sandeep kadaganchi

LIVER TARGETING: 

LIVER TARGETING Presented By Kadaganchi Sandeep, M. Pharmacy (Pharmaceutics) II-Semester, JANGAON INSTITUTE OF PHARMACEUTICAL SCIENCES (2010-2011) 1

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Concept Introduction Hepatic Inflammation and Fibrosis Liver Cirrhosis Drug Targeting to the Liver Anti-inflammatory Drugs Anti-fibrotic Drugs Targeting of Anti-inflammatory Drugs for the Treatment of Liver Fibrosis Selective Drug Delivery for the Treatment of Other Hepatic Disorders Conclusion References CONTENTS 2

Targeting concept originated from ‘Magic bullet idea’ proposed by Paul Ehrlich in 1902. Targeted drug delivery is an event where, a drug carrier complex / conjugate delivers the drug (s) exclusively to preselected cells in a specific manner.: 

Targeting concept originated from ‘Magic bullet idea’ proposed by Paul Ehrlich in 1902. Targeted drug delivery is an event where, a drug carrier complex / conjugate delivers the drug (s) exclusively to preselected cells in a specific manner. In 1981, Gregoriadis described targeting using novel drug delivery systems as ‘old drugs in new clothes’. TARGETING CONCEPT 3

Targeted drug delivery: 

Targeted drug delivery It implies for selective and effective localization of pharmacologically active moiety at a predetermined (preselected) in therapeutic concentration, while restricting its access to non-target normal cellular linings, thus minimizing toxic effects and maximizing therapeutic index (Gregoriadis & Florence, 1993). 4

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Drug targeting is the ability of the drug to accumulate in the target organ or tissue selectively and quantitatively, independent of the site and methods of its administration. In general, the aim of targeted therapies is to increase the efficacy and reduce the toxicity of drugs. The choice of carrier system to be used in drug targeting strategies depends on which target cells should be reached and what drug needs to be delivered. INTRODUCTION 5

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Targeting drugs to specific organs, tissues, or cells is an attractive strategy for enhancing drug efficacy and reducing side effects. Site-specific drug delivery is a concept that has the potential to increase local drug concentrations and thereby produce more effective medicines with fewer side effects. Most of the chronic liver diseases eventually result in excess scarring leading to liver cirrhosis . Fibrosis or scarring of the liver occurs after damage to liver tissue. Chronic liver diseases are characterized by an inflammatory and a fibrotic component, both of which can be targets for pharmacological intervention. 6

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7 Since drug targeting implies the manipulation of drug distribution in the whole body, emphasis should be put on in vivo studies. This fatal disease, to date, can only be effectively treated with a liver transplantation . Since this is a costly procedure, hampered by the lack of donor organs among other technical factors, much effort has been put into developing new drugs. The drugs available are not sufficiently effective and/or cause too many adverse side-effects . Therefore drug targeting is an option in trying to maximize efficacy and minimize (ADR) adverse drug reactions.

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A Targeted drug delivery system is preferred in the following situations: 

A Targeted drug delivery system is preferred in the following situations 9

Important Properties Influencing Drug Targeting: 

Important Properties Influencing Drug Targeting Drug -Concentration, Particulate location and Distribution -Molecular Weight, Physiochemical properties -Drug Carrier Interaction Carrier -Type, Amount of Excipients - Surface, Surface Characteristics, size, -Density In Vivo Environment -PH, Polarity, Ionic Strength -Surface Tension, Viscosity -Temperature -Enzyme -Electric Field 10

Rationale of drug targeting / Advantages: 

Rationale of drug targeting / Advantages Exclusive delivery to predetermined sites with maximum intrinsic activity of drug. Reduced access of drugs to irrelevant non-target cells. Targeted delivery to previously inaccessible domains. E.g.: intracellular sites, virus, bacteria and parasites. Controlled rate of drug delivery to pharmacological receptor and specific binding with target cells. Bioenvironmental protection of drug en route to site of action. 11

Strategies of drug targeting: 

Strategies of drug targeting 12

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The liver is one of the two major glands associated with the digestive tract. It is the largest internal organ (weight 1500 g) and the largest exocrine gland in the human body. Its major exocrine function is the formation and secretion of bile. The liver is located in the upper right quadrant of the abdominal cavity just beneath the diaphragm. It consists of four lobes. The left and right lobes are the major ones, and are separated by the falciform ligament. Because of its interposition, the liver has a dual blood supply. Nutrient-rich blood arrives through the portal vein and oxygen-rich blood through the hepatic artery. Together these channels import a large variety of endobiotics and xenobiotics, ranging from nutrients to toxic substances derived from the digestive system. LIVER 13

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Anatomy of liver 14

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15 Weighs about 1 pound. Carries out 1000s of functions per day. Effects the emotions. Cleanses the blood. Helps regulate blood sugar. Metabolizes fats. Synthesizes vitamin A. Breaks down toxic substances. Stores iron for the body. Stores glycogen (converted glucose). Metabolizes carbohydrates. Metabolizes proteins . LIVER FACTS

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THE MAJOR LIVER FUNCTIONS Formation and secretion of bile Detoxification and inactivation of drugs and toxic substances Processing and storage of nutrients and minerals Synthesis of plasma proteins and coagulation factors Production of hormones Phagocytosis of debris and bacteria Storage of Vitamin A LIVER CELLS The Parenchymal Cell (PC) The Sinusoidal Endothelial Cell (SEC) The Kupffer Cell (KC) The Hepatic Stellate Cell (HSC) 16

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Schematic representation of the architecture of the liver Blood enters the liver through the portal vein (PV) and hepatic arteries (HA), flows through the sinusoids, and leaves the liver again via the central vein (CV). KC, Kupffer cells; SEC, sinusoidal endothelial cells; HSC, hepatic stellate cells; BD, bile duct. 17

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The Parenchymal Cell (PC) The liver consists mainly of parenchymal cells, or hepatocytes (60-70%). Most drug-targeting preparations designed for liver targeting of therapeutic compounds are directed towards this cell type, generally aiming at the asialoglycoprotein receptor using galactose residues coupled to a core molecule for binding. The Sinusoidal Endothelial Cell (SEC) The endothelial lining of the sinusoids in the liver differs from the other capillaries in the body and is adapted to form a selective barrier between blood and hepatocytes(20%) SECs play an important role in the pathogenesis of several acute and chronic inflammatory liver diseases. Consequently they are attractive target cells for anti-inflammatory therapies. 18

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The Kupffer Cell (KC) Kupffer cells are the largest reservoir of fixed-tissue macrophages and are quantitatively the most important cell type for the removal of circulating microorganisms, LPS, tumour cells, immune complexes, and other circulating tissue and microbial debris. They account for about 15% of the liver cell population in number and they are preferentially located in the periportal areas. The Hepatic Stellate Cell (HSC) Another resident hepatic cell that is important in the pathogenesis of chronic liver diseases is the hepatic stellate cell (also known as fat-storing cell, Ito cell, lipocyte, perisinusoidal cell). They produce and secrete matrix proteins such as collagens I, III, IV,V and VI, fibronectin, laminin, tenascin, undulin, hyaluronic acid and proteoglycans , as well as extracellular matrix degrading metalloproteinases and their inhibitors, the tissue inhibitors of metalloproteinases (TIMPs). 19

HEPATIC INFLAMMATION AND FIBROSIS: 

HEPATIC INFLAMMATION AND FIBROSIS Virtually any damage to the liver can cause hepatocyte destruction and parenchymal inflammation. If the damage is minor and occurs only once, local restoration mechanisms will suffice to repair the damage. If, however, the damage is major or persistent, an inflammatory response will be generated. This inflammation is the result of cytokine-mediated activation of sinusoidal cells, their subsequent release of pro-inflammatory cytokines and their expression of adhesion molecules for the recruitment of circulating leucocytes. During conditions of chronic liver injury, however, the repair process does lead to scar tissue formation, which is deposited within the liver until impairment of liver function occurs. This process is called liver fibrogenesis and the end stage, or irreversible stage, is referred to as liver cirrhosis. 20

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Diagram outlining the pathogenesis of liver fibrosis Injury to parenchymal cells (PC) results in the activation of Kupffer cells (KC) and sinusoidal endothelial cells (SEC) and the recruitment on inflammatory cells (IC). These cells release cytokines, growth factors and reactive oxygen species that induce activation and proliferation of hepatic stellate cells (HSC). HSCs gradually transform into myofibroblasts (MF), the major producers of extracellular matrix (ECM) proteins. 21

LIVER CIRRHOSIS: 

LIVER CIRRHOSIS This is largely the result of alcohol abuse, viral hepatitis and biliary diseases. The causes for cirrhosis are Chronic exposure to toxins such as alcohol, drugs or chemicals. Viral hepatitis resulting from infection with the hepatitis B, C or D viruses. Metabolic disorders such as Wilson’s disease (copper storage disease) and haemochromatosis (iron overload disease). Autoimmune diseases such as primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC) and autoimmune hepatitis. Venous outflow obstruction. Cirrhosis of unknown causes. 22

DRUGS TARGETING TO THE LIVER: 

DRUGS TARGETING TO THE LIVER Targeting of drugs to cells with in the liver, there are several ways to intervene in the fibrotic process. One way is the targeting of drugs to SECs and KCs to modulate their release of pro-inflammatory mediators, this may arrest the inflammatory process leading to cirrhosis. Another way is the delivery of drugs to HSCs to inhibit collagen production or to enhance their extracellular matrix degrading capabilities. Targeting to KCs and SECs to influence the inflammatory process that is the basis of most forms of liver cirrhosis. A number of specific entry mechanisms that could be used for cell-specific delivery of drugs, by either enclosing drugs in particles or by coupling drugs to macromolecular carriers with high affinity for certain uptake mechanisms, drugs can be concentrated in the target cells without causing side-effects elsewhere in the body. The choice of type of carrier depending on the specificity of the carrier, the potency of the drug and the entry mechanism during pathological conditions. 23

CARRIERS DIRECTED AT SECs AND KCs: 

CARRIERS DIRECTED AT SECs AND KCs Albumins : Albumin is one of the soluble macromolecular carriers available for drug targeting purposes, it is small in size as compared to other potential carriers. It can be derivatized with molecules that will determine its cell specificity, and with drug molecules. A maximum of about 60 molecules can be coupled to albumin through the ε-NH 2 of the lysine residues. Albumin modified with negatively charged groups like succinic acid (Suc-HSA) and aconitic acid (Aco-HSA) are avidly taken up by SECs via the scavenger receptors type A. After interaction of the carriers with specific receptors, the carrier is then taken up by endocytosis and transported intracellularly to acidified endosomes and lysosomes. The carrier is proteolytically degraded in the lysosomes and if a drug is coupled to the carrier, it is then released to diffuse into the cytoplasmic compartment. 24

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Liposomes: Liposomes are small vesicles composed of unilamellar or multilamellar phospholipid bilayers enclosing an aqueous space. Soluble drugs can readily be incorporated into this aqueous space and lipophilic drugs can be incorporated into the lipid bilayer. The loading capacity for drugs is therefore much greater than that of the modified albumins. Elimination from the circulation is dependent on the lipid composition, charge, and size of the liposomes. Liposomes such as neutral and negatively-charged liposomes, are however, primarily cleared by the phagocytotic processes of the cells of the reticuloendothelial system (RES), the KCs having the greatest responsibility for this process. This feature of liposomes can seriously limit the use of liposomes in targeting other sites in the body. 25

ANTI-INFLAMMATORY DRUGS: 

ANTI-INFLAMMATORY DRUGS Nonsteroidal Anti-inflammatory Drugs (NSAIDs) NSAIDs are drugs related to acetylsalicylic acid which inhibit cyclooxygenase (COX), the enzyme in the synthesis of PGs and thromboxanes from arachidonic acid.There are two isoforms of cyclooxygenase, COX-1 and COX-2. COX-1 constitutively expressed in blood vessels, stomach and kidney, while COX-2 is induced under inflammatory conditions by certain serum factors, cytokines, and growth factors. Most of the currently used NSAIDs non-selectively inhibit both COX- 1 and COX-2. They are widely used in inflammatory disorders of the joints such as arthritis, of the tendons. 26

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Glucocorticosteroids Glucocorticosteroids are the synthetic derivatives of the adrenal gland hormone cortisol. At pharmacological doses they prevent or suppress inflammation and other immunologically mediated processes. These drugs are therefore used for a variety of inflammatory diseases such as allergic diseases, rheumatic disorders, renal diseases, bronchial asthma, skin and gastrointestinal diseases. The anti-inflammatory and immunosuppressive activities of glucocorticosteroids are most likely due to the inhibition of the production of a wide range of cytokines, chemokines, eicosanoids, and metalloproteinases in many cell types. In macrophages they block the release of numerous cytokines (IL-1, IL-6, TNFα), inhibit the expression of the MHC class II antigens, depress production and release of pro-inflammatory PGs and LTs, and depress tumouricidal and microbicidal activities of activated macrophages. In the case of neutrophils they inhibit neutrophil adhesion to endothelial cells, thereby reducing the infiltration of neutrophils at inflamed sites. 27

ANTI-FIBROTIC DRUGS: 

ANTI-FIBROTIC DRUGS HSCs are the major contributors to the deposition of extracellular matrix in fibrotic livers and should therefore be the target for anti-fibrotic therapy. Using the carriers that are internalized by activated HSCs, potential anti-fibrotic drugs include collagen synthesis inhibitors, e.g. the prolyl hydroxylase inhibitors, inhibitors of HSC activation, e.g. NFκB inhibitors or histone deacetylase inhibitors (trichostatin A), and inhibitors of portal hypertension, the endothelin antagonists. 28

TARGETING OF ANTI-INFLAMMATORY DRUGS FOR THE TREATMENT OF LIVER FIBROSIS: 

TARGETING OF ANTI-INFLAMMATORY DRUGS FOR THE TREATMENT OF LIVER FIBROSIS There are several carriers available for targeting the key cells in the hepatic inflammatory process. The method of loading a carrier with anti-inflammatory drugs largely depends on the proposed entry mechanism of the carrier into the cell. In the case of drug-filled liposomes and drug molecules covalently linked to albumin this means the carrier must be degraded in the target cell for the drug to be released. After receptor-mediated uptake most of the carrier is thus lysosomally degraded and a pharmacologically active drug can be released. For covalently attached drugs this means enzymatic (lysosomal hydrolases or reductases) or hydrolytic (acid environment) degradation of the chemical bond between the drug and the carrier. 29

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Targeting of NSAIDs For targeting with a soluble macromolecular carrier, the NSAID naproxen (Nap) was coupled via its carboxyl groups to the free amino groups of the lysine residues in the (Man-)HAS molecule, resulting in a direct amide linkage. This type of bond is not very sensitive to proteolytic degradation and incubation with lysosomal lysates showed release of a lysine conjugate of Nap. This Nap-lysine, however, was equipotent to Nap itself with respect to inhibition of PGE 2 synthesis. As compared to free Nap, Nap coupled to HSA was preferentially taken up by the liver, mainly by SECs, but to a lesser extent also by KCs. Scavenger receptors were responsible for this uptake. Liver fibrosis induced significant alterations in the pharmacokinetic behaviour of Nap20-HSA. 30

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The chemical synthesis of naproxen-HSA Naproxen is first converted to an ester and is then coupled to the free ε-NH2 of the lysine residues in human serum albumin (HSA). NHS: Nhydroxysuccinimide, DCC: dicyclohexylcarbodiimide . 31

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Targeting of Glucocorticosteroids The glucocorticosteroid dexamethasone (Dexa) was coupled to HSA and Man10-HSA for targeting to SECs and KCs. Dexa itself could not be coupled directly to the protein, and therefore had to be derivatized to create a reactive compound. succinic acid was coupled to the alcohol group on C21 yielding Dexa hemisuccinate. The introduced carboxyl group could then easily be coupled to the free amino groups of the lysine residues in the HSA molecule yielding Dexa 10 -HSA and Dexa 5 -Man 10 -HSA. The ester bond between native Dexa and the succinate spacer proved to be more sensitive to proteolytic enzymes than the amide bond between the succinate spacer and the protein. Lysosomal degradation of the Dexa-HSA conjugate, therefore, yielded the native Dexa. Dexa incorporated into several particle-type carriers, Dexa-21-palmitate into lipid microspheres for targeting inflammatory cells and macrophages in the treatment of rheumatoid arthritis . 32

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The chemical synthesis of dexamethasone-HSA Dexamethasone hemisuccinate is first converted to a reactive intermediate with isobutylchlorocarbonate and is then coupled to the free ε-NH2 of the lysine residues in human serum albumin(HSA). 33

SELECTIVE DRUG DELIVERY FOR THE TREATMENT OF OTHER HEPATIC DISORDERS: 

SELECTIVE DRUG DELIVERY FOR THE TREATMENT OF OTHER HEPATIC DISORDERS Drug targeting preparations have been given to patients with various infectious diseases. For the treatment of Leishmaniasis, liposomes as well as mannosylated HSA have been used to deliver antiparasitic drugs, such as methotrexate, amphotericin B, doxorubicin and muramyl dipeptide to KCs. Liposomal amphotericin B was also tested in immunocompetent patients with visceral Leishmaniasis and was proven to be an effective treatment. Drug targeting preparations based on lactosylated HSA have been used for the treatment of chronic viral hepatitis, because these viruses reside in hepatocytes, several anti-viral nucleoside analogues coupled to this carrier for the treatment of hepatitis. 34

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The treatment of tumours in the liver with drug targeting preparations is hampered by the lack of tumour specifity of most preparations. Liposomes incorporating the immunomodulator muramyl tripeptide phosphatidylethanolamine have been used as an ‘aspecific’ approach to increasing the number of tumouricidal macrophages in the liver in order to prevent the development of metastases. 35

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Nearly every medication that is prescribed has its hepato-toxic effect. 36

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37 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. Drug-induced liver injury is responsible for 5% of all hospital admissions and 50% of all acute liver failures.

CONCLUSION: 

CONCLUSION Hepatic inflammation and fibrosis of the liver are multi factorial processes that cannot be treated successfully with drugs currently on the market. These drugs either lack suitable efficacy or cause too many side-effects. New directions for therapy include the targeting of anti inflammatory drugs to the key players in the chronic inflammatory process ( the Kupffer cells and liver endothelial cells ). The major challenge in the near future will be to establish the relevance of the concept of drug targeting in experimental models of disease, in human tissue in vitro, and finally in patients with liver diseases. Targeted therapies is to increase the drug efficacy and reduce the side effects and toxicity of drugs. 38

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REFERENCE Batrarbro N. Melgert , Leonie Beljaars , Dirk K. F. Meijer, Klaas Poelstra , Cell specific Delivary of Anti-inflammatory Drugs to Hepatic Endothelial and Kupffer Cells for the Treatment of Inflammatory Liver Diseases, 2001. Kawada N, Histol . Histopathol . 1997, 12, 1069–1080. Vogl S, Petermann H, Dargel R, Liver 1996, 16, 313–320. van Oosten M, van de Bilt E, de Vries HE, Van Berkel TJC, Kuiper J, Hepatology 1995, 22, 481–488. Vogl S, Petermann H, Dargel R, Liver 1996, 16, 313–320. Rockey DC, Weisiger RA, Hepatology 1996, 24, 233–240. Rockey DC, Weisiger RA, Hepatology 1996, 24, 233–240. Ramadori , Knittel T, Saile B, Digestion 1998, 59, 372–375. Rieder H, Meyer zum Büschenfelde K-H, Ramadori G, J. Hepatol . 1992, 15, 237–250. 39

“confidence and hardwork” are the best medicines to kill the disease called failure… it will make you a sucessful person.: 

“ confidence and hardwork ” are the best medicines to kill the disease called failure… it will make you a sucessful person. 40