The acromegaly lipodystrophy

Abstract

Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) are essential to normal growth, metabolism, and body composition, but in acromegaly, excesses of these hormones strikingly alter them. In recent years, the use of modern methodologies to assess body composition in patients with acromegaly has revealed novel aspects of the acromegaly phenotype. In particular, acromegaly presents a unique pattern of body composition changes in the setting of insulin resistance that we propose herein to be considered an acromegaly-specific lipodystrophy. The lipodystrophy, initiated by a distinctive GH-driven adipose tissue dysregulation, features insulin resistance in the setting of reduced visceral adipose tissue (VAT) mass and intra-hepatic lipid (IHL) but with lipid redistribution, resulting in ectopic lipid deposition in muscle. With recovery of the lipodystrophy, adipose tissue mass, especially that of VAT and IHL, rises, but insulin resistance is lessened. Abnormalities of adipose tissue adipokines may play a role in the disordered adipose tissue metabolism and insulin resistance of the lipodystrophy. The orexigenic hormone ghrelin and peptide Agouti-related peptide may also be affected by active acromegaly as well as variably by acromegaly therapies, which may contribute to the lipodystrophy. Understanding the pathophysiology of the lipodystrophy and how acromegaly therapies differentially reverse its features may be important to optimizing the long-term outcome for patients with this disease. This perspective describes evidence in support of this acromegaly lipodystrophy model and its relevance to acromegaly pathophysiology and the treatment of patients with acromegaly.

Keywords: AgRP; acromegaly; adipose tissue; body composition; ghrelin; growth hormone; insulin resistance; lipodystrophy.

Figure 1

(A) Model of the acromegaly lipodystrophy that is present when the disease is active (i.e., elevated levels of GH and IGF-1). The lipodystrophy is initiated by a GH-induced accelerated lipolysis leading to insulin resistance, adipose tissue inflammation, and reduced adipose tissue mass, especially that of the VAT depot. Hepatic lipid is reduced, but hepatic insulin resistance occurs. Lipid is redistributed from VAT and SAT depots to ectopic deposition in muscle and may contribute to muscle insulin resistance. (B) Model of recovery of the lipodystrophy with biochemical remission after acromegaly treatment. After normalization of GH by surgery or medical therapy, adipose tissue lipolysis is reduced, permitting a re-accumulation of VAT and SAT lipid stores, a rise in intra-hepatic lipid and reduction in insulin resistance. Muscle lipid may not decrease due to the rise in total adipose tissue mass with acromegaly therapy despite improvement in insulin resistance.