A Nonthiazolidinedione Peroxisome Proliferator-Activated Receptor γ Agonist Reverses Endothelial Dysfunction in Diabetic (db/db-/-) Mice

Pioglitazone Attenuates Ischemic Stroke Aggravation By Blocking PPARγ Reduction and Inhibiting Chronic Inflammation in Diabetic Mice

Diabetes can cause vascular remodeling and is associated with worse outcome after ischemic stroke. Pioglitazone is a commonly used anti-diabetic agent. However, it is not known whether pioglitazone use before ischemia could reduce brain ischemic injury. Pioglitazone was administered to 5-week-old db⁺ or db/db mice. Cerebral vascular remodeling was examined at the age of 9 weeks. Expression of peroxisome proliferator-activated receptor-γ (PPARγ), p-PPARγ (S112 and S273), nucleotide-binding domain (NOD)-like receptor protein 3 (Nlrp3), interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) was evaluated in the somatosensory cortex of mice. Neurological outcome was evaluated 24 h after brain ischemia. Results showed that early pioglitazone treatment provided a long-lasting effect of euglycemia but enhanced hyperlipidemia in the db/db mice. Diabetic mice exhibited increased vascular tortuosity, narrower middle cerebral artery (MCA) width and IgG leakage in the brain. These changes were blocked by early pioglitazone treatment. In diabetic animals, PPARγ expression was reduced and p-PPARγ at S273 but not S112, Nlrp3, IL-1β and TNF-α were increased in the somatosensory cortex. PPARγ decrease and Nlrp3 increase were mainly in the neurons of the diabetic brain, which was reversed by early pioglitazone treatment. Pioglitazone attenuated the aggravated neurological outcome after stroke in diabetic mice. But this protective effect was abolished through restoring cerebral inflammation by intracerebroventricular administration of IL-1β and TNF-α in pioglitazone treated diabetic mice before MCAO. In summary, early pioglitazone treatment attenuates cerebral vascular remodeling and ischemic brain injury possibly via blocking chronic neuroinflammation in the db/db mice.

Targeting Early Atherosclerosis: A Focus on Oxidative Stress and Inflammation

Atherosclerosis is a chronic vascular inflammatory disease associated to oxidative stress and endothelial dysfunction. Oxidation of low-density lipoprotein (LDL) cholesterol is one of the key factors for the development of atherosclerosis. Nonoxidized LDL have a low affinity for macrophages, so they are not themselves a risk factor. However, lowering LDL levels is a common clinical practice to reduce oxidation and the risk of major events in patients with cardiovascular diseases (CVD). Atherosclerosis starts with dysfunctional changes in the endothelium induced by disturbed shear stress which can lead to endothelial and platelet activation, adhesion of monocytes on the activated endothelium, and differentiation into proinflammatory macrophages, which increase the uptake of oxidized LDL (oxLDL) and turn into foam cells, exacerbating the inflammatory signalling. The atherosclerotic process is accelerated by a myriad of factors, such as the release of inflammatory chemokines and cytokines, the generation of reactive oxygen species (ROS), growth factors, and the proliferation of vascular smooth muscle cells. Inflammation and immunity are key factors for the development and complications of atherosclerosis, and therefore, the whole atherosclerotic process is a target for diagnosis and treatment. In this review, we focus on early stages of the disease and we address both biomarkers and therapeutic approaches currently available and under research.

A protective role of ciglitazone in ox-LDL-induced rat microvascular endothelial cells via modulating PPARγ-dependent AMPK/eNOS pathway

Thiazolidinediones, the antidiabetic agents such as ciglitazone, has been proved to be effective in limiting atherosclerotic events. However, the underlying mechanism remains elucidative. Ox-LDL receptor-1 (LOX-1) plays a central role in ox-LDL-mediated atherosclerosis via endothelial nitric oxide synthase (eNOS) uncoupling and nitric oxide reduction. Therefore, we tested the hypothesis that ciglitazone, the PPARγ agonist, protected endothelial cells against ox-LDL through regulating eNOS activity and LOX-1 signalling. In the present study, rat microvascular endothelial cells (RMVECs) were stimulated by ox-LDL. The impact of ciglitazone on cell apoptosis and angiogenesis, eNOS expression and phosphorylation, nitric oxide synthesis and related AMPK, Akt and VEGF signalling pathway were observed. Our data showed that both eNOS and Akt phosphorylation, VEGF expression and nitric oxide production were significantly decreased, RMVECs ageing and apoptosis increased after ox-LDL induction for 24 hrs, all of which were effectively reversed by ciglitazone pre-treatment. Meanwhile, phosphorylation of AMP-activated protein kinase (AMPK) was suppressed by ox-LDL, which was also prevented by ciglitazone. Of interest, AMPK inhibition abolished ciglitazone-mediated eNOS function, nitric oxide synthesis and angiogenesis, and increased RMVECs ageing and apoptosis. Further experiments showed that inhibition of PPARγ significantly suppressed AMPK phosphorylation, eNOS expression and nitric oxide production. Ciglitazone-mediated angiogenesis and reduced cell ageing and apoptosis were reversed. Furthermore, LOX-1 protein expression in RMVECs was suppressed by ciglitazone, but re-enhanced by blocking PPARγ or AMPK. Ox-LDL-induced suppression of eNOS and nitric oxide synthesis were largely prevented by silencing LOX-1. Collectively, these data demonstrate that ciglitazone-mediated PPARγ activation suppresses LOX-1 and moderates AMPK/eNOS pathway, which contributes to endothelial cell survival and function preservation.

Effects of a Western diet versus high glucose on endothelium-dependent relaxation in murine micro- and macro-vasculature

Vascular contractility and endothelium-dependent vasodilatation were studied in mesenteric, aorta and coronary vasculature from male and female LDL receptor deficient (LDLR(-/-)) and wild type C57BL/6 mice fed either a high-fat Western Diet (WD) or regular animal chow (RD). Endothelium-dependent vasodilatation was also studied in small mesenteric arteries and aorta from C57BL/6 mice following a 20 h exposure in vitro to 30 mM glucose. Compared with RD-fed animals, WD-fed LDLR-/- animals had increased body weights, elevated triglycerides and total cholesterol, but not glucose. Control C57BL6 animals had elevated body weight without increased cholesterol, triglyceride or glucose levels. The contractile sensitivity to cirazoline (pD(2)) of small mesenteric arteries was the same for RD-fed LDLR-/- and RD-fed C57BL6 mice, but was reduced in WD-fed male LDLR-/- and WD-fed female C57BL/6 mice. Maximum mesenteric contractile values for cirazoline (Emax) were unchanged; however, the Emax for phenylephrine in the aorta from WD-fed male C57BL/6 (but not LDLR-/- or female C57BL/6) mice was reduced. The Emax for acetylcholine-mediated endothelium-dependent vasodilatation in micro- and macro vessels (small mesenteric artery, coronary artery and aorta) from WD-fed LDLR-/- and C57BL/6 mice was unaltered, in contrast to the reduction in Emax for glucose-exposed tissues. Furthermore, the component of acetylcholine-mediated vasodilatation resistant to the combination of inhibitors of nitric oxide synthase, cyclooxygenase and guanylyl cyclase (nitro L-arginine methyl ester - 100 microM; indomethacin 10 microM and 1H-[1,2,4]-oxadiazolo[4,3,-a]quinoxalin-1-one, ODQ - 10 microM, respectively) was generally greater in WD-fed mice. Thus, vasculature from WD-fed mice with short-term dyslipidaemia do not exhibit reduced endothelium-dependent vasodilatation, but the WD is associated with changes in the overall endothelial-dependent relaxation and contractile responses thus suggesting an impact of diet rather than dyslipidaemia on cellular signalling pathways in vascular tissue. In contrast, acute hyperglycaemia resulted in endothelial dysfunction in both small mesenteric arteries and thoracic aorta.

Neuronatin: a new inflammation gene expressed on the aortic endothelium of diabetic mice

OBJECTIVE

Identification of arterial genes and pathways altered in obesity and diabetes.

RESEARCH DESIGN AND METHODS

Aortic gene expression profiles of obese and diabetic db/db, high-fat diet-fed C57BL/6J, and control mice were obtained using mouse Affymetrix arrays. Neuronatin (Nnat) was selected for further analysis. To determine the function of Nnat, a recombinant adenovirus (Ad-Nnat) was used to overexpress the Nnat gene in primary endothelial cells and in the mouse aorta in vivo.

RESULTS

Nnat, a gene of unknown vascular function, was upregulated in the aortas of db/db and high-fat diet-fed mice. Nnat gene expression was increased in db/db mouse aorta endothelial cells. Nnat protein was localized to aortic endothelium and was selectively increased in the endothelium of db/db mice. Infection of primary human aortic endothelial cells (HAECs) with Ad-Nnat increased expression of a panel of nuclear factor-kappaB (NF-kappaB)-regulated genes, including inflammatory cytokines, chemokines, and cell adhesion molecules. Infection of mouse carotid arteries in vivo with the Ad-Nnat increased expression of vascular cell adhesion molecule 1 protein. Nnat activation of NF-kappaB and inflammatory gene expression in HAECs was mediated through pathways distinct from tumor necrosis factor-alpha. Nnat expression stimulated p38, Jun NH(2)-terminal kinase, extracellular signal-related kinase, and AKT kinase phosphorylation. Phosphatidylinositol 3-kinase and p38 inhibitors prevented Nnat-mediated activation of NF-kappaB-induced gene expression.

CONCLUSIONS

Nnat expression is increased in endothelial cells of obese and diabetic mouse blood vessels. The effects of Nnat on inflammatory pathways in vitro and in vivo suggest a pathophysiological role of this new gene in diabetic vascular diseases.

Impairment of endothelium-dependent ACh-induced relaxation in aorta of diabetic db/db mice--possible dysfunction of receptor and/or receptor-G protein coupling

Diabetes is a risk factor of ischemic heart disease, cerebral ischemia, and atherosclerosis, in which endothelial dysfunction plays a role in the pathogenesis. We examined vascular responses in the aorta of pre-diabetic db/db mice with normoglycemia, hyperlipidemia, and hyperinsulinemia (6 weeks old), and diabetic db/db mice with hyperglycemia, hyperlipidemia, and hyperinsulinemia (11 weeks old) in comparison with age-matched non-diabetic db/+ mice. Prostaglandin F2alpha (PGF2alpha)-induced contraction was significantly enhanced in the aorta of diabetic but not pre-diabetic db/db mice compared to age-matched non-diabetic db/+ mice. Acetylcholine (ACh), adenosine-5'-diphosphate (ADP), NaF, a G protein activator and A-23187, a Ca-ionophore, caused endothelium-dependent and nitric oxide (NO)-mediated relaxation, and sodium nitroprusside (SNP), an NO donor, caused endothelium-independent relaxation in the pre-contracted aorta of db/db mice. Maximal endothelium-dependent ACh-induced relaxation was reduced in diabetic but not pre-diabetic db/db mice compared to age-matched db/+ mice, while maximal SNP-induced relaxation was not different between diabetic and non-diabetic mice. ACh-induced relaxation in diabetic db/db mice was not affected by ozagrel, a thromboxane A2 (TXA2) synthetase inhibitor, or acetylsalicylic acid (aspirin), a cyclooxygenase inhibitor, suggesting no involvement of endogenous TXA2 or prostanoids in the reduction of relaxation. Maximal endothelium-dependent ADP-, A-23187-, and NaF-induced relaxation was not reduced in diabetic db/db mice. EC50 values for ACh- and SNP-induced relaxation were increased in diabetic but not pre-diabetic db/db mice, suggesting decreases in sensitivity to NO in diabetic mice. Two-week treatment with KV-5070, a PPARgamma agonist, lowered plasma glucose, triglyceride (TG), and insulin but not cholesterol, and reversed the reduced ACh-induced relaxation. In conclusion, ACh-induced endothelium-dependent relaxation is impaired in diabetic db/db mice, probably due to the dysfunction of ACh receptors and/or receptor-G protein coupling. Endothelial dysfunction was not genetic and was considered to be initiated primarily by hyperglycemia, and was improved by anti-diabetic treatment with a PPARgamma agonist.

Endothelin stimulates vascular hydroxyl radical formation: effect of obesity

Reactive oxygen species (ROS) and endothelin-1 (ET-1) contribute to vascular pathophysiology in obesity. In this context, whether ET-1 modulates hydroxyl radical (•OH) formation and the function of ROS/•OH in obesity is not known. In the present study, formation and function of ROS, including •OH, were investigated in the aorta of lean and leptin-deficient obese ob/ob mice. Hydroxyl radical formation was detected ex vivo using terephthalic acid in intact aortic rings and the involvement of ROS in ET-1-mediated vasoreactivity was analyzed using the antioxidant EPC-K1, a combination of α-tocopherol and ascorbic acid. Generation of either •OH, •O2−, and H2O2was strongly inhibited by EPC-K1 (all P < 0.05). In obese mice, basal vascular •OH formation and ROS activity were reduced by 3-fold and 5-fold, respectively ( P < 0.05 vs. lean). ET-1 markedly enhanced •OH formation in lean (6-fold, P < 0.05 vs. untreated) but not in obese mice. Obesity increased ET-1-induced contractions ( P < 0.05 vs. lean), and ROS scavenging further enhanced the response ( P < 0.05 vs. untreated). Exogenous ROS, including •OH caused stronger vasodilation in obese animals ( P < 0.05 vs. lean), whereas endothelium-dependent relaxation was similar between lean and obese animals. In conclusion, we present a sensitive method allowing ex vivo measurement of vascular •OH generation and provide evidence that ET-1 regulates vascular •OH formation. The data indicate that in obesity, vascular formation of ROS, including •OH is lower, whereas the sensitivity to ROS is increased, suggesting a novel and important role of ROS, including •OH in the regulation of vascular tone in disease status associated with increased body weight.