The heterogeneity of bone disease in cirrhosis: a multivariate analysis.

This study aimed to assess the clinical, biochemical and hormonal factors contributing to low bone density in a large ambulatory group of patients with cirrhosis of diverse aetiology. Bone density of the lumbar spine, neck of femur, total hip, total body, as well as total body fat, was measured by dual X-ray (DEXA) absorptiometry in 81 men and 32 women (average age 50.3 years). Morning blood and urine samples were taken for hormonal and biochemical analysis. Viral hepatitis was the most common cause of cirrhosis (54%) and the severity of cirrhosis ranged from Child-Pugh A5-C14. Osteoporosis was most common in the lumbar spine but was present at any site in 31% of women and 22% of men, with osteopenia present in another 40% of both genders. Urinary deoxypyridinoline, a marker of bone resorption, was elevated in 56% of patients and was associated with increasing severity of cirrhosis and a higher prevalence of osteoporosis, particularly of the lumbar spine. Hip-bone density was primarily affected by low 25-hydroxyvitamin D levels and was associated with secondary hyperparathyroidism in one third of these patients. Additional important predictors for low bone density at all sites were age in women and testosterone in men. These findings indicate that, although the pathophysiology of osteoporosis in chronic liver disease is heterogeneous, high bone turnover may be the underlying pathophysiological mechanism in a significant subgroup of cirrhotic patients and may reflect metabolic effects of hypogonadism or secondary hyperparathyroidism on bone.

Insulin-like growth factor bioactivity and its modification in growth hormone resistant states.

Acquired growth hormone (GH) resistance is an increasingly recognized feature of catabolic states. Low circulating levels of the insulin-like growth factors (IGF-I and II) have been shown to be associated with changes in the IGF binding proteins (IGFBP-1 to -6) that may significantly impact on IGF bioactivity. IGFBP-3 binds IGF and a third glycoprotein, the acid labile subunit (ALS), to form a stable 150 kDa ternary complex that serves as an intravascular store for IGFs and prolongs IGF half-life. IGFBP-1 is present at much lower concentration in serum but levels fluctuate acutely, suggesting regulation of IGF bioactivity in response to short-term metabolic changes. The function of IGFBP-2 remains unclear, but studies suggest that this protein may act as an alternative carrier for IGF when IGFBP-3 levels are low. Multiple regulatory influences on circulating IGFBP levels have been identified but three appear prominent. Nutritional influences, in particular substrate availability, appear to be a central regulatory influence on IGFBP levels in catabolic states. Low substrate availability increases IGFBP-1 levels acutely and decreases IGFBP-3 and IGFBP-2 levels in the intermediate term, with each of these changes likely to further limit IGF bioactivity. End organ failure, particularly of liver and kidney significantly affects production and clearance rates of the circulating IGFBPs and may contribute to the catabolism frequently seen in these states. Severe protein catabolism often accompanies malignancy and chronic sepsis and it is likely that additional ill-defined factors influence IGF bioactivity in this setting. Recent studies have identified post-translational modifications to the IGFBPs such as proteolysis and phosphorylation, which appear to further impact on IGF bioactivity. The relative contributions of these changes to the overall impairment of IGF bioactivity in GH-resistant states remains to be fully elucidated.