Cilostazol improves endothelial dysfunction by increasing endothelium-derived hyperpolarizing factor response in mesenteric arteries from Type 2 diabetic rats

Cilostazol Ameliorates Peripheral Neuropathic Pain in Streptozotocin-Induced Type I Diabetic Rats

Background: Cilostazol is an antiplatelet agent with vasodilating, endothelial function restoration, and anti-inflammatory effects. This study aims to investigate the efficacy of oral cilostazol for preventing the development of diabetic peripheral neuropathy (DPN).

Materials and Methods: Ninety adult male Sprague-Dawley rats were divided into five groups: 1) naïve (control); 2) diabetic (DM); 3) DM receiving 10 mg/kg cilostazol (cilo-10); 4) DM receiving 30 mg/kg cilostazol (cilo-30); and 5) DM receiving 100 mg/kg cilostazol (cilo-100). Hindpaw responses to thermal and mechanical stimuli were measured. Activation of microglia and astrocytes in the spinal dorsal horn (SDH) and expression of NaVs in the dorsal root ganglia (DRG) were examined with Western blots and immunofluorescence.

Results: DM rats displayed decreased withdrawal thresholds to mechanical stimuli (mechanical allodynia) and blunted responses to thermal stimuli. In addition, the expression of microglia increased, but astrocytes were reduced in the SDH. Upregulation of Nav −1.1, 1.2, −1.3, −1.6, and −1.7 and downregulation of Nav-1.8 were observed in the DRG. The DM rats receiving cilostazol all returned DM-induced decrease in withdrawal threshold to mechanical stimuli and attenuated neuropathic pain. Additionally, all cilostazol treatments suppressed the level of activated microglial cells and ameliorated the DM-induced decline in astrocyte expression levels in the SDH. However, only the rats treated with cilo-100 demonstrated significant improvements to the aberrant NaV expression in the DRG.

Conclusion: Oral cilostazol can blunt the responses of mechanical allodynia and has the potential to treat diabetic neuropathy by attenuating NaV and glial cell dysregulation.

Update on Cilostazol: A Critical Review of Its Antithrombotic and Cardiovascular Actions and Its Clinical Applications

Cilostazol, a phosphodiesterase III inhibitor, has vasodilating and antiplatelet properties with a low rate of bleeding complications. It has been used over the past 25 years for improving intermittent claudication in patients with peripheral artery disease (PAD). Cilostazol also has demonstrated efficacy in patients undergoing percutaneous revascularization procedures for both PAD and coronary artery disease. In addition to its antithrombotic and vasodilating actions, cilostazol also inhibits vascular smooth muscle cell proliferation via phosphodiesterase III inhibition, thus mitigating restenosis. Accumulated evidence has shown that cilostazol, due to its "pleiotropic" effects, is a useful, albeit underutilized, agent for both coronary artery disease and PAD. It is also potentially useful after ischemic stroke and is an alternative in those who are allergic or intolerant to classical antithrombotic agents (eg, aspirin or clopidogrel). These issues are herein reviewed together with the pharmacology and pharmacodynamics of cilostazol. Large studies and meta-analyses are presented and evaluated. Current guidelines are also discussed, and the spectrum of cilostazol's actions and therapeutic applications are illustrated.

Phosphodiesterase-3 inhibitor cilostazol reverses endothelial dysfunction with ageing in rat mesenteric resistance arteries

Ageing impairs endothelial function, which is considered a hallmark of the development of cardiovascular diseases in elderly. Cilostazol, a phosphodiesterase-3 inhibitor, has antiplatelet, antithrombotic and protective effects on endothelial cells. Here, we hypothesized that cilostazol could improve endothelial function in mesenteric resistance arteries (MRA) from old rats. Using eight-week cilostazol-treated (100mg/kg/day) or untreated 72-week-old Wistar rats, we evaluate the relaxation to acetylcholine, sodium nitroprusside (SNP), forskolin and isoproterenol and the noradrenaline-induced contraction in MRA. Superoxide anion and nitric oxide (NO) was measured by dihydroethidium- and diaminofluorescein-2-emitted fluorescence, respectively. Normotensive old rats had impaired acetylcholine-induced NO- and EDHF-mediated relaxation and increased noradrenaline vasoconstriction than young rats. This age-associated endothelial dysfunction was restored by cilostazol treatment. Relaxation to SNP, forskolin or isoproterenol remained unmodified by cilostazol. Diaminofluorescein-2-emitted fluorescence was increased while dihydroethidium-emitted was decreased by cilostazol, indicating increased NO and reduced superoxide generation, respectively. Cilostazol improves endothelial function in old MRA without affecting blood pressure. This protective effect of cilostazol could be attributed to reduced oxidative stress, increased NO bioavailability and EDHF-type relaxation. Although these results are preliminary, we believe that should stimulate further interest in cilostazol as an alternative for the treatment of age-related vascular disorders.

Alterations of voltage-dependent K(+) channels in the mesenteric artery during the early and chronic phases of diabetes

This study investigated the alteration of voltage-dependent K(+) (Kv) channels in mesenteric arterial smooth muscle cells from control (Long-Evans Tokushima Otsuka [LETO]) and diabetic (Otsuka Long-Evans Tokushima Fatty [OLETF]) rats during the early and chronic phases of diabetes. We demonstrated alterations in the mesenteric Kv channels during the early and chronic phase of diabetes using the patch-clamp technique, the arterial tone measurement system, and RT-PCR in Long-Evans Tokushima (LETO; for control) and Otsuka Long-Evans Tokushima Fatty (OLETF; for diabetes) type 2 diabetic model rats. In the early phase of diabetes, the amplitude of mesenteric Kv currents induced by depolarizing pulses was greater in OLETF rats than in LETO rats. The contractile response of the mesenteric artery induced by the Kv inhibitor, 4-aminopyridine (4-AP), was also greater in OLETF rats. The expression of most Kv subtypes- including Kv1.1, Kv1.2, Kv1.4, Kv1.5, Kv1.6, Kv2.1, Kv3.2, Kv4.1, Kv4.3, Kv5.1, Kv6.2, Kv8.1, Kv9.3, and Kv10.1-were increased in mesenteric arterial smooth muscle from OLETF rats compared with LETO rats. However, in the chronic phase of diabetes, the Kv current amplitude did not differ between LETO and OLETF rats. In addition, the 4-AP-induced contractile response of the mesenteric artery and the expression of Kv subtypes did not differ between the two groups. The increased Kv current amplitude and Kv channel-related contractile response were attributable to the increase in Kv channel expression during the early phase of diabetes. The increased Kv current amplitude and Kv channel-related contractile response were reversed during the chronic phase of diabetes.

Bridging Type 2 Diabetes and Alzheimer's Disease: Assembling the Puzzle Pieces in the Quest for the Molecules With Therapeutic and Preventive Potential

Type 2 diabetes (T2D) and Alzheimer's disease (AD) are two age-related amyloid diseases that affect millions of people worldwide. Broadly supported by epidemiological data, the higher incidence of AD among type 2 diabetic patients led to the recognition of T2D as a tangible risk factor for the development of AD. Indeed, there is now growing evidence on brain structural and functional abnormalities arising from brain insulin resistance and deficiency, ultimately highlighting the need for new approaches capable of preventing the development of AD in type 2 diabetic patients. This review provides an update on overlapping pathophysiological mechanisms and pathways in T2D and AD, such as amyloidogenic events, oxidative stress, endothelial dysfunction, aberrant enzymatic activity, and even shared genetic background. These events will be presented as puzzle pieces put together, thus establishing potential therapeutic targets for drug discovery and development against T2D and diabetes-induced cognitive decline-a heavyweight contributor to the increasing incidence of dementia in developed countries. Hoping to pave the way in this direction, we will present some of the most promising and well-studied drug leads with potential against both pathologies, including their respective bioactivity reports, mechanisms of action, and structure-activity relationships.

Impaired endothelium-derived hyperpolarization-type relaxation in superior mesenteric arteries isolated from female Otsuka Long-Evans Tokushima Fatty rats

Endothelium-derived hyperpolarization (EDH) is an important signaling mechanism of endothelium-dependent vasorelaxation, and little attention has been paid to the EDH-type responses in female metabolic syndrome such as that observed with type-2 diabetes. We previously reported that EDH-type relaxation was impaired in superior mesenteric arteries from male Otsuka Long-Evans Tokushima Fatty (OLETF) rat, a model of type-2 diabetes, however, the response was unclear in female OLETF rat. Thus, the aim of this study was to examine if EDH-type relaxation was altered in superior mesenteric arteries isolated from female OLETF rats compared to age-matched, control female Long-Evans Tokushima Otsuka (LETO) rats at age 50-59 weeks. We investigated concentration-relaxation curves for acetylcholine (at age 50-53 weeks), NS309 (an activator of small- and intermediate-conductance calcium-activated potassium channels) (at age 50-53 weeks), and GSK1016790A (an agonist of transient receptor potential vanilloid type 4, TRPV4) (at age 58 or 59 weeks) in the presence of the nitric oxide synthase inhibitor N^G-nitro-L-arginine and the cyclooxygenase inhibitor indomethacin to investigate EDH-type responses in the superior mesenteric artery. Obesity, mild hyperglycemia, hyperinsulinemia, and hyperlipidemia (i.e., increased total cholesterol, triglyceride, and non-esterified fatty acids) were more frequent in OLETF rats than in age-matched LETO rats at age 50-53 weeks. Acetylcholine-, NS309-, and GSK1016790A-induced relaxations in arteries from OLETF rats were all significantly reduced compared to those in LETO rats. These results indicated that EDH-type relaxations were impaired in female OLETF rats. This novel experimental model may provide new insights into vascular dysfunction in metabolic syndrome in females.

The Protective Effect of Antioxidants Consumption on Diabetes and Vascular Complications

Obesity and diabetes is generally accompanied by a chronic state of oxidative stress, disequilibrium in the redox balance, implicated in the development and progression of complications such as micro- and macro-angiopathies. Disorders in the inner layer of blood vessels, the endothelium, play an early and critical role in the development of these complications. Blunted endothelium-dependent relaxation and/or contractions are quietly associated to oxidative stress. Thus, preserving endothelial function and oxidative stress seems to be an optimization strategy in the prevention of vascular complications associated with diabetes. Diet is a major lifestyle factor that can greatly influence the incidence and the progression of type 2 diabetes and cardiovascular complications. The notion that foods not only provide basic nutrition but can also prevent diseases and ensure good health and longevity is now attained greater prominence. Some dietary and lifestyle modifications associated to antioxidative supply could be an effective prophylactic means to fight against oxidative stress in diabesity and complications. A significant benefit of phytochemicals (polyphenols in wine, grape, teas), vitamins (ascorbate, tocopherol), minerals (selenium, magnesium), and fruits and vegetables in foods is thought to be capable of scavenging free radicals, lowering the incidence of chronic diseases. In this review, we discuss the role of oxidative stress in diabetes and complications, highlight the endothelial dysfunction, and examine the impact of antioxidant foods, plants, fruits, and vegetables, currently used medication with antioxidant properties, in relation to the development and progression of diabetes and cardiovascular complications.

Cerebral hypoperfusion and glucose hypometabolism: Key pathophysiological modulators promote neurodegeneration, cognitive impairment, and Alzheimer's disease

Aging, hypertension, diabetes, hypoxia/obstructive sleep apnea (OSA), obesity, vitamin B12/folate deficiency, depression, and traumatic brain injury synergistically promote diverse pathological mechanisms including cerebral hypoperfusion and glucose hypometabolism. These risk factors trigger neuroinflammation and oxidative-nitrosative stress that in turn decrease nitric oxide and enhance endothelin, Amyloid-β deposition, cerebral amyloid angiopathy, and blood-brain barrier disruption. Proinflammatory cytokines, endothelin-1, and oxidative-nitrosative stress trigger several pathological feedforward and feedback loops. These upstream factors persist in the brain for decades, upregulating amyloid and tau, before the cognitive decline. These cascades lead to neuronal Ca²⁺ increase, neurodegeneration, cognitive/memory decline, and Alzheimer's disease (AD). However, strategies are available to attenuate cerebral hypoperfusion and glucose hypometabolism and ameliorate cognitive decline. AD is the leading cause of dementia among the elderly. There is significant evidence that pathways involving inflammation and oxidative-nitrosative stress (ONS) play a key pathophysiological role in promoting cognitive dysfunction. Aging and several comorbid conditions mentioned above promote diverse pathologies. These include inflammation, ONS, hypoperfusion, and hypometabolism in the brain. In AD, chronic cerebral hypoperfusion and glucose hypometabolism precede decades before the cognitive decline. These comorbid disease conditions may share and synergistically activate these pathophysiological pathways. Inflammation upregulates cerebrovascular pathology through proinflammatory cytokines, endothelin-1, and nitric oxide (NO). Inflammation-triggered ONS promotes long-term damage involving fatty acids, proteins, DNA, and mitochondria; these amplify and perpetuate several feedforward and feedback pathological loops. The latter includes dysfunctional energy metabolism (compromised mitochondrial ATP production), amyloid-β generation, endothelial dysfunction, and blood-brain-barrier disruption. These lead to decreased cerebral blood flow and chronic cerebral hypoperfusion- that would modulate metabolic dysfunction and neurodegeneration. In essence, hypoperfusion deprives the brain from its two paramount trophic substances, viz., oxygen and nutrients. Consequently, the brain suffers from synaptic dysfunction and neuronal degeneration/loss, leading to both gray and white matter atrophy, cognitive dysfunction, and AD. This Review underscores the importance of treating the above-mentioned comorbid disease conditions to attenuate inflammation and ONS and ameliorate decreased cerebral blood flow and hypometabolism. Additionally, several strategies are described here to control chronic hypoperfusion of the brain and enhance cognition. © 2016 Wiley Periodicals, Inc.

Efficacy of cilostazol on uncontrolled coronary vasospastic angina: a pilot study

BACKGROUND

Although an angina attack by vasospastic angina (VSA) can usually be relieved or controlled with nitrates and calcium channel blockers (CCBs), there are some patients who cannot be controlled even by higher doses and combinations of these drugs. Cilostazol is a selective inhibitor of phosphodiesterase 3 that increases intracellular cyclic adenosine monophosphate (cAMP) contents. A stimulation of cAMP signal transduction increases coronary nitric oxide production. We examined whether cilostazol improved angina symptoms in patients with VSA uncontrolled by conventional treatment.

METHODS

This study was conducted in a prospective, multicenter, nonrandomized manner. The subject consisted of 21 patients (13 men, 57 ± 9 year-old) who were diagnosed with VSA and had at least two angina attacks during the past 1 week despite of conventional medications such as CCBs and/or nitrates. They took cilostazol 100 mg twice daily for 2 weeks in addition to the conventional medications. The patients recorded the frequency of angina attack and wrote down the numeric rating scale of a "severity of angina attack" while taking conventional medications and cilostazol for 2 weeks, and also recorded an averaged scale or total number of event during the last week at the time of the assessment. Using the Wilcoxon rank-sum test, we compared the changes in the scores of frequency and severity of angina attack before and after adding cilostazol to the conventional medications.

RESULTS

After adding cilostazol to the conventional medications, there were 78.9% relative reduction of the score of angina intensity and 73.5% of angina frequency (P < 0.001). There were four patients (19%) who were forced to stop cilostazol due to headache as an adverse event.

CONCLUSIONS

Cilostazol appears to be an effective therapy in VSA uncontrolled with conventional medical treatment. A further prospective, randomized, placebo-controlled study will be needed to validate this result.

Effect of cilostazol in the treatment of acute ischemic stroke in the lenticulostriate artery territory

BACKGROUND

Cilostazol, an inhibitor of phosphodiesterase 3, has various pleiotropic effects besides its antiplatelet activity. This study examined the efficacy of cilostazol for the treatment of acute perforating artery infarction.

METHODS

In this prospective, randomized, open-label, blinded-end point trial, 100 patients with cerebral infarction in the territory of the lenticulostriate arteries were enrolled within 48 h of onset. Patients were randomly treated with both cilostazol and ozagrel for 14 days (n = 50, cilostazol group) or ozagrel alone for 14 days (n = 50, control group). The primary end point was the proportion of favorable outcomes 30 days after randomization as defined by a modified Rankin Scale (mRS) score of 0-2. Secondary end points included the incidence of neurological deterioration (an increase of ≥ 2 on the National Institutes of Health Stroke Scale within 7 days).

RESULTS

Favorable outcomes (mRS scores 0-2) were similar in both groups (81.3 and 82.0% in the cilostazol and control groups, respectively). The incidence of neurological deterioration was lower in the cilostazol group than the control group (12.5 and 16.0%, respectively) with a 21.9% relative risk reduction, although the difference was not statistically significant.

CONCLUSIONS

Cilostazol did not prevent the neurological deterioration of perforating artery infarction.

Aminoguanidine normalizes ET-1-induced aortic contraction in type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats by suppressing Jab1-mediated increase in ET(A)-receptor expression

Circulating levels of endothelin (ET)-1 are increased in the diabetic state, as is endogenous ET(A)-receptor-mediated vasoconstriction. However, the responsible mechanisms remain unknown. We hypothesized that ET-1-induced vasoconstriction is augmented in type 2 diabetes with hyperglycemia through an increment in advanced glycation end-products (AGEs). So, we investigated whether treatment with aminoguanidine (AG), an inhibitor of AGEs, would normalize the ET-1-induced contraction induced by ET-1 in strips of thoracic aortas isolated from OLETF rats at the chronic stage of diabetes. In such aortas (vs. those from age-matched genetic control LETO rats): (1) the ET-1-induced contraction was enhanced, (2) the levels of HIF1α/ECE1/plasma ET-1 and plasma CML-AGEs were increased, (3) the ET-1-stimulated ERK phosphorylation mediated by ET(A)-R was increased, (4) the expression level of Jab1-modified ET(A)-R protein was reduced, and (5) the expression level of O-GlcNAcylated ET(A)-R protein was increased. Aortas isolated from such OLETF rats that had been treated with AG (50mg/kg/day for 10 weeks) exhibited reduced ET-1-induced contraction, suppressed ET-1-stimulated ERK phosphorylation accompanied by down-regulation of ET(A)-R, and increased modification of ET(A)-R by Jab1. Such AG-treated rats exhibited normalized plasma ET-1 and CML-AGE levels, and their aortas exhibited decreased HIF1α/ECE1 expression. However, such AG treatment did not alter the elevated levels of plasma glucose or insulin, or systolic blood pressure seen in OLETF rats. These data from the OLETF model suggest that within the timescale studied here, AG normalizes ET-1-induced aortic contraction by suppressing ET(A)-R/ERK activities and/or by normalizing the imbalance between Jab1 and O-GlcNAc in type 2 diabetes.

Endothelium-derived hyperpolarizing factor and diabetes

In addition to its role as a barrier between blood and tissues, the vascular endothelium is responsible for the synthesis and released of a number of vasodilators including prostaglandins, nitric oxide and endothelium-derived hyperpolarizing factor (EDHF). As one of these vasodilators, the specific nature of EDHF has not been fully elucidated, although a number of roles have been proposed. Importantly, many conditions, such as hypertension, hyperlipidemia, heart failure, ischemia-reperfusion and diabetes mellitus comprise vascular endothelial dysfunction with EDHF dysregulation. This article reviews reports on the role of EDHF in diabetes-related endothelial dysfunction.

[Therapeutic target for endothelium-derived hyperpolarizing factor signaling in diabetic vascular complication]

Vascular tone is tightly regulated by endothelium-derived factors. These include relaxing factors (EDRFs) such as nitric oxide (NO), hyperpolarizing factors (EDHFs), and contracting factors (EDCFs). Although EDHF is a prominent vasodilator, particularly in smaller arteries, little attention has been paid to the potential role of EDHF responses in diabetes. EDHF signaling may involve various factors, including several diffusible factors and non-diffusible factors (e.g., gap junctions). It has been demonstrated that the alterations in EDHF relaxation seen in mesenteric arteries from diabetic rats may be attributable to an increase in phosphodiesterase 3 (PDE3) activity, leading to a reduction in the action of adenosine 3',5'-cyclic monophosphate (cAMP), and consequently the activity of protein kinase A (PKA) is decreased in such arteries. Moreover, it has been suggested that the imbalance between EDRFs and EDCFs is present in mesenteric arteries from type 2 diabetic rats and the EDHF relaxation can be partly reversed by suppression of EDCF signaling. Indeed, chronic treatment with metformin, eicosapentaenoic acid, or thromboxane synthase inhibitor can reduce EDCF signaling and normalize EDHF signaling in mesenteric arteries from type 2 diabetic rats. Although the improvement or restoration of EDHF responses has not been the direct subject of any pharmaceutical effort, increasing cAMP/PKA signaling (e.g., by inhibiting PDE3 activity) or reducing EDCFs signaling has potential as an interesting therapeutic target in diabetic vasculopathy.

Mechanisms underlying the losartan treatment-induced improvement in the endothelial dysfunction seen in mesenteric arteries from type 2 diabetic rats

It is well known that type 2 diabetes mellitus is frequently associated with vascular dysfunction and an elevated systemic blood pressure, yet the underlying mechanisms are not completely understood. We previously reported that in mesenteric arteries from established type 2 diabetic Otsuka Long-Evans Tokushima fatty (OLETF) rats, which exhibit endothelial dysfunction, there is an imbalance between endothelium-derived vasodilators [namely, nitric oxide (NO) and hyperpolarizing factor (EDHF)] and vasoconstrictors [contracting factors (EDCFs) such as cyclooxygenase (COX)-derived prostanoids]. Here, we investigated whether the angiotensin II receptor antagonist losartan might improve endothelial dysfunction in OLETF rats at the established stage of diabetes. In mesenteric arteries isolated from OLETF rats [vs. those from age-matched control Long-Evans Tokushima Otsuka (LETO) rats]: (1) the acetylcholine (ACh)-induced relaxation was impaired, (2) the NO- and EDHF-mediated relaxations were reduced, (3) the ACh-induced EDCF-mediated contraction and the production of prostanoids were increased, and (4) superoxide generation was increased. After such OLETF rats had received losartan (25 mg/kg/day p.o. for 4 weeks), their isolated mesenteric arteries exhibited: (1) improvements in ACh-induced NO- and EDHF-mediated relaxations, (2) reduced EDCF- and arachidonic acid-induced contractions, (3) suppressed production of prostanoids, (4) reduced PGE(2)-mediated contraction, and (5) reduced superoxide generation. Within the timescale studied here, losartan did not change the protein expressions of endothelial NO synthase, COX1, or COX2 in mesenteric arteries from either OLETF or LETO rats. Losartan thus normalizes vascular dysfunction in this type 2 diabetic model, and the above effects may contribute to the reduction of adverse cardiovascular events seen in diabetic patients treated with angiotensin II receptor blockers.

Intrinsic sex-specific differences in microvascular endothelial cell phosphodiesterases

The importance of gonadal hormones in the regulation of vascular function has been documented. An alternate and essential contribution of the sex chromosomes to sex differences in vascular function is poorly understood. We reported previously sex differences in microvessel permeability (P(s)) responses to adenosine that were mediated by the cAMP signaling pathway (Wang J, PhD thesis, 2005; Wang J and Huxley V, Proceedings of the VIII World Congress of Microcirculation, 2007; Wang J and Huxley VH, Am J Physiol Heart Circ Physiol 291: H3094-H3105, 2006). The two cyclic nucleotides, cAMP and cGMP, central to the regulation of vascular barrier integrity, are hydrolyzed by phosphodiesterases (PDE). We hypothesized that microvascular endothelial cells (EC) would retain intrinsic and inheritable sexually dimorphic genes with respect to the PDEs modulating EC barrier function. Primary cultured microvascular EC from skeletal muscles isolated from male and female rats, respectively, were used. SRY (a sex-determining region Y gene) mRNA expression was observed exclusively in male, not female, cells. The predominant isoform among PDE1-5, present in both XY and XX EC, was PDE4. Expression mRNA levels of PDE1A (male > female) and PDE3B (male < female) were sex dependent; PDE2A, PDE4D, and PDE5A were sex independent. Barrier function, P(s), was determined from measures of albumin flux across confluent primary cultured microvessel XY and XX EC monolayers. Consistent with intact in situ microvessels, basal monolayer P(s) did not differ between XY (1.7 +/- 0.2 x 10(-6) cm/s; n = 8) and XX (1.8 +/- 0.1 x 10(-6) cm/s; n = 10) EC. Cilostazol, a PDE3 inhibitor, reduced (11%, P < 0.05) P(s) in XX, not XY, cells. These findings demonstrate the presence and maintenance of intrinsic sex-related differences in gene expression and cellular phenotype by microvascular EC in a gonadal-hormone-free environment. Furthermore, intrinsic cell-sex likely contributes significantly to sexual dimorphism in cardiovascular function.