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Biochemistry of homocysteine in health and diseases

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Title Biochemistry of homocysteine in health and diseases
 
Creator Ramakrishnan, S
Sulochana, K N
Lakshmi, S
Selvi, R
Angayarkanni, N
 
Subject Homocysteine metabolism
Homocystinurias
Homocysteinemias
Clinical manifestations
Thrombotic disorders
Cardiovascular diseases
Diabetes
Ocular diseases
Smokers
Oxidant stress
Protein thiolation
Protein homocysteinylation
Cystine
Vitamins B6
B12
folate
 
Description 275-283
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-b-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.
 
Date 2009-03-20T04:41:27Z
2009-03-20T04:41:27Z
2006
 
Type Article
 
Identifier 0301-1208
http://hdl.handle.net/123456789/3401
 
Language en_US
 
Publisher CSIR
 
Source IJBB Vol.43(5) [October 2006]