LIVER DISEASE AND ABNORMAL METAL METABOLISM
Abnormal metal metabolism, which is related to liver disease, has long been a subject of pathological study, particularly storage diseases such as iron metabolism in hemochromatosis[1] and copper metabolism in Wilson’s disease[2].
As nutrition science has advanced, it has recently been pointed out that trace metallic elements in blood play essential roles, and abnormal metal metabolism involving metal deficiency in various diseases has been studied.
Zinc is an essential trace element in the human body, with approximately 2 g distributed throughout the body of a healthy adult, including many organs[3-5]. In vivo, this element stimulates the activity of as many as 300 metal enzymes and metal-activated enzymes, and is crucial for nucleic acids and protein metabolism. Zinc plays an important role in the activity of many enzyme proteins, and a deficiency of zinc causes various pathologic disorders in the human body.
Regarding zinc metabolism abnormality in liver disease, in 1951 Vikbladh pointed out that the zinc content in serum was low in the case of various liver diseases[6], and conjectured that serum contains albumin loosely bound to zinc and globulin firmly bound to zinc, and that the albumin is associated with a lower zinc content. In 1957, Bartholomay et al[7] claimed that hypozincemia in liver disease might be associated with increased urinary zinc excretion. In 1979, Sullivan et al[8] pointed out that decreased zinc absorption was observed in cases of alcoholic cirrhosis, and in 1988, Grüngreiff et al[9,10] reported that poor zinc absorption was observed in cases of non-alcoholic cirrhosis.
It is known that among liver disease cases, those with chronic hepatitis C show lower zinc concentrations in blood as their pathologic condition worsens from chronic hepatitis, to compensated cirrhosis, to decompensated cirrhosis, to hepatocellular carcinoma (HCC). Serum and hepatic zinc concentrations are decreased in chronic liver diseases, and zinc depletion has been suggested to be a cause of liver fibrosis[11,12]. Particularly, cases with liver failure[13] or cases of HCC[14,15] are known to show conspicuous hypozincemia, and zinc supplementation therapy improves liver disease.
CORRELATION OF HEPATITIS C VIRUS WITH ZINC
A study of the relationship of the existence of hepatitis C virus (HCV) with zinc concentration in serum suggested that zinc concentration was not related to HCV genotypes or HCV-RNA values, and thus the existence of HCV did not affect the serum zinc concentration. However, it was reported that the serum zinc concentrations of untreated asymptomatic carrier (ASC) cases were significantly lower than those of healthy people[16]. From this report, it can be inferred that the existence of HCV may be related to the serum zinc concentration even if the former does not directly affect the latter.
It has recently been reported that nonstructural 3 proteinase[17-20], which is involved in the replication of HCV, is a zinc-containing enzyme, and that the nonstructural 5A protein is a zinc metalloprotein[21]. Accordingly, it is necessary to examine and control the serum zinc concentration when treating cases of refractory chronic hepatitis C. In addition, in ASC cases, their progress may need to be observed by monitoring the serum zinc concentration and other means.
It has been reported that zinc in blood is closely related to hepatic fibrosis in cases of liver disease. It has also been reported that drug therapy or gene therapy that increases the serum zinc concentration can inhibit the progress of hepatic fibrosis[22]. Many studies, including those noted above, suggest that pathologic conditions of the liver are closely related to zinc in blood. However, although there have been basic researches, its relationship with hepatic fibrosis has not been clinically studied.
CHRONIC HEPATITIS C AND ZINC
Some 60% to 70% of cases of hepatitis C progress to chronic hepatitis, and then to cirrhosis and hepatocellular carcinoma over 20 years to 30 years. Following the 1986 report of Hoofnagle et al[23] on the effects of interferon (IFN) on HCV infection in patients with chronic hepatitis, IFN therapy has been employed throughout the world to treat chronic hepatitis C. The treatment of choice for chronic hepatitis C is antiviral therapy using IFN[24,25].
In Japan, many cases of hepatitis C have been treated with IFN since 1992, when treatment using IFN drugs became covered by the public health insurance system. IFN monotherapy, which was used initially, successfully resulted in low sustained HCV-negative condition of all cases treated[26]. Sustained virological response (SVR) was gained in merely 6% of patients with HCV-1b in high viral loads when the practice of administering a 6-mo regimen of natural IFN was started in 1992; it increased to 20% with the 6-mo regimen of standard IFN combined with ribavirin (RBV) implemented in 2001[27,28]. Finally, the introduction of the 12-mo regimen of pegylated IFN (PEG-IFN) and RBV approved in 2004 achieved SVR in 50%[29,30].
The viral factors that affect the effectiveness of IFN therapy include HCV genotype and HCV-RNA quantity, and the host factors that do so include the histological condition of the liver, age and degree of fatness.
Generally, genotype Ib virus is more resistant to IFN than genotype IIa or IIb viruses. In Japan, genotype Ib in high viral loads accounts for more than 70% of HCV infections, making it difficult to treat patients with chronic hepatitis C[27,28].
With regard to the effect of the combination therapy of oral administration of zinc with IFN for chronic hepatitis C, Nagamine et al[31] reported on the roles of zinc and metallothionein in IFN-α therapy for hepatitis C in 1997. Takagi et al[32] treated 68 cases of chronic hepatitis C with genotype Ib virus of an HCV-RNA quantity of at least 100 Kcopy/mL with a dose of 10 million units of IFN-α once daily for four weeks, and then the same dose three times weekly for the subsequent 20 wk, by intramuscular injection. They combined the IFN administration with an oral dose of 150 mg of polaprezinc (Promac；Zeria Pharmaceutical, Company Ltd., Tokyo, Japan) daily (equivalent to 34 mg of zinc) in 32 of the 68 cases. The effects of the treatment were evaluated six months after completion, with the criteria of complete response (CR) for disappearance of HCV-RNA and normal alanine aminotransferase (ALT) levels; incomplete response (IR) for HCV-RNA that did not disappear, but normal ALT levels; and non-responder for other cases. The IFN monotherapy group (IFN) was compared with the IFN and zinc combination group (IFN + Zn) in terms of those criteria, with the following results. The IFN group showed CR: 11.1% (4/36) and IR: 11.1% (4/36), totaling 22.2% (8/36), while the IFN + Zn group showed CR: 37.5% (12/32) and IR: 18.8% (6/32), totaling 56.3% (18/32). Thus, they concluded that the zinc combination group had a significantly higher effective rate[32].
Murakami et al[33] treated cases of chronic hepatitis C with a high virus quantity of genotype Ib with the PEG-IFN/RBV therapy, and analyzed the proportion of cases that became HCV-RNA negative after eight weeks of treatment by using groups with and without combination with zinc administration with an oral dose of 150 mg of polaprezinc (containing 34 mg of zinc) daily. They reported that the proportion of cases in whom ALT lowered to 35 U/L or less by the eighth week was 91% (10/11) in the zinc combination group and 58% (7/12) in the non-zinc administration group; however, the proportions of cases that became HCV-RNA negative were 18% (2/11) and 25% (3/12) respectively, showing no significant difference. Furthermore, they continued to observe the cases, and reported that all the cases (9/9) in the group with combination with zinc administration and 67% (8/12) of the cases in the group without combination with zinc administration showed normal ALT levels after 24 wk, and that all the cases (7/7) in the group with zinc and 60% (6/10) of the cases in the group without zinc did so after 48 wk. Interferon therapy for chronic hepatitis C has improved in many ways such as combination with ribavirin, and the rate of virus disappearance resulting from such therapy has increased conspicuously in comparison with the initial results. This therapy now achieves an SVR of approximately 50% even for cases with a high virus quantity of genotype Ib, and a viral clearance rate of nearly 90% for other cases. However, this therapy has shown poor results for cases with severe hepatic histological fibrosis or thrombocytopenia, or for elderly patients, so its combination with zinc administration should be attempted in refractory cases.
HEPATIC FIBROSIS AND ZINC
In cirrhosis, the quantity of hydroxyproline in liver tissues increases while that of zinc decreases. Boyett et al[34] reported that the concentration of zinc per unit nitrogen not derived from collagen was correlated with the concentration of zinc in liver tissues. Himoto et al[35] examined the effects of zinc administration on inflammatory activity and fibrosis of the liver in patients with HCV-related chronic liver disease (CLD). Treatment with polaprezinc significantly decreased serum aminotransferase levels (aspartate aminotransferase: 92 ± 33 IU/L vs 63 ± 23 IU/L, P = 0.0004; ALT: 106 ± 43 IU/L vs 65 ± 32 IU/L, P = 0.0002), whereas alkaline phosphatase levels were significantly increased (305 ± 117 IU/L vs 337 ± 118 U/L, P = 0.0020). There was a tendency toward a decrease in serum type IV collagen 7S levels after treatment with polaprezinc. However, administration of polaprezinc did not affect peripheral blood cell counts, other liver function tests, or HCV-RNA loads. These findings suggest that polaprezinc exerts an anti-inflammatory effect on the liver in patients with HCV-related CLD by reducing iron overload.
Furthermore, Matsuoka et al[36] reported that zinc supplementation improves the outcome of chronic hepatitis C and liver cirrhosis. Takahashi et al[37] investigated the effect of oral zinc supplementation on liver fibrosis in patients with advanced chronic liver disease. The serum levels of type IV collagen and the activity of tissue inhibitors of metalloproteinase-1 were significantly reduced. This suggests that oral zinc supplement therapy is safe and may be a novel and useful strategy for antifibrosis therapy in patients with early liver cirrhosis.
Generally, the oxidative stress is high in hepatitis patients, and significant correlations among HCV-RNA. Oxidant stress is a significant feature of hepatitis C infection[38]. There is evidence that the production of free radicals increases while anti-oxidant defense decreases significantly in all types of liver damage. Alongside the direct effect of the HCV core protein, hepatocellular iron accumulation and the production of reactive oxygen species associated with the immune response are considered to be of crucial significance for the creation of oxidative stress in chronic HCV. Mitochondrial effects may contribute to liver injury and oxidative stress seen in chronic hepatitis C[39]. Zinc plays an important role in the redox process as a signal molecule and second messenger.
Decrease of supportive nutrients such as zinc have been documented in patients with viral or alcoholic liver disease. These markers may contribute to the monitoring the degree of liver damage, the response to antiviral therapies and to the design of new therapeutic strategies[40]. Effects of zinc in the treatment of chronic hepatitis C are produced via immunological reactions, antiviral defence mechanisms and the role of zinc as an antioxidant[41]. Furthermore, Yuasa et al[42] have shown that zinc substitution negatively influences HCV replication. Zinc supplementation thus appears to offer a novel approach to the development of future strategies for the treatment of intractable chronic hepatitis C.
TREATMENT FOR CHRONIC HEPATITIS C BY ADMINISTERING ZINC
Leucopenia or thrombocytopenia is often found in elderly patients with chronic hepatitis C with severe fibrosis, and in many such cases, the IFN therapy must be discontinued due to side effects.
According to the results of a study in which zinc was administered in applying IFN and RBV therapy to cases of chronic hepatitis C with a tendency toward zinc deficiency to assess its effects on cytopenia, zinc served to protect against a reduction in white blood cells or platelets and thus effectively inhibited side effects.
The reduction in the number of peripheral blood cells due to IFN therapy seems to be caused by inhibition of the hematopoietic function of bone marrow. When RBV is combined with IFN therapy, hemolytic anemia due to the accumulation of RBV in red blood cells also seems to cause such a reduction. In cases of chronic hepatitis C with severe fibrosis, the number of blood cells tends to be already low before the administration of IFN or RBV, and therefore how to prevent the reduction in blood cells as a side effect is important.
Nagamine et al[43] conducted a basic study on the activity of IFN-α in U937 cells in order to elucidate whether zinc would enhance the action of interferon. They found that zinc chloride and polaprezinc increased IFNAR mRNA by 30% to 40%, whereas monotherapy of L-carnosine had no such effect, suggesting that zinc enhanced the action of interferon and induced the production of anti-viral proteins. Hence, many cases of liver disease are accompanied by complaints of symptoms in the mouth such as dysgeusia, dry mouth and stomatitis when treated with PEG-IFN/RBV. Zinc supplement seems to be effective against oral mucosa disorders in IFN therapy treatment.
A new antiviral drug called DAA became covered by the public health insurance system in Japan. Hence, the treatment of choice for cases with a high quantity of genotype 1 virus is likely to be DAA + PEG-IFN α-2b + RBV combination therapy (the “3-drug therapy”). However, it has been reported that this therapy causes side effects such as severe hemoglobin reduction or severe rash, and many side effects in elderly patients.
Zinc supplementation to reduce such side effects may be the key to developing more effective anti-viral therapies. As this paper has suggested, the administration of zinc in many clinical cases requires further study. Prospective double-blind studies with large sample sizes are necessary.
Peer reviewers: Heitor Rosa, Professor, Department of Gastroenterology and Hepatology, Federal University School of Medicine, Rua 126 n.21, Goiania-GO 74093-080, Brazil; Natalia A Osna, MD, PhD, Liver Study Unit, Research Service (151), VA Medical Center, 4101 Woolworth Avenue, Omaha, NE 68105, United States
S- Editor Cheng JX L- Editor A E- Editor Zhang DN
