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Prostaglandin metabolite induces inhibition of TRPA1 and channel-dependent nociception.

Weng Y, Batista-Schepman PA, Barabas ME, Harris EQ, Dinsmore TB, Kossyreva EA, Foshage AM, Wang MH, Schwab MJ, Wang VM, Stucky CL, Story GM - Mol Pain (2012)

Bottom Line: Ca2+ imaging studies of DRG neurons demonstrated that 15d-PGJ2 pre-exposure reduced the magnitude and number of neuronal responses to AITC, but not CAP.AITC responses were not reduced when neurons were pre-exposed to 15d-PGJ2 combined with HC-030031 (TRPA1 antagonist), demonstrating that inhibitory effects of 15d-PGJ2 depend on TRPA1 activation.Collectively, our studies support that TRPA1 agonists may be useful as pain therapeutics.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anesthesiology, Washington University Pain Center, St. Louis, MO 63110, USA.

ABSTRACT

Background: The Transient Receptor Potential (TRP) ion channel TRPA1 is a key player in pain pathways. Irritant chemicals activate ion channel TRPA1 via covalent modification of N-terminal cysteines. We and others have shown that 15-Deoxy-Δ12, 14-prostaglandin J2 (15d-PGJ2) similarly activates TRPA1 and causes channel-dependent nociception. Paradoxically, 15d-PGJ2 can also be anti-nociceptive in several pain models. Here we hypothesized that activation and subsequent desensitization of TRPA1 in dorsal root ganglion (DRG) neurons underlies the anti-nociceptive property of 15d-PGJ2. To investigate this, we utilized a battery of behavioral assays and intracellular Ca2+ imaging in DRG neurons to test if pre-treatment with 15d-PGJ2 inhibited TRPA1 to subsequent stimulation.

Results: Intraplantar pre-injection of 15d-PGJ2, in contrast to mustard oil (AITC), attenuated acute nocifensive responses to subsequent injections of 15d-PGJ2 and AITC, but not capsaicin (CAP). Intraplantar 15d-PGJ2-administered after the induction of inflammation-reduced mechanical hypersensitivity in the Complete Freund's Adjuvant (CFA) model for up to 2 h post-injection. The 15d-PGJ2-mediated reduction in mechanical hypersensitivity is dependent on TRPA1, as this effect was absent in TRPA1 knockout mice. Ca2+ imaging studies of DRG neurons demonstrated that 15d-PGJ2 pre-exposure reduced the magnitude and number of neuronal responses to AITC, but not CAP. AITC responses were not reduced when neurons were pre-exposed to 15d-PGJ2 combined with HC-030031 (TRPA1 antagonist), demonstrating that inhibitory effects of 15d-PGJ2 depend on TRPA1 activation. Single daily doses of 15d-PGJ2, administered during the course of 4 days in the CFA model, effectively reversed mechanical hypersensitivity without apparent tolerance or toxicity.

Conclusions: Taken together, our data support the hypothesis that 15d-PGJ2 induces activation followed by persistent inhibition of TRPA1 channels in DRG sensory neurons in vitro and in vivo. Moreover, we demonstrate novel evidence that 15d-PGJ2 is analgesic in mouse models of pain via a TRPA1-dependent mechanism. Collectively, our studies support that TRPA1 agonists may be useful as pain therapeutics.

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Homologous desensitization of 15d-PGJ2 vs. AITC is dependent on agonist concentration. Homologous sensitization and desensitization are agonist- and concentration-dependent. In contrast to 50 μM 15d-PGJ2 (A), responses to 50 μM AITC sensitize (B) significantly (C). Traces show mean ± SEM of ~30-60 DRG neurons. Values in C represent the peak response of neurons under each condition. **p < 0.01, ***p < 0.001. Data were analyzed using a paired, two-tailed Student’s t-test.
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Figure 5: Homologous desensitization of 15d-PGJ2 vs. AITC is dependent on agonist concentration. Homologous sensitization and desensitization are agonist- and concentration-dependent. In contrast to 50 μM 15d-PGJ2 (A), responses to 50 μM AITC sensitize (B) significantly (C). Traces show mean ± SEM of ~30-60 DRG neurons. Values in C represent the peak response of neurons under each condition. **p < 0.01, ***p < 0.001. Data were analyzed using a paired, two-tailed Student’s t-test.

Mentions: We conducted cross- and homologous-inhibition experiments utilizing two bath applied pulses of 50–100 μM 15d-PGJ2 or AITC. As shown in Figure 4, 100 μM 15d-PGJ2 strongly inhibits subsequent responses to a pulse of 100 μM AITC applied up to 8 min later (Figure 4A) and to itself (Figure 4B). Similarly, 100 μM ATIC strongly desensitizes subsequent responses to 100 μM 15d-PGJ2 (Figure C) and to itself (Figure 4D). Cross-desensitization was maintained when we applied two pulses of 50 μM of each compound (data not shown). In experiments utilizing two 50 μM pulses of 15d-PGJ2 or two 50 μM pulses of AITC, homologous desensitization of 15d-PGJ2, but not AITC, was maintained (Figure 5). With up to an 8 min inter-stimulus interval, two 50 μM 15d-PGJ2 pulses revealed a significant homologous desensitization of the second 15d-PGJ2 response (Figure 5A). Intriguingly, the reverse was not evident—50 μM AITC did not inhibit the percentage of neurons responding (39.7% vs. 38.2%) or reduce the overall magnitude of responses to a subsequent stimulus of 50 μM ATIC (Figure 5B). Instead, the second response to 50 μM AITC was significantly sensitized relative to the first (Figure 5C). These experiments reveal complex concentration- and stimulus-dependent variables that affect TRPA1 activation.


Prostaglandin metabolite induces inhibition of TRPA1 and channel-dependent nociception.

Weng Y, Batista-Schepman PA, Barabas ME, Harris EQ, Dinsmore TB, Kossyreva EA, Foshage AM, Wang MH, Schwab MJ, Wang VM, Stucky CL, Story GM - Mol Pain (2012)

Homologous desensitization of 15d-PGJ2 vs. AITC is dependent on agonist concentration. Homologous sensitization and desensitization are agonist- and concentration-dependent. In contrast to 50 μM 15d-PGJ2 (A), responses to 50 μM AITC sensitize (B) significantly (C). Traces show mean ± SEM of ~30-60 DRG neurons. Values in C represent the peak response of neurons under each condition. **p < 0.01, ***p < 0.001. Data were analyzed using a paired, two-tailed Student’s t-test.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3526547&req=5

Figure 5: Homologous desensitization of 15d-PGJ2 vs. AITC is dependent on agonist concentration. Homologous sensitization and desensitization are agonist- and concentration-dependent. In contrast to 50 μM 15d-PGJ2 (A), responses to 50 μM AITC sensitize (B) significantly (C). Traces show mean ± SEM of ~30-60 DRG neurons. Values in C represent the peak response of neurons under each condition. **p < 0.01, ***p < 0.001. Data were analyzed using a paired, two-tailed Student’s t-test.
Mentions: We conducted cross- and homologous-inhibition experiments utilizing two bath applied pulses of 50–100 μM 15d-PGJ2 or AITC. As shown in Figure 4, 100 μM 15d-PGJ2 strongly inhibits subsequent responses to a pulse of 100 μM AITC applied up to 8 min later (Figure 4A) and to itself (Figure 4B). Similarly, 100 μM ATIC strongly desensitizes subsequent responses to 100 μM 15d-PGJ2 (Figure C) and to itself (Figure 4D). Cross-desensitization was maintained when we applied two pulses of 50 μM of each compound (data not shown). In experiments utilizing two 50 μM pulses of 15d-PGJ2 or two 50 μM pulses of AITC, homologous desensitization of 15d-PGJ2, but not AITC, was maintained (Figure 5). With up to an 8 min inter-stimulus interval, two 50 μM 15d-PGJ2 pulses revealed a significant homologous desensitization of the second 15d-PGJ2 response (Figure 5A). Intriguingly, the reverse was not evident—50 μM AITC did not inhibit the percentage of neurons responding (39.7% vs. 38.2%) or reduce the overall magnitude of responses to a subsequent stimulus of 50 μM ATIC (Figure 5B). Instead, the second response to 50 μM AITC was significantly sensitized relative to the first (Figure 5C). These experiments reveal complex concentration- and stimulus-dependent variables that affect TRPA1 activation.

Bottom Line: Ca2+ imaging studies of DRG neurons demonstrated that 15d-PGJ2 pre-exposure reduced the magnitude and number of neuronal responses to AITC, but not CAP.AITC responses were not reduced when neurons were pre-exposed to 15d-PGJ2 combined with HC-030031 (TRPA1 antagonist), demonstrating that inhibitory effects of 15d-PGJ2 depend on TRPA1 activation.Collectively, our studies support that TRPA1 agonists may be useful as pain therapeutics.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anesthesiology, Washington University Pain Center, St. Louis, MO 63110, USA.

ABSTRACT

Background: The Transient Receptor Potential (TRP) ion channel TRPA1 is a key player in pain pathways. Irritant chemicals activate ion channel TRPA1 via covalent modification of N-terminal cysteines. We and others have shown that 15-Deoxy-Δ12, 14-prostaglandin J2 (15d-PGJ2) similarly activates TRPA1 and causes channel-dependent nociception. Paradoxically, 15d-PGJ2 can also be anti-nociceptive in several pain models. Here we hypothesized that activation and subsequent desensitization of TRPA1 in dorsal root ganglion (DRG) neurons underlies the anti-nociceptive property of 15d-PGJ2. To investigate this, we utilized a battery of behavioral assays and intracellular Ca2+ imaging in DRG neurons to test if pre-treatment with 15d-PGJ2 inhibited TRPA1 to subsequent stimulation.

Results: Intraplantar pre-injection of 15d-PGJ2, in contrast to mustard oil (AITC), attenuated acute nocifensive responses to subsequent injections of 15d-PGJ2 and AITC, but not capsaicin (CAP). Intraplantar 15d-PGJ2-administered after the induction of inflammation-reduced mechanical hypersensitivity in the Complete Freund's Adjuvant (CFA) model for up to 2 h post-injection. The 15d-PGJ2-mediated reduction in mechanical hypersensitivity is dependent on TRPA1, as this effect was absent in TRPA1 knockout mice. Ca2+ imaging studies of DRG neurons demonstrated that 15d-PGJ2 pre-exposure reduced the magnitude and number of neuronal responses to AITC, but not CAP. AITC responses were not reduced when neurons were pre-exposed to 15d-PGJ2 combined with HC-030031 (TRPA1 antagonist), demonstrating that inhibitory effects of 15d-PGJ2 depend on TRPA1 activation. Single daily doses of 15d-PGJ2, administered during the course of 4 days in the CFA model, effectively reversed mechanical hypersensitivity without apparent tolerance or toxicity.

Conclusions: Taken together, our data support the hypothesis that 15d-PGJ2 induces activation followed by persistent inhibition of TRPA1 channels in DRG sensory neurons in vitro and in vivo. Moreover, we demonstrate novel evidence that 15d-PGJ2 is analgesic in mouse models of pain via a TRPA1-dependent mechanism. Collectively, our studies support that TRPA1 agonists may be useful as pain therapeutics.

Show MeSH
Related in: MedlinePlus