Euphausia pacifica (North Pacific Krill): Review of Chemical Features and Potential Benefits of 8-HEPE against Metabolic Syndrome, Dyslipidemia, NAFLD, and Atherosclerosis.

Marine n-3 fatty acids are well known to have health benefits. Recently, krill oil, which contains phospholipids, has been in the spotlight as an n-3 PUFA-containing oil. Euphausia pacifica (E. pacifica), also called North Pacific krill, is a small, red crustacean similar to shrimp that flourishes in the North Pacific Ocean. E. pacifica oil contains 8-hydroxyeicosapentaenoic acid (8-HEPE) at a level more than 10 times higher than Euphausia superba oil. 8-HEPE can activate the transcription of peroxisome proliferator-activated receptor alpha (PPARα), PPARγ, and PPARδ to levels 10, 5, and 3 times greater than eicosapentaenoic acid, respectively. 8-HEPE has beneficial effects against metabolic syndrome (reduction in body weight gain, visceral fat area, amount of gonadal white adipose tissue, and gonadal adipocyte cell size), dyslipidemia (reduction in serum triacylglycerol and low-density lipoprotein cholesterol and induction of serum high-density lipoprotein cholesterol), atherosclerosis, and nonalcoholic fatty liver disease (reduction in triglyceride accumulation and hepatic steatosis in the liver) in mice. Further studies should focus on the beneficial effects of North Pacific krill oil products and 8-HEPE on human health.

Mizagliflozin, a selective SGLT1 inhibitor, improves vascular cognitive impairment in a mouse model of small vessel disease.

Previously, we showed that sodium/glucose cotransporter 1 (SGLT1) participates in vascular cognitive impairment in small vessel disease. We hypothesized that SGLT1 inhibitors can improve the small vessel disease induced-vascular cognitive impairment. We examined the effects of mizagliflozin, a selective SGLT1 inhibitor, and phlorizin, a non-selective SGLT inhibitor, on vascular cognitive impairment in a mouse model of small vessel disease. Small vessel disease was created using a mouse model of asymmetric common carotid artery surgery (ACAS). Two and/or 4 weeks after ACAS, all experiments were performed. Cerebral blood flow (CBF) was decreased in ACAS compared with sham-operated mice. Phlorizin but not mizagliflozin reversed the decreased CBF of ACAS mice. Both mizagliflozin and phlorizin reversed the ACAS-induced decrease in the latency to fall in a wire hang test of ACAS mice. Moreover, they reversed the ACAS-induced longer escape latencies in the Morris water maze test of ACAS mice. ACAS increased SGLT1 and proinflammatory cytokine gene expressions in mouse brains and phlorizin but not mizagliflozin normalized all gene expressions in ACAS mice. Hematoxylin/eosin staining demonstrated that they inhibited pyknotic cell death in the ACAS mouse hippocampus. In PC12HS cells, IL-1ß increased SGLT1 expression and decreased survival rates of cells. Both mizagliflozin and phlorizin increased the survival rates of IL-1ß-treated PC12HS cells. These results suggest that mizagliflozin and phlorizin can improve vascular cognitive impairment through the inhibition of neural SGLT1 and phlorizin also does so through the improvement of CBF in a mouse model of small vessel disease.

Chronic HDAC6 Activation Induces Atrial Fibrillation Through Atrial Electrical and Structural Remodeling in Transgenic Mice.

Atrial fibrillation (AF) is a relatively common complication of hypertension. Chronic hypertension induces cardiac HDAC6 catalytic activity. However, whether HDAC6 activation contributes to hypertension-induced AF is still uncertain. We examined whether chronic cardiac HDAC6 activation-induced atrial remodeling, leading to AF induction.The HDAC6 constitutively active transgenic (TG) (HDAC6 active TG) mouse overexpressing the active HDAC6 protein, specifically in cardiomyocytes, was created to examine the effects of chronic HDAC6 activation on atrial electrical and structural remodeling and AF induction in HDAC6 active TG and non-transgenic (NTG) mice. Left atrial burst pacing (S1S1 = 30 msec) for 15-30 sec significantly increased the frequency of sustained AF in HDAC6 active-TG mice compared with NTG mice. Left steady-state atrial pacing (S1S1 = 80 msec) decreased the atrial conduction velocity in isolated HDAC6 active TG compared with NTG mouse atria. The atrial size was similar between HDAC6 active TG and NTG mice. In contrast, atrial interstitial fibrosis increased in HDAC6 active TG compared with that of NTG mouse atria. While protein expression levels of both CX40 and CX43 were similar between HDAC6 active TG and NTG mouse atria, a heterogeneous distribution of CX40 and CX43 occurred in HDAC6 active-TG mouse atria but not in NTG mouse atria. Gene expression of interleukin 6 increased in HDAC6 active TG compared with NTG mouse atria.Chronic cardiac HDAC6 activation induced atrial electrical and structural remodeling, and sustained AF. Hypertension-induced cardiac HDAC6 catalytic activity may play important roles in the development of AF.

8-HEPE-Concentrated Materials from Pacific Krill Improve Plasma Cholesterol Levels and Hepatic Steatosis in High Cholesterol Diet-Fed Low-Density Lipoprotein (LDL) Receptor-Deficient Mice.

Eicosapentaenoic acid (EPA), one of the N-3 polyunsaturated fatty acids (n-3 PUFAs), is a major active ingredient of fish that contributes to improve dyslipidemia. Recently, we demonstrated that 8-hydroxyeicosapentaenoic acid (8-HEPE) had a more positive effect on metabolic syndrome than EPA, and that 8-HEPE induced peroxisome proliferator-activated receptor (PPAR)α activation in the liver. We investigated the effects of 8-HEPE-concentrated materials from Pacific krill on dyslipidemia and hepatic steatosis in low-density lipoprotein (LDL) receptor-deficient (LDLR-KO) mice. Eight-week-old male LDLR-KO mice were fed a Western diet (0.15% cholesterol, WD), WD supplemented with 8-HEPE-concentrated materials from Pacific krill (8-HEPE included; WD +8-HEPE), or a standard diet (SD) for eighteen weeks, respectively. Murine J774.1 macrophages were incubated in the absence or presence of 8-HEPE (50 µM) or EPA (50 µM). 8-HEPE-concentrated materials significantly increased the plasma high-density lipoprotein (HDL)-cholesterol level, and decreased the plasma LDL-cholesterol and hepatic triglyceride levels in WD-fed LDLR-KO mice. Moreover, the rate of Oil Red O-positive staining was higher in the liver of WD-fed LDLR-KO mice than in that of 8-HEPE + WD-fed LDLR-KO mice. 8-HEPE but not EPA significantly increased gene expression levels of ABCA1, CD36, and interleukin 6 (IL-6) in murine J774.1 macrophages compared with those in the control. These results suggest that 8-HEPE-concentrated materials improve dyslipidemia and hepatic steatosis increasing ABCA1, CD36, and IL-6 gene expressions in macrophages.

SGLT1 participates in the development of vascular cognitive impairment in a mouse model of small vessel disease.

Sodium/glucose cotransporter 1 (SGLT1) participates in ischemia-reperfusion-induced cerebral injury. However, whether SGLT1 participates in the development of small vessel disease induced-vascular cognitive impairment is unknown. We examined the roles of SGLT1 in the development of vascular cognitive impairment in a mouse model of small vessel disease. Small vessel disease was created by placement of an ameroid constrictor around the right common carotid artery (CCA) and placement of a microcoil around the left CCA (ACAS) in wild-type (WT) and SGLT1-knock out (KO) mice. Two and/or 4 weeks after ACAS, all experiments were performed. Hematoxylin/eosin staining demonstrated that the number of pyknotic cell deaths was greater in the ACAS WT than ACAS SGLT1-KO hippocampus. The latency to fall in a wire hang test was significantly shorter in ACAS than sham-operated WT mice, whereas it was similar between ACAS and sham-operated SGLT1-KO mice. The Morris water maze test revealed that ACAS WT mice exhibited longer escape latencies than ACAS SGLT1-KO mice. ACAS significantly increased SGLT1 gene expression in WT mouse brains. Gene expressions of MCP-1, IL-1ß, TNF-α, and IL-6 were increased in ACAS WT compared with sham-operated WT mouse brains. Their increased gene expressions were significantly decreased in ACAS SGLT1-KO compared with ACAS WT mice. These results suggest that SGLT1 plays important roles in the development of small vessel dementia.

Pretreatment with KGA-2727, a selective SGLT1 inhibitor, is protective against myocardial infarction-induced ventricular remodeling and heart failure in mice.

Recent studies demonstrated that sodium-glucose co-transporter 1 (SGLT1) is associated with human ischemic cardiomyopathy. However, whether SGLT1 blockade is effective against ischemic cardiomyopathy is still uncertain. We examined the effects of KGA-2727, a selective SGLT1 inhibitor, on myocardial infarction (MI)-induced ischemic cardiomyopathy. To create MI, left anterior descending coronary artery (LAD) ligation with or without KGA-2727 administration was performed in C57BL/6J mice. Four weeks after the operation, all mice were investigated. Left ventricular fractional shortening (LVFS) was reduced and KGA-2727 significantly improved it in LAD-ligated MI mice. The cardiomyocyte diameter, and ANP, BNP, ß-MHC, and IL-18 gene expressions significantly increased in LAD-ligated mouse left ventricles compared with those of sham-operated mouse left ventricles, and KGA-2727 inhibited increases in them. Myocardial fibrosis and upregulation of CTGF and MMP-3 gene expressions in the left ventricle were increased in LAD-ligated mice compared with sham-operated mice, and KGA-2727 decreased them in the LAD-ligated left ventricles. SGLT1 protein expression level was significantly higher in LAD-ligated compared with sham-operated mouse ventricles regardless of KGA-2727 treatment. These results suggest that KGA-2727 pretreatment protects against MI-induced left ventricular remodeling through SGLT1 blockade and that it may become a new pharmacological therapy for ischemia-induced cardiomyopathy.

IL-1ß Plays an Important Role in Pressure Overload-Induced Atrial Fibrillation in Mice.

Hypertension is one risk for atrial fibrillation (AF) and induces cardiac inflammation. Recent evidence indicates that pressure overload-induced ventricular structural remodeling is associated with the activation of nucleotide binding-oligomerization domain (NOD)-like receptor P3 (NLRP3) inflammasomes, including an apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC). We hypothesized that NLRP3 inflammasomes are an initial sensor for danger signals in pressure overload-induced atrial remodeling, leading to AF. Transverse aortic constriction (TAC) or a sham procedure was performed in mice deficient for ASC-/- and interleukin-1ß (IL-1ß-/-). One week after the procedure, electrical left atrial burst pacing from the esophagus was performed for 30 s to induce AF. IL-1ß, monocyte chemotactic protein 1 (MCP-1), connective tissue growth factor (CTGF), and collagen 1 gene expression were also examined. The electrical burst pacing induced AF in TAC-operated wild-type (WT) (p < 0.001) and ASC-/- (p < 0.05) mice, compared to no AF in the sham-operated WT and ASC-/- mice, respectively. In contrast, the number of mice in which sustained AF was induced was similar between TAC-operated IL-1ß-/- and sham-operated IL-1ß-/- mice (p > 0.05). The expression of all genes tested was increased in TAC-operated WT and ASC-/- mice compared with sham-operated WT and ASC-/- mouse atria, respectively. CTGF and collagen 1, but not MCP-1, gene expressions were increased in TAC-operated IL-1ß-/- mouse atria compared with sham-operated WT and IL-1ß-/- mouse atria. In contrast, the IL-1ß gene was not detected in either TAC-operated or sham-operated IL-1ß-/- mouse atria. These results suggest that an IL-1ß activation pathway, different from NLRP3 inflammasomes, plays an important role in pressure overload-induced sustained AF.

Chronic Pressure Overload Induces Cardiac Hypertrophy and Fibrosis via Increases in SGLT1 and IL-18 Gene Expression in Mice.

Increased gene expression levels of sodium-glucose cotransporter 1 (SGLT1) are associated with hypertrophic and ischemic cardiomyopathy. However, it remains unclear whether chronic pressure overload increases SGLT1 expression, which in turn induces hypertrophic cardiomyopathy. We hypothesized that pressure overload could increase SGLT1 gene expression, leading to the development of hypertrophic cardiomyopathy.To create pressure overload-induced cardiomyopathy, transverse aortic constriction (TAC) was performed in SGLT1-deficient (SGLT1-/-) and wild-type (WT) mice. Six weeks after surgery, all mice were investigated. We observed a reduction of left ventricular fractional shortening and left ventricular dilatation in TAC-operated WT but not in TAC-operated SGLT1-/- mice. SGLT1, interleukin 18, connective tissue growth factor, and collagen type 1 gene expression levels were increased in TAC-operated WT mouse hearts compared with that of sham-operated WT mouse hearts. Moreover, heart/body weight ratio and ventricular interstitial fibrosis were increased in TAC-operated WT mice compared with that of sham-operated WT mice. Interestingly, these factors did not increase in TAC-operated SGLT1-/- mice compared with that of sham-operated WT and SGLT1-/- mice. Phenylephrine, an adrenergic α1 receptor agonist, caused cardiomyocyte hypertrophy in neonatal WT mouse hearts to a significantly larger extent than in neonatal SGLT1-/- mouse hearts.In conclusion, the results indicate that chronic pressure overload increases SGLT1 and IL-18 gene expressions, leading to the development of hypertrophic cardiomyopathy. These results make SGLT1 a potential candidate for the therapeutic target for hypertension-induced cardiomyopathy.

[Roles of Sodium-Glucose Cotransporter 1 (SGLT1) in the Induction of Cardiac Remodeling].

　It is well-known that metabolic remodeling occurs in the presence of cardiomyopathy induced by cardiac ischemia and hypertrophy, and diabetes mellitus. It is also known that a novel cardiac glucose transporter, sodium-glucose co-transporter 1 (SGLT1), is expressed in the human heart. However, the role of SGLT1 in the development of cardiac metabolic remodeling is still unclear. Recent studies demonstrated that SGLT1 activation improves ischemia-reperfusion-induced cardiac injury, and increased SGLT1 gene expression is observed in hypertrophic, ischemic, and diabetic cardiomyopathy in human hearts. Moreover, increases in SGLT1 protein expression cause cardiac remodeling such as hypertrophy and increased interstitial fibrosis in mice. We demonstrated that ischemia-reperfusion-induced cardiac injury was potentiated in SGLT1-deficient mice. In contrast, chronic pressure overload induced by transverse aortic constriction (TAC) caused cardiac hypertrophy and reduced left ventricular fractional shortening in C57BL/6J wild-type mice. Moreover, the TAC-induced hypertrophied heart showed increased SGLT1 and AMPKαprotein expressions. These results suggest the different effects of SGLT1 activation on cardiac diseases such as acute ischemia-reperfusion-induced cardiac injury and chronically-induced cardiac hypertrophy. Thus, SGLT1 may be a novel therapeutic target for the treatment of patients with cardiac diseases such as ischemic and hypertrophic cardiomyopathy.