Measurement of the intestinal permeability in chronic kidney disease

Table 1 Characteristics of the used methods assessing the intestinal permeability

Marker for intestinal permeability	Mechanism of action	Advantages	Disadvantages	Influence renal function	Part of the intestine evaluated	Ref.
D-lactate (plasma)	Produced by bacteria in the colon. Present in human blood at very low concentrations as a product of methylglyoxal metabolism. In case of increased intestinal permeability levels will rise due to increased translocation across the intestinal mucosa	Non-invasive Low levels in healthy subjects, high specificity Mainly large intestine; thus focusing on part of the bowel with the highest bacterial load	Possibly increased fermentation of undigested carbohydrates to D-lactate in case of bacterial overgrowth	Influenced by renal function to some extent	Mainly large intestine	[18,19]
Sugar absorption test (urine)	Method based on calculating the urinary excretion of orally administered test substance that reflects the non-mediated diffusion of that probe across the intestinal barrier. Most commonly used combination of sugars is a oligosaccharide or disaccharide (lactulose, cellobiose) combined with a monosaccharide (mannitol). By adding sucralose to the test, which is not degraded by the bacteria of the colon, the colonic permeability can be assessed	Non-invasive Different sugar combinations can assess different parts of the gastrointestinal tract	Relative impractical in use Results could be influenced by decreased bowel motility 32 Used according to different protocols and different combinations of sugars which makes the comparison of studies difficult Relative large inter- and intra-individual variety	Influenced by renal function. Corrected by using the ratio of administered sugars. It is however not clarified whether this correction is sufficient due to possible different renal clearance of the administered sugars	Small intestine, large intestine (only if sucralose, is added)	[14-17]
5¹Cr-EDTA (urine)	Method based on calculating the urinary excretion of orally administered test substance that reflects the non-mediated diffusion of that probe across the intestinal barrier	Not degraded by bacteria in the colon, useful marker for both the small and large intestinal permeability	Radioactivity Not commonly used nowadays due to radioactivity	Influenced by renal function. Corrected in included studies: 24-h Cr-EDTA excretion = 100% of the total oral dose excreted in the urine in 24 h/creatinine	Both small and large intestine	[20-23]
Endotoxin level (blood), LPS (plasma)	Indirect measurement of translocation of bacterial products	High specificity	Not eligible to use among patients with inflammation in the GI tract	Unlikely to be influenced by renal function	Both small and large intestine	[18,25,26]
Bacterial derived DNA (16S rRNA PCR) (blood)	Direct measurement of bacterial products in blood	Optimal tool for detection and identification of bacterial isolates	Not eligible to use among patients with inflammation in the GI tract	Unlikely to be influenced by renal function	Both small and large intestine	[18,19,24]
Polyethylene glycols (PEG) (urine)	Method based on calculating the urinary excretion of orally administered test substance that reflects the non-mediated diffusion of that probe across the intestinal barrier. It is hypothesized that, as saccharides in sugar absorption test, molecular PEG will only cross the intestinal mucosa to the circulation in case of barrier integrity loss. Increased urinary levels of large PEGs therefore reflect an increased intestinal permeability	Biologically inert and not degraded by bacteria, thus providing information of the whole intestinal permeability	High inter- and intra-individual variations have been reported, even in healthy controls[34]	Influenced by renal function	Both small and large intestine	[28]

AVF: Arteriovenous fistula; CAPD: Continuous ambulatory peritoneal dialysis; CKD: Chronic kidney disease; CVC: Central venous catheter; ESRD: End stage renal disease; HD: Hemodialysis; IgAN: IgA nephropathy; IgA GN: IgA glomerulonephritis; IC-GN: Immunocomplex glomerulonephritis; INS: Idiopathic nephrotic syndrome; Li: Lithium; LPS: Lipopolysaccharide; PD: Peritoneal dialysis; PEG: Polyethylene glycols; TER: Trans epithelial electrical resistance.

Table 2 Results considering the intestinal permeability published in the included studies

Ref.	Population	Study size	Marker used to assess intestinal permeability (values provided as mean ± SD)	Results	Part of the intestine evaluated
Shi et al[18]	ESRD (both HD and non-HD) vs healthy controls ESRD group further divided patients with bacterial DNA and without bacterial DNA in their blood samples	ESRD n = 52 (HD n = 22, ND n = 30) Controls n = 10	D-lactate (plasma) Endotoxins (blood) Bacterial DNA (blood)	D-lactate plasma levels higher: ESRD HD vs controls P = 0.039 ESRD non-HD vs controls P = 0.044 HD vs non-HD P > 0.05 ESRD with bacterial DNA vs ESRD without bacterial DNA P < 0.05 ESRD HD with bacterial DNA vs ESRD non-HD with bacterial DNA P > 0.05 Endotoxin significantly higher: ESRD HD vs controls P < 0.05 ESRD non-HD vs controls P < 0.05 ESRD HD 0.95 ± 0.12 EU/mL ESRD non-HD 0.70 ± 0.15 EU/mL Controls 0.17 ± 0.10 EU/mL Presence of bacterial 16S rDNA: ESRD HD 6/22 patients ESRD non-HD 6/30 patients Controls: 0/10 patients	Large intestine Mostly large intestine Mostly large intestine
Wang et al[19]	ESRD patients (non-HD) vs healthy controls ESRD group further divided patients with bacterial DNA and without bacterial DNA in their blood samples	ESRD n = 30 Controls n = 10	D-lactate (plasma) Bacterial 16s rDNA (blood)	Plasma D-lactate higher: ESRD with bacterial DNA vs ESRD without bacterial DNA P = 0.0233 ESRD with bacterial DNA vs controls P =0.067 ESRD with bacterial DNA: 13.53 ± 1.47 μg/mL ESRD without bacterial DNA: 5.71 ± 2.28 μg/mL Controls: 4.82 ± 0.93 μg/mL D-lactate plasma levels both ESRD groups combined: 7.274 ± 2.16 μg/mL1 ESRD: 6/30 bacterial DNA in blood Controls: no bacterial DNA in blood	Large intestine
Bossola et al[24]	HD patients (AVF en CVC) vs healthy controls	HD n = 58 (AVF n = 44, CVC n = 14) Controls n = 30	Bacterial 16S rDNA (blood)	HD patients: 12/58 bacterial DNA in blood (= 20.7%) Healthy controls: No bacterial DNA in blood AVF patients 5/44 (= 15.9%) CVC patients 5/14 (35.7) P = 0.22	Both small and large intestine
McIntyre et al[25]	HD patients, PD patients, CKD patients (stage 3-5) vs healthy controls	HD n = 120 PD n =25 CKD stage 3-5 n = 90 Controls n = 14	Endotoxin level (blood)	Significant higher endotoxin levels in HD vs PD P < 0.008 Dialysis patients (HD + PD) vs CKD P < 0.001 CKD vs controls P > 0.05 HD patients: 0.64 EU/mL PD patients: 0.56 EU/mL HD + PD patients: 0.62 ± 0.37 EU/mL CKD patients: 0.11 ± 0.68 EU/mL Controls: Not provided	Both small and large intestine
Feroze et al[26]	HD patients, follow up for 42 mo	HD n = 303	Endotoxin level (blood)	No significant association between elevated circulating endotoxin levels and mortality Mean endotoxin levels: 2.31 ± 3.10 EU/mL	Both small and large intestine
Zuckerman et al[20]	No control group CAPD patients vs healthy controls	CAPD patients n = 11 (5 with significant urine output) Controls n = 32	Cr-EDTA recovery (24 h urine + dialysate)	Significant less recovery of Cr-EDTA: CAPD vs controls P < 0.0005	Both small and large intestine
Szeto et al[27]	New PD patients vs IgAN patients (mild to moderate CKD) and healthy controls Mean creatinine level IgAN group: 151.2 ± 116.68 μmol/L	PD n = 30 IgAN n = 10 Controls n = 6	LPS (plasma)	CAPD patients: Mean 0.57% (0%-1.24%) Healthy controls: Mean 1.99% (0.59-3.48) Significantly higher LPS levels PD vs IgAN P < 0.0001 PD vs controls P < 0.0001 IgAN vs controls: Not provided PD: 0.44 ± 0.18 EU/mL IgAN: 0.0035 ± 0.009 EU/mL Controls: 0.013 ± 0.007 EU/mL	Both small and large intestine
Cobden et al[17]	CKD patients vs healthy controls CKD group: Serum creatinine levels ranging from 140 to 1050 μmol/L	CKD n = 6 Controls n = 55	Cellobiose and mannitol recovery (urine)	No significant difference recovery cellobiose and mannitol CKD vs controls P > 0.05 Cellobiose: CKD: Recovery range 0.09%-0.44% Controls: Not provided Mannitol: CKD: Recovery range 12.8%-52.3% Controls: Not provided	Small intestine
Magnusson et al[28]	Asymptomatic uremic CKD vs healthy volunteers Mean serum creatinine level IgAN group: 503 μmol/L, range 274-796 μmol/L	CKD n = 9 Controls n = 6	PEGs (urine) Computer model was used to predict the PEG recovery adjusted for eGFR	Significant lower urinary recovery of PEG’s CKD vs controls P < 0.05 More heavy PEG’s were harvest in urine CKD patients: indicating that intestinal permeability in CKD patients is more increased for larger molecules	Both small and large intestine
Kovacs et al[21] and Kovacs et al[23]	IgAN patients (both uremic and non-uremic) vs healthy controls	1989: IgAN patients n = 29: (uremic n = 24 non-uremic n = 5) Controls n = 20	Cr-EDTA recovery (urine)	Significantly higher Cr-EDTA recovery in IgAN patients vs controls P < 0.005, both in 1989 and in follow up after 5 yr	Both small and large intestine
These two studies published results measured in the same patient group. Provided data by the two articles are summarized	Both in 1989 and after a four year follow up in 1994 No mean serum creatinine levels of total IgAN group provided	1996: IgAN patients n = 21 No controls Follow up patients further divided an analyzed in two groups; increased intestinal permeability group vs non-increased intestinal permeability		IgAN (1989): 3.86% ± 0.29% IgAN (1994): 4.57% ± 0.63% Controls: 2.72% ± 0.23% Only in the increased permeability group significant decrease in eGFR (Baseline eGFR 84.4 ± 6.1 mL/min vs 65.4 ± 8.6 mL/min after four years, P < 0.01)
Rostoker et al[22]	Patients with Primary IgA glomerulonefritis and permanent proteinuria (IgA GN), INS IC-GN: Membranous + membranoproliferative) vs healthy controls and alcohol abusers (positive controls)	IgA GN n = 30 INS n = 25 IC-GN n = 20 Controls n = 20 Alcohol abusers n = 5	Cr-EDTA recovery (urine)	Significantly higher Cr-EDTA recovery in IgA GN vs controls P < 0.005 INS vs controls P < 0.005 IC-GN vs controls P < 0.005 Alcohol abusers vs controls P < 0.005 IgA GN: Median 3.25% (0.7-17.8) INS: Median 3.71% (0.82-10) IC-GN: 3.40% (0.30-16) Alcohol abusers: 4.9% (7-30) Controls: 2% (0.4-3.9)	Both small and large intestine
Layward et al[15]	Histologically proven IgAN with proteinuria and microscopic hematuria vs healthy No mean serum creatinine levels provided controls	IgAN patients n = 18 Controls n = 17	Cellobiose/mannitol ratio (urine)	No significant difference cellobiose/mannitol ratio IgA NP patients vs controls P = 0.42 IgA NP: 0.015 ± 0.008 Controls: 0.022 ± 0.015	Small intestine
De Maar et al[14]	Renal transplant patients assessed before transplantation and in the follow up during active CMV infection and CMV negative controls	Permeability assessed before transplantation n = 104 Permeability assessed during active infection n = 12 (primary infections: 5, secondary infections: 7) Controls (CMV-): n = 9	Lactulose/mannitol ratio (urine)	L/M ratio increased during active CMV infection in 9/12 patients P < 0.01 L/M ratio active CMV infection compared to patients without CMV P < 0.01	Small intestine Small intestine
Ponda et al[16]	CKD stadium III patients vs healthy controls CKD patients: mean eGFR: 51 mL/min per 1.73² All patients and controls had a vitamin D deficiency	CKD n = 5 Controls n = 4	Endotoxin activity; expressed as fraction of the maximum response to endotoxin (plasma) Lactulose/mannitol ratio (urine)	No significant difference endotoxin activity CKD vs controls P > 0.05 CKD: 0.23 ± 0.15 Healthy controls: 0.20 ± 0.13 L/M ratio increased with D3 therapy P = 0.02 (reflecting an increase in permeability) L/M ratio not assessed in control group

¹Value not provided in article. Calculated as followed: sqrt((6-1)*1.47^2+(24-1)*2.28^2)/(6-1+24-1). Sp = √(n1 – 1) x S1² + (N2 - 1) x S2²/(n1 - 1 + n2 - 1).

AVF: Arteriovenous fistula; CAPD: Continuous ambulatory peritoneal dialysis; CKD: Chronic kidney disease; CVC: Central venous catheter; ESRD: End stage renal disease; HD: Hemodialysis; IgAN: IgA nephropathy; IgA GN: IgA glomerulonephritis; IC-GN: Immunocomplex glomerulonephritis; INS: Idiopathic nephrotic syndrome; Li: Lithium; LPS: Lipopolysaccharide; PD: Peritoneal dialysis; PEG: Polyethylene glycols; TER: Trans epithelial electrical resistance.