Urinary organic acids

In the severely ill infant, measurements of serum ammonia and lactate, urinary organic acids, urinary and serum amino acids and erythrocyle galacto.se I-phosphale uridyl transferase will be required. If the baby has a problem which is apparent intermittently, then blood and urine should be collected for analysis during the acute phase. 

Fig. 3.13. Organic acid urinary profiles of a patient with hereditary progressive deafness and a control patient both individuals were administered orally 20 g of leucine. 3-HIVA, 3-hydroxyisovaleric acid 3-MCG, 3-methyl-crotonylglycine. Reproduced from [164].

Recently, multidimensional GC has been employed in enantioselective analysis by placing a chiral stationary phase such as a cyclodextrin in the second column. Typically, switching valves are used to heart-cut the appropriate portion of the separation from a non-chiral column into a chiral column. Heil et al. used a dual column system consisting of a non-chiral pre-column (30 m X 0.25 mm X 0.38 p.m, PS-268) and a chiral (30 m X 0.32 mm X 0.64 p.m, heptakis(2,3-di-(9-methyl-6-(9-tert-butyldimethylsilyl)-(3-cyclodextrin) (TBDM-CD) analytical column to separate derivatized urinary organic acids that are indicative of metabolic diseases such as short bowel syndrome, phenylketonuria, tyrosinaemia, and others. They used a FID following the pre-column and an ion trap mass-selective detector following the... 

Figure 15.8 Multidimensional GC-MS separation of urinary acids after derivatization with methyl chloroformate (a) pre-column cliromatogram after splitless injection (h) Main-column selected ion monitoring cliromatogram (mass 84) of pyroglutamic acid methyl ester. Adapted from Journal of Chromatography, B 714, M. Heil et ai, Enantioselective multidimensional gas chromatography-mass spectrometry in the analysis of urinary organic acids , pp. 119-126, copyright 1998, with permission from Elsevier Science.

M. Heil, E. Podehrad, T. Beck, A. Mosandl, A. C. Sewell and H. Bohles, Enantioselective multidimensional gas clnomatography-mass spectrometiy in the analysis of urinary organic acids , 7. Chromatogr. 714 119-126 (1998). 

The answer is a. (Hardman, pp 16-20.) Sodium bicarbonate is excreted principally in the urine and alkalinizes it. Increasing urinary pH interferes with the passive renal tubular reabsorption of organic acids (such as aspirin and phenobarbital) by increasing the ionic form of the drug in the tubular filtrate. This would increase their excretion. Excretion of organic bases (such as amphetamine, cocaine, phencyclidine, and morphine) would be enhanced by acidifying the urine. 

HALKET, J.M., PRZYBOROWSKA, A., STEIN, S.E., MALLARD, W.G., DOWN, S., CHALMERS, R.A., Deconvolution gas chromatography/mass spectrometry of urinary organic acids—potential for patem recognition and automated identification of metabolic disorders, Rapid Commun. Mass Spectrom., 1999,13,279-284. 

Karjalinen EJ, Karjalinen UP. Speeding up the identification of anomalies in urinary organic acids. J Inherit Metab Dis 2003 26 Suppl 2 49... 

Many laboratories use quantitative urinary organic acid analysis as an alternative to a qualitative approach and may not use stable isotope dilution as a more rigorous means of quantitation. The results from EQA schemes in the area reflect this variability of practice and the lack of internationally agreed standardisation. 

Some important assays commonly used in biochemical genetics laboratories do not provide quantitative data (e.g. MPS-EP, qualitative urinary organic acid analysis, AA-TLC). In addition, all successful investigations depend heavily upon selection of the correct analytes to measure and the appropriate interpretation of the quantitative or qualitative results in their clinical context. These challenges suggest a requirement for external quality assessment or proficiency testing schemes that can inform participants about their performance in these areas when compared with other centres. 

Similarly, there is an increasing degree of consistency of methodological approach between laboratories. For instance, a recent survey of those undertaking qualitative urinary organic acid analysis revealed that more than 90% (83 of 91) of laboratories indicated that they extracted the samples with ethylacetate or ethylacetate/ether, formed trimethylsilyl derivatives and employed gas chromatography-mass spectrometry as a means of analysis. 

Downing M, Bonham JR, Allen JC, Heap SJ, Manning NJ, Olpin SE, Pollitt RJ (1999) Is quality assurance for quality urinary organic acid analysis improving performance J Inherit Metab Dis 22 148... 

Guneral L, Bachmann C (1994) Age-related reference values for urinary organic acids in a healthy Turkish pediatric population. Clin Chem 1994 40 862-866... 

Kumps A, Duez P, Mardens Y (2002) Metabolic, nutritional, iatrogenic, andartifactual sources of urinary organic acids a comprehensive table. Clin Chem 48 708-717... 

Sewell AC, Bohles HJ (1991) 4-Hydroxycyclohexanecarboxylic acid a rare compound in urinary organic acid analysis. Clin Chem 37 1301-1302... 

Chalmers RA, Roe CR, Stacey , Hoppel CL (1988) Urinary excretion of L-carnitine and acylcarnitines by patients with disorders of organic acid metabolism evidence for secondary insufficiency of L-carnitine. Pediatr Res 18 1325-1328... 

With regard to AADC, vanillactic acid (a metabolite of 3-MD) appears in the urine and can be detected by organic acid analysis. As predicted, an increase in urinary vanillactic acid has also been reported in PNPO deficiency. The PLP concentration in CSF, which can be determined by HPLC, is also reported to be decreased in PNPO deficiency. Mutation analysis can also now confirm or refute a suggestion of PNPO deficiency. 

In patients affected with GAMT deficiency, GA is elevated in urine, plasma and CSF. In addition, Cr is decreased or in the low-normal range in urine, plasma and CSF. Creatinine in urine (expressed as excretion per 24 h) and plasma is decreased. This low urinary creatinine results in increased concentration of other metabolites (e.g. amino acids, organic acids, uric acid) when expressed per mol creatinine. During treatment by Cr supplementation, GA in plasma decreases, but does not normalise. Cr in plasma and urine becomes increased. 

On the other hand, acidic drugs tend to ionize under conditions of alkaline pH and so are unable to permeate the renal tubular epithelium and are preferentially excreted. Tire converse applies to conditions of acidic urinary pH. This has been demonstrated experimentally for many drugs weak bases are excreted more rapidly in acidic urine, whereas weak acids are excreted more rapidly in alkaline urine. In the horse, phenylbutazone, which is a weak organic acid with a pKa of 4.6, has a more delayed clearance time under conditions of aciduria than under conditions of alkaline urine. 

Acetazolamide can produce severe lactic acidosis, with an increased lactaterpyruvate ratio, ketosis with a low beta-hydroxybutyrateracetoacetate ratio, and a urinary organic acid profile consistent with pyruvate carboxylase deficiency. The acquired enzymatic injury that results from inhibition of mitochondrial carbonic anhydrase V, which provides bicarbonate to pyruvate carboxylase, can damage the tricarboxylic acid cycle. 

Maitani T, Kubota H, Hori N, et al. 1994. Distribution and urinary excretion of aluminum injected with several organic acids into mice Relationship with chemical state in serum studied by the HPLC-ICP method. J Appl Toxicol 14 257-261. 

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