In particular we focused our

In particular, we focused our attention on beta2 adrenergic receptors, since their commercial inhibitors are effective in lowering IOP, the primary indication of glaucoma. The hypotensive action of a commercial sequence of beta2 adrenergic receptor siRNA was tested in rabbits. The results confirmed the reduction of the IOP in rabbits, in a marked and sustained way. The frequency of application is a factor to be considered to achieve this IOP reduction in a reproducible mode. In this case, beta2 adrenergic receptor siRNA was administered daily in a single dose on four consecutive days in rabbits. This approach, the use of siRNA to reduce IOP has been also observed by other authors, with similar results to the ones here presented. In a clear difference with those works, the reduction in IOP observed at the highest siRNA concentration showed a decreased in IOP around 30% while in the work by Moreno-Montañes and co-workers it only reduced around 20%. Also, the concentrations used by these authors, up to 900μg/day are far from the doses here studied, which were 250μg/day. The present study was performed in rabbits while the one of 900μg/day was carried out in humans. Although the aqueous humors in rabbits and humans are not so different, it would be interesting to carry out experiments in humans to confirm the potential higher efficacy of the siRNA used in our work. The effect of beta2 adrenergic siRNA treatment was significantly longer in terms of time-effect as compared to conventional pharmacological agents. While the commercial compounds reduced IOP for a few hours, the siRNA effect lasted for several days. In a previous study, a single dose of a siRNA for the beta receptor, provided a mean time effect of 91h, while in our case it was about 120h. Therefore, it seems that comparing commercial compounds as well as other siRNA treatments already published, it seems that the characteristics of the sequence we use is also better producing a longer lasting effect. This long-lasting reduction of IOP may be one of the most attractive features of this new approach for the treatment of ocular Ethacrynic Acid and glaucoma since it could allow reducing the frequency of instillation and improving patient compliance. Moreover, taking into account that the frequent application of some commercial drugs currently used at high concentrations to achieve the desired therapeutic effects, can lead to adverse side effects due to systemic absorption (e.g., timolol can generate deleterious effect in the heart) the use of siRNA therapy could minimize these side effects. Likewise, it has been demonstrated that, on the contrary to an isolated compartment as the eye, siRNA stability in serum is decreased as a consequence of RNases activity. Thus, a reduced siRNA half-life in serum also would contribute to reduce the likelihood of systemic side effects. A potential limitation of our study is that we have not evaluated those possible systemic side effects. However, previous reports suggest the safety of siRNA treatment. In animal biodistribution studies only trace amounts of siRNA were detected in systemic organs (lung, liver and kidney) and the absence of 5′-phosphorylated antisense strand of siRNA (a marker of intracellular delivery of the siRNA) indicated that the siRNAs were not internalized by the cells and accordingly they are not biologically active. In addition, the analysis of several parameters (clinical signs, electrocardiogram, hematology) in toxicity studies performed with animals that received ocular administration of siRNA did not reveal any alterations, indicating the safety of siRNA treatment. Supporting these data, in a study with humans using a siRNA targeting the β2 adrenergic receptor, no significant changes were observed during the comprehensive clinical evaluations, monitoring of vital signs or electrocardiograms.
Conflicts of interest
Introduction Psychostimulant abuse and addiction remain a societal problem in the United States. The latest statistics from the National Survey on Drug Use and Health indicate that slightly less than one million people over the age of 12 report having a cocaine use disorder (NSDUH, 2016). Additionally, about 11% of American children have been diagnosed with Attention Deficit Hyperactivity Disorder (ADHD), with over 70% being treated with stimulant medications (Visser et al., 2014). A problem that has arisen is the misuse of ADHD medications for nonmedical purposes, with recent surveys finding approximately 1.7 million individuals in the United States abusing stimulant drugs without a prescription (NSDUH, 2016). A goal in understanding the mechanisms behind dependency and abuse of psychostimulant drugs is to explore relevant underlying circuitry, receptors and neurochemistry in the brain.