Modification of innervation pattern by fluoroquinolone treatment in the rat salivary glands

Pefloxacin induced changes in serotonergic innervation and mast cell number in rat salivary glands

Pefloxacin is a second-generation fluoroquinolone antibiotic. Besides its advantageous characteristics, side effects including the hypofunction of salivary glands, decreased saliva production, and peripheral neuropathy were observed during the administration of pefloxacin. The aim of this study was to investigate the changes in the number of serotonergic immunoreactive fibers and mast cells after pefloxacin treatment in the parotid and sublingual glands of rats to detect the possible neurotoxic effect of pefloxacin. The adult female rats were treated with intraperitoneal (i.p.) injection of pefloxacin for three or seven days (at a concentration of 20 mg/100g body weight) and the serotonergic innervation pattern along with the change in mast cell number were evaluated by using histochemistry and immunohistochemistry in the parotid and sublingual glands. We found that a three-day treatment significantly increased the number of immunoreactive serotonergic nerve fibers, but after a seven-day treatment the number of serotonin positive nerve fibers decreased almost to values of the control group. The alteration of mast cell number was parallel with the changes of the serotonin positive fibers during the treatment. These results suggest that pefloxacin treatment can modify the finely controlled communication between the immune- and the peripheral nervous systems, resulting neurogenic inflammatory process. The background of this process is the altered serotonergic innervation and the increased number of activated mast cells releasing different mediators for example histamine, which can finally lead to reduced number of serotonin positive nerve fibers after a seven-day treatment of pefloxacin leading to atrophy and hypofunction of the salivary glands.

Radiation-Induced Loss of Salivary Gland Function Is Driven by Cellular Senescence and Prevented by IL6 Modulation

Head and neck cancer patients treated by radiation commonly suffer from a devastating side effect known as dry-mouth syndrome, which results from the irreversible loss of salivary gland function via mechanisms that are not completely understood. In this study, we used a mouse model of radiation-induced salivary hypofunction to investigate the outcomes of DNA damage in the head and neck region. We demonstrate that the loss of salivary function was closely accompanied by cellular senescence, as evidenced by a persistent DNA damage response (γH2AX and 53BP1) and the expression of senescence-associated markers (SA-βgal, p19ARF, and DcR2) and secretory phenotype (SASP) factors (PAI-1 and IL6). Notably, profound apoptosis or necrosis was not observed in irradiated regions. Signs of cellular senescence were also apparent in irradiated salivary glands surgically resected from human patients who underwent radiotherapy. Importantly, using IL6 knockout mice, we found that sustained expression of IL6 in the salivary gland long after initiation of radiation-induced DNA damage was required for both senescence and hypofunction. Additionally, we demonstrate that IL6 pretreatment prevented both senescence and salivary gland hypofunction via a mechanism involving enhanced DNA damage repair. Collectively, these results indicate that cellular senescence is a fundamental mechanism driving radiation-induced damage in the salivary gland and suggest that IL6 pretreatment may represent a promising therapeutic strategy to preserve salivary gland function in head and neck cancer patients undergoing radiotherapy.