Xanthines are a group of compounds that are derivatives of xanthine, a purine base. These compounds are alkaloids and include such common mild stimulants as caffeine and theobromine, which is found in chocolate. Some are used medicinally to treat asthma and other respiratory conditions. Xanthine is involved in human physiology and is an intermediate in the production of uric acid. There is a genetic disorder known as xanthinuria that interferes with xanthine metabolism.
The basic chemical structure of these compounds is a purine base. This is a type of molecule that has two fused aromatic rings that contain nitrogen, carbon, and hydrogen molecules. They are very common, since two of these bases are components of DNA and RNA. These are guanine and adenine. Xanthine appears to also be found extraterrestrially, given an analysis of its inclusion in the Murchison meteorite found in Australia.
Xanthines act as mild stimulants and help to improve breathing. This makes them useful to treat asthma, emphysema, and chronic bronchitis. The derivatives of xanthine that are used most commonly in medicine have a methyl, or CH3, group on them. There are multiple modes of action, and different drugs exert varying selectivities.
These compounds also stimulate heart rate and affect the central nervous system, however, and can have toxic side effects. Due to this, they are not the first class of drugs typically chosen for treating asthma. Synthetic xanthines with fewer side effects have been developed. To limit the chances of side effects, one should reduce the intake of caffeine and chocolate when taking medicinal xanthines.
Xanthine is an important intermediate in purine degradation, and is subsequently found in most fluids and tissues of the human body. Uric acid is the final product of the breakdown of purines and is normally expelled in urine. Under some conditions, this compound can build up in the joints to cause a painful condition called gout.
The metabolism of xanthine takes place by a liver enzyme known as xanthine oxidase (XO), also known as xanthine dehydrogenase. This enzyme carries out two different reactions. It transforms hypoxanthine, an intermediate breakdown product from adenine, to xanthine in a reversible reaction. It can also reversibly transform xanthine to uric acid. An inhibitor of XO, known as allopurinol, is sometimes used to treat gout by preventing uric acid buildup.
Some people have the genetic disorder xanthinuria and lack the ability to produce XO. They build up high concentrations of xanthine in the blood, which can lead to the build-up of uric acid in the muscles and kidneys. The kidneys may develop xanthine stones, and complete kidney failure is a possibility. There is no treatment for this rare condition. Patients are advised to avoid foods that have a lot of purines, and to drink a lot of fluids.