The Protective Effects And Mechanisms Of1,25（OH）₂D₃on The Lung In STZ-induced Diabetic Rats

Background:Diabetes mellitus is a metabolic disease characterized by persistent hyperglycemia, and long-term metabolism of carbohydrate, protein and fat can induce tissue and organ damage, for instance, the heart, kidney, lung et al. TLR4is one of innate immune pattern recognition receptor family members and can be involved in the body’s natural immune response and the pathophysiology process of a variety of chronic inflammation diseases. Diabetic nephropathy, diabetic retinopathy, diabetic neuropathy and diabetic macrovascular complications are all associated with TLR4.1,25-(OH)2D3, Calcitriol, a kind of bioactive steroid hormones, not only can regulates calcium and phosphorus metabolism, but also plays an important role in cell prolifera-tion and differentiation, the defense of inflammation and the regulation of immune function. However, current research on diabetic lung lesion is less and has no clear about that the protective effects and mechanisms of1,25(OH)2D3on the lung in STZ-induced diabetic rats.Objective:To observe the effect of1,25-hydroxyvitaminD3(1,25-(OH)2D3) on inflammatory level and TLR4expression of lung tissue in diabetic rats, and to investigate the mechanism of the lung protective effect.Methods:Ninety SD rats were randomly divided into the control group(Group C, n=10) and diabetic model group(n=80). Streptozotocin(STZ) was injected into caudal veins to generate diabetic models, with75diabetic rats generated. Citrate buffer was injected into Group C. Seventy-five diabetic rats were randomly divided into five groups, including diabetic group (Group D), high-dose (Group H), middle-dose (Group M) and low-dose1,25-(OH)2D3intervention group (Group L) and protamine zinc insulin group (Group Y). Rats in group H, M and L group were given0.3μg·kg-1·d-1,0.15μg·kg-1·d-1,0.025μgkg-1·d-11,25-(OH)2D3intragastric administration respectively. Group Y was given16U·kg-1·d-1insulin hypodermic injection in posterior of the neck. Group D and C were given distilled water intragastric administration. All the rats were sacrificed after16weeks by femoral artery hemorrhage. Lung samples were placed in10%Neutral formalin and liquid nitrogen. Blood glucose and serum CRP levels were determined. Pathological alterations in lung tissue were observed through HE and Masson Stain. Protein expression of TLR4and NF-κB p65were investigated by immunohistochemistry. Expression of TLR4, MyD88and NF-κB p65mRNA were quantitatively measured by PCR.Results:Blood glucose and serum CRP levels were significantly higher in diabetic groups than in Group C (P<0.01), and lower in all intervention groups, especially in Group H, than in Group D (P<0.01). There are no statistically significant difference on the serum calcium and phosphorus levels in each group rats (P>0.05). Urinary calcium level in diabetic groups are higher than group C (P<0.05), especially in Group M. PTH level in diabetic groups are higher than group C (P<0.05), especially in Group D. Group D showed severe alveolar wall thickening, significant interstitial proliferation and massive inflammatory cell infiltration. Group H, Y, M and L showed mild to moderate alveolar wall thickening and inflammatory cell infiltration. TLR4and NF-κB p65protein expression were significantly higher in all5diabetic modeled groups than in Group C, and significantly lower in Group H and Y than in Group D. The expression levels of TLR4, MyD88, and NF-κB p65mRNA were significantly higher in Group D than in Group C (P<0.01), and lower in all intervention groups than in Group D. TLR4mRNA expression was positively correlated with both MyD88(r=0.610, P<0.001) and NF-κB p65(r=0.744, P<0.001) mRNA expression. MyD88and NF-κB p65mRNA expression was also positively correlated(r=0.609, P<0.001)Conclusions:1,25-(OH)2D3may exert lung protective effect in STZ-induced diabetic rats by downregulating TLR4-mediated inflammatory pathway.