Biocatalytic conversion and detoxification of imipramine by the laccase-mediated system

- Laccase showed a high potential activity to remove imipramine and clomipramine.
- Amitriptyline, doxepin, and nortriptyline are resistant to laccase-mediated system.
- Reduction in toxicity on Caco-2 cells was observed in the case of imipramine.
- Main factors affecting the biotreatment of imipramine were optimized.
- Metabolite was purified and identified on the basis of its spectroscopic analyses.

This study describes the enzymatic elimination of imipramine and four other tricyclic antidepressants (TCAs) by laccase-mediated catalysis in aqueous solution. The results showed that TCAs demonstrated dissimilar enzymatic elimination behavior: up to 67% of clomipramine and 82% of imipramine were significantly removed during the first 6 h. The elimination percentages of amitriptyline, doxepin, and nortriptyline were 11%, 6%, and 23%, respectively, after 72 h laccase-based treatment. Due to the rapid and high percentage of removal, imipramine was selected for detailed toxicity evaluation. Optimal levels for the main factors in the enzymatic removal process of imipramine were obtained as pH (4.9), incubation time (5.7 h), imipramine concentration (0.12 μg mL−1), and enzyme activity (1.63 U mL−1). Laccase-catalyzed transformation of imipramine led to the formation of an unknown metabolite which was subsequently purified and spectroscopically characterized as 3-(2,7-dihydroxy-10,11-dihydro-5H-dibenzo[b,f]azepin-5-yl)-1-hydroxy-N,N-dimethyl-3-oxopropan-1-amine oxide. The toxicity reduction of the bio-product was assessed by MTT cell and Caco-2 cell line.