Diet gel-based oral drug delivery system for controlled dosing of small molecules for microglia depletion and inducible Cre recombination in mice

Abstract

Small molecules like PLX5622 for microglia depletion and Tamoxifen for inducible Cre recombination are commonly used in mouse research. Traditional application methods, such as chow or oral gavage and injections, have limitations, including uncontrolled dosage and risk of injury. To address this issue, we have developed an alternative oral drug delivery system using a gel-based rodent maintenance diet that allows for controlled consumption and adjustment of dosage and is suitable for water-insoluble small molecules. We tested DietGel(R) 93M (93M) infused with PLX5622 (0.8 mg/g and 2.0 mg/g) in the Cx3cr1gfp/+ retinal microglia reporter mouse and Tamoxifen-infused 93M (0.3125 mg/g) in the Rlbp1-CreERT2;Rosaai14 mouse with an inducible tdTomato reporter in retinal Muller glia. Mice were single-caged and received daily batches of PLX5622-infused 93M over 14 days or Tamoxifen-infused 93M for one or three days followed by a 14-day observation period. Longitudinal scanning laser ophthalmoscopy in vivo and fixed tissue imaging were used to track GFP and tdTomato expression. Following evaluation of a suitable 93M consumption rate (g/d) to sustain body weight, the PLX5622-93M diet at both concentrations showed a 94% microglia depletion rate at 3 days and >99% after one and two weeks. The Tamoxifen-93M diet confirmed suitability for inducible Cre recombination, with significant treatment-time dependent efficacy and a positive correlation between total Tamoxifen dose and tdTomato expression. This study demonstrates that a diet gel-based drug delivery system offers a controllable and less invasive alternative to current drug application methods for PLX5622 and Tamoxifen.