Effects of Edible Insect Tenebrio molitor Larva Fermentation Extract as a Substitute Protein on Hepatosteatogenesis and Proteomic Changes in Obese Mice Induced by High-Fat Diet

Abstract

Mealworms (Tenebrio molitor larva) are an edible insect and a protein-rich food; however, research on mealworms as a substitute protein is insufficient. In this study, mealworm fermentation extract (TMP) was assessed as a replacement for soy protein (SP) in a control diet (CON) or a high-fat diet (HFD) of mice for 12 weeks. TMP substitution reduced body weight, body weight gain, body fat mass (perirenal and mesenteric), fat size, glucose intolerance, and insulin resistance compared to the HFD-SP group. TMP alleviated hepatic steatosis (lipid contents and lipid droplets) in high-fat-fed mice and down-regulated the PPARγ, CD36, and DGAT2 gene levels. Proteomic analysis showed that a HFD for 12 weeks up-regulated 20 proteins and down-regulated 17 proteins in mice fed SP. On the other hand, TMP reversed the protein profiles. TMP significantly down-regulated KHK, GLO1, ATP5H, SOD, and DDAH1 and up-regulated DLD, Mup1, CPS1, Ces3b, PDI, and HYOU1 compared to the HFD-SP group. These proteins are involved in the glucose, lipid, and amino acid metabolism, as well as in oxidative stress and endoplasmic reticulum stress. Thus, substituting SP for TMP helped improve HFD-induced obesity, steatosis, and insulin resistance in mice. These results suggest that TMP is a potential substitute for commonly used protein sources.

Keywords: Tenebrio molitor larva; alternative protein; hepatosteatosis; mealworm; obesity.

Figure 1

Body weight, body weight gain, fat mass, and adipocyte size. The values are expressed as the means ± S.E. (n = 10 per group). ^† vs. CON-SP, ^†† vs. CON-TMP and ^††† vs. HFD-SP by two-way ANOVA followed by a Turkey post hoc test (p < 0.05). * p < 0.05 vs. HFD-SP by Student’s t-test. Histological analysis magnification 200×. 2WA FAT, fat diet effect in two-way ANOVA (p < 0.05); 2WA TMP, TMP effect in two-way ANOVA (p < 0.05); 2WA TMP × FAT, interaction between TMP and fat diet in two-way ANOVA (p < 0.05); CON-SP, control diet containing SP; CON-TMP, control diet containing TMP; HFD-SP, high-fat diet containing SP; HFD-TMP, high-fat diet containing TMP.

Figure 2

Serum insulin, glucose, and leptin levels; HOMA-IR; and OGTT. The values are expressed as the means ± S.E. (n = 10 per group). * p < 0.05, *** p < 0.001 vs. HFD-SP by Student’s t-test. 2WA FAT, fat diet effect in two-way ANOVA (p < 0.05); 2WA TMP, TMP effect in two-way ANOVA (p < 0.05); CON-SP, control diet containing SP; CON-TMP, control diet containing TMP; HFD-SP, high-fat diet containing SP; HFD-TMP, high-fat diet containing TMP; HOMA-IR, homeostasis model assessment of insulin resistance; OGTT, oral glucose tolerance test.

Figure 3

Histology, lipid contents, and lipid metabolism-related gene expression in the liver. The values are expressed as the means ± S.E. (n = 10 per group). ^† vs. CON-SP and ^††† vs. HFD-SP by two-way ANOVA followed by a Turkey post hoc test (p < 0.05). ### p < 0.001 vs. CON-SP, *** p < 0.001 vs. HFD-SP by Student’s t-test. Histological analysis magnification 200×. Yellow arrows indicated the lipid droplets or fibrosis. 2WA FAT, fat diet effect in two-way ANOVA (p < 0.05); 2WA TMP, TMP effect in two-way ANOVA (p < 0.05); 2WA TMP × FAT, interaction between TMP and fat diet in two-way ANOVA (p < 0.05); CON-SP, control diet containing SP; CON-TMP, control diet containing TMP; HFD-SP, high-fat diet containing SP; HFD-TMP, high-fat diet containing TMP; H&E, hematoxylin and eosin.

Figure 4

Two-dimensional electrophoresis of proteins in the liver. The 2-D PAGE image from the liver was used as a master gel and reference map. The HFD caused 37 spots to change. The protein spots were identified by MALDI-TOF (arrow) and are marked by their spot numbers. pI, isoelectric point.

Figure 5

Two-dimensional electrophoresis patterns of the proteins in the liver.