Passiflora incarnata attenuation of neuropathic allodynia and vulvodynia apropos GABA-ergic and opioidergic antinociceptive and behavioural mechanisms.

BACKGROUND: Passiflora incarnata is widely used as an anxiolytic and sedative due to its putative GABAergic properties. Passiflora incarnata L. methanolic extract (PI-ME) was evaluated in an animal model of streptozotocin-induced diabetic neuropathic allodynia and vulvodynia in rats along with antinociceptive, anxiolytic and sedative activities in mice in order to examine possible underlying mechanisms. METHODS: PI-ME was tested preliminary for qualitative phytochemical analysis and then quantitatively by proximate and GC-MS analysis. The antinociceptive property was evaluated using the abdominal constriction assay and hot plate test. The anxiolytic activity was performed in a stair case model and sedative activity in an open field test. The antagonistic activities were evaluated using naloxone and/or pentylenetetrazole (PTZ). PI-ME was evaluated for prospective anti-allodynic and anti-vulvodynic properties in a rat model of streptozotocin induced neuropathic pain using the static and dynamic testing paradigms of mechanical allodynia and vulvodynia. RESULTS: GC-MS analysis revealed that PI-ME contained predominant quantities of oleamide (9-octadecenamide), palmitic acid (hexadecanoic acid) and 3-hydroxy-dodecanoic acid, among other active constituents. In the abdominal constriction assay and hot plate test, PI-ME produced dose dependant, naloxone and pentylenetetrazole reversible antinociception suggesting an involvement of opioidergic and GABAergic mechanisms. In the stair case test, PI-ME at 200 mg/kg increased the number of steps climbed while at 600 mg/kg a significant decrease was observed. The rearing incidence was diminished by PI-ME at all tested doses and in the open field test, PI-ME decreased locomotor activity to an extent that was analagous to diazepam. The effects of PI-ME were antagonized by PTZ in both the staircase and open field tests implicating GABAergic mechanisms in its anxiolytic and sedative activities. In the streptozotocin-induced neuropathic nociceptive model, PI-ME (200 and 300 mg/kg) exhibited static and dynamic anti-allodynic effects exemplified by an increase in paw withdrawal threshold and paw withdrawal latency. PI-ME relieved only the dynamic component of vulvodynia by increasing flinching response latency. CONCLUSIONS: These findings suggest that Passiflora incarnata might be useful for treating neuropathic pain. The antinociceptive and behavioural findings inferring that its activity may stem from underlying opioidergic and GABAergic mechanisms though a potential oleamide-sourced cannabimimetic involvement is also discussed.

HPLC-based activity profiling approach for the discovery of GABAA receptor ligands using an automated two microelectrode voltage clamp assay on Xenopus oocytes.

An approach for rapid HPLC-based profiling for new GABA (A) ligands of natural origin has been developed. Active extracts are separated by a single injection of 3-10 mg of extract onto a semi-preparative (150 x 10 mm i. d.) HPLC column with gradient elution and time-based fractionation. The microfractions are tested in an automated two-microelectrode voltage-clamp assay on Xenopus oocytes expressing recombinant GABA (A) channels composed of alpha (1), beta (2) and gamma (2S) subunits. The protocol has been validated by spiking experiments with inactive extract and the GABA (A) receptor ligand magnolol, and by profiling of active extracts such as valerian extract containing the known GABA (A) receptor ligand valerenic acid. For dereplication of GABA containing extracts, we established a rapid and simple procedure by which GABA is analyzed as OPA derivative by reversed-phase HPLC. This dereplication protocol was validated with plant and fungal extracts which had been previously tested active or inactive in the oocyte assay and with spiking experiments.