Emilia Fugassa

Thyroid status affects rat liver regeneration after partial hepatectomy by regulating cell cycle and apoptosis.

In rats, various growth factors and hormones, as well as partial hepatectomy (PH) are able to trigger the proliferative response of hepatocytes. Although recent evidence highlights the important role of thyroid hormones and thyroid status in regulating the growth of liver cells in vitro and in vivo models, the mechanism involved in the pro-proliferative effects of thyroid hormones is still unclear. Here we have investigated how in rats made hypo- and hyperthyroid after prolonged treatment respectively with propylthiouracil (PTU) and triiodothyronine (T3), the thyroid status affects liver regeneration after PH by regulating cell cycle and apoptosis proteins. Our results show that both in control and partially hepatectomized animals hyperthyroidism increases the cyclin D1, E and A levels and the activity of cyclin-cdk complexes, and decreases the levels of cdk inhibitors such as p16 and p27. On the contrary hypothyroidism induces a down-regulation of the activity of cyclin cdk complexes decreasing cyclin levels. Thyroid hormones control also p53 and p73, two proteins involved in apoptosis and growth arrest which are induced by PH. In particular, hypothyroidism increases and T3 treatment decreases p73 levels. The analysis of the phosphorylated forms of p42/44 and p38 MAPK revealed that they are induced during hepatic regeneration in euthyroid and hyperthyroid rats whereas they are negatively regulated in hypothyroid rats. In conclusion our data demonstrate that thyroid status can affects liver regeneration, altering the expression and the activity of the proteins involved in the control of cell cycle and growth arrest.

Effects of 3,5-diiodo-L-thyronine administration on the liver of high fat diet-fed rats.

In rats fed a high fat diet (HFD), long-term administration of 3,5-diiodo-L-thyronine (T2), a naturally occurring iodothyronine, was shown to reduce body-weight gain, fat mass, and hepatic lipid accumulation. This work was aimed at investigating the mechanisms of T2 action in the liver of HFD rats. The results show that HFD induces liver lipid peroxidation and stimulates the activity of enzymes involved in hydrogen peroxide (H2O2) metabolism, catalase in particular. Moreover, quantitative RT-PCR revealed HFD-induced upregulation of the transcription factor PPARα, as well as of metallothionein isoforms (MT-1 and MT-2). T2 administration prevented the HDF-induced lipid peroxidation, as well as the increase in H2O2 metabolism, and reduced the upregulation of both PPARα and MT-2. These data demonstrate that in the liver of HFD rats, T2 prevents both lipid accumulation and oxidative stress associated with increased fat metabolism.

Collagenase perfusion of rat liver induces DNA damage and DNA repair in hepatocytes

Evidence is presented that the collagenase perfusion of adult rat liver results in significant damage to nuclear DNA as evaluated by the alkaline elution technique. The extent of the damage is related to the perfusion time as well as to the clostridial enzyme preparation used. The DNA structure of isolated cells is almost completely repaired within 12 h of their culture in chemically defined medium.

Influence of the culture time of DNA damage and repair in isolated rat hepatocytes exposed to nitochlorobenzene derivatives

The induction of DNA damage on 1.5- and 24-h cultured hepatocytes was tested after a 3-h exposure to 5 and 50 microM mono-, di-, and trinitrochlorobenzene (100-00-5; 97-00-7; 88-88-0). DNA-repair synthesis, elicited by nitrochlorobenzene treatment, was also estimated 24 and 48 h after the withdrawal of the nitro-aryl halides. DNA damage and repair were evaluated by determining the DNA elution rate in alkali. A dose-related rate of DNA damage was obtained by exposure of 1.5-h-cultured hepatocytes to 5 and 50 microM nitrochlorobenzenes . DNA of 24-h-cultured cells was not affected by nitrochlorobenzene treatment. The data obtained by exposure to 5 microM methyl methanesulfonate (66-27-3) and nitrosodimethylamine (62-75-9), direct and indirect methylating agents, suggest that 24-h-cultured liver cells are still able to transform nitrosodimethylamine but not nitrochlorobenzenes . Isolated hepatocytes maintain their capability of repairing the induced DNA damage when cultured for 24 and 48 h in fresh medium. The system offers an interesting model to investigate the perturbations related to the metabolism of xenobiotics.

Uncoupling protein-2 induction in rat hepatocytes after acute carbon tetrachloride liver injury

This study is focused on the role of UCP‐2 in hepatic oxidative metabolism following acute CCl4 administration to rats. UCP‐2 mRNA, almost undetectable in the liver of controls, was significantly increased 24 h after CCl4 administration, peaked at 72 h and then tended to disappear. UCP‐2 protein, undetectable in controls, increased 48–72 h after CCl4 treatment. Experiments with isolated liver cells indicated that in control rats UCP‐2 was expressed in non‐parenchymal cells and not in hepatocytes, whereas in CCl4‐treated rats UCP‐2 expression was induced in hepatocytes and was not affected in non‐parenchymal cells. Addition of CCl4 to the culture medium of hepatocytes from control rats failed to induce UCP‐2 expression. Liver mitochondria from CCl4‐treated rats showed an increase of H2O2 release at 12–24 h, followed by a rise of TBARS. Vitamin E protected liver from CCl4 injury and reduced the expression of UCP‐2. Treatment with GdCl3 prior to CCl4, in order to inhibit Kupffer cells, reduced TBARS and UCP‐2 mRNA increase in hepatic mitochondria. Our data indicate that CCl4 induces the expression of UCP‐2 in hepatocytes with a redox‐dependent mechanism involving Kupffer cells. A role of UCP‐2 in moderating CCl4‐induced oxidative stress during tissue regeneration after injury is suggested. J. Cell. Physiol. 216: 413–418, 2008.

Is the platelet serotonin transporter different in venous vs. arterial blood

The binding of labelled paroxetine to the serotonin transporter (SERT) of platelet membranes has been studied in both venous and mixed venous/arterial blood of the rat. In addition, we studied the inhibition of paroxetine binding to SERT by quipazine and N-methyl-quipazine (NMQ). The results indicate differences in affinity for the two test drugs, quipazine and NMQ, in venous vs. mixed venous/arterial blood. This suggests different post-translational modifications of SERT in platelets of arterial vs. venous blood.