In-vivo metabolic labeling

The use of the in vivo labeling methods described above is limited by the fact that the sample must be grown in the presence of the labeling isotopes. In many cases, it is not feasible to perform in vivo metabolic labeling. For example, for human clinical samples it is not possible to perform in vivo labeling and yet it is highly desirable to obtain accurate quantitative information on protein expression levels within these samples. Therefore, robust methods are needed for quantitation of protein levels in the absence of in vivo labeling with isotopes. 

Experiments of in vivo metabolic labelling showed that unusual neutral and anionic glycolipids were synthesized by carrot cells [10]. The synthetic rate of these glycolipids seemed to depend both on the differentiation stage and on the embryogenic potential of the... 

Davit, B., Reynolds, K., Yuan, R., Ajayi, F., Conner, D. et al., FDA evaluations using in vitro metabolism to predict and interpret in vivo metabolic drug-drug interactions impact on labeling, J. Clin. Pharmacol. 

A drin and Dieldrin Metabolism.— The in vivo metabolism of the chlorinated alicyclic insecticides, aldrin and dieldrin, has been measured. Fish were exposed to l c-labelled aldrin or dieldrin for 6 hours. The metabolism of each compound was monitored by thin layer chromatography of hexane and chloroform-methanol extracts of liver homogenates, followed by liquid scintillation counting of the spots (5,15,16). 

Such stability is only relative, however, given the possibility of the acid-catalyzed 1,2-shift of a proton observed in some olefin epoxides of general structure 10.10 (Fig. 10.3) [12], Such a reaction occurs in the in vivo metabolism of styrene to phenylacetic acid the first metabolite formed is styrene oxide (10.10, R = Ph, Fig. 10.3, also 10.6), whose isomerization to phenyl-acetaldehyde (10.11, R = Ph, Fig. 10.3) and further dehydrogenation to phenylacetic acid has been demonstrated by deuterium-labeling studies. A com-... 

H. Pereira, P. C. Lemos, M. J. T. Carrondo, J. P. S. Crespo, M. A. M. Peis and H. Santos (1996). Model for carbon metabolism in biological phosphorus removal processes based on in vivo 13C labelling experiment. Water Res., 30, 2128-2138. 

Both these 5-hydroxyindoles are natural compounds, playing an important role in the brain. 5-hydroxytryptophan (5-HTP) 315 is the metabolic precursor for the neurotransmitter serotonin melatonin 316 is a neurohormone involved in the regulation of chronobiological rhythms such as sleep and fertility306. They have been labelled with F-18, for in vivo metabolic imaging with PET, in reaction of dilute [18F]fluorine gas with melatonin or with 5-hydroxytryptophan in hydrogen fluoride307 at — 70 °C (equation 134). 

FDA Guidance for Industry. In Vivo Metabolism/Drug Interaction Studies - Study Design, Data Analysis and Recommendations for Dosing and Labelling. Rockville, MD, USA FDA, 1999. 

The biological uptake pattern of the radioiodinated peptide indicates urinary as well as gastrointestinal excretion. In vivo metabolization is evidenced by the thyroid uptake (see Table 16.2), which reached 10.2 8.5% of the injected dose at 24 h. In the case of the Lu labelled peptide, the elimination is mainly through urinary excretion. Dose estimates for the radioiodinated peptide are shown in Table 16.4. 

Schwender, J., and J.B. Ohlrogge. 2002. Probing in vivo metabolism by stable isotope labeling of storage lipids and proteins in developing Brassica napus embryos. Plant Physiol. 130 347-361. 

FDA. In Vivo metabolism/drug interaction studies — study design, data analysis, and recommendations for dosing and labeling 1999. 

Through the study of Roth el al. with carboxyl C -labeled niacin, it has been estimated that the turnover time of niacin in tissues is from 4 to 8 days 19ff). More recent data, however, indicate that in liver the half-life of the pyridine nucleotides may be considerably shorter 197). The observation that the injection of nicotinamide into mice can produce large increases in the levels of liver DPN has provided a useful means of studying the in vivo metabolism of the P3uidine coenzymes. The results obtained with this method of approach are presented in this section. 

In-vitro models can provide preliminary insights into some pharmacodynamic aspects. For example, cultured Caco 2 cell lines (derived from a human colorectal carcinoma) may be used to simulate intestinal absorption behaviour, while cultured hepatic cell lines are available for metabolic studies. However, a comprehensive understanding of the pharmacokinetic effects vfill require the use of in-vivo animal studies, where the drug levels in various tissues can be measured after different dosages and time intervals. Radioactively labelled drugs (carbon-14) may be used to facilitate detection. Animal model studies of human biopharmaceutical products may be compromised by immune responses that would not be expected when actually treating human subjects. 

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