Impact of genetic and nongenetic factors on interindividual variability in 4ß-hydroxycholesterol concentration.

PURPOSE: Individual variability in the endogenous CYP3A metabolite 4ß-hydroxycholesterol (4ßOHC) is substantial, but to which extent this is determined by genetic and nongenetic factors remains unclear. The aim of the study was to evaluate the explanatory power of candidate genetic variants and key nongenetic factors on individual variability in 4ßOHC levels in a large naturalistic patient population. METHODS: We measured 4ßOHC concentration in serum samples from 655 patients and used multiple linear regression analysis to estimate the quantitative effects of CYP3A4*22, CYP3A5*3, and POR*28 variant alleles, comedication with CYP3A inducers, inhibitors and substrates, sex, and age on individual 4ßOHC levels. RESULTS: 4ßOHC concentration ranged >100-fold in the population, and the multiple linear regression model explained about one fourth of the variability (R 2 = 0.23). Only comedication with inducers or inhibitors, sex, and POR genotype were significantly associated with individual variability in 4ßOHC level. The estimated quantitative effects on 4ßOHC levels were greatest for inducer comedication (+>313%, P < 0.001), inhibitor comedication (-34%, P = 0.021), and female sex (+30%, P < 0.001), while only a modestly elevated 4ßOHC level was observed in carriers vs. noncarriers of POR*28 (+11%, P = 0.023). CONCLUSIONS: These findings suggest that the CYP3A4*22, CYP3A5*3, and POR*28 variant alleles are of limited importance for overall individual variability in 4ßOHC levels compared to nongenetic factors.

4ß-Hydroxycholesterol Level in Patients With Rheumatoid Arthritis Before vs. After Initiation of bDMARDs and Correlation With Inflammatory State.

Systemic inflammation has been linked to suppressed CYP3A(4) activity. We determined 4ß-hydroxycholesterol (4ßOHC), an endogenous CYP3A4 metabolite, in patients with rheumatoid arthritis (RA) before and after treatment with biological disease-modifying antirheumatic drugs (bDMARDs). The 4ßOHC was compared in 41 patients before and 2-5 months after initiating TNFα inhibitors (n = 31), IL-6 inhibitors (n = 5), or B-cell inhibitors (n = 5). Correlations between 4ßOHC and inflammatory markers (C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR)) were also tested before and after bDMARDs. 4ßOHC did not differ following bDMARD treatment (P = 0.6), nor in patients who started with IL-6 inhibitors (median 51.6 vs. 50.6 nmol/L). The 4ßOHC and CRP/ESR did not correlate before treatment (P > 0.5), but correlated significantly after bDMARDs (CRP = Spearman r -0.40; P < 0.01; ESR = r -0.34; P = 0.028) suggesting that mainly non-CYP3A4-suppressive cytokines were reduced during treatment. Thus, this study does not support a generally regained CYP3A4 phenotype in patients with RA following initiation of bDMARDs.