Pyrazine-Fused Triterpenoids Block the TRPA1 Ion Channel in Vitro and Inhibit TRPA1-Mediated Acute Inflammation in Vivo

Abstract

TRPA1 is a non-selective cation channel, most famously expressed in non-myelinated nociceptors.In addition to being an important chemical and mechanical pain sensor, TRPA1 has more recently appeared to have a role in inflammation as well. Triterpenoids are natural products with antiinflammatory and anti-cancer effects in experimental models. In this paper, thirteen novel triterpenoids were created by synthetically modifying betulin, an abundant triterpenoid of the genus Betula L. and their TRPA1-modulating features were examined. Fluo 3-AM protocol was used in the initial screening, in which six out of the fourteen tested triterpenoids inhibited TRPA1 in a statistically significant manner. In subsequent whole-cell patch clamp recordings, the two most effective compounds (pyrazine-fused triterpenoids 8 and 9) displayed a reversible and dose and voltage-dependent effect to block the TRPA1 ion channel at submicromolar concentrations. Interestingly, the TRPA1-blocking action was also evident in vivo, as compounds 8 and 9 both alleviated TRPA1-agonist induced acute paw inflammation in mice. The results introduce betulinderived pyrazine-fused triterpenoids as promising novel antagonists of TRPA1 that are potentially useful in treating diseases with a TRPA1-mediated adverse component.

HIF-1α Dependent Upregulation of ZIP8, ZIP14, and TRPA1 Modify Intracellular Zn2+ Accumulation in Inflammatory Synoviocytes

“…TRPA1 is widely expressed in neuronal and non-neuronal cells, and it acts as a biological sensor that is activated by environmental irritants and oxidative-and thiol-reactive compounds [13][14][15][16][17]. Because transgenic mice lacking TRPA1 exhibit suppressed sensitivity to mechanical stimulation, cold stimuli, and TNF-α-induced mechanical hyperalgesia [18][19][20][21][22], TRPA1 has been identified as a nociceptor mediating acute and inflammatory pain [21][22][23][24][25]. On the other hand, a previous study from our group revealed the transcriptional induction of TRPA1 by inflammation via HIF-1α as a mechanism controlling inflammatory cytokine release [26].…”

Transient Receptor Potential Ankyrin 1 (TRPA1) Is Involved in Upregulating Interleukin-6 Expression in Osteoarthritic Chondrocyte Models

“…We have also shown that TRPA1 is expressed in primary human osteoarthritic chondrocytes, and that its expression is downregulated by the antiinflammatory drugs aurothiomalate and dexamethasone [8,20]. In addition to OA, TRPA1 is also implicated in the development of other inflammatory conditions and joint diseases, such as gout and chronic arthritis [21][22][23][24][25][26].…”

Donor–Acceptor Bicyclopropyls as 1,6-Zwitterionic Intermediates: Synthesis and Reactions with 4-Phenyl-1,2,4-triazoline-3,5-dione and Terminal Acetylenes

“…Transisomer: 1 H NMR (300 MHz, CDCl 3 ): δ 7.45 (br.d, J = 8.4 Hz, 2H, o-C 6 H 4 ), 7.00 (br.d, J = 8. 4 Hz, 2H, H m-C 6 H 4 ), 6.55 (d, J = 10.5 Hz, 1H, (CH)), 3.80 and 3.78 (both s, 2 × 3H, 2 OMe), 2.42−2.12 (m, 2H, HC−CH), 1.63−1.47 and 1.44−1.31 (both m, 2 × 1H, CH 2 ). 2)), 24.9 (C(1)), 18.6 (C(3)).…”

“…Silica gel column chromatography (eluent: CHCl 3 −MeOH, 25:1) gave the desired product 12. 3,5,2,4]triazolo[1,2-a]pyridazin-5-yl)methyl)-2-(3,5-dioxo-4-phenyl-1,2,4-triazolidin-1-yl)malonate (12a). Reaction time: 2 h, yield: 60% (250 mg), yellow oil, cis/trans ≈ 3.5:1.…”

“…Donor−acceptor cyclopropanes (DACs) 1,2 are widely used in organic synthesis 3,4 owing to their ability to react as synthetic equivalents of 1,3-zwitterions (Scheme 1A). Recently, reactions of DACs where they exhibit other reactivity types have also been studied intensely.…”