PubMed Health⌕ Search

Biomedical subjects

A S Chong

Publications and source records attributed to A S Chong.

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

Induction of species-specific host accommodation in the hamster-to-rat xenotransplantation model.

The combination of two immunosuppressants, leflunomide and cyclosporin A (CsA), completely inhibits immune xenoreactions in the hamster-to-Lewis rat xenotransplantation model. In addition, the control of acute xenograft rejection with this combination of immunosuppressants subdues early T-independent xenoreactivity and uncovers a late immune response that can be controlled by CsA alone. We attribute this acquired responsiveness to CsA to a modification in the recipient's humoral response to the xenograft, and refer to this change as host accommodation. Host accommodation can be induced in Lewis rats receiving hamster hearts by the combination of leflunomide and CsA. A 7-day treatment with leflunomide and CsA was able to convert xenoreactivity from one that was resistant to CsA treatment into one that was controlled by CsA. The presence of the hamster xenograft was critical for the induction of host accommodation since the immunosuppressive regimen, either alone or in combination with a transfusion with donor-specific spleen cells, was unable to modify the anti-hamster reactivity in Lewis rats. When accommodation was induced in the presence of hamster hearts, these accommodated rats were able to acutely reject third-party mouse hearts while under CsA therapy, thus indicating that the host accommodation is species specific. Finally, we demonstrate that host accommodation is associated with a loss in the ability to produce species-specific, T-independent xenoantibodies. These novel observations suggest that xenoreactive T-independent humoral responses can be deleted selectively without significant loss of other innate, Ag-specific T-independent humoral responses.

Acute Disease↗
PubMed1998

Protective effect of ischemic preconditioning on liver preservation-reperfusion injury in rats.

BACKGROUND: Ischemic-preconditioning is a process whereby a brief ischemic episode confers a state of protection against subsequent long-term ischemia-reperfusion injury. Ischemic preconditioning has been studied in heart and liver ischemia-reperfusion injury; however, few studies have been performed in the model of preservation-reperfusion injury in liver transplantation. The current study was designed to evaluate the ability of ischemic preconditioning to protect liver grafts from long-term preservation-reperfusion injury. METHODS: Male Sprague Dawley rats were used as donors and recipients of orthotopic liver transplantation. Ischemic preconditioning was done by interruption of the portal vein and hepatic artery for 5, 10, and 20 min (5-10, 10-10, and 20-10 groups). Reflow was initiated by removal of the clamp for another 10 min in all groups. The liver was removed and placed in a bath with Euro-Collins solution for different preservation times. Tolerance of the transplanted liver to cold ischemia was determined by survival time and liver function tests. Rat tumor necrosis factor was analyzed by a bioassay. Nomega-Nitro-L-arginine methyl ester, L-arginine, or adenosine was administered to block or stimulate the synthesis of nitric oxide (NO) in the rats that received long-term-preserved liver grafts. RESULTS: Twenty percent of syngeneic rats (n=10) that received a liver graft with a 16-hr cold ischemia time in Euro-Collins solution survived for more than 1 day and 10% survived for more than 5 days. In contrast, 87.5% of rats (n=8) that received a liver graft with ischemic preconditioning (10-10 group) and 16 hr of cold ischemia survived for more than 1 day and 75% for more than 5 days. Recipients of liver grafts with ischemic preconditioning had significantly reduced levels of serum aspartate transaminase and tumor necrosis factor-alpha, as well as increased bile flow, compared with recipients of liver grafts without ischemic preconditioning. Blockage of the NO pathway using Nomega-nitro-L-arginine methyl ester, a stereospecific competitive inhibitor of NO formation, attenuated the protective effect of ischemic preconditioning. Administration of one of two precursors of NO synthesis, L-arginine or adenosine, prolonged the survival of rats that received 16-hr-preserved liver grafts. In addition, L-arginine synergized with short-term ischemic pre conditioning (5-10 group) to increase the survival of rats that received a liver graft with a 16-hr cold ischemia time, and the survival rate was 83% after 5 days. Finally, prolonged ischemic preconditioning (> or = 20 min; 20-10 group) resulted in liver damage and loss of function. CONCLUSION: The current results show that ischemic preconditioning protects the liver graft from subsequent long-term cold preservation-reperfusion injury in a rat liver transplantation model. The protective role of ischemic preconditioning may be mediated by the endogenous production of NO.

Animals↗
PubMed1998

Anti-CD4 therapy in combined heart-kidney, heart-liver, and heart-small bowel allotransplants in high-responder rats.

BACKGROUND: In these experiments, we studied the role of anti-CD4 (Ox38) monoclonal antibody in the induction of allograft unresponsiveness in high-responder Lewis rats in the single liver, kidney, small bowel, and heart versus the combined heart-kidney, heart-liver, and heart-small bowel transplantation models. METHODS: ACI heart, kidney, liver, and small bowel allografts were transplanted into untreated and anti-CD4 treated Lewis rats. In selected animals bearing long-surviving ACI liver or kidney allografts for over 3 months, donor-matched second heart or third-party (Brown Norway) heart allografts were transplanted. Simultaneously, heart-liver, heart-kidney, and heart-small bowel transplants were performed on the day of operation. Rejected allografts were verified by autopsy and pathology. RESULTS: ACI liver allografts were permanently accepted by Lewis recipients treated with either regular-dose (5 mg/kg for 4 days) or low-dose (5 mg/kg for 2 days) of anti-CD4 monoclonal antibody. Pretransplant anti-CD4 therapy (5 mg/kg for 4 days but not 5 mg/kg for 2 days) resulted in a long-term survival of kidney allografts (mean survival time [MST] > 100.0 days, n=5). Pretransplant anti-CD4 treatment (5 mg/kg for 4 days) could not induce tolerance when single ACI hearts were transplanted; however, long-term survival of ACI heart allografts could be induced when heart transplants were combined with liver (n=7) or kidney (n=8) transplants. The survival of both ACI heart allografts (MST=25.0 days, n=4) and small bowel allografts (MST=28.0 days, n=4) was also prolonged when simultaneous heart and small bowel transplantation was performed in anti-CD4-treated recipients. The second ACI heart allograft was permanently accepted by tolerant Lewis recipients of ACI liver or kidney allografts induced by anti-CD4 treatment, and third-party heart grafts were acutely rejected without affecting survival of the primary allografts. CONCLUSION: Our current results show that: (1) there is a vigorous rejection of heart > or = small bowel > kidney > liver in high-responder Lewis rats after pretransplant anti-CD4 therapy; and (2) simultaneous or metachronous combined liver-heart and kidney-heart transplants may protect heart allografts from rejection.

Animals↗
PubMed1998

IFN-gamma induces cell growth inhibition by Fas-mediated apoptosis: requirement of STAT1 protein for up-regulation of Fas and FasL expression.

The mechanism by which IFN-gamma inhibits tumor cell growth has not been fully understood. Here we report that IFN-gamma up-regulated the expression of Fas and Fas ligand (FasL) on HT29 cells, a human colon adenocarcinoma cell line, and subsequently induced apoptosis of these cells. The kinetics of cell death in IFN-gamma-treated HT29 cells paralleled the increase in the levels of Fas and FasL expression. We further show that IFN-gamma up-regulated the expression of Fas and FasL in STAT1-transfected U3A cells but not in STAT1-deficient U3A cells. Correspondingly, IFN-gamma induced cell death in STAT1-transfected U3A cells but not in STAT1-deficient U3A cells. IFN-gamma-induced cell death was inhibited by caspase-1 inhibitors. Our results suggest that cell growth inhibition by IFN-gamma is due to apoptosis mediated by Fas and FasL interaction.

Antineoplastic Agents↗
PubMed1998

Immunosuppression preventing concordant xenogeneic islet graft rejection is not sufficient to prevent recurrence of autoimmune diabetes in nonobese diabetic mice.

BACKGROUND: We and others have reported previously that the immunosuppressant, leflunomide (Lef), can prevent allogeneic and xenogeneic islet graft rejection in streptozocin (STZ)-induced diabetic animals. However, whether Lef required to prevent islet graft rejection is sufficient to prevent the recurrence of autoimmune diabetes has not been addressed. METHODS: The effect of Lef on concordant xenogeneic islet graft in STZ-induced diabetic mice and autoimmune nonobese diabetic (NOD) mice were studied. Then, whether Lef prevents the onset of spontaneous diabetes in young NOD mice and the recurrence of diabetes after major histocompatibility complex (MHC)-matched islet transplantation in diabetic NOD mice were investigated. RESULTS: In STZ-induced diabetic BALB/c mice, Lef treatment significantly prolonged rat islet graft survival. However, Lef could not significantly prolong rat islet graft survival in autoimmune diabetic NOD mice. For prevention studies, treatment with Lef at 30 mg/ kg/day from 4 weeks to 20 weeks of age significantly reduced the incidence of spontaneous diabetes in NOD mice. However, when the NOD mice were treated from 8 to 24 weeks of age, the incidence of spontaneous diabetes was not significantly reduced as compared to the incidence of diabetes in the untreated female NOD mice at 28 weeks of age. Finally, in the MHC-matched islet transplant model, Lef could not significantly prolong MHC-matched nonobese diabetes-resistant mice islet graft survival in NOD mice. CONCLUSIONS: Lef preventing concordant xenogeneic islet graft rejection is not sufficient to prevent the recurrence of autoimmune diabetes in NOD mice. We believe that controlling autoimmunity after islet transplantation will lead the way to promote successful clinical islet transplantation in the future.

Animals↗
PubMed1998

Inhibition of JAK3 and STAT6 tyrosine phosphorylation by the immunosuppressive drug leflunomide leads to a block in IgG1 production.

Leflunomide is an immunosuppressive drug capable of inhibiting T and B cell responses in vivo. A number of studies demonstrate that leflunomide functions both as a pyrimidine synthesis inhibitor and as a tyrosine kinase inhibitor. We previously reported that leflunomide inhibits LPS-stimulated B cell proliferation, cell cycle progression, and IgM secretion. This inhibition can be reversed by the addition of exogenous uridine, suggesting that leflunomide functions as a pyrimidine synthesis inhibitor in B cells. We report here that while the addition of uridine restored proliferation and IgM secretion to leflunomide-treated LPS-stimulated B cells, as determined by metabolic labeling and immunoprecipitation, it did not completely restore secretion of IgG Ab. We hypothesized that leflunomide inhibits LPS-induced IgG secretion by inhibiting tyrosine kinase activity required for isotype switch. We tested this hypothesis in a well-defined model of isotype switch, LPS plus IL-4 induction of IgG1. Leflunomide inhibited IgG1 secretion in this model in a dose-dependent manner. The signal transduction pathway utilized by IL-4 to induce IgG1 involves tyrosine phosphorylation of the IL-4 receptor, JAK1, JAK3, and STAT6 proteins induced by IL-4 binding to the IL-4R. Leflunomide diminished the tyrosine phosphorylation of JAK3 and STAT6 in the absence or presence of uridine. In gel mobility shift studies, STAT6 binding to the STAT6 DNA binding site in the IgG1 promoter decreased in the presence of leflunomide or leflunomide plus uridine. Taken together, these data suggest that leflunomide acts as a tyrosine kinase inhibitor to block IgG1 production.

Animals↗
PubMed1998

In vitro and in vivo mechanisms of action of the antiproliferative and immunosuppressive agent, brequinar sodium.

Intracellular pyrimidine nucleotides (PyN) can be synthesized de novo from glutamine, CO2, and ATP, or they can be salvaged from preformed pyrimidine nucleosides. The antiproliferative and immunosuppressive activities of brequinar sodium (BQR) are thought to be due to the inhibition of the activity of dihydroorotate dehydrogenase, which results in a suppression of de novo pyrimidine synthesis. Here we describe the effects of the pyrimidine nucleoSide, uridine, on the antiproliferative and immunosuppressive activities of BQR. In vitro reduction of PyN levels in Con A-stimulated T cells and inhibition of cell proliferation by low concentrations of BQR (< or =65 microM) are reversed by uridine. However, uridine is unable to reverse the effects of high concentrations of BQR (> or =65 microM). The ability of BQR to induce anemia in BALB/c mice is prevented by the coadministration of uridine. In contrast, the immunosuppressive activity of BQR is unaffected by similar doses of uridine. PyN levels in the bone marrow, but not in the spleen, are depressed in mice treated with BQR. These observations suggest that the induction of anemia by BQR is due to depletion of intracellular PyN in hemopoietic stem cells located in the bone marrow. They also suggest that the mechanism of immunosuppression by BQR may be only marginally dependent on depletion of intracellular PyN in lymphocytes located in the periphery. We report a novel activity of BQR: inhibition of tyrosine phosphorylation, and hypothesize that the immunosuppressive activity may be due, in part, to this unsuspected ability of BQR to inhibit tyrosine phosphorylation in lymphocytes.

Animals↗
PubMed1998

Field efficacy of a new repellent, KBR 3023, against Aedes albopictus (SKUSE) and Culex quinquefasciatus (SAY) in a tropical environment.

Two new repellent formulations, KBR 3023 10% and 20% from Bayer AG, Germany, were evaluated together with DEET 10% and 20% as standard repellent formulations. Evaluation was based on two separate field studies: a daytime study (0900-1700 hr) in a forested orchard on Penang Island and a nighttime study (2100-0100 hr) in a squatter residential area on the adjacent mainland of peninsular Malaysia. Both studies were carried out by exposing humans with bare arms and legs to mosquitoes landing/biting for an eight hour period. Right arms and legs of the human baits were treated with different repellent formulations (KBR 3023 10%, 20% and DEET 10%, 20%) and the left limbs were left untreated to act as controls. The daytime study indicated that all four formulations were equally effective (P < 0.05) as repellents against the predominant Aedes albopictus with greater than 88.5% reduction in landing/biting in the first four hours and not less than 65.0% in the next four hours of the assessment period. In the night study, all four formulations were also found to be equally effective (P < 0.05) in repelling Culex quinquefasciatus, the predominant species. All four formulations provided complete protection against Cx. quinquefasciatus in the first two hours of exposure. The percentage reduction values were maintained above 90.0% for the next six hours of the assessment period. In conclusion, both the KBR 3023 and DEET formulations were found to be equally effective (P < 0.05) in providing a long-lasting reduction in human-mosquito contact in both the day and night field studies.

Aedes↗
PubMed1997

Modification of humoral responses by the combination of leflunomide and cyclosporine in Lewis rats transplanted with hamster hearts.

BACKGROUND: Vigorous antibody-mediated responses prevent the successful engraftment of hamster hearts transplanted into Lewis rats. Early antibody responses mediating acute rejection of the xenograft are T cell-independent and resistant to the T-cell immunosuppressant, cyclosporine (CsA). Immunosuppression with the combination of leflunomide plus CsA completely prevents xenograft rejection, but when such immunosuppression is stopped the hamster heart is rejected by a process that we term late xenograft rejection. We report here on some of the immunological features of late xenograft rejection. METHODS: Lewis rats transplanted with hamster hearts were treated with leflunomide (5 mg/kg/day by gavage) for 14-21 days and CsA (20 mg/kg/day by gavage) continuously from the day of transplant. Serum was harvested and the functional activities of the xenoreactive antibodies were quantitated by in vivo passive transfer of sera, flow cytometry, in vitro C3 deposition assays, and Western blotting. RESULTS: CsA alone prevented late xenograft rejection and the accompanying production of xenoreactive antibodies. The xenoreactive antibodies accompanying acute or late xenograft rejection were predominantly IgM, but only serum from rats undergoing acute xenograft rejection was able to induce hyperacute rejection. The ability of serum to induce hyperacute rejection correlated with its ability to induce C3 deposition on hamster lymphocytes in vitro. The repertoire of hamster antigens recognized by IgM in the serum of rats undergoing late xenograft rejection is more restricted than that of IgM in the serum of rats undergoing acute xenograft rejection. We additionally demonstrate that long-term graft survival is not dependent on graft accommodation. CONCLUSIONS: These studies demonstrate that a brief treatment with the combination of leflunomide and CsA profoundly modifies the humoral xenoreactivity in the recipient, converting it from a T-independent into a T cell-dependent response. Differences in functional activity of sera from acute or late xenograft rejection suggest that antigenic specificity defines the ability of IgM to induce complement activation and hyperacute rejection.

Animals↗
PubMed1997

Quantitation of the changes in splenic architecture during the rejection of cardiac allografts or xenografts.

BACKGROUND: The spleen plays a central role in the generation of both cellular and antibody responses during graft rejection. Although changes in lymphocyte function have been extensively analyzed in vitro, there have been limited attempts at quantitating the structural changes in the lymphoid compartments within the spleen during graft rejection. METHODS: We describe here a means of quantitating the histological changes in the spleen using immunohistochemical techniques and computerized image analysis. RESULTS: Allograft rejection at 6 days after transplant is characterized by a threefold increase in the T cell-rich areas of the periarteriolar lymphoid sheaths (PALs). The follicular areas are enlarged and germinal centers appear in 55% of the white pulp regions. Acute xenograft rejection, 4 days after transplant, is specifically accompanied by a 2.3-fold increase in the marginal zone (MZ) and an increase in the numbers of B cells in the red pulp of the spleen. The expansion of both PALs and follicular/germinal centers during xenograft rejection is comparable to that observed during allograft rejection. We also investigated the effect of two immunosuppressants, leflunomide and cyclosporine, on the spleen of rats with hamster hearts. Leflunomide, which prevents acute xenograft rejection, prevented the increase in PALs and significantly reduced the areas comprising the MZ and follicles. Cyclosporine, which does not alter the tempo of xenograft rejection and only partially inhibited xenospecific antibody production, inhibited the increase in PALs and the appearance of germinal centers, while permitting a modest increase in the area of MZ and follicles. CONCLUSIONS: These observations collectively suggest that both T cell-dependent and T cell-independent responses are stimulated by the transplanted xenograft. However, the T cell-independent responses that initiate xenograft rejection are characterized by very modest increases in the area of MZ and follicles within the white pulp of the spleen.

Animals↗
PubMed1997

Effect of anti-CD4 monoclonal antibody combined with human CTLA4Ig on the survival of hamster liver and heart xenografts in Lewis rats.

We investigated the effects of pretransplant anti-CD4 monoclonal antibody (mAb) combined with human (h) CTLA4Ig on the survival of hamster heart and liver xenografts. Pretransplant anti-CD4 mAb (5 mg/kg x 4 days) or hCTLA4Ig (0.5 mg/rat on days 1, 3, and 5 after transplantation) treatment alone prolonged the survival of hamster liver xenografts in Lewis rats (mean survival time [MST]=10.5 days, n=6, and MST=9.0 days, n=5, respectively, compared with untreated Lewis recipients of hamster liver grafts, MST=6.0 days, n=6). The same regimen could not prevent hamster heart xenorejection. Pretransplant anti-CD4 mAb (5 mg/kg x 4 days) combined with hCTLA4Ig (0.5 mg/rat x 4) treatments increased survival of hamster liver xenograft fourfold (MST=24.2 days, n=5). The current results also show that IgG in the sera from Lewis recipients of hamster liver grafts treated with anti-CD4 mAb and hCTLA4Ig was threefold reduced at 6 days after transplantation compared with untreated Lewis rats. These results suggest a synergistic effect of anti-CD4 mAb combined with hCTLA4Ig in a liver xenograft transplantation model.

Abatacept↗
PubMed1997

The immunosuppressive metabolite of leflunomide, A77 1726, affects murine T cells through two biochemical mechanisms.

The immunosuppressive metabolite of leflunomide, A77 1726, inhibits the enzymatic activity of protein tyrosine kinases and of dihydro-orotic acid dehydrogenase, an enzyme involved in pyrimidine biosynthesis. Here murine CTLL cell lines were studied to determine which of the biochemical targets of A77 1726 was responsible for the observed inhibition of proliferation and cytotoxic activity. At low concentrations of A77 1726, pyrimidine biosynthesis is the target, since inhibition of proliferation correlates with a reduction in pyrimidine NTP levels and is reversed by uridine. At higher concentrations of A77 1726, uridine no longer reverses the inhibition of proliferation even though pyrimidine NTP levels are restored. This second mechanism for inhibiting proliferation is probably inhibition of protein tyrosine kinases, since these higher concentrations of A77 1726 inhibit IL-2-induced tyrosine phosphorylation of Jak1 and Jak3, the protein tyrosine kinases initiating signaling by the IL-2R. Tyrosine phosphorylation of the beta-chain of the IL-2R, which is required for IL-2-driven proliferation, is also inhibited by A77 1726. Cytotoxicity of a CTLL line that overexpresses the Lck protein tyrosine kinase is inhibited by A77 1726; this inhibition is not affected by uridine, but does correlate with inhibition of an Lck in vitro kinase reaction. These studies establish that inhibition of pyrimidine biosynthesis and that of protein tyrosine kinase both contribute to the effects of A77 1726 on CTLL cell lines.

Aniline Compounds↗
PubMed1997

In vivo mechanism by which leflunomide controls lymphoproliferative and autoimmune disease in MRL/MpJ-lpr/lpr mice.

Two activities have been identified for the immunosuppressive metabolite of leflunomide, A77 1726: inhibition of dihydroorotate dehydrogenase (DHO-DHase), an enzyme involved in the biosynthesis of pyrimidine nucleotides (PyN); and inhibition of protein tyrosine kinases. The in vitro potency of A77 1726 as a DHO-DHase inhibitor is reported to be 10- to 500-fold greater than as a tyrosine kinase inhibitor. These observations suggested that the immunosuppressive efficacy of leflunomide in vivo is related to inhibition of DHO-DHase. However, observations that patients with disorders in the PyN synthetic pathway are not overtly immunodeficient militate against this hypothesis. We investigated the effects of leflunomide in vivo and report that amelioration of lymphoproliferative and autoimmune diseases in MRL/MpJ-lpr/lpr (lpr/lpr) mice by leflunomide is not accompanied by reduced PyN concentrations in lymph node cells. Our hypothesis that lymphocytes could salvage serum uridine to counter the effects of reduced PyN synthesis in vivo was supported by in vitro studies. Finally, we observed that amelioration of disease correlated with a reduction of tyrosine phosphorylated proteins in lymph node cells of lpr/lpr mice. These observations suggest that the primary mechanism by which leflunomide prevents autoimmune and lymphoproliferative diseases in lpr/lpr mice is not depletion of PyN, but correlates with reduced tyrosine phosphorylation concentrations in lymph node cells.

Aniline Compounds↗
PubMed1997

Prolongation of rat islet allograft survival by the immunosuppressive agent leflunomide.

The purpose of this study was to investigate the effect of Leflunomide (Lef), alone or in combination with a suboptimal dose of cyclosporine (CsA), on rat allogeneic islet transplantation. Two thousands islets were transplanted under the left kidney capsule of a streptozocin-induced diabetic Lewis recipient. In the ACI to Lewis combination, the mean survival time (MST) of the untreated group was 5.2 +/- 0.8 days. Lef at 2.5, 5, and 10 mg/kg/day for 14 days significantly prolonged MSTs to 19.0 +/- 1.6, 29.8 +/- 3.7, and 29.0 +/- 5.3 days (P<0.01), respectively. CsA at 5 mg/kg/day also prolonged graft survival to 21 +/- 3.5 days. When CsA (5 mg/ kg/day) was combined with Lef (5 or 10 mg/kg/day) and administered for 14 days, the survival rate of the islet allografts was further increased to 34.8 -/+ 4.7 and 36.0 -/+ 6.6 days, respectively. When Lef or CsA monotherapy was extended to 28 days at a dose of 5 mg/kg/ day, MSTs were further increased to 45.8 -/+ 8.8 or 37.4 -/+ 4.7 days, respectively. Graft MST was 56.4 -/+ 9.9 days when Lef and CsA combination therapy was administered for 28 days. In the Brown-Norway to Lewis combination, MST of the allogeneic islets in untreated rats was 6.2 -/+ 0.8 days. When Lef or CsA alone, at 5 mg/kg/day, was administered for 28 days, two of seven Lef-treated rats remained normoglycemia for more than 100 days. Graft survival longer than 100 days occurred in one of five CsA-treated rats, and in five of eight rats treated with the combination of Lef and CsA. The graft-bearing left kidney was removed after 100 days in rats with functional islet allografts, and a second Brown-Norway islet graft was transplanted into the right kidney. In all recipients, the second graft was rejected by 9.8 -/+ 1.5 days. In summary, our findings demonstrate that Lef prolonged allogeneic islet graft survival, and its immunosuppressive effect was improved when combined with CsA.

Animals↗
PubMed1997

In vivo effects of leflunomide on normal pancreatic islet and syngeneic islet graft function.

Leflunomide (Lef) is a novel immunosuppressant that can prevent islet allograft and xenograft rejection. In this study, we investigated the in vivo effects of Lef on the function of normal pancreatic islets and syngeneic islet grafts in rats and compared its effect to cyclosporine (CsA) and FK506. Different groups of rats were treated with Lef (10 and 20 mg/kg/day), CsA (20 mg/kg/day), or FK506 (2 mg/kg/day). After 4 and 6 weeks, nonfasting blood glucose (BG) levels of all the treatment groups were not different from that of the control group. Intravenous glucose tolerance test revealed that the rate of glucose disappearance was normal in Lef-treated groups. However, the rate of glucose disappearance in the CsA- and FK506-treated rats was impaired. In contrast, long-term (7 months) treatment of rats with CsA (10 mg/kg/day) resulted in five of seven rats developing hyperglycemia. However, normal BG was observed in all rats treated for 7 months with Lef (10 mg/kg/day). In the second experimental model, streptozocin-induced diabetic ACI rats were grafted with an average of 1200 syngeneic islets into the liver or kidney capsule. Diabetes in these ACI recipients was stably reversed for 6 months, then these rats were treated with Lef (20 mg/kg/day), CsA (20 mg/kg/day), and FK506 (2 mg/kg/day). After 14 days of treatment, nonfasting BG levels were significantly increased in rats treated with CsA (before: 105 +/- 2.9 mg/ dl, after: 275.8 +/- 60 mg/dl) as well as in rats treated with FK506 (before: 108 +/- 2.4 mg/dl, after: 209 +/- 10.1 mg/dl). In contrast, the BG levels of the Lef-treated rats were indistinguishable from those of the untreated control groups. Site of transplantation, i.e., liver and kidney, did not affect the results. Our results indicating that Lef has no diabetogenic property in vivo lends support to the promise that leflunomide may be effective for clinical islet transplantation.

Animals↗