Study Reveals Biomarkers for Fibrosis Detection in Homozygous ZZ AATD Liver Disease

Jeffrey Teckman, MD

Credit: Saint Louis University

Findings from a recent study are providing clinicians with an overview of factors associated with increased fibrosis in homozygous ZZ alpha-1-antitrypsin deficiency (AATD).¹

The prospective cohort study enrolled nearly 100 adult patients with ZZ AATD at 3 sites across the US and described the relationship between liver biopsy results and hepatic content of the toxic Z protein polymer with fibrosis and other parameters based on findings from protocol liver biopsies and 5 subsequent annual visits.¹

“Liver biopsy is currently the gold standard to study fibrosis, although data relating liver biopsy and other clinical parameters are lacking,” Jeffrey Teckman, MD, a physician and professor of biochemistry and molecular biology at Saint Louis University School of Medicine, and colleagues wrote, acknowledging limitations to previous research efforts to document the natural history of liver injury in patients with AATD.¹

A hereditary disorder characterized by low levels of alpha-1 antitrypsin in the blood, AATD may predispose an individual to several illnesses and most commonly manifests as chronic obstructive pulmonary disease or liver disease. Most patients with AATD-related liver disease are homozygous for the Z allele, underscoring the need for research specific to this patient population to better understand factors impacting liver injury and biomarkers for detecting it.²

In an effort to increase the understanding of liver disease in homozygous ZZ AATD, investigators conducted a prospective cohort study enrolling adult patients ≥ 18 years of age with or without lung disease and with no restrictions on gender, race, or ethnicity. Patients were required to agree to protocol liver biopsy and 5 annual visits for inclusion in the study. Patients with established cirrhosis in whom a repeat biopsy without benefit was not ethical were included in the “known severe” arm of the study and were enrolled without a liver biopsy. Instead, investigators collected their medical records and previous liver biopsy results to confirm the presence of cirrhosis and significant fibrosis.¹

Investigators used the Ishak score (0–6) to assess fibrosis and validated metrics to assess steatosis and inflammation. To optimize statistical power, they analyzed data in the following Ishak groupings: 0%–19.8% (1); 1%–29.2% (2); 2%–21.9% (3); 3%–8.3% (4); and ≥4%–20.8% (5). Additionally, they used Brunt's steatosis score to grade the degree and type of steatosis on liver biopsy.¹

In total, the study enrolled 95 homozygous ZZ AATD adult patients at 3 US sites with standardized clinical evaluations and protocol liver biopsies. Of these, 14 patients were included in the “known severe” group. Among the cohort, the mean age at AATD diagnosis was 45.9 ± 17.7 years and the mean age at study enrollment was 54.6 ± 14.1 years. The majority of participants were female (50.5%) and Caucasian (94.8%).¹

Investigators divided the cohort into 3 fibrosis groups: Ishak 0–1 (49%); Ishak 2–3 (36%); and Ishak ≥ 4 (15%). Upon analysis, clinical signs of advanced liver disease detected during follow-up were significantly associated with Ishak ≥4 compared to Ishak 2–3, including variceal bleed (P <.0004), splenomegaly (P <.0001), portal hypertension (P <.01) and ascites (P <.04). Although biochemical markers of liver injury ALT, AST and GGT were associated with the degree of fibrosis, clinically relevant values were only observed in patients with Ishak ≥4. Additionally, increased mean AST Platelet ratio index (APRI) and Fibrosis index 4 (FIB 4) scores were significantly associated with the degree of fibrosis.¹

Investigators noted BMI at enrollment was greater in those with significant fibrosis (29.2 ± 6.5 kg/m2 vs 26.4 ± 6.1 kg/m2; P = .0384) and was associated with degree of fibrosis. (26.4 ± 6.1 Ishak 0–1 vs 27.5 ± 4.8 Ishak 2–3 vs 31.7 ± 7.9 kg/m2 Ishak ≥4; P = .0083). They additionally pointed out metabolic syndrome was associated with an increased degree of fibrosis and none of the subjects in the minimal fibrosis group had metabolic syndrome (P = .0058).¹

Further analysis revealed Brunt's macrovesicular steatosis score did not correlate with the degree of fibrosis (P = .5731) but greater mean circulating Z polymer levels were associated with an increased degree of fibrosis (9.7 ± 6.8 μg/mL Ishak 0–1 vs 12.1 ± 4.3 μg/mL Ishak 2–3 vs 16.1 ± 8.1 μg/mL Ishak ≥4; P = .0194).¹

Additionally, investigators most frequently observed portal inflammation (70.7% prevalent) and lobular inflammation (61% prevalent) on biopsies, and these were the most common histological findings other than AAT protein accumulation, although the degree of inflammation was typically mild.¹

Increased fibrosis was also significantly associated with increased biopsy area of mutant Z polymer ‘globular’ inclusions (P = .002) and increased diffuse cytoplasmic Z polymer area (P = .0029). Univariate analysis revealed increased serum Z polymer was significantly associated with increased biopsy area of mutant Z polymer ‘globular’ inclusions (P = .0001) but also increased diffuse cytoplasmic Z polymer area to a lesser degree (P = .014). Additional analysis revealed higher serum AST was significantly associated with increased globular inclusion area (P = .0064) but not with diffuse cytoplasmic stain area, and ALT had no significant relationship to liver Z polymer accumulation.¹

Investigators outlined multiple limitations to these findings, including the limited number of events in the study and the subsequent negative impact on certain analyses as well as the ability to measure serum Z polymer in participants who were not on exogenous alpha-1 intravenous protein replacement for lung disease.¹

“Clinical signs of liver disease and elevations of liver enzymes are often delayed until fibrosis is significant. Early detection of increasing fibrosis, which might require a liver biopsy to fully clarify, and would then more strongly encourage close follow-up, is necessary… Serum Z polymer levels appear to be a promising, non-invasive, disease-specific biomarker,” investigators concluded.¹ “Further study, including 5-year follow-up data and correlation to biopsy are needed to determine use in clinical care and study enrolments.”

References

1. ^{Suri A, Zhang Z, Neuschwander-Tetri B, et al. Fibrosis, biomarkers and liver biopsy in AAT deficiency and relation to liver Z protein polymer accumulation. Liver International. https://doi.org/10.1111/liv.16094}
2. ^{Meseeha M, Sankari A, Attia M. Alpha-1 Antitrypsin Deficiency. StatPearls. February 12, 2024. Accessed July 24, 2024. https://www.ncbi.nlm.nih.gov/books/NBK442030/}