Original ArticleLaurolitsine ameliorates type 2 diabetes by regulating the hepatic LKB1-AMPK pathway and gut microbiota
Graphical Abstract
Introduction
Type 2 diabetes mellitus (DM) is characterized by high blood glucose level added to a group of metabolic disorders. It is one of the most prevalent health problems, affecting a total of 537 million patients worldwide (Sun et al., 2022). Hyperglycemia and hyperlipidemia are the main clinical manifestations of DM, usually caused by pancreatic islet β-cells being unable to secrete sufficient amounts of insulin to match the progressing severity of insulin resistance (IR) (Loria et al., 2013). Glucolipid metabolism and IR in diabetes are lengthy and complex processes that mainly occur in the liver, muscles, and adipose tissues. Although drugs such as metformin, rosiglitazone, and acarbose are widely used for the control of blood glucose, they do not meet all clinical needs, and new antidiabetic drugs are still needed to expand and improve the available treatment options.
Natural products are an important source of new antidiabetic drugs. Classic examples include galegine and phlorizin, which have been isolated from plants (Ríos et al., 2015). In traditional Chinese medicine (TCM), DM has been treated with extracts from plants or other natural resources. Extracts of TCMs such as Gynostemma pentaphyllum, Coptis chinensis, and Salvia miltiorrhiza showed significant clinical effects in treating DM (Wang et al., 2018). Importantly, natural products obtained from TCMs, such as berberine and mangiferin, are very attractive antidiabetic drug candidates (Wang et al., 2019). The leaves and bark of Litsea glutinosa (Lour.) C.B.Rob. (Lauraceae) are traditionally used to treat diabetes and other diseases in China (Wu et al., 2017; Zhang et al., 2018). In our previous study, the alkaloid-rich extract from Litsea glutinosa bark (CG) was found to have antidiabetic effects. Furthermore, eight alkaloids were identified in the CG, and laurolitsine (LL) was the most abundant (Zhang et al., 2018). However, there have been no reports regarding the antidiabetic activities of LL, indicating a need for systematic investigation of its effects and mechanisms of action.
In the present study, we evaluated its antidiabetic effects in vitro using HL-7702 cells and in vivo using db/db diabetic mice, an established animal model of DM (Sharma et al., 2003). We also investigated the potential mechanisms underlying the antidiabetic effects of LL.
Section snippets
Materials
The human liver HL-7702 cell line was purchased from the Institute of Cell Biology of the Chinese Academy of Sciences (Shanghai, China). RPMI-1640 medium, fetal bovine serum (FBS), trypsin, antibiotics, and phosphate buffer solution were purchased from Gibco-Invitrogen (Grand Island, NY, USA). 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) was purchased from KeyGEN Biotech Co., Ltd. (Nanjing, China). The cell and tissue triglyceride (TG) assay kit was purchased from Applygen
LL shows no cytotoxicity in HL-7702 hepatocytes and potently stimulates glucose consumption
The MTT assay showed that LL with a purity of 99.5% (Fig. 1) was not toxic to HL-7702 hepatocytes at concentrations up to 320 μM (Fig. 2A). Treatment with LL (2.5 μM) for 24 h significantly stimulated glucose consumption in HL-7702 hepatocytes compared with the vehicle control (6.99 ± 0.57 mM vs. 5.84 ± 0.59 mM, p < 0.05). The efficiency of LL at 5 μM was comparable to that of 2 mM metformin (Fig. 2B).
LL potently alleviates diabetic symptoms in db/db mice
Compared to C57BL/KsJ mice, diabetic db/db mice showed typical diabetic symptoms, such as
Discussion
The leaves and bark of L. glutinosa are traditional medicines in Hainan Province of China and are traditionally used to treat diabetes. Our previous study found that CG has antidiabetic effects and that its key component was LL (Zhang et al., 2018). In this work, we demonstrated the antidiabetic effects of LL and explored its potential mechanism via a systematic investigation including biochemical and molecular analyses, RNA-seq assays and metagenomics.
Obesity, polydipsia and increased food
Conclusion
The present study demonstrated that LL could stimulate glucose consumption without inducing lactic acid production in vitro. Meanwhile, it exhibited potent antidiabetic effects, including hypoglycemic activity, weight loss, alleviation of insulin resistance, improvement of lipid metabolism, and protection of liver, kidney and pancreatic islet functions in vivo. A potential mechanism of this antidiabetic activity may be related to the decreasing abundances of M. schaedleri and
CRediT authorship contribution statement
Zhang Yong and Wang Ruiqi wrote this paper draft. Zhang xiaopo, Wu chongming and Lu weiying corrected the draft. Zhang Yong, Zhang Xiaopo supervised the experimentators. Zhang Yong, Wang Ruiqi, Yang Yanan, Maning, Zhou Zhi, Tan Yinfeng, Li Yiying and Dong Lin performed the experiments. All data were generated inhouse, and no paper mill was used. All authors agree to be accountable for all aspects of work ensuring integrity and accuracy.
Declaration of Competing Interest
All authors report no conflict of interest.
Acknowledgment
This work was financially supported by Hainan Provincial Natural Science Foundation of China (2019RC208), and the National Natural Science Foundation of China (81760628), and Project Supported by Hainan Province Clinical Medical Center (QWYH202175).
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Authors contributed equally to this paper.