Cystic Fibrosis (CF) is the most common life-limiting, autosomal recessive genetic disease affecting the U.S. population, and is due to mutations in the cystic fibrosis transmembrane regulator (CFTR) gene. The consequence of the deltaF508CFTR mutation, the most common in the population, is a failure of the mutant CFTR protein to traffick correctly to the apical plasma membrane of epithelial cells in lung and elsewhere. A profoundly morbid consequence of an intrinsic proinflammatory phenotype occurs in the CF lung. We have designed and synthesized pyridinium salts that inhibit the formation of interleukin-8 in lung epithelial cells that act as a model of cystic fibrosis. These antagonists are amphiphilic pyridinium derivatives, and the mechanism of action is being explored. Members of this class of pyridinium derivatives have been found to block of neuronal calcium channels formed by aggregates of amyloid proteins. The P2X ion channels are receptor channels activated by extracellular ATP and mediate a number of potent and possibly important biological effects in the cardiovascular, inflammatory, and central nervous systems. Previous studies have shown that extracellular ATP can cause an ionic current in murine, rat and guinea pig cardiac ventricular myocytes. The receptor that mediates this current appears to be a P2X receptor, of which the P2X4 receptor is an important subunit. Activation of P2X receptors leads to the opening of a nonselective cation channel permeable to sodiumn, potassium, and calcium ions. The current is inward at negative membrane potentials, reverses near 0 mV, and becomes outward at positive potentials. The continuous activation of this receptor channel by endogenous extracellular ATP may assume an important biological function. This constant activation under the resting or negative membrane potentials would produce an inward current, whereas its activation during depolarized portions of the action potential should lead to an outward current. These currents represent a possible ionic mechanism by which the cardiac P2X channel achieves its biological effects. A potential biologically important role of the cardiac P2X receptor was suggested by the finding that cardiac myocyte-specific overexpression of the P2X4 receptor can rescue the hypertrophic and heart failure phenotype of the calsequestrin (CSQ) model of cardiomyopathy. However, little is known regarding regulation of the cardiac P2X receptor in cardiac hypertrophy or failure. Furthermore, it is not clear whether an increased activation of the endogenous P2X receptor channel is beneficial or harmful in the progression of heart failure. In collaboration with Dr. Bruce Liang (Univ.of Connecticut) we investigated the regulation of the P2X receptor-mediated ionic current and its potential role in heart failure using several novel nucleotide agonists. Chronic administration of a novel nucleotidase-resistant P2 receptor agonist MRS2339, which was capable of inducing this ionic current and devoid of any vasodilator action, reduced cardiac hypertrophy and increase lifespan. The data suggest that an important biological function of the cardiac P2X current is to favorably modulate the progression of cardiac hypertrophy and failure. The structure activity relationship of MRS2339 is currently being explored. We have discovered analogues of this monophosphate derivative that have a stable C-P bond in place of the C-O-P bond, which is subject to cleavage in vivo. These are phosphonate derivatives that are equally cardioprotective in comparison to the lead compound MRS2339. The P2X7 receptor, a ligand gated ion channel that responds to ATP and other nucleotide derivatives, is involved in the inflammatory process. In the brain it occurs on microglial cells. Antagonists of the P2X7 receptor, based on tyrosine derivatives are being designed as functionalized congeners. In these antagonists, a reactive chain forms an extension of the Tyr side chain. Since the receptor likely consists of higher order bundles of multiple subunits, and we might expect more that one binding site for agonists or for antagonists to occur on each functional ion channel, we have designed dimers ofthese antagonists that still act as potent blockers of the actions of ATP. Vanilloid agonists such as capsaicin activate ion flux through the TRPV1 channel, a heat- and ligand-gated cation channel that transduces painful chemical or thermal stimuli applied to peripheral nerve endings in skin or deep tissues. We have probed the SAR of a variety of 1,4-dihydropyridine (DHP) derivatives as novel enhancers of TRPV1 activity by examining changes in capsaicin-induced elevations in calcium-uptake in either cells ectopically expressing TRPV1 or in cultured dorsal root ganglion (DRG) neurons. The enhancers increased the maximal capsaicin effect on 45Ca2+-uptake by typically 2- to 3-fold without producing an action when used alone. The DHP enhancers contained 6-aryl substitution and small alkyl groups at the 1 and 4 positions, and a 3-phenylalkylthioester was tolerated. Levels of free intracellular calcium ions, as measured by calcium imaging, were also increased in DRG neurons when exposed to the combination of capsaicin and the most efficacious enhancer 23 compared to capsaicin alone. Thus, DHPs can modulate TRPV1 channels in a positive fashion.
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