Plasma nitric oxide levels used as an indicator of doxorubicin-induced cardiotoxicity in rats Jhon Guerra* ,1 , Ana De Jesus 1 , Pedro Santiago-Borrero 1 , Angel Roman-Franco 2 , Edwin Rodrı´guez 1 and Maria J Crespo 3 1 Department of Pediatrics, University of Puerto Rico-School of Medicine, San Juan, Puerto Rico; 2 Department of Pathology, University of Puerto Rico-School of Medicine, San Juan, Puerto Rico; 3 Department of Physiology, University of Puerto Rico- School of Medicine, San Juan, Puerto Rico Introduction: The clinical efficacy of doxorubicin is severely limited by its cardiotoxicity. The currently noninvasive techniques used to detect this complication lack sensitivity to identify its early stages. Nitric oxide (NO) is a free radical that has been implicated in the etiology of doxorubicin-induced cardiotoxicity. In the present study, we investigated whether plasmatic NO levels can be used as a noninvasive and reliable biomarker of doxorubicin-induced cardiotoxicity. Materials and methods: Two groups of six spontaneously hypertensive rats (SHR) were used for the experiment. Group 1 received 1.5 mg/kg intraperitoneal (IP) doxorubicin weekly for up to 9 weeks. Group 2 (Control) received nine weekly IP injection of 0.5 cm 3 saline. Plasmatic NO levels and cardiac ejection fraction (EF%) were determined. Ventricular biopsies were analyzed by light microscopy according with the Billinghan score. Results: Doxorubicin treatment significantly increased plasmatic NO concentration (35.3075.63 mM versus 14.7272.66 mM in control animals, n ¼ 6, Po0.05). In addition, doxorubicin decreased EF by 23% approximately (from 77.0073.89 in controls, to 59.0075.61 in doxorubicin-treated animals, n ¼ 6, Po0.05). The mean score of histological cardiac damage was 2.3370.33 for doxorubicin-treated versus 0.0870.08 for controls, n ¼ 6, Po0.001. Discussion: Our results revealed a correlation between plasmatic NO levels, systolic function and histopathological myocardial damage. Therefore, it is plausible to postulate that plasmatic NO levels could be used as a biomarker for myocardial damage in doxorubicin-treated SHR, and may be a potential tool for noninvasive evaluation of doxorubicin-induced toxicity in humans. The Hematology Journal (2005) 5, 584–588. doi:10.1038/sj.thj.6200573 Keywords: doxorubicin; nitric oxide; biomarker; cardiomyopathy; ejection fraction Introduction Doxorubicin, a broad spectrum antineoplasic antibiotic, has been widely used in the treatment of several types of cancer. 1 The clinical efficacy of this drug is limited due to the development of a severe form of cardiotoxicity, which is believed to be mediated via oxidative mechan- isms. 2–4 Many patients exhibit cumulative dose-depen- dent toxicities, but others experience acute life- threatening reactions or delayed cardiomyopathy arising months to years after cessation of therapy. 5,6 Although there are different techniques to detect cardiotoxicity, investigations are ongoing for noninva- sive sensitive methods. At present, echocardiography is the method of choice among noninvasive studies for monitoring cardiac function in many centers, but it lacks the sensitivity required to detect early stages of this cardiomyopathy, when decrease in cardiac function have not yet developed. 7 In an effort to detect this cardiac damage early, many studies have been per- formed to find a correlation between this anthracyclin- induced cardiomyopathy with different serological biomarkers, including measurements of the MB iso- enzyme, creatine kinase, lactate dehydrogenase, and troponin-T, which are released from damaged myocar- dial cells, but conclusive evidence regarding their applicability is lacking. 8–10 Nitric oxide (NO), a diatomic free radical that is known to be an important determinant of vascular tone and may have different roles in cardiac function and disease, has been found to play a crucial role in the pathophysiology of many forms of cardiovascular diseases. It has been recently demonstrated that excessive NO depresses systolic function by decreasing Received 4 May 2004; accepted 20 September 2004 *Correspondence: J Guerra, Department of Pediatrics, Hematology- Oncology Section, University of Puerto Rico School of Medicine, GPO Box 365067, San Juan, PR 00936-5067, Puerto Rico; Fax: þ 809 787 751 5812; E-mail: jhonguerra@wartech-pro.com The Hematology Journal (2005) 5, 584–588 & 2005 The European Hematology Association All rights reserved 1466-4680/05 $30.00 www.nature.com/thj