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Biomedical subjects

N M Kneteman

Publications and source records attributed to N M Kneteman.

At least 73 records · Page 4Linked to original sources
PubMed1993

The efficacy and toxicity of rapamycin in murine islet transplantation. In vitro and in vivo studies.

We performed an in vivo and in vitro dose-response study of the novel immunosuppressive macrolide antibiotic rapamycin looking at murine islet allograft survival, impact on glucose homeostasis, and possible tissue toxicity. A total of 300 islets were isolated from CBA/J mice (H-2k) and transplanted beneath the renal capsule of streptozotocin-induced diabetic BALB/c (H-2d) recipients. Seven groups of allografted mice received intraperitoneally for 7 days post-transplant: no immunosuppression (n = 8); vehicle only (carboxymethyl-cellulose) (n = 6); or rapamycin at dosages of 0.05 (n = 8), 0.1 (n = 8), 0.3 (n = 8), 1.0 (n = 8), or 5.0 (n = 6) mg/kg/day. Blood glucose was monitored on alternate days, with graft failure defined by the first day of persistently high blood glucose (> 14 mmol/L). The 0.1 and 0.3 mg/kg/day groups showed statistically significant prolongation of diet allograft survival (P < 0.01) when compared to the controls and vehicle-treated mice. Three mice in both the 0.1 and 0.3 mg/kg/day groups and one mouse in the 0.05 mg group reached 100 days normoglycemia and, following nephrectomy of the islet-bearing kidney, returned to hyperglycemia. The 0.05, 1.0, and 5.0 mg/kg/day groups showed no statistically significant prolongation of graft survival. In addition, the higher dosage (1.0 and 5.0 mg/kg/day) groups had erratic blood glucose control. Histologically, there was no evidence of toxicity seen in any of the multiple organ samples. In the in vitro analysis, BALB/c (H-2k) islets cultured in either 0, 10, 30, or 100 ng/ml rapamycin had no significant differences in insulin secretion following a 24-hr culture period; however, there was a significant deterioration in glucose stimulated insulin release after 72 hr culture at high rapamycin concentration (100 ng/ml). Rapamycin significantly prolonged murine islet allograft survival. At doses 10 to 50 times the effective antirejection dosage, we demonstrated adverse impact on glucose homeostasis without histological evidence of end-organ toxicity. We also demonstrated an adverse impact on insulin release in vitro following prolonged culture (72 hr) in a high concentration of rapamycin.

Animals↗
PubMed1993

Prolongation of canine pancreatic islet allograft survival with combined rapamycin and cyclosporine therapy at low doses. Rapamycin efficacy is blood level related.

We studied the survival of 5 groups of apancreatic mongrel dogs that received 30 days of treatment with CsA adjusted to 300 micrograms/L, rapamycin (0.05 mg/kg/day), both, or no immunosuppression after intrasplenic allotransplantation with purified pancreatic islets. Autografts survived indefinitely. Neither CsA nor rapamycin alone at low doses showed significant increase in islet allograft survival: 6.2 +/- 1.7 and 5.0 +/- 1.1, respectively, versus 3.4 +/- 1.0 days in controls. Dogs treated with low doses of both CsA and rapamycin demonstrated prolongation of graft function to 23.6 +/- 13.2 days (P < 0.05). These findings support synergism between these 2 agents, especially as CsA was not shown to increase trough rapamycin blood concentration when given together. In the combined treatment group, a significant (r = 0.90, P < 0.001) relationship was found between rapamycin blood levels and graft survival. Animals having trough rapamycin concentrations > 10 micrograms/L had significantly (P < 0.05) prolonged graft survival, which suggests that dosing of rapamycin according to blood levels may optimize the effectiveness of the drug. Given at these low doses, combination CsA and rapamycin gave no evidence of adverse effects as measured by hepatic and renal function tests, histology, or electron microscopy.

Animals↗
PubMed1992

Long-term follow-up after transplantation of insulin-producing pancreatic islets into patients with type 1 (insulin-dependent) diabetes mellitus.

Purified human islets and a kidney from the same donor were transplanted into four patients with Type 1 (insulin-dependent) diabetes mellitus. Two of the patients received additional islets that were isolated from multiple donors, cryopreserved, and stored in a tissue bank. The islets were embolized into the liver via the portal vein. Immunosuppression was induced with antilymphocyte globulin and maintained with azathioprine, prednisone and cyclosporine. In the first two patients, fasting serum C-peptide rose to levels of 0.5-2.0 ng/ml during the first 4-8 weeks and mixed meal feeding elicited increases to 2-3 ng/ml. C-peptide secretion persisted for 8 months, but at progressively lower levels and insulin therapy could not be withdrawn. In the next two patients who received cryopreserved islets in addition to fresh islets, serum C-peptide levels (fasting/post-meal) rose to 4-7 ng/ml and serum glucose was more stable, allowing withdrawal of insulin therapy after 69 days in one patient, and reduced insulin doses in the other. The insulin-independent patient has maintained normal fasting glucose, glycosylated haemoglobin, and oral glucose tolerance at 1 year following cessation of daily insulin therapy. Episodes of renal graft rejection occurred in three patients, including the insulin-independent patient. High-dose steroid therapy reversed the rejection in all instances, with apparent preservation of C-peptide secretion. These data show that transplantation of purified freshly-prepared and cryopreserved islets into Type 1 diabetic patients results in prolonged insulin secretion, and that sufficient function could be provided in one patient to sustain euglycaemia in the absence of insulin therapy at 1 year of follow-up.

Adult↗
PubMed1992

Intestinal function following allogeneic small intestinal transplantation in the rat.

This study tests the hypothesis that small bowel transplantation alters the function of the intestine. The function of the small intestine was investigated after syngeneic (BN----BN or Lew----Lew) and fully allogeneic (BN----Lew) orthotopic total small intestinal transplantation (SIT) using a two-stage model. All animals were treated with cyclosporine A throughout the 60-day study period. Syngeneic transplantation reduced weight gain in the (BN----BN) rats, but not in the (Lew----Lew) animals. Allogeneic transplantation caused a reduction in weight gain for the first 30 days posttransplantation, which may have been associated with graft-versus-host disease. Thereafter, the rate of growth of allogeneic SIT animals was normal. Dietary fat absorption was reduced in all groups of transplanted animals. Intestinal permeability to mannitol and polyethylene glycol 400 (PEG-400) was increased by syngeneic transplantation in all groups, with further permeability increases to mannitol, lactulose, PEG-400, and 51Cr-EDTA after allogeneic SIT. The glucose-stimulated intestinal short circuit current was reduced by both syngeneic and allogeneic SIT, but the maximal active transport rate for glucose uptake was increased, as was the passive uptake of fatty acids. These functional alterations were not associated with changes in intestinal morphology or evidence of rejection. These findings demonstrate that: (1) SIT results in significant changes in the transport characteristics of the bowel, but these have a minimal impact on the well-being of the animal overall; (2) SIT induces an increase in intestinal permeability to mannitol and PEG-400, with a further increase in permeability to all markers following allogeneic SIT; (3) following SIT, and the immune events associated with allogeneic SIT, significant adaptation of the transplanted intestine occurs. We suggest that denervation of the small intestine after SIT is the underlying cause of the changes observed.

Animals↗
PubMed1992

Reduction of nutrient absorption in normal rats by cyclosporine.

The indications for using cyclosporine are expanding rapidly beyond immune suppression for transplantation. We have previously described reduced active glucose uptake by small bowel following CsA treatment in rats. This study examined the effect of varying the dose and route of administration of CsA on bowel function. Male Lewis rats were given CsA via subcutaneous injection at doses of 5 mg/kg or 30 mg/kg on alternate days, or orally via gavage at 0 (control solvent oil), 7.5 mg/kg, or 30 mg/kg daily. Weight gain and feed intake were followed for 1 month when a balance study was performed to quantify in vivo nutrient absorption from the feed. In vitro studies of glucose and fatty acid uptake studies were then performed. Weight gain was reduced by high-dose CsA whether given orally or by subcutaneous injection. Oral CsA reduced in vivo fat and energy absorption from the diet, and all doses and routes of administration of CsA caused a reduction in both active glucose uptake and passive fatty acid absorption by the bowel in vitro. Thus, CsA has significant effects on bowel function in the normal rat. We suggest that further studies are indicated to determine the effects of CsA in man, especially in conditions with already-impaired bowel function.

Animals↗
PubMed1992

Small bowel transplantation: past, present and future.

As techniques for immune suppression improve, the clinical utility of small bowel transplantation will increase. Recent reports of long-term (over 1 year) survival with totally enteral nutrition following bowel transplantation have increased interest in this area and prompted the present review of the state of the art of small bowel transplantation. Background methodology is emphasized, in order to allow for more critical review of reported models, and to provide a framework for comparing results. The functional capacity of bowel following transplantation, and the effects of immune suppression on bowel function are reviewed in detail. Prospects for future direction in basic and clinical research are discussed.

Animals↗
PubMed1992

Effects of cyclosporine on insulin secretion and insulin sensitivity in dogs with intrasplenic islet autotransplants.

Concern about cyclosporine causing adverse effects on glucose metabolism is based mainly on in vitro studies and in vivo data in rodents. However, data on large mammals and humans are much more controversial. Because the drug is used as therapy accompanying pancreatic or isolated islet transplantations, studies in large animals are needed to assess whether cyclosporine inhibits beta-cell function and causes glucose intolerance. To address these issues, we examined intravenous glucose tolerance, islet beta-cell function, and insulin sensitivity in a group of adult mongrel dogs with intrasplenic islet autografts, with and without cyclosporine treatment. Similar fasting plasma glucose and insulin values were found before and after pancreatectomy and islet transplantation. After intravenous glucose, plasma glucose values decreased more slowly in dogs that had undergone transplantation, but no additional adverse effect as a result of cyclosporine was observed. During euglycemic clamp studies, performed at both physiologic and pharmacologic insulin concentrations, the drug had no effect on the total amount of metabolized glucose, and glucose production was unaffected by cyclosporine treatment. Thus intramuscular cyclosporine therapy does not seem to inhibit insulin secretion from heterotopic islets or to affect peripheral and hepatic insulin sensitivity in dogs with intrasplenic islet autografts.

Animals↗
PubMed1991

Normoglycaemia after transplantation of freshly isolated and cryopreserved pancreatic islets in type 1 (insulin-dependent) diabetes mellitus.

Purified islets of Langerhans and a kidney were transplanted into a 36-year-old patient who suffered from renal failure secondary to a 25 year history of Type 1 (insulin-dependent) diabetes mellitus. The islet graft contained 243,000 fresh islets (mean islet diameter 150 microns) that were syngeneic with the kidney graft and 368000 cryopreserved islets that had been collected from four other donors. The total of 10,000 islets/kg body weight was infused into the liver via the umbilical vein. Immunosuppression was induced with antilymphocyte globulin and maintained with prednisone, cyclosporine and azathioprine. Serum C-peptide levels (ng/ml) during fasting and after standard mixed meal feeding (Sustacal) were less than 0.12 preoperatively. Postoperatively, insulin secretion was restored: fasting C-peptide rose during the first 4 weeks to levels of 4 to 5 and Sustacal elicited a further rise to 6 to 7. Transplant renal function was stable. Daily fasting glucose (mmol/l, mean +/- SD) was 5.6 +/- 1 and 5.3 +/- 0.6 during the first and second months respectively and post-Sustacal glucose was 5.7 +/- 0.8. Exogenous insulin therapy was progressively withdrawn and stopped during the ninth week. Thereafter, fasting glucose was 4.7 +/- 0.5, 24 h mean glucose was 6.6 +/- 0.5, and normoglycaemia was maintained after Sustacal. These data show that this mass of freshly isolated and cryopreserved islets from multiple donors provided sustained function (3 months) that reversed insulin-dependence in an immunosuppressed Type 1 diabetic patient treated with simultaneous islet-kidney transplantation.

Adult↗
PubMed1991

Major histocompatibility complex antigens and murine islet allograft survival.

Immunomodulation of rodent islets can significantly prolong allograft survival. We utilized a murine model of primary islet transplantation to study the relationship between allograft survival and the quantitative pretransplant expression of class I and II MHC antigens in freshly isolated CBA/J islets, and islets subjected to 37 degrees C tissue culture, brief culture at 7 degrees C, or exposure of the donor to lipopolysaccharide. Seven-day culture resulted in decreased class II expression, a tendency to decreased class I expression, and a significant prolongation of allograft survival. Brief culture at 7 degrees C resulted in increased class I expression, a trend to decreased class II expression, and no significant change in allograft survival. Donor pretreatment with LPS resulted in increased class I expression without significant change in class II expression and was correlated with prolongation of allograft survival. These studies demonstrate that an upregulation of MHC class I by in vitro or in vivo islet pretreatment is not associated with an acceleration of islet rejection. Reduction of class II was associated with delayed rejection. These results do not support a major role of the indirect pathway of antigen presentation in islet rejection in vivo. Certain protocols that alter the usual expression of class I and II on pancreatic islets are associated with alteration in the initiation and/or propagation of the normal cell-mediated rejection process, suggesting that the concept of pretransplant treatment should continue to be pursued.

Animals↗