What is Homocysteine?
is a naturally occurring, sulfur containing amino acid, formed from methionine,
an essential amino acid, via transmethylation.
Homocysteine may be irreversibly metabolized to cysteine or can be converted
back to methionine by transfer a methyl group from a derivative of the vitamin,
folic acid) in a reaction that involves Vitamin B12.
on arteries of both animals and humans with an elevated level of homocysteine
showed that homocysteine level in blood is an independent risk factor for
atherosclerotic vascular disease affecting the coronary (arteries supplying the
heart), cerebral (arteries supplying the brain) and peripheral arteries
(supplying the rest of the body). Homocysteine contributes to in many ways that
lead to this disease.
- Homocysteine prevents small
arteries from dilating, thereby making them more vulnerable to obstruction
by clot or plaque
- Homocysteine changes coagulation
factor levels, which encourages blood clot formation
- Homocysteine generates superoxide
and hydrogen peroxide, both of which have been linked to damage the
endothelial lining of arterial vessels.
- Homocysteine causes the smooth
muscle cells that support the arterial wall to multiply, which is part of
the narrowing process.
- In its reactive form, homocysteine
thiolactone, causes platelets to aggregate,
which is part of the clotting process.
- The active form of excess
homocysteine reacts with Low Density Lipoprotein (LDL, which is sometimes referred to as the 'bad' cholesterol) to form
LDL-homocysteine thiolactone aggregates. These
are taken up by macrophages, which in turn promotes atherothrombosis.
homocysteine levels also may be associated with spina
bifida. rheumatoid arthritis
and some cancers. Elevated homocysteine levels, has inverse relationship to the
plasma levels of both folate and vitamin B12. Dietary
supplementation with foIic acid B 12 and B6 reduces
the plasma homocysteine levels by about 30% in almost all subjects.
Who should have their Homocysteine
who has early symptoms or strong family history of atherosclerosis should be
screened for elevated homocysteine"
populations with low plasma levels of vitamin B6, vitamin B12
and folic acid, homocysteine levels and incidence of atherosclerosis are
occurs in plasma as the free thiol (free homocysteine about 1%), its
symmetrical disulfide (homocysteine) asymmetrical disulfide and conjugated with
protein through disulfide link-age. The bulk of plasma homocysteine thus occurs
in conjugated form, making it inaccessible to common analytical techniques.
Sample must therefore be treated with reacting agent before analysis to
liberate homocysteine as the free thiol.
study on about 600 Norwegian patients with coronary heart disease, heart
attacks and deaths rose in straight line relation to plasma homocysteine level.
In other words, the higher the homocysteine the higher the risk for death
from heart disease. (Stampfer MJ. Malinow MR- Willett WC, et al. A prospective study of
plasma homocysteine and risk of myocardial infarction in US physicians. JAMA.
international study of healthy middle aged men from 11 countries convincingly
shows that the risk of dying from arteriosclerotic
cardiovascular disease (ACVD) increased with average homocysteine level in a
given nation. (Alfthan G. Aro A. Gey KF. Plasma
Homocysteine and cardiovascular disease mortality. Lancet 1997:349:397.)
each 5-umolA increase in blood homocysteine content, the risk of middle-aged
men dying of ischemic heart diseases by one third.
(Wald NJ, Watt HC. Law MR- et al.
homocysteine and ischemic heart disease: results of
prospective study with implications regarding prevention. Arch lnternal Med. 1998:158:862-867.)
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