Johannes P. van Hooff

Clinical Relevance of Pretransplant Donor-Directed Antibodies Detected by Single Antigen Beads in Highly Sensitized Renal Transplant Patients

Background. Highly sensitized (HS) patients (>85% panel-reactive antibodies) have a lower chance of receiving a donor kidney. Within Eurotransplant the Acceptable Mismatch (AM) program was developed to increase the chances of HS patients to receive a crossmatch-negative donor kidney. The standard crossmatch in the AM program is based on complement-dependent cytotoxicity. Methods. In this study we wanted to determine the clinical relevance of human leukocyte antigen donor-directed antibodies (DDA) detected by the single antigen (SA) bead technique, in the pretransplant sera of HS patients transplanted in our center through the Eurotransplant AM program. Results. From 34 AM patients, 27 were transplanted with 1 to 5 mismatches and 7 received a 0-mismatched graft. From the mismatched patients, retrospectively, 13 proved to possess pretransplant DDA by SA whereas 14 did not. No antibodies were found in the 0-mismatched group. Comparison of the DDA+ and DDA− patients in the human leukocyte antigen-mismatched donor/recipient combinations revealed a trend to an earlier and higher number of rejection episodes in DDA+ patients (P=0.08). No detrimental effect of DDA on graft survival was observed. Conclusions. This single-center study showed that in the AM program DDA detected by SA, and not by less-sensitive methods, may be related to acute rejection episodes but is not detrimental to long-term graft outcome. These findings question the increasing use of more-sensitive screening techniques for the allocation of organs.

Effect of immunosuppressive agents on long-term survival of renal transplant recipients: Focus on the cardiovascular risk

In the control of acute rejection, attention is being focused more and more on the long-term adverse effects of the immunosuppressive agents used. Since cardiovascular disease is the main cause of death in renal transplant recipients, optimal control of cardiovascular risk factors is essential in the long-term management of these patients. Unfortunately, several commonly used immunosuppressive drugs interfere with the cardiovascular system. In this review, the cardiovascular adverse effects of the immunosuppressive agents currently used for maintenance immunosuppression are thoroughly discussed.Optimising immunosuppression means finding a balance between efficacy and safety. Corticosteroids induce endothelial dysfunction, hypertension, hyperlipidaemia and diabetes mellitus, and impair fibrinolysis. The use of corticosteroids in transplant recipients is undesirable, not only because of their cardiovascular effects, but also because they induce such adverse effects as osteoporosis, obesity, and atrophy of the skin and vessel wall. Calcineurin inhibitors are the most powerful agents for maintenance immunosuppression. The calcineurin inhibitor ciclosporin (cyclosporine) not only induces these same adverse effects as corticosteroids but is also nephrotoxic. Tacrolimus has a more favourable cardiovascular risk profile than ciclosporin and is also less nephrotoxic. It has little or no effect on blood pressure and serum lipids; however, its diabetogenic effect is more prominent in the period immediately following transplantation, although at maintenance dosages, the diabetogenic effect appears to be comparable to that of ciclosporin. The diabetogenic effect of tacrolimus can be managed by reducing the dose of tacrolimus and early corticosteroid withdrawal. The effect of tacrolimus on endothelial function has not been completely elucidated. The proliferation inhibitors azathioprine and mycophenolate mofetil (MMF) have little effect on the cardiovascular system. Yet, indirectly, by inducing anaemia, they may lead to left ventricular hypertrophy. MMF is an attractive alternative to azathioprine because of its higher potency and possibly lower risk of malignancies. Sirolimus also induces anaemia, but may be promising because of its antiproliferative features. Whether the hyperlipidaemia induced by sirolimus counteracts its beneficial effects is, as yet, unknown. It may be combined with MMF, however, initial attempts resulted in severe mouth ulcers.

Minimization of Immunosuppressive Therapy After Renal Transplantation: Results of a Randomized Controlled Trial

Modern immunosuppressive regimens reduce the acute rejection rate by combining a cornerstone immunosuppressant like tacrolimus or cyclosporine with adjunctive agents like corticosteroids, mycophenolate mofetil (MMF) or azathioprine, often associated with untoward side effects.

Tacrolimus pharmacokinetics and pharmacogenetics: influence of adenosine triphosphate‐binding cassette B1 (ABCB1) and cytochrome (CYP) 3A polymorphisms

Tacrolimus, an immunosuppressant used after organ transplantation, has a narrow therapeutic range and its pharmacokinetic variability complicates its daily dose assessment. P‐glycoprotein (P‐gp), encoded by the adenosine triphosphate‐binding cassette B1 (ABCB1) and the cytochrome (CYP) 3A4 and 3A5 enzymes appears to play a role in the tacrolimus metabolism. In the present study, two different renal transplant recipient groups were used to examine the influence of ABCB1 and CYP3A polymorphisms on the daily tacrolimus dose and several pharmacokinetic parameters. In total 63 Caucasian renal transplant recipients divided into 26 early [median (range) of the days since transplantation – 16 (3–74)] and 37 late [median (range) of the days since transplantation – 1465 (453–4128)] post‐transplant recipients were genotyped for ABCB1 and CYP3A polymorphisms. The pharmacokinetic parameters of tacrolimus were determined for all renal transplant recipients and correlated with their corresponding genotypes. A significant difference in allele frequencies of the CYP3A4*1B (P = 0.028) and CYP3A5*1 (P = 0.022) alleles was observed between the early and late post‐transplant recipient groups. Significantly higher dose‐normalized trough levels (dnC0), dose‐normalized area under the curve (dnAUC0−12), and dose‐normalized maximum concentration (dnCmax) were observed for carriers of the CYP3A5*3 variant allele in both renal transplant patient groups. Except for the daily tacrolimus dose (P = 0.025) no significant differences were observed for carriers of the CYP3A4*1B variant allele. Neither the individual ABCB1 polymorphisms nor the ABCB1 haplotypes were associated with any pharmacokinetic parameter. We noticed that patients carrying a CYP3A5*1 allele require a twofold higher tacrolimus dose compared with homozygous carriers of the CYP3A5*3 variant allele to maintain the target dnAUC0−12. Therefore, genotyping for the CYP3A5*3 variant allele can contribute to a better and more individualized immunosuppressive therapy in transplant patients.

Similarities in skeletal muscle strength and exercise capacity between renal transplant and hemodialysis patients

Exercise intolerance is common in hemodialysis (HD) and renal transplant (RTx) patients. Aim of the study was to assess to what extent exercise capacity and skeletal muscle strength of RTx patients differ from HD patients and healthy controls and to elucidate potential determinants of exercise capacity in RTx patients. Exercise capacity, muscle strength, lean body mass (LBM) and physical activity level (PAL) were measured by cycle‐ergometry, isokinetic dynamometry, DEXA and Baecke Questionnaire, respectively, in 35 RTx, 16 HD and 21 controls. VO2peak and muscle strength of the RTx patients were significantly lower compared to controls (p < 0.01), but not different compared to HD patients. In RTx patients, strength (p < 0.001), PAL (p = 0.001) and age (p = 0.045) were significant predictors of VO2peak. Muscle strength was related to LBM (p = 0.001) and age (p = 0.001), whereas gender (p < 0.001) and renal function (p = 0.01) turned out to be significant predictors of LBM. No effects of corticosteroids were observed. Exercise capacity and muscle strength seem equally reduced in RTx and HD patients compared to controls. In RTx patients, muscle strength and PAL are highly related to exercise capacity. Renal function appears to be a significant predictor of LBM, and through the LBM, of muscle strength and exercise capacity.

A prospective randomized multicenter study of tacrolimus in combination with sirolimus in renal-transplant recipients.

Background. Recently, sirolimus (SRL) was introduced as an immunosuppressant in solid-organ transplantation. This study evaluated combinations of SRL and tacrolimus (Tac). Methods. This 6-month study investigated the safety and efficacy of Tac and steroids in combination with three different doses of SRL in renal-transplant recipients. A total of 104 patients were randomized in four groups: one group received Tac and steroids (control n=28), and three groups also received the following daily SRL doses: 0.5 mg (TacSRL0.5, n=25), 1 mg (TacSRL1, n=25), or 2 mg (TacSRL2, n=26). Tac doses were adjusted to whole-blood trough levels. Steroids were tapered from 20 mg per day to 5 mg per day. The SRL groups underwent a second randomization to discontinue SRL at either month 3 or 5. Results. At month 6, patient survival rates were 100%, 100%, 96.0%, and 100%, and graft survival rates were 96.4%, 84.0%, 88.0%, and 84.6%, respectively. The overall safety profile was similar in all groups. The incidences of infections during months 1 to 3 were similar in all groups (control 46.4%, TacSRL0.5 32.0%, TacSRL1 56.0%, TacSRL2 46.2%). The 3-month incidences of hypercholesteremia (cholesterol >240 mg/dL or low-density lipoprotein cholesterol >160 mg/dL) were 21.4%, 36.0%, 48.0%, and 50.0% (P =0.019). Lipid levels improved after withdrawal of SRL. The 3-month incidences of biopsy-proven acute rejection were 28.6% (control), 8.0% (TacSRL0.5), 8.0% (TacSRL1), and 3.8% (TacSRL2) (P =0.014). Conclusion. Tac in combination with low doses of SRL provides a very effective and safe regimen.

Tacrolimus and posttransplant diabetes mellitus in renal transplantation

The most prominent side effect of tacrolimus is the induction of posttransplant diabetes mellitus (PTDM). In this review, the authors discuss the incidence, mechanism, prevention, and treatment of tacrolimus-induced PTDM in renal patients.

Outcome of Nonheart‐Beating Donor Kidneys with Prolonged Delayed Graft Function after Transplantation

Nonheart‐beating donor (NHBD) kidneys are frequently associated with delayed graft function (DGF), with a deleterious effect on kidney function and allograft survival. The influence and the duration of DGF on the outcome of NHBD kidneys are assessed.

Dried blood spot measurement: application in tacrolimus monitoring using limited sampling strategy and abbreviated AUC estimation

Dried blood spot (DBS) sampling and high‐performance liquid chromatography tandem–mass spectrometry have been developed in monitoring tacrolimus levels. Our center favors the use of limited sampling strategy and abbreviated formula to estimate the area under concentration–time curve (AUC0–12). However, it is inconvenient for patients because they have to wait in the center for blood sampling. We investigated the application of DBS method in tacrolimus level monitoring using limited sampling strategy and abbreviated AUC estimation approach. Duplicate venous samples were obtained at each time point (C0, C2, and C4). To determine the stability of blood samples, one venous sample was sent to our laboratory immediately. The other duplicate venous samples, together with simultaneous fingerprick blood samples, were sent to the University of Maastricht in the Netherlands. Thirty six patients were recruited and 108 sets of blood samples were collected. There was a highly significant relationship between AUC0–12, estimated from venous blood samples, and fingerprick blood samples (r2 = 0.96, P < 0.0001). Moreover, there was an excellent correlation between whole blood venous tacrolimus levels in the two centers (r2 = 0.97; P < 0.0001). The blood samples were stable after long‐distance transport. DBS sampling can be used in centers using limited sampling and abbreviated AUC0–12 strategy as drug monitoring.

The influence of early steroid withdrawal on body composition and bone mineral density in renal transplantation patients

Abstract.Corticosteroid treatment may have an important effect on body composition and bone mineral density (BMD) in renal transplantation (RTx) patients. We investigated the effect of early steroid withdrawal on body composition and BMD of RTx patients in a prospective design. Post-transplant immunosuppression consisted of tacrolimus, mycophenolate mofetil, and prednisolone. Three months after RTx, 27 patients participating in a multi-center trial were randomized either to continue steroids (at a dose of 10 mg/day, n=17; steroid+) or be withdrawn from steroids within 2 weeks (n=10; steroid–). Body composition and BMD (lumbar spine (L2–L4) and femoral neck) were measured by dual-energy X-ray absorptiometry (DEXA) just before and 3 months after randomization. With regard to body composition, fat mass tended to increase in the steroid+ group (1.1±2.3 kg; P=0.084), but did not change in the steroid– group. Increase in body fat percentage tended to be higher (P=0.08) in the steroid+ group (0.6±2.7%) than in the steroid– group (–0.7±2.1%). The change in lean body mass was not significantly different between the two groups. BMD of the lumbar spine and femoral neck decreased significantly in the steroid+ group (–1.4±3.2% and –2.3±2.9%, respectively, P<0.05) while no changes were observed in the steroid– group. The change in BMD of the lumbar spine was significantly different between the steroid+ and the steroid– group, whereas the change in BMD of the femoral neck was not significantly different. Thus, the increase in fat mass tended to be higher in the group continuing on steroids, though not significant, due to large inter-individual variation. In general, the effect of early steroid withdrawal on body composition after RTx appears to be modest. In addition, early steroid withdrawal seems to have beneficial effects on BMD in RTx patients, especially in the lumbar region.