mass spectrometry raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2025-12-26 and is reviewed periodically as new material appears.
Proposed mechanisms centre on modulation of the GABAergic system, with reports of altered expression of genes related to GABA-A receptor subunits and changed monoamine turnover. Some studies describe inhibition of enkephalinase, the enzyme that degrades endogenous enkephalins, which may prolong opioid peptide signalling. Effects on brain-derived neurotrophic factor and on cytokine expression have also been reported. These findings come largely from animal models and small human studies, and the precise primary target remains unresolved.
Published clinical evidence is limited. Most controlled trials were conducted in Russia, enrolled modest numbers of participants, and appeared in Russian-language journals, which restricts independent verification. Reported outcomes include lower anxiety scores, improved attention and memory measures, and changes in fatigue ratings. Reviews written in English note methodological limitations such as small samples and inconsistent endpoints. Whether the compound produces clinically meaningful benefit relative to established anxiolytics is therefore an open question rather than an established finding.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. It was designed at the Institute of Molecular Genetics of the Russian Academy of Sciences as a structural analogue of tuftsin, a naturally occurring tetrapeptide fragment of the immunoglobulin heavy chain. The added Pro-Gly-Pro tail was intended to slow enzymatic degradation and extend biological activity. In Russia it is registered as an anxiolytic nasal preparation, while regulators elsewhere have not approved it for clinical use.
Proposed mechanisms center on modulation of the GABA system, but no single molecular target has been confirmed. Rodent studies report changes in GABA-A receptor expression and in the turnover of serotonin, dopamine, and norepinephrine in several brain regions. Increases in brain-derived neurotrophic factor and its receptor have also been described after repeated administration. These findings come largely from animal models, and the degree to which they describe human neurochemistry remains an open question. The mechanism is best characterized as multi-system and not fully resolved.
Pharmacokinetic data are limited. Like most short peptides, Selank is vulnerable to plasma and tissue peptidases, and its measured half-life in circulation is short, on a minutes scale. The Pro-Gly-Pro tail slows this degradation but does not eliminate it. Intranasal administration is the route described in most reports, with absorption through the nasal mucosa and a hypothesized path into the central nervous system that avoids the blood-brain barrier. Direct measurements of human brain exposure are unavailable, so distribution claims rest on inference from animal work.
Clinical evidence comes mainly from small studies conducted in Russia, several of which were open-label or lacked robust blinding. Reported outcomes include lower anxiety scores, changes in attention measures, and effects on asthenic states following illness. Sample sizes are typically in the tens of participants, and independent replication outside the region is scarce. Reviews published in English generally note the limited methodological quality of the underlying trials. Whether the compound produces clinically meaningful effects under rigorous conditions remains unresolved.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C33H57N11O9 | Free peptide form |
| Molecular mass | About 751.9 Da | Calculated average mass |
| Amino acid sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Single-letter form TKPRPGP |
| Structural basis | Tuftsin analogue | Extended version of a natural tetrapeptide |
| Development origin | Russian Academy of Sciences | Work carried out from the 1980s onward |
Once dissolved, the peptide is markedly less stable than the dry powder. Aqueous solutions are subject to backbone hydrolysis and to microbial growth when they are handled without sterile technique. Buffered solutions near neutral pH are common for short-term laboratory work, while acidic conditions are sometimes used to improve solubility. Analytical laboratories generally prepare working solutions fresh rather than storing them, and a residual water film left in a reopened vial can seed degradation even when the container appears dry.
Reversed-phase high-performance liquid chromatography is the standard technique for estimating peptide purity. The result is a peak-area percentage, which describes how much of the detected material elutes as the main peak in one run. Mass spectrometry confirms the molecular mass and can reveal truncated, adducted, or otherwise modified species. Amino acid analysis or tandem mass spectrometry can address sequence fidelity when identity is in doubt. None of these measurements, taken alone, establishes that a sample is fit for any specific purpose.
Lyophilized selank is normally supplied as a dry powder and is considered stable for extended periods when kept cold and dry. Moisture uptake is the main practical threat, because absorbed water promotes both hydrolysis and aggregation in the solid state. Vials are usually warmed to room temperature before opening so that condensation does not form on the powder. Supplier documentation commonly specifies -20 °C for routine storage, with -80 °C used for material intended to be archived for years.
Solubility behavior is a practical concern for handling. Selank dissolves readily in water and in common aqueous buffers, which simplifies preparation of working solutions. The choice of solvent, ionic strength, and pH can influence aggregation over time, particularly at higher concentrations. Aqueous solutions are typically sterile-filtered before use. Because stability depends on several variables, storage and handling notes should be treated as general guidance rather than fixed rules, and specific values are best confirmed against a certificate of analysis for each batch.
Characterization of Selank in a laboratory setting relies on standard peptide methods. Reverse-phase high-performance liquid chromatography separates the target from related impurities and provides a purity figure, commonly reported as 95 percent or higher. Mass spectrometry, typically electrospray ionization or matrix-assisted laser desorption, confirms the molecular mass and helps detect truncation or modification. Amino acid analysis can verify composition when a sequence-level check is needed. These techniques together establish identity and purity for a given lot.
Lyophilized Selank, the dry powder form, is generally stored frozen at minus 20 degrees Celsius or colder for long-term keeping. The solid is hygroscopic and should stay sealed, dry, and protected from light. Once dissolved, the peptide is less stable and is usually held refrigerated at 2 to 8 degrees Celsius for short periods. Repeated freezing and thawing is avoided because it can promote aggregation and loss of activity. Buffers and pH choice also affect how long a solution remains usable.
Regulatory treatment varies by jurisdiction. In Russia the compound is a registered prescription product, while in the European Union and the United States it is generally handled as a research chemical without a marketing authorization. Suppliers therefore operate outside pharmaceutical oversight, and buyers rely on supplier documentation for purity and identity claims. Chain of custody and third-party testing are the main verification tools. Analysts note that the absence of a pharmacopoeial monograph for research-grade material limits standardization across vendors.
Purity assessment relies mainly on reverse-phase high-performance liquid chromatography with ultraviolet detection. Because the peptide lacks a strong chromophore, detection often uses backbone absorbance near 214 nm. Identity is confirmed by mass spectrometry, typically electrospray ionization or matrix-assisted laser desorption, comparing the measured mass against the expected value. Amino acid analysis can verify composition after acid hydrolysis. Diastereomer content and residual counterions are reported less often, although both can influence biological assays.
Last but not least, specific cleavage of poly (ADP-ribose) polymerase (PARP) and a decrease in pro-caspase9 and 3 were also induced by arenobufagin treatment. PARP is mainly involved in cell repair and programmed cell death. After treatment with arenobufagin, some cells make more autophagosomes and lysosomes, whereas other cells undergo apoptosis. Arenobufagin also leads to increased expression of LC3-II, Biclin1(initial vesicle formation), Atg5 (elongation and completion), Atg9, Atg16L1 and p62/SQSTM1, all proteins which induce autophagy. Blockers of autophagy increase the cytotoxic effect of arenobufagin. Addition of 3-MA increases the proportion of cells in which there in enlarged PARP cleavage and limited caspase-9 and caspase-3 cleavage. This indicates that autophagy pathways protect the cell against apoptosis by arenobufagin. It was hypothesized that arenobufagin may inhibit the PI3K/Akt pathway in controlling cell death and differentiation in response to external stimuli. It was found that arenobufagin inhibited the proteins Akt, PDK1 and PI3K, whereas it stimulated the PHEN-protein. It does this by altering the degree of phosphorylation. All these proteins are involved in the PI3/Akt pathway. Further down the pathway, arenobufagin indirectly inhibits the mTOR-protein, which is involved in apoptosis as well as in autophagy. The biotransformation of arenobufagin by Alternaria alternata leads to the following three metabolites: 3-oxo-arenobufagin (1a), ψ-bufarenogin (1b), and 3- oxo- ψ-bufarenogin (1c).
Topical solutions can be marketed as drops, rinses, or sprays, are generally of low viscosity, and often use alcohol or water in the base. These are usually a powder dissolved in alcohol, water, and sometimes oil; although a solution that uses alcohol as a base ingredient, as in topical steroids, can cause drying of the skin. There is significant variability among brands, and some solutions may cause irritation, depending on the preservative(s) and fragrances used in the base. Some examples of topical solutions are given below:
Holick helped develop the first clinical assays for 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, determined how vitamin D3 is made in the skin from sun exposure, and established how season, time of day, skin pigmentation, sunscreen use, and latitude influenced this vital cutaneous process. He established that the skin was not only the organ responsible for making vitamin D3 but was also a target tissue for its active form, 1,25-dihydroxyvitamin D3. He determined the extremely inhibitory effects of 1,25-dihydroxyvitamin D3 on keratinocyte proliferation and the promoting effects on differentiation, and translated these seminal observations by demonstrating that the topical application of 1,25-dihydroxyvitamin D3 and several of its analogs were effective for the treatment of psoriasis. He demonstrated that macrophages and prostate cells have the enzymatic machinery to produce 1,25-dihydroxyvitamin D3, and established that the extrarenal production of 1,25-dihydroxyvitamin D3 may play a crucial role not only in cancer prevention but also in regulating the immune system. He developed a vitamin D absorption test and demonstrated that vitamin D was bioavailable in orange juice, leading to fortification of juice products in the United States. He also used the test to demonstrate the major cause of vitamin D deficiency in obesity is sequestration of vitamin D in the fat. He helped perform dose escalation studies establishing how much vitamin D is required to maintain blood levels of 25-hydroxyvitamin D in the sufficient range for adults.
Sources: en.wikipedia.org
=== Structure determination === Incorporation of selenomethionine into proteins in place of methionine aids the structure elucidation of proteins by X-ray crystallography using single- or multi-wavelength anomalous diffraction (SAD or MAD). The incorporation of heavy atoms such as selenium helps solve the phase problem in X-ray crystallography. Incorporation is achieved with the help of a selenomethionine-tolerant microbial expression system: the recombinant DNA for the protein in question is put into a microbe, which is then given large amounts of selenomethionine.
903), Catanzaro was occupied by the Saracens, who founded an emirate and took the Arab name of قطنصار – Qaṭanṣār. An Arab presence is evidenced by findings at an eighth-century necropolis which had items with Arabic inscriptions. Around the 1050, Catanzaro rebelled against Saracen dominance and briefly returned to Byzantine control.
Henriksen states that ice-nine represents a collaboration between science and the military that, as with the atomic bomb, proves their "indifference to the fate of the human race", and the "inhuman and immoral results of [...] pure research". The book notes that the pure search for knowledge without "living human principles" as depicted in Cat's Cradle ultimately tarnishes science.
After neutrophils have finished phagocytosing and clearing the antigen at the end of the immune response, they undergo apoptosis, and macrophages are recruited from blood monocytes to help clear apoptotic debris. Macrophages also recruit other immune cells such as monocytes, dendritic cells, natural killer cells, basophils, eosinophils, and T cells through chemokines such as CCL2, CCL4, CCL5, CXCL8, CXCL9, CXCL10, and CXCL11. Along with dendritic cells, macrophages help activate natural killer (NK) cells through secretion of type I interferons (IFN-α and IFN-β) and IL-12. IL-12 acts with IL-18 to stimulate the production of proinflammatory cytokine interferon gamma (IFN-γ) by NK cells, which serves as an important source of IFN-γ before the adaptive immune system is activated. IFN-γ enhances the innate immune response by inducing a more aggressive phenotype in macrophages, allowing macrophages to more efficiently kill pathogens. Some of the T cell chemoattractants secreted by macrophages include CCL5, CXCL9, CXCL10, and CXCL11.
Sources: en.wikipedia.org
=== Mouse-human hybrid === A mouse-human hybrid is a genetically modified mouse whose genome has both mouse and human genes, thus being a murine form of a human-animal hybrid. For example, genetically modified mice may be born with human leukocyte antigen genes in order to provide a more realistic environment when introducing human white blood cells into them in order to study immune system responses. One such application is the identification of hepatitis C virus (HCV) peptides that bind to HLA, and that can be recognized by the human immune system, thereby potentially being targets for future vaccines against HCV.
=== Glutathione's impact on cellular balance, diseases, and drug development === Townsend's research has focused on the multifaceted role of glutathione and glutathione S-transferase (GST) in human disease, particularly their involvement in anti-cancer drug resistance, protein S-glutathionylation, and redox stress. She explored GSH's role in maintaining cellular balance, serving as a co-factor for enzymes, and influencing posttranslational modifications. This work emphasized GSH's crucial role in combating reactive oxygen species (ROS), implicated in diseases such as cancer, neurodegenerative diseases, cystic fibrosis (CF), HIV, and aging. Collaborating with Tew, she investigated the role of GSTs in the development of resistance to chemotherapy agents, proposing them as inhibitors of the MAP kinase pathway and potential therapeutic targets for various diseases, including neurodegenerative diseases, multiple sclerosis, and asthma. Her studies identified a role for GSTs as enzymatic mediators of S-glutathionylation of proteins. In her further research on cancer chemotherapy, she explored how cisplatin selectively kills proximal tubule cells, identified its metabolic pathway to a nephrotoxin, and showed that the metabolism in these cells is crucial for cisplatin-induced kidney damage, suggesting new targets for inhibition.
The United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances was adopted in 1988, entered into force on November 11, 1990, has been joined by 191 countries. The convention addressed concern over the rapid growth in international drug trafficking. According to the UNODC, it "provides comprehensive measures against drug trafficking, including provisions against money laundering and the diversion of precursor chemicals". The treaty essentially "criminalized the entire drug market chain, from cultivation/production to shipment, sale, and possession".
== Isotope vs. nuclide == A nuclide is a species of an atom with a specific number of protons and neutrons in the nucleus, for example, carbon-13 with 6 protons and 7 neutrons. Thus the terms are roughly the same, but the nuclide concept (referring to individual nuclear species) emphasizes nuclear properties over chemical properties, whereas the isotope concept (grouping all atoms of each element) emphasizes chemical over nuclear. The neutron number greatly affects nuclear properties, but its effect on chemical properties is negligible for most elements. Even for the lightest elements, whose ratio of neutron number to atomic number varies the most between isotopes, it usually has only a small effect although it matters in some circumstances (for hydrogen, the lightest element, the isotope effect is large enough to affect biology strongly). The term isotopes (originally also isotopic elements, now sometimes isotopic nuclides) is intended to imply comparison (like synonyms or isomers). For example, the nuclides 126C, 136C, 146C are isotopes (nuclides with the same atomic number but different mass numbers), but 4018Ar, 4019K, 4020Ca are isobars (nuclides with the same mass number). As the older and better-known term, isotope is however still used in some contexts where nuclide might be more appropriate, such as in nuclear technology and nuclear medicine.
=== Pharmacodynamics === Loratadine is a tricyclic antihistamine, which acts as a selective inverse agonist of peripheral histamine H1 receptors. The potency of second generation histamine antagonists is (from strongest to weakest) desloratadine (Ki 0.4 nM) > levocetirizine (Ki 3 nM) > cetirizine (Ki 6 nM) > fexofenadine (Ki 10 nM) > terfenadine > loratadine. However, the onset of action varies significantly and clinical efficacy is not always directly related to only the H1 receptor potency, as the concentration of free drug at the receptor must also be considered. Loratadine also shows anti-inflammatory properties independent of H1 receptors. The effect is exhibited through suppression of the NF-κB pathway, and by regulating the release of cytokines and chemokines, thereby regulating the recruitment of inflammatory cells.
Sources: en.wikipedia.org
It is a seven-amino-acid peptide, Thr-Lys-Pro-Arg-Pro-Gly-Pro, produced by chemical synthesis rather than extracted from biological tissue. Its design is based on tuftsin, a natural immunomodulatory tetrapeptide. The C-terminal Pro-Gly-Pro segment is a common stabilising motif in short regulatory peptides.
The core four residues correspond to tuftsin, which occurs naturally as part of immunoglobulin G. The full seven-residue sequence, however, is not a known endogenous peptide. It is a laboratory-designed analogue intended to combine tuftsin-like activity with greater resistance to breakdown.
No single receptor has been confirmed as the primary target. Reports describe involvement of the GABAergic system, interference with enkephalin degradation, and shifts in neurotrophic factor expression. Because these observations come from different models and assays, they have not yet been integrated into one accepted mechanism.
Reports describe effects on GABA-A receptor expression, monoamine turnover, and neurotrophic factor levels. These are proposed mechanisms drawn mainly from animal models. No single molecular target has been established.