Functional markers method

The Functional Marker Method (26) was developed with the specific goal to determining directly and specifically organic functional groups in kerogens. 

Figure 5. Pictorial representation of the functional markers method.

As it was mentioned in the general definition of the objectives of the Geochemistry of oil shales the final goal in the stuparticular case, the Functional Marker Method may be of help in trying to locate relative positions of functional groups in microuniverses of the tridimensional network. 

A plethora of methods has been developed to evaluate renal function by dynamic renography and remote analysis of the excretion of renal function markers. The underlying principle is that the kidneys excrete a majority of small hydrophilic molecules and their clearance, secretion, or fixation in the kidney is quantifiable. When a renal marker in plasma is filtered through the glomeruli, the accumulation of the filtrate in the Bowman s capsule. One or more of the following events may occur in the renal tubule once a marker is filtered or is in plasma [171] ... 

Several analytes are known to be indicative of folate metabolism. Plasma total homocysteine increases when there is a deficiency of 5-MTHF, such that the methylation of homocysteine to methionine is compromised. However, though plasma homocysteine is considered to be a sensitive functional indicator, it is not specific because its concentration can be influenced by deficiency of other vitamins (Bg and B12) involved in the metabolism of homocysteine. Similarly the methylation of DNA is dependent upon adequate 5-MTHF. A sensitive new method for the rapid detection of abnormal methylation patterns in global DNA patterns has been reported and may have promise as a functional marker, as may the measurement of the degree of uracil incorporation into DNA, 5,10-metliylene THF being required for die conversion of deoxyuridine monophosphate (dUMP) to dTMP by thymidylate synthetase. ... 

Direct determination of functional groups by the Functional Group Marker Method. 

It is well accepted that MDMA produces 5-HT depletions in rat CNS, but much less attention has been devoted to the effects of MDMA on established markers of neurotoxicity such as cell death, silver-positive staining, and reactive gliosis. Support for the hypothesis of MDMA-induced axotomy relies heavily on immunohistochemical analysis of 5-HT levels, which could produce misleading results if not validated by other methods. For example, MDMA-induced loss of 5-HT could be due to persistent adaptive changes in gene expression or protein function, reflecting a state of metabolic quiescence rather than neurotoxic damage. Table 7.3 summarizes the effects of MDMA on hallmark measures of neurotoxicity. 

To test the irritancy potential of substances, two tests which can reliably distinguish between skin corrosives and noncorrosives are endorsed by the European Centre for the Validation of Alternative Methods (ECVAM). The testing procedures are based on the transcutaneous electrical resistance (TER) measurements of rat skin and on a human skin model. Both test systems [141-145] will be briefly outlined below. Nevertheless, these tests are not suited for the group of mild irritants which do not induce an acute effect on the barrier function. For those substances, new markers need to be evaluated. First results are available for heat shock protein 27 where higher levels were observed in skin models after exposure to mildly irritating chemicals [146, 147]. 

Because of the possible effects of active and carrier-mediated processes and metabolic biotransformation, the issue of tissue viability is important for in vitro buccal mucosal experiments. The barrier nature of the buccal mucosa resides in the upper layers of the epithelium, where unlike in the stratum corneum, the cells contain a variety of functional organelles [119, 122, 125, 150], and so tissue viability may be an important component of the barrier function of the tissue. Various methods have been employed to assess the viability of excised buccal mucosa, including measurement of biochemical markers, microscopic methods, and linearity of transport data [42], While biochemical methods, including measurement of adenosine 5 -triphosphate (ATP) levels and utilization of glucose, provide information on the metabolic activity of the tissue, this does not necessarily relate to the barrier function of the tissue. In excised rabbit buccal mucosa, levels of ATP were measured and found to decline by 40% in 6 h, and this correlated well with transmission electron microscopic evaluation of the tissue (intact superficial cells) [32], In addition, the permeability of a model peptide was unaltered up to 6 h postmortem, but at 8 h, a significant change in permeability was observed [32], These investigators therefore claimed that excised rabbit buccal mucosa could be used for diffusion studies for 6 h. 

A functional method for detection depends upon competition for the activity of the and desaturases between a non-essential fatty acid (e.g. oleic acid) and an essential fatty acid (see above). If the latter is deficient, oleic acid is readily converted, via the desaturases, to Mead acid, since there is little competition (Figure 11.14). Hence the amount of the latter can be used as a marker for deficiency of essential fatty acids, although it is better to use the ratio of double bonds only three are present in Mead acid (i.e. a triene) but four are present in arachidonic acid (i.e. a tetraene). A ratio in plasma, triene/tetraene >4.0 is an indication of a deficiency of essential fatty acids. This method has shown that a deficiency can occur in a number of conditions which can lead to disease (Table 11.5). 

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