Metabolites quantitative information

The application areas for LC-MS, as will be illustrated later, are diverse, encompassing both qualitative and quantitative determinations of both high-and low-molecular-weight materials, including synthetic polymers, biopolymers, environmental pollutants, pharmaceutical compounds (drugs and their metabolites) and natural products. In essence, it is used for any compounds which are found in complex matrices for which HPLC is the separation method of choice and where the mass spectrometer provides the necessary selectivity and sensitivity to provide quantitative information and/or it provides structural information that cannot be obtained by using other detectors. 

In clinical chemistry, interpretation of the data can be quite simple or complex. In the case of MS/MS applications pertaining to a single analyte, all that is needed is the intensity value from the mass of a peak of interest and its internal standard. Viewing of a spectrum is not necessary. For profile methods such as full-scan acylcarni-tines, amino acids, or other compound families, the interpretation is more complex. With multiple related components, calculation of the concentration of many key metabolites is required. The system generally has multiple internal standards, external standards, or both. In addition to the concentration calculations, examination of a profile is often best achieved by viewing the spectra together with the quantitative information. 

Metabolic profiling approaches are developed for the determination and quantitation of metabolites of a particular pathway or for a class of compounds. This strategy generates quantitative information of metabolites... 

Quantitative information on metabolites that have been identified to have pharmacological and/or toxicological activities is very important during the drug discovery and development process. One limitation of LC-MS for metabolite quantification... 

In addition to providing quantitative information on the parent drug, HPLC-MS/ MS is used to analyze biological samples within drug discovery and monitor for select metabolites. This serves two functions, to help chemists identify metabolic hot spots and help identify a new lead compound or prodrug. 

Toxicity and dose-response to an exogenous chemical are dependent upon the concentration of the toxicant at the site(s) of action (e.g. the target organ). The disposition of a chemical in an organism is dependent upon the processes of absorption, distribution, metabolism, and excretion, defined as toxicokinetic data. Qualitative and quantitative information on each of these processes would be useful in risk assessment. For autoimmune diseases, toxicokinetic data may be helpful in identifying the potential organ systems that are likely to be involved or the responsible metabolite. 

ADME studies provide information on absorption, distribution, metabolism, and excretion for the compound of interest in animals and humans. In drug development, these studies are performed with either C-14- or tritium-labeled material to provide detailed quantitative information on the circulating metabolites, the extent of metabolism and routes of excretion for drug and its metabolites. Readers are encouraged to refer Chapter 18 of this book for more detailed discussion on ADME study design and data presentation. 

If urine or blood samples are to be used to determine the absorbed dose, it is helpful to have pre-study information which will give the researcher an opportunity to design his sample collection scheme in a manner which will be simplest to achieve and which will provide the most quantitative information. Much has been written with regard to the excretion rates, quantitative nature of the excretion, and other data on the phenoxy herbicides. For other compounds where less is known, if the manufacturer can not provide detailed information on the excretion data, the researcher may be required to conduct a small controlled study, evaluating excretion rate, and other important characteristics of the compound prior to conducting full-scale field study. It is necessary to know if one should analyze for the parent compound or a metabolite. If a metabolite is to be analyzed, it is necessary to know if its amount can be related to the dose of the parent compound. 

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