Dog-specific hemorrhagic changes induced by liposomal formulations, in the liver and the gallbladder

Abstract

Although several liposomal drugs, including liposomal doxorubicin, have been approved, the etiology of the pathological responses caused by their physicochemical properties remains unknown. Herein, we investigated the pathological changes in the liver and the gallbladder of dogs following a single injection of liposomal doxorubicin (1 or 2.5 mg/kg) or an empty liposomal formulation (i.e., liposomal formulation without doxorubicin, ca. 21 mg/kg as lipid content). Injection of liposomal doxorubicin or the empty liposomal formulation induced hemorrhagic changes in the liver and the gallbladder. These changes were accompanied by minimal cellular infiltration with no obvious changes in the blood vessels. As there were no differences in the incidence and severity of hemorrhage between the groups administered comparable amounts of total lipid, the physicochemical properties of the liposomal formulation rather than an active pharmacological ingredient, doxorubicin, were associated with the hemorrhagic changes. Furthermore, decreased cytoplasmic granules with low electron density in mast cells beneath the endothelium of the hepatic vein were observed in the liver of dogs treated with liposomal doxorubicin or empty liposomal formulation. Injection of compound 48/80, a histamine releaser induced comparable hemorrhage in dogs, implying that hemorrhage caused by injection of liposomal doxorubicin or the empty liposomal formulation could be attributed to the histamine released from mast cells. The absence of similar hemorrhagic lesions in other species commonly used in toxicology studies (i.e., rats and monkeys), as well as humans, is due to the lack of mast cells beneath the endothelium of the hepatic vein in these species.

Nonclinical Testing Evaluation of Liposomes as Drug Delivery Systems

“…More recent work has indicated a sensitivity for dogs from intravenous dosing of the doxorubicin-free liposomal formulation of Doxil ® (empty liposome). 39 Macroscopical observations of reddish foci in liver and gall bladder correlated to histopathological changes of perivascular hemorrhage and dilated lymphatic vessels in liver and hemorrhage in gall bladder. Decreased cytoplasmic granules in mast cells beneath endothelium of hepatic vein were noted.…”

“…These effects were considered to be related to reactions to the physicochemical properties of liposomes such as their particle size, surface charges, PEG and cholesterol ratio. 39,40 Investigation has shown that the complement system is activated by phospholipid bilayers after liposomal injections, which leads to complement production, mediated by anaphylatoxins, and subsequent release of histamine from mast cells; this phenomenon has been named C activation-related pseudoallergy (CARPA). 41 In addition, for PEGylated liposomes, work with Caelyx TM /Doxil ® using plasma from mice and human volunteers has demonstrated that anti-PEG antibodies may contribute to complement activation.…”