α-lipoic acid ameliorates hepatotoxicity induced by chronic ammonia toxicity in crucian carp (Carassius auratus gibelio) by alleviating oxidative stress, inflammation and inhibiting ERS pathway.

High environment ammonia (HEA) poses a deadly threat to aquatic animals and indirectly impacts human healthy life, while nutritional regulation can alleviate chronic ammonia toxicity. α-lipoic acid exhibits antioxidative effects in both aqueous and lipid environments, mitigating cellular and tissue damage caused by oxidative stress by aiding in the neutralization of free radicals (reactive oxygen species). Hence, investigating its potential as an effective antioxidant and its protective mechanisms against chronic ammonia stress in crucian carp is highly valuable. Experimental fish (initial weight 20.47 ± 1.68 g) were fed diets supplemented with or without 0.1% α-lipoic acid followed by a chronic ammonia exposure (10 mg/L) for 42 days. The results revealed that chronic ammonia stress affected growth (weight gain rate, specific growth rate, and feed conversion rate), leading to oxidative stress (decreased the activities of antioxidant enzymes catalase, superoxide dismutase, glutathione peroxidase; decreased total antioxidant capacity), increased lipid peroxidation (accumulation of malondialdehyde), immune suppression (decreased contents of nonspecific immune enzymes AKP and ACP, 50% hemolytic complement, and decrease of immunoglobulin M), impaired ammonia metabolism (reduced contents of Glu, GS, GSH, and Gln), imbalance of expression of induced antioxidant-related genes (downregulation of Cu/Zu SOD, CAT, Nrf2, and HO-1; upregulation of GST and Keap1), induction of pro-apoptotic molecules (transcription of BAX, Caspase3, and Caspase9), downregulation of anti-apoptotic gene Bcl-2 expression, and induction of endoplasmic reticulum stress (upregulation of IRE1, PERK, and ATF6 expression). The results suggested that the supplementation of α-lipoic acid could effectively induce humoral immunity, alleviate oxidative stress injury and endoplasmic reticulum stress, and ultimately alleviate liver injury induced by ammonia poisoning (50-60% reduction). This provides theoretical basis for revealing the toxicity of long-term ammonia stress and provides new insights into the anti-ammonia toxicity mechanism of α-lipoic acid.

New insight into the effect of nitrogen on hydrocarbon degradation in petroleum-contaminated soil revealed through 15N tracing and flow cytometry.

Nitrogen (N) has been widely used to dissipate total petroleum hydrocarbons (TPH) in the oil-contaminated soil, but the relationships of hydrocarbon transformation, N cycling and utilization, and microbial characteristics during TPH biodegradation still remain unclear. In this study, 15N tracers (K15NO3 and 15NH4Cl) were used as stimulants for TPH degradation to compare the bioremediation potential of TPH in the historically (5 a) and freshly (7 d) petroleum-contaminated soils. During bioremediation process, TPH removal and carbon balance, N transformation and utilization, as well as microbial morphologies were investigated using 15N tracing and flow cytometry. Results showed that TPH removal rates were higher in the freshly polluted soils (61.59 % for K15NO3 amendment and 48.55 % for 15NH4Cl amendment) than in the historically polluted soils (35.84 % for K15NO3 amendment and 32.30 % for 15NH4Cl amendment), and TPH removal rate through K15NO3 amendment was higher than that of 15NH4Cl in the freshly polluted soils. This result was attributed to the higher N gross transformation rates in the freshly contaminated soils (0.0034-0.432 mmol N kg-1 d-1) when compared with that in the historically contaminated soils (0.009-0.04 mmol N kg-1 d-1), which led to more TPH transformation to residual carbon (51.84 %-53.74 %) in the freshly polluted soils than that in the historically polluted soils (24.67 %-33.47 %). Based on the fluorescence intensity displayed by the combination of stains and cellular components to indicate microbial morphology and activity, flow cytometry analysis showed that nitrogen addition was beneficial for the membrane integrity of TPH-degrading bacteria, and nitrogen also enhanced DNA synthesis and activity of TPH-degrading fungi in freshly polluted soil. Correlation and structural equation modeling analysis identified that K15NO3 was beneficial to synthesize DNA of the TPH-degrading fungi but not the bacteria, which contributed to enhance TPH bio-mineralization in the soils with K15NO3 amendment.