Tag: NOVEL

  • MitoQ

    Plain-language summaryIntrigue 75 / 100

    MitoQ is mitochondria-targeted ubiquinone (a derivative of CoQ10 with a positively charged triphenylphosphonium group that drives accumulation in mitochondria). Concentrates antioxidant activity at the mitochondrial inner membrane where oxidative damage occurs. Not stocked by Kodiac. This monograph is provided for research and educational reference.

    Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

    Mitochondria-targeted ubiquinone-derived antioxidant conjugated to a triphenylphosphonium cation

    A synthetic coenzyme Q10 analog covalently linked to a lipophilic triphenylphosphonium moiety that drives selective mitochondrial accumulation, enabling targeted quenching of reactive oxygen species at the inner mitochondrial membrane with demonstrated vascular, hepatoprotective, and anti-inflammatory activity in human clinical studies.

    Abstract

    Mitoquinone mesylate (MitoQ) is a mitochondria-targeted antioxidant composed of a ubiquinone moiety covalently linked via a ten-carbon alkyl chain to a triphenylphosphonium (TPP+) cation, enabling rapid permeation of lipid bilayers and accumulation within the mitochondrial matrix at concentrations up to several hundred-fold above extracellular levels, driven by the large negative mitochondrial membrane potential (approximately negative 150 to negative 180 millivolts). The compound was developed in the 1990s by Robin Smith and Michael Murphy at the University of Otago, New Zealand, as an approach to overcoming the failure of conventional untargeted antioxidants (including native coenzyme Q10) to achieve therapeutically meaningful concentrations within mitochondria, the principal intracellular source of reactive oxygen species (ROS). Within the mitochondrion, MitoQ adsorbs to the matrix-facing leaflet of the inner mitochondrial membrane, where the ubiquinone head group is reduced to the active antioxidant ubiquinol form by complex II (succinate:ubiquinone oxidoreductase) of the electron transport chain. The ubiquinol form scavenges superoxide, hydroxyl radicals, and peroxyl radicals, preventing lipid peroxidation of cardiolipin and other mitochondrial membrane phospholipids. Following oxidation during radical quenching, the resulting ubiquinone is re-reduced by complex II, establishing a catalytic antioxidant cycle that permits repeated radical neutralization from a single molecule. This recycling mechanism distinguishes MitoQ from stoichiometric antioxidants such as alpha-tocopherol that are consumed in the quenching reaction. Preclinical pharmacology has demonstrated protective effects in rodent models of ischemia-reperfusion injury, diabetic nephropathy, nonalcoholic fatty liver disease, sepsis-associated organ failure, pulmonary hypertension, Alzheimer’s disease, doxorubicin-induced cardiomyopathy, cisplatin nephrotoxicity, and metabolic syndrome, with consistent reductions in mitochondrial oxidative damage markers, preservation of mitochondrial membrane potential, and attenuation of downstream inflammatory signaling through suppression of NF-kappaB activation and NLRP3 inflammasome assembly. Four completed human clinical trials define the current clinical evidence base. The Snow et al. (2010) PROTECT study, a 12-month randomized double-blind placebo-controlled trial in 128 newly diagnosed untreated Parkinson’s disease patients at 40 or 80 mg per day, found no difference between MitoQ and placebo on any measure of disease progression, establishing an important negative result for the oxidative stress hypothesis in early Parkinson’s disease. The Gane et al. (2010) phase II trial in 30 patients with chronic hepatitis C virus infection demonstrated significant decreases in serum alanine aminotransferase and aspartate aminotransferase at 40 and 80 mg per day over 28 days, without change in viral load, suggesting hepatoprotective activity through reduction of mitochondrial oxidative necroinflammation. The Rossman et al. (2018) randomized crossover trial in 20 healthy older adults (60 to 79 years) with impaired endothelial function demonstrated that 6 weeks of MitoQ at 20 mg per day produced a 42 percent improvement in brachial artery flow-mediated dilation versus placebo, with concurrent reductions in plasma oxidized low-density lipoprotein and aortic pulse wave velocity, establishing the first human evidence for mitochondria-targeted antioxidant improvement of age-related vascular dysfunction. A 2024 exploratory pilot trial (Jain et al. 2024) of MitoQ as post-exposure prophylaxis against SARS-CoV-2 infection reported reduced infection rates and symptom duration in the treatment group versus matched controls. The compound is well tolerated in human studies at doses up to 80 mg per day for 12 months, with nausea and gastrointestinal discomfort as the principal dose-limiting adverse events. MitoQ is not approved as a pharmaceutical by any regulatory authority; it is marketed globally as a dietary supplement at doses of 5 to 10 mg per day and is available as a research-grade compound from multiple chemical suppliers. This monograph reviews the chemistry, synthesis, and mitochondrial targeting mechanism of MitoQ; the comprehensive preclinical pharmacology across disease models; the complete human clinical evidence base; pharmacokinetics including the low oral bioavailability and extensive first-pass metabolism; sourcing, reconstitution, and handling; stack-interaction considerations; adverse-event signal; and a structured comparative assessment of five mitochondria-targeted antioxidant candidates (SkQ1, elamipretide, MitoTEMPO, MitoVitE, idebenone) against MitoQ on five competency standards.

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    FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

  • SRT2104

    Plain-language summaryIntrigue 50 / 100

    SRT2104 is a small-molecule sirtuin 1 (SIRT1) activator developed at Sirtris Pharmaceuticals (later acquired by GSK). It was designed as a more potent and drug-like successor to resveratrol, the natural compound that started the sirtuin-aging story. Sirtuins are NAD+-dependent enzymes that deacetylate metabolic and stress-response targets, hypothesized to mediate calorie-restriction-like longevity effects. SRT2104 activates SIRT1 allosterically and produced metabolic and inflammatory benefits in mouse studies. Phase 2 trials in diabetes, ulcerative colitis, and cardiovascular disease showed modest signals at best, and GSK shut down Sirtris in 2013 amid skepticism about the sirtuin-activator concept. Of mainly historical interest as a flagship compound of a faded program. Not stocked by Kodiac. This monograph is provided for research and educational reference.

    Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

    Selective small-molecule allosteric activator of NAD-dependent protein deacetylase sirtuin 1 (SIRT1)

    A second-generation imidazothiazole-scaffold sirtuin 1 activator developed by Sirtris Pharmaceuticals and advanced through multiple Phase 2 clinical programs by GlaxoSmithKline, distinguished from first-generation sirtuin-activating compounds by high target selectivity and favorable oral pharmacokinetics.

    Abstract

    SRT2104 (GSK2245840) is a synthetic, orally bioavailable, small-molecule allosteric activator of the NAD-dependent protein deacetylase sirtuin 1 (SIRT1, silent mating type information regulation 2 homolog 1), developed at Sirtris Pharmaceuticals and subsequently advanced into clinical trials by GlaxoSmithKline following the 2008 acquisition of Sirtris for approximately 720 million United States dollars. The compound is a second-generation sirtuin-activating compound (STAC) built on an optimized imidazo[2,1-b]thiazole scaffold and is reported to activate SIRT1 deacetylase activity approximately 1000-fold more potently than the natural polyphenol resveratrol in fluorophore-tagged peptide substrate assays, with minimal activity against a panel of more than 180 non-SIRT1 targets including kinases, G-protein-coupled receptors, nuclear receptors, ion channels, enzymes, and transporters [1, 2]. The allosteric mechanism involves binding to the N-terminal domain of SIRT1, lowering the Michaelis constant (Km) for the acetylated protein substrate without competing with either the NAD cofactor or the substrate acetyl-lysine site [3]. Downstream consequences of SIRT1 activation by SRT2104 include deacetylation and functional modulation of the transcription factor p53, the RelA/p65 subunit of nuclear factor kappa B (NF-kB), forkhead box protein O3 (FOXO3), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1alpha), and signal transducer and activator of transcription 3 (STAT3), producing composite anti-inflammatory, metabolic, and cytoprotective effects that have been characterized across a broad range of preclinical disease models [4, 5].

    Pharmacokinetics in humans are characterized by oral absorption with time to peak plasma concentration of 1 to 3 hours after single dosing, a terminal elimination half-life of 8 to 24 hours depending on dose, and substantial inter-individual variability that is not dose-proportional across the studied range of 0.03 to 3.0 grams [6]. The variable and non-dose-proportional pharmacokinetic profile has been identified as a principal limitation of the compound for clinical development in its current oral formulation. SRT2104 is poorly soluble in water and is formulated as a lipid-based oral capsule to improve bioavailability.

    Clinical evaluation has spanned at least seven registered clinical trials across multiple indications. In a Phase 1 trial in healthy elderly volunteers (60 to 80 years of age), 28 days of oral SRT2104 at 0.5 or 2.0 grams daily produced reductions in serum cholesterol, low-density lipoprotein, and triglycerides, with trends toward improved mitochondrial oxidative phosphorylation capacity as measured by phosphorus-31 magnetic resonance spectroscopy of skeletal muscle [7]. A Phase 2 randomized, placebo-controlled trial in 37 subjects with type 2 diabetes mellitus treated for 28 days at doses of 0.25, 0.5, 1.0, or 2.0 grams daily did not demonstrate improved glycemic control but produced a statistically significant reduction in total cholesterol and triglycerides at the 1.0 gram dose [8]. A separate cardiometabolic study in type 2 diabetic subjects reported trends toward improved endothelial function and arterial stiffness [9]. A Phase 2 trial in 40 subjects with moderate to severe psoriasis treated for 84 days at escalating doses of 250, 500, or 1000 milligrams daily reported 35 percent of SRT2104-treated patients achieving good to excellent histological improvement on skin biopsy, but three serious adverse events were reported including pneumonitis and pancreatitis [10]. A trial in mild to moderate ulcerative colitis (31 subjects, 50 or 500 milligrams daily for 8 weeks) demonstrated tolerability but limited clinical efficacy, with only 3 of 26 evaluable subjects achieving endoscopic remission [11]. In a human endotoxemia model, SRT2104 pretreatment significantly reduced lipopolysaccharide-induced cytokine release (interleukin-6, interleukin-8) and coagulation activation, representing the first human demonstration of anti-inflammatory and anticoagulant activity consistent with pharmacological SIRT1 activation [12].

    Preclinical pharmacology is extensive. The Mercken et al. (2014) study at the National Institute on Aging demonstrated that SRT2104 extends both mean and maximum lifespan of male mice fed a standard diet by 9.7 percent and 4.9 percent respectively, with preserved bone mineral density, muscle mass, motor coordination, and insulin sensitivity [13]. The Jiang et al. (2014) study demonstrated blood-brain barrier penetration, attenuation of brain atrophy, improvement of motor function, and extension of median lifespan by approximately 16 percent in N171-82Q Huntington disease model mice [14]. Additional preclinical evidence spans emphysema, sepsis, neonatal white matter injury, microglia polarization, dendritic outgrowth, and auditory cell senescence. GlaxoSmithKline discontinued active clinical development of SRT2104 following the 2013 closure of the Sirtris unit, though the compound remains widely used as a reference SIRT1 activator in academic and preclinical research. This monograph reviews chemistry, molecular pharmacology, pharmacokinetics, the complete clinical evidence base, sourcing and handling, stack interactions, adverse events, and a comparative assessment of five SIRT1 modulators against SRT2104 on five competency standards.

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    FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

  • P7C3-A20

    Aminopropyl carbazole neuroprotective agent functioning as a nicotinamide phosphoribosyltransferase (NAMPT) positive allosteric modulator

    A synthetic 3,6-dibromocarbazole derivative discovered through target-agnostic in vivo neurogenesis screening, distinguished by its activation of the NAD+ salvage enzyme NAMPT and broad neuroprotective efficacy across preclinical models of traumatic brain injury, ischemic stroke, Parkinson disease, amyotrophic lateral sclerosis, and Alzheimer disease.

    Abstract

    P7C3-A20, the fluorinated and methoxylated analog of the parent aminopropyl carbazole P7C3, is a synthetic neuroprotective compound identified through iterative structure-activity optimization of a chemical series originally discovered in a target-agnostic in vivo screen for enhancers of adult hippocampal neurogenesis conducted by Pieper, McKnight, and colleagues at the University of Texas Southwestern Medical Center [1]. The parent compound P7C3 was one of eight hits from a library of approximately 1,000 small molecules screened for their ability to augment the survival of newborn neurons in the subgranular zone of the murine dentate gyrus. Subsequent medicinal chemistry optimization, principally the replacement of the central hydroxyl with fluorine and the introduction of a methoxy substituent on the aniline ring, yielded P7C3-A20, which demonstrated approximately ten-fold greater proneurogenic potency than the parent compound while retaining favorable oral bioavailability, blood-brain barrier penetration, and tolerability in chronic dosing studies in rodents and nonhuman primates [2, 3]. The molecular target of P7C3-A20 was identified by Wang et al. (2014) as nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in the nicotinamide adenine dinucleotide (NAD+) salvage pathway [4]. P7C3-A20 functions as a positive allosteric modulator of NAMPT, enhancing the conversion of nicotinamide to nicotinamide mononucleotide (NMN) and thereby augmenting intracellular NAD+ levels under conditions of metabolic stress without elevating NAD+ to supraphysiologic concentrations. This mechanism distinguishes P7C3-A20 from direct NAD+ precursor supplementation strategies (nicotinamide riboside, nicotinamide mononucleotide) by preserving endogenous feedback regulation of the salvage pathway. The downstream consequences of NAMPT activation and NAD+ restoration include maintenance of sirtuin deacetylase activity (particularly SIRT1 and SIRT3), protection of mitochondrial bioenergetics, suppression of oxidative stress and DNA damage, attenuation of neuroinflammation through microglial modulation, and enhancement of the survival of newly generated neurons during adult hippocampal neurogenesis. The preclinical pharmacology of P7C3-A20 has been characterized across an unusually broad spectrum of neurodegenerative and neurotraumatic disease models. In the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson disease, P7C3-A20 substantially preserved dopaminergic neurons in the substantia nigra [5]. In the G93A-SOD1 transgenic mouse model of amyotrophic lateral sclerosis (ALS), P7C3-A20 reduced motor neuron cell death in the spinal cord [6]. In models of traumatic brain injury (TBI), P7C3-A20 blocked axonal degeneration and preserved neurological function when administered acutely [7], and, in a landmark 2020 study, restored blood-brain barrier integrity, arrested chronic neurodegeneration, and recovered normal cognitive function when treatment was initiated a full twelve months after the initial injury [8]. In rat models of focal ischemic stroke, P7C3-A20 promoted post-ischemic neurogenesis, restored cortical NAD+ levels, and improved chronic sensorimotor and cognitive outcomes [9]. In retinal degeneration models, the P7C3 class protected retinal ganglion cells from optic nerve injury [10]. In 2025, Vazquez-Rosa et al. published a study in Cell Reports Medicine demonstrating that P7C3-A20 treatment of 5xFAD and PS19 transgenic mice with advanced Alzheimer-like pathology produced comprehensive reversal of tau phosphorylation, blood-brain barrier deterioration, oxidative stress, DNA damage, and neuroinflammation, with full cognitive recovery and normalization of the clinical biomarker p-tau217 [11]. P7C3-A20 has not entered human clinical trials as of the most recent monograph revision. The compound is not approved by any regulatory authority for any indication. It is available as a research-grade preparation from multiple chemical suppliers at high purity. This monograph reviews the chemistry, synthesis, and structure-activity relationships of P7C3-A20; the NAMPT-mediated mechanism of action; the preclinical pharmacokinetic profile; the extensive preclinical pharmacology across neurodegenerative and neurotraumatic models; the current clinical development status; sourcing and quality considerations; reconstitution and handling; stack interactions; the adverse-event and safety profile from preclinical studies; and a comparative assessment of five neuroprotective or NAD-augmenting compounds against P7C3-A20 on five competency standards.

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    FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

  • AF710B

    Allosteric M1 muscarinic acetylcholine receptor agonist and sigma-1 receptor agonist with disease-modifying preclinical efficacy in Alzheimer’s disease models

    A dual-target allosteric M1 muscarinic and sigma-1 receptor agonist developed at the Israel Institute for Biological Research and advanced by Anavex Life Sciences as ANAVEX 3-71, distinguished from earlier orthosteric muscarinic agonists by allosteric M1 selectivity, picomolar-range potency, sigma-1 chaperone engagement, and disease-modifying activity across amyloid, tau, and neuroinflammatory pathologies in transgenic rodent models of Alzheimer’s disease.

    Abstract

    AF710B (ANAVEX 3-71) is a highly potent and selective allosteric agonist of the M1 subtype of the muscarinic acetylcholine receptor (M1 mAChR) and a concurrent agonist of the sigma-1 receptor (sigma-1R), first reported by Fisher et al. (2016) in Neurodegenerative Diseases as a next-generation candidate for cognitive enhancement and disease modification in Alzheimer’s disease [1]. The compound emerged from a decades-long medicinal chemistry program at the Israel Institute for Biological Research (IIBR) that previously produced the orthosteric M1 agonists AF102B (cevimeline, approved for Sjogren’s syndrome), AF267B, and AF292, each of which demonstrated procognitive and anti-amyloidogenic activity in preclinical and early clinical settings but was limited by insufficient M1 selectivity, dose-limiting cholinergic adverse events, or both. AF710B was designed to overcome these limitations through an allosteric mechanism of M1 receptor engagement: at nanomolar concentrations the compound potentiates the binding and efficacy of the endogenous agonist acetylcholine (and of the reference orthosteric agonist carbachol) at the M1 receptor, amplifying downstream signaling through phospho-ERK1/2 and phospho-CREB pathways without producing the gastrointestinal and cardiovascular cholinergic toxicity that constrained the earlier orthosteric series [1, 2]. Selectivity screening at 10 micromolar against 83 additional G-protein-coupled receptors, ion channels, and transporters produced no significant off-target hits, establishing a pharmacological selectivity profile substantially cleaner than that of xanomeline and other earlier M1-preferring agonists [1]. The sigma-1 receptor agonism adds a second, mechanistically independent neuroprotective axis. Sigma-1R is an endoplasmic reticulum chaperone protein concentrated at the mitochondria-associated endoplasmic reticulum membrane (MAM), where it regulates calcium transfer between the endoplasmic reticulum and mitochondria, modulates the unfolded protein response, and activates anti-inflammatory and antiapoptotic signaling cascades [3, 4]. Activation of sigma-1R by AF710B has been linked to rescue of mushroom spine loss in presenilin-1 knock-in and APP knock-in neuronal cultures, reduction of neuroinflammatory markers, and normalization of brain-derived neurotrophic factor (BDNF) signaling in transgenic models [1, 5]. In the seminal Fisher et al. (2016) study, AF710B administered to female 3xTg-AD mice at 10 micrograms per kilogram intraperitoneally daily for two months mitigated cognitive impairment in the Morris water maze and reduced BACE1 expression, GSK3-beta activity, p25/CDK5 levels, neuroinflammation, soluble and insoluble amyloid-beta 40 and 42, amyloid plaques, and phosphorylated tau pathology [1]. A subsequent study by Hall et al. (2018) in Alzheimer’s and Dementia extended these findings to the McGill-R-Thy1-APP transgenic rat model, demonstrating that chronic oral AF710B at 10 micrograms per kilogram daily for 4.5 months in 13-month-old (post-plaque) rats reversed cognitive deficits, reduced hippocampal amyloid plaque burden and cortical amyloid-beta 40 and 42 levels, decreased neuroinflammatory markers, increased cerebrospinal fluid amyloid clearance, and elevated the synaptic marker synaptophysin [6]. The disease-modifying character of the effect was underscored by its persistence through a five-week drug washout period following treatment cessation. A third study (Bhatt et al., 2024, Neurobiology of Aging) confirmed that early treatment with AF710B in the same rat model prevented cognitive decline when treatment was initiated before overt plaque deposition [7]. Anavex Life Sciences Corporation acquired exclusive worldwide rights to the AF710B intellectual property in 2014 and advanced the compound under the designation ANAVEX 3-71 through a first-in-human Phase 1 single ascending dose study in 42 healthy volunteers (2020 to 2021), which demonstrated safety and tolerability at oral doses of 5 to 200 mg with no serious adverse events, no clinically significant electrocardiogram changes, and linear, dose-proportional pharmacokinetics with a mean terminal elimination half-life of approximately 3.56 hours [8, 9]. A Phase 1b study subsequently confirmed the bioavailability of a once-daily oral tablet formulation. In 2024, Anavex initiated a placebo-controlled Phase 2 study (ANAVEX3-71-SZ-001) in adults with schizophrenia, and in October 2025 reported positive topline results demonstrating safety, tolerability, reduction in the neuroinflammatory biomarker glial fibrillary acidic protein (GFAP), and encouraging trends in EEG and event-related potential biomarkers [10, 11]. The compound has received orphan drug designation from the FDA for frontotemporal dementia. No registration-enabling Phase 3 trial has been completed for any indication as of the most recent monograph revision. This monograph documents the chemistry, synthesis, dual-receptor pharmacology, pharmacokinetics, preclinical and clinical evidence, sourcing and handling considerations, stack interactions, adverse-event profile, and a structured comparative assessment of AF710B against five muscarinic and sigma-1 receptor candidates on five competency standards.

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    FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

  • SkQ1 (Visomitin)

    Plain-language summaryIntrigue 72 / 100

    SkQ1 (Visomitin) is a mitochondria-targeted plastoquinone developed in Russia by Vladimir Skulachev. Approved as eye drops for dry eye in Russia. Concentrates antioxidant activity in mitochondria similar to MitoQ. Not stocked by Kodiac. This monograph is provided for research and educational reference.

    Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

    Mitochondria-targeted plastoquinone-based antioxidant conjugated to a penetrating lipophilic cation (triphenylphosphonium)

    A rechargeable, mitochondria-accumulating plastoquinone derivative developed at Lomonosov Moscow State University as a direct scavenger of reactive oxygen species at the inner mitochondrial membrane, with preclinical geroprotective, cytoprotective, and anti-inflammatory activity across multiple organ systems and a registered ophthalmic formulation (Visomitin) for dry eye syndrome.

    Abstract

    SkQ1 (10-(6′-plastoquinonyl)decyltriphenylphosphonium), designated a “Skulachev ion” after its principal developer Vladimir P. Skulachev, is a synthetic mitochondria-targeted antioxidant composed of a plastoquinone moiety linked by a ten-carbon aliphatic chain to a triphenylphosphonium cation. The triphenylphosphonium group exploits the large negative-inside mitochondrial membrane potential (approximately 180 millivolts) to drive electrophoretic accumulation of the compound within the mitochondrial matrix at concentrations estimated to reach 10(8)-fold above extracellular levels. Within the inner mitochondrial membrane, the plastoquinone headgroup intercalates near the cardiolipin fatty acid chains and directly quenches peroxyl radicals, with regeneration of the reduced (antioxidant-active) form by Complex I at the IQ site and by Complex III at the Qi site of the electron transport chain. This rechargeable antioxidant cycle distinguishes SkQ1 from stoichiometric scavengers and positions it as a catalytic antioxidant with sustained activity at nanomolar external concentrations. The compound was developed beginning in the early 2000s at the A. N. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, within a research framework centered on Skulachev’s hypothesis that aging represents a form of programmed organismal death (phenoptosis) mediated by mitochondrial reactive oxygen species (mtROS). Preclinical studies in organisms spanning fungi (Podospora anserina), crustaceans (Ceriodaphnia affinis), insects (Drosophila melanogaster), fish (Nothobranchius furzeri), and mammals (mice and rats) have demonstrated lifespan extension, delay or reversal of age-related pathologies, and suppression of mtROS-driven tissue damage under a variety of experimental conditions. In the senescence-accelerated OXYS rat strain, SkQ1 prevented or reversed cataracts, retinopathy resembling age-related macular degeneration, osteoporosis, and neurodegenerative phenotypes resembling Alzheimer’s disease. In outbred and inbred mouse strains, SkQ1 extended median and maximum lifespan under non-specific-pathogen-free housing conditions, with effect sizes dependent on ambient pathogen exposure. The compound prevented rapid death caused by mechanistically diverse acute shocks including bacterial lipopolysaccharide, intravenous mitochondrial injection, cold exposure, and toxic insult. The ophthalmic formulation of SkQ1 (Visomitin, 0.155 micrograms per milliliter ophthalmic solution) was approved by the Russian Ministry of Health in December 2011 for the treatment of dry eye syndrome and early cataracts. In the United States, Mitotech S.A. advanced SkQ1 ophthalmic solution through a positive Phase 2 clinical trial demonstrating statistically significant improvement in corneal fluorescein staining and lissamine green staining relative to placebo in 91 subjects with mild to moderate dry eye disease. Two subsequent Phase 3 studies (VISTA-1, 452 subjects; VISTA-2, 610 subjects) did not meet their co-primary endpoints, although VISTA-2 demonstrated statistically significant superiority in a pre-specified secondary endpoint of central corneal fluorescein staining change in a Schirmer’s score-defined subpopulation. Phase 1 oral formulation studies were conducted in Russia in 2016. Preclinical pharmacology extends beyond ophthalmology to include cardioprotection (hemorrhagic shock, doxorubicin-induced cardiomyopathy), nephroprotection (cisplatin-induced and ischemia-reperfusion acute kidney injury with ferroptosis inhibition), neuroprotection (stroke, Alzheimer’s disease models in OXYS rats), hepatoprotection, suppression of experimental colitis and autoimmune arthritis, wound healing acceleration, tumor growth inhibition in fibrosarcoma and rhabdomyosarcoma models, and antibacterial activity at micromolar concentrations. Safety pharmacology in rats and dogs has demonstrated a wide therapeutic window with no adverse effects on the central nervous system, cardiovascular system, or respiratory system at doses orders of magnitude above the efficacious range. The compound does not induce hepatic cytochrome P450 enzymes. This monograph reviews the chemistry, structural pharmacology, and rechargeable antioxidant mechanism of SkQ1; the comprehensive preclinical evidence across geroprotective, cytoprotective, and anti-inflammatory applications; the clinical evidence base in dry eye disease; the pharmacokinetic characteristics; sourcing and quality considerations; reconstitution and handling protocols; stack-interaction implications; the adverse-event and safety profile; and a structured comparative assessment of five mitochondria-targeted antioxidant candidates against SkQ1 on five competency standards (novelty, effect size, promising potential, side-effect profile, and overall validation).

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  • Pirenzepine

    Selective M1 muscarinic acetylcholine receptor antagonist of the pyridobenzodiazepinone structural class

    A peripherally selective, M1-preferring muscarinic antagonist developed at Dr. Karl Thomae GmbH (Boehringer Ingelheim) as a gastric antisecretory agent for peptic ulcer disease, subsequently investigated as a topical ophthalmic intervention for the retardation of progressive myopia in children.

    Abstract

    Pirenzepine (LS 519, Gastrozepin) is a tricyclic pyridobenzodiazepinone and the prototypical selective antagonist of the M1 subtype of the muscarinic acetylcholine receptor. Synthesized at Dr. Karl Thomae GmbH, a subsidiary of Boehringer Ingelheim, in the mid-1970s, the compound was the first muscarinic antagonist demonstrated to discriminate pharmacologically between what were subsequently classified as M1 and M2 receptor subtypes, a finding reported by Hammer et al. in 1980 in Nature and foundational to the modern subtype classification of muscarinic receptors [1]. Pirenzepine binds the M1 muscarinic receptor with a dissociation constant (Ki) of approximately 5 to 14 nanomolar and displays 5- to 20-fold selectivity over the M2, M3, and M5 subtypes, with intermediate affinity at M4 receptors [2, 3]. The compound is peripherally selective, exhibiting negligible penetration of the blood-brain barrier at therapeutic oral doses, a property that minimizes central anticholinergic adverse effects and distinguishes it from atropine and other non-selective muscarinic antagonists. The primary registered indication is peptic ulcer disease. Pirenzepine inhibits vagally mediated and pentagastrin-stimulated gastric acid secretion through antagonism of M1 receptors on intramural gastric plexus neurons, reducing basal acid output by approximately 50 percent at oral doses of 50 mg twice daily [4, 5]. Extensive controlled trials conducted through the late 1970s and 1980s demonstrated duodenal ulcer healing rates of 60 to 76 percent at 4 to 8 weeks on pirenzepine 100 to 150 mg per day, broadly comparable to cimetidine 1 g per day and superior to placebo and gefarnate [6, 7]. The compound was registered as Gastrozepin in numerous European, Asian, and Latin American jurisdictions but was never approved by the United States Food and Drug Administration. The clinical importance of pirenzepine as a gastric antisecretory agent has diminished substantially following the introduction of histamine H2 receptor antagonists and proton pump inhibitors, which offer superior acid suppression and ulcer healing rates. A second, more recent research application is the retardation of progressive myopia (axial elongation of the globe) in children aged 8 to 12 years. Two multicenter, randomized, double-masked, placebo-controlled trials of 2% pirenzepine ophthalmic gel, conducted by Siatkowski et al. (2004, 2008), demonstrated approximately 50 percent reduction in the rate of myopia progression over 1- and 2-year treatment periods, with a clinically acceptable safety profile dominated by mild pupil dilation and accommodation difficulty [8, 9]. The mechanism of the antimyopic effect is incompletely characterized but is attributed to M1 and possibly M4 muscarinic receptor antagonism in the retina and sclera, modulating signaling cascades that regulate scleral extracellular matrix remodeling and axial elongation [10]. The ophthalmic application has not received regulatory approval; the compound remains investigational for myopia control, with atropine (a non-selective muscarinic antagonist applied at low concentrations) having advanced further in clinical development for this indication. Pharmacokinetics are characterized by low oral bioavailability (20 to 30 percent in fasted subjects, further reduced by food), a plasma elimination half-life of approximately 10 to 12 hours, negligible hepatic first-pass metabolism, predominant renal elimination of unchanged drug, and low plasma protein binding (approximately 12 percent) [11, 12]. The compound does not undergo significant cytochrome P450-mediated metabolism and has a correspondingly limited drug-drug interaction profile. The principal adverse events at registered oral doses are mild anticholinergic effects: dry mouth (approximately 14 percent), blurred vision (1 to 5 percent, dose-dependent), and constipation (approximately 3 percent), with an overall discontinuation rate of approximately 2 percent in controlled trials [6]. Serious adverse events are rare. This monograph reviews the chemistry, synthesis, and structural pharmacology of pirenzepine; the molecular pharmacology at muscarinic receptor subtypes; comprehensive human pharmacokinetics; the clinical evidence base across peptic ulcer and myopia indications; sourcing and quality verification; reconstitution and handling; stack-interaction considerations; adverse-event signal; and a structured comparative assessment of five gastric antisecretory and muscarinic antagonist alternatives (telenzepine, atropine, cimetidine, ranitidine, omeprazole) against pirenzepine on five competency standards.

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    FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

  • Pridopidine

    Plain-language summaryIntrigue 62 / 100

    Pridopidine started life as a dopamine stabilizer for Huntington disease and was later reclassified as a high-affinity sigma-1 agonist when its true binding profile was characterized. Originally developed at NeuroSearch and now at Prilenia Therapeutics, it failed the phase 3 PRIDE-HD trial in Huntington but has continued in ALS development based on encouraging phase 2 signals in that population. The reclassification story is interesting because it changed how investigators think about both pridopidine and the sigma-1 target itself. Whether the current ALS program produces meaningful efficacy remains an open question. Not stocked by Kodiac. This monograph is provided for research and educational reference.

    Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

    Selective sigma-1 receptor agonist with low-affinity dopamine D2 receptor antagonism and CYP2D6 auto-inhibition

    A 4-phenylpiperidine sigma-1 receptor agonist originally developed as a dopaminergic stabilizer, repositioned on the basis of high-affinity sigma-1 binding and neuroprotective activity in Huntington disease and amyotrophic lateral sclerosis models, with Phase 3 clinical data in Huntington disease and an FDA-cleared Phase 3 program in ALS.

    Abstract

    Pridopidine (ACR16; 4-[3-(methylsulfonyl)phenyl]-1-propylpiperidine; CAS 346688-38-8; molecular formula C15H23NO2S; molecular weight 281.41) is a selective sigma-1 receptor (S1R) agonist with a binding affinity (Ki) of approximately 57 nM at the human sigma-1 receptor and substantially lower affinity at the dopamine D2 receptor (Ki approximately 2950 nM), the dopamine D3 receptor (Ki approximately 1630 nM), the adrenergic alpha-2C receptor (Ki approximately 1580 nM), and the sigma-2 receptor (Ki approximately 5450 nM). The compound was synthesized at A. Carlsson Research (later NeuroSearch) as part of a structure-activity exploration of 4-phenylpiperidine dopamine D2 receptor ligands with fast dissociation kinetics and was originally classified as a “dopaminergic stabilizer” on the basis of its state-dependent modulation of dopaminergic tone in behavioral models. Subsequent binding, functional, and positron emission tomography studies established that the principal pharmacological target at clinically relevant concentrations is the sigma-1 receptor, an endoplasmic reticulum chaperone protein located at the mitochondria-associated membrane that regulates calcium homeostasis, mitochondrial function, brain-derived neurotrophic factor (BDNF) trafficking and secretion, endoplasmic reticulum stress responses, autophagy, and synaptic plasticity. Pridopidine has demonstrated neuroprotective and neurorestorative activity in preclinical models of Huntington disease (YAC128 transgenic mice, R6/2 mice), amyotrophic lateral sclerosis (SOD1G93A mice), Parkinson disease (6-OHDA lesioned mice), and glaucoma (optic nerve crush and microbead occlusion models), with effects dependent on sigma-1 receptor activation and abolished in sigma-1 receptor knockout animals.

    Clinical development has focused primarily on Huntington disease. Four randomized controlled trials (Lundin 2010, MermaiHD, HART, PRIDE-HD) evaluated pridopidine at doses of 20 to 112.5 mg per day in a combined population of over 1,100 patients. The Phase 3 MermaiHD trial (437 patients, 26 weeks) did not meet its primary motor endpoint (modified Motor Score) but demonstrated nominally significant improvement on the total Unified Huntington’s Disease Rating Scale (UHDRS) Total Motor Score. The Phase 2 PRIDE-HD trial (408 patients, 52 weeks) reported that pridopidine 45 mg twice daily was associated with maintenance of Total Functional Capacity (TFC) compared to placebo at 52 weeks, a finding extended to five years in the Open-HART open-label extension. The Phase 3 PROOF-HD trial (499 patients, 65 weeks) did not meet its primary endpoint (TFC change) in the overall population but demonstrated statistically significant benefit on TFC, composite UHDRS score, and multiple secondary endpoints in the pre-specified subgroup of participants not receiving antidopaminergic medications. A European Marketing Authorisation Application was submitted in 2024 for the treatment of adults with Huntington disease; the Committee for Medicinal Products for Human Use recommended refusal in July 2025, and Prilenia Therapeutics has announced plans for a confirmatory global Phase 3 study.

    In amyotrophic lateral sclerosis, pridopidine was evaluated in the Phase 2 HEALEY ALS Platform Trial (121 participants, 24 weeks). The primary endpoint (ALSFRS-R total score change) was not met in the full analysis set, but subgroup analyses in patients with early and rapidly progressive disease demonstrated a 32 percent slowing of ALSFRS-R decline, a 62 percent slowing of respiratory decline, and a prolongation of median survival from approximately 300 to 600 days. The United States Food and Drug Administration cleared a pivotal Phase 3 trial (PREVAiLS, 500 patients) in December 2025, with recruitment planned for early 2026.

    Pharmacokinetics are characterized by oral absorption, hepatic CYP2D6-mediated N-depropylation, and a single-dose elimination half-life of approximately 6 hours in extensive CYP2D6 metabolizers and 15 hours in poor metabolizers. Pridopidine is a metabolism-dependent inhibitor of CYP2D6, producing auto-inhibition that extends the effective half-life to 10 to 14 hours regardless of CYP2D6 genotype on repeated dosing, an unusual pharmacokinetic property that reduces inter-individual variability at steady state and eliminates the requirement for CYP2D6 genotype-based dose adjustment. The compound is well tolerated at doses up to 112.5 mg per day; the most common adverse events are insomnia, diarrhea, nausea, and dizziness, with no clinically significant differences from placebo in serious adverse event rates across pooled trial data. QTc prolongation at the 45 mg twice daily dose is not considered clinically relevant.

    This monograph reviews the chemistry and synthesis of pridopidine; the sigma-1 receptor mechanism in molecular and cellular detail; the comprehensive pharmacokinetic record including CYP2D6 auto-inhibition; the preclinical neuroprotective evidence across multiple disease models; the clinical evidence base across Huntington disease, amyotrophic lateral sclerosis, and exploratory indications; sourcing and quality verification considerations; reconstitution and handling; stack-interaction implications; adverse-event signal; and a structured comparative assessment of five sigma-1 receptor candidates against pridopidine on five competency standards (novelty, effect size, promising potential, side-effect profile, and overall validation). The compound is not approved by any regulatory authority as of the monograph revision date. It is available as a research-grade preparation from multiple chemical suppliers; investigators should obtain analytical confirmation of identity and purity on every lot.

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  • PRE-084

    Selective sigma-1 receptor agonist derived from phencyclidine with neuroprotective, nootropic, and neurotrophic activity

    A phencyclidine-derived sigma-1 receptor agonist developed as a pharmacological tool compound, distinguished by high selectivity over sigma-2 and PCP receptors and by a broad preclinical literature spanning neuroprotection in motor neuron disease, stroke, Parkinson’s disease, cognitive impairment, and antidepressant activity.

    Abstract

    PRE-084 (2-(4-morpholino)ethyl 1-phenylcyclohexane-1-carboxylate) is a selective agonist of the sigma-1 receptor (sigma-1R) originally identified in 1991 by Su and colleagues at the National Institute on Drug Abuse through a systematic structure-activity program that sought to separate sigma receptor affinity from phencyclidine (PCP) receptor binding in the parent cyclohexylamine scaffold [1]. The compound binds the sigma-1 receptor with an IC50 of approximately 44 nM in radioligand displacement assays and exhibits selectivity ratios exceeding 2000-fold over the PCP binding site (IC50 greater than 100,000 nM) and approximately 300-fold over the sigma-2 receptor subtype (IC50 approximately 13,091 nM), establishing it as one of the most widely used pharmacological tools for interrogating sigma-1 receptor function in vitro and in vivo [1, 2]. The sigma-1 receptor itself is a ligand-regulated chaperone protein resident at the mitochondria-associated endoplasmic reticulum membrane (MAM), where it modulates calcium signaling through interactions with inositol 1,4,5-trisphosphate receptors, regulates protein folding and endoplasmic reticulum stress responses, and participates in diverse signal transduction cascades including the NF-kappaB, ERK/CREB, and protein kinase C pathways [3, 4]. PRE-084 has not been advanced to human clinical trials and carries no regulatory approval in any jurisdiction; its utility is exclusively as a research-grade pharmacological probe. The preclinical literature on PRE-084 is nonetheless substantial and spans multiple therapeutic domains. In amyotrophic lateral sclerosis, daily administration of PRE-084 to SOD1-G93A transgenic mice from eight weeks of age preserved spinal motoneuron survival, maintained compound muscle action potential amplitudes, improved locomotion, and extended overall survival, with neuroprotective effects attributed to protein kinase C-mediated phosphorylation of the NMDA receptor NR1 subunit and reduction of microglial reactivity [5, 6]. Comparable neuroprotection was demonstrated in the wobbler mouse model of motor neuron disease not linked to SOD1 mutation, broadening the mechanistic generalizability [7]. In ischemic stroke models, PRE-084 at 5 mg/kg intraperitoneally reduced infarct volume and neurological deficit scores after embolic middle cerebral artery occlusion in rats, with the mechanism involving suppression of pro-inflammatory cytokines (interleukin-1 beta, tumor necrosis factor alpha) and enhancement of anti-inflammatory cytokines [8]. In Parkinson’s disease models, PRE-084 administration normalized motor dysfunction and prevented dopaminergic neuron loss in both 6-hydroxydopamine and MPTP paradigms through sigma-1 receptor-mediated promotion of PINK1/Parkin mitophagy and enhancement of dopamine transporter expression [9, 10]. Cognitive and nootropic effects have been characterized across multiple paradigms: PRE-084 attenuated MK-801-induced amnesia, amyloid-beta peptide-induced learning impairment, and spatial learning deficits in aged rats, with mechanisms involving upregulation of NMDA receptor expression in the hippocampus and activation of the ERK/CREB/BDNF signaling axis [11, 12, 13]. Antidepressant-like activity has been demonstrated in the forced swim test in multiple mouse strains at doses of 30 to 60 mg/kg, with enhanced efficacy in amyloid-beta-treated animals [14, 15]. Additional preclinical applications include cardioprotection in myocardial ischemia-reperfusion injury, neuroprotection in perinatal excitotoxic brain injury, glial modulation in spinal muscular atrophy, protection against Huntington’s disease-associated cellular degeneration through NF-kappaB-mediated calpastatin upregulation, and attenuation of sepsis-associated encephalopathy [16, 17, 18, 19, 20]. Pharmacokinetic characterization in mice after intraperitoneal administration at 10 mg/kg reveals rapid central nervous system penetration (brain concentration 773.6 ng/g at five minutes), a plasma elimination half-life of approximately 195 minutes, and stability in biological matrices for at least 24 hours [2]. The compound is supplied as the hydrochloride salt by multiple research chemical vendors at greater than 98 percent purity and is reconstituted in aqueous solution or dimethyl sulfoxide for experimental use. This monograph reviews the chemistry, synthesis, and selectivity of PRE-084; the sigma-1 receptor chaperone pharmacology in molecular detail; the pharmacokinetic profile; the full preclinical evidence base across neurodegenerative, cerebrovascular, cognitive, affective, and cardioprotective domains; sourcing and quality verification; reconstitution and handling; stack interaction considerations; adverse event and safety signal from preclinical data; and a comparative assessment of five sigma-1 receptor candidates (SA4503/cutamesine, ANAVEX2-73/blarcamesine, pridopidine, igmesine, and fluvoxamine) against PRE-084 on five competency standards.

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  • Noopept

    Plain-language summaryIntrigue 70 / 100

    Noopept is a Russian-developed dipeptide nootropic that gets metabolized to cycloprolylglycine in the body. It supports BDNF and NGF expression and has memory-enhancing effects in animal studies at very low doses. Not stocked by Kodiac. This monograph is provided for research and educational reference.

    Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

    Synthetic dipeptide nootropic and neuroprotectant derived from cycloprolylglycine with AMPA receptor positive allosteric modulation and neurotrophic factor upregulation

    A proline-glycine dipeptide cognitive enhancer (GVS-111) developed at the Zakusov Institute of Pharmacology in Russia, distinguished from classical racetam nootropics by approximately 1000-fold greater mass potency, rapid conversion to the endogenous neuropeptide cycloprolylglycine, and a multifactorial mechanism encompassing AMPA receptor positive allosteric modulation, NMDA receptor modulation, NGF and BDNF upregulation, HIF-1 transcription factor activation, and neuroprotection against amyloid-beta toxicity and tau hyperphosphorylation.

    Abstract

    Noopept (INN: omberacetam; development code GVS-111; N-phenylacetyl-L-prolylglycine ethyl ester; CAS 157115-85-0; molecular formula C17H22N2O4; molecular weight 318.37 g/mol) is a synthetic dipeptide nootropic and neuroprotectant developed in the mid-1990s at the V.V. Zakusov Research Institute of Pharmacology of the Russian Academy of Medical Sciences by Tatyana Gudasheva, Rita Ostrovskaya, and Sergei Seredenin using a drug-based peptide design strategy that models the pyrrolidone ring of piracetam as the central element of a beta-turn dipeptide. The compound is approved in the Russian Federation (registration 2006) and several former Soviet states for the treatment of cognitive impairment of vascular and post-traumatic origin at oral doses of 10 to 30 mg per day, doses approximately 1000-fold lower by mass than the effective doses of piracetam (1200 to 4800 mg per day), its structural prototype. Noopept is not approved by the United States Food and Drug Administration, the European Medicines Agency, or the regulatory authorities of Japan, Australia, or Canada. It is sold internationally as a research-grade compound and as an unregulated dietary supplement in several jurisdictions.

    The pharmacological mechanism of noopept is multifactorial and operates through both the parent compound and its principal active metabolite, cycloprolylglycine (cyclo-L-prolylglycine, CPG), an endogenous brain dipeptide. The parent compound and CPG function as positive allosteric modulators of AMPA-subtype ionotropic glutamate receptors, increasing glutamate sensitivity without direct agonist binding. Noopept modulates NMDA receptor expression and function, upregulates the expression of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) in hippocampal and cortical neurons on chronic administration, activates the transcription factor hypoxia-inducible factor 1 (HIF-1) through inhibition of prolyl hydroxylase, and provides direct neuroprotection against amyloid-beta peptide toxicity, glutamate excitotoxicity, oxidative stress, and calcium overload in cellular and animal models. In Alzheimer’s disease cellular models, noopept attenuates tau hyperphosphorylation at Ser396 and reduces apoptosis through suppression of the mitochondrial apoptotic pathway.

    Pharmacokinetics in humans are characterized by rapid oral absorption (time to peak plasma concentration approximately 15 to 20 minutes), extensive first-pass metabolism yielding an oral bioavailability of approximately 10 percent relative to parenteral administration, rapid hydrolysis of the parent ester to the active metabolite cycloprolylglycine, and a short plasma half-life of the parent compound. The pharmacological effect persists for 3 to 6 hours after oral dosing, substantially longer than the plasma residence of the parent compound, consistent with the contribution of the longer-lived CPG metabolite and downstream transcriptional effects on neurotrophic factor expression. The compound does not appear to undergo significant cytochrome P450-mediated metabolism; the principal biotransformation is peptidase-mediated ester hydrolysis and amide cleavage.

    The clinical evidence base is concentrated in Russian-language literature and is modest by Western regulatory standards. The principal English-language clinical study is the Neznamov and Teleshova (2009) comparative trial of noopept (20 mg per day) and piracetam (1200 mg per day) in 53 patients with mild cognitive disorders of vascular and traumatic origin over 56 days, which demonstrated comparable cognitive improvement with a 1.8-fold lower incidence of adverse events in the noopept arm. Preclinical evidence is more extensive, spanning rodent models of ischemic brain injury, Alzheimer’s disease (both amyloid-beta infusion and transgenic models), traumatic brain injury, and age-related cognitive decline. The compound is well tolerated at recommended doses; the principal adverse events are sleep disturbance, irritability, and transient blood pressure elevation, all at low incidence. No serious adverse events have been reported in published clinical studies at doses up to 30 mg per day for periods up to 56 days. Long-term safety data beyond 56 days of continuous administration are not available.

    This monograph reviews the chemistry, synthesis, and structural pharmacology of noopept; the multifactorial mechanism of action including AMPA receptor modulation, NMDA receptor effects, neurotrophic factor upregulation, HIF-1 activation, and amyloid-beta neuroprotection; the pharmacokinetic profile with emphasis on the cycloprolylglycine metabolite; the preclinical pharmacology across ischemic, neurodegenerative, and traumatic models; the clinical evidence base; sourcing and quality verification; reconstitution and handling; stack interactions and combinations; adverse events and safety signal; and a comparative assessment of five nootropic alternatives (piracetam, aniracetam, phenylpiracetam, semax, and cerebrolysin) against noopept on five competency standards.

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  • GDF-11

    TGF-beta superfamily growth differentiation factor

    A growth differentiation factor in the TGF-beta superfamily originally implicated in parabiosis-mediated rejuvenation and subsequently a focus of contested replication studies in cardiac and skeletal muscle aging.

    Abstract

    GDF-11 (growth differentiation factor 11; bone morphogenetic protein 11, BMP-11; CAS 268544-12-9; mature peptide molecular weight approximately 12.5 kDa as a homodimer) is a member of the transforming growth factor beta (TGF-beta) superfamily, closely related to myostatin (GDF-8) with which it shares approximately 90 percent amino acid identity in the mature C-terminal domain. The compound came to prominence in 2013 when a heterochronic parabiosis study by Amy Wagers and Richard Lee at the Harvard Stem Cell Institute identified GDF-11 as a putative young-blood-borne rejuvenation factor that reversed age-related cardiac hypertrophy when administered to old mice. Subsequent studies extended the proposed rejuvenation activity to skeletal muscle and the central nervous system. The original GDF-11 papers triggered substantial follow-up research and substantial contested replication: independent groups (notably the Glass laboratory at Eli Lilly and the Wagers laboratory’s own subsequent work) reported that the original immunoassays did not adequately distinguish GDF-11 from myostatin, that circulating GDF-11 levels do not in fact decline with age, and that recombinant GDF-11 administered to old mice produces muscle wasting at high doses (consistent with the myostatin-like activity expected from the structural homology) rather than rejuvenation. The contested literature has not produced consensus; some groups continue to report modest pro-cardiac and pro-cognitive effects of GDF-11 at carefully titrated doses, while others find no effect or harmful effects. Mechanism is canonical TGF-beta superfamily signaling through ActRIIA/B receptors and downstream SMAD2/3 transcription factor activation; GDF-11 and myostatin share the same receptor and signaling pathway, distinguishing them principally through tissue-specific expression patterns and post-translational propeptide regulation. The compound is research-grade with no regulatory approval and no active clinical development. Investigators studying GDF-11 should be aware of the contested replication literature and the importance of distinguishing GDF-11 from myostatin in immunoassays.

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