Use of verapamil as a potential P-glycoprotein inhibitor in a patient with refractory epilepsy.

OBJECTIVE: To describe a patient in whom we used adjunctive verapamil therapy was used for its P-glycoprotein inhibitory effects. CASE SUMMARY: Verapamil was added to the antiepileptic drug regimen of a 24-year-old woman with intractable epilepsy. The average time interval between hospitalizations for complex partial status doubled. The addition of verapamil greatly improved overall seizure control and subjective quality of life in this pharmacoresistant patient. DISCUSSION: The overexpression of P-glycoprotein in the central nervous system may be one mechanism of pharmacoresistance in patients with epilepsy. The calcium-channel blocker verapamil is a known inhibitor of P-glycoprotein and may function to block P-glycoprotein-modulated efflux of antiepileptic drugs in the brain, thereby raising the intracellular concentration of antiepileptic drugs and ultimately decreasing seizure burden in patients with refractory epilepsy. CONCLUSIONS: Verapamil may offer pharmacoresistant patients hope of improved seizure control due to its potential P-glycoprotein inhibitory effects.

A lymphocyte-generated fragment of vasoactive intestinal peptide with VPAC1 agonist activity and VPAC2 antagonist effects.

Vasoactive intestinal peptide receptors 1 (VPAC1) and 2 (VPAC2) have been identified in humans. Cell lines expressing only VPAC1 (HT-29) or VPAC2 (Molt-4b) were identified using real-time reverse transcriptase polymerase chain reaction. Vasoactive intestinal peptide (VIP) and related peptides, VIP-6-28, VIP4-28, and VIP10-28, previously isolated from cultures of human leukocytes, were evaluated for their ability to bind to VPAC1 and VPAC2 and to increase the levels of cAMP in HT-29 and Molt-4b cells. VIP bound to membranes of HT-29 colon carcinoma cells and Molt-4b lymphoblasts with high affinity (KD = 1.6 +/- 0.2 and 1.7 +/- 0.9 nM, respectively). VIP4-28 also demonstrated high-affinity binding (KD = 1.7 +/- 0.2 and 1.7 +/- 0.7 nM in HT-29 and Molt-4b, respectively). VIP and VIP4-28 are potent VPAC1 agonists, inducing maximal 200- and 400-fold increases in cAMP, respectively. VIP demonstrated weak VPAC2 agonist activity, inducing a maximal 14-fold increase in cAMP. VIP4-28 had no VPAC2 agonist activity but demonstrated potent VPAC2 antagonist activity. VIP4-28 inhibited VPAC2-mediated increases in cAMP in Molt-4b cells up to 95%, but had no antagonistic effect on VPAC1. Lymphoblasts did not hydrolyze VIP4-28 to a form with VPAC1 antagonist activity. VIP4-28 thus is a lymphocyte-generated VIP fragment with potent agonist activity for VPAC1 and potent antagonist activity for VPAC2.