Interactions of acid sphingomyelinase and lipid bilayers in the presence of the tricyclic antidepressant desipramine

Abstract

The tricyclic antidepressant desipramine causes a decrease in cellular acid sphingomyelinase (A-SMase, EC 3.1.4.12) activity when added to culture medium of human ¢bro-blasts. This e¡ect can be prevented by incubation of the cells with the protease inhibitor leupeptin, which suggests that desipramine induces proteolytic degradation of the lysosomal enzyme. By using surface plasmon resonance (SPR, Biacore) we were able to monitor the interactions of A-SMase and substrate-containing lipid bilayers immobilized on the surface of a Pioneer1 1 L1 sensor chip. SPR binding curves show that the enzyme hardly dissociates from the lipid surface at acidic pH values. On the other hand, a drop in binding signals (resonance units, RU) of approximately 50% occurred after injection of 20 mM desipramine. Our ¢ndings indicate that desipramine interferes with the binding of A-SMase to the lipid bilayers and thereby displaces the enzyme from its membrane-bound substrate. The application of control substances suggests a key role for the cationic moiety of desipramine. We hypothesize that the displacement of the glycoprotein A-SMase from the inner membranes of late endosomes and lysosomes by desipramine renders it susceptible to proteolytic cleavage by lysosomal proteases. ß 2004 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.

Acid sphingomyelinase–ceramide system mediates effects of antidepressant drugs

“…1b,c; Supplementary Fig. 1a,b,d, Supplementary note 1), a finding consistent with the induction of partial proteolysis of Asm by amitriptyline and fluoxetine 15,16 . Mice transgenic for Asm (tAsm) exhibited increased Asm activity and protein levels in the hippocampus, and amitriptyline and fluoxetine reduced Asm activity and protein levels ( Fig.…”

Regulated Secretion of Acid Sphingomyelinase

“…Desipramine is an established in vivo, but not in vitro, inhibitor of L-SMase that destabilizes the interaction between L-SMase and anionic lipids thus rendering L-SMase more susceptible to the action of lysosomal proteases (49,50). To confirm that S508A aSMase was indeed successfully trafficked to the acidic compartment, V5-LacZ, V5-aSMase WT , and V5-aSMase S508A cells were treated with increasing doses of desipramine, and L-SMase activity was measured.…”

The Role of Sphingolipids and Ceramide in Pulmonary Inflammation in Cystic Fibrosis

“…Several studies [77-80] identified pharmacological inhibitors of the acid sphingomyelinase; the acid sphingomyelinase seems to interact with intra-lysosomal membranes, thereby being protected against proteolytic inactivation [77]. Weak bases such as amitriptyline diffuse into cells, are protonated in lysosomes and concentrated in these organelles.…”

“…High pKa- and high logP-values of the drugs are necessary but not sufficient to functionally inhibit the acid sphingomyelinase [80]. These drugs interfere with binding of the acid sphingomyelinase to the membrane, which results in a detachment of the acid sphingomyelinase and subsequent proteolytic degradation [77-80]. The lipophilic ring structures that are present in all acid sphingomyelinase inhibitors are embedded in the lysosomal membrane, while the cationic amino group linked through an aliphatic chain to the ring system of all acid sphingomyelinase inhibitors interferes with binding of the enzyme to the membrane finally resulting in detachment and subsequent proteolytic degradation in the lysosome [80].…”