Zonulin, Iron Status, and Anemia in Kidney Transplant Recipients: Are They Related?

Iron status and anemia control are related to peritoneal membrane properties in peritoneally dialyzed patients

Background

Characteristics of peritoneal membrane is unique and individually different in peritoneal dialysis patients. Relationship between specific nature of peritoneal transport, anemia and inflammation has not yet been extensively studied. We attempted to outline the complex interplay of several biomarkers of iron status and their association with peritoneal transport, degree of inflammation and residual renal function.

Methods

A total of 58 patients treated with peritoneal dialysis either CAPD or APD for at least 3 months were enrolled in this study. Full blood count, traditional markers of iron status (transferrin saturation-TSAT and ferritin), serum erythroferrone-ERFE, soluble transferrin receptor (sTfR), hepcidin, zonulin, growth differentiation factor -15 (GDF15), IL-16, hsCRP and hypoxia-inducible factor-α (HIF-1-α; in serum and dialysate) were measured using commercially available tests. We also performed Peritoneal Equilibrium Test and assessed GFR level.

Results

Hb levels above 10 g/dL was found in 74% of patients. Hb levels positively correlated with residual renal function and nutritional status. Adequate iron status was diagnosed in 69% of subjects, only in 9% of patients, criteria for absolute iron deficiency were met. Serum ERFE correlated inversely with hepcidin levels but was not associated with erythropoietin stimulating agent dose. Peritoneal transport had strong correlation with dialysate sTfR (p < 0.05), dialysate hepcidin (p < 0.05), dialysate GDF15 (p < 0.01) and dialysate zonulin (p < 0.001) levels, as well as serum IL6 (p = 0.03), serum hs-CRP (p = 0.04) and dialysate hs-CRP (p = 0.04).

Conclusion

Residual kidney function contributes considerably to better control of anemia. Various degree of inflammation is inherent to PD patients. Additionally, fast-average peritoneal transport is associated with greater degree of inflammation and higher concentration of markers of iron status, GDF15 and zonulin in dialysate. This finding may indicate more effective clearance of higher-range middle molecules in fast-average transporters. The role of ERFE as a marker of erythropoiesis in PD patients requires further investigation.

Zonulin levels in complicated pregnancy: a systematic review and meta-analysis

Zonulin is a novel biomarker of intestinal permeability. The existing data suggest that upregulation of zonulin might be linked to systemic inflammation and pregnancy complications. A systematic search was performed in medical electronic databases to identify eligible studies that reported circulating zonulin levels in complicated pregnancies compared to controls. Eight studies with 1196 serum samples of pregnant women were included in the systematic review. Meta-analysis on four studies revealed a significant increase in serum zonulin in women with Gestational diabetes mellitus (GDM) compared to healthy controls (Cohen's d = 2.06; 95% Confidence Interval (CI): 0.15, 3.98). By pooling four studies that investigated zonulin levels in Hypertensive disorders of pregnancy (HDP), higher zonulin concentrations were found in cases, while the difference was not significant (Cohen's d = 0.86; 95% CI: -0.04, 1.75). Current evidence suggests that higher levels of zonulin during pregnancy seem to be associated with inflammation-related complications, including GDM and HDP.Impact StatementWhat is already known on this subject? Increased zonulin levels are considered as a marker of intestinal hyper-permeability. Upregulation of zonulin and concurrent systemic inflammation, are known to be associated with some pregnancy complications.What do the results of this study add? We performed a meta-analysis to evaluate changes in serum zonulin levels in pregnancies complicated with Gestational diabetes mellitus (GDM), Hypertensive disorders of pregnancy (HDP), and Intrahepatic cholestasis of pregnancy (ICP). According to our results, zonulin levels were significantly higher in complicated pregnancies than in normal pregnancies, particularly for GDM.What are the implications of these findings for clinical practice and/or further research? Our findings revealed a probable association between increased zonulin levels and inflammation-related complications during pregnancy. Moreover, zonulin could serve as a reliable diagnostic clinical biomarker to identify (or predict) complications during pregnancy. Further studies are needed to examine the clinical accuracy of zonulin for detecting pregnancy-related complications.

Could serum zonulin be an intestinal permeability marker in diabetes kidney disease?

Zonulin is a protein associated with the tight junction complex opening at the intestinal epithelium, previously linked to obesity, cardiovascular diseases, type 2 diabetes mellitus (T2DM) and chronic kidney disease (CKD). However, its role in CKD has not been totally elucidated. This study aimed to evaluate zonulin levels in subjects with diabetic kidney disease (DKD). This case-control study included two cases groups: 1) Advanced DKD cases: T2DM patients with estimated glomerular filtration rate (eGFR) <60ml/min/1.73m²; 2) Albuminuric T2DM cases: diabetic patients with urinary albumin excretion (UAE) >30mg/g creatinine, but with eGFR>60ml/min/1.73m². Two control groups were also included: 1) T2DM controls: patients with T2DM without impaired kidney function; 2) Non-T2DM controls: subjects without T2DM and normal renal function. Serum levels of zonulin were measured by ELISA. Eighty-six individuals were included. Zonulin levels was different among study groups (P = 0.003). T2DM controls presented higher zonulin levels than non-T2DM controls [(131.35 (83.0–170.5) vs. 87.25 (54.7–111.8), P = 0.018] and advanced DKD cases [63.72 (45.03–106.0); P = 0.007]. Zonulin showed a positive correlation with eGFR (r = 0.222; P = 0.040), total cholesterol (r = 0.299; P = 0.034), LDL (r = 0.258; P = 0.021), and negative with albuminuria (r = -0.243; P = 0.024) and body fat (r = -0.271; P = 0.014). In the multivariate logistic regression analyses, zonulin levels were independently associated to renal outcomes [OR 0.99 (0.98–0.99, P = 0.012)] after 5-year inclusion. In conclusion, increased zonulin levels in patients with TD2M without renal disease suggest an impaired intestinal permeability. Moreover, its association with renal outcomes could indicate its use as a disease monitoring marker. However, the mechanisms behind this association should be better understood.

Advances in the role and mechanism of zonulin pathway in kidney diseases

The intestinal barrier is the first line of defense against foreign antigens. Tight junctions play an important role in maintaining the function of the intestinal wall. Zonulin is the only physiological protein discovered in recent years that can reversibly regulate tight junctions in human body. It changes the permeability of intestinal epithelial cells by regulating the state of tight junctions. Increased intestinal permeability can lead to abnormal activation of intestinal mucosal immune and bacterial translocation, then inducing systemic inflammation. It has already been reported that zonulin plays an important pathogenic role in a variety of diseases by regulating tight junctions leading to an abnormal increase of intestinal permeability. However, the research on the pathogenic role and mechanism of zonulin pathway in kidney disease is still in its infancy. Therefore, we reviewed the progress on pathophysiological characteristics of zonulin as well as the pathogenesis of zonulin in kidney disease in this paper.

Zonulin as marker of pregnancy induced hypertension: a case control study

Background

Zonulin has been implicated in many metabolic disorders including hypertension and obesity. However, there is insufficient information about the involvement of zonulin in pregnancy induced hypertension (PIH) which comprises preeclampsia (PE) and gestational hypertension (GH). This study was therefore aimed at finding the level of this biochemical marker of regulation of tight junctions among women with PIH.

Methods

A total of 88 women with PIH and 60 age and body mass index (BMI) matched healthy pregnant women controls were enrolled. Blood pressure at 11–13 weeks and after 20 weeks of gestation, body mass index (BMI) in addition to serum Zonulin levels and lipid profile were compared between the groups. Student’s t-test was used for comparisons of the mean between the two groups. Correlation analyses were performed using Pearson’s correlation and binary logistic regression was used to evaluate the factors associated with PIH.

Results

Zonulin level was significantly higher in the participants with PIH as compared to the normal pregnant controls 56.81 ± 7.72 ng/ml vs 40.4 ± 8.60 ng/ml p < 0.0001 and had strong positive correlation with PIH (OR = 1.805; CI1.139–1.275; p < 0.0001). However, the association between first trimester lipids and PIH was weak.

Conclusion

The results showed a strong positive correlation between zonulin and PIH, thus changes in intestinal permeability occur in early stages of pregnancy and may be involved in the pathogenesis of PIH.

Effect of prebiotic (fructooligosaccharide) on uremic toxins of chronic kidney disease patients: a randomized controlled trial

BACKGROUND

Microbial-derived uremic toxins, p-cresyl sulfate (PCS), indoxyl sulfate (IS) and indole 3-acetic acid (IAA), have been associated with the burden of chronic kidney disease (CKD). Prebiotics have emerged as an alternative to modulate the gut environment and to attenuate toxin production. This trial aims to investigate the effect of a prebiotic fructooligosaccharide (FOS) on uremic toxins of non-dialysis-dependent CKD (NDD-CKD) patients.

METHODS

A double-blind, placebo-controlled, randomized trial was conducted for 3 months. In all, 50 nondiabetic NDD-CKD patients [estimated glomerular filtration rate (eGFR) <45 mL/min/1.73 m2], aged 18-80 years, were allocated to prebiotic (FOS, 12 g/day) or placebo (maltodextrin, 12 g/day) groups. Primary outcomes were changes in serum (total and free) and urinary (total) PCS. Secondary outcomes included changes in IS, IAA, serum markers of intestinal permeability (zonulin), gut-trophic factors (epidermal growth factor and glucagon-like peptide-2), eGFR, inflammation (high sensitive c-reactive protein and interleukin-6), homeostatic model assessment-insulin resistance, lipid profile and gastrointestinal symptoms.

RESULTS

From 50 participants (54% men, 57.3 ± 14.6 years and eGFR 21.4 ± 7.6 mL/min/1.73 m2), 46 completed the follow-up. No changes in dietary intake or gastrointestinal symptoms were observed. There was a trend in the difference of serum total ΔPCS (treatment effect adjusted for baseline levels: -12.4 mg/L; 95% confidence interval (-5.6 to 0.9 mg/L; P = 0.07) and serum-free Δ%PCS [intervention -8.6 (-41.5 to 13.9%) versus placebo 3.5 (-28.8 to 85.5%); P = 0.07] between the groups. The trend in the difference of serum total ΔPCS was independent of eGFR and dietary protein:fiber ratio intake. No difference was found in urinary PCS. Aside from the decreased high-density lipoprotein cholesterol in the intervention, no differences were observed in the change of IS, IAA or other secondary outcome between the groups.

CONCLUSIONS

Our result suggests the potential of FOS in reducing serum total and free PCS in nondiabetic NDD-CKD patients.

New Biomarkers of Ferric Management in Multiple Myeloma and Kidney Disease-Associated Anemia

Multiple myeloma (MM) is a malignancy of clonal plasma cells accounting for approximately 10% of haematological malignancies. MM mainly affects older patients, more often males and is more frequently seen in African Americans. The most frequent manifestations of MM are anaemia, osteolytic bone lesions, kidney failure and hypercalcemia. The anaemia develops secondary to suppression of erythropoiesis by cytokine networks, similarly to the mechanism of anaemia of chronic disease. The concomitant presence of kidney failure, especially chronic kidney disease (CKD) and MM per se, leading to anaemia of chronic disease (ACD) in combination, provoked us to pose the question about their reciprocal dependence and relationship with specific biomarkers; namely, soluble transferrin receptor (sTfR), growth differentiation factor 15 (GDF15), hepcidin 25 and zonulin. One or more of these are new biomarkers of ferric management may be utilized in the near future as prognostic predictors for patients with MM and kidney failure.

Risk factors associated with intestinal permeability in an adult population: A systematic review

BACKGROUND

Increased intestinal permeability (IP) involves the loss of integrity between the cells of the small intestine. IP has been suggested to contribute to the pathogenesis and exacerbation of many chronic diseases. Many potential risk factors for IP are proposed in contemporary literature. The purpose of this review is to identify the most significant risk factors for IP.

METHODS

A systematic search of literature published up until September 2018 in the PubMed, EMBASE, CINAHL, and Scopus databases was conducted.

RESULTS

A total of 47 articles met the inclusion criteria. Elevated levels of proinflammatory markers, dyslipidaemia, hyperglycaemia, insulin resistance, anthropometric measurements resembling obesity, advanced disease severity, comorbidity and the consumption of a Western-style diet were identified as the strongest risk factors for altered intestinal integrity. The risk of IP increases when coupled with a multiple disease state or combined with other environmental risk factors. Furthermore, many of the identified risk factors such as anthropometric measurements and biomarkers were external from intestinal health and rather resembled a metabolic-like condition.

CONCLUSIONS

This review identified a number of potential risk factors for IP, ranging from biomarkers to anthropometric measurements, demographics, dietary intake and chronic diseases. These risk factors warrant the attention of clinicians and other healthcare providers to aid the identification of potential patients at risk of altered IP. Further research needs to examine whether the identified risk factors are homogeneous with the diagnosis of IP or whether the disease state influences the association.

Zonulin, inflammation and iron status in patients with early stages of chronic kidney disease

Background/aims

Zonulin is the only known regulator of intestinal permeability. It is also considered as a potential inflammatory marker in several conditions such as diabetes and inflammatory bowel syndrome. The aim of the study was to investigate zonulin levels in patients with early stages of CKD and its possible correlation with inflammation, anemia and iron status parameters.

Methods

Eighty-eight patients with early stages of CKD and 23 healthy volunteers were enrolled in the study. Zonulin, hepcidin-25, soluble transferrin receptor, interleukin-6 and high-sensitivity C-reactive protein were measured using commercially available assays.

Results

Zonulin was significantly lower among patients with CKD in comparison with healthy volunteers. There were no statistically significant differences in zonulin concentration between patients with and without inflammation. Zonulin was significantly correlated with hepcidin only in patients with inflammation. Zonulin was neither related to iron nor related to ferritin.

Conclusions

Zonulin cannot be considered as an inflammatory marker in CKD. It does not play a role in the disturbances of iron metabolism in CKD. Its physiological role remains to be elucidated.

Higher Levels of Serum Zonulin May Rather Be Associated with Increased Risk of Obesity and Hyperlipidemia, Than with Gastrointestinal Symptoms or Disease Manifestations

Zonulin is considered a biomarker of increased intestinal permeability, and elevated levels have been found in celiac disease. The primary aim of this study was to examine the association between serum zonulin levels and gastrointestinal (GI) symptoms, and secondarily, between zonulin levels and anthropometric and metabolic factors. The offspring (n = 363) of the participants of the Malmö Diet and Cancer cardiovascular cohort (MDC-CV) were invited to an anthropometric and clinical examination, where fasting plasma glucose levels were measured. Questionnaires about lifestyle factors and medical history were completed along with the Visual Analog Scale for Irritable Bowel Syndrome (VAS-IBS). Zonulin levels were measured in serum by ELISA. Neither GI symptoms nor GI diseases had any influence on zonulin levels. Higher zonulin levels were associated with higher waist circumference (p = 0.003), diastolic blood pressure (p = 0.003), and glucose levels (p = 0.036). Higher zonulin levels were associated with increased risk of overweight (p < 0.001), obesity (p = 0.047), and hyperlipidemia (p = 0.048). We cannot detect altered zonulin levels among individuals reporting GI symptoms or GI diseases, but higher zonulin levels are associated with higher waist circumference, diastolic blood pressure, fasting glucose, and increased risk of metabolic diseases.

Calprotectin in serum and zonulin in serum and feces are elevated after introduction of a diet with lower carbohydrate content and higher fiber, fat and protein contents

Calprotectin is a marker of inflammation and zonulin is a marker of intestinal permeability. Diets with lower carbohydrate content and higher contents of fat, fiber and protein, e.g., Okinawan-based diet, are considered to reduce inflammation and intestinal permeability. The aim of the present study was to evaluate calprotectin and zonulin levels in serum and feces after intervention with an Okinawan-based Nordic diet. Thirty patients (17 women) with type 2 diabetes, mean age 57.5±8.2 years, BMI 29.9±4.1 kg/m², were served the diet during 12 weeks, and were followed for another 16 weeks. Anthropometric and metabolic parameters were registered. Fasting levels of calprotectin and zonulin in serum and feces, and hormones in plasma, were measured by Luminex or ELISA before study start and after 12 and 28 weeks. Calprotectin in serum tended to be increased (P=0.074) after 12 weeks. Zonulin in serum and feces were elevated after 12 weeks (P=0.019 vs. P<0.001), and remained elevated in serum after 28 weeks (P=0.014). In contrast to baseline, there was a correlation between calprotectin and zonulin in serum and feces after dietary intervention (P=0.025 vs. P=0.079). Energy percentage of protein in breakfast correlated with serum calprotectin (P=0.008) and tended to correlate with serum zonulin (P=0.059). Calprotectin in serum tended to be elevated, and zonulin in serum and feces are elevated after introduction of an Okinawan-based Nordic diet. These biomarkers correlate with energy percentage of protein.