Treatment of Schizophrenia With L-tetrahydropalmatine (l-THP): a Novel Dopamine Antagonist With Anti-inflammatory and Antiprotozoal Activity

Schizophrenia is a devastating and complex illness, with multiple symptom and behavioral manifestations. Antipsychotic medications are the mainstay of treatment; however, many patients only partially respond to treatment. Development of new treatment has not progressed rapidly, in part, because the underlying etiopathophysiology of the illness is not well understood. To date, all pharmacological treatments approved for use in schizophrenia involve primary modulation of the dopamine system. Many agents without dopamine action have failed to demonstrate efficacy. There is growing evidence that schizophrenia may be, in part, due to an inflammatory process and pharmacological treatment approaches that decrease inflammation have shown promise. Thus, treatments that may have anti-inflammatory properties (e.g., TNF-alpha inhibition), but also possess dopamine modulation may prove to be beneficial. This novel medication, l-tetrahydropalmatine (l-THP), has robust anti-inflammatory properties, particularly TNF-alpha and ICAM inhibition; has antiprotozoal activity; and possesses an antipsychotic-like pharmacological profile of D1, D2 and D3 receptor antagonism. The high affinity of l-THP for D1 versus D2 receptors distinguishes it from first generation antipsychotics and its D1 to D2 ratio resembles that of the superior antipsychotic, clozapine. Also, an almost identical compound, l-stepholindine (l-SPD), demonstrates robust antipsychotic activity in humans (both positive and negative symptoms) and is currently used clinically in China. l-THP has been used for over 40 years clinically in China, has a good safety profile to date, and represents a novel and exciting mechanism for schizophrenia treatment. Initial safety data from our phase I study of l-THP (20 healthy controls) shows excellent tolerability and lack of any substantial side effects. L-THP has been tested in outpatient drug abuse trials for 4 weeks with good safety data, (Hu et al 2006, Yang et al 2003). Yang et al (2003) randomized this medication in over 120 participants for 4 weeks with 4 week observation without any notable side effects.

We will test this compound (30 mg BID) as an adjunct treatment in a randomized, double-blind, 4-week trial, in which we will assess treatment efficacy, changes in peripheral cytokine concentrations, and, secondarily, antiprotozoal effects, (antibody titers to Toxoplasma gondii), an infection that is known to occur at higher rates in schizophrenia than healthy controls and may be related in part to the illness.