Metabolic activity of cells

MTT assay is a standard colorimetric assay used to determine cytotoxicity of potential medicinal agents and other toxic materials. It is based on the reduction of the tetrazolium salt MTT by viable cells. A mitochondrial dehydrogenase enzyme is able to cleave the tetrazolium rings of the pale yellow MTT and form dark purple formazan crystals, which are largely impermeable to cell membranes resulting in the accumulation of these crystals within healthy cells. Solubilization of the cells by the addition of a detergent results in the liberation of crystals, which are solubilized. The metabolic activity of cells is directly proportional to the concentration of the created formazan product (22), whose color is quantified in a colorimetric assay. 

Much of the metabolic activity of cells consists largely of central metabolic pathways that transform large amounts of proteins, fats and carbohydrates. Foremost among these pathways are glycolysis, which can occur in either aerobic or anaerobic conditions, and the Krebs cycle, which is coupled to the electron transport chain, which accepts electrons removed from reduced coenzymes of glycolysis and the Krebs cycle. The final electron acceptor of the chain is usually oxygen, but some bacteria use specific, oxidized ions as the final acceptor in anaerobic conditions. 

A recent study has shown that membranes made of a modified polyetheretherketone (PEEK-WC) are interesting materials for biomedical applications [23,24]. The cytocompatibility of PEEK-WC membranes was evaluated by culturing hepatocytes isolated from rat liver (Figure 43.6). The properties of PEEK-WC membranes were compared to polyurethane membranes prepared using the same technique, and commercial membranes (made of Nylon, polyethersulphone, and polyester). The results have shown that PEEK-WC membranes promoted hepatocyte adhesion most effectively and metabolic activities of cells cultured on these membranes improved significantly. 

Plot the different specific rates as a function of time and analyse the evolution of the metabolic activities of cells during the culture... 

The long range goal continues to be to relate the metabolic activities of cell cultures to bioreactor control. Early studies focused on measuring the respiration quotient and rate of ammonia addition for pH control and combining these measurements with elemental and microscopic balances to predict behavior of batch, fed-batch, and continuous yeast cultures. Cybernetic models continue to be studied with the goal of using these models to control bioreactors. ... 

Problem 15.67. The normal metabolic activity of cells results in the production of carboxylic acids, which would alter the pH of blood and other biological fluids if unchecked. This is a potential danger to proteins and other biologically important compounds whose structures and physiological functions depend on pH (See. 20.3.4). The pH of blood and other biological fluids is maintained within very narrow limits to avoid such changes in structure and fimction. How is pH control achieved ... 

It is important to ensure the maximum metabolic activity of the microbe suspension. The ATP (adenosine triphosphate) content reflects the metabolic activity of cells. Thus, the measurement of ATP content is a good indicator of the viability of bacteria. The measured ATP content must be expressed on the basis of one of the cellular attributes (protein content or cell number). The bacterial suspensions are the most suitable for coating the TLC plates when their growth is in the exponential log phase, and their OD... 

Studies on the biological perfomiance of ferroelectric hydroxyapatite-barium titanate (HABT) ceramics (< 33 = 58 pC/N) showed that the attachment, proliferation, viability, morphology and metabolic activity of cells cultured on unpoled HABT were comparable to those observed on commercially available HAp, at all time points. However, there were no striking differences between the properties of poled and non-poled ceramics, at least not during the short incubation times employed (Baxter et al., 2009). 

This bicarbonate buffer system is quantitatively the most important of the three because of the high bicarbonate concentration in blood which results from the large amounts of CO2 produced by the metabolic activity of cells. Loss of CO2 in the lungs displaces the equation to the left once more and prevents build up of hydrogen ions. The p/sT value of this system is considerably below pH 7-4, the normal physiological value for blood, and can be evaluated by applying the Henderson-Hasselbalch equation. The normal plasma bicarbonate value is 27 m-equiv per litre, approximately twenty times the total solubility of carbon dioxide of 1-35 mmol per litre (at a partial pressure of 40mmHg) From Equation (3-11)... 

A potentially toxic alkaline gas which is formed from amino acids or urea by (1) intestinal bacteria, or (2) metabolic activities of cells. Normally, the accumulation of ammonia in the body is prevented by enzymes which convert the ammonia to safer compounds such as urea or amino acids. However, ammonia intoxication is a common occurrence in certain liver diseases. 

ProUferation/Viability Assays Based on Metabolic Activity of Cells Besides the incorporation of nucleosides into DNA, cell-viability dyes and kits have become valid options to monitor cell viability, activation and the increasing number of viable cells during cell proHferation. Table 5 Hsts the assays that are based on the metabolic activity of cells. They are also used as an indirect measure of cytotoxicity. The viability/metabolic reagents based on redox indication dyes like tetrazolium (MTT, XTT, MTS WST-1) and resazurin (Alamar Blue) are popular substitutes for radioactive compovmds. The tetrazolium assays are colorimetric assays based on bioreduction of tetrazolium salt into a either insoluble (MTT) or soluble (XTT, MTS,WST-1) colored substance formazan by mitochondrial succinate dehydrogenase. The reaction occurs only in live cells, and the... 

The assays based on metabolic activity using the vital dyes are simple, sensitive and, in most cases, provide an accurate measure of the number of live cells. In recent years the metabolic activity methods have been improved with introduction of the commercial reagents and kits, which were used to monitor cell viability and proliferation in simple add-mix-measure assay protocols. These simple assay formats allow for a wider cell-based assay application and automation. However, one should exercise caution when developing any assay based on metabolic activity of cells because there are several drawbacks with these types of... 

The use of additional methods during bioassay development is highly recommended to verify suitability of the method based on metabolic activity of cells. 

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