Islet autoantibodies and insulin dependent diabetes mellitus in cystic fibrosis

ZnT8 antibodies in patients with cystic fibrosis: an expression of secondary beta-cell damage?

Cystic Fibrosis-Related Diabetes (CFRD) is caused by a severe insulin deficiency with associated different degrees of insulin resistance. Data concerning the potential impact of autoimmunity are conflicting. Ninety subjects with cystic fibrosis (CF) were tested for glucose tolerance and autoantibodies against insulin (IAA), glutamic acid decarboxylase (GADA), protein tyrosine phosphatase (IA2) and zinc transporter 8 (Znt8A). Eighty-three subjects showed a normal glucose tolerance (92.2%), 6 subjects (6.6%) impaired glucose tolerance and 1 subject (1.1%) newly diagnosed CFRD. Four subjects were found positive for both IAA and GADA (4.4%), one subject (1.1%) for both IA2 and GADA, and one subject (1.1%) for isolated GADA. Three subjects (3.3%) showed isolated ZnT8A positivity. ZnT8A positivity in CF patients is uncommon and not associated with other autoantibodies. ZnT8A may not represent a specific indicator of a primary autoimmune beta-cell destruction, but possibly the expression of a secondary damage of the pancreatic islets with autoantigen release.

Managing diabetes in cystic fibrosis

Cystic fibrosis related diabetes (CFRD) is the most common co-morbidity in persons with cystic fibrosis (CF). As the life expectancy of persons with CF continues to increase, the need to proactively diagnose and aggressively treat CFRD and its potential complications has become more apparent. CFRD negatively impacts lung function, growth and mortality, making its diagnosis and management crucial in a population already at high risk for early mortality. Compared to type 1 and type 2 diabetes, CFRD is a unique entity, requiring a thorough understanding of its unique pathophysiology to facilitate the creation and utilization of an effective medical treatment plan. The physiology of CFRD is complex, likely consisting of a combination of insulin deficiency, insulin resistance and a genetic predisposition towards the development of diabetes. However, the hallmark of CFRD is insulin deficiency, necessitating the use of exogenous insulin as the mainstay of therapy. Insulin administration, in combination with a multidisciplinary team of health professionals with expertise in the care of patients with CF and CFRD, is the cornerstone of the care for these patients. The goals of treatment of the CFRD population are to reverse protein catabolism, maintain a healthy weight, and reduce acute and chronic diabetes complications. Creating a partnership between the treatment team and the patient is the ideal way to accomplish these goals and is essential for successful diabetes care.

A susceptibility gene for type 2 diabetes confers substantial risk for diabetes complicating cystic fibrosis

AIMS/HYPOTHESIS

Insulin-requiring diabetes affects 25-50% of young adults with cystic fibrosis (CF). Although the cause of diabetes in CF is unknown, recent heritability studies in CF twins and siblings indicate that genetic modifiers play a substantial role. We sought to assess whether genes conferring risk for diabetes in the general population may play a risk modifying role in CF.

METHODS

We tested whether a family history of type 2 diabetes affected diabetes risk in CF patients in 539 families in the CF Twin and Sibling family-based study. A type 2 diabetes susceptibility gene (transcription factor 7-like 2, or TCF7L2) was evaluated for association with diabetes in CF using 998 patients from the family-based study and 802 unrelated CF patients in an independent case-control study.

RESULTS

Family history of type 2 diabetes increased the risk of diabetes in CF (OR 3.1; p = 0.0009). A variant in TCF7L2 associated with type 2 diabetes (the T allele at rs7903146) was associated with diabetes in CF in the family study (p = 0.004) and in the case-control study (p = 0.02; combined p = 0.0002). In the family-based study, variation in TCF7L2 increased the risk of diabetes about three-fold (HR 1.75 per allele, 95% CI 1.3-2.4; p = 0.0006), and decreased the mean age at diabetes diagnosis by 7 years. In CF patients not treated with systemic glucocorticoids, the effect of TCF7L2 was even greater (HR 2.9 per allele, 95% CI 1.7-4.9, p = 0.00011).

CONCLUSIONS/INTERPRETATION

A genetic variant conferring risk for type 2 diabetes in the general population is a modifier of risk for diabetes in CF.

Anti-GAD65 reactive peripheral blood mononuclear cells in the pathogenesis of cystic fibrosis related diabetes mellitus

OBJECTIVE

A role of autoreactive T cells for type 1 diabetes pathogenesis is considered crucial. In our pilot study we addressed if autoreactive mononuclear cells are present also in peripheral blood of patients with other specific forms of diabetes as cystic fibrosis related diabetes (CFRD).

METHODS

Cellular immune responses to a known beta-cell autoantigen (GAD65 and GAD65 derived peptides) were analysed by ELISPOT (IFN-gamma) and by protein microarray analysis in four patients suffering from CFRD, in four cystic fibrosis (CF) patients without diabetes, in eight type 1 diabetes patients (without CF) and in four healthy controls.

RESULTS

Response to the autoantigen GAD65 (protein and peptides) was observed in 7/8 patients suffering from CF and in all type 1 diabetes patients. Post-stimulation production of Th1 cytokines (IFN-gamma, TNF-beta) was observed in 2/4 CFRD, 1/4 CF patients and in 7/8 type 1 diabetes patients. All these patients carry prodiabetogenic HLA-DQ genotype. Th2- and Th3 type of cytokine pattern was observed in 2/4 CF patients. Production of IL-8 was observed in the third CFRD as well as in the third CF patient and in 1/8 type 1 diabetes patient and borderline production of this chemokine was also observed in 2/4 healthy controls. No reaction was observed in the other 2/4 healthy controls and in the fourth CFRD patient who carried a strongly protective genotype and did not produce autoantibodies. The most potent peptide of GAD65 was amino acids 509-528.

CONCLUSIONS

We consider our observations as a sign of a reaction directed against the self-antigen GAD65 that are closely connected to type 1 diabetes. In CF patients who do not develop diabetes autoreactive mechanisms are very probably efficiently suppressed by immune self-tolerance mechanisms. CFRD patients are a heterogenic group. To disclose those who may display features of autoimmune diabetes could have an impact for their therapy and prognosis.

Beta-cell autoantibodies and diabetes mellitus family history in cystic fibrosis

OBJECTIVE

To verify whether autoimmunity against beta-cells and family history of type 1 and/or type 2 diabetes mellitus (DM) play a role in the pathogenesis of cystic fibrosis (CF)-related diabetes mellitus (CFRD).

PATIENTS AND METHODS

The prevalence of beta-cell autoantibodies (GADA and IA-2A) was investigated in a group of patients with CF compared with patients with type 1 DM (DM1) and controls. Family history of DM1 and/or DM2 was investigated among patients with CF.

RESULTS

Frequency of beta-cell autoantibodies was significantly lower (p = 0.0001) in patients with CF with CFRD (IA-2A: 0%; GADA 12.5%) than in patients with DM1 (64.1% vs 52.8%, respectively) and it did not differ from the frequency in patients with CF without CFRD. Prevalence of family history for DM1 or DM2 was not significantly higher in CF patients with CFRD than in CF patients without CFRD.

CONCLUSIONS

The investigated factors did not show correlation with the pathogenesis of CFRD.

Clinical importance of cystic fibrosis-related diabetes

The prevalence of cystic fibrosis-related diabetes (CFRD) and glucose intolerance (IGT) has risen dramatically over the past 20 years as survival has increased for people with cystic fibrosis (CF). Diabetes is primarily caused by pancreatic damage, which reduces insulin secretion, but glucose tolerance is also modified by factors that alter insulin resistance, such as intercurrent illness and infection. CFRD not only causes the symptoms and micro and macrovascular complications seen in type 1 and type 2 diabetes in the general population, but also is associated with accelerated pulmonary decline and increased mortality. Pulmonary effects are seen some years before the diagnosis of CFRD, implying that impaired glucose tolerance may be detrimental. Current practice is to screen for changes in glucose tolerance by regular measurement of fasting blood glucose, by oral glucose tolerance test or a combination of these approaches with symptom review and measurement of HbA1C. Treatment is clearly indicated for those with CFRD and fasting hyperglycaemia to control symptoms and reduce complications. As nutrition is critical in people with CF to maintain body mass and lung function, blood glucose should be controlled in CFRD by adjusting insulin doses to the requirements of adequate food intake and not by calorie restriction. It is less clear whether blood glucose control will have clinical benefits in the management of patients with CFRD without fasting hyperglycaemia or with impaired glucose tolerance and further studies are required to establish the best treatment for this patient group.

Diabetes in an infant with cystic fibrosis

Cystic fibrosis (CF)-related diabetes mellitus is an unusual complication in very young pediatric patients with CF. It is generally associated with more severe clinical manifestations of CF. In this report, we describe a case of diabetes and CF starting in infancy. The patient manifested a form of intermittent diabetes without fasting hyperglycemia, which was exacerbated by steroid treatment during pulmonary disease and occasionally required insulin therapy. Insulin responses to oral and intravenous glucose challenge were low. The clinical and radiological status was stable during the 9-yr follow-up. Our patient demonstrates that diabetes may not only represent a complication of CF, as previously maintained, but can also be a co-morbid condition proceeding along with the exocrine disease. The early occurrence of hyperglycemia in this case may highlight an impairment of beta-cell function, which might be genetically determined. Careful monitoring of the glucose profile and of beta-cell function is indicated in patients with CF to avoid late recognition of diabetes.

Autoantibodies to pancreatic hsp60 precede the development of glucose intolerance in patients with cystic fibrosis

Persons expressing the genetic disease cystic fibrosis (CF) suffer from a high risk of developing impaired glucose tolerance and diabetes. The development of diabetes in CF has been attributed, in the past, to the destruction of pancreatic islets and their resident beta-cells secondary to the destruction of the surrounding tissue by mechanical clogging of the pancreatic exocrine ducts. However, the discovery that autoimmunity to the 60-kDa heat shock protein (hsp60) may cause type I diabetes in NOD mice raises the possibility that hsp60 autoimmunity may be involved in CF diabetes too; could the hyperimmunization to bacterial hsp60 characteristic of CF spread to self-hsp60 and hence to autoimmune diabetes? We now report that rising levels of IgG autoantibodies to hsp60 do indeed precede the appearance of glucose intolerance and diabetes in CF patients. We produced a recombinant human pancreatic hsp60 protein and investigated the IgG antibody response to hsp60 in prediabetic and non-diabetic patients with CF. To detect hsp60 autoantibodies in the presence of high levels of antibodies to bacterial hsp60, we absorbed test sera with the 60-kDa GroEL of Pseudomonas aeruginosa and used an immunostaining technique. Using this technique, 32 prediabetic CF patients were evaluated over a five-year period, three years, on the average, before the onset of glucose intolerance. We found that a significant increase in hsp60 autoantibody preceded impaired glucose tolerance (P=0.042, n=17), diabetes (P=0.011, n=15) and glucose intolerance (P=0.005, n=32). As has been observed in NOD mice and in type I diabetic patients, the hsp60 autoantibodies decline at the outbreak of glucose intolerance in the CF patients. The association of CF diabetes with the rise and fall of hsp60 autoimmunity suggests that the pathogenesis of the diabetes may not be merely mechanical, but arise in the wake of bacterial hyperimmunisation.

Rethinking cystic fibrosis pathology: the critical role of abnormal reduced glutathione (GSH) transport caused by CFTR mutation

Though the cause of cystic fibrosis (CF) pathology is understood to be the mutation of the CFTR protein, it has been difficult to trace the exact mechanisms by which the pathology arises and progresses from the mutation. Recent research findings have noted that the CFTR channel is not only permeant to chloride anions, but other, larger organic anions, including reduced glutathione (GSH). This explains the longstanding finding of extracellular GSH deficit and dramatically reduced extracellular GSH:GSSG (glutathione disulfide) ratio found to be chronic and progressive in CF patients. Given the vital role of GSH as an antioxidant, a mucolytic, and a regulator of inflammation, immune response, and cell viability via its redox status in the human body, it is reasonable to hypothesize that this condition plays some role in the pathogenesis of CF. This hypothesis is advanced by comparing the literature on pathological phenomena associated with GSH deficiency to the literature documenting CF pathology, with striking similarities noted. Several puzzling hallmarks of CF pathology, including reduced exhaled NO, exaggerated inflammation with decreased immunocompetence, increased mucus viscoelasticity, and lack of appropriate apoptosis by infected epithelial cells, are better understood when abnormal GSH transport from epithelia (those without anion channels redundant to the CFTR at the apical surface) is added as an additional explanatory factor. Such epithelia should have normal levels of total glutathione (though perhaps with diminished GSH:GSSG ratio in the cytosol), but impaired GSH transport due to CFTR mutation should lead to progressive extracellular deficit of both total glutathione and GSH, and, hypothetically, GSH:GSSG ratio alteration or even total glutathione deficit in cells with redundant anion channels, such as leukocytes, lymphocytes, erythrocytes, and hepatocytes. Therapeutic implications, including alternative methods of GSH augmentation, are discussed.