Download Hurdles for clinical validation

Prevention of Liver Fibrosis to
Cirrhosis
Hongqun Liu
University of Calgary
Categories
• Eliminate the causative agent(s) of liver injury;
• Directly downregulate HSC activation;
• Reduce inflammation or modulate inflammatory
cells;
• “Hepatoprotection” to reduce hepatocyte injury;
• Inhibit fibrogenesis;
• Neutralize proliferative, fibrogenic, contractile and/or
proinflammatory factors;
• Induce apoptosis of activated HSC;
• Increase the degradation of extracellular matrix
(ECM).
Proliferation
Quiescent
HSC
Injury (inflammation)
Activated
HSC
Matrix synthesis
Apoptosis
Anti-fibrosis
Ideal drugs:
“Anti-fibrosis”
Anti-inflammation
Anti-angiogenesis
Anti-inflammatory drugs
Corticosteroids
• Useful for autoimmune hepatitis. But long term
administration is not recommended.
Interleukin 10
• Shifts cytokines from proinflammatory to antiinflammatory, decreases TNFα, IL-1 and 2 and IFNγ.
However, increases viral load and therefore, not suiltabe
for viral hepatitis.
Anti-TNFα
• Effective in cell culture of fibroblasts and HSC, not human
Antioxidants
“in vitro” and in experimental animals; limited
evidence in humans.
• N-acetyl-cysteine (NAC): in cell cultures and in
experimental animals, its antifibrosing properties is
limited in humans
• Cu-Zn superoxide dismutase: Emerit mentioned the
clinical trail in 2006 but so far no further document.
• Curcumin and silymarin: natural products, anti
oxidant and inflammation (experimental)
HSC proliferation
•
•
•
•
•
•
•
•
•
•
TGFβ (Transforming Growth Factor beta)
PDGF (Platelet derived growth factor)
EGF (Epidermal Growth Factor),
CTGF (Connective Tissue Growth Factor),
VEGF (Vascular Endothelial Growth Factor),
IGF (Insulin-like Growth Factor),
bFGF (basic Fibroblast Growth Factor),
RAAS (renin-angiotensin-aldosterone system)
TGFα (Transforming Growth Factor alpha)
Leptin, endothelin, thrombin, IL-1, endocannabinoids
TGFβ
The most powerful fibrogenic factor
• Inducing hepatic oval cells to HSC (You hong)
• Inducing fibrogenic related gene transcriptions
• Favoring HSC activation
• Reducing ECM degradation
Side effects of TGFβ blockage:
Affecting the tissue and organ architecture such
as bone integrity; excessive inflammation.
Collagen
• Synthesis: 4-prolylhydroxylase. Safironil.
Activated in liver, experimentally useful, not in
human.
• Secretion: colchicin, inconclusive in human
• Formation of cross-linking among collagen
molecules: D-Penicillamine good for Wilson’s
disease.
HSC inactivation
• PPARγ (Peroxisome Proliferator-Activated Receptors): PPARγ ligands reduce activation of HSC,
intensity of fibrosis, expression of TGFβ and proinflammatory cytokines TNFα and IL-6, and increases
PPARγ expression in HSC
• Retinoic acid ( in cell culture only, not animal and
human)
• IL-10
• Trans-resveratrol,
• Pentoxifylline inhibits HSCs proliferation
HSC apoptosis
• Fas ligand and TNFα, P53, BCL2/Bax, NK and
NKTγδ cells, MMPs, IFNγ
• RAIL receptor 2 (TNF-related apoptosisinduced ligand) (TRAIL-R2)
• Inhibition of PI 3-K/Akt signaling pathway
induces apoptosis in HSC (Jiang)
• NF-κB knockdown enhances hepatic stellate
cell apoptosis (Jiang)
Drugs for HSC apoptosis
Sorafenib (Tumor) J Hepatol. 2010;53:132-44
• reduces HSC proliferation; induces apoptosis.
downregulates Cyclin D1 and Cyclin-dependent
kinase 4 (Cdk-4), Bcl-2/Bax, collagen synthesis. ERK,
Akt phosphorylation
• increases Fas, Fas-L, and Caspase-3, increases
MMPs/TIMPs.
Nilotinib (Leukemia) J Hepatol. 2011;55:612-25
• Ursolic acid (tumor) J Hepatol. 2011;55:379-87.
• Gliotoxin (immunosuppressant) J Hepatol. 2007;
47:103-13.
Is the fibrosis/cirrhosis
reversible?
• Animal experiments
CCL4, fibrosis/cirrhosis disappears
spontaneously when CCl4 discontinue
Bile duct ligation, liver will be back to when bile
duct ligation is released.
• Human
Spontaneous regression of liver fibrosis when
causative agent of disease is eliminated
Hurdles for clinical validation
1. Slow progression of liver fibrosis
2. Lack of sensitive and specific
markers to evaluate progression
and regression.
3. Well-stratified, high number of
patients, long term treatment.
Well-stratified (1)
• Recent fibrosis, as characterized by the
presence of thin reticulin (collagen) fibres,
often in the presence of a diffuse
inflammatory infiltrate, appears to be fully
reversible;
• Histopathological evidence of significant
fibrosis (F ≥2) incurs a high risk for progression
to cirrhosis and is thus an indication for antifibrotic treatment.
Well-stratified (2)
Patients suitable for the anti-fibrogenic clinical
trials:
• Rapidly progressing fibrosis such as in HCV reinfection after liver transplant or in HCV–HIV
coinfection; 1–2 years trial;
• NASH,
• Cholestatic CLD such as PBC, PSC or pediatric
biliary liver diseases;
• Nonresponders to standard antiviral
treatment
Well-stratified (3)
• Long-standing fibrosis, as characterized by
thick collagen fibrils embedded in an acellular
or paucicellular ECM and consequent
decreased expression and/or activity of
fibrolytic MMPs, is not easy to reverse
Challenges from basic study to
clinical application
• Time for progression and regression in humans is measurable
in years
• Genetic differences affecting fibrosis progression and
regression
• Insufficient performance of both liver biopsy and noninvasive
methods to differentiate within and between a single stage of
fibrosis (0-4),
• Ethical problems to include a placebo group;
• Lack of data on the efficiency of a given treatment in CLD
with different etiologies
• Difficulty to assess the impact of contributing factors (i.e.
obesity/overweight/insulin resistance, alcohol and tobacco
consumption
• Realistic endpoints
Hepatic stellate cell activation
•
As a result of liver injury, quiescent
vitamin-A-rich hepatic stellate cells
Fibrosis “scores” correlated with HVPG, ascites,
INR,'activation'
bilirubin and inversely
with
undergo
towards
albumin; as well as Child-Pugh class
proliferative, fibrogenic and
contractile myofibroblasts
excessive amounts of collagens,
downregulate matrix
metalloproteinases (MMPs) and
show an enhanced expression of the
tissue inhibitors of the MMPs
(TIMP-1 & -2).
During resolution of liver injury,
hepatic stellate cells might revert to
a quiescent phenotype and/or be
selectively cleared by apoptosis.
24
Scott L Friedman : Nat Clin Pract Gastroenterol
Hepatol 1(2),2004.