Lipid metabolism in acromegalic patients before and after selective pituitary adenomectomy

Postoperative Changes in Metabolic Parameters of Patients with Surgically Controlled Acromegaly: Assessment of New Stringent Cure Criteria

The criteria for surgical cure of acromegaly have become more stringent during the past decades and a change from Cortina to new consensus criteria has recently been proposed. However, the superiority of the new consensus over Cortina criteria with respect to postoperative metabolic parameters remains to be ascertained. We retrospectively assessed metabolic parameters, the body habitus, and other health-related parameters of 48 patients with surgically controlled acromegaly who met the Cortina criteria [normalized insulin-like growth factor-1 (IGF-1) level and nadir growth hormone (GH) level <1.0 ng/ml during postoperative oral glucose tolerance test]. The 48 patients were divided into two groups. Group A (n = 33) met the new consensus criteria (normalized IGF-1 and nadir GH level <0.4 ng/ml). Group B (n = 15) met Cortina criteria, but their nadir GH ranged from 0.4 to 1.0 ng/ml. In both groups, the level of triglyceride and homeostasis model assessment-insulin resistance (HOMA-IR) was significantly decreased 1 year after the operation (P < 0.05). High-density lipoprotein cholesterol showed a significant increase only in group B (P = 0.02). However, the two groups did not differ with respect to the postoperative improvement rate of these parameters and the other health-related parameters including body mass index, blood pressure, anterior pituitary function, and self-estimated quality of life scale. In conclusion, our findings show that with respect to changes in metabolic parameters and the body habitus assessed 1 year after surgery, the stricter consensus criteria seemed not to be superior to Cortina criteria.

Serum lipoprotein changes following IGF-I normalization using a growth hormone receptor antagonist in acromegaly

OBJECTIVE

Active acromegaly is associated with altered lipid metabolism. The purpose of this study was to investigate the effect of serum IGF-I normalization on serum lipoproteins and insulin, in patients with acromegaly receiving the GH receptor antagonist pegvisomant.

PATIENTS

Twenty patients (9 male, mean age 58.7 years, range 28-79) with active acromegaly (baseline serum IGF-I > 130% the age-related upper limit of normal) received pegvisomant and achieved a normal serum IGF-I [585.2 +/- 54.3 (mean +/- SEM) to 169.2 +/- 13.9 ng/ml, P < 0.0001].

MEASUREMENTS

Total cholesterol (TC), high-density lipoprotein (HDL) cholesterol, triglyceride (TG), apolipoprotein B (apo B), apolipoprotein A1 (apo A1), lipoprotein a [Lp(a)] and insulin were measured in a single batch analysis on samples obtained at baseline and the first occasion of serum IGF-I normalization. Low-density lipoprotein (LDL) was calculated using the Friedewald formula. Paired analysis was performed using Student's paired t-test and the Wilcoxon signed rank test.

RESULTS

Normalization of serum IGF-I resulted in an increase in TC (5.0 +/- 0.3 to 5.7 +/- 0.4 mmol/l, P = 0.0068), an increase in LDL (3.0 +/- 0.25 to 3.7 +/- 0.31 mmol/l, P = 0.0093) and an increase in apo B (110.6 +/- 7.76 to 127.1 +/- 8.86 mg/l, P = 0.014). TC and LDL increased in all but four patients. Despite a significant fall in fasting insulin levels (9.9 to 8.3 mU/l, range 8.85-19.8 to 6.33-11.6, P < 0.001) and insulin resistance (2.7 to 1.9, range 1.2-10.4 to 1-6.2, P < 0.001), mean serum TG and HDL levels were unaffected by IGF-I normalization. The protein component of HDL, apo A1, increased (153 +/- 4 to 166.4 +/- 5.43 mg/l, P = 0.026) and Lp(a) declined (median 342 to 235 mg/l, range 60-1013 to 74-671), P = 0.0035). Baseline serum TC and LDL were below the age- and sex-matched mean population value but after normalization of serum IGF-I the distribution of serum TC and LDL values was similar to that of the general population.

CONCLUSIONS

Active acromegaly is associated with lowered mean serum TC and LDL. Successful management using pegvisomant increases lowered baseline serum TC and LDL levels, restoring the distribution of values to that of the general population, and improves insulin resistance. These findings are consistent with the reported lipoprotein changes following GH administration to normal and GH-deficient individuals.

Long-term growth hormone excess induces marked alterations in lipoprotein metabolism in mice

The effects of long-term chronic growth hormone (GH) excess on lipid and lipoprotein metabolism were investigated in 8-mo-old bovine GH (bGH)-transgenic mice. Total body weight, serum cholesterol, insulin-like growth factor-I, and insulin levels were higher, whereas serum levels of glucose, free fatty acids, and triglycerides were lower in transgenic mice. Very low-density lipoprotein (VLDL) cholesterol levels were lower, and low-density lipoprotein (LDL) cholesterol levels were higher, in transgenic mice irrespective of gender, whereas only transgenic male mice had higher high-density lipoprotein cholesterol levels. Total serum apolipoprotein B (apoB) levels were not affected, but the amount of apoB in the LDL fraction was higher in transgenic mice. Hepatic LDL receptor expression was unchanged, whereas apoB mRNA editing and hepatic triglyceride secretion rate were reduced in bGH-transgenic male mice. Both lipoprotein lipase activity in adipose and heart tissue and beta-adrenergic-stimulated lipolysis were increased in transgenic male mice. The relative weight of adipose tissue was lower in transgenic mice, whereas hepatic triglyceride content was unchanged. Fat feeding of the mice equalized serum triglycerides and free fatty acids in bGH-transgenic and control mice. In summary, long-term GH excess is associated with marked alterations in lipid and lipoprotein metabolism, indicating decreased production and increased degradation of VLDL and preferential flux of fatty acids to muscle tissues.

Epidemiology of acromegaly

Acromegaly is a consequence of chronic growth hormone (GH) excess, due in the majority of cases to a GH-secreting pituitary adenoma, and occurring with a population prevalence of 60 per million and an incidence of 3-4 per million per year. Males and females appear to be equally affected with an average age of presentation of 44 years. Younger patients may have more aggressive tumours and higher GH concentrations. There is co-existent hyperprolactinaemia in about one third of cases, and a variable proportion of [figure: see text] tumours appear to have activating mutations of the gsp gene or other genetic abnormalities. Acute complications such as carpal tunnel syndrome, sweating and obstructive sleep apnoea are usually readily reversible with treatment of the condition, but chronic complications such as hypertension, diabetes and heart disease are less readily corrected and post-treatment GH levels of < 2.5 ug/L (5 mU/L) are needed to achieve the prevalence found in the general community. Such 'curative' levels of GH are achieved in only about 50% of patients with current therapies, and as a result there is an ongoing excess of patients with chronic complications of acromegaly leading to increased morbidity and mortality from the disorder, with observed-to-expected mortality ratios ranging from 1.6-3.3 and only approaching unity in those with growth hormone levels < 2.5 ug/L following treatment. Prognostic factors include in some studies the presence of diabetes and [table: see text] hypertension prior to diagnosis as well as measures of exposure to excessive growth hormone derived from the product of preoperative serum GH and the time from first symptoms to treatment. Overall, however, the most important prognostic variable appears to be the serum GH concentration achieved by treatment, with an increasing consensus that this needs to be < 2.5 ug/L (5 mU/L) to achieve cure of the condition.

Serum lipoproteins in acromegaly before and 6-15 months after transsphenoidal adenomectomy

OBJECTIVES

Acromegaly is a rare disorder characterized by over-secretion of GH, most often because of a pituitary adenoma. The disease is associated with disturbances in lipoprotein metabolism and an increased cardiovascular mortality. The aim of the present study was to investigate whether treatment of acromegaly results in changes in serum concentrations of lipids and apolipoproteins, including lipoprotein(a) (Lp(a)).

DESIGN

Fourteen patients with clinical features of acromegaly and increased GH secretion were studied 1-10 months before and 6-15 months after transsphenoidal adenomectomy in an open study.

PATIENTS

Three patients had diabetes mellitus before surgery and two of these patients had normalized serum glucose levels post-operatively. Mean and baseline plasma GH levels were determined from 24-hour GH profiles. Serum samples were taken in the morning after an overnight fast. All patients were normocholesterolaemic, and four patients were hypertriglyceridaemic before treatment.

RESULTS

Mean plasma GH levels decreased from 34.5 +/- 7.4 to 2.1 +/- 0.4 mU/l (mean +/- SEM). Serum IGF-I, insulin and free T3 levels decreased and serum SHBG concentrations increased post-operatively. There was no effect of treatment on serum cholesterol concentrations, but serum triglyceride concentrations decreased. Serum apolipoprotein (apo) B and apoE levels were unaffected by treatment. Serum apoA-I levels increased and Lp(a) levels decreased post-operatively.

CONCLUSIONS

Successful treatment of acromegaly, resulting in normal mean GH values (< 5 mU/l) and/or normal responsiveness to TRH, have beneficial effects on serum lipoproteins with increased serum apoA-I levels and decreased serum levels of triglycerides and Lp(a). These effects seem to be independent of improvement in glucose tolerance, since patients with diabetes mellitus before surgery and normal fasting blood glucose levels post-operatively had similar lipoprotein responses to treatment as those with normal fasting blood glucose levels before surgery.