An efficient preparation and biocatalytic synthesis of novel C-glycosylflavonols kaempferol 8-C-glucoside and quercetin 8-C-glucoside through using resting cells and macroporous resins

Exploring the mechanisms of kaempferol in neuroprotection: Implications for neurological disorders

Kaempferol, a flavonoid compound found in various fruits, vegetables, and medicinal plants, has garnered increasing attention due to its potential neuroprotective effects in neurological diseases. This research examines the existing literature concerning the involvement of kaempferol in neurological diseases, including stroke, Parkinson's disease, Alzheimer's disease, neuroblastoma/glioblastoma, spinal cord injury, neuropathic pain, and epilepsy. Numerous in vitro and in vivo investigations have illustrated that kaempferol possesses antioxidant, anti-inflammatory, and antiapoptotic properties, contributing to its neuroprotective effects. Kaempferol has been shown to modulate key signaling pathways involved in neurodegeneration and neuroinflammation, such as the PI3K/Akt, MAPK/ERK, and NF-κB pathways. Moreover, kaempferol exhibits potential therapeutic benefits by enhancing neuronal survival, attenuating oxidative stress, enhancing mitochondrial calcium channel activity, reducing neuroinflammation, promoting neurogenesis, and improving cognitive function. The evidence suggests that kaempferol holds promise as a natural compound for the prevention and treatment of neurological diseases. Further research is warranted to elucidate the underlying mechanisms of action, optimize dosage regimens, and evaluate the safety and efficacy of this intervention in human clinical trials, thereby contributing to the advancement of scientific knowledge in this field.

Efficient and Economic Utilization of Cellobiose for Glycosylation Modification by Regulating Carbon Source Supply and Metabolic Pathway In Vivo

Glycosylation, one of the most common and significant modifications in nature, has prompted the development of a cellobiose phosphorolysis route for glycosylation in vivo. However, the process of glycosylation is hampered by the notably low conversion rate of cellobiose. In this work, regulation of the carbon source supply by changing the ratio of glucose to cellobiose improved the conversion rate of cellobiose, resulting in enhancing the efficiency of glycosylation and the production of vitexin. Moreover, three genes (pgm, agp, and ushA) involved in the degradation of UDP-glucose were knocked out to relieve the degradation and diversion of the cellobiose phosphorolysis route. Finally, through the optimization of conversion conditions, we observed a continuous enhancement in cellobiose conversion rate and vitexin production in BL21ΔushAΔagp-TcCGT-CepA, corresponding to an increased concentration of added glucose. The maximum production of vitexin reached 2228 mg/L with the addition of 2 g/L cellobiose and 6 g/L glucose, which was 312% of that in BL21-TcCGT-CepA with the addition of 2 g/L cellobiose. The conversion rate of cellobiose in BL21ΔushAΔagp-TcCGT-CepA reached 88%, which was the highest conversion rate of cellobiose to date. Therefore, this study presents a cost-effective and efficient method to enhance the conversion rate of cellobiose during the glycosylation process.

Engineering Escherichia coli for efficient and economic production of C-glycosylflavonoids by deleting YhhW and regulating pH

C-glycosylflavonoids have a number of pharmacological activities. An efficient method for the preparation of C-glycosylflavonoids is through metabolic engineering. Thus, it is important to prevent the degradation of C-glycosylflavonoids for producing C-glycosylflavonoids in the recombinant strain. In this study, two critical factors for the degradation of C-glycosylflavonoids were clarified. The quercetinase (YhhW) gene from Escherichia coli BL21(DE3) was expressed, purified, and characterized. YhhW effectively degraded quercetin 8-C-glucoside, orientin, and isoorientin, while the degradation of vitexin and isovitexin was not significant. Zn²⁺ can significantly reduce the degradation of C-glycosylflavonoids by inhibiting the activity of YhhW. pH was another key factor causing the degradation of C-glycosylflavonoids, and C-glycosylflavonoids were significantly degraded with pH exceeding 7.5 in vitro or in vivo. On this basis, two strategies, deleting YhhW gene from the genome of E. coli and regulating pH during the bioconversion, were developed to relieve the degradation of C-glycosylflavonoids. Finally, the total degradation rates for orientin and quercetin 8-C-glucoside decreased from 100 to 28% and 65% to 18%, respectively. The maximum yield of orientin reached 3353 mg/L with luteolin as substrate, and the maximum yield of quercetin 8-C-glucoside reached 2236 mg/L with quercetin as substrate. Therefore, the method described herein for relieving the degradation of C-glycosylflavonoids may be widely used for the biosynthesis of C-glycosylflavonoids in recombinant strains.

Production of Four Flavonoid C-Glucosides in Escherichia coli

Flavonoid C-glucosides, which are found in several plant families, are characterized by several biological properties, including antioxidant, anticancer, anti-inflammatory, neuroprotective, hepatoprotective, cardioprotective, antibacterial, antihyperalgesic, antiviral, and antinociceptive activities. The biosynthetic pathway of flavonoid C-glucosides in plants has been elucidated. In the present study, a pathway was introduced to Escherichia coli to synthesize four flavonoid C-glucosides, namely, isovitexin, vitexin, kaempferol 6-C-glucoside, and kaempferol 8-C-glucoside. A five- or six-step metabolic pathway for synthesizing flavonoid aglycones from tyrosine was constructed and two regioselective flavonoid C-glycosyltransferases from Wasabia japonica (WjGT1) and Trollius chinensis (TcCGT) were used. Additionally, the best shikimate gene module construct was selected to maximize the titer of each C-glucoside flavonoid. Isovitexin (30.2 mg/L), vitexin (93.9 mg/L), kaempferol 6-C-glucoside (14.4 mg/L), and kaempferol 8-C-glucoside (38.6 mg/L) were synthesized using these approaches. The flavonoid C-glucosides synthesized in this study provide a basis for investigating and unraveling their novel biological properties.