Margaret T. Behme

Glucagon-Like Peptide I Reduces Postprandial Glycemic Excursions in IDDM

Effects of human glucagon-like peptide I (GLP-I)(7–36)amide were examined in volunteers having insulin-dependent diabetes mellitus (IDDM) with residual C-peptide (CP) secretion (n = 8, 7 men and 1 woman; age, 31 ± 1.4 years; body mass index, 24.7 ± 0.7 kg/m2; duration of diabetes, 3.2 ± 0.8 years; insulin dose, 0.41 ± 0.05 U · kg−1· day−1; meal-stimulated CP, 1.0 ± 0.2 nmol/l [means ± SE]). After a mixed meal (Sustacal, 30 kJ/kg body wt), intravenous injection of GLP-I, 1.2 pmol · kg−1 · min−1 through 120 min, virtually abolished increments of plasma glucose, CP, pancreatic polypeptide (PP), and glucagon concentrations, with no significant effect on plasma gastrin levels during the infusions. At reduced dosage (0.75 pmol · kg−1 · min−1), GLP-I had lesser effects on plasma glucose and CP levels. On cessation of intravenous GLP-I infusions after the meals, plasma glucose, CP, PP, and glucagon concentrations rebounded toward control levels by 180 min, and the response of plasma gastrin was prolonged. These rebound responses are consistent with intestinal delivery of food retained in the stomach on escape from inhibition of gastric emptying by GLP-I. Infusion of 1.2 pmol · kg−1 · min−1 GLP-I with 20 g glucose (10% dextrose in water) injected intravenously over 60 min enhanced plasma responses of immunoreactive CP; the mean incremental areas under concentration curves (0–60 min) increased sixfold, but the glycemic excursion was not affected. Thus, in CP-positive IDDM, pharmacological doses of GLP-I reduce glycemic excursions after meals by a mechanism(s) not dependent on stimulation of insulin secretion, presumably involving delayed gastric emptying. This effect of the peptide on blood glucose levels after meals may have therapeutic implications in both IDDM and non-insulin-dependent diabetes.

Dietary fish oil enhances insulin sensitivity in miniature pigs

The effects of dietary fish oil, MaxEPA, and corn oil on insulin sensitivity were examined in male miniature pigs. The pigs (20-35 kg) received 750 g of nonpurified diet per day (160 g/kg protein, 50 g/kg fat) with the addition of either 30 g corn oil or 30 g MaxEPA, resulting in 90 g total fat per kg diet for 4-5 wk. The MaxEPA diet provided 12.6 g (n-3) polyunsaturated fatty acids per kg diet (6.7 g eicosapentaenoic acid, 4.8 g docosahexaenoic acid), 4.7 g (n-3) polyunsaturated fatty acids and 147 mg cholesterol. The corn oil diet provided 22.7 g (n-6) polyunsaturated fatty acids per kg diet and no (n-3) polyunsaturated fatty acids; cholesterol was added to equal the amount in the MaxEPA. After overnight withdrawal of food, intravenous glucose tolerance tests were conducted in conscious pigs by using previously placed jugular vein catheters. Plasma glucose responses and the areas under the plasma glucose curves were similar in seven MaxEPA- and five corn oil-fed pigs. However, the incremental areas under the insulin curves were significantly lower for the pigs fed MaxEPA. Thus values for insulin sensitivity (SI), determined with Bergmans minimal model, were significantly higher for MaxEPA than for corn oil-fed pigs, whereas the rate of glucose disappearance (KG), did not differ between the two groups. Therefore, substitution of (n-3) for (n-6) polyunsaturated fatty acids in dietary lipids is associated with enhanced insulin sensitivity in male pigs.

Subcutaneous Glucagon-Like Peptide I Combined With Insulin Normalizes Postcibal Glycemic Excursions in IDDM

OBJECTIVE To determine whether a subcutaneous injection of truncated glucagon-like peptide 1 (tGLP-I)(7–36) amide that delays gastric emptying transiently can prevent postcibal hyperglycemia in IDDM without causing hypoglycemia when administered with insulin. RESEARCH DESIGN AND METHODS The postcibal increase in plasma human pancreatic polypeptide (HPP) was used as a presumptive indicator of arrival of nutrient in the small intestine. Studies in seven normal human volunteers established the dose of tGLP-I that delayed the postcibal rise in HPP by 30 min. This dose was tested in six patients with IDDM with a range of residual endogenous insulin secretion. The patients received a standard liquid test meal with or without subcutaneous tGLP-I and their usual dose of regular insulin before the meal. Blood samples collected at timed intervals were assayed for plasma concentrations of glucose, C-peptide (CP), immunoreactive insulin (IR1), HPP, and glucagon (GLN). RESULTS In normal subjects after administration of tGLP-I, postcibal plasma glucose concentration at 20 min fell below fasting levels in a dose-dependent manner. At 10 and 20 min, transient increments in plasma CP and IRI, and decrements in GLN, occurred. Subsequently, through 60 min, the excursions of plasma HPP, CP, and IRI were negatively correlated to the dose of tGLP-I. In subjects with IDDM, the selected dose of tGLP-I given with insulin before the meal delayed the plasma HPP response for 30 min and confined excursions of plasma glucose within the range observed in normal subjects receiving saline injections, whereas administration of insulin with saline injections in IDDM was followed by supranormal increases of plasma glucose. In IDDM, this dose of subcutaneous tGLP-I had no effect on plasma CP, IRI, or GLN. CONCLUSIONS In normal subjects, transient hypoglycemia after injections of tGLP-I with a meal was associated with transient stimulation of insulin secretion and inhibition of glucagon secretion. These actions together with delayed gastric emptying may account for the hypoglycemia, but other unidentified mechanisms cannot be excluded. In the subjects with IDDM, the selected relatively low dose of tGLP-I delayed excursions of plasma HPP as in normal subjects, but did not reduce the plasma glucose below the fasting level and had no effect on plasma CP, IRI, or GLN. However, injection of tGLP-I reduced the postcibal glycemic excursion and confined it within the normal range. Thus, in IDDM, a pharmacological dose of subcutaneous tGLP-I that presumably delays gastric emptying by ∼30 min can normalize glycemic excursions after a meal when given in combination with insulin. Because this cannot be achieved with regular insulin alone without risk of hypoglycemia, this combination of glucoregulatory peptides has therapeutic potential in insulin-requiring diabetes.

Insulin Resistance in Latent Autoimmune Diabetes of Adulthood

Abstract: Insulin resistance in patients with latent autoimmune diabetes of adulthood (LADA) was determined by homeostasis model assessment (HOMA). LADA was identified by a clinical phenotype of type 2 diabetes with antibodies to GAD65 and/or IA‐2/ICA512. All patients were managed with insulin therapy. Insulin resistance in LADA was lower than in antibody‐negative type 2 diabetes, higher than in normal humans and in recent‐onset type 1 diabetes, and similar to that in long‐term type 1 diabetes. Mean values for HOMA varied linearly with mean values for BMI, which accounted for much of the insulin resistance in these forms of diabetes. LADA resembles long‐term type 1 diabetes with respect to insulin resistance and BMI, but occurs at an older age.

A DNA-dependent ATPase from E.coli infected with bacteriophage T4

A DNA-dependent ATPase has been purified from E.coli infected with bacteriophage T4. The enzyme has a low molecular weight and is not detectable in uninfected E.coli. In the presence of DNA, ATP is cleaved to ADP and inorganic phosphate. Calf thymus DNA, E.coli DNA and heat-denatured T4 and T7 bacteriophage DNAs stimulate the ATPase. However, native T4 and T7 DNAs do not activate the enzyme. In addition to ATP breakdown, the enzyme catalyzes dATP and, to a lesser extent, CTP degradation to their respective diphosphates. No exo- or endonucleolytic activity has been detected. The role of DNA in the reaction is currently under investigation.

Pathways of DNA repair in T4 phage. I. Methyl methanesulfonate sensitive mutant.

Abstract A new T4 phage mutant with increased sensitivity to methyl methanesulfonate (MMS) and ultraviolet (UV) irradiation is described. From a study of the relationship of this mutant to other DNA repair mutants, we have speculated on the pathways of repair of MMS-and UV-damaged T4 phage.

Insulin Resistance Prevented by Portal Delivery of Insulin in Rats With Renal Subcapsular Islet Grafts

We determined the metabolic effects of insulin derived from renal subcapsular islet grafts, either with systemic delivery of insulin through renal venous drainage (REN) or with portal delivery of insulin after renal vein–to–superior mesenteric vein anastomosis (RMA), in streptozotocin-induced diabetic Lewis rats, in comparison with normal rats. After gavage glucose, the plasma glucose responses were similar to normal in REN and RMA rats; however, hyperinsulinemia occurred in REN rats (area under the concentration curves [AUCs] of insulin, 27 ± 3 nmol · l−1 · min) in comparison with RMA (14 ± 2) and normal rats (19 ± 2), P < 0.003, with no difference in C-peptide responses. The ratio of AUC C-peptide to AUC insulin was lower in REN (2.0 ± 0.2) than in RMA (3.4 ± 0.3) and normal animals (3.2 ± 0.3), P < 0.0005. In euglycemic-hyperinsulinemic clamp studies using the same insulin infusion rate (10 pmol · kg−1 · min−1), insulin resistance was found in REN animals (mean glucose infusion rate [GIR], REN: 7.5 ± 1.2; RMA: 12.0 ± 1.2; normal: 12.7 ± 1.0 mg · kg−1 · min−1; P < 0.008), with higher steady-state insulin levels in REN (554 ± 63 pmol/l) than in RMA (291 ± 26) and normal rats (269 ± 60), P < 0.0001. With matching steady-state insulin levels in RMA and REN rats during infusion of insulin at 20 pmol · kg−1 · min−1 in RMA rats (steady-state insulin 623 ± 64 pmol/l), GIR was 15.7 ± 0.7 mg · kg−1 · min−1. Thus, systemic delivery of insulin from islet grafts is associated with hyperinsulinemia, insulin resistance, and decreased metabolic clearance of insulin. These abnormalities are prevented by portal delivery of insulin from islet grafts in the same site. The findings are consistent with the hypothesis that portal delivery of insulin is important in maintenance of normal whole-body insulin sensitivity.

Hepatic extraction of insulin after stimulation of secretion with oral glucose or parenteral nutrients.

To determine whether hepatic extraction of insulin differs when glucose is administered by parenteral and physiological routes, we studied responses to oral glucose and to intravenous (IV) infusion of glucose or glucose plus arginine in normal volunteers. As in earlier studies, when IV glucose infusions were empirically programmed to to produce isoglycemic responses with 50 or 75 g oral glucose, ratios of integrated areas under concentration curves for immunoreactive C-peptide (CP) to insulin in the plasma were higher with IV than with oral glucose. Mean values +/- standard errors for these ratios in paired experiments with 50 g oral glucose were 5.6 +/- 0.66 compared with 8.3 +/- 1.4 with IV glucose (P < .03). With 75 g oral glucose, the corresponding values were 4.3 +/- 0.38 and 7.8 +/- 0.50 (P < .001). These results suggest that hepatic extraction of insulin is diminished when insulin secretion is potentiated by enteroinsular mechanisms after oral glucose administration. To determine whether this phenomenon is related to the route of administration of glucose or to the enhancement of insulin secretion with oral glucose, programmed IV infusions of glucose were used to elicit excursions of plasma CP similar to those obtained after 50 g oral glucose, and programmed infusions of glucose plus arginine were used to elicit excursions of plasma CP similar to those obtained after 75 g oral glucose. Plasma levels of immunoreactive gastric inhibitory polypeptide (GIP) increased substantially after ingestion of 75 g glucose, but did not change during isoglycemic IV glucose infusions or during IV infusions of glucose plus arginine.(ABSTRACT TRUNCATED AT 250 WORDS)

Rats with portal-caval vein transposition show hyperinsulinemia and insulin resistance.

To compare the metabolic effects of portal and systemic delivery of insulin, we used portal-caval transposition (PCT) in rats to provide total systemic diversion of splanchnic venous blood. PCT rats exhibited normal weight gain, liver histology, liver-function tests, glycosylated hemoglobin, arterial blood pressure, and hepatic blood flow. Mean liver weight relative to body weight was 12% lower in PCT rats than in sham-operated control (CTR) rats 30 days following transposition. Indwelling venous catheters were established to facilitate metabolic studies in conscious, minimally restrained animals. Postabsorptive plasma glucose and C-peptide (CPEP) levels were similar in PCT and CTR rats; however, postabsorptive immunoreactive insulin (IRI) levels were elevated in PCT rats (67 +/- 3.1 v 49 +/- 3.5 pmol.L-1, P < .002, n = 11 v 11), as were postabsorptive plasma glucagon levels (570 +/- 67 v 240 +/- 11 ng.L-1, P < .001, n = 11 v 16) at similar body weights. The postabsorptive CPEP/IRI concentration ratio was lower in PCT than in CTR rats (4.0 +/- 0.3 v 6.0 +/- 0.6, P < .02), suggesting reduced hepatic extraction of insulin. Insulin sensitivity (IS), determined by minimal model analysis of frequently sampled intravenous glucose tolerance tests yielding the sensitivity index (SI), was reduced in PCT compared with CTR (61 +/- 5.6 v 86 +/- 9.0 (mumol.L-1)-1.min-1, P < .04, n = 9 v 10). During euglycemic-hyperinsulinemic clamps, glucose infusion rates (GIRs) from 60 to 120 minutes were lower in PCT than in CTR rats (6.0 +/- 0.3 v 8.0 +/- 0.4 g.kg-1.min-1, P < .002, n = 9 v 7) with matching plasma IRI levels, confirming the reduced IS in PCT rats. Areas under the concentration curves ([AUCs] 0 to 150 minutes) for glucose tolerance tests (gavage) indicated that plasma glucose excursion was similar in PCT and CTR rats whereas AUC IRI was significantly higher in PCT than in CTR rats (23 +/- 1.3 v 18 +/- 0.6 nmol.L-1.min, P < .009, n = 11 v 11). However, AUC CPEP for oral glucose tolerance tests was lower in PCT than in CTR rats (55 +/- 3.4 v 68 +/- 4.8 nmol.L-1.min, P < .05), indicating decreased insulin secretion. Thus, the mean ratio AUC CPEP/AUC IRI was significantly lower in PCT rats (2.5 +/- 0.2 v 3.8 +/- 0.3, P < .002), again suggesting reduced hepatic extraction of insulin. Thus, euglycemia after PCT was accompanied by elevated postabsorptive and glucose-stimulated levels of IRI in systemic blood, postabsorptive hyperglucagonemia, and decreased insulin secretion in response to glucose challenge (gavage), with diminished hepatic extraction of insulin and decreased IS. The PCT model illustrates the insulin-resistant adaptive state that results from systemic delivery of insulin, and indicates the importance of hepatic portal delivery of insulin and possibly of other gastroenteropancreatic hormones in the maintenance of IS and physiological metabolic control.

Continued Insulin Dependence Despite Normal Range Insulin Sensitivity and Insulin Connecting Peptide Levels in a Kidney/Islet Transplant Patient

OBJECTIVE The majority of islet transplant recipients remain insulin-requiring, although many have near-normal connecting peptide (CP) levels. Insulin resistance may be one possible cause of the continuing need for exogenous insulin in islet transplant recipients. To assess this, we have studied the insulin sensitivity index (S1) in one patient with near-normal CP levels after islet transplant who remained insulin-requiring. RESEARCH DESIGN AND METHODS The islet transplant recipient is a 36-year-old woman with no residual CP who received a kidney transplant, followed 7 days later by an islet transplant. The islets were infused into the liver via the umbilical vein. Induction immunosuppression consisted of OKT3, prednisone, cyclosporin A, and azathioprine, with maintenance on the latter three. RESULTS Maximum CP levels after a standardized Sustacal meal were 2.09, 1.18, 0.85, and 0.81 nmol/l at 1,6,18, and 24 months posttransplant, respectively. Insulin requirements at the same times were 0.27, 0.45, 0.49, and 0.62 U·kg−1·d−1, while S1 was 36.3, 53.3, and 13.2 min −1·nmol−1·ml at 6,18, and 24 months, respectively. This compares with S1 values of 43.3 ± 10.0 min−1·nmol−1·ml for normal subjects. CONCLUSIONS This patient had near-normal S1 and CP levels, but she was unable to discontinue insulin therapy, suggesting that other factors are critical. Despite this, she maintained normal or near-normal glycated hemoglobins, indicating metabolic benefit from the islet transplant.