Capsaicinoids prevent intestinal fluid secretion and motility by inhibiting chloride channels

In traditional Chinese medicine, chili peppers and their seeds have been utilized for the treatment of watery diarrhea and malaria. Capsaicinoids, as the major bioactive compounds of these plants, possess diverse pharmacological activities. However, the specific effects of capsaicinoids on intestinal fluid secretion and motility remain unclear.

The chloride channels play a crucial role in regulating intestinal motility and fluid secretion. They are also major targets for the treatment of diarrhea and constipation. The aim of this study is to elucidate the role of capsaicinoids in regulating intestinal function and their correlation with chloride channel activity.

Cell-based fluorescence quenching assays, short-circuit current experiments, and intracellular [Ca²⁺]_i assays were conducted to reveal the effects and pathways of capsaicinoids on transmembrane protein 16A (TMEM16A). Short-circuit current experiments were employed to investigate the impact of capsaicinoids on Ca²⁺-activated chloride channels (CaCCs), cystic fibrosis transmembrane conductance regulator (CFTR), Na⁺/K⁺ ATPase, and K⁺ channels in intestinal epithelial cells and isolated mouse intestinal tissues. The influence of capsaicinoids on intestinal fluid secretion was evaluated using ileal closed-loop experiments in cholera toxin (CT)-injected mice. Immunohistochemistry and isolated intestinal contractility assays were performed to investigate the effects of capsaicinoids on intestinal motility, with a focus on TMEM16A-mediated smooth muscle contraction.

In vitro, capsaicinoids significantly inhibited TMEM16A, Ca²⁺-activated, and CFTR-mediated chloride currents, K⁺ channel-mediated K⁺ currents in intestinal epithelial cells and tissues. Capsaicinoids inhibited TMEM16A via both direct and indirect ways. In vivo, capsaicinoids attenuated CT-induced intestinal fluid secretion and reduced the amplitude of spontaneous ileal contractions, with minimal effect on contraction frequency. Furthermore, capsaicinoids suppressed contractile force induced by TMEM16A activation.

Our results demonstrate that capsaicinoids inhibit intestinal fluid secretion and smooth muscle contraction by mainly targeting chloride channels, including TMEM16A, CaCCs, and CFTR. It also suggested that capsaicinoids can serve as lead compounds for chloride ion channel inhibitors.