The insulin-like growth factors and their binding proteins in a case of non-islet-cell tumour-associated hypoglycaemia

Glycosylation Analysis of Urinary Peptidome Highlights IGF2 Glycopeptides in Association with CKD

Chronic kidney disease (CKD) is prevalent in 10% of world’s adult population. The role of protein glycosylation in causal mechanisms of CKD progression is largely unknown. The aim of this study was to identify urinary O-linked glycopeptides in association to CKD for better characterization of CKD molecular manifestations. Urine samples from eight CKD and two healthy subjects were analyzed by CE-MS/MS and glycopeptides were identified by a specific software followed by manual inspection of the spectra. Distribution of the identified glycopeptides and their correlation with Age, eGFR and Albuminuria were evaluated in 3810 existing datasets. In total, 17 O-linked glycopeptides from 7 different proteins were identified, derived primarily from Insulin-like growth factor-II (IGF2). Glycosylation occurred at the surface exposed IGF2 Threonine 96 position. Three glycopeptides (DVStPPTVLPDNFPRYPVGKF, DVStPPTVLPDNFPRYPVG and DVStPPTVLPDNFPRYP) exhibited positive correlation with Age. The IGF2 glycopeptide (tPPTVLPDNFPRYP) showed a strong negative association with eGFR. These results suggest that with aging and deteriorating kidney function, alterations in IGF2 proteoforms take place, which may reflect changes in mature IGF2 protein. Further experiments corroborated this hypothesis as IGF2 increased plasma levels were observed in CKD patients. Protease predictions, considering also available transcriptomics data, suggest activation of cathepsin S with CKD, meriting further investigation.

Non-islet cell tumor hypoglycemia concurrent with acromegalic features: A case report and literature review

Background

Non-islet cell tumor hypoglycemia (NICTH) is a rare cause of hypoglycemia due to the overproduction of high molecular weight insulin-like growth factor (big-IGF2), which activates the insulin receptor and subsequently caused hypoglycemia. But NICTH with acromegaly had rarely been reported. We firstly reported a rare case of NICTH concurrent with acromegalic facial features induced by a retroperitoneal hemangiopericytoma and reviewed similar cases in the literature.

Case presentation

A 30-year old man was admitted to hospital because of recurrent unconscious, which usually occurred in the late afternoon or early morning before supper or breakfast. On one unconscious occasion, his blood glucose was 2.4 mmol/L. His consciousness recovered rapidly with intravenous 50% glucose administration. Physical examination showed that he had coarse oily facial features with acne, prominent forehead and brow, broad nose, prominent nasolabial folds. At the time of hypoglycemia, suppressed serum insulin, GH and IGF-1 levels was found. Computed Tomography further revealed a large left retroperitoneal mass measuring 7.0 cm × 12.3 cm × 13.0 cm. He underwent complete surgical resection of the mass. Surgical pathology demonstrated a hemangiopericytoma and strong positive for IGF-2. He did not experience further episodes of hypoglycemia after the operation during the 2.5 years follow-up.

Conclusions

Fibrous origin is the most common tumor type for NICTH with acromegaly features. NICTH should be considered in non-diabetic patients who have recurrent hypoglycemia along with suppressed serum insulin and IGF-1 levels.

The Neglected Insulin: IGF-II, a Metabolic Regulator with Implications for Diabetes, Obesity, and Cancer

When originally discovered, one of the initial observations was that, when all of the insulin peptide was depleted from serum, the vast majority of the insulin activity remained and this was due to a single additional peptide, IGF-II. The IGF-II gene is adjacent to the insulin gene, which is a result of gene duplication, but has evolved to be considerably more complicated. It was one of the first genes recognised to be imprinted and expressed in a parent-of-origin specific manner. The gene codes for IGF-II mRNA, but, in addition, also codes for antisense RNA, long non-coding RNA, and several micro RNA. Recent evidence suggests that each of these have important independent roles in metabolic regulation. It has also become clear that an alternatively spliced form of the insulin receptor may be the principle IGF-II receptor. These recent discoveries have important implications for metabolic disorders and also for cancer, for which there is renewed acknowledgement of the importance of metabolic reprogramming.

Solitary fibrous tumor of the ischioanal fossa-a multidisciplinary approach to management with radiologic-pathologic correlation

Solitary fibrous tumors are primary mesenchymal tumors, which may occur in any part of the body. Overall, these tumors are considered to have intermediate malignant potential with 5- and 10-year metastasis-free and overall disease-specific survival rates of 74% and 55%, and 89% and 73%, respectively (Demicco et al, 2012). Herein we present an unusual case of solitary fibrous tumors involving the ischioanal fossa in a 19-year-old woman with radiologic-pathologic correlation. This case was complicated by extensive tumor vascularity and was thus managed with preoperative embolization followed by en bloc surgical resection.

Management of non-islet-cell tumor hypoglycemia: a clinical review

CONTEXT

Non-islet cell tumor hypoglycemia (NICTH) is a rare but serious paraneoplastic syndrome in which a tumor secretes high molecular weight IGF-II, causing hypoglycemia. Complete tumor resection is curative but is often delayed or unfeasible. There is no clear "standard of care" for managing these patients.

EVIDENCE ACQUISITION

PubMed searches were conducted for: "non-islet-cell tumor hypoglycemia," "NICTH," "Doege-Potter," "Doege-Potter syndrome," "high molecular weight IGF-II," and "big IGF-II." Relevant articles were reviewed in detail. We limited our review to English-language articles, focusing on 1988-2013 (corresponding with the elucidation of the pathophysiology of NICTH).

EVIDENCE SYNTHESIS

The available literature exists as case reports or small case series, with a void of higher-order treatment studies. Thus, an evidence-based approach to data synthesis was difficult. Nevertheless, the available literature is presented objectively with an attempt to describe clinically useful trends and findings in the management of NICTH.

CONCLUSIONS

Appropriate identification of NICTH and prompt and complete tumor resection represents ideal management. However, when prompt resection is not feasible, iv glucose or dextrose often does not suffice to prevent hypoglycemia. In such cases, we suggest consideration of local antitumor therapies for disease control and trial of glucocorticoids alone or in combination with GH. Continuous glucagon infusion can be successful if the patient has a positive response to a glucagon stimulation test, and parenteral nutrition may allow higher glucose delivery, but both are limited by the need for continuous iv infusion. Diazoxide and octreotide have no role in NICTH.

Rectal hemangiopericytoma in a 37-year-old woman: a case report and review of the literature

Introduction

Hemangiopericytoma is an uncommon perivascular tumor. Rectal Hemangiopericytomas are extremely rare. To the best of our knowledge, only two cases have been reported in the literature.

Case presentation

We report the case of a 37-year-old Asian woman with an Hemangiopericytoma rising from the anterior wall of her rectum. Abdominopelvic computed tomography showed a 7.4 cm solid mass between her uterus and her rectum. Heterogeneous gradual enhancement after intravenous injection of contrast material was noted with several tortuous vessels around her tumor. Intra-operative findings indicated a capsule and well-circumscribed solid tumor connecting with the anterior wall of her rectum by a small pedicle. With immunohistochemical stains, her tumor cells reacted positive for Bcl-2, CD34, and ki67 and negative for CD10, CD117, S100, and Desmin. Follow-up computed tomography scans have shown no tumor recurrence or metastasis signs.

Conclusions

Rectal Hemangiopericytoma is a rare tumor with non-specific imaging findings. Hemangiopericytomas should be included in the differential list when a massive tumor with heterogeneously gradual enhancement in the regions of the rectum is encountered.

The role of insulin-like growth factor system in soft tissue sarcomas: from physiopathology to targeted therapeutic approaches

Purpose/Results. Although surgical, chemo- and radiotherapeutic treatment regimens in patients with soft tissue sarcomas have constantly been refined over the past two decades, the survival rate for these patients is rather low.

Discussion. There is a great need to investigate the mechanisms for oncogenesis and to identify the factors involved in malignant transformation in sarcomas. Among these factors, IGFs are thought to play a pivotal role as progression factors in various types of sarcomas. The dysregulation of the IGF-II synthesis, e.g. by loss of imprinting which occurs in most types of sarcomas, is a permissive effect through the suppression of cell death. In addition, cells that overexpress the type I IGF receptors are more susceptible to transformation by oncogenes. As TP53 suppresses the activity of IGF-II P3 and P4, as well as the type I IGF receptor promoter, mutations of TP53 in sarcomas may alternatively lead to the activation of these factors. Finally, the phenomenon of non-islet cell tumour hypoglycaemia that occurs in patients with sarcomas, and which is related to the secretion of IGF-II prohormones, is discussed. Future therapeutic strategies may be based upon the application of antibodies or antisense oligonucleotides directed against the type I IGF receptors, with the common goal of inducing apoptosis in sarcoma cells. Ultimately, these and other therapeutic approaches may lead to a better outcome in patients suffering from sarcoma.

How growth hormone may be linked to cancer: concerns and perspective

Recent evidence from epidemiology indicates that inter-individual variations in the growth hormone (GH)/IGF-I pathway affect the risk of individuals developing common epithelial cancers. This is supported by associations between normal common variants within genes from the pathway and these cancers, which excludes many potential confounding issues, such as reverse causality. This raises concern for the increasing numbers of patients treated with GH; although replacement therapy for GH-deficiency should aim to restore normality, which should then only incur a normal risk. The links with cancer also offers promising new opportunities. Clinical trials treating cancer patients with pharmaceuticals targeting the IGF-I receptor are well advanced with promising initial findings. In the future, there has to be much more emphasis within oncology on prevention and the GH/IGF-I pathway is one of few identified risk factors that are modifiable, not just by pharmaceutical, but also nutritional, interventions that may, in the long term, be more appropriate. Assessing the status of the GH/IGF-I pathway in individuals may also provide a means for targeting screening programs and preventative measures.

A rapid method for analyzing serum pro-insulin-like growth factor-II in patients with non-islet cell tumor hypoglycemia

CONTEXT

Non-islet cell tumor hypoglycemia (NICTH) results from the hypersecretion of pro-IGF-II by a large, usually mesenchymal tumor. Detection of pro-IGF-II in serum is a potential tumor marker in these patients.

OBJECTIVE

The aim of this study was to validate a rapid and reliable method for determining serum pro-IGF-II.

PATIENTS

Serum samples from 16 patients with NICTH were studied.

MAIN OUTCOME MEASURE

The main outcome measure was serum concentration of pro-IGF-II determined by immunoblot analysis of pro-IGF-II and mature IGF-II after 16.5% tricine-SDS-PAGE, which was compared with pro-IGF-II measured by standard RIA after size-exclusion acid chromatography.

RESULTS

The analyses of patients' sera by size-exclusion acid chromatography showed that 68 +/- 19% of IGF-II were present in the pro-IGF-II form, whereas only 18 +/- 4% corresponded to pro-IGF-II in controls. Scanning densitometry of immunoblots showed 67 +/- 16% in the bands corresponding to pro-IGF-II in patients' sera, compared with 27 +/- 9% in controls. The detection sensitivity of tricine-SDS-PAGE method was the same as for size-exclusion chromatography, but the tricine-SDS-PAGE method is quicker and requires smaller amounts of serum.

CONCLUSION

Tricine-SDS-PAGE followed by IGF-II immunoblot analysis provides a rapid, reproducible, and sensitive method for the separation of serum pro-IGF-II from mature IGF-II and is a useful laboratory evaluation of patients with a clinical diagnosis of NICTH.

Plasma levels of insulin-like growth factor binding protein-4 (IGFBP-4) under normal and pathological conditions

OBJECTIVE

Insulin-like growth factor binding protein-4 (IGFBP-4) belongs to a family of six structurally related IGF-binding proteins that are involved in the modulation of the biological effects of the IGFs. In order to obtain more insight into the clinical significance and regulation of IGFBP-4 in vivo we determined the levels of this protein by a specific radioimmunoassay in the human circulation under normal and various pathological conditions.

DESIGN AND PATIENTS

Selected human biological fluids and plasma samples from 804 normal healthy males and females, ranging from 0 to 78 years of age, were analysed. In addition, plasma samples from patients with several disorders (i.e. hypothyroidism, hyperthyroidism, GH-deficiency, acromegaly, cancer, chronic renal failure corticosteroid-treatment) were investigated.

MEASUREMENTS

A specific RIA for hIGFBP-4 was developed, using a rabbit polyclonal antibody raised against a synthetic peptide containing amino acids 80-103 of the mature hIGFBP-4 sequence.

RESULTS

In normal individuals circulating IGFBP-4 levels in males did not change with age. For females the values tended to increase slightly in older age. Overall, the mean +/- SD for males and females (189 +/- 83 microg/l and 193 +/- 72 microg/l, respectively) were not different. Normative range values of IGFBP-4 correlated weakly with those of IGF-II (r = 0.31, P < 0.001). Neither hypothyroidism nor hyperthyroidism appeared to influence circulating IGFBP-4 levels since the levels were within the normal range. Both GH status and pharmacological doses of glucocorticoids, as employed in various chronic diseases, did not seriously affect plasma IGFBP-4 either. Under conditions with increased circulating PTH levels, i.e. dialysed adult patients with chronic renal failure (CRF) and subjects with hyperparathyroidism, a weak positive relationship was noted between the plasma contents of IGFBP-4 and PTH. An excess of IGFBP-4 was found in plasma of both nondialysed and dialysed prepubertal growth retarded children with chronic renal failure (CRF) (mean SDS: 10.75 and 5.78, respectively). IGFBP-4 levels were inversely related to glomerular filtration rate. Similar results were obtained for dialysed adults with CRF. In a group of CRF children who had undergone renal transplantation, circulating IGFBP-4 levels were markedly lower (mean SDS: 3.75). There was no evidence for an increased secretion of IGFBP-4 in the circulation of most of the cancer patients with solid tumours. Several children with acute lymphoblastic leukaemia, however, showed elevated plasma IGFBP-4 levels (mean SDS: 1.27). The presence of IGFBP-4 could also be demonstrated in other human biological fluids. The highest amounts were found in amniotic fluid (391-717 microg/l) and follicular fluid (249-500 microg/l).

CONCLUSIONS

Measurement of plasma IGFBP-4 has been shown so far to be of minor clinical relevance. However, the results indicate that different concentration gradients between plasma and various other body fluids may exist. Therefore, it may well be that certain pathophysiological stimuli induce significant alterations in the local turnover rate of IGFBP-4 but that they are not reflected by changes in the circulating levels. The possibility of quantifying IGFBP-4 by RIA will facilitate further in vitro and in vivo studies on its regulation and function in humans.

Liver transplantation for metastatic hemangiopericytoma associated with hypoglycemia

We report a case of successful liver transplantation in a young man with metastatic hemangiopericytoma confined to the liver. He had a primary retroperitoneal hemangiopericytoma removed in 1982 and was diagnosed as having liver metastases 8 years later. Subsequently, he developed hypoglycemia, which did not respond to chemotherapy. Hepatectomy and transplantation resolved his hypoglycemic attacks. He remained well and symptom free for 4 years. Liver transplantation can provide effective palliation and should be considered in carefully selected patients with localized metastatic cancer.

Gene expression and serum levels of insulin-like growth factors (IGFs) and IGF-binding proteins in a case of non-islet cell tumour hypoglycaemia

We describe a case of non-islet cell tumour hypoglycaemia (NICTH) associated with a renal cell carcinoma. Serum insulin-like growth factors (IGFs) (including IGF-II E peptide), IGF-binding proteins (IGFBPs), insulin and C-peptide were measured before and after surgical removal of the tumour. IGFBPs were visualized by Western ligand blotting. Preoperatively 'big' IGF-II and IGFBP-2 levels were raised. IGF-I, IGFBP-1 and IGFBP-3 were low, while insulin, C-peptide and GH were undetectable. These changes were reversed by 2 days postoperatively. Protease assays showed little IGFBP-3 protease activity preoperatively. Preoperatively, neutral chromatography demonstrated most of the immunoassayable IGFBP-3 in a high molecular weight form with a small amount of IGF-II. Most of the IGF-II and big IGF-II eluted in lower molecular weight forms. Postoperative samples showed a shift in IGF-II which became increasingly associated with IGFBP-3 in both low and high molecular weight complexes. By Northern blotting, expression of all species of IGF-II mRNA in the tumour was 10-fold greater than in normal human liver. The tumour did not express IGFBP-1 or IGFBP-2. IGFBP-3 was expressed in small amounts, while the expression of IGFBP-4 was two-fold higher than in liver. In conclusion, we have confirmed high levels of big IGF-II and IGFBP-2 in NICTH, changes which are reversed postoperatively. The IGF-II is derived from the tumour which overexpresses these genes but IGFBP-2 probably arises from extratumour upregulation.

Case report: Insulin-like growth factor II expression in hepatocellular carcinoma with alcoholic liver fibrosis accompanied by hypoglycaemia

This case of hepatocellular carcinoma (HCC) with alcoholic liver fibrosis, which was not associated with hepatitis viruses, was accompanied by hypoglycaemia. The immunoreactive insulin level was low and other hormonal examinations were almost normal. Immunohistochemical studies showed a high level of insulin-like growth factor II (IGF2) peptide in the HCC section and the size heterogeneity of serum IGF2 investigated by western blot revealed a large form at approximately 15 kDa. These results suggest that the HCC with alcoholic liver fibrosis produced IGF2 and that the hypoglycaemia was caused by tumour-associated IGF2.

Insulin-like growth factor II expression in primary meningeal hemangiopericytoma and its metastasis to the liver accompanied by hypoglycemia

In situ hybridization and immunohistochemistry were performed to detect insulin-like growth factor II (IGF2) in tissue sections obtained from a patient with hypoglycemia in association with primary meningeal hemangiopericytoma and metastatic foci in the liver. High levels of IGF2 mRNA and IGF2 peptide were detected in both primary and metastatic tumor cells, although the serum IGF2 level was within the normal range. Because the serum level of IGF binding protein-3 was low, whereas the serum insulin level and other endocrinological examinations were normal, we speculate that the mechanism of the hypoglycemia was associated with the tumor-produced IGF2.

Expression of a high molecular weight form of insulin-like growth factor II in a Beckwith-Wiedemann syndrome associated adrenocortical adenoma

Beckwith-Wiedemann syndrome is a rare condition (1/13,700 live births) occurring in both inherited and sporadic forms in the population. It is manifest as a fetal overgrowth syndrome, in which hypertrophy dominates the clinical picture. An additional complication is that these children are predisposed to a specific subset of childhood neoplasms, amongst which are Wilms' tumour and adrenocortical carcinoma. We report here the synthesis by an associated adrenal tumour of large quantities of a high molecular weight form of insulin-like growth factor II (IGF-II), associated with profound suppression of circulating IGFs in the patient's serum. As with other tumours of this type, the tumours showed loss of material on chromosome 11p.

Abnormal serum IGF-II transport in non-islet cell tumor hypoglycemia results from abnormalities of both IGF binding protein-3 and acid labile subunit and leads to elevation of serum free IGF-II

The syndrome of non-islet cell tumor hypoglycemia (NICTH) is the result of hypersecretion of IGF-II by a tumor although serum IGF-II is seldom elevated. This is attributable to abnormalities of the IGF binding proteins (IGFBPs) present in NICTH which is characterized by a marked decrease in the fraction of IGFBP-3 present in the 150 kD complex with acid labile subunit (ALS) and a 2- to 4-fold increase in IGFBP-2. We studied the impact of these changes in IGFBPs on the concentration of free IGF-II using a neutral C-18 Sep-Pak extraction procedure. We found that free IGF-II was increased 8- to 20-fold in NICTH. Thus there is no limitation of free IGF-II for complex formation. Additional experiments were conducted to determfine whether ALS deficiency limits 150 kD complex formation. We observed that addition of purified ALS to NICTH sera only partially succeeded in converting smaller complexes containing IGFBP-3 to large 150 kD complexes. We conclude that both a functional deficiency of ALS and IGFBP-3 are present in NICTH sera. The increased free IGF-II in NICTH sera contributes greatly to bioactivity and largely explains the marked hypoglycemia of NICTH patients even when total serum IGF-II concentrations may remain within normal limits.

Recurrent hemangiopericytoma of the liver: report of a case

We present herein the case of a 63-year-old man with a locally recurrent hemangiopericytoma in the hepatic hilum. The patient presented to our hospital for the investigation of elevated transaminases 6 years after undergoing resection of a hemangiopericytoma followed by chemotherapy at another hospital. Various imaging techniques demonstrated a well-circumscribed, hypervascular tumor with central necrosis in the hepatic hilum. Establishing a preoperative diagnosis would have been difficult without the information that he had previously had a hemangiopericytoma of the abdominal cavity. An extended right hepatic lobectomy was performed and histopathological examination confirmed the diagnosis of recurrent hemangiopericytoma. Although hemangiopericytoma is a rare tumor, the clinical presentation and radiologic features of this case were fairly typical.

A case of hepatoma associated with hypoglycaemia and overproduction of IGF-II (E-21): beneficial effects of treatment with growth hormone and intrahepatic adriamycin

We describe a case of recurrent hypoglycaemia associated with a hepatoma. During hypoglycaemia serum insulin was undetectable. Plasma insulin-like growth factor II (IGF-II) was not elevated although 71% of plasma IGF-II was present as big IGF-II (molecular weight 11 kDa) which probably represents a non-glycated form of pro-IGF-II. The GH response to hypoglycaemia was impaired and plasma levels of both IGF-I and the GH-dependent IGF binding protein (IGFBP-3) were low. A recently described unextracted assay directed against the first 21 amino acids of the E-domain (E-21) of proinsulin-like growth factor-II (pro-IGF-II) allows direct plasma estimation (plasma E-21) of larger molecular forms of IGF-II without interference from normal IGF-II and IGF binding proteins. Basal values were grossly elevated (23.7 and 23.8 nmol/l). Treatment with GH led to an increase in the mean plasma glucose across 24 hours (4.25 +/- 0.21 mol/l (mean +/- SEM) before treatment, compared with 4.86 mmol/l +/- 0.17 following GH (P < 0.01)) and a reduction in hypoglycaemic attacks. The treatment was associated with a rise in IGFBP-3 and small increases in insulin like growth factors. Subsequent treatment with the somatostatin analogue octreotide did not produce a significant change in plasma glucose levels or insulin-like growth factors. Two courses of intrahepatic adriamycin restored elevated levels of E-21 to normal. Total IGF-II remained normal and IGF-I increased. GH treatment was successfully withdrawn with no effect on plasma glucose or growth factor levels. The patient remained free from hypoglycaemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in serum levels of insulin-like growth factors and insulin-like growth-factor-binding proteins in patients with colorectal cancer

It has been reported that insulin-like growth factor (IGF) II is associated with human primary colorectal tumors and colon-carcinoma cell lines. Here, we examine alterations in circulating levels of IGFs and IGF binding proteins (IGFBPs) in patients with colorectal carcinoma, and compare them to age- and nutrition-adjusted references. We report (i) an increase in serum IGF-II concentrations (about 2-fold), whereas IGF-I concentrations are regarded as normal when aging is taken into account; (ii) an apparent increase in serum IGFBP-3 levels when compared to those of healthy elderly subjects, IGFBP-3 only being detected in the 150-kDa IGFBP ternary complex as in normal serum; (iii) abnormally elevated serum IGFBP-2 levels taking into account the apparent concentrations of IGFBP-3. This simultaneous elevation of IGFBP-3 and IGFBP-2 in the serum of patients with colorectal tumors appears to be unique in that it reflects a break in the inverse relationship between the serum IGFBP-3 and IGFBP-2 levels that is observed in normal and in several physiopathological conditions. Moreover, it enables a distinction to be made between 76.5% (13/17) of patients with colorectal carcinoma and normal adults, age-related healthy aged and malnourished patients. We propose that the disturbed serum IGFBP profile observed in the patients with colorectal cancer may be a consequence of oversecretion of IGF-II by the tumor cells. The usefulness of IGFs and IGFBPs as potential colorectal tumor-associated metabolic markers should be further investigated.

Role of the insulin-like growth factors in the endocrine control of glucose homeostasis

There is a growing body of evidence that the insulin-like growth factors (IGF-I and IGF-II) are dynamically involved in the regulation of glucose homeostasis, with one of their binding proteins, IGFBP-1, playing a counterregulatory role. The IGFs are structurally and functionally related to insulin and in the circulation they represent a huge hypoglycemic potential which is buffered by their association with the IGFBPs. The predominant IGFBP in serum, IGFBP-3, is able to form a high molecular weight complex with the IGFs and this complex is retained in the circulation and appears to act as a reservoir of IGFs. The IGFs and IGFBP-3 are regulated in the long term by changes in nutritional status. In contrast, IGFBP-1 is acutely regulated in a manner similar to glucose counterregulatory hormones. IGFBP-1 is able to block the insulin-like actions of the circulating IGFs and when administered alone as a bolus infusion causes an increase in blood glucose levels. There is recent evidence that more IGFs are available for an endocrine glucoregulatory role than indicated by estimates of steady-state 'free' IGF levels. The IGF/IGFBP system may thus play a complementary role to insulin and the classical counterregulatory hormones in the control of blood glucose.

Serum "big insulin-like growth factor II" from patients with tumor hypoglycemia lacks normal E-domain O-linked glycosylation, a possible determinant of normal propeptide processing

The insulin-like growth factor II (IGF-II) gene is overexpressed in many mesenchymal tumors and can lead to non-islet-cell tumor hypoglycemia (NICTH). ProIGF-II consists of the 67 aa of IGF-II with a carboxyl 89-aa extension, the E domain. A derivative of proIGF-II containing only the first 21 aa of the E domain [proIGF-II-(E1-21)] has been isolated by others from normal serum and has O-linked glycosylation. We found that the "big IGF-II" of normal serum, as detected by an RIA directed against residues 1-21 of the E domain of proIGF-II, was reduced in size by treatment with neuraminidase and O-glycosidase. The big IGF-II, which is greatly increased in NICTH sera, was unaffected by neuraminidase and O-glycosidase treatment. We have also shown that big IGF-II from normal serum is retained by jacalin lectin columns and that big IGF-II from NICTH serum was not retained, indicating that it lacked O-glycosylation. Normal O-linked glycosylation may be required for proper peptidase processing of proIGF-II. The lack of normal O-linked glycosylation by tumors may explain the predominance of big IGF-II in NICTH sera. In normal serum, most of the IGF-II is present in a 150-kDa ternary complex with IGF-II binding protein (IGFBP) 3 and alpha subunit. In NICTH serum, however, the complexes carrying big IGF-II are < 50 kDa. We investigated whether big IGF-II of NICTH was responsible for this abnormality. Tumor big IGF-II and IGF-II were equally effective in forming the 150-kDa complex with purified IGFBP-3 and 125I-labeled alpha subunit. Both 125I-labeled IGF-II and 125I-labeled proIGF-II-(E1-21), when incubated with normal serum, formed the 150-kDa complex as detected by Superose 12 exclusion chromatography. We conclude that the nonglycosylated big IGF-II of NICTH serum can form normal complexes with serum IGFBPs. The defective binding in NICTH is attributable to defective IGFBP-3 binding.

Alleviation of non-islet cell tumour hypoglycaemia by growth hormone therapy is associated with changes in IGF binding protein-3

The hypoglycaemia caused by non-islet cell tumours is often associated with an increase in plasma insulin-like activity. In many cases there is a relative if not always absolute increase in plasma insulin-like growth factor II (IGF-II). Growth hormone (GH) secretion is almost invariably depressed as is the plasma insulin response to oral glucose. Despite the high concentration of IGFs (i.e. IGF-I and IGF-II) normally found in the plasma of healthy people their potential hypoglycaemic effect is not manifest due to the tightness with which they are bound to specific binding proteins (IGFBPs). Plasma levels of the major binding protein (IGFBP-3), which is GH-dependent, were depressed in three patients with tumour induced hypoglycaemia. Treatment with biosynthetic GH restored IGFBP-3 to levels which were approximately equimolar to total plasma IGF concentrations, alleviated the hypoglycaemia and restored the plasma insulin responses to oral glucose. We suggest that after GH treatment IGF-II is sequestered by stimulated IGFBP-3 in association with a pre-existing acid-labile subunit to form high molecular weight complexes which prevent IGF-II gaining access to tissues receptors through which it exerts its hypoglycaemic effects.