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

Population pharmacokinetic study in children with vascular anomalies: body weight as a key variable in predicting the initial dose and dosing frequency of sirolimus

Background

The main challenges faced when using sirolimus in children with vascular anomalies (VAs) still include significant pharmacokinetic (PK) variability, uncertainty in the target concentration range, as well as inconsistencies in initial dosing and dosing frequency. The aim of this study is to establish a new population pharmacokinetic (PPK) model for children with VAs to guide the individualized use of sirolimus.

Methods

A PPK study was performed using data from children with VAs who received sirolimus between July 2017 and April 2022. A nonlinear mixed-effect modeling with a one-compartment model structure was applied. Monte Carlo simulation was employed to propose specific dosing recommendations to achieve the target trough concentrations (C trough) of 5-15 ng/mL.

Results

In total, 134 blood concentrations from 49 pediatric patients were used to characterize the sirolimus pharmacokinetics. Covariate analysis identified body weight (BW) as a significant factor affecting clearance (CL) in the final PPK model. The typical clearance rate and distribution volume, standardized to a BW of 16 kg, were 4.06 L/h (4% relative standard error, RSE) and 155 L (26% RSE), respectively. Optimal dosing regimens were simulated for different BWs. For a twice-daily regimen, the recommended doses were 0.05, 0.06, 0.07, and 0.08 mg/kg/day for BW of <10, 10-20, 20-40, and ≥40 kg, respectively; for a once-daily regimen, the recommended doses were 0.06, 0.07, 0.08, and 0.09 mg/kg/day for BW of <10, 10-30, 30-50, and ≥50 kg, respectively. Notably, sirolimus C trough could be maintained between 5-15 ng/mL across various dosing frequencies based on the recommended dosing regimen.

Conclusion

We established a PPK model of sirolimus for children with VAs and proposed an initial dosing strategy. Integrating initial dose and medication frequency recommendations into sirolimus' guidelines will broaden its clinical options and simplify the clinical management for childhood VAs.

Model-Informed individualized dosage regimen of sirolimus in pediatric patients with intractable lymphatic malformations

Intractable lymphatic malformations (iLM) pose a significant threat to affected children, demonstrating limited responses to conventional treatments. Sirolimus, effectively inhibiting endothelial cell proliferation in lymphatic vessels, plays a crucial role in iLM treatment. However, the drug's narrow therapeutic window and substantial interindividual variability necessitate customized dosing strategies. This study aims to establish a Population Pharmacokinetic Model (PopPK model) for sirolimus in pediatric iLM patients, identifying quantitative relationships between covariates and sirolimus clearance and volume of distribution. Initial dosages are recommended based on a target concentration range of 5-15 ng/mL. Retrospective data from our institution, encompassing 53 pediatric patients with 275 blood concentration results over the past five years (average age: 4.64 ± 4.19 years), constituted the foundation of this analysis. The final model, adopting a first-order absorption and elimination single-compartment model, retained age as the sole covariate. Results indicated a robust correlation between apparent clearance (CL/F) at 5.56 L/h, apparent volume of distribution (V/F) at 292.57 L, and age. Monte Carlo simulation guided initial dosages for patients aged 0-18 years within the target concentration range. This study presents the first PopPK model using a large Therapeutic Drug Monitoring (TDM) database to describe personalized sirolimus dosing for pediatric iLM patients, contributing to pharmacokinetic guidance and potentially improving long-term clinical outcomes.

Influence of genetic variants on the pharmacokinetics and pharmacodynamics of sirolimus: a systematic review

Sirolimus is an antiproliferative and immunosuppressive compound inhibiting the mTOR pathway, which is often activated in congenital low-flow vascular malformations. Studies have demonstrated the efficacy of sirolimus for this disease. Studies in kidney transplant patients suggest that genetic variants can influence these pharmacokinetic parameters. Therefore, a systematic literature search was performed to gain insight into pharmacogenetic studies with sirolimus. Most studies investigated CYP3A4 and CYP3A5, with inconsistent results. No pharmacogenetic studies focusing on sirolimus have been performed for low-flow vascular malformations. We analyzed two common variants of CYP3A4 and CYP3A5 (CYP3A4*22 and CYP3A5*3, respectively) in patients (n = 59) with congenital low-flow vascular malformations treated with sirolimus. No association with treatment outcome was identified in this small cohort of patients.

Evaluation of Pharmacogenetics of Drug-Metabolizing Enzymes and Drug Efflux Transporter in Renal Transplants Receiving Immunosuppressants

Cytochrome P450 (CYP) enzymes, such as CYP3A4, and CYP3A5, P450 oxidoreductase (POR), peroxisome proliferator activated receptor alpha (PPAR-alpha), and drug transporter (ABCB1) were observed to influence concentrations of immunosuppressants (cyclosporine, everolimus, sirolimus, and tacrolimus) and outcomes in renal transplants. We carried out the present study to evaluate the prevalence and impact of these single nucleotide polymorphisms (SNPs) in adult renal transplants. SNPs were evaluated using commercial TaqMan^® assays. Serum drug concentrations were estimated using immunoassays. One hundred and forty-six patients were recruited. SNPs in CYP3A5*3 were significantly associated with greater dose-adjusted cyclosporine and tacrolimus concentrations. SNPs in POR*28 were observed with significantly lower dose-adjusted concentrations, particularly with cyclosporine and tacrolimus. ABCB1 homozygous polymorphisms were observed with significantly lower time spent in the therapeutic range with cyclosporine and everolimus/sirolimus. Cyclosporine was observed in a significantly greater proportion of patients with elevated GGT, and SNPs in PPAR-alpha were significantly associated with an increased risk of this adverse event. Hypertriglyceridemia with everolimus was significantly associated with POR*28 polymorphisms. There is a need to validate the influence of these SNPs in a prospective study and develop an algorithm predicting the achievement of target concentrations.

CYP3A4∗22 Genotyping in Clinical Practice: Ready for Implementation?

Cytochrome P450 3A4 (CYP3A4) is the most important drug metabolizing enzyme in the liver, responsible for the oxidative metabolism of ∼50% of clinically prescribed drugs. Therefore, genetic variation in CYP3A4 could potentially affect the pharmacokinetics, toxicity and clinical outcome of drug treatment. Thus far, pharmacogenetics for CYP3A4 has not received much attention. However, the recent discovery of the intron 6 single-nucleotide polymorphism (SNP) rs35599367C > T, encoding the CYP3A4^∗22 allele, led to several studies into the pharmacogenetic effect of CYP3A4^∗22 on different drugs. This allele has a relatively minor allele frequency of 3-5% and an effect on CYP3A4 enzymatic activity. Thus far, no review summarizing the data published on several drugs is available yet. This article therefore addresses the current knowledge on CYP3A4^∗22. This information may help in deciding if, and for which drugs, CYP3A4^∗22 genotype-based dosing could be helpful in improving drug therapy. CYP3A4^∗22 was shown to significantly influence the pharmacokinetics of several drugs, with currently being most thoroughly investigated tacrolimus, cyclosporine, and statins. Additional studies, focusing on toxicity and clinical outcome, are warranted to demonstrate clinical utility of CYP3A4^∗22 genotype-based dosing.

Significance of Ethnic Factors in Immunosuppressive Therapy Management After Organ Transplantation

Clinical outcomes after organ transplantation have greatly improved in the past 2 decades with the discovery and development of immunosuppressive drugs such as calcineurin inhibitors, antiproliferative agents, and mammalian target of rapamycin inhibitors. However, individualized dosage regimens have not yet been fully established for these drugs except for therapeutic drug monitoring-based dosage modification because of extensive interindividual variations in immunosuppressive drug pharmacokinetics. The variations in immunosuppressive drug pharmacokinetics are attributed to interindividual variations in the functional activity of cytochrome P450 enzymes, UDP-glucuronosyltransferases, and ATP-binding cassette subfamily B member 1 (known as P-glycoprotein or multidrug resistance 1) in the liver and small intestine. Some genetic variations have been found to be involved to at least some degree in pharmacokinetic variations in post-transplant immunosuppressive therapy. It is well known that the frequencies and effect size of minor alleles vary greatly between different races. Thus, ethnic considerations might provide useful information for optimizing individualized immunosuppressive therapy after organ transplantation. Here, we review ethnic factors affecting the pharmacokinetics of immunosuppressive drugs requiring therapeutic drug monitoring, including tacrolimus, cyclosporine, mycophenolate mofetil, sirolimus, and everolimus.

The Genetic Polymorphism of CYP3A4 rs2242480 is Associated with Sirolimus Trough Concentrations Among Adult Renal Transplant Recipients

BACKGROUND

The large interindividual variability in the genetic polymorphisms of sirolimus (SIR)- metabolizing enzymes, transporters, and receptors can lead to qualitatively and quantitatively distinct therapeutic responses.

OBJECTIVE

We examined the impact of numerous candidate single-nucleotide polymorphisms (SNPs) involved in the trough concentration of SIR-based immunosuppressant regimen.

METHODS

This is a retrospective, long-term cohort study involving 69 renal allograft recipients. Total DNA was isolated from recipient blood samples and trough SIR concentrations were measured by microparticle enzyme immunoassay. Genome sequence reading was targeted based on next-generation sequencing. The association of tagger SNPs to SIR trough concentrations with non-genetic covariate adjusting was analyzed using logistic regression.

RESULTS

A total of 300 SNPs were genotyped in the recipient DNA samples using target sequencing analysis. Only the SNP of CYP3A4 (Ch7: 99361466 C>T, rs2242480) had a significantly higher association with SIR trough concentration as compared to the other 36 tagger SNPs. The mean trough SIR concentration of patients in the CYP3A4 rs2242480-CC group was more significant compared to that of the CYP3A4 rs2242480-TC and TT group, respectively 533.3; 157.4 and 142.5 (ng/ml)/mg/kg, P<0.0001. After adjusting the SNPs, there was no significant association between clinical factors such as age, follow-up period, the incidence of delayed graft function, immunosuppression protocol, and sex with SIR trough concentration.

CONCLUSION

These findings indicated a significant association of polymorphism in the CYP3A4 (Ch7: 99361466 C>T, rs2242480) with SIR trough concentration after 1-year administration in patients who have undergone kidney transplantation.

Clinical implementation of pharmacogenetics and model-informed precision dosing to improve patient care

Providing maximal therapeutic efficacy without toxicity is a universal goal of rational drug therapy. However, substantial between-patient variability in drug response often impedes such successful treatments and brings the necessity of tailoring drug dose to individual needs for more precise therapy. In many cases plenty of patient characteristics, such as body size, genetic makeup and environmental factors, need to be taken into consideration to find the optimal dose in clinical practice. A pharmacokinetics and pharmacodynamics (PK/PD) model-informed approach offers integration of various patient information to provide an expectation of drug response and derive practical dose estimates to support clinicians' dosing decisions. Such an approach was pioneered in the late 1970s, but its broad clinical acceptance and implementation have been hampered by the lack of widespread computer technology, including user-friendly software tools. This has significantly changed in recent years. With the advent of electronic health records (EHRs) and the ubiquity of user-friendly software tools, we now experience a convergence of clinical information, pharmacogenetics, systems pharmacology and pharmacometrics, and technology. Advanced pharmacometrics research is now more appliable and implementable to improve health care. This article presents examples of successful development and implementation of pharmacogenetics-guided and PK/PD model-informed decision support to facilitate precision dosing, including the development of an EHR-embedded decision support tool. Through the integration of clinical decision support tools in EHRs, clinical pharmacometrics support can be brought directly to the clinical team and the bedside.

A Novel PCR-RFLP Method for Detection of POR*28 Polymorphism and its Genotype/Allele Frequencies in a Turkish Population

BACKGROUND

The Cytochrome P450 (CYP) enzymes are involved in the metabolism of many endogenous and exogenous substances. They need electrons for their activity. CYP mediated oxidation reactions require cytochrome oxidoreductase (POR) as an electron donor. A common genetic variation identified in the coding region of POR gene (POR*28) leads to an alteration in POR activity by causing amino acid change. The current study aimed to determine the allele and genotype frequencies of POR*28 in a healthy Turkish population by using a novel genotyping assay.

METHODS

A novel PCR-RFLP assay was developed for the detection of POR*28 (rs1057868) polymorphism and the obtained frequencies were compared with the data established in various ethnic groups.

RESULTS

Genotypic analysis revealed that of 209 healthy, unrelated individuals tested for POR*28 polymorphism, 55.5% of the studied subjects were homozygous for the CC genotype, 34.9% were heterozygous for the CT genotype and 9.6% were homozygous for the TT genotype. The allele frequencies were 0.73 (C) and 0.27 (T). The present results were in accordance with the Hardy- Weinberg equilibrium. The distribution of POR*28 allele varies between populations. The frequency of the T allele among members of the Turkish population was similar to frequencies in Caucasian populations but was lower than in Japanese and Chinese populations.

CONCLUSIONS

In this study, a novel method was developed, which could be applied easily in every laboratory for the genotyping of POR *28 polymorphism. The developed genotyping method and documented allele frequencies may have potential in understanding and predicting the variations in drug response/adverse reactions in pharmacotherapy and susceptibility to diseases in POR-mediated metabolism reactions.

Genetic Polymorphisms and In Silico Mutagenesis Analyses of CYP2C9, CYP2D6, and CYPOR Genes in the Pakistani Population

Diverse distributions of pharmacogenetically relevant variants of highly polymorphic CYP2C9, CYP2D6 and CYPOR genes are responsible for some varied drug responses observed across human populations. There is limited data available regarding the pharmacogenetic polymorphisms and frequency distributions of major allele variants in the Pakistani population. The present in silico mutagenesis study conducted on genotype pharmacogenetic variants and comparative analysis with a global population aims to extend the currently limited pharmacogenetic available evidence for the indigenous Pakistani population. Extracted genomic DNA from 244 healthy individuals' venous blood samples were amplified for distinct variant loci in the CYP2C9, CYP2D6 and CYPOR genes. Two-way sequencing results were compared with standard PubMed data and sequence variant loci confirmed by Chromas. This study revealed significant variations in CYP2C9 (rs1799853, rs1057910 and rs72558189), CYP2D6 (rs16947 and rs1135840), and CYPOR (rs1057868, rs781919285 and rs562750402) variants in intraethnic and interethnic frequency distributions. In silico mutagenesis and three-dimensional protein structural alignment analysis approaches clearly exposed the possible varied impact of rare CYPOR (rs781919285 and rs562750402) single nucleotide polymorphisms (SNPs) and confirmed that the influences of CYP2C9 and CYP2D6 variants are consistent with what was found in earlier studies. This investigation highlighted the need to study pharmacogenetic relevance loci and documentation since evidence could be utilized to elucidate genetic backgrounds of drug metabolism, and provide a basis for future pharmacogenomic studies and adequate dose adjustments in Pakistani and global populations.

Immunologic Monitoring to Personalize Immunosuppression After Liver Transplant

Although immunosuppressive drugs have enhanced patient outcomes in transplantation, the liver transplant community has made significant research efforts into the discovery of more accurate and precise methods of posttransplant monitoring and diagnosing. Current research in biomarkers reveals many promising approaches.

Association of NR1I2, CYP3A5 and ABCB1 genetic polymorphisms with variability of temsirolimus pharmacokinetics and toxicity in patients with metastatic bladder cancer

PURPOSE

Temsirolimus is a mammalian target of rapamycin (mTOR) inhibitor that exhibits antitumor activity in renal cell carcinoma and mantle cell lymphoma. The metabolism of temsirolimus and its active metabolite sirolimus mainly depends on cytochrome P450 3A4/5 (CYP3A4/A5) and the ABCB1 transporter. Differently from sirolimus, no pharmacogenetic study on temsirolimus has been conducted. Therefore, the aim of this pilot study was to identify genetic determinants of the inter-individual variability in temsirolimus pharmacokinetics and toxicity.

METHODS

Pharmacokinetic profiles were obtained for 16 patients with bladder cancer after intravenous infusion of 25 mg temsirolimus. Non-compartmental analysis was performed to calculate the pharmacokinetic parameters of temsirolimus and sirolimus, its main metabolite. The presence of single nucleotide polymorphisms (SNPs) in CYP3A5, ABCB1 and in their transcriptional regulator NR1I2 (PXR) was assessed by genotyping. Non-parametric statistical tests were used to assess associations between candidate SNPs and temsirolimus pharmacokinetics and toxicity.

RESULTS

The ratio between sirolimus AUC and temsirolimus AUC was 1.6-fold higher in patients who experienced serious toxic events (p = 0.034). The frequency of adverse events was significantly higher in patients homozygous for the NR1I2-rs6785049 A allele (OR = 0.065, p = 0.04) or NR1I2-rs3814055 C allele (OR = 0.032, p = 0.006). These NR1I2 SNPs were also predictive of temsirolimus half-life and global exposure to temsirolimus and sirolimus. Finally, the effect of the ABCB1-rs1128503, ABCB1-rs2032582 and CYP3A5*3 SNPs on sirolimus pharmacokinetics was confirmed.

CONCLUSIONS

Our findings suggest that SNPs of NR1I2 and its target genes CYP3A5 and ABCB1 are genetic determinants of temsirolimus pharmacokinetics and toxicity in patients with bladder cancer.

Pharmacogenetics of immunosuppressants: State of the art and clinical implementation - recommendations from the French National Network of Pharmacogenetics (RNPGx)

Therapeutic drug monitoring is already widely used for immunosuppressive drugs due to their narrow therapeutic index. This article summarizes evidence reported in the literature regarding the pharmacogenetics of (i) immunosuppressive drugs used in transplantation and (ii) azathioprine used in chronic inflammatory bowel disease. The conditions of use of currently available major pharmacogenetic tests are detailed and recommendations are provided based on a scale established by the RNPGx scoring tests as "essential", "advisable" and "potentially useful". Other applications for which the level of evidence is still debated are also discussed.

Barcelona Consensus on Biomarker-Based Immunosuppressive Drugs Management in Solid Organ Transplantation

With current treatment regimens, a relatively high proportion of transplant recipients experience underimmunosuppression or overimmunosuppression. Recently, several promising biomarkers have been identified for determining patient alloreactivity, which help in assessing the risk of rejection and personal response to the drug; others correlate with graft dysfunction and clinical outcome, offering a realistic opportunity for personalized immunosuppression. This consensus document aims to help tailor immunosuppression to the needs of the individual patient. It examines current knowledge on biomarkers associated with patient risk stratification and immunosuppression requirements that have been generally accepted as promising. It is based on a comprehensive review of the literature and the expert opinion of the Biomarker Working Group of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology. The quality of evidence was systematically weighted, and the strength of recommendations was rated according to the GRADE system. Three types of biomarkers are discussed: (1) those associated with the risk of rejection (alloreactivity/tolerance), (2) those reflecting individual response to immunosuppressants, and (3) those associated with graft dysfunction. Analytical aspects of biomarker measurement and novel pharmacokinetic-pharmacodynamic models accessible to the transplant community are also addressed. Conventional pharmacokinetic biomarkers may be used in combination with those discussed in this article to achieve better outcomes and improve long-term graft survival. Our group of experts has made recommendations for the most appropriate analysis of a proposed panel of preliminary biomarkers, most of which are currently under clinical evaluation in ongoing multicentre clinical trials. A section of Next Steps was also included, in which the Expert Committee is committed to sharing this knowledge with the Transplant Community in the form of triennial updates.

[Applied pharmacogenetic]

Pharmacokinetics is the link between genetic data and the use of treatments. It can be use on several relevant aspects in the clinic, including the treatment selection, efficacy or toxicity prediction and the choice of the dose. Pharmacogenetics has been applied in clinical nephrology since a long time by the genetic prediction of azathiorpine associated myelotoxicity. However, despite an extensive literature describing the links between genetics and metabolism and transport of drugs, genetic tests are little used in clinical practice. One reason for this poor implementation is the current lack of evidence of improved clinical outcomes with pharmacogenetic tests. In addition, with an effective therapeutic drug monitoring, it is possible to correct the effect of genotype on the pharmacokinetic differences, thus reducing the usefulness of the assay based on the genotype. The future of pharmacogenetics will be treatment models in which patient characteristics are combined with data on polymorphisms in multiple genes including pharmacodynamic parameters, drug transporter proteins, and predictors of toxicity.

Effects of major transporter and metabolizing enzyme gene polymorphisms on carbamazepine metabolism in Chinese patients with epilepsy

AIM

The present study aimed to evaluate the effects of SNPs of major transporter and metabolizing enzyme genes on carbamazepine (CBZ) metabolism in Chinese patients with epilepsy.

MATERIALS & METHODS

For 210 epileptic patients treated with CBZ as monotherapy, nine SNPs in candidate genes ABCB1, CYP3A4, CYP3A5, POR and EPHX1 were analyzed by PCR-RFLP or direct sequencing. Serum concentrations of CBZ, carbamazepine-10,11-epoxide (CBZE) and carbamazepine-10,11-trans dihydrodiol (CBZD) were determined by HPLC. Dose-adjusted concentrations of CBZ (CDRCBZ), CBZE (CDRCBZE), CBZD (CDRCBZ D) and CBZD:CBZE ratio were used as evaluation parameters for CBZ metabolism.

RESULTS

The ABCB1 c.3435C>T was significantly associated with the CDR of CBZ and its major metabolites. CYP3A4*1G and CYP3A5*3 could influence CBZ metabolism, while POR*28 had no effect on it. The EPHX1 c.416A>G and c.128G>C variants were significantly associated with CBZD:CBZE ratio.

CONCLUSION

Our data suggest that certain polymorphisms of major transporter and metabolizing enzyme genes could in part influence interindividual variability of CBZ metabolism in Chinese patients with epilepsy.

A clinical approach to solving discrepancies in therapeutic drug monitoring results for patients on sirolimus or tacrolimus: Towards personalized medicine, immunosuppression and pharmacogenomics

BACKGROUND

Unexpected clinical laboratory concentrations often need to be investigated before they are acted upon in a clinical setting. Therapeutic drug monitoring (TDM) frequently involves drugs with narrow therapeutic windows and can be harmful to the patient if changes are made based on erroneous serum drug concentrations. Too little of the drug will result in ineffective therapy and too much of the drug can cause life threatening toxicities. There are many factors that can result in unexpected serum drug concentrations including differences in analytical methods being used, diet, timing of blood draw, genotype and compliance. All these factors should all be considered before deciding if changes should be made in a patient's therapeutic course.

CASE REPORT

We determined the cause of 2 patient's unexpected TDM concentrations for sirolimus and tacrolimus. Using this approach in 2 patient cases, we describe how co-treatment and uncommon genotypes result in unexpected drug concentrations.

CONCLUSIONS

Both cases involved unexpected drug values. In the first case, the cause was revealed to be a drug that was added to the patient's treatment regimen (posaconazole) that inhibits CYP3A4 which is responsible for sirolimus metabolism. In the second case, the patient was revealed to have an uncommon genotype for CYP3A5, causing higher metabolism and lower serum tacrolimus concentrations than the general population.

Role of pharmacogenomics in dialysis and transplantation

PURPOSE OF REVIEW

Pharmacogenomics is the study of differences in drug response on the basis of individual genetic background. With rapidly advancing genomic technologies and decreased costs of genotyping, the field of pharmacogenomics continues to develop. Application to patients with kidney disease provides growing opportunities for improving drug therapy.

RECENT FINDINGS

Pharmacogenomics studies are lacking in patients with chronic kidney disease and dialysis, but are abundant in the kidney transplant field. A potentially clinically actionable genetic variant exists in the CYP3A5 gene, with the initial tacrolimus dose selection being optimized based on CYP3A5 genotype. Although many pharmacogenomics studies have focused on transplant immunosuppression pharmacokinetics, an expanding literature on pharmacodynamic outcomes, such as calcineurin inhibitor toxicity and new onset diabetes, is providing new information on patients at risk.

SUMMARY

Appropriately powered pharmacogenomics studies with well-defined phenotypes are needed to validate existing studies and unearth new findings in patients with kidney disease, especially the chronic kidney disease and dialysis population.

Role of peroxisome proliferator-activated receptors gene polymorphisms in type 2 diabetes and metabolic syndrome

Metabolic syndrome (MetS) and type 2 diabetes mellitus (T2DM) are the serious public health problems worldwide. Moreover, it is estimated that MetS patients have about five-fold greater risk of the T2DM development compared with people without the syndrome. Peroxisome proliferator-activated receptors are a subgroup of the nuclear hormone receptor superfamily of ligand-activated transcription factors which play an important role in the pathogenesis of MetS and T2DM. All three members of the peroxisome proliferator-activated receptor (PPAR) nuclear receptor subfamily, PPARα, PPARβ/δ and PPARγ are critical in regulating insulin sensitivity, adipogenesis, lipid metabolism, and blood pressure. Recently, more and more studies indicated that the gene polymorphism of PPARs, such as Leu¹⁶²Val and Val²²⁷Ala of PPARα, +294T > C of PPARβ/δ, Pro¹²Ala and C1431T of PPARγ, are significantly associated with the onset and progressing of MetS and T2DM in different population worldwide. Furthermore, a large body of evidence demonstrated that the glucose metabolism and lipid metabolism were influenced by gene-gene interaction among PPARs genes. However, given the complexity pathogenesis of metabolic disease, it is unlikely that genetic variation of a single locus would provide an adequate explanation of inter-individual differences which results in diverse clinical syndromes. Thus, gene-gene interactions and gene-environment interactions associated with T2DM and MetS need future comprehensive studies.

Use of pharmacogenomics in pediatric renal transplant recipients

Transplant recipients receive potent immunosuppressive drugs in order to prevent graft rejection. Therapeutic drug monitoring is the current approach to guide the dosing of calcineurin inhibitors, mammalian target of rapamycin inhibitors (mTORi) and mofetil mycophenolate. Target concentrations used in pediatric patients are extrapolated from adult studies. Gene polymorphisms in metabolizing enzymes and drug transporters such as cytochromes CYP3A4 and CYP3A5, UDP-glucuronosyl transferase, and P-glycoprotein are known to influence the pharmacokinetics and dose requirements of immunosuppressants. The implications of pharmacogenomics in this patient population is discussed. Genetic information can help with achieving target concentrations in the early post-transplant period, avoiding adverse drug reactions and drug-drug interactions. Evidence about genetic studies and transplant outcomes is revised.

Personalization of the immunosuppressive treatment in renal transplant recipients: the great challenge in "omics" medicine

Renal transplantation represents the most favorable treatment for patients with advanced renal failure and it is followed, in most cases, by a significant enhancement in patients’ quality of life. Significant improvements in one-year renal allograft and patients’ survival rates have been achieved over the last 10 years primarily as a result of newer immunosuppressive regimens. Despite these notable achievements in the short-term outcome, long-term graft function and survival rates remain less than optimal. Death with a functioning graft and chronic allograft dysfunction result in an annual rate of 3%–5%. In this context, drug toxicity and long-term chronic adverse effects of immunosuppressive medications have a pivotal role. Unfortunately, at the moment, except for the evaluation of trough drug levels, no clinically useful tools are available to correctly manage immunosuppressive therapy. The proper use of these drugs could potentiate therapeutic effects minimizing adverse drug reactions. For this purpose, in the future, “omics” techniques could represent powerful tools that may be employed in clinical practice to routinely aid the personalization of drug treatment according to each patient’s genetic makeup. However, it is unquestionable that additional studies and technological advances are needed to standardize and simplify these methodologies.

Pharmacogenetics and immunosuppressive drugs in solid organ transplantation

The transplantation literature includes numerous papers that report associations between polymorphisms in genes encoding metabolizing enzymes and drug transporters, and pharmacokinetic data on immunosuppressive drugs. Most of these studies are retrospective in design, and although a substantial number report significant associations, pharmacogenetic tests are hardly used in clinical practice. One of the reasons for this poor implementation is the current lack of evidence of improved clinical outcome with pharmacogenetic testing. Furthermore, with efficient therapeutic drug monitoring it is possible to rapidly correct for the effect of genotypic deviations on pharmacokinetics, thereby decreasing the utility of genotype-based dosing. The future of pharmacogenetics will be in treatment models in which patient characteristics are combined with data on polymorphisms in multiple genes. These models should focus on pharmacodynamic parameters, variations in the expression of drug transporter proteins, and predictors of toxicity. Such models will provide more information than the relatively small candidate gene studies performed so far. For implementation of these models into clinical practice, linkage of genotype data to medication prescription systems within electronic health records will be crucial.

Impact of PPARA and POR polymorphisms on tacrolimus pharmacokinetics and new-onset diabetes in kidney transplant recipients

Recent efforts have been made to identify genetic markers of CYP3A4 enzymatic activity within genes encoding for regulatory elements. The aim of the current study was to investigate the impact of polymorphism of PPARA and POR genes on tacrolimus (TAC) dose-adjusted trough concentration and risk of new-onset diabetes after transplantation (NODAT). A total of 241 White kidney transplant patients were genotyped for three functional single nucleotide polymorphisms: rs1057868 (*28) in POR, rs4253728:G>A, and rs4823613:A>G in PPARA. No significant genotype-dependent differences in TAC dose-adjusted trough concentration were observed for either POR or PPARA variants. No significant differences in the incidence of NODAT were observed between patients stratified by PPARA and POR genotypes. The frequency of NODAT among PPARA rs4253728 AA homozygotes (42%) was higher compared with heterozygotes (22%) and GG homozygotes (19%), but the difference was not significant. Testing TAC-medicated renal transplant recipients for POR and PPARA variants seems to have limited clinical application.

Functional gene variants of CYP3A4

Cytochrome P450 3A4 (CYP3A4) is involved in the metabolism of more drugs in clinical use than any other foreign compound-metabolizing enzyme in humans. Recently, increasing evidence has been found showing that variants in the CYP3A4 gene have functional significance and--in rare cases--lead to loss of activity, implying tremendous consequences for patients. This review article highlights the functional consequences of all CYP3A4 variants recognized by the Human Cytochrome P450 (CYP) Allele Nomenclature Database.