Gene therapy of bladder pain with herpes simplex virus (HSV) vectors expressing preproenkephalin (PPE)

Abstract

Interstitial cystitis (IC) and bladder pain have been a major challenge to understand and treat. We propose a new concept in the treatment of IC and bladder pain. We hypothesize that targeted and localized expression of enkephalin in afferent nerves that innervate the urinary bladder by preproenkephalin (PPE) gene transfer using herpes simplex virus (HSV) vectors can treat bladder pain. SHZ vectors (HSV-1 with lacZ insert, 5 ×108 plaque forming units [pfu]) or SHPE vectors (HSV-1 with PPE cDNA insert, 5 × 108 pfu) were injected into the bladder wall of adult female rats. β-Galactosidase staining, which detects lacZ expression, was observed in the bladder and L6 dorsal root ganglia (DRG) 1 week after bladder injection with SHZ. At 7, 14, and 30 days after bladder injection with SHPE, PPE transgene levels in the bladder and L4, L6, S1 DRGs, which were quantified by PCR techniques using primers specific for human PPE, revealed that PPE transgene expression elevated in the bladder and L6>S1>>L4 DRGs at all time points, consistent with afferent innervation of the rat urinary bladder. Cystometrograms under urethane anesthesia exhibited that intrathecal met-enkephalin (10 μg) blocks bladder hyperactivity induced by intravesical capsaicin (15 μmol/L) in untreated rats. This effect was antagonized by intrathecal naloxone, an opioid antagonist (4 μg). SHPE-injected rats demonstrated a significantly increased intercontraction interval (ICI), compared with SHZ-injected rats (15.1 ± 3.0 vs 6.1 ± 0.97 minutes; P = 0.009). Moreover, reduction in the ICI induced by intravesical capsaicin was significantly smaller in SHPE-injected rats than SHZ-injected rats (24% vs 35% change; P = 0.04). This reduced response to capsaicin in the ICI of SHPE-injected rats was antagonized by intramuscular naloxone (0.5 mg/kg), indicating that enkephalinergic mechanisms were upregulated to suppress capsaicin-induced bladder hyperactivity in SHPE-injected animals. These results suggest that the PPE gene can be transferred and maintained in the bladder and bladder afferent nerves using HSV vectors and that increased expression of enkephalin in bladder afferent pathways can suppress nociceptive responses induced by bladder irritation. This technique of gene transfer may be useful for treating IC and other types of visceral pain.