Celiac disease or positive tissue transglutaminase antibodies in patients undergoing renal biopsies

Causality between Celiac disease and kidney disease: A Mendelian Randomization Study

Celiac disease, characterized as an autoimmune disorder, possesses the capacity to affect multiple organs and systems. Earlier research has indicated an increased risk of kidney diseases associated with celiac disease. However, the potential causal relationship between genetic susceptibility to celiac disease and the risk of kidney diseases remains uncertain. We conducted Mendelian randomization analysis using nonoverlapping European population data, examining the link between celiac disease and 10 kidney traits in whole-genome association studies. We employed the inverse variance-weighted method to enhance statistical robustness, and results' reliability was reinforced through rigorous sensitivity analysis. Mendelian randomization analysis revealed a genetic susceptibility of celiac disease to an increased risk of immunoglobulin A nephropathy (OR = 1.44; 95% confidence interval [CI] = 1.17-1.78; P = 5.7 × 10-4), chronic glomerulonephritis (OR = 1.15; 95% CI = 1.08-1.22; P = 2.58 × 10-5), and a decline in estimated glomerular filtration rate (beta = -0.001; P = 2.99 × 10-4). Additionally, a potential positive trend in the causal relationship between celiac disease and membranous nephropathy (OR = 1.37; 95% CI = 1.08-1.74; P = 0.01) was observed. Sensitivity analysis indicated the absence of pleiotropy. This study contributes novel evidence establishing a causal link between celiac disease and kidney traits, indicating a potential association between celiac disease and an elevated risk of kidney diseases. The findings provide fresh perspectives for advancing mechanistic and clinical research into kidney diseases associated with celiac disease.

Advancements in understanding the role of intestinal dysbacteriosis mediated mucosal immunity in IgA nephropathy

IgA nephropathy, presently recognized as the foremost primary glomerular disorder, emerges as a principal contributor to renal failure globally, with its pathogenesis yet to be fully elucidated. Extensive research has highlighted the critical role of gut microbiome in the onset and progression of IgA nephropathy, underscoring its importance in accurately delineating the disease's etiology. For example, gut microbiome dysbacteriosis can lead to the production of nephritogenic IgA1 antibodies, which form immune complexes that deposit in the kidneys, causing inflammation and damage. The gut microbiome, a source of numerous bioactive compounds, interacts with the host and plays a regulatory role in gut-immune axis modulation, earning it the moniker of the "second brain." Recent investigations have particularly emphasized a significant correlation between IgA nephropathy and gut microbiome dysbacteriosis. This article offers a detailed overview of the pathogenic mechanisms of IgA nephropathy, specifically focusing on elucidating how alterations in the gut microbiome are associated with anomalies in the intestinal mucosal system in IgA nephropathy. Additionally, it describes the possible influence of gut microbiome on recurrent IgA nephropathy following kidney transplantation. Furthermore, it compiles potential therapeutic interventions, offering both theoretical and practical foundations for the management of IgA nephropathy. Lastly, the challenges currently faced in the therapeutic approaches to IgA nephropathy are discussed.

Indirect Markers of Intestinal Damage in IgA Nephropathy

INTRODUCTION

Presence of subclinical intestinal inflammation has repeatedly been shown in IgA nephropathy (IgAN) and the degree of histological inflammation has correlated with abnormal urinary findings. There is lack of noninvasive biomarkers evaluating the presence of subclinical intestinal damage in IgAN. We conducted this study hypothesizing that selected biomarkers regarded as indirect markers of intestinal damage could be elevated in IgAN.

METHODS

Eighty-five primary IgAN patients (median age 55 years, 54% men) participated in this single-center study in Tampere, Finland. None had end-stage kidney disease or previously diagnosed enteropathies. Celiac disease was excluded with serum transglutaminase 2 antibody (TG2Ab) and endomysial antibody tests and inflammatory bowel disease with fecal calprotectin. Intestinal damage was evaluated from sera with analyses of intestinal fatty-acid binding protein (I-FABP), soluble cluster of differentiation molecule 14 (sCD14), and lipopolysaccharide binding protein. Fourteen people suffering from dyspepsia and 15 healthy people served as controls.

RESULTS

I-FABP levels among IgAN patients were higher than in the healthy controls (median 830 pg/mL vs. 289 pg/mL, p < 0.001). Also, sCD14 was increased in IgAN patients compared to dyspepsia controls. Although TG2Ab levels were within the normal range among IgAN patients, they were higher than in the healthy controls (median 1.3 U/mL vs. 0.6 U/mL, p < 0.001).

CONCLUSIONS

Elevated serum levels of I-FABP were present in primary IgAN patients without known enteropathies. Serum I-FABP may indicate the presence of subclinical intestinal damage. These findings encourage further investigation into the role of the intestine in the pathophysiology of IgAN.

Unraveling chronic kidney disease in children: a surprising manifestation of celiac disease

Celiac disease, firstly described in children, is a type of T-cell enteropathy that occurs in individuals genetically predisposed to gluten exposure. The estimated global prevalence of celiac disease is continuously increasing. Although, traditionally, celiac disease was diagnosed in children with failure to thrive and digestive issues, it is now recognized that may present with a wide range of symptoms beyond gastrointestinal ones. Celiac disease continues to pose significant challenges due to the continuous advancement of knowledge in understanding its pathophysiology, diagnosing the condition, managing its effects, and exploring potential therapeutic approaches. The prevalence of celiac disease is increased among individuals with chronic kidney disease, also. The most frequent associations are with diabetic nephropathy, IgA nephropathy and urolithiasis. A gut-kidney axis has been recognized to play a significant role in chronic kidney diseases. This literature review aims to review the chronic renal pathology associated with celiac disease, with emphasis on childhood.

Current understanding of IgA antibodies in the pathogenesis of IgA nephropathy

Immunoglobulin A (IgA) is the most abundant isotype of antibodies, provides a first line of defense at mucosal surfaces against pathogens, and thereby contributes to mucosal homeostasis. IgA is generally considered as a non-inflammatory antibody because of its main function, neutralizing pathogenic virus or bacteria. Meanwhile, IgA can induce IgA-mediated diseases, such as IgA nephropathy (IgAN) and IgA vasculitis. IgAN is characterized by the deposition of IgA and complement C3, often with IgG and/or IgM, in the glomerular mesangial region, followed by mesangial cell proliferation and excessive synthesis of extracellular matrix in glomeruli. Almost half a century has passed since the first report of patients with IgAN; it remains debatable about the mechanism how IgA antibodies selectively bind to mesangial region-a hallmark of IgAN-and cause glomerular injuries in IgAN. Previous lectin- and mass-spectrometry-based analysis have revealed that IgAN patients showed elevated serum level of undergalactosylated IgA1 in O-linked glycans of its hinge region, called galactose-deficient IgA1 (Gd-IgA1). Thereafter, numerous studies have confirmed that the glomerular IgA from IgAN patients are enriched with Gd-IgA1; thus, the first hit of the current pathogenesis of IgAN has been considered to increase circulating levels of Gd-IgA1. Recent studies, however, demonstrated that this aberrant glycosylation alone is not sufficient to disease onset and progression, suggesting that several additional factors are required for the selective deposition of IgA in the mesangial region and induce nephritis. Herein, we discuss the current understanding of the characteristics of pathogenic IgA and its mechanism of inducing inflammation in IgAN.

Presence of gastrointestinal symptoms in IgA nephropathy: a cross-sectional study

BACKGROUND

Gastrointestinal (GI) symptoms are common in end-stage kidney disease. Mounting evidence indicates that the intestine plays an important role in the pathogenesis of IgA nephropathy (IgAN). However, no studies have addressed the obvious question; do IgAN patients suffer from GI symptoms?

METHODS

Presence of GI symptoms and health-related quality of life were evaluated using the validated Gastrointestinal Symptom Rating Scale (GSRS) and Psychological General Well-Being (PGWB) questionnaires in 104 patients with kidney biopsy-verified IgAN and in 147 healthy controls. A person was regarded to experience 'increased GI symptoms' if the GSRS score exceeded plus 1 standard deviation of the mean of the corresponding score in the healthy controls.

RESULTS

According to the GSRS total score, the IgAN patients had more GI symptoms than the healthy controls (2.0 vs. 1.7, p < 0.001). Female IgAN patients had higher GSRS total score than male patients (2.2 vs. 1.7, p = 0.001). More IgAN patients with preserved kidney function (eGFR > 60ml/min/1.73m²) suffered from increased symptoms of diarrhoea (76 vs. 25%, p = 0.028), constipation (81 vs. 19%, p = 0.046) and reflux (85 vs. 15%, p = 0.004) than did IgAN patients with reduced kidney function (eGFR < 60ml/min/1.73m²).

CONCLUSIONS

IgAN patients and especially female IgAN patients experienced more GI symptoms than healthy controls. More prevalent GI symptoms were already observed before kidney function was clearly reduced. Systematic enquiry of GI symptoms might increase the standard of care among IgAN patients. Moreover, GI symptoms may provide clues for future studies that examine the pathophysiology of IgAN.

Role of gut-kidney axis in renal diseases and IgA nephropathy

PURPOSE OF REVIEW

Growing evidence show the importance of gut/kidney axis in renal diseases. Advances in gut microbiome sequencing, associated metabolites, detection of gut permeability and inflammation provide new therapeutic strategies targeting gut for kidney diseases and particularly for Immunoglobulin A (IgA) nephropathy (IgAN).

RECENT FINDINGS

The diversity and composition of gut flora have been recently deeply explored in kidney diseases. Modulation and depletion of microbiota in animal models allowed the understanding of molecular mechanisms involved in the crosstalk between gut, immune system and kidney. New clinical trials in order to positively modulate microbiota result in improvement of gastrointestinal disorders and inflammation in patients suffering with kidney diseases.

SUMMARY

The investigation of gut alterations in kidney diseases open new therapeutic strategies. In IgAN, targeted treatments for intestinal inflammation and modifications of gut microbiota seem promising.

Celiac Disease-Type Tissue Transglutaminase Autoantibody Deposits in Kidney Biopsies of Patients with IgA Nephropathy

An association between celiac disease and IgA nephropathy (IgAN) has been suggested. In celiac disease, in addition to circulating in serum, IgA-class tissue transglutaminase (tTG) autoantibodies are deposited in the small bowel mucosa and extraintestinal organs. In this case series of IgAN patients with or without celiac disease, we studied whether celiac disease-type IgA-tTG deposits occur in kidney biopsies. The study included nine IgAN patients, four of them with celiac disease. At the time of the diagnostic kidney biopsy serum tTG autoantibodies were measured and colocalization of IgA and tTG was investigated in the frozen kidney biopsies. Three IgAN patients with celiac disease had IgA-tTG deposits in the kidney even though in two of these the celiac disease diagnosis had been set years later. These deposits were not found in a patient with already diagnosed celiac disease following a gluten-free diet. Of the five non-celiac IgAN patients, three had IgA-tTG deposits in the kidney. We conclude that tTG-targeted IgA deposits can be found in the kidney biopsies of gluten-consuming IgAN patients but their specificity to celiac disease seems limited.

Prevalence of Inflammatory Bowel Disease and Celiac Disease in Patients with IgA Nephropathy over Time

INTRODUCTION

IgA nephropathy (IgAN) has been connected with increased intestinal permeability and subclinical intestinal mucosal inflammation as well as with inflammatory bowel disease (IBD) and celiac disease - nevertheless, the results are controversial. The prevalence of bowel diseases has increased over time in Western populations. Whether similar trend is seen among IgAN patients remains obscure. Our aim was to study the prevalence of IBD and celiac disease in IgAN patients over time.

METHODS

The study cohort consisted of altogether 629 patients with newly diagnosed IgAN during years 1976-2012. Data on diagnosis of IBD and celiac disease were retrospectively collected from medical records. Further, to detect unrecognized celiac disease, IgA-class tissue transglutaminase antibodies (tTGA) were measured from serum samples taken at the time of kidney biopsy during years 1980-2012 (defined as screen-detected celiac disease autoimmunity).

RESULTS

The prevalence of IBD among IgAN patients increased over time from 0 to 4.4%, while the prevalence of clinically diagnosed celiac disease decreased from 2.6 to 0.6%. Moreover, the number of screen-detected tTGA-positive cases decreased from the 1980s to the 21st century (2.8-0.7%).

CONCLUSION

The prevalence of IBD increased over time in IgAN patients, which exceeds the prevalence of 0.6% in Finnish general population. In parallel, the prevalence of celiac disease and screen-detected celiac disease autoimmunity decreased over time. The coexistence of IBD and IgAN is not negligible. Whether this finding is caused by the increase in the prevalence of IBD in the population or shared pathophysiology between IgAN and IBD remains a matter of further studies.

Food antigens and Transglutaminase 2 in IgA nephropathy: Molecular links between gut and kidney

The transglutaminase 2 (TG2) is one of the enigmatic enzymes with important functional diversity. It plays an important role in several pathologies such as celiac disease (CD). In patients with active CD, the abnormal retrotranscytosis of IgA/gliadin complexes is mediated by Transferrin Receptor 1 (TfR1). This triad association takes also place in IgA nephropathy (IgA-N). IgA-N is characterized by the formation of nephrotoxic complexes of IgA1 and soluble CD89 (sCD89). These complexes are abnormally deposited in the kidney. Using a humanized mouse model of IgA-N (α1KI-CD89Tg), we showed that IgA1-sCD89 complexes engender mesangial cell activation and proliferation with TfR1 and TG2 up-regulation, associated with IgA-N features. This TG2-TfR1 interaction enhances mesangial IgA1 deposition promoting inflammation. Humanized α1KI-CD89Tg mice deficient for TG2 show a decrease in TfR1 expression in kidney leading to reduced IgA1-sCD89 deposits and an improvement in IgA-N features. Moreover, TG2 is active and overexpressed in the intestine of IgA-N mice and gliadin participates to this renal pathology. In kidney as in intestine, the TG2 has a crucial role in the cooperation between TfR1-IgA and a central role in the pathogenic amplification.

Inflammatory bowel disease in patients undergoing renal biopsies

BACKGROUND

There are no good data in the literature on the prevalence of inflammatory bowel disease (IBD) in patients with kidney disease and we do not know whether IBD affects the course of kidney disease or if the type of IBD is an influential factor. The aim of this study was to evaluate the prevalence of IBD among patients who have undergone renal biopsies due to clinical indications and to elucidate whether the presence of IBD influences renal and patient outcomes.

METHODS

We collected retrospective data on concomitant diseases, especially IBD, from adult patients undergoing renal biopsy for any clinical indication between 2000 and 2012 at Tampere University Hospital, Tampere, Finland. Information was systematically collected on the activity of IBD, medication for IBD, surgery performed for IBD and markers of kidney function.

RESULTS

Of the 819 patients biopsied, 35 (4.3%) had IBD. The prevalence of IBD was 13.3 and 4.6% in patients with tubulointerstitial nephritis (TIN) and immunoglobulin A nephropathy (IgAN), respectively. In comparison, the prevalence of IBD in the Finnish population is 0.6%. Ulcerative colitis and Crohn's disease were equally represented. The presence of IBD showed no impact on renal and patient outcomes.

CONCLUSIONS

IBD should not be overlooked in patients undergoing renal biopsies, especially those diagnosed with TIN or IgAN. The renal findings did not associate with the activity of intestinal inflammation. Whether a concomitant IBD truly affects the course of chronic kidney disease should be examined in further studies.

The Gut-Renal Connection in IgA Nephropathy

The connection between a dysregulated gut-associated lymphoid tissue and IgA nephropathy (IgAN) was supposed decades ago after the observation of increased association of IgAN with celiac disease. Pivotal studies have shown a role for alimentary antigens, particularly gliadin in developing IgAN in BALB/c mice, and a reduction in IgA antigliadin antibodies and proteinuria was reported after gluten free-diet in patients with IgAN. Recently a genome-wide association study showed that most loci associated with IgAN also are associated with immune-mediated inflammatory bowel diseases, maintenance of the intestinal barrier, and response to gut pathogens. Transgenic mice that overexpress the B-cell activating factor develop hyper-IgA with IgAN modulated by alimentary components and intestinal microbiota. Mice expressing human IgA1 and a soluble form of the IgA receptor (sCD89) develop IgAN, which is regulated by dietary gluten. Recent observations have confirmed gut-associated lymphoid tissue hyper-reactivity in IgAN patients with IgA against alimentary components. Interesting results were provided by the NEFIGAN randomized controlled trial, which adopted an enteric controlled-release formulation of the corticosteroid budesonide targeted to Peyer's patches. After 9 months of treatment, a reduction in proteinuria was observed with stabilized renal function and limited adverse events. The gut-renal connection is an area of promising new treatment approaches for patients with IgAN.

The Gut-Kidney Axis: Putative Interconnections Between Gastrointestinal and Renal Disorders

Diabetic kidney disease (DKD) is a devastating condition associated with increased morbidity and premature mortality. The etiology of DKD is still largely unknown. However, the risk of DKD development and progression is most likely modulated by a combination of genetic and environmental factors. Patients with autoimmune diseases, like type 1 diabetes, inflammatory bowel disease, and celiac disease, share some genetic background. Furthermore, gastrointestinal disorders are associated with an increased risk of kidney disease, although the true mechanisms have still to be elucidated. Therefore, the principal aim of this review is to evaluate the impact of disturbances in the gastrointestinal tract on the development of renal disorders.