A Mechanistic Approach to the Development of Gene Therapy for Chronic Pain.

Treatment of chronic pain has created a "silent epidemic," a term that describes the serious public health problem of the abuse of opioid painkillers and other prescription drugs. Conventional pharmacotherapy is limited by the loss of effectiveness in the long-term and by potentially lethal side effects. Efforts need to be focused on the development of nonpharmacological approaches. As significant progress is made in the viral vector technology, gene therapy involving recombinant viruses as vehicles may become a viable alternative for treatment of severe pain. Virus-based gene therapy has several advantages: (1) the transfer of a therapeutic gene to produce/release bioactive therapeutic molecules in a specific location in the nervous system thus minimizing the risks of off-target side effects, and (2) sustained long-term production of the therapeutic agent. This review compiles recently developed strategies for gene therapy targeting specific mechanisms of specific chronic pain conditions. A few successful studies on animal models of chronic pain have been translated to human clinical trials.

Endogenous steroid production in the spinal cord and potential involvement in neuropathic pain modulation.

It has recently been demonstrated that the spinal cord (SC) is an active production center of neuroactive steroids including pregnenolone, dehydroepiandrosterone, progesterone and allopregnanolone. Indeed, anatomical, cellular and biochemical investigations have shown that the SC dorsal horn (DH), a pivotal structure in nociception, contains various active steroidogenic enzymes such as cytochrome P450side-chain-cleavage, cytochrome P450c17, 3beta-hydroxysteroid dehydrogenase, 5alpha-reductase and 3alpha-hydroxysteroid oxido-reductase. Reviewed here are several data obtained with in vitro and vivo experiments showing that endogenous steroids synthesized in the SC are involved in the modulation of nociceptive mechanisms. Various approaches were used as the real-time polymerase chain reaction after reverse transcription to determine the effects of neuropathic pain on the expression of genes encoding steroidogenic enzymes in the DH. Combination of the pulse-chase technique with high performance liquid chromatography and continuous flow scintillation detection allowed investigations of the impact of noxious signals on the activity of steroid-producing enzymes in the SC in vitro. Radioimmunological analyses of spinal tissue extracts contributed to determine the link between the painful state and endogenous steroid secretion in the SC in vivo. Finally, the physiological relevance of the modification of endogenous steroid formation in the SC during painful situation was discussed.