Effect of cyclosporine A on cytochrome P-450-mediated drug metabolism in the partially hepatectomized rat.

Despite its hepatotoxic potential, cyclosporine A (CsA) has been reported to positively influence compensatory liver growth. To probe the physiological consequences of CsA on the recovery of liver function, studies were initiated in the 2/3 partially hepatectomized (PHx) rat, taking the recovery of cytochromes P-450-dependent drug metabolism as primary outcome. CsA was administered at a dose of 3. 33 mg/kg/day for 10 days. Drug metabolism was evaluated by the recovery of 14CO2 after administration of isotopically labeled model drugs and by studying the expression of the P-450 transcripts involved in their biotransformation before and 24 to 96 h after PHx. Before PHx, neither the steady-state mRNA nor the in vivo disposition of caffeine (CYP1A2), erythromycin (CYP3A2 and 3A1), or aminopyrine (CYP2B1 and 2C11) were influenced by CsA. Studies 24 h after PHx revealed a 29 to 39% reduction in the elimination of [14C]aminopyrine and [14C]erythromycin, which was unaffected by CsA. Their metabolism at 48 to 96 h after PHx also remained unaffected by CsA. By contrast, postPHx, [14C]caffeine elimination decreased to a level closely proportional to the loss in liver mass. In addition, CsA accelerated the recovery and/or prevented the decrease of caffeine elimination 24 h after PHx but not at later time points, indicating an early, but unsustained, beneficial effect of CsA on the recovery of CYP1A2-mediated activities. These data show that at the critical time of greatest loss in liver mass, CsA has only a selective influence on the biotransformation of cytochrome P-450 protein-dependent activities and that its effect on the regeneration process does not translate into an overall accelerated recovery of the hepatic drug-metabolizing function.

Hypocalcemia decreases the early and late responses to epidermal growth factor in rat hepatocytes.

Extreme variations in extracellular Ca2+ concentrations ([Ca2+]e) modify the signaling generated by many hormones and growth factors. However, the influence of physiological changes in [Ca2+]e on the response to hepatic mitogens remains largely unknown. To study the influence of [Ca2+]e on the response to epidermal growth factor (EGF), hepatocytes from normal rat livers were equilibrated in vitro at [Ca2+]e similar to those observed in normocalcemia or hypocalcemia. To further investigate the effect of hypocalcemia in vivo, hepatocytes were obtained from chronically hypocalcemic rats and kept in vitro at the [Ca2+]e prevailing in vivo. Intracellular Ca2+ concentrations ([Ca2+]i) and DNA synthesis were evaluated after increasing doses of EGF. [Ca2+]e strongly influenced the [Ca2+]i response to EGF with significantly smaller [Ca2+]i increases in hepatocytes of normal rats kept in low [Ca2+]e compared with those kept in normal [Ca2+]e. In hypocalcemic rat hepatocytes, the response was further decreased and found to be significantly lower than that obtained in control cells kept in vitro at either 1.25 mmol/L or 0.8 mmol/L [Ca2+]e. In normal [Ca2+]e, the EGF-induced increases in [Ca2+]i were abolished by inhibiting EGF receptor autophosphorylation and by blocking calcium channels. Low in vitro [Ca2+]e significantly dampened the EGF-mediated DNA synthesis in normal rat hepatocytes but hypocalcemia in vivo further reduced the proliferative response compared with that obtained in control rat hepatocytes maintained in normal, or low [Ca2+]e. Furthermore, the blunted responses in [Ca2+]i mobilization and DNA synthesis associated with hypocalcemia could not be overcome by increasing concentrations of EGF nor by normalization of [Ca2+]e in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic hypocalcemia of vitamin D deficiency leads to lower intracellular calcium concentrations in rat hepatocytes.

Several lines of evidence indicate that calcium deficiency is associated with cellular defects in many tissues and organs. Owing to the large in vivo gradient between ionized extra- and intracellular Ca2+ concentrations ([Ca2+]i), it is generally recognized that the prevailing circulating Ca2+ does not significantly affect resting cytosolic Ca2+. To probe the consequences of hypocalcemia on [Ca2+]i, a model of chronic hypocalcemia secondary to vitamin D (D) deficiency was used. Hepatocytes were isolated from livers of hypocalcemic D-deficient, of normocalcemic D3-repleted, or of normal control rats presenting serum Ca2+ of 0.78 +/- 0.02, 1.24 +/- 0.03, or 1.25 +/- 0.01 mM, respectively (P < 0.0001). [Ca2+]i was measured in cell couplets using the fluorescent probe Fura-2. Hepatocytes of normocalcemic D3-repleted and of normal controls exhibited similar [Ca2+]i of 227 +/- 10 and 242 +/- 9 nM, respectively (NS), whereas those of hypocalcemic rats had significantly lower resting [Ca2+]i (172 +/- 10 nM; P < 0.0003). Stimulation of hepatocytes with the alpha 1-adrenoreceptor agonist phenylephrine illicited increases in cytosolic Ca2+ leading to similar [Ca2+]i and phosphorylase a (a Ca(2+)-dependent enzyme) activity in all groups but in contrast to normocalcemia, low extracellular Ca2+ was often accompanied by a rapid decay in the sustained phase of the [Ca2+]i response. When stimulated with the powerful hepatic mitogen epidermal growth factor (EGF), hepatocytes isolated from hypocalcemic rat livers responded with a blunted maximal [Ca2+]i of 237.6 +/- 18.7 compared with 605.2 +/- 89.9 nM (P < 0.0001) for their normal counterparts, while the EGF-mediated DNA synthesis response was reduced by 50% by the hypocalcemic condition (P < 0.03). Further studies on the possible mechanisms involved in the perturbed [Ca2+]i homeostasis associated with chronic hypocalcemia revealed the presence of an unchanged plasma membrane Ca2+ ATPase but of a significant decrease in agonist-stimulated Ca2+ entry as indicated using Mn2+ as surrogate ion (P < 0.03). Our data, thus indicate that, in rat hepatocytes, the in vivo calcium status significantly affects resting [Ca2+]i, and from this we raise the hypothesis that this lower than normal [Ca2+]i may be linked, in calcium disorders, to inappropriate cell responses mediated through the calcium signaling pathway as illustrated by the response to phenylephrine and EGF.