Tomoaki Nagao

Osteopontin deficiency protects against aldosterone-induced inflammation, oxidative stress, and interstitial fibrosis in the kidney

Osteopontin (OPN) has been implicated in the pathology of several renal conditions. Recently, we demonstrated in vitro that aldosterone has important roles in collagen synthesis by inducing OPN (Irita J, Okura T, Kurata M, Miyoshi K, Fukuoka T, Higaki J. Hypertension 51: 507-513, 2008). The aim of the present study was to clarify the roles of OPN in aldosterone-mediated renal fibrosis by infusing aldosterone into either wild-type (WT) or OPN knockout mice (OPN(-/-)). We used uninephrectomized mice treated with aldosterone and high salt to exacerbate renal fibrosis. After 4 wk of treatment with aldosterone, we showed similar increases in systolic blood pressure in both strains of mice. Urine albumin excretion was greater in aldosterone-infused WT mice than in aldosterone-infused OPN(-/-) mice. Immunohistochemical analysis showed high levels of OPN expression in aldosterone-infused WT mice. Interstitial fibrosis and inflammatory infiltrations were increased in aldosterone-infused WT mice compared with either vehicle-infused WT or aldosterone-infused OPN(-/-) mice. These changes were ameliorated markedly by eplerenone treatment in aldosterone-infused WT mice. Aldosterone-infused WT mice also had increased expression of NADPH oxidase subunits compared with aldosterone-infused OPN(-/-) mice. We observed a marked increase in oxidative stress markers in aldosterone-infused WT mice compared with aldosterone-infused OPN(-/-) mice. These results indicate that OPN is a promoter of aldosterone-induced inflammation, oxidative stress, and interstitial fibrosis in the kidney and suggest that inhibition of OPN may be a potential therapeutic target for prevention of renal injury.

Hyperhomocysteinemia is one of the risk factors associated with cerebrovascular stiffness in hypertensive patients, especially elderly males

Hyperhomocystemia has been reported to be associated with cardiovascular disease, especially stroke. The resistive index (RI) estimated by carotid ultrasound is an established variable for estimating the risk of cerebral infarction. The aim of this study was to evaluate the relationship between homocysteine concentration and carotid RI, a marker of cerebral vascular resistance in essential hypertensive patients. We measured serum total homocysteine and carotid RI in 261 patients. Multiple linear regression analysis was used to determine the association of homocysteine with carotid RI and intima media thickness (IMT). Age, sex, BMI, systolic blood pressure (SBP), homocysteine, total cholesterol, high density lipoprotein-cholesterol (HDL-C), uric acid, CRP, HbA1c, estimated glomerular filtration rate, and use of antihypertensive agents were included as independent variables. Age, sex, use of antihypertensive agents, HDL-C and homocysteine levels were shown to be significant predictors of carotid RI, but not IMT. Multiple regression analysis in men older than 65 years showed homocysteine and SBP were associated significantly with carotid RI. In elderly male patients, homocysteine was the strongest predictor of carotid RI (B = 0.0068, CI = 0.0017–0.0120, P = 0.011) in the multivariate model. In conclusion, hyperhomocysteinemia is associated with carotid RI, a surrogate marker of cerebral vascular resistance, especially in elderly men.

Undercarboxylated osteocalcin is a biomarker of carotid calcification in patients with essential hypertension.

The development of vascular calcification is an active, highly regulated process with similarities to bone formation. Osteocalcin (OC), a vitamin K-dependent protein expressed by osteoblasts, contains 3 γ-carboxyglutamic acid residues derived from the vitamin K-dependent posttranslational modification of glutamic acid residues. Circulating undercarboxylated OC (ucOC) is increased in vitamin K deficiency and serum ucOC is reported to be a clinical marker of vitamin K status. Vitamin K deficiency is associated with vascular calcification as well as osteoporosis. We evaluated the relationship between ucOC and carotid artery calcification in 92 patients with essential hypertension. Ultrasound of the common carotid artery was performed to identify vascular calcification and subjects were divided into 2 groups: a calcification (+) group and a calcification (–) group. Serum creatinine and ucOC levels were higher in the calcification (+) group than in the calcification (–) group and serum ucOC correlated with serum creatinine. To identify the independent determinant factor for carotid artery calcification, we applied both ucOC and estimated glomerular filtration rate as independent factors in logistic regression analysis. Serum ucOC was an independent determinant of carotid calcification, suggesting that circulating ucOC may be an important biomarker of carotid artery calcification.

The Relationship Between Osteopontin and Adiponectin in Patients with Essential Hypertension

The renin angiotensin aldosterone system (RAAS) induces inflammation and accelerates atherosclerosis, contributes to both pro- and anti-inflammatory cytokines. Osteopontin (OPN) is known as a pro-inflammatory cytokine and adiponectin is known as an anti-inflammatory cytokine. C-reactive protein (CRP) not only reflects an inflammatory state but also leads to inflammation. Previous studies clarified that OPN and adiponectin were regulated by RAAS. In this study, we hypothesized that plasma OPN level relates to serum adiponectin level in patients with essential hypertension (EHT). Sixty-two patients (32 females) with EHT were enrolled in this study. They were evaluated for conventional risk factors for atherosclerosis, further plasma aldosterone, plasma OPN, serum adiponectin, and CRP levels were assayed. There were significant gender differences in creatinine, total cholesterol, high-density lipoprotein (HDL) cholesterol, low-denisty lipoprotein(LDL) cholesterol, log transformed (ln) adiponectin and ln CRP. Osteopontin was correlated positively with aldosterone and ln CRP (r = 0.277, p = 0.029, r = 0.278, p = 0.029, respectively), negatively with adiponectin (r = −0.346, p = 0.006). Ln adiponectin was correlated positively with HDL cholesterol (r = 0.373, p = 0.003) and negatively with gender (male as 1), creatinine, triglyceride, aldosterone, and ln CRP (r = −0.55, p < 0.001, r = −0.279, p = 0.028, r = −0.406, p = 0.001, r = −0.307, p < 0.015, r = −0.289, p = 0.023, respectively). Stepwise regression analysis showed that adiponectin was an independent predictor of OPN β= −0.0339, p = 0.004). Our results suggest that OPN and adiponectin are related to each other underlying the mechanisms of RAAS and inflammation.

Osteopontin deficiency reduces kidney damage from hypercholesterolemia in Apolipoprotein E-deficient mice

Hypercholesterolemia is a well-established risk factor for kidney injury, which can lead to chronic kidney disease (CKD). Osteopontin (OPN) has been implicated in the pathology of several renal conditions. This study was to evaluate the effects of OPN on hypercholesterolemia induced renal dysfunction. Eight-week-old male mice were divided into 4 groups: apolipoprotein E knockout (ApoE−/−) and ApoE/OPN knockout (ApoE−/−/OPN−/−) mice fed a normal diet (ND) or high cholesterol diet (HD). After 4 weeks, Periodic acid-Schiff (PAS) and oil red O staining revealed excessive lipid deposition in the glomeruli of ApoE−/−HD mice, however, significantly suppressed in ApoE−/−/OPN−/−HD mice. Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) expression was lower in the glomeruli of ApoE−/−/OPN−/−HD mice than ApoE−/−HD mice. In vitro study, primary mesangial cells were incubated with recombinant mouse OPN (rmOPN). RmOPN induced LOX-1 mRNA and protein expression in primary mesangial cells. Pre-treatment with an ERK inhibitor suppressed the LOX-1 gene expression induced by rmOPN. These results indicate that OPN contributes to kidney damage in hypercholesterolemia and suggest that inhibition of OPN may provide a potential therapeutic target for the prevention of hypercholesterolemia.

Perivascular Adipose Tissue Angiotensin II Type 1 Receptor Promotes Vascular Inflammation and Aneurysm FormationNovelty and Significance

Perivascular adipose tissue exhibits characteristics of active local inflammation, which contributes to the development of atherosclerotic disease as a complication of obesity/metabolic syndrome. However, the precise role of perivascular adipose tissue in the progression of abdominal aortic aneurysm remains unclear. To test the hypothesis that genetic deletion of angiotensin II type 1a (AT1a) receptor in perivascular visceral adipose tissue (VAT) can attenuate aortic aneurysm formation in apolipoprotein E–deficient (ApoE−/−) mice, we performed adipose tissue transplantation experiments by using an angiotensin II–induced aneurysm murine model, in which we transplanted VAT from ApoE−/− or ApoE−/− AT1a−/− donor mice onto the abdominal aorta of ApoE−/− recipient mice. Compared with ApoE−/− VAT transplantation, ApoE−/− AT1a−/− VAT transplantation markedly attenuated aortic aneurysm formation, macrophage infiltration, and gelatinolytic activity in the abdominal aorta. AT1a receptor activation led to the polarization of macrophages in perivascular VAT toward the proinflammatory phenotype. Moreover, osteopontin expression and gelatinolytic activity were considerably lower in ApoE−/− AT1a−/− perivascular VAT than in ApoE−/− perivascular VAT, and angiotensin II–induced osteopontin secretion from adipocytes was eliminated after deletion of AT1a receptor in adipocytes. Notably, induction of macrophage migration by conditioned medium from angiotensin II–stimulated wild-type adipocytes was suppressed by treatment with an osteopontin-neutralizing antibody, and ApoE−/− OPN−/− VAT transplantation more potently attenuated aortic aneurysm formation than ApoE−/− VAT transplantation. Our findings indicate a previously unrecognized effect of AT1a receptor in perivascular VAT on the pathogenesis of abdominal aortic aneurysm.

Osteopontin plays a critical role in interstitial fibrosis but not glomerular sclerosis in diabetic nephropathy.

Background/Aims: Osteopontin (OPN) has been implicated in the pathology of several renal conditions. The aim of this study was to clarify the roles of OPN in diabetic nephropathy. Methods: Diabetes mellitus (DM) was induced in wild-type (WT) and OPN knockout (KO) mice by injecting streptozotocin. The mice were killed 20 weeks after induction of DM and their kidneys removed. Results: Renal mRNA expression of OPN was increased in WT-DM mice compared to WT-sham mice. Immunohistochemistry showed high levels of OPN expression in the proximal tubules of WT-DM mice. Kidney weight and urinary albumin excretion increased to similar levels in the WT-DM and KO-DM mice. Interstitial fibrosis was increased in WT-DM mice compared to KO-DM mice. However, there were no differences in the degree of mesangial expansion or glomerular hypertrophy between the two groups. F4/80-positive cells (macrophages) and FSP-1-positive cells (fibroblasts) showed significantly higher infiltration in WT-DM mice than in KO-DM mice. Renal mRNA expression of NADPH oxidase subunits and urinary 8-isoprostane excretion were also increased in WT-DM mice. Conclusions: These results indicated that OPN is a key molecule that induces interstitial fibrosis in the diabetic kidney, but does not induce glomerular sclerosis.

Fibrillary glomerulonephritis associated with monoclonal gammopathy of undetermined significance showing lambda-type Bence Jones protein

A 79-year-old woman was admitted to our hospital because of leg edema due to a nephrotic syndrome. Urinary and serum immunoelectrophoresis showed positive for the lambda type of Bence Jones protein. A bone marrow aspiration test revealed mild plasmacytosis (6.4% of the total cells). These findings confirmed her diagnosis of monoclonal gammopathy of undetermined significance (MGUS). Her renal biopsy specimen revealed mild mesangial cell proliferation and an increase in the mesangial matrix. Immunofluorescence studies showed positive staining for IgG, IgA, C3, and kappa and lambda light chains in the capillary wall and mesangium area. Electron microscopy showed that the electron deposits in the thickened basement membrane were formed by randomly arranged 16- to 18-nm nonbranching fibrils. A Congo red stain for amyloid was negative. These findings corresponded with the diagnosis of fibrillary glomerulonephritis. Therefore, this case showed a rare combination of fibrillary glomerulonephritis and MGUS.

Usefulness of the renal resistive index to predict an increase in urinary albumin excretion in patients with essential hypertension.

Microalbuminuria is a risk factor for cardiovascular events and death in hypertensive patients. Patients who are expected to increase albuminuria need strict blood pressure control. In the present study, we assessed the association between the renal resistive index (RI) and future increases in albuminuria in patients with essential hypertension. Sixty-six patients with essential hypertension were included in the study. Univariate and multivariate logistic regression analyses were used to identify the factors, including renal RI, that were significant independent determinants of increased in urinary albumin excretion (UAE), defined as an increase of >50% in the urinary albumin-to-creatinine ratio over 2 years. Receiver operator characteristics curve analysis was used to select the optimal cut-off point that predicted an increase in UAE. RI was the only significant variable that predicted the increase in UAE, with the optimal cut-off value of renal RI that predicted this increase being 0.71 (sensitivity 52.4% and specificity 84.4%). Renal RI is associated with the future increase in albuminuria in patients with essential hypertension.

Comparison of the Effect of Combination Therapy with an Angiotensin II Receptor Blocker and Either a Low-Dose Diuretic or Calcium Channel Blocker on Cardiac Hypertrophy in Patients with Hypertension

Left ventricular hypertrophy (LVH) regression is an important issue in hypertensive patients. Patients with LVH who had received the angiotensin receptor blocker (ARB) treatment for 8 weeks and had not reached the target blood pressure level were enrolled in the study. Patients were assigned to either losartan (50 mg)/hydrochlorothiazide (HCTZ, 12.5 mg) group or ARB + CCB group (usual dose of ARB and calcium channel blocker, CCB). After 48 weeks, LV mass index was found to be reduced significantly in the losartan/HCTZ group but not in the ARB + CCB group. These results suggest that combination therapy of an ARB and diuretic has greater potential to cause regression compared with an ARB and CCB.