Metabolic activation and toxicological evaluation of polychlorinated biphenyls in Drosophila melanogaster

Abstract

Degradation of polychlorinated biphenyls (PCBs) is initiated by cytochrome P450 (CYP) enzymes and includes PCB oxidation to OH-metabolites, which often display a higher toxicity than their parental compounds. In search of an animal model reflecting PCB metabolism and toxicity, we tested Drosophila melanogaster, a well-known model system for genetics and human disease. Feeding Drosophila with lower chlorinated (LC) PCB congeners 28, 52 or 101 resulted in the detection of a human-like pattern of respective OH-metabolites in fly lysates. Feeding flies high PCB 28 concentrations caused lethality. Thus we silenced selected CYPs via RNA interference and analyzed the effect on PCB 28-derived metabolite formation by assaying 3-OH-2′,4,4′-trichlorobiphenyl (3-OHCB 28) and 3′-OH-4′,4,6′-trichlorobiphenyl (3′-OHCB 28) in fly lysates. We identified several drosophila CYPs (dCYPs) whose knockdown reduced PCB 28-derived OH-metabolites and suppressed PCB 28 induced lethality including dCYP1A2. Following in vitro analysis using a liver-like CYP-cocktail, containing human orthologues of dCYP1A2, we confirm human CYP1A2 as a PCB 28 metabolizing enzyme. PCB 28-induced mortality in flies was accompanied by locomotor impairment, a common phenotype of neurodegenerative disorders. Along this line, we show PCB 28-initiated caspase activation in differentiated fly neurons. This suggested the loss of neurons through apoptosis. Our findings in flies are congruent with observation in human exposed to high PCB levels. In plasma samples of PCB exposed humans, levels of the neurofilament light chain increase after LC-PCB exposure, indicating neuronal damage. In summary our findings demonstrate parallels between Drosophila and the human systems with respect to CYP mediated metabolism and PCB mediated neurotoxicity.

Ecdysteroid kinase-like (EcKL) paralogs confer developmental tolerance to caffeine in Drosophila melanogaster

“…While caffeine metabolites and other methylxanthines can have physiological effects in humans sometimes equal or exceeding that of caffeine itself ( Benowitz et al., 1995 ; Geraets et al., 2006 ; Malki et al., 2006 ), only limited data currently exist on the differential toxicity of caffeine and its metabolites in insects: theobromine appears less toxic than caffeine in D. melanogaster adults ( Matsagas et al., 2009 ); while caffeine, theophylline and theobromine are toxic to the pupal CNS of giant silkmoths (Lepidoptera: Bombycoidea), caffeine and theophylline are 3- to 4-fold more toxic than theobromine ( Blaustein and Schneiderman, 1960 ); and theophylline and theobromine are not toxic at daily doses of 5–10 µg in Vespa orientalis (Hymenoptera: Vespoidea) and Apis mellifera (Hymenoptera: Apoidea), unlike caffeine ( Ishay and Paniry, 1979 ). Additionally, despite being a canonical phase I detoxification reaction, hydroxylation can bioactivate some pro-toxic xenobiotic compounds ( Harrop et al., 2018 ; Idda et al., 2020 ; Salgado and David, 2017 ). As the metabolism of caffeine is poorly understood at a fine level of detail even in model insect species like D. melanogaster , the relative change in toxicity of caffeine at each step of its metabolism in insects remains to be determined.…”

A cell atlas of the fly kidney

“…Cyp4e3 has been associated with permethrin insecticide resistance (Terhzaz et al, 2015) and Cyp12a5 in Nitenpyram resistance (Harrop et al 2018). Cyp307a2 , Cyp18a1 , and Cyp312a1 are involved in degradation of polychlorinated biphenyls (Idda et al, 2020), and Cyp12d1 impacts caffeine resistance (Najarro et al, 2015). Among these genes, Cyp6g1 , Cyp6A2 , Cyp4e3 , Cyp12a5 , Cyp307a2 , and Cyp12d1 are mainly expressed in PCs (Fig.…”

“…(A) Insecticide- and drug-related P450 genes in the fly (based on Seong et al, 2020; Bergé et al, 1998; Terhzaz et al, 2015; Harrop et al 2018; Idda et al, 2020; Najarro et al, 2015). (B) Expression levels of each P450 gene visualized by UMAP plots.…”

The use of fly artifacts in a crime scene: Is there any application for forensic toxicology?

“…This might be due both to the spontaneous degradation of cocaine to benzoylecgonine at room temperature once deposited onto the surface, and/or to the influence of the digesting activity of flies (i.e., defecated FA). Although flies are evolutionally distant from human, fly tissues, and biological processes showed equivalent and in some studies flies are used as model system for human disease [20,21]. On this base, we can assume that enzymes and metabolic pathways involved in cocaine and heroin detoxification are similar to humans, producing the same metabolites.…”

“…Although flies are evolutionally distant from human, fly tissues, and biological processes showed equivalent and in some studies flies are used as model system for human disease [20,21]. On this base, we can assume that enzymes and metabolic pathways involved in cocaine and heroin detoxification are similar to humans, producing the same metabolites.…”