Nootropics are drugs, supplements, and other substances that may improve cognitive function, particularly executive functions, memory, creativity, or motivation, in healthy individuals. While many substances are purported to improve cognition, research is at a preliminary stage as of 2019, and the effects of the majority of these agents are not fully determined.
Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal redox state of cells can cause toxic effects through the production of peroxides and free radicals that damage all components of the cell, including proteins, lipids, and DNA. Oxidative stress from oxidative metabolism causes base damage, as well as strand breaks in DNA. Base damage is mostly indirect and caused by reactive oxygen species (ROS) generated, e.g. O2− (superoxide radical), OH (hydroxyl radical) and H2O2 (hydrogen peroxide). Further, some reactive oxidative species act as cellular messengers in redox signaling. Thus, oxidative stress can cause disruptions in normal mechanisms of cellular signaling.
Neuroprotection refers to the relative preservation of neuronal structure and/or function. In the case of an ongoing insult the relative preservation of neuronal integrity implies a reduction in the rate of neuronal loss over time, which can be expressed as a differential equation. It is a widely explored treatment option for many central nervous system (CNS) disorders including neurodegenerative diseases, stroke, traumatic brain injury, spinal cord injury, and acute management of neurotoxin consumption. Neuroprotection aims to prevent or slow disease progression and secondary injuries by halting or at least slowing the loss of neurons. Despite differences in symptoms or injuries associated with CNS disorders, many of the mechanisms behind neurodegeneration are the same. Common mechanisms include increased levels in oxidative stress, mitochondrial dysfunction, excitotoxicity, inflammatory changes, iron accumulation, and protein aggregation. Of these mechanisms, neuroprotective treatments often target oxidative stress and excitotoxicity—both of which are highly associated with CNS disorders. Not only can oxidative stress and excitotoxicity trigger neuron cell death but when combined they have synergistic effects that cause even more degradation than on their own. Thus limiting excitotoxicity and oxidative stress is a very important aspect of neuroprotection. Common neuroprotective treatments are glutamate antagonists and antioxidants, which aim to limit excitotoxicity and oxidative stress respectively.
Human enhancement (HE) can be described as the natural, artificial, or technological alteration of the human body in order to enhance physical or mental capabilities.
Xaliproden is a drug which acts as a 5HT1A agonist. It has neurotrophic and neuroprotective effects in vitro, and has been proposed for use in the treatment of several neurodegenerative conditions including amyotrophic lateral sclerosis (ALS) and Alzheimer's disease.
SCH-58261 is a drug which acts as a potent and selective antagonist for the adenosine receptor A2A, with more than 50x selectivity for A2A over other adenosine receptors. It has been used to investigate the mechanism of action of caffeine, which is a mixed A1 / A2A antagonist, and has shown that the A2A receptor is primarily responsible for the stimulant effects of caffeine, but blockade of both A1 and A2A receptors is required to accurately replicate caffeine's effects in animals. SCH-58261 has also shown antidepressant and neuroprotective effects in a variety of animal models, and has been investigated as a possible treatment for Parkinson's disease.
Taltirelin is a thyrotropin-releasing hormone (TRH) analog, which mimics the physiological actions of TRH, but with a much longer half-life and duration of effects, and little development of tolerance following prolonged dosing. It has nootropic, neuroprotective and analgesic effects.
Zacopride is a potent antagonist at the 5-HT3 receptor and an agonist at the 5-HT4 receptor. It has anxiolytic and nootropic effects in animal models, with the (R)-(+)-enantiomer being the more active form. It also has antiemetic and pro-respiratory effects, both reducing sleep apnea and reversing opioid-induced respiratory depression in animal studies. Early animal trials have also revealed that administration of zacopride can reduce preference for and consumption of ethanol.
Neramexane is a drug related to memantine, which acts as an NMDA antagonist and has neuroprotective effects. It is being developed for various possible applications, including treatment of tinnitus, Alzheimer's disease, drug addiction and as an analgesic. Animal studies have also suggested antidepressant and nootropic actions, so there are a wide range of potential applications this drug may be used for. It also acts as a nicotinic acetylcholine receptor antagonist.
Leteprinim is a hypoxanthine derivative drug with neuroprotective and nootropic effects. It stimulates release of nerve growth factors and enhances survival of neurons in the brain, and is under development as a potential treatment for neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and stroke.
Icariin is a chemical compound classified as a prenylated flavonol glycoside, a type of flavonoid. It is the 8-prenyl derivative of kaempferol 3,7-O-diglucoside. The compound has been isolated from several species of plant belonging to the genus Epimedium which are commonly known as Horny Goat Weed or Yin Yang Huo. Extracts from these plants are reputed to produce aphrodisiac effects, and are used in traditional Chinese medicine to enhance erectile function.
SB-399885 is a drug which is used in scientific research. It acts as a potent, selective and orally active 5-HT6 receptor antagonist, with a Ki of 9.0nM. SB-399885 and other 5-HT6 antagonists show nootropic effects in animal studies, as well as antidepressant and anxiolytic effects which are comparable to and synergistic with drugs such as imipramine and diazepam, and have been proposed as potential novel treatments for cognitive disorders such as schizophrenia and Alzheimer's disease.
SB-271046 is a drug which is used in scientific research. It was one of the first selective 5-HT6 receptor antagonists to be discovered, and was found through high-throughput screening of the SmithKline Beecham Compound Bank using cloned 5-HT6 receptors as a target, with an initial lead compound being developed into SB-271046 through a structure-activity relationship (SAR) study. SB-271046 was found to be potent and selective in vitro and had good oral bioavailability in vivo, but had poor penetration across the blood–brain barrier, so further SAR work was then conducted, which led to improved 5-HT6 antagonists such as SB-357,134 and SB-399,885.
3-( ethynyl)pyridine (MTEP) is a research drug that was developed by Merck & Co. as a selective allosteric antagonist of the metabotropic glutamate receptor subtype mGluR5. Identified through structure-activity relationship studies on an older mGluR5 antagonist MPEP, MTEP has subsequently itself acted as a lead compound for newer and even more improved drugs.
S-18986 is a positive allosteric modulator of the AMPA receptor related to cyclothiazide. It has nootropic and neuroprotective effects in animal studies, and induces both production of BDNF and AMPA-mediated release of noradrenaline and acetylcholine in the hippocampus and frontal cortex of the brain.
Aceglutamide, or aceglutamide aluminum, also known as acetylglutamine, is a psychostimulant, nootropic, and antiulcer agent that is marketed in Spain and Japan. It is an acetylated form of the amino acid L-glutamine, the precursor of glutamate in the body and brain. Aceglutamide functions as a prodrug to glutamine with improved potency and stability.
Solanum anguivi is a plant indigenous to non-arid parts of Africa, and is commonly known as Forest Bitterberry or African Eggplant, although the latter moniker is most commonly associated with Solanum aethiopicum.
Bacopasides are triterpene saponins isolated from Bacopa monnieri.
