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Protein engineering brings the clinical laboratory to the patients fingertip

The treatment of numerous diseases could be improved if the blood concentration of disease-relevant metabolites would be monitored at the point-of-care (POC), ideally even by the patient. A team of scientists led by researchers at the Max Planck Institute for Medical Research in Heidelberg and the École Polytechnique Fédérale de Lausanne, and initiated at the NCCR Chemical Biology, now introduces a biosensor for the accurate quantification of metabolites in small blood samples obtained from a simple finger prick. This biosensor could become an important tool for the diagnosis and management of various diseases.

Diseases or injuries can result in dramatic changes in metabolite blood levels. For example, increased blood levels of the amino acid phenylalanine are characteristic for the genetic disorder phenylketonuria (PKU). Infants suffering from PKU need to control phenylalanine levels through dietary management to avoid irreversible brain damage. It is therefore essential to have means of regularly monitoring phenylalanine levels in blood. However, such monitoring currently requires blood samples to be sent to clinical laboratories with results taking several days to come back to the patient. This time-delay often complicates disease management for both PKU patients and their physicians. A team of scientists lead by Kai Johnsson of the Max Planck Institute for Medical Research (MPIMR) in Heidelberg has now introduced a simple paper-based assay that can measure concentrations of metabolites such as phenylalanine in small blood samples within minutes. The approach was validated with patient samples obtained from the Heidelberg and Lausanne University Hospitals. The work, published this week in Science, represents an important advance towards POC-monitoring of metabolites in blood.

Molecular engineering

“We introduce a fundamentally new mechanism to measure metabolites for blood analysis,” says Dr. Qiuliyang Yu, first author of the paper and scientist at the Department of Chemical Biology at the MPIMR. “Instead of miniaturizing available technologies for POC applications, we developed a new molecular tool,” he explains further. The tool is a light-emitting, engineered protein that changes its color in the presence of the reduced cofactor nicotinamide adenine dinucleotide, known to biochemists under its acronym NADPH. As NADPH can be produced in an enzyme-catalyzed reaction specific for the metabolite of interest, analyzing the color of the emitted light reveals the metabolite concentration. Using different enzyme-catalyzed reactions, the same sensor can be used to establish quantitative POC assays for various metabolites, as shown for phenylalanine, glutamate and glucose.

How to use it?

In the case of phenylalanine, a droplet of blood is first taken from the patient through a painless finger pick. In a second step, a fraction of the blood sample is added into a reaction buffer and applied onto a paper containing the immobilized biosensor. When phenylalanine is consumed and NADPH is produced, the light emitted by the sensor changes its color from blue to red, which can be detected by a simple digital camera or a smartphone. The ratio of blue to red light is then used to calculate the concentration of phenylalanine. The whole procedure takes only 10-15 minutes,  can be done at the POC and yields accurate results when compared to standard methods used in clinical laboratories.

Original article

Qiuliyang Yu, Lin XueJulien HiblotRudolf GrissSebastian FabritzClothilde RouxPierre-Alain BinzDorothea HaasJürgen G. OkunKai Johnsson, Semisynthetic sensor proteins enable metabolic assays at the point of care“, Science, DOI: 10.1126/science.aat7992

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