Turnover rates of hepatic collagen and circulating collagen-associated proteins in humans with chronic liver disease.

Accumulation and degradation of scar tissue in fibrotic liver disease occur slowly, typically over many years. Direct measurement of fibrogenesis, the rate of scar tissue deposition, may provide valuable therapeutic and prognostic information. We describe here results from a pilot study utilizing in vivo metabolic labeling to measure the turnover rate of hepatic collagen and collagen-associated proteins in plasma for the first time in human subjects. Eight subjects with chronic liver disease were labeled with daily oral doses of 2H2O for up to 8 weeks prior to diagnostic liver biopsy and plasma collection. Tandem mass spectrometry was used to measure the abundance and fractional synthesis rate (FSR) of proteins in liver and blood. Relative protein abundance and FSR data in liver revealed marked differences among subjects. FSRs of hepatic type I and III collagen ranged from 0.2-0.6% per day (half-lives of 4 months to a year) and correlated significantly with worsening histologic fibrosis. Analysis of plasma protein turnover revealed two collagen-associated proteins, lumican and transforming growth factor beta-induced-protein (TGFBI), exhibiting FSRs that correlated significantly with FSRs of hepatic collagen. In summary, this is the first direct measurement of liver collagen turnover in vivo in humans and suggests a high rate of collagen remodeling in advanced fibrosis. In addition, the FSRs of collagen-associated proteins in plasma are measurable and may provide a novel strategy for monitoring hepatic fibrogenesis rates

Subject Demographics.

<p>*both scores 0 to 4 (Batts Ludwig, 1995)</p><p>Details regarding diagnosis, heavy water labeling duration, pathology scoring and tissue samples analyzed from each clinical subject. Abbreviations: autoimmune hepatitis (AIH); hepatitis C virus (HCV); human immunodeficiency virus (HIV); orthotopic liver transplantation (OLT).</p><p>Subject Demographics.</p

Comparison of Plasma Lumican FSR to Hepatic Collagen Kinetics and Histopathologic Fibrosis Score.

<p>(A) Linear regression of FSR of plasma lumican vs FSR of hepatic collagen in human subjects with chronic liver disease. (B) Linear regression of plasma lumican FSR vs histopathologic fibrosis score in human subjects with chronic liver disease. (C) Comparison of FSRs of liver and plasma lumican in individual subjects in whom liver values were measurable. Abbreviation: fractional synthesis rate (FSR).</p

List of 10 hepatic proteins with fractional synthesis rates (FSRs) that most significantly positively correlate with histological fibrosis score.

<p>List of 10 hepatic proteins with fractional synthesis rates (FSRs) that most significantly positively correlate with histological fibrosis score.</p

Hepatic Protein Turnover Rate vs Abundance.

<p>Heat maps displaying hepatic protein FSR (A) and relative abundance (B) for 6 human subjects with chronic liver disease. Protein data are row-scaled, with the columns representing each subject sorted by increasing histological fibrosis score. Abbreviation: fractional synthesis rate (FSR).</p

Comparison of Plasma TGFBI FSR to Hepatic Collagen Kinetics.

<p>(A) Linear regression of FSR of plasma TGFBI vs FSR of hepatic type I collagen in human subjects with chronic liver disease. (B) Linear regression of FSR of plasma TGFBI vs FSR of hepatic type III collagen in human subjects with chronic liver disease. (C) Comparison of FSRs of liver and plasma TGFBI in individual subjects in whom liver values were measurable. Abbreviations: fractional synthesis rate (FSR); transforming growth factor beta-induced protein (TGFBI).</p

Overview of Study Design.

<p>Overview of the stable-isotope labeling strategy employed to measure hepatic and plasma protein turnover in human subjects with chronic liver disease.</p

List of 20 hepatic proteins with relative abundances observed to most significantly positively correlate with histological fibrosis score.

<p>List of 20 hepatic proteins with relative abundances observed to most significantly positively correlate with histological fibrosis score.</p

Comparison of Hepatic Collagen Kinetics and Histologic Fibrosis Score.

<p>(A) Linear regression of hepatic type I collagen FSR (% new per day) and histopathologic fibrosis score in human subjects with chonic liver disease. (B,C) Bar graphs depicting the relative abundance of unlabeled (old) and labeled (new) hepatic type I collagen (B) and type III collagen (C) per unit mass of liver protein, normalized to 30 days of labeling <i>in vivo</i>. Collagen FSR values (% new per 30 days) are displayed above each bar. Values shown represent the subject or the mean of subjects with each histopathology score. Abbreviation: fractional synthesis rate (FSR).</p