Peter H. Winocour

Serum paraoxonase activity in familial hypercholesterolaemia and insulin-dependent diabetes mellitus

The activity of serum paraoxonase, an enzyme located on high-density lipoprotein, has been investigated in familial hypercholesterolaemia (FH) and insulin dependent diabetes mellitus (IDDM). Increases in total serum cholesterol and apolipoprotein B were present in both FH and IDDM compared to healthy controls and in the patients with IDDM, serum triglycerides were also raised. The serum HDL-cholesterol concentrations in controls and patients with FH and IDDM did not differ significantly. Serum paraoxonase activity was significantly lower in both the FH and IDDM populations than in controls (P less than 0.001 and P less than 0.01, respectively). 72% of the FH population and 67% of the IDDM population were in the lower half of the frequency distribution for serum paraoxonase (activity of less than 112 U/l). It is likely that the common factor related to low paraoxonase activity is hyperlipidaemia. It is possible that paraoxonase has a physiological role in lipid metabolism and that decreases in its activity may accelerate atherogenesis.

Lipoprotein (a) and Microvascular Disease in Type 1 (Insulin-dependent) Diabetes

The influence of albuminuria and proliferative retinopathy on concentrations of serum lipoprotein (a) was examined cross‐sectionally in 90 Type 1 diabetic patients. Concentrations of lipoprotein (a) were less in those with normoalbuminuria (90 (8–882) (median (range)) U l−1) than in those with micro‐ or macro‐albuminuria (137 (19–1722) U l−1, p < 0.05). The prevalence of patients whose lipoprotein (a) concentrations were greater than 200 U l−1 was also greater (45% vs 24%, p = 0.03) among patients with albuminuria, but no difference was found between the microalbuminuric and macroalbuminuric groups (53 and 41%, respectively), or between those with or without proliferative retinopathy. The present finding that lipoprotein (a) concentrations may be increased at an early stage of diabetic renal disease may in part account for the excess ischaemic heart disease associated with diabetic nephropathy.

Abnormalities of VLDL, IDL, and LDL characterize insulin-dependent diabetes mellitus.

To identify abnormalities of serum lipoprotein composition and concentration that were specific to insulin-dependent diabetes mellitus (IDDM), the procedure of discontinuous gradient ultracentrifugation was employed to isolate lipoprotein fractions in 44 patients with IDDM, 24 nondiabetic subjects with similar lipid and lipoprotein concentrations, and 19 healthy normocholesterolemic (less than 5.2 mmol/l [less than 200 mg/dl]) subjects. The mass concentration of low density lipoprotein (LDL) was greater in IDDM than in both control groups. The free cholesterol to phospholipid ratio in large very low density lipoprotein (VLDL) was greatest in IDDM in comparison with both of the other groups. The contribution of triglyceride to total large VLDL mass was greater, whereas that of phospholipids was lower, in IDDM than in the dyslipidemic nondiabetic group. Protein concentration was reduced and phospholipid increased in small VLDL in IDDM in comparison with both control groups, and the contribution from protein to lipoprotein mass was least in IDDM. Similarly in intermediate density lipoprotein (IDL), the protein concentration and its contribution to overall mass was also lower in IDDM than in either control group, but by contrast, the phospholipid content was increased. The cholesteryl ester to protein ratio was highest in both small VLDL and IDL in IDDM in comparison with both control groups, whereas the free cholesterol to phospholipid ratio in IDL was least in IDDM. In LDL, total cholesterol and triglyceride concentrations were greatest and the contribution from protein to lipoprotein mass was least in IDDM in comparison with both control groups. The LDL free cholesterol to phospholipid ratio was greater in IDDM than in dyslipidemic control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

The relationship between autonomic neuropathy and urinary sodium and albumin excretion in insulin-treated diabetics.

There is evidence to suggest that renal function may alter in the presence of autonomic neuropathy. Albumin excretion rate (AER) and sodium excretion rate (NaER) in timed daytime (erect) and night‐time (supine) urine collections were assessed in 20 insulin‐treated diabetics with and in 20 without established autonomic neuropathy, matched for age, sex, duration of diabetes, diabetic control, and systolic blood pressure. All patients were free of proteinuria on albustix testing and had normal serum levels of urea and creatinine.

Precise measurement of glycated serum albumin by column affinity chromatography and immunoturbidimetry

A precise and easy method for measuring glycated serum albumin using affinity chromatography and immunoturbidimetry on a centrifugal analyser, ensuring complete recovery of serum albumin is described.

A cross-sectional evaluation of cardiovascular risk factors in coronary heart disease associated with Type 1 (insulin-dependent) diabetes mellitus

The contribution from lipoproteins, blood pressure, albuminuria and demographic variables to coronary heart disease in 90 adult subjects with and 172 without Type 1 diabetes mellitus was examined in order to investigate whether risk factors were of equivalent importance in diabetic and non-diabetic coronary heart disease. Coronary heart disease (CHD) was present in roughly 25% of subjects in each group. In Type 1 diabetes those with CHD had significantly higher levels of systolic blood pressure, albumin excretion, serum creatinine, triglycerides, VLDL cholesterol and C-peptide, and reductions in serum concentrations of HDL and HDL2 cholesterol, in comparison to those without. However, the prevalence of smokers, and concentrations of Lp(a), ApoB and fibrinogen were comparable. Blood pressure and HDL cholesterol were higher in the CHD group with Type 1 diabetes in comparison to the nondiabetic group with CHD, although LDL concentrations and the prevalence of Lp(a) concentrations > 200 mg/l were lower. Logistic regression analysis revealed the strongest independent predictors of CHD in Type 1 diabetes were serum triglycerides, systolic blood pressure, age, serum LDL cholesterol, and the daily insulin dosage, whereas in the non-diabetic control group HDL2 cholesterol, Lp(a), ApoA1 and ApoB, total serum cholesterol and body mass index were additional predictors. CHD in Type 1 diabetes appears to be most closely associated with increasing age and levels of blood pressure and total serum lipids. Apolipoproteins and albuminuria did not seem to be important independent predictors of CHD in Type 1 diabetes, whereas the former were more clearly associated with CHD in non-diabetic controls.

Influence of early diabetic nephropathy on very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL), and low density lipoprotein (LDL) composition.

The procedure of discontinuous gradient ultracentrifugation (DGU) was used to characterize the influence of early diabetic nephropathy on the composition of very low density lipoprotein (VLDL, flotation density 60-400 Svedberg (Sf) units), low density lipoprotein (LDL, flotation density 0-12 Sf) and subfractions of intermediate density lipoprotein (IDL1 and IDL2, 20-60 and 12-20 Sf, respectively). Forty-six subjects with type 1 (insulin-dependent) diabetes and serum creatinine, less than 140 mumol/l were studied, of whom 23 consistently had normal rates of albumin excretion (AER less than 15 micrograms/min), and 23 had persistent albuminuria (AER 20.0-960.6 micrograms/min). The two groups were similar with respect to total serum lipids, glycaemic control, age and body mass. The composition (lipid, protein and phospholipid) and mass of VLDL, LDL and IDL2 was not appreciably altered by early nephropathy, but free and total cholesterol concentration in IDL1 (Sf 20-60) was increased (total cholesterol 0.68 (0.09) (mean (SE)) vs. 0.47 (0.07) mmol/l, and free cholesterol 0.27 (0.04) vs. 0.17 (0.03) mmol/l, both P less than 0.05). The explanation of these findings was probably an accumulation in the circulation of the remnants of chylomicron metabolism and/or intermediates in the conversion from VLDL to IDL1. In addition, there was a decrease in serum high density lipoprotein (HDL) cholesterol in early nephropathy (1.27 (0.06) vs. 1.38 (0.10) mmol/l, P less than 0.05), due to a decrease in the HDL2 cholesterol subfraction (P less than 0.05). These findings may in part explain the increased risk of premature atherosclerosis associated with the development of albuminuria.

Apolipoprotein E polymorphism and lipoproteins in insulin-treated diabetes mellitus

Apolipoprotein E (apo E), a component of VLDL, HDL and chylomicron remnants, is inherited at a single genetic locus with 3 common alleles (epsilon 2, epsilon 3 and epsilon 4). epsilon 2 homozygosity is found in 0-2% of healthy populations, but in 75-100% of subjects with type III hyperlipoproteinaemia, in whom an increased prevalence of glucose intolerance has previously been reported. The lipoprotein abnormality associated with diabetes mellitus has features in common with type III hyperlipoproteinaemia and both conditions lead to accelerated atherogenesis with a similar anatomical distribution. We have therefore examined the frequency of apo E genotypes in 120 subjects with insulin-treated diabetes mellitus (ITDM) and 107 healthy controls, and examined the effect of apo E polymorphism on lipoproteins in the diabetic group. As in the general population, the apo E phenotype in ITDM was a significant determinant of the total serum and LDL cholesterol concentrations which were lowest in patients possessing the epsilon 2 allele, intermediate in those homozygous for epsilon 3 and highest in those with an epsilon 4 allele. The observed gene frequencies of epsilon 2 (0.091), epsilon 3 (0.780) and epsilon 4 (0.130) were similar to those of the healthy control group and those in the general population. However, there was an unexpected increase (P less than 0.0002) in epsilon 2 homozygosity of 6.7% compared to a prevalence of 0.8% predicted both from the Hardy-Weinberg equilibrium and the 0.9% prevalence observed in the healthy control group. This suggests either that epsilon 2 homozygosity increases susceptibility to the development of ITDM or that the two conditions are genetically linked.(ABSTRACT TRUNCATED AT 250 WORDS)

The relevance of persistent C-peptide secretion in type 1 (insulin-dependent) diabetes mellitus to glycaemic control and diabetic complications

The effect of residual C-peptide secretion in longer standing IDDM on glycaemic control and the prevalence and evolution of complications over 2 years was evaluated. Thirty-one subjects with IDDM of 15.4 (1.5) years duration (mean SEM)) and residual C-peptide secretion, were matched for age, duration of diabetes and body mass index with 31 subjects without detectable C-peptide secretion. At trial entry and over 2 years, levels of HbA1, fructosamine and mean blood glucose were essentially similar in both groups. Levels of glycated albumin (GSA) were significantly higher in the C-peptide negative group after 3 and 9 months (P less than 0.05). An increased prevalence of proliferative retinopathy in the C-peptide negative group and of peripheral vascular disease in the C-peptide secretor group was apparent at entry to the study (both P less than 0.05), although no significant differences were observed after 1 or 2 years. There was no difference in the prevalence of peripheral or autonomic neuropathy, hypertension, nephropathy or ischaemic heart disease. Subjects with C-peptide concentrations greater than 0.100 pmol/ml at entry to this study had lower daily insulin requirements after 1 and 2 years, but behaved like the larger group with any detectable C-peptide secretion in all other respects. Residual C-peptide secretion was lost after 1 year in 7 patients, in whom glycaemic control during the year had been particularly poor. Insulin antibody titres were no different in the 2 groups at any time point. This study suggests that residual C-peptide secretion in longer standing IDDM confers the potential for limited improvements in glycaemic control. This effect appears to be insufficient to prevent the evolution of microvascular complications over a 2-year period. Residual C-peptide secretion and relative hyperinsulinaemia may be associated with an excess of peripheral vascular disease.

An analysis of glycosylated blood proteins and blood glucose profiles over one year in patients with type 1 diabetes.

The clinical value of prospective measurement of several direct and indirect measures of blood glucose control in the management of Type 1 diabetes has been investigated. Ninety‐eight Type 1 diabetic patients were followed over a period of 1 year after a 6‐week period of intensification of management, with monthly measurements of blood glucose profiles and 3‐monthly HbA1, glycosylated serum albumin, and fructosamine measurements. All measures improved markedly after the initial 6‐week period (p < 0.001), and all except glycosylated serum albumin and fructosamine then remained relatively stable. Of fourteen serial comparisons, glycosylated blood proteins were significantly correlated more often with levels of mean blood glucose and M value (on 4–7 occasions, rs 0.30‐0.58) than with fasting blood glucose levels (on only 2–3 occasions, rs 0.34‐0.44). Serum fructosamine levels correlated significantly with mean blood glucose on four occasions (rs 0.30‐0.50), whilst glycosylated serum albumin and HbA1 correlated with mean blood glucose on six occasions (rs 0.36‐0.54). Glycosylated serum albumin correlated with HbA1 and fructosamine levels throughout the year (rs 0.47‐0.68 and 0.48‐0.76, respectively), but HbA1 and fructosamine were less clearly correlated with each other (rs 0.38‐0.44), with no significant association immediately after the period of intensive management or 3 months later. When the various measures were used to categorize blood glucose control, HbA1 was more often discordant with fructosamine than with glycosylated albumin. Over the year glycosylated albumin and fructosamine values were discordant on 6–15% of comparisons. Significant intra‐individual variations in levels of glycosylated albumin, fructosamine, mean blood glucose, and the M value were observed during the stable year of the study. Cluster analyses revealed that fructosamine values were least closely associated with other variables. In 19 patients with normal HbA1 levels and near normal mean blood glucose and M values throughout the year following intensified management, a substantial proportion had persistently high levels of fructosamine and glycosylated albumin. We conclude that the use of several measures of blood glucose control in the management of Type 1 diabetes provides complementary information. Fructosamine is a less appropriate measure of blood glucose control in Type 1 diabetes than glycosylated serum albumin.