Animal assays Subject

The bioavailability of iron from any source (e.g., iron supplement, food or meal composite) is considered to be that portion of the total iron which is metabolizable. Philosophically, this concept is important because the amount of iron utilized by avian and mammalian species is directly associated with iron need. When assaying iron bioavailability, it is therefore necessary to use an organism whose need will exceed the amount provided. In animal assays of iron bioavailability, iron need is assured by a growth phase and/or creation of iron deficiency through feeding an iron deficient diet and phlebotomy. Because healthy subjects are usually used in human assays of iron bioavailability (Cook et al., 1981 Cook and Monson, 1976 Radhakrishman and Sivaprasad, 1980), it is inappropriate to compare the data obtained from animal and human assays. In fact it is questionable if assays of iron bioavailability yield good information on the quantities of metabolizable iron available when healthy human subjects are used. 

Effect of Heat Processing on Bioavailability of Added Iron. Several studies in Table III measured directly the effect of heat processing on added iron. These studies compared processed foods to a control group of identical unprocessed food. Studies in Table 111 utilizing unprocessed controls include 15, 19, and 23. Other studies did not employ an unprocessed control, but used a reference dose to enable comparisons from study to study. Reference doses of ferrous sulfate (most animal assays) or ferrous ascorbate (most human tests) were frequently used. Preparation of ferrous ascorbate, usually a 2 1 molar ascorbic acid iron solution, has been detailed by Layrisse et al. (25). These controls enabled measurement of variation in iron absorption from subject to subject, important in view of greater absorption of an iron deficient versus an iron replete subject. When a reference dose was fed as a radiolabeled salt (55Fe), and on alternate times the test diet was fed with a different radiolabel (59Fe), errors due to variation in subject absorption were eliminated, as each subject served as its own control. The different availabilities of various iron sources from baked enriched rolls were established in this manner (17). 

Part of the strength of the cytochemical bioassays is that they are within-animal assays. But normally only six, or at the most eight, segments can be obtained from one animal, four being required for the standard graph and the rest for the two dilutions of the plasma from one, or at the most two, subjects. To increase the throughput of some of these bioassays, it was found possible to use sections, instead of segments. 

Inasmuch as the chief difficulty in the work on the purification of active materials has been the relative scarcity of pernicious anemia patients, many worthy attempts have been made to develop an animal assay the guinea pig, dog, cat, pigeon, swine, monkey, and rabbit have all been tried without definite success if any. Creskoff and Fritz Hugh have covered this subject admirably in their review of standardization and assay of liver extracts (20). At any rate the clinical assay still is the only reliable way of following the fractionation procedures. 

Assessment and definition of sensitivity are often described for quantitative analysis but are of equal importance for qualitative devices of the dip-stick type that are very popular for farm- or field-based screening assays. Because of the somewhat subjective nature of visually assessed assays, the assay s sensitivity must be validated using a number of observers to determine at what level a test is deemed positive. The number of false positives and false negatives must be carefully determined in order to balance consumer safety and potential economic loss to animal producers. 

Recent guidelines entitled Non-clinical Local Tolerance Testing of Medicinal Product from the CPMP refer to the murine local l)unph node assay as a method for the assessment of the induction phase of skin sensitisation. This method measures the ability of compoimds to induce proliferative responses in skin-draining lymph nodes. This method uses fewer animals than alternative in vivo methods and reduces the trauma to which animals are potentially subjected. ... 

Throughout their lifetimes all assays are subjected to improvements. In case of an animal species change or a major protocol change, the assay is fully revalidated and all BioPrint compounds retested. 

Another important contributor to the development of toxicology was the Spanish physician Orfila (1787-1853). He was one of the first scientists to make systematic use of test animals and autopsy material. Orfila was the first to treat toxicology as a separate scientific subject and was also responsible for the development of numerous chemical assays for detecting the presence of poisons, thus providing an early foundation for forensic toxicology. In 1815 Orfila published the first major work dealing with the toxicity of natural agents. 

Of importance the sulfatides can be further distinguished by a more sophisticated procedure. This would entail intraperitoneal injection of 35S04 into small animals. A quite rapid incorporation of label into brain lipids, for example, will provide support for the presence of a sulfatide. The isolated sulfatide-containing fraction is subjected to thin-layer chromatography, and the lanes are sectioned and assayed for radioactivity. Location of labeled material migrating at the same Rf value of standards (nonlabeled) would be... 

Our currently poor understanding of the mechanisms leading to autoimmunity and autoimmune diseases following drug therapy is a major hurdle. To date, no animal model or assay can reliably predict the potential, of biopharmaceuticals or pharmaceuticals, for inducing autoimmunity reactions in human subjects. 

---