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Title: RELATIONSHIP OF NITROTYROSINE IN MILK TO INFLAMMATION OF THE BOVINE MAMMARY GLAND

Author
item Ledbetter, Tonya
item Paape, Max
item DOUGLASS, L - UNIV. MD
item RAINARD, P - INRA TOURS, FRANCE

Submitted to: Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/2002
Publication Date: 12/1/2002
Citation: LEDBETTER, T.K., PAAPE, M.J., DOUGLASS, L.W., RAINARD, P. RELATIONSHIP OF NITROTYROSINE IN MILK TO INFLAMMATION OF THE BOVINE MAMMARY GLAND. VETERINARY RESEARCH. 2002.

Interpretive Summary: Infecting bacteria that invade the lactating mammary gland settle next to epithelial cells lining the convoluted ducts of the gland, absorbing the abundant nutrients that are readily available and expelling their own toxic excretions into the delicate environment of the mammary gland. These toxic excretions act like acid and burn away ductal and secretory epithelial cells. Almost immediately, chemicals are released by epithelial cells that result in a massive influx of specialized cells from blood called granulocytes. These cells combat the bacteria directly and release more chemicals like hydrogen peroxide and potent oxygen radicles. These chemicals combine to from peroxynitrite, a powerful oxidant that has detrimental effects on both the granulocytes and epithelial cells. As peroxynitrite breaks down, nitrogen dioxide is formed which nitrates tyrosine residues. Researchers at the USDA, Beltsville discovered the presence of nitrotyrosine residues in the milk of dairy cows. Further, they found that the residues were higher in milk from healthy udders compared to diseased udders. These residues were found to inhibit epithelial cell death and may be an important link between viability and nitration of tyrosine residues in cells. Tyrosine nitration may represent the normal state of many proteins in the bovine mammary gland.

Technical Abstract: The relationships of whey protein nitrotyrosine concentration with milk somatic cell count (SCC), clinical mastitis and intramammary infection were investigated. Composite milk samples were collected from 42 lactating Holstein cows and SCC were determined. Total nitrotyrosine concentrations of whey prepared from composite milk samples were determined by ELISA. Bacteriology was performed on aseptically collected quarter milk samples. Nitrotyrosine concentration was negatively correlated with log10SCC (r = -0.49, p # 0.001). Somatic cell count was positively correlated with clinical mastitis (r = 0.51, p # 0.001) and parity (r = 0.31, p # 0.05). Clinical mastitis was positively correlated with log10SCC (r = 0.51, p # 0.001), intramammary infection (r = 0.38, p # 0.05) and parity (r = 0.32, p # 0.05). Intramammary infection and SCC were not correlated (p > 0.8). The decrease in whey protein nitrotyrosine residues with increased log10SCC was likely due to cleavage of nitrotyrosine residues from milk proteins by proteases. Tyrosine nitration in whey proteins was associated with low SCC. Tyrosine nitration may represent the normal state of many proteins in the mammary gland.