**4. Discussion**

Zinc is an essential trace element to human health. It plays an important role in membrane stabilization and in cell protection against oxidative stress because it is part of structure of superoxide dismutase, the main enzyme in endogenous control of some types of free oxygen radicals. It also inhibits transition metals, such as copper and iron, from producing reactive types of oxygen (Powell, 2000). This metal is also essential for DNA and RNA polymerase, which has an important effect in hepatic regeneration (Sato et al., 2005).

The liver is one of the main organs in the metabolism of zinc. Disorders in zinc metabolism have been described in patients with chronic liver disease, and several studies found a decrease in plasma, serum or liver zinc concentrations (Loguercio et al., 2001; Halifeoglu et al., Schneider et al., 2009; Matsuoka et al., 2009, Milman et al., 1986; Göksu & Özsoylu, 1986; Sharda & Bhandari, 1986; Bode et al., 1988; Kollmeier et al., 1992). The decrease of zinc in liver disease seems to be associated with decreased intake, poor absorption associated with portal hypertension, and greater urinary excretion (Loguercio et al., 2001). Collagenase is a zinc-metalloenzyme and zinc is the most effective inhibitor for prolylhydroxylase, an

10 168.0 200.2 11 188.2 215.4 12 221.6 212.9 13 136.6 216.4 14 299.0 744.7 15 170.0 523.7 16 179.8 166.5 17 160.5 260.8 18 151.1 153.1 19 155.9 220.2 20 163.8 175.0 21 124.1 141.9 22 145.6 161.4 23 140.0 164.4 24 190.3 179.9 25 174.2 149.0 26 103.7 169.3 27 184.3 225.2 Mean 173.6 220.2 SDa 37.9 127.0 RSDb 21.9 57.5

*g/g dry tissue) Concentration deparaffinized liver* 

*(*μ

*g/g dry tissue)* 

*Concentration fresh liver*

a SD = standard deviation,b RSD = relative standard deviation (%).

which has an important effect in hepatic regeneration (Sato et al., 2005).

Table 1. Liver zinc concentration in samples of fresh and deparaffinized bovine liver tissue.

Zinc is an essential trace element to human health. It plays an important role in membrane stabilization and in cell protection against oxidative stress because it is part of structure of superoxide dismutase, the main enzyme in endogenous control of some types of free oxygen radicals. It also inhibits transition metals, such as copper and iron, from producing reactive types of oxygen (Powell, 2000). This metal is also essential for DNA and RNA polymerase,

The liver is one of the main organs in the metabolism of zinc. Disorders in zinc metabolism have been described in patients with chronic liver disease, and several studies found a decrease in plasma, serum or liver zinc concentrations (Loguercio et al., 2001; Halifeoglu et al., Schneider et al., 2009; Matsuoka et al., 2009, Milman et al., 1986; Göksu & Özsoylu, 1986; Sharda & Bhandari, 1986; Bode et al., 1988; Kollmeier et al., 1992). The decrease of zinc in liver disease seems to be associated with decreased intake, poor absorption associated with portal hypertension, and greater urinary excretion (Loguercio et al., 2001). Collagenase is a zinc-metalloenzyme and zinc is the most effective inhibitor for prolylhydroxylase, an

*(*μ

*Samples* 

**4. Discussion** 

enzyme which plays a key role in collagen synthesis. These two assumptions could explain the role of zinc in collagen deposition and reabsorption in liver disease, the role played by zinc in liver fibrosis and in the evolution of chronic hepatitis toward cirrhosis (Faa et al., 2008).

Some reports found an increase in liver zinc concentrations in chronic liver disease. An increase in copper and zinc liver concentrations was found in Canadian children with chronic cholestasis (Phillips et al., 1996). Another case report described the increase in zinc concentration in hepatic tissue of a child with hepatosplenomegaly and symptoms of zinc deficiency, and the authors speculated about the existence of a zinc metabolism disorder (Sampson et al., 1997). A study that investigated the concentration of metals in liver tissue of adults with hereditary hemochromatosis found an increase in zinc in the liver parenchyma. The authors suggested that the concurrent increase in iron and zinc might be explained by the greater intestinal absorption of these metals (Adams et al., 1991).

The test usually conducted to determine body zinc is the measurement of plasma zinc concentration. However, plasma zinc concentrations do not seem to reflect the concentration found in the liver parenchyma (Göksu & Özsoylu, 1986; Sato et al., 2005). This may be explained by the fact that there are very efficient homeostatic mechanisms to correct plasma or serum zinc deficiencies, which makes it difficult to diagnose marginal deficiency by using this method. Therefore, the investigation of zinc concentration in liver tissue is important.

Studies report a great variation in liver zinc concentrations, maybe due to the different techniques used (Table 2). Kollmeier et al. (1992) studied the distribution of zinc in adult liver parenchyma from necropsy material, and found a small variation in intraorgan metal concentrations. They reported that zinc concentrations in the liver do not seem to be associated with sex or age (Kollmeier et al., 1992). Another study, conducted with children by Coni et al. (1996), confirmed these findings. They measured the concentration of metal in necropsy material from infants that died of sudden infant death syndrome and from pediatric control subjects, and found that a small liver sample is representative of liver concentration in the whole liver.


a AAS = atomic absorption spectrophotometry.

b ICP-ES = inductively coupled plasma emission spectroscopy.

Table 2. Zinc concentration in hepatic tissue according to the literature.

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Fresh tissue is not always available for chemical analysis, but formalin-fixed tissue often is. In our study, zinc concentration measurements in fresh liver tissue and deparaffinized tissue have been shown to be concordant. We have found in fresh e deparaffinized tissues respectively, 173,6 ± 37,9 µg/g dry weight and 220,2 ± 127 µg/g dry weight. Two deparaffinized tissue samples showed higher values of zinc than the others samples, causing a higher standard deviation. There was no evidence of mineral contamination during the embedding process to account for these divergent values.

We found only one study in the literature, conducted at the Mayo Clinic by Bush et al. (1995) that compared zinc concentration in fresh and deparaffinized liver tissue. Their study investigated the concentration of metals in several organs using material obtained from autopsy of 30 presumably healthy individuals. Zinc concentration found in fresh liver tissue was 191 ± 56.3 µg/g dry weight, and, in formalin-fixed tissue, 204 ± 63.2 µg/g dry weight. They concluded that formalin fixation long-term storage has little effect on zinc concentrations in tissue and that zinc was homogeneously distributed in liver.

Due to the clinical importance of zinc in liver diseases, the use of paraffin-embedded specimens for analysis is extremely useful when fresh tissue is not available. Stored material for analysis may be available even years after the biopsy or autopsy sample was obtained.
