The effect of azithromycin on acute and chronic inflammation in an in vivo experimental model.

Abstract

Background: Macrolide antibiotics have been found to have both antimicrobial and antiinflammatory properties. They may be useful adjuncts in the treatment of conditions in which both these factors play a role, such as periodontitis. Objectives: The aim of this study was to evaluate the effect of azithromycin in a rat model of experimentally induced acute and chronic inflammation. Material and methods: Polyurethane sponges loaded with either heat killed Porphyromonas gingivalis (HKPG), Mycobacterium tuberculosis (HKTB) or Phosphate Buffered Saline (PBS) were surgically implanted into the fore flanks of rats. To determine any acute inflammatory effects animals received azithromycin 4 days prior to surgery, while to determine the effects on chronic inflammation animals did not receive azithromycin until day 25 post operatively. The control groups did not receive azithromycin. The sponges were retrieved at days 7, 14, 21, 35 and 49, wet weights recorded and then processed for histological evaluation of acute and chronic inflammation and fibrosis. Additionally, immunohistochemical staining was used to identify macrophages using CD163 and CD68 macrophage markers at days 21 and 35. Biochemical analyses were used to determine serum levels of C-reactive protein (CRP) and hydroxyproline (HP) content in the retrieved sponges. Results: No differences were found between wet and dry weights of sponges for any of the groups. Acute Inflammation: A trend for lower inflammation and infiltration scores was observed for all azithromycin treated groups compared to untreated groups, although this was not statistically significant. Azithromycin reduced neutrophil infiltration in all groups, but this reduction was only significant in the acute HKTB group (p= 0.008). Although azithromycin reduced CD68 cell counts between treated and untreated animals in all groups, this was found to be significant only for animals with PBS sponges at day 21 as well as day 35 and TB sponges at day 35. Similarly, for CD163 it was found that although azithromycin reduced counts of CD163 positive cells, this was only significant at day 35 for PBS (p<0.001) and HKTB (p<0.001). The hydroxyproline content differed within sponges for rats with HKTB 66 sponges at days 7 (p=0.001), 14 (p=0.04) and 21 (p=0.001) as well as PBS sponge implants was at all time points (p<0.05) for animals that had received azithromycin, compared to control animals. CRP levels increased between 32-58% in all groups after sponge implantation, but a significant difference was only observed between the azithromycin treated and untreated groups at day 21 for animals with PBS sponge implants. Chronic Inflammation: Animals in this part of the study received the late (day 25) administration of azithromycin. No statistically significant effects were demonstrated on any of the measured (histological or biochemical) parameters, except the sponge hydroxyproline content, which was significantly reduced at day 35 for animals that had received HKTB (p=0.012) and HKPG (p=0.025) sponges. Conclusions: Azithromycin has the potential to suppress neutrophil infiltration and thus modulate acute inflammation in a subcutaneous rat model for inflammation. The drug has a limited effect on macrophage infiltration and the collagen content of the resulting scar tissue, but no significant impact on serum CRP levels. Once chronic inflammation has ensued, the anti-inflammatory effect of azithromycin was less marked than effects on acute inflammation, although a tendency for reduction of inflammation was observed.