Metabolic activation and cytochrome P450 inhibition of piperlonguminine mediated by CYP3A4.

Piperlonguminine (PLG) is a major alkaloid found in Piper longum fruits. It has been shown to possess a variety of biological activities, including anti-tumor, anti-hyperlipidemic, anti-renal fibrosis and anti-inflammatory properties. Previous studies have reported that PLG inhibits various CYP450 enzymes. The main objective of this study was to identify reactive metabolites of PLG in vitro and assess its ability to inhibit CYP450. In rat and human liver microsomal incubation systems exposed to PLG, two oxidized metabolites (M1 and M2) were detected. Additionally, in microsomes where N-acetylcysteine was used as a trapping agent, N-acetylcysteine conjugates (M3, M4, M5 and M6) of four isomeric O-quinone-derived reactive metabolites were found. The formation of metabolites was dependent on NADPH. Inhibition and recombinant CYP450 enzyme incubation experiments showed that CYP3A4 was the primary enzyme responsible for the metabolic activation of PLG. This study characterized the O-dealkylated metabolite (M1) through chemical synthesis. The IC50 shift assay showed time-dependent inhibition of CYP3A4, 2C9, 2E1, 2C8 and 2D6 by PLG. This research contributes to the understanding of PLG-induced enzyme inhibition and bioactivation.

Feeding behavior toxicity in the marine rotifer Brachionus plicatilis caused by 2,2',4,4'-tetrabromodiphenyl ether (BDE-47): Characteristics and mechanisms.

Polybrominated diphenyl ether contamination in marine environments has received special attention due to its accumulation and magnification in the marine food web and toxicity to organisms. In the present study, a series of short-term toxicological tests were conducted with the marine rotifer Brachionus plicatilis to assess the effects on ingestion and digestive performance after treatment with 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) at nonlethal concentrations under controlled laboratory conditions and to analyze the possible mechanism. The results showed that with accumulation in rotifers, BDE-47 caused a significant decline in the filtration and feeding rates in a concentration-dependent manner. Moreover, the activities of amylase (AMS) and protease were affected, indicating that BDE-47 impaired ingestion and digestion efficiency. BDE-47 exposure did not lead to abnormal microstructures in the main digestive tract (e.g., cilia around the corona, mastax, stomach, digestive gland and esophagus), but the gastric parietal cells shrank, suggesting nutritional deficiency. BDE-47 prominently induced the occurrence of irregular mitochondria at the cilia root, and mitochondrial and isocitrate dehydrogenase activity declined, indicating mitochondrial dysfunction. Furthermore, the activity of ATPase, which catalyzes ATP hydrolysis, decreased as the BDE-47 concentration rose, implying that BDE-47 retarded rotifer ATP dynamics, inevitably interfering with cilia movement to ingest food. Additionally, a significant decline in acetylcholine esterase activity was observed, which led to a hindrance in neurotransmission involved in food intake and digestion. Altogether, our results demonstrated that nonlethal concentrations of BDE-47 could induce feeding depression in rotifers, which is mainly attributed to stymied energy metabolism and nerve conduction.

Evaluation of the toxic response induced by BDE-47 in a marine alga, Phaeodactylum tricornutum, based on photosynthesis-related parameters.

The pollution of polybrominated diphenyl ethers (PBDEs) is becoming a pressing environmental problem in aquatic environments, and its threat to aquatic organism has received much attention. In this study, Phaeodactylum tricornutum was treated with 0.8 and 4 mg L-1 2,2',4,4'-tetrabrominated biphenyl ether (BDE-47), the most toxic PBDEs, for 96 h. BDE-47 inhibited cell growth in a time- and concentration-dependent manner. Observation of cell ultrastructure suggested the damage of the chloroplasts morphology. BDE-47 also decreased the chlorophyll content and the oxygen evolution rate, and altered the performance of photosystems. Transcriptomic analysis revealed differential expression of 62 genes related to photosynthesis in BDE-47 treatments (4 mg L-1) and transcription suppression of 58 genes involved in chlorophyll synthesis, antenna proteins, oxygen evolution, electron transport and downstream carbon fixation, implying potential toxicity targets in cells. Additionally, the levels of reactive oxygen species (ROS) and lipid peroxidation increased under BDE-47 stress and were positively correlated with photosynthesis inhibition. Pretreatment with the ROS scavenger N-acetyl-l-cysteine reduced the extent of inhibition, suggesting that ROS was responsible for these effects. Another experiment with the electron transport chain inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea showed that the generation of ROS was partially blocked, primarily indicating that photosynthetic inhibition induced by BDE-47 contributed to ROS overproduction. Thus, BDE-47 inhibited the photosynthesis by down-regulating the gene expression. This change stimulated ROS production, further leading to chloroplast membrane damage to aggravate this inhibition via a feedback loop. These effects of BDE-47 had adverse outcomes on the entire physiological state and the population growth of the microalgae.

Changes in the immune function of rainbow trout (Oncorhynchus mykiss) provide insights into strategies against BDE-47 stress.

Polybrominated diphenyl ethers (PBDEs) are ubiquitous in marine ecosystems and have been suggested to bioaccumulate in aquatic food webs, with potentially negative impacts on marine organism. In this study, a 21-day experiment was performed under controlled laboratory conditions, in which 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), the most biotoxic PBDE in the marine environment, was fed to rainbow trout (Oncorhynchus mykiss) at concentrations of 50 and 500 ng g-1 in the diet. BDE-47 significantly decreased the specific growth rate of O. mykiss and was highly concentrated in the liver and head kidney, as evidenced by increased bioaccumulation factor (BAF) values. Tissue observation revealed impairment of the microstructure of the head kidney. Important immune factors in the skin, blood and head kidney were significantly inhibited by BDE-47 treatment (p < 0.05), whereas the respiratory burst activity of macrophages was enhanced. Additionally, immune-related genes were strongly downregulated following BDE-47 exposure (p < 0.05). In a bacterial challenge, the treatment groups had much higher mortality than did the control group (p < 0.05). BDE-47 accumulated and impaired immune organs, and the hierarchy of immune responses was impaired, consequently reducing O. mykiss resistance to pathogen invasion.

Responses of the rotifer Brachionus plicatilis to flame retardant (BDE-47) stress.

A series of short-term toxicological tests were conducted on the rotifer Brachionus plicatilis to assess the toxicity of the flame retardant 2,2',4,4'-tetrabrominated biphenyl ether (BDE-47). BDE-47 increased mortality, morphological damage, and altered population dynamics and fecundity of rotifer. Antioxidant enzymes were differentially changed to maintain the balance between antioxidant and pro-oxidant activity. However, with increases in the concentration of BDE-47, the metabolic and antioxidant activity decreased. Moreover, the reactive oxygen species (ROS) and malondialdehyde contents increased and the ratio between glutathione and glutathione-SH decreased, indicating oxidative stress. The addition of the ROS-inhibitor N-acetylcysteine alleviated the degree of damage and stimulated the activity of xenobiotic-metabolizing and antioxidant system, which suggested that ROS were the most important loop in the stress response.