Evaluation of the ability of antioxidants to counteract lipid oxidation: Existing methods, new trends and challenges

Formação de toxinas durante o processamento de alimentos e as possíveis conseqüências para o organismo humano

A produção de alimentos envolve inúmeras reações químicas, durante as quais podem ser geradas substâncias tóxicas ao organismo humano. A produção destas substâncias pode ocorrer de diferentes maneiras, variando em quantidade e em grau de toxicidade. Este trabalho objetivou estudar a produção de toxinas no processamento de alimentos, assim como as conseqüências da ingestão dessas substâncias para o ser humano. O estudo foi realizado a partir de extensa pesquisa bibliográfica. As principais reações na formação de compostos tóxicos apresentadas no decorrer do estudo são: degradação de lipídios, hidrogenação, pirólise e defumação. Entre as substâncias formadas, destacam-se: peróxidos, ácidos graxos trans, aminas heterocíclicas e hidrocarbonetos aromáticos policíclicos. O profissional nutricionista necessita conhecer como ocorre a formação de toxinas durante os variados processamentos que envolvem alimentos, assim como os riscos para a saúde de quem consome essas substâncias. Também é preciso propor técnicas de processamento adequadas, visando ao bem-estar do consumidor e à manutenção das propriedades nutricionais do alimento.

Antioxidant activity of liver growth factor, a bilirubin covalently bound to albumin

We previously reported that treatment of spontaneously hypertensive rats (SHR) with liver growth factor (LGF), an albumin-bilirubin complex with a covalent bond, reduces blood pressure, improves nitric oxide (NO)-dependent vasodilatation, and exerts vascular antifibrotic actions. Because bilirubin, albumin, and albumin-bound bilirubins have antioxidant properties, we hypothesize that LGF might exert its cardiovascular actions through an antioxidant mechanism. We have tested in vitro the capacity of LGF to scavenge ABTS cation and peroxyl and hydroxyl radicals and to protect vascular NO from degradation by superoxide anion. We have also compared the antioxidant capacity of LGF with that of its molecular components albumin and bilirubin and the reference antioxidant trolox. LGF exhibited antioxidant capacity against all free radicals tested at lower concentrations than albumin, bilirubin, and trolox. LGF, bilirubin, and albumin were also able to protect endothelial NO from superoxide anion degradation in a fashion similar to that of superoxide dismutase or tiron, but at much lower concentrations. These data, together with our previous results in SHR, suggest that LGF might exert its cardiovascular regenerative actions, at least in part, through an antioxidant mechanism and that LGF could be a relevant circulating antioxidant in situations of oxidative stress.

Kinetic and stoichiometry of the reaction of chlorogenic acid and its alkyl esters against the DPPH radical

The lipophilization of polar antioxidants such as phenolics is an efficient way to enhance their solubility in apolar media. Thus, in emulsified systems, lipophilized antioxidants are supposed to locate at the lipid/aqueous phase interface and to lead to a better protection of unsaturated lipids. Herein, the antiradical activity of chlorogenic acid (5-CQA) and its corresponding esters with seven fatty alcohols (from methanol to eicosanol) have been achieved using the well-known 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. Hydrophobation was shown to significantly improve the antiradical activity of 5-CQA esters which reached a maximum for butyl- and octyl-chlorogenate. In addition, for both 5-CQA and its esters, it was demonstrated that the global mechanism of DPPH* stabilization proceeded likely by electron transfer (ET), while it appeared that the pathways of DPPH* stabilization were different between 5-CQA and its esters, as confirmed by the LC-MS characterization of reaction products. Finally, strong differences were found between the tested molecules allowing the proposal of different DPPH* stabilization pathways by electron transfer for 5-CQA and its esters.

Conjugated autoxidizable triene (CAT) assay: a novel spectrophotometric method for determination of antioxidant capacity using triacylglycerol as ultraviolet probe

Described here is a novel spectrophotometric method for estimating antioxidant capacity in a 96-well microplate using as UV probes the conjugated triene triacylglycerols (TAGs) naturally present in tung oil. The TAGs of this commercially available oil contain around 86% eleostearic acid, an octadecatrienoic acid with conjugated trienes exhibiting strong UV absorption at 273 nm. In an oil-in-water emulsion at 37 degrees C, the azo initiator 2,2'-azobis(2-amidinopropane) dihydrochloride generated a constant flux of peroxy radicals, which destroyed the conjugated trienes. The absorbance decay at 273 nm, related to oxidative degradation of conjugated triene TAGs, was monitored in the absence and presence of various concentrations of antioxidants. To validate this new method, the antioxidant capacity of four phenolic compounds (gallic acid, (-)-epicatechin, chlorogenic acid, and rosmarinic acid) was measured using an area-under-the-curve calculation and expressed as Trolox equivalents, the value for Trolox being taken as reference. The order of efficacy was found to be rosmarinic acid > chlorogenic acid approximately epicatechin>Trolox>gallic acid, which can be partially explained by the number of catecholic moieties and the polarity of these antioxidants. Moreover, the conjugated autoxidizable triene (CAT) assay provided good insight into antioxidant behavior (i.e., retarder or chain breaker). The same molecules were then analyzed in 2,2-diphenyl-1-picrylhydrazyl and fluorescein-based oxygen radical absorbance capacity assays, and the results are discussed critically with respect to those obtained with the CAT assay. This new method may constitute an easy-to-use, sensitive, and high-throughput in vitro protocol for evaluation of the antioxidant capacity of pure molecules and natural extracts in lipid oxidation.

How to standardize the multiplicity of methods to evaluate natural antioxidants

A great multiplicity of methods has been used to evaluate the activity of natural antioxidants by using different techniques of inducing and catalyzing oxidation and measuring the end point of oxidation for foods and biological systems. Antioxidant in vitro protocols for foods should be based on analyses at relatively low levels of oxidation under mild conditions and on the formation and decomposition of hydroperoxides. For antioxidant in vivo protocols, widely different methods have been used to test the biological protective activity of phenolic compounds. Unfortunately, many of these protocols have been based on questionable methodology to accurately measure oxidative damage and to assess relevant changes in biological targets. Many studies testing the ex vivo activity of phenolic compounds to inhibit human low-density lilpoprotein (LDL) oxidation have been difficult to evaluate because of the structural complexity of LDL particles and because a multitude of markers of oxidative damage have been used. Although studies with animal models of atherosclerosis have demonstrated the antioxidant effect of phenolic compounds in delaying the progress of this disease, human clinical trials of antioxidants have reported inconsistent and mixed results. Complex mixtures of plant polyphenols have been shown to be absorbed to varying degrees as metabolites in the intestine, but little is known about their interactions, bioavailability, and their in vivo antioxidant activity. Several metabolites identified in human plasma after consuming flavonoids need to be tested for possible nonantioxidant activities. More research and better-designed human studies are required to clarify the complex questions of bioavailability of polyphenols and the factors affecting their in vivo activities. Until we know what relevant in vivo activities to measure, any claims on the biological and health protective effects of natural polyphenolic compounds in our diet are premature.

A review of natural antioxidants and their effects on oxidative status, odor and quality of fresh beef produced in Argentina

Meat derived from pasture feeding, is associated with a high level of antioxidants. Antioxidants are incorporated within cell membranes and protect tissues against oxidation from reactive oxygen species. This maintains the overall quality of meat and secondary products. This paper reviews the implications of incorporating natural antioxidants into fresh beef, focusing on the benefits of feeding cattle good quality pasture. Pasture samples typically have higher levels of α-tocopherol, β-carotene, ascorbic acid and glutathione than feedlot samples. These compounds retard lipid and protein oxidation in fresh and stored meat, and preserve the color and odor quality of beef. The significance of antioxidant enzymes is variable, because their behavior depends on individual redox status before slaughter. Understanding total antioxidant activity requires information on antioxidant and pro-oxidant status. With an abundance of pasture, Argentina has a natural advantage in producing meat with a high antioxidant value.

Autoantibodies in children with chronic hepatitis B infection and the influence of interferon alpha

BACKGROUND/AIMS

One of the serious side effects of interferon-a (IFN) is the possible induction of autoimmunity. However, data concerning children with chronic hepatitis B (HBV) infection is limited with conflicting results. The aim of this study was to evaluate the frequency of autoantibody positivity in children with chronic HBV infection and to assess whether IFN treatment has any influence on exacerbation of serological or clinical parameters of autoimmunity.

METHODS

61 children (32 female, mean age 7.5+/-3.8 years) were evaluated in two groups. Group I (29 patients) received 5 x 106 U/m2 IFN-a and group II (32 patients) 10 x 106 U/m2 IFN-a three times per week for six months. Autoantibody levels (anti-TPO, anti-Tg, AMA, ASMA, LKM-1, ANA, ds-DNA) and Ig G, A and M were analyzed before and after IFN treatment and 12 months after completion of therapy.

RESULTS

No significant difference in autoimmune antibody positivity rate was observed between the two groups when compared at the beginning of the study and at the end of IFN treatment separately. SMA positivity rate was shown to significantly increase in group I after treatment was completed (p<0.05). None of the patients positive for autoantibodies showed further laboratory or clinical signs of autoimmunity. Thyroid hormones were within normal range in patients positive for anti-thyroid antibodies; however, thyrotropin-releasing hormone (TRH) stimulation test revealed subclinical hypothyroidism. All antibodies disappeared 12 months after completion of therapy. Overall, autoantibody positivity, pre- and posttreatment, were 16.3% and 54%, respectively (p<0.05). Age, sex, hepatitis activity index (HAI) score, HBV load and the dose of IFN had no influence on autoantibody formation. Complete and sustained response rates were similar in children with and without autoantibody.

CONCLUSIONS

Autoantibody formation may occur in children with chronic HBV infection. IFN treatment leads to significant autoantibody formation, but this causes no organ dysfunction except for antithyroid antibodies associated with subclinical hypothyroidism. These results suggest that neither the presence of autoantibodies in choronic hepatitis B nor their development during IFN therapy is associated with severe autoimmune disorders in children with chronic HBV infection.