Insulin action and insulin binding following pancreas transplantation

IRS-1 serine phosphorylation and insulin resistance in skeletal muscle from pancreas transplant recipients

Insulin-dependent diabetic recipients of successful pancreas allografts achieve self-regulatory insulin secretion and discontinue exogenous insulin therapy; however, chronic hyperinsulinemia and impaired insulin sensitivity generally develop. To determine whether insulin resistance is accompanied by altered signal transduction, skeletal muscle biopsies were obtained from pancreas-kidney transplant recipients (n = 4), nondiabetic kidney transplant recipients (receiving the same immunosuppressive drugs; n = 5), and healthy subjects (n = 6) before and during a euglycemic-hyperinsulinemic clamp. Basal insulin receptor substrate (IRS)-1 Ser (312) and Ser (616) phosphorylation, IRS-1-associated phosphatidylinositol 3-kinase activity, and extracellular signal-regulated kinase (ERK)-1/2 phosphorylation were elevated in pancreas-kidney transplant recipients, coincident with fasting hyperinsulinemia. Basal IRS-1 Ser (312) and Ser (616) phosphorylation was also increased in nondiabetic kidney transplant recipients. Insulin increased phosphorylation of IRS-1 at Ser (312) but not Ser (616) in healthy subjects, with impairments noted in nondiabetic kidney and pancreas-kidney transplant recipients. Insulin action on ERK-1/2 and Akt phosphorylation was impaired in pancreas-kidney transplant recipients and was preserved in nondiabetic kidney transplant recipients. Importantly, insulin stimulation of the Akt substrate AS160 was impaired in nondiabetic kidney and pancreas-kidney transplant recipients. In conclusion, peripheral insulin resistance in pancreas-kidney transplant recipients may arise from a negative feedback regulation of the canonical insulin-signaling cascade from excessive serine phosphorylation of IRS-1, possibly as a consequence of immunosuppressive therapy and hyperinsulinemia.

MATURITY-ONSET DIABETES OF THE YOUNG WITH END-STAGE NEPHROPATHY: A NEW INDICATION FOR SIMULTANEOUS PANCREAS AND KIDNEY TRANSPLANTATION?

BACKGROUND AND CASE: Simultaneous pancreas and kidney transplantation (SPK) is applied almost exclusively in C-peptide-negative type 1 diabetic patients, although some data on SPK in type 2 diabetes have been published as well. Nothing is known about SPK in the autosomal diabetes form, maturity-onset diabetes of the young (MODY). SPK was performed in a 47-year old man who has MODY3 because of a Arg272His mutation in the hepatocyte nuclear factor-1alphagene. He developed overt diabetes mellitus at 19 years and end-stage diabetic nephropathy 26 years thereafter. Before SPK, the patient had measurable fasting serum C-peptide levels, but lacked beta-cell response to intravenous glucose and glucagon. He was treated with 34 IU of insulin per day. At 2 years post-transplantation, the patient remains normoglycemic and insulin independent. A hyperglycemic clamp test showed a normal beta-cell function.

CONCLUSION

Identification of MODY3 among all C-peptide-positive patients with advanced diabetic nephropathy might help to select a specific group profiting from SPK.

The circulating hormonal milieu of the endocrine pancreas in healthy individuals, organ donors, and the isolated perfused human pancreas

Although basal circulating levels of individual islet cell hormones have been measured, few studies compared the molar ratios of the major hormones secreted by the endocrine pancreas. This study examined the basal levels of four major islet hormones: insulin, C-peptide (C-P), glucagon (G), and pancreatic polypeptide (PP) in normal subjects, in organ donors with brain death, and in the isolated perfused human pancreas. Basal blood samples were taken from normal, fasted control subjects (NCs). Pancreata were obtained from 17 organ donors (ODs) with donor portal vein (DPV) and radial arterial (DRA) blood samples taken before organ procurement. Single-pass perfusion was performed on the procured pancreata, and after rewarming and equilibration, basal samples were collected from the splenic vein (SV) for 30 min. Radioimmunoassays of insulin, C-P, G, and PP were performed on all samples, and basal levels of all hormones were expressed as a common unit, femtomoles per milliliter. The data suggest that in the basal state, these four major islet hormones circulate in a relatively constant molar ratio. The ratio of the hormones is altered in brain death and with in vitro perfusion of the pancreas. The isolated perfused human pancreas secretes a relatively constant molar ratio of these hormones; however, this ratio is markedly different from the circulating ratio seen in either the NC group or the OD group. We conclude that a relatively constant hormonal milieu is secreted from the normal endocrine pancreas, and this hormonal milieu is altered after brain death and with isolation and perfusion of the human pancreas.

The metabolic effects of cyclosporin and tacrolimus

The introduction of cyclosporin and, more recently, tacrolimus in the immunosuppression of transplanted patients has lead to prolonged graft survival and increased patients' life expectancy. It has been therefore possible to evaluate the effects of long-term treatment with these drugs and metabolic alterations in patients on cyclosporin or tacrolimus have been reported by several authors. In particular, the use of these drugs is associated with abnormalities of glucose and lipid metabolism. Post-transplant diabetes is more common with tacrolimus, probably due to more marked effects on the pancreatic beta-cells, whereas increased levels of cholesterol and triglycerides are more frequently associated with cyclosporin treatment, even though, in this latter case, steroid treatment seems to play a major role. Comparison and intervention studies must be planned to evaluate the best therapeutical approaches to control these abnormalities and to assess the possibility to further increase graft and patient survival by appropriate treatment of diabetes and hyperlipidemia.

Insulin secretion and sensitivity after simultaneous pancreas-kidney transplantation estimated by continuous infusion of glucose with model assessment

BACKGROUND

Monitoring of insulin secretion and sensitivity after pancreas transplantation remains a practical problem.

METHODS

We introduced the simple structural model, continuous infusion of glucose with model assessment (CIGMA), to obtain insulin secretion and insulin sensitivity estimations after 35 successful simultaneous pancreas-kidney transplantations. Eighteen non-diabetic kidney transplant recipients were used as control group.

RESULTS

The baseline characteristics were equal between the two groups except for higher fasting insulin levels in the pancreas transplant group. After the 1-hr CIGMA glucose load, the pancreas transplant group reached a mean +/- SD blood glucose of 8.2+/-1.7 mmol/L compared with 7.3+/-1.0 mmol/L in the control group (P = 0.05). Concurrent stimulated insulin and C-peptide levels were 48+/-28 mU/L and 2.3+/-0.9 nmol/L in the pancreas transplant group compared with 36+/-21 mU/L and 2.9+/-1.1 nmol/L in the control group (P = 0.1 and P = 0.03, respectively). Both the CIGMA estimation for secretion as well as the CIGMA estimation for sensitivity were lower in pancreas transplant group (P = 0.003 and P = 0.01, respectively). Mean +/- SE coefficients of variation for the model estimations were 15+/-4% for secretion and 17+/-6% for sensitivity.

CONCLUSIONS

We conclude that CIGMA can be used clinically to evaluate carbohydrate metabolism in pancreas-kidney transplant recipients. These patients have a reduction in insulin secretory capacity and evidence of more insulin resistance than non-diabetic kidney transplant recipients.

Clinical determinants of glucose homeostasis after pancreas transplantation

Although successful simultaneous pancreas and kidney transplantation (SPK) achieves normoglycemia in the majority of diabetic recipients with end-stage renal disease, little is known about the factors that influence long-term endocrine function. In this prospective study of 48 bladder-drained SPK patients, 209 oral glucose tolerance tests were performed between 3 months and 6 years after transplantation. Normal fasting glucose levels and systemic hyperinsulinemia were stable for up to 6 years after SPK. Multivariate analysis revealed that increased area-under-curve (AUC) levels of C-peptide 3 months after transplantation were predicted by short surgical pancreas anastomosis time, greater recipient body weight, and total HLA mismatch score. Episodes of acute pancreas rejection were not associated with reduced allograft insulin output in the long term. Insulin output, stimulated by oral glucose tolerance tests and assessed by the ratio of AUC insulin to AUC glucose, fell gradually after transplantation and was decreased by an elevated serum calcium level and high cyclosporine dose. The ratio of fasting insulin to glucose, which acts as a marker of peripheral insulin resistance, fell with time after transplantation and was increased by greater body weight, higher prednisolone dose, and lower cyclosporine dose. The inhibitory effect of cyclosporine on both fasting and postprandial insulin output was, however, minor when quantified by multivariate analysis. Endocrine function of the transplanted pancreas was not correlated with its exocrine function measured by urinary amylase excretion, nor was there a correlation with change in renal function measured by isotopic glomerular filtration rate. In summary, simultaneous pancreas and kidney transplantation leads to excellent long-term glucose homeostasis maintained at the expense of systemic hyperinsulinemia. The key factors adversely affecting peripheral resistance in SPK were corticosteroid therapy, body weight, and time after transplantation. The susceptibility of islets to ischemia-reperfusion injury, as quantitated by surgical anastomosis time, may have implications for islet transplantation programs, as may the relative resistance of islets to allograft rejection. Glucose homeostasis after SPK, while remaining abnormal, may be used as the standard against which islet transplantation must be measured.

Sequential evaluation of islet cell responses to glucose in the transplanted pancreas in humans

We evaluated the hormonal and metabolic responses of denervated pancreas allografts in nine volunteers 3 to 12 months after the transplant (initial) and again 1 year later (follow-up). Eight of the patients received simultaneous pancreas-kidney transplants. The glucose clamp technique was used to create a square wave of hyperglycemia 5.5 mmol/L above the basal glucose level for 2 hours. A biphasic insulin response was evident in each subject, both initially and at follow-up. The initial plasma insulin response was fourfold higher in patients with pancreas-kidney transplants than in normal volunteers. However, the plasma insulin response of the patients with pancreas-kidney transplants at the follow-up study was more similar to that of the normal controls. The plasma glucagon levels were elevated in follow-up clamp studies. Hepatic glucose production and glucose disposal were similar in both studies. At the follow-up examination only, GLUT4, the major insulin-sensitive glucose transporter, was measured in muscle homogenates by immunoblotting. GLUT4 levels in the patients with pancreas-kidney transplants were only 55% as abundant as in normal volunteers. This may be due, in part, to immunosuppressive therapy or to persistent, albeit reduced, levels of hyperinsulinemia even 2 years after transplantation. We concluded that, despite systemic drainage of the pancreas and immunosuppressive therapy, pancreatic insulin secretion, peripheral insulin levels, and muscle insulin responsiveness are restored toward normal levels approximately 2 years after the transplant.

Minimal model analysis of insulin sensitivity and glucose-mediated glucose disposal in type 1 (insulin-dependent) diabetic pancreas allograft recipients

Decreased insulin sensitivity and glucose-dependent glucose disposal (glucose effectiveness) have been demonstrated in poorly-controlled Type 1 (insulin-dependent) diabetic patients. We have therefore examined the effects of successful pancreas transplantation that results in long-term physiologic normoglycaemia as measured by insulin sensitivity index and glucose effectiveness in 14 Type 1 diabetic recipients (Group 1) using the Bergman minimal model method. Their results were compared with those of five non-diabetic patients with kidney transplant alone (Group 2) and 10 healthy control subjects (Group 3). Mean plasma glucose levels were indistinguishable in Group 1 when compared to Groups 2 and 3. However, mean basal plasma insulin levels were two- and eight-fold greater in Group 1 (36 +/- 6 microU/ml) than in Group 2 (17 +/- 7 microU/ml) and Group 3 (4.5 +/- 0.6 microU/ml), respectively. Following intravenous glucose (t = 0 min) and tolbutamide (t = 20), peak incremental insulin levels were significantly (p less than 0.001) greater in Group 1 vs Groups 2 and 3. Mean insulin sensitivity index was 65% and 50% lower in Group 1 (2.89 +/- 0.45) and Group 2 (4.11 +/- 1.30), respectively, when compared to Group 3 (8.40 +/- 1.24 x 10(-1) min-1 (microU/ml)-1. In contrast, glucose effectiveness was similar in the three groups (Group 1, 2.48 +/- 0.26; Group 2, 2.05 +/- 0.21; and Group 3, 2.10 +/- 0.17 x 10(-2).min-1). We conclude that, despite prednisone-induced insulin resistance, normal glucose tolerance is achieved by hyperinsulinaemia and normalisation of glucose-dependent glucose disposal following pancreas-kidney transplantation in Type 1 diabetic patients.

Pancreas and islet transplantation in man

The results of pancreas transplantation have greatly improved, the overall patient and graft 1-year survival rates now being 89 and 62%, respectively. A technically successful graft ensures a near-normal glucose metabolism in most cases, and improves the patient's quality of life. However, pancreas transplantation is not a life-saving procedure and because of the necessary permanent immunosuppression it is usually performed in patients in whom a kidney transplant is needed or has been previously established. In such patients the other diabetic chronic complications are often advanced and limit the potential benefit of pancreas transplantation, but it seems premature to extend the indications to early stage diabetes. Islet transplantation has many potential advantages, mainly the possibilities of immune alteration and immune protection of the transplant that could allow transplantation to be performed without immunosuppression and the use of xenogenic tissue. Major limiting factors are the high numbers of islets necessary to ensure insulin independence and the low yield of islet isolation from adult pancreas. Encouraging, albeit preliminary results have been recently reported in man.