AGL9: A Novel Hepatoprotective Peptide from the Larvae of Edible Insects Alleviates Obesity-Induced Hepatic Inflammation by Regulating AMPK/Nrf2 Signaling

Abstract

In this study, we investigated the anti-obesity properties of the novel peptide Ala-Gly-Leu-Gln-Phe-Pro-Val-Gly-Arg (AGL9), isolated from the enzymatic hydrolysate of Allomyrina dichotoma larvae. To investigate the preventive effects of AGL9 against hepatic steatosis and its possible mechanisms of action, we established an nonalcoholic fatty liver disease (NAFLD) model by feeding C57BL/6 mice a high-fat diet. NAFLD mice were administered 100 mg/kg AGL9 and 60 mg/kg orlistat via gavage (10 mL/kg) for 5 weeks, followed by the collection of blood and liver tissues. We found that AGL9 normalized the levels of serum alanine aminotransferase, aspartate aminotransferase, triglyceride, total cholesterol, high-density lipoprotein, very low-density lipoprotein (LDL)/LDL, adiponectin, and leptin in these mice. Additionally, AGL9 activated the protein-level expression of 5’ AMP-activated protein kinase and acetyl-CoA carboxylase phosphorylation and the transcript-level expression of sterol regulatory element-binding protein-1c, fatty acid synthase, superoxide dismutase, glutathione peroxidase, glucocorticoid receptor, nuclear respiratory factor 2, tumor necrosis factor-α, interleukin-1β, interleukin-6, and monocyte chemoattractant protein-1 in hepatocytes. These results showed that AGL9 exhibited hepatoprotective effects by attenuating lipid deposition, oxidative stress, and inflammation via inhibition of AMPK/Nrf2 signaling, thereby reducing the production of hepatic proinflammatory mediators and indicating AGL9 as a potential therapeutic strategy for NAFLD.

Bioactive Peptide Discovery from Edible Insects for Potential Applications in Human Health and Agriculture

“…Ultrafiltration was often the first step in peptide purification, probably because of its simplicity and cost-effectiveness. The ultrafiltration membranes used mostly had molecular weight cut-offs (MWCO) of 1, 3, 5, and 10 kDa [ 30 , 31 , 33 , 34 , 35 , 36 , 37 , 38 ]. The peptide fraction with the lowest molecular weight very often showed the highest bioactivity, and thus, was chosen to proceed to the next purification step.…”

“…Other than the fractionation of peptides by size, the separation of peptides by the charges and hydrophobicity was performed in some investigations. Anion exchange chromatography was frequently used to isolate negatively-charged bioactive peptides, such as GNPWM, an anti-ACE peptide [ 31 ], EIAQDFKTDL, an anti-obesity peptide [ 37 ], and AGLQFPVGR, a hepatoprotective peptide [ 36 , 37 ]. Phosphate buffers were used as the mobile eluent for the bioactive peptide separation in anion exchange columns; therefore, a desalting step was essential to eliminate the excess salt before the next purification [ 31 , 37 ].…”

“…Databases such as UniProt, SwissProt, BIOPEP-UWM, and NCBI were used for peptide identification by searching against the molecular mass-to-charge information from MS or MS/MS [ 29 , 30 , 33 , 37 , 39 ]. Some studies also used in-house or specific databases of edible insects for more specific identification [ 29 , 36 , 37 ].…”

“…Peptides can be synthesized by peptide synthesizer equipment or through a conventional fluorenylmethoxycarbonyl protecting group (FMOC) solid-phase approach or FMOC/ tert -butyl-based solid-phase protocols [ 31 , 37 , 39 ]. Usually, the peptides synthesized would be analyzed with HPLC and LC-MS to ensure that the purity of the synthetic peptides ranges from 95 to 99.8% [ 30 , 33 , 34 , 36 , 37 , 39 ].…”

“…They used this in vivo model to study the mechanism of action of AGLQFPVGR ( Figure 3 ), a novel anti-obesity peptide isolated from Allomyrina dichotoma . AGLQFPVGR acted by activating AMPK/Nrf2 signaling to regulate lipid levels, inhibiting lipid metabolism, and reducing oxidative stress [ 36 ]. This peptide also possessed hepatoprotective properties due to its ability to attenuate oxidative stress [ 36 ].…”