A molecular marker of physiological aging

Scientists develop a light-emitting biosensor for the point-of-care quantification of a central biochemical cofactor

December 16, 2019

It is present in all of our cells and it is a central cofactor of metabolism and signaling - Nicotinamide adenine dinucleotide (NAD+). Decreases in its cellular concentrations are associated with pathologies such as neurodegeneration and physiological aging. Due to its great importance in a large number of molecular processes, measuring the concentration during those is critical for understanding cellular mechanisms in health and disease. Researchers at the Max Planck Institute for Medical Research in Heidelberg, the École Polytechnique Fédérale de Lausanne and the University Hospital of Lausanne have now introduced a bioluminescent biosensor for the rapid quantification of cellular NAD+ levels, which can be used either in laboratories or at the point of care. The work should facilitate studies on the role of NAD+ levels in human health and enable point-of-care quantification of clinically relevant biomarkers.

Change of color of the emitted light from blue to red upon the sensor binding to NAD+.

At present, NAD+ levels in cells are routinely measured by mass spectrometry or enzymatic assays. However, both methods are labor-intensive and require expensive equipment, making them unsuitable for point-of-care applications at patients’ homes or on the go. To address these limitations, Qiuliyang Yu from the Department of Chemical Biology at the Max Planck Institute for Medical Research designed a semisynthetic, light-emitting sensor protein. The color of emitted light changes from blue to red upon binding to NAD+. This NAD+-dependent color change enables the use of the biosensor in paper-based assays in which NAD+ is quantified, by simply measuring the color of the emitted light using a regular digital camera. It requires only a very small amount of sample, such as a drop of blood, and a few seconds to get the results, which also makes it a promising tool for point-of-care applications.

According to Yu, “the biggest challenge was to optimize the sensor to a point where it was accurate and consistent enough for measuring clinical samples. To improve the sensitivity, we screened a large number of mutants to identify the protein variant that fitted our need.” Testing the new tool, scientists at the Max Planck Institute for Medical Research and EPFL quantified NAD+ levels in cell culture, tissue and blood samples, yielding results that agreed with standard testing methods. “The simplicity of the approach should greatly facilitate basic research on this vital cofactor,” says Qiuliyang Yu. “And I am particularly excited about the idea of developing a point-of-care system for patient self-testing. This would enable us to study the role of NAD+ levels in physiological aging and neurodegenerative diseases.”

The Max Planck Institute in Heidelberg has now started a collaboration with scientists at the Fraunhofer Institute of Cell Therapy and Immunology to develop a more automated version of the paper-based assay. “This is a great opportunity for us to bring the biosensor into the clinic and to patients,” says Corentin Gondrand, a co-author of the paper and project coordinator of the collaboration with the scientists at the Fraunhofer Institute. A broad availability of the biosensor will advance research on the role of NAD+ in health and disease.

Flow diagram of NAD+ paper assay using a digital camera for the read out.

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