We investigated the concept of using bioactive substrates as templates for in vitro synthesis of bone tissue for transplantation by assessing the osteogenic potential of a melt-derived bioactive glass ceramic (Bioglass 45S5) in vitro. Bioactive glass ceramic and bioinert (plastic) substrates were seeded with human primary osteoblasts and evaluated after 2, 6, and 12 days. Flow cytometric analysis of the cell cycle suggested that the bioactive glass-ceramic substrate induced osteoblast proliferation, as indicated by increased cell populations in both S (DNA synthesis) and G2/M (mitosis) phases of the cell cycle. Biochemical analysis of the osteoblast differentiation markers alkaline phosphatase (ALP) and osteocalcin indicated that the bioactive glass-ceramic substrate augmented osteoblast commitment and selection of a mature osteoblastic phenotype. Scanning electron microscopic observations of discrete bone nodules over the surface of the bioactive material, from day 6 onward, further supported this notion. A combination of fluorescence, confocal, transmission electron microscopy, and X-ray microprobe (SEM-EDAX) examinations revealed that the nodules were made of cell aggregates which produced mineralized collagenous matrix. Control substrates did not exhibit mineralized nodule formation at any point studied up to 12 days. In conclusion, this study shows that Bioglass 45S5 has the ability to stimulate the growth and osteogenic differentiation of human primary osteoblasts. These findings have potential applications for tissue engineering where this bioactive glass substrate could be used as a template for the formation of bioengineered bone tissue.

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Background-In animal models of cirrhosis, altered activity of nitric oxide (NO) has been implicated in the pathogenesis of increased intrahepatic portal vascular resistance and abnormal mesenteric vasodilatation. Aims-To investigate NO activity in the liver and splanchnic vascular bed of patients with cirrhosis. Methods-Activity of the calcium dependent constitutive and calcium independent inducible isoforms of NO synthase (cNOS and iNOS, respectively) was assayed biochemically in biopsy specimens of liver and a vascular portion of the greater omentum (representative of mesenteric vasculature) obtained from patients with cirrhosis undergoing liver transplantation (n=14) and non-cirrhotic control patients undergoing liver resection for metastases (n=9). The concentration of NO metabolites (NO 2 + NO 3 ) in portal and peripheral venous plasma was measured. Results-The activity of cNOS was lower in cirrhotic compared with non-cirrhotic subjects for both liver and omentum. Hepatic and omental iNOS activities did not diVer significantly between the two groups. Portal (NO 2 + NO 3 ) was threefold higher in cirrhotic than non-cirrhotic patients, but no diVerences were observed in systemic venous samples from the two groups. Conclusions-The activity of cNOS is diminished in the cirrhotic human liver. The resultant decrease in constitutive NO release may promote an increase in the intrahepatic portal vascular resistance. Elevated portal venous (NO 2 + NO 3 ) indicates enhanced splanchnic vascular release of NO in cirrhotic patients, but the absence of increased NOS activity in the mesenteric vasculature suggests diVerential regulation of NO synthesis within the splanchnic vascular bed. (Gut 1999;44:749-753)

Aseptic loosening is a major cause of failure of total hip arthroplasty. The adverse tissue response to prosthetic wear particles, with activation of cytokine and prostanoid production, contributes to bone loss around the implants. We have investigated the possibility that inducible nitric oxide synthase (iNOS) and cyclo-oxygenase-2 (COX-2) are expressed in macrophages in the pseudomembrane at the bone-implant interface, thereby contributing to the periprosthetic bone resorption.We also assessed whether peroxynitrite, a nitric oxide (NO)-derived oxidant associated with cellular injury, is generated in the membrane. Enzymatic activity of iNOS was measured using the arginine-citrulline assay technique and prostaglandin E 2 (PGE 2 ), as an indicator of COX-2 activity, was measured using an enzyme immunoassay.Cellular immunoreactivity for iNOS, nitrotyrosine (a marker of peroxynitrite-induced cellular injury) and COX-2 was assessed by quantitative peroxidase immunocytochemistry while immunofluorescence methods were used for subsequent co-localisation studies with CD68 + macrophages.