Increased expression of glucagon-like peptide-1 and cystic fibrosis transmembrane conductance regulator in the ileum and colon in mouse treated with metformin.

Metformin, an oral medication, is prescribed to patients with type 2 diabetes mellitus. Although the efficacy, safety, and low economic burden of metformin on patients have long been recognized, approximately 5% of the patients treated with this drug develop severe diarrhea and discontinue the treatment. We previously reported that 1,000 mg·kg-1·day-1 of metformin induced diarrhea in diabetic obese (db/db) mice and wood creosote (traditional medication for diarrhea) ameliorated the symptoms. In this study, we attempted to elucidate the molecular mechanisms by which metformin induces diarrhea. Cystic fibrosis transmembrane conductance regulator (CFTR) is a key ion (chloride) channel in cyclic adenosine monophosphate (cAMP)-induced diarrhea. Metformin treatment increased bile flow (bile acids and bilirubin) in the ileum of mice. In addition, the treatment was accompanied by an increase in mRNA and protein levels of CFTR in the mucosa of the ileum and colon in both wild-type (C57BL/6J) and db/db mice. Glucagon-like peptide-1 (GLP-1), as well as cholic acid, induces CFTR mRNA expression in human colon carcinoma Caco-2 cells through cAMP signaling. Although wood creosote (10 mg/kg) ameliorated diarrhea symptoms, it did not alter the mRNA levels of Glp-1 or Cftr. Similar to overeating, metformin upregulated GLP-1 and CFTR expression, which may have contributed to diarrhea symptoms in mice. Although we could not identify db/db mouse-specific factors associated with metformin-induced diarrhea, these factors may modulate colon function. Wood creosote may not interact with these factors but ameliorates diarrhea symptoms.

Visualization of mitophagy using LysoKK, a 7-nitro-2,1,3-benzoxadiazole-(arylpropyl)benzylamine derivative.

7-Nitro-2,1,3-benzoxadiazole (NBD) is an environmentally responsive fluorophore. We have reported that GIF2114 and GIF2115, anti-ferroptotic N,N-dimethylaniline-compounds, localize to lysosome when they are visualized by NBD. Here we show that the NBD fluorescence of GIF2259, a hybrid derivative of GIF2114 and GIF2115, was quenched in aqueous buffer. However, the fluorescence was recovered when GIF2259 was localized on lysosomes. Although the dimethylamine group of GIF2259 is not essential for the lysosome localization, it contributes to a high specific/nonspecific ratio of fluorescence. Under a normal condition, the lysosomal signal visualized by GIF2259 did not overlap with mitochondria, while, under starved or depolarization conditions, it overlapped with mitochondria, suggesting that GIF2259 could be used as a simple tool for monitoring lysosomal metabolism and mitochondrial turnover, that is mitophagy.