Thermodynamic interpretation of effects of alcohols on membrane lipid fluidity

The effect of alcohols on red blood cell mechanical properties and membrane fluidity depends on their molecular size

The role of membrane fluidity in determining red blood cell (RBC) deformability has been suggested by a number of studies. The present investigation evaluated alterations of RBC membrane fluidity, deformability and stability in the presence of four linear alcohols (methanol, ethanol, propanol and butanol) using ektacytometry and electron paramagnetic resonance (EPR) spectroscopy. All alcohols had a biphasic effect on deformability such that it increased then decreased with increasing concentration; the critical concentration for reversal was an inverse function of molecular size. EPR results showed biphasic changes of near-surface fluidity (i.e., increase then decrease) and a decreased fluidity of the lipid core; rank order of effectiveness was butanol > propanol > ethanol > methanol, with a significant correlation between near-surface fluidity and deformability (r = 0.697; p<0.01). The presence of alcohol enhanced the impairment of RBC deformability caused by subjecting cells to 100 Pa shear stress for 300 s, with significant differences from control being observed at higher concentrations of all four alcohols. The level of hemolysis was dependent on molecular size and concentration, whereas echinocytic shape transformation (i.e., biconcave disc to crenated morphology) was observed only for ethanol and propanol. These results are in accordance with available data obtained on model membranes. They document the presence of mechanical links between RBC deformability and near-surface membrane fluidity, chain length-dependence of the ability of alcohols to alter RBC mechanical behavior, and the biphasic response of RBC deformability and near-surface membrane fluidity to increasing alcohol concentrations.

Influence of the active compounds of Perilla frutescens leaves on lipid membranes

The leaves of the annual plant Perilla frutescens are used widely as a spice and a preservative in Asian food as well as in traditional medicine. The active compounds in the leaves are the cyclic monoterpene limonene (1) and its bio-oxidation products, perillaldehyde (2), perillyl alcohol (3), and perillic acid (4). These compounds are known to be biologically active and exhibit antimicrobial, anticancer, and anti-inflammatory effects that could all be membrane mediated. In order to assess the possible biophysical effects of these compounds on membranes quantitatively, the influence of limonene and its bio-oxidation products has been investigated on a membrane model composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) using differential scanning calorimetry (DSC), isothermal titration calorimetry (ITC), and electron paramagnetic resonance spectroscopy (EPR). It was found that limonene (1), perillyl alcohol (2), and perillaldehyde (3) partitioned into the DMPC membrane, whereas perillic acid (4) did not. The DSC results demonstrated that all the partitioning compounds strongly perturbed the phase transition of DMPC, whereas no perturbation of the local membrane order was detected by EPR spectroscopy. The results of the study showed that limonene (1) and its bio-oxidation products affect membranes in rather subtle ways.

Ca-efflux, from direct membrane injury by CCl4, is elicited by amphiphilic vehicles in vitro

Direct membrane injury by CCl4, in situations excluding metabolic activation, was evaluated in saponin-permeabilized hepatocytes and in microsomes by measuring immediate Ca2+ efflux. A good correlation appears between the Ca2+ efflux and the level of CCl4 in the membrane and also the variations in fluidity. Mixtures of CCl4 with water-soluble vehicles were used to improve the dispersion of CCl4 in the medium. The mixtures varied in their ability to elicit the membrane effects of CCl4. The performance of ethanol and, to a lesser degree, other alcohols, suggests the existence of a water stable structural organization between CCl4 and these amphiphilic vehicles, facilitating the transfer of CCl4 to the membrane.

Experimental pathogenesis: drugs and chemical lesions in the gastric mucosa

The goals of this article are to review the similarities and differences in the pathogenesis of acute gastric mucosal injury induced by alcohol, exemplified mostly by ethanol, and aspirin, as a representative of nonsteroidal anti-inflammatory drugs, and to deduce implications from pathogenetic studies for a better understanding of the concept of gastric cytoprotection. The main similarity between the hemorrhagic erosions caused by ethanol and aspirin is their localization in the acid-producing glandular stomach, the rate-limiting step in their pathogenesis being the extent of microvascular injury in the gastric mucosa. The major differences include the fast healing and low probability of transition into chronic gastritis after a single exposure to aspirin. On the other hand, perforated ulcer may develop, especially in the elderly, after chronic aspirin but not ethanol consumption. The main implications of pathogenetic investigations include the relative nature of gastroprotection: that is, initially, the superficial epithelial layer is not protected against concentrated luminal solutions, but it is rapidly replaced by migrating, adjacent, surviving cells if blood flow is maintained and the basement membrane is relatively intact. Vascular changes thus seem to be the rate-limiting step both in the pathogenesis and prevention of chemically induced acute gastric mucosal injury. The ultimate biochemical mechanisms of gastroprotection seem to include an effect on structural and enzymic proteins, and vascular mediators which influence vascular permeability and, indirectly, the extent of tissue injury.

Activity of liver microsomal Ca2+-ATPase in relation to perturbation of membrane hydrophobic interactions induced by methoxybenzene derivatives and n-aliphatic alcohols

Changes in the activity of liver microsomal Ca2+-ATPase were studied in the presence of two series of lipophilic compounds: four flavouring substances derived from methoxybenzene and four n-aliphatic alcohols. With each compound the activity was stimulated at lower concentrations and inhibited at higher concentrations. The linear relationship between equiactive concentrations of the compounds and their partition coefficients showed that the enzyme activity was modulated by perturbation of membrane hydrophobic interactions. Measurements carried out by electron-spin resonance (ESR) showed evidence of a decrease in the membrane order induced by these compounds. However, results obtained with the methoxybenzene derivatives showed that the modification in ATPase activity cannot be directly related to the decrease in membrane order. This decrease did not only reflect perturbation of hydrophobic interactions.