الفهرس 
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Abstract
Skin, as the largest organ of the body, is constantly exposed to both intrinsic and extrinsic factors of aging. Intrinsic aging is associated with impairment of cellular proliferative capacity. Extrinsic factors like air pollution, smoking, and ultraviolet radiation exposure which considered the main cause of extrinsic aging (photo-aging).
Spirulina platensis unicellular blue-green algae have a variety of biological and nutritional activities because of their high level of nutrients. The current study aims to investigate the mechanism by which Spirulina extract (SE) may act as an anti-aging in female albino rats.
In the present study, forty-two female albino rats were used. They divided into six groups (7 animals each) fed on a standard diet and supplied with water ad libitum:
First group: (GI): control young albino rats were (only subjected to shaving).
Second group: (GII): Young albino rats received SE (20 mg/ml) daily for a week.
Third group: (GIII): Young albino rats were administered a daily dose of saline and an hour later exposed to UVR (2.16 J/cm2), daily for a week.
Fourth group: (GIV): Young albino rats received SE (20mg/ml) and an hour later exposed to UVR (2.16 J/cm2), daily for a week.
Fifth group: (GV): control old albino rats were (only subjected to shaving), considering (GI) as a young control.
Sixth group: (GVI): old albino rats received SE (20 mg/ml) daily for a week.
All treatments were carried out by injecting subcutaneously to shaved dorsal skins before UVA irradiation.
The study includes:
(1) Histopathological study
(a) The epidermal thickness:
Hematoxylin and eosin (H&E) staining showed increased epidermal thickness and the formation of tough wrinkles in the UVA-irradiated groups. While the SE administration group showed abundant photo-protective activity and could retain the epidermal layer of the skin intact. On the other hand, the results show slightly decreasing atrophy of the epidermis and relative improvement in skin wrinkle formation of the old treated group.
(b) The density of collagen fibers:
Using Massonʼs trichrome stain, the effect of SE administration showed a significant abundance of dermal collagen fibers in the dorsal skin. However, In the UVA group showed collagen destructed. The intrinsic aging showed no great change in collagen layer in old groups.
(2) 0xidative markers
The excess levels of reactive oxygen species (ROS) in UVA- irradiated group and control old group significantly decreased in SE-administrated groups; the activities of superoxide dismutase (SOD), and reduced glutathione (GSH) were evaluated in the homogenate skin. There were significant improvements in the activities of antioxidants in SE-administrated groups when compared to UVA group and old untreated group.
(3) Anti-inflammatory cytokines
There was a significant excess in the Interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) levels of the UVA-irradiated group. Prominently, SE suppressed the expressions of inflammatory cytokines (IL-1𝛽 and TNF-𝛼) and restores them to control levels. The same results were represented in old-treated albino rats.
(4) Collagen degradation
The matrix metalloprotease-1 (MMP-1) content of skin tissue homogenate increased significantly in the UVA group while decreasing significantly with SE administration. Dramatically reduced levels of MMP-1 in old albino rats treated with SE returned to levels of control in young albino rats.
(5) Collagen production
The levels of hydroxyproline (Hyp) were significantly decreased in the UVA-irradiated group. Meanwhile, young and old albino rats administered with SE exhibited significantly higher levels of Hyp.
Conclusion
The current study demonstrated that the subcutaneous injection of SE significantly shows anti-aging effects by enhancing collagen production as well as antioxidant activities and inhibiting collagen degradation and inflammation due to its high contents of antioxidant substances such as phycocyanine and β-carotene. Based on this study we suggest that SE is a useful material for application in dermal-cosmetic formulations to protect the skin from the damaging effects of aging and UV exposure.