Do genetic variations in antioxidant enzymes influence the course of hereditary hemochromatosis?

Characterization of ferroptosis in murine models of hemochromatosis

Ferroptosis is a recently identified iron-dependent form of nonapoptotic cell death implicated in brain, kidney, and heart pathology. However, the biological roles of iron and iron metabolism in ferroptosis remain poorly understood. Here, we studied the functional role of iron and iron metabolism in the pathogenesis of ferroptosis. We found that ferric citrate potently induces ferroptosis in murine primary hepatocytes and bone marrow-derived macrophages. Next, we screened for ferroptosis in mice fed a high-iron diet and in mouse models of hereditary hemochromatosis with iron overload. We found that ferroptosis occurred in mice fed a high-iron diet and in two knockout mouse lines that develop severe iron overload (Hjv^-/- and Smad4^Alb/Alb mice) but not in a third line that develops only mild iron overload (Hfe^-/- mice). Moreover, we found that iron overload-induced liver damage was rescued by the ferroptosis inhibitor ferrostatin-1. To identify the genes involved in iron-induced ferroptosis, we performed microarray analyses of iron-treated bone marrow-derived macrophages. Interestingly, solute carrier family 7, member 11 (Slc7a11), a known ferroptosis-related gene, was significantly up-regulated in iron-treated cells compared with untreated cells. However, genetically deleting Slc7a11 expression was not sufficient to induce ferroptosis in mice. Next, we studied iron-treated hepatocytes and bone marrow-derived macrophages isolated from Slc7a11^-/- mice fed a high-iron diet.

CONCLUSION

We found that iron treatment induced ferroptosis in Slc7a11^-/- cells, indicating that deleting Slc7a11 facilitates the onset of ferroptosis specifically under high-iron conditions; these results provide compelling evidence that iron plays a key role in triggering Slc7a11-mediated ferroptosis and suggest that ferroptosis may be a promising target for treating hemochromatosis-related tissue damage. (Hepatology 2017;66:449-465).

Progress in understanding association of PNPLA3 I148M (rs738409) single nucleotide polymorphism with hepatocellular carcinoma and hepatic cirrhosis

Patatin-like phospholipase domain containing 3 (PNPLA3), also called adiponutrin, is mainly expressed in the hepatocellular membrane and involved in lipid metabolism. The rs738409 genetic variant causes an isoleucine-to-methionine substitution at amino acid position 148 (I148M). Recently, genome-wide association studies have described associations of PNPLA3 I148M with plasma liver enzyme levels, steatosis and fibrosis severity. Studies found that PNPLA3 I148M is associated with progression of alcoholic liver cirrhosis, clinical outcome and prognosis of alcohol related hepatocellular carcinoma (HCC), and clinical outcomes of chronic hepatitis C. PNPLA3 I148M plays an important role in liver disease progression, which can be an independent risk factor for HCC.

Impact of hemochromatosis gene mutations on cardiac status in doxorubicin-treated survivors of childhood high-risk leukemia

BACKGROUND

Doxorubicin is associated with progressive cardiac dysfunction, possibly through the formation of doxorubicin-iron complexes leading to free-radical injury. The authors determined the frequency of hemochromatosis (HFE) gene mutations associated with hereditary hemochromatosis and their relationship with doxorubicin-associated cardiotoxicity in survivors of childhood high-risk acute lymphoblastic leukemia.

METHODS

Peripheral blood was tested for 2 common HFE allelic variants: C282Y and H63D. Serum cardiac troponin-T (cTnT) and N-terminal pro-brain natriuretic peptide (NT-proBNP), which are biomarkers of cardiac injury and cardiomyopathy, respectively, were assayed during therapy. Left ventricular (LV) structure and function were assessed with echocardiography.

RESULTS

A total of 184 patients had DNA results for at least 1 variant, and 167 had DNA results for both: 24% carried H63D and 10% carried C282Y. Heterozygous C282Y genotype was associated with multiple elevations in cTnT concentrations (P = .039), but not NT-proBNP. At a median of 2.2 years (range, 1.0 years-3.6 years) after diagnosis, the mean Z-scores for LV fractional shortening (-0.71 [standard error (SE), 0.25]; P = .008), mass (-0.84 [SE, 0.17]; P < .001), and end-systolic (-4.36 [SE, 0.26], P < .001) and end-diastolic (-0.68 [SE, 0.25]; P = .01) posterior wall thickness were found to be abnormal in children with either allele (n = 32). Noncarriers (n = 63) also were found to have below-normal LV mass (-0.45 [SE, 0.15]; P = .006) and end-systolic posterior wall thickness (-4.06 [SE, 0.17]; P < .001). Later follow-up demonstrated similar results.

CONCLUSIONS

Doxorubicin-associated myocardial injury was associated with C282Y HFE carriers. Although LV mass and wall thickness were found to be abnormally low overall, they were even lower in HFE carriers, who also had reduced LV function. Screening newly diagnosed cancer patients for HFE mutations may identify those at risk for doxorubicin-induced cardiotoxicity.

PNPLA3 I148M variant and hepatocellular carcinoma: a common genetic variant for a rare disease

Hepatocellular carcinoma (HCC) is highly associated with chronic liver disease. The rs738409 genetic variant in the patatin-like phospholipase domain-containing 3 (PNPLA3, adiponutrin) gene has been implicated as a genetic determinant of the entire spectrum of liver diseases, ranging from steatosis, chronic hepatitis, cirrhosis and ultimately to HCC. In this review, first we will examine the current genetic theories of disease susceptibility. Next, we will analyze the evidences for the association between PNPLA3 I148M variant and HCC. Moreover, we will exploit this association to propose a new paradigm in human genetics: a common genetic variant contributing to a rare disease. Finally, we will examine the molecular genetics of PNPLA3 and, specifically, the theories that have been proposed to explain the function of PNPLA3 in health and disease.

Effect of hereditary haemochromatosis genotypes and iron overload on other trace elements

PURPOSE

Hereditary haemochromatosis is a common genetic disorder involving dysregulation of iron absorption. There is some evidence to suggest that abnormal iron absorption and metabolism may influence the status of other important trace elements. In this study, the effect of abnormal HFE genotypes and associated iron overload on the status of other trace elements was examined.

METHODS

Dietary data and blood samples were collected from 199 subjects (mean age = 55.4 years; range = 21-81 years). Dietary intakes, serum selenium, copper and zinc concentrations and related antioxidant enzymes (glutathione peroxidase and superoxide dismutase) in subjects with normal HFE genotype (n = 118) were compared to those with abnormal HFE genotype, with both normal iron status (n = 42) and iron overload (n = 39).

RESULTS

For most dietary and biochemical variables measured, there were no significant differences between study groups. Red cell GPx was significantly higher in male subjects with normal genotypes and normal iron status compared to those with abnormal genotypes and normal iron status (P = 0.03) or iron overload (P = 0.001). Red cell GPx was also highest in normal women and significantly lower in the abnormal genotype and normal iron group (P = 0.016), but not in the iron overload group (P = 0.078).

CONCLUSION

Although it may not be possible to exclude a small effect between the genotype groups on RBC GPx, overall, haemochromatosis genotypes or iron overload did not appear to have a significant effect on selenium, copper or zinc status.