維他命C是一種水溶性的化合物，在自然界有左旋和右旋之分，其中唯有左旋性具有生理活性。左旋維他命C在皮膚上的功能包括了抗氧化、抗老化、減少黑色素形成、以及促進膠原蛋白的產生，膠原蛋白存在於皮膚的形式主要是第一型和第三型，由真皮層的纖維母細胞所分泌以穩定真皮骨架提供彈性和調節細胞的分化。由於左旋維他命C容易受光線、空氣影響而氧化分解，化妝品工業上亦已開發了相關的劑型和衍生物。
　　
　　高分子聚合物作為藥物的載體或賦型劑已非常普遍，可以依照不同的需求製造成不同的劑型，例如：水膠、貼片、錠劑、奈米微粒等；在選擇上必須考慮聚合物的物理化學性質、取得來源、生物相容性、生體崩解性、與藥物之間的交互作用等因素。
　　
　　本研究之主要目的在於利用in vitro cell culture方式，探討帶有不同電荷的水溶性聚合物對於左旋維他命C在人類皮膚纖維母細胞之吸收以及第一型、第三型膠原蛋白合成之影響。選擇的三種水溶性聚合物分別是帶正電荷的chitosan 100、不帶電荷的hydroxypropyl-methylcellulose (HPMC)、以及帶負電荷的carbopol 940。首先採用細胞毒性試驗篩選各個聚合物的適合濃度；在細胞吸收實驗部份利用了L -[1-14C]-ascorbic acid為測量的材料，另一方面則是採用了聚合酵素鏈鎖反應測量細胞第一型和第三型膠原蛋白mRNA之表現量。接著進一步評估以簡易的ionotropic gelation方法製備的chitosan 100奈米微粒包覆左旋維他命C之可行性。
　　
　　研究結果顯示，HPMC即使在濃度高達10 mg/ml時也不會對fibroblasts造成細胞毒性；chitosan 100和carbopol 940可維持細胞90 %以上存活率的濃度分別是100及300 μg/ml。此外，chitosan 100和carbopol 940兩種聚合物均可以對於左旋維他命C之吸收以及細胞膠原蛋白之合成有促進的效果，HPMC則沒有顯著的影響，且兩種試驗的結果具有一致性。比較三種聚合物在相同濃度(10 μg/ml)下，carbopol 940促進左旋維他命C吸收約2.1倍，而第一型和第三型膠原蛋白的合成則是約增加1.6倍；chitosan 100則是能夠促進約1.6倍的左旋維他命C吸收，增加膠原蛋白表現約1.4倍。總之，三種聚合物對細胞吸收藥物和膠原蛋白mRNA表現的影響為carbopol 940 > chitosan 100 > HPMC。在奈米微粒製備方面，以各種不同比例所製備出的粒子，其左旋維他命C的包埋率均不理想(3.0至22.9%)；可能是製備方法未最適化、或是chitosan 100與左旋維他命C之間的交互作用不夠緊密所造成的。
　　
　　本研究結果可提供資訊作為製備左旋維他命C凝膠劑型之參考，以進一步評估其in vitro穿皮速率或in vivo活體動物模式之影響。此外，在製備包覆左旋維他命C之幾丁聚醣奈米微粒部分，仍待進一步探討以改變實驗條件改善藥物包覆率之可行性。

　Vitamin C, a water soluble compound, has levorotary and dextrorotary forms in the nature. Only the levorotary form has the biological activity, and it’s called L-ascorbic acid. Pertinent to dermatology its roles are anti-oxidant, anti-aging, to inhibit melanin synthesis, and to stimulate the production of collagen. The major types of collagen in human skin are type I and III. They are secreted by the fibroblasts in dermal tissue. The function of collagen is to stabilize scaffold of dermal connective tissues, as well as a regulator of differentiation and migration of dermal cells. Due to the poor stability of L-ascorbic acid, which is easily affected by the light、temperature、and air, there have been many formulations and derivatives of L-ascorbic acid developed in the cosmetics industry.
　　
　Polymers as drug carriers or excipients are widely used in many fields. They can be formulated into various types depending on different requirements, for example： hydrogels, patches, tablets, and nanoparticles. The selection of appropriate polymers should take account of the physicochemical properties of polymers, sources, biocompatibility, and the interaction with drugs.
　　
　The major purpose of this study was to investigate the effects of hydrophilic polymers with different charges on the uptake of L-ascorbic acid and collagen synthesis in human skin fibroblasts. The polymers used were chitosan 100, a positively-charged polymer, hydroxypropyl-methylcellulose (HPMC), and carbopol 940, a negatively-charged polymer. The cytotoxicity of polymers was evaluated using MTT assay. L-[1-14C]-ascorbic acid was employed in cell uptake studies. In addition, we used reverse transcription-polymerase chain reaction to determine the expression of Type I and III procollagen mRNA. Furthermore, we evaluated the feasibility of chitosan 100 nanoparticles prepared using ionotropic gelation technique by determination of the association efficiency of L-ascorbic acid encapsulated in those nanoparticles.
　　
　The results indicated that HPMC did not lead to any cytotoxicity even at high concentrations up to 10 mg/ml. The concentrations of chitosan 100 and carbopol 940 when fibroblasts could maintain > 90% cell viability was 100 and 300 μg/ml, respectively. In addition, both chitosan 100 and carbopol 940 enhanced the uptake of L-ascorbic acid and type I either III procollagen mRNA levels. HPMC was shown to have no effects on both aspects. The effect on expression of procollagen synthesis was similar to the results of uptake studies. Comparing the effects of polymers at the same concentration of 10 μg/ml, carbopol 940 stimulated the greatest uptake of L-ascorbic acid, about 2.1-fold of control. It also increased the expression of Type I and III procollagen mRNA by 1.6-fold. For chitosan 100, it enhanced the L-ascorbic ascid uptake by 1.6-fold, and increased the expression of Type I and III procollagen mRNA by 1.4-fold. In summary, the uptake of L-ascorbic acid and Type I and III procollagen mRNA expression in fibroblasts decreased in the order of carbopol 940 > chitosan 100 > HPMC. In the preparation of nanoparticles, the association efficiency of L-ascorbic acid was not high (3.0-22.9 %) at various L-ascorbic acid/chitosan ratio. The phenomenon may be attributed to the sub-optimal preparation conditions, or the weak interaction between L-ascorbic acid and chitosan 100.
　　
　In conclusion, the results from the study may provide references for the selection of hydrophilic polymers to prepare L-ascorbic acid gel formulations. In addition, the feasibility of chitosan 100 nanoparticles to encapsulate L-ascorbic acid requires further investigation and evaluation.

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