{"doi":"10.1021/acs.jproteome.5c00679","title":"Development and Validation of a Novel LC-MS/MS-Based Proteomics Method for Quantitation of Retinol Binding Protein 4 (RBP4) and Transthyretin (TTR)","abstract":"Retinol binding protein 4 (RBP4), the circulating carrier of retinol, complexes with transthyretin (TTR) and is a potential biomarker of cardiometabolic disease. However, RBP4 quantitation relies on immunoassays and Western blots without retinol and TTR measurement. A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the simultaneous absolute quantitation of circulating RBP4 and TTR is critical to establishing their biomarker potential. Surrogate peptides with reproducible, linear LC-MS/MS response were selected. Purified proteins were used as quantitation standards and heavy-labeled peptides as internal standards. Matrix effects were evaluated. The validated method was applied to measure inter- and intraindividual variability in RBP4 and TTR concentrations in healthy individuals and patients with diabetic kidney disease. Quantitation was linear for the clinically relevant concentration ranges of RBP4 (0.5-6 μM) and TTR (5.8-69 μM). Assay interday variability was <12% and precision within 5%. The interindividual variability for RBP4 and TTR concentrations was 18-26%, while intraindividual variability was similar to assay variability. RBP4 and TTR quantitation correlated with commercially available enzyme-linked immunoassays (ELISA) assays. The developed LC-MS/MS method enables simultaneous absolute quantitation of RBP4 and TTR in serum and plasma. It can be applied to clinical biomarker studies and stoichiometric measurements of circulating RBP4, TTR, and retinol.","journal":"Journal of Proteome Research","year":2025,"id":574479,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":0,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9509,"is_data_producer":false,"deposit_databanks":null,"is_oa":false,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2025-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":385939,"name":"Katya B. Rubinow","orcid":"0000-0002-6505-5657","position":1,"is_corresponding":false},{"id":565814,"name":"Alex Zelter","orcid":"0000-0002-5331-0577","position":2,"is_corresponding":false},{"id":1062947,"name":"Aurora K. Authement","orcid":"0000-0003-3677-5214","position":3,"is_corresponding":false},{"id":268748,"name":"Bryan Kestenbaum","orcid":"0000-0003-4799-5968","position":4,"is_corresponding":false},{"id":462850,"name":"John K. Amory","orcid":"0000-0002-7419-435X","position":5,"is_corresponding":false},{"id":126655,"name":"Nina Isoherranen","orcid":"0000-0002-9548-3126","position":6,"is_corresponding":false},{"id":905880,"name":"Aprajita S. Yadav","orcid":"0000-0002-4181-7522","position":0,"is_corresponding":true}],"reference_count":36,"raw_metadata":null,"created_at":"2026-07-19T02:57:40.686992Z","pmid":"40928833","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}