Izu Gloria O, Mapasa Nomonde P, Nambooze Jennifer, Chukwuma Maria S, Njoya Emmanuel Mfotie, Tabakam Gaetan T, Bonnet Susanna L, Makhafola Tshepiso J, Mashele Samson S, Chukwuma Chika I
Department of Health Sciences, Faculty of Health and Environmental Sciences, Central University of Technology, Bloemfontein 9301, Free State, South Africa.
Centre for Quality of Health and Living (CQHL), Faculty of Health and Environmental Sciences, Central University of Technology, Bloemfontein 9301, Free State, South Africa.
Antioxidants (Basel). 2024 Oct 14;13(10):1233. doi: 10.3390/antiox13101233.
Bioactive flavonoid epicatechin has been reported in the peel of litchi fruit but isolated from its hydroalcoholic extracts. This study isolated epicatechin with cellular glucose uptake modulatory and ROS production inhibitory properties from the ethyl acetate (EtOAc) extract using a bioassay-guided approach. The fruit peel was defatted with hexane and sequentially extracted using dichloromethane (DCM), EtOAc, methanol (MeOH) and water. In vitro phytochemical models, namely antioxidant (Fe reducing, radical scavenging and anti-linoleic acid peroxidative) and glycaemic control (α-glucosidase and α-amylase inhibitory and glucose uptake modulatory), were employed for the bioassay-guided isolation, while the isolated compound was characterised using NMR and mass spectrometry and assessed for dose-dependent inhibition of α-glucosidase and lipopolysaccharide (LPS)-induced cellular ROS production, as well as modulation of cellular glucose uptake. Relative to the other extracts, the EtOAc extract had appreciable phenol and flavonoid contents, which perhaps influenced its potent anti-lipid peroxidative (65.0%) and α-glucosidase inhibitory (52.4%) effects. The α-glucosidase inhibitory potency of the fractions (1-8) from the EtOAc extracts correlated with their flavonoid contents, with fraction 5 outperforming other fractions. The fraction comprised a pool of fractions obtained from the DCM:MeOH:water (7:3:0.281 //) solvent system. LC-MS revealed the predominant presence of epicatechin in fraction 5, which was later isolated from one of the sub-fractions (sub-fraction 4) of fraction 5. This sub-fraction had stronger anti-lipid peroxidative (65.5%), α-glucosidase inhibitory (65.8%) and glucose uptake modulatory (38.2%) effects than the other sub-fractions from fraction 5, which could have been influenced by the isolated epicatechin. Moreover, the isolated epicatechin inhibited α-glucosidase (IC = 35.3 µM), modulated cellular glucose uptake (EC = 78.5 µM) and inhibited LPS-induced ROS production in RAW 264.7 macrophages in a dose-dependent fashion [IC = 18.9 µM; statistically comparable ( > 0.05) to ascorbic acid, IC = 9.57 µM]. Epicatechin from litchi peel EtOAc extract could potentiate glucose uptake modulatory, α-glucosidase inhibitory and ROS suppressive capacities, which could be influential in the use of litchi fruit peel for managing diabetes and associated oxidative damage.
生物活性类黄酮表儿茶素已在荔枝果皮中被报道，但从其水醇提取物中分离得到。本研究采用生物活性导向法从乙酸乙酯（EtOAc）提取物中分离出具有调节细胞葡萄糖摄取和抑制ROS生成特性的表儿茶素。将果皮用己烷脱脂，然后依次用二氯甲烷（DCM）、乙酸乙酯、甲醇（MeOH）和水进行提取。采用体外植物化学模型，即抗氧化（铁还原、自由基清除和抗亚油酸过氧化）和血糖控制（α-葡萄糖苷酶和α-淀粉酶抑制以及葡萄糖摄取调节）模型进行生物活性导向分离，同时利用核磁共振和质谱对分离得到的化合物进行表征，并评估其对α-葡萄糖苷酶和脂多糖（LPS）诱导的细胞ROS生成的剂量依赖性抑制作用以及对细胞葡萄糖摄取的调节作用。相对于其他提取物，乙酸乙酯提取物具有可观的酚类和黄酮类含量，这可能影响了其强大的抗脂质过氧化（65.0%）和α-葡萄糖苷酶抑制（52.4%）作用。乙酸乙酯提取物的各馏分（1 - 8）的α-葡萄糖苷酶抑制效力与其黄酮类含量相关，馏分5的表现优于其他馏分。该馏分包含从DCM:MeOH:水（7:3:0.281 //）溶剂系统获得的一组馏分。液相色谱-质谱联用（LC-MS）显示馏分5中主要存在表儿茶素，随后从馏分5的一个子馏分（子馏分4）中分离得到表儿茶素。该子馏分比馏分5的其他子馏分具有更强的抗脂质过氧化（65.5%）、α-葡萄糖苷酶抑制（65.8%）和葡萄糖摄取调节（38.2%）作用，这可能受到分离得到的表儿茶素的影响。此外，分离得到的表儿茶素以剂量依赖性方式抑制α-葡萄糖苷酶（IC = 35.3 μM）、调节细胞葡萄糖摄取（EC = 78.5 μM）并抑制RAW 264.7巨噬细胞中LPS诱导的ROS生成[IC = 18.9 μM；与抗坏血酸（IC = 9.57 μM）具有统计学可比性（> 0.05）]。荔枝果皮乙酸乙酯提取物中的表儿茶素可增强葡萄糖摄取调节、α-葡萄糖苷酶抑制和ROS抑制能力，这可能对利用荔枝果皮管理糖尿病及相关氧化损伤具有重要意义。
