Search PubMed⌕ Search

Biomedical subjects

R Ghobrial

Publications and source records attributed to R Ghobrial.

14 recordsLinked to original sources
PubMed1997

Synergistic mechanisms by which sirolimus and cyclosporin inhibit rat heart and kidney allograft rejection.

The studies presented herein examined the mechanism(s) whereby sirolimus (SRL) and cyclosporin (CsA) act synergistically to block allograft rejection. Combination index (CI = 1 reflects additive, CI > 1 antagonistic, and CI < 1 synergistic, effects) analysis documented potent synergism between SRL and CsA to block allograft rejection. Combinations of the two drugs produced synergistic prolongation of heart (CI = 0.001-0.2) or kidney (CI = 0.03-0.5) allograft survival at SRL/CsA ratios ranging from 1:12.5 to 1:200. Pharmacokinetic analysis of the individual drugs showed that CsA does not affect the blood levels of SRL, and SRL mildly increases the levels of CsA in SRL/CsA-treated rats. Quantitative polymerase chain reaction analysis was used to document that both subtherapeutic (1.0 mg/kg) and therapeutic (2.0 or 4.0 mg/kg) CsA doses inhibited the expression of interferon-gamma (IFN-gamma) (P < 0.03) and IL-2 (P < 0.003) mRNA produced by T helper (Th) 1 cells, as well as IL-10 (P < 0.001), but not IL-4 (NS) mRNA produced by Th2 cells. Contrariwise, all tested SRL doses (0.02, 0.04 or 0.08 mg/kg) did not affect cytokine mRNA expression. However, heart allografts from rat recipients treated with synergistic SRL/CsA doses displayed reduced levels of IFN-gamma (P < 0.01), IL-2 (P < 0.001) and IL-10 (P < 0.001) mRNA. Thus, because subtherapeutic doses of CsA reduce Th1/Th2 activity, thereby facilitating the inhibition of signal transduction by low does of SRL, the two agents act synergistically to inhibit allograft rejection.

Animals↗
PubMed1997

Long-term survival after retransplantation of the liver.

OBJECTIVE: The authors determined the long-term outcome of patients undergoing hepatic retransplantation at their institution. Donor, operative, and recipient factors impacting on outcome as well as parameters of patient resource utilization were examined. SUMMARY BACKGROUND DATA: Hepatic retransplantation provides the only available option for liver transplant recipients in whom an existing graft has failed. However, such patients are known to exhibit patient and graft survival after retransplantation that is inferior to that expected using the same organs in naiive recipients. The critical shortage of donor organs and resultant prolonged patient waiting periods before transplantation prompted the authors to evaluate the results of a liberal policy of retransplantation and to examine the factors contributing to the inferior outcome observed in retransplanted patients. METHODS: A total of 2053 liver transplants were performed at the UCLA Medical Center during a 13-year period from February 1, 1984, to October 1, 1996. A total of 356 retransplants were performed in 299 patients (retransplant rate = 17%). Multivariate regression analysis was performed to identify variables associated with survival. Additionally, a case-control comparison was performed between the last 150 retransplanted patients and 150 primarily transplanted patients who were matched for age and United Network of Organ Sharing (UNOS) status. Differences between these groups in donor, operative, and recipient variables were studied for their correlation with patient survival. Days of hospital and intensive care unit stay, and hospital charges incurred during the transplant admissions were compared for retransplanted patients and control patients. RESULTS: Survival of retransplanted patients at 1, 5, and 10 years was 62%, 47%, and 45%, respectively. This survival is significantly less than that seen in patients undergoing primary hepatic transplantation at the authors' center during the same period (83%, 74%, and 68%). A number of variables proved to have a significant impact on outcome including recipient age group, interval to retransplantation, total number of grafts, and recipient UNOS status. Recipient primary diagnosis, cause for retransplantation, and whether the patient was retransplanted before or after June 1, 1992, did not reach statistical significance as factors influencing survival. In the case-control comparison, the authors found that of the more than 25 variables studied, only preoperative ventilator status showed both a significant difference between control patients and retransplanted patients and also was a factor predictive of survival in retransplanted patients. Retransplant patients had significantly longer hospital and intensive care unit stays and accumulated total hospitalization charges more than 170% of those by control patients. CONCLUSIONS: Hepatic retransplantation, although life-saving in almost 50% of patients with a failing liver allograft, is costly and uses scarce donor organs inefficiently. The data presented define patient characteristics and preoperative variables that impact patient outcome and should assist in the rational application of retransplantation.

Adolescent↗
PubMed1996

Kinetics of in vitro immune responses of T and B cells during tolerance induction by sirolimus.

OBJECTIVES: The purpose of the study presented herein was to examine immune performances of rat heart allograft recipients immunosuppressed with sirolimus (SRL, rapamycin; Rapamune, Wyeth-Ayerst, Princeton, NJ). METHODS: The immune performances of lymphocytes harvested from SRL-treated Wistar Furth (WF; RT1u) recipients of Buffalo (BUF; RT1b) heart allografts were examined on days 7, 14, and 90 postgrafting. RESULTS: Whether derived from normal WF rats, SRL-treated WF heart recipients, or SRL-untreated WF heart recipients, pan-T cell population purified from the lymph nodes or spleens on day 7 or 14 displayed similar responses to phytohemaglutinin, anti-T cell receptor R73 monoclonal antibody, donor-type BUF, or third-party Brown Norway alloantigenic stimulators. There was no in vitro evidence of suppressor T cells in SRL-treated recipients. The frequencies of anti-BUF-specific cytotoxic T cells, as shown by limiting dilution analysis, were similar in the short- (days 7 or 14) and in the long- (day 90) term surviving recipients. SRL treatment did not affect the expression of interleukin-2 (IL-2) messenger RNA (mRNA) by T helper 1 (Th1) or of IL-4 and IL-10 mRNA by Th2 cells on days 7 and 14 postgrafting, but did induce selective activation of Th2 cells on day 60 postgrafting. Administration of SRL induced the production of non-complement (C')-fixing IgG2c BUF-specific alloantibodies that appeared in the sera of unresponsive recipients on day 14 postgrafting and reached a peak concentration on day 120 postgrafting. In contrast to untreated recipients that rejected BUF heart allografts, all SRL-treated WF recipients failed to produce C'-fixing BUF-specific alloantibodies. CONCLUSIONS: SRL promotes long-term selective activation of Th2 cells and the production of non-C'-fixing IgG2c blocking antibodies.

Animals↗
PubMed1995

Membrane-bound or soluble truncated RT1.Aa rat class I major histocompatibility antigens induce specific alloimmunity.

Transfectants that express membrane-bound (MB) or secrete soluble truncated (TR) rat class I RT1.Aa major histocompatibility (MHC) antigens induce alloimmunity in vivo. The MB-RT1.Aa was produced by transfecting the full-length RT1.Aa cDNA, including the alpha 1, alpha 2, and alpha 3, transmembrane and intracellular domains. The TR-RT1.Aa cDNA insert included only the extracellular alpha 1, alpha 2, and alpha 3 domains; a stop codon was placed in front of the transmembrane domain. Following full-length sequencing, MB-RT1.Aa and TR-RT1.Aa cDNAs were translated in vitro into glycosylated MB-RT1.Aa (45 kDa) and TR-RT1.Aa (36 kDa) proteins, respectively. Each cDNA construct was individually subcloned into the pSG5 vector before transfection into Buffalo (BUF; RT1b) hepatoma cells. FACscan analysis with anti-RT1.Aa-specific R2/15S monoclonal antibody (MAb) confirmed surface expression of RT1.Aa molecules on the MB-RT1.Aa, but not on the TR-RT1.Aa, transfectants. In contrast, enzyme-linked immunoadsorbent assays documented the presence of soluble RT1.Aa molecules in supernates from cells transfected with the TR-RT1.Aa, but not from cells transfected with the MB-RT1.Aa, cDNA. Subcutaneous injection of MB-RT1.Aa or TR-RT1.Aa transfectants to BUF or Wistar Furth (WF; RT1u) rats induced accelerated rejection of ACI (RT1a) but not third-party Brown Norway (RT1n) heart allografts. Furthermore, supernates of TR-RT1.Aa, but not of MB-RT1.Aa, transfectants immunized WF hosts toward ACI hearts. Thus, both intact MB-RT1.Aa and soluble TR-RT1.Aa class I alloantigens induce potent sensitization against alloantigens.

Amino Acid Sequence↗
PubMed1994

Rapamycin inhibits production of cytotoxic but not noncytotoxic antibodies and preferentially activates T helper 2 cells that mediate long-term survival of heart allografts in rats.

Rapamycin (RAPA) induces unresponsiveness toward heart allografts by at least two mechanisms: selective production of noncytotoxic IgG2c-blocking Ab and preferential activation of Th2 cells. RAPA (0.8 mg/kg/day) delivered via a 14-day osmotic pump to Wistar Furth (WF; RT-1u) recipients prolongs Buffalo (BUF; RT-1b) heart allograft survival from a mean survival time (MST) of 6.5 +/- 0.5 days to 75.0 +/- 18.9 days (n = 18; p < 0.001), with 6 of 18 grafts beating for more than 100 days. Recipient sera or their IgG but not IgM fraction, obtained after postgrafting day 40, passively transfer the unresponsive state to sublethally irradiated secondary recipients in a dose-dependent and immunologically-specific fashion. Sera obtained after untreated WF hosts rejected BUF hearts contained IgG moieties of all subclasses that bound to class I MHC BUF epitopes. In contrast, the unresponsive sera contained predominantly non-C'-fixing IgG2c and only marginal amounts of activated (C') fixing IgG1, IgG2a, and IgG2b Ab. The transcription of IL-2, IL-4, and IL-10 mRNAs was assessed using a PCR method. There were similar increases in the levels of IL-2, IL-4, and IL-10 mRNA in heart allografts from both untreated and RAPA-treated recipients on day 5 postgrafting. In contrast, on days 60 and 300 postgrafting heart allografts from RAPA-treated unresponsive recipients showed increased levels of IL-10 and IL-4 but not of IL-2 mRNA, suggesting preferential activation of Th2 cells. Thus, RAPA treatment selectively inhibits the synthesis of C'-binding of IgG subclasses, spares the non C-binding blocking IgG2c Ab, and preferentially activates Th2 cells.

Animals↗
PubMed1994

Immunosuppressive agents.

The present success of organ transplantation is largely due to advances in immunosuppressive therapy. Progress has been made from a cytotoxic strategy associated with a high morbidity rate to a strategy that seeks to alter the activity of cells that regulate the immune response, in order to selectively dampen antidonor responses. This article presents a comprehensive review of the clinical matrix of immunosuppressive agents, which includes various combinations of pharmacologic agents tailored to minimize toxicity and to enhance efficacy.

Antigen Presentation↗
PubMed1993

Effect of atrial natriuretic peptide on urine flow and glomerular filtration during acute renal allograft rejection.

The effect of exogenous atrial natriuretic peptide (ANP) on urine excretion and glomerular filtration rate (GFR) during acute renal allograft rejection was evaluated in a canine model. Eight animals underwent simultaneous allotransplantation and unilateral native nephrectomy. No preoperative or postoperative immunosuppressive therapy was given. Acute renal function studies were performed on the allografts and companion, native kidneys following surgical exposure and mobilization on the third postoperative day. At reexploration, the allografts were found to be grossly enlarged (138 +/- 10 gm.) and contained moderate-to-marked perivascular interstitial infiltration. Glomerular filtration rate, determined by measurement of urinary inulin clearance, was significantly reduced from prenephrectomy baseline values (19 +/- 4 ml. per minute versus 32 +/- 5 ml. per minute, p < .05). During a 30 minute, intravenous ANP infusion, allograft urine flow rates increased from 1.4 +/- 0.5 ml. per minute to 3.3 +/- 0.4 ml. per minute (p < .01), and GFR increased from 19 +/- 4 ml. per minute to 24 +/- 4 ml. per minute (p < .05). During ANP infusion, mean arterial pressure declined from 136 +/- 7 mm. Hg to 116 +/- 7 mm. Hg (p < .05), and the hematocrit remained unchanged. These observations are consistent with previously described, ameliorative effects of ANP in other models of acute ischemic renal injury and provide an experimental basis for more extended studies examining the potential usefulness of ANP as adjunctive therapy in the treatment of acute renal allograft rejection.

Acute Disease↗
PubMed1993

The mechanism of unresponsiveness to allografts induced by rapamycin and rapamycin/cyclosporine treatment in rats.

The mechanisms by which rapamycin (RAPA) and/or cyclosporine induce unresponsiveness to allografts were investigated in a rat model. Buffalo (BUF, RT-1b) heart allografts were rejected by Wistar-Furth (WFu, RT-1u) recipients at a mean survival time (MST) of 6.5 +/- 0.5 days. A 14-day course of RAPA (0.8 mg/kg) delivered intravenously by an osmotic pump prolonged BUF allograft survival to 76.1 +/- 23.4 days (P < 0.001). Adoptive transfer of 30-50 x 10(6) spleen and lymph node T cells that had been isolated on day 40 postgrafting from CsA- or RAPA/CsA-treated hosts into lightly irradiated (6 Gray) secondary WFu recipients prolonged BUF graft survival from 9.8 +/- 1.2 to 29.2 +/- 11.0 (P < 0.01) and 58.2 +/- 38.9 days (P < 0.004), respectively. T cells transferred from animals treated with RAPA alone failed to prolong graft survival. In contrast, sera isolated on day 40 postgrafting from WFu primary hosts treated with RAPA alone or with the RAPA/CsA combination, but not with CsA alone, extended the survival of BUF hearts: 3 ml serum from RAPA-treated hosts prolonged BUF heart survival to 76.6 +/- 31.3 days (P < 0.002) and from RAPA/CsA-treated hosts to 47.1 +/- 12.8 days (P < 0.001). The effect of serum was immunologically specific: it did not prolong the survival of third-party outbred Sprague Dawley heart allografts. Although the IgM fraction (0.2 mg) purified from the serum of RAPA-treated recipients was ineffective (10.6 +/- 0.8 days; NS), an equal amount of the IgG fraction significantly (P < 0.002) prolonged BUF heart allograft survival to 26 days (n = 4). Thus, hosts treated with RAPA or a RAPA/CsA combination develop IgG antibodies that mediate the unresponsive state toward allogeneic heart allografts.

Animals↗
PubMed1992

Percutaneous endoscopic gastrostomy with jejunal extension: a new technique.

Percutaneous endoscopic gastrostomies (PEG) with jejunal extensions are placed in patients at risk for aspiration of gastric contents. Current methods used are difficult and often ineffective in preventing aspiration, and frequently result in substantial morbidity and mortality. In this study, a new method of jejunal extension from a PEG was evaluated with regard to efficacy and prevention of aspiration of gastric contents while providing adequate enteral nutrition. Twelve patients with recent aspiration pneumonitis underwent PEG placement with a jejunal extension by this new method. The technique was accomplished rapidly and without difficulty in an average time of 26.2 min (range 17-31 min). In all instances, the jejunal extension remained functional for the first 8 wk after placement, and there were no instances of aspiration of gastric contents while nutritional requirements were met. None of the patients died from complications of the procedure. The method described was effective in preventing aspiration of gastric contents, was easily performed, and was associated with minimal complications.

Enteral Nutrition↗
PubMedDate not supplied

Concomitant placement of percutaneous endoscopic gastrostomy and jejunostomy.

Percutaneous endoscopic gastrostomies have gained wide use for long-term enteral nutrition. However, gastroesophageal reflux and aspiration pneumonia have occurred following this procedure. Initial enthusiasm concerning the ability of intrajejunal feeding to negate the risk of aspiration has been challenged by some reports. In this report, a new method is described for concomitant placement of endoscopic gastrostomy and feeding jejunostomy wherein the tip of the feeding jejunostomy is placed at least 40 cm distal to the pylorus while the gastrostomy tube is used for drainage. Twenty critically ill patients underwent the procedure utilizing general or local anesthesia. Sixty-day follow-up showed one uneventful episode of pulmonary aspiration (5%) after retrograde migration of the jejunal tube into the duodenum. All but two patients (90%) tolerated their tube feedings well. This technique can be easily performed with accurate placement of the PEJ tube distal to the pylorus and is associated with minimal risk of aspiration.

Adolescent↗