A partial agonist for retinoid X receptor mitigates experimental colitis.

Inflammatory bowel disease (IBD), including ulcerative colitis and Crohn's disease, is an intractable disease of the gastrointestinal tract. Multiple environmental factors, including food ingredients, have been implicated in the development of these diseases. For example, animal fat-rich diets are predisposing factors for ulcerative colitis, whereas n-3 unsaturated fatty acids such as docosahexaenoic acid (DHA) show protective effects in experimental colitis and are negatively correlated with the incidence of ulcerative colitis and Crohn's disease. Given that DHA exhibits agonistic activity on retinoid X receptor (RXR), activation of RXR could be a therapeutic strategy for IBD. However, conventional full RXR agonists are known to show considerable adverse effects. We therefore took advantage of a partial RXR agonist, CBt-PMN, to minimize the adverse effects, and evaluated its efficacy in dextran sodium sulfate-induced colitis. Administration of CBt-PMN efficiently ameliorated the symptoms of colitis. This effect was attributed to the down-regulation of pro-inflammatory cytokines such as Tnf and Il6 in colon-infiltrating monocytes. Down-regulation of pro-inflammatory cytokines by CBt-PMN was also evident in lipopolysaccharide-stimulated bone marrow-derived macrophages (BMDMs). Among many RXR-associated nuclear receptors, activation of peroxisome proliferator-activated receptor δ (PPARδ) and nuclear hormone receptor 77 (Nur77) suppressed cytokine production by BMDMs. These observations suggest that the activation of PPARδ/RXR and Nur77/RXR heterodimers by CBt-PMN through the permissive mechanism is responsible for diminishing the monocyte-mediated inflammatory response in the gut. Our data highlight the importance of RXR activation in the regulation of colitis.

3H-Imidazo[4,5-b]pyridine-6-carboxylic acid derivatives as rexinoids with reduced teratogenicity.

Several retinoid X receptor (RXR) ligands (rexinoids), such as bexarotene (1), exhibit teratogenicity, which is a serious impediment to their clinical application. We considered that rexinoids with a lower level of maximal RXR transcription activation (i.e., partial agonists) and lower lipid solubility might show weaker adverse side effects. Based on this idea, we modified our previously reported pentamethyltetralin-type RXR partial agonists 5 and 6 to reduce their lipophilicity. Here, we report a new RXR partial agonist, 3-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydronaphthalen-2-yl)-2-(trifluoromethyl)-3H-imidazo[4,5-b]pyridine-6-carboxylic acid (8, CATF-PMN), which showed greatly reduced teratogenicity in zebrafish embryos.

Arm span-height difference is correlated with gastroesophageal reflux symptoms in aged Japanese subjects.

Previous studies have indicated an association between the symptoms of gastroesophageal reflux disease (GERD) and aging plus height. In this study we investigated whether the arm span-height difference was related to GERD symptoms with a focus on aged subjects in the general population, since the arm span reflects the height in young adulthood before decreasing due to vertebral deformities from aging. A total of 285 elderly individuals (105 females) who visited nursing homes for the elderly in Japan were enrolled in this study. The GERD symptoms were evaluated by the Frequency Scale for the Symptoms of GERD (FSSG). The body weight, height and arm span were measured, and information regarding medications and complications were reviewed in each nursing record. 50.5% of women had more than 3 cm of arm span-height difference. In contrast, only 37.3% of men had more than 3 cm of arm span-height difference. The FSSG scores indicated more than 70% of subjects complained of any GERD symptoms. There was a significant correlation between the FSSG score and the arm span-height difference in the subjects with more than 3 cm of arm span-height difference (r = 0.236; p = 0.012). The correlation between the arm span-height difference and the FSSG score was significant only in women in females in the present study. In conclusion, our findings indicate that vertebral deformity evaluated by the arm span-height difference might have some positive relationship to the pathogenesis of GERD symptoms in elderly Japanese individuals.

Teratogenicity and Fetal-Transfer Assessment of the Retinoid X Receptor Agonist Bexarotene.

Bexarotene, a retinoid X receptor (RXR) agonist, is used to treat cutaneous T-cell lymphoma, and drug repositioning research has also been reported, despite warnings of teratogenicity. However, fetal transfer of bexarotene and its effect on rat fetal bone formation have not been examined. In this study, we conducted a detailed teratogenicity and fetal transferability assessment of bexarotene in rats. Repeated administration of bexarotene during pregnancy caused marked fetal atrophy and bone dysplasia. Although fetal transfer was not detectable by dynamic imaging of [11C]bexarotene by means of positron emission tomography, transfer to the fetus was confirmed by using a gamma counter. Similar levels were found in mother and fetus. In addition, we found that bexarotene was accumulated in the placenta. These findings will be useful for the toxicity assessment of bexarotene as well as for drug discovery research targeting RXR agonists, which are expected to have therapeutic effects in various diseases.