Nitric oxide (NO) from constitutive NO synthase (NOS) has been postulated to be a homeostatic regulator of leukocyte-endothelial cell interactions. By contrast, the inducible NO synthase (iNOS) isoform has been invoked as a potential pathogenic enzyme in numerous inflammatory diseases. The objective of this study was to determine whether the iNOS isoform is also capable of functioning as a regulator of leukocyte recruitment. Mice received endotoxin (LPS, 30 microg/kg, i.v.); 2-4 h later, intravital microscopy was used to examine leukocyte rolling and adhesion in postcapillary venules of the cremaster muscle and the sinusoids and postsinusoidal venules of the hepatic microcirculation. Leukocyte recruitment into the lung was also examined. RT-PCR confirmed that this treatment induced iNOS mRNA expression in wild-type mice as early as 2 h after LPS treatment. Between 2 and 4 h after LPS administration, the number of rolling and adherent leukocytes in cremasteric postcapillary venules and of adherent cells in liver postsinusoidal venules of iNOS-deficient mice were significantly higher than in wild-type mice. Leukocyte accumulation in the lung (measured by myeloperoxidase assay) was also significantly elevated in iNOS-deficient animals. These effects could not be attributed to differences in systemic blood pressure, shear rates, circulating leukocyte numbers, or baseline levels of rolling and adhesion because these parameters were not different between the two groups. To establish whether the differences in leukocyte recruitment were related to the leukocytes per se, perfusion of iNOS+/+ or iNOS-/- septic blood over purified E-selectin (using parallel plate flow chambers) revealed much larger recruitment of iNOS-/- leukocytes. These results suggest that iNOS induced in response to LPS releases NO that is capable of reducing leukocyte accumulation by affecting leukocytes directly and raises the possibility that induction of iNOS is a homeostatic regulator for leukocyte recruitment.

Background-Studies using inhibitors of nitric oxide synthase (NOS) to date are inconclusive regarding the role of inducible NOS (iNOS) in intestinal inflammation. Aims-(1) To examine the role of iNOS in the development of chronic intestinal inflammation; (2) to identify the cellular source(s) of iNOS. Methods-Colitis was induced by an intrarectal instillation of trinitrobenzene sulphonic acid (TNBS, 60 mg/ml, 30% ethanol), in wild type (control) or iNOS deficient mice. Mice were studied over 14 days; the colons were scored for injury and granulocyte infiltration was quantified. Blood to lumen leakage of 51 Cr-EDTA was measured as a quantitative index of mucosal damage. Results-At 24 and 72 hours, iNOS deficient mice had significantly increased macroscopic inflammation compared with wild type mice. Granulocyte infiltration increased significantly at 24 hours and remained elevated in iNOS deficient mice at 72 hours, but significantly decreased in controls. However, by seven days post-TNBS macroscopic damage, microscopic histology, granulocyte infiltration, and mucosal permeability did not diVer between wild type and iNOS deficient mice. A four-to fivefold increase in iNOS mRNA was observed in wild type mice at 72 hours and seven days post-TNBS and was absent in iNOS deficient mice. Immunohistochemistry techniques showed that iNOS expression was predominantly localised in neutrophils, with some staining also in macrophages. Conclusions-These results suggest that leucocyte derived iNOS ameliorates the early phase, but does not impact on the chronic phase of TNBS induced colitis despite the presence of iNOS. (Gut 1999;45:864-873)

Mice deficient in both inducible nitric oxide synthase (iNOS) and interleukin (IL)-10 (iNOS(-/-)/IL-10(-/-)) were created to examine the role of iNOS in spontaneously developing intestinal inflammation. IL-10(-/-)/iNOS(-/-) mice were compared with IL-10(-/-) (iNOS(+/+)) littermates over 6 mo. RT-PCR, Western blot analysis, and immunohistochemistry were performed to measure iNOS message and protein levels. Plasma nitrate/nitrite (NO(x)) levels were assessed by HPLC. Damage scores (macroscopic and microscopic) and granulocyte infiltration were assessed. At 3-4 wk, IL-10(-/-) and IL-10(-/-)/iNOS(-/-) mice had no signs of colonic inflammation or granulocyte infiltration. Plasma NO(x) levels were not different from controls. By 3-4 mo, IL-10(-/-) mice had increased damage scores and granulocyte infiltration concurrent with increased mRNA and protein synthesis (restricted to the epithelium) for iNOS in intestinal tissues but not other tissues. Plasma NO(x) levels increased fivefold. Interestingly, in the absence of iNOS induction or increased plasma NO(x), iNOS(-/-)/IL-10(-/-) mice had damage and granulocyte infiltration equivalent to those observed in IL-10(-/-) littermates. These data suggest that iNOS does not impact on the development or severity of spontaneous chronic inflammation in IL-10-deficient mice.

Staphylokinase is a promising blood-clot dissolving agent for the treatment of patients suffering from a heart attack. It would be desirable to produce this protein in large quantities for biochemical characterization and clinical trials. Production of intact, biologically active staphylokinase from bacterial expression systems has been a challenge because of N-terminal microheterogeneity, plasmid instability, or low-production yield. By using a seven-extracellular-protease deficient Bacillus subtilis strain, WB700, intact staphylokinase can be produced via secretion. However, native staphylokinase gene (sak) in a high-copy number plasmid was found to be unstable in B. subtilis. To optimize the production and the stability of the expression vectors, both the promoter and the signal sequence of sak were replaced by B. subtilis promoters (P43, a constitutively expressed promoter; Pamy, a stationary-phase promoter; and PsacB, a sucrose-inducible promoter) and the levansucrase-signal sequence, respectively. This overcame the plasmid instability problem. To enhance transcription from the sacB promoter, degQ encoding a transcriptional activator for sacB and other protease genes was also installed in the expression vector. The use of WB700 as the expression host allowed enhanced production of staphylokinase from the sucrose-inducible plasmid without causing any obvious degradation of staphylokinase. Both the P43 and PsacB (with DegQ) promoters worked well. Over 90% of staphylokinase synthesized can be secreted effectively. With the optimization of both the culture media and the fermentation conditions, production of staphylokinase reached a level of 337 mg/L, and staphylokinase could be purified to homogeneity by a simple three-step purification scheme. Secreted staphylokinase did not show any N-terminal heterogeneity. This presents an attractive system for the production of staphylokinase in both high quality and quantity.