Weight loss and metabolic effects of an ALDH1A1-specific inhibitor, FSI-TN42, in a diet induced mouse model of obesity.

Background: Retinoic acid (RA) participates in weight regulation and energy metabolism. Mice lacking ALDH1A1, one of the major enzymes responsible for RA biosynthesis, are resistant to diet-induced obesity. Previously, we identified FSI-TN42 (N42) as an ALDH1A1-specific inhibitor and reported its pharmacokinetics and pharmacodynamics as well as its efficacy in weight suppression.

Methods: In the first study, C57BL/6 J male mice were fed a high fat diet for 8 weeks to induce obesity. Mice were then divided into three groups and fed (1) moderate fat diet (MFD), (2) MFD + WIN 18,446 (1 g/kg diet), or (3) MFD + N42 (1 g/kg diet) for 8 weeks. A control group of mice were fed a low-fat diet for the entire period. Mice were weighed weekly and fasting glucose was determined every 4 weeks. Tissues were examined for potential toxicity using histopathology and complete blood counts. In the second study, we examined influences of N42 on energy balance and/or appetite by determining food intake, activity and energy expenditure in mice with obesity treated with MFD or MFD + N42. Lastly, we tested fertility with a mating study.

Results: N42 significantly accelerated weight loss compared to MFD alone in mice with obesity by reducing fat mass without decreasing lean mass. N42 did not alter food intake or activity levels. While mice treated with N42 lost significantly more weight, they maintained a similar level of energy expenditure compared to mice fed MFD only. Mice fed N42 preferentially used fat postprandially, especially under thermoneutral or mild cold challenge. N42 did not affect male fertility.

Conclusions: N42 promotes weight loss when used with MFD in mice with diet-induced obesity without causing significant organ toxicity or male infertility. Future studies will determine if N42 can be used to promote further weight loss if combined with current weight loss drugs.