Diminished insulin receptors on monocytes and erythrocytes in hypertriglyceridemia

Gene-environment interaction in type 2 diabetes in Korean cohorts: Interaction of a type 2 diabetes polygenic risk score with triglyceride and cholesterol on fasting glucose levels

Type 2 diabetes (T2D) is caused by genetic and environmental factors as well as gene-environment interactions. However, these interactions have not been systematically investigated. We analyzed these interactions for T2D and fasting glucose levels in three Korean cohorts, HEXA, KARE, and CAVAS, using the baseline data with a multiple regression model. Two polygenic risk scores for T2D (PRS_T2D ) and fasting glucose (PRS_FG ) were calculated using 488 and 82 single nucleotide polymorphisms (SNP) for T2D and fasting glucose, respectively, which were extracted from large-scaled genome-wide association studies with multiethnic data. Both lifestyle risk factors and T2D-related biochemical measurements were assessed. The effect of interactions between PRS_T2D -triglyceride (TG) and PRS_T2D -total cholesterol (TC) on fasting glucose levels was observed as follows: β ± SE = 0.0005 ± 0.0001, p = 1.06 × 10^-19 in HEXA, β ± SE = 0.0008 ± 0.0001, p = 2.08 × 10^-8 in KARE for TG; β ± SE = 0.0006 ± 0.0001, p = 2.00 × 10^-6 in HEXA, β ± SE = 0.0020 ± 0.0004, p = 2.11 × 10^-6 in KARE, β ± SE = 0.0007 ± 0.0004, p = 0.045 in CAVAS for TC. PRS_T2D -based classification of the participants into four groups showed that the fasting glucose levels in groups with higher PRS_T2D were more adversely affected by both the TG and TC. In conclusion, blood TG and TC levels may affect the fasting glucose level through interaction with T2D genetic factors, suggesting the importance of consideration of gene-environment interaction in the preventive medicine of T2D.

Alpha-lipoic acid and its protective role in fructose induced endocrine-metabolic disturbances

In recent decades a worldwide increase has been reported in the consumption of unhealthy high calorie diets associated with marked changes in meal nutrient composition, such as a higher intake of refined carbohydrates, which leads to the speculatation that changes in food habits have contributed to the current epidemic of obesity and type 2 diabetes. Among these refined carbohydrates, fructose has been deeply investigated and murine models of high fructose diet have emerged as useful tools to study dietary-induced insulin resistance, impaired glucose tolerance, dyslipidemia and alterations in glucose metabolism. Since oxidative stress has been demonstrated to play a key pathogenic role in the alterations described above, several lines of research have focused on the possible preventive effects of antioxidant/redox state regulation therapy, among which alpha-lipoic acid has been extensively investigated. The following references discussed support the fact that co-administration of alpha-lipoic acid normalized the changes generated by fructose rich diets, thereby making this compound a good therapeutic tool, also administered as a food supplement, to prevent endocrine-metabolic disturbances triggered by high fructose associated with obesity and type 2 diabetes at an early stage of development (prediabetes).

Albiflorin Granule significantly decreased the cholesterol gallstone formation by the regulation of insulin transduction signal

OBJECTIVE

To study the mechanism of insulin resistance in the cholesterol gallstone formation from insulin signal transduction pathway so as to reveal the possible mechanism and the effective role of Albiflorin Granule on preventing the cholesterol gallstones.

METHODS

Serum triglycerides (TG), free fatty acid (FFA), and total cholesterol (TC) from different groups were measured and liver cells InsR, PKB, IKK-β protein expression levels were detected by western blotting.

RESULTS

Albiflorin significantly decreased the cholesterol gallstone formation rate, increased glucose infusion rate in gallstone guinea pigs and improved insulin resistance. Compared with the normal group, insulin receptor and PKB protein expression in GS group were significantly reduced. IKK-β protein in the GS group increased significantly and Albiflorin could reduce IKK-β protein expression in guinea pig liver cells.

CONCLUSIONS

The model of insulin resistance in cholesterol gallstone guinea pig was successfully established, which plays an important role in the cholesterol gallstone formation. All aspects of insulin signaling pathway are involved in gallstone formation. Albiflorin can regulate various aspects of insulin signal transduction pathway to prevent the formation of gallbladder.

Quercetin-Rich Guava (Psidium guajava) Juice in Combination with Trehalose Reduces Autophagy, Apoptosis and Pyroptosis Formation in the Kidney and Pancreas of Type II Diabetic Rats

We explored whether the combination of anti-oxidant and anti-inflammatory guava (Psidium guajava) and trehalose treatment protects the kidney and pancreas against Type II diabetes (T2DM)-induced injury in rats. We measured the active component of guava juice by HPLC analysis. T2DM was induced in Wistar rats by intraperitoneal administration of nicotinamide and streptozotocin and combination with high fructose diets for 8 weeks. The rats fed with different dosages of guava juice in combination with or without trehalose for 4 weeks were evaluated the parameters including OGTT, plasma insulin, HbA1c, HOMA-IR (insulin resistance) and HOMA-β (β cell function and insulin secretion). We measured oxidative and inflammatory degrees by immunohistochemistry stain, fluorescent stain, and western blot and serum and kidney reactive oxygen species (ROS) by a chemiluminescence analyzer. High content of quercetin in the guava juice scavenged H2O2 and HOCl, whereas trehalose selectively reduced H2O2, not HOCl. T2DM affected the levels in OGTT, plasma insulin, HbA1c, HOMA-IR and HOMA-β, whereas these T2DM-altered parameters, except HbA1c, were significantly improved by guava and trehalose treatment. The levels of T2DM-enhanced renal ROS, 4-hydroxynonenal, caspase-3/apoptosis, LC3-B/autophagy and IL-1β/pyroptosis were significantly decreased by guava juice and trehalose. The combination with trehalose and guava juice protects the pancreas and kidney against T2DM-induced injury.

Hypothyroidism associated with acromegaly and insulin-resistant diabetes mellitus in a Samoyed

BACKGROUND

The aetiology of insulin resistance (IR) in naturally occurring canine hypothyroidism is poorly understood and likely multifactorial. Excess secretion of growth hormone (GH) by transdifferentiated pituitary cells may contribute to IR in some hypothyroid dogs, but although this has been demonstrated in experimental studies, it has not yet been documented in clinical cases.

CASE REPORT

A 4-year-old male entire Samoyed presented with an 8-month history of pedal hyperkeratosis and shifting lameness, which had been unresponsive to zinc supplementation, antibiotics and glucocorticoid therapy. The dog also exhibited exercise intolerance and polydipsia of 12 and 2 months duration, respectively. On physical examination, obesity, poor coat condition, widened interdental spaces and mild respiratory stridor were noted. Initial laboratory test results revealed concurrent hypothyroidism and diabetes mellitus (DM). Further investigations showed IR, GH excess and a paradoxical increase of GH following stimulation with thyrotropin-releasing hormone.

CONCLUSIONS

To the authors' knowledge, this is the first reported case that suggests that GH alterations may have clinical significance in naturally occurring hypothyroidism. Among other factors, hypothyroidism-induced GH excess should be considered as a possible cause of IR in patients suffering from hypothyroidism and concurrent DM. In such cases, DM may reverse with treatment of hypothyroidism, as was documented in this case.

Attenuated alpha-adrenoceptor-mediated arterial and venous constrictions in rat models of diabetes

Diabetes is associated with metabolic and vascular abnormalities. We investigated if arterial and venous constrictions are impaired in rat models of diabetes. Wistar rats (5 weeks old) were fed a normal or high-fructose diet (60% of caloric intake). On Day 14, half of the animals in each diet regimen were given streptozotocin (60 mg/kg, i.v.). On Day 35, plasma insulin and triglyceride were measured, and on Day 42, insulin sensitivity (via hyperinsulinemic euglycemic clamp), and pressor as well as mean circulatory filling pressure (index of venous tone) responses to noradrenaline were determined. The rats treated with streptozotocin or fructose-streptozotocin were hyperglycemic, hypoinsulinemic and insulin resistant, and they also had reduced potency (increased ED(50)) of pressor response and reduced venoconstriction to noradrenaline compared to the two groups not given streptozotocin. Plasma triglyceride was unchanged in streptozotocin-treated rats, moderately increased in fructose-fed rats, and markedly increased in fructose-streptozotocin-treated rats. Hyperglycemia, insulin resistance and alpha-adrenoceptor-mediated venous contractile dysfunction were more pronounced in the group given fructose-streptozotocin than that given streptozotocin alone. The presence of marked hypertriglyceridemia, insulin resistance and vascular dysfunction makes the fructose-streptozotocin-treated rats a suitable model for study of metabolic and vascular abnormalities in advanced type 2 diabetes.

Food seasoning spices mixture improves glucose metabolism and lipid profile in fructose-fed hyperinsulinemic rats

Fructose feeding has been shown to induce insulin resistance in rats, associated with hyperinsulinemia, hyperglycemia, and hypertriglyceridemia. We have investigated the effect of administering food seasoning spices mixture (SM) on glucose, insulin, and lipids in circulation and carbohydrate enzymes in the erythrocytes of high fructose-fed rats. Additionally, we also measured the protein glycation status by assaying the levels of glycated hemoglobin, fructosamine, and plasma protein glycation. Male Wistar rats received a daily diet containing either 60% fructose or 60% starch (control). The rats were administered SM at three different doses (10, 30, or 50 mg/day per rat) orally 15 days later. At the end of the 45-day experimental period, fructose-fed rats showed significantly higher levels of plasma glucose and insulin, dyslipidemia, and alterations in enzyme activities. Treatment with SM significantly reduced plasma glucose and insulin levels and brought about a favorable lipid profile. In these rats, the activities of enzymes of glucose metabolism were normal. These effects were observed at all three doses of SM. High homeostasis model assessment (HOMA) values indicated insulin resistance in fructose-fed rats, while the HOMA values in SM-treated fructose-fed rats were comparable to those of control rats. We conclude that administration of SM improves glucose metabolism and plasma lipid profile in fructose-fed rats, possibly through improved insulin-sensitizing actions of the active constituents.

Dietary fructose: implications for dysregulation of energy homeostasis and lipid/carbohydrate metabolism

Fructose intake and the prevalence of obesity have both increased over the past two to three decades. Compared with glucose, the hepatic metabolism of fructose favors lipogenesis, which may contribute to hyperlipidemia and obesity. Fructose does not increase insulin and leptin or suppress ghrelin, which suggests an endocrine mechanism by which it induces a positive energy balance. This review examines the available data on the effects of dietary fructose on energy homeostasis and lipid/carbohydrate metabolism. Recent publications, studies in human subjects, and areas in which additional research is needed are emphasized.

Substituting dietary linoleic acid with alpha-linolenic acid improves insulin sensitivity in sucrose fed rats

This study describes the effect of substituting dietary linoleic acid (18:2 n-6) with alpha-linolenic acid (18:3 n-3) on sucrose-induced insulin resistance (IR). Wistar NIN male weanling rats were fed casein based diet containing 22 energy percent (en%) fat with approximately 6, 9 and 7 en% saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) respectively for 3 months. IR was induced by replacing starch (ST) with sucrose (SU). Blends of groundnut, palmolein, and linseed oil in different proportions furnished the following levels of 18:3 n-3 (g/100 g diet) and 18:2 n-6/18:3 n-3 ratios respectively: ST-220 (0.014, 220), SU-220 (0.014, 220), SU-50 (0.06, 50), SU-10 (0.27, 10) and SU-2 (1.1, 2). The results showed IR in the sucrose fed group (SU-220) as evidenced by increase in fasting plasma insulin and area under the curve (AUC) of insulin in response to oral glucose load. In SU-220, the increase in adipocyte plasma membrane cholesterol/phospholipid ratio was associated with a decrease in fluidity, insulin stimulated glucose transport, antilipolytic effect of insulin and increase in basal and norepinephrine stimulated lipolysis in adipocytes. In SU-50, sucrose induced alterations in adipocyte lipolysis and antilipolysis were normalized. However, in SU-2, partial corrections in plasma insulin, AUC of insulin and adipocyte insulin stimulated glucose transport were observed. Further, plasma triglycerides and cholesterol decreased in SU-2. In diaphragm phospholipids, the observed dose dependent increase in long chain (LC) n-3 PUFA was associated with a decrease in LC-n-6 PUFA but insulin stimulated glucose transport increased only in SU-2. Thus, this study shows that the substitution of one-third of dietary 18:2 n-6 with 18:3 n-3 (SU-2) results in lowered blood lipid levels and increases peripheral insulin sensitivity, possibly due to the resulting high LCn-3 PUFA levels in target tissues of insulin action. These findings suggest a role for 18:3 n-3 in the prevention of insulin resistant states. The current recommendation to increase 18:3 n-3 intake for reducing cardiovascular risk may also be beneficial for preventing IR in humans.

Dietary trans-fatty acids alter adipocyte plasma membrane fatty acid composition and insulin sensitivity in rats

The present study was designed to investigate the effects of dietary trans-fatty acids (TFA) present in Indian vanaspati (partially hydrogenated vegetable oils) in comparison with saturated fatty acids (SFA) on adipocyte plasma membrane fatty acid composition, fluidity, and insulin action. The effects of 3% energy (% en) TFA was studied at 2% and 4% en of linoleic acid (18:2 n-6). WNIN male weanling rats were divided into 4 groups and fed casein-based diet containing 10% groundnut oil control (CON), palmolein (SFA), blend of vanaspati and safflower oil (3% en TFA and 2% en 18:2 n-6, TFA-1), or blend of vanaspati and safflower oil (3% en TFA and 4% en 18:2 n-6, TFA-2) for 12 weeks. Compared with CON, rats fed TFA and SFA diets had high levels of fasting plasma insulin and triglycerides. Both TFA- and SFA-fed groups had low levels of arachidonic acid (20:4 n-6) in adipocyte plasma membrane phospholipids. However, adipocyte plasma membrane fluidity decreased only in TFA-fed rats. Norepinephrine-stimulated lipolysis was high, whereas the antilipolytic effect of insulin and insulin-stimulated glucose transport were low in the adipocytes of SFA- and TFA-fed rats. However, the extent of decrease in the antilipolytic effect of insulin and insulin-stimulated glucose transport was greater in TFA-fed rats. These findings suggest that diet providing approximately 10% en SFA (PUFA/SFA [P/S] ratio 0.2) decreased adipocyte insulin sensitivity in rats. In these diets, replacement of approximately 2% en SFA (16:0) and approximately 1% en monounsaturated fatty acid (18:1 cis) with TFA decreased adipocyte insulin sensitivity to a greater extent. However, increasing dietary 18:2 n-6 did not prevent or reduce the TFA-induced adipocyte insulin resistance.

Cardiac lipids and antioxidant status in high fructose rats and the effect of alpha-lipoic acid

BACKGROUND AND AIMS

The development of insulin resistance has been shown to be an early step in the development of cardiovascular diseases in diabetic patients. Oxidative stress may be important in the development of coronary artery disease. Fructose loaded rats, which show the characteristic features of insulin resistance, also display an imbalance between the peroxidation process and the antioxidant system. Alpha-lipoic acid (LA)--a co-enzyme--is known for its potent antioxidant effects. The present study examined whether LA mitigates fructose-induced oxidative stress in heart tissue.

METHODS AND RESULTS

Male Wistar rats with a body weight of 150-170g were divided into 4 groups of 6 rats each. Control rats received a control diet containing starch and water ad libitum. Fructose rats received a fructose-enriched diet (>60% of total calories). Fructose + LA rats received a fructose diet and alpha-lipoic acid (35mg/kg b.w i.p.). Control + LA rats received control diet and alpha-lipoic acid. After the 20-day treatment period, we assessed the insulin sensitivity index in terms of HOMA. The levels of lipid peroxidation markers and the enzymatic and non-enzymatic antioxidant status in the heart tissue were measured. Plasma and heart tissue lipids were also analysed. Fructose rats showed decreased insulin sensitivity as reflected by high values of HOMA, increased peroxidation, impaired antioxidant status and lipid abnormalities in the cardiac tissue. These abnormalities were attenuated and the antioxidant levels were enhanced by LA. The reduction in HOMA values suggests LA improves insulin sensitivity.

CONCLUSIONS

Improvement of insulin sensitivity and enhancement of cardiac antioxidant status suggest that LA may be useful as a cardioprotective agent in insulin-resistant states.

Influence of alpha-lipoic acid on lipid peroxidation and antioxidant defence system in blood of insulin-resistant rats

BACKGROUND

High fructose feeding induces insulin resistance and hyperinsulinaemia in rats. A role for oxidative stress in the occurrence of insulin resistance has been suggested by several workers.

AIM

The aim of this study was to investigate the effect of alpha-lipoic acid (LA) on oxidant-antioxidant balance in rats fed on a high-fructose diet that showed characteristic features of insulin resistance.

METHODS

Male Wistar rats weighing 150-170 g were divided into seven groups. The control group received the control diet containing starch. The fructose group was given a high-fructose diet (>60% of total calories). The third and fourth groups were given fructose diet and were administered two different doses of LA at a low dose (35 mg/kg body weight) and high dose (70 mg/kg body weight) using olive oil as vehicle. The fifth group received fructose diet and olive oil. The sixth group received control diet and was administered LA (70 mg/kg body weight). And, the seventh group received the control diet and olive oil. Products of lipid peroxidation and activities of enzymic antioxidants, namely superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase and glutathione reductase, in red blood cells were assayed. Levels of non-enzymic antioxidants alpha-tocopherol, ascorbic acid and reduced glutathione were determined in plasma.

RESULTS

The levels of lipid peroxides, diene conjugates and thiobarbituric acid-reactive substances were significantly higher in fructose-fed rats. Inadequate antioxidant system was observed in high-fructose-fed rats. Treatment of fructose rats mitigated the imbalance between peroxidation and antioxidant defence system at both the doses tested. Increases in glucose, triglycerides, free fatty acids, insulin and insulin resistance were observed in fructose-fed rats. LA administration prevented these alterations and improved insulin sensitivity. Significant positive correlations were obtained between insulin resistance and lipid peroxidation indices.

CONCLUSIONS

Increased lipid peroxidation and deficient antioxidant system are observed in high-fructose-fed rats. LA administration preserves the antioxidant system and lowers lipid peroxidation. The findings suggest an interrelationship between lipid peroxidation and insulin resistance.

Fructose, weight gain, and the insulin resistance syndrome

This review explores whether fructose consumption might be a contributing factor to the development of obesity and the accompanying metabolic abnormalities observed in the insulin resistance syndrome. The per capita disappearance data for fructose from the combined consumption of sucrose and high-fructose corn syrup have increased by 26%, from 64 g/d in 1970 to 81 g/d in 1997. Both plasma insulin and leptin act in the central nervous system in the long-term regulation of energy homeostasis. Because fructose does not stimulate insulin secretion from pancreatic beta cells, the consumption of foods and beverages containing fructose produces smaller postprandial insulin excursions than does consumption of glucose-containing carbohydrate. Because leptin production is regulated by insulin responses to meals, fructose consumption also reduces circulating leptin concentrations. The combined effects of lowered circulating leptin and insulin in individuals who consume diets that are high in dietary fructose could therefore increase the likelihood of weight gain and its associated metabolic sequelae. In addition, fructose, compared with glucose, is preferentially metabolized to lipid in the liver. Fructose consumption induces insulin resistance, impaired glucose tolerance, hyperinsulinemia, hypertriacylglycerolemia, and hypertension in animal models. The data in humans are less clear. Although there are existing data on the metabolic and endocrine effects of dietary fructose that suggest that increased consumption of fructose may be detrimental in terms of body weight and adiposity and the metabolic indexes associated with the insulin resistance syndrome, much more research is needed to fully understand the metabolic effect of dietary fructose in humans.

Effect of eicosapentaenoic acid ethyl ester v. oleic acid-rich safflower oil on insulin resistance in type 2 diabetic model rats with hypertriacylglycerolaemia

The purpose of the present study was to test whether hyperlipidaemia and insulin resistance in type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats can be improved by dietary supplementation with purified eicosapentaenoic acid (EPA) or oleic acid (OA). Male OLETF rats were fed powdered chow (510 g fat/kg) alone (n 8) or chow supplemented with 10 g EPA- (n 8) or OA- (n 8) rich oil/kg per d from 5 weeks until 30 weeks of age. An oral glucose tolerance test and hyperinsulinaemic euglycaemic clamp was performed at 25 and 30 weeks of age. EPA supplementation resulted in significantly (P<0.05) reduced plasma lipids, hepatic triacylglycerols, and abdominal fat deposits, and more efficient in vivo glucose disposal compared with OA supplementation and no supplementation. OA supplementation was associated with significantly increased insulin response to oral glucose compared with EPA supplementation and no supplementation. Inverse correlation was noted between glucose uptake and plasma triacylglycerol levels (r -086, P<0.001) and abdominal fat volume (r -0.80, P<0.001). The result of oral glucose tolerance test study showed that the rats fed EPA tended to improve glucose intolerance, although this was not statistically significant. Levels of plasma insulin at 60 min after glucose was significantly increased in rats fed OA compared with the other two groups. The results indicate that long-term feeding of EPA might be effective in preventing insulin resistance in diabetes-prone rats, at least in part, due to improving hypertriacylglycerolaemia.

Diagnosis and management of insulin resistance in dogs and cats with diabetes mellitus

Both dogs and cats with diabetes occasionally develop resistance to the action of insulin during treatment. Clinical insulin resistance should be suspected in any animal in which marked hyperglycemia persists throughout the day despite insulin doses of greater than 1.5 U/kg per injection. In a clinical setting it may be difficult to determine the underlying cause for insulin resistance, which makes management difficult. This article reviews the known causes for insulin resistance and outlines recommendations for diagnosis and management of diabetic dogs and cats.

Insulin binding in non-insulin-dependent diabetes mellitus (NIDDM) is correlated with glycemic control: clinical evidence for abnormal receptor regulation in NIDDM

Insulin binding has been reported to be decreased in non-insulin-dependent diabetes mellitus (NIDDM). Although elevated basal insulin concentrations have been correlated with decreased insulin binding in obesity, this relationship has not been found in NIDDM. To determine the potential cause(s) of the decrease, we measured 125I-insulin binding to circulating monocytes isolated from 31 non-insulin-treated patients with NIDDM who had a fasting plasma glucose (FPG) concentration greater than 7.8 mmol/L and 13 control subjects. We examined the influence of obesity, insulin concentration, glycemic control, and treatment with oral hypoglycemic agents on insulin binding in a cross-sectional study. Insulin binding was significantly decreased in the entire NIDDM group (mean +/- SEM, %/10(7) monocytes: 4.65 +/- 0.33) as compared with controls (6.45 +/- .70, P < .02). Subgroups defined by obesity (relative body weight > 1.2) and poor glycemic control (FPG > 11.1 mmol/L) and those not taking oral hypoglycemic agents had significantly lower insulin binding (P < .02). However, neither relative body weight nor insulin concentrations (basal or stimulated) correlated with insulin binding. Stepwise linear regression analysis showed that only FPG significantly correlated with insulin binding (r = -.45, P = .002) even when oral hypoglycemic agent-treated patients were removed from the analysis (r = -.50, P = .003). There was no significant contribution to explain insulin binding by the other variables, including diagnosis of diabetes, obesity, insulin concentration, or treatment with oral hypoglycemic agents. We conclude that poor metabolic control is associated with an alteration in insulin receptor regulation in NIDDM.

Relation of angiographically defined coronary artery disease and plasma concentrations of insulin, lipid, and apolipoprotein in normolipidemic subjects with varying degrees of glucose tolerance

We investigated the association between hyperinsulinemia and changes in lipid, lipoprotein, and apolipoprotein that would increase the risk of coronary artery disease (CAD) independent of glucose tolerance. A coronary angiogram was recorded in 127 male subjects, including 41 with normal glucose tolerance, 41 with impaired glucose tolerance, and 45 with non-insulin-dependent diabetes mellitus (NIDDM). Subjects were divided into 2 groups according to results: the group with CAD (n = 94) and the group with normal coronary arteries (n = 33). All subjects were normolipidemic (total cholesterol < 230 mg/dl and triglycerides < 150 mg/dl). The CAD group had a significantly lower plasma level of high-density lipoprotein (HDL) cholesterol and apolipoprotein A-I (apo A-I) and a higher level of apolipoprotein B (apo B) than the normal group with normal glucose tolerance. In considering subjects with impaired glucose tolerance or NIDDM, the CAD group had a significantly lower plasma level of HDL cholesterol and apo A-I and a significantly higher plasma level of total cholesterol, triglycerides, and apo B than the normal group. In each of the subjects with normal and impaired glucose tolerance, and NIDDM, the elevation of plasma insulin concentration during both the complete test period and the early phase of an oral glucose challenge was significantly higher in the CAD than in the normal group. In all subjects, graded reductions in HDL cholesterol and apo A-I and graded increases in plasma total cholesterol, triglycerides, and apo B were observed with increasing tertiles of the postglucose challenge measurements of insulinemia.(ABSTRACT TRUNCATED AT 250 WORDS)

The dyslipoproteinemias of diabetes

Atherosclerosis is the most frequent complication of diabetes. There are many potentially atherogenic factors in diabetes that may underlie this problem. Of these, one is the group of dyslipoproteinemias. In diabetes there are both qualitative and quantitative changes in the plasma lipoproteins. Based on pathophysiological and epidemiological data, these may be among the many factors that can result in early macrovascular disease. Furthermore, at least one of the dyslipoproteinemias--hypertriglyceridemia--is associated with insulin resistance and therefore could aggravate glucose intolerance. Thus, on theoretical grounds it is reasonable to postulate that treating the dyslipoproteinemias of diabetes would reduce atherosclerotic disease. However, to date there have been no intervention studies specifically designed to test this postulate in the diabetic population. One such study, the Diabetes Atherosclerosis Intervention Study, is currently in progress.

The effect of an antilipolytic agent (acipimox) on the insulin resistance of lipid and glucose metabolism in hypertriglyceridaemic patients

Hypertriglyceridaemia is associated with insulin resistance of both lipid and glucose metabolism. It is not known whether the insulin resistance affects both glucose oxidation and glycogen formation. To study the oxidative and non-oxidative pathways of non-esterified fatty acids (NEFA) and glucose metabolism, eight male hypertriglyceridaemic subjects were studied during insulin infusion (75 and 340 pmol/m2.min) in combination with indirect calorimetry and infusions of [3-3H]glucose and [1-14C]palmitate before and after 4 weeks of treatment with the antilipolytic agent acipimox (250 mg three times daily). Compared with eight healthy subjects the hypertriglyceridaemic subjects were resistant to the antilipolytic effect of insulin, both in the basal state (P < 0.05) and during insulin infusion (P < 0.05). This was associated with impaired insulin-stimulated glucose uptake (P < 0.05), predominantly in the non-oxidative pathway (P < 0.05). Acipimox decreased basal NEFA concentrations (P < 0.01) and reduced lipid oxidation during low-dose insulin infusion (P < 0.05). Glucose uptake, predominantly glycogen formation, was stimulated by acipimox (P < 0.05). In conclusion, the insulin resistance of glucose metabolism associated with hypertriglyceridaemia is largely due to a defect in non-oxidative glucose metabolism. Acipimox improves glucose metabolism both by affecting glucose oxidation (low-dose insulin) and non-oxidative glucose metabolism (high-dose insulin).

Effects of vanadate administration on the high sucrose diet-induced aberrations in normal rats

Effects of feeding sucrose rich diet supplemented with and without the insulinmimetic agent vanadate for a period of six weeks were studied in rats. Sucrose diet caused hypertriglyceridemia (140% increase), hyperinsulinemia (120% increase) and significant elevations in the levels of glucose (p < 0.001) and cholesterol (p < 0.05) in plasma as compared to control starch fed rats. Activities of hepatic lipogenic enzymes, ATP-citrate lyase, glucose 6-phosphate dehydrogenase and malic enzyme increased by 100-150% as a result of sucrose feeding. However, glycogen content and the activities of glycogen synthase and phosphorylase in liver remained unaltered in these animals. The plasma levels of triacylglycerols and insulin in the rats fed on vanadate supplemented sucrose diet were 65% and 85% less, respectively as compared to rats on sucrose diet without vanadate. The concentrations of glucose and cholesterol in plasma and the activities of lipogenic enzymes in liver did not show any elevation in sucrose fed rats when supplemented with vanadate. These data indicate that the sucrose diet-induced metabolic aberrations can be prevented by the insulin-mimetic agent, vanadate.

Insulin resistance in type 2 (non-insulin-dependent) diabetic patients with hypertriglyceridaemia

Hypertriglyceridaemia, which is frequently seen in Type 2 (non-insulin-dependent) diabetes mellitus, is associated with insulin resistance. The connection between hypertriglyceridaemia and insulin resistance is not clear, but could be due to substrate competition between glucose and lipids. To address this question we measured glucose and lipid metabolism in 39 Type 2 diabetic patients with hypertriglyceridaemia, i.e. mean fasting serum triglyceride level equal to or above 2 mmol/l (age 59 +/- 1 years, BMI 27.4 +/- 0.5 kg/m2, HbA1c 8.0 +/- 0.2%, serum triglycerides 3.2 +/- 0.2 mmol/l) and 41 Type 2 diabetic patients with normotriglyceridaemia, i.e. mean fasting serum triglyceride level below 2 mmol/l (age 58 +/- 1 years, BMI 27.0 +/- 0.7 kg/m2, HbA1c 7.8 +/- 0.2%, serum triglycerides 1.4 +/- 0.1 mmol/l). Insulin sensitivity was assessed using a 340 pmol.(m2)-1 x min-1 euglycaemic insulin clamp. Substrate oxidation rates were measured with indirect calorimetry and hepatic glucose production was estimated using a primed (25 microCi)-constant (0.25 microCi/min) infusion of [3-3H]-glucose. Suppression of lipid oxidation by insulin was impaired in patients with hypertriglyceridaemia vs patients with normal triglyceride levels (3.5 +/- 0.2 vs 3.0 +/- 0.2 mumol.kg-1 x min-1; p < 0.05). Stimulation of glucose disposal by insulin was reduced in hypertriglyceridaemic vs normotriglyceridaemic patients (27.0 +/- 1.3 vs 31.9 +/- 1.6 mumol.kg-1 x min-1; p < 0.05) primarily due to impaired glucose storage (9.8 +/- 1.0 vs 14.6 +/- 1.4 mumol.kg-1 x min-1; p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Red blood cell insulin receptors in health and disease

CONTENTS

Structure and characteristics of erythrocyte insulin receptor. Red blood cell age and insulin receptors. Insulin receptors in human disease states. Obesity. Chronic renal failure. Acanthosis nigricans. Miscellaneous disease states. Insulin receptors in children. Insulin receptors in women during pregnancy. Insulin binding and other hormones. Comparison of biosynthetic insulin, pancreatic human insulin and porcine insulin binding to erythrocytes. Effect of exercise on insulin binding to red blood cells of normal human volunteers. Miscellaneous insulin binding studies. Insulin internalization and degradation. Insulin and erythrocyte metabolism. Summary and conclusion.

The assessment of hepatic and peripheral insulin sensitivity in hypertriglyceridemia

Peripheral insulin resistance is a common finding in hypertriglyceridemia. However, hepatic insulin sensitivity has rarely been investigated. We measured hepatic and peripheral insulin sensitivity in eight nondiabetic, nonobese hypertriglyceridemic subjects (HT) with raised triglyceride concentrations (4.3 +/- 0.6 mmol.L-1, mean +/- SEM) and eight age-, sex-, and weight-matched control subjects (C) with normal triglyceride concentrations (1.2 +/- 0.2 mmol.L-1). Insulin secretion was assessed during a 75-g oral glucose tolerance test (OGTT). Glucose turnover was determined using 3(3H) glucose in the postabsorptive state and during euglycemic glucose clamps at insulin infusion rates of 0.25 and 1.0 mU.kg-1.min-1. At identical fasting glucose concentrations (HT, 5.2 +/- 0.2; C, 5.2 +/- 0.2 mmol.L-1), the glucose responses to OGTT were similar in both groups. Fasting plasma insulin (HT, 8.3 +/- 1.2; C, 4.6 +/- 0.4 mU.L-1; P = .02), and C-peptide (HT, 1.7 +/- 0.2; C, 1.1 +/- 0.1 microgram.L-1; P = .006) concentrations were higher in hypertriglyceridemic subjects. The insulin and C-peptide responses to OGTT were greater in hypertriglyceridemic subjects (insulin, P = .005; C-peptide; P = .01). Hepatic glucose appearance in the postabsorptive state was similar (HT, 11.4 +/- 0.3; C, 10.9 +/- 0.7 mumol.kg-1.min-1; NS). At low insulin concentrations (HT, 20.7 +/- 1.4; C, 20.5 +/- 1.4 mU.L-1), hepatic glucose appearance was equally suppressed (HT, 9.6 +/- 0.9; C, 10.5 +/- 1.3 mumol.kg-1.min-1; NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin resistance is associated with lipid and lipoprotein abnormalities in subjects with varying degrees of glucose tolerance

We tested the hypothesis that insulin resistance, rather than high insulin level, is associated with lipid and lipoprotein changes favoring atherosclerosis independently of the glucose tolerance status. To this aim, 50 subjects with normal glucose tolerance, 28 subjects with impaired glucose tolerance, and 54 subjects with noninsulin-dependent diabetes (NIDDM) were studied. Subjects with low glucose disposal rate (GDR) or a high degree of insulin resistance as measured by the euglycemic hyperinsulinemic clamp technique had lower high density lipoprotein (HDL) cholesterol and higher total and very low density lipoprotein (VLDL) triglycerides than did subjects with high GDR (highest GDR tertile). These associations were independent of fasting insulin level and other confounding factors. In stepwise multiple linear regression analysis, GDR was the most important single variable associated with HDL cholesterol and VLDL triglyceride level independently of age, obesity, distribution of obesity (waist/hip ratio), 2-hour glucose level, and free fatty acid concentration. We conclude: 1) insulin resistance measured by the euglycemic clamp technique is associated with adverse lipid and lipoprotein changes favoring atherosclerosis not only in nondiabetic subjects (as shown in previous studies) but also in impaired glucose tolerance and NIDDM subjects; 2) the association of high insulin level with adverse lipid and lipoprotein changes indirectly reflects the association of insulin resistance with lipid and lipoprotein levels; and 3) HDL cholesterol and VLDL triglycerides are independently associated with insulin-mediated glucose uptake, which may indicate that these lipoproteins have separate sites of interaction with insulin action.

Insulin, body mass index, and cardiovascular risk factors in premenopausal women

This study assessed the relationship between insulin, glucose, body mass index, and cardiovascular risk factors in a sample of 489 white premenopausal women. All women were participants in the Healthy Women Study (University of Pittsburgh) and had normal blood pressure and fasting blood glucose of less than 140 mg/dl and a 2-hour value after a 75-g glucose load of less than 200 mg/dl. Both body mass index and fasting insulin were significantly and independently associated with blood pressure, triglycerides, and high density lipoprotein (HDL) cholesterol and its subfractions. Body mass index and fasting insulin were more strongly associated with coronary heart disease (CHD) risk factors than were 2-hour insulin, or fasting or 2-hour glucose; glucose levels did not contribute independently to multivariate predictions of any of the CHD risk factors. When patients were divided into tertiles according to fasting insulin and body mass index, there were significant main effects of insulin and body mass index on blood pressure, triglycerides, and HDL cholesterol and its subfractions; the interaction of insulin times body mass index was also significant for systolic blood pressure, triglycerides, and apoprotein B. These data confirm the previous findings of a strong association between insulin and CHD risk factors and extend this to healthy premenopausal women.

Lack of a lipoprotein-induced insulin resistance in hepatoma cells in culture

A lipoprotein-induced resistance to the action of insulin has been postulated. To test this hypothesis, cultured rat-derived hepatoma cells, designated FAO, and human-derived hepatoma cells, designated HEP-G2, were incubated for 20 h in the presence or absence of lipoprotein; specific 125I-insulin receptor binding and labeled glucose incorporation into glycogen were then measured. Very low density lipoproteins (d less than 1.006 g/ml) in physiologic (0.5 mg/ml) or pathophysiologic (5 mg/ml) concentrations did not modify insulin receptor binding of FAO or HEP-G2 cells. This was true for very low density lipoproteins derived from normal human, diabetic human, and streptozotocin-diabetic rat plasma. Low density lipoproteins (d = 1.019 - 1.063 g/ml) isolated from normal human plasma similarly failed to modify insulin receptor binding. Concerning insulin action, the different very low density lipoprotein preparations did not modulate either basal or insulin-stimulated glucose incorporation into glycogen of the cells. Thus, very low density lipoproteins and low density lipoproteins did not induce insulin resistance in cultured hepatoma cells either at the insulin receptor level or at the post-receptor level.

Hypertriglyceridemia and carbohydrate intolerance: interrelations and therapeutic implications

Atherosclerosis, the most frequent complication of diabetes, could be the result of hyperlipidemia, among other factors. Mounting evidence suggests that reducing the concentration of triglyceride-rich lipoprotein, which influences the production of the possibly atherogenic intermediate density lipoprotein (IDL), might diminish the circulating level of potentially atherogenic lipoproteins. Hypertriglyceridemia, even in the absence of obesity, is associated with insulin resistance. To compensate, pancreatic B cells respond to glucose challenge by producing hyperinsulinemia. If the B cells cannot respond adequately, carbohydrate intolerance ensues. Insulin-treated diabetics may also become hyperinsulinemic because routine insulin injection may not reflect physiologic need and because the insulin is administered peripherally rather than portally. Hyperinsulinemia increases the production of circulating triglyceride. It appears to do this in rats by causing the production of more triglyceride-rich lipoprotein particles rather than by increasing the triglyceride content of each particle. Further, at least in rats, the insulin-induced increase in triglyceride production requires the presence of supplementary dietary fructose. Hyperinsulinemia also increases the activity of adipose tissue lipoprotein lipase and the degradation of very low density lipoprotein (VLDL). The concentration of VLDL depends on balance of production and degradation. Accelerated VLDL degradation leads to an increase in IDL production. Because there is mounting evidence that IDL may be atherogenic, this cycle could accelerate atherogenesis. As such, it is reasonable to postulate that reducing the concentration of triglyceride-rich lipoproteins would break this cycle and would diminish the circulating level of potentially atherogenic lipoproteins.