Effects of ethanol alone or after pretreatment with 20% ethanol on phospholipid metabolism in rat gastric mucosa

High α-tocopherol dosing increases lipid metabolism by changing redox state in damaged rat gastric mucosa and liver after ethanol treatment

Regeneration of ethanol-injured rat gastric mucosa must undergo changes in major metabolic pathways to achieve DNA replication and cell proliferation. These events are highly dependent on glucose utilization and inhibited by vitamin E (VE) (α-tocopherol) administration. Therefore, the present study aimed at assessing lipid metabolism in the gastric mucosa and ethanol-induced gastric damage and the effect of α-tocopherol administration. For this, rates of fatty acid β-oxidation and lipogenesis were tested in gastric mucosa samples. Through histological analysis, we found loss of the mucosa's superficial epithelium, which became gradually normalized during the recovery period. Proliferation of gastric mucosa occurred with augmented formation of β-oxidation by-products, diminished synthesis of triacylglycerols (TGs), as well as of phospholipids, and a reduced cytoplasmic NAD/NADH ratio, whereas the mitochondrial redox NAD/NADH ratio was much less affected. In addition, α-tocopherol increased palmitic acid utilization in the gastric mucosa, which was accompanied by the induction of 'mirror image' effects on the cell redox state, reflected in an inhibited cell gastric mucosa proliferation by the vitamin administration. In conclusion, the present study shows, for the first time, the role of lipid metabolism in the adaptive cell gastric mucosa changes that drive proliferation after a chronic insult. Moreover, α-tocopherol increased gastric mucosa utilization of palmitic acid associated with energy production. These events could be associated with its antioxidant properties in co-ordination with regulation of genes and cell pathways, including changes in the cell NAD/NADH redox state.

Ethanol and lipid metabolism. Differential effects on liver and brain microsomes

We have determined the effect of prolonged ethanol treatment on several enzyme activities related to lipid metabolism in chick-brain and liver microsomes. Ethanol increased microsome cholesterol levels in both organs. The treatment caused a marked increase in the hepatic HMG-CoA reductase and ACAT activities while in the brain a clear decrease was found in these enzyme activities. At the same time the activity of reacylation of phospholipids, was clearly modified in both brain and liver. Thus, while in the liver the turnover of acyl moieties of phosphatidylethanolamine, sphingomyelin and phosphatidylinositol was enhanced by ethanol consumption, in the brain only the reacylation of phosphatidylserine increased to any significant extent. These results indicate that ethanol exerts a differential action in brain and liver, namely cholesterol synthesis and esterification decreased in brain and increased in chick liver. Ethanol also induces faster phospholipid metabolism in both brain and liver microsomes.

Effects of 16,16-dimethyl prostaglandin E2 on glycoprotein and lipid synthesis of gastric epithelial cells grown in a primary culture

We investigated the biosynthesis of phospholipid, neutral lipids, glycoproteins, and DNA in primary cultures of rat oxyntic mucosal cells. In addition, responses of these biosynthetic pathways to the gastric protective agent 16,16-dimethyl prostaglandin E2 (dmPGE2) were studied. Cultured gastric cells under control conditions synthesized glycoprotein in a linear manner over time. The cells responded to dmPGE2 with an increase in glycoprotein synthesis without an effect on DNA synthesis. Investigations of lipid synthesis showed that phospholipid was produced in a linear fashion by these cells, however, no effect of exogenously administered dmPGE2 on its rate of formation was discernible. In contrast, the incorporation of labeled palmitate into neutral lipids revealed that triglyceride biosynthesis was significantly increased by the addition of dmPGE2 to the culture medium, which could be further enhanced by the administration of the phosphodiesterase inhibitor, isobutyl methyl xanthine. Cyclic nucleotide involvement was further suggested by our finding that triglyceride synthesis in cultured gastric mucous cells could be increased a comparable amount by the addition of both dbcAMP and dbcGMP to the medium. The possible relationship between these biochemical alterations and the gastric protective action of dmPGE2 is discussed.

Gastric protective activity of mixtures of saturated polar and neutral lipids in rats

It has been shown that intragastric treatment of rats with a suspension of dipalmitoylphosphatidylcholine and tripalmitin at a 1:4 ratio (5 mg lipid/mL per rat) provided rats with highly efficaceous and consistent protection against a variety of ulcerogenic agents and conditions. The gastric protective activity of this mixture was of long duration (t 1/2 approximately 9 hours. In an attempt to understand the mechanism of protection, it was determined that the ulcerogen-induced reduction in gastric surface hydrophobicity was reversed in rats pretreated with the mixture. However, the lipid mixture did not affect the gastric emptying rate and maintained its cytoprotective activity in indomethacin-treated rats. These results indicate that the mixture's protective effect was not mediated by alterations in either gastrointestinal motility or the gastric accumulation of lipids or "cytoprotective" metabolites (prostaglandins). The mixture also appreciably reduced gastric lesion score in response to acid if one or both the lipids was substituted for a metabolically inert ether analogue, suggesting that lipid metabolism makes a negligible contribution to the protective response. Electron microscopic observation indicated that the predominent structure in the mixture is a microemulsion in which a dipalmitoylphosphatidylcholine monolayer encapsulates a tripalmitin core. Last, the improved gastric protective activity of the mixture in comparison to dipalmitoylphosphatidylcholine liposomes is discussed regarding marked differences in the physical structure of the two suspensions and the rate at which lipids in these states adsorb to a surface to enhance its hydrophobic properties.

Effects of 15(S)-15-methyl prostaglandin E2 methyl ester on phospholipid metabolism in rat gastric mucosa

The effects of 15(S)-15-methyl prostaglandin E2 (PGE2) methyl ester on gastric mucosal metabolism of phospholipids in intact rats and rats injured by intragastric instillation of acidified taurocholic acid were examined by using radioisotope-labeled precursors. The incorporation of palmitic, oleic and arachidonic acids into phosphatidylcholine (PC) and phosphatidylethanolamine (PE) was reduced by treatment with 15(S)-15-methyl PGE2 methyl ester in the intact rats, but the incorporation of glycerol was unaffected or affected only slightly. Instillation of acidified taurocholic acid resulted in decreased incorporation of palmitic acid and glycerol into PC and PE, whereas pretreatment with 15(S)-15-methyl PGE2 methyl ester caused the incorporations of these precursors to be maintained after acidified taurocholic acid treatment. These results suggest that 15(S)-15-methyl PGE2 methyl ester may reduce the incorporation of fatty acids into PC and PE by inhibition of the deacylation-reacylation cycle either directly or indirectly, whereas acidified taurocholic acid decreases de novo synthesis of PC and PE, and probably also the reacylation of fatty acid into phospholipids. Pretreatment with 15(S)-15-methyl PGE2 methyl ester protected the PC- and PE-synthesizing activity against the injury induced by acidified taurocholic acid, and this effect may be involved in the prevention of mucosal damage.

Effects of taurocholic acid/HCl alone or after pretreatment with geranylgeranylacetone on phospholipid metabolism in rat gastric mucosa

Changes in phospholipid metabolism in gastric mucosa caused by instillation of taurocholic acid (TCA)/HCl (80 mM/300 mM) into the stomach of rats and the effects of pretreatment with an antiulcer agent, geranylgeranylacetone (GGA), were studied after intravenous injection of radioisotope-labeled precursors. The instillation of TCA/HCl rapidly reduced the incorporation of labeled fatty acids and glycerol into phosphatidylcholine and phosphatidylethanolamine, indicating the inhibition of de novo synthesis of phospholipids. These changes were restored by 120-150 min after the TCA/HCl treatment. Pretreatment with GGA enhanced the incorporation of precursors into phosphatidylcholine immediately after the instillation of TCA/HCl. Experiments in which the mucosal lipids were labeled with fatty acids prior to the instillation of TCA/HCl showed that the degradation of cellular lipids and release of the products into the gastric lumen were induced by TCA/HCl and that these changes were not prevented by GGA. Since GGA almost completely inhibited the gastric lesions induced by TCA/HCl, the enhancement of synthesis of mucosal phosphatidylcholine induced by GGA may be involved in the prevention of gastric damage. The incorporation of labeled fatty acids into free fatty acid fraction and diacylglycerol was increased quickly by the TCA/HCl treatment, suggesting early damage to the blood vessels of the gastric mucosa; these changes were inhibited significantly by GGA.