Mercury, with the chemical symbol Hg (from Greek "Hydrargyros"), is the only metal adopting liquid form in room temperature. Mercury appears in seven natural isotopic forms. The metal is extracted from the mineral cinnabar, mercuric sulfide, in former times used also for paint. Mercury has fascinated people for millennia, as a heavy liquid metal. However, because of its toxicity, many uses of mercury are being phased out or are under review. It is now mainly used in the chemical industry as catalysts. It is also used in some electrical switches and rectifiers. Previously its major use was in the manufacture of sodium hydroxide and chlorine by electrolysis of brine. These plants will all be phased out by 2020. Elemental mercury is used in thermometers, blood pressure devices, and thermostats because its ability to expand and contract uniformly makes it useful for measuring changes in temperature and pressure. Mercury is also used in dental fillings, paints, soaps, batteries, and fluorescent lighting. Mercury will dissolve numerous metals to form amalgams and is used to extract gold dust from rocks by dissolving the gold and then boiling off the mercury. The amalgam used in dental fillings contains tin and silver alloyed with mercury. Because it works as a biocide, mercury has been used as a fungicide in paint, though this kind of paint is no longer sold. Mercury and its compounds used in dental practice may be responsible for release of mercury into the oral cavity. Compounds of mercury tend to be much more toxic than the element itself, and organic compounds of mercury (e.g., dimethyl-mercury) are often extremely toxic and may be responsible in causing brain and liver damage. Human exposure to mercury has increased through anthropogenic mercury emissions from fuel combustion, municipal incinerators, and chemical industries. Mercury is considered a major environmental toxicant throughout the world. Mercury is harmless in insoluble form, but vapor or soluble forms such as inorganic mercury or methylmercury can be extremely toxic to humans. Most human mercury exposure occurs through inhalation of elemental mercury vapor released from dental amalgam and through the consumption of fish contaminated with methylmercury.

Bilirubin is an orange-yellow pigment made during the normal breakdown of red blood cells. Bilirubin passes through the liver and is excreted out of the body. Occasionally, higher bilirubin levels may indicate an increased rate of destruction of red blood cells (hemolysis). A high level of bilirubin in the blood is called hyperbilirubinemia. High bilirubin levels can cause jaundice. Jaundice makes the skin and the whites of the eyes appear yellow, due to the brown and yellow bilirubin in the blood. Phototherapy for neonatal is one of the treatment methods against hyperbilirubinemia. Light absorption by bilirubin in the skin transforms the native Z,Z-bilirubin to conformational photoisomers Z,E-bilirubin and E,Z-bilirubin and structural photoisomers E,Z-lumirubin and E,E-lumirubin. Formation and excretion of Z,E-bilirubin and E,Z-lumirubin are both important routes of elimination of bilirubin through bile and urine, although the precise contributions of the various photoisomers to the overall elimination of bilirubin are still unknown.

Uric acid, generated from the metabolism of purines, has proven and emerging roles in human disease. Humans produce large quantities of uric acid. Excess serum accumulation of uric acid can lead to a type of arthritis known as gout. Hyperuricemia may increase risk factors for cardiovascular disease. High serum uric acid was associated with higher risk of type 2 diabetes and other diseases.

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.

Carbon monoxide (CO) is a colorless, odorless, tasteless, and nonirritating but highly toxic gas generated by both natural and manufactured processes. CO displays many physiological roles in the neuronal, cardiovascular, and immune systems, as well as in the respiratory, reproductive, gastrointestinal, and urogenital apparatus, including anti‐apoptotic, anti‐inflammatory, anti‐oxidant, anti‐proliferative, and vasodilator effects. Although many pathologies, including cancer, hematological diseases, hypertension, heart failure, inflammation, sepsis, neurodegeneration, and sleep disorders, have been linked to abnormal endogenous CO metabolism and functions, CO displays therapeutic actions. CO has demonstrated therapeutic potential against a wide range of human diseases. However, development of CO as a therapeutic agent is severely impeded, primarily due to the lack of pharmaceutically acceptable delivery forms of CO. The therapeutic use of CO is based on (i) the induction or gene transfer of HO‐1, (ii) the inhalation of gaseous CO, and (iii) the use of CO‐releasing molecules (CO‐RMs). There is a large amount of broad preclinical evidence of the benefits of CO in large and small animal models. Importantly, CO is effective both as a prophylactic and as a therapeutic in diverse models, such as malaria, organ transplantation and pulmonary hypertension. Inhaled CO and CO-RMs are in development as therapeutics; inhaled CO is being tested in Phase II clinical trials for kidney transplantation and various CO-RMs are under preclinical evaluation. The precise molecular targets for CO remain unclear with a wide range of evidence for both haem and non-haem targets. A commonality revolves around the contributions of the mitochondria and alterations in cellular bioenergetics. Inhaled CO delivery can be accomplished with an innovative delivery device. In addition strong medicinal chemistry is driving CO-RM development with efforts towards tissue specificity and the appropriate pharmacokinetic and pharmacodynamic profiling. Inhaled CO has found wide applications in basic research in examining CO’s physiological and pathological roles, yet its application in human has many limitations, such as difficulty in precise dose control, lack of portability and inability for targeted delivery, among others. In order to mitigate these limitations, a family of transition metal based CO-releasing molecules (CO-RMs) have been elegantly devised, and have shown CO-associated biological outcomes both in vitro and in vivo. Proterris is developing an inhaled carbon monoxide (CO) therapy for the treatment of idiopathic pulmonary fibrosis (IPF), delayed graft function (DGF), acute kidney injury and renal fibrosis.

L-carnitine (L-beta-hydroxy-gamma-N,N,N-trimethylaminobutyric acid) is conditionally necessary for mitochondrial transport and metabolism of long-chain fatty acids, and thus for myocardial energetic metabolism. D-carnitine is not biologically active and might interfere with proper utilization of the L isomer, and so there are claims that the racemic mixture (DL-carnitine) should be avoided. The pharmacological effects of carnitine are stereospecific: L-carnitine was effective in various animal and clinical studies, while D- and DL-carnitine was found to be ineffective or even toxic to some cells and tissues, such as muscle cells and the myocardium. DL-carnitine caused symptoms of myasthenia and cardiac arrhythmias, which disappeared after L-carnitine administration.

Creatine is an amino acid that occurs in vertebrate tissues and in urine. It is synthesized mainly in the liver from three different amino acids: arginine, glycine, and methionine. In skeletal muscles, which store 95% of it, creatine generally occurs as phosphocreatine. The rest is stored in the brain, heart, and testes. Creatine functions as part of the cell's energy shuttle. It is excreted as creatinine in the urine.

Glutathione (GSH, also called as reduced glutathione) is a tripeptide with many roles in cells. It conjugates to drugs to make them more soluble for excretion, is a cofactor for some enzymes such as, glutathione reductase, glutathione peroxidases, peroxiredoxins. Glutathione S-transferases catalyse the conjugation of GSH via a sulfhydryl group to electrophilic centers on a wide variety of substrates in order to make the compounds more water-soluble. As a part of homeopathic product, glutathione is used for temporary relief of symptoms related to Free Radical Toxicity including tingling in hands and feet, mood changes, frequent colds, poor digestion, fatigue, and constipation. In addition, for temporary relief of pain in the back from urinating, constant urging and frequent urination, kidneys sensitive to pressure, and pain from back extending down the thigh. Glutathione is an important nutrient for brain function and loss of glutathione has been implicated in Parkinson's disease. In phase II of the clinical trial was investigated whether administration of either dose of glutathione, as a nasal spray, improves PD symptoms over time in a population of individuals with Parkinson's disease (PD). In addition in phase II of clinical trial was shown, that reduced glutathione, an ingredient of RayGel™, has been helpful in decreasing some radiation therapy side effects to the skin. Reduced glutathione plays a vital role in both making DNA and cell repair. Cystic fibrosis (CF) is the most common inherited disease among the Caucasian population with considerable morbidity and reduced life expectancy. Glutathione (GSH) represents the first-line defence of the lung against oxidative stress-induced cell injury. Therapeutic approaches with inhaled GSH could improve the reduced lung antioxidant capacity in order to counterbalance the oxidant stress linked to the chronic airway inflammation and bacterial infection.

Glycocholic acid (GCA) is an important metabolite of bile acids, a conjugate of cholic acid with glycine. GCA urine levels are expected to be a specific diagnostic biomarker for hepatocellular carcinoma (HCC). The average GCA concentrations of HCC patients in plasma and urine were about 25 and 2.8 times than that of healthy volunteers.