Hansmeier et al. We demonstrated that as little as 240 μ L cord blood serum is suitable for obtaining proteome information at confidence levels comparable with those attained in adult blood studies. Use of this relatively low sample vol- ume is not anticipated to adversely affect the possibility of further diagnostic tests. Because clinical approval and validation of biomarkers are costly and time consuming (Chao et al. 2010), prioritization is important. Of highest priority are UCB proteins already approved by the FDA for diagnosis in adults. Among these were protein biomarkers for differ- ent organ diseases such as deficiency of thyroid binding (thyroxine-binding globulin), chronic kidney dysfunctions (cystatin C), hypercoagula- tion disorders (plasminogen), and cardiovascular diseases (apolipoprotein A1, B). In addition, deficiencies in coagulation factors X or VII may indicate bleeding disorders that, without proper therapy, can lead to liver failure, internal bleed- ing, or sudden death (Morley 2011). It is con- ceivable that these established biomarkers are also of diagnostic value in infants. Second in importance are proteins with known functions in metabolic pathways to inform about disruptions of normal cellular processes. Although not approved by the FDA for diagnostic purposes, a number of the pro- teins identified in the UCB proteome are either known to play a role in certain diseases or can be diagnostic of exposure to toxic substances. Among the proteins found in disease pathways is the cardiac ryanodine receptor 2, whose dys- function is directly linked to cardiac arrhythmia and sudden heart failure (Betzenhauser and Marks 2010; Durham et al. 2007; Wehrens and Marks 2003). Also of interest are homeobox protein NKX6.1 for MODY (Donelan et al. 2010); protein S and platelet-derived growth factor BB for acute kidney injury (Thurman et al. 2009); WNT target-gene promoter TBL1XR1 (F-box-like/WD repeat contain- ing protein) for acute lymphoblastic leukemia (Parker et al. 2008); and proto-oncogene serine/ threonine-protein kinase PIM1, which is pro- posed as a marker for mutated K-ras signaling activity in pancreatic cancer (Xu et al. 2011). Furthermore, peroxisome proliferator-activated receptor (PPAR) and calcium-signaling path- ways are associated with metabolic diseases such as diabetes mellitus type 2 and cardiovascular disorders (Benkusky et al. 2007; Biscetti et al. 2009; Bulhak et al. 2009). Platelet factor 4, pro- platelet basic protein precursor, and comple- ment component 3 are known to be diagnostic in a panel for acute lymphoblastic leukemia in children (Shi et al. 2009). Interestingly, lower adiponectin levels in UCB also have been found to be a predictor of adiposity in children at 3 years of age (Mantzoros et al. 2009). We also detected several proteins associated with different kinds of toxic exposures. Toxic exposures can often have varied unspecific 768 effects on human health. Accordingly, their effects on the molecular level are largely unknown. Potential biomarkers of exposure identified in here include proteins involved in lipid metabolism disruptable by smoking (Craig et al. 1989), alcohol (Través et al. 2007), or bisphenol A exposure (Chou et al. 2011). Specifically, we detected all previously pro- posed protein biomarkers of in utero exposure to tobacco products from maternal smoking (Colquhoun et al. 2009). Other identified proteins of interest included alpha-fetoprotein, whose expression is affected by cigarette smoke exposure but has also been found to be elevated after exposure to dioxins and phenols (Colquhoun et al. 2009; El Far et al. 2006), and endothelin B, which is elevated after inhalation of diesel exhaust (Langrish et al. 2009; Peretz et al. 2008). Antenatal administration of the drug betame- thasone was associated with an increase in UCB of retinol-binding protein, transthyretin, and transferrin (Georgieff et al. 1988). Increased levels of IgG were found to be associated with a range of environmental exposures—for exam- ple, to mold (Rydjord et al. 2007), organo- chlorines (Karmaus et al. 2005), tobacco-smoke products (Colquhoun et al. 2009), and methyl- mercury (Nyland et al. 2011). Overall, the presented data indicate that proteome analyses may provide a window to current physiological status of patients and also offer opportunities for detecting molecu- lar malfunctions related to diseases. In par- ticular, protein biomarkers with mechanistic linkage to disturbed signaling and metabolic pathways have proved to be of diagnostic value. Diagnostics in the form of protein assays provide a spectrum of clinical data, including information on acute events such as forecasting of coronary diseases, myocardial infarction, and cancer (Anderson 2010). Ideally, the results of this study will be supplemented with quantitative information on a population basis. Knowledge of normal and aberrant protein abundance at the pro- teome level, together with pathway-centered analyses of adverse health effects in diverse population, will continue to drive the develop- ment of mechanistically based biomarkers of health status. 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Nat Biotechol 28:710–721. ovlume 120 | number 5 | May 2012 • Environmental Health Perspectives