Involvement of Cathepsins in Osteoporosis and Allergy and Cathepsin Inhibitors as the New Therapeutic Drugs

许多激素和局部因素已被报道参与骨吸收的调节。然而，其机制仍不清楚。本研究以钙缺乏饲料喂养的骨质疏松大鼠为模型，探讨溶酶体半胱氨酸蛋白酶及其抑制剂在骨胶原溶解中的作用。这些大鼠股骨重量下降，血液中羟脯氨酸（Hyp）水平升高。此外，组织蛋白酶B和L的活性在其股骨提取物中显示出轻微的增加，而组织蛋白酶H的活性保持不变。组织蛋白酶抑制剂E-64 a或半胱氨酸蛋白酶抑制剂能显著降低组织蛋白酶B、H和L的活性。这些蛋白酶抑制剂的施用也降低了血液中的Ca-和Hyp-level，并且不影响胶原酶的活性。另一方面，我们寻找了溶酶体半胱氨酸蛋白酶的选择性抑制剂，并发现了一种新的选择性组织蛋白酶B抑制剂（CA-074，E-64的衍生物）。CA-074可特异性抑制烟曲霉组织蛋白酶B的活性，但对H和L的活性无明显抑制作用。但这种特异性抑制剂不影响胎内Ca ~（2+）和Hyp ~（2+）水平。提示组织蛋白酶B可能不参与胶原溶解。因此，组织蛋白酶L可能参与骨基质胶原纤维的降解，因为胶原对组织蛋白酶L非常敏感。组织蛋白酶L的选择性抑制剂可作为治疗骨质疏松症的药物。

Many hormones and local factors have been reported to be involved in the regulation of bone resorption. However, their mechanisms have remained unclear. This study focused on lysosomal cysteine proteinases and their inhibitors that are thought to play roles in bone collagenolysis.Osteoporotic rats were prepared by feeding a ca-deficient diet. These rats show a decrease in the weight of their femur and increase in the level of hydroxyproline (Hyp) in blood. Furthermore, the activities of cathepsin B and L show a slight invrease in their femur extract, whereas the activity of cathepsin H remained unchanged. Administration of inhibitor of cathepsin, such as E-64a or cystatin to osteoporotic rats caused a dramatic decrease in the activities of cathepsin B, H and L in extract of the femur. Administration of these proteinase inhibitors also reduced the ca- and Hyp-level in blood and do not affect the activity of collagenase. On the other hand, we searched for selective inhibitors of lysosomal cysteine proteinases and discovered a new selective inhibitor (CA-074, derivative of E-64) of cathepsin B in vivo. Administration of CA-074 caused the specific inhibition of cathepsin B in fumer, while H and L activities were not inhibited. However, this specific inhibitor boes not affect the Ca- and Hyp=level in bolld. There results suggest that Cathepsin B may not be involved in collagenolysis. Therefore, cathepsin L might be implicated in degradation of the collagen fibers of bone matric because the collagen is quite susceptible to cathepsin L. The selective inhibitor (s) of cathepsin L might be used for osteoporosis as therapeutic drugs.