Effects of cholesterol and docosahexaenoic acid on cell viability and (Ca(2+))(i) levels in acutely isolated mouse thymocytes

Highly Selective Anti-Cancer Activity of Cholesterol-Interacting Agents Methyl-β-Cyclodextrin and Ostreolysin A/Pleurotolysin B Protein Complex on Urothelial Cancer Cells

Cholesterol content can vary distinctly between normal and cancer cells, with elevated levels in cancer cells. Here, we investigated cholesterol sequestration with methyl-β-cyclodextrin (MCD), and pore-formation with the ostreolysin A/pleurotolysin B (OlyA/PlyB) protein complex that binds to cholesterol/sphingomyelin-rich membrane domains. We evaluated the effects on viability of T24 invasive and RT4 noninvasive human urothelial cancer cells and normal porcine urothelial (NPU) cells. Cholesterol content strongly correlated with cancerous transformation, as highest in the T24 high-grade invasive urothelial cancer cells, and lowest in NPU cells. MCD treatment induced prominent cell death of T24 cells, whereas OlyA/PlyB treatment resulted in greatly decreased viability of the RT4 low-grade noninvasive carcinoma cells. Biochemical and transmission electron microscopy analyses revealed that MCD and OlyA/PlyB induce necrotic cell death in these cancer cells, while viability of NPU cells was not significantly affected by either treatment. We conclude that MCD is more toxic for T24 high-grade invasive urothelial cancer cells, and OlyA/PlyB for RT4 low-grade noninvasive urothelial cancer cells, and neither is toxic for NPU cells. The cholesterol and cholesterol/sphingomyelin-rich membrane domains in urothelial cancer cells thus constitute a selective therapeutic target for elimination of urothelial cancer cells.

Fatty acid-binding protein 4 (FABP4) and FABP5 modulate cytokine production in the mouse thymic epithelial cells

Thymic stromal cells, including cortical thymic epithelial cells (cTEC) produce many humoral factors, such as cytokines and eicosanoids to modulate thymocyte homeostasis, thereby regulating the peripheral immune responses. In this study, we identified fatty acid-binding protein (FABP4), an intracellular fatty acid chaperone, in the mouse thymus, and examined its role in the control of cytokine production in comparison with FABP5. By immunofluorescent staining, FABP4(+) cells enclosing the thymocytes were scattered throughout the thymic cortex with a spatial difference from the FABP5(+) cell that were distributed widely throughout the cTEC. The FABP4(+) cells were immunopositive for MHC class II, NLDC145 and cytokeratin 8, and were identified as part of cTEC. The FABP4(+) cells were identified as thymic nurse cells (TNC), a subpopulation of cTEC, by their active phagocytosis of apoptotic thymocytes. Furthermore, FABP4 expression was confirmed in the isolated TNC at the gene and protein levels. To explore the function of FABP in TNC, TSt-4/DLL1 cells stably expressing either FABP4 or FABP5 were established and the gene expressions of various cytokines were examined. The gene expression of interleukin (IL)-7 and IL-18 was increased both in FABP4 and FABP5 over-expressing cells compared with controls, and moreover, the increase in their expressions by adding of stearic acids was significantly enhanced in the FABP4 over-expressing cells. These data suggest that both FABPs are involved in the maintenance of T lymphocyte homeostasis through the modulation of cytokine production, which is possibly regulated by cellular fatty acid-mediated signaling in TEC, including TNC.

Oleic acid versus linoleic and α-linolenic acid. different effects on Ca2+ signaling in rat thymocytes

BACKGROUND

Oleic acid is the principal fatty acid of olive oil composition and is reported to play a crucial role in its healthy aspects. However, the detailed mechanism of action is poorly understood.

AIMS

This study aims to elucidate the role of oleic acid in calcium signaling in rat thymocytes, in comparison to linoleic and linolenic acid.

METHODS

Fatty acids were applied to thymocytes isolated from wistar rats and loaded with Fura-2 to measure calcium signals.

RESULTS

The main results showed a concentration-dependent increase in [Ca(2+)](i) induced by the 3 fatty acids. Raising the number of unsaturations resulted in greater increases. Two different pathways contributed to the increase induced by the polyunsaturated fatty acids: an IP(3)- independent release from the thapsigargin-sensitive stores and an extracellular calcium entry by econazole and nifedipine-insensitive channels. However, the OA-induced increases in [Ca(2+)](i) seemed to be due mostly to the Ca(2+) recruited from the intracellular stores.

CONCLUSION

This study demonstrates that the fatty acids tested induce increases in [Ca(2+)](i) in rat thymocytes, with differences in close relation to the degree of unsaturation. Such differences could be responsible for their different physiological action.

Role of calcium and ROS in cell death induced by polyunsaturated fatty acids in murine thymocytes

We investigated the mechanisms whereby omega-3 and -6 polyunsaturated fatty acids (PUFAs) cause cell death of mouse thymocytes using flow cytometry, focusing on the respective roles of intracellular calcium concentration, [Ca(2+)](i) and reactive oxygen species (ROS). We applied the C-22, 20, and 18 carbon omega-3 (DHA, EPA, ALA) and omega-6 (DTA, ARA, and LNA) fatty acids to isolated thymocytes and monitored cell death using the DNA-binding dye, propidium iodide. When applied at 20 µM concentration, omega-3 fatty acids killed thymocytes over a period of 1 h with a potency of DHA > EPA > ALA. The omega-6 PUFAs were more potent. The C18 omega-6 fatty acid, LNA, was the most potent, followed by DHA and ARA. Cell death was always accompanied by an increase in the levels of [Ca(2+)](i) and ROS. Both increases were in proportion to the potency of the PUFAs in inducing cell death. Removing extracellular calcium did not prevent the elevation in [Ca(2+)](i) nor cell death. However, the intracellular calcium chelator, BAPTA, almost totally reduced both the elevation in [Ca(2+)](i) and cell death, while vitamin E reduced the elevation in ROS and cell death. BAPTA also prevented the elevation in ROS, but vitamin E did not prevent the elevation in [Ca(2+)](i). Thapsigargin, which depletes endoplasmic reticulum calcium, blocked the elevation in [Ca(2+)](i), but CCCP, a mitochondrial calcium uptake inhibitor, did not. These results suggest that the six PUFAs we studied kill thymocytes by causing release of calcium from endoplasmic reticulum, which causes release of ROS from mitochondria which leads to cell death.

Intracellular mechanisms involved in docosahexaenoic acid-induced increases in tight junction permeability in Caco-2 cell monolayers

We recently showed that enrichment of Caco-2 cells with docosahexaenoic acid (DHA) increases lipid peroxidation and the formation of hydrogen peroxide and peroxynitrite, which disrupt the epithelial barrier function. Studies were designed to test whether the participation of phospholipase C (PLC)/Ca(2+)/protein kinase C (PKC), cyclooxygenase (COX), and 5-lipooxygenase pathways are involved in mediating the effects of DHA. Paracellular permeability was assessed from D-mannitol flux and transepithelial electrical resistance (TER) in differentiated Caco-2 cell monolayers incubated in control or DHA-enriched conditions (100 micromol/L). The effect of DHA was prevented by U73122 (PLC inhibitor), chelerytrine (PKC inhibitor), and 1-[5-iodonaphtalene-1-sulfonyl]-1H-hexahydro-1,4-diazepine hydrochloride (myosin light chain kinase inhibitor). In contrast, the effect of DHA was enhanced by A23187 (Ca(2+) ionophore) and BAPTA-AM (Ca(2+) chelator). Indomethacin (COX inhibitor) and AA961 (5-lipooxygenase inhibitor) also prevented the changes in D-mannitol flux induced by DHA, but no effect was detected for TER. Moreover, occludin and ZO-1 immunogold staining microscopy showed that the increase in paracellular permeability was accompanied by the redistribution of both tight junction proteins. We conclude that the disruption of epithelial barrier function by DHA is partly mediated by the PLC/Ca(2+)/PKC pathway and by the formation of eicosanoids.

Benefits versus risks associated with consumption of fish and other seafood

Fish provide nutrition for much of the world's population, and when not contaminated with chemicals, fish is a very good food. A major benefit of fish is that they are high in polyunsaturated fatty acids (PUFAs), low in saturated fat, and they contain other critical nutrients. Much of the benefit of fish consumption derives from their high levels of long chain omega-3 PUFAs, which are produced by aquatic microorganisms and bioconcentrate in the aquatic food supply. The PUFAs are essential, in that humans and other vertebrates are not able to synthesize them and therefore must obtain them from the diet. The PUFAs particularly concentrate in the nervous system, alter immune system function reduce serum triglyceride levels and have been reported to reduce the risk of sudden death after a myocardial infarction. But the problem is that most fish have at least some degree of chemical contamination with methylmercury, (which binds to muscle) and/or with persistent organic pollutants such as dioxins, polychlorinated biphenyls, polybrominated diphenyl ethers, chlorinated pesticides (which concentrate in fish fat). These chemicals have adverse effects on nervous system function, modulate the immune system, and are associated with elevations in risk of cardiovascular disease. Thus the question of benefits and risk from fish consumption is complex but very important.