Biomechanical Performance of Charcot-Specific Implants.

Over the past 2 decades, an increased number of diabetic Charcot neuroarthropathy reconstructions have been performed. Despite advances in implant technology, arthrodesis complication rates remain high. This study examined the biomechanical properties (4-point bending, cantilever bending, and thread pullout resistance) of intramedullary implants designed for midfoot reconstruction. Large implants included A1 (7.4 mm cannulated stainless steel beam), B1 (6.5 mm solid titanium bolt), and C1 (7.0 mm cannulated titanium beam). Smaller implants included A2 (5.4 mm cannulated stainless steel beam) and C2 (5.0 mm solid titanium bolt). Four-point bending testing compared flexural properties of the body of the implants. Cantilever-bending testing was performed with the maximum bending moment being applied off the main thread of the implant to assess the thread portion. Thread pullout strength was tested by fixing the implants to a Sawbone block on a platform, and the distal portion of the implant in a clamp connected to loading actuator. Implant A1 demonstrated higher stiffness, force to failure, and fatigue compared to implants B1 and C1 (p < .05). Pullout strength of implant A1 was higher than implant B1 (p < .05). Thread fatigue strength of implant A1 was higher than implant C1 (p < .05). Implant A2 demonstrated higher stiffness, force to failure, tip fatigue strength, and thread pullout strength compared to implant C2 (p < .05), while implant C2 demonstrated higher body fatigue failure than implant A2 (p < .05). Alteration of beam/bolt parameters influences the biomechanical performance of implants used in Charcot reconstruction. Greater stiffness resists deformation, providing improved stability. Greater static failure load and fatigue limit improves the implant's ability to withstand higher and repetitive loads before failing This study should stimulate further clinical research to determine if these biomechanical properties translate into reduced implant failure rates and improved clinical outcomes in patients with diabetic Charcot neuroarthropathy.

Oral absorption enhancement of probucol by PEGylated G5 PAMAM dendrimer modified nanoliposomes.

Probucol (PB), an antioxidant drug, is commonly used as a lipid concentration lowering drug to reduce blood plasma cholesterol levels in the clinic. However, the therapeutic effects of this drug are negatively impacted by its poor water solubility and low oral absorption efficiency. In this study, a PEGylated G5 PAMAM dendrimer (G5-PEG) modified nanoliposome was employed to increase water solubility, transepithelial transport, and oral absorption of PB. The uptake mechanism was explored in vitro in Caco-2 cells with the results suggesting that the absorption improvement of G5-PEG modified PB-liposome (PB-liposome/G5-PEG) was related to P-glycoprotein (P-gp) efflux pump but was independent of caveolae endocytosis pathways. Additionally, plasma lipid concentration lowering effects of PB-liposome/G5-PEG were evaluated in vivo in a LDLR-/- hyperlipidemia mouse model. Compared with saline treated group, treatment with PB-liposome/G5-PEG significantly inhibited the increase of plasma total cholesterol (TC) and triglyceride (TG) of mice induced by a high fat diet. Moreover, its lipid concentration lowering effects and plasma drug concentration were greater than PB alone or commercial PB tablets. Our results demonstrated that PB-liposome/G5-PEG significantly increased the oral absorption of PB and therefore significantly improved its pharmacodynamic effects.

G5 PAMAM dendrimer versus liposome: a comparison study on the in vitro transepithelial transport and in vivo oral absorption of simvastatin.

This study compared formulation effects of a dendrimer and a liposome preparation on the water solubility, transepithelial transport, and oral bioavailability of simvastatin (SMV). Amine-terminated G5 PAMAM dendrimer (G5-NH2) was chosen to form SMV/G5-NH2 molecular complexes, and SMV-liposomes were prepared by using a thin film dispersion method. The effects of these preparations on the transepithelial transport were investigated in vitro using Caco-2 cell monolayers. Results indicated that the solubility and transepithelial transport of SMV were significantly improved by both formulations. Pharmacokinetic studies in rats also revealed that both the SMV/G5-NH2 molecular complexes and the SMV-liposomes significantly improved the oral bioavailability of SMV with the liposomes being more effective than the G5-NH2. The overall better oral absorption of SMV-liposomes as compared to SMV/G5-NH2 molecular complexes appeared to arise from better liposomal solubilization and encapsulation of SMV and more efficient intracellular SMV delivery. FROM THE CLINICAL EDITOR: Various carrier systems have been designed to enhance drug delivery via the oral route. In this study, the authors compared G5 PAMAM dendrimers to liposome preparations in terms of solubility, transepithelial transport, and oral bioavailability of this poorly water-soluble drug. This understanding has improved our knowledge in the further development of drug carrier systems.

Liposomal encapsulation of vancomycin improves killing of methicillin-resistant Staphylococcus aureus in a murine infection model.

OBJECTIVES: Methicillin-resistant Staphylococcus aureus (MRSA) poses a major problem to public health worldwide. MRSA strains with increased resistance to vancomycin cause infections that are associated with greater morbidity and threaten the use of this once gold-standard antistaphylococcal drug. We investigated whether encapsulation of vancomycin within liposomes could improve its antistaphylococcal activity. METHODS: Two liposomal formulations of vancomycin were prepared using a rehydration-dehydration method. MICs and MBCs of the liposomal vancomycin for strains of MRSA were determined. The efficacy of one of the liposomal vancomycin formulations was also investigated in a time-kill assay in vitro and in a murine systemic infection model. RESULTS: Encapsulation in either liposome preparation decreased the vancomycin MICs and MBCs for MRSA strains by approximately 2-fold. Liposomal vancomycin increased killing of MRSA in vitro in a kinetic study. In a systemic murine infection model, treatment with a 50 mg/kg intraperitoneal injection of liposomal vancomycin improved kidney clearance of a USA300 strain by 1 log compared with an injection of 50 mg/kg of free vancomycin. CONCLUSIONS: Our findings suggest that entrapment within liposomes could improve the antistaphylococcal efficacy of vancomycin.

Efficient in vitro siRNA delivery and intramuscular gene silencing using PEG-modified PAMAM dendrimers.

Although siRNA techniques have been broadly applied as a tool for gene knockdown, substantial challenges remain in achieving efficient delivery and in vivo efficacy. In particular, the low efficiency of target gene silencing in vivo is a critical limiting step to the clinical application of siRNA therapies. Poly(amidoamine) (PAMAM) dendrimers are widely used as carriers for drug and gene delivery; however, in vivo siRNA delivery by PAMAM dendrimers remains to be carefully investigated. In this study, the effectiveness of G5 and G6 PAMAM dendrimers with 8% of their surface amines conjugated to MPEG-5000 was studied for siRNA delivery in vitro and for intramuscular in vivo delivery in mice. The results from the PEG-modified dendrimers were compared to the results from the parent dendrimers as well as Lipofectamine 2000 and INTERFERin. Both PEG-modifed dendrimers protect the siRNA from being digested by RNase and gave high transfection efficiency for FITC-labeled siRNA in the primary vascular smooth muscle cells (VSMC) and mouse peritoneal macrophages. The PEG-modified dendrimers achieved knockdown of both plasmid (293A cells) and adenovirus-mediated green fluorescence protein (GFP) expression (Cos7 cells) in vitro with efficiency similar to that shown for Lipofectamine 2000. We further demonstrated in vivo that intramuscular delivery of GFP-siRNA using PEG-modified dendrimer significantly suppressed GFP expression in both transiently adenovirus infected C57BL/6 mice and GFP transgenic mice.

Efficient siRNA Delivery Using PEG-conjugated PAMAM Dendrimers Targeting Vascular Endothelial Growth Factor in a CoCl2-induced Neovascularization Model in Retinal Endothelial Cells.

BACKGROUND: Choroidal neovascularization (CNV), also known as subretinal neovascularization, causes serious damage to the central vision as it happens more commonly in macula. The most important factor involved in angiogenesis is vascular endothelial growth factor (VEGF). By an RNAi technique, VEGF gene knockdown can be used to treat CNV. PEG-conjugated poly (amidoamine) (PEGPAMAM) dendrimers as a new type of synthetic polymers are very promising to be gene delivery carriers. METHODS: To investigate siRNA delivery efficacy of PEG-PAMAM dendrimers, we prepared dendriplexes of PEG-PAMAM dendrimers with a fluorescence-labelled siRNA (PEG-PAMAM/FAM siRNA) or VEGF siRNA (PEG-PAMAM/VEGF siRNA), and studied transfection and downregulation efficacy of the dendriplexes in a cobalt chloride (CoCl2)-induced neovascularization model in retinal vascular endothelial cells (RF/6A). RESULTS: Our results demonstrate that PEG-PAMAM dendrimers had significantly higher transfection efficiency to FAM siRNA than a commercial transfection reagent PEI (1.4-fold, P<0.001) measured by flow cytometry. Compared to the PEI/VEGF siRNA polyplexes, the dendriplexes of the PEG-PAMAM/VEGF siRNA more significantly downregulated VEGF gene expression (P < 0.01) at both mRNA and protein expression level. A tube formation assay also proved that the PEG-PAMAM/VEGF siRNA dendriplexes more significantly inhibited vascular-like formation than PEI/VEGF siRNA did (P < 0.001) in RF/6A. CONCLUSION: This study demonstrated that G5-PEG was more efficient than PEI in facilitating siRNA delivery, downregulating VEGF expression and inhibiting vascular-like formation on RF/6A.

The role of caveolin-1 and syndecan-4 in the internalization of PEGylated PAMAM dendrimer polyplexes into myoblast and hepatic cells.

To improve gene delivery efficiency of PEGylated poly(amidoamine) dendrimers in livers and muscles, the roles of syndecan-4 receptor and caveolin-1 protein in the endocytosis of PEGylated generation 5 (G5-PEG) or 7 (G7-PEG) dendrimers and plasmid DNA polyplexes were explored in C2C12 and HepG2 cells. Expression levels of syndecan-4 for both cell lines were downregulated by transfection of the cells with syndecan-4 specific siRNA. Caveolin-1 was upregulated by infecting the cells with adenovirus vector expressed caveolin-1 (Ad-CAV-1). The impact of syndecan-4 and caveolin-1 on endocytosis of G5-PEG/DNA or G7-PEG/DNA polyplexes was then measured by flow cytometry. Our results demonstrate that downregulation of syndecan-4 and upregulation of caveolin-1 significantly improved internalization of PEG-PAMAM dendrimer polyplexes in HepG2 cells; however, in C2C12 cells, downregulation of syndecan-4 decreased the internalization of the polyplexes while upregulation of caveolin-1 had no effect on internalization. Gene expression results for G5-PEG/pGFP on the two cell lines exhibited the same trends for syndecan-4 and caveolin-1 as was observed for endocytosis of the polyplexes. This study gives a clue how to take strategies by up- or down-regulation of the expressions of syndecan-4 and caveolin-1 to improve in vivo gene delivery efficiency of the PEG-PAMAM dendrimers in clinical transgenic therapy.

PEG-conjugated PAMAM dendrimers mediate efficient intramuscular gene expression.

Generations 5 and 6 (G5 and G6) poly(amidoamine) (PAMAM) dendrimers have been shown to be highly efficient nonviral carriers in in vitro gene delivery. However, their high toxicity and unsatisfied in vivo efficacy limit their applications. In this study, to improve their characteristics as gene delivery carriers, polyethylene glycol (PEG, molecular weight 5,000) was conjugated to G5 and G6 PAMAM dendrimers (PEG-PAMAM) at three different molar ratios of 4%, 8%, and 15% (PEG to surface amine per PAMAM dendrimer molecular). Compared with unconjugated PAMAM dendrimers, PEG conjugation significantly decreased the in vitro and in vivo cytotoxicities and hemolysis of G5 and G6 dendrimers, especially at higher PEG molar ratios. Among all of the PEG-PAMAM dendrimers, 8% PEG-conjugated G5 and G6 dendrimers (G5-8% PEG, G6-8% PEG) resulted in the most efficient muscular gene expression when polyplexes were injected intramuscularly to the quadriceps of neonatal mice. Consistent with the in vivo results, these two 8% PEG-conjugated PAMAM dendrimers could also mediate the highest in vitro transfection in 293A cells. Therefore, G5-8% PEG and G6-8% PEG possess a great potential for gene delivery both in vivo and in vitro.

Electrostatic forward-viewing scanning probe for Doppler optical coherence tomography using a dissipative polymer catheter.

A novel flexible scanning optical probe is constructed with a finely etched optical fiber strung through a platinum coil in the lumen of a dissipative polymer. The packaged probe is 2.2 mm in diameter with a rigid length of 6mm when using a ball lens or 12 mm when scanning the fiber proximal to a gradient-index (GRIN) lens. Driven by constant high voltage (1-3 kV) at low current (< 5 microA), the probe oscillates to provide wide forward-viewing angle (13 degrees and 33 degrees with ball and GRIN lens designs, respectively) and high-frame-rate (10-140 fps) operation. Motion of the probe tip is observed with a high-speed camera and compared with theory. Optical coherence tomography (OCT) imaging with the probe is demonstrated with a wavelength-swept source laser. Images of an IR card as well as in vivo Doppler OCT images of a tadpole heart are presented. This optomechanical design offers a simple, inexpensive method to obtain a high-frame-rate forward-viewing scanning probe.