S100A9 is a Biliary Protein Marker of Disease Activity in Primary Sclerosing Cholangitis

<div><h3>Background and Aims</h3><p>Bile analysis has the potential to serve as a surrogate marker for inflammatory and neoplastic disorders of the biliary epithelium and may provide insight into biliary pathophysiology and possible diagnostic markers. We aimed to identify biliary protein markers of patients with primary sclerosing cholangitis (PSC) by a proteomic approach.</p> <h3>Methods</h3><p>Bile duct-derived bile samples were collected from PSC patients (n = 45) or patients with choledocholithiasis (n = 24, the control group). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was performed to analyse the proteins, 2-D-gel patterns were compared by densitometry, and brush cytology specimens were analysed by RT-PCR.</p> <h3>Results</h3><p>A reference bile-duct bile proteome was established in the control group without signs of inflammation or maligancy comprising a total of 379 non-redundant biliary proteins; 21% were of unknown function and 24% had been previously described in serum. In PSC patients, the biliary S100A9 expression was elevated 95-fold (p<0.005), serum protein expression was decreased, and pancreatic enzyme expression was unchanged compared to controls. The S100A9 expression was 2-fold higher in PSC patients with high disease activity than in those with low activity (p<0.05). The brush cytology specimens from the PSC patients with high disease activity showed marked inflammatory activity and leukocyte infiltration compared to the patients with low activity, which correlated with S100A9 mRNA expression (p<0.05).</p> <h3>Conclusions</h3><p>The bile-duct bile proteome is complex and its analysis might enhance the understanding of cholestatic liver disease. Biliary S100A9 levels may be a useful marker for PSC activity, and its implication in inflammation and carcinogenesis warrants further investigation.</p> </div

Correlation between biliary proteins and disease activity in PSC patients.

<p>Bile from PSC patients showed a marked increase in biliary protein content. (<b>A</b>) Box plots of the protein concentration per volume show a marked increase for the PSC patients. If the PSC patients were classified based on disease activity, either by endoscopic findings (<b>C</b>) or by Mayo Risk score (<b>E</b>), the corresponding biliary protein concentrations showed significantly greater concentrations in the patients with high PSC activity than in those with low activity. If the bile samples were normalised by the bile-acid content, the results were similar (<b>B,</b> controls versus all the PSC patients; <b>D,</b> PSC patients classified by endoscopic findings; <b>F,</b> PSC patients classified by Mayo Risk Score). Box plots of the protein concentration normalised by the BA concentration. (control = 24, PSC = 45, low MRS = 25, intermediate MRS = 20; low endoscopic = 26; high endoscopy activity = 19; ns = not significant; *p<0.05; **p<0.005).</p

Identification of S100A9 as a marker of disease activity.

<p>The protein patterns among the PSC and choledocholithiasis (control) patients were compared. Intensities of 25 spots uniquely identified by mass spectrometry were measured using densitometry. The spot resembling S100A9 was markedly upregulated in the PSC patients with high activity (<b>B</b>) compared to those with low activity (<b>A</b>). Circled spots: haemoglobin (red), S100A9 (yellow), serum proteins (black), pancreatic enzymes (green), and others (blue). An evaluation of the relative amount of S100A9 in the spots demonstrated a clear upregulation of S100A9 in the PSC patients (<b>C</b>). Subgroup analyses of the PSC patients performed according to disease activity revealed a distinct increase in S100A9 in the PSC patients with high disease activity relative to those with low disease activity (<b>D</b>). The PSC patients were also stratified by their Mayo risk scores. (n: control = 6; PSC = 18; low MRS = 13; intermediate MRS = 5; low endoscopic = 12; high endoscopic = 6). The total S100 levels were significantly elevated in the PSC patients PSC (<b>F</b>) (*p<0.05; **p<0.005). The RT-PCR analyses of the brush cytology samples demonstrated marked upregulation of S100A9 expression (n = 8, 4 in the low activity group and 4 in the high activity group; p<0.05) (<b>G</b>).The brush cytology from the patients with unclear strictures demonstrated corresponding cytological findings. The cytology from a patient with low disease activity showed regular epithelial cells (arrowheads) (<b>H</b>), whereas the cytology from a patient with high disease activity showed leukocyte infiltrate (arrows) and altered epithelial cells (<b>I</b>).</p

Patient characteristics.

<p>MRS Mayo risk score; PSC low and high activities refer to the endoscopic finding.</p

Bile purification and identification of biliary proteins.

<p>(<b>A</b>) Comparison of serum (S), plasma (P), and bile duct-derived bile proteins (B) from two choledocholithiasis patients demonstrates many similar expressed proteins; however, the protein composition differs between the serum and bile samples. (<b>B</b>) Albumin and IgG depletion and purification for the crude bile duct-derived bile samples. The purification of the bile samples was monitored using 1-D silver stained gels, and the crude bile samples (Lane 1) were compared to the precipitated samples depleted of albumin and IgG. The arrow indicates the marked reduction in albumin. (<b>C</b>) A mixture of bile samples was separated by 1-D Gel electrophoresis, cut into the depicted slices and analysed by mass spectrometry. The 301 identified proteins with a Mascot score >100 were classified according to reported subcellular localisation (<b>D</b>), the biological processes in which they are involved (<b>E</b>) and the pathways the majority of proteins are involved (<b>F</b>).</p

2-D SDS-PAGE analysis of purified bile.

<p>2-D gels of biliary proteins. pH range of the first-dimension isoelectric focusing gel is shown at the bottom, and the sizes of the molecular mass standards (in kDa) for the second dimension are indicated on the left. The proteins corresponding to the spots on the gels (circled in blue) were identified by mass spectrometry. (<b>A</b>) 500 µg of protein was separated on a gradient from pH 3–11 (non-linear). To identify less abundant proteins, (<b>B</b>), 1 mg of protein was separated; more prominent spots were excluded, and the less prominent spots were identified by mass spectrometry.</p

A Frequent <em>PNPLA3</em> Variant Is a Sex Specific Disease Modifier in PSC Patients with Bile Duct Stenosis

<div><p>Background & Aims</p><p>Primary sclerosing cholangitis predominantly affects males and is an important indication for liver transplantation. The rs738409 variant (I148M) of the <i>PNPLA3</i> gene is associated with alcoholic and non-alcoholic liver disease and we evaluated its impact on the disease course of PSC.</p> <p>Methods</p><p>The I148M polymorphism was genotyped in 121 German PSC patients of a long-term prospective cohort and 347 Norwegian PSC patients.</p> <p>Results</p><p>In the prospective German cohort, actuarial survival free of liver transplantation was significantly reduced for I148M carriers (p = 0.011) compared to wildtype patients. This effect was restricted to patients with severe disease, as defined by development of dominant stenosis (DS) requiring endoscopic intervention. DS patients showed markedly decreased survival (p = 0.004) when carrying the I148M variant (I148M: mean 13.8 years; 95% confidence interval: 11.6–16.0 vs. wildtype: mean 18.6 years; 95% confidence interval: 16.3–20.9) while there was no impact on survival in patients without a DS (p = 0.87). In line with previous observations of sex specific effects of the I148M polymorphism, the effect on survival was further restricted to male patients (mean survival 11.9 years; 95% confidence interval: 10.0–14.0 in I148M carriers vs. 18.8 years; 95% confidence interval: 16.2–21.5 in wildtype; p<0.001) while female patients were unaffected by the polymorphism (p = 0.65). These sex specific findings were validated in the Norwegian cohort (p = 0.013).</p> <p>Conclusions</p><p>In male PSC patients with severe disease with bile duct stenosis requiring intervention, the common I148M variant of the <i>PNPLA3</i> gene is a risk factor for reduced survival.</p> </div

Kaplan – Meier estimate for the I148M variant and dominant stenosis.

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058734#pone-0058734-g001" target="_blank"><u>Figure 1A:</u></a><u> In patients with a DS, the I148M variant markedly impairs actuarial survival free of liver transplantation</u>: Kaplan – Meier estimate of all patients in the prospective study cohort with a DS (n = 81) shows markedly impaired actuarial survival free of liver transplantation in the presence of a DS (p = 0.004). <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058734#pone-0058734-g001" target="_blank"><u>Figure 1B:</u></a><u> In patients without a DS, the I148M variant does not affect actuarial survival free of liver transplantation</u>: Kaplan–Meier estimate of all patients in the prospective study cohort without a DS (n = 40) showed no difference in actuarial survival free of liver transplantation in the presence of a DS (p = 0.87).</p

Allele frequencies in PSC patients of the prospective study cohort and the Norwegian cohort as well as a Norwegian control population for the rs738409 polymorphism investigated.

*<p>Pearson's chi-square test for differences in allele frequencies.</p><p>Genotypes were in Hardy-Weinberg equilibrium (p_prospective = 0.19, p_norway = 0.43, p_controls = 0.26).</p

Gender specific Kaplan–Meier estimate for the I148M variant.

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058734#pone-0058734-g002" target="_blank"><u>Figure 2A:</u></a><u> In male PSC patients with a DS, the I148M variant impairs actuarial survival free of liver transplantation in the German prospective study cohort:</u> Kaplan-Meier estimate of all male PSC patients with a DS (n = 55) in the prospective study cohort shows markedly impaired actuarial survival free of liver transplantation (p = 0.002) when carrying the I148M genotype (n = 23) compared to male wildtype patients (n = 32). <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058734#pone-0058734-g002" target="_blank"><u>Figure 2B:</u></a><u> In female PSC patients with a DS, the I148M variant does not affect actuarial survival free of liver transplantation in the German prospective study cohort:</u> Kaplan-Meier estimate of all female PSC patients with a DS (n = 26) in the prospective study cohort shows no difference in actuarial survival free of liver transplantation (p = 0.38) when carrying the I148M genotype (n = 10) compared to the wildtype genotype (n = 16). <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058734#pone-0058734-g002" target="_blank"><u>Figure 2C:</u></a><u> In male PSC patients with endoscopic intervention, the I148M variant impairs actuarial survival free of liver transplantation in the Norwegian study cohort:</u> Kaplan-Meier estimate of all male PSC patients with endoscopic intervention (n = 101) in the Norwegian study cohort shows markedly impaired actuarial survival free of liver transplantation (p = 0.013) when carrying the I148M genotype (n = 32) compared to the wildtype genotype (n = 69). <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058734#pone-0058734-g002" target="_blank"><u>Figure 2D:</u></a><u> In female PSC patients without endoscopic intervention, the I148M variant does not affect actuarial survival free of liver transplantation in the Norwegian study cohort:</u> Kaplan-Meier estimate of all female PSC patients with endoscopic intervention (n = 22) in the Norwegian study cohort shows no difference in actuarial survival free of liver transplantation (p = 0.65) when carrying the I148M genotype (n = 9) compared to the wildtype genotype (n = 13).</p