The influence of pharmacogenetics and cofactors on clinical outcomes in kidney transplantation

Effects of Wuzhi Capsule on Whole-Blood Tacrolimus Concentration Levels: A Systematic Review and Meta-Analysis

BACKGROUND

Wuzhi Capsule (WZC) is a traditional Chinese medicinal herb widely used to treat drug-induced hepatitis or liver dysfunction and is usually prescribed in China to increase tacrolimus concentration. Several studies with small sample sizes have shown that WZC can increase tacrolimus concentration levels in clinical practice. This study aimed to evaluate the effect of WZC on whole-blood tacrolimus concentration levels and safety.

METHODS

We searched 7 databases for randomized clinical trials (RCTs) and observational studies (OSs) comparing whole-blood tacrolimus concentration levels between WZC and non-WZC treatments. Data analysis was performed using Review Manager version 5.3. This study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses reporting guidelines.

RESULTS

Eleven studies involving 6 RCTs and 5 OSs were included. The meta-analysis indicated that whole-blood tacrolimus concentration levels in the WZC group was significantly higher than that of the non-WZC group [weighted mean difference = 1.38, 95% CI (confidence interval), 1.21-1.56, P < 0.001], and similar results were shown in all the subgroups of follow-up time, different primary disease, and different WZC doses. In the self-control OSs, the whole-blood tacrolimus concentration levels in the WZC group was significantly higher than the non-WZC group (weighted mean difference = 1.17, 95% CI, 0.71-1.64, P < 0.001). WZC was generally well tolerated and there was no significant difference in the incidence of adverse reactions between the 2 groups.

CONCLUSIONS

WZC can increase whole-blood tacrolimus concentration levels. This may be an economical and practical treatment choice for patients, especially those with poor oral tacrolimus absorption capabilities. Nevertheless, RCTs and OSs with large sample sizes and high quality are needed in the future to confirm these positive results.

Effects and safety evaluation of Wuzhi Capsules combined with tacrolimus for the treatment of kidney transplantation recipients

WHAT IS KNOWN AND OBJECTIVE

Tacrolimus (FK506), an effective and potent calcineurin inhibitor, is the cornerstone of immunosuppression after kidney transplantation. Wuzhi capsule (WZC), a prescribed ethanol extract of Nan-Wuweizi (Schisandra sphenanthera), is widely prescribed for kidney transplant recipients for the maintenance of tacrolimus concentration in clinical settings. Previous studies have demonstrated that WZC can increase the blood concentration of tacrolimus. However, it remains controversial whether to use WZC can be used to increase tacrolimus concentration in clinical practice. Our study aimed to evaluate the efficacy and safety of WZC combined with tacrolimus in the treatment of kidney transplant recipients.

METHODS

One hundred and ninety four Chinese kidney transplant recipients were included in this retrospective study. The recipients were divided into two groups (non-WZC group and WZC group). We investigated the effects of WZC on tacrolimus in terms of tacrolimus metabolism, laboratory tests, pharmacogenomics, renal function and adverse reactions.

RESULTS AND DISCUSSION

The concentration/dose (C₀ /D) of tacrolimus was significantly higher in the WZC group than the non-WZC group. The laboratory findings of blood routine tests, liver and kidney function were not significantly different between the two groups. The CYP3A5 genotype showed clearly associated with tacrolimus C₀ /D, whereas no significant difference was observed in patients with CYP3A4*1B, CYP3A4*22, ABCB1, ABCC2, POR*28 or PXR alleles. The improvement of C₀ /D by administration of WZC was significant in CYP3A5 expressers compared to non-expressers. Furthermore, the WZC group had a remarkably higher proportion of subjects who reached the target tacrolimus concentration than the non-WZC group. No significant differences in renal function and adverse reactions were observed between the groups.

WHAT IS NEW AND CONCLUSION

Wuzhi capsule can increase tacrolimus concentration without negative effects on renal function and adverse reactions, especially in CYP3A5 expressers. Efficient and economical synergistic effects can be achieved by the combined administration of WZC in kidney transplant recipients.

Beyond Single Nucleotide Polymorphisms: CYP3A5∗3∗6∗7 Composite and ABCB1 Haplotype Associations to Tacrolimus Pharmacokinetics in Black and White Renal Transplant Recipients

Interpatient variability in tacrolimus pharmacokinetics is attributed to metabolism by cytochrome P-450 3A5 (CYP3A5) isoenzymes and membrane transport by P-glycoprotein. Interpatient pharmacokinetic variability has been associated with genotypic variants for both CYP3A5 or ABCB1. Tacrolimus pharmacokinetics was investigated in 65 stable Black and Caucasian post-renal transplant patients by assessing the effects of multiple alleles in both CYP3A5 and ABCB1. A metabolic composite based upon the CYP3A5 polymorphisms: ^∗3(rs776746), ^∗6(10264272), and ^∗7(41303343), each independently responsible for loss of protein expression was used to classify patients as extensive, intermediate and poor metabolizers. In addition, the role of ABCB1 on tacrolimus pharmacokinetics was assessed using haplotype analysis encompassing the single nucleotide polymorphisms: 1236C > T (rs1128503), 2677G > T/A(rs2032582), and 3435C > T(rs1045642). Finally, a combined analysis using both CYP3A5 and ABCB1 polymorphisms was developed to assess their inter-related influence on tacrolimus pharmacokinetics. Extensive metabolizers identified as homozygous wild type at all three CYP3A5 loci were found in 7 Blacks and required twice the tacrolimus dose (5.6 ± 1.6 mg) compared to Poor metabolizers [2.5 ± 1.1 mg (P < 0.001)]; who were primarily Whites. These extensive metabolizers had 2-fold faster clearance (P < 0.001) with 50% lower AUC^∗ (P < 0.001) than Poor metabolizers. No differences in C_{12 h} were found due to therapeutic drug monitoring. The majority of blacks (81%) were classified as either Extensive or Intermediate Metabolizers requiring higher tacrolimus doses to accommodate the more rapid clearance. Blacks who were homozygous for one or more loss of function SNPS were associated with lower tacrolimus doses and slower clearance. These values are comparable to Whites, 82% of who were in the Poor metabolic composite group. The ABCB1 haplotype analysis detected significant associations of the wildtype 1236T-2677T-3435T haplotype to tacrolimus dose (P = 0.03), CL (P = 0.023), CL/LBW (P = 0.022), and AUC^∗ (P = 0.078). Finally, analysis combining CYP3A5 and ABCB1 genotypes indicated that the presence of the ABCB1 3435 T allele significantly reduced tacrolimus clearance for all three CPY3A5 metabolic composite groups. Genotypic associations of tacrolimus pharmacokinetics can be improved by using the novel composite CYP3A5^∗3^∗4^∗5 and ABCB1 haplotypes. Consideration of multiple alleles using CYP3A5 metabolic composites and drug transporter ABCB1 haplotypes provides a more comprehensive appraisal of genetic factors contributing to interpatient variability in tacrolimus pharmacokinetics among Whites and Blacks.

Association Between CYP3A4 and CYP3A5 Genotypes and Cyclosporine's Blood Levels and Doses among Jordanian Kidney Transplanted Patients

BACKGROUND

Cyclosporine is used as an immunosuppressive agent in kidney transplantation. It has a narrow therapeutic window. Cyclosporine is predominantly metabolized by CYP3A4 and CYP3A5. The most common Single Nucleotide Polymorphisms (SNPs) affecting cyclosporine metabolism (CYP3A4*1B, CYP3A4*1G, CYP3A4*22 and CYP3A5*3) were investigated among Jordanian kidney transplanted patients to find out the genotypes and allele frequencies of these SNPs. Additionally, this study investigated whether genotypes of CYP3A4 and CYP3A5 affect C2 blood levels, dosing of cyclosporine and the prevalence of acute rejection.

METHODS

Blood samples of 109 adult patients taking cyclosporine as their primary immunosuppressant for kidney transplantation were collected from the Prince Hamzah Hospital, Amman, Jordan. Patients' first C2 blood levels and their first two given doses were collected. Patients were genotyped for the four SNPs using Polymerase Chain Reaction- restriction Fragment Length Polymorphism (PCR-RFLP) assay method.

RESULTS

Allele frequencies among Jordanian patients for CYP3A4*1B, CYP3A4*1G, CYP3A4*22 and CYP3A5*3 were 0.037, 0.399, 0.037 and 0.271, respectively. There was a significant association between CYP3A4*22 and mean difference in the second and first given doses (P=0.034). There was a big difference between CYP3A4*22 and the mean of the first C2 blood levels (P=0.063).

CONCLUSION

There was a strong association between CYP3A4*22 and the mean difference between the second and first given doses. There was a trend of significant difference between the mean of the first C2 blood levels among heterozygous CYP3A4*22 patients. Pharmacogenomics may hold promise in assisting the prediction of the best cyclosporine dose and C2 blood level among Jordanian kidney transplant patients.

Effects of Wuzhi Capsules on Blood Concentration of Tacrolimus in Renal Transplant Recipients

BACKGROUND Tacrolimus is a widely used immunosuppressant in renal transplant recipients. It was demonstrated in rats and healthy volunteers that Wuzhi capsules could inhibit metabolism and maintain blood concentration of tacrolimus. However, there are no clinical studies of Wuzhi capsules in renal transplant recipients. This research aimed to assess the effect of Wuzhi capsules on the blood concentration of tacrolimus in renal transplant recipients. MATERIAL AND METHODS A total of 158 Chinese renal transplant recipients receiving tacrolimus with or without Wuzhi capsules were included in this retrospective study. The cohort study included 126 recipients, with 86 recipients receiving Wuzhi capsules (WZCs) and the other 40 recipients not receiving WZCs. Another 32 recipients were involved in a self-control study. RESULTS Dose- and body weight-adjusted trough concentrations (C0/D/W) of tacrolimus in the WZC group were found to be significantly higher than that in the non-WZC group (P<0.05). The improvement of C0/D/W by administration of Wuzhi capsules was more significant in CYP3A5 expressers than in non-expressers following subgroup analysis. Furthermore, the WZC group had a remarkably higher proportion of subjects who reached target tacrolimus concentration than in the non-WZC group, both in CYP3A5 expressers (P=0.01) and non-expressers (P<0.001). Multiple linear regression analysis and self-control analysis confirmed the positive impact of Wuzhi capsules on tacrolimus concentration (P<0.001). CONCLUSIONS Wuzhi capsules can increase tacrolimus trough concentration without adverse effects on allograft function, especially in CYP3A5 expressers. Efficient and convenient immunosuppressive effects on renal transplant recipients can be achieved by treatment including administration of Wuzhi capsules.

Pharmacokinetics and pharmacogenomics of mycophenolic acid and its clinical correlations in maintenance immunosuppression for lupus nephritis

Background

There is little data on mycophenolic acid (MPA) pharmacokinetics and pharmacogenomics and optimal MPA exposure in lupus nephritis (LN) patients during long-term maintenance.

Methods

We measured blood MPA levels at 1, 2, 4, 8, 10 and 12-h post-dose (i.e. C1, C2, C4, C8, C10 and C12) in 88 stable LN patients receiving maintenance prednisolone and mycophenolate mofetil, repeated every 6 months. The relationship between MPA exposure and single nucleotide polymorphisms (SNPs) of adenosine triphosphate–binding cassette subfamily C member 2 (ABCC2; rs2273697, rs3740066, rs717620 and rs17222723), organic anion-transporting polypeptides (OATPs; rs7311358 and rs4149117) and uridine diphosphate glucuronosyltransferase (UGT; rs17863762, rs6714486, rs17868320 and rs72551330) was also investigated.

Results

C1, C2 and C12 were 8.3 ± 6.6 , 7.2 ± 5.2 and 2.0 ± 1.4 mg/L and all correlated with the 12-h area under the curve (AUC0–12; r = 0.51, 0.85 and 0.73; P = 0.02, &lt;0.001 and &lt;0.001, respectively). C12 inversely correlated with hemoglobin, immunoglobulins and leukocyte levels (P &lt; 0.05 for all). Five renal flares, 11 episodes of infection and 10 episodes of anemia (hemoglobin &lt;10 g/dL) occurred over 96 weeks, with a corresponding C12 of 1.3 ± 0.5, 4.3 ± 2.6 and 2.9 ± 1.5 mg/L, respectively (versus 2.4 ± 1.2, 1.8 ± 1.2 and 1.7 ± 1.1 mg/L in patients without these complications; P = 0.041, &lt;0.001 and 0.004). SNP rs2273697 A/G in the ABCC2 gene was associated with lower MPA exposure compared with G/G (1075.9 ± 239.9 versus 1891.5 ± 918.9 mgh/L per g/kg; P = 0.003). SNPs of OATP and UGT were unrelated to MPA level.

Conclusion

MPA C12 correlates with the AUC0–12 and is related to renal flare, infection and anemia. SNP rs2273697 A/G is associated with lower MPA exposure.

Gene Variations of Sixth Complement Component Affecting Tacrolimus Metabolism in Patients with Liver Transplantation for Hepatocellular Carcinoma

BACKGROUND

Orthotopic liver transplantation (OLT) improves the prognosis of patients with hepatocellular carcinoma (HCC). Moreover, the complement system is a powerful immune effector that can affect liver function and process of liver cirrhosis. However, studies correlating the complement system with tacrolimus metabolism after OLT are scarce. In this study, the role of single nucleotide polymorphisms (SNPs) associated with the sixth complement component (C6) in tacrolimus metabolism was investigated during the early stages of liver transplantation.

METHODS

The study enrolled 135 adult patients treated with OLT for HCC between August 2011 and October 2013. Ten SNPs in C6 gene and rs776746 in cytochrome P450 3A5 (CYP3A5) gene were investigated. The tacrolimus levels were monitored daily during 4 weeks after transplantation.

RESULTS

Both donor and recipient CYP3A5 rs776746 allele A were correlated with decreased concentration/dose (C/D) ratios. Recipient C6 rs9200 allele G and donor C6 rs10052999 homozygotes were correlated with lower C/D ratios. Recipient CYP3A5 rs776746 allele A (yielded median tacrolimus C/D ratios of 225.90 at week 1 and 123.61 at week 2), C6 rs9200 allele G (exhibited median tacrolimus C/D ratios of 211.31 at week 1, 110.23 at week 2, and 99.88 at week 3), and donor CYP3A5 rs776746 allele A (exhibited median C/D ratios of 210.82 at week 1, 111.06 at week 2, 77.49 at week 3, and 85.60 at week 4) and C6 rs10052999 homozygote (exhibited median C/D ratios of 167.59 at week 2, 157.99 at week 3, and 155.36 at week 4) were associated with rapid tacrolimus metabolism. With increasing number of these alleles, patients were found to have lower tacrolimus C/D ratios at various time points during the 4 weeks after transplantation. In multiple linear regression analysis, recipient C6 rs9200 group (AA vs. GG/GA) was found to be related to tacrolimus metabolism at weeks 1, 2, and 3 (P = 0.005, P = 0.045, and P = 0.033, respectively), whereas donor C6 rs10052999 group (CC/TT vs. TC) was demonstrated to be correlated with tacrolimus metabolism only at week 4 (P = 0.001).

CONCLUSIONS

Recipient C6 gene rs9200 polymorphism and donor C6 gene rs10052999 polymorphism are new genetic loci that affect tacrolimus metabolism in patients with HCC after OLT.

Influence of CYP3A4 and CYP3A5 polymorphisms on tacrolimus and sirolimus exposure in stable kidney transplant recipients

BACKGROUND

Polymorphisms in genes encoding for drug-metabolizing enzymes and drug transporters are among multiple factors that modulate the pharmacokinetic variability of tacrolimus (TAC) and sirolimus (SRL). This study aimed to evaluate the influence of single nucleotide polymorphisms (SNPs) on TAC and SRL dose-adjusted concentrations (C0/D) in stable kidney transplant recipients.

METHODS

This is an exploratory and prospective study, which includes 46 stable kidney transplant recipients. These patients were monitored from the 3rd to the 24th month after transplantation. The SRL group consisted of 25 patients receiving TAC, prednisone (PRED), and mycophenolate sodium (MPS), which were converted from TAC to SRL at 3rd month after transplantation. The TAC group consisted of 21 patients who underwent treatment with TAC, PRED, and MPS. Both groups were genotyped for CYP3A4 rs2242480 (g.20230G>A), CYP3A5 rs15524 (g.31611C>T), CYP2C8 rs10509681 (c.1196A>G) and ABCB1 rs1045642 (c.3435C>T), rs1128503 (c.1236C>T), and rs2032582 (c.2677G>T/A) polymorphisms.

RESULTS

In the TAC group, CYP3A4 rs2242480 A allele carriers were associated with lower TAC C0/D. For CYP3A5 rs15524 SNP, C0/D was higher among patients carrying TT genotype when compared with CT and CC genotype carriers in the SRL and, more consistently, in the TAC groups. For ABCB1 rs1045642 SNP, TT genotype was associated with reduced SRL C0/D, but only at month 15.

CONCLUSIONS

CYP3A4 rs2242480 and CYP3A5 rs15524 SNPs resulted in significant changes in SRL and TAC C0/D at different times after transplantation.

A candidate gene approach of the calcineurin pathway to identify variants associated with clinical outcomes in renal transplantation

AIM

To investigate the potential influence of variants in genes involved in the calcineurin pathway on the efficacy and toxicity of calcineurin inhibitors in renal transplantation.

MATERIALS & METHODS

Twenty-three polymorphisms in thirteen genes were tested in 381 renal transplant recipients receiving ciclosporin (n = 221) or tacrolimus (n = 160) and mycophenolate mofetil. Data were collected prospectively over the first year post-transplantation.

RESULTS

Multivariate survival analyses revealed no genetic associations with biopsy proven acute graft rejection and serious infections. Donor-recipient Cytomegalovirus mismatch was the only variable associated with serious infection.

CONCLUSION

This large exploratory study casts doubts on the potential interest of genetic biomarkers related to CNI pharmacodynamics but associations with other phenotypes in transplantation deserve further studies.

Impact of CYP3A5 and MDR-1 gene polymorphisms on the dose and level of tacrolimus among living-donor liver transplanted patients: single center experience

AIM OF WORK

To assess the impact of Cytochrome P450 3A5 (CYP3A5) and multidrug resistance-1 gene (MDR-1) single nucleotide polymorphisms on the dose and blood level of tacrolimus among liver transplanted patients.

PATIENTS AND METHODS

We enrolled a prospective study of 41 liver transplanted patients. Dose-adjusted trough blood concentration (C/D ratio) was calculated. Polymerase chain reaction-restriction fragment length polymorphism followed by sequencing was done for genotyping of CYP3A5*3 (6986A > G).

RESULTS

At 1 week, 1 and 3 months C/D ratio were significantly lower in CYP3A5 expressers *1/*1 patients compared to non-expressers *3/*3.

CONCLUSION

CYP3A5 (6986A > G) genotype, rather than MDR-1 (2677G > A/T) variant, has an impact on tacrolimus pharmacokinetics.

Donor ABCB1 3435 C>T genetic polymorphisms influence early renal function in kidney transplant recipients treated with tacrolimus

AIM

Determine the effect of genetic variants of donors and recipients on early renal function and tacrolimus pharmacokinetics in kidney transplant recipients.

PATIENTS & METHODS

We measured CYP3A5 (6986A>G), ABCB1 (3435C>T, 2677G>T/A, 1236C>T) genetic polymorphisms in 120 renal transplant recipients and donors by high-resolution melting curve analysis. The renal function and tacrolimus trough concentrations were analyzed.

RESULTS

The genotype of CYP3A5 (6986A>G) in recipients showed strong influence on tacrolimus pharmacokinetics. The ABCB1 3435 CC genotype in donor was significantly associated with lower estimated glomerular filtration in recipients within 1 month (p < 0.05) and correlated with delayed creatinine recovery (p = 0.007).

CONCLUSIONS

ABCB1 3435 CC genotype in donor influences early renal function and creatinine recovery in tacrolimus-treated kidney transplant recipients.

Association of Extrarenal Adverse Effects of Posttransplant Immunosuppression With Sex and ABCB1 Haplotypes

Extrarenal adverse effects (AEs) associated with calcineurin inhibitor (CNI) and mycophenolic acid (MPA) occur frequently but are unpredictable posttransplant complications. AEs may result from intracellular CNI accumulation and low activity of P-glycoprotein, encoded by the ABCB1 gene. Since ABCB1 single nucleotide polymorphisms (SNPs) and sex influence P-glycoprotein, we investigated haplotypes and extrarenal AEs. A prospective, cross-sectional study evaluated 149 patients receiving tacrolimus and enteric coated mycophenolate sodium or cyclosporine and mycophenolate mofetil. Immunosuppressive AE assessment determined individual and composite gastrointestinal, neurologic, aesthetic, and cumulative AEs. Lipids were quantitated after 12-hour fast. ABCB1 SNPs: c.1236C>T (rs1128503), c.2677G>T/A (rs2032582), and c.3435C>T (rs1045642) were determined with haplotype associations computed using the THESIAS program, and evaluated by immunosuppression, sex and race using multivariate general linear models. Tacrolimus patients exhibited more frequent and higher gastrointestinal AE scores compared with cyclosporine with association to CTT (P = 0.018) and sex (P = 0.01). Aesthetic AE score was 3 times greater for cyclosporine with TTC haplotype (P = 0.005). Females had higher gastrointestinal (P = 0.022), aesthetic (P < 0.001), neurologic (P = 0.022), and cumulative AE ratios (P < 0.001). Total cholesterol (TCHOL), low-density lipoproteins (LDL), and triglycerides were higher with cyclosporine. The TTC haplotype had higher TCHOL (P < 0.001) and LDL (P = 0.005). Higher triglyceride (P = 0.034) and lower high-density lipoproteins (P = 0.057) were associated with TTT with sex-adjusted analysis. ABCB1 haplotypes and sex were associated with extrarenal AEs. Using haplotypes, certain female patients manifested more AEs regardless of CNI. Haplotype testing may identify patients with greater susceptibility to AEs and facilitate CNI individualization.

Relationship between pharmacokinetics and pharmacodynamics of calcineurin inhibitors in renal transplant patients

The calcineurin inhibitors (CNIs) cyclosporine A (CsA) and tacrolimus (Tac) are immunosuppressive drugs, which are typically employed in the field of organ transplantation. Both drugs have narrow therapeutic indices, highly variable pharmacokinetics, and are associated with severe adverse effects. In current clinical routine, the dose finding of CNIs is based on the measurement of their blood concentrations. However, this method is limited in its ability to determine the biological impact of the drug. Alternative monitoring strategies, focusing on the pharmacodynamics of CNIs, could help to personalize drug dosing and optimize the treatment with CNIs. Therefore, we analyzed the relationship between pharmacokinetic and pharmacodynamic of the CNIs CsA (n = 9) and Tac (n = 8) in stable renal transplant patients during a 12-h dosing period. We observed a significant decrease in the drug-blood concentration during the course of the day and in parallel a significant recovery of T cell function. In addition, our data document that analysis of intracellular interleukin (IL)-2 production and determination of the IL-2 release are accurate parameters for monitoring the pharmacodynamics of CNIs.

Clinical implementation of pharmacogenetics in kidney transplantation: calcineurin inhibitors in the starting blocks

Pharmacogenetics has generated many expectations for its potential to individualize therapy proactively and improve medical care. However, despite the huge amount of reported genetic associations with either pharmacokinetics or pharmacodynamics of drugs, the translation into patient care is still slow. In fact, strong evidence for a substantial clinical benefit of pharmacogenetic testing is still limited, with a few exceptions. In kidney transplantation, established pharmacogenetic discoveries are being investigated for application in the clinic to improve efficacy and to limit toxicity associated with the use of immunosuppressive drugs, especially the frequently used calcineurin inhibitors (CNIs) tacrolimus and ciclosporin. The purpose of the present review is to picture the current status of CNI pharmacogenetics and to discuss the most promising leads that have been followed so far.

Association between interleukin-18 promoter variants and tacrolimus pharmacokinetics in Chinese renal transplant patients

PURPOSE

Interleukin 18 (IL-18) is a potent proinflammatory cytokine thought to down-regulate cytochrome P450 (CYP) enzyme activities. This study aimed to assess the potential influence of two functional single nucleotide polymorphisms (SNPs) in the IL-18 promoter region on the tacrolimus pharmacokinetics in Chinese renal transplant patients.

METHODS

We enrolled 96 renal allograft recipients receiving tacrolimus-based immunosuppressive regiments. Two functional SNPs in the IL-18 gene promoter region at the positions -137G/C (rs187283) and -607A/C (rs1946518) and one SNP (rs776746) of CYP3A5 were genotyped using a Mass ARRAY platform. Tacrolimus daily doses (mg/day) and trough tacrolimus concentration (ng/ml) were continuously recorded for 1 month after transplantation.

RESULTS

The tacrolimus C/D ratio was significantly associated with the IL-18 rs1946518 gene polymorphism in the first month after transplantation (P = 0.0225). We studied the influence of its polymorphism on tacrolimus C/D ratios in subjects with different CYP3A5 genotype backgrounds, and among patients with CYP3A5 expressers, the difference among the three genotypes was even more striking (P < 0.001). We did not find significant differences in tacrolimus C/D ratios between the IL-18 rs187238 genotypes, either nominally or according to the CYP3A5 genotype. In a simple linear regression model, age, hemoglobin (Hb), CYP3A5 gene polymorphisms, and IL-18 A-607C gene polymorphisms were associated with log-transformed tacrolimus C/D ratios (P < 0.05). In the final multiple linear regression model, CYP3A5 polymorphisms were the most important variant, accounting for 19.5 % of total variation involved in tacrolimus pharmacokinetics.

CONCLUSION

Our findings suggest that a combined analysis of CYP3A5 and IL-18 promoter polymorphisms may help clinicians develop individualized tacrolimus treatment, which is based on determining CYP3A5 genotype.

Associations between polymorphisms in target, metabolism, or transport proteins of mycophenolate sodium and therapeutic or adverse effects in kidney transplant patients

OBJECTIVES

Different associations between single nucleotide polymorphisms (SNPs) in cellular target, metabolism enzymes or transport proteins, and biopsy-proven acute rejection (BPAR) or adverse events have been reported in transplant patients receiving mycophenolate mofetil. This work aimed to study these in patients on enteric-coated mycophenolate sodium (EC-MPS).

PATIENTS AND METHODS

The study included 189 renal transplant patients from the DOMINOS trial. Fifteen SNPs in IMPDH2, IMPDH1, ABCC2, SLCO1B3, UGT1A8, UGT1A9, UGT2B7, CYP2C8, HUS1, and IL12A were genotyped in all patients. Associations between SNPs and the first event of BPAR or diarrhea were investigated using multivariate logistic regressions. Associations between SNPs and leukopenia or anemia at nine different visits between days 0 and 190 after transplantation were studied using time-dependent Cox proportional hazards regression models.

RESULTS

Multivariate analyses showed that the CYP2C8 rs11572076 wild-type genotype was associated significantly with a lower risk of leukopenia [GG vs. GA: hazard ratio (95% confidence interval) 0.14 (0.03, 0.59), P=0.00783]. Higher EC-MPS doses and the UGT2B7 c.-840 G>A variant allele were associated with an increased risk of anemia [EC-MPS per unit dose increase: 1.004 (1.003, 1.005), P<0.0001; UGT2B7 GA vs. AA: 1.65 (1.12, 2.43), P=0.01043; GG vs. AA: 1.88 (1.23, 2.88), P=0.00343]. However, no significant association was found between any of the SNPs studied and diarrhea or BPAR.

CONCLUSION

Two pharmacogenetic associations reported previously with mycophenolate mofetil were found in a population of 189 renal transplant patients treated with EC-MPS.

Pharmacogenetics and immunosuppressive drugs

Several candidate genes have been proposed as potential biomarkers for altered pharmacodynamics or pharmacokinetics of immunosuppressive drugs. However, there is usually only limited clinical evidence substantiating the implementation of biomarkers into clinical practice. Testing for thiopurine-S-methyltransferase polymorphisms has been put into routine clinical use quite widely, while the other pharmacogenetic tests are much less frequently used. Relatively good evidence appeared for tacrolimus-related biomarkers; thus, their utilization may be envisaged in the near future. Although the biomarkers related to mycophenolate, sirolimus or other drugs in the therapeutic class may be promising, further research is necessary to provide more robust evidence. The present review focuses on immunosuppressive drugs, excluding biological treatment.

Pharmacology and toxicology of mycophenolate in organ transplant recipients: an update

This review aims to provide an update of the literature on the pharmacology and toxicology of mycophenolate in solid organ transplant recipients. Mycophenolate is now the antimetabolite of choice in immunosuppressant regimens in transplant recipients. The active drug moiety mycophenolic acid (MPA) is available as an ester pro-drug and an enteric-coated sodium salt. MPA is a competitive, selective and reversible inhibitor of inosine-5'-monophosphate dehydrogenase (IMPDH), an important rate-limiting enzyme in purine synthesis. MPA suppresses T and B lymphocyte proliferation; it also decreases expression of glycoproteins and adhesion molecules responsible for recruiting monocytes and lymphocytes to sites of inflammation and graft rejection; and may destroy activated lymphocytes by induction of a necrotic signal. Improved long-term allograft survival has been demonstrated for MPA and may be due to inhibition of monocyte chemoattractant protein 1 or fibroblast proliferation. Recent research also suggested a differential effect of mycophenolate on the regulatory T cell/helper T cell balance which could potentially encourage immune tolerance. Lower exposure to calcineurin inhibitors (renal sparing) appears to be possible with concomitant use of MPA in renal transplant recipients without undue risk of rejection. MPA displays large between- and within-subject pharmacokinetic variability. At least three studies have now reported that MPA exhibits nonlinear pharmacokinetics, with bioavailability decreasing significantly with increasing doses, perhaps due to saturable absorption processes or saturable enterohepatic recirculation. The role of therapeutic drug monitoring (TDM) is still controversial and the ability of routine MPA TDM to improve long-term graft survival and patient outcomes is largely unknown. MPA monitoring may be more important in high-immunological recipients, those on calcineurin-inhibitor-sparing regimens and in whom unexpected rejection or infections have occurred. The majority of pharmacodynamic data on MPA has been obtained in patients receiving MMF therapy in the first year after kidney transplantation. Low MPA area under the concentration time from 0 to 12 h post-dose (AUC0-12) is associated with increased incidence of biopsy-proven acute rejection although AUC0-12 optimal cut-off values vary across study populations. IMPDH monitoring to identify individuals at increased risk of rejection shows some promise but is still in the experimental stage. A relationship between MPA exposure and adverse events was identified in some but not all studies. Genetic variants within genes involved in MPA metabolism (UGT1A9, UGT1A8, UGT2B7), cellular transportation (SLCOB1, SLCO1B3, ABCC2) and targets (IMPDH) have been reported to effect MPA pharmacokinetics and/or response in some studies; however, larger studies across different ethnic groups that take into account genetic linkage and drug interactions that can alter a patient's phenotype are needed before any clinical recommendations based on patient genotype can be formulated. There is little data on the pharmacology and toxicology of MPA in older and paediatric transplant recipients.

Effect of CYP3A4*22, POR*28, and PPARA rs4253728 on Sirolimus In Vitro Metabolism and Trough Concentrations in Kidney Transplant Recipients

BACKGROUND

Recent studies have identified new candidate polymorphisms in the genes related to CYP3A activity or calcineurin inhibitor dose requirements in kidney transplant recipients. These genes and polymorphisms are CYP3A4 (cytochrome P450, family 3, subfamily A, polypeptide 4) (rs35599367-C&gt;T; *22); POR [P450 (cytochrome) oxidoreductase] (rs1057868-C&gt;T; *28); and PPARA (peroxisome proliferator-activated receptor alpha) (rs4253728-G&gt;A). We investigated the impact of these polymorphisms on sirolimus (SRL) in vitro hepatic metabolism, SRL trough concentrations (C0), and SRL adverse events in kidney transplant recipients.

METHODS

The clinical study included 113 stable kidney transplant patients switched from a calcineurin inhibitor to SRL (SRL C0 measured at 1, 3, and 6 months thereafter). We investigated SRL metabolism in vitro using human liver microsomes derived from individual donors (n = 31). Microsomes and patients were genotyped by use of Taqman® allelic discrimination assays. The effects of polymorphisms and covariates were studied using multilinear regression imbedded in linear mixed-effect models or logistic regressions.

RESULTS

In vitro, the CYP3A4*22 allele resulted in approximately 20% lower metabolic rates of SRL (P = 0.0411). No significant association was found between CYP3A4, CYP3A5, or PPARA genotypes and SRL dose, C0, or C0/dose in kidney transplant patients. POR*28 was associated with a minor but significant decrease in SRL log-transformed C0 [CT/TT vs CC, β = −0.15 (0.05); P = 0.0197] but this did not have any impact on the dose administered, which limited the relevance of the finding. After adjustment for nongenetic covariates and correction for false discovery finding, none of the single-nucleotide polymorphisms tested showed significant association with SRL adverse events.

CONCLUSIONS

These recently described polymorphisms do not seem to substantially influence the pharmacokinetics of SRL or the occurrence of SRL adverse events in kidney transplant recipients.

Do drug transporter (ABCB1) SNPs and P-glycoprotein function influence cyclosporine and macrolides exposure in renal transplant patients? Results of the pharmacogenomic substudy within the symphony study

The function of the efflux pump P-glycoprotein (Pgp) and ABCB1 single nucleotide polymorphisms (SNPs) should be considered as important tools to deepen knowledge of drug nephrotoxicity and disposition mechanisms. The aim of this study is to investigate the association of C3435T, G2677T, C1236T, and T129C ABCB1 SNPs with Pgp activity and exposure to different immunosuppressive drugs in renal transplant patients. Patients included in the Symphony Pharmacogenomic substudy were genotyped for ABCB1 SNPs. According to the design, patients were randomized into four immunosuppressive regimens: low and standard dose of cyclosporine (n = 30), tacrolimus (n = 13), and sirolimus (n = 23) concomitantly with mycophenolate and steroids. Pgp activity was evaluated in PBMC using the Rhodamine 123 efflux assay. TT carrier patients on C3435T, G2677T, and C1236T SNPs (Pgp-low pumpers) showed lower Pgp activity than noncarriers. Pgp-high pumpers treated with cyclosporine showed lower values of Pgp function than macrolides. There was a negative correlation between cyclosporine AUC and Pgp activity at 3 months. Results did not show any correlation between tacrolimus and sirolimus AUC and Pgp activity at 3 months. We found an important role of the ABCB1 SNPs Pgp function in CD3(+) peripheral blood lymphocytes from renal transplant recipients. Pgp activity was influenced by cyclosporine but not macrolides exposure.

Influence of CYP3A4, CYP3A5 and MDR-1 polymorphisms on tacrolimus pharmacokinetics and early renal dysfunction in liver transplant recipients

OBJECTIVES

Tacrolimus is a widely used immunosuppressive drug in organ transplantation. The oral bioavailability of tacrolimus varies greatly between individuals and depends largely on the activity of both the cytochrome P450 3A (CYP3A) subfamily and P-glycoprotein (P-gp). The possible influence of single nucleotide polymorphisms (SNPs) of CYP3A subfamily and P-gp (MDR-1) in liver transplant recipients has recently been indicated as one of the most important variables affecting the pharmacokinetics of tacrolimus and the renal injury induced by tacrolimus.

METHODS

A total of 216 liver transplant recipients were enrolled in this study. The recipients' mean follow-up time was 52 mo (range from 16 to 96 mo). All liver transplant recipients were all in a stable stage with normal serum creatinine (SCr). All liver transplant recipients treated with tacrolimus were genotyped for CYP3A5 (6986A>G), CYP3A4 intron 6 (CYP3A4*22), MDR-1 exon 26 (3435C>T) and exon 12 (1236 C>T) SNPs by HRM analysis (high-resolution melting curve analysis). Recipients were defined as the early renal injury by the elevation of different microproteins in the urine including microalbumin (MA), urine immunoglobulin G (IGU), urine transferrin (TRU) and α1-microglobulin (A1M).

RESULTS

The daily dose of tacrolimus was higher for recipients with CYP3A5 1/1 (AA) genotype than those with CYP3A5 3/ 3 (GG) genotype [3.0 (2.0-4.0) versus 2.0 (1.5-2.5) mg/d, P<0.05]. The concentration/dose ratio of recipients with CYP3A5 1 homozygotes was lowest compared to recipients with CYP3A5 3/ 3 and CYP3A5 1/ 3 genotypes. Furthermore, the recipients carrying CYP3A5 3 allele were associated with increased risk of early renal glomerular injury compared to the recipients carrying CYP3A5 1 allele (P=0.01). MDR-1 polymorphisms were not related with tacrolimus pharmacokinetics and early renal injury.

CONCLUSION

CYP3A5 6986A>G genetic polymorphism affected daily dose requirements, concentration and nephrotoxicity of tacrolimus. Screening for this single nucleotide polymorphism before the transplantation might be helpful for the selection of adequate initial daily dose and to achieve the desired immunosuppression outcome.

Meta-analysis of the effect of MDR1 C3435 polymorphism on tacrolimus pharmacokinetics in renal transplant recipients

BACKGROUND

The published data revealed conflicting results of the polymorphism of MDR1 exon 26 SNP C3435T on the pharmacokinetics of tacrolimus in different post transplant times; thus, the aim was to perform a meta-analysis of different post transplant times to investigate the influence of SNP C3435T on the tacrolimus pharmacokinetics.

METHODS

A literature search was conducted to locate the relevant papers by using the PUBMED and EMBASE electronic source until 2011. The pharmacokinetic parameters, including dose administration, concentration and concentration to dose ratio were extracted and a meta-analysis was performed by using STATA10.0.

RESULTS

A total of 13 papers concerning 1327 individuals were included in the meta-analysis. The overall results showed SNP C3435T could influence the pharmacokinetic parameters in different post transplant times, the subjects with CC genotype had lower concentration dose ratio and need higher tacrolimus dose than the CT and TT genotype.

CONCLUSIONS

Our meta-analysis of available studies has demonstrated a definite correlation between the SNP C3435T in MDR1 gene and pharmacokinetics of tacrolimus. However, additional studies with large sample size and better study designs are warranted to verify our finding.

Maximum a posteriori Bayesian estimation of mycophenolic Acid area under the concentration-time curve: is this clinically useful for dosage prediction yet?

This review seeks to summarize the available data about Bayesian estimation of area under the plasma concentration-time curve (AUC) and dosage prediction for mycophenolic acid (MPA) and evaluate whether sufficient evidence is available for routine use of Bayesian dosage prediction in clinical practice. A literature search identified 14 studies that assessed the predictive performance of maximum a posteriori Bayesian estimation of MPA AUC and one report that retrospectively evaluated how closely dosage recommendations based on Bayesian forecasting achieved targeted MPA exposure. Studies to date have mostly been undertaken in renal transplant recipients, with limited investigation in patients treated with MPA for autoimmune disease or haematopoietic stem cell transplantation. All of these studies have involved use of the mycophenolate mofetil (MMF) formulation of MPA, rather than the enteric-coated mycophenolate sodium (EC-MPS) formulation. Bias associated with estimation of MPA AUC using Bayesian forecasting was generally less than 10%. However some difficulties with imprecision was evident, with values ranging from 4% to 34% (based on estimation involving two or more concentration measurements). Evaluation of whether MPA dosing decisions based on Bayesian forecasting (by the free website service https://pharmaco.chu-limoges.fr) achieved target drug exposure has only been undertaken once. When MMF dosage recommendations were applied by clinicians, a higher proportion (72-80%) of subsequent estimated MPA AUC values were within the 30-60 mg · h/L target range, compared with when dosage recommendations were not followed (only 39-57% within target range). Such findings provide evidence that Bayesian dosage prediction is clinically useful for achieving target MPA AUC. This study, however, was retrospective and focussed only on adult renal transplant recipients. Furthermore, in this study, Bayesian-generated AUC estimations and dosage predictions were not compared with a later full measured AUC but rather with a further AUC estimate based on a second Bayesian analysis. This study also provided some evidence that a useful monitoring schedule for MPA AUC following adult renal transplant would be every 2 weeks during the first month post-transplant, every 1-3 months between months 1 and 12, and each year thereafter. It will be interesting to see further validations in different patient groups using the free website service. In summary, the predictive performance of Bayesian estimation of MPA, comparing estimated with measured AUC values, has been reported in several studies. However, the next step of predicting dosages based on these Bayesian-estimated AUCs, and prospectively determining how closely these predicted dosages give drug exposure matching targeted AUCs, remains largely unaddressed. Further prospective studies are required, particularly in non-renal transplant patients and with the EC-MPS formulation. Other important questions remain to be answered, such as: do Bayesian forecasting methods devised to date use the best population pharmacokinetic models or most accurate algorithms; are the methods simple to use for routine clinical practice; do the algorithms actually improve dosage estimations beyond empirical recommendations in all groups that receive MPA therapy; and, importantly, do the dosage predictions, when followed, improve patient health outcomes?