Glucuronides Hydrolysis by Intestinal Microbial β-Glucuronidases (GUS) Is Affected by Sampling, Enzyme Preparation, Buffer pH, and Species

Detection of β-D-glucuronidase activity in environmental samples using 4-fluorophenyl β-D-glucuronide and 19F NMR

Common methods for establishing the presence of enteric bacteria polluting water supplies, or in other samples, rely on detecting the hydrolysis of model glucuronide substrates by glucuronidases to release a phenolic product quantifiable by absorbance or fluorescence. Substrates include the β-D-glucuronides of p-nitrophenol, and umbelliferyl or quercetin derivatives. One limitation is that it may be difficult or impossible to quantify the released phenolic moiety in samples that are strongly coloured or, that contain fluorescent compounds. Exploiting the sensitivity available from the 19F nucleus to changes in chemical environment which can be detected by 19F NMR spectroscopy, and the almost complete absence of 19F from naturally-occurring samples containing organic matter, which provides background-free signals, we propose a model substrate; 4-fluorophenyl β-D-glucuronide (4FP-glucuronide). The 19F NMR chemical shift position of 4FP-glucuronide changes from -121.0 ppm upon hydrolysis to release 4-fluorophenol, at -124.9 ppm (at pH 6.8), enabling detection of β-glucuronidase activity. We illustrate the use of this substrate with environmental samples from forest soil, standing water, and mud from cattle pasture. Each of these would challenge conventional methods, owing to their opacity or the presence of coloured organic material. The technique enables detection of glucuronidases, a widely-used proxy for enteric bacteria, extending the scope of testing beyond water to include environmental and other challenging samples.

A Metformin-Ferulic Acid Salt with Improved Biopharmaceutical Parameters

Though ferulic acid presents great hypoglycemic potential, it possesses limited aqueous solubility, and low oral bioavailability. When associated with metformin, the first-choice drug in Type 2 diabetes treatment, FA demonstrates synergistic hypoglycemic effects, however, it also causes certain undesirable dose-related effects. This study aimed to develop a new ferulic acid - metformin multicomponent system, and incorporate it into a solid dosage form with improved biopharmaceutical parameters. A novel metformin: ferulate (1:1) salt (MFS) was produced, which was properly characterized using differing analytical techniques, including single crystal analysis. Also during the course of the study, a new polymorph of the metformin free base was observed. The MFS was obtained using solvent evaporation methods, which achieved high yields in reproducible process, as well as a 740-fold increase in ferulic acid aqueous solubility. The MFS tablets developed met quality control requirements for this dosage form, as well as revealing excellent performance in vitro dissolution tests, presenting dissolution efficiency values of 95.4 ± 0.5%. Additionally, physicochemical instability was not observed in a study at 40 °C for 3 months for both MFS powder and its tablet form. The MFS product developed is a promising candidate for further Type 2 diabetes clinical study.

The role of gut microbial β-glucuronidase in drug disposition and development

Gut microbial β-glucuronidase (gmGUS) is involved in the disposition of many endogenous and exogenous compounds. Preclinical studies have shown that inhibiting gmGUS activity affects drug disposition, resulting in reduced toxicity in the gastrointestinal tract (GIT) and enhanced systemic efficacy. Additionally, manipulating gmGUS activity is expected to be effective in preventing/treating local or systemic diseases. Although results from animal studies are promising, challenges remain in developing drugs by targeting gmGUS. Here, we review the role of gmGUS in host health under physiological and pathological conditions, the impact of gmGUS on the disposition of phenolic compounds, models used to study gmGUS activity, and the perspectives and challenges in developing drugs by targeting gmGUS.

Inhibitory Activity of 4-O-Benzoyl-3'-O-(OMethylsinapoyl) Sucrose from Polygala tenuifolia on Escherichia coliβ-Glucuronidase

Bacterial β-glucuronidase in the intestine is involved in the conversion of 7-ethyl-10- hydroxycamptochecin glucuronide (derived from irinotecan) to 7-ethyl-10-hydroxycamptothecin, which causes intestinal bleeding and diarrhea (side effects of anti-cancer drugs). Twelve compounds (1-12) from Polygala tenuifolia were evaluated in terms of β-glucuronidase inhibition in vitro. 4-O-Benzoyl-3'-O-(O-methylsinapoyl) sucrose (C3) was highly inhibitory at low concentrations. C3 (an uncompetitive inhibitor) exhibited a k_i value of 13.4 μM; inhibitory activity increased as the substrate concentration rose. Molecular simulation revealed that C3 bound principally to the Gln158-Tyr160 enzyme loop. Thus, C3 will serve as a lead compound for development of new β- glucuronidase inhibitors.