Development of Therapy for Refractory Hyperlipidemia with LDL Receptor Gene Introduction by Lipofection Method

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In this report, we tried to develop a gene therapy for famillial hypercholesterolemia (FH) which is caused by the abnormality in the low density lipoprotein (LDL) receptor gene. First, we developed a highly efficient in vivo gene introduction system, HVJ-liposome method. Second, we introduced human LDL receptor gene into adult rat liver with this method. HVJ-liposome particles containing human LDL receptor gene were introduced to the liver through portal vein or tail vein and the expression of human LDL receptor mRNA was confirmed in the liver with RT-PCR method. Furthermore, serum cholesterol was decreased about 20% in the intravenously transfected rats compared with control rats which were loaded with a high-cholesterol diet. However, the efficiency of transfection with HVJ-liposome method was a little lower than expected and was considered to be insufficient for the gene therapy for FH.So, we tried to improve the expression vector. The vector we used first (pMy3) was long and its promoter (transferrin promoter) could be regulated in the liver, so we developed a new vector which contains chicken beta actin promoter and included human LDL receptor cDNA and compared in vitro the efficiency of these two vectors. Northern blot analysis demonstrated that the new vector (pCL1) was more efficient than pMy3. So we used this vector for transfection in vivo, but serum cholesterol was not reduced markedly compared with pMy3. Now, we are trying to develop another new expression vector, using Epstein-Barr virus or retrovirus vector and improve HVJ-liposome method by changing the lipid composition of liposomes.