Activity-Based Protein Profiling to Probe Relationships between Cytochrome P450 Enzymes and Early-Age Metabolism of Two Polycyclic Aromatic Hydrocarbons (PAHs): Phenanthrene and Retene.

A growing body of literature has linked early-life exposures to polycyclic aromatic hydrocarbons (PAH) with adverse neurodevelopmental effects. Once in the body, metabolism serves as a powerful mediator of PAH toxicity by bioactivating and detoxifying PAH metabolites. Since enzyme expression and activity vary considerably throughout human development, we evaluated infant metabolism of PAHs as a potential contributing factor to PAH susceptibility. We measured and compared rates of phenanthrene and retene (two primary PAH constituents of woodsmoke) metabolism in human hepatic microsomes from individuals ≤21 months of age to a pooled sample (n = 200) consisting primarily of adults. We used activity-based protein profiling (ABPP) to characterize cytochrome P450 enzymes (CYPs) in the same hepatic microsome samples. Once incubated in microsomes, phenanthrene demonstrated rapid depletion. Best-fit models for phenanthrene metabolism demonstrated either 1 or 2 phases, depending on the sample, indicating that multiple enzymes could metabolize phenanthrene. We observed no statistically significant differences in phenanthrene metabolism as a function of age, although samples from the youngest individuals had the slowest phenanthrene metabolism rates. We observed slower rates of retene metabolism compared with phenanthrene also in multiple phases. Rates of retene metabolism increased in an age-dependent manner until adult (pooled) metabolism rates were achieved at ∼12 months. ABPP identified 28 unique CYPs among all samples, and we observed lower amounts of active CYPs in individuals ≤21 months of age compared to the pooled sample. Phenanthrene metabolism correlated to CYPs 1A1, 1A2, 2C8, 4A22, 3A4, and 3A43 and retene metabolism correlated to CYPs 1A1, 1A2, and 2C8 measured by ABPP and vendor-supplied substrate marker activities. These results will aid efforts to determine human health risk and susceptibility to PAHs exposure during early life.

Profiling How the Gut Microbiome Modulates Host Xenobiotic Metabolism in Response to Benzo[a]pyrene and 1-Nitropyrene Exposure.

The gut microbiome is a key contributor to xenobiotic metabolism. Polycyclic aromatic hydrocarbons (PAHs) are an abundant class of environmental contaminants that have varying levels of carcinogenicity depending on their individual structures. Little is known about how the gut microbiome affects the rates of PAH metabolism. This study sought to determine the role that the gut microbiome has in determining the various aspects of metabolism in the liver, before and after exposure to two structurally different PAHs, benzo[a]pyrene and 1-nitropyrene. Following exposures, the metabolic rates of PAH metabolism were measured, and activity-based protein profiling was performed. We observed differences in PAH metabolism rates between germ-free and conventional mice under both unexposed and exposed conditions. Our activity-based protein profiling (ABPP) analysis showed that, under unexposed conditions, there were only minor differences in total P450 activity in germ-free mice relative to conventional mice. However, we observed distinct activity profiles in response to corn oil vehicle and PAH treatment, primarily in the case of 1-NP treatment. This study revealed that the repertoire of active P450s in the liver is impacted by the presence of the gut microbiome, which modifies PAH metabolism in a substrate-specific fashion.

Evaluation of materials for iodine and technetium immobilization through sorption and redox-driven processes.

Radioactive iodine-129 (129I) and technetium-99 (99Tc) pose a risk to groundwater due to their long half-lives, toxicity, and high environmental mobility. Based on literature reviewed in Moore et al. (2019) and Pearce et al. (2019), natural and engineered materials, including iron oxides, low-solubility sulfides, tin-based materials, bismuth-based materials, organoclays, and metal organic frameworks, were tested for potential use as a deployed technology for the treatment of 129I and 99Tc to reduce environmental mobility. Materials were evaluated with metrics including capacity for IO3- and TcO4- uptake, selectivity and long-term immobilization potential. Batch testing was used to determine IO3- and TcO4- sorption under aerobic conditions for each material in synthetic groundwater at different solution to solid ratios. Material association with IO3- and TcO4- was spatially resolved using scanning electron microscopy and X-ray microprobe mapping. The potential for redox reactions was assessed using X-ray absorption near edge structure spectroscopy. Of the materials tested, bismuth oxy(hydroxide) and ferrihydrite performed the best for IO3-. The commercial Purolite A530E anion-exchange resin outperformed all materials in its sorption capacity for TcO4-. Tin-based materials had high capacity for TcO4-, but immobilized TcO4- via reductive precipitation. Bismuth-based materials had high capacity for TcO4-, though slightly lower than the tin-based materials, but did not immobilize TcO4- by a redox-drive process, mitigating potential negative re-oxidation effects over longer time periods under oxic conditions. Cationic metal organic frameworks and polymer networks had high Tc removal capacity, with TcO4- trapped within the framework of the sorbent material. Although organoclays did not have the highest capacity for IO3- and TcO4- removal in batch experiments, they are available commercially in large quantities, are relatively low cost and have low environmental impact, so were investigated in column experiments, demonstrating scale-up and removal of IO3- and TcO4- via sorption, and reductive immobilization with iron- and sulfur-based species.

Technetium and iodine aqueous species immobilization and transformations in the presence of strong reductants and calcite-forming solutions: Remedial action implications.

At the Hanford Site in southeastern Washington, discharge of radionuclide laden liquid wastes resulted in vadose zone contamination, providing a continuous source of these contaminants to groundwater. The presence of multiple contaminants (i.e., 99Tc and 129I) increases the complexity of finding viable remediation technologies to sequester contaminants in situ and protect groundwater. Although previous studies have shown the efficiency of zero valent iron (ZVI) and sulfur modified iron (SMI) in reducing mobile Tc(VII) to immobile Tc(IV) and iodate incorporation into calcite, the coupled effects from simultaneously using these remedial technologies have not been previously studied. In this first-of-a-kind laboratory study, we used reductants (ZVI or SMI) and calcite-forming solutions to simultaneously remove aqueous Tc(VII) and iodate via reduction and incorporation, respectively. The results confirmed that Tc(VII) was rapidly removed from the aqueous phase via reduction to Tc(IV). Most of the aqueous iodate was transformed to iodide faster than incorporation into calcite occurred, and therefore the I remained in the aqueous phase. These results suggested that this remedial pathway is not efficient in immobilizing iodate when reductants are present. Other experiments suggested that iodate removal via calcite precipitation should occur prior to adding reductants for Tc(VII) removal. When microbes were included in the tests, there was no negative impact on the microbial population but changes in the makeup of the microbial community were observed. These microbial community changes may have an impact on remediation efforts in the long-term that could not be seen in a short-term study. The results underscore the importance of identifying interactions between natural attenuation pathways and remediation technologies that only target individual contaminants.