Thymulin and zinc (Zn2+)-mediated inhibition of endotoxin-induced production of proinflammatory cytokines and NF-kappaB nuclear translocation and activation in the alveolar epithelium: unraveling the molecular immunomodulatory, anti-inflammatory effect of thymulin/Zn2+ in vitro.
The immunomodulatory potential of thymulin and zinc (Zn(2+)) in the perinatal alveolar epithelium is not well characterized. In an in vitro model of fetal alveolar type II epithelial cells (FATEII), we have investigated the exhibition of an anti-inflammatory activity of this peptide hormone. Thymulin selectively ameliorated, in a dose-dependent manner, the endotoxin (ET/LPS [lipopolysaccharide])-induced release of IL-1beta, but not IL-6 or TNF-alpha. Furthermore, Zn(2+), an anti-inflammatory antioxidant, which is required for the biological activity of thymulin, independently reduced the secretion of IL-1beta, TNF-alpha and, to a lesser extent, at a supraphysiologic dose (1 mM), IL-6. The underlying cellular and molecular pathways associated with the anti-inflammatory effect of thymulin and Zn(2+) in the alveolar epithelium are not well established. Further in this study, the role of cyclic AMP (cAMP) in the anti-inflammatory effect of thymulin was investigated, in addition to unraveling the possible involvement of the NF-kappaB pathway. Interestingly, thymulin upregulated, in a dose- and time-dependent manner, the release of the nucleotide cAMP. To understand whether the inhibitory effect of thymulin on cytokine release is cAMP-dependent, Forskolin, a labdane diterpene known to elevate intracellular cAMP, was shown to reduce the secretion of IL-1beta and TNF-alpha, but not IL-6, an effect mimicked by dibutyryl-cAMP (dbcAMP), an analog of cAMP. Alveolar epithelial cells treated with thymulin markedly showed a downregulation of the nuclear translocation of RelA (p65), the major transactivating member of the NF-kappaB family, in addition to NF-kappaB(1) (p50) and c-Rel (p75), an effect mildly substantiated with Zn(2+). Furthermore, thymulin/Zn(2+) reduced, in a dose-dependent manner, the DNA-binding activity of NF-kappaB (RelA/p65). These results indicate that the anti-inflammatory effect of thymulin, which is mediated by cAMP, is NF-kappaB-dependent and involves the downregulation of the release of proinflammatory cytokines, particularly IL-1beta, an effect synergistically amplified, at least in part, by Zn(2+). The molecular regulation of thymulin via a NF-kappaB-dependent pathway is critical to understanding the anti-inflammatory alleviating role of this nonapeptide in regulating proinflammatory signals.
Haddad
John J
JJ
Cellular and Molecular Signaling Research Group, Department of Clinical Laboratory Science, Faculty of Health Sciences, American University of Science and Technology, Aschrafieh, Beirut, Lebanon. john.haddad@yahoo.co.uk
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D003994:Bucladesine / Q000494:pharmacology; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D016207:Cytokines / Q000096:biosynthesis*; D004247:DNA / Q000378:metabolism; D004731:Endotoxins / Q000276:immunology*; D004848:Epithelium / Q000187:drug effects / Q000276:immunology*; D056747:Immunomodulation / Q000187:drug effects / Q000276:immunology*; D018836:Inflammation Mediators / Q000276:immunology; D008070:Lipopolysaccharides / Q000494:pharmacology; D016328:NF-kappa B / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D021122:Protein Subunits / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D011650:Pulmonary Alveoli / Q000187:drug effects / Q000276:immunology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects; D013935:Thymic Factor, Circulating / Q000494:pharmacology*; D015032:Zinc / Q000494:pharmacology*
D000893:Anti-Inflammatory Agents; D016207:Cytokines; D004731:Endotoxins; D018836:Inflammation Mediators; D008070:Lipopolysaccharides; D016328:NF-kappa B; D021122:Protein Subunits; D005576:Colforsin; D003994:Bucladesine; D004247:DNA; D013935:Thymic Factor, Circulating; D000242:Cyclic AMP; D015032:Zinc