Inhibitory effects of flavonoids on aldehyde oxidase activity

Flavonoids are an important group of natural compounds that can interfere with the activity of some enzymes. In this study, effects of various flavonoids on aldehyde oxidase (AO) activity were evaluated in vitro. AO was partially purified from guinea pig liver. The effects of 12 flavonoids from three subclasses of flavon-3-ol, flavan-3-ol and flavanone on the oxidation of vanillin and phenanthridine as substrates of AO and xanthine as a substrate of xanthine oxidase (XO) were investigated spectrophotometrically. Among the 12 flavonoids, myricetin and quercetin were the most potent inhibitors of both AO and XO. In general, the oxidation of vanillin was more inhibited by flavonoids than that of phenanthridine. Almost all of the flavonoids inhibited AO activity more potently than XO, which was more evident with non-planner flavanols. A planner structure seems to be essential for a potent inhibitory effect and any substitution by sugar moieties reduces the inhibitory effects. This study could provide a new insight into AO natural inhibitors with potential to lead to some food-drug interactions.     

Substrate specificity,plasma membrane localization,and lipid modification of the aldehyde dehydrogenase ALDH3B1

The accumulation of reactive aldehydes is implicated in the development of several disorders. Aldehyde dehydrogenases (ALDHs) detoxify aldehydes by oxidizing them to the corresponding carboxylic acids. Among the 19 human ALDHs, ALDH3A2 is the only known ALDH that catalyzes the oxidation of long-chain fatty aldehydes including C16 aldehydes (hexadecanal and trans-2-hexadecenal) generated through sphingolipid metabolism. In the present study, we have identified that ALDH3B1 is also active in vitro toward C16 aldehydes and demonstrated that overexpression of ALDH3B1 restores the sphingolipid metabolism in the ALDH3A2-deficient cells. In addition, we have determined that ALDH3B1 is localized in the plasma membrane through its C-terminal dual lipidation (palmitoylation and prenylation) and shown that the prenylation is required particularly for the activity toward hexadecanal. Since knockdown of ALDH3B1 does not cause further impairment of the sphingolipid metabolism in the ALDH3A2-deficient cells, the likely physiological function of ALDH3B1 is to oxidize lipid-derived aldehydes generated in the plasma membrane and not to be involved in the sphingolipid metabolism in the endoplasmic reticulum.     

DNA repair mechanisms in dividing and non-dividing cells

DNA damage created by endogenous or exogenous genotoxic agents can exist in multiple forms, and if allowed to persist, can promote genome instability and directly lead to various human diseases, particularly cancer, neurological abnormalities, immunodeficiency and premature aging. To avoid such deleterious outcomes, cells have evolved an array of DNA repair pathways, which carry out what is typically a multiple-step process to resolve specific DNA lesions and maintain genome integrity. To fully appreciate the biological contributions of the different DNA repair systems, one must keep in mind the cellular context within which they operate. For example, the human body is composed of non-dividing and dividing cell types, including, in the brain, neurons and glial cells. We describe herein the molecular mechanisms of the different DNA repair pathways, and review their roles in non-dividing and dividing cells, with an eye toward how these pathways may regulate the development of neurological disease.     

Association of genetic polymorphisms in ADH and ALDH2 with risk of coronary artery disease and myocardial infarction: A meta-analysis

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) are the major enzymes responsible for alcohol metabolism in humans. Emerging evidences have shown that functional polymorphisms in ADH and ALDH genes might play a critical role in increasing coronary artery disease (CAD) and myocardial infarction (MI) risks; however, individually published studies showed inconclusive results. The aim of this meta-analysis is to evaluate the associations between the genetic polymorphisms of ADH and ALDH genes with susceptibility to CAD and MI. A literature search was conducted on PubMed, Embase, Web of Science and Chinese BioMedical databases from inception through December 1st, 2012. Crude relative risks (RRs) with 95% confidence intervals (CIs) were calculated. Twelve case–control studies were included with a total of 9616 subjects, including 2053 CAD patients, 1436 MI patients, and 6127 healthy controls. Meta-analysis showed that mutant genotypes (GA + AA) of the rs671 polymorphism in the ALDH2 gene were associated with increased risk of both CAD and MI (CAD: RR = 1.20, 95%CI: 1.03–1.40, P = 0.021; MI: RR = 1.32, 95%CI: 1.11–1.57, P = 0.002). However, there were no significant associations of ADH genetic polymorphisms to CAD and MI risks (CAD: RR = 0.92, 95%CI: 0.73–1.15, P = 0.445; MI: RR = 0.93, 95%CI: 0.84–1.03, P = 0.148). In conclusion, this meta-analysis provides strong evidence that ALDH2 rs671 polymorphism may be associated with increased risks of CAD and MI. However, further studies are still needed to accurately determine whether ADH genetic polymorphisms are associated with susceptibility to CAD and MI.     

Structure and activity of the NAD(P)+‐dependent succinate semialdehyde dehydrogenase YneI from Salmonella typhimurium

Aldehyde dehydrogenases are found in all organisms and play an important role in the metabolic conversion and detoxification of endogenous and exogenous aldehydes. Genomes of many organisms including Escherichia coli and Salmonella typhimurium encode two succinate semialdehyde dehydrogenases with low sequence similarity and different cofactor preference (YneI and GabD). Here, we present the crystal structure and biochemical characterization of the NAD(P)⁺‐dependent succinate semialdehyde dehydrogenase YneI from S. typhimurium. This enzyme shows high activity and affinity toward succinate semialdehyde and exhibits substrate inhibition at concentrations of SSA higher than 0.1 mM. YneI can use both NAD⁺ and NADP⁺ as cofactors, although affinity to NAD⁺ is 10 times higher. High resolution crystal structures of YneI were solved in a free state (1.85 Å) and in complex with NAD⁺ (1.90 Å) revealing a two domain protein with the active site located in the interdomain interface. The NAD⁺ molecule is bound in the long channel with its nicotinamide ring positioned close to the side chain of the catalytic Cys268. Site‐directed mutagenesis demonstrated that this residue, as well as the conserved Trp136, Glu365, and Asp426 are important for activity of YneI, and that the conserved Lys160 contributes to the enzyme preference to NAD⁺. Our work has provided further insight into the molecular mechanisms of substrate selectivity and activity of succinate semialdehyde dehydrogenases. © 2012 Wiley Periodicals, Inc.     

Hydrogen sulfide protects SH-SY5Y neuronal cells against d-galactose induced cell injury by suppression of advanced glycation end products formation and oxidative stress

d-Galactose is widely used as an agent to cause aging effects in experimental animals. The present study aims to investigate the effects of hydrogen sulfide (H₂S) in human neuroblastoma SH-SY5Y cells exposed to d-galactose. Cells were pretreated with NaHS, an H₂S donor, and then exposed to d-galactose (25–400 mM for 48 h). We found that NaHS pretreatment significantly reversed the d-galactose-induced cell death and cellular senescence. MTT assay shows that NaHS significantly increased cell viability from 62.31 ± 1.29% to 72.34 ± 0.46% compared with d-galactose (200 mM) treatment group. The underlying mechanism appeared to involve a reduction by NaHS in the formation of advanced glycation end products (AGEs), which are known to contribute to the progression of age-related diseases. In addition, NaHS decreased the elevation of reactive oxygen species from 151.17 ± 2.07% to 124.8 ± 2.89% and malondialdehyde from 1.72 ± 0.07 to 1.10 ± 0.08 (nmol/mg protein) in SH-SY5Y cells after d-galactose exposure. NaHS also stimulated activities of superoxide dismutase from 0.42 ± 0.05 to 0.73 ± 0.04 (U/mg protein) and glutathione peroxidase from 3.98 ± 0.73 to 14.73 ± 0.77 (nmol/min/mg protein) and upregulated the gene expression levels of copper transport protein ATOX1, glutathione synthetase (GSS) and thioredoxin reductase 1 (TXNRD1) while down-regulated aldehyde oxidase 1 (AOX1). In summary, our data indicate that H₂S may have potentially anti-aging effects through the inhibition of AGEs formation and reduction of oxidative stress.     

A single amino acid determines the catalytic efficiency of two alkenal double bond reductases produced by the liverwort Plagiochasma appendiculatum

Alkenal double bond reductases (DBRs) catalyze the NADPH-dependent reduction of the α,β-unsaturated double bond of many secondary metabolites. Two alkenal double bond reductase genes PaDBR1 and PaDBR2 were isolated from the liverwort species Plagiochasma appendiculatum. Recombinant PaDBR2 protein had a higher catalytic activity than PaDBR1 with respect to the reduction of the double bond present in hydroxycinnamyl aldehydes. The residue at position 56 appeared to be responsible for this difference in enzyme activity. The functionality of a C56 to Y56 mutation in PaDBR1 was similar to that of PaDBR2. Further site-directed mutagenesis and structural modeling suggested that the phenol ring stacking between this residue and the substrate was an important determinant of catalytic efficiency.     

Inhibitor selectivity between aldo–keto reductase superfamily members AKR1B10 and AKR1B1: Role of Trp112 (Trp111)

The antineoplastic target aldo–keto reductase family member 1B10 (AKR1B10) and the critical polyol pathway enzyme aldose reductase (AKR1B1) share high structural similarity. Crystal structures reported here reveal a surprising Trp112 native conformation stabilized by a specific Gln114-centered hydrogen bond network in the AKR1B10 holoenzyme, and suggest that AKR1B1 inhibitors could retain their binding affinities toward AKR1B10 by inducing Trp112 flip to result in an “AKR1B1-like” active site in AKR1B10, while selective AKR1B10 inhibitors can take advantage of the broader active site of AKR1B10 provided by the native Trp112 side-chain orientation.     

Measurement of Free Choline in Plant Leaves by Capillary Electrophoresis

A low pH capillary electrophoresis (CE) was used for the measurement of free choline in plant leaves. Choline in the leaf extract was first converted to the benzoyl ester and put into CE. A well-resolved peak in the electropherogram was easily obtained. Involvement of enzymes in a two-step oxidation of choline to glycine betaine was evaluated in different plant species with the same mehod developed for glycine betaine and betaine aldehyde.