Relationship between insulin sensitivity and plasma leptin concentration in lean and obese men

Exercise and diet enhance fat oxidation and reduce insulin resistance in older obese adults

Older, obese, and sedentary individuals are at high risk of developing diabetes and cardiovascular disease. Exercise training improves metabolic anomalies associated with such diseases, but the effects of caloric restriction in addition to exercise in such a high-risk group are not known. Changes in body composition and metabolism during a lifestyle intervention were investigated in 23 older, obese men and women (aged 66 +/- 1 yr, body mass index 33.2 +/- 1.4 kg/m(2)) with impaired glucose tolerance. All volunteers undertook 12 wk of aerobic exercise training [5 days/wk for 60 min at 75% maximal oxygen consumption (Vo(2max))] with either normal caloric intake (eucaloric group, 1,901 +/- 277 kcal/day, n = 12) or a reduced-calorie diet (hypocaloric group, 1,307 +/- 70 kcal/day, n = 11), as dictated by nutritional counseling. Body composition (decreased fat mass; maintained fat-free mass), aerobic fitness (Vo(2max)), leptinemia, insulin sensitivity, and intramyocellular lipid accumulation (IMCL) in skeletal muscle improved in both groups (P < 0.05). Improvements in body composition, leptin, and basal fat oxidation were greater in the hypocaloric group. Following the intervention, there was a correlation between the increase in basal fat oxidation and the decrease in IMCL (r = -0.53, P = 0.04). In addition, basal fat oxidation was associated with circulating leptin after (r = 0.65, P = 0.0007) but not before the intervention (r = 0.05, P = 0.84). In conclusion, these data show that exercise training improves resting substrate oxidation and creates a metabolic milieu that appears to promote lipid utilization in skeletal muscle, thus facilitating a reversal of insulin resistance. We also demonstrate that leptin sensitivity is improved but that such a trend may rely on reducing caloric intake in addition to exercise training.

Impact of reduced meal frequency without caloric restriction on glucose regulation in healthy, normal-weight middle-aged men and women

An unresolved issue in the field of diet and health is if and how changes in meal frequency affect energy metabolism in humans. We therefore evaluated the influence of reduced meal frequency without a reduction in energy intake on glucose metabolism in normal-weight, healthy male and female subjects. The study was a randomized crossover design, with two 8-week treatment periods (with an intervening 11-week off-diet period) in which subjects consumed all of their calories for weight maintenance distributed in either 3 meals or 1 meal per day (consumed between 4:00 pm and 8:00 pm). Energy metabolism was evaluated at designated time points throughout the study by performing morning oral glucose tolerance tests and measuring levels of glucose, insulin, glucagon, leptin, ghrelin, adiponectin, resistin, and brain-derived neurotrophic factor (BDNF). Subjects consuming 1 meal per day exhibited higher morning fasting plasma glucose levels, greater and more sustained elevations of plasma glucose concentrations, and a delayed insulin response in the oral glucose tolerance test compared with subjects consuming 3 meals per day. Levels of ghrelin were elevated in response to the 1-meal-per-day regimen. Fasting levels of insulin, leptin, ghrelin, adiponectin, resistin, and BDNF were not significantly affected by meal frequency. Subjects consuming a single large daily meal exhibit elevated fasting glucose levels and impaired morning glucose tolerance associated with a delayed insulin response during a 2-month diet period compared with those consuming 3 meals per day. The impaired glucose tolerance was reversible and was not associated with alterations in the levels of adipokines or BDNF.

Circulating leptin levels predict the development of metabolic syndrome in middle-aged men: an 8-year follow-up study

BACKGROUND

Because high circulating plasma leptin is associated with many features of the metabolic syndrome (MS), such as abdominal obesity, insulin resistance and high blood pressure (BP), we analysed the ability of plasma leptin concentration to predict the risk of developing MS in a prospective investigation of adult male participants of the Olivetti Heart Study (OHS).

METHODS AND RESULTS

Three hundred and sixty out of 907 men participating in the 1994-95 and 2002-04 OHS examinations (mean age at baseline 50.4 years, range 25-73 years) were free of MS at first visit according to NCEP-ATP III criteria (modified for the lack of high-density lipoprotein cholesterol measurement at baseline). During an average follow-up period of 8 years, there were 52 incident cases of MS (14.5%) due, in particular, to a rise in the prevalence of high BP (+42.4%), abdominal obesity (+16.4%) and impaired fasting glucose (IFG, +6.1%). In multivariate analyses, a one standard deviation difference in baseline plasma leptin concentration was associated with a 1.58-fold greater risk of developing MS (95% confidence interval = 1.10-2.30, P = 0.016) accounting for age, waist circumference, homeostatic assessment model index, smoking, alcohol consumption and physical activity. In particular, plasma leptin was positively associated with the risk of developing high BP (0.006) and IFG (0.014), after adjustment for confounders.

CONCLUSION

In this sample of an adult male population free of MS at baseline, circulating plasma leptin was a significant predictor of the risk of MS and, in particular, of its high BP and IFG components, independently of potential confounders.

Leptin and coronary heart disease risk: prospective case control study of British women

OBJECTIVE

Prospective studies have shown a positive association between leptin concentrations and coronary heart disease (CHD) in men, but its effect in women is unclear. Our objective was to examine the association of serum leptin levels with CHD in a prospective study of women.

RESEARCH METHODS AND PROCEDURES

We conducted a prospective (4 year) case (N=165) control (N=335) study nested within a cohort of 4286 British women.

RESULTS

With mutual adjustment for each other and age, social class, smoking, and physical activity, leptin was positively associated with BMI, fasting insulin, total cholesterol, low-density lipoprotein-cholesterol, triglycerides, and hypertension and was inversely associated with homeostasis model assessment insulin sensitivity. Leptin was not associated with CHD risk (age-adjusted relative risk for a doubling of leptin: 1.08 [95% confidence interval (CI): 0.91, 1.29]). This changed little with adjustment for childhood and adult social class, smoking, alcohol, and physical activity but attenuated to 1.00 (95% CI: 0.80, 1.26) with further adjustment for other metabolic risk factors (waist-to-hip ratio, low-density lipoprotein-cholesterol, triglycerides, C-reactive protein, fasting insulin, hypertension).

DISCUSSION

We found no strong statistical evidence that leptin is associated with CHD risk in this study population of older British women. Further research is needed to compare associations of leptin with CHD in men and women and to determine whether the effect varies by gender.

Physical activity energy expenditure may mediate the relationship between plasma leptin levels and worsening insulin resistance independently of adiposity

Leptin regulates a constellation of neuroendocrine processes that control energy homeostasis. The infusion of leptin in rodents lacking endogenous leptin promotes physical activity energy expenditure (PAEE) and improves insulin signaling, whereas hyperleptinemia is associated with physical inactivity and insulin resistance (IR). We tested whether baseline leptin levels predict changes in PAEE and IR over time, independent of obesity. We also assessed whether the relationship between leptin and change in IR is mediated by PAEE. The population consisted of 288 nondiabetic UK Caucasian adults (mean age: 49.4 yr; SD: 0.7 yr), in whom leptin, insulin, glucose, PAEE (via heart rate monitoring with individual calibration by indirect calorimetry), and anthropometric characteristics had been measured at baseline and 5 yr later. In linear regression models, baseline leptin levels inversely predicted follow-up PAEE ( P = 0.033). On average, individuals with low leptin levels (below sex-specific median) increased their daily activity 35% more during the 5-yr follow-up period than those with above-median leptin levels. Baseline leptin level also predicted worsening IR (fasting, 30-min, and 2-h insulins, and homeostasis model assessment-IR; all P < 0.01). Associations were independent of potential confounders, such as adiposity, age, and sex. Including baseline PAEE as a cofactor in the leptin-insulin models reduced the strength (1–4% reduction) and significance of the associations, suggesting that PAEE mediates the leptin-insulin relationships. Hyperleptinemia predicts a relative decline in PAEE and worsening insulin resistance, possibly via shared molecular pathways.

The role of hypoxia inducible factor-1 in cell metabolism--a possible target in cancer therapy

In many cancer types, intratumoural hypoxia is linked to increased expression and activity of the transcription factor hypoxia-inducible factor (HIF-1alpha), which is associated with poor patient prognosis. This increased the interest in HIF-1alpha as a cancer drug target. Further, HIF-1alpha has also a central role in the adaptive cellular programme responding to hypoxia in normal tissues. Many of the HIF-1alpha-regulated genes encode enzymes of metabolic pathways. Therefore, studying the link and the feedback mechanisms between metabolism and HIF-1alpha is of major importance to find new and specific therapeutic strategies.

Fat cell enlargement is an independent marker of insulin resistance and 'hyperleptinaemia'

AIMS/HYPOTHESIS

The aim of this study was to explore whether fat cell size in human subcutaneous and omental adipose tissue is independently related to insulin action and adipokine levels.

MATERIALS AND METHODS

Fat cells were prepared from abdominal subcutaneous biopsies obtained from 49 type 2 diabetic and 83 non-diabetic subjects and from omental biopsies obtained from 37 non-diabetic subjects. Cell size and insulin action on glucose uptake capacity in vitro were assessed in isolated fat cells. Insulin sensitivity in vivo was assessed with euglycaemic-hyperinsulinaemic clamps. Fasting blood samples were collected and adipokines and NEFA were measured.

RESULTS

Negative correlations were found between subcutaneous fat cell size and insulin sensitivity assessed as M-value during clamp and as insulin action on glucose uptake in fat cells in vitro. This was seen in non-diabetic subjects after including age, sex and BMI in the analyses. No such relationship was found in type 2 diabetic subjects. In both groups, subcutaneous fat cell size correlated positively and independently with plasma levels of leptin but not to any of the other assessed adipokines. In non-diabetic subjects, omental fat cell size was independently and negatively correlated with insulin action in subcutaneous, but not omental, fat cells in vitro.

CONCLUSIONS/INTERPRETATION

Fat cell enlargement is associated with insulin resistance in non-diabetic individuals independently of BMI. This was not seen in type 2 diabetic subjects, suggesting that after development of type 2 diabetes other factors, not related to fat cell size, become more important for the modulation of insulin resistance.

Influence of serum leptin on weight and body fat growth in children at high risk for adult obesity

OBJECTIVE

Our objective was to examine serum leptin prospectively as a predictor of weight and body fat growth in children at high risk for adult obesity. We hypothesized that leptin measurements would be positively associated with increased growth of adipose tissue because children with high baseline leptin for their body fat mass have greater leptin resistance and thus would have greater susceptibility to weight gain.

METHODS

Children ages 6-12 yr at high risk for adult obesity because of early-onset childhood overweight and/or parental overweight were recruited from 1996-2004. Growth in body mass index (BMI) was studied in 197 children, and growth in total body fat mass was examined in 149 children over an average follow-up interval of 4.4 yr (range, 1-8 yr). Longitudinal analyses accounted for sex, race, socioeconomic status, initial body composition, age, skeletal age, and physical activity and included all available interim visits for each individual so that a total of 982 subject visits were included in the analysis.

RESULTS

At baseline, 43% of children studied were overweight (BMI > or = 95th percentile); during follow-up, an additional 14% became overweight. Independent of initial body composition, baseline leptin was a statistically significant positive predictor of increased BMI (P = 0.0147) and increased total body fat mass (P < 0.007).

CONCLUSIONS

High serum leptin, independent of body fat, may be an indicator of increased leptin resistance, which predisposes children at high risk for adult obesity to somewhat greater growth in weight and body fat during childhood.

Enhanced food intake regulatory responses after a glucose drink in hyperinsulinemic men

OBJECTIVE

To determine the effect of hyperinsulinemia on food intake and plasma concentrations of glucose and food intake regulatory hormones in men after a glucose drink.

DESIGN

Cross-sectional clinical intervention study of the effect of a glucose drink on food intake regulation.

SUBJECTS

Thirty-three normoinsulinemic (NI) (body mass index (BMI)=25.3+/-0.6; age=41.4+/-2.4) and 32 hyperinsulinemic (HI) men (BMI=29.5+/-0.6; age=43.4+/-2.6).

MEASUREMENTS

Food intake was measured from a pizza meal 1 h after subjects consumed either a noncaloric sweetened drink or a glucose-containing drink (75 g/300 ml) in random order on two occasions. On another occasion, blood samples were taken every 30 min for 2 h after the glucose drink.

RESULTS

Fasting insulin in the HI and NI men was 65+/-3 (mean+/-s.e.m.) and 26+/-1.5 pmol/l, respectively. Food intake at the pizza meal was reduced by the glucose drink (P<0.01), but more so in HI (-9.7+/-4.1 %) than NI men (-5.4+/-3.4 %) (P=0.06). The increase in plasma insulin and cholecystokinin (CCK) after the glucose drink was greater and the plasma concentrations of leptin were higher, and ghrelin and adiponectin were lower in HI men than in NI men (P<0.05).

CONCLUSION

These results support epidemiological data suggesting that hyperinsulinemia, at least in the early stages, may provide resistance to weight gain, possibly through physiological mechanisms of food intake control.

Changes in serum sex hormone profiles after short-term low-dose administration of dehydroepiandrosterone (DHEA) to young and elderly persons

In man, serum concentrations of dehydroepiandrosterone (DHEA) and DHEA sulfate (DHEAS) decrease with age after the twenties. For this reason, the decline in DHEA and DHEAS concentrations may be related to the development of some chronic diseases that are prevalent in the older age population. In this study, we evaluate the benefit and safety level of DHEA administration to men as a hormone replacement therapy. Twenty-two healthy Japanese males (age 26-63; mean +/- SD, 41.0 +/- 10.0 yrs.) received 25 mg DHEA once a day orally in the morning for two weeks. Serum concentrations of steroid hormones and cytokines were measured before and after the DHEA administration. Glucose tolerance and insulin resistance were also assessed before and after the DHEA administration using a 75 g oral glucose tolerance test and homeostasis model assessment (HOMA-R), respectively. Serum DHEA and DHEAS levels were significantly elevated after the DHEA administration for all ages of test subjects. In subjects who were older than 41 yrs. (older group) serum androstenedione and estradiol levels were elevated after the DHEA administration. Significant negative correlations were observed between the serum DHEA concentration and the serum concentration of fasting insulin, HOMA-R, leptin, and high-sensitivity C-reactive protein for all subjects. Daily administration of 25 mg DHEA increased the serum DHEA, DHEAS, androstenedione, and estradiol levels of the subjects of the older group to the same level as that of younger subjects.

Insulin resistance with hormone replacement therapy: associations with markers of inflammation and adiposity

OBJECTIVE

This study was undertaken to determine whether insulin resistance associated with combination hormone replacement therapy (HRT) is mediated by changes in serum markers of inflammation or in serum adipocyte hormones.

STUDY DESIGN

Forty-five postmenopausal women, aged 55 +/- 7 years, were examined from a randomized, double-blind placebo-controlled trial evaluating the effect of HRT on insulin-stimulated glucose disposal and body composition. Volunteers were randomly assigned to conjugated estrogens 0.625 mg plus medroxyprogesterone acetate 2.5 mg vs placebo for 1 year. At baseline and at 1 year, body composition was assessed by dual photon x-ray absorptiometry scans; body fat distribution was measured by computed tomographic scans at the L4/L5 vertebral disk space; insulin sensitivity was measured by euglycemic hyperinsulinemic clamp; interleukin-6 (IL-6), leptin, and adiponectin were measured by enzyme-linked immunosorbent assay; and c-reactive protein (CRP) was measured by radioimmunoassay.

RESULTS

HRT increased CRP by 121% compared with a 32% increase with placebo (P = .03); HRT decreased glucose disposal by 17% compared with no change with placebo (P = .04) as reported previously. HRT did not affect body composition, body fat distribution, IL-6, leptin, or adiponectin. The increase in CRP did not correlate with the decrease in glucose disposal in the HRT group (R = 0.11, P = .65).

CONCLUSION

Treatment with HRT for one year increases CRP, but does not alter IL-6, adiponectin, or leptin. The change in CRP was not, however, related to the decrease in glucose disposal with HRT treatment.

Leptin receptors in human skeletal muscle

Human skeletal muscle expresses leptin receptor mRNA; however, it remains unknown whether leptin receptors (OB-R) are also expressed at the protein level. Fourteen healthy men (age = 33.1 +/- 2.0 yr, height = 175.9 +/- 1.7 cm, body mass = 81.2 +/- 3.8 kg, body fat = 22.5 +/- 1.9%; means +/- SE) participated in this investigation. The expression of OB-R protein was determined in skeletal muscle, subcutaneous adipose tissue, and hypothalamus using a polyclonal rabbit anti-human leptin receptor. Three bands with a molecular mass close to 170, 128, and 98 kDa were identified by Western blot with the anti-OB-R antibody. All three bands were identified in skeletal muscle: the 98-kDa and 170-kDa bands were detected in hypothalamus, and the 98-kDa and 128-kDa bands were detected in thigh subcutaneous adipose tissue. The 128-kDa isoform was not detected in four subjects, whereas in the rest its occurrence was fully explained by the presence of intermuscular adipose tissue, as demonstrated using an anti-perilipin A antibody. No relationship was observed between the basal concentration of leptin in serum and the 170-kDa band density. In conclusion, a long isoform of the leptin receptor with a molecular mass close to 170 kDa is expressed at the protein level in human skeletal muscle. The amount of 170-kDa protein appears to be independent of the basal concentration of leptin in serum.

Relationships between glycaemic abnormalities, obesity and insulin resistance in nondiabetic Polynesians of New Caledonia

OBJECTIVE

Polynesians in New Caledonia have an increased risk for developing diabetes, compared to Melanesians or Europeans. They are also more prone to obesity. The aim of this study was to analyse differences in the pre-diabetic state that may explain the varying susceptibility to diabetes between these three ethnic groups, focusing on the balance between insulin resistance and capacity of pancreatic cells to secrete insulin.

DESIGN AND SUBJECTS

The CALDIA Study is a population-based cross-sectional survey of diabetes prevalence conducted in New Caledonia. All participants who did not have diabetes, according to the results of a 0-2 h oral glucose tolerance test (n=392), were selected for analysis.

RESULTS

Compared to Europeans, Polynesians and Melanesians had significantly higher body mass indices (BMI) and waist-to-hip ratios (WHRs). Polynesians had higher fasting plasma glucose values than Europeans or Melanesians (6.03 mmol/l, vs 5.78 and 5.46, respectively; P<0.0001). Fasting plasma insulin level and the estimate of insulin resistance by homeostasis model assessment were not significantly different between the three ethnic groups. Homeostasis model assessment estimate of beta-cell secretory capacity was lower in Polynesians compared to the two other ethnic groups (83.1 mU/mmol, vs 119.3 and 125.2, respectively; P<0.02).

CONCLUSION

Despite a high prevalence of central obesity, as judged by high BMI and WHR, in Polynesians of New Caledonia, their high risk of diabetes may be more strongly related to a defect in insulin secretion capacity than to insulin resistance.

Acute effect of exercise on plasma leptin level and insulin resistance in obese women with stable caloric intake

Obese individuals are frequently hyperleptinemic and insulin resistant. Chronic exercise is associated with improvements in plasma leptin level and insulin sensitivity; however, little is known about the acute effect of exercise on these parameters. The aim of this study was to evaluate the acute effect of aerobic exercise on plasma leptin and insulin sensitivity in obese women with stable caloric intake.

PATIENTS AND METHODS

Twenty-three obese women (age 41.2 +/- 10.3 years, body mass index 40.7 +/- 6.7 kg/m2) were included to the study. All subjects were admitted to an exercise program (45-minute walking sessions at 60-80% of maximum heart rate) every day except weekends for four weeks (total 20 exercise sessions). Insulin resistance was evaluated by HOMA model. Plasma glucose, insulin and leptin levels were determined at baseline and at the end of the first, seventh, and twentieth exercise session.

RESULTS

Baseline and at the end of the first, seventh, and twentieth exercise session plasma leptin levels were 59.1 +/- 20.1, 58.5 +/- 21.0, 53.4 +/- 21.9, and 51.2 +/- 20.5 ng/ml and HOMA-r were 2.75 +/- 1.47, 1.77 +/- 0.71, 1.73 +/- 0.89, 1.62 +/- 0. 70, respectively. Compared to baseline, at the end of the seventh (p = 0.021) and twentieth exercise session (p = 0.003), plasma leptin levels were significantly low. Plasma leptin level did not change significantly at the end of the first exercise session (p > 0.05). At the end of the first exercise session (p = 0.005), end of the seventh (p = 0.003) and twentieth exercise session (p = 0.007) HOMA-r was lower than baseline. There was no correlation between weight loss during exercise period and the change of leptin, and HOMA-r. Fasting plasma glucose, insulin and leptin levels were determined at baseline and at the end of the first, seventh, and twentieth exercise session.

CONCLUSION

Our study suggests that acute exercise decreases insulin resistance at the first exercise session with no effect on leptin levels. Significant leptin decrement was evident at the first week and lasted during the entire four weeks exercise session.

Beneficial impact of crocetin, a carotenoid from saffron, on insulin sensitivity in fructose-fed rats

Crocetin, a unique carotenoid with potent antioxidative and anti-inflammatory activities, is a major ingredient of saffron which is used as an important spice and food colorant in various parts of the world. In the present study, the effect of crocetin on insulin resistance and its related abnormalities induced by high-fructose diet were investigated in male Wistar rats. Compared to the control rats fed on normal laboratory diet, fructose-fed rats developed a series of pathological changes including insulin resistance, hyperinsulinemia, dyslipidemia and hypertension. Although having no evident effect on the body weight, fructose feeding caused a marked increase in the weight of epididymal white adipose tissue. Furthermore, a significant reduction in the expression of both protein and mRNA of adiponectin (an insulin-sensitizing adipocytokine) was observed, whereas those of tumor necrosis factor (TNF)-alpha and leptin were enhanced in epididymal white adipose tissue in fructose-fed rats. These disorders were effectively normalized in crocetin-treated rats. Crocetin was also demonstrated here to alleviate free fatty acid (FFA)-induced insulin insensitivity and dysregulated mRNA expression of adiponectin, TNF-alpha and leptin in primary cultured rat adipocytes. These findings suggest the possibility of crocetin treatment as a preventive strategy of insulin resistance and related diseases. The favorable impact on adiponectin, TNF-alpha and leptin expression in white adipose tissue may be involved in the improvement of insulin sensitivity observed in crocetin-treated rats.

Sleep and the metabolic syndrome

The metabolic syndrome represents a clustering of several interrelated risk factors of metabolic origin that are thought to increase cardiovascular risk. It is still uncertain whether this clustering results from multiple underlying risk factors or whether it has a single cause. One metabolic abnormality that may underlie several clinical characteristics of the metabolic syndrome is insulin resistance. This review discusses the evidence that sleep disturbances (obstructive sleep apnoea, sleep deprivation and shift work) may independently lead to the development of both insulin resistance and individual clinical components of the metabolic syndrome. The converse may also be true, in that metabolic abnormalities associated with the metabolic syndrome and insulin resistance may potentially exacerbate sleep disorders. The notion that sleep disturbances exert detrimental metabolic effects may help explain the increasing prevalence of the metabolic syndrome and insulin resistance in the general population and may have important implications for population-based approaches to combat the increasing epidemic of metabolic and cardiovascular disease.

Obesity-related cardiovascular disease: implications of obstructive sleep apnea

Obesity and obstructive sleep apnea (OSA) often coexist. OSA has been linked to cardiovascular disease. Thus, OSA may contribute to the cardiovascular consequences of obesity. In this review, we explore clinical and pathophysiological interactions between obesity, cardiovascular disease and OSA. We discuss the mechanisms whereby OSA may contribute to hypertension, atherosclerosis, insulin resistance and atrial fibrillation associated with obesity, and emphasize the potential implications for understanding why only a subgroup of obese patients develop cardiovascular disease. Identification of the OSA-dependent and OSA-independent pathways in the cardiovascular pathophysiology of obesity may hold clinical and therapeutic promise.

Pathways leading to muscle insulin resistance--the muscle--fat connection

Type 2 diabetes is a heterogeneous disease characterized by hyperglycemia and insulin resistance in peripheral tissues such as adipose tissue and skeletal muscle. This review focuses on obesity as one of the major environmental factors contributing to the development of diabetes. It has become evident that adipose tissue represents an active secretory organ capable of releasing a variety of cytokines such as TNFalpha, IL-6, adiponectin and other still unknown factors that might constitute the missing link between adipose tissue and insulin resistance. In fact, adipocyte-derived factors are significantly increased in obesity and represent good predictors of the development of type 2 diabetes. The negative crosstalk between adipocytes and skeletal muscle cells leads to disturbances in muscle cell insulin signalling and insulin resistance involving major pathways in inflammation, cellular stress and mitogenesis. Positive regulators of insulin sensitivity include the adipocyte hormone adiponectin and inhibitors of inflammatory pathways such as JNK-, IKK- and ERK-inhibitors. In summary, a better knowledge of intracellular and intercellular mechanisms by which adipose tissue affects skeletal muscle cell physiology may help to develop new strategies for diabetes treatment.

Changes in C-reactive protein predict insulin sensitivity in severely obese individuals after weight loss surgery

The production of inflammatory mediators by abdominal adipose tissue may link obesity and insulin resistance. We determined the influence of systemic levels of interleukin-6 and C-reactive protein on insulin sensitivity after weight loss via Roux-en-Y gastric bypass surgery. Severely obese individuals (n = 15) were evaluated at baseline and at 6 months after surgery. Insulin sensitivity was determined by frequently sampled intravenous glucose tolerance testing at the same time points. Visceral and subcutaneous adipose tissue volumes were quantified by computed tomography. Interleukin-6 and C-reactive protein were measured by enzyme-linked immunoassay in plasma and in adipose tissue biopsies. Correlation analysis was used to determine associations between insulin sensitivity and other outcome variables. Significance was set at P < 0.05. Plasma interleukin-6 concentrations were significantly correlated to the IL-6 content of subcutaneous adipose tissue (r = 0.71). At 6 months postsurgery, subcutaneous and visceral adipose tissue volumes were significantly reduced (34.7% and 44.1%, respectively) and insulin sensitivity had improved by 160.9%. Significant longitudinal correlations were found between insulin sensitivity and plasma C-reactive protein (r = -0.61), but not plasma interleukin-6 at 6 months. These findings offer insights that link obesity and insulin resistance via the activity of inflammatory mediators.

Beneficial effects of icodextrin on plasma level of adipocytokines in peritoneal dialysis patients

OBJECTIVE

Leptin and adiponectin, well-recognized adipocytokines, are reported to contribute to the pathogenesis of atherosclerosis. The aim of this study was to elucidate the effects of icodextrin-based dialysis solution on adipocytokine metabolism.

METHODS

In 12 non-diabetic anuric patients on peritoneal dialysis, dialysis solution was changed from glucose-based dialysis solution to icodextrin-based dialysis solution for 6 months. Plasma levels of leptin, adiponectin, lipids (total cholesterol, HDL-cholesterol and triglyceride), insulin, blood glucose and insulin sensitivity index by the homeostasis model assessment (HOMA-IR) were compared before and after the use of the icodextrin solution.

RESULTS

Plasma leptin level was decreased from 15.6 (2.5-69.0) to 7.3 (2.9-45.9) ng/ml (P = 0.018) and plasma adiponectin level increased from 11.6 (6.2-19.6) to 17.6 (7.8-33.0) microg/ml (P = 0.002). A reduction in plasma insulin level from 33.1 (13.8-54.1) to 19.1 (5.8-37.3) muU/ml (P = 0.009) and HOMA-IR from 8.22 (3.68-15.09) to 5.15 (1.40-13.78) (P = 0.015) was observed. While plasma total cholesterol level remained similar, HDL-cholesterol level increased, from 36.0 (22-45) to 43.5 (30-69) mg/dl (P = 0.008) and the triglyceride level decreased, from 174.0 (140-250) to 116.5 (81-207) mg/dl (P = 0.012).

CONCLUSION

Icodextrin-based dialysis solution improves abnormal adipocytokine metabolism, dyslipidaemia and insulin resistance, which are known to be associated with atherosclerosis. These results suggest that the use of icodextrin-based dialysis solution might be useful in preventing atherosclerosis in PD patients. Long-term effects of icodextrin-based dialysis solution on the atherosclerosis in peritoneal dialysis patients should be tested.

Comparison of the effects of valsartan and felodipine on plasma leptin and insulin sensitivity in hypertensive obese patients

Aim of this study was to compare the effect of valsartan and felodipine on blood pressure (BP), plasma leptin (L), insulin sensitivity and plasma norepinephrine (NE) in obese hypertensive patients. Ninty-six obese patients (body mass index [BMI] > or = 30 kg/m2) with mild to moderate essential hypertension (diastolic blood pressure [DBP] > 90 and < 110 mmHg, as evaluated with an appropriately sized cuff) aged 31-60 years, were randomized to a valsartan (80 mg/day for 16 weeks; n = 48) or felodipine (5 mg/day for 16 weeks; n = 48) treatment group after a 2-week wash-out period. After the first 4 weeks of treatment there was a titration with dose-doubling in non responder patients (DBP > 90 mmHg). At the end of the placebo period and of active treatment period, BP and BMI were evaluated and a venous sample was drawn at the same hour in the morning to evaluate plasma L and NE. Insulin resistance index (HOMA-IR) was calculated. No dietary advice was prescribed. Both valsartan and felodipine significantly decreased BP values (-19.3/15 mmHg and -18.9/13.6 mmHg, respectively p < 0.001 vs. placebo), with no difference between treatments. However, felodipine increased plasma NE (+124 pg/ml, +38.2%, p < 0.05 vs. placebo and < 0.01 vs. valsartan) and had no effect on L, body weight and HOMA-IR index, while valsartan did not modify NE and produced a significant reduction in L (-3.7 ng/ml, -10.1%, p < 0.05 vs. placebo), BMI (-1.7 kg/m2, -4.7%, p < 0.01 vs. placebo) and HOMA-IR index (-1.6, -20%, p < 0.05 vs. placebo). These results suggest that in hypertensive obese subjects, treatment with valsartan might offer an advantage over treatment with felodipine, since valsartan may help to improve obesity-related disorders in addition to lowering BP.

Leptin repletion restores depressed {beta}-adrenergic contractility in ob/ob mice independently of cardiac hypertrophy

Impaired leptin signalling in obesity is increasingly implicated in cardiovascular pathophysiology. To explore mechanisms for leptin activity in the heart, we hypothesized that physiological leptin signalling participates in maintaining cardiac beta-adrenergic regulation of excitation-contraction coupling. We studied 10-week-old (before development of cardiac hypertrophy) leptin-deficient (ob/ob, n=12) and C57Bl/6 (wild-type (WT), n=15) mice at baseline and after recombinant leptin infusion (0.3 mg kg-1 day-1 for 28 days, n=6 in each group). Ob/ob-isolated myocytes had attenuated sarcomere shortening and calcium transients ([Ca2+]i) versus WT (P<0.01 for both) following stimulation of the beta-receptor (with isoproterenol (isoprenaline)) or at the post-receptor level (with forskolin and dibutryl-cAMP). In addition, sarcoplasmic reticulum (SR) Ca2+ stores were depressed. Leptin replenishment in ob/ob mice restored each of these abnormalities towards normal without affecting gross (wall thickness) or microscopic (cell size) measures of cardiac architecture. Immunoblots revealed alterations of several proteins involved in excitation-contraction coupling in the ob/ob mice, including decreased abundance of Gsalpha-52 kDa, as well as alterations in the expression of Ca2+ cycling proteins (increased SR Ca2+-ATPase, and depressed phosphorylated phospholamban). In addition, protein kinase A (PKA) activity in ob/ob mice was depressed at baseline and correctable towards the activity found in WT with leptin repletion, a finding that could account for impaired beta-adrenergic responsiveness. Taken together, these data reveal a novel link between the leptin signalling pathway and normal cardiac function and suggest a mechanism by which leptin deficiency or resistance may lead to cardiac depression.

Leptin, from fat to inflammation: old questions and new insights

Leptin is 16 kDa adipokine that links nutritional status with neuroendocrine and immune functions. Initially thought to be a satiety factor that regulates body weight by inhibiting food intake and stimulating energy expenditure, leptin is a pleiotropic hormone whose multiple effects include regulation of endocrine function, reproduction, and immunity. Leptin can be considered as a pro-inflammatory cytokine that belongs to the family of long-chain helical cytokines and has structural similarity with interleukin-6, prolactin, growth hormone, IL-12, IL-15, granulocyte colony-stimulating factor and oncostatin M. Because of its dual nature as a hormone and cytokine, leptin links the neuroendocrine and the immune system. The role of leptin in the modulation of immune response and inflammation has recently become increasingly evident. The increase in leptin production that occurs during infection and inflammation strongly suggests that leptin is a part of the cytokine network which governs the inflammatory-immune response and the host defense mechanisms. Leptin plays an important role in inflammatory processes involving T cells and has been reported to modulate T-helper cells activity in the cellular immune response. Several studies have implicated leptin in the pathogenesis of autoimmune inflammatory conditions, such as experimental autoimmune encephalomyelitis, type 1 diabetes, rheumatoid arthritis, and intestinal inflammation. Very recently, a key role for leptin in osteoarthritis has been demonstrated: leptin indeed exhibits, in concert with other pro-inflammatory cytokines, a detrimental effect on articular cartilage by promoting nitric oxide synthesis in chondrocytes. Here, we review the recent advances regarding leptin biology with a special focus on those actions relevant to the role of leptin in the pathophysiology of inflammatory processes and immune responses.

Plasma leptin and prognosis in patients with established coronary atherosclerosis

OBJECTIVES

This study was designed to evaluate the relationship between plasma leptin and prognosis in patients with angiographically confirmed coronary atherosclerosis.

BACKGROUND

Experimental studies suggest that leptin, an adipose tissue-derived hormone, exerts important cardiovascular effects.

METHODS

Study subjects were recruited prospectively from a cohort of patients undergoing clinically indicated coronary angiography (n = 382). The median duration of follow-up was four years. Follow-up information was available for 361 patients.

RESULTS

The combined end point of cardiac death, myocardial infarction (MI), cerebrovascular accident, or re-vascularization occurred in 44 subjects. In the simple Cox model, leptin had a significant (p < 0.001) non-linear/cubic univariate relationship with the combined end point. Other variables associated with prognosis in the univariate analysis were body mass index (BMI), prior MI, insulin resistance, C-reactive protein (CRP), fibrinogen, and number of coronary vessels with >50% stenosis. A positive relationship between leptin and prognosis was also seen when leptin levels were split by quintiles, with a hazard ratio of 6.46 for the highest quintile. The only two variables significantly associated with the combined end point in the multivariate Cox model were leptin (p = 0.004) and number of coronary vessels with >50% stenosis (p < 0.001). A similar relationship between leptin and prognosis was observed when leptin was adjusted for BMI.

CONCLUSIONS

In patients with angiographically confirmed coronary atherosclerosis, leptin is a novel predictor of future cardiovascular events independent of other risk factors, including lipid status and CRP.

A Case-control Pilot Study on n-3 Polyunsaturated Fatty Acid as a Negative Risk Factor for Myocardial Infarction

The relation between n-3 polyunsaturated fatty acid (PUFA) and nonfatal myocardial infarction is still controversial. A multicenter case-control pilot study on n-3 PUFA as a negative risk factor for myocardial infarction was performed in Niigata prefecture. Seventy-three patients with acute myocardial infarction (AMI) and age and gender matched controls (n = 84) were recruited. Serum leptin levels were significantly higher in patients with AMI than the controls (8.1 +/- 6.7 ng/mL versus 5.8 +/- 3.7 ng/mL, P < 0.01), and serum high-density lipoprotein cholesterol (HDLc) levels were significantly lower in patients with AMI than the controls (46 +/- 10.5 mg/dL versus 60 +/- 15 mg/dL, P < 0.00001). Statistically significant differences were preserved in leptin and HDLc when the data were analyzed separately by gender. Serum levels (%weight) of linolenic acid (C18:3:n3), eicosapentaenoic acid (C20:5:n3), docosapentaenoic acid (C22:5:n3), and total n-3 PUFA were significantly lower in patients with AMI than the control group (P < 0.000001, < 0.05, < 0.05, < 0.05, respectively). The serum n-3 PUFA/saturated fatty acid (SF) ratio and n-3 PUFA/n-9 monounsaturated fatty acid (MUFA) ratio were significantly lower in patients with AMI than the controls (P < 0.05 and < 0.01, respectively). When the subjects were separated into two categories according to an n-3/n-6 PUFA ratio below 0.3 or above 0.3, patients with AMI were more frequently in the former while the controls were more frequently in the latter (P < 0.05). N-3 PUFA may be a negative risk factor for AMI. The results suggest leptin is a risk factor for AMI irrespective of ethnicity and gender.

Resistin expression in 3T3-L1 adipocytes is reduced by arachidonic acid

The resistin gene is expressed in adipocytes and encodes a protein proposed to link obesity and type 2 diabetes. Increased plasma FFA is associated with insulin resistance. We examined the effect of separate FFAs on the expression of resistin mRNA in cultured murine 3T3-L1 adipocytes. The FFAs tested did not increase resistin expression, whereas both arachidonic acid (AA) and eicosapentaenoic acid (EPA) reduced resistin mRNA levels. AA was by far the most potent FFA, reducing resistin mRNA levels to approximately 20% of control at 60-250 muM concentration. Selective inhibitors of cyclooxygenase-1 and of mitogen-activated protein kinase kinase counteracted AA-induced reduction in resistin mRNA levels. Transient overexpression of sterol-regulatory element binding protein-1a (SREBP-1a) activated the resistin promoter, but there was no reduction in the abundance of approximately 65 kDa mature SREBP-1 after AA exposure. Actinomycin D as well as cycloheximide abolished the AA-induced reduction of resistin mRNA levels, indicating dependence on de novo transcription and translation. Our data suggest that reductions in resistin mRNA levels involve a destabilization of the resistin mRNA molecule. An inhibitory effect of AA and EPA on resistin expression may explain the beneficial effect of ingesting PUFAs on insulin sensitivity.

Effect of fish diets and weight loss on serum leptin concentration in overweight, treated-hypertensive subjects

BACKGROUND

Leptin, a circulating hormone secreted from adipocytes, is an index of adiposity and is reduced by caloric restriction and weight loss. A recent population study suggested that dietary-derived omega3 fatty acids lower leptin levels independent of body fat.

OBJECTIVE

To examine whether dietary fish enhanced the effects of weight loss on serum leptin levels, in 69 overweight, treated hypertensive men and women.

METHODS

Participants were randomized to a daily fish meal, a weight-reduction regimen, the two regimens combined or a control group for 16 weeks.

RESULTS

A total of 63 individuals completed the study. Weight fell 5.6 +/- 0.8 kg with energy-restriction. Blood pressure (BP) reductions in the combined fish-weight loss group were twice that seen with either intervention alone. At baseline, in all groups combined, serum leptin levels correlated with serum insulin (r = 0.307, P = 0.014), but not with body weight. The greatest change in serum leptin occurred in the fish-weight loss group (control, 0.60 +/- 0.76 ng/ml; fish, 1.20 +/- 0.79 ng/ml; weight loss, -1.40 +/- 1.05 ng/ml; fish-weight loss, -5.08 +/- 1.64 ng/ml). In the fish-weight loss group, the change in serum leptin was predicted by changes in serum insulin (r = 0.488, P = 0.038), 24-h BP (systolic BP (SBP): r = 0.435, P = 0.060; diastolic BP (DBP): r = 0.563, P = 0.018) and 24-h heart rate (0.584, P = 0.028). Using general linear models, there was a significant fish x weight-loss interaction (P = 0.008) on post-intervention serum leptin after adjustment for baseline levels, independent of post-intervention insulin.

CONCLUSION

A daily fish meal as part of a weight-reducing regimen was more effective than either measure alone at reducing leptin levels. Reductions in leptin may be related to the substantial fall in BP seen with the fish-weight loss program.

Improvement of insulin resistance by troglitazone ameliorates cardiac sympathetic nervous dysfunction in patients with essential hypertension

BACKGROUND

It was recently suggested that insulin resistance is significantly correlated with activation of the cardiac sympathetic nervous system in patients with essential hypertension.

OBJECTIVES

To examine the effects of troglitazone, an agent used to treat insulin resistance, on cardiac sympathetic nervous dysfunction and insulin resistance in patients with essential hypertension.

METHODS

The study participants included 34 patients (14 men, 20 women) with mild essential hypertension and 17 normal controls (group C, seven men). The patients were randomly divided into two groups, one treated with 400 mg troglitazone and antihypertensive drugs (group T, n = 17) and the other treated with antihypertensive drugs only (group N, n = 17). We evaluated insulin resistance and cardiac sympathetic nervous function before and after 6 months of treatment. Insulin resistance was evaluated using steady-state plasma glucose (SSPG; mg/dl) concentrations and cardiac sympathetic nervous function was evaluated using the heart-to-mediastinum ratio (H : M) and mean washout rate measured by 123I-meta-iodobenzylguanidine (MIBG) cardiac imaging.

RESULTS

There were significant differences in SSPG (P < 0.01), early (P < 0.05) and delayed (P < 0.05) phases of H : M and washout rate (P < 0.05) between the hypertensive patients and group C. The SSPG concentration was significantly improved after treatment only in group T, from 153.3 to 123.7 mg/dl (P < 0.01). The early and delayed phases of H : M and washout rate also were significantly improved (P < 0.05) (from 2.59 to 2.63, from 2.12 to 2.27 and from 18.1 to 13.7%, respectively) in only group T.The change in SSPG was significantly correlated with the changes in H : M and washout rate (r = -0.639 and 0.577, respectively).

CONCLUSION

Troglitazone had a beneficial effect on cardiac sympathetic nervous function through a decrease in insulin resistance in patients with essential hypertension.

Guidelines for prevention and treatment of adverse effects of antipsychotic drugs on glucose-insulin homeostasis and lipid metabolism

RATIONALE

With the antipsychotic drugs available today, especially with some of the newer, atypical antipsychotics, metabolic side effects, such as weight gain, diabetes mellitus and lipid abnormalities, have become a complication to the drug therapy that have to be recognized and treated.

OBJECTIVE

The aim of this article is to suggest guidelines for prevention and treatment of adverse effects of antipsychotics on glucose-insulin homeostasis and lipid metabolism, whereas strategies for management of antipsychotic-induced weight gain are summarized elsewhere.

METHOD

The guidelines are based on results of experimental and clinical studies presented in the article, as well as on a recently published review of 180 articles in the field.

RESULTS

Both conventional and atypical antipsychotics can indirectly, by causing obesity, promote development of insulin resistance and type-2 diabetes. In addition, some atypical agents probably directly induce hyperinsulinemia, followed by weight gain, insulin resistance and drug-induced, sometimes insulin-dependent, diabetes.

CONCLUSION

In this article, guidelines for the management of adverse metabolic effects of antipsychotics are described.

[Future targets in the treatment of type 2 diabetes]

Prevention and treatment of type 2 diabetes mellitus (T2DM) and the metabolic syndrome represent a major clinical challenge, because effective strategies such as fat restriction and exercise are difficult to implement into diabetes treatment. Based on the increasing knowledge on the pathogenesis of T2DM, new therapeutic approaches are currently under investigation. Potential targets of new therapeutic approaches include: (i) Inhibition of hepatic glucose production, (ii) stimulation of glucose-dependent insulin secretion, (iii) enhancement of insulin signal transduction, and (iv) reduction of body fat mass. Agonists of glucagon-like-peptide 1 (GLP-1) and antagonists of dipeptidylpeptidase IV, which inactivates GLP-1, stimulate glucose-dependent insulin secretion, improve hyperglycemia and are already tested in clinical trials. In humans, glucagon antagonists and an amylin analogue reduce glucagon-dependent glucose production. The glucose-lowering effect of current modulators of lipid oxidation is not pronounced and their use could be limited by side effects. In addition to clinically approved thiazolidendiones, new agonists of the peroxisome proliferator activator receptor gamma (PPAR gamma) as well as combined PPAR alpha/gamma agonists are developed at present. The direct modulation of insulin signal transduction is still limited to experimental studies.

Is there a rationale for angiotensin blockade in the management of obesity hypertension?

Obesity, currently affecting >20% of the adult population in most Western countries, is a major risk factor for the development of hypertension. Hypertension in obese patients is, in the majority of instances, further complicated by the concomitant presence of dyslipidemia and insulin resistance. The latter is reflected by derangement of glucose homeostasis, ranging from hyperinsulinemia to frank type 2 diabetes. Hypertension in obese patients is also associated with an increased risk for left ventricular hypertrophy, endothelial dysfunction, renal hyperfiltration, microalbuminuria, and elevated markers of inflammation. Sodium retention, volume expansion, and increased cardiac output are common findings in obese individuals. These changes are largely attributable to increased activity of the sympathetic nervous system and insufficient suppression of the renin-angiotensin system. Recent data show increased expression of angiotensin II-forming enzymes in adipose tissue, and increased activity of the renin-angiotensin system has recently been implicated in the development of insulin resistance and type 2 diabetes. Accordingly, antihypertensive agents that block the renin-angiotensin system might be a beneficial strategy for treatment of obesity-related hypertension. Both angiotensin-converting enzyme inhibitors and angiotensin type-1 receptor blockers have been associated with favorable metabolic properties and end-organ protection in addition to their antihypertensive effects. Data from ongoing large trials will provide an indication of the protective and preventive effects of these treatment strategies while offering insights into the mechanisms linking obesity, hypertension, and other facets of the metabolic syndrome.

Respiratory complications of obesity

Obesity is known to be a major risk factor of a whole range of cardiovascular, metabolic and respiratory disorders. It has been recognised that the pattern of regional fat distribution plays an important role in the pre-disposition of obese subjects to certain obesity-related complications. Derangement of parameters of lung function is determined to a large extent by the quantity and distribution of excess body fat with its potential to interfere with the mechanics of pulmonary physiology. Clinical, laboratory and epidemiological observations have established links between obesity and several breathing problems including obstructive sleep apnoea, obesity hypoventilation syndrome and asthma. However, in many respects, the pathophysiology of these links is not fully explored. In this article, the impact of obesity on pulmonary physiology and its association with the above-mentioned clinical conditions is discussed.

Adverse Metabolic Effects Associated with Atypical Antipsychotics

Adverse metabolic effects, such as diabetes mellitus, lipid abnormalities and weight gain, have increasingly been recognised with the use of the newer, so-called atypical antipsychotic drugs. This article reviews the current literature in the field and attempts to answer the question of whether the atypical antipsychotics differ in their effects on glucose-insulin homeostasis and lipid metabolism. It also addresses how then to manage the use of the atypical antipsychotics that do interfere with these metabolic systems. Differences in effects of atypical antipsychotics on leptin levels are also summarised and put into context; bodyweight gain associated with atypical antipsychotics is reviewed elsewhere. In summary, there are no large controlled trials published quantifying the prevalence of adverse effects on glucose-insulin homeostasis and lipid metabolism in patients receiving atypical antipsychotics. Nevertheless, the published articles and case reports reviewed in this article give a fairly good view of those adverse effects occurring with clozapine, olanzapine and risperidone, whereas little data are available regarding quetiapine, ziprasidone and zotepine, and no data exist for amisulpride and aripiprazole. Estimated rankings of the atypical agents, based on the available literature, show that the relative risk of glucose intolerance/diabetes mellitus, hyperlipidaemia and hyperleptinaemia is highest for clozapine and olanzapine, moderately high for quetiapine, rather low for risperidone and lowest for ziprasidone. Since adverse metabolic effects of atypical antipsychotics may have a negative influence on both the antipsychotic treatment outcome as well as the physical health of the patient, these effects have to be recognised and adequately managed. In this review, recommendations for prevention and treatment of the adverse metabolic effects are outlined.

Case-control study of anthropometric measures and prostate cancer risk

A population-based case-control study of 988 stage T2 or greater prostate cancer cases and 1063 controls was conducted in Alberta from November 1997 to December 2000 to examine the influence of anthropometric risk factors on the risk of prostate cancer using several different measures. An in-person interview was conducted, and all anthropometric measurements were taken using standardized methods. Respondents also recalled their body weight at each decade from age 20 to the referent year. Several anthropometric variables were derived, and unconditional logistic regression analyses were performed. The multivariable odds ratios, when comparing the highest to the lowest quartile were: for body mass index, OR = 1.12 (95% CI 0.85-1.47); for waist-hip ratio, OR = 1.07 (0.83-1.38); for height, OR = 0.78 (0.60-1.02); for weight, OR = 0.91 (0.70-1.18); for weight gain since age 20, OR = 0.91 (0.70-1.19); and for difference between minimum and maximum adult weight, OR = 0.89 (0.69-1.16). Our study provides evidence for no association between any measures of anthropometry including several derived measures of changes in weight over lifetime and prostate cancer risk.

Serum leptin is elevated in Saudi Arabian patients with metabolic syndrome and coronary artery disease

AIMS

To compare plasma leptin in Saudi subjects with Type 2 diabetes and coronary heart disease (CHD) with non-diabetic control subjects and to examine the relationship of plasma leptin to other CHD risk factors.

RESEARCH DESIGN AND METHOD

Serum leptin concentrations were measured in 144 Saudi men. Subjects studied included 59 with Type 2 diabetes mellitus [BMI 27.5 (3.7) kg/m2 mean (sd)], 34 with coronary heart disease [BMI 29.6 (1.8) kg/m2], and 51 non-diabetic controls [BMI 28.0 (3.5) kg/m2]. There was no significant difference in BMI between the groups. Fasting serum leptin, lipids, insulin, apolipoproteins and glucose were measured. BMI, blood pressure; smoking habit and age were also recorded. Insulin resistance was assessed using the HOMA model.

RESULTS

Leptin concentrations were significantly higher in diabetic and CHD patients than in controls (P = 0.024 and 0.016, respectively). Multiple regression analysis showed that body weight (P < 0.0006), serum triglyceride concentration (P = 0.046) and systolic blood pressure (P = 0.013) were all significantly related to the logarithm of the serum leptin concentration (R2 = 0.549) in CHD patients. A subgroup analysis, comparing those patients who had the metabolic syndrome, as defined by WHO, with controls, showed higher serum leptin in those with metabolic syndrome (P = 0.05).

CONCLUSIONS

Serum leptin is increased in Saudi subjects with diabetes mellitus, metabolic syndrome and CHD. Leptin may be a marker of risk of CHD, at least in men, and contribute to the CHD risk profile in subjects with insulin resistance. Further studies are needed to evaluate this relationship prospectively.

Leptin and insulin modulate nutrient partitioning and weight loss in ob/ob mice through regulation of long-chain fatty acid uptake by adipocytes

Leptin treatment of ob/ob mice leads to weight loss appreciably greater than that in pair-fed mice. To test whether this "extra" weight loss is mediated by leptin-induced alterations in nutrient partitioning, the effects in ob/ob mice of subcutaneous leptin infusion (500 ng/h for <or=21 d) on adipocyte fatty acid uptake and transporter gene expression were examined. Mice were initially hyperinsulinemic (5.25 +/- 1.57 nmol/L). Plasma insulin decreased by 55 +/- 10% within 8 h of leptin infusion, declining progressively to normal by d 14. The V(max) for saturable adipocyte fatty acid uptake fell from 31.1 +/- 5.6 to 25.2 +/- 4.0 pmol/(s. 50000 cells) (P < 0.05) by 24 h, and to a normal rate (8.0 +/- 0.8 pmol/(s. 50000 cells) by d 21 (P > 0.5 vs. normal C57BL/6J controls). Adipocyte mRNA levels for plasma membrane fatty acid binding protein and fatty acid translocase, putative fatty acid transporters that are up-regulated three- to fourfold in adipocytes from ob/ob mice, had also normalized by d 21. The initial changes in V(max) preceded decreases in food intake and body weight by at least 24 h. In pair-fed mice, insulin levels, V(max) and body weight all declined more slowly than in leptin-treated mice, and all remained significantly elevated compared with normal values at d 21. The data suggest that insulin up-regulates and leptin down-regulates adipocyte fatty acid uptake, leading to alterations in fatty acid partitioning that affect adiposity.

The effect of pegvisomant-induced serum IGF-I normalization on serum leptin levels in patients with acromegaly

BACKGROUND

In humans, serum leptin correlates positively with fat mass. GH is lipolytic and patients with active acromegaly have lowered serum leptin compared to age, sex and body mass index (BMI)-matched controls, but a direct influence of GH on serum leptin remains unclear. In patients with acromegaly, total leptin increases following successful pituitary surgery and during somatostatin (SMS) analogue therapy (despite no change in BMI) but whether this represents changes in soluble leptin receptor, bound or free leptin is unclear. Pegvisomant, a GH receptor antagonist capable of normalizing serum IGF-I in over 97% of patients, represents a novel treatment strategy in acromegaly and its effect on leptin has not previously been reported.

PATIENTS

Sixteen patients (nine male (M), seven female (F), median age 52 years, range 27-78 years) with active acromegaly (serum IGF-I at least 30% above the upper limit of an age-related reference range) were studied. Serum IGF-I was normalized in all subjects with pegvisomant [mean duration 7 months (range 3-11 months), median dose 20 mg/day (range 10-40 mg/day)]. A single batch measurement of leptin, bound leptin (BL), soluble leptin receptor (SLR), insulin and glucose were performed on samples from baseline and first occurrence of serum IGF-I normalization.

RESULTS

As in normal subjects, females with acromegaly had higher baseline serum leptin [median M = 6.1 (range 1.6-58.7), F = 25.9 (range 3.19-54.1) ng/ml; P = 0.04], which correlated positively with BMI (R = 0.78, P = 0.0004). Forward step-wise regression analysis demonstrated that BMI and gender accounted for 90% of the variance in mean serum log10 leptin. Pegvisomant-induced serum IGF-I normalization was associated with a rise in serum leptin [8.9 (range 1.6-58.3) to 12.7 (range 2.3-90.8) ng/ml, P < 0.0001]. Although the absolute increase was not significantly different, mean percentage increase was greater in men (M = 66.6 +/- 51%, F = 11.8 +/- 16%, P = 0.017) despite similar serum IGF-I and BMI in male and female subjects at baseline. No change in BL or SLR accompanied serum IGF-I normalization [0.27 (range 0.15-1.26) to 0.27 (range 0.14-1.2) nmol/l, P = 0.27 and 3.2 (range 1.2-6.8) to 2.7 (range 1-7.4) nmol/l, P = 0.5, respectively]. After normalization of serum IGF-I, a correlation between BMI and leptin remained (R = 0.86, P < 0.0001) and together BMI and gender accounted for 87% of the variance in mean log10 serum leptin (P = 0.0002).

CONCLUSION

Pegvisomant-induced serum IGF-I normalization in patients with active acromegaly is associated with a significant increase in total, and by implication, free leptin.

Aspectos neuroendócrinos na síndrome dos ovários policísticos

A síndrome dos ovários policísticos (PCOS) é a endocrinopatia mais freqüente na mulher em idade reprodutiva. O quadro clínico é variável, mas em geral apresenta-se com hirsutismo, acne e/ou alopecia androgênica, anovulação crônica associada a distúrbio menstrual e infertilidade. A resistência insulínica pode estar presente em mais da metade dos casos, em especial nas pacientes obesas. A etiopatogenia ainda não foi totalmente esclarecida, mas mecanismos neuroendócrinos vêm sendo estudados nos últimos anos. Embora esteja bem estabelecida a presença de secreção inapropriada do eixo GnRH-LH em pacientes com PCOS, algumas delas, especialmente as obesas/hiperinsulinêmicas, exibem níveis normais de LH e uma atenuação de sua resposta aos testes de estímulo. Recentemente, descrevemos uma correlação negativa entre leptina e LH em pacientes com PCOS, sugerindo que a atenuação nos níveis de LH nestas pacientes possa estar relacionada a um estado de resistência à leptina. Por outro lado, evidências sugerem que o eixo somatotrófico participe também dos mecanismos fisiopatológicos envolvidos na PCOS. Dados recentes do nosso grupo demonstram que pacientes de peso normal e normoinsulinêmicas apresentam uma maior resposta do GH à clonidina do que pacientes com hirsutismo idiopático. Um mecanismo possível seria uma ação co-gonadotrófica do GH, contribuindo para o hiperandrogenismo clínico e a anovulação. Outra possibilidade é que a elevação da secreção de GH seja somente um epifenômeno vinculado ao aumento de androgênios ovarianos e sua conversão periférica em estrogênios. Estudos futuros são necessários para esclarecer os mecanismos subjacentes associados às alterações descritas neste trabalho e sua relevância na etiopatogenia, diagnóstico e tratamento desta síndrome.

Short-term effects of prednisolone and dexamethasone on circulating concentrations of leptin and sex hormone-binding globulin in children being treated for acute lymphoblastic leukaemia

OBJECTIVE

Disturbances in body weight regulation are often encountered during glucocorticoid treatment and are associated with increased insulin resistance and truncal fat accumulation. Children were investigated who were receiving glucocorticoid treatment for acute lymphoblastic leukaemia (ALL). They were randomized to receive either prednisolone or dexamethasone as part of induction of remission. This randomization process provided a suitable opportunity to compare the effects of these two administered steroid on surrogate markers of adipocyte activity (leptin) and hyperinsulinaemia/insulin resistance (SHBG).

DESIGN AND PATIENTS

Prospective study over 16 weeks of children randomized to receive prednisolone (40 mg/m2) or dexamethasone (6.5 mg/m2) as part of the MRC-ALL97/99 induction chemotherapy for ALL. Nineteen children (8 male, 11 female) with a median age 5.9 years (range 2.6-13 years) were recruited into the study. Main outcome measures were body mass index (BMI), serum leptin and sex hormone binding globulin (SHBG).

RESULTS

Glucocorticoid administration for 5 weeks resulted in significant (P < 0.05) increases in BMI, leptin (corrected for BMI) and the leptin : SHBG ratio and lowering of SHBG. Dose for dose, dexamethasone was significantly more potent than prednisolone in altering these parameters.

CONCLUSIONS

Short-term glucocorticoid treatment has significant effects on BMI, leptin and SHBG. The leptin : SHBG ratio increase indicates that this may be a novel and sensitive biochemical marker of metabolic change. Our results suggest that glucocorticoid treatment regimens should be kept as short as possible to avoid possible detrimental effects associated with increased adiposity and insulin resistance.

Effects of angiotensin II receptor antagonists on insulin resistance syndrome and leptin in sucrose-fed spontaneously hypertensive rats

In order to investigate the usefulness of angiotensin II type 1 receptor (AT1) antagonists (ARA) in the treatment of hypertension with insulin resistance syndrome, we studied the effects of a high dose sucrose diet and ARA on insulin sensitivity, plasma lipids, and leptin in spontaneous hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). SHR and WKY were divided into three groups and treated for 12 weeks: those fed a standard chow, those given a sucrose-rich chow or those given a sucrose-rich chow and ARA. While in SHR the weight of both subcutaneous and mesenteric adipose tissue was greater in the sucrose-rich chow fed animals than in the standard chow fed animals, ARA treatment significantly decreased the weights of both subcutaneous and mesenteric adipose tissue. ARA treatment decreased free fatty acid and triglyceride in SHR, and increased high density lipoprotein cholesterol in SHR and WKY. Homeostasis model assessment-insulin resistance (HOMA-IR) index, plasma levels of leptin, and leptin mRNA in mesenteric adipose tissue were significantly greater in the sucrose-rich chow fed animals than in the standard chow fed animals, and significantly lower in the ARA-treated sucrose-rich chow fed animals than in the sucrose-rich chow fed animals in both SHR and WKY. ARA improved insulin resistance, and reduced plasma leptin and leptin mRNA in adipose tissue. These results suggest that the improvement of insulin resistance by ARA may be attributed, at least in part, to the reduction of adipose tissue weight. It is concluded that ARA is useful in the treatment of patients with hypertension and concomitant insulin resistance syndrome.

Plasma leptin, fatty acids, and tumor necrosis factor-receptor and insulin resistance in children

OBJECTIVE

To evaluate the effect of plasma leptin, nonsterified fatty acids (NEFAs), and tumor necrosis factor-receptor 1 (TNFR1) on plasma insulin and insulin-resistance status in children.

RESEARCH METHODS AND PROCEDURES

One thousand thirty-two children (521 boys and 511 girls) were included in this study. We measured plasma insulin and leptin levels by radioimmunoassay, plasma NEFA levels by enzymatic acyl-coenzyme A synthase-acyl-coenzyme A oxidase spectrophotometric methods, and TNFR1 levels by enzyme-linked immunosorbent assay. We calculated insulin resistance index (IRI) using homeostasis model assessment and calculated insulin-resistance syndrome summary score (IRS) by adding the quartile ranks from the distribution of systolic blood pressure (BP), serum triglyceride, high-density lipoprotein-cholesterol (inverse), and insulin levels.

RESULTS

Overweight children had higher BP, plasma leptin, and insulin levels and higher IRI and IRS than normal-weight children. Plasma leptin and TNFR1 were positively correlated with insulin levels, IRI, and IRS. The correlation coefficients of leptin and TNFR1 in IRI were 0.53 and 0.12, respectively, for boys and 0.25 and 0.18, respectively, for girls. In multivariate regression analyses, TNFR1 was positively associated with insulin level and IRI in girls; NEFA was positively associated only with IRS. Plasma leptin levels were significantly positively associated with insulin levels, IRI, and IRS, even after adjusting for BMI and other potential confounders.

DISCUSSION

Overweight children had higher BP, plasma insulin, and leptin levels and adverse insulin-resistance status than normal-weight children. Plasma leptin levels, rather than NEFA and TNFR1, may play a significant role in the development of hyperinsulinemia and insulin resistance in children.

Relationship among systolic blood pressure, serum insulin and leptin, and visceral fat accumulation in obese children

The aim of this study was to clarify the relation among systolic blood pressure (SBP), serum insulin, leptin, visceral fat accumulation and family history of hypertension, and to elucidate the pathophysiologic mechanism of blood pressure elevation in obese children. This study examined 109 obese children with a family history of hypertension (OF: 77 boys and 32 girls), and 83 obese children without such a history (ON: 60 boys and 23 girls). Body height and weight, and percent of body fat were measured and the percent of relative weight was calculated. Both boys and girls, the two groups were matched with respect to age, height, and weight. SBP was measured in the seated position using an automated recorder. Abdominal fat thickness (maximum preperitoneal fat thickness: Pmax; minimum subcutaneous fat thickness: Smin) were measured using ultrasonography. The fasting serum levels of insulin and leptin were measured by radioimmunoassay. All subjects were simply obese, without diabetic states. In both OF and ON, SBP was associated with insulin levels, leptin levels, and Pmax by simple regression analysis, and with insulin levels by stepwise regression analysis. Insulin levels were associated with leptin levels and Pmax by simple regression analysis, and with leptin levels by stepwise regression analysis. These findings indicated that SBP was associated with hyperinsulinemia, hyperleptinemia and visceral accumulation regardless of a family history of hypertension in obese children, as well as later in adult obesity. For primary prevention of hypertension, these results support the importance of implementation of a strategy to prevent obesity, especially visceral obesity. An effective strategy for preventing childhood obesity will contribute to a future decrement in cases of metabolic syndrome, including adulthood hypertension.

Serum leptin concentrations are decreased and correlated with disease severity in age-related macular degeneration: a preliminary study

BACKGROUND

Age-related maculopathy (ARM) or degeneration (ARMD) is the leading cause of irreversible blindness in developed countries. Despite several studies on the morphology of ARMD, the aetiology is unknown and factor(s) contributing to the pathogenesis remain to be characterised. More recent studies have demonstrated that cholesterol esters and lipids are present within Bruch's membrane deposits and drusen, and dietary fat intake is associated with ARMD. The product of Ob gene, leptin, is a recently discovered peptide participating in human metabolism. There is a direct relationship between serum leptin and diet, and lipoprotein metabolism, but the role of leptin in the course of ARMD has not previously been investigated.

PURPOSE

This cross-sectional case-control study investigated whether serum leptin level was associated with ARMD as a new possible risk factor and to assess its relationship with disease severity. Methods A total of 32 patients with ARM or ARMD (17 men, 15 women) and 20 age- and sex-matched healthy control subjects without ARMD (11 men, nine women) from a similar ethnic background were enrolled in this multicentre study. Body mass index (BMI) (weight (kg)/height (m(2))) was calculated for each group. The presence of maculopathy was assessed on the basis of colour fundus photographs using an international classification system. Patients were classified as early-ARM (n=16) or late-ARMD (n=16) using clinical examination and grading of photographs. Serum leptin levels were measured by an enzyme-linked immunosorbent assay kit. The Mann-Whitney U test or chi(2) test was used for statistics as indicated, and P&<0.05 was considered to be significant.

RESULTS

The age, sex ratio, and BMI between groups were comparable. Patients with maculopathy had significantly (P&<0.001) lower leptin levels (mean+/-SD, 6.01+/-2.55 ng/ml) than control subjects (13.21+/-2.27 ng/ml). In addition, late-ARMD patients had significantly lower leptin levels (3.81+/-0.58 ng/ml) than early-ARM patients (8.21+/-1.68 ng/ml, P&<0.001) or control subjects (P&<0.001).

CONCLUSION

Leptin seems to be a possible newly associated factor in the course of ARM and may be involved in the lipid composition of the macular lesions, especially in late-ARMD.

The changes in serum leptin, body fat mass and insulin resistance after renal transplantation

BACKGROUND

In this prospective-controlled study, we aimed to investigate the effect of changes in insulin resistance and anthropometrical parameters on serum leptin levels (SLL) after renal transplantation (Tx).

PATIENTS AND METHODS

Thirty-four patients (M/F: 19/15, mean age: 29 +/- 9 yr) and 30 age and sex-matched healthy controls (C) were included. Body weight, subscapular, suprailiac, periumbilical, biceps and triceps skinfold thicknesses, neck, wrist, hip and waist circumferences, as well as body mass index and body fat mass were measured as anthropometrical parameters. In order to measure the serum glucose, insulin and SLL, blood samples were obtained before and 1 wk, 1 and 6 months after Tx. Homeostasis Model Assessment (HOMA) values were calculated as an index of insulin resistance.

RESULTS

Serum leptin levels (SLL) of the patients at pre-Tx were significantly higher than C (21.5 +/- 3.5 vs. 7.8 +/- 0.9 ng/mL, p = 0.002) and decreased at first week after Tx (from 21.5 +/- 3.5 to 8.4 +/- 1.5 ng/mL, p < 0.001). Thereafter, it gradually increased to 12.8 +/- 2.1 ng/mL in the first month and to 14.4 +/- 2.1 ng/mL in the sixth month after Tx. Serum leptin levels at sixth month were significantly higher than C (p = 0.005). Serum insulin and HOMA values changed similar to SLL after Tx. Correlations between SLL and HOMA persisted during the study period [pre-Tx (r: 0.40) and at first (r: 0.38) and sixth (r: 0.47) months]. In linear regression analysis, HOMA and fat mass were found as independent variables for predicting SLL at the sixth month after Tx.

CONCLUSION

Serum leptin levels dramatically decreased immediately after Tx and significantly correlated with serum insulin levels and HOMA during the entire study. Increase in SLL at sixth months was probably because of increase in fat mass, insulin resistance and steroid use in renal transplant recipients.

Adipocyte-Derived Hormone Levels in HIV Lipodystrophy

Objective

Despite evidence for the role of adipocyte-derived hormones in insulin resistance, little is known about their levels in human lipodystrophic states. We examined the relationships of plasma leptin and adiponectin levels to fat distribution and insulin sensitivity in the HIV lipodystrophy syndrome.

Design

Cross-sectional study

Setting

HIV primary care practices

Patients

HIV-infected men with (n=13) and without (12) lipodystrophy and healthy uninfected controls (12). Main outcome measures: Plasma adiponectin and leptin levels were measured in the fasting state. Body composition was assessed by physical examination, dual-energy x-ray absorptiometry and computed tomography. Insulin sensitivity (SI) was measured using the insulin-modified frequently sampled intravenous glucose tolerance test.

Results

Leptin levels were significantly higher in HIV-infected men with lipodystrophy as compared to HIV-infected controls (5.2 vs 3.0 ng/ml, P=0.01). Across the entire study population, leptin levels were positively correlated with measures of general adiposity. In the HIV-infected patients, leptin levels were negatively correlated with SI after adjustment for fat mass (r=-0.38, P=0.07). Adiponectin levels were significantly lower in HIV-infected men with lipodystrophy as compared to both HIV-infected and healthy controls (1.6 vs 3.4 μg/ml, P<0.05 and 1.6 vs 6.7 μg/ml, P<0.001, respectively). Adiponectin levels, after adjustment for fat mass, were correlated with measures of fat distribution. Finally, in the HIV-infected patients, adiponectin levels were significantly and positively correlated with SI after adjustment for fat mass (r=0.75, P≤0.001), and adiponectin level was also an independent determinant of SI.

Conclusions

Plasma leptin and adiponectin levels are altered in the HIV lipodystrophy syndrome. Adiponectin deficiency may play a role in the insulin resistance associated with HIV lipodystrophy.

Clinical evaluation of pioglitazone in patients with type 2 diabetes using alpha-glucosidase inhibitor and examination of its efficacy profile

AIM

Pioglitazone is considered to reduce insulin resistance. This study was conducted to evaluate the efficacy, safety and clinical profile of pioglitazone in patients whose type 2 diabetes were poorly controlled with alpha-glucosidase inhibitor alone or alpha-glucosidase in combination with sulfonylurea.

METHODS

Twenty patients with type 2 diabetes were treated with pioglitazone (30 mg q.d.) orally for 16 weeks.

RESULTS

There were significant reductions in HbA1C, FPG and postprandial plasma glucose at week 16. As adverse events, oedema, hypoglycaemia-like reaction, increases in LDH, CPK, etc. were noted. There was no significant change in TNF-alpha. Leptin levels increased significantly at week 16 and were still increasing 4 weeks after the treatment. Per cent body fat was almost constant throughout the study period. When efficacy was classified by demographic variables, pioglitazone was found to be more effective in the subjects who had a higher postprandial 2-h plasma glucose level, leptin level or per cent body fat value.

CONCLUSION

Pioglitazone was considered to be effective when used in patients whose type 2 diabetes were poorly controlled with alpha-glucosidase inhibitor alone or alpha-glucosidase in combination with sulfonylurea.

Hypertension and insulin disorders

Insulin resistance and/or compensatory hyperinsulinemia are associated with hypertension, obesity, dyslipidemia, and glucose intolerance. Insulin resistance and hyperinsulinemia are considered to increase blood pressure through sympathetic nervous system activation, renin-angiotensin system stimulation, and vascular smooth muscle cell proliferation. Leptin, magnesium ions, nitric oxide, endothelin, peroxisome proliferator-activated receptor gamma, and tumor necrosis factor-alpha also modulate blood pressure. Decreasing insulin resistance by lifestyle modification including diet, weight loss, and physical exercise has been shown to reduce blood pressure. Angiotensin-converting enzyme inhibitors have a beneficial effect on insulin resistance. On the other hand, the angiotensin II antagonist, losartan, does not affect insulin sensitivity. The selective alpha1-blockers have a favorable metabolic profile producing increases in insulin sensitivity. A short-acting type calcium channel blocker seems to decrease insulin sensitivity. On the other hand, long-acting type calcium channel blockers improve insulin sensitivity. Thiazide diuretics and most of the beta-blockers decrease insulin sensitivity. Vasodilatory beta-blockers have been reported to improve insulin sensitivity. Use of low-dose diuretics avoids the adverse effects seen with conventional doses.