Abstract:

【Objective】 The aim of this study was to evaluate the polysaccharide nucleic acid fraction of Bacillus Calmette Guerin (BCG-PSN) in protection of rat mastitis induced by endotoxin (or lipopolysaccharide,LPS). 【Method】 Seventy-two lactating SD rats were randomly divided into control and treatment groups (n=36). BCG-PSN (treatment group, TG) or sterile pyrogen-free physiological saline solution (control group, CG) were injected at 0.33 mL into the left tibialis anterior muscle of rats 14 days after conception. The administration was repeated for five consecutive times every other day. Seventy-two hours after parturition, 30 rats of each group were inoculated with 10 μg Escherichia coli LPS dissolved in 100 μL physiological saline solution into the left 4 (L4) and right 4 (R4) mammary glands and six as control. Just before the inoculation (control group defined as 0 h) and 3, 6, 9, 12 and 24 h after inoculation, six rats at every time point were euthanatized and samples were collected. 【Results】 The histopathological observation indicated that treatment with BCG-PSN made a rapid renovation of mammary tissue compared with CG. Milk secretion elevated with an increasing of the luminal spaces with milk at the later stage of inflammation in TG. RT-PCR analysis showed that BCG-PSN decreased the toll-like receptor-4 (TLR-4) mRNA expression level from 3 h PI and significant reduction was observed at 6 h, 9 h and 24 h PI. In mammary tissue, the activity of iNOs peaked at 6 h in TG and 9 h in CG, whereas serum iNOs activity reached nadir level at 6 h and 3 h PI, respectively. Administration BCG-PSN reduced the peak level of TNF-α, in mammary tissue compared with CG, whereas no significant changes were observed in serum after LPS challenge. 【Conclusion】 These findings suggested that BCG-PSN has a general protective effect against LPS-induced local mammary injury by reducing TLR-4 mRNA expression level and further inhibiting the release of inflammatory factors (TNF-α, iNOs) that cause damage to mammary gland.

Key words: BCG-PSN, endotoxin, mastitis, rats