Dissolved organic carbon diminishes manganese oxide-driven oxidation of chromium

Oxidation of chromium (Cr)-bearing minerals by manganese (Mn) oxides is viewed as the dominant mechanism controlling geogenic production of Cr(VI) and its contamination of groundwater. This process may be modulated by other chemical constituents found in the natural environment, but such confounding factors have not been quantified. Here, we evaluated the mechanism of Cr(III) oxidation by mixed-valence Mn oxide in the presence of citric and gallic acids, two natural organic matter (NOM) constituents commonly found in the soil environment. Incubation experiments showed that each organic acid enhanced solubilization of Cr(III) and Mn over controls without organic addition but increasing organic acid concentration decreased production of Cr(VI), with approximately 8.5 times less Cr(VI) produced in the citric acid than gallic acid experiments. X-ray absorption spectroscopy showed that negligible Cr(VI) was present in solid-phase reaction products, regardless of treatment. Geochemical modeling revealed that in the citric acid experiments, unprotonated Cr(III)-citrate was the dominant organo-metallic complex in solution, while (CrOH)2+ distribution positively correlated with concentrations of Cr(VI) produced. Collectively, these results illustrate how NOM can modify expected chemical pathways driving Cr cycling, and such mechanistic information should be better integrated into models predicting Cr redox dynamics and availability in the environment.

Oral Squamous Cell Carcinoma as a Complication of Treatment for Recurrent High-Grade Serous Cancer

OBJECTIVES/HYPOTHESIS

Advances in cancer treatment have increased survival for many patients, prompting a need for greater recognition of the long-term complications of treatment. Chemotherapy agents have the potential to induce carcinogenesis and can increase the risk of secondary malignancy. Pegylated liposomal doxorubicin (PLD) used for maintenance treatment of recurrent high-grade serous cancers has been associated with the development of oral cavity squamous cell carcinoma (SCC).

STUDY DESIGN

Retrospective review.

METHODS

Cases of oral cavity SCC in patients with recurrent high-grade serous cancer treated with PLD between 1997 and 2017 at a single institution were reviewed.

RESULTS

Eight of 16 patients treated with PLD developed oral cavity SCC. The duration of PLD use ranged from 1.3 to 15 years (mean = 5.8 years) and cumulative dose ranged from 405 to 3,000 mg/m² (mean = 1,542 mg/m² ). Seven patients tested positive for BRCA mutations (four BRCA 1+, three BRCA 2+). No patients had a history of alcohol or tobacco use. All had early-stage oral cavity disease; five were T1N0, two were T2N0, and one had carcinoma in situ. All patients underwent surgery, and two received adjuvant radiation. Four developed locoregional recurrence requiring additional treatment. Of these, one patient died from complications of oral SCC, one developed recurrent ovarian cancer, and two had no evidence of disease of the oral cavity or ovarian cancer at the last follow-up.

CONCLUSIONS

Long-term PLD therapy may be associated with the development of oral cavity SCC. A high index of suspicion and routine head and neck examination should be included in follow-up for exposed patients.

LEVEL OF EVIDENCE

4 Laryngoscope, 130:2607-2610, 2020.

DNA resection proteins Sgs1 and Exo1 are required for G1 checkpoint activation in budding yeast

Double-strand breaks (DSBs) in budding yeast trigger activation of DNA damage checkpoints, allowing repair to occur. Although resection is necessary for initiating damage-induced cell cycle arrest in G2, no role has been assigned to it in the activation of G1 checkpoint. Here we demonstrate for the first time that the resection proteins Sgs1 and Exo1 are required for efficient G1 checkpoint activation. We find in G1 arrested cells that histone H2A phosphorylation in response to ionizing radiation is independent of Sgs1 and Exo1. In contrast, these proteins are required for damage-induced recruitment of Rfa1 to the DSB sites, phosphorylation of the Rad53 effector kinase, cell cycle arrest and RNR3 expression. Checkpoint activation in G1 requires the catalytic activity of Sgs1, suggesting that it is DNA resection mediated by Sgs1 that stimulates the damage response pathway rather than protein-protein interactions with other DDR proteins. Together, these results implicate DNA resection, which is thought to be minimal in G1, as necessary for activation of the G1 checkpoint.