An In Vivo Method for Evaluating the Gut-Blood Barrier and Liver Metabolism of Microbiota Products

Summary

The access of nutrients, microbiota metabolites and medicines to the circulation is controlled by the gut-blood barrier (GBB). We describe a direct method for measuring the GBB permeability in vivo, which, in contrast to commonly used indirect methods, is virtually not affected by liver and kidney functions.

Abstract

The gut-blood barrier (GBB) controls the passage of nutrients, bacterial metabolites and drugs from intestinal lumen to the bloodstream. The GBB integrity is disturbed in gastrointestinal, cardiovascular and metabolic diseases, which may result in easier access of biologically active compounds, such as gut bacterial metabolites, to the bloodstream. Thus, the permeability of the GBB may be a marker of both intestinal and extraintestinal diseases. Furthermore, the increased penetration of bacterial metabolites may affect the functioning of the entire organism.

Commonly used methods for studying the GBB permeability are performed ex vivo. The accuracy of those methods is limited, because the functioning of the GBB depends on intestinal blood flow. On the other hand, commonly used in vivo methods may be biased by liver and kidney performance, as those methods are based on evaluation of urine or/and peripheral blood concentrations of exogenous markers. Here, we present a direct measurement of GBB permeability in rats using an in vivo method based on portal blood sampling, which preserves intestinal blood flow and is virtually not affected by the liver and kidney function.

Polyurethane catheters are inserted into the portal vein and inferior vena cava just above the hepatic veins confluence. Blood is sampled at baseline and after administration of a selected marker into a desired part of the gastrointestinal tract. Here, we present several applications of the method including (1) evaluation of the colon permeability to TMA, a gut bacterial metabolite, (2) evaluation of liver clearance of TMA, and (3) evaluation of a gut-portal blood-liver-peripheral blood pathway of gut bacteria-derived short-chain fatty acids. Furthermore, the protocol may also be used for tracking intestinal absorption and liver metabolism of drugs or for measurements of portal blood pressure.

Introduction

The gut-blood barrier (GBB), also known as the intestinal barrier, is a complex multilayer system that separates the gut lumen from the bloodstream in order to limit the passage of harmful compounds while allowing the absorption of nutrients¹. It consists of the three main layers: the mucus layer, epithelium and lamina propria.

Numerous factors may affect the GBB integrity and function². It has been shown that GBB is disturbed in both gastrointestinal and extraintestinal diseases, including cardiovascular and metabolic diseases³, which may lead to an increased passage o....

Protocol

The experiments were performed on male Wistar Kyoto rats according to Directive 2010/63 EU on the protection of animals used for scientific purposes and were approved by the I Local Bioethical Committee in Warsaw.

1. Insertion of the Line for Intraintestinal Administration

NOTE: Here we propose intracolonic administration of a marker using a catheter. It may be modified by oral administration or gavage at various levels of the digestive tract e.g. stomach or duodenum. Remember to use disposable surgical clothing, including surgical gown, hood and gloves, and ensure to follow the safety pre....

Results

We have successfully measured the GBB permeability and liver clearance of TMA in rats. We have demonstrated that hypertensive rats have an increased colon permeability to TMA in comparison to normotensive rats (Figure 2)⁴. In another study we found that high salt intake does not affect the GBB permeability and liver clearance of TMA (Figure 3)¹⁴.

Discussion

The described direct, in vivo, method of measuring the GBB permeability maintains closetophysiological conditions in the gastrointestinal system (preserves the intestinal blood flow), and is virtually not influenced by liver and kidney function.

The critical step of this technique is the insertion of the portal catheter. This must be done gently and decisively at the same time. A mild, short bleeding may occur from the correctly performed puncture of the portal vein; however, it stops.......

Materials

Name	Company	Catalog Number	Comments
Needle OD: 9 mm	Becton Dickinson  S.A.	301300
Polyethylene catheter ID: 0.025", OD: 0.040"	Scientific Commodities, Inc.	#BB520-40
Polyethylene catheter ID: 0.012", OD: 0.025"	Scientific Commodities, Inc.	#BB520-25
C-Flex Tubing,Opaque White 1/50"ID x 1/12 " OD	Cole-Parmer Instrument Co.	06424-59
Pediatric Foley catheter (size 10F or 8F)	Sigmed	0000 80305
Surgical ligatures 3/0	Yavo Sp. Z o.o.	P48JE
Absorbable surgical sutures - Polyglactine 910 4/0	KRUUSE Polska Sp. Zo.o.	152336
Tissue glue - Loctite 454Cyanoacrylate Adhesive	Loctite	1370127
Povidone iodine	EGIS Pharmaceuticals PLC	4449 11
Heparin - Heparinium WZF	WZF Polfa S.A.	02BK0417	Dilute 10 times with physiological saline
Glycerin 86%	Laboratorium Farmaceutyczne Avena	5.90999E+12	Serves as a lubricant in colon catheterization
Xylocaine 2%	AstraZenca	9941342
Urethane	Sigma-Aldrich (Merck)	U2500-500G
Trimethylamine solution 45%	Sigma-Aldrich (Merck)	92262-1L
Syringes 2 mL	B.Braun Melsungen AG	4606027V
Saline 250 mL	Fraesenius Kabi Polska Sp. Z o.o.	15LL707WL
Surgical scissors, straight, length 115 mm, 4 1/2 "blunt ends	Braun	NS-010-115-PKM
Artery forceps type Micro-Adson bent, length 140 mm 5 1/2 "	Braun	KN-008-140-ZMK
Anatomic forceps, lenght 95 mm, 3 3/4" sharp 0.7x0.55	Braun	PO-001-007-ZMK
Micro Scissors type Vannas,  straight, lenght 85 mm, 3 3/8 " the length of the blades 6 mm	Braun	NO-010-085-PMK
Towel clamps type Backhouse, lenght 130 mm, 5 1/8"	Braun	HO-128-130-PMK
Needle holders, lenght 150 mm, 6" t=0.4 1/2	Braun	IM-927-150-PZMK
Delicate Scissors, lenght 110 mm , straight, 4 3/8” sharp	Braun	NO-052-110-PMK
Anatomic forceps, lenght 95 mm, 3 3/4" sharp	Braun	PO-022-001-PMK