RESUMEN
Astrocytes have been recognized as important elements in controlling inflammatory as well as immune processes in the central nervous system (CNS). Recently, glial cells have been shown to produce cysteinyl leukotrienes (CysLTs) which are known lipid mediators of inflammation and whose extracellular concentrations rise under different pathological conditions in the brain. In the same conditions also extracellular concentrations of ATP dramatically increase reaching levels able to activate P2X7 ionotropic receptors for which an emerging role in neuroinflammation and neurodegeneration has been claimed. RTPCR analysis showed that primary cultures of rat brain astrocytes express P2X7 receptors. Application of the selective P2X7 agonist benzoyl benzoly ATP (BzATP) markedly increased [Ca2+]i which was mediated by a calcium influx from the extracellular milieu. The P2X7 antagonist, oATP, suppressed the BzATP-induced calcium increase. Consistent with the evidence that increased calcium levels activate the leukotriene biosynthetic pathway, challenge of astrocytes with either the calcium ionophore A23187 or BzATP significantly increased CysLT production and the cell pre-treatment with EGTA abolished these effects. Again the P2X7 antagonist prevented the BzATP-mediated CysLT efflux, whereas the astrocyte pretreatment with MK-571, a CysLT1 receptor antagonist, was ineffective. The astrocyte pre-treatment with a cocktail of inhibitors of ATP binding cassette (ABC) proteins reduced the BzATP-mediated CysLT production confirming that ABC transporters are involved in the release of CysLTs. The astrocyte P2X7- evoked rise of CysLT efflux was abolished in the presence of MK-886, an inhibitor of 5-lipoxygenase activating protein (FLAP) whose expression, along with that of 5-lipoxygenase (5-LO) was reported by Northern Blot analysis. The stimulation of P2X7 induced an up-regulation of FLAPmRNA that was reduced by the antagonist oATP. These data suggest that in rat brain cultured astrocytes P2X7ATP receptors may participate in the control of CysLT release thus further supporting a role for extracellular ATP as an integral component of the inflammatory brain response.
Asunto(s)
Astrocitos/metabolismo , Encéfalo/citología , Cisteína/biosíntesis , Cisteína/metabolismo , Leucotrienos/biosíntesis , Leucotrienos/metabolismo , Receptores Purinérgicos P2/metabolismo , Proteínas Activadoras de la 5-Lipooxigenasa , Adenosina Trifosfato/análogos & derivados , Adenosina Trifosfato/farmacología , Marcadores de Afinidad/farmacología , Animales , Astrocitos/citología , Astrocitos/efectos de los fármacos , Calcimicina/farmacología , Proteínas Portadoras/metabolismo , Células Cultivadas , Corteza Cerebral/citología , Quelantes/farmacología , Cisteína/química , Relación Dosis-Respuesta a Droga , Ácido Egtácico/farmacología , Indoles/farmacología , Ionóforos/farmacología , Antagonistas de Leucotrieno/farmacología , Leucotrienos/química , Inhibidores de la Lipooxigenasa/farmacología , Proteínas de la Membrana/metabolismo , Propionatos/farmacología , Antagonistas del Receptor Purinérgico P2 , Quinolinas/farmacología , ARN Mensajero/metabolismo , Ratas , Regulación hacia ArribaRESUMEN
Total triterpenic fraction of Centella asiatica (TTFCA) is effective in improving venous wall alterations in chronic venous hypertension and in protecting the venous endothelium. TTFCA is active on connective tissue modulation, improves the synthesis of collagen and other tissue proteins by modulating the action of fibroblasts in the vein wall, and stimulates collagen remodeling in and around the venous wall. This is due to the modulating action of TTFCA on fibroblasts as shown by experiments on the growth of human embryonal fibroblasts. TTFCA has a moderate in-vitro and in-vivo stimulating effect on collagen synthesis and, at higher dosages, an inhibition on the synthesis of collagen and acid mucopolysaccharides. Studies have indicated the role of TTFCA on the synthesis of specific venous wall elements by cell cultures of human embryonal fibroblasts. The tissue-stimulating action is shown by the increased collagen production independent from the stimulation of cell proliferation (this differentiates the action of TTFCA from cell growth factors). TTFCA is active on the microcirculation in venous and diabetic microangiopathy. Signs and symptoms of venous hypertension and edema are improved by treatment. The remodeling on collagen synthesis could be one of the possible mechanisms of actions of TTFCA in the remodeling of echolucent (soft; therefore, with risk of thrombosis and embolization) plaques at the carotid and femoral bifurcation. This compound is safe and well tolerated. In conclusion, several actions of TTFCA in vascular diseases makes the use of this compound very interesting in venous and arterial problems.