Elevated excretion of N-acetylated branched-chain amino acids in maple syrup urine disease

Biosynthesis, degradation and pharmacological importance of the fatty acid amides

The identification of two biologically active fatty acid amides, N-arachidonoylethanolamine (anandamide) and oleamide, has generated a great deal of excitement and stimulated considerable research. However, anandamide and oleamide are merely the best-known and best-understood members of a much larger family of biologically occurring fatty acid amides. In this review, we will outline which fatty acid amides have been isolated from mammalian sources, detail what is known about how these molecules are made and degraded in vivo, and highlight their potential for the development of novel therapeutics.

Development of a class-selective enzyme-linked immunosorbent assay for mercapturic acids in human urine

Epidemiological and toxicological studies often require the analysis of large numbers of samples for biological markers of exposure. The goal of this work was to develop a class-selective ELISA to detect groups of structurally closely related mercapturic acids with small nonpolar S-substituents. An assay was developed with strong recognition for mercapturates including S-benzylmercapturic acid (IC50 = 0.018 micromol/L), S-n-hexylmercapturic acid (IC50 = 0.021 micromol/L), S-phenylmercapturic acid (IC50 = 0.024 micromol/L), and S-cyclohexylmethylmercapturic acid (IC50 = 0.042 micromol/L). The same assay also showed weaker recognition for S-(1-hydroxynaphthal-2-yl)mercapturic acid and S-allylmercapturic acid (IC50 = 1.1 and 1.7 micromol/L, respectively). Subtle modifications to the hapten linker structure of the coating antigen proved to have a strong impact on the selectivity and the specificity of the assay. A slightly modified assay showed high recognition for S-benzylmercapturic acid (IC50 = 0.018 micromol/L) and weaker recognition for seven other mercapturic acids (IC50 = 0.021-10 micromol/L). Strong positive assay responses were detected in 12 urine samples obtained from persons with no known occupational exposure to exogenous electrophilic xenobiotics. Solid phase extraction and cross-reactivity indicated that the presumptive immunoreactive materials were similar in size and polarity to S-benzylmercapturic acid. The assay was more selective to mercapturic acids than the spectrophotometric thioether assay.

Renal clearance of branched-chain L-amino and 2-oxo acids in maple syrup urine disease

In maple syrup urine disease (MSUD), branched-chain L-amino (BCAA) and 2-oxo acids (BCOA) accumulate in body fluids owing to an inherited deficiency of branched-chain 2-oxo acid dehydrogenase complex activity. In MSUD, little information is available on the significance of urinary disposal of branched-chain compounds. We examined the renal clearance of leucine, valine, isoleucine and alloisoleucine, and their corresponding 2-oxo acids 4-methyl-2-oxopentanoate (KIC), 3-methyl-2-oxobutanoate (KIV), (S)-(S-KMV), and (R)-3-methyl-2-oxopentanoate (R-KMV), using pairs of plasma and urine samples (n = 63) from 10 patients with classical MSUD. The fractional renal excretion of free BCAA was in the normal range (< 0.5%) and independent of the plasma concentrations. The excretion of bound (N-acylated) BCAA was normal and not significantly dependent on the BCAA plasma concentrations. The fractional renal excretion of BCOA was in the order KIC << KIV < R-KMV < or = S-KMV (range (%): KIC 0.1-25; KIV 0.14-21.3; S-KMV 0.26-24.6; R-KMV 0.1-35.9), significantly correlated with the KIC plasma concentrations, and generally higher than that of the related BCAA. The results show that the renal excretion of free BCAA as well as of the acylated derivatives is negligible. The renal excretion of BCOA, however, to some extent counteracts increases in BCAA concentrations and thus contributes to the lowering of total BCAA pools in MSUD.