Characterization of 24-hour growth hormone secretion in acromegaly: implications for diagnosis and therapy

Consensus on criteria for acromegaly diagnosis and remission

PURPOSE

The 14th Acromegaly Consensus Conference was convened to consider biochemical criteria for acromegaly diagnosis and evaluation of therapeutic efficacy.

METHODS

Fifty-six acromegaly experts from 16 countries reviewed and discussed current evidence focused on biochemical assays; criteria for diagnosis and the role of imaging, pathology, and clinical assessments; consequences of diagnostic delay; criteria for remission and recommendations for follow up; and the value of assessment and monitoring in defining disease progression, selecting appropriate treatments, and maximizing patient outcomes.

RESULTS

In a patient with typical acromegaly features, insulin-like growth factor (IGF)-I > 1.3 times the upper limit of normal for age confirms the diagnosis. Random growth hormone (GH) measured after overnight fasting may be useful for informing prognosis, but is not required for diagnosis. For patients with equivocal results, IGF-I measurements using the same validated assay can be repeated, and oral glucose tolerance testing might also be useful. Although biochemical remission is the primary assessment of treatment outcome, biochemical findings should be interpreted within the clinical context of acromegaly. Follow up assessments should consider biochemical evaluation of treatment effectiveness, imaging studies evaluating residual/recurrent adenoma mass, and clinical signs and symptoms of acromegaly, its complications, and comorbidities. Referral to a multidisciplinary pituitary center should be considered for patients with equivocal biochemical, pathology, or imaging findings at diagnosis, and for patients insufficiently responsive to standard treatment approaches.

CONCLUSION

Consensus recommendations highlight new understandings of disordered GH and IGF-I in patients with acromegaly and the importance of expert management for this rare disease.

Excess Growth Hormone Triggers Inflammation-Associated Arthropathy, Subchondral Bone Loss, and Arthralgia

Growth hormone (GH) is a key mediator of skeletal growth. In humans, excess GH secretion due to pituitary adenoma, seen in patients with acromegaly, results in severe arthropathies. This study investigated the effects of long-term excess GH on the knee joint tissues. One year-old wild-type (WT) and bovine GH (bGH) transgenic mice were used as a model for excess GH. bGH mice showed increased sensitivity to mechanical and thermal stimuli, compared with WT mice. Micro-computed tomography analyses of the distal femur subchondral bone revealed significant reductions in trabecular thickness and significantly reduced bone mineral density of the tibial subchondral bone-plate associated with increased osteoclast activity in both male and female bGH compared with WT mice. bGH mice showed severe loss of matrix from the articular cartilage, osteophytosis, synovitis, and ectopic chondrogenesis. Articular cartilage loss in the bGH mice was associated with elevated markers of inflammation and chondrocyte hypertrophy. Finally, hyperplasia of synovial cells was associated with increased expression of Ki-67 and diminished p53 levels in the synovium of bGH mice. Unlike the low-grade inflammation seen in primary osteoarthritis, arthropathy caused by excess GH affects all joint tissues and triggers severe inflammatory response. Data from this study suggest that treatment of acromegalic arthropathy should involve inhibition of ectopic chondrogenesis and chondrocyte hypertrophy.

Neurofibromatosis Type 1 Has a Wide Spectrum of Growth Hormone Excess

Overgrowth due to growth hormone (GH) excess affects approximately 10% of patients with neurofibromatosis type 1 (NF1) and optic pathway glioma (OPG). Our aim is to describe the clinical, biochemical, pathological, and genetic features of GH excess in a retrospective case series of 10 children and adults with NF1 referred to a tertiary care clinical research center. Six children (median age = 4 years, range of 3−5 years), one 14-year-old adolescent, and three adults (median age = 42 years, range of 29−52 years) were diagnosed with NF1 and GH excess. GH excess was confirmed by the failure to suppress GH (<1 ng/mL) on oral glucose tolerance test (OGTT, n = 9) and frequent overnight sampling of GH levels (n = 6). Genetic testing was ascertained through targeted or whole-exome sequencing (n = 9). Five patients (all children) had an OPG without any pituitary abnormality, three patients (one adolescent and two adults) had a pituitary lesion (two tumors, one suggestive hyperplasia) without an OPG, and two patients (one child and one adult) had a pituitary lesion (a pituitary tumor and suggestive hyperplasia, respectively) with a concomitant OPG. The serial overnight sampling of GH levels in six patients revealed abnormal overnight GH profiling. Two adult patients had a voluminous pituitary gland on pituitary imaging. One pituitary tumor from an adolescent patient who harbored a germline heterozygous p.Gln514Pro NF1 variant stained positive for GH and prolactin. One child who harbored a heterozygous truncating variant in exon 46 of NF1 had an OPG that, when compared to normal optic nerves, stained strongly for GPR101, an orphan G protein-coupled receptor causing GH excess in X-linked acrogigantism. We describe a series of patients with GH excess and NF1. Our findings show the variability in patterns of serial overnight GH secretion, somatotroph tumor or hyperplasia in some cases of NF1 and GH excess. Further studies are required to ascertain the link between NF1, GH excess and GPR101, which may aid in the characterization of the molecular underpinning of GH excess in NF1.

Correlation Between Clinical and Biochemical Markers in Patients With Acromegaly on Different Modalities of Treatment

Background

Acromegaly is a disabling disease caused by growth hormone (GH) over-secretion, associated with increased morbidity and mortality through different metabolic and somatic consequences involving soft tissue, acral overgrowth, and skin thickening, which will lead to different clinical manifestations. The study aimed to assess the correlation between biochemical markers of acromegaly with different clinical findings and biochemical control with the clinical findings.

Methods

A cross-sectional study was done on 56 patients with acromegaly attending a tertiary center for diabetes, endocrine, and metabolism in Southern Iraq Basrah. They were 32 (57.1%) males. Fatigue, headache, excessive sweating, joint pain, backache, soft tissue swelling, numbness, snoring, and visual problems were assessed on a four-point Likert scale. In addition, biochemical dynamic GH testing was done using a five-point random GH curve and/or standard GH suppression under the oral glucose tolerance test (OGTT).

Results

No significant correlation was found between symptoms severity and five-point GH parameters in respect of mean, peak, and nadir. Only backache showed a significant correlation with GH under OGTT suppression parameters in respect to mean, peak, and nadir (P-values < 0.01, < 0.01, and < 0.01), respectively. No particular biochemical control cut-off value in the 9 am random GH, mean five-point GH curve, or nadir GH under OGTT was correlated with the degree of severity for any of the clinical symptoms, as there was no difference between the biochemically controlled and uncontrolled groups in respect to any of the clinical symptom’s severity scale.

Conclusion

Only backache correlated with the biochemical tests of disease activity in the form of GH under OGTT. It appears in this study that the severity of the clinical symptoms does not correlate with biochemical control so that thorough evaluation and treatment of clinical complaints besides biochemical control is an essential part of the management plan in patients with acromegaly.

Prognostic factors of biochemical remission after transsphenoidal surgery for acromegaly: a structured review

PURPOSE

Biochemical control is the main determinant of survival, clinical manifestations and comorbidities in acromegaly. Transsphenoidal selective adenomectomy (TSA) is the initial treatment of choice with reported biochemical remission rates varying between 32 and 85%. Understanding the limiting factors is essential for identification of patients who require medical treatment.

METHODS

We reviewed the English literature published in Medline/Pubmed until Dec 31, 2019 to identify eligible studies that described outcomes of TSA as primary therapy and performed analyses to determine the main predictors of remission.

RESULTS

Most publications reported single-institution, retrospective studies. The following preoperative parameters were consistently associated with lower remission rates: cavernous sinus invasion by imaging, larger tumor size and higher GH levels. Young age and preoperative IGF-1 levels were predictive in some studies. When controlled for covariates, the best single preoperative predictor was cavernous sinus invasion, followed by preoperative GH levels. Conversely, low GH level in the first few days postoperatively was a robust predictor of durable remission. The influence of tumor histology (sparsely granular pattern, co-expression of prolactin and proliferation markers) on surgical remission remains to be established. Few studies developed predictive models that yielded much higher predictive values than individual parameters.

CONCLUSION

Surgical outcome prognostication systems could be further generated by machine learning algorithms in order to support development and implementation of personalized care in patients with acromegaly.

Prevalence, Clinical and Biochemical Spectrum, and Treatment Outcome of Acromegaly With Normal Basal GH at Diagnosis

CONTEXT

The term micromegaly has been used to describe a subset of patients who have elevated IGF-1 levels but apparently normal basal GH (bGH) concentrations and often a glucose-suppressed GH of <1 ng/mL.

OBJECTIVE

To evaluate the prevalence, clinical spectrum, and therapeutic outcome of acromegaly with normal bGH at diagnosis.

DESIGN AND METHODS

Retrospective analysis of a cohort of patients with acromegaly diagnosed and treated at a tertiary care center.

RESULTS

A cohort of 528 patients with acromegaly was stratified according to bGH at diagnosis: group 1, <2 ng/mL, n = 16; group 2, 2 to 9.9 ng/mL, n = 202; group 3, 10 to 99 ng/mL, n = 294; and group 4, ≥100 ng/mL, n = 16. Patients in group 1 (normal bGH) constituted 3% of the total cohort and were significantly older and more likely to be male than patients in the other groups. The frequency of acromegalic symptoms, signs, and comorbidities was similar between the four patient groups. Patients in group 1 more often harbored microadenomas (75%) and had significantly lower median IGF-1 and postglucose GH levels. Surgical success rates were similar between patients from groups 1 (53.8%), 2 (54.1%), and 3 (36.9%), whereas only 13.3% of patients in group 4 achieved remission.

CONCLUSION

Normal bGH acromegaly is uncommon in real life. These patients have some distinctive features that argue against this being simply acromegaly in its early stages.

Twenty-four-hour growth hormone profiling in the assessment of acromegaly

OBJECTIVES AND BACKGROUND

Recent guidelines recommend insulin-like growth factor (IGF-1), random growth hormone (GH) and nadir GH on an oral glucose tolerance test (OGTT) for assessment of acromegaly. At this Regional Centre, the 24-hour GH profile has also been used.

DESIGN PATIENTS AND MEASUREMENTS

We evaluated 57 GH profiles from 34 patients from 2008 to 2012. Samples were drawn every 2 hour and matched with 0800 GH, nadir GH after OGTT and IGF-1.

RESULTS

Correlations between the mean 13-point profiles and mean 5-point profile, OGTT nadir and 0800 GH were as follows: r = .99, .99 and .90, respectively (P < .01 for all). The correlation between the mean 13-point profiles and IGF-1 was r = .32 P = .02.Of 5 patients with very high 0800 GH preoperatively (≥20 μg/L), mean 13-point GH reduced by 88%-99% postoperatively. IGF-1 did not normalize in these patients, and all required extra treatment. Preoperatively, all patients had concordant 0800 GH and IGF-1. Postoperatively, 6 patients had 0800 GH <1 μg/L and high IGF-1; only 2 of these had a 13-point mean >1 μg/L, but 5 required further treatment.

CONCLUSIONS

Growth hormone profiling is not necessary for assessing the majority of patients with acromegaly if there is confidence in the local IGF-1 assay. When undertaken, a 5-point profile is adequate. In patients with very high 0800 GH, 24-hour profiling was useful in demonstrating partial therapeutic success but did not alter management. Further work is needed to explore the possible role of GH profiling in stratifying patients with discordant IGF-1 and GH results.

A two-step deconvolution-analysis-informed population pharmacodynamic modeling approach for drugs targeting pulsatile endogenous compounds

Pharmacodynamic modeling of pulsatile endogenous compounds (e.g. growth hormone [GH]) is currently limited to the identification of a low number of pulses. Commonly used pharmacodynamic models are not able to capture the complexity of pulsatile secretion and therefore non-compartmental analyses are performed to extract summary statistics (mean, AUC, C_max). The aim of this study was to develop a new quantification method that deals with highly variable pulsatile data by using a deconvolution-analysis-informed population pharmacodynamic modeling approach. Pulse frequency and pulse times were obtained by deconvolution analysis of 24 h GH profiles. The estimated pulse times then informed a non-linear mixed effects population pharmacodynamic model in NONMEM V7.3. The population parameter estimates were used to perform simulations that show agonistic and antagonistic drug effects on the secretion of GH. Additionally, a clinical trial simulation shows the application of this method in the quantification of a hypothetical drug effect that inhibits GH secretion. The GH profiles were modeled using a turnover compartment in which the baseline secretion, k_out, pulse secretion width, amount at time point 0 and pulse amplitude were estimated as population parameters. Population parameters were estimated with low relative standard errors (ranging from 2 to 5%). Total body water (%) was identified as a covariate for pulse amplitude, baseline secretion and the pulse secretion width following a power relationship. Simulations visualized multiple gradients of a hypothetical drug that influenced the endogenous secretion of GH. The established model was able to fit and quantify the highly variable individual 24 h GH profiles over time. This pharmacodynamic model can be used to quantify drug effects that target other endogenous pulsatile compounds.

Growth hormone and risk for cardiac tumors in Carney complex

Carney complex (CNC) is a multiple neoplasia syndrome that is caused mostly by PRKAR1A mutations. Cardiac myxomas are the leading cause of mortality in CNC patients who, in addition, often develop growth hormone (GH) excess. We studied patients with CNC, who were observed for over a period of 20 years (1995-2015) for the development of both GH excess and cardiac myxomas. GH secretion was evaluated by standard testing; dedicated cardiovascular imaging was used to detect cardiac abnormalities. Four excised cardiac myxomas were tested for the expression of insulin-like growth factor-1 (IGF-1). A total of 99 CNC patients (97 with a PRKAR1A mutation) were included in the study with a mean age of 25.8 ± 16.6 years at presentation. Over an observed mean follow-up of 25.8 years, 60% of patients with GH excess (n = 46) developed a cardiac myxoma compared with only 36% of those without GH excess (n = 54) (P = 0.016). Overall, patients with GH excess were also more likely to have a tumor vs those with normal GH secretion (OR: 2.78, 95% CI: 1.23-6.29; P = 0.014). IGF-1 mRNA and protein were higher in CNC myxomas than in normal heart tissue. We conclude that the development of cardiac myxomas in CNC may be associated with increased GH secretion, in a manner analogous to the association between fibrous dysplasia and GH excess in McCune-Albright syndrome, a condition similar to CNC. We speculate that treatment of GH excess in patients with CNC may reduce the likelihood of cardiac myxoma formation and/or recurrence of this tumor.

60 YEARS OF NEUROENDOCRINOLOGY: Acromegaly

Acromegaly (ACM) is a chronic, progressive disorder caused by the persistent hypersecretion of GH, in the vast majority of cases secreted by a pituitary adenoma. The consequent increase in IGF1 (a GH-induced liver protein) is responsible for most clinical features and for the systemic complications associated with increased mortality. The clinical diagnosis, based on symptoms related to GH excess or the presence of a pituitary mass, is often delayed many years because of the slow progression of the disease. Initial testing relies on measuring the serum IGF1 concentration. The oral glucose tolerance test with concomitant GH measurement is the gold-standard diagnostic test. The therapeutic options for ACM are surgery, medical treatment, and radiotherapy (RT). The outcome of surgery is very good for microadenomas (80-90% cure rate), but at least half of the macroadenomas (most frequently encountered in ACM patients) are not cured surgically. Somatostatin analogs are mainly indicated after surgical failure. Currently their routine use as primary therapy is not recommended. Dopamine agonists are useful in a minority of cases. Pegvisomant is indicated for patients refractory to surgery and other medical treatments. RT is employed sparingly, in cases of persistent disease activity despite other treatments, due to its long-term side effects. With complex, combined treatment, at least three-quarters of the cases are controlled according to current criteria. With proper control of the disease, the specific complications are partially improved and the mortality rate is close to that of the background population.

Discordance between growth hormone and insulin-like growth factor-1 after pituitary surgery for acromegaly: a stepwise approach and management

INTRODUCTION

Follow-up management of patients with acromegaly after pituitary surgery is performed by conducting biochemical assays of growth hormone (GH) and insulin-like growth factor-1 (IGF1). Despite concordant results of these two tests in the majority of cases, there is increasing recognition of patients who show persistent or intermittent discordance between GH and IGF1 (normal GH and elevated IGF1 or vice versa).

METHOD

In this narrative review, the last three decades materials on the issue of discrepancy between GH and IGF1 were thoroughly assessed.

RESULTS

Various studies have obtained different discordance rates, ranging from 5.4 to 39.5%. At present, despite the use of current sensitive assays and more stringent criteria to define remission, the rate of discordance still remains high. A number of mechanisms have been proposed to explain the postoperative discordance of GH and IGF1 including; altered dynamics of the GH secretion after surgery, early postoperative hormone assay, inaccurate or less sensitive tests and laboratory errors, too high cut-off point for GH suppression in the GH assays, GH nadir values not adjusted to age, sex, and body mass index, the influence of concomitant medication, co-existing physiologic and pathologic conditions, and many other proposed reasons. Nevertheless, the underlying mechanisms are still far from clear, and the solution continues to evade complete elucidation. Similarly, the impacts of such a discrepancy over mortality and morbidity and the risk of biochemical and/or clinical recurrence are unclear.

CONCLUSION

As a challenging clinical problem, a stepwise evaluation and management of these patients appears to be more rational.

[Consensus on the change of criteria for cure of acromegaly during the last decade]

The Acromegaly Consensus Group redefined the consensus criteria for cure of acromegaly. 74 neurosurgeons and experienced endocrinologists summarized the latest results on diagnosis and treatment of acromegaly. In this consensus statement the reliable growth hormone and insulin-like growth factor-1 assays were established. Definition of disease control was discussed based on the available publications and evidence. This short communication summarizes the clinical aspects of consensus criteria for diagnosis and cure of acromegaly based on the original article.

Clinical laboratory indices in the treatment of acromegaly

Measurement of serum growth hormone (GH) and insulin-like growth factor-I (IGF-) is used to monitor the degree of improvement that occurs following treatment of patients with acromegaly. Improvement in GH assay sensitivity has led to changes in the definition of normal GH however many studies that assess the predictive value of GH were conducted in an era where assays were less sensitive. Other problems that have occurred with GH measurements include utilization of different standards and failure to prove commutability of commonly accepted standard. GH reference ranges vary in their quality and are not stratified for age, sex or body mass index. IGF-I measurements are associated with similar problems. They do not use a common standard that has been proven to be commutable and results can vary widely when the same specimens are assayed in different laboratories. Although age and sex stratified reference ranges exist, these do not always have adequate numbers of subjects and BMI adjusted ranges are not available. These problems have led to significant discordance in a significant number of patients wherein the IGF-I and GH values may yield a discrepant prediction of disease stabilization. In these cases in general the IGF-I values correlate better with the presence of persistent symptoms. Patients who fail to suppress GH to normal but have a normal IGF-I have to be monitored carefully for recurrence but usually do not require further therapy if they are asymptomatic. For the long term assessment of outcome and clinical disease activity measurement of both hormones is recommended.

A consensus on criteria for cure of acromegaly

OBJECTIVE

The Acromegaly Consensus Group met in April 2009 to revisit the guidelines on criteria for cure as defined in 2000.

PARTICIPANTS

Participants included 74 neurosurgeons and endocrinologists with extensive experience of treating acromegaly. EVIDENCE/CONSENSUS PROCESS: Relevant assays, biochemical measures, clinical outcomes, and definition of disease control were discussed, based on the available published evidence, and the strength of consensus statements was rated.

CONCLUSIONS

Criteria to define active acromegaly and disease control were agreed, and several significant changes were made to the 2000 guidelines. Appropriate methods of measuring and achieving disease control were summarized.

Basal, but not pulsatile, growth hormone secretion determines the ambient circulating levels of insulin-like growth factor-I

CONTEXT

Previous studies have shown that mean 24-h GH concentrations determine plasma IGF-I levels in patients with acromegaly. However, we have recently shown that continuous GH infusion, mimicking the interpulse GH levels, was significantly more effective than the pulsatile GH administration at increasing IGF-I concentrations.

OBJECTIVE

The aim of the study was to ascertain relative roles of total GH output (24-h mean), GH pulses, and interpulse GH level in determining plasma IGF-I concentrations.

DESIGN AND SETTING

We conducted a point-in-time observational inpatient study in the General Clinical Research Center at the University of Michigan.

PATIENTS OR OTHER PARTICIPANTS

Eighteen patients with acromegaly and 19 healthy control subjects participated in the study.

INTERVENTION(S)

We performed frequent (every 10 or 20 min) blood sampling over 24 h.

MAIN OUTCOME MEASURE(S)

Before data collection, we hypothesized that interpulse nadir levels of GH would correlate with IGF-I levels in normal and acromegalic subjects.

RESULTS

Mean and valley levels of GH correlated with serum IGF-I levels (r(2) = 0.44 and 0.48, respectively) in normal and acromegalic patients in a log-linear fashion. The strongest correlation, however, was observed between the log of nadir GH and IGF-I concentrations (r(2) = 0.77). GH pulse mass did not significantly correlate with IGF-I (r(2) = 0.001).

CONCLUSIONS

Plasma IGF-I concentrations correlated with mean 24-h GH concentrations. This relationship is dependent exclusively on the basal GH levels. GH pulses do not determine plasma IGF-I concentrations.

The value of the oral glucose tolerance test, random serum growth hormone and mean growth hormone levels in assessing the postoperative outcome of patients with acromegaly

BACKGROUND

The nadir GH value following an oral glucose tolerance test (OGTT) and the mean GH levels obtained from a GH day curve (GHDC) are among the tools currently used for assessing therapeutic end-points in surgically treated acromegaly. The latter test, however, is cumbersome and costly.

OBJECTIVES

To evaluate, by using a modern, two-site chemiluminescent immunometric GH assay, the degree of discordance between the nadir GH following an OGTT and the mean GH obtained from a GHDC after surgical treatment of acromegaly and to check whether the OGTT can replace reliably the GHDC for the assessment of the disease status postoperatively.

PATIENTS AND METHODS

Forty-nine patients [25 males/24 females, median age 52 years (range 18-70)] with a GH-secreting pituitary adenoma who had been surgically treated previously underwent hormonal evaluation of their disease status. The GHDC comprised of 9 x 30-min samples for GH collected in the morning after an overnight fast and rest.

RESULTS

Seven per cent of patients with mean GH <1.7 mug/l (5 mU/l) in the GHDC had nadir GH >0.7 mug/l (2 mU/l) in the OGTT, and 10% of those with mean GH >1.7 mug/l had nadir GH <0.7 mug/l in the OGTT (all cases with discrepancies had normal IGF-I). GH value at time 0 min <0.6 mug/l in the OGTT had positive predictive value 100% and negative predictive value 75% in predicting nadir GH <0.3 mug/l (1 mU/l) in the OGTT. Nadir GH <0.8 mug/l in the OGTT had positive predictive value 97% and negative predictive value 95% in predicting mean GH <1.7 mug/l in the GHDC. Mean GH in the OGTT <1.4 mug/l had a positive predictive value 90% and negative predictive value 95% in predicting mean GH <1.7 mug/l in the GHDC. Mean GH in the OGTT <2.5 mug/l had positive predictive value 100% and negative predictive value 81% in predicting normal IGF-I. GH at time 0 min in the GHDC <2.1 mug/l had positive predictive value 90% and negative predictive value 90% in predicting mean GH <1.7 mug/l in the GHDC.

CONCLUSIONS

The hormonal data obtained from an OGTT (mean and nadir GH) can provide comprehensive information on the status of acromegaly following surgery and can replace the GHDC cost-effectively. Furthermore, a morning fasting GH sample has an excellent positive predictive value in predicting biochemical cure and an optimal prognostic profile in predicting "safe" mean GH levels.

Monitoring of acromegaly: what should be performed when GH and IGF-1 levels are discrepant?

Monitoring of a patient with acromegaly requires periodic evaluation of levels of GH and IGF-1, the biochemical markers of this disease. Although the results of these two tests are usually concordant, they can be discrepant and how to proceed when they are can be a challenging clinical problem. In some cases, IGF-1 levels are normal yet GH suppression after oral glucose is abnormal; this pattern may be due to persistent GH dysregulation despite remission. In other cases, IGF-1 levels are elevated yet GH suppression appears to be normal; this pattern may be observed if the cutoff for GH suppression is inappropriately high for the GH assay being used. Various conditions known to alter GH and IGF-1 including malnutrition, thyroid disease and oestrogen use as well as the potential for methodological or normative data issues with the GH and IGF-1 assays should be considered in the interpretation of discrepant results. When a known cause of the discrepancy other than acromegaly is not identified, a clinical decision about the patient's therapy needs to be made. We adjust treatment in most patients whose results are discrepant based on the IGF-1 level, continuing current treatment if it is persistently normal or modifying this if it is elevated. The clinical picture of the patient, however, also needs to be incorporated into this decision. All patients should have continued periodic surveillance of both GH and IGF-1 levels.

Influence of growth hormone receptor d3 and full-length isoforms on biochemical treatment outcomes in acromegaly

CONTEXT

In acromegaly, a discrepancy between what are defined as "normal" levels of GH and IGF-I for every given patient is observed in up to 35% of subjects at diagnosis and during the follow-up.

OBJECTIVE

The aim of the study was to evaluate the impact of GH receptor (GHR) polymorphism on the biochemical assessment of the treatment of acromegaly and on prevalence of discordant levels of GH and IGF-I.

SETTING

The study was performed in an institutional referral center at a tertiary care hospital.

DESIGN, PATIENTS, AND METHODS

We studied prospectively and retrospectively 84 consecutive acromegalic patients with active disease after neurosurgery and treated them with somatostatin analogs. The GHR genotype (flfl, fld3, or d3d3) was determined from peripheral blood.

RESULTS

Lack of exon 3 of GH receptor (d3-GHR) was found in 40 of 84 patients (47.6%). After neurosurgery, 67 subjects (79.8%) of the study population, concordant active acromegalic patients, had high IGF-I and mean GH levels above 2 ng/ml, whereas the remaining 17 patients (20.2%, discordant active acromegalic patients) showed discordance between these two parameters (high IGF-I and GH levels < or = 2 ng/ml). Overall, 70.6% of discordant patients were carriers of the d3-GHR. After somatostatin analogs, discordant active acromegalic patients increased to 30.9%, 69.2% of whom were carriers of the d3-GHR. Logistic regression analysis demonstrated that d3-GHR carriers maintained the significant correlation with discordant GH and IGF-I values either after neurosurgery or after somatostatin analog treatment, independently of the effects of age, sex, duration of acromegaly, serum GH, and IGF- I values either at diagnosis of acromegaly or after neurosurgery.

CONCLUSION

The GHR polymorphism seems to have a relevant impact on the posttreatment biochemical assessment of acromegaly. Moreover, the d3-GHR isoform could be an independent predictor of GH and IGF-I discrepancy during the follow-up in acromegaly.

Therapeutic options in the management of acromegaly: focus on lanreotide Autogel

BACKGROUND

In acromegaly, expert surgery is curative in only about 60% of patients. Postoperative radiation therapy is associated with a high incidence of hypopituitarism and its effect on growth hormone (GH) production is slow, so that adjuvant medical treatment becomes of importance in the management of many patients.

OBJECTIVE

To delineate the role of lanreotide in the treatment of acromegaly.

METHODS

Search of Medline, Embase, and Web of Science databases for clinical studies of lanreotide in acromegaly.

RESULTS

Treatment with lanreotide slow release and lanreotide Autogel((R)) normalized GH and insulin-like growth factor-I (IGF-I) concentrations in about 50% of patients. The efficacy of 120 mg lanreotide Autogel((R)) on GH and IGF-I levels was comparable with that of 20 mg octreotide LAR. There were no differences in improvement of cardiac function, decrease in pancreatic beta-cell function, or occurrence of side effects, including cholelithiasis, between octreotide LAR and lanreotide Autogel(R). When postoperative treatment with somatostatin analogs does not result in normalization of serum IGF-I and GH levels after noncurative surgery, pegvisomant alone or in combination with somatostatin analogs can control these levels in a substantial number of patients.

Two hour mean GH is not superior to basal GH for the follow-up of acromegalic patients treated with Octreotide LAR

BACKGROUND

GH secretion, in acromegaly, is characterized by increased basal levels, as well as by increased frequency and amplitude of pulses. Evaluation of disease activity during follow-up of treated patients is frequently done with mean GH levels, although there is no established protocol for sample collection.

OBJECTIVE

Determine mean GH value of 5 blood samples collected 30 min apart for 2 consecutive hours in the follow-up of acromegalic patients treated with octreotide LAR.

METHODS

Ninety-one GH curves of 44 patients (25 women) were evaluated as were the respective IGF-I values (basal). Normal IGF-I for age and sex was considered standard for control of disease activity. Correlations between basal and mean GH were studied as were correlations between both values and %IGF-I above the upper limit of reference values (%ULRV).

RESULTS

Median age of the group was 45.5 years (range 28-73). Twenty-five patients (56.8%) had previous surgery and 7 (15.9%) had both surgery and radiotherapy. A positive correlation was found between mean and basal GH (r=0.953; p<0.001). Both basal and mean GH were correlated to %ULRV (r=0.645 and 0.661; p<0.001 for both). In only 3 of the 91 curves (3.3%) there were discordances between basal GH and IGF-I, however the latter was concordant with mean GH. In 3 other curves there was concordance between basal GH and IGF-I although the latter was discordant with mean GH.

CONCLUSIONS

There was no benefit to perform GH curves with the present protocol. It may be due to our established outpatient follow up protocol. The use of more complex protocols and the cost of multiple GH assays should be acknowledged, and probably reserved for patients with basal GH levels between 1 and 5 microg/L with discordant GH and IGF-I.

Growth hormone measurements in the diagnosis and monitoring of acromegaly

Before the availability of immunoassays for IGF-I, growth hormone (GH) measurement was the sole method used in the biochemical assessment of acromegaly. IGF-I has since been established as the most reliable biochemical indicator of acromegaly. The last 25 years has seen important advances in the understanding of the neuroregulation and in the characterization of GH secretion in acromegaly. The availability of supersensitive GH has changed many aspects of the interpretation of GH-value in the management of acromegaly. Hypersecretion and abnormal neuroregulation characterize GH secretion in acromegaly. GH can be measured in many ways: as a single random sample, as multiple samples, either spontaneously or as an integral part of a dynamic test. These approaches give useful information on diagnosis, therapy, and prognosis. There is a place for measuring GH in the management of acromegaly although it complements that of IGF-I.

Serum IGF-I levels in the diagnosis and monitoring of acromegaly

Insulin-Like Growth Factor-I (IGF-I) is a reliable marker of disease activity and growth hormone (GH) status in acromegaly, but its clinical utility has been hampered over the years by various issues including a lack of robust reference range data and variability in assay sensitivity and specificity. In acromegaly IGF-I correlates well with GH activity and nadir GH on oral glucose tolerance test (OGTT) and is the most sensitive and specific test in diagnosis, where serum IGF-I is persistently seen to be elevated to a range that is distinct from that in healthy individuals. However it should not be relied on exclusively for diagnosis or used as the sole indication of disease severity and GH burden. Successful medical or surgical treatment of acromegaly is usually associated with normalisation of serum IGF-I but there is discordance between GH and IGF-I in some patients. Patients with a normal IGF-I but an abnormal GH suppression to OGTT are at risk of relapse and therefore it should not be used alone to establish disease remission. In contrast to the diagnosis of acromegaly, there is also considerable overlap in serum IGF-I with normality after primary treatment of disease, even in the presence of persisting GH excess. Gender, age and prior radiotherapy alters the relationship between GH and IGF-I and reliance on one marker of disease activity such as IGF-I is particularly precarious in certain disease states. However an elevated serum IGF-I has been shown to be associated with excess mortality and normalising IGF-I normalises mortality making it a useful marker. The tightening up of the assays means that establishing absolute concentrations as well as standard deviation scores are essential to allow cross-study comparisons. This becomes especially important in the use of Pegvisomant, where IGF-I becomes the sole biochemical marker of disease activity.

Newer options in the management of acromegaly

Paradigms for managing acromegaly have undergone major changes in the past two decades. This has been brought about by combining surgical, pharmacological and radiotherapeutic approaches that provide tight biochemical control to reduce mortality to that of the general population. The biochemical targets for treatment are a growth hormone of <2.5 ng/mL (approximately 7.5 mU/L) and a normal, age-adjusted insulin-like growth factor-1. Until 20 years ago, dopamine agonists were the only class of pharmaceutical agents available to control acromegaly. They have a limited adjunctive role, even with the development of second-generation selective agonists such as cabergoline. Surgery and radiotherapy were the mainstay of acromegaly management before the advent of the effective pharmacological therapies of the modern era: somatostatin analogues and pegvisomant, a growth hormone receptor antagonist. Somatostatin analogues achieve biochemical control in approximately 60% of patients. Pegvisomant, which is available in the USA and Europe and has just been registered in Australia, normalizes insulin-like growth factor-1 in nearly all patients but has no effect on tumour mass. Surgery is an appropriate first-line therapy for microadenomas as the chance of success is high. For large and/or invasive tumours where the prospect of surgical cure is remote, first-line therapy is somatostatin analogue treatment with debulking surgery having an adjunctive role to achieve tight control or to alleviate compression of the optic chiasm. Although acromegaly remains a challenging disease to manage, the expanding range of therapeutic options is likely to result in a better outcome for patients and offers the potential to tailor therapy based on a patient's individual requirements.

Role of radiotherapy in the management of acromegaly

Active acromegaly can be treated effectively by transsphenoidal surgery, radiotherapy and medical treatment in the form of somatostatin analogs and growth hormone receptor antagonists. Many patients will require a combination of treatment modalities to normalize growth hormone excess and associated increased mortality, and to improve comorbidity. Following postoperative radiotherapy, growth hormone and insulin-like growth factor-I levels gradually decrease and normalization of growth hormone and insulin-like growth factor-I is achieved in 50% of patients after 5 years and 75% after 10 years. Disadvantages of radiotherapy include the long interval until hormone levels have sufficiently decreased and the high incidence of radiation-induced hypopituitarism. Radiotherapy was associated with increased mortality in some but not other studies. Limitations in the design and confounding factors, such as years spent with active disease and changing treatment strategies, make it impossible to draw conclusions on this topic. Gamma knife radiosurgery may combine faster decline of growth hormone excess with a lower incidence of hypopituitarism in eligible cases, but long-term results of this radiation technique are lacking. At present, patients will preferentially be treated by primary surgery and/or somatostatin analog treatment, followed, if necessary, by growth hormone receptor antagonist treatment, while radiotherapy is reserved for selected cases only. The indications for radiotherapy and radiosurgery need to be revisited in the near future, when longer follow-up results for medical treatment and radiosurgery have become available. This review summarizes the recent literature on efficacy and side effects of radiotherapy and radiosurgery in acromegaly and discusses the place of radiation treatment in the treatment algorithm of acromegaly.

Individual IGF-I Responsiveness to a Fixed Regimen of Low-Dose Growth Hormone Replacement Is Increased with Less Variability in Obese Compared to Non-Obese Adults with Severe Growth Hormone Deficiency

BACKGROUND/AIMS

Decreased GH and IGF-I levels and increased GH responsiveness are frequently reported in obesity. As GH-deficient adults are commonly obese, the role of obesity in affecting hepatic responsiveness of IGF-I generation to GH stimulation is unclear in severe GH-deficient states. To address this question, we challenged a cohort of severely GH-deficient non-obese and obese adults with a fixed low GH dose (0.2 mg/day), and examined the relationship of body mass index (BMI) with IGF-I response.

METHODS

12 non-obese (6 males, median BMI 24.7 kg/m2) and 14 obese (7 males, median BMI 45.2 kg/m2) adults with severe GH deficiency were studied for 8 weeks. Blood samples were collected at baseline, and weeks 4 and 8.

RESULTS

There was a larger increment and reduced variability of IGF-I levels in obese compared to non-obese GH-deficient adults at week 8, but not at week 4. A similar but smaller increment and less variability was observed with IGFBP-3. Increment IGF-I positively correlated with baseline BMI at weeks 4 (r=0.49, p<0.02) and 8 (r=0.47, p<0.02). No gender differences were observed with the IGF-I and IGFBP-3 response.

CONCLUSIONS

This study demonstrates that there is a larger increment and deceased individual variability of IGF-I to the low GH replacement dose in obese compared to non-obese adults with severe GH deficiency, regardless of gender. The positive association of IGF-I increment with BMI implies a greater impact of obesity rather than GH deficiency in enhancing hepatic sensitivity to GH. These findings, thus, question the reliability of interpreting single serum IGF-I levels in non-obese adults with severe GH deficiency treated with low GH replacement doses.

Nanomedicines in the treatment of acromegaly: focus on pegvisomant

This article examines the role of pegvisomant in the treatment of acromegaly. This syndrome, caused by excessive growth hormone (GH) secretion by a pituitary adenoma, is associated with a doubled mortality rate and poor quality of life. Pituitary microsurgery has long been the first choice of treatment since it cures many patients, especially those with localized tumors. Adjuvant irradiation was given if insulin-like growth factor-I (IGF-I) or GH did not normalize. The introduction of long-acting slow- release somatostatin analogs was a breakthrough for adjuvant treatment, although not always effective. Rather, targeting excessive GH production, muting the GH signal at its receptor, was a totally different approach. The development of GH antagonists (by mutation ofglycine at position 120) and other modifications to enhance receptor binding, and subsequent pegylation of the molecule led to the development of B2036. After pegylation of B2036 at 5 positions the distribution volume is restricted and its serum half-life considerably increased. In short-term clinical studies performed in selected, mostly pretreated, acromegalic patients, IGF-I normalized in the majority of cases. Combination therapy with long-acting somatostatin analogs and weekly rather than daily pegvisomant injections appears to be successful in one clinical study and might limit the high cost of pegvisomant. Long-term efficacy and safety has to be demonstrated. The drug does not cross the blood-brain barrier, and whether it distributes freely into the extracellular space of other organs than the liver has not been investigated, which might have implications for persistent local IGF-I production under unrestrained GH concentrations.

Clinical indicators of biochemical remission in acromegaly: does incomplete disease control always mean therapeutic failure?

OBJECTIVE

Correction of GH and IGF-I levels are associated with improvements in insulin secretion, cardiac performance and body composition in patients with acromegaly, but whether these parallel post-treatment levels of GH-IGF-I axis activity is undefined. We investigate whether various biochemical outcomes after transsphenoidal pituitary surgery (TSS) in these patients are associated with clinically relevant differences in cardiac performance, insulin resistance and body composition.

DESIGN

Cross-sectional study of consecutive patients with acromegaly admitted to the hospital between 2001 and 2002.

PATIENTS AND METHODS

Forty-one patients after TSS for somatotroph pituitary adenoma and 23 patients with naive acromegaly serving as positive controls were enrolled in the study. Mean daily GH levels (mGH), IGF-I, leptin and lipid levels, glucose, insulin and GH concentrations during oral glucose tolerance test (oGTT) were measured in all study participants. Insulin resistance was measured by homeostatic model index (R(HOMA)). Body composition was assessed by dual-energy X-ray absorptiometry. Left ventricular mass index (LVM(i)) and cardiac index (C(i)) were determined by echocardiography.

RESULTS

We found no difference in cardiac indices, insulin resistance, body composition and leptin levels between patients with complete biochemical remission and those with inadequately controlled disease (P > 0.05 for all) after TSS. Cured patients had lower values (mean +/- SD) of cardiac index (2.2 +/- 0.7 vs. 3.0 +/- 1.0 l/min/m(2); P = 0.04) compared with naive patients. A similar decrease in LVM(i) was observed in controlled (108.4 +/- 30.0 g/m(2); P = 0.015) and inadequately controlled disease (108.8 +/- 30.7 g/m(2); P = 0.03) in comparison with naive disease (160.3 +/- 80.6 g/m(2)). Insulin resistance and leptin changed in opposite ways. In controlled and inadequately controlled disease, R(HOMA) index was lower (2.2 +/- 1.4; P = 0.001 and 3.1 +/- 2.0; P = 0.05 vs. 5.1 +/- 3.1) while leptin concentration was higher (14.9 +/- 8.7 microg/l, P = 0.004 and 12.8 +/- 7.8 microg/l, P = 0.05 vs. 7.4 +/- 3.8 microg/l) than in naive disease. In all patients, leptin correlated negatively with cardiac index (r = -0.46; P = 0.001) and IGF-I levels (r = -0.45; P < 0.001). Independent predictors of biochemical remission, based on normal IGF-I levels only, were cardiac [P = 0.04, odds ratio (OR) 0.4; 95% confidence interval (CI) 0.2-0.9] and R(HOMA) index (P = 0.009, OR 0.6; 95% CI 0.4-0.8). Similar results were obtained if the definition of cure included both normal IGF-I levels and the ability to achieve GH nadir < 1 microg/l during oGTT. Insulin resistance (P = 0.02, OR 0.6; 95% CI 0.4-0.9) and leptin level (P = 0.002, OR 1.3; 95% CI 1.1-1.6) were independent predictors of normalized mGH values.

CONCLUSION

This study shows that cardiac indices, insulin resistance and body composition were not different between patients with complete biochemical remission and those with discordant GH and IGF-I levels. It appears that even incomplete disease control after TSS can result in improvement of these clinical markers.

[Usefulness of subcutaneous or long-acting octreotide as a predictive test and in the treatment of acromegaly]

We evaluated GH, IGF-1 and IGFBP-3 concentrations in ten acromegalic patients before and after treatment with subcutaneous octreotide (OCT-sc) and long-acting octreotide (OCT-LAR). We also evaluated the acute and short-period treatment (post 21 days) with octreotide as an index to test tolerance and responsiveness to both formulations. Patients were also evaluated after 6 months of treatment with each drug. Pre-treatment fasting GH (microg/l; IFMA), GH nadir during oGTT and IGF-1 (microg/l; IRMA) levels were 13.9+/-6.3; 11.4+/-6.3; 717+/-107, respectively. Fasting GH and IGF-1 were reduced after short treatment with OCT-sc or OCT-LAR (2.9+/-1.1 and 4.4+/-1.2; 491+/-80 and 512+/-80). All parameters were also reduced after a six-month period with OCT-sc or OCT-LAR (2.8+/-0.9 and 1.9+/-0.5; 1.6+/-0.4 and 1.6+/-0.5; 583+/-107 and 515+/-83), respectively. The efficacy of the two drugs was similar. IGFBP-3 was not a good parameter during follow-up of these patients. The acute test with OCT-sc was not a valuable index to predict tolerance, however, as well as the short-period test, it could predict the long-term GH responsiveness to OCT.

Early postoperative indicators of late outcome in acromegalic patients

OBJECTIVE

According to current criteria, normalised serum IGF-1 and glucose-suppressed GH < 1 ng/ml are indicators of biochemical cure in acromegalic patients. We performed a retrospective study to assess whether the attainment of these values in the early postoperative period was predictive of future IGF-1 normalisation and disease inactivity.

PATIENTS, MEASUREMENTS AND RESULTS

Between 1978 and 1999, 78 acromegalic patients underwent resection for pituitary adenomas. At the end of the mean follow-up period of 7 years, 43 (55.1%) showed normalised IGF-1 levels and no disease activity. In 51 cases, both IGF-1 and glucose-suppressed GH were examined within the first postoperative month. Of this group, all 19 patients who had early glucose-suppressed GH < 1 ng/ml and were treated by surgery alone maintained normal IGF-1 levels throughout the follow-up; four of them demonstrated delayed (i.e. more than 30 days after the operation) IGF-1 normalisation. In 19 patients with early glucose-suppressed GH levels of 1-4 ng/ml, seven of 11 patients with early normalised IGF-1 and two of eight patients with early IGF-1 elevation manifested eventual IGF-1 normalisation. However, none of the 13 patients with early glucose-suppressed GH > 4 ng/ml attained IGF-1 normalisation. Both univariate and multivariate analyses indicated that early glucose-suppressed GH was a significant factor for predicting late normalised IGF-1; the cut-off value was 1.5 ng/ml (sensitivity: 0.97; specificity: 0.75; odds ratio: 90).

CONCLUSION

The attainment of both normalised IGF-1 and glucose-suppressed GH < 1 ng/ml, even during the early postoperative period, suggests absolute cure in acromegalic patients. However, even in patients who do not meet both criteria within the first postoperative month, glucose-suppressed GH < 1.5 ng/ml, or glucose-suppressed GH < 4 ng/ml coupled with early IGF-1 normalisation indicate the possibility of eventual normalisation of IGF-1 and disease inactivity without adjuvant therapy. These postoperative parameters may be useful for assessing the desirability of further treatment.

Prolactin and the prolactin receptor: new targets of an old hormone

Prolactin (PRL) is one of a family of related hormones including growth hormone (GH) and placental lactogen (PL) that are hypothesized to have arisen from a common ancestral gene about 500 million years ago. Over 300 different functions of PRL have been reported, highlighting the importance of this pituitary hormone. PRL is also synthesized by a number of extra-pituitary tissues including the mammary gland and the uterus. Most of PRL's actions are mediated by the unmodified 23 kDa peptide, however, PRL may be modified post-translation, thereby altering its biological effects. PRL exerts these effects by binding to its receptor, a member of the class I cytokine receptor super-family. This activates a number of signaling pathways resulting in the transcription of genes necessary for the tissue specific changes induced by PRL. Mouse knockout models of the major forms of the PRL receptor have confirmed the importance of PRLs role in reproduction. Further knockout models have provided insight into the importance of PRL signaling intermediates and the advent of transcript profiling has allowed the elucidation of a number of PRL target genes.

Octreotide represses secretory-burst mass and nonpulsatile secretion but does not restore event frequency or orderly GH secretion in acromegaly

Octreotide is a potent somatostatin analog that inhibits growth hormone (GH) release and restricts somatotrope cell growth. The long-acting octreotide formulation Sandostatin LAR is effective clinically in approximately 60% of patients with acromegaly. Tumoral GH secretion in this disorder is characterized by increases in pulse amplitude and frequency, nonpulsatile (basal) release, and irregularity. Whether sustained blockade by octreotide can restore physiological secretion patterns in this setting is unknown. To address this question, we studied seven patients with GH-secreting tumors during chronic receptor agonism. Responses were monitored by sampling blood at 10-min intervals for 24 h, followed by analyses of secretion and regularity by multiparameter deconvolution and approximate entropy (ApEn). The somatostatin agonist suppressed GH secretory-burst mass, nonpulsatile (basal) GH release, and pulsatile secretion, thereby decreasing total GH secretion by 86% (range 70-96%). ApEn decreased from 1.203 +/- 0.129 to 0.804 +/- 0.141 (P = 0.032), denoting greater regularity. None of GH pulse frequency, basal GH secretion rates, or ApEn normalized. In summary, chronic somatostatin agonism is able to repress amplitude-dependent measures of excessive GH secretion in acromegaly. Presumptive tumoral autonomy is inferred by continued elevations of event frequency, overall pattern disruption (irregularity), and nonsuppressible basal GH secretion.

Optimizing control of acromegaly: integrating a growth hormone receptor antagonist into the treatment algorithm

Acromegaly is associated with significant morbidities and a 2- to 3-fold increase in mortality because of the excessive metabolic action of GH and IGF-I, a marker of GH output. Reductions in morbidity correspond with decreases in IGF-I, and mortality is lowered following normalization of IGF-I or GH levels. Therefore, this has become an important end point. Current guidelines for the treatment of acromegaly have not considered recent advances in medical therapy, in particular, the place of pegvisomant, a GH receptor antagonist. Treatment goals include normalizing biochemical markers, controlling tumor mass, preserving pituitary function, and relieving signs and symptoms. Surgery reduces tumor volume and is considered first-line therapy. Radiation reduces tumor volume and GH and IGF-I levels, but the onset of action is slow and hypopituitarism typically develops. Therefore, pharmacotherapy is often used following surgery or as first-line therapy for nonresectable tumors. Dopamine agonists can be considered in patients exhibiting minimal disease or those with GH-prolactin-cosecreting tumors but will not achieve hormone normalization in most patients. Somatostatin analogs effectively suppress GH and IGF-I in most patients, but intolerance (e.g. diarrhea, cramping, gallstones) can occur. Pegvisomant, the newest therapeutic option, blocks GH action at peripheral receptors, normalizes IGF-I levels, reduces signs and symptoms, and corrects metabolic defects. Pegvisomant does not appear to affect tumor size and has few adverse effects. Pegvisomant is the most effective drug treatment for acromegaly in normalizing IGF-I and producing a clinical response; it is the preferred agent in patients resistant to or intolerant of somatostatin analogs.

Current concepts in the biochemical assessment of the patient with acromegaly

Biochemical assessment of a patient for acromegaly aims to definitively establish or exclude the presence of growth hormone excess. Whether applied to a newly recognized patient or to detect residual disease after therapy, this assessment is best accomplished by measurement of both the degree of GH suppression after oral glucose administration (OGTT) and levels of the GH dependent peptide, insulin-like growth factor I (IGF-I). When measured properly and compared to a well-characterized, age-adjusted normative database, elevation of the serum IGF-I level is a sensitive and specific indicator for the presence of acromegaly or persistent disease after therapy. The diagnosis of acromegaly can be confirmed by documenting an elevated IGF-I level in combination with failure of GH to suppress after oral glucose to below 0.3 microg/l, when GH is measured with a highly sensitive and specific assay. Persistently, normal IGF-I levels along with a nadir GH <0.3 microg/l should exclude the diagnosis. In assessing disease status during or after treatment, normalization of IGF-I is an essential criterion for biochemical control. It is important to recognize that nadir GH levels are >0.3 microg/l in some healthy subjects, so this criterion alone is not diagnostic of acromegaly. Also, because of heterogeneity of clinically available GH assays, this GH criterion, which was developed with a research assay, may not be applicable to use with all other assays. A nadir GH cut off of 1 microg/l has been found to be reliable for use with some standard immunoassays. It is recommended that glucose-suppressed GH levels be interpreted in conjunction with those of IGF-I and with consideration of conditions other than acromegaly that can alter them. With greater assay standardization and the use of IGF-I levels along with new rigorous criteria for interpretation of GH suppression during a OGTT we can improve our identification of patients with acromegaly in earlier stages of the disease as well as better recognize residual disease during therapy.

Biochemical definitions of disease activity in acromegaly

In acromegaly the therapeutic outcome is difficult to assess and depends on the biochemical method. We have ascertained disease activity in 70 acromegalic patients by means of a GH profile (8 hourly samples) and a single IGF-I measurement as compared to a healthy control group. As an estimate of the "stiffness" of the GH profile we calculated the SD/nadir(GH) from the GH profile. In the control group the following upper normal limits were obtained: IGF-I (microg/l) 217; mean GH (microg/l) 2.16; nadir GH (g/l) 0.3. Based on ROC plot analysis a value of 2.0 for the SD/nadir ratio was used as cut-off. This translated into the following surgical cure rates (%): IGF-I 47; mean GH 77; nadir GH 65; SD/nadir 30. Some of the patients post-surgery had elevated IGF-I levels despite "normal" GH levels. Abnormal SD/nadir versus normal IGF-I and vice versa were recorded in many patients post-surgery.

IN CONCLUSION

(1) cure rates of acromegaly depend strongly on the criteria being used and (2) estimates of GH secretion pattern may yield important information about GH status in acromegaly.

Three-hour spontaneous GH secretion profile is as reliable as oral glucose tolerance test for the diagnosis of acromegaly

The diagnosis of acromegaly, in an appropriate clinical context, usually relies on lack of GH suppression below 1 microg/l during OGTT coupled with elevated IGF-I levels. On the other hand, in normal subjects glucose-induced inhibition of GH secretory bursts without any further decrease of interpulse GH levels had already been shown. Based on the foregoing, we aimed to compare the diagnostic reliability of OGTT-induced GH nadir with that recorded during 3-h spontaneous GH secretion. In 59 acromegalic patients (17 male and 42 female, age, mean +/- SE 51.5 +/- 1.9, range 21-76 yr) and in 82 normal subjects (43 male and 39 female, age, mean +/- SE 35.7 +/- 1.5, range 15-72 yr) GH secretion was evaluated every 30 min from 0 to 180 min during slow saline infusion or OGTT (75 g at 0 min). A nadir GH concentration below 1 microg/l was recorded in all normal subjects either during OGTT or saline infusion if GH secretion was evaluated over 180 min. In contrast in acromegalic patients a nadir GH concentration below 1 microg/l never occurred in both conditions. This study shows that a 3-h spontaneous GH profile is as reliable as OGTT in the diagnosis of active acromegaly.

Pitfalls in the biochemical assessment of acromegaly

The biochemical assessment for newly recognized acromegaly is in most, but not all patients straightforward. Although significant improvements in the methods of biochemical testing for acromegaly have recently been made, major pitfalls to the assessment of this disease still exist. A number of different schemes have been employed for the assessment of GH secretion in clinical practice. Random GH levels have been often used, but remain unreliable for the assessment of acromegaly. Mean GH levels are also frequently used to assess GH status, but are not specific for the diagnosis of acromegaly. Measurement of glucose suppressed GH levels is the preferred method for assessing GH secretion in acromegaly. However, it is essential to recognize that when using highly sensitive and specific GH assays, nadir GH levels can be < 1 microg/L after oral glucose in some patients with newly diagnosed acromegaly and postoperative patients with active disease. On the other hand, when using most clinically available commercial GH assays which are less sensitive and specific than those used in research studies, failure of GH suppression into the normal range set in these studies is not alone diagnostic of active acromegaly. In order to diagnose acromegaly, documentation of GH excess should be accompanied by elevation in levels of the GH dependent peptide, insulin-like growth factor I (IGF-I). Consideration also needs to be given to the clinical context in which GH and IGF-I are being measured as both can be altered in a number of clinical settings other than acromegaly. Both IGF-I and GH evaluations are important and complimentary parts of the biochemical assessment of acromegaly.

Gender and age influence the relationship between serum GH and IGF-I in patients with acromegaly

BACKGROUND

In patients with acromegaly serum IGF-I is increasingly used as a marker of disease activity. As a result, the relationship between serum GH and IGF-I is of profound interest. Healthy females secrete three times more GH than males but have broadly similar serum IGF-I levels, and women with GH deficiency require 30-50% more exogenous GH to maintain the same serum IGF-I as GH-deficient men. In a selected cohort of patients with active acromegaly, studied off medical therapy using a single fasting serum GH and IGF-I measurement, we have reported previously that, for a given GH level, women have significantly lower circulating IGF-I.

OBJECTIVE

To evaluate the influence of age and gender on the relationship between serum GH and IGF-I in an unselected cohort of patients with acromegaly independent of disease control and medical therapy.

METHODS

Sixty (34 male) unselected patients with acromegaly (median age 51 years (range 24-81 years) attending a colonoscopy screening programme were studied. Forty-five had previously received pituitary radiotherapy. Patients had varying degrees of disease control and received medical therapy where appropriate. Mean serum GH was calculated from an eight-point day profile (n = 45) and values obtained during a 75-g oral glucose tolerance test (n = 15). Serum IGF-I, IGFBP-3 and acid-labile subunit were measured and the dependency of these factors on covariates such as log10 mean serum GH, sex, age and prior radiotherapy was assessed using regression techniques.

RESULTS

The median calculated GH value was 4.7 mU/l (range 1-104). A significant linear association was observed between serum IGF-I and log10 mean serum GH for the cohort (R = 0.5, P < 0.0001). After simultaneous adjustment of the above covariates a significant difference in the relationship between mean serum GH and IGF-I was observed for males and females. On average, women had serum IGF-I levels 11.44 nmol/l lower than men with the same mean serum GH (P = 0.03, 95% CI 1.33-21.4 nmol/l). Age significantly influenced the relationship and for a given serum GH, IGF-I was estimated to fall by 0.37 nmol/l per year (P = 0.04, 95% CI 0.015-0.72).

CONCLUSIONS

In keeping with previous observations of relative GH resistance in normal and GH-deficient females we have observed lower serum IGF-I levels for equivalent mean serum GH levels in females patients with acromegaly. This gender-dependent difference is independent of disease activity and the use of concomitant medical therapy. Additionally, we have demonstrated that for a given serum GH level, age significantly influences IGF-I concentrations in patients with acromegaly. These data have important implications for the use of serum IGF-I and GH as markers of disease activity in acromegaly.

Diagnosis of acromegaly in a patient with type 1 diabetes mellitus

OBJECTIVE

To describe a case of acromegaly in a young patient with poorly controlled diabetes mellitus and suggest guidelines to distinguish acromegaly and high growth hormone (GH) levels previously reported in poorly controlled type 1 diabetes.

METHODS

We present a detailed case report, including clinical findings and serial laboratory results in a patient with type 1 diabetes and a GH-secreting pituitary tumor.

RESULTS

A 28-year-old woman with type 1 diabetes underwent assessment for secondary amenorrhea and worsening glycemic control. A low estradiol level and an inappropriately low level of follicle-stimulating hormone prompted magnetic resonance imaging of the head, which demonstrated a pituitary adenoma. Subsequent endocrine investigation revealed a high insulin-like growth factor I (IGF-I) level (849 mg/L; normal range, 122 to 400). The concentration of insulin-like growth factor-binding protein-3 (IGFBP-3) was also elevated (5.5 mg/L; normal range, 2.0 to 4.2). GH levels measured during episodes of spontaneous hyperglycemia (>180 mg/dL) were in the range of 3 to 5 ng/mL and failed to suppress to below 2 ng/mL after a bromocriptine suppression test. The patient underwent transsphenoidal resection of a pituitary tumor, which stained positively for GH by immunohistochemistry. Postoperatively, glycemic control improved, with decreased fluctuations of hypoglycemia and hyperglycemia, despite a decrease in insulin requirements.

CONCLUSION

This report highlights the difficulty in interpreting GH and IGF-I levels in patients with type 1 diabetes. In addition, a detailed review of the literature suggests that IGFBP-3 measurements may be helpful in confirming the diagnosis of concurrent acromegaly and distinguishing it from high GH levels attributable to poor control of diabetes.

O Laboratório no Diagnóstico e Seguimento da Acromegalia

Acromegalia é uma síndrome clínica característica, que na maior parte das vezes resulta de um macroadenoma hipofisário produtor de hormônio de crescimento (GH, growth hormone). A hipersecreção tumoral crônica de GH provoca deformidades esqueléticas, distúrbios metabólicos, complicações em vários órgãos e sistemas, e acaba reduzindo a expectativa de vida do paciente. O diagnóstico presuntivo baseia-se nos achados clínicos característicos da doença, com a confirmação vindo através de exames laboratoriais e da avaliação radiológica. Do ponto de vista laboratorial, a abordagem diagnóstica inclui dosagens basais e testes endócrinos que comprovem o excesso de GH, através de dosagens diretas do GH e/ou de fatores circulantes GH-dependentes, cujo melhor exemplo é o fator de crescimento insulina-símile-1 (IGF-1, insulin-like growth factor-1). A adenomectomia transesfenoidal permanece como o tratamento inicial de escolha na acromegalia, mas infelizmente a cura cirúrgica ocorre em menos da metade dos pacientes portadores de macroadenomas. Conseqüentemente, os exames laboratoriais têm um papel muito importante no seguimento dos pacientes após a cirurgia, para definir os critérios de cura e monitorar a atividade da doença durante tratamento complementar com radioterapia ou medicamentos. Neste artigo, revisaremos os exames laboratoriais mais freqüentemente utilizados no diagnóstico da acromegalia e alguns métodos experimentais que vêm sendo testados na sua abordagem. Na parte final, apresentaremos as principais recomendações de dois workshops internacionais realizados nos últimos anos com o objetivo de padronizar a avaliação diagnóstica e a conduta terapêutica na acromegalia.

Medical management of growth hormone-secreting pituitary adenomas

The primary treatment of acromegaly remains transsphenoidal adenomectomy, yet the tissue overgrowth of acromegaly often progresses following surgery, and responds to radiotherapy only after significant delay. Persistently elevated serum growth hormone (GH) and insulin-like growth factor-I (IGF-I) concentrations can be normalized in about half of post-surgery acromegalics using the pharmacologic alternatives presently available, the dopamine agonists (DA) and somatostatin (SST) analogs. Cabergoline, the most efficacious DA, normalizes IGF-I in approximately 37% of patients, whereas the long-acting SST analogs, Octreotide LAR and Lanreotide SR, do so in 66%. Significant tumor shrinkage may be attained with SST analogs in particular, and when necessary, the primary medical treatment of acromegaly may be successfully addressed with this class of drugs. Greatly enhanced efficacy is expected from the GH receptor antagonist pegvisomant, which is nearing market availability and will enable the normalization of serum IGF-I in virtually all patients treated. We review here the pharmacologic treatments of excessive GH secretion.

Measurement of growth hormone, insulin-like growth factor I and their binding proteins: the clinical aspects

BACKGROUND

Growth hormone (GH) secreted from the pituitary stimulates the production of insulin-like growth factor I (IGF-I) from the liver and extrahepatic tissues, which in turn regulates tissue proliferation and differentiation in an endocrine or autocrine/paracrine manner. Both GH and IGF-I circulates as complexes with specific binding proteins. The GH binding protein (GHBP) corresponds to the extracellular, ligand-binding domain of the GH receptors in tissues and its serum concentration may reflect the status of the tissue receptors. Most serum IGF-I associates with IGF binding protein 3 (IGFBP-3) and another protein, the acid labile subunit (ALS). Like IGF-I, serum concentrations of IGFBP-3 and ALS are tightly regulated by GH. GH secretion (both spontaneous and stimulated), IGF-I, IGFBP-3, and ALS have been assessed as potential biochemical markers for diagnosis of GH-related disorders.

CONCLUSIONS

In acromegaly, IGF-I is the most reliable marker. The peak GH response to insulin tolerance test is the diagnostic test of choice, GH deficiency. GHBP has no diagnostic value in acromegaly or GH deficiency. However, it may be a potential biochemical marker for GH insensitivity syndrome as serum GHBP concentrations are undetectable or reduced in >75% of these patients. Other biochemical tests may also prove to be useful in these disorders, but require further validation.

Gender and age in the biochemical assessment of cure of acromegaly

The principal biochemical criteria for cure in acromegaly are normalization of both glucose-suppressed GH levels and IGF-I levels. As we have reported previously, measurement of GH by highly sensitive assay in conjunction with IGF-I levels has led to a re-appraisal of "normal" GH suppression criteria during an OGTT in subjects with acromegaly. In some patients with active acromegaly, glucose-suppressed GH levels as measured by highly sensitive assay are much lower than could previously be appreciated with less sensitive GH assays and some other patients in apparent remission have subtle abnormalities of GH suppression. A question to arise is whether gender differences in glucose-suppressed GH levels as found by others in young healthy subjects should be considered in our interpretation of OGTT criteria for cure in acromegaly. Therefore, we have evaluated parameters of GH secretion in a larger number of subjects from our cohort of postoperative patients with acromegaly and in healthy subjects in order to determine if gender or age associated differences in these parameters exist. Ninety-two subjects with acromegaly (49 men, 43 women) and 46 age-matched healthy subjects (26 men, 20 women) were evaluated with baseline GH and IGF-I levels and nadir GH levels after a 100 g. OGTT. GH was assayed by highly sensitive IRMA (DSL). Basal GH levels were higher in female than in male healthy subjects, but the fall in GH from baseline (% suppression) was also greater in females resulting in no significant difference in mean nadir GH levels in female vs. male healthy subjects (0.09 vs. 0.08 microg/L). In the subjects with acromegaly, there were no significant gender differences in basal, %GH suppression or nadir GH levels. Basal and nadir GH levels correlated significantly only in subjects with active disease (r=0.84, p<.0001). Similarly, IGF-I levels correlated significantly with basal (r=0.573, p=.0012), and nadir (r=.702, p<.0001) GH levels only in subjects with active disease. Gender differences in IGF-I levels were not apparent in any group of subjects. As expected, IGF-I levels declined with age in those groups of subjects with normal IGF-I levels. Nadir GH levels did not vary with age. In conclusion, we have not found significant gender or age-related differences in nadir GH levels and thus our data does not support separate OGTT criteria for cure in men and women with acromegaly.

Clinical implications of pulsatile hormone signals

In all biological systems, the information content of hormonal signals is conveyed by the modalities of pulsatile hormone secretion. New mathematical tools for the analysis of pulsatile behaviour and increasing knowledge of the sources of signal variability have enabled us to recognize altered hormonal pulsatility associated with human disease. Its consequences for our understanding of disease mechanisms, for diagnostic procedures and for therapeutic decisions are discussed at the level of single hormones. Increased disorderliness of hormone secretion is a hallmark of pituitary adenomas, indicating functional subsystem autonomy. The effects on target tissues of changing growth hormone therapy from low-frequency administration to long-acting preparations are still incompletely understood. In contrast, the gonadotropic axis is a paradigm for the successful therapeutic use of induced pulsatility changes, where therapy with long-acting gonadotropin-releasing hormone (GnRH) agonists suppresses endogenous gonadotropin pulses and gonadal function, and pulsatile GnRH administration is used to restore normal gonadal function. Future development of endocrine therapies will depend on our knowledge of hormonal pulsatility.

Growth hormone responses to oral glucose and intravenous thyrotropin-releasing hormone in acromegalic patients treated by slow-release lanreotide

The aim of this study was to assess GH response to oral glucose tolerance test (OGTT) and TRH stimulation test in a group of 10 patients with active post-operative acromegaly before and after long-term slow-release (SR) lanreotide therapy (30 mg im every 10-14 days). Seven patients (2 males, 5 females, 29-71 yr), who during therapy maintained plasma GH and IGF-I concentrations under 5 microg/l and 450 microg/l, respectively, were considered as responders and studied for 24 (1 patient) to 36 months (6 patients). Three patients (1 male, 2 females, 46-61 yr) with levels of GH and IGF-I above those values were studied for 12 months. The OGTT (75 g po) and TRH test (400 microg iv) were repeated before and after 6, 12, 24 and 36 months. The GH response to OGTT was abnormal (nadir: >2 microg/l) at 6 and 12 months in poorly responsive patients. This response was normalized in all responsive patients. Nonetheless, 2 responsive patients showed abnormal GH values after OGTT once each throughout the 36-month study period. The GH response to TRH was characterized by great variability and exhibited unpredictable behavior throughout the study period both in responsive and in poorly responsive patients. Only 2 patients in the responsive group showed persistent normal GH levels (peak: < or =5 microg/l) after TRH for 3 yr. In conclusion, SR lanreotide treatment gave rise to a correct control of GH hypersecretion and to a normalization of GH response to oral glucose in 7 out of 10 patients, although it did not abolish the paradoxical reaction of GH to TRH in all responders. The effect of SR lanreotide on GH response to glucose tolerance test was not paralleled by GH response to TRH.