Insulin resistance is associated with decreased clinical status in cystic fibrosis

Associations Between Glucose Tolerance, Insulin Secretion, Muscle and Fat Mass in Cystic Fibrosis

Background:

A frequent comorbidity in cystic fibrosis (CF) is CF related diabetes (CFRD) caused by a gradual decline in insulin secretion. The reduction in the anabolic hormone, insulin, might explain the weight loss that precedes onset of CFRD. We investigated the association between muscle and fat mass in relation to glucose tolerance and insulin function.

Methods:

In a cross-sectional study with CF patients (⩾18 years), we conducted an oral glucose tolerance test and dual energy X-ray absorptiometry scan (DXA). Based on plasma glucose, glucose tolerance was defined as normal (NGT): 1-hour <11.1 mmol/L and 2-hour <7.8 mmol/L, impaired (IGT): 2-hour ⩾7.8 and <11.1 mmol/L or CFRD: 2-hour ⩾11.1 mmol/L. Insulin resistance (HOMA-IR) was derived from fasting levels of plasma glucose and plasma insulin, and fat-free and fat mass index (kg/m²) from DXA. Associations were evaluated using linear regression models adjusted for age, sex, and pancreas insufficiency.

Results:

Among 79 CF patients with exocrine pancreas insufficiency, impairment of glucose tolerance corresponded to reduced insulin secretion. In the IGT group the fat-free mass index (FFMI) was 1.2 kg/m² (95% CI: [−2.3, −0.03] kg/m², P = .044) lower compared to the NGT group. FFMI increased insignificantly by 0.4 kg/m² (95% CI: [−0.6, 1.5] kg/m², P = .422) among the insulin-treated CFRD group compared to IGT. Fat mass index (FMI) was not different between groups but tended to decrease with glucose tolerance impairment. For each 100 pmol/L increase in fasting insulin FFMI increased by 1.77 kg/m² (95% CI: [0.21, 3.33] kg/m²/pmol/L/100) and FMI increased by 6.15 kg/m² (95% CI: [3.87, 8.44] kg/m²/pmol/L/100). In multivariate analyses, HOMA-IR was positively associated with FFMI (β = 0.5 kg/m²/HOMA-IR, 95% CI: [0.08, 0.92] kg/m²/HOMA-IR, P = .021) and FMI (β = 1.5 kg/m²/HOMA-IR, 95% CI: [0.87, 2.15] kg/m²/HOMA-IR, P < .001).

Conclusions:

Muscle mass was significantly lower among participants with impaired glucose tolerance (IGT), while muscle mass was normalized among those treated with insulin.

CFTR Deficiency Affects Glucose Homeostasis via Regulating GLUT4 Plasma Membrane Transportation

Cystic Fibrosis (CF) is an autosomal recessive disorder caused by mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene. CF-related diabetes (CFRD) is one of the most prevalent comorbidities of CF. Altered glucose homeostasis has been reported in CF patients. The mechanism has not been fully elucidated. Besides the consequence of pancreatic endocrine dysfunction, we focus on insulin-responsive tissues and glucose transportation to explain glucose homeostasis alteration in CFRD. Herein, we found that CFTR knockout mice exhibited insulin resistance and glucose tolerance. Furthermore, we demonstrated insulin-induced glucose transporter 4 (GLUT4) translocation to the cell membrane was abnormal in the CFTR knockout mice muscle fibers, suggesting that defective intracellular GLUT4 transportation may be the cause of impaired insulin responses and glucose homeostasis. We further demonstrated that PI(4,5)P₂ could rescue CFTR related defective intracellular GLUT4 transportation, and CFTR could regulate PI(4,5)P₂ cellular level through PIP5KA, suggesting PI(4,5)P₂ is a down-stream signal of CFTR. Our results revealed a new signal mechanism of CFTR in GLUT4 translocation regulation, which helps explain glucose homeostasis alteration in CF patients.

Incidence and risk factors of paediatric cystic fibrosis-related diabetes

INTRODUCTION

Cystic fibrosis-related diabetes (CFRD) is a common complication of cystic fibrosis (CF) directly linked to increased morbidity and mortality. Both the incidence of type I and type II diabetes has been shown to increase in the general population. In this study, we investigated the incidence and risk factors of CFRD in a paediatric CF population.

METHODS

Prospectively collected data from the Canadian CF Registry (CCFR) from 2000 to 2016 for patients ages 10 to 18 years was used to determine the incidence of CFRD. Risk factors for CFRD in the Canadian population were investigated using a nested case-control design. Conditional logistic regression analysis with a 4:1 control: case matching was used.

RESULTS

From 2000 to 2016, 2326 patients with CF aged between 10 through 18 years were included in the CCFR, during this time the overall incidence rate of CFRD was 2.1 cases per 100 patient-years (95% confidence interval 1.8 to 2.3). Incidence rates were stable in the Canadian cohort over three consecutive time periods 2000-2005, 2006-2010; 2011-2016. Worse lung function, female gender, history of allergic bronchopulmonary aspergillosis, Gastrostomy tube insertion and liver disease were statistically significant risk factors for CFRD.

CONCLUSION

The incidence of CFRD in the Canadian paediatric population has been stable over time, in contrast to the rising rates of Type 1 and Type 2 diabetes in the general paediatric population. The risk factor for CFRD in this contemporary population were consistent with previous studies.

Oxygen dependence of glucose sensing: role in glucose homeostasis and related pathology

In glucose homeostasis, glucose concentration is sensed by its metabolism through glucokinase (GCK) and oxidative phosphorylation. Because oxidative phosphorylation is an integral part of the sensory system, glucose sensing is necessarily dependent on oxygen pressure. Much of the dependence on oxygen is suppressed by location of glucose sensing cells in tissues with well-regulated blood flow. In healthy individuals the oxygen dependence is primarily observed in response to transient global hypoxia events such as during birth or transition to high altitude. The GCK sensing system is, however, used to control release of both insulin and glucagon, the preeminant hormonal regulators of blood glucose, as well as glucose sensitive neuronal activity. Suppression of oxygen delivery to glucose-sensing cells or interference with regulation of tissue blood flow by either local or systemic causes, stresses the glucose regulatory system. This is true whether the stress is imposed locally, such as by altered oxygen delivery to the pancreas, or globally, as in pulmonary insufficiency or exposure to high altitude. It may be expected that chronic application of this stress predisposes individuals to developing diabetes. Type 2 diabetes is a broad class of diseases characterized by disturbance of glucose homeostasis, i.e., having either hyperglycemia and/or decreased sensitivity to insulin. Given the role of oxidative phosphorylation in glucose sensing, tissue oxygen deprivation may predispose individuals to developing diabetes as well as contributing to the disease itself. This is particularly true in age-related diabetes because the incidence of vascular insufficiency increases markedly with increasing age. NEW & NOTEWORTHY Glucose sensing requires glucose metabolism through glycolysis and oxidative phosphorylation. Dependence of the latter on oxygen concentration imposes an oxygen dependence on glucose sensing. We have used a validated computational model to quantify that dependence. Evidence is presented that tissue oxygenation plays an important role in predisposition of individuals to developing type 2 diabetes and in progression of the disease.

Expression of Cystic Fibrosis Transmembrane Conductance Regulator in Ganglia of Human Gastrointestinal Tract

CF is caused by mutations of the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) which is an anion selective transmembrane ion channel that mainly regulates chloride transport, expressed in the epithelia of various organs. Recently, we have demonstrated CFTR expression in the brain, the spinal cord and the sympathetic ganglia. This study aims to investigate the expression and distribution of CFTR in the ganglia of the human gastrointestinal tract. Fresh tissue and formalin-fixed paraffin-embedded normal gastrointestinal tract samples were collected from eleven surgical patients and five autopsy cases. Immunohistochemistry, in situ hybridization, laser-assisted microdissection and nested reverse transcriptase polymerase chain reaction were performed. Expression of CFTR protein and mRNA was detected in neurons of the ganglia of all segments of the human gastrointestinal tract examined, including the stomach, duodenum, jejunum, ileum, cecum, appendix, colon and rectum. The extensive expression of CFTR in the enteric ganglia suggests that CFTR may play a role in the physiology of the innervation of the gastro-intestinal tract. The presence of dysfunctional CFTRs in enteric ganglia could, to a certain extent, explain the gastrointestinal symptoms frequently experienced by CF patients.

The ΔF508 Mutation in the Cystic Fibrosis Transmembrane Conductance Regulator Is Associated With Progressive Insulin Resistance and Decreased Functional β-Cell Mass in Mice

Cystic fibrosis (CF) is the result of mutations in the cystic fibrosis transmembrane conductance regulator (CFTR). CF-related diabetes affects 50% of adult CF patients. How CFTR deficiency predisposes to diabetes is unknown. Herein, we examined the impact of the most frequent cftr mutation in humans, deletion of phenylalanine at position 508 (ΔF508), on glucose homeostasis in mice. We compared ΔF508 mutant mice with wild-type (WT) littermates. Twelve-week-old male ΔF508 mutants had lower body weight, improved oral glucose tolerance, and a trend toward higher insulin tolerance. Glucose-induced insulin secretion was slightly diminished in ΔF508 mutant islets, due to reduced insulin content, but ΔF508 mutant islets were not more sensitive to proinflammatory cytokines than WT islets. Hyperglycemic clamps confirmed an increase in insulin sensitivity with normal β-cell function in 12- and 18-week-old ΔF508 mutants. In contrast, 24-week-old ΔF508 mutants exhibited insulin resistance and reduced β-cell function. β-Cell mass was unaffected at 11 weeks of age but was significantly lower in ΔF508 mutants versus controls at 24 weeks. This was not associated with gross pancreatic pathology. We conclude that the ΔF508 CFTR mutation does not lead to an intrinsic β-cell secretory defect but is associated with insulin resistance and a β-cell mass deficit in aging mutants.

Cystic fibrosis related diabetes

Improved life expectancy in cystic fibrosis (CF) has led to an expanding population of adults with CF, now representing almost 50 % of the total CF population. This creates new challenges from long-term complications such as diabetes mellitus (DM), a condition that is present in 40 %-50 % of adults with CF. Cystic fibrosis-related diabetes (CFRD) results from a primary defect of insulin deficiency and although sharing features with type 1 (DM1) and type 2 diabetes (DM2), it is a clinically distinct condition. Progression to diabetes is associated with poorer CF clinical outcomes and increased mortality. CFRD is not associated with an increased risk of cardiovascular disease and the prevalence of microvascular complications is lower than DM1 or DM2. Rather, the primary goal of insulin therapy is the preservation of lung function and optimization of nutritional status. There is increasing evidence that appropriate screening and early intervention with insulin can reverse weight loss and improve pulmonary function. This approach may include targeting postprandial hyperglycemia not detected by standard diagnostic tests such as the oral glucose tolerance test. Further clinical research is required to guide when and how much to intervene in patients who are already dealing with the burden of one chronic illness.

Cystic fibrosis-related diabetes in adults: inpatient management of 121 patients during 410 admissions

BACKGROUND

With improved longevity, cystic fibrosis (CF)-related diabetes (CFRD) has emerged as the most common nonpulmonary complication of CF. Patients with CFRD are frequently admitted to the hospital with infections and deterioration of pulmonary function, during which time glycemic control might have an impact on pulmonary function, recovery from infection, and survival.

METHODS AND RESULTS

In an attempt to share our insight into inpatient management of CFRD, this article summarizes the experience of our inpatient glucose management team with hospital management of 121 adult CFRD patients who were hospitalized on 410 occasions at the University of Colorado Hospital between January 2009 and September 2011. This is a retrospective chart review descriptive study of inpatient management of CFRD in our center. Our cohort includes CFRD patients treated with basal and mealtime insulin through multiple daily injections or continuous subcutaneous insulin infusion (CSII), as well as patients receiving steroids or enteral nutrition, which adds complexity to the management of CFRD during hospitalization.

CONCLUSIONS

Multiple hospitalizations and intensive inpatient management of CF are integral elements of treatment. Inpatient therapy for CFRD requires a customized approach that is uniquely different from that of type 1 or type 2 diabetes. Our experience highlights clinical circumstances such as irregular food intake, high dose steroid therapy, and supplemental tube feeding. For many patients, it is possible to continue CSII therapy during hospitalization through a combination of mutual trust between the patient and hospital staff and oversight provided by the glucose management team.

Update on cystic fibrosis-related diabetes

PURPOSE OF REVIEW

The aim is to provide a detailed review of recent publications on cystic fibrosis-related diabetes (CFRD) with a particular focus on the interplay between cystic fibrosis (CF) lung disease and diabetes.

RECENT FINDINGS

CFRD is a form of diabetes that is distinct from type 1 or type 2 diabetes. CFRD remains very common and increases in prevalence with increasing age so that one in two middle-aged CF persons have CFRD. People with CFRD have lower lung function, worse nutrition, more frequent hospitalization, and worse mortality than CF people without diabetes. The excess mortality previously noted in women with CFRD compared with CF women without diabetes or CF men is much less apparent. CFRD is due to insulin deficiency and peripheral insulin resistance is much less a factor. Genetic susceptibility and oxidant stress are key risk factors for developing CFRD. The lung is the prime end organ target in CFRD and mortality is due to respiratory failure, not vascular complications. Insulin is the mainstay of therapy and early recognition and institution of therapy appear to improve health outcomes.

SUMMARY

CFRD remains one of the most important co-morbidities in CF. Early recognition of the disease and therapeutic intervention may diminish the negative impact that diabetes has on lung health in CF. Although a clearer understanding of the role of oxidant stress and genetics in the pathogenesis of CFRD is being elucidated, much needs to be learned before more targeted, specific therapies can be developed for this distinct form of diabetes.

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.

Recent trends in cystic fibrosis-related diabetes

PURPOSE OF REVIEW

To provide an updated literature review highlighting important aspects of cystic fibrosis-related diabetes (CFRD) including epidemiology, pathogenesis, complications, screening, and management.

RECENT FINDINGS

Although CFRD continues to be associated with increased rates of mortality in the cystic fibrosis (CF) population, this has improved over the past several years, and the previous sex difference is no longer present. Recent studies support that CFRD is primarily caused by insulin deficiency due to loss of beta cells, which may occur via a number of mechanisms including oxidative stress. Aggressive screening programs with oral-glucose tolerance testing and early treatment with insulin for patients with CFRD with or without fasting hyperglycemia have led to improvements in nutritional states and lung function. Oral agents do not appear to be effective in CFRD.

SUMMARY

CFRD is the most common comorbidity in the CF population and is associated with microvascular complications and protein catabolism leading to worse health outcomes. Recognition of glycemic abnormalities through aggressive screening has led to improvements in nutritional status, pulmonary function, and mortality rates.

Pharmacotherapy of diabetes in cystic fibrosis patients

IMPORTANCE OF THE FIELD

Cystic fibrosis-related diabetes (CFRD) is a unique type of diabetes. In this article I review the pathophysiology of CFRD to gain insight as to why these patients have clinical features of both type 1 and 2 diabetes (DM). The reader will also learn that, although CFRD is different from type 1 and 2 DM, the development of diabetes-induced complications is similar to other types of DM. These complications can include retinopathy, nephropathy and neuropathy resulting from uncontrolled hyperglycemia; however, hyperglycemia and/or insulin deficiency in people with CFRD may exacerbate underlying CF problems, such as decreased pulmonary function and weight loss.

AREAS COVERED IN THIS REVIEW

Review medical therapy of CFRD including the over-riding goal of maintaining blood glucose levels in a range as close to normal as possible. The other important goal for diabetes management is to prevent diabetes complications and to encourage psychological wellbeing of the patient. However, as reviewed in this article, the underlying medical condition of people with CF and the basic metabolic differences caused by the disease often provide challenges in maintaining optimal diabetes control.

WHAT THE READER WILL GAIN

The reader will gain an understanding of how CFRD physically affects the patient with CF and the various pharmacologic therapies available for treatment of this type of diabetes. Furthermore they will gain insight into areas where more research is needed.

TAKE HOME MESSAGE

Cystic fibrosis-related diabetes is unique to CF and thus deserves disease specific medical therapy.

Pharmacological correction of a defect in PPAR-gamma signaling ameliorates disease severity in Cftr-deficient mice

Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (encoded by Cftr) that impair its role as an apical chloride channel that supports bicarbonate transport. Individuals with cystic fibrosis show retained, thickened mucus that plugs airways and obstructs luminal organs as well as numerous other abnormalities that include inflammation of affected organs, alterations in lipid metabolism and insulin resistance. Here we show that colonic epithelial cells and whole lung tissue from Cftr-deficient mice show a defect in peroxisome proliferator-activated receptor-gamma (PPAR-gamma, encoded by Pparg) function that contributes to a pathological program of gene expression. Lipidomic analysis of colonic epithelial cells suggests that this defect results in part from reduced amounts of the endogenous PPAR-gamma ligand 15-keto-prostaglandin E(2) (15-keto-PGE(2)). Treatment of Cftr-deficient mice with the synthetic PPAR-gamma ligand rosiglitazone partially normalizes the altered gene expression pattern associated with Cftr deficiency and reduces disease severity. Rosiglitazone has no effect on chloride secretion in the colon, but it increases expression of the genes encoding carbonic anhydrases 4 and 2 (Car4 and Car2), increases bicarbonate secretion and reduces mucus retention. These studies reveal a reversible defect in PPAR-gamma signaling in Cftr-deficient cells that can be pharmacologically corrected to ameliorate the severity of the cystic fibrosis phenotype in mice.

Cystic fibrosis related diabetes

Diabetes is a frequent complication seen in cystic fibrosis patients as they reach adulthood. Cystic fibrosis related diabetes (CFRD) is distinguished as a separate entity with features that include progressive loss of islet beta cell mass and insulin deficiency, as well as insulin resistance. Abnormalities in glucose tolerance may be detectable for many years prior to the development of overt diabetes. Therefore oral glucose tolerance testing is the preferred screening method for the identification of those patients at the highest risk for progression to diabetes. Progression to diabetes has been linked to poor outcomes in CF including loss of pulmonary function and increased mortality among females. Given the role that insulin deficiency plays in CFRD, insulin replacement therapy remains the only recommended intervention. In the absence of definitive supportive data, the use of oral antidiabetic agents is not considered standard therapy and needs further study. As with other forms of diabetes, CFRD patients also experience microvascular complications and should be periodically evaluated for manifestations.

Mechanisms of glucose intolerance in cystic fibrosis

AIMS

Although cystic fibrosis-related diabetes (CFRD), a poor prognostic factor in cystic fibrosis (CF), is characterized by insulinopenia, the role of insulin resistance is unclear. Using a prospective study design, we measured insulin resistance, pancreatic beta-cell function and correlated glycaemic status with clinical parameters.

METHODS

Oral glucose tolerance test was performed in 60 stable adult CF patients. Insulin sensitivity and beta-cell function were measured using the homeostatic model assessment (HOMA2), Stumvoll and oral glucose insulin sensitivity (OGIS) indices.

RESULTS

Forty-two (70%) had normal glucose tolerance (NGT), 10 (17%) impaired glucose tolerance (IGT) and eight (13%) CFRD. There was no difference in insulin sensitivity among the three groups (HOMA2: NGT 280, IGT 250, CFRD 339, P = 0.42; Stumvoll: NGT 0.128, IGT 0.126, CFRD 0.129, P = 0.76; and OGIS: NGT 515, IGT 472, CFRD 472, P = 0.12). Pancreatic beta-cell function (CFRD 50% vs. NGT 67%; P < 0.05) and first-phase insulin secretion were reduced in CFRD (250 vs. NGT 509; P = 0.004). First-phase insulin secretion was inversely correlated with 1-h (r = -0.74; P < 0.0001) and 2-h glucose levels (r = -0.34; P < 0.05). There was no difference in body mass index or poor lung function (forced expiratory volume in 1 s: CFRD 54% vs. NGT 65%; P = 0.43). However, there were more hospital admissions in the CFRD group (three vs. NGT one per patient per year; P < 0.05).

CONCLUSIONS

CFRD is characterized by qualitative and quantitative defects in insulin secretion, but not insulin resistance, and is associated with increased hospital admissions for pulmonary exacerbations.

Clinical practice and genetic counseling for cystic fibrosis and CFTR-related disorders

Cystic fibrosis transmembrane conductance regulator-related disorders encompass a disease spectrum from focal male reproductive tract involvement in congenital absence of the vas deferens to multiorgan involvement in classic cystic fibrosis. The reproductive, gastrointestinal, and exocrine manifestations of cystic fibrosis transmembrane conductance regulator deficiency are correlated with CFTR genotype, whereas the respiratory manifestations that are the main cause of morbidity and mortality in cystic fibrosis are less predictable. Molecular genetic testing of CFTR has led to new diagnostic strategies and will enable targeting of molecular therapies now in development. Older diagnostic methods that measure sweat chloride and nasal potential difference nonetheless remain important because of their sensitivity and specificity. In addition, the measurement of immunoreactive trypsinogen and the genotyping of CFTR alleles are key to newborn screening programs because of low cost. The multiorgan nature of cystic fibrosis leads to a heavy burden of care, thus therapeutic regimens are tailored to the specific manifestations present in each patient. The variability of cystic fibrosis lung disease and the variable expressivity of mild CFTR alleles complicate genetic counseling for this autosomal recessive disorder. Widespread implementation of newborn screening programs among populations with significant cystic fibrosis mutation carrier frequencies is expected to result in increasing demands on genetic counseling resources.

Prior diabetes mellitus is associated with increased morbidity in cystic fibrosis patients undergoing bilateral lung transplantation: an 'orphan' area? A retrospective case-control study

BACKGROUND

The aim of this study was to determine whether pre-existing diabetes mellitus increases the risk of rejection, infection and/or death in cystic fibrosis patients undergoing bilateral sequential single-lung transplantation.

METHODS

A retrospective audit of 25 consecutive patients with cystic fibrosis who underwent bilateral sequential single-lung transplantation between 1 January 2003 and 31 December 2005 at a tertiary referral hospital was carried out.

RESULTS

Although 32% patients had diabetes diagnosed before lung transplantation, 92% had random blood glucose levels > or =11.1 mmol/L requiring insulin during admission. Patients with pre-existing diabetes had increased infection-related (3.9 vs 1.2, P= 0.01) and putative rejection-related (1.4 vs 0.5, P= 0.04) hospital admissions post-transplantation compared with those without diabetes pre-transplant. During the period of observation, four of eight patients with a prior diagnosis of diabetes died compared with none of 17 patients without prior diabetes (P= 0.0055).

CONCLUSION

Almost all cystic fibrosis patients develop hyperglycaemia after lung transplantation, but patients with prior diabetes have more complication-related admissions to hospital and a higher mortality rate.

OGTT-derived measures of insulin sensitivity are confounded by factors other than insulin sensitivity itself

Insulin resistance is an important risk factor for diabetes and other diseases. It has been important to estimate insulin resistance in epidemiological and genetic studies involving significant number of individuals. Complex and invasive protocols are impractical. Therefore, insulin sensitivity indices based on the oral glucose-tolerance test (OGTT) have been introduced. The aim of the present study was to assess the accuracy with which OGTT-derived indices would reflect changes in insulin sensitivity in the face of changes in other factors, such as rate of glucose absorption and/or B-cell function. A computer model was employed to predict excursions of plasma glucose and insulin after a 75-g oral glucose load. The model was then used to predict changes in these excursions, which would be observed with altered insulin resistance, with alterations in beta-cell sensitivity to glucose and/or alterations in glucose absorption rates. Published indices of insulin sensitivity could then be calculated from the predicted curves, to ask whether changes in beta-cell function or glucose absorptions rates might be misinterpreted (using the indices) as changes in insulin sensitivity. The model accurately represented OGTT data for a normal glucose tolerant subject, closely matching published data. Imposed 50% reductions or increases in insulin sensitivity alone in the model were reflected in only small changes in OGTT-derived insulin sensitivity values. More important, imposed alterations in beta-cell sensitivity and glucose absorption without simulated changes in insulin sensitivity did change insulin sensitivity indices. These results indicate that caution is required for the interpretation of differences in OGTT-derived values of insulin sensitivity, because variation in factors other than insulin sensitivity per se appear to have the greatest effects on indices calculated from the OGTT alone.

Glucose tolerance and insulin secretion, morbidity, and death in patients with cystic fibrosis

OBJECTIVES

To describe the history, mechanisms, and consequences of cystic fibrosis (CF)-related diabetes, from childhood to early adulthood.

STUDY DESIGN

Pancreatic beta-cell function was estimated from the plasma insulin/glucose ratios during oral glucose tolerance test (total area under the curve and deltaI(30-0min)/G(30min), homeostasis model assessment [HOMA]%B), insulin sensitivity with the HOMA%S index, in 237 children with CF (109 boys, 128 girls). Progression of glucose metabolism abnormalities was evaluated by analysis for interval censored data; rates of pulmonary transplantation and death by Kaplan-Meier analysis.

RESULTS

Impaired glucose tolerance was found in 20% of patients at 10 years, 50% at 15 years, 75% at 20 years, 82% at 30 years; for diabetes, >20% at 15 year, 45% at 20 years, 70% at 30 years; for insulin treatment, 30% at 20 years, 40% at 30 years. Early impairment was associated with lower survival rates and higher rates of lung transplantation. The area under the curve(glucose) correlated with decreased body mass index and height. Decrease in early insulin secretion (deltaI(30-0min)/G(30min)) was associated with impaired glucose tolerance, in all estimates of insulin secretion with diabetes. HOMA%S did not differ between the groups. Increased inflammation correlated with insulin resistance and impaired glucose tolerance.

CONCLUSIONS

CF-related diabetes, mainly because of beta-cell deficiency, is frequent early in life and associated with impaired nutritional state and growth, increased rates of terminal respiratory failure, and death.

O diabetes melito na fibrose cística: uma comorbidade cada vez mais freqüente

O diabetes melito (DM) é a principal comorbidade relacionada à fibrose cística (FC) e costuma acontecer após os 15 anos de idade, associando-se ao aumento da morbimortalidade. Sua fisiopatologia inclui destruição do tecido exócrino, insuficiência endócrina e aumento da resistência insulínica, determinando inicialmente a alteração da cinética secretora da insulina, até o comprometimento de sua secreção total. A hiperglicemia pós-prandial é a alteração clínica mais precoce e sintomas do DM podem não ser reconhecidos. A investigação anual deve ser realizada por meio da glicemia de jejum ou de glicemias ao acaso e do teste oral de tolerância à glicose (OGTT). São reconhecidas duas categorias de diabetes relacionadas à FC: o DRFC sem hiperglicemia de jejum (HJ) (glicemia de jejum < 126 mg/dL e glicemia de 2 horas OGTT > 200 mg/dL) e DRFC com HJ (glicemia de jejum > 126 mg/dL). O tratamento inclui o manejo nutricional especializado e a correção da hiperglicemia. A insulinoterapia é recomendada para a categoria DRFC com HJ, não existindo ainda evidências do benefício de drogas secretagogas ou sensibilizantes da ação insulínica.

Glucose tolerance, insulin secretion, and insulin sensitivity in children and adolescents with cystic fibrosis and no prior history of diabetes

OBJECTIVE

To determine the prevalence of abnormalities of glucose metabolism in pediatric outpatients with cystic fibrosis (CF).

STUDY DESIGN

Children and adolescents (n = 73, mean age 15.0 +/- 3.7 years) with CF not previously diagnosed with diabetes underwent 3-hour oral glucose tolerance testing. All subjects with CF were clinically stable and were not being treated for active infection. A reference group of young lean adults was used for comparison. Subjects were classified as having normal glucose tolerance (NGT) or abnormal glucose metabolism (AGM), including impaired glucose tolerance (IGT), impaired fasting glucose (IFG), or diabetes, by standard criteria. The insulinogenic index was calculated as a measure of beta-cell function, and insulin resistance was estimated with the homeostatic model assessment.

RESULTS

The reference group was significantly older than the patients with CF, but in the control subjects, the AGM and NGT were comparable in body mass index z-scores (-0.8 +/- 1.3, -0.6 +/- 1.1, -0.21 +/- 0.9 kg/m2). Thirty-eight percent of subjects with CF had AGM: 43% IGT, 29% IFG, 14% IGT/IFG, and 14% diabetes. In spite of distinct differences in glycemic response, the subjects with NGT and AGM had marked abnormalities of insulin secretion relative to the control subjects (Insulinogenic index 5.8 +/- 1.0, 5.3 +/- 0.8, and 53.5 +/- 10.0 uU/mL/mmol/L, respectively; P < .0001). Insulin sensitivity did not differ among the 3 groups, although there was a trend toward greater insulin resistance in the subjects with AGM (homeostatic model assessment: CF-NGT 1.5 +/- 0.2, CF-AGM 1.9 +/- 0.3, REF 1.3 +/- 0.1, P = NS).

CONCLUSION

Abnormalities in glucose metabolism are frequent in young patients with CF without a prior diagnosis of diabetes and are associated with marked defects in insulin secretion. Given the poor beta-cell function in patients with CF, even small reductions in insulin sensitivity may be an important determinant of AGM.

Glucose homeostasis and genotype-phenotype interplay in cystic fibrosis patients with CFTR gene deltaF508 mutation

OBJECTIVE

We sought to determine the clinical phenotype of adolescent/adult patients with cystic fibrosis, according to heterozygosity or homozygosity for cystic fibrosis transmembrane regulator (CFTR) deltaF508 mutation, and to analyze their characteristics according to glucose tolerance status.

RESEARCH DESIGN AND METHODS

A total of 76 cystic fibrosis patients with CFTR deltaF508 mutation (33 heterozygous and 43 homozygous) stratified according to normal glucose tolerance (NGT) (n = 51) or abnormal glucose homeostasis (AGH) (impaired fasting glucose, impaired glucose tolerance, or diabetes; n = 25) had their homeostasis model assessment (HOMA) of beta-cell function and of insulin sensitivity and hyperbolic product (beta-cell function x insulin sensitivity [B x S]) measured. Pancreatic exocrine insufficiency was inferred from pancreatine requirements. Clinical effects of insulin therapy on weight and lung function were recorded.

RESULTS

AGH was observed in 24 and 40% of heterozygous and homozygous subjects, respectively. AGH patients were older than NGT patients (mean +/- SD age 29 +/- 10 vs. 23 +/- 8 years, P = 0.006), and their beta-cell function was lower (93 +/- 49 vs. 125 +/- 51%, P = 0.011). Insulin sensitivity values were comparable in NGT and AGH patients. A lower B x S product was observed in AGH, although it was nonsignificant when adjusted for error propagation. Pancreatic insufficiency was observed in 52 and 100% of heterozygous and homozygous patients (P = 0.001).

CONCLUSIONS

Pre-diabetes and diabetes represent frequent comorbidities in CFTR deltaF508 mutation in the homozygous or heterozygous states. Impairment of insulin secretion, as shown by HOMA, is an important determinant when compared with the magnitude of compensation from insulin sensitivity. Given the high prevalence of abnormal glucose tolerance, screening for (pre-)diabetes is mandatory. Insulin supplementation in diabetic subjects with CFTR deltaF508 mutation seems a rational therapy for consideration, although this does not preclude that therapy directed toward insulin resistance could also interact.

Carbohydrate metabolism changes in cystic fibrosis

AIMS

To assess the prevalence of impaired glucose tolerance (ITG) and diabetes mellitus (DMRCF) in a group of patients with cystic fibrosis (CF). To study clinical status-related variables and to compare age with the evolution of their carbohydrate metabolism (CHM).

PATIENTS AND METHODS

Thirty patients with CF (1.5-26 years). Oral glucose tolerance test (OGTT) in 28 patients.

RESULTS

Three patients (10%) showed ITG and four DMRCF (13.3%). CF patients with impaired CHM (ICHM) were older (p = 0.006), and had longer times since diagnosis and first sputum colonization (p = 0.001, p < 0.001). Homozygous deltaF508 mutation was significant (p = 0.001). Insulin peak, area under the curve for insulin, insulin resistance, insulin sensitivity, and pancreatic beta-cell function were all significant.

CONCLUSIONS

ICHM was present in 23.3%. Age, time since diagnosis of CF, first sputum colonization and homozygous deltaF508 mutation were significantly associated. CHM in patients with CF is similar to that in the population without CF in the early years.

Microvascular complications in cystic fibrosis-related diabetes

OBJECTIVE

The incidence of cystic fibrosis-related diabetes (CFRD) and the prevalence of diabetic microvascular complications were determined at the University of Minnesota.

RESEARCH DESIGN AND METHODS

Cystic fibrosis patients have undergone annual oral glucose tolerance testing since 1990. Database review was performed to determine diabetes duration and the results of annual urine albumin-to-creatinine ratio (U(alb:Cr)) screening and dilated retinal exams. In addition, 59 individuals underwent detailed retinopathy, nephropathy, neuropathy, and gastroenteropathy screening.

RESULTS

During 1990-2005, 775 patients aged > or = 6 years were followed. CFRD was diagnosed by an oral glucose tolerance test or fasting hyperglycemia in 285 subjects (52% female), 64% of whom had fasting hyperglycemia. Most patients with CFRD without fasting hyperglycemia progressed to CFRD with fasting hyperglycemia over time. No subject with CFRD without fasting hyperglycemia had retinopathy or abnormal U(alb:Cr). In CFRD subjects with fasting hyperglycemia and diabetes for > or = 10 years, 14% had microalbuminuria and 16% had retinopathy. Autonomic neuropathy and gastrointestinal symptoms each were seen in 52% and somatic abnormalities in 22% of patients with or without fasting hyperglycemia.

CONCLUSIONS

Diabetic microvascular complications occur in CFRD, although the prevalence of retinopathy and nephropathy appears to be less than that found in other forms of diabetes. Annual complication screening should occur after known diabetes duration of 5 years in patients with CFRD with fasting hyperglycemia.

Normal adiponectin levels despite abnormal glucose tolerance (or diabetes) and inflammation in adult patients with cystic fibrosis

RATIONALE

Circulating adiponectin levels are negatively associated with glucose intolerance, inflammation and central adiposity. Since these conditions are common in cystic fibrosis (CF), we examined whether adiponectin values are altered in these patients.

AIM

To determine if CF patients have altered adiponectin levels and if these levels correlate with glucose tolerance categories (normal, impaired glucose tolerance (IGT) and cystic fibrosis-related diabetes (CFRD)), insulin resistance or inflammatory markers such as fibrinogen and C-reactive protein (CRP).

METHODS

Oral glucose tolerance tests (OGTTs) were performed and adiponectin levels were measured in 90 CF patients not known to be diabetic and 15 healthy controls matched for age, sex and body mass index (BMI). Inflammatory markers, serum albumin concentrations and the clinical status of CF patients (i.e. pulmonary function) were also examined.

RESULTS

CF pathology was characterized by a high prevalence (43.5%) of glucose tolerance abnormalities: 26.5% of IGT and 17.0% of newly diagnosed CFRD. CF patients also presented systemic inflammation as revealed by a significant increase of fibrinogen (P=0.029) in all patients and higher CRP levels in CFRD patients compared to the controls (P<0.05). On the other hand, CF and control subjects had similar albumin serum concentration. While CF patients and controls had similar serum adiponectin values, women had significantly higher hormone levels than men (P<0.001). Adiponectin levels did not correlate with glucose tolerance, inflammatory markers or insulin resistance. On the other hand, they correlated positively with both total and HDL-cholesterol (P<0.001).

CONCLUSION

CF patients did not show any alterations in adiponectin levels despite insulin resistance, glucose intolerance and sub clinical chronic inflammation. Thus, CF appears to be one of the rare conditions in which discordance between adiponectin values and insulin resistance or inflammation is evident.

Increased glucose excursion in cystic fibrosis and its association with a worse clinical status

BACKGROUND

Abnormal glucose tolerance is a frequent co-morbidity in cystic fibrosis patients (CF), and is associated with a worse prognosis. The objectives are to investigate (a) the relative contribution of insulinopenia and insulin resistance (IR) for glucose tolerance and (b) the association between various glucose parameters and CF clinical status.

METHODS

Oral glucose tolerance tests were performed in 114 consecutive CF patients not known to be diabetic as well as 14 controls similar for age and BMI.

RESULTS

Abnormal glucose tolerance was found in 40% of patients with CF: 28% had impaired glucose tolerance (IGT) and 12% had new cystic fibrosis related diabetes (CFRD). Compared to control subjects, all CF patients were characterized by an increased glucose excursion (AUC). While reduced early insulin release characterised CF, IGT and CFRD patients also present IR thus both mechanisms significantly contribute to glucose tolerance abnormalities. Increased glucose AUC and reduced early insulin release but not glucose tolerance categories were associated with a reduced pulmonary function (FEV(1)).

CONCLUSION

In CF, early insulin secretion defect but also IR contribute to glucose intolerance. Early in the course of the disease, increased glucose AUC and reduced early insulin secretion are more closely associated with a worse clinical status than conventional glucose tolerance categories.

Inflammation is a modulator of the insulin-like growth factor (IGF)/IGF-binding protein system inducing reduced bioactivity of IGFs in cystic fibrosis

OBJECTIVE

In inflammatory bowel diseases, increased serum interleukin (IL)-6 levels are associated with high serum insulin-like growth factor-binding protein 2 (IGFBP-2) levels, and cytokines modify the insulin-like growth factor (IGF)/IGFBP system in models in vitro. In cystic fibrosis (CF) the IGF/IGFBP system has not been extensively studied, and relationships with proinflammatory cytokines have not been explored. The aim of this study was to investigate the IGF/IGFBP system and verify changes dependent on IL-1beta, IL-6, tumour necrosis factor alpha (TNFalpha), and insulin.

METHODS

Eighteen subjects with CF (mean age 26.6 +/- 1.1 years) and 18 controls, comparable for age, sex, and body mass index, were enrolled. Serum IGF-I, IGF-II, IGFBP-2, IGFBP-3, IL-1beta, IL-6, TNFalpha, insulin and C-peptide were measured. Different molecular forms of IGFBP-2 and IGFBP-3 were investigated by Western immunoblotting. The patients were analysed as a whole and as two subgroups depending on established clinical criteria (Swachman-Kulczycki score).

RESULTS

Patients had higher serum concentrations of IL-1beta, IL-6, TNFalpha and IGFBP-2 than controls. Serum concentrations of IGF-I and IGF-II were significantly lower and insulin and C-peptide levels significantly increased in CF compared with healthy controls whereas IGFBP-3 serum concentrations were similar, with comparable IGF-I/IGFBP-3 and decreased IGF-I/IGFBP-2 and IGF-II/IGFBP-2 molar ratios. From correlation analysis we detected a significant positive correlation between IGFBP-2 and IL-6 and a negative correlation between IGFBP-2 and IGFBP-3.

CONCLUSIONS

Our findings suggest that inflammation is an important modulator of the IGF/IGFBP system with an overall reduction in IGF bioactivity in CF.

The metabolic effects of pregnancy in cystic fibrosis

OBJECTIVE

Our purpose was to determine glucose tolerance in pregnant women with cystic fibrosis (CF) and to relate glucose tolerance to insulin sensitivity, hepatic glucose production, and protein turnover.

METHODS

We studied 8 CF women during pregnancy (CFPreg). Results were compared with those from 9 pregnant controls (PregCont) and 8 nonpregnant CF women (CFCont). The following metabolic studies were conducted: oral glucose tolerance test (OGTT), hyperinsulinemic euglycemic clamp, stable isotope infusion of [1-13C]leucine and [6,6-2H2]glucose for measurement of whole body protein turnover and hepatic glucose production (HGP), respectively. Indirect calorimetry was used to measure resting energy expenditure (REE), and food intake was measured by 3-day food journals. Fat-free mass was measured by total body potassium 40K scan.

RESULTS

All but one CFPreg developed diabetes by the end of the second trimester and had significantly lower insulin secretion and more insulin resistance than PregCont. Hepatic glucose production was significantly higher and suppression by insulin was less in CF subjects, and protein breakdown was significantly higher. Insulin resistance and HGP increased during pregnancy similarly in CFPreg and PregCont groups.

CONCLUSION

Pregnancy in CF is associated with decreased insulin sensitivity and high HGP, in addition to inherent decreased insulin secretion. Pregnancy in CF is also associated with increased protein turnover and less response to insulin's anticatabolic effect. These changes appear to predispose the pregnant CF women to early development of diabetes and poor weight gain.

Diabetes: a major co-morbidity of cystic fibrosis

Cystic fibrosis-related diabetes (CFRD) is a frequent complication of cystic fibrosis, its prevalence increases with age of patient and is close to 30% at the age of 30 years. As life expectancy greatly increases, the number of cystic fibrosis patients developing diabetes will increase too. CFRD shares some features with type 1 and type 2 diabetes, initial phase is characterised by postprandial hyperglycaemia followed by a progression toward insulin deficiency. Insulin deficiency is an essential factor in the development of diabetes with an additional contribution of insulin resistance. Systematic screening with an oral glucose tolerance test is recommended from the age of 14 years because clinical signs of CFRD are often confused with signs of pulmonary infection and CFRD occurrence is associated with weight and pulmonary function deterioration. In observational studies CFRD diagnosis is associated with a significant increase in mortality, while treatment allow correction of weight and lung deterioration suggesting that CFRD has a significant impact on CF evolution. Microvascular complications are recognised, although paucity of data does not permit a clear description of their natural history. Annual screening for microvascular complication is recommended. There is no evidence by now that CF patients develop macrovascular complications. The only recommended pharmacological treatment is insulin therapy.

Epidemiology of cystic fibrosis-related diabetes

OBJECTIVES

Cystic fibrosis-related diabetes (CFRD) has emerged as an important complication of CF. To better understand who is at risk of developing CFRD, to gain insight into the impact of CFRD on pulmonary and nutritional status, and to assess the association of CFRD with various practice patterns and comorbid conditions, we characterized the Epidemiologic Study of Cystic Fibrosis (ESCF) patient population.

STUDY DESIGN

Analyses were performed on the 8247 adolescents and adults who were evaluated at one of 204 participating sites during 1998. CFRD was defined as the use of insulin or an oral hypoglycemic agent at any time during the year.

RESULTS

Previously reported risk factors for CFRD including age, gender (female), and pancreatic insufficiency were confirmed in this study. Patients with CFRD had more severe pulmonary disease, more frequent pulmonary exacerbations, and poorer nutritional status as compared with those without diabetes. CFRD also was associated with liver disease.

CONCLUSIONS

CFRD is a common complication in adolescents and adults that is associated with more severe disease.

Insulin-secretion abnormalities and clinical deterioration related to impaired glucose tolerance in cystic fibrosis

OBJECTIVE

To evaluate insulin-secretion kinetics and insulin sensitivity in cystic fibrosis (CF) patients with normal glucose tolerance (CF-NGT), impaired glucose tolerance (CF-IGT) or CF-related diabetes (CFRD), and the potential effects of moderate hyperglycemia on clinical and nutritional status.

DESIGN AND METHODS

Cross-sectional study including 50 outpatients with CF. Patients underwent both oral (OGGT) and intravenous (IVGTT) glucose tolerance tests in order to assess insulin secretion and peripheral insulin sensitivity. Homeostasis assessment model and OGGT were used to investigate insulin sensitivity. Forced expiratory volume in the first second (FEV(1)) and forced vital capacity (FVC) were measured to evaluate pulmonary function. Body mass index (BMI) was determined to assess nutritional status.

RESULTS

Insulin secretion was significantly decreased (and delayed at OGTT) in the CFRD group (n = 9) versus the CF-IGT group (n = 10) and the CF-IGT versus the CF-NGT group (n = 31). Insulin sensitivity was significantly different in the CF-IGT and CFRD groups versus the CF-NGT group. FEV(1), FVC and BMI presented a significant linear correlation with plasma glucose value at 120 min at OGTT and were significantly lower in both CF-IGT and CFRD versus the CF-NGT group, whereas no differences were found between the CF-IGT and CFRD groups.

CONCLUSIONS

CF patients with IGT present diminished insulin secretion and increased peripheral insulin resistance, correlating with a worse clinical status, undernutrition and impaired pulmonary function. These findings open the question of whether early treatment of mild alterations of glucose metabolism with insulin secretagogues or short-action insulin may lead to improvement of clinical status in CF patients.

Acquired non-type 1 diabetes in childhood: subtypes, diagnosis, and management

Over the past 30 years it has become apparent that not all diabetes presenting in childhood is autoimmune type 1. Increasingly type 2 diabetes, maturity onset diabetes of the young, iatrogenic diabetes, and rare syndromic forms of diabetes such as Wolfram's syndrome have been identified in children. This review is aimed at the general paediatrician looking after children with diabetes, and aims to provide an algorithm for assessment, investigation, and suggested management for the newly diagnosed child with suspected non-type 1 diabetes. This article will also be relevant to the child with atypical diabetes-that is, on low insulin doses outside the honeymoon period.

Insulin regulation of free fatty acid kinetics in adult cystic fibrosis patients with impaired glucose tolerance

Cystic fibrosis (CF) patients are insulin-resistant with regards to suppression of hepatic glucose production and proteolysis, but the effect of insulin on adipose free fatty acid (FFA) release has not been studied. [9,10-(3)H]palmitate kinetics were measured in 11 stable adult CF patients with impaired glucose tolerance (IGT) and 9 normal control subjects. Baseline plasma palmitate concentrations [CF = 99 +/- 13 (median 74, range 65 to 187); control = 88 +/- 9 (88, 46 to 138) micromol/L, P = .9] and palmitate flux [CF = 114 +/- 11 (100, 72 to 171); control = 105 +/- 12 (106, 54 to 182) micromol/min, P = 0.9] were not different between CF patients and controls. During a euglycemic clamp with infusion of insulin to physiologic postprandial levels, however, palmitate concentrations tended to be higher in CF patients: CF = 18 +/- 3 (13, 10 to 47), control = 12 +/- 1 (11, 8 to 18) micromol/L, P = 0.08. The higher palmitate concentrations during hyperinsulinemia appeared to be due to reduced suppression of adipose tissue palmitate release, because mean palmitate flux was 33% greater in CF subjects [32 +/- 5 (26, 17 to 66) micromol/min] than controls: [24 +/- 2 (23, 17 to 34) micromol/min], P = .20. There was considerably greater heterogeneity in insulin-induced suppression of plasma palmitate concentration and flux in CF patients compared to normal control subjects. In summary, a defect in insulin suppression of lipolysis was seen in clinically stable CF patients with IGT, similar to what has been described in CF for amino acid and glucose metabolism. This quantitative difference in lipolysis may account for inadequate insulin-induced suppression of hepatic glucose production in CF, and may be a metabolic adaptation to increased energy needs.

Decreased expression of peroxisome proliferator activated receptor gamma in cftr-/- mice

Some of the pathological manifestations of cystic fibrosis are in accordance with an impaired expression and/or activity of PPARgamma. We hypothesized that PPARgamma expression is altered in tissues lacking the normal cystic fibrosis transmembrane regulator protein (CFTR). PPARgamma mRNA levels were measured in colonic mucosa, ileal mucosa, adipose tissue, lung, and liver from wild-type and cftr-/- mice by quantitative RT-PCR. PPARgamma expression was decreased twofold in CFTR-regulated tissues (colon, ileum, and lung) from cftr-/- mice compared to wild-type littermates. In contrast, no differences were found in fat and liver. Immunohistochemical analysis of PPARgamma in ileum and colon revealed a predominantly nuclear localization in wild-type mucosal epithelial cells while tissues from cftr-/- mice showed a more diffuse, lower intensity labeling. A significant decrease in PPARgamma expression was confirmed in nuclear extracts of colon mucosa by Western blot analysis. In addition, binding of the PPARgamma/RXR heterodimer to an oligonucletotide containing a peroxisome proliferator responsive element (PPRE) was also decreased in colonic mucosa extracts from cftr-/- mice. Treatment of cftr-/- mice with the PPARgamma ligand rosiglitazone restored both the nuclear localization and binding to DNA, but did not increase RNA levels. We conclude that PPARgamma expression in cftr-/- mice is downregulated at the RNA and protein levels and its function diminished. These changes may be related to the loss of function of CFTR and may be relevant to the pathogenesis of metabolic abnormalities associated with cystic fibrosis in humans.

Hypoxia causes glucose intolerance in humans

Hypoxic respiratory diseases are frequently accompanied by glucose intolerance. We examined whether hypoxia is a cause of glucose intolerance in healthy subjects. In a double-blind within-subject crossover design, hypoxic versus normoxic conditions were induced in 14 healthy men for 30 minutes by decreasing oxygen saturation to 75% (versus 96% in control subjects) under the conditions of a euglycemic clamp. The rate of dextrose infusion needed to maintain stable blood glucose levels was monitored. Neurohormonal stress response was evaluated by measuring catecholamine and cortisol concentrations as well as cardiovascular parameters, and symptoms of anxiety. To differentiate between the effects of stress hormonal response, and hypoxia itself, on glucose intolerance, we performed hypoglycemic clamps as a nonspecific control. We found a significant decrease in dextrose infusion rate over a period of 150 minutes after the start of hypoxia (p < 0.01). Hypoxia also increased plasma epinephrine concentration (p < 0.01), heart rate (p < 0.01), and symptoms of anxiety (p < 0.05), whereas the other parameters remained unaffected. Glucose intolerance was closely comparable between hypoxic and hypoglycemic conditions (p < 0.9) despite clear differences in stress hormonal responses. Hypoxia acutely causes glucose intolerance. One of the factors mediating this effect could be an elevated release of epinephrine.

Dietary intakes in adult patients with cystic fibrosis–do they achieve guidelines?

BACKGROUND

Most patients with cystic fibrosis (CF) require a higher energy and protein intake than their healthy peer group. There are few data on dietary intakes of adult patients. The aim of this study was to determine nutritional intakes in an adult population with CF. The impact of nutritional intervention and disease on macronutrient intake was examined.

METHODS

Retrospective cross-sectional analysis of 94 unweighed food diaries at annual review (1995-2000). Energy and protein intakes were compared to the estimated average requirement (EAR) for energy and reference nutrient intake (RNI) for protein. The effect of diet alone, oral supplements, enteral tube feeding, and cystic fibrosis related diabetes (CFRD), on macronutrient intake was examined and impact of pancreatic sufficency (PS) and lung transplantation.

RESULTS

Mean energy and protein intakes approached recommended CF guidelines, but in 72% of assessments these values were not achieved. Mean energy and protein intakes for patients on diet alone and protein intake for those with CFRD failed to meet recommendations. Oral supplementation and enteral tube feeding regimens increased energy and protein intake above recommended levels. No group achieved 40% total energy from fat. Patients receiving enteral tube feeds had the highest mean energy and protein intakes but lowest body mass index (BMI) and lung function.

CONCLUSION

Adequate mean energy and protein intakes in adult patients with CF mask subgroups of patients who fail to meet recommendations ie. diet alone, diabetic. Oral supplementation and enteral tube feeding increase energy and protein intake but fail to achieve an adequate BMI level in subjects with a decreased clinical status. Individual nutritional assessment remains essential.

Cystic fibrosis-related diabetes

Diabetes mellitus (DM) has been recognized as a complication of cystic fibrosis (CF) for almost 50 years and commonly develops around 20 years of age. The prevalence increases with age and, with improved survival of those with CF, approaches 30% in certain centres. Its development appears to have a significant impact on pulmonary function and may increase mortality by up to six-fold. Subjects with CF are rarely ketosis-prone and phenotypically lie between Type 1 and Type 2 DM. Microvascular complications are recognized, although paucity of data does not permit a clear description of their natural history. An annual oral glucose tolerance test from the age of 10 years is recommended for screening, but logistical difficulties have led some groups to develop specific algorithms to aid diagnosis. Insulin sensitivity in CF is much debated and may depend upon the degree of glucose intolerance. Insulin resistance occurs in the presence of infection, corticosteroid usage and hyperglycaemia, whilst hepatic insulin resistance is considered an adaptation to CF. There is no universal consensus on the treatment of hyperglycaemia. With increased longevity of individuals with CF, greater numbers will develop diabetes and the diabetes physician is destined to play a greater role in the multidisciplinary CF team.