TY - JOUR AU - Cui, Xiaoxing AU - Gong, Jicheng AU - Han, Hailong AU - He, Linchen AU - Teng, Yanbo AU - Tetley, Teresa AU - Sinharay, Rudy AU - Chung, Kian Fan AU - Islam, Talat AU - Gilliland, Frank AU - Grady, Stephanie AU - Garshick, Eric AU - Li, Zhen AU - Zhang, Junfeng (Jim) PY - 2018 TI - Relationship between free and total malondialdehyde, a well-established marker of oxidative stress, in various types of human biospecimens JF - Journal of Thoracic Disease; Vol 10, No 5 (May 31, 2018): Journal of Thoracic Disease Y2 - 2018 KW - N2 - Background: Oxidative stress is involved in thoracic diseases and health responses to air pollution. Malondialdehyde (MDA) is a well-established marker of oxidative stress, but it may be present in unconjugated and conjugated forms. To our knowledge, no studies have conducted a systemic evaluation of both free MDA (unconjugated MDA) and total MDA (the sum of both unconjugated and conjugated MDA) across various types of human biospecimens. Methods: Free MDA and total MDA were simultaneously measured in a range of human biospecimens, including nasal fluid (N=158), saliva (N=158), exhaled breath condensate (N=40), serum (N=232), and urine (N=429). All samples were analyzed using an HPLC-fluorescence method with high sensitivity and specificity. Due to the right skewed distribution of free MDA and total MDA, we performed natural-log transformation before subsequent statistical analyses. The relationship between the natural log of free and total MDA was evaluated by R 2 of simple linear regression. T test was used for comparisons of means between two groups. One-way analysis of variance was used in combination with Tukey’s test to compare the natural log of the ratio of free MDA to total MDA across various types of biospecimens. Results: For exhaled breath condensate, serum, urine, nasal fluid and saliva samples, the R 2 between free and total MDA were 0.61, 0.22, 0.59, 0.47 and 0.06, respectively; the medians of the free MDA to total MDA ratio were 48.1%, 17.4%, 9.8%, 5.1% and 3.0%, respectively; the free MDA to total MDA ratio in EBC > serum > urine > nasal fluid > saliva (P Conclusions: For exhaled breath condensate and urine samples, using either free or total MDA can provide information regarding the level of oxidative stress; however, that is not the case for serum, nasal fluid, and saliva given the low correlations between free and total MDA. UR - https://jtd.amegroups.org/article/view/21482