[Low density lipoprotein rich in triglycerides and hepatic lipase activity in insulin-dependent diabetic patients]. / Lipoproteína de baja densidad rica en triglicéridos y actividad de lipasa hepática en pacientes diabéticos insulino-dependientes.

Genetic hepatic lipase (HL) deficiency is associated with low density lipoprotein (LDL) rich in triglycerides (TG), whose affinity for B:E receptors is decreased. In rats, experimental hypoinsulinemia produces HL deficiency. However, the relation between human insulin-dependent Diabetes Mellitus (IDDM), HL activity and the characteristics of LDL have not been studied. The objective of our study is to evaluate the relation between HL activity and the chemical composition of LDL in treated IDDM patients. Subjects were 15 IDDM patients and 15 controls (C), matched for sex and body mass index (BMI). The IDDM patients were classified by the WHO criteria, were free of nephropathy and hypothyroidism, and received no medication except insulin. Controls were clinically healthy and normolipidemic with no family history of diabetes. The IDDM group was divided into two subgroups: subgroup IDDM-A (n = 9) with HL values > or = 4.3 and IDDM-B (n = 6) with HL < or = than 4.2 mumoles glycerol/ml h. the HL in IDDM was lower than in C (p < 0.001). Table 1 shows clinical data. Blood samples were drawn after 12 h fasting. Percentage of HbA1c and plasma concentrations of glucose, total cholesterol, LDL-cholesterol, HDL-cholesterol and TG were assayed. LDL was separated by sequential ultracentrifugation at densities of 1.019-1.063 g/ml and its chemical composition was analyzed. The most relevant results were: plasma TG concentration was higher in IDDM than in C (p < 0.05) (Table 2), although average values DMID not exceed the reference values of 200 mg/dl. The TG-LDL were higher in IDDM than in C: 24.8 +/- 2.7 vs 17.5 +/- 1.1 mg/dl plasma, media +/- SE, (p < 0.02). This difference reflected the values of IDDM-B, whose plasma concentrations of TG-LDL were higher than in C: 32.3 +/- 3.6 vs 17.5 +/- 1.1 mg/dl (p < 0.001), and also higher than in IDDM-A (p < 0.02). (Table 3). The chemical composition of LDL in IDDM-B contained a higher percentage of TG than C: 8.5 +/- 0.7 vs 6.8 +/- 0.3% (p < 0.05), a lower percentage of cholesterol than IDDM-A: 39.0 +/- 1.7 vs 45.2 +/- 2.2% (p < 0.05) and also a larger percentage of proteins than IDDM-A: 28.9 +/- 1.9 vs 20.8 +/- 1.0% (p < 0.01). The correlations between TG/cholesterol and HL activity in IDDM were r = -0.53 (p < 0.05) and in IDDM-B, r = -0.81 (p = 0.05). The noteworthy result of this study is the modification of the LDL particle in IDDM, rich in TG in patients with low HL activity. Anomalies in the chemical composition of LDL like those described decrease the uptake of this particle by its physiological B:E receptors. It has recently been demonstrated that LDL is an indisoluble association of lipids and apoproteins, and that both act simultaneously to hold the apoB in a spatial position that expresses normal epitopes. It has been described that particles of LDL rich in TG and poor in cholesterol, shows low affinity for LDL receptors in human fibroblasts. Also in IDDM the interaction of LDL rich in TG with B:E receptors is decreased. This might be one more mechanism contributing to the accelerated atherosclerosis of these patients. Our results suggest that there may be a threshold of HL activity for the complete hydrolysis of the TG of LDL, for the normalization of the TG/cholesterol relation and for the conformation of typical LDL particles.

New method for isolating and quantifying intermediate and beta-very-low-density lipoprotein cholesterol.

We describe a new method, useful to clinical laboratories, for assessing intermediate density (IDL) or beta-very-low-density (beta-VLDL) lipoprotein cholesterol. The technique involves selective precipitation properties of the qualitative Wieland and Seidel post-electrophoretic method that immobilizes IDL and beta-VLDL in the beta-zone of an agarose slide (Clin Chem 1973;19:1139-41). In our method, we separate low-density lipoprotein (LDL) in a second electrophoretic step, in which LDL moves toward the anode, and then quantify the cholesterol of the above lipoproteins remaining in the precipitate band at the beta-zone. Replicate within-run precision (CV) of 15 aliquots of a sera pool was 10.1%. The correlation with sequential ultracentrifugation of 30 samples was r = 0.96 (P less than 0.001). Serum reference values for 30 normal individuals are 57 +/- 7.0 mg/L. Seven phenotype III hyperlipoproteinemic patients had the highest concentrations of IDL or beta-VLDL cholesterol in serum, 1620 +/- 346 mg/L.

Alterations in dense LDL subfractions in normolipidemic IDDM patients.

Low density lipoproteins (LDL) of human plasma, consist of a continuum of particles subclasses with distinct physicochemical, immunological and hydrodynamic characteristics. Such structural differences are intimately linked to atherogenesis. The current study was designated to investigated the LDL subclasses profile in 12 normolipidemic IDDM patients, and compare it with 11 healthy controls. Four plasma LDL subfractions were isolated by sequential ultracentrifugation in the density range (1.025-1.063 g/ml) and were characterized by their content of free and esterified cholesterol, triglycerides, phospholipids, and proteins. The net electrical charge was evaluated. Plasma concentration of the two denser LDL subfractions were higher in IDDM patients vs control subjects, due to an increase in cholesterol (free and esterified) and phospholipids, while more buoyant subfractions in the two groups were not different. In IDDM patients the LDL profile was skewed towards the dense subclasses LDL-III and LDL-IV, being significant this increase for LDL-IV: 22.3 +/- 5.2 vs 18.3 +/- 4.0%, p < 0.05, X +/- DS. In the healthy controls the LDL profile was skewed toward the lighter subclasses (LDL-I and LDL-II), being significant for LDL-II: 30.0 +/- 4.3 vs 23.3 +/- 4.2%, p < 0.005. Diabetic patients, even those who are normolipidemic, present increased risk of premature atherosclerosis. This suggest that normal values in lipid and lipoprotein profile can mask deeper alterations, such as changes in the composition and distribution of the denser subclasses, whose characteristics make them potentially more atherogenic. Despite the apparently normolipidemic status, dense LDL particles considered to be atherogenic, are increased in IDDM patients.

Alterations in dense LDL subfractions in normolipidemic IDDM patients

Low density lipoproteins (LDL) of human plasma, consist of a continuum of particles subclasses with distinct physicochemical, immunological and hydrodynamic characteristics. Such structural differences are intimately linked to atherogenesis. The current sludy was designated to investigate the LDL subclasses profile in 12 normolipidemic IDDM patients, and compare it with 11 healthy controls. Four plasma LDL subfractions were isolated by sequential ultracentrifugation in the density range (1.025- 1.063 g/ml) and were characterized by their content of free and esterified cholesterol, triglycerides, phospholipids, and proteins. The net electrical charge was evaluated. Plasma concentration of the two denser LDL subfractions were higher in IDDM patients vs control subjects, due to an increase in cholesterol (free and esterified and phospholipids, while more buoyant subfractions in the two groups were not diferent. In IDDM patients the LDL profile was skewed towards the dense subclasses LDL-III and LDL-IV, being significant this increase for LDL-IV: 22.3 ñ 5.2 vs 18.3 ñ 4.0 per cent, p<0.05, XñDS. In the healthy controls the LDL profile was skewed toward the lighter subclasses (LDL-I and LDL-II), being significant for LDL-II: 30.0 ñ 4.3 vs 23.3 ñ 4.2 per cent, p<0.005. Diabetic patients, even those who are normolipidemic, present increased risk of premature atherosclerosis. This suggest that normal values in lipid and lipoprotein profile can mask deeper alterations, such as changes in the composition and distribution of the denser subclasses, whose characteristics make them potentially more atherogenic. Despite the apparently normolipidemic status, dense LDL particles considered to be atherogenic, are increased in IDDM patients.