Abstract
In this study, milk protein casein was glycated by oligochitosan through the catalysis of transglutaminase (TGase) and then hydrolyzed by trypsin. The obtained glycated casein hydrolysates (GCNH) were assessed for their anti-inflammatory activities, using the lipopolysaccharide (LPS)-stimulated rat intestinal epithelial cells (IEC-6) as cell models and the casein hydrolysates (CNH) without TGase catalysis as controls. The results showed that GCNH had oligochitosan incorporation and thus possessed a glucosamine content of 5.74 g/kg protein. In general, GCNH at dose levels of 25–100 μg/mL could elevate IEC-6 cell growth, and at dose levels of 25–50 μg/mL, they were also able to alleviate the LPS-induced cytotoxicity by increasing cell viability efficiently. Although LPS caused clear inflammation in the LPS-stimulated cells, GCNH were capable of reducing the secretion of three pro-inflammatory mediators including interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α, or promoting the secretion of two anti-inflammatory mediators like IL-10 and transforming growth factor-β, demonstrating their anti-inflammatory activities to the stimulated cells. Moreover, GCNH also could down-regulate the expression of three inflammation-related proteins including TLR4, p-p38, and p-p65 in the stimulated cells, and thus possessed a capacity to suppress the phosphorylation of p38 and p65 proteins as well as to inactivate the NF-κB and MAPK signaling pathways. Additionally, a higher GCNH dose level consistently led to higher anti-inflammatory effect in the cells, while GCNH were always more potent than CNH at performing anti-inflammatory function targets. It is thus suggested that the TGase-catalyzed casein oligochitosan-glycation could enhance the anti-inflammatory activities of casein hydrolysates efficiently. TGase-catalyzed protein glycation thus might enhance the healthcare function of protein ingredients in the body.
Highlights
Proteins as one main component of dietary foodstuffs are vital to the body, because they can provide the essential nutrients for life growth
The results showed that the conjugated glucosamine amount of glycated casein hydrolysates (GCNH) was 5.74 g/kg protein, suggesting that GCNH contained oligochitosan-glycated peptides
When IEC-6 cells were incubated with casein hydrolysates (CNH) and GCNH at three doses of 25–100 μg/mL for three set time periods (12–48 h), all treated cells were detected with viability values larger than 100% (Figure 1), indicating that the two samples did not have a toxic effect on cells
Summary
Proteins as one main component of dietary foodstuffs are vital to the body, because they can provide the essential nutrients for life growth. The transglutaminase (TGase)-mediated protein glycation using the saccharides with amino groups was explored in the previous studies [1,8,9,10,11]. The results of our group showed that TGase-mediated casein oligochitosan-glycation could endow the casein hydrolysates with better barrier protection, higher growth proliferation and differentiation in the rat intestinal epithelial cells (IEC-6 cells) [12,13]. Whether the TGase-induced protein glycation has a positive or negative impact on the anti-inflammatory function of the target proteins or protein hydrolysates is still insufficiently investigated so far. Such a study using the TGase-mediated case in oligochitosan-glycation deserves our consideration
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