PHARMACOLOGY OF OCULAR COMPLICATIONS

糖尿病是一个日益严重的公共卫生问题，糖尿病引起的神经病变、肾病、微血管病变、视网膜病变和白内障等长期并发症会导致视力丧失、生活质量下降、肢体和运动功能丧失以及死亡率增加。糖尿病眼部并发症包括白内障、角膜病变和视网膜病变。在工业化国家，由于视网膜病变导致的失明是成人失明的主要原因，糖尿病患者比非糖尿病患者更频繁地接受白内障手术。过去30年进行的研究已经确定了细胞内山梨醇水平的过度积累与糖尿病并发症的发生之间的明显联系。山梨醇是一种糖醇，由葡萄糖在醛糖还原酶(AR)的作用下形成。我们发现哺乳动物组织中含有一种内源性的醛糖还原酶抑制物(IARI)。IARI的发现意义重大，因为它代表了一种新的无毒(或毒性明显较低)的抑制剂。研究表明，IARI是一种热稳定的化合物，它对醛糖还原酶的抑制明显在微微到纳摩尔范围内。它的相对分子质量似乎不到1000，有证据表明它是一种小的多肽。用部分纯化的IARI进行的体外晶状体培养研究表明，这种化合物可以跨膜抑制晶状体内山梨醇的产生。初步的老鼠研究也表明，这种IARI在体内是活跃的。将含牛晶状体IARI的部分纯化提取物注射给饲喂半乳糖24小时的大鼠，3只大鼠注射约0.3毫升的提取物对半乳糖形成的抑制率为94%，注射约0.1毫升的大鼠的抑制率为54%。估计只有不到0.1%的物质代表紧束缚缓蚀剂，注射水平低于6g/kg。关于醛糖还原酶如何引发糖尿病并发症的病理生理机制也在进行研究。由于目前尚无犬体内多元醇途径酶的序列信息可用于基础分子生物学研究，故对犬的醛糖还原酶、乙醛还原酶和山梨醇脱氢酶进行了克隆和测序。此外，为了开发抑制醛糖还原酶的新方法，设计并筛选了一些反义寡聚体来抑制人和大鼠AR基因在细胞培养中的表达。核磁共振成像研究也在进行，以确定醛糖还原酶是否会引发人类糖性白内障。利用磁化传递对比(MTC)增强磁共振成像(MRI)这一无创性工具，我们获得了喂食半乳糖的狗眼睛的高对比度图像，表明在白内障形成过程中，这些狗的晶状体中发生了与醛糖还原酶有关的渗透性变化。这项技术目前正在应用于临床环境中，使用的是年龄从28岁到72岁的正常志愿者。初步研究表明，MTC-MRI获得的高对比度图像是临床研究白内障改变的良好工具。-醛糖还原酶、糖尿病、视网膜病变、半乳糖血症、白内障、晶状体、乙醛还原酶-人类受试者

Diabetes is a rapidly increasing public health problem and the long-term complications such as neuropathy, nephropathy, microangiopathy, retinopathy and cataract associated with diabetes result in loss of vision, decreased quality of life, loss of limbs and motor function and increased mortality. Ocular diabetic complications include cataract, keratopathy and retinopathy. Blindness due to retinopathy is the leading cause of blindness in of adults industrialized countries, and diabetics undergo cataract surgery more often than non- diabetics. Studies conducted over the last 30 years have established a clear link between the excess accumulation of intracellular sorbitol levels and the onset of diabetic complications. Sorbitol is a sugar alcohol formed from glucose by the enzyme aldose reductase (AR). We have discovered that mammalian tissues contain an intrinsic aldose reductase inhibitor (IARI). The discovery of an IARI is significant because this represents a new class of nontoxic (or significantly less toxic) inhibitor. Studies indicate that the IARI is a heat-stable compound which inhibits aldose reductase in apparently the pico- to nanomolar range. Its molecular weight appears to be less than 1,000 and evidence suggests that it is a small polypeptide. In vitro lens culture studies with partially purified IARI indicate that this compound can cross membranes to inhibit the intralenticular production of sorbitol. Preliminary rat studies also indicate that this IARI is active in vivo. When the partially purified extract containing the IARI from bovine lenses was injected intraperitoneally into 24 hr galactose-fed rats, galactitol formation was inhibited by 94 % in the three rats receiving ca. 0.3 mL injection of extract and 54% in the rat receiving ca. 0.1 mL injection. Estimating that less than 0.1% of the material represents the tight-binding inhibitor, the injected level was under 6 ?g/kg. Studies are also being conducted on the pathophysiological mechanism of how aldose reductase initiates diabetic complications. Since no sequence information on the enzymes of the polyol pathway in the dog is available for basic molecular biological studies, canine aldose reductase, aldehyde reductase and sorbitol dehydrogenase have been cloned and sequenced. In addition, to develop new methods of inhibition of aldose reductase, a number of antisense oligomers to suppress human and rat AR gene expression in cell cultures have been designed and screened. Magnetic resonance imaging studies are also being conducted to determine if aldose reductase initiates human sugar cataracts. Using the noninvasive tool of magnetization transfer contrast (MTC) enhanced magnetic resonance imaging (MRI), we have obtained high contrast images of the eyes of galactose-fed dogs that indicate that osmotic changes linked to aldose reductase occur in the lenses of these dogs during cataract formation. This technique is now being applied to a clinical setting using normal volunteers ranging from 28 to 72 years in age. Preliminary studies indicate that the high contrast images obtained by MTC-MRI are a good tool for clinically investigating cataractous changes. - aldose reductase, diabetes, retinopathy, galactosemia, cataract, lens, aldehyde reductase, - Human Subjects