Capsaicinoids Cause Inflammation and Epithelial Cell Death through Activation of Vanilloid Receptors

Abstract

Capsaicinoids, found in less-than-lethal self-defense weapons, have been associated with respiratory failure and death in exposed animals and people. The studies described herein provide evidence for acute respiratory inflammation and damage to epithelial cells in experimental animals, and provide precise molecular mechanisms that mediate these effects using human bronchiolar and alveolar epithelial cells. Inhalation exposure of rats to pepper sprays (capsaicinoids) produced acute inflammation and damage to nasal, tracheal, bronchiolar, and alveolar cells in a dose-related manner. In vitro cytotoxicity assays demonstrated that cultured human lung cells (BEAS-2B and A549) were more susceptible to necrotic cell death than liver (HepG2) cells. Transcription of the human vanilloid receptor type-1, VR1 or TRPV1, was demonstrated by RT-PCR in all of these cells, and the relative transcript levels were correlated to cellular susceptibility. TRPV1 receptor activation was presumably responsible for cellular cytotoxicity, but prototypical functional antagonists of this receptor were cytotoxic themselves, and did not ameliorate capsaicinoid-induced damage. Conversely, the TRPV1 antagonist capsazepine, as well as calcium chelation by EGTA ablated cytokine (IL-6) production after capsaicin exposure. To address these seemingly contradictory results, recombinant human TRPV1 was cloned and overexpressed in BEAS-2B cells. These cells exhibited dramatically increased cellular susceptibility to capsaicinoids, measured using IL-6 production and cytotoxicity, and an apoptotic mechanism of cell death. Surprisingly, the cytotoxic effects of capsaicin in TRPV1 overexpressing cells were also not inhibited by TRPV1 antagonists or by treatments that modified extracellular calcium. Thus, capsaicin interacted with TRPV1 expressed by BEAS-2B and other airway epithelial cells to cause the calcium-dependent production of cytokines and, conversely, calcium-independent cell death. These results have demonstrated that capsaicinoids contained in pepper spray products produce airway inflammation and cause respiratory epithelial cell death. The mechanisms of these cellular responses to capsaicinoids appear to proceed via distinct cellular pathways, but both pathways are initiated by TRPV1.

Calcium‐dependent and independent mechanisms of capsaicin receptor (TRPV1)‐mediated cytokine production and cell death in human bronchial epithelial cells

“…TRPV1 expression was initially demonstrated in peripheral afferent sensory nerve fibers (C-and Aδ-) originating from dorsal root ganglia [1], but ongoing studies have also revealed expression and function in a variety of nonneuronal tissues and cell types [4] including keratinocytes [5] and lung epithelial cells [6][7][8]. TRPV1 subunits consist of six transmembrane domains, a putative pore loop region, and cytosolic N-and C-terminal domains that possess a variety of regulatory features including multiple phosphorylation sites [9][10][11][12], subcellular localization sequences [13], a calcium/ calmodulin binding site [14], and a phosphatidylinositol diphosphate (PiP 2 ) binding site [15].…”

“…Our laboratory has investigated mechanisms by which pepper sprays produce toxicity in respiratory tissues; the active ingredients in pepper spray products are the capsaicinoids [7]. Rats exposed to capsaicin by nose-only inhalation exhibited marked inflammation, the appearance of neutrophils and proliferating macrophages, and extensive damage to tracheal epithelial, bronchial epithelial, and alveolar cells [7].…”

The protective effect of genistein postconditioning on hypoxia/reoxygenation-induced injury in human gastric epithelial cells

“…Recent research, however, has indicated that VR1 is also distributed in some non-nervous tissues, such as liver, lungs, gastric epithelial cells [17] , bronchi [18] , bladder epithelium [19] , mast cells, skin cells [20] , and macrophages [21] . This finding suggests that VR1 might be involved in regulating a variety of physiological functions of different tissues and organs.…”

Is TRPV1 a useful target in respiratory diseases?

“…TRPV1 expression in the lung is not confined to sensory nerves, as this receptor is A c c e p t e d m a n u s c r i p t 6 also present in immortalized human bronchial epithelial cells [36][37][38], airway smooth muscle cells [35] and mast cells [39]. Recently, parietal pleura afferents were found in the intercostal nerves of rabbits, and these myelinated and unmyelinated fibers had multi-modal properties [40].…”

“…A c c e p t e d m a n u s c r i p t 13 In vitro studies using human bronchial epithelial cells have demonstrated increased production of pro-inflammatory cytokines, such as interleukin-6 and interleukin-8, and oncotic cell death associated with TRPV1 activation [37,98]. Other studies have also demonstrated that particulate matter increases intracellular Ca 2+ and induces apoptosis of cultured lung epithelial cells via activation of TRPV1 [38,99].…”