Robert A. Rizza

Influence of body fat distribution on free fatty acid metabolism in obesity.

UNLABELLED In order to determine whether differences in body fat distribution result in specific abnormalities of free fatty acid (FFA) metabolism, palmitate turnover, a measure of systemic adipose tissue lipolysis, was measured in 10 women with upper body obesity, 9 women with lower body obesity, and 8 nonobese women under overnight postabsorptive (basal), epinephrine stimulated and insulin suppressed conditions. RESULTS Upper body obese women had greater (P less than 0.005) basal palmitate turnover than lower body obese or nonobese women (2.8 +/- 0.2 vs. 2.1 +/- 0.2 vs. 1.8 +/- 0.2 mumol.kg lean body mass (LBM)-1.min-1, respectively), but a reduced (P less than 0.05) net lipolytic response to epinephrine (59 +/- 7 vs. 79 +/- 5 vs. 81 +/- 7 mumol palmitate/kg LBM, respectively). Both types of obesity were associated with impaired suppression of FFA turnover in response to euglycemic hyperinsulinemia compared to nonobese women (P less than 0.005). These specific differences in FFA metabolism may reflect adipocyte heterogeneity, which may in turn affect the metabolic aberrations associated with different types of obesity. These findings emphasize the need to characterize obese subjects before studies.

Meal Simulation Model of the Glucose-Insulin System

A simulation model of the glucose-insulin system in the postprandial state can be useful in several circumstances, including testing of glucose sensors, insulin infusion algorithms and decision support systems for diabetes. Here, we present a new simulation model in normal humans that describes the physiological events that occur after a meal, by employing the quantitative knowledge that has become available in recent years. Model parameters were set to fit the mean data of a large normal subject database that underwent a triple tracer meal protocol which provided quasi-model-independent estimates of major glucose and insulin fluxes, e.g., meal rate of appearance, endogenous glucose production, utilization of glucose, insulin secretion. By decomposing the system into subsystems, we have developed parametric models of each subsystem by using a forcing function strategy. Model results are shown in describing both a single meal and normal daily life (breakfast, lunch, dinner) in normal. The same strategy is also applied on a smaller database for extending the model to type 2 diabetes.

β-Cell Replication Is the Primary Mechanism Subserving the Postnatal Expansion of β-Cell Mass in Humans

OBJECTIVE— Little is known about the capacity, mechanisms, or timing of growth in β-cell mass in humans. We sought to establish if the predominant expansion of β-cell mass in humans occurs in early childhood and if, as in rodents, this coincides with relatively abundant β-cell replication. We also sought to establish if there is a secondary growth in β-cell mass coincident with the accelerated somatic growth in adolescence. RESEARCH DESIGN AND METHODS— To address these questions, pancreas volume was determined from abdominal computer tomographies in 135 children aged 4 weeks to 20 years, and morphometric analyses were performed in human pancreatic tissue obtained at autopsy from 46 children aged 2 weeks to 21 years. RESULTS— We report that 1) β-cell mass expands by severalfold from birth to adulthood, 2) islets grow in size rather than in number during this transition, 3) the relative rate of β-cell growth is highest in infancy and gradually declines thereafter to adulthood with no secondary accelerated growth phase during adolescence, 4) β-cell mass (and presumably growth) is highly variable between individuals, and 5) a high rate of β-cell replication is coincident with the major postnatal expansion of β-cell mass. CONCLUSIONS— These data imply that regulation of β-cell replication during infancy plays a major role in β-cell mass in adult humans.

Intensive Intraoperative Insulin Therapy versus Conventional Glucose Management during Cardiac Surgery: A Randomized Trial

Context Intensive insulin therapy used to maintain normoglycemia during intensive care after cardiac surgery improves perioperative outcomes. Its effect during cardiac surgery is unknown. Contributions The authors randomly assigned 400 cardiac surgical patients to tight glycemic control (blood glucose level, 4.4 to 5.6 mmol/L [80 to 100 mg/dL]) during surgery or usual intraoperative care. All patients received tight glycemic control in the cardiac intensive care unit. The groups had the same risk for perioperative adverse events (risk ratio, 1.0 [95% CI, 0.8 to 1.2]). The intensive treatment group had more strokes (8 vs. 1) and more deaths (4 vs. 0) than the conventional treatment group. Caution The authors performed the study at a single center. Implications Maintaining normoglycemia during cardiac surgery does not improve outcomes and might worsen them. The Editors Hyperglycemia occurs frequently in patients with and without diabetes during cardiac surgery, especially during cardiopulmonary bypass surgery (1, 2). In a study by Van den Berghe and colleagues (3), intensive insulin therapy after surgery reduced morbidity and death in critically ill patients, most of whom underwent cardiac surgery. As a result, professional organizations have recommended rigorous glycemic control in hospitalized patients (4) and strict glycemic control is now routine practice during the postoperative period in cardiac surgical patients. However, no consensus exists on the optimal management of intraoperative hyperglycemia in cardiac surgical patients because of the lack of evidence from randomized trials. Researchers are increasingly extrapolating evidence from studies that assess the role of strict postoperative glycemic control in critically ill patients to advocate for intravenous insulin therapy for patients in the operating room (3, 57). Evidence, strictly from observational studies, suggests that tight intraoperative glycemic control may reduce postoperative complications (810). We recently reported, in a retrospective, observational study of 409 cardiac surgical patients, that intraoperative hyperglycemia was an independent risk factor for perioperative complications, including death, after adjustment for postoperative glucose concentrations. Each 1.1-mmol/L (20 mg/dL) increase in glucose concentration greater than 5.6 mmol/L (>100 mg/dL) during surgery was associated with a 34% increase in the likelihood of postoperative complications (8). An association between intraoperative hyperglycemia and adverse outcomes based on observational studies does not prove causality. Because hyperglycemia can adversely affect immunity, wound healing, and vascular function, the concept that normoglycemia be maintained during the relatively brief duration of cardiac surgery seems plausible (1116). On the other hand, the degree of intraoperative hyperglycemia may merely reflect the severity of underlying stress. If so, prevention of hyperglycemia might not reduce perioperative complications, and the risks and costs of intensive intraoperative glycemic management may outweigh the benefits. Simple, safe, and effective insulin infusion algorithms that achieve rigorous intraoperative glycemic control are lacking. To address these questions, we conducted a randomized, controlled trial at 1 center to determine whether maintenance of near normoglycemia during cardiac surgery by using intraoperative intravenous insulin infusion reduced perioperative death and morbidity when added to rigorous postoperative glycemic control. Methods Design Overview This was a randomized, open-label, controlled trial with blinded assessment. We randomly assigned patients to receive intensive insulin therapy to maintain intraoperative glucose levels between 4.4 (80 mg/dL) and 5.6 mmol/L (100 mg/dL) or conventional treatment. By design, both groups were postoperatively treated with strict glycemic control to ensure that the observed difference in outcome could be attributed to the effects of intraoperative glycemic control. Setting We performed the study at St. Marys Hospital, Rochester, Minnesota, which is a tertiary care teaching hospital with 1157 beds and an average of more than 41000 admissions per year. Participants Adults undergoing elective cardiac surgery between July 2004 and April 2005 were eligible for enrollment in our study. We excluded patients who had off-pump cardiopulmonary bypass procedures. The Mayo Foundation Institutional Review Board, Rochester, Minnesota, approved the protocol. Randomization and Interventions Before we enrolled patients in our randomized trial, we enrolled 20 patients in a 2-week pilot trial to ensure that the anesthesiologists in the operating room and the nursing staff in the intensive care units (ICUs) had adequate experience with the study insulin infusion algorithm. The 20 patients received intensive insulin therapy during surgery and for 24 hours after surgery. The pilot period data allowed us to modify the graded insulin infusion to achieve desired glucose concentration goals. We built safety features into our infusion protocol to minimize hypoglycemia. We discontinued the infusion when glucose levels were less than 4.4 mmol/L (<80 mg/dL) and initiated dextrose infusion. When glucose levels decreased to less than 3.3 mmol/L (<60 mg/dL), we treated hypoglycemia according to a standardized hypoglycemia protocol. Per protocol, patients treated in the pilot phase were not included in the analyzed cohort. Study coordinators obtained written informed consent from all patients who met eligibility criteria. We randomly assigned patients to receive intensive or conventional intraoperative insulin therapy. Randomization was computer-generated with permuted blocks of 4, with stratification according to surgeon, surgical procedure (coronary artery bypass grafting [CABG] with or without other procedures and no CABG), and diabetes. The randomization assignments were concealed in opaque, sealed, tamper-proof envelopes that were opened sequentially by study personnel after participants signed the patient consent form. We could not possibly know, before obtaining consent, the few patients who would not have intraoperative hyperglycemia (glucose concentration of 5.6 mmol/L or more [100 mg/dL]). Therefore, per protocol, patients who gave consent were randomly assigned, and those whose glucose levels were less than 5.6 mmol/L (<100 mg/dL) during surgery were not included in the final analyses. Intraoperative Period Intensive Treatment Patients in the intensive treatment group received a continuous intravenous insulin infusion, 250 units of NovoLin R (Novo Nordisk, Princeton, New Jersey) in 250 mL of 0.45% sodium chloride, when their blood glucose levels exceeded 5.6 mmol/L (>100 mg/dL). We adjusted the infusions to maintain blood glucose levels between 4.4 (80 mg/dL) and 5.6 mmol/L (100 mg/dL). We adjusted the dose according to a standardized algorithm used by anesthesiologists (Appendix Table 1). Appendix Table 1. Insulin Infusion Protocol* Conventional Treatment Patients in the conventional treatment group did not receive insulin during surgery unless their glucose levels exceeded 11.1 mmol/L (200 mg/dL). If glucose concentration was between 11.1 (200 mg/dL) and 13.9 mmol/L (250 mg/dL), patients received an intravenous bolus of 4 units insulin every hour until the glucose concentration was less than 11.1 mmol/L (<200 mg/dL). If the intraoperative glucose concentration was greater than 13.9 mmol/L (>250 mg/dL), patients received an intravenous infusion of insulin that was continued until the glucose level was less than 8.3 mmol/L (<150 mg/dL). In both study groups, we measured arterial plasma glucose concentration every 30 minutes, starting just before anesthetic induction by using hexokinase method on a Double P Modular System (Roche Diagnostics, Indianapolis, Indiana). Intraoperative procedures, including cardiopulmonary bypass, monitoring, laboratory testing, and treatment, were left to the discretion of anesthesiologists and cardiac surgeons. There was no standard protocol for monitoring and managing intraoperative potassium levels. Postoperative Period Intravenous insulin infusion was started in patients in the conventional treatment group on their arrival in the ICU. Thereafter, both study groups were treated identically, with the intravenous insulin infusion rates adjusted by a nursing staff that was not involved with the study according to a standard protocol. The target blood glucose range was 4.4 (80 mg/dL) to 5.6 mmol/L (100 mg/dL) (Appendix Table 1). Arterial blood glucose levels were measured every 1 to 2 hours by using the Accu-Check Inform blood glucose monitoring system (glucometer) (Roche Diagnostics). During the first 24 hours after surgery, patients were given only clear liquids by mouth; we did not administer subcutaneous insulin or oral diabetic medications during this time. Thereafter, the hospital diabetes consulting service saw all patients and provided individualized recommendations for ongoing care. Outcomes and Measurements The primary outcome variable was a composite of death, sternal wound infections, prolonged pulmonary ventilation, cardiac arrhythmias (new-onset atrial fibrillation, heart block requiring permanent pacemaker, or cardiac arrest), stroke, and acute renal failure within 30 days after surgery. Secondary outcome measures were length of stay in the ICU and hospital. Trained study personnel identified the occurrence of a complication through chart abstraction by using confirmable, objective criteria in accordance with standardized definitions from the Society of Thoracic Surgeons (STS) database committee (17). Personnel who assessed outcomes were not aware of patient treatment assignment or of the study hypothesis. Follow-up Procedures We contacted patients by telephone and used a standardized telephone survey at 30 days after surgery to assess outcomes that occurred after discharge. We considered pat

Intraoperative Hyperglycemia and Perioperative Outcomes in Cardiac Surgery Patients

OBJECTIVE To estimate the magnitude of association between intraoperative hyperglycemia and perioperative outcomes in patients who underwent cardiac surgery. PATIENTS AND METHODS We conducted a retrospective observational study of consecutive adult patients who underwent cardiac surgery between June 10, 2002, and August 30, 2002, at the Mayo Clinic, a tertiary care center in Rochester, Minn. The primary independent variable was the mean intraoperative glucose concentration. The primary end point was a composite of death and infectious (sternal wound, urinary tract, sepsis), neurologic (stroke, coma, delirium), renal (acute renal failure), cardiac (new-onset atrial fibrillation, heart block, cardiac arrest), and pulmonary (prolonged pulmonary ventilation, pneumonia) complications developing within 30 days after cardiac surgery. RESULTS Among 409 patients who underwent cardiac surgery, those experiencing a primary end point were more likely to be male and older, have diabetes mellitus, undergo coronary artery bypass grafting, and receive insulin during surgery (P< or =.05 for all comparisons). Atrial fibrillation (n=105), prolonged pulmonary ventilation (n=53), delirium (n=22), and urinary tract infection (n=16) were the most common complications. The initial, mean, and maximal intraoperative glucose concentrations were significantly higher in patients experiencing the primary end point (P<.01 for all comparisons). In multivariable analyses, mean and maximal glucose levels remained significantly associated with outcomes after adjusting for potentially confounding variables, including postoperative glucose concentration. Logistic regression analyses indicated that a 20-mg/dL increase in the mean intraoperative glucose level was associated with an increase of more than 30% in outcomes (adjusted odds ratio, 1.34; 95% confidence Interval, 1.10-1.62). CONCLUSION Intraoperative hyperglycemia is an independent risk factor for complications, including death, after cardiac surgery.

Sustained beta cell apoptosis in patients with long-standing type 1 diabetes: indirect evidence for islet regeneration?

Aims/hypothesisType 1 diabetes is widely held to result from an irreversible loss of insulin-secreting beta cells. However, insulin secretion is detectable in some people with long-standing type 1 diabetes, indicating either a small population of surviving beta cells or continued renewal of beta cells subject to ongoing autoimmune destruction. The aim of the present study was to evaluate these possibilities.Materials and methodsPancreatic sections from 42 individuals with type 1 diabetes and 14 non-diabetic individuals were evaluated for the presence of beta cells, beta cell apoptosis and replication, T lymphocytes and macrophages. The presence and extent of periductal fibrosis was also quantified.ResultsBeta cells were identified in 88% of individuals with type 1 diabetes. The number of beta cells was unrelated to duration of disease (range 4–67 years) or age at death (range 14–77 years), but was higher (p<0.05) in individuals with lower mean blood glucose. Beta cell apoptosis was twice as frequent in type 1 diabetes as in control subjects (p<0.001), but beta cell replication was rare in both groups. The increased beta cell apoptosis in type 1 diabetes was accompanied by both increased macrophages and T lymphocytes and a marked increase in periductal fibrosis (p<0.001), implying chronic inflammation over many years, consistent with an ongoing supply of beta cells.Conclusions/interpretationMost people with long-standing type 1 diabetes have beta cells that continue to be destroyed. The mechanisms underlying increased beta cell death may involve both ongoing autoimmunity and glucose toxicity. The presence of beta cells despite ongoing apoptosis implies, by definition, that concomitant new beta cell formation must be occurring, even after long-standing type 1 diabetes. We conclude that type 1 diabetes may be reversed by targeted inhibition of beta cell destruction.

Effects of Growth Hormone on Insulin Action in Man: Mechanisms of Insulin Resistance, Impaired Suppression of Glucose Production, and Impaired Stimulation of Glucose Utilization

The present studies were undertaken to assess the mechanisms responsible for growth hormone-induced insulin resistance in man. The insulin dose-response characteristics for suppression of glucose production and stimulation of glucose utilization and their relationship to monocyte insulin binding were determined in six normal volunteers after 12-h infusion of growth hormone and 12-h infusion of saline. The infusion of growth hormone (2 μg · kg−1 · h−1) increased plasma growth hormone nearly threefold (to ≃9 ng/ml) within the range observed during sleep and exercise. This increased plasma insulin (14 ± 1 versus 8 ± 1 μU/ml, P < 0.005) concentrations without significantly altering plasma glucose concentrations or basal rates of glucose production and utilization. Insulin dose-response curves for both suppression of glucose production (half-maximal response at 37 ± 3 versus 20 ± 3 μu/ml, P < 0.01) and stimulation of glucose utilization (half-maximal response at 98 ± 8 versus 52 ± 8 μU/ml, P / 0.01) were shifted to the right with preservation of normal maximal responses to insulin. Monocyte insulin binding was unaffected. Thus, except at near maximal insulin receptor occupancy, the action of insulin on glucose production and utilization per number of monocyte insulin receptors occupied was decreased. These results indicate that increases in plasma growth hormone within the physiologic range can cause insulin resistance in man, which is due to decreases in both hepatic and extrahepatic effects of insulin. Assuming that insulin binding to monocytes reflects insulin binding in insulin sensitive tissues, this decrease in insulin action can be explained on the basis of a postreceptor defect.

Role of Glucagon, Catecholamines, and Growth Hormone in Human Glucose Counterregulation: EFFECTS OF SOMATOSTATIN AND COMBINED α- AND β-ADRENERGIC BLOCKADE ON PLASMA GLUCOSE RECOVERY AND GLUCOSE FLUX RATES AFTER INSULIN-INDUCED HYPOGLYCEMIA

To further characterize mechanisms of glucose counterregulation in man, the effects of pharmacologically inducd deficiencies of glucagon, growth hormone, and catecholamines (alone and in combination) on recovery of plasma glucose from insulin-induced hypoglycemia and attendant changes in isotopically ([3-(3)H]glucose) determined glucose fluxes were studied in 13 normal subjects. In control studies, recovery of plasma glucose from hypoglycemia was primarily due to a compensatory increase in glucose production; the temporal relationship of glucagon, epinephrine, cortisol, and growth hormone responses with the compensatory increase in glucose appearance was compatible with potential participation of all these hormones in acute glucose counterregulation. Infusion of somatostatin (combined deficiency of glucagon and growth hormone) accentuated insulin-induced hypoglycemia (plasma glucose nadir: 36+/-2 ng/dl during infusion of somatostatin vs. 47+/-2 mg/dl in control studies, P < 0.01) and impaired restoration of normoglycemia (plasma glucose at min 90: 73+/-3 mg/dl at end of somatostatin infusion vs. 92+/-3 mg/dl in control studies, P<0.01). This impaired recovery of plasma glucose was due to blunting of the compensatory increase in glucose appearance since glucose disappearance was not augmented, and was attributable to suppression of glucagon secretion rather than growth hormone secretion since these effects of somatostatin were not observed during simultaneous infusion of somatostatin and glucagon whereas infusion of growth hormone along with somatostatin did not prevent the effect of somatostatin. The attenuated recovery of plasma glucose from hypoglycemia observed during somatostatin-induced glucagon deficiency was associated with plasma epinephrine levels twice those observed in control studies. Infusion of phentolamine plus propranolol (combined alpha-and beta-adrenergic blockade) had no effect on plasma glucose or glucose fluxes after insulin administration. However, infusion of somatostatin along with both phentolamine and propranolol further impaired recovery of plasma glucose from hypoglycemia compared to that observed with somatostatin alone (plasma glucose at end of infusions: 52+/-6 mg/dl for somatostatin-phentolamine-propranolol vs. 72+/-5 mg/dl for somatostatin alone, P < 0.01); this was due to further suppression of the compensatory increase in glucose appearance (maximal values: 1.93+/-0.41 mg/kg per min for somatostatin-phentolamine-propranolol vs. 2.86+/-0.32 mg/kg per min for somatostatin alone, P < 0.05). These results indicate that in man (a) restoration of normoglycemia after insulin-induced hypoglycemia is primarily due to a compensatory increase in glucose production; (b) intact glucagon secretion, but not growth hormone secretion, is necessary for normal glucose counterregulation, and (c) adrenergic mechanisms do not normally play an essential role in this process but become critical to recovery from hypoglycemia when glucagon secretion is impaired.

High Expression Rates of Human Islet Amyloid Polypeptide Induce Endoplasmic Reticulum Stress–Mediated β-Cell Apoptosis, a Characteristic of Humans With Type 2 but Not Type 1 Diabetes

OBJECTIVE—Endoplasmic reticulum (ER) stress–induced apoptosis may be a common cause of cell attrition in diseases characterized by misfolding and oligomerisation of amyloidogenic proteins. The islet in type 2 diabetes is characterized by islet amyloid derived from islet amyloid polypeptide (IAPP) and increased β-cell apoptosis. We questioned the following: 1) whether IAPP-induced β-cell apoptosis is mediated by ER stress and 2) whether β-cells in type 2 diabetes are characterized by ER stress. RESEARCH DESIGN AND METHODS—The mechanism of IAPP-induced apoptosis was investigated in INS-1 cells and human IAPP (HIP) transgenic rats. ER stress in humans was investigated by β-cell C/EBP homologous protein (CHOP) expression in 7 lean nondiabetic, 12 obese nondiabetic, and 14 obese type 2 diabetic human pancreata obtained at autopsy. To assure specificity for type 2 diabetes, we also examined pancreata from eight cases of type 1 diabetes. RESULTS—IAPP induces β-cell apoptosis by ER stress in INS-1 cells and HIP rats. Perinuclear CHOP was rare in lean nondiabetic (2.6 ± 2.0%) and more frequent in obese nondiabetic (14.6 ± 3.0%) and obese diabetic (18.5 ± 3.6%) pancreata. Nuclear CHOP was not detected in lean nondiabetic and rare in obese nondiabetic (0.08 ± 0.04%) but six times higher (P < 0.01) in obese diabetic (0.49 ± 0.17%) pancreata. In type 1 diabetic pancreata, perinuclear CHOP was rare (2.5 ± 2.3%) and nuclear CHOP not detected. CONCLUSIONS—ER stress is a mechanism by which IAPP induces β-cell apoptosis and is characteristic of β-cells in humans with type 2 diabetes but not type 1 diabetes. These findings are consistent with a role of protein misfolding in β-cell apoptosis in type 2 diabetes.

Adrenergic Mechanisms for the Effects of Epinephrine on Glucose Production and Clearance in Man

THE PRESENT STUDIES WERE UNDERTAKEN TO ASSESS THE ADRENERGIC MECHANISMS BY WHICH EPINEPHRINE STIMULATES GLUCOSE PRODUCTION AND SUPPRESSES GLUCOSE CLEARANCE IN MAN: epinephrine (50 ng/kg per min) was infused for 180 min alone and during either alpha (phentolamine) or beta (propranolol)-adrenergic blockade in normal subjects under conditions in which plasma insulin, glucagon, and glucose were maintained at comparable levels by infusion of somatostatin (100 mug/h), insulin (0.2 mU/kg per min), and variable amounts of glucose. In additional experiments, to control for the effects of the hyperglycemia caused by epinephrine, variable amounts of glucose without epinephrine were infused along with somatostatin and insulin to produce hyperglycemia comparable with that observed during infusion of epinephrine. This glucose infusion suppressed glucose production from basal rates of 1.8+/-0.1 to 0.0+/-0.1 mg/kg per min (P < 0.01), but did not alter glucose clearance. During infusion of epinephrine, glucose production increased transiently from a basal rate of 1.8+/-0.1 to a maximum of 3.0+/-0.2 mg/kg per min (P < 0.01) at min 30, and returned to near basal rates at min 180 (1.9+/-0.1 mg/kg per min). Glucose clearance decreased from a basal rate of 2.0+/-0.1 to 1.5+/-0.2 ml/kg per min at the end of the epinephrine infusion (P < 0.01). Infusion of phentolamine did not alter these effects of epinephrine on glucose production and clearance. In contrast, infusion of propranolol completely prevented the suppression of glucose clearance by epinephrine, and inhibited the stimulation of glucose production by epinephrine by 80+/-6% (P < 0.001). These results indicate that, under conditions in which plasma glucose, insulin, and glucagon are maintained constant, epinephrine stimulates glucose production and inhibits glucose clearance in man predominantly by beta adrenergic mechanisms.