title: A comparison of methods for the measurement of 8-isoPGF(2α): a marker of oxidative stress.
abstract: BACKGROUND
  Oxidative stress describes the cellular damage caused by excess reactive oxygen species not adequately inactivated by antioxidants. Oxidative stress has been implicated in playing a role in many disorders. Lipid peroxidation end-products are employed as markers of oxidative stress, of which the isoprostane, 8-iso-PGF(2α), is widely used. 8-iso-PGF(2α) is measured in plasma or urine by gas chromatography-mass spectrometry (GC/MS), liquid chromatography-mass spectrometry (LC/MS), tandem-mass spectrometry or enzyme-linked immunosorbent assay (ELISA). However, discrepancies between the specificity of these methods means correlation is poor.
  
  
  METHODS
  A tandem-mass spectrometric (LC/MS/MS) method, using immunoaffinity purification, for urinary 8-iso-PGF(2α) was developed and compared with two commercial ELISAs (A--Cayman Chemicals, B--Oxford Biomedical Research) in urine samples (n = 156).
  
  
  RESULTS
  An LC/MS/MS method coupled to immunoaffinity purification was developed with satisfactory performance and comparison to ELISAs A and B. Spearman rank correlation demonstrated significant correlation between all methods (P = <0.0001); however, r² values ranged from 0.68 to 0.72. Bland-Altman plots revealed a proportional positive bias of ELISA B when compared with ELISA A and LC/MS/MS. Furthermore, the agreement between ELISA A and LC/MS/MS was poor.
  
  
  CONCLUSIONS
  The poor agreement between methods for measurement of 8-iso-PGF(2α) highlights differences in selectivity. 8-iso-PGF(2α) is an isoprostane, a family of isomeric end-products of arachidonic acid peroxidation, which are produced by peroxidation or enzymatically. This makes avoiding cross-reactivity between 8-iso-PGF(2α) and related isomers challenging. When assessing oxidative stress studies, the selectivity of the methods used should be taken into account, particularly when comparing studies.
authors.affiliation: Department of Clinical Biochemistry, Hull Royal Infirmary, Anlaby Road, Hull HU32JZ, UK.
authors.forename: K A
authors.initials: KA
authors.lastname: Smith
authors.forename: J
authors.initials: J
authors.lastname: Shepherd
authors.forename: A
authors.initials: A
authors.lastname: Wakil
authors.forename: E S
authors.initials: ES
authors.lastname: Kilpatrick
mesh_terms: D015415:Biomarkers / Q000652:urine; D002853:Chromatography, Liquid; D015237:Dinoprost / Q000031:analogs & derivatives* / Q000652:urine; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D018384:Oxidative Stress; D053719:Tandem Mass Spectrometry; D016482:Urinalysis / Q000379:methods*
chemical_list: D015415:Biomarkers; C075750:8-epi-prostaglandin F2alpha; D015237:Dinoprost