S.A.B.E. van Acker

Doxorubicin-induced cardiotoxicity monitored by ECG in freely moving mice A new model to test potential protectors

Abstract In laboratory animals, histology is most commonly used to study doxorubicin-induced cardiotoxicity. However, for monitoring during treatment, large numbers of animals are needed. Recently we developed a new method to measure ECG values in freely moving mice by telemetry. With this model we investigated the effect of chronic doxorubicin administration on the ECG of freely moving BALB/c mice and the efficacy of ICRF-187 as a protective agent. The ST interval significantly widened from 15.0±1.5 to 56.8±11.8 ms in week 10 (7 weekly doses of 4 mg/kg doxorubicin given i.v. plus 3 weeks of observation). The ECG of the control animals did not change during the entire study. After sacrifice the hearts of doxorubicin-treated animals were enlarged and the atria were hypertrophic. As this schedule exerted more toxicity than needed to investigate protective agents, the protection of ICRF-187 was determined using a dose schedule with lower general toxicity (6 weekly doses of 4 mg/kg doxorubicin given i.v. plus 2 weeks of observation). On this schedule, the animals’ hearts appeared normal after sacrifice and ICRF-187 (50 mg/kg given i.p. 1 h before doxorubicin) provided almost full protection. These data were confirmed by histology. The results indicate that this new model is very sensitive and enables monitoring of the development of cardiotoxicity with time. These findings result in a model that allows the testing of protectors against doxorubicin-induced cardiotoxicity as demonstrated by the protection provided by ICRF-187.

Monohydroxyethylrutoside as protector against chronic doxorubicin‐induced cardiotoxicity

1 The clinical use of the antitumour agent, doxorubicin, is largely limited by the development of a cumulative dose‐related cardiotoxicity. This toxicity is generally believed to be caused by the formation of oxygen free radicals. In earlier studies it was established that flavonoids, naturally occurring antioxidants, can provide some degree of protection. In this study we investigated whether 7‐monohydroxyethylrutoside (monoHER), a powerful antioxidative flavonoid with extremely low toxicity, can provide protection to an extent comparable to the clinically successful Cardioxane (ICRF‐187). 2 Balb/c mice of 20–25 g were equipped i.p. with a telemeter to measure ECG. They were given 6 i.v. doses of doxorubicin (4 mg kg −1) at weekly intervals. ICRF‐187 (50 mg kg−1) or monoHER (500 mg kg−1) were administered i.p. 1 h before doxorubicin administration. In the 2 monoHER groups the treatment continued with either 1 or 4 additional injections per week. A saline and monoHER treated group served as controls. After these 6 weeks, they were observed for another 2 weeks. 3 At the end of this study (week 8) the ST interval had increased by 16.7 ±2.7 ms (mean ± s.e.mean) in doxorubicin‐treated mice. At that time, the ST interval had increased by only 1.8 ±0.9 ms in ICRF‐187 co‐mediated mice and in monoHER co‐medicated mice by only 1.7 ±0.8 and 5.1 ± 1.7 ms (5‐ and 2‐day schedule, respectively, all P< 0.001 relative to doxorubicin and not significantly different from control). The ECG of the control animals did not change during the entire study. The QRS complex did not change in either group. 4 It can be concluded that monoHER protects against doxorubicin‐induced cardiotoxicity and merits further evaluation in this respect.

Effect of dimethyl sulfoxide (DMSO) on the electrocardiogram (ECG) in freely moving male balb/c mice

1. Since dimethyl sulfoxide (DMSO) is a solvent which is often used for drugs in animal studies, we investigated the effect of a daily administration of DMSO on the telemetrically obtained electrocardiogram (ECG) in freely moving male Balb/c mice. 2. During treatment with 4.5 ml 100% DMSO/kg i.p. 5 days per week during 3 weeks, DMSO caused substantial cardiotoxicity. The ST-interval increased significantly after 1 week by 2.2 +/- 1.3 msec and also the ECG wave form changed completely in time. 3. During treatment with 4.5 ml 50% DMSO/kg i.p. 5 days per week during 3 weeks, no significant difference was observed compared with the control animals. 4. During the entire study the maximal heart rate and body weight remained constant in all treated groups. 5. The data indicate that DMSO can not be used in a 100% concentration to dissolve compounds that are tested for protection against the cardiotoxicity of cytostatics.