Microencapsulation for the Therapeutic Delivery of Drugs, Live Mammalian and Bacterial Cells, and Other Biopharmaceutics: Current Status and Future Directions

Microencapsulation is a technology that has shown significant promise in biotherapeutics, and other applications. It has been proven useful in the immobilization of drugs, live mammalian and bacterial cells and other cells, and other biopharmaceutics molecules, as it can provide material structuration, protection of the enclosed product, and controlled release of the encapsulated contents, all of which can ensure efficient and safe therapeutic effects. This paper is a comprehensive review of microencapsulation and its latest developments in the field. It provides a comprehensive overview of the technology and primary goals of microencapsulation and discusses various processes and techniques involved in microencapsulation including physical, chemical, physicochemical, and other methods involved. It also summarizes the state-of-the-art successes of microencapsulation, specifically with regard to the encapsulation of microorganisms, mammalian cells, drugs, and other biopharmaceutics in various diseases. The limitations and future directions of microencapsulation technologies are also discussed.

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.

Microencapsulated Saccharomyces cerevisiae column bioreactor for potential use in renal failure uremia

A novel bioreactor containing viable APA microencapsulated yeast cells was designed. Rat plasma was used for perfusion. Yeast cell loading and perfusion flow rate were studied to maximize urea removal. An increase in column loading from 25% to 100%, increased urea removal from 5.67 ± 1.34% to 30.45 ± 0.48%. An increase in flow rate from low to high, increased urea removal from 30.46% to 40.4%. At 100% column loading and high flow rate, the creatinine and phosphate concentrations decreased by 22% and 10%, respectively, while ammonia concentrations increased by 58.9% (p < 0.05). Our in-vitro perfusion study demonstrates that microencapsulated yeast cells can remove urea efficiently.

The use of hollow fiber membranes combined with cytometry in analysis of bacteriological samples

To avoid destruction of the implanted biological material it may be separated from host immunological system by enclosure within a permiselective membrane. Two-directional diffusion through the membrane of nutrients, metabolic products, as well as bioactive products of encapsulated cells is required to ensure their survival and functional activities. The system of cells encapsulated within the membrane releasing the biologically active substance may be applied either locally to give an opportunity of therapeutic agent activity in the specified place and/or at some convenient site (tissue) for a prolonged period of time.The novel system of bacteria bio-encapsulation using modified membranes, and its assessment by flow cytometry is described and discussed. The encapsulated in membrane bacteria, functioning and releasing their products were evaluated in the systems in vitro and in vivo. The bacteria cells products impact on Eukariotic cells was evaluated. The cytometric evaluation demonstrates the membrane ability to avoid the release of bacteria enclosed within the membrane wall. In experiments with treatment of the bacteria with antibiotic to release products from damaged bacteria it was possible to distinguish stages of the applied antibiotic impact on encapsulated bacteria cells. In E. coli following stages were distinguished: induction of membrane permeability to PI, activation of proteases targeting GFP (protein) and subsequent nucleic acids degradation. In the another experiment the evidence was presented of the cytotoxic activity of live Bacillus subtilis encapsulated within the membrane system. The Bacilus products mediated by secreted listeriolysin O (LLO) on the chosen eukaryotic cells was evaluated. Similar systems releasing bacterial products locally and continuously may selectively affect different types of cells and may have possible application in the anticancer treatment at localized sites.

Evaluation of Two Protocols of Uremic Rat Model: Partial Nephrectomy and Infarction

Animal models of chronic renal failure have been mostly achieved by partial ablation of renal parenchyma, the two most common techniques employed being surgical resection or infarction. Evaluation of the uremic model using these two techniques was carried out in Wistar rats. Two weeks after operative procedure, measured serum urea levels in the resection and infarction models were 59.1 and 64.3 mg/dL (normal range 15.6-24.4 mg/dL) respectively. However, the standard deviation in the former was significantly lower, 6.3 vs. 97.1 mg/dL from infarction model, p = 0.007. A consistent degree of glomerular filtration rate reduction was obtained in the resection model, resulting in 20-30% of normal creatinine clearance. This compared favorably with the creatinine clearance range (0.3-74% of normal) from the infarction model, in which two animals died of uremia and seven had higher than 50% of normal creatinine clearance. It is reasonable to attribute reproducibility and homogeneity demonstrated in the resection model to (i) more precise control of renal ablation extent with surgical techniques and (ii) less interplay of confounding injury mechanism to remnant kidney. These data support superiority of the resection model as an experimental tool for pathophysiological and/or interventional investigations of chronic renal failure.

Recombinant Saccharomyces cerevisiae strain expressing a model cytochrome P450 in the rat digestive environment: viability and bioconversion activity

An innovative "biodrug" concept, based on the oral administration of living recombinant microorganisms, has recently emerged for the prevention or treatment of various diseases. An engineered Saccharomyces cerevisiae strain expressing plant P450 73A1 (cinnamate-4-hydroxylase [CA4H] activity) was used, and its survival and ability to convert trans-cinnamic acid (CIN) into p-coumaric acid (COU) were investigated in vivo. In rats, the recombinant yeast was resistant to gastric and small intestinal secretions but was more sensitive to the conditions found in the large intestine. After oral administration of yeast and CIN, the CA4H activity was shown in vivo, with COU being found throughout the rat's digestive tract and in its urine. The bioconversion reaction occurred very fast, with most of the COU being produced within the first 5 min. The gastrointestinal sac technique demonstrated that the recombinant yeast was able to convert CIN into COU (conversion rate ranging from 2 to 5%) in all the organs of the rat's digestive tract: stomach, duodenum, jejunum, ileum, cecum, and colon. These results promise new opportunities for the development of drug delivery systems based on engineered yeasts catalyzing a bioconversion reaction directly in the digestive tract.

Probing the role of microenvironment for microencapsulated Sacchromyces cerevisiae under osmotic stress

Cell encapsulation opens a new avenue to the oral delivery of genetically engineered microorganism for therapeutic purpose. Osmotic stress is one of the universal chemical stress factors in the application of microencapsulation technology. In order to understand the effect and mechanism of the encapsulated microenvironment on protecting cells from hyper-osmotic stress, yeast cells of Saccharomyces cerevisiae Y800 were encapsulated in calcium alginate micro-gel beads (MB), alginate-chitosan-alginate (ACA) solid core microcapsules (SCM), and ACA liquid core microcapsules (LCM), respectively. The stress-induced intracellular components and enzyme activity including trehalose, glycerol and super oxide dismutase (SOD) were measured. Free cell culture was used as control. The survival of encapsulated cells and the cells released from MB, SCM and LCM after osmotic shock induced by NaCl solution (1, 2 and 3M) was evaluated. An analysis method was established to probe the effect of encapsulated microenvironment on the cell tolerance to osmotic stress. The results showed that LCM gave rise to the highest level of intracellular trehalose and glycerol, and SOD activity, as well as the highest survival rate of encapsulated cells or cells released from microcapsule. It was demonstrated that LCM was able to induce the highest stress response and stress tolerance of cells, which was adapted during culture, while SCM failed. The theoretical analysis revealed that it was the liquid alginate matrix in microcapsule that played a central role in domesticating the cells to adapt to hyper-osmotic stress. This finding provides a very useful guideline to cell encapsulation.

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.

Probiotics and Prebiotics in Human Health

Probiotic bacteria are found in the intestines of humans and other mammals where they provide health benefits to the host. They do so by (1) providing nutrients and cofactors, (2) successfully competing with pathogens, and (3) stimulating host immune responses by producing specific polysaccharides. These bacteria can also alleviate the symptoms of disease-related metabolic disorders. Prebiotics are substances, usually poorly metabolized polysaccharides and oligosaccharides, that cannot be ingested effectively by the animal. They stimulate the growth of intestinal probiotic bacteria, which can utilize these carbohydrates, thereby promoting health of the organism. Genetic engineering has proven useful for the design of probiotic bacteria that counteract the symptoms of genetic and age-related diseases. Can these bacteria be engineered, through human-promoted accelerative evolution, so that they stimulate their own growth and that of other probiotic bacteria so as to crowd pathogens out of the intestine?

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.

Low water-soluble uremic toxins

The uremic syndrome is the result of the retention of solutes, which under normal conditions are cleared by the healthy kidneys. Uremic retention products are arbitrarily subdivided according to their molecular weight. Low-molecular-weight molecules are characterized by a molecular weight below 500 D. The purpose of the present publication is to review the main water soluble, nonprotein bound uremic retention solutes, together with their main toxic effects. We will consecutively discuss creatinine, glomerulopressin, the guanidines, the methylamines, myo-inositol, oxalate, phenylacetyl-glutamine, phosphate, the polyamines, pseudouridine, the purines, the trihalomethanes, and urea per se.

Genetically engineered probiotics

Probiotic micro-organisms have been used for many years. Originating as food supplements, they are now most often administered orally and offer an attractive alternative for treating of intestinal disorders. A better understanding of the mechanisms by which these micro-organisms act has now opened up possibilities for designing new probiotic strains. Through genetic engineering, it is possible not only to strengthen the effects of existing strains, but also to create completely new probiotics. These need not necessarily be composed only of bacterial products but can also include elements of regulatory systems or enzymes derived from a foreign-human-source. If designed carefully and with absolute attention to biological safety in its broadest sense, the development of genetically modified probiotics has the potential to revolutionize alimentary health.

Recombinant Saccharomyces cerevisiae expressing P450 in artificial digestive systems: a model for biodetoxication in the human digestive environment

The use of genetically engineered microorganisms such as bacteria or yeasts as live vehicles to carry out bioconversion directly in the digestive environment is an important challenge for the development of innovative biodrugs. A system that mimics the human gastrointestinal tract was combined with a computer simulation to evaluate the survival rate and cinnamate 4-hydroxylase activity of a recombinant model of Saccharomyces cerevisiae expressing the plant P450 73A1. The yeasts showed a high level of resistance to gastric and small intestinal secretions (survival rate after 4 h of digestion, 95.6% +/- 10.1% [n = 4]) but were more sensitive to the colonic conditions (survival rate after 4 h of incubation, 35.9% +/- 2.7% [n = 3]). For the first time, the ability of recombinant S. cerevisiae to carry out a bioconversion reaction has been demonstrated throughout the gastrointestinal tract. In the gastric-small intestinal system, 41.0% +/- 5.8% (n = 3) of the ingested trans-cinnamic acid was converted into p-coumaric acid after 4 h of digestion, as well as 8.9% +/- 1.6% (n = 3) in the stomach, 13.8% +/- 3.3% (n = 3) in the duodenum, 11.8% +/- 3.4% (n = 3) in the jejunum, and 6.5% +/- 1.0% (n = 3) in the ileum. In the large intestinal system, cinnamate 4-hydroxylase activity was detected but was too weak to be quantified. These results suggest that S. cerevisiae may afford a useful host for the development of biodrugs and may provide an innovative system for the prevention or treatment of diseases that escape classical drug action. In particular, yeasts may provide a suitable vector for biodetoxication in the digestive environment.

Present status of modified hemoglobin as blood substitutes and oral therapy for end stage renal failure using artificial cells containing genetically engineered cells

Artificial cell or bioencapsulation has been developed for use in bioartificial organs, drug delivery, blood substitutes, and other areas. Recent rapid advances in modified hemoglobin blood substitutes have resulted in advance stages of Phase III clinical trials. Another area of use is in oral therapy, using artificial cells microencapsulated with genetically engineered cells for use in end stage renal failure and other conditions.

The 'biodrug' concept: an innovative approach to therapy

Cell engineering technology using recombinant microorganisms has created new opportunities in the development of innovative drugs. This article presents the use of living genetically engineered microorganisms, such as bacteria or yeasts, as a new delivery vehicle to the gastrointestinal tract. This 'biodrug' concept was demonstrated using recombinant Saccharomyces cerevisiae expressing the plant cytochrome P450 73A1. This enzyme provides a relevant model for potential therapeutic applications, such as 'biodetoxication' in the digestive environment. An artificial gastrointestinal tract simulating human digestion was chosen as a powerful tool to validate the biodrug concept. This approach offers a novel strategy for drug discovery and testing.