Valproate antinociceptive and anti-inflammatory effect in female rodents
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Abstract
Valproate, an indirect γ-aminobutiric acid agonist has been successfully used in various painful conditions. Despite its frequent use, limited pre-clinical and clinical data exist about its analgesic effect. We tested valproate p.o. in increasing doses (10, 25, 50, 100 mg/kg) in acute nociception models in mice (writhing test and formalin licking-paw test) and in acute primary thermal hyperalgesia induced by carrageenan in rats, comparing its effects to a non-treated control and morphine (5 mg/kg), amitriptyline (10 mg/kg) or indomethacin (10 mg/kg). Valproate showed a statiscally significant (p<0.001) dose-response effect in these models, both in male and female mice and in female rats. Antihyperalgesic effect of valproate in the plantar model was not reverted by reserpine pre-treatment. Interestingly, the maximum effect of valproate on this model occurred at a dose of 50mg/kg and the higher dose of 100mg/kg showed a minor effect. Additionally, we demonstrated that valproate has anti-inflammatory effect in the carrageenan-induced oedema model in male and female mice. Valproate antinociceptive and anti-inflammatory effects seem not to be gender-specific in animal models.
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2015. Valproate antinociceptive and anti-inflammatory effect in female rodents. PeerJ PrePrints 3:e1613v1 https://doi.org/10.7287/peerj.preprints.1613v1Author comment
This manuscript is a previously unpublished version, based on original research of our lab.
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Figure 1: Valproate reversal of acetic acid-induced nociception (male)
The writhing test was performed as described in methods. Male Swiss mice (25-30g) were injected intraperitoneally with 0.6% acetic acid (10ml/kg) and the number of writhings was recorded over a period of 20 min. Animals were treated orally with valproate sodium in increasing doses of 10, 25, 100, and 250 mg/kg, or with morfine 5 mg/kg (positive control) 1h before acetic acid administration. Negative control animals were treated with the diluent of VPA. Number of writhings (mean ± SD) was registered.
Figure 1: Valproate reversal of acetic acid-induced nociception (female)
The writhing test was performed as described in methods. Female Swiss mice (25-30g) were injected intraperitoneally with 0.6% acetic acid (10ml/kg) and the number of writhings was recorded over a period of 20 min. Animals were treated orally with valproate sodium in increasing doses of 10, 25, 100, and 250 mg/kg, or with morfine 5 mg/kg (positive control) 1h before acetic acid administration. Negative control animals were treated with the diluent of VPA. Number of writhings (mean ± SD) was registered.
Figure 2: Valproate reversal of formalin-induced nociception
Formalin-induced paw-licking test was determined as described in methods. Female Swiss mice (25-30g) were injected by na intraplantar route in the right hindpaw with formalin (1%, 20 µl). The duration of paw licking was measured 0-5 min (first phase) and 20-25 min (second phase) after formalin administration. Animals were treated orally with valproate sodium in increasing doses of 10, 50, and 100 mg/kg 1 h before formalin administration, or with morfine 5 mg/kg (positive control) 30 min before formalin administration. Negative control animals were treated with the diluent of VPA. Lickng time is registered.
Figure 3: Valproate reversal of carrageenan-induced acute thermal hyperalgesia (A)
Plantar test was performed as described in methods. SHAM group (SHAM) had no pharmacological treatment. Control group had a 1.0 mg carrageenan plantar injection in right hindpaw 2 h before the test. Treatment groups (VPA 50, AMI 10, and INDO 10) were treated with valproate 50 mg/kg, ), amitriptyline 10 mg/kg or indomethacin 10 mg/kg at the same time of carrageenan injection. Reaction time to thermal stimulus (mean ± SD) was registered.
Figure 3: Valproate reversal of carrageenan-induced acute thermal hyperalgesia (B)
Plantar test was performed as described in methods. SHAM group (SHAM) had no pharmacological treatment. Control group had a 1.0 mg carrageenan plantar injection in right hindpaw 2 h before the test. Treatment groups (VPA 10, VPA 25, VPA 50, VPA 100) were treated with valproate 10 to 100 mg/kg at the same time of carrageenan injection. Reaction time to thermal stimulus (mean ± SD) was registered.
Figure 4: Reserpine did not modify the effect of valproate in the plantar test
Plantar test was performed as described in methods. Animals were pre-treated with reserpine (Sigma), 5.0 mg/kg, administered i.p. (0.2 ml/animal), 6 h before plantar test. Treatment groups (VPA 50) were treated with valproate 50 mg/kg at the same time of carrageenan injection. Reaction time to thermal stimulus (mean ± SD) was registered.
Figure 5: Valproate reversal of carrageenan-induced paw oedema (male)
Valproate was administered orally (10, 50 and 100 mg/kg) to mice, 60 min before intraplantar injection of 0.1 mL 1% carrageenan solution in the right hind paw. Indomethacin (2 mg/kg , p.o.) was used as a reference drug. Inflammatory oedema was evaluated by the measurement of the hind paw swelling induced by the injection of carrageenan using a plethysmometer (Ugo Basile, Italy). The hind paw was submerged to the tibiotarsal joint into the liquid-filled cell of the instrument. The volume of the displacement, which is equal to the paw volume, was then read on a digital display. The oedema (µL) was defined as the difference between the paw volume before and 1, 2, 3, 4 and 24 h after the carrageenan administration and registered.
Figure 5: Valproate reversal of carrageenan-induced paw oedema (female)
Valproate was administered orally (10, 50 and 100 mg/kg) to mice, 60 min before intraplantar injection of 0.1 mL 1% carrageenan solution in the right hind paw. Indomethacin (2 mg/kg , p.o.) was used as a reference drug. Inflammatory oedema was evaluated by the measurement of the hind paw swelling induced by the injection of carrageenan using a plethysmometer (Ugo Basile, Italy). The hind paw was submerged to the tibiotarsal joint into the liquid-filled cell of the instrument. The volume of the displacement, which is equal to the paw volume, was then read on a digital display. The oedema (µL) was defined as the difference between the paw volume before and 1, 2, 3, 4 and 24 h after the carrageenan administration and registered.
Additional Information
Competing Interests
The authors declare that they have no competing interests.
Author Contributions
Karolinne S Figueiredo performed the experiments, analyzed the data, wrote the paper, reviewed drafts of the paper.
Maria LAO Sales performed the experiments, analyzed the data, wrote the paper, reviewed drafts of the paper.
Juvenia B Fontenele conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, wrote the paper, reviewed drafts of the paper.
Glauce SB Viana conceived and designed the experiments, contributed reagents/materials/analysis tools, reviewed drafts of the paper.
Francisco H Felix conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.
Animal Ethics
The following information was supplied relating to ethical approvals (i.e., approving body and any reference numbers):
All experiments were conducted in accordance with the brazilian regulations of animal care and experimentation covered by CONCEA (National Council for Control of Animal Experimentation) documentations, and were approved by the local Institutional Animal Care and Use Committee.
Data Deposition
The following information was supplied regarding data availability:
Raw data in the supplemental files.
Funding
The authors received no funding for this work.
