Lahiri D K, Farlow M R, Sambamurti K
Institute of Psychiatric Research, Departments of Psychiatry and Neurology, 791 Union Drive, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
Brain Res Mol Brain Res. 1998 Nov 20;62(2):131-40. doi: 10.1016/s0169-328x(98)00236-8.
The amyloid beta-protein (Abeta) is an approximately 4 kD secreted protein normally found in human plasma and cerebrospinal fluid. Abeta is invariably deposited as insoluble amyloid fibrils in the brains of patients with Alzheimer's disease (AD), and there is increasing evidence that Abeta deposition plays an important role in AD pathogenesis. Abeta is released from the larger beta-amyloid precursor protein (betaAPP) through cleavage on the amino and carboxyl side of Abeta by proteolytic activities referred to as beta and gamma secretase, respectively. betaAPP is also cleaved at Abeta16 by a third protease, alpha secretase, which may prevent amyloid deposition by bisecting the Abeta peptide. Tacrine, a cholinesterase inhibitor, has been shown to improve memory and cognitive functions in some patients with AD, and we have previously demonstrated that it significantly reduces the levels of the secretion of soluble betaAPP fragments (sAPP) in cultured cells. In this study, we extended our studies by analysis of Abeta40 and Abeta42 and report that in a human neuroblastoma cell line tacrine reduced the levels of total Abeta, Abeta40 and Abeta42 in addition to sAPP. These inhibitory results cannot be attributed to a reduction in total betaAPP synthesis as tacrine treatment did not cause a significant change in the rate of betaAPP synthesis. Furthermore, significant toxicity was not observed in tacrine-treated cultures as determined by analysis of lactate dehydrogenase (LDH) in the conditioned media. Taken together, these results suggest that tacrine affects the processing of betaAPP by alterations in betaAPP trafficking and/or increased intracellular proteolysis. This study raises the possibility that tacrine may aid in the treatment of AD due to its effects on betaAPP processing as well as by its effects on the cholinergic pathway.
淀粉样β蛋白（Aβ）是一种分子量约为4kD的分泌蛋白，正常情况下存在于人体血浆和脑脊液中。在阿尔茨海默病（AD）患者的大脑中，Aβ总是以不溶性淀粉样纤维的形式沉积，越来越多的证据表明Aβ沉积在AD发病机制中起重要作用。Aβ是通过分别被称为β和γ分泌酶的蛋白水解活性在Aβ的氨基和羧基侧进行切割，从较大的β淀粉样前体蛋白（βAPP）释放出来的。βAPP还会被第三种蛋白酶α分泌酶在Aβ16处切割，这可能通过将Aβ肽一分为二来防止淀粉样沉积。他克林是一种胆碱酯酶抑制剂，已被证明能改善一些AD患者的记忆和认知功能，我们之前已经证明它能显著降低培养细胞中可溶性βAPP片段（sAPP）的分泌水平。在这项研究中，我们通过分析Aβ40和Aβ42扩展了我们的研究，并报告在人神经母细胞瘤细胞系中，他克林除了降低sAPP水平外，还降低了总Aβ、Aβ40和Aβ42的水平。这些抑制结果不能归因于总βAPP合成的减少，因为他克林处理并未导致βAPP合成速率发生显著变化。此外，通过分析条件培养基中的乳酸脱氢酶（LDH），未在他克林处理的培养物中观察到明显的毒性。综上所述，这些结果表明他克林通过改变βAPP的运输和/或增加细胞内蛋白水解来影响βAPP的加工过程。这项研究提出了一种可能性，即他克林可能因其对βAPP加工的影响以及对胆碱能途径的影响而有助于AD的治疗。
