Sc Riemens

Elevated plasma cholesteryl ester transfer in NIDDM: relationships with apolipoprotein B-containing lipoproteins and phospholipid transfer protein

Lecithin:cholesteryl acyl transferase (LCAT) and cholesteryl ester transfer protein (CETP) are key factors in the esterification of cholesterol and the subsequent transfer of cholesteryl ester from high density lipoproteins (HDL) towards very low and low density lipoproteins (VLDL + LDL). Phospholipid transfer protein (PLTP), lipoprotein lipase (LPL) and hepatic lipase (HL) are involved in plasma phospholipid and triglyceride metabolism and also affect HDL. Equivocal changes in plasma cholesteryl ester transfer have been reported in non-insulin-dependent diabetes mellitus (NIDDM). In 16 NIDDM men with plasma triglycerides < or = 4.5 mmol/l and cholesterol < or = 8.0 mmol/l. plasma cholesteryl ester transfer (CET), cholesterol esterification rate, LCAT and PLTP activity levels were higher (P < 0.05 to P < 0.02) in conjunction with higher plasma triglycerides (P < 0.01) and lower HDL cholesterol and cholesteryl ester levels (P < 0.05) compared to 16 matched healthy men. Multiple stepwise regression analysis demonstrated that CET was positively related to VLDL + LDL cholesterol (P < 0.001), triglycerides (P = 0.001), PLTP activity (P = 0.007) and CETP activity (P = 0.008, multiple r = 0.94). NIDDM had no effect on CET, independently from these parameters. HDL cholesteryl ester was negatively related to CET (P= 0.017), HL activity (P = 0.033) and NIDDM (P = 0.047) and positively to LCAT activity levels (P = 0.034, multiple r = 0.68). It is concluded that the elevated CET in plasma from NIDDM patients is associated with higher plasma triglycerides and PLTP activity levels. Furthermore, our data suggest that in normo- and moderately dyslipidaemic subjects PLTP and CETP activity levels per se may influence the rate of cholesteryl ester transfer in plasma. Plasma cholesteryl ester transfer appears to be a determinant of HDL cholesteryl ester, but other factors are likely to contribute to lower HDL cholesteryl ester levels in NIDDM.

Plasma phospholipid transfer protein activity is related to insulin resistance : impaired acute lowering by insulin in obese Type II diabetic patients

Summary Cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) have important functions in high density lipoprotein (HDL) metabolism. We determined the association of plasma CETP and PLTP activities (measured with exogenous substrate assays) with insulin resistance, plasma triglycerides (TG) and non-esterified fatty acids (NEFA), and assessed the lipid transfer protein response to insulin during a 6–7 h hyperinsulinaemic euglycaemic clamp in non-obese and obese healthy subjects and patients with Type II (non-insulin-dependent) diabetes mellitus (n = 8 per group). Plasma PLTP activity was higher in obese healthy subjects and obese Type II diabetic patients compared with non-obese healthy subjects (p < 0.05 to 0.01) and was correlated with insulin resistance, plasma TG and NEFA (p = 0.02 to < 0.01). In non-obese healthy subjects, insulin decreased plasma TG and increased the HDL cholesteryl ester (CE)/TG ratio (p < 0.01 compared with saline infusion). Plasma PLTP activity fell by 14 % at the end of the clamp (p < 0.01 compared with saline) but CETP activity did not change. The decreases in plasma NEFA, TG and PLTP activity and the rise in HDL CE/TG were smaller in obese Type II diabetic patients than in non-obese healthy subjects (p < 0.01 for all). Baseline HDL CE/TG was negatively correlated with plasma TG (p < 0.001, n = 32) and PLTP activity (p < 0.01) but not with CETP activity. Likewise, the rise in HDL CE/TG during the clamp was related to the fall in plasma TG (p < 0.001) and in PLTP activity (p < 0.02). It is concluded that plasma PLTP, but not CETP, is regulated by insulin in an acute setting. High plasma PLTP activity is associated with insulin resistance in conjunction with altered NEFA and triglyceride metabolism. High plasma TG and PLTP activity have coordinate effects on HDL metabolism. [Diabetologia (1998) 41: 929–934]

Lack of relationship between 11β-hydroxysteroid dehydrogenase setpoint and insulin sensitivity in the basal state and after 24h of insulin infusion in healthy subjects and type 2 diabetic patients

OBJECTIVES To test whether insulin resistance in type 2 diabetes mellitus is associated with an altered overall setpoint of the 11β‐hydroxysteroid dehydrogenase (11βHSD) mediated cortisol to cortisone Inter‐conversion towards cortisol, and to evaluate whether changes in insulin sensitivity induced by antecedent hyperinsulinaemia are related to changes in the 11βHSD setpoint.

Enhanced escape of non-esterified fatty acids from tissue uptake: its role in impaired insulin-induced lowering of total rate of appearance in obesity and Type II diabetes mellitus

Aims/hypothesis. To estimate non-esterified fatty acids kinetics in patients with Type II (non-insulin-dependent) diabetes mellitus and obese subjects in the postabsorptive state and during hyperinsulinaemia using non-equlibrium tracer conditions.¶Methods. We evaluated the effect of hyperinsulinaemia [euglycaemic clamp with insulin infused at 30 mU · kg–1· h–1 (3–4 h) and 150 mU · kg–1· h–1 (3 h)] on non-esterified fatty acid kinetics, traced with [14C]-palmitate using non-equlibrium tracer conditions in non-obese and obese healthy subjects and Type II diabetic patients (10 per group). Michaelis-Menten kinetics were applied for total non-esterified fatty acid disposal, which was assumed to be composed of total arterial plasma non-esterified fatty acid rate of appearance (equalling the rate of disappearance) and tissue uptake of non-esterified fatty acids derived from intravascular triglyceride hydrolysis. A model was developed to calculate the rate of escape of non-esterified fatty acids from tissue uptake and the net rate of tissue lipolysis.¶Results. Total arterial plasma non-esterified fatty acid rate of appearance was lower in non-obese healthy subjects than in the other groups at low insulin infusion (p < 0.05) and in obese Type II diabetic patients at high insulin infusion (p < 0.05). Plasma triglycerides were also lowest in non-obese healthy subjects during hyperinsulinaemia (p < 0.05 from other groups). The rate of escape from tissue uptake decreased during hyperinsulinaemia (p < 0.05 for each group) but remained higher in obese Type II diabetic patients (p < 0.05 from non-obese healthy subjects). In contrast, net rate of tissue lipolysis was not different between the groups at baseline and its decline during hyperinsulinaemia (p < 0.05 for each group) was similar in all groups.¶Conclusion/interpretation. This study challenges the view that the antilipolytic effect of insulin is impaired in Type II diabetes and obesity. We suggest that a high plasma triglyceride concentration causes a higher escape of non-esterified fatty acids from tissue uptake, leading to an impaired suppression of total arterial plasma rate of appearance during a low degree of hyperinsulinaemia in obese subjects and Type II diabetic patients and during a high degree of hyperinsulinaemia in obese Type II diabetic patients. [Diabetologia (2000) 43: 416–426]

Lowering of plasma phospholipid transfer protein activity by acute hyperglycaemia-induced hyperinsulinaemia in healthy men

Human plasma contains two lipid transfer proteins involved in the remodelling of plasma lipoproteins; cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP). CETP mediates the transfer/exchange of cholesterylesters, triglycerides and phospholipids between high-density lipoproteins (HDL) and chylomicron (remnants), very low-density lipoproteins (VLDL) and low density lipoproteins (LDL). The physiological function of PLTP is unknown. It is able to transfer phospholipids (but not neutral lipids) between lipoproteins and to modulate HDL particle size in vitro. The effects of acute endogenous hyperinsulinaemia on plasma CETP and PLTP activity, as well as on lipid and lipoprotein levels, were assessed in eight healthy men during a 3-h hyperglycaemic clamp. Another group of seven men received an infusion of an equal volume of saline in order to detect possible dilution effects or effects on lipoprotein changes over time (control group). Plasma cholesterol and triglyceride concentrations fell during the clamp and the decreases were significantly different from the minor changes during saline infusion in the control group (p < 0.05 and p < 0.01, respectively). Plasma CETP activity levels did not change, but plasma PLTP activity levels decreased by 7.7 and 5.1% after 2 and 3 h of hyperglycaemia (p < 0.01 for each time-point). The hyperglycaemia-induced mean percentage change in PLTP activity levels during the 3 h of the clamp was greater than the essentially absent change during the NaCl infusion (p < 0.05). Plasma PLTP activity during the clamp was related negatively to the insulin sensitivity index (p < 0.01 by analysis of covariance). It is concluded that acute hyperglycaemia-induced hyperinsulinaemia lowers plasma PLTP, but not CETP activity levels, either directly or in conjunction with an effect on plasma lipoproteins.

Insulin decreases plasma cholesteryl ester transfer but not cholesterol esterification in healthy subjects as well as in normotriglyceridaemic patients with type 2 diabetes.

Plasma cholesterol esterification (EST) and subsequent cholesteryl ester transfer (CET) from high‐density lipoproteins (HDLs) towards apolipoprotein (apo) B‐containing lipoproteins are key steps in HDL metabolism.

Cholesteryl Ester Transfer Protein Gene Polymorphism Is a Determinant of HDL Cholesterol and of the Lipoprotein Response to a Lipid-Lowering Diet in Type 1 Diabetes

The TaqlB cholesteryl ester transfer protein (CETP) gene polymorphism (B1B2) is a determinant of HDL cholesterol in nondiabetic populations. Remarkably, this gene effect appears to be modified by environmental factors. We evaluated the effect of this polymorphism on HDL cholesterol levels and on the lipoprotein response to a linoleic acid-enriched, low-cholesterol diet in patients with type 1 diabetes. In 44 consecutive type 1 diabetic patients (35 men), CETP polymorphism, apolipoprotein (apo) E genotype, serum lipoproteins, serum CETP activity (measured with an exogenous substrate assay, n = 30), clinical variables, and a diet history were documented. The 1-year response to diet was assessed in 14 type 1 diabetic patients, including 6 B1B1 and 6 B1B2 individuals. HDL cholesterol was higher in 10 B2B2 than in 14 B1B1 homozygotes (1.63 ± 0.38 vs. 1.24 ± 0.23 mmol/l, P < 0.01). HDL cholesterol, adjusted for triglycerides and smoking, was 0.19 mmol/l higher for each B2 allele present. CETP activity levels were not significantly different between CETP genotypes. Multiple regression analysis showed that VLDL + LDL cholesterol was associated with dietary polyunsaturated: saturated fatty acids ratio (P < 0.02) and total fat intake (P < 0.05) in the B1B1 homozygotes only and tended to be related to the presence of the apo E4 allele (P < 0.10). In response to diet, VLDL + LDL cholesterol fell (P < 0.05) and HDL cholesterol remained unchanged in 6 B1B1 homozygotes. In contrast, VLDL + LDL cholesterol was unaltered and HDL cholesterol decreased (P < 0.05) in 6 B1B2 heterozygotes (P < 0.05 for difference in change in VLDL + LDL/HDL cholesterol ratio). This difference in response was unrelated to the apo E genotype. Thus, the TaqlB CETP gene polymorphism is a strong determinant of HDL cholesterol in type 1 diabetes. This gene effect is unlikely to be explained by a major influence on the serum level of CETP activity, as an indirect measure of CETP mass. Our preliminary data suggest that this polymorphism may be a marker of the lipoprotein response to dietary intervention.

Higher high density lipoprotein cholesterol associated with moderate alcohol consumption is not related to altered plasma lecithin:cholesterol acyltransferase and lipid transfer protein activity levels

Lecithin:cholesterol acyltransferase (LCAT), cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) are important factors involved in HDL metabolism. Altered plasma activity levels of these factors could play a role in the increase in high density lipoprotein (HDL) cholesterol associated with moderate alcohol consumption. We measured plasma LCAT, CETP and PLTP activities with exogenous substrate assays, as well as lipoproteins and HDL lipids in 6 alcohol-abstaining men, 18 matched men who used < or = 1 and 18 men who used > or = 1 alcohol-containing drinks per day. Plasma cholesterol and triglycerides were similar in the three groups. HDL total cholesterol, HDL cholesteryl ester, HDL free cholesterol and HDL triglycerides were higher in the alcohol drinkers compared to the abstainers (all P < 0.05). No differences in plasma LCAT, CETP and PLTP activity levels were observed between the three groups. Analysis of covariance also demonstrated that the use of alcohol was associated with higher HDL cholesterol (P < 0.04), whereas plasma LCAT, CETP and PLTP activity levels were not related to alcohol consumption. Furthermore, HDL cholesteryl ester was positively associated with LCAT activity (P < 0.001), PLTP activity (P < 0.01) and alcohol intake (P < 0.04) and negatively with plasma triglycerides (P < 0.001) and CETP activity (P < 0.03); indicating that alcohol influenced HDL cholesteryl ester independently from these biochemical parameters. The higher HDL cholesterol associated with moderate alcohol consumption is, therefore, unlikely to be caused by and effect on plasma LCAT, CETP or PLTP activity levels.

Plasma cholesteryl ester transfer and hepatic lipase activity are related to high-density lipoprotein cholesterol in association with insulin resistance in type 2 diabetic and non-diabetic subjects

We evaluated the hypothesis that plasma cholesteryl ester transfer (CET) and lipase activities are influenced by insulin sensitivity and contribute to the low high-density lipoprotein (HDL) cholesterol observed in type 2 diabetic patients and insulin-resistant non-diabetic subjects. Sixteen type 2 diabetic and 16 non-diabetic subjects participated. Diabetic and non-diabetic subjects were divided in equal groups of eight subjects with low or high insulin sensitivity, which was documented as the glucose infusion rate (M-value) during the last hour of a 3-h euglycaemic hyperinsulinaemic clamp (150 mU kg(-1) h(-1), blood glucose target 4.6 mmol L(-1)). Post-heparin plasma lipoprotein lipase (LPL) and hepatic lipase (HL) activities were measured in samples obtained 1-2 weeks before the clamp. Plasma CET was measured by a radioisotope method. Compared to non-diabetic men with high insulin sensitivity (n = 8) HDL cholesterol was lower in type 2 diabetic men (n=8, p<0.01) and non-diabetic men (n=8, p <0.05) with low insulin sensitivity, and the HDL cholesterylester content was lower in type 2 diabetic men with high insulin sensitivity (n=8, p<0.05). In non-diabetic subjects with high insulin sensitivity, plasma CET was lower than in the other groups (p<0.05 for all). Multiple regression analysis showed that plasma CET (p=0.001) and HL activity (p=0.02) were independently and negatively associated with the M-value. No association between the M-value and LPL activity was observed. Independent negative relationships of HDL cholesterol with plasma CET (p = 0.04) and HL activity (p=0.03) were observed. This study supports the hypothesis that a low HDL cholesterol associated with insulin resistance in type 2 diabetic and non-diabetic subjects is related to a high plasma CET and a high HL activity.We evaluated the hypothesis that plasma cholesteryl ester transfer (CET) and lipase activities are influenced by insulin sensitivity and contribute to the low high-density lipoprotein (HDL) cholesterol observed in type 2 diabetic patients and insulin-resistant non-diabetic subjects. Sixteen type 2 diabetic and 16 nondiabetic subjects participated. Diabetic and non-diabetic subjects were divided in equal groups of eight subjects with low or high insulin sensitivity, which was documented as the glucose infusion rate (M-value) during the last hour of a 3-h euglycaemic hyperinsulinaemic clamp (150 mU kg

Effect of insulin on apolipoprotein(a) synthesis

Summary Raised plasma lipoprotein(a) (lp(a)) concentrations have been reported in patients with Type I (insulin-dependent) diabetes mellitus, which were lowered by insulin therapy. To investigate the biochemical background of these changes, we studied the effect of insulin on apolipoprotein(a) (apo(a)) synthesis and mRNA levels in primary cultures of cynomolgus monkey hepatocytes. Low concentrations of insulin (10 nmol/l) had a small but significant decreasing effect (p < 0.046) on apolipoprotein(a) secretion (–16 %). Maximum inhibition (–33 %) was obtained after incubation for 72 h with 1000 nmol/l insulin. Apolipoprotein B-100 secretion was 30 %–36 % decreased when using 10–1000 nmol/l and no change was observed for the secretion of apolipoprotein A-1 and albumin which were measured as control proteins. Steady state apolipoprotein(a) mRNA concentrations paralleled the decrease in apolipoprotein(a) synthesis (–29 % after incubating the cells for 48 h with 100 nmol/l insulin) indicating that the decreased synthesis is regulated at the (post)-transcriptional level. Concentrations of apolipoprotein B-100 and apolipoprotein A-1 mRNA were not changed after incubation with insulin. We conclude that high concentrations of insulin suppress apolipoprotein(a) synthesis in monkey hepatocytes at the (post)-transcriptional level. These data may provide an explanation for the increased plasma concentrations of lipoprotein(a) as found in patients with insulin dependent diabetes mellitus. [Diabetologia (1999) 42: 41–44]