Longan extract suppresses food intake through regulation of POMC/AgRP neuronal activities and endoplasmic reticulum stress in hypothalamus of db/db mice

Abstract

Type 2 diabetes mellitus (T2DM) is one of the biggest public health issues worldwide and closely related to development of other chronic diseases such as cardiovascular diseases, cancer and neurodegenerative diseases. Considerable percentage of T2DM patients undergo have suffered from binge eating disorder which exacerbates insulin resistance and metabolic challenges. Longan (Dimocarpus longan L.) and its constituents are reported for their various health benefits. However, it is still unknown whether longan fruit supplementation can ameliorate glucose homeostasis and binge eating disorder found in T2DM. The current study aimed to investigate whether longan fruit extract (LE) supplementation can improve diabetic hyperglycemia through modulation of feeding center located in hypothalamus of db/db T2DM mice. As a result, LE supplementation ameliorated fasting blood glucose levels and reduced excessive epididymal fat accumulation. In addition, LE administration improved glucose tolerance and insulin sensitivity in db/db mice. Especially, LE supplemented mice showed less food consumption which was in line with increase of pro-opiomelanocortin (POMC) neuronal activities and decrease of agouti-related peptide (AgRP) neuronal activities. Furthermore, LE supplementation reduced hypothalamic endoplasmic reticulum (ER) stress which was stimulated in db/db mice. As ER stress is a crucial factor involving in appetite control and glucose homeostasis, the effect of LE supplementation on circulating glucose levels and feeding behavior might be mediated by suppression of hypothalamic ER stress. Collectively, these findings suggest that LE could be a potential nutraceutical for improvement of T2DM as well as patients with satiety issues.

Keywords: ER stress; POMC/AgRP; appetite; binge eating disorder; longan; type 2 diabetes.

Figure 1

Fasting blood glucose levels before and after the LE supplementation in db/db mice. Mice were treated with vehicle, 50 mg/kg of LE or 250 mg/kg of metformin for 28 days (N = 5 per group). The data were analyzed by one-way ANOVA followed by Dunnett’s multiple comparison test: ^**p < 0.01 and ^***p < 0.001 vs. the CON group; ^##p < 0.01 and ^###p < 0.001 vs. the DB group.

Figure 2

Effect of LE supplementation on glucose tolerance after oral glucose injection in db/db mice. Mice were treated with vehicle, 50 mg/kg of LE or 250 mg/kg of metformin for 28 days (N = 5 per group). 2 g/kg glucose provided orally after 16 h of fasting and then blood glucose was measured from tail blood at each time point. (A) Left panel shows blood glucose level 0, 15, 30, 60, 90, and 120 min after oral glucose injection. (B) Right panel shows the area under the curve calculated from panel (A). The data were analyzed by one-way ANOVA followed by Dunnett’s multiple comparison test: ^**p < 0.01 and ^***p < 0.001 vs. the CON group; #p < 0.05, ^##p < 0.01 and ^###p < 0.001 vs. the DB group.

Figure 3

Effect of LE supplementation on response to insulin after intraperitoneal insulin injection in db/db mice. Mice were treated with vehicle, 50 mg/kg of LE or 250 mg/kg of metformin for 28 days (N = 5 per group). 1 U/kg of insulin was injected intraperitoneally after 4 h of fasting and then the blood glucose levels were measured from tail blood at each time point. (A) Left panel shows blood glucose level 0, 15, 30, 60, 90, and 120 min after insulin injection. (B) Right panel shows the area under the curve calculated from panel (A). The data were analyzed by one-way ANOVA followed by Dunnett’s multiple comparison test: ^***p < 0.001 vs. the CON group; ^#p < 0.05, ^##p < 0.01 and ^###p < 0.001 vs. the DB group.

Figure 4

Effect of LE supplementation on mRNA expression of POMC/AgRP related genes in hypothalamus of db/db mice. Mice were treated with vehicle, 50 mg/kg of LE or 250 mg/kg of metformin for 28 days (N = 5 per group). mRNA expression was measured by real-time PCR and quantification of (A) POMC, (B) AgRP, (C) NPY, (D) spexin and (E) miR-200a is shown individually. The data were analyzed by one-way ANOVA followed by Dunnett’s multiple comparison test: ^**p < 0.01 and ^***p < 0.001 vs. the CON group; ^##p < 0.01 and ^###p < 0.001 vs. the DB group.

Figure 5

Effect of LE supplementation on mRNA expression of ER stress related genes in hypothalamus of db/db mice. Mice were treated with vehicle, 50 mg/kg of LE or 250 mg/kg of metformin for 28 days (N = 5 per group). mRNA expression was measured by real-time PCR and quantification of (A) CHOP, (B) ATF4, (C) ATF6, (D) spliced XBP-1 and (E) μXBP-1 is shown individually. (F) XBP-1 splicing ratio was calculated by dividing gene expression of sXBP-1 by μXBP-1 and then shown as ratio compared to the CON group. The data were analyzed by one-way ANOVA followed by Dunnett’s multiple comparison test: ^**p < 0.01 and ^***p < 0.001 vs. the CON group; ^##p < 0.01 and ^###p < 0.001 vs. the DB group.