Topical application of disodium isostearyl 2-O-L-ascorbyl phosphate, an amphiphilic ascorbic acid derivative, reduces neuropathic hyperalgesia in rats.
OBJECTIVE
Ca(v) 3.2 T-type calcium channels, targeted by H(2) S, are involved in neuropathic hyperalgesia in rats and ascorbic acid inhibits Ca(v) 3.2 channels. Therefore, we evaluated the effects of intraplantar (i.pl.) administration of ascorbic acid or topical application of disodium isostearyl 2-O-L-ascorbyl phosphate (DI-VCP), a skin-permeable ascorbate derivative on hyperalgesia induced by NaHS, an H(2) S donor, and on neuropathic hyperalgesia.


METHODS
In rats mechanical hyperalgesia was evoked by i.pl. NaHS, and neuropathic hyperalgesia was induced by L5 spinal nerve cutting (L5SNC) or by repeated administration of paclitaxel, an anti-cancer drug. Dermal ascorbic acid levels were determined colorimetrically.


RESULTS
The NaHS-evoked Ca(v) 3.2 channel-dependent hyperalgesia was inhibited by co-administered ascorbic acid. Topical application of DI-VCP, but not ascorbic acid, prevented the NaHS-evoked hyperalgesia, and also increased dermal ascorbic acid levels. Neuropathic hyperalgesia induced by L5SNC or paclitaxel was reversed by i.pl. NNC 55-0396, a selective T-type calcium channel blocker, ascorbic acid or DI-VCP, and by topical DI-VCP, but not by topical ascorbic acid. The effects of i.pl. ascorbic acid and topical DI-VCP in the paclitaxel-treated rats were characterized by the faster onset and greater magnitude, compared with their effects in the L5SNC rats. Dermal ascorbic acid levels in the hindpaw significantly decreased after paclitaxel treatment, but not L5SNC, which was reversed by topical DI-VCP.


CONCLUSIONS
Ascorbic acid, known to inhibit Ca(v) 3.2 channels, suppressed neuropathic hyperalgesia. DI-VCP ointment for topical application may be of benefit in the treatment of neuropathic pain.
Division of Pharmacology and Pathophysiology, Kinki University School of Pharmacy, Higashi-Osaka, Japan.
Kazumasa
K
Okubo
Hiroki
H
Nakanishi
Maho
M
Matsunami
Hiroharu
H
Shibayama
Atsufumi
A
Kawabata
D000287:Administration, Topical; D000818:Animals; D001205:Ascorbic Acid / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000627:therapeutic use; D002121:Calcium Channel Blockers / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000627:therapeutic use*; D020908:Calcium Channels, R-Type; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors*; D004195:Disease Models, Animal; D006930:Hyperalgesia / Q000209:etiology / Q000378:metabolism / Q000517:prevention & control*; D008297:Male; D009437:Neuralgia / Q000150:complications / Q000188:drug therapy* / Q000378:metabolism; D009824:Ointments; D017288:Pain Threshold / Q000187:drug effects; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000378:metabolism; D012867:Skin / Q000378:metabolism; D012869:Skin Absorption
C498917:Cacna1e protein, rat; D002121:Calcium Channel Blockers; D020908:Calcium Channels, R-Type; D027682:Cation Transport Proteins; D009824:Ointments; C528521:disodium isostearyl 2-O-L-ascorbyl phosphate; D001205:Ascorbic Acid