Inhibition of mitochondrial respiration by model phenolic compounds

5: Final Report on the Safety Assessment of 2-Methylresorcinol and Resorcinol

2-Methylresorcinol and Resorcinol are most frequently used in cosmetic hair dye formulations at concentrations between 1 and 5%. The results of cutaneous and oral feeding studies have indicated that both 2-Methylresorcinol and resorcinol are readily absorbed by rodents and are rapidly eliminated. Acute oral toxicity studies indicate that 2-Methylresorcinol is moderately toxic and Resorcinol is slightly to moderately toxic. Subchronic feeding and dermal studies of bothingredients produced no significant effects. A chronic dermal study was uneventful. Significant skin effects were observed in mice, but not in rabbits, following dermal application of Resorcinol at 5%. A 10% Resorcinol solution was not irritating to guinea pigs. A 2.5% 2-Methylresorcinol solution was classified as a primary irritant in rabbits, but 10% 2-Methylresorcinol was not irritating to guinea pigs. 2-Methylresorcinol was not an ocular irritant at 2.5%, but irritation was produced at 5% concentration in unwashed rabbit eyes. Neither 2-Methylresorcinol at 5% nor Resorcinol at 3% produced sensitization in guinea pigs. 2-Methylresorcinol was not photoallergenic to guinea pigs but was a sensitizer at 10%. Resorcinol was not photoallergenic to guinea pigs but was a sensitizer at 10%. Resorcinol and 2-Methylresorcinol were nonmutagenic in microbial and tissue culture assays for mutagenicity. Topically applied hair dyes containing 2-Methylresorcinol and Resorcinol were negative for carcinogenicity. Resorcinol showed no cocarcinogenic potential when tested on mice and rats. 2-Methylresorcinol at 3% concentration produced no evidence of irritation or sensitization in human subjects. Resorcinol was a mild skin irritant and rare sensitizer in clinical testing, but not when tested on nonclinical groups. On the basis of the available animal and clinical data, it is concluded that 2-Methylresorcinol and Resorcinol are safe as cosmeticingredients in the present practices of use and concentrations.

Fragrance material review on cinnamic acid

A toxicologic and dermatologic review of cinnamic acid when used as a fragrance ingredient is presented.

Inhibition of tumoral cell respiration and growth by nordihydroguaiaretic acid

The effects of nordihydroguaiaretic acid (NDGA), best known as an inhibitor of lipoxygenase activities, on the culture growth, oxygen consumption, ATP level, viability, and redox state of some electron carriers of intact TA3 and 786A ascites tumor cells have been studied. NDGA inhibited the respiration rate of these two tumor cell lines by preventing electron flow through the respiratory chain. Consequently, ATP levels, cell viability and culture growth rates were decreased. NDGA did not noticeably inhibit electron flow through both cytochrome oxidase and ubiquinone-cytochrome b-c1 complex. Also, the presence of NDGA changed to redox state of NAD(P)+ to a more reduced level, and the redox states of ubiquinone, cytochrome b and cytochromes c + c1 changed to a more oxidized level. These observations suggest that the electron transport in the tumor mitochondria was inhibited by NDGA at the NADH-dehydrogenase-ubiquinone level (energy-conserving site 1). As a consequence, mitochondrial ATP synthesis would be interrupted. This event could be related to the cytotoxic effect of NDGA.

Evidence for involvement of amino acid neurotransmitters in anesthesia and naloxone induced reversal of respiratory paralysis

General anesthetics render a person unconscious and may produce respiratory paralysis at therapeutic doses. No pharmacological agent is available to restore respiration and the mechanism/s of anesthesia or apnea is not clearly understood. In this report, we present evidence to show that naloxone reversed respiratory failure induced by thiopental, ketamine, halothane but not that induced by phenobarbital. Furthermore, 25 mg/kg, i.v. thiopental, 140 mg/kg, i.v. ketamine, and 3% halothane produced anesthesia without significantly altering respiratory rate, increased GABA and decreased glutamate (except ketamine and phenobarbital) levels in rat brain stem and cortex, but not in caudate and cerebellum. Aspartate, glycine and alanine levels were not affected in four brain regions studied. Pretreatment with TSC for 30 minutes did not change GABA or glutamate contents, but abolished the anesthetic as well as the respiratory depressant actions of the anesthetics. Increasing the doses of anesthetics produced respiratory failure with further rise in GABA and fall in glutamate in brain stem and cortex. Naloxone reversed respiratory paralysis and restored GABA close to control values in rat brain stem and cortex with no changes in caudate or cerebellum. Data presented here suggest that GABA may be necessary to produce loss of consciousness and naloxone reverses anesthetic induced respiratory failure.

Interaction of butylated hydroxyanisole with mitochondrial oxidative phosphorylation

The antioxidant, butylated hydroxyanisole (BHA), has a number of effects on mitochondrial oxidative phosphorylation. In this study we apply the novel approach developed by Brand (Brand MD, Biochim Biophys Acta 1018: 128-133, 1990) to investigate the site of action of BHA on oxidative phosphorylation in rat liver mitochondria. Using this approach we show that BHA increases the proton leak through the mitochondrial inner membrane and that it also inhibits the delta p (proton motive force across the mitochondrial inner membrane) generating system, but has no effect on the phosphorylation system. This demonstrates that compounds having pleiotypic effects on mitochondrial oxidative phosphorylation in vitro can be analysed and their many effects distinguished. This approach is of general use in analysing many other compounds of pharmacological interest which interact with mitochondria. The implications of these results for the mechanism of interaction of BHA with mitochondrial oxidative phosphorylation are discussed.

t-butyl-4-hydroxyanisole as an inhibitor of tumor cell respiration

The effect of t-butyl-4-hydroxyanisole (BHA), a widely used food antioxidant additive, on the culture growth, oxygen consumption, and redox state of some electron carriers of intact TA3 and 786A ascites tumor cells has been studied. BHA inhibited culture growth and respiration of these two tumor cell lines, by inhibiting the electron flow through the respiratory chain. Experiments to determine its site of action showed that BHA did not inhibit noticeably the electron flow through cytochrome oxidase, due to the ability of N,N,N',N'-tetramethyl-p-phenylenediamine to bypass the BHA inhibition of the respiration. Electron flow through the ubiquinone-cytochrome b-c1 complex also was unaffected by BHA; in fact, BHA failed to inhibit the oxidation of duroquinol. Spectrophotometric experiments are in accordance with studies carried out using synthetic electron donors. The redox state of NAD(P)+, determined in steady-state conditions, changed to a more reduced level, and the redox states of ubiquinone, cytochrome b, cytochromes c + c1 and cytochromes a + a3 changed to a more oxidized level. These observations suggest that the electron transport in the tumor mitochondria was inhibited by BHA at the NADH-dehydrogenase-ubiquinone level (energy-conserving site 1). These findings could explain, in part, the cytotoxic effect of BHA.

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.

GABA involvement in naloxone induced reversal of respiratory paralysis produced by thiopental

No agent is yet available to reverse respiratory paralysis produced by CNS depressants, such as general anesthetics. In this study naloxone reversed respiratory paralysis induced by thiopental in rats. 25 mg/kg, i.v. thiopental produced anesthesia without altering respiratory rate, increased GABA, decreased glutamate, and had no effect on aspartate or glycine levels compared to controls in rat cortex and brain stem. Pretreatment of rats with thiosemicarbazide for 30 minutes abolished the anesthetic action as well as the respiratory depressant action of thiopental. 50 mg/kg, i.v. thiopental produced respiratory arrest with further increase in GABA and decrease in glutamate again in cortex and brain stem without affecting any of the amino acids studied in four regions of rat brain. Naloxone (2.5 mg/kg, i.v.) reversed respiratory paralysis, glutamate and GABA levels to control values in brain stem and cortex with no changes in caudate or cerebellum. These data suggest naloxone reverses respiratory paralysis produced by thiopental and involves GABA in its action.

Inhibitory effect of phenolic compounds on aflatoxin B1 metabolism and induced mutagenesis

The interaction between phenolic compounds and the food-borne carcinogenic mycotoxin, aflatoxin B1 (AFB1), was examined. 6 phenolic compounds (gallic acid, chlorogenic acid, caffeic acid, dopamine, p-hydroxybenzoic acid and salicylic acid) inhibited AFB1-induced mutagenesis in Salmonella typhimurium strain TA98 in a suspension assay in the presence of rat-liver microsomes (S9). The inhibitory effect was observed when the phenolic compound and the mutagen (AFB1 plus S9) were administered concurrently, but not when exposure to the mutagen was followed by the phenolic compound. The concentrations of the phenolic compounds used were not mutagenic to S. typhimurium strain TA98 and had no effect on the survival of the bacteria. The inhibition of AFB1 metabolism was studied using high-pressure liquid chromatography. Increasing the concentration of all 6 phenolic compounds resulted in a dose-dependent reduction of both major AFB1 metabolite peaks. The results are consistent with the hypothesis that the phenolic compounds do not react covalently with AFB1, and the inhibitory effect of phenolic compounds on AFB1-induced mutagenesis may be due to the inhibition of the activation enzymes.

Inhibition of mitochondrial respiration and production of toxic oxygen radicals by flavonoids. A structure-activity study

A series of fourteen flavonoids were employed in a systematic structure-activity study to assess their abilities to inhibit succinoxidase and generate toxic oxygen species in beef heart mitochondria. By comparing I50 values toward succinoxidase activity, flavonoids with a catechol moiety on the b ring exhibited the following general order of potency: chalcone greater than flavone greater than flavonol greater than dihydroflavonol greater than anthocyanidin. Catechins were inactive. In a series of 3,5,7-trihydroxyflavones containing various configurations of the b ring hydroxyl groups, it was found that the flavonoids possessing adjacent trihydroxy (pyrogallol) and b ring ortho-hydroxy(catechol) configurations were the most potent inhibitors of succinoxidase, followed by those with meta-hydroxyl, monohydroxyl and unhydroxylated configurations. Four of the fifteen flavonoids tested exhibited substrate-independent, KCN-insensitive respiration. Two flavonols with a pyrogallol configuration, myricetin and quercetagetin, produced the largest respiratory bursts and were found to auto-oxidize. Evidence is presented that the mitochondrial respiratory bursts induced by both flavonols and their auto-oxidation resulted in the generation of O-2 and H2O2.

Reinterpretation of the literature indicates differential sensitivities of long-sleep and short-sleep mice are not specific to alcohol

This paper reviews the findings and conclusions of the literature pertinent to the Long-Sleep and Short-Sleep selectively-bred lines of mice and challenges the widely-held notion that the selective breeding program was successful in separating alleles for specific sensitivities to just alcohol. Rather, it is argued that these lines of mice were selected for differing activity of a more general process. Recent evidence, as well as reevaluated previous evidence, indicates that Long-Sleep mice are more sensitive to the soporific effects of three major classes of CNS depressants (alcohols, barbiturates, and benzodiazepines), as well as many other anesthesia-inducing compounds (adenosine, chloral hydrate, trichloroethanol, paraldehyde, nitrous oxide, enflurane, and isoflurane). Further, much evidence also supports the conclusion that most of these hypnotic-depressants and anesthetics could exert their soporific influence by a potentiation of GABA activity. The other characteristic of interest in this regard is susceptibility to convulsions. Short-Sleep mice have significantly lower thresholds to both flurothyl-induced and bicuculline-induced convulsions, as well as being more likely to suffer from paroxysms during ethanol withdrawal.

In vivo and in vitro activity by diverse chelators against Trypanosoma brucei brucei

A system of prescreens and screen has been developed to select chelators as potential drugs against Trypanosoma brucei brucei EATRO 110. The chelators tested were nearly all commercially available, low molecular, and having moderate to high affinity for Fe(III). We prescreened 70 compounds showing heme-sparing or inhibitory activity in a Crithidia fasciculata growth system having excess Fe and minimal hemin. Of these, 45 were highly trypanocidal for suspensions of bloodstream T. b. brucei; criteria of activity here were immobilization, lysis, and loss of infectivity. Eighteen of the chelators highly active in the suspension prescreen were tried in T. b. brucei-infected mice. Thirteen of these chelators were curative in mice with 24-h infections, that is, they allowed survival greater than 30 days beyond the untreated controls. 3,4-Dihydroxycinnamic acid (caffeic acid), 2,9-dimethyl-1, 10 phenanthroline (neocuproine), and 2-pyridinecarboxaldehyde-2-pyridyl-hydrazone cured five out of five mice after an i.v dose of 100 mg/kg. Salicylaldehyde thiosemicarbazone cured five out of five mice at an i.p. dose of 500 mg/kg. Lesser activity was shown by several other chelators.