A practical reference on sirtuins: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-06-14. Anything still debated is marked as such rather than presented as settled.
Research on NAD+ spans biochemistry, aging biology, and metabolism. Studies often examine how NAD+ levels change with age, diet, exercise, or disease states, and whether precursor supplementation alters those levels. Findings in animal models do not automatically translate to humans, and measurement methods vary across studies. Questions about tissue-specific effects, long-term consequences, and causal relationships remain open. NAD+ itself is not established as a single therapeutic agent with a broad clinical role.
Nicotinamide adenine dinucleotide, abbreviated NAD+, is a dinucleotide composed of two nucleotides joined by phosphate groups. One nucleotide contains adenine; the other contains nicotinamide. The molecule exists in oxidized (NAD+) and reduced (NADH) forms, and the reversible hydride transfer between them underlies many metabolic oxidation-reduction reactions. In cells, NAD+ serves as an electron acceptor in pathways such as glycolysis, the citric acid cycle, and oxidative phosphorylation. Its concentration and redox ratio vary by compartment, tissue, and metabolic state.
Beyond redox chemistry, NAD+ is consumed as a substrate by enzymes that transfer ADP-ribose or remove acetyl groups. Sirtuins use NAD+ in deacylation reactions, poly(ADP-ribose) polymerases use it in DNA damage responses, and CD38 hydrolases convert it to signaling metabolites. Because these enzymes compete for the same pool, changes in NAD+ availability can influence multiple cellular processes. The relative contribution of each consumption route differs by cell type and condition, and precise quantitative links remain an active area of study.
Beyond redox chemistry, NAD+ serves as a substrate for enzymes that transfer ADP-ribose or remove acetyl groups. Sirtuins, PARPs, and CD38-family enzymes consume NAD+ and produce nicotinamide and ADP-ribose-related products. These reactions link NAD+ availability to DNA repair, chromatin modification, and cellular signaling. Because the molecule is central to energy metabolism and regulation, changes in its concentration are studied in aging, immunity, and metabolic research. The balance between synthesis and consumption varies by tissue, developmental stage, and physiological state.
In humans, NAD+ can be synthesized from nicotinic acid, nicotinamide, nicotinamide riboside, and tryptophan through overlapping pathways. The salvage pathway recycles nicotinamide back to NAD+ and is often considered a major route in many tissues. Dietary precursors and intracellular recycling both contribute to the pool, but the quantitative importance of each source remains an active research question. NAD+ levels are not uniform across organs or cell compartments. Measurements in blood do not necessarily reflect concentrations inside tissues.
| Property | Value | Notes |
|---|---|---|
| Chemical formula | C21H27N7O14P2 | Free acid form; salt and hydrate forms differ in mass. |
| Molar mass | 663.43 g/mol | Anhydrous free acid; counterions and water change the value. |
| Appearance | White to off-white powder | Typical solid reagent; exact color varies by purity and form. |
| Solubility class | Highly water-soluble | Aqueous solutions are acidic; organic solubility is generally limited. |
| Common synonyms | DPN, coenzyme I, NAD | Older literature often uses diphosphopyridine nucleotide or DPN. |
Research on NAD+ often examines changes with age, diet, exercise, and disease states, but causal relationships are difficult to establish. Some studies measure NAD+ levels, while others assess enzyme activity or downstream markers. In the literature, terms such as "NAD+ decline" and "NAD+ boosting" appear in both scientific and commercial contexts, sometimes without precise definitions. Whether changes in measured NAD+ directly produce health effects remains an open question. Results from cells, animals, and humans cannot be assumed to translate directly.
Measuring NAD+ in biological samples requires rapid processing because the compound can degrade or interconvert after collection. Common approaches include enzymatic cycling assays, high-performance liquid chromatography, and mass spectrometry. Each method has different sensitivity, specificity, and susceptibility to interference from related nucleotides. Sample type matters: cultured cells, animal tissues, and human blood present distinct challenges. Reported values can vary widely across laboratories because of differences in extraction, normalization, and analytical platform. Standardization remains an open issue in the field.
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.
== Drug addiction == Family-based, adoption, and twin studies have indicated that there is a strong (50%) heritable component to vulnerability to substance abuse addiction. Especially among genetically vulnerable individuals, repeated exposure to a drug of abuse in adolescence or adulthood causes addiction by inducing stable downregulation or upregulation in expression of specific genes and microRNAs through epigenetic alterations. Such downregulation or upregulation has been shown to occur in the brain's reward regions, such as the nucleus accumbens.
=== Advanced treatment plant technology === For some emerging contaminants, several advanced technologies—sonolysis, photocatalysis, Fenton-based oxidation and ozonation—have treated pollutants in laboratory experiments. Another technology is "enhanced coagulation" in which the treatment entity would work to optimize filtration by removing precursors to contamination through treatment. In the case of THMs, this meant lowering the pH, increasing the feed rate of coagulants, and encouraging domestic systems to operate with activated carbon filters and apparatuses that can perform reverse osmosis. Although these methods are effective, they are costly, and there have been many instances of treatment plants being resistant to pay for the removal of pollution, especially if it wasn't created in the water treatment process as many EC's occur from runoff, past pollution sources, and personal care products. It is also difficult to incentivize states to have their own policies surrounding contamination because it can be burdensome for states to pay for screening and prevention processes. There is also an element of environmental injustice, in that lower income communities with less purchasing and political power cannot buy their own system for filtration and are regularly exposed to harmful compounds in drinking water and food. However, recent treads for light-based systems shows great potential for such applications. With the decrease in cost of UV-LED systems and growing prevalence of solar powered systems, it shows great potential to remove CEC while keeping costs low.
=== Pharmacokinetics === Bimatoprost is well absorbed through the cornea. It starts lowering intraocular pressure after four hours, lasting for at least 24 hours. A low percentage enters the bloodstream. In the blood plasma, peak concentrations are reached after 10 minutes, then drop below the detection limit of 25 pg/ml after 1.5 hours. The substance does not accumulate in the body. Plasma protein binding is 88%. Bimatoprost is metabolized by oxidation, N-deethylation and glucuronidation, forming a variety of metabolites. Biological half-life was measured to be 45 minutes after intravenous infusion. 67% are eliminated via the kidney, and 25% via the feces.
== Legality, ethics and politics == The results of federally mandating drug testing were similar to the effects of simply extending to the trucking industry the right to perform drug tests, and it has been argued that the latter approach would have been as effective at lower cost. Psychologist Tony Buon has criticized the use of workplace drug testing on a number of grounds, including:
Sources: en.wikipedia.org
Portal is a series of first-person puzzle-platform video games developed by Valve. Set in the Half-Life universe, the two main games in the series, Portal (2007) and Portal 2 (2011), center on a woman, Chell, who is forced to undergo a series of tests within the Aperture Science Enrichment Center by a malicious artificial intelligence, GLaDOS, that controls the facility. Most of the tests involve using the "Aperture Science Handheld Portal Device" – nicknamed the portal gun – that creates a human-sized, wormhole-like connection between two flat surfaces. The player-character or objects in the game world may move through portals while conserving their momentum. This allows complex "flinging" maneuvers to be used to cross wide gaps or perform other feats to reach the exit for each test chamber. A number of other mechanics, such as lasers, light bridges, high energy pellets, buttons, cubes, tractor funnels and turrets, exist to aid or hinder the player's goal to reach the exit. The Portal games originated through bringing students and their projects from the DigiPen Institute of Technology into Valve and expanding upon the ideas in Valve's Source engine. The concept was introduced by the game Narbacular Drop, which became the basis for the first game. Another DigiPen game, Tag: The Power of Paint, formed the basis of the "Mobility gels" introduced in Portal 2. Both games have received near-universal praise and have sold millions of copies. The first game was released as part of a five-game compilation, The Orange Box.
== Further reading == Insulin Basics for Diabetes American Diabetes Association (diabetes.org). Retrieved 2026-04-27. Insulin, Medicines, & Other Diabetes Treatments". National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Retrieved 2026-04-27.
In April 2012, the Xinjiang Border Defense Corps Female Special Service team (新疆公安边防总队女子特勤分队) was founded. In March 2015 it was renamed to the "Snowy Eagle Female Special Service team" (雪鹰女子特勤分队) at the Xinjiang Border Corps Training Base. At its founding in 2012, it only had 6 members, and by March 2015 it had 34 members. It assisted in security at the China Eurasia Expo multiple times. The Shenzhen Border Defense Detachment operated the Maritime Special Service Team (Nicknamed "Maritime Jiaolongs"), a police tactical unit which is dedicated to maritime anti-terrorism, search and rescue, combat diving and VBSS.
=== Post-mortem === After fatal accidents, it is common to check the blood alcohol levels of involved persons. Soon after death, however, the body begins to putrefy, a biological process that produces ethanol. This can make it difficult to conclusively determine the blood alcohol content in autopsies, particularly in bodies recovered from water. For instance, following the 1975 Moorgate tube crash, the driver's kidneys had a blood alcohol concentration of 80 mg/100 mL, but it could not be established how much of this could be attributed to natural decomposition. Newer research has shown that vitreous (eye) fluid provides an accurate estimate of blood alcohol concentration that is less subject to the effects of decomposition or contamination.
== History == Octreotide acetate was approved for use in the United States in 1988. In January 2020, approval of octreotide acetate in the United States was granted to Sun Pharmaceutical under the brand name Bynfezia Pen for the treatment of:
Sources: en.wikipedia.org
=== Fleet telematics and remote monitoring === Refrigerated trucks, railcars, and reefer containers are typically equipped with advanced fleet telematics systems. A telematic control unit installed in the vehicle or container serves as the central hub for data collection. Unlike standard systems, these units often interface directly with the refrigeration unit's microprocessor, allowing for two-way communication. This enables dispatchers and fleet managers to not only receive data but also remotely adjust settings, such as the temperature setpoint. The specialized telemetry data transmitted in real-time is crucial for cold chain oversight. This includes:
The inner workings of The Culture are not especially described in detail though it is shown that the society is populated by an empowered, educated and augmented citizenry in a direct democracy or highly democratic and transparent system of self-governance. In comparisons to the real world, intended or not, the Culture could resemble various posited egalitarian societies including in the writings of Karl Marx, the end condition of communism after a withering away of the state, the anarchism of Bakunin and Fourier et al., libertarian socialism, council communism and anarcho-communism. Other characteristics of The Culture that are recognisable in real world politics include pacifism, post-capitalism, and transhumanism. Banks deliberately portrayed an imperfect utopia whose imperfection or weakness is related to its interaction with the 'other', that is, exterior civilisations and species that are sometimes variously warred with or mishandled through the Culture's Contact section which cannot always control its intrigues and the individuals it either 'employs' or interacts with. This 'dark side' of The Culture also alludes to or echoes mistakes and tragedies in 20th century Marxist–Leninist countries, although the Culture is generally portrayed as far more 'humane' and just.
It is not always distinguished from hematoidin, which one modern dictionary defines as synonymous with it but another defines as "apparently chemically identical with bilirubin but with a different site of origin, formed locally in the tissues from hemoglobin, particularly under conditions of reduced oxygen tension." The synonymous identity of bilirubin and hematoidin was confirmed in 1923 by Fischer and Steinmetz using analytical crystallography. In the 1930s, significant advances in bilirubin isolation and synthesis were described by Hans Fischer, Plieninger, and others, and pioneering work pertaining to endogenous formation of bilirubin from heme was likewise conducted in the same decade. The suffix IXα is partially based on a system developed Fischer, which means the bilin's parent compound was protoporphyrin IX cleaved at the alpha-methine bridge (see protoporphyrin IX nomenclature). Origins pertaining to the physiological activity of bilirubin were described by Ernst Stadelmann in 1891, who may have observed the biotransformation of infused hemoglobin into bilirubin possibly inspired by Ivan Tarkhanov's 1874 works. Georg Barkan suggested the source of endogenous bilirubin to be from hemoglobin in 1932. Plieninger and Fischer demonstrated an enzymatic oxidative loss of the alpha-methine bridge of heme resulting in a bis-lactam structure in 1942. It is widely accepted that Irving London was the first to demonstrate endogenous formation of bilirubin from hemoglobin in 1950, and Sjostrand demonstrated hemoglobin catabolism produces carbon monoxide between 1949 and 1952.
Inorganic elements play critical roles in metabolism; some are abundant (e.g. sodium and potassium) while others function at minute concentrations. About 99% of a human's body weight is made up of the elements carbon, nitrogen, calcium, sodium, chlorine, potassium, hydrogen, phosphorus, oxygen and sulfur. Organic compounds (proteins, lipids and carbohydrates) contain the majority of the carbon and nitrogen; most of the oxygen and hydrogen is present as water. The abundant inorganic elements act as electrolytes. The most important ions are sodium, potassium, calcium, magnesium, chloride, phosphate and the organic ion bicarbonate. The maintenance of precise ion gradients across cell membranes maintains osmotic pressure and pH. Ions are also critical for nerve and muscle function, as action potentials in these tissues are produced by the exchange of electrolytes between the extracellular fluid and the cell's fluid, the cytosol. Electrolytes enter and leave cells through proteins in the cell membrane called ion channels. For example, muscle contraction depends upon the movement of calcium, sodium and potassium through ion channels in the cell membrane and T-tubules. Transition metals are usually present as trace elements in organisms, with zinc and iron being most abundant of those. Metal cofactors are bound tightly to specific sites in proteins; although enzyme cofactors can be modified during catalysis, they always return to their original state by the end of the reaction catalyzed.
Sources: en.wikipedia.org
NAD+ is a coenzyme found in all living cells. It carries electrons in metabolic reactions and also serves as a substrate for enzymes involved in signaling and DNA repair. Its oxidized and reduced forms are central to energy metabolism.
NAD+ is the oxidized form and NADH is the reduced form. The pair accepts and donates electrons in redox reactions. Their ratio helps indicate the metabolic state of a cell or compartment.
No. Nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) are precursors that cells can convert into NAD+. They are distinct molecules with different absorption and metabolism profiles.
The plus sign indicates the oxidized form of nicotinamide adenine dinucleotide, which can accept electrons. When it accepts electrons, it becomes NADH. The two forms together support redox reactions in cells.