Valproic Acid Causes Redox-Regulated Post-Translational Protein Modifications That Are Dependent upon P19 Cellular Differentiation States.

Valproic acid (VPA) is a common anti-epileptic drug and known neurodevelopmental toxicant. Although the exact mechanism of VPA toxicity remains unknown, recent findings show that VPA disrupts redox signaling in undifferentiated cells but has little effect on fully differentiated neurons. Redox imbalances often alter oxidative post-translational protein modifications and could affect embryogenesis if developmentally critical proteins are targeted. We hypothesize that VPA causes redox-sensitive post-translational protein modifications that are dependent upon cellular differentiation states. Undifferentiated P19 cells and P19-derived neurons were treated with VPA alone or pretreated with D3T, an inducer of the nuclear factor erythroid 2-related factor 2 (NRF2) antioxidant pathway, prior to VPA exposure. Undifferentiated cells treated with VPA alone exhibited an oxidized glutathione redox couple and increased overall protein oxidation, whereas differentiated neurons were protected from protein oxidation via increased S-glutathionylation. Pretreatment with D3T prevented the effects of VPA exposure in undifferentiated cells. Taken together, our findings support redox-sensitive post-translational protein alterations in undifferentiated cells as a mechanism of VPA-induced developmental toxicity and propose NRF2 activation as a means to preserve proper neurogenesis.

Gut Metabolite Trimethylamine N-Oxide Protects INS-1 ß-Cell and Rat Islet Function under Diabetic Glucolipotoxic Conditions.

Serum accumulation of the gut microbial metabolite trimethylamine N-oxide (TMAO) is associated with high caloric intake and type 2 diabetes (T2D). Impaired pancreatic ß-cell function is a hallmark of diet-induced T2D, which is linked to hyperglycemia and hyperlipidemia. While TMAO production via the gut microbiome-liver axis is well defined, its molecular effects on metabolic tissues are unclear, since studies in various tissues show deleterious and beneficial TMAO effects. We investigated the molecular effects of TMAO on functional ß-cell mass. We hypothesized that TMAO may damage functional ß-cell mass by inhibiting ß-cell viability, survival, proliferation, or function to promote T2D pathogenesis. We treated INS-1 832/13 ß-cells and primary rat islets with physiological TMAO concentrations and compared functional ß-cell mass under healthy standard cell culture (SCC) and T2D-like glucolipotoxic (GLT) conditions. GLT significantly impeded ß-cell mass and function by inducing oxidative and endoplasmic reticulum (ER) stress. TMAO normalized GLT-mediated damage in ß-cells and primary islet function. Acute 40µM TMAO recovered insulin production, insulin granule formation, and insulin secretion by upregulating the IRE1α unfolded protein response to GLT-induced ER and oxidative stress. These novel results demonstrate that TMAO protects ß-cell function and suggest that TMAO may play a beneficial molecular role in diet-induced T2D conditions.