Clinical Biochemicals> HCY
Total Homocysteine (tHcy) Biochemical Assay Kit
Introduction:

Over 1 million of Americans died of cardiovascular disease (CVD) such as heart attack or stoke. It was long thought that CVD is related to the increased level of cholesterol in the blood , but yet 25% patients with heart attack have no obviously elevated blood cholesterol level or other risk factors been observed. However, the metabolism of homocysteine is found to be related to the CVD or stoke in recent study.

Homocysteine (Hcy) is a thiol-containing amino acid produced by the intracellular demethylation of methionine. Hcy is exported into plasma where it circulates mostly in its oxidized forms bound to plasma proteins. Smaller amounts of reduced homocysteine and disulfide homocystin (Hcy-SSHcy) are present. Total homocysteine represents the sum of all Hcy species found in plasma and serum (free plus protein-bound). Hcy is either metabolised to cysteine or to methionine. In the vitamin B6 dependent transsulphuration pathway Hcy is irreversibly catabolised to cysteine. A major part of Hcy is remethylated to methionine, mainly by the folate and cobalamin- dependent enzyme methionine synthase. Hcy accumulates and is excreted into the blood when these reactions are impaired. The elevated concentration of homocysteine in the blood is considered an independent risk factor of CVD.

Epidemiological studies have investigated the relationship between Hcy levels in blood and CVD. A meta analysis of 27 epidemiological studies, including more than 4000 patients, estimated that a 5 μM increase in Hcy was associated with an odds ratio for coronary artery disease (CAD) of 1.6 for men and 1.8 for women. Peripheral arterial disease also showed a strong association.

Certain patient groups with anemia and/or asthenia also demonstrate increased levels of plasma or serum Hcy. Patients with chronic renal disease experience an excess morbidity and mortality due to arteriosclerotic CVD. Elevated concentration of Hcy is a frequently observed finding in the blood of these patients. Although such patients may lack some of the vitamins involved in the metabolism of Hcy, the increased levels of Hcy are mainly due to impaired removal of Hcy from the blood by the kidney.

Severely elevated concentrations of Hcy are found in subjects with homocystinuria, a rare genetic disorder of the enzymes involved in the metabolism of Hcy. Patients with homocystinuria exhibit mental retardation, early arteriosclerosis and arterial and venous thromboembolism. Drugs such as methotrexate, carbamazepine, phenytoin, nitrous oxide and penicillamine interfere with the Hcy metabolism and may give elevated levels of Hcy.


Product description:

The Total Homocysteine (tHcy) Biochemical Assay Kit is based on an enzymatic conversion method instead of immunoassay by antibodies. The oxidized form of homocysteine is first reduced by DTT, and then converted by a genetic recombinant enzyme to react with chromophore reagent to produce a fluorescent compound with an excitation wavelength of 660nm and an emission wavelength of 710nm. The resulting fluorescence can be measured in a fluorescence microtiter plate reader. The quantitative linear range of the Total Homocysteine (tHcy) Biochemical Assay Kit is between 1μM and 60μM.


Reference:

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2) Han Q, Lenz M, Tan Y, Xu M, Sun X, Tan XZ, Tan XY, Tang L, Miljkovic D, and Hoffman RM. High expression, purification and properties of recombinant homocysteine, α, γ-lyase. Protein Expression and Purification 14,267-274, 1998.

3) Malinow MR. Plasma homocyst(e)ine and arterial occlusive diseases: A mini-review. Clin. Chem. 40, 173-176, 1995.

4) Ueland PM. Homocysteine species as components of plasma redox thiol status. Clin. Chem. 41, 340-342, 1995.

5) Perry IJ, Refsum H, Morris RW, Ebrahim SB, Ueland PM, Shaper AG. Prospective study of serum total homocystein concentration and risk of stroke in middle-aged British men. The Lancet 346, 1395-98, 1995.

6) Finkelstein JD. Methionine metabolism in mammals. J. Nutr. Biochem. 1, 228-237, 1990.

7) Clark R, Daly L, Robinson K, Naughten E, Cahalane S, Fowler B, Graham I. Hyperhomocysteinemia: An independent risk factor for vascular disease. N. Engl. J. Med. 324, 1149-55, 1991.

8) Schmitz C, Lindpainter K, Verhoef P, Gaziano JM, Buring JS. Genetic polymorphism of methyleneterahydrofolate reductase and myocardial infarction. Circulation 94, 1812-1814, 1996.

9) Boushey CJ, Beresford SAA, Omenn CS, Motulsky AG. A quantitative assessment of plasma homocysteine as a risk factor for vascular disease. JAMA 274:13, 1049-1057, 1995.

10) Refsum H, Ueland PM. Clinical significance of pharmacological modulation of homocysteine metabolism. TIPS 11, 411-416, 1990.

11) Frantzen F, Faaren AL, Alfheim I, and Nordhei AK. An enzyme conversion immunoassay for determining total homocysteine in plasma or serum. Clin. Chem. 44, 311-316, 1998.

12) Ueland PM, Refsum H, Stabler SP, Malinow R, Anderson A, Allen RH. Total homocysteine in plasma or serum: Methods and clinical applications. Clin. Chem. 39, 1764-1779, 1993.

13) Ubbink JB, Vermaak WJH, van der Merwe A, Becker PJ. The effect of blood sample aging and food consumption on plasma total homocysteine levels. Clinica Chimica Acta 207, 119-128, 1992.

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15) Willems HPJ, Gerrits WBJ, Blom HJ. Stability of homocysteine in full blood: A comparison of six collection media. Thrombosis and Haemostasis Supplement, 531, 1997.

16) Fiskerstrand T, Refsum H, Kvalheim G, Ueland PM. Homocysteine and other thiols in plasma and urine: Automated determination and sample stability. Clin. Chem. 39, 263-271, 1993.

For 100 tests


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