Prediction and Chemical Interpretation of Singlet-Oxygen-Scavenging Activity of Small Molecule Compounds by Using Machine Learning

A chemically explainable machine learning model was constructed with a small dataset to quantitatively predict the singlet-oxygen-scavenging ability. In this model, ensemble learning based on decision trees resulted in high accuracy. For explanatory variables, molecular descriptors by computational chemistry and Morgan fingerprints were used for achieving high accuracy and simple prediction. The singlet-oxygen-scavenging mechanism was explained by the feature importance obtained from machine learning outputs. The results are consistent with conventional chemical knowledge. The use of machine learning and reduction in the number of measurements for screening high-antioxidant-capacity compounds can considerably improve prediction accuracy and efficiency.

Neurosporaxanthin Overproduction by Fusarium fujikuroi and Evaluation of Its Antioxidant Properties

Neurosporaxanthin (NX) is a carboxylic carotenoid produced by some filamentous fungi, including species of the genera Neurospora and Fusarium. NX biosynthetic genes and their regulation have been thoroughly investigated in Fusarium fujikuroi, an industrial fungus used for gibberellin production. In this species, carotenoid-overproducing mutants, affected in the regulatory gene carS, exhibit an upregulated expression of the NX pathway. Based on former data on a stimulatory effect of nitrogen starvation on carotenoid biosynthesis, we developed culture conditions with carS mutants allowing the production of deep-pigmented mycelia. With this method, we obtained samples with ca. 8 mg NX/g dry mass, in turn the highest concentration for this carotenoid described so far. NX-rich extracts obtained from these samples were used in parallel with carS-complemented NX-poor extracts obtained under the same conditions, to check the antioxidant properties of this carotenoid in in vitro assays. NX-rich extracts exhibited higher antioxidant capacity than NX-poor extracts, either when considering their quenching activity against [O2(1g)] in organic solvent (singlet oxygen absorption capacity (SOAC) assays) or their scavenging activity against different free radicals in aqueous solution and in liposomes. These results make NX a promising carotenoid as a possible feed or food additive, and encourage further studies on its chemical properties.

Kinetic Study of Singlet-Oxygen Quenching and Aroxyl-Radical Scavenging Activities of Vitamin E Homologs and Fatty Acids Present in Vegetable Oils

Recently, singlet-oxygen (¹O₂) quenching and aroxyl-radical (ArO·) scavenging rates (k_Q and k_S, respectively) of eight vegetable oils were measured in the ethanol/chloroform/D₂O solution. Furthermore, the k_Q and k_S values and concentrations of four tocopherols and four tocotrienols contained in the vegetable oils were measured. In this study, the concentrations of nine fatty acids (including stearic, oleic, linoleic, and linolenic acids) comprising the above-mentioned eight vegetable oils were determined by gas chromatography. The k_Q and k_S values for ethyl stearate, ethyl oleate, ethyl linoleate, methyl linolenate, and glyceryl trioleate in the ethanol/chloroform/D₂O solution were measured by UV-vis spectrophotometry. Based on the results obtained for the above-mentioned fatty acid esters, the k_Q and k_S values were estimated for nine fatty acids. Furthermore, comparisons of k_Q values observed for the vegetable oils with the sum of the product {∑k_Q^AO-i [AO-i]} of the k_Q^AO-i values obtained for each antioxidant-i (AO-i) and the concentrations ([AO-i]) of AO-i (i.e., four tocopherols (& four tocotrienols) and nine fatty acids) contained in vegetable oils were performed. Based on the results, a detailed comparison of the contributions of the tocopherols (and tocotrienols) and the fatty acids to the ¹O₂-quenching rate constants (k_Q) was performed. This indicated that both the tocopherols (and tocotrienols) and the fatty acids contribute to the ¹O₂- quenching. A similar comparison was conducted for the ArO· -scavenging rate constants (k_S). The results suggested that only the tocopherols (and tocotrienols) contained in the oils contributed to the ArO· -scavenging, with negligible contribution from the fatty acids.