Publications

The development of progressive glomerulosclerosis in the renal ablation model has been ascribed to a number of humoral and hemodynamic events, including the peptide growth factor, transforming growth factor-beta 1 (TGF-beta 1). An important role has also been attributed to angiotensin II (AII), which, in addition to its hemodynamic effects, can stimulate transcription of TGF-beta 1. We postulated that increased glomerular production of AII, resulting from enhanced intrinsic angiotensinogen expression, stimulates local TGF-beta 1 synthesis, activating glomerular matrix protein synthesis, and leads to sclerosis. Using in situ reverse transcription, the glomerular cell sites of alpha-1 (IV) collagen, fibronectin, laminin B1, angiotensinogen, and TGF-beta 1 mRNA synthesis were determined at sequential periods following renal ablation. The early hypertrophic phase was associated with global, but transient, increases in the mRNA for alpha-1 (IV) collagen. No changes were noted for fibronectin, TGF-beta 1, and angiotensinogen mRNAs. At 24 d after ablation, at which time sclerosis is not evident, endothelial cells, particularly in the dilated capillaries at the vascular pole, expressed angiotensinogen and TGF-beta 1 mRNAs, as well as fibronectin and laminin B1 RNA transcripts. By 74 d after ablation angiotensinogen and TGF-beta 1 mRNAs were widely distributed among endothelial and mesangial cells, and were particularly prominent in regions of evolving sclerosis. These same regions were also notable for enhanced expression of matrix protein mRNAs, particularly fibronectin. All receptor blockade inhibited angiotensinogen, TGF-beta 1, fibronectin, and laminin B1 mRNA expression by the endothelium. We conclude that, as a result of hemodynamic changes, injured or activated endothelium synthesizes angiotensinogen, triggering a cascade of TGF-beta 1 and matrix protein gene expression with resultant development of the segmental glomerular sclerotic lesion.

The integrin alpha v beta 6 was initially identified from primary cultures of airway epithelial cells. This integrin is expressed in bronchiolar and alveolar epithelium during development and in settings of injury and/or inflammation and mediates attachment of epithelial cells to fibronectin and tenascin. Like other integrins, this receptor localizes to structures called focal contacts in cells plated on appropriate ligands. In the present study, we produced a mutant beta 6 cDNA (beta 6m) containing a single substitution of Asp140 with Ala and transfected mutant (or wild-type) beta 6 cDNA into the human colon carcinoma cell line SW480. In parallel, we used cDNAs truncated just proximal to the transmembrane domain to generate secreted forms of mutant alpha v beta 6 in Chinese hamster ovary (CHO) cells. The mutant beta 6, like the wild type, formed heterodimers with human alpha v that were expressed on the cell surface of SW480 cells and secreted by CHO cells. Secreted alpha v beta 6 containing this point mutation did not bind to fibronectin-Sepharose. Furthermore, in contrast to wild-type beta 6, the mutant form did not allow SW480 cells to bind to fibronectin in the presence of beta 1-blocking antibody and did not localize to focal contacts. Our results confirm that the Asp140 of beta 6, like the corresponding residues in beta 1 (Asp130) and beta 3 (Asp119), is critical for interactions of alpha v beta 6 with ligand, and also suggest that ligand binding to alpha v beta 6 is necessary for localization of this receptor to focal contacts.

BACKGROUND

Metal fume fever is a flu-like illness caused by zinc oxide fume inhalation and mediated by unknown mechanisms. It is one of a group of work-related febrile inhalational syndromes. We studied bronchoalveolar lavage (BAL) obtained from cigarette smoking and nonsmoking human volunteers after controlled exposure to purified zinc oxide fume to explore the possible roles of proinflammatory cytokines in this condition.

METHODS

We studied 14 volunteers after inhalation exposure to purified zinc oxide fume and after sham exposure to air. The mean cumulative exposure was 537 +/- 232 mg min per cubic meter elemental zinc. Twenty hours after exposure we performed BAL. We analyzed BAL cells and studied BAL supernatant for cytokines including tumor necrosis factor-alpha (TNF alpha), interleukin(IL)-8, and IL-1 by enzyme-linked immunosorbant assay (ELISA).

RESULTS

Polymorphonuclear leukocytes (PMNs) were significantly increased in the BAL fluid obtained post-exposure compared to sham (mean difference = 41.3 +/- 16.8 x 10(3) per mL; p < 0.05). Cumulative zinc exposure positively correlated with exposure-sham differences in BAL supernatant concentrations of both TNF (r2 = 0.58; p = .002) and IL-8 (r2 = 0.44, p = 0.01). Exposure-sham concentration differences in BAL supernatant IL-8 and BAL PMNs were also positively correlated (r2 = 0.60; p < 0.001). Cigarette smoking was not associated with exposure-sham differences in BAL TNF or IL-8, but did demonstrate a packs-per-day dependent increase in BAL supernatant IL-1 (t = 2.3, p = 0.04) post-exposure compared to sham, after taking into account the zinc exposure response.

CONCLUSIONS

Purified zinc oxide fume inhalation causes an exposure-dependent increase in proinflammatory cytokines and PMNs in the lung. This supports a role for cytokine networking in mediating metal fume fever.