Phenylephrine Alleviates 131I Radiation Damage in Submandibular Gland Through Maintaining Mitochondrial Homeostasis

Glycyrrhizin Protects Submandibular Gland Against Radiation Damage by Enhancing Antioxidant Defense and Preserving Mitochondrial Homeostasis

Aims: Radiotherapy inevitably causes radiation damage to the salivary glands (SGs) in patients with head and neck cancers (HNCs). Excessive reactive oxygen species (ROS) levels and imbalanced mitochondrial homeostasis are serious consequences of ionizing radiation in SGs; however, there are few mitochondria-targeting therapeutic approaches. Glycyrrhizin is the main extract of licorice root and exhibits antioxidant activity to relieve mitochondrial damage in certain oxidative stress conditions. Herein, the effects of glycyrrhizin on irradiated submandibular glands (SMGs) and the related mechanisms were investigated. Results: Glycyrrhizin reduced radiation damage in rat SMGs at both the cell and tissue levels, and promoted saliva secretion in irradiated SMGs. Glycyrrhizin significantly downregulated high-mobility group box-1 protein (HMGB1) and toll-like receptor 5 (TLR5). Moreover, glycyrrhizin significantly suppressed the increases in malondialdehyde and glutathione disulfide (GSSG) levels; elevated the activity of some critical antioxidants, including superoxide dismutase, catalase, glutathione peroxidase, and glutathione (GSH); and increased the GSH/GSSG ratio in irradiated cells. Importantly, glycyrrhizin effectively enhanced thioredoxin-2 levels and scavenged mitochondrial ROS, inhibited the decline in mitochondrial membrane potential, improved adenosine triphosphate synthesis, preserved the mitochondrial ultrastructure, activated the proliferator-activated receptor-gamma coactivator-1alpha (PGC-1α)/nuclear respiratory factor 1/2 (NRF1/2)/mitochondrial transcription factor A (TFAM) signaling pathway, and inhibited mitochondria-related apoptosis in irradiated SMG cells and tissues. Innovation: Radiotherapy causes radiation sialadenitis in HNC patients. Our data suggest that glycyrrhizin could be a mitochondria-targeted antioxidant for the prevention of radiation damage in SGs. Conclusion: These findings demonstrate that glycyrrhizin protects SMGs from radiation damage by downregulating HMGB1/TLR5 signaling, maintaining intracellular redox balance, eliminating mitochondrial ROS, preserving mitochondrial homeostasis, and inhibiting apoptosis.

The underlying mechanisms and strategies of DNA damage and repair in radiation sialadenitis

Radiation therapy is a critical strategy for the treatment of malignant tumors. X-ray external radiation has been successfully used to treat head and neck cancer. On the other hand, ¹³¹ I internal radiation has been effective in managing differentiated thyroid cancer. However, these therapies cause radiation damage to salivary glands. Radiation sialadenitis is the most common complication associated with radiotherapy applied to the head and neck and it severely affects patients' quality of life. Since DNA is the main intracellular target of radiation, and the integrity of the DNA structure is critical to genomic stability and the cellular survival of salivary glands, regulating radiation-induced DNA damage offers great promise in preventing and managing radiation sialadenitis. In this review, we summarize recent progress in DNA damage and repair in irradiated salivary glands.

SPECT/CT-based dosimetry of salivary glands and iodine-avid lesions following 131I therapy

Objective

The purpose was to provide uptake and radiation dose estimates to salivary glands (SG) and pathologic lesions following radioiodine therapy (RIT) of differentiated thyroid cancer patients (DTC).

Methods

A group of DTC patients (n = 25) undergoing ¹³¹I therapy joined this study with varying amounts of therapeutic activity. Sequential SPECT/CT scans were acquired at 4 ± 2, 24 ± 2, and 168 ± 3 h following administration of 3497-9250 MBq 131I. An earlier experiment with Acrylic glass body phantom (PET Phantom NEMA 2012 / IEC 2008) was conducted for system calibration including scatter, partial volume effect and count loss correction. Dose calculation was made via IDAC-Dose 2.1 code.

Results

The absorbed dose to parotid glands was 0.04-0.97 Gy/GBq (median: 0.26 Gy/GBq). The median absorbed dose to submandibular glands was 0.14 Gy/GBq (0.05 to 0.56 Gy/GBq). The absorbed dose to thyroid residues was from 0.55 to 399.5 Gy/GBq (median: 21.8 Gy/GBq), and that to distal lesions ranged from 0.78 to 28.0 Gy/GBq (median: 3.12 Gy/GBq). 41% of the thyroid residues received dose > 80 Gy, 18% between 70-80 Gy, 18% between 40-70 Gy, and 23% has dose < 40 Gy. In contrast, 18% of the metastases exhibited a dose > 80 Gy, 9% between 40-60 Gy, and the dose to the vast majority of lesions (64%) was < 40 Gy.

Conclusion

It was inferred that dose estimation after RIT with SPECT/CT is feasible to apply, together with good agreement with published ¹²⁴I PET/CT dose estimates. A broad and sub-effective dose range was estimated for thyroid residues and distal lesions. Moreover, the current methodology might be useful for establishing a dose-effect relationship and radiation-induced salivary glands damage after RIT.

Nicotinamide mitigates radiation injury in submandibular gland by protecting mitochondrial structure and functions

BACKGROUND

Radiation damage to salivary gland (SG) is inevitable in head and neck cancer patients receiving radiotherapy. Safe and effective treatments for protecting SGs from radiation are still unavailable. Mitochondrial damage is a critical mechanism in irradiated SG, however, treatment targeting mitochondria has not received much attention. Nicotinamide (NAM) is a key component of the mitochondrial metabolism. Here, we investigated the effects and underlying mechanisms of NAM on protecting irradiated submandibular gland (SMG).

METHODS

SMG cells and tissues were randomly divided into four groups: control, NAM alone, radiation alone, and radiation with NAM pretreatment. Cell viability was detected by PrestoBlue™ cell viability reagent. Histopathological alterations were observed with HE staining. Pilocarpine-stimulated saliva was measured from Wharton's duct. Cell apoptosis was determined by flow cytometry and TUNEL assay. Nicotinamide phosphoribosyl transferase (NAMPT) was examined with immunofluorescence. The levels of nicotinamide adenine dinucleotide (NAD), mitochondrial membrane potential (MMP) and ATP were measured with the relevant kits. The mitochondrial ultrastructure was observed under transmission electron microscopy.

RESULTS

NAM significantly mitigated radiation damage both in vitro and in vivo. Also, NAM improved saliva secretion and reduced radiation-induced apoptosis in irradiated SMGs. Moreover, NAM improved NAMPT and the levels of NAD/ATP and MMP, all of which were decreased by radiation in SMG cells. Importantly, NAM protected the mitochondrial ultrastructure from radiation.

CONCLUSION

These findings demonstrate that NAM alleviates radiation damage in SMG by replenishing NAD and maintaining mitochondrial function and ultrastructure, suggesting that NAM could be used as a prospective radioprotectant for preventing radiation sialadenitis.

Salidroside Ameliorates Radiation Damage by Reducing Mitochondrial Oxidative Stress in the Submandibular Gland

Radiotherapy for patients with head and neck cancer inevitably causes radiation damage to salivary glands (SGs). Overproduction of reactive oxygen species (ROS) leads to mitochondrial damage and is critical in the pathophysiology of SG radiation damage. However, mitochondrial-targeted treatment is unavailable. Herein, both in vitro and in vivo models of radiation-damaged rat submandibular glands (SMGs) were used to investigate the potential role of salidroside in protecting irradiated SGs. Cell morphology was observed with an inverted phase-contrast microscope. Malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), mitochondrial ROS, mitochondrial membrane potential (MMP), and ATP were measured using relevant kits. The mitochondrial ultrastructure was observed under transmission electron microscopy. Cell apoptosis was determined by Western blot and TUNEL assays. Saliva was measured from Wharton’s duct. We found that salidroside protected SMG cells and tissues against radiation and improved the secretion function. Moreover, salidroside enhanced the antioxidant defense by decreasing MDA, increasing SOD, CAT, and GSH, and scavenging mitochondrial ROS. Furthermore, salidroside rescued the mitochondrial ultrastructure, preserved MMP and ATP, suppressed cytosolic cytochrome c and cleaved caspase 3 expression, and inhibited cell apoptosis. Together, these findings first identify salidroside as a mitochondrial-targeted antioxidant for preventing SG radiation damage.

Dual Roles of Nicotinamide Phosphoribosyltransferase as a Promising Target for Cancer Radiotherapy

Nicotinamide phosphoribosyltransferase (NAMPT) is the key rate-limiting enzyme in the regulation of nicotinamide adenine dinucleotide (NAD) biosynthesis, and its activity is critical for the replenishment of NAD level as well as cell survival or death. As one of the most important components in the electron transport chain of complex I in mitochondrion, sustained supply of NAD is essential to the maintenance of energy metabolism both in normal and cancer cells. Recent research showed that X-ray radiation sharply downregulated the expression of NAMPT, which may be the main cause of radiation damage in salivary gland. Consistently, upregulation of NAMPT by phenylephrine restored the function and tissue structure of salivary gland, indicating the cytoprotective role of NAMPT in preventing radiation damage in normal tissues of patients with head and neck cancer during radiotherapy. On the other hand, NAMPT downregulation and NAD depletion could induce cell death in oral squamous cell cancer, suggesting that a combination of NAMPT inhibitor and radiotherapy presents a promising therapeutic strategy for cancer treatment. Based on our and other's studies, NAMPT may have dual roles in cancer radiotherapy: the upregulation of NAMPT could serve to suppress radiotherapy complications such as radiation sialadenitis, and combination regimens that involve NAMPT inhibitors may enhance efficacy of radiotherapy for cancer treatment.

Progressive changes in the major salivary gland after radioiodine therapy for differentiated thyroid cancer: a single-center retrospective ultrasound cohort study

This study aimed to determine the prevalence of radioiodine-induced salivary gland damage by evaluating progressive changes in salivary glands using ultrasound. Four hundred forty-six patients with differentiated thyroid carcinoma who underwent total or near-total thyroidectomy and postoperative radioiodine therapy were retrospectively reviewed. From the first to the fifth follow-up visits, the positive rate of major salivary gland changes on ultrasound gradually increased from 2.0% to 33.0% (P<0.001) and possibly stabilized at the fifth visit (approximately 36 months). The first positive result was detected at an average of 20.78±8.72 months. Only 21 of the 161 positive cases eventually achieved negative ultrasound results (Fisher's test, P<0.001), and the 21 cases simply showed a coarse echotexure. In conclusion, ultrasound changes appeared late, and most of these changes were not reversed.

Protective Effect of Sirt1 against Radiation-Induced Damage

Radiotherapy is an important method for the treatment of malignant tumors. It can directly or indirectly lead to the formation of free radicals and DNA damage, resulting in a series of biological effects, including tumor cell death and normal tissue damage. These radiation effects are typically accompanied by the abnormal expression of sirtuin 1 (Sirt1), which deacetylates histones and non-histones. These Sirt1 substrates, including transcription factors and some catalytic enzymes, play a crucial role in anti-oxidative stress, DNA damage repair, autophagy regulation, anti-senescence, and apoptosis, which are closely related to triggering cell defense and survival in radiation-induced damage. In this article, we review the mechanisms underlying cellular responses to ionizing radiation and the role of Sirt1 in the process, with the aim of providing a theoretical basis for protection against radiation by Sirt1 as well as novel targets for developing radioprotective agents.

Clinical and Sialographic Imaging Features of 131I Radiation-induced Submandibular Gland Sialadenitis

PURPOSE

¹³¹I radiation-induced sialadenitis is the most frequent complication of ¹³¹I treatment for papillary thyroid carcinoma, but little is known about ¹³¹I radiation-induced submandibular gland sialadenitis. The purpose of this study was to compare and contrast the clinical and sialographic imaging features of ¹³¹I radiation-induced submandibular gland sialadenitis to ¹³¹I radiation-induced parotitis.

PATIENTS AND METHODS

This retrospective cross-sectional study included patients with ¹³¹I radiation-induced submandibular gland sialadenitis and parotitis. Clinical records and sialographic image features were evaluated. The predictor variables included age at the time of diagnosis, gender, course of the disease, site of symptoms, and sialographic image grades. The outcome variable was the location of sialadenitis. A student t-test was conducted to analyze the associations between predictor variables and the outcome.

RESULTS

The sample was composed of 4 patients with submandibular gland sialadenitis (100% female), 28 with parotitis (85.7% female), and 1 with submandibular gland sialadenitis and parotitis (P < .05). The occurrence of bilateral glands dysfunction was less often in submandibular glands (SMG: 1/4; PG: 19/28). The age and course of disease were not different between submandibular gland sialadenitis and parotitis (Age, SMG: 46.00 ± 13.59 years; PG: 50.04 ± 10.71 years, P > .05; Course of the disease, SMG: 11.00 ± 16.69 months; PG: 6.96 ± 11.18 months, P > .05). Radiographically, 7 of 16 patients with parotitis were identified as grade 2 and 9 patients as grade 3. In 3 patients with submandibular gland sialadenitis, 1 patient was identified as grade 2 and 2 patients as grade 3. The postoperative pathological results showed that the proliferation of glandular tissue from the hilum of the submandibular gland caused duct stenosis.

CONCLUSION

The results suggest ¹³¹I radiation-induced submandibular gland sialadenitis has a lower incidence compared with parotitis and ¹³¹I radiation-induced submandibular gland sialadenitis might be related to duct stenosis caused by proliferative glandular tissue after ¹³¹I radiation treatment.

Phenylephrine alleviates 131I damage in submandibular gland through promoting endogenous stem cell regeneration via lissencephaly-1 upregulation

Thyroid cancer is the most common endocrine malignancy. ¹³¹I ablation therapy is an effective treatment for patients with differentiated thyroid cancer (DTC) but frequently causes radiation damage in salivary glands (SGs). Stem cell-based regenerative therapy has been found to reduce radiation sialadenitis. We hypothesize that microtubule motor-regulating protein lissencephaly-1 (LIS1) may be a key stem cell regulator responsible for its efficacy and that upregulating LIS1 would decrease¹³¹I-induced radiation sialadenitis. Here, we report that LIS1 was reduced by ¹³¹I in submandibular glands (SMGs) of rats, using both proteomic analysis and Western blot approach. Moreover, the levels of LIS1-Sca-1 and LIS1-SOX2 were downregulated by ¹³¹I together with the decrease of LIS1. In contrast, phenylephrine pretreatment enhanced LIS1 and improved the co-expressions and co-localizations of LIS1-Sca-1 and LIS1-SOX2 in ¹³¹I-irradiated SMGs. Since Sca-1 and SOX2 are the established stem cell biomarkers in salivary gland, our findings demonstrate that LIS1 may be a potential target for regulating stem cell maintenance in irradiated SGs. Importantly, phenylephrine may have the ability to promote endogenous stem cell regeneration in SMGs via upregulating the LIS1/Sca-1 and LIS1/SOX2 signaling pathways, suggesting that phenylephrine application before ¹³¹I ablation therapy may provide a practical and effective way to prevent radiation sialadenitis for DTC patients.