Point-of-Care Monitoring of Colitis Using Intestinal Alkaline Phosphatase in Inflammatory Bowel Disease

Toward the point-of-care testing of alkaline phosphatase in human serum

This work addresses challenges of simple but reliable determination of enzyme alkaline phosphatase (ALP) in μL-sized serum samples. The single-tube assay and plate-based immunoassay were developed by using a commercial glucose test strip (GTS) to transduce analytical signal from the ALP + glucose-6-phosphate (G6P) reaction. The glucose released from G6P contributed to the flow of anodic charge Q20s through GTS. The interferences from serum matrix including those from native glucose were eliminated by devising a signal ΔQ20s = Q20s (total) - Q20s (matrix). The ΔQ20s was proportional to ALP activity within a linear range of 7.4-720 IU L-1 for assay (R2, 0.995) and 10-300 IU L-1 for immunoassay (R2, 0.983), which far exceeded a normal clinical range for ALP in adult human serum (30-150 IU L-1). Both methods required no auxiliary enzymes or labels, and were accurate (93-99 % signal recovery) and precise (RSD ≤10%). The assay was a simpler option because it required only one 20-min incubation step to determine ALP. The immunoassay involved three steps but it was still less laborious (by ∼70%) than a traditional enzyme-linked immunosorbent assay (ELISA) of ALP due to the substitution of ELISA detection antibody with GTS. The GTS-G6P-based methods bring ALP testing closer to the point-of-care locations, which is important considering the growing role of ALP as a prophylactic, therapeutic, and anti-inflammatory agent, and a marker of human diseases.

The role of fecal biomarkers in individuals with inflammatory bowel disease

INTRODUCTION

Inflammatory bowel disease (IBD), encompassing Crohn's disease (CD) and Ulcerative Colitis (UC), is a relapsing and remitting condition. Noninvasive biomarkers have an increasingly important role in the diagnosis of IBD and in the prediction of future disease course in individuals with IBD. Strategies for the management of IBD increasingly rely upon close monitoring of gastrointestinal inflammation.

AREAS COVERED

This review provides an update on the current understanding of established and novel stool-based biomarkers in the diagnosis and management of IBD. It also highlights key gaps, identifies limitations, and advantages of current markers, and examines aspects that require further study and analysis.

EXPERT OPINION

Current noninvasive inflammatory markers play an important role in the diagnosis and management of IBD; however, limitations exist. Future work is required to further characterize and validate current and novel markers of inflammation. In addition, it is essential to better understand the roles and characteristics of noninvasive markers to enable the appropriate selection to accurately determine the condition of the intestinal mucosa.

Self-Immolative Electrochemical Redox Substrates: Emerging Artificial Receptors in Sensing and Biosensing

The development of artificial receptors has great significance in measurement science and technology. The need for a robust version of natural receptors is getting increased attention because the cost of natural receptors is still high along with storage difficulties. Aptamers, imprinted polymers, and nanozymes are some of the matured artificial receptors in analytical chemistry. Recently, a new direction has been discovered by organic chemists, who can synthesize robust, activity-based, self-immolative organic molecules that have artificial receptor properties for the targeted analytes. Specifically designed trigger moieties implant selectivity and sensitivity. These latent electrochemical redox substrates are highly stable, mass-producible, inexpensive, and eco-friendly. Combining redox substrates with the merits of electrochemical techniques is a good opportunity to establish a new direction in artificial receptors. This Review provides an overview of electrochemical redox substrate design, anatomy, benefits, and biosensing potential. A proper understanding of molecular design can lead to the development of a library of novel self-immolative redox molecules that would have huge implications for measurement science and technology.

Electroanalysis of Enzyme Activity in Small Biological Samples: Alkaline Phosphatase

The discovery of sulfite-stabilized anodic current of hydroquinone (HQ) at high pH was used to develop two new methods for measuring the activity of the key biomarker alkaline phosphatase (ALP). Both approaches relied on the monitoring of ALP-triggered release of HQ from a substrate hydroquinone diphosphate (HQDP) into a pH 10.00 solution. One detected the released HQ via the internally calibrated electrochemical continuous enzyme assay (ICECEA) at a glassy carbon (GC) electrode with no sample incubation. The other used sample incubation with HQDP and quantified the released HQ via a coulometric assay at a commercial glucose test strip (GTS). The assay solution was optimized by investigating the ALP/HQDP/HQ system at a GC electrode. The ICECEA revealed high affinity of ALP for HQDP (K_m^app, 87 μM; V_max, 0.36 μM min^-1) and detected ALP down to 0.022 U L^-1. At GTS, ALP was detected down to 0.064 U L^-1 in a 1 μL sample of human serum after a 20 min incubation at room temperature. The linear range (R², 0.994) extended at least up to 1.7 U L^-1 ALP, which covered more than the clinical range for ALP in serum. The interferences from the sample matrix including those from indigenous glucose were eliminated using a charge difference ΔQ (=Q_total - Q_{sample matrix}) as a signal for ALP. Both advances proposed here are direct (no auxiliary enzymes or labels required), accurate (98 ± 3% ALP signal recovery), and precise (relative standard deviation (RSD), <7%). The HQDP-GTS-based assay advances the analysis of ALP activity in microsized real-life samples.