Methylglyoxal

Biochemistry

Biosynthesis and biodegradation

In organisms, methylglyoxal is formed as a side-product of several metabolic pathways. Methylglyoxal mainly arises as side products of glycolysis involving glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. It is also thought to arise via the degradation of acetone and threonine. Illustrative of the myriad pathways to MGO, aristolochic acid caused 12-fold increase of methylglyoxal from 18 to 231 μg/mg of kidney protein in poisoned mice. It may form from 3-aminoacetone, which is an intermediate of threonine catabolism, as well as through lipid peroxidation. However, the most important source is glycolysis. Here, methylglyoxal arises from nonenzymatic phosphate elimination from glyceraldehyde phosphate and dihydroxyacetone phosphate (DHAP), two intermediates of glycolysis. This conversion is the basis of a potential biotechnological route to the commodity chemical 1,2-propanediol.

Since methylglyoxal is highly cytotoxic, several detoxification mechanisms have evolved. One of these is the glyoxalase system. Methylglyoxal is detoxified by glutathione. Glutathione reacts with methylglyoxal to give a hemithioacetal, which converted into S-D-lactoyl-glutathione by glyoxalase I. This thioester is hydrolyzed to D-lactate by glyoxalase II.

Biochemical function

Methylglyoxal is involved in the formation of advanced glycation end products (AGEs). In this process, methylglyoxal reacts with free amino groups of lysine and arginine and with thiol groups of cysteine forming AGEs. Histones are also heavily susceptible to modification by methylglyoxal and these modifications are elevated in breast cancer.

DNA damages are induced by reactive carbonyls, principally methylglyoxal and glyoxal, at a frequency similar to that of oxidative DNA damages. Such damage, referred to as DNA glycation, can cause mutation, breaks in DNA and cytotoxicity. In humans, a protein DJ-1 (also named PARK7), has a key role in the repair of glycated DNA bases.

Biomedical aspects

Due to increased blood glucose levels, methylglyoxal has higher concentrations in diabetics and has been linked to arterial atherogenesis. Damage by methylglyoxal to low-density lipoprotein through glycation causes a fourfold increase of atherogenesis in diabetics. Methylglyoxal binds directly to the nerve endings and by that increases the chronic extremity soreness in diabetic neuropathy.

Occurrence, other

Methylglyoxal is a component of some kinds of honey, including manuka honey; it appears to have activity against E. coli and S. aureus and may help prevent formation of biofilms formed by P. aeruginosa.

Research suggests that methylglyoxal contained in honey does not cause an increased formation of advanced glycation end products (AGEs) in healthy persons.