Cell cytotoxicity assays measure the ability of certain compounds or chemical mediators to reduce the viability of the cells. The term cell cytotoxicity assay can sometimes be used interchangeably with cell proliferation assay. Healthy living cells can be identified by the use of formazan dyes, protease biomarkers or by measuring ATP content. The formazan dyes are chromogenic products formed by the reduction of tetrazolium salts by dehydrogenases, such as lactate dehydrogenase (LDH) and reductases that are released during cell death. Common tetrazolium salts include INT, MTT, MTS and XTT. Cell cytotoxicity can also be measured by using the SRB and WST-1 assays. These assays can usually be used in a high-throughput fashion and can be quantitated by measuring absorbance, colorimetry or luminescence. All these assays require similar numbers of cell plating at the initiation, a time course of treatment with the cytotoxic agent and at least triplicates for each condition at every point of analysis. Cell shrinkage, plasma membrane blebbing, cell detachment, externalization of phosphatidylserine, nuclear condensation and ultimately DNA fragmentation are well-described features of apoptosis. The assays that rely on cell membrane integrity for their function, may not be able to quantify early apoptosis. Therefore, in order to distinguish early apoptotic vs. late apoptotic or necrotic cells, additional flow cytometry techniques can be used. A combination of Annexin V and PI (propidium iodide) can be used to distinguish early (Annexin V+/PI-) and late apoptotic (Annexin V+/PI+) cells. Sometimes, caspase assays are used in order to differentiate the stages of apoptosis.
Reporter gene assays are designed to test the regulation of the expression of a gene of interest. This is usually done by linking the promoter of the gene of interest with a gene such as a firefly luciferase, which can be easily detected by addition of luciferin that leads to an enzymatic reaction to produce luminescence. The enzymatic reaction can be correlated to the expression of the gene of interest. Another luciferase gene that can be used is Renilla luciferase. For an appropriate luciferase assay: 1. the reporter should express uniformly in all cells, 2. specifically respond to effectors that the assay intends to monitor, 3. have low intrinsic stability to quickly reflect transcriptional dynamics. It is important to have an equal number of cells plated in each testing condition to avoid any incorrect readouts. Reporter assays could be single or dual reporter assays. The reporter could be both luciferases. Most dual-luciferase assays involve adding two reagents to each sample and measuring luminescence following each addition. Adding the first reagent activates the first luciferase reporter reaction; adding the second reagent extinguishes first luciferase reporter activity and initiates the second luciferase reaction. Dual-luciferase assays have some advantages, including 1. reduces variability, 2. reduces background, 3. normalizes differences in transfection efficiencies between samples.
Cell cytotoxicity assays measure the ability of certain compounds or chemical mediators to reduce the viability of the cells. The term cell cytotoxicity assay can sometimes be used interchangeably with cell proliferation assay. Healthy living cells can be identified by the use of formazan dyes, protease biomarkers or by measuring ATP content. The formazan dyes are chromogenic products formed by the reduction of tetrazolium salts by dehydrogenases, such as lactate dehydrogenase (LDH) and reductases that are released during cell death. Common tetrazolium salts include INT, MTT, MTS and XTT. Cell cytotoxicity can also be measured by using the SRB and WST-1 assays. These assays can usually be used in a high-throughput fashion and can be quantitated by measuring absorbance, colorimetry or luminescence. All these assays require similar numbers of cell plating at the initiation, a time course of treatment with the cytotoxic agent and at least triplicates for each condition at every point of analysis. Cell shrinkage, plasma membrane blebbing, cell detachment, externalization of phosphatidylserine, nuclear condensation and ultimately DNA fragmentation are well-described features of apoptosis. The assays that rely on cell membrane integrity for their function, may not be able to quantify early apoptosis. Therefore, in order to distinguish early apoptotic vs. late apoptotic or necrotic cells, additional flow cytometry techniques can be used. A combination of Annexin V and PI (propidium iodide) can be used to distinguish early (Annexin V+/PI-) and late apoptotic (Annexin V+/PI+) cells. Sometimes, caspase assays are used in order to differentiate the stages of apoptosis.
Cell cytotoxicity assays measure the ability of certain compounds or chemical mediators to reduce the viability of the cells. The term cell cytotoxicity assay can sometimes be used interchangeably with cell proliferation assay. Healthy living cells can be identified by the use of formazan dyes, protease biomarkers or by measuring ATP content. The formazan dyes are chromogenic products formed by the reduction of tetrazolium salts by dehydrogenases, such as lactate dehydrogenase (LDH) and reductases that are released during cell death. Common tetrazolium salts include INT, MTT, MTS and XTT. Cell cytotoxicity can also be measured by using the SRB and WST-1 assays. These assays can usually be used in a high-throughput fashion and can be quantitated by measuring absorbance, colorimetry or luminescence. All these assays require similar numbers of cell plating at the initiation, a time course of treatment with the cytotoxic agent and at least triplicates for each condition at every point of analysis. Cell shrinkage, plasma membrane blebbing, cell detachment, externalization of phosphatidylserine, nuclear condensation and ultimately DNA fragmentation are well-described features of apoptosis. The assays that rely on cell membrane integrity for their function, may not be able to quantify early apoptosis. Therefore, in order to distinguish early apoptotic vs. late apoptotic or necrotic cells, additional flow cytometry techniques can be used. A combination of Annexin V and PI (propidium iodide) can be used to distinguish early (Annexin V+/PI-) and late apoptotic (Annexin V+/PI+) cells. Sometimes, caspase assays are used in order to differentiate the stages of apoptosis.
Cell cytotoxicity assays measure the ability of certain compounds or chemical mediators to reduce the viability of the cells. The term cell cytotoxicity assay can sometimes be used interchangeably with cell proliferation assay. Healthy living cells can be identified by the use of formazan dyes, protease biomarkers or by measuring ATP content. The formazan dyes are chromogenic products formed by the reduction of tetrazolium salts by dehydrogenases, such as lactate dehydrogenase (LDH) and reductases that are released during cell death. Common tetrazolium salts include INT, MTT, MTS and XTT. Cell cytotoxicity can also be measured by using the SRB and WST-1 assays. These assays can usually be used in a high-throughput fashion and can be quantitated by measuring absorbance, colorimetry or luminescence. All these assays require similar numbers of cell plating at the initiation, a time course of treatment with the cytotoxic agent and at least triplicates for each condition at every point of analysis. Cell shrinkage, plasma membrane blebbing, cell detachment, externalization of phosphatidylserine, nuclear condensation and ultimately DNA fragmentation are well-described features of apoptosis. The assays that rely on cell membrane integrity for their function, may not be able to quantify early apoptosis. Therefore, in order to distinguish early apoptotic vs. late apoptotic or necrotic cells, additional flow cytometry techniques can be used. A combination of Annexin V and PI (propidium iodide) can be used to distinguish early (Annexin V+/PI-) and late apoptotic (Annexin V+/PI+) cells. Sometimes, caspase assays are used in order to differentiate the stages of apoptosis.
miRNA is the inherent gene silencing machinery which can have more than one mRNA target, whereas siRNA can be designed to target a particular mRNA target. By design, both siRNA and miRNA are 20-25 nucleotides in length. The target sequence for siRNAs is usually located within the open reading frame, between 50 and 100 nucleotides downstream of the start codon. There are two ways in which cells can be transfected with desired RNAi: 1. Direct transfection (with calcium phosphate co-precipitation or cationic lipid mediated transfection using lipofectamine or oligofectamine), and 2. Making RNAi lentiviral constructs (followed by transformation and transduction). Lentiviral constructs are time consuming, but provide a more permanent expression of RNAi in the cells, and consistent gene silencing. Direct transfection of oligonucleotides provides temporary genetic suppression. Traditional methods like calcium phosphate co-precipitation have challenges like low efficiency, poor reproducibility and cell toxicity. Whereas, cationic lipid-based transfection reagents are able to overcome these challenges, along with applicability to a large variety of eukaryotic cell lines. When using oligos, the ideal concentration lies between 10-50nM for effective transfection.
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