Apo B-containing lipoprotein particles in poorly controlled insulin-dependent diabetes

Metabolism of very-low-density lipoprotein and low-density lipoprotein containing apolipoprotein C-III and not other small apolipoproteins

OBJECTIVE

We aimed to clarify the influence of apolipoprotein C-III (apoCIII) on human apolipoprotein B metabolism.

METHODS AND RESULTS

We studied the kinetics of 4 very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and low-density lipoprotein (LDL) types containing: (1) otherApos-CIII-: none of apoCIII, apoAII, apoCI, apoCII, or apoE; (2) otherApos+CIII-: no apoCIII but at least one of the others; (3) otherApos-CIII+: apoCIII, but not any others; and (4) otherApos+CIII+: apoCIII and at least one other. VLDL and IDL otherApos-CIII+ and otherApos-CIII- had similar rates of lipolytic conversion to smaller particles. However, light LDL otherApos-CIII+ compared with otherApos-CIII- had much faster conversion to dense LDL as did light LDL otherApos+CIII+ compared with otherApos+CIII-. VLDL and IDL otherApos-CIII+ had minimal direct removal from circulation, whereas VLDL and IDL otherApos+CIII-, rich in apoE, showed fast clearance. Lipoproteins in fraction otherApos+CIII+ also rich in apoE had very low clearance.

CONCLUSIONS

The results suggest that apoCIII strongly inhibits hepatic uptake of VLDL and IDL overriding the opposite influence of apoE when both are present. The presence of apoCIII on dense VLDL is not associated with slow conversion to IDL, a lipoprotein lipase-dependent process; but when on light LDL, apoCIII is associated with enhanced conversion to dense LDL, a process involving hepatic lipase.

Lipoprotein composition in children and adolescents with type 1 diabetes mellitus

Atherosclerotic cardiovascular diseases are the major causes of morbidity and mortality in patients with diabetes mellitus. Both quantitative and qualitative abnormalities of lipo-proteins are associated with the development of atherogenesis. In this study, the prevalence of dyslipidemia and the relative levels of glycosylated lipoproteins in 20 children and adolescents with type 1 diabetes mellitus were determined. Lipid profile, apolipoproteins A-I and B, Lp(a) and LpA-I in plasma were assayed. LpB and glycosylated HDL and LDL were evaluated by ELISA. Diabetic patients and controls had normal lipid profiles, but the diabetic group showed significantly higher LpA-I and lower LpA-I:A-II concentrations than controls. The diabetic group showed a significantly higher glycosylation level of HDL than controls and did not show a statistical difference for glycosylated LDL. No significant correlation between glycosylated lipoproteins, glycemia or HbA1c was found. In conclusion, these results suggest that type 1 diabetic patients develop important qualitative lipid abnormalities.

Are predictors of coronary heart disease and lower-extremity arterial disease in type 1 diabetes the same? A prospective study

In the Type 1 diabetes population, coronary heart disease (CHD) and lower-extremity arterial disease (LEAD) are the two common macrovascular complications leading to early mortality and morbidity. However, it is not clear if these two complications share the same risk factors. The Pittsburgh Epidemiology of Diabetes Complications (EDC) Study prospectively examined and compared the risk factors for LEAD and CHD (including CHD morbidity and mortality). EDC subjects (332 men and 325 women), all diagnosed at Children's Hospital of Pittsburgh between 1950 and 1980, were first examined at baseline (1986-1988), and then biennially, for diabetes complications and their risk factors. Data used in the current analysis were from the first 6 years of follow-up, 98% provided at least some follow-up data for these analyses. CHD was defined as the presence of angina (diagnosed by the EDC examining physician) or a history of confirmed myocardial infarction or CHD death. An ankle-to-arm ratio of less than 0.9 at rest was considered to be evidence of LEAD. Among 635 subjects without CHD at baseline, 57 developed CHD (1.69/100 person-years), and among 579 without LEAD at baseline, 70 developed LEAD (2.31/100 person-years). CHD incidence rate was slightly higher in males, while LEAD incidence rate was slightly higher in females. Compared to non-incident cases, subjects who developed either complication were older, had a longer diabetes duration, higher LDL and total cholesterol, and were more likely to be hypertensive. In multivariate analyses, hypertension, low HDL cholesterol level, high white cell count, depression, and nephropathy were the independent risk factors for CHD (including morbidity and mortality). For LEAD, higher HbA1 level, higher LDL cholesterol level and smoking were the important contributing factors. In conclusion, the risk factor patterns differ between the two vascular complications. Glycemic control does not predict CHD overall but does predict LEAD, while hypertension and inflammatory markers are more closely related to CHD than to LEAD.

Effects of insulin deficiency on lipoproteins and their hepatic receptors in Rico rats

The present study was designed to examine the effect of streptozotocin (STZ)-induced diabetes on the plasma lipoprotein profile and hepatic expression of the LDL receptor and HDL binding protein (HB2) in hypercholesterolemic Rico rats. The plasma level of HDL1 (density range 1.040-1.063), which is particularly high in this rat strain, decreased (-25%) 28 d after STZ administration (50 mg/kg). In contrast, the treatment increased (+54%) the plasma concentration of HDL2 (density range 1.063-1.210). These variations in the lipoprotein concentrations were associated with inverse changes in the hepatic protein levels of the LDL receptor (+118%) and HB2 (-46%). These results suggest that the hepatic expression of HB2, a putative HDL receptor, can influence the plasma level of apo Al-rich HDL as has already been shown for the LDL receptor for apo B/E containing lipoproteins.