In-vitro conditions

FIGURE 16A Daily rate of release of naltrexone from a poly-e-caprolactone-co-lactic acid capsule (reservoir device) under in vitro conditions. (From Ref. 89.)... 

More definitive evidence of enzymatic attack was obtained with 1 1 copolymers of e-caprolactone and 6-valerolactone crosslinked with varying amounts of a dilactone (98,99). The use of a 1 1 mixture of comonomers suppressed crystallization and, together with the crosslinks, resulted in a low-modulus elastomer. Under in vitro conditions, random hydrolytic chain cleavage, measured by the change in tensile properties, occurred throughout the bulk of the samples at a rate comparable to that experienced by the other polyesters no weight loss was observed. However, when these elastomers were implanted in rabbits, the bulk hydrolytic process was accompanied by very rapid surface erosion. Weight loss was continuous, confined to the... 

Chemical structure of monomers and intermediates was confirmed by FT-IR and FT-NMR. Molecular weight distribution of polymers was assessed by GPC and intrinsic viscosity. The thermal property was examined by differential scanning calorimetry. The hydrolytic stability of the polymers was studied under in vitro conditions. With controlled drug delivery as one of the biomedical applications in mind, release studies of 5-fluorouracil and methotrexate from two of these polymers were also conducted. 

For a long time one question remained unanswered the efficiency of the Fenton reaction as the in vivo producer of hydroxyl radicals due to the low rate of Reaction (2) (the rate constant is equal to 42.11 mol 1 s 1 [18]). It is known that under in vitro conditions the rate of Fenton reaction can be sharply enhanced by chelators such as EDTA, but for a long time no effective in vivo chelators have been found. From this point of view new findings obtained by Chen and Schopfer [19] who found that peroxidases catalyze hydroxyl radical formation in plants deserve consideration. These authors showed that horseradish peroxidase (HRP) compound III is a catalyst of the Fenton reaction and that this compound is one to two orders of magnitude more active than Fe EDTA. 

HOC1 is probably not a single active MPO oxidant able to chlorinate LDL. Hazen et al. [166] have shown that such a powerful oxidant as molecular chlorine is formed under in vitro conditions during the reaction of MPO-hydrogen peroxide-chloride system of phagocytes with LDL. They pointed out that there is an equilibrium between HOC1 and Cl2, which is shifted to the right under acidic conditions ... 

It has been proposed that a major source of oxygen radicals in sickle erythrocytes is mutant hemoglobin HbS. However, although HbS showed an accelerated autoxidation rate under in vitro conditions, its in vivo oxidative activity was not determined. Sheng et al. [401] suggested that the observed oxidation rate of HbS is exaggerated by adventitious iron. Dias-Da-Motta et al. [402] proposed that another source of enhanced superoxide production in sickle cells are monocytes in contrast, there is no difference in superoxide release by sickle... 

Amyloid in the original medical sense of the term refers to certain disease-related protein aggregates (Westermark et al., 2005). Nowadays, it is applied more broadly to protein aggregates that have certain biophysical and biochemical properties in common. The original amyloids have been found to consist mainly of polymerized fragments of about 20 different proteins, each amyloid containing one of these polypeptides. More recently, it has emerged that many other proteins may be converted into amyloid artificially under in vitro conditions that involve prior denaturation (Chiti et al., 1999 Stefani and Dobson, 2003). 

Choice of Potential Bioavailability Criterion. It is usually assumed that calcium must be soluble and probably ionized in order to be available for absorption ( ). For the in vitro procedure, as a first approximation we chose calcium solubility after centrifugation at 18,000 x g as the measure of potential bioavailability (Figure 1). We assumed that this would probably overestimate the available calcium and later work based on fractionation might define the bioavailable calcium more precisely. The data in Table IV illustrate how the choice of criterion for "solubility" could affect the in vitro estimate of potential availability, even if in vitro conditions closely resembled in vivo conditions. Since our in vitro criterion unexpectedly underestimated calcium bioavailability for two of the three foods in the direct in vivo - in vitro comparison (8), it was necessary to determine the in vitro digestion conditions which might be limiting solubility before addressing the choice of appropriate criterion. 

Assay of Homogenate for Aldrin Epoxidation. The following experimental sequence was designed to determine the optimum in vitro conditions for aldrin epoxidation in larval whole body homogenates 1) the effect of component chemicals generally included in an incubation mixture, 2) a pH profile, 3) a temperature profile, 4) a molarity profile, 5) a reaction time profile, 6) a larval concentration (enzyme concentration) profile, 7) a substrate concentration profile, and 8) a restudy of the effects of component chemicals in the initial incubation mixture (Step 1) upon aldrin epoxidation under optimum conditions as defined by steps 2-7 above. The effect of PBO, FMN, and FAD upon enzyme activity was also tested. 

Nicolazzo JA, Reed BL, Finnin BC (2003) The effect of various in vitro conditions on the permeability characteristics of the buccal mucosa. J Pharm Sci 92 2399-2410... 

U. Werner and T. Kissel. Development of a human nasal cell culture model and its suitability for transport and metabolism studies under in vitro conditions. Pharm Res 12 565-571 (1995). 

Fig. 3.4. Formation of peptide bonds by peptidases under special in vitro conditions...

The kinetics of disappearance from the circulation of intravenously administered human insulin (Fig. 6.32) is nonlinear [145]. Within a few minutes after injection, it becomes localized in the liver, heart, and kidneys, where it is rapidly metabolized. Indeed, the hepatic extraction could be as high as 70% on a single passage, whereas kidneys could account for 10-40% degradation. Enzymatic reduction of the disulfide bridges appears to be the first step in the in vivo metabolism of insulin, although this reaction appears of limited significance under in vitro conditions. 

Emergent plants (helophytes) showed a potential for removal of TNT from contaminated water under in vitro conditions with small differences in the formation of the major degradation products - monoaminodinitrotoluenes. Most of TNT degradation products (using " C-radiolabelled TNT) were localized in the roots of reed (53% of total radioactivity) as insoluble compounds (33% of total radioactivity) (Nepovim et al. 2005). 

Attention must be paid to the viability of the exeised tissue under in vitro conditions. Electrophysiologic characterization appears to be a valuable tool to indicate the viability of the tissue following excision. The viability of the tissue can be retained by continuous bubbling with O2/CO2 mixtures and addition of glucose to the buffer medium [11]. 

Advances in technology and improvements in imaging techniques have provided many approaches for imaging chromatin under in vitro conditions and in situ in fixed or living cells. Some of these techniques are described below. 

---