# Melatonin free form versus its chitosan-loaded nano formula impact on wound healing of albino rat’s parotid gland “a histological study”

## TL;DR

This study compares free melatonin and melatonin-loaded chitosan nanoparticles in healing rat parotid gland wounds, finding the nanoparticles more effective.

## Contribution

The novel contribution is demonstrating that melatonin-loaded chitosan nanoparticles enhance wound healing in rat parotid glands compared to free melatonin.

## Key findings

- Melatonin-loaded chitosan nanoparticles (MET-CNPs) promoted better regeneration of acini and ducts in parotid gland wounds.
- MET-CNPs reduced fibrosis and inflammation, as shown by lower vimentin immunoreactivity.
- AQP5 expression was higher in MET-CNPs-treated groups, indicating improved gland function.

## Abstract

This study was carried out in rat’s parotid glands to compare the regenerative effect of melatonin (MET) as a free drug and when loaded on chitosan nanoparticles (CNPs).

Seventy-two male albino rats were divided into four groups. Circular wounds were created (5 mm diameter*2 mm depth) in right parotid glands using biopsy puncher. Wounds in group I were left to heal spontaneously while in group II received topical MET treatment. Wounds in group III received topical nanoparticles (NPs), while group IV received topical melatonin loaded chitosan nanoparticles (MET-CNPs). Rats in four groups were euthanized 3, 14, 30 days post-surgery. Salivary glands (SGs) specimens were processed for ordinary Hematoxylin and eosin (H&E) and anti-vimentin immunohistochemical (IHC) staining. Other specimens were used to demonstrate Aquaporin 5 (AQP5) expression using real time polymerase chain reaction (RT-PCR).

H&E findings were fibrosis, dilated, congested blood vessels, massive inflammation, and loss of the normal outline of acini with pyknosis and vacuolation after 3 days in all groups. After 14 days in group IV there were newly developed ducts and acini in the wound area. After 30 days in group IV, there was an increase in the development of ducts and acini with restoration of normal acini outline. Anti-vimentin findings were the least immunoreactivity in group IV, with means and standard deviation (SD), 1.466 ± 0.107, and highest in positive control 8.330 ± 0.214. AQP5 expression was highest after 3 days, 13.836 ± 0.004, and lowest after 14 days in group IV 8.612 ± 0.004, while in group II it was lowest after 30 days 0.256 ± 0.003.

MET-CNPs have better healing and regenerative effects in surgical wounds of rats’ parotid glands, by enhancing the formation of new acini and ductal tissue. Also, through decreasing fibrosis as indicated by suppressed vimentin, and propagating function, as shown by increased expression of AQP5.

The online version contains supplementary material available at 10.1186/s12903-025-06869-4.