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

The role of blood vessels, endothelial cells, and vascular pericytes in insulin secretion and peripheral insulin action

The pathogenesis of type 2 diabetes is intimately intertwined with the vasculature. Insulin must efficiently enter the bloodstream from pancreatic beta-cells, circulate throughout the body, and efficiently exit the bloodstream to reach target tissues and mediate its effects. Defects in the vasculature of pancreatic islets can lead to diabetic phenotypes. Similarly, insulin resistance is accompanied by defects in the vasculature of skeletal muscle, which ultimately reduce the ability of insulin and nutrients to reach myocytes. An underappreciated participant in these processes is the vascular pericyte. Pericytes, the smooth muscle-like cells lining the outsides of blood vessels throughout the body, have not been directly implicated in insulin secretion or peripheral insulin delivery. Here, we review the role of the vasculature in insulin secretion, islet function, and peripheral insulin delivery, and highlight a potential role for the vascular pericyte in these processes.

Ischemia/reperfusion injury in kidney transplantation: mechanisms and prevention

Ischemia has been an inevitable event accompanying kidney transplantation. Ischemic changes start with brain death, which is associated with severe hemodynamic disturbances: increasing intracranial pressure results in bradycardia and decreased cardiac output; the Cushing reflex causes tachycardia and increased blood pressure; and after a short period of stabilization, systemic vascular resistance declines with hypotension leading to cardiac arrest. Free radical-mediated injury releases proinflammatory cytokines and activates innate immunity. It has been suggested that all of these changes-the early innate response and the ischemic tissue damage-play roles in the development of adaptive responses, which in turn may lead to an acute font of kidney rejection. Hypothermic kidney storage of various durations before transplantation add to ischemic tissue damage. The final stage of ischemic injury occurs during reperfusion. Reperfusion injury, the effector phase of ischemic injury, develops hours or days after the initial insult. Repair and regeneration processes occur together with cellular apoptosis, autophagy, and necrosis; the fate of the organ depends on whether cell death or regeneration prevails. The whole process has been described as the ischemia-reperfusion (I-R) injury. It has a profound influence on not only the early but also the late function of a transplanted kidney. Prevention of I-R injury should be started before organ recovery by donor pretreatment. The organ shortage has become one of the most important factors limiting extension of deceased donor kidney transplantation worldwide. It has caused increasing use of suboptimal deceased donors (high risk, extended criteria [ECD], marginal donors) and uncontrolled non-heart-beating (NHBD) donors. Kidneys from such donors are exposed to much greater ischemic damage before recovery and show reduced chances for proper early as well as long-term function. Storage of kidneys, especially those recovered from ECD (or NHBD) donors, should use machine perfusion.

Acute insulin response to arginine in deceased donors predicts the outcome of human islet isolation

Despite a stringent donor selection, human islet isolation remains frustratingly unpredictable. In this study, we measured acute insulin response to arginine (AIRarg), an in vivo surrogate measure of islet mass, in 29 human deceased donors before organ donation, and correlated values with the outcome of islet isolation. Thirteen isolations (45%) met the threshold for clinical islet transplantation. Among all measured donor characteristics, the only discriminating variable between successful or unsuccessful isolations was donor AIRarg (p < 0.01). Using a threshold of 55 microIU/mL (ROC curve AUC: 72%), isolation was successful in 12/19 donors with high AIRarg and in 1/10 donors with low AIRarg (p < 0.001). The negative and positive predictive values were 90 and 63%, respectively. If used to select donors in the entire cohort, AIRarg would have increased our success rate by 40% and avoided 56% of unsuccessful isolations while missing only 8% of successful preparations. Our results suggest that donor AIRarg is markedly superior to body mass index (BMI) and other criteria currently used to predict isolation outcome. If routinely performed in deceased donors, this simple test could significantly reduce the failure rate of human islet isolation.

Islet Vasculature as a Regulator of Endocrine Pancreas Function

The islets of Langerhans consist of endocrine cells embedded in a network of specialized capillaries that regulate islet blood flow. Despite evidence for a critical role of islet perfusion in endocrine pancreas function, there is information to support no fewer than three models of endocrine cell perfusion, emphasizing the lack of a universally accepted physiological theory. Islet blood flow is regulated by signals, such as hormones and nutrients that reach the islet vasculature from distant tissues via the bloodstream. In addition, islet perfusion determines communication between endocrine and exocrine cells and between different types of endocrine cells within islets. Interest in islet microcirculation has increased after improvements in islet transplantation, a therapy for diabetes mellitus that requires revascularization of grafted islets in a new host organ. Abnormal revascularization is thought to be partly responsible for differences in graft and native islet function. Similarly, angiogenesis has been shown to be a critical step in the transformation of islet hyperplasia to neoplasia.

Pancreatic polypeptide administration reduces insulin requirements of artificial pancreas in pancreatectomized dogs

An artificial endocrine pancreas is a mechanical device that frequently measures blood glucose and adjusts the rate of insulin infusion to maintain normoglycemia. In this study, we evaluated the effect of pancreatic polypeptide (PP) on insulin requirements after total pancreatectomy. However, other endocrine hormones are needed not only to facilitate the effect of insulin, but also to regulate insulin functions in vivo. In this study, the effect of PP infusion on insulin requirements after total pancreatectomy in dogs is examined. After total pancreatectomy, five dogs were supported by artificial endocrine pancreas model STG-22 for 72 h. In a second group of five dogs, both insulin and PP were infused. Mean blood glucose levels and insulin requirements were compared between the two groups. There was no difference in mean plasma glucose levels between the two groups. In all 10 dogs, the mean blood glucose level for 72 h was 110 +/- 4 mg/dL and was tightly controlled between 65 and 190 mg/dL. However, the insulin requirement for the first and second postoperative days in the group treated with PP was significantly less than that of the control group (90.0 +/- 20.8 mU/kg vs. 445.0 +/- 151.9 mU/kg; P < 0.05, and 562.7 +/- 126.5 mU/kg vs. 1007.7 +/- 144.9 mU/kg; P < 0.05, respectively). We conclude that infusion of PP reduces the insulin requirement for the initial 48 h in pancreatectomized dogs treated with an artificial endocrine pancreas.

Donor Care before Pancreatic Tissue Transplantation

Publications are reviewed to identify factors related to donor care that may optimize the function of pancreatic tissue (whole or segmental organ or islet cells) after transplantation. Short cold ischemia time, avoidance of hypotension, and treatment of donor hyperglycemia appear to be beneficial, although additional properly designed studies are needed to verify those findings.

Endocrine pancreatic insufficiency in chronic pancreatitis

Chronic pancreatitis (CP) is considered to be a rare cause of diabetes mellitus. However, in both the developed and developing world, there is an increasing number of patients suffering from pancreatitis probably due to lifestyle changes, which is partially associated with both social factors and the poor health status of immigrants. Owing to these circumstances, CP has evolved with one of the possible causes of diabetes in a selected group of patients and should be included in the differential diagnosis of diabetes. Several studies have shown that the long-term rate of diabetic complications in patients with CP and insulin-dependent diabetes is similar to that in patients with type 1 diabetes of equal duration. The hypothesis that early diagnosis of CP should result in better prognosis is not validated and may complicate the issue, since the risk of diabetes has been shown to increase significantly only once pancreatic calcification has developed. Accumulative evidence suggests that the risk of diabetes is not influenced by elective pancreatic surgical procedures other than distal pancreatectomy. The lack of contemporary data points to the urgent need for large prospective studies in order to accurately evaluate the special characteristics of disorders in glucose homeostasis in patients with CP.