Toward personalized medicine in renal transplantation

BACKGROUND

The pharmacokinetics of tacrolimus (TRL) are clearly affected by genetic polymorphisms in drug-metabolizing enzymes, which lead to large interindividual differences in dose-response relations. In addition, TRL has a narrow therapeutic index requiring monitoring of blood levels. The objective of the present observational, retrospective study was to associate maintenance TRL doses with various genetic markers seeking to guide optimization of the initial dose.

METHODS

Results of DNA samples from 15 kidney transplant patients were correlated retrospectively with clinical information from medical records. Samples were genotyped using PHARMAchip. Association studies were performed with χ2 and Pearson tests and by analysis of variance. The study was carried out in accordance with international ethical standards of the Helsinki Declaration and approved by our ethics committee.

RESULTS

Two patient groups were identified to show a difference in TRL dose requirements: a control (0.014-0.10 mg/kg/per day) and an high-dose group (0.14-0.15 mg/kg/per day). The presence of CYP3A5*1 and the null allele in GSTM1 were significantly associated (P=.01 and P=.04) with the need for higher immunosuppressive doses (>0.10 mg/kg/per day). There were no differences in plasma levels of TRL or other clinical variables between the patient groups.

CONCLUSION

Determination of the CYP3A5 genotype might be used to predict initial TRL requirements, although other genetic variants also provide important information to adjust the drug dose.

Errors and reproducibility of DNA array-based detection of allelic variants in ADME genes: PHARMAchip™

Aims: Differences in adverse drug reactions can be explained by genetic variations, especially if they determine the expression of certain protein effectors and/or drug-metabolizing enzymes. Over the last decade, several tests screening for the most frequent polymorphisms in drug-metabolizing enzymes have been marketed for research and diagnostic purposes. The aim of this study was to assess the suitability of PHARMAchip™ for the genotyping of polymorphisms of genes associated with drug metabolism and response as an alternative to Jurilab Ltd’s DrugMEt® Test. Materials & methods: In this observational study, performed using 100 previously genotyped DNA samples, we report on common genes included in the two different tests examined: the former DrugMEt test and the recently introduced PHARMAchip test. Results & conclusion: Although these tests are based on different methodological approaches, we have found a high concordance of results between both methods. Some of the discrepancies between tests were related to allelic variants not monitored in a particular microarray and the quality of the genomic DNA used.

Alpha-tocopherol transport in the lung is affected by the apoE genotype--studies in transgenic apoE3 and apoE4 mice

Apolipoprotein E (apoE) is a major constituent of lipoproteins mediating peripheral uptake of lipids including the lipid-soluble vitamin alpha-tocopherol (alpha-toc). In a recent study, we observed significant lower alpha-toc concentrations in the lung of apoE4 compared with apoE3 transgenic mice. In this study, we determined the mRNA levels of genes encoding for proteins centrally involved in the uptake, export, and degradation of vitamin E. Receptors of alpha-toc uptake including scavenger receptor B1 (SR-B1), LDL receptor (LDLrec), and LDLrec-related protein 1 (LRP1) were lower in apoE4 when compared with apoE3 mice with statistical significance for SR-B1 and LRP1. Lung mRNA levels of the ATP-binding cassette A1 and the multidrug resistance transporter 1, surfactant proteins mediating the export of alpha-toc, were lower in apoE4 than in apoE3 mice. In addition, the mRNA levels of cytochrome P450 3A, a microsomal enzyme family involved in the degradation of alpha-toc, tended to be higher in the apoE4 when compared with the apoE3 genotype. Current data indicate that genes encoding for proteins involved in peripheral alpha-toc transport and degradation are affected by the apoE genotype probably accounting for thelower alpha-toc tissue concentration as observed in apoE4 mice.

Impact of apoE genotype on oxidative stress, inflammation and disease risk

Although in developing countries an apolipoprotein E4 (apoE4) genotype may offer an evolutionary advantage, as it has been shown to offer protection against certain infectious disease, in Westernised societies it is associated with increased morbidity and mortality, and represents a significant risk factor for cardiovascular disease, late-onset Alzheimer's disease and other chronic disorders. ApoE is an important modulator of many stages of lipoprotein metabolism and traditionally the increased risk was attributed to higher lipid levels in E4 carriers. However, more recent evidence demonstrates the multifunctional nature of the apoE protein and the fact that the impact of genotype on disease risk may be in large part due to an impact on oxidative status or the immunomodulatory/anti-inflammatory properties of apoE. An increasing number of studies in cell lines, targeted replacement rodents and human volunteers indicate higher oxidative stress and a more pro-inflammatory state associated with the epsilon4 allele. The impact of genotype on the antioxidant and immunomodulatory/anti-inflammatory properties of apoE is the focus of the current review. Furthermore, current information on the impact of environment (diet, exercise, smoking status, alcohol) on apoE genotype-phenotype associations are discussed with a view to identifying particular lifestyle strategies that could be adapted to counteract the 'at-risk' E4 genotype.

Effect of apoE genotype and vitamin E on biomarkers of oxidative stress in cultured neuronal cells and the brain of targeted replacement mice

The aetiology of apoE4 genotype-Alzheimer's disease (AD) association are complex. The current study emphasizes the impact of apoE genotype and potential beneficial effects of vitamin E (VE) in relation to oxidative stress. Agonist induced neuronal cell death was examined 1) in the presence of conditioned media containing equal amounts of apoE3 or apoE4 obtained from stably transfected macrophages, and 2) after pretreatment with alpha- and gamma-tocopherol, and -tocotrienol. ApoE3 and apoE4 transgenic mice were fed a diet poor or rich in VE to study the interplay of both apoE genotype and VE status, on membrane lipid peroxidation, antioxidative enzyme activity and glutathione levels in the brain. Cytotoxicity of hydrogen peroxide and glutamate was higher in neuronal cells cultured with apoE4 than apoE3 conditioned media. VE pre-treatment of neurons counteracted the cytotoxicity of a peroxide challenge but not of nitric oxide. No significant effects of apoE genotype or VE supplementation were observed on lipid peroxidation or antioxidative status in the brain of apoE3 and apoE4 mice. VE protects against oxidative insults in vitro, however, no differences in brain oxidative status were observed in mice. Unlike in cultured cells, apoE4 may not contribute to higher neuronal oxidative stress in the brain of young targeted replacement mice.

Differential effects of apolipoprotein E3 and E4 on markers of oxidative status in macrophages

ApoE is secreted by macrophages at the lesion site of the atherosclerotic plaque, where it is thought to play a protective role against atherosclerosis independently of its effects on lipid metabolism. Of the three common isoforms for apoE, apoE4 is associated with higher risk of cardiovascular disease (CVD). In vitro studies have shown that recombinant apoE may act as an antioxidant in an isoform-dependent manner (E2 > E3 > E4). The oxidative status of the macrophages plays a key role in the process of atherosclerosis. In the present study the possible differential actions of apoE3 and apoE4 on several parameters of oxidative status were determined in stably transfected murine macrophages (RAW 264-7-apoE3 and - apoE4). No differences between genotypes were observed after peroxide challenge in either protection against cytotoxicity or in cell membrane oxidation, and modest differences were observed in the non-enzymatic antioxidants (glutathione and alpha-tocopherol) in apoE3 v. apoE4 macrophages. Importantly, cells secreting apoE4 showed increased membrane oxidation under basal conditions, and produced more NO and superoxide anion radicals than the apoE3 macrophages after stimulation. The present data suggest that apoE genotype influences the oxidative status of macrophages, and this could partly contribute to the higher CVD risk observed in apoE4 carriers.

ApoE genotype, cardiovascular risk and responsiveness to dietary fat manipulation

Cardiovascular risk is determined by the complex interactions between genetic and environmental factors. The apoE genotype represents the most-widely-studied single nucleotide polymorphism in relation to CVD risk, with >3600 publications cited in PubMed. Although originally described as a mediator of lipoprotein metabolism, the lipoprotein-independent functions of apoE are being increasingly recognised, with limited data available on the potential impact of genotype on these metabolic processes. Furthermore, although meta-analyses suggest that apoE4 carriers may have a 40-50% increased CVD risk, the associations reported in individual studies are highly heterogeneous and it is recognised that environmental factors such as smoking status and dietary fat composition influence genotype-phenotype associations. However, information is often derived from observational studies or small intervention trials in which retrospective genotyping of the cohort results in small group sizes in the rarer E2 and E4 subgroups. Either larger well-standardised intervention trials or smaller trials with prospective recruitment according to apoE genotype are needed to fully establish the impact of diet on genotype-CVD associations and to establish the potential of dietary strategies such as reduced total fat, saturated fat, or increased antioxidant intakes to counteract the increased CVD burden in apoE4 carriers.

Effects of apoE genotype on macrophage inflammation and heme oxygenase-1 expression

In order to gain a more comprehensive understanding of the aetiology of apolipoprotein E4 genotype-cardiovascular disease (CVD) associations, the impact of the apoE genotype on the macrophage inflammatory response was examined. The murine monocyte-macrophage cell line (RAW 264.7) stably transfected to produce equal amounts of human apoE3 or apoE4 was used. Following LPS stimulation, apoE4-macrophages showed higher and lower concentrations of tumour necrosis factor alpha (pro-inflammatory) and interleukin 10 (anti-inflammatory), respectively, both at mRNA and protein levels. In addition, increased expression of heme oxygenase-1 (a stress-induced anti-inflammatory protein) was observed in the apoE4-cells. Furthermore, in apoE4-macrophages, an enhanced transactivation of the key redox sensitive transcription factor NF-kappaB was shown. Current data indicate that apoE4 macrophages have an altered inflammatory response, which may contribute to the higher CVD risk observed in apoE4 carriers.