Citations

Wheelchair propulsion is a man-machine interaction in which chair design and fit affect the relative positions and orientations of the upper extremity relative to the handrim and wheel axle. To understand these relationships better, experimental data were collected in five hand positions from five subjects exerting maximal effort to propel an instrumented wheelchair with its wheel in a locked position. The results of experiments revealed that the progression moment was greater at both initial and terminal propulsion positions and smaller in the mid-propulsion position. The vertical and horizontal force components were directed radially away from the wheel axle posterior to the dead centre position and radially towards the wheel axle anterior to top dead centre. Subsequently, a subject-specific quasi-static model of the upper extremity which maximized wheel progression moment was developed to augment our understanding of experimental measures. Model-predicted trends in progression moments and hand force direction were similar to experiment. Model predictions revealed that the optimal progression moment generation could potentially be affected by an individual's anthropometric parameters, joint strengths and also the direction of force applied by the hand on the handrim. Through wheelchair fitting and training of wheelchair users, it may be possible to improve propulsion technique.

Gene transfer involves the use of an engineered biologic vehicle known as a vector to introduce a gene encoding a protein of interest into a particular tissue. In diseases with known defects at a genetic level, gene transfer offers a potential means of restoring a normal molecular environment via vector-mediated entry (transduction) and expression of genes encoding potentially therapeutic proteins selectively in diseased tissues. The technology of gene transfer therefore underlies the concept of gene therapy and falls under the umbrella of the current genomics revolution. Particularly since 1995, numerous attempts have been made to introduce genes into intracranial blood vessels to demonstrate and characterize viable transduction. More recently, in attempting to translate cerebrovascular gene transfer technology closer to the clinical arena, successful transductions of normal human cerebral arteries ex vivo and diseased animal cerebral arteries in vivo have been reported using vasomodulatory vectors. Considering the emerging importance of gene-based strategies for the treatment of the spectrum of human disease, the goals of the present report are to overview the fundamentals of gene transfer and review experimental studies germane to the clinical translation of a technology that can facilitate genetic modification of cerebral blood vessels.

The current study was designed to determine the effect of recombinant heme oxygenase-1 (HO-1) gene expression on endothelial function in cerebral arteries. Isolated canine basilar arteries were exposed ex vivo (30 minutes at 37°C) to an adenoviral vector (10 10 PFU/mL, total volume 300 μL) encoding either the HO-1 gene (AdCMVHO-1) or the β-galactosidase (β-Gal) reporter gene (AdCMVβ-Gal). Twenty-four hours after transduction, arterial rings were suspended in organ chamber for isometric force recording. Endothelium-dependent relaxations were obtained in response to bradykinin (10 −10 to 10 −6 mol/L) during contraction to uridine-5′-triphosphate (UTP; 3 × 10 −6 to 3 × 10 −5 mol/L). Certain rings were incubated with oxyhemoglobin (OxyHb; 10 −5 mol/L) overnight (16 to 18 hours of 24 hours). Expression and localization of recombinant protein were shown by Western blot analysis and immunohistochemistry. Endothelium-dependent relaxation to bradykinin and endothelium-independent relaxation to forskolin (10 −9 to 10 −5 mol/L) and DEA-NONOate (10 −10 to 10 −5 mol/L) were identical in β-Gal– and HO-1–transduced arteries. Exposure to OxyHb caused impairment of endothelium-dependent relaxation to bradykinin ( P < 0.01). In contrast, OxyHb did not affect endothelium-dependent relaxation in arteries expressing recombinant HO-1 ( P > 0.05). This protective effect of HO-1 was reversed by coincubation with tin protoporphyrin (SnPP9; 10 −5 mol/L), a selective inhibitor of HO-1 ( P < 0.01). Basal levels of 3′,5′-cyclic monophosphate (cGMP) in HO-1–transduced vessels were not significantly different from those in β-Gal–transduced vessels. Pretreatment with OxyHb significantly reduced cGMP level in β-Gal–transduced rings ( P < 0.01), whereas it had no effect in HO-1–transduced rings. These results demonstrate that HO-1 gene transfer does not affect endothelial and smooth muscle function of normal arteries, and that expression of recombinant HO-1 in cerebral arteries protects vasomotor function against OxyHb-induced injury.

This study was designed to determine the effect of subarachnoid hemorrhage (SAH) on potassium (K + ) channels involved in relaxations of cerebral arteries to nitrovasodilators. The effects of K + channel inhibitors on relaxations to 3-morpholinosydnonimine (SIN-1) and sodium nitroprusside (SNP) were studied in rings of basilar arteries obtained from untreated dogs and dogs exposed to SAH. The levels of cyclic GMP were measured by radioimmunoassay. In rings without endothelium, concentration-dependent relaxations to SIN-1 (10 −9 − 10 −4 mol/L) and SNP (10 −9 − 10 −4 mol/L) were not affected by SAH, whereas increase in cyclic GMP production stimulated by SIN-1 (10 −6 mol/L) was significantly suppressed after SAH. The relaxations to SIN-1 and SNP were reduced by charybdotoxin (CTX; 10 −7 mol/L), a selective Ca 2+ -activated K + channel inhibitor, in both normal and SAH arteries; however, the reduction of relaxations by CTX was significantly greater in SAH arteries. By contrast, the relaxations to these nitrovasodilators were not affected by glyburide (10 −5 mol/L), an ATP-sensitive K + channel inhibitor, in both normal and SAH arteries. These findings suggest that in cerebral arteries exposed to SAH, Ca 2+ -activated K + channels may play a compensatory role in mediation of relaxations to nitric oxide. This may help to explain mechanisms of relaxations to nitrovasodilators in arteries with impaired production of cyclic GMP.

This experiment examined the effects of nitric oxide (NO) synthase inhibition on brain intracellular pH, regional cortical blood flow, and NADH fluorescence before and during 3 h of focal cerebral ischemia using in vivo fluorescence imaging. Thirty fasted rabbits under 1% halothane were divided into four treatment groups receiving N ω -nitro-L-arginine methyl ester (L-NAME) intravenously at 20 min prior to ischemia (0.1, I, and 10 mg/kg and 1 mg/kg + 5 mg/kg L-arginine) and two control groups (nonischemic and ischemic). In ischemic controls, brain pH i declined to 6.73 ± 0.03 at 30 min and remained acidotic through the remainder of the ischemic period. In the 0.1 mg/kg group, brain pH i fell after 30 min of ischemia to 6.76 ± 0.05 ( p < 0.05), but then improved progressively despite occlusion. In the 1 mg/kg group, brain pH i remained normal despite middle cerebral artery (MCA) occlusion. In the 10 mg/kg group and in the combined L-NAME + L-arginine group, pH i fell after 30 min of ischemia to 6.81 ± 0.03 ( p < 0.05) and remained acidotic. During occlusion, regional cortical blood flow dropped in a dose-dependent manner. After 3 h of ischemia, regional cortical blood flow was 33.9 ± 10.9 and 25.1 ± 8.9 ml/100 g/min at doses of 0.1 and 10.0 mg/kg, respectively. L-NAME treatment did not significantly alter the increased NADH fluorescence that accompanied occlusion. This study shows that L-NAME can prevent intracellular brain acidosis during focal cerebral ischemia independent from regional cortical blood flow changes. This experiment suggests that NO is involved in pH i regulation during focal cerebral ischemia.

Heat shock protein 90 (HSP90), an essential component of several signal transduction systems, participates in the activation of endothelial nitric oxide synthase (eNOS) in cells. The objective of the current study was to determine if HSP90 and eNOS were functionally interdependent and colocalized in the cerebral circulation. The authors used isometric force recording, cyclic 3′5′-guanosine monophosphate (cGMP) radioimmunoassay (RIA), and immunogold electron microscopy (EM) to study canine basilar artery. They found that geldanamycin (0.1 to 10 μg/mL), a selective HSP90 inhibitor, caused concentration-dependent contractions in arterial rings (n = 6 dogs). Contractions to geldanamycin were unaffected by a cyclooxygenase inhibitor, indomethacin (10 μmol/L; P < 0.05, n = 6). Functional evidence for interaction between HSP90 and nitric oxide (NO)-mediated signaling included observations that the contractile effect of geldanamycin was the following: (1) endothelium-dependent, (2) abolished by N g -nitro-l-arginine methylester (L-NAME; 0.3 mmol/L), and (3) nonadditive with the contractile effect of this NOS inhibitor ( P < 0.01, n = 6 for each). Furthermore, RIA showed significant reduction in cGMP levels in arteries treated with geldanamycin (3 μg/mL; P < 0.02, n = 8), whereas immunogold EM demonstrated areas of colocalization of HSP90 and eNOS selectively in the cytoplasm of endothelial cells. The current findings suggest that in cerebral arteries, endothelial HSP90 plays an important role in modulation of basal NO-mediated signaling. This interaction may be particularly important in stress-induced up-regulation of HSP90 with subsequent alteration of vasomotor function.