Essay: Hepatoprotective, liver disease, Hepatocytes

Abstract
The liver is the principal organ for maintaining the body’s internal environment and it plays a role in the metabolism of carbohydrate, proteins and fats, control the flow of nutrients, It is also the major reticulo- endothelial organ in the body as such has an important immune function in maintaining body authenticity. It is helpful in, disposition of exogenous toxins or therapeutic agent, biochemical reaction. Hepatotoxicity is produced due to chemicals. Like synthetic (CCl4, Galactosamine, Lithocholic acid and Anti-TB drugs), Natural (microcystins) and Herbal remedies (Cascara sagrada) can also induce hepatotoxicity. In this review some of the plants with their extract studied for the protective effect in liver diseases were summerised along with isolated compounds like Andrographolide, neoandrographolide, bacoside-A, colchicine, populnin, naringenin, echinacoside, kolaviron, ternatin, indigtona, rubiadin, bacicalein, baicalin, wogonin, punicalagin, punicalin for their hepatoprotective activity.
Key word:- Hepatoprotective, liver disease, Hepatocytes.
INTRODUCTION
The liver is the largest organ of the body and it performs hundreds of critical functions to maintain homeostasis and health. These functions include production of serum proteins and hormones, detoxification of foreign and naturally occurring chemicals, glucose and lipid metabolism, etc. because of this many functions the liver diseases severely affect health and can be life threatening. There are four major types of liver disease, cirrhosis, fatty liver, hepatitis and liver cancer, from this heaptais and liver cancer being among the most serious global public health problems.Hepatitis means ‘inflammation of the liver’ in Latin, and the most common etiologies are infections by one of five viruses, called hepatitis A, B, C, D and E. All of these viruses can cause acute diseases with symptoms lasting several weeks, including yellowish skin and eyes (jaundice), dark urine, extreme fatigue, nausea, vomiting and abdominal pain. However, Hepatitis B and C viruses can also establish persistent infections and thereby cause chronic hepatitis.1
Fig.1
More than 900 drugs have been implicated in causing liver injury and it is the most common reason for a drug to be withdrawn from the market. Hepatotoxicity and drug-induced liver injury also account for a substantial number of compound failures, highlighting the need for drug screening assays, such as stem cell-derived hepatocyte-like cells, that are capable of detecting toxicity early in the drug development process. Drug metabolism is usually divided into two phases: phase 1 and phase 2. Phase 1 reaction is thought to prepare a drug for phase 2. However, many compounds can be metabolized by phase 2 directly.Phase 1 reaction involves oxidation, reduction, hydrolysis, hydration and many other rare chemical reactions. These processes tend to increase water solubility of the drug and can generate metabolites that are more chemically active and potentially toxic. Most of phase 2 reactions take place in the cytosol and involve conjugation with endogenous compounds via transferase enzymes. Chemically active phase 1 products are rendered relatively inert and suitable for elimination by this step.
Fig.2
A group of enzymes located in the endoplasmic reticulum, known as cytochrome P-450, is the most important family of metabolizing enzymes in the liver. Cytochrome P-450 is the terminal oxidase component of an electron transport chain. It is not a single enzyme, but rather consists of a closely related family of 50 isoforms; six of them metabolize 90% of drugs. There is a tremendous diversity of individual P-450 gene products, and this heterogeneity allows the liver to perform oxidation in a vast array of chemicals (including almost all drugs) in phase 1. Three important characteristics of the P450 system have roles in drug-induced toxicity:
1. Genetic diversity:
Each of the P-450 proteins is unique and accounts (to some extent) for the variation in drug metabolism between individuals. Genetic variations (polymorphism) in P-450 metabolism should be considered when patients exhibit unusual sensitivity or resistance to drug effects at normal doses. Such polymorphism is also responsible for variable drug response among patients of differing ethnic backgrounds.
Cytochrome P-450 enzyme induction and inhibition
Potent inducers Potent inhibitors Substrates
Rifampicin, Carbamazepine,
Phenobarbital, Phenytoin,
(St John’s wort),
Amiodarone, cimetidine,
ciprofloxacin, fluconazole,
fluoxetine, erythromycin,
isoniazid, diltiazem
Caffeine, clozapine,
omeprazole, losartan,
theophylline
2. Change in enzyme activity:
Many substances can influence the P-450 enzyme mechanism. Drugs interact with the enzyme family in several ways. 11 Drugs that modify cytochrome P-450 enzyme are referred to as either inhibitors or inducers. Enzyme inhibitors block the metabolic activity of one or several P-450 enzymes. This effect usually occurs immediately. On the other hand, inducers increase P-450 activity by increasing its synthesis. Depending on the inducing drug’s half life, there is usually a delay before enzyme activity increases.
3. Competitive inhibition:
Some drugs may share the same P-450 specificity and thus competitively block their bio transformation. This may lead to accumulation of drugs metabolized by the enzyme. This type of drug interaction may also reduce the rate of generation of toxic substrate.
ETIOLOGICAL FACTORS FOR HEPATOTOXICITY
When the drugs administered orally or intravenously are focus to first pass metabolism in the liver which causes their biological inactivation. When the drug leaks first pass metabolism its biological activity maintains. Due to the absences of P450s and hepatic metabolic inactivation a stage will come when there is a prolonged response to a drug takes place .The presence of P450 in liver can have a major influence on the efficacy and toxicicity of a drug. Several of the xenobiotics metabolizing P450 including CYP2A6, CYP2C9, CYP2C19and CYP 2D6, with the exemption of CYP2A6 that are having the capability to activate certain nitrosamine
From human liver specimens studies, it was concluded that there is still a high degree of difference in their expression. When a limited number of P450s are involved in xenobiotics metabolism, Several P450s are involved in the synthesis of steroid hormones. When P450s is activating several genes like CYP1A1, CYP1A2, CYP1B1, CYP2A6, CYP2E1 is involved in the process.
Drug interactions occur when two drugs are co administered and both are processed by the same P450. One drug can then inhibit the metabolism of another drug significantly to high serum levels and prolonged biological activity and occasionally toxicity. This depends on the drug activity as either inducer or inhibitor. When the effect is immediate, several P450 enzymes block metabolic activity. On the other hand enzymes inducers chemical drug increase P450 activity by cumulative its synthesis. Other factors are:-
‘ Inherited birth imperfections
‘ Metabolic complaints
‘ Bacterial infections.
‘ Alcohol or poisoning by toxins.
‘ Certain medications that are toxic to the liver.
‘ Nutritional paucities.
‘ Injury
Mechanism of Hepatotoxicity Caused By Different Agents
Several mechanisms are responsible for inducing hepatic injury. Many chemicals damage mitochondria, an intracellular organelle that produces energy. Its dysfunction releases excessive amount of oxidants which in turn injures hepatic cells. Activation of some enzymes in the cytochrome P-450 system such as CYP2E1 also leads to oxidative stress. Injury to hepatocyte and bile duct cells lead to accumulation of bile acid in liver. This endorses further liver damage. Non-parenchyma cells, such as Kupffer cells also have a role in the mechanism of hepatotoxicity. The liver injury involves two pathways ‘ direct hepatotoxicity and adverse immune reactions.
Direct Hepatotoxicity: Drug induced liver injury is originated by the bio activation of drugs to chemically reactive metabolites, which have the ability to interconnect with cellular macromolecules such as proteins, lipids, and nucleic acids, leading to protein dysfunction, lipid per oxidation, DNA damage, and oxidative stress. These reactive metabolites may induce interruption of ion gradients and intracellular calcium stores, resulting in mitochondrial dysfunction and loss of energy production. This damage of cellular function can dismiss in cell death and likely liver failure.
Immunological Reaction: liver cell dysfunction and cell death also have the ability to produce immunological reactions, including both innate and adaptive immune responses. Damaging hepatocyte result in the activation of innate immune system like Kupffer cells, natural killer cells result in producing proinflammatory mediators and secreting chemokine to further recruit inflammatory cells to the liver. It has been confirmed that various inflammatory cytokines, such as tumor necrosis factor (TNF) -Alfa, interferon (IFN) – gamma, and interleukin (IL)-1beeta produced during drug induced liver injury are involved in promoting tissue damage. Innate immune cells are also the main source of IL-10, IL-6, and convinced prostaglandins, all have been shown to display hepatoprotective role.6 It is the subtle equilibrium of inflammatory and hepatoprotective mediators produced after activation of the innate immune system that determines an individual susceptibility and adaptation to drug induced liver injury. The major procedures of drug induced liver injury include acute hepatitis, Cholestasis, and a mixed pattern.
These are the factors influencing drug induced hepatotoxicity. Like Age,Ethnicity & race,Gender,Nutritional status,Underlying liver disease,Renal function,Pregnancy,Duration and dosage of drug,Enzyme induction and Drug to drug interact.
Development of liver injury takes place in three stages i.e. necrosis, fibrosis and cirrhosis. Cirrhosis of the liver is one of the major health problems in developed countries. Although extensive work is being done in the field of cirrhosis the molecular mechanisms leading to cell death and increased collagen accumulation is still not clear. Therefore, treatment and prevention of the cirrhotic process are still elusive.
Most of the hepatotoxic chemicals damage liver cells mainly by inducing lipid peroxidation and other oxidative damages in liver. Toxic effects of drugs on the liver or its function may mimic almost every naturally occurring hepatic disease. Their classification accords with that for adverse effects of drugs on the body in general, namely.
Type A (Augmented)
Liver injury occurs as the dose of some drugs is raised causing
‘ Centrizonal necrosis with paracetamol and also caused by carbon tetrachloride.
‘ Hepatocelluar necrosis with salicylates
‘ Fatty change in liver cells and cells and hepatic failure with tetracycline.
‘ Hepatitis with alcohol.
Type B (Bizarre)
Many drugs can cause hepatic damage at therapeutic doses
‘ Acute hepatocellular necrosis.(General Anesthetics like halothane)
‘ Anticonvulsants (phenytoin, phenobarbitone)
‘ Antiinflammatory
‘ Cholesatic hepatitis (Phenotiazine, Chlorpromazine)
Type C (Continued use)
‘ Chronic active hepatitis ( Isoniazide Methyldopa)
‘ Hepatic fibrosis or cirrhosis( Alcohol, Mthotrexate)
Type D (Delayed effect)
Benign liver tumors may develop
‘ When synthetic androgens (anabolic steroids) usually in high dose
‘ Oral contraceptives are used for more than 5 years.
Some Models To Screen Hepatotoxicity
Hepatotoxins are generally causes the necrosis, cirrhosis, carcinogenesis and hepatobilary dysfunction in experimental animal. The following are some of the experimental models explained by employing some of the important hepatotoxins.
a) Carbon tetrachloride model:- Acute liver damage caused by oral or subcutaneous administration of CCl4 dose of about 1.25mg/ml. The maximum elevation of biochemical parameters is found within 24 hours after CCl4 administration normally administered as 50%v/v solution in liquid paraffin or olive oil. Chronic reversible hepatic damage cases when administration of CCl4 of dose 1 ml/kg subcutaneously twice a week for continues 8 weeks. Chronic irreversible hepatic damage causes when administration of CCl4 of dose 1ml/kg for twice continuously 12 weeks.
b) Paracetamol model: – IT produces dose dependant hepatotoxicity through different routes of administration like the 800 mg/kg dose of paracetamol intraperitonially cause centrilobular necrosis without steatosis, a single dose of 3 g/kg leads to the acute hepatic damage within 48 hours.
c) Chloroform model: – it produces hepatotoxicity by inhalation or by subcutaneous route when the dose of 0.4 to 1.5ml/kg administered.
d) Ethanol model:- it produces dose dependent hepatotoxicity a single dose of ethanol about 1ml/kg induces fatty degeneration, an administration of 40% v/v ethanol 2ml/100g/day for 21 days produces fatty liver. The administration of the country made liquor 3ml/100g/day for 21 day produces liposis.
e) D-galactosamine model: – it produces hepatotoxicity when a dose of 800mg/kg intraperitonially after 48 hours of administration by causing diffuse necrosis and steatosis.
f) Thioacetamide model: – it produces hepatotoxicity when the 100mg/kg subcutaneous dose administration it requires 48 hours by causing sinusoidal congestion and hydropic swelling with increase mitosis.
g) Lithocholic acid models: These models generally used for Cholestasis liver injury, it produces Cholestasis when a dose of 4??mol/100gof body weight administered intravenously.
h) Antimicrobial drug models:- Dose of antitubercular drug (Isoniazid 7.5mg/kg, rifampicin 10mg/kg, pyrazinamide 35 mg/kg, p.o.) for 2 weeks40. Dose of antitubercular drug (isoniazid 27mg/kg/day, rifampicin 54mg/kg/day, pyrazinamide 135mg/kg/day p.o.) administrated for 30 days, dose extrapolated from daily human dose using the conversion table based on body surface area. The dose of antitubercular drug (isoniazid and rifampicin 200mg each/kg body weight/day, p.o.) for 45 days.
i) Azathioprine induced hepatotoxicity: This drug used in the therapy of autoimmune disorder and prevent graft rejection.
j) Ranitidine induced Hepatotoxicity: Liver injury induced by ranitidine is due to its metabolite which may lead to hepatic oxidative damage and one of its metabolite is generating immunoallergic reaction. It also produces a reaction as reflected by infiltration of hepatocyte with ranitidine dose of either 50 or 30 mg/kg.
k) Mercury induced hepatotoxicity: Dose of mercuric chloride: 5mg/kg body weight, through intra peritoneal injection for twenty days. Mercuric chloride dose: 2mg/kg body weight, administrated orally for thirty days45.
l) Lead induced hepatotoxicity: Oral treatment with lead nitrate at a dose of 50mg/kg body weight daily for 40 days.
m) Bromobenzene induced hepatotoxicity: (0.5, 2.0 and 5.0mmole/kg body weight, dissolved in corn oil, 40%v/v) administered orally for 10 ’12 weeks.
Evaluation of Hepatoprotective Activity
The literature revel that several chemical substances and drugs having specific actions on liver are used as hepatotoxins in animals to generate the diseased conditions. In all test model systems, conditions for liver damage are implemented and an attempt is made to counteract these toxicities with the substance under test. The protective effect can be measured by estimating the enzyme activity and the rate of survival verified by histological method. The available method is in-vivo, ex vivo, and in vitro methods.
a. In-vivo methods: – This method used to study the nature of giving compound and mechanism of the toxicant. Hepatotoxicity is produced by in experimental animal by the administration of a known dose of hepatotoxins like CCl4, galactosamine, Thioacetamide, ethanol and paracetamol etc.which causes marked measurable effects, the magnitude of which can be measured by carrying out various liver function test like morphological, fuctional, biochemical and histopathological determinations. These methods are very convenient laboratory method. In this method reproducibility of the result is very poor.
b. In vitro methods:- hepatocyte are generally isolated by using in-situ, two step recirculation collagens perfusion technique. These seeded in small container and expose to test sample and toxins. After particular time period, the degree of toxicity assed by viability tests and enzyme levels such as SGOT, SGPT, ALP, Total protein, bilirubin and Cholesterol.
c. Ex-vivo:- in this after completion of preselected in vivo test protocol hepatocyte are isolated and the percentage of viable cells and biochemical parameters are determined as a liver function testes. These methods are somewhat better correlated to clinical models than in vitro or in vivo methods.
Pharmacotherapy for Hepatotoxicity:
In recent years the use of herbal drug for the treatment of liver diseases has increased all over the world because of herbal drugs are believed to be harmless and free from serious adverse reactions as they are obtained from nature and are easily available. Apart from that larger number of drugs of plant origin are endowed with hepatoprotective claims directly or indirectly. Many research has examined the effects of plants used traditionally by many traditional remedies from plant origin have been used for the treatment of liver diseases. In most cases, research has confirmed traditional experience and wisdom by discovering the mechanisms and mode of action of these plants as well as re affirm the therapeutic effectiveness of certain plants or plant extracts in clinical studies. Several hundred plants have been examined for use in a wide variety of liver disorders. Just a handful has been fairly well researched.There are about 600 commercial herbal formulations, which are claimed to have hepatoprotective activity and many of them are being sold in markets all over the world.
In India, about 40 patented polyherbal formulations representing a variety of combinations of 93 herbs from 44 families are available Liver protective herbal drugs contain a variety of chemical constituents like phenols, coumarins, lignans, essential oil, monoterpenes, carotenoids, glycosides, flavonoids, organic acids, lipids, alkaloids and xanthone derivatives.
Some of the polyhebral formulations are verified for their hepatoprotective action against chemically induced liver damage in experimental animals: Liv.52, Liv.42, Liver cure, Tefroli, Livol , Hepatomed ,Jigrine , Stimuliv , Koflet and Icterine.
In present urosodeoxycholic acid is only one allopathic compound approved by US FDA for treatment of primary biliary cirrhosis or hepatoprotection.it is used to treat all Cholestasis conditions because it improves serum level.
Clinical Uses of UDCA
1. Biliary cirrhosis
2. Biliary disease secondary to cystic fibrosis
3. Non-alcoholic steatohepatitis, idiopathic chronic hepatitis
4. Autoimmune hepatitis
5. Primary sclerosing cholangitis.
6. Alcoholic hepatitis
List of some medicinal plant which shows hepatoprotective activity.
Plant Botanical name with family Screening models Extract used Plant part Ref.
Accacia catechu Leguminose Carbon tetrachloride induces Ethyl acetate Powder pale catechu 45
Aegle marmelos Rutaceae Paracetamol induces Ethanol Fruit pulp 46
Aerva lanata linn.
Amaranthaceae Paracetamol induces Hydro alcoholic Coarse powder 47
Annona squamosa linn.
Annonaceae Isoniazide + rifampicin Alcoholic Leaves 48
Alocasia indica linn.
Araceae Paracetamol induces Hydro alcoholic Leaves 49
Anogeissus latiafolia
Annonaceae Carbon tetrachloride induces Hydro alcoholic Bark 50
Aloe barbadensis
Liliaceae Carbon tetrachloride induces Aqueous extract Dried areal part 51
Azardirachta indiaca linn.
Meliaceae Paracetamol induced Ethanol Leaf 52
Boerhavia diffusa
Nyctaginaceae Thioacetamide Aqueous Roots 53
Capparis decudua
Capparaceae Carbon tetrachloride induces Aqueous and methanolic Stems 54
Bixa orellana Bixxaceae Carbon tetrachloride induces Methanolic Plant material 55
Cajanus scarabaeoide Fabaeceae
Paracetamol induced 84 Ethanol Whole plant 56
Carissa carindas Linn Apocyanaceae
Carbon tetrachloride induces 85 13 Ethanol Root 57
Carum copticum Apiaceae Carbon tetrachloride induces, paracetamol 86
Aqueous methanolic extract Seed 58
Calotropis procera Asclepediaceae Carbon tetrachloride induces 87
Ethanol Root bark 59
Cassia fistula Leguminosae Carbon tetrachloride induces 88
Methanolic Leaf 60
Capparis
decudua
Capparaceae
Carbon tetrachloride induces Aqueous and
Methanolic
Stems 61
Chamomile
capitula
Asteraceae Paracetamol Aqueous
Ethanol Fresh plant 62
Decalepis hamiltonii Asclepiadaceae Carbon tetrachloride induces 99
Aqueous Roots 63
Equisetum arvense equisetaceae Carbon tetrachloride induces 101
Metahnolic Aerial parts 64
Embelia ribes myrsinaceae Paracetamol induced 102
Water Fruits 65
Enicostemma axillare Gentianaceae D-galactosamine 103 Ethanol Whole plant 66
Ginkgo biloba Ginkgoaceae Carbon tetrachloride induces 109
Ethanol Dried extract 67
Glyrrhiza glabra Fabaceae Carbon tetrachloride induces 110
Crude drug Root powder 68
Hibiscus Sabdariffa Malvaceae Paracetamol induced 115
Water Leaves 69
Hypericum japonicum Clusiaceae Carbon tetrachloride induces 117
Water Whole plant 70
Momordica
charantiaLi
nn.
Cucurbitaceae 34
Carbon tetrachloride induces Hydroalcoholic Leaves 71
Plumbago
zeylanicaLi
nn.
Plumbaginaceae 35 Carbon tetrachloride induces Methanolic Aerial part 72
Premna
serratifolia
Lamiaceae 36
Carbon tetrachloride induces Ethanol Leaves 73
Rhododend
ron
Arboreum
Headaches.
Ericaceae 37
Carbon tetrachloride induces Ethanol Leaves 74
Scoparia
dulcis L.
Scrophulariaceae
38
Carbon tetrachloride induces Petroleum ether,
Diethyl ether,
And methanol Whole
Fresh plant
75
Spondias
pinnata
Anacardiaceae 39 Carbon tetrachloride induces Methanolic Stem 76
Ocimum sanctum Lamiaceae 135
Paracetamol induced Hydroalcoholic Leaf 77
Orthosiphan stamineus Lamiaceae 136 Acetaminophen Methanol
Leaves 78
Oroxylum indicum linn.
bignoniacec Carbon tetrachloride induces Ethanol Leave 79
Phyllanthus amarus schum Euphorbiaceae 137
Ehanol Ethanol Aerial part 80
Phyllanthus amarus Euphorbiaceae 138 Aflatoxin b1 induced liver
damage
Ethanol Whole plant except root 81
Picrorhiza kurrooa Scrophulariaceae 142
Alcohol ‘carbon tetra chloride Ethanol Root and rhizomes 82
Picrorrhiza rhizome Scrophulariaceae 143
Poloxamer(PX)-407 Water Dried underground stem 83
Piper chaba Piperaceae 144
D-galactosamine Aqueous acetone Fruit 84
Piper longum Piperaceae 145
Carbon tetrachloride induces Milk extract Fruits and roots 85
Pittosporum neelgherrense Pittospoaceae
146
Carbontetra chloride,
D-galactosamine and
acetaminophen Induced
Methanolic Stem bark 86
Pterocarpus marsupium Papilionaceae 148
Carbon tetrachloride induces Methanol and aqueous Stem bark 87
Plantago major Plantaginaceae 147
Carbon tetrachloride induces Ethanol Seeds 88
Ptrospermum acerifolium Sterculiaceae 149
Carbon tetrachloride induces Ethanol Leaves 89
Ricinus communis Euphorbiaceae 150
Carbon tetrachloride induces Cold aqueous extract Leaves 90
Sarcostemma brevistigma Asclepiadaceae 152
Carbon tetrachloride induces Ethyl acetate Stem 91
Saururus chinensis Sauruaceae 153
Carbon tetrachloride induces Ethanol Whole plant 92
Scoparia dulcis Scrophulariaceae 154
Carbon tetrachloride induces Methanol,diethyl ether,pt.ether Whole plant 93
Solanum nigram Linn Solsnaceae 156
Carbon tetrachloride induces Aqueous -Methanol Fruits 94
Tecomella undulate Bignoniaceae 157
Thioacetamide Aqueous-ethanolic Stem, bark 95
Tephrosia purpurea Linn Fabaceae 158 Thioacetamide Aqueous -methanol Aerial parts 96
Thunbergia laurifolia Acanthaceae 159
Ethanol Aqueous extract Leaves 97
Tridax procumbens Asteraceae 160
Carbon tetrachloride induces Ethanol Leaves 98
Tylophora indica Asclepiadaceae 161
Ethanol Methanolic Leaf powder 99
Vitex trifolia Verbenaceae 162
Carbon tetrachloride induces Ethanol and water Leaves 100
Vitis vinifera Vitaceae 163 Carbon tetrachloride induces Etylacetate n-butanol ,water Leaves 101
CONCLUSION:
Hepatic diseases remains a major worldwide health problem thus the search of new medicine is still going many formulations of medicinal plants are used to treat liver disorder in Chinese ethno medical and traditional medicine practices. The goal of ethnopharmacological studies on medicinal plants should not be restricted to find new prototype pure compounds as drugs. Active extracts or mixture of extracts may prove very effective drugs.
Plant drugs for liver diseases should possess sufficient efficacy to cure severe liver diseases caused by toxic chemicals, viruses, excess alcohol intake, and repeated administration of drugs like paracetamol, Rifampicin and Isoniazid. Various herbal plants and plants extracts have significant hepatoprotective activity in animal models was proved by research. The hepatoprotective activity of the plants probably due to the presence of phenols, coumarins, lignans, essential oil, monoterpenes, carotenoids, glycosides, flavonoids, organic acids, lipids, alkaloids and xanthone derivatives.
Effective formulations have to be developed using indigenous medicinal plants, with proper pharmacological experiments and clinical trials. The manufacture of plant products should be governed by standards of safety and efficacy. Along with all more allopathic drugs like urosodeoxycholic acid need to be develop for treatment of liver disease and hepatotoxicity.