Herbal and polymeric approaches for liver-targeting drug delivery: novel strategies and their significance

Abstract

The liver is a vital organ present in vertebrates, which performs many functions including detoxification, protein synthesis and production of various bio-chemicals which are very important for digestion. A large number of serious liver disorders affect millions of people worldwide which are very difficult to treat properly despite many efforts. There are several factors which are responsible for liver injuries, include plants (Crotalaria Senecio Heliotropium Symphytum officinale), drugs (analgesic and antibiotics), industrial toxins (mercury and lead), water, alcohol and so on. Herbal medicinal preparations can be used for the treatment of a large number of human liver disorders like cirrhosis, hepatitis, carcinomas, etc. Indian Medicinal Practitioner’s Co-operative pharmacy and Stores (IMPCPS) approved herbal-based systems (Unani, Siddha and Ayurveda) for the treatment of various chronic liver disorders. Different types of the receptors are found on the surface of hepatocytes, Kupffer cell, hepatic stellate cell and sinusoidal endothelial cells, etc., which can be used for achieving liver targeting. These receptors bind to different types of ligands (galactosylated, lactobionic acid, asialofetuin, etc.) which can be used in the formulation to achieve targeted delivery of the drug. Various novel particulate approaches (liposomes, niosomes, nanoparticles, micelles, nanosuspensions, etc.) can be used to enhance the targeting efficiency of systems to receptors found on the surface of different cells present in the liver. In this review, we focused on the status of liver targeting via herbal and nanotechnology inspired formulation approaches.

• Herbal approach
• liver targeting
• nanotechnological approach
• targeted drug delivery

Introduction

The liver is a vital organ present in vertebrates which perform many functions including detoxification, protein synthesis and production of various bio-chemicals which are very important for digestion (Singh et al., 2014b). Liver has highly specialized tissues which regulate a wide variety of high volume biochemical reactions like synthesis and breakdown of various small and complex molecules (Maton et al., 1993). Many serious liver disorders affect millions of people worldwide, which are very difficult to treat effectively after many efforts. A large number of drugs, especially potent drugs may not be effective enough in vivo or may show high adverse effects. Enhanced delivery of drug into the target cells may improve the activity of the drug at the target site (Singh et al., 2014a). Therefore, it is important to understand the morphology of liver before explaining the targeting of the drug to liver. Similarly, before designing a novel drug delivery system, it is important to understand the molecular scale of the target tissues. The liver performs large number of metabolic, immunological and endocrine functions which are very important for normal functions of body (Parnami et al., 2013). Blood circulation in the liver occurs through a permeable discontinuous capillary network known as sinusoids which small blood vessels (5–10 μm wide) are having radiating rows of hepatocytes in between them. Inside the sinusoid capillaries, Kupffer cells are present which are responsible for phagocytic activity in the liver (Abe et al., 1988). Hence, liver cells are divided into two major categories which are parenchymal cells (hepatocytes) and non-parenchymal cells. Parenchymal cells occupy about 80% of the total liver volume. Non-parenchymal cells occupy about 6.5% of the total liver volume (Kmiec, 2001). A non-parenchymal cell consists of sinusoidal hepatic endothelial cells, Kupffer cells and hepatic stellate cells. Targeting of drugs to liver can be done by combining the drug along with targeting moieties which are recognized by the receptors found on the surface of the liver cells (Kaur et al., 2014c). Hepatic-targeted drug delivery system (HTDDS) can be achieved using a variety of vehicles such as microspheres, emulsions, liposomes, nanoparticles, albumin, lipoproteins, polymer conjugates and recombinant chylomicrons, which are actively absorbed by the liver (Garg et al., 2013). Receptor–ligand drug targeting systems which is well used to achieve targeted drug delivery to liver (Garg et al., 2012). The HTDDS will not only distribute drugs to the liver but also result in enhancing bioavailability of the drugs as well as in reduction of various side effects of drugs. It is very well known that there are many receptors present on the surface of hepatic cells. Abundant receptor, which is specific to hepatic parenchymal cells, is asialoglycoprotein receptors, which have ability to recognize the galactosylated ligands, lactobionic acid ligand, asialofetuin ligands, soybean derived stearyl glycoside (SG) ligands and many more. Similarly, glycyrrhetinic acid receptors are mainly found on the sinusoidal surface of mammalian hepatocytes. It has ability to recognize the glycyrrhetinic acid ligands. The hepatic non-parenchymal cells also have various receptors present on their surface such as mannose receptors that are located on the surface of Kupffer cells. Chemically, mannosylated albumins have received high attention because of albumin receptors present in them, which specifically recognize ligands containing N-acetyl glucosamine (Kawakami et al., 2000) or l-fructose, non-reducing d-mannose (Nishikawa et al., 2000; Hashida et al., 2001). These receptors are mainly expressed on the surface of non-parenchymal liver cells like Kupffer cells and sinusoidal endothelial cells (Higuchi et al., 2004). Various receptors, which are found in the different liver cells, are shown in Table 1.

Table 1. List of receptors which are found on different liver cells.

Hepatic cells	Receptors on different cells	References
Hepatocytes	1. Asialoglycoprotein receptor (ASGP-R) 2. IgA-Receptors 3. Transferrin receptors 4. HDL receptors 5. LDL receptors 6. Insulin receptors 7. Scavenger receptors	Yang et al. (2014) Liu et al. (2014) McDonald et al. (2014) Martinez et al. (2003) Goldstein & Brown (2009) Jiang et al. (2014) Li et al. (2014)
Endothelial cells	1. Scavenger receptors 2. Mannose/N-acetyl glucosamine receptors 3. Fc Receptors immune complexes 4. Hyaluronan fibronectin, denatured collagen receptors	Li et al. (2014) Ramirez-Garcia et al. (2013) Storch et al. (2002) Rost & Sumanas (2014)
Hepatic stellate cells	1. Uroplasminogen receptors 2. Thrombin receptors 3. Ferritin receptors 4. α2-macroglobulin receptors 5. IGF II receptors	Friedman (2008) Kallis et al. (2014) Moss et al. (1992) Strickland et al. (2014) List et al. (2014)
Kupffer cells	1. LDL receptors 2. Mannose receptors 3. Galactose receptors 4. Scavenger receptors (Class AI, BI, BII, MARCO CD3 etc.) 5. Complement receptors (C3b, C1q) 6. Fc receptors (opsonized materials, immune complexes receptors)	Goldstein & Brown, 2009) Ramirez-Garcia et al. (2013) Coombs et al. (2006) Li et al. (2014) Woods & Greally (1979) Storch et al. (2002)

Mechanism of hepatotoxicity

Many chemicals damage mitochondria whose dysfunction results in release of excessive amount of oxidants leading to hepatic cells injury (Kaur et al., 2014b). Activation of some enzymes like CYP2E1 also leads to oxidative stress (Jaeschke et al., 2002). Accumulation of bile salts inside the liver may be due to the injury to hepatocyte and bile duct cells which itself promotes liver damage (Patel et al., 1998). Two important pathways may be responsible for toxicity – direct hepatotoxicity and adverse immune reactions (Kaur et al., 2014a). In most of the cases, hepatic toxicity is generally initiated by the bioactivation of drugs into chemically reactive metabolites (Goyal et al., 2013b). These produced reactive metabolites have high ability to interact with cellular macromolecules like proteins, lipids and nucleic acids which result in lipid peroxidation, DNA damage, protein dysfunction and oxidative stress (Lynch & Price, 2007). Disruption of ionic gradients as well as disruption in intracellular calcium stores may be caused by the presence of these metabolites which may result in the loss of energy production as well as mitochondrial dysfunction. Various inflammatory cytokines like interferon (IFN)-γ, interleukin (IL)-1β and tumor necrosis factor (TNF)-α, which are produced during hepatic injury, may promote1 tissue damage (Bourdi et al., 2002; Goyal et al., 2013a). Several types of hepatic injuries are discussed in Table 2.

Table 2. Main patterns of liver injury during hepatotoxicity.

Liver injury	Characteristics of liver injury during hepatotoxicity
Zonal necrosis	• Substances like Paracetamol (Deng et al., 2009) and carbon tetrachloride (Kedderis, 1996; Bleibel et al., 2007) may  cause this type of injury. • Amatoxins cause necrosis of liver due to the inhibition of RNA synthesis (Chang & Schiano, 2007). • Herbal plants like Atractylis gummifera and Callilepsis laureola (Naruse et al., 2007), Larrea trdentata (Uetrecht, 2005)  and Teucrium polium (Olson et al., 2000) also cause necrosis. • Such injury is largely confined to a particular zone of the liver lobule. • It may manifest as a very high level of alanine amino transferase and severe disturbance of liver function leading to acute  liver failure.
Hepatitis	• Viral hepatitis may be caused by halothane (Murray et al., 2008), isoniazid, acetaminophen, bromofenac, nevirapine,  ritonavir, troglitazone (Kaplowitz, 2004) and phenytoin (Saukkonen et al., 2006). • Focal hepatitis where scattered foci of cell necrosis may accompany lymphocytic infiltration may be caused by aspirin. • Chronic hepatitis, may be caused by methyldopa, diclofenac, dantrolene, minocycline and nitrofurantoin  (Kaplowitz, 2004).
Cholestasis	• This type of liver injury leads to harm of bile flow, itching and jaundice. • Kaplowitz (2004) reported angiotensin-converting enzyme (ACE) inhibitors, amoxicillin, chlorpromazine,  erythromycins and sulindac to be associated with etiology of cholestasis.
Steatosis	• This type of liver injury may manifest as triglyceride accumulation (Angulo, 2002; Saukkonen et al., 2006). • Aspirin, ketoprofen, tetracycline, nucleoside reverse transcriptase inhibitors and valproic acid (Kaplowitz, 2004;  Chang & Schiano, 2007) may lead to micro vesicular steatosis while acetaminophen and methotrexate  (Langman et al., 2001) may lead to macro vesicular steatosis (Garg et al., 2011).
Granuloma	• Drugs like allopurinol, sulfonamides pyrazinamide, phenytoin, isoniazid, penicillin and quinidine have been found  to cause such injury (Saukkonen et al., 2006; Chang & Schiano, 2007).
Vascular lesions	• Such condition is caused by injury to the vascular endothelium and may be caused by chemotherapeutic agents  (King & Perry, 2001) bush tea [Crotalaria spp.] and anabolic steroids (Ishak & Zimmerman, 1995).
Neoplasm	• Some medications and toxins like vinyl chloride, anabolic steroids, arsenic and thorotrast may cause neoplasms  like hepatocellular carcinoma, angiosarcoma and liver adenomas (Brind, 2007).
Veno-occlusive	• The hepatic vein becomes clogged, blocking off the blood supply to the liver. • It is a non-thrombotic obliteration of small intra-hepatic veins by sub endothelial fibrin (Rollins, 1986) associated  with congestion and potentially fatal necrosis of centrilobular hepatocytes. • The pyrrolizidine alkaloids cause this hepatotoxicity (Kaplowitz, 2001). • Busulfan and cyclophosphamide also cause veno occlusive disease (King & Perry, 2001; Kaplowitz, 2004).

There are several factors which are responsible for liver injuries, include plants, drugs, industrial toxins, water, alcohol and many more.

Hepatotoxicity causing plants

Plants such as Crotalaria Senecio, Chelidonum majus and Callilepsis laureola are also responsible for causing hepatotoxicity. Some of the most common examples are discussed in Table 3.

Table 3. Plants having hepatotoxicity.

Plants	Toxic agents	Mechanism	Effects	Reference
Crotalaria Senecio Heliotropium Symphytum officinale (Comfrey)	Pyrrolizidine alkaloids	Endothelial cell glutathione depletion, central vein necrosis, thrombosis and fibrosis	Veno-occlusive disease	Arzt & Mount (1999)
Atractylis gummifera	Atractylate, gummiferin	Inhibition of oxidative phosphorylation, hepatic necrosis	Hepatitis	Stickel et al. (2001)
Callilepsis laureola	Atractylate	Hepatocyte necrosis	Hepatitis	Stickel et al. (2000)
Chelidonum majus (greater celandine)	Chelidonine, sanguinarine, berberine, coptisine	Lymphocyte infiltration	Hepatitis (cholestatic)	Teschke et al. (2012)
Larreatridentata (chaparral)	Guaiaretic acid derivatives	–	Hepatitis	Haller et al. (2002)
Teucrium chamaedrys(germander)	Furano-diterpenoids	Hepatocyte glutathione depletion and apoptosis	Hepatitis	Kouzi et al. (1994)
Chinese herbal mixtures (Artemisia, hare’s ear, chrysanthemum, plantago seed)	Largely undefined	–	Hepatitis	Jeong et al. (2013)
Lantana Camara	Lantadene A and B	Affect bile canalicular membrane	Jaundice	Sharma et al. (1988)
Aconitum carmichaeli (chuanwu) Aconitum kusnezoffi (caowu)	Pyrrolizidine alkaloids	Central vein necrosis	Aconitine poisoning	Chan et al. (1994)
Aflatoxin – contaminant of plant materials grown/stored in humid areas.	Lipopolysaccharide (LPS) augments AFB(1)	Occurs as a mycotoxin from growth of Aspergillus flavus mould on stored nuts and other foods.	Liver cancer-causing agent	Henry et al. (1999)
Atractylis gummifera (African remedy)	Atractyloside and carboxy atractyloside	Inhibiting mitochondrial oxidative phosphorylation	Diffuse hepatic necrosis	Daniele et al. (2005)
Azadirachta indica (margosa oil)	Chelidonium majus	–	Reye’s Syndrome and steatosis	Chitturi & Farrell (2002)
Bajiaolian	Podophyllo toxin	Podophyllum glycosides are directly toxic to cells	Abnormal liver function tests	Kao et al. (1992)
Heliotropium lasocarpium	Pyrrolizidine alkaloids	–	Hepatotoxicity, veno-occlusive disease	Larrey (1997)
Larreatridentata (Chaparral, creosote bush, grease wood)	Creosote bush	Cytochrome P450- dependent metabolism of NDGA	Hepatic necrosis and chronic hepatitis	Gordon et al. (1995)
Lycopodiumserratum	Pyrrolizidine alkaloids, tetrahydropalmatine	Non-nucleoside reverse transcriptase inhibitors	Acute/chronic hepatitis, fibrosis and steatosis	Om (2011)
Petasites hybridus (butterbur)	Pyrrolizidine alkaloids.	–	Hepatotoxic and carcinogenic	Kälin (2003)
Symphytum officinale, Symphytum uplandicum	Hepatotoxic pyrrolizidine alkaloids.	Reduction of N-oxides	Hepatic veno-occlusive disease	Yeong et al. (1990)

Hepatotoxicity causing drugs

Some class of drugs also shows toxicity in liver. Table 4 shows liver toxicity due to drugs along with its mechanism.

Table 4. Drugs having hepatotoxicity.

Class	Drug	Mechanism	Effect	References
Aniline analgesics	Acetaminophen	A toxic metabolite, NABQI, which is produced by cytochrome P-450 enzymes in the liver	Hydro alcoholic extract of Aervalanata has been reported to possess hepatoprotective activity against paracetamol-induced hepatotoxicity.	Wallace (2004), Manokaran et al. (2008)
Aniline antibiotics	Sulfonamides	By increasing the oxidation to toxic metabolites by the P 450 system	Wide range of adverse reaction and hepatotoxicity	Navarro & Senior (2006)
Anticoagulants	Warfarin, Ximelagatran, Enoxaparin, Acenocoumarin, Phenprocoumon and Heparin	Asymptomatic elevation of serum transaminases, Cytochrome P-450 enzymes, causing decline of adenosine triphosphate levels, loss of ionic gradients, cell swelling and rupture.	Anticoagulants, Showing hepatotoxicity	Arora & Goldhaber (2006), Schimanski et al. (2004)
Anesthesia	Halothane	Toxicity by forming a reactive trifluoroacetyl chloride reactive metabolite by cytochrome P450	Clinical investigations reveal elevated transaminases compatible with hepatitis	Chitturi & Farrell (2002)
Anti-hyperlipidemic drugs	Atorvastatin, Lovastatin, simvastatin, provastatin, Fenofibrate, Ezetimibe	Dose-related toxicity	Cholestatic hepatitis and acute autoimmune hepatitis, acute intrahepatic cholestasis	Bhardwaj & Chalasani (2007), Ricaurte et al. (2006)
Antimalarial drugs	Amodiaquine, iminoquinone	Oxidation to a reactive metabolite, can irreversibly bind to proteins which lead to direct toxicity by disrupting the cell function	Can induce immune response, cause hepatotoxicity	Shimizu et al. (2009)
Antiretroviral	Didanosine and Stavudine	Mitochondrial damage	Hepatotoxicity	Brind (2007)
	Nevirapine, Efavirenz and Abacavir	Hypersensitivity reactions	Hepatotoxicity	Moses (2005)
	Stavudine, Didanosine Zidovudine	Lactic acidosis and hepatic steatosis	Hepatotoxicity	Piroth (2005)
	Fosamprenavir, Ritonavir, Nelfinavir, Tipranavir	Protease inhibitors	Low-hepatotoxicity	Sulkowski et al. (2004)
Anti-tubercular drugs	Isoniazid, Rifampicin, Pyrazinamide, Ethambutol	Increased levels of transaminases	Liver cholestatic jaundice, hepatotoxicity	Khalili et al. (2009)
Arthritis medication	Methotrexate	Transaminase elevation	Hepatotoxicity	Kremer et al. (1989)
Cortico-steroids or glucocorticoids and anabolic androgenic steroids	Glucocorticoids	Promote glycogen storage in the liver	Serious hepatotoxicity, steatosis	Edmondson & Peters (1983), Iancu et al. (1986)
Non-steroidal anti-inflammatory drugs	Aspirin, Phenylbutazone, Ibuprofen, Sulindac, Piroxicam, Diclofenac, Indomethacin	ATP synthesis by mitochondria, and the production of active metabolites, particularly N,5-dihydroxydiclofenac	Jaundice, intrinsic hepatotoxicity, idiosyncratic reaction	O'connor et al. (2003)

Alcohol-induced hepatotoxicity

Alcohol consumption causes hepatotoxicity worldwide (Lieber, 1994). Ethanol metabolism results in protein conjugation, free radical generation and lipid peroxidation (MacGregor et al., 1989). Ethanol plays an important role in methionine metabolism leading to progressive liver injury (Garg et al., 2014). In some species, it has been seen that ethanol can enhance the activity of different enzymes like betaine homocysteine methyl transferase which catalyzes an alternate pathway of methionine metabolism leading to decreased hepatocyte level and increased S-adenosyl homocysteine and homocysteine (toxic metabolites). It shows that betaine has protective effect against ethanol induced vitamin A depletion. It also protects from peroxidative injury in experimental models affected from liver disorders (Barak et al., 2003; Kanbak et al., 2009; Kharbanda, 2009). Smoking is also a major factor in hepatotoxicity (Lee, 2003).

Industrial toxins

Industrial toxins are also responsible for liver toxicity (Garg & Goyal, 2014a). Some examples of toxins are shown in Table 5, which are mainly responsible for causing hepatotoxicity.

Table 5. Industrial toxins causing hepatotoxicity.

Metals	Characteristics	Treatment	References
Mercury	Show Hazardous effect both in animals and humans Mercuric chloride is highly toxic to liver function	Zingiber officinalis	Ezeuko Vitalis et al. (2007)
Lead	Hepatotoxicity caused by lead causes generation of reactive oxygen species and decreased antioxidant defense system	Etlingera elatior	Haleagrahara et al. (2010)
Arsenic	Oxidative stress is causative factor in the development of arsenic-induced hepatotoxicity	Phenyl propanoid compound	Pari & Mohamed Jalaludeen (2011)
Carbon Tetra-chloride	Trichloromethyl is a type of free radical obtained from the oxidation of Carbon tetrachloride which causes degradation in adipose tissue leading to fatty infiltration of hepatocytes (Boll et al., 2001; Klaassen, 2001; Mochizuki et al., 2009)	Spirulina laxissima West, Phenolic extract of chnocarpus frutescense	Kuriakose & Kurup (2011)
Chloroform	Lead to cellular glutathione depletion and increased covalent binding to hepatocellular macromolecules	Rhododendron arboretum	Purushotham et al. (1988)
Vinyl chloride	It is more potent, faster acting than carbon tetrachloride or 1,2-dichloroethylene	Schisandra chinensis	Jenkins et al. (1972), Jaeger et al. (1973)

Water causing hepatotoxicity

Cylindrospermopsis raciborskii was isolated from the domestic water supply reservoir. This species was shown to be severely hepatotoxic for mice (Hawkins et al., 1985). Note: Drugs like troglitazone, bromfenac, ticrynafen, benoxaprofen, trovafloxacin, ebrotidine, nimesulide, nefazodone, ximelagatran and pemoline have been withdrawn due to hepatotoxicity (Xu et al., 2004; Smith et al., 2005; Goldkind & Laine, 2006).

Treatment of liver disorders

Herbal drugs used in treatment of various liver disorders

In ancient China (during Xia period) and India (during Vedic period), use of herbal medicines can be traced about 2100 BC ago. About 600 BC ago, the first written evidence was seen with Charakasamhita of India and in China about 400 BC ago, written evidence was seen in India. Ayurveda forces are agni and ama, where agni representing strength, health as well as innovation and ama representing weakness, disease and intoxication. In India, various other systems of traditional medicine are also found, e.g. Siddha, Unani. All such systems primarily focus on the curative potential of their medicinal preparation which can be used for the treatment of large number of human liver disorders like cirrhosis, hepatitis, carcinomas etc. In the Indian systems of medicine, there are about more than 300 preparations which can be used for the treatment of jaundice and various chronic liver diseases. Some of such preparations have been discussed in Table 6.

Table 6. List of some medicinal preparations, which are approved by the IMPCPS (Indian Medicinal Practitioner’s Co-operative pharmacy and Stores), used for the treatment of various chronic liver disorders.

Unani medicinal system	Siddha medicinal system	Ayurvedic medicinal system
Sherbeth-e-anarshreen	Loha mandooram	Guduchi satwam
Muffarah-e-Ahmedi	Ayakantha chendooram	Panchatiktakwatha churnam
Bhoi-Amla	Karisalai lehyam	Tapyadi loham
Jawarish-e-Amilasada	Kantha chendooram	Saptamiruda loham
Kurs-e-gul	Arumuga chendooram	Bhringarajasava
Rue-e-amila	Ayabringaraja karpam	Drakahadi rasayam
Jawarish-e-Amilaluluvi	Mandooradi kudineer	Chandraprabhavati
Sherbeth-e-deenar	Annabedhi chendooram no. 1 and 2	Jambeeradi panakam

Hepatoprotective plants

A large number of herbal plants have been tested for their hepatoprotective activity. However, no plants are being tested for their pharmacological and antiviral efficacy but, some of the plants have been tested for their hepatoprotective activity. Some examples of such plants that have been discussed are listed in Table 7.

Table 7. List of some medicinal important plants found in India which are having hepatoprotective properties.

Plant name	Common name	Family	Chemical constituents	Hepatoprotective constituent	Other uses	References
Acacia catechu	Catechu	Fabaceae	Catechins, Catechol’s and Catecholamine	Catechins	Anti-dyslipidemia, anti-inflammatory, anthelminthic, anti-diuretic, anti-pruritic, coolant, curing skin disorders	Shen et al. (2006)
Azadirachta indica	Neem	Meliaceae	Nimbin, Nimbinin, Nimbidin	Azadirachtin, Margolone	Anthelmintic, antifungal, antibacterial, antidiabetic, antibacterial, antiviral, contraceptive sedative	Raphael (2012)
Boerhaaviadiffusa	Punarnava	Nyctaginaceae	β-Sitosterol, α-2-sitosterol, Palmitic acid, ester of β-sitosterol	β-Sitosterol	Improve and protect eyesight, diuretic properties, anti-diabetes, antibacterial activity, antioxidant, hepatoprotective properties, anticancer, antiestrogenic, immunomodulatory, antiamoebic activity.	Mahesh et al. (2012)
Chelidonium majus	–	Papaveraceae	Coptisine, allocryptopine, stylopine, protopine, norchelidonine, berberine, chelidonine, sanguinarine	–	Antimicrobial, antiviral and antiparasitic effects, cardiovascular effects, anti-inflammatory and analgesic activity, choleretic effects	Colombo & Bosisio (1996)
Daucuscarota	Wild carrot	Apiaceae	Camphene, Sabinene, α-pinene, Limonene, Terpinolene	–	Phytophotodermatitis, lower heart attack risk, intestinal parasites, persistent diarrhea	Bishayee et al. (1995)
Withaniasomnifera	Ashwagandha	Solanaceae	Withanolides, withaferin A, withanolide D, Anaferine	Withanolides	Anti-carcinogenic, anti-oxidant, cardio protective activity, anti-aging activity, osteoarthritis	Singh et al. (2010)
Verbena officinalis	Mosquito plant	Verbenaceae	Apigenin, Luteolin, 3α,24-dihydroxy-urs-12-en-28-oic acid	–	Use during pregnancy, antiperiodic, diaphoretic, expectorant, anthelmintic	Verma & Siddiqui (2011)
Tephrosiapurpuria	Auhola	Fabaceae	Aromatic ester, prenylated flavonoid, sesquiterpene, Tephrosiapurpuria	Tephrosim, Quercetin	Hepatoprotective, anthelmintic, alexiteric, dyspepsia, diarrhea	Khatri et al. (2009)
Sidarhombifolia	Indian hemp	Malvaceae	Ephedrine, pseudoephedrine, palmitic, stearic and hexacosanoic acids, Vasicinol, Vasicinone, Hypaphorine	–	Antimicrobial agents, anticancerous agent, anti-bacterial activity	Joseph (2011)
Picrorhizakurroa	Katuka	Scrophulariaceae	Iridoid glycosides and cucurbitacins, apocynin, andorsin and cucurbitacin glycosides	Picroside I, Picroside II, Kutkosides	Asthma, liver damage, wound healing, vitiligo, digestive problems	Luper (1998), Gagandeep et al. (2014)
Ricinuscommunis	Castor oil plant	Euphorbiaceae	Alkaloid ricinin, toxalbumin ricin	–	Antimicrobial, antihistamine, anti-inflammatory, analgesic	Singh et al. (2013)
Ocimum sanctum	Tulasi	Lamiaceae	Ursolic acid, apigenin, luteolin	–	Antimicrobial, antimalarial, antiallergic, immunomodulator, antifertility, antidiabetic	Lahon & Das (2011)
Phyllanthusniruri/amarus	Stonebreaker	Phyllanthaceae	Phyllanthin, hypophyllanthin, flavonoids, glycosides, tannins, alkaloids, ellagitannins	Phyllanthin, Niranthin	Anti-spasmodic, laxative, diuretic, carminative, against constipation	Narendra et al. (2012)
Mikaniacordata	Mile-a-Minute Vine	Asteraceae	Linalool and α-pinene, terpineol, camphene, α-felandrene, geraniol	Felandrene	Antibacterial and anti-inflammatory	Perez-Amador et al. (2010)
Cichoriumintybus	Chicory	Asteraceae	Lactucin, lactucopicrin, loliolide, artesin, cichoriolide, malic acid	Lactucin, lactucopicrin	Antimicrobial activity, anthelmintic activity, antimalarial and hepatoprotective activity, antidiabetic activity, anti-inflammatory activity	Street et al. (2013)
Achilleamillfolium	Yarrow	Asteraceae	Α-Pinene, Camphene, Sabinene, β-Pinene, Myrcene, p-Cymene, Limonene, 1,8-Cineole, methanol, Cyclohexane	–	Antiphlogistic, gastrointestinal disorders, choleretic	Nadim et al. (2011)
Eclipta alba	Bhringraj	Asteraceae	Wedelolactone, Desmethylwedelolactone, Desmethyl-wedelolactone-7-glucoside, stigmasterol, Wedelolactone	Wedelolactone	Improve hair growth, uterine hemorrhage and monnorrage, remedy for jaundice, in liver cirrhosis	Shaikh et al. (2012)
Swertiachirata	Chirayata	Gentianaceae	Sawertiamarine, mangeferin and amarogenitine, balanophonin, oleanolic acid, maslinic acid, sumaresinolic acid	Sawertiamarine	Hepatoprotective, digestive, astringent, laxative, anti-inflammatory and anti-malarial	Tabassum et al. (2012)
Boerhaviadiffusa	Punarnava	Nyctaginaceae	Punarnavine, arachidic acid, Sitosterol, 2-sitosterol, palmitic acid, ester of sitosterol	Punarnavine	Antibacterial, antidiabetic, antistress, antitumor, anticonvulsant, analgesic, anti-inflammatory	Rawat et al. (1997)
Fumaria officinalis	–	Papaveraceae	Canadine, fumaricine, protopine, allocryptopine	Canadine, fumaricine	Treat skin diseases, conjunctivitis, treating gallbladder	Mortazavi et al. (2007)
Glycyrrhiza glabra	Liquorice	Leguminosae	Saponin, glycyrrhizin, glycyrrhetinic acid	Saponin, glycyrrhizin	Hepatoprotective, stomach ulcers, sore throat, bronchitis, cough and infections caused by bacteria or viruses	Lee et al. (2007)
Hydrastiscanadeni	Yellow puccoon	Berberidaceae	Hydrastine, berberine, hydrastine, berberine, berberastine, hydrastinine	Hydrastine, berberine	Hepatic, alterative, anticatarrhal, anti-inflammatory, antimicrobial, laxative	Yamaura et al. (2011)
Schisandra chinensis	Five flavor berry	Schisandraceae	Lignans, schizandrin, lignansschizandrin, deoxyschizandrin, gomisins and pregomisin	Lignans, schizandrin, deoxyschizandrin	In pregnancy, treat diarrhea, arrest excessive sweating, treating liver disease (hepatitis)	Cheng et al. (2013c)
Taraxacum officinale	Dandelion	Compositae	Taraerol, taraxol, laevulin, inulin	Taraerol, taraxol	Diuretic, in kidney and liver disorders, mild laxative	You et al. (2010)
Mallotusjaponicus	Akamegashiwa	Euphorbiaceae	Bergenin, mallotophenonemallotojaponin, isomallotochromeneandmalloto chroman	Bergenin	Gastric ulcer, duodenal ulcer, gastric hyperacidity, hepatoprotective	Kim et al. (2000)

Various targeting ligands used to liver targeting

Different types of cells, namely hepatocytes, Kupffer cell, hepatic stellate cell and sinusoidal endothelial cells, etc., are found in liver. On the surface of these cells, different types of the receptors are found which can be used for achieving liver targeting. These receptors bind with different types of ligands which can be used in the formulation to achieve targeted delivery of the drug. Hence, it becomes very important to design or to select proper materials which can be used to target the drug into these different diseased cells. Various novel materials, which can be used to enhance the targeting efficiency of systems to receptors found on the surface of different cells present on the liver, have been discussed with some appropriate cases.

Galactosylated ligand

This ligand is very important in achieving liver targeting as there is the specific interaction between galactose moiety and the asialoglycoprotein receptors which are found on the surface of hepatocytes (Garg, 2014). The major determinant of attachment of the galactose to the hepatocytes is the density of galactose (Ashwell & Harford, 1982) asialoglycoprotein receptor of hepatocytes bind with the galactose residues on de-asialylated glycoproteins (Baenziger & Fiete, 1980). The binding between the galactose ligand-asialoglycoprotein receptors is not only influenced by the ligand density but also by the spatial orientation of the ligand (Kobayashi et al., 1995). It was seen that the hepatocytes cultured on the surface of the polymer recognize galactose moieties of the polymer, even at low galactose concentration (Ise et al., 2001), which have well due to the galactose orientation (Cho et al., 1996). The result showed that the spatial micro-distribution of the galactose is important for the regulation of the cell adhesion.

Lactobionic acid ligand

Lactobionic acid has a galactose moiety in its chemical structure which can be recognized by the asialoglycoprotein receptors found on the surface of hepatocytes, which leads to liver targeting. Super paramagnetic magnetite nanoparticles were modified using lactobionic acid which leads to the improved intracellular uptake and target ability of the conjugate to the hepatocytes, and hence lactobionic acid-modified magnetite nanoparticles have been shown to have great potential to be used as contrast agent for liver diagnosis (Kamruzzaman Selim et al., 2007). Similarly, a novel galactosylated moiety was used for the selective targeting of doxorubicin (DOX) which showed that the galactosylated liposomes have high liver-targeting ability value of about 64.6%, while doxorubicin drug with simple conventional liposome gave only 21.8% of target ability value (Wang et al., 2006). Later in 2009, lactobionic acid having beta galactose moiety was conjugated on the surface of mercapto acetic acid which was coated with cadmium sulfide nanoparticles (CSNPs) to check the specific recognition of liver cells (hepatocytes) and to increase the biocompatibility. It was found that the uptake amount of lactobionic acid-immobilized nanoparticles into hepatocytes was higher than that of simple non-lactobionic acid-reacted nanoparticles (Selim et al., 2009).

Asialofetuin ligand

It is an example of a natural ligand that possesses three asparagine-linked triantennary complex carbohydrate chains having N-acetyl-lactosamine as terminal residues. The targeted protein having asialofetuin shows affinity to the asialoglycoprotein receptors found on the surface of hepatocytes and then get internalized by endocytosis. It was found that the receptor dissociation constant of such compounds is 200-fold lower than that of glycoproteins with biantennary N-linked oligosaccharide chains. Hence, it has been used as a competitive inhibitor of various other polysaccharides which show high affinity to the receptors (Díez et al., 2009). Cationic nanoparticles were prepared using asialofetuin as targeting ligand and found that targeted-nanoparticles showed about 5- to 12-fold higher transfection activity as compared to non-targeted (plain) complexes in the liver. Similarly, poly (d,l-lactic-co-glycolic acid) nanoparticles were prepared using the double emulsion method. To modify the targeted delivery of the drug into the hepatic parenchymal cells, the nanoparticles were coated with asialofetuin ligands. Covalently conjugated protein on nanoparticles were labeled with rhodamine and used for cell-based studies. Results proved that asialofetuin conjugated with nanoparticles showed high and selective uptake by hepatic parenchymal cells as compared to the nanoparticles conjugated with bovine serum albumin (BSA; Gagandeep, 2010).

Soybean-derived ligand

This ligand is derived from soybeans. To check the liver targeting activity of this ligand, the liposomes of a drug was prepared by interaction of liposomal surface with soybean-derived sterylglucoside along with HepG2 cells. It was found that the sterylglucoside-derived liposomes are potentially more useful drug carriers to target the liver cells as compared to the conventional liposomes. This is because the glucose residue of the ligand may work as the targeting ligand for asialoglycoprotein receptors (Maitani et al., 2001). A liposomal liver targeting delivery system was prepared by adding soybean-derived sterylglucoside as targeting ligand to the cationic liposomes and the results showed that SG/Brij-35-modified cationic liposomes are potentially more useful as drug carrier to deliver the drug to the liver (Shi et al., 2006).

Glycyrrhetinic acid ligand

Liquorice is having two main bioactive chemical constituents named as glycyrrhizin (GL) and glycyrrhetinic acid (GA) which are widely used in medicine for the treatment of many disorders (Rensen et al., 2001; Wu et al., 2002). These are mainly used as anti-inflammatory, antiallergic, antigastric, antihepatitis and antihepatotoxic effects. It was proved that there are specific binding sites for both GL and GA on the cellular membrane of hepatocytes. It was found that the number of binding sites for GA is much more than that for GL binding sites (Negishi et al., 1991). Recently, chitosan nanoparticles modified were prepared which were modified using glycyrrhizin as liver-targeting ligand and the results confirmed that glycyrrhizin conjugate nanoparticles were accumulated more in the rat hepatocytes by ligand receptor interaction as compared to that of conventional nanoparticles of chitosan (Wolfrum et al., 2007). It was also found that the cellular uptake of liposomes modified with glycyrrhetinic acid showed about 3.3-fold higher uptake than that of unmodified ones (Akinc et al., 2010).

Lactoferrin targeting ligand

In general, lactoferrin receptors were used as targeting ligand for delivery of drug to the brain due to the presence of various lactoferrin receptors on blood brain barrier (BBB; Huang et al., 2008; Chen et al., 2010). Recently, it was seen that lactoferrin ligands also have efficiency to bind with the multiple receptors found on the hepatocytes. Lactoferrin-PEGylated liposomes were prepared for achieving the target delivery of the drug and was seen that the results showed higher liver targeting to hepatic cells with lower toxicity and enhanced efficacy (Gorria et al., 2008; Wei et al., 2012). This is because the lactoferrin receptors bind with the asialoglycoprotein receptors found on the surface of the hepatocytes (McAbee et al., 1998, 2000). These exciting evidences suggested that lactoferrin receptors may become a promising candidate for hepato-cellular carcinoma targeting due to its high affinity for asialoglycoprotein receptor.

Bile acid receptor targeting ligands

These receptors are important in achieving target drug delivery of drugs for the treatment of large number of human liver disorders like cholestatic and fatty liver diseases. It was found that bile acids activate a nuclear receptor, farnesoid X receptor, which is further responsible in the induction of an a typical nuclear receptor (Popielarski et al., 2005). Modified phospholipid (PC)/Chol liposomes were prepared using a novel polymer bile salts – (polyethylene glycol) 2000 bile salt by the N,N′-dicyclohexylcarbodiimide/4-dimethylaminopyridine (4-DMAP) esterification method. The results showed that the MRT of the liposomes, was longer than that of traditional liposomes (Zhipeng et al., 2012). The mean plasma concentration time profile was also higher than that of traditional liposomes. A large number of formulations have been prepared till date for liver targeting using above carries as targeting ligands. Some of these formulations have been discussed in Table 8.

Table 8. Clinical significance of nanotechnological approaches which are having hepatoprotective properties.

S. No.	Targeting ligand	Targeting cells	API used	Clinical significance	Result	References
Liposomal preparations for achieving liver targeting
1	Polyaspartic acid, poly-l-glutamic acid, chondroitin sulfate C modified with cholesterol	Hepatocytes	Small interfering (siRNA)	siRNA therapy	Cholesterol-modified polyaspartic acid, poly-l-glutamic acid, chondroitin sulfate coated liposomes showed high liver targeting with lesser kidney targeting after i.v. injection. No increase in GOT and GPT level was observed representing least toxicity.	Hattori et al. (2014), Garg & Goyal (2014b)
2	Cyclic peptide (pPB)	Human stellate cells	Interferon-γ	Anti-fibrotic agent	The tissue distribution study shows the prepared liposomal conjugate mostly accumulated in liver until 24 h and showed more significant remission of hepatic fibrosis.	Bansal et al. (2014)
3	Galactose	Hepatocytes	Small interfering (siRNA)	siRNA therapy	siRNA accumulated concentration was found to be 45 µg/ml, which was 30 times higher than the concentration required for silencing in vitro.	Sonoke et al. (2011)
4	Asialofetuin	Hepatocytes	–	Anti-cancer therapy	In vivo study in rat model confirmed the hepatocyte specific targeting and high internalization of prepared liposomes which could be competitively inhibited by co injection of unbounded asialofetuin.	Detampel et al. (2013)
5	β-Sitosterol	Parenchymal cells of liver	Silymarin	Hepatoprotective action	The formulation showed high liver targeting. Antihepatoprotective action of prepared preparation was checked on CCl4 induced liver toxicity and was found that PEGylated targeting silymarin-loaded liposome did not affect silymarin hepatoprotective action.	Samy et al. (2014)
6	β-sitosterol β-d-glucoside (Sito-G)	Hepatocytes	Silymarin	Hepatoprotective action	The cellular drug uptake of PEGylated formulation was found to be 18% achieved at 0.17 and 0.33 M ratio of added Sito-G. The formulation when stored in HEPES buffer (pH 7.4) showed stability for at least 2 months.	Elmowafy et al. (2013)
7	Glycyrrhetinic acid	Hepatocytes	Wogonin	Anti-tumor effect	Glycyrrhetinic acid modified liposomes showed rapid accumulation in liver with long retention time. Preparation showed modified accumulation in tumor, modified bio-distribution with high therapeutic efficacy.	Garg & Goyal (2012), Tian et al. (2013)
8	Infusion in bile duct	Hepatic stellate cells	Growth factor gene	Anti-fibrosis	Dimethyl nitrosamine-induced liver fibrosis was treated using prepared formulation targeted to hepatic stellate cells which showed increased transgene expression at the fibrotic foci leading to enhanced antifibrotic effects.	Narmada et al. (2013)
9	Galactose	Hepatocytes	Doxorubicin	Anti-cancer therapy	The results showed that the specific cell uptake by human hepatocellular carcinoma HepG2 cells was stronger of galactose containing liposomes as compared to the non-targeted liposomes.	Zhao et al. (2013)
10	Antibody domain specific to hepatocytes (DOM26h-196-61)	Hepatocytes	Interferon α (INFα)	Against hepatitis C infection	The prepared liposomes showed desirable biophysical properties and high activity in vitro. The preparation showed high liver targeting as compared to non-targeted system in vivo with improved safety and patient compliance.	Coulstock et al. (2013)
Nanoparticles for liver targeting
1	Galactose	Hepatocytes	Oridonin	Anti-tumor therapy	The prepared spherical nanoparticles showed size distribution below 200 nm having zeta potential of about −30 mv. DSC and X-ray diffraction confirmed the amorphous state of nanoparticles. In vitro showed biphasic pattern with initial burst effect and then sustained release.	Li et al. (2013)
2	Galactose	Hepatocytes	Doxorubicin	Anti-cancer therapy	Prepared spherical nanoparticles (mean size of 181.9 nm) showed sustained and pH-dependent drug release in vitro. In vivo study showed higher AUC value and residence time in blood circulation. Nanoparticles showed high uptake of drug in liver and spleen as compared to heart, lung and kidney.	Guo et al. (2014)
3	Glycyrrhizin	Hepatocytes	Lamivudine	Hepatitis B treatment	Drug release from nanoparticles showed first burst release and consequently sustained release. In-vivo biodistribution study showed high target ability and hematological study showed lesser tissue damage.	Mishra et al. (2014)
4	Lactic acid, glycyrrhetinic acid and chitosan	Hepatocytes	5-Fluoro uracil	Anti-cancer therapy	Prepared nanoparticles showed particle size of 239.9 nm, PDI of 0.040, zeta potential of +21.2 mV with drug loading of 3.90%. Nanoparticles showed drug release pattern of small burst release, gentle release, second burst release, steady release and slow release with high liver targeting.	Cheng et al. (2013a)
5	Lactobionic acid	Hepatocytes	5-Fluoro uracil	Anti-cancer therapy	The prepared nanoparticles showed proper particle morphology, particle size (below 150 nm), PDI ∼0.35, entrapment efficiency (∼60.23%). In vivo studies showed higher drug concentration (37.52 ± 0.68%) in liver as compared to other organs and plasma.	Dangi et al. (2014)
6	–	Reticulo-endothelial cells	Buparvaquone	Theleriosis	DSC and powder X-ray diffraction showed decreased crystallinity of nanoparticles and spherical morphology. High RES targeting (about 75%). Good stability at 4 and 25°C.	Soni et al. (2014)
7	Galactose	Hepatocytes	Acyclovir	Liver cancer	The spherical nanoparticles showed size (198.1 nm), electrical charge (−8.5 mV), entrapment efficiency (84.1%) and in vitro drug release (40% over 48 h). Nanoparticles were remarkably targeted to liver, the accumulation in the liver was found to be 36.71 ± 0.68% at 24 h.	Jain & Kumar (2013)
8	Glycyrrhetinic acid	Cancerous cells of liver	5-Fluoro uracil	Anti-cancer therapy	The preparation showed particle size (193.7 nm), drug loading 1.56% and PDI 0.003 and show sustained release of drug. The preparation showed high liver targeting with less effects on non-cancerous cells.	Cheng et al. (2013b)
9	Galactose	Hepatocytes	Gene delivery	Genetic disorders in liver	The preparation showed asialoglycoprotein mediated endocytosis of the polyplexes with minimum cytotoxicity to HepG2 cells making it potential non-viral gene delivery to liver.	Ong et al. (2013)
10	Galactose	Hepatocytes	Adenosine triphosphate	Hepatocellular carcinoma treatment	The prepared nanoparticles showed average diameter and zeta potential of about 51.03 ± 3.26 nm and 30.50 ± 1.25 mV, respectively. The preparation showed high liver targeting through asialoglycoprotein receptors with least cytotoxicity to normal cells.	Zhu et al. (2013)
Micelles for achieving liver targeting
1	Glycyrrhetinic acid	Cancerous cells of liver	Doxorubicin	Anti-cancer therapy	IC50 of prepared conjugate against HepG2 cells was 54.7 ng/mL, which was extremely lower than without GA loaded micelles. In addition, prepared micelles showed higher affinity for liver cancer cells (HepG2 cells) than normal cells.	Tian et al. (2012)
2	Lactose and glycyrrhetinic acid	Hepatocytes	Diammonium glycyrrhizinate	Hepatic disorders	Both glycyrrhetinic and lactose conjugated micelles showed encapsulation efficiency of 97.4 and 96.7%, respectively, having spherical micelles of size 21.6 and 26.4 nm. Through TEM, lactose conjugated system showed high liver targeting as compared to glycyrrhetinic acid conjugated system.	Tian et al. (2012)
3	Glycyrrhetinic acid	Hepatocytes	Doxorubicin	Anti-cancer therapy	In vitro drug release study of the prepared formulation showed the pH dependent release with Fickian diffusion kinetics. The prepared micelles showed high liver targeting of about 4.9-fold higher than that of free doxorubicin solution.	Huang et al. (2011)
4	N-acetyl galactosamine	Hepatocytes	siRNA	siRNA therapy	Successful down-regulation of liver-specific Apo lipoprotein B at both transcriptional and protein level was found in mouse liver after i.v. injection of prepared micelles. Systemic delivery of prepared preparation did not show any innate immune response or hepatotoxicity.	Wang et al. (2013)
5	Lactobionic acid	Hepatocytes	Silybin	Hepatoprotective action	The prepared formulation showed remarkable increase in the dissolubility of silybin in lactobionic acid conjugated system (627 µg/ml) as compared to water (4.6 µg/ml). Bio-distribution study showed high liver targeting as compared to the other organs.	Li et al. (2009)
6	Galactose	Hepatocytes	Prednisone	Anti-inflammatory action	TEM study showed spherical shape of the micelles. Size of micelles was found to be 120 nm. The study showed high liver targeting using HepG2 micelles. In vivo study showed high liver uptake as compared to other cells.	Wu et al. (2009)
7	Glycyrrhetinic acid	Hepatocytes	Paclitaxel	Anti-cancer therapy	The prepared nanosized micelles showed mean diameter of about 159.21 ± 2.2 nm. Prepared micelles showed low cytotoxicity and high ability of delivering drug to hepatic cells both in vivo and in vitro by the targeting moiety glycyrrhetinic acid.	Wu et al. (2013)
8	Lactose	Hepatocytes	Harmine	Anti-cancer therapy	Self-assembled micelles showed particle size (∼200 nm). In vivo study showed that the prepared micelles significantly inhibit tumor growth and lifetime of mice bearing H22 tumors was extended after i.v. administration. In vivo near-infrared fluorescence showed satisfactory liver tumor-targeting effect.	Bei et al. (2014)
9	Galactose	Hepatocytes	Sorafenib	Hepatocarcinoma treatment	Liver-targeted sorafenib-loaded micelles showed nanometer size and positive zeta potential. Biodistribution studies on mice showed that after oral administration, the drug sorafenib mainly accumulated into the liver as compared to other organs.	Craparo et al. (2014)
10	Galactose	Hepatic stellate cells and hepatocytes	siRNA	siRNA therapy	It was found that the prepared conjugate could silence luciferase gene expression (40%) without any transfection reagents, while with the help of cationic liposomes, the gene silencing effects reached more than 98% at the same dose. The prepared conjugate showed targeted delivery to hepatocytes and hepatic stellate cells of siRNAs for efficient gene silencing in vivo.	Zhu & Mahato (2010)
Nanosuspensions, polymeric conjugates and niosomes used for liver targeting
1	–	Hepatocytes	Silybin	Hepatoprotective activity	The prepared nanosuspension when given orally or i.v. produces hepatoprotective action by reducing enzymes like AST, ALT, TBIL, ALP and GGT. Prepared nanosuspension showed high targeting at liver and spleen.	Wang et al. (2012b)
2	Folate	Cancerous cells	Docetaxel	Anti-cancer activity	The particle size of prepared nanosuspension was found to be 220.6 ± 9.54 nm. The cytotoxicity of the prepared nanosuspension against B16 (FR+) cell line was higher. In vivo study showed that the nanosuspension showed higher antitumor efficacy by reducing the tumor volume (p < 0.01) as compared to PEG-modified preparation.	Wang et al. (2012a)
3	Coating with Serum albumin, polysaccharides	Viral infected cells	Nevirapine	Anti-viral therapy	The biodistribution study of the prepared nanosuspension showed high organ-specific targeting as compared to plain drug solution when given intravenously. The preparation showed high MRT, enhanced bioavailability and high residence of drug in targeted organs.	Shegokar & Singh (2011)
4	Galactose	Hepatocytes	Primaquine and chloroquine	Antimalarial activity	The conjugate was prepared using polymer polyamidoamine. Final preparation showed twice antimalarial action and low unspecific toxicity as compared to free drug combinations. The preparation showed high selective internalization into parasite infected RBC’s.	Vale et al. (2009)
5	Galactosamine	Hepatocytes	Doxorubicin	Anticancer activity	The prepared conjugate was prepared using polymer HPMA N-(2-hydroxy propyl) methacryl-amide which shows about 16.9 ± 3.9% drug targeting. Conjugate prepared without the galactosamine showed no liver targeting.	Jiwpanich (2011)
6	Glycyrrhetinic acid	Hepatocytes	Paclitaxel	Anticancer activity	Nanoparticles were prepared using glycyrrhetinic acid as targeting ligand and hyaluronic acid as polymer. Prepared nanoparticles showed high efficiency up to 31.16% and entrapment efficiency of 92.02%. The prepared conjugate showed high liver targeting as compared to other organs.	Huang et al. (2010)
7	–	Liver cells	Ribavirin	Chronic hepatitis C	The niosomes were prepared using thin film hydration method using span 60 and cholesterol (1:1). The results showed that the liver targeting of the drug was about 6-fold higher as compared to the normal ribavirin-free solution without any targeting.	Hashim et al. (2010)
8	Mannose	Non-parenchymal cells	Oral vaccination	Hepatitis B	The serum anti-HBsAg obtained after oral administration of niosomal formulations was less as compared to naked DNA, but the mice were seroprotective within 2 weeks. Intramuscular naked DNA did not elicit sIgA titer in mucosal secretions which were induced by oral administration of niosomes. Niosomes produced humoral and cellular immune response after oral administration.	Jain et al. (2005)
9	–	Liver cells	Hydroxycamptothecin	Anti-tumor effect	The prepared niosomes showed strongest cytotoxicity to KB, K562 and S180 carcinomatous cell lines and greatest intracellular uptake, especially in nuclei. The preparation showed most powerful anti-tumor activity by inhibiting the S180 tumor in mice of about 70%.	Hong et al. (2009)

Conclusions

Many significant approaches have been developed for the therapy of liver diseases. Both systems (herbal and nanocarriers) exhibit a higher specificity in terms of delivering the drug load to the site of action. Nanocarriers show great potential for selective drug delivery to targeting cells. A large number of formulations have been prepared till date for liver targeting by polymeric nanocarriers as targeting ligands. To date, very few delivery systems are marketed as liver targeted drug delivery system. In future, liver-targeted drug delivery system will be available to serve the mankind.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.