Dexamethasone and 1,25-dihydroxyvitamin D3, but not cyclosporine A, inhibit production of granulocyte-macrophage colony-stimulating factor in human fibroblasts

Tumor necrosis factor alpha (TNF alpha) stimulates granulocyte- macrophage colony-stimulating factor (GM-CSF) production in human fibroblasts and other mesenchymal cells. However, relatively little is known about agents that downregulate cytokine production in these cells. In the present report we show that dexamethasone (Dexa), a synthetic glucocorticoid, markedly reduced GM-CSF production in TNF alpha-stimulated fibroblasts at both the protein and the RNA levels. CSF activity, GM-CSF protein, and RNA levels, determined by an in vitro colony-forming assay in normal human bone marrow cells, by an enzyme immunoassay, and by Northern blotting assay, were reduced to greater than 90% of control values by Dexa (1 mumol/L). Similarly, 1,25- dihydroxyvitamin D3 [1,25(OH)2D3], a hormone with possible physiologic immunoregulatory significance, reduced GM-CSF expression in a concentration- and time-dependent manner. However, this repression was less pronounced than that of Dexa, and in part due to a decreased proliferative activity. In contrast, cyclosporine A (CsA), another immunosuppressive agent, did not alter GM-CSF expression in TNF alpha- stimulated fibroblasts. Our in vitro studies suggest that by inhibiting GM-CSF production in fibroblasts, glucocorticoids and possibly 1,25(OH)2D3, but not CsA, may attenuate TNF alpha-mediated inflammatory processes and influence the regulation of hematopoiesis.</jats:p

Dexamethasone and 1,25-dihydroxyvitamin D3, but not cyclosporine A, inhibit production of granulocyte-macrophage colony-stimulating factor in human fibroblasts

Abstract Tumor necrosis factor alpha (TNF alpha) stimulates granulocyte- macrophage colony-stimulating factor (GM-CSF) production in human fibroblasts and other mesenchymal cells. However, relatively little is known about agents that downregulate cytokine production in these cells. In the present report we show that dexamethasone (Dexa), a synthetic glucocorticoid, markedly reduced GM-CSF production in TNF alpha-stimulated fibroblasts at both the protein and the RNA levels. CSF activity, GM-CSF protein, and RNA levels, determined by an in vitro colony-forming assay in normal human bone marrow cells, by an enzyme immunoassay, and by Northern blotting assay, were reduced to greater than 90% of control values by Dexa (1 mumol/L). Similarly, 1,25- dihydroxyvitamin D3 [1,25(OH)2D3], a hormone with possible physiologic immunoregulatory significance, reduced GM-CSF expression in a concentration- and time-dependent manner. However, this repression was less pronounced than that of Dexa, and in part due to a decreased proliferative activity. In contrast, cyclosporine A (CsA), another immunosuppressive agent, did not alter GM-CSF expression in TNF alpha- stimulated fibroblasts. Our in vitro studies suggest that by inhibiting GM-CSF production in fibroblasts, glucocorticoids and possibly 1,25(OH)2D3, but not CsA, may attenuate TNF alpha-mediated inflammatory processes and influence the regulation of hematopoiesis.</jats:p

Agonist-Induced Hump Current Production In Heterologously-Expressed Human α4β2-Nicotinic Acetylcholine Receptors

Aim: To characterize the functional and pharmacological features of agonist-induced hump currents in human α4β2-nicotinic acetylcholine receptors (nAChR). Methods: Whole-cell and outside-out patch recordings were performed using human α4β2-nAChR heterologously expressed in stably-transfected, native nAChR-null subclonal human epithelial 1 (SH-EP1) cells. RT-PCR was used to test the mRNA expression of transfected nAChR. Homology modeling and ace-tylcholine (ACh) docking were applied to show the possible ACh-binding site in the channel pore. Results: The rapid exposure of 10 mmol/L ACh induced an inward current with a decline from peak to steady-state. However, after the removal of ACh, an additional inward current, called \ hump\ current, reoccurred. The ability of agonists to produce these hump currents cannot be easily explained based on drug size, charge, acute potency, or actions as full or partial agonists. Hump currents were associated with a rebound increase in whole-cell conductance, and they had voltage dependence-like peak currents induced by agonist action. Hump currents blocked by the α4β2-nAChR antagonist dihydro-β-erythroidine were reduced when α4β2-nAChR were desensitized, and were more pronounced in the absence of external Ca2+. Outside-out single-channel recordings demonstrated that compared to 1 μmol/L nicotine, 100 μmol/L nicotine reduced channel current amplitude, shortened the channel mean open time, and prolonged the channel mean closed time, supporting an agonist-induced open-channel block before hump current production. A docking model also simulated the agonist-binding site in the channel pore. Conclusion: These results support the hypothesis that hump currents reflect a rapid release of agonists from the α4β2-nAChR channel pore and a rapid recovery from desensitized α4β2- nAChR. © 2008 CPS and SIMM