Progressive glycosylation of albumin and its effect on the binding of homocysteine may be a key step in the pathogenesis of vascular damage in diabetes mellitus

Homocysteine enhances LDL fatty acid peroxidation, promoting microalbuminuria in type 2 diabetes

Background

We aimed to establish the relationship between glycated haemoglobin (HbA1c), hypertension and microalbuminuria onset in type 2 diabetes. We also intended to ascertain the metabolic action of homocysteine on LDL fatty acids and on renal function.

Methods

The study was carried out on 200 patients with type 2 diabetes and 200 healthy subjects. HbA1c, apolipoprotein B (apo B) and microalbuminuria were measured using immunoturbidimetric methods. Cholesterol, peroxide, urea and uric acid were assayed using colorimetric methods. Creatinine clearance was calculated using the Cockroft-Gault equation. Homocysteine was measured by immunological fluorescence polarization. LDL fatty acids were quantified by gas chromatography.

Results

Creatinine and microalbuminuria significantly increased in type 2 diabetes when compared with controls. Microalbuminuria was significantly correlated with HbA1c and with the presence of high blood pressure. Homocysteinaemia significantly correlated with creatinine clearance in diabetes. Linoleic acid (C18:2ω6) did not differ between groups. C18:2ω6/C18:3ω3 ratio was three times higher in diabetics than in controls. Total saturated fatty acids, homocysteine, H2O2 and LDL-thiobarbituric reactive substances significantly increased in microalbuminuric when compared with normoalbuminuric diabetes. Total polyunsaturated fatty acids, arachidonic acid (C20:4ω6), LDL-cholesterol, apo B and creatinine clearance significantly decreased in microalbuminuric when compared with normoalbuminuric diabetes.

Conclusion

Microalbuminuria onset is associated with renal protein oxidation that is preceded by LDL fatty acid oxidation. The latter is initiated by H2O2 produced from an auto-oxidation of homocysteine and increased metabolism of arachidonic acid towards its pro-inflammatory eicosanoids. An oxidative stress state is the common ground of diffused vasculopathy.