Action of 6-amino-3-pyridinols as novel antioxidants against free radicals and oxidative stress in solution,plasma, and cultured cells

Free radical-mediated lipid peroxidation has been implicated in the pathogenesis of various diseases. Lipid peroxidation products are cytotoxic and they modify proteins and DNA bases, leading eventually to degenerative disorders. Various synthetic antioxidants have been developed and assessed for their capacity to inhibit lipid peroxidation and oxidative stress induced by free radicals. In this study, the capacity of novel 6-amino-2,4,5-trimethyl-3-pyridinols for scavenging peroxyl radicals, inhibiting plasma lipid peroxidation in vitro, and preventing cytotoxicity induced by glutamate, 6-hydroxydopamine, 1-methyl-4-phenylpyridium (MPP⁺ ), and hydroperoxyoctadecadienoic acid was assessed. It was found that they exerted higher reactivity toward peroxyl radicals and more potent activity for inhibiting the above oxidative stress than α-tocopherol, the most potent natural antioxidant, except against the cytotoxicity induced by MPP⁺. These results suggest that the novel 6-amino-3-pyridinols may be potent antioxidants against oxidative stress.     

Effects of antioxidants against atherosclerosis

It is generally accepted that the oxidative modification of low density lipoprotein (LDL) plays a pivotal role in the progression of atherosclerosis. This suggests that the antioxidants which suppress the oxidative modification of LDL should be effective in preventing atherogenesis. This brief article reviews the role and potency of antioxidants against the oxidation of LDL. It is emphasized that the LDL can be oxidized by different oxidants by different mechanisms and the efficacy of antioxidants depends on the type of oxidants.     

Tumor delivery of liposomal doxorubicin prepared with poly-L-glutamic acid as a drug-trapping agent

Context: Poly-l-glutamic acid (PGA) is an anionic polymer with a large number of carboxyl groups that can interact electrostatically with cationic drugs such as doxorubicin (DOX).

Objective: For stable encapsulation of DOX into liposomes, we prepared triethylamine (TEA)-PGA-liposomes using PGA as an internal trapping agent.

Methods: We prepared TEA-PGA-liposomes by remote loading of DOX with a TEA gradient into preformed liposomes prepared with 1, 2, or 4?mg/mL PGA (molecular weights 4800, 9800, and 20 500), and evaluated their biodistribution and antitumor effects on Lewis lung carcinoma (LLC) tumor-bearing mice.

Results: TEA-PGA-liposomes using the higher the molecular weight or concentration of PGA showed a slower release of DOX from the liposomes. TEA-PGA-liposomes prepared with a high concentration of PGA could enhance DOX accumulation in tumors and prolonged DOX circulation in the serum, indicating that DOX may be retained stably in the liposomal interior by interaction with PGA. Furthermore, injection of TEA-PGA-liposomes prepared with 4?mg/mL of PGA₉₈₀₀ or 2?mg/mL PGA₂₀₅₀₀ strongly inhibited tumor growth in LLC tumor-bearing mice.

Conclusions: PGA may be a potential trapping agent for liposomal DOX for tumor drug delivery.     

Determination of D- and L-alanine concentrations using a pyruvic acid sensor

The concentrations of D- and L-alanine in bivalves are useful as indicators of environmental pollution. Amino acid oxidase with a low substrate specificity catalyzes the oxidation of various amino acids. Among the various amino acids, pyruvic acid can be generated from alanine only by the catalytic oxidative reaction of this oxidase. Therefore, in this study, the concentrations of D- and L-alanine were determined from the concentration of pyruvic acid, which was determined from the consumption of oxygen based on the oxidative reaction of pyruvate oxidase. From this point of view, there is a very strong possibility that biosensors utilizing enzymes with a low substrate specificity can be developed. The results obtained were as follows. (1) The optimum conditions for the use of pyruvic acid sensor were as follows: temperature of 25 degrees C, pH of 6.8, flow rate of 0.1 ml/min, thiamin diphosphate concentration of 1.5 mM, and injection volume of 50 microl. (2) D-Alanine and L-alanine optimally reacted with D- and L-amino acid oxidase at 30 degrees C, pH 8.2, for 30 min and at 37 degrees C, pH 7.8, for 90 min, respectively. (3) The linear relationships between the concentrations of D- and L-alanine and the output of the sensor were obtained at 3.56-106.8 microg of D-alanine and 5.34-71.3 microg of L-alanine. (4) The concentrations of D- and L-alanine in Meretrix iusoria, Patinopecten yessonsi, and Corbicula leana obtained by the proposed assay were in good agreement with those determined by a conventional method.     

Mitochondrial aspartate aminotransferase: a third kynurenate-producing enzyme in the mammalian brain

The tryptophan metabolite kynurenic acid (KYNA), which is produced enzymatically by the irreversible transamination of l-kynurenine, is an antagonist of alpha7 nicotinic and NMDA receptors and may thus modulate cholinergic and glutamatergic neurotransmission. Two kynurenine aminotransferases (KAT I and II) are currently considered the major biosynthetic enzymes of KYNA in the brain. In this study, we report the existence of a third enzyme displaying KAT activity in the mammalian brain. The novel KAT had a pH optimum of 8.0 and a low capacity to transaminate glutamine or alpha-aminoadipate (the classic substrates of KAT I and KAT II, respectively). The enzyme was inhibited by aspartate, glutamate, and quisqualate but was insensitive to blockade by glutamine or anti-KAT II antibodies. After purification to homogeneity, the protein was sequenced and the enzyme was identified as mitochondrial aspartate aminotransferase (mitAAT). Finally, the relative contributions of KAT I, KAT II, and mitAAT to total KAT activity were determined in mouse, rat, and human brain at physiological pH using anti-mitAAT antibodies. KAT II was most abundant in rat and human brain, while mitAAT played the major role in mouse brain. It remains to be seen if mitAAT participates in cerebral KYNA synthesis under physiological and/or pathological conditions in vivo.     

S-allyl cysteine prevents CCl(4)-induced acute liver injury in rats

Aged garlic extract (AGE) possesses multiple biological activities. We evaluated the protective effect of S-allyl cysteine (SAC), one of the organosulfur compounds of AGE, against carbon tetrachloride (CCl₄)-induced acute liver injury in rats. SAC was administrated intraperitoneally (50-200 mg/kg). SAC significantly suppressed the increases of plasma ALT and LDH levels. SAC also attenuated histological liver damage. CCl₄ administration induced lipid peroxidation accompanied by increases in the plasma malondialdehyde and hepatic 4-hydroxy-2-nonenal levels, and SAC dose-dependently attenuated these increases. The hepatic total level of hydroxyoctadecadienoic acid (HODE), a new oxidative stress biomarker, was closely correlated with the amount of liver damage. These results suggest that SAC decreased CCl₄-induced liver injury by attenuation of oxidative stress, and may be a better therapeutic tool for chronic liver disease.