The desert woodrat (Neotoma lepida) induces a diversity of biotransformation genes in response to creosote bush resin

Liver biotransformation enzymes have long been thought to enable animals to feed on diets rich in xenobiotic compounds. However, despite decades of pharmacological research in humans and rodents, little is known about hepatic gene expression in specialized mammalian herbivores feeding on toxic diets. Leveraging a recently identified population of the desert woodrat (Neotoma lepida) found to be highly tolerant to toxic creosote bush (Larrea tridentata), we explored the expression changes of suites of biotransformation genes in response to diets enriched with varying amounts of creosote resin. Analysis of hepatic RNA-seq data indicated a dose-dependent response to these compounds, including the upregulation of several genes encoding transcription factors and numerous phase I, II, and III biotransformation families. Notably, elevated expression of five biotransformation families - carboxylesterases, cytochromes P450, aldo-keto reductases, epoxide hydrolases, and UDP-glucuronosyltransferases - corresponded to species-specific duplication events in the genome, suggesting that these genes play a prominent role in N. lepida's adaptation to creosote bush. Building on pharmaceutical studies in model rodents, we propose a hypothesis for how the differentially expressed genes are involved in the biotransformation of creosote xenobiotics. Our results provide some of the first details about how these processes likely operate in the liver of a specialized mammalian herbivore.

Characteristics of cytochrome P450-dependent metabolism against acetamiprid in the musk shrew (Suncus murinus)

Soricidae spp. (shrews) play an essential role in soil ecosystems and, due to their habitat and behavior, are exposed to soil pollutants, such as pesticides. Still, toxicity risk in Soricidae spp. has not been appropriately assessed. In this study, the musk shrew (Suncus murinus) was used as a model organism for toxicity assessment in Soricidae. Considering their carnivorous diet, it is reasonable to assume that the musk shrew has unique metabolic traits that are different from those of other common experimental models. This study describes the cytochrome P450 (CYP)-dependent metabolism affected by acetamiprid (ACP), a neonicotinoid insecticide. Pharmacokinetics analysis, an in vitro metabolic assay, and genetic analysis of CYP were performed and compared with data from mice and rats. Through phylogenetic and syntenic analyses, three families of CYP were identified in the musk shrew. Pharmacokinetic analysis showed that the blood concentration of ACP decreased more quickly in musk shrews than in mice. Moreover, the in vitro metabolic assay suggested more efficient metabolic responses toward ACP in musk shrews than in mice or rats. One of the CYP2A isoforms in musk shrews might be linked to a better ACP metabolism. From the results above, we describe novel metabolic traits of the musk shrew. Future research on recombinant CYP enzymes is necessary to fully understand CYP-dependent metabolism of xenobiotics in musk shrews.

Characteristics of cytochrome P450-dependent metabolism in the liver of the wild raccoon, Procyon lotor

Wildlife is exposed to a wide range of xenobiotics in the natural environment. In order to appropriately assess xenobiotic-induced toxicity in wildlife, it is necessary to understand metabolic capacities. Carnivores, in general, have low metabolic abilities, making them vulnerable to a variety of chemicals. Raccoons (Procyon lotor) in the wild have been found to have high levels of xenobiotics. However, little is known about the metabolic capacity of the cytochrome P450 (CYP) enzymes in this species. Thus, this study used liver samples to investigate the characteristics of CYP enzymes in wild raccoons. In 22 wild raccoons, CYP concentrations in hepatic microsomes were examined. To better understand the properties of CYP-dependent metabolism, in vitro metabolic activity studies were performed using ethoxyresorufin, pentoxyresorufin and testosterone as substrates. In addition, three raccoons were fed commercial dog food in the laboratory for one week, and the effects on CYP-dependent metabolism were investigated. In comparison to other mammalian species, raccoons had very low concentrations of CYP in their livers. In an in vitro enzymatic analysis, raccoons' ethoxyresorufin O-deethylase (EROD) and pentoxyresorufin O-depentylase (PROD) metabolic capacities were less than one-fifth and one-tenth of rats', respectively. These results indicate the possible high risk in raccoons if exposed to high levels of environmental xenobiotics because of their poor CYP activity. In this study, the features of CYP-dependent metabolism in wild raccoons are described for the first time.

Duplication, Loss, and Evolutionary Features of Specific UDP-Glucuronosyltransferase Genes in Carnivora (Mammalia, Laurasiatheria)

UDP-glucuronosyltransferases (UGTs) are one of the most important enzymes for xenobiotic metabolism or detoxification. Through duplication and loss of genes, mammals evolved the species-specific variety of UGT isoforms. Among mammals, Carnivora is one of the orders that includes various carnivorous species, yet there is huge variation of food habitat. Recently, lower activity of UGT1A and 2B were shown in Felidae and pinnipeds, suggesting evolutional loss of these isoforms. However, comprehensive analysis for genetic or evolutional features are still missing. This study was conducted to reveal evolutional history of UGTs in Carnivoran species. We found specific gene expansion of UGT1As in Canidae, brown bear and black bear. We also found similar genetic duplication in UGT2Bs in Canidae, and some Mustelidae and Ursidae. In addition, we discovered contraction or complete loss of UGT1A7–12 in phocids, some otariids, felids, and some Mustelids. These studies indicate that even closely related species have completely different evolution of UGTs and further imply the difficulty of extrapolation of the pharmacokinetics and toxicokinetic result of experimental animals into wildlife carnivorans.