Posts Tagged ‘Monash University’

Reported by: Dr. Venkat S. Karra, Ph.D.

Mitochondria are responsible for more than 90% of a cell’s energy production via ATP (adenosine triphosphate) generation, in addition to playing a significant role in respiration and many signaling events within most eukaryotic cells. These intracellular powerhouses range in size and quantity within each cell depending on the organism and overall cell function.

Mitochondria consist of a semi-permeable outer membrane, a thin inter-membrane space where oxidative phosphorylation occurs, an impermeable inner membrane that is intricately folded to create layered compartments—or christae—and the matrix that contains ATP-producing enzymes and the organelle’s own independent genome. Each section has a highly specialized function, and any impairment within the organelle can lead to disease or disorders within the overall organism.

Mitochondrial dysfunction may be due to:

1. Hereditary:

Inherited mitochondrial disorders can play a role in prevalent diseases such as cardiac disease and diabetes, and can also result in rare diseases such as Pearson syndrome or Leigh’s disease.

2. Drug Toxicity:

Mitochondrial toxicity as a result of pharmaceutical use may damage key organs, such as the liver and heart. For example:

nefazodone—a depression treatment—was withdrawn from the U.S. market after it was shown to significantly inhibit mitochondrial respiration in liver cells, leading to liver failure.

Troglitazone, an anti-diabetic and anti-inflammatory, was withdrawn from all markets after research concluded that it caused acute mitochondrial membrane depolarization, also leading to liver failure.

Drug recalls are costly to a manufacturer’s bottom line and reputation, and more importantly, can be harmful or even fatal to users. As drug discovery continues to evolve, much lead compound research now includes careful review of its interaction and potential toxicity with mitochondria.

Cell-based mitochondrial assays in microplate format may include mitochondrial membrane potential, total energy metabolism, oxygen consumption, and metabolic activity; and offer a truer environment for mitochondrial function in the presence of drug compounds compared to isolated mitochondria-based tests. Combining more than one assay in a multiplex format increases the amount of data per well while decreasing data variability arising from running the assays separately. The aggregated data also provides a more encompassing analysis of the drug’s effect on mitochondria than a single test.

One example, when testing compound effects on mitochondria, would be to measure cell membrane integrity as a function of cytotoxicity and mitochondrial function via ATP production concurrently, thus distinguishing between compounds that exhibit mitochondrial toxicity versus overt cytotoxicity.

General cytotoxicity is characterized by a decrease in ATP production and a loss of membrane integrity whereas mitochondrial toxicity results in decreased ATP production with little to no change in membrane integrity.

The assay’s efficiency is further enhanced via automation.

Robotic instrumentation ensures repeatable operation within the microplate wells when performing tasks such as cell dispensing, serial titration and transfer of compounds, and reagent dispensing. Additionally, by automating tasks within the assay process, researchers are free to attend to other tasks, reducing overall active time spent on the assay. Multi-mode microplate readers are compact instruments that can detect both fluorescent and luminescent signals. In addition, an automated process—including liquid handling and detection—can increase throughput capacity compared to manual methods.

Multiplexed cell-based mitochondrial assays increase sample throughput and decrease variability, costs, and overall time for project completion. Automating the process with robotic instrumentation allows for rapid compound profiling, repeatability, further throughput increase, and decreased per-assay and overall project time.



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