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Vascular NADPH oxidases have been shown to be a major source of reactive oxygen species (ROS). Recent studies have also implicated ROS in the proliferation of vascular smooth muscle cells. However, the components required for activation of the NADPH oxidase complex have not been clearly elucidated. Here we demonstrate that ROS generation in ovine pulmonary arterial smooth muscle cells (PASMCs) requires the activation of Rac1, implicating this protein as an important subunit of the NADPH oxidase complex. Our results, using a geranylgeranyl transferase inhibitor (GGTI-287), demonstrated a dose-dependent inhibition of Rac1 activity and ROS production. This was associated with an inhibition of PASMC proliferation with an arrest at G2/M. The inhibition of Rac1 by GGTI-287 led us to more specifically target Rac1 to investigate its role in the generation of ROS and cellular proliferation. To accomplish this, we utilized a dominant negative Rac1 (N17Rac1) and a constitutively active Rac1 (V12Rac1). These two forms of Rac1 were transiently expressed in PASMCs using adenovirus-mediated gene transfer. N17Rac1 expression resulted in decreased cellular Rac1 activity, whereas V12Rac1 infection showed increased activity. Compared with controls, the V12Rac1-expressing cells had higher levels of ROS production and increased proliferation, whereas the N17Rac1-expressing cells had decreased ROS generation and proliferation and cell cycle arrest at G2/M. However, the inhibition of cell growth produced by N17Rac1 overexpression could be overcome if cells were co-incubated with the Cu,Zn superoxide dismutase inhibitor DETC. These results indicate the importance of Rac1 in ROS generation and proliferation of vascular smooth muscle cells.

Machining of titanium alloys generates enormous amount of heat at the chip-tool interface leading to poor machinability. The current research investigates the effect of dry machining of Ti6Al4V on surface integrity of machined workpiece. A change in subsurface deformation was assessed by varying cutting speed and feed rate keeping the cut depth constant. Various output responses viz. cutting temperature, surface finish, induced strain, deformed depth, microhardness, etc. were discussed to evaluate the surface integrity. An optical microscopy, SEM and EBSD analysis performed on the machined edge showed deformation induced damage with microstructural restructuring which was correlated with chip microstructure. At lower cutting parameters, work hardening phenomenon however; at high cutting parameters thermal softening phenomenon becomes more dominant. This was derived with increased surface roughness, reduction in microhardness values beneath the machined surface and coarse microstructure obtained at higher cutting parameters. A Chip microstructural analysis validates the thermal softening and work hardening phenomenon where at high cutting speeds and feed rate the shear band formation is increased accompanied with increased chip segmentation frequency. However, at lower cutting parameters the reduction segmentation frequency and more deformed grains near shear band were observed.