ELABELA measurements by commercial ELISA kits require sample extraction

Danai Georgiadou, Souad Boussata, Marie van Dijk
2019 American Journal of Physiology. Endocrinology and Metabolism  
TO THE EDITOR: We read with great interest the article by Zhou and coworkers (10) in American Journal of Physiology-Endocrinology and Metabolism, entitled "ELABELA, as a potential diagnostic biomarker of preeclampsia, regulates abnormally shallow placentation via APJ." The authors measured levels of the peptide hormone ELABELA in serum and urine of after nonpregnant, and normal and preeclamptic pregnant women. They nicely demonstrate an increase of ELABELA levels upon pregnancy, while in
more » ... mptic women the serum levels of ELABELA were found to be significantly lower. We were, however, confused by the serum concentrations of ELABELA as measured in this study; levels were all between log 0.5 and log 2.0 ng/ml, converting to concentrations between 3 and 100 ng/ml. When measuring ELABELA levels in serum of pregnant women with a custom ELISA (3), we do obtain levels up to 100 ng/ml, but the majority is much lower, down to 10 pg/ml, and in about half of the samples ELABELA is even undetectable. Based on the results obtained by Zhou et al. (10), we tested the ELABELA ELISA kit by Phoenix Pharmaceuticals as used in this article and measured pregnant serum samples that by our custom ELISA were either after undetectable, around 0.1 ng/ml and around 100 ng/ml. We noted that the kit recommended a sample preparation by peptide extraction, which we also attempted. Interestingly, without sample extraction all our samples gave values ranging between 10 and 150 ng/ml and not following the same pattern of levels as observed by using the custom ELISA. By using the recommended sample extraction, we measured ELABELA levels mirroring the values as found by the custom assay. The method section of the article by Zhou et al. (10) is inconclusive to the fact if the recommended sample extraction was performed; they state that the ELISA kit was used according to the manufacturer's instructions. However, based on the concentrations they measured, it appears that sample extraction was not undertaken. To our knowledge, in total eight articles (1, 4 -10) have so far been published presenting data on circulating ELABELA in human plasma or serum. These articles used ELISA kits from three different companies (Phoenix Pharmaceuticals, Peninsula Laboratories International and Creative Diagnostics), all recommending sample peptide extraction by C18 columns. In two articles (4, 8), the method section indirectly states that sample extraction was not performed. In the remaining papers the use of sample extraction is unclear. It now appears that when comparing ELABELA data obtained using commercial ELISA kits without or with peptide extraction we are actually looking at different appearances of the peptide, of which the latter identifies the same peptide as the custom ELISA without peptide extraction. This fact potentially leads to ambiguous findings like we recently encountered by performing a systematic review on ELABELA levels in preeclamptic pregnancies (2). Hence, in future studies measuring ELABELA by commercial ELISA kits we strongly recommend that the use of peptide extraction is clearly stated so we are not comparing apples and oranges. DISCLOSURES No conflicts of interest, financial or otherwise, are declared by the authors. AUTHOR CONTRIBUTIONS M.v.D. drafted manuscript; D.G. and S.B. edited and revised manuscript; D.G., S.B., and M.v.D. approved final version of manuscript. REFERENCES 1. Deniz R, Baykus Y, Ustebay S, Ugur K, Yavuzkir Ş , Aydin S. Evaluation of elabela, apelin and nitric oxide findings in maternal blood of normal pregnant women, pregnant women with pre-eclampsia, severe pre-eclampsia and umbilical arteries and venules of newborns. CD. ELABELA plasma concentrations are increased in women with late-onset preeclampsia. . 6. Pritchard N, Kaitu'u-Lino TJ, Gong S, Dopierala J, Smith GCS, Charnock-Jones DS, Tong S. ELABELA/APELA levels are not decreased in the maternal circulation or placenta among women with preeclampsia.
doi:10.1152/ajpendo.00257.2019 pmid:31808726 fatcat:gtogm7vwb5hsrg3glv3zmdf6pm