Saliva panel of protein candidates: A comprehensive study for assessing high altitude acclimatization

Altitude acclimatization describes the processes whereby lowland humans respond to decreased partial pressure of oxygen. It refers to the changes seen as beneficial and involves a series of physiological adjustments that compensate for reduced ambient PO₂, as opposed to changes that are pathological. Although numerous reports document the physiological effects of exposure to hypobaric hypoxia of varying durations but an interesting aspect overlooked by many researchers is that of acclimatization related studies. As proteome, a dynamic entity responds immediately to external stimuli, protein markers and their trends can be studied to assess acclimatization status of an individual. Compared to blood, the use of saliva is advantageous because sample collection and processing are easy, minimally invasive, low cost and better tolerated by individuals. In this study, we employed iTRAQ based LC-MS/MS technique for comparing saliva samples from humans exposed to hypobaric hypoxia from 7 to 120 days with normoxic controls followed by analysis using Ingenuity Pathway Analysis software and validation by immunoassays. Nearly 67 proteins were found to be differentially expressed in the exposed groups as compared to normoxia indicating modulated canonical pathways as lipid metabolism; acute phase response signalling and proteins as carbonic anhydrase 6, alpha-enolase, albumin, and prolactin inducible protein. Collectively, this study provides the proof of concept for the non-invasive assessment of high altitude acclimatization.