In vivo environments

It has been demonstrated that a variety of different polyphosphazenes can be developed as biomaterials, membranes or hydrogels, bioactive polymers, and bioerodible polymers. As with most new areas of polymer chemistry and biomaterials science, molecular design forms the basis of most new advances, but the rate-controlling step is the testing and evaluation of the materials in both in vitro and in vivo environments. This is particularly true for polyphosphazenes where the availability of research quantities only has limited the... 

The bioavailability of drugs from tablets can be markedly influenced by the rate and efficiency of the initial disintegration and dissolution process. Unfortunately, one is faced with a compromise situation — a structure that has both a durable structure prior to administration and the ability to readily break down when placed in the in vivo environment. One of the major factors affecting both these properties is the structure of the tablet, in particular its density (or porosity) and the pore structure. Study of the significance of such measurements and interpretation of the results is a relatively recent field of interest. 

The in vivo environment of the GIT is characterized by a pH gradient the pH value is constant at 7.4 in the receiving compartment (blood), and varying in the donor compartment (lumen) from 5 to 8 from the start to the end of the small intestine. In contrast, the BBB has a constant iso-pH 7.4. Modeling the two environments requires proper pH adjustment in the in vitro model, as indicated in Table 7.22. 

Al Dhaheri AH, El-Sabban F, Fahim MA. 1995. Chronic lead treatment accelerates photochemically induced platelet aggregation in cerebral microvessels of mice, in vivo. Environ Res 69 51-58. 

On the other hand, pDNA/PEI polyplexes were found to be not stable enough in the extracellular in vivo environment. Unpackaging of PEI and PEG-PEI polyplexes was observed [64, 65, 81], for example by serum proteins, soluble glycosaminoglycans, or extracellular matrix components. The situation is even worse in the case of siRNA polyplexes, where PEI polyplexes are dissociated in full human serum, as monitored by fluorescence fluctuation spectroscopy [66, 67]. 

In contrast to other analytical methods, ion-selective electrodes respond to an ion activity, not concentration, which makes them especially attractive for clinical applications as health disorders are usually correlated to ion activity. While most ISEs are used in vitro, the possibility to perform measurements in vivo and continuously with implanted sensors could arm a physician with a valuable diagnostic tool. In-vivo detection is still a challenge, as sensors must meet two strict requirements first, minimally perturb the in-vivo environment, which could be problematic due to injuries and inflammation often created by an implanted sensor and also due to leaching of sensing materials second, the sensor must not be susceptible to this environment, and effects of protein adsorption, cell adhesion, and extraction of lipophilic species on a sensor response must be diminished [13], Nevertheless, direct electrolyte measurements in situ in rabbit muscles and in a porcine beating heart were successfully performed with microfabricated sensor arrays [18],... 

Fig. 4.1). Since the P450s are membrane-bound enzymes in vivo, adding lipid to reconstitute a functional enzyme system in vitro more closely mirrors the in vivo environment and presumably serves as a matrix to allow the two enzymes, P450 and P450 reductase, to interact properly. 

For the dissolution test to be used as an effective drug product characterization and quality control tool, the method must be developed with the various end uses in mind. In some cases, the method used in the early phase of product and formulation development could be different from the final test procedure utilized for control of the product quality. Methods used for formulation screening or BA and/or bioequivalency evaluations may simply be impractical for a quality control environment. It is essential that with the accumulation of experience, the early method be critically re-evaluated and potentially simplified, giving preference to compendial apparatus and media. Hence, the final dissolution method submitted for product registration may not necessarily closely imitate the in vivo environment but should still test the key performance indicators of the formulation. 

Morimoto K, Koizumi A. 1983. Trihalomethanes induce sister chromatid exchanges in human lymphocytes in vitro and mouse bone marrow cells in vivo. Environ Res 32 72-79. 

The interpretation of in vitro drng release prohles also has to take the specific in vivo environment into account. Then a possible enzymatic degradation of lipid particles may be influenced to a relevant extent by the composition of the particles [31]. 

Loprieno, N., Boncristiani, G, Forster, R. Goldstein, B. (1985) Assays for forward mutation in Schizosaccharomycespombe strain PL Prog. Mutat Res., 5, 297-306 Lutz, W.K. (1986) Investigation of the potential for binding of di(2-ethylhexyl) phthalate (DEHP) to rat liver DNA in vivo. Environ. Health Perspect., 65, 267-269 Malcolm, A.R. Mills, L.J. (1989) Inhibition of gap-jnnctional intercellular communication between Chinese hamster lung fibroblasts by di(2-ethylhexyl) phthalate (DEHP) and trisodinm nitrilotriacetate monohydrate (NTA). Cell Biol. Toxicol., 5, 145-153 Malcolm, A.R., Mills, L.J. McKeima, E.J. (1983) Inhibition of metabolic cooperation between Chinese hamster V79 cells by tnmor promoters and other chemicals. Ann. N.Y. Acad. Set, 407, 448-450... 

Lahdetie, J., Peltonen, K. Sjoblom, T. (1997) Germ cell mutagenicity of tlirce metabolites of 1,3-butadiene in the rat induction of spermatid micronuclei by butadiene mono-, di-, and diol-epoxides in vivo. Environ, mol. Mutag., 29, 230-239... 

Xiao, Y. Tates, A.D. (1995) Clastogenic effects of 1.3-butadiene and its metabolites 1,2-epoxy-butene and 1,2,3,4-diepoxybutane in splenocytes and germ cells of rats and mice in vivo. Environ. Health Perspect., 26, 97-108... 

Henschler, R., Glatt, H.R. Heyworth, C.M. (1996) Hydroquinone stimulates granulocyte-macrophage progenitor cells in vitro and in vivo. Environ. Health Perspect., 104 (Suppl. 6), 1271-1274... 

At the conclusion of an experiment, a DT/MH-functionalized AgFON was removed after being incubated in bovine plasma or implanted in the rat for 5h and placed in a flow cell containing bovine plasma to simulate the in vivo environment. 

The P450 enzymes are found primarily in the outer membrane of the endoplasmic reticulum. Enzyme activity requires that the enzyme be integrated into a membrane that contains P450 reductase and, for some reactions, cytochrome b5. Characterization of the saturation kinetics for the P450 enzymes can be determined using a variety of enzyme preparations, including tissue slices, whole cells, microsomes, and reconstituted, purified enzymes. The more intact the in vitro preparation, the more it is likely that the environment of the enzyme will represent the in vivo environment. However, intact cell preparations do not... 

These same peptide amphiphiles have been shown to assist mice to recover from spinal cord injuries (Tysseling-Mattiace et al., 2008). Both motor and sensory axons were able to cross the site of injury when peptide amphiphiles were injected and the peptide amphiphiles were stable in this in vivo environment for 1-2 weeks. Although recovery was only partial, this represents a remarkable achievement. 

Sanchez-Dardon J, Voccia I, Hontela A, Chilmonczyk S, Dunier M, Boermans H, Blakley B, Fournier M. 1999. Immunomodulation by heavy metals tested individually or in mixtures in rainbow trout (Oncorhynchus mykiss) exposed in vivo. Environ Toxicol Chem 18 1492-1497. 

If one accepts that the concept of an isolated receptor is meaningful (i.e., that a receptor retains its integrity outside its in vivo environment), then attempts to achieve this condition must form an important step in receptor investigations. To date, only modest progress has been made in attempts to isolate opioid receptor material as characterized by its ability to bind ligands in a manner similar to that of intact nervous tissue. The problem is to devise a method of solubilizing the receptor from its supporting tissue (usually assumed to be a coll membrane) in a manner in which it retains its ability to... 

Morimoto Y, Tsuda T, Nakamura H, et al. 1997. Expression of matrix metalloproteinases, tissue inhibitors of metalloproteinases, and extracellular matrix mRNA following exposure to mineral fibers and cigarette smoke in vivo. Environ Health Perspect Suppl 105 1247-1251. 

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