Abstract
According to previous reports, flavonoids and nutraceuticals correct defective electrolyte transport in cystic fibrosis (CF) airways. Traditional medicinal plants from China and Thailand contain phytoflavonoids and other bioactive compounds. We examined herbal extracts of the common Thai medicinal euphorbiaceous plant Phyllanthus acidus for their potential effects on epithelial transport. Functional assays by Ussing chamber, patch-clamping, double-electrode voltage-clamp and Ca2+ imaging demonstrate activation of Cl- secretion and inhibition of Na+ absorption by P. acidus. No cytotoxic effects of P. acidus could be detected. Mucosal application of P. acidus to native mouse trachea suggested transient and steady-state activation of Cl- secretion by increasing both intracellular Ca2+ and cAMP. These effects were mimicked by a mix of the isolated components adenosine, kaempferol, and hypogallic acid. Additional experiments in human airway cells and CF transmembrane conductance regulator (CFTR)-expressing BHK cells and Xenopus laevis oocytes confirm the results obtained in native tissues. Cl- secretion was also induced in tracheas of CF mice homozygous for Phe508del-CFTR and in Phe508del-CFTR homozygous human airway epithelial cells. Taken together, P. acidus corrects defective electrolyte transport in CF airways by parallel mechanisms including 1) increasing the intracellular levels of second messengers cAMP and Ca2+, thereby activating Ca2+-dependent Cl- channels and residual CFTR-Cl- conductance; 2) stimulating basolateral K+ channels; 3) redistributing cellular localization of CFTR; 4) directly activating CFTR; and 5) inhibiting ENaC through activation of CFTR. These combinatorial effects on epithelial transport may provide a novel complementary nutraceutical treatment for the CF lung disease.
Footnotes
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This work was supported by the Bayerische Forschungsstiftung, Mukoviszidose e.V., the Else Kröner-Fresenius Stiftung, Deutsche Forschungsgemeinschaft SFB699 and by the research grant POCTI/MGI/47382/2002 and Centro de Investigação em Genética Molecular Humana (Fundação do Ministério de Ciência e Tecnologia de Portugal, Portugal and Fondo Europeo de Desarrollo Regional, European Union).
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R.S. and K.K. share senior authorship. M.S. and J.O. contributed equally to the present work.
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ABBREVIATIONS: CF, cystic fibrosis; CFTR, cystic fibrosis transmembrane conductance regulator; ENaC, epithelial Na+ channels; 8-SPT, 8-sulfophenyltheophylline; DPC-PX, 1,3-dipropyl-8-cyclopentylxanthine; DMEM, Dulbecco's modified Eagle's medium; DHBA, 2,3-dihydroxybenzoic acid (hypogallic acid); Vte, transepithelial voltage; Rte, transepithelial resistance; Isc, short-circuit current; BHK, baby hamster kidney; wt, wild-type; IBMX, 3-isobutyl-1-methylxanthine; DIDS, 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid; CPA, cyclopiazonic acid; MRS2179, 2′-deoxy-N6-methyl adenosine 3′,5′-diphosphate; U73122, 1-[6-((17β-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione; NFA, niflumic acid; BAPTA, 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid; AM, acetoxymethyl ester; CCH, carbachol.
- Received April 4, 2006.
- Accepted October 25, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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