Caffeic acid (CA) is a phenolic compound widely found in coffee beans with known beneficial effects in vivo. Many studies showed that CA has anti-inflammatory, anti-mutagenic, antibacterial and anti-carcinogenic properties, which could be linked to its antioxidant activity. Taking in consideration the reported in vitro antioxidant mechanism of other polyphenols, our working hypothesis was that the CA antioxidant activity could be related to its metal-chelating property. With that in mind, we sought to investigate the chemical antioxidant mechanism of CA against in vitro iron-induced oxidative damage under different assay conditions. CA was able to prevent hydroxyl radical formation promoted by the classical Fenton reaction, as determined by 2-deoxyribose (2-DR) oxidative degradation and DMPO hydroxylation. In addition to its ability to prevent hydroxyl radical formation, CA had a great inhibition of membrane lipid peroxidation. In the lipid peroxidation assays CA acted as both metal-chelator and as hydrogen donor, preventing the deleterious action promoted by lipid-derived peroxyl and alkoxyl radicals. Our results indicate that the observed antioxidant effects were mostly due to the formation of iron-CA complexes, which are able to prevent 2-DR oxidation and DMPO hydroxylation. Noteworthy, the formation of iron-CA complexes and prevention of oxidative damage was directly related to the pH of the medium, showing better antioxidant activity at higher pH values. Moreover, in the presence of lipid membranes the antioxidant potency of CA was much higher, indicating its enhanced effectiveness in a hydrophobic environment. Overall, our results show that CA acts as an antioxidant through an iron chelating mechanism, preventing the formation of free hydroxyl radicals and, therefore, inhibiting Fenton-induced oxidative damage. The chemical properties of CA described here—in association with its reported signaling effects—could be an explanation to its beneficial effects observed in vivo.

We used the spin label electron spin resonance technique to monitor the hydration effect on the molecular dynamics of lipids at C-5, C-12, and C-16 positions of the alkyl chain. Increase in water content of neonatal rat SC leads to an increase in membrane fluidity, especially in the region near the membrane-water interface. The effect is less pronounced deeper inside the hydrophobic core. The reorientational correlation time at the C-16 position of hydrocarbon chains showed a higher change up to approximately 18% (w/w) of water content. This behavior was accompanied by an exponential decay both in elastic modulus and electrical resistance with water content. On the contrary, the segmental motion at C-5 and C-12 positions of the chain and the permeability constant increased in the range of around 18% w/w) up to the fully hydrated condition (58 +/- 7%). Our results give a better characterization of the fluidity of SC and show that it is the principal parameter involved in the mechanism of the permeability of different compounds through skin.

No abstract

No abstract

Tropical and sub-tropical higher plant species show marked growth inhibition when exposed to chilling temperatures. In root tip segments of coffee seedlings which were subjected for 6 days to temperatures of 10, 15, 20 and 25 degrees C, in darkness, we have detected an increased amount of malondialdehyde formed in the 10 degrees C treatment, accompanied by higher electrolyte leakage. The electron paramagnetic resonance (EPR) technique and the fatty acid spin probes 5-, 12- and 16-doxylstearic acid were used to assess cellular membrane fluidity. At the depth of the 5th and 16th carbon atom of the alkyl chains the nitroxide radical detected more rigid membranes in seedlings subjected to 10 degrees C compared with 15 and 25 degrees C. At the C-12 position of the chains the probe showed very restricted motion and was insensitive to chilling induced membrane alterations. EPR parameters for intact tissues and microsome preparations from root tips showed that the fluidity was essentially the same when evaluated at C-5 and C-16 positions of the chains, and was considerably more fluid for microsomal membranes in the region of the C-12 position of the bilayers. The rotational motion of the nitroxide at C-16 position of the chains experienced a phase transition at about 15 degrees C. The calculated energy barriers for reorientational motion of the probe 16-doxylstearic acid were higher at temperatures of 5-15 degrees C than in the interval of 15-25 degrees C, suggesting that below the phase transition the membrane lipids assume a more ordered and compacted array. Membrane rigidity induced by chilling was interpreted as due to lipid peroxidation that could have been facilitated by higher density of peroxidizable chains below the membrane phase transition.