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Rahnama S, Spence R, Vathsangam N, Baskerville CL, Bailey SR, de Laat MA, Anderson ST, Pollitt CC, Sillence MN. Effects of insulin on IGF-1 receptors in equine lamellar tissue in vitro. Domest Anim Endocrinol 2021; 74:106530. [PMID: 32818904 DOI: 10.1016/j.domaniend.2020.106530] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Revised: 07/23/2020] [Accepted: 07/23/2020] [Indexed: 11/21/2022]
Abstract
Although it is understood that equine endocrinopathic laminitis can be triggered by high concentrations of insulin, it is unclear whether this represents a direct action on lamellar tissue via insulin receptors (InsR), an interaction with IGF-1 receptors (IGF-1R), or some other, indirect action. This uncertainty is because of the reported scarcity of InsR in lamellar tissue and the low affinity of insulin for equine IGF-1R. In the present study, the effects of insulin and IGF-1 (as a positive control) were examined using lamellar explants isolated from the hooves of healthy horses and incubated in cell culture medium for between 2 min and 48 h. In this system, a low physiological concentration of IGF-1 (10 nM; 1.31 ng/mL) caused a marked increase in the appearance of phosphorylated IGF-1R after 5 min (P < 0.05), and this effect was blocked by a human anti-IGF-1R monoclonal antibody (mAb). However, a high concentration of insulin (10 nM; 1,430 μIU/mL) appeared to cause dephosphorylation of the IGF-1R after 5 min (P < 0.01), 15 min, and 30 min (P < 0.001). Using 3H-thymidine as a marker, it was also demonstrated that insulin and IGF-1-stimulated cell proliferation in lamellar explants over the same concentration range as each other (1-100 nM), implying that each peptide acts via its own receptor (P < 0.001). Conversely, the effect of both peptides could be blocked using a selective anti-IGF-1R mAb (P < 0.001), implying that insulin acts via IGF1-R (either directly or indirectly). Notwithstanding this conundrum, the results demonstrate that insulin acts directly on lamellar tissue and suggest that a therapeutic anti-IGF-1R mAb could be useful in treating or preventing endocrinopathic laminitis.
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Affiliation(s)
- S Rahnama
- School of Biology and Environmental Science, Queensland University of Technology, Brisbane, Queensland, Australia
| | - R Spence
- School of Biology and Environmental Science, Queensland University of Technology, Brisbane, Queensland, Australia
| | - N Vathsangam
- Department of Veterinary Biosciences, The University of Melbourne, Melbourne, Victoria, Australia
| | - C L Baskerville
- Department of Veterinary Biosciences, The University of Melbourne, Melbourne, Victoria, Australia
| | - S R Bailey
- Department of Veterinary Biosciences, The University of Melbourne, Melbourne, Victoria, Australia
| | - M A de Laat
- School of Biology and Environmental Science, Queensland University of Technology, Brisbane, Queensland, Australia
| | - S T Anderson
- School of Biomedical Sciences, The University of Queensland, St Lucia, Queensland, Australia
| | - C C Pollitt
- School of Veterinary Science, The University of Queensland, Gatton, Australia
| | - M N Sillence
- School of Biology and Environmental Science, Queensland University of Technology, Brisbane, Queensland, Australia.
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Rahnama S, Vathsangam N, Spence R, Anderson ST, de Laat MA, Bailey S, Sillence MN. Identification of monoclonal antibodies suitable for blocking IGF-1 receptors in the horse. Domest Anim Endocrinol 2021; 74:106510. [PMID: 32652390 DOI: 10.1016/j.domaniend.2020.106510] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 06/11/2020] [Accepted: 06/11/2020] [Indexed: 01/19/2023]
Abstract
Prolonged hyperinsulinemia is thought to be the cause of equine endocrinopathic laminitis, a common and crippling disease of the foot, for which there are no pharmacologic treatments other than pain relief. It has been suggested that insulin causes its effects on the lamellae by activating IGF-1 receptors (IGF-1R), as insulin receptors (InsR) are scarce in this tissue, whereas IGF-1R are abundant and become downregulated after prolonged insulin infusion. As a first step toward confirming this mechanism and beginning to develop a therapeutic anti-IGF-1R monoclonal antibody (mAb) for horses, it was necessary to identify available human IGF-1R mAbs that would recognize equine receptors. Four IGF-1R mAbs were tested using soluble equine IGF-1R, with ELISA and flow cytometry. Frozen equine lamellar and liver tissue was also used in radioligand binding assays. The results demonstrated that only one of the mAbs tested (mAb1) was able to compete effectively with IGF-1 for binding to its receptors in equine lamellar tissue, with an IC50 of 5 to 159 ng/mL. None of the 4 mAbs were able to bind to equine hepatic InsR. This study has generated valuable structure-activity information and has identified a prototype anti-IGF-1R mAb suitable for further development.
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Affiliation(s)
- S Rahnama
- School of Biology and Environmental Science, Queensland University of Technology, Brisbane, Queensland, Australia
| | - N Vathsangam
- Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Melbourne, Victoria, Australia
| | - R Spence
- School of Biology and Environmental Science, Queensland University of Technology, Brisbane, Queensland, Australia
| | - S T Anderson
- School of Biomedical Sciences, The University of Queensland, St Lucia, Queensland, Australia
| | - M A de Laat
- School of Biology and Environmental Science, Queensland University of Technology, Brisbane, Queensland, Australia
| | - S Bailey
- School of Biomedical Sciences, The University of Queensland, St Lucia, Queensland, Australia
| | - M N Sillence
- School of Biology and Environmental Science, Queensland University of Technology, Brisbane, Queensland, Australia.
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Nanayakkara SN, Rahnama S, Harris PA, Anderson ST, de Laat MA, Bailey S, Sillence MN. Characterization of insulin and IGF-1 receptor binding in equine liver and lamellar tissue: implications for endocrinopathic laminitis. Domest Anim Endocrinol 2019; 66:21-26. [PMID: 30205269 DOI: 10.1016/j.domaniend.2018.05.008] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Revised: 05/25/2018] [Accepted: 05/31/2018] [Indexed: 01/19/2023]
Abstract
Although it is well established that equine laminitis can be triggered by extreme hyperinsulinemia, the mechanism of insulin action is not known. High concentrations of insulin lead to separation of the weight-bearing apparatus from the hoof wall and are associated with an increased cycle of cell death and proliferation in the lamellae. Gene expression and immunohistochemistry studies have indicated that the lamellae are sparsely populated with insulin receptors, whereas IGF-1 receptors (IGF-1R) are abundant, suggesting that the action of insulin may be mediated by insulin binding to the IGF-1R. To investigate this possibility, cell membrane fragments containing IGF-1R were extracted from the livers of 6 horses and the lamellae of >50 horses euthanized for nonresearch purposes at an abattoir. Radioligand-binding studies using 125I-IGF-1 and 125I-insulin confirmed an abundance of high-affinity IGF-1R in the liver (KD 0.11 nM, Bmax 223 fmol/mg protein) and lamellae (KD 0.16 nM, Bmax 243 fmol/mg protein). However, the affinity of insulin for binding to the lamellar IGF-1R (Ki 934 nM) was >5,800 fold less than that of IGF-1, suggesting that insulin is unlikely to bind to equine IGF-1R at physiological concentrations. Although insulin receptors could be detected in the liver (KD 0.48 nM, Bmax 123 fmol/mg protein), they were barely detectable in lamellae (estimated Bmax 14 fmol/mg protein). There was no evidence to support the presence of insulin/IGF-1 hybrid receptors in either tissue. These findings suggest that insulin does not act directly through IGF-1 receptors and that an alternative theory is required to explain the mechanism of insulin action in laminitis.
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Affiliation(s)
- S N Nanayakkara
- Earth, Environmental and Biological Sciences School, Queensland University of Technology, Brisbane, Queensland, Australia
| | - S Rahnama
- Earth, Environmental and Biological Sciences School, Queensland University of Technology, Brisbane, Queensland, Australia
| | - P A Harris
- Equine Studies Group, WALTHAM Centre for Pet Nutrition, Waltham-on-the-Wolds, UK
| | - S T Anderson
- School of Biomedical Sciences, The University of Queensland, St Lucia, Queensland, Australia
| | - M A de Laat
- Earth, Environmental and Biological Sciences School, Queensland University of Technology, Brisbane, Queensland, Australia
| | - S Bailey
- Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Melbourne, Victoria, Australia
| | - M N Sillence
- Earth, Environmental and Biological Sciences School, Queensland University of Technology, Brisbane, Queensland, Australia.
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Rahnama S, Deuis JR, Cardoso FC, Ramanujam V, Lewis RJ, Rash LD, King GF, Vetter I, Mobli M. The structure, dynamics and selectivity profile of a NaV1.7 potency-optimised huwentoxin-IV variant. PLoS One 2017; 12:e0173551. [PMID: 28301520 PMCID: PMC5354290 DOI: 10.1371/journal.pone.0173551] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2016] [Accepted: 02/23/2017] [Indexed: 12/19/2022] Open
Abstract
Venom-derived peptides have attracted much attention as potential lead molecules for pharmaceutical development. A well-known example is Huwentoxin-IV (HwTx-IV), a peptide toxin isolated from the venom of the Chinese bird-eating spider Haplopelma schmitdi. HwTx-IV was identified as a potent blocker of a human voltage-gated sodium channel (hNaV1.7), which is a genetically validated analgesic target. The peptide was promising as it showed high potency at NaV1.7 (IC50 ~26 nM) and selectivity over the cardiac NaV subtype (NaV1.5). Mutagenesis studies aimed at optimising the potency of the peptide resulted in the development of a triple-mutant of HwTx-IV (E1G, E4G, Y33W, m3-HwTx-IV) with significantly increased potency against hNaV1.7 (IC50 = 0.4 ± 0.1 nM) without increased potency against hNaV1.5. The activity of m3-HwTx-IV against other NaV subtypes was, however, not investigated. Similarly, the structure of the mutant peptide was not characterised, limiting the interpretation of the observed increase in potency. In this study we produced isotope-labelled recombinant m3-HwTx-IV in E. coli, which enabled us to characterise the atomic-resolution structure and dynamics of the peptide by NMR spectroscopy. The results show that the structure of the peptide is not perturbed by the mutations, whilst the relaxation studies reveal that residues in the active site of the peptide undergo conformational exchange. Additionally, the NaV subtype selectivity of the recombinant peptide was characterised, revealing potent inhibition of neuronal NaV subtypes 1.1, 1.2, 1.3, 1.6 and 1.7. In parallel to the in vitro studies, we investigated NaV1.7 target engagement of the peptide in vivo using a rodent pain model, where m3-HwTx-IV dose-dependently suppressed spontaneous pain induced by the NaV1.7 activator OD1. Thus, our results provide further insight into the structure and dynamics of this class of peptides that may prove useful in guiding the development of inhibitors with improved selectivity for analgesic NaV subtypes.
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Affiliation(s)
- Sassan Rahnama
- Centre for Advanced Imaging, The University of Queensland, St Lucia, QLD, Australia
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD, Australia
| | - Jennifer R. Deuis
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD, Australia
| | - Fernanda C. Cardoso
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD, Australia
| | | | - Richard J. Lewis
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD, Australia
| | - Lachlan D. Rash
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD, Australia
- School of Biomedical Sciences, The University of Queensland, St Lucia, QLD, Australia
| | - Glenn F. King
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD, Australia
| | - Irina Vetter
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD, Australia
| | - Mehdi Mobli
- Centre for Advanced Imaging, The University of Queensland, St Lucia, QLD, Australia
- * E-mail:
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