Z and Mmalton-1-antitrypsin deficiency-associated hepatocellular carcinoma: a genetic study

The Recruitment-Secretory Block ("R-SB") Phenomenon and Endoplasmic Reticulum Storage Diseases

In this article, we review the biological and clinical implication of the Recruitment-Secretory Block (“R-SB”) phenomenon. The phenomenon refers to the reaction of the liver with regard to protein secretion in conditions of clinical stimulation. Our basic knowledge of the process is due to the experimental work in animal models. Under basal conditions, the protein synthesis is mainly carried out by periportal (zone 1) hepatocytes that are considered the “professional” synthesizing protein cells. Under stimulation, midlobular and centrolobular (zones 2 and 3) hepatocytes, are progressively recruited according to lobular gradients and contribute to the increase of synthesis and secretion. The block of secretion, operated by exogenous agents, causes intracellular retention of all secretory proteins. The Pi MZ phenotype of Alpha-1-antitrypsin deficiency (AATD) has turned out to be the key for in vivo studies of the reaction of the liver, as synthesis and block of secretion are concomitant. Indeed, the M fraction of AAT is stimulated for synthesis and regularly exported while the Z fraction is mostly retained within the cell. For that reason, the phenomenon has been designated “Recruitment-Secretory Block” (“R-SB”). The “R-SB” phenomenon explains why: (a) the MZ individuals can correct the serum deficiency; (b) the resulting immonohistochemical and electron microscopic (EM) patterns are very peculiar and specific for the diagnosis of the Z mutation in tissue sections in the absence of genotyping; (c) the term carrier is no longer applicable for the heterozygous condition as all Pi MZ individuals undergo storage and the storage predisposes to liver damage. The storage represents the true elementary lesion and consequently reflects the phenotype-genotype correlation; (d) the site and function of the extrahepatic AAT and the relationship between intra and extracellular AAT; (e) last but not least, the concept of Endoplasmic Reticulum Storage Disease (ERSD) and of a new disease, hereditary hypofibrinogenemia with hepatic storage (HHHS). In the light of the emerging phenomenon, described in vitro, namely that M and Z AAT can form heteropolymers within hepatocytes as well as in circulation, we have reviewed the whole clinical and experimental material collected during forty years, in order to evaluate to what extent the polymerization phenomenon occurs in vivo. The paper summarizes similarities and differences between AAT and Fibrinogen as well as between the related diseases, AATD and HHHS. Indeed, fibrinogen gamma chain mutations undergo an aggregation process within the RER of hepatocytes similar to AATD. In addition, this work has clarified the intriguing phenomenon underlying a new syndrome, hereditary hypofibrinogenemia and hypo-APO-B-lipoproteinemia with hepatic storage of fibrinogen and APO-B lipoproteins. It is hoped that these studies could contribute to future research and select strategies aimed to simultaneously correct the hepatocytic storage, thus preventing the liver damage and the plasma deficiency of the two proteins.

Hepatic and Extrahepatic Sources and Manifestations in Endoplasmic Reticulum Storage Diseases

Alpha-1-antitrypsin (AAT) and fibrinogen are secretory acute phase reactant proteins. Circulating AAT and fibrinogen are synthesized exclusively in the liver. Mutations in the encoding genes result in conformational abnormalities of the two molecules that aggregate within the rough endoplasmic reticulum (RER) instead of being regularly exported. That results in AAT-deficiency (AATD) and in hereditary hypofibrinogenemia with hepatic storage (HHHS). The association of plasma deficiency and liver storage identifies a new group of pathologies: endoplasmic reticulum storage disease (ERSD).

Alpha-1 antitrypsin deficiency: an update on clinical aspects of diagnosis and management

Clinical heterogeneity has been demonstrated in alpha-1 antitrypsin deficiency (AATD), such that clinical suspicion plays an important role in its diagnosis. The PiZZ genotype is the most common severe deficiency genotype and so tends to result in the worst clinical presentation, hence it has been the major focus of research. However, milder genotypes, especially PiSZ and PiMZ, are also linked to the development of lung and liver disease, mainly when unhealthy behaviors are present, such as smoking and alcohol use. Monitoring and managing AATD patients remains an area of active research. Lung function tests or computed tomography (CT) densitometry may allow physicians to identify progressive disease during follow up of patients, with a view to decision making about AATD-specific therapy, like augmentation therapy, or eventually surgical procedures such as lung volume reduction or transplant. Different types of biological markers have been suggested for disease monitoring and therapy selection, although most need further investigation. Intravenous augmentation therapy reduces the progression of emphysema in PiZZ patients and is available in many European countries, but its effect in milder deficiency is less certain. AATD has also been suggested to represent a risk factor and trigger for pulmonary infections, like those induced by mycobacteria. We summarize the last 5-10 years' key findings in AATD diagnosis, assessment, and management, with a focus on milder deficiency variants.

Mineralization of alpha-1-antitrypsin inclusion bodies in Mmalton alpha-1-antitrypsin deficiency

Background

Alpha-1-antitrypsin (AAT) deficiency (AATD) of Z, Mmalton, Siiyama type is associated with liver storage of the mutant proteins and liver disease. The Z variant can be diagnosed on isoelectric focusing (IEF) while Mmalton and Siiyama may be missed or misdiagnosed with this technique. Therefore, molecular analysis is mandatory for their characterization. In particular, that holds true for the Mmalton variant as on IEF profile it resembles the wild M2 subtype.

Methods

This is a retrospective analysis involving review of medical records and of liver biopsy specimens from a series of Mmalton, Z and Siiyama Alpha-1-antitrypsin deficiency patients. The review has been implemented by additional histological stains, electron microscopic observations and 3-D modeling studies of the sites of the mutations.

Results

Z, Mmalton and Siiyama liver specimen contained characteristic intrahepatocytic PAS-D globules. The globules differed in the three variants as only Mmalton cases showed dark basophilic precipitates within the AAT inclusions. The precipitates were visualized in haematoxylin-eosin (H.E.) stained preparations and corresponded to calcium precipitates as demonstrated by von Kossa staining. On immunohistochemistry, ZAAT inclusions were stained by polyclonal as well as monoclonal noncommercial anti-AAT antibody (AZT11), whilst Mmalton and Siiyama inclusion bodies remained negative with the monoclonal anti-Z antibody. 3-D protein analysis allowed to predict more severe misfolding of the Mmalton molecule as compared to Z and Siiyama that could trigger anomalous interaction with endoplasmic reticulum chaperon proteins, namely calcium binding proteins.

Conclusions

Mmalton AAT inclusion bodies contain calcium precipitates inside them that allow the differential diagnosis with Siiyama and ZAAT inclusions in routine histological sections. The study has confirmed the specificity of the monoclonal AZT11 for the Z mutant. Thus, the combination of these two features is crucial for the distinction between the three variants and for predicting the genotype, whose confirmation would definitely require molecular analysis. Our study provides new data on the pathomorphogenesis of Mmalton inclusion bodies whose mineralization could play a central role in disease pathogenesis of Mmalton that is distinct from the Z and Siiyama variants. Calcium is known to be a major effector of cell death either via the increased intracellular concentration or the alteration of homeostasis.

Alpha-1-antitrypsin deficiency: from genoma to liver disease. PiZ mouse as model for the development of liver pathology in human

BACKGROUND & AIMS

Homozygous individuals with alpha-1-antitrypsin deficiency (AATD) type PiZ have an increased risk of chronic liver disease and hepatocellular carcinoma (HCC). It is noteworthy that HCCs are composed by hepatocytes without accumulation of AAT, but the reason for this remains unclear. The aim of this study was to determine liver pathology in PiZ mice, focusing the attention on the distribution of AAT globules in normal liver, regenerative foci and neoplastic nodules.

METHODS

Liver of 79 PiZ mice and 18 wild type (Wt) was histologically analysed for steatosis, clear cell foci, hyperplasia and neoplasia. The expression of human-AAT transgene and murine AAT, in non-neoplastic liver and in hyperplastic/neoplastic nodules was tested by qPCR and qRT-PCR. RT-PCR was used to study expression of hepatic markers: albumin, α-foetoprotein, transthyretin, AAT, glucose-6-phospate, tyrosine aminotransferase.

RESULTS

Liver pathology was seen more frequently in PiZ (47/79) than in Wt (5/18) and its development was age related. In older PiZ mice (18-24 m), livers showed malignant tumours (HCC and angiosarcoma) (17/50), hyperplastic nodules (28/50), non-specific changes (33/50), whereas only 9/50 were normal. Both human-AATZ DNA and mRNA showed no differences between tumours/nodules and normal liver, while murine-AAT mRNA was reduced in tumours/nodules.

CONCLUSION

Accumulation of AAT is associated with an increased risk of liver nodules. The presence of globule-devoid hepatocytes and the reduced expression of murine-AAT mRNA in hyperplastic and neoplastic nodules suggest that these hepatic lesions in AATD could originate from proliferating dedifferentiated cells, lacking AAT storage and becoming capable of AFP re-expression.

Challenging identification of a novel PiISF and the rare PiMmaltonZ α1-antitrypsin deficiency variants in two patients

OBJECTIVES

α1-Antitrypsin (AAT) deficiency is associated with an increased risk for lung and liver disease. Identification of AAT deficiency as the underlying cause of these diseases is important in correct patient management.

METHODS

AAT deficiency is commonly diagnosed by demonstrating low concentrations of AAT followed by genotype and/or phenotype testing. However, this algorithm may miss novel AAT phenotypes.

RESULTS

We report two cases of AAT deficiency in two patients: a case of the novel phenotype PiISF, misclassified as PiII by phenotyping, and a case of the rare phenotype PiMmaltonZ misclassified as PiM2Z.

CONCLUSIONS

These cases highlight the importance of understanding the limitations of a commonly used diagnostic algorithm, use of further gene sequencing in applicable cases, and the potential for underdiagnosis of AAT deficiency in patients with chronic obstructive pulmonary disease.

Diagnosis and management of patients with α1-antitrypsin (A1AT) deficiency

Alpha(1)-antitrypsin (A1AT) deficiency is an autosomal codominant disease that can cause chronic liver disease, cirrhosis, and hepatocellular carcinoma in children and adults and increases risk for emphysema in adults. The development of symptomatic disease varies; some patients have life-threatening symptoms in childhood, whereas others remain asymptomatic and healthy into old age. As a result of this variability, patients present across multiple disciplines, including pediatrics, adult medicine, hepatology, genetics, and pulmonology. This can give physicians the mistaken impression that the condition is less common than it actually is and can lead to fragmented care that omits critical interventions commonly performed by other specialists. We sought to present a rational approach for hepatologists to manage adult patients with A1AT deficiency.

Performance of enhanced liver fibrosis plasma markers in asymptomatic individuals with ZZ α1-antitrypsin deficiency

OBJECTIVES

Alpha1-antitrypsin deficiency (AATD) is a common genetic cause of chronic liver disease. According to retrospective studies, up to 25% of those with homozygous ZZ (Glu 342 to Lys) AATD suffer from liver cirrhosis and/or liver cancer in late adulthood. We hypothesized that the plasma markers for liver fibrosis, necrosis, and apoptosis may identify AATD individuals at higher risk for liver diseases.

METHODS

The study cohort included 52 clinically healthy ZZ AATD individuals of 34 years of age, identified in the Swedish neonatal screening of 1972-1974, and 81 age-matched controls with normal MM AAT variant. We analyzed plasma levels of the enhanced liver fibrosis (ELF) panel, including plasma tissue inhibitor of metalloprotease-1, amino-terminal propeptide of type III collagen and hyaluronic acid (HA), and the M30 and M65 antigens, markers for apoptosis/necrosis.

RESULTS

Higher levels of tissue inhibitor of metalloprotease-1 (52%, P<0.001), amino-terminal propeptide of type III collagen (12%, P<0.05), HA (17% not significant), and M65 (13.4%, P=0.043) were found in ZZ than in MM patients. In the ZZ group, plasma levels of AAT correlated with M65 (P<0.01) and with HA (P<0.05). On the basis of the ELF panel, M30 and M65, a logistic regression model enabled us to correctly classify 81.2% of the originally grouped ZZ and MM cases with a sensitivity of 73.1% and a specificity of 86.4%.

CONCLUSION

The ELF markers are associated with ZZ AATD at early adulthood, and can be considered as a useful tool to identify ZZ cases at an increased risk of developing liver diseases later in life.