Significant increase in plasma 4β-hydroxycholesterol concentration in patients after kidney transplantation

Abstract

This article is available online at http://www.jlr.org Phenotyping of cytochrome CYP3A seems to be of special importance because enzymes belonging to this family, particularly CYP3A4, are involved in the metabolism of more than 50% of currently prescribed drugs. However, the selection of an appropriate CYP3A phenotyping substrate and metric is still a matter of discussion, although some CYP3A test substrates, including midazolam, erythromycin, alprazolam, and nifedipine have been proposed ( 15 ). However, administration of these drugs poses challenges in specifi c patient populations such as pediatric and elderly patients, transplant recipients, and cancer patients, in whom administration of probe drugs may have a negative impact on patient safety. Identifi cation of an appropriate endogenous CYP3A substrate and corresponding metrics would be a promising alternative, allowing simple and possibly broader application of the phenotyping approach. Oxidation of the endogenous compound cortisol to 6 ␤ -hydroxycortisol has been shown to be a CYP3A-dependent pathway in humans. Consequently, a urinary 6 ␤ -hydroxycortisol-to-cortisol ratio has been proposed as a suitable phenotyping marker for the assessment of CYP3A activity ( 16,17 ). However, the sensitivity of the method to detect small changes in enzyme activity is low because of pronounced background variation ( 17 ). Another compound, 4 ␤ -hydroxycholesterol, which is identifi ed as one of the major oxysterols in humans, was reported to be formed solely by CYP3A4 ( 18 ). Markedly elevated concentrations of 4 ␤ -hydroxycholesterol were found in patients treated with CYP3A4 inducers ( 19-23 ), and decreased concentrations in patients treated with CYP3A4 inhibitors ( 22-24 ). Furthermore, a relationship between blood 4 ␤ -hydroxycholesterol concentration and the number of active CYP3A5*1 alleles has been demonstrated, suggesting that 4 ␤ -hydroxycholesterol is formed not only by CYP3A4 but also by CYP3A5 ( 25 ). Accordingly, 4 ␤ -hydro xycholesterol has been proposed to be a potential endogenous biomarker of CYP3A activity. Impaired renal function alters the clearance of many drugs mainly by decreasing their renal elimination. However, several studies in rats ( 1-6 ) and in patients ( 7-9 ) have shown that renal failure also decreases the metabolic clearance of drugs, particularly those metabolized by cytochrome P450 (CYP). The underlying causes of altered CYP functional expression observed in kidney disease remain unclear, but several studies indicate that uremic toxins ( 10-13 ) and infl ammation ( 14 ) may play a role via transcriptional or translational modifi cations of CYP enzymes.

CYP3A5 Polymorphism affects the increase in CYP3A activity after living Kidney transplantation in patients with end stage renal disease

“…Especially, 4β-hydroxycholesterol may be useful in patients with renal failure because the kinetics of 4β-hydroxycholesterol seem to be unaffected by renal function due to the slow elimination by 7α-hydroxylation [20]. We have previously reported a significant increase in plasma concentration of 4β-hydroxycholesterol as an endogenous marker of CYP3A activity in patients with end stage renal disease (ESRD) after kidney transplantation [21]. However, wide interindividual variability in the degree of increase was observed.…”

“…Plasma concentration of 4β-hydroxycholesterol was determined using a gas chromatography/mass spectrometry (GC/MS) system according to the procedures that we reported previously [21]. One hundred μl of plasma sample was mixed with 20 μl of internal standard (1000 nM 4β-hydroxycholesterol-d7 in 2-propanol) and 200 μl of 2 M sodium methoxide solution in ethanol, and the mixture was left at room temperature for 20 min to convert esterified to free 4β-hydroxycholesterol.…”

Association of Plasma Concentration of 4β-Hydroxycholesterol with CYP3A5 Polymorphism and Plasma Concentration of Indoxyl Sulfate in Stable Kidney Transplant Recipients

“…Plasma concentration of 4b-hydroxycholesterol was determined using a gas chromatography/mass spectrometry system according to the procedures that we reported previously (Suzuki et al, 2013). Inter-assay coefficients of variation for 20 and 200 ng/ml samples were 3.8% and 4.2%, respectively (n = 6).…”

“…Hence, 4b-hydroxycholesterol is suitable for the evaluation of CYP3A activity in stable kidney transplant recipients. We defined stable kidney transplant recipients as those who underwent transplantation more than 90 days prior to the study, because we have previously shown in patients with end-stage renal disease that plasma concentration of 4b-hydroxycholesterol becomes stable 90 days after kidney transplantation (Suzuki et al, 2013). Dowling et al (2003) used the erythromycin breath test and showed that CYP3A activity in patients with end-stage renal disease was significantly lower than that in controls.…”

“…Several studies in rats (Rege et al, 2003;Kusaba et al, 2012;Velenosi et al, 2012) and in patients (Dowling et al, 2003;Kirwan et al, 2009Kirwan et al, , 2012 have shown that renal failure decreases CYP3A expression and function. We have previously reported a significant increase in plasma concentration of 4b-hydroxycholesterol as an endogenous marker of CYP3A activity in patients with end-stage renal disease after kidney transplantation (Suzuki et al, 2013). The underlying causes of altered CYP expression and function observed in kidney disease remain unclear, but several studies indicate that uremic toxins may play a role via transcriptional or translational modifications of CYP enzymes and direct inhibition of CYP-mediated metabolism (Guévin et al, 2002;Hanada et al, 2006;Nolin et al, 2006;Michaud et al, 2008).…”