Effect of cholesterol feeding on membrane fluidity, (Na+ + K+)ATPase, adenylate cyclase, [3H]-ouabain-, and [3H]-dihydroalprenolol-binding in rat submandibular salivary glands

In vivo influence of extract from Aronia melanocarpa on the erythrocyte membranes in patients with hypercholesterolemia

Background

Hypercholesterolemia increases cholesterol concentration in erythrocyte membranes, which results in decrease of membrane fluidity and decreases the deformability of red blood cells. The fruits of Arona melanocarpa contains many of polyphenols and other compounds that have beneficial health effects.

Material/Methods

The aim of the study was to estimate the influence of 2-month supplementation of extract from Aronia melanocarpa (100 mg Aronox, three times per day) on cholesterol concentration, lipid peroxidation, membrane fluidity, level of thiol groups and activity of ATPase in erythrocytes from patients with hypercholesterolemia. The study involved 25 patients with hypercholesterolemia without pharmacological treatment and 20 healthy individuals as a control group. Blood samples were collected before, and after 1 and 2 months of Aronia administration.

Results

The 2-month Aronia supplementation resulted in a decrease of cholesterol concentration (by 22%) and a decrease of lipid peroxidation (by 40%), and an increase of membrane fluidity. No statistically significant increase of the concentration of thiol groups and of ATPase activity were observed.

Conclusions

Our study shows that supplementation of extract from Aronia melanocarpa has a beneficial effect on rheological properties of erythrocytes.

Cholecystosteatosis: an explanation for increased cholecystectomy rates

INTRODUCTION

Over the past decade, obesity has become epidemic, and the number of cholecystectomies as well as the percentage with acalculous cholecystitis have increased. We have recently reported that congenitally obese mice and lean mice fed a high fat diet have increased gallbladder wall lipids and poor gallbladder emptying. Therefore, we tested the hypothesis that compared to patients with a normal gallbladder, patients with both acalculous and calculous cholecystitis would have increased gallbladder wall fat.

METHODS

Sixteen patients who underwent cholecystectomy for acalculous cholecystitis were identified. Sixteen nondiseased controls who underwent incidental cholecystectomy during surgery for liver or pancreatic disease and 16 diseased controls whose gallbladder was removed for chronic calculous cholecystitis were chosen to match the acalculous patients for gender and Body Mass Index. Pathology specimens were reviewed in a blinded fashion for gallbladder wall fat, thickness, and inflammation.

RESULTS

Acalculous cholecystitis patients were younger (p < 0.01) than nondiseased or diseased controls. Gallbladder wall fat was significantly increased (p < 0.02) in the acalculous and calculous cholecystitis patients compared to the nondiseased controls. Gallbladder wall thickness (p < 0.02) and inflammatory score (p < 0.01) were highest in the calculous cholecystitis patients.

CONCLUSIONS

These data suggest that compared to nondiseased controls, (1) patients with acalculous cholecystitis are younger and have increased gallbladder fat and (2) patients with calculous cholecystitis have increased gallbladder fat and inflammation. We conclude that increased gallbladder fat may lead to poor gallbladder emptying and biliary symptoms. Thus, cholecystosteatosis may explain, in part, the increased need for cholecystectomy and the higher percentage of these patients with acalculous cholecystitis.

Excess membrane cholesterol alters human gallbladder muscle contractility and membrane fluidity

BACKGROUND & AIMS

The relationship between muscle contractility, plasma membrane cholesterol, and fluidity was investigated in human gallbladders with gallstones.

METHODS

Isolated gallbladder muscle cells were used to measure contraction. Plasma membranes of gallbladder muscle were purified in a sucrose gradient and measured for cholesterol content and cholesterol/phospholipid mole ratio. Membrane fluidity was determined by using fluorescence polarization and was expressed as the reciprocal of anisotropy.

RESULTS

The maximal contraction induced by cholecystokinin octapeptide was significantly less in gallbladders with cholesterol stones than in those with pigment stones. The membrane cholesterol content and cholesterol/phospholipid mole ratio were significantly higher in gallbladders with cholesterol stones than in those with pigment stones. Membrane anisotropy was also higher than in gallbladders with pigment stones, reflecting lower membrane fluidity in gallbladders with cholesterol stones. After muscle cells from cholesterol stone gallbladders were incubated with cholesterol-free liposomes for 4 hours, cholecystokinin octapeptide-induced contraction, membrane cholesterol content and cholesterol/phospholipid ratio, and membrane fluidity returned to normal levels.

CONCLUSIONS

Gallbladder muscle from patients with cholesterol stones has increased membrane cholesterol/phospholipid mole ratio and decreased membrane fluidity resulting in impaired muscle contractility. These abnormalities are corrected by removing the excess cholesterol from the plasma membranes.

The role of diet cholesterol changes on EEG

Thirty three male albino rats, weight between 200 and 220 g were used in this experiment. Control animals consisting of 11 rats were fed with a normal lab diet for a period of 14 weeks and the others (22) were fed with a diet containing 1% cholesterol for the same period. At the end of the experimental period, plasma cholesterol level (Mean +/- SD) was 141.29 +/- 34.5 mg/dl in the cholesterol group and 70.66 +/- 10 mg/dl in the control group. Eleven of the rats from the cholesterol group were transferred to the normal diet for 14 weeks (normocholesterolemic group). Spectral analysis of EEG records from parietal lobes of animals showed that there was an obvious depression in the brain waves of hypercholesterolemic rats whereas no depression in normocholesterolemic rats.

Reversal of diet-induced changes in adenylate cyclase activity and fatty acid composition of rat submandibular salivary gland lipids

This study sought to determine if the diet-induced changes in submandibular salivary glands can be reversed. Two groups of male weanling Sprague-Dawley rats were fed purified diets containing 9% butter + 1% corn oil (group I, control) or 9% ethyl ester concentrate of n-3 fatty acids + 1% corn oil (group II, experimental). After 5 weeks of feeding the respective diets, rats in group I were divided into two subgroups: Ia, which was maintained on the control diet, and Ib, which was shifted to the experimental diet for the reversal study. The rats in the experimental group were kept on their original diet. After five further weeks of feeding, the rats were killed, and membranes from submandibular glands were prepared and assayed for adenylate cyclase activity and for the fatty acid composition of total phospholipids. Changes characteristic of feeding n-3 fatty acids, including a significant increase in membrane fluidity as measured by the degree of unsaturation of fatty acids, were observed in the total phospholipids of membranes from the experimental group. The adenylate cyclase activity was two- to three-fold higher in membranes of rats fed the experimental diet (group II) than the control diet (group Ia). Whereas the diet-induced changes in fatty acid composition and membrane fluidity were largely reversed (group Ib, reversal study), changes in adenylate cyclase activity were only partially reversed. The results suggest that, in addition to the fatty acid composition and membrane fluidity, other factors may also be important in modifying adenylate cyclase activity.

Ceratitis capitata brain adenylate cyclase and its membrane environment

Adenylate cyclase activation by GTP and octopamine as well as basal activity (in the presence of Mg2+) have been studied as a function of membrane structure in plasma membranes from brain of the dipterous Ceratitis capitata. Benzyl alcohol and lidocaine, but not phenobarbital, inhibited the three activities to the same extent. Triton X-100-solubilized adenylate cyclase was also inhibited by benzyl alcohol and lidocaine, but not by phenobarbital. Results could be explained by an effect on the catalytic unit lipid environment, which would be maintained after solubilization, counteracting the effect of these drugs to facilitate lateral diffusion and coupling of adenylate cyclase components in the lipid bilayer. The observation that the insect adenylate cyclase is relatively insensitive to changes in bulk bilayer fluidity is strengthened by the absence of effect of phenobarbital on enzyme activities. Indeed, this compound was as active as lidocaine or benzyl alcohol in increasing bulk membrane fluidity. The response of C. capitata adenylate cyclase to changes in membrane fluidity is different from that recorded in mammalian systems. This may be functionally important and result from the fact that insects are not warm-blooded.

Fatty acid incorporation into membranes of dispersed rat submandibular salivary gland cells and their effect on adenylate cyclase activity

Dispersed cells from rat submandibular salivary glands were incubated in medium supplemented with different fatty acids, such as stearic (18:0), oleic (cis 18:1 omega 9) and elaidic acid (trans 18:1 omega 9). The exogenous fatty acids were incorporated into the membrane lipids. A comparison of the adenylate cyclase activity in membranes of cells incubated with different fatty acids revealed the following order (from highest to lowest specific activity): stearic, elaidic, oleic. The findings suggest that changes in adenylate cyclase activity in these dispersed membranes enriched with different fatty acids may be related to the possible changes in membrane fluidity. The synthesis of glycoproteins was studied by measuring the incorporation of [1-14C]-glucosamine into TCA-PTA-precipitable material in the presence or absence of fatty acids. No effect of the exogenous fatty acids on glycoprotein synthesis was observed.

Adenylate cyclase and beta-receptors in salivary glands of rats fed diets containing trans fatty acids

The effects of trans fatty acids on adenylate cyclase were determined in the submandibular salivary glands (SMSG) of rats fed diets containing 20% corn oil, 20% partially hydrogenated soybean oil (PHSBO) or 18% PHSBO + 2% corn oil. The fluoride- and isoproterenol-stimulated adenylate cyclase activities were higher in the SMSG from rats fed 20% PHSBO than in the control group fed 20% corn oil. The feeding of 2% corn oil with the diet containing 18% PHSBO resulted in a complete restoration of isoproterenol-stimulated and a partial restoration of fluoride-stimulated adenylate cyclase activity. There was no significant difference in the concentration of the beta-adrenergic receptor or in the receptor-binding affinity constants among the three dietary groups as measured by [3H]dihydroalprenolol (DHA)-binding. Higher fluorescence polarization of diphenyl hexatriene (DPH) was observed in SMSG membranes of rats fed diet containing 20% PHSBO than in the other two oils, suggesting that membrane fluidity may play a role in adenylate cyclase activity.

In-vivo incorporation of omega 3 fatty acids into membrane lipids of rat salivary glands and changes in adenylate-cyclase activity

Dietary omega 3 fatty acids from menhaden oil were incorporated into membrane phospholipids of submandibular salivary glands (SMSG). Eicosapentaenoic (20:5), docosapentaenoic (22:5) and docosahexaenoic (22:6) acids constituted about 20 per cent of the total fatty acids in phospholipids, phosphatidylcholine and phosphatidylethanolamine fractions of the SMSG plasma membranes of rats fed for 6 weeks a diet containing 10 per cent menhaden oil. The changes in fatty-acid composition of the membrane phospholipids were accompanied by higher adenylate-cyclase activity in the SMSG membranes of rats fed 10 per cent menhaden oil than in rats fed 10 per cent corn oil or 8 per cent coconut oil + 2 per cent corn oil. However, there were no diet-related differences in the fold-stimulation of adenylate-cyclase activity.