Abstract
Chinese propolis (CP), an important hive product, can alleviate inflammatory responses. However, little is known regarding the potential of propolis treatment for mastitis control. To investigate the anti-inflammatory effects of CP on bovine mammary epithelial cells (MAC-T), we used a range of pathogens to induce cellular inflammatory damage. Cell viability was determined and expressions of inflammatory/antioxidant genes were measured. Using a cell-based reporter assay system, we evaluated CP and its primary constituents on the NF-κB and Nrf2-ARE transcription activation. MAC-T cells treated with bacterial endotoxin (lipopolysaccharide, LPS), heat-inactivated Escherichia coli, and Staphylococcus aureus exhibited significant decreases in cell viability while TNF-α and lipoteichoic acid (LTA) did not. Pretreatment with CP prevented losses in cell viability associated with the addition of killed bacteria or bacterial endotoxins. There were also corresponding decreases in expressions of proinflammatory IL-6 and TNF-α mRNA. Compared with the mastitis challenged cells, enhanced expressions of antioxidant genes HO-1, Txnrd-1, and GCLM were observed in CP-treated cells. CP and its polyphenolic active components (primarily caffeic acid phenethyl ester and quercetin) had strong inhibitive effects against NF-κB activation and increased the transcriptional activity of Nrf2-ARE. These findings suggest that propolis may be valuable in the control of bovine mastitis.
Highlights
Inflammation of the mammary gland caused by invading pathogens is common among lactating dairy cows and leads to considerable economic loss through reduced milk yield, impaired milk quality, and increased veterinary costs [1]
We studied the impact of the effect propolis when bovine mammary epithelial cells were challenged with heat-killed mastitis-causing bacterial cells, as well as selected agents associated with tissue response to mastitis
We found that tumor necrosis factor- (TNF-)α and lipoteichoic acid (LTA) stimulation did not cause any significant losses on the cell viability or cell apoptosis to bovine mammary epithelial cells (bMECs), coinciding with other in vitro studies using bovine mammary cells [1, 5]
Summary
Inflammation of the mammary gland (mastitis) caused by invading pathogens is common among lactating dairy cows and leads to considerable economic loss through reduced milk yield, impaired milk quality, and increased veterinary costs [1]. Mastitis is primarily categorized as subclinical or clinical mastitis The differences in these types of mastitis are based on the invading pathogen(s) and resolution of the infection. Clinical mastitis is stronger and more acute than the subclinical mastitis, and it is caused mainly by Gram-negative bacteria such as Escherichia coli. To suppress proliferation of invading pathogenic mastitiscausing bacteria, modern dairy practice employs several strategies, including teat disinfection, antibiotic therapy, and Mediators of Inflammation culling of persistently infected cows [7]. Considering the risks associated with antibiotic therapies for bovine mastitis, development of alternative treatment strategies for management of clinical and subclinical mastitis are warranted. We studied the impact of the effect propolis when bovine mammary epithelial cells were challenged with heat-killed mastitis-causing bacterial cells, as well as selected agents associated with tissue response to mastitis. Several isolated compounds from propolis were investigated to clarify the mechanism of action
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