BackgroundThis study aimed to measure the gait abnormalities in GRMD (Golden retriever muscular dystrophy) dogs during growth and disease progression using an ambulatory gait analyzer (3D-accelerometers) as a possible tool to assess the effects of a therapeutic intervention.MethodsSix healthy and twelve GRMD dogs were evaluated twice monthly, from the age of two to nine months. The evolution of each gait variable previously shown to be modified in control and dystrophin-deficient adults was assessed using two-ways variance analysis (age, clinical status) with repeated measurements. A principal component analysis (PCA) was applied to perfect multivariate data interpretation.ResultsSpeed, stride length, total power and force significantly already decreased (p < 0.01) at the age of 2 months. The other gait variables (stride frequency, relative power distributions along the three axes) became modified at later stages. Using the PCA analysis, a global gait index taking into account the main gait variables was calculated, and was also consistent to detect the early changes in the GRMD gait patterns, as well as the progressive degradation of gait quality.ConclusionThe gait variables measured by the accelerometers were sensitive to early detect and follow the gait disorders and mirrored the heterogeneity of clinical presentations, giving sense to monitor gait in GRMD dogs during progression of the disease and pre-clinical therapeutic trials.

Cardiomyopathy in GRMD dogs is characterized by profound LV subendocardial dysfunction, abnormal sarcomeric protein phosphorylation, and impaired e/nNOS, which can be normalized by bradykinin treatment. These data provide new insights into the pathophysiological mechanisms accounting for DMD cardiomyopathy and open new therapeutic perspectives.

Little is known about the vascular function and expression of endothelial and neuronal nitric oxide synthases (eNOS and nNOS) in Duchenne muscular dystrophy (DMD). Bradykinin is involved in the regulation of eNOS expression induced by angiotensin-converting enzyme inhibitors. We characterized the vascular function and eNOS and nNOS expression in a canine model of DMD and evaluated the effects of chronic bradykinin treatment. Vascular function was examined in conscious golden retriever muscular dystrophy (GRMD) dogs with left ventricular dysfunction (measured by echocardiography) and in isolated coronary arteries. eNOS and nNOS proteins in carotid arteries were measured by western blot and cyclic guanosine monophosphate (cGMP) content was analyzed by radioimmunoassay. Compared with controls, GRMD dogs had an impaired vasodilator response to acetylcholine. In isolated coronary artery, acetylcholine-elicited relaxation was nearly absent in placebo-treated GRMD dogs. This was explained by reduced nNOS and eNOS proteins and cGMP content in arterial tissues. Chronic bradykinin infusion (1 μg/min, 4 weeks) restored in vivo and in vitro vascular response to acetylcholine to the level of control dogs. This effect was NO-mediated through upregulation of eNOS and nNOS expression. In conclusion, this study is the first to demonstrate that DMD is associated with NO-mediated vascular endothelial dysfunction linked to an altered expression of eNOS and nNOS, which can be overcome by bradykinin.