Induction of endoplasmic reticulum-derived oxidative stress by an occult infection related S surface antigen variant

Preliminary analysis of the role of small hepatitis B surface proteins mutations in the pathogenesis of occult hepatitis B infection via the endoplasmic reticulum stress-induced UPR-ERAD pathway

A growing body of evidence has shown that hepatitis B surface antigen (HBsAg) mutations can influence the occurrence of occult hepatitis B infection (OBI), particularly amino acid substitutions in small hepatitis B surface proteins (SHBs). The mechanistic basis for these results, however, remains unclear. This study was designed to explore the potential impact and mechanisms of OBI-related SHBs mutations on serum HBsAg. Huh7 and HepG2 cells were transfected with plasmids encoding wild-type (WT) or OBI-related SHB mutation-containing sequences, after which a chemiluminescence approach was used to detect HBsAg levels in cell culture supernatants. Western blotting was further used to assess HBsAg and endoplasmic reticulum stress (ERS)-related protein levels in lysates prepared from these cells, while the localization of HBsAg within cells was assessed via immunofluorescent staining. Cells transfected with OBI-related SHB mutation-encoding plasmids exhibited lower supernatant HBsAg levels than cells transfected with WT plasmids. Intracellular and extracellular HBsAg levels in these mutant plasmid-transfected cells were lower relative to those for WT plasmid-transfected cells, and HBsAg accumulation within the ER was detected via immunofluorescent staining in cells transfected with OBI-related SHB mutation-encoding plasmids, ERS-related protein content was also significantly increased in mutant plasmid-transfected cells as compared to those in the WT group. These results suggest that proteins harboring OBI-related mutations may tend to accumulate in the ER, thereby triggering an ERS response and impairing the transcription and translation of HBsAg via the activation of the unfolded protein response and ER-associated protein degradation pathway. These effects ultimately reduce the overall assembly of HBV virions in the ER and their associated secretion.

Inherent symmetry and flexibility in hepatitis B virus subviral particles

Chronic hepatitis B virus (HBV) infection poses a major global health challenge with massive morbidity and mortality. Despite a preventive vaccine, current treatments provide limited virus clearance, necessitating lifelong commitment. The HBV surface antigen (HBsAg) is crucial for diagnosis and prognosis, yet its high-resolution structure and assembly on the virus envelope remain elusive. Utilizing extensive datasets and advanced cryo-electron microscopy analysis, we present structural insights into HBsAg at a near-atomic resolution of 3.7 angstroms. HBsAg homodimers assemble into subviral particles with D2- and D4-like quasisymmetry, elucidating the dense-packing rules and structural adaptability of HBsAg. These findings provide insights into how HBsAg assembles into higher-order filaments and interacts with the capsid to form virions.

Mitochondrial Oxidative Phosphorylation in Viral Infections

Mitochondria have been identified as the "powerhouse" of the cell, generating the cellular energy, ATP, for almost seven decades. Research over time has uncovered a multifaceted role of the mitochondrion in processes such as cellular stress signaling, generating precursor molecules, immune response, and apoptosis to name a few. Dysfunctional mitochondria resulting from a departure in homeostasis results in cellular degeneration. Viruses hijack host cell machinery to facilitate their own replication in the absence of a bonafide replication machinery. Replication being an energy intensive process necessitates regulation of the host cell oxidative phosphorylation occurring at the electron transport chain in the mitochondria to generate energy. Mitochondria, therefore, can be an attractive therapeutic target by limiting energy for viral replication. In this review we focus on the physiology of oxidative phosphorylation and on the limited studies highlighting the regulatory effects viruses induce on the electron transport chain.

Oxidative stress sensor Keap1 recognizes HBx protein to activate the Nrf2/ARE signaling pathway, thereby inhibiting hepatitis B virus replication

IMPORTANCE

The Kelch-like ECH-associated protein 1 (Keap1)/NF-E2-related factor 2 (Nrf2)/antioxidant response element (ARE) signaling pathway is one of the most important defense mechanisms against oxidative stress. We previously reported that a cellular hydrogen peroxide scavenger protein, peroxiredoxin 1, a target gene of transcription factor Nrf2, acts as a novel HBV X protein (HBx)-interacting protein and negatively regulates hepatitis B virus (HBV) propagation through degradation of HBV RNA. This study further demonstrates that the Nrf2/ARE signaling pathway is activated during HBV infection, eventually leading to the suppression of HBV replication. We provide evidence suggesting that Keap1 interacts with HBx, leading to Nrf2 activation and inhibition of HBV replication via suppression of HBV core promoter activity. This study raises the possibility that activation of the Nrf2/ARE signaling pathway is a potential therapeutic strategy against HBV. Our findings may contribute to an improved understanding of the negative regulation of HBV replication by the antioxidant response.

Antioxidants and Calcium Modulators Preclude in Vitro Hepatitis B Virus-Induced Mitochondrial Damage

BACKGROUND/AIMS

Hepatitis B virus induces mitochondrial damage via the production of reactive oxygen species and concomitant with deregulation of calcium homeostasis. The current study evaluates the potential of antioxidant and calcium modulators for inhibition of hepatitis B virus-induced mitochondrial damage using in vitro cell culture models.

MATERIALS AND METHODS

Hepatitis B virus-induced mitochondrial fragmentation was observed by immunofluorescence confocal micros- copy in hepatitis B virus-infected cell lines (HepG2 and HepAD38). Differential protein expression of mitochondrial fragmentation mark- ers, dynamin-related protein 1 and phospho-dynamin-related protein 1, were evaluated both pre- and posttreatment with antioxidant N-acetyl-l-cysteine and calcium modulators like 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakisacetoxymethyl ester, ethylene-bis (oxyethylenenitrilo) tetraacetic acid glycol ether diamine tetraacetic acid-acetoxymethyl ester, and ruthenium amine complex by western blot analysis.

RESULTS

A slight reduction in mitochondrial fragmentation in both cell lines was observed post-antioxidant treatment with a partial prevention observed with calcium modulators. The expression of phospho-dynamin-related protein 1 was significantly upregulated (P = .0007, P = .003) in both hepatitis B virus-infected cell lines compared to uninfected cells. In line with these observations, the expres- sion of dynamin-related protein 1 and phospho-dynamin-related protein 1 was found to be significantly downregulated with N-acetyl- l-cysteine treatment in both cell lines (P = .003, P = .002), respectively. A nonsignificant trend was observed in the case of calcium modulators treatment.

CONCLUSIONS

Current study indicates that the mitochondrial fragmentation induced by hepatitis B virus infection can be reduced after antioxidant treatment pointing toward exploring better drug targets for the prevention of hepatitis B virus-induced mitochondrial frag- mentation and associated liver damage.

Small Hepatitis B Virus Surface Antigen Promotes Hepatic Gluconeogenesis via Enhancing Glucagon/cAMP/Protein Kinase A/CREB Signaling

Hepatitis B virus (HBV) is a major risk factor for serious liver diseases. The liver plays a unique role in controlling carbohydrate metabolism to maintain the glucose level within the normal range. Chronic HBV infection has been reported to associate with a high prevalence of diabetes. However, the detailed molecular mechanism underlying the potential association remains largely unknown. Here, we report that liver-targeted delivery of small HBV surface antigen (SHBs), the most abundant viral protein of HBV, could elevate blood glucose levels and impair glucose and insulin tolerance in mice by promoting hepatic gluconeogenesis. Hepatocytes with SHB expression also exhibited increased glucose production and expression of gluconeogenic genes glucose-6-phosphatase (G6pc) and phosphoenolpyruvate carboxykinase (PEPCK) in response to glucagon stimulation. Mechanistically, SHBs increased cellular levels of cyclic AMP (cAMP) and consequently activated protein kinase A (PKA) and its downstream effector cAMP-responsive element binding protein (CREB). SHBs-induced activation of CREB enhanced transcripts of gluconeogenic genes, thus promoting hepatic gluconeogenesis. The elevated cAMP level resulted from increased transcription activity and expression of adenylyl cyclase 1 (AC1) by SHBs through a binary E-box factor binding site (BEF). Taken together, we unveiled a novel pathogenic role and mechanism of SHBs in hepatic gluconeogenesis, and these results might highlight a potential target for preventive and therapeutic intervention in the development and progression of HBV-associated diabetes. IMPORTANCE Chronic HBV infection causes progressive liver damage and is found to be a risk factor for diabetes. However, the mechanism in the regulation of glucose metabolism by HBV remains to be established. In the current study, we demonstrate for the first time that the small hepatitis B virus surface antigen (SHBs) of HBV elevates AC1 transcription and expression to activate cAMP/PKA/CREB signaling and subsequently induces the expression of gluconeogenic genes and promotes hepatic gluconeogenesis both in vivo and in vitro. This study provides a direct link between HBV infection and diabetes and implicates that SHBs may represent a potential target for the treatment of HBV-induced metabolic disorders.

Signaling Induced by Chronic Viral Hepatitis: Dependence and Consequences

Chronic viral hepatitis is a main cause of liver disease and hepatocellular carcinoma. There are striking similarities in the pathological impact of hepatitis B, C, and D, although these diseases are caused by very different viruses. Paired with the conventional study of protein-host interactions, the rapid technological development of -omics and bioinformatics has allowed highlighting the important role of signaling networks in viral pathogenesis. In this review, we provide an integrated look on the three major viruses associated with chronic viral hepatitis in patients, summarizing similarities and differences in virus-induced cellular signaling relevant to the viral life cycles and liver disease progression.

Hepatitis B virus small envelope protein promotes HCC angiogenesis via ER stress signaling to upregulate VEGFA expression

Hepatocellular carcinoma (HCC) is a hypervascular tumor and accumulating evidence has indicated that stimulation of angiogenesis by HBV may contribute to HCC malignancy. The small protein of hepatitis B virus surface antigen (HBsAg), SHBs, is the most abundant HBV viral protein and has a close clinical association with HCC, however, whether SHBs contributes to HCC angiogenesis remains unknown. This study reports that forced expression of SHBs in HCC cells promoted xenograft tumor growth and increased the microvessel density (MVD) within the tumors. Consistently, HBsAg was also positively correlated with MVD count in HCC patients' specimens. The conditioned media from the SHBs-transfected HCC cells increased the capillary tube formation and migration of human umbilical vein endothelial cells (HUVECs). Intriguingly, overexpression of SHBs increased VEGFA expression at both mRNA and protein levels. A higher VEGFA expression level was also observed in the xenograft tumors transplanted with SHBs-expressing HCC cells and in HBsAg-positive HCC tumor tissues as compared to their negative controls. As expected, in the culture supernatants, the secretion of VEGFA was also significantly enhanced from HCC cells expressing SHBs, which promoted HUVECs migration and vessel formation. Furthermore, all the three unfolded protein response (UPR) sensors IRE1α, PERK and ATF6 associated with endoplasmic reticulum (ER) stress were found activated in the SHBs-expressing cells and correlated with VEGFA protein expression and secretion. Taken together, these results suggest an important role of SHBs in HCC angiogenesis and may highlight a potential target for preventive and therapeutic intervention of HBV-related HCC and its malignant progression. IMPORTANCE Chronic hepatitis B virus infection is one of the important risk factors for the development and progression of hepatocellular carcinoma (HCC). HCC is characteristic of hypervascularization even at early phases of the disease due to overexpression of angiogenic factors like vascular endothelial growth factor-A (VEGFA). However, a detailed mechanism in the HBV-induced angiogenesis remains to be established. In this study, we demonstrate for the first time that the most abundant HBV viral protein, i.e. small surface antigens (SHBs) can enhance the angiogenic capacity of HCC cells by upregulation of VEGFA expression both in vitro and in vivo. Mechanistically, SHBs induced endoplasmic reticulum (ER) stress which consequently activated unfolded protein response (UPR) signaling to increase VEGFA expression and secretion. This study suggests that SHBs plays an important pro-angiogenic role in HBV-associated HCC and may represent a potential target for anti-angiogenic therapy in the HCC.

Dysregulation of host cell calcium signaling during viral infections: Emerging paradigm with high clinical relevance

Viral infections are one of the leading causes of human illness. Viruses take over host cell signaling cascades for their replication and infection. Calcium (Ca2+) is a versatile and ubiquitous second messenger that modulates plethora of cellular functions. In last two decades, a critical role of host cell Ca2+ signaling in modulating viral infections has emerged. Furthermore, recent literature clearly implicates a vital role for the organellar Ca2+ dynamics (influx and efflux across organelles) in regulating virus entry, replication and severity of the infection. Therefore, it is not surprising that a number of viral infections including current SARS-CoV-2 driven COVID-19 pandemic are associated with dysregulated Ca2+ homeostasis. The focus of this review is to first discuss the role of host cell Ca2+ signaling in viral entry, replication and egress. We further deliberate on emerging literature demonstrating hijacking of the host cell Ca2+ dynamics by viruses. In particular, a variety of viruses including SARS-CoV-2 modulate lysosomal and cytosolic Ca2+ signaling for host cell entry and replication. Moreover, we delve into the recent studies, which have demonstrated the potential of several FDA-approved drugs targeting Ca2+ handling machinery in inhibiting viral infections. Importantly, we discuss the prospective of targeting intracellular Ca2+ signaling for better management and treatment of viral pathogenesis including COVID-19. Finally, we highlight the key outstanding questions in the field that demand critical and timely attention.

In Vitro Analysis of the Antioxidant and Antiviral Activity of Embelin against Herpes Simplex Virus-1

Herpes simplex virus-1 (HSV-1) causes a wide range of infections from mild to life-threatening in the human population. There are effective treatments for HSV-1 infections that are limited due HSV-1 latency and development of resistance to current therapeutics. The goal of this study was to investigate the antioxidant and antiviral effects of embelin on HSV-1 in cultured Vero cells. Oxidative stress was verified by an extensive production of a reactive oxygen species (ROS) H2O2. Vero cells were infected with a recombinant strain of HSV-1 and antiviral assays, time course attachment, penetration, and post penetration assays, confocal microscopy, qPCR, and antioxidant assays were conducted. Our results lead to the conclusion that embelin is noncytotoxic at concentrations tested ranging from 20 to 70 µM. Treatment of HSV-1 virions with embelin resulted in 98.7-100% inhibition and affected the early stage of HSV-1 infection of Vero cells, by inhibiting the attachment and penetration of HSV-1 virions to host cells. Treatment of virions with concentrations of embelin ranging from 35 to 60 µM significantly reduced the production of H2O2. In conclusion, embelin reduces oxidative damage caused by HSV-1 infection and is an effective antiviral to reduce the infection of HSV-1 in cultured Vero cells. Further studies are needed to explore the possibility of embelin as a medicinal agent.

Small hepatitis B virus surface antigen promotes malignant progression of hepatocellular carcinoma via endoplasmic reticulum stress-induced FGF19/JAK2/STAT3 signaling

Chronic hepatitis B virus (HBV) infection is one of the major global health problems. Although the small protein of hepatitis B virus surface antigen (HBsAg), SHBs, is the most abundant HBV viral protein, its pathogenic role and molecular mechanism in malignant progression of HBV-related hepatocellular carcinoma (HCC) remain largely unknown. Here we reported that SHBs expression induced epithelial-mesenchymal transition (EMT) process in HCC cells and significantly increased their migratory and invasive ability as well as metastatic potential. Mechanistically, SHBs expression in HCC cells induced endoplasmic reticulum (ER) stress that activated the activating transcription factor 4 (ATF4) to increase the expression and secretion of fibroblast growth factor 19 (FGF19). The autocrine released FGF19 in turn activated JAK2/STAT3 signaling for induction of EMT process in HCC. Notably, SHBs was positively correlated with the expression of mesenchymal markers, the phosphorylation status of JAK2 and STAT3 as well as FGF19 levels in human HCC samples. HCC patients with SHBs positive had a more advanced clinical stage and worse prognosis. These results suggest an important role of SHBs in the metastasis and progression of HCC and may highlight a potential target for preventive and therapeutic intervention of HBV-related HCC and its malignant progression.

Redox-Modulating Agents in the Treatment of Viral Infections

Viruses use cell machinery to replicate their genome and produce viral proteins. For this reason, several intracellular factors, including the redox state, might directly or indirectly affect the progression and outcome of viral infection. In physiological conditions, the redox balance between oxidant and antioxidant species is maintained by enzymatic and non-enzymatic systems, and it finely regulates several cell functions. Different viruses break this equilibrium and induce an oxidative stress that in turn facilitates specific steps of the virus lifecycle and activates an inflammatory response. In this context, many studies highlighted the importance of redox-sensitive pathways as novel cell-based targets for therapies aimed at blocking both viral replication and virus-induced inflammation. In the review, we discuss the most recent findings in this field. In particular, we describe the effects of natural or synthetic redox-modulating molecules in inhibiting DNA or RNA virus replication as well as inflammatory pathways. The importance of the antioxidant transcription factor Nrf2 is also discussed. Most of the data reported here are on influenza virus infection. We believe that this approach could be usefully applied to fight other acute respiratory viral infections characterized by a strong inflammatory response, like COVID-19.

Flaviviridae Viruses and Oxidative Stress: Implications for Viral Pathogenesis

Oxidative stress is induced once the balance of generation and neutralization of reactive oxygen species (ROS) is broken in the cell, and it plays crucial roles in a variety of natural and diseased processes. Infections of Flaviviridae viruses trigger oxidative stress, which affects both the cellular metabolism and the life cycle of the viruses. Oxidative stress associated with specific viral proteins, experimental culture systems, and patient infections, as well as its correlations with the viral pathogenesis attracts much research attention. In this review, we primarily focus on hepatitis C virus (HCV), dengue virus (DENV), Zika virus (ZIKV), Japanese encephalitis virus (JEV), West Nile virus (WNV), and tick-borne encephalitis virus (TBEV) as representatives of Flaviviridae viruses and we summarize the mechanisms involved in the relevance of oxidative stress for virus-associated pathogenesis. We discuss the current understanding of the pathogenic mechanisms of oxidative stress induced by Flaviviridae viruses and highlight the relevance of autophagy and DNA damage in the life cycle of viruses. Understanding the crosstalk between viral infection and oxidative stress-induced molecular events may offer new avenues for antiviral therapeutics.

Naturally Occurring Hepatitis B Virus Mutations Leading to Endoplasmic Reticulum Stress and Their Contribution to the Progression of Hepatocellular Carcinoma

Hepatitis B virus (HBV) infection is a global health problem that causes a wide range of pathological outcomes, including cirrhosis and hepatocellular carcinoma (HCC). Endoplasmic reticulum (ER) stress induction by HBV infection has been implicated in liver carcinogenesis and disease progression with chronic inflammation via enhanced inflammation, oxidative stress-mediated DNA damage, and hepatocyte proliferation. In the natural course of HBV infection, the accumulation of naturally occurring mutations in the HBV genome can generate several mutant types of HBV-encoded proteins, including three different proteins in the S ORF (SHBs, MHBs, and LHBs) and HBcAg in the C ORF, which could contribute to enhanced ER stress in infected hepatocytes mainly via increased ER accumulation of mutant proteins. However, it seems that there may be distinct capacity and pathway in ER stress-induction and distinct resulting clinical outcomes between HBV variants. In addition, the role of HBxAg mutations in ER stress remains unknown. However, it has been reported that HBxAg itself could exert ER stress in infected cells, resulting in HCC generation in chronic HBV patients. To date, review papers regarding ER stress-mediated HBV mutation have been limited into a specific mutation type: preS2 deletion. So, in this review, we will discuss details about various mutation types in all four regions of the HBV genome (preS1, preS2, S, and C) related to ER stress and their distinct ER stress mechanisms and clinical outcomes in terms of mutation types.

SVCV impairs mitochondria complex Ⅲ resulting in accumulation of hydrogen peroxide

Spring viraemia of carp virus (SVCV) is a deadly pathogen of common carp. SVCV infection is found to be associated with excess reactive oxygen species (ROS) generation and induces oxidative stress in EPC and FHM cells, which contributes to its pathogenesis. In this study, ROS production and mitochondria function as well as antioxidant enzymes in mitochondria were investigated during SVCV infection in EPC cells. Dysfunction of mitochondria and inactivation of mitochondria electron transport chain complex Ⅲ to augment O₂^-∙ and H₂O₂ accumulation were observed in SVCV infected EPC cells. Treatment of Antimycin A reduced the activity of mitochondria complex Ⅲ in EPC cells, which also inhibited the transcription of SVCV glycoprotein gene (SVCV-G) and production of SVCV. Our studies explain the production of ROS following SVCV infection and also suggest that integrate mitochondrial function is important for SVCV infection.

Oxidative stress, a trigger of hepatitis C and B virus-induced liver carcinogenesis

Virally induced liver cancer usually evolves over long periods of time in the context of a strongly oxidative microenvironment, characterized by chronic liver inflammation and regeneration processes. They ultimately lead to oncogenic mutations in many cellular signaling cascades that drive cell growth and proliferation. Oxidative stress, induced by hepatitis viruses, therefore is one of the factors that drives the neoplastic transformation process in the liver. This review summarizes current knowledge on oxidative stress and oxidative stress responses induced by human hepatitis B and C viruses. It focuses on the molecular mechanisms by which these viruses activate cellular enzymes/systems that generate or scavenge reactive oxygen species (ROS) and control cellular redox homeostasis. The impact of an altered cellular redox homeostasis on the initiation and establishment of chronic viral infection, as well as on the course and outcome of liver fibrosis and hepatocarcinogenesis will be discussed The review neither discusses reactive nitrogen species, although their metabolism is interferes with that of ROS, nor antioxidants as potential therapeutic remedies against viral infections, both subjects meriting an independent review.

eNOS/iNOS and endoplasmic reticulum stress-induced apoptosis in the placentas of patients with preeclampsia

Disruption of nitric oxide pathway and endoplasmic reticulum (ER) stress had been observed in preeclampsia (PE). However, the correlation and overall detailed expression profiles of ER stress-related markers and endothelial nitric oxide synthase/inducible nitric oxide synthase (eNOS/iNOS) in patients with PE were poorly understood. In this study, placental protein expression of ER stress-related markers as well as eNOS/iNOS in normotensive control (n=32) and PE pregnancies (n=32) was examined by western blot. In addition, apoptosis was detected by terminal deoxynucleotidyl transferase-mediated nick-end labelling (TUNEL) staining in placentas. Compared with control, we found elevated ER stress response was agreeable with iNOS upregulation in placenta tissue of PE patients. Placental protein expression of ER stress-related markers, including GRP78, GRP94, p-PERK, eIF2a, p-eIF2a, XBP1, CHOP, Ire1, p-Ire1 and iNOS, was higher, and eNOS expression was lower in PE (P<0.05 for all); however, the expression of ATF6 and PERK was similar in the PE and control groups. Upregulation of CHOP and iNOS was consistent of apoptosis increasing indicated by TUNEL staining and caspase 4 expression upregulation in PE placenta. Our datas suggest that the exaggerated ER stress response and upregulated iNOS are probably associated with increased apoptosis in placenta of PE patients and may contribute to the pathophysiology of PE.

Hepatitis B Virus Middle Protein Enhances IL-6 Production via p38 MAPK/NF-κB Pathways in an ER Stress-Dependent Manner

During hepatitis B virus (HBV) infection, three viral envelope proteins of HBV are overexpressed in the endoplasmic reticulum (ER). The large S protein (LHBs) and truncated middle S protein (MHBs^t) have been documented to play roles in regulating host gene expression and contribute to hepatic disease development. As a predominant protein at the ultrastructural level in biopsy samples taken from viremic patients, the role of the middle S protein (MHBs) remains to be understood despite its high immunogenicity. When we transfected hepatocytes with an enhanced green fluorescent protein (EGFP)-tagged MHBs expressing plasmid, the results showed that expression of MHBs cause an upregulation of IL-6 at the message RNA and protein levels through activating the p38 mitogen-activated protein kinase (p38 MAPK) and nuclear factor-kappa B (NF-κB) pathways. The use of specific inhibitors of the signaling pathways can diminish this upregulation. The use of BAPTA-AM attenuated the stimulation caused by MHBs. We further found that MHBs accumulated in the endoplasmic reticulum and increased the amount of glucose regulated protein 78 (GRP78/BiP). Our results provide a possibility that MHBs could be involved in liver disease progression.

Association of preS/S Mutations with Occult Hepatitis B Virus (HBV) Infection in South Korea: Transmission Potential of Distinct Occult HBV Variants

Occult hepatitis B virus infection (HBV) is characterized by HBV DNA positivity but HBV surface antigen (HBsAg) negativity. Occult HBV infection is associated with a risk of HBV transmission through blood transfusion, hemodialysis, and liver transplantation. Furthermore, occult HBV infection contributes to the development of cirrhosis and hepatocellular carcinoma. We recently reported the characteristic molecular features of mutations in the preS/S regions among Korean individuals with occult infections caused by HBV genotype C2; the variants of preS and S related to severe liver diseases among chronically infected patients were also responsible for the majority of HBV occult infections. We also reported that HBsAg variants from occult-infected Korean individuals exhibit lower HBsAg secretion capacity but not reduced HBV DNA levels. In addition, these variants exhibit increased ROS-inducing capacity compared with the wild-type strain, linking HBV occult infections to liver cell damage. Taken together, our previous reports suggest the transmission potential of distinct HBV occult infection-related variants in South Korea.