Hydroxycitric acid (HCA) is a derivative of

citric acid Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in t ...

that is found in a variety of tropical plants including '' Garcinia cambogia'' and ''

Hibiscus sabdariffa Roselle (''Hibiscus sabdariffa'') is a species of flowering plant in the genus ''Hibiscus'' that is native to Africa, most likely West Africa and also found in India especially Maharashtra with local name ambali. In the 16th and early 17th cent ...

''. There are four isomers, (+)- and (-)-hydroxycitric acid, and (+)- and (-)-allo-hydroxycitric acid. The (-)-hydroxycitric acid isomer is the one found in ''

Garcinia ''Garcinia'' is a genus of flowering plants in the family Clusiaceae native to Asia, America, Australia, tropical and southern Africa, and Polynesia. The number of species is disputed; Plants of the World Online (POWO) recognise up to 400. Common ...

''.

Chemistry

Hydroxy citric acid as such cannot be isolated from garcinia fruits or hibiscus sabdariffa fruits. Hydroxy citric acid exist in both the open and lactone forms. The presence of two chiral centres in the molecule is exploited to construct molecular skeletons that are otherwise difficult to synthesize, thus demonstrating the lactones use as chirons.

Biological effects

(-)-HCA is a competitive inhibitor of

ATP citrate lyase ATP citrate synthase (also ATP citrate lyase (ACLY)) is an enzyme that in animals represents an important step in fatty acid biosynthesis. By converting citrate to acetyl-CoA, the enzyme links carbohydrate metabolism, which yields citrate as an ...

, which converts citrate into

oxaloacetate Oxaloacetic acid (also known as oxalacetic acid or OAA) is a crystalline organic compound with the chemical formula HO2CC(O)CH2CO2H. Oxaloacetic acid, in the form of its conjugate base oxaloacetate, is a metabolic intermediate in many processes ...

and

acetyl CoA Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for ...

. The reverse of this conversion is a step in the

citric acid cycle The citric acid cycle (CAC)—also known as the Krebs cycle or the TCA cycle (tricarboxylic acid cycle)—is a series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins ...

. Laboratory and animal studies of HCA have produced results that indicate a potential for modulation of lipid metabolism. However, a clinical study has demonstrated that HCA has no effect in terms of weight loss or reduction of fat mass. A meta-analysis published in 2010 revealed that gastrointestinal adverse effects were twice as likely for users of hydroxycitric acid. The use of HCA is contraindicated in patients suffering Colitis or Inflammatory Bowel Disease. One

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Iso ...

of HCA, known as (2''S'',3''R'')-HCA, inhibits pancreatic

alpha-amylase α-Amylase is an enzyme (EC 3.2.1.1; systematic name 4-α-D-glucan glucanohydrolase) that hydrolyses α bonds of large, α-linked polysaccharides, such as starch and glycogen, yielding shorter chains thereof, dextrins, and maltose: :Endohyd ...

and intestinal

alpha-glucosidase α-Glucosidase (EC 3.2.1.20, maltase, glucoinvertase, glucosidosucrase, maltase-glucoamylase, α-glucopyranosidase, glucosidoinvertase, α-D-glucosidase, α-glucoside hydrolase, α-1,4-glucosidase, α-D-glucoside glucohydrolase; systematic n ...

, leading to a reduction in carbohydrate metabolism ''

in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology an ...

''. In a study in

Zucker rat A laboratory rat or lab rat is a brown rat of the subspecies '' Rattus norvegicus domestica'' which is bred and kept for scientific research. While less commonly used for research than mice (see laboratory mouse), rats have served as an importa ...

s, which are genetically predisposed to obesity, ''Garcinia cambogia'' extract containing HCA showed that high doses led to significant suppression of epididymal fat accumulation, but also had high testicular toxicity. However, this study has been criticized because of possible contamination of the HCA used and various design flaws. Researchers at the

University of Houston The University of Houston (UH) is a Public university, public research university in Houston, Texas. Founded in 1927, UH is a member of the University of Houston System and the List of universities in Texas by enrollment, university in Texas ...

reported hydroxycitrate is capable of dissolving

calcium oxalate Calcium oxalate (in archaic terminology, oxalate of lime) is a calcium salt of oxalic acid with the chemical formula . It forms hydrates , where ''n'' varies from 1 to 3. Anhydrous and all hydrated forms are colorless or white. The monohydrate ...

crystals, a component of human kidney stones. Recent studies (2019) shows kidney stones are layered and the stones may form and dissolve with time. The researchers believe the effect could lead to the development of new drugs for human kidney stones.

References

{{DEFAULTSORT:Hydroxycitric Acid Dietary supplements Tricarboxylic acids Alpha hydroxy acids