Effects Of Air Mixed Pollutants On The Expression Of SP-D In Lung Tissue And Serum Of Rats

Air pollution is one of the main risking factors which affect humanhealth. Air pollutants are complicated mixture of contents such as particles,SO₂, NOx, CO and O₃. Particles with diameter less than or equal to2.5μm （PM2.5） are more hazardous to human health. PM2.5can easilyconcentrates on poisonous heavy metal, organic pollutant, virus bacteriaand acidic oxide in the air. PM2.5can reach deep into lung tissue. This isthe direct reason of bronchial inflammation. Pulmonary surfactant isreduced mainly by Alveolar type II epithelial cells and Clara cell in whichthe main contents are10%surfactant protein and90%phospholipids. SPhas four types of SP-A, SP-B, SP-C, SP-D. SP-D adjusts lunginflammation, allergy, immunity, participates in clearing pathogen.Probably SP-D is a potential biological index for the completeness ofpulmonary epithelial cell.Objective:The animal model of rats treated by mixed air pollutants of PM2.5,SO₂, NO₂, CO were prepared to study the SP-D level in serum and lungtissue of damaged rats, to search sensitive biomarkers. This will developthe pure detection of atmospheric pollutants into detection of index ofdisease.Methods:90Wistar rats were randomly divided into12groups: experimentalgroups （D1, D7, D30）（low dose, middle dose, high dose） and controlgroups （D1, D7, D30）. Rats in experimental groups were injectedphysiological saline with polluted dust （PM2.5） for1day,7days and30 days respectively. Rats in control groups were given physiological salineand air. The SP-D levels both in pulmonary tissue and serum of rats weredetected using immunohistochemical method, ELISA and RT-PCR.Results1. SP-D levels in serum of ratsIn1day group, SP-D levels in serum of rats of the low dose andmiddle dose experimental group are higher than control group, but there isno significant difference （P＞0.05）, SP-D level of high dose experimentalgroup is higher than control group, their difference is significant （P<0.05）;In7day group, SP-D levels in the low dose and middle dose experimentalgroup are lower than control group, but there is no significant difference,SP-D level of the high dose experimental group is lower than controlgroup, their difference is significant; In30day group, SP-D levels of thelow dose and middle dose experimental group are lower than controlgroup, but there is no significant difference SP-D level of the high doseexperimental group is lower than control group, their difference issignificant. Comparison of each group affected for different time of1day,7days and30days shows that SP-D level first increased then decreasedover time.2. SP-D levels in pulmonary tissue of ratsIn1day and7day groups, SP-D levels in the high dose experimentalgroup is lower than control group, their difference is significant （P<0.05）.There is no significant difference between SP-D levels of low dose,middle dose experimental groups and control group （P＞0.05）; In30daygroup, there is no significant difference between SP-D levels ofexperimental group and control group. Comparison of each groupaffected for different time of1day,7days and30days shows that SP-Dlevel first decreased from1day to7days then increased from7days to30 days.3. SP-D mRNA expression in pulmonary tissue of ratsIn1day group, the expression level of SP-D mRNA in experimentalgroup is higher compared to control group （P＜0.05）; In7day group,there is no significant difference of expression level of SP-D mRNAbetween experimental group and control group; In30day group, theexpression level of SP-D mRNA in low dose experimental group is lowerthan control group （P＜0.05）, the expression level of SP-D mRNA in highdose and middle dose experimental group are lower than control group,but there is no significant difference. Comparison of each group affectedfor different time of1day,7days and30days shows that the expressionlevel of SP-D mRNA first increased then decreased.Conclusion:1. In acute inflammation caused by air pollution, SP-D level in serumof the high dose experimental group is higher than control group in1day,and is lower than control group in7days and30days, but there is nosignificant difference in low dose and middle dose experimental groups.This indicates that SP-D level in serum can serve as a indicator forpulmonary damage and it relates to the concentration of air mixedpollutants.2. Immunohistochemistry shows that SP-D level in pulmonary tissueof high dose experimental group is lower in early inflammatory stage （1day and7days） because of the tissue damage. There is no significantdifference between low dose, middle dose and experimental group. Thisindicates that SP-D level in the lung tissue of rats changed after the lungdamage, and associated with the concentration of polluted dust. When theconcentration of polluted dust is high, the damage to type Ⅱ alveolarepithelial cell is heavy, the synthesis and secretion of SP-D is reduced. Furthermore, the body plays a compensatory function and increases theSP-D content in the lung tissue of rats with dust exposure time, which isbeneficial to protect the lung by SP-D.3. When rats were infected with PM2.5for1day the expression levelof SP-DmRNA was raised compared to control level. This indicates thatSP-D transcriptional level changed at the super-early stage of pulmonarydamage. Besides, low dose can cause change confirmed that SP-D has anatural immune function at early stage of pulmonary damage and canprotect lung tissue. Hence, SP-D mRNA level change can be as a sensitivebiological indicator of early pulmonary damage.In summary, SP-D reacts quickly, the SP-DmRNA expression levelsincreased significantly in1day. This rapid gene rising will help to reducepulmonary damage. SP-D content of lung tissue in rats of the high dosegroup decreased and SP-D in serum rose in1day. This indicates that thealveolar type II epithelial cell damage is fast and heavy, synthesis andsecretion of SP-D of lung tissue is reduced, SP-D gets into bloodcirculation. The experiments show that SP-D reacts rapidly; it is sensitivebiomarkers of pulmonary damage and related to the dust concentration.