Dose-dependent and time-course evaluation of surfactant proteins A (SP-A) and B (SP-B) expression in human lung cells exposed to dexamethasone (DXM)

Abstract

(SP-A) AND B (SP-B) EXPRESSION IN HUMAN LUNG CELLS EXPOSED TO DEXAMETHASONE (DXM) LINDA FONSECA, ALEX VIDAEFF, ALCORN JOSEPH, BISHOP KAREN, GILSTRAP LARRY, RAMIN SUSAN, University of Texas Health Science Center at Houston, Houston, Texas, University of Texas Health Science Center at Houston, Obstetrics, Gynecology and Reproductive Sciences, Houston, Texas OBJECTIVE: Previous in vitro studies have shown that physiologic concentrations of corticosteroids significantly influence surfactant proteins gene expression after 48 hours of exposure. The purpose of this study was to determine if shorter exposures at lower concentrations elicit the same genomic effects on SP-A and B mRNA. STUDY DESIGN: NCI-H441 cells were exposed to varying concentrations of DXM (10-11 to 10-7 M) in combination with dibutyryl cAMP (1mM) an agent which promotes surfactant gene expression. The measured outcome was SP-A and SP-B mRNA expression at different time points in cell culture (6, 12, 24, 36 and 48 hours). The experiment was conducted three times in parallel with control, and mRNA levels were quantified by quantitative reverse transcriptase polymerase chain reaction. Two-way ANOVA and Kruskal-Wallis test were used for statistical analysis. RESULTS: Both time and concentration significantly influenced SP-A and SP-B mRNA levels (ANOVA, P=0.01 and P=0.03, respectively for SP-A and p=0.001 and p!0.001, respectively for SP-B). When SP-A mRNA levels were considered relative to concentration alone, significant inhibition was evident at higher concentration (10-7 M) compared to control and lower concentration (10-11 M) (P=0.001 and P=0.01, respectively). Also, a dose-dependent effect of DXM on SP-B mRNA upregulation compared to control was first noticeable at 10 -9 M and maximal at 10-7 M concentration (P!0.001 and P=0.001, respectively). Analysis of time impact alone showed that the significant influence of DXM on SP-A and SP-B was not observed until 48 hours (P=0.001 and P=0.008, respectively). CONCLUSION: The dose-dependent effect of DXM on inhibition of SP-A mRNAsteady-state levels andupregulationofSP-BmRNAlevels doesnotappear to manifest earlier than 48 hours from exposure. The inhibition of SP-A mRNA expression at higher concentrations may be relevant to the human fetus. These results suggests that prenatal overexposure to corticosteroids may unfavorably impact thenon-immunehost defense in the lung,which is theprimary role ofSP-A.