Estimation of hydrogen sulphide in the human lymphocytes.

Hydrogen sulphide (H2S), a signaling gasotransmitter and a potent vasorelaxant is endogenously produced by the enzymes cystathionine-beta-synthase (CBS) and cystathionine-gamma-lyase (CSE). CBS is a predominant source of H2S in the central nervous system, while CSE is the major H2S producing enzyme in the brain and other nervous tissues. Though the expression of these enzymes in the blood lymphocytes is known, H2S formation in the lymphocytes has not been reported so far. In the present study, H2S levels in the lymphocytes of healthy control subjects were estimated, after suitable modifications in a routine method [Stipanuk M H & Beck P W (1982) Biochem J 206, 267-277] used for detecting tissue levels of H2S. In this method, homocysteine (Hcys) due to its higher solubility was used as the substrate in place of L-cysteine and NaOH was used in place of zinc acetate to increase the entrapment of H2S in the central well. A mean H2S level of 11.64 +/- 6.36 microM/min/mg protein was detected in the lymphocytes of 8 subjects (mean age, 24 +/- 2; 2 male, 6 female). The modified method was found to be more sensitive for H2S estimation in human lymphocytes. As endogenous H2S is reported to be involved in the pathogenesis of various cardiovascular and pulmonary diseases, the levels of H2S in lymphocytes can be a marker of the endogenous tissue levels.

Biochemistry of homocysteine in health and diseases.

The amino acid homocysteine (Hcy), formed from methionine has profound importance in health and diseases. In normal circumstances, it is converted to cysteine and partly remethylated to methionine with the help of vit B12 and folate. However, when normal metabolism is disturbed, due to deficiency of cystathionine-beta-synthase, which requires vit B6 for activation, Hcy is accumulated in the blood with an increase of methionine, resulting into mental retardation (homocystinuria type I). A decrease of cysteine may cause eye diseases, due to decrease in the synthesis of glutathione (antioxidant). In homocystinurias type II, III and IV, there is accumulation of Hcy, but a decrease of methionine, thus, there is no mental retardation. Homocysteinemia is found in Marfan syndrome, some cases of type I diabetes and is also linked to smoking and has genetic basis too. In hyperhomocysteinemias (HHcys), clinical manifestations are mental retardation and seizures (type I only), ectopia lentis, secondary glaucoma, optic atrophy, retinal detachment, skeletal abnormalities, osteoporosis, vascular changes, neurological dysfunction and psychiatric symptoms. Thrombotic and cardiovascular diseases may also be encountered. The harmful effects of homocysteinemias are due to (i) production of oxidants (reactive oxygen species) generated during oxidation of Hcy to homocystine and disulphides in the blood. These could oxidize membrane lipids and proteins. (ii) Hcy can react with proteins with their thiols and form disulphides (thiolation), (iii) it can also be converted to highly reactive thiolactone which could react with the proteins forming -NH-CO- adducts, thus affecting the body proteins and enzymes. Homocystinuria type I is very rare (1 in 12 lakhs only) and is treated with supplementation of vit B6 and cystine. Others are more common and are treated with folate, vit B12 and in selected cases as in methionine synthase deficiency, methionine, avoiding excess. In this review, the role of elevated Hcy levels in cardiovascular, ocular, neurologial and other diseases and the possible therapeutic measures, in addition to the molecular mechanisms involved in deleterious manifestations of homocysteinemia, have been discussed.