Irreversible hypofunction of salivary glands is a common side effect of radiotherapy for head and neck cancer and is difficult to remedy. Recent studies indicate that transient activation of Hedgehog signaling rescues irradiation-impaired salivary function in animal models, but the underlying mechanisms are largely unclear. Here, we show in mice that activation of canonical Gli-dependent Hedgehog signaling by Gli1 gene transfer is sufficient to recover salivary function impaired by irradiation. Salivary gland cells responsive to Hedgehog/Gli signaling comprised small subsets of macrophages, epithelial cells, and endothelial cells, and their progeny remained relatively rare long after irradiation and transient Hedgehog activation. Quantities and activities of salivary gland resident macrophages were substantially and rapidly impaired by irradiation and restored by Hedgehog activation. Conversely, depletion of salivary gland macrophages by clodronate liposomes compromised the restoration of irradiation-impaired salivary function by transient Hedgehog activation. Single-cell RNA sequencing and qRT-PCR of sorted cells indicated that Hedgehog activation greatly enhances paracrine interactions between salivary gland resident macrophages, epithelial progenitors, and endothelial cells through Csf1, Hgf, and C1q signaling pathways. Consistently, expression of these paracrine factors and their receptors in salivary glands decreased following irradiation but were restored by transient Hedgehog activation. These findings reveal that resident macrophages and their prorepair paracrine factors are essential for the rescue of irradiation-impaired salivary function by transient Hedgehog activation and are promising therapeutic targets of radiotherapy-induced irreversible dry mouth. Significance: These findings illuminate a novel direction for developing effective treatment of irreversible dry mouth, which is common after radiotherapy for head and neck cancer and for which no effective treatments are available.

Heinz body formation has been reported in cats repeatedly administered propofol for anesthesia induction, although the resultant changes were deemed of little clinical significance (1, 2). This report suggests repeated propofol administration to some individual cats might induce anemia with clinical signs and cessation of propofol administration may result in rapid resolution. A 9-years-old American Domestic Shorthair cat receiving a 20-fraction radiation protocol for lateral thoracic fibrosarcoma showed lethargy, decreased appetite and activity, and Heinz body (3+ on blood smear examination) anemia (packed cell volume 22%; reference interval 24–45%) after 12 repeated propofol anesthesia inductions. The anesthesia induction protocol was adjusted to exclude propofol. Over the following week, the anemia resolved (packed cell volume, 30%), and the cat's activity level, appetite and attitude improved. The total dose of propofol received over the 12 treatments was 62.4 mg/kg.

Objective: To describe cardiovascular intra-anesthetic complications and ultrasensitive serum cardiac troponin I (cTnI) concentrations in dogs anesthetized repeatedly for radiation therapy (RT). Animals: 12 client-owned dogs anesthetized once daily (Monday through Friday) for 10 to 20 sessions, totaling 218 general anesthesia (GA) episodes. Clinical Presentation: American Society of Anesthesiologists III sevoflurane-anesthetized dogs (median age, 10 years [range, 2 to 11]; body weight, 27.5 kg [range, 6.0 to 42.3]) undergoing RT. Results: Comparing the first 5 to the last 5 GA episodes, the incidence of bradycardia (heart rate [HR] < 60 beats/min) decreased from 58.3% to 43.8%, hypotension (mean arterial pressure [MAP] < 60 mm Hg) from 28.3% to 16.3%, and hypertension (MAP > 120 mm Hg) from 20.0% to 9.4%. Tachycardia (HR > 160 beats/min [10%]) and ventricular arrhythmias (2.3%) remained infrequent. Fluid bolus administration increased from 5.0% to 20.8%; anticholinergics and inotropes decreased from 35.0% to 15.0%. Median (range) cTnI concentrations were (ng/mL) 0.073 (0.007 to 0.685) at baseline and 0.083 (0.006 to 0.685), 0.073 (0.018 to 0.286), 0.062 (0.010 to 0.265), and 0.033 (0.026 to 0.121) after 5, 10, 15, and 20 GA episodes, respectively. Two dogs had transient elevations after 5 GA episodes (0.132 and 0.500 ng/mL), which normalized; 3 had elevated baseline cTnI (0.135 to 0.685 ng/mL), which decreased during RT; 1 had cardiac disease. Clinical Relevance: With cardiovascular monitoring and timely support, intra-anesthetic complication decreased, and cTnI remained stable or declined with repeated anesthetics. These findings support owner-informed decision-making regarding repeated GA for RT in dogs.

Irreversible hypofunction of salivary glands is a common side effect of radiotherapy for head and neck cancer and is difficult to remedy. Recent studies indicate that transient activation of Hedgehog signaling rescues irradiation-impaired salivary function in animal models, but the underlying mechanisms are largely unclear. Here, we show in mice that activation of canonical Gli-dependent Hedgehog signaling by Gli1 gene transfer is sufficient to recover salivary function impaired by irradiation. Salivary gland cells responsive to Hedgehog/Gli signaling comprised small subsets of macrophages, epithelial cells, and endothelial cells, and their progeny remained relatively rare long after irradiation and transient Hedgehog activation. Quantities and activities of salivary gland resident macrophages were substantially and rapidly impaired by irradiation and restored by Hedgehog activation. Conversely, depletion of salivary gland macrophages by clodronate liposomes compromised the restoration of irradiation-impaired salivary function by transient Hedgehog activation. Single-cell RNA sequencing and qRT-PCR of sorted cells indicated that Hedgehog activation greatly enhances paracrine interactions between salivary gland resident macrophages, epithelial progenitors, and endothelial cells through Csf1, Hgf, and C1q signaling pathways. Consistently, expression of these paracrine factors and their receptors in salivary glands decreased following irradiation but were restored by transient Hedgehog activation. These findings reveal that resident macrophages and their prorepair paracrine factors are essential for the rescue of irradiation-impaired salivary function by transient Hedgehog activation and are promising therapeutic targets of radiotherapy-induced irreversible dry mouth.Significance:These findings illuminate a novel direction for developing effective treatment of irreversible dry mouth, which is common after radiotherapy for head and neck cancer and for which no effective treatments are available.