SERINE, D- (D-serine) is a non-essential amino acid occurring in natural form as the L-isomer. It is synthesized from glycine or threonine. It is involved in the biosynthesis of purines, pyrimidines and other amino acids. A considerable level of D-serine was discovered, surprisingly, in the mammalian brain in the early 1990s. Since then, D-serine has been considered to be a co-agonist of glutamate at the glycine site of NMDA receptors. D-serine plays an important role in the central nervous system as an endogenous ligand for the glycine site of glutamate N-Methyl-D-Aspartate (NMDA) receptors. D-serine is synthetized by racemization of L-serine in most neural and non-neural cells, and modulates a variety of physiological functions in mammals. D-Serine synthesis is attributed to Serine Racemase (SR), which catalyses the synthesis of D-serine from L-serine. D-serine may play a role in the pathophysiology of neuropsychiatric disorders, such as schizophrenia, which may be linked to NMDA receptor hypo-function. Studies in genetic and pharmacological animal models with decreased D-serine levels have shown that these animals displayed behavioural abnormalities similar to those seen in schizophrenia. Moreover, exogenous administration of D-serine and related compounds improved several phenotypes relevant to schizophrenia, which could have positive clinical implications in humans. The results of a clinical trial in Taiwanese schizophrenic patients who received D-serine as adjuvant treatment indicated that those patients who received D-serine treatment, improved positive, negative and cognitive symptoms seen in schizophrenia. In addition, this clinical trial showed that D-serine did not worsen side effects from other antipsychotics, which may be due to its selective action at the NMDA-glycine site. Therefore, D-serine could be considered as a therapeutic approach for schizophrenia, which is different from the dopaminergic approach. It has also been shown that exogenous d-serine administration can suppress appetite and alter food preference. Thus NMDA receptor and its co-agonist d-seine participate in the control of appetite and food preference, which can be used to suppress obesity. D-serine has been shown to have cognitive-enhancing properties in different brain disorders and in age-related cognitive decline. From a clinical perspective, it is important to highlight that in a recent double-blind placebo-controlled cross-over study our group observed that an acute oral administration of 30 mg/kg of d-serine improved spatial learning and problem solving. D-serine may be especially useful for depression because of its acute and chronic antidepressant effects,

Estriol (E3), also spelled oestriol, is a steroid, a weak agonist of the estrogen receptors ERα and ERβ., and a minor female sex hormone. According to in vitro study, the relative binding affinity (RBA) of estriol for the human ERα and ERβ was 11.3% and 17.6% of that estradiol, respectively, and the relative transactivational capacity of estrone at the ERα and ERβ was 10.6% and 16.6% of that of estradiol, respectively. Estriol is marketed widely in Europe and elsewhere throughout the world under the brand names Ovestin, Ortho-Gynest, and a variety of others. It is available in oral tablet, vaginal cream, and vaginal suppository form, and is used in menopausal hormone therapy for the treatment of menopausal symptoms. Estriol is also available in some countries as estriol succinate (brand name Synapause), a dosage-equivalent ester prodrug of estriol. Estriol and estriol succinate are not approved for use in the United States and Canada, although they have been produced and sold by compounding pharmacies in North America for use as a component of bioidentical hormone therapy. Estriol can be measured in maternal blood or urine and can be used as a marker of fetal health and well-being. If levels of unconjugated estriol (uE3 or free estriol) are abnormally low in a pregnant woman, this may indicate chromosomal or congenital anomalies like Down syndrome or Edward's syndrome. It is included as part of the triple test and quadruple test for antenatal screening for fetal anomalies.

Cytosine is a pyrimidine nucleobase, one of the five main bases of nucleic acids. In DNA and RNA cytosine is paired with guanine. Only small amounts of cytosine administered with food are incorporated in DNA. The majority of cytosine is synthesized de-novo starting from carbamoyl phosphate.

Citrulline (name derived from citrullus, the Latin word for watermelon, from which it was first isolated) is an amino acid. It is made from ornithine and carbamoyl phosphate in one of the central reactions in the urea cycle. It is also produced from arginine as a by-product of the reaction catalyzed by nitric oxide synthase (NOS) family. Citrulline supplements have been claimed to promote energy levels, stimulate the immune system and help detoxify ammonia (a cell toxin). Citrulline is not involved in protein synthesis. Several pharmacokinetic studies have confirmed that citrulline is efficiently absorbed when administered orally. Oral citrulline could be used to deliver arginine to the systemic circulation or as a protein anabolic agent in specific clinical situations (for example in case of malnourishment), because recent data have suggested that citrulline, although not a component of proteins, stimulates protein synthesis in skeletal muscle through the mammalian target of rapamycin signaling pathway. Citrulline is converted to L-arginine by argininosuccinate synthase. L-arginine is in turn responsible for citrulline's therapeutic effects. Many of L-arginine's activities, including its possible anti-atherogenic actions, may be accounted for by its role as the precursor to nitric oxide (NO).

D-ribose, a naturally occurring pentose carbohydrate, and a key component in the adenosine triphosphate (ATP) molecule. D-ribose was studied for congestive heart failure. In addition was discovered, that D-ribose significantly reduced clinical symptoms in patients suffering from fibromyalgia and chronic fatigue syndrome. Recently was published an article where were described, that d-Ribose reacted with the N-terminal valinyl residues of hemoglobin (Hb), thus producing glycated hemoglobin (HbA1c). It is known, that HbA1c is the most important marker of hyperglycemia in diabetes mellitus, which prompts future studies to explore whether D-ribose could also lead to diabetic complications.

D-mannose is a simple sugar found naturally in fruits such as cranberries and pineapples. Unlike many sugars, it is not metabolised or stored in the liver. Much of it is excreted in the urine, where it interferes with particle attachment and prevents certain kind of bacteria from sticking to the walls and causing infection. Mannose supplement is also indicated for treatment of carbohydrate-deficient glycoprotein syndrome, however clinical trials failed to prove its efficacy.