Bioactive agents

Eig. 1. Schematic bioactive polyphosphazenes. (a) General stmcture, where X = hydrophilic /hydrophobic group that hydrolyzes with concurrent polymer breakdown, Y = difunctional group for attaching bioactive agent to polymer, and T = bioactive agent, (b) Actual example where X = —OC H, Y = and... 

P-OCH2CH2OCH3 P-NHCOCH2NHCOCH3 Polymers Carrying Bioactive Agents ... 

Controlled Release of Bioactive Agents from Lactide/Glycolide Polymers... 

Occasionally, an unusual combination of polymeric excipient and bioactive agent can lead to unexpected biodegradation profiles. 

Several investigators have utilized the 85 15 DL-lactide/glycolide copolymer for 90-day delivery of bioactive agents. This polymer is essentially bioeroded by about 150 days, thus making the 85 15 a useful matrix for 90-day systems. 

Processes based on fluidized bed coating have been developed (49). In this process, the bioactive agent is dissolved in an organic solvent along with the polymer. This solution is then processed through a Wurster air suspension coater apparatus to form the final microcapsule product. A solvent partition technique based on continuous injection of a polymer-drug solution into flowing mineral oil has been reported (50). 

There are literally dozens of patents and literature references addressing the microencapsulation of bioactive agents in polymers. 

It appears that none of these process techniques is dominant, at least with the lactide/glycolide materials. Researchers have considerable choices available in regard to fabrication of microspheres from these polymers. The most commonly used procedures employ relatively mild conditions of pH and temperature and are usually quite compatible with the bioactive agents to be entrapped, including proteins and other macromolecules. Only in the case of live virus and living cell encapsulation have serious deactivation problems been encountered and those problems were due to solvents used in the process. 

Although implants are rather easily fabricated, problems have occurred in instances when care is not taken in maintaining an ultradry processing environment. It is extremely important to thoroughly dry the bulk polymer and the bioactive agent, usually at ambient temperature under vacuum, prior to processing. Dry nitrogen... 

Classical or conventional pharmaceutical agents in combination with lactide/glycolide polymers have been widely studied since about 1973. In general, these compounds are bioactive agents usually produced by synthetic chemistry, with molecular weights of less than a few hundred and relatively stable structures. Examples include steroid hormones, antibiotics, narcotic antagonists, anticancer agents, and anesthetics. 

Biomaterials cover a broad range of properties from those that are designed to be inert to those that are intended to elicit a particular set of biological responses. In the latter category are materials with surfaces tailored to retard blood clotting, or surfaces that bear covalently bound bioactive agents such as enzymes or antigens. 

Bidlack, W.R. et al.. Phytochemicals as Bioactive Agents, Technomic Lancaster, PA, 2000. 

Mayer, L. D. Bally, M. B. Hope, M. J. Cullis, P R., Techniques for encapsulating bioactive agents into liposomes, Chem. Phys. Lipids 40, 333-345 (1986). 

This subject can be considered in terms of five different types of molecules or materials (a) biologically inert, water-insoluble polymers (b) water-insoluble polymers that bear biologically active surface groups (c) water-swellable polymeric gels, or amphiphilic polymers that function as membranes (d) water-insoluble but bioerodable polymers that erode in aqueous media with concurrent release of a linked or entrapped bioactive molecule and (e) water-soluble polymers that bear bioactive agents as side groups. 

IPs are very useful for DDS because IP systems allow easy entrapment of pharmaceuticals and bioactive agents and can be used as a depot for their sustained release after a simple injection with a syringe at the target site in a human body. Such a system can minimize the requirement for surgical operations for... 

Figure 22.17 Antibody-liposome conjugates may be used as targeting reagents for detection or therapeutic applications. The liposome may be constructed to contain fluorescent molecules for detection purposes or bioactive agents for therapy. The antibody component targets the complex for binding to specific antigenic determinants.

Some active materials are carriers for drugs (drug delivery systems), some have immobilized peptides to enable cell adhesion or migration, some are degradable by hydrolysis or by specific enzyme action. Some contain bioactive agents (e.g., heparin, thrombomodulin) to prevent coagulation or platelet activation while others incorporate bioactive groups to enhance osteo-conduction. Many include polyethylene oxide to retard protein adsorption and this is perhaps the closest we have come to a kind of inertness. 

By definition, a nutraceutical (derived from the term nutritional pharmaceutical ) is a foodstuff (fortified food or dietary supplement) that is held to provide health or medical benefits in addition to its basic nutritional value [1], Nutraceuticals derived from botanicals deliver a concentrated form of presumed bioactive agents from plants that are not generally part of the food supply. The term nutraceutical has no regulatory definition. Similarly, functional foods, as defined by the International Life Sciences Institute (ILSI), are foods that by virtue of physiologically active food components, provide health benefits beyond basic nutrition [2], For the purposes of this review, these two terms will be differentiated by the form in which they are consumed. Nutraceuticals refers to dietary supplements most often found in pill or capsule form functional foods are ingested as part of a normal food pattern. Both are intended to provide beneficial effects beyond their nutritional value, and contribute to an improved state of health and/or reduction of risk of disease. 

Ariens, E. J. Stereospecificity of bioactive agents General aspects of exemplified by pesticides and drugs. In Stereoselectivity of Pesticides, Biological and Chemical Problems Chemicals in Agriculture, Vol. 1, Ariens, E. J., van Rensoen, J. J. S. W. W., Eds., Elsevier Science, New York, 1988. 

It appears that cyclic dipeptides are indeed an unexplored class of bioactive agents that may hold great promise for the future. ... 

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