Assessment of the degree of interference of polyphenolic compounds on glucose oxidation/peroxidase assay.

The glucose oxidase/peroxidase assay (GOP) is a coupled enzymatic assay commonly used in measuring glucose concentrations in biological sciences and food chemistry, particularly for quantification of α-glucosidase activity. However, we found that the GOP assay is prone to interference, especially from reducing substances such as polyphenolic compounds, which are commonly found in botanical materials. To establish the scope and limitation of the assay in measuring α-glucosidase inhibition activity, we systematically investigated the structural features of the polyphenolic compounds that can lead to false positives. Utilizing sodium dodecyl sulfate (SDS) as surrogate for the meriquinone intermediate formed during the reaction, we measured the reactivity of this redox active intermediate toward common flavonoids. Our results show that flavonoids with o-dihydroxy groups in the B-ring cause strong interference and that compounds with little DPPH scavenging activity do not have interference. Our results highlight the need for checking the suitability of the GOP assay first before it is applied in measuring α-glucosidase inhibition activity. In addition, when the literature data on α-glucosidase inhibition activity of botanical extracts or polyphenolic compounds using GOP assay are interpreted, potential false positives due to interference on the assay will need to be taken into consideration.

A disposable tear glucose biosensor--part 3: assessment of enzymatic specificity.

BACKGROUND: A concept for a tear glucose sensor based on amperometric measurement of enzymatic oxidation of glucose was previously presented, using glucose dehydrogenase flavin adenine dinucleotide (GDH-FAD) as the enzyme. Glucose dehydrogenase flavin adenine dinucleotide is further characterized in this article and evaluated for suitability in glucose-sensing applications in purified tear-like saline, with specific attention to the effect of interfering substances only. These interferents are specifically saccharides that could interact with the enzymatic activity seen in the sensor's performance. METHODS: Bench top amperometric glucose assays were performed using an assay solution of GDH-FAD and ferricyanide redox mediator with samples of glucose, mannose, lactose, maltose, galactose, fructose, sucrose, and xylose at varying concentrations to evaluate specificity, linear dynamic range, signal size, and signal-to-noise ratio. A comparison study was done by substituting an equivalent activity unit concentration of glucose oxidase (GOx) for GDH-FAD. RESULTS: Glucose dehydrogenase flavin adenine dinucleotide was found to be more sensitive than GOx, producing larger oxidation currents than GOx on an identical glucose concentration gradient, and GDH-FAD exhibited larger slope response (-5.65 × 10(-7) versus -3.11 × 10(-7) A/mM), signal-to-noise ratio (18.04 versus 2.62), and linear dynamic range (0-30 versus 0-10 mM), and lower background signal (-7.12 versus -261.63 nA) than GOx under the same assay conditions. GDH-FAD responds equally to glucose and xylose but is otherwise specific for glucose. CONCLUSION: Glucose dehydrogenase flavin adenine dinucleotide compares favorably with GOx in many sensor-relevant attributes and may enable measurement of glucose concentrations both higher and lower than those measurable by GOx. GDH-FAD is a viable enzyme to use in the proposed amperometric tear glucose sensor system and perhaps also in detecting extreme hypoglycemia or hyperglycemia in blood.

Aspiration assessment and prevention in critically ill enterally fed patients: evidence-based recommendations for practice.

Providing nutrition to patients is a vitally important aspect of care. Enterally feeding even critically ill patients remains the method of choice for most prescribers; however, the decision to provide nutrition via the enteral route comes with the added concern of bronchopulmonary aspiration as a complication. The majority of the literature and research on enteral feeding is out of date and focuses primarily on ways to identify aspiration, rather then preventing it. Although much of this research and literature is not current, many valid and useful recommendations have been made that can be applied to current practice. These recommendations are synthesized in this article in an effort to improve the quality and safety of administration of enteral nutrition to critically ill patients. However, this compiled information is limited to the current resources. More research should be done to decrease the risk of aspiration in this delicate population.