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J A H Wass

Elevated growth hormone is a cardinal feature of acromegaly from the biological view point. Growth hormone stimulates IGF-I secretion and that of its major binding protein IGFBP-3. In these circumstances, where hyperinsulinaemia is present, IGFBP-1 levels, which are inversely related to insulin, are suppressed.

Failure of suppression of growth hormone after oral glucose (>2 mU/1 (1 μg/l)) is the cardinal biochemical feature of acromegaly. IGF-I values at diagnosis are almost invariably raised. There is some overlap in the value of basal IGFBP-3 between normal subjects and acromegalics.

For monitoring purposes, growth hormone values, either basal or during the day are useful. There is overlap in the values of IGF-I and IGFBP-3 between normal subjects and patients on treatment.

Prognosis in acromegaly is determined by persistent elevation of growth hormone levels above 5 mU/l (2·5 μg/l). More data are required for the prognostic use of IGF-I.

Journal of Endocrinology (1997) 155, S17–S19

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J A H Wass

Radiotherapy most frequently uses an external beam, though interstitial irradiation with yttrium or gold has also been used, and heavy particle irradiation with alpha particles or protons is also practised in a few centres. Radiosurgery is a recent development and data on long-term use and cure rates are lacking.

External beam radiotherapy is administered after careful planning and delineation of the pituitary tumour, including the position of the diaphragm, the slope of the floor and, in particular, the lateral margins. An individual face mask immobilises the patient and irradiation is administered through a 4 or 10 MeV linear accelerator using three portals (two temporal, one frontal) at 180 cGy/fraction in 26 fractions over 35 days, to deliver a total tumour dose of 4500 cGy. This is now the accepted means worldwide for giving radiotherapy. Parallel opposed-field radiotherapy results in the delivery of greater doses of radiation to the temporal lobes

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J. M. P. Holly and J. A. H. Wass

Introduction

The list of growth factors which have generalized effects on the development and proliferation of many cells throughout the body has grown considerably; however, the insulin-like growth factors (IGFs) are still considered as a class in their own right. They are peptides with a high degree of structural homology to proinsulin with important effects on cell metabolism (insulin-like effects) and on cell growth, differentiation and mitosis. In man, there are two main forms which are known to exist; IGF-I, which is synonymous with somatomedin C, and IGF-II which in the human circulation is the most prevalent form. This review is not intended to cover the entire subject comprehensively but attempts to bring together some of the more recent developments in a cohesive manner to update our concepts on the mode of action of the IGFs. Although there have been many major advancements regarding IGF-II, particularly pertaining to its receptor,

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V. J. Frost, V. M. Macaulay, J. A. H. Wass and J. M. P. Holly

ABSTRACT

Proteolytic modification of circulating insulin-like growth factor binding protein-3 (IGFBP-3) has been described in a number of conditions. Using Western ligand blotting and SDS-PAGE analysis of fragmentation patterns of 125I-labelled IGFBP-3 and 125-labelled IGFBP-1, we have examined conditioned media from cultured human cell lines for the presence of proteolytic activity and compared this with the action of circulating proteases and with characterized enzymes including cathepsin D, kallikrein, plasmin and tissue plasminogen activator.

125I-labelled IGFBP-3 was incubated with serum from pregnant women, patients following heart surgery and patients with cancer of the breast, lung or head/neck. Following separation of the preincubated samples by SDS-PAGE, a distinct pattern of degradation fragments was observed which was similar in all cases. This proteolytic activity was inhibited in the presence of EDTA, phenanthroline and 4(-2-aminoethyl)-benzenesulphonylfluoride,HCl. These proteases had no detectable effect on IGFBP-1. Serum-free conditioned medium from a human dermal fibroblast cell line, a rabdomyosarcoma, a cervical, a bladder, a chorio- and two-tongue squamous cell carcinoma cell lines all contained proteolytic activity which fragmented IGFBP-3. The pattern of fragments was similar in all cell lines but different from that produced by the circulating proteases. Six out of nine cell lines produced protease(s) which degraded IGFBP-1 in addition to IGFBP-3. Whilst all the characterized enzymes tested also fragmented IGFBP-3 and plasmin cleaved IGFBP-1, none of these acted in the same way as either circulating or cell line-derived proteolytic activity. The activity associated with the characterized enzymes and cell lines was inhibited in the presence of serum from normal healthy subjects.

These results demonstrate that the serum of pregnant women, post-operative patients and patients with cancer contain circulating proteases which cause fragmentation of IGFBP-3 but have little effect on IGFBP-1. Cell-derived proteases were shown to act on IGFBP-3 and IGFBP-1 in a number of instances but are not active in the presence of circulating inhibitors. These proteases may play an important role in regulating the availability of IGFs to normal and neoplastic tissues.

Journal of Endocrinology (1993) 138, 545–554

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S. C. Cwyfan Hughes, J. A. H. Wass and J. M. P. Holly

ABSTRACT

The presence of proteolytic activity in the circulation directed against insulin-like growth factor binding protein-3 (IGFBP-3) was originally described in pregnancy but has subsequently been described in a number of catabolic and other pathological conditions. However, detection of this proteolytically modified IGFBP-3 has been demonstrated, in most cases, following separation using SDS-PAGE and this has led to speculation that its occurrence may be an artefact of the harsh conditions employed. Using two sitespecific antisera, one of which recognizes as its antigenic site a region of IGFBP-3 which is close to that of the IGF-binding domain, we have developed two radioimmunoassays which, when compared, can reveal alterations in the IGF-binding domain of IGFBP-3. The presence of IGFBP-3 modified by the circulating protease is denoted in this system by a divergence in the IGFBP-3 levels observed; this divergence has been shown to coincide with protease activity as determined by Western ligand blotting. The use of these assays has confirmed that the IGF-binding site of IGFBP-3 undergoes proteolytic modification in the circulation during a number of pathologies.

Journal of Endocrinology (1993) 137, 321–328

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A. M. Cotterill, J. M. P. Holly, S. C. Davies, V. J. Coulson, P. A. Price and J. A. H. Wass

ABSTRACT

Non-islet-cell tumours which induce hypoglycaemia are rare. Insulin-like growth factor-II (IGF-II) produced by some tumours is thought to be responsible for the hypoglycaemia and other systemic effects, despite normal or even low serum IGF-II levels. We studied a 44-year-old woman presenting with symptomatic hypoglycaemia associated with a large intraabdominal haemangiopericytoma. The serum IGF-II level was 455 μg/l when measured after acid-ethanol extraction (normal range (NR) 450–750 μg/l) and 1063 μg/l after acid chromatography (normal human serum pool 1068 μg/l). Levels of fasting plasma insulin, C-peptide, glucose and serum IGF-I levels were low before the operation (< 2 mU/l (NR <2-14), 0·23 nmol/l (NR 0-4-1-2), 3-1 mmol/l, (NR 3-7-5-9) and 002 U/ml respectively). After tumour removal, the symptoms resolved rapidly and the patient made a full recovery. Secretion of both insulin and growth hormone was suppressed before the operation in response to a 75 g glucose meal and to an infusion of 100 μg GH-releasing hormone (GHRH) respectively in comparison with studies after the operation. Serum IGF-II levels 6 weeks and 12 weeks after the operation fell to 385 μg/1 (777 μg/1; acid chromatography) and 280 μg/1 (647 μg/1; acid chromatography) and serum IGF-I levels increased to 0-35 U/ml and 0-26 U/ml. Serum before the operation and tumour extract contained chiefly a large molecular weight precursor IGF-II (molecular weight 15 000–20 000) which disappeared from the serum after the operation. The IGF-binding proteins (IGFBP-1, IGFBP-2, IGFBP-3 and IGFBP-4) were examined. The preoperation fasting serum IGFBP-1 level was lower than expected (31 μg/l (NR 20–70 μg/l)) and similar to levels at 6 weeks after the operation (33 μg/l). This was surprising given the differences in plasma insulin levels before and after the operation (< 2 mU/l versus 13 mU/l). Using Western ligand blotting techniques, serum IGFBP-3 levels were found to be low and IGFBP-2 appeared to be the dominant IGFBP before the operation. Serum IGFBP-3 levels after the operation fell further. This further decrease appeared, in part, to be due to the presence of a cation-dependent IGFBP-3-specific protease which has previously only been described in late pregnancy.

We conclude that in this subject, despite normal serum IGF-II levels, the hypoglycaemia and systemic effects on insulin and GH secretion were due to increased bioavailability of a circulating tumour-produced precursor form of IGF-II. This increased bioavailability appears to be due to alterations in the circulating levels and perhaps affinities of the IGFBPs.

Journal of Endocrinology (1991) 131, 303–311

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J. M. P. Holly, S. A. Amiel, R. R. Sandhu, L. H. Rees and J. A. H. Wass

Summary

The insulin and growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis are two endocrine systems that are interlinked at many levels. GH is one of the glucose counter-regulatory hormones, rising in response to hypoglycaemia, it has both intrinsic hyperglycaemic actions and causes insulin resistance. Both IGF-I and its receptor have high structural and functional homology to insulin and its receptor. Insulin can regulate IGF-I production, acting on the GH receptor or at a post-receptor site. Conversely IGF-I is thought to have a permissive effect on the pancreatic insulin response to glucose.

Growth is compromised in poorly controlled diabetic children; however, a causal link with altered GH/IGF-I levels has not been proven. Insulin-dependent diabetes clearly causes derangements in the GH/IGF-I axis. In poorly controlled diabetics GH levels are invariably raised whilst normal or low levels of IGF-I are found, indicating a dissociation between the two factors. Altered IGF-binding protein levels are also found, with high levels of small binding protein and low levels of large binding protein. These derangements are probably the result of interactions at many levels although the exact mechanisms are not fully understood.

Raised GH levels could result from altered hypothalamic/pituitary control or reduced feedback inhibition. The latter could, in turn, result from low IGF-I levels, reduced availability of IGF-I to relevant receptors or increased levels of inhibitors (possibly the small binding protein). Low IGF-I levels could be directly due to deficient insulin levels or simply to lack of available circulating binding protein.

Alternative or altered molecular forms of circulating GH in diabetes seem unlikely on present evidence.

That GH has an effect on glycaemic control is most evident from the abnormal glucose tolerance seen in acromegalics, but is also seen with physiological GH variations such as during the pubertal growth spurt. In diabetics the derangements to the GH/IGF-I axis, caused by poor metabolic control, leads to aggravation of the metabolic problems.

Altered GH/IGF-I levels have been implicated in the long-term complications associated with diabetes, and whilst GH/IGF-I are not essential for the early changes involved in these complications they may still play an important role in their development, especially proliferative retinopathy.

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E. S. Penny, A. M. Sopwith, R. L. Patience, J. A. H. Wass, G. M. Besser and L. H. Rees

ABSTRACT

Four forms of circulating immunoreactive human GH-releasing factor (ir-hGRF) have been identified in each of four normal subjects, with a mean increase in total ir-hGRF of twofold over basal levels following a mixed meal. Plasma samples (200 ml) from each individual were subjected to large-scale Vycor extraction with initial purification by high-performance liquid chromatography on a reversed-phase C18 column, followed by analytical separation of the ir-hGRF components using a C3 wide-pore reversed-phase column, and subsequent radioimmunoassay of the fractions. The mean recovery of total ir-hGRF from the plasma (fasted and non-fasted) was 76±16% (2×s.e.m.). Analytical separation of the ir-hGRF revealed four components which co-eluted with synthetic hGRF-37, hGRF-40 and hGRF-44, and a peak eluting between hGRF-40 and -44 which may represent hGRF-42. The hGRF-40 was shown to be the predominant circulating molecular form in the fasted state in each subject, and in three out of four subjects following a mixed meal. The hGRF-44 showed the greatest percentage increase over basal in all four individuals.

J. Endocr. (1986) 111, 507–511

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E.S. Penny, R.L. Patience, A.M. Sopwith, J.A.H. Wass, G.M. Besser and L.H. Rees

ABSTRACT

Three forms of circulating immunoreactive human growth hormone-releasing factor (ir-hGRF) have been identified from a patient whose acromegaly was associated with a disseminated carcinoid tumour. This is the first known report of the molecular forms of ir-hGRF in human plasma. High performance liquid chromatography (HPLC) on a C3, wide pore reversed-phase column and gel filtration chromatography were used in conjunction with a sensitive radioimmunoassay (RIA). The greatly elevated concentration of the ir-hGRF in plasma from this patient was 25,000 ng/l (normal range <60 ng/l). Gel filtration (G50) chromatography of the plasma revealed a single peak which coeluted with synthetic hGRF-40. However, reversed-phase HPLC of Vycorextracted plasma resolved the ir-hGRF into three components, which coeluted with synthetic hGRF-40 (69%), hGRF-44 (22%) and hGRF-37 (9%). At present it is not clear if the three forms are natural variants or whether either or both hGRF-40 and hGRF-37 are cleavage products of hGRF-44.

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S. C. Cwyfan Hughes, A. M. Cotterill, A. R. Molloy, T. B. Cassell, N. Braude, C. J. Hinds, J. A. H. Wass and J. M. P. Holly

ABSTRACT

Insulin-like growth factors (IGF-I and IGF-II) circulate bound to specific high-affinity binding proteins (IGFBPs). Recent evidence has shown that in pregnancy and severe illness, specific proteases modify these binding proteins, reducing their affinity for IGFs. We have studied 12 patients, undergoing elective coronary artery vein-bypass graft surgery, for the appearance of these proteases and have demonstrated the induction of two independent, heat-labile, cationdependent proteases. Proteolytic activity directed against IGFBP-3 was detected in all patients between 24 h and 5 days after surgery; the second IGFBP-4 specific protease was active 1 h after sternotomy. The total IGF-I levels were found to decrease following surgery, with the IGF-I distribution in the plasma being radically altered from that seen prior to the operation. One day after the operation the majority of the IGF-I, instead of being bound in the relatively inert 150 kDa complex, was associated with the smaller binding proteins which are more readily accessible to the tissues. These findings are in contrast to pregnancy where, despite similar proteases, the majority of the IGF-I remains in the 150 kDa complex. The alteration seen in IGF-I distribution after surgery did not appear to be a direct result of the IGFBP-3 proteolytic activity or an effect of the addition of heparin to the circulation. The potential increase in bioavailability of IGFs caused by the alteration in carrier protein may play a pivotal role in countering the catabolic state induced by surgery.

Journal of Endocrinology (1992) 135, 135–145.