Morphological and functional changes of islets of Langerhans in FK506-treated rats

The effects of maintenance doses of FK506 versus cyclosporin A on glucose and lipid metabolism after orthotopic liver transplantation

BACKGROUND

Posttransplant diabetes mellitus (PTDM) has gained widespread attention due to the micro and macro-vascular complications that increase the morbidity and mortality of patients receiving solid organs. The higher incidence of PTDM has been mainly attributed to the immunosuppressive therapy. Therefore, this study compares the metabolic side effects of low dose maintenance therapy of FK-506 and Cyclosporin A (CsA) in 14 patients 1 year after orthotopic liver transplant and analyzes possible factors that contribute to the development of PTDM.

METHODS

Two groups (n=7) differing in their immunosuppressive regimen (FK506 or CsA) were matched to eight control subjects and compared to each other. The effects of in vivo insulin action were assessed by means of the euglycemic hyperinsulinemic clamp technique. Arginine stimulation tests at normo- (5.5 mM) and hyperglycemic (15 mM) levels were performed and the acute insulin, C-peptide, and glucagon response (2-5 min) to arginine were determined.

RESULTS

Insulin sensitivity (total glucose disposal) was statistically lower in patients treated with FK-506 and CsA (5.05+/-0.47 and 5.05+/-0.42 mg/kg/min) as compared to controls (6.62+/-0.38 mg/kg/min) (P<0.02), with a significantly higher nonoxidative glucose disposal for the control group (P<0.01), and lower free fatty acid levels (P<0.05). Absolute values for acute insulin response were higher but not significantly different for the transplanted groups. The lower percentage of increase of insulin release after arginine stimulation observed in the FK-506 and CsA groups as compared with controls (754%+/-100, 644%+/-102 vs. 1191%+/-174) (P<0.03 and 0.02, respectively), suggests a reduced beta cell secretory reserve in both treated groups. Also, the acute glucagon response to arginine during hyperglycemia declined less in the FK-506 (28%) and CsA groups (29%) compared with controls (48%) (P<0.05) indicating a defect in the pancreatic beta cell-alpha cell axis.

CONCLUSIONS

There are no major metabolic differences on low maintenance doses between FK-506 and CsA. Both immunosuppressant agents contribute to the development of PTDM at different levels.

Islet cell damage associated with tacrolimus and cyclosporine: morphological features in pancreas allograft biopsies and clinical correlation

BACKGROUND

The introduction of the potent immunosuppressive drugs tacrolimus (FK) and cyclosporine (CSA) has markedly improved the outcome of solid organ transplantation. However, these drugs can cause posttransplantation diabetes mellitus. Abnormalities in the glucose metabolism are of particular significance in pancreas transplantation.

METHODS

We studied 26 pancreas allograft biopsies, performed 1-8 months posttransplantation, from 20 simultaneous kidney-pancreas transplant recipients, randomized to receive either FK or CSA. The biopsies were studied by light microscopy, immunoperoxidase stains for insulin and glucagon, in situ DNA-end labeling for detection of apoptosis, and electron microscopy. The islet morphology was correlated with the mean and peak levels of CSA and FK in serum, with corticosteroid administration and with glycemia.

RESULTS

On light microscopy cytoplasmic swelling, vacuolization, apoptosis, and abnormal immunostaining for insulin were seen in biopsies from patients receiving either FK or CSA. The islet cell damage was more frequent and severe in the group receiving FK than in the group receiving CSA (10/13 and 5/13, respectively) but the differences were not statistically significant. Significant correlation was seen between the presence of islet cell damage and serum levels of CSA or FK during the 15 days previous to the biopsy, as well as with the peak level of FK. Toxic levels of CSA or FK and administration of pulse steroids were associated with hyperglycemia when these occurred concurrently (P=0.005). Toxic levels of CSA or FK by themselves were associated with hyperglycemia in a minority of cases (8 and 26%, respectively). Electron microscopy showed cytoplasmic swelling and vacuolization, and marked decrease or absence of dense-core secretory granules in beta cells; the changes were more pronounced in patients on FK. Serial biopsies from two hyperglycemic patients receiving FK and evidence of islet cell damage demonstrated reversibility of the damage when FK was discontinued.

CONCLUSIONS

The structural damage to beta cells demonstrated in this study is similar to morphological and functional abnormalities previously described in experimental animal models and can at least partially account for the glucose metabolism abnormalities seen in patients receiving these drugs. Toxic levels of CSA or FK and higher steroid doses potentiate each others' diabetogenic effects.

Risk for posttransplant Diabetes mellitus with current immunosuppressive medications

With improvements in the practice of transplantation and the introduction of new immunosuppressive medications, there has been a substantial increase in 1-year allograft survival rates. Consequently, the pool of potential candidates for organ transplants continues to grow and a greater preponderance of older patients with more comorbidities are undergoing transplantation. As a result, there is interest in such medical complications as posttransplantation diabetes mellitus (PTDM) that develop after the transplantation of a successful allograft. PTDM is an undesirable consequence of transplantation because of its associated morbidity and impairment of both patient and graft survival. Although some controversy exists, it is likely that glucose intolerance after transplantation results in both macrovascular and microvascular disease, and there is an increasing risk for infectious and cardiovascular diseases, to which transplant recipients are already at increased susceptibility. Both experimental and clinical observations have shown that immunosuppressive agents currently used in transplantation account for a large degree of the increased risk for PTDM. Consequently, improved understanding of the effects of currently used immunosuppressive medicines on glycemic tolerance is of interest in clinical transplantation.

Clinical islet cell transplantation. Are we there yet?

Diabetes mellitus is perhaps the most devastating chronic disease of all time. A brief history of the evolution of treatment modalities is provided, culminating in the rationale for the physiologic replacement of a functioning beta-cell mass by transplantation. Vascularized pancreas transplantation is discussed briefly as an introduction to the transplantation of the isolated islet. A detailed review of the current state of human islet transplantation for the cure of diabetes is then described. Finally, areas for future development are highlighted.

Post-transplant diabetes with anti-glutamic acid decarboxylase antibody during tacrolimus therapy

A 54-year-old man undergoing hemodialysis because of end-stage renal failure was transplanted with a cadaver kidney in November 1997. He had no history of diabetes. Tacrolimus was used as the primary immunosuppressant. Three weeks after transplantation, he developed insulin-requiring diabetes mellitus. Anti-glutamic acid decarboxylase antibody was not detected on the third post-operative day, but appeared 4 weeks after transplantation. The recipient had DNA haplotypes that indicated susceptibility to Type 1 diabetes in Japanese subjects. Immunosuppressive therapy was changed from tacrolimus to cyclosporin. Thereafter, titer of anti-glutamic acid decarboxylase antibody disappeared and the patient's insulin requirement was notably reduced. The mechanism underlying the development of diabetes in this case appears to be, in part, direct beta-cell toxicity due to tacrolimus therapy, resulting in secondary beta-cell autoimmunity. This case suggests that tacrolimus therapy after transplantation should be used with caution in patients with genetic susceptibility to Type 1 diabetes.

Cataract development induced by repeated oral dosing with FK506 (tacrolimus) in adult rats

FK506 (tacrolimus), a potent immunosuppressant, is used for inhibiting allograft rejection in the organ transplantation field. In a preclinical toxicity study in rats, FK506 induced various toxicities, including renal and pancreatic injuries. One of these toxic findings was cataract, and we have found that cataract appeared in rats dosed orally with FK506 for 13 weeks and more. Therefore, to better elucidate the onset mechanism of FK506-induced cataract, we measured biochemical parameters, such as sorbitol, Na,K-ATPase and glutathione in the lens of rats. Rats were dosed with FK506 in oral daily doses of 0.2, 1 or 5 mg/kg for 13 weeks, the lowest dose of which approximated the expected clinical dosage. Cataract developed in the 5-mg/kg/day group, with an incidence of 25%, whereas no cataract formation was observed in the 0.2- or 1-mg/kg/day groups. Five mg/kg/day led an increase of sorbitol and a decrease of reduced type glutathione, but did not affect Na,K-ATPase activity of the lens. FK506 is known to have diabetogenicity mediated through pancreatic injury, which appears as vacuolation of islet cell in rats. Five mg/kg/day of FK506 induced an elevation of blood glucose associated with glucose intolerance, and decrease of both basal insulin level and insulin content in the pancreas, and the changes were in parallel with the cataract development in the present study. On the other hand, diabetic parameters did not change in the 0.2- or 1-mg/kg/day groups. These observation suggest that diabetes developed in the rats dosed with 5 mg/kg/day of FK506. Coadministration of a novel aldose reductase inhibitor, Zenarestat, at an oral dose of 50 mg/kg/day resulted in a reduction of incidence of the FK506-induced cataract and a decrease of sorbitol levels in the lens when compared to that in the lens of rats dosed with 5 mg/kg/day of FK506. These results suggest that FK506-induced cataract in rats is due to an accumulation of sorbitol in the lens, secondary to the diabetogenic effect of FK506. FK506 treatment at the doses of 0.2 and 1 mg/kg/day neither affected parameters indicative of diabetes nor induced cataract in rats, suggesting that the cataract would not develop with FK506 if diabetic parameters were kept under control.

A comparison of tacrolimus (FK506) and cyclosporine for immunosuppression after cadaveric renal transplantation. FK506 Kidney Transplant Study Group

BACKGROUND

Tacrolimus (FK506), a macrolide molecule that potently inhibits the expression of interleukin 2 by T lymphocytes, represents a potential major advance in the management of rejection following solid-organ transplantation. This randomized, open-label study compared the efficacy and safety of tacrolimus-based versus cyclosporine-based immunosuppression in patients receiving cadaveric kidney transplants.

METHODS

A total of 412 patients were randomized to tacrolimus (n=205) or cyclosporine (n=207) after cadaveric renal transplantation and were followed for 1 year for patient and graft survival and the incidence of acute rejection.

RESULTS

One-year patient survival rates were 95.6% for tacrolimus and 96.6% for cyclosporine (P=0.576). Corresponding 1-year graft survival rates were 91.2% and 87.9% (P=0.289). There was a significant reduction in the incidence of biopsy-confirmed acute rejection in the tacrolimus group (30.7%) compared with the cyclosporine group (46.4%, P=0.001), which was confirmed by blinded review, and in the use of antilymphocyte therapy for rejection (10.7% and 25.1%, respectively; P<0.001). Impaired renal function, gastrointestinal disorders, and neurological complications were commonly reported in both treatment groups, but tremor and paresthesia were more frequent in the tacrolimus group. The incidence of posttransplant diabetes mellitus was 19.9% in the tacrolimus group and 4.0% in the cyclosporine group (P<0.001), and was reversible in some patients.

CONCLUSIONS

Tacrolimus is more effective than cyclosporine in preventing acute rejection in cadaveric renal allograft recipients, and significantly reduces the use of antilymphocyte antibody preparations. Tacrolimus was associated with a higher incidence of neurologic events, which were rarely treatment limiting, and with posttransplant diabetes mellitus, which was reversible in some patients.

Post-transplant diabetes mellitus. The role of immunosuppression

Immunosuppressive agents increase the risk of death due to coronary disease or stroke by their ability to cause 3 different adverse effects: dyslipidaemia, hypertension and hyperglycaemia. Post-transplant diabetes mellitus has emerged as a major adverse effect of immunosuppressants. As recipients of organ transplants survive longer, the secondary complications of diabetes mellitus have assumed greater importance. There is a need for a precise definition of post-transplant diabetes mellitus to facilitate inter-centre comparison and to study the natural history of post-transplant diabetes mellitus. We recommend broad criteria to define hyperglycaemia, as a fasting blood glucose level of > 400 mg/dl at any point or > 200 mg/dl for 2 weeks, or a need for insulin treatment for at least 2 weeks. We also recommend serial measurements of HbA1c. Cyclosporin and tacrolimus cause post-transplant diabetes mellitus by a number of mechanisms, including decreased insulin secretion, increased insulin resistance or a direct toxic effect on the beta cell. For corticosteroids, the induction of insulin resistance seems to be the predominant factor. However, few studies have examined the mechanism of diabetogenicity at the molecular level. This may hold the key for pharmacological manipulation of current immunosuppressive regimens which may result in decreased metabolic complications. Corticosteroid sparing regimens have been shown to reduce the metabolic complications of immunosuppressants including post-transplant diabetes mellitus. However, their use should be balanced against the increased incidence of transplant rejections. Post-transplant diabetes mellitus may be organ-specific irrespective of the immunosuppressant used. Tacrolimus causes a high incidence of post-transplant diabetes mellitus in recipients of kidney transplants (upto 20% in some reports); the diabetogenicity of cyclosporin-based regimens is comparable with that of tacrolimus-based regimens in recipients of liver transplants. A few clinical studies in which attempts were made to discontinue cyclosporin resulted in an unacceptable loss of the transplant. In the case of tacrolimus, complete withdrawal of immunosuppression may be possible in selected patients with liver transplants. However, post-transplant recipients who may benefit from this approach are difficult to identify. In some early series, patients received doses of tacrolimus that were approximately 2 to 3 times higher than those currently used, which may have resulted in a higher incidence of post-transplant diabetes mellitus. More recently, it has been shown that tacrolimus was successful in salvaging whole pancreatic grafts which were maintained on cyclosporin. Tacrolimus-based immunosuppression as primary therapy was also used with remarkable success in solitary whole pancreas transplants. Strategies to reduce the metabolic complications of immunosuppressants should be pursued aggressively as this will directly lead to a decrease in long term cardiovascular adverse effects.

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.

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.

Effects of tacrolimus (FK506) on human insulin gene expression, insulin mRNA levels, and insulin secretion in HIT-T15 cells

FK506 (tacrolimus) is an immunosuppressive drug which interrupts Ca2+-calmodulin-calcineurin signaling pathways in T lymphocytes, thereby blocking antigen activation of T cell early activation genes. Regulation of insulin gene expression in the beta cell may also involve Ca2+-signaling pathways and FK506 has been associated with insulin-requiring diabetes mellitus during clinical use. The purpose of this study was to characterize the effects of FK506 on human insulin gene transcription, insulin mRNA levels, and insulin secretion using as a model the HIT-T15 beta cell line. FK506 had no acute effect on insulin secretion in the HIT cell, but caused a reversible time- and dose-dependent (10(-9)-10(-6) M) decrease in HIT cell insulin secretion. Decreased insulin secretion in the presence of FK506 was also accompanied by a dose-dependent decrease in HIT cell insulin content, insulin mRNA levels, and expression of a human insulin promoter-chloramphenicol acetyl transferase (CAT) reporter gene. FK506 decreased HIT cell expression of the human insulin promoter-CAT reporter gene by 40% in the presence of both low (0.4 mM) at high (20 mM) glucose concentrations. Western blot analysis of HIT cell proteins gave evidence for the presence of calcineurin in the HIT cell. These findings suggest that FK506 may have direct effects to reversibly inhibit insulin gene transcription, leading to a decline in insulin mRNA levels, insulin synthesis, and ultimately insulin secretion.

A multicenter analysis of the first experience with FK506 for induction and rescue therapy after pancreas transplantation

Between May 1, 1993 and April 5, 1995, 154 pancreas allograft recipients at 9 institutions were given FK506 posttransplant. Three groups were studied: (1) recipients given FK506 initially for induction and maintenance therapy (n = 82), (2) recipients switched to FK506 for antirejection or rescue therapy (n = 61), and (3) recipients converted to FK506 for other reasons (n = 11). Of 82 patients in the induction group, 7 (9%) had simultaneous bone marrow (BM) and pancreas-kidney (SPK-BM) transplants, 54 (66%) had SPK transplants without BM, 14 (17%) had pancreas transplants alone (PTA), and 7 (9%) had pancreas after previous kidney transplants (PAK). All but 1 recipient was given quadruple immunosuppression (anti-T cell agents plus azathioprine and prednisone) for induction. The median FK506 starting dose was 4 mg/day p.o.; the median average FK506 blood level, 12 ng/ml. The most common side effects were neurotoxicity (16%), nephrotoxicity (13%), and gastrointestinal toxicity (9%). New-onset diabetes mellitus requiring permanent insulin therapy did not occur. Of 61 transplants in the rescue group, 44 (72%) were SPK, 11 (18%) PTA, and 6 (10%) PAK. All but 3 (95%) of the recipients had been on cyclosporine-azathioprine-prednisone triple immunosuppression before substitution of FK506 for cyclosporine; 46% of the recipients had one, and 54% > or = 2, rejection episodes preconversion. The most common side effects were nephrotoxicity (25%), neurotoxicity (23%), and gastrointestinal toxicity (21%). Two recipients were reconverted to cyclosporine because of transient hyperglycemia, and one recipient is on insulin. In the induction group, patient survival at 6 months was 90% for SPK, 100% for PTA, and 100% for PAK. According to a matched-pair analysis, pancreas graft survival for SPK recipients at 6 months was 87% for FK506 versus 70% for cyclosporine recipients (P = 0.04); for PTA recipients, 84% versus 66% (P = n.s.); and for PAK recipients, 80% versus 14% (P = 0.11). When technical failures and death with functioning grafts were censored, pancreas graft survival remained significantly better in the FK506 group. The incidence of first reversible rejection episodes by 6 months in FK506 recipients was 35% for SPK, 40% for PTA, and 20% for PAK. Of 75 pancreas grafts, 64 are currently functioning; in 5 recipients the pancreas failed (1 from rejection); 6 recipients died with a functioning pancreas graft. There were 3 posttransplant lymphomas (all EBV-positive); 2 recipients died and 1 is alive after subtotal colectomy and transplant pancreatectomy. In the antirejection rescue group, patient survival rates at 6 months were 91% for SPK, 100% for PTA, and 80% for PAK (P = n.s.). Pancreas graft survival rates at 6 months were 90% for SPK, 72% for PTA, and 40% for PAK. The incidence of first reversible rejection episodes after conversion to FK506 at 6 months was 44% in SPK, 54% in PTA, and 50% in PAK. Of 61 pancreas grafts, 51 are currently functioning; in 7 recipients the pancreas failed (5 from rejection); 3 recipients died with a functioning graft. There were no posttransplant lymphomas in the rescue group. This multicenter survey shows that FK506 in pancreas transplantation is associated with (1) a low rate of graft loss from rejection when used for induction therapy, (2) a high rate of graft salvage when used for rescue or rejection therapy, and (3) a very low rate of new-onset insulin-dependent diabetes mellitus. These encouraging results are tarnished by 3 posttransplant lymphomas in the induction group; a possible explanation is overimmunosuppression, but further (randomized) studies are necessary to analyze the long-term risk-benefit ratio of FK506 after pancreas transplantation.

Use of FK 506 in pancreas transplantation

Until recently, FK 506 was used only for rescue therapy after pancreas transplantation. We report our initial experience with FK 506 for 67 pancreas recipients (treated between 1 May 1993 and 30 April 1995). Of these recipients, 49 (73%) received FK 506 for induction and maintenance therapy, 12 (18%) for rescue or antirejection therapy, and 6 (9%) for reasons other than rescue or antirejection therapy. In our induction and maintenance therapy group, 32 recipients (65%) underwent a simultaneous pancreas-kidney transplant (SPK), 8 (16%) a pancreas transplant alone (PTA), and 9 (19%) a pancreas after previous kidney transplant (PAK). Quadruple immunosuppression was used for induction; the median FK 506 starting dose was 4 mg/day p.o. and target levels were 10-20 ng/ml. The most common side effects were nephrotoxicity (16%) and neurotoxicity (14%); transient episodes of hyperglycemia were also noted (12%), in particular in the presence of concurrent rejection and infection episodes. A matched-pair analysis was done to compare graft outcome with FK 506 versus cyclosporin A (CsA). For SPK recipients, pancreas graft survival at 6 months was 79% with FK 506 versus 65% with CsA (P = 0.04), for PTA, 100% versus 63% (P > 0.35), and for PAK, 88% versus 33% (P > 0.01). Pancreas graft loss due to rejection at 6 months posttransplant was lower with FK 506 versus CsA. Two FK 506 recipients died from B-cell lymphomas (Epstein-Barr virus positive) at 6 and 7 months posttransplant. In our rescue or anti-rejection group, 5 recipients underwent SPK, 3 PTA, and 4 PAK. The mean average FK 506 dose was 10 mg/day p.o. and the mean average FK 506 blood level was 11 ng/ml. The most common side effects were nephrotoxicity (33%) and neurotoxicity (16%). Two recipients developed hyperglycemic episodes, of whom 1 has remained on insulin with good exocrine pancreas graft function. Graft survival at 6 months after conversion was 75% for SPK, 67% for PTA, and 50% for PAK. Only one graft was lost due to chronic rejection. Our single-center experience shows that FK 506 after pancreas transplantation is associated with: (1) a low rate of graft loss due to rejection when used for induction, in particular for solitary pancreas transplants, (2) a high rate of graft salvage when used for rescue, (3) a 1% rate of new-onset insulin-dependent diabetes mellitus, and (4) a 3% rate of posttransplant lymphoma. Further studies are necessary to analyze the long-term impact of FK 506 on pancreas transplant outcome.

Pancreatic and nephrotoxicity of immunomodulator compounds

Increasing clinical experience of FK 506 in transplantation therapy has revealed a number of potentially restrictive adverse effects associated with its use. The mechanisms of action underlying 2 prominent toxic effects of FK 506, namely diabetogenesis and renal dysfunction, were investigated. A simple model system based on the effect of FK 506 on isolated rat pancreatic islets was utilised to study the relationship between inhibition of insulin biosynthesis, inhibition of interleukin 2 (IL-2) activation and FK binding protein (FKBP-12) binding of FK 506 and a number of FK 506 analogues. Results indicate that the action of these compounds on inhibition of insulin biosynthesis (and by implication, diabetogenesis) may be related to their immunosuppressive potential. Observations on the FK 506-induced release of endothelin-1 from isolated rat kidney mesangial cells suggest that this cell may be an important target associated with the nephrotoxic potential of the drug, and that this action may be mediated via the FKBP.

Intraportal delivery of immunosuppression to intrahepatic islet allograft recipients

Local delivery of immunosuppressive agents may dampen local alloreactive events with avoidance of systemic toxicity. We investigated the innovative strategy of intraportal (IPO) delivery of three immunosuppressive agents in streptozotocin diabetic rat recipients of islet allografts (Lewis to Wistar-Furth) transplanted intrahepatically. IPO budesonide (BUD, 240 or 360 micrograms/kg per day), a potent steroid, and cyclosporin (CyA, 2 or 4 mg/kg per day) did not prolong graft mean survival time [MST +/- standard deviation (SD)] as compared to nonimmunosuppressed recipients. Fourteen days of IPO FK 506 (0.16 mg/kg per day) significantly increased MST as compared with untreated controls (49 +/- 29 vs 7 +/- 1 days, P < 0.01) and was more effective than intravenous (IV) FK 506 (17 +/- 7 days, P < 0.01). When FK 506 was given for 28 days, the benefit of IPO over IV delivery was reaffirmed (MST 81 +/- 32 vs 34 +/- 4 days, P < 0.01). The potential for toxicity was lessened by lower mean systemic levels in the IPO group as compared to the IV group (1.3 +/- 0.6 vs 3.5 +/- 0.9 ng/mg, P < 0.02). The strategy of continuous IPO FK 506 was effective in the prevention of rejection of intrahepatic islet allografts.

Effect of FK506 and anti-CD4 therapy on fetal pig pancreas xenografts and host lymphoid cells in nod/Lt, CBA, and BALB/c mice

Varying doses of FK506, and a cell-depleting anti-CD4 monoclonal antibody, GK1.5, were tested as either monotherapy or in combination for their effect on the survival of renal subcapsular xenografts of organ-cultured fetal pig pancreas in three strains of mice. Subcutaneous injections of FK506 at 4.0 mg/kg/day for 28 d prevented graft rejection to day 35 posttransplantation (i.e., 7 days after cessation of treatment in NOD/Lt, and CBA mice) while BALB/c mice had intact grafts at 28 days. Lower doses were less effective and immunosuppression was less effective in NOD mice than in the other strains. Even 2.0 mg/kg/day of FK506 prevented rejection in CBA mice until day 35, but not in NOD/Lt mice. GK1.5 alone did not prevent rejection in NOD/Lt mice but when a low dose of FK506 (2.0 mg/day) was added, the grafts were present, essentially intact, at 35 days. There were no obvious toxic effects of FK506 in NOD/Lt and CBA mice. With FK506 treatment there was no significant difference in absolute numbers of total leucocytes or lymphocytes in peripheral blood and spleen, but there was a decrease in thymus cellularity. Flow cytometric analysis of lymphocyte subsets in blood and spleen also showed no significant differences, but in the thymus the percentage of immature CD4/CD8 "double positive" cells increased while the more mature CD3"high", and CD4 or CD8 "single-positive" cells decreased. Thus, prolonged discordant xenograft survival in mice is possible and the use of two agents that act on different parts of the immune system allows a reduction in the dose of FK506 to safe levels.

Diabetogenic effects of FK506 on renal subcapsular islet isografts in rat

Previously we demonstrated prevention of immune rejection in rat islet allografts by continuous subcutaneous (s.c.) administration of FK506 and also showed that FK506 might have diabetogenic effects (Ryu and Yasunami (1991) Transplantation, 52, 599-605). The purpose of the present study was to characterize further diabetogenic effects of FK506 on renal subcapsular islet isografts in rat. Continuous s.c. administration of FK506 (3 mg/kg/day) for 35 days produced glucose intolerance in the recipients as demonstrated by intravenous (i.v.) glucose tolerance test at the end (35 days) and after discontinuation (90 days) of FK506 administration. Morphologically, beta cells in the grafts of FK506-treated group were degranulated at 35 and 120 days after transplantation. Electron microscopically, degranulation, marked swelling of rough endoplasmic reticulum, Golgi apparatus and mitochondria were detected in beta cells of the grafts treated with FK506 at 35 days, and at 120 days there was moderate structural recovery in the organella. These findings clearly demonstrate that FK506 has diabetogenic effects on renal subcapsular islet isografts in rat and also suggests potential reversibility of damages by FK506 in beta cells of the grafts.