Electrochemistry of flavonoids. Relationships between redox potentials, inhibition of mitochondrial respiration, and production of oxygen radicals by flavonoids

We have investigated the redox behavior of a series of structurally related flavonoids employing cyclic voltammetry under physiological conditions. The flavonoids that auto-oxidized and produced oxygen radicals had oxidation potentials (E 1/2) significantly lower [-30 to +60 mV vs (SCE)] than those that did not undergo auto-oxidation (+130 to +340 mV vs SCE). The range of E 1/2 values for the auto-oxidizable flavonoids was comparable to the E 1/2 range reported for the optimum quinone induced production of superoxide (O2 pi) in mitochondrial NADH-CoQ reductase (complex I). The most potent flavonoid inhibitors of mitochondrial succinate-CoQ reductase (complex II) possessed hydroxyl configurations capable of supporting redox reactions. For a series of 3,5,7-trihydroxyflavones that differed by b-ring hydroxylation it was found that decreasing E 1/2 of the flavonoids was associated with decreasing I50 values towards succinoxidase. These findings suggest that the electrochemical properties of the flavonoids may contribute to their biological activity.     

Protection of mitochondrial respiration activity by bilobalide.

Mitochondria alteration is an early event in ischemia-induced damage, and its prevention improves tissue survival upon reperfusion. Adenine translocase and complex I activities are rapidly affected by ischemia. Ginkgo biloba extract demonstrates anti-ischemic properties attributable to the terpenoid fraction, mainly due to the presence of bilobalide. The mechanism of the protection afforded by bilobalide is not yet known. In this work, the effects of bilobalide on mitochondrial respiration were investigated. Mitochondria isolated from rats treated with bilobalide (2 to 8 mg/kg) showed a dose-dependent increase in the respiratory control ratio, due to a lower oxygen consumption during state 4. Bilobalide also decreased the sensitivity of oxygen consumption to inhibition of complex I by Amytal or to inhibition of complex III by antimycin A or myxothiazol. There was no protection of complexes IV and V. It also increased the activity of complex I but not of adenine translocase. Similar effects were also obtained in vitro when control mitochondria were preincubated for 1 hr with 0.8 microg/mL bilobalide. Treatment of the rats with 8 mg/kg bilobalide also prevented the ischemia-induced decrease in state 3 of the mitochondrial respiration and thus the decrease in RCR. The protective effect of bilobalide on cellular ATP content observed under ischemic conditions can be correlated with the above observations. By protecting complex I and III activities, bilobalide allows mitochondria to maintain their respiratory activity under ischemic conditions as long as some oxygen is present, thus delaying the onset of ischemia-induced damage. This mechanism provides a possible explanation for the anti-ischemic properties of bilobalide and of Ginkgo biloba extract in therapeutic interventions.     

羟基喜树碱内酯环形式与其抗癌活性的关系

目的：研究10－羟基喜树碱（HCPT）的内酯环形式与抗癌活性之间的关系。方法：采用MTT和台盼蓝排染法测定两种内酯环形式的HCPT在体外对多种肿瘤细胞的作用,并在体内（0．5、1．0和2．0mg/kg,ip）评价它们对S180肉瘤和HepS肝癌的抑瘤效果;应用HPLC方法观察了HCPT内酯环在肿瘤细胞内的转化情况。结果：两种形式的HCPT对同一种肿瘤细胞均显示类似的细胞毒性（P＞0．05）;但在体内实验中,闭环HCPT（C－HCPT）的抑瘤率明显高于（约两倍）开环HCPT（O－HCPT）。采用HPLC方法分析证明,两种类型的HCPT能在一定条件（如pH改变等）下相互转化。因此,O－HCPT体内、外作用的明显差异可归因于其在偏酸性环境（包括肿瘤细胞体外培养时）可较多地转化成C－HCPT,而在偏碱性环境（如正常体液pH约为7．40）中多呈开环形式。结论：闭环和开环HCPT羟基喜树碱均具有抗癌活性,但前者的活性较强;开环HCPT可在一定条件下转化成闭环形式。     

Leukotriene biosynthesis inhibition by aryl and aroyl substituted naphthoquinones.

Naphthoquinones are known to inhibit 5-lipoxygenase. In particular, CGS 8515 (methyl 2-[(3,4-dihydro-3,4-dioxo-1-naphthalenyl)amino]benzoate) has been studied in detail. However this potent and selective 5-lipoxygenase inhibitor has a short duration of action and poor bioavailability. To improve the duration of action we have prepared a series of carbon substituted naphthoquinones. Several members of this series have demonstrated potent in vitro inhibition of 5-LO (IC50's less than 10(-6) M) and at doses of 1 mg/kg iv completely inhibited LTB4 production measured in ex vivo A23187-stimulated blood from dogs. The duration of action measured by the ex vivo assay was improved up to threefold over CGS 8515.     

Structure-activity relationships for N,N'-bis(dichloroacetyl) diamines and substituted naphthoquinones in the inhibition of mitochondrial electron transport

The inhibition of mitochondrial electron transport was measured with four homologous series of N,N′-bis(dichloroacetyl) diamines and one homologous series of substituted naphthoquinones. Partition coefficients between acetone-water and silicone for these compounds were estimated by their R_m values in reversed-phase thin-layer chromatography. Parabolic correlations between a log function of biological activity and R_m were obtained with all series. A statistical analysis suggested that a homologous series of secondary amide derivatives of the N,N′-bis(dichloroacetyl) diamines differed from 3 homologous series of tertiary amide derivatives of the N,N'-bis(dichloroacetyl) diamines. Although N,N'-bis(dichloroacetyl) diamines and substituted napthoquinones affected the respiratory chain at different points and the substituted naphthoquinones were more effective inhibitors of electron transport, R_m values for maximum inhibition differed by only two methylene elements between the most widely separated series. Similarities between R_m values for maximum inhibition suggest that penetration of the mitochondrial membrane is a highly significant determinant for structure-activity relationships.     

Nitrofurantoin inhibition of mouse liver mitochondrial respiration involving NAD-linked substrates

In our study, nitrofurantoin (NF) and nitrofurazone (NZ) inhibited respiration of isolated mouse (C57B/6J, adult, male) liver mitochondria. Other aromatic nitro compounds, nitroimidazole, metronidazole, and p-nitrobenzoic acid, did not have any significant effect. The primary site of activity for NF was complex I NADH-ubiquinone oxidoreductase mediated respiration, since only complex I substrates, glutamate, beta-hydroxybutyrate, and alpha-ketoglutarate-mediated respiration were decreased. Respiration supported by succinate, a complex II substrate, was not affected by any of the compounds. NF at a concentration of 50 microM decreased state 3 and dinitrophenol-uncoupled respiration to 28 +/- 1 and 25 +/- 5% of control, respectively, of mitochondria oxidizing glutamate. Studies with mitoplasts oxidizing glutamate showed that NF inhibited both state 3 and 4 respiration. The inhibition of state 3 was prevented by the simultaneous addition of superoxide dismutase (240 micrograms/ml) and catalase (200 micrograms/ml). These results suggest that the mitochondrion, in particular complex I of the electron transport system, is a target for NF toxicity. The effect on respiration may be mediated by NF redox cycling and the generation of reactive oxygen intermediates resulting in the interference of electron flow.     

In vitro activity of Brazilian medicinal plants,naturally occurring naphthoquinones and their analogues,against methicillin-resistant Staphylococcus aureus

Fourteen extracts from Brazilian traditional medicinal plants used to treat infectious diseases were used to look for potential antimicrobial activity against multiresistant bacteria of medical importance. Staphylococcus aureus strains were susceptible to extracts of Punica granatum and Tabebuia avellanedae. The minimum inhibitory concentrations (MICs) of the total extracts and of additional fractions of these plants were determined by employing strains of methicillin-resistant (MRSA) and -sensitive (MSSA) S. aureus, including isolates of the PFGE clone A, which is prevalent in Brazil and two ATCC reference strains. A mixture of ellagitannins isolated from P. granatum and two naphthoquinones isolated from T. avellanedae demonstrated antibacterial activity against all S. aureus strains tested. Semi-synthetic furanonaphthoquinones (FNQs) showed lower MICs than those exhibited by natural occurring naphthoquinones. The results indicate that these natural products can be effective potential candidates for the development of new strategies to treat MRSA infections.     

小檗碱抗肿瘤作用与Wnt/-βcaten in信号转导关系

目的证明小檗碱抗肿瘤作用机制可能与信号转导过程的调控有关。方法采用细胞增殖抑制和Hoechst 33258染色凋亡实验比较小檗碱和黄连总碱对人结肠癌HCT116和SW 480细胞的作用。利用Tcf-4报告基因研究小檗碱对肿瘤细胞的信号转导影响。结果小檗碱在5~40 mg.L-1浓度范围内呈浓度依赖性和时间依赖性抑制人结肠癌HCT116和SW 480细胞的增殖;小檗碱(20 mg.L-1)处理72 h后的HCT116和SW 480细胞出现明显凋亡;相当于小檗碱浓度的黄连总碱有类似于小檗碱的作用。20~40 mg.L-1小檗碱和黄连总碱均能明显抑制-βcaten in/Tcf介导的转录活性。结论黄连总碱的抗肿瘤作用可能与其主要成分小檗碱有关;其抗肿瘤作用机制至少与抑制W nt/-βcaten in信号通路有关。     

Amethocaine-induced inhibition of mitochondrial monoamine oxidase activity

Amethocaine (tetracaine) (1-10 microM) produces a concentration-dependent in-vitro inhibition of mitochondrial membrane-bound MAO activity towards tyramine (18-84% in brain and 19-84% in liver) and 5-hydroxytryptamine (5-HT) (23-94% in brain and 20-100% in liver). At relatively higher concentrations (25-300 microM) of amethocaine, benzylamine oxidation is inhibited in brain (24-91%) and liver (29-100%). The extent of MAO inhibition is appreciably reduced when preincubation time of the enzyme with a low concentration (7.5 microM) of amethocaine is increased from zero to 45 min. This inhibition is reversible. The Km of MAO for tyramine is increased in brain (106-473%) and liver (121-352%) in the presence of amethocaine (2-7.5 microM) accompanied by a decrease in Vmax (21-51% in brain and 18-57% in liver). Similarly the Km of MAO for 5-HT is increased to the extent of 79-336% in brain and 51-225% in liver and the corresponding Vmax is decreased by 35-55% and 39-74%, respectively, in the presence of 2-5 microM amethocaine. At relatively higher concentrations (25-100 microM), amethocaine increases the Km of MAO for benzylamine in brain (25-101%) and liver (26-85%) and decreases the Vmax by 28-64% and 32-63% in the respective tissues. Thus these results suggest that amethocaine preferentially inhibits MAO-A and the nature of inhibition is reversible and of mixed type.