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Pharmacological suppression of RA synthesis via inhibition of ALDH1A1 may be a potential target for treatment of obesity.

Many inflammatory bowel disease (IBD) patients require surgical intervention due to limited pharmacological treatment options. Antibodies targeting α4ß7, a gut-homing integrin, are one of the most promising IBD treatments. As retinoic acid (RA) regulates expression of gut-homing proteins including α4ß7 integrin, we tested if ALDH1A enzymes in the RA synthesis pathway could be targeted for IBD treatment using a potent inhibitor, WIN 18,446. Age- and sex-matched Smad3−/− mice were fed a diet with and without WIN 18,446 for 3 weeks before triggering inflammation with Helicobacter bilis infection. Colitis was evaluated by histopathology one week following the IBD trigger, and T cell subsets were evaluated before and after the IBD trigger. WIN 18,446 treatment significantly reduced IBD severity in Smad3−/− mice and reduced expression of α4ß7 integrin on multiple activated CD4+ T cell subsets. This change was associated with increased ratios of induced regulatory T cells to Th17 cells during the inflammatory response in the draining lymph nodes. These studies indicate that RA reduction via ALDH1A enzyme inhibition is a potential new target for IBD treatment. Further studies are needed to examine its effects on other types of immune cells, to evaluate the efficacy window for this target, and to determine its efficacy in other animal models of IBD.

Background: Retinoic acid (RA) controls diverse physiological functions including weight regulation and energy metabolism. It has been reported that mice lacking ALDH1A1, one of the aldehyde dehydrogenases (ALDH) that synthesize RA, are healthy and resistant to weight gain, raising the possibility that inhibiting this enzyme might treat obesity. We previously demonstrated that treatment with a pan-ALDH1A enzyme inhibitor, WIN18446, suppressed weight gain in mice fed a high fat diet (HFD), but caused increased hepatic lipidosis and reversible male infertility. Methods: A series of piperazine compounds that inhibited ALDH1A1 were identified and their inhibitory activity was characterized in vitro using purified recombinant enzymes and cell-based assay systems. One potent compound, FSI-TN42 (N42) was examined for its oral bioavailability and pharmacodynamic effects. In addition, its effect on weight gain was investigated by daily oral administration to C57BL/6 male mice receiving a HFD, and compared with mice receiving WIN18446 or vehicle alone (n=6/group, 200 mg compound/kg body weight) for 5 weeks. Body weights were measured weekly, and a glucose tolerance test was performed after 4 weeks of treatment. Tissues were collected to determine changes in adipose weight, hepatic lipidosis, retinoid metabolism, and expression of genes associated with RA and lipid metabolism. Results: N42 irreversibly binds and inhibits ALDH1A1 in vitro with a low nM IC 50 and 800-fold specificity for ALDH1A1 compared to ALDH1A2. Daily oral administration of N42 significantly suppressed weight gain (P<0.05) and reduced visceral adiposity (p<0.05) in mice fed a HFD without the hepatic lipidosis observed with WIN18446 treatment. Conclusions: We developed a potent and specific inhibitor of ALDH1A1 that suppressed weight gain in mice fed a HFD. These findings demonstrate that inhibition of ALDH1A1 is a feasible target for drug development to treat and/or prevent obesity.

Retinoic acid (RA), the active form of vitamin A (retinol), is indispensable for maintaining many essential biological processes. RA formation depends on a complex network of enzymes. The rate limiting step is irreversible formation of RA by aldehyde dehydrogenase1A (ALDH1A1‐1A3). However, the specific roles, tissue expression, and localization of these enzymes are not well understood. While RA is necessary for spermatogenesis in animal models, the source of intratesticular RA is unknown. Sertoli cell specific ALDH1A knockouts have demonstrated intratesticular RA formation is required for male fertility. Due to the requirement for intratesticular RA formation and presence of mRNA for all three ALDH1A enzymes in the human testis, the human testis was chosen as a model of the biochemistry of RA formation. In order to model RA formation, a novel LC‐MS/MS based peptide quantification method was developed to quantify ALDH1A in a cohort of 18 men. Each ALDH1A concentration was used to predict the velocity of RA formation in each donor. The accuracy of our predictions was confirmed by measuring intrinsic RA formation and RA concentrations in the same samples. Additionally, weidentified a distinct localization pattern for ALDH1A enzymes in the human testis using immunohistochemistry. In conclusion, these novel techniques were successfully used to model RA formation in human testicular tissue. In the future, RA formation in other tissues can be investigated using the assays developed. Grant Funding Source: Supported by NIH/NICHD grant U54 HD042454 and TL1TR000422

WIN 18,446 treatment significantly reduces fecundity, but teratogenicity in the setting of contraceptive failure limits the appeal of this approach to female contraception.