The liver plays the major role in detoxification process; hepatocytes are considered as a massive detoxification center for degrading alcohol, toxins and drugs protecting the body from their deleterious effects 1. Therefore liver cellular damage commonly resulted from the metabolites of such toxins.

Nanotechnology is a fast developing field that has been used in a wide range of applications including; engineering, agriculture and medicine 2. Nanoparticles are used in some drugs to maximize their bioavailability such as sunscreens, toothpastes, cosmetics, food additives, furniture varnishes and in optic industry e.g. the anti-reflective ultra-thin sunglasses, as well as construction materials 3. ZnONPs are commonly used in food stuffing due to their antifungal properties. In addition, ZnONPs are added to fungicides to increase their effectiveness. They are commonly applied as antibacterial agents in lotions, ointments, and mouthwashes to prevent micro-organisms growth by their bacteriostatic properties 4.

ZnONPs have different physicochemical properties compared to zinc (ZnO) which can affect bioactivity and toxicity of ZnONPs 5. It is suggested that the size of nanoparticles and its surface area greatly increase their ability to produce reactive oxygen species (ROS) 6.

Reactive oxygen species (ROS) that include free radicals are frequently created in cells in normal circumstances as a result of aerobic metabolism. Once cells are exposed to a physical or chemical insult, it causes overproduction of ROS 7. ROS play an important role in nanomaterial induced cytotoxicity. Exposure to NPs leads to occurrence of imbalance between ROS production and antioxidant defense system 8.

The nanoparticles enter the blood circulation in an ionic form and localize in organs as zinc ions. Liver is among the possible target organs for accumulation of zinc ions. They spread to various organs such as kidney and lungs within 72 hours regardless of particle size or charge 9. Toxicity of ZnONPs depends on not only the dose, but also the physicochemical properties of these nanoparticles such as: shape, size, chemical composition, their solubility and route of exposure 10. The gastrointestinal tract is one of the important NPs, oral exposure of nanomaterial can occur directly from water, food, or orally administered medicines 11.

Zinc plays an important role in controlling apoptosis; however excess of zinc may cause cell death due to apoptosis or necrosis. This process is triggered, when the concentrations of intracellular zinc increase 12. Administration of ZnONPs has been suggested to cause apoptosis which considers a key event after oxidative DNA damage. There was evident by marked increase in the activity of the apoptotic biomarker (Caspase 3) in liver tissue 13.

Acute exposure to ZnONPs shows hepatic damage and liver dysfunction demonstrated by increasing alanine transaminase (ALT) and aspartate transaminase (AST) which is located primarily in the cytosol of hepatocytes 14. These results reveal that ZnONPs interrupt the functions of liver cells. Hepatotoxic symptoms included fever, suppression of bile flow in addition to enlargement of liver are common sequences 15.

Vitamin E (VE) is considered to be one of the most potent radical scavengers and a chain breaking antioxidant that interrupts the chain propagation of lipid oxidation, thus protecting polyunsaturated fatty acids and low density lipoproteins from oxidation, hence it stabilize lipid portion of cell membrane and maintains its integrity. For this reason, there is an increasing interest in fortifying many foods with VE 16. In liver, VE (especially α tocophrol) is incorporated into very low density lipoproteins and excreted back into circulation 17. This study aimed to demonstrate the possible adverse effects of ZnONPs on the liver structure and the possible protective role of VE in such case.

It has been documented that the tissue structure and biochemical changes as well as the body and organ weights are the determinant factors in evaluating the toxicity of nanoparticles 26. In this study, we investigated the liver structure and some enzymes in animals exposed to ZnONPs to determine such toxicity. Adult albino rats were selected in the current study as they have relatively long life span free from diseases and they are easily handled. In addition, male animals were favored as they have relatively constant hormone levels which help to pass over the role that could such hormones play in many inflammatory conditions 27.

Regarding the weights of the animals and their livers, it was noticed that marked reduction occurred in ZnONPs exposed animals that relatively improved with administration of VE. These findings are in the line with previous study 19. This is an indication of toxicological effect in ZnONPs-treated animals.

In the present work, H&E-stained liver sections of the ZnONPs-treated group showed disruption of normal architecture with congestion and dilatation of central as well as blood sinusoids. These results are in accordance with Johar et al., 28 who suggested that the destruction of lobular structure, vacuolization of hepatocytes (fat deposits), and infiltration of leukocytes indicate necrotic effects of ZnONPs on liver tissue. On the other hand, Puche et al., 29 attributed sinusoidal dilatation to the activation of perisinusoidal cells which had contractile properties. On contrary to the current results, Wang et al 26 found minimal toxicity through their biodistribution assays in liver tissue of mice exposed to 50 and 500 mg/kg ZnONPs.

Some hepatocytes appeared ballooned with dark stained nuclei. This finding is in consistence with Abbasalipourkabir et al., 30 who gave 50, 100, 150 and 200 mg/kg ZnONPs attributed ballooning of hepatocytes to apoptosis induced by ZnONPs. Ma et al. 31 revealed that swelling of hepatocytes indicates that these nanoparticles may affect permeability of the cell membrane in hepatocytes. Al-Rasheed et al., 13 stated that the liver of rats treated with a high dose of ZnONPs showed numerous hepatocytes with karyolysis and pyknotic nuclei in addition to inflammatory cellular infiltration.

Foci of cellular infiltration were detected in the liver parenchyma. Such result is parallel with Sharma et al., 14 who stated that the liver revealed hepatocellular necrosis and accumulation of mixed inflammatory cells around the necrotic area. Edinger and Thompson 32 attributed the presence of necrotic foci to lysis of cells and formation of cell debris, which could initiate phagocytic infiltration. In the current study the portal area revealed portal vein dilatation and congestion. Hu et al. 33 explained that the congestion and dilatation of central and portal veins may be due to portal hypertension. Bile duct proliferation was evident in the current ZnONPs- treated group. This result is in agreement with Pati et al. 34 who documented that a ductular reaction is the proliferative response to many types of liver injuries. It is now generally accepted that the liver contains hepatic stem cells/ progenitor cells in which are considered as a subpopulation of liver cells termed oval cells. Under the condition of severe and chronic liver injury caused by drugs, toxins and viruses, these oval cells are induced to proliferate and differentiate both into biliary epithelial cells and into mature hepatocytes 35.

In the current study, portal veins of rat treated with ZnONPs revealed elongation of their endothelial lining. Wen et al. 36 attributed this result to smooth muscle cell (SMC) proliferation and hypertrophy in the portal vein. They indirectly proved that nitric oxide (NO) is closely related with portal venous vascular remodeling that will lead to SMC proliferation and hypertrophy. Also, the wall of hepatic artery showed increasing of its muscular wall. Reneman et al., 37 explained this result to that Shear stress can promote remodeling of the arterial walls, possibly through regulation of endothelial cells (EC) gene expression and intracellular bioactive substances.

In the 4^th group, there was some improvement of liver architecture when compared with group III. Preservation of normal structures in the protected groups was attributed to the anti-inflammatory role of VE which associated with the amelioration of oxidative damage 38. The binucleated hepatocytes seen the ZnONPs+VE treated groups may be due to the regenerative attempt of the degeneration of cells as reported earlier in the liver of carbaryl treated rats by Munglang et al., 39.

Regarding Masson’s trichrome-stained sections, there was marked increase collagen fibers around the portal area in ZnONPs- treated group. These results are in agreement with that of Al-Rasheed et al., 13. Galli et al., 40 stated that ROS are incriminated in the development of hepatic fibrosis as they stimulate hepatic stellate cells (HSCs) proliferation and collagen synthesis.Hepatic stellate cells which are relatively inactive fibroblasts in liver lobules play an important role in liver fibrosis. Apparent reduction in collagen fibers content around the portal area was obvious in group IV.

Caspase 3 stained liver sections of ZnONPs- treated rats showed strong positive reactions in the cytoplasm of hepatocytes. These findings are in accordance with those of Yousef and Mohamed 41, who stated that the liver apoptosis biomarker caspase3 was significantly up-regulated in rats administered either ZnO-bulk or its NPs orally (500 mg/kg bw) for 10 successive days. These findings confirmed statistically by morphometric analysis of the number of hepatocytes with caspase 3 positive immunoreaction and area percentage of collagen fiber that showed a highly significant increase (P<0.001) in ZnONPs- treated group when compared with that of the control group. In addition, there was a non-significant difference between the control and ZnONPs+VE- treated groups, this is in accordance with Al-Rasheed et al., 13.

In the present study, both liver and body weights showed highly significant decrease in the ZnONPs- treated group when compared with the control groups. However, no significant difference was observed between the control animals and both VE and ZnONPs plus VE- treated groups. This result is in accordance with that of Ko et al. 42. However, Sharma et al., 14 observed that there was no significant difference in the body weights between control and ZnONPs- treated groups. Similarly, no obvious difference was observed in the organ weights.

On the other hand, the changes in ALT and AST levels were statistically decreased in ZnONPs+VE treated group when compared with ZnONPs animals. This result is in agreement with Al-Rasheed et al. 13 who reported that VE has the ability to normalize levels of such enzymes.

It was concluded that ZnONPs might induce some histological and biochemical adverse effects on liver of adult male albino; and VE alleviated most of these changes. Eventually, the study suggests the use of VE as a protective approach against the toxic effects of ZnONPs. Future studies using large numbers and different models of animals are recommended with follow up of the animals for longer period to investigate the recovery from such adverse effects.

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