Publications by authors named "Andrew M Hoff"

7 Publications

  • Page 1 of 1

Real-time impedance feedback to enhance cutaneous gene electrotransfer in a murine skin model.

Bioelectrochemistry 2021 Jul 13;142:107885. Epub 2021 Jul 13.

Department of Chemical, Biological, and Materials Engineering, University of South Florida, 4202 E. Fowler Ave ENG 030, Tampa, FL 33620, USA; Center for Molecular Delivery at USF, University of South Florida, 4202 E. Fowler Ave ENG 030, Tampa, FL 33620, USA; Department of Medical Engineering, University of South Florida, 4202 E. Fowler Avenue ENG 030, Tampa, FL 33620, USA. Electronic address:

Electric field mediated gene delivery methods have the ability to efficiently transfect cells in vivo with an excellent safety profile. The method has historically used a fixed number of electric pulses with identical characteristics in induce delivery. Electrical treatment does not typically compensate for subject-to-subject variation and other differences. This study was designed to investigate if delivery/expression could be increased using a novel electropulsation method that compensated for variation using real-time electrical impedance measurements. The method involved delivering plasmid DNA encoding luciferase to murine skin. Tissue impedance in a 1-3 KHz range was measured before electric pulses were applied. Impedance was also measured after each successive pulse. Pulsation was stopped when impedance values were reduced by either 80% or 95% relative to prepulse values. Standard/fixed pulsing parameters were also used for comparison. The results indicated that up to 15-fold increases in luciferase expression could be obtained when electrical treatment was ceased based upon impedance reductions. Furthermore, peak expression levels of all treatment groups pulsed using the novel pulsing method were statistically higher than those that employed standard pulsing. These results strongly suggest that applying pulses until a defined impedance-based endpoint results in higher expression.
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http://dx.doi.org/10.1016/j.bioelechem.2021.107885DOI Listing
July 2021

Impedance spectroscopy as an indicator for successful in vivo electric field mediated gene delivery in a murine model.

Bioelectrochemistry 2017 Jun 27;115:33-40. Epub 2017 Jan 27.

Department of Chemical and Biomedical Engineering, University of South Florida, 4202 E. Fowler Ave. ENB 118, Tampa, FL 33620, USA; Center for Molecular Delivery at USF, University of South Florida, 4202 E. Fowler Ave. ENB 118, Tampa, FL 33620, USA.

In vivo gene electro transfer technology has been very successful both in animal models and in clinical trials over the past 20years. However, variable transfection efficiencies can produce inconsistent outcomes. This can be due to differences in tissue architecture and/or chemical composition which may effectively create unique biological environments from subject to subject that may respond differently to the identical electric pulses. This study investigates the integration of impedance spectroscopy into the gene electro transfer process to measure murine skin impedance spectra before, during (after pulse delivery), and after gene electro transfer pulse application to determine if changes in impedance correlate with reporter gene expression. Both post-treatment impedance spectra and gene expression were dependent upon the applied electric field strength. These results indicate that alterations in tissue impedance produced by the applied electric field represent an excellent parameter to predict degrees of transfection and gene expression. These results could ultimately be used to alter pulsing parameters in order to optimize delivery/expression.
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http://dx.doi.org/10.1016/j.bioelechem.2017.01.004DOI Listing
June 2017

Optimization of a plasma facilitated DNA delivery method.

Bioelectrochemistry 2015 Jun 13;103:15-21. Epub 2014 Oct 13.

Department of Chemical and Biomedical Engineering, College of Engineering, University of South Florida, 4202 East Fowler Avenue, Tampa, FL 33620, United States. Electronic address:

Plasma-based methods have recently emerged as a technique for augmenting plasmid DNA delivery to skin. This delivery modality relies on the deposition of ionized gas molecules on to targeted cells or tissue to establish an electric field. It is hypothesized that this electric field results in the dielectric breakdown of cell membranes, making cells permeable to exogenous molecules. This in vivo investigation sought to optimize the intradermal delivery of a luciferase expressing plasmid DNA by modulating the total exposure to the plasma source and the plasmid DNA dose. Varying the plasma exposure time from 2, 5, 10, and 20 min allowed the conditions resulting in the highest expression of luciferase to be found. These conditions correlated to the 10 minute exposure time for a plasma derived from either +8 kV or -8 kV, when the generator was operated 3 cm from the epidermal tissue surface with a helium flow rate of 15 L/min. Exposing the injected flank skin for 10 min resulted in a rise of 37.3-fold for a plasma created with +8 kV and 27.1-fold for a plasma created with -8 kV. When using this treatment time with 50, 100, or 200 μg of a luciferase expressing plasmid, it was found that 100 μg resulted in the highest peak luminescence.
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http://dx.doi.org/10.1016/j.bioelechem.2014.09.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4346600PMC
June 2015

Non-contact helium-based plasma for delivery of DNA vaccines. Enhancement of humoral and cellular immune responses.

Hum Vaccin Immunother 2012 Nov 16;8(11):1729-33. Epub 2012 Aug 16.

Center for Molecular Delivery, University of South Florida; Tampa, FL, USA.

Non-viral in vivo administration of plasmid DNA for vaccines and immunotherapeutics has been hampered by inefficient delivery. Methods to enhance delivery such as in vivo electroporation (EP) have demonstrated effectiveness in circumventing this difficulty. However, the contact-dependent nature of EP has resulting side effects in animals and humans. Noncontact delivery methods should, in principle, overcome some of these obstacles. This report describes a helium plasma-based delivery system that enhanced humoral and cellular antigen-specific immune responses in mice against an intradermally administered HIV gp120-expressing plasmid vaccine (pJRFLgp120). The most efficient plasma delivery parameters investigated resulted in the generation of geometric mean antibody-binding titers that were 19-fold higher than plasmid delivery alone. Plasma mediated delivery of pJRFLgp120 also resulted in a 17-fold increase in the number of interferon-gamma spot-forming cells, a measure of CD8+ cytotoxic T cells, compared with non-facilitated plasmid delivery. This is the first report demonstrating the ability of this contact-independent delivery method to enhance antigen-specific immune responses against a protein generated by a DNA vaccine.
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http://dx.doi.org/10.4161/hv.21624DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3601149PMC
November 2012

Characterization of plasma mediated molecular delivery to cells in vitro.

Int J Pharm 2010 Apr 18;389(1-2):53-7. Epub 2010 Jan 18.

Department of Chemical and Biomedical Engineering, University of South Florida, ENB 118, 4202 E. Fowler Avenue, Tampa, FL 33620, USA.

Ion-based strategies have recently emerged as a method to facilitate molecular delivery. These methods are attractive as they separate the applicator from the treatment site avoiding some issues encountered with other electrically driven methods. Current literature on plasma delivery has shown utility in vitro and in vivo for both drugs and genes. To advance this technology more information must become available on the mechanism responsible for delivery and the effects of ion exposure on eukaryotic cells. This in vitro investigation found that molecular delivery facilitated by a DC-based plasma follows a dose-response behavior, with optimum uptake of Sytox Green occurring in two cell lines after 600 s of exposure. In both cell lines exposure to the discharge caused no adverse effects in viability for exposure times up to 600 s. It was also found that membranes treated with ions remained permeabilized for several minutes following plasma treatment and that membrane resealing exhibited first order kinetics.
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http://dx.doi.org/10.1016/j.ijpharm.2010.01.016DOI Listing
April 2010

Plasma facilitated delivery of DNA to skin.

Biotechnol Bioeng 2009 Dec;104(5):1034-40

Department of Chemical and Biomedical Engineering, University of South Florida, ENB 118, Tampa, Florida 33620, USA.

Non-viral delivery of cell-impermeant drugs and DNA in vivo has traditionally relied upon either chemical or physical stress applied directly to target tissues. Physical methods typically use contact between an applicator, or electrode, and the target tissue and may involve patient discomfort. To overcome contact-dependent limitations of such delivery methodologies, an atmospheric helium plasma source was developed to deposit plasma products onto localized treatment sites. Experiments performed in murine skin showed that samples injected with plasmid DNA encoding luciferase and treated with plasma demonstrated increased levels of expression relative to skin samples that received injections of DNA alone. Increased response relative to injection alone was observed when either positive or negative voltage was used to generate the helium plasma. Quantitative results over a 26-day follow-up period showed that luciferase levels as high as 19-fold greater than the levels obtained by DNA injection alone could be achieved. These findings indicate that plasmas may compete with other physical delivery methodologies when skin is the target tissue.
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http://dx.doi.org/10.1002/bit.22451DOI Listing
December 2009

Molecular delivery to cells facilitated by corona ion deposition.

IEEE Trans Nanobioscience 2008 Sep;7(3):233-9

Department of Chemical Engineering, University of South Florida, Tampa, FL 33620 USA.

A novel method of inducing the delivery of nonpermeant molecules to the cytosol of cells is presented in this paper. Corona discharge in air was utilized to produce ions that in turn were deposited onto the liquid surface of media containing cultured cells. Murine B16 melanoma cells were used to demonstrate the molecular delivery of fluorescent dye calcein, the drug bleomycin, and a nucleic acid stain SYTOX-green. None of these molecules penetrate cells with intact membranes. Following the corona treatment, cells were observed to admit significant quantities of these molecules from the culture media, relative to control samples. Further, greater than 95% viability of treated cells was observed by Trypan Blue assay. This method may provide an attractive alternative to electroporation where a physical contact between electrodes and cells is needed to deliver molecules to the cytosol.
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http://dx.doi.org/10.1109/TNB.2008.2002290DOI Listing
September 2008
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