In vivo toxicology of excipients commonly employed in drug discovery in rats.

INTRODUCTION: Toxicology and pharmacology studies conducted in the early stages of drug discovery often require formulation strategies involving the use of excipients with limited knowledge regarding their preclinical safety liabilities. The use of excipients is vital to efforts to solubilize and deliver small molecules in drug discovery. Whilst excipients can have a significant impact on pharmacology and toxicology studies by enabling solubility to maximize systemic exposure, they also have the potential to obscure clinical pathology endpoints. In this article, we report on the in vivo safety in rats for 18 excipients commonly employed in formulations for preclinical pharmacology and toxicology studies. METHODS: The test articles were administered once daily for five days, by oral gavage to male Sprague Dawley rats, and the animals monitored for visible clinical signs. At the end of the study, routine necropsy and clinical pathology endpoints were investigated. RESULTS: None of the excipients tested were acutely toxic. However, there were effects on parameters commonly evaluated as indicators of health and/or toxicological response in regulated preclinical safety studies. DISCUSSION: While the excipients tested were generally well tolerated, several were found to affect common clinical pathology endpoints in a manner that might confound or conceivably mask the interpretation of compound mediated adverse/pharmacological effects.

Improved glycemic control in mice lacking Sglt1 and Sglt2.

Sodium-glucose cotransporter 2 (SGLT2) is the major, and SGLT1 the minor, transporter responsible for renal glucose reabsorption. Increasing urinary glucose excretion (UGE) by selectively inhibiting SGLT2 improves glycemic control in diabetic patients. We generated Sglt1 and Sglt2 knockout (KO) mice, Sglt1/Sglt2 double-KO (DKO) mice, and wild-type (WT) littermates to study their relative glycemic control and to determine contributions of SGLT1 and SGLT2 to UGE. Relative to WTs, Sglt2 KOs had improved oral glucose tolerance and were resistant to streptozotocin-induced diabetes. Sglt1 KOs fed glucose-free high-fat diet (G-free HFD) had improved oral glucose tolerance accompanied by delayed intestinal glucose absorption and increased circulating glucagon-like peptide-1 (GLP-1), but had normal intraperitoneal glucose tolerance. On G-free HFD, Sglt2 KOs had 30%, Sglt1 KOs 2%, and WTs <1% of the UGE of DKOs. Consistent with their increased UGE, DKOs had lower fasting blood glucose and improved intraperitoneal glucose tolerance than Sglt2 KOs. In conclusion, 1) Sglt2 is the major renal glucose transporter, but Sglt1 reabsorbs 70% of filtered glucose if Sglt2 is absent; 2) mice lacking Sglt2 display improved glucose tolerance despite UGE that is 30% of maximum; 3) Sglt1 KO mice respond to oral glucose with increased circulating GLP-1; and 4) DKO mice have improved glycemic control over mice lacking Sglt2 alone. These data suggest that, in patients with type 2 diabetes, combining pharmacological SGLT2 inhibition with complete renal and/or partial intestinal SGLT1 inhibition may improve glycemic control over that achieved by SGLT2 inhibition alone.

Increased intraocular pressure in mice treated with dexamethasone.

PURPOSE: Glucocorticoids are potent modulators of the immune system and are useful in treating systemic and ocular diseases, but they can increase intraocular pressure (IOP) in susceptible persons. Steroid-induced ocular hypertension resembles several characteristics observed in primary open angle glaucoma (POAG). Elucidating genetic and environmental mechanisms impacting steroid-induced ocular hypertension may provide important insight into pathophysiological drivers of POAG. The purpose of this study was to create a mouse model of steroid-induced ocular hypertension. METHODS: Osmotic mini-pumps delivering dexamethasone or PBS were implanted into C57BL/6J-Tyr(c-Brd) × 129S5/SvEvBrd (B6.129) mice. Repeated IOP measurements were obtained over a 4-week study using a tonometer before and after pump implantation. Body weights, complete blood counts (CBCs), and blood pressure were obtained to further characterize the model. Pharmacologic effects of timolol, latanoprost, and Y-39983 were studied in hypertensive mice. RESULTS: Administration of dexamethasone to B6.129 hybrid mice resulted in significant increases in IOP in most animals compared with baseline or mice treated with PBS. No significant change in IOP was observed in PBS-treated mice. Interestingly, dexamethasone failed to increase IOP in a subset of mice, though steroid delivery was successful as measured using CBC analysis. Moreover, topical agents that lower IOP in normotensive mice also produced significant decreases in mice exhibiting elevated IOP in response to dexamethasone. CONCLUSIONS: Systemic treatment with dexamethasone significantly increased IOP in most genetically heterogeneous mice used in this study. This mouse model should facilitate studies aimed at understanding mechanisms affecting steroid-induced ocular hypertension in humans.