Commercial plant extracts may act as antioxidants or pro-oxidants in cosmetic emulsions based on argan oil.

Cosmetic emulsions containing plant extracts should be tested in a range of temperatures from 5°C to 40°C to be sure that they will be stable during general use by consumers and that plant extracts used as antioxidants do not accelerate oxidative degradation of their oil base. The oxidative stability of argan oil-in-water emulsions containing 1% and 5% commercial acerola, willow, and rose extracts [or 0.01% butylhydroxytoluene (BHT)], stored at 5°C and 20°C for 6 months and at 40°C for 4 weeks, was monitored by the determination of peroxide content. The antioxidant or pro-oxidant activities of extracts or BHT in emulsions were expressed as the protection factor (PF) and inhibition of peroxide formation (Ip). At the end of storage, 5% willow, 0.01% BHT, 1% willow, and 5% acerola were the most protective for emulsions stored at 5°C. At 20°C, the most effective was 0.01% BHT, 5% rose, and 5% acerola. At 40°C, inhibition of peroxide formation calculated for 1% rose, 5% acerola, and 0.01 % BHT was similar. Altogether, the results show that some plant extracts, depending on storage conditions, may act as pro-oxidants, whereas the others can be applied as natural antioxidants instead of synthetic BHT.

Evaluation of the acute oral toxicity class of trinuclear chromium(III) glycinate complex in rat.

Chromium(III) is considered as an essential element playing a role in carbohydrate and lipid metabolism, and various chemical forms of this element are widely used in dietary supplements. A new trinuclear chromium(III) glycinate complex [Cr(3)O(NH(2)CH(2)CO(2))(6)(H(2)O)(3)](+)NO(3)(-) (CrGly), an analogue of Cr3 (trinuclear Cr(III) propionate complex) has been synthesized as a potential source of supplementary Cr. In this study, we evaluated the acute toxicity class of CrGly in Wistar rats applying the OECD 423 procedure. Male and female Wistar rats (n = 12, 6 ♀ and 6 ♂) were given by gavage either a single dose of CrGly 2,000 mg/kg body mass (equals to 300 mg Cr(III)/kg body mass; in aqueous solution) or equivalent volumes of distilled water and fed ad libitum commercial Labofeed B diet, and observed carefully for 14 days, then sacrificed to collect blood and internal organs for biochemical and histologic examination. No death cases were detected. No abnormalities in animal behavior, body mass gains, gross organ histology, or blood morphology and biochemistry were observed. The results demonstrate that LD(50) of CrGly is greater than 2,000 mg/kg when administrated orally to rat; thus, this compound appears to belong to the fifth category in the GHS system or the fourth class ("unclassified") in the EU classification system.

Evaluation of insulin binding and signaling activity of newly synthesized chromium(III) complexes in vitro.

In the present study, the influence of chromium(III) complexes (acetate, chloride, glycinate, histidinate, lactate and propionate) on insulin binding and signal transduction [phosphorylation of tyrosine and serine in the insulin receptor substrate (IRS)-1] was investigated in vitro using three experimental models: isolated rat liver membranes and cultured mouse C2C12 myoblasts or 3T3-L1 preadipocytes. The examined complexes did not elevate the binding of insulin to the liver membranes. Moreover, chromium histidinate, lactate, acetate and propionate complexes diminished the specific binding of insulin. Simultaneously, chromium chloride, which did not significantly elevate insulin binding, increased the number of membrane accessible particles of the insulin receptors. However, it was accompanied by slightly diminished affinity of the receptor to the hormone. Chromium acetate and propionate significantly diminished the binding capacity of the low-affinity insulin receptor class. Investigations with the myoblast cell line C2C12 and preadipocyte cell line 3T3-L1 did not allow differentiation of the influence of the examined complexes on insulin binding. Immunodetection of phosphorylated forms of IRS-1 showed that the chromium compounds modulated the transduction of the insulin signal. Chromium glycinate, acetate and propionate decreased the amount of IRS-1 phosphorylated at serine. Since it is generally thought that phosphorylation of serine in IRS-1 may moderate insulin action, the above mentioned chromium complexes may, in this way, enhance insulin effects inside target cells. Phosphorylation of tyrosine in IRS-1, which acts as a stimulatory signal for further steps of insulin action, was elevated after the incubation of 3T3-L1 cells with insulin. Chromium supplementation did not additionally intensify this process. However, in the absence of insulin, chromium glycinate and acetate slightly elevated the level of IRS-1 phosphorylated at tyrosine. This fact may be important in vivo at low levels of insulin in blood. The results indicate that the action of chromium(III) complexes involves a direct effect on the number of receptors accessible to insulin, their affinity to the hormone and the modulation of the signal multiplying proteins by their phosphorylation.

pH-Dependent radical scavenging capacity of green tea catechins.

The effect of pH on the radical scavenging capacity of green tea catechins was investigated using experimental as well as theoretical methods. It was shown that the radical scavenging capacity of the catechins, quantified by the TEAC value, increases with increasing pH of the medium. Comparison of the pKa values to theoretically calculated parameters for the neutral and deprotonated forms indicates that the pH-dependent increase in radical scavenging activity of the catechins is due to an increase of electron-donating ability upon deprotonation. The data also reveal that the radical scavenging activity of the catechins containing the pyrogallol (or catechol) and the galloyl moiety over the whole pH range is due to an additive effect of these two independent radical scavenging structural elements. Altogether, the results obtained provide better insight into the factors determining the radical scavenging activity of the catechins and reveal that the biological activity of green tea catechins will be influenced by the pH of the surrounding medium or tissues.

Role of catechin quinones in the induction of EpRE-mediated gene expression.

In the present study, the ability of green tea catechins to induce electrophile-responsive element (EpRE)-mediated gene expression and the role of their quinones in the mechanism of this induction were investigated. To this end, Hepa1c1c7 mouse hepatoma cells were used, stably transfected with a luciferase reporter gene under the expression regulation of an EpRE from the human NAD(P)H:quinone oxidoreductase 1 (NQO1) gene. The results obtained show that several, but not all, catechins tested are able to induce EpRE-mediated gene transcription, with epigallocatechin gallate (EGCG) and gallocatechin gallate (GCG), both containing a pyrogallol and a galloyl moiety, being the most powerful inducers. Moreover, it was demonstrated that the EpRE-mediated response to catechins was increased in cells with reduced cellular glutathione (GSH) levels and decreased in cells with increased levels of GSH, corroborating a role for catechin quinones. The intrinsic capacity of catechins to form quinone type metabolites upon their oxidation was demonstrated using incubations of epigallocatechin (EGC) and EGCG with tyrosinase and the GSH-trapping method. Glutathione conjugates formed in these incubations were identified as 2'-glutathionyl-EGC, 2',6'-diglutathionyl-EGC, 2'-glutathionyl-EGCG, and 2',6'-diglutathionyl-EGCG, supporting the formation of quinone type metabolites involving especially the pyrogallol moiety of these catechins. Formation of the EGCG-quinone-glutathionyl adducts was also observed in the EpRE-LUX cellular system. This further supports the importance of the pyrogallol moiety for the quinone chemistry of the catechins. Finally, the presence of the pyrogallol moiety in the catechins also results in a relatively lower half-wave oxidation potential (E1/2) and calculated heat of formation (DHF) for conversion of the catechins to their corresponding quinones, pointing at an increased ability to become oxidized. Altogether, our studies reveal that catechins, especially those containing a pyrogallol moiety, induce EpRE-mediated detoxifying gene expression and that this induction is likely to be the result of their quinone chemistry.

Radical scavenging capacity of wine anthocyanins is strongly pH-dependent.

The radical scavenging capacity of red wine anthocyanins was quantified by the so-called TEAC assay with special emphasis on the influence of pH and conjugation on this activity. The pH appears to be a dominant factor in the radical scavenging capacity of wine anthocyanins, with higher pH values increasing this capacity significantly. On the basis of the pKa values for deprotonation and theoretical calculations, it could be concluded that the effect is due to an increase in intrinsic radical scavenging capacity upon deprotonation. The data also reveal that the reduction in radical scavenging activity of anthocyanins upon their conjugation can, at least in part, be ascribed to an increase in pKa values upon conjugation. Altogether, the results obtained provide molecular insight into factors that influence radical scavenging potential of anthocyanins and reveal that the radical scavenging-mediated supposed beneficial health effects of these wine pigments will be influenced by the pH of the surrounding matrix or tissue.

The effect of catechol O-methylation on radical scavenging characteristics of quercetin and luteolin--a mechanistic insight.

The biological effect of flavonoids can be modulated in vivo due to metabolism. The O-methylation of the catechol group in the molecule by catechol O-methyl transferase is one of the important metabolic pathways of flavonoids. In the present study, the consequences of catechol O-methylation for the pH-dependent radical scavenging properties of quercetin and luteolin were characterized both experimentally and theoretically. Comparison of the pKa values to the pH-dependent TEAC profiles reveals that O-methylation not only affects the TEAC as such but also modulates the effect of changing pH on this radical scavenging activity due to an effect on the pKa for deprotonation. The pH-dependent TEAC curves and computer calculated electronic parameters: bond dissociation energy (BDE) and ionisation potential (IP) even indicate that O-methylation of the luteolin catechol group affects the radical scavenging potential only because it shifts the pKa for deprotonation. O-Methylation of the quercetin catechol moiety affects radical scavenging capacity by both an effect on the pKa, and also by an effect on the electron and hydrogen atom donating properties of the neutral (N) and the anionic (A) form of the molecule. Moreover, O-methylation of a catechol OH-group in quercetin and luteolin has a similar effect on their TEAC profiles and on calculated parameters as replacement of the OH-group by a hydrogen atom. Altogether, the results presented provide new mechanistic insight in the effect of catechol O-methylation on the radical scavenging characteristics of quercetin and luteolin.