Effect of Sitagliptin on Islet Function in Pancreatic Insufficient Cystic Fibrosis With Abnormal Glucose Tolerance

Glycemia and Insulin Secretion in Cystic Fibrosis Two Years After Elexacaftor/Tezacaftor/Ivacaftor: PROMISE-ENDO

BACKGROUND

Elexacaftor/tezacaftor/ivacaftor (ETI) is a highly effective therapy that improves lung disease in people with cystic fibrosis (pwCF), but its effect on glucose tolerance and insulin secretion is unclear.

METHODS

PROMISE is a multicenter prospective, observational study of ETI in pwCF ≥12 years and at least one F508del allele. The PROMISE Endocrine sub-study (PROMISE-ENDO) enrolled participants at 10 CF Centers where hemoglobin A1c (HbA1c) was collected and 3-hour oral glucose tolerance tests (OGTT) conducted to examine glucose tolerance, glucose excursions, insulin secretory rates (deconvolution of C-peptide) and sensitivity (oral minimal model) prior to ETI and 12-18 months (mos) and 24-30 mos following ETI initiation. Longitudinal mixed effects models were used to test within-subject ETI effects.

RESULTS

At baseline, 79 participants completed OGTTs [39 (49%) male, median (IQR) age 19.6 (14.7, 27.3) years, BMI z-score 0.12 (-0.51, 0.65)]. At 12-18 mos n=68 and at 24-30 mos n=58 completed OGTTs. At 24-30 mos, fasting glucose (mg/dL) decreased [94 (92, 96) to 90 (88, 93), p=0.02] in the subset not on insulin therapy (n=61), but no differences in 1-hr or 2-hr glucose were found. HbA1c (%) decreased from 5.8 (5.6, 5.9) to 5.5 (5.4, 5.6), p<0.001 by 24-30 mos. Although insulin sensitivity (mU/L-1.min-1) decreased [8.4 (7.2, 9.5) vs. 6.8 (5.8, 7.9), p=0.03], no changes in oral disposition index were found, p=0.14.

CONCLUSIONS

After two years of ETI, fasting glucose and HbA1c showed modest decreases. Glucose tolerance varied, and overall measures of insulin secretion did not deteriorate.

Cystic fibrosis-related diabetes is associated with reduced islet protein expression of GLP-1 receptor and perturbation of cell-specific transcriptional programs

Insulin secretion is impaired in individuals with cystic fibrosis (CF), contributing to high rates of CF-related diabetes (CFRD) and substantially increasing disease burden. To develop improved therapies for CFRD, better knowledge of pancreatic pathology in CF is needed. Glucagon like peptide-1 (GLP-1) from islet α cells potentiates insulin secretion by binding GLP-1 receptors (GLP-1Rs) on β cells. We determined whether expression of GLP-1 and/or its signaling components are reduced in CFRD, thereby contributing to impaired insulin secretion. Immunohistochemistry of pancreas from humans with CFRD versus no-CF/no-diabetes revealed no difference in GLP-1 immunoreactivity per islet area, whereas GLP-1R immunoreactivity per islet area or per insulin-positive islet area was reduced in CFRD. Using spatial transcriptomics, we observed several differentially expressed α- and/or β-cell genes between CFRD and control pancreas. In CFRD, we found upregulation of α-cell PCSK1 which encodes the enzyme (PC1/3) that generates GLP-1, and downregulation of α-cell PCSK1N which inhibits PC1/3. Gene set enrichment analysis also revealed α and β cell-specific pathway dysregulation in CFRD. Together, our data suggest intra-islet GLP-1 is not limiting in CFRD, but its action may be restricted due to reduced GLP-1R protein levels. Thus, restoring β-cell GLP-1R protein expression may improve β-cell function in CFRD.

Nutritional status in the era of highly effective CFTR modulators

Advances in cystic fibrosis (CF) diagnostics and therapeutics have led to improved health and longevity, including increased body weight and decreased malnutrition in people with CF. Highly effective CFTR modulator therapies (HEMT) are associated with increased weight through a variety of mechanisms, accelerating trends of overweight and obesity in the CF population. Higher body mass index (BMI) is associated with improved pulmonary function in CF, yet the incremental improvement at overweight and obese BMIs is not clear. Improvements in pulmonary health with increasing BMI are largely driven by increases in fat-free mass (FFM), and impact of HEMT on FFM is uncertain. While trends toward higher weight and BMI are generally seen as favorable in CF, the increased prevalence of overweight and obesity has raised concern for potential risk of traditional age- and obesity-related comorbidities. Such comorbidities, including impaired glucose tolerance, hypertension, cardiac disease, hyperlipidemia, fatty liver, colon cancer, and obstructive sleep apnea, may occur on top of pre-existing CF-related comorbidities. CF nutrition recommendations are evolving in the post-modulator era to more individualized approaches, in contrast to prior blanket high-fat, high-calorie prescriptions for all. Ultimately, it will be essential to redefine goals for optimal weight and nutritional status to allow for holistic health and aging in people with CF.

Overnutrition in persons with cystic fibrosis on modulator therapy and the relationship to obstructive sleep apnea

Cystic fibrosis (CF) care is evolving with the ubiquitous use of modulator therapy and resultant increase in lifespan. It is important for CF clinicians to monitor the pathologic weight gain that is concomitantly being seen as obesity is a known risk factor for multiple other diseases. In this review we focus on obesity in CF, discuss screening and lifestyle considerations, outline CF-specific concerns with weight loss medications, and describe the vicious cycle of obesity and obstructive sleep apnea (OSA). We discuss screening and treatment for OSA, as it directly correlates with weight fluctuation. We offer interim recommendations for CF teams as they continue to care for this population.

Role for DPP4 inhibitor therapy in cystic fibrosis related diabetes: A single centre experience

INTRODUCTION

Insulin remains the only recommended medical treatment for cystic fibrosis related diabetes (CFRD) Whilst there is an established role for orally bioavailable incretin mimetic agents such as the dipeptidyl peptidase-4 inhibitors (DPP4-I) in Type 2 diabetes mellitus, there exists little data on their utility in CFRD.

AIM

To examine the use of DPP4-I therapy in patients with CFRD at a single large adult cystic fibrosis center.

METHOD

People with CFRD prescribed a DPP4-I were identified from our specialist CFRD clinic and records were retrospectively examined for indication for therapy, tolerability and effectiveness. Analysis of continuous glucose monitoring data Libre 2 was done for these patients (CGM) pre and at least 3 months post therapy was performed.

RESULTS

23 people with CF (PwCF) with a mean (SD) age of 35.0 ± 2.4 years were included in this analysis . In 21 patients DPP4-I was prescribed as a monotherapy and it was given in combination with insulin in 2 others. Indications for therapy included reactive hypoglycaemia (n = 10) post prandial hyperglycaemia (8), insulin avoidance (3), metformin intolerance (1) and unclear (1). Therapy was well tolerated with no discontinuations due to adverse effects. Significant improvements were noted in Time in Range- Pre vs Post: 78.0 [67.5 - 84.0] vs 89.0 [79.8 - 96.0]%, p = 0.005, Time above Range -Pre vs Post: 19.5 [12.5 - 30.8] vs 6.0 [2.5 - 16.5]%, p = 0.006 and glucose variability Pre versus Post: 28.3 [25.4 - 31.1] vs 26.9 [23.1 - 31.3], p = 0.021, Of the 10 subjects who initiated therapy for hypoglycaemia, 7 reported an improvement in symptoms. No significant difference was found in weight pre and post: 61.5 ± 15.0 kg vs 62.5 ± 15.3 kg, p = 0.326 or Hba1c pre vs post: 41.0 [36.0 - 53.3] mmol/mol versus 40.5 [36.8 - 47.3], p = 0.727.

CONCLUSION

DPP4-I is well tolerated in CFRD and can lead to an improved glycaemic control in these patients with significant improvement in validated CGM metrics.

The Changing Landscape of Treatment for Cystic Fibrosis Related Diabetes

Objective

Patients with Cystic Fibrosis related diabetes [CFRD] are treated with insulin and high calorie diets to maintain body mass. The combined CFTR modulator elexacaftor/tezacaftor/ivacaftor [ETI] decreases pulmonary exacerbations and improves nutritional status. We reviewed the effects of ETI on BMI, HbA1c and diabetes regimen in patients with CFRD over a period of three years.

Methods

Data of previously CFTR-modulator-naïve patients with CFRD and pancreatic insufficiency on ETI therapy were retrieved from an electronic health record database. Patients were followed for a mean duration of 2.7 ± 0.8 years after ETI initiation. Data pertaining to weight, BMI, HbA1c and diabetes regimen were collected at 6 months, 12 months, 2 years and at 3 years post-ETI initiation. Patients were then dichotomized based on their baseline BMI into a low BMI group and an "at target" BMI group. The effects of ETI on changes in weight, BMI, A1c and diabetes regimen were compared in both groups over a period of three years.

Results

Twenty-seven patients with CFRD (15 men/12 women), age 30.6 ± 11.5 (SD) years, BMI 22.4 ± 4.0 kg/m2, were included. Fifteen patients had low BMI (<22 kg/m2 for women, <23 kg/m2 for men) and 12 patients had at target BMI (≥22 kg/m2for women, ≥BMI 23 kg/m2 for men). Patients with low BMI had an increase in their BMI from 19.5 ± 1.7 to 21.4 ± 2.2 kg/m2 at one year (p = 0.002), and 21.8 ± 1.8 kg/m2 at three years (p = 0.004) after ETI initiation. Four patients (out of 15) in the low BMI group had achieved normal BMI by the end of study follow up. There was no change in weight in the at target BMI group. HbA1c and basal insulin requirements did not change in either group. Five patients started non-insulin therapies.

Conclusion

BMI increased after ETI therapy in CFRD patients with low BMI, but not in those with at target BMI. The use of non-insulin therapies is increasing in CFRD and should be evaluated in future studies.

Early-phase insulin secretion during mixed-meal tolerance testing predicts β-cell function and secretory capacity in cystic fibrosis

Insulin secretion within 30 minutes of nutrient ingestion is reduced in people with cystic fibrosis (PwCF) and pancreatic insufficiency and declines with worsening glucose tolerance. The glucose potentiated arginine (GPA) test is validated for quantifying β-cell secretory capacity as an estimate of functional β-cell mass but requires technical expertise and is burdensome. This study sought to compare insulin secretion during mixed-meal tolerance testing (MMTT) to GPA-derived parameters in PwCF.

Methods

Secondary data analysis of CF-focused prospective studies was performed in PwCF categorized as 1) pancreatic insufficient [PI-CF] or 2) pancreatic sufficient [PS-CF] and in 3) non-CF controls. MMTT: insulin secretory rates (ISR) were derived by parametric deconvolution using 2-compartment model of C-peptide kinetics, and incremental area under the curve (AUC) was calculated for 30, 60 and 180-minutes. GPA: acute insulin (AIR) and C-peptide responses (ACR) were calculated as average post-arginine insulin or C-peptide response minus pre-arginine insulin or C-peptide under fasting (AIRarg and ACRarg), ~230 mg/dL (AIRpot and ACRpot), and ~340 mg/dL (AIRmax and ACRmax) hyperglycemic clamp conditions. Relationships of MMTT to GPA parameters were derived using Pearson's correlation coefficient. Predicted values were generated for MMTT ISR and compared to GPA parameters using Bland Altman analysis to assess degree of concordance.

Results

85 PwCF (45 female; 75 PI-CF and 10 PS-CF) median (range) age 23 (6-56) years with BMI 23 (13-34) kg/m2, HbA1c 5.5 (3.8-10.2)%, and FEV1%-predicted 88 (26-125) and 4 non-CF controls of similar age and BMI were included. ISR AUC30min positively correlated with AIRarg (r=0.55), AIRpot (r=0.62), and AIRmax (r=0.46) and with ACRarg (r=0.59), ACRpot (r=0.60), and ACRmax (r=0.51) (all P<0.001). ISR AUC30min strongly predicted AIRarg (concordance=0.86), AIRpot (concordance=0.89), and AIRmax (concordance=0.76) at lower mean GPA values, but underestimated AIRarg, AIRpot, and AIRmax at higher GPA-defined β-cell secretory capacity. Between test agreement was unaltered by adjustment for study group, OGTT glucose category, and BMI.

Conclusion

Early-phase insulin secretion during MMTT can accurately predict GPA-derived measures of β-cell function and secretory capacity when functional β-cell mass is reduced. These data can inform future multicenter studies requiring reliable, standardized, and technically feasible testing mechanisms to quantify β-cell function and secretory capacity.

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.

Preservation of β-cell Function in Pancreatic Insufficient Cystic Fibrosis With Highly Effective CFTR Modulator Therapy

CONTEXT

Elexacaftor/tezacaftor/ivacaftor (ETI; Trikafta) enhances aberrant cystic fibrosis transmembrane conductance regulator function and may improve the insulin secretory defects associated with a deterioration in clinical outcomes in pancreatic insufficient cystic fibrosis (PI-CF).

OBJECTIVE

This longitudinal case-control study assessed changes in β-cell function and secretory capacity measures over 2 visits in individuals with PI-CF who were initiated on ETI after the baseline visit (2012-2018) and (1) restudied between 2019 and 2021 (ETI group) vs (2) those restudied between 2015 and 2018 and not yet treated with cystic fibrosis transmembrane conductance regulator modulator therapy (controls).

METHODS

Nine ETI participants (mean ± SD age, 25 ± 5 years) and 8 matched controls were followed up after a median (interquartile range) 5 (4-7) and 3 (2-3) years, respectively (P < .01), with ETI initiation a median of 1 year before follow-up. Clinical outcomes, glucose-potentiated arginine, and mixed-meal tolerance test measures were assessed with comparisons of within- and between-group change by nonparametric testing.

RESULTS

Glucose-potentiated insulin and C-peptide responses to glucose-potentiated arginine deteriorated in controls but not in the ETI group, with C-peptide changes different between groups (P < .05). Deterioration in basal proinsulin secretory ratio was observed in controls but improved, as did the maximal arginine-induced proinsulin secretory ratio, in the ETI group (P < .05 for all comparisons). During mixed-meal tolerance testing, early insulin secretion improved as evidenced by more rapid insulin secretory rate kinetics.

CONCLUSION

ETI preserves β-cell function in CF through effects on glucose-dependent insulin secretion, proinsulin processing, and meal-related insulin secretion. Further work should determine whether early intervention with ETI can prevent deterioration of glucose tolerance in PI-CF.

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.

Continuous Glucose Monitoring as an Additional Tool in Early Cystic Fibrosis-Related Diabetes Monitoring and in Evaluation of Short-Term Sitagliptin Response

Cystic fibrosis-related diabetes (CFRD) is a complication associated with a negative prognosis in patients with cystic fibrosis (CF). Although the oral glucose tolerance test (OGTT) is the widely recommended screening test for CFRD diagnosis, continuous glucose monitoring (CGM) is increasingly considered a useful and easy-to-perform test for diagnosis and follow-up in clinical practice. Regarding CFRD treatment, although insulin is the classic approved pharmacological option, incretins could also be a helpful alternative in early stages. CGM could be also a useful tool to measure the early response to this therapy.

METHODS

We studied 25 CF patients with abnormal OGTT results and compared glucose and insulin levels during the OGTTs with CGM results as a tool for early CFRD diagnosis. In addition, we evaluated glycaemic control with CGM before and after treatment with sitagliptin.

RESULTS

A correlation was found between lower plasma insulin levels during the OGTTs and higher average sensor glucose (p = 0.009) and hyperglycaemic excursions (p = 0.017). The CGM data on sitagliptin treatment (n = 25) showed an average glycaemic improvement from 124.2 to 117.2 mg/dL (p = 0.002) with a 5.6-point standard deviation of glucose decrease (p < 0.001). Hyperglycaemic excursions ≥200 mg/dL diminished 57.1% (p = 0.021). Both time in range and time above 180 mg/dL improved during treatment (p = 0.036 and p = 0.006, respectively).

CONCLUSION

CGM is a useful tool that offers valuable information for both the diagnosis and the management of CFRD. Lower plasma insulin levels during OGTTs are associated with a poor ambulatory glucose profile in CGM. Sitagliptin could play an important role in the treatment of the early stages of CFRD.

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.

Endocrine Complications of Cystic Fibrosis

Endocrine comorbidities have become increasingly important medical considerations as improving cystic fibrosis (CF) care increases life expectancy. Although the underlying pathophysiology of CF-related diabetes remains elusive, the use of novel technologies and therapeutics seeks to improve both CF-related outcomes and quality of life. Improvements in the overall health of those with CF have tempered concerns about pubertal delay and short stature; however, other comorbidities such as hypogonadism and bone disease are increasingly recognized. Following the introduction of highly effective modulator therapies there are many lessons to be learned about their long-term impact on endocrine comorbidities.

Bone metabolism and incretin hormones following glucose ingestion in young adults with pancreatic insufficient cystic fibrosis

Background

Gut-derived incretin hormones, including glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide 1 (GLP-1), regulate post-prandial glucose metabolism by promoting insulin production. GIP, GLP-1, and insulin contribute to the acute bone anti-resorptive effect of macronutrient ingestion by modifying bone turnover. Cystic fibrosis (CF) is associated with exocrine pancreatic insufficiency (PI), which perturbs the incretin response. Cross-talk between the gut and bone ("gut-bone axis") has not yet been studied in PI-CF. The objectives of this study were to assess changes in biomarkers of bone metabolism during oral glucose tolerance testing (OGTT) and to test associations between incretins and biomarkers of bone metabolism in individuals with PI-CF.

Methods

We performed a secondary analysis of previously acquired blood specimens from multi-sample OGTT from individuals with PI-CF ages 14-30 years (n = 23). Changes in insulin, incretins, and biomarkers of bone resorption (C-terminal telopeptide of type 1 collagen [CTX]) and formation (procollagen type I N-terminal propeptide [P1NP]) during OGTT were computed.

Results

CTX decreased by 32% by min 120 of OGTT (P < 0.001), but P1NP was unchanged. Increases in GIP from 0 to 30 mins (rho = -0.48, P = 0.03) and decreases in GIP from 30 to 120 mins (rho = 0.62, P = 0.002) correlated with decreases in CTX from mins 0-120. Changes in GLP-1 and insulin were not correlated with changes in CTX, and changes in incretins and insulin were not correlated with changes in P1NP.

Conclusions

Intact GIP response was correlated with the bone anti-resorptive effect of glucose ingestion, represented by a decrease in CTX. Since incretin hormones might contribute to development of diabetes and bone disease in CF, the "gut-bone axis" warrants further attention in CF during the years surrounding peak bone mass attainment.

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.

Effects of GLP-1 and GIP on Islet Function in Glucose-Intolerant, Pancreatic-Insufficient Cystic Fibrosis

Impaired insulin and incretin secretion underlie abnormal glucose tolerance (AGT) in pancreatic insufficient cystic fibrosis (PI-CF). Whether the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) can enhance pancreatic islet function in cystic fibrosis (CF) is not known. We studied 32 adults with PI-CF and AGT randomized to receive either GLP-1 (n = 16) or GIP (n = 16) during glucose-potentiated arginine (GPA) testing of islet function on two occasions, with either incretin or placebo infused, in a randomized, double-blind, cross-over fashion. Another four adults with PI-CF and normal glucose tolerance (NGT) and four matched control participants without CF underwent similar assessment with GIP. In PI-CF with AGT, GLP-1 substantially augmented second-phase insulin secretion but without effect on the acute insulin response to GPA or the proinsulin secretory ratio (PISR), while GIP infusion did not enhance second-phase or GPA-induced insulin secretion but increased the PISR. GIP also did not enhance second-phase insulin in PI-CF with NGT but did so markedly in control participants without CF controls. These data indicate that GLP-1, but not GIP, augments glucose-dependent insulin secretion in PI-CF, supporting the likelihood that GLP-1 agonists could have therapeutic benefit in this population. Understanding loss of GIP's insulinotropic action in PI-CF may lead to novel insights into diabetes pathogenesis.

Characterization of glucose metabolism in youth with vs. without cystic fibrosis liver disease: A pilot study

•

Severe CF-liver disease may exaggerate glucose abnormalities in patients with CFRD.

•

CF-liver disease may decrease insulin clearance that fosters insulin resistance.

•

Patients with CFRD and liver disease may warrant treatment other than insulin.

Background

Diabetes and liver disease are life-threatening complications of cystic fibrosis (CF). CF-liver disease is a risk factor for CF related diabetes (CFRD) development, but the underlying mechanisms linking the two co-morbidities are not known. The objective of this pilot study was to characterize glucose metabolism in youth with CF with and without liver disease.

Methods

In this two-center cross-sectional study, 20 youth with CF with and without liver disease underwent a 3-hour oral glucose tolerance test. Subjects were categorized by liver disease (LD) status [no LD, mild LD, severe LD] and diabetes status. Measures of glucose excursion, islet cell secretory responses, insulin sensitivity and clearance were obtained.

Results

Participants with severe LD had the highest fasting, peak, and glucose area under the curve over 3 h (AUC_3h) among individuals with CFRD (interaction p < 0.05). In parallel with glycemic changes, prandial β-cell secretory response (AUC _{C-peptide 3h}) was lower in those with severe LD compared to mild or no LD (p < 0.01). There was a trend of higher HOMA-IR in those with severe LD (p = 0.1) as well as lower fasting insulin clearance in those with mild and severe LD compared to no LD (p = 0.06) and lower prandial insulin clearance in severe LD among those with CFRD (interaction p = 0.1).

Conclusion

In this small cohort, subjects with severe LD tended to have more impaired glycemia, insulin secretion, insulin sensitivity and clearance. Larger studies are imperative to define the pathogenesis to inform clinical care guidelines in terms of CFRD screening, diagnosis, and treatment options.