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

The role of circulating zonulin levels in patients with chronic kidney disease stages 3 to 5 not on dialysis

Zonulin (Zo) has recently been identified as a marker of intestinal permeability. It has previously been linked to type 2 diabetes mellitus, obesity, and cardiovascular disease; however, its role in chronic kidney disease (CKD) remains unclear. This study aimed to investigate the relationship between Zo and systemic inflammation (SI), endothelial dysfunction (ED), and renal function in CKD patients. One hundred sixty-three participants were enrolled in this study and divided into 2 groups (patient and control) according to the presence of CKD stage 3 to 5 not on dialysis. Circulating Zo levels have been investigated as markers of intestinal permeability. Furthermore, vascular cell adhesion molecule 1 (VCAM-1) and Interleukin-6 (IL-6) have been used as biomarkers for ED and SI assessments, respectively. A total of 104 patients with CKD (mean age: 58.9 ± 1.4) and 59 control subjects (mean age: 59.0 ± 1.1) were included, with similar age (P = .934) and sex (P = .196) between the groups. In the comparison analysis, plasma Zo levels in the CKD group (166.16 ± 53.54) were significantly higher than those in the control group (143.30 ± 60.92) (P < .001). In the correlation analysis, the serum Zo level showed a positive correlation with claudin-3 (R = 0.612, P < .001), IL-6 (R = 0.307, P < .001), and creatinine (R = 0.313, P < .001) and a negative correlation with glomerular filtration rate (GFR) (r = -0.320, P < .001). On the other hand, there was no correlation between circulating Zo and VCAM-1 levels (r = -0.139, P = .081). Additionally, according to linear regression analysis, Zo level was significantly associated with GFR after adjusting for age and systolic blood pressure (β = -0.918, P = .012). High serum Zo levels in patients with CKD reflect increased intestinal permeability and are associated with impaired renal function. Moreover, it was thought that Zo levels could be associated with SI; however, novel clinical studies are needed to elucidate their relationship with ED.

Effect of Probiotic Supplementation on Intestinal Permeability in Overweight and Obesity: A Systematic Review of Randomized Controlled Trials and Animal Studies

Overweight and obesity are associated with increased intestinal permeability, characterized by loss of gut epithelial integrity, resulting in unregulated passage of lipopolysaccharide (LPS) and other inflammatory triggers into circulation, i.e., metabolic endotoxemia. In obesity, shifts in the gut microbiome negatively impact intestinal permeability. Probiotics are an intervention that can target the gut microbiome by introducing beneficial microbial species, potentially restoring gut barrier integrity. Currently, the role of probiotic supplementation in ameliorating obesity- and overweight-associated increases in gut permeability has not been reviewed. This systematic review aimed to summarize findings from both animal and clinical studies that evaluated the effect of probiotic supplementation on obesity-induced impairment in intestinal permeability (International Prospective Register of Systematic Reviews, CRD42022363538). A literature search was conducted using PubMed (Medline), Web of Science, and CAB Direct from origin until August 2023 using keywords of intestinal permeability, overweight or obesity, and probiotic supplementation. Of 920 records, 26 eligible records were included, comprising 12 animal and 14 clinical studies. Clinical trials ranged from 3 to 26 wk and were mostly parallel-arm (n = 13) or crossover (n = 1) design. In both animal and clinical studies, plasma/serum LPS was the most common measure of intestinal permeability. Eleven of 12 animal studies reported a positive effect of probiotic supplementation in reducing intestinal permeability. However, results from clinical trials were inconsistent, with half reporting reductions in serum LPS and half reporting no differences after probiotic supplementation. Bifidobacterium, Lactobacillus, and Akkermansia emerged as the most common genera in probiotic formulations among the animal and clinical studies that yielded positive results, suggesting that specific bacteria may be more effective at reducing intestinal permeability and improving gut barrier function. However, better standardization of strain use, dosage, duration, and the delivery matrix is needed to fully understand the probiotic impact on intestinal permeability in individuals with overweight and obesity.

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 as a Potential Therapeutic Target in Microbiota-Gut-Brain Axis Disorders: Encouraging Results and Emerging Questions

The relationship between dysbiosis and central nervous diseases has been proved in the last 10 years. Microbial alterations cause increased intestinal permeability, and the penetration of bacterial fragment and toxins induces local and systemic inflammatory processes, affecting distant organs, including the brain. Therefore, the integrity of the intestinal epithelial barrier plays a central role in the microbiota-gut-brain axis. In this review, we discuss recent findings on zonulin, an important tight junction regulator of intestinal epithelial cells, which is assumed to play a key role in maintaining of the blood-brain barrier function. In addition to focusing on the effect of microbiome on intestinal zonulin release, we also summarize potential pharmaceutical approaches to modulate zonulin-associated pathways with larazotide acetate and other zonulin receptor agonists or antagonists. The present review also addresses the emerging issues, including the use of misleading nomenclature or the unsolved questions about the exact protein sequence of zonulin.

Relevance of biomarkers indicating gut damage and microbial translocation in people living with HIV

The intestinal barrier has the daunting task of allowing nutrient absorption while limiting the entry of microbial products into the systemic circulation. HIV infection disrupts the intestinal barrier and increases intestinal permeability, leading to microbial product translocation. Convergent evidence has shown that gut damage and an enhanced level of microbial translocation contribute to the enhanced immune activation, the risk of non-AIDS comorbidity, and mortality in people living with HIV (PLWH). Gut biopsy procedures are invasive, and are not appropriate or feasible in large populations, even though they are the gold standard for intestinal barrier investigation. Thus, validated biomarkers that measure the degree of intestinal barrier damage and microbial translocation are needed in PLWH. Hematological biomarkers represent an objective indication of specific medical conditions and/or their severity, and should be able to be measured accurately and reproducibly via easily available and standardized blood tests. Several plasma biomarkers of intestinal damage, i.e., intestinal fatty acid-binding protein (I-FABP), zonulin, and regenerating islet-derived protein-3α (REG3α), and biomarkers of microbial translocation, such as lipopolysaccharide (LPS) and (1,3)-β-D-Glucan (BDG) have been used as markers of risk for developing non-AIDS comorbidities in cross sectional analyses and clinical trials, including those aiming at repair of gut damage. In this review, we critically discuss the value of different biomarkers for the estimation of gut permeability levels, paving the way towards developing validated diagnostic and therapeutic strategies to repair gut epithelial damage and to improve overall disease outcomes in PLWH.

Zonulin — regulation of tight contacts in the brain and intestine — facts and hypotheses

In recent years, the interrelationship between the brain and the gut has become an area of high scientific interest. The intestine is responsible not only for digestion, as it contains millions of neurons, its own immune system, and affects the emotional and cognitive processes. The relationship between the gut and the brain suggests that the processes carried out by the gut microbiota play a significant role in the regulation of brain function, and vice versa. A special role here is played by intercellular tight junctions (TJ), where the zonulin protein holds an important place. Zonulin, an unprocessed precursor of mature haptoglobin, is the only physiological modulator of intercellular TJ that can reversibly regulate the permeability of the intestinal (IB) and blood-brain (BBB) barriers in the human body. BBB disruption and altered microbiota composition are associated with many diseases, including neurological disorders and neuroinflammation. That is, there is a gut-brain axis (GBA) — a communication system through which the brain modulates the functions of the gastrointestinal tract (GIT) and vice versa. GBA is based on neuronal, endocrine, and immunological mechanisms that are interconnected at the organismal, organ, cellular, and molecular levels.

Assessment of Gut leakage Induced Systemic Inflammation in Children on Chronic Hemodialysis

BACKGROUND: Children with chronic kidney disease (CKD) are at high risk to develop GIT complications such as intestinal wall edema and increased permeability which contributes to chronic systemic inflammation that increases morbidity and mortality burden. AIM: This study aim was to show the relationship between inflammation and increased intestinal permeability in children on hemodialysis (HD). METHODS: The study included 50 children with CKD on regular HD of variable duration; their age range was (5−16) years and 40 controls. They were followed up at Nephrology clinic- Eldemerdash hospital. Complete history taking, physical examination were done. Laboratory measurement in the form of zonulin, tumor necrosis factor-alpha (TNF-alpha), high sensitive C-reactive protein (hs-CRP), and alpha1-antitrypsin (AAT) were quantified in serum by ELISA method. RESULTS: There was a highly significant decrease in anthropometric measures (weight, height and BMI) and their corresponding z score in cases compared to controls with p ≤ 0.001. Furthermore, there was significant increase of levels of zonulin, TNF-alpha, AAT, and hs-CRP in cases compared to controls with p value of 0.009, 0.001, 0.002, and 0.003, respectively. There was significant positive correlation between zonulin and (TNF-alpha, AAT, hs-CRP, and creatinine) with P values (0.003, 0.001, 0.001, and 0.001), respectively. Zonulin is negatively correlated with weight for age Z score (WAZ) and height with p value (0.01 and 0.018), respectively. TNF-alpha and hs-CRP were negatively correlated with WAZ with P-values of 0.02 and 0.01, respectively. CONCLUSION: Children with CKD on chronic hemodialysis had elevated levels of zonulin, TNF-alpha, hs-CRP, and AAT which reflects gut permeability induced systemic inflammatory state.