# Cardiotoxicity prevention in thoracic radiotherapy: The effect of different melatonin doses on the level of oxidation markers -in vivo animal study

## TL;DR

This study finds that a low dose of melatonin (5 mg/kg) helps protect the heart from radiation damage in rats by reducing oxidative stress and improving antioxidant defenses.

## Contribution

The study identifies 5 mg/kg as the optimal melatonin dose for cardioprotection against radiation-induced oxidative stress in an animal model.

## Key findings

- A 5 mg/kg melatonin dose reduced protein and lipid peroxidation more effectively than higher doses.
- Melatonin at 5 mg/kg significantly increased antioxidant markers like Cu-Zn superoxide dismutase and total thiol groups.
- All melatonin-treated groups showed reduced cardiac damage, with the strongest protection at 5 mg/kg.

## Abstract

Radiation-induced cardiotoxicity (RIC) is a significant adverse effect of thoracic radiotherapy (RT), leading to oxidative stress, inflammation, endothelial dysfunction, myocardial fibrosis, vascular damage, and cardiac dysfunction. Melatonin (MLT), a potent antioxidant and radioprotective agent, has been suggested to mitigate these effects. This study aims to evaluate the optimal dosage of MLT for cardioprotection following RT in a rat model.

Forty-five adult male Sprague-Dawley rats were divided into five groups. The control group received 1 mL saline solution and sham irradiation. The RT-only group received 12 Gy RT in a single fraction with saline. Three experimental groups received the same RT dose with MLT at 100 mg/kg, 50 mg/kg, or 5 mg/kg. Eight weeks post-irradiation, protein oxidation, lipid peroxidation, glycoxidation, non-enzymatic redox homeostasis biomarkers, and histological changes in heart tissues were examined.

In MLT-treated groups, 5 mg/kg dose was found to be more effective in preventing protein oxidation and lipid peroxidation. The levels of advanced glycation end products were significantly lower in 5 mg/kg and 50 mg/kg MLT groups compared to the RT only group, whereas no difference was found at the high dose (100 mg/kg). When Cu-Zn superoxide dismutase activity, iron ion reducing antioxidant power and total thiol groups were evaluated, we found that 5 mg/kg MLT caused a significant increase in these antioxidant parameters, while 50 mg/kg and 100 mg/kg dose caused significant increase in superoxide dismutase. Evaluation heart tissues showed that the RIC was significantly lower in all MLT-treated groups.

5 mg/kg melatonin reduces oxidative markers and RIC in rats, indicating its potential as a low-dose cardioprotective agent after RT.

•Optimal Dose for Oxidative Stress: A 5 mg/kg dose of melatonin effectively reduced oxidative markers like protein and lipid peroxidation and advanced glycation end products. It outperformed higher doses, demonstrating its potential as a low dose radioprotective agent.•Antioxidant Activity Boost: Melatonin at 5 mg/kg significantly enhanced antioxidant defenses, increasing Cu-Zn superoxide dismutase activity and total thiol groups. This highlights its role in maintaining redox balance during radiotherapy.•Reduced Cardiac Damage: All melatonin-treated groups showed reduced cardiac damage, with 5 mg/kg providing the strongest protection. This suggests melatonin's effectiveness in preventing radiotherapy-induced cardiotoxicity.

Optimal Dose for Oxidative Stress: A 5 mg/kg dose of melatonin effectively reduced oxidative markers like protein and lipid peroxidation and advanced glycation end products. It outperformed higher doses, demonstrating its potential as a low dose radioprotective agent.

Antioxidant Activity Boost: Melatonin at 5 mg/kg significantly enhanced antioxidant defenses, increasing Cu-Zn superoxide dismutase activity and total thiol groups. This highlights its role in maintaining redox balance during radiotherapy.

Reduced Cardiac Damage: All melatonin-treated groups showed reduced cardiac damage, with 5 mg/kg providing the strongest protection. This suggests melatonin's effectiveness in preventing radiotherapy-induced cardiotoxicity.