Benzo[a]pyrene and Benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide induced locomotor and reproductive senescence and altered biochemical parameters of oxidative damage in Canton-S Drosophila melanogaster

Abstract

Benzo[a]pyrene (B[a]P) is a polycyclic aromatic hydrocarbon (PAH) commonly found in cigarette smoke, automobile exhaust fumes, grilled meat, and smoked food among others. Exposure to B[a]P is associated with a range of toxic effects including developmental, neurological, oxidative, inflammatory, mutagenic, carcinogenic and mortal. Efficient and more affordable experimental models like Drosophila melanogaster could provide more insight into the mechanism of PAH toxicity and help develop new strategies for prevention, diagnosis and treatment of PAH-related conditions. In this study, we examined the induction of some biochemical changes along with mortality and functional senescence by B[a]P and its metabolite, benzo[a]pyrene- 7,8-dihydrodiol-910-epoxide (BPDE) in the Canton-S strain of Drosophila melanogaster, with the aim to establish an alternative assay medium for B[a]P toxicity in flies. Flies were exposed to 2-200 μM of B[a]P and 1-10 μM of BPDE through diet for a seven-day survival assay followed by a four-day treatment to determine the effects of the compounds on negative geotaxis, fecundity and some biochemical parameters of oxidative damage. BPDE significantly reduced the survival rate of flies along the 7 days of exposure whereas B[a]P did not cause any significant change in the survival rate of flies. B[a]P and BPDE significantly reduced the climbing ability of flies after 4 days of exposure. Rate of emergence of flies significantly reduced at 10-200 μM of B[a]P and 5-10 μM of BPDE. Both compounds caused various levels of alterations in the values of reduced glutathione (GSH), total thiol (T-SH), glutathione-S-transferase (GST), catalase (CAT), hydrogen peroxide (H₂O₂), nitric oxide (NO) and acetylcholinesterase (AChE) of the flies. The compounds also exhibited high binding affinities and molecular interactions with the active site amino acid residues of Drosophila GST and the inhibitor binding site of Drosophila AChE in an in silico molecular docking analysis, with BPDE forming stable hydrogen bonds with AChE. Hence, the Canton-S strain of Drosophila melanogaster could offer a simple and affordable assay medium to study B[a]P toxicity.

Keywords: Acetylcholinesterase; Benzo[a]pyrene; Benzo[a]pyrene- 7, 8-dihydrodiol-9,10-epoxide; Canton-S; Drosophila melanogaster; Glutathione-S-transferase; Molecular docking.

Graphical abstract

Fig. 1

Percentage Survival of flies exposed to various concentrations of B[a]P for 7 days.

Fig. 2

Percentage Survival of flies exposed to various concentrations of BPDE for 7 days. * Significantly lower (p < 0.05) compared with the control.

Fig. 3

Percentage negative geotaxis and rate of emergence of flies exposed to B[a]P for 4 days. * Significantly lower (p < 0.05) compared with the control.

Fig. 4

Percentage negative geotaxis and rate of emergence of flies exposed to BPDE for 4 days. * Significantly lower (p < 0.05) compared with the control.

Fig. 5

Changes in the levels of biochemical parameters (Glutathione-S-Transferase, catalase and acetylcholinesterase activities; and reduced glutathione, total thiol, hydrogen peroxide and nitric oxide concentrations) after 4 days exposure of D. melanogaster to B[a]P. * Significantly different (p < 0.05) compared with the control.

Fig. 6

Changes in the levels of biochemical parameters (Glutathione-S-Transferase, catalase and acetylcholinesterase activities; and reduced glutathione, total thiol, hydrogen peroxide and nitric oxide concentrations) after 4 days exposure of D. melanogaster to BPDE. * Significantly lower (p < 0.05) compared with the control.

Fig. 7

3D (left) and 2D (right) views of the molecular interactions of amino-acid residues of glutathione – S - transferase with the substrate (glutathione), the standard inhibitor (NBDHEX), B[a]P and BPDE.

Fig. 8

3D (left) and 2D (right) views of the molecular interactions of amino-acid residues of acetylcholinesterase with the substrate (acetylcholine), the standard inhibitor (galantamine), B[a]P and BPDE.