Evidence Of Hepatic Flavin Containing Monooxygenases In Food Producing Species

Benzydamine hydrochloride (BZ) is an anti-inflammatory drug used in human and veterinary therapy. Its main metabolites reported in man and rodents are N-demethylbenzydamine (Nor-BZ) and benzydamine N-oxide (BZ-NO) [1]. The latter is the most important unconjugated metabolite of BZ and its production is catalysed in vitro by flavin-containing monooxygenases (FMO) [1; 2]. Despite the use of BZ in veterinary practice, no information is available on its metabolism in domestic animals. Thus to assess the role played by hepatic FMO and cytochrome P450 enzymes and to check whether BZ could be a specific FMO substrate marker also in veterinary species, BZ (1-1000µM) oxidation was studied in microsomes prepared from livers of cattle, pigs, horses, turkeys and rabbits. In all species at least two main metabolites were produced and identified as Nor-BZ and BZ-NO by matching the LC-MS spectra of authentic compounds [3]. Table 1. Kinetic parameters of BZ-NO production in liver microsomes. Bovine Rabbit Swine Horse Turkey Km (µM) 16.16±0.28 39.40±0.49 19.62±1.78 15.27±2.38 47.37±10.3 Vmax (nmoli/mg.min) 4.32±0.52 4.99±0.54 10.75±0.34 1.26±0.06 3.06±0.31 Following heat inactivation of microsome protein, the decrease of BZ-NO production, by incubated BZ (2.5-100µM), was up to 80% in swine, horse, cattle and rabbits, but only 35% in turkeys. Methimazole (2.5–50µM) incubation reduced the BZ-NO production up to 50%. Preliminary results with trimethylamine up to 50 µM did not inhibit the production of BZ-NO. To date the results obtained could support the role of BZ as a marker of FMO. Whether the demethylation of BZ to Nor-BZ occurs by dealkylation catalysed by P450 or via N-oxide dealkylation and subsequent reduction, or by both reactions is still under investigation. Researches supported by MURST grants (ex 40% and ex 60% 1998).