Hydroxycitric Acid (HCA)
Hydroxycitric acid is found in the fruits of the genus Garcinia. Supplemental hydroxycitric acid is typically an extract of the rinds of Garcinia cambogia fruit, also called Brindle berry. Fruit of this plant has long been used in India as a condiment, and the dried rind is used as a flavoring agent. The dried fruit rind is also used in Indian folk medicine for gastrointestinal complaints and rheumatism. Hydroxycitric acid is the principal acid in the fruits of Garcinia cambogia and makes up to 16% of the content of the dried fruit.
Hydroxycitric acid, in addition to being called (-)- hydroxycitric acid, is also known as hydroxycitrate, (-) -- threohydroxycitric acid and 4S-hydroxycitric acid. It is abbreviated as (-)-HCA and sometimes as HCA. It is a different substance than either citric acid or isocitric acid, which are key intermediates in the tricarboxylic acid or Krebs cycle. The terms for the acid and anion forms, hydroxycitric acid and hydroxycitrate, respectively, are used interchangeably. However, the anion form is the form that occurs under biological conditions.
Hydroxycitric acid (HCA) is the active ingredient in the herbal compound Garcinia cambogia. It should competitively inhibit the extramitochondrial enzyme adenosine triphosphate-citrate (pro-3S)-lyase. As a citrate cleavage enzyme that may play an essential role in de novo lipogenesis inhibition. As a result, G cambogia is claimed to lower body weight and reduce fat mass in humans. Hydroxycitric acid is an 'additive' ingredient of many weight-loss drugs, and is promoted as an appetite suppressant. It is especially important in ephedra-free products as thermogenic weight-loss is nowhere near as efficient with only caffeine and aspirine being used.
HCA exerts its weight control effect through its inhibition of the enzyme ATP citrate lyase, playing a critical role in energy storage. When calorie intake exceeds the body's energy needs, the excess glucose is converted into glycogen, which is stored in the liver and muscles for future conversion into energy. Weight gain occurs after the body's capacity for glycogen storage is reached. At this point, glucose from excessive calorie intake is converted into acetyl coenzyme A via a metabolic pathway involving ATP-citrate lyase and then into fat molecules, which are stored in fat cells. HCA has been shown to bind to ATP-citrate lyase to reduce the production of acetyl coenzyme A and also increase the ability of the liver and muscles to synthesize and store glycogen.
Hydroxycitric acid is a competitive inhibitor of the enzyme adenosine triphosphate-citrate (pro-3S) — lyase or ATP citrate lyase. In the cytosol, ATP citrate lyase catalyzes the conversion of citrate and coenzyme A to oxaloacetate and acetyl coenzyme A (acetyl CoA). Acetyl CoA is used in the synthesis of fatty acids, cholesterol and triglycerides and also in the synthesis of acetylcholine in the central nervous system. Oxaloacetate may enter the gluconeogenic pathway, which can lead to the production of glucose and glycogen. It is believed that the putative antiobesity effect of hydroxycitric acid is due to suppression of fatty acid and fat synthesis. In addition, hydroxycitric acid is thought to suppress food intake via an anorectic effect. This is believed to be accounted for by hydroxycitric acid's stimulation of liver gluconeogenesis.