Metabolism screening

Cerep evaluates hits, leads, and new compounds from the metabolic point of view using liver microsomes and recombinant cytochrome P450s (275). The results of these metabolic screening studies offer insight to the rate of metabolic pathways, in vivo pharmacokinetic properties, and drug-drug interactions. 

Shih VE, Mandell R, Sheinhait I (1991) General metabolic screening tests. In Hommes FA (ed) Techniques in Diagnostic Human Biochemical Genetics. Wiley-Liss, New York, pp 45-68... 

Pitfalls associated with metabolic screening are numerous. They can result from proximal tubulopathy, causing a reduction in blood lactate and an increase in urinary lactate from diabetes mellitus, hampering entry of pyruvate into the citric acid cycle from tissue-specific involvement or partial deficiency, which may barely alter the redox status in plasma. When metabolic tests are negative, respiratory chain deficiency may be misdiagnosed. 

Janiszewski, J. S., Rogers, K. J., Whalen, K. M., Cole, M. J., Liston, T. E., Duchoslav, E., and Fouda, H. G. (2001). A high-capacity LC/MS system for the bioanalysis of samples generated from plate-based metabolic screening. Anal. Chem. 73 1495-1501. 

Acceptable hits do not need to show ideal behavior, but problem compounds will be removed from consideration. If all the hits fail initial pharmacokinetic screening, several options are possible. First, the search for hits could start over with screening of a new library. Second, the threshold for selection of hits could be lowered to enlarge the pool of hits, some of which may pass the permeability and metabolic screens. Third, the criteria for passing the Caco-2 and microsome screens may be softened to allow some hits to pass.18... 

One of the earliest and perhaps most rewarding introductions of metabolomics in pediatric medicine has occurred with the bioanalysis of endogenous substrates and altered metabolism that may be indicative or predictive of significant disease states. Newborn and metabolic screening of inherited disorders of metabolism has, in many respects, served as a cornerstone for innovative... 

Today, many of the older methods used historically in clinical chemistry are being replaced by methods that utilize MS. In 2013, some areas of interest in clinical chemistry include steroid and vitamin D analyses that require a high selectivity and relative sensitivity. For example, the improved selectivity is essential in the analysis of testosterone in infants due to low concentrations. Immunoassays are not sufficiently selective to provide an accurate measurement of the true concentrations of these metabolites. There are many more assays being used or that are now in development in clinical chemistry, but a discussion of this growing use of metabolic screening is too broad and too evolutionary to be included here. Therefore, this chapter focuses on those proteins and metabolites (e.g., amino acids and acylcamitines) that are part of a classic newborn screening panel. 

As previously noted, MS technology was first applied in the broad area of metabolic screening for neonatal diseases. The value of this approach has been seen from the fact that it is still used extensively for this purpose around the world. This application, however, may ultimately be viewed as merely the tip of the iceberg, given the potential that analysis of proteins and metabolites has in refining our understanding of diseases and active disease states during clinical care. 

An example for an automated stability test in plasma is described by Linget and du Vignaud (1999). Incubations are performed on a 215 Gilson liquid handler. Incubation was done at substrate concentrations of 50 pM on 96 deep well plates. Each incubation tube contained 375 pL of a 200 pM test compound solution (in 0.1 M Tris buffer with 3% BSA, added to assist dissolution of compounds with poor solubility) and 1125 pL of plasma. Samples are taken after incubation times of 0, 1, 2, 3, 4 and 5 min. At each of these time points an aliquot of the incubation mixture was transferred from the incubation tube into a well in a 96 deep well plate containing an equal volume of acetonitrile for quenching by protein precipitation followed by centrifugation of the plates. Supernatants were analyzed by HPLC for metabolic screening. 

Valproate should not be prescribed for children with metabolic defects possibly associated with Reye-like symptoms, including acyl CoA-dehydrogenase deficiency (SEDA-22, 92) (75). In patients under 2 years old and in children with psychomotor retardation metabolic screening should be performed before therapy, and the drug should be avoided whenever a metabolic defect is known or suspected. 

R.B. van Breemen, D. Nikohc, J.L.Bolton, Metabolic screening using on-line ultrafiltration MS, Drug Metab. Disp., 26 (1998) 85. 

PJ Eddershaw, M Dickins. Advances in in vitro drug metabolism screening. Pharm Sci Technol Today 2 13—19, 1999. 

Aside from investigating structure/pharmacokinetic relationships, cassette dosing can also be used as a high-throughput screen for diverse compounds. These compounds are passed through one or more preliminary screens, such as in vitro efficacy, permeability (Chap. 8), or metabolic screening (Chap. 9). These... 

Van Breemen, RB. Nikolic, D. Bolton, J.L. Metabolic Screening Using Online Ultrafiltration Mass Spectrometry, DrugMetab. Dispos. 26, 85-90 (1998). 

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