Inhibition of cytochrome P450 1A2-mediated metabolism and production of reactive oxygen species by heme oxygenase-1 in rat liver microsomes

Bifenthrin induces changes in clinical poisoning symptoms, oxidative stress, DNA damage, histological characteristics, and transcriptome in Chinese giant salamander (Andrias davidianus) larvae

Bifenthrin (BF) is a broad-spectrum insecticide that has gained widespread use due to its high effectiveness. However, there is limited research on the potential toxic effects of bifenthrin pollution on amphibians. This study aimed to investigate the 50 % lethal concentration (LC50) and safety concentration of Chinese giant salamanders (CGS) exposed to BF (at 0, 6.25,12.5,25 and 50 μg/L BF) for 96 h. Subsequently, CGS were exposed to BF (at 0, 0.04, and 4 μg/L BF) for one week to investigate its toxic effects. Clinical poisoning symptoms, liver pathology, oxidative stress factors, DNA damage, and transcriptome differences were observed and analyzed. The results indicate that exposure to BF at 4 μg/L significantly decreased the adenosine-triphosphate (ATP), superoxide dismutase (SOD), glutathione (GSH), and catalase (CAT) contents in the brain, liver, and kidney of CGS. Additionally, the study found that the malondialdehyde (MDA), reactive oxygen species (ROS), and 8-hydroxydeoxyguanosine (8-OHdG) contents were increased. The liver tissue exhibited significant inflammatory reactions and structural malformations. RNA-seq analysis of the liver showed that BF caused abnormal antioxidant indices of CGS. This affected molecular function genes such as catalytic activity, ATP-dependent activity, metabolic processes, signaling and immune system processes, behavior, and detoxification, which were significantly upregulated, resulting in the differential genes significantly enriched in the calcium signaling pathway, PPARα signaling pathway and NF-kB signaling pathway. The results suggest that BF induces the abnormal production of free radicals, which overwhelms the body's self-defense system, leading to varying degrees of oxidative stress. This can result in oxidative damage, DNA damage, abnormal lipid metabolism, autoimmune diseases, clinical poisoning symptoms, and tissue inflammation. This work provides a theoretical basis for the rational application of bifenthrin and environmental risk assessment, as well as scientific guidance for the conservation of amphibian populations.

Identification of the contact region responsible for the formation of the homomeric CYP1A2•CYP1A2 complex

Previous studies showed that cytochrome P450 1A2 (CYP1A2) forms a homomeric complex that influences its metabolic characteristics. Specifically, CYP1A2 activity exhibits a sigmoidal response as a function of NADPH-cytochrome P450 reductase (POR) concentration and is consistent with an inhibitory CYP1A2•CYP1A2 complex that is disrupted by increasing [POR] (Reed et al. (2012) Biochem. J. 446, 489-497). The goal of this study was to identify the CYP1A2 contact regions involved in homomeric complex formation. Examination of X-ray structure of CYP1A2 implicated the proximal face in homomeric complex formation. Consequently, the involvement of residues L91-K106 (P1 region) located on the proximal face of CYP1A2 was investigated. This region was replaced with the homologous region of CYP2B4 (T81-S96) and the protein was expressed in HEK293T/17 cells. Complex formation and its disruption was observed using bioluminescence resonance energy transfer (BRET). The P1-CYP1A2 (CYP1A2 with the modified P1 region) exhibited a decreased BRET signal as compared with wild-type CYP1A2 (WT-CYP1A2). On further examination, P1-CYP1A2 was much less effective at disrupting the CYP1A2•CYP1A2 homomeric complex, when compared with WT-CYP1A2, thereby demonstrating impaired binding of P1-CYP1A2 to WT-CYP1A2 protein. In contrast, the P1 substitution did not affect its ability to form a heteromeric complex with CYP2B4. P1-CYP1A2 also showed decreased activity as compared with WT-CYP1A2, which was consistent with a decrease in the ability of P1-CYP1A2 to associate with WT-POR, again implicating the P1 region in POR binding. These results indicate that the contact region responsible for the CYP1A2•CYP1A2 homomeric complex resides in the proximal region of the protein.

Heteromeric complex formation between human cytochrome P450 CYP1A1 and heme oxygenase-1

P450 and heme oxygenase-1 (HO-1) receive their necessary electrons by interaction with the NADPH-cytochrome P450 reductase (POR). As the POR concentration is limiting when compared with P450 and HO-1, they must effectively compete for POR to function. In addition to these functionally required protein-protein interactions, HO-1 forms homomeric complexes, and several P450s have been shown to form complexes with themselves and with other P450s, raising the question, 'How are the HO-1 and P450 systems organized in the endoplasmic reticulum?' Recently, CYP1A2 was shown to associate with HO-1 affecting the function of both proteins. The goal of this study was to determine if CYP1A1 formed complexes with HO-1 in a similar manner. Complex formation among POR, HO-1, and CYP1A1 was measured using bioluminescence resonance energy transfer, with results showing HO-1 and CYP1A1 form a stable complex that was further stabilized in the presence of POR. The POR•CYP1A1 complex was readily disrupted by the addition of HO-1. CYP1A1 also was able to affect the POR•HO-1 complex, although the effect was smaller. This interaction between CYP1A1 and HO-1 also affected function, where the presence of CYP1A1 inhibited HO-1-mediated bilirubin formation by increasing the KmPOR•HO-1 without affecting the Vmaxapp. In like manner, HO-1 inhibited CYP1A1-mediated 7-ethoxyresorufin dealkylation by increasing the KmPOR•CYP1A1. Based on the mathematical simulation, the results could not be explained by a model where CYP1A1 and HO-1 simply compete for POR, and are consistent with the formation of a stable CYP1A1•HO-1 complex that affected the functional characteristics of both moieties.

Improving Antibody Production in Stably Transfected CHO Cells by CRISPR-Cas9-Mediated Inactivation of Genes Identified in a Large-Scale Screen with Chinese Hamster-Specific siRNAs

The Chinese hamster ovary (CHO) cell line is commonly used for the production of biotherapeutics. As cell productivity directly affects the cost of production, methods are developed to manipulate the expression of specific genes that are known to be involved in protein synthesis, folding, and secretion to increase productivity. However, there are no large-scale CHO-specific functional screens to identify novel gene targets that impact the production of secreted recombinant proteins. Here, a large-scale, CHO cell-specific small interfering RNA screen is performed to identify genes that consistently enhance antibody production when silenced in a panel of seven CHO cell lines. Four genes, namely, Cyp1a2, Atp5s, Dgki, and P3h2, are identified, and then selected for CRISPR-Cas9 knockout validation in recombinant CHO cell lines. Single knockout of Cyp1a2, Atp5s, or Dgki, but not P3h2, results in a more than 90% increase in specific antibody productivity. Overall, the knockout of Cyp1a2 demonstrates the most significant improvement of antibody production, with a minimal impact on cell growth.

Occurrence, formation, environmental fate and risks of environmentally persistent free radicals in biochars

Biochars are used globally in agricultural crop production and environmental remediation. However, environmentally persistent free radicals (EPFRs), which are stable emerging pollutants, are generated as a characteristic feature during biomass pyrolysis. EPFRs can induce the formation of reactive oxygen species, which poses huge agro-environmental and human health risks. Their half-lives and persistence in both biochar residues and in the atmosphere may lead to potentially adverse risks in the environment. This review highlights the comprehensive research into these bioreactive radicals, as well as the bottlenecks of biochar production leading up to the formation and persistence of EPFRs. Additionally, a way forward has been proposed, based on two main recommendations. A global joint initiative to create an all-encompassing regulations policy document that will improve both the technological and the quality control aspects of biochars to reduce EPFR generation at the production level. Furthermore, environmental impact and risk assessment studies should be conducted in the extensive applications of biochars in order to protect the environmental and human health. The highlighted key research directions proposed herein will shape the production, research, and adoption aspects of biochars, which will mitigate the considerable concerns raised on EPFRs.

T-2 toxin neurotoxicity: role of oxidative stress and mitochondrial dysfunction

Mycotoxins are highly diverse secondary metabolites produced in nature by a wide variety of fungi. Mycotoxins cause animal feed and food contamination, resulting in mycotoxicosis. T-2 toxin is one of the most common and toxic trichothecene mycotoxins. For the last decade, it has garnered considerable attention due to its potent neurotoxicity. Worryingly, T-2 toxin can cross the blood-brain barrier and accumulate in the central nervous system (CNS) to cause neurotoxicity. This review covers the current knowledge base on the molecular mechanisms of T-2 toxin-induced oxidative stress and mitochondrial dysfunction in the CNS. In vitro and animal data have shown that induction of reactive oxygen species (ROS) and oxidative stress plays a critical role during T-2 toxin-induced neurotoxicity. Mitochondrial dysfunction and cascade signaling pathways including p53, MAPK, Akt/mTOR, PKA/CREB and NF-κB contribute to T-2 toxin-induced neuronal cell death. T-2 toxin exposure can also result in perturbations of mitochondrial respiratory chain complex and mitochondrial biogenesis. T-2 toxin exposure decreases the mitochondria unfolded protein response and dampens mitochondrial energy metabolism. Antioxidants such as N-acetylcysteine (NAC), activation of Nrf2/HO-1 and autophagy have been shown to provide a protective effect against these detrimental effects. Clearly, translational research and the discovery of effective treatment strategies are urgently required against this common food-borne threat to human health and livestock.

Assessing Anticancer Potential of Blueberry Flavonoids, Quercetin, Kaempferol, and Gentisic Acid, Through Oxidative Stress and Apoptosis Parameters on HCT-116 Cells

In recent years, natural products gained popularity with their anti-inflammatory and antioxidant effects mediated by chemical compounds within their composition. Study results offering them as palliative therapy options in cancer or as anticancer agents with high levels of cytotoxicity brought a new approach to combine cancer treatment protocols with these products. From a different perspective, edible types of these products are suggested in daily diets due to their potential cancer preventive effects. Our preliminary work was on blueberry extracts (Vaccinium myrtillus) as a main representative of these natural products, and the contents of the extracts were analyzed with liquid chromatography tandem mass spectrometry (LC MS/MS) to reveal the composition and distribution of polyphenolic compounds within. The most abundant polyphenols detected in V. myrtillus extracts were quercetin, kaempferol, and a phenolic acid, gentisic acid (GA). The compounds were further evaluated on treated HCT-116 cells for their potential anticancer effects by measuring total antioxidant status, total oxidant status, and 8-hydroxydeoxyguanosine levels for evaluation of oxidative stress and through protein array analysis and flow cytometric analysis for evaluation of apoptosis. In analysis of oxidative stress parameters, reduced total oxidant levels and reduced oxidative stress index levels were found in cells treated with the compounds in comparison with untreated cells. In apoptosis-related protein profiles, at least twofold reduction in various apoptotic proteins was observed after quercetin and kaempferol treatment, whereas a different profile was observed for GA. Overall, results of this study showed that quercetin and kaempferol have strong cytotoxic, antioxidant, and apoptotic effects, although GA is mostly effective as an antioxidant polyphenol on HCT-116 cells.

Oxidative stress and cell death induction by amitraz and its metabolite BTS-27271 mediated through cytochrome P450 and NRF2 pathway alteration in primary hippocampal cell

Amitraz is a neurotoxic formamidine pesticide that induces cell death in hippocampal neurons, although its mechanisms are unknown. Amitraz produces reactive oxygen species (ROS), which could lead to cell death. Amitraz was shown to induce different cytochrome P450 (CYP) isoenzymes involved with ROS and apoptotic cell death induction. Finally, amitraz was described to decrease the activity of antioxidant enzymes regulated through KEAP1/NRF2 pathway, thus likely leading to a reduction of ROS elimination and to cell death induction. We evaluated the effect of amitraz or BTS-27271 co-treatment with or without the antioxidant N-acetylcysteine and/or the unspecific CYP inhibitor 1-aminobenzotriazole on cell viability and its related mechanisms in wild type and silenced primary hippocampal neurons after 24 h treatment. We observed that amitraz produced oxidative stress and CYPs induction leading to apoptotic cell death. ROS generation was partially mediated by CYPs induction and downregulation of NRF2-pathway through KEAP1 overexpression. These data could help explain the mechanism by which amitraz induces cell death and oxidative stress and provide a therapeutic strategy to protect against this effect in case of poisoning.

The role of mitochondrial defects and oxidative stress in Alzheimer's disease

Alzheimer's disease (AD) is a complex, progressive, and irreversible neurodegenerative disorder. Recent reports suggest that it affects more than 36 million people worldwide and accounts 60-80% of all cases of dementia. It is characterised by aberrations of multiple interactive systems and pathways, which ultimately lead to memory loss and cognitive dysfunction. The exact mechanisms and initial triggering factors that underpin the known pathological defects in AD remain to be fully elucidated. In addition, an effective treatment strategy to reduce the progression of AD is yet to be achieved. In the light of above-mentioned facts, our article deals with the exploration of the mitochondrial defect and oxidative stress leading to this devastating disease. In this communication, we have highlighted specific mitochondrial and antioxidant-directed approach to ameliorate and manage AD. Nonetheless, new approaches should also be investigated that could tackle various molecular events involved in AD pathogenicity.

Behavioral, molecular and physiological responses of embryo-larval zebrafish exposed to types I and II pyrethroids

Pyrethroids are potent neurotoxicants that may elicit multiple pathways of toxicity in non-target organisms. Comparative studies on the mechanistic and developmental effects of types I and II pyrethroids against non-target aquatic species are limited. This study assessed the effects of the two pyrethroid types against embryo-larval zebrafish (Danio rerio) at environmentally relevant and laboratory concentrations. Zebrafish embryos were exposed to type-I (permethrin, bifenthrin) and type-II (deltamethrin, λ-cyhalothrin, fenvalerate, esfenvalerate) pyrethroids at 1000, 10, 0.1, 0.01, 0.0 μg/L, starting at 5-h post-fertilization (hpf) through 5-d post-fertilization (dpf) under static exposure conditions. Swimming behavior (distance traveled and velocity) was assessed at 5-dpf. The relative expression of Nrf2a, GST, Casp-9 and p53 mRNA transcripts, carboxyl esterase (CES) activity and total reactive oxygen species (ROS) were measured. The stability of the pyrethroids across 5 days was analyzed. Bifenthrin-(10 μg/L) and esfenvalerate-(1000 μg/L) significantly (p < 0.05) reduced total distance traveled by larvae while 1000 μg/L deltamethrin and λ-cyhalothrin were lethal causing body axis curvature and pericardial edema. At environmentally relevant concentrations-(μg/L) compared to control, permethrin-(0.122) upregulated Nrf2a and Casp-9 expressions while λ-cyhalothrin-(0.053) downregulated Nrf2a and fenvalerate-0.037 downregulated GST. At laboratory concentrations-(μg/L), permethrin-(1000) upregulated Nrf2a, Casp-9 and p53 expressions, bifenthrin-(10) upregulated Casp-9 while fenvalerate-(0.1) and esfenvalerate-(1000) downregulated GST. There was concentration dependent increase in CES activity which correlated positively with total ROS. Pyrethroid concentrations decreased significantly by day 5. This study showed disparity in the mechanistic effects across the pyrethroids types and their instability in aqueous media may underestimate toxicity against non-target aquatic species when exposed in their natural environment.

Cardiovascular Disease: An Introduction

Cardiovascular disease (CVD) is a collective term designating all types of affliction affecting the blood circulatory system, including the heart and vasculature, which, respectively, displaces and conveys the blood.

Characterization of Interactions Among CYP1A2, CYP2B4, and NADPH-cytochrome P450 Reductase: Identification of Specific Protein Complexes

Cytochromes P450s (P450s) catalyze oxygenation reactions via interactions with their redox partners. However, other proteins, particularly other P450s, also have been shown to form complexes that modulate P450 function. Previous studies showed that CYP1A2 and CYP2B4 form a complex when reconstituted into phospholipid vesicles; however, details of the interactions among the P450s and NADPH-cytochrome P450 reductase (POR) have not been fully characterized. The goal of this study was to examine P450 complex formation in living cells, using bioluminescence resonance energy transfer (BRET). Various pairs of P450 and POR constructs were tagged with either green fluorescent protein or Renilla luciferase, and transfected into human embryonic kidney 293T cells. Complexes were demonstrated by measuring energy transfer between the tags, and disruption of the complex was verified by cotransfection with unlabeled P450-system proteins. CYP1A2 and CYP2B4 formed a stable complex that could not be disrupted by cotransfection of untagged POR. Interactions of both P450s with POR were detected, with untagged CYP1A2 disrupting the POR-CYP2B4 interaction. In contrast, untagged CYP2B4 did not affect the POR-CYP1A2 interaction. These data are consistent with POR preferentially binding to the CYP1A2 moiety of CYP1A2-CYP2B4. BRET-detectable homomeric CYP1A2-CYP1A2 also was detected, and was disrupted by cotransfection of either POR or CYP2B4. Both CYP1A2 and CYP2B4 activities were affected by their coexpression in a manner consistent with formation of the high-affinity POR-CYP1A2-CYP2B4 complex. These findings demonstrate that CYP1A2 and CYP2B4 form a heteromeric POR-CYP1A2-CYP2B4 complex in living cells that has altered catalytic activities relative to the homomeric enzymes.

The functional effects of physical interactions involving cytochromes P450: putative mechanisms of action and the extent of these effects in biological membranes

Cytochromes P450 represent a family of enzymes, which are responsible for the oxidative metabolism of a wide variety of xenobiotics. Although the mammalian P450s require interactions with their redox partners in order to function, more recently, P450 system proteins have been shown to exist as multi-protein complexes that include the formation of P450•P450 complexes. Evidence has shown that the metabolism of some substrates by a given P450 can be influenced by the specific interaction of the enzyme with other forms of P450. Detailed kinetic analysis of these reactions in vitro has shown that the P450-P450 interactions can alter metabolism by changing the ability of a P450 to bind to its cognate redox partner, NADPH-cytochrome P450 reductase; by altering substrate binding to the affected P450; and/or by changing the rate of a catalytic step of the reaction cycle. This review summarizes the known examples of P450-P450 interactions that have been shown in vitro to influence metabolism and categorizes them according to the mechanism(s) causing the effects. P450-P450 interactions have the potential to cause major changes in the metabolism and elimination of drugs in vivo. This review summarizes the evidence that the P450-P450 interactions influence metabolism in biological membranes and discusses the studies, which will provide further insight into the extent of these effects in the future.

Dual character of flavonoids in attenuating and aggravating ischemia-reperfusion-induced myocardial injury

The concept that flavonoids exert cardioprotection against myocardial ischemia-reperfusion (I/R) injury has been acknowledged by a large body of evidence. However, recent studies reported cardiotoxic effects of certain flavonoids, while the underlying mechanisms have remained largely elusive. Flavonoids have been demonstrated to activate aryl hydrocarbon receptor (Ahr), which is implicated in an array of cell signaling processes. The present study examined the cardioprotective roles of quercetin (Qu) and β-naphthoflavone (β-NF) against I/R injury and explored whether the underlying mechanism proceeds via molecular signaling downstream of Ahr. An oxygen glucose deprivation/reoxygenation (OGD/R) model of I/R was established in myocardial H9c2 cells in the absence or presence of Qu or β-NF. Qu as well as β-NF reversed OGD/R-induced overproduction of reactive oxygen species by increasing the anti-oxidative capacity of the cells and protected them from lethal injury, as demonstrated by a decreased cell death rate, lactate hydrogenase leakage and caspase-3 activity as determined by flow cytometry, colorimetric assay and western blot analysis, respectively. Immunocytochemistry, co-immunoprecipitation and western blot assays collectively revealed that Qu and β-NF engendered the translocation of Ahr from the cytoplasm into the cell nucleus, where binding of Ahr with the Ahr nuclear translocator (ARNT) blocked its binding to hypoxia-inducible factor (HIF)-1α, which inhibited the cardioprotection of HIF-1α, including the induction of nitric oxide (NO) and inhibition of vascular endothelial growth factor (VEGF) production. Ahr knockdown recovered the binding of ARNT to HIF-1α and the generation of NO and VEGF. The results of the present study suggested a dual character of Qu and β-NF in the process of myocardial I/R.

Assembly of Dynamic P450-Mediated Metabolons-Order Versus Chaos

Purpose of Review

We provide an overview of the current knowledge on cytochrome P450-mediated metabolism organized as metabolons and factors that facilitate their stabilization. Essential parameters will be discussed including those that are commonly disregarded using the dhurrin metabolon from Sorghum bicolor as a case study.

Recent Findings

Sessile plants control their metabolism to prioritize their resources between growth and development, or defense. This requires fine-tuned complex dynamic regulation of the metabolic networks involved. Within the recent years, numerous studies point to the formation of dynamic metabolons playing a major role in controlling the metabolic fluxes within such networks.

Summary

We propose that P450s and their partners interact and associate dynamically with POR, which acts as a charging station possibly in concert with Cytb5. Solvent environment, lipid composition, and non-catalytic proteins guide metabolon formation and thereby activity, which have important implications for synthetic biology approaches aiming to produce high-value specialized metabolites in heterologous hosts.

α- and β-Naphthoflavone synergistically attenuate H2O2-induced neuron SH-SY5Y cell damage

Previous studies have demonstrated an association between neurological diseases and oxidative stress (OS). Naphthoflavone is a synthetic derivative of naturally occurring flavonoids that serves an important role in the treatment and prevention of OS-related diseases. The current study was designed to apply α- and β-Naphthoflavone individually and in combination to counteract the detrimental effects of OS on neurons in vitro. Neuronal SH-SY5Y cells were subjected to 20 µM H₂O₂, followed by exposure to 20 µM α-Naphthoflavone and/or 10 µM β-Naphthoflavone. Results indicated that α- and β-Naphthoflavone effectively antagonized the apoptosis-promoting effect of H₂O₂ on neuronal SH-SY5Y cells, and that β-Naphthoflavone significantly (P<0.05) reversed H₂O₂-inhibited cell viability. Notably, co-treatment of α- and β-Naphthoflavone reversed the H₂O₂-induced apoptosis rate elevation and cell viability reduction. Further analysis demonstrated that H₂O₂ inhibited the activities of antioxidant enzymes including catalase, superoxide dismutase and glutathione peroxidase, but this was reversed by the co-treatment with α- and β-Naphthoflavone and selectively enhanced by the treatment with α- or β-Naphthoflavone. H₂O₂-stimulated p38 mitogen-activated protein kinase activation was repressed following treatment with α- and/or β-Naphthoflavone, along with a decreased expression of the apoptosis-related factors and inhibited caspase-3 activation. In conclusion, co-treatment with α- and β-Naphthoflavone minimized H₂O₂-led neuron damage compared with treatment with α- or β-Naphthoflavone, suggesting a synergetic effect between α- and β-Naphthoflavone. This indicates that utilizing α- and β-Naphthoflavone together in the clinical setting may provide a novel therapeutic for neurological disease.

Immobilized Cytochrome P450 for Monitoring of P450-P450 Interactions and Metabolism

Cytochrome P450 (P450) protein-protein interactions have been shown to alter their catalytic activity. Furthermore, these interactions are isoform specific and can elicit activation, inhibition, or no effect on enzymatic activity. Studies show that these effects are also dependent on the protein partner cytochrome P450 reductase (CPR) and the order of protein addition to purified reconstituted enzyme systems. In this study, we use controlled immobilization of P450s to a gold surface to gain a better understanding of P450-P450 interactions between three key drug-metabolizing isoforms (CYP2C9, CYP3A4, and CYP2D6). Molecular modeling was used to assess the favorability of homomeric/heteromeric P450 complex formation. P450 complex formation in vitro was analyzed in real time utilizing surface plasmon resonance. Finally, the effects of P450 complex formation were investigated utilizing our immobilized platform and reconstituted enzyme systems. Molecular modeling shows favorable binding of CYP2C9-CPR, CYP2C9-CYP2D6, CYP2C9-CYP2C9, and CYP2C9-CYP3A4, in rank order.KDvalues obtained via surface plasmon resonance show strong binding, in the nanomolar range, for the above pairs, with CYP2C9-CYP2D6 yielding the lowestKD, followed by CYP2C9-CYP2C9, CYP2C9-CPR, and CYP2C9-CYP3A4. Metabolic incubations show that immobilized CYP2C9 metabolism was activated by homomeric complex formation. CYP2C9 metabolism was not affected by the presence of CYP3A4 with saturating CPR concentrations. CYP2C9 metabolism was activated by CYP2D6 at saturating CPR concentrations in solution but was inhibited when CYP2C9 was immobilized. The order of addition of proteins (CYP2C9, CYP2D6, CYP3A4, and CPR) influenced the magnitude of inhibition for CYP3A4 and CYP2D6. These results indicate isoform-specific P450 interactions and effects on P450-mediated metabolism.

The Localization of Cytochrome P450s CYP1A1 and CYP1A2 into Different Lipid Microdomains Is Governed by Their N-terminal and Internal Protein Regions

In cellular membranes, different lipid species are heterogeneously distributed forming domains with different characteristics. Ordered domains are tightly packed with cholesterol, sphingomyelin, and saturated fatty acids, whereas disordered domains contain high levels of unsaturated fatty acids. Our laboratory has shown that membrane heterogeneity affects the organization of cytochrome P450s and their cognate redox partner, the cytochrome P450 reductase (CPR). Despite the high degree of sequence similarity, CYP1A1 was found to localize to disordered regions, whereas CYP1A2 resided in ordered domains. We hypothesized that regions of amino acid sequence variability may contain signal motifs that direct CYP1A proteins into ordered or disordered domains. Thus, chimeric constructs of CYP1A1 and CYP1A2 were created, and their localization was tested in HEK293T cells. CYP1A2, containing the N-terminal regions from CYP1A1, no longer localized in ordered domains, whereas the N terminus of CYP1A2 partially directed CYP1A1 into ordered regions. In addition, intact CYP1A2 containing a 206-302-residue peptide segment of CYP1A1 had less affinity to bind to ordered microdomains. After expression, the catalytic activity of CYP1A2 was higher than that of the CYP1A1-CYP1A2 chimera containing the N-terminal end of CYP1A1 with subsaturating CPR concentrations, but it was approximately equal with excess CPR suggesting that the localization of the CYP1A enzyme in ordered domains favored its interaction with CPR. These data demonstrate that both the N-terminal end and an internal region of CYP1A2 play roles in targeting CYP1A2 to ordered domains, and domain localization may influence P450 function under conditions that resemble those found in vivo.

Environmentally persistent free radical-containing particulate matter competitively inhibits metabolism by cytochrome P450 1A2

Combustion processes generate different types of particulate matter (PM) that can have deleterious effects on the pulmonary and cardiovascular systems. Environmentally persistent free radicals (EPFRs) represent a type of particulate matter that is generated after combustion of environmental wastes in the presence of redox-active metals and aromatic hydrocarbons. Cytochromes P450 (P450/CYP) are membrane-bound enzymes that are essential for the phase I metabolism of most lipophilic xenobiotics. The EPFR formed by chemisorption of 2-monochlorophenol to silica containing 5% copper oxide (MCP230) has been shown to generally inhibit the activities of different forms of P450s without affecting those of cytochrome P450 reductase and heme oxygenase-1. The mechanism of inhibition of rat liver microsomal CYP2D2 and purified rabbit CYP2B4 by MCP230 has been shown previously to be noncompetitive with respect to substrate. In this study, MCP230 was shown to competitively inhibit metabolism of 7-benzyl-4-trifluoromethylcoumarin and 7-ethoxyresorufin by the purified, reconstituted rabbit CYP1A2. MCP230 is at least 5- and 50-fold more potent as an inhibitor of CYP1A2 than silica containing 5% copper oxide and silica, respectively. Thus, even though PM generally inhibit multiple forms of P450, PM interacts differently with the forms of P450 resulting in different mechanisms of inhibition. P450s function as oligomeric complexes within the membrane. We also determined the mechanism by which PM inhibited metabolism by the mixed CYP1A2-CYP2B4 complex and found that the mechanism was purely competitive suggesting that the CYP2B4 is dramatically inhibited when bound to CYP1A2.

Safety assessment of potential food ingredients in canine hepatocytes

This research aimed to develop in vitro methods to assess hazard of canine food ingredients. Canine hepatocytes were harvested and cell viability of clove-leaf oil (CLO), eugenol (EUG), lemongrass oil (LGO), guanosine monophosphate (GMP), inosine monophosphate (IMP), sorbose, ginger-root extract (GRE), cinnamon-bark oil (CBO), cinnamaldehyde (CINA), thymol oil (TO), thymol (THYM), and citric acid were assessed with positive controls: acetaminophen (APAP), aflatoxin B1 and xylitol. Molecular Toxicology PathwayFinder array (MTPF) analyzed toxicity mechanisms for LGO. LC50 for APAP was similar among human (3.45), rat (2.35), dog (4.26 mg/ml). Aflatoxin B1 had an LC50 of 4.43 (human), 5.78 (rat) and 6.05 (dog) µg/ml; xylitol did not decrease viability. LC50 of CLO (0.185 ± 0.075(SD)), EUG (0.165 ± 0.112), LGO (0.220 ± 0.012), GRE (1.54 ± 0.31) mg/ml; GMP (166.03 ± 41.83), GMP + IMP (208.67 ± 15.27) mM; CBO (0.08 ± 0.03), CINA (0.11 ± 0.01), TO (0.21 ± 0.03), THYM (0.05 ± 0.01), citric acid (1.58 ± 0.08) mg/ml, while sorbose was non-toxic. LGO induced upregulation of 16 and down-regulation of 24 genes, which CYP and heat shock most affected. These results suggest that in vitro assays such as this may be useful for hazard assessment of food ingredients for altered hepatic function.

Inhibition of cytochrome P450 2B4 by environmentally persistent free radical-containing particulate matter

Combustion processes generate particulate matter (PM) that can affect human health. The presence of redox-active metals and aromatic hydrocarbons in the post-combustion regions results in the formation of air-stable, environmentally persistent free radicals (EPFRs) on entrained particles. Exposure to EPFRs has been shown to negatively influence pulmonary and cardiovascular functions. Cytochromes P450 (P450/CYP) are endoplasmic reticulum resident proteins that are responsible for the metabolism of foreign compounds. Previously, it was shown that model EPFRs, generated by exposure of silica containing 5% copper oxide (CuO-Si) to either dicholorobenzene (DCB230) or 2-monochlorophenol (MCP230) at ≥ 230 °C, inhibited six forms of P450 in rat liver microsomes (Toxicol. Appl. Pharmacol. (2014) 277:200-209). In this study, the inhibition of P450 by MCP230 was examined in more detail by measuring its effect on the rate of metabolism of 7-ethoxy-4-trifluoromethylcoumarin (7EFC) and 7-benzyloxyresorufin (7BRF) by the purified, reconstituted CYP2B4 system. MCP230 inhibited the CYP2B4-mediated metabolism of 7EFC at least 10-fold more potently than non-EPFR controls (CuO-Si, silica, and silica generated from heating silica and MCP at 50 °C, so that EPFRs were not formed (MCP50)). The inhibition by EPFRs was specific for the P450 and did not affect the ability of the redox partner, P450 reductase (CPR) from reducing cytochrome c. All of the PM inhibited CYP2B4-mediated metabolism noncompetitively with respect to substrate. When CYP2B4-mediated metabolism of 7EFC was measured as a function of the CPR concentration, the mechanism of inhibition was competitive. EPFRs likely inhibit CYP2B4-mediated substrate metabolism by physically disrupting the CPR·P450 complex.

Inhibition of lipopolysaccharide-induced liver injury in rats treated with a hepatic drug-metabolizing enzyme inducer p,p'-DDT

Hepatocellular hypertrophy in association with drug-metabolizing enzyme induction is considered to be an adaptive change associated with drug metabolism. To improve our understanding of liver hypertrophy, we determined the effect of a single ip injection of either lipopolysaccharide (LPS) or vehicle in male F344 rats with hepatocellular hypertrophy induced by oral delivery of p,p'-DDT for 2 weeks. The rats were sacrificed 3h or 24h after LPS or vehicle injection. LPS induced a focal hepatocellular necrosis in rats fed the control diet. When rats pre-treated with p,p'-DDT were injected with LPS, necrotic foci surrounded by ballooned hepatocytes were observed in the liver. The change was consistent with reduced LPS-mediated increases in plasma hepatic biomarkers, neutrophil influx, and apoptosis, and also associated with hepatic mRNA levels of TNF-α, CYPs, and NOS2. By contrast, when combined with p,p'-DDT and LPS, faint hepatocellular fatty change was extended, together with a synergistic increase in total blood cholesterol. These results suggest that hepatocytes exposed to p,p'-DDT are protected from the cell-lethal toxic effects of an exogenous stimulus, resulting in cell ballooning rather than necrosis in association with reduced inflammation and apoptosis, but compromised by an adverse effect on lipid metabolism.

Distributing a metabolic pathway among a microbial consortium enhances production of natural products

Metabolic engineering of microorganisms such as Escherichia coli and Saccharomyces cerevisiae to produce high-value natural metabolites is often done through functional reconstitution of long metabolic pathways. Problems arise when parts of pathways require specialized environments or compartments for optimal function. Here we solve this problem through co-culture of engineered organisms, each of which contains the part of the pathway that it is best suited to hosting. In one example, we divided the synthetic pathway for the acetylated diol paclitaxel precursor into two modules, expressed in either S. cerevisiae or E. coli, neither of which can produce the paclitaxel precursor on their own. Stable co-culture in the same bioreactor was achieved by designing a mutualistic relationship between the two species in which a metabolic intermediate produced by E. coli was used and functionalized by yeast. This synthetic consortium produced 33 mg/L oxygenated taxanes, including a monoacetylated dioxygenated taxane. The same method was also used to produce tanshinone precursors and functionalized sesquiterpenes.

Plasticity of specialized metabolism as mediated by dynamic metabolons

The formation of specialized metabolites enables plants to respond to biotic and abiotic stresses, but requires the sequential action of multiple enzymes. To facilitate swift production and to avoid leakage of potentially toxic and labile intermediates, many of the biosynthetic pathways are thought to organize in multienzyme clusters termed metabolons. Dynamic assembly and disassembly enable the plant to rapidly switch the product profile and thereby prioritize its resources. The lifetime of metabolons is largely unknown mainly due to technological limitations. This review focuses on the factors that facilitate and stimulate the dynamic assembly of metabolons, including microenvironments, noncatalytic proteins, and allosteric regulation. Understanding how plants organize carbon fluxes within their metabolic grids would enable targeted bioengineering of high-value specialized metabolites.

Role of protein-protein interactions in cytochrome P450-mediated drug metabolism and toxicity

Through their unique oxidative chemistry, cytochrome P450 monooxygenases (CYPs) catalyze the elimination of most drugs and toxins from the human body. Protein–protein interactions play a critical role in this process. Historically, the study of CYP–protein interactions has focused on their electron transfer partners and allosteric mediators, cytochrome P450 reductase and cytochrome b5. However, CYPs can bind other proteins that also affect CYP function. Some examples include the progesterone receptor membrane component 1, damage resistance protein 1, human and bovine serum albumin, and intestinal fatty acid binding protein, in addition to other CYP isoforms. Furthermore, disruption of these interactions can lead to altered paths of metabolism and the production of toxic metabolites. In this review, we summarize the available evidence for CYP protein–protein interactions from the literature and offer a discussion of the potential impact of future studies aimed at characterizing noncanonical protein–protein interactions with CYP enzymes.

Environmentally persistent free radicals inhibit cytochrome P450 activity in rat liver microsomes

Combustion processes generate particulate matter that affects human health. When incineration fuels include components that are highly enriched in aromatic hydrocarbons (especially halogenated varieties) and redox-active metals, ultrafine particulate matter containing air-stable, environmentally persistent free radicals (EPFRs) is generated. The exposure to fine EPFRs (less than 2.5 μm in diameter) has been shown to negatively influence pulmonary and cardiovascular functions in living organisms. The goal of this study was to determine if these EPFRs have a direct effect on cytochrome P450 function. This was accomplished by direct addition of the EPFRs to rat liver microsomal preparations and measurement of several P450 activities using form-selective substrates. The EPFRs used in this study were formed by heating vapors from an organic compound (either monochlorophenol (MCP230) or 1,2-dichlorobenzene (DCB230)) and 5% copper oxide supported on silica (approximately 0.2 μm in diameter) to 230°C under vacuum. Both types of EPFRs (but not silica, physisorbed silica, or silica impregnated with copper oxide) dramatically inhibited the activities of CYP1A, CYP2B, CYP2E1, CYP2D2 and CYP3A when incubated at concentrations less than 0.1 mg/ml with microsomes and NADPH. Interestingly, at the same concentrations, the EPFRs did not inhibit HO-1 activity or the reduction of cytochrome c by NADPH-cytochrome P450 reductase. CYP2D2-selective metabolism by rat liver microsomes was examined in more detail. The inhibition of CYP2D2-selective metabolism by both DCB230- and MCP230-EPFRs appeared to be largely noncompetitive and was attenuated in the presence of catalase suggesting that reactive oxygen species may be involved in the mechanism of inhibition.

Relevance of Liver Failure for Anti-Infective Agents: From Pharmacokinetic Alterations to Dosage Adjustments

The liver is a complex organ with great ability to influence drug pharmacokinetics. Due to its wide array of function, its impairment has the potential to affect bioavailability, enterohepatic circulation, drug distribution, metabolism, clearance, and biliary elimination. These alterations differ widely depending on the cause of the liver failure, if it is acute or chronic in nature, the extent of impairment, and comorbid conditions. In addition, effects on liver functions do not occur in a proportional or predictable manner for escalating degrees of liver impairment. The ability of hepatic alterations to influence PK is also dependent on drug characteristics, such as administration route, chemical properties, protein binding, and extraction ratio, among others. This complexity makes it difficult to predict what these effects have on drugs. Unlike certain classes of agents, efficacy of anti-infectives is most often dependent on fulfilling pharmacokinetic/pharmacodynamic targets, such as C_max/MIC, AUC/MIC, T_>MIC, IC₅₀/EC₅₀, or T>EC₉₅. Loss of efficacy, or conversely, increased risk of toxicity may occur in certain circumstances of liver injury. Although important to consider these potential alterations and their effects on specific anti-infectives, many lack data to constitute specific dosing adjustments, making it important to monitor patients for effectiveness and toxicities of therapy.

Interactions between cytochromes P450 2B4 (CYP2B4) and 1A2 (CYP1A2) lead to alterations in toluene disposition and P450 uncoupling

The goal of this study was to characterize the effects of CYP1A2·CYP2B4 complex formation on the rates and efficiency of toluene metabolism by comparing the results from simple reconstituted systems containing P450 reductase (CPR) and a single P450 to those using a mixed system containing CPR and both P450s. In the mixed system, the rates of formation of CYP2B4-specific benzyl alcohol and p-cresol were inhibited, whereas that of CYP1A2-specific o-cresol was increased, results consistent with the formation of a CYP1A2·CYP2B4 complex in which the CYP1A2 moiety has a higher affinity for CPR binding. Comparison of the rates of NADPH oxidation and production of hydrogen peroxide and excess water by the simple and mixed systems indicated that excess water formed at a much lower rate in the mixed system. The commensurate increase in the rate of CYP1A2-specific product formation suggested the P450·P450 interaction increased the rate of the putative rate-limiting step of CYP1A2 catalysis, abstraction of a hydrogen radical from the substrate. Cumene hydroperoxide-supported metabolism was measured to determine whether the effects of the P450·P450 interaction required the presence of CPR. Peroxidative metabolism was not affected by the interaction of the two P450s, even with CPR present. However, CPR did stimulate peroxidative metabolism by the simple system containing CYP1A2. These results suggest the major functional effects of the P450·P450 interaction are mediated by changes in the relative abilities of the P450s to receive electrons from CPR. Furthermore, CPR may play an effector role by causing a conformational change in CYP1A2 that makes its metabolism more efficient.

Heme oxygenase isoforms differ in their subcellular trafficking during hypoxia and are differentially modulated by cytochrome P450 reductase

Heme oxygenase (HO) degrades heme in concert with NADPH cytochrome P450 reductase (CPR) which donates electrons to the reaction. Earlier studies reveal the importance of the hydrophobic carboxy-terminus of HO-1 for anchorage to the endoplasmic reticulum (ER) which facilitates the interaction with CPR. In addition, HO-1 has been shown to undergo regulated intramembrane proteolysis of the carboxy-terminus during hypoxia and subsequent translocation to the nucleus. Translocated nuclear HO-1 was demonstrated to alter binding of transcription factors and to alter gene expression. Little is known about the homologous membrane anchor of the HO-2 isoform. The current work is the first systematic analysis in a eukaryotic system that demonstrates the crucial role of the membrane anchor of HO-2 for localization at the endoplasmic reticulum, oligomerization and interaction with CPR. We show that although the carboxy-terminal deletion mutant of HO-2 is found in the nucleus, translocation of HO-2 to the nucleus does not occur under conditions of hypoxia. Thus, we demonstrate that proteolytic regulation and nuclear translocation under hypoxic conditions is specific for HO-1. In addition we show for the first time that CPR prevents this translocation and promotes oligomerization of HO-1. Based on these findings, CPR may modulate gene expression via the amount of nuclear HO-1. This is of particular relevance as CPR is a highly polymorphic gene and deficiency syndromes of CPR have been described in humans.

Formation of P450 · P450 complexes and their effect on P450 function

Cytochromes P450 (P450) are membrane-bound enzymes that catalyze the monooxygenation of a diverse array of xenobiotic and endogenous compounds. The P450s responsible for foreign compound metabolism generally are localized in the endoplasmic reticulum of the liver, lung and small intestine. P450 enzymes do not act alone but require an interaction with other electron transfer proteins such as NADPH-cytochrome P450 reductase (CPR) and cytochrome b(5). Because P450s are localized in the endoplasmic reticulum with these and other ER-resident proteins, there is a potential for protein-protein interactions to influence P450 function. There has been increasing evidence that P450 enzymes form complexes in the ER, with compelling support that formation of P450 · P450 complexes can significantly influence their function. Our goal is to review the research supporting the formation of P450 · P450 complexes, their specificity, and how drug metabolism may be affected. This review describes the potential mechanisms by which P450s may interact, and provides evidence to support each of the possible mechanisms. Additionally, evidence for the formation of both heteromeric and homomeric P450 complexes are reviewed. Finally, direct physical evidence for P450 complex formation in solution and in membranes is summarized, and questions directing the future research of functional P450 interactions are discussed with respect to their potential impact on drug metabolism.

Mutations of human cytochrome P450 reductase differentially modulate heme oxygenase-1 activity and oligomerization

Genetic variations in POR, encoding NADPH-cytochrome P450 oxidoreductase (CYPOR), can diminish the function of numerous cytochromes P450, and also have the potential to block degradation of heme by heme oxygenase-1 (HO-1). Purified full-length human CYPOR, HO-1, and biliverdin reductase were reconstituted in lipid vesicles and assayed for NADPH-dependent conversion of heme to bilirubin. Naturally-occurring human CYPOR variants queried were: WT, A115V, Y181D, P228L, M263V, A287P, R457H, Y459H, and V492E. All CYPOR variants exhibited decreased bilirubin production relative to WT, with a lower apparent affinity of the CYPOR-HO-1 complex than WT. Addition of FMN or FAD partially restored the activities of Y181D, Y459H, and V492E. When mixed with WT CYPOR, only the Y181D CYPOR variant inhibited heme degradation by sequestering HO-1, whereas Y459H and V492E were unable to inhibit HO-1 activity suggesting that CYPOR variants might have differential binding affinities with redox partners. Titrating the CYPOR-HO-1 complex revealed that the optimal CYPOR:HO-1 ratio for activity was 1:2, lending evidence in support of productive HO-1 oligomerization, with higher ratios of CYPOR:HO-1 showing decreased activity. In conclusion, human POR mutations, shown to impact P450 activities, also result in varying degrees of diminished HO-1 activity, which may further complicate CYPOR deficiency.