Makiko Oboshi

Aortic Iron Overload With Oxidative Stress and Inflammation in Human and Murine Abdominal Aortic Aneurysm

Objective—Although iron is an essential element for maintaining physiological function, excess iron leads to tissue damage caused by oxidative stress and inflammation. Oxidative stress and inflammation play critical roles for the development of abdominal aortic aneurysm (AAA). However, it has not been investigated whether iron plays a role in AAA formation through oxidative stress and inflammation. We, therefore, examined whether iron is involved in the pathophysiology of AAA formation using human AAA walls and murine AAA models. Approach and Results—Human aortic walls were collected from 53 patients who underwent cardiovascular surgery (non-AAA=34; AAA=19). Murine AAA was induced by infusion of angiotensin II to apolipoprotein E knockout mice. Iron was accumulated in human and murine AAA walls compared with non-AAA walls. Immunohistochemistry showed that both 8-hydroxy-2′-deoxyguanosine and CD68-positive areas were increased in AAA walls compared with non-AAA walls. The extent of iron accumulated area positively correlated with that of 8-hydroxy-2′-deoxyguanosine expression area and macrophage infiltration area in human and murine AAA walls. We next investigated the effects of dietary iron restriction on AAA formation in mice. Iron restriction reduced the incidence of AAA formation with attenuation of oxidative stress and inflammation. Aortic expression of transferrin receptor 1, intracellular iron transport protein, was increased in human and murine AAA walls, and transferrin receptor 1–positive area was similar to areas where iron accumulated and F4/80 were positive. Conclusions—Iron is involved in the pathophysiology of AAA formation with oxidative stress and inflammation. Dietary iron restriction could be a new therapeutic strategy for AAA progression.

Increased renal iron accumulation in hypertensive nephropathy of salt-loaded hypertensive rats.

Although iron is reported to be associated with the pathogenesis of chronic kidney disease, it is unknown whether iron participates in the pathophysiology of nephrosclerosis. Here, we investigate whether iron is involved in the development of hypertensive nephropathy and the effects of iron restriction on nephrosclerosis in salt- loaded stroke-prone spontaneously hypertensive rats (SHRSP). SHRSP were given either a normal or high-salt diet for 8 weeks. Another subset of SHRSP were fed a high-salt with iron-restricted diet. SHRSP given a high-salt diet developed severe hypertension and nephrosclerosis. As a result, survival rate was decreased after 8 weeks diet. Importantly, massive iron accumulation and increased iron content were observed in the kidneys of salt-loaded SHRSP, along with increased superoxide production, urinary 8-Hydroxy-2′-deoxyguanosine excretion, and urinary iron excretion; however, these changes were markedly attenuated by iron restriction. Of interest, expression of cellular iron transport proteins, transferrin receptor 1 and divalent metal transporter 1, was increased in the tubules of salt-loaded SHRSP. Notably, iron restriction attenuated the development of severe hypertension and nephrosclerosis, thereby improving survival rate in salt-loaded SHRSP. Taken together, these results suggest a novel mechanism by which iron plays a role in the development of hypertensive nephropathy and establish the effects of iron restriction on salt-induced nephrosclerosis.

Association between renal iron accumulation and renal interstitial fibrosis in a rat model of chronic kidney disease

Iron accumulation is associated with the pathophysiology of chronic kidney disease (CKD). Renal fibrosis is a final common feature that contributes to the progression of CKD; however, little is known about the association between renal iron accumulation and renal interstitial fibrosis in CKD. Here we investigate the effects of iron chelation on renal interstitial fibrosis in a rat model of CKD. CKD was induced by 5/6 nephrectomy in Sprague–Dawley rats. At 8 weeks after operation, 5/6 nephrectomized rats were administered an oral iron chelator, deferasirox (DFX), in chow for 8 weeks. Other CKD rats were given a normal diet. Sham-operative rats given a normal diet served as a control. CKD rats exhibited hypertension, glomerulosclerosis and renal interstitial fibrosis. Iron chelation with DFX did not change hypertension and glomerulosclerosis; however, renal interstitial fibrosis was attenuated in CKD rats. Consistent with these findings, renal gene expression of collagen type III and transforming growth factor-β was increased in CKD rats compared with the controls, while iron chelation suppressed these increments. In addition, a decrease in vimentin along an increase in E-cadherin in renal gene expression was observed in CKD rats with iron chelation. CKD rats also showed increased CD68-positive cells in the kidney, whereas its increase was attenuated by iron deprivation. Similarly, increased renal gene expression of CD68, tumor necrosis factor-α and monocyte chemoattractant protein-1 was suppressed in CKD rats with iron chelation. Renal iron accumulation seems to be associated with renal interstitial fibrosis in a rat model of CKD.

Iron restriction inhibits renal injury in aldosterone/salt-induced hypertensive mice

Excess iron is associated with the pathogenesis of several renal diseases. Aldosterone is reported to have deleterious effects on the kidney, but there have been no reports of the role of iron in aldosterone/salt-induced renal injury. Therefore, we investigated the effects of dietary iron restriction on the development of hypertension and renal injury in aldosterone/salt-induced hypertensive mice. Ten-week-old male C57BL/6J mice were uninephrectomized and infused with aldosterone for four weeks. These were divided into two groups: one fed a high-salt diet (Aldo) and the other fed a high-salt with iron-restricted diet (Aldo-IR). Vehicle-infused mice without a uninephrectomy were also divided into two groups: one fed a normal diet (control) and the other fed an iron-restricted diet (IR) for 4 weeks. As compared with control and IR mice, Aldo mice showed an increase in both systolic blood pressure and urinary albumin/creatinine ratio, but these increases were reduced in the Aldo-IR group. In addition, renal histology revealed that Aldo mice exhibited glomerulosclerosis and tubulointerstitial fibrosis, whereas these changes were attenuated in Aldo-IR mice. Expression of intracellular iron transport protein transferrin receptor 1 was increased in the renal tubules of Aldo mice compared with control mice. Dietary iron restriction attenuated the development of hypertension and renal injury in aldosterone/salt-induced hypertensive mice.

Interleukin-18 gene deletion protects against sepsis-induced cardiac dysfunction by inhibiting PP2A activity

BACKGROUND Interleukin-18 (IL-18) neutralization protects against lipopolysaccharide (LPS)-induced injuries, including myocardial dysfunction. However, the mechanism is yet to be fully elucidated. The aim of the present study was to determine whether IL-18 gene deletion prevents sepsis-induced cardiac dysfunction and to elucidate the potential mechanisms underlying IL-18-mediated cardiotoxicity by LPS. METHODS AND RESULTS Ten-week-old male wild-type (WT) and IL-18 knockout (IL-18 KO) mice were intraperitoneally administered LPS. Serial echocardiography showed better systolic pump function and less left ventricular (LV) dilatation in LPS-treated IL-18 KO mice compared with those in LPS-treated WT mice. LPS treatment significantly decreased the levels of phospholamban (PLN) and Akt phosphorylation in WT mice compared with those in saline-treated WT mice, while the LPS-induced decrease in the phosphorylation levels was attenuated in IL-18 KO mice compared with that in WT mice. IL-18 gene deletion also attenuated an LPS-induced increase of type 2 protein phosphatase 2A (PP2A) activity, a molecule that dephosphorylates PLN and Akt. There was no difference in type 1 protein phosphatase (PP1) activity. To address whether IL-18 affects PLN and Akt phosphorylation via PP2A activation in cardiomyocytes, rat neonatal cardiac myocytes were cultured and stimulated using 100ng/ml of recombinant rat IL-18. Exogenous IL-18 decreased the level of PLN and Akt phosphorylation in cardiomyocytes. PP2A activity but not PP1 activity was increased by IL-18 stimulation in cardiomyocytes. CONCLUSIONS IL-18 plays a pivotal role in advancing sepsis-induced cardiac dysfunction, and the mechanisms underlying IL-18-mediated cardiotoxicity potentially involve the regulation of PLN and Akt phosphorylation through PP2A activity.

Transferrin Receptor 1 in Chronic Hypoxia-Induced Pulmonary Vascular Remodeling

BACKGROUND Iron is associated with the pathophysiology of several cardiovascular diseases, including pulmonary hypertension (PH). In addition, disrupted pulmonary iron homeostasis has been reported in several chronic lung diseases. Transferrin receptor 1 (TfR1) plays a key role in cellular iron transport. However, the role of TfR1 in the pathophysiology of PH has not been well characterized. In this study, we investigate the role of TfR1 in the development of hypoxia-induced pulmonary vascular remodeling. METHODS PH was induced by exposing wild-type (WT) mice and TfR1 hetero knockout mice to hypoxia for 4 weeks and evaluated via assessment of pulmonary vascular remodeling, right ventricular (RV) systolic pressure, and RV hypertrophy. In addition, we assessed the functional role of TfR1 in pulmonary artery smooth muscle cells in vitro. RESULTS The morphology of pulmonary arteries did not differ between WT mice and TfR1 hetero knockout mice under normoxic conditions. In contrast, TfR1 hetero knockout mice exposed to 4 weeks hypoxia showed attenuated pulmonary vascular remodeling, RV systolic pressure, and RV hypertrophy compared with WT mice. In addition, the depletion of TfR1 by RNA interference attenuated human pulmonary artery smooth muscle cells proliferation induced by platelet-derived growth factor-BB (PDGF-BB) in vitro. CONCLUSIONS These results suggest that TfR1 plays an important role in the development of hypoxia-induced pulmonary vascular remodeling.

Interleukin-18 disruption suppresses hypoxia-induced pulmonary artery hypertension in mice

Article history: Received 31 July 2015 Received in revised form 24 September 2015 Accepted 28 September 2015 Available online 03 October 2015 atria, RV free wall was removed from left ventricle (LV). Each ventricle was weighed and the ratio of RV weight to LV plus septum weight (RV/LV + Sp) was calculated. Lungs were fixed with 4% buffered paraformaldehyde for 24 h, embedded in paraffin, and cut into 4-μm-thick sections. Hematoxylineosin (HE) and Elastica van Gieson (EVG) stainings were performed using standard protocols. Immunofluorescence staining was performed using a primary anti-α-smooth muscle actin (α-SMA) mouse antibody

Temporary dietary iron restriction affects the process of thrombus resolution in a rat model of deep vein thrombosis.

Background Deep vein thrombosis (DVT) is a major cause of pulmonary thromboembolism and sudden death. Thus, it is important to consider the pathophysiology of DVT. Recently, iron has been reported to be associated with thrombotic diseases. Hence, in this study, we investigate the effects of dietary iron restriction on the process of thrombus resolution in a rat model of DVT. Methods We induced DVT in 8-week-old male Sprague-Dawley rats by performing ligations of their inferior venae cavae. The rats were then given either a normal diet (DVT group) or an iron-restricted diet (DVT+IR group). Thrombosed inferior venae cavae were harvested at 5 days after ligation. Results The iron-restricted diet reduced venous thrombus size compared to the normal diet. Intrathrombotic collagen content was diminished in the DVT+IR group compared to the DVT group. In addition, intrathrombotic gene expression and the activity of matrix metalloproteinase-9 were increased in the DVT+IR group compared to the DVT group. Furthermore, the DVT+IR group had greater intrathrombotic neovascularization as well as higher gene expression levels of urokinase-type plasminogen activator and tissue-type plasminogen activator than the DVT group. The iron-restricted diet decreased intrathrombotic superoxide production compared to the normal diet. Conclusions These results suggest that dietary iron restriction affects the process of thrombus resolution in DVT.

Combination of hypertonic saline and low-dose furosemide is an effective treatment for refractory congestive heart failure with hyponatremia

Hyponatremia often associates with heart failure. Although severe salt restriction is generally recommended in heart failure treatment, it may promote hyponatremia which is a risk factor for increased morbidity and mortality in heart failure patients. Therefore, it is not yet clear whether correction of hyponatremia is an effective treatment in congestive heart failure with hyponatremia. We experienced a successful case of refractory congestive heart failure with hyponatremia treated with hypertonic saline and furosemide. A 45-year-old man, suffering from dilated cardiomyopathy, was admitted to our hospital for heart failure worsening with hyponatremia. We started diuretics therapy without correction of hyponatremia, but his clinical status of heart failure was not improved. Therefore, we additionally started to correct hyponatremia by continuous injection of hypertonic saline. The correction of hyponatremia increased urinary volume dramatically, and improved cardiac output and clinical status of heart failure. This case strongly suggests that combination of hypertonic saline and furosemide could enhance diuretic effect, and improve the clinical status of heart failure in congestive heart failure patients with hyponatremia. <Learning objective: Hyponatremia is a major problem associated with heart failure, but it is not yet clear whether correction of hyponatremia is an effective treatment in patients with congestive heart failure. We experienced a successful case of refractory congestive heart failure with hyponatremia treated with hypertonic saline and low dose furosemide. This case strongly suggests that aggressive correction of hyponatremia can be an effective treatment for refractory congestive heart failure with hyponatremia.>.

Altered expression of intestinal duodenal cytochrome b and divalent metal transporter 1 might be associated with cardio-renal anemia syndrome

The interaction among heart failure (HF), chronic kidney disease (CKD), and anemia is called cardio-renal anemia syndrome. The mechanism of anemia in cardio-renal anemia syndrome is complex and remains completely unknown. We have previously reported that impaired intestinal iron transporters may contribute to the mechanism of anemia in HF using in vivo HF model rats. In this study, we assessed intestinal iron transporters in CKD model rats to investigate the association of intestinal iron transporters in the mechanism of cardio-renal anemia syndrome. CKD was induced by 5/6 nephrectomy in Sprague–Dawley rats. Sham-operated rats served as a control. After 24-week surgery, CKD rats exhibited normocytic normochromic anemia and normal serum erythropoietin levels despite of anemia. Serum iron levels were decreased in CKD rats compared with the controls. Of interest, intestinal expression of critical iron importers, such as duodenal cytochrome b (Dcyt-b) and divalent metal transporter 1 (DMT-1), was decreased in CKD rats compared with the controls. On the other hand, intestinal expression of ferroportin, an intestinal iron exporter, was not different in the control and CKD groups. Moreover, hepatic expression of hepcidin, a regulator of iron homeostasis, did not differ between the control and CKD groups. These results suggest that impaired intestinal expression of Dcyt-b and DMT-1 might be associated with the reduction of an iron uptake in CKD. Taken together, impaired these intestinal iron transporters may become a novel therapeutic target for cardio-renal anemia syndrome.