Effects Of Milk-derived Bioactive Peptide VPP On Intestinal Inflammation Of Pre-weaning Calves

Milk-derived peptide Val-Pro-Pro(VPP)is known as a classic bioactive peptide with good anti-inflammatory,antihypertension,and anti-hydrolysis functions.However,whether VPP can alleviate intestinal inflammation in calves is unclear.In this study,Holstein calves and SPF C57BL/6 mice were used as animal models to explore the effects of VPP on the growth,health,blood biochemistry,and intestinal microbial construction of calves with diarrhea and related mechanisms.A random block design was adopted in experiment 1.According to the principle of similar birth date,body weight and genetic background,18 newborn Holstein calves were randomly divided into two treatment groups(n = 9): The Ctrl group given 50 m L PBS before morning feeding;and the VPP group given 50 m L of VPP solution(100 mg/kg BW/d)before morning feeding.The trial period is 17 d,of which the actual period is 3 d,and the trial period is 14 d.The initial body weight of the calf and that at the end of the experiment were weighed,and the daily dry matter intake and fecal score were recorded.Determination of serum hormone levels,antioxidant and immune indicators on the 3 and 9 d,and determination of fecal microorganisms on the 3,7 and 11 d.The results showed that: 1)VPP administration had no significant effect on the average daily feed intake and body weight of pre-weaning calves,and the weight growth rate of the VPP group on the d 7 of the test was significantly higher than that of the Ctrl group(P < 0.05).2)The contents of proinflammatory factors IL-6 and TNF-α in the serum of pre-weaning calves could be significantly reduced by feeding VPP(P < 0.05),and the contents of NO and IL-1β also had a tendency of decrease.3)After 7 days of feeding VPP,the relative abundance of g＿Lachnoclostridi,umuncultured＿bac-terium＿,g＿Streptococcu and other bacterial species in the fecal sample of pre-weaning calves were significantly increased.4)VPP administration increased the concentrations of butyric acid and isovaleric acid in the feces of pre-weaning calves(P < 0.05).In order to further study the mechanism by which VPP alleviates intestinal inflammation in calves,18 SPF-grade healthy C57BL/6 male mice(weighing 18-20 g)was chosen in experiment 2 and randomly divided into Ctrl,DSS and DSS+VPP group.The three groups were fed basal diets.The Ctrl group was given water and DSS group was given3% DSS water,and the DSS+VPP group was added 100 mg/kg BW/d VPP on the basis of DSS group.At the end of the experimental period,the mice were sacrificed by necking,and the entire colon was taken to measure the length.The intestinal tissue section was HE stained to observe the intestinal tissue morphology.Blood samples were collected to detect inflammatory cytokines.Colon contents were collected to detect short-chain fatty acids.The results showed that: 1)Compared with the Ctrl group,the weight of the mice in DSS group significantly decreased(P < 0.001),and the VPP administration had a tendency to alleviate the weight loss of the mice(0.05 < P < 0.1).The DAI score of the mice in DSS group was significantly higher than that in the DSS+VPP group(P < 0.001).The colon length of mice in DSS group was significantly shorter than that in Ctrl group and DSS+VPP group(P < 0.001).2)HE staining results of colon tissue showed that the colon of DSS group mice was significantly damaged.The intestinal mucosal epithelial damage was absent,and ulcers.The crypt base was severely damaged,the edema is obvious,and the glands were disorderly arranged with a large number of neutrophils infiltrated.Whereas,the colon structure of mice fed with VPP was complete,and the inflammation was alleviated,and the colon score was significantly lower than that of DSS group(P < 0.05).3)Compared with the Ctrl group,the contents of Ig A,Ig G,IL-6,IL-8,IL-1β and TNF-α in the mice colon tissues of DSS group mice were significantly increased(P < 0.05).Compared with DSS group,the contents of Ig A,Ig G,IL-6,IL-8,IL-1β and TNF-α in the DSS+VPP group were significantly decreased(P < 0.001).4)Compared with the Ctrl group,the contents of acetic acid,valeric acid and total volatile fatty acids in the feces of the mice in the DSS+VPP group were significantly increased(P < 0.01).In summary,VPP can alleviate gut inflammation in both newborn calves and DSSinduced mice.The milk-derived active peptide VPP reduces the concentration of serum inflammatory factors,and protects the integrity of the intestinal tissue structure,thereby alleviating gut inflammation.