Short small-interfering RNAs produce interferon-α-mediated analgesia.
BACKGROUND
There is increasing interest in RNA interference in pain research using the intrathecal route to deliver small-interfering RNA (siRNA). An interferon (IFN) response is a common side-effect of siRNA. However, the IFN response in the spinal cord after intrathecal administration of siRNA remains unknown. We hypothesized that high doses of siRNAs can elicit off-target analgesia via releasing IFN-α. We investigated the IFN response and its role in regulating pain sensitivity in the spinal cords after intrathecal administration of siRNAs.


METHODS
Male Sprague-Dawley rats were given intrathecal injections of non-targeting (NT) siRNAs or IFN-α and tested for complete Freund's adjuvant (CFA)-induced mechanical allodynia and heat hyperalgesia. IFN-α in the spinal cord after injection of NT siRNAs was measured by western blotting and immunohistochemical staining.


RESULTS
IFN-α was up-regulated in the spinal cord after intrathecal treatment of NT siRNAs. Intrathecal injection of NT siRNAs, at high doses of 10 or 20 μg, reduced CFA-induced inflammatory pain (P<0.05). Intrathecal application of IFN-α inhibited pain hypersensitivity in inflamed rats and produced analgesia in naïve rats (P<0.05). Notably, the anti-nociceptive effects elicited by NT siRNAs and IFN-α were reversed by IFN-α neutralizing antibody and naloxone.


CONCLUSIONS
Our data suggest that (i) intrathecal administration of high doses of siRNA (≥ 10 μg) induced up-regulation of IFN-α in the spinal cord and produced analgesic effects through IFN-α, and (ii) IFN-α's analgesic effect is mediated via opioid receptors. Caution must be taken to avoid IFN-α-mediated analgesic effects of siRNAs in pain research.
Department of Anesthesiology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA. tanphphd@hotmail.com
P H
PH
Tan
Y J
YJ
Gao
T
T
Berta
Z Z
ZZ
Xu
R R
RR
Ji
D000698:Analgesia / Q000379:methods*; D000818:Animals; D015153:Blotting, Western; D004195:Disease Models, Animal; D005620:Freund's Adjuvant / Q000008:administration & dosage / Q000494:pharmacology; D006930:Hyperalgesia / Q000188:drug therapy; D007155:Immunologic Factors / Q000494:pharmacology; D007249:Inflammation / Q000150:complications / Q000188:drug therapy; D007278:Injections, Spinal; D016898:Interferon-alpha / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D010146:Pain / Q000150:complications / Q000188:drug therapy*; D059408:Pain Management / Q000379:methods; D017288:Pain Threshold / Q000187:drug effects; D034741:RNA, Small Interfering / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects
D007155:Immunologic Factors; D016898:Interferon-alpha; D034741:RNA, Small Interfering; D005620:Freund's Adjuvant