Comparison of impedance to insulin-mediated glucose uptake in normal subjects and in subjects with latent diabetes

Effects of moderate variations in macronutrient composition on weight loss and reduction in cardiovascular disease risk in obese, insulin-resistant adults

BACKGROUND

Obese, insulin-resistant persons are at risk of cardiovascular disease. How best to achieve both weight loss and clinical benefit in these persons is controversial, and recent reports questioned the superiority of low-fat diets.

OBJECTIVE

We aimed to ascertain the effects of moderate variations in the carbohydrate and fat content of calorie-restricted diets on weight loss and cardiovascular disease risk in obese, insulin-resistant persons.

DESIGN

Fifty-seven randomly assigned, insulin-resistant, obese persons completed a 16-wk calorie-restricted diet with 15% of energy as protein and either 60% and 25% or 40% and 45% of energy as carbohydrate and fat, respectively. Baseline and postweight-loss insulin resistance; daylong glucose, insulin, and triacylglycerol concentrations; fasting lipid and lipoprotein concentrations; and markers of endothelial function were quantified.

RESULTS

Weight loss with 60% or 40% of energy as carbohydrate (5.7 +/- 0.7 or 6.9 +/- 0.7 kg, respectively) did not differ significantly, and improvement in insulin sensitivity correlated with the amount of weight lost (r = 0.50, P < 0.001). Subjects following the diet with 40% of energy as carbohydrate had greater reductions in daylong insulin and triacylglycerol (P < 0.05) and fasting triacylglycerol (0.53 mmol/L; P = 0.04) concentrations, greater increases in HDL-cholesterol concentrations (0.12 mmol/L; P < 0.01) and LDL particle size (1.82 s; P < 0.05), and a greater decrease in plasma E-selectin (5.6 ng/L; P = 0.02) than did subjects following the diet with 60% of energy as carbohydrate.

CONCLUSIONS

In obese, insulin-resistant persons, a calorie-restricted diet, moderately lower in carbohydrate and higher in unsaturated fat, is as efficacious as the traditional low-fat diet in producing weight loss and may be more beneficial in reducing markers for cardiovascular disease risk.

Relationship between the adiponectin-leptin ratio and parameters of insulin resistance in subjects without hyperglycemia

We previously reported that the adiponectin-leptin (A/L) ratio was more efficacious as a parameter of insulin resistance than adiponectin or leptin alone, and a more sensitive and reliable marker of insulin resistance than homeostasis model assessment (HOMA-R) as the fasting plasma glucose (FPG) level elevated in type 2 diabetes mellitus. In this study, we examined the usefulness of the A/L ratio as compared to HOMA-R for assessing insulin resistance in Japanese subjects without hyperglycemia. A total of 411 Japanese adults without hyperglycemia (205 men, aged 49 +/- 10 years; 206 women, aged 48 +/- 10 years) were enrolled. We investigated the correlation between fasting serum insulin level, FPG, leptin or adiponectin, and body mass index (BMI), fat mass (FM), triglycerides (TGs), high-density lipoprotein (HDL) cholesterol, or preheparin serum lipoprotein lipase (LPL) as parameters of insulin resistance. Next, we examined the relationships between parameters of insulin resistance and the A/L ratio or HOMA-R. By simple regression of the correlation between serum insulin level, FPG, leptin or adiponectin, and each parameter of insulin resistance, the best correlation coefficients were seen in leptin (men, r = 0.501; women, r = 0.667) as compared with BMI, in leptin (men, r = 0.658; women, r = 0.747) as compared with FM, in adiponectin (r = -0.285) in men and leptin (r = 0.299) in women as compared with TGs, in adiponectin (men, r = 0.405; women; r = 0.442) as compared with HDL cholesterol, and in adiponectin (men, r = 0.228; women, r = 0.452) as compared with LPL. By simple regression of the correlation between A/L ratio or HOMA-R and each parameter of insulin resistance, the highest correlation coefficients were seen with the A/L ratio except HDL cholesterol in men. Next, we carried out multiple linear regression to analyze the association between A/L ratio or HOMA-R and FM, TGs, HDL cholesterol, and LPL, excluding BMI, simultaneously. In men, the A/L ratio was significantly correlated with FM and TGs, and HOMA-R was significantly correlated with FM. This model explained 34% of the variance in the A/L ratio and 17% of the variance in HOMA-R. In women, the A/L ratio was significantly correlated with FM and LPL, and HOMA-R was significantly correlated with FM and LPL. This model explained 39% of the variance in A/L ratio and 14% of the variance in HOMA-R. In conclusion, the present study suggested that the A/L ratio might be more useful than HOMA-R to accurately assess insulin resistance in subjects without hyperglycemia.

The effect of acute, chronic, and prenatal ethanol exposure on insulin sensitivity

Ethanol has been considered as a lifestyle factor that may influence the risk of type 2 diabetes mellitus. In healthy adults, acute ethanol consumption results in insulin resistance. Acute ethanol consumption causes insulin resistance selectively in skeletal muscle by an indirect mechanism. Possible mediators include triglycerides (TGs), catecholamines, acetaldehyde, alterations in insulin binding, and hepatic insulin sensitizing substance (HISS). Recent studies in rats showed that acute administration of ethanol causes insulin resistance in a dose-dependent manner that is secondary to the blockade of insulin-induced HISS release. Chronic ethanol consumption may improve insulin sensitivity, but the results from the randomized controlled trials are mixed. Differences in ethanol dose, consumption period, and abstention period may account for the discrepant results. Epidemiological studies have suggested that the relationship between ethanol and insulin sensitivity is either an inverted U-shape or a positive linear relationship. Future randomized controlled trials should consider the dose of ethanol and the duration of ethanol consumption and abstention in the experimental design. Chronic prenatal and postnatal (nursing) ethanol exposure results in insulin resistance that is secondary to the absence of HISS release/action with the HISS-independent insulin action and insulin-like growth factor-1 (IGF-1)-mediated glucose disposal action remaining unimpaired. The impaired HISS release may be related to a reduction in hepatic glutathione (GSH) levels. The effect of chronic ethanol consumption on HISS has not been evaluated.

Longitudinal assessment of insulin sensitivity in pregnancy. Validation of the homeostasis model assessment

OBJECTIVE

To validate the use of the homeostasis model assessment (HOMA) for measurement of insulin sensitivity in obese women during gestation and the postpartum period.

DESIGN

Three consecutive measurements of insulin resistance (IR) were performed during and after pregnancy to compare the homeostasis model assessment insulin sensitivity index (HOMA-IR) to glucose utilization rates obtained during hyperinsulinaemic euglycaemic clamps (G(Rd)).

PATIENTS

Six obese women (mean second trimester BMI = 30.4 kg/m(2)) with normal glucose tolerance were studied during the second and third trimesters of pregnancy and once in the postpartum period. Thus, there were a total of 18 measurements for analysis.

RESULTS

Correlations between the rate of glucose disappearance (G(Rd)) (the gold standard) and the HOMA-derived metabolic parameters of insulin sensitivity were significant, with a multiple R(2) of 43.5% (P = 0.003). However, when controlling for variations between patients using dummy variables, we observed that one patient differed from the other five in the relationship between G(Rd) and HOMA-IR. Applying this regression we obtained a R(2) of 72.6% (P < 0.001). When the regression constant was omitted, we observed that the individual trends during pregnancy and postpartum in two patients differed statistically from the other patients between the two assessments, and we obtained a multiple R(2) of 97.3% (< 0.001).

CONCLUSIONS

HOMA estimation of insulin resistance is appropriate for use during both the second and third trimesters of pregnancy and postpartum in obese women with normal glucose tolerance. It lacks sensitivity for the evaluation of individuals, where more precise measures of insulin sensitivity should be utilized.

The metabolic syndrome: is this diagnosis necessary?

Values of insulin-mediated glucose disposal vary continuously throughout a population of apparently healthy persons, and a difference of > or = 600% exists between the most insulin-sensitive and the most insulin-resistant persons. Approximately 50% of this variability can be attributed to differences in adiposity (25%) and fitness (25%), with the remaining 50% likely of genetic origin. The more insulin-resistant a person, the more likely that he or she will develop some degree of glucose intolerance, high triacylglycerol and low HDL concentrations, essential hypertension, and procoagulant and proinflammatory states, all of which increase the risk of cardiovascular disease (CVD). To identify persons at greater CVD risk because of these abnormalities, the World Health Organization, the Adult Treatment Panel III, and the International Diabetes Federation created a new diagnostic category, the metabolic syndrome. Although the components of the 3 versions of the metabolic syndrome are similar, the specific values for those components that define an abnormality are somewhat different, and the manner in which the abnormalities are used to make a positive diagnosis varies dramatically from version to version. This review will summarize the similarities in and differences between the 3 versions of the metabolic syndrome, point out that the clustering of components that make up all 3 definitions of the metabolic syndrome is not accidental and occurs only in insulin-resistant persons, develop the argument that diagnosing the metabolic syndrome in a person has neither pedagogical nor clinical utility, and suggest that the clinical emphasis should be on treating effectively any CVD risk factor that is present.

Avaliação laboratorial e diagnóstico da resistência insulínica

Em virtude da associação entre resistência à insulina (RI) e aterosclerose, existe interesse no desenvolvimento de técnicas para se avaliar a sensibilidade à insulina (SI) in vivo. Por ser uma medida de fácil utilização em grandes populações, a insulinemia de jejum tem sido usada para avaliar a SI e fornece uma boa avaliação da sensibilidade hepática, embora não da muscular. O HOMA é um modelo matemático que prediz a SI pelas simples medidas da glicemia e da insulina no jejum e tem boa correlação com o método do clamp euglicêmico hiperinsulinêmico, considerado padrão-ouro na medida da SI. Assim, mostra-se como valiosa alternativa às técnicas mais sofisticadas e trabalhosas na avaliação da RI em humanos, como o método descrito por Bergman. Em nosso meio, encontramos o valor de corte para o diagnóstico da RI quando o Homa-IR for maior que 2,71. O QUICKI é outro método simples, baseado também nas medidas da glicemia e da insulina no jejum, que apresenta boas correlações com marcadores da síndrome metabólica, conseguindo discriminar satisfatoriamente diferentes estados de RI, como graus de obesidade e tolerância à glicose. Métodos diretos de avaliação da SI incluem o teste de tolerância à insulina (K ITT), o teste de supressão de insulina e as técnicas de clamp hiperglicêmico e euglicêmico que são descritas neste artigo. A técnica do clamp euglicêmico e hiperinsulinêmico fornece a mais pura e reprodutível informação sobre a ação da insulina. Os custos envolvidos na sua realização, entretanto, limitam o seu uso.

The metabolic syndrome: a glance at its history

Although the modern era of what we now call the 'metabolic syndrome' or the 'insulin resistance syndrome' seems to have started less than two decades ago with the description of syndrome X by G.M. Reaven in the late 1980s, the history of this syndrome is much longer. In particular, a considerable number of scientists, starting as early as almost 90 years ago, have described the very common coexistence of the various components of the syndrome, including hypertension, and some of them gave several names to this clustering. On the other hand, during the past few years several international organizations have tried to form a reference context of what is included under the terms 'metabolic syndrome' and 'insulin resistance syndrome', proposing various 'definitions' for them. This review summarizes the history of the syndrome, from the early descriptions and other valuable contributions to the recent attempts to define it, as a small piece in honour of the pioneer workers in this field during the twentieth century.

Body mass index and waist circumference both contribute to differences in insulin-mediated glucose disposal in nondiabetic adults

BACKGROUND

Overweight and obese individuals are more likely to be insulin resistant and at increased risk of adverse clinical outcomes. Questions remain as to whether waist circumference (WC) or body mass index (BMI) most effectively identifies insulin-resistant individuals.

OBJECTIVE

This study quantified insulin-mediated glucose uptake (IMGU) in 330 apparently healthy volunteers and compared the relation between this value and measurements of WC and BMI.

DESIGN

IMGU was quantified via determination of the steady-state plasma glucose (SSPG) concentration during the insulin-suppression test. Differences in SSPG concentrations due to variations in WC within a given BMI category, as well as those due to differences in BMI within a given WC classification, were then compared.

RESULTS

BMI and WC correlated with each other (r = 0.78, P < 0.001) and equally with SSPG concentrations (r = 0.58 and 0.57, respectively; P < 0.001). When stratified by BMI, abdominally obese subjects within the overweight BMI category had higher SSPG concentrations than did those with a normal WC (P < 0.05). When classified by WC, subjects in the overweight BMI category had greater SSPG concentrations than did subjects in the normal BMI category within the normal WC category (P < 0.01), as did subjects in the obese BMI category in comparison with subjects in the overweight BMI category within the obese WC category (P < 0.01).

CONCLUSIONS

The more overweight or obese a person, the greater the degree of insulin resistance; differences in adiposity accounted for approximately one-third of the variation in IMGU, irrespective of the index used. Furthermore, there was no difference in the relation between the degree of insulin resistance and either index of adiposity.

The relationships between insulin resistance and components of metabolic syndrome in Taiwanese Asians

Metabolic syndrome (MetS) is a complicated clinicopathological entity with clustering of cardiovascular and metabolic risk factors, which includes central obesity, hypertension, dyslipidemia and glucose intolerance. There were many studies investigating a wide variety of clinical and pathophysiological aspects of this syndrome. However, the cutoffs of the components of MetS are not yet being evaluated by measured the insulin resistance (IR) directly. In this study, we enrolled 564 (male/female: 250/314) middle-aged healthy subjects. Each of the male and the female group was further divided into four subgroups (group 1 to group 4). Group 4 had the top 25 percentile of most severe IR determined by insulin suppression test. We then obtain the mean values of each component of the MetS in group 4 and compared them with the definitions of World Health Organization, National Cholesterol Education Program Adult Treatment Panel III, European Study Group of Insulin Resistance and International Diabetes Federation. The means of the blood pressure (BP) (male, 125/81; female, 125/80 mmHg) and the triglyceride (TG) (male, 1.6; female, 1.4 mmol/l) in group 4 were lower, and the fasting plasma glucose (6.2 mmol/l) was higher than the cutoffs of the other four sets of the criteria. The means of the high-density lipoprotein cholesterol (male, 0.9; female, 1.03 mmol/l) and the body mass index (male, 26.9; female 26.1 kg/m(2)) in group 4 were consistent with the cutoffs of other four groups and also the Taiwan Health Department criteria. In conclusion, we suggest to lower the cutoffs of the BP from 140/90 to 125/80 mmHg, TG from 1.7 to 1.6 mmol/l for males and 1.4 mmol/l for females for MetS definition, at least in Taiwan. This may help to early detect subjects under high risk of future coronary heart disease and diabetes. Still, these newly proposed cutoffs need larger-scale epidemiological studies to confirm.

All obese individuals are not created equal: insulin resistance is the major determinant of cardiovascular disease in overweight/obese individuals

The ability of insulin to mediate glucose disposal varies more than six-fold in an apparently healthy population, and approximately one third of the most insulin-resistant of these individuals are at increased risk to develop cardiovascular disease. Differences in degree of adiposity account for approximately 25% of this variability, and another 25% varies as a function of level of physical fitness. The more overweight/obese the person, the more likely they are to be insulin-resistant and at increased risk of cardiovascular disease, but substantial numbers of overweight/obese individuals remain insulin-sensitive, and not all insulin-resistant persons are obese. Of greater clinical relevance is evidence that the metabolic benefit and decrease in risk of cardiovascular disease following weight loss occurs primarily in those overweight/obese individuals that are also insulin-resistant. The relationship between insulin resistance and overall obesity, as assessed by measurement of body mass index, is essentially the same as the relationship between insulin action and abdominal obesity as quantified by determining waist circumference. Finally, there appears to be a comparable relationship between insulin-mediated glucose disposal and amount of visceral fat, subcutaneous fat, and total fat as quantified by various imaging techniques, and the magnitude of these relationships is no greater than that between insulin action and simple measure of body mass index.

Body mass index and waist circumference correlate to the same degree with insulin-mediated glucose uptake

To compare the relationship between insulin-mediated glucose uptake (IMGU) and excess adiposity as determined by measurement of either body mass index (BMI) or waist circumference (WC), IMGU was quantified by determining the steady-state plasma glucose (SSPG) concentration with the insulin suppression test and the relationship between the SSPG concentration and BMI or WC evaluated in a study of 208 healthy individuals (128 women/80 men). The results indicated that BMI and WC were correlated (P < .001) to a similar degree in both men (r = 0.90) and women (r = 0.86). Steady-state plasma glucose and both indices of excess adiposity were also significantly correlated (P < .001) to an essentially identical extent in men (r values of 0.71 vs 0.70) and women (r values of 0.54 vs 0.53). When the population was divided into tertiles on the basis of SSPG concentrations, 96% of those in the most insulin-resistant tertile were identified as being overweight/obese by BMI criteria and 84% as abdominally obese by WC criteria. However, a substantial number of those in the most insulin-sensitive tertile also demonstrated excess adiposity as defined by either BMI (45%) or WC (33%). To summarize, (1) BMI and WC correlate closely within an individual and equally well with IMGU, and (2) BMI is as effective as WC in identifying insulin-resistant individuals.

The metabolic syndrome: time for a critical appraisal: joint statement from the American Diabetes Association and the European Association for the Study of Diabetes

The term "metabolic syndrome" refers to a clustering of specific cardiovascular disease (CVD) risk factors whose underlying pathophysiology is thought to be related to insulin resistance. Since the term is widely used in research and clinical practice, we undertook an extensive review of the literature in relation to the syndrome's definition, underlying pathogenesis, and association with CVD and to the goals and impact of treatment. While there is no question that certain CVD risk factors are prone to cluster, we found that the metabolic syndrome has been imprecisely defined, there is a lack of certainty regarding its pathogenesis, and there is considerable doubt regarding its value as a CVD risk marker. Our analysis indicates that too much critically important information is missing to warrant its designation as a "syndrome." Until much needed research is completed, clinicians should evaluate and treat all CVD risk factors without regard to whether a patient meets the criteria for diagnosis of the "metabolic syndrome."

The metabolic syndrome: time for a critical appraisal. Joint statement from the American Diabetes Association and the European Association for the Study of Diabetes

BACKGROUND

The term 'metabolic syndrome' refers to a clustering of specific cardiovascular disease (CVD) risk factors whose underlying pathophysiology is thought to be related to insulin resistance.

METHODS

Since the term is widely used in research and clinical practice, we undertook an extensive review of the literature in relation to the syndrome's definition, underlying pathogenesis, association with cardiovascular disease and to the goals and impact of treatment.

DISCUSSION

While there is no question that certain CVD risk factors are prone to cluster, we found that the metabolic syndrome has been imprecisely defined, there is a lack of certainty regarding its pathogenesis, and there is considerable doubt regarding its value as a CVD risk marker. Our analysis indicates that too much critically important information is missing to warrant its designation as a 'syndrome'.

CONCLUSION

Until much-needed research is completed, clinicians should evaluate and treat all CVD risk factors without regard to whether a patient meets the criteria for diagnosis of the 'metabolic syndrome'.

Characteristics of type 2 diabetes in terms of insulin resistance in Korea

The aim of this study was to assess the implications of insulin resistance on the clinical and biochemical profiles of Korean type 2 diabetic patients. 122 patients with type 2 diabetes underwent a short insulin tolerance test to assess insulin resistance. Subjects were classified in tertiles according to ISI (insulin sensitivity index), and the tertile I (the insulin- resistant group) and tertile III (the insulin-sensitive group) clinical and biochemical parameters were compared. Age, waist circumference (WC), systolic blood pressure (SBP), HbA1c, body fat content, and fasting plasma glucose were significantly higher in tertile I than tertile III (all p < 0.05). The frequency of hypertension and family history of cerebrovascular disease (CVD) were greater in tertile I than III (p < 0.05). To evaluate the factors affecting ISI, multiple regression was performed, and age, WC, SBP, HbA1c, and body fat content were found to be independently related to insulin resistance (p < 0.05). Old age, hypertension, central obesity, and poor glycemic control were identified as clinical parameters of insulin resistance in Korean type 2 diabetic patients.

Is there a simple way to identify insulin-resistant individuals at increased risk of cardiovascular disease?

The goal of this study was to evaluate the ability of various routine measures of lipoprotein metabolism to identify patients who were insulin resistant and dyslipidemic, and therefore, at increased risk of cardiovascular disease. For this purpose, insulin resistance was quantified by determining the steady-state plasma glucose concentration during the insulin suppression test in 449 apparently healthy patients. The low-density lipoprotein (LDL) particle diameter and subclass phenotype were measured by gradient gel electrophoresis in 1,135 patients. Pearson's correlation coefficients and receiver-operating characteristic curves were used to evaluate measures of lipoprotein metabolism as potential markers of insulin resistance and LDL phenotype. The results indicated that the ratio of the plasma concentrations of triglyceride to high-density lipoprotein cholesterol was the best predictor of insulin resistance and LDL particle diameter. The optimal triglyceride/high-density lipoprotein cholesterol ratio for predicting insulin resistance and LDL phenotype was 3.5 mg/dl; a value that identified insulin-resistant patients with a sensitivity and specificity comparable to the criteria currently proposed to diagnose the metabolic syndrome. The sensitivity and specificity were even greater for identification of patients with small, dense, LDL particles. In conclusion, a plasma triglyceride/high-density lipoprotein cholesterol concentration ratio > or =3.5 provides a simple means of identifying insulin-resistant, dyslipidemic patients who are likely to be at increased risk of cardiovascular disease.

Rosiglitazone reduces glucose-stimulated insulin secretion rate and increases insulin clearance in nondiabetic, insulin-resistant individuals

Compensatory hyperinsulinemia permitting insulin-resistant individuals to maintain normal glucose tolerance is associated with a left shift in the glucose-stimulated insulin secretion rate (GS-ISR) dose-response curve and decrease in the insulin metabolic clearance rate (I-MCR). To see whether these changes would reverse with improvement in insulin sensitivity, 14 nondiabetic insulin-resistant subjects received rosiglitazone for 12 weeks (4 mg daily for 4 weeks and then 8 mg daily for 8 weeks). Insulin-mediated glucose uptake was quantified by measuring the steady-state plasma glucose concentration during the insulin suppression test. GS-ISR and I-MCR were determined during a 240-min graded intravenous glucose infusion. I-MCR was also calculated during the insulin suppression test. After rosiglitazone treatment, insulin sensitivity improved with significant fall in steady-state plasma glucose (means +/- SE from 13.5 +/- 0.62 to 9.8 +/- 1.02 mmol/l, P < 0.001). In response, the integrated GS-ISR decreased by 21% (P < 0.001), with a right shift in the dose-response curve. Calculated I-MCR increased by 34% (P = 0.008) during the insulin suppression test and by 21% (P = 0.03) during the graded glucose infusion. In conclusion, enhanced insulin sensitivity in rosiglitazone-treated nondiabetic insulin-resistant individuals was associated with a shift to the right in the GS-ISR dose-response curve and an increase in I-MCR.

Prevalence of insulin resistance and the metabolic syndrome with alternative definitions of impaired fasting glucose

We sought to evaluate the effect of the new definition of impaired fasting glucose (IFG = fasting glucose concentration 100-125 mg/dL among people without diabetes) on the ability to identify insulin resistance, as well as the prevalence of the metabolic syndrome in apparently healthy individuals. From the Stanford General Clinical Research Center data-base, we used data from 230 men and 260 women aged 19-79 years who had had an insulin suppression test to measure insulin resistance. From the Third National Health and Nutrition Examination Survey (1988-1994), we used data from 8814 participants aged > or =20 years to estimate the impact of adopting the new IFG criteria on the prevalence of the metabolic syndrome. Among the 490 participants, the prevalence of IFG increased from 5.5% under the old definition of IFG to 20.4% under the new definition. Using the old definition of IFG, the sensitivity, specificity, and positive predictive value (PPV) of IFG of identifying an individual as being insulin resistant were 10%, 97%, and 63%, respectively. Using the new definition, these parameters were 33%, 88%, and 61%, respectively. If the new IFG criteria were adopted, the prevalence of the metabolic syndrome would increase from 21.8% to 26.3%. The new definition of IFG expands the population with insulin resistance by almost four-fold and could expand the population with the metabolic syndrome by about 20%. The clinical and public health implications of the new IFG definition remain to be elucidated.

Insulin control of glucose metabolism in man: a new kinetic analysis

Analyses of the control of glucose metabolism by insulin have been hampered by changes in bloog glucose concentration induced by insulin administration with resultant activation of hypoglycemic counterregulatory mechanisms. To eliminate such mechanisms, we have employed the glucose clamp technique which allows maintenance of fasting blood glucose concentration during and after the administration of insulin. Analyses of six studies performed in young healthy men in the postabsorptive state utilizing the concurrent administration of [14C]glucose and 1 mU/kg per min (40 mU/m2 per min) porcine insulin led to the development of kinetic models for insulin and for glucose. These models account quantitatively for the control of insulin on glucose utilization and on endogenous glucose production during nonsteady states. The glucose model, a parallel three-compartment model, has a central compartment (mass = 68 +/- 7 mg/kg; space of distribution = blood water volume) in rapid equilibrium with a smaller compartment (50 +/- 17 mg/kg) and in slow equilibrium with a larger compartment (96 +/-21 mg/kg). The total plasma equivalent space for the glucose system averaged 15.8 liters or 20.3% body weight. Two modes of glucose loss are introduced in the model. One is a zero-order loss (insulin and glucose independent) from blood to the central nervous system; its magnitude was estimated from published data. The other is an insulin-dependent loss, occurring from the rapidly equilibrating compartment and, in the basal period, is smaller than the insulin-independent loss. Endogenous glucose production averaged 1.74 mg/kg per min in the basal state and enters the central compartment directly. During the glucose clamp experiments plasma insulin levels reached a plateau of 95 +/-8 microU/ml. Over the entire range of insulin levels studied, glucose losses were best correlated with levels of insulin in a slowly equilibrating insulin compartment of a three-compartment insulin model. A proportional control by this compartment on glucose utilization was adequate to satisfy the observed data. Insulin also rapidly decreased the endogenous glucose production to 33% of its basal level (0.58 mg/kg per min), this suppression being maintained for at least 40 min after exogenous insulin infusion was terminated and after plasma insulin concentrations had returned to basal levels. The change in glucose utilization per unit change in insulin in the slowly equilibrating insulin compartment is proposed as a new measure for insulin sensitivity. This defines insulin effects more precisely than previously used measures, such as plasma glucose/plasma insulin concentration ratios. Glucose clamp studies and the modeling of the coupled kinetics of glucose and insulin offers a new and potentially valuable tool to the study of altered states of carbohydrate metabolism.

Correlation between the adiponectin-leptin ratio and parameters of insulin resistance in patients with type 2 diabetes

We studied the correlation between the adiponectin-leptin (A/L) ratio and parameters of insulin resistance in 220 Japanese patients with type 2 diabetes (138 men and 82 women). Body mass index (BMI), triglycerides (TGs), HDL cholesterol (HDL), and preheparin serum lipoprotein lipase (LPL mass) were examined as laboratory parameters of the insulin resistance. The correlations between these laboratory parameters and adiponectin, leptin, or A/L ratio were studied. Adiponectin levels correlated significantly with BMI (r = -0.298, P = .0003), TGs (r = -0.221, P = .0092), HDL (r = 0.31, P = .0002), and LPL mass (r = 0.26, P = .0021) in men, and with TGs (r = -0.29, P = .0093), HDL (r = 0.239, P = .0338), and LPL mass (r = 0.499, P < .0001) in women. Leptin levels correlated significantly with only BMI (r = 0.31, P = .0002) in men, and with BMI (r = 0.71, P < .0001) and TGs (r = 0.26, P = .0201) in women. Adiponectin and leptin levels tended to correlate with these parameters in an opposite manner. On the other hand, A/L ratio significantly correlated with BMI (r = -0.4, P < .0001), TG (r = -0.199, P = .0192), HDL (r = 0.235, P = .0054), and LPL mass (r = 0.244, P = .0390) in men, and with BMI (r = -0.482, P < .0001), TG (r = -0.402, P = .0002), HDL (r = 0.358, P = .0011), and LPL mass (r = 0.487, P < .0001) in women. Next, the patients were divided into 3 groups classified by their fasting plasma glucose (FPG) level, and the correlations between the parameters and A/L ratio or homeostasis model assessment (HOMA-R), and the correlation between A/L ratio and HOMA-R were investigated in each group. Significant correlations between the parameters and A/L ratio were tended to be observed as the FPG level rose; however, the significant correlations between the parameters and HOMA-R were no longer seen as FPG level elevated. The results suggested that the A/L ratio was effective in relevance as a parameter of insulin resistance to adiponectin or leptin alone, and a more sensitive and reliable marker of insulin resistance than HOMA-R as the FPG level elevated, in patients with type 2 diabetes.

Identification of individuals with insulin resistance using routine clinical measurements

Insulin resistance is a treatable precursor of diabetes and potentially of cardiovascular disease as well. To identify insulin-resistant patients, we developed decision rules from measurements of obesity, fasting glucose, insulin, lipids, and blood pressure and family history in 2,321 (2,138 nondiabetic) individuals studied with the euglycemic insulin clamp technique at 17 European sites; San Antonio, Texas; and the Pima Indian reservation. The distribution of whole-body glucose disposal appeared to be bimodal, with an optimal insulin resistance cutoff of <28 micromol/min . kg lean body mass. Using recursive partitioning, we developed three types of classification tree models: the first, based on clinical measurements and all available laboratory determinations, had an area under the receiver operator characteristic curve (aROC) of 90.0% and generated a simple decision rule: diagnose insulin resistance if any of the following conditions are met: BMI >28.9 kg/m(2), homeostasis model assessment of insulin resistance (HOMA-IR) >4.65, or BMI >27.5 kg/m(2) and HOMA-IR >3.60. The fasting serum insulin concentrations corresponding to these HOMA-IR cut points were 20.7 and 16.3 microU/ml, respectively. This rule had a sensitivity and specificity of 84.9 and 78.7%, respectively. The second model, which included clinical measurements but no laboratory determinations, had an aROC of 85.0% and generated a decision rule that had a sensitivity and specificity of 78.7 and 79.6%, respectively. The third model, which included clinical measurements and lipid measurements but not insulin (and thus excluded HOMA-IR as well), had a similar aROC (85.1%), sensitivity (81.3%), and specificity (76.3%). Thus, insulin-resistant individuals can be identified using simple decision rules that can be tailored to specific needs.

Effect of rosiglitazone treatment on circulating vascular and inflammatory markers in insulin-resistant subjects

Thiazolidinedione (TZD) compounds enhance insulin sensitivity and attenuate inflammation. The effect of the TZD compound, rosiglitazone (RSG) on both actions was evaluated in two groups of insulin-resistant subjects with minimal elevations of fasting plasma glucose (PG) concentration: group A (n=15, PG < 7.0 mmol/L) and group B (n=14, PG 7.0-8.3 mmol/L). Insulin action, quantified by the insulin suppression test, improved after three months of treatment in both groups, and concentrations of C-reactive protein, plasminogen activator inhibitor-1 and Eselectin all fell. Significant decreases in L-selectin and P-selectin were confined to group B, and concentrations of interleukin-6, intercellular adhesion molecule-1 and vascular cellular adhesion molecule-1 did not fall in either group. Significant relationships were not discerned between enhanced insulin sensitivity and related variables and decreases in inflammatory/vascular markers, suggesting that RSG-induced changes in the latter variables in insulin-resistant individuals might be at least partly independent of the effects of the drug on insulin action.

Comparative effects of rosuvastatin and gemfibrozil on glucose, insulin, and lipid metabolism in insulin-resistant, nondiabetic patients with combined dyslipidemia

To evaluate the pharmacologic intervention most likely to decrease cardiovascular disease risk in insulin-resistant patients with combined dyslipidemia, 39 patients with this abnormality were assessed before and after 3 months of treatment with gemfibrozil (1,200 mg/day) or rosuvastatin (40 mg/day) with regard to: (1) steady-state plasma glucose concentration at the end of a 180-minute infusion of octreotide, insulin, and glucose; (2) fasting lipid, lipoprotein, and apolipoprotein concentrations; and (3) daylong glucose, insulin, triglyceride, and remnant lipoprotein cholesterol concentrations in response to breakfast and lunch. The 2 groups were similar at baseline in age, gender, body mass index and in measurements of carbohydrate and lipoprotein metabolism. Neither gemfibrozil nor rosuvastatin enhanced insulin sensitivity or lowered daylong glucose and insulin concentrations in insulin-resistant patients with combined dyslipidemia, but both drugs significantly decreased fasting triglyceride concentrations. However, only rosuvastatin treatment significantly (p <0.05 to <0.001) reduced fasting low-density lipoprotein cholesterol, apolipoprotein B-100, apolipoprotein C-III, apolipoprotein C-III:B particles, the apolipoprotein B-100:apolipoprotein A-I ratio, and increased apolipoprotein A-I (p <0.05). The degree of improvement in fasting and postprandial remnant lipoprotein cholesterol concentrations was significantly greater (p <0.05) in rosuvastatin-treated patients, and this difference in the relative effectiveness of the drugs was also true of the decrease in non-high-density lipoprotein cholesterol concentrations.

Why Syndrome X? From Harold Himsworth to the insulin resistance syndrome

Although the concept of Syndrome X was introduced in the Banting Medal address of 1988 (Reaven, 1988), the notion that led to its genesis had started approximately 50 years earlier. In this short history, an attempt will be made to trace the two paths of scientific discovery that were formally merged in New Orleans in 1988 to form the scientific foundation of Syndrome X. In addition, the developments in the last 16 years that have led from the notion of Syndrome X to the broader concept of an Insulin Resistance Syndrome (IRS) will be briefly summarized.

Impact of degree of obesity on surrogate estimates of insulin resistance

OBJECTIVE

To evaluate the role of adiposity in the relationship between specific and surrogate estimates of insulin-mediated glucose uptake (IMGU) in a large nondiabetic population.

RESEARCH DESIGN AND METHODS

Healthy volunteers were classified by BMI into normal weight (<25.0 kg/m(2), n = 208), overweight (25.0-29.9 kg/m(2), n = 168), and obese (>or=30.0 kg/m(2), n = 109) groups. We then assessed how differences in BMI affect the correlation between steady-state plasma glucose (SSPG) concentration at the end of a 180-min infusion of octreotide, glucose, and insulin (a specific measure of IMGU) and five surrogate estimates: fasting plasma glucose, fasting plasma insulin, homeostasis model assessment of insulin resistance (HOMA-IR), quantitative insulin sensitivity check index (QUICKI), and area under the curve for insulin in response to oral glucose (I-AUC).

RESULTS

Correlation coefficients (r values) between SSPG and surrogate measures of IMGU were all significant (P < 0.05), but the magnitude varied between BMI groups: normal weight: fasting plasma glucose 0.20, fasting plasma insulin 0.33, HOMA-IR 0.36, QUICKI -0.33, and I-AUC 0.69; overweight: fasting plasma glucose 0.19, fasting plasma insulin 0.55, HOMA-IR 0.55, QUICKI -0.54, and I-AUC 0.72; and obese: fasting plasma glucose 0.40, fasting plasma insulin 0.56, HOMA-IR 0.60, QUICKI -0.61, and I-AUC 0.69.

CONCLUSIONS

The relationship between direct and surrogate estimates of IMGU varies with BMI, with the weakest correlations seen in the normal-weight group and the strongest in the obese group. In general, I-AUC is the most useful surrogate estimate of IMGU in all weight groups. Fasting plasma insulin, HOMA-IR, and QUICKI provide comparable information about IMGU. Surrogate estimates of IMGU based on fasting insulin and glucose account for no more than 13% of the variability in insulin action in the normal-weight group, 30% in the overweight group, and 37% in the obese group.

The metabolic syndrome or the insulin resistance syndrome? Different names, different concepts, and different goals

The goal of this article is to differentiate the insulin resistance syndrome from the metabolic syndrome. In the case of the insulin resistance syndrome, the abnormalities and clinical syndromes that are increased in prevalence in insulin-resistant individuals have been summarized, with a brief discussion of the causal relationship between insulin resistance, compensatory hyperinsulinemia, and associated consequences. Discussion of the metabolic syndrome has focused on the five criteria chosen by the adult treatment panel III to diagnose the syndrome, evaluating them in terms of their relationship to insulin resistance and their role as cardiovascular disease risk factors.

Relationship to insulin resistance of the adult treatment panel III diagnostic criteria for identification of the metabolic syndrome

The Adult Treatment Panel III (ATP III) has published criteria for diagnosing the metabolic syndrome, a cluster of closely related abnormalities related to insulin resistance that increase cardiovascular disease risk. The present analysis was performed to evaluate the ability of these criteria to identify insulin-resistant individuals. The population consisted of 443 healthy volunteers, with measurements of BMI, blood pressure, fasting plasma glucose, triglycerides, HDL cholesterol concentrations, and steady-state plasma glucose (SSPG) concentration. Insulin resistance was defined as being in the top tertile of SSPG concentrations. Of the population, 20% satisfied ATP III criteria for the metabolic syndrome. Although insulin resistance and the presence of the metabolic syndrome were significantly associated (P < 0.001), the sensitivity and positive predictive value equaled 46% (69 of 149) and 76% (69 of 91), respectively. Being overweight, with high triglycerides, low HDL cholesterol, or elevated blood pressure, most often resulted in a diagnosis of the metabolic syndrome. Thus, the ATP III criteria do not provide a sensitive approach to identifying insulin-resistant individuals. The individual components vary both in terms of their utility in making a diagnosis of the metabolic syndrome and their relationship to insulin resistance, with the obesity and lipid criteria being most useful.

Prevalence of insulin resistance and associated cardiovascular disease risk factors among normal weight, overweight, and obese individuals

Obese individuals tend to be both insulin resistant and at increased risk to develop cardiovascular disease (CVD). Given the increased prevalence of obesity in the US population, we thought it important to define the relationship between degree of obesity and insulin-mediated glucose disposal in the population at large, as well as the relationship between obesity, insulin resistance, and CVD risk in these individuals. To do this we quantified insulin-mediated glucose disposal in 465 healthy volunteers by determining the steady-state plasma glucose (SSPG) concentrations at the end of a 180-minute infusion of somatostatin, insulin, and glucose. Adiposity was estimated by body mass index (BMI) and the relationship between BMI and SSPG defined. In addition, a series of CVD risk factors were measured, including blood pressure, plasma glucose, and insulin concentrations, before and after 75 g of oral glucose, and fasting plasma lipid and lipoprotein concentrations. The results indicated that SSPG concentration and BMI were significantly correlated (r = 0.54, P >.001), and 36% of individuals in the most insulin-resistant tertile were obese (BMI >/= 30.0 kg/m(2)). However, 16% of those in the most insulin-resistant tertile were of normal weight (BMI < 25.0 kg/m(2)). Although CVD risk factors were accentuated in general with progressive increases in either BMI or SSPG concentration, important differences were noted. Thus, the higher the SSPG concentration, the more the increase in plasma glucose, insulin, and triglyceride (TG) concentrations, whereas the greater the BMI, the higher the low-density lipoprotein concentration. Furthermore, while CVD risk factors increased significantly with each tertile of insulin resistance, significant differences in CVD risk were only apparent when the lowest BMI tertile was compared with the other 2, with the values in the middle and upper BMI differing from each other. These results show that while BMI and insulin resistance are related, they are not synonymous, and that they make independent and different contributions to increasing CVD risk.

Plasma adiponectin concentrations do not increase in association with moderate weight loss in insulin-resistant, obese women

Plasma adiponectin concentrations were measured before and after moderate weight loss in 20 obese women, divided at baseline into insulin-resistant (IR) and insulin-sensitive (IS) subgroups on the basis of their steady-state plasma glucose (SSPG) concentration at the end of a 180-minute infusion of octreotide, glucose, and insulin. The groups were similar in age and body weight and lost comparable amounts of weight (8 to 9 kg) during the weight loss period. Fasting plasma insulin and SSPG concentrations were significantly higher (P <.001) and adiponectin concentrations somewhat lower (P =.10) in the IR group (P <.001) at baseline. Both SSPG and plasma insulin concentrations decreased in IR subjects (P <.001), but did not change in IS individuals. Adiponectin concentrations did not change with weight loss in either group. Thus, neither weight loss, per se, nor enhanced insulin sensitivity resulted in a change in plasma adiponectin concentrations.

Usefulness of plasma glucose and insulin concentrations in identifying patients with insulin resistance

In this study, a specific measurement of insulin-mediated glucose disposal was used in 490 healthy volunteers to classify subjects as being insulin resistant. We then made standard measurements of plasma glucose and insulin concentrations to see how useful they would be as surrogate markers of insulin resistance.

Minimal model-based insulin sensitivity has greater heritability and a different genetic basis than homeostasis model assessment or fasting insulin

Insulin resistance is an important risk factor for development of type 2 diabetes as well as other chronic conditions, including hypertension, cardiovascular disease, and colon cancer. To find genes for insulin resistance it is necessary to assess insulin action in large populations. We have previously measured insulin action in a large cohort of subjects (Insulin Resistance and Atherosclerosis Study [IRAS] Family Study) using the minimal model approach. In this study, we compare sensitivity from the minimal model (insulin sensitivity index [S(I)]) with the measure of insulin resistance emanating from the homeostasis model assessment (HOMA) approach. The former measure emerges from the glycemic response to endogenous and exogenous insulin; the latter is based solely on fasting measures of glucose and insulin. A total of 112 pedigrees were represented, including 1,362 individuals with full phenotypic assessment. Heritability of S(I) was significantly greater than that for HOMA (0.310 vs. 0.163) and for fasting insulin (0.171), adjusted for age, sex, ethnicity, and BMI. In addition, correlation between S(I) and either HOMA or fasting insulin was only approximately 50% accounted for by genetic factors, with the remainder accounted for by environment. Thus S(I), a direct measure of insulin sensitivity, is determined more by genetic factors rather than measures such as HOMA, which reflect fasting insulin.

Quantification of insulin-mediated glucose disposal in HIV-infected individuals: comparison of patients treated and untreated with protease inhibitors

To describe the distribution of insulin sensitivity and glucose tolerance in HIV-infected patients, the authors measured insulin-mediated glucose disposal (IMGD) in 51 subjects (24 protease inhibitor (PI)-treated subjects and 27 non-PI-treated subjects). IMGD was determined by measuring the steady-state plasma glucose (SSPG) concentration during the last 30 minutes of a 180-minute intravenous infusion of octreotide, glucose, and insulin. In addition, oral glucose tolerance testing was performed. SSPG concentrations varied six-fold in both groups, and the mean values +/- SEM did not differ between PI-treated and non-PI-treated groups (8.7 +/- 0.9 vs. 8.0 +/- 0.7 mmol/L, respectively). The mean fasting plasma glucose concentration +/- SEM was higher in the PI-treated subjects than in the non-PI-treated subjects (5.44 +/- 0.11 vs. 5.05 +/- 0.11 mmol/L, respectively; p =.01), whereas fasting plasma insulin concentrations did not differ. PI-treated patients also had significantly higher plasma glucose (p =.001) and insulin (p =.03) responses to the oral glucose challenge. However, whereas the incremental plasma glucose response during the first 30 minutes was significantly higher in PI-treated patients, the incremental insulin response in the two groups was identical. In conclusion, insulin sensitivity varies widely in HIV-infected patients irrespective of PI treatment, and the adverse effect of PIs on insulin sensitivity is likely to be of modest magnitude. Finally, PI treatment may have an inhibitory effect on insulin secretion.

Differentiation between obesity and insulin resistance in the association with C-reactive protein

BACKGROUND

Plasma C-reactive protein (CRP) concentrations are increased in obese and/or hyperinsulinemic individuals. The goal of this study was to determine if the relation between insulin resistance and CRP was independent of obesity.

METHODS AND RESULTS

Plasma CRP concentrations were measured before and after 3 months of calorie restriction in 38 healthy, obese women. Steady-state plasma glucose (SSPG) concentration during a 180-minute infusion of octreotide, glucose, and insulin was used to stratify participants into insulin-resistant (IR, n=20) or insulin-sensitive (n=18) groups, similar in terms of mean age (46+/-2 versus 44+/-2 years), body mass index (32.0+/-0.4 versus 31.4+/-0.3 kg/m2), and waist circumference (96+/-2 versus 95+/-2 cm). Mean CRP (0.39+/-0.08 versus 0.12+/-0.03 mg/dL, P=0.003) concentrations were higher in the IR group, as were day-long plasma glucose and insulin responses (P<0.001). There was a significant correlation at baseline between CRP and day-long plasma integrated insulin response (r=0.47, P=0.001) but not between CRP and body mass index (r=0.14) or waist circumference (r=0.10). Weight loss was similar in the two groups (8.7+/-0.9 versus 8.4+/-0.8 kg) but was associated with significant (P<0.001) decreases in SSPG and CRP concentrations in the IR group only. Regression analysis showed that SSPG and day-long plasma insulin response were the only significant predictors of CRP concentration.

CONCLUSIONS

CRP concentrations are elevated predominantly in obese individuals who are also insulin resistant and fall in parallel with weight loss-associated improvements in insulin resistance. The relation between CRP concentrations and insulin resistance is independent of obesity.

Assessment of beta-cell function during the oral glucose tolerance test by a minimal model of insulin secretion

OBJECTIVE

To characterise the performance of beta-cell during a standard oral glucose tolerance test (OGTT).

DESIGN

Fifty-six subjects were studied. A minimal analogic model of beta-cell secretion during the OGTT was applied to all OGTTs (see below). The amount of insulin secreted over 120' in response to oral glucose (OGTT-ISR; Insulin Units 120'-1 m-2 BSA) and an index of beta-cell secretory 'force' (beta-Index; pmol.min-2.m-2 BSA) were computed with the aid of the model. In protocol A, 10 healthy subjects underwent two repeat 75 g OGTT with frequent (every 10'-15') blood sampling for glucose and C-peptide to test the reproducibility of OGTT-ISR and beta-Index with a complete or a reduced data set. In protocol B, 7 healthy subjects underwent three OGTTs (50, 100 or 150 g), to test the stability of the beta-Index under different glucose loads. In protocol C, 29 subjects (15 with normal glucose tolerance, 7 with impaired glucose tolerance and 7 with newly diagnosed type 2 diabetes) underwent two repeat 75 g OGTT with reduced (every 30' for 120') blood sampling to compare the reproducibility and the discriminant ratio (DR) of OGTT-ISR and beta-index with the insulinogenic index (IG-Index: Delta Insulin 30' - Basal/Delta Glucose 30' - Basal). In protocol D, 20 subjects (14 with normal glucose tolerance, 5 with impaired glucose tolerance and 1 with newly-diagnosed type 2 diabetes) underwent a 75 g OGTT and an intravenous glucose tolerance test (IVGTT) on separate days to explore the relationships between acute (0'-10') insulin response (AIR) during the IVGTT and beta-index and OGTT-ISR during the OGTT.

RESULTS

In all protocols, the minimal analogic model of C-peptide secretion achieved a reasonable fit of the experimental data. In protocol A, a good reproducibility of both beta-index and OGTT-ISR was observed with both complete and reduced (every 30') data sets. In protocol B, increasing the oral glucose load caused progressive increases in OGTT-ISR (from 2.63 +/- 0.70 to 5.11 +/- 0.91 Units.120'-1.m-2 BSA; P < 0.01), but the beta-index stayed the same (4.14 +/- 0.35 vs. 4.29 +/- 0.30 vs. 4.30 +/- 0.33 pmol.min-2.m-2 BSA). In protocol C, both OGTT-ISR and beta-index had lower day-to-day CVs (17.6 +/- 2.2 and 12.4 +/- 2.4%, respectively) and higher DRs (2.57 and 1.74, respectively) than the IG-index (CV: 35.5 +/- 6.3%; DR: 0.934). OGTT-ISR was positively correlated to BMI (P < 0.03), whereas beta-index was inversely related to both fasting and 2 h plasma glucose (P < 0.01 for both). In protocol D, beta-index, but not OGTT-ISR, was significantly correlated to AIR (r = 0.542, P < 0.02).

CONCLUSIONS

Analogically modelling beta-cell function during the OGTT provides a simple, useful tool for the physiological assessment of beta-cell function.

A comparison of insulin suppression tests performed with somatostatin and octreotide with particular reference to tolerability

To evaluate the tolerability of insulin suppression test (IST) using octreotide instead of somatostatin, we compared the steady-state plasma glucose (SSPG) values and the safety during and after the test in 17 normal volunteers. The subject received IST twice (with somatostatin or with octreotide) in random order. During the test, all subjects were infused with regular insulin and glucose simultaneously for 180 min. In addition, either somatostatin or octreotide was infused intravenously over the same period of time. Plasma glucose, insulin and C-peptide were measured. The subject response to the test was recorded during and one day after the test by a structured questionnaire. The SSPG and the steady-state plasma insulin (SSPI) values reached during IST were similar, irrespective of the use of somatostatin or octreotide. There was a positive correlation between the SSPG values obtained from both methods (r = 0.67, P = 0.003). However, the mean intra-individual coefficient of variation is 17.9% for SSPG. The SSPG levels, no matter from which method, correlated positively with the 2-h insulin after oral glucose challenge. Most adverse events (especially gastrointestinal discomfort) occurred after the test, and increased much more after using octreotide than somatostatin (P = 0.002 by chi 2 test). In conclusion, the SSPG values measured by IST using octreotide or somatostatin are similar in normal healthy subjects. Yet, the octreotide method has more adverse events after the test.

Diet-induced change in fatty acid composition of plasma triacylglycerols is not associated with change in glucagon-like peptide 1 or insulin sensitivity in people with type 2 diabetes

BACKGROUND

Polyunsaturated fatty acids (PUFAs) and monounsaturated fatty acids (MUFAs) have been shown to positively affect blood lipids; however, their comparative effects on insulin sensitivity are unclear.

OBJECTIVE

Our objective was to investigate whether chronic intake of MUFAs or PUFAs improves insulin sensitivity in people with type 2 diabetes via stimulation of the endogenous gut hormone glucagon-like peptide 1 [7-36] amide (GLP-1).

DESIGN

Nine overweight people with type 2 diabetes received isoenergetic high-MUFA (20.3 +/- 3.5% of total energy) or high-PUFA (13.4 +/- 1. 3%) diets for 24 d in a randomized, double-blind crossover design.

RESULTS

Weight and glycemic control remained stable throughout the study. Despite a significant change in the plasma triacylglycerol linoleic-oleic acid ratio (L:O) with both diets (MUFA: from 0.46 +/- 0.03 to 0.29 +/- 0.02, P: < 0.005; PUFA: from 0.36 +/- 0.04 to 0.56 +/- 0.05, P: < 0.05) and the phospholipid L:O (1.7 +/- 0.1 to 2.0 +/- 0.3; P: = 0.04) during consumption of the PUFA diet, this change was not associated with a change in insulin sensitivity, measured by the short-insulin-tolerance test. There was a significant reduction in the ratio of total to HDL cholesterol during consumption of the PUFA diet (5.2 +/- 0.4 compared with 4.7 +/- 0.3; P: = 0.005) but no change with the MUFA diet. There was no change in the fasting or postprandial incremental area under the curve in response to an identical standard test meal for glucose, insulin, triacylglycerol, nonesterified fatty acids, or GLP-1.

CONCLUSIONS

Over the 3-wk intervention period, diet-induced change in the triacylglycerol or phospholipid L:O was not associated with either increased stimulation of GLP-1 or a change in insulin sensitivity in people with type 2 diabetes.

Validation of the insulin sensitivity index (ISI(0,120)): comparison with other measures

The purpose of this study was to explore possible calculations using oral glucose tolerance test (OGTT) values in order to develop a simple measure of insulin sensitivity. We devised a formula for an insulin sensitivity index, ISI(0,120), that uses the fasting (0 min) and 120 min post-oral glucose (OGTT) insulin and glucose concentrations. It appears to be generalizable across a spectrum of glucose tolerance and obesity. Most importantly, our data show that ISI(0,120) correlates well, when applied prospectively in comparative studies, with the insulin sensitivity index obtained from the euglycemic hyperinsulinemic clamp (r = 0.63, P < 0.001). This correlation was demonstrably superior to other indices of insulin sensitivity such as the HOMA formula presented by Matthews, and performed comparably to the computerized HOMA index. Measurement of insulin sensitivity has traditionally been possible only in research settings because of the invasiveness and expense of the methods used. Clinical investigators have therefore sought more practical methods to obtain an index of insulin sensitivity. Such an index should approximate insulin sensitivity as measured by the euglycemic hyperinsulinemic clamp (M). We present ISI(0,120), a simple yet sensitive measure of insulin sensitivity which is adaptable for use in clinical settings as well as large epidemiologic studies.

Roles of insulin resistance and obesity in regulation of plasma insulin concentrations

Plasma glucose, insulin, and C-peptide concentrations were determined in response to graded infusions of glucose, and insulin secretion rates were calculated over each sampling period. Measurements were also made of insulin clearance, resistance to insulin-mediated glucose, uptake, and the plasma glucose, insulin, and C-peptide concentrations at hourly intervals from 8:00 AM to 4:00 PM in response to breakfast and lunch. Plasma glucose, insulin, and C-peptide concentrations were significantly (P < 0.01) higher in obese women in response to the graded intravenous glucose infusion, associated with a 40% (P < 0.005) greater insulin secretory response. Degree of insulin resistance correlated positively (P < 0.05) with the increase in insulin secretion rate in both nonobese (r = 0.52) and obese (r = 0.58) groups and inversely (P < 0.05) with the decrease in insulin clearance in obese (r = -0.46) and nonobese (r = -0.39) individuals. Weight loss was associated with significantly lower plasma glucose, insulin, and C-peptide concentrations in response to graded glucose infusions and in day-long insulin concentrations. Neither insulin resistance nor the insulin secretory response changed after weight loss, whereas there was a significant increase in the rate of insulin clearance during the glucose infusion. It is concluded that 1) obesity is associated with a shift to the left in the glucose-stimulated insulin secretory dose-response curve as well as a decrease in insulin clearance and 2) changes in insulin secretion and insulin clearance in obese women are more a function of insulin resistance than obesity.

Coronary artery disease risk predicted by insulin resistance, plasma lipids, and hypertension in people without diabetes

BACKGROUND

It has been shown that insulin resistance syndrome, including glucose intolerance, dyslipidemia, and hypertension, is frequently associated with coronary artery disease (CAD). However, their relative contributions and predictive power in the development of CAD are still unclear, particularly in persons without diabetes.

METHOD

We examined these risk factors between 96 patients without diabetes but with angiographically documented CAD and 96 age-, sex-, and body mass index-matched healthy control subjects. Fasting plasma lipoprotein, glucose, and insulin concentrations in response to a 75-g oral glucose tolerance test were determined, and insulin sensitivity was measured by the insulin suppression test.

RESULTS

Patients with CAD had significantly higher values of fasting glucose, glucose and insulin responses to oral glucose tolerance test, total cholesterol, low-density lipoprotein (LDL) cholesterol, and triglyceride and decreased high-density lipoprotein (HDL) cholesterol concentrations compared with those of healthy people (P < 0.02-0.001). Although the steady-state plasma insulin values were similar in both groups, the steady-state plasma glucose (SSPG) concentrations were significantly higher in patients with CAD (12.2+/-0.4 versus 8.1+/-0.4 mmol/L, P < 0.001) compared with healthy subjects. When HDL < 0.9 mmol/L, LDL cholesterol > or = 4.1 mmol/L, triglyceride > or = 2.3 mmol/L, SSPG > or = 10.5 mmol/L, and presence of hypertension were defined as separate risk factors for CAD, significantly higher odds-ratio values were observed in patients with CAD compared with healthy people. From logistic multiple regression analysis, SSPG was the strongest risk, followed by lowered HDL cholesterol, elevated triglyceride and LDL cholesterol, and hypertension, to predict CAD. These 5 factors accounted for 36% of total risk for development of CAD in persons without diabetes.

CONCLUSIONS

Patients without diabetes with CAD have abnormal glucose metabolism, hyperinsulinemia, and insulin resistance. Degree of insulin resistance (SSPG values), plasma lipid values, and history of hypertension together accounted for one third of all risk for CAD, although degree of insulin resistance was the strongest risk factor.

Insulin regulation of plasma free fatty acid concentrations is abnormal in healthy subjects with muscle insulin resistance

This study evaluated the ability of insulin to regulate free fatty acid (FFA) concentrations in healthy nondiabetic subjects selected to be either insulin-resistant or -sensitive on the basis of insulin-mediated glucose disposal by muscle. Comparisons of steady-state plasma glucose (SSPG), insulin (SSPI), and FFA concentrations were made at the end of 3 infusion periods: (1) under basal insulin conditions (approximately 10 microU/mL), (2) in response to isoproterenol-induced stimulation of lipolysis at the same basal insulin concentration, and (3) following inhibition of isoproterenol-induced lipolysis by a 2-fold increase in the insulin concentration. The results showed that steady-state FFA concentrations were significantly higher under basal conditions (360 +/- 73 v 158 +/- 36 microEq/L, P = .02), in response to isoproterenol-induced lipolysis (809 +/- 92 v433 +/- 65 microEq/L, P = .005), and following insulin inhibition of isoproterenol-induced lipolysis (309 +/- 65 v 159 +/- 37 microEq/L, P = .06). These differences were found despite the fact that SSPG concentrations were also higher in insulin-resistant individuals during all 3 infusion periods. These results demonstrate that the ability of insulin to regulate plasma FFA concentrations is impaired in healthy subjects with muscle insulin resistance, indicating that insulin-resistant individuals share defects in the ability of insulin to stimulate muscle glucose disposal and to inhibit adipose tissue lipolysis.