TLR4 Mediates Endotoxin-induced Pulmonary Inflammation And Airway Mucus Hypersecretion In Rats

Part 1 Endotoxin induced pulmonary inflammation andmucus hypersecretion in ratsObjective To investigate endotoxin-induced lung inflammatory injury andairway mucus hypersecretion in rats.Methods Twenty four rats were divided into two experimental groups. Ratsin LPS group (n =12) were intratracheal administered 200 μg of LPSdissolved in 100 μl saline after anesthetization, rats in control group(n = 12 )were given intratracheal 100 μl saline.Pulmonary inflammation scoring,cellcounts in bronchoalveolar lavage fluid (BALF) , and mucus secretionwere evaluated on Day 2, 4, and 7 post-treatment.Results Pulmonary inflammation scoring, cell counts in BALF in LPSgroup was peaked on Day 2 and decreased dramatically on Day 4 and furtheron Day 7 post-treatment. Mucus secretion in LPS group was significantlyenhanced on Day 2, peaked on Day 4, and decreased on Day 7, comparedwith rats treated with saline alone(P<0.05).Conclusions Endotoxin may stimulate pulmonary inflammation and mucushypersecretion in rats.Part 2 TLR4 mediates endotoxin-induced pulmonary inflammation in rats treated with dexamethasoneObjective To investigate the role of TLR4 and TLR2 in endotoxin-induced pulmonary inflammation in rats treated with dexamethasone(DEX). Methods Forty eight rats were divided into four experimental groups. Rats in LPS group (n = 12) were intratrachealy administered 200 μg of LPS dissolved in 100 μl saline after anesthetization, rats in control group(n = 12 ) were given intratracheal 100 μl saline.Rats in LPS plus DEX group(n = 12)were pretreated with DEX 5mg/kg by intraperitonial injection (ip)before intratracheal administration of LPS, rats that were treated with DEX 5mg/kg by ip served as DEX control (n = 12 ).Pulmonary inflammation scoring, the expression of TLR4 mRNA and protein in lung tissue were detected evaluated on Day 2, 4, and 7 post-treatment.Results The expression of TLR4 mRNA and TLR4 positive staining of lung tissue in LPS group was peaked on Day 2 and decreased dramatically on Day 4 and further on Day 7 post-treatment. Pulmonary inflammation scoring, the expression of TLR4 mRNA and protein of lung tissue in LPS plus DEX group was significantly lower than those of LPS group on Days 2, 4, and 7 post-treatment(P<0.05).Conclusions Dexamethasone inhibits endotoxin-induce pulmonary inflammation mediated by TLR4 in rats.Part 3 TLR4 mediates endotoxin-induced airway mucushypersecretion in rats treated with dexamethasoneObjective To investigate role of TLR4 in endotoxin-induced airway mucus hypersecretion in rats treated with dexamethasone(DEX).Methods Forty eight rats were divided into four experimental groups. Rats in LPS group (n = 12) were intratrachealy administered 200 μg of LPS dissolved in 100 μl saline after anesthetization, rats in control group(n = 12 ) were given intratracheal 100 μl saline.Rats in LPS plus DEX group(n = 12)were pretreated with DEX 5mg/kg by intraperitonial injection (ip)before intratracheal administration of LPS, rats that were treated with DEX 5mg/kg by ip served as DEX control (n = 12 ).Mucus secretion and Muc5ac mRNA expression in airway,the of TLR4 and TLR4 in lung tissue were detected on Day 2, 4, and 7 post-treatment.Results The expression of TLR4 mRNA and TLR4 positive staining of lung tissue in LPS group was peaked on Day 2 and decreased dramatically on Day 4 and further on Day 7 post-treatment. Mucus secretion and Muc5ac mRNA expression in airway,the expression of TLR4 mRNA and TLR4 positive staining of lung tissue in LPS plus DEX group was significantly lower than those of LPS group on Days 2, 4, and 7 post-treatment(P<0.05). Conclusions The current study suggests that dexamethasone may inhibit endotoxin-induce airway mucus hypersecretion in rats,which were mediated by TLR4.