Gingerols: a novel class of vanilloid receptor (VR1) agonists

Abstract

1. Gingerols, the pungent constituents of ginger, were synthesized and assessed as agonists of the capsaicin-activated VR1 (vanilloid) receptor. 2. [6]-Gingerol and [8]-gingerol evoked capsaicin-like intracellular Ca(2+) transients and ion currents in cultured DRG neurones. These effects of gingerols were blocked by capsazepine, the VR1 receptor antagonist. 3. The potency of gingerols increased with increasing size of the side chain and with the overall hydrophobicity in the series. 4. We conclude that gingerols represent a novel class of naturally occurring VR1 receptor agonists that may contribute to the medicinal properties of ginger, which have been known for centuries. The gingerol structure may be used as a template for the development of drugs acting as moderately potent activators of the VR1 receptor.

Figure 1

Comparison of capsaicin, [6]-gingerol, [8]-gingerol and zingerone. The molecules are divided into ‘A', ‘B' and ‘C' regions, as described for capsaicin by Walpole et al. (1993a, 1993b, 1993c). Log P values were calculated using Molecular Modeling Pro software (ChemSW, version 3.23). EC₅₀ values for plasma membrane current flow were determined as described in the Results.

Figure 2

[Ca²⁺]_i transients in Fura-2 loaded DRG neurones evoked by capsaicin and constituents of ginger. Drugs were applied for 1 min where indicated by bars, following extensive wash out with physiological solutions. Successive drug applications were: (A) 500 nM capsaicin (Cap), 10 μM capsaicin, 50 mM KCl, 2 μM ionomycin; (B) 10 μM [6]-gingerol ([6]-G), 10 μM capsaicin, 50 mM KCl; (C) 10 μM [8]-gingerol ([8]-G), 10 μM capsaicin, 50 mM KCl. Data from Fura-2 loaded DRG neurones typical of 10–20 cells from at least three separate cultures represent capsaicin and gingerol evoked [Ca²⁺]_i transients (trace 1) and capsaicin and gingerol-insensitive [Ca²⁺]_i transients (trace 2).

Figure 3

Effect of pre-treatment of DRG neurones with capsaicin and capsazepine on gingerol [Ca²⁺]_i transient responses. [Ca²⁺]_i transients are represented as an increase in fluorescence ratio (F/F_max; basal amplitude=0.3±0.09) of Fluo-4 loaded DRG neurones (typical of 20–30 cells from at least three separate cultures) evoked by capsaicin, [6]-gingerol and [8]-gingerol. Drugs were applied for 5–10 s, as shown by bars in the Figure, following a 3-min wash out with physiological solutions between additions. Capsazepine applications are shown as indicated by bars. Successive drug applications were: (A) 100 nM capsaicin (Cap), 10 μM [6]-gingerol ([6]-G) and 50 mM KCl; (B) 100 nM capsaicin, 10 μM capsazepine (Cpz), 10 μM [6]-gingerol, 100 nM capsaicin and 50 mM KCl; (C) 100 nM capsaicin, 10 μM [8]-gingerol ([8]-G) and 50 mM KCl; (D) 100 nM capsaicin, 10 μM capsazepine, 10 μM [8]-gingerol, 100 nM capsaicin and 50 mM KCl.

Figure 4

Ion currents evoked by capsaicin and gingerols in whole-cell patch clamped DRG neurones. (A) Voltage ramp was applied to patch-clamped DRG neurons in the presence of 10 μM capsaicin, 30 μM [8]-gingerol and 300 μM [6]-gingerol. Note the same I/V characteristics for all three drugs. (B) Ion current dose response to capsaicin, [8]-gingerol, [6]-gingerol and zingerone calculated as percentage to the amplitude of current evoked by 10 μM capsaicin. Data are presented as mean±s.d of at least six neurones per data point.