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In vivo USPIO magnetic resonance imaging shows that minocycline mitigates macrophage recruitment to a peripheral nerve injury.

Ghanouni P, Behera D, Xie J, Chen X, Moseley M, Biswal S - Mol Pain (2012)

Bottom Line: Minocycline has proven anti-nociceptive effects, but the mechanism by which minocycline delays the development of allodynia and hyperalgesia after peripheral nerve injury remains unclear.Behavioral measurements confirmed the presence of allodynia in the neuropathic pain model while the uninjured and minocycline-treated injured group had significantly higher paw withdrawal thresholds (p < 0.011).Decreased MR signal is observed in the SNI group that received USPIOs (3.3+/-0.5%) compared to the minocycline-treated SNI group that received USPIOs (15.2+/-4.5%) and minocycline-treated group that did not receive USPIOs (41.2+/-2.3%) (p < 0.04).

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiology, Molecular Imaging Program at Stanford (MIPS) Stanford, Stanford University School of Medicine, California, USA.

ABSTRACT

Background: Minocycline has proven anti-nociceptive effects, but the mechanism by which minocycline delays the development of allodynia and hyperalgesia after peripheral nerve injury remains unclear. Inflammatory cells, in particular macrophages, are critical components of the response to nerve injury. Using ultrasmall superparamagnetic iron oxide-magnetic resonance imaging (USPIO-MRI) to monitor macrophage trafficking, the purpose of this project is to determine whether minocycline modulates macrophage trafficking to the site of nerve injury in vivo and, in turn, results in altered pain thresholds.

Results: Animal experiments were approved by Stanford IACUC. A model of neuropathic pain was created using the Spared Nerve Injury (SNI) model that involves ligation of the left sciatic nerve in the left thigh of adult Sprague-Dawley rats. Animals with SNI and uninjured animals were then injected with/without USPIOs (300 μmol/kg i.v.) and with/without minocycline (50 mg/kg i.p.). Bilateral sciatic nerves were scanned with a volume coil in a 7 T magnet 7 days after USPIO administration. Fluid-sensitive MR images were obtained, and ROIs were placed on bilateral sciatic nerves to quantify signal intensity. Pain behavior modulation by minocycline was measured using the Von Frey filament test. Sciatic nerves were ultimately harvested at day 7, fixed in 10% buffered formalin and stained for the presence of iron oxide-laden macrophages. Behavioral measurements confirmed the presence of allodynia in the neuropathic pain model while the uninjured and minocycline-treated injured group had significantly higher paw withdrawal thresholds (p < 0.011). Decreased MR signal is observed in the SNI group that received USPIOs (3.3+/-0.5%) compared to the minocycline-treated SNI group that received USPIOs (15.2+/-4.5%) and minocycline-treated group that did not receive USPIOs (41.2+/-2.3%) (p < 0.04). Histology of harvested sciatic nerve specimens confirmed the presence USPIOs at the nerve injury site in the SNI group without minocycline treatment.

Conclusion: Animals with neuropathic pain in the left hindpaw show increased trafficking of USPIO-laden macrophages to the site of sciatic nerve injury. Minocycline to retards the migration of macrophages to the nerve injury site, which may partly explain its anti-nociceptive effects. USPIO-MRI is an effective in vivo imaging tool to study the role of macrophages in the development of neuropathic pain.

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Minocycline administration prevents development of mechanical allodynia after peripheral nerve injury. Mechanical sensitivity was assessed by the von Frey test before, and 1, 3, 7, 13, 15, and 16 days after nerve injury. The 50% response threshold of the injured left hindpaw decreased to 3.86 ± 0.34 by 72 hours (squares). The response threshold of rats receiving daily intraperitoneal injections of minocycline did not change (4.90 ± 0.08, triangles) and was similar to the threshold of the uninjured rats (4.85 ± 0.16, triangles, red line). Minocycline administration was stopped after seven days; one week later, all injured rats demonstrated the same threshold. Averages and standard deviations of data collected from 3 – 6 animals at each time point are presented.
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Figure 1: Minocycline administration prevents development of mechanical allodynia after peripheral nerve injury. Mechanical sensitivity was assessed by the von Frey test before, and 1, 3, 7, 13, 15, and 16 days after nerve injury. The 50% response threshold of the injured left hindpaw decreased to 3.86 ± 0.34 by 72 hours (squares). The response threshold of rats receiving daily intraperitoneal injections of minocycline did not change (4.90 ± 0.08, triangles) and was similar to the threshold of the uninjured rats (4.85 ± 0.16, triangles, red line). Minocycline administration was stopped after seven days; one week later, all injured rats demonstrated the same threshold. Averages and standard deviations of data collected from 3 – 6 animals at each time point are presented.

Mentions: Minocycline is known to prevent allodynia in both inflammatory and mechanical nerve injury models, and has been shown to decrease macrophage recruitment after nerve injury [1]. Before testing the impact of this drug on macrophage trafficking by MR, we first confirmed minocycline’s ability to prevent allodynia after sciatic nerve injury in our model of neuropathic pain. Behavioral measurements confirmed the presence of allodynia in the neuropathic pain model (50% paw withdrawal threshold of 3.86 ± 0.34) while the paw withdrawal threshold of the minocycline-treated injured group was significantly higher (4.90 ± 0.08, p < 0.011), and was similar to the threshold of the uninjured paw (4.85 ± 0.16). Without minocycline, the injured rat demonstrated increased sensitivity to previously innocuous stimuli within 72 hours after injury, reaching a plateau within one week. In order to determine the persistence of the effect of the drug, minocycline administration was then stopped at this point, one week after injury. One week after termination of minocycline treatment, all injured rats demonstrated the same level of allodynia (3.90 ± 0.17 for previously minocycline treated rats compared to 3.97 ± 0.22 for the untreated rats, Figure 1).


In vivo USPIO magnetic resonance imaging shows that minocycline mitigates macrophage recruitment to a peripheral nerve injury.

Ghanouni P, Behera D, Xie J, Chen X, Moseley M, Biswal S - Mol Pain (2012)

Minocycline administration prevents development of mechanical allodynia after peripheral nerve injury. Mechanical sensitivity was assessed by the von Frey test before, and 1, 3, 7, 13, 15, and 16 days after nerve injury. The 50% response threshold of the injured left hindpaw decreased to 3.86 ± 0.34 by 72 hours (squares). The response threshold of rats receiving daily intraperitoneal injections of minocycline did not change (4.90 ± 0.08, triangles) and was similar to the threshold of the uninjured rats (4.85 ± 0.16, triangles, red line). Minocycline administration was stopped after seven days; one week later, all injured rats demonstrated the same threshold. Averages and standard deviations of data collected from 3 – 6 animals at each time point are presented.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3472277&req=5

Figure 1: Minocycline administration prevents development of mechanical allodynia after peripheral nerve injury. Mechanical sensitivity was assessed by the von Frey test before, and 1, 3, 7, 13, 15, and 16 days after nerve injury. The 50% response threshold of the injured left hindpaw decreased to 3.86 ± 0.34 by 72 hours (squares). The response threshold of rats receiving daily intraperitoneal injections of minocycline did not change (4.90 ± 0.08, triangles) and was similar to the threshold of the uninjured rats (4.85 ± 0.16, triangles, red line). Minocycline administration was stopped after seven days; one week later, all injured rats demonstrated the same threshold. Averages and standard deviations of data collected from 3 – 6 animals at each time point are presented.
Mentions: Minocycline is known to prevent allodynia in both inflammatory and mechanical nerve injury models, and has been shown to decrease macrophage recruitment after nerve injury [1]. Before testing the impact of this drug on macrophage trafficking by MR, we first confirmed minocycline’s ability to prevent allodynia after sciatic nerve injury in our model of neuropathic pain. Behavioral measurements confirmed the presence of allodynia in the neuropathic pain model (50% paw withdrawal threshold of 3.86 ± 0.34) while the paw withdrawal threshold of the minocycline-treated injured group was significantly higher (4.90 ± 0.08, p < 0.011), and was similar to the threshold of the uninjured paw (4.85 ± 0.16). Without minocycline, the injured rat demonstrated increased sensitivity to previously innocuous stimuli within 72 hours after injury, reaching a plateau within one week. In order to determine the persistence of the effect of the drug, minocycline administration was then stopped at this point, one week after injury. One week after termination of minocycline treatment, all injured rats demonstrated the same level of allodynia (3.90 ± 0.17 for previously minocycline treated rats compared to 3.97 ± 0.22 for the untreated rats, Figure 1).

Bottom Line: Minocycline has proven anti-nociceptive effects, but the mechanism by which minocycline delays the development of allodynia and hyperalgesia after peripheral nerve injury remains unclear.Behavioral measurements confirmed the presence of allodynia in the neuropathic pain model while the uninjured and minocycline-treated injured group had significantly higher paw withdrawal thresholds (p < 0.011).Decreased MR signal is observed in the SNI group that received USPIOs (3.3+/-0.5%) compared to the minocycline-treated SNI group that received USPIOs (15.2+/-4.5%) and minocycline-treated group that did not receive USPIOs (41.2+/-2.3%) (p < 0.04).

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiology, Molecular Imaging Program at Stanford (MIPS) Stanford, Stanford University School of Medicine, California, USA.

ABSTRACT

Background: Minocycline has proven anti-nociceptive effects, but the mechanism by which minocycline delays the development of allodynia and hyperalgesia after peripheral nerve injury remains unclear. Inflammatory cells, in particular macrophages, are critical components of the response to nerve injury. Using ultrasmall superparamagnetic iron oxide-magnetic resonance imaging (USPIO-MRI) to monitor macrophage trafficking, the purpose of this project is to determine whether minocycline modulates macrophage trafficking to the site of nerve injury in vivo and, in turn, results in altered pain thresholds.

Results: Animal experiments were approved by Stanford IACUC. A model of neuropathic pain was created using the Spared Nerve Injury (SNI) model that involves ligation of the left sciatic nerve in the left thigh of adult Sprague-Dawley rats. Animals with SNI and uninjured animals were then injected with/without USPIOs (300 μmol/kg i.v.) and with/without minocycline (50 mg/kg i.p.). Bilateral sciatic nerves were scanned with a volume coil in a 7 T magnet 7 days after USPIO administration. Fluid-sensitive MR images were obtained, and ROIs were placed on bilateral sciatic nerves to quantify signal intensity. Pain behavior modulation by minocycline was measured using the Von Frey filament test. Sciatic nerves were ultimately harvested at day 7, fixed in 10% buffered formalin and stained for the presence of iron oxide-laden macrophages. Behavioral measurements confirmed the presence of allodynia in the neuropathic pain model while the uninjured and minocycline-treated injured group had significantly higher paw withdrawal thresholds (p < 0.011). Decreased MR signal is observed in the SNI group that received USPIOs (3.3+/-0.5%) compared to the minocycline-treated SNI group that received USPIOs (15.2+/-4.5%) and minocycline-treated group that did not receive USPIOs (41.2+/-2.3%) (p < 0.04). Histology of harvested sciatic nerve specimens confirmed the presence USPIOs at the nerve injury site in the SNI group without minocycline treatment.

Conclusion: Animals with neuropathic pain in the left hindpaw show increased trafficking of USPIO-laden macrophages to the site of sciatic nerve injury. Minocycline to retards the migration of macrophages to the nerve injury site, which may partly explain its anti-nociceptive effects. USPIO-MRI is an effective in vivo imaging tool to study the role of macrophages in the development of neuropathic pain.

Show MeSH
Related in: MedlinePlus