Response to Letter to the Editor regarding “GC-MS with ethyl chloroformate derivatization for comprehensive analysis of metabolites in serum and its application to human uremia”

Abstract

Dear Sir, Dr Husek Petr argued that “Ourmethod should not be pursued as a general tool suitable for serum-based metabolic profiling study due to several possible defects for amino acid measurement although he believed that our method might be applied to identify the metabolites associated with human uremia” [1]. We are pleased to know scientists from areas of conventional analytical chemistry are also interested in our work in addition to those from the emerging metabolomics field [1–4]. We acknowledge the contribution made by many pioneering researchers, including Husek’s group. However, the purpose of our study [5] was to identify differential metabolites between subjects diagnosed with uremia and healthy controls by use of a global profiling approach—“metabolomics” and/or “metabonomics”. To ensure the efficiency, reproducibility, and reliability of sample-preparation procedures that are capable of handling hundreds of clinical samples, we selected the ECF method developed by Husek [6] in preference to many other methods and optimized it for global metabolite analysis of human serum samples. Before addressing technical concerns raised by Husek [1], we would like to provide a brief introduction to metabolomics because this field is rather different from routine analytical chemistry. Metabolomics/metabonomics has evolved quickly in recent years and can be defined as “the quantitative measurement of the dynamic multiparametric metabolic response of living systems to pathophysiological stimuli or genetic modification” [7]. The strength of metabolomics lies in its capability to identify a metabolic fingerprint, which provides global metabolic information associated with a pathophysiological state. The ability to acquire the complete set of smallmolecule metabolites (the whole metabolome) from biospecimens by use of appropriate analytical instrumentation will ensure the discovery of abnormally regulated key metabolites and metabolic pathways most relevant to the specific disease and useful for mechanistic interpretation [7, 8]. In reality, however, it is not possible to recover all metabolites of a great variety of chemical classes from biological samples. Additionally, the concentration ranges of these metabolites span more than a dozen orders of magnitude with compounds such as glucose in the millimolar range in blood and compounds such as some lipids in the femtomolar range [9]. Therefore, optimum sample-preparation procedures in metabolic profiling studies are usually a compromise among sensitivity, number of samples analyzed, number of metabolites detected, and specific aims of the study design. In this scenario, it is very This article is the response to the “Letter to the Editor” to be found at http://dx.doi.org/10.1007/s00216-011-5615-x