Cardiac autonomic modulation induced by doxorubicin in a rodent model of colorectal cancer and the influence of fullerenol pretreatment

<div><p>The very effective anticancer drug doxorubicin (DOX) is known to have cardiotoxic side effects, which could be accompanied by autonomic modulation. Autonomic disbalance might even be an initiating mechanism underlying DOX-induced cardiotoxicity and can be studied noninvasively by the analysis of heart rate variability (HRV). A number of strategies have been assessed to predict chemotherapy-induced cardiac dysfunction while HRV, a potential detecting tool, has not yet been tested. Thus, we aimed to determine the effect of DOX treatment on HRV in a rat model of colorectal cancer. While pretreatment with fullerenol (Frl) acts protectively on DOX-induced cardiotoxicity, we aimed to test the effect of Frl pretreatment on DOX-induced HRV alterations. After the induction of colorectal cancer, adult male Wistar rats were treated with saline (n = 7), DOX (1.5 mg/kg per week, n = 7) or DOX after pretreatment with Frl (25 mg/kg per week, n = 7) for three weeks (cumulative DOX dose 4.5 mg/kg). One week after treatment rats were anaesthetized, standard ECG was measured and HRV was analyzed in time and frequency domain. During autopsy the intestines and hearts were gathered for biochemical analysis and histopathological examination. DOX treatment significantly decreased parasympathetically mediated high-frequency component (p<0.05) and increased the low-frequency component of HRV (p<0.05), resulting in an increased LF/HF ratio (p<0.05) in cancerous rats. When pretreated with Frl, DOX-induced HRV alterations were prevented: the high-frequency component of HRV increased (p<0.01), the low-frequency decreased (p<0.01), LF/HF ratio decreased consequently (p<0.01) compared to DOX only treatment. In all DOX-treated animals, disbalance of oxidative status in heart tissue and early myocardial lesions were found and were significantly reduced in rats receiving Frl pretreatment. Autonomic modulation accompanied the development of DOX-induced cardiotoxicity in rat model of colorectal cancer and was prevented by Frl pretreatment. Our results demonstrated the positive prognostic power of HRV for the early detection of DOX-induced cardiotoxicity.</p></div

Representative histologic pictures of the heart sections.

<p>(a) DMH-treated Wistar rats, control group; (b) after DOX therapy; (c) DOX therapy in combination with Frl pretreatment, haematoxylin-eosin staining, magnification 400x.</p

Representative histologic pictures of the colon lesions.

<p>All DMH-treated Wistar rats developed small microscopically visible colon lesions such as hyperplastic (a) or dysplastic crypts (b), adenomas (c) and adenocarcinomas (d). Kreyberg staining, magnification 400x (a,b), 200x (c,d).</p

Frequency domain indices in control, DOX and Frl/DOX groups of animals.

<p>Statistically significant differences of control and Frl/DOX group were found in nLF, nHF and LF/HF compared to DOX. Control: group of rats with colorectal carcinoma without anticancer treatment, DOX: group of rats with colon cancer, treated with doxorubicin (DOX), Frl/DOX: group of rats with colon cancer, treated with doxorubicin, pretreated with Fullerenol. *—statistically significant difference of control group compared to DOX (p<0.05), #—statistically significant difference of Frl/DOX group compared to DOX (p<0.01). nLF: integral under the low-frequency (LF) part of the power spectral density function expressed in normalized units (NU), nHF: integral under the high frequency (HF) part of the power spectral density function expressed in NU; LF/HF: the ratio between power spectrum density in HF part and LF part of the total power spectrum.</p

Body weight of rats throughout the experiment.

<p>Each curve represents one group of animals. Control: group of rats with colon cancer without anticancer treatment; DOX: doxorubicin-treated group; Frl/DOX: doxorubicin-treated group with fullerenol pretreatment. *:<i>p</i> < 0.05 weight gain at 19th week compared to 16th week in control group, no significant weight gain in the same time interval in both DOX group. Arrows indicate time of Dox administration.</p

Cardiac lesion scores in cancer controls, rats treated with doxorubicin and doxorubicin pretreated with fullerenol.

<p>Cardiac lesion scores in cancer controls, rats treated with doxorubicin and doxorubicin pretreated with fullerenol.</p

Heart rate and heart rate variability parameters in time and frequency domains.

<p>Heart rate and heart rate variability parameters in time and frequency domains.</p

Biochemical evaluation of the heart oxidative status in cancerous rats treated with DOX alone or with Frl pretreatment.

<p>MDA: malondialdehyde; GSH/GSSG: free glutathione to free glutathione disulfide ratio; SOD: superoxide dismutase; CAT: catalase. *: p < 0.05 compared to DOX; #: p < 0.01 compared to DOX; &: p < 0.05 compared to control group.</p