Artificial cells with emphasis on cell encapsulation of genetically engineered cells

Artificial cells for the treatment of liver diseases

Liver diseases have become an increasing health burden and account for over 2 million deaths every year globally. Standard therapies including liver transplant and cell therapy offer a promising treatment for liver diseases, but they also suffer limitations such as adverse immune reactions and lack of long-term efficacy. Artificial cells that mimic certain functions of a living cell have emerged as a new strategy to overcome some of the challenges that liver cell therapy faces at present. Artificial cells have demonstrated advantages in long-term storage, targeting capability, and tuneable features. This article provides an overview of the recent progress in developing artificial cells and their potential applications in liver disease treatment. First, the design of artificial cells and their biomimicking functions are summarized. Then, systems that mimic cell surface properties are introduced with two concepts highlighted: cell membrane-coated artificial cells and synthetic lipid-based artificial cells. Next, cell microencapsulation strategy is summarized and discussed. Finally, challenges and future perspectives of artificial cells are outlined. STATEMENT OF SIGNIFICANCE: Liver diseases have become an increasing health burden. Standard therapies including liver transplant and cell therapy offer a promising treatment for liver diseases, but they have limitations such as adverse immune reactions and lack of long-term efficacy. Artificial cells that mimic certain functions of a living cell have emerged as a new strategy to overcome some of the challenges that liver cell therapy faces at present. This article provides an overview of the recent progress in developing artificial cells and their potential applications in liver disease treatment, including the design of artificial cells and their biomimicking functions, two systems that mimic cell surface properties (cell membrane-coated artificial cells and synthetic lipid-based artificial cells), and cell microencapsulation strategy. We also outline the challenges and future perspectives of artificial cells.

Droplet-based microfluidics for artificial cell generation: a brief review

Artificial cells are best defined as micrometre-sized structures able to mimic many of the morphological and functional characteristics of a living cell. In this mini-review, we describe progress in the application of droplet-based microfluidics for the generation of artificial cells and protocells.

Protein-based blood substitutes: recent attempts at controlling pro-oxidant reactivity with and beyond hemoglobin

Reviewed here are recent attempts to produce protein-based artificial oxygen carriers (“blood substitutes”). Most of these involve chemical or physical modifications on hemoglobin, although a recent line of research using hemerythrin instead of hemoglobin is also described. The focus is set on the extent to which these modifications alter the redox reactivity of the proteins, and on ways in which this can be done systematically and purposefully, within the framework of a working hypothesis where redox side-reactions hold an important role in the physiological outcome of experimental transfusions with artificial oxygen carriers.

Oral administration of biochemically active microcapsules to treat uremia: new insights into an old approach

This paper begins with an extensive review of previous research on the degradation of non-protein nitrogen compounds for improved therapy of renal failure. During the 1970s, Malchesky established that naturally occurring strains of microorganisms were highly effective for the in vitro degradation of urea and other compounds found in urine, and that these bacteria could be conditioned with selected media to enhance growth and degradation efficiency. A few years later, Setala introduced the concept of oral delivery of lyophilized bacteria, harvested from soil, to uremic patients, for degradation of non-protein nitrogen compounds. In the 1990s, Chang proposed delivery of encapsulated genetically modified bacteria for removal of uremic waste products in vitro and in vivo. Recently, our group has pursued the idea of orally delivering formulated combinations of enzymes or modified bacteria. A new study is also described, which characterizes the capacity of a single alginate microcapsule containing a mixture of genetically modified cells and enzyme to degrade urea, uric acid and creatinine. The combination capsules were found to be effective in vitro and in vivo in a rodent model of chemically-induced renal failure. Reduction of urea concentration in vivo required co-administration of a cation exchange resin to adsorb ammonia. Increased investigative effort is warranted for these approaches which offer significant potential as an adjunct to conventional forms of dialysis.

Impact of Orally Administered Microcapsules on Gastrointestinal Microbial Flora: In-Vitro Investigation Using Computer Controlled Dynamic Human Gastrointestinal Model

Oral administration of artificial cell microcapsules has been proposed for various therapy procedures using biologically active materials. Recently we have designed novel APPPA microcapsules using alginate, poly-L-lysine, pectin, poly-L-lysine and alginate that have shown superior oral delivery features. This article investigates, in-vitro using a computer controlled dynamic gastrointestinal (GI) model, effects of APPPA microcapsules on health of gastrointestinal (GI) microbial flora. The impact of APPPA microcapsules on GI bacterial population, total anaerobes, total aerobes, Escherichia coli, Lactobacillus sp. and Staphylococcus sp. has been analyzed. In addition, the effects of microcapsules on GI microbial extracellular enzymatic activities have been investigated. Result shows the altered activities of microbial flora and enzymes due to the use of APPPA microcapsule. The most disparity is observed in the colon ascendans microbial activities. This study would have significant impact on future microcapsule design. However, further in-vivo studies are required.

Microcalorimetric study on the growth and metabolism of microencapsulated microbial cell culture

The rate of heat output is one of the suitable measurements of metabolic activity of the organism or its parts, down to the cellular or even the sub-cellular levels. In this paper, microcalorimetry was first applied to study the metabolic activity of microbial in both alginate-polylysine-alginate and alginate-chitosan-alginate microencapsulated cultures as well as in free non-encapsulated culture. The organisms used for the measurements were Escherichia coli and Saccharomyces cerevisiae. As a result of this work, it was found that, despite E. coli cell in free non-encapsulated culture has the highest metabolic rate due to the highest value of heat output, the proliferation of the cells terminates quickly with a lowest biomass formed. And we found also an obviously longer stationary phase in microencapsulated culture. As far as S. cerevisiae was concerned, it was found that there was also the highest value of heat output in free non-encapsulated culture, but the cell density was lower than that in microencapsulated culture. On account of the microcalorimetric and metabolic measurements, it can be concluded that more substrate can be used to convert to biomass in microencapsulated culture which means a higher biomass yield existed.

In Vivoandin VitroDegradation of Urea and Uric Acid by Encapsulated Genetically Modified Microorganisms

This study was undertaken to characterize the capacity of a combination of genetically modified bacteria to lower elevated levels of urea and uric acid and thus to serve as a potential adjunct to maintenance dialysis in patients with chronic renal failure. Two strains of genetically modified bacteria expressing enzymes, urease to degrade urea and uricase to degrade uric acid, were identified, combined, and dispersed in 600-microm alginate microcapsules suitable for oral administration. In 24 h in vitro experiments, 5 mL of these capsules completely cleared 95% of the urea and >99% of the uric acid from 100 mL of a challenge solution formulated to the concentration of these solutes in a presenting hemodialysis patient. The process of urea degradation was found to be intracellular and each bacterial strain was specific for its substrate. Solute degradation in vivo was evaluated with a chemically induced model of acute renal failure, using Sprague-Dawley rats. Orally administered capsules were found to remain in the gastrointestinal tract for at least 6 h. The severity of azotemia and hyperuricaemia after chemical induction of acute renal failure was reduced by 64 and 31%, respectively, on administration of the capsules. Reduction of urea concentration (but not uric acid concentration) in vivo required coadministration of an ion-exchange resin to adsorb ammonia. Oral delivery of a combination of genetically modified microorganisms should be further explored in chronic renal failure models as a useful adjunct to dialysis or to immunosorption for the treatment of uremia.

Progress and challenges for cell encapsulation in brain tumour therapy

Cell encapsulation provides a method to circumvent the host immune system by encapsulating cells or tissues in immunoisolating, semipermeable membranes before implantation. The technology has been widely studied with an aim of developing bio-organs transplantable into patients without the need of immunosuppression, and in cancer therapy, the principle of cell encapsulation may be further exploited. Encapsulated recombinant cells represent factories or bioreactors for the production of therapeutic proteins. By implanting the bioreactors in the vicinity of the tumour, long-term local de novo delivery of the therapeutic proteins may be achieved. Malignant brain tumours such as glioblastoma multiforme (GBM) remain highly lethal neoplasms, refractory to current therapies. Researchers and medical professionals are working on developing translational therapies to combat these aggressive tumours. Numerous clinical trials on gene therapy for glioma patients have been conducted over the last decade, but the results have largely been disappointing. Cell encapsulation represents an alternative method for local delivery of therapeutic proteins with antineoplastic properties to glioma patients. The concept has not yet reached clinical trials, but encouraging results have been achieved in rats bearing gliomas when implanting endostatin-secreting encapsulated cells into the rat brain. This review primarily focuses on the recent progress that has been made with cell encapsulation technology. In addition, the challenges this field faces before clinical application in brain tumour patients is discussed.

Rationalizing the design of polymeric biomaterials

Polymers are a promising class of biomaterials that can be engineered to meet specific end-use requirements. They can be selected according to key 'device' characteristics such as mechanical resistance, degradability, permeability, solubility and transparency, but the currently available polymers need to be improved by altering their surface and bulk properties. The design of macromolecules must therefore be carefully tailored in order to provide the combination of chemical, interfacial, mechanical and biological functions necessary for the manufacture of new and improved biomaterials.