Insulin secretion and insulin-like growth factor-I levels in active and controlled acromegaly

Correlation analysis between short-term insulin-like growth factor-I and glucose intolerance status after transsphenoidal adenomectomy in acromegalic patients: a large retrospective study from a single center in China

OBJECTIVES

Our study aimed to investigate the associations of glucose tolerance status with insulin-like growth factor-I (IGF-I) and other clinical laboratory parameters of acromegalic patients before and after the patients underwent transsphenoidal adenomectomy (TSA) by conducting a single-center, retrospective study.

SUBJECTS AND METHODS

A total of 218 patients with acromegaly who had undergone TSA as the first treatment were retrospectively analyzed. Serum IGF-I, growth hormone (GH) and glucose levels were measured before and after surgery.

RESULTS

The follow-up levels for random GH, GH nadir, and the percentage of the upper limit of normal IGF-I (%ULN IGF-I) were decreased significantly. The percentages of normal (39.0%), early carbohydrate metabolism disorders (33.0%) and diabetes mellitus (28.0%) changed to 70.2%, 16.5% and 13.3%, respectively, after TSA. %ULN IGF-I at baseline was higher in the diabetes mellitus (DM) group than in the normal glucose tolerance group and impaired glucose tolerance (IGT) /impaired fasting glucose (IFG) groups before TSA, and the DM group exhibited a greater reduction in %ULN IGF-I value after surgery. The follow-up %ULN IGF-I value after surgery was significantly lower in the improved group, and Pearson's correlation analysis revealed that the reductions in %ULN IGF-I corresponded with the reductions in glucose level.

CONCLUSION

This study examined the largest reported sample with complete preoperative and follow-up data. The results suggest that the age- and sex-adjusted IGF-I level, which reflects altered glucose metabolism, and the change of it are associated with improved glucose tolerance in acromegalic patients both before and after TSA.

Diabetes in Patients With Acromegaly

Acromegaly is a clinical syndrome which results from growth hormone excess. Uncontrolled acromegaly is associated with cardiovascular mortality, due to an excess of risk factors including diabetes mellitus, hypertension and cardiomegaly. Diabetes mellitus is a frequent complication of acromegaly with a prevalence of 12-37%. This review will provide an overview of a number of aspects of diabetes mellitus and glucose intolerance in acromegaly including the following: 1. Epidemiology and pathophysiology of abnormalities of glucose homeostasis 2. The impact of different management options for acromegaly on glucose homeostasis 3. The management options for diabetes mellitus in patients with acromegaly RECENT FINDINGS: Growth hormone and IGF-1 have complex effects on glucose metabolism. Insulin resistance, hyperinsulinaemia and increased gluconeogenesis combine to produce a metabolic milieu which leads to the development of diabetes in acromegaly. Treatment of acromegaly should ameliorate abnormalities of glucose metabolism, due to reversal of insulin resistance and a reduction in gluconeogenesis. Recent advances in medical therapy of acromegaly have varying impacts on glucose homeostasis. These adverse effects influence management choices in patients with acromegaly who also have diabetes mellitus or glucose intolerance. The underlying mechanisms of disorders of glucose metabolism in patients with acromegaly are complex. The aim of treatment of acromegaly is normalisation of GH/IGF-1 with reduction of co-morbidities. The choice of therapy for acromegaly should consider the impact of therapy on several factors including glucose metabolism.

Insulin-like growth factor-I correlates more closely than growth hormone with insulin resistance and glucose intolerance in patients with acromegaly

In normal subjects growth hormone (GH) and insulin-like growth factor-I (IGF-I) have opposing effects on glucose metabolism. Active acromegaly is associated with insulin resistance (IR) and glucose intolerance although both GH and IGF-I are elevated. Our objective was to compare whether GH or IGF-I correlates more closely with IR and glucose intolerance in acromegaly. Basal serum IGF-I and GH, glucose and insulin during an oral glucose tolerance test were measured in 70 normoglycemic and 44 hyperglycemic acromegalic patients (21 impaired fasting glucose, 11 impaired glucose tolerance and 12 diabetes mellitus) according to American Diabetes Association criteria. 55 patients were assessed before any treatment for acromegaly and 59 after surgery and/or radiotherapy (15 patients had normal IGF-I after treatment). Patients treated with somatostatin analogs, GH-receptor antagonists or antidiabetic drugs were excluded. IR was assessed by various basal and stimulated indices. Homeostatic Model Assessment 2-Insulin Resistance (HOMA2-IR) index correlated more closely with IGF-I (r = 0.65, p < 0.0001) than nadir (r = 0.23, p = 0.008) or random GH (r = 0.26, p = 0.002). HOMA2-IR correlated better with IGF-I than nadir or random GH also in normoglycemic (n = 70; r = 0.74, p < 0.0001 vs. r = 0.36, p = 0.001 vs. r = 0.39, p < 0.001) and hyperglycemic patients (n = 44; r = 0.54, p = 0.0002 vs. r = 0.09, p = 0.4 vs. r = 0.14, p = 0.26). In multivariate logistic regression analysis IGF-I but not GH was a significant risk factor for glucose intolerance after adjusting for age, sex, weight and acromegaly duration (OR = 1.56, p = 0.01). In acromegaly IGF-I correlates more closely than GH with IR. IGF-I levels but not GH are associated with glucose intolerance.

Hyperproinsulinaemia in acromegaly: evidence for abnormal pancreatic beta-cell function?

We investigated whether pancreatic beta-cell dysfunction has a role in the pathogenesis of glucose intolerance in acromegaly by comparing plasma intact proinsulin, immunoreactive insulin, C-peptide and glucose concentrations during a 75 g oral glucose load in six patients with active acromegaly and eight healthy volunteers. Only acromegalic patients with normal glucose tolerance were studied. Glucose concentrations were similar in acromegalic patients and controls. Acromegalic patients had higher fasting insulin (P < 0.005) and fasting C-peptide (P < 0.005) concentrations than controls. Although fasting proinsulin levels were higher in acromegalic patients than controls, this did not achieve statistical significance. Integrated insulin (P < 0.05), C-peptide (P < 0.05) and proinsulin (P < 0.005) concentrations were greater in acromegalic patients than control subjects. Integrated (P < 0.05) proinsulin:insulin molar ratios were higher in acromegalic patients than controls. Fasting and integrated insulin:C-peptide molar ratios were similar in acromegalic patients and controls. These results indicate that hyperproinsulinaemia contributes to the hyperinsulinaemia which characterizes active acromegaly. The disproportionate hyperproinsulinaemia in acromegaly suggests that prolonged and excessive growth hormone secretion may result in pancreatic beta-cell dysfunction which may predispose acromegalic subjects to glucose intolerance.

Beta-cell function and insulin sensitivity in tropical calcific pancreatitis from north India

Tropical calcific pancreatitis (TCP) is a variant of chronic pancreatitis, occurring only in developing countries. It frequently leads to diabetes at a young age. To determine the pathogenesis of glucose intolerance, beta-cell function and insulin sensitivity were measured in 11 TCP patients with normal glucose tolerance (TCP-NGT), six TCP patients with mild hyperglycemia [TCP-DM] median fasting plasma glucose, 6.1 mmol/L), and 16 healthy control subjects. The technique of continuous infusion of glucose with model assessment (CIGMA) was used to calculate beta-cell function (%B) and insulin sensitivity (%S), based on plasma glucose and insulin levels achieved after an intravenous infusion of glucose. %S was similar in both groups of TCP patients and controls. In contrast, %B was significantly lower in TCP-DM patients (median, 53; interquartile range, 41 to 62) compared with controls (90; 65 to 143; P < .01) and with TCP-NGT patients (119; 91 to 159; P < .01). TCP-NGT and control subjects had similar beta-cell function. Among patients with TCP, %B negatively correlated with the duration of pancreatitis (r = -.63, P < .05). Our results suggest that patients with TCP develop diabetes due to a diminution in beta-cell function, and that insulin resistance does not play a significant role in its pathogenesis.

Inverse correlation between insulin-like growth factor binding protein-1 and insulin in patients with acromegaly during treatment with the somatostatin analogue octreotide

OBJECTIVE

Previous reports have shown an inverse relation between IGFBP-1 and insulin levels in healthy men, patients with insulin dependent diabetes mellitus, and insulinoma. We have investigated whether this inverse relation also exists in acromegaly, before and during treatment with octreotide, and whether changes in IGFBP-1 levels relate to GH and IGF-I levels.

DESIGN

We studied short-term treatment with octreotide in a double-blind placebo-controlled 14-day clinical trial.

PATIENTS

Eighteen patients with acromegaly were studied.

MEASUREMENTS

Plasma GH and serum IGFBP-1 levels were measured at hourly intervals from 0700 to 1800 h before randomization (day 0) and on days 4, 6, 8, 14 and 20. Serum insulin was determined at 0700, 0800 and 0900 h, and serum IGF-I at 0700 h.

RESULTS

Octreotide increased the daily mean IGFBP-1 level by 43% on day 8 and by 35% on day 14. The IGFBP-1 levels during octreotide were significantly higher (P < 0.05) compared to placebo, 29.9 +/- 3.9 vs 19.9 +/- 1.7 micrograms/l (mean +/- SEM) on day 8, and 28.3 +/- 3.2 vs 19.9 +/- 1.6 micrograms/l on day 14. Octreotide treatment significantly suppressed the insulin levels on all observation days by 40-48% compared to placebo. There was a significant inverse correlation between IGFBP-1 levels and insulin levels, both before treatment and on the last day of treatment (r = 0.79, P = 0.04; r = -0.90, P = 0.02, respectively). GH and IGF-I were significantly decreased in the octreotide group compared to the placebo group during the entire treatment period. The mean of age related standard deviation scores of IGF-I in the octreotide group decreased from a pretreatment value of 6.47 +/- 0.74 to 3.60 +/- 1.20 on day 14. There was no significant correlation between IGFBP-1 levels and levels of GH and IGF-I, either before or during treatment.

CONCLUSIONS

Octreotide treatment, in addition to reducing GH, IGF-I and insulin levels, is associated with an increase in IGFBP-1 concentrations in patients with acromegaly, and it is suggested that the rise in serum IGFBP-1 is a consequence of the decrease in insulin secretion.

The ratio between serum levels of insulin-like growth factor (IGF)-I and the IGF binding proteins (IGFBP-1, 2 and 3) decreases with age in healthy adults and is increased in acromegalic patients

OBJECTIVE

Several in-vitro studies have suggested that the biological actions of IGF-I can be modified by the presence of specific IGF binding proteins. In man, the 24-hour serum levels of IGF-I and IGFBP-3 remain constant, but short-term changes in the IGF-I/IGFBP-3 ratio have been described following GH administration. Serum levels of IGF-I and IGFBP-3 decrease with age in normal adults and are elevated in active acromegaly due to excessive GH secretion. However, the individual ratios between serum levels of IGF-I and IGFBP-3 in acromegalic and healthy adults have not been described previously.

METHODS AND MATERIALS

We studied this ratio in 198 healthy adults and in 56 acromegalic patients, grouped according to their serum GH levels (group I GH < 2mIU/l II GH 2-10 mIU/l; III GH > 10 mIU/l). In all subjects a single blood sample was drawn for IGF-I, IGF-II, IGFBP-1, IGFBP-2, IGFBP-3 and GH measurements by specific RIAs. In 38 of the patients a 24-hour urinary collection was performed for GH determination.

RESULTS

In healthy adults serum levels of IGF-I and IGFBP-3 decreased with increasing age (r = -0.52 and r = -0.34, respectively, P < 0.0001). In addition, the molar IGF-I/IGFBP-3 ratio declined with increasing age (r = -0.44, P = 0.0001). In patients with acromegaly and high serum GH levels (group III), circulating IGF-I was increased 7.97 standard deviations (SDS) and IGFBP-3 was increased 4.20 SDS (P < 0.0001). Serum levels of IGF-II were normal in all three groups (588 +/- 240 micrograms/l) whereas IGFBP-1 and IGFBP-2 levels were low and IGFBP-2 levels decreased significantly with increasing serum GH levels (P < 0.0001). The molar IGF-I/IGFBP-3 ratio in the acromegalic patients was significantly higher than in the controls (P < 0.0001) and correlated significantly with urinary GH excretion (r = 0.67, P < 0.0001) as well as with serum GH levels (r = 0.73, P < 0.0001).

CONCLUSION

We demonstrated a decreasing molar IGF-I/IGFBP-3 ratio with increasing age in healthy adults and an increased ratio between serum IGF-I and IGFBP-3 levels in acromegalic patients. As IGF-II is normal and IGFBP-1 and IGFBP-2 are inversely correlated to the serum GH levels in the acromegalic patients, we speculate that the molar ratio between IGF-I and IGFBP-3 reflects free (biologically active) IGF-I and is dependent on GH levels.