Hypothesis: Extra-hepatic acromegaly: a new paradigm?

European Journal of Endocrinology (2011) 164 11–16 ISSN 0804-4643

COMMENTARY

Hypothesis: Extra-hepatic acromegaly: a new paradigm?Sebastian J Neggers, John J Kopchick1, Jens O L Jørgensen2 and Aart J van der LelyDepartment of Internal Medicine, Erasmus University MC, PO Box 2040, 3000 CA Rotterdam, The Netherlands, 1Edison Biotechnology Institute,Ohio University, Athens, Ohio 45701, USA and 2Medical Department MEA, Aarhus University Hospital, DK-8000 C Aarhus, Denmark

(Correspondence should be addressed to A J van der Lely; Email: [email protected])

q 2011 European Society of E

Abstract

Medical treatment of acromegaly with long-acting somatostatin analogs (LA-SMSA) and the GHreceptor antagonist, pegvisomant (PEGV), has made it possible to achieve normal serum IGF1concentrations in a majority of patients with acromegaly. These two compounds, however, impact theGH–IGF1 axis differently, which challenges the traditional biochemical assessment of the therapeuticresponse. We postulate that LA-SMSA in certain patients normalizes serum IGF1 levels in the presenceof elevated GH actions in extra-hepatic tissues. This may result in persistent disease activity for whichwe propose the term extra-hepatic acromegaly. PEGV, on the other hand, blocks systemic GH actions,which are not necessarily reliably reflected by serum IGF1 levels, and this treatment causes a furtherelevation of serum GH levels. Medical treatment is therefore difficult to monitor with the traditionalbiomarkers. Moreover, the different modes of actions of LA-SMSA and PEGV make it attractive to usethe two drugs in combination. We believe that it is time to challenge the existing concepts of treatmentand monitoring of patients with acromegaly.

European Journal of Endocrinology 164 11–16

Introduction

Acromegaly is a rare disease, most often caused by aGH-producing tumor of the anterior pituitary (1).Available treatment modalities to date aim at normal-izing serum insulin-like growth factor 1 (IGF1) levelsvia reduction of either GH overproduction or GH actions(2–5). The obvious advantage is that the efficacy ofdifferent treatments can be easily compared by means ofserum IGF1 measurements, as this is more practicalthan frequent GH measurements. This also applies tocomparisons between the effects of long-acting somato-statin therapies (LA-SMSA) and the GH receptor (GHR)antagonist, pegvisomant (PEGV). This approach,however, is based on the assumption that serum IGF1levels adequately and uniformly reflect disease activity.This assumption, however, is not necessarily valid.In this paper, we address the relationship between theGH–IGF1 axis with a specific emphasis on the significantdifferences in the modes of action of LA-SMSA and PEGV.In doing so, we will introduce the novel hypotheticparadigm of hepatic and extra-hepatic acromegaly andits potential clinical implications.

The effects of GH are tissue specific andconcentration dependent

The physiological effects of GH versus IGF1 remaincontroversial. Historically, it has been difficult to isolate

ndocrinology

the individual effects of GH and IGF1 at the tissue levelduring physiological conditions. But the fact that GHpossesses a diabetogenic or ‘anti-insulin’ activity (6),while IGF1 (as the name implies) is similar to insulin inits actions, clearly demonstrates that physiologicaldifferences exist between the actions of the two peptidehormones. Below, we cite results of animal studies thataddress specific effects of GH and physiological effects ofGH versus IGF1.

Animal studies of the actions of GHversus IGF1

Since GH is a diabetogenic molecule, it would not bepredicted to be used as a pharmaceutical to treat type 2diabetes. Yet its lipolytic and anti-lipogenic actions couldhave potential positive outcomes in type 2 diabetic indi-viduals. Two reports have documented beneficial effects ofGH on glucose metabolism in type 2 diabetic patients (7, 8).

A mouse model attempting to determine the effect ofGH on diet-induced type 2 diabetes parameters has beenpresented (9). In this model, male C57BL/6J mice wereplaced on a high-fat diet to induce obesity and type 2diabetes. During the studies, mice were treated withvarious doses of GH. Body weight and composition,fasting blood glucose, insulin and IGF1 levels, glucosetolerance, liver triacylglycerol, tissue weights, and bloodchemistries were determined. Several important findingswere reported (9). First, a GH dose-dependent decrease

DOI: 10.1530/EJE-10-0969

Online version via www.eje-online.org

12 S J Neggers and others EUROPEAN JOURNAL OF ENDOCRINOLOGY (2011) 164

in fat and an increase in lean mass were found. Theseeffects on body composition were seen at the highest twodoses of GH administered, even though only the highestdose of GH resulted in elevated circulating IGF1 levels.These results indicate that certain effects of GH areindependent of circulating IGF1 levels. Second, theincrease in lean mass was observed before the decreasein white adipose tissue (WAT); thus, physiological effectsof GH were not observed at the same time points. Third,GH-induced WAT loss was specific to subcutaneous andmesenteric fat. This result agrees with previouslypublished work in which subcutaneous WAT depotswere found to be increased in mice that lacked GH action(10–12). Thus, these data further support the notionthat ‘not all WAT depots are treated equally’ in terms ofGH action and should be evaluated independently instudies with GH or other treatments.

The finding that GH can affect body compositionindependent of elevations in total serum IGF1 levels isimportant. However, we must point out that theseGH-dependent changes in body composition may be dueto the autocrine/paracrine actions of IGF1 and not thedirect action of GH. The importance of the autocrine orparacrine production of IGF1 has been documented inthe liver-specific IGF1 gene-deficient mouse (13).

Other mouse studies attempting to discriminate theeffect of GH versus IGF1 were carried out nearly 20years ago. These studies showed that animals that havehigh GH and IGF1 levels display glomerulosclerosis;however, glomerulosclerosis is not observed in micewith increased levels of IGF1 alone (14, 15).

A continuation of these studies was carried outemploying transgenic mice that express analogs of GH.For example, when a bovine (b) GH analog containingthe following changes (L121P and E126G) is expressedin the transgenic mice, the resulting animals are ofnormal size with normal levels of IGF1; yet they displaykidney glomerulosclerosis as severe as mice that expresswild-type bGH (16). These data suggest that GH canaffect the kidney independent of increases in IGF1.

Additionally, diabetic kidney disease can be induced inmice using streptozotocin. This kidney pathology wasnot seen in mice that express a GHR antagonist (17, 18)or in mice injected with PEGV (19). Important in thislatter study was the fact that kidney pathology wasprevented by PEGV, even in the absence of a decrease inserum IGF1 (19). Again, this implies that GH has a directeffect on the kidney independent of serum IGF1 levels.

The above data derived from mouse models of GHaction suggest that GH can have temporal and tissue-specific effects independent of elevations of serum IGF1.

The relationship between portal insulinand GH sensitivity of the liver

Human and other mammals are capable of prolongedfasting because they can recruit and utilize lipid stores

www.eje-online.org

when they exhaust readily available carbohydrates(20–22). Prolonged fasting is associated with a gradualdecline in hepatic IGF1 production, which makesteleological sense due to the insulin-like effects ofIGF1. A study by Leung et al. suggests that GH-inducedhepatic IGF1 production is regulated by portal insulinlevels (23). They reported that insulin promotes thetranslocation of the hepatic GHR to the surface.

When portal insulin levels are high, the liver becomesGH sensitive, regardless of the cause of the elevation ininsulin production (23). In addition, portal insulin alsoinhibits hepatic IGFBP1 production, which mayincrease the bioavailability of circulating IGF1 (24, 25).

In conclusion, high portal insulin levels increase liverGH sensitivity (via up-regulation of surface GHRs) and,therefore, ultimately increase liver IGF1 productionwith concomitant increases in serum IGF1 levels. Incontrast, low portal insulin levels reduce the sensitivityof liver for GH and, therefore, reduce serum IGF1 levels.

Why do acromegaly patients haveelevated IGF1 levels

Acromegaly patients have elevated IGF1 levels as aconsequence of GH hypersecretion (1). In addition, theelevated GH levels stimulate lipolysis and induceresistance to the effects of insulin on glucose metabolismin liver and muscle. The net result is a hypermetabolicstate characterized by elevated levels of glucose, freefatty acids, and insulin (26, 27).

The GH-induced hyperinsulinemia, in turn, is likely tofurther stimulate hepatic IGF1 production and to lowerIGFBP1 levels (28, 29). The importance of this effect issupported by the observation that prolonged fasting-induced hypoinsulinemia can completely normalizeserum IGF1 levels in acromegaly patients (30).

In conclusion, acromegaly patients have elevatedserum IGF1 levels because of the pathological hyperse-cretion of GH by the pituitary tumor, which isaggravated by the accompanying hyperinsulinemia.

How somatostatin analogs work

Somatostatin analogs (SMSA) bind to somatostatinreceptors of which subtypes 2 (sst2) and 5 (sst5) are themost important ones for mediating the actions of theavailable LA-SMSAs (31–33). Because of the expression ofsst2 and sst5 on the somatotroph cells, pathological GHsecretion can be inhibited by SA, which translates intoreduced hepatic IGF1 production (31–34). When thisreduction is sufficient to normalize IGF1 levels, thetreatment is traditionally considered adequate (31, 35–37).

However, SMSA also binds to sst2 and sst5 receptorson the pancreatic islet, which will reduce glucagon andinsulin secretion (38, 39). This occasionally results in aworsening of the glycemic control in acromegaly

Somatostatinanalogues (SMSA) (GH)

(a)

(b)

GH actions ,but degree of

is tissue specificUnaltered

GH sensitivityin the periphery

WAT

Bone

WAT

Kidney

Kidney

Bone

Suppressedperipheral GH actions

(IGF1) becomesnormal, but othertissues might be

already GH deficient

Low (pegvisomant)already blocks

peripheral tissues

Residual peripheraldisease activity,

i.e. 'extra-hepatic acromegaly'

(IGF1) becomes normal,but other tissues still encounter

too much GH actions,i.e. 'extra-hepatic acromegaly'

Insulin asdirect effect

of SMSA

Hepatic GH sensitivityvia direct SMSA

effects and becauseof low (insulin)

(GH) , but GH actionsPegvisomant

Only high(pegvisomant) blocks

IGF1 production

GH actions ,but degree of

is tissue specific

GH sensitivityof liver does

not

Only slightin (insulin) as

result oflower GHactions

Figure 1 (a) Effects of somatostatin analogs (SMSA) in SMSA-sensitive acromegalic subjects. Red arrows indicate inhibitoryeffects; green arrows indicate stimulatory effects, while thickness ofarrow indicates level of inhibition. (b) Effects of pegvisomant inacromegalic subjects. Red arrows indicate inhibitory effects; green

Extra-hepatic acromegaly 13EUROPEAN JOURNAL OF ENDOCRINOLOGY (2011) 164

patients during long-term LA-SMSA (40). Moreover, asuppression of insulin secretion by SMSA also selectivelyresults in hepatic GH resistance, which itself decreaseshepatic IGF1 production (23). Therefore, the ensuingreduction in circulating IGF1 does not necessarilyreflect GH activity in peripheral tissues.

A GH-independent suppressive effect of SMSA onserum IGF1 levels has been documented in two studiesin humans (41, 42). Both studies involved adminis-tration of octreotide for 7 days during continued GHtreatment in adult GH deficiency (GHD) patients. Thisresulted in a significant 16–18% reduction in serumIGF1 levels with a concomitant reduction in insulinlevels and elevated levels of IGFBP1 (41, 42).

In the context of acromegaly, it is therefore plausiblethat normalization of serum IGF1 levels duringLA-SMSA not necessarily implies control of diseaseactivity in peripheral tissues, i.e. a condition for whichwe propose the term ‘extra-hepatic acromegaly’(Fig. 1a). This is further supported by a recent reportby Rubeck et al. (43). They compared traditional andnovel biomarkers and health status in patients withacromegaly treated with either surgery alone or SMSA.They reported that despite similar and normalized IGF1levels, SMSA treatment compared with surgery alonewas associated with less suppressed GH levels and lesssymptom relief. They concluded that this discordancemay be due to specific suppression of hepatic IGF1production by SMSA (43).

In the absence of a convenient bioassay for diseaseactivity in acromegaly, it is not easy to validate whetherextra-hepatic acromegaly is a clinical entity rather thana semantic issue, but it is noteworthy that impairedquality of life (QoL) has been reported in LA-SMSApatients despite normal IGF1 levels (44).

arrows indicate stimulatory effects, while thickness of arrowindicates level of inhibition.

How GHR antagonists work

As described above, the GHR antagonist, PEGV,competitively blocks the GHRs in all peripheral tissues(45–47). Thus, the higher the endogenous GH level, themore PEGV is needed to effectively block GH actions (4).PEGV, however, does not block all tissues equallyeffective for the actions of GH. Adipose tissue, thekidneys, and skeletal muscle seem to require less PEGVto reduce GH actions compared to the liver where morePEGV is required in order to reduce IGF1 production(19). In further support of this, it was recently reportedthat short-term PEGV administration in healthy subjectscan suppress lipolysis without affecting either circulat-ing or local IGF1 (48).

It is therefore possible that PEGV treatment inacromegaly is subject to tissue-specific differences in adose-dependent manner. In particular, it is possible thatperipheral suppression of GH activity is obtained prior tonormalization of hepatic IGF1 production. Such acondition during PEGV therapy could be denoted

‘hepatic acromegaly’, which in essence is reciprocal tothe putative conditions during LA-SMSA (Fig. 1b).However, unlike extra-hepatic acromegaly, data inhumans are lacking to suggest that hepatic acromegalyindeed does occur during PEGV monotherapy.

Lessons from diabetes type I and II

The effects of restoring portal insulin levels on serum IGF1have been studied in type I diabetes (49). Only with portalinsulin administration, did IGF1 levels increase to withinthe normal range, which resulted in a decrease in GHlevels. However, diabetic patients on conventional insulintherapy had low IGF1 and elevated GH levels (49).

Wurzburger et al. (50) also studied GH-stimulated IGF1levels in type 1 diabetes. The patients were divided intoC-peptide-negative patients without residual b-cell activityand C-peptide-positive patients with preserved b-cellactivity. A GH-induced increase in serum IGF1 levels wasonly observed in patients with remnantb-cell activity (50).

www.eje-online.org

14 S J Neggers and others EUROPEAN JOURNAL OF ENDOCRINOLOGY (2011) 164

There are similarities between type I diabetes andLA-SMSA-treated acromegalic subjects: both exhibitelevated systemic GH activity together with relativehepatic GH resistance due to low portal insulin levels.The difference is that type I diabetic subjects have lowIGF1 levels, while LA-SMSA-treated acromegalic sub-jects have normal or elevated IGF1 levels. There are alsosimilarities between type 2 diabetes and PEGV-treatedacromegalic subjects: both exhibit low systemic GHactivity in the presence of relatively high hepatic GHsensitivity due to normal or elevated portal insulin levels.

What about combining SMSA and PEGV

Several papers have presented data on combinationtherapy with LA-SMSA and PEGV. To date, the focus inthese reports has been on patients with an insufficientresponse to LA-SMSA (51, 52), but we believe thatcombination treatment may offer benefit to otherpatients. The strongest evidence for this is presented byNeggers et al. (53). They hypothesized that weeklyadministration of 40 mg PEGV could improve QoL andmetabolic parameters in acromegalic patients withnormal age-adjusted IGF1 concentrations duringLA-SMSA treatment. In a double-blind, placebo-con-trolled, crossover study, 20 acromegalic subjectsreceived either PEGV or placebo for two consecutivetreatment periods of 16 weeks, separated by a wash-outperiod of 4 weeks. Efficacy was assessed as a significantchange in disease-specific QoL between baseline and atthe end of each treatment period. QoL was assessed bythe acromegaly QoL questionnaire (AcroQoL) and thepatient-assessed acromegaly symptom questionnaire(PASQ). Interestingly, the AcroQoL and AcroQolimproved significantly after PEGV was added. Theaddition of PEGV also significantly improved the PASQand the single PASQ questions dealing with perspiration,soft tissue swelling, and overall health status. Bycontrast, no significant changes in IGF1 levels wereobserved during the addition of PEGV. As the age-dependent normal range for IGF1 is still relatively wide,it might be possible, however, that some patients mayhave a statistically normal IGF1 level that is in fact toohigh for them. Addition of weekly PEGV might induce ashort-lived decline of IGF1 for 2 days, which does notregister if the blood is drawn 7 days after PEGVadministration, but the clinical effects might bemanifested in QoL questionnaires. Thus, low-dosePEGV treatment improved the signs and symptoms of‘extra-hepatic acromegaly’ without impacting hepaticIGF1 production consistent with our hypothesis of extra-hepatic acromegaly. It is noteworthy that the largestimprovement in QoL was observed in patients who alsoresponded to PEGV with alleviation of fluid retention(53). It remains to be studied whether the samefavourable effects could be obtained by an increase inthe dose of LA-SMSA.

www.eje-online.org

Conclusions and future directions

SMSA have stood the test of time as a safe and effectivetreatment for acromegaly; however, adequate control ofthe disease is not always achieved. With the recentintroduction of PEGV, it is now possible to obtainbiochemical control of the disease in most patients.Thus, now is an appropriate moment for criticalevaluation of the proper assessment of the therapeuticoutcome with these two different treatment modalities.In particular, we postulate that circulating IGF1 is notnecessarily the most reliable biomarker of diseaseactivity. SMSA have at least three tissue-specific effects:i) decreased GH secretion from the pituitary tumor,ii) decreased insulin secretion from the pancreas, andiii) decreased hepatic IGF1 production that may lead toa normalization of serum IGF1 levels despite insufficientcontrol of disease activity in peripheral tissues. Thecombination of these effects may lead to a state ofnormalized serum IGF1 levels and residual peripheraldisease activity, i.e. extra-hepatic acromegaly. Whetherthis is of clinical significance and whether it may beovercome by simply increasing the dose of LA-SMSAmerits are to be addressed in a controlled clinical trial. Itwould be obvious to compare the outcome of LA-SMSAin patients who are randomized to dosing according toeither serum IGF1 levels or GH levels.

The use of PEGV also is challenging since thistreatment is accompanied by a further elevation in GHlevels. Moreover, there is evidence to suggest that PEGVin some cases may induce significant blockade ofperipheral GH actions prior to blockade of the hepaticGHRs. In this context, it is also noteworthy thatthe dose requirements of PEGV are subject to a wideinter-individual variation. Novel biomarkers in additionto IGF1 for this individual variation are needed. It alsoremains to be determined whether assessment of serumPEGV levels would be useful. We believe that patientsusing combination therapy of SMSA and PEGV shouldbe monitored with more specific ways. This mightinclude procollagen II levels or another parameter thatcan integrate GH actions on the ‘extra-hepatic’ tissuessuch as bone.

The fact that LA-SMSA and PEGV exert comp-lementary suppressive effects on the GH–IGF1 axismakes combination therapy with the two modalitiesan interesting option. Indeed, there is evidence tosuggest that combination therapy is superior tomonotherapy with LA-SMSA in terms of glucosehomeostasis (52) and disease-specific QoL (53). Thelatter observation also suggests that assessment of QoLcould be considered as routine practice during medialtherapy. Our hope is that the introduction of thehypothetic paradigm of extra-hepatic acromegaly willchallenge basic scientists, clinicians, and pharma-ceutical industries to design and perform studies thatshow that we are wrong, because if we are not,medical treatment of acromegalic patients might need

Extra-hepatic acromegaly 15EUROPEAN JOURNAL OF ENDOCRINOLOGY (2011) 164

a significant update. Last but not least, we believethere is a need for novel biomarkers (either genomic,metabolomic, proteomic, or others), which ideallyintegrate hepatic as well as peripheral disease activity.

Declaration of interest

The authors declare that there is no conflict of interest that could beperceived as prejudicing the impartiality of the research reported.

Funding

This work did not receive any specific grant from any funding agencyin the public, commercial, or not-for-profit sector.

References

1 Melmed S. Acromegaly pathogenesis and treatment. Journal of ClinicalInvestigation 2009 119 3189–3202. (doi:10.1172/JCI39375)

2 Melmed S, Colao A, Barkan A, Molitch M, Grossman AB,Kleinberg D, Clemmons D, Chanson P, Laws E, Schlechte J,Vance ML, Ho K & Giustina A. Guidelines for acromegalymanagement: an update. Journal of Clinical Endocrinology andMetabolism 2009 94 1509–1517. (doi:10.1210/jc.2008-2421)

3 Trainer PJ, Drake WM, Katznelson L, Freda PU, Herman-Bonert V,van der Lely AJ, Dimaraki EV, Stewart PM, Friend KE, Vance ML,Besser GM, Scarlett JA, Thorner MO, Parkinson C, Klibanski A,Powell JS, Barkan AL, Sheppard MC, Malsonado M, Rose DR,Clemmons DR, Johannsson G, Bengtsson BA, Stavrou S,Kleinberg DL, Cook DM, Phillips LS, Bidlingmaier M,Strasburger CJ, Hackett S, Zib K, Bennett WF & Davis RJ. Treatmentof acromegaly with the growth hormone-receptor antagonistpegvisomant [see comments]. New England Journal of Medicine2000 342 1171–1177. (doi:10.1056/NEJM200004203421604)

4 van der Lely AJ, Hutson RK, Trainer PJ, Besser GM, Barkan AL,Katznelson L, Klibanski A, Herman-Bonert V, Melmed S, Vance ML,Freda PU, Stewart PM, Friend KE, Clemmons DR, Johannsson G,Stavrou S, Cook DM, Phillips LS, Strasburger CJ, Hackett S, Zib KA,Davis RJ, Scarlett JA & Thorner MO. Long-term treatment ofacromegaly with pegvisomant, a growth hormone receptorantagonist. Lancet 2001 358 1754–1759. (doi:10.1016/S0140-6736(01)06844-1)

5 Castinetti F, Nagai M, Morange I, Dufour H, Caron P, Chanson P,Cortet-Rudelli C, Kuhn JM, Conte-Devolx B, Regis J & Brue T. Long-term results of stereotactic radiosurgery in secretory pituitaryadenomas. Journal of Clinical Endocrinology and Metabolism 200994 3400–3407. (doi:10.1210/jc.2008-2772)

6 Rabinowitz D, Merimee TJ, Burgess JA & Riggs L. Growth hormoneand insulin release after arginine: indifference to hyperglycemiaand epinephrine. Journal of Clinical Endocrinology and Metabolism1966 26 1170–1172. (doi:10.1210/jcem-26-10-1170)

7 Nam SY, Kim KR, Cha BS, Song YD, Lim SK, Lee HC & Huh KB.Low-dose growth hormone treatment combined with dietrestriction decreases insulin resistance by reducing visceral fatand increasing muscle mass in obese type 2 diabetic patients.International Journal of Obesity and Related Metabolic Disorders 200125 1101–1107. (doi:10.1038/sj.ijo.0801636)

8 Ahn CW, Kim CS, Nam JH, Kim HJ, Nam JS, Park JS, Kang ES,Cha BS, Lim SK, Kim KR, Lee HC & Huh KB. Effects of growthhormone on insulin resistance and atherosclerotic risk factors inobese type 2 diabetic patients with poor glycaemic control. ClinicalEndocrinology 2006 64 444–449. (doi:10.1111/j.1365-2265.2006.02490.x)

9 List EO, Palmer AJ, Berryman DE, Bower B, Kelder B & Kopchick JJ.Growth hormone improves body composition, fasting bloodglucose, glucose tolerance and liver triacylglycerol in a mousemodel of diet-induced obesity and type 2 diabetes. Diabetologia2009 52 1647–1655. (doi:10.1007/s00125-009-1402-z)

10 Berryman DE, List EO, Palmer AJ, Chung MY, Wright-Piekarski J,Lubbers E, O’Connor P, Okada S & Kopchick JJ. Two-year bodycomposition analyses of long-lived GHR null mice. Journals ofGerontology. Series A, Biological Sciences and Medical Sciences 201065 31–40. (doi:10.1093/gerona/glp175)

11 Berryman DE, List EO, Kohn DT, Coschigano KT, Seeley RJ &Kopchick JJ. Effect of growth hormone on susceptibility to diet-induced obesity. Endocrinology 2006 147 2801–2808. (doi:10.1210/en.2006-0086)

12 Berryman DE, List EO, Coschigano KT, Behar K, Kim JK &Kopchick JJ. Comparing adiposity profiles in three mouse modelswith altered GH signaling. Growth Hormone & IGF Research 200414 309–318. (doi:10.1016/j.ghir.2004.02.005)

13 Yakar S, Liu JL, Stannard B, Butler A, Accili D, Sauer B &LeRoith D. Normal growth and development in the absence ofhepatic insulin-like growth factor I. PNAS 1999 96 7324–7329.(doi:10.1073/pnas.96.13.7324)

14 Yang CW, Striker LJ, Kopchick JJ, Chen WY, Pesce CM, Peten EP &Striker GE. Glomerulosclerosis in mice transgenic for native ormutated bovine growth hormone gene. Kidney International.Supplement 1993 39 S90–S94.

15 Yang CW, Striker GE, Chen WY, Kopchick JJ & Striker LJ.Differential expression of glomerular extracellular matrix andgrowth factor mRNA in rapid and slowly progressive glomerulo-sclerosis: studies in mice transgenic for native or mutated growthhormone. Laboratory Investigation 1997 76 467–476.

16 Yang CW, Striker LJ, Pesce C, Chen WY, Peten EP, Elliot S, Doi T,Kopchick JJ & Striker GE. Glomerulosclerosis and body growth aremediated by different portions of bovine growth hormone. Studiesin transgenic mice. Laboratory Investigation 1993 68 62–70.

17 Chen NY, Chen WY & Kopchick JJ. A growth hormone antagonistprotects mice against streptozotocin induced glomerulosclerosiseven in the presence of elevated levels of glucose and glycatedhemoglobin. Endocrinology 1996 137 5163–5165. (doi:10.1210/en.137.11.5163)

18 Esposito C, Liu ZH, Striker GE, Phillips C, Chen NY, Chen WY,Kopchick JJ & Striker LJ. Inhibition of diabetic nephropathy by aGH antagonist: a molecular analysis. Kidney International 1996 50506–514. (doi:10.1038/ki.1996.342)

19 Flyvbjerg A, Bennett WF, Rasch R, Kopchick JJ & Scarlett JA.Inhibitory effect of a growth hormone receptor antagonist(G120K-PEG) on renal enlargement, glomerular hypertrophy,and urinary albumin excretion in experimental diabetes in mice.Diabetes 1999 48 377–382. (doi:10.2337/diabetes.48.2.377)

20 Moller N, Vendelbo MH, Kampmann U, Christensen B, Madsen M,Norrelund H & Jorgensen JO. Growth hormone and proteinmetabolism. Clinical Nutrition 2009 28 597–603. (doi:10.1016/j.clnu.2009.08.015)

21 Salgin B, Marcovecchio ML, Humphreys SM, Hill N, Chassin LJ,Lunn DJ, Hovorka R & Dunger DB. Effects of prolonged fasting andsustained lipolysis on insulin secretion and insulin sensitivity innormal subjects. American Journal of Physiology. Endocrinologyand Metabolism 2009 296 E454–E461. (doi:10.1152/ajpendo.90613.2008)

22 Boyle PJ, Shah SD & Cryer PE. Insulin, glucagon, andcatecholamines in prevention of hypoglycemia during fasting.American Journal of Physiology 1989 256 E651–E661.

23 Leung KC, Doyle N, Ballesteros M, Waters MJ & Ho KK. Insulinregulation of human hepatic growth hormone receptors:divergent effects on biosynthesis and surface translocation.Journal of Clinical Endocrinology and Metabolism 2000 854712–4720. (doi:10.1210/jc.85.12.4712)

24 Frystyk J, Delhanty PJ, Skjaerbaek C & Baxter RC. Changes in thecirculating IGF system during short-term fasting and refeeding inrats. American Journal of Physiology 1999 277 E245–E252.

25 Ogilvy-Stuart AL, Hands SJ, Adcock CJ, Holly JM, Matthews DR,Mohamed-Ali V, Yudkin JS, Wilkinson AR & Dunger DB. Insulin,insulin-like growth factor I (IGF-I), IGF-binding protein-1, growthhormone, and feeding in the newborn. Journal of ClinicalEndocrinology and Metabolism 1998 83 3550–3557. (doi:10.1210/jc.83.10.3550)

www.eje-online.org

16 S J Neggers and others EUROPEAN JOURNAL OF ENDOCRINOLOGY (2011) 164

26 Moller N & Jorgensen JO. Effects of growth hormone on glucose,lipid, and protein metabolism in human subjects. EndocrineReviews 2009 30 152–177. (doi:10.1210/er.2008-0027)

27 Jorgensen JO, Krag M, Jessen N, Norrelund H, Vestergaard ET,Moller N & Christiansen JS. Growth hormone and glucosehomeostasis. Hormone Research 2004 62 (Supplement 3) 51–55.

28 Jorgensen JO, Moller N, Moller J, Weeke J & Blum WF. Insulin-likegrowth factors (IGF)-I and -II and IGF binding protein-1, -2, and -3 inpatients with acromegaly before and after adenomectomy. Metabolism1994 43 579–583. (doi:10.1016/0026-0495(94)90199-6)

29 Parkinson C, Flyvbjerg A & Trainer PJ. High levels of 150-kDainsulin-like growth factor binding protein three ternary complexin patients with acromegaly and the effect of pegvisomant-inducedserum IGF-I normalization. Growth Hormone & IGF Research 200414 59–65. (doi:10.1016/j.ghir.2003.08.004)

30 Ho PJ, Friberg RD & Barkan AL. Regulation of pulsatile growthhormone secretion by fasting in normal subjects and patients withacromegaly. Journal of Clinical Endocrinology and Metabolism 199275 812–819. (doi:10.1210/jc.75.3.812)

31 Castinetti F, Saveanu A, Morange I & Brue T. Lanreotide for thetreatment of acromegaly. Advances in Therapy 2009 26 600–612.(doi:10.1007/s12325-009-0035-4)

32 Freda PU, Katznelson L, van der Lely AJ, Reyes CM, Zhao SH &Rabinowitz D. Long-acting somatostatin analog therapy ofacromegaly: a meta-analysis. Journal of Clinical Endocrinology andMetabolism 2005 90 4465–4473. (doi:10.1210/jc.2005-0260)

33 Melmed S, Sternberg R, Cook D, Klibanski A, Chanson P, Bonert V,Vance ML, Rhew D, Kleinberg D & Barkan A. A critical analysis ofpituitary tumor shrinkage during primary medical therapy inacromegaly. Journal of Clinical Endocrinology and Metabolism 200590 4405–4410. (doi:10.1210/jc.2004-2466)

34 Lamberts SW, van der Lely AJ, de Herder WW & Hofland LJ.Octreotide. New England Journal of Medicine 1996 334 246–254.(doi:10.1056/NEJM199601253340408)

35 Toledano Y, Rot L, Greenman Y, Orlovsky S, Pauker Y,Olchovsky D, Eliash A, Bardicef O, Makhoul O, Tsvetov G,Gershinsky M, Cohen-Ouaqnine O, Ness-Abramof R, Adnan Z,Ilany J, Guttmann H, Sapir M, Benbassat C & Shimon I. Efficacy oflong-term lanreotide treatment in patients with acromegaly.Pituitary 2009 12 285–293. (doi:10.1007/s11102-009-0172-4)

36 Lombardi G, Minuto F, Tamburrano G, Ambrosio MR, Arnaldi G,Arosio M, Chiarini V, Cozzi R, Grottoli S, Mantero F, Bogazzi F,Terzolo M, Tita P, Boscani PF & Colao A. Efficacy of the newlong-acting formulation of lanreotide (lanreotide Autogel) insomatostatin analogue-naive patients with acromegaly. Journal ofEndocrinological Investigation 2009 32 202–209.

37 Giustina A, Bonadonna S, Bugari G, Colao A, Cozzi R, Cannavo S,de Marinis L, Degli Uberti E, Bogazzi F, Mazziotti G, Minuto F,Montini M & Ghigo E. High-dose intramuscular octreotide inpatients with acromegaly inadequately controlled on conventionalsomatostatin analogue therapy: a randomised controlled trial.European Journal of Endocrinology 2009 161 331–338. (doi:10.1530/EJE-09-0372)

38 Presti ME, Burton FR, Niehoff ML, Rioux J & Garvin PJ. Effect ofoctreotide on stimulated insulin release from pancreatic tissueslices. Pancreas 1998 16 141–147. (doi:10.1097/00006676-199803000-00006)

39 Krentz AJ, Boyle PJ, Macdonald LM & Schade DS. Octreotide: along-acting inhibitor of endogenous hormone secretion for humanmetabolic investigations. Metabolism 1994 43 24–31. (doi:10.1016/0026-0495(94)90153-8)

40 Koop BL, Harris AG & Ezzat S. Effect of octreotide on glucosetolerance in acromegaly. European Journal of Endocrinology 1994130 581–586. (doi:10.1530/eje.0.1300581)

41 Laursen T, Moller J, Fisker S, Jorgensen JO & Christiansen JS.Effects of a 7-day continuous infusion of octreotide on circu-lating levels of growth factors and binding proteins in growth

www.eje-online.org

hormone (GH)-treated GH-deficient patients. Growth Hormoneand IGF Research 1999 9 451–457. (doi:10.1054/ghir.1999.0131)

42 Pokrajac A, Frystyk J, Flyvbjerg A & Trainer PJ. Pituitary-independent effect of octreotide on IGF1 generation. EuropeanJournal of Endocrinology 2009 160 543–548. (doi:10.1530/EJE-08-0822)

43 Rubeck KZ, Madsen M, Andreasen CM, Fisker S, Frystyk J &Jorgensen JO. Conventional and novel biomarkers of treatmentoutcome in patients with acromegaly: discordant results aftersomatostatin analog treatment compared with surgery. EuropeanJournal of Endocrinology 2010 163 717–726. (doi:10.1530/EJE-10-0640)

44 Bonapart IE, van DR, Ten Have SM, de Herder WW, Erdman RA,Janssen JA & van der Lely AJ. The ‘bio-assay’ quality of life mightbe a better marker of disease activity in acromegalic patients thanserum total IGF-I concentrations. European Journal of Endocrinology2005 152 217–224. (doi:10.1530/eje.1.01838)

45 Dattani MT, Hindmarsh PC, Brook CG, Robinson IC, Kopchick JJ &Marshall NJ. G120R, a human growth hormone antagonist,shows zinc-dependent agonist and antagonist activity on Nb2cells. Journal of Biological Chemistry 1995 270 9222–9226.(doi:10.1074/jbc.270.16.9222)

46 Chen XZ, Shafer AW, Yun JS, Li YS, Wagner TE & Kopchick JJ.Conversion of bovine growth hormone cysteine residues to serineaffects secretion by cultured cells and growth rates in transgenicmice. Molecular Endocrinology 1992 6 598–606. (doi:10.1210/me.6.4.598)

47 Chen WY, Wight DC, Mehta BV, Wagner TE & Kopchick JJ. Glycine119 of bovine growth hormone is critical for growth-promotingactivity. Molecular Endocrinology 1991 5 1845–1852. (doi:10.1210/mend-5-12-1845)

48 Moller L, Norrelund H, Jessen N, Flyvbjerg A, Pedersen SB,Gaylinn BD, Liu J, Thorner MO, Moller N & Lunde Jorgensen JO.Impact of growth hormone receptor blockade on substratemetabolism during fasting in healthy subjects. Journal of ClinicalEndocrinology and Metabolism 2009 94 4524–4532. (doi:10.1210/jc.2009-0381)

49 Shishko PI, Dreval AV, Abugova IA, Zajarny IU & Goncharov VC.Insulin-like growth factors and binding proteins in patients withrecent-onset type 1 (insulin-dependent) diabetes mellitus: influ-ence of diabetes control and intraportal insulin infusion. DiabetesResearch and Clinical Practice 1994 25 1–12. (doi:10.1016/0168-8227(94)90155-4)

50 Wurzburger MI, Prelevic GM, Sonksen PH, Wheeler M & Balint-Peric L. Effect of recombinant human growth hormone treatmenton insulin-like growth factor (IGF-I) levels in insulin-dependentdiabetic patients. Acta Diabetologica 1995 32 131–134. (doi:10.1007/BF00569572)

51 Feenstra J, de Herder WW, Ten Have SM, van den Beld AW,Feelders RA, Janssen JA & van der Lely AJ. Combined therapy withsomatostatin analogues and weekly pegvisomant in active acrome-galy (Erratum in: Lancet. 2005 May;365(9471):1620). Lancet2005365 1644–1646. (doi:10.1016/S0140-6736(05)63011-5)

52 Jorgensen JO, Feldt-Rasmussen U, Frystyk J, Chen JW,Kristensen LO, Hagen C & Orskov H. Cotreatment of acromegalywith a somatostatin analog and a growth hormone receptorantagonist. Journal of Clinical Endocrinology and Metabolism 200590 5627–5631. (doi:10.1210/jc.2005-0531)

53 Neggers SJ, van Aken MO, de Herder WW, Feelders RA, Janssen JA,Badia X, Webb SM & van der Lely AJ. Quality of life in acromegalicpatients during long-term somatostatin analog treatment withand without pegvisomant. Journal of Clinical Endocrinology andMetabolism 2008 93 3853–3859. (doi:10.1210/jc.2008-0669)

Received 27 October 2010

Accepted 2 November 2010