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Mechanisms underlying clinical efficacy of Angiotensin II type 2 receptor (AT2R) antagonist EMA401 in neuropathic pain: clinical tissue and in vitro studies.

Anand U, Yiangou Y, Sinisi M, Fox M, MacQuillan A, Quick T, Korchev YE, Bountra C, McCarthy T, Anand P - Mol Pain (2015)

Bottom Line: Neurite lengths were significantly increased in the presence of NGF, AngII and C21 in cultured DRG neurons.AngII and, as expected, NGF significantly increased signal intensity of p38 and p42/44 MAPK, which was reversed by EMA401.EMA401 may act on paracrine/autocrine mechanisms at peripheral nerve terminals, or intracrine mechanisms, to reduce neuropathic pain signalling in AngII/NGF/TRPV1-convergent pathways.

View Article: PubMed Central - PubMed

Affiliation: Peripheral Neuropathy Unit, Centre for Clinical Translation, Hammersmith Hospital, Imperial College London, Area A, Ground Floor, Du Cane Rd, London, W12 ONN, UK. u.anand@imperial.ac.uk.

ABSTRACT

Background: The clinical efficacy of the Angiotensin II (AngII) receptor AT2R antagonist EMA401, a novel peripherally-restricted analgesic, was reported recently in post-herpetic neuralgia. While previous studies have shown that AT2R is expressed by nociceptors in human DRG (hDRG), and that EMA401 inhibits capsaicin responses in cultured hDRG neurons, the expression and levels of its endogenous ligands AngII and AngIII in clinical neuropathic pain tissues, and their signalling pathways, require investigation. We have immunostained AngII, AT2R and the capsaicin receptor TRPV1 in control post-mortem and avulsion injured hDRG, control and injured human nerves, and in cultured hDRG neurons. AngII, AngIII, and Ang-(1-7) levels were quantified by ELISA. The in vitro effects of AngII, AT2R agonist C21, and Nerve growth factor (NGF) were measured on neurite lengths; AngII, NGF and EMA401 effects on expression of p38 and p42/44 MAPK were measured using quantitative immunofluorescence, and on capsaicin responses using calcium imaging.

Results: AngII immunostaining was observed in approximately 75% of small/medium diameter neurons in control (n = 5) and avulsion injured (n = 8) hDRG, but not large neurons i.e. similar to TRPV1. AngII was co-localised with AT2R and TRPV1 in hDRG and in vitro. AngII staining by image analysis showed no significant difference between control (n = 12) and injured (n = 13) human nerves. AngII levels by ELISA were also similar in control human nerves (4.09 ± 0.36 pmol/g, n = 31), injured nerves (3.99 ± 0.79 pmol/g, n = 7), and painful neuromas (3.43 ± 0.73 pmol/g, n = 12); AngIII and Ang-(1-7) levels were undetectable (<0.03 and 0.05 pmol/g respectively). Neurite lengths were significantly increased in the presence of NGF, AngII and C21 in cultured DRG neurons. AngII and, as expected, NGF significantly increased signal intensity of p38 and p42/44 MAPK, which was reversed by EMA401. AngII mediated sensitization of capsaicin responses was not observed in the presence of MAP kinase inhibitor PD98059, and the kinase inhibitor staurosporine.

Conclusion: The major AT2R ligand in human peripheral nerves is AngII, and its levels are maintained in injured nerves. EMA401 may act on paracrine/autocrine mechanisms at peripheral nerve terminals, or intracrine mechanisms, to reduce neuropathic pain signalling in AngII/NGF/TRPV1-convergent pathways.

No MeSH data available.


Related in: MedlinePlus

IHC in human DRG tissues. Serial sections of post-fixed human avulsion injured DRG immunostained with rabbit antibodies to AngII (a) and TRPV1 (c). Arrows indicate co-localising cells. Similar serial sections of post-fixed human avulsion injured DRG immunostained with antibodies to AngII (b) and AT2R (d). Arrows indicate co-localising cells. Scale bar 50 microns.
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Fig1: IHC in human DRG tissues. Serial sections of post-fixed human avulsion injured DRG immunostained with rabbit antibodies to AngII (a) and TRPV1 (c). Arrows indicate co-localising cells. Similar serial sections of post-fixed human avulsion injured DRG immunostained with antibodies to AngII (b) and AT2R (d). Arrows indicate co-localising cells. Scale bar 50 microns.

Mentions: All results are given as mean ± sem unless otherwise stated. Antibodies to AngII (Table 1) were first evaluated by titration on tissue sections of human DRG. Rabbit antibodies to AngII showed strong staining of small/medium diameter (≤50 µm) sensory neurons but not large diameter neurons (Figure 1a, b), and showed co-localisation with TRPV1 (Figure 1c). Mouse antibodies showed very similar strongly immunoreactive sensory neurons (not shown). Counts of AngII immunoreactive small/medium diameter (≤50 µm) neurons showed that 78.54 ± 2.0% were positive in control hDRG (n = 5) and 72.13 ± 5.4% in avulsion injured hDRG (n = 8, p = 0.95). A comparison of serial sections immunostained with AngII (Figure 1b) and AT2R antibody showed that AngII and AT2R were co-localised in some small/medium diameter (≤50 µm) cells (Figure 1d).Table 1


Mechanisms underlying clinical efficacy of Angiotensin II type 2 receptor (AT2R) antagonist EMA401 in neuropathic pain: clinical tissue and in vitro studies.

Anand U, Yiangou Y, Sinisi M, Fox M, MacQuillan A, Quick T, Korchev YE, Bountra C, McCarthy T, Anand P - Mol Pain (2015)

IHC in human DRG tissues. Serial sections of post-fixed human avulsion injured DRG immunostained with rabbit antibodies to AngII (a) and TRPV1 (c). Arrows indicate co-localising cells. Similar serial sections of post-fixed human avulsion injured DRG immunostained with antibodies to AngII (b) and AT2R (d). Arrows indicate co-localising cells. Scale bar 50 microns.
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4482278&req=5

Fig1: IHC in human DRG tissues. Serial sections of post-fixed human avulsion injured DRG immunostained with rabbit antibodies to AngII (a) and TRPV1 (c). Arrows indicate co-localising cells. Similar serial sections of post-fixed human avulsion injured DRG immunostained with antibodies to AngII (b) and AT2R (d). Arrows indicate co-localising cells. Scale bar 50 microns.
Mentions: All results are given as mean ± sem unless otherwise stated. Antibodies to AngII (Table 1) were first evaluated by titration on tissue sections of human DRG. Rabbit antibodies to AngII showed strong staining of small/medium diameter (≤50 µm) sensory neurons but not large diameter neurons (Figure 1a, b), and showed co-localisation with TRPV1 (Figure 1c). Mouse antibodies showed very similar strongly immunoreactive sensory neurons (not shown). Counts of AngII immunoreactive small/medium diameter (≤50 µm) neurons showed that 78.54 ± 2.0% were positive in control hDRG (n = 5) and 72.13 ± 5.4% in avulsion injured hDRG (n = 8, p = 0.95). A comparison of serial sections immunostained with AngII (Figure 1b) and AT2R antibody showed that AngII and AT2R were co-localised in some small/medium diameter (≤50 µm) cells (Figure 1d).Table 1

Bottom Line: Neurite lengths were significantly increased in the presence of NGF, AngII and C21 in cultured DRG neurons.AngII and, as expected, NGF significantly increased signal intensity of p38 and p42/44 MAPK, which was reversed by EMA401.EMA401 may act on paracrine/autocrine mechanisms at peripheral nerve terminals, or intracrine mechanisms, to reduce neuropathic pain signalling in AngII/NGF/TRPV1-convergent pathways.

View Article: PubMed Central - PubMed

Affiliation: Peripheral Neuropathy Unit, Centre for Clinical Translation, Hammersmith Hospital, Imperial College London, Area A, Ground Floor, Du Cane Rd, London, W12 ONN, UK. u.anand@imperial.ac.uk.

ABSTRACT

Background: The clinical efficacy of the Angiotensin II (AngII) receptor AT2R antagonist EMA401, a novel peripherally-restricted analgesic, was reported recently in post-herpetic neuralgia. While previous studies have shown that AT2R is expressed by nociceptors in human DRG (hDRG), and that EMA401 inhibits capsaicin responses in cultured hDRG neurons, the expression and levels of its endogenous ligands AngII and AngIII in clinical neuropathic pain tissues, and their signalling pathways, require investigation. We have immunostained AngII, AT2R and the capsaicin receptor TRPV1 in control post-mortem and avulsion injured hDRG, control and injured human nerves, and in cultured hDRG neurons. AngII, AngIII, and Ang-(1-7) levels were quantified by ELISA. The in vitro effects of AngII, AT2R agonist C21, and Nerve growth factor (NGF) were measured on neurite lengths; AngII, NGF and EMA401 effects on expression of p38 and p42/44 MAPK were measured using quantitative immunofluorescence, and on capsaicin responses using calcium imaging.

Results: AngII immunostaining was observed in approximately 75% of small/medium diameter neurons in control (n = 5) and avulsion injured (n = 8) hDRG, but not large neurons i.e. similar to TRPV1. AngII was co-localised with AT2R and TRPV1 in hDRG and in vitro. AngII staining by image analysis showed no significant difference between control (n = 12) and injured (n = 13) human nerves. AngII levels by ELISA were also similar in control human nerves (4.09 ± 0.36 pmol/g, n = 31), injured nerves (3.99 ± 0.79 pmol/g, n = 7), and painful neuromas (3.43 ± 0.73 pmol/g, n = 12); AngIII and Ang-(1-7) levels were undetectable (<0.03 and 0.05 pmol/g respectively). Neurite lengths were significantly increased in the presence of NGF, AngII and C21 in cultured DRG neurons. AngII and, as expected, NGF significantly increased signal intensity of p38 and p42/44 MAPK, which was reversed by EMA401. AngII mediated sensitization of capsaicin responses was not observed in the presence of MAP kinase inhibitor PD98059, and the kinase inhibitor staurosporine.

Conclusion: The major AT2R ligand in human peripheral nerves is AngII, and its levels are maintained in injured nerves. EMA401 may act on paracrine/autocrine mechanisms at peripheral nerve terminals, or intracrine mechanisms, to reduce neuropathic pain signalling in AngII/NGF/TRPV1-convergent pathways.

No MeSH data available.


Related in: MedlinePlus