Eavri Ronen, Lorberboum-Galski Haya
Department of Cellular Biochemistry and Human Genetics, Faculty of Medicine, Hebrew University, Ein-Kerem, Jerusalem 91120, Israel.
J Biol Chem. 2007 Aug 10;282(32):23402-9. doi: 10.1074/jbc.M703367200. Epub 2007 Jun 12.
Metabolic diseases arise from mutations in key enzymes of major metabolic pathways. One promising approach for the treatment of such diseases is based on the administration of a wild-type enzyme to substitute the activity of the impaired enzyme by the use of enzyme replacement therapy, yet it is important to deliver this enzyme to the specific deficient tissue. We suggest a new concept for the treatment of metabolic diseases using fusion proteins. We examined the feasibility of this concept in the well characterized metabolic disease, phenylketonuria (PKU), which results from a mutation in the liver enzyme phenylalanine hydroxylase (PAH). PAH is a key enzyme in the metabolic pathway of phenylalanine. Deficiency in PAH leads to high and persistent levels of this amino acid in the plasma of PKU patients, causing permanent neurological damage. Currently a low protein diet is still considered the only effective treatment for most PKU patients. To restore PAH activity in the liver of PKU patients, we constructed PAH-based fusion proteins with delivery moieties based on the HIV-transactivator of transcription peptide, and fragments of human hepatocyte growth factor aiming to specifically target PAH to the liver. We show that these new fusion proteins can be delivered into a variety of human liver cell lines and retain PAH activity after being internalized. We also show that plasma phenylalanine levels were dramatically lowered in mice treated with PAH-based fusion proteins after intravenous administration. We therefore suggest an alternative concept for the treatment of PKU using targeted fusion proteins, which may also be applied to the treatment of other metabolic diseases.
代谢性疾病源于主要代谢途径中关键酶的突变。治疗此类疾病的一种有前景的方法是基于给予野生型酶，通过酶替代疗法来替代受损酶的活性，但将这种酶递送至特定的缺陷组织很重要。我们提出了一种使用融合蛋白治疗代谢性疾病的新概念。我们在特征明确的代谢性疾病苯丙酮尿症（PKU）中检验了这一概念的可行性，该疾病由肝脏酶苯丙氨酸羟化酶（PAH）的突变引起。PAH是苯丙氨酸代谢途径中的关键酶。PAH缺乏导致PKU患者血浆中这种氨基酸水平持续升高，引起永久性神经损伤。目前，低蛋白饮食仍被认为是大多数PKU患者唯一有效的治疗方法。为了恢复PKU患者肝脏中的PAH活性，我们构建了基于PAH的融合蛋白，其带有基于HIV转录激活因子肽的递送部分以及人肝细胞生长因子的片段，旨在将PAH特异性靶向至肝脏。我们表明，这些新的融合蛋白可以递送至多种人肝细胞系，并在被内化后保留PAH活性。我们还表明，静脉注射基于PAH的融合蛋白后，治疗的小鼠血浆苯丙氨酸水平显著降低。因此，我们提出了一种使用靶向融合蛋白治疗PKU的替代概念，这也可能适用于其他代谢性疾病的治疗。
