Lymphocyte subsets in irradiation-induced sialadenitis of the submandibular gland

Evaluating the transcriptional landscape and cell-cell communication networks in chronically irradiated parotid glands

Understanding the transcriptional landscape that results in chronic salivary hypofunction after irradiation will help identify injury mechanisms and develop regenerative therapies. We present scRNA-seq analysis from control and irradiated murine parotid glands collected 10 months after irradiation. We identify a population of secretory cells defined by specific expression of Etv1, which may be an acinar cell precursor. Acinar and Etv1+ secretory express Ntrk2 and Erbb3, respectively while the ligands for these receptors are expressed in myoepithelial and stromal cells. Furthermore, our data suggests that secretory cells and CD4+CD8+T-cells are the most transcriptionally affected during chronic injury with radiation, suggesting active immune involvement. Lastly, evaluation of cell-cell communication networks predicts that neurotrophin, neuregulin, ECM, and immune signaling are dysregulated after irradiation, and thus may play a role in the lack of repair. This resource will be helpful to understand cell-specific pathways that may be targeted to repair chronic damage in irradiated glands.

Long-term functional regeneration of radiation-damaged salivary glands through delivery of a neurogenic hydrogel

Salivary gland acinar cells are severely depleted after radiotherapy for head and neck cancer, leading to loss of saliva and extensive oro-digestive complications. With no regenerative therapies available, organ dysfunction is irreversible. Here, using the adult murine system, we demonstrate that radiation-damaged salivary glands can be functionally regenerated via sustained delivery of the neurogenic muscarinic receptor agonist cevimeline. We show that endogenous gland repair coincides with increased nerve activity and acinar cell division that is limited to the first week after radiation, with extensive acinar cell degeneration, dysfunction, and cholinergic denervation occurring thereafter. However, we found that mimicking cholinergic muscarinic input via sustained local delivery of a cevimeline-alginate hydrogel was sufficient to regenerate innervated acini and retain physiological saliva secretion at nonirradiated levels over the long term (>3 months). Thus, we reveal a previously unknown regenerative approach for restoring epithelial organ structure and function that has extensive implications for human patients.

Diagnostic Accuracy of 18F-FDG-PET/CT and 18F-FDG-PET/MRI in Detecting Locoregional Recurrence of HNSCC 12 Weeks after the End of Chemoradiotherapy: Single-Center Experience with PET/MRI

Purpose

In head and neck squamous cell carcinoma (HNSCC), the early diagnosis and efficient detection of recurrences and/or residual tumor after treatment play a very important role in patient's prognosis. Positron emission tomography (PET) using 2-deoxy-2-¹⁸F-fluoro-D-glucose (¹⁸F-FDG) has become an established method for the diagnosis of suspected recurrence in head and neck carcinomas. In particular, integrated PET/MRI imaging that provides optimal soft tissue contrast and less dental implant artifacts compared to PET/CT is an intriguing technique for the follow-up imaging of HNSCC patients. The aim of this study was to evaluate the benefit of PET/MRI compared to PET/CT in post-treatment follow-up imaging of HNSCC patients.

Methods

This retrospective observational cohort study consists of 104 patients from our center with histologically confirmed HNSCC. All patients received chemoradiotherapy (CRT) and underwent ¹⁸F-FDG-PET/CT (n = 52) or ¹⁸F-FDG-PET/MRI (n = 52) scan 12 weeks after the end of treatment. Image analysis was performed by two independent readers according to a five-point Likert scale analysis.

Results

PET/MRI was more sensitive (1.00 vs. 0.77) than PET/CT in the detection of locoregional recurrence. PET/MRI also had better negative (1.00 vs. 0.87) predictive values. AUCs for PET/MRI and PET/CT on patient-based analysis were 0.997 (95% CI 0.989–1.000) and 0.890 (95% CI 0.806–0.974), respectively. The comparison of sensitivity, AUCs, and negative predictive values revealed a statistically significant difference, p < 0.05. In PET/CT, false-negative and positive findings were observed in the more advanced disease stages, where PET/MRI performed better. Also, false-negative findings were located in the oropharyngeal, laryngeal, and nasopharyngeal regions, where PET/MRI made no false-negative interpretations.

Conclusion

Based on these results, PET/MRI might be considered the modality of choice in detecting locoregional recurrence in HNSCC patients, especially in the more advanced stages in the oral cavity, larynx, or nasopharynx.

Salivary Gland Function, Development and Regeneration

Salivary glands produce and secrete saliva, which is essential for maintaining oral health and overall health. Understanding both the unique structure and physiological function of salivary glands, as well as how they are affected by disease and injury will direct the development of therapy to repair and regenerate them. Significant recent advances, particularly in the OMICS field, increase our understanding of how salivary glands develop at the cellular, molecular and genetic levels; the signaling pathways involved, the dynamics of progenitor cell lineages in development, homeostasis and regeneration and the role of the extracellular matrix microenvironment. These provide a template for cell and gene therapies as well as bioengineering approaches to repair or regenerate salivary function.

Radiation-Induced Salivary Gland Dysfunction: Mechanisms, Therapeutics and Future Directions

Salivary glands sustain collateral damage following radiotherapy (RT) to treat cancers of the head and neck, leading to complications, including mucositis, xerostomia and hyposalivation. Despite salivary gland-sparing techniques and modified dosing strategies, long-term hypofunction remains a significant problem. Current therapeutic interventions provide temporary symptom relief, but do not address irreversible glandular damage. In this review, we summarize the current understanding of mechanisms involved in RT-induced hyposalivation and provide a framework for future mechanistic studies. One glaring gap in published studies investigating RT-induced mechanisms of salivary gland dysfunction concerns the effect of irradiation on adjacent non-irradiated tissue via paracrine, autocrine and direct cell-cell interactions, coined the bystander effect in other models of RT-induced damage. We hypothesize that purinergic receptor signaling involving P2 nucleotide receptors may play a key role in mediating the bystander effect. We also discuss promising new therapeutic approaches to prevent salivary gland damage due to RT.

P2 Receptors as Therapeutic Targets in the Salivary Gland: From Physiology to Dysfunction

Although often overlooked in our daily lives, saliva performs a host of necessary physiological functions, including lubricating and protecting the oral cavity, facilitating taste sensation and digestion and maintaining tooth enamel. Therefore, salivary gland dysfunction and hyposalivation, often resulting from pathogenesis of the autoimmune disease Sjögren's syndrome or from radiotherapy of the head and neck region during cancer treatment, severely reduce the quality of life of afflicted patients and can lead to dental caries, periodontitis, digestive disorders, loss of taste and difficulty speaking. Since their initial discovery in the 1970s, P2 purinergic receptors for extracellular nucleotides, including ATP-gated ion channel P2X and G protein-coupled P2Y receptors, have been shown to mediate physiological processes in numerous tissues, including the salivary glands where P2 receptors represent a link between canonical and non-canonical saliva secretion. Additionally, extracellular nucleotides released during periods of cellular stress and inflammation act as a tissue alarmin to coordinate immunological and tissue repair responses through P2 receptor activation. Accordingly, P2 receptors have gained widespread clinical interest with agonists and antagonists either currently undergoing clinical trials or already approved for human use. Here, we review the contributions of P2 receptors to salivary gland function and describe their role in salivary gland dysfunction. We further consider their potential as therapeutic targets to promote physiological saliva flow, prevent salivary gland inflammation and enhance tissue regeneration.

Xanthomatous sialadenitis: Autoimmune- or treatment-induced lesions?

Xanthomatous sialadenitis (XS) is rarely reported. Here we report XS in a case of HLA-B27-positive ankylosing spondylitis showing also anti-MAG-positive polyneuropathy with IgM-kappa dysimmunoglobulinemia/paraproteinemia, lung small cell carcinoma and buccal squamous cell carcinoma (SCC). The lesions were identified in submandibular and labial minor salivary glands of a neck dissection specimen (made during a buccal 1.7 cm large SCC resection procedure). The oral SCC was resected at 8 months after the diagnosis of the lung small cell carcinoma (with skull dome metastases, revealed by a superior cava syndrome) and at 2 months after radiotherapy. The microscopic XS-lesions consisted in multifocal accumulations of CD68-positive macrophages. Plasmocyte-abundant foci (CD138-positive) were extra-xanthomatous (atrophic parenchyma, zones of adipose involution). CD138 was also expressed in ductal cells and in acini (focally). In conclusion, we report XS of submandibular and labial minor salivary glands, occurring in the context of a HLA-B27-positive ankylosing spondylitis, polyneuropathy with IgM-kappa dysimmunoglobulinemia and anti-MAG antibodies in a case of small cell lung carcinoma (treated by radio-chemotherapy) and oral SCC.

A Century of Radiation Therapy and Adaptive Immunity

The coming of age for immunotherapy (IT) as a genuine treatment option for cancer patients through the development of new and effective agents, in particular immune checkpoint inhibitors, has led to a huge renaissance of an old idea, namely to harness the power of the immune system to that of radiation therapy (RT). It is not an overstatement to say that the combination of RT with IT has provided a new conceptual platform that has re-energized the field of radiation oncology as a whole. One only has to look at the immense rise in sessions at professional conferences and in grant applications dealing with this topic to see its emergence as a force, while the number of published reviews on the topic is staggering. At the time of writing, over 97 clinical trials have been registered using checkpoint inhibitors with RT to treat almost 7,000 patients, driven in part by strong competition between pharmaceutical products eager to find their market niche. Yet, for the most part, this enthusiasm is based on relatively limited recent data, and on the clinical success of immune checkpoint inhibitors as single agents. A few preclinical studies on RT-IT combinations have added real value to our understanding of these complex interactions, but many assumptions remain. It seems therefore appropriate to go back in time and pull together what actually has been a long history of investigations into radiation and the immune system (Figure 1) in an effort to provide context for this interesting combination of cancer therapies.

Radiation and inflammation

The immune system has the power to modulate the expression of radiation-induced normal and tumor tissue damage. On the one hand, it can contribute to cancer cure, and on the other hand, it can influence acute and late radiation side effects, which in many ways resemble acute and chronic inflammatory disease states. The way radiation-induced inflammation feeds into adaptive antigen-specific immune responses adds another dimension to the tumor-host cross talk during radiation therapy and to possible radiation-driven autoimmune responses. Understanding how radiation affects inflammation and immunity is therefore critical if we are to effectively manipulate these forces for benefit in radiation oncology treatments.

Diffusion-weighted and PET/MR Imaging after Radiation Therapy for Malignant Head and Neck Tumors

Interpreting imaging studies of the irradiated neck constitutes a challenge because of radiation therapy-induced tissue alterations, the variable appearances of recurrent tumors, and functional and metabolic phenomena that mimic disease. Therefore, morphologic magnetic resonance (MR) imaging, diffusion-weighted (DW) imaging, positron emission tomography with computed tomography (PET/CT), and software fusion of PET and MR imaging data sets are increasingly used to facilitate diagnosis in clinical practice. Because MR imaging and PET often yield complementary information, PET/MR imaging holds promise to facilitate differentiation of tumor recurrence from radiation therapy-induced changes and complications. This review focuses on clinical applications of DW and PET/MR imaging in the irradiated neck and discusses the added value of multiparametric imaging to solve diagnostic dilemmas. Radiologists should understand key features of radiation therapy-induced tissue alterations and potential complications seen at DW and PET/MR imaging, including edema, fibrosis, scar tissue, soft-tissue necrosis, bone and cartilage necrosis, cranial nerve palsy, and radiation therapy-induced arteriosclerosis, brain necrosis, and thyroid disorders. DW and PET/MR imaging also play a complementary role in detection of residual and recurrent disease. Interpretation pitfalls due to technical, functional, and metabolic phenomena should be recognized and avoided. Familiarity with DW and PET/MR imaging features of expected findings, potential complications, and treatment failure after radiation therapy increases diagnostic confidence when interpreting images of the irradiated neck. Online supplemental material is available for this article.

Ultrasonic Nakagami-parameter characterization of parotid-gland injury following head-and-neck radiotherapy: a feasibility study of late toxicity

PURPOSE

The study aims to investigate whether Nakagami parameters--estimated from the statistical distribution of the backscattered ultrasound radio-frequency (RF) signals--could provide a means for quantitative characterization of parotid-gland injury resulting from head-and-neck radiotherapy.

METHODS

A preliminary clinical study was conducted with 12 postradiotherapy patients and 12 healthy volunteers. Each participant underwent one ultrasound study in which ultrasound scans were performed in the longitudinal, i.e., vertical orientation on the bilateral parotids. For the 12 patients, the mean radiation dose to the parotid glands was 37.7 ± 9.5 Gy, and the mean follow-up time was 16.3 ± 4.8 months. All enrolled patients experienced grade 1 or 2 late salivary-gland toxicity (RTOG/EORTC morbidity scale). The normal parotid glands served as the control group. The Nakagami-scaling and Nakagami-shape parameters were computed from the RF data to quantify radiation-induced parotid-gland changes.

RESULTS

Significant differences in Nakagami parameters were observed between the normal and postradiotherapy parotid glands. Compared with the control group, the Nakagami-scaling parameter of the postradiotherapy group decreased by 25.8% (p < 0.001), and the Nakagami-shape parameter decreased by 31.3% (p < 0.001). The area under the receiver operating characteristic curve was 0.85 for the Nakagami-scaling parameter and was 0.95 for the Nakagami-shape parameter, which further demonstrated the diagnostic efficiency of the Nakagami parameters.

CONCLUSIONS

Nakagami parameters could be used to quantitatively measure parotid-gland injury following head-and-neck radiotherapy. Moreover, the clinical feasibility was demonstrated and this study provides meaningful preliminary data for future clinical investigation.

Ultrasound GLCM texture analysis of radiation-induced parotid-gland injury in head-and-neck cancer radiotherapy: an in vivo study of late toxicity

PURPOSE

Xerostomia (dry mouth), secondary to irradiation of the parotid glands, is one of the most common side effects of head-and-neck cancer radiotherapy. Diagnostic tools able to accurately and efficiently measure parotid gland injury have yet to be introduced into the clinic. This study's purpose is to investigate sonographic textural features as potential imaging signatures for quantitative assessment of parotid-gland injury after head-and-neck radiotherapy.

METHODS

The authors have investigated a series of sonographic features obtained from the gray level co-occurrence matrix (GLCM) - a second order statistical method of texture analysis. These GLCM textural features were selected based on empirical observations that the normal parotid gland exhibits homogeneous echotexture, whereas the postradiotherapy parotid gland often exhibits heterogeneous echotexture. We employed eight sonographic features: (1) angular second moment (ASM), (2) inverse differential moment (IDM), (3) contrast, (4) variance, (5) correlation, (6) entropy, (7) cluster shade, and (8) cluster prominence. Altogether, sonographic properties of the parotid glands were quantified by their degrees of homogeneity (ASM and IDM), heterogeneity (contrast and variance), smoothness (correlation), randomness (entropy), and symmetry (cluster shade and prominence). The sonographic features were tested in a pilot study of 12 postradiotherapy patients and 7 healthy volunteers. The mean follow-up time for the postradiotherapy patients was 17.2 months (range: 12.1-23.9 months) and the mean radiation dose to the parotid glands was 32.3 Gy (range: 11.0-63.4 Gy). Each participant underwent one ultrasound study in which longitudinal (vertical) ultrasound scans were performed on the bilateral parotids - a total of 24 postirradiation and 14 normal parotid glands were examined. The 14 normal parotid glands served as the control group. A radiologist contoured the parotid glands on the B-mode images and the sonographic features were computed from the contoured region-of-interest.

RESULTS

The authors observed significant differences (p < 0.05) in all sonographic features between the normal and postradiotherapy parotid glands. The sonographic findings were consistent with the clinical observations of the ultrasound images: normal parotid glands exhibited homogeneous texture, while the postradiotherapy parotid glands exhibited heterogeneous echotexture (e.g., hyperechoic lines and spots), which likely represents fibrosis.

CONCLUSIONS

The authors have demonstrated the feasibility of ultrasonic texture evaluation of parotid glands; and the sonographic features may serve as imaging signatures to assess radiation-induced parotid injury.

T lymphocytes and normal tissue responses to radiation

There is compelling evidence that lymphocytes are a recurring feature in radiation damaged normal tissues, but assessing their functional significance has proven difficult. Contradictory roles have been postulated in both tissue pathogenesis and protection, although these are not necessarily mutually exclusive as the immune system can display what may seem to be opposing faces at any one time. While the exact role of T lymphocytes in irradiated normal tissue responses may still be obscure, their accumulation after tissue damage suggests they may be critical targets for radiotherapeutic intervention and worthy of further study. This is accentuated by recent findings that pathologically damaged “self,” such as occurs after exposure to ionizing radiation, can generate danger signals with the ability to activate pathways similar to those that activate adoptive immunity to pathogens. In addition, the demonstration of T cell subsets with their recognition radars tuned to “self” moieties has revolutionized our ideas on how all immune responses are controlled and regulated. New concepts of autoimmunity have resulted based on the dissociation of immune functions between different subsets of immune cells. It is becoming axiomatic that the immune system has the power to regulate radiation-induced tissue damage, from failure of regeneration to fibrosis, to acute and chronic late effects, and even to carcinogenesis. Our understanding of the interplay between T lymphocytes and radiation-damaged tissue may still be rudimentary but this is a good time to re-examine their potential roles, their radiobiological and microenvironmental influences, and the possibilities for therapeutic manipulation. This review will discuss the yin and yang of T cell responses within the context of radiation exposures, how they might drive or protect against normal tissue side effects and what we may be able do about it.

Ultrasound histogram assessment of parotid gland injury following head-and-neck radiotherapy: a feasibility study

Xerostomia (dry mouth), resulting from radiation damage to the parotid glands, is one of the most common and distressing side effects of head-and-neck cancer radiotherapy. A noninvasive, objective imaging method to assess parotid injury is lacking, but much needed in the clinic. Therefore, we investigated echo histograms to quantitatively evaluate the morphologic and microstructural integrity of the parotid glands. Six sonographic features were derived from the echo-intensity histograms to assess the echogenicity, homogeneity and heterogeneity of the parotid gland: (1) peak intensity value (I(peak)), (2) -3-dB intensity width (W(3-dB)), (3) the low (<50% I(peak)) intensity width (W(low)), (4) the high (>50% I(peak)) intensity width (W(high)), (5) the area of low intensity (A(low)) and (6) the area of high intensity (A(high)). In this pilot study, 12 post-radiotherapy patients and seven healthy volunteers were enrolled. Significant differences (p < 0.05) were observed in four sonographic features between 24 irradiated and 14 normal parotid glands. In summary, we developed a family of sonographic features derived from echo histograms and demonstrated the feasibility of quantitative evaluation of radiation-induced parotid-gland injury.

Changes of parotid and submandibular glands caused by radiotherapy--an ultrasound evaluation

OBJECTIVE

Radiotherapy may alter the normal morphology of salivary glands located in the radiation field. These changes could be evaluated safely by sonography; however, there have been few studies in this regard. This study is aimed at evaluating the sonographic changes of the parotid and submandibular glands in patients undergoing radiotherapy for head and neck malignancies.

METHODS

20 patients (16 males and 4 females) with head and neck malignancies who had been referred for radiotherapy to the Qaem Hospital in Mashhad, Iran, entered the study. Length, height, depth, echotexture, echogenicity and margins of parotid and submandibular glands were evaluated in three stages (I, before radiotherapy; II, 2 weeks after radiotherapy; and III, 6-7 weeks after radiotherapy) using sonography. Peak systolic velocity (PSV), end diastolic velocity (EDV) and resistive index (RI) were also evaluated by Doppler sonography.

RESULTS

Significant differences in length, height and depth (p = 0.000, p = 0.000, and p = 0.39, respectively) and also echotexture, echogenicity and gland margins (p = 0.000) were observed before and after radiotherapy. Doppler sonography results showed no significant differences regarding PSV, EDV and RI between sonographic stages. Echotexture and echogenicity were the only independent parameters that showed significant differences in sonographic stages I and II (p = 0.000). Length in stage I and II (p = 0.000) and echogenicity in stage III (p = 0.038) were the only parameters that showed significant differences between the two glands.

CONCLUSION

Radiotherapy may change the echotexture, echogenicity and margins of the salivary glands from homogenic to heterogenic, hyperechoic to hypoechoic and regular to irregular, respectively, and may reduce their size.

Sonographic appearance of parotid glands in patients treated with intensity-modulated radiotherapy or conventional radiotherapy for nasopharyngeal carcinoma

This study aimed to investigate and compare the sonographic appearances of parotid glands in nasopharyngeal carcinoma patients treated with conventional radiotherapy (RT) or intensity-modulated radiotherapy (IMRT), and to compare them with healthy subjects. Totally 43 patients treated with conventional RT, 38 patients treated with IMRT and 58 healthy subjects were recruited and underwent parotid ultrasonography. Parotid glands were assessed for their size, echogenicity and internal architectures. The mean transverse dimension of parotid glands in patients treated with conventional RT and those treated with IMRT were significantly smaller than that in healthy subjects (p < 0.05). Parotid glands of the IMRT group tended to be hyperechoic (93%), homogenous (62%), without hypoechoic areas (64%) and with marginally-seen intra-parotid ducts (89%), which are similar to those in healthy subjects. Parotid glands in the conventional RT group tended to be hypoechoic (51%), heterogeneous (98%), with hypoechoic areas (94%) and had obviously-seen intra-parotid ducts (64%). For accurate diagnosis, post-RT changes of parotid glands should be noted in ultrasound examination of patients with previous radiotherapy.

Botulinum toxin prevents radiotherapy-induced salivary gland damage

Radiotherapy of head and neck malignancies results in severe damage to salivary glands. Irradiation-induced sialadenitis with xerostomia leads to a significant deterioration of the quality of life which lasts life-long. Here we show in a preliminary study that intraglandular application of botulinum toxin performed prior to radiation reduces significantly the radiation induced toxicity of the glandular tissue in rats.

Comparison of sonographic appearance of normal and postradiotherapy parotid glands: a preliminary study

This study was undertaken to evaluate and compare the grey-scale and Doppler sonographic features of postradiotherapy (RT) and normal parotid glands. A total of 10 patients with previous head and neck RT and with different degrees of xerostomia were included. Another 10 healthy subjects, who are age and gender-matched with the 10 patients, were also recruited. Grey-scale and Doppler ultrasound examinations of parotid glands were performed on both the patients and healthy subjects. The parotid glands were assessed for their size, echogenicity, echotexture, conspicuity of intraparotid ducts, blood flow velocity and vascular resistance. Results showed that post-RT parotid glands tended to be smaller than normal parotid glands with a significant difference in the transverse dimension (p < 0.05). Normal parotid glands appeared homogeneous, hyperechoic relative to the adjacent muscles and had marginally seen intraparotid ducts. Post-RT parotid glands were heterogeneous, isoechoic (50%) or hypoechoic (50%) relative to the adjacent muscles, and the intraparotid ducts were either marginally (50%) or obviously (50%) seen on ultrasound. The PSV, RI and PI of normal parotid glands were significantly higher than that of post-RT parotid glands (p < 0.05). However, the difference in EDV between normal and post-RT parotid glands was not significant (p > 0.05). In conclusion, ultrasound is useful in assessing parotid glands. To avoid image misinterpretation, post-RT changes in the sonographic appearance of parotid glands should be considered in examining patients with previous head and neck RT.