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  • Title: Salivary aldehyde dehydrogenase--reversible oxidation of the enzyme and its inhibition by caffeine, investigated using fluorimetric method.
    Author: Wierzchowski J, Pietrzak M, Szelag M, Wroczyński P.
    Journal: Arch Oral Biol; 2008 May; 53(5):423-8. PubMed ID: 18154860.
    Abstract:
    OBJECTIVE: We have applied fluorimetric method to monitor aldehyde dehydrogenase (ALDH*) activity in human saliva samples to study inactivation, reactivation and inhibition of the enzyme. DESIGN: Saliva samples were collected to buffer stock solution, containing various thiols, and assayed in the presence of the fluorogenic substrate 6-dimethylamino-2-naphthaldehyde and NAD(+). Fluorescence of the produced 6-dimethylamino-2-naphthalene carboxylate was used to measure the reaction rate. RESULTS: Kinetic parameters for the highly fluorogenic substrate, 6-dimethylamino-2-naphthaldehyde were measured, with apparent K(m) of 7.9 microM at pH 7.3. The apparent K(m) for NAD(+) was 1.2 microM. The observed ALDH activity is unstable in the absence of thiols, but can be stabilized by 1mM glutathione, and inactivated enzyme can be re-activated within 10 min by treatment of 0.5 mM DTT. Two-assay procedure was applied to measure degree of inactivation of ALDH in saliva samples. It was found that degree of ALDH inactivation in fresh samples, stabilized by glutathione, is between 0% and 90%, with average value ca. 40%. Caffeine and theophylline were shown to be moderate inhibitors of salivary ALDH. CONCLUSIONS: Oxidation of the salivary ALDH in fresh saliva may be reliably measured using fluorimetric two-assay procedure. Preliminary statistics indicate that in most individuals this enzyme is partially inactive. Inhibition of the salivary ALDH by caffeine may have consequences for nutrition safety.
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