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.
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
John J
JJ
Haddad
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