Estimation in-vitro

The in vitro release comparison should be carried out as a two-stage test. At the first stage, two mns of the (six cells) in vitro apparatus should be carried out, yielding six slopes (estimated in vitro release rates) for the prechange lot (R) and six slopes for the postchange lot (T). A 90% confidence interval (to be described below) for the ratio of the median in vitro release rate (in the population) for the postchange lot over the median in vitro release rate (in the population) for the... 

Ludden LK, Ludden TM, Collins JM, et al. Effect of albumin on the estimation, in vitro, of phenytoin Vmax and Km values implications for clinical correlation. J Pharmacol Exp Ther 1997 282 391-396. 

DeJongh, J., Verhaar, H.J.M., and Hermens, J.L.M., A quantitative property-property (QPPR) approach to estimate in vitro tissue-blood partition coefficients of organic chemicals in rats and humans, Arch. Toxicol., 72, 17-25, 1997. 

In contrast to the type I deiodinase which shows a high preference for rT4 over T4 as the substrate (Table II), the type II enzyme is somewhat more effective in the deiodination of T4 than of rT3 (Table III). Under the conditions tested, the Km value of T4 for the type II enzyme is three orders of magnitude lower than the Km of T4 for the type I deiodinase. The Km of rT3 for the type II deiodinase is somewhat greater than that of T4 and differs less from the Km of rT3 for the type I enzyme. The Umax of the conversion of T4 to T3 by the type II enzyme depends on the tissue and the thyroid status of the animal (see below). In cerebral cortex of hypothyroid rats [82] it is roughly one-thousandth of the maximum T3 production by the hepatic type I deiodinase of euthyroid animals determined under similar conditions [32]. The VmiJKm ratio of this reaction is, therefore, similar for the type II deiodinase of hypothyroid rat brain and the type I deiodinase of euthyroid rat liver and much greater than that for the hepatic enzyme of hypothyroid rats [86], In view of the reaction kinetics of the type II deiodinase (see below), it is questionable if the Vm,JKm ratios estimated in vitro also apply to physiological conditions with unknown cofactor availability. 

Eastes W., Potter R. M., and Hadley J. G. (2000a) Estimating in-vitro glass fiber dissolution rate from composition. Inhalat. Toxicol. 12, 269-280. 

As discussed above, the rate-limiting step in the oral absorption of Class II drug substances is likely to be the in vivo dissolution [23-25]. For Class II dissolution rate limited drugs, hence, if in vivo dissolution can be estimated in vitro, an in vitro-in vivo correlation may be established. As discussed in Section 3.5, such media have been developed, and an adequate IVIVC was shown for number of Class II drugs. However, due to the numerous in vivo parameters involved, it appears that more research is needed to develop uniform dissolution media reflecting in vivo dissolution conditions, to establish an adequate IVIVC, and to asses the risk of bioinequivalence [86, 88], In addition, the relationship between the hydrodynamics in the currently available dissolution tests and the actual in vivo situation is not adequately characterized and might interfere to obtain the correlation. 

A few words of caution are required, however. The estimate in vitro of brain/ blood concentration ratios is subject to many errors and has to be regarded as a gross approximatioa Although compounds are administered intravenously by infusion over an extended period (2-3 h) so that near steady state equilibrium is produced, they are subject to different rates of metabolism, elimination (excretion) and protein binding. All these factors will affect the concentration of drag available for brain penetration and will operate differently for each compound. In each case a check was made to determine the proportion of parent drag in the peripheral blood and in the brain by thin-layer chromatography. In most cases, the parent compound was still present at 90% for a few compounds, the proportion of parent present in the blood had decreased to 50%, so that the ratios for these could be underestimated by a factor of up to twofold with respect to metabohsm. 

There do not appear to have been any reports of hormonal contraceptive or NRTI failure during concurrent use. Tenofovir does not appear to affect the pharmacokinetics of ethinylestradiol or noi estimate. In-vitro evidence suggests that ethinylestradiol might possibly reduce the metabolism of zidovudine but the significance of this is unclear. 

Abraham MH. 2014. A simple method for estimating in vitro air-tissue and in vivo blood-tissue partition coefficients. Chemosphere 120C 188-191. 

Chaudhry, A.S., 2005. Comparing commercial enzymes to estimate in vitro proteolysis of purified and semi purified proteins. J. Anim. Physiol. Anim. Nutr. 89, 403-412. 

Other investigations performed with AOS include estimations of haemolytic concentrations [147,148], effect on methemoglobin concentration [156], and in vitro estimation of immunological potential [157]. None of these investigations gave any reason to suspect a toxic hazard of AOS. 

Working with rats, Lntz et al. (1977) compared the rates of loss from blood of 4,-CB (rapidly metabolized) with that of 2,2, 4,4, 5 -HCB (slowly metabolized). Both showed biphasic elimination, with the former disappearing much more rapidly than the latter. Estimations were made of the rates of hepatic metabolism in vitro, which were then incorporated into toxicokinetic models to predict rates of loss. The predictions for HCB were very close to actual rates of loss for the entire period of... 

Looking at the foregoing results overall, the rates of loss in vivo are related to the rates of metabolism in vitro, measured or estimated. As with the OC insecticides, problems of persistence are associated with compounds that are not readily metabolized, for example, 2,2, 4,4, 5,5 -HCB in the foregoing examples. For further discussion of the dependence of elimination of lipophilic xenobiotics on metabolism, see Walker (1981). 

Toxic equivalency factors (TEFs) are estimated relative to 2,3,7,8-TCDD, which is assigned a value of 1. They are measures of the toxicity of individual compounds relative to that of 2,3,7,8-TCDD. A variety of toxic indices, measured in vivo or in vitro, have been used to estimate TEFs, including reproductive effects (e.g., embryo toxicity in birds), immunotoxicity, and effects on organ weights. The degree of induction of P450 lAl is another measure from which estimations of TEF values have been made. The usual approach is to compare a dose-response curve for a test compound with that of the reference compound, 2,3,7,8-TCDD, and thereby establish the concentrations (or doses) that are required to elicit a standard response. The ratio of concentration of 2,3,7,8-TCDD to concentration of test chemical when both compounds produce the same degree of response is the TEF. Once determined, a TEF can be used to convert a concentration of a dioxin-like chemical found in an environmental sample to a toxic equivalent (TEQ). 

The quality control of immunoglobuhns includes potency tests and conventional tests of safety and sterihty. The potency tests consist of neutrahzation tests that parallel those used for the potency assay of immunosera, except that in the cases of some immimoglobulins the assays are made in vitro, fit addition to the safety and sterihty tests, total protein is determined by nitrogen estimations, the protein composition by... 

Ticlopidine inhibits the P2Yj2 platelet ADP receptor, thus inhibiting ADP-dependent activation of the GP Ilb/IIIa receptor. It has a slow onset of action and takes 3-7 days to reach its maximal antiplatelet effect. It is inactive in vitro and must undergo activation by the hepatic cytochrome p450 enzyme system. Secondary prevention trials have found that ticlopidine-treated patients have an estimated RRR of 33% for the composite endpoint of stroke, myocardial infarction, or vascular death after ischemic stroke. Significant adverse effects include bone marrow depression, rash, diarrhea, and thrombotic thrombocytopenic purpura. No clinical trials have studied ticlopidine for the treatment of stroke in the acute phase. 

The antioxidant activities of carotenoids and other phytochemicals in the human body can be measured, or at least estimated, by a variety of techniques, in vitro, in vivo or ex vivo (Krinsky, 2001). Many studies describe the use of ex vivo methods to measure the oxidisability of low-density lipoprotein (LDL) particles after dietary intervention with carotene-rich foods. However, the difficulty with this approach is that complex plant foods usually also contain other carotenoids, ascorbate, flavonoids, and other compounds that have antioxidant activity, and it is difficult to attribute the results to any particular class of compounds. One study, in which subjects were given additional fruits and vegetables, demonstrated an increase in the resistance of LDL to oxidation (Hininger et al., 1997), but two other showed no effect (Chopra et al, 1996 van het Hof et al., 1999). These differing outcomes may have been due to systematic differences in the experimental protocols or in the populations studied (Krinsky, 2001), but the results do indicate the complexity of the problem, and the hazards of generalising too readily about the putative benefits of dietary antioxidants. 

In this module, an emphasis is placed on the different methods that have been used for assessing the bioavailability of food pigments such as carotenoids. Different in vivo and in vitro approaches can be used to estimate pigment bioavailability from foods in humans. 

In the in vitro digestion method, the compound of interest is transferred from the food matrix to a bile salt micelle suspension that simulates the in vivo digestion process. This in vitro digestion procedure was first developed to estimate iron availability from meals and since then has been modified and applied to studying carotenoid bioaccessibility from various food matrices. This approach assesses the bioaccessibility of the compound from a certain meal before it is presented to and taken up by intestinal cells. 

Hedren, F., Diaz, V., and Svanberg, U., Estimation of carotenoid accessibility from carrots determined by an in vitro digestion method, Eur. J. Clin. Nutr, 56, 425, 2002. 

Garrett, D.A., Failla, M.L., and Sarama, R.J., Estimation of carotenoid bioavailability from fresh stir-fried vegetables using an in vitro digestion/Caco-2 cell culture model, J. Nutr. Biochem., 11, 574, 2000. 

---