Demonstration of normal plasma somatomedin concentrations in cystic fibrosis

Growth failure and treatment in cystic fibrosis

Poor growth has long been a characteristic feature of cystic fibrosis (CF) and is significantly linked to lung function and overall health status. Improvements in pulmonary and nutrition care for patients with cystic fibrosis (CF) have resulted in better growth outcomes; however, height gains have not paralleled the improvements in weight in children with CF, and patients with more severe CF mutations remain significantly more affected. Many factors affect the growth hormone-IGF-1 axis and the growth plate of the long bones, including the chronic inflammatory state associated with CF. There are also increasing data on the direct effects of CFTR on bone and implications for CFTR modulators in attaining optimal growth. Treatments aimed at improving growth in CF are also reviewed here.

Plasma insulin-like growth factor-I determinations in patients with cystic fibrosis: Influence of the nutritional and liver status

Insulin-like growth factor-1 (Igf1), a useful and early marker of undernutrition in inflammatory diseases, is dependent on the calorie and protein content of the diet. In 31 children and adolescents with cystic fibrosis (CF), a chronic inflammatory disease, the influence of the degree of liver dysfunction and the protein and calorie content of the diet on the circulating Igf1 was evaluated. No significant difference in the median plasma Igf1 concentration, measured by RIA, between the CF children (0.80 U/ml) and a for age and puberty matched control group (0.61 U/ml) was found. Expressing the Igf1 concentration as a percentage of normal for age, gave for the CF patients with liver involvement a lower level (median: 76%) than in those without (median: 101%). No correlation existed between the circulating Igf1 levels and the body height SDS, the body weight index and the calorie or protein intake of the patients.

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 relationship between insulin, IGF-I and weight gain in cystic fibrosis

OBJECTIVE

In cystic fibrosis, reduced body mass is related to low levels of IGF-I and changes in the IGF binding proteins. Our aim was to determine whether these abnormalities are linked to pancreatic endocrine dysfunction.

PATIENTS AND DESIGN

We measured serum levels of insulin, IGF-I, IGFBP-I, IGFBP-3 and IGF bioactivity in 77 fasting subjects (43 male) mean age 9.6 years (range 2.99-17.98 years). Data were analysed with respect of body mass, puberty and stature and compared with control data established in the same laboratory.

RESULTS

The mean height standard deviation score (SDS (SD)) was -0.54 (0.97) and the body mass index SDS -0.24 (1.09). Both body mass index SDS (r = -0.40, P = 0.0003) and IGF-I SDS (r = - 0.32, P = 0.009) declined with age. Insulin levels were also low and correlated with IGF-I and IGFBP-3 (r = 0.42, P = 0.0004, and r = 0.45, P = 0.0002, respectively) whereas levels of IGFBP-I were inversely related to those of IGF-I and insulin (r = - 0.43, P = 0. 0004, r = - 0.52, P < 0.0001). IGF bioactivity was reduced and inversely related to IGFBP-I (r = - 0.31, P = 0.009). In multiple regression analysis, body mass index SDS was negatively related to age (P < 0.0001) and positively related to insulin and IGF-I (P = 0. 04, P = 0.03, respectively). Height SDS was correlated with IGF bioactivity (P = 0.003) and negatively with IGFBP-I (P = 0.01).

CONCLUSIONS

We conclude that progressive insulin deficiency may result in reduced IGF-I levels and IGF-bioactivity and may determine weight gain and statural growth in cystic fibrosis.

Serum leptin and IGF-I levels in cystic fibrosis

The role of leptin in states of negative energy balance such as cystic fibrosis (CF) has not been explored. We hypothesized that leptin levels in patients with CF would be low due to correlation with body weight. Despite the importance of IGF-I in normal growth and anabolism, there are few data on IGF-I in CF. We studied 27 CF patients (25+/-5 yrs, 57+/-9 kg, 10M/17F) and 12 control subjects (25+/-4 yrs, 57+/-9 kg, 6M/6F). Each subject underwent analysis of lean body mass (LBM) and percent body fat by dual-energy x-ray absorptiometry (DEXA). Serum leptin and IGF-I levels were measured by radioimmunoassay. Serum leptin levels were similar both in CF and in controls (CF=5.3+/-4.1 ng/ml, C=4.4+/-3.6ng/ml; p=0.3), and there was no difference in percent body fat between the two groups (CF=26+/-13%, C=21+/-7%; p=0.3). Leptin levels were significantly lower in CF males than females corresponding to lower fat levels in males in both CF and controls. Leptin levels were positively correlated with percent body fat both in CF and controls (CF: r=0.8; p=0.01, CONTROL: r=0.8; p =0.2). Serum IGF-I levels were significantly lower in CF patients than in controls (CF=1.13+/-0.41 ng/ml, C=6.72+/-3.62 ng/ml; p=<0.01). We conclude that the physiological regulation of leptin is maintained in relation to body fat even in chronic illness and that the negative energy balance in CF is not caused by high leptin levels.

Relation between insulin-like growth factor-I, body mass index, and clinical status in cystic fibrosis

OBJECTIVES

Despite improved nutrition and intensive treatment, subjects with cystic fibrosis have difficulty in maintaining anabolism during intercurrent infections, which can result in reduced body mass index and impaired skeletal growth. Insulin-like growth factor-I (IGF-I) and its binding protein IGFBP3 are sensitive to changes in nutritional status. The aim of this study was to determine the relation between circulating concentrations of these peptides, body mass index, and clinical status in cystic fibrosis.

METHODS

Serum concentrations of IGF-I and IGFBP3 were measured in 197 subjects (108 males, 89 females; mean age 9.69 years, range 0.41-17.9 years) and these data were analysed with respect to body mass index, pubertal stage, and clinical status as assessed by Shwachman score and forced expiratory volume in one second (FEV1).

RESULTS

The mean height SD score of the children studied was -0.2 (SD 1.14) and the body mass index SD score -0.26 (1.4). The body mass index SD score declined with increasing age (r = -0.18) and paralleled changes in IGF-I concentrations, which also declined. The IGF-I SD score (calculated from control data) correlated with age (r = -0.53). The abnormalities were most obvious during late puberty, when IGF-I and IGFBP3 concentrations were significantly reduced compared with those in control subjects matched for pubertal stage. The IGF-I SD score correlated with height SD score (r = 0.14) and the decline in IGF-I concentrations with the fall in body mass index SD score (r = 0.42). IGF-I SD scores also correlated with the Shwachman score (r = 0.33) and FEV1 (r = 0.17).

CONCLUSIONS

The close relation between declining IGF-I and IGFBP3 concentrations and body mass index in patients with cystic fibrosis may simply reflect poor nutritional status and insulin hyposecretion. Nevertheless, IGF-I deficiency could also contribute towards the catabolism observed in these patients, and IGF-I SD scores correlated with other measures of clinical status such as the Shwachman score and FEV1.

Diminished concentrations of insulin-like growth factor I in cystic fibrosis

Cystic fibrosis is frequently accompanied by a catabolic condition with low body mass index caused by a number of disease complications. Insulin-like growth factor-I (IGF-I) is an anabolic hormone and an important marker of nutritional status, liver function, and linear growth. Available data on IGF-I in cystic fibrosis are sparse and conflicting. From 1990-3, 235 of our 240 patients (114 males, 121 females, median age 16.2 years, ranged 0.1-44.0 years) had IGF-I measured once by radioimmunoassay. IGF-I was significantly reduced compared with a healthy Scandinavian control population: mean (-2 SD to +2 SD) IGF-I SD score was -0.97 (-3.7 to 1.7) in males and -0.67 (-3.2 to 1.9) in females. Height SD score was -0.95 (-3.3 to 1.4) in males and -0.81 (-3.2 to 1.6) in females. In patients who were still in the growth period a significant correlation of IGF-I SD score to height SD score (r = 0.28, p < 0.001) was found. The low IGF-I concentrations may reflect the catabolic state of many patients with cystic fibrosis and play a part in their abnormal growth pattern.

Linear growth in children with cystic fibrosis. I. Birth to 8 years of age

The linear growth of Swedish children with cystic fibrosis (CF), is described using the infancy-childhood-puberty (ICP) growth model. Length/height was studied in 51 patients during their first 8 years of life. The median age at diagnosis was 0.4 years (range 0.0-6.1 years). At birth, their mean length was close to normal, but the gain in length over the first 0.25 years of life was significantly below normal, resulting in a mean length SDS of -1.3. Length remained subnormal up to 1.0 year of age. Thereafter, catch-up growth occurred, resulting in almost normal height (mean SDS-0.3) at 5.0 years of age. Between 5.0 and 8.0 years of age growth was normal. The mean age at onset of the childhood component was not significantly different from the controls. Hence, the catch-up growth did not occur until after the onset of the childhood component. This study shows that the postnatal linear growth rate is retarded in children with CF during the first months of life. This is almost completely compensated for by a supranormal growth rate that starts at the end of the first year of life.

[Principles and clinical significance of insulin-like growth factors/somatomedins]

The Insulin-like Growth Factors (IGFs) or Somatomedins are polypeptide growth factors which are similar to insulin in respect to their aminoacid sequence, structure and biologic activities. The IGFs bind to high affinity receptors which are present on many cells and in many tissues. In the circulation the IGFs are bound to transport (binding) proteins (IGF-BPs). In this review the physiologic role, the basic chemistry and the gene expression of this family of growth factors is summarized systematically. The pathophysiology of growth disorders, diabetes mellitus, malnutrition, liver and kidney disease in relation to the IGFs as well as the therapeutic and diagnostic potentials of these peptides are discussed in detail.

Oral correction of essential fatty acid deficiency in cystic fibrosis

A combination of pancreatic insufficiency and inadequate caloric intake may produce essential fatty acids (EFA) deficiency in patients with cystic fibrosis. Seventy-five percent of the adolescents and young adults with poor weight gain in our clinic were EFA-deficient by total plasma linoleic acid criteria. Twenty of these patients were placed on an oral hyperalimentation regimen containing 230% of calories required for basal energy expenditure, 40% as fat. Forty percent of these (8/20) achieved normal EFA levels on this diet. Eight of the nonresponding patients were given an additional 5% of their caloric intake as linoleic acid monoglyceride. All who maintained caloric intake achieved normal EFA levels. Normalization of EFA levels was associated with a number of clinical benefits including increase in weight and activity and, in five teenage girls, regulation of menses. The 16 control patients who received standard pancrelipase therapy and nutritional supplements remained fatty acid deficient. We conclude that oral hyperalimentation can restore EFA levels in cystic fibrosis patients if adequate calories are available to provide energy needs.