Bilirubin and ferritin as protectors against hemin-induced oxidative stress in rat liver.

The in vivo effect of hemin on both hepatic oxidative stress and heme oxygenase induction was studied. A marked increase in lipid peroxidation was observed 1 hr after hemin administration. Heme oxygenase-1 activity and expression appeared 6 hr after treatment, reaching a maximum between 12 and 15 hr after hemin administration. Such induction was preceded by a decrease in the soluble and enzymatic defenses, both effects taking place some hours before induction of heme oxygenase. Ferritin content began to increase 6 hr after heme oxygenase induction, and these increases were significantly higher 15 hr after treatment and remained high for at least 24 hr after hemin injection. Co-administration of tin protoporphyrin IX, a potent inhibitor of heme oxygenase, completely prevented the enzyme induction and the increase in ferritin levels, increasing the appearance of oxidative stress parameters. Administration of bilirubin, prevented the heme oxygenase induction as well as the decrease in hepatic GSH and the increase of lipid peroxidation when it was administered 2 hr before hemin treatment. These results indicate that the induction of heme oxygenase by hemin may be a general response to oxidant stress, by increasing bilirubin and ferritin levels and could therefore provide a major cellular defense mechanism against oxidative damage.

Effect of acetaminophen on heme metabolism in rat liver.

BACKGROUND AND AIMS: Acetaminophen (APAP) or paracetamol is a hepatotoxic drug through mechanisms involving oxidative stress. To know whether mammalian cells possess inducible pathways for antioxidant defense, we have to study the relationship between heme metabolism and oxidative stress. METHODS: fasted female Wistar rats received a single injection of APAP (3.3 mmol kg(-1) body weight) and then were killed at different times. Heme oxygenase-1 (HO), delta-aminolevulinic acid (ALA) synthase, ALA dehydratase, and porphobilinogenase activities, lipid peroxidation, GSH, catalase and glutathione peroxidase, were measured in liver homogenates. The antioxidant properties of bilirubin and S-adenosyl-L-methionine were also evaluated. RESULTS: APAP increased lipid peroxidation (115% +/- 6; S.E.M., n=12 over control values) 1 h after treatment. GSH reached a minimum at 3 h (38% +/- 5) increasing thereafter. At the same time antioxidant enzymes reached minimum values (catalase, 5. 6 +/- 0.4 pmol mg(-1) protein, glutathione peroxidase, 0.101 +/- 0.006 U mg(-1) protein). HO induction was observed 6 h after treatment reaching a maximum value of 2.56 +/- 0.12 U mg(-1) protein 15 after injection. ALA synthase (ALA-S) induction occurred after enhancement of HO, reaching a maximum at 18 h (three-fold the control). ALA dehydratase activity was first inhibited (31 +/- 3%) showing a profile similar to that of GSH, while porphobilinogenase activity was not modified along the whole period of the assay. Administration of bilirubin (5 micromol kg(-1) body weight) or S-adenosyl L-methionine (46 micromol kg(-1) body weight) 2 h before APAP treatment entirely prevented the increase in malondialdehyde (MDA) content, the decrease in GSH levels as well as HO and ALA-S induction. CONCLUSION: This study shows that oxidative stress produced by APAP leads to increase in ALA-S and HO activities, indicating that toxic doses of APAP affect both heme biosynthesis and degradation.

Non-essential activation of rat liver porphobilinogen-deaminase by folic acid.

This report demonstrates the ability of folic acid to activate rat liver porphobilinogen-deaminase (PBG-D). Lineweaver-Burk analysis revealed an increase in Vmax (38%) without affecting the Km. In the concentration range assayed, secondary replots of 1/delta slope and 1/delta intersect versus 1/[folic acid] yielded straight lines, indicating the binding of a single molecule of activator to the enzyme PBG-D, with a KA = 1.66 mM. Results presented here show that folic acid acts as a non-essential activator (alpha = 1; beta = 1.6). The activating effect of folic acid has been observed employing the 35-70% ammonium sulphate precipitated fraction, desalted by dialysis or gel filtration, whereas no action was detected when other partially purified PBG-D preparations were utilized as the enzyme source, suggesting either the presence of sites saturated for the activator, or the existence of a different structural protein conformation, or both.