GLP-1 agonists such as exendin-4 (EX4) are used in the treatment of type 2 diabetes and have the additional benefit of promoting weight loss. GLP-1 agonists decrease feeding through peripheral affects, but recent evidence suggests they may also influence sweet or high fat preference, as well as the motivation to obtain these tastants. Yet it remains unclear how GLP-1 induced alterations in food preference influences the decrease in overall feeding. The current study sought to determine if EX4 affects the reinforcing strength and consumption of a highly palatable sweet/fat reinforcer. Rats were trained to self-administer sweetened vegetable shortening (SVS) under fixed (FR) and progressive ratio (PR) schedules of reinforcement. EX4 (0.3 - 2.4 μg/kg, IP) administered one hour prior to operant sessions significantly reduced responding for SVS under both FR and PR schedules (e.g. total reinforcers and breakpoints, respectively), although the lowest active dose (0.6 μg/kg) significantly suppressed FR responding only. EX4 also dose dependently decreased locomotor activity (0.6-2.4 μg/kg doses), but did not enhance acute kaolin intake, indicating that EX4-induced nausea did not influence the self-administration results. Analysis of ED50 values show that EX4 is more effective at inhibiting FR responding versus PR, indicating that EX4 may have more potent effects on consummatory versus appetitive feeding behaviors. Although EX4 caused generalized behavioral suppression, these results cannot fully explain the decreases in operant responding. For example, the 0.6 μg/kg dose inhibited only FR responding, even though the rats were physically capable of responding at a higher rate during PR sessions. In addition, the rate of intake was constant at the beginning of the sessions in both PR and FR schedules, regardless of the dose. Together these data suggest that EX4 inhibits consumption of a palatable high sweet/high fat reinforcer potentially through altering satiety.
PurposeTo systematically evaluate human rod opsin (hRHO) mRNA for potential target sites sensitive to posttranscriptional gene silencing (PTGS) by hammerhead ribozyme (hhRz) or RNA interference (RNAi) in human cells. To develop a comprehensive strategy to identify and optimize lead candidate agents for PTGS gene therapeutics.MethodsIn multidisciplinary RNA drug discovery, computational mRNA accessibility and in vitro experimental methods using reverse transcription–polymerase chain reaction (RT-PCR) were used to map accessibility in full-length hRHO transcripts. HhRzs targeted predicted accessible and inaccessible sites and were screened for cellular knockdown using a bicistronic reporter construct. Lead hhRz and RNAi PTGS agents were rationally optimized for target knockdown in human cells.ResultsSystematic screening of hRHO mRNA targeting agents resulted in lead candidate identification of a novel hhRz embedded in an RNA scaffold. Rational optimization strategies identified a minimal 725 hhRz as the most active agent. Recently identified tertiary accessory elements did not enhance activity. A 725-short-hairpin RNA (shRNA) agent exerts log-order knockdown. Silent modulation of the 725-hhRz target site in hRHO mRNA resulted in resistance to knockdown.ConclusionsCombining rational RNA drug design with cell-based screening allowed rapid identification of lead agents targeting hRHO. Optimization strategies identified the agent with highest intracellular activity. These agents have therapeutic potential in a mutation-independent strategy for adRP, or other degenerations where hRHO is a target. This approach can be broadly applied to any validated target mRNA, regardless of the disease.Translational RelevanceThis work establishes a platform approach to develop RNA biologicals for the treatment of human disease.
Hammerhead ribozymes (hhRzs), RNA enzymes capable of site-specific cleavage of arbitrary target mRNAs, have faced significant hurdles in development and optimization as gene therapeutics for clinical translation. Chemical and biological barriers must be overcome to realize an effective therapeutic. A new Facilitated ribozyme has been identified with greatly enhanced kinetic properties that lead new insight on the capacity of ribozymes to target mutant genes to treat inherited retinal degenerations.
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