Plasma low density lipoprotein transport kinetics in noninsulin-dependent diabetes mellitus

Modification of lipoprotein metabolism and function driving atherogenesis in diabetes

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease, characterized by raised blood glucose levels and impaired lipid metabolism resulting from insulin resistance and relative insulin deficiency. In diabetes, the peculiar plasma lipoprotein phenotype, consisting in higher levels of apolipoprotein B-containing lipoproteins, hypertriglyceridemia, low levels of HDL cholesterol, elevated number of small, dense LDL, and increased non-HDL cholesterol, results from an increased synthesis and impaired clearance of triglyceride rich lipoproteins. This condition accelerates the development of the atherosclerotic cardiovascular disease (ASCVD), the most common cause of death in T2DM patients. Here, we review the alteration of structure, functions, and distribution of circulating lipoproteins and the pathophysiological mechanisms that induce these modifications in T2DM. The review analyzes the influence of diabetes-associated metabolic imbalances throughout the entire process of the atherosclerotic plaque formation, from lipoprotein synthesis to potential plaque destabilization. Addressing the different pathophysiological mechanisms, we suggest improved approaches for assessing the risk of adverse cardiovascular events and clinical strategies to reduce cardiovascular risk in T2DM and cardiometabolic diseases.

Insulin Prevents Hypercholesterolemia by Suppressing 12a-Hydroxylated Bile Acid Production

Background: The risk of cardiovascular disease in type 1 diabetes remains extremely high, despite marked advances in blood glucose control and even the widespread use of cholesterol synthesis inhibitors. Thus, a deeper understanding of insulin regulation of cholesterol metabolism, and its disruption in type 1 diabetes, could reveal better treatment strategies. Methods: To define the mechanisms by which insulin controls plasma cholesterol levels, we knocked down the insulin receptor, FoxO1, and the key bile acid synthesis enzyme, CYP8B1. We measured bile acid composition, cholesterol absorption, and plasma cholesterol. In parallel, we measured markers of cholesterol absorption and synthesis in humans with type 1 diabetes treated with ezetimibe and statins in a double-blind crossover study. Results: Mice with hepatic deletion of the insulin receptor showed marked increases in 12α-hydroxylated bile acids (12HBAs), cholesterol absorption, and plasma cholesterol. This phenotype was entirely reversed by hepatic deletion of FoxO1. FoxO1 is inhibited by insulin, and required for the production of 12HBAs, which promote intestinal cholesterol absorption and suppress hepatic cholesterol synthesis. Knockdown of Cyp8b1 normalized 12HBA levels and completely prevented hypercholesterolemia in mice with hepatic deletion of the insulin receptor (n=5-30) as well as mouse models of type 1 diabetes (n=5-22). In parallel, the cholesterol absorption inhibitor, ezetimibe, normalized cholesterol absorption and LDL-cholesterol in patients with type 1 diabetes as well as, or better than, the cholesterol synthesis inhibitor, simvastatin (n=20). Conclusions: Insulin, by inhibiting FoxO1 in the liver, reduces 12HBAs, cholesterol absorption, and plasma cholesterol levels. Thus, type 1 diabetes leads to a unique set of derangements in cholesterol metabolism, with increased absorption rather than synthesis. These derangements are reversed by ezetimibe, but not statins, which are currently the first line of lipid-lowering treatment in type 1 diabetes. Taken together, these data suggest that a personalized approach to lipid lowering in type 1 diabetes may be more effective and highlight the need for further studies specifically in this group of patients.

Treatment of Hyperlipidemia Changes With Level of Kidney Function-Rationale

Lipoprotein abnormalities such as low levels of high-density lipoprotein (HDL) and high triglycerides (TGs), associated with the metabolic syndrome, are also associated with subsequent decline in kidney function. Patients with end-stage kidney disease also exhibit low HDL and high TGs and a modest reduction in low-density lipoprotein (LDL), although the mechanisms responsible for these changes differ when patients with end-stage kidney disease are compared with those having metabolic syndrome with normal kidney function, as do lipoprotein structures. Among dialysis patients, oxidized LDL, levels of TG-rich intermediate-density lipoprotein, and low HDL are associated with aortic pulsewave velocity and other markers of atherosclerosis. Statins are effective in reducing LDL and do decrease risk of cardiovascular events in patients with CKD not requiring dialysis but have no significant effect on outcomes, including all-cause mortality among dialysis patients. Similarly gemfibrozil and other fibrates lower TGs, increase HDL, and reduce cardiovascular events, but not mortality, among patients with CKD not requiring dialysis but have no significant effect on cardiovascular outcomes in dialysis patients. There is potential clinical benefit in treating elevated LDL, TGs, and low HDL in patients with CKD using statins or fibrates in those not yet requiring dialysis.

The Identification of Novel Protein-Protein Interactions in Liver that Affect Glucagon Receptor Activity

Glucagon regulates glucose homeostasis by controlling glycogenolysis and gluconeogenesis in the liver. Exaggerated and dysregulated glucagon secretion can exacerbate hyperglycemia contributing to type 2 diabetes (T2D). Thus, it is important to understand how glucagon receptor (GCGR) activity and signaling is controlled in hepatocytes. To better understand this, we sought to identify proteins that interact with the GCGR to affect ligand-dependent receptor activation. A Flag-tagged human GCGR was recombinantly expressed in Chinese hamster ovary (CHO) cells, and GCGR complexes were isolated by affinity purification (AP). Complexes were then analyzed by mass spectrometry (MS), and protein-GCGR interactions were validated by co-immunoprecipitation (Co-IP) and Western blot. This was followed by studies in primary hepatocytes to assess the effects of each interactor on glucagon-dependent glucose production and intracellular cAMP accumulation, and then in immortalized CHO and liver cell lines to further examine cell signaling. Thirty-three unique interactors were identified from the AP-MS screening of GCGR expressing CHO cells in both glucagon liganded and unliganded states. These studies revealed a particularly robust interaction between GCGR and 5 proteins, further validated by Co-IP, Western blot and qPCR. Overexpression of selected interactors in mouse hepatocytes indicated that two interactors, LDLR and TMED2, significantly enhanced glucagon-stimulated glucose production, while YWHAB inhibited glucose production. This was mirrored with glucagon-stimulated cAMP production, with LDLR and TMED2 enhancing and YWHAB inhibiting cAMP accumulation. To further link these interactors to glucose production, key gluconeogenic genes were assessed. Both LDLR and TMED2 stimulated while YWHAB inhibited PEPCK and G6Pase gene expression. In the present study, we have probed the GCGR interactome and found three novel GCGR interactors that control glucagon-stimulated glucose production by modulating cAMP accumulation and genes that control gluconeogenesis. These interactors may be useful targets to control glucose homeostasis in T2D.

New insights into the pathophysiology of dyslipidemia in type 2 diabetes

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality for patients with type 2 diabetes, despite recent significant advances in management strategies to lessen CVD risk factors. A major cause is the atherogenic dyslipidemia, which consists of elevated plasma concentrations of both fasting and postprandial triglyceride-rich lipoproteins (TRLs), small dense low-density lipoprotein (LDL) and low high-density lipoprotein (HDL) cholesterol. The different components of diabetic dyslipidemia are not isolated abnormalities but closely linked to each other metabolically. The underlying disturbances are hepatic overproduction and delayed clearance of TRLs. Recent results have unequivocally shown that triglyceride-rich lipoproteins and their remnants are atherogenic. To develop novel strategies for the prevention and treatment of dyslipidaemia, it is essential to understand the pathophysiology of dyslipoproteinaemia in humans. Here, we review recent advances in our understanding of the pathophysiology of diabetic dyslipidemia.

Decreased Insulin Sensitivity and Impaired Fibrinolytic Activity in Type 2 Diabetes Patients and Nondiabetics with Ischemic Stroke

We analyzed (a) insulin sensitivity (IS), (b) plasma insulin (PI), and (c) plasminogen activator inhibitor-1 (PAI-1) in type 2 diabetes (T2D) patients with (group A) and without (group B) atherothrombotic ischemic stroke (ATIS), nondiabetics with ATIS (group C), and healthy controls (group D). IS was determined by minimal model (Si). Si was lower in A versus B (1.18 ± 0.67 versus 2.82 ± 0.61 min-1/mU/L × 104; P < 0.001) and in C versus D (3.18 ± 0.93 versus 6.13 ± 1.69 min-1/mU/L × 104; P < 0.001). PI and PAI-1 were higher in A versus B (PI: 19.61 ± 4.08 versus 14.91 ± 1.66 mU/L; P < 0.001, PAI-1: 7.75 ± 1.04 versus 4.57 ± 0.72 mU/L; P < 0.001) and in C versus D (PI: 15.14 ± 2.20 versus 7.58 ± 2.05 mU/L; P < 0.001, PAI-1: 4.78 ± 0.98 versus 3.49 ± 1.04 mU/L; P < 0.001). Si correlated with PAI-1 in T2D patients and nondiabetics, albeit stronger in T2D. Binary logistic regression identified insulin, PAI-1, and Si as independent predictors for ATIS in T2D patients and nondiabetics. The results imply that insulin resistance and fasting hyperinsulinemia might exert their atherogenic impact through the impaired fibrinolysis.

The regulation of ApoB metabolism by insulin

The leading cause of death in diabetic patients is cardiovascular disease. Apolipoprotein B (ApoB)-containing lipoprotein particles, which are secreted and cleared by the liver, are essential for the development of atherosclerosis. Insulin plays a key role in the regulation of ApoB. Insulin decreases ApoB secretion by promoting ApoB degradation in the hepatocyte. In parallel, insulin promotes clearance of circulating ApoB particles by the liver via the low-density lipoprotein receptor (LDLR), LDLR-related protein 1 (LRP1), and heparan sulfate proteoglycans (HSPGs). Consequently, the insulin-resistant state of type 2 diabetes (T2D) is associated with increased secretion and decreased clearance of ApoB. Here, we review the mechanisms by which insulin controls the secretion and uptake of ApoB in normal and diabetic livers.

Lipoprotein metabolism in patients with type 1 diabetes under intensive insulin treatment

Background

Type 1 diabetes (T1DM) is frequently accompanied by dyslipidemia related with insulin-dependent steps of the intravascular lipoprotein metabolism. T1DM dyslipidemia may predispose to precocious cardiovascular disease and the lipid status in T1DM under intensive insulin treatment has not been sufficiently explored. The aim was to investigate the plasma lipids and the metabolism of LDL and HDL in insulin-treated T1DM patients with high glycemic levels.

Methods

Sixteen male patients with T1DM (26 ± 7 yrs) with glycated hemoglobin >7%, and 15 control subjects (28 ± 6 yrs) were injected with a lipid nanoemulsion (LDE) resembling LDL and labeled with ¹⁴C-cholesteryl ester and ³H-free-cholesterol for determination of fractional clearance rates (FCR, in h^-1) and cholesterol esterification kinetics. Transfer of labeled lipids from LDE to HDL was assayed in vitro.

Results

LDL-cholesterol (83 ± 15 vs 100 ± 29 mg/dl, p=0.08) tended to be lower in T1DM than in controls; HDL-cholesterol and triglycerides were equal. LDE marker ¹⁴C-cholesteryl ester was removed faster from plasma in T1DM patients than in controls (FCR=0.059 ± 0.022 vs 0.039 ± 0.022h-1, p=0.019), which may account for their lower LDL-cholesterol levels. Cholesterol esterification kinetics and transfer of non-esterified and esterified cholesterol, phospholipids and triglycerides from LDE to HDL were also equal.

Conclusion

T1DM patients under intensive insulin treatment but with poor glycemic control had lower LDL-cholesterol with higher LDE plasma clearance, indicating that LDL plasma removal was even more efficient than in controls. Furthermore, HDL-cholesterol and triglycerides, cholesterol esterification and transfer of lipids to HDL, an important step in reverse cholesterol transport, were all normal. Coexistence of high glycemia levels with normal intravascular lipid metabolism may be related to differences in exogenous insulin bioavailabity and different insulin mechanisms of action on glucose and lipids. Those findings may have important implications for prevention of macrovascular disease by intensive insulin treatment.

Removal from the plasma of the free and esterified forms of cholesterol and transfer of lipids to HDL in type 2 diabetes mellitus patients

BACKGROUND

The aim was to investigate new markers for type 2 diabetes (T2DM) dyslipidemia related with LDL and HDL metabolism. Removal from plasma of free and esterified cholesterol transported in LDL and the transfer of lipids to HDL are important aspects of the lipoprotein intravascular metabolism. The plasma kinetics (fractional clearance rate, FCR) and transfers of lipids to HDL were explored in T2DM patients and controls, using as tool a nanoemulsion that mimics LDL lipid structure (LDE).

RESULTS

14C- cholesteryl ester FCR of the nanoemulsion was greater in T2DM than in controls (0.07 ± 0.02 vs. 0.05 ± 0.01 h-1, p = 0.02) indicating that LDE was removed faster, but FCR 3 H- cholesterol was equal in both groups. Esterification rates of LDE free-cholesterol were equal. Cholesteryl ester and triglyceride transfer from LDE to HDL was greater in T2DM (4.2 ± 0.8 vs. 3.5 ± 0.7%, p = 0.03 and 6.8 ± 1.6% vs. 5.0 ± 1.1, p = 0.03, respectively). Phospholipid and free cholesterol transfers were not different.

CONCLUSIONS

The kinetics of free and esterified cholesterol tended to be independent in T2DM patients and the lipid transfers to HDL were also disturbed. These novel findings may be related with pathophysiological mechanisms of diabetic macrovascular disease.

Regulation of hepatic LDL receptors by mTORC1 and PCSK9 in mice

Individuals with type 2 diabetes have an increased risk of atherosclerosis. One factor underlying this is dyslipidemia, which in hyperinsulinemic subjects with early type 2 diabetes is typically characterized by increased VLDL secretion but normal LDL cholesterol levels, possibly reflecting enhanced catabolism of LDL via hepatic LDLRs. Recent studies have also suggested that hepatic insulin signaling sustains LDLR levels. We therefore sought to elucidate the mechanisms linking hepatic insulin signaling to regulation of LDLR levels. In WT mice, insulin receptor knockdown by shRNA resulted in decreased hepatic mTORC1 signaling and LDLR protein levels. It also led to increased expression of PCSK9, a known post-transcriptional regulator of LDLR expression. Administration of the mTORC1 inhibitor rapamycin caused increased expression of PCSK9, decreased levels of hepatic LDLR protein, and increased levels of VLDL/LDL cholesterol in WT but not Pcsk9-/- mice. Conversely, mice with increased hepatic mTORC1 activity exhibited decreased expression of PCSK9 and increased levels of hepatic LDLR protein levels. Pcsk9 is regulated by the transcription factor HNF1α, and our further detailed analyses suggest that increased mTORC1 activity leads to activation of PKCδ, reduced activity of HNF4α and HNF1α, decreased PCSK9 expression, and ultimately increased hepatic LDLR protein levels, which result in decreased circulating LDL levels. We therefore suggest that PCSK9 inhibition could be an effective way to reduce the adverse side effect of increased LDL levels that is observed in transplant patients taking rapamycin as immunosuppressive therapy.

n-3 PUFA prevent metabolic disturbances associated with obesity and improve endothelial function in golden Syrian hamsters fed with a high-fat diet

Glucose intolerance and dyslipidaemia are independent risk factors for endothelium dysfunction and CVD. The aim of the present study was to analyse the preventive effect of n-3 PUFA (EPA and DHA) on lipid and carbohydrate disturbances and endothelial dysfunction. Three groups of adult hamsters were studied for 20 weeks: (1) control diet (Control); (2) high-fat diet (HF); (3) high-fat diet enriched with n-3 PUFA (HFn-3) groups. The increase in body weight and fat mass in the HF compared to the Control group (P < 0.05) was not found in the HFn-3 group. Muscle TAG content was similar in the Control and HF groups, but significantly lower in the HFn-3 group (P = 0.008). Glucose tolerance was impaired in the HF compared to the Control group, but this impairment was prevented by n-3 PUFA in the HFn-3 group (P < 0.001). Plasma TAG and cholesterol were higher in the HF group compared to the Control group (P < 0.001), but lower in the HFn-3 group compared to the HF group (P < 0.001). HDL-cholesterol was lower in the HFn-3 group compared to the Control and HF groups (P < 0.0005). Hepatic secretion of TAG was lower in the HFn-3 group compared to the HF group (P < 0.005), but did not differ from the Control group. Hepatic gene expression of sterol regulatory element-binding protein-1c, diacylglycerol O-acyltransferase 2 and stearyl CoA desaturase 1 was lower in the HFn-3 group, whereas carnitine palmitoyl transferase 1 and scavenger receptor class B type 1 expression was higher (P < 0.05). In adipocytes and adipose macrophages, PPARγ and TNFα expression was higher in the HF and HFn-3 groups compared to the Control group. Endothelium relaxation was higher in the HFn-3 (P < 0.001) than in the HF and Control groups, and was correlated with glucose intolerance (P = 0.03) and cholesterol (P = 0.0003). In conclusion, n-3 PUFA prevent some metabolic disturbances induced by high-fat diet and improve endothelial function in hamsters.

Nephrotic syndrome in diabetic kidney disease: an evaluation and update of the definition

BACKGROUND

Nephrotic syndrome is defined as urine total protein excretion greater than 3.5 g/d or total protein-creatinine ratio greater than 3.5 g/g, low serum albumin level, high serum cholesterol level, and peripheral edema. These threshold levels have not been rigorously evaluated in patients with diabetic kidney disease or by using urine albumin excretion, the preferred measure of proteinuria in patients with diabetes.

STUDY DESIGN

Diagnostic test study.

SETTING & PARTICIPANTS

Adults with type 2 diabetes, hypertension, and urine total protein level greater than 0.9 g/d enrolled in the Irbesartan in Diabetic Nephropathy Trial.

INDEX TEST

Baseline measures of proteinuria (total protein and albumin excretion and protein-creatinine and albumin-creatinine ratios). Linear regression to relate measures.

REFERENCE TEST

Other signs and symptoms of nephrotic syndrome at baseline (serum albumin < 3.5 g/dL, serum total cholesterol > 260 mg/dL or use of a statin, and edema or use of a loop diuretic); progression of chronic kidney disease during follow-up (doubling of baseline serum creatinine level or requirement for dialysis or kidney transplantation). Logistic regression to relate index and reference tests.

RESULTS

In 1,608 participants, total urine protein level of 3.5 g/d was equivalent to urine albumin level of 2.2 g/d (95% confidence interval, 1.4 to 3.5). Of 1,467 participants, 641 (44%) had urine total protein level of 3.5 g/d or greater at baseline, 132 (9%) had other signs and symptoms of nephrotic syndrome at baseline, and 385 (26%) had progression of kidney disease during a mean follow-up of 2.6 years. Areas under the receiver operating curves for measures of proteinuria were 0.80 to 0.83 for other signs and symptoms of nephrotic syndrome and 0.72 to 0.74 for kidney disease progression. Threshold levels for nephrotic-range proteinuria and albuminuria were close to the points of maximal accuracy for both outcomes.

LIMITATIONS

Study population limits generalizability; inability to adjust for several variables known to affect serum albumin levels; lack of spot urine samples.

CONCLUSIONS

The historical definition of nephrotic-range proteinuria appears reasonable in patients with diabetic kidney disease. Equivalent thresholds for nephrotic-range albuminuria and albumin-creatinine ratio are 2.2 g/d and 2.2 g/g, respectively.

Overproduction of very low-density lipoproteins is the hallmark of the dyslipidemia in the metabolic syndrome

Insulin resistance is a key feature of the metabolic syndrome and often progresses to type 2 diabetes. Both insulin resistance and type 2 diabetes are characterized by dyslipidemia, which is an important and common risk factor for cardiovascular disease. Diabetic dyslipidemia is a cluster of potentially atherogenic lipid and lipoprotein abnormalities that are metabolically interrelated. Recent evidence suggests that a fundamental defect is an overproduction of large very low-density lipoprotein (VLDL) particles, which initiates a sequence of lipoprotein changes, resulting in higher levels of remnant particles, smaller LDL, and lower levels of high-density liporotein (HDL) cholesterol. These atherogenic lipid abnormalities precede the diagnosis of type 2 diabetes by several years, and it is thus important to elucidate the mechanisms involved in the overproduction of large VLDL particles. Here, we review the pathophysiology of VLDL biosynthesis and metabolism in the metabolic syndrome. We also review recent research investigating the relation between hepatic accumulation of lipids and insulin resistance, and sources of fatty acids for liver fat and VLDL biosynthesis. Finally, we briefly discuss current treatments for lipid management of dyslipidemia and potential future therapeutic targets.

Effect of n-3 fatty acids on metabolism of apoB100-containing lipoprotein in type 2 diabetic subjects

The effect of long-chain n-3 PUFA on the metabolism of apoB100-containing lipoprotein in diabetic subjects is not fully understood. The objective of the present study was to determine the effect of a daily intake of 1080 mg EPA and 720 mg DHA for diabetic subjects on the kinetics of apoB100-containing lipoprotein in the fasting state. A kinetic study was undertaken to determine the mechanisms involved in the effects of n-3 fatty acids in terms of a decrease in triacylglycerol level in type 2 diabetic patients. We have studied the effect of fish oils on the metabolism of apoB100 endogenously labelled by [5,5,5-2H3]-leucine in type 2 diabetic patients in the fasting state. The kinetic parameters of apoB100 in VLDL, intermediate-density lipoprotein and LDL were determined by compartmental modelling in five diabetic subjects before and 8 weeks after n-3 fatty acid treatment. Treatment did not change the plasma cholesterol level (0.801 (sd 0.120) v. 0.793 (sd 0.163) mmol/l) but lowered the plasma triacylglycerol level (1.776 (sd 0.280) v.1.356 (sd 0.595) mmol/l; P < 0.05). Treated patients showed a decrease in VLDL apoB100 concentration (0.366 (sd 0.030) v.0.174 (sd 0.036) g/l; P < 0.05) related to a decrease in VLDL 1 production (1.49 (sd 0.23) v.0.44 (sd 0.19) mg/kg per h; P < 0.05) and an increase in the VLDL conversion rate (0.031 (sd 0.024) v.0.052 (sd 0.040) per h; P < 0.05), with no change in fractional catabolic rates. Treatment led to a higher direct production of intermediate-density lipoprotein (0.02 (sd 0.01) v.0.24 (sd 0.12) mg/kg per h; P < 0.05). In conclusion, the present study, conducted in the fasting state, showed that supplementation with n-3 fatty acids in type 2 diabetic patients induced beneficial changes in the metabolism of apoB100-containing lipoprotein.

Low-density lipoprotein subclass and its correlating factors in diabetics

OBJECTIVES

Small dense LDL, low density lipoprotein (LDL) particles with small size and high density, is regarded as a significant risk factor for cardiovascular diseases. Diabetes mellitus is one of the conditions accompanied by increased small dense LDL. We analyzed LDL subclass in type 2 diabetics and normal controls with LipoPrint LDL System to investigate the LDL heterogeneity in diabetics and factors affecting it.

DESIGN AND METHODS

We selected 40 normal controls and 40 type 2 diabetics with fasting blood glucose level over 7.0 mmol/L and HbA1c level over 7%. LDL subclass was determined with LipoPrint LDL System. LipoPrint LDL System fractionates LDL into seven parts (LDL1-7) by size and LDL3 to LDL7 are defined as small-sized LDL. In addition we estimated 'the percent of small-sized LDL over whole LDL' and defined it as 'small-sized LDL proportion'.

RESULTS

Mean small-sized LDL proportion was significantly higher in diabetics (23.4%) than in controls (11.8%) (p<0.001) and small-sized LDL proportion showed positive correlation with blood levels of glucose, HbA1c, total cholesterol, triglyceride, and oxidized LDL and negative correlation with HDL cholesterol level in univariate analysis (p<0.001). Of these parameters, triglyceride, HbA1c, oxidized LDL were statistically significant variables contributing to the small-sized LDL proportion in stepwise multiple regression analysis.

CONCLUSIONS

We analyzed small-sized LDL proportion in type 2 diabetics and found that it was significantly increased in diabetics than control subjects and it was independently correlated with triglyceride, HbA1c, oxidized LDL in descending order, which are reflecting lipid metabolism, glycation, and oxidative stress, respectively.

Cell surface expression of LDL receptor is decreased in type 2 diabetic patients and is normalized by insulin therapy

OBJECTIVE

In type 2 diabetic patients with poor metabolic control, kinetic studies have demonstrated that LDL fractional catabolic rate (FCR) is slowed down, whereas it is normalized on insulin therapy. This study was designed to analyze whether variations in the expression of LDL receptors at the cell surface could explain the results observed in kinetic studies.

RESEARCH DESIGN AND METHODS

LDL receptors were quantified at the surface of mononuclear cells in fresh fasting blood samples by a flow cytometry method in 21 control subjects and 21 type 2 diabetic patients before and 3 months after the introduction of insulin therapy and concomitant removal of oral antidiabetic drugs.

RESULTS

Before insulin treatment, monocyte LDL receptor expression was reduced by 41% (6,439 +/- 2,310 vs. 10,846 +/- 2,764 receptors per monocyte, P < 0.001) in type 2 diabetic patients compared with control subjects. It increased by 57% after 3 months of insulin therapy (10,096 +/- 5,657 vs. 6,439 +/- 2,310, P < 0.01) and was similar to that observed in control subjects.

CONCLUSIONS

Our results suggest that insulin plays an important role in the in vivo expression of LDL receptors. Moreover, modulations in the expression of LDL receptors in type 2 diabetic patients either with poor metabolic control or on insulin therapy are likely to contribute to the variations of LDL FCR demonstrated by kinetic studies under those circumstances.

Dietary and plasma lipid, lipoprotein, and apolipoprotein profiles among elderly Hispanics and non-Hispanics and their association with diabetes

BACKGROUND

There are limited data about dietary intakes and plasma lipids of elderly US Hispanics.

OBJECTIVE

The disparity in prevalence of type 2 diabetes among population groups underscored our need to assess dietary and plasma risk factors for cardiovascular disease.

DESIGN

Plasma lipids and apolipoproteins and dietary intakes of macronutrients were measured in elderly subjects (60-98 y): 490 Hispanics of Caribbean origin (Puerto Ricans and Dominicans) and 163 non-Hispanic whites. Plasma values were related to ethnicity and to macronutrient intake. Differences in plasma lipids due to diabetes were assessed among the Hispanics.

RESULTS

Intakes of carbohydrate and polyunsaturated fatty acids were higher and intakes of cholesterol and saturated and monounsaturated fatty acids were lower in Hispanics than in non-Hispanic whites. Concentrations of total cholesterol, HDL cholesterol, and apolipoprotein A-I were significantly lower among Hispanic women than among non-Hispanic white women; a similar trend was seen in men. Dyslipidemia (high triacylglycerols and low HDL cholesterol) was more prevalent among Hispanics with than without diabetes.

CONCLUSIONS

Ethnic differences in serum lipids exist and appear to be associated with differences in dietary intakes. However, both Hispanics and non-Hispanic whites had lipid profiles indicating a high risk of cardiovascular disease. Hispanics with diabetes were at higher risk of dyslipidemia than were those without diabetes. Our data suggest that lifestyle changes, including diet modification and exercise, could be of significant benefit to both ethnic groups.

High plasma insulin and lipids profile in older individuals: the Italian longitudinal study on aging

BACKGROUND

The inverse relationship of insulin level to high-density lipoprotein (HDL)-cholesterol and its positive association with hypertriglyceridemia has been demonstrated in several studies; however, the relationship of insulin to low-density lipoprotein (LDL)-cholesterol in elderly persons is not clear. This study investigates the relationships of fasting plasma insulin and selected metabolic and biological risk factors in an aged population.

METHODS

The present study is based on a cross-sectional analysis of the data collected at baseline of the Italian Longitudinal Study on Aging in 1992 on a random sample of 5632 Italians aged 65-84 years. Analyses were performed to compare the distribution of risk factors, such as blood level of lipids, creatinine, albumin, fibrinogen, apolipoprotein A-1 and B, blood pressure, and body mass index (BMI), by quartiles of insulin, in both diabetic and nondiabetic participants.

RESULTS

Significantly higher levels of triglycerides and BMI and lower levels of HDL-cholesterol were found in the upper quartile of insulin among nondiabetic individuals. In men, we also found significantly higher levels of systolic and diastolic blood pressure. The same trend for these variables, although not significant for HDL-cholesterol and blood pressure, was seen in diabetic men. In diabetic women, total and LDL-cholesterol were significantly lower in the highest insulin quartile (p <.001), while no significant differences were seen in nondiabetic women or in men. We also found higher levels of white blood cells in the highest insulin quartile of diabetic women.

CONCLUSIONS

These results, apparently in disagreement with earlier reports on the clustering of cardiovascular disease risk factors in hyperinsulinemic individuals, could be due to the high frequency of chronic inflammation and the high prevalence of urinary infections in older diabetic women.

The db/db mouse, a model for diabetic dyslipidemia: molecular characterization and effects of Western diet feeding

Diabetic dyslipidemia is a major factor contributing to the accelerated atherosclerosis in type 2 diabetes mellitus. Although several mouse models are available, the plasma lipoproteins in response to diet have not been fully characterized in these animals. In this study, we have characterized the plasma lipoproteins and related apolipoproteins, as well as the vascular lipases, in diabetes (db/db) mice and their nondiabetic controls (+/?) in the C57BL/KsJ strain. Within 6 weeks of age, db/db mice developed significant obesity, fasting hyperglycemia, and hyperinsulinemia. By FPLC analysis, db/db mice showed a prominent peak in the low-density lipoprotein (LDL) range that was absent in +/? mice, although high-density lipoprotein (HDL) was the predominant species in both groups of animals. Postheparin lipoprotein lipase (LPL) activity in db/db mice was 28% of the level in +/? mice. Upon feeding a human-like 0.15% (wt/wt) cholesterol and 21% (wt/wt) fat "Western" diet, db/db mice developed elevated plasma cholesterol, accompanied by an exaggerated apolipoprotein E (apoE) response compared with +/? mice. FPLC analysis showed that the marked hypercholesterolemic response in db/db mice was the result of a massive increase in the LDL region, which overshadowed a moderate increase in HDL. We next isolated lipoproteins by ultracentrifugation and characterized them by nondenaturing gradient gel electrophoresis. With regular chow, db/db mice had almost exclusively small dense LDL with a peak size at 21.4 nm, as compared with 26.6 nm in nondiabetic controls. On the Western diet, the small dense LDLs persisted but larger particles also appeared in db/db mice, whereas the size distribution in +/? mice was unchanged by the diet. Our results suggest that db/db mice fed a Western diet have a plasma lipoprotein phenotype that shows some similarities to that in patients with type 2 diabetes mellitus, and that db/db mice are a useful model to study the pathogenesis and treatment of diabetic dyslipidemia.

Association between low-density lipoprotein composition and its metabolism in non-insulin-dependent diabetes mellitus

Atheroma is related to low-density lipoprotein (LDL) composition. LDL in diabetic patients-a group with increased risk of severe atheroma-has been shown by our group and others to have various compositional alterations that are potentially atherogenic. Little is known about the relationship between LDL turnover and composition. This study examined the relationship between LDL composition and turnover in non-insulin-dependent diabetes mellitus (NIDDM) patients. Twenty-two NIDDM patients with a mean plasma cholesterol of 6.6+/-1.5 mmol/L were studied. Twelve subjects were hypercholesterolemic (mean cholesterol, 7.7+/-0.8 mmol/L), and eight of these agreed to be studied a second time after 4 weeks of treatment with simvastatin. LDL was isolated by density gradient ultracentrifugation, iodinated, and reinjected into the patient. LDL turnover was determined by measuring the clearance of [125I]-LDL from plasma over a 10-day period. The LDL residence time, determined using a biexponential model, correlated negatively with the body mass index (BMI) (r = -.73, P<.001) and serum triglycerides (r = - .57, P<.01). There was a significant inverse correlation between LDL residence time and the LDL esterified to free cholesterol ratio in hypercholesterolemic subjects (r = -.94, P<.001). There was a significant inverse relationship between LDL residence time and both hemoglobin A1c (HbA1c) and fasting blood glucose in these subjects before treatment (P<.005). After simvastatin therapy, the relationships were no longer significant. Simvastatin treatment was associated with a shorter LDL residence time (P<.01) and a decrease in LDL glycation (P<.001) with virtually no change in diabetic control (HbA1c, 6.0%+/-3.1% v. 6.3%+/-3.3%, NS). This study suggests that a decrease in residence time by upregulation of the LDL receptor with simvastatin alters LDL composition in a way that is likely to render the particle less atherogenic.

Hyperlipidemia and diabetes mellitus

The increased risk of coronary artery disease in subjects with diabetes mellitus can be partially explained by the lipoprotein abnormalities associated with diabetes mellitus. Hypertriglyceridemia and low levels of high-density lipoprotein are the most common lipid abnormalities. In type 1 diabetes mellitus, these abnormalities can usually be reversed with glycemic control. In contrast, in type 2 diabetes mellitus, although lipid values improve, abnormalities commonly persist even after optimal glycemic control has been achieved. Screening for dyslipidemia is recommended in subjects with diabetes mellitus. A goal of low-density lipoprotein cholesterol of less than 130 mg/dL and triglycerides lower than 200 mg/dL should be sought. Several secondary prevention trials, which included subjects with diabetes, have demonstrated the effectiveness of lowering low-density lipoprotein cholesterol in preventing death from coronary artery disease. The benefit of lowering triglycerides is less clear. Initial approaches to lowering the levels of lipids in subjects with diabetes mellitus should include glycemic control, diet, weight loss, and exercise. When goals are not met, the most common drugs used are hydroxymethylglutaryl coenzyme A reductase inhibitors or fibrates.

Low density lipoprotein binding and uptake by human and rat islet beta cells

Abnormalities in lipoprotein metabolism are common in diabetes. It is unknown whether variations in form or concentration of lipoproteins influence the function of pancreatic beta cells. This study investigates whether low density lipoproteins (LDL) exhibit specific interactions with islet beta cells. Radioactively labeled LDL (125I-LDL) and fluorescently labeled LDL (DiI-LDL) were used as tracers. Rat islet cells express high affinity LDL binding sites (K(d) = 9 nM), which are also recognized by very low density lipoproteins and which are down-regulated by LDL. Binding of LDL appears restricted to the beta cells, as it was not detected on islet endocrine non-beta cells. At 37 C, LDL is taken up and lysosomally degraded by islet beta cells but not by islet non-beta cells. Human islet cells were also found to present LDL binding, uptake, and degradation. Compared with rat islet cells, human islet cells exhibit 10-fold less binding sites (2.10(7) vs. 2.10(8) per 10(3) cells) with a 2-fold lower K(d) value (5 nM) and an equal sensitivity to LDL-induced down-regulation. In conclusion, human and rat islet beta cells express LDL receptors that can internalize the lipoprotein. This pathway should be examined for its potential role in (dys)regulating pancreatic beta cell functions.

High plasma insulin is associated with lower LDL cholesterol in elderly individuals

To investigate possible relationships between plasma low density lipoprotein (LDL) cholesterol and fasting plasma insulin in the elderly, cross-sectional random samples of age cohorts (65, 75, 80 and 85 years, n = 1188, M/F 38/62 percent) were studied in the neighbouring cities of Helsinki and Vantaa, Finland. Plasma total and high density lipoprotein (HDL) cholesterol, plasma triglycerides, blood glucose and plasma insulin were measured after an overnight fast. LDL cholesterol was calculated using the Friedewald equation. Statistical analyses were performed separately in subjects with non-insulin-dependent diabetes mellitus (NIDDM, n = 219) and non-diabetic subjects (n = 969). Comparison of lipid levels by insulin quartile (I < 7.4 IU/1, II 7.4-10.0, III 10.1-15.0, IV > 15.0) showed that total and LDL cholesterol decreased in the highest insulin quartile (P = 0.003). This trend prevailed after adjustments for age, gender, body mass index, blood glucose and serum triglycerides, and it was significant also in normotriglyceridemic (serum triglycerides <2.3 mmol/l) subjects. Furthermore, the association between high insulin and lower cholesterol was seen in normoglycemic (fasting blood glucose <6.7 mmol/l) and diabetic subjects. Lower LDL cholesterol in elderly subjects with higher fasting insulin may reflect poor health or a 'harvesting' effect, but the results may also be due to effects of insulin on LDL catabolism and/or cholesterol absorption.

Low-density lipoprotein binding assay using the calf adrenocortical low-density lipoprotein receptor

The low-density lipoprotein (LDL) receptor was purified to a semipure solubilized form from calf adrenocortical tissue. This receptor was found to be a suitable substitute for the human LDL receptor for studying human LDL binding. The apparent dissociation constant of the receptor from calf adrenocortical cells, using human LDL as the ligand, was found to be 8.8 +/- 1.0 micrograms 125I-LDL/mL, similar to that reported for the human LDL receptor (4-10 micrograms LDL/mL). The calf adrenocortical LDL receptor demonstrated specificity toward human lipoprotein fractions that was identical with that of the human LDL receptor. A competitive binding assay was optimized using the semipurified solubilized calf adrenocortical receptor. This facilitated the study of nonenzymatically glycosylated human LDL by a binding assay that is much simpler and faster than previous studies, which used intact cultured cells. The present assay requires only a 1-h incubation of LDL with the receptor and a simple filtration procedure to remove unbound LDL. Using the present assay, it was shown that nonenzymatic glycosylation of LDL on the order of what is seen in diabetics, that is, modification of 2-5% of lysine residues, caused a decreased ability of the LDL to bind to the receptor.

Non-esterified fatty acids regulate lipid and glucose oxidation and glycogen synthesis in healthy man

We examined the interrelationship of lipid and glucose metabolism in the basal state and during insulin stimulus in 19 healthy men (27 +/- 2 years, body mass index 23.6 +/- 0.6 kg/m2). In each subject, we performed a 4-h euglycaemic (5.3 +/- 0.1 mmol/l) hyperinsulinaemic (647 +/- 21 pmol/l) insulin clamp with indirect calorimetry in the basal state and during insulin infusion, and muscle biopsies before and at the end of the clamp. In the basal state, serum non-esterified fatty acid levels correlated directly with lipid oxidation (r = 0.56, p < 0.05) and indirectly with glucose oxidation (r = -0.80, p < 0.001). Lipid and glucose oxidation rates were inversely related in the basal state (r = -0.47, p < 0.05) and during insulin infusion (r = -0.65, p < 0.01). Basal lipid oxidation and glycogen synthase total activity correlated inversely (r = -0.54, p < 0.05). Lipid oxidation both in the basal state (r = -0.61, p < 0.01) and during insulin infusion (r = -0.62, p < 0.05) was inversely related to muscle glycogen content after the insulin clamp. Fasting plasma triglyceride concentration correlated directly to fasting insulin (r = 0.55, p < 0.05) and C-peptide (r = 0.50, p < 0.03) concentrations and inversely to non-oxidative glucose disposal rate at the end of clamp (r = -0.54, p < 0.05).

IN CONCLUSION

1) Serum non-esterified fatty acid concentration enhances lipid and reduces glucose oxidation. 2) Lipid oxidation is inversely related to total glycogen synthase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Familial hypercholesterolaemia-like syndrome with apolipoprotein E-7 associated with marked Achilles tendon xanthomas and coronary artery disease: a report of two cases

We observed two patients with hypercholesterolaemia and tendon xanthomas associated with apolipoprotein (apoE-7) E-7, a rare variant of the apoE isoforms. Both suffered from coronary artery disease and had undergone a coronary bypass operation. Their cholesterol levels were 268 and 310 mg dl-1, respectively. Both patients had marked xanthomas in the Achilles tendons. Both also suffered from diabetes. Although their clinical and laboratory findings were compatible with typical familial hypercholesterolaemia (FH), the analysis of low-density lipoprotein (LDL) receptors in cultured fibroblasts showed no abnormality of binding, internalization or degradation of 125I-LDL. Diabetic control with a low-calorie, low-fat diet led to the rapid reduction of serum cholesterol. Other family members of the patients with apoE-7, who were normoglycaemic, showed normal cholesterol levels and no xanthomas. These findings suggest that coexistent diabetes mellitus may induce overt hyperlipidaemia and accumulation of lipids in tissues in subjects with apoE7.

Lipoprotein disorders in diabetes mellitus

In IDDM or NIDDM, the total plasma cholesterol and triglycerides are usually within normal limits when the blood glucose is controlled. Marked hypertriglyceridemia can develop with loss of glycemic control and is often due to superimposed genetic abnormalities in lipoprotein metabolism. Tight control in IDDM usually reduces LDL and VLDL to normal levels and may raise HDL above the normal range. Low HDL cholesterol and mild to moderate elevations of VLDL triglyceride are common in NIDDM if obesity or proteinuria is also present. Both HDL and LDL may be smaller and more dense and may be enriched with triglyceride as compared with cholesterol. These abnormalities may require weight loss for control. The increased incidence of cardiovascular disease in diabetes is unexplained but is amplified by the well-defined cardiovascular risk factors. The new American Diabetes Association guidelines call for treatment of high triglycerides and LDL cholesterol to be aggressively reduced. Triglycerides should be under 200 mg/dL, are considered borderline high between 200 and 400 mg/dL, and high when above 400 mg/dL. Low HDL is defined as less than 35 mg/dL. Control of obesity with diet and exercise and reduced intake of saturated fat and cholesterol are important first steps. If needed, drug therapy is appropriate to reduce LDL to levels below 130 mg/dL in all adult diabetics and below 100 mg/dL in those with cardiovascular disease.

Lipids and lipoproteins predicting coronary heart disease mortality and morbidity in patients with non-insulin-dependent diabetes

BACKGROUND

The aim of this study was to investigate the association of lipoprotein fractions with the future risk of coronary heart disease (CHD) in patients with non-insulin-dependent diabetes (NIDDM).

METHODS AND RESULTS

At baseline, lipoprotein fractions were determined in 313 diabetic patients with NIDDM (153 men and 160 women), and these patients were followed up for 7 years with respect to CHD events (CHD death or all CHD events including CHD death or nonfatal myocardial infarction). Altogether, 56 NIDDM patients (28 men and 28 women) died from CHD and 25 had a nonfatal myocardial infarction (17 men and 8 women) during the follow-up. NIDDM patients having these CHD events during the follow-up had higher levels of total and very-low-density lipoprotein (VLDL) triglycerides and VLDL cholesterol and lower levels of high-density lipoprotein (HDL) and HDL2 cholesterol than those without CHD events. The risk for CHD death was fourfold and for all CHD events, twofold higher among diabetics with low HDL cholesterol (< 0.9 mmol/L) than among diabetics with HDL cholesterol > or = 0.9 mmol/L. High triglyceride level (> 2.3 mmol/L) was associated with a twofold increase in the risk of CHD events. In multiple logistic regression analyses, HDL was inversely associated with CHD events and VLDL triglycerides with CHD events in NIDDM patients with low HDL cholesterol level (< or = 1.12 mmol/L).

CONCLUSIONS

Our 7-year follow-up study gives evidence that low HDL and HDL2 cholesterol, high VLDL cholesterol, and high total and VLDL triglycerides are powerful risk indicators for CHD events in patients with NIDDM:

Two patterns of LDL metabolism in normotriglyceridemic patients with hypoalphalipoproteinemia

The objective of this study was to determine whether normotriglyceridemic patients with low levels of high density lipoprotein (HDL) cholesterol have concomitant defects in the metabolism of low density lipoproteins (LDLs). To address this question, measurements of turnover rates of apolipoprotein A-I (apo A-I) and LDL apolipoprotein B (apo B) were made in 36 middle-aged men with low HDL cholesterol (< 40 mg/dL), normal triglyceride (< 250 mg/dL), and normal total cholesterol (< or = 90th percentile) levels. Similar measurements were made in eight hypertriglyceridemic men having low HDL levels. For control, turnover rates of LDL apo B were measured in 24 healthy, normolipidemic men, and apo A-I kinetics were determined in 20 other healthy men with normal HDL cholesterol levels. In all patients with low HDL levels, fractional catabolic rates (FCRs) for apo A-I were increased compared with control subjects; in contrast, input rates for apo A-I in low-HDL patients were similar to control. Hypertriglyceridemic patients had significantly higher FCRs for LDL (0.463 +/- 0.040 pool/day, [mean +/- SEM]) than control subjects (0.328 +/- 0.008 pool/day, p < 0.001). In normolipidemic patients having low HDL, a bimodal pattern of LDL-apo B kinetics was observed. For 23 low-HDL patients, FCRs for LDL apo B averaged 0.450 +/- 0.017 pool/day and were significantly higher than control values. Additionally, in these patients, levels of very low density lipoprotein plus intermediate density lipoprotein (VLDL+IDL) cholesterol and VLDL+IDL apo B were higher than in control subjects (54 +/- 3 versus 32 +/- 3 mg/dL and 25 +/- 2 versus 18 +/- 1 mg/dL, respectively). The remaining 13 low-HDL patients had lower and essentially normal FCRs for LDL (0.300 +/- 0.009 pool/day); these patients also had relatively low levels of cholesterol and apo B in VLDL+IDL. Thus, two patterns of LDL kinetics were present in normotriglyceridemic patients with low HDL levels. One pattern was indistinguishable from that typically present in patients with hypertriglyceridemia, whereas the other was similar to normal control subjects. These two patterns of LDL-apo B kinetics may reflect different mechanisms for the causation of low HDL cholesterol concentrations.

Glycated low density lipoprotein catabolism is increased in rabbits with alloxan-induced diabetes mellitus

Hyperglycaemia in diabetes mellitus is responsible for the process of non-enzymatic glycosylation of different proteins. Since we did not find elevated glycated apolipoprotein B levels in diabetic patients, an altered glycated apolipoprotein B metabolism was suspected in diabetic patients. Experiments in normal rabbits showed that non-reductive (in vitro) glycated low density lipoprotein (gly-LDL) was cleared at a slower rate than control LDL and thus stayed longer in the circulation (vascular mean residence time: 10 vs 8 h, p less than 0.001). The body mean residence time for gly-LDL was 22 h vs 17 h for control LDL. In diabetic animals the catabolic parameters of both LDL preparations changed towards a faster clearance, the effect being greatest for gly-LDL (total mean residence times of gly-LDL pre-diabetic: 19 h, diabetic: 16 h; control LDL pre-diabetic and diabetic: 14 h). The difference in clearance between glycated and control LDL was thus strongly reduced. Virtually no antibody complexed to gly-LDL could be measured. The results suggest an increased activity of the non-receptor mediated pathway in diabetes mellitus, possibly co-responsible for an increased atherosclerotic risk.

[Anomalies of lipid metabolism in diabetes mellitus]

Atheroma is by far the most common cause of mortality in diabetic patients (66 to 75% of deaths). Several physiopathological mechanisms are suspected to account for the greater frequency and severity of atheroma in diabetes. Among these, lipid abnormalities hold first rank and include not only quantitative but also qualitative abnormalities of lipoproteins altering their kinetics and bindings to membrane receptors. The main quantitative abnormalities are an increase of triglycerides and very low density lipoproteins (VLDL) and a fall in high density lipoproteins (HDL) and their HDL2 subfraction. Qualitative abnormalities include non-enzymatic glucosylation of apoproteins, changes in lipoprotein size and increase in their triglyceride content, and excessive oxidation of low density lipoproteins (LDL). Both quantitative and qualitative abnormalities of lipoproteins are present in non-insulin-dependent diabetes, whereas only qualitative abnormalities are observed, as a rule, in treated insulin-dependent diabetes. The physiopathology of lipid metabolism disorders is complex, possibly multifactorial and still imperfectly known. However, such factors as modification of insulin status, hyperglycaemia and obesity frequently associated with diabetes, are thought to be involved.

Comparison of the effects of lovastatin and gemfibrozil on lipids and glucose control in non-insulin-dependent diabetes mellitus

Patients with non-insulin dependent diabetes mellitus have an increased incidence of coronary artery disease which may, in part, be associated with abnormalities in plasma lipids. In a double-blind, parallel, randomized study, lovastatin and gemfibrozil were compared in 102 diabetic patients with primary hypercholesterolemia; two-thirds of the patients were treated with oral hypoglycemic agents and one-third received diet therapy alone for their diabetes. Mean pretreatment total and low-density lipoprotein (LDL) cholesterol values were 273 and 193 mg/dl, respectively. Lovastatin significantly reduced total, LDL and very low density lipoprotein cholesterol (20, 26 and 28%, respectively) and raised high-density lipoprotein (HDL) cholesterol (14%). Gemfibrozil significantly reduced triglycerides and very low density lipoprotein cholesterol (36 and 41%, respectively) and, to a lesser extent, total cholesterol (9%); it also increased HDL cholesterol (21%). Lovastatin therapy was not associated with a significant change in triglycerides, and gemfibrozil did not significantly lower LDL cholesterol. The decrease in the ratio of total to HDL cholesterol tended to be greater with lovastatin than with gemfibrozil (26.5 and 20.4%, respectively; p = 0.053). Changes in lipid profiles with both agents were of a degree similar to those reported in nondiabetic patients. Neither agent had a clinically important effect on fasting glucose or hemoglobin A1c. Both drugs were well tolerated with the exception of 2 patients treated with gemfibrozil who developed symptoms of cholecystitis.

[Intolerance to carbohydrates: the seven questions]

The borderline between diabetes and intolerance to carbohydrates has been drawn on the basis of prospective studies which determined a glycaemic threshold marking the risk for microangiopathy. On the other hand, the borderline between intolerance to carbohydrates and normal glucose tolerance remains arbitrary: 25% for subjects who are intolerant to carbohydrates return to normal glucose tolerance within 10 years. This is due to the fact that intolerance to carbohydrates is a heterogeneous entity which should be dismembered according to the severity of insulin deficiency and to the degree of insulin resistance. Alteration of insulin secretion is perhaps the most specific marker of susceptibility to non insulin dependent diabetes, but insulin resistance is certainly the principal factor exhausting insulin secretion and leading to non insulin dependent diabetes. Insulin resistance and the hyperinsulinism it creates seem to facilitate atherogenesis, even when glucose tolerance is still normal, so that the oral glucose tolerance test is not only poorly reproducible but loses a great deal of its value in the early detection of vascular risk. Measurements of fasting and post-prandial glucose levels and of A1C haemoglobin, cholesterol, triglyceride, and HDL cholesterol levels usually make it possible to classify subjects into one of the three following categories: (1) no risk of macro- or microangiopathy; (2) diabetes with a risk of macro- or microangiopathy; (3) intolerance to glucose with risk of atherogenesis but no risk of microangiopathy. The oral glucose tolerance test probably remains useful within a small set of values that are either very slightly above normal or dissociated. Measuring blood insulin levels might be a better way of assessing the risk of atherogenesis, but the clinical use of this test requires evaluation.

Isoform patterns of apolipoprotein E in diabetes mellitus

Apolipoproteins in delipidated VLDL preparations from normal, diabetic, and non-diabetic hyperlipidaemic subjects were analysed by SDS-polyacrylamide gel electrophoresis, and by isoelectric focusing. On electrophoresis, diabetic VLDL contained more apolipoprotein E (17.3 +/- 7.3 (+/- SD) %, n = 54) than did VLDL from hyperlipidaemic (13.4 +/- 4.2%, n = 52; p less than 0.005) or normal (12.4 +/- 2.6%, n = 29; p less than 0.001) subjects. Apolipoprotein E excess was also seen when subgroups were characterized by apolipoprotein E phenotype. In diabetic patients of E3/E3 phenotype, apolipoprotein E was 16.4 +/- 6.0% (n = 25), compared with 12.9 +/- 2.5% in control subjects (n = 14; p = 0.008). Acidic isoforms were more common in 44 diabetic patients with E3/E3 phenotype; E3, E2, E1, and E1' as percentage of total E apolipoprotein were 58.3 +/- 7.6, 24.5 +/- 4.4, 13.7 +/- 4.5, and 3.8 +/- 4.3% respectively, compared with 63.5 +/- 10.4 (p = 0.034), 19.1 +/- 5.3 (p less than 0.001), 13.7 +/- 6.5 (NS), and 3.7 +/- 2.1% (NS) in 21 normal subjects. In 31 diabetic patients, of apolipoprotein E3/E3 phenotype, E3, E2, E1 and E1' were 60.2 +/- 7.3, 23.4 +/- 9.4, 11.1 +/- 4.1, and 5.4 +/- 3.7%, respectively, compared with 68.0 +/- 7.1 (p less than 0.001), 21.9 +/- 6.4 (NS), 6.3 +/- 3.9 (p less than 0.001), and 3.7 +/- 2.5 (p less than 0.05) % in 32 hyperlipidaemic patients. Diabetic patients of E3/E2 phenotype showed less apolipoprotein E3 than normal or hyperlipidaemic subjects, with a similar trend for apolipoprotein E4 in those of E4/E3 phenotype.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma insulin, serum lipids and lipoproteins in gall stone disease in non-insulin dependent diabetic subjects: a case control study

Fasting insulin, lipids and lipoproteins were measured in 22 middle aged female non-insulin dependent diabetics with gall stone disease (cases) and in 22 non-insulin dependent diabetics without gall stone disease (controls). The groups were matched for sex, age, obesity, and fasting glucose concentrations. No differences were observed between the cases and controls in duration of diabetes, glycated haemoglobin A1, alcohol intake, smoking, use of cardiovascular drugs or a history of myocardial infarction. Diabetics with gall stone disease had higher fasting insulin concentrations (p less than 0.5), lower total (p less than 0.01) and low density lipoprotein cholesterol (p less than 0.01) and high density lipoprotein cholesterol (not statistically significant) concentrations than diabetics without gall stone disease. These changes in insulin, lipids and lipoproteins are similar to reported changes in non-diabetic subjects with gall stone disease. Therefore, they are characteristic for gall stone disease and not as such explanatory to an increased risk of gall stones in patients with non-insulin dependent diabetes.

Heterogeneity of low density lipoprotein responses to fish-oil supplementation in hypertriglyceridemic subjects

Previous studies have demonstrated a variable effect of fish oil on low density lipoprotein (LDL) cholesterol and apolipoprotein (apo) B levels, particularly in hypertriglyceridemic subjects. Since heterogeneity of LDL composition and metabolism in hypertriglyceridemic subjects is well described, the present study was undertaken to determine if the response of LDL to dietary fish-oil supplementation is dependent upon pretreatment differences in LDL composition. A single-blind, cross-over design was used with 18 hypertriglyceridemic subjects, who were given supplements of a safflower-oil placebo or a fish-oil concentrate (4.0 g omega-3 fatty acids; [F4 dose]) for 1 month. Sixteen subjects then received an additional month of fish-oil supplementation at a higher dose (7.5 g omega-3 fatty acids [F7.5 dose]). The initial LDL cholesterol/apo B ratio, an index of LDL composition, was correlated positively with changes in LDL apo B levels (F4.0 dose: r = 0.41, p = 0.06; F7.5 dose: r = 0.51, p = 0.03) and negatively with changes in LDL cholesterol concentrations (F4.0 dose: r = -0.51, p = 0.01; F7.5 dose: r = -0.50, p = 0.02). Twelve subjects with LDL cholesterol/apo B ratios above 1.4 had large increases in LDL apo B (51% at both doses, p less than 0.05) but much smaller changes in LDL cholesterol levels during fish-oil treatment. Six subjects with LDL cholesterol/apo B ratios below 1.4 showed a trend toward increased LDL cholesterol (12% increase from baseline at F4 dose, 10% increase from baseline at F7.5 dose, p greater than 0.05) but not in LDL apo B levels during fish-oil therapy. These data suggest that LDL responses to fish oil may be linked to underlying differences in LDL composition and, presumably, to differences in LDL metabolic behavior.

Long-term treatment of hypercholesterolemic non-insulin dependent diabetics (NIDDM) with pravastatin (CS-514)

We examined the long-term effect of pravastatin, a new potent inhibitor of endogenous cholesterol biosynthesis, on glucose and lipid metabolism in hyperlipidemic NIDDM. Ten patients (5 on sulfonylurea, 5 on diet) were studied over 12 months. Five were WHO type IIa and 5 were type IIb. Blood was taken before and then 1, 6 and 12 months after initiating 10 or 20 mg daily of pravastatin. The cholesterol concentration in whole plasma and very low density lipoprotein (VLDL), plasma triglyceride and apolipoprotein (apo) B were all significantly decreased within the first month. These changes lasted for 1 year. High density lipoprotein (HDL)-cholesterol increased in the first month but returned to base line thereafter. Low density lipoprotein (LDL)-cholesterol tended to decrease in the first month, and was suppressed significantly from the 6th month (11%) to the 12th month (16%). The effect of pravastatin on LDL-cholesterol in NIDDM was slower and weaker than that published for non-diabetic hypercholesterolemia. Therefore, the mechanism by which pravastatin suppresses plasma cholesterol levels in these two conditions may differ. After 1 year, no adverse effects were noted on hematopoietic, hepatic or renal function. Blood glucose level, hemoglobin A1c and the insulin response to oral glucose were unchanged. In addition, serum creatine phosphokinase showed no abnormal increase. Careful ophthalmological examinations before and after pravastatin treatment revealed no development of new lenticular opacities. Thus, pravastatin appears to be a safe and effective drug for the long-term treatment of NIDDM with hypercholesterolemia.

Health risks of obesity

Evidence implicating obesity as a risk-factor disease is critically reviewed. Possible reasons for the many conflicting findings are addressed. The classification of obesity, based upon the site of body fat distribution, and possible biologic mechanisms associating regional adiposity with morbidity, are discussed.

Treatment of lipid disorders in diabetes mellitus

One reason for premature atherosclerosis in patients with diabetes mellitus is abnormal lipid metabolism. This article discusses the plasma lipid disorders associated with diabetes mellitus, and how to apply the new guidelines from the National Cholesterol Education Program for treatment of hypercholesterolemia in patients with diabetes mellitus.

Hyperinsulinemia is characterized by jointly disturbed plasma VLDL, LDL, and HDL levels. A population-based study

Plasma very low density lipoprotein (VLDL) cholesterol and triglyceride, low density lipoprotein (LDL) cholesterol and triglyceridea, high density lipoprotein (HDL) cholesterol, glucose and insulin response (sums of 1- and 2-hour postload oral glucose levels), body mass index (BMI), and blood pressure were determined in a representative sample (n = 542) of the adult Israeli Jewish population. Persons with diabetes or on antihypertensive medications were excluded. Total VLDL and LDL fractions were estimated from their cholesterol and triglyceride subfraction levels that were standardized relative to the mean of the reference group (participants free of glucose intolerance, obesity, and hypertension--the GOH conditions). Hyperinsulinemia and disturbed levels of VLDL and LDL were defined as levels equal to or greater than the 75th percentile and those of HDL, equal to or less than the 25th percentile of their respective reference group distributions. When VLDL was disturbed jointly with LDL and HDL, the mean insulin response adjusted for age, gender, glucose response, BMI, blood pressure, and smoking was high compared to the reference group (166.0 vs. 122.5, p less than 0.001). With isolated disturbed VLDL, or disturbed LDL and HDL but normal VLDL, the mean insulin response resembled the reference group. The adjusted risk ratio for this jointly disturbed lipoprotein profile among hyperinsulinemic individuals was 3.4 (95% confidence limits 2.6 to 4.4, p less than 0.001) with no further association with the GOH conditions. We conclude that hyperinsulinemia is characterized by an atherogenic lipoprotein profile.

Hyperinsulinemia, upper body adiposity, and cardiovascular risk factors in non-diabetics

Previous studies have suggested that hyperinsulinemia and upper body adiposity are each separately associated with elevated BP and triglyceride (TG) levels, and with lower high density lipoprotein (HDL) cholesterol levels. The joint effect of hyperinsulinemia and upper body adiposity on lipids, lipoproteins, and BP, however, has not been previously studied. We hypothesized that the effect of body fat distribution on cardiovascular risk factors might be mediated through hyperinsulinemia. We measured BP, lipids and lipoproteins, HDL subfractions, and insulin and glucose concentrations as part of the San Antonio Heart Study, a population-based study of diabetes and cardiovascular risk factors. Insulinemia and glycemia were assessed as the sum of the fasting, half-hour, one-hour, and two-hour insulin and glucose levels, respectively, measured during a standardized oral glucose tolerance test. Individuals who had diabetes according to National Diabetes Data Group criteria were excluded from the analyses. In univariate analyses, both hyperinsulinemia and waist-to-hip ratio (WHR), a measure of upper body adiposity, were positively associated with TG and negatively associated with total HDL and HDL2 cholesterol levels. However, when the effects of glycemia and insulinemia were controlled for by analysis of variance, WHR was no longer significantly related to TG levels. By contrast, WHR continued to be inversely related to total HDL and HDL2 cholesterol even after adjustment for glycemia and insulinemia. Hyperinsulinemia was only weakly related to HDL cholesterol. These results suggest that insulinemia and glycemia might mediate the effects of upper body adiposity on TG, although not on HDL and HDL2 cholesterol. Hyperinsulinemia was also positively associated with diastolic and systolic BP in men.