Sanae Saka

Relationship between silent brain infarction and chronic kidney disease

Background. The presence of silent brain infarction (SBI) increases the risk of symptomatic stroke and dementia. The association between SBI and chronic kidney disease (CKD) has not been clarified. Moreover, little is known about what factors are related to SBI in CKD patients and whether the prevalence of SBI differs in CKD stage or cause of CKD. Methods. This is a cross-sectional study. A total of 375 subjects—335 with CKD and 40 with essential hypertension—were included. All subjects underwent magnetic resonance imaging (MRI) of the brain to detect SBI. Glomerular filtration rate (GFR) was estimated using Modification of Diet in Renal Disease equation, and cardiovascular risk factors were examined. Results. The prevalence of SBI was 56.5% in all subjects. Among causes of CKD, hypertensive nephrosclerosis had a strong association with SBI. According to the estimated GFR (eGFR) stage, the more severe the stage of eGFR, the higher the prevalence of SBI (age-adjusted odds ratio [95% confidence interval] for eGFR 30–59, 15–29 and <15 versus ≥60 mL/min/1.73 m2: 1.34 [0.68–1.99], 1.94 [1.30–2.57] and 2.51 [1.91–3.10]). In multivariate logistic analysis, eGFR was related to SBI independently, in addition to age and blood pressure (P = 0.025). However, other traditional and non-traditional risk factors were not. Conclusion. There was an independent association between eGFR and SBI. CKD patients should receive active detection of SBI and more intensive preventive management, especially for hypertension, should be needed in CKD patients to prevent SBI.

Mice Lacking Hypertension Candidate Gene ATP2B1 in Vascular Smooth Muscle Cells Show Significant Blood Pressure Elevation

We reported previously that ATP2B1 was one of the genes for hypertension receptivity in a large-scale Japanese population, which has been replicated recently in Europeans and Koreans. ATP2B1 encodes the plasma membrane calcium ATPase isoform 1, which plays a critical role in intracellular calcium homeostasis. In addition, it is suggested that ATP2B1 plays a major role in vascular smooth muscle contraction. Because the ATP2B1 knockout (KO) mouse is embryo-lethal, we generated mice with vascular smooth muscle cell-specific KO of ATP2B1 using the Cre-loxP system to clarify the relationship between ATP2B1 and hypertension. The KO mice expressed significantly lower levels of ATP2B1 mRNA and protein in the aorta compared with control mice. KO mice showed significantly higher systolic blood pressure as measured by tail-cuff method and radiotelemetric method. Similar to ATP2B1, the expression of the Na+-Ca2+ exchanger isoform 1 mRNA was decreased in vascular smooth muscle cells of KO mice. However, ATP2B4 expression was increased in KO mice. The cultured vascular smooth muscle cells of KO mice showed increased intracellular calcium concentration not only in basal condition but also in phenylephrine-stimulated condition. Furthermore, phenylephrine-induced vasoconstriction was significantly increased in vascular rings of the femoral artery of KO mice. These results suggest that ATP2B1 plays important roles in the regulation of blood pressure through alteration of calcium handling and vasoconstriction in vascular smooth muscle cells.

Impaired nitric oxide production and increased blood pressure in systemic heterozygous Atp2b1 null mice

Background: In the ‘Millennium Genome Project’, we identified ATP2B1 as a gene responsible for hypertension through single-nucleotide polymorphism analysis. The ATP2B1 gene encodes the plasma membrane calcium ATPase isoform 1, which contributes to the maintenance of intracellular calcium homeostasis by removing calcium ions. Method: Since ATP2B1 knockout mice are reported to be embryo-lethal, we generated systemic heterozygous ATP2B1 null (ATP2B1+/−) mice, and evaluated the implication of ATP2B1 in blood pressure. Results: ATP2B1+/− mice revealed significantly higher SBP as measured by a radiotelemetric method. Phenylephrine-induced vasoconstriction was significantly increased in vascular rings from ATP2B1+/− mice, and the difference in this contraction disappeared in the presence of a nitric oxide synthase (NOS) inhibitor. Vasorelaxation to acetylcholine was significantly attenuated in vascular rings from ATP2B1+/− mice. In addition, cultured endothelial cells of ATP2B1+/− mice showed that the phosphorylation (Ser-1177) level of endothelial NOS protein was significantly lower, and nitric oxide production in endothelial cells and aorta was lower compared with those in control mice. In contrast, neural NOS expression in vascular smooth muscle cells from ATP2B1+/− mice and control mice were not significantly different. Conclusion: These results suggest that decreased ATP2B1 gene expression is associated with impaired endothelial NOS activity and nitric oxide production, and the ATP2B1 gene plays a crucial role in the regulation of blood pressure.

Long‐Term Efficacy and Safety of the Small‐Sized β2‐Microglobulin Adsorption Column for Dialysis‐Related Amyloidosis

Dialysis‐related amyloidosis (DRA) is one of the major complications often seen in long‐term dialysis patients, and is one of the factors that decreases quality of life. β2‐microglobulin (β2‐m) is considered to be a major pathogenic factor in dialysis‐related amyloidosis. The Lixelle adsorbent column, with various capacities, has been developed to adsorb β2‐m from the circulating blood of patients with dialysis‐related amyloidosis. Using a minimum type of β2‐m‐adsorbing column (Lixelle S‐15), we evaluated its therapeutic efficacy and safety in dialysis patients. Seventeen hemodialysis patients with DRA were treated with the S‐15 column for one year. Treatment was performed three times a week in this study. During the study period, pinch strength, visual analog scale for joint pain, and activities of daily living were evaluated every three months, and blood sampling was performed every six months. After one years treatment with the S‐15 column, the β2‐m level decreased from 29.3 ± 9.6 mg/L to 24.7 ± 5.1 mg/L (P < 0.05), and the high sensitive C‐reactive protein level decreased from 2996 ± 4380 ng/mL to 1292 ± 1774 ng/mL. After one year of S‐15 column use, pinch strength increased from 5.9 ± 3.0 pounds to 7.2 ± 3.2 pounds (P < 0.05), and the visual analog scale for joint pain and activities of daily living score also improved. Long‐term use of the Lixelle S‐15 column is safe and effective for improvement of quality of life in chronic dialysis patients. Improvement of chronic inflammation may be one of the mechanisms through which the beneficial effects of the column is effected.

Loss of nocturnal decline of blood pressure in non-diabetic patients with nephrotic syndrome in the early and middle stages of chronic kidney disease

In non-diabetic patients with nephrotic syndrome (NS) at early stages of chronic kidney disease, it remains unclear whether the degree of proteinuria affects the nocturnal blood pressure (BP) dip. We evaluated the relationship among circadian BP rhythm, proteinuria and hypoalbuminemia in these patients. We also evaluated the autonomic nervous activity. Twenty-four-hour BP was measured in NS patients (8 men and 13 women; mean age, 58.5±14.8 years) and age- and sex-matched normal subjects (11 men and 13 women; mean age, 54.3±18.2 years) as controls. Serum albumin and urinary protein concentrations were measured. Power spectral analysis of the heart rate was performed, and the high frequency (HF) and low frequency (LF) components were calculated as indices of sympathovagal balance. There were no differences in waking BP between the NS and the control groups (131±13/78±9 vs. 130±17/76±7 mm Hg; P>0.05). However, sleeping BP was significantly higher in the NS group than in the control group (127±18/75±9 vs. 115±14/66±7 mm Hg; P<0.05). Sleeping/waking BP ratios were higher in the NS group than in the control group (P<0.01). In the NS group, these ratios correlated significantly with serum albumin level (r=−0.54, P=0.011 for systolic BP; r=−0.48, P=0.030 for diastolic BP) and urinary protein excretion (r=0.47, P=0.027 for systolic BP; r=0.60, P=0.003 for diastolic BP). Both HF components and LF/HF ratios were not significantly different between the two groups. In non-diabetic NS patients, loss of nocturnal BP reduction correlates with proteinuria and hypoalbuminemia but not with circadian autonomic nervous rhythm.

Relationship between Arterial Stiffness and Blood Pressure Drop During the Sit-to-stand Test in Patients with Diabetes Mellitus.

Aim: Patients with orthostatic hypotension (OH) have high arterial stiffness. Patients with diabetes mellitus (DM) often have cardiac autonomic neuropathy that leads to OH; however, whether OH is an indicator of arterial stiffness progression is unclear. We aimed to investigate whether the cardioankle vascular index (CAVI) varies between DM patients with and without OH using the sit-to-stand test (STST). Methods: One hundred and fifty-nine patients with DM underwent CAVI assessment and blood pressure (BP) and heart rate change evaluation during the STST. OH was defined as a decline in systolic BP (SBP) and/or diastolic BP of at least 20 mmHg or 10 mmHg, respectively, in the initial and late upright positions compared with that in the sitting position. Results: OH was diagnosed in 42 patients (26.4%). DM patients with OH had significantly higher CAVI (9.36 ± 1.15 versus 8.89 ± 1.18, p = 0.026) than those without OH. CAVI was significantly inversely correlated with systolic and diastolic BP changes (R = −0.347, p <0.001 and R = −0.314, p <0.001, respectively) in the initial upright position. Multivariate regression analysis revealed that age, SBP changes, and low frequency component in the initial upright position were independent determinants of CAVI. Conclusion: Patients with DM having large BP drops occurring when moving from sitting to standing have high arterial stiffness. A significant BP drop during the STST necessitates careful evaluation of advanced arterial stiffness in patient with DM.

Genome-wide association study of IgA nephropathy using 23 465 microsatellite markers in a Japanese population.

Immunoglobulin A nephropathy (IgAN) is the most common form of primary glomerulonephritis in many parts of the world. Although previous genome-wide association studies (GWAS) identified the major susceptibility loci for IgAN, the causal genes currently remain unknown. We performed a GWAS using 23 465 microsatellite (MS) markers to identify genes related to IgAN in a Japanese population. A pooled sample analysis was conducted in three-stage screenings of three independent case–control populations, and after the final step of individual typing, 11 markers survived. Of these, we focused on two regions on 6p21 and 12q21 because they (i) showed the strongest relationship with IgAN, and (ii) appeared to be highly relevant to IgAN in view of several previous studies. These regions contained the HLA, TSPAN8 and PTPRR genes. This study on GWAS, using >20 000 MS markers, provides a new approach regarding susceptible genes for IgAN for investigators seeking new tools for the prevention and treatment of IgAN.

Kidney Diseases Enhance Expression of Tetraspanin-8: A Possible Protective Effect against Tubular Injury

Background/Aims:TSPAN8 encoding tetraspanin-8 was identified as a candidate gene for immunoglobulin A nephropathy (IgAN) by a genome-wide association study using microsatellites in the Japanese population. Tetraspanin-8 is a cell surface protein that contributes to the migration and invasion of epithelial cells. Methods: We performed immunohistochemistry for tetraspanin-8 on human renal biopsy specimens associated with IgAN, antineutrophil cytoplasmic antibody-associated nephropathy and interstitial nephritis, as well as normal renal tissue. Furthermore, to study the potential function of tetraspanin-8, we performed cell migration and invasion assays using human renal tubule cells transfected with tetraspanin-8. Results: Tetraspanin-8 was often expressed in vascular smooth muscle cells and occasionally in tubule cells in normal kidney. In the kidneys of all types of nephropathy, tetraspanin-8 staining in the arteries was unaffected, but that in the tubules was enhanced. The degree of tubular staining negatively correlated with the estimated glomerular filtration rate, independently of the type of nephropathy. Tetraspanin-8-expressing tubule cells were found predominantly in distal and collecting tubules, identified by cytokeratin 7 or aquaporin 2 staining. In vitro studies using cultured tubule cells revealed that tetraspanin-8 promoted migration by 2.7-fold without laminin, by 2.8-fold with laminin and invasion into Matrigel by 3.5-fold, suggesting that enhanced tetraspanin-8 may be involved in the repair of tubules. Conclusion: The obtained findings indicate that tetraspanin-8 expression is enhanced in injured distal tubules, which may be involved in the repair of tubules by facilitating migration and invasion.

Effects of doxazosin as the third agent on morning hypertension and position-related blood pressure changes in diabetic patients with chronic kidney disease

Abstract We conducted a prospective study to assess the effects of doxazosin, as the third agent, on morning and position-related blood pressure (BP) in 77 diabetic patients with chronic kidney disease, who were allocated randomly to doxazosin and diuretics groups. Doxazosin decreased morning BP but diuretics could not decrease pre-awakening diastolic BP. Only doxazosin improved sympathovagal balance. Doxazosin and diuretics decreased standing and sitting BP but only doxazosin improved sympathovagal balance regardless of body positions. Doxazosin did not decrease absolute BP changes shortly after standing. In diabetic patients, doxazosin decreased morning BP through improving sympathovagal balance without causing significant orthostatic hypotension (ClinicalTrials.gov number, NCT00295555). Trial registration: ClinicalTrials.gov identifier: NCT00295555.

Reduced secretion of parathyroid hormone and hypocalcemia in systemic heterozygous ATP2B1-null hypertensive mice

The ATP2B1 gene is associated with hypertension. We previously reported that systemic heterozygous ATP2B1-null (ATP2B1+/−) mice exhibited hypertension due to impaired endothelial nitric oxide synthase (eNOS) activity and decreased nitric oxide (NO) production. The ATP2B1 gene encodes plasma membrane calcium ATPase 1 (PMCA1), which has been thought to regulate only intracellular Ca2+ concentration. However, recently, it has been suggested that ATP2B1 works not only at cellular levels, but also throughout the entire body, including in the calcium metabolism, using small intestine-specific ATP2B1 knockout mice. To clarify the roles of ATP2B1 in the entire body and the effects of ATP2B1 on blood pressure, we examined the alterations of calcium related factors in ATP2B1+/− mice. ATP2B1+/− mice exhibited hypocalcemia. The expression of ATP2B1 in the kidney and small intestine decreased, and hypercalciuria was confirmed in ATP2B1+/− mice. The intact-PTH levels were lower, and bone mineral density was increased in these mice. These results suggest that hypocalcemia is mainly a result of inhibited bone resorption without compensation by PTH secretion in the case of ATP2B1 knockout. Moreover, NO production may be affected by reduced PTH secretion, which may cause the increase in vascular contractility in these mice. The ATP2B1 gene is important for not only intra-cellular calcium regulation but also for calcium homeostasis and blood pressure control.