The Neuroprotective Effect of L-Carnitine against Glyceraldehyde-Induced Metabolic Impairment: Possible Implications in Alzheimer's Disease.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive regression and memory loss. Dysfunctions of both glucose metabolism and mitochondrial dynamics have been recognized as the main upstream events of the degenerative processes leading to AD. It has been recently found that correcting cell metabolism by providing alternative substrates can prevent neuronal injury by retaining mitochondrial function and reducing AD marker levels. Here, we induced an AD-like phenotype by using the glycolysis inhibitor glyceraldehyde (GA) and explored whether L-carnitine (4-N-trimethylamino-3-hydroxybutyric acid, LC) could mitigate neuronal damage, both in SH-SY5Y neuroblastoma cells and in rat primary cortical neurons. We have already reported that GA significantly modified AD marker levels; here we demonstrated that GA dramatically compromised cellular bioenergetic status, as revealed by glycolysis and oxygen consumption rate (OCR) evaluation. We found that LC ameliorated cell survival, improved OCR and ATP synthesis, prevented the loss of the mitochondrial membrane potential (Δψm) and reduced the formation of reactive oxygen species (ROS). Of note, the beneficial effect of LC did not rely on the glycolytic pathway rescue. Finally, we noticed that LC significantly reduced the increase in pTau levels induced by GA. Overall, these findings suggest that the use of LC can promote cell survival in the setting of the metabolic impairments commonly observed in AD. Our data suggest that LC may act by maintaining mitochondrial function and by reducing the pTau level.

In vitro toxicity of reuterin, a potential food biopreservative.

Reuterin has a high potential as a food preservative due to both its chemical characteristics and its antimicrobial activity against food-borne pathogens and spoilage bacteria. However, there is a lack of information about its toxicity and its capacity to interfere with the metabolism of drugs by inhibiting cytochrome P450 (CYP) activity. The results of this study indicated that reuterin exhibited a moderate cytotoxicity in the human hepatoma cell line HepG2 according to assays measuring three different endpoints in the same set of cells. Reuterin was much less toxic than acrolein and only four times more toxic than diacetyl, a generally recognized as safe flavoring compound. In vitro experiments utilizing human liver microsomes showed that reuterin presents low possibility of displaying in vivo drug interactions by inhibition of CYP3A4, CYP2D6, and CYP2C9. Therefore, reuterin can be considered a promising food biopreservative, although additional toxicology research is needed before permission for use can be granted.

Experimental scleral cross-linking increases glaucoma damage in a mouse model.

The purpose of this study was to assess the effect of a scleral cross-linking agent on susceptibility to glaucoma damage in a mouse model.CD1 mice underwent 3 subconjunctival injections of 0.5 M glyceraldehyde (GA) in 1 week, then had elevated intraocular pressure (IOP) induced by bead injection. Degree of cross-linking was measured by enzyme-linked immunosorbent assay (ELISA), scleral permeability was measured by fluorescence recovery after photobleaching (FRAP), and the mechanical effects of GA exposure were measured by inflation testing. Control mice had buffer injection or no injection in 2 separate glaucoma experiments. IOP was monitored by Tonolab and retinal ganglion cell (RGC) loss was measured by histological axon counting. To rule out undesirable effects of GA, we performed electroretinography and detailed histology of the retina. GA exposure had no detectable effects on RGC number, retinal structure or function either histologically or electrophysiologically. GA increased cross-linking of sclera by 37% in an ELISA assay, decreased scleral permeability (FRAP, p = 0.001), and produced a steeper pressure-strain behavior by in vitro inflation testing. In two experimental glaucoma experiments, GA-treated eyes had greater RGC axon loss from elevated IOP than either buffer-injected or control eyes, controlling for level of IOP exposure over time (p = 0.01, and 0.049, multivariable regression analyses). This is the first report that experimental alteration of the sclera, by cross-linking, increases susceptibility to RGC damage in mice.

Cytotoxic molecular mechanisms and cytoprotection by enzymic metabolism or autoxidation for glyceraldehyde, hydroxypyruvate and glycolaldehyde.

Previously, we showed that dietary fructose or its carbonyl metabolites, glyceraldehyde and glycolaldehyde, could be oxidized by inflammatory reactive oxygen species (ROS), products of immune cells, to form highly toxic and genotoxic products, such as glyoxal. Glycolaldehyde-caused hepatocyte protein carbonylation likely resulted from glyoxal, an autoxidation product formed by ROS. Although hepatocyte protein carbonylation by glyoxal or d-glycolaldehyde was rapid, the product was unstable. Glyceraldehyde-induced protein carbonylation was slower and was also less cytotoxic. Non-toxic concentrations of H(2)O(2) were then used to mimic inflammation and oxidative stress associated with fructose-induced non-alcoholic steatohepatitis (NASH). A slow infusion of H(2)O(2) markedly increased glyoxal, glyceraldehyde, and glycolaldehyde-induced cytotoxicity and protein carbonylation. However, it had a smaller effect on glyceraldehyde-induced protein carbonylation. The cytotoxicities of both aldehydes were increased if glutathione (GSH)-depleted hepatocytes were used, presumably because of the increased ROS formation and subsequent glyoxal-induced protein carbonylation. Catalytic amounts of Cu or Fe increased the glycolaldehyde and glyceraldehyde-induced cytotoxicity and protein carbonylation resulting from autoxidation to glyoxal. Glyceraldehyde and glycolaldehyde were also detoxified by mitochondrial aldehyde dehydrogenase (ALDH2) as ALDH2 inhibitors increased their cytotoxicity. Hydroxypyruvate has not been previously tested for toxicity and was found to be the most toxic fructose metabolite. Catalytic amounts of Cu or Fe caused hydroxypruvate autoxidation, which formed extensive ROS, glycolaldehyde and glyoxal. Iron chelators EGTA or deferoxamine inhibited cytotoxicity as well as the extensive ROS formation. The Girard assay confirmed that glyoxal was a common autoxidation product from glyceraldehyde, glycolaldehyde and hydroxypyruvate.

Influence of environmental parameters on production of the acrolein precursor 3-hydroxypropionaldehyde by Lactobacillus reuteri DSMZ 20016 and its accumulation by wine lactobacilli.

Lactic acid bacteria belonging to the genus Lactobacillus are known to convert glycerol into 3-hydroxypropionaldehyde (3-HPA) during anaerobic glycerol fermentation. Wine quality can be gravely compromised by the accumulation of 3-HPA, due to its spontaneous conversion to acrolein under wine making conditions. Acrolein is not only a dangerous substance for the living cell, but has been implicated in the development of unpleasant bitterness in beverages. This study evaluates the effect of individual environmental parameters on 3-HPA production by Lactobacillus reuteri DSMZ 20016, which only proved possible under conditions that allow accumulation well below the threshold concentration affecting cell viability. 3-HPA production was optimal at pH 6 and in the presence of 300 mM glycerol. Production increased with an increase in cell concentration up to an OD(600) of 50, whereas higher cell concentrations inhibited accumulation. Data presented in this study suggest that 3-HPA plays a role in regulating its own production through quorum sensing. Glycerol dehydratase possessing bacterial strains isolated from South African red wine, L. pentosus and L. brevis, tested positive for 3-HPA accumulation. 3-HPA is normally intracellularly reduced to 1,3-propanediol. This is the first study demonstrating the ability of wine lactobacilli to accumulate 3-HPA in the fermentation media. Recommendations are made on preventing the formation of acrolein and its precursor 3-HPA in wine.

Cytotoxicity and oxidative stress induced by the glyceraldehyde-related Maillard reaction products for HL-60 cells.

We demonstrated the cytotoxicity of glyceraldehyde-related Maillard reaction products for HL-60 cells. Glyceraldehyde-modified bovine serum albumin and glyceraldehyde-modified casein inhibited the proliferation of HL-60 cells. The reaction products formed from glyceraldehyde and Nalpha-acetyllysine had also a cytotoxic effect on HL-60 cells. The cytotoxic effect was prevented by N-acetylcysteine or pyrrolidinedithiocarbamate as the antioxidants. In addition, the reaction products depressed the intracellular glutathione level, and induced the reactive oxygen species (ROS) production. These results suggested that the glyceraldehyde-related advanced glycation end products (AGEs) induced the cytotoxicity and the oxidative stress. We previously reported that the glyceraldehyde-related AGE was identified as 1-(5-acetylamino-5-carboxypentyl)-3-hydroxy-5-hydroxymethyl-pyridinium, named GLAP (glyceraldehyde-derived pyridinium compound), formed from glyceraldehyde and Nalpha-acetyllysine (Biosci. Biotechnol. Biochem., 67, 930-932 (2003)). In this study, GLAP inhibited the proliferation of HL-60 cells, and the inhibitory effect was prevented by the antioxidants. Furthermore, GLAP depressed the intracellular glutathione level, and induced the ROS production. This work indicated the possibility that the cytotoxicity and the oxidative stress in the progression of diabetic complications and chronic renal disease might be induced by GLAP.