Phosphodiesterase 5A inhibitors improve functional recovery after stroke in rats: optimized dosing regimen with implications for mechanism.

Phosphodiesterase 5A (PDE5A) inhibitors improve functional recovery after middle cerebral artery occlusion (MCA-o) in rats. We used the PDE5A inhibitor 3-(4-(2-hydroxyethyl)piperazin-1-yl)-7-(6-methoxypyridin-3-yl)-1-(2-propoxyethyl)pyrido[3,4-b]pyrazin-2(1H)-one hydrochloride (PF-5) to determine the timing, duration, and degree of inhibition that yields maximum efficacy. We also investigated the localization of PDE5A to determine the tissues and cells that would be targets for PDE5 inhibition and that may mediate efficacy. Nearly complete inhibition of PDE5A, starting 24 h after MCA-o and continued for 7 days, resulted in nearly complete recovery of sensorimotor function that was sustained for 3 months. Delaying administration until 72 h after MCA-o resulted in equivalent efficacy, whereas delaying treatment for 14 days was ineffective. Treatment for 7 days was equivalently efficacious to 28 or 84 days of treatment, whereas treatment for 1 day was less effective. In the normal forebrain, PDE5A immunoreactivity was prominent in smooth muscle of meningeal arteries and a few smaller blood vessels, with weak staining in a few widely scattered cortical neurons and glia. At 24 and 48 h after MCA-o, the number and intensity of blood vessel staining increased in the infarcted cortex and striatum. PDE5A immunoreactivity also was increased at 48 h in putative microglia in penumbra, whereas there was no change in staining of the scattered cortical neurons. Given the window for efficacy and the PDE5A distribution, we hypothesize that efficacy results from an effect on vasculature, and perhaps modulation of microglial function, both of which may facilitate recovery of neuronal function.

Phase response curve to melatonin in a putatively diurnal rodent, Octodon degus.

The degu (Octodon degus) is a diurnal rodent, although phase inversions to nocturnal behavior have been reported under specific laboratory conditions. The reliability of this animal as a diurnal model of sleep therefore requires further characterization of intrinsic circadian pacemaker properties. A phase response curve to light has been reported in the degu, and is consistent with other diurnal animals. This study reports a phase response curve to melatonin in the degu, which is distinct in orientation from the light curve.

Targeting the role of the endosome in the pathophysiology of Alzheimer's disease: a strategy for treatment.

Membrane-bound endosomal vesicles play an integral role in multiple cellular events, including protein processing and turnover, and often critically regulate the cell-surface availability of receptors and other plasma membrane proteins in many different cell types. Neurons are no exception, being dependent on endosomal function for housekeeping and synaptic events. Growing evidence suggests a link between neuronal endosomal function and Alzheimer's disease (AD) pathophysiology. Endosomal abnormalities invariably occur within neurons in AD brains, and endocytic compartments are one likely site for the production of the pathogenic beta-amyloid peptide (Abeta), which accumulates within the brain during the disease and is generated by proteolytic processing of the amyloid precursor protein (APP). The enzymes and events involved in APP processing are appealing targets for therapeutic agents aimed at slowing or reversing the pathogenesis of AD. The neuronal endosome may well prove to be the intracellular site of action for inhibitors of beta-amyloidogenic APP processing. We present here the view that knowledge of the endosomal system in the disease can guide drug discovery of AD therapeutic agents.

Personalized medicine for pathological circadian dysfunctions.

The recent approval of a therapeutic for a circadian disorder has increased interest in developing additional medicines for disorders characterized by circadian disruption. However, previous experience demonstrates that drug development for central nervous system (CNS) disorders has a high failure rate. Personalized medicine, or the approach to identifying the right treatment for the right patient, has recently become the standard for drug development in the oncology field. In addition to utilizing Companion Diagnostics (CDx) that identify specific genetic biomarkers to prescribe certain targeted therapies, patient profiling is regularly used to enrich for a responsive patient population during clinical trials, resulting in fewer patients required for statistical significance and a higher rate of success for demonstrating efficacy and hence receiving approval for the drug. This personalized medicine approach may be one mechanism that could reduce the high clinical trial failure rate in the development of CNS drugs. This review will discuss current circadian trials, the history of personalized medicine in oncology, lessons learned from a recently approved circadian therapeutic, and how personalized medicine can be tailored for use in future clinical trials for circadian disorders to ultimately lead to the approval of more therapeutics for patients suffering from circadian abnormalities.

A non-brain penetrant PDE5A inhibitor improves functional recovery after stroke in rats.

PURPOSE: Phosphodiesterase 5A (PDE5A) inhibitors improve functional recovery in experimental models of stroke in rats when treatment is delayed and without effect on infarct volume. PDE5A is expressed to only a very limited extent in forebrain tissues, raising the possibility that the locus of effect for the inhibitors is outside the brain. To start to address this question, we determined whether PDE5A inhibitors must have the ability to cross the blood brain barrier to improve recovery. METHOD: After permanent middle cerebral artery occlusion in rats, PF-5 and UK-489,791, PDE5A inhibitors that do or do not pass the blood brain barrier, were administered starting 24 h after occlusion and continued for 1 week. Motor function was assessed at intervals to 28 days using body swing and limb placement measures. RESULTS: Both PF-5 and UK-489,791 produced improvement in motor scores over 28 days that were significantly greater than in vehicle treated animals. There was no difference in efficacy between the two PDE5A inhibitors. CONCLUSIONS: Brain penetrability appears not to be critical to the ability of a PDE5A inhibitor to improve functional recovery after experimental stroke in rats. This finding is discussed with regard to the cellular target(s) for PDE5A inhibitors mediating this effect.