Sangi Co., Ltd, Central Research Laboratory, Kasukabe, Saitama, Japan.
PLoS One. 2019 Apr 23;14(4):e0215681. doi: 10.1371/journal.pone.0215681. eCollection 2019.
Nano-hydroxyapatite is used in oral care products worldwide. But there is little evidence yet whether nano-hydroxyapatite can enter systemic tissues via the oral epithelium. We investigated histologically the ability of two types of nano-hydroxyapatite, SKM-1 and Mi-HAP, to permeate oral epithelium both with and without a stratum corneum, using two types of three-dimensional reconstituted human oral epithelium, SkinEthic HGE and SkinEthic HOE respectively with and without a stratum corneum. Both types of nano-hydroxyapatite formed aggregates in solution, but both aggregates and primary particles were much larger for SKM-1 than for Mi-HAP. Samples of each tissue model were exposed to SKM-1 and Mi-HAP for 24 h at concentrations ranging from 1,000 to 50,000 ppm. After treatment, paraffin sections from the samples were stained with Dahl or Von Kossa stains. We also used OsteoSense 680EX, a fluorescent imaging agent, to test for the presence of HAP in paraffin tissue sections for the first time. Our results for both types of nano-hydroxyapatite showed that the nanoparticles did not penetrate the stratum corneum in SkinEthic HGE samples and penetrated only the outermost layer of cells in SkinEthic HOE samples without stratum corneum, and no permeation into the deeper layers of the epithelium in either tissue model was observed. In the non-cornified model, OsteoSense 680EX staining confirmed the presence of nano-hydroxyapatite particles in both the cytoplasm and extracellular matrix of outermost cells, but not in the deeper layers. Our results suggest that the stratum corneum may act as a barrier to penetration of nano-hydroxyapatite into the oral epithelium. Moreover, since oral epithelial cell turnover is around 5-7 days, superficial cells of the non-keratinized mucosa in which nanoparticles are taken up are likely to be deciduated within that time frame. Our findings suggest that nano-hydroxyapatite is unlikely to enter systemic tissues via intact oral epithelium.
纳米羟基磷灰石在全球范围内被用于口腔护理产品。但目前几乎没有证据表明纳米羟基磷灰石是否可以通过口腔上皮进入全身组织。我们使用两种类型的三维重建人口腔上皮分别为 SkinEthic HGE 和 SkinEthic HOE（有和没有角质层），研究了两种类型的纳米羟基磷灰石 SKM-1 和 Mi-HAP 是否能够穿透口腔上皮，同时也研究了有和没有角质层的情况下纳米羟基磷灰石的穿透能力。两种类型的纳米羟基磷灰石在溶液中形成聚集体，但 SKM-1 的聚集体和初级颗粒都比 Mi-HAP 大得多。每种组织模型的样本均在浓度为 1,000 至 50,000 ppm 的范围内暴露于 SKM-1 和 Mi-HAP 24 小时。处理后，用 Dahl 或 Von Kossa 染色剂对样品的石蜡切片进行染色。我们还首次使用荧光成像剂 OsteoSense 680EX 测试石蜡组织切片中 HAP 的存在。对于两种类型的纳米羟基磷灰石，我们的结果均表明，纳米颗粒未穿透 SkinEthic HGE 样本中的角质层，仅穿透无角质层的 SkinEthic HOE 样本的最外层细胞，并且在两种组织模型中均未观察到穿透上皮的更深层。在非角化模型中，OsteoSense 680EX 染色证实纳米羟基磷灰石颗粒存在于最外层细胞的细胞质和细胞外基质中，但不存在于更深层。我们的结果表明，角质层可能是纳米羟基磷灰石穿透口腔上皮的屏障。此外，由于口腔上皮细胞的更新周期约为 5-7 天，因此在那段时间内，摄取纳米颗粒的非角化黏膜的浅层细胞可能会脱落。我们的研究结果表明，纳米羟基磷灰石不太可能通过完整的口腔上皮进入全身组织。
