The distribution of squalene and non-cholesterol sterols in lipoproteins in type 2 diabetes

Background: Lipoprotein distribution of non-cholesterol sterols was studied to evaluate in which lipoproteins they are carried in type 2 diabetes with body weight ranging from normal to overweight. Methods: Serum and lipoprotein squalene and non-cholesterol sterols were quantitated with gas-liquid chromatography in 33 diabetic subjects separated into normal (BMI <= 25 kg/m(2), n = 10) and overweight (BMI > 25 ka/m(2), n = 23) groups. Results: Two-thirds of the non-cholesterol sterols were carried in LDL and one-fifth in HDL, whereas squalene was mainly in VLDL and LDL in both groups. In overweight versus normal weight subjects, the absorption marker concentrations and ratios to cholesterol in serum and lipoproteins were lower and those of synthesis higher. In both groups the synthesis and absorption markers were interrelated in all lipoproteins suggesting intact regulation of cholesterol metabolism. The absorption marker ratios to cholesterol were mostly carried in HDL (cholestanol) and IDL (campesterol and sitosterol), and synthesis markers in VLDL and IDL regardless of overweight. Synthesis marker ratios were underestimated in serum versus VLDL and IDL, and those of absorption markers in serum versus IDL and HDL (p < 0.05 for all). Squalene was related to lathosterol in all lipoprotein fractions (e.g., in LDL r = +0.501, p < 0.01) suggesting that in diabetes squalene, too, is an indicator of cholesterol synthesis. Conclusions: The absorption sterols are carried in IDL and HDL, and the synthesis markers in VLDL and IDL regardless of weight. The lipoprotein squalene and non-cholesterol sterol ratios were under- or overestimated in serum, and whether their evaluation in lipoprotems versus in serum only gives better information on cholesterol metabolism should be investigated further also in normal population. (C) 2006 Elsevier Ireland Ltd. All rights reserved.