Novel carbonic anhydrase autoantibodies and renal manifestations in patients with primary Sjogren's syndrome

Oxidative modification of carbonic anhydrase by peroxynitrite trigger immune response in mice and rheumatic disease patients

BACKGROUND

Carbonic anhydrases (CA) are metalloenzymes with wide tissue distribution, involved in many important physiological processes, and in some rheumatic diseases, autoantibodies are formed against these enzymes. Recent studies have suggested that oxidative stress triggers anti-CA antibody formation. In this study, we aimed to investigate the effects of modification with oxidative/nitrosative stress end products on CA antigenicity in mice and the relationship between the modified CA autoantibodies and oxidant-antioxidant status in patients with rheumatoid arthritis (RA) and Sjögren's syndrome (SjS).

METHODS

CA I and CA II isoenzymes were isolated from human erythrocytes and modified with 4-hydroxynonenal (4-HNE), malondialdehyde (MDA), and peroxynitrite (PN). Balb-c mice were immunized with these agents to determine the effects of modification on CA antigenicity. The autoantibody titers of modified CA isoenzymes were detected in patients. In addition MDA, 4-HNE, 3-nitrotyrosine (3-NT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) activities were measured to assess the oxidant-antioxidant status in patients.

RESULTS

Modifications of carbonic anhydrase with oxidative stress end products, HNE, MDA and PN, lead to alterations in the immune response to these enzymes in mice. It was found that HNE and MDA decreased the antigenicity while PN increased. In addition, PN-modified CA autoantibody levels were found to be significantly different in both RA and SjS patients compared to their controls (p<0.05).

CONCLUSIONS

PN modifications can also trigger an immune response against CA isoenzymes in mice, and PN-modified CA I and CA II autoantibody titers were found at a significantly high level in both RA and SjS patients.

Serum biomarkers for the differentiation of autoimmune pancreatitis from pancreatic ductal adenocarcinoma

Autoimmune pancreatitis (AIP), a chronic inflammation caused by the immune system attacking the pancreas, usually presents imaging and clinical features that overlap with those of pancreatic ductal adenocarcinoma (PDAC). Serum biomarkers, substances that quantitatively change in sera during disease development, are a promising non-invasive tool with high utility for differentiating between these diseases. In this way, the presence of AIP is currently suspected when serum concentrations of immunoglobulin G4 (IgG4) antibody are elevated. However, this approach has some drawbacks. Notably, IgG4 antibody concentrations are also elevated in sera from some patients with PDAC. This review focuses on the most recent and relevant serum biomarkers proposed to differentiate between AIP and PDAC, evaluating the usefulness of immunoglobulins, autoantibodies, chemokines, and cytokines. The proposed serum biomarkers have proven useful, although most studies had a small sample size, did not examine their presence in patients with PDAC, or did not test them in humans. In addition, current evidence suggests that a single serum biomarker is unlikely to accurately differentiate these diseases and that a set of biomarkers will be needed to achieve adequate specificity and sensitivity, either alone or in combination with clinical data and/or radiological images.

Anti-carbonic anhydrase II antibody reflects urinary acidification defect especially in proximal renal tubules in patients with primary Sjögren syndrome

Primary Sjögren syndrome (pSS) is a systemic autoimmue disease featured by excessive autoantibody production. It has been demonstrated that anti-carbonic anhydrase II (anti-CA II) antibody is correlated with renal tubular acidosis in pSS; however, no further details about urinary acidification defect have been reported, and the antibody's relationship with other organ impairments remains unknown. This case-control study aimed to examine anti-CA II antibody levels in relation to various systemic complications in pSS, and evaluate its potential role as a organ-specific biomarker in a Chinese cohort. Serum anti-CA II antibody levels were determined using ELISA in 123 patients with pSS and 72 healthy controls. The medical records of the patients were collected, and the correlation between serum anti-CA II antibody and clinical/immunological parameters was investigated. Serum anti-CA II antibody level and its positive rate were significantly increased in pSS patients compared with controls, and ANA-positive patients presented even higher titers of the antibody. In anti-CA II positive group, remarkably higher urine pH and bicarbonate, as well as lower urine titratable acid and serum potassium were observed, which indicated renal tubular acidification dysfunction both involving bicarbonate reabsorption and acid secretion. In addition, platelet count and complement 3, complement 4 levels decreased, whereas serum IgG, IgA and γ-globulin levels increased notably in accord with a higher EULAR SS disease activity index score in these patients. Further analysis showed that anti-CA II antibody was most elevated in patients with defect in bicarbonate reabsorption, reflecting proximal renal tubular injury, rather than in patients with distal renal tubular acidosis as previously reported. In conclusion, anti-CA II antibody reflects renal (especially proximal renal tubular) and hematologic impairment as well as increased disease activity in pSS. It may act as a serum biomarker of systemic damage of pSS.

Mechanistic insights into the primary and secondary alterations of renal ion and water transport in the distal nephron

The kidneys, by equilibrating the outputs to the inputs, are essential for maintaining the constant volume, pH, and electrolyte composition of the internal milieu. Inability to do so, either because of internal kidney dysfunction (primary alteration) or because of some external factors (secondary alteration), leads to pathologies of varying severity, leading to modification of these parameters and affecting the functions of other organs. Alterations of the functions of the collecting duct (CD), the most distal part of the nephron, have been extensively studied and have led to a better diagnosis, better management of the related diseases, and the development of therapeutic tools. Thus, dysfunctions of principal cell-specific transporters such as ENaC or AQP2 or its receptors (mineralocorticoid or vasopressin receptors) caused by mutations or by compounds present in the environment (lithium, antibiotics, etc.) have been demonstrated in a variety of syndromes (Liddle, pseudohypoaldosteronism type-1, diabetes insipidus, etc.) affecting salt, potassium, and water balance. In parallel, studies on specific transporters (H⁺ -ATPase, anion exchanger 1) in intercalated cells have revealed the mechanisms of related tubulopathies like distal renal distal tubular acidosis or Sjögren syndrome. In this review, we will recapitulate the mechanisms of most of the primary and secondary alteration of the ion transport system of the CD to provide a better understanding of these diseases and highlight how a targeted perturbation may affect many different pathways due to the strong crosstalk and entanglements between the different actors (transporters, cell types).

Idiopathic Hypokalemia in Lupus Nephritis: A Newly Recognized Entity

Background

Various causes of hypokalemia (HK) from renal potassium wasting, including distal renal tubular acidosis (RTA), have been described in lupus nephritis (LN). We report a phenomenon of otherwise unexplained HK among a population with LN.

Methods

From our population of 403 patients with LN, we identified a cohort of 20 patients with idiopathic HK, defined by serum potassium <3.5 mmol/L without any apparent explanation. This cohort is compared with 90 LN controls (CON) and ten patients with LN with distal RTA from the same population.

Results

The patients with HK had lower median serum potassium compared with CON and RTA subjects (3.26 versus 4.00 versus 3.75 mmol/L, respectively; P<0.001). The median serum bicarbonate was normal in HK and CON, but low in RTA (26.0 versus 25.0 versus 19.4 mmol/L; P<0.001). The median urine pH was abnormally high only in the RTA group (6.00 versus 6.25 versus 6.67; P=0.012). The median serum magnesium was modestly lower in HK compared with the CON and RTA groups (1.73 versus 2.00 versus 1.85 mg/dl; P=0.002). Although both HK and RTA showed a higher rate of seropositivity than CON for anti-Ro/SSA (79% and 80% versus 37%, respectively; P<0.001), only HK revealed a higher rate of seropositivity than CON for anti-RNP (84% versus 42%; P=0.003) and only RTA showed a higher rate of seropositivity than CON for anti-La/SSB (40% versus 12%; P=0.05).

Conclusions

A syndrome of idiopathic HK was revealed in 20 out of 403 (5%) of patients within our LN population, and proved to be distinct from the RTA that occurs in LN. Furthermore, it was associated with a distinct pattern of autoantibodies. We speculate that idiopathic HK is the result of a novel target of autoimmunity in LN, affecting renal tubular potassium transport.

The Diagnostic Performance of Early Sjögren's Syndrome Autoantibodies in Juvenile Sjögren's Syndrome: The University of Florida Pediatric Cohort Study

Objectives

The aim of this study was to evaluate the clinical validity of early Sjögren's syndrome (SS) autoantibodies (eSjA), which were originally marketed for early diagnosis of SS, for juvenile SS (JSS) in a recently identified pediatric cohort.

Methods

A total of 105 symptomatic subjects with eSjA results available were evaluated at the Center for Orphaned Autoimmune Disorders at the University of Florida and enrolled for this study. JSS diagnosis was based on the 2016 ACR/EULAR SS criteria. Demographic/clinical/laboratory parameters were compared between JSS (n = 27) and non-JSS (n = 78) for % positivity, sensitivity, and specificity of eSjA (SP1, anti-salivary protein; CA6, anti-carbonic anhydrase VI; PSP, anti-parotid secretory protein) and classic SS-autoantibodies (cSjA; ANA, SSA/SSB, RF, and others) either alone or in combination. Associations between eSjA and diagnostic/glandular parameters were also determined by Fisher's exact test.

Results

Compared to non-JSS, JSS patients exhibited sicca symptoms demonstrating reduced unstimulated salivary flow rate (USFR) and abnormal glandular features revealed by salivary gland ultrasound (SGUS). Among cSjA, ANA demonstrated the highest sensitivity of 69.2%, while SSA, SSB, and RF showed around 95% specificities for JSS diagnosis. The % positive-SSA was notably higher in JSS than non-JSS (56% vs. 5%). Of eSjA, anti-CA6 IgG was the most prevalent without differentiating JSS (37%) from non-JSS (32%). Sensitivity and specificity of eSjA were 55.6 and 26.9%, respectively. Autoantibodies with potentially applicable specificity/sensitivity for JSS were seen only in cSjA without a single eSjA included. There were no associations detected between eSjA and focus score (FS), USFR, SSA, SGUS, and parotitis/glandular swelling analyzed in the entire cohort, JSS, and non-JSS. However, a negative association between anti-PSP and parotitis/glandular swelling was found in a small group of positive-SSA (n = 19, p = 0.02) whereas no such association was found between anti-PSP-positive compared to anti-PSP-negative. JSS and non-JSS groups differed in FS, USFR, and EULAR SS Patient Reported Index Dryness/Mean in CA6/PSP/ANA, SP1, and SSA-positive groups, respectively. Additionally, a higher FS was found in RF-positive than RF-negative individuals.

Conclusions

eSjA underperformed cSjS in differentiating JSS from non-JSS. The discovery of clinical impact of eSjA on early diagnosis of JSS necessitates a longitudinal study.

From Hypokalemic Crisis to Sjogren's Syndrome: A Case Report and Literature Review

Renal involvement occurs in approximately 5% of patients with Sjögren's syndrome (SS). We reported the case of a 20-year-old African woman who was received for paralysis of 4 limbs secondary to hypokalemia. The diagnosis of renal tubular acidosis type 1 complicated by hypokalemia was retained. In the etiologic research of renal tubular acidosis type 1, primary SS was retained. The patient received symptomatic treatment based on potassium chloride, sodium bicarbonate, hydration, and a low protein diet. In terms of etiological treatment, she was put on corticosteroid and hydroxychloroquine. The outcome was favorable with correction of acidosis and hypokalemia.

Hypokalaemic paralysis and metabolic alkalosis in a patient with Sjögren syndrome: a case report and literature review

Background

Acquired Gitelman syndrome is a very rare disorder reported in association with autoimmune disorders, mostly Sjögren syndrome. It is characterized by the presence of hypokalaemic metabolic alkalosis, hypocalciuria, hypomagnesaemia and hyper-reninaemia, in the absence of typical genetic mutations associated with inherited Gitelman syndrome.

Case presentation

A 20 year old woman who was previously diagnosed with primary Sjögren syndrome and autoimmune thyroiditis presented with two week history of lower limb weakness and salt craving. Examination revealed upper limb and lower limb muscle weakness with muscle power of 3/5 on MRC scale and diminished deep tendon reflexes. On evaluation, she had hypokalaemia with high trans-tubular potassium gradient, metabolic alkalosis and hypocalciuria, features suggestive of Gitelman syndrome. New onset hypokalaemic alkalosis in a previously normokalaemic patient with Sjögren syndrome strongly favored a diagnosis of acquired Gitelman syndrome. Daily potassium supplementation and spironolactone resulted in complete clinical recovery.

Conclusions

Acquired Gitelman syndrome associated with Sjögren syndrome is rare. It should be considered as a differential diagnosis during evaluation of acute paralysis and hypokalaemic metabolic alkalosis in patients with autoimmune disorders, especially Sjögren syndrome.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02371-5.

[Immunity and tubular dysfunction in case of systemic disease]

The immune renal tubular diseases are known since five decades, but their prevalence remains to be defined. They are caused by humoral and cellular effectors of innate and adaptative immunities on several targets of the renal tubule: protein channels, co or counter transporters, luminal or cytosolic enzymes, tight junctions. Genetic or epigenetic variations are also involved. Clinical manifestations are various and make the diagnosis difficult. They can precede the causal affection and they worsen the prognosis. The classical model consists in hypokalemic tubular distal acidosis observed in Sjögren's syndrome which illustrates the auto-immune epithelitis concept. Cellular immunity can act through other ways, like tertiary lymphoid neogenesis in systemic lupus. Humoral immunity through autoantibodies targets several membrane, cytosolic or nuclear proteins, causing specific tubular dysfonctions. It is also implied in the epithelial-mesenchymal transition of tubular cells. Innate immunity through cytokines may be involved. Treatment consists in electrolytic disorders correction and immunosupppressive medication: the choice should be guided at best by physiopathology.

Factors Associated With Renal Involvement in Primary Sjögren's Syndrome: A Meta-Analysis

Background: Renal impairment is a critical complication in primary Sjögren's syndrome (pSS), resulting in chronic renal disease and even death. This meta-analysis was designed to find out the relevant factors of renal involvement in pSS.

Methods: PubMed, EMBASE, Cochrane Library, Scopus, and Web of Science were systemically searched until August 30, 2019. Studies were selected according to inclusion criteria, and data was extracted by two researchers independently. The Newcastle-Ottawa Scale was applied for quality assessment. Random- and fixed-effects models were used in this meta-analysis based on the result of the heterogeneity test. Meanwhile, a sensitivity analysis was conducted to investigate the cause of heterogeneity. Publication bias was shown in the funnel plot and evaluated further by Begg's and Egger's tests.

Results: Of the 9,989 articles identified, five articles enrolling 1,867 pSS patients were included in the final analysis, 533 with and 1,334 without renal involvement. There was no statistical significance in age and gender between these two groups. According to the meta-analysis, anti-SSB antibody, and arthralgia showed a significant association with renal involvement in pSS, the overall odds ratio (OR) values of which were 1.51 (95% CI, 1.16–1.95) and 0.59 (95% CI, 0.46–0.74), respectively. On the other hand, the overall OR values of anti-SSA antibody, rheumatoid factor, dry eyes, and labial salivary gland biopsy were just 0.90 (95% CI, 0.49–1.64), 1.05 (95% CI, 0.59–1.86), 0.60 (95% CI, 0.34–1.06), and 1.38 (95% CI, 0.98–1.95), respectively.

Conclusion: The presence of anti-SSB antibody is positively associated with renal involvement in pSS, while arthralgia is inversely associated. Large-scale prospective cohort studies are needed in the future to identify further risk factors.

[Renal involvement in Sjögren's syndrome]

Primary Sjögren syndrome is an autoimmune disorder characterized by lymphoplasmacytic infiltration of the exocrine (salivary and lachrymal) glands resulting in sicca symptoms (dryness). Systemic complications can occur in primary Sjögren syndrome, but renal involvement is rare, affecting<10% patients. The most frequent form of nephropathy in primary Sjögren syndrome is tubulointerstitial nephritis, where infiltration of the kidney by plasma cells is a key feature and shows similarity to the lymphoplasmacytic infiltration of the salivary glands. Electrolyte disturbances may occur in primary Sjögren syndrome, such as renal distal tubular acidosis, diabetes insipidus, Gitelman syndrome, or Fanconi syndrome. Glomerular involvement is less frequently detected in patients with primary Sjögren syndrome, but can take the form of membranoproliferative glomerulonephritis secondary to cryoglobulinaemia. The renal prognosis in patients with primary Sjögren syndrome and TIN or glomerular disease is usually good, but the risk of chronic kidney disease remains significant for some patients. Appropriate screening must be performed at least once a year in patients with systemic primary Sjögren syndrome in order to facilitate the early detection of renal complications. In this Review, we discuss the epidemiology, pathophysiology, differential diagnosis, and treatment of renal disease in primary Sjögren syndrome.

Incomplete distal renal tubular acidosis in children

AIM

To describe incomplete distal renal tubular acidosis (iDRTA) in paediatric patients, a term used for the diagnosis of patients who do not develop spontaneous overt metabolic acidosis but are unable to acidify the urine in response to an ammonium chloride load.

METHODS

Tests used to explore urinary acidification were revised. In addition, publications in English extracted from 161 entries yielded by a PubMed database search, using 'incomplete distal renal tubular acidosis' as keyword, were reviewed.

RESULTS

Incomplete distal renal tubular acidosis has mostly been identified in adults with autoimmune diseases, nephrolithiasis, nephrocalcinosis and/or osteopenia. iDRTA has been reported in few paediatric patients with rickets, congenital abnormalities of kidney and urological tract and/or growth failure. The pathophysiological mechanisms potentially responsible for the defect of urinary acidification are discussed as well as the clinical and biochemical findings of iDRTA described in children.

CONCLUSION

The presentation of iDRTA in children differs from adults. The clinical and biochemical features of iDRTA are not well characterised in paediatric patients. The detection of iDRTA in groups of population such as heterozygous carriers of primary DRTA gene mutations and children with hypocitraturia or hypercalciuria might be of clinical interest to better know the pathophysiology and natural history of iDRTA.

Primary Sjogren's syndrome presenting as hypokalemic paralysis: A case series

Primary Sjögren's syndrome (pSS) primarily involves exocrine glands, and renal tubular acidosis (RTA) is seen in one-third of the cases. RTA with hypokalemic paralysis as a presenting feature of pSS is described in few case reports in literature. We report 13 cases who presented as hypokalemic paralysis, and on evaluation were diagnosed to be pSS, as per the diagnostic criteria laid by the Sjögren's International Collaborative Clinical Alliance (2012). All patients were female, with a mean age at presentation being 33.1 ± 8.22 years (range, 25–48 years). Eleven patients had a complete distal RTA and two patients had incomplete distal RTA at the time of presentation. 62% (8/13) of patients had no signs and symptoms of exocrine gland involvement. All the cases were managed with oral alkali therapy, and six patients received additional immunomodulating agents. No improvement in renal tubular dysfunction (in the form of a reduction in the alkali dose) after immunomodulating therapy was observed over a mean follow-up of 2.8 years. Renal tubular dysfunction can be the presenting manifestation of pSS. It is important to consider the possible presence of this disorder in adults with otherwise unexplained distal RTA or hypokalemia.

Carbonic anhydrases as disease markers

INTRODUCTION

The physiologic importance of fast CO₂/HCO₃^- interconversion in various tissues requires the presence of carbonic anhydrase (CA, EC 4.2.1.1). Fourteen CA isozymes are present in humans, all of them being used as biomarkers.

AREAS COVERED

A great number of patents and articles were focused on the use of CA isozymes as biomarkers for various diseases and syndromes in the recent years, in an ascending trend over the last decade. The review highlights the most important studies related with each isozyme and covers the most recent patent literature.

EXPERT OPINION

The CAs biomarker research area expanded significantly in recent years, shifting from the predominant use of CA IX and CA XII in cancer diagnostic, staging, and prognosis towards a wider use of CA isozymes as disease biomarkers. CA isozymes are currently used either alone, in tandem with other CA isozymes and/or in combination with other proteins for the detection, staging, and prognosis of a huge repertoire of human dysfunctions and diseases, ranging from mild transformation of the normal tissues to extreme shifts in tissue organization and function. The techniques used for their detection/quantitation and the state-of-the-art in each clinical application are presented through relevant clinical examples and corresponding statistical data.

Distal renal tubular acidosis and severe hypokalemia: a case report and review of the literature

Background

Distal renal tubular acidosis is a relatively infrequent condition with complex pathophysiology that can present with life-threatening electrolyte abnormalities.

Case presentation

We describe a case of a 57-year-old Caucasian woman with previous episodes of hypokalemia, severe muscle weakness, and fatigue. Upon further questioning, symptoms of dry eye and dry mouth became evident. Initial evaluation revealed hyperchloremic metabolic acidosis, severe hypokalemia, persistent alkaline urine, and a positive urinary anion gap, suggestive of distal renal tubular acidosis. Additional laboratory workup and renal biopsy led to the diagnosis of primary Sjögren’s syndrome with associated acute tubulointerstitial nephritis. After potassium and bicarbonate supplementation, immunomodulatory therapy with hydroxychloroquine, azathioprine, and prednisone was started. Nonetheless, her renal function failed to improve and remained steady with an estimated glomerular filtration rate of 42 ml/min/1.73 m². The literature on this topic was reviewed.

Conclusions

Cases of renal tubular acidosis should be carefully evaluated to prevent adverse complications, uncover a potentially treatable condition, and prevent the progression to chronic kidney disease. Repeated episodes of unexplained hypokalemia could be an important clue for diagnosis.

Carbonic Anhydrase 6 Gene Variation influences Oral Microbiota Composition and Caries Risk in Swedish adolescents

Carbonic anhydrase VI (CA6) catalyses the reversible hydration of carbon dioxide in saliva with possible pH regulation, taste perception, and tooth formation effects. This study assessed effects of variation in the CA6 gene on oral microbiota and specifically the acidophilic and caries-associated Streptococcus mutans in 17-year old Swedish adolescents (n = 154). Associations with caries status and secreted CA6 protein were also evaluated. Single Nucleotide Polymorphisms (27 SNPs in 5 haploblocks) and saliva and tooth biofilm microbiota from Illumina MiSeq 16S rDNA (V3-V4) sequencing and culturing were analysed. Haploblock 4 (rs10864376, rs3737665, rs12138897) CCC associated with low prevalence of S. mutans (OR (95% CI): 0.5 (0.3, 0.8)), and caries (OR 0.6 (0.3, 0.9)), whereas haploblock 4 TTG associated with high prevalence of S. mutans (OR: 2.7 (1.2, 5.9)) and caries (OR: 2.3 (1.2, 4.4)). The TTG-haploblock 4 (represented by rs12138897(G)) was characterized by S. mutans, Scardovia wiggsiae, Treponema sp. HOT268, Tannerella sp. HOT286, Veillonella gp.1 compared with the CCC-haploblock 4 (represented by rs12138897(C)). Secreted CA6 in saliva was weakly linked to CA6 gene variation. In conclusion, the results indicate that CA6 gene polymorphisms influence S. mutans colonization, tooth biofilm microbiota composition and risk of dental caries in Swedish adolescents.

The Human Carbonic Anhydrase II in Platelets: An Underestimated Field of Its Activity

Carbonic anhydrases constitute a group of enzymes that catalyse reversible hydration of carbon dioxide leading to the formation of bicarbonate and proton. The platelet carbonic anhydrase II (CAII) was described for the first time in the '80s of the last century. Nevertheless, its direct role in platelet physiology and pathology still remains poorly understood. The modulation of platelet CAII action as a therapeutic approach holds promise as a novel strategy to reduce the impact of cardiovascular diseases. This short review paper summarises the current knowledge regarding the role of human CAII in regulating platelet function. The potential future directions considering this enzyme as a potential drug target and important pathophysiological chain in platelet-related disorders are described.

Investigation of autoantibodies to SP-1 in Chinese patients with primary Sjögren's syndrome

In order to evaluate autoantibody to SP-1 as an early biomarker in pSS, we investigated autoantibody to SP-1 in Chinese patients with primary Sjögren's syndrome (pSS). Autoantibodies to SP-1 are significantly increased in pSS patients compared to RA patients, SLE patients, and healthy people without secondary SS. The presence of anti SP-1 antibodies was negatively correlated with the focus score (FS), RF, and salivary gland function. It was positively correlated with FS=0, RF≤20, and normal salivary gland function. In further studies, the autoantigen SP-1 was identified in ductal epithelia of salivary glands in il14α TG mice by IIF. SP-1 mRNAs expression increased with growing age in il14α TG mice. SP-1 mRNA was also identified in labial biopsies of patients with pSS. In conclusion, autoantibody to SP-1 is an early marker in pSS. It is useful to diagnose pSS patients who lack RF or antibodies to Ro/La.

Hypokalemic Paralysis: A Hidden Card of Several Autoimmune Diseases

Acute hypokalemic paralysis is a rare and potentially fatal condition, with few related causes, one of which highlights distal renal tubular acidosis (dRTA). Distal renal tubular acidosis is a rare complication of several autoimmune diseases such as systemic lupus erythematosus, Sjögren's syndrome, and Hashimoto thyroiditis. We report a case of a lupic patient who presented rapidly progressive quadriparesis in the context of active renal disease. Research revealed severe refractory hypokalemia, metabolic acidosis, and alkaline urine suggestive of dRTA. We diagnosed Sjögren's syndrome based on sicca symptoms, an abnormal salivary glands' nuclear scan and the presence of anti-Ro/SSA and anti-La/SSB. In addition, the finding of thyroid peroxidase, thyroglobulin antibodies, and hypothyroidism led us to the diagnosis of Hashimoto thyroiditis. Due to the active renal involvement on the context of systemic lupus erythematosus and Sjögren's syndrome, the patient received immunosuppression with rituximab, resulting in a progressive and complete improvement.

Renal involvement in primary Sjögren syndrome

Primary Sjögren syndrome (pSS) is an autoimmune disorder characterized by lymphoplasmacytic infiltration of the exocrine (salivary and lachrymal) glands that results in sicca symptoms (dryness of the eyes and mouth). Systemic complications can occur in pSS, but renal involvement is rare, affecting <10% patients. The most frequent form of nephropathy in pSS is tubulointerstitial nephritis (TIN), in which infiltration of the kidney by plasma cells is a key feature and shows similarity to the lymphoplasmacytic infiltration of the salivary glands. Electrolyte disturbances may occur in pSS, such as renal distal tubular acidosis, diabetes insipidus, Gitelman syndrome or Fanconi syndrome. Glomerular involvement is less frequently detected in patients with pSS, but usually takes the form of membranoproliferative glomerulonephritis secondary to cryoglobulinaemia. The renal prognosis in patients with pSS and TIN or glomerular disease is usually favourable, but the risk of chronic kidney disease remains high in patients with TIN. Appropriate screening must be performed at least once a year in patients with systemic pSS in order to facilitate the early detection of renal complications. In this Review we discuss the epidemiology, pathophysiology, differential diagnosis and treatment of renal disease in pSS.

Proteomic surveillance of putative new autoantigens in thyroid orbitopathy

AIMS

Thyroid orbitopathy (TO) is an autoimmune inflammatory disorder characterised by several ocular manifestations. Several autoantigens have been proposed to be involved in the pathogenesis of TO, but the autoantigen system and the mechanism of TO would be rather complex. In this study, an immunoproteomic method was used to survey novel autoantigens expressed in the orbital fat tissue of patients with TO.

METHODS

We used immunoproteomic, ELISA and immunohistochemical staining methods to survey novel autoantigens expressed in the orbital fat tissue of patients with TO.

RESULTS

Six protein spots showing high reactivity with the serum from the patients with TO were detected as candidate orbital autoantigens, and two of them (carbonic anhydrase 1 (CA1) and alcohol dehydrogenase 1B (ADH1B)) were further verified by ELISA and immunohistochemical staining. We found that CA1 and ADH1B could attribute target autoantigens in this autoimmune disease. We discovered anti-CA1 and anti-ADH1B antibody prevalence to be higher in patients with TO (68.57%/51.43%) or Graves' disease (GD) (72%/48%) than in healthy controls respectively. Immunohistochemical staining study revealed the significantly enhanced expressions of CA1 and ADH1B in orbital fat of TO compared with that in healthy controls.

CONCLUSIONS

We found that CA1 and ADH1B could attribute target autoantigens in this autoimmune disease. The high prevalence of these autoantibodies against CA1 and ADH1B in patients with TO and GD clarifies the potential clinical role for anti-CA1 and anti-ADH1B antibodies as biomarkers for GD and TO.

Mitochondrial-dependent Autoimmunity in Membranous Nephropathy of IgG4-related Disease

The pathophysiology of glomerular lesions of membranous nephropathy (MN), including seldom-reported IgG4-related disease, is still elusive. Unlike in idiopathic MN where IgG4 prevails, in this patient IgG3 was predominant in glomerular deposits in the absence of circulating anti-phospholipase A₂ receptor antibodies, suggesting a distinct pathologic process. Here we documented that IgG4 retrieved from the serum of our propositus reacted against carbonic anhydrase II (CAII) at the podocyte surface. In patient's biopsy, glomerular CAII staining increased and co-localized with subepithelial IgG4 deposits along the capillary walls. Patient's IgG4 caused a drop in cell pH followed by mitochondrial dysfunction, excessive ROS production and cytoskeletal reorganization in cultured podocytes. These events promoted mitochondrial superoxide-dismutase-2 (SOD2) externalization on the plasma membrane, becoming recognizable by complement-binding IgG3 anti-SOD2. Among patients with IgG4-related disease only sera of those with IgG4 anti-CAII antibodies caused low intracellular pH and mitochondrial alterations underlying SOD2 externalization. Circulating IgG4 anti-CAII can cause podocyte injury through processes of intracellular acidification, mitochondrial oxidative stress and neoantigen induction in patients with IgG4 related disease. The onset of MN in a subset of patients could be due to IgG4 antibodies recognizing CAII with consequent exposure of mitochondrial neoantigen in the context of multifactorial pathogenesis of disease.

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In a patient with IgG4-related disease, glomerular CAII increases and colocalizes with IgG4 deposits.

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IgG4 from patient's serum reacts against CAII expressed by podocytes.

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IgG4 causes acidification, mitochondrial dysfunction and ROS-dependent cytoskeletal alterations in cultured podocytes.

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IgG4 induces the externalization on the plasma membrane of clustered SOD2, becoming recognizable by complement-binding IgG3.

Distal renal tubular acidosis associated with Sjogren syndrome

Renal tubular acidosis is a common cause of normal anion gap metabolic acidosis but these disorders can be easily missed or misdiagnosed. We highlight the approach to assessing renal tubular acidosis by discussing a case study with a temporal data set collected over more than 5 weeks. We highlight the principles and the necessary information required for a diagnosis of classic distal renal tubular acidosis. We also briefly review several aspects of type 1 renal tubular acidosis related to autoimmune disease, drugs and thyroid disorders.

Xerophthalmia of Sjogren's Syndrome Diagnosed with Anti-Salivary Gland Protein 1 Antibodies

Purpose

The purpose of this report is to describe 2 patients with persistent severe dry eyes, positive Schirmer tests for Sjogren's syndrome (SS) but lacking antibodies to either Ro or La. These patients were diagnosed to have SS by detecting antibodies to salivary gland protein 1 (Sp1) and parotid secretory protein (PSP). This report emphasizes the existence of patients with SS who lack antibodies to either Ro or La and may therefore be misdiagnosed. Detection of novel autoantibodies, including antibodies to Sp1 and PSP, are helpful in identifying these patients. Initial presentation may simply be dry eyes.

Methods

Two patients who presented to our ophthalmology clinic are described. One of the patients underwent multiple procedures over a period of 10 years for severe xerophthalmia. The other patient had rheumatoid arthritis and xerophthalmia. However, in both patients, chronic xerophthalmia had been considered to be idiopathic because antibodies Ro and La were negative. Further serologic testing revealed antibodies to Sp1 and PSP.

Results

Two patients who lacked antibodies to Ro and La but not to Sp1 and PSP were diagnosed as having SS.

Conclusion

Patients presenting with unexplained dry eyes may not always show the serology markers in the current criteria for SS, anti-Ro and anti-La. In these cases, investigation for novel, early antibodies to Sp1 and PSP is of importance in the diagnosis of SS.

Sjögren's syndrome: where do we stand, and where shall we go?

Primary Sjögren's syndrome (pSS) is one of the most frequent autoimmune systemic diseases, mainly characterized by ocular and oral dryness due to the progressive destruction of lachrymal and salivary glands by an inflammatory process. A noteworthy proportion of patients also features extraglandular manifestations, sometimes severe and life-threatening. Until now, its management relies mostly on symptomatic interventions, long-term monitoring, and, in patients with severe systemic complications, immunosuppressive drugs can be provided. However, recent years have seen great progresses in the understanding of the pathological processes of the disease. The central role of regulatory lymphocytes, the implication of the type 1 interferon pathway in some patients or the importance of epigenetics have been highlighted. New classification criteria have been recently published and have shed in light an international attempt for a better recognition of the patients, probably thanks to the development of new diagnostic procedures such as salivary gland ultrasonography. To facilitate the detection of treatment efficacy in clinical trials and to help in determining which subgroups of patients would have benefits from intensive therapies, a better definition of activity scores and the availability of new prognostic markers are urgent. Thereby, the development of future therapies should be based on specific molecular signatures that will enable a personalized management of each patient. This review focuses on the most striking advances in the fields of pathophysiology, diagnosis and treatment of pSS, which generate a great hope for pSS patients.

Isolation and sequencing of swine carbonic anhydrase VI, an enzyme expressed in the swine kidney

Background

Carbonic anhydrase VI (CA-VI) is produced by the salivary gland and is secreted into the saliva. Although CA-VI is found in the epithelial cells of distal straight tubule of swine kidneys, the exact function of CA-VI in the kidneys remains unclear.

Results

CA-VI was located in the epithelial cells of distal straight tubule of swine kidneys.

A full-length cDNA clone of CA-VI was generated from the swine parotid gland by reverse transcription polymerase chain reaction, using degenerate primers designed based on conserved regions of the same locus in human and bovine tissues.

The cDNA sequence was 1348 base pairs long and was predicted to encode a 317 amino acid polypeptide with a putative signal peptide of 17 amino acids. The deduced amino acid sequence of mature CA-VI was most similar (77.4%) to that of human CA-VI. CA-VI expression was confirmed in both normal and nephritic kidneys, as well as parotid. As the primers used in this study spanned two exons, the influence of genomic DNA was not detected. The expression of CA-VI was demonstrated in both normal and nephritic kidneys, and mRNA of CA-VI in the normal kidneys which was the normalised to an endogenous β–actin was 0.098 ± 0.047, while it was significantly lower in the diseased kidneys (0.012 ± 0.007). The level of CA-VI mRNA in normal kidneys was 19-fold lower than that of the parotid gland (1.887).

Conclusions

The localisation of CA-VI indicates that it may play a specialised role in the kidney.

Anti-carbonic anhydrase II antibodies in end-stage renal disease patients

OBJECTIVE

The aim of this study was to investigate the presence of anti-carbonic anhydrase (CA II) autoantibodies in patients with end-stage renal disease (ESRD) and relationships between the autoantibody titers and ghrelin, glucose, blood urea nitrogen (BUN) and creatinine.

SUBJECTS AND METHODS

Serum CA II autoantibody titers, malondialdehyde (MDA), BUN, creatinine and ghrelin levels were measured in 45 ESRD patients and 45 healthy subjects.

RESULTS

The CA II autoantibody titers in the ESRD group (0.170 ± 0.237) were significantly higher than those in the control group (0.079 ± 0.032; p = 0.035). MDA and ghrelin levels were also significantly higher in the ESRD group (p < 0.001). A weak positive correlation was determined between anti-CA II antibody titers and MDA, and a negative correlation was observed between ghrelin levels and anti-CA II antibody titers (r = 0.287, p = 0.028 and r = -0.278, p = 0.032, respectively).

CONCLUSIONS

In ESRD patients, the results showed the development of an autoimmune response against CA II. This suggests that anti-CA II antibodies could be involved in the pathogenesis of ESRD.

Novel autoantibodies in Sjogren's syndrome

Sjogren's syndrome (SS) is defined by autoantibodies to Ro and La. The current studies identified additional autoantibodies in SS to salivary gland protein 1 (SP-1), carbonic anhydrase 6 (CA6) and parotid secretory protein (PSP). These autoantibodies were present in two animal models for SS and occurred earlier in the course of the disease than antibodies to Ro or La. Patients with SS also produced antibodies to SP-1, CA6 and PSP. These antibodies were found in 45% of patients meeting the criteria for SS who lacked antibodies to Ro or La. Furthermore, in patients with idiopathic xerostomia and xerophthalmia for less than 2 years, 76% had antibodies to SP-1 and/or CA6 while only 31% had antibodies to Ro or La. Antibodies to SP-1, CA6 and PSP may be useful markers for identifying patients with SS at early stages of the disease or those that lack antibodies to either Ro or La.

Subgroups of Sjögren syndrome patients according to serological profiles

Sjögren Syndrome (SS) is a systemic, autoimmune disorder characterized by lymphocytic infiltration of the exocrine glands. Different clinical associations have been described for each of the diverse autoantibodies found in SS patients. Antibodies directed against the Ro/La ribonucleoprotein complexes have been correlated with younger age, more severe dysfunction of the exocrine glands and a higher prevalence of extraglandular manifestations. Anti-nuclear antibodies and rheumatoid factors have been associated to extraglandular manifestations and an active immunological profile, while cryoglobulins are markers of more severe disease and correlate to lymphoma development and death. Antibodies to cyclic citrullinated peptides are scarce in SS and have been linked in some cases to the development of non-erosive arthritis. Furthermore, the presence of anti-mitochondrial antibodies and anti-smooth muscle antibodies in the sera of primary SS patients is considered indicative of primary biliary cirrhosis and autoimmune hepatitis, respectively. In addition, anti-centromere antibodies have been associated with a clinical phenotype intermediate between primary SS and systemic sclerosis, while antibodies against carbonic anhydrase have been related to renal tubular acidosis. Finally, an association of anti-muscarinic antibodies with cytopenias and a higher disease activity has also been described in primary SS. In conclusion, although not all of the above mentioned antibodies are useful for predicting distinct patient subgroups in SS, knowledge of the clinical associations of the different autoantibody specificities encountered in SS can advance our understanding of the disease and improve patient management.

Successful treatment of osteomalacia caused by renal tubular acidosis associated with Sjögren's syndrome

A 62-year-old woman was diagnosed with severe osteomalacia caused by renal tubular acidosis associated with Sjögren's syndrome. She was treated with sodium bicarbonate, risedronate, alfacalcidol, and prednisolone (1 mg/kg). By 24 months, renal tubular acidosis was improved and the bone density had normalized. Here we report the successful amelioration of bone lesions through a multidisciplinary approach that improved renal tubular acidosis, with a special focus on treatment of the underlying inflammatory disorder with glucocorticoids.