Hyaluronan uptake and degradation

Hyaluronan (HA) turnover can occur locally at the tissue of origin, where it is taken up by cells to be degraded, or released into the lymphatic and vascular systems, where it can be eliminated by the liver and kidneys. Uptake of HA into cells for degradation involves receptor-mediated processes. Once HA enters lysosomes, the acidic conditions favour hyaluronidases to cleave it into small oligosaccharides, the most common size being a tetrasaccharide. Beta-glucuronidases participate in degrading the small oligosaccharides in the lysosome. Ultimately, HA is degraded into its constituent sugars (glucuronic acid and N-acetylglucosamine) which can be used to reform many glycosaminoglycans (GAGs) when released from the lysosome.<br>A third of the total HA content in humans is turned over daily and it has a short half life of minutes in circulation up to days in many tissues. The reasons why the body eliminates HA so rapidly are unknown but one possible explanation could be HA's role as a reactive oxygen species (ROS) scavenger. Removing these toxic compounds could explain the rapid elimination of HA (Lepperdinger et al. 2004, Menzel & Farr 1998, Erickson & Stern 2012, Stern 2003).

透明质酸（HA）的代谢周转可在起源组织局部进行，其中细胞摄取以进行降解，或释放至淋巴和血管系统，该系统中的透明质酸可由肝脏和肾脏排除。透明质酸进入细胞进行降解的过程涉及受体介导的过程。一旦透明质酸进入溶酶体，酸性环境有利于透明质酸酶将其切割成小寡糖，其中最常见的分子量为四糖。β-葡萄糖苷酸酶参与降解溶酶体中的小寡糖。最终，透明质酸降解为其组成糖类（葡萄糖醛酸和N-乙酰葡萄糖胺），这些糖类在从溶酶体释放后可用于重组多种糖胺聚糖（GAGs）。人类体内总透明质酸含量中三分之一每日进行代谢周转，其在循环中的半衰期短至数分钟，而在许多组织中的半衰期则长达数天。身体快速排除透明质酸的原因尚不明确，但一种可能的解释是透明质酸作为活性氧（ROS）清除剂的作用。移除这些有毒化合物可能解释了透明质酸快速排除的现象（Lepperdinger 等人，2004年，Menzel 和 Farr，1998年，Erickson 和 Stern，2012年，Stern，2003年）。