The Study On Blood-brain Barrier Permeability Of Endomorphin-2 Using Nanodiamond Strategy

The endomorphins(EMs)not only possess highly μ-opioid receptor affinity and selectivity,but also elicit equipotent analgesia effect to morphine.By virtue of the relatively simple structures and strong analgesic effect,EMs have gained attention as potential lead compounds and hopefully develop into new analgesic drugs.However,EMs still suffered from serious limitations because of poor metabolic stability,relative inability to cross the blood-brain barrier(BBB)and short duration of action,which limited their application.Among the strategies to enhance drug across the BBB,nanoparticles technology provide a significant advantage.Nanoparticles are able to cross the BBB without destroying the integrity of BBB.In this thesis,the nanodiamonds were applied as a drug delivery system.The endomorphin-2 was loaded on nanodiamonds in two different ways,aimed to use nanodiamonds transport endomorphin-2 across the BBB.Firstly,the endomorphin-2 was loaded on nanodiamonds via physical adsorption and covalently linked respectively.The contents of endomorphin-2 on the nanodiamonds were calculated and the particle size distribution and zeta potential of the complex were determinated.Then a series of spectroscopy and analysis techniques were used for characterization.The results showed that the encapsulation efficiency of endomorphin-2 on nanodiamonds via physical adsorption and covalently linked was 0.45mg·mg-1 and 0.27mg·mg-1 respectively.The endomorphin-2 was further confirmed the successful attachment to nanodiamonds by Fourier transform infrared spectroscopy,elemental analysis and thermogravimetric analysis,respectively.To further assess the blood-brain barrier permeability of the endomorphin-2-nanodiamond complex,the efficacy of the complex was evaluated using mouse tail-flick test and an in vitro BBB model—parallel artificial membrane permeability assay(PAMPA)was established to evaluate the BBB permeability of the complex.The results of antinociception assay showed that intravenous(i.v.)administration of endomorphin-2 or nanodiamonds to mice had no analgesic response,while the physical adsorption complex and covalently linked complex exhibited approximately 4-fold and 5-fold increase of antinociception respectively,and the duration of action was extend also.The maximum analgesic effect of the covalently linked complex was higher than the physical adsorption complex,yet the latter had a longer duration of action.The results of PAMPA showed that the permeability coefficient of nanodiamonds(12.15%)was close to the positive drug carbamazepine(14.7%),and significantly higher than the negative drug atenolol(1.48%).It is shown that nanodiamonds were able to transport endomorphin-2 through the BBB as a drug delivery system and it provided a new idea for clinical preparations of the peptide drugs.