Aim: To explore the signalling pathways involved in aldosterone-induced inflammation and fibrosis in rat vascular smooth muscle cells (VSMCs). Methods: Using Western blotting and real-time RT-PCR, we investigated the effects of aldosterone on the expression of cyclooxygenase-2 (Cox-2) and IL-6, two important proinflammatory factors, and TGFβ1, a critical profibrotic factor, in VSMCs. Results: Aldosterone treatment significantly increased the expression of Cox-2 and IL-6 and activation of p38MAPK and NF-κB. The expression of both Cox-2 and IL-6 could be blocked by the mineralocorticoid receptor (MR) antagonist spironolactone and the p38MAPK inhibitor SB203580. Also, the rapid phosphorylation of p38MAPK could be suppressed by SB203580 but not by spironolactone, implicating in nongenomic effects of aldosterone. Similar to SB203580 and spironolactone, the NF-κB inhibitor α-p-tosyl-L-lysine chloromethyl ketone (TLCK) markedly attenuated expression of Cox-2, indicating that MR, p38MAPK and NF-κB are associated with aldosterone-induced inflammatory responses. Furthermore, aldosterone enhanced expression of TGFβ1 in rat VSMCs. This result may be related to activation of the MR/ERK-Sp1 signalling pathway because PD98059, an ERK1/2 inhibitor, significantly blocked the rapid phosphorylation of ERK1/2 and function of Sp1 and led to reduced expression of TGFβ1. Spironolactone was also shown to significantly inhibit TGFβ1 and Sp1 expression but not ERK1/2 phosphorylation. Conclusion: These results suggest that aldosterone-induced inflammatory responses and fibrotic responses may be mediated by the MR/p38MAPK-NF-κB pathways and the MR/ERK-Sp1 pathways in VSMCs, respectively.

The pharmacokinetics of clausenamide (CLA) enantiomers and their metabolites were investigated in Wistar rat. After intravenous and oral administration at a dose of 80 and 160 mg/kg each enantiomer, plasma concentrations of (-)- or (+)-CLA and its major metabolites were simultaneously determined by reverse-phase HPLC with UV detection. Notably, stereoselective differences in pharmacokinetics were found. The mean plasma levels of (+)-CLA were higher at almost all time points than those of (-)-CLA. (+)-CLA also exhibited greater t(max), C(max), t(1/2beta), AUC(0-12h), and AUC(0--> infinity) and smaller CL (or CL/F) and V(d) (or V(d)/F), than its antipode. The (+)/(-) isomer ratios for t(1/2beta), t(max), AUC(0-12 h), and AUC(0--> infinity), which ranged from 1.26 to 2.08. The ratio for CL (or CL/F) was about 0.5, and there were significant differences in these values between CLA enantiomers (P < 0.05), implying that the absorption, distribution, and elimination of (-)-CLA were more rapid than those of (+)-CLA. Similar findings for (-)-7-OH-CLA, the major metabolite of (-)-CLA, and (+)-4-OH-CLA, the major metabolite of (+)-CLA, can be also seen in rat plasma. The contributing factors for the differences in stereoselective pharmacokinetics of CLA enantiomers appeared to be involved in their different plasma protein binding, first-pass metabolism and interaction with CYP enzymes, especially with their metabolizing enzyme CYP 3A isoforms.

To identify which cytochrome P450 (CYP) isoform(s) are responsible for the metabolism of clausenamide (CLA) enantiomers in rats, effects of various CYP isoform inducers and inhibitors on the formation of CLA metabolites were investigated in liver microsomes. In incubations with rat liver microsomes, CLA enantiomers were mainly converted to 4-hydroxy, 5-hydroxy, and 7-hydroxy-metabolites. 4-OH-CLA was the major metabolite of (+)-3R, 4S, 5S, 6R-CLA [(+)-CLA], while 7-OH-CLA was the major one of (-)-3S, 4R, 5R, 6S-CLA [(-)-CLA]. In induction studies, enzymatic parameters were used to assess the role of different CYP forms in CLA hydroxylation reactions. A marked increase in the rate of metabolism of CLA enantiomers was observed in microsomes of dexamethasone treated rats, V(max)/K(m) values for 4-OH-(+)-CLA, 7-OH-, 5-OH-, and 4-OH-(-)-CLA were 5.3, 6.5, 3.0, and 5.9 times higher than those in control microsomes, respectively. Rifampicin treatment caused corresponding 1.7-, 2.6-, 3.1-, and 2.8-fold increases. Dex and Rif also increased in the amount of (+)-5- and (+)-7-OH-CLA that were not detectable in the control group. These results suggested that inducible CYP3A1 was involved in the hydroxylation of CLA enantiomers. In inhibition studies, ketoconazone (6.25 microM) completely inhibited the production of main metabolites of (-)-CLA (100%) and (+)-CLA (97%). Triacetyloleandomycin (12.5 microM) strongly inhibited the corresponding metabolites by 34-85%. These findings also indicated that institutive CYP3A2 shared a major role in the hydroxylation of CLA enantiomers with CYP3A1 in untreated rats. Together, the data suggested that CYP3A was the predominant isoform responsible for the metabolism of CLA enantiomers.

Stereoselective differences in pharmacokinetics between clausenamide (CLA) enantiomers have been found after intravenous and oral administration of each enantiomer to rats. The differences could be associated with protein binding of CLA enantiomers. By equilibrium dialysis methods, the binding of CLA enantiomers to rat plasma protein was investigated. The results showed that mean percentages of (-) and (+)CLA in the bound form were 28.5% and 38.0%, respectively, indicating that the unbound fraction of (-)CLA was higher than that of (+)CLA, which provided an explanation for stereoselective pharmacokinetics of CLA enantiomers in rats. The results also showed that there were species differences in plasma protein binding of (-)-isomer between rats (28.5%) and rabbits (47.2%). Furthermore, effects of plasma protein binding on the distribution of CLA enantiomers to their possible target tissues were observed. The amount of (-)CLA in brain was greater than that of (+)CLA 15 min after administration of each enantiomer to rats. But the results were reverse at 4 h postdose. Further studies in distributional kinetics showed that (-)CLA had a more rapid absorption and distribution to hippocampus, cortex, and cerebellum than (+) CLA. (+)CLA had greater values for T(max), t(1/2) (beta), and AUC(0) (-->infinity), and smaller ones for CL/F and V(d)/F than its antipode. The data indicated that the distribution of (-) and (+)CLA in their target tissues was stereoselective. The stereoselective distribution might be involved in the metabolism and transport of two enantiomers in the central nerve system.

These results indicate that istradefylline 40 mg/day as augmentation shows potential promise on clinical applicability, and is worthy of further study. Limited by the number of included RCTs, future studies are needed to verify and support this conclusion, and assess the long-term effect of istradefylline, the effect of istradefylline as monotherapy and other dose of istradefylline.