CncC-Keap1-P450s pathway is involved in the detoxification of emamectin benzoate in the spongy moth Lymantria dispar

The detoxification of insecticides in insects is dependent on the expression and activity of multiple detoxification enzymes. As an important modulator of detoxification enzymes, the CncC-Keap1 pathway was involved in the detoxification of various pesticides. However, whether the CncC-Keap1 pathway is involved in the detoxification of emamectin benzoate (EMB) is unclear. In this study, we cloned the LdCncC and LdKeap1 from spongy moths (Lymantria dispar). Our results showed that EMB exposure induced oxidative stress, and activated the CncC-Keap1 pathway at mRNA and protein levels. Removing ROS by N-acetylcysteine remarkably decreased H2O2 levels and restored the expression of LdCncC and LdKeap1. The silencing LdCncC, not LdKeap1, by dsRNA significantly decreased the cytochrome P450 activities, and increased the sensitivity of larvae to EMB. Besides, the expression of CYP6B7v1, CYP321A7 and CYP4S4v1 were significantly decreased after silencing LdCncC. Notably, the knockdown of CYP6B7v1, CYP321A7 or CYP4S4v1 significantly increased the mortality induced by EMB exposure. Therefore, we proposed that activation of CncC-Keap1 pathway induced by ROS increased the detoxification of EMB in spongy moths by regulating the expression of CYP6B7v1, CYP321A7 and CYP4S4v1. Our study strengthened the understanding of the detoxification of EMB from the perspective of CncC-Keap1-P450s pathway.

Geranium intoxication induces detoxification enzymes in the Japanese beetle, Popillia japonica Newman

Popillia japonica is a generalist herbivore that feeds on >300 host plant species in at least 72 plant families. It is unknown why P. japonica, despite possessing active detoxification enzymes in its gut, is paralyzed when feeding on the petals of one of its preferred host plant, Pelargonium×hortorum, or on artificial diet containing quisqualic acid (QA), the active compound in zonal geranium. We hypothesized that Pelargonium×hortorum or QA do not induce activity of the cytochrome P450, glutathione S transferase (GST), and carboxylesterase (CoE) detoxification enzymes in P. japonica. In this study, P. japonica were fed petals of zonal geranium or agar plugs containing QA, or rose petals, another preferred but non-toxic host. Midgut enzyme activities of P450, GST, and CoE were then assayed after 6, 12, or 24h of feeding. In most cases, P450, GST, and CoE activities were significantly induced in P. japonica midguts by geranium petals and QA, though the induction was slower than with rose petals. Induced enzyme activity reached a peak at 24h after consumption, which coincides with the period of highest recovery from geranium and QA paralysis. This study shows that toxic geranium and QA induce detoxification enzyme activity, but the induced enzymes do not effectively protect P. japonica from paralysis by QA. Further investigation is required through in vitro studies to know if the enzymes induced by geranium are capable of metabolizing QA. This study highlights a rare physiological mismatch between the detoxification tool kit of a generalist and its preferred host.

Use of HμREL Human Coculture System for Prediction of Intrinsic Clearance and Metabolite Formation for Slowly Metabolized Compounds

Design of slowly metabolized compounds is an important goal in many drug discovery projects. Standard hepatocyte suspension intrinsic clearance (CLint) methods can only provide reliable CLint values above 2.5 μL/min/million cells. A method that permits extended incubation time with maintained performance and metabolic activity of the in vitro system is warranted to allow in vivo clearance predictions and metabolite identification of slowly metabolized drugs. The aim of this study was to evaluate the static HμREL coculture of human hepatocytes with stromal cells to be set up in-house as a standard method for in vivo clearance prediction and metabolite identification of slowly metabolized drugs. Fourteen low CLint compounds were incubated for 3 days, and seven intermediate to high CLint compounds and a cocktail of cytochrome P450 (P450) marker substrates were incubated for 3 h. In vivo clearance was predicted for 20 compounds applying the regression line approach, and HμREL coculture predicted the human intrinsic clearance for 45% of the drugs within 2-fold and 70% of the drugs within 3-fold of the clinical values. CLint values as low as 0.3 μL/min/million hepatocytes were robustly produced, giving 8-fold improved sensitivity of robust low CLint determination, over the cutoff in hepatocyte suspension CLint methods. The CLint values of intermediate to high CLint compounds were at similar levels both in HμREL coculture and in freshly thawed hepatocytes. In the HμREL coculture formation rates for five P450-isoform marker reactions, paracetamol (CYP1A2), 1-OH-bupropion (CYP2B6), 4-OH-diclofenac (CYP2C9), and 1-OH-midazolam (3A4) were within the range of literature values for freshly thawed hepatocytes, whereas 1-OH-bufuralol (CYP2D6) formation rate was lower. Further, both phase I and phase II metabolites were detected and an increased number of metabolites were observed in the HμREL coculture compared to hepatocyte suspension. In conclusion, HμREL coculture can be applied to accurately estimate intrinsic clearance of slowly metabolized drugs and is now utilized as a standard method for in vivo clearance prediction of such compounds in-house.