Age-related changes to vascular protease-activated receptor 2 in metabolic syndrome: a relationship between oxidative stress, receptor expression, and endothelium-dependent vasodilation

Endothelium dysfunction in hind limb arteries of male Zucker Diabetic-Sprague Dawley rats

Endothelium dysfunction produces peripheral vascular disease comorbidities in type 2 diabetes, including hypertension, and critical limb ischemia. In this study we aimed to test endothelial dysfunction, the vasodilator effects of a proteinase-activated receptor 2 (PAR2) agonist (2fLIGRLO), and thromboxane A₂ synthase inhibitor (ozagrel) on PAR2 vasodilation in hind limb arteries ex vivo, using Zucker Diabetic-Sprague Dawley (ZDSD) rats, a model of type 2 diabetes. Male Sprague Dawley rats (SD) and ZDSD were fed a high-fat content 'Western diet' from 16 to 20 weeks of age (wks) then fed a standard laboratory diet. We identified diabetic ZDSD rats by two consecutive blood glucose measurements > 12.5 mM, based on weekly monitoring. We used acetylcholine, 2fLIGRLO, and nitroprusside with wire-myograph methods to compare relaxations of femoral, and saphenous arteries from diabetic ZDSD (21-23 wks) to age-matched normoglycemic SD. All arteries showed evidence of endothelium dysfunction using acetylcholine (reduced maximum relaxations, reduced sensitivity), and higher sensitivities to 2fLIGRLO, and nitroprusside in ZDSD vs SD. Ozagrel treatment of ZDSD distal segments, and end-branches of saphenous arteries decreased their sensitivities to 2fLIGRLO. We tested aortas for altered expression of endothelium-specific gene targets using PCR array and qPCR. PAR2, and placental growth factor gene transcripts were 1.5, and 4-times higher in ZDSD than SD aortas. Hind limb arteries of ZDSD exhibit endothelium dysfunction having less GPCR agonist induced vasodilation by endothelial NO-release. Different expression of several endothelial genes in ZDSD vs SD aortas, including PAR2, suggests altered inflammatory, and angiogenesis signaling pathways in the endothelium of ZDSD.

Characterization of Endothelium-Dependent Relaxation in the Saphenous Artery and Its Caudal Branches in Young and Old Adult Sprague Dawley Rats

Ageing is associated with reduced endothelium-derived nitric oxide (NO) production in the femoral artery of Sprague Dawley (SD) rats. In the current study, we examined endothelium-dependent relaxation (EDR) in the saphenous artery and its caudal branches. We used acetylcholine and the Proteinase-Activated receptor-2 (PAR2)-specific agonist (2fLIGRLO) with nitroarginine methylester (L-NAME) to assess EDR in two groups of male SD rats (age in weeks: young, 10–12; old, 27–29). Acetylcholine and 2fLIGRLO were potent NO-dependent relaxant agents in all arteries. For all arteries, EDR by acetylcholine decreased significantly in old compared to young SD rats. Interestingly, PAR2-induced EDR of proximal saphenous artery segments and caudal branches decreased significantly in old compared to young, but did not differ for the in-between middle and distal ends of the saphenous artery. L-NAME treatment increased subsequent contractions of proximal and middle segments of saphenous arteries by phenylephrine and U46619 in young, but not in old, SD rats. We conclude the SD saphenous artery and caudal branches exhibit regional characteristics that differ in response to specific EDR agonists, endothelial NO synthase inhibitor, and changes to endothelium function with increased age, which are, in part, attributed to decreased sensitivity of vascular smooth muscle to the gaseous transmitter NO.

A Sodium Glucose Cotransporter 2 Inhibitor Fails to Improve Perivascular Adipose Tissue-Mediated Modulation of Vasodilation and Cardiac Function in Rats With Metabolic Syndrome

Arterial perivascular adipose tissue (PVAT) can elicit vasodilator signals complementary to those elicited by the endothelium in SHRSP.Z-Lepr^fa/IzmDmcr (SHRSP.ZF) rats, an animal model of metabolic syndrome (MetS). Here, we tested whether a glucose cotransporter 2 inhibitor (SGLT2-i; tofogliflozin) increased this PVAT effect to prevent the deterioration of cardiac function in aging SHRSP.ZF rats. Tofogliflozin treatments (1 or 10 mg/kg/day) or vehicle (control) were administered for 10 weeks by oral gavage to SHRSP.ZF rats, starting at 13 weeks of age. At 23 weeks of age, glucose levels in the serum and urine (24 h after the last administration) were determined using commercial kits. Vasodilator responsiveness of PVAT-surrounded or PVAT-free superior mesenteric arteries was determined using acetylcholine with organ-bath methods. Cardiac ventricular function and coronary flow were determined using Langendorff heart preparations. Serum and urine glucose levels in SGLT2-i treatment groups did not differ from those in the controls, but the ratios of glycated to non-glycated albumin were lower than those in the controls. Tofogliflozin treatments did not alter relaxations in the presence of PVAT or affect relaxations of PVAT-free arteries. Left ventricular systolic pressures, maximum rate of pressure decline, and coronary flow in ex vivo hearts did not differ among the treatment groups. PVAT effects and cardiac dysfunction were not altered by tofogliflozin treatment in SHRSP.ZF rats with MetS. These results do not provide strong evidence to support the use of SGLT2-i as a cardiovascular protective therapy in MetS, which occurs prior to the onset of type 2 diabetes.

Evaluation of Enhanced Lipid Oxidation and Compensatory Suppression using Natriuretic Peptide in Patients with Cardiovascular Diseases

Malondialdehyde-modified low-density lipoprotein (MDA-LDL) is recognized as a surrogate marker of lipid oxidation and is associated with arteriosclerosis. However, there are limited reports on the relationship between heart failure and MDA-LDL. Therefore, we aimed to determine whether MDA-LDL is activated in patients with left ventricular (LV) dysfunction and examine our hypothesis that the B-type natriuretic peptide (BNP) masks the enhancement of MDA-LDL in patients with LV dysfunction by its strong antioxidative action. The study population comprised 2,976 patients with various cardiovascular diseases. Patients were divided into four groups depending on the LV ejection fraction (LVEF) or plasma BNP level. A nonparametric analysis with the Kruskal-Wallis test was used to perform an interquartile comparison. In addition, structural equation modeling and Bayesian estimation were used to compare the effects of LVEF and BNP on MDA-LDL. MDA-LDL levels did not significantly change (P > 0.05) with respect to the degree of LVEF among the four groups. In contrast, MDA-LDL levels were significantly decreased (P < 0.001) with respect to the degree of BNP among the four groups. A path model based on structural equation modeling clearly showed a significant effect of LVEF (standardized regression coefficient; β: -0.107, P < 0.001) and BNP (β: -0.114, P < 0.001) on MDA-LDL, with a significant inverse association between LVEF and BNP (correlation coefficient -0.436, P < 0.001). MDA-LDL should be activated in patients with LV dysfunction; however, BNP is thought to exert a strong compensatory suppression on lipid oxidation, masking the relationship between heart failure and lipid oxidation.

Activation of protease-activated receptor 2 is associated with blood pressure regulation and proteinuria reduction in metabolic syndrome

Metabolic syndrome (MetS) increases the risk of kidney disease. In SHRSP.Z-Lepr^fa /IzmDmcr (SHRSP.ZF) rats with MetS, protease-activated receptor 2 (PAR2)-mediated vasorelaxation is preserved in the aorta at 20 weeks of age (weeks) via enhancement of nitric oxide production but impaired at 30 weeks by oxidative stress. However, impairment of PAR2-mediated vasorelaxation of renal arteries and its possible implications for kidney disease are unclear. We used organ baths to assess PAR2-mediated vasorelaxation of isolated renal arteries, colorimetric methods to measure urinary protein levels as an index of renal function, and western blot to determine expression of PAR2 and nephrin proteins in the kidneys of SHRSP.ZF rats at 10, 20, and 30 weeks. We assessed renal arteries and kidney function for effects of orally administered GB88, a pathway-dependent PAR2 antagonist, from 10 to 18 weeks, and azilsartan, an angiotensin II type 1 receptor blocker, from 13 to 23 weeks. PAR2-mediated vasorelaxation was slightly lower at 20 weeks and attenuated significantly at 30 weeks compared with those at 10 weeks. Urinary protein levels were increased at 20 and 30 weeks. Decreased protein expression of PAR2 and nephrin in the kidney were observed at 30 weeks. Administration of GB88 increased blood pressure (BP) and proteinuria. Azilsartan reduced the high BP and the impaired PAR2-mediated vasorelaxation, but did not restore the increase in urinary protein levels and decreased PAR2 and nephrin protein expression in the kidney. PAR2 activation in the kidney may be associated with maintenance of BP and urinary protein excretion in MetS.

FoxO6-mediated IL-1β induces hepatic insulin resistance and age-related inflammation via the TF/PAR2 pathway in aging and diabetic mice

FoxO has been proposed to play a role in the promotion of insulin resistance, and inflammation. FoxO is a pro-inflammatory transcription factor that is a key mediator of generation of inflammatory cytokines such as IL-1β in the liver. However, the detailed association of FoxO6 with insulin resistance and age-related inflammation has not been fully documented. Here, we showed that FoxO6 was elevated in the livers of aging rats and obese mice that exhibited insulin resistance. In addition, virus-mediated FoxO6 activation led to insulin resistance in mice with a notable increase in PAR2 and inflammatory signaling in the liver. On the other hand, FoxO6-KO mice showed reduced PAR2 signaling with a decrease in inflammatory cytokine expression and elevated insulin signaling. Because FoxO6 is closely associated with abnormal production of IL-1β in the liver, we focused on the FoxO6/IL-1β/PAR2 axis to further examine mechanisms underlying FoxO6-mediated insulin resistance and inflammation in the liver. In vitro experiments showed that FoxO6 directly binds to and elevates IL-1β expression. In turn, IL-1β treatment elevated the protein levels of PAR2 with a significant decrease in hepatic insulin signaling, whereas PAR2-siRNA treatment abolished these effects. However, PAR2-siRNA treatment had no effect on IL-1β expression induced by FoxO6, indicating that IL-1β may not be downstream of PAR2. Taken together, we assume that FoxO6-mediated IL-1β is involved in hepatic inflammation and insulin resistance via TF/PAR2 pathway in the liver.