Annexin V detection of lipopolysaccharide-induced cardiac apoptosis

Acute inflammatory response to lipopolysaccharide (LPS) exposure is typically associated with cardiac myocyte apoptosis, which is difficult to quantify because of heart tissue specificity. We report here that radioiodinated Annexin V (I-AnxV), a specific ligand of phosphatidylserine exposed by apoptotic cells, allows tissue detection of apoptosis in LPS-treated rat hearts. Heart I-AnxV uptake was significantly increased in all cardiac territories of LPS-treated rats. In contrast, I-human serum albumin myocardial uptake was only slightly increased in LPS-treated rat hearts, suggesting limited changes in vascular protein permeability. Autoradiography of endotoxin-treated rat heart sections with I-AnxV in association with deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling and caspase 3 staining allows identification of double positive cardiac myocytes. Inhibition of apoptosis by caspase inhibitors (i.e., ZVAD.fmk and DEVD.cmk) reduced I-AnxV myocardial uptake in LPS-treated rats. Eventually, endotoxin-treated rats displayed pathological uptake of Tc-annexin in the cardiac mediastinal region whereas zVAD.fmk reduced Tc-annexin mediastinal uptake. Our results show that radioactive I-AnxV signal emerging from LPS-treated rat hearts could be related to the activation of caspase-dependent apoptotic pathway in cardiac myocytes.