A Rapid and Reliable Spectrofluorimetric Method to Measure the Urinary Lactulose/Mannitol Ratio for Dysbiosis Assessment

Gut microbiota plays a crucial role in human health homeostasis, and the result of its alteration, known as dysbiosis, leads to several pathologies (e.g., inflammatory bowel disease, metabolic syndrome, and Crohn's disease). Traditional methods used to assess dysbiosis include the dual sugar absorption test and the urinary lactulose/mannitol ratio (LMR) measurement using mass spectrometry. Despite its precision, this approach is costly and requires specialized equipment. Hence, we developed a rapid and reliable spectrofluorimetric method for measuring LMR in urine, offering a more accessible alternative. This spectrofluorimetric assay quantifies the fluorescence of nicotinamide adenine dinucleotide (NADH) and nicotinamide adenine dinucleotide phosphate (NADPH) produced during the enzymatic oxidation of mannitol and lactulose, respectively. The assay requires 100 mu L of urine samples and detects LMR values lower (eubiosis) and higher (dysbiosis) than 0.05, ultimately being amenable to high-throughput screening and automatization, making it practical for clinical and research settings. A validation of the method demonstrated its high precision, accuracy, and robustness. Additionally, this study confirmed analyte stability under various storage conditions, ensuring reliable results even with delayed analysis. Overall, this spectrofluorimetric technique reduces costs, time, and the environmental impact associated with traditional mass spectrometry methods, making it a viable option for widespread use in the assessment of dysbiosis.