Redox activity of caffeic acid towards iron(III) complexed in a polygalacturonate network

The transfer of several metal ions from the soil to the plant absorbing cells is mediated principally by organic molecules of low molecular weight with complexing and reducing activity, among which caffeic acid (CAF) is particularly important. Here we report the results of a survey which deals with the oxidation of CAF by the Fe(III) ions bound to a polygalacturonate network (Fe(III)-PGA network). The interaction between Fe(III) and CAF was studied by using Fe(III)-PGA networks equilibrated in the 2.4-7.0 pH range by means of kinetic and spectroscopic methods. The reducing power was found to depend on the nature of the Fe(III)-PGA network complexes: when the ferric ion was complexed only by the PGA carboxylic groups, a high redox activity was observed, whereas the Fe(III) reduction was found to be lower when a hydroxylic group was inserted in the Fe(III) coordination sphere. The iron complexed in the network was protected from hydrolysis reactions, as shown by the high pH values at which its reduction occurred. Two different fractions of Fe(II) produced were identified, one diffusible and another exchangeable with CaCl₂ 6.0 mM. The existence of the exchangeable form was attributed to the electrostatic interaction of the Fe(II) ions with the carboxylate groups of the fibrils and with the degradation products of CAF. The arrangement of the fibrils was altered following the substitution of Ca(II) by Fe(III) ions and was restored following the reduction of Fe (III) by CAF.     

The fate of olive oil polyphenols in the gastrointestinal tract: Implications of gastric and colonic microflora-dependent biotransformation

We have conducted a detailed investigation into the absorption, metabolism and microflora-dependent transformation of hydroxytyrosol (HT), tyrosol (TYR) and their conjugated forms, such as oleuropein (OL). Conjugated forms underwent rapid hydrolysis under gastric conditions, resulting in significant increases in the amount of free HT and TYR entering the small intestine. Both HT and TYR transferred across human Caco-2 cell monolayers and rat segments of jejunum and ileum and were subject to classic phase I/II biotransformation. The major metabolites identified were an O-methylated derivative of HT, glucuronides of HT and TYR and a novel glutathionylated conjugate of HT. In contrast, there was no absorption of OL in either model. However, OL was rapidly degraded by the colonic microflora resulting in the formation of HT. Our study provides additional information regarding the breakdown of complex olive oil polyphenols in the GI tract, in particular the stomach and the large intestine.     

Mitotic and meiotic chromosomes of the American lobster Homarus americanus (Nephropidae, Decapoda)

The chromosomes of H. americanus have been characterised by C-banding, fluorochrome banding and restriction endonuclease banding. Thanks to these techniques, it has been possible to identify mitotic and meiotic figures clearly and to study the distribution and structure of heterochromatic regions. Moreover, we have identified small supernumerary chromosomes, variable in number and often asynaptic in first meiotic metaphase.     

HDL2 and HDL3 cholesterol in hepatic cirrhosis

In order to further investigate plasma lipoproteins abnormalities secondary to serious liver damage, we studied plasma lipids and lipoproteins, and in particular HDL subfractions (HDL2, HDL3), in 12 patients with cirrhosis of the liver and in 12 sex, age and weight matched healthy volunteers. Enzymatic methods were used to determine total cholesterol and triglycerides, while the extractive method of Abell et al. was used for the determination of HDL-cholesterol levels after LDL and VLDL precipitation with polyanions (MnCl2 and Na-heparin) and of HDL3-cholesterol values after HDL2 precipitation with dextran-sulphate 15,000 m.w. Total cholesterol and HDL-cholesterol levels were significantly lower in cirrhotic patients compared to normal subjects. We must emphasize that only HDL3-cholesterol was decreased in cirrhotics, whereas HDL2-cholesterol values were normal or high. We suggest that a diminished activity of hepatic triglyceride lipase might account for the decrease in HDL3-cholesterol in liver cirrhosis.     

Accumulation and mobilization of arsenate by Fe(III) polyions trapped in a Ca-polygalacturonate network

The role of Fe(III) stored at the soil–root interface in the accumulation of arsenate and the influence of citric acid on the As(V) mobility were investigated by using Ca-polygalacturonate networks (PGA). The results indicate that in the 2.5–6.2 pH range Fe(III) interacts with As(V) leading to the sorption of As(V) on Fe(III) precipitates or Fe–As coprecipitates. The FT-IR analysis of these precipitates evidenced that the interaction produces Fe(III)–As(V) inner-sphere complexes with either monodentate or bidentate binuclear attachment of As(V) depending on pH.In the 3.0–6.0 pH range, As(V) diffuses freely through the polysaccharidic matrix that was found to exert a negligible reducing action towards As(V). At pH 6.0 citric acid is able to mobilize arsenate from the As–Fe–PGA network through the complexation of the Fe(III) polyions that leads to the release of As(V).