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Biomedical subjects

Y Calmus

Publications and source records attributed to Y Calmus.

At least 37 records · Page 2Linked to original sources
PubMed2000

Suppression of humoral immunization against encapsulated xenogeneic hepatocytes and prolongation of their function by 2-week cyclosporine treatment in the rat.

BACKGROUND: Xenogeneic liver transplantation may induce immune reactions not only against the grafted liver but also against the proteins that it synthesizes. We investigated whether 2-week cyclosporine treatment could suppress immunization and improve graft function in a xenogeneic hepatocyte transplantation model. METHODS: Free or encapsulated human hepatoma cells (HepG2) were cocultured for 28 days with splenocytes from Lewis rats or implanted for 60 days into the peritoneum of Lewis rats. RESULTS: Anti-HepG2 and antialbumin antibodies were detected in the supernatants of rat splenocytes that were cocultured with HepG2 cells and in the serum of rats that had undergone transplantation with HepG2 cells. Cyclosporine suppressed this antibody production both in vitro and in vivo. Human alpha-GST blood levels, which reflect hepatocyte injury, were low in cyclosporine-treated animals but high when encapsulated HepG2 cells were transplanted without cyclosporine therapy. Western blots revealed human albumin from day 3 to day 60 in the serum of rats treated with cyclosporine, but not after day 30 in untreated rats. CONCLUSIONS: Xenogeneic hepatocytes induce a humoral response that impairs their viability and function. A 2-week course of cyclosporine suppresses this immune response and improves graft function for up to 60 days.

Animals↗
PubMed2000

[Xenotransplantation: physiopathology of hyperacute and differentiated rejection, and therapeutic perspectives].

The mechanisms of xenograft rejection involved in closely related species of donors and recipients are not the same as in disparate combinations. When the donor and the recipient are phylogenetically close, such as the monkey and the human being, the rejection of xenografts is essentially mediated by a cellular immune response, and is clinically similar to a strong allograft rejection. When the donor and the recipient belong to widely disparate species, such as in the pig-to-human combination, the graft is destroyed by a hyperacute rejection before a cellular rejection has started. Hyperacute rejection is triggered by the fixation of the recipient's preformed antibodies on the graft endothelium, and subsequent activation of the recipient's complement. The activation of endothelial cells that ensues leads to the formation of an extensive thrombosis within the graft and to its necrosis within minutes or hours after grafting. When hyperacute rejection is overcome by means of complement inhibitors, a delayed vascular rejection occurs within 36 to 48 hours, mainly involving antibody-dependent cellular cytotoxicity and contributing to the extension of the thrombosis. Both hyperacute and delayed vascular rejections can be prevented by depletion of preformed antibodies, inhibition of complement activation, or by masking the dominant xeno-epitope Gal alpha 1,3 Gal. Transgenic pigs expressing molecules that inhibit xenogeneic rejection are being produced. However, prior to any clinical use, the infectious risks, and particularly the viral risk must be evaluated.

Acute Disease↗
PubMed1999

Bile acids modulate the interferon signalling pathway.

We have previously shown that cholestasis and bile acids inhibit 2', 5' oligoadenylate synthetase (OAS) activity in the liver and in primary hepatocyte cultures. Here, we assessed the influence of bile acids on interferon (IFN) pathway activation in three hepatoma cell lines. In HepG2 cells, bile acids (100-200 micromol/L) inhibited IFN-induced 2',5' OAS activity to an extent depending on their surface activity index. In Western blot analysis, IFN-induced expression of two major antiviral proteins, MxA and OAS p100, was reduced by 54% +/- 8% and 44% +/- 12%, respectively, when cells were preincubated for 4 hours with 100 micromol/L chenodeoxycholic acid (CDCA). In the same conditions, CDCA did not modify the IFN-induced signal transducers and activators of transcription (STAT)s tyrosine phosphorylation. In contrast, it reduced IFN-induced MxA promoter activity by 60%. The inhibitory effect of CDCA was not mediated by a 4beta-phorbol 12beta-myristate 13alpha-acetate (PMA)-sensitive protein kinase C (PKC)-dependent pathway. Finally, using CHO cells stably expressing a functional human bile acid carrier (Na+-dependent taurocholate cotransporting polypeptide [NTCP]), we found that bile acid inhibition of the IFN pathway occurred in the range of more physiological concentrations (12-50 micromol/L). In summary, our results provide strong evidence that bile acids inhibit the induction of proteins involved in the antiviral activity of IFN. This might partly explain the lack of responsiveness to IFN therapy in some patients with advanced chronic viral liver diseases.

2',5'-Oligoadenylate Synthetase↗
PubMed1999

Increased expression of interleukin-4 during liver allograft rejection.

BACKGROUND/AIMS: To investigate the respective roles of interleukin-2 (IL-2) and IL-4 during rejection, we evaluated the expression of IL-2, IL-2 receptor and IL-4 in human liver allografts. METHODS: Immunohistochemistry and RT-PCR were performed in liver biopsies. To determine the effects of immunosuppression and cholestasis in IL-4 production, in vitro experiments were also designed. RESULTS: IL-2 protein and its mRNA were absent in the liver, with minimal expression of IL-2 receptor, during rejection. In contrast, IL-4 protein and its mRNA were highly expressed during acute and chronic rejection, whereas this expression was absent in stable liver transplant recipients. In vitro, cyclosporine potently inhibited IL-2 and IL-2 receptor expression of activated mononuclear blood cells, but poorly inhibited IL-4 expression. Chenodeoxycholic acid decreased IL-2 and IL-2 receptor expression, but increased IL-4 expression. CONCLUSIONS: During liver allograft rejection, IL-2 pathway is down-regulated, while IL-4 expression is increased by cholestasis and poorly inhibited by cyclosporine. These data suggest that IL-4 is involved in the mechanisms of liver allograft rejection in patients treated with cyclosporine.

Acute Disease↗
PubMed1999

Evaluation of efficacy of liver transplantation in alcoholic cirrhosis using matched and simulated controls: 5-year survival. Multi-centre group.

BACKGROUND/AIMS: Alcoholic cirrhosis is the most common cause of liver transplantation in US males. The limited number of donor livers calls for "prioritisation", favouring those patients who will benefit most. The aim was to assess the efficacy of liver transplantation in patients with alcoholic cirrhosis. METHODS: We compared the survival of 169 transplanted patients with two conservatively treated control groups, one of 169 patients matched for prognostic factors (age, cirrhosis severity, bleeding history) and one of 169 simulated patients. RESULTS: The probability of survival to 5 years in the transplanted group was 66% (95% confidence interval 58-74%) vs. 52% (44-60; p = 0.03) in the matched group and 54% (51-57; p = 0.01) in the simulated controls. Transplantation was associated with survival (relative risk = 1.51; p = 0.02), independently of risk score (risk = 2.07; p<0.001), indication, period of inclusion, centre experience, and alcohol abstinence. Patients with severe disease (Pugh C11-15) benefited most in terms of 5-year survival: 58% (44-72) vs. 31% (17-45; p = 0.008) in the matched and 35% (30-40; p<0.001) in the simulated control groups. For patients at lower risk there was no significant difference. CONCLUSIONS: Liver transplantation increases the 5-year survival of patients with severe alcoholic cirrhosis. In patients at lower risk, efficacy of transplantation should be confirmed by longer follow-up or by randomised trial.

Case-Control Studies↗
PubMed1999

A short induction regimen of interferon-alpha is not effective for treatment of relapse in chronic hepatitis C: a randomized trial. For the multicentre GER-CYT-01 group.

The aim of this work was to assess the effect of a high-dose (10 million units, MU) short-duration (14 weeks) interferon-alpha2b (IFN-alpha2b) regimen in relapsers compared with the standard IFN regimen of 3 MU three times weekly (t.i.w.) for 6 months. Fifty-eight non-cirrhotic patients (who had relapsed after previous treatment with IFN) with chronic hepatitis were randomized: 29 to the high-dose, short-duration regimen and 29 to the standard regimen. By the end of IFN therapy, in the high-dose, short-duration group alanine aminotransferase (ALT) normalization was observed in 23 (79%) of 29 patients, and undetectable hepatitis C virus (HCV) RNA in eight (28%) vs 25 (86%) and 11 (38%) of the 29 patients in the standard group, respectively (P = NS). At the end of the 72-week follow-up, in the high-dose, short-duration group a sustained ALT normalization was observed in two (7%) patients, and undetectable HCV RNA in 0 (0%) vs five (17%) and four (14%) patients in the standard group (P = NS). There was less fibrosis improvement in the high-dose, short-duration group (two of 26 patients, 8%) than in the standard group (eight of 25 patients, 32%) (P = 0.04). Tolerance to IFN was good and similar in the two groups. In conclusion, in IFN relapsers, high-dose, short-duration treatment with IFN-alpha has no advantage when compared to a 6-month treatment with 3 MU IFN t.i.w.

Adult↗
PubMed1999

[Biological monitoring of liver transplantation].

Liver transplantation is now a widely used therapeutic option that has been proved effective, although the inadequate supply of transplants remains a problem. Laboratory tests are important at three different periods in time: prior to transplantation to aid in patient selection and to look for contra-indications to transplantation; during the transplant procedure to ensure real-time evaluation of vital metabolic parameters; and, above all, after the procedure to assist in the detection of complications. These can occur early (preservation lesions, acute rejection, side effects of immuno-suppressive agents, infections, renal failure, etc.), as a direct result of the surgical procedure (blood vessel or bile duct injury), or late (chronic rejection, recurrence of the initial disease, treatment-induced cancer).

Contraindications↗
PubMed1998

A newly established porcine aortic endothelial cell line: characterization and application to the study of human-to-swine graft rejection.

The establishment of cell lines allows reproductible in vitro studies that would be far more difficult to perform using primary cells that rapidly undergo phenotypical alterations in culture. The purpose of this work was to establish an endothelial cell line appropriate for in vitro study of endothelial cell activation during xenograft rejection. Porcine aortic endothelial cells were transfected with the early region of SV40 and selected on the basis of morphological, phenotypical, and functional features. By light and electron microscopy, the porcine aortic endothelial cell line (PAEC11) and primary cells were similar except that PAEC11 was slightly smaller. PAEC11 displayed endothelial cell characteristics since it endocytosed acetylated low density lipoproteins, produced von Willebrand factor, and expressed E-selectin. Human natural antibodies bound to the same xenoantigens on PAEC11 and primary cells. That binding was followed by human complement activation and cell lysis. In addition, PAEC11 was found appropriate for genetic engineering since it could be transfected with a plasmid encoding a foreign gene. Therefore, this cell line should be a useful model for in vitro study of endothelial cell function in general and human-to-swine xenograft rejection in particular.

Animals↗
PubMed1998

Human preformed IgG combining with membrane-bound porcine serotransferrin lyse porcine endothelial cells through antibody-dependent cellular cytotoxicity.

Preformed antibodies are involved in xenograft rejection. The purpose of this work was to characterize porcine xenoantigens recognized by human preformed IgG (hpIgG), and to investigate the role of hpIgG in xenogeneic rejection. IgG eluted from porcine livers perfused with human plasma, human sera and total human IgG were immunoblotted on porcine aortic endothelial cell extracts. The amino acid sequence of a 76-kDa antigen constantly revealed was 100% homologous with porcine serotransferrin (psTf). hpIgG from human sera, human IgG1 and IgG2 and F(ab')2gamma specifically bound to psTf. Neutralization by psTf abolished that binding. Although alpha1,3-linked galactose residues (Gal(alpha)1,3Gal) is the dominant epitope recognized by preformed antibodies in the swine-to-human combination, the analysis of carbohydrate composition of psTf showed that the molecule was devoid of Gal(alpha)1,3Gal moieties and that preformed anti-psTf IgG bound to epitopes localized on the peptide core of the molecule. Purified human anti-psTf IgG antibodies were able to bind to psTf linked to its receptor on porcine endothelial cells, and to kill those cells through antibody-dependent cellular cytotoxicity.

Amino Acid Sequence↗
PubMed1998

Beneficial hemodynamic effects of bosentan, a mixed ET(A) and ET(B) receptor antagonist, in portal hypertensive rats.

In patients with cirrhosis, the plasma level of endothelin, a potent vasoconstrictor peptide, is elevated, and endothelin plays a role in increased intrahepatic vascular resistance. Thus, the aim of this study was to evaluate the hemodynamic effects of bosentan, a mixed ET(A) and ET(B) endothelin receptor antagonist in three models of portal hypertension. In all groups of rats, endothelin (2 microg/kg intravenously) administration significantly increased intrahepatic vascular resistance. In rats with secondary biliary cirrhosis, bosentan (30 mg/kg) significantly reduced portal pressure from 14.6 +/- 1.2 to 12.1 +/- 0.6 mm Hg, while portal blood flow and cardiac output increased by 45% and 57%, respectively. Thus, hepatocollateral vascular resistance decreased significantly from 177 +/- 19 to 101 +/- 9 dyn x s x cm(-5) x 10(-3). Similar results were observed in rats with CCl4-induced cirrhosis. In isolated perfused cirrhotic rat livers, bosentan (1 to 100 micromol/L) had no significant effect on hepatic vascular resistance. In portal vein-stenosed rats, bosentan administration significantly decreased portal pressure from 13.1 +/- 0.6 to 11.4 +/- 0.5 mm Hg by reducing portosystemic vascular resistance, because bosentan had no effect on vascular resistance of normal rat liver. In conclusion, bosentan administration decreased portal pressure in vivo by reducing hepatocollateral vascular resistance in rats with cirrhosis. Thus, mixed endothelin receptor antagonists might be a new approach in the pharmacological treatment of portal hypertension.

Animals↗
PubMed1998

[Intraperitoneal transplantation of isolated hepatocytes of the pig: the implantable bioartificial liver].

The general aim is to prepare a bioartificial liver to treat acute hepatic failure using allo- and xenogeneic hepatocytes, immunoprotected by macroencapsulation and transplanted into the peritoneal cavity. The goal of this study was to prepare a large amount of isolated porcine hepatocytes, to encapsulate them within biocompatible membranes for transplant in allo- and xenogeneic combinations and to examine the viability and functionality of the cells 6 weeks later. Hepatocyte isolation was performed in 12 kg pigs (n = 15) by dissociation of the liver with collagenase D (1 g) without oxygenation. Encapsulation of the hepatocyte suspension (10(7)/mL) was performed in hydrogel membranes AN69; hollow fibers (2 m x 0.8 mm) and flaskes (1.8 cm), and transplanted to Yucatan pigs (n = 4) and Lewis rats (n = 12). Six weeks later, they were removed to study the cell viability by histological examination, and the production of albumin by immunonephelometry. The rate of isolated hepatocytes was 38 +/- 5 x 10(9)/mL by liver of pig and the mean viability was 93 +/- 2%. Six weeks after transplantation, hepatocytes were viable, organized in lobules, and showed conserved albumin production. The same results were observed for allogenic and xenogeneic combinations. In conclusion, this method of liver dissociation allowed for preparation of a large amount of isolated hepatocytes from a single pig liver, theoretically sufficient to treat a patient with acute liver failure. Hydrogel membranes were well tolerated and allowed immunoprotection without immunosuppression. Transplanted hepatocytes remained functional. This work is an important step in progress toward clinical application.

Animals↗
PubMed1998

Encapsulated xenogeneic hepatocytes remain functional after peritoneal implantation despite immunization of the host.

BACKGROUND/AIMS: Xenogeneic hepatocytes encapsulated in semipermeable membranes could be used in the future for the treatment of acute liver failure and congenital liver defects. However, host immune response could affect the viability and function of transplanted cells. The purpose of this study was to investigate the immunological consequences of intraperitoneal implantation of encapsulated xenogeneic hepatocytes and their effects. METHODS: Recipient Lewis rats received 2 x 10(7) human hepatocytes encapsulated in semipermeable hydrogel-based hollow fibers, 2 x 10(7) free human hepatocytes or 2 x 10(7) encapsulated Lewis rat hepatocytes. The presence of human albumin in rat sera was assessed by Western blot and the presence of anti-human hepatocytes and anti-human albumin antibodies by ELISA. RESULTS: Anti-hepatocyte antibodies were detected on the 7th day, and their level increased progressively on days 21 and 28 in rats grafted with encapsulated or free human hepatocytes. Anti-albumin antibodies were detected on day 7 and increased progressively in rats grafted with encapsulated human hepatocytes, but were not detected in the other groups. No immune complexes or complement components of donor origin were detected by immunofluorescence in the recipients' tissues. Despite immunization of the host, encapsulated xenogeneic hepatocytes survived and produced albumin, whereas free hepatocytes had been lysed. CONCLUSION: Transplantation of encapsulated xenogeneic hepatocytes resulted in immunization of the host with production of anti-hepatocyte and anti-albumin antibodies. However, hepatocytes could be efficiently protected by the membrane and remained viable and functional during the study.

Animals↗
PubMed1998

Is acute rejection deleterious to long-term liver allograft function?

BACKGROUND/AIMS: The decreasing incidence of chronic rejection after liver transplantation emphasizes the need for an alternative end-point to assess the long-term consequences of acute rejection. The purpose of this study was to determine the effects of resolved episodes of acute rejection on late liver allograft function. METHODS: Parameters of hepatic function (liver biochemistry, indocyanine green and sulfobromophthalein clearances, histology) were analyzed in 170 consecutive adult recipients, who were followed prospectively on the basis of repeat annual work-up. Mean follow-up was 3.7+/-0.2 years. RESULTS: The rates of acute and chronic rejection were 51% and 4.1%, respectively. At the last follow-up, there was no significant difference in graft function between patients with a single episode of acute rejection (n=56) and those without rejection (n=84). Among patients treated for a single episode of acute rejection, late hepatic function was not influenced by the severity of acute rejection and the response to corticosteroids. In contrast, patients with recurrent acute rejection (n=30) had significant impairment of liver function tests (aspartate aminotransferase, p<0.05; alanine aminotransferase, p<0.01; alkaline phosphatase, p<0.01; gamma-glutamyl transpeptidase, p<0.001), lower dye clearances (indocyanine green, p<0.01; sulfobromophthalein, p<0.01) and more severe histologic damage (p<0.001). CONCLUSIONS: Single episodes of acute rejection do not impair the long-term hepatic function, whereas recurrent episodes leave sequellar damage to the liver allograft. These results provide a rationale for converting patients with rejection to a heavier immunosuppressive regimen, while leaving nearly half the recipients on a lifelong light immunosuppressive regimen.

Adolescent↗