Augmentation of hepatocyte proliferation by immunosuppressant pretherapy is associated with up-regulation of malondialdehyde production

Changes in mitochondrial ultrastructure and malondialdehyde level in regenerating liver tissue in rats

AIM: To investigate the role of mitochondria permeability transition (MPT) in liver regeneration.

METHODS: One hundred and five male Sprague-Dawley rats were randomly divided into three groups: partial hepatectomy (PH) group, cyclosporin A (CsA) group and sham-operated (SH) group. Animals in the PH and CsA groups underwent 2/3 partial hepatectomy. Animals in the CsA group were administered CsA before the surgery. The animals in each group were further divided into seven sub-groups. Ultrastructural morphology of mitochondria in remnant liver after PH was determined by electron microscopy. The content of malondialdehyde (MDA) in liver tissue was also measured.

RESULTS: Remarkable changes were observed in the morphology and ultrastructure of the liver mitochondria at 24 h after PH, including conspicuous swelling, increased membrane permeability, reduced number of cristae, and matrix vacuolation. At 72 h, moderate mitochondrial swelling was observed, while, at other time points, mild mitochondrial swelling was seen. Mitochondrial permeability increased at 0, 3 and 6 h in the CsA group, but decreased at 24 and 72 h when compared with the PH group. Similar changes in endoplasmic reticulum were also noted. The content of MDA increased at 3 h after PH, peaked at 24 h, and then decreased and returned to normal level at 120 h. The contents of MDA at all time points in the CsA group were significantly higher than those in the PH group.

CONCLUSION: The changes in mitochondrial ultrastructure and MDA level are closely associated with MPT during live regeneration in rats, especially prominent at 24 h after PH. The changes in mitochondrial ultrastructure and MDA level in liver tissue is possibly related to the initiation of liver regeneration after PH.

Short-term and long-term FK506 treatment alters the vascular reactivity of renal and mesenteric vascular beds

The aims of this study were to investigate the role of endothelin-1 in FK506-induced hypertension and vascular dysfunction of rats treated with the drug for 8 (short-term) or 30 (long-term) days and to measure malondialdehyde levels in the kidneys. Kidney and mesentery of rats were perfused. In the short-term treated groups, there was no significant change in systolic blood pressure. The response to noradrenaline only in renal vascular beds was significantly increased by FK506 and this increase was prevented by Bosentan. FK506 had no significant effect on sodium nitroprusside-induced vasodilation in comparison with solvent in both vascular beds. Bosentan failed to prevent these responses. In the long-term treated groups, at the end of the treatment with FK506, there was a significant increase in blood pressure, but no change in the response to noradrenaline in either kidneys or mesentery. The increase in blood pressure was prevented by bosentan treatment. FK506 increased malondialdehyde levels in the kidneys of the rats from only the long-term treated groups. Bosentan did not change this increase. Our results indicated that endothelin-1 plays a key role in the FK506-induced change in vascular reactivity to noradrenaline in renal vascular beds and drug-induced hypertension in the rats. There was no relationship between oxidative stress and FK506-induced hypertension.

Liver regeneration enhanced by orally administered ursodesoxycholic acid is mediated by immunosuppression in partially hepatectomized rats

The relationship of liver regeneration to immunoactivity was examined after ursodesoxycholic acid (UDCA) administration to partially (about 66%) hepatectomized rats. The UDCA was given orally. Liver regeneration was evaluated by the hepatocyte mitotic index (MI) and immunoactivity by natural killer cell (NK) activity in the blood. When UDCA 12.5 mg/kg/day was administered, a significant increase in the MI was observed 2 and 3 days after hepatectomy, and the MI response 2 days after bepatectomy tended to be dose-dependent in the range of 0-25 mg/kg/day. NK activity was decreased 2 days after hepatectomy when UDCA was given, and a significant correlation between MI and NK activity was obtained. The increase in MI and decrease in NK activity was blocked completely or partially (respectively) by interleukin-2 administration. It was also noted that UDCA did not affect serum parameters indicating liver and kidney function. These findings suggest that liver regeneration can be modified by orally administered UDCA through a change in immunoactivity.

Hepatic branch vagotomy can block liver regeneration enhanced by ursodesoxycholic acid in 66% hepatectomized rats

The effect of hepatic branch vagotomy on liver regeneration induced by ursodesoxycholic acid was examined in 66% hepatectomized rats. A standard feeding was obtained from animals with hepatic branch vagotomy, and all rats examined received pair food intake. Liver regeneration was evaluated by the hepatocyte mitotic index. When ursodesoxycholic acid 12.5 mg kg(-1) day(-1) was administered orally, a significant increase in the mitotic index was observed 2 and 3 days after hepatectomy, and the mitotic index response 2 days after hepatectomy was dose-dependent in the range of 0-25 mg kg(-1) day(-1). Hepatic branch vagotomy suppressed the mitotic index 2 days after hepatectomy, and the mitotic index increase due to ursodesoxycholic acid was blocked by hepatic branch vagotomy, but not by gastric branch vagotomy. It was also noted that hepatic branch vagotomy or ursodesoxycholic acid or both did not affect serum parameters indicating liver and kidney function. Because ursodesoxycholic acid exists in the bile juice, these results suggest that the hepatic vagus nerve is specifically active with endogenous bile acids in the control of liver regeneration.

Induction of cell proliferation by cyclosporine A in primary cultures of rat hepatocytes

Cyclosporine A (CsA) has been reported to be able to promote cell proliferation, although the precise mechanism by which CsA stimulates cell growth remains uncertain. In the present study, we examined, in hepatocyte cultures, the effect of CsA on parameters related to the cell cycle as well as the levels of proteins involved in the control and progression of the cycle. Flow cytometry analysis detected an increase in the percentage of cells involved in the S phase of the cycle, which correlated with increases in the levels of cyclins D1 and E (two G1-progression regulators), as well as in those of PCNA (proliferating cell nuclear antigen), and without modification in p27, an inhibitory protein of CDKs. We also examined in nucleus the levels of nuclear factor kappaB (a nuclear factor involved in the transcription of the cyclin D1 gene) and found that this transcription factor increased in the presence of CsA. We conclude that the increases in cyclin D1, PCNA, and cyclin E, together with the invariable level of p27, clearly show that CsA induces hepatocytes to proliferate. These results reinforce the idea of the growth-promoting effect of CsA in cultured hepatocytes.