Arterial Calcifications in Patients with Liver Cirrhosis Are Linked to Hepatic Deficiency of Pyrophosphate Production Restored by Liver Transplantation

Abstract

Liver fibrosis is associated with arterial calcification (AC). Since the liver is a source of inorganic pyrophosphate (PPi), an anti-calcifying compound, we investigated the relationship between plasma PPi ([PPi]pl), liver fibrosis, liver function, AC, and the hepatic expression of genes regulating PPi homeostasis. To that aim, we compared [PPi]pl before liver transplantation (LT) and 3 months after LT. We also assessed the expression of four key regulators of PPi in liver tissues and established correlations between AC, and scores of liver fibrosis and liver failure in these patients. LT candidates with various liver diseases were included. AC scores were assessed in coronary arteries, abdominal aorta, and aortic valves. Liver fibrosis was evaluated on liver biopsies and from non-invasive tests (FIB-4 and APRI scores). Liver functions were assessed by measuring serum albumin, ALBI, MELD, and Pugh–Child scores. An enzymatic assay was used to dose [PPi]pl. A group of patients without liver alterations from a previous cohort provided a control group. Gene expression assays were performed with mRNA extracted from liver biopsies and compared between LT recipients and the control individuals. [PPi]pl negatively correlated with APRI (r = −0.57, p = 0.001, n = 29) and FIB-4 (r = −0.47, p = 0.006, n = 29) but not with interstitial fibrosis index from liver biopsies (r = 0.07, p = 0.40, n = 16). Serum albumin positively correlated with [PPi]pl (r = 0.71; p < 0.0001, n = 20). ALBI, MELD, and Pugh–Child scores correlated negatively with [PPi]pl (r = −0.60, p = 0.0005; r = −0.56, p = 0.002; r = −0.41, p = 0.02, respectively, with n = 20). Liver fibrosis assessed on liver biopsies by FIB-4 and by APRI positively correlated with coronary AC (r = 0.51, p = 0.02, n = 16; r = 0.58, p = 0.009, n = 20; r = 0.41, p = 0.04, n = 20, respectively) and with abdominal aorta AC (r = 0.50, p = 0.02, n = 16; r = 0.67, p = 0.002, n = 20; r = 0.61, p = 0.04, n = 20, respectively). FIB-4 also positively correlated with aortic valve calcification (r = 0.40, p = 0.046, n = 20). The key regulator genes of PPi production in liver were lower in patients undergoing liver transplantation as compared to controls. Three months after surgery, serum albumin levels were restored to physiological levels (40 [37–44] vs. 35 [30–40], p = 0.009) and [PPi]pl was normalized (1.40 [1.07–1.86] vs. 0.68 [0.53–0.80] µmol/L, p = 0.0005, n = 12). Liver failure and/or fibrosis correlated with AC in several arterial beds and were associated with low plasma PPi and dysregulation of key proteins involved in PPi homeostasis. Liver transplantation normalized these parameters.

The Purinergic Nature of Pseudoxanthoma Elasticum

“…PXE and GACI are rare diseases that have been extensively studied over the last 2 decades and from which much has been learned. The gained knowledge is progressively being extended and applied to other diseases with ectopic calcification, for example the development Randall's plaque and kidney stones, and arterial calcification resulting from kidney or liver failure as well as systemic sclerosis [235,[240][241][242]253]. We have described in this review a series of well-documented evidence reporting the dysregulation of purinergic signaling and related gene expression as a result of ABCC6 deficiency.…”

“…Despite the effective role of PPi in the prevention of calcification [11,13,89,90,133,210,[233][234][235][236][237][238], plasma PPi is not the main determinant of ectopic calcification severity [19,239]. Therefore, establishing methods to determine local concentrations and the exact in situ molecular determinants seems essential to fully understand PXE, GACI and other pathological calcifications such as Randall's plaque and kidney stones, as well as in arterial calcification resulting from liver failure [240][241][242].…”

Identification of a DBA/2 Mouse Sub-strain as a Model for Pseudoxanthoma Elasticum-Like Tissue Calcification

“…1, Table 1). To clarify the differences between the three sub-strains, we evaluated hepatic gene expression associated with calcification according to the previous report, 15,19,20) in which the severity of calcification after cardiac injury was determined using mice with different hepatic Abcc6 expression levels. 15) As a result, male DBA/2CrSlc mice showed lower expression of Abcc6, Enpp1, and Spp1 than did male C57BL6J mice that developed little calcification, whereas no difference was observed in Akp2 expression (Fig.…”