Mediators of the effect of ertugliflozin on a composite kidney outcome in patients with type 2 diabetes and atherosclerotic cardiovascular disease: analyses from VERTIS CV

Introduction

Sodium–glucose cotransporter 2 (SGLT2) inhibitors have been shown to slow the decline of kidney function in outcome trials, but the biological mediator(s) underlying the therapeutic benefit are not well established.

Purpose

We performed a post-hoc analysis exploring potential mediators of the effects of the SGLT2 inhibitor ertugliflozin on the VERTIS CV exploratory kidney composite outcome (sustained 40% decrease from baseline in estimated glomerular filtration rate [eGFR], chronic kidney replacement therapy or kidney death).

Methods

In VERTIS CV, 8246 participants with type 2 diabetes mellitus and established atherosclerotic cardiovascular disease were randomised to placebo, ertugliflozin 5 mg or 15 mg (pooled for analyses, as prospectively planned), and were followed for a mean of 3.5 years. The hazard ratio (HR; 95% confidence interval) for the pre-specified exploratory kidney composite outcome was 0.66 (0.50, 0.88). Cox regression models were used to evaluate covariates that were significantly differentially changed from baseline with ertugliflozin treatment as candidate mediators, with a mediator identified as a covariate when added to an unadjusted model of randomised treatment assignment a) yielded a larger hazard ratio; and b) the mediator retained P<0.05 in the model (eGFR was excluded as a covariate). The percentage of mediation was determined by the proportional increase in the HR between the unadjusted and adjusted models for each post-randomisation period: early (first change from baseline measurement) and average (weighted average of change from baseline from all post-baseline measurements). Each potential mediator was tested individually, so across analyses, mediation % sums to >100%.

Results

Of 22 covariates significantly changed by ertugliflozin, nine were identified as potential mediators (Table). The covariates with a high percentage of mediation were those related to changes in blood erythrocytes (haemoglobin, haematocrit and red blood cell mass), with average changes in haemoglobin having the highest percentage of mediation (61.8%). Serum uric acid was associated with a mediation of 29.4% and 50.0% for the early and average post-randomisation effect periods, respectively. Early changes in glycated haemoglobin had a large mediation (50%), but the average change during the trial was not significant. Average change in serum albumin had a large mediation (29.4%). Average changes in body weight and systolic blood pressure had percentages of mediation of 41.2% and 14.7%, respectively.

Conclusion

Multiple factors may be involved in the reduction of the kidney composite outcome observed with ertugliflozin. In the short-term, changes in glycaemia had a high mediation effect. Over the long-term, changes suggestive of haemoconcentration and/or haematopoiesis (natriuresis-related effects), showed the highest percentage of mediation, followed by changes in serum uric acid and body weight (glucosuria-related effects).

Funding Acknowledgement

Type of funding sources: Private company. Main funding source(s): Sponsored by Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA in collaboration with Pfizer Inc., New York, NY, USA

Mediation analyses of the effect of ertugliflozin on hospitalisation for heart failure in patients with type 2 diabetes and atherosclerotic cardiovascular disease from the VERTIS CV trial

Introduction

Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce risk of hospitalisation for heart failure (HHF) in outcome trials, but the biological mediators underlying the therapeutic benefit are not well established.

Purpose

To identify potential biological mediators through which ertugliflozin reduces risk of HHF.

Methods

In VERTIS CV, 8246 patients with type 2 diabetes and atherosclerotic cardiovascular disease were randomised to ertugliflozin 5 or 15 mg (observations pooled as prospectively planned) or placebo. Cox regression models were used to evaluate the associations between changes in 26 potential mediators with outcomes. Potential mediators were selected based on proposed mechanisms and/or differential change from baseline with SGLT2 inhibitors. Mediation criteria required 1) significant (P<0.05 for change from baseline) effects of ertugliflozin vs placebo on each potential mediator; and 2) significant (P<0.05) association of change in post-randomisation levels of the potential mediator with risk of HHF when added to an unadjusted model of randomised treatment assignment. Percent mediation was determined by comparing the unadjusted hazard ratio and hazard ratio adjusted for change in the potential mediator of interest. Each covariate was tested individually, such that percent mediation across the analyses summed to >100%. Time-dependent models were used to evaluate associations between early (change from baseline for the first post-baseline measurement) and average (weighted average of change from baseline using all post-baseline measurements) changes in covariates with clinical outcomes.

Results

Over a mean of 3.5 years, the incidence rate of HHF was 0.7 and 1.1 per 100 patient-years with ertugliflozin and placebo, respectively. Among 26 candidate mediators, 9 and 13 met the mediation criteria based on early and average changes, respectively. The 3 covariates with the largest mediating effects of early changes included haematocrit (40%), haemoglobin (27%) and HDL-C (23%) (Table); other significant biomarkers included urine albumin/creatinine ratio, and serum albumin, uric acid, chloride, protein and sodium. The 3 biomarkers with the largest mediating effects in average changes included haemoglobin (63%), albumin (50%) and uric acid (47%) (Table); other significant biomarkers included haematocrit, urine albumin/creatinine ratio, body weight, serum protein and chloride, systolic blood pressure, ALT, BUN, eGFR and heart rate.

Conclusions

In these analyses from the VERTIS CV trial, potential markers of volume status and haemoconcentration and/or haematopoiesis were the strongest mediators of the effect of ertugliflozin on reducing risk of HHF in the early and average change periods. Other potential mediators included uric acid, lipid markers and kidney parameters. These findings provide insights into potential mechanisms through which ertugliflozin, and potentially the SGLT2 inhibitor class, may prevent HHF.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): Sponsored by Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, and Pfizer Inc., New York, NY, USA.

Cardiorenal outcomes with ertugliflozin by baseline metformin use: post-hoc analyses of the VERTIS CV trial

Introduction

We analysed data from the VERTIS CV trial that investigated the CV and kidney safety and efficacy of the sodium-glucose cotransporter 2 (SGLT2) inhibitor ertugliflozin (ERTU) vs placebo (PBO) to assess the impact of metformin (MET) use at baseline (BL). These analyses are timely because the recent ESC guidelines recommendation to use SGLT2 inhibitor or GLP-1 RAs as initial glucose-lowering therapy in patients with type 2 diabetes (T2D) with or at high risk for atherosclerotic cardiovascular disease (ASCVD) has been questioned because outcome trials of these drug classes included a large proportion of patients with MET as background therapy, yet MET was not used at BL in approximately 25% of patients in each trial.

Purpose

These analyses determined cardiorenal endpoints of VERTIS CV according to use of BL MET to assess for evidence of treatment effect modification for ERTU by BL MET use, adjusting for the probability (propensity) of BL MET use.

Methods

VERTIS CV was an international, double-blind, PBO-controlled trial of 2 doses of ERTU (5 mg; 15 mg) vs PBO in patients with T2DM and ASCVD. As prospectively planned, the 2 ERTU dose groups were combined for all analyses vs PBO. Differences in risk of CV and kidney outcomes between ERTU and PBO across subgroups by BL MET use were conducted using Cox proportional hazards model along with propensity adjustment using inverse probability for treatment weighting to account for differences in patient mix between those with and without BL MET influenced by individual BL characteristics and risk factors. Treatment (categorical), BL MET use (categorical) and the interaction term between treatment and BL MET use subgroup (no or yes) were used in each model to assess effect modification by BL MET use. Hazard ratio and 95% CI are presented along with Pinteraction for evaluation of treatment effect modification by BL MET use.

Results

In VERTIS CV, 8246 patients were randomised to ERTU 5 mg, 15 mg or PBO. Of these, 6286 (76%) patients used MET (alone or with other glucose-lowering agents [GLA]) at BL. Differences in BL characteristics by BL MET use subgroup (no or yes) included a higher mean UACR (204.4 vs 129.8 mg/g), more patients with eGFR <60 mL/min/1.73 m2 (34.8% vs 17.9%), more patients on a single GLA (76.9% vs 18.3%), higher insulin use (67.6% vs 40.9%), lower sulphonylurea use (32.2% vs 43.8%) and a slightly longer disease duration (14.4 vs 12.5 years) in the subgroup without vs with BL MET, respectively. No significant differences in the relative risk for cardiorenal outcomes were observed with or without BL MET use (Figure; all Pinteraction values >0.05).

Conclusions

In VERTIS CV, there was no evidence for effect modification by BL MET use on the effects of ERTU on cardiorenal outcomes in patients with T2D and ASCVD.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): Sponsored by Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, and Pfizer Inc., New York, NY, USA.

Exploring residual risk for diabetes and microvascular disease in the Diabetes Prevention Program Outcomes Study (DPPOS)

AIM

Approximately half of the participants in the Diabetes Prevention Outcomes Study (DPPOS) had diabetes after 15 years of follow-up, whereas nearly all the others remained with pre-diabetes. We examined whether formerly unexplored factors in the DPPOS coexisted with known risk factors that posed additional risk for, or protection from, diabetes as well as microvascular disease.

METHODS

Cox proportional hazard models were used to examine predictors of diabetes. Sequential modelling procedures considered known and formerly unexplored factors. We also constructed models to determine whether the same unexplored factors that associated with progression to diabetes also predicted the prevalence of microvascular disease. Hazard ratios (HR) are per standard deviation change in the variable.

RESULTS

In models adjusted for demographics and known diabetes risk factors, two formerly unknown factors were associated with risk for both diabetes and microvascular disease: number of medications taken (HR = 1.07, 95% confidence intervals (95% CI) 1.03 to 1.12 for diabetes; odds ratio (OR) = 1.10, 95% CI 1.04 to 1.16 for microvascular disease) and variability in HbA_1c (HR = 1.02, 95% CI 1.01 to 1.03 for diabetes; OR = 1.06, 95% CI 1.04 to 1.09 for microvascular disease per sd). Total comorbidities increased risk for diabetes (HR = 1.10, 95% CI 1.04 to 1.16), whereas higher systolic (OR = 1.22, 95% CI 1.13 to 1.31) and diastolic (OR = 1.14, 95% CI 1.05 to 1.22) blood pressure, as well as the use of anti-hypertensives (OR = 1.41, 95% CI 1.23 to 1.62), increased risk of microvascular disease.

CONCLUSIONS

Several formerly unexplored factors in the DPPOS predicted additional risk for diabetes and/or microvascular disease - particularly hypertension and the use of anti-hypertensive medications - helping to explain some of the residual disease risk in participants of the DPPOS.

Combination of Recreational Soccer and Caloric Restricted Diet Reduces Markers of Protein Catabolism and Cardiovascular Risk in Patients with Type 2 Diabetes

BACKGROUND

Moderate calorie-restricted diets and exercise training prevent loss of lean mass and cardiovascular risk. Because adherence to routine exercise recommendation is generally poor, we utilized recreational soccer training as a novel therapeutic exercise intervention in type 2 diabetes (T2D) patients.

OBJECTIVE

We compared the effects of acute and chronic soccer training plus calorie-restricted diet on protein catabolism and cardiovascular risk markers in T2D.

DESIGN, SETTING AND SUBJECTS

Fifty-one T2D patients (61.1±6.4 years, 29 females: 22 males) were randomly allocated to the soccer+diet-group (SDG) or to the diet-group (DG). The 40-min soccer sessions were held 3 times per week for 12 weeks.

RESULTS

Nineteen participants attended 100% of scheduled soccer sessions, and none suffered any injuries. The SDG group showed higher levels of growth hormone (GH), free fatty acids and ammonia compared with DG. After 12 weeks, insulin-like growth factor binding protein (IGFPB)-3 and glucose levels were lower in SDG, whereas insulin-like growth factor (IGF)-1/ IGFBP-3 ratio increased in both groups. After the last training session, an increase in IGF-1/IGFBP-3 and attenuation in ammonia levels were suggestive of lower muscle protein catabolism.

CONCLUSIONS

Recreational soccer training was popular and safe, and was associated with decreased plasma glucose and IGFBP-3 levels, decreased ammoniagenesis, and increased lipolytic activity and IGF-1/IGFBP-3 ratio, all indicative of attenuated catabolism.

Predicting, managing and preventing new-onset diabetes after transplantation

New-onset diabetes after transplantation (NODAT) or posttransplant diabetes mellitus is a frequent metabolic complication of organ transplantation. Diabetes incidence rates among transplant recipients are higher than in the general population. The estimated rates are 9-18% after kidney, 20-33% after liver, 26-40% after lung, and 29% after heart transplants, respectively. In retrospective studies, NODAT was associated with higher costs of posttransplant care and increased risks of graft failure, infection, cardiovascular disease, and death. The incidence of NODAT is influenced by both traditional risk factors for type 2 diabetes (age, family history, obesity, hepatitis C infection, and ethnicity) and transplant-specific risk factors. Managing NODAT is challenging because posttransplant care is complex and characterized by multiple variables including immunosuppressive regimens, choice of antidiabetes agents, and optimal use of insulin therapy. Therefore, predicting and preventing NODAT would be a compelling objective for improving care of posttransplant patients. During the pretransplant period, lifestyle modifications in patients at risk for NODAT should be considered, recognizing that no randomized controlled trials exist to inform specific modalities or cost-effectiveness of such an approach. After hospital discharge, close monitoring of blood glucose during the first month, and every 3 months thereafter for the first year, is recommended for those without prior history of diabetes mellitus. Future areas of investigation include clinical validation of NODAT risk score engines, validation of interventions for primary prevention of NODAT, the development of immunosuppressive regimens with minimal diabetogenic effects, and prospective determination of the role of glycemic control on graft survival and cardiovascular outcomes.

Metabolic syndrome, prediabetes and the science of primary prevention

This review provides an update on the metabolic syndrome and prediabetes. Compared to the downstream disorders, namely type 2 diabetes and cardiovascular disease (including coronary artery disease, cerebrovascular disease and peripheral vascular disease), prediabetes and the metabolic syndrome represent intermediate cardiometabolic states. The generally accepted working definitions, epidemiology, pathophysiology and clinical relevance of these intermediate conditions are discussed. Importantly, the review focuses on evidence-based strategies for preventing the cardiometabolic sequelae associated with prediabetes and the metabolic syndrome. The importance of lifestyle modification in the primary prevention of the metabolic syndrome and prediabetes is emphasized, and the interaction between genetics and lifestyle intervention in predicting outcomes is presented. In addition to discussing the evidence from landmark clinical trials, we identify methods for translating the success achieved in clinical trials to the community with regard to the prevention of diabetes and cardiometabolic risk. Future research needs are also highlighted. The overall goal is to foster an increased understanding of the prominent role of primary prevention in stemming the tide of cardiometabolic disorders in the society.

Comparison of vildagliptin and thiazolidinedione as add-on therapy in patients inadequately controlled with metformin: results of the GALIANT trial--a primary care, type 2 diabetes study

AIM

To assess the efficacy and tolerability of vildagliptin compared with thiazolidinediones (TZDs) as an add on to metformin treatment in a primary care patient population with type 2 diabetes.

METHODS

This was a randomized, 12-week, open-label study comparing vildagliptin (100 mg, n = 1653) and TZD (agent and dose at the investigators' discretion, n = 825) add-on therapy in patients inadequately controlled [haemoglobin A(1C) (HbA(1c)): 7-10%] on a stable dose of metformin (> or =1000 mg/day). The primary objective was to test non-inferiority of vildagliptin to TZDs for the difference in change in HbA(1c) from baseline [established if the upper limit of the two-sided 95% confidence intervals (CI) did not exceed 0.4%].

RESULTS

Mean (+/- s.e.) change in HbA(1c) from baseline to study endpoint was -0.68 +/- 0.02% in the vildagliptin group and -0.57 +/- 0.03% in the TZD group. The difference between groups was -0.11% (95% CI: -0.17% and -0.04%), establishing the non-inferiority of vildagliptin (p = 0.001) after 3 months of treatment. Vildagliptin was non-inferior to TZDs for subgroups of race, age and body mass index. Body weight increased in the TZD group (0.33 +/- 0.11 kg) and decreased in the vildagliptin group (mean: -0.58 +/- 0.09 kg; p < 0.001 for difference). Adverse events occurred in similar proportions of patients in both groups (vildagliptin: 39.5% and TZD: 36.3%) Hypoglycaemia and abnormal changes in liver enzymes were uncommon.

CONCLUSIONS

This short-term study suggests that vildagliptin is as effective as TZDs after 3-month treatment as an add-on to metformin in a primary care population that included diverse patient subgroups.

Multiple drug targets in the management of type 2 diabetes

Diabetes mellitus (DM) is being diagnosed at an alarming rate around the world. More than 90% of the estimated 200 million affected persons with diabetes worldwide have type 2 DM, an often clinically silent disorder. In the United States, nearly half of the estimated 16 million persons with diabetes remain undiagnosed. Type 2 diabetes is preceded by a long period of impaired glucose tolerance (IGT), a potentially reversible metabolic state associated with increased risk for macrovascular complications. At the time of diagnosis more than one-third of patients have already developed long-term complications of diabetes. Genetic and acquired factors contribute to the pathogenesis of type 2 diabetes. The pathophysiological hallmarks consist of progressive insulin resistance, pancreatic beta-cell dysfunction, and excessive hepatic glucose production. The ideal treatment for type 2 diabetes should correct insulin resistance, beta-cell dysfunction, and normalize hepatic glucose output, as well as prevent, delay, or reverse diabetic complications. Emerging targets for therapy of type 2 diabetes include inhibition of gluconeogenesis, lipolysis, and fatty acid oxidation, as well as stimulation of beta3-adrenergic receptors. Drug intervention for obesity is a legitimate adjunct to diabetes management. Additional drug targets include interventions to prevent or delay the progression of specific complications. Finally, primary prevention of type 2 diabetes is an important emerging strategy. The specific pharmacological agents acting at the various targets are discussed in this review. A targeted approach to the multiple underlying pathophysiologic processes offers the best chance of controlling diabetes and complications.

Human leptin regulation and promise in pharmacotherapy

In rodents leptin inhibits food intake, stimulates energy expenditure, reverses obesity, ameliorates insulin resistance, and accelerates sexual maturation. These potent and diverse effects have stimulated interest in exploring a role for leptin in the treatment of human metabolic disorders. However, the significance of leptin in human (patho)physiology is still being investigated. The present review summarizes current knowledge of leptin regulation, provides a critical assessment of initial experience with leptin therapy, and discusses potential targets for recombinant leptin therapy in humans. The results of numerous studies indicate that leptin is indeed a regulated human hormone: The physiological factors that influence leptin secretion include gender, adiposity, physical exercise, feeding, and caloric restriction. Several hormones, including insulin, glucocorticoids, estradiol, growth hormone, testosterone, somatostatin, and insulin-like growth factor-I also modulate leptin secretion. The results of initial trials of leptin therapy in humans have become available. Treatment with recombinant human leptin (0.028 mg/kg) induced a progressive weight loss (without evidence of tachyphylaxis) in a morbidly obese patient with congenital leptin deficiency. The weight loss averaged 1-2 kg/month, was associated with preservation of lean muscle mass, and was almost exclusively accounted for by depletion of body fat. Administration ofrecombinant leptin (0.01-0.3 mg/kg) also resultedin a dose-dependentweight loss among lean and obese humans with presumably normal leptin genotype. Thus leptin may have a therapeutic role in humans, but its physiological functions and regulation first need to be fully unravelled.

Physiological responses during hypoglycaemia induced by regular human insulin or a novel human analogue, insulin glargine

AIM

Glargine, a product of recombinant technology, has different structural and physicochemical properties compared with native human insulin. We determined whether such differences are associated with alterations in the responses to hypoglycaemia induced by glargine.

METHODS

Nineteen adults (six healthy and 13 with type 1 diabetes) underwent a 5-h hyperinsulinaemic (2 mU/kg/min(-1)) stepped hypoglycaemic clamps (hourly targets of 4.7, 4.2, 3.6, 3.1 and 2.5 mmol/l, respectively) on two occasions using intravenous infusion of regular human insulin or glargine, in random sequence. Hypoglycaemic symptoms, counter-regulatory hormones and glucose disposal rates were assessed at intervals throughout the clamps. A 1-week 'wash out' period was observed between studies.

RESULTS

The peak total symptoms scores (mean +/- s.e.m.) at nadir blood glucose (2.5 mmol/1) were 18.83 +/- 2.68 (healthy) and 17.46 +/- 3.62 (diabetic) during regular insulin, and 18.50 +/- 3.20 (healthy) and 19.08 +/- 3.83 (diabetic) during glargine infusion. The peak epinephrine levels during hypoglycaemia were 767.8 +/- 140.4 pg/ml (regular insulin) and 608.8 +/- 129.9 pg/ml (glargine) among healthy subjects, and 332.5 +/- 54.8 pg/ml (regular insulin) and 321.8 +/- 67.4 pg/ml (glargine) in diabetic patients. Diabetic patients had blunted glucagon responses during hypoglycaemia with either insulin. Both insulins also elicited similar rates of glucose disposal.

CONCLUSIONS

We conclude that insulin glargine and regular human insulin elicit comparable symptomatic and counter-regulatory hormonal responses during hypoglycaemia in healthy or diabetic subjects, and induce similar rates of glucose disposal. Since glargine is designed for subcutaneous (s.c.) use, it is possible (though unlikely) that our findings obtained using an intravenous protocol could differ from responses to hypoglycaemia induced by the s.c. route.

Impaired leptin response to glucocorticoid as a chronic complication of diabetes

Leptin has anorectic, anti-obesity, and insulin-sensitizing properties. We recently reported subnormal responses to the leptin secretagogue dexamethasone in diabetes (DM). To determine whether this defect precedes or follows the occurrence of diabetes, we have studied 37 adults: 11 with type 2 DM diagnosed within 6 months prior to study, 16 with chronic (> or =20 years) DM, and 10 healthy controls. After baseline measurements, subjects ingested dexamethasone (4 mg), followed by blood sampling 16 and 40 h later. Nadir plasma cortisol levels (<2.5 mg/dl) occurred 16 h after dexamethasone ingestion in all study groups; this period of maximal biological action of dexamethasone was associated with peak plasma leptin levels. The peak dexamethasone-stimulated plasma leptin responses (% baseline, +/-SEM) were 188+/-18.7% among healthy controls, 180+/-13.8% among new DM patients, and 127+/-10.5% (P<0.01) in chronic DM patients. Following dexamethasone ingestion, plasma glucose remained stable in the control and new DM groups but increased by 240% in the chronic DM patients; in contrast, plasma insulin increased significantly in controls and new DM patients but not in patients with chronic DM. These results indicate that plasma leptin responses to secretagogue are preserved in newly diagnosed diabetes patients but markedly attenuated in patients with long-standing diabetes, who also were unable to augment insulin secretion during glucocorticoid treatment. Thus, defective glucocorticoid augmentation of plasma leptin, probably related to beta-cell failure, may be a novel chronic complication of diabetes. Theoretically, such a defect could contribute to the obesity and insulin resistance associated with diabetes.

Hormonal regulation of human leptin in vivo: effects of hydrocortisone and insulin

OBJECTIVE

To investigate the effects of continuous i.v. infusion of hydrocortisone or insulin on leptin secretion in humans.

SUBJECTS

Six, nonfasting healthy adults (four women, two men), aged (mean +/- s.e.m.) 36.6 +/- 1.7 y; body mass index (BMI) 27.6 +/- 0.9 kg/m2.

DESIGN

Randomized, placebo-controlled, cross-over study, with a 2-week 'wash-out' period.

INTERVENTIONS

Intravenous infusion of hydrocortisone (3.3 microg/(kg min)), insulin (1 mU/(kg min)) or normal saline (placebo) for 24 h.

MEASUREMENTS

Blood sampling every 1-2 h for measurement of glucose, insulin, cortisol and leptin; subcutaneous abdominal fat biopsy for determination of leptin mRNA expression.

RESULTS

Plasma cortisol increased to 50.0 +/- 0.4 microg/dl during hydrocortisone infusion, but was unaltered during saline or insulin infusion. The plasma insulin levels were: 28.5 +/- 4.7 microU/ml (placebo), 40.8 +/- 9.2 microU/ml (hydrocortisone, P=0.214), and 243 +/- 23.0 microU/ml (insulin, P=0.0002). Peak hyperleptinemia occurred after 16h of insulin and 20h of hydrocortisone infusion; peak/baseline plasma leptin levels (ng/ml) were 18.2 +/- 4.2/15.1 +/- 3.3 (placebo, P=0.056), 42.1 +/- 7.0/16.0 +/- 3.8 (hydrocortisone, + 163%, P= 0.008) and 30.2 +/- 4.3/16.6 +/- 2.7 (insulin, +83%, P= 0.024). Adipocyte leptin mRNA increased by 350% after the hydrocortisone infusion.

CONCLUSION

Hydrocortisone, a natural glucocorticoid, induces hyperleptinemia in vivo, with a potency greater than that of insulin. The interaction between glucocorticoids and leptin may be of metabolic significance in humans.

Thyroid function during pregnancy

BACKGROUND

This Case Conference reviews the normal changes in thyroid activity that occur during pregnancy and the proper use of laboratory tests for the diagnosis of thyroid dysfunction in the pregnant patient.

CASE

A woman in the 18th week of pregnancy presented with tachycardia, increased blood pressure, severe vomiting, increased total and free thyroid hormone concentrations, a thyroid-stimulating hormone (TSH) concentration within the reference interval, and an increased human chorionic gonadotropin (hCG) beta-subunit concentration.

ISSUES

During pregnancy, normal thyroid activity undergoes significant changes, including a two- to threefold increase in thyroxine-binding globulin concentrations, a 30-100% increase in total triiodothyronine and thyroxine concentrations, increased serum thyroglobulin, and increased renal iodide clearance. Furthermore, hCG has mild thyroid stimulating activity. Pregnancy produces an overall increase in thyroid activity, which allows the healthy individual to remain in a net euthyroid state. However, both hyper- and hypothyroidism can occur in pregnant patients. In addition, two pregnancy-specific conditions, hyperemesis gravidarum and gestational trophoblastic disease, can lead to clinical hyperthyroidism. The normal changes in thyroid activity and the association of pregnancy with conditions that can cause hyperthyroidism necessitates careful interpretation of thyroid function tests during pregnancy.

CONCLUSION

Assessment of thyroid function during pregnancy should be done with a careful clinical evaluation of the patient's symptoms as well as measurement of TSH and free, not total, thyroid hormones. Measurement of thyroid autoantibodies may also be useful in selected cases to detect maternal Graves disease or Hashimoto thyroiditis and to assess risk of fetal or neonatal consequences of maternal thyroid dysfunction.

Basal and stimulated plasma leptin in diabetic subjects

OBJECTIVE

To determine whether leptin secretion is impaired in diabetes, we compared basal and stimulated plasma leptin levels in diabetic subjects and healthy controls.

RESEARCH METHODS AND PROCEDURES

Blood samples for assay of leptin and other hormones were obtained at baseline in 54 diabetic patients and 65 controls, and 8 hours, 16 hours, and 40 hours following ingestion of dexamethasone (4 mg) in 6 healthy and 12 controls. C-peptide status was defined as "negative" if < or =0.1 ng/mL or "positive" if > or =0.3 ng/mL, in fasting plasma.

RESULTS

Basal plasma leptin levels were 19.7+/-2.2 ng/mL in nondiabetic subjects, 13.4+/-1.5 ng/ml in C-peptide negative (n = 28) and 26.1+/-3.7 ng/mL in C-peptide positive (n = 26, p = 0.001) diabetic patients. Dexamethasone increased leptin levels of controls (n = 6) to 145+/-17% of baseline values at 8 hours (p = 0.03), 224+/-18% at 16 hours (p = 0.01), and 134+/-18% at 40 hours (p=0.05). The corresponding changes were 108+/-13%, 126+/-23%, and 98+/-16% in C-peptide negative (n=6), and 121+/-10%, 144+/-16% (p=0.03), and 147+/-23% (p=0.11) in C-peptide positive (n = 6) diabetic patients, respectively. The peak stimulated leptin levels were lower in the diabetic patients, compared with controls. Plasma insulin increased (p = 0.02) in controls, but not in the diabetic patients, following dexamethasone.

DISCUSSION

Although diabetic patients have normal plasma leptin levels under basal conditions, their leptin responses to glucocorticoid are impaired, probably because of the concomitant insulin secretory defect. A subnormal leptin secretory response could worsen obesity and insulin resistance in diabetes.

Insulin resistance in HIV protease inhibitor-associated diabetes

BACKGROUND

Fasting hyperglycemia has been associated with HIV protease inhibitor (PI) therapy.

OBJECTIVE

To determine whether absolute insulin deficiency or insulin resistance with relative insulin deficiency and an elevated body mass index (BMI) contribute to HIV PI-associated diabetes.

DESIGN

Cross-sectional evaluation.

PATIENTS

8 healthy seronegative men, 10 nondiabetic HIV-positive patients naive to PI, 15 nondiabetic HIV-positive patients receiving PI (BMI = 26 kg/m2), 6 nondiabetic HIV-positive patients receiving PI (BMI = 31 kg/m2), and 8 HIV-positive patients with diabetes receiving PI (BMI = 34 kg/m2). All patients on PI received indinavir.

MEASUREMENTS

Fasting concentrations of glucoregulatory hormones. Direct effects of indinavir (20 microM) on rat pancreatic beta-cell function in vitro.

RESULTS

In hyperglycemic HIV-positive subjects, circulating concentrations of insulin, C-peptide, proinsulin, glucagon, and the proinsulin/insulin ratio were increased when compared with those of the other 4 groups (p < .05). Morning fasting serum cortisol concentrations were not different among the 5 groups. Glutamic acid decarboxylase (GAD) antibody titers were uncommon in all groups. High BMI was not always associated with diabetes. In vitro, indinavir did not inhibit proinsulin to insulin conversion or impair glucose-induced secretion of insulin and C-peptide from rat beta-cells.

CONCLUSIONS

The pathogenesis of HIV PI-associated diabetes involves peripheral insulin resistance with insulin deficiency relative to hyperglucagonemia and a high BMI. Pancreatic beta-cell function was not impaired by indinavir. HIV PI-associated diabetes mirrors that of non-insulin-dependent diabetes mellitus and impaired insulin action in the periphery.

Tumor-Grade Hyperprolactinemia Induced by Multiple Medications in The Setting of Renal Failure

OBJECTIVE

To describe a patient with galactorrhea and severe hyperprolactinemia in whom workup revealed a nontumoral mechanism.

METHODS

We present the medical history of a woman with long-standing diabetes in whom bilateral galactorrhea and hyperprolactinemia developed. In addition, the details of her clinical course and management are reviewed.

RESULTS

A 33-year-old woman with diabetes, end-stage renal disease, and gastroparesis was admitted to the hospital because of intractable nausea and vomiting. Several months before admission, she had been noted to have galactorrhea and irregular menses. Routine medications included captopril, verapamil, furosemide, prochlorperazine, metoclopramide, cisapride, and Ortho-Novum. Laboratory evaluation showed normal thyroid function, increased serum prolactin levels (up to 1,197 ng/mL), and normal findings on magnetic resonance imaging of the pituitary. Electrophoresis of the patient's serum on a protein A Sepharose column showed no evidence of macro-prolactinemia. Orally administered medications were discontinued, and the patient was given total parenteral nutrition. These measures resulted in a decrease of 300 ng/mL in serum prolactin levels in 4 days. The prolactin levels eventually normalized after withdrawal of verapamil, prochlorperazine, and metoclopramide.

CONCLUSION

A modest increase in serum prolactin level often can be produced by a variety of medications, but gross hyperprolactinemia of 200 ng/mL or higher usually raises suspicion of an underlying prolactin-secreting tumor. This case report demonstrates that conventional limits for nontumoral hyperprolactinemia can be exceeded by concurrent exposure to multiple lactotropic medications in the setting of renal failure.

Leptin elimination in hyperleptinaemic peritoneal dialysis patients

BACKGROUND

Elevated plasma concentrations of leptin, a hormone thought to regulate body composition by influencing food intake/metabolic rate, are prevalent in renal failure patients. The mechanism for these increases is not known, but evidence suggests that simple accumulation due to decreased elimination is insufficient explanation.

METHODS

We studied the incidence of hyperleptinaemia in 28 end-stage renal disease patients treated with continuous ambulatory peritoneal dialysis (CAPD), compared with body-mass-index-and sex-matched controls. Results were separated by gender because women have higher leptin concentrations than men. Excretion of leptin and other substances in dialysis fluid was also studied.

RESULTS

Hyperleptinaemia was prevalent in women CAPD subjects, but not in men. Plasma leptin concentrations correlated strongly with the daily excretion of leptin in dialysis fluid. Clearance of leptin in dialysis fluid was greater in men than women CAPD subjects. Single regression analysis found that fasting insulin, glucose content of dialysis fluid, plasma albumin, C-reactive protein, erythropoietin dose, urinary creatinine clearance and plasma beta2-microglobulin were not determinants of plasma leptin concentrations. Stepwise forward multiple regression, examining the dependence of plasma leptin on body mass index, renal creatinine clearance, plasma albumin, daily dialysis fluid glucose load, daily leptin in dialysis fluid, erythropoietin dose and plasma C-reactive protein found only erythropoietin dose as a consistent negative predictor of plasma leptin concentrations.

CONCLUSIONS

The results suggest that hyperleptinaemia of CAPD was due to predisposing loss of renal elimination capacity combined with increased production due to obesity (more prevalent in women subjects of this study) and potentially female gender.

Reproducibility of fasting plasma leptin concentration in lean and obese humans

We determined the reproducibility of plasma leptin levels in 20 healthy subjects (10 men, 10 women; 10 lean, 10 obese) at stable body weight. Blood samples were obtained, after an overnight fast, between 0700 and 0800 on days 1, 2, 3, 4, 5, 12, 19, and 26. Body weights were recorded on the same days. Plasma leptin was measured using a specific radioimmunoassay. The mean +/- SE baseline body weights (kg) were 65.8 +/- 3.6 (lean) and 96.4 +/- 7.1 (obese). The body mass indices (BMI) were 22.9 +/- 2.8 kg/m2 (lean) and 32.7 +/- 2.2 kg/m2 (obese). The mean daily fasting plasma glucose level was 98.7 +/- 3.7 mg/dl. Baseline plasma leptin levels (ng/ml) were 5.3 +/- 0.75 in lean men, 14.9 +/- 4.6 in obese men, 11.2 +/- 2.8 in lean women, and 27.1 +/- 8.4 in obese women. Fasting leptin levels on days 2 to 26 were highly correlated with the baseline levels on day 1 (r2 = 0.9, P<0.0001). Body weights remained within 98%-102% of baseline, whereas intra-individual leptin levels fluctuated between 80% and 120% of baseline values, throughout the 26 days of study. We conclude that fasting plasma leptin levels are reproducible, with a maximum day-to-day variation of approximately 20%, in healthy, free-living, lean and obese persons who maintain a stable body weight.

High-flux dialysis lowers plasma leptin concentration in chronic dialysis patients

Leptin is a protein produced by fat cells and involved in body weight regulation. Plasma leptin is significantly higher in some hemodialysis (HD) patients than in normal controls. We examined the influence of dialyzer membrane biocompatibility and flux on elevated plasma leptin concentrations in hemodialysis patients. Employing a crossover design, leptin and tumor necrosis factor-alpha (TNF-alpha) levels were serially determined in eight chronic dialysis patients. Patients were dialyzed sequentially on low-flux cellulosic (TAF) dialyzers, low-flux (F8) polysulfone, high-flux (F80B) polysulfone, then low-flux polysulfone and cellulosic dialyzers again. Mean leptin concentrations were similar when low-flux polysulfone or cellulosic dialyzers were employed (141.9+/-24.2 microg/L versus 137.8+/-18.4 microg/L, respectively (P=NS). In contrast, leptin fell significantly on the high-flux polysulfone dialyzer (99.4+/-16.2 microg/L) compared with cellulosic (P < 0.005), and low-flux polysulfone dialyzers (P < 0.02). Leptin clearance by the high-flux polysulfone dialyzer was significantly higher than the low-flux dialyzers (50.4+/-21.5 v -9.6+/-10.3 mL/min; P=0.043), but did not account fully for the 30% decline in plasma leptin during the high-flux arm of the study. Concentrations of TNF-alpha were lower when high-flux polysulfone dialyzers were employed, but there was no correlation of individual TNF-alpha levels with leptin concentrations. High-flux dialysis lowers plasma leptin concentrations an average of 30%, but biocompatibility does not influence leptin levels. The decrease in plasma leptin on high-flux dialysis cannot be explained solely by enhanced clearance.

Recombinant human insulin-like growth factor-I (IGF-I) therapy decreases plasma leptin concentration in patients with chronic renal insufficiency

OBJECTIVE

To determine the relationship between plasma leptin and insulin-like growth factor-I (IGF-I) levels in healthy subjects and patients with chronic renal insufficiency at baseline, and during administration of recombinant human IGF-I in the renal impaired patients.

SUBJECTS

20 healthy subjects (six men, 14 women, age: 42.7 +/- 3.2 y) and nine subjects with chronic renal insufficiency (five men, four women, age: 53.6 +/- 3.7 y).

INTERVENTION

Daily s.c. injection of recombinant human IGF-I (50 micrograms/kg) for 24 d.

MEASUREMENTS

Fasting plasma levels of leptin, IGF-I, growth hormone, C-peptide, glucagon and IGF binding proteins by specific radioimmunoassays at baseline in all subjects and serially during IGF-I therapy in the renal impaired subjects.

RESULTS

Baseline leptin levels were correlated with body mass index (BMI, R = 0.72, P = 0.0001) but not IGF-I levels (R = 0.02). During IGF-I therapy, plasma IGF-I levels increased from 128 +/- 17.4 ng/ml at baseline to 250 +/- 36.8 ng/ml on day 3 (P = 0.003) and 323 +/- 61.6 ng/ml on day 24 (P = 0.01), whereas leptin levels declined: 24.4 +/- 10.3 ng/ml (baseline), 19.5 +/- 6.2 ng/ml (day 3, P = 0.028), and 17.2 +/- 4.9 ng/ml (day 24, P = 0.05).

CONCLUSION

Basal plasma leptin and IGF-I levels are not correlated; however, chronic administration of recombinant IGF-I is associated with an early and sustained decrease in plasma leptin levels. IGF-I may have an inhibitory effect on leptin secretion in humans.

Dose-dependent cortisol-induced increases in plasma leptin concentration in healthy humans

BACKGROUND

Leptin is a hormone that regulates fat metabolism and appetite. The secretion of leptin is regulated by adiposity and, in the rodent, by factors such as insulin, beta-adrenergic agonists, and glucocorticoids (GCs). Increased secretion of the endogenous human GC, cortisol, occurs during stress and in disorders such as major depression. Pharmacological GCs can robustly increase plasma leptin concentrations in humans, leading us to hypothesize that cortisol may serve as a physiological regulator of human leptin secretion.

METHODS

A randomized double-blind placebo-controlled comparison of 2 fixed oral dosages of cortisol (40 mg/d and 160 mg/d), given for 4 days to matched groups of healthy subjects (n=47). Low-dose treatment approximated GC output during mild stress, while high-dose treatment approximated GC output during maximal stress, spanning a range of GC secretion relevant to physiological stress.

RESULTS

Cortisol produced dose-dependent and time-dependent increases in plasma leptin concentrations (time x treatment condition x body mass index; F6,123=10.73; P<.001). Initial treatment-induced increases in plasma leptin concentration returned toward baseline values during 4 treatment days, suggesting tolerance to this GC effect in these healthy subjects.

CONCLUSIONS

The results indicate an important role for GCs in the short-term regulation of human leptin secretion. Glucocorticoid-induced increases in leptin secretion suggest a mechanism that may contribute to anorexia and weight loss during stress and disease states such as major depression, if these conditions are associated with sustained increases in plasma leptin concentrations.

Hyperleptinaemia of end-stage renal disease is corrected by renal transplantation

BACKGROUND

Previous studies have reported that patients with end-stage renal disease (ESRD) have elevated plasma leptin concentrations, but the cause and significance of the elevations are unknown. We studied leptin concentrations in 29 adults undergoing renal transplantation, to determine if restoration of renal function reduced leptin concentrations in ESRD.

METHODS

Leptin concentrations were measured by radioimmunoassay in plasma specimens collected within 1 week before transplant, 6 days post-transplant, and 60 days post-transplant.

RESULTS

Mean plasma leptin concentrations were higher in both male and female ESRD patients compared with a control population of similar age and body mass index (BMI), but most of the disparity was due to a minority of patients with grossly elevated concentrations; the majority of ESRD patients had normal or near-normal leptin concentrations after accounting for their adiposity with BMI. Six days after successful renal transplantation, average plasma leptin concentrations decreased to control levels. The grossly elevated pretransplant concentrations in a minority of patients were greatly reduced in relation to BMI, and the reduction persisted to 60 days post-transplant. The decrease in creatinine with transplant did not correlate with the decrease in leptin.

CONCLUSIONS

These results demonstrate that restoration of renal function in ESRD patients reduces hyperleptinaemia, which provides further evidence of a cause/effect relationship between impaired renal function and abnormal leptin metabolism.

Hyperleptinemia in patients with end-stage renal disease undergoing continuous ambulatory peritoneal dialysis

OBJECTIVE

To determine whether the increased plasma leptin levels reported in hemodialyzed patients is a feature of end-stage renal disease or an artifact of hemodialysis, we studied plasma levels in patients treated exclusively by continuous ambulatory peritoneal dialysis (CAPD).

DESIGN

Prospective comparison of end points in CAPD patients and matched healthy subjects.

SETTING

Tertiary care institutional dialysis center.

PARTICIPANTS

Fifty-six healthy subjects, age 50.8 +/- 2.3 years, body mass index (BMI) 27.7 +/- 1.3 kg/m2, recruited through public announcement, and 36 patients with end-stage renal disease, age 51.0 +/- 2.4 yr, BMI 28.2 +/- 1.3 kg/m2, enrolled in a CAPD treatment program.

INTERVENTION

Four exchanges of CAPD per day, using 2.0, 2.5, or 3.0 L of dialysate over a period of 1 - 96 months (median 22 mth).

MAIN OUTCOME MEASURES

The primary outcome measure was plasma leptin concentration. Secondary measures included plasma glucose, insulin, C-peptide, and cortisol concentrations; and residual renal function and dialysis adequacy (Kt/V).

RESULTS

Plasma leptin levels in CAPD patients were 27.1 - 490 ng/mL (women) and 1.3 - 355 ng/mL (men); the levels in healthy subjects were 2.0 - 84.7 ng/mL (women) and 1.8 - 55.4 ng/mL (men). The mean leptin levels were 5-fold higher among CAPD-treated men than control men (49.9 +/- 18.4 vs 9.8 +/- 2.5 ng/mL, p < 0.001) and 7.5-fold higher among CAPD-treated women than control women (220 +/- 28.1 vs 29.3 +/- 3.7 ng/mL, p < 0.0001). Female gender and BMI were the strongest predictors of hyperleptinemia in CAPD patients.

CONCLUSION

These results indicate that hyperleptinemia is a feature of terminal renal failure, not an artifact of hemodialysis.

Whole body leptin kinetics and renal metabolism in vivo

Leptin metabolism was investigated in male Sprague-Dawley rats by use of 125I-labeled leptin plasma kinetic and arteriovenous balance studies. When conscious rats received bolus venous injections of 125I-leptin, intact (precipitable) leptin quickly disappeared from circulation in a biexponential manner during the 2-h experimental period. After substantial delay, most of the injected radioactivity appeared in the urine. The data were described by a two-compartment model, which postulated that plasma leptin exchanged with a nonplasma pool and that all of the tracer cleared from plasma appeared in urine or in a degraded form in plasma. The half-life of leptin was 9.4 +/- 3.0 min, and the leptin production rate was 3.6 +/- 1.2 ng 100 g fat-1.min-1. The left kidney extracted 21 +/- 1.5% of intact arterial 125I-leptin 5 min after femoral venous injection. Endogenous arterial leptin was reduced 21 +/- 8 and 18 +/- 12%, respectively, in simultaneously sampled left and right renal veins. Renal elimination appears to be the major elimination mechanism for leptin in normal rats, and the kinetic studies suggest that uptake of leptin by renal tissue rather than glomerular filtration is the predominant elimination mechanism.

Reversible muscle weakness in patients with vitamin D deficiency

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Robust leptin secretory responses to dexamethasone in obese subjects

Although leptin reverses obesity in rodents, its function and regulation in humans are unknown. Glucocorticoids have been reported to stimulate leptin production in both rodents and humans, but data assessing the effect of obesity on dynamic leptin secretory responses are unavailable. We, therefore, studied 52 lean and obese subjects [20 men and 32 women; aged 19-84 yr; body mass index (BMI) range, 16-47 kg/m2] randomized to treatment with dexamethasone (total dose, 10 mg/4 days) or placebo. Compared with placebo, dexamethasone increased (P = 0.0001) plasma leptin levels by 64-111% above baseline values within 2-4 days. The increases occurred in all ages, showed no sexual dimorphism, and were particularly robust in obese subjects. After dexamethasone treatment, significant interactions were observed between the change in plasma leptin and BMI (P = 0.0001), baseline plasma leptin (P = 0.0006) and plasma dexamethasone levels (P = 0.04), but not age (P = 0.28); an apparent interaction with plasma insulin no longer was significant after controlling for BMI. These results confirm dexamethasone-induced hyperleptinemia in humans and further demonstrate that the response is not defective in obesity.

Pathophysiology of type 2 diabetes and modes of action of therapeutic interventions

At least 90% of the 12 to 15 million persons with diabetes mellitus in the United States, half of whose condition remains undiagnosed, have type 2 diabetes. Type 2 diabetes is preceded by a long period of impaired glucose tolerance, a reversible metabolic state associated with increased prevalence of macrovascular complications. Thus, at the time of diagnosis, long-term complications have developed in almost one fourth of patients. Susceptibility to type 2 diabetes requires genetic (most likely polygenic) and acquired factors, and its pathogenesis involves an interplay of progressive insulin resistance and beta-cell failure. The ideal treatment of type 2 diabetes should reverse insulin resistance and beta-cell dysfunction in most treated patients and prevent, delay, or reverse long-term complications. Current strategies are aimed at amelioration of insulin resistance (diet, exercise, weight loss, and metformin and troglitazone therapy), augmentation of insulin supply (sulfonylurea and insulin therapy), or limitation of postprandial hyperglycemia (acarbose therapy). Future therapies probably will target (1) insulin resistance, using a multifaceted approach; (2) hepatic glucose production, using gluconeogenesis inhibitors; (3) excess nonesterified fatty acid production, using lipolysis inhibitors; and (4) fat oxidation, using carnitine palmitoyltransferase I and II inhibitors. Attempts also could be made to stimulate energy expenditure and increase nonoxidative glucose disposal by means of beta 3-adrenoceptor agonists. One promising strategy is an attack on multiple pathophysiological processes by combining antidiabetic agents with disparate mechanisms of action. Thus, we now have unprecedented resources for drug therapy for diabetes, with great opportunity for innovative combinations. It is hoped that these expanded choices will provide the tools necessary for a more efficient management of type 2 diabetes and prevention of its long-term complications.

Augmentation of bone mineral density in hirsute women

Hirsutism is associated with both hyperandrogenism and oligomenorrhea or amenorrhea, which have opposing effects on bone mineral density (BMD). We tested the hypothesis that hyperandrogenism in hirsute women counteracts the osteopenic effects of menstrual dysfunction. Using dual energy x-ray absorptiometry, we measured BMD and total bone mineral content (BMC) in 32 young women referred for hirsutism. The control group consisted of 25 matched, nonhirsute women. Among the hirsute women, 21 reported regular menses, and 11 gave a history of oligomenorrhea; all members of the control group reported regular menses. Compared with controls, hirsute women had higher total BMD (1.202 +/- 0.02 vs. 1.116 +/- 0.02 g/cm2, P < 0.01), lumbar spine BMD (1.183 +/- 0.02 vs. 1.125 +/- 0.02 g/cm2, P < 0.01), and total BMC (2700 +/- 66 vs. 2400 +/- 70 g, P < 0.001). Serum total testosterone levels were similar, but androstenedione levels were higher (11.7 +/- 0.80 vs. 7.9 +/- 0.79 nmol/L, P < 0.005) and sex hormone binding globulin levels lower (22.0 +/- 3.0 vs. 57.6 +/- 8.5 nmol/L, P < 0.001) in hirsute women than controls. Oligomenorrheic hirsute women had higher BMD than nonhirsute women, although the augmentation was less pronounced than in eumenorrheic hirsute women. These results indicate that hirsutism is associated with higher bone density and mineral content, consistent with a net positive effect of hyperandrogenism on skeletal mass.

Increased plasma leptin concentration in end-stage renal disease

Leptin is a 16-kDa protein recently identified as the obese gene product involved in body weight regulation. Administration of recombinant leptin to ob/ob mice, which have a genetic defect in leptin production, reduces food intake and increases energy expenditure. Leptin is synthesized by fat cells, and in normal humans, plasma concentrations are proportional to adiposity. The physiological actions and the degradation pathways of leptin in humans are unknown. We investigated renal elimination of leptin by comparing plasma leptin concentrations in end-stage renal disease (ESRD) patients with normal controls. Our hypothesis was that if renal filtration is a significant route of elimination, the hormone would accumulate in ESRD patients. Mean plasma levels in 141 ESRD patients (26.8 +/- 5.7 and 38.3 +/- 5.6 micrograms/L for males and females, respectively) were significantly higher (P < 0.001) than mean values obtained in normal controls (11.9 +/- 3.1 and 21.2 +/- 3.0 micrograms/L for males and females, respectively). Leptin concentrations in ESRD patients correlated directly with body mass index (BMI; r = 0.77 for men and 0.78 for women). The rate of increase in leptin concentrations with BMI was significantly greater in ESRD patients (5.5 and 6.6 micrograms/L/U BMI for men and women, respectively) than in normal controls (1.4 and 2.6 micrograms/L/U for men and women, respectively). Pre- and postdialysis leptin levels in hemodialysis patients were similar. Western blot of plasma from ESRD patients with high leptin levels showed bands corresponding to the intact protein (16 kDa) with no lesser or greater molecular mass species observed. Leptin concentrations in patients with ESRD did not correlate with measures of residual renal function (serum creatinine, beta 2-microglobulin, PTH, or GH levels). Similarly, we found no correlation between leptin levels and the number of years patients had been on dialysis or with recent weight changes. We conclude that intact leptin is increased in ESRD patients, but does not appear to cause decreased weight. As leptin levels did not correlate with residual renal function, increased production may account for the high levels observed.

Plasma leptin and insulin relationships in obese and nonobese humans

Hyperinsulinemia. is associated with an overexpression of mRNA for the ob protein leptin in rodent models of genetic obesity, and insulin has been reported to directly stimulate leptin mRNA in rat adipocytes. Human obesity is also associated with increased leptin mRNA as well as plasma levels, but there have been no reports of the effect of insulin on leptin secretion. We, therefore, tested the hypothesis that insulin stimulates leptin secretion in humans. Using a newly developed leptin assay, immunoreactive leptin was measured in fasting and postprandial plasma samples from 27 healthy adults and in samples before and during euglycemic-hyperinsulinemic then stepped hypoglycemic (hourly steps at 85, 75, 65, 55, and 45 mg/dl) clamps from 10 healthy subjects and 11 patients with IDDM. Plasma leptin was correlated (r = 0.84, P = 0.0005) with BMI in obese but not nonobese subjects and with fasting (r = 0.75, P = 0.008) but not postprandial plasma insulin levels. (Leptin levels did not change postprandially.) Euglycemic hyperinsulinemia did not alter leptin levels, nor did hyperinsulinemic hypoglycemia. Thus, because circulating leptin levels are not increased during postprandial hyperinsulinemia or during euglycemic (or hypoglycemic) hyperinsulinemia, we conclude that, at least in the short term, insulin does not increase leptin secretion in humans and that hyperleptinemia in obese individuals is not likely the result of hyperinsulinemia.

Memory improvement following induced hyperinsulinemia in Alzheimer's disease

Dementia of the Alzheimer type (DAT) is accompanied by disruption in glucose regulation and utilization that may contribute to its characteristic memory impairment. Increasing glucose availability by raising plasma glucose improves memory in patients with DAT. Such memory improvement is associated with a secondary elevation in plasma insulin levels, raising the question of whether improvement is due to changes in insulin levels, independent of hyperglycemia. Distributions of insulin receptors in the hippocampus and insulin-mediated increases in glucose utilization in entorhinal cortex provide potential mechanisms for such improvement. We show that raising plasma insulin through intravenous infusion while keeping plasma glucose at a fasting baseline level produces striking memory enhancement for patients with DAT. Previous findings of hyperglycemic memory enhancement were also replicated. Patients with DAT also showed abnormal plasma levels of glucoregulatory hormones and metabolites at baseline and during metabolic manipulations. Our findings suggest that neuroendocrine factors play an important role in the pathophysiology of DAT.

Cerebral transport and metabolism of 1-11C-D-glucose during stepped hypoglycemia

Attempts to measure blood-to-brain glucose transport and cerebral glucose metabolism with 11C-glucose have been hampered by methods that require jugular venous sampling or do not adequately account for the efflux of labeled metabolites from the brain. We performed eight positron emission tomography studies with 1-11C-D-glucose in macaques at arterial plasma glucose concentrations of 8.43 to 1.51 mumol ml-1 (152-27 mg dl-1) using a model that includes a fourth rate constant to account for regional egress of all 11C-metabolites. Values for blood-to-brain glucose influx, cerebral glucose metabolism, and brain free glucose concentration agreed closely with values obtained in mammals by other investigators. Values for net extraction fraction corresponded closely to simultaneously measured arteriovenous values. We demonstrated that utilization of a model that includes a fourth rate constant to account for regional egress of all 11C-metabolites with positron emission tomography and 1-11C-D-glucose provides accurate measurements of blood-to-brain glucose transport and cerebral glucose metabolism in vivo without need for jugular venous sampling, even under conditions of severe hypoglycemia.

Salivary epidermal growth factor concentration in thyrotoxicosis

Epidermal growth factor (EGF) was first isolated from the mouse submaxillary gland, and later from human urine. The synthesis of mouse EGF is stimulated by thyroid hormone and inhibited by antithyroid therapy. EGF in turn stimulates the growth of thyroid cells. The objective of the present study was to determine whether salivary EGF levels are affected by thyroid hormone level in man. Unstimulated saliva was obtained from 13 (1 male, 12 females) untreated thyrotoxic patients (age 19-64 yr) and from 21 (2 males, 19 females) healthy controls (age 19-68 yr). After centrifugation at 1000 x g, the supernatants were assayed for human (h) EGF in a homologous radioimmunoassay. The mean +/- SEM concentration of hEGF was 0.42 +/- 0.05 nmol/L in controls compared with 0.71 +/- 0.25 nmol/L in thyrotoxic patients (p > 0.05). Thyrotoxic patients with goiter secreted significantly higher concentrations of hEGF (0.92 +/- 0.24 nmol/L) in saliva than did euthyroid controls or nongoitrous thyrotoxic patients (0.31 +/- 0.11 nmol/L, p < 0.01).

A new understanding of goitrogenesis: role of cytokines in the regulation of normal and aberrant thyroid growth

Several cytokines and growth factors together with their binding proteins and/or receptors are being increasingly detected in mammalian thyroid tissue. These include epidermal growth factor, insulin-like growth factors, transforming growth factors, fibroblast growth factor, interleukins, interferons, and tumour necrosis factor-alpha. Their exact role in relation to thyroid regulation has not been fully elucidated but it is clear that many of these peptide regulatory factors are mitogenic for cultured thyrocytes. Recent evidence suggests that some thyroid cancers and benign goiters over-express receptors for a number of these growth factors. Transforming growth factor-beta is unique for its dominant anti-proliferative effect on thyrocytes concurrently exposed to potent thyroid mitogens. The mammalian thyroid cell is clearly a source as well as target of myriad polypeptide factors that probably co-regulate its normal growth and differentiation. Aberrant expression of these growth factors or their receptors might be a factor in the development of goiter.

Reversal of hypoglycemia unawareness, but not defective glucose counterregulation, in IDDM

To test the hypothesis that the neuroendocrine (including autonomic) responses to hypoglycemia are dissociated from the symptomatic responses to hypoglycemia in insulin-dependent diabetes mellitus (IDDM) patients with hypoglycemia awareness and during reversal of hypoglycemia unawareness in IDDM, we used the hyperinsulinemic stepped hypoglycemic (5.0, 4.4, 3.9, 3.3, 2.8, and 2.2 mmol/l) clamp technique to quantitate these responses in nondiabetic control subjects and IDDM patients with hypoglycemia awareness and with hypoglycemia unawareness. The latter were restudied after 3 days, 3-4 weeks, and 3 months of scrupulous avoidance of iatrogenic hypoglycemia. At baseline, symptom responses were virtually nil in unaware patients (P = 0.0001 vs. nondiabetic); these were increased in aware patients (P = 0.0183 vs. nondiabetic). In contrast, several neuroendocrine responses were comparably reduced in both unaware and aware patients: epinephrine (P = 0.0222 and 0.0156), pancreatic polypeptide (P = 0.0004 and 0.0003), glucagon (P = 0.0112 and 0.0109), and cortisol (P = 0.0214 and 0.0450). In initially unaware patients, symptom responses increased (P = 0.0001) during avoidance of hypoglycemia. Demonstrable after 3 days, these were entirely normal after 3-4 weeks and 3 months. In contrast, none of the neuroendocrine responses increased. Thus, we conclude that several neuroendocrine responses to hypoglycemia (including the adrenomedullary and parasympathetic components of the autonomic response) can be dissociated from symptomatic responses in IDDM patients with hypoglycemia awareness and during reversal of hypoglycemia unawareness in IDDM. Avoidance of iatrogenic hypoglycemia sufficient to reverse the clinical syndrome of hypoglycemia unawareness did not reverse the key elements (deficient glucagon and epinephrine responses) of the clinical syndrome of defective glucose counterregulation. This implies that the mechanisms of hypoglycemia unawareness and of defective glucose counterregulation are, at least in part, different in IDDM.

Dietary iodine affects epidermal growth factor levels in mouse thyroid and submaxillary glands

To determine whether dietary iodine intake affects the levels of immunoreactive epidermal growth factor (EGF) in vivo in two mouse tissues known to be thyroid hormone responsive, 24 adult BALB/c mice were randomized into groups of six animals and fed a) an iodine-deficient diet, b) normal laboratory chow (controls), c) an iodine-deficient diet with high physiological iodine supplementation (approximately 300 micrograms/day), and d) an iodine-deficient diet with pharmacological doses of iodine (approximately 3 mg/day). After 21 days on the various regimens, the mice were killed and the concentration of mouse (m) EGF in the thyroid and submaxillary glands (SMG) measured by radioimmunoassay. The mean (+/- SEM) SMG mEGF level (micrograms/mg wet weight) in the different groups were: a) 7.58 +/- 1.87, b) 12.46 +/- 4.7, c) 19.79 +/- 4.47, and d) 24.36 +/- 5.96. The thyroid mEGF concentrations (ng/mg wet weight) were: a) 3.65 +/- 0.75, b) 5.23 +/- 1.84, c) 8.07 +/- 1.18, and d) 6.43 +/- 0.95, respectively. Analysis of variance revealed that dietary iodine status had a significant effect on mEGF levels in both the SMG (p < 0.001) and the thyroid gland (p < 0.001). Compared to controls, tissue mEGF levels decreased by 30-40% in the mice fed an iodine-deficient diet, and increased by 60-150% following physiologic iodine replacement.

Isolation of the human LIM/homeodomain gene islet-1 and identification of a simple sequence repeat polymorphism [corrected]

The islet-1 (Isl-1) gene encodes a protein that binds to the enhancer region of the insulin gene. Isl-1 is a member of the LIM/homeodomain family of transcription factors. Because insulin deficiency, either relative or absolute, is a cardinal feature of non-insulin-dependent diabetes mellitus (NIDDM), this study addressed the question of whether mutations in genes that regulate insulin production could be involved. Rat Isl-1 was the first insulin enhancer binding protein to be isolated, and, in this study, the rat gene was used to isolate a partial human islet Isl-1 cDNA and subsequently to isolate genomic clones. A simple sequence repeat was found in the Isl-1 gene, and polymerase chain reaction amplification of this region of genomic DNA revealed 12 alleles in St. Louis African-Americans (het = 0.87), 14 alleles in black Nigerians (het = 0.89), 8 alleles in Japanese (het = 0.69), and 8 alleles in Caucasians (het = 0.81). Genetic linkage analysis uniquely placed Isl-1 on chromosome 5q (D5S395[12.8 cM]Isl-1 [11.6 cM]D5S407). The simple sequence repeat polymorphism at the Isl-1 locus was used to evaluate mutations in this gene as a possible contributor to the pathogenesis of NIDDM. Allelic frequencies did not differ between patients with NIDDM (n = 165) and nondiabetic control subjects (n = 163) in two black populations (St. Louis African-Americans and Nigerians). Linkage analyses in 15 nonglucokinase maturity-onset diabetes of the young pedigrees indicated that linkage could be rejected (LOD score < -3.0) over a distance of 15 cM.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypoglycemia-induced autonomic failure in IDDM is specific for stimulus of hypoglycemia and is not attributable to prior autonomic activation

We hypothesized, first, that recent antecedent hypoglycemia causes reduced autonomic responses to subsequent hypoglycemia in patients with well-controlled insulin-dependent diabetes mellitus (IDDM) and that the reduced responses are specific for the stimulus of hypoglycemia while the responses to other stimuli are unaltered and, second, that reduced autonomic responses, specifically sympathochromaffin, so-induced are not simply the result of prior activation of the system. To test the first hypothesis, eight patients with IDDM, selected for HbA1c levels < 8.0% and the absence of classic diabetic autonomic neuropathy, were studied twice. On one occasion, clamped hypoglycemia (approximately 2.8 mM) was produced at 1400-1600 on days 2 and 3; on the other occasion clamped euglycemia (approximately 5.6 mM) was produced at those times. On both occasions, autonomic responses to hypoglycemia (approximately 2.8 mM) were determined the morning of day 3 and those to standing, exercise, and a formula meal the morning of day 4. Following afternoon hypoglycemia, 1) the adrenomedullary epinephrine (EPI) response to hypoglycemia was reduced (P = 0.0397) but that to standing, exercise, and a meal were unaltered; 2) the sympathetic neural norepinephrine (NE) response to standing and to exercise was unaltered; and 3) the partially parasympathetic neural-mediated pancreatic polypeptide response to a meal was unaltered. To test the second hypothesis, seven nondiabetic subjects were studied twice, once with cycle exercise (60% peak VO2 x 60 min) and once without exercise 90 min before clamped hypoglycemia (approximately 2.8 mM). Prior exercise had no effect on the EPI, NE, or pancreatic polypeptide responses to hypoglycemia. We conclude, first, that the phenomenon of hypoglycemia-associated autonomic failure can be induced in patients with well-controlled IDDM and is specific for the stimulus of hypoglycemia and, second, that this is not simply the result of prior activation of the system.

Acute and long-term effects of octreotide in patients with ACTH-dependent Cushing's syndrome

PURPOSE

Octreotide is of proven efficacy in the management of patients with acromegaly, thyrotropin-secreting pituitary adenomas, and certain gastrointestinal tumors, but its effect in Cushing's syndrome is less clear.

PATIENTS AND METHODS

We studied 10 patients who presented with adrenocorticotropic hormone (ACTH)-dependent Cushing's syndrome, 3 of whom were previously adrenalectomized. Serum cortisol or ACTH levels were measured before and during the administration of octreotide 50 to 500 micrograms every 8 hours for 24 to 72 hours.

RESULTS

Treatment was effective in four patients: serum cortisol levels decreased to within or below the normal range in Patients 1, 2, and 3, and ACTH levels were substantially lowered in Patient 4, who had previously been adrenalectomized for a metastatic islet cell tumor. These responses were sustained during long-term treatment for 2 to 72 weeks. All four patients showed no evidence of a pituitary tumor on computed tomographic or magnetic resonance imaging and had proven (Patients 3 and 4) or presumed ectopic disease. Of the six patients who did not respond, four had pituitary tumors and two had presumed ectopic ACTH production.

CONCLUSION

We conclude that a short trial of octreotide is warranted in patients with ACTH-dependent Cushing's syndrome who have no demonstrable pituitary tumor. A response to treatment should alert the physician to the possibility of an ectopic ACTH source and will identify patients whose disease may be controllable using octreotide.

Sialoadenectomy increases the concentration of immunoreactive epidermal growth factor in the mouse thyroid gland

The mouse thyroid gland contains significant concentrations of immunoreactive epidermal growth factor (EGF). To determine whether thyroidal EGF represents material obtained from the SMG via the circulation, we have compared EGF concentrations in sialoadenectomized (Sx) and sham-operated (Sh) BALB/c mice 30 days after surgical removal of the SMG. We found that the thyroids of Sx male and female mice had a significant increase in EGF concentration. The mean thyroidal EGF concentration (ng/mg wet weight) was 3.67 +/- 0.58 for Sx males, 1.53 +/- 0.47 for Sh males (p less than 0.02), 3.03 +/- 0.64 for Sx females, and 1.08 +/- 0.54 for Sh females (p less than 0.001), respectively. Thus EGF found in the mouse thyroid gland does not appear to arise from the SMG, and the thyroid appears to be an independent source of EGF synthesis.

Testosterone regulates epidermal growth factor levels in the thyroid gland of hypothyroid mice

The effects of testosterone (TP) and thyroxine (T4) on the level of epidermal growth factor (mEGF) in the thyroid were compared in a hypothyroid mouse model. Groups of five adult female BALB/c mice were given a "severe" hypothyroid regimen consisting of an iodine deficient diet together with oral and s.c propylthiouracil (PTU). Sialoadenectomy or sham operation was performed after 18 days on the hypothyroid regimen. The mice convalesced on normal diet for 5 days and beginning from day 23 received either T4, 1 ug/g or 2 ug/g, s.c daily or TP, 0.3 mg or 0.75 mg, i.m. every third day until day 33, while continuing the hypothyroid regimen. Control mice received normal diet and vehicles for the various injections. The mice were killed on day 33 and thyroidal EGF levels determined by radioimmunoassay. The mean+S.E. levels of mEGF in the thyroid were 10.12 +/- 1.75 ng/mg protein (control), 3.82 +/- 0.67 ng/mg (hypothyroid; p < 0.01), 3.07 +/- 1.52 (T4, 1 ug/g; p < 0.02), 2.59 +/- 0.46 ng/mg (T4, 2 ug/g; p < 0.01), 8.58 +/- 2.48 (TP, 0.3 mg), and 9.65 +/- 1.86 (TP, 0.75 mg). Thus thyroidal mEGF levels decreased significantly in all groups except those subsequently treated with testosterone; T4 was ineffective in reversing the tissue depletion of mEGF in this model. These results show that mEGF levels in the thyroid could be depleted by hypothyroidism and may also be androgen responsive.