On the joys of combining pediatric clinical chemistry and research on inborn errors of metabolism.
Sometimes a new assay is born in a research setting and then finds a clinical home. The assay measuring 3-hydroxy-fatty acids (30HFAs) is such an assay. Developed as a research tool, this assay was found to be clinically useful for helping to diagnose disorders in the t,-3hydroxyacyl-CoA dehydrogenases, which are involved in the third enzymatic step in mitochondrial FAO (1). Subsequently, we have found the assay to be useful not only as a diagnostic tool, but also for monitoring treatment and health status in long-chain 3-hydroxyacyl CoA dehydrogenase (LCHAD)-deficient patients. The assay continues to be an extremely useful research tool.
Since the assay's inception, we have added the quantification of 3-hydroxy-octadecanoic acid (3-OHC18) to the assay profile. This has given us quantitative assays for the 3-OH species with chain lengths from C6 to C18 and has added to the diagnostic usefulness and research capability of the assay (2). Research on the utilization and metabolism of stearate (C18 fatty acid) is ongoing.
Another research area that uses this assay involves the quantification of 30HFAs in culture media of skin fibroblasts from healthy and LCHAD-deficient individuals. The result of feeding the cultured cells with medium-chain triglycerides (MCTs), which is the treatment of choice for LCHAD-deficient patients, has provided information about the effectiveness and possible actions of this treatment in patients. We have shown that MCTs not only bypass the long-chain defect, but actually decrease the amount of accumulation of long-chain intermediates by an as yet unknown mechanism (3). Decanoate (C10 fatty acid) shows this effect to a greater extent than octanoate (C8). We have also shown that although odd-numbered MCTs (C7 and C9 fatty acids) also demonstrate this effect, they do so much less efficiently than even-numbered MCTs (4).
A particularly intriguing recent finding with the 30HFA assay has become the center of a new line of research. We are finding that normal fibroblasts, when fed intermediate-chain-length fatty acids, actually add two-carbon units to the molecule in the process of oxidizing it. Fig. 1 illustrates this completely unexpected finding. When C10 fatty acid is fed to the cells, they accumulate 3-OH-C12; feeding the cells C12 fatty acid leads to the accumulation of 3-OH-C14. The implication of this finding is that the FAO pathway is functioning in an unexpected and unknown way, involving steps that will have to be elucidated. This line of research beautifully illustrates the fun of performing research that may end up having wide-reaching implications in a clinical field.
[FIGURE 1 OMITTED]
As a clinical tool, this assay quickly established itself as an important part of the laboratory evaluation of patients suspected of having a FAO defect. We expect it to continue to provide us with new insights into the workings of this complex pathway.
This is only a small example of how clinical chemists work at the interface between basic research and clinical science, but it makes concrete for me the joy that comes from seeing one's scientific work applied for the benefit of patients.
(1.) Jones PM, Quinn R, Fennessey PV, Tjoa S, Goodman SI, Fiore S, et al. Improved stable isotope dilution-gas chromatography-mass spectrometry method for serum or plasma free 3-hydroxy-fatty acids and its utility for the study of disorders of mitochondrial fatty acid 0-oxidation. Clin Chem 2000;46:149-55.
(2.) Jones PM, Tjoa S, Fennessey PV, Goodman SI, Bennett MJ. Addition of quantitative 3-hydroxyoctadecanoic acid (3-0H-C18) to the stable isotope gas chromatography-mass spectrometry method for measuring 3-hydroxy-fatty acids. Clin Chem 2002;48:176-9.
(3.) Jones PM, Butt Y, Bennett MJ. Accumulation of 3-hydroxy-fatty acids in the culture medium of long-chain L-3-hydroxyacyl CoA dehydrogenase and mitochondrial trifunctional protein deficient skin fibroblasts: Implications for medium chain triglyceride dietary treatment of LCHAD deficiency. Pediatr Res 2003;53:783-7.
(4.) Jones PM, Butt YM, Bennett MJ. Effects of odd-numbered medium-chain fatty acids on the accumulation of long-chain 3-hydroxy-fatty acids in long-chain L-3-hydroxyacyl CoA dehydrogenase (LCHAD) and mitochondrial trifunctional protein (MTFP) deficient skin fibroblasts. Mol Genet Metab; in press (doi: 10.1016/j.ymgme.2003. 11.009).
Patricia M. Jones
Department of Pathology University of Texas Southwestern Medical Center and Children's Medical Center of Dallas Dallas, TX 75235
|Printer friendly Cite/link Email Feedback|
|Title Annotation:||The Clinical Chemist|
|Author:||Jones, Patricia M.|
|Date:||Mar 1, 2004|
|Previous Article:||The Short Road to Great Presentations.|
|Next Article:||2005 IFCC-Roche Diagnostics Award for Advances in Critical Care Testing.|