Acute kidney injury accounts for 20% of all hospitalized adults, and 14 to 26% is drug-induced, emphasizing the importance of proper nephrotoxicity assessment. The ‘gold standard’ MTT assay is widely used to measure cell viability, but depends on cellular metabolic activity. Consequently, MTT may not be most optimal to assess cytotoxicity, as nephrotoxicity often involves mitochondrial dysfunction. We compared MTT with a direct cell death assay based on a compromised plasma membrane permeability. Mature conditionally immortalized proximal tubule epithelial cells were dose- (0.1-1,000 µM) and time- (0.5, 1, 2, 4, 8 and 24 hours) dependently exposed to a selection of prototypic nephrotoxicants. Dose-dependent reductions in cellular metabolic activity were stronger compared to declines in fluorescence-based cell death, most prominently for cisplatin (1.6 ± 2.0% and 68 ± 4% (mean ± SEM), respectively) and chloroacetaldehyde (2.13 ± 0.05% and 61.0 ± 0.8%). Similar, but more pronounced time-dependent effects were observed, particularly for sanguinarine. We show that assessing cellular metabolic activity by MTT provides a composite readout of cellular metabolic activity and cell death. A nuclear staining approach is preferable when assessing nephrotoxicity of metabolically active compounds. We recommend both assays during drug development to discriminate between metabolically active versus non-active compounds.

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Competing interest reported. F.G.M.R. is co-inventor on patent EP2010/066792 ‘Novel conditionally immortalized human proximal tubule cell line expressing functional influx and efflux transporters’ assigned to Radboud University Medical Center and has conflict of interest through commercialization of ciPTEC models via Cell4Pharma. J.A.M.S. is the founding CEO of Khondrion BV, a Radboud University Medical Center spin-out company founded by J.A.M.S. Other authors do not have any conflict of interest.
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Posted 12 Apr, 2021
Posted 12 Apr, 2021
Acute kidney injury accounts for 20% of all hospitalized adults, and 14 to 26% is drug-induced, emphasizing the importance of proper nephrotoxicity assessment. The ‘gold standard’ MTT assay is widely used to measure cell viability, but depends on cellular metabolic activity. Consequently, MTT may not be most optimal to assess cytotoxicity, as nephrotoxicity often involves mitochondrial dysfunction. We compared MTT with a direct cell death assay based on a compromised plasma membrane permeability. Mature conditionally immortalized proximal tubule epithelial cells were dose- (0.1-1,000 µM) and time- (0.5, 1, 2, 4, 8 and 24 hours) dependently exposed to a selection of prototypic nephrotoxicants. Dose-dependent reductions in cellular metabolic activity were stronger compared to declines in fluorescence-based cell death, most prominently for cisplatin (1.6 ± 2.0% and 68 ± 4% (mean ± SEM), respectively) and chloroacetaldehyde (2.13 ± 0.05% and 61.0 ± 0.8%). Similar, but more pronounced time-dependent effects were observed, particularly for sanguinarine. We show that assessing cellular metabolic activity by MTT provides a composite readout of cellular metabolic activity and cell death. A nuclear staining approach is preferable when assessing nephrotoxicity of metabolically active compounds. We recommend both assays during drug development to discriminate between metabolically active versus non-active compounds.

Figure 1

Figure 2

Figure 3
Competing interest reported. F.G.M.R. is co-inventor on patent EP2010/066792 ‘Novel conditionally immortalized human proximal tubule cell line expressing functional influx and efflux transporters’ assigned to Radboud University Medical Center and has conflict of interest through commercialization of ciPTEC models via Cell4Pharma. J.A.M.S. is the founding CEO of Khondrion BV, a Radboud University Medical Center spin-out company founded by J.A.M.S. Other authors do not have any conflict of interest.
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