Maarten H. L. Christiaans

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.

Conversion from Cyclosporine to Tacrolimus Improves Quality of Life Indices, Renal Graft Function and Cardiovascular Risk Profile

Long‐term use of cyclosporine after renal transplantation results in nephrotoxicity and an increased cardiovascular risk profile. Tacrolimus may be more favorable in this respect. In this randomized controlled study in 124 renal transplant patients, the effects of conversion from cyclosporine to tacrolimus on renal function, cardiovascular risk factors, and perceived side‐effects were investigated after a follow‐up of 2 years. After conversion from cyclosporine to tacrolimus renal function remained stable, whereas continuation of cyclosporine was accompanied by a rise in serum creatinine from 142 ± 48 μmol/L to 157 ± 62 μmol/L (p < 0.05 comparing both groups). Conversion to tacrolimus resulted in a sustained reduction in systolic and diastolic blood pressure, and a sustained improvement in the serum lipid profile, leading to a reduction in the Framingham risk score from 5.7 ± 4.3 to 4.8 ± 5.3 (p < 0.05). Finally, conversion to tacrolimus resulted in decreased scores for occurrence of and distress due to side‐effects. In conclusion, conversion from cyclosporine to tacrolimus in stable renal transplant patients is beneficial with respect to renal function, cardiovascular risk profile, and side‐effects. Therefore, for most renal transplant patients tacrolimus will be the drug of choice when long‐term treatment with a calcineurin inhibitor is indicated.

Improved Cardiovascular Risk Profile and Renal Function in Renal Transplant Patients after Randomized Conversion from Cyclosporine to Tacrolimus

Cyclosporine is considered to contribute to the high cardiovascular morbidity and mortality in patients after renal transplantation. Tacrolimus may be more favorable in this respect, but controlled data are scarce. In this prospective randomized study in 124 stable renal transplant patients, the effects of conversion from cyclosporine to tacrolimus on cardiovascular risk factors and renal function were investigated. Follow-up was 6 mo. Statistical analysis was performed by ANOVA for repeated measurements. The serum creatinine level decreased from 137 +/- 30 micromol/L to 131 +/- 29 micromol/L (P < 0.01). Three months after conversion from cyclosporine to tacrolimus, mean BP significantly decreased from 104 +/- 13 to 99 +/- 12 mmHg (P < 0.001). Serum LDL cholesterol decreased from 3.48 +/- 0.80 to 3.11 +/- 0.74 mmol/L (P < 0.001,) and serum apolipoprotein B decreased from 1018 +/- 189 to 935 +/- 174 mg/L (P < 0.001). Serum triglycerides decreased from 2.11 +/- 1.12 to 1.72 +/- 0.94 mmol/L (P < 0.001). In addition, both rate and extent of LDL oxidation were reduced. The fibrinogen level decreased from 3638 +/- 857 to 3417 +/- 751 mg/L (P < 0.05). Plasma homocysteine concentration did not change. Three months after conversion, plasma fasting glucose level temporarily increased from 5.4 +/- 1.3 mmol/L to 5.8 +/- 1.9 mmol/L (P < 0.05). Conversion to tacrolimus resulted in a significant reduction of the Framingham risk score. In conclusion, conversion from cyclosporine to tacrolimus in stable renal transplant patients has a beneficial effect on renal function, BP, serum concentration and atherogenic properties of serum lipids, and fibrinogen.

Therapeutic drug monitoring of everolimus using the dried blood spot method in combination with liquid chromatography–mass spectrometry

An assay of everolimus based on finger prick sampling and consecutive application as a blood spot on sampling paper has been developed. We explored several methods [K. Hoogtanders, J. van der Heijden, M. Christiaans, P. Edelbroek, J. van Hooff, L. Stolk, J. Pharm. Biomed. Anal. 44 (2006) 658-664; A. Allanson, M. Cotton, J. Tettey, et al., J. Pharm. Biomed. Anal. 44 (2007) 963-969] and developed a new method, namely the impregnation of sampling paper with a solution of plasma-protein, formic acid and ammonium acetate, in combination with the extraction of the blood spot by filter filtration. This kind of sample preparation provides new possibilities for blood spot sampling especially if analytes are adsorbed to the paper. The dried blood spot was analysed using the HPLC-electrospray-tandem mass spectrometry method, with 32-desmethoxyrapamycin as the internal standard. The working range of our study was 2-30 microg/l. Within this range, intra-and inter-assay variability for precision and accuracy was <15%. Everolimus blood spot samples proved stable for 3 days at 60 degrees C and for 32 days at 4 degrees C. Everolimus concentrations of one stable out-patient were compared after both blood spot sampling and conventional venous sampling on various occasions. Results indicate that this new method is promising for therapeutic drug monitoring in stable renal transplant patients.

The influence of obesity on short- and long-term graft and patient survival after renal transplantation

To determine short‐ and long‐term patient and graft survival in obese [body mass index (BMI) ≥ 30 kg/m2] and nonobese (BMI < 30 kg/m2) renal transplant patients we retrospectively analyzed our national‐database. Patients 18 years or older receiving a primary transplant after 1993 were included. A total of 1871 patients were included in the nonobese group and 196 in the obese group. In the obese group there were significantly more females (52% vs. 38.6%, P < 0.01) and patients were significantly older [52 years (43–59) vs. 48 years (37–58); P < 0.05]. Patient survival and graft survival were significantly decreased in obese renal transplant recipients (1 and 5 year patient survival were respectively 94% vs. 97% and 81% vs. 89%, P < 0.01; 1 and 5 year graft survival were respectively 86% vs. 92% and 71% vs. 80%, P < 0.01). Initial BMI was an independent predictor for patient death and graft failure. This large retrospective study shows that both graft and patient survival are significantly lower in obese renal transplant recipients.

Kidneys from Donors after Cardiac Death Provide Survival Benefit

The continuing shortage of kidneys for transplantation requires major efforts to expand the donor pool. Donation after cardiac death (DCD) increases the number of available kidneys, but it is unknown whether patients who receive a DCD kidney live longer than patients who remain on dialysis and wait for a conventional kidney from a brain-dead donor (DBD). This observational cohort study included all 2575 patients who were registered on the Dutch waiting list for a first kidney transplant between January 1, 1999, and December 31, 2004. From listing until the earliest of death, living-donor kidney transplantation, or December 31, 2005, 459 patients received a DCD transplant and 680 patients received a DBD transplant. Graft failure during the first 3 months after transplantation was twice as likely for DCD kidneys than DBD kidneys (12 versus 6.3%; P=0.001). Standard-criteria DCD transplantation associated with a 56% reduced risk for mortality (hazard ratio 0.44; 95% confidence interval 0.24 to 0.80) compared with continuing on dialysis and awaiting a standard-criteria DBD kidney. This reduction in mortality translates into 2.4-month additional expected lifetime during the first 4 years after transplantation for recipients of DCD kidneys compared with patients who await a DBD kidney. In summary, standard-criteria DCD kidney transplantation associates with increased survival of patients who have ESRD and are on the transplant waiting list.

Everolimus plus early tacrolimus minimization: a phase III, randomized, open-label, multicentre trial in renal transplantation

There is increasing interest in tacrolimus‐minimization regimens. ASSET was an open‐label, randomized, 12‐month study of everolimus plus tacrolimus in de‐novo renal‐transplant recipients. Everolimus trough targets were 3–8 ng/ml throughout the study. Tacrolimus trough targets were 4–7 ng/ml during the first 3 months and 1.5–3 ng/ml (n = 107) or 4–7 ng/ml (n = 117) from Month 4. All patients received basiliximab induction and corticosteroids. The primary objective was to demonstrate superior estimated glomerular filtration rate (eGFR; MDRD‐4) at Month 12 in the tacrolimus 1.5–3 ng/ml versus the 4–7 ng/ml group. Secondary endpoints included incidence of biopsy‐proven acute rejection (BPAR; Months 4–12) and serious adverse events (SAEs; Months 0–12). Statistical significance was not achieved for the primary endpoint (mean eGFR: 57.1 vs. 51.7 ml/min/1.73 m2), potentially due to overlapping of achieved tacrolimus exposure levels (Month 12 mean ± SD, tacrolimus 1.5–3 ng/ml: 3.4 ± 1.4; tacrolimus 4–7 ng/ml: 5.5 ± 2.0 ng/ml). BPAR (months 4–12) and SAE rates were comparable between groups (2.7% vs. 1.1% and 58.7% vs. 51.3%; respectively). Everolimus‐facilitated tacrolimus minimization, to levels lower than previously investigated, achieved good renal function, low BPAR and graft‐loss rates, and an acceptable safety profile in renal transplantation over 12 months although statistically superior renal function of the 1.5–3 ng/ml tacrolimus group was not achieved. (ClinicalTrials.gov: NCT00369161) is registered at http://www.clinicaltrials.gov.

Kidney transplantation from donors after cardiac death: a 25-year experience.

Background. The shortage of organ donors presents a major obstacle for adequate treatment of patients with end-stage renal disease. Donation after cardiac death (DCD) has been shown to increase the number of kidneys available for transplantation. The present article reports on the first 25 years of our experience with DCD kidney transplantation. Methods. This observational cohort study included all DCD kidney transplantations recovered in our procurement area from January 1, 1981 until December 31, 2005 (n=297). Patients were followed up until the earliest of death or December 31, 2006. Clinical outcomes were compared with matched kidney transplantations from brain dead donors (DBD, n=594), using multivariable regression models to adjust for potential confounders. Results. DCD activity resulted in a 44% increase in the number of deceased donor kidneys from our organ procurement area. After adjustment for potential confounders, the odds of primary nonfunction and delayed graft function were 7.5 (95% CI, 4.0–14.1; P<0.001) and 10.3 (95% CI, 6.7–15.9; P<0.001) times greater, respectively, for DCD kidneys compared with DBD kidneys. The high incidence of primary nonfunction of DCD kidneys resulted in an increased rate of graft loss (HR, 1.82; 95% CI, 1.37–2.42; P<0.001). However, DCD kidneys that did not experience primary nonfunction functioned as long as DBD kidneys (HR, 1.05; 95% CI, 0.73–1.51; P=0.79). Patient survival of DCD and DBD kidney recipients was equivalent (HR, 1.16; 95% CI, 0.87–1.54; P=0.32). Conclusions. The benefits of DCD kidney transplantation outweigh the increased risk of early graft loss. Expansion of the supply of DCD kidneys is likely to improve the treatment of wait-listed dialysis patients.

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.