Ultrastructural evaluation of the radioprotective effects of melatonin against X-ray-induced skin damage in Albino rats

Abstract

Our knowledge about the radioprotective effects of melatonin against X-ray-induced skin damage is still lacking. To examine these effects, an animal model of 60 Albino rats was used. The animals were divided into five groups: Group 1, nonirradiated; Group 2, X-ray irradiated (XRI, 8 Gy); Group 3, XRI pretreated with solvent (ethanol and phosphate-buffered saline); Group 4, nonirradiated group treated with melatonin; and Group 5, XRI pretreated with melatonin. The skin was evaluated for ultrastructural changes using transmission electron microscopy (TEM). When compared to the nonirradiated skin (Groups 1 and 4), XRI skin (Groups 2 and 3) showed features of both cell injury and increased metabolic activity. The former included changes such as condensation of the nuclei, vacuolization of the cytoplasm, dilatation of the rough endoplasmic reticulum, swelling of the mitochondria with cristolysis, destruction of the ribosomes and intermediate filaments, fragmentation of the keratohyaline granules and loss of the irregularity of the basal cell borders. The central cells of the sebaceous gland alveoli had larger irregular nuclei and few lipid droplets in their cytoplasm. The hair follicle cells had heterochromatic nuclei and less electron dense cytoplasm containing few complements of the organelles. The features of increased metabolic activity included increased euchromatin, irregularity of the nuclear membrane and increased branching of the melanocytes. Also, an increased number of the Birbeck granules were seen in the Langerhans cells. When compared to the irradiated skin (Groups 2 and 3), these changes were mild or absent in the skin of XRI animals pretreated with melatonin (Group 5). The ability of melatonin to minimize the injurious effects of XRI suggests a radioprotective role. The clinical ramifications of these observations warrant further studies.

Figure 1

(a) Non-irradiated skin. The basal cells had euchromatic nuclei and conspicuous nucleoli. The cytoplasm contained full complements of organelles. The basal borders of the cells were irregular (×4000). (b) X-ray-irradiated skin. The basal cells were relatively small with small-condensed, irregular heterochromatic nuclei. The cytoplasm contained numerous vacuoles representing swollen mitochondria and dilated RER. The irregularity of the basal borders were markedly lost (×4000). (c) X-ray-irradiated skin pretreated with melatonin. The basal cells were large with euchromatic nuclei. The cytoplasm contained almost similar numbers of organelles as compared to the nonirradiated group. There was mild loss in the irregularity of the basal membrane (×4000). (d) Non-irradiated skin. The spinous cells were polyhedral with euchromatic nuclei. The cytoplasm contained full complements of organelles. The lateral borders of the cells had numerous desmosomes (×15,000). (e) X-ray-irradiated skin. The spinous cells were polyhedral with small heterochromatic nuclei. The cytoplasm contained numerous vacuoles and few organelles. The lateral borders of the cells had few desmosomes (×10,000). (f) X-ray-irradiated skin pretreated with melatonin. The spinous cells were polyhedral, with euchromatic nuclei. The cytoplasm contained slightly fewer numbers of organelles as compared to nonirradiated cells. The lateral borders of the cells had numerous desmosomes (×10,000).

Figure 2

(a) Non-irradiated skin. The granular cells were elongated, slightly flattened with flattened nuclei, masked by electron dark nonmembranous granules (NMG). The corneocytes were squamous cells with thick plasma membranes (×4000). (b) X-ray-irradiated skin. The granular cells were flattened, contained small, few NMG and fragmented keratohyaline granules. The corneocytes were squamous cells with very irregular outlines (×4000). (c) X-ray-irradiated skin pretreated with melatonin. The granular layer contained considerable numbers of NMG with mild fragmentation of the keratohyaline granules. The corneocytes had similar appearance to those of the nonirradiated group (×4000). (d) Non-irradiated skin. The fibroblasts were elongated; branched cells with elongated heterochromatic nuclei. The cytoplasm contained well-developed Golgi, RER cisternae and some mitochondria (×10,000). (e) X-ray-irradiated skin. The fibroblasts were relatively small in size, with more heterochromatic nuclei, ballooning of Golgi saccules and RER cisternae (×10,000). (f) X-ray-irradiated skin pretreated with melatonin. The fibroblasts had euchromatic nuclei. The cytoplasm contained full complement of organelles (×10,000).

Figure 3

(a) Non-irradiated skin. Langerhans cells were large, rounded, with highly convoluted nuclei. The cytoplasm contained moderate profile of organelles and some Birbecks granules (×12,000). (b) X-ray-irradiated skin. Langerhans cells were relatively large with more numerous Birbecks granules and less electron-dense cytoplasm (×12000). (c) X-ray-irradiated skin pretreated with melatonin. Langerhans cells were more frequent and had similar features as the nonirradiated group (×6000). (d) Non-irradiated skin. The melanocytes appeared as small oval cells with short and few branches, convoluted nuclei and prominent nucleoli. The cytoplasm contained small Golgi, some profiles of RER and few melanosomes (×12,000). (e) X-ray-irradiated skin. The melanocytes appeared as large cells. Their cytoplasm contained numerous cisternae of RER, Golgi saccules and melanosomes at different stages of maturation (X12000). (f) X-ray irradiated skin pretreated with melatonin. The melanocytes appeared as slightly large cells. Their cytoplasm contained moderate sized Golgi, RER and some melanosomes (×12,000).

Figure 4

(a) Non-irradiated skin. The sebaceous gland alveolus (SGA) consisted of basal cell, differentiating cells and a part of well-differentiated central cell full of lipid droplets, electron dense (×4000). (b) X-ray-irradiated skin. The SGA consisted of basal cells, differentiating cells and a part of a central cell. The lipid droplets are smaller in size and less electron dense as compared to the nonirradiated group (×4000). (c) X-ray-irradiated skin pretreated with melatonin. The SGA central cells contained a considerable number of lipid droplets, which were electron dense and similar to those of the nonirradiated group. (d) Non-irradiated skin. The cells of the hair follicle had euchromatic nuclei, numerous desmosomes, and electron-dense cytoplasm. The cytoplasm contained numerous mitochondria, ribosomes, IF and some profiles of RER (×4000). (e) X-ray-irradiated skin. The cells of the hair follicle had heterochromatic nuclei and less electron-dense cytoplasm containing few complements of organelles. There was marked widening of the intercellular spaces with few desmosomes joining the adjacent cells together (×4000). (f) X-ray-irradiated skin pretreated with melatonin. The cells of the hair follicle were almost similar to those of the nonirradiated group with numerous desmosomes joining them together (×4000).

Figure 5

(a) Non-irradiated skin. The endothelial lining cells with euchromatic nuclei, desmosomes between them with some overlapping (×8000). (b) X-ray-irradiated skin. The endothelial cells with marked irregular surfaces, heterochromatic irregular nuclei, numerous pinocytotic vesicles and marked widening of the intercellular spaces (×8000). (c) X-ray-irradiated skin pretreated with melatonin. The endothelial cells had slightly heterochromatic nuclei and minimal widening of the intercellular spaces (×8000). (d) Non-irradiated skin. The epidermis is formed of one basal, two spinous and one granular cell layers (×400). (e) X-ray-irradiated skin. The epidermis is formed of basal, spinous and granular cell layers (one layer each). Marked oedema of the dermis and disruption of the dermal connective tissue (×400). (f) X-ray-irradiated skin pretreated with melatonin. The epidermis was formed of one basal, two spinous and one granular layers. The dermal connective tissue is similar to the nonirradiated group (×400).