探討薏仁油乳液製備以及抑制黑色素生成功效之研究

Abstract

近年紫外線日益增強，誘使黑色素細胞生成黑色素造成黑色素沉積，導致曬斑、老人斑、黑色素瘤等疾病發生，黑色素為酪胺酸與L-Dopa經酪胺酸酶反應後產生，抑制酪胺酸酶活性被視為是否能抑制黑色素生成的指標。經皮藥物遞送系統在治療皮膚疾病時，為最佳的藥物使用途徑，其中乳液凝膠為新穎的劑型，具有包覆疏水性藥物、增加穩定性、具黏附性與搖變性的功能，並因為可增加藥物皮膚滲透率的優點而漸漸被研究。薏仁油是薏苡麩皮中的副產物，為低極性物質，具有抗氧化的生理活性。文獻指出利用超臨界萃取的低極性薏苡子實萃取物具有抑制B16F10細胞生成黑色素的能力，故推測薏仁油可能具有抑制黑色素生成的效果。本研究目的為製備不同薏仁油與Tween 80比例之薏仁油乳液與奈米乳液，分析其物性並用於B16F10細胞與斑馬魚中，以探討薏仁油抑制黑色素生合成與酪胺酸酶活性的能力。確定薏仁油功效後，進行乳液、奈米乳液、奈米乳液凝膠等經皮給藥劑型製備，分析其物理性質與經皮吸收率。在細胞實驗中，薏仁油濃度為50 μg/mL時有29.5%與31.6%的黑色素生成與酪胺酸酶活性抑制率，且與正控制組50 μg/mL 麴酸無顯著性差異。在斑馬魚實驗中，薏仁油濃度為2,000 μg/mL時有46.5%與31.7%的黑色素生成與酪胺酸酶活性抑制率，顯示薏仁油具有抑制黑色素生成與酪胺酸酶活性的功效。在經皮給藥劑型製備實驗中，當水、薏仁油與Tween 80比例為60:28:12 (%) 時，粒徑可達73.70 nm，並添加18% Pluronic® F-127後可形成凝膠，凝膠溫度約為30℃。比較薏仁油、乳液、奈米乳液、奈米乳液凝膠之經皮吸收率後，以奈米乳液最佳，而穩定性則為奈米乳液與奈米乳液凝膠較佳。綜合上述實驗結果，推測薏仁油可抑制酪胺酸酶活性而降低黑色素生成，而奈米乳液能提高薏仁油功能性成分的經皮吸收率，雖然奈米乳液凝膠無法提高經皮吸收率，其流變性質仍較適用於皮膚上。

Uraviolet could induce melanocytes to produce melanin which will result in sunspots, age spots and melanoma, etc. Melanin is produced by tyrosine and L-Dopa oxidation to dopaquinone catalyzed by tyrosinase, and inhibition of tyrosinase activity is considered as a key point of whether melanin production is inhibited. Transdermal delivery is the best route for administrating active ingredient to skin upon treating various skin diseases. Emulsion gel is a novel carrier which possesses the property of both emulsions and gel, and it can encapsulate hydrophobic drugs, improving stability, showing mucoadhesive and thixotropic properties to improve penetration ability. Adlay oil, exhibiting antioxidant capacity, is a by-product of adlay bran. It has been reported that the lipophilic fractions from supercritical fluid extract of adlay seeds could suppress intracellular tyrosinase activity and decrease the amount of melanin in B16F10 cells. This study aims at preparing adlay oil emulsions and nanoemulsions with different ratios of Tween 80, and analyzing their physical properties as well as in vitro and in vovo whitening activities. The results from B16F10 cells indicates that adlay oil at 50 μg/mL could reduce the cellular melanin production and tyrosinase activity by 29.5% and 31.6%, whereas in the zebrafish embryos model, 2,000 μg/mL of adlay oil significantly suppressed the melanin contents and tyrosinase activity by 46.5% and 31.7% while not causing toxicity effects on zebrafish. In the experiment of preparation of transdermal formulation, emulsion containing 60:28:12% water, adlay oil and Tween 80 had the smallest particle size (73.70 nm) after being homogenized by high pressure homogenization for 2 cycles at 1,000 bar pressure, and the addition of 18% Pluronic® F-127 could make nanoemulsion into nanoemulsion gel which formed gel at 30℃. We further used in vitro guinea pig skins to examine the permeation ability of different samples. The nanoemulsion significantly enhanced the skin penetration rate of active components when compared to adlay oil, emulsion, and nanoemulsion gel, while the stability of the nanoemulsion and nanoemulsion gel were better. According the aforementioned results, adlay oil is a potential tyrosinase inhibitor and potent skin whitening agent as proven by our in vitro and in vivo screening systems. Moreover, nanoemulsion system could enhance skin permeability of active compounds due to its smaller particle size. Although the percutaneous absorption rate of nanoemulsion gel is not the best, it is still a suitable route for administrating active ingredient to skin because of its rheological properties like thixotropic and mucoadhesive abilities.