Hepatic glucuronidation of 4-tert-octylphenol in humans: inter-individual variability and responsible UDP-glucuronosyltransferase isoforms

Integrated Metabolomics and Transcriptomics Analyses Reveal Metabolic Changes in Primary Angiitis of the Central Nervous System

Purpose

Metabolic characterization of primary angiitis of the central nervous system (PACNS) is crucial for understanding the disease pathogenesis and progression mechanisms, but it has not been reported in patients. This study aimed to explore changes in the plasma metabolome during the active and remission phases of PACNS and identify potential biomarkers.

Methods

We collected plasma samples from 35 patients with PACNS during the active and remission phases and 22 samples from patients with non-inflammatory disease as controls. Liquid and gas chromatography-mass spectrometry were used to analyze 63 plasma samples from 57 patients metabolically. Meanwhile, we cross-validated the metabolomics results with brain tissue transcriptomic data from comprehensive gene expression databases, enhancing the reliability of our conclusions.

Results

A total of 3,233 metabolites were identified. Enrichment analysis showed significant changes in lactate/amino acid/glycerol-pyruvic-tricarboxylic acid, glycerophospholipid/sphingolipid-membrane metabolism, lysine/tryptophan-essential amino acid metabolism, and uracil metabolism pathways during the active phase of PACNS. These findings were confirmed in both the remission phase of PACNS patients and the transcriptomic samples. Meanwhile, metabolic abnormalities in patients with PACNS were observed with benzoxazole, sesquiterpenoid, and octyl-phenolic products, and enrichment of environmental pollutants and their estrogen-like effects. Twelve metabolites, including D-Ribose, 13s-HPODE, and C16 Sphinganine, showed potential diagnostic and therapeutic evaluation value.

Conclusion

Our study identified potential biomarkers and metabolic characteristics of PACNS using integrated metabolomics and transcriptomics approaches. These findings highlight the importance of understanding PACNS from a metabolic perspective and guide future diagnostic and therapeutic strategies.

Toxicity of tire rubber-derived pollutants 6PPD-quinone and 4-tert-octylphenol on marine plankton

The impacts of tire wear particles and their associated chemicals on the aquatic systems are a major environmental concern. In this study, we investigated the acute toxicity of two pollutants derived from tire rubber, 6PPD-quinone and 4-tert-octylphenol, on marine plankton. Specifically, we determined the acute effects of these pollutants on various organisms within the plankton food web: the microalgae Rhodomonas salina, the adult copepod Acartia tonsa, and the early life stages of the echinoderms Arbacia lixula and Paracentrotus lividus and the fish Sparus aurata. Exposure to 6PPD-quinone did not affect the microalgae growth, copepod survival, or fish embryo viability after 48 h of exposure at concentrations up to 1000 µgL-1. However, 6PPD-quinone significantly inhibited the growth of early developmental stages of both echinoderm species, with median effective concentrations of 7 and 8 µgL-1. Conversely, 4-tert-octylphenol was toxic to all studied organisms, with median lethal and effective concentrations ranging from 21 to 79 µgL-1 depending on the species and endpoints. The most sensitive planktonic organisms to 4-tert-octylphenol were echinoderm embryos and copepods, which exhibited negative effects at concentrations as low as 1 and 25 µgL-1, respectively. Our results demonstrate that acute exposure to 6PPD-quinone and 4-tert-octylphenol can cause harmful effects on key planktonic organisms at environmentally relevant concentrations. Overall, our findings highlight the need for develop ecologically safer tire rubber additives and reduce traffic-related tire particle emissions to mitigate their entry and potential impacts on aquatic ecosystems.

The structural basis of conserved residue variant effect on enzyme activity of UGT2B15

UDP-glucuronosyltransferase 2B15 (UGT2B15) is a crucial phase II drug-metabolizing enzyme, which glucuronidates various compounds, including clinical drugs and hormones. Mutants might affect glucuronidation, leading to a disruption of drug metabolism in vivo and decrease of therapeutic effect. Here, we mainly analyzed two representative mutants, H401P and L446S, on UGT2B15 activity using glucuronidation assays, molecular dynamic (MD) simulation and X-ray diffraction methods. The enzyme activity of L446S obviously increased six-fold than the wild type, although the enzyme activities of P191L, T374A, and H401P were lost apparently. Furthermore, we used MD simulations to calculate the energy change in the catalytic process of H401P and L446S, and the results indicated the free binding energies of H401P mutant to oxazepam and UDPGA were -30.98 ± 1.00 kcal/mol and -36.42 ± 1.04 kcal/mol, respectively, increased obviously compared to wild type, suggesting the mutation on position 401 had a crucial effect on the catalysis. Moreover, the three-dimensional structure of UGT2B15 C-terminal domain L446S was determined through protein crystallography and X-ray diffraction technology and the results suggested that one more hydrogen bonding between S446 and K410 was formed in the S446 crystal structure, compared to the wild type. Isothermal titration calorimetry assay further revealed the K_d values of C-terminal domain of UGT2B15 harbored L446S towards the cofactor UDPGA was similar to the value of wild type. Above all, our results pointed out that H401P and L446S affected the enzyme activity by different mechanism. Our work provided a helpful mechanism for variance explained in the UGTs catalyzation process.

Sulfonation and glucuronidation of hydroxylated bromodiphenyl ethers in human liver

Hydroxylated bromodiphenyl ethers (OH-BDEs) can arise from monooxygenation of anthropogenic BDEs or through natural biosynthetic processes in marine organisms, and several OH-BDEs have been shown to be toxic. OH-BDEs are expected to form sulfate and glucuronide conjugates that are readily excreted, however there is little information on these pathways. We examined the human hepatic glucuronidation and sulfonation of 6-OH-BDE47, 2-OH-BDE68, 4-OH-BDE68 and 2-OH-6'methoxy-BDE68. Human liver microsomes and cytosol were from de-identified female and male donors aged 31 to 75 under an exempt protocol. Recombinant human SULT1A1, 1B1, 1E1 and 2A1 enzymes were prepared from bacterial expression systems. Sulfonation and glucuronidation of each OH-BDE were studied using radiolabeled co-substrates, 3'phosphoadenosine-5'phospho-³⁵S-sulfate or uridine diphospho-β-D-¹⁴C-glucuronic acid in order to quantify the sulfated or glucuronidated products. The OH-BDEs studied were more efficiently glucuronidated than sulfonated. Of the compounds studied, 2-OH-BDE68 was the most readily conjugated, and exhibited an efficiency (V_max/K_M) of glucuronidation of 0.274 ± 0.125 mL/min/mg protein, mean ± S.D., n = 3, while that for sulfonation was 0.179 ± 0.030 mL/min/mg protein. For both pathways, all K_m values were in the low μM range. Studies with human SULT enzymes showed that sulfonation of these four substrates was readily catalyzed by SULT1B1 and SULT1E1. Much lower activity was found with SULT1A1 and SULT2A1. Assuming that the glucuronide and sulfate conjugates are non-toxic and readily excreted, as is the case for most such conjugates, these studies suggest that OH-BDEs should not accumulate in people to the same extent as the parent BDEs.