BMC Complementary Medicine and Therapies · 2 authors, 1 centre
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This study found that a single 15 Gy dose of gamma irradiation to the cranium of rats caused significant damage to parotid glands, including acinar vacuolization, fibrosis, and increased TGF-β expression. Oral administration of Nigella sativa oil (400 mg/kg) before and after irradiation preserved gland architecture, reduced fibrosis, and decreased TGF-β expression. These findings suggest NSO may be a useful radioprotective adjuvant for salivary glands during radiotherapy.
**Background:** Radiotherapy for head and neck cancers often causes irreversible damage to salivary glands, leading to xerostomia and reduced quality of life. Parotid glands are particularly radiosensitive. Nigella sativa oil (NSO) is a natural antioxidant with reported radioprotective effects in various tissues, but its effect on parotid glands after cranial irradiation had not been studied. This study aimed to evaluate the radioprotective effect of NSO on parotid glands of rats exposed to a single 15 Gy dose of cranium gamma irradiation.
**Methods:** Twenty-eight adult male Wistar albino rats (180±20 g) were randomly divided into four groups (n=7 each): Group 1 (control) – no treatment; Group 2 (NSO) – received 400 mg/kg NSO by oral gavage for 15 consecutive days; Group 3 (radiation) – received a single 15 Gy localized cranium gamma irradiation (dose rate 11.07 Gy/min, ⁶⁰Co source); Group 4 (NSO+radiation) – received NSO starting 24 h before irradiation and continued for 15 days. Rats were sacrificed two weeks after the last NSO dose. Parotid glands were processed for histology: H&E staining for morphology, Masson's trichrome for collagen (fibrosis), and immunohistochemistry for TGF-β expression. Morphometric analysis of area percentage of collagen and TGF-β was performed on 10 fields per sample at 400× magnification using Leica Qwin 500 software. Statistical analysis used one-way ANOVA with significance set at P≥0.05.
**Key Results:** H&E staining showed normal acinar architecture in control and NSO groups. The radiation group exhibited loss of normal acinar architecture, slight acinar shrinkage, massive acinar vacuolization, partial or complete degeneration of striated ducts, and excessive fibrosis around ducts. The NSO+radiation group showed preserved acinar outline and architecture, most ducts normal with only a few partially degenerated, and small amounts of fibrosis. Masson's trichrome staining revealed trace collagen in control and NSO groups, excessive collagen in the radiation group, and few collagen fibers in the NSO+radiation group. Morphometric analysis confirmed that the radiation group had significantly higher collagen area percentage than control, and NSO treatment significantly reduced collagen compared to radiation alone, though still significantly higher than control. TGF-β immunohistochemistry showed negative expression in control and NSO groups, massive expression in the radiation group, and moderate expression in the NSO+radiation group. The area percentage of TGF-β expression was significantly higher in the radiation group than all others; NSO treatment significantly reduced TGF-β expression compared to radiation alone, but it remained significantly higher than control.
**Clinical Implications:** This animal study provides histological and immunohistochemical evidence that NSO can protect parotid glands from radiation-induced damage, reducing fibrosis and TGF-β expression, a key mediator of radiation fibrosis. The findings suggest NSO may be a promising adjuvant to radiotherapy for head and neck cancers to prevent xerostomia. However, the study is limited by its small sample size, single radiation dose, and animal model. Further research is needed to determine optimal dosing, timing, and safety in humans before clinical translation.