In vitro immuno-modulatory ability of tryptic caseinate hydrolysate affected by prior caseinate glycation using the Maillard reaction or transglutaminase

Maillard-type glycated collagen with alginate oligosaccharide suppresses inflammation and oxidative stress by attenuating the expression of LPS receptors Tlr4 and Cd14 in macrophages

Inflammation and oxidative stress contribute to noncommunicable diseases (NCDs), with macrophages playing pivotal roles. Glycated collagen through Maillard-type glycation holds promise for enhancing anti-inflammatory properties, but its mechanism remains unclear. This study investigates the cellular mechanism and aims to contribute to expanding collagen utilization. Collagen was glycated with alginate oligosaccharide (AO) and glucose (Glc: as a comparative case) at 60 °C and 35% relative humidity for up to 24 h (C-AO and C-Glc, respectively). The anti-inflammatory activities of both C-AO and C-Glc were evaluated using an LPS-stimulated macrophage model. 18 h AO-glycated collagen (C-AO18 h) was found to significantly reduce the production of nitric oxide and proinflammatory cytokines (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β). In contrast, C-Glc did not exhibit enhanced anti-inflammatory activity during any of the glycation periods. The enhanced anti-inflammatory activity of C-AO18 h was attributed to its downregulating effect on LPS receptors (toll-like receptor 4, Tlr4; cluster of differentiation 14, Cd14) and myeloid differentiation primary response 88 (Myd88) mRNA expression, with suppression in receptor expression resulting in decreased phagocytic ability of macrophages against E. coli. In addition, compared with intact collagen, C-AO18 h exhibited improved antioxidant activity in the LPS-stimulated macrophage model, as it significantly upregulated superoxide dismutase (SOD) and catalase (CAT) activities while reducing malondialdehyde (MDA) levels. Overall, this study contributes to the development of collagen-based functional foods for mitigating inflammation and oxidative stress in NCDs.

Casein Lactose-Glycation of the Maillard-Type Attenuates the Anti-Inflammatory Potential of Casein Hydrolysate to IEC-6 Cells with Lipopolysaccharide Stimulation

During the thermal processing of dairy products, the Maillard reaction occurs between milk proteins and lactose, resulting in the formation of various products including glycated proteins. In this study, lactose-glycated casein was generated through the Maillard reaction between casein and lactose and then hydrolyzed by a trypsin preparation. The anti-inflammatory effect of the resultant glycated casein hydrolysate (GCH) was investigated using the lipopolysaccharide (LPS)-sitmulated rat intestinal epithelial (IEC-6) cells as a cell model and corresponding casein hydrolysate (CH) as a control. The results indicated that the preformed glycation enabled lactose conjugation to casein, which endowed GCH with a lactose content of 12.61 g/kg protein together with a lower activity than CH to enhance the viability value of the IEC-6 cells. The cells with LPS stimulation showed significant inflammatory responses, while a pre-treatment of the cells with GCH before LPS stimulation consistently led to a decreased secretion of three pro-inflammatory mediators, namely, IL-6, IL-1β and tumor necrosis factor-α (TNF-α) but an increased secretion of two anti-inflammatory mediators, including IL-10 and transforming growth factor-β (TGF-β), demonstrating the anti-inflammatory potential of GCH in LPS-stimulated cells. In addition, GCH up-regulated the expression of TLR4, p-p38, and p-p65 proteins in the stimulated cells, resulting in the suppression of NF-κB and MAPK signaling pathways. Collectively, GCH was mostly less efficient than CH to exert these assessed anti-inflammatory activities in the cells and more importantly, GCH also showed an ability to cause cell inflammation by promoting IL-6 secretion and up-regulating the expression of TLR4 and p-p65. The casein lactose-glycation of the Maillard-type was thereby concluded to attenuate the anti-inflammatory potential of the resultant casein hydrolysate. It is highlighted that the casein lactose-glycation of the Maillard-type might cause a negative impact on the bioactivity of casein in the intestine, because the glycated casein after digestion could release GCH with reduced anti-inflammatory activity.

Transglutaminase-Mediated Caseinate Oligochitosan Glycation Enhances the Effect of Caseinate Hydrolysate to Ameliorate the LPS-Induced Damage on the Intestinal Barrier Function in IEC-6 Cells

Some food components can regulate the intestinal barrier function. Herein, the effect of transglutaminase-type oligochitosan glycation on caseinate hydrolysate for its ability to maintain intestinal epithelial integrity and the tight junction (TJ) structure was investigated by assessing and comparing the bioactivities of glycated caseinate hydrolysate and caseinate hydrolysate against the lipopolysaccharide-induced barrier damage in the model cells (rat intestinal epithelial IEC-6 cells). The results from liquid chromatography with tandem mass spectrometry (LC-MS/MS) analysis demonstrated that oligochitosan glycation occurred at the Gln residues of α-S1-casein and α-S2-casein. The two hydrolysates retarded the lipopolysaccharide cytotoxicity toward IEC-6 cells and enhanced the barrier integrity by increasing the transepithelial electrical resistance or decreasing the paracellular permeability. In addition, these two hydrolysates could upregulate both mRNA and protein expression of three TJ proteins in IEC-6 cells. More importantly, the glycated caseinate hydrolysate had higher potential than caseinate hydrolysate to protect IEC-6 cells against the lipopolysaccharide-induced barrier damage, suggesting that the transglutaminase-mediated oligochitosan glycation of proteins is a useful approach to enforce protein biofunctions in the intestine.

The impact of caseinate oligochitosan-glycation by transglutaminase on amino acid compositions and immune-promoting activity in BALB/c mice of the tryptic caseinate hydrolysate

Caseinate was glycated with oligochitosan via transglutaminase (TGase) action and then hydrolyzed by trypsin to generate glycated caseinate hydrolysate (GCNH) that was investigated for in vivo immune-promoting activity. Caseinate hydrolysate (CNH) containing glucosamine of 5.7 g/kg had amino acid compositions similar to GCNH. In normal BALB/c mice, GCNH at 100-400 mg/(kg d) showed higher immune-promoting activity than CNH via increasing serum IgM, IgA, and IgG by 1.5-24.5%, enhancing spleen and thymus indices by 9.7-26.2%, or increasing splenocyte lymphocyte proliferation and natural killer (NK) cell activity by 1.2-11.5%. GCNH also exerted higher activity than CNH in the suppressed BALB/c mice through increasing serum IgM, IgA, and IgG by 2.6-10.5%, enhancing spleen and thymus indices by 0.4-50.1%, or increasing splenocyte lymphocyte proliferation and NK cell activity by 3.4-18.9%. The results highlight that this TGase-type oligochitosan-glycation is potential to generate functional protein ingredients that possess improved immune-promoting activity once hydrolyzed by trypsin.

Glycation sites and bioactivity of lactose-glycated caseinate hydrolysate in lipopolysaccharide-injured IEC-6 cells

During the thermal processing of milk, Maillard reactions occur between proteins and lactose to generate glycated proteins. In this study, a lactose-glycated caseinate was hydrolyzed by trypsin. The obtained glycated caseinate (GCN) hydrolysate had a lactose content of 10.8 g/kg of protein. We identified its glycation sites and then assessed it for its protective effect against lipopolysaccharide-induced barrier injury using a rat intestinal epithelial cell line (IEC-6 cells) as a cell model and unglycated caseinate (CN) hydrolysate as a reference. Results from our liquid chromatography-mass spectrometry analysis of the GCN hydrolysate verified that lactose glycation occurred at the Lys residues in 3 casein components (α_S1-casein, β-casein, and κ-casein), and this resulted in the formation of 5 peptides with the following amino acid sequences: EMPFPKYPKYPVEPF, HIQKEDVPSE, GSENSEKTTMPL, NQDKTEIPT, and EGIHAQQKEPM. The results from cell experiments showed that the 2 hydrolysates could promote cell growth and decrease lactate dehydrogenase release in the lipopolysaccharide-injured cells; more importantly, they could partially protect the damaged barrier function of the cells by increasing trans-epithelial electrical resistance, decreasing epithelial permeability, and upregulating the expression of the 3 tight junction proteins zonula occludens-1, occludin, and claudin-1. However, compared with CN hydrolysate, GCN hydrolysate showed lower efficacy in protecting against cellular barrier dysfunction. We propose that the different chemical characteristics of the CN hydrolysate and the GCN hydrolysate (i.e., amino acid loss and lactose conjugation) contributed to the lower barrier-protective efficacy of the GCN hydrolysate. During dairy processing, protein glycation of the Maillard type might have a non-negligible, unfavorable effect on dairy proteins, in view of the resulting protein glycation we found and the critical function of proteins for maintaining the integrity of the intestinal barrier.

Preparation and Evaluation of New Glycopeptides Obtained by Proteolysis from Corn Gluten Meal Followed by Transglutaminase-Induced Glycosylation with Glucosamine

New glycopeptides were generated by proteolysis from corn gluten meal (CGM) followed by transglutaminase (TGase)-induced glycosylation with glucosamine (GlcN). The glycopeptides exhibited desirable antioxidant and intracellular ROS-scavenging properties. The amount of conjugated GlcN quantified by high-performance liquid chromatography (HPLC) was 23.0 g/kg protein. The formed glycopeptides contained both glycosylated and glycation types, as demonstrated by the electrospray ionization time-of-flight mass spectrometry (ESI-TOF MS/MS). The glycopeptides exhibited scavenging capabilities against free radical diphenylpicrylhydrazyl (DPPH) and hydroxyl radicals by reducing their power. The potential protection of glycopeptides against ethanol-induced injury in LO2 cells was assessed In Vitro based on methyl thiazole tetrazolium (MTT) testing and intracellular reactive oxygen species (ROS) scavenging capacity, respectively. Glycopeptide cytoprotection was expressed in a dose-dependent manner, with the glycopeptides exhibiting good solubility ranging from 74.8% to 83.2% throughout a pH range of 2-10. Correspondingly, the glycopeptides showed good emulsifying activity (36.0 m2/g protein), emulsion stability (74.9%), and low surface hydrophobicity (16.3). These results indicate that glycosylation of CGM significantly improved its biological and functional properties. Glycopeptides from CGM could be used as potential antioxidants as well as comprising a functional food ingredient.

Effect of the Zn Supplementation on Immuno-Modulatory Activities of Bovine Lactoferrin in the Murine Splenocytes and RAW264.7 Macrophages

Lactoferrin (LF) has important bio-functions including immuno-modulation, while essential trace metals may interact with LF and thereby induce property especially bio-activity changes. Bovine LF was thus supplemented with Zn²⁺ at 0.16, 0.32, and 0.64 mg/g LF to yield 10%, 20%, and 40% Zn-saturation, respectively. Afterwards, bovine LF and the Zn-supplemented LF products at 10-40-μg/mL doses were compared for their immuno-modulatory activities in two immune cells (murine splenocytes and RAW264.7 macrophages), using the stimulation index of the splenocytes, T lymphocyte subpopulations, macrophage phagocytosis, and cytokine production as evaluation reflectors. The results showed that bovine LF and the Zn-supplemented LF products had suppressive effect on the splenocytes and concanavalin A (ConA)- and lipopolysaccharide-stimulated splenocytes, but lower Zn-saturation and lower dose could alleviate and even counteract this suppressive effect (P < 0.05). More importantly, the Zn-supplemented LF product with lower Zn-saturation at lower dose exerted slightly higher macrophage stimulation, increased CD4⁺/CD8⁺ ratio of T lymphocyte subpopulations, and were capable of enhancing the interleukin-2 (IL-2), IL-4, and interferon-γ production in the splenocytes or the IL-1β, IL-6, and tumor necrosis factor-α production in the macrophages significantly (P < 0.05). Contrary to its counterpart at lower dose, the Zn-supplemented LF product with higher Zn-saturation at higher dose mostly showed opposite effects in the two cell models. It is concluded that Zn supplementation has an impact on the immuno-modulation of bovine LF, while Zn-saturation is a key factor to modulate these assessed immune activities.

Modulatory Effect of the Supplemented Copper Ion on In Vitro Activity of Bovine Lactoferrin to Murine Splenocytes and RAW264.7 Macrophages

Bovine lactoferrin (LF) was supplemented with Cu²⁺ at three contents of 0.16, 0.32, and 0.64 mg/g LF, respectively. After then, LF and Cu-supplemented LF products were assessed for immuno-modulation in murine splenocytes and RAW264.7 macrophages, using dose levels of 10-40 μg/mL and four evaluation reflectors including stimulation index of splenocytes, T lymphocyte subpopulations, macrophage phagocytosis, and cytokine secretion. The results indicated that LF and Cu-supplemented LF products had suppression on splenocytes as well as concanavalin A (ConA)- or lipopolysaccharide-stimulated splenocytes; however, using lower Cu-supplementation content (i.e., 0.16 mg/g LF) and lower dose level (10 μg/mL) alleviated this suppression significantly (P &lt; 0.05). Compared to LF, Cu-supplemented LF product of lower Cu-supplementation content at lower dose level yielded slightly enhanced macrophage stimulation, increased CD4⁺/CD8⁺ ratio of T lymphocyte subpopulations in ConA-stimulated splenocytes, and significant secretion enhancement for interleukin-2 (IL-2), IL-4, interferon-γ (in splenocytes), IL-1β, and tumor necrosis factor-α (in macrophages) (P &lt; 0.05). Furthermore, Cu-supplemented LF product of higher Cu-supplementation content (i.e., 0.64 mg/g LF) at higher dose level mostly showed opposite effects in the cells, in comparison with its counterpart at lower dose level. It is concluded that Cu-supplementation of LF can alleviate or increase LF's effects on the two immune cells, and moreover, Cu content of supplemented LF is a key factor that modulates these effects.

Chemical features of the oligochitosan-glycated caseinate digest and its enhanced protection on barrier function of the acrylamide-injured IEC-6 cells

Whether caseinate oligochitosan-glycation of the transglutaminase-type followed by trypsin digestion could lead to better protection against the acrylamide-induced cell barrier damage was investigated. Compared with caseinate digest, glycated caseinate digest had similar amount of Lys and Arg but lower -NH₂ (0.557 versus 0.508 mol/kg protein) and total amide (1.12 versus 1.05 mol/kg protein) contents, and contained glucosamine at 5.74 g/kg protein. Acrylamide damaged barrier function of IEC-6 cells efficiently, leading to increased paracellular permeability and lactate dehydrogenase release, decreased trans-epithelial electrical resistance, and destroyed tight junction. The two digests alleviated these barrier dysfunctions via reversing index values. Three cellular proteins (ZO-1, occludin, and claudin-1) crucial to tight junction were up-regulated by the two digests. Furthermore, glycated caseinate digest was always more effective than caseinate digest to improve cell barrier function. This oligochitosan glycation is thus desired, as it ensures glycated protein digest with higher potential to protect intestinal barrier function.