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Biomedical subjects

N M Kneteman

Publications and source records attributed to N M Kneteman.

At least 37 records · Page 2Linked to original sources
PubMed1998

Metabolic adaptations of a lower vertebrate to long-term hypothermic hypoxia provide clues to successful clinical liver preservation.

This study was designed to determine whether the metabolic adaptations developed by frogs to tolerate natural events of hypothermic hypoxia would precondition its liver for ex vivo organ storage. The metabolic responses of the frog, Rana castabiena, were compared to those of a mammalian system (rat) throughout a prolonged period of organ storage. Livers from rats and frogs were flushed and stored in UW solution at 5 degrees C for periods of 24-96 h. In frog livers, ATP was maintained high and constant over the first 24 h of storage; values ranged from 2.7 to 3.0 micro mol/g. Even after 96 h cold storage, ATP remained > 1.0 micro mol/g. In contrast, ATP levels in stored rat livers dropped rapidly, and by 4 h ATP was 1.2 micro mol/g. In terms of anaerobic endproduct accumulation, lactate levels rose 5.8 micro mol/g in frog liver (over 96 h) and by 8.6 micro mol/g in rat liver (over 24 h). This difference in flux through glycolysis was also reflected in relative rates of carbohydrate catabolism (i.e., glucose + lactate production). The rate of carbohydrate catabolism for frog liver was 0.74 micro mol/g/h compared to 2.26 micro mol/g/h for rat liver; a Q10 value of 6.2 was estimated for livers from R. castabiena. An assessment of glycolytic enzyme activities revealed that key differences in the responsiveness of pyruvate kinase to allosteric modifiers may have been responsible for the marked drop in the rate of anaerobic energy production in frog tissues. Although the concept of depressed metabolism in a lower vertebrate is not new, the data presented in this study demonstrate that a depressed metabolic state can be achieved in isolated livers from R. castabiena simply through cold exposure. With respect to clinical relevance, the results of this study indicate that energetics of stored livers can be maintained effectively through an efficient reduction in energy use in combination with a slow, yet continuous, rate of energy production facilitated by glycolysis.

Adaptation, Physiological↗
PubMed1998

Effects of hypothermic hypoxia on anaerobic energy metabolism in isolated anuran livers.

Many lower vertebrates (reptilian and amphibian species) are capable of surviving natural episodes of hypoxia and hypothermia. It is by specific metabolic adaptations that anurans are able to tolerate prolonged exposure to harsh environmental stresses. In this study, it was hypothesized that livers from an aquatic frog would possess an inherent metabolic ability to sustain high levels of ATP in an isolated organ system, providing insight into a metabolic system that is well-adapted for low temperature in vitro organ storage. Frogs of the species, R. pipiens were acclimated at 20 degrees C and at 5 degrees C. Livers were preserved using a clinical preservation solution after flushing. Livers from 20 degrees C-acclimated frogs were stored at 20 degrees C and 5 degrees C and livers from 5 degrees C-acclimated frogs were stored at 5 degrees C. The results indicated that hepatic adenylate status was maintained for 96 h during 5 degrees C storage, but not longer than 4-10 h during 20 degrees C storage. In livers from 5 degrees C-acclimated animals subjected to 5 degrees C storage, ATP was maintained at 100% throughout the 96-h period. Warm acclimation (20 degrees C) and 20 degrees C storage resulted in poorer maintenance of ATP; energy charge values dropped to 0.50 within 2 h and by 24 h, only 24% of control ATP remained. Lactate levels remained less than 25 mumol/g dry weight in all 5 degrees C-stored livers; 20 degrees C-stored livers exhibited greater accumulation of this anaerobic endproduct (lactate reached 45-50 mumol/g by 10 h). The data imply that hepatic adenylate status is largely dependent on exposure to hypothermic hypoxia and although small amounts of ATP were accounted for by anaerobic glycolysis, there must have been either a substantial reduction in cellular energy-utilization or an efficient use of low oxygen tensions.

Adenine Nucleotides↗
PubMed1998

Postliver transplant allograft reinfection with a lamivudine-resistant strain of hepatitis B virus: long-term follow-up.

Lamivudine is a nucleoside analogue with efficacy in the suppression of hepatitis B viral (HBV) replication. In a previously reported study, lamivudine was administered to patients with chronic, actively replicating HBV infection who subsequently underwent liver transplantation. Patients became serum HBV DNA-negative in response to lamivudine before transplantation, which was continued in the post-transplant period. Two of four patients surviving the immediate postoperative period developed allograft reinfection 240 and 409 days post-transplant. The strain of the reinfecting virus was analyzed, and a mutation in the YMDD region of the viral polymerase conferring resistance to lamivudine was discovered. The long term follow-up of these two patients is reported. The first patient developed ascites 16.5 months after allograft reinfection. A transjugular liver biopsy performed 18 months after the emergence of the lamivudine-resistant strain revealed cirrhosis and lobular hepatitis without rejection. The gradient between hepatic vein wedged and free pressures was 13 mmHg, consistent with portal hypertension. The second patient, 16 months after allograft reinfection with the lamivudine-resistant strain, is without clinical evidence of portal hypertension, although liver enzymes remain elevated. Both patients were given a trial of famciclovir, which did not significantly suppress HBV viremia. In conclusion, lamivudine-resistant HBV strains with the YMDD mutation may have an aggressive clinical course with rapid progression to cirrhosis. Famciclovir did not appear to be an effective rescue agent in these two patients.

2-Aminopurine↗
PubMed1998

[A comparative randomized prospective multicenter study of Sandimmune vs Neoral in liver transplantation].

Despite two decades of use, there are limited data on the best way to administer and monitor cyclosporine for orthotopic liver transplantation (OLT). The present study was undertaken: 1) to establish the safety of a new formulation of cyclosporine, Neoral, 2) to determine if treatment with Neoral will improve the results of liver transplantation and 3) to study the relationship between pharmacokinetic parameters and clinical outcomes after OLT. A double-blind, randomized, comparison of Sandimmune and Neoral was conducted at 5 Canadian centers in 188 consecutive adults undergoing OLT. Patients were induced with intravenous cyclosporine (CsA) then switched to Neoral or Sandimmune. Dose adjustments were made daily, or as needed, to reach a target trough CsA level (C0) of 350 ng/mL in both groups. Pharmacokinetic studies were performed on days 5, 10, 15 and 30 after transplantation. The Neoral group stopped intravenous CsA earlier (p < 0.0001), and these patients required a lower median daily oral dose (p < 0.01) to maintain comparable trough CsA levels. Five Sandimmune patients, but no Neoral patients discontinued the study because of the inability to reach target trough levels of CsA within the prescribed time (p < 0.05). At 4 months, there were no differences between the two groups with respect to patient survival, graft survival or rejection-free survival. The incidence of serious adverse events was also similar and did not correlate with CsA profiles. The Neoral group had a higher area under the drug concentration curve (AUC) and peak CsA levels (Cmax). There was a correlation between freedom from graft rejection and both AUC and Cmax at days 5 and 10 post-transplant. In contrast, there was a poor correlation between C0 and graft rejection. In summary, Neoral appears to be safe and well tolerated by patients. Cmax and/or AUC maybe better markers for monitoring cyclosporine based immunosuppression after liver transplantation.

Administration, Oral↗
PubMed1997

Minimal criteria for placement of adults on the liver transplant waiting list: a report of a national conference organized by the American Society of Transplant Physicians and the American Association for the Study of Liver Diseases.

This report summarizes a recent meeting cosponsored by the American Society of Transplant Physicians and the American Association for the Study of Liver Diseases to formulate minimal criteria by which patients with severe liver disease will be placed on the waiting list for liver transplantation. The participants agreed that only patients in immediate need of liver transplantation should be placed on the waiting list. Patients should not be placed in anticipation of some future need for such therapy. It was agreed that minimal criteria could assist but not replace the clinical judgment of the transplant professionals at individual centers. The criteria will be summarized below for adult patients with acute or chronic liver disease. The most important non-disease-specific criterion for placement on the transplant waiting list was an estimated 90% chance of surviving 1 year. This translated into a Child-Pugh score of > or = 7 for patients with cirrhosis which places the patient in Child-Pugh class B or C. Cirrhotic patients who have experienced gastrointestinal bleeding caused by portal hypertension or a single episode of spontaneous bacterial peritonitis would meet the minimal criteria irrespective of their Child-Pugh score. There were disease-specific criteria also. These include a sole minimal criterion for patients with fulminant hepatic failure regardless of etiology of the onset of stage 2 hepatic encephalopathy. A requirement for 6 months abstinence from alcohol before placement on the transplant waiting list was considered appropriate for most patients with alcoholic liver disease. Exceptional cases could get access to the waiting list through a regional review process. Chronic cholestatic diseases present difficulties because of a different natural history than that of chronic hepatocellular diseases. The use of specific risk scores for primary biliary cirrhosis and primary sclerosing cholangitis will likely replace Childs-Pugh classification as the scoring systems become refined. Minimal criteria for any patient with a primary hepatocellular cancer would admit any patient with a tumor confined to the liver irrespective of size or number of tumors, after careful investigation had failed to show spread to lymph nodes, the portal vein, or distant organs. Unusual or rare indications for liver transplantation, including Budd-Chiari syndrome, Wilson's disease, and other hereditary disorders, were also discussed. Finally, it was agreed that there should be no absolute contraindications to placement of patients on the liver transplant waiting list. These criteria should be open to regular review to accommodate advances in the field.

Adult↗
PubMed1996

Efficacy of lamivudine in chronic hepatitis B patients with active viral replication and decompensated cirrhosis undergoing liver transplantation.

Liver transplantation for endstage hepatitis B virus (HBV) infection has been associated with survival inferior to that of liver transplantation in other chronic liver diseases due to HBV reinfection of the graft. Lamivudine is a new nucleoside analog with potent antiviral effects against hepatitis B. Our aim was to test its efficacy when used pre- and posttransplantation in HBV-DNA positive patients with endstage liver disease. Patients received oral lamivudine 100 mg daily both pretransplant and posttransplant. Viral serology, serum and tissue HBV-DNA and liver histology were assessed sequentially. Five consecutive patients with endstage hepatitis B were entered into the trial. Serum HBV-DNA was cleared pretransplant in all patients. Three of four transplanted patients cleared HBeAg and HBsAg postoperatively, whereas all four became negative for serum HBV-DNA (dot-blot and PCR). Liver biopsies were negative for HBV-DNA by PCR in 3 of 4 cases. Lymphocytes were negative for HBV-DNA by PCR in all cases. With follow-up of 3, 14, 16, and 26 months, two patients have normal liver enzymes and normal liver histology and two have developed recurrent hepatitis B. No significant side effects were seen. This pilot study shows that lamivudine can effectively inhibit hepatitis B virus in cirrhotic patients pretransplant and posttransplant. A lamivudine resistant mutant developed in two patients. Transplant recipients with actively replicating HBV related cirrhosis may achieve a good outcome after liver transplantation using lamivudine, but viral resistance is likely to be a significant problem.

Adult↗
PubMed1996

Rapid resolution of chylous ascites after liver transplantation using somatostatin analog and total parenteral nutrition.

Chylous ascites is the accumulation of chylomicronrich lymphatic fluid within the peritoneal cavity. It is a rare complication of retroperitoneal surgery, and may occur spontaneously in 0.5% of patients with cirrhosis. Its management is controversial, and despite a variety of treatment options with limited efficacy, the course is usually indolent. In this article, we report a case of rapid resolution of chylous ascites after liver transplantation following 10 days of treatment using somatostatin analog (Octreotide, 100 micrograms sc. t.i.d.) and total parenteral nutrition (TPN). A 55-year-old man underwent liver transplantation for hepatitis C cirrhosis, and developed an infected chylous fistula on the 10th day. Treatment by fasting, TPN, and somatostatin analog resulted in a rapid falloff in fistula output, with complete resolution of ascites within 2 days. This is the first report, to our knowledge, of somatostatin analog and TPN used in combination for rapid and successful closure of a chylous fistula.

Ascites↗
PubMed1996

The metabolic impact of rapamycin (sirolimus) in chronic canine islet graft recipients.

The objective of this study was to analyze the impact of rapamycin and/or cyclosporine on the metabolic efficiency of intrasplenic islet autografts in dogs. An insulin modified frequently sampled intravenous glucose tolerance test was carried out before, on the last of 30 days treatment with drug and 30 days after cessation of drug therapy in dogs with stable function 1 to 7 years after total pancreatectomy and intrasplenic islet autografting. Analyses were performed for glucose clearance, insulin release, insulin sensitivity, and other variables. Rapamycin treatment was associated with increased glucose clearance, increased total and stimulated insulin release in response to glucose, and increased fasting plasma insulin level, as well as reduced insulin clearance. Cyclosporine at 300 micrograms/L had little impact on the measured variables. Treatment with rapamycin and cyclosporine showed a similar (although less-marked) pattern of changes to rapamycin alone. Rapamycin, with or without concomitant cyclosporine, was not associated with adverse impact on islet function or glucose metabolism in this canine model of pancreatic islet transplantation.

Animals↗
PubMed1996

Variables in organ donors that affect the recovery of human islets of Langerhans.

In an attempt to reduce the variability in the yields of human islets isolations and to identify donor factors that were potentially deleterious, we retrospectively reviewed 153 human islets isolations in our center over a 3-year period. Isolations were performed using controlled collagenase perfusion via the duct, automated dissociation, and Ficoll purification. Factors leading to successful isolations (recovery of >100,000 islet equivalents at a purity >50%) were analyzed retrospectively using univariate and multivariate analysis. Critical factors in the multiorgan cadaveric donors that were identified using univariate analysis included donor age (P<0.01), body mass index (BMI)(P<0.01), cause of death (P<0.01), and prolonged hypotensive episodes (systolic blood pressure <90 mmHg or mean arterial pressure <60 mmHg for > 15 min) requiring high vasopressors (>15 microgram/kg/min dopamine or >5 microgram/kg/min Levophed) (P>0.01). Independent analysis of 19 donor variables using multivariate logistic stepwise regression showed six factors were statistically significant. Odds ratio (OR) showed that donor age (OR 1.1, P<0.01), local procurement team (OR 10.9, P<0.01), and high BMI (OR 1.4, P<0.01) had a positive correlation with islet recovery. In contrast, hyperglycemia (all blood glucose >10 mmol/L) (OR 0.63, P<0.01), frequency and duration of cardiac arrest (OR 0.7, P<0.01), and increased duration of cold storage before islet isolation (OR 0.83, P<0.01) had negative correlation. Using these combinations of factors, the prediction of success was 85% accurate. By donor age, success was 13% for 2.5- to 18-year-old donors (n=23), 37% for 19- to 28-year-old donors (n=30), 65% for 29- to 50-year-old donors (n=70), and 83% for 51- to 65-year-old (n=29) donors. However, when vitro function was assessed by perifusion, the insulin secretory capabilities of islets isolated from the >50-year-old donor group was significantly reduced as compared with the 2.5- to 18-year-old group (P<0.02). Multiple regression analysis using postdigestion and postpurification islet recovery as outcome variables identified BMI, procurement team, pancreas weight, and collagenase digestion time factors tht can affect the recovery of human islets. Locally procured pancreases and donors with elevated minimum blood glucose levels were identified as factors that affect the insulin secretory capabilities of the isolated islets. This review of parameters suggests an improved approach to the prediction of successful islet isolation from human pancreases. Selection of suitable pancreases for processing may improve consistency in human islet isolation and thereby decrease costs.

Adult↗
PubMed1996

Tacrolimus (FK506)--its effects on intestinal glucose transport.

Tacrolimus (FK506) is at present the mainstay of immunosuppression for small intestinal transplantation. This study investigates the effects of chronic treatment with varying dosages of tacrolimus on animal well-being, weight gain, intestinal permeability, and the active transport of nutrients as measured by in vitro studies quantifying glucose flux. The effect of acute treatment with high-dose tacrolimus on glucose flux was also investigated. In the chronic studies, juvenile male Lewis rats were given tacrolimus in a dosage of 0.1 mg/kg, 0.5 mg/kg, and 2 mg/kg q. second day by subcutaneous injection for five weeks. In the acute studies, animals were treated with 2 mg/kg given q. 24 hr [mult] 48 hr, 24 hr and 12 hr prior to sacrifice. In the acute treatment groups, tacrolimus caused no change in glucose flux. In the chronically treated animals, FK506 levels were within the clinically relevant range. Chronic treatment with 0.5 and 2 mg/kg caused a significant reduction in weight gain. These same groups of animals had a significant increase in intestinal permeability as measured by absorption of 99Te-DTPA. Glucose flux was affected in all chronically treated groups, with net flux increasing in the jejunum and decreasing in the ileum. These findings show that chronic treatment with low-dose tacrolimus is well tolerated, but in higher doses there are significant effects in intestinal permeability and nutrient uptake, and animal weight gain. We suggest that these changes are due to alterations in intestinal permeability that do not appear to be mediated by an acute drug effect and more likely represent chronic changes, possibly from alterations in gene expression. These findings suggest that further studies regarding the effects of tacrolimus on nutrient transport, intestinal permeability, and the known immunologically related functions of tacrolimus should be done.

Animals↗
PubMed1996

Pharmacodynamic assessment of mycophenolic acid-induced immunosuppression by measurement of inosine monophosphate dehydrogenase activity in a canine model.

The combination of pharmacokinetic and pharmacodynamic (measurement of the biological effect) monitoring of immunosuppressive drugs provides a method for the optimization of drug dosing. We chose to investigate this using mycophenolic acid (MPA), an immunosuppressive drug that mediates its effect by the inhibition of inosine monophosphate dehydrogenase (IMPDH), a key enzyme in the de novo biosynthesis of purines. Using an assay developed for measurement of IMPDH activity in whole blood, the concentration required for 50% inhibition of IMPDH activity was approximately 200 mg/L (58 +/- 8.3% for whole blood [n = 6] and 55 +/- 10.0% for isolated lymphocytes). To ascertain the relationship between MPA concentration and IMPDH inhibition in vivo, dogs were administered a single dose of mycophenolate mofetil, the pro-drug of MPA, at 20 or 40 mg/kg orally. Pharmacokinetic analysis revealed that the Cmax of the 40-mg/kg group was statistically greater than that of the 20-mg/kg group (P < 0.05). There were no statistical differences in the other parameters investigated (area under the curve, beta half-life, mean residence time, volume of distribution at steady state, and clearance) between the two treatment groups. The half-life was calculated at approximately 8 hr for both dose groups. There was also substantial variability among the dogs in the absorption and clearance of MPA. An inverse relationship was found between the MPA concentration and IMPDH. Maximal inhibition of IMPDH activity of 30-40% occurs approximately 2-4 hr after dosing, followed by a gradual restoration in enzyme activity. After 24 hr, there is an increase in IMPDH activity that exceeds the pre-dosing levels in some cases by 3-fold. Evaluation of the pharmacokinetic and the pharmacodynamic responses to MPA in the canine model suggests that the drug should be administered ever 8 hr to optimize its immunosuppressive efficacy. This combined approach can be used for optimization of doses of this and other immunosuppressive drugs.

Animals↗
PubMed1996

Mutation in HBV RNA-dependent DNA polymerase confers resistance to lamivudine in vivo.

The (-) enantiomer of 3'-thiacytidine (lamivudine) has been found to be a potent inhibitor of hepatitis B virus (HBV) and human immunodeficiency virus (HIV) replication. Mutation of methionine to valine or isoleucine at the YMDD (tyrosine, methionine, aspartate, aspartate) motif of the HIV reverse transcriptase has been shown to be responsible for lamivudine resistance in HIV. The hepadnaviruses also have the YMDD motif in their DNA polymerase. Therefore, it is possible that hepadnaviruses could develop lamivudine resistance by a similar mutation at this motif. We analyzed the HBV from a liver transplantation patient who developed recurrent HBV viremia during lamivudine treatment. The polymerase gene was amplified by polymerase chain reaction (PCR), and the region coding for the YMDD motif was sequenced. The pretreatment HBV sequence coded for YMDD, while the lamivudine-resistant mutant HBV coded for YIDD (tyrosine, isoleucine, aspartate, aspartate). With the documented changes in the YMDD motif of lamivudine-resistant HIV, it is likely that the methionine-to-isoleucine mutation in the YMDD motif of the HBV polymerase contributes significantly to the lamivudine-resistance of HBV isolated from this patient.

Adult↗
PubMed1996

Nutritional and intestinal effects of the novel immunosuppressive agents: deoxyspergualin, rapamycin, and mycophenolate mofetil.

OBJECTIVES: Transplantation of the small intestine would be an attractive therapeutic option for treatment of short bowel syndrome if effective, nontoxic immunosuppressive agents could be developed. This study examines the effect of three newly developed immuno-suppressive agents: rapamycin, deoxyspergualin, and mycophenolate mofetil, on the nutritional status and intestinal function of normal juvenile rats. DESIGN & METHODS: Rapamycin (2 mg/kg every second day), deoxyspergualin (2 mg/kg every second day) and mycophenolate mofetil (MM) (25 mg/kg every second day) were injected subcutaneously for six weeks. RESULTS: Rapamycin and deoxyspergualin caused significant reductions in weight gain without impairing feed intake. Both drugs caused small decreases in fat absorption; treatment with DSG induced an increase in permeability to 99Tc-DTPA. However, the permeability to other markers, such as mannitol and lactulose, was decreased in the rapamycin and mycophenolate mofetil-treated animals. Intestinal function in vitro was quantified using glucose flux (absorption). In the rapamycin group, there was a significant decrease in ileal uptake of glucose, with the net flux (absorption) being zero; there was an associated loss of villous size histologically. In the deoxyspergualin-treated groups, there was a decrease in the jejunal glucose flux. In the mycophenolate mofetil-treated animals, there was a decrease in jejunal with a compensatory increase in ileal glucose absorption. There were minor variations in intestinal morphology, but these were not consistent. CONCLUSIONS: Rapamycin and deoxyspergualin in these doses cause a significant reduction in weight gain in healthy juvenile animals, and all the drugs caused changes in the active transport characteristics of the intestine. Accordingly, the use of these drugs for intestinal transplantation should be evaluated carefully for their nutritional impact.

Animals↗