Reversal of liver cirrhosis: a desirable clinical outcome and its pathogenic background

Effect of different driver power amplitudes on liver stiffness measurement in pediatric liver MR elastography

PURPOSE

To assess how different driver power amplitudes affect the measurement of liver stiffness in pediatric liver magnetic resonance elastography (MRE).

METHODS

From January 2018 to May 2018, pediatric patients (≤ 18 years) who underwent liver MRE with 20% and 56% driver power amplitudes were included in this retrospective study. Region-of-interests (ROIs) were drawn on four stiffness maps to include the largest area of the liver parenchyma. Intraclass correlation coefficients (ICCs) were used to assess agreements for the area, mean, maximum, minimum and standard deviation of liver stiffness between the driver power amplitudes.

RESULTS

128 MRE stiffness maps from 16 patients (M:F = 10:6, median 12.5 years old) were included. On MRE, median ROI areas of liver were 83.1 cm² (range, 46.9-144.1 cm²) and 63.0 cm² (range, 5.4-123.4 cm²) for the driver power amplitudes of 20% and 56%, respectively. Median liver stiffness values were 2.3 kPa (range, 1.7-8.0 kPa) and 2.8 kPa (range, 1.7-8.5 kPa). Maximum and minimum liver stiffness values were 5.3 kPa and 1.0 kPa for 20% and 7.8 kPa and 1.1 kPa for 56%. Standard deviation was 0.6 kPa for 20% and 1.0 kPa for 56%. ICC values between the two power amplitudes were 0.33-0.51 for the ROI area and the maximum, minimum and standard deviation values of liver stiffness. The ICC value for liver stiffness was 0.857 (95% confidence interval, 0.760-0.915).

CONCLUSION

Liver stiffness with two driver power amplitudes on MRE showed good reliability in pediatric patients. Driver power amplitudes need to be optimized according to the pediatric liver size.

Astragaloside IV combating liver cirrhosis through the PI3K/Akt/mTOR signaling pathway

Astragaloside IV (AS-IV) in improving liver cirrhosis injury in rats and its effect on the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mechanistic target of rapamycin (mTOR) signaling pathway were observed. Rat model of liver cirrhosis was induced by injection of carbon tetrachloride (CCl₄). A total of 36 Sprague-Dawley (SD) rats were randomly divided into three groups: the normal control group (n=10), the model control group (n=13), and the AS-IV group (n=13). The normal control group was injected with olive oil and given carboxymethyl cellulose (CMC)-Na (10 ml/kg/day), the model control group was given CMC-Na (10 ml/kg/day), and the AS-IV group underwent intragastric administration of AS-IV (20 ml/kg/day). The content of alanine transaminase (ALT) and aspartate transaminase (AST) of rats was detected. The levels of tumor necrosis factor-α (TNF-α), interleukin (IL)-6 and IL-1β in serum were detected via enzyme-linked immunosorbent assay (ELISA). Hematoxylin and eosin (H&E) staining was applied to observe morphological changes in liver tissues. The expression of collagens in liver tissues was detected via Masson's trichrome staining. Additionally, the expression of proteins in liver tissues was detected via western blotting. Compared with those in the blank group, the levels of AST, ALT, TNF-α, IL-6 and IL-1β were higher, the expression level of collagens in liver tissues was increased, and the expression ratios of phosphorylated (p)-PI3K/PI3K, p-Akt/Akt and p-mTOR/mTOR proteins were increased in the model group. Compared with the model group, AS-IV could significantly decrease the content of AST, ALT, TNF-α, IL-6 and IL-β in serum of rats, obviously inhibit the expression of collagens in liver tissues and decrease the expression ratios of p-PI3K/PI3K, p-Akt/Akt and p-mTOR/mTOR proteins in liver tissues. AS-IV can inhibit the inflammatory response so as to reduce the expression of collagens, and its mechanism may play a key role by inhibiting the PI3K/Akt/mTOR signaling pathway.

Cholic acid for primary bile acid synthesis defects: a life-saving therapy allowing a favorable outcome in adulthood

Background

Oral cholic acid (CA) replacement has been shown to be an effective therapy in children with primary bile acid synthesis defects, which are rare and severe genetic liver diseases. To date there has been no report of the effects of this therapy in children reaching adulthood. The aim of the study was to evaluate the long-term effectiveness and safety of CA therapy.

Methods

Fifteen patients with either 3β-hydroxy-Δ⁵-C₂₇-steroid oxidoreductase (3β-HSD) (n = 13) or Δ⁴–3-oxosteroid 5β-reductase (Δ⁴–3-oxo-R) (n = 2) deficiency confirmed by mass spectrometry and gene sequencing received oral CA and were followed prospectively.

Results

The median age at last follow-up and the median time of follow-up with treatment were 24.3 years (range: 15.3–37.2) and 21.4 years (range: 14.6–24.1), respectively. At last evaluation, physical examination findings and blood laboratory test results were normal in all patients. Liver sonograms were normal in most patients. Mean daily CA dose was 6.9 mg/kg of body weight. Mass spectrometry analysis of urine showed that excretion of the atypical metabolites remained low or traces in amount with CA therapy. Liver fibrosis scored in liver biopsies or assessed by elastography in 14 patients, after 10 to 24 years with CA therapy, showed a marked improvement with disappearance of cirrhosis (median score < F1; range: F0-F2). CA was well tolerated in all patients, including five women having 10 uneventful pregnancies during treatment.

Conclusions

Oral CA therapy is a safe and effective long-term treatment of 3β-HSD and Δ⁴–3-oxo-R deficiencies and allows affected children to reach adulthood in good health condition without the need for a liver transplantation.

Regression of fibrosis in pediatric liver diseases

The concept of irreversibility of cirrhosis has been challenged in the recent past with literature in this regard, albeit still scarce, now being accumulated across all age groups, etiologies, and geographical regions. This small series of nine pediatric cases elegantly recapitulates the concept of regression of hepatic fibrosis/cirrhosis and paves way for further detailed studies to enable development of therapeutic anti-fibrotic modalities in future.

Correlating liver stiffness with disease severity scoring system (DS3) values in Gaucher disease type 1 (GD1) patients

Gaucher disease (GD) is an autosomal-recessive lysosomal storage disease caused by a deficiency of the enzyme, glucocerebrocidase, resulting in accumulation of lipid-laden storage cells in multiple organs such as bone marrow, liver, spleen, and lungs. Type 1 Gaucher disease is the most common form of this condition in which the brain and spinal cord (the central nervous system) are not affected. The Gaucher disease severity scoring system (GD-DS3) is typically used to assess disease severity accounting for skeletal, hematologic, and visceral disease. In addition to being time consuming for the clinician to calculate the scores, some of the assessments are subjective and may falsely increase or decrease disease severity. The purpose of this study was to determine if there is a correlation between liver stiffness values obtained from MR elastography (MRE) and the GD-DS3 score. An IRB approved, HIPAA compliant retrospective study was performed. All patients with type 1 GD imaged with MRE between 2011 and 2016 were included in this study. Clinical and imaging data was collected. Two pediatric radiologists analyzed MR images from abdomen and thigh studies independently to determine bone marrow involvement using a semi-quantitative scoring system with one reviewer analyzing a subset of studies to determine inter-observer reliability. The collected data was used to calculate a GD-DS3 score for all patients. GD-DS3 scores were compared with liver MRE stiffness values. Clinical MRE scores were plotted against GD-DS3 severity scores for 31 patients (15 males, 16 females; median age 27years, age range: 4-67years). The median GD-DS3 score was 4 (range: 1-10.1) and median MRE value was 2.43kPa (range: 1.30-5.20kPa). A significant positive correlation was found between MRE and GD-DS3 scores; Pearson's correlation coefficient value of r=0.47, p<0.001 for all scores, r=0.68, p<0.001 for complete scores and r=0.46, p<0.07 for incomplete scores. The inter-observer variation of bone marrow burden showed only fair agreement with a Kappa coefficient of 0.26. There is a significant positive correlation between increasing liver stiffness and increasing composite GD-DS3 scores. This supports the use of MRE, a non-invasive reproducible quantitative test, as both an additional assessment and independent marker for monitoring disease severity and progression in GD.

Gluten-Free hepatomiracle in "celiac hepatitis": A case highlighting the rare occurrence of nutrition-induced near total reversal of advanced steatohepatitis and cirrhosis

Regression of hepatic fibrosis is increasingly becoming a reality, both in clinical as well as experimental models. Reversal or near-total regression of marked liver steatohepatitis and fibrosis, however, remains a rare event. We report the case of a 20-year-old female presenting with diarrhea due to celiac disease and biopsy proven cirrhosis with portal hypertension who had a remarkable clinical improvement in response to a gluten free diet (GFD). A follow-up liver biopsy 9 months after the initiation of GFD revealed a remarkable regression of both fibrosis as well as steatosis. Villous atrophy, as seen in patients with celiac disease, could lead to a deprivation of trophic factors leading to liver injury and subsequent cirrhosis. A gluten-free dietary regimen can produce a reversal of fibrosis leading to the amelioration of symptoms associated even with advanced liver disease.

Natural regression of fibrosis in chronic hepatitis B

The fibrosis of liver cirrhosis was considered to be irreversible before the anti-viral drugs showed that it is reversible when they lead to continuous suppression of viral replication and inflammation. However, several reports previously showed that fibrosis of type B liver cirrhosis was almost completely absorbed after the natural remission of chronic inflammation. This phenomenon might not be limited to exceptional patients, but rather occur commonly, considering the dynamic clinical features of chronic hepatitis B (CHB), where inactive carrier stage normally follows aggravation of hepatitis and progression of fibrosis at the time of HBeAg seroconversion. Thus, fibrosis levels of CHB as a hepatocellular carcinoma (HCC)-surveillance marker, particularly those of the inactive stage, could be underestimated, because some of them might have been (pre)cirrhotic in the past and recovered with the natural regression of fibrosis. We argue that cirrhosis-induced HCC mechanisms, rather than direct action of viral genome, may be more common than generally considered in CHB patients. This may have some impact on reconsidering the surveillance rationale for HCC in CHB, from where advanced HCCs tended to be missed. In addition, a molecular marker to assess the cancer-prone characteristics of the liver will definitely be needed to resolve the issue.

Cross-vendor validation of liver magnetic resonance elastography

PURPOSE

To evaluate and validate the reproducibility of MR Elastography (MRE)-derived liver stiffness values on two different MR vendor platforms performed on the same subject on the same day.

METHODS

This investigation was approved by the hospital IRB. MRE exams were performed twice in identical fashion in eight volunteers and in five clinical patients on two different 1.5 T MR scanners-once on a Philips MR scanner and immediately afterward in back-to-back fashion on a General Electric MR scanner, or vice versa. All scan parameters were kept identical on the two platforms to the best extent possible. After the MRE magnitude and phase images were obtained, the data were converted into quantitative images displaying the stiffness of the liver parenchyma. Mean liver stiffness values between the two platforms were compared using interclass correlation with a p value <0.05 considered statistically significant.

RESULTS

Interclass correlation coefficient (ICC) value of 0.994 was obtained for 13 subjects with p value <0.001 indicating a significantly positive correlation.

CONCLUSION

As MRE gains in acceptance and as its availability becomes more widespread, it is important to ascertain and confirm that liver stiffness values obtained on different MRE vendor platforms are consistent and reproducible. In this small pilot investigation, we demonstrate that liver stiffness measurement with MRE is reproducible and has very good consistency across two vendor platforms.

Magnetic resonance imaging of the pediatric liver: imaging of steatosis, iron deposition, and fibrosis

Traditionally, many diffuse diseases of the liver could only be diagnosed by liver biopsy. Although still considered the gold standard, liver biopsy is limited by its small sample size, invasive nature, and subjectivity of interpretation. There have been significant advances in functional magnetic resonance (MR) imaging of the liver. These advances now provide radiologists with the tools to evaluate the liver at the molecular level, allowing quantification of hepatic fat and iron, and enabling the identification of liver fibrosis at its earliest stages. These methods provide objective measures of diffuse liver processes and aid hepatologists in the diagnosis and management of liver disease.

Regression effect of hepatocyte nuclear factor 4α on liver cirrhosis in rats

OBJECTIVE

The aim of this study was to determine whether cirrhosis could be reversed after treated with hepatocyte nuclear factor 4α (HNF4α), a key transcriptional regulator of hepatocyte differentiation and function.

METHODS

Early and advanced stages of liver cirrhosis were induced by thioacetamide (TAA) administration. The adenovirus carrying HNF4α gene was injected into cirrhotic rats via the tail vein. The effect of HNF4α on cirrhosis was evaluated by histological and immunohistochemical examination.

RESULTS

Early stage of cirrhosis was remarkably resolved by HNF4α to a nearly-normal extent and advanced cirrhosis was partially ameliorated in vivo. The enforced expression of HNF4α downregulated profibrogenic factors remarkably including α-smooth muscle actin (α-SMA), transforming growth factor (TGF)-β1, fibroblast-specific protein (FSP)-1, collagen I and III. In vivo and in vitro studies revealed that HNF4α administration inhibited extracellular signal-regulated kinase (ERK) signaling pathway through the downregulation of phosphorated ERK and phosphorated JunD. In addition, HNF4α readjusted the balance between extracellular matrix deposition and degradation through the upregulation of matrix metalloproteinase and downregulation of its inhibitors. Moreover, HNF4α treatment inhibited angiogenesis as determined by CD31 and CD34 immunostaining.

CONCLUSIONS

Our findings broaden the knowledge on the reversibility of different stages of cirrhosis as HNF4α could present a promising alternative for the treatment of liver cirrhosis.

Pediatric liver MR elastography

INTRODUCTION

Many chronic pediatric liver disorders are complicated by the development of fibrosis and ultimately cirrhosis. Although hepatic fibrogenesis progresses along a common pathway irrespective of the specific etiology, fibrosis in pediatric liver diseases has different histopathological patterns than in adults. In pediatric liver disease, as in adults, management choices may depend upon the stage of fibrosis at diagnosis. With early intervention, the progression of hepatic fibrosis can be slowed or halted, and in some situations, reversed. While liver biopsy is the gold standard for diagnosing and assessing the presence and degree of fibrosis, it has several disadvantages including the potential for sampling error, the risk of complications, the relatively high cost, and general poor acceptance by pediatric patients and their parents. MR elastography (MRE) is a relatively new imaging technique with the potential for allowing a safe, rapid, cost-effective, and non-invasive evaluation of a wide variety of hepatic diseases by quantitatively evaluating the stiffness of the liver parenchyma. The purpose of this article is to present our initial clinical experience and illustrate our modified technique for the application of liver MRE in pediatric patients at our medical center.

METHODS AND MATERIALS

Pediatric MRE techniques were developed and applied to over 45 patients scanned with our new protocol.

CONCLUSION

Liver MRE is a safe, non-invasive method for assessing hepatic fibrosis in pediatric patients.

Quantitative evaluation of liver cirrhosis using T1 relaxation time with 3 tesla MRI before and after oxygen inhalation

PURPOSE

To quantify liver T1 relaxation times before and after oxygen inhalation in patients with and without liver cirrhosis using a 3 Tesla (T) MRI.

MATERIALS AND METHODS

Institutional Review Board approval and written informed consent were obtained. Ninety-two noncirrhotic patients and 87 patients with hepatitis B viral liver cirrhosis (72 Child-Pugh class A and 15 Child-Pugh class B or C) underwent MRI with a 3.0T system before and after the supply of 100% oxygen at a rate of 15 L/min by means of a nonrebreather ventilation mask for 3 min. T1 maps were acquired using three-dimensional spoiled gradient echo sequences with two different flip angles (2° and 14°) and a fixed TR/TE (2.54 ms/0.95 ms). Liver T1 values were obtained using a T1 processing tool (MapIT software). The mean baseline T1 values of three groups (control, Child-Pugh class A, and Child-Pugh class B/C) were compared using an analysis of variance test. Liver T1 value before and after oxygenation was compared using a paired t-test for each group.

RESULTS

The baseline liver T1 value was significantly higher in the control group (941 ± 136 ms) than in Child-Pugh A (858 ± 143 ms) and Child-Pugh B/C (783 ± 164 ms) group (P < 0.001 and P < 0.0001). The reduction in the liver T1 value after oxygen inhalation was significant in the control group (P = 0.012) but not significant in Child-Pugh class A (P = 0.079) and Child-Pugh class B/C (P = 0.752).

CONCLUSION

The baseline liver T1 relaxation time was significantly different between the patients with and without liver cirrhosis. The shortening effect of oxygen on the liver T1 value was significant in the control group but not in the cirrhotic patients.

Reversal of hepatic fibrosis: pathophysiological basis of antifibrotic therapies

Chronic liver injuries of different etiologies eventually lead to fibrosis, a scarring process associated with increased and altered deposition of extracellular matrix in the liver. Progression of fibrosis has a major worldwide clinical impact due to the high number of patients affected by chronic liver disease which can lead to severe complications, expensive treatment, a possible need for liver transplantation, and death. Liver fibrogenesis is characterized by activation of hepatic stellate cells and other extracellular matrix producing cells. Liver fibrosis may regress following specific therapeutic interventions. Other than removing agents causing chronic liver damage, no antifibrotic drug is currently available in clinical practice. The extent of liver fibrosis is variable between individuals, even after controlling for exogenous factors. Thus, host genetic factors are considered to play an important role in the process of liver scarring. Until recently it was believed that this process was irreversible. However, emerging experimental and clinical evidence is starting to show that even cirrhosis in its early stages is potentially reversible.

Reversal of hepatic fibrosis: pathophysiological basis of antifibrotic therapies

Chronic liver injuries of different etiologies eventually lead to fibrosis, a scarring process associated with increased and altered deposition of extracellular matrix in the liver. Progression of fibrosis has a major worldwide clinical impact due to the high number of patients affected by chronic liver disease which can lead to severe complications, expensive treatment, a possible need for liver transplantation, and death. Liver fibrogenesis is characterized by activation of hepatic stellate cells and other extracellular matrix producing cells. Liver fibrosis may regress following specific therapeutic interventions. Other than removing agents causing chronic liver damage, no antifibrotic drug is currently available in clinical practice. The extent of liver fibrosis is variable between individuals, even after controlling for exogenous factors. Thus, host genetic factors are considered to play an important role in the process of liver scarring. Until recently it was believed that this process was irreversible. However, emerging experimental and clinical evidence is starting to show that even cirrhosis in its early stages is potentially reversible.

Liver fibrosis in paediatric liver diseases

Numerous paediatric liver diseases from different origins may be complicated by development of liver fibrosis and progression to cirrhosis. Although fibrogenesis, which represents a major driving force for the development of liver fibrosis, has common tracts whatever the aetiology, liver fibrosis has different histopathological patterns in paediatric liver disease. In these diseases management choices may depend upon the stage of liver fibrosis. Thus, the accurate estimation of histological pattern of liver fibrosis is important for the prevention of the subsequent complications. Liver biopsy has long been considered as a gold standard diagnostic method for assessing liver fibrosis. However, due to its several disadvantages, in the last decades alternative and accurate non-invasive means to estimate fibrosis are developed. In this review, we characterised the most frequent histological patterns of liver fibrosis in paediatric liver diseases. Furthermore, we describe use of liver biopsy in diagnosis and staging of liver fibrosis, list the alternative non-invasive techniques that have an emerging role in the assessment of liver fibrosis, and propose a management algorithm.

[Reversibility of hepatitis B virus-induced liver cirrhosis after prolonged antiviral therapy]

Reversibility of liver fibrosis or cirrhosis involves complete restoration of normal liver architecture. This phenomenon has been well documented in chronic liver diseases such as autoimmune hepatitis, biliary obstruction, hemochromatosis, nonalcoholic steatohepatitis, and viral hepatitis. There are very few reports of reversal of cirrhosis after antiviral therapy in patients with chronic hepatitis B virus (HBV) infection. We report a case of disappearance of HBV-induced liver cirrhosis after years of treatment with distinct antiviral drugs, documented by successive biopsy results. This disappearance was accompanied by normalization of platelet count, gammaglobulin titers, and radiologic findings.

Hepatic stellate cell activation and hepatic fibrosis in children with type 1 autoimmune hepatitis: an immunohistochemical study of paired liver biopsies before treatment and after clinical remission

OBJECTIVES

The activation of hepatic stellate cells (HSC) is considered the most important event in hepatic fibrogenesis. The precise mechanism of this process is unknown in autoimmune hepatitis (AIH), and more evidence is needed on the evolution of fibrosis. The aim of this study was to assess these aspects in children with type 1 AIH.

METHODS

We analyzed 16 liver biopsy samples from eight patients, paired before treatment and after clinical remission, performed an immunohistochemical study with anti-alpha actin smooth muscle antibody and graded fibrosis and inflammation on a scale of 0-4 (Batts and Ludwig scoring system).

RESULTS

There was no significant reduction in fibrosis scores after 24+/-18 months (2.5+/-0.93 vs. 2.0+/-0.53, P=0.2012). There was an important decrease in inflammation: portal (2.6+/-0.74 vs. 1.3+/-0.89, P=0.0277), periportal/periseptal (3.0+/-0.76 vs. 1.4+/-1.06, P=0.0277), and lobular (2.8+/-1.04 vs. 0.9+/-0.99, P=0.0179). Anti-alpha actin smooth muscle antibodies were expressed in the HSC of the initial biopsies (3491.93+/-2051.48 mum), showing a significant reduction after remission (377.91+/-439.47 microm) (P=0.0117).

CONCLUSION

HSC activation was demonstrated in the AIH of children. The reduction of this activation after clinical remission, which may precede a decrease in fibrosis, opens important perspectives in the follow-up of AIH.

Oral cholic acid for hereditary defects of primary bile acid synthesis: a safe and effective long-term therapy

BACKGROUND & AIMS

Oral bile acid replacement has been shown to be an effective therapy in primary bile acid synthesis defects, but to date there have been no reports of the long-term effects of this therapy. The aim of the study was to evaluate the long-term effectiveness and safety of cholic acid (CA) therapy.

METHODS

Fifteen patients with either 3beta-hydroxy-Delta(5)-C(27)-steroid oxidoreductase (3beta-HSD) (n = 13) or Delta(4)-3-oxosteroid 5beta-reductase (Delta(4)-3-oxo-R) (n = 2) deficiency confirmed by mass spectrometry and gene sequencing received oral CA and were followed up prospectively.

RESULTS

CA therapy was started at a median age of 3.9 years (range, 0.3-13.1 years). The median follow-up with treatment was 12.4 years (range, 5.6-15 years). The mean daily dose of CA was initially 13 mg/kg and was 6 mg/kg at last evaluation. During CA therapy, physical examination findings, laboratory test results, and findings on sonography normalized. Mass spectrometry analysis of urine showed that excretion of the atypical metabolites was reduced by 500-fold and 30-fold in 3beta-HSD and Delta(4)-3-oxo-R deficiency, respectively, and total urinary bile acid excretion decreased dramatically. Liver biopsies performed in 14 patients after at least 5 years of CA therapy showed marked improvement, especially in patients with the 3beta-HSD deficiency. CA was well tolerated with all children developing normally, including 2 women having 4 normal pregnancies during treatment.

CONCLUSIONS

Oral CA therapy is a safe and effective long-term treatment of the most common primary bile acid synthesis defects.

Bone marrow stromal cells control the growth of hepatic stellate cells in vitro

Liver cirrhosis is characterized by hepatic dysfunction, with extensive accumulation of fibrous tissue in the liver. Hepatic stellate cells (HSCs) are the major source of fibrillar matrix proteins and play an important role in the progress of liver cirrhosis. In our study, the growth of HSCs is inhibited by bone marrow stromal cells (BMSCs). The inhibition is irreversible and is followed by apoptosis. The effect of BMSCs on the apoptosis of HSCs is possibly via the JNK pathway activated by nerve growth factor (NGF) and hepatocyte growth factor (HGF) secreted by BMSCs. Meanwhile, the apoptosis effect is enhanced by transforming growth factor-beta blocking.

The case for combination antiviral therapy for chronic hepatitis B virus infection

The treatment of hepatitis B virus (HBV) infection has been revolutionised in the past decade by the increased availability of effective antiviral agents. Many studies have shown the benefits of single agent therapy, but there is an alarming and rising rate of viral resistance, and clear evidence that viruses that harbour resistant mutations can cause liver disease and death. Current national guidelines for the treatment of HBV recommend a programme that starts with monotherapy, followed by sequential monotherapy or add-on therapy for those infections in which mutations have arisen. Very few studies starting with combination therapy have been undertaken, so there is little evidence of the clinical benefit of this approach to treatment. The studies that have been done have been short term and have concentrated on clinical parameters rather than virological resistance, which is likely to be the key determinant in the longer term. We argue that we should not wait for the evidence to use combination therapy for the treatment of HBV, since such trials may never be done and it would take several years for a benefit to become apparent. In the meantime, multidrug-resistant strains continue to hinder HBV control.