Cell-Based Galactosemia Diagnosis System Based on a Galactose Assay Using a Bioluminescent Escherichia coli Array

Genetic regulatory element based whole-cell biosensors for the detection of metabolic disorders

Clinicians require simple, and cost-effective diagnostic tools for the quantitative determination of amino acids in physiological fluids for the detection of metabolic disorder diseases. Besides, amino acids also act as biological markers for different types of cancers and cardiovascular diseases. Herein, we applied an in-silico based approach to identify potential amino acid-responsive genetic regulatory elements for the detection of metabolic disorders in humans. Identified sequences were further transcriptionally fused with GFP, thus generating an optical readout in response to their cognate targets. Screening of genetic regulatory elements led us to discover two promoter elements (pmetE::GFP and ptrpL::GFP) that showed a significant change in the fluorescence response to homocysteine and tryptophan, respectively. The developed biosensors respond specifically and sensitively with a limit of detection of 3.8 μM and 3 μM for homocysteine and tryptophan, respectively. Furthermore, the clinical utility of this assay was demonstrated by employing it to identify homocystinuria and tryptophanuria diseases through the quantification of homocysteine and tryptophan in plasma and urine samples within 5 h. The precision and accuracy of the biosensors for disease diagnosis were well within an acceptable range. The general strategy used in this system can be expanded to screen different genetic regulatory elements present in other gram-negative and gram-positive bacteria for the detection of metabolic disorders.

Effective Cryopreservation of a Bioluminescent Auxotrophic Escherichia coli-Based Amino Acid Array to Enable Long-Term Ready-to-Use Applications

Amino acid arrays comprising bioluminescent amino acid auxotrophic Escherichia coli are effective systems to quantitatively determine multiple amino acids. However, there is a need to develop a method for convenient long-term preservation of the array to enable its practical applications. Here, we reported a potential strategy to efficiently maintain cell viability within the portable array. The method involves immobilization of cells within agarose gel supplemented with an appropriate cryoprotectant in individual wells of a 96-well plate, followed by storage under freezing conditions. Six cryoprotectants, namely dimethyl sulfoxide, glycerol, ethylene glycol, polyethylene glycol, sucrose, and trehalose, were tested in the methionine (Met) auxotroph-based array. Carbohydrate-type cryoprotectants (glycerol, sucrose, and trehalose) efficiently preserved the linearity of determination of Met concentration. In particular, the array with 5% trehalose exhibited the best performance. The Met array with 5% trehalose could determine Met concentration with high linearity (R² value = approximately 0.99) even after storage at −20 °C for up to 3 months. The clinical utilities of the Met and Leu array, preserved at −20 °C for 3 months, were also verified by successfully quantifying Met and Leu in spiked blood serum samples for the diagnosis of the corresponding metabolic diseases. This long-term preservation protocol enables the development of a ready-to-use bioluminescent E. coli-based amino acid array to quantify multiple amino acids and can replace the currently used laborious analytical methods.

Homogentisic Acid-Based Whole-Cell Biosensor for Detection of Alkaptonuria Disease

Clinicians require simple quantitative tools for the detection of homogentisic acid in alkaptonuria patients, a rare inherited disorder of amino acid metabolism. In this study, we report a whole-cell biosensor for homogentisic acid to detect alkaptonuria disease through the expression of green fluorescence protein. The assay system utilizes a promoter sequence (hmgA) isolated from the Pseudomonas aeruginosa genome. To increase the sensitivity, the sensor module harboring phmgA::GFP was further transformed into various transposon mutants debilitated in steps involved in the metabolism of phenylalanine and tyrosine via homogentisic acid as a central intermediate. The proposed biosensor was further checked for analytical features such as sensitivity, selectivity, linearity, and precision for the quantification of homogentisic acid in spiked urine samples. The limit of detection for the developed biosensor was calculated to be 3.9 μM, which is comparable to that of the various analytical techniques currently in use. The sensor construct showed no interference from all of the amino acids and its homolog molecules. The accuracy and precision of the proposed biosensor were validated using high-performance liquid chromatography (HPLC) with satisfactory results.

Reagent-Free Colorimetric Assay for Galactose Using Agarose Gel Entrapping Nanoceria and Galactose Oxidase

A reagent-free colorimetric method for galactose quantification using a composite of cerium oxide nanoparticles (nanoceria) and galactose oxidase (Gal Ox) entrapped in an agarose gel was developed. In the presence of galactose, the Gal Ox entrapped within the agarose gel catalyzed the oxidation of galactose to generate H₂O₂, which induced a color change from white to intense yellow. This reaction occurred without any chromogenic substrate. This color transition is presumed to be due to the H₂O₂-mediated alteration of the oxidation state of cerium ions present on the surface of the nanoceria. The intensity of color change was quantified by acquiring an image with a conventional smartphone, converting the image to cyan-magenta-yellow-black (CMYK) mode, and subsequently analyzing the image using the ImageJ software. Using this strategy, galactose concentration was specifically determined with excellent sensitivity of as low as 0.05 mM. The analytical utility of the assay was successfully verified by correctly determining diverse levels of galactose in human serum, which is enough to diagnose galactosemia, a genetic disorder characterized by the malfunctioning of enzymes responsible for galactose metabolism. The assay employing a hydrogel composite with entrapped nanoceria and Gal Ox, is a simple, cost-effective, and rapid colorimetric assay for galactose quantification, without using any chromogenic reagent. This cost-effective method has great potential for the diagnosis of galactosemia and is highly promising in comparison to the laborious instrumentation-based methods currently in use.

Galactose-1-phosphate uridyltransferase deficiency: A literature review of the putative mechanisms of short and long-term complications and allelic variants

Galactosemia type 1 is an autosomal recessive disorder of galactose metabolism, determined by a deficiency in the enzyme galactose-1-phosphate uridyltransferase (GALT). GALT deficiency is classified as severe or variant depending on biochemical phenotype, genotype and potential to develop acute and long-term complications. Neonatal symptoms usually resolve after galactose-restricted diet; however, some patients, despite the diet, can develop long-term complications, in particular when the GALT enzyme activity results absent or severely decreased. The mechanisms of acute and long-term complications are still discussed and several hypotheses are presented in the literature like enzymatic inhibition, osmotic stress, endoplasmic reticulum stress, oxidative stress, defects of glycosylation or epigenetic modification. This review summarizes the current knowledge of galactosemia, in particular the putative mechanisms of neonatal and long-term complications and the molecular genetics of GALT deficiency.

Recent Advances in Genetic Technique of Microbial Report Cells and Their Applications in Cell Arrays

Microbial cell arrays have attracted consistent attention for their ability to provide unique global data on target analytes at low cost, their capacity for readily detectable and robust cell growth in diverse environments, their high degree of convenience, and their capacity for multiplexing via incorporation of molecularly tailored reporter cells. To highlight recent progress in the field of microbial cell arrays, this review discusses research on genetic engineering of reporter cells, technologies for patterning live cells on solid surfaces, cellular immobilization in different polymers, and studies on their application in environmental monitoring, disease diagnostics, and other related fields. On the basis of these results, we discuss current challenges and future prospects for novel microbial cell arrays, which show promise for use as potent tools for unraveling complex biological processes.