Alexander Weymann

p21 is Required for Dextrose-Mediated Inhibition of Mouse Liver Regeneration

The inhibitory effect of dextrose supplementation on liver regeneration was first described more than 4 decades ago. Nevertheless, the molecular mechanisms responsible for this observation have not been elucidated. We investigated these mechanisms using the partial hepatectomy model in mice given standard or 10% dextrose (D10)‐supplemented drinking water. The results showed that D10‐treated mice exhibited significantly reduced hepatic regeneration compared with controls, as assessed by hepatocellular bromodeoxyuridine (BrdU) incorporation and mitotic frequency. D10 supplementation did not suppress activation of hepatocyte growth factor (HGF), induction of transforming growth factor alpha (TGF‐α) expression, or tumor necrosis factor alpha–interleukin‐6 cytokine signaling, p42/44 extracellular signal‐regulated kinase (ERK) activation, immediate early gene expression, or expression of CCAAT/enhancer binding protein beta (C/EBPβ), but did augment expression of the mito‐inhibitory factors C/EBPα, p21Waf1/Cip1, and p27Kip1. In addition, forkhead box M1 (FoxM1) expression, which is required for normal liver regeneration, was suppressed by D10 treatment. Finally, D10 did not suppress either FoxM1 expression or hepatocellular proliferation in p21 null mice subjected to partial hepatectomy, establishing the functional significance of these events in mediating the effects of D10 on liver regeneration. Conclusion: These data show that the inhibitory effect of dextrose supplementation on liver regeneration is associated with increased expression of C/EBPα, p21, and p27, and decreased expression of FoxM1, and that D10‐mediated inhibition of liver regeneration is abrogated in p21‐deficient animals. Our observations are consistent with a model in which hepatic sufficiency is defined by homeostasis between the energy‐generating capacity of the liver and the energy demands of the body mass, with liver regeneration initiated when the functional liver mass is no longer sufficient to meet such demand. (HEPATOLOGY 2009.)

Evidence for non-traditional activation of complement factor C3 during murine liver regeneration.

UNLABELLED Complement signaling has been implicated as important for normal hepatic regeneration. However, the specific mechanism by which complement is activated during liver regeneration remains undefined. To address this question, we investigated the hepatic regenerative response to partial hepatectomy in wildtype mice, C3-, C4-, and factor B-null mice, and C4-null mice treated with a factor B neutralizing antibody (mAb 1379). The results showed that following partial hepatectomy, C3-null mice exhibit reduced hepatic regeneration compared to wildtype mice as assessed by quantification of hepatic cyclin D1 expression and hepatocellular DNA synthesis and mitosis. In contrast, C4-null mice and factor B-null mice demonstrated normal liver regeneration. Moreover, animals in which all of the traditional upstream C3 activation pathways were disrupted, i.e. C4-null mice treated with mAb 1379, exhibited normal C3 activation and hepatocellular proliferation following partial hepatectomy. In order to define candidate non-traditional mechanisms of C3 activation during liver regeneration, plasmin and thrombin were investigated for their abilities to activate C3 in mouse plasma in vitro. The results showed that both proteases are capable of initiating C3 activation, and that plasmin can do so independent of the classical and alternative pathways. CONCLUSIONS These results show that C3 is required for a normal hepatic regenerative response, but that disruption of the classical- or lectin-dependent pathways (C4-dependent), the alternative pathway (factor B-dependent), or all of these pathways does not impair the hepatic regenerative response, and indicate that non-traditional mechanisms by which C3 is activated during hepatic regeneration must exist. In vitro analysis raises the possibility that plasmin may contribute to non-traditional complement activation during liver regeneration in vivo.

Liver regeneration is impaired in lipodystrophic fatty liver dystrophy mice

We previously reported that mice subjected to partial hepatectomy exhibit rapid development of hypoglycemia followed by transient accumulation of fat in the early regenerating liver. We also showed that disrupting these metabolic alterations results in impaired liver regeneration. The studies reported here were undertaken to further characterize and investigate the functional importance of changes in systemic adipose metabolism during normal liver regeneration. The results showed that a systemic catabolic response is induced in each of two distinct, commonly used experimental models of liver regeneration (partial hepatectomy and carbon tetrachloride treatment), and that this response occurs in proportion to the degree of induced hepatic insufficiency. Together, these observations suggest that catabolism of systemic adipose stores may be essential for normal liver regeneration. To test this possibility, we investigated the hepatic regenerative response in fatty liver dystrophy (fld) mice, which exhibit partial lipodystrophy and have diminished peripheral adipose stores. The results showed that the development of hypoglycemia and hepatic accumulation of fat was attenuated and liver regeneration was impaired following partial hepatectomy in these animals. The fld mice also exhibited increased hepatic p21 expression and diminished plasma levels of the adipose‐derived hormones adiponectin and leptin, which have each been implicated as regulators of liver regeneration. Conclusion: These data suggest that the hypoglycemia that develops after partial hepatectomy induces systemic lipolysis followed by accumulation of fat derived from peripheral stores in the early regenerating liver, and that these events may be essential for initiation of normal liver regeneration. (HEPATOLOGY 2010)

Biliary strictures in pediatric liver transplant recipients – Early diagnosis and treatment results in excellent graft outcomes

Anderson CD, Turmelle YP, Darcy M, Shepherd RW, Weymann A, Nadler M, Guelker S, Chapman WC, Lowell JA. Biliary strictures in pediatric liver transplant recipients – Early diagnosis and treatment results in excellent graft outcomes.
Pediatr Transplantation 2010: 14:358–363.

Analysis of the role of hepatic PPARγ expression during mouse liver regeneration

Mice subjected to partial hepatectomy (PH) develop hypoglycemia, followed by increased systemic lipolysis and hepatic fat accumulation, prior to onset of hepatocellular proliferation. Strategies that disrupt these metabolic events inhibit regeneration. These observations suggest that alterations in metabolism in response to hepatic insufficiency promote liver regeneration. Hepatic expression of the peroxisome proliferator‐activated receptor gamma (PPARγ) influences fat accumulation in the liver. Therefore, the studies reported here were undertaken to assess the effects of disruption of hepatic PPARγ expression on hepatic fat accumulation and hepatocellular proliferation during liver regeneration. The results showed that liver regeneration was not suppressed, but rather modestly augmented in liver‐specific PPARγ null mice maintained on a normal diet. These animals also exhibited accelerated hepatic cyclin D1 expression. Because hepatic PPARγ expression is increased in experimental models of fatty liver disease in which liver regeneration is impaired, regeneration in liver‐specific PPARγ null mice with chronic hepatic steatosis was also examined. In contrast to the results described above, disruption of hepatic PPARγ expression in mice with diet‐induced hepatic steatosis resulted in significant suppression of hepatic regeneration. Conclusion: The metabolic and hepatocellular proliferative responses to PH are modestly augmented in liver‐specific PPARγ null mice, thus providing additional support for a metabolic model of liver regeneration. Furthermore, regeneration is significantly impaired in liver‐specific PPARγ null mice in the setting of diet‐induced chronic steatosis, suggesting that pharmacological strategies to augment hepatic PPARγ activity might improve regeneration of the fatty liver. (HEPATOLOGY 2012)

Hepatic venous outflow obstruction in pediatric liver transplantation: Technical considerations in prevention, diagnosis, and management

HVOO creates significant diagnostic and management dilemmas in pediatric liver transplant recipients, particularly with TVGs (split or reduced‐size grafts). Numerous technical variations for the hepatic vein to IVC anastomosis have been described to minimize the incidence of this complication, but no consensus for an optimal anastomotic technique exists. One hundred and thirty‐four liver transplants (70 TVGs) were performed in 124 patients between 1994 and 2011. These were divided into two cohorts. Group 1 (95 transplants, 41 TVGs) utilized a continuous running anastomosis. Group 2 (39 transplants, 29 TVGs) implemented a triangulated (three‐stitch) anastomosis. All were reviewed for demographics, diagnostics, interventions, and outcome. The overall HVOO incidence was seven of 134 transplants (5.2%) and six of 70 transplants utilizing TVGs (8.6%). Group 1 incidence was five of 41 (12.2%) compared with one of 29 (3.4%; p = 0.20, OR 3.89) in Group 2. Liver Doppler was employed in all patients, and only three suggested HVOO. All patients with HVOO underwent venogram, at a median of 81 days post‐transplant. All underwent percutaneous venoplasty and required 1–6 treatments, all resulting in HVOO resolution. Incidence of HVOO has improved since adopting the triangulated anastomosis, although not to a level of statistical significance. US is not adequately sensitive to exclude HVOO. Venogram is recommended in patients with prolonged ascites, and venoplasty has been highly successful in HVOO treatment.

Baseline Ultrasound and Clinical Correlates in Children with Cystic Fibrosis

OBJECTIVE To investigate the relationship between abdominal ultrasound findings and demographic, historical, and clinical features in children with cystic fibrosis (CF). STUDY DESIGN Children age 3-12 years with CF without known cirrhosis, were enrolled in a prospective, multicenter study of ultrasound to predict hepatic fibrosis. Consensus ultrasound patterns were assigned by 3 radiologists as normal, heterogeneous, homogeneous, or cirrhosis. Data were derived from direct collection and US or Toronto CF registries. χ(2) or ANOVA were used to compare variables among ultrasound groups and between normal and abnormal. Logistic regression was used to study risk factors for having abnormal ultrasound. RESULTS Findings in 719 subjects were normal (n = 590, 82.1%), heterogeneous (64, 8.9%), homogeneous (41, 5.7%), and cirrhosis (24, 3.3%). Cirrhosis (P = .0004), homogeneous (P < .0001), and heterogeneous (P = .03) were older than normal. More males were heterogeneous (P = .001). More heterogeneous (15.0%, P = .009) and cirrhosis (25.0%, P = .005) had CF-related diabetes or impaired glucose tolerance vs normal (5.4%). Early infection with Pseudomonas aeruginosa (<2 years old) was associated with a lower risk (OR 0.42, P = .0007) of abnormal. Ursodeoxycholic acid use (OR 3.69, P < .0001) and CF-related diabetes (OR 2.21, P = .019) were associated with increased risk of abnormal. CONCLUSIONS Unsuspected cirrhosis is seen in 3.3% of young patients with CF, heterogeneous in 8.9%. Abnormal ultrasound is associated with CF-related diabetes, and early P aeruginosa is associated with normal ultrasound. Prospective assessment of these risk factors may identify potential interventional targets. TRIAL REGISTRATION ClinicalTrials.gov: NCT01144507.

Variceal hemorrhage and adverse liver outcomes in patients with cystic fibrosis cirrhosis

Objectives: Cirrhosis occurs in 5% to 10% of cystic fibrosis (CF) patients, often accompanied by portal hypertension. We analyzed 3 adverse liver outcomes, variceal bleeding (VB), liver transplant (LT), and liver-related death (LD), and risk factors for these in CF Foundation Patient Registry subjects with reported cirrhosis. Methods: We determined 10-year incidence rates for VB, LT, LD, and all-cause mortality (ACM), and examined risk factors using competing risk models and Cox-proportional hazard regression. Results: From 2003 to 2012, 943 participants (41% females, mean age 18.1 years) had newly reported cirrhosis; 24.7% required insulin, 85% had previous pseudomonas. Seventy-three subjects had reported VB: 38 with first VB and new cirrhosis reported simultaneously and 35 with VB after cirrhosis report. Ten-year cumulative VB, LT, and LD rates were 6.6% (95% confidence interval [CI]: 4.0, 9.1%), 9.9% (95% CI: 6.6%, 13.2%), and 6.9% (95% CI: 4.0%, 9.8%), respectively, with an ACM of 39.2% (95% CI: 30.8, 36.6%). ACM was not increased in subjects with VB compared to those without (hazard ratio [HR] 1.10, 95% CI: 0.59, 2.08). CF-related diabetes (HR: 3.141, 95% CI:1.56, 6.34) and VB (HR: 4.837, 95% CI: 2.33, 10.0) were associated with higher LT risk, whereas only worse lung function was associated with increased LD in multivariate analysis. Death rate among subjects with VB was 24% with LT and 20.4% with native liver. Conclusions: VB is an uncommon complication of CF cirrhosis and can herald the diagnosis, but does not affect ACM. Adverse liver outcomes and ACM are frequent by 10 years after cirrhosis report.