Auto- and alloimmune reactivity to human islet allografts transplanted into type 1 diabetic patients.
(1/1227)
Allogeneic islet transplantation can restore an insulin-independent state in C-peptide-negative type 1 diabetic patients. We recently reported three cases of surviving islet allografts that were implanted in type 1 diabetic patients under maintenance immune suppression for a previous kidney graft. The present study compares islet graft-specific cellular auto- and alloreactivity in peripheral blood from those three recipients and from four patients with failing islet allografts measured over a period of 6 months after portal islet implantation. The three cases that remained C-peptide-positive for >1 year exhibited no signs of alloreactivity, and their autoreactivity to islet autoantigens was only marginally increased. In contrast, rapid failure (<3 weeks) in three other cases was accompanied by increases in precursor frequencies of graft-specific alloreactive T-cells; in one of them, the alloreactivity was preceded by a sharply increased autoreactivity to several islet autoantigens. One recipient had a delayed loss of islet graft function (33 weeks); he did not exhibit signs of graft-specific alloimmunity, but developed a delayed increase in autoreactivity. The parallel between metabolic outcome of human beta-cell allografts and cellular auto- and alloreactivity in peripheral blood suggests a causal relationship. The present study therefore demonstrates that T-cell reactivities in peripheral blood can be used to monitor immune mechanisms, which influence survival of beta-cell allografts in diabetic patients. (+info)
Prolonged elevation of plasma free fatty acids desensitizes the insulin secretory response to glucose in vivo in rats.
(2/1227)
Prolonged exposure of pancreatic islets to free fatty acids (FFAs) inhibits glucose-stimulated insulin secretion (GSIS) in vitro. However, FFA inhibition of GSIS has not been clearly demonstrated in vivo. We examined the in vivo effect of prolonged elevation of plasma FFAs on GSIS using a two-step hyperglycemic clamp in rats treated with a 48-h intravenous infusion of either 20% Intralipid plus heparin (INT) (5 microl/min plus heparin, 0.1 U/min; n = 8), oleate (OLE) (1.3 microEq/min; n = 6), saline (SAL) (n = 6), or bovine serum albumin (BSA) (vehicle for OLE; n = 5). Because there was no difference in any of the parameters between BSA and SAL rats, these groups were combined as control rats (CONT) (n = 11). At the end of the 48-h OLE/INT/CONT infusions, after an overnight fast, plasma glucose was clamped for 2 h at 13 mmol/l and for another 2 h at 22 mmol/l. Preclamp plasma FFAs were elevated twofold (P < 0.01) versus CONT with both INT and OLE (NS, INT vs. OLE). Preclamp glucose, insulin, and C-peptide levels were higher in INT than in CONT rats (P < 0.05), suggesting insulin resistance, but they were not different in OLE and CONT rats. The insulin and C-peptide responses to the rise in plasma glucose from basal to 13 mmol/l were lower in OLE (336 +/- 72 pmol/l and 1.2 +/- 0.1 nmol/l, P < 0.01 and P < 0.05, respectively) than in CONT (552 +/- 54 and 1.9 +/- 0.1) rats, but they were not different between CONT and INT rats (648 +/- 150 and 2.0 +/- 0.4). The insulin and C-peptide responses to the rise in plasma glucose from 13 to 22 mmol/l were lower in both INT (1,188 +/- 204 pmol/l and 3.0 +/- 0.3 nmol/l, P < 0.01 and P < 0.001) and OLE (432 +/- 60 and 1.7 +/- 0.2, P < 0.001 vs. CONT or INT) rats than in CONT rats (1,662 +/- 174 and 5.0 +/- 0.6). In summary, 1) both INT and OLE decreased GSIS in vivo in rats, and 2) the impairing effect of INT on GSIS was less than that of OLE, which might be due to the different type of fatty acid (mostly polyunsaturated in INT versus monounsaturated as OLE) and/or to differential effects of INT and OLE on insulin sensitivity. In conclusion, prolonged elevation of plasma FFAs can desensitize the insulin secretory response to glucose in vivo, thus inducing a beta-cell defect that is similar to that found in type 2 diabetes. (+info)
Resistance to insulin's acute direct hepatic effect in suppressing steady-state glucose production in individuals with type 2 diabetes.
(3/1227)
We and others have shown that insulin acutely suppresses glucose production in fasting nondiabetic humans and dogs, by both a direct hepatic effect and an indirect (extrahepatic) effect, and in diabetic dogs by an indirect effect alone. In type 2 diabetes, there is resistance to insulin's ability to suppress hepatic glucose production, but it has not previously been determined whether the resistance is primarily at the level of the hepatocyte or the peripheral tissues. To determine whether the diabetic state reduces the direct effect of insulin in humans, we studied nine patients with untreated type 2 diabetes who underwent three studies each, 4-6 weeks apart. 1) Portal study (POR): intravenous tolbutamide was infused for 3 h with calculation of pancreatic insulin secretion from peripheral plasma C-peptide. 2) Peripheral study (PER): equidose insulin was infused by peripheral vein. 3) Half-dose peripheral insulin study (1/2 PER): matched peripheral insulin levels with study 1. In all studies, glucose was clamped at euglycemia, glucose turnover was measured with the constant specific activity method, and 3-[3H]glucose was purified by high-performance liquid chromatography. Peripheral insulin was lower in POR versus PER but slightly higher in POR versus 1/2 PER, although most of the difference could be accounted for by higher proinsulin levels in POR (stimulated by tolbutamide). Calculated portal insulin was approximately 1.3-fold higher in POR versus PER and approximately 2.2-fold higher in POR versus 1/2 PER. In the final 30 min of the clamp, glucose production reached a lower steady-state level in PER than in POR (4.0 +/- 0.4 vs. 5.3 +/- 0.5 pmol(-1) x kg(-1) x min(-1), P < 0.05), despite the higher hepatic insulin level in POR. In contrast with our studies in nondiabetic individuals, glucose production was not more suppressed at steady state in POR versus 1/2 PER (5.3 +/- 0.4 micromol x kg(-1) x min(-1)), despite much higher hepatic insulin levels in POR. In conclusion, this is the first study in patients with type 2 diabetes to characterize insulin resistance to the acute direct suppressive effect of insulin on hepatic glucose production. (+info)
Effects of fatty acids and ketone bodies on basal insulin secretion in type 2 diabetes.
(4/1227)
The objective of this study was to assess the role of free fatty acids (FFAs) as insulin secretagogues in patients with type 2 diabetes. To this end, basal insulin secretion rates (ISR) in response to acute increases in plasma FFAs were evaluated in patients with type 2 diabetes and in age- and weight-matched nondiabetic control subjects during 1) intravenous infusion of lipid plus heparin (L/H), which stimulated intravascular lipolysis, and 2) the FFA rebound, which followed lowering of plasma FFAs with nicotinic acid (NA) and was a consequence of increased lipolysis from the subject's own adipose tissue. At comparable euglycemia, diabetic patients had similar ISR but higher plasma beta-hydroxybutyrate (beta-OHB) levels during L/H infusion and higher plasma FFA and beta-OHB levels during the FFA rebound than nondiabetic control subjects. Correlating ISR with plasma FFA plus beta-OHB levels showed that in response to the same changes in FFA plus beta-OHB levels, diabetic patients secreted approximately 30% less insulin than nondiabetic control subjects. In addition, twice as much insulin was secreted during L/H infusion as during the FFA rebound in response to the same FFA/beta-OHB stimulation by both diabetic patients and control subjects. Glycerol, which was present in the infused lipid (272 mmol/l) did not affect ISR. We concluded that 1) assessment of FFA effects on ISR requires consideration of effects on ISR by ketone bodies; 2) ISR responses to FFA/beta-OHB were defective in patients with type 2 diabetes (partial beta-cell lipid blindness), but this defect was compensated by elevated plasma levels of FFAs and ketone bodies; and 3) approximately two times more insulin was released per unit change in plasma FFA plus beta-OHB during L/H infusion than during the FFA rebound after NA. The reason for this remains to be explored. (+info)
Within- and between-subject variation in commonly measured anthropometric and biochemical variables.
(5/1227)
BACKGROUND: The biological variation of some commonly assessed metabolic variables in healthy subjects has not been studied extensively. The aim of the study was to assess, in 12 healthy subjects (6 male and 6 female; mean (SD) age; 22.7 (1.5) years) following an overnight fast, the day-to-day variation of body fat (impedance method), triglycerides, nonesterified fatty acid (NEFAs), glycerol, 3-hydroxybutyrate (3-OHB), lactate, glucose, insulin (RIA), C-peptide, and glucagon on 12 consecutive days. METHODS: Between- and within-subject coefficients of variation (CVG and CVW) were estimated using a random effects analysis of variance, and assay variation was subtracted to give the coefficient of within-subject biological variation (CVI). Individuality indices were calculated as CVW/CVG. RESULTS: The overall means, CVI, and individuality indices were as follows: for body fat, 24.2%, 10%, and 0.3; for triglycerides, 0.61 mmol/L, 21%, and 1.1; for NEFAs, 376 micromol/L, 45%, and 1.4; for glycerol, 48 micromol/L, 36%, and 0.8; for 3-OHB, 43 micromol/L, 61%, and 1.5; for lactate, 0.88 mmol/L, 31%, and 1.1; for glucose, 4.9 mmol/L, 4.8%, and 0.7; for insulin, 52 pmol/L, 26%, and 1.0; for C-peptide, 0.39 nmol/L, 24%, and 0.9; and for glucagon, 53 ng/L, 19%, and 0.8. CONCLUSIONS: The data presented here are necessary for the evaluation of several important metabolic variables in individual and group studies. The biological variation of some metabolites makes it difficult to characterize the status of healthy subjects with a single measurement. (+info)
Intact proinsulin and beta-cell function in lean and obese subjects with and without type 2 diabetes.
(6/1227)
OBJECTIVE: Type 2 diabetes is a heterogeneous disease in which both beta-cell dysfunction and insulin resistance are pathogenetic factors. Disproportionate hyperproinsulinemia (elevated proinsulin/insulin) is another abnormality in type 2 diabetes whose mechanism is unknown. Increased demand due to obesity and/or insulin resistance may result in secretion of immature beta-cell granules with a higher content of intact proinsulin. RESEARCH DESIGN AND METHODS: We investigated the impact of obesity on beta-cell secretion in normal subjects and in type 2 diabetic patients by measuring intact proinsulin, total proinsulin immunoreactivity (PIM), intact insulin, and C-peptide (by radioimmunoassay) by specific enzyme-linked immunosorbent assays in the fasting state and during a 120-min glucagon (1 mg i.v.) stimulation test. Lean (BMI 23.5 +/- 0.3 kg/m2) (LD) and obese (30.1 +/- 0.4 kg/m2) (OD) type 2 diabetic patients matched for fasting glucose (10.2 +/- 0.6 vs. 10.3 +/- 0.4 mmol/l) were compared with age- and BMI-matched lean (22.4 +/- 0.6 kg/m2) (LC) and obese (30.8 +/- 0.9 kg/m2) (OC) normal control subjects. RESULTS: Diabetic patients (LD vs. LC and OD vs. OC) had elevated fasting levels of intact proinsulin 6.6 +/- 1.0 vs. 1.6 +/- 0.3 pmol/l and 7.7 +/- 2.0 vs. 1.2 +/- 0.2 pmol/l; PIM: 19.9 +/- 2.5 vs. 5.4 +/- 1.0 pmol/l and 29.6 +/- 6.1 vs. 6.1 +/- 0.9 pmol/l; and total PIM/intact insulin: 39 +/- 4 vs. 15 +/- 2% and 35 +/- 5 vs. 13 +/- 2%, all P < 0.01. After glucagon stimulation, PIM levels were disproportionately elevated (PIM/intact insulin based on area under the curve analysis) in diabetic patients (LD vs. LC and OD vs. OC): 32.6 +/- 6.7 vs. 9.2 +/- 1.1% and 22.7 +/- 5.2 vs. 9.1 +/- 1.1%, both P < 0.05. Intact insulin and C-peptide net responses were significantly reduced in type 2 diabetic patients, most pronounced in the lean group. The ratio of intact proinsulin to PIM was higher in diabetic patients after stimulation in both LD versus LC: 32 +/- 3 vs. 23 +/- 2%, and OD versus OC: 28 +/- 4 vs. 16 +/- 2%, both P < 0.01. In obese normal subjects, intact proinsulin/PIM was lower both in the fasting state and after glucagon stimulation: OC versus LC: 22 +/- 3 vs. 33 +/- 3% (fasting) and 16 +/- 2 vs. 23 +/- 2% (stimulated), both P < 0.05. CONCLUSIONS: Increased secretory demand from obesity-associated insulin resistance cannot explain elevated intact proinsulin and disproportionate hyperproinsulinemia in type 2 diabetes. This abnormality may be an integrated part of pancreatic beta-cell dysfunction in this disease. (+info)
Effect of calorie restriction on in vivo glucose metabolism by individual tissues in rats.
(7/1227)
We evaluated the effects of 8 mo of calorie restriction [CR: 60% of ad libitum (AL) food intake] on glucose uptake by 14 tissues in unanesthetized, adult (12 mo) F344xBN rats. Glucose metabolism was assessed by the 2-[3H]deoxyglucose tracer technique at 1500 or 2100. Despite an approximately 60% decline in insulinemia with CR, plasma 2-[3H]deoxyglucose clearance for CR was greater than for AL at both times. A small, CR-related decrease in glucose metabolic index (R'g) occurred only at 1500 in the spleen and heart, and this decrease was reversed at 2100. In some tissues (cerebellum, lung, kidney, soleus, and diaphragm), R'g was unaffected by diet, regardless of time. In the other tissues (brown fat, 3 white fat pads, epitrochlearis, plantaris, and gastrocnemius), R'g was higher or tended to be higher for CR vs. AL at one or both times. These findings indicate that 8 mo of CR did not cause a continuous reduction in in vivo glucose uptake by any tissue studied, and, in several insulin-sensitive tissues, glucose uptake was at times greater for CR vs. AL rats. (+info)
C-peptide induces a concentration-dependent dilation of skeletal muscle arterioles only in presence of insulin.
(8/1227)
In this study we tested the hypothesis that C-peptide alone or in conjunction with insulin may cause a dilation of skeletal muscle arterioles. First-order arterioles (88 microm) isolated from rat cremaster muscles were pressurized (65 mmHg), equilibrated in a Krebs bicarbonate-buffered solution (pH 7.4), gassed with 10% O2 (balance 5% CO2, 85% N2), and studied in a no-flow state. C-peptide administered at concentrations of 0.3, 1, 3, 10, 100, 300, and 1,000 ng/ml evoked arteriolar dilation that was not concentration dependent. In contrast, the administration of the four lower physiological concentrations of C-peptide to arterioles exposed to a nondilating concentration of insulin evoked a significant concentration-dependent increase in arteriolar diameter from 8.6 to 42.3% above control. The arteriolar dilation to C-peptide in the presence of insulin was completely inhibited by administration of NG-nitro-L-arginine (10(-4) M). Responses to ACh and adenosine were not enhanced when these drugs were administered in the presence of insulin. These results indicate that C-peptide has the capacity to evoke arteriolar dilation in skeletal muscle via a nitric oxide-mediated mechanism that appears to be enhanced by an interaction with insulin. Furthermore, the effects of insulin appear to be specific for C-peptide and are not the result of a general enhancement of endothelium-dependent or endothelium-independent dilation. (+info)