Our study presents, for the first time, a comparative analysis of liver metallomic profiles among patients from different geographical locations and genetic background, affected by HCC-NC, a disease that escapes the conventional profile of HCC and representing merely 20% of cases of HCC.14 However in the Peruvian context, HCC-NC represents 90% of cases of liver cancer.3
The impact of metals on biological cell processes is a phenomenon not completely understood. Metals are involved in many beneficial functions like maintenance of pH, enzymatic cofactor, metabolism trigger, and reactive oxygen species formation as a product of normal metabolism.15–17 However, while present in excess, metals may have harmful effects. The principal impact of metals is the disruption of intracellular redox balance, debt to increase of reactive oxigen species production.18
Our data shows that concentrations of metals were higher in NTL of Peruvian patients compared to French individuals. Among those metals, some of them, such as As and Cd, are known to exert harmful effects on health.19,20 Indeed, As and Cd are considered as carcinogenic to human according to WHO. The mechanism by which As contributes to the process of carcinogenesis is DNA damage with chromosomal aberrations, deletion mutations, and aneuploidy.21,22 A strong link between exposure to arsenic and the development of HCC has been demonstrated in animal models, which also evidenced an increase in lipid peroxidation levels, prior to the onset of the fibrosis process and subsequent development of HCC.21,23,24 The mechanism of Cd related injury involves the interaction and possible inactivation of thiol groups, leading to functional alteration of the metallo-enzymes of the superoxide dismutase family and to subsequent depletion of antioxidant agents such as glutathione.25,26
We cannot assess whether HCC-NC and its spectrum of mutated genes are directly caused by the presence of heavy metals.27 It is likely that metals could play an enhancing role in the carcinogenic process in association with hepatic carcinogenic agents, such the hepatitis B virus infection in Peruvian patients,28 and/or alcohol intake that we were not able to assess with sufficient confidence.
However, due to the absence of liver fibrosis in these series of patients, the role of ethanol is predicted to be marginal in the patho-physiological process.
Another important highlight is the common metallome profile of HCC compared to NTL, with lower concentrations of metals in tumor tissue in both cohorts. Such findings suggest that whatever the etiological factors, the geographic origin or other different parameters between cohorts, cancer cells have similar adaptive process regarding metal metabolisms. Whether the concentration decrease of most of these metals are related to a lower uptake, an increase release, and/or an increased turnover related especially to the enhanced cell cycle and cell metabolism remains not known.
The increase of Cu concentration, mostly in cancer tissues, was already reported in HCC,10 and other cancers affecting especially breast, cervix, ovarian, and lung.23,29,30 A hypothesis aiming to explain the behavior of Cu in cancer has been proposed by Fisher and collaborators, who states that the increase of this metal is due to a decrease in the catabolism in tumoral cells of ceruloplasmin (Cp) in tumor cells.31 This phenomenon affecting the multicopper-carrying protein, might be due to increased sialylation produced by free sialic acid from cell membranes of neoplastic cells. This hypothesis was later supported in an animal model by Bernacki et al.32 Another hypothesis concerns the role of copper as angiogenic agent.33 McAuslan et al. showed that copper acts as promoter of endothelial cells migration.34 Martin et al. consolidated both hypotheses, describing the link between Cu, ceruloplasmin and HIF-1α.35 The authors showed that Cu acts as a stabilizer of the HIF-1α, mediating inhibition of prolyl-4-hydroylation. The HIF-1α is eventually responsible for regulating transcription of many genes, including the Cp gene. Meanwhile, Himoto proposed a possible mechanism whereby Cu is required for binding HIF-1α to p300 and prevents the effect of Factor Inhibiting HIF-1 (FIH-1).36
Another finding is the relationship between Se concentration in tumor tissues and survival in the Peruvian group. Se plays a major role in cell homeostasis, mainly through selenoproteins that are anti-inflammatory, chemo-preventive, and immune modulators.37 Cox regression model suggests a beneficial effect in overall survival for patients with higher levels of Se in HCC. This result is corroborated by a meta-analysis displaying the negative correlation between Se concentration and HCC.38 Indeed, low levels of Se have been associated with high risk of developing HCC. Our model developed on a relatively small number of patients give us a significative outcome only in the Peruvian cohort. This could be explained by the fact that, in these patients, a “natural evolution of the disease” is observed,4 since in this group of patients received only surgery, unlike the French patients who received additional local or systemic treatments that could modify HCC development.39,40 Such findings shall be corroborated in larger cohorts.
Finally, we must highlight the possible role of environment in the hepatocarcinogenic process due to the high mineral content of the subsoil and rivers. This statment was endorsed by several studies showing the presence of high heavy metal concentrations in the Andean regions of Peru.41–43 In Egypt, Elwakil et al. have also described high concentrations of Cd, Pb, As, and Hg in blood samples from HCC patients who were exposed to the consumption of contaminated plants.44 Therefore, we cannot rule out the relationship between the presence of metal in environment and natural history HCC.
Altogether, our findings show that Peruvian and French cohorts of HCC patients have different metallomic profiles in NTLs, suggesting a putative impact of environmental and/or genetic factors. Whether these elements play a role in the very peculiar phenotype of HCC in Peru should be further explored. In addition, the modulation of metal concentration in HCC, that is shared by the two cohort suggests a coordinated modulation of metal metabolism in liver cancer cells during the carcinogenesis. Additional studies will allow to progress in understanding the role of metal metabolisms alterations in the hepatocarcinogenic process.