salvage pathway raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2026-08-01. Anything still debated is marked as such rather than presented as settled.
Laboratory handling of NAD+ follows standard practices for hygroscopic fine chemicals. Personnel typically avoid inhalation and skin contact, use gloves and eye protection, and work in a ventilated area. Quality control may include ultraviolet absorbance at the nicotinamide maximum, chromatographic purity, water content, and identity confirmation by mass spectrometry. Because commercial preparations can contain counterions, residual solvents, or related nucleotides, a certificate of analysis helps verify the material. Researchers should confirm that the form supplied matches the intended assay.
Measuring NAD+ in biological samples requires care because the molecule is chemically reactive and present at low concentrations in some tissues. Common approaches include enzymatic cycling assays, high-performance liquid chromatography, and liquid chromatography coupled to mass spectrometry. Each method has different sensitivity and specificity, and sample preparation can affect results. Acidic or alkaline extraction steps are used in some protocols, but the choice depends on the analyte and matrix. No single method is universally optimal for every tissue or fluid.
Solid NAD+ is relatively stable when kept dry, cold, and protected from light. Aqueous solutions are more vulnerable to hydrolysis and can lose activity during repeated freeze-thaw cycles or prolonged storage at ambient temperature. Stability depends on pH, ionic strength, and the presence of degrading enzymes or metal ions. For many laboratory uses, aliquots are stored frozen and thawed only once. Exact degradation rates vary by matrix, so stability should be checked for each application rather than assumed.
Commercial NAD+ is available at research grade, often with purity specifications determined by high-performance liquid chromatography. Certificates of analysis may report water content, residual solvents, and counterion identity. Identity can be confirmed by ultraviolet absorbance near 260 nm, mass spectrometry, or enzymatic activity. Because different salt forms and hydration states exist, researchers should verify that the product matches the intended molecular form. Lot-to-lot variation in purity can affect quantitative assays and should be documented.
Solid NAD+ is usually supplied as a white to off-white powder or lyophilized preparation. It is hygroscopic and should be kept desiccated at low temperature, commonly -20 °C or below for long-term storage. Aqueous solutions are less stable than dry material and are often prepared fresh or stored frozen in aliquots. Light exposure and repeated freeze-thaw cycles can promote degradation, so amber containers and single-use aliquots are preferred. Buffered solutions near neutral pH are generally less stable than acidic or frozen preparations.
Quantification of NAD+ in biological samples typically uses liquid chromatography coupled to mass spectrometry. Enzymatic cycling assays offer higher throughput and rely on NAD+ dependent dehydrogenases to amplify signal. Both approaches require careful sample quenching because NAD+ can be rapidly consumed or converted after collection. Acidic extraction is common for NAD+, while alkaline conditions favor NADH in some protocols. Isotopically labeled internal standards help correct for losses during extraction and ionization.
| Property | Value | Notes |
|---|---|---|
| UV absorbance maximum | ~259 nm | Nicotinamide ring; spectrum depends on pH. |
| Primary analytical method | LC-MS | Separates and identifies nucleotides with high specificity. |
| Alternative method | Enzymatic cycling | Amplifies signal for low-abundance samples. |
| Typical storage | −20 °C or below | Dry powder, desiccated and protected from light. |
| Degradation products | Nicotinamide and ADP-ribose | Hydrolysis products can interfere with assays. |
Stability studies show that NAD+ can hydrolyze under prolonged heat, extreme pH, or microbial contamination. Phosphate buffers near neutral pH are often used for short-term handling, though exact stability depends on concentration, temperature, and matrix. In biological samples, endogenous enzymes can rapidly degrade NAD+, making cold chain and fast processing important. Analytical reports should state extraction conditions, internal standards, and validation parameters. Without those details, comparisons across studies remain difficult and potentially misleading.
Laboratory measurement of NAD+ often begins with rapid quenching of cell or tissue samples to prevent enzymatic conversion. Acidic or alkaline extraction can precipitate proteins, but the chosen method affects recovery of oxidized and reduced forms. Enzymatic cycling assays provide high sensitivity by amplifying a NAD+-dependent reaction. High-performance liquid chromatography and mass spectrometry offer separation and structural confirmation. Each method has trade-offs in throughput, specificity, and the ability to distinguish NAD+ from close analogues.
Purified NAD+ is typically supplied as a white to off-white powder and stored desiccated at low temperature. Airtight containers limit moisture uptake, while protection from light reduces degradation of the nicotinamide ring. Aqueous stock solutions are less stable than solid material and are often aliquoted before freezing. Repeated freeze-thaw cycles can lower integrity, so working portions are kept separate. Purity is commonly checked by ultraviolet absorbance near 260 nm, high-performance liquid chromatography, or mass spectrometry.
Beyond redox chemistry, NAD+ acts as a substrate for several enzyme families. ADP-ribosyltransferases, sirtuins, and CD38 ectoenzymes cleave the molecule into nicotinamide and ADP-ribose or related products. These reactions connect NAD+ availability to processes such as DNA repair, chromatin modification, and calcium signaling. Because the coenzyme is used in both electron transfer and signaling, cells maintain separate pools in compartments including the cytosol, mitochondria, and nucleus. The relative sizes and regulation of those pools remain active areas of study.
Cells produce NAD+ through several biosynthetic routes. The salvage pathway recycles nicotinamide, while the Preiss-Handler pathway uses nicotinic acid, and a de novo route can start from tryptophan in some organisms. In mammals, the salvage pathway is generally considered the main source under ordinary conditions. Tissue concentrations vary widely by cell type and compartment, and measured declines with age have been reported in some studies. Whether such changes drive aging or mainly accompany it remains an open question.
Nicotinamide adenine dinucleotide, commonly abbreviated NAD+, is a coenzyme present in all living cells. The molecule consists of two nucleotides linked by phosphate groups, with adenine and a nicotinamide ring as its principal features. In its oxidized form, the nicotinamide ring can accept a hydride ion, becoming NADH. This reversible conversion places NAD+ at the center of many electron-transfer reactions. Its role as a redox carrier is well established across bacteria, plants, fungi, and animals.
Beyond electron transfer, NAD+ serves as a substrate for enzymes that cleave the molecule and transfer ADP-ribose units. Sirtuins, poly(ADP-ribose) polymerases, and CD38 consume NAD+ in regulatory reactions. These activities link NAD+ availability to DNA repair, chromatin modification, calcium signaling, and metabolic stress responses. Because consumption can exceed biosynthesis under some conditions, cellular NAD+ levels are dynamic rather than fixed. Enzyme affinity and local synthesis also influence how much NAD+ is available for signaling.
NAD+ is a dinucleotide composed of adenine, ribose, and nicotinamide moieties linked by phosphate groups. Its oxidized form carries a positive charge on the nicotinamide ring, which enables reversible hydride transfer. The molecule functions as a coenzyme in oxidoreductase reactions rather than as a dietary vitamin in its intact form. Cells maintain separate pools in cytoplasm, mitochondria, and nucleus. This compartmentalization allows distinct redox environments while preserving a shared chemical identity.
Beyond redox catalysis, NAD+ is a substrate for enzymes that transfer ADP-ribose or remove acetyl groups from proteins. Sirtuins and poly(ADP-ribose) polymerases consume NAD+ and release nicotinamide as a byproduct. These reactions connect cellular energy status to gene regulation, DNA repair, and stress responses. Because NAD+ is used rather than merely recycled in such signaling, its concentration reflects both biosynthesis and consumption. The balance between salvage and de novo synthesis pathways determines available pools in different tissues.
Biosynthesis of NAD+ starts from nicotinamide, nicotinic acid, or nicotinamide riboside through salvage pathways. A rate-limiting enzyme, nicotinamide phosphoribosyltransferase, converts nicotinamide to nicotinamide mononucleotide. Further coupling with ATP yields NAD+. In mammals, the liver and muscle can synthesize NAD+ from dietary precursors, but tissue levels vary widely. Researchers study these pathways to understand age-related changes, metabolic disorders, and neurodegeneration. Direct causal links between NAD+ decline and disease remain an active area of investigation.
=== 10 February === Seventeen Russian missiles hit Zaporizhzhia in an hour. Other missiles hit Khmelnytskyi, Kharkiv and Dnipropetrovsk regions, targeting the power grid and forcing emergency blackouts. Valerii Zaluzhnyi said two Kalibr missiles launched from the Black Sea entered Moldovan airspace before re-entering Ukraine. The Defense Ministry of Moldova confirmed that a missile had crossed its airspace, and summoned the Russian ambassador. The Ukrainian government claimed to have shot down 61 of the 71 cruise missiles that Russian forces fired at Ukrainian targets, using a mixture of Kh-101, Kh-555 and Kalibr missiles; eight Tu-95 bombers were used as well as elements of the Black Sea fleet. 35 countries, including United States, Germany, and Australia, have demanded that Belarus and Russia be banned from the 2024 Paris Olympics due to the war in Ukraine. The IOC suggested that athletes from these countries could compete as "neutrals". Ukraine threatened to boycott the games if Russian athletes were allowed to compete. Celeste Wallander, United States Assistant Secretary of Defense for International Security Affairs, estimates that Russia had "likely" lost half of its main battle tanks, but was adapting to these losses. The Zatoka Bridge, in which it crosses the Dniester Estuary, was struck by "marine unmanned drones" according to Russian and Ukrainian media. It was filled with explosives, and footage released showed an explosion. The amount of damage inflicted was not released.
Research into automated cell counting began in the early 20th century. A method developed in 1928 used the amount of light transmitted through a diluted blood sample, as measured by photometry, to estimate the red blood cell count, but this proved inaccurate for samples with abnormal red blood cells. Other unsuccessful attempts, in the 1930s and 1940s, involved photoelectric detectors attached to microscopes, which would count cells as they were scanned. In the late 1940s, Wallace H. Coulter, motivated by a need for better red blood cell counting methods following the bombing of Hiroshima and Nagasaki, attempted to improve on photoelectric cell counting techniques. His research was aided by his brother, Joseph R. Coulter, in a basement laboratory in Chicago. Their results using photoelectric methods were disappointing, and in 1948, after reading a paper relating the conductivity of blood to its red blood cell concentration, Wallace devised the Coulter principle—the theory that a cell suspended in a conductive medium generates a drop in current proportional to its size as it passes through an aperture. That October, Wallace built a counter to demonstrate the principle. Owing to financial constraints, the aperture was made by burning a hole through a piece of cellophane from a cigarette package. Wallace filed a patent for the technique in 1949, and in 1951 applied to the Office of Naval Research to fund the development of the Coulter counter.
==== Smoking ==== Dry leaves can be smoked in a pipe, or through the use of a water pipe to cool the smoke. The temperature required to release salvinorin from the plant material is quite high (about 240 °C). A cooler flame will work, but the direct application of a more intense flame, such as that of a torch lighter, is often preferred. Some find that untreated dry leaf produces unnoticeable or only light effects. Concentrated preparations or extracts which may be smoked in place of untreated leaves, have become widely available. This enhanced (or "fortified") leaf is described by a number followed by an x (e.g. 5x, 10x), the multiplicative factors being generally indicative of the relative amounts of leaf concentrate, though there is no accepted standard for these claims. Other sources may use a system of color codes to form their own standards of potency; for example, "green", "yellow", and "red." These grades of potency may be roughly indicative of the relative concentration of the active principle, (salvinorin A), but the measure should not be taken as absolute. Overall extract potency will depend on the (naturally varying) strength of the untreated leaf used in preparing the extract, as well as the efficiency of the extraction process itself. Extracts reduce the overall amount of inhalations needed to ingest a given amount of active principle, thus facilitating more powerful experiences. If salvia is smoked, then the main effects are experienced quickly.
==== Selective androgen receptor modulator-like activity ==== Although bicalutamide has been characterized as a silent antagonist of the AR in prostate tissue and other contexts, and despite its overall antiandrogenic profile, there is evidence that the drug may activate the AR to some degree in certain other tissues, such as muscle and bone among others. This would make bicalutamide a selective androgen receptor modulator (SARM), or a tissue-selective mixed agonist/antagonist or partial agonist of the AR, with antiandrogenic effects in some tissues and androgenic effects in other tissues, rather than a pure antiandrogen. This would be similar to certain other SARMs structurally related to bicalutamide, like enobosarm, which in animals have potent anabolic effects in muscle and bone but show partially agonistic or antagonistic effects in the prostate or seminal vesicles. Bicalutamide has been found to not oppose testosterone-induced increases in levator ani muscle weight in immature castrated male rats at doses of the drug (e.g., 0.08–2 mg/kg) that reduce or even completely block testosterone-induced prostate gland and seminal vesicle growth. In other studies, higher doses of bicalutamide (e.g., 10–30 mg/kg) reduced levator ani muscle weight (by ~40% or more) in gonadally intact male rats but had no effect on lean body mass (a surrogate of muscle mass), whereas castration reduced levator ani weight by around 70% and lean body mass by around 25%.
Darren Keith McGuire, MD, MHSc is an American cardiologist and clinical trialist specializing in cardiovascular disease prevention and cardiometabolic medicine, particularly the relationship between diabetes and heart disease. He is a Distinguished Teaching Professor of Internal Medicine in the Division of Cardiology at the University of Texas Southwestern Medical Center. He also serves as lead physician of the Parkland Health cardiology clinics and holds the Jere H. Mitchell Distinguished Chair in Cardiovascular Science.
Sources: en.wikipedia.org
Chelation therapy is a medical procedure that involves the administration of chelating agents to remove or deactivate heavy metals from the body. Chelating agents are molecules that form particularly stable coordination complexes with metal ions. Complexation prevents the metal ions from reacting with molecules in the body, and enable them to be dissolved in blood and eliminated in urine.
== Mechanism of action == Blasticidin prevents the growth of both eukaryotic and prokaryotic cells. It works by inhibiting termination step of translation and peptide bond formation (to lesser extent) by the ribosome. This means that cells can no longer produce new proteins through translation of mRNA. It is competitive with puromycin suggesting a highly similar binding site.
=== Biochemical applications === In general, SEC is considered a low-resolution chromatography as it does not discern similar species very well, and is therefore often reserved for the final step of a purification. The technique can determine the quaternary structure of purified proteins that have slow exchange times, since it can be carried out under native solution conditions, preserving macromolecular interactions. SEC can also assay protein tertiary structure, as it measures the hydrodynamic volume (not molecular weight), allowing folded and unfolded versions of the same protein to be distinguished. For example, the apparent hydrodynamic radius of a typical protein domain might be 14 Å and 36 Å for the folded and unfolded forms, respectively. SEC allows the separation of these two forms, as the folded form elutes much later due to its smaller size.
This article was submitted to WikiJournal of Medicine for external academic peer review in 2021 (reviewer reports). The updated content was reintegrated into the Wikipedia page under a CC-BY-SA-3.0 license (2021). The version of record as reviewed is: Kholhring Lalchhandama; et al. (2021). "History of penicillin" (PDF). WikiJournal of Medicine. 8 (1): 3. doi:10.15347/wjm/2021.003. Wikidata Q107303937.
Signs of androgen excess, either clinical (visible signs such as facial hair or acne) or biochemical (detected through a blood test). Androgens are "male" hormones like testosterone. Irregular or absent menstrual cycles Polycystic ovaries on ultrasound or high levels of anti-Müllerian hormone (AMH) Other causes of these issues need to be excluded for diagnosis. In adolescents, both androgen excess and irregular or absent periods are required, as it is normal for adolescents to have many follicles ("cysts") visible in their ovaries, so it does not help with diagnosis. Adolescents who only meet one criterion are considered 'at risk', and are to be reassessed when they are adults. Older criteria are the 1990 NIH criteria and the 2006 Androgen Excess Society criteria. The Androgen Excess Society criteria were never widely adopted. The old NIH criteria are stricter than the Rotterdam criteria, as both infrequent or irregular cycles and signs of androgen excess need to be present:
Sources: en.wikipedia.org
Common laboratory methods include enzymatic cycling, high-performance liquid chromatography, and liquid chromatography with mass spectrometry. The choice depends on sample type, expected concentration, and available equipment.
Frozen storage slows hydrolysis and other degradation reactions that occur more quickly in solution at warmer temperatures. Dry powder is generally more stable than aqueous solutions, which can lose activity over time.
Purity tests can reveal related nucleotides, water content, counterions, and other impurities that may affect an experiment. They do not by themselves establish biological activity or suitability for a specific assay.
Aqueous NAD+ solutions are best kept frozen in aliquots and protected from light. Repeated freezing and thawing is avoided because it can accelerate breakdown. Dry powder stored desiccated at -20 °C or lower typically remains stable for longer periods.