Role of COX-2 in the enhanced vasoconstrictor effect of arachidonic acid in the diabetic rat kidney

Peripheral Neuropathy in Diabetes Mellitus: Pathogenetic Mechanisms and Diagnostic Options

Diabetic neuropathy (DN) is one of the main microvascular complications of both type 1 and type 2 diabetes mellitus. Sometimes, this could already be present at the time of diagnosis for type 2 diabetes mellitus (T2DM), while it appears in subjects with type 1 diabetes mellitus (T1DM) almost 10 years after the onset of the disease. The impairment can involve both somatic fibers of the peripheral nervous system, with sensory-motor manifestations, as well as the autonomic system, with neurovegetative multiorgan manifestations through an impairment of sympathetic/parasympathetic conduction. It seems that, both indirectly and directly, the hyperglycemic state and oxygen delivery reduction through the vasa nervorum can determine inflammatory damage, which in turn is responsible for the alteration of the activity of the nerves. The symptoms and signs are therefore various, although symmetrical painful somatic neuropathy at the level of the lower limbs seems the most frequent manifestation. The pathophysiological aspects underlying the onset and progression of DN are not entirely clear. The purpose of this review is to shed light on the most recent discoveries in the pathophysiological and diagnostic fields concerning this complex and frequent complication of diabetes mellitus.

A pleiotropic hypoxia-sensitive EPAS1 enhancer is disrupted by adaptive alleles in Tibetans

In Tibetans, noncoding alleles in EPAS1-whose protein product hypoxia-inducible factor 2α (HIF-2α) drives the response to hypoxia-carry strong signatures of positive selection; however, their functional mechanism has not been systematically examined. Here, we report that high-altitude alleles disrupt the activity of four EPAS1 enhancers in one or more cell types. We further characterize one enhancer (ENH5) whose activity is both allele specific and hypoxia dependent. Deletion of ENH5 results in down-regulation of EPAS1 and HIF-2α targets in acute hypoxia and in a blunting of the transcriptional response to sustained hypoxia. Deletion of ENH5 in mice results in dysregulation of gene expression across multiple tissues. We propose that pleiotropic adaptive effects of the Tibetan alleles in EPAS1 underlie the strong selective signal at this gene.

A Thromboxane A2 Receptor-Driven COX-2-Dependent Feedback Loop That Affects Endothelial Homeostasis and Angiogenesis

BACKGROUND

TP (thromboxane A₂ receptor) plays an eminent role in the pathophysiology of endothelial dysfunction and cardiovascular disease. Moreover, its expression is reported to increase in the intimal layer of blood vessels of cardiovascular high-risk individuals. Yet it is unknown, whether TP upregulation per se has the potential to affect the homeostasis of the vascular endothelium.

METHODS

We combined global transcriptome analysis, lipid mediator profiling, functional cell analyses, and in vivo angiogenesis assays to study the effects of endothelial TP overexpression or knockdown/knockout on the angiogenic capacity of endothelial cells in vitro and in vivo.

RESULTS

Here we report that endothelial TP expression induces COX-2 (cyclooxygenase-2) in a G_i/o- and G_q/11-dependent manner, thereby promoting its own activation via the auto/paracrine release of TP agonists, such as PGH₂ (prostaglandin H₂) or prostaglandin F₂ but not TxA₂ (thromboxane A₂). TP overexpression induces endothelial cell tension and aberrant cell morphology, affects focal adhesion dynamics, and inhibits the angiogenic capacity of human endothelial cells in vitro and in vivo, whereas TP knockdown or endothelial-specific TP knockout exerts opposing effects. Consequently, this TP-dependent feedback loop is disrupted by pharmacological TP or COX-2 inhibition and by genetic reconstitution of PGH₂-metabolizing prostacyclin synthase even in the absence of functional prostacyclin receptor expression.

CONCLUSIONS

Our work uncovers a TP-driven COX-2-dependent feedback loop and important effector mechanisms that directly link TP upregulation to angiostatic TP signaling in endothelial cells. By these previously unrecognized mechanisms, pathological endothelial upregulation of the TP could directly foster endothelial dysfunction, microvascular rarefaction, and systemic hypertension even in the absence of exogenous sources of TP agonists.

Endothelium-dependent contraction: The non-classical action of endothelial prostacyclin, its underlying mechanisms, and implications

Although commonly thought to produce prostacyclin (prostaglandin I₂ ; PGI₂ ) that evokes vasodilatation and protects vessels from the development of diseases, the endothelial cyclooxygenase (COX)-mediated metabolism has also been found to release substance(s) called endothelium-derived contracting factor(s) (EDCF) that causes endothelium-dependent contraction and implicates in endothelial dysfunction of disease conditions. Various mechanisms have been proposed for the process; however, the major endothelial COX metabolite PGI₂ , which has been classically considered to activate the I prostanoid receptor (IP) that mediates vasodilatation and opposes the effects of thromboxane (Tx) A₂ produced by COX in platelets, emerges as a major EDCF in health and disease conditions. Our recent studies from genetically altered mice further suggest that vasomotor reactions to PGI₂ are collectively modulated by IP, the vasoconstrictor Tx-prostanoid receptor (TP; the prototype receptor of TxA₂ ) and E prostanoid receptor-3 (EP3; a vasoconstrictor receptor of PGE₂ ) although with differences in potency and efficacy; a contraction to PGI₂ reflects activities of TP and/or EP3 outweighing that of the concurrently activated IP. Here, we discuss the history of endothelium-dependent contraction, evidences that support the above hypothesis, proposed mechanisms for the varied reactions to endothelial PGI₂ synthesis as well as the relation of its dilator activity to the effect of another NO-independent vasodilator mechanism, the endothelium-derived hyperpolarizing factor. Also, we address the possible pathological and therapeutic implications as well as questions remaining to be resolved or limitations of our above findings obtained from genetically altered mouse models.

Eicosanoid blood vessel regulation in physiological and pathological states

Arachidonic acid can be metabolized in blood vessels by three primary enzymatic pathways; cyclooxygenase (COX), lipoxygenase (LO), and cytochrome P450 (CYP). These eicosanoid metabolites can influence endothelial and vascular smooth muscle cell function. COX metabolites can cause endothelium-dependent dilation or constriction. Prostaglandin I2 (PGI2) and thromboxane (TXA2) act on their respective receptors exerting opposing actions with regard to vascular tone and platelet aggregation. LO metabolites also influence vascular tone. The 12-LO metabolite 12S-hydroxyeicosatrienoic acid (12S-HETE) is a vasoconstrictor whereas the 15-LO metabolite 11,12,15-trihydroxyeicosatrienoic acid (11,12,15-THETA) is an endothelial-dependent hyperpolarizing factor (EDHF). CYP enzymes produce two types of eicosanoid products: EDHF vasodilator epoxyeicosatrienoic acids (EETs) and the vasoconstrictor 20-HETE. The less-studied cross-metabolites generated from arachidonic acid metabolism by multiple pathways can also impact vascular function. Likewise, COX, LO, and CYP vascular eicosanoids interact with paracrine and hormonal factors such as the renin-angiotensin system and endothelin-1 (ET-1) to maintain vascular homeostasis. Imbalances in endothelial and vascular smooth muscle cell COX, LO, and CYP metabolites in metabolic and cardiovascular diseases result in vascular dysfunction. Restoring the vascular balance of eicosanoids by genetic or pharmacological means can improve vascular function in metabolic and cardiovascular diseases. Nevertheless, future research is necessary to achieve a more complete understanding of how COX, LO, CYP, and cross-metabolites regulate vascular function in physiological and pathological states.

Altered cyclooxygenase-1 and enhanced thromboxane receptor activities underlie attenuated endothelial dilatory capacity of omental arteries in obesity

AIMS

Obesity is a risk factor for endothelial dysfunction, the severity of which is likely to vary depending on extent and impact of adiposity on the vasculature. This study investigates the roles of cyclooxygenase isoforms and thromboxane receptor activities in the differential endothelial dilatory capacities of arteries derived from omental and subcutaneous adipose tissues in obesity.

MAIN METHODS

Small arteries were isolated from omental and subcutaneous adipose tissues obtained from consented morbidly obese patients (n = 65, BMI 45 ± 6 kg m^-2 [Mean ± SD]) undergoing bariatric surgery. Relaxation to acetylcholine was studied by wire myography in the absence or presence of indomethacin (10 μM, cyclooxygenase inhibitor), FR122047 (1 μM, cyclooxygenase-1 inhibitor), Celecoxib (4 μM, cyclooxygenase-2 inhibitor), Nω-Nitro-L-arginine methyl ester (L-NAME, 100 μM, nitric oxide synthase inhibitor) or combination of apamin (0.5 μM) and charybdotoxin (0.1 μM) that together inhibit endothelium-derived hyperpolarizing factor (EDHF). Contractions to U46619 (thromboxane A₂ mimetic) were also studied.

KEY FINDINGS

Acetylcholine relaxation was significantly attenuated in omental compared with subcutaneous arteries from same patients (p < 0.01). Indomethacin (p < 0.01) and FR122047 (p < 0.001) but not Celecoxib significantly improved the omental arteriolar relaxation. Cyclooxygenase-1 mRNA and U46619 contractions were both increased in omental compared with subcutaneous arteries (p < 0.05). L-NAME comparably inhibited acetylcholine relaxation in both arteries, while apamin+charybdotoxin were less effective in omental compared with subcutaneous arteries.

SIGNIFICANCE

The results show that the depot-specific reduction in endothelial dilatory capacity of omental compared with subcutaneous arteries in obesity is in large part due to altered cyclooxygenase-1 and enhanced thromboxane receptor activities, which cause EDHF deficiency.

Activation of 20-HETE/PPARs involved in reno-therapeutic effect of naringenin on diabetic nephropathy

Naringenin is a flavanone compound found in citrus fruits. Recent researches showed that naringenin has many potentially pharmacological effects. However, the therapeutic effect and the potential mechanism of naringenin on diabetic nephropathy (DN) remain to be elucidated. DN model was established by a high-fat diet combined with streptozotocin (STZ), which was confirmed by the levels of fasting blood glucose (FBG, more than 11.1 mmol/L) and urinary albumin (10 times higher than the normal mice). After 5 weeks of STZ injection, the DN was developed in model mice. Then naringenin (25 or 75 mg/kg·d) were supplemented for 4 weeks. At the end of the experiment, the injury of the renal function and structure was deteriorated. Concomitantly, peroxisome proliferators-activated receptors (PPARs) protein expression was down-regulated, and CYP4A expression and 20-hydroxyeicosatetraenoic acid (20-HETE) level were reduced in DN mice. Naringenin administration improved the renal damage of DN mice, and up-regulated PPARs expression, increased CYP4A-20-HETE level. Consistent with the results of in vivo, glucose at 30 mmol/L (high glucose, HG) significantly induced cell proliferation and hypertrophy in NRK-52E cells, following the reductive PPARs protein expression and the downward CYP4A-20-HETE level. Naringenin (0.01, 0.1, 1 μmol/L) reversed these changes induced by HG in a dose-dependent manner. HET0016, a selective inhibitor of 20-HETE synthase, partially blocked the effects of naringenin. In conclusion, naringenin has a therapeutic effect on DN, which may be, at least partly, related to the activation of CYP4A-20-HETE and the up-regulation of PPARs.

Meloxicam fails to augment the reno-protective effects of soluble epoxide hydrolase inhibition in streptozotocin-induced diabetic rats via increased 20-HETE levels

The pro-inflammatory cyclooxygenase (COX)-derived prostaglandins and the anti-inflammatory cytochrome P450 epoxygenase-derived epoxyeicosatrienoic acids (EETs) play an important role in the regulation of renal injury. The current study examined whether COX inhibition augments the reno-protective effects of increased EETs levels via inhibiting EETs degradation by soluble epoxide hydrolase (sEH) in diabetic rats. Streptozotocin (50mg/kg, i.v) was used to induce diabetes in male Sprague Dawley rats. Rats were then divided into 5 groups (n=6-8); control non diabetic, diabetic, diabetic treated with the sEH inhibitor trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB), diabetic treated with the COX inhibitor meloxicam and diabetic treated with meloxicam plus t-AUCB for 2 months. Glomerular albumin permeability and urinary albumin and nephrin excretion levels were significantly elevated in diabetic rats together with decreased glomerular α3 integrin and nephrin expression levels. Inhibition of sEH reduced glomerular albumin permeability, albumin and nephrin excretion levels and restored the decrease in glomerular α3 integrin and nephrin expression in diabetic rats. Meloxicam failed to reduce renal injury or even to synergize the reno-protective effects of sEH inhibition in diabetic rats. Furthermore, inhibition of sEH reduced the elevation in renal collagen deposition and urinary MCP-1 excretion levels together with a reduction in the number of renal TUNEL positive cells in diabetic vs. control rats (P<0.05). Meloxicam did not reduce renal inflammation or apoptosis in diabetic rats or even exacerbate the anti-inflammatory and anti-apoptotic effects of sEH inhibition. Renal 20-hydroxyeicosatetranoic acid (20-HETE) levels were elevated in diabetic rats and meloxicam further exacerbated this elevation. In conclusion, our study suggests that inhibition of COX failed to provide renal protection or to augment the reno-protective effects of sEH inhibition in diabetic rats, at least in part, via increased inflammatory 20-HETE levels.

The endothelial cyclooxygenase pathway: Insights from mouse arteries

To date, cyclooxygenase-2 (COX-2) is commonly believed to be the major mediator of endothelial prostacyclin (prostaglandin I2; PGI2) synthesis that balances the effect of thromboxane (Tx) A2 synthesis mediated by the other COX isoform, COX-1 in platelets. Accordingly, selective inhibition of COX-2 is considered to cause vasoconstriction, platelet aggregation, and hence increase the incidence of cardiovascular events. This idea has been claimed to be substantiated by experiments on mouse models, some of which are deficient in one of the two COX isoforms. However, results from our studies and those of others using similar mouse models suggest that COX-1 is the major functional isoform in vascular endothelium. Also, although PGI2 is recognized as a potent vasodilator, in some arteries endothelial COX activation causes vasoconstrictor response. This has again been recognized by studies, especially those performed on mouse arteries, to result largely from endothelial PGI2 synthesis. Therefore, evidence that supports a role for COX-1 as the major mediator of PGI2 synthesis in mouse vascular endothelium, reasons for the inconsistency, and results that elucidate underlying mechanisms for divergent vasomotor reactions to endothelial COX activation will be discussed in this review. In addition, we address the possible pathological implications and limitations of findings obtained from studies performed on mouse arteries.

Role of cyclooxygenase-1 and -2 in endothelium-dependent contraction of atherosclerotic mouse abdominal aortas

The objective of this study was to determine the role of cyclooxygenase (COX)-1 or -2 in endothelium-dependent contraction under atherosclerotic conditions. Atherosclerosis was induced in apoE knockout (apoE(-/-)) mice and those with COX-1(-/-) (apoE(-/-)-COX-1(-/-)) by feeding with high fat and cholesterol food. Aortas (abdominal or the whole section) were isolated for functional and/or biochemical analyses. As in non-atherosclerotic conditions, the muscarinic receptor agonist acetylcholine (ACh) evoked an endothelium-dependent, COX-mediated contraction following NO synthase (NOS) inhibition in abdominal aortic rings from atherosclerotic apoE(-/-) mice. Interestingly, COX-1 inhibition not only abolished such a contraction in rings showing normal appearance, but also diminished that in rings with plaques. Accordingly, only a minor contraction (<30% that of apoE(-/-) counterparts) was evoked by ACh (following NOS inhibition) in abdominal aortic rings of atherosclerotic apoE(-/-)-COX-1(-/-) mice with plaques, and none was evoked in those showing normal appearance. Also, the contraction evoked by ACh in apoE(-/-)-COX-1(-/-) abdominal aortic rings with plaques was abolished by non-selective COX inhibition, thromboxane-prostanoid (TP) receptor antagonism, or endothelial denudation. Moreover, it was noted that ACh evoked a predominant production of the prostacyclin (PGI2, which mediates abdominal aortic contraction via TP receptors in mice) metabolite 6-keto-PGF1α, which was again sensitive to COX-1 inhibition or COX-1(-/-). Therefore, in atherosclerotic mouse abdominal aortas, COX-1 can still be the major isoform mediating endothelium-dependent contraction, which probably results largely from PGI2 synthesis as in non-atherosclerotic conditions. In contrast, COX-2 may have only a minor role in such response limited to areas of plaques under the same pathological condition.

Constrictor prostanoids and uridine adenosine tetraphosphate: vascular mediators and therapeutic targets in hypertension and diabetes

Vascular dysfunction plays a pivotal role in the development of systemic complications associated with arterial hypertension and diabetes. The endothelium, or more specifically, various factors derived from endothelial cells tightly regulate vascular function, including vascular tone. In physiological conditions, there is a balance between endothelium-derived factors, that is, relaxing factors (endothelium-derived relaxing factors; EDRFs) and contracting factors (endothelium-derived contracting factors; EDCFs), which mediate vascular homeostasis. However, in disease states, such as diabetes and arterial hypertension, there is an imbalance between EDRF and EDCF, with a reduction of EDRF signalling and an increase of EDCF signalling. Among EDCFs, COX-derived vasoconstrictor prostanoids play an important role in the development of vascular dysfunction associated with hypertension and diabetes. Moreover, uridine adenosine tetraphosphate (Up4 A), identified as an EDCF in 2005, also modulates vascular function. However, the role of Up4 A in hypertension- and diabetes-associated vascular dysfunction is unclear. In the present review, we focused on experimental and clinical evidence that implicate these two EDCFs (vasoconstrictor prostanoids and Up4 A) in vascular dysfunction associated with hypertension and diabetes.

COX-2 is involved in vascular oxidative stress and endothelial dysfunction of renal interlobar arteries from obese Zucker rats

Obesity is related to vascular dysfunction through inflammation and oxidative stress and it has been identified as a risk factor for chronic renal disease. In the present study, we assessed the specific relationships among reactive oxygen species (ROS), cyclooxygenase 2 (COX-2), and endothelial dysfunction in renal interlobar arteries from a genetic model of obesity/insulin resistance, the obese Zucker rats (OZR). Relaxations to acetylcholine (ACh) were significantly reduced in renal arteries from OZR compared to their counterpart, the lean Zucker rat (LZR), suggesting endothelial dysfunction. Blockade of COX with indomethacin and with the selective blocker of COX-2 restored the relaxations to ACh in obese rats. Selective blockade of the TXA2/PGH2 (TP) receptor enhanced ACh relaxations only in OZR, while inhibition of the prostacyclin (PGI2) receptor (IP) enhanced basal tone and inhibited ACh vasodilator responses only in LZR. Basal production of superoxide was increased in arteries of OZR and involved NADPH and xanthine oxidase activation and NOS uncoupling. Under conditions of NOS blockade, ACh induced vasoconstriction and increased ROS generation that were augmented in arteries from OZR and blunted by COX-2 inhibition and by the ROS scavenger tempol. Hydrogen peroxide (H2O2) evoked both endothelium- and vascular smooth muscle (VSM)-dependent contractions, as well as ROS generation that was reduced by COX-2 inhibition. In addition, COX-2 expression was enhanced in both VSM and endothelium of renal arteries from OZR. These results suggest that increased COX-2-dependent vasoconstriction contributes to renal endothelial dysfunction through enhanced (ROS) generation in obesity. COX-2 activity is in turn upregulated by ROS.

Vasoconstrictor role of cyclooxygenase-1-mediated prostacyclin synthesis in non-insulin-dependent diabetic mice induced by high-fat diet and streptozotocin

This study tested the hypothesis that in diabetic arteries, cyclooxygenase (COX)-1 mediates endothelial prostacyclin (PGI2) synthesis, which evokes vasoconstrictor activity under the pathological condition. Non-insulin-dependent diabetes was induced to C57BL/6 mice and those with COX-1 deficiency (COX-1−/− mice) using a high-fat diet in combination with streptozotocin injection. In vitro analyses were performed 3 mo after. Results showed that in diabetic aortas, the endothelial muscarinic receptor agonist ACh evoked an endothelium-dependent production of the PGI2 metabolite 6-keto-PGF1α, which was abolished in COX-1−/− mice. Meanwhile, COX-1 deficiency or COX-1 inhibition prevented vasoconstrictor activity in diabetic abdominal aortas, resulting in enhanced relaxation evoked by ACh. In a similar manner, COX-1 deficiency increased the relaxation evoked by ACh in nitric oxide synthase-inhibited diabetic renal arteries. Also, in diabetic abdominal aortas and/or renal arteries, both PGI2 and the COX substrate arachidonic acid evoked contractions similar to those of nondiabetic mice. However, the contraction to arachidonic acid, but not that to PGI2, was abolished in vessels from COX-1−/− mice. Moreover, we found that 3 mo after streptozotocin injection, systemic blood pressure increased in diabetic C57BL/6 mice but not in diabetic COX-1−/− mice. These results explicitly demonstrate that in the given arteries from non-insulin-dependent diabetic mice, COX-1 remains a major contributor to the endothelial PGI2 synthesis that evokes vasoconstrictor activity under the pathological condition. Also, our data suggest that COX-1 deficiency prevents or attenuates diabetic hypertension in mice, although this could be related to the loss of COX-1-mediated activities derived from both vascular and nonvascular tissues.

A vasoconstrictor role for cyclooxygenase-1-mediated prostacyclin synthesis in mouse renal arteries

This study was to determine whether prostacyclin [prostaglandin I2 (PGI2)] evokes mouse renal vasoconstriction and, if so, the underlying mechanism(s) and how its synthesis via cyclooxygenase-1 (COX-1) influences local vasomotor reaction. Experiments were performed on vessels from C57BL/6 mice and/or those with COX-1 deficiency (COX-1−/−). Results showed that in renal arteries PGI2 evoked contraction more potently than in carotid arteries, where COX-1 is suggested to mediate prominent endothelium-dependent contraction. A similar result was observed with the thromboxane-prostanoid (TP) receptor agonist U46619. However, in renal arteries TP receptor antagonism, which inhibited the contraction, did not result in any relaxation in response to PGI2. Moreover, we noted that the endothelial muscarinic receptor agonist ACh evoked an increase in the production of the PGI2 metabolite 6-keto-PGF1α, which was prevented by endothelial denudation or COX-1−/−. Interestingly, COX-1−/− was further found to abolish a force development that was sensitive to TP receptor antagonism and result in enhanced relaxation evoked by ACh following NO synthase inhibition. Also, in renal arteries the COX substrate arachidonic acid evoked a vasoconstrictor response, which was again abolished by COX-1−/−. Meanwhile, nonselective COX inhibition did not show any effect in vessels from COX-1−/− mice. Thus, in mouse renal arteries, high expression of TP receptors together with little functional involvement from the vasodilator PGI2 receptors results in a potent vasoconstrictor effect evoked by PGI2. Also, our data imply that endogenous COX-1-mediated PGI2 synthesis leads to vasoconstrictor activity and this could be an integral part of endothelium-derived mechanisms in regulating local renal vascular function.

Eicosanoid post-mortem induction in kidney tissue is prevented by microwave irradiation

Previously, we, and others, have demonstrated a rapid and significant post-mortem increase in brain prostanoid (PG) levels analyzed without microwave fixation, and this is not the result of PG trapping or destruction in microwave-irradiated brain tissue. In the present study, we demonstrate a dramatic increase in kidney eicosanoid levels when analyzed without microwave fixation which was mainly accounted for by the 142-, 81-, and 62-fold increase in medullary 6-ketoPGF1α, PGE2, and PGF2α, levels, respectively, while PGD2 and TXB2 levels were increased ~7-fold. Whole kidney and cortex PG were also significantly increased in non-microwaved tissue, but at lesser extent. Arachidonic acid and the lipoxygenase products hydroxyeicosatetraenoic acids (HETE) were also induced in whole kidney, cortex, and medulla 1.5- to 5.5-fold depending upon tissue and metabolite. Cyclooxygenase inhibition with indomethacin decreased PG mass in non-microwaved tissue to basal levels, however HETE and arachidonic acid were not decreased. These data demonstrate the critical importance of kidney tissue fixation to limiting artifacts during kidney eicosanoid analysis.

Cyclo-oxygenase-1 or -2-mediated metabolism of arachidonic acid in endothelium-dependent contraction of mouse arteries

This study aimed to determine whether the cyclo-oxygenase (COX) substrate arachidonic acid (AA) evokes endothelium-dependent contraction and, if so, the specific COX isoform(s) involved and whether prostacyclin (prostaglandin I2; PGI2), a mediator of endothelium-derived vasoconstrictor activity, can be generated in medial smooth muscle from the intermediate COX product prostaglandin H2 (PGH2) that might diffuse from the endothelium. Aortae and/or carotid arteries were isolated from C57BL/6 mice or those lacking one of the two COX isoforms (COX-1(-/-) or COX-2(-/-)) for functional and/or biochemical analyses. Results showed that in vessels from C57BL/6 mice, exogenous AA evoked not only endothelium-dependent production of the PGI2 metabolite 6-keto-PGF1α, but also contractions reduced by thromboxane-prostanoid receptor antagonism or endothelial denudation. The minimal concentration for AA to evoke contraction was 0.3 μm, a level thought to activate only COX-2. However, neither the contraction nor 6-keto-PGF1α production was altered in vessels from COX-2(-/-) mice, while both were reduced in COX-1(-/-) counterparts. In vessels from COX-1(-/-) mice, AA also caused minor contractions that were sensitive to non-selective COX inhibition. Real-time PCR showed that like COX-1, COX-2 mainly existed in the endothelium, but it was unaltered in COX-1(-/-) mice. Also, we noted that in endothelium-denuded aortae, PGH2 generated PGI2 as in intact vessels. These results demonstrate a predominant role for COX-1 and suggest that in the given mouse arteries, metabolites from either COX isoform cause contraction. Moreover, our results imply that some of the PGI2 involved in vasoconstrictor activity of endothelial COX-mediated metabolism could possibly be generated from PGH2 in medial smooth muscle.

Effect of celecoxib on cyclooxygenase-1-mediated prostacyclin synthesis and endothelium-dependent contraction in mouse arteries

This study aimed to determine whether a cyclooxygenase-2 (COX-2) inhibitor celecoxib influences endothelium-dependent contraction independent of its action on COX-2 and, if so, the underlying mechanism(s). Abdominal aortas and/or carotid arteries from C57BL/6 mice or those with genetic COX-2 deficiency (COX-2(-/-)) were isolated for functional and/or biochemical analyses. Result showed that following NO synthase inhibition celecoxib not only reduced the contraction evoked by acetylcholine in C57BL/6 abdominal aorta, but also that in COX-2 (-/-) mice showing a comparable magnitude. Notably, the IC(50) of celecoxib obtained in COX-2 (-/-) abdominal aorta was only ~0.364 μM. Also, celecoxib exhibited a similar effect on COX-2 (-/-) carotid arteries. Interestingly, celecoxib was not only found to inhibit the production of the prostacyclin (PGI(2)) metabolite 6-keto-PGF (1α) in COX-2 (-/-) aortas, but also caused a reduction in the contraction evoked by PGI(2), by the α(1)-adrenergic agonist phenylephrine, or by 30 mM K(+)-induced depolarization in COX-2 (-/-) and/or C57BL/6 abdominal aorta. Moreover, N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide (NS398), another COX-2 inhibitor, also reduced the contraction evoked by acetylcholine or by 30 mM K(+)-induced depolarization in COX-2 (-/-) mice. These results demonstrate explicitly that in mouse arteries celecoxib not only inhibits COX-1-mediated synthesis of PGI(2) and probably some other prostanoids, but also causes a reduction in vessel contractility that is independent of either COX-2 or COX-1, leading to an inhibition of COX-1-mediated endothelium-dependent contraction with an IC(50) value far below that of it considered for COX-1 . Also, our data suggest that such effects of celecoxib could be possibly shared by some other COX-2 inhibitors, such as NS398.

Inflammatory mediators involved in the progression of the metabolic syndrome

The metabolic syndrome is often associated with type 2 diabetes mellitus, dyslipidemia, atherosclerosis, hypertension, steatosis of the liver and other organs, as well as hypertension, type 2 diabetes mellitus, and atherosclerosis. Recent studies have implicated a number of inflammatory mediators including cytokines, adipokines and eicosanoids in the inflammatory responses that accompany the metabolic syndrome. Measurements of the circulating levels of the inflammatory molecules that accompany this syndrome might provide leads to therapeutic approaches to modulate the inflammatory responses and thereby alter disease progression. In this review, we summarize recent studies on classical and newer inflammatory mediators in the pathogenesis of the metabolic syndrome in humans and experimental models.

Effect of glycine on the cyclooxygenase pathway of the kidney arachidonic acid metabolism in a rat model of metabolic syndrome

The kidneys are organs that can be severely impaired by metabolic syndrome (MS). This is characterized by the association of various pathologies such as hypertension, dyslipidemia, and type-2 diabetes. Glycine, a nonessential amino acid, is known to possess various protective effects in the kidney, such as a decrease in the deterioration of renal function and a reduction of the damage caused by hypoxia. In a rat model of MS, the effect of glycine on the cyclooxygenase (COX) pathway of arachidonic acid (AA) metabolism was studied in isolated perfused kidney. MS was induced in Wistar rats by feeding them a 30% sucrose solution for 16 weeks. The addition of 1% glycine to their drinking water containing 30% sucrose, for 8 weeks, reduced high blood pressure, triglyceride levels, insulin concentration, homeostatis model assessment (HOMA) index, albuminuria, AA concentration in kidney homogenate, renal perfusion pressure, prostaglandin levels, PLA2 expression, and COX isoform expression, compared with MS rats that did not receive the glycine supplement. Glycine receptor expression decreased significantly with MS, but glycine treatment increased it. The results suggest that in the MS model, 1% glycine treatment protects the kidney from damage provoked by the high sucrose consumption, by acting as an anti-inflammatory on the COX pathway of AA metabolism in kidney.

Renal protective effect of chronic inhibition of COX-2 with SC-58236 in streptozotocin-diabetic rats

The induction of renal cyclooxygenase-2 (COX-2) in diabetes has been implicated in the renal functional and structural changes in models where hypertension or uninephrectomy was superimposed. We examined the protective effects of 3 mo treatment of streptozotocin-diabetic rats with a highly selective COX-2 inhibitor (SC-58236) in terms of albuminuria, renal hypertrophy, and the excretion of TNF-α and TGF-β, which have also been implicated in the detrimental renal effects of diabetes. SC-58236 treatment (3 mg·kg(-1)·day(-1)) of diabetic rats resulted in reduced urinary excretion of PGE(2), 6-ketoPGF(1α), and thromboxane B(2), all of which were increased in the diabetic rat compared with age-matched nondiabetic rats. However, serum thromboxane B(2) levels were unchanged, confirming the selectivity of SC-58236 for COX-2. The renal protective effects of treatment of diabetic rats with the COX-2 inhibitor were reflected by a marked reduction in albuminuria, a reduction in kidney weight-to-body weight ratio, and TGF-β excretion and a marked decrease in the urinary excretion of TNF-α. The protective effects of SC-58236 were independent of changes in plasma glucose levels or serum advanced glycation end-product levels, which were not different from those of untreated diabetic rats. In an additional study, the inhibition of COX-2 with SC-58236 for 4 wk in diabetic rats resulted in creatinine clearance rates not different from those of control rats. These results confirm that the inhibition of COX-2 in the streptozotocin-diabetic rat confers renal protection and suggest that the induction of COX-2 precedes the increases in cytokines, TNF-α, and TGF-β.

Treatment of diabetic rats with a peroxynitrite decomposition catalyst prevents induction of renal COX-2

Cyclooxygenase (COX)-2 expression is increased in the kidney of rats made diabetic with streptozotocin and associated with enhanced release of prostaglandins stimulated by arachidonic acid (AA). Treatment of diabetic rats with nitro-L-arginine methyl ester (L-NAME) to inhibit nitric oxide synthase or with tempol to reduce superoxide prevented these changes, suggesting the possibility that peroxynitrite (ONOO) may be the stimulus for the induction of renal COX-2 in diabetes. Consequently, we tested the effects of an ONOO decomposition catalyst, 5,10,15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron(III) (FeTMPyP), which was administered for 3-4 wk after the induction of diabetes. FeTMPyP treatment normalized the twofold increase in the expression of nitrotyrosine, a marker for ONOO formation, in the diabetic rat and prevented the increase in renal COX-2 expression without modifying the two- to threefold increases in renal release of prostaglandins PGE(2) and 6-ketoPGF(1α) in response to AA. FeTMPyP treatment of diabetic rats reduced the elevated creatinine clearance and urinary excretion of TNF-α and transforming growth factor (TGF)-β, suggesting a renoprotective effect. Double immunostaining of renal sections and immunoprecipitation of COX-2 and nitrotyrosine suggested nitration of COX-2 in diabetic rats. In cultured human umbilical vein endothelial cells (HUVECs) exposed to elevated glucose (450 mg/dl) or ONOO derived from 3-morpholinosydnonimine (SIN-1), expression of COX-2 was increased and was prevented when endothelial cells were treated with FeTMPyP. These results indicate that elevated glucose increases the formation of ONOO, which contributes to the induction of renal COX-2 in the diabetic rat.

Curcumin improves prostanoid ratio in diabetic mesenteric arteries associated with cyclooxygenase-2 and NF-κB suppression

BACKGROUND

Curcumin, the active ingredient from turmeric rhizomes, has been shown to have a wide range of pharmacological properties including antioxidant and anti-inflammatory effects. Curcumin has been reviewed for its multiple molecular action on inhibiting tumor angiogenesis via its mechanisms of cyclooxygenase (COX)-2, and vascular endothelial growth factor (VEGF) inhibition. In this present study, we aimed to assess the effects of curcumin on preventing diabetes-induced vascular dysfunction in association with COX-2, nuclear factor-κB (NF-κB) expression, and prostanoid production.

METHODS

Twelve-week-old male Wistar rats were separated into five groups: 1) diabetes with 0.9% normal saline (DM-NSS; n =10), 2) diabetes treated with curcumin 30 mg/kg (n =10), 3) diabetes treated with curcumin 300 mg/kg (n =10), 4) the control with 0.9% normal saline (n =10), and 5) the control treated with 300 mg/kg (n =10). Daily oral feeding of curcumin was started at 6 weeks after the streptozotocin injection. Levels of 6-keto prostaglandin (PG) F(1α)and thromboxane (TX) B(2) were determined from mesenteric perfusates using enzyme immunoassay kits. Protein kinase C (PKC)-β II and COX-2 with NF-κB levels were analyzed in the mesenteric arteries by immunofluorescent staining and immunohistochemistry, respectively.

RESULTS

The ratio of 6-keto-PGF(1α)and TXB(2) was significantly decreased in DM-NSS compared with the control (P < 0.05). Double-immunofluorescent staining with specific antibodies for PKC-βII and α-smooth muscle actins showed that the diabetic mesenteric arteries contained increased of PKC-βII within the vascular wall. Also, COX-2 expression and activated NF-κB in the small mesenteric artery of diabetes mellitus rats were markedly increased when compared with the control. Interestingly, curcumin could inhibit the upregulation of all of these biomarkers.

CONCLUSION

These findings show that curcumin can attenuate diabetes-induced vascular dysfunction in association with its potential for COX-2 and NF-κB suppression, PKC inhibition, and improving the ratio of prostanoid products PGI(2)/TXA(2).

Immunohistochemical examination of cyclooxygenase-2 and renin in a KK-A(y) mouse model of diabetic nephropathy

The renin-angiotensin system plays a central role in the pathological mechanisms of diabetic nephropathy and is regulated by renal expression of cyclooxygenase-2 (COX-2). In the present study, the kidneys of diabetic KK-A(y) mice, a model of human type 2 diabetes, were investigated histologically and immunohistochemically at 8, 12, 16, and 20 weeks of age, and changes in renal lesions and expression of COX-2 and renin were evaluated quantitatively. Glomerular damage, characterized by expansion of mesangial matrices and nodular lesions, was observed in the kidneys of these mice. The glomerular sclerosis score gradually increased with age and was significantly higher than those of age-matched control C57BL/6 mice at 12, 16, and 20 weeks of age. Although mild tubulointerstitial damage was observed, there was no significant change in the interstitial fibrosis score. These findings were considered early diabetic nephropathy changes. COX-2-positive signals were consistently detected in the macula densa cells of the thick ascending limbs in all KK-A(y) mice, with a slightly higher score observed at 8 weeks of age. No COX-2-positive signals were detected in C57BL/6 mice. Renin-positive signals were commonly detected in the juxtaglomerular arterioles, and the scores in KK-A(y) mice increased at 16 weeks and decreased at 20 weeks of age. The present study demonstrated activation of renal COX-2 and renin expression in diabetic KK-A(y) mice at different stages. This finding suggests that these two enzymes contribute to the development and progression of diabetic nephropathy via different mechanisms.

Effects of aspirin and nimesulide on tissue damage in diabetic rats

This study was designed to compare the effect of Aspirin (AS) and Nimesulide (NM) on renal failure and vascular disorder in streptozotocin (STZ)-induced diabetic rats. Rats were divided into four groups; control, diabetic rats, diabetic rats plus AS and diabetic rats plus NM, which are COX inhibitors. The renal and aorta tissues morphology were investigated by light microscopy. Trunk blood was also obtained to determine plasma lipid peroxidation product malondialdehyde (MDA) and plasma activity of antioxidant enzymes. MDA levels were increased in the diabetic rats when compared to the control group. AS and NM administration caused a significant decrease in MDA production. Morphological damage in diabetic rats was severe in the kidney and in the aorta tissue. Treatment of AS reduced these damages, but NM did not exert positive effect on these damages in diabetic rats. As a result, although both AS and NM corrected lipid peroxidation parameters such as MDA via their antioxidant properties, only AS ameliorated pathological alteration in tissues. These findings indicate that there may be another mechanism in beneficial effect of AS in diabetic rats.

Effect of gonadectomy on the metabolism of arachidonic acid in isolated kidney of a rat model of metabolic syndrome

Influence of sex on arachidonic acid metabolism, a pathway involved in the link between metabolic syndrome (MS) and renal damage, was studied in isolated perfused kidney. Metabolic syndrome was induced by feeding 30% sucrose solution for 24 weeks to intact and gonadectomized female (Ovx) and male (Cas) rats. Systolic blood pressure, albuminuria, as well as prostaglandin E(2) and thromboxane B(2) from urine and perfusate increased in MS male and MS ovariectomized females; castration reduced them in MS males. Perfusion of arachidonic acid in kidneys from MS males increased perfusion pressure compared with controls. No difference appeared in perfusion pressure between control and MS females. Castration diminished perfusion pressure in MS; the opposite was observed in Ovx MS. Perfusion with arachidonic acid plus indomethacin decreased perfusion pressure in MS male kidneys and in Cas MS. In Ovx MS, arachidonic acid plus indomethacin decreased perfusion pressure, but not in female control, MS, and Ovx control. Increase in perfusion pressure with arachidonic acid in both male MS and Ovx MS was related to cyclooxygenase (COX)-1 and COX-2 overexpression in kidney. Castration reduced the expression of COX-1 and COX-2 in MS to control levels. The results suggest that the alteration in arachidonic acid metabolism associated with changes in the expression of COX-1 and COX-2 induced by sucrose intake, and influenced by sex hormones, may contribute to renal damage.

Endothelial dysfunction in mice with streptozotocin-induced type 1 diabetes is opposed by compensatory overexpression of cyclooxygenase-2 in the vasculature

Cardiovascular complications of diabetes result from endothelial dysfunction secondary to persistent hyperglycemia. We investigated potential compensatory mechanisms in the vasculature that oppose endothelial dysfunction in diabetes. BALB/c mice were treated with streptozotocin (STZ) to induce type 1 diabetes (T1D). In mesenteric vascular beds (MVBs), isolated ex vivo from mice treated with STZ for 1 wk, dose-dependent vasorelaxation to acetylcholine (ACh) or sodium nitroprusside was comparable with that in age-matched control mice (CTRL). By contrast, MVBs from mice treated with STZ for 8 wk had severely impaired vasodilator responses to ACh consistent with endothelial dysfunction. Pretreatment of MVBs from CTRL mice with nitric oxide synthase inhibitor nearly abolished vasodilation to ACh. In MVB from 1-wk STZ-treated mice, vasodilation to ACh was only partially impaired by L-N(omega)-arginine methyl ester. Thus, vasculature of mice with T1D may have compensatory nitric oxide-independent mechanisms to augment vasodilation to ACh and oppose endothelial dysfunction. Indeed, pretreatment of MVBs isolated from 1-wk STZ-treated mice with NS-398 [selective cyclooxygenase (COX)-2 inhibitor] unmasked endothelial dysfunction not evident in CTRL mice pretreated without or with NS-398. Expression of COX-2 in MVBs, aortic endothelial cells, and aortic vascular smooth muscle cells from STZ-treated mice was significantly increased (vs. CTRL). Moreover, concentrations of the COX-2-dependent vasodilator 6-keto-prostaglandin F-1alpha was elevated in conditioned media from aorta of STZ-treated mice. We conclude that endothelial dysfunction in a mouse model of T1D is opposed by compensatory up-regulation of COX-2 expression and activity in the vasculature that may be relevant to developing novel therapeutic strategies for diabetes and its cardiovascular complications.

Effects of cyclooxygenase-2 gene inactivation on cardiac autonomic and left ventricular function in experimental diabetes

Glucose-mediated oxidative stress and the upregulation of cyclooxygenase (COX)-2 pathway activity have been implicated in the pathogenesis of several vascular complications of diabetes including diabetic neuropathy. However, in nondiabetic subjects, the cardiovascular safety of selective COX-2 inhibition is controversial. The aim of this study was to explore the links between hyperglycemia, oxidative stress, activation of the COX-2 pathway, cardiac sympathetic integrity, and the development of left ventricular (LV) dysfunction in experimental diabetes. R wave-to-R wave interval (R-R interval) and parameters of LV function measured by echocardiography using 1% isoflurane, LV sympathetic nerve fiber density, LV collagen content, and markers of myocardial oxidative stress, inflammation, and PG content were assessed after 6 mo in control and diabetic COX-2-deficient (COX-2(-/-)) and littermate, wild-type (COX-2(+/+)) mice. There were no differences in blood glucose, LV echocardiographic measures, collagen content, sympathetic nerve fiber density, and markers of oxidative stress and inflammation between nondiabetic (ND) COX-2(+/+) and COX-2(-/-) mice at baseline and thereafter. After 6 mo, diabetic COX-2(+/+) mice developed significant deteriorations in the R-R interval and signs of LV dysfunction. These were associated with a loss of LV sympathetic nerve fiber density, increased LV collagen content, and a significant increase in myocardial oxidative stress and inflammation compared with those of ND mice. Diabetic COX-2(-/-) mice were protected against all these biochemical, structural, and functional deficits. These data suggest that in experimental diabetes, selective COX-2 inactivation confers protection against sympathetic denervation and LV dysfunction by reducing intramyocardial oxidative stress, inflammation, and myocardial fibrosis.

Deficient renal 20-HETE release in the diabetic rat is not the result of oxidative stress

We confirmed that release of 20-hydroxyeicosatetraenoic acid (20-HETE) from the isolated perfused kidney of diabetic rats is greatly reduced compared with age-matched control rats. The present studies were undertaken to examine potential mechanisms for the deficit in renal 20-HETE in rats with streptozotocin-induced diabetes of 3-4 wk duration. A role for oxidative stress was excluded, inasmuch as treatment of diabetic rats with tempol, an SOD mimetic, for 4 wk did not affect the renal release of 20-HETE. Similarly, chronic inhibition of nitric oxide formation with nitro-l-arginine methyl ester or aldose reductase with zopolrestat failed to alter the release of 20-HETE from the diabetic rat kidney. Inasmuch as 20-HETE may be metabolized by cyclooxygenase (COX), the expression/activity of which is increased in diabetes, we included indomethacin in the perfusate of the isolated kidney to inhibit COX but found no effect on 20-HETE release. Diabetic rats were treated for 3 wk with fenofibrate to increase expression of cytochrome P-450 (CYP4A) in an attempt to find an intervention that would restore release of 20-HETE from the diabetic rat kidney. However, fenofibrate reduced 20-HETE release in diabetic and control rat kidneys but increased expression of CYP4A. Only insulin treatment of diabetic rats for 2 wk to reverse the hyperglycemia and maintain blood glucose levels at <200 mg/dl reversed the renal deficit in 20-HETE. We conclude that oxidative stress, increased aldose reductase activity, or increased COX activity does not contribute to the renal deficit of 20-HETE in diabetes, which may be directly related to insulin deficiency.

Protective effects of cyclooxygenase-2 gene inactivation against peripheral nerve dysfunction and intraepidermal nerve fiber loss in experimental diabetes

OBJECTIVE

Activation of the cyclooxygenase (COX) pathway with secondary neurovascular deficits are implicated in the pathogenesis of experimental diabetic peripheral neuropathy (DPN). The aim of this study was to explore the interrelationships between hyperglycemia, activation of the COX-2 pathway, and oxidative stress and inflammation in mediating peripheral nerve dysfunction and whether COX-2 gene inactivation attenuates nerve fiber loss in long-term experimental diabetes.

RESEARCH DESIGN AND METHODS

Motor and sensory digital nerve conduction velocities, sciatic nerve indexes of oxidative stress, prostaglandin content, markers of inflammation, and intraepidermal nerve fiber (IENF) density were measured after 6 months in control and diabetic COX-2-deficient (COX-2(-/-)) and littermate wild-type (COX-2(+/+)) mice. The effects of a selective COX-2 inhibitor, celecoxib, on these markers were also investigated in diabetic rats.

RESULTS

Under normal conditions, there were no differences in blood glucose, peripheral nerve electrophysiology, markers of oxidative stress, inflammation, and IENF density between COX-2(+/+) and COX-2(-/-) mice. After 6 months, diabetic COX-2(+/+) mice experienced significant deterioration in nerve conduction velocities and IENF density and developed important signs of increased oxidative stress and inflammation compared with nondiabetic mice. Diabetic COX-2(-/-) mice were protected against functional and biochemical deficits of experimental DPN and against nerve fiber loss. In diabetic rats, selective COX-2 inhibition replicated this protection.

CONCLUSIONS

These data suggest that selective COX-2 inhibition may be useful for preventing or delaying DPN.

Fenofibrate treatment of diabetic rats reduces nitrosative stress, renal cyclooxygenase-2 expression, and enhanced renal prostaglandin release

Renal cyclooxygenase (COX)-2 expression is increased in the diabetic rat and has been linked to increased glomerular filtration rate (GFR) and renal injury. Our studies indicate that oxidative stress in the form of peroxynitrite (ONOO) may be the stimulus for induction of COX-2. In this study, we addressed the effects of a peroxisome proliferator-activated receptor alpha agonist on renal COX-2 expression as fibrates exert renal protective effects. Forty-eight hours after the induction of diabetes with streptozotocin in male Wistar rats, fenofibrate treatment (100 mg/kg/day) was started, and the effects were compared with untreated diabetic rats and treated and untreated age-matched control rats (n = 5 per group). After 12 to 14 weeks of treatment, the right kidney was perfused to determine prostaglandin release in response to arachidonic acid (AA), and the left kidney was used to examine the expression of COX-2 and nitrotyrosine, an index of ONOO formation. Release of prostaglandin (PG) E(2) in response to AA was enhanced in the diabetic rat kidney compared with control (4.8 +/- 0.7 versus 1.9 +/- 0.7 ng/min) and reduced by fenofibrate to 0.6 +/- 0.2 ng/min. A similar pattern was obtained for AA-stimulated release of 6-ketoPGF(1alpha). The effects of fenofibrate were associated with reduced renal expression of COX-2 and nitrotyrosine in diabetic rats. We used creatinine clearance as an index of GFR, which was increased in the diabetic rat, 3.09 +/- 0.4 versus 1.15 +/- 0.1 ml/min for control, and reduced by fenofibrate treatment to 1.87 +/- 0.3 ml/min. These results show that fenofibrate treatment of diabetic rats decreases renal COX-2 expression, possibly by reducing nitrosative stress, and is associated with a reduction of the enhanced GFR.

H2O2 increases production of constrictor prostaglandins in smooth muscle leading to enhanced arteriolar tone in Type 2 diabetic mice

Our previous study showed that arteriolar tone is enhanced in Type 2 diabetes mellitus (T2-DM) due to an increased level of constrictor prostaglandins. We hypothesized that, in mice with T2-DM, hydrogen peroxide (H2O2) is involved in the increased synthesis of constrictor prostaglandins, hence enhanced basal tone in skeletal muscle arterioles. Isolated, pressurized gracilis muscle arterioles (∼100 μm in diameter) of mice with T2-DM (C57BL/KsJ- db−/ db−) exhibited greater basal tone to increases in intraluminal pressure (20–120 mmHg) than that of control vessels (at 80 mmHg, control: 25 ± 5%; db/ db: 34 ± 4%, P < 0.05), which was reduced back to control level by catalase ( db/ db: 24 ± 4%). Correspondingly, in carotid arteries of db/ db mice, the level of dichlorofluorescein-detectable and catalase-sensitive H2O2 was significantly greater. In control arterioles, exogenous H2O2 (0.1–100 μmol/l) elicited dilations (maximum, 58 ± 10%), whereas in arterioles of db/ db mice H2O2 caused constrictions (−28 ± 8%), which were converted to dilations (maximum, 16 ± 5%) by the thromboxane A2/prostaglandin H2 (TP) receptor antagonist SQ-29548. In addition, arteriolar constrictions in response to the TP receptor agonist U-46619 were not different between the two groups of vessels. Endothelium denudation did not significantly affect basal tone and H2O2-induced arteriolar responses in either control or db/ db mice. Also, in arterioles of db/ db mice, but not in controls, 3-nitrotyrosine staining was detected in the endothelial layer of vessels. Thus we propose that, in mice with T2-DM, arteriolar production of H2O2 is enhanced, which leads to increased synthesis of the constrictor prostaglandins thromboxane A2/prostaglandin H2 in the smooth muscle cells, which enhance basal arteriolar tone. These alterations may contribute to disturbed regulation of skeletal muscle blood flow in Type 2 diabetes mellitus.

Chronic hyperglycemia impairs functional vasodilation via increasing thromboxane-receptor-mediated vasoconstriction

Individuals with hyperglycemia exhibit impaired exercise performance and functional vasodilatory response. Based on the importance of arachidonic acid (AA) metabolites in functional vasodilation and the increased thromboxane-to-prostacyclin ratio in diabetes, we hypothesized that chronic hyperglycemia in diabetes increases thromboxane-receptor (TP)-mediated vasoconstriction, resulting in an attenuated functional vasodilation. Three groups of lean Zucker rats (8 wk) were used to test the effects of chronic hyperglycemia on endothelial function: normal, streptozotocin (STZ; 70 mg/kg ip), and STZ + insulin (2 U/day). After 4 wk of treatment, spinotrapezius arcade arterioles were chosen for microcirculatory observation. Arteriolar diameter was measured following muscle stimulation and 10 μM AA application in the absence and presence of 1 μM SQ-29548 (TP antagonist). STZ rats exhibited significantly higher fasting glucose levels and attenuated functional and AA-induced dilation compared with normal animals. SQ-29548 improved the vasodilatory responses in STZ rats but had no effect in controls. Insulin treatment normalized both the glucose levels and the vasodilatory responses, and SQ-29548 treatment had no effect on functional or AA-mediated vasodilation in STZ + insulin animals. These results suggest that the impaired functional vasodilation in diabetic rats is due to hyperglycemia-mediated increases in TP-mediated vasoconstriction.

Mechanisms of endothelial dysfunction with development of type 1 diabetes mellitus: role of insulin and C-peptide

Complications associated with insulin-dependent diabetes mellitus (type-1diabetes) primarily represent vascular dysfunction that has its origin in the endothelium. While many of the vascular changes are more accountable in the late stages of type-1diabetes, changes that occur in the early or initial functional stages of this disease may precipitate these later complications. The early stages of type-1diabetes are characterized by a diminished production of both insulin and C-peptide with a significant hyperglycemia. During the last decade numerous speculations and theories have been developed to try to explain the mechanisms responsible for the selective changes in vascular reactivity and/or tone and the vascular permeability changes that characterize the development of type-1diabetes. Much of this research has suggested that hyperglycemia and/or the lack of insulin may mediate the observed functional changes in both endothelial cells and vascular smooth muscle. Recent studies suggest several possible mechanisms that might be involved in the observed decreases in vascular nitric oxide (NO) availability with the development of type-1 diabetes. In addition more recent studies have indicated a direct role for both endogenous insulin and C-peptide in the amelioration of the observed endothelial dysfunction. These results suggest a synergistic action between insulin and C-peptide that facilitates increase NO availability and may suggest new clinical treatment modalities for type-1 diabetes mellitus.

Effect of inhibition of nitric oxide synthase on renal cyclooxygenase in the diabetic rat

Renal cyclooxygenase (COX)-2 expression and arachidonic acid-stimulated prostaglandin release are increased in streptozotocin-diabetic rats and are reduced by tempol treatment, indicating a role for superoxide. Generation of nitric oxide (NO) and its product with superoxide, peroxynitrite, is also increased in diabetes and can induce COX-2. To investigate a role of NO, rats were treated with L-nitroarginine methyl ester (L-NAME; 100 mg/kg/day) to inhibit NO synthase (NOS) for 14-18 days. In isolated perfused kidneys from diabetic rats, prostaglandin release and vasoconstrictor responses to arachidonic acid were increased and renal cortical expression of COX-2 was 2-fold that of control rats. Treatment of diabetic rats with L-NAME reduced arachidonic acid-stimulated release of prostaglandins and the expression of COX-2. L-NAME increased vasoconstrictor responses to AA in diabetic and non-diabetic rats but abolished the differences between the two. These results, coupled with those using tempol, suggest that NO or its product with superoxide may contribute to the induction of renal COX-2 in the diabetic rat.

Neuronal nitric oxide synthase and cyclooxygenase-2 in diabetic nephropathy of type 2 diabetic OLETF rats

Neuronal nitric oxide synthase (nNOS) and cyclooxygenase-2 (COX-2) regulate the tubuloglomerular feedback (TGF) and renin-angiotensin system (RAS) in the kidney. In type 1 diabetic rats, renal overproduction of these enzymes and their relationship to the pathogenesis of diabetic nephropathy has been demonstrated. In the present study, we histologically and immunohistochemically investigated the kidneys of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, as a model of type 2 diabetes, at 62 weeks of age (chronic phase of diabetes). The kidneys of OLETF rats showed typical diabetic nephropathy. Quantitative scores for glomerulosclerosis and interstitial fibrosis in OLETF rats were significantly higher than those of age-matched control Long-Evans Tokushima Otsuka (LETO) rats. nNOS- and COX-2-positive immunoreactions were observed in the distal tubules and collecting ducts. These reactions appeared to be more widely distributed in OLETF, and the number of nNOS-and COX-2-positive sites in the OLETF were significantly more than those in LETO rats. Expression of renin, angiotensin II, and inducible nitric oxide synthase (iNOS) were also examined immunohistochemically, and no differences between OLETF and LETO rats were observed in the distributions and the number of immunoreactive-sites. In conclusion, the overproduction of nNOS and COX-2 in the kidney of OLETF rats was confirmed, suggesting that the overproduction of nNOS and/or COX-2 does not affect the intrarenal RAS or iNOS production but does affect TGF.

Contribution of endothelin receptors and cyclooxygenase-derivatives to the altered response of the rabbit renal artery to endothelin-1 in diabetes

The influence of diabetes on regulatory mechanisms and specific receptors implicated in the response of isolated rabbit renal artery to endothelin-1 was examined. Endothelin-1 induced a concentration-dependent contraction that was less potent in arteries from diabetic rabbits than in arteries from control rabbits. Endothelium removal or N(G)-nitro-L-arginine (L-NOARG) enhanced contractions to endothelin-1 either in control and diabetic arteries. Indomethacin inhibited endothelin-1-induced response in control arteries, but enhanced it in diabetic arteries. In contrast to that observed in rubbed and in L-NOARG treated arteries, in the presence of indomethacin the contractile action of endothelin-1 was higher in diabetic arteries than in control arteries. Nimesulide enhanced endothelin-1 contractions both in control and diabetic arteries. Cyclo-(D-Asp-Pro-D-Val-Leu-D-Trp) (BQ-123, endothelin ET(A) receptor antagonist), attenuated endothelin-1 vasoconstriction in control rabbits, while vasoconstriction resulted increased in diabetic rabbits. 2,6-Dimethylpiperidinecarbonyl-gamma-Methyl-Leu-N(in)-(Methoxycarbonyl)-D-Trp-D-Nle (BQ-788, endothelin ET(B) receptor antagonist), enhanced the contractile response in control rabbit arteries without modifying this response in diabetic rabbits. In summary, diabetes decreases the sensitivity of the rabbit renal artery to endothelin-1 by decreasing the ratio between vasoconstrictor and vasodilator prostanoids released after activation of endothelin ET(A) receptors.

Efeitos da metformina na disfunção endotelial da circulação renal induzida pela hiperglicemia em coelhos não diabéticos

OBJETIVO: Avaliar o efeito da metformina (Met) na disfunção endotelial da circulação renal de coelhos não diabéticos induzida por concentrações de glicose usualmente observadas em pacientes com diabetes tipo 2 (DM2) em tratamento ambulatorial. METODOLOGIA: Rins isolados de coelhos não diabéticos foram expostos por 3h a concentrações normais (100mg/dl) e elevadas (270mg/dl) de glicose na presença ou ausência de Met (100µM). Os níveis de glicose utilizados correspondem à mediana da glicemia pós-prandial (270mg/dl) obtida 2h após o café da manhã em 780 pacientes com DM2 atendidos em nosso serviço. A reatividade vascular (RV) dependente do endotélio (DE) foi avaliada com acetilcolina (ACh) e independente do endotélio (IE) com nitroprussiato de sódio (NPS). RESULTADO: Houve redução significativa na vasodilatação DE no grupo com infusão elevada de glicose em comparação ao controle (redução máxima na pressão de perfusão de respectivamente 25 ± 3 vs. 41 ± 3%; p< 0,01). No grupo de infusão com concentrações elevadas de glicose associada à infusão contínua de Met, a resposta vasodilatadora DE foi restaurada sem haver diferença significativa com o grupo controle (redução da pressão de perfusão respectivamente de 43 ± 1,5% e 41 ± 3%, p> 0,05). A Met não alterou a vasodilatação induzida pela ACh na presença de níveis normais de glicose. Finalmente, a vasodilatação renal induzida por NPS não foi modificada pela infusão conjunta de glicose e Met. CONCLUSÃO: Níveis de glicose observados em pacientes com DM2 em tratamento ambulatorial são capazes de provocar alterações agudas na RV no modelo experimental estudado, sendo estes efeitos totalmente abolidos pela Met. Os mecanismos envolvidos nesta ação protetora da Met merecem investigações específicas.

Metformin prevents the impairment of endothelium-dependent vascular relaxation induced by high glucose challenge in rabbit isolated perfused kidneys

High glucose concentrations are involved in the development of diabetic-associated vascular complications. We have previously reported that acute high glucose challenge, corresponding to post-prandial glycemia levels observed in patients with type 2 diabetes, blunts ACh-induced endothelium-dependent relaxation of the renal circulation of non-diabetic rabbits. Isolated perfused kidneys from non-diabetic rabbits were acutely exposed (3 h) to normal (5.5 mM--control group) or high (15 mM) D-glucose concentrations in the presence or absence of a continuous infusion of metformin (20 or 100 microM). Renal vascular reactivity was evaluated with endothelium-dependent (acetylcholine, ACh) and -independent (sodium nitroprusside, SNP) vasodilating agents. ACh-induced maximal renal vasodilation was reduced by high glucose infusion (15 mM) in comparison to the control group (25+/-3% and 41+/-3% respectively; P<0.01), being restored to 41+/-4% and 43+/-2% by a simultaneous 3-h infusion of 20 or 100 microM of metformin respectively (P>0.05). Perfusion of the kidneys with the angiotensin II-converting enzyme inhibitor captopril (10 microM) also significantly prevented the deleterious effects of high glucose challenge in the renal circulation. The use of a continuous infusion of N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM) did not affect the protective effect of metformin in the renal circulation (39+/-4%; P>0.05), while tetraethylammonium (TEA, 10 mM) partially blunted this effect (33+/-4, P<0.01). Renal vasodilation induced by SNP was not modified by simultaneous infusion of high glucose and/or metformin. It is concluded that the impairment of ACh-induced endothelium-dependent renal vasodilation observed after acute exposure to high glucose concentrations is abolished by metformin administration. These alterations of renal vascular reactivity can be accounted for, at least in part, by the activation of the renal renin-angiotensin system during hyperglycemia. The protective effects of metformin present some EDHF-dependent component and are not related to metabolic pathways dependent on nitric oxide.

Type 2 Diabetic Mice Have Increased Arteriolar Tone and Blood Pressure

OBJECTIVE

Type 2 diabetes mellitus (T2-DM) is frequently associated with vascular dysfunction and elevated blood pressure, yet the underlying mechanisms are not completely understood. We hypothesized that in T2-DM, the regulation of peripheral vascular resistance is altered because of changes in local vasomotor mechanisms.

METHODS AND RESULTS

In mice with T2-DM (C57BL/KsJ-(db-)/db-), systolic and mean arterial pressures measured by the tail cuff method were significantly elevated compared with those of control (db+/db-) animals (db/db, 146+/-5 and 106+/-2 mm Hg versus control, 133+/-4 and 98+/-4 mm Hg, respectively; P<0.05). Total peripheral resistance, calculated from cardiac output values (measured by echocardiography) and mean arterial pressure were significantly elevated in db/db mice (db/db, 25+/-6 versus control, 15+/-1 mm Hg[middot]mL(-1)[middot]min(-1)). In isolated, pressurized gracilis muscle arterioles (diameter approximately 80 microm) from db/db mice, stepwise increases in intraluminal pressure (from 20 to 120 mm Hg) elicited a greater reduction in diameter than in control vessels at each pressure step (at 80 mm Hg, db/db, 66+/-4% versus control, 79+/-3%). The passive diameters of arterioles (obtained in Ca2+-free solution) and the calculated myogenic index were not significantly different in the 2 groups. The presence of the prostaglandin H2/thromboxane A2 receptor antagonist SQ29548 did not affect arteriolar diameters of control mice but reduced the enhanced arteriolar tone of db/db mice back to control levels (at 80 mm Hg, 80+/-4%). The inhibitor of cyclooxygenase-1 (COX-1), SC-560, did not affect the basal tone of arterioles, whereas NS-398, an inhibitor of COX-2, caused a significant shift in the arteriolar pressure-diameter curve of vessels from db/db mice (at 80 mm Hg, 76+/-3%) but not in those of control mice. Also, in aortas of db/db mice, expression of COX-2 was enhanced compared with controls.

CONCLUSIONS

Collectively, these findings suggest that in mice with T2-DM, the basal tone of skeletal muscle arterioles is increased because of an enhanced COX-2-dependent production of constrictor prostaglandins. These alterations in microvascular prostaglandin synthesis may contribute to the increase in peripheral resistance and blood pressure in T2-DM.

Effect of Tempol on Renal Cyclooxygenase Expression and Activity in Experimental Diabetes in the Rat

Renal cyclooxygenase (COX)-2 expression is increased in the streptozotocin (STZ)-diabetic rat and is associated with enhanced renal prostaglandin release in response to arachidonic acid (AA). Endoperoxide-mediated vasoconstrictor responses to AA were also enhanced in the diabetic rat kidney. Because oxidative stress is increased in diabetes and has been shown to induce COX-2, we assessed its contribution to prostaglandin release by treating diabetic rats with tempol (120 mg/kg/day) for 28 days. Release of AA-stimulated prostaglandins PGE(2) and 6-ketoPGF(1alpha) from the isolated perfused kidney was used as an index of COX activity, and Western analysis was used to determine COX-2 protein expression. In untreated diabetic rats, the release of prostaglandins in response to AA was markedly enhanced; the increase in release of both 6-ketoPGF(1alpha) and PGE(2) after AA was twice that in control rats. Renal cortical COX-2 expression in diabetic rats was 3-fold that of control rats. Tempol treatment reduced the AA-stimulated release of prostaglandins to levels seen in control rats; this was associated with reduced expression of COX-2 protein to levels not different from that in control rats. However, the enhanced vasoconstrictor response to AA in diabetic rats was unaffected by tempol treatment but abolished by inhibition of COX-1 with SC58560 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole]. The addition of tempol to the perfusate of kidneys from diabetic and control rats had only a slight effect on prostaglandin release. We conclude that oxidative stress is an integral component of the mechanism involved in the induction of renal COX-2 in diabetes.

Cyclooxygenase-2 and an early stage of chronic hypoxia-induced pulmonary hypertension in newborn pigs

Our objective was to determine whether cyclooxygenase (COX)-2-dependent metabolites contribute to the altered pulmonary vascular responses that manifest in piglets with chronic hypoxia-induced pulmonary hypertension. Piglets were raised in either room air (control) or hypoxia for 3 days. The effect of the COX-2 selective inhibitor NS-398 on responses to arachidonic acid or acetylcholine (ACh) was measured in endothelium-intact and denuded pulmonary arteries (100- to 400-microm diameter). Pulmonary arterial production of the stable metabolites of thromboxane and prostacyclin was assessed in the presence and absence of NS-398. Dilation to arachidonic acid was greater for intact control than for intact hypoxic arteries, was unchanged by NS-398 in intact arteries of either group, and was augmented by NS-398 in denuded hypoxic arteries. ACh responses, which were dilation in intact control arteries but constriction in intact and denuded hypoxic arteries, were diminished by NS-398 treatment of all arteries. NS-398 reduced prostacyclin production by control pulmonary arteries and reduced thromboxane production by hypoxic pulmonary arteries. COX-2-dependent contracting factors, such as thromboxane, contribute to aberrant pulmonary arterial responses in piglets exposed to 3 days of hypoxia.

Effects of exercise training on the vascular reactivity of the whole kidney circulation in rabbits

Exercise training is known to improve vasodilating mechanisms mediated by endothelium-dependent relaxing factors in the cardiac and skeletal muscle vascular beds. However, the effects of exercise training on visceral vascular reactivity, including the renal circulation, are still unclear. We used the experimental model of the isolated perfused rabbit kidney, which involves both the renal macro- and microcirculation, to test the hypothesis that exercise training improves vasodilator mechanisms in the entire renal circulation. New Zealand White rabbits were pen confined (Sed; n = 24) or treadmill trained (0% grade) for 5 days/wk at a speed of 18 m/min during 60 min over a 12-wk period (ExT; n = 24). Kidneys isolated from Sed and ExT rabbits were continuously perfused in a nonrecirculating system under conditions of constant flow and precontracted with norepinephrine (NE). We assessed the effects of exercise training on renal vascular reactivity using endothelial-dependent [acetylcholine (ACh) and bradykinin (BK)] and -independent [sodium nitroprusside (SNP)] vasodilators. ACh induced marked and dose-related vasodilator responses in kidneys from Sed rabbits, the reduction in perfusion pressure reaching 41 ± 8% ( n = 6; P < 0.05). In the kidneys from ExT rabbits, vasodilation induced by ACh was significantly enhanced to 54 ± 6% ( n = 6; P < 0.05). In contrast, BK-induced renal vasodilation was not enhanced by training [19 ± 8 and 13 ± 4% reduction in perfusion pressure for Sed and ExT rabbits, respectively ( n = 6; P > 0.05)]. Continuous perfusion of isolated kidneys from ExT animals with Nω-nitro-l-arginine methyl ester (l-NAME; 300 μM), an inhibitor of nitric oxide (NO) biosynthesis, completely blunted the additional vasodilation elicited by ACh [reduction in perfusion pressure of 54 ± 6 and 38 ± 5% for ExT and l-NAME + ExT, respectively ( n = 6; P < 0.05)]. On the other hand, l-NAME infusion did not affect ACh-induced vasodilation in Sed animals. Exercise training also increased renal vasodilation induced by SNP [36 ± 7 and 45 ± 10% reduction in perfusion pressure for Sed and ExT rabbits, respectively ( n = 6; P < 0.05)]. It is concluded that exercise training alters the rabbit kidney vascular reactivity, enhancing endothelium-dependent and -independent renal vasodilation. This effect seems to be related not only to an increased bioavailability of NO but also to the enhanced responsiveness of the renal vascular smooth muscle to NO.