Does verapamil act as an immunomodulatory drug in vivo?

Area of Science:

• Immunology
• Pharmacology
• Cell Biology

Background:

• Previous in vitro studies suggested calcium (Ca2+) entry blockers might impact lymphocyte activation, proliferation, and effector functions.
• This hypothesis stemmed from observations of Ca2+ channel blocker effects on immune cells in laboratory settings.

Purpose of the Study:

• To investigate the in vitro and in vivo effects of the Ca2+ entry blocker verapamil on human lymphocytes.
• To determine if the in vitro inhibitory effects of verapamil on lymphocytes translate to in vivo clinical relevance.

Main Methods:

• In vitro experiments assessed the impact of verapamil, diltiazem, and nifedipine on mitogen-stimulated human lymphocyte Ca2+ influx, inositol phosphate generation, and proliferation.
• In vivo studies involved healthy volunteers treated with verapamil, followed by analysis of circulating lymphocyte counts, subset distribution, and in vitro responses.

Main Results:

• High concentrations of verapamil (100 microM) inhibited in vitro lymphocyte activation, including Ca2+ influx, inositol phosphate generation, and proliferation.
• In vivo verapamil treatment in healthy volunteers did not alter lymphocyte numbers, subset distribution, or in vitro mitogen-stimulated proliferation and IL-2 receptor expression.

Conclusions:

• The in vitro inhibitory effects of verapamil on lymphocyte activation are unlikely to be therapeutically relevant in vivo.
• The observed in vitro effects may not be directly linked to the Ca2+ entry blocking properties of verapamil.