Modification of hepatic iron metabolism induced by pravastatin during obstructive cholestasis in rats

Development and validation of a prediction model for iron status in a large U.S. cohort of women

Serum iron levels can be important contributors to health outcomes, but it is not often feasible to rely on blood-based measures for a large epidemiologic study. Predictive models that use questionnaire-based factors such as diet, supplement use, recency of blood donation, and medical conditions could potentially provide a noninvasive alternative for studying health effects associated with iron status. We hypothesized that a model based on questionnaire data could predict blood-based measures of iron status biomarkers. Using iron (mcg/dL), ferritin (mcg/dL), and transferrin saturation (%) based on blood collected at study entry, in a subsample from the U.S.-wide Sister Study (n = 3171), we developed and validated a prediction model for iron with multivariable linear regression models. Model performance based on these cross-sectional data was weak, with R2 less than 0.10 for serum iron and transferrin saturation, but better for ferritin, with an R2 of 0.13 in premenopausal women and 0.19 in postmenopausal women. When menopause was included in the predictive model for the sample, the R2 was 0.31 for ferritin. Internal validation of the estimates indicated some optimism present in the observed prediction model, implying there would be worse performance when applied to new samples from the same population. Serum iron status is hard to assess based only on questionnaire data. Reducing measurement error in both the exposure and outcome may improve the prediction model performance, but environmental heterogeneity, temporal variation, and genetic heterogeneity in absorption and storage may contribute substantially to iron status.

The Link between Iron Turnover and Pharmacotherapy in Transplant Patients

Iron is a transition metal that plays a crucial role in several physiological processes. It can also exhibit toxic effects on cells, due to its role in the formation of free radicals. Iron deficiency and anemia, as well as iron overload, are the result of impaired iron metabolism, in which a number of proteins, such as hepcidin, hemojuvelin and transferrin, take part. Iron deficiency is common in individuals with renal and cardiac transplants, while iron overload is more common in patients with hepatic transplantation. The current knowledge about iron metabolism in lung graft recipients and donors is limited. The problem is even more complex when we consider the fact that iron metabolism may be also driven by certain drugs used by graft recipients and donors. In this work, we overview the available literature reports on iron turnover in the human body, with particular emphasis on transplant patients, and we also attempt to assess the drugs’ impact on iron metabolism, which may be useful in perioperative treatment in transplantology.

Deposition of Iron in the Bone Marrow of a Murine Model of Hematopoietic Acute Radiation Syndrome

Exposure to high-dose total body irradiation (TBI) can result in hematopoietic acute radiation syndrome (H-ARS), characterized by leukopenia, anemia, and coagulopathy. Death from H-ARS occurs from hematopoietic insufficiency and opportunistic infections. Following radiation exposure, red blood cells (RBCs) undergo hemolysis from radiation-induced hemoglobin denaturation, causing the release of iron. Free iron can have multiple detrimental biological effects, including suppression of hematopoiesis. We investigated the impact of radiation-induced iron release on the bone marrow following TBI and the potential impact of the ACE inhibitor captopril, which improves survival from H-ARS. C57BL/6J mice were exposed to 7.9 Gy, ⁶⁰Co irradiation, 0.6 Gy/min (LD_70-90/30). RBCs and reticulocytes were significantly reduced within 7 days of TBI, with the RBC nadir at 14-21 days. Iron accumulation in the bone marrow correlated with the time course of RBC hemolysis, with an ∼10-fold increase in bone marrow iron at 14-21 days post-irradiation, primarily within the cytoplasm of macrophages. Iron accumulation in the bone marrow was associated with increased expression of genes for iron binding and transport proteins, including transferrin, transferrin receptor 1, ferroportin, and integrin αMβ2. Expression of the gene encoding Nrf2, a transcription factor activated by oxidative stress, also increased at 21 days post-irradiation. Captopril did not alter iron accumulation in the bone marrow or expression of iron storage genes, but did suppress Nrf2 expression. Our study suggests that following TBI, iron is deposited in tissues not normally associated with iron storage, which may be a secondary mechanism of radiation-induced tissue injury.

Iron depletion induces hepatic secretion of biliary lipids and glutathione in rats

Iron depletion (ID) has been shown to induce the liver expression of Cyp7a1, the rate-limiting enzyme initiating conversion of cholesterol to bile acids (BA), although the effect on bile acids metabolism and bile production is unknown. Therefore, we investigated changes in bile secretion and BA synthesis during diet-induced iron depletion (ID) in rats. ID increased bile flow along with augmented biliary excretion of bile acids, glutathione, cholesterol and phospholipids. Accordingly, we found transcriptional upregulation of the Cyp7a1, Cyp8b1, and Cyp27a1 BA synthetic enzymes, as well as induction of the Abcg5/8 cholesterol transporters in ID rat livers. In contrast, intravenous infusion of ³H-taurocholate failed to elicit any difference in biliary secretion of this compound in the ID rats. This corresponded with unchanged expression of canalicular rate-limiting transporters for BA as well as glutathione. We also observed that ID substantially changed the spectrum of BA in bile and decreased plasma concentrations of BA and cholesterol. Experiments with differentiated human hepatic HepaRG cells confirmed human CYP7A1 orthologue upregulation resulting from reduced iron concentrations. Results employing a luciferase reporter gene assay suggest that the transcriptional activation of the CYP7A1 promoter under ID conditions works independent of farnesoid X (FXR), pregnane X (PXR) and liver X (LXRα) receptors activation. It can be concluded that this study characterizes the molecular mechanisms of modified bile production as well as cholesterol as along with BA homeostasis during ID. We propose complex upregulation of BA synthesis, and biliary cholesterol secretion as the key factors affected by ID.

Boldine Attenuates Cholestasis Associated With Nonalcoholic Fatty Liver Disease in Hereditary Hypertriglyceridemic Rats Fed by High-Sucrose Diet

The aim of the current study was to clarify the effect of high sucrose diet (HSD) on bile formation (BF) in rats with hereditary hypertriglyceridemia (HHTg). Potentially positive effects were studied for boldine, a natural choleretic agent. Administration of HSD to HHTg rats led to increased triglyceride deposition in the liver. HSD reduced BF as a consequence of decreased biliary secretion of bile acids (BA) and glutathione. Responsible mechanism was down-regulation of hepatic transporters for BA and glutathione, Bsep and Mrp2, respectively. Moreover, gene expressions of transporters for other constituents of bile, namely Abcg5/8 for cholesterol, Abcb4 for phospholipids, and Oatp1a4 for xenobiotics, were also reduced by HSD. Boldine partially attenuated cholestatic effect of HSD by promotion of biliary secretion of BA through up-regulation of Bsep and Ntcp, and by increase in biliary secretion of glutathione as a consequence of its increased hepatic disposition. This study demonstrates mechanisms of impaired BF during nonalcoholic fatty liver disease induced by HSD. Altered function of responsible transporters suggests also potential for changes in kinetics of drugs, which may complicate pharmacotherapy in subjects with high intake of sucrose, and with fatty liver disease. Sucrose induced alterations in BF may be alleviated by administration of boldine.

Ezetimibe increases hepatic iron levels in mice fed a high-fat diet

Accumulating evidence suggests that ezetimibe may be a promising agent for treatment of nonalcoholic fatty liver disease and steatohepatitis (NAFLD/NASH). Phlebotomy and dietary iron restriction reduce serum transaminase in NAFLD/NASH patients. Recent studies have shown that a mutual effect exists between lipid metabolism and iron metabolism. Accordingly, we examined the effect of ezetimibe on iron metabolism in mice fed a high-fat diet with or without iron. We fed C57BL/6 mice the following diets for 12 weeks. Experiment 1 comprised [1] a control diet (C), [2] C plus ezetimibe (0.3 mg/day; 4 weeks) (CE), [3] a high-fat diet (H), and [4] H plus ezetimibe (HE). Experiment 2 comprised [1] C containing carbonyl iron (average; 22.4 mg/day; 6 weeks) (CI), [2] CI plus ezetimibe (CIE), [3] H containing carbonyl iron (HI), and [4] HI plus ezetimibe (HIE). Blood, livers, and duodenum were removed after 12 weeks. In experiment 1, the hepatic iron levels were higher in HE than H, whereas there was no difference between C and CE. Hepatic mRNA expression of transferrin receptor 1 and 2, ferritins, and hepcidin were increased more in CE than C, and more in HE than H. In the duodenum, divalent metal transporter 1, ferritin H, and hephaestin mRNA levels were increased in CE compared with C. In experiment 2, hepatic iron concentrations were higher in HIE than HI. Hepatic mRNA expression of ferritin L and hepcidin were increased in HIE compared with HI. In duodenum, ferritin L mRNA was increased in HIE compared with CIE. Ezetimibe induced hepatic iron uptake transporter expression in mice fed a high-fat diet, causing increased hepatic iron concentrations.

Pravastatin attenuates hypertension, oxidative stress, and angiogenic imbalance in rat model of placental ischemia-induced hypertension

Preeclampsia is a pregnancy-specific condition characterized by an imbalance of circulating angiogenic factors and new-onset hypertension. Although current treatment options are limited, recent studies suggest that pravastatin may improve angiogenic profile and reduce blood pressure in preeclampsia. We hypothesized pravastatin would restore angiogenic balance and reduce mean arterial pressure (MAP) in rats with reduced utero-placental perfusion pressure (RUPP)-induced hypertension. Pravastatin was administered intraperitoneally (1 mg/kg per day) in RUPP (RUPP+P) and normal pregnant rats (NP+P) from day 14 to 19 of pregnancy. On day 19, MAP was measured via catheter, conceptus data were recorded, and tissues collected. MAP was increased (P<0.05) in RUPP compared with NP dams, and pravastatin ameliorated this difference. Pravastatin attenuated decreased fetal weight and plasma vascular endothelial growth factor and the RUPP-induced increased soluble fms-like tyrosine kinase-1 when compared with NP dams. Pravastatin treatment did not improve angiogenic potential in RUPP serum and decreased (P<0.05) endothelial tube formation in NP rats. RUPP rats presented with indices of oxidative stress, such as increased placental catalase activity and plasma thiobarbituric acid reactive substances along with decreased plasma total antioxidant capacity compared with NP controls, and pravastatin attenuated these effects. MAP, fetal weight, plasma vascular endothelial growth factor, and plasma soluble fms-like tyrosine kinase-1 were unchanged in NP+P compared with NP controls. The present data indicate that treatment with pravastatin attenuates oxidative stress and lowers MAP in placental ischemia-induced hypertension, but may have negative effects on circulating angiogenic potential during pregnancy. Further studies are needed to determine whether there are long-term deleterious effects on maternal or fetal health after pravastatin treatment during pregnancy-induced hypertension or preeclampsia.