Screening and identification of high bioavailable oligopeptides from rapeseed napin (Brassica napus) protein-derived hydrolysates via Caco-2/HepG2 co-culture model

Amelioration of Type 2 Diabetes Mellitus Using Rapeseed (Brassica napus)-Derived Peptides through Stimulating Calcium-Sensing Receptor: Effects on Glucagon-Like Peptide-1 Secretion and Hepatic Lipid Metabolism

The potential of rapeseed-derived peptides (RDPs) in the amelioration of type 2 diabetes mellitus (T2DM) has been hypothesized. However, the mechanisms of the intestinal endocrine hormones activated by RDPs have not been fully understood. This study aimed to explore the amelioration of T2DM and associated hepatic lipid metabolism disorders using RDPs by affecting glucagon-like peptide-1 (GLP-1) secretion. Eight RDPs were prepared by different stepwise enzymatic hydrolysis, wherein RCPP-3 (sequential using alcalase/flavourzyme) and RNPP-1 (sequential using alcalase/trypsin) maintained the normal blood glucose level, significantly increased the body weight (27.17 ± 0.19%) in T2DM mice compared to the positive group (p < 0.05). Western blotting and immunofluorescence experiments indicated that RCPP-3 and RNPP-1 regulated the intestinal endocrine hormones GLP-1 secretion through the calcium-sensing receptor (CaSR). Additionally, the PI3K-Akt pathway was significantly activated by GLP-1, leading to marked improvements in hepatic lipid parameters (TC, TG, LDL-c, and HDL-c) and mitigated fat accumulation (p < 0.05). Notably, the stimulating effect of RCPP-3 on GLP-1 was 10.05% ± 0.71% higher than RNPP-1. G2-R3, a fraction separated from RCPP-3, which contained 14 peptides with the best capacity to stimulate GLP-1 secretion, was identified using HPLC-QTOF-MS/MS. This study suggests the potential of RDPs as novel functional food supplements for ameliorating T2DM.

Metabolomics reveals the effects of Lactiplantibacillus plantarum dy-1 fermentation on the lipid-lowering capacity of barley β-glucans in an in vitro model of gut-liver axis

Bioactive polysaccharides known as the biological response modifiers, can directly interact with intestinal epithelium cells (IEC) and regulate key metabolic processes such as lipid metabolism. Here, the coculture of Caco-2/HT29 monolayer (>400 Ω × cm2) and HepG2 cells was developed to mimic the gut-liver interactions. This system was used to investigate the effects of raw and fermented barley β-glucans (RBG and FBG) on lipid metabolism by directly interacting with IEC. Both RBG and FBG significantly and consistently reduced the lipid droplets and triacylglycerol levels in monoculture and coculture of HepG2 overloaded with oleic acid. Notably, FBG significantly and distinctly elevated PPARα (p < 0.05) and PPARα-responsive ACOX-1 (p < 0.01) gene expressions, promoting lipid degradation in cocultured HepG2. Moreover, the metabolomics analyses revealed that FBG had a unique impact on extracellular metabolites, among them, the differential metabolite thiomorpholine 3-carboxylate was significantly and strongly correlated with PPARα (r = -0.68, p < 0.01) and ACOX-1 (r = -0.76, p < 0.01) expression levels. Taken together, our findings suggest that FBG-mediated gut-liver interactions play a key role in its lipid-lowering effects that are superior to those of RBG. These results support the application of Lactiplantibacillus fermentation for improving hypolipidemic outcomes.

Evaluating the In Situ Insulinotropic Effects of Pea Protein Hydrolysates Mediated by Active GLP-1 via a 2D and Dual-Layered Coculture Cell Model

The aim of this study was to evaluate the in situ insulinotropic effects of pea protein hydrolysates (PPHs) mediated by active glucagon-like peptide-17-36 (active GLP-1) using a 2D and dual-layered coculture cell model. Following this model, a mixed Caco-2 and NCI-H716 cell monolayer was differentiated on the apical side to study the effects of PPHs on active GLP-1 levels; meanwhile, the beta-TC-6 cells were seeded on the basolateral side to investigate the insulin responses induced by active GLP-1. The in situ DPP-4 half-maximal inhibitory concentration (IC50) of PPHs, PPHs-120G, and PPHs-120I was 2.94, 3.43, and 2.26 mg/mL, respectively. They directly stimulated active GLP-1 secretion in NCI-H716 cells by 3.03 ± 0.21, 1.99 ± 0.03, and 2.24 ± 0.02 times, respectively. Insulin release in beta-TC-6 cells was directly stimulated by PPHs but not by PPHs-120G and PPHs-120I. Interestingly, PPHs-120G and PPHs-120I indirectly stimulated insulin release in this coculture cell model by enhancing active GLP-1 concentrations. More importantly, PPHs, PPHs-120G, and PPHs-120I increase active GLP-1 levels by their dual function of stimulating active GLP-1 secretion and DPP-4 inhibition. This study suggests that the 2D and dual-layered coculture cell model supports a more comprehensive assessment of in situ insulinotropic effects of protein hydrolysates mediated by active GLP-1.

Heat-Killed Lacticaseibacillus paracasei Repairs Lipopolysaccharide-Induced Intestinal Epithelial Barrier Damage via MLCK/MLC Pathway Activation

Intestinal epithelial barrier function is closely associated with the development of many intestinal diseases. Heat-killed Lacticaseibacillus paracasei (HK-LP) has been shown to improve intestinal health and enhance immunity. However, the function of HK-LP in the intestinal barrier is still unclear. This study characterized the inflammatory effects of seven HK-LP (1 μg/mL) on the intestinal barrier using lipopolysaccharide (LPS) (100 μg/mL)-induced Caco-2 cells. In this study, HK-LP 6105, 6115, and 6235 were selected, and their effects on the modulation of inflammatory factors and tight junction protein expression (claudin-1, zona occludens-1, and occludin) were compared. The effect of different cultivation times (18 and 48 h) was investigated in response to LPS-induced intestinal epithelial barrier dysfunction. Our results showed that HK-LP 6105, 6115, and 6235 improved LPS-induced intestinal barrier permeability reduction and transepithelial resistance. Furthermore, HK-LP 6105, 6115, and 6235 inhibited the pro-inflammatory factors (TNF-α, IL-1β, IL-6) and increased the expression of the anti-inflammatory factors (IL-4, IL-10, and TGF-β). HK-LP 6105, 6115, and 6235 ameliorated the inflammatory response. It inhibited the nuclear factor kappa B (NF-κB) signaling pathway-mediated myosin light chain (MLC)/MLC kinase signaling pathway by downregulating the Toll-like receptor 4 (TLR4)/NF-κB pathway. Thus, the results suggest that HK-LP 6150, 6115, and 6235 may improve intestinal health by regulating inflammation and TJ proteins. Postbiotics produced by these strains exhibit anti-inflammatory properties that can protect the intestinal barrier.

Assessment of Novel Oligopeptides from Rapeseed Napin (Brassica napus) in Protecting HepG2 Cells from Insulin Resistance and Oxidative Stress

Oligopeptides (Thr-His-Leu-Pro-Lys (THLPK), His-Pro-Leu-Lys (HPLK), Leu-Pro-Lys (LPK), His-Leu-Lys (HLK), and Leu-His-Lys (LHK)) are newly identified from rapeseed napin (Brassica napus) protein-derived hydrolysates with the capability of upregulating glucose transporter-4 (GLUT4) expression and translocation. However, whether each of them enhances GLUT4 expression and translocation and their specific mechanisms remain unclear. Here, we assess the effects of the oligopeptides against insulin resistance (IR) and oxidative stress in hepatocytes and screen out the most antidiabetic one. Specifically, compared with other oligopeptides, LPK not only remarkably elevated glucose consumption to 8.45 mmol/L protein; superoxide dismutase (SOD) activity to 319 U/mg protein; GLUT4 expression and translocation; and phosphorylated level of insulin receptor substrate-1 (IRS-1), phosphatidylinositol 3-kinase (PI3K), and protein kinase B (Akt) (P < 0.05) but also remarkably attenuated the reactive oxygen species (ROS) level to 2255, lactate dehydrogenase (LDH) activity to 20.5 U/mg protein, malondialdehyde (MDA) content to 241 nmol/mg protein, and NO content to 1302 μmol/mL protein (P < 0.05). These findings demonstrated that antidiabetic oligopeptide LPK possessed the most potential to protect HepG2 cells from IR and oxidative stress via activating IRS-1/PI3K/Akt/GLUT4 and regulating common oxidative markers in vitro.

Evaluation of the Effect of Wheat Germ Oil and Olmutinib on the Thioacetamide-Induced Liver and Kidney Toxicity in Mice

Thioacetamide (TAA) intoxication produces a reproducible standard animal model of induced liver and kidney injuries where free radicals are produced by phase I oxidation reactions, which eventually leads to liver and kidney failure. Wheat germ oil (WGO) is a unique food supplement with concentrated nutrient efficiency and has remarkable antioxidant functions. Olmutinib, on the other hand, is a chemotherapy drug considered safe for kidneys and the liver. Therefore, in this study, WGO and olmutinib were investigated for their effect on TAA-induced liver and kidney damage. Inflammatory markers; interleukin-1 beta (IL-1β); IL-6; and the levels of enzymatic markers ALT (Alanine aminotransferase), AST (Aspartate aminotransferase), LDH (Lactate dehydrogenase), and CK (creatinine kinase) in serum for liver and kidney were analyzed and evaluated along with histopathological changes in the tissue. Thirty male mice 4–6 weeks of age were grouped into five groups of six animals: the control group (saline) and the other groups (Groups II to V), which were given thioacetamide for two weeks. In addition, Group II continued with TAA; Group III was given olmutinib (30 mg/kg), Group IV was given the wheat germ oil (WGO) (1400 mg/kg), and Group V was given (olmutinib (30 mg/kg) + WGO (1400 mg/kg)) for five days. The results suggested that olmutinib treatment potentiated TAA-induced liver and kidney injury. At the same time, WGO efficiently alleviated TAA and TAA–olmutinib toxicity in Groups IV and V. The histological studies also showed reduced damage with WGO in the animal model. Hence, it was concluded that WGO could significantly reduce liver and kidney damage caused by TAA and olmutinib in mice.