Rapid small intestinal permeability assay based on riboflavin and lactulose detected by bis-boronic acid appended benzyl viologens

[Synthetic Studies on Developments for Bioactive New Leads of Oligovalent Symmetrical Molecules]

Interactions between carbohydrate-containing glycoproteins, proteoglycans, and glycolipids on the cell surface are important biological stages for the processes of bacterial or viral infection and tumor metastasis. Moreover, supramolecular interaction by macromolecules with two-fold (C₂) or three-fold (C₃) geometry is one of the common interactions in many important biological responses. To develop new multivalent symmetrical bioactive compounds or leads, we designed and synthesized several new molecules with these geometries and evaluated their bioactivities in an attempt to find new types of bioactive leads that may interfere with the sugar recognition process. We evaluated bioactivities including antibacterial, antiviral, and anticancer activities of targeted molecules in vitro using biological assay systems. Among the synthesized target derivatives examined, some bivalent symmetrical derivatives showed high levels of bioactivities. In this review, the author describes the results of synthesis of oligovalent symmetrical target compounds and some interesting guiding results of evaluation of their biological activities and structure-activity relationships.

Tests of intestinal mucosal hyperpermeability: Many diseases, many biomarkers and a bright future

The number of disorders now linked to increased intestinal mucosal permeability implies that a substantial percent of the population is affected. Drug interventions targeting reduced tight junctional permeability are being pursued. Although hyper-permeability in itself is not a clinically recognized disease entity, its relationship to disease processes has driven interest in measuring, and even monitoring mucosal permeability in vivo. Along with improved knowledge of gut barrier physiology, advances have been made in tests and biomarkers of barrier function. Drawing from our experiences in the past decade, considerations and challenges faced in assessing in vivo intestinal permeability are discussed herein, along with indications of what the future might hold.

Boronic acid recognition of non-interacting carbohydrates for biomedical applications: increasing fluorescence signals of minimally interacting aldoses and sucralose

To address carbohydrates that are commonly used in biomedical applications with low binding affinities for boronic acid based detection systems, two chemical modification methods were utilized to increase sensitivity. Modified carbohydrates were analyzed using a two component fluorescent probe based on boronic acid-appended viologen-HPTS (4,4'-o-BBV). Carbohydrates normally giving poor signals (fucose, l-rhamnose, xylose) were subjected to sodium borohydride (NaBH₄) reduction in ambient conditions for 1 h yielding the corresponding sugar alcohols from fucose, l-rhamnose and xylose in essentially quantitative yields. Compared to original aldoses, apparent binding affinities were increased 4-25-fold. The chlorinated sweetener and colon permeability marker sucralose (Splenda), otherwise undetectable by boronic acids, was dechlorinated to a detectable derivative by reactive oxygen and hydroxide intermediates by the Fenton reaction or by H₂O₂ and UV light. This method is specific to sucralose as other common sugars, such as sucrose, do not contain any carbon-chlorine bonds. Significant fluorescence response was obtained for chemically modified sucralose with the 4,4'-o-BBV-HPTS probe system. This proof of principle can be applied to biomedical applications, such as gut permeability, malabsorption, etc.

Parallel Changes in Harvey-Bradshaw Index, TNFα, and Intestinal Fatty Acid Binding Protein in Response to Infliximab in Crohn's Disease

Intestinal fatty acid binding protein (I-FABP) indicates barrier integrity.

AIMS

determine if I-FABP is elevated in active Crohn's disease (CD) and if I-FABP parallels anti-TNFα antibody (infliximab) induced lowering of TNFα and Harvey-Bradshaw Index (HBI) as potential indicator of mucosal healing. I-FABP distribution along human gut was determined. Serum from 10 CD patients collected during first three consecutive infliximab treatments with matched pretreatment and follow-up samples one week after each treatment and corresponding HBI data were analyzed. I-FABP reference interval was established from 31 healthy subjects with normal gut permeability. I-FABP and TNFα were measured by ELISA; CRP was measured by nephelometry. Healthy tissue was used for I-FABP immunohistochemistry. Pretreatment CD patient TNFα was 1.6-fold higher than in-house reference interval, while I-FABP was 2.5-fold higher, which lowered at follow-ups. Combining all 30 infusion/follow-up pairs also revealed changes in I-FABP. HBI followed this pattern; CRP declined gradually. I-FABP was expressed in epithelium of stomach, jejunum, ileum, and colon, with the highest expression in jejunum and ileum. I-FABP is elevated in active CD with a magnitude comparable to TNFα. Parallel infliximab effects on TNFα, HBI, and I-FABP were found. I-FABP may be useful as an intestine selective prognostic marker in CD.

Validation of SmartPill® wireless motility capsule for gastrointestinal transit time: Intra-subject variability, software accuracy and comparison with video capsule endoscopy

BACKGROUND

There is interest in ultimately combining endoscopy and motility assessments. Gastric emptying (GET), small bowel (SBTT), colon (CTT) and whole gut transit (WGTT) times are conveniently obtained by SmartPill^® wireless motility capsule (WMC) that records luminal pH, temperature and pressure. Reproducibility within same subjects and accuracy of software derived times (MotiliGI^® ) were investigated for diagnostic application. GET and SBTT were separately measured using video capsule endoscopy (VCE). The aim of this investigation was to assess same subject reproducibility of WMC, accuracy of software derived transit times and relate to Pillcam^® SB (small bowel) VCE motility data.

METHODS

Seventy three healthy adults ingested a 260 kcal mixed meal followed by WMC tests. Food intake was permitted after 6 hours. Regional transit data was obtained for GET, SBTT and CTT, the sum yielding WGTT. Nineteen subjects repeated WMC tests 2 or 4 weeks later; a separate 70 underwent VCE while fasted.

KEY RESULTS

Visually derived data from WMC yielded GET 3.46±0.27, SBTT 5.15±0.21, CTT 20.76±1.19 and WGTT 29.53±1.28 hours (mean±SEM). Pearson's correlation coefficients (r) against software derived results were: GET 0.78 (P<.0001), SBTT 0.28 (P<.05), CTT 0.96 (P<.0001), WGTT 0.99 (P<.0001). VCE yielded lower GET (0.71±0.08 hours) and SBTT (4.15±0.13 hours).

CONCLUSIONS AND INFERENCES

GET, SBTT, CTT and WGTT obtained by WMC are commensurate with literature values, including by other methods. Visually and software derived transit times have strongest correlations for CTT and WGTT. WMC yields longer GET and SBTT than VCE, perhaps due to meal related effects on motility.

Multiwell Assay for the Analysis of Sugar Gut Permeability Markers: Discrimination of Sugar Alcohols with a Fluorescent Probe Array Based on Boronic Acid Appended Viologens

With the aim of discerning between different sugar and sugar alcohols of biomedical relevance, such as gut permeability, arrays of 2-component probes were assembled with up to six boronic acid-appended viologens (BBVs): 4,4'-o-BBV, 3,3'-o-BBV, 3,4'-o-BBV, 4,4'-o,m-BBV, 4,7'-o-PBBV, and pBoB, each coupled to the fluorophore 8-hydroxypyrene, 1,3,6-trisulfonic acid trisodium salt (HPTS). These probes were screened for their ability to discriminate between lactulose, l-rhamnose, 3-O-methyl-d-glucose, and xylose. Binding studies of sugar alcohols mannitol, sorbitol, erythritol, adonitol, arabitol, galactitol, and xylitol revealed that diols containing threo-1,2-diol units have higher affinity for BBVs relative diols containing erythro-1,2 units. Those containing both threo-1,2- and 1,3-syn diol motifs showed high affinity for boronic acid binding. Fluorescence from the arrays were examined by principle component analysis (PCA) and linear discriminant analysis (LDA). Arrays with only three BBVs sufficed to discriminate between sugars (e.g., lactulose) and sugar alcohols (e.g., mannitol), establishing a differential probe. Compared with 4,4'-o-BBV, 2-fold reductions in lower limits of detection (LOD) and quantification (LOQ) were achieved for lactulose with 4,7-o-PBBV (LOD 41 μM, LOQ 72 μM). Using a combination of 4,4'-o-BBV, 4,7-o-PBBV, and pBoB, LDA statistically segregated lactulose/mannitol (L/M) ratios from 0.1 to 0.5, consistent with values encountered in small intestinal permeability tests. Another triad containing 3,3'-o-BBV, 4,4'-o-BBV, and 4,7-o-PBBV also discerned similar L/M ratios. This proof-of-concept demonstrates the potential for BBV arrays as an attractive alternate to HPLC to analyze mixtures of sugars and sugar alcohols in biomedical applications and sheds light on structural motifs that make this possible.

Gastrointestinal Safety Pharmacology in Drug Discovery and Development

Although the basic structure of the gastrointestinal tract (GIT) is similar across species, there are significant differences in the anatomy, physiology, and biochemistry between humans and laboratory animals, which should be taken into account when conducting a gastrointestinal (GI) assessment. Historically, the percentage of cases of drug attrition associated with GI-related adverse effects is small; however, this incidence has increased over the last few years. Drug-related GI effects are very diverse, usually functional in nature, and not limited to a single pharmacological class. The most common GI signs are nausea and vomiting, diarrhea, constipation, and gastric ulceration. Despite being generally not life-threatening, they can greatly affect patient compliance and quality of life. There is therefore a real need for improved and/or more extensive GI screening of candidate drugs in preclinical development, which may help to better predict clinical effects. Models to identify drug effects on GI function cover GI motility, nausea and emesis liability, secretory function (mainly gastric secretion), and absorption aspects. Both in vitro and in vivo assessments are described in this chapter. Drug-induced effects on GI function can be assessed in stand-alone safety pharmacology studies or as endpoints integrated into toxicology studies. In silico approaches are also being developed, such as the gut-on-a-chip model, but await further optimization and validation before routine use in drug development. GI injuries are still in their infancy with regard to biomarkers, probably due to their greater diversity. Nevertheless, several potential blood, stool, and breath biomarkers have been investigated. However, additional validation studies are necessary to assess the relevance of these biomarkers and their predictive value for GI injuries.