hepatoprotective agents
TRANSCRIPT
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HEPATOPROTECTIVE AGENTS
Dr Priyank shah, Jr 1, Dept of pharmacology
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Introduction Liver is one of the largest organs in human body
and the chief site for intense metabolism and excretion.
It has a surprising role in the maintenance, performance and regulating homeostasis of the body.
It is involved with almost all the biochemical pathways to growth, fight against disease, nutrient supply, energy provision and reproduction.
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Liver Toxicity The main causes of liver damage are
The major cause in India is ethanol and it is suspected that more than half of the cases of hepatotoxicity is caused by alcohol.
Chemicals like carbon tetrachloride CCL4, phosphorous , aflatoxins, chlorinated hydrocarbon etc
Drugs i.e. DILI ( drugs induced liver injury )
Autoimmune disorders
Infections like viral hepatitis
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Drugs
Liver Disease
Drug Metabolites (the good, the bad and the ugly)
Drug Elimination
Drugs and the Liver
Drug-Drug InteractionsLIVER
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Drugs causing DILI Anti tuberculosis drugs
All drugs causes hepatotoxicity except ethambutol
Anti convulsant drugs Carbamazepine and valproic
acid NSAIDS
Paracetamol , diclofenac , indomethacin , oxicam group
Anti microbials Dapsone , ketoconazole ,
Sulfonamides, anti retrovirals Anaesthetics
Enflurane , Isoflurane
Miscellaneous drugs Disulfuram Flutamide Statins Labetlol Nicotinic acid Propylthiouracil OC pills
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Clinical PresentationsAsymptomatic elevation in hepatic enzymes
No progress despiteContinued use of the Medication.
(Drug tolerance)
•INH•Phenytoin•Chlopromazine
Progression to Hepatic injury withContinued use of themedication
AST & ALT 3-5 timesUpper limit of normal
May progress to Hepatic failure
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Acute Hepatocellular Injury by Drugs
Characterized by Marked elevation in ALT and AST Normal or minimally elevated alkaline phosphatase Bilirubin variably increased-----›worse prognosis.
Comprise 1/3 of all cases of fulminant hepatic failure in the US. 20% due to Acetominophen 12%-15% due to other drugs
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Acute Hepatocellular Injury Alcohol
AST is always 2-3 times higher than ALT AST remains less than 300 IU. ALT is almost always less than 100 IU.
Towering elevation of ALT&AST(5000-10000 IU) Drugs (acetaminophen) Differential:
Chemical toxins Toxic Mushrooms Shock liver
Unusual with other causes of liver diseases including Viral Hepatitis.
11 Mechanism of Hepatotoxicity
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Markers of Hepatotoxicity Aspartate Serum
Transferase (AST),
Alanine Amino Transferase (ALT),
Alkaline Phosphatase (ALP)
Lactate dehydrogenase (LDH)
Total Bilirubin (TB)
Total protein (TP),
Triglycerides (TG)
Gammaglutamyl transferase (GGT) levels
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Mechanism of hepatotoxicity Most of the hepatotoxic chemicals damage liver
cells mainly by inducing lipid per oxidation and other oxidative damages in liver.
By forming the reactive free oxygen radicals which directly induces hepatotoxicity
Increasing the apoptosis
Reducing Glutathione stores an antioxidant of human body
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DILI
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19 Hepatoprotective agents
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List of Hepatoprotective agents N acetylcysteine vitamins
Penicillamine
Anti oxidants melatonin
cardiotropin 1 glutathione
Herbal medications beta carotene
S adenosyl methionine (SAM) many more
21 N acetyl cysteine
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Description N-acetyl derivative of
L-cysteine
Pharmacologic category Antidote
Mucolytic
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Indications FDA labeled indications
Acetaminophen (APAP) overdose Adjunctive mucolytic therapy Diagnostic bronchial studies
Off-label use Prevention of contrast-induced
nephrotoxicity (CIN) Helicobacter pylori infection
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Pathophysiology of APAP Overdose APAP primarily metabolized via Glucoronidation
or sulphation
Secondary metabolism by CYP 450 system In OD, primary route saturated → CYP 450 system →
NAPQI production
NAPQI converted to non-toxic form by glutathione In OD, glutathione stores consumed → excess NAPQI
→ covalent binding to hepatocytes
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NAPQI causes1. Protein binding cytoplasm loss /damage of
protein
Apoptosis pro apoptotic factors
2. Formation ROS lipid peroxidation Liver necrosis DNA damage
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N-acetylcysteine (NAC) has been used for several decades and has proven to be the antidote of choice in treating acetaminophen-induced hepatotoxicity.
oral and intravenous NAC are equally efficacious in the prevention of hepatotoxicity.
An important factor in assessing the efficacy of NAC is the timing of therapy initiation in relation to the ingestion. Pt should receive NAC within 8hours of APAP poisoning.
Metabolism of NAC
N-Acetylcysteine 12/2002
Society For Free Radical Biology and Medicine
Ercal & Gurer-Orhan 28
Oral NAC administration
Extensive first-pass metabolism in
liver and intestine
3% of NACexcreted in
feces
Rapid absorption
LIVER
INTESTINE
NACdeacetylation
cysteineglutamate
Glutamylcysteinee
+
glycine
GSH
+
GSHsynthase
glutamate-cysteine ligase
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N Acetyl cysteine Prevents hepatic injury primarily by restoring
hepatic glutathione
N acetyl cysteine improves hemodynamics and oxygen use,
Decreases cerebral edema.
It may involve scavenging of free radicals or changes in hepatic blood flow
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Adverse Reactions Oral
Drowsiness Chills/fever Nausea / Vomiting Bronchospasm Rhinorrhea Unpleasant odor
IV Anaphylactoid
reactions Vomiting
31 Penicillamine
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Penicillamine is a degradation product of penicillin but has no antimicrobial activity.
It was first isolated in 1953 from the urine of a patient with liver disease who was receiving penicillin.
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Mechanism of action Penicillamine chelates several metals including
copper, lead, iron, and mercury, forming stable water soluble complexes that are renally excreted.
It also combines chemically with cystine to form a stable, soluble, readily excreted complex.
It may also have antifibrotic effects as it inhibits lysyl oxidase, an enzyme necessary for collagen production.
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It also directly binds to collagen fibrils, preventing cross-linking into stable collagen fibers.
Penicillamine may have immunomodulatory effects and has been demonstrated to reduce IgM rheumatoid factor in humans with rheumatoid arthritis.
35 S Adenosyl Metheonine (SAM)
Methionine & SAMe Methionine is an essential amino acid that is
primarily metabolized in the liver. SAM biosynthesis is the first step in methionine metabolism in a reaction catalyzed by methionine adenosyltransferase (MAT)
In mammals, this reaction in the liver catabolizes nearly half of the daily intake of methionine
The liver is the main source of SAM biosynthesis and metabolism, turning over nearly 8 gm per day in a normal adult
SAM is used in transmethylation reactions and is converted to S-adenosylhomocysteine (SAH)
Hepatic methonine metabolism and SAME biosynthesis
S Adenosyl Methionine SAM is the principal biological methyl donor
required for methylation of DNA, RNA, biogenic amines, phospholipids, histones, and other proteins
It is the precursor for synthesis of polyamines, which are required for cell proliferation and the maintenance of cell viability
In the liver, SAM is a precursor for glutathione, a major endogenous antioxidant that protects cells against injury by scavenging free radicals.
Thus, SAM deficiency can impair many vital functions of liver, which render it susceptible to injury by toxic agents, including alcohol
SAMe (S-adenosylmethionine) SAMe (S-adenosylmethionine) is the main methyl donor
group in the cell. MAT (methionine adenosyltransferase) is the unique enzyme responsible for the synthesis of SAMe from methionine and ATP
SAMe is the common point between the three principal metabolic pathways: polyamines, transmethylation and transsulfuration that converge into the methionine cycle
SAMe is now also considered a key regulator of metabolism, proliferation, differentiation, apoptosis and cell death
SAM functions as an antioxidant Additionally, SAM functions as an antioxidant not
only because of its role as a precursor for GSH biosynthesis, but also because of its capacity to interact directly with reactive oxygen species
Evidence to support this role comes from studies on the capacity of SAM to diminish ischemia/ reperfusion injuries in clinical trials during liver transplantation
These studies demonstrated that SAM was more effective than GSH in scavenging hydroxyl radicals and in chelating iron ions to inhibit generation of these radicals and, unlike GSH, SAM did not stimulate formation of scavenging hydroxyl radicals at lower concentrations
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Other mechanisms Abnormal inflammatory cytokine metabolism is a
major feature of both alcoholic and non-alcoholic steatohepatitis.
Apoptotic cell death of hepatocytes is emerging as an important mechanism contributing to the progression of human liver diseases.
SAM effectively reduces Apoptosis and inflammatory cytokines.
Therapeutic potential of SAM in ALD
The therapeutic potential of SAM was tested in a 24-month randomized, placebo-controlled, double-blind, multicenter clinical trial in patients with alcoholic cirrhosis
SAM treatment improved survival or delayed the need for liver transplantation in alcoholic liver cirrhosis, especially those with less advanced liver disease
Mechanism of protection was not investigated in this trial, increased hepatic concentrations of glutathione may have contributed to beneficial effect of SAM
This notion is supported by another study in which oral 1.2 g SAM/d for 6 months significantly increased hepatic glutathione concentrations in ALD patients
Authors evaluated whether SAMe infusion improved methionine clearance in patients with stable ALD
43 Herbal medication
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List of herbal medication used in hepatic diseases
Silybum marinum Eclipta alba Foeniculum vulgare Trigonella foenum graecum Jatropha curcas Garcinia mangostana Linn Chamomile capitula
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Silybum marianum
Silybum marianum, commonly known as ‘milk thistle’ (Family: Asteraceae/Compositae) is one of the oldest and thoroughly researched plants in the treatment of liver diseases.
The extracts of milk thistle is being used as a general medicinal herb from as early as 4th century B.C. and first reported by Theophrastus.
Silymarin, a single herbal drug formulation which is mostly used in liver diseases amounts to about 240 million US dollars in Germany alone.
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Silymarin is a complex mixture of four flavonolignan isomers, namely silybin, isosilybin, silydianin and silychristin with an empirical formula C25H22O10
Among the isomers silybin is the major and most active component and represents about 60-70 per cent, followed by silychristin (20%), silydianin (10%), and isosilybin (5%).
The structural similarity of silymarin to steroid hormones is believed to be responsible for its protein synthesis facilitatory actions
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Mechanism of action Stimulation of protein synthesis:-
Silymarin can enter inside the nucleus and act on RNA polymerase enzymes resulting in increased ribosomal formation.
This in turn hastens protein and DNA synthesis.
This action has important therapeutic implications in the repair of damaged hepatocytes and restoration of normal functions of liver.
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Anti-inflammatory actions: The inhibitory effect on 5-lipoxygenase pathway
resulting in inhibition of leukotriene synthesis is a pivotal pharmacological property of silymarin.
Strong inhibitory effect on LTB4 but not on TNF alpha or on prostaglandin formation
In vivo study in mice treated with silymarin suggested that parenteral exposure to silymarin results in suppression of T-lymphocytes at low doses and stimulation of inflammatory process at higher doses.
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Antifibrotic action: Liver fibrosis can result in remodeling of liver architecture
leading to hepatic insufficiency, portal hypertension and hepatic encephalopathy.
The conversion of hepatic stellate cells (HSC) into myofibroblast is considered as the central event in fibrogenesis. Silymarin inhibits HSC activation
It also inhibits protein kinases and other kinases involved in signal transduction and may interact with intracellular signaling pathways.
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Drug and toxin related liver damage : Hepatocellular injury due to drugs seems to be the
primary event.
This is rarely due to the drug itself and a toxic metabolite is usually responsible.
The drug metabolizing enzymes activate chemically stable drugs to produce electrophilic metabolites.
All this leads to reduction in glutathione stores, lipid peroxidation, and membrane damage.
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Silymarin has a regulatory action on cellular and mitochondrial membrane permeability in association with an increase in membrane stability against xenobiotic injury.
prevent the absorption of toxins into the hepatocytes by occupying the binding sites as well as inhibiting many transport proteins at the membrane
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As an antioxidant : Free radicals, including the superoxide radical, hydroxyl
radical (.OH), hydrogen peroxide (H2O2), and lipid peroxide radicals have been implicated in liver diseases.
The cytoprotective effects of silymarin are mainly attributable to its antioxidant and free radical scavenging properties.
Silymarin can also interact directly with cell membrane components to prevent any abnormalities in the content of lipid fraction responsible for maintaining normal fluidity.
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Adverse Drug Reactions Silymarin is reported to have a very good safety profile.
Both animal and human studies showed that silymarin is non toxic even when given at high doses (>1500 mg/day).
gastrointestinal tract side effects like bloating, dyspepsia, nausea, irregular stool , diarrhoea
It also produced pruritus, headache, exanthema, malaise, asthenia, and vertigo.
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Liv 52 Key ingrediants
The caper Bush ( Himsra) It contains p- methoxy benzoic acid which is a potent
Hepatoprotective. It prevents the elevation of malondialdehyde (biomarker for oxidative stress)
It also inhibits the elevation of ALT and AST
Chicory (Kasani) Potent antioxidant It suppresses the oxidative degradation of DNA
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Mechanism of action Potent Hepatoprotective against chemical induced
hepatotoxicity
It protects liver parenchyma and promotes hepatocellular regenration
It maintains cytochrome p450, hastens the early recovery period and maintains functional integrity
Rapid clearance of aldehyde and protects from alcohol liver disease
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Side effects Only mild GI symptoms bloating, dyspepsia, nausea, irregular stool , Diarrhoea
When taken at prescribed dose it is totally side effects free
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As a supplementary therapy
Anti oxidants
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The mechanism of free radical damage include
ROS- induced peroxidation of polyunsaturated fatty acid in the cell membrane bilayer, which causes a chain reaction of lipid peroxidation, thus damaging the cellular membrane and causing further oxidation of membrane lipids and proteins.
Subsequently cell contents including DNA, RNA, and other cellular components are damaged.
Antioxidants Prevents the transfer of electron from O2
to organic molecules
Stabilizes free radicals
Terminates free radical reactions
63 Cardiotrophin 1
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Phase I study in healthy volunteers completed
Orphan Drug status granted for solid organ transplantation and acute liver failure by FDA and EMA
IP protection granted for liver diseases, and filed for solid organs transplantation and kidney diseases
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Cardiotrophin 1 (CT-1) belongs to the IL-6 family of cytokines.
CT-1 receptor activation (gp 130-LIF-R) induce cell survival through signal transduction mechanisms mediated by Stat3, MAPK y PI3K.
CT-1 is induced in the context of cell damage in several tissues. Strong anti-apoptotic effects on hepatocytes. Reduce the cellular damage cause by ischemia/reperfusion. Decrease oxidative damage. Potent anti-inflammatory agent.
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Cardiotropin 1 has FDA and EMA orphan drug designation for transplantation and acute liver failure.
It has been granted for its use in hepatic regenration.
67 Vaccines
HEPATITIS VACCINES
HEPATITIS A
Inactivated viral vaccineNot given < 1 year2 doses, 6 – 18 months apart
Combination VaccineInactivated Hep – A + Recombinant Hep – B3 doses, 0, 1 & 6 months, > 1 year older.
HEPATITIS BrDNA – Yeast derived VaccineAdults – 10 -20 mcg IM at 0, 1, 6 months< 10 yr – 5 – 10 mcg IM95 % immunity till 40 yrsNot contraindicated in pregnancyFor Immunodeficient :Recombivax HB(1 dose, 40g)
Engerix B (2 dose 20 g)New Vaccines Status• HBc VLP+ cochleates, nasal - Phase I• HBV polyepitope vaccine - Phase I• DNA coding for T-cell epitopes - Phase I
HEPATITIS CNo Vaccine yet availableNew Vaccine StatusVaccine Stage of
DevelopmentRecombinant E1/E2 + MF59 subunit vaccine Phase IRecombinant E1glycopro-tein subunit vaccine Phase IIHCcAg/E1/E2 VLPs PreclinicalMultiepitope synthetic peptides in virosomes PreclinicalMultigene recombinant Adenovirus PreclinicalLive recombinant MVA-NS3-NS4-NS5 antigens vaccine
Preclinical
HEPATITIS E
New Vaccines Status
Vaccine Stage of Development
56 kD ORF-2 protein VLPs (baculovirus) Phase II/III
DNA vaccine (ORF-2) Preclinical
72 Evaluation of hepatoprotective drugs
73 In vitro metho
Hepatocytes are isolated and placed in HEPES (N-2-hydroxyethylpiperazine – N- 2 ethanesulphonic acid)
Hepatocytes are exposed to test samples and toxins CCL4, alcohol or paracetamol.
Degree of protection is assesed by viability tests (Trypan blue dye exclusion method) and measurement of enzymes levels.
Ex vivo method After completion of in
vivo test, hepatocytes are isolated and % of viable cells and biochemical parameters are determined
Better correlated to clinical models than in vitro or in vivo
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Paracetamol model
Ethanol model
Ccl4 model
Thioacetamide model
D- galactosamine model
Experimental rat models
75 Future direction
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Hepatotoxicity will remain clinical and controlling significance.
With increasing the incidence of hepatotoxicity the need for new , potent and efficacious Hepatoprotective agents arises.
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NAC for anti TB hepatotoxicity
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NAC for statins
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It also showed Hepatoprotective activity against Carabamazepine All in preclinical
phase N-N dimethylformaide
Anti retroviral agents
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Cannabinoids A very attractive target for modulating hepatic fibrosis.
CB1 receptor – up regulated in myelofibroblast and promote fibrosis
CB2 receptor – antifibrotic but may amplify inflammation.
As a result of these findings, CB1 antagonism is a more promising strategy than CB2 agonism
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Rimonabant CB1 antagonist showed significant weight loss and improved metabolic
function, decreased triglycerides and improved insulin resistance.
But it lead to increased neuropsychiatric complication so was withdrawn from market.
As a result, current efforts are directed towards CB1 antagonists that do not cross the bloodbrain barrier.
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Endothelin (ET1) receptor antagonist
High levels of ET-1 and endothelin receptors are present during cirrhosis.
The blockade of ET-1 type A receptor and the administration of vasodilators (prostaglandins E2 and NO donor) exert an antifibrotic activity in rodents and in humans also improves portal hypertension.
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Hormones Adipokines
Metabolic abnormalities are considered the ‘first hit’ of liver injury in obesity-related liver disease, followed by oxidative stress and inflammation.
Leptin and its natural antagonist adiponectin are key adipokines secreted by adipose tissue and stromal cells, especially HSC.
Elevated leptin levels signal through their specific receptors to promote fibrogenesis by JAK/STAT signalling.
While adipokines are inversely related to body fat and inhibit inflammation
Gherlin ( a gut hormone) has also showed anti inflammatory activity in rats
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Tyrosine kinase receptors inhibitors Many proliferative cytokines, including PDGF,
fibroblast growth factor (FGF), and TGF-a signal through tyrosine kinase receptors.
Antagonism of pathways that mediate PDGF or VEGF signals reduces HSC proliferation.
Sorafenib, a multiple receptor tyrosine kinase inhibitor approved for therapy in hepatocellular carcinoma, targets the PDGF receptor and Raf/ERK signaling pathways
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References 87
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