Tetsuhiko Nagao

BACKGROUND:Diabetic macular edema (DME) causes serious visual impairments in diabetic patients. The standard treatments of DME are intra-vitreous injections of corticosteroids or anti-vascular endothelial growth factor antibodies and pan-photocoagula...

Retinopathy and nephropathy are life-threatening diabetic complications that decrease patient quality of life. Although the mechanisms underlying these conditions have been extensively studied, they remain unknown. Recent reports have demonstrated the presence of sodium glucose cotransporter 2 (SGLT2) in retinal pericytes and mesangial cells. Hyperglycemia results in functional and morphological changes in these cells, but these effects are attenuated by phlorizin, a nonselective SGLT inhibitor. Based on these findings, we hypothesized that SGLT2 plays a pivotal role in the development of diabetic nephropathy and retinopathy and that SGLT2 inhibitors may directly protect against these complications.

Mesangial cells play an important role in regulating glomerular filtration by altering their cellular tone. We report the presence of a sodium glucose cotransporter (SGLT) in rat mesangial cells. This study in rat mesangial cells aimed to evaluate the expression and role of SGLT2. The SGLT2 expression in rat mesangial cells was assessed by Western blotting and reverse transcription-polymerase chain reaction (RT-PCR). Changes in the mesangial cell surface area at different glucose concentrations and the effects of extracellular Na⁺ and Ca²⁺ and of SGLT and Na⁺/Ca²⁺ exchanger (NCX) inhibitors on cellular size were determined. The cellular sizes and the contractile response were examined during a 6-day incubation with high glucose with or without phlorizin, an SGLT inhibitor. Western blotting revealed an SGLT2 band, and RT-PCR analysis of SGLT2 revealed the predicted 422-bp band in both rat mesangial and renal proximal tubular epithelial cells. The cell surface area changed according to the extracellular glucose concentration. The glucose-induced contraction was abolished by the absence of either extracellular Na⁺ or Ca²⁺ and by SGLT and NCX inhibitors. Under the high glucose condition, the cell size decreased for 2 days and increased afterwards; these cells did not contract in response to angiotensin II, and the SGLT inhibitor restored the abolished contraction. These data suggest that SGLT2 is expressed in rat mesangial cells, acts as a normal physiological glucose sensor and regulates cellular contractility in rat mesangial cells.

Thiazide diuretics are reported to have antioxidant effects and reduce pulse pressure (PP). The aim of this study was to elucidate whether hydrochlorothiazide additionally exerts such effects in stroke patients under treatment with losartan. This study was an open-label, randomized, multicenter study. Patients with a history of chronic stroke and treatment with angiotensin receptor blockers or angiotensin-converting enzyme inhibitors for essential hypertension were enrolled. Fifty-five hypertensive patients were randomly assigned to two groups: those further treated with hydrochlorothiazide and those further treated with non-diuretic antihypertensive drugs. Both groups showed a significant decrease in PP over six months (hydrochlorothiazide group: 67±12 mmHg to 58±12, p<0.001; non-diuretic group: 72±12 to 61±12, p<0.001), although no significant differences were observed between the two groups. The malondialdehyde-modified low-density lipoprotein levels did not change significantly after treatment in either group. In this study, hydrochlorothiazide treatment did not provide any additional benefits over non-diuretic antihypertensive drugs in terms of antioxidant effects or reducing PP.

Background and purpose: Sorbin and SH3‐domain‐containing‐1 (SORBS1) is an important adaptor protein in insulin‐signalling pathway, and its genetic polymorphism may regulate the activity of insulin resistance. We investigated the association between the SORBS1 T228A polymorphism and ischaemic stroke. Methods: Genotyping was achieved by a rapid‐cycle PCR and melting curve analysis using fluorescent probes in 1049 incident cases of ischaemic stroke and 1049 age‐ and sex‐matched control subjects recruited from the Hisayama study. Results: The allele distributions of the SORBS1 T228A polymorphism were similar amongst cases and controls. The multivariate‐adjusted odds ratio (OR) of the AA genotype for ischaemic stroke was 2.897 (95% CI, 0.907–8.018) compared with the TT genotype. In terms of stroke subtype, there was a trend toward a difference in the AA genotypes for lacunar infarction, compared with the TT genotype (OR = 8.740, P = 0.0510), and combined TT and TA genotypes (OR = 8.768, P = 0.0505). The other polymorphisms genotyped were not associated with any subtypes of ischaemic stroke. T228A polymorphism of SORBS1 was not associated with the prevalence of diabetes. Conclusions: The AA genotype of SORBS1 T228A polymorphism may play a role in lacunar infarction in the Japanese population.

Background and Purpose: Lymphotoxin α (LTA), one of the tumor necrosis factor family proteins, is an important proinflammatory cytokine and appears to play a putative role in the inflammatory process of atherosclerosis. Recent genetic studies have suggested that variations in the gene encoding LTA, which affect its expression and biological function, may contribute to the development of vascular diseases. We conducted a case-control study to clarify the association of LTA gene polymorphisms with ischemic stroke in a large Japanese population. Methods: Genotyping for LTA A252G and C804A polymorphisms was achieved by a rapid-cycle polymerase chain reaction and melting curve analysis using fluorescent probes in 1,044 incident cases of ischemic stroke recruited from the Fukuoka Stroke Registry and 1,044 age- and sex-matched control subjects recruited from the Hisayama Study. Results: The overall distribution of allele and genotype for each polymorphism was similar between stroke patients and control subjects. The allele frequencies of 252G and 804A were slightly lower in stroke patients than in control subjects; however, conditional logistic regression analysis adjusted for potential risk factors found no association between the risk of ischemic stroke and either polymorphism. In terms of stroke subtype, we also found no association of these polymorphisms with any subtypes of ischemic stroke. Conclusions: Neither the A252G nor C804A polymorphism of the LTA gene was associated with stroke overall and any subtypes of ischemic stroke in the Japanese population.

The C242T polymorphism of p22^phox, a component of NAD(P)H oxidase, may have an impact on cardiovascular diseases; however, the association between this polymorphism and brain infarction is not fully understood. Here, we investigate the relationship between the C242T polymorphism and brain infarction in Japan. We recruited 1055 patients with brain infarction and 1055 control subjects. A chi‐squared test revealed that the T‐allele frequency was lower in patients with cardioembolic infarction (5.6%) than in control subjects (11.0%, P < 0.001); however, allele frequencies in patients with lacunar and atherothrombotic infarction (11.2%) were not significantly different from those in control subjects (11.0%). A multivariate‐adjusted conditional logistic regression analysis also revealed no association between CT + TT genotype, and lacunar and atherothrombotic infarction (odds ratio = 0.97, 95% confidence interval: 0.72–1.32). To investigate the functional effects of the C242T polymorphism, we examined superoxide production in COS‐7 cells cotransfected with Nox4 and p22^phox of each genotype. The superoxide‐producing activity in those cells expressing p22^phox with the T allele was not significantly different from that in cells expressing p22^phox with the C allele. The present results suggest that the p22^phox C242T polymorphism may have a protective effect against cardioembolic infarction, but is not related to lacunar and atherothrombotic infarction in Japan.

SUMMARY: 1. Ionic channels appear to play an important role in contractile responses of the cerebral arteries and, thereby, contribute to the regulation of cerebral circulation. In the present study, we investigated the role of large‐conductance Ca²⁺‐activated K⁺ (BK_Ca) channels in the regulation of cerebral arterial tone during chronic hypertension.2. Ring segments of the basilar artery from spontaneously hypertensive rats (SHR) and normotensive Wistar‐Kyoto (WKY) rats were placed in bath chambers and the isometric tension of each ring was measured.3. Application of inhibitors of BK_Ca channels, namely tetraethylammonium (TEA; ≥ 0.1 mmol/L) and charybdotoxin (CTX; ≥ 0.1 nmol/L), produced spontaneous contraction with rhythmic oscillation in the basilar artery from SHR.4. The oscillatory contraction was not induced by 5‐hydroxytryptamine (0.01–10 μmol/L) or depolarization by external high K⁺ (20–60 mmol/L).5. The rhythmic contraction was completely abolished by either the removal of external Ca²⁺ or the application of nicardipine (10 nmol/L).6. The oscillation was not affected by the substitution of external Cl^– by various equimolar anions (i.e. acetate, benezenesulphonate, bromide and isethianate).7. The amplitude of the oscillation was dose‐dependently increased by the vasodilators forskolin and sodium nitroprusside, as well as by stimulation of the endothelium with histamine and acetylcholine, whereas the frequency was decreased.8. In contrast, the oscillation was eliminated by depletion of Ca²⁺ stores by caffeine. Neither TEA (10 mmol/L) nor CTX (10 nmol/L) produced any significant contraction of the basilar artery in WKY rats.9. These results suggest that BK_Ca channels may play an important role in regulating the resting tone of the cerebral artery in SHR.

Background and Purpose—In patients with stroke and long-standing hypertension, the autoregulation curve of cerebral blood flow (CBF) shifts toward higher blood pressure levels. Angiotensin-converting enzyme (ACE) inhibitors reduce blood pressure and shift the autoregulation curve back to normal in hypertensive patients. ACE inhibitors have 2 major pharmacological properties: they inhibit both the production of angiotensin II and the breakdown of kinins. Hence, we investigated whether the effect of an ACE inhibitor on the lower limit of CBF autoregulation is mediated by the potentiation of bradykinin-mediated vasodilatation.Methods—In 28 male Sprague-Dawley rats, CBF was measured by laser-Doppler flowmetry during stepwise controlled hypotension. The lower limit of CBF autoregulation was defined as the mean arterial pressure at which CBF decreased by 20% of the baseline value. The rats were treated with an ACE inhibitor, captopril, in the captopril group; a bradykinin BK2-receptor antagonist, Hoe140, in the Hoe140 group; and both agents in the captopril+Hoe140 group. Other rats served as a control group. The lower limits of CBF autoregulation were compared among the 4 groups.Results—In the captopril group, the lower limit of CBF autoregulation was 43±8 mm Hg (mean±SD), which was significantly lower than that in the control group (57±14 mm Hg). Inhibition of bradykinin abolished the effect of captopril on the lower limit of CBF autoregulation. Hoe140 alone had no significant effect on the lower limit of CBF autoregulation.Conclusions—These results suggest that the shift of the lower limit of CBF autoregulation by captopril is mediated, at least in part, by bradykinin.

Activity of daily living (ADL) and cognitive are indices of physical and psychological activity in elderly subjects. The present study was performed to clarify the relationship among ADL, cognitive function, and ambulatory blood pressure (ABP) in the elderly. Study subjects were 77 females and 22 males (aged 60 to 101 years) with various levels of ADL and cognition, who were in nursing homes or geriatric hospitals. ABP was recorded every 30 min for 24 h by a noninvasive device. Mini-mental state examination (MMSE) and Barthel index measurement were used to evaluate cognitive function and ADL, respectively. Both the MMSE and Barthel index values showed a significant positive correlation with daytime ABP but not with nighttime ABP. The dip in nighttime BP correlated negatively with age, and positively with MMSE and Barthel index. In the multiple regression analysis, age and Barthel index values remained significant determinants of the dip in nighttime BP. Presence of stroke and MMSE became significant when the Barthel index values were removed from the analyses. When subjects were classified by tertiles of MMSE or Barthel index, subjects in the lowest MMSE group and those in the lowest Barthel index group had both lower daytime ABP and smaller nighttime BP dip than those of the other groups. A low BP level during the daytime was associated with altered diurnal variation of BP in elderly subjects with greater age, impaired cognitive function, and/or decreased ADL. ADL had a greater influence on diurnal BP variation than did cognitive function.