In vitro scavenger effect of dihydroquinoline type derivatives in different free radical generating systems

Oxidative stress in the liver and biliary tract diseases

Oxidative stress plays an important role in the pathogenesis of toxic liver diseases and of other hepatic alterations. We summarize the pathomechanism of free radical reactions in liver diseases and the results of experimental and clinical observations. Most of the hepatoprotective drugs belong in the group of free-radical scavengers, their mechanism of action involving membrane stabilization, neutralization of free radicals and immunomodulation. We demonstrate the effects of the different drugs used in the therapy of liver diseases in animal experiments and in human clinicopharmacological studies. The scavenger effect of these drugs has been demonstrated in the subcellular fractions of liver cells in animal experiments. In vitro incubation with some hepatoprotective drugs inhibit lectin-induced lymphocyte transformation while others decrease the antibody-dependent, spontaneous, and lectin-induced lymphocytotoxicity. Dihydroquinolin-type antioxidants and silymarin enhanced the superoxide dismutase activity of erythrocytes and lymphocytes. In addition, in a 6-month double-blind clinical trial of patients with chronic alcoholic liver disease, we studied the effects of silymarin therapy on liver function tests, on the parameters characterizing the oxidative stress and immune reaction, on serum procollagen III peptide level, and on liver histology. A wide range of methods was used. The silymarin preparate corrected the altered immune reaction and the decreased superoxide-dismutase activity of erythrocytes and lymphocytes in patients with alcoholic liver cirrhosis. The results indicate that these drugs exert hepatoprotective activity and can improve liver functions in alcoholic patients and in toxic liver diseases. We found a correlation between the bilirubin concentration and lipid peroxidation in cases with toxic liver and biliary tract diseases, and assume that there are two kinds of bilirubin, an antioxidant and a prooxidant form, on the basis of diene conjugates in the bile.

The role of free radicals in the pathogenesis of amiodarone toxicity

INTRODUCTION

In vitro and in vivo studies were performed to elucidate the pathogenesis of amiodarone toxicity.

METHODS AND RESULTS

Rats were treated with amiodarone alone (500 mg/kg body weight per day) or together with antioxidants (silibinin or MTDQ-DA: 50 mg/kg body weight per day) or with either antioxidant alone. They received amiodarone for 30 days and antioxidant for 33 days (3 days pretreatment). In vitro, amiodarone induced a dose-dependent chemiluminescence signal, which was inhibited by the two dihydroquinolin-type antioxidants (MTDQ-DA, CH 402). Chemiluminometric results from liver homogenate demonstrated that simultaneous treatment with silibinin partially prevented the liver homogenate superoxide anion radical scavenger capacity decreasing effect of amiodarone. Amiodarone treatment caused a significant increase of NADPH and Fe3+ induced lipid peroxidation in the liver microsomal fraction, which antioxidants (silibinin, MTDQ-DA) were unable to prevent. Light microscopy of the lung tissue in amiodarone-treated rats showed accumulation of foamy macrophages with thickening of the interalveolar septa, pneumonitis, and variable interstitial fibrosis. Antioxidant treatment did not prevent these changes. Electron micrographs of lung from amiodarone-treated rats showed lysosomal phospholipoidosis, intralysosomal electron dense deposits, and increased lysosome number and size. In contrast to rats treated with amiodarone alone, those treated with both amiodarone and silibinin had significantly fewer lysosomes (P < 0.01); the lysosome size, shape, and internal characteristics remained the same. Simultaneous treatment with silibinin and amiodarone decreased lysosomal phospholipoidosis compared to amiodarone treatment alone. Simultaneous treatment with MTDQ-DA and amiodarone did not show any beneficial effect. Pulse radiolysis and cobalt 60-gamma (60Co-gamma) radiolysis studies showed that the main free radical product in a reducing environment was a very reactive aryl radical formed after the partial deiodination of the amiodarone molecule. The radiosensitizing effect of amiodarone was also verified in rat liver microsomal preparations using in vivo amiodarone with or without MTDQ-DA pretreatment and 60Co-gamma irradiation with or without the in vitro addition of antioxidants (CH 402, MTDQ-DA). In vivo, the MTDQ-DA treatment also had a radiosensitizing effect; however, the in vitro addition of both antioxidants resulted in a radioprotective effect. The aryl radical also may emerge in vivo during the metabolism of amiodarone.

CONCLUSION

These observations suggest that amiodarone in vitro and in vivo generates free radicals that may play a role in the pathogenesis of amiodarone toxicity beside other well-established mechanisms, and antioxidants may have a partial protective effect against amiodarone toxicity.

The superoxide scavenging activity of dihydroquinoline type derivatives (CH402 and MTDQ-DA)

Electron paramagnetic resonance/spin trapping studies were applied, to verify the superoxide radical scavenging activity of two non-toxic, water soluble dihydroquinoline type antioxidants, CH402 (Na-2,2-dimethyl-1,2-dihydroquinoline-4-yl methane sulphonate and MTDQ-DA (6,6-methylene bis 2,2-dimethyl-4-methane sulphonic acid: Na-1,2-dihydroquinoline). Results were compared with other indirect methods such as the amperometric, spectrophotometric and luminometric methods, respectively. Both dihydroquinoline type antioxidants scavenged superoxide in vitro specifically. MTDQ-DA scavenged superoxide an order of magnitude faster than CH-402. Neither CH402 nor MTDQ-DA affected the hypoxanthine/xanthine oxidase superoxide generating system, nor did they inhibit xanthine oxidase directly.