2-Hydroxybutyric acid, also known as ''alpha''-hydroxybutyrate and α-hydroxybutyrate, is a
hydroxybutyric acid with the
hydroxyl
In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydrox ...
group on the carbon adjacent to the
carboxyl
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxyl ...
. It is a
chiral
Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object.
An object or a system is ''chiral'' if it is distinguishable from i ...
compound having two
enantiomers
In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical ant ...
,
D-2-hydroxybutyric acid and
L-2-hydroxybutyric acid.
(R)-2-Hydroxybutanic Acid Structural Formula V1.svg, (''R'')-2-hydroxybutyric acid
(S)-2-Hydroxybutanic Acid Structural Formula V1.svg, (''S'')-2-hydroxybutyric acid
2-Hydroxybutyrate, the
conjugate base
A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid donates a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as in the reverse reaction it loses a ...
of 2-hydroxybutyric acid, is produced in mammalian tissues (principally hepatic) that catabolize
L-threonine or synthesize
glutathione
Glutathione (GSH, ) is an antioxidant in plants, animals, fungi, and some bacteria and archaea. Glutathione is capable of preventing damage to important cellular components caused by sources such as reactive oxygen species, free radicals, pe ...
.
Oxidative stress
Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal re ...
or detoxification demands can dramatically increase the rate of hepatic glutathione synthesis. Under such metabolic stress conditions, supplies of
L-cysteine for glutathione synthesis become limiting, so
homocysteine
Homocysteine is a non-proteinogenic α-amino acid. It is a homologue of the amino acid cysteine, differing by an additional methylene bridge (-CH2-). It is biosynthesized from methionine by the removal of its terminal Cε methyl group. In th ...
is diverted from the
transmethylation pathway forming methionine into the
transsulfuration pathway forming cystathionine. 2-Hydroxybutyrate is released as a byproduct when
cystathionine
Cystathionine is an intermediate in the synthesis of cysteine.
Cystathionine is produced by the transsulfuration pathway which converts homocysteine into cystathionine. Cystathionine is then used by the enzymes cystathionine gamma-lyase (CTH), c ...
is cleaved to cysteine that is incorporated into glutathione. Chronic shifts in the rate of glutathione synthesis may be reflected by urinary excretion of 2-hydroxybutyrate.
α-hydroxybutyrate may be useful as an early indicator of
insulin resistance
Insulin resistance (IR) is a pathological condition in which cells fail to respond normally to the hormone insulin.
Insulin is a hormone that facilitates the transport of glucose from blood into cells, thereby reducing blood glucose (blood suga ...
in
non-diabetic subjects.
Moreover, elevated serum α-hydroxybutyrate predicts worsening
glucose tolerance
Prediabetes is a component of the metabolic syndrome and is characterized by elevated blood sugar levels that fall below the threshold to diagnose diabetes mellitus. It usually does not cause symptoms but people with prediabetes often have obesit ...
.
References
{{DEFAULTSORT:Hydroxybutyric acid, 2-
Alpha hydroxy acids