We examined transcript expression and post-transcriptional regulation of human ADAM33, a recently identified asthma gene. A detailed messenger RNA (mRNA) expression profile was obtained using Northern, reverse transcription polymerase chain reaction, and in situ hybridization analyses. ADAM33 mRNA was expressed significantly in smooth muscle-containing organs, minimally in immune organs and hematopoietic cells, and highly in repairing duodenal granulation tissue. Expression was seen in asthmatic subepithelial fibroblasts and smooth muscle but not in respiratory epithelium. In all tissues, transcripts of approximately 5 kb predominated over those of approximately 3.5 kb by 2- to 5-fold. The effect of the 3' untranslated region (UTR) on ADAM33 protein expression and maturation was examined. The presence of the 3'UTR in untagged full-length constructs promoted prodomain removal, detected as mature approximately 100 kD protein by ADAM33-reactive antibodies; in its absence, maturation was 2- to 3-fold less in HEK293 cells. His-tagged and untagged constructs lacking the 3'UTR demonstrated that lack of maturation was not a result of tag-mediated effects. Minimal maturation of ADAM33 occurred in primary lung and MRC5 fibroblasts following adenoviral-mediated expression of ADAM33 lacking the 3'UTR. In contrast, prodomain removal was observed with plasmids and adenovirus encoding only the pro- and catalytic domains. Thus, the 3'UTR of ADAM33 and domains downstream of the catalytic domain regulate potential ADAM33 activity. Mechanisms of regulation of ADAM33, distinct from closely related ADAMs, thus include mRNA localization and processing and protein maturation.
AimsTwo clinical studies were conducted to determine possible drug−drug interactions between apremilast and a strong CYP3A4 inhibitor, ketoconazole, or a potent CYP3A4 inducer, rifampicin. The main objectives of these two studies were to evaluate the impact of multiple doses of ketoconazole on the pharmacokinetics of apremilast and its metabolites, and the effect of multiple oral doses of rifampicin on the pharmacokinetics of apremilast.MethodsThese single centre, open label, sequential treatment studies in healthy subjects included two treatment periods for ketoconazole and three treatment periods for rifampicin. Apremilast was administered as a 20 mg (ketoconazole study) or 30 mg (rifampicin study) single oral dose.ResultsKetoconazole increases overall exposure (AUC(0,∞)) of apremilast by ≈36% (2827 vs. 2072 ng ml−1 h, 90% CI = 126.2, 147.5) and peak exposure (Cmax) by 5% (247 vs. 236 ng ml−1). Multiple doses of rifampicin increase apremilast clearance ≈3.6-fold and decrease apremilast mean AUC(0,∞) by ≈72% (3120 vs. 869 ng ml−1 h, 90% CI = 25.7, 30.4) and Cmax (from 290 vs. 166 ng ml−1) relative to that of apremilast given alone. A 30 min intravenous infusion of rifampicin 600 mg had negligible effects on the overall exposure (AUC(0,∞)) of apremilast (2980 vs. 3120 ng ml−1 h, 90% CI = 88.0, 104.1).ConclusionKetoconazole slightly decreased apremilast clearance, resulting in a small increase in AUC which is probably not meaningful clinically. However, the effect of CYP3A4 induction by rifampicin on apremilast clearance is much more pronounced than that of CYP3A4 inhibition by ketoconazole. Strong CYP3A4 inducers may result in a loss of efficacy of apremilast because of decreased drug exposure.
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