Purple lettuce (Lactuca sativa L.) attenuates metabolic disorders in diet induced obesity

Volume 45, June 2018, Pages 462-470 Journal of Functional Foods Author links open overlay panelYingyanHana1ChanghuiZhaoc1XiaoyunHebYaoShengbTianshiMabZhifanSunaXueyingLiuaChaojieLiuaShuangxiFanaWentaoXubKunlunHuangb a Beijing Key Laboratory of New Technology in Agricultural Application, National Demonstration Center for Experimental Plant Production Education, Beijing University of Agriculture, Beijing 102206, China b Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China c Department of Food Quality and Safety, College of Food Science and Engineering, Jilin University, Changchun, Jilin Province 130062, China Received 21 December 2017, Revised 13 April 2018, Accepted 14 April 2018, Available online 25 April 2018. crossmark-logo Show less https://doi.org/10.1016/j.jff.2018.04.027Get rights and content Highlights • Purple lettuce reduces the body weight gain of DIO mice. • Purple lettuce protects DIO mice from metabolic risk factors. • Purple lettuce contains more esculin and chlorogenic acid than green lettuce. • Purple lettuce modifies the intestinal microbiota structure in DIO mice. Abstract Purple lettuce (Lactuca sativa L.) is a type of low caloric vegetable often consumed freshly, whereas its function in metabolic control has been little studied. To investigate the protective effect of a type of purple lettuce against metabolic risk factors, we treated the C57BL/6J DIO mice with or without purple lettuces for 8 weeks. Results showed that purple lettuce effectively attenuated many metabolic risk factors in DIO mice. Typically, purple lettuce prevented the body weight gain by reducing fat mass accumulation and increasing energy expenditure. Additionally, consumption of purple lettuces enhanced glucose homeostasis, increased insulin sensitivity and improved the lipid profile in the DIO mice. This was, at least partly, attributable to its abundance of bioactive molecules like esculin and chlorogenic acid. High intake of purple lettuces modulated the intestinal microbiota composition like decreased Lachnospiraceae. We conclude that purple lettuce has great potential as functional foods in prevention of metabolic disorders. Previous article in issueNext article in issue Keywords Energy expenditureGlucose toleranceInsulin sensitivityLipid profileDiabetesMicrobiota 1. Introduction With increasing need for high quality life and many factors that affect it, various functional foods are developed to boost physical and mental well-being and prevent nutrition-related diseases (Bigliardi & Galati, 2013). For example, exploring the kingdom of natural plants that may prevent the metabolic risk factors is a popular strategy to curb the trend for obesity development and associated metabolic diseases (Hasaniranjbar et al., 2009, Park et al., 2011; Wang, Feng, & Xiong, 2013). High intakes of fruits and vegetables are frequently shown to be associated with a lower risk of chronic diseases, including metabolic diseases (Rodriguez-Casado, 2016). The lettuce (Lactuca sativa L.) is one of the most popular leafy vegetables predominantly consumed freshly. However, little is known on the beneficial functions of lettuces beyond its basic nutritional property. Lactuca sativa includes many identified taxonomic groups, subspecies and varieties, which delineates various cultivar groups of domesticated edible lettuces but also different visual characteristics as well as nutritional quality (Mulabagal et al., 2010). A number of factors, including the plant genotype and growing conditions, can have a large impact on the quality of vegetable crops, especially on phytochemical levels (Kim, Fonseca, Choi, Kubota, & Kwon, 2008). The amount of the bioactive compounds in lettuces can change during processing and storage (Ferreres, Gil, Castaner, & Tomasbarberan, 1997) and differ in different types (López, Javier, Fenoll, Hellín, & Flores, 2014). This indicated that different species or processed lettuces may have distinct properties. Lettuces have been reported to have health beneficial effects. Typically, the lettuce can decrease intracellular lipid peroxidation, reduce DNA damage and inhibit proapoptotic pathways (Asadpour et al., 2014, Ghorbani et al., 2014). Consumption of lettuces also improves glucose control in a polyphenol independent way (Meyer et al., 2015). Leafy purple lettuce is a type of lettuces with high anthocyanin content and potent antioxidant activity (Hao et al., 2014). Up to now, no study has been dealt with the possible beneficial effect of purple lettuces. We recently evaluated the nutritional value of sixteen varieties of lettuces and found that the flavonoid content and antioxidant activity in purple leafy lettuces were higher than that in green and red leafy lettuces, while the vitamin C and E contents in red leafy lettuces were higher. By comprehensive analysis, two purple leafy varieties (Naiyouzicui and Beizisheng NO.4) are of higher nutritional value (Xie et al., 2017). Therefore, in the current study we intended to systematically evaluate the protective effect of purple lettuce (Beizisheng NO. 4) against metabolic disorders in diet induced obese (DIO) mice model. 2. Materials and methods 2.1. Lettuce preparation and composition analysis The purple lettuce (Beizisheng No. 4) and green leafy lettuce were harvested in October in a farm of Beijing Academy of Agricultural Sciences, thoroughly washed, and then dried at 45 °C for 36 h. The sample was ground to fine powder in a multifunctional electric grinder and adulterated into high fat diet (60% fat; w/w) prepared by Beijing HFK Bioscience Co. Ltd. (Beijing, China). The contents of typical bioactive molecules (esculin, chlorogenic acid, aesculetine, lactucin, cymaroside, chicoric acid and lactucopicin apigenin) in two types of lettuces – purple lettuce (Beizisheng No.4) and green leafy lettuce were quantified using a high performance liquid chromatography Agilent 1100 HPLC system (Agilent Technologies Inc., California, USA) equipped with a diode array detector.