Study objectives: A potential pathogenetic cofactor for the development of high-altitude pulmonary edema (HAPE) is an increase in capillary permeability, which could occur as a result of an inflammatory reaction and/or free-radical-mediated injury to the lung. Pulmonary surfactant protein A (SP-A), the most abundant surfactant protein, has potent antioxidant properties and protects unsaturated phospholipids and growing cells from oxidative injury. Single-nucleotide polymorphisms (SNPs) in SP-A1 and SP-A2, genes encoding SP-A, have been associated with susceptibility to respiratory distress syndrome, COPD, and pulmonary infections. In view of the protective role of SP-A against inflammatory reactions and oxidative damage, the two underlying mechanisms in development of HAPE, we examined the association of constitutional susceptibility to HAPE with polymorphisms in SP-A1 and SP-A2.
Design: A cross-sectional case-control study.
Setting: Blood samples were collected at an altitude (≥ 3,500 m).
Participants: Twelve low-altitude native (LAN) subjects with a history of HAPE, 15 healthy LAN sojourners without a history of HAPE (LAN control subjects), and 19 healthy high-altitude natives (HANs) without a history of HAPE (HAN control subjects).
Measurements: The SNPs in four exons and intermediate introns of the SP-A1 and SP-A2 were screened by polymerase chain reaction and sequencing. Biochemical parameters related to oxidative stress (malondialdehyde and reduced glutathione in RBC) and membrane permeability (circulating levels of lactate dehydrogenase) were measured in plasma.
Results: Allele frequencies of three loci in SP-A1 and one in SP-A2 were significantly different between LAN HAPE patients (SP-A1 C1101T: C allele, 36.4% and T allele, 63.6%; SP-A1 T3192C: T allele, 61.1% and C allele, 38.9%; SP-A1 T3234C: T allele, 61.1% and C allele, 38.9%; and SP-A2 A3265C: A allele, 21.4% and C allele, 78.6%) and LAN control subjects (SP-A1 C1101T: C allele, 8.3% and T allele, 91.7%; SP-A1 T3192C: T allele, 15% and C allele, 85%; SP-A1 T3234C: T allele, 15% and C allele, 85%; and SP-A2 A3265C: A allele, 37.5% and C allele, 62.5%) [C1101T odds ratio [OR], 6.3 with 95% confidence interval (CI), 2.8 to 14.3; T3192C OR, 8.9 with 95% CI, 4.5 to 17.6; T3234C OR, 8.9 with 95% CI, 4.5 to 17.6; and A3265C OR, 2.2 with 95% CI, 1.2 to 4.1 (p ≤ 0.01)]. Heterozygous individuals, with respect to SP-A1 C1101T and SP-A2 A3265C, showed less severity in oxidative damage in comparison with homozygous subjects (SP-A1 T1101 and SP-A2 C3265).
Conclusion: The polymorphisms in SP-A1 (C1101T, T3192C, and T3234C) and SP-A2 (A3265C) might be one of the genetic factors contributing to susceptibility to HAPE.