Pharmacokinetics of bound and unbound telaprevir in cirrhotic patients with moderate and severe hepatic impairment.

This study aimed to characterize the pharmacokinetic parameters of telaprevir (TVR) in patients with moderate and severe hepatic impairment, measure the unbound (pharmacologically active) plasma concentrations of TVR, and determine if any changes in TVR exposure were of clinical relevance. Ten patients with moderate (Child-Pugh B) hepatic impairment, 10 matched healthy control volunteers, and 4 nonmatched patients with severe (Child-Pugh C) hepatic impairment received 750 mg TVR every 8 hours for 6 days. Venous blood samples were collected at various times throughout the study. Single-dose and steady-state pharmacokinetics of total and unbound TVR were calculated. Safety and tolerability of TVR were also assessed. The mean maximum plasma concentration and area under the curve values of total and unbound TVR were lower in patients with moderate hepatic impairment compared with matched healthy controls following a single dose and at steady state but did not consistently meet statistical significance. This trend was also present when patients with severe hepatic impairment were compared with the nonmatched healthy controls. However, the safety profile of TVR in the patient and healthy volunteer groups was comparable with previously published data. These results indicate that reduced plasma concentrations of total and unbound TVR in patients with hepatic impairment are unlikely to be clinically relevant.

NO-induced activation of cyclic GMP-dependent pathway down regulates ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) protein in rat C6 glioma.

In rat C6 glioma cells, the ecto-nucleotide pyrophosphatase/phosphodiesterase-1 (NPP1), a modulator of purinergic receptor signaling, is down regulated after an increase in intracellular cAMP by addition of dibutyryl cAMP, a membrane-permeable cAMP-analog, or by activation of the ß-adrenoceptor receptor with (-)-isoproterenol (Aerts et al., 2011, Eur. J. Pharmacol. 654, 1-9). In this communication we studied the effect of nitric oxide (NO)/cGMP, a pathway also affecting purinergic receptor signaling, on the level of NPP1 protein. Sodium nitroprusside (SNP), a NO donor, reduces NPP1 protein in a dose-dependent manner. A combination of SNP and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, an inhibitor of soluble guanylate cyclase, demonstrated that NO-dependent down regulation of NPP1 was caused by NO-sensitive guanylyl cyclase. Treatment with Rp-pCPT-cGMPS, an inhibitor of protein kinase G (PKG), showed that PKG is not involved in the down regulation of NPP1. In addition, we have shown that the cAMP- and cGMP-dependent decrease in NPP1 expression is unrelated. These results indicate that NO/cGMP regulates the level of NPP1 protein by a pathway that differs from the cAMP-induced decrease in NPP1.

The expression of ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (E-NPP1) is correlated with astrocytic tumor grade.

OBJECTIVE: Astrocytic brain tumors are subdivided in four grades. The most aggressive and invasive one is grade IV or glioblastoma multiforme (GBM). Ecto-nucleotide pyrophosphatase/phosphodiesterase-1 (E-NPP1), a membrane-bound enzyme, is involved in many cellular processes such as modulation of purinergic signalling, nucleotide recycling, regulation of extracellular pyrophosphate levels and stimulation of cell motility. In this study, the use of anti-NPP1 antibody in the determination of astrocytic tumor grade is evaluated. MATERIALS AND METHODS: Paraffin-embedded surgical specimens from 41 primary human astrocytic brain tumors (grade I=2; grade II=10; grade III=9; grade IV=20) and 5 control samples are immunostained against NPP1 and glial fibrillary acid protein an astrocytic marker. RESULTS: In this communication, we report the expression of NPP1 in human astrocytic brain tumors. No expression could be detected in control tissue. We observed a remarkable up regulated expression of NPP1 in GBM. Taking the latter as 100%, grade I has a relative NPP1 staining of 7%, whereas grade II and III have a similar NPP1 expression level of 53% and 47% respectively. CONCLUSION: A correlation is found between the up-regulated expression of NPP1 and the grade of the astrocytic tumor. Further investigation of NPP1 expression, especially in GBM, is necessary to determine the role of NPP1 in astrocytic brain tumor progression.

Cyclic AMP-dependent down regulation of ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) in rat C6 glioma.

In this communication, we demonstrate that an increase in intracellular cAMP by 1) addition of dibutyrylic cAMP (dbcAMP), a membrane-permeable cAMP-analogue, or 2) activation of the ß-adrenoceptor with (-)-isoproterenol, down regulates the levels of ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) mRNA, NPP1 protein and ecto-NPPase activity in rat C6 glioma cells. DbcAMP and (-)-isoproterenol inhibit NPP1 expression in a time and dose-dependent manner. After 48h of stimulation, 1mM dbcAMP or 5µM (-)-isoproterenol decreases the amount of NPP1 protein by 75±3% and 81±1% respectively. Contrary to down regulation of NPP1, we observe an up regulation of glial fibrillary acidic protein (GFAP), a differentiation marker for astrocytic cells. Using specific inhibitors and activators, we have shown that Ca(2+), PKA, PI 3-K/PKB/GSK-3, Epac/Rap1/PP2A and MAP kinase modules are not involved in the inhibition of NPP1 gene expression. The transcription factor c-jun is significantly reduced while c-fos becomes up regulated after cAMP elevation. However an electrophoretic mobility shift assay with the activator protein-1 motif present in the promoter of the rat NPP1 gene indicates that this motif is not involved in the cAMP-dependent inhibition of NPP1 expression. In conclusion, these results indicate that intracellular cAMP levels regulate the expression of NPP1 in rat C6 glioma cells by a signalling pathway that is different from the GFAP signal transduction pathway.