Abstract  Intrastriatal injections of the mitochondrial toxins malonate and 3-nitropropionic acid produce selective cell death similar to that seen in transient ischemia and Huntington's disease. The extent of cell death can be attenuated by pharmacological or surgical blockade of cortical glutamatergic input. It is not known, however, if dopamine contributes to toxicity caused by inhibition of mitochondrial function. Exposure of primary striatal cultures to dopamine resulted in dose-dependent death of neurons. Addition of medium supplement containing free radical scavengers and antioxidants decreased neuronal loss. At high concentrations of the amine, cell death was predominantly apoptotic. Methyl malonate was used to inhibit activity of the mitochondrial respiratory chain. Neither methyl malonate (50 microM) nor dopamine (2.5 microM) caused significant toxicity when added individually to cultures, whereas simultaneous addition of both compounds killed 60% of neurons. Addition of antioxidants and free radical scavengers to the incubation medium prevented this cell death. Dopamine (up to 250 microM) did not alter the ATP/ADP ratio after a 6-h incubation. Methyl malonate, at 500 microM, reduced the ATP/ADP ratio by approximately 30% after 6 h; this decrease was not augmented by coincubation with 25 microM dopamine. Our results suggest that dopamine causes primarily apoptotic death of striatal neurons in culture without damaging cells by an early adverse action on oxidative phosphorylation. However, when combined with minimal inhibition of mitochondrial function, dopamine neurotoxicity is markedly enhanced.

Abstract  The functioning of the propionate pathway of oxidation substrate metabolism in the norm and under vitamin B12 deficiency has been studied. This pathway has been shown to play an important role in oxidative processes occurring in normal organisms, for its inhibition in B12-deficient animals is associated with a reduction of respiration as well as with noticeable decreases in palmitoylcarnitine and succinate oxidation rates and oxidation phosphorylation coupling. Succinate, the end product of the propionate pathway, normalizes the respiration and restores the rate of palmitoylcarnitine oxidation in B12-deficient animals, which is suggestive of its crucial role in the propionate pathway. In vivo propionate inhibits, whereas methyl malonate stimulates palmitoylcarnitine respiration, however only in intact animals. In B12-deficient animals the sensitivity to these metabolites is decreased.

Abstract  Glutamate-induced excitotoxicity is implicated as playing a key role in the pathogenesis of amyotrophic lateral sclerosis (ALS), and mitochondrial dysfunction is also found in ALS patients. We investigated the relationship between glutamate excitotoxicity and mitochondrial dysfunction elicited by rotenone (a complex I inhibitor), malonate (a complex II inhibitor), or antimycin (a complex III inhibitor), in primary cultures of the embryonic rat spinal cord. Rotenone and malonate induced relatively selective toxicity against motor neurons as compared to non-motor neurons, whereas antimycin caused non-selective toxicity. The toxicity of rotenone was prevented by a non-N-methyl-D-aspartate (NMDA) receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) but not by an NMDA receptor antagonist, 5-methyl-10, 11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801). The toxicity of malonate was blocked by both CNQX and MK-801. The toxicity of antimycin was affected by neither CNQX nor MK-801. When mitochondrial complex I was mildly inhibited by a sub-lethal concentration of rotenone, AMPA-induced motor neuron death was significantly exacerbated. A sub-lethal concentration of malonate exacerbated both NMDA- and AMPA-induced motor neuron death. These data suggest that mitochondrial dysfunction predisposes motor neurons to ionotropic glutamate receptor-mediated excitotoxicity.

Abstract  The influence of the selective adenosine A(2A) receptor antagonist ZM 241385 on exogenous l-DOPA-derived dopamine (DA) release in intact and dopamine-denervated rats was studied using an in vivo microdialysis in freely moving animals. Local infusion of l-DOPA (2.5 microM) produced a marked increase in striatal extracellular DA level in intact and malonate-lesioned rats. Intrastriatal perfusion of ZM 241385 (50-100 microM) had no effect on basal extracellular DA level, but enhanced dose-dependently the l-DOPA-induced DA release in intact and malonate-lesioned animals. A non-selective adenosine A(2A) receptor antagonist DMPX (100 microM), similarly to ZM 241385, accelerated conversion of l-DOPA in intact and malonate-denervated rats. This effect was not produced by the adenosine A(1) receptor antagonist, CPX (10-50 microM). However, ZM 241385 did not affect the l-DOPA-induced DA release in rats pretreated with reserpine (5 mg/kg i.p.) and alpha-methyl-p-tyrosine (AMPT, 300 mg/kg i.p.). Obtained results indicate that blockade of striatal adenosine A(2A) receptors increases the l-DOPA-derived DA release possibly by indirect mechanism exerted on DA terminals, an effect dependent on striatal tyrosine hydroxylase activity. Selective antagonists of adenosine A(2A) receptors may exert a beneficial effect at early stages of Parkinson's disease by enhancing the therapeutic efficacy of l-DOPA applied exogenously.

Abstract  The relative contribution of glycolysis vs. oxidative metabolism to the stimulus secretion coupling mechanism of P-cells was investigated in isolated islets. For that purpose, the secretory and intracellular calcium responses of islets to both glucose and succinic acid dimethyl ester (SAD) were compared. After 45 min of rat islet perifusion in the absence of substrates, the maximum secretory responses to Glucose (20 mmol/L) and SAD (10 mmol/L) were qualitatively and quantitatively indistinguishable. Malonic acid dimethyl ester (a permeable citric acid cycle inhibitor) suppressed the insulin secretory response to both 20 mmol/L glucose and 10 mmol/L SAD (-70% on average). The inhibitor decreased within 70% the rate of (CO2)-C-14-production from 10 mmol/L [2-C-14]pyruvate without affecting the rate of 20 mmol/L D-[5-H-3]glucose utilization. Both, 11.1 mmol/L glucose and 10 mmol/L SAD, elevated the intracellular calcium concentration and induced a similar pattern of oscillations that were rapidly ablated by 20 mmol/L malonic acid dimethyl ester. However. the intracellular concentration of calcium declined to basal values several minutes after the introduction of the inhibitor in the presence of SAD whereas it remained elevated in the case of glucose. In conclusion: (1) An exclusive increase of mitochondrial metabolism in pancreatic islets was sufficient to mimic the effects of glucose on intracellular calcium and insulin secretion. (2) Islet glycolysis and/or the re-oxidation of cytoplasmic NADH allowed the maintenance of an elevated, though non-oscillating, intracellular calcium concentration, but a reduced response to glucose. (C) 2003 Elsevier Inc. All rights reserved.

Abstract  The uptake of dimethyl malonate and dimethyl succinate on aqueous surfaces was measured between 266 and 279 K, using the droplet train technique coupled with mass spectrometric detection. The uptake coefficients gamma were found to be independent of the aqueous phase composition and of the gas-liquid contact times. In addition, the uptake coefficients and the derived mass accommodation coefficients a show a negative temperature dependence in the temperature ranges studied. The mass accommodations decrease from 7.8 x 10(-2) to 5.0 x 10(-2) and from 4.5 x 10(-1) to 2.3 x 10(-2) for dimethyl malonate and succinate, respectively. These results are used to discuss the incorporation of oxygenated volatile organic compounds (VOCs) into the liquid using the nucleation theory. Henry's law constants of both compounds were directly measured between 283 and 298 K using a dynamic equilibrium system. Their values exponentially decrease when temperature increases, from (2.60 +/- 0.30) x 10(4) to (0.40 +/- 0.05) x 10(4) and from (1.20 +/- 0.10) x 10(4) to (0.30 +/- 0.03) x 10(4) for dimethyl malonate and succinate, respectively (in units of M atm(-1)). The partitioning of both dibasic esters between gas and aqueous phases and the corresponding atmospheric lifetimes have then been derived.

Abstract  The microbial capacity to degrade simple organic compounds with quaternary carbon atoms was demonstrated by enrichment and isolation of five denitrifying strains on dimethylmalonate as the sole electron donor and carbon source. Quantitative growth experiments showed a complete mineralization of dimethylmalonate. According to phylogenetic analysis of the complete 16S rRNA genes, two strains isolated from activated sewage sludge were related to the genus Paracoccus within the alpha-Proteobacteria (98.0 and 98.2% 16S rRNA gene similarity to Paracoccus denitrificans(T)), and three strains isolated from freshwater ditches were affiliated with the beta-Proteobacteria (97.4 and 98.3% 16S rRNA gene similarity to Herbaspirillum seropedicae(T) and Acidovorax facilis(T), respectively). Most-probable-number determinations for denitrifying populations in sewage sludge yielded 4.6 x 10(4) dimethylmalonate-utilizing cells ml(-1), representing up to 0.4% of the total culturable nitrate-reducing population.

Abstract  To determine the potential environmental persistence and toxic effects of agent simulants Diethyl Malonate (DEM) and Methyl Salicylate (MS), plants, soils, earthworms, and oil microbial populations were exposed to projected aerosolized simulant concentrations of (approximately)100 (low) and (approximately)1000 (high) mg/m(sup 3). Both simulants exhibited biphasic residence times on foliar and soil surfaces following aerosol exposure. Half-times of DEM on soil and foliar surfaces were 1 to 3 h and 5 to 22 H, respectively, and 2 to 2 h and 5 to 31 h for the MS, respectively. Persistence was longer on the foliar surfaces than that of the soils. Both simulants proved phytotoxic to vegetation with a lower threshold of 1 to 2 (mu)m/cm(sup 2) for the MS versus that of 10 (mu)g/cm(sup 2) for the DEM. However, neither significantly affected chloroplast electron transport in vitro at concentrations of up to 100 (mu)g/mL. Results from in vitro testing of DEM indicated concentrations below 500 (mu)g/g dry soil generally did not adversely impact soil microbial activity, while the theshold was 100 (mu)g/g dry soil for MS. Earthworm bioassays indicated survival rates of 66% at soil doses of 204 (mu)g DEM/cm(sup 2) soil and 86% at soil doses of 331 (mu)g MS/cm(sup 2).

Abstract  This substance is manufactured and/or imported in the European Economic Area in 1 000+ tonnes per year. This substance is used by consumers, in articles, by professional workers (widespread uses), in formulation or re-packing, at industrial sites and in manufacturing.

Abstract  Enteric bacterial and hepatic azoreductase enzymes are capable of reducing azo dyes to yield the constituent aromatic amines. Azo dyes based on benzidine and benzidine congeners have received particular attention because of their widespread use and the known carcinogenicity of benzidine to humans. Azo dyes based on beta-diketone coupling components exist preferentially as the tautomeric hydrazones. A series of hydrazone dyes based on benzidine and benzidine congeners was prepared and characterized by NMR and UV-visible spectroscopy. These dyes were tested for mutagenicity using a modified Ames assay and, unlike the true azo dyes, showed no significant mutagenic activity. The hydrazone dyes were resistant to enzymatic reduction by FMN-supplemented hamster-liver post-mitochondrial supernatant (S-9); under identical conditions, azo dyes such as trypan blue were rapidly reduced.

Abstract  Summary: The use of this material under current conditions is supported by existing information. The material diethyl malonate was evaluated for genotoxicity, repeated dose toxicity, reproductive toxicity, local respiratory toxicity, phototoxicity/photoallergenicity, skin sensitization, as well as environmental safety. Target data show that diethyl malonate is not genotoxic. The repeated dose and reproductive toxicity endpoints were completed using dimethyl malonate (CAS# 108-59-8) as a read-across analog, which provided an MOE > 100. Data from target material and read-across analog, pentanedioic acid, 1,5-dimethyl ester (CAS# 1119-40-0) show that is material is not a concern for skin sensitization. The local respiratory toxicity endpoint was completed using the TTC (Threshold of Toxicological Concern) for a Cramer Class I material (1.4 mg/day). The phototoxicity/photoallergenicity endpoint was completed based on UV spectra. The environmental endpoints were evaluated; diethyl malonate was found not to be a PBT as per the IFRA Environmental Standards, and its risk quotients, based on its current volume of use in Europe and North America (i.e., PEC/PNEC) are < 1.

Abstract  Isoxazolidine-3,5-dione 2 (JTT-501), one of the cyclic malonic acid derivatives, was found to decrease blood glucose at an oral dose of 38 mg/kg/day in KKAy mice and is currently undergoing evaluation in phase II clinical trials. Further studies on a series of malonic acids and related compounds showed that the 1,3-dicarbonyl structure was important for insulin-sensitizing activity. Dimethyl malonate 10, which was selected as a successor for 2, was the optimum compound in a series of 1,3-dicarbonyl compounds and was more potent than the corresponding thiazolidine-2,4-dione 1.