Association between Serum Cholesterol and Leucocyte Lysosomal Function

Abstract

Wycombe, UK); between-batch ev 5· 0% at 6'4070 HbAl c ' We observed significant correlations (P 0·05). Stepwise multiple regression analysis (n = 36 complete data sets) determined the dependence of each enzyme activity on serum cholesterol, age, sex and HbAl c as explanatory variables. {3-D-Nacetylglucosaminidase, {3-D-glucuronidase and {3-Dgalactosidase all showed significant associations with cholesterol (respectively, F= 12· 84, P=O·OOI; F= 13'04, P=O'OOI; F=4'70, P=0·037), independent of age, sex or HbAl c concentration. Sialidase (a-neuraminidase) activity was significantly associated both with cholesterol and, less strongly, with HbAl c (F=7·93; P=O·013 and 0'041, respectively). Neither age nor sex had a significant independent influence on sialidase (P>0·05). It should be noted that MNL sialidase activity, although chiefly lysosomal, may contain a minor contribution from a non-lysosomal isoenzyme.P Lysosomal enzymes are responsible for intracellular breakdown of complex macromolecules, and can also act extracellularly to degrade endothelial glycoconjugates, thus influencing membrane permeability. Increased plasma lysosomal enzyme activities may contribute to the development of vascular disease in diabetic and non-diabetic subjects. The sources of such activities remain to be defined, but circulating leucocytes or platelets represent likely candidates. We therefore studied lysosomal enzymes in mononuclear leucocytes (MNLs), and measured serum total cholesterol, a recognized risk factor for atherogenesis. Blood was drawn from 36 non-fasting healthy control subjects (21 men, 15 women), always between 9.15-10.00a.m., and MNLs (>98% pure, platelet-free) were immediately prepared by Dextran sedimentation and Isopaque-Ficoll centrifugation. The activities of seven lysosomal glycosidases in cell sonicates were assayed fluorimetrically (within-batch coefficients of variation [Cvs] <3,2%) using methylumbelliferyl derivatives, I and related to protein measured by a Lowry method. Serum total cholesterol was measured by a cholesterol oxidase/paminophenazone method on a Hitachi analyser (Boehringer Mannheim UK Ltd, Lewes, UK); between-batch ev 2·5070 at 6· 9 mmol/L. Glycated haemoglobin (HbA1c ) was also assayed (Novoclone ELISA method Dako, High