title: DNA hydroxymethylation age of human blood determined by capillary hydrophilic-interaction liquid chromatography/mass spectrometry.
abstract: BACKGROUND
  Aging is a complex phenomenon and characterized by a progressive decline in physiology and function of adult tissues. However, it hasn't been well established of the correlation between aging and global DNA methylation and hydroxymethylation that regulate the growth and development of higher organisms.
  
  
  RESULTS
  We developed an on-line trapping/capillary hydrophilic-interaction liquid chromatography/electrospray ionization-mass spectrometry method for ultra-sensitive and simultaneous quantification of 5-methylcytosine (5-mC) and 5-hydroxymethylcytosine (5-hmC) in genomic DNA from human blood. Limits of detection for 5-mC and 5-hmC were 0.04 and 0.13 fmol, respectively. The imprecision and recovery of the method were determined with the relative standard deviations (RSDs) and relative errors being <11.2 and 14.0 %, respectively. We analyzed the contents of 5-mC and 5-hmC in genomic DNA of blood from 238 healthy people aged from 1 to 82 years. The results showed that 5-hmC content was significantly decreased and highly correlated with aging process, while 5-mC only showed slight correlation with age. We then established a DNA hydroxymethylation age model according to 5-hmC content with a mean absolute deviation (MAD) of approximate 8.9 years. We also calculated the mean relative error (MRE) using the predicted ages based on the age model and the chronological ages. The results showed that the MRE was 18.3 % for samples with ages from 20 to 82 years (95 % confidence interval, N = 190).
  
  
  CONCLUSIONS
  The global DNA hydroxymethylation represents a strong and reproducible mark of chronological age, which could be potentially applied in health assessment and prevention of diseases. The identification of biological or environmental factors that influence DNA hydroxymethylation aging rate may permit quantitative assessments of their impacts on health.
authors.affiliation: Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of education), Department of Chemistry, Wuhan University, Wuhan, 430072 China.
authors.forename: Jun
authors.initials: J
authors.lastname: Xiong
authors.affiliation: Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of education), Department of Chemistry, Wuhan University, Wuhan, 430072 China.
authors.forename: Han-Peng
authors.initials: HP
authors.lastname: Jiang
authors.affiliation: Center for Gene Diagnosis, Zhongnan Hospital of Wuhan University, Wuhan, 430071 China.
authors.forename: Chun-Yan
authors.initials: CY
authors.lastname: Peng
authors.affiliation: Center for Gene Diagnosis, Zhongnan Hospital of Wuhan University, Wuhan, 430071 China.
authors.forename: Qian-Yun
authors.initials: QY
authors.lastname: Deng
authors.affiliation: Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of education), Department of Chemistry, Wuhan University, Wuhan, 430072 China.
authors.forename: Meng-Dan
authors.initials: MD
authors.lastname: Lan
authors.affiliation: Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of education), Department of Chemistry, Wuhan University, Wuhan, 430072 China.
authors.forename: Huan
authors.initials: H
authors.lastname: Zeng
authors.affiliation: Center for Gene Diagnosis, Zhongnan Hospital of Wuhan University, Wuhan, 430071 China.
authors.forename: Fang
authors.initials: F
authors.lastname: Zheng
authors.affiliation: Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of education), Department of Chemistry, Wuhan University, Wuhan, 430072 China.
authors.forename: Yu-Qi
authors.initials: YQ
authors.lastname: Feng
authors.affiliation: Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of education), Department of Chemistry, Wuhan University, Wuhan, 430072 China.
authors.forename: Bi-Feng
authors.initials: BF
authors.lastname: Yuan
keywords: 5-hydroxymethylcytosine; 5-methylcytosine; Aging; Hydrophilic-interaction liquid chromatography; Mass spectrometry