Effects of recombinant human growth hormone on adipose tissue in adults with growth hormone deficiency

Alterations of protein metabolism in acromegaly

PURPOSE OF REVIEW

Growth hormone is a powerful anabolic hormone necessary for normal growth, but its importance in maintaining the cellular and protein mass in adult life is still unclear. However, it is viewed as a drug capable of combating the tissue loss and some metabolic derangements of aging. Growth hormone excess causes acromegaly, a disease characterized by overgrowth of some tissues and multiple metabolic abnormalities. The purpose of this article is to review recent knowledge in acromegaly considering it as a model for clarifying aspects of growth hormone action on body composition, protein dynamics and molecular mechanisms in adult life.

RECENT FINDINGS

Acromegaly induces well-documented changes in body fat (decreased), and bone density and water retention (increased), but there are less-clear changes in protein and body cell-mass accretion. Recent studies related insulin resistance to glucose metabolism to accelerated fat oxidation and described the reversibility of such alterations after surgical or pharmacologic therapy. Less attention was paid to changes in protein metabolism. Acromegalics are profoundly insulin-resistant to the antiproteolytic action of insulin, but amino acids are channelled towards protein synthesis because they are still normally spared from oxidation by insulin. This insulin resistance persists months after the surgical cure of acromegaly when glucose metabolism is already normalized. Recent studies suggested that increased use of fat for fuel by growth hormone may also promote protein anabolism and reduce amino acid oxidation.

SUMMARY

Despite important advances in understanding molecular mechanisms in acromegaly, the specific effects on body cell and protein mass and the specific modulation of local protein dynamics remain poorly defined.

Assessment of quality of life in adults receiving long-term growth hormone replacement compared to control subjects

OBJECTIVE

There are few studies of quality of life (QOL) in adults with growth hormone deficiency (GHD) compared to matched control populations without GHD. These have shown impairments in a variety of QOL measures, which improve but do not normalize after short-term replacement with GH. There is little information on QOL in long-term treated GHD patients compared with controls without GHD.

PATIENTS AND METHODS

A total of 120 adults with GHD who had received GH replacement for at least 1 year were identified from the neuroendocrine clinic. Patients were asked to complete eight QOL questionnaires and an Energy Visual Analogue Scale (VAS). Results were compared with 83 control subjects without GHD from the local population who agreed to complete seven of the QOL questionnaires (excluding Disease Impact scale) and the energy VAS. The eight questionnaires were a combination of generic and disease-specific questionnaires used to assess health related QOL, namely: Short Form-36 (SF-36), Nottingham Health Profile (NHP), Disease Impact, Life Fulfilment and Satisfaction scales, Mental Fatigue Questionnaire (MFQ) and Self Esteem scale, Hospital Anxiety Depression (HAD) scale and QOL-AGHDA (assessment of GHD in adults).

RESULTS

Eighty-nine patients returned questionnaires and 85 (71%) had complete data for analysis. The mean (SD) duration of GH replacement was 36.0 +/- 26.4 (range 13-159) months. Mean age was 43.9 +/- 15.8 years (37 males) in treated GHD patients compared to a mean age 41.7 +/- 10.5 years (32 males) in the controls. Mean IGF-1 levels were 22.5 +/- 13.6 nmol/l in the GHD patients and the mean dose of GH replacement was 1.2 +/- 0.4 IU daily. Analysis of the QOL questionnaires from the GH treated patients revealed highly significant impairments in all measures (most P </= 0.0001, except life fulfilment-material, P = 0.33) compared to the control population.

CONCLUSIONS

This large population with treated GH deficiency have significant impairments in multiple aspects of QOL despite replacement with GH and other pituitary hormones for at least 1 year (mean 3 years). It is likely therefore that other factors in addition to GH deficiency must influence QOL in these patients. Further strategies to improve QOL in these individuals should therefore be considered, e.g. psychological support and treatments and physical treatments (such as exercise programmes).

The mechanism of effect of growth hormone on preadipocyte and adipocyte function

Growth hormone (GH) is not only the major regulator of postnatal somatic growth but also exerts profound effects on body composition through a combination of anabolic, lipolytic and antinatriuretic actions. GH enhancement of the lipolytic activity of adipose tissue in combination with a reduction of triglyceride accumulation via inhibition of lipoprotein lipase activity appears to be the major mechanism by which GH results in a reduction of the total fat mass. Recently, much progress has been made in understanding the molecular mechanism by which GH affects cellular function. This review provides a brief discourse and summary of the mechanism of effects of GH on preadipocyte/adipocyte function. It is intended to provide a functional understanding of the mechanism of action of GH as it relates to adipogenesis and adipocyte function.