NDT Advance Access originally published online on April 10, 2008
Nephrology Dialysis Transplantation 2008 23(8):2699-2700; doi:10.1093/ndt/gfn202
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Increased serum advanced glycation end products are associated with impairment in HDL antioxidative capacity in diabetic nephropathy
E-mail: connellyp{at}smh.toronto.on.caSir,
I read with interest the paper by Zhou et al. [1] in which an inverse relationship between organophosphatase activity and concentration of advanced glycation end products was reported. The organophosphatase assay used in that study is the commercially available EnzChek® Paraoxonase Assay Kit from InvitrogenTM. The samples used for the assay were the supernatant from serum after precipitation of the non-high-density lipoproteins using dextran-sulfate magnesium. Somewhat surprisingly, there was no citation for the use of this novel combination of reagent and sample for measuring human serum paraoxonase-1 activity. I have been unable to find any published reports validating this assay for the measurement of human serum paraoxonase-1 activity. This contrasts with other published works with novel paraoxonase-1 substrates, such as that by Gaidukov and Tawfik [2]. The EnzChek® assay has been used in one other study, where the results were corroborated by measurement of enzyme mass, but not by serum arylesterase activity [3]. Soukharev and Hammond report the development of a fluorogenic organophosphatase substrate [4] that is hydrolysed by purified human paraoxonase 1. However, no data have been published validating the substrate used in that paper, 7-diethylphospho-6,8-difluor-4-methylumbelliferyl (DEPFMU), in the context of a human serum matrix or the serum matrix remaining after divalent cation/polyvalent anion precipitations.
I would propose that the results of this type of assay be referred to as organophosphatase activity in the same way as results for phenyl acetate hydrolysis are referred to as arylesterase activity. Referring to this activity as paraoxonase would require rigorous validation and comparison with serum hydrolysis of paraoxon. I would also make an appeal that the introduction of novel assays be accompanied by the validation data with conditions described in sufficient detail to allow replication in subsequent studies.
Conflict of interest statement. None declared.
Department of Medicine, St. Michael's Hospital, Toronto, Canada
References
- Zhou H, Tan KC, Shiu SW, et al. Increased serum advanced glycation end products are associated with impairment in HDL antioxidative capacity in diabetic nephropathy. Nephrol Dial Transplant (2008) 23:927–933.
[Abstract/Free Full Text] - Gaidukov L, Tawfik DS. The development of human sera tests for HDL bound serum PON1 and its lipolactonase activity. J Lipid Res (2007) 48:1637–1646.
[Abstract/Free Full Text] - Rector RS, Warner SO, Liu Y, et al. Exercise and diet induced weight loss improves measures of oxidative stress and insulin sensitivity in adults with characteristics of the metabolic syndrome. Am J Physiol Endocrinol Metab (2007) 293:E500–E506.
[Abstract/Free Full Text] - Soukharev S, Hammond DJ. A fluorogenic substrate for detection of organophosphatase activity. Anal Biochem (2004) 327:140–148.[CrossRef][Web of Science][Medline]
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