Peak glucose during an oral glucose tolerance test is associated with future diabetes risk in adults with cystic fibrosis

The effect of a pre-meal snack and/or postprandial exercise on breakfast glycemic excursion in adults with cystic fibrosis: A pilot study

BACKGROUND & AIMS

Cystic fibrosis (CF)-related diabetes (CFRD), a common comorbidity in CF, is often preceded and characterized with elevated postprandial glycemic (PPG) excursions. In the general population, the consumption of a pre-meal protein snack and/or physical activity (PA) hinder the elevation of PPG levels. Our objective is to evaluate the effect of a pre-meal snack and/or post-meal PA on PPG excursions in CF.

METHODS

This is a double-blinded randomized controlled crossover interventional study in 14 adults with CF, with 4 interventions: placebo pre-meal snack + no PA (control: CTL), pre-meal soy snack + no PA (SK), placebo pre-meal snack + PA (PA), and pre-meal soy snack + PA (SK + PA). The pre-meal soy snack or placebo beverage (vanilla flavoured water) is served at 8 AM, followed by a standardized breakfast at 9 AM and, postprandially, 5 repeated bouts of 3-min walk every 30 min or sedentary activity. Blood glucose and insulin were measured every 15-30 min during the interventions.

RESULTS

Plasma glucose (PG) was higher 30 min after snack consumption compared to placebo beverage. One-hour post-breakfast, PG levels were lower during both PA interventions than with sedentary behavior. However, the overall 3 h post-breakfast glucose area under the curve (AUC) was similar between interventions. Post-breakfast 3 h insulin AUC was significantly lower during the SK + PA intervention compared to the sedentary behavior interventions.

CONCLUSION

Repeated short bouts of post-meal physical activity may positively impact PPG control in adults with CF, with or without the addition of a pre-meal soy snack. A pre-meal snack alone does not improve PPG.

Feasibility and accuracy of at-home glucose tolerance tests for cystic fibrosis related diabetes screening

BACKGROUND

Adult people living with Cystic Fibrosis (CF) undergo annual screening for CF-related diabetes. These tests represent a burden and can lead to undesirable effects resulting in low adherence. The objectives of this study were to 1) compare gold-standard in-hospital oral glucose tolerance testing (OGTT) with at-home options, and 2) evaluate acceptability of at-home options.

METHODS

A total of 34 adults living with CF undertook 3 types of OGTTs in standardized conditions within two weeks: 1) in a hospital using a 75 g glucose beverage, 2) at home with the same glucose beverage, and 3) at home using a standardized quantity of candy. Glucose levels were measured prior to the OGTT, after 1 and 2 hours. Concordance of glucose measurement, side effects and general appreciation were assessed across the three options.

RESULTS

Mean blood glucose was comparable among the three tests. Glucose tolerance categorization (normal, impaired glucose tolerance, or diabetes) was concordant with the hospital reference test in 59 % of participants for the glucose beverage and 75 % for the candies. Side effects were mild with all types of OGTTs, and 94 % of participants preferred the home options. Among the at-home OGTTs, the glucose beverage was preferred to the candy option.

CONCLUSIONS

Home-based OGTT could be an alternative to gold standard hospital-based OGTT testing, improving adherence to annual testing and reducing costs. However, the discrepancy between various OGTT testing methods could lead to diagnosis dilemma. This approach should be tested on a larger sample size.

Continuous glucose monitoring and advanced glycation endproducts for prediction of clinical outcomes and development of cystic fibrosis-related diabetes in adults with CF

Introductions

Cystic fibrosis-related diabetes (CFRD) is associated with pulmonary decline, compromised nutritional status, and earlier mortality. Onset is often insidious, so screening for early detection of glycemic abnormalities is important. Continuous glucose monitoring (CGM) has been validated in people with CF and has been shown to detect early glycemic variability otherwise missed on 2-hour oral glucose tolerance testing (OGTT). We previously reported that CGM measures of hyperglycemia and glycemic variability are superior to hemoglobin A1c (HbA1c) in distinguishing those with and without CFRD. However, little is known about the long-term predictive value of CGM measures of glycemia for both the development of CFRD and their effect on key clinical outcomes such as weight maintenance and pulmonary function. In addition, there have been no studies investigating advanced glycation endproducts (AGE) assessed by skin autofluorescence in people with CF.

Methods

In this prospective observational study, CGM and HbA1c were measured at 2 to 3 time points 3 months apart in 77 adults with CF. Participants who did not have CFRD at the time of enrollment underwent OGTT at the baseline visit, and all participants had AGE readings at baseline. Follow up data including anthropometric measures, pulmonary function and CFRD status were collected by review of medical records 1- and 2-years after the baseline visits. We applied multivariable linear regression models correlating glycemic measures to change in key clinical outcomes (weight, BMI, FEV1) accounting for age, gender and elexacaftor/tezacaftor/ivacaftor (ETI) use. We also conducted logistic regression analyses comparing baseline glycemic data to development of CFRD during the 2-year follow up period.

Results

Of the 77 participants, 25 had pre-existing CFRD at the time of enrollment, and six participants were diagnosed with CFRD by the OGTT performed at the baseline visit. When adjusting for age, gender, and ETI use, multiple CGM measures correlated with weight and BMI decline after one year but not after two years. CGM and HbA1c at baseline did not predict decline in FEV1 (p>0.05 for all). In the 46 participants without a diagnosis of CFRD at baseline, two participants were diagnosed with CFRD over the following two years, but CGM measures at baseline did not predict progression to CFRD. Baseline AGE values were higher in individuals with CFRD and correlated with multiple measures of dysglycemia (HbA1c, AG, SD, CV, TIR, % time >140, >180, >250) as well as weight. AGE values also correlated with FEV1 decline at year 1 and weight decline at year 1 and year 2.

Conclusions

Several key CGM measures of hyperglycemia and glycemic variability were predictive of future decline in weight and BMI over one year in this population of adults with CF with and without CFRD. None of the baseline glycemic variables predicted progression to CFRD over 2 years. To our knowledge, this is the first report correlating AGE levels with key clinical and glycemic measures in CF. Limitations of these analyses include the small number of participants who developed CFRD (n=2) during the follow up period and the initiation of ETI by many participants, affecting their trajectory in weight and pulmonary function. These results provide additional data supporting the potential role for CGM in identifying clinically significant dysglycemia in CF. Future studies are needed to investigate CGM as a diagnostic and screening tool for CFRD and to understand the implications of AGE measures in this patient population.

ESPEN-ESPGHAN-ECFS guideline on nutrition care for cystic fibrosis

BACKGROUND

Nutritional status is paramount in Cystic Fibrosis (CF) and is directly correlated with morbidity and mortality. The first ESPEN-ESPGHAN-ECFS guidelines on nutrition care for infants, children, and adults with CF were published in 2016. An update to these guidelines is presented.

METHODS

The study was developed by an international multidisciplinary working group in accordance with officially accepted standards. Literature since 2016 was reviewed, PICO questions were discussed and the GRADE system was utilized. Statements were discussed and submitted for on-line voting by the Working Group and by all ESPEN members.

RESULTS

The Working Group updated the nutritional guidelines including assessment and management at all ages. Supplementation of vitamins and pancreatic enzymes remains largely the same. There are expanded chapters on pregnancy, CF-related liver disease, and CF-related diabetes, bone disease, nutritional and mineral supplements, and probiotics. There are new chapters on nutrition with highly effective modulator therapies and nutrition after organ transplantation.

Advances in cystic fibrosis-related diabetes: Current status and future directions

AIMS

The aim of this review is to give an update of the recent advances in the pathophysiology, prognosis, diagnosis and treatments of cystic fibrosis-related diabetes (CFRD).

METHODS

The literature survey focuses on original and review articles dealing with CFRD between 2006 and 2023, and in particular with: pathophysiology, risk and predictive factors, screening, chronic complications of CFRD, management and the effects of CFTR channel modulator therapies on glucose homeostasis, using PubMed®.

RESULTS

The rising prevalence of CFRD is due to prolonged life survival among patients with cystic fibrosis (CF). Advances in the understanding of the pathophysiology highlight the singularity of CFRD. Adherence to diagnostic guidelines remains challenging. Besides the classical OGTT, alternative diagnostic tests are being considered: HbA1c measurement, continuous glucose monitoring (CGM), intermediate measurements of alternative glucose tolerance stages through OGTT and homeostatic model assessment (HOMA). Early treatment of (pre)diabetes in CF patients is mandatory. The advent of CFTR channel modulator therapies have created a paradigm shift in the management of CF: they seem to improve glucose homeostasis, but the mechanism remains unclear.

CONCLUSION

CFRD management is an ongoing concern. Optimal care has reduced the negative impact of CFRD on lung function, nutrition, and survival. Increasing prevalence of CFRD and prolonged lifespan lead to more microvascular complications. New screening tools (Hba1c, CGM, HOMA) show potential for better classification of patients. The effect of CFTR modulators on glucose metabolism warrants further research.

A glycosylated hemoglobin A1c above 6% (42 mmol/mol) is associated with a high risk of developing Cystic Fibrosis-Related Diabetes and a lower probability of weight gain in both adults and children with Cystic Fibrosis

OBJECTIVES

The classical glycosylated hemoglobin A1c threshold of 6.5% is an insensitive screening test for cystic fibrosis-related diabetes (CFRD). We sought to identify CF-specific A1C thresholds associated with 1) risk of progression to CFRD and 2) changes in body mass index (BMI) and forced expiratory volume (FEV1).

METHODS

We studied the cross sectional and longitudinal associations between A1c, BMI, and FEV1 in 2 cohorts of 223 children (followed for up to 8 years) and 289 adults (followed for a mean of 7.5 ± 4.3 years) with CF but without diabetes at baseline and undergoing regular assessments including Oral Glucose Tolerance Test (OGTT).

RESULTS

For the onset of OGTT-defined CFRD optimal A1c threshold was 5.9% in adults (sensitivity: 67% and specificity: 71%) and 5.7% for children (sensitivity: 60% and specificity: 47%). Kaplan-Meier analysis of progression to CFRD according to baseline A1C showed increased the risk of developing CFRD for A1c ≥ 6.0% in adults (P = 0.002) and ≥ 5.5% in children (p = 0.012). Temporal changes in BMI and FEV1 according to baseline A1C in adults were assessed with a linear mixed-effect model, BMI significantly increased over time in subjects with a baseline A1c < 6%, but those with a A1C ≥ 6.0% gained significantly less weight over time (P = 0.05). There was no difference in FEV1 according to baseline A1c category.

CONCLUSION

An A1C above 6% may be associated with a high risk of developing CFRD and a lower probability of weight gain in both adults and children with CF.

Cystic Fibrosis-Related Diabetes Workshop: Research Priorities Spanning Disease Pathophysiology, Diagnosis, and Outcomes

Cystic fibrosis (CF) is a recessive disorder arising from mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein. CFTR is expressed in numerous tissues, with high expression in the airways, small and large intestine, pancreatic and hepatobiliary ducts, and male reproductive tract. CFTR loss in these tissues disrupts regulation of salt, bicarbonate, and water balance across their epithelia, resulting in a systemic disorder with progressive organ dysfunction and damage. Pancreatic exocrine damage ultimately manifests as pancreatic exocrine insufficiency that begins as early as infancy. Pancreatic remodeling accompanies this early damage, during which abnormal glucose tolerance can be observed in toddlers. With increasing age, however, insulin secretion defects progress such that CF-related diabetes (CFRD) occurs in 20% of teens and up to half of adults with CF. The relevance of CFRD is highlighted by its association with increased morbidity, mortality, and patient burden. While clinical research on CFRD has greatly assisted in the care of individuals with CFRD, key knowledge gaps on CFRD pathogenesis remain. Furthermore, the wide use of CFTR modulators to restore CFTR activity is changing the CFRD clinical landscape and the field's understanding of CFRD pathogenesis. For these reasons, the National Institute of Diabetes and Digestive and Kidney Diseases and the Cystic Fibrosis Foundation sponsored a CFRD Scientific Workshop, 23-25 June 2021, to define knowledge gaps and needed research areas. This article describes the findings from this workshop and plots a path for CFRD research that is needed over the next decade.

Cystic Fibrosis-Related Diabetes Workshop: Research Priorities Spanning Disease Pathophysiology, Diagnosis, and Outcomes

Cystic fibrosis (CF) is a recessive disorder arising from mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein. CFTR is expressed in numerous tissues, with high expression in the airways, small and large intestine, pancreatic and hepatobiliary ducts, and male reproductive tract. CFTR loss in these tissues disrupts regulation of salt, bicarbonate, and water balance across their epithelia, resulting in a systemic disorder with progressive organ dysfunction and damage. Pancreatic exocrine damage ultimately manifests as pancreatic exocrine insufficiency that begins as early as infancy. Pancreatic remodeling accompanies this early damage, during which abnormal glucose tolerance can be observed in toddlers. With increasing age, however, insulin secretion defects progress such that CF-related diabetes (CFRD) occurs in 20% of teens and up to half of adults with CF. The relevance of CFRD is highlighted by its association with increased morbidity, mortality, and patient burden. While clinical research on CFRD has greatly assisted in the care of individuals with CFRD, key knowledge gaps on CFRD pathogenesis remain. Furthermore, the wide use of CFTR modulators to restore CFTR activity is changing the CFRD clinical landscape and the field's understanding of CFRD pathogenesis. For these reasons, the National Institute of Diabetes and Digestive and Kidney Diseases and the Cystic Fibrosis Foundation sponsored a CFRD Scientific Workshop, 23-25 June 2021, to define knowledge gaps and needed research areas. This article describes the findings from this workshop and plots a path for CFRD research that is needed over the next decade.

The Glycemic Curve during the Oral Glucose Tolerance Test: Is It Only Indicative of Glycoregulation?

The shape of the glycemic curve during the oral glucose tolerance test (OGTT), interpreted in the correct context, can predict impaired glucose homeostasis. Our aim was to reveal information inherent in the 3 h glycemic trajectory that is of physiological relevance concerning the disruption of glycoregulation and complications beyond, such as components of metabolic syndrome (MS).

METHODS

In 1262 subjects (1035 women, 227 men) with a wide range of glucose tolerance, glycemic curves were categorized into four groups: monophasic, biphasic, triphasic, and multiphasic. The groups were then monitored in terms of anthropometry, biochemistry, and timing of the glycemic peak.

RESULTS

Most curves were monophasic (50%), then triphasic (28%), biphasic (17.5%), and multiphasic (4.5%). Men had more biphasic curves than women (33 vs. 14%, respectively), while women had more triphasic curves than men (30 vs. 19%, respectively) (p < 0.01). Monophasic curves were more frequent in people with impaired glucose regulation and MS compared to bi-, tri-, and multiphasic ones. Peak delay was the most common in monophasic curves, in which it was also most strongly associated with the deterioration of glucose tolerance and other components of MS.

CONCLUSION

The shape of the glycemic curve is gender dependent. A monophasic curve is associated with an unfavorable metabolic profile, especially when combined with a delayed peak.

Screening strategies for glucose tolerance abnormalities and diabetes in people with cystic fibrosis

The increase in life expectancy of patients with cystic fibrosis has come with new comorbidities, particularly diabetes. The gradual development of glucose tolerance abnormalities means that 30 to 40% of adults will be diabetic. Cystic fibrosis-related diabetes is a major challenge in the care of these patients because it is a morbidity and mortality factor at all stages of the disease. Early glucose tolerance abnormalities observed from childhood, before the stage of diabetes, are also associated with a poor pulmonary and nutritional outcome. The long asymptomatic period justifies systematic screening with an annual oral glucose tolerance test from the age of 10 years. However, this strategy does not take into account the new clinical profiles of patients with cystic fibrosis, recent pathophysiological knowledge of glucose tolerance abnormalities, and the emergence of new diagnostic tools in diabetology. In this paper, we summarise the challenges of screening in the current context of new patient profiles - patients who are pregnant, have transplants, or are being treated with fibrosis conductance transmembrane regulator modulators - and put forward an inventory of the various screening methods for cystic fibrosis-related diabetes, including their applications, limitations and practical implications.

The utility of glucose area under the curve from the oral glucose tolerance test as a screening tool for cystic fibrosis-related diabetes

BACKGROUND

Consistently abnormal glucose levels on oral glucose tolerance test (OGTT) are the most effective screening tool for cystic fibrosis-related diabetes (CFRD). However, some cystic fibrosis (CF) patients demonstrate abnormal glucose profiles not reaching levels required for CFRD diagnosis and are, therefore, left untreated. Since CFRD is associated with disease deterioration, early diagnosis and treatment are desirable.

AIM

To explore the association between the area under the curve of glucose (G-AUC) obtained during a five-point 2-h standard OGTT and CF disease severity parameters.

METHODS

All CF patients referred for an annual routine OGTT at the Hadassah CF Center between 2002 and 2018, were included. Disease severity parameters were correlated with the G-AUC.

RESULTS

Two hundred forty-two OGTTs were performed in 81 patients (mean age 19.7 ± 9.0 years); 54% were normal, 14% showed impaired glucose tolerance (IGT), 5% had values in the indeterminate range (INDET), 11% had both IGT and INDET and 16% were diagnosed with CFRD. A gradual increase in mean G-AUC was observed among the groups. In multivariate regression models, G-AUC ≥ 295 mg h/dl was independently associated with an increased number of pulmonary exacerbations (PEx). Not all the patients having this value met the CFRD definition.

CONCLUSION

Patients who do not fulfill the criteria for CFRD may have abnormal glucose metabolism identifiable by abnormally high G-AUC values, which may be associated with more PEx. The potential advantage of treating these patients with insulin and the subsequent reduction in PEx needs further investigation.

Cystic Fibrosis-Related Diabetes: Clinical approach and knowledge gaps

Cystic Fibrosis-Related Diabetes (CFRD) is a unique type of diabetes mellitus that shares some features with both type 1 and type 2 diabetes. Yet, its distinguishing feature of acute pulmonary complications associated with hyperglycemia and the catabolic metabolism associated with a relative insulin deficiency poses challenges to the application of traditional definitions and treatments for diabetes mellitus. People with CF (pwCF) undergo rigorous annual screening starting at age 10, a process that is challenging for patients and limited by sensitivity, specificity, and reproducibility. As pwCF continue to live longer, over 50% are expected to develop CFRD over their lifetime, including up to 20% of adolescents. Increasing numbers of people with CFRD will make this disease increasingly relevant to diabetes practitioners. Evidence-guided practice in CFRD care is limited by small and short studies. Our current understanding of CFRD may change significantly with the recent introduction of CF Transmembrane Regulator (CFTR) modulator medications. This review will explore current challenges in the diagnosis and management of CFRD, specifically highlighting knowledge gaps in the pathophysiology of CFRD, optimal screening methods, priorities for research and provide guidance with regards to screening, diagnosis, and treatment.

Comparison of Continuous Glucose Monitoring in Cystic Fibrosis Patients With or Without Pancreatic Exocrine Insufficiency

This study aimed to compare continuous glucose monitoring (CGM) in cystic fibrosis (CF) according to pancreatic exocrine status.CGM and oral glucose tolerance testing (OGTT) were realized annually over five years in people with CF (pwCF) aged≥10 years without cystic fibrosis-related diabetes (CFRD). CGM parameters in patients with normal glucose tolerance (NGT), impaired glucose tolerance (IGT), and newly diagnosed CFRD were compared according to presence of pancreatic sufficiency (PS) or insufficiency (PI).Overall, 547 OGTTs and 501 CGMs were performed in 147 CF patients, comprising 122 PI and 25 PS. In PS patients, 84% displayed NGT, 12% IGT, and 4% CFRD vs. 58%, 32%, and 10% (p=0.05) in PI. Among participants displaying normal OGTT, time in glucose range (70-140 mg/dl) was significantly increased, 97% (93, 99) vs. 92% (85, 96), p<0.001, and time above glucose range > 140 mg/dl significantly decreased, 1% (0, 2) % vs. 6% (2, 13), in patients with PS compared to those with PI. No significant differences were highlighted in patients with IGT.CGM revealed significant different glucose tolerance abnormalities in PI versus PS, which were undetected by standard 2-hour OGTT glucose.

Combined Indeterminate and Impaired Glucose Tolerance Is a Novel Group at High Risk of Cystic Fibrosis-Related Diabetes

BACKGROUND

Indeterminate glycemia (INDET) and impaired glucose tolerance (IGT) are independently associated with cystic fibrosis-related diabetes (CFRD) risk. We determined whether patients meeting both criteria have increased risk of diabetes in 2 separate adult cohorts.

METHODS

The Montreal Cystic Fibrosis Cohort (MCFC; n = 293 baseline and 198 for prospective analysis excluding subjects identified with incident CFRD at baseline) and the Lyon cystic fibrosis cohort [Determination of the Predictive Factors in the Reversibility or the Aggravation in the Disorders of the Glucose Metabolism in Cystic Fibrosis Patients (DIAMUCO); n = 144/105] are prospective observational cohorts.

RESULTS

In the MCFC and DIAMUCO cohorts, mean age was 25.5 ± 7.7 and 25.0 ± 8.6 years; body mass index, 21.7 ± 3.0 and 20.2 ± 2.2 kg/m2; percentage of forced expiratory volume expired in 1 sec, 73.2 ± 22.1 and 62.5 ± 21.9; and follow-up, 6.9 ± 3.8 and 2.4 ± 1.2 years, respectively. In the MCFC cohort, the IGT only and combined INDET and IGT (INDET + IGT) groups had greater risk of CFRD (P = 0.0109). In the DIAMUCO cohort, there was lower diabetes-free survival in the INDET + IGT group (P = 0.0105). In both cohorts, CFRD risk ranged from 17% in normal glucose tolerance patients up to 42% to 56% in patients with INDET + IGT.

CONCLUSION

Patients who meet combined criteria have a higher risk of developing diabetes probably justifying closer follow-up.

The Potential Causes of Cystic Fibrosis-Related Diabetes

Cystic fibrosis (CF) is a genetic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR). Cystic fibrosis-related diabetes (CFRD) is the most common comorbidity, affecting more than 50% of adult CF patients. Despite this high prevalence, the etiology of CFRD remains incompletely understood. Studies in young CF children show pancreatic islet disorganization, abnormal glucose tolerance, and delayed first-phase insulin secretion suggesting that islet dysfunction is an early feature of CF. Since insulin-producing pancreatic β-cells express very low levels of CFTR, CFRD likely results from β-cell extrinsic factors. In the vicinity of β-cells, CFTR is expressed in both the exocrine pancreas and the immune system. In the exocrine pancreas, CFTR mutations lead to the obstruction of the pancreatic ductal canal, inflammation, and immune cell infiltration, ultimately causing the destruction of the exocrine pancreas and remodeling of islets. Both inflammation and ductal cells have a direct effect on insulin secretion and could participate in CFRD development. CFTR mutations are also associated with inflammatory responses and excessive cytokine production by various immune cells, which infiltrate the pancreas and exert a negative impact on insulin secretion, causing dysregulation of glucose homeostasis in CF adults. In addition, the function of macrophages in shaping pancreatic islet development may be impaired by CFTR mutations, further contributing to the pancreatic islet structural defects as well as impaired first-phase insulin secretion observed in very young children. This review discusses the different factors that may contribute to CFRD.