Sialic Acid-mediated Drug Delivery For The Targeted Treatment Of Acute Kidney Injury

Acute kidney injury(AKI)occurs during rapid renal function impairment.Although treatment strategies for AKI are improved constantly,its morbidity and mortality rates are still high,which forces more and more clinicians to focus on the novel and effective therapeutic approaches for AKI.Recent studies revealed renal vascular endothelial cell injury was of great importance to AKI.Therefore,identifying more effective therapeutic approach to ameliorate cell injury via reducing the production and release of pro-inflammatory cytokines,strengthening anti-apoptotic effect and improving oxidative stress injury is remains a primary aim.In this study,sialic acid is used to construct sialic acid-mediated kidney-targeted drug delivery systems for the treatment of AKI via increasing drug distribution in renal tissues.Sialic acid-polyethylene glycol-dexamethasone(SA-PEG-DXM)conjugate was synthesized via the esterification reaction.The obtained conjugate could spontaneously form blank micelles with 50 nm in aqueous medium,and its critical micelle concentration was 63.9 ± 4.1 ?g/mL determined by pyrene fluorescence mensuration.The low CMC value could ensure conjugate to form micelles with a core-shell structure in aqueous medium,and keep integrity and stability during systemic circulation.The conjugated DXM content in SA-PEG-DXM conjugate was 15.9 ± 2.4%,and its release SA-PEG-DXM conjugate could be sustained for more than 48 h.Then,dexamethasone-loaded sialic acid-polyethylene glycol-dexamethasone(SA-PEG-DXM/DXM)micelles were prepared via the solvent diffusion method.The DXM content in SA-PEG-DXM/DXM micelles was 22.5 ± 2.1%during 10%DXM-feeding amount.The obtained SA-PEG-DXM/DXM micelles had a uniform spherical shape with 30 nm and were well dispersed as individual nanoparticles.In vitro drug release results showed the encapsulated DXM released rapidly at initial 24 h,which indicated that SA-PEG-DXM/DXM micelles had the dual characteristics of drug release,including repad release and sustained release.The cytotoxicity of SA-PEG-DXM was assessed in human umbilical vein endothelial cells(HUVECs)for a range of concentrations via the MTT assay,and the results showed SA-PEG-DXM displays minimum cytotoxicity with over 80%HUVECs remaining viable at the highest concentration of 800 ?g/mL.Cellular uptake test for SA-PEG-DXM and PEG-DXM micelles on lipopolysaccharide(LPS)-activated HUVECs was performed,and the results showed more SA-PEG-DXM micelles were internalized into HUVECs,which was consistent with the expression of E-selectin receptors.The internalization of SA-PEG-DXM micelles by HUVECs was reduced after free sialic acid blockage.To investigate the kidney-targeting efficacy of SA-PEG-DXM micelles in vivo,AKI murine models were built and then injected indocyanine green-loaded SA-PEG-DXM micelles.At 24 h after administration,mice were sacrificed,and their organs were collected.Compared with mice without AKI,the higher renal fluorescence signal was observed in AKI murine model treated with SA-PEG-DXM micelles.Moreover,the renal fluorescence intensity in AKI murine model treated with SA-PEG-DXM micelles was higher than that treated with PEG-DXM micelles.The ICR mice were used as model animals,and AKI murine models were built by LPS.The in vivo pharmacodynamics of free DXM,PEG-DXM/DXM and SA-PEG-DXM/DXM micelles were investigated subsequently after intravenous administration.The kidney index,renel function index,pro-inflammatory factor and oxidative stress parameter were investigated at day 2 and day 7 after intravenous administration,and the results showed SA-PEG-DXM/DXM micelles achieved the better therapeutic outcomes in comparison to free DXM and PEG-DXM/DXM micelles.HE and PAS staining showed that SA-PEG-DXM/DXM micelles effectively improved renal injury,as evidenced widespread by tubular expansion,interstitial edema and inflammatory cells infiltration.TUNEL staining and western blot demonstrated the best anti-apoptotic effects of SA-PEG-DXM/DXM micelles.Matrix metalloproteinase(MMP)-2-responsive sialic acid-dextran-PVGLIG-curcumin(SA-DEX-PVGLIG-CUR)polymeric drug was prepared on the basis of the successful development of SA-PEG-DXM/DXM micelles with excellent kidney-targeting efficacy.CUR content in SA-DEX-PVGLIG-CUR was 5.38 ± 0.25%determined by fluorescence spectrophotometry.In vitro drug release results showed that 84.4 ± 5.1%CUR was released from SA-DEX-PVGLIG-CUR under the effects of MMP-2 enzyme within 48 h,which was significantly higher than that from MMP-2-independent sialic acid-dextran-curcumin(SA-DEX-CUR)polymeric drug.SA-DEX-PVGLIG-CUR could be specifically internalized by inflamed HUVECs in co-culture systems of HUVECs and renal tubular epithelial cells(HK-2).Biodistribution results showed that CUR content in renal tissues of AKI mice treated with SA-DEX-PVGLIG-CUR was 16.2-and 3.1-fold than those treated with free CUR and DEX-PVGLIG-CUR,respectively.It was also observed that more CUR was distributed in renal tubular of AKI mice treated with SA-DEX-PVGLIG-CUR than that of mice treated with SA-DEX-CUR,which indicated that MMP-2-responsive SA-DEX-PVGLIG-CUR had benefits on other functional cells in renal tissue.ICR mice were used as model animals to construct AKI murine models.The in vivo pharmacodynamics of free CUR,SA-DEX-CUR and SA-DEX-PVGLIG-CUR were investigated subsequently after intravenous administration.The kidney index,renel function index,pro-inflammatory factor,oxidative stress and pathological histology were investigated at day 2 after intravenous administration,and the results showed SA-DEX-PVGLIG-CUR achieved the better therapeutic outcomes in comparison to free CUR and SA-DEX-CUR.In conclusion,it was demonstrated that SA-PEG-DXM/DXM micelles and SA-DEX-PVGLIG-CUR polymeric prodrug were effective for the treatment of AKI via the increased drug distribution in kidney tissues.Hopefully,the safe and effective treatment for AKI could be realized via sialic acid-mediated drug delivery system.