Activation of the phenylpropanoid pathway in Citrus sinensis collapsed vesicles during segment drying revealed by physicochemical and targeted metabolomics analysis

Segment drying is a common internal physiological disorder in citrus fruit, and vesicles get granulated or collapsed. This study aimed to probe whether and how the phenylpropanoid metabolism changes in vesicles during collapse of blood orange (Citrus sinensis cv. Tarocco). Vesicle collapse led to a decrease in the content of nutrients and flavonoids, while an increase in lignin content. This disorder was further associated with the increasing enzyme activities and gene expression levels of both the general phenylpropanoid pathway and branch pathway of lignin synthesis, while decreasing enzyme activities and gene expression levels of branch pathway of flavonoids synthesis. Targeted metabolomics analysis of 14 metabolites of the lignin pathway revealed that lignin precursors were accumulated in collapsed vesicles. We provide solid evidence that phenylpropanoid metabolism could be activated, and, intriguingly, metabolic flux may be shuttled to lignin precursors synthesis rather than flavonoids synthesis in vesicles during collapse of blood orange.

Discovery of polymethoxyflavones as potential cyclooxygenase-2 (COX-2), 5-lipoxygenase (5-LOX) and phosphodiesterase 4B (PDE4B) inhibitors

Non-steroidal anti-inflammatory drugs (NSAIDs) are widely prescribed to treat inflammatory-related diseases, pain and fever. However, the prolong use of traditional NSAIDs leads to undesirable side effects such as gastric, ulceration, and renal toxicity due to lack of selectivity toward respective targets for COX-2, 5-LOX, and PDE4B. Thus, targeting multiple sites can reduce these adverse effects of the drugs and increase its potency. A series of methoxyflavones (F1-F5) were synthesized and investigated for their anti-inflammatory properties through molecular docking and inhibition assays. Among these flavones, only F2 exhibited selectivity toward COX-2 (Selectivity Index, SI: 3.90, COX-2 inhibition: 98.96 ± 1.47%) in comparison with celecoxib (SI: 7.54, COX-2 inhibition: 98.20 ± 2.55%). For PDEs, F3 possessed better selectivity to PDE4B (SI: 4.67) than rolipram (SI: 0.78). F5 had the best 5-LOX inhibitory activity among the flavones (33.65 ± 4.74%) but less than zileuton (90.81 ± 0.19%). Docking analysis indicated that the position of methoxy group and the substitution of halogen play role in determining the bioactivities of flavones. Interestingly, F1-F5 displayed favorable pharmacokinetic profiles and acceptable range of toxicity (IC₅₀>70 µM) in cell lines with the exception for F1 (IC₅₀: 16.02 ± 1.165 µM). This study generated valuable insight in designing new anti-inflammatory drug based on flavone scaffold. The newly synthesized flavones can be further developed as future therapeutic agents against inflammation.