William T. Cefalu

Contribution of visceral fat mass to the insulin resistance of aging

Recent studies have shown that central obesity (increased waist to hip ratio [WHR]) is related to insulin resistance and aging. Furthermore, in central-obesity states, the intraabdominal fat (IAF) depot has been postulated to contribute most to the development of insulin resistance. Therefore, the observed insulin resistance of aging may be related more to changes in body composition than to aging per se. The purpose of this study was to explore the association of IAF with age and insulin sensitivity (SI) after controlling for obesity. We examined 60 healthy nondiabetic subjects (normal 75-g oral glucose tolerance test, aged 23 to 83, 15 men and 45 women). We chose subjects so that those < or = 125% and greater than 125% of ideal body weight were equally represented in each age decade. We quantified total and subcutaneous abdominal fat and IAF at the umbilicus using a validated magnetic resonance imaging (MRI) scanning technique and determined SI using a modified minimal model. IAF correlated significantly with age (r = .49, P = .0001) in the group as a whole, as well as in men (r = .58, P = .022) and women (r = .48, P = .0008) separately. In all subjects, SI was significantly related to IAF (r = -.50, P < .0001) but was not related to age (r = .00, P = .98). In multivariate analysis for various combinations of age, sex, and measures of fat distribution, WHR accounted for 28% and IAF for 51% of the variance in SI, whereas age, sex, and interactions of age and sex accounted for only 1%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of chromium picolinate on insulin sensitivity in vivo

This study assessed the effect of chromium (Cr) supplementation on insulin sensitivity and body composition in subjects at high risk for Type 2 diabetes because of family history and obesity. Twenty-nine subjects (14 men, 15 women) were evaluated in a double-blind, randomized, placebo-controlled trial using chromium picolinate (CrPic) (1,000 μg/day), or placebo for 8 months of study. Clinical and metabolic evaluations consisted of insulin sensitivity (SI) and glucose effectiveness (Sg); measurement of glucose tolerance and insulin response to an oral glucose tolerance test (75 g OGTT); and 24-hour glucose and insulin profiles. Anthropometric measures and magnetic resonance imaging (MRI) assessed abdominal fat distribution. Fasting plasma glucose and insulin levels and measures of glycemia (glycated hemoglobin and fructosamine) were also assessed. The CrPic group showed a significant increase in insulin sensitivity at midpoint (P < .05) and end of study (P < .005) compared with controls, which had no significant changes. No change in Sg was seen in either group. There was no effect of CrPic on body weight, abdominal fat distribution, or body mass index. However, CrPic significantly improved insulin sensitivity in these obese subjects with a family history of Type 2 diabetes. Improvement in insulin sensitivity without a change in body fat distribution suggests that Cr may alter insulin sensitivity independent of a change in weight or body fat percentage, thereby implying a direct effect on muscle insulin action. Definitive double-blinded, placebo-controlled trials are currently being conducted to confirm this observation in Type 2 diabetic subjects and evaluate the effects of Cr supplementation on insulin action and glycemic control. J. Trace Elem. Exp. Med. 12:71–83, 1999.

The effects of hormone replacement therapy on carbohydrate metabolism and cardiovascular risk factors in surgically postmenopausal cynomolgus monkeys

Controversy exists regarding the effects of estrogen and estrogen/progestin replacement therapies on glucose tolerance and insulin resistance. Also unknown are whether changes in glucose tolerance and insulin resistance with hormone therapy affect arterial glycation and atherosclerosis. We studied ovariectomized female monkeys fed a lipid-lowering diet and given either no hormone replacement therapy (n = 25) or conjugated equine estrogens (CEE) alone (n = 22) or combined with medroxyprogesterone acetate ([MPA] n = 21) for 30 months. Monkeys receiving combined hormone replacement had significantly higher fasting glucose and insulin levels and higher insulin responses to a glucose challenge compared with controls or those given estrogen alone. Monkeys given estrogen-only therapy had lower body weights, lower measures of abdominal adiposity, and decreased serum androgen concentrations. However, due to the effective dietary lipid decrease, there was no additional effect of hormone treatment on atherosclerosis. Also, there was no correlation between either arterial glycation or insulin levels and atherosclerosis extent. Thus, although there were adverse effects of combined hormone replacement therapy on carbohydrate metabolism, we were unable to determine whether these effects altered the extent of atherosclerosis.

Effect of age and caloric restriction on insulin receptor binding and glucose transporter levels in aging rats

We report on the effect of age and chronic caloric restriction (CR) on insulin binding and glucose transporter content in both diaphragm and heart muscle membrane of young (11 months), mid-age (17 months), and old (29 month) ad libitum fed and CR Brown-Norway rats. The control animals received rat chow ad lib and CR animals were allowed 60% of ad libitum food. The CR regimen was initiated at four months of age and the animals were maintained on their respective diets until necropsy. There was no effect of age on insulin binding for either ad libitum or CR animals at each age evaluated. Caloric restriction significantly lowered insulin levels at each age studied when compared to the ad libitum-fed rats. However, CR animals were noted to have increased insulin binding (p < 0.001) compared to ad libitum-fed animals at each age for diaphragm muscle. For the heart, there appeared to be a decreased binding, particularly at higher insulin concentrations, in CR-fed animals. There was no net change in Glut-1 or Glut-4 levels for heart muscle membrane, or Glut-4 levels for diaphragm muscle membrane between ad libitum or CR animals. This data indicates that caloric restriction may have tissue-specific effects for insulin receptor binding, and that the improved insulin sensitivity in CR states is not a result of altered glucose transporter protein content.

Chronic hyperglycemia increases arterial low-density lipoprotein metabolism and atherosclerosis in cynomolgus monkeys

Diabetes mellitus confers a threefold to fivefold increased risk of mortality from vascular disease. The primary cause of this increased incidence of vascular disease is atherosclerosis, but the mechanisms accounting for the increase are unclear. Chronic hyperglycemia is a common feature of all forms of diabetes mellitus and may contribute greatly to the increased incidence of atherosclerosis, via promotion of both lipoprotein and tissue glycation, which may have atherogenic effects. The present study investigated the effect of chronic hyperglycemia on measures of low-density lipoprotein (LDL) metabolism and atherosclerosis in streptozotocin-induced diabetic (STZ-DM) and control cynomolgus monkeys after 6 months of study. Consistent with a chronic hyperglycemic state, diabetic monkeys had significant increases in glycated hemoglobin (GHb) and glycated plasma LDL concentrations, but had minimal changes in total plasma cholesterol (TPC) or triglyceride (TG) concentrations during the study. Forty-eight hours before necropsy, control and in vitro-glycated LDL were differentially radiolabeled and coinjected into diabetic and control monkeys. There was a significant increase in arterial LDL accumulation in femoral arteries from diabetic monkeys compared with controls, with similar trends in other arterial sites. The effect of LDL glycation on arterial LDL accumulation was minimal in both groups. Arterial segments from diabetic monkeys also had greater amounts of arterial cholesterol content compared with controls. Histomorphometric analyses showed that diabetic monkeys had significantly greater intimal areas in the femoral artery and abdominal aorta compared with controls. Diabetic monkeys also had reduced arterial remodeling, or compensation, in the femoral artery and abdominal aorta. However, there was no difference in advanced glycation end products (AGE) in arterial collagen between groups. In conclusion, experimentally induced diabetes mellitus increases arterial LDL accumulation and atherosclerosis extent in cynomolgus monkeys before changes in AGE formation. The increased atherogenesis may be due to changes in lipoproteins or direct effects of hyperglycemia on the artery wall.

Islet Amyloid and Islet Amyloid Polypeptide in Cynomolgus Macaques (Macaca fascicularis): An Animal Model of Human Non-insulin-dependent Diabetes Mellitus

To further characterize spontaneous diabetes mellitus in cynomolgus macaques (Macaca fascicularis) as a model for human non-insulin-dependent diabetes mellitus (NIDDM), we evaluated the morphologic characteristics of the endocrine pancreas of 4 diabetic and 12 age-matched nondiabetic cynomolgus macaques. In addition, the cDNA-predicted amino acid sequence for islet amyloid polypeptide (IAPP) of this species was determined. Islet amyloid deposits exhibiting typical congophilia and green birefringence were found in 4/4 diabetic animals and in 8/12 nondiabetics. Islet amyloid deposits were significantly more extensive in the diabetic macaques (P = 0.001), in which they occupied a mean of 60% of the islet area. In contrast, in the nondiabetic group the maximum islet area occupied by amyloid was 24% (group mean = 6.8%), with four animals having no detectable islet amyloid. Amyloid deposits consistently showed immunoreactivity for IAPP but not for insulin. Comparisons between group means for diabetic versus nondiabetic macaques showed significantly greater islet area (P = 0.01, 85,390 versus 36,540 μm2) and significantly greater islet area fraction (P = 0.02, 0.065 versus 0.032) for the diabetic group. The cDNA-predicted amino acid sequence for cynomolgus IAPP was identical to that previously reported for pig-tail macaques (M. nemestrina) and had 92%, 86%, and 84% amino acid sequence identity with human, domestic cat, and murine IAPPs, respectively. These findings support the use of cynomolgus macaques as an animal model of human NIDDM.

Effect of obesity and fertility status on sex steroid levels in men

Endocrine studies were performed on fertile and infertile obese men and compared with fertile and infertile nonobese men in order to determine the independent and codependent effects of obesity and fertility status on the male hypothalamic-pituitary gonadal axis. The obese infertile group exhibited significant endocrinologic changes as compared with fertile nonobese control group which was not observed in any of the other three groups. Serum testosterone was significantly lower. The testosterone/estradiol ratio was significantly lower despite a lack of significant change in serum estradiol levels. Serum steroid hormone binding globulin (SHBG) was significantly lower which correlated with elevated bioavailability of both testosterone and estradiol in the obese infertile group. Serum luteinizing hormone levels were no different, suggesting that free testosterone levels were unchanged. Obese infertile men exhibit endocrinologic changes that are not observed in men with either obesity or infertility alone. Reduction of serum SHBG, total testosterone, and testosterone/estradiol ratio appear to be a marker of infertility among obese men.

The effects of hormonal replacement therapy on insulin sensitivity in surgically postmenopausal cynomolgus monkeys (Macaca fascicularis)

OBJECTIVE Our purpose was to evaluate the effect of hormone replacement therapy on insulin resistance in postmenopausal cynomolgus monkeys (Macaca fascicularis). STUDY DESIGN We studied 37 surgically postmenopausal cynomolgus monkeys that were fed a moderately atherogenic diet for 12 weeks with either no treatment (control), conjugated equine estrogens, medroxyprogesterone acetate, combination conjugated equine estrogens and medroxyprogesterone acetate, or tamoxifen. Insulin sensitivity and glucose effectiveness were determined by the frequent-sampling intravenous tolerance test by means of the minimal model analysis. RESULTS There were no differences in body weight, total plasma cholesterol, or body fat distribution between control and conjugated equine estrogens, medroxyprogesterone acetate, or combination treatment groups. However, compared with control animals (insulin sensitivity = 5.9 +2- 1.2 x 10(-4) min-1 microU-1 ml) or conjugated equine estrogens treatment (6.3 +/- 1.1 x 10(-4) min-1 microU-1 ml) insulin sensitivity was significantly decreased in animals treated with medroxyprogesterone acetate (2.9 +/- 0.4 x 10(-4) min-1 microU-1 ml, p < 0.001) or conjugated equine estrogens and medroxyprogesterone acetate (2.8 +/- 0.6 x 10(-4) min-1 microU-1 ml, p < 0.001). Although insulin sensitivity was shown to be decreased in the tamoxifen-treated animals (insulin sensitivity = 4.6 +/- 0.6 x 10(-4) min-1 microU -1 ml), the difference was not statistically significant compared with the control or conjugated equine estrogens-treated animals. No significant differences were seen for glucose effectiveness comparing control animals (glucose effectiveness = 0.043 +/- 0.006 min-1) to animals treated with medroxyprogesterone acetate (glucose effectiveness = 0.046 +/- 0.009 min-1), conjugated equine estrogens and medroxyprogesterone acetate (0.048 +/- 0.008 min-1) or tamoxifen (0.039 +/- 0.006 min-1). CONCLUSION These results suggest that progestins alone or in combination with estrogens can induce insulin resistance in postmenopausal monkeys while having no effect on plasma lipid concentrations or glucose effectiveness.

Intensive Glycemic Control and Cardiovascular Disease Observations From the ACCORD Study: Now What Can a Clinician Possibly Think?

It goes without saying that the results of randomized clinical trials over the past few years evaluating specific diabetic regimens have been nothing short of surprising. For example, with specific regard to the use of thiazolidinediones, all the data up to the point of conducting randomized, controlled clinical trials for hard cardiovascular outcomes suggest that these agents would more than fulfill their promise to reduce clinical events. Specifically, the effects of these drugs on the surrogate markers, e.g., endothelial function, coagulopathy, and inflammation, all favored a strong clinical result. What was found in clinical studies that assessed hard end points was less than impressive. Interestingly, the expected favorable outcomes with use of thiazolidinediones were not routinely seen, and in some studies and using certain agents, the observation was made that event rates increased. Now, more recently, come the startling findings that intensive glycemic control in a high-risk cohort failed to live up to its promise in the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial. Surprising? Yes! Unexpected? Certainly! Will the findings really impact clinical recommendations and have far reaching implications? We will first need to take a step back and evaluate the study more carefully, and we will only be in a position to suggest changes to current clinical recommendations after the dust settles. There is no question regarding the benefit of glycemic control in reducing the progression and development of microvascular complications in subjects with type 1 and type 2 diabetes. But, with all data considered, there has been a question of whether glycemic control will have a major impact on cardiovascular disease or all-cause mortality. In this regard, data have clearly demonstrated that hyperglycemia may predict a higher likelihood of fatal and nonfatal cardiovascular events. Studies such as the Diabetes Control and Complication Trial/Epidemiology of Diabetes …

Inflammation, Insulin Resistance, and Type 2 Diabetes: Back to the Future?

In this issue of Diabetes , two articles highlight the emergence of inflammations contribution to insulin resistance and to chronic diseases in humans. The common feature in each article is the inflammation–obesity–insulin resistance connection, but each article approaches the investigation from a completely different perspective. Specifically, the study of Ortega Martinez de Victoria et al. (1) comments on factors related to macrophage activation in adipocytes as a source for cytokines for systemic inflammatory effects. In contrast, the study of Haus et al. (2) provides data on systemic effects resulting from inflammatory activation, namely, the relationship of cytokines with circulating lipid intermediates. Approximately 2,000 years ago, Aulus (Aurelius) Cornelius Celsus, a Roman physician, was credited with the first recording of the cardinal signs of inflammation, which included calor (warmth), dolor (pain), tumor (swelling), and rubor (redness and hyperemia) (3). This general description of inflammation appears to have served clinical medicine well for most of the 2,000 years since it was first described. Until the recent past, no one would have ever envisioned that inflammation would be considered a root cause of the pathogenesis of metabolic abnormalities associated with obesity or a potential molecular target for diabetes therapies. But these statements for the inflammatory pathway represent present-day reality for basic and clinical human investigation. The association of inflammation with carbohydrate metabolism can actually be traced back to reports from the 1800s. Shoelson et al. (4) describe these reports in a historical review. Specifically, they cite reports from over a century ago in which high-dose salicylates appeared to decrease glycosuria in individuals classified as diabetic (presumably type 2 diabetes). The works of Ebstein in 1876 and Williamson in 1901 were also cited. These works …