Measuring treatment effects of cilostazol on clinical trial endpoints in patients with intermittent claudication

Approaches for Increasing Cerebral Efflux of Amyloid-β in Experimental Systems

Amyloid protein-β (Aβ) concentrations are increased in the brain in both early onset and late onset Alzheimer's disease (AD). In early onset AD, cerebral Aβ production is increased and its clearance is decreased, while increased Aβ burden in late onset AD is due to impaired clearance. Aβ has been the focus of AD therapeutics since development of the amyloid hypothesis, but efforts to slow AD progression by lowering brain Aβ failed until phase 3 trials with the monoclonal antibodies lecanemab and donanemab. In addition to promoting phagocytic clearance of Aβ, antibodies lower cerebral Aβ by efflux of Aβ-antibody complexes across the capillary endothelia, dissolving Aβ aggregates, and a "peripheral sink" mechanism. Although the blood-brain barrier is the main route by which soluble Aβ leaves the brain (facilitated by low-density lipoprotein receptor-related protein-1 and ATP-binding cassette sub-family B member 1), Aβ can also be removed via the blood-cerebrospinal fluid barrier, glymphatic drainage, and intramural periarterial drainage. This review discusses experimental approaches to increase cerebral Aβ efflux via these mechanisms, clinical applications of these approaches, and findings in clinical trials with these approaches in patients with AD or mild cognitive impairment. Based on negative findings in clinical trials with previous approaches targeting monomeric Aβ, increasing the cerebral efflux of soluble Aβ is unlikely to slow AD progression if used as monotherapy. But if used as an adjunct to treatment with lecanemab or donanemab, this approach might allow greater slowing of AD progression than treatment with either antibody alone.

Phosphodiesterase in heart and vessels: from physiology to diseases

Phosphodiesterases (PDEs) are a superfamily of enzymes that hydrolyze cyclic nucleotides, including cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Both cyclic nucleotides are critical secondary messengers in the neurohormonal regulation in the cardiovascular system. PDEs precisely control spatiotemporal subcellular distribution of cyclic nucleotides in a cell- and tissue-specific manner, playing critical roles in physiological responses to hormone stimulation in the heart and vessels. Dysregulation of PDEs has been linked to the development of several cardiovascular diseases, such as hypertension, aneurysm, atherosclerosis, arrhythmia, and heart failure. Targeting these enzymes has been proven effective in treating cardiovascular diseases and is an attractive and promising strategy for the development of new drugs. In this review, we discuss the current understanding of the complex regulation of PDE isoforms in cardiovascular function, highlighting the divergent and even opposing roles of PDE isoforms in different pathogenesis.

Cilostazol does not improve peripheral arterial disease-linked oxidative stress

AIM

Cilostazol is a drug widely used to treat peripheral arterial disease (PAD) in patients with advanced atherosclerosis. It is an inhibitor of platelet aggregation and causes arterial vasodilatation. It has been speculated that cilostazol might act to improve oxidative stress in these patients.

METHODS

We analyzed 25 patients with demonstrated lower limb peripheral arterial disease to determine whether lipid peroxidation (LPO) or total antioxidant capacity (TAC) were modified after 6 months of cilostazol treatment (postintervention phase) with respect to the basal phase.

RESULTS

Analysis of plasma samples determined that LPO levels decreased significantly over the postintervention phase (26±15 vs. 11±7 pM, P=0.0003). However, when TAC levels were analyzed, no significant differences were observed (0.80±0.21 vs. 0.85±0.17 mM, P=0.42). Under basal conditions, LPO showed a positive correlation to treatment as judged by the ankle-brachial index (r=0.800, P=0.002) as well as uric acid (r=0.508, P=0.03) and CRP (r=0.481, P=0.05) levels. In contrast, TAC negatively correlated with triglycerides (r=-0.879, P<0.0001) and microalbuminuria (r=-0.868, P<0.0001). In the postintervention phase, TAC negatively correlated with HbA1c (r=-0.570, P=0.02) and triglycerides (r=-0.864, P<0.0001).

CONCLUSIONS

Our data indicate that cilostazol treatment does not improve oxidative stress in PAD patients after 6 months of treatment. However, lipid peroxidation and total antioxidant capacity were affected by cilostrazol treatment, which could be related to altered reactive oxygen species production. Further research may be needed to determine the critical dose of cilostazol to clarify the protective role of this drug in PAD.

Phosphodiesterase III inhibition increases cAMP levels and augments the infarct size limiting effect of a DPP-4 inhibitor in mice with type-2 diabetes mellitus

PURPOSE

We assessed whether phosphodiesterase-III inhibition with cilostazol (Cil) augments the infarct size (IS)-limiting effects of MK0626 (MK), a dipeptidyl-peptidase-4 (DPP4) inhibitor, by increasing intracellular cAMP in mice with type-2 diabetes.

METHODS

Db/Db mice received 3-day MK (0, 1, 2 or 3 mg/kg/d) with or without Cil (15 mg/kg/d) by oral gavage and were subjected to 30 min coronary artery occlusion and 24 h reperfusion.

RESULTS

Cil and MK at 2 and 3 mg/kg/d significantly reduced IS. Cil and MK had additive effects at all three MK doses. IS was the smallest in the MK-3+Cil. MK in a dose dependent manner and Cil increased cAMP levels (p < 0.001). cAMP levels were higher in the combination groups at all MK doses. MK-2 and Cil increased PKA activity when given alone; however, PKA activity was significantly higher in the MK-2+Cil group than in the other groups. Both MK-2 and Cil increased myocardial levels of Ser(133) P-CREB, Ser(523) P-5-lipoxygenase, Ser(473)P-Akt and Ser(633) P-eNOS. These levels were significantly higher in the MK-2+Cil group. Myocardial PTEN (Phosphatase and tensin homolog on chromosome ten) levels were significantly higher in the Db/Db mice compared to nondiabetic mice. MK-2 and Cil normalized PTEN levels. PTEN levels tended to be lower in the combination group than in the MK and Cil alone groups.

CONCLUSION

MK and Cil have additive IS-limiting effects in diabetic mice. The additive effects are associated with an increase in myocardial cAMP levels and PKA activity with downstream phosphorylation of Akt, eNOS, 5-lipoxygenase and CREB and downregulation of PTEN expression.

A scientific rationale for the CREST trial results: evidence for the mechanism of action of cilostazol in restenosis

The Cilostazol for RESTenosis (CREST) clinical trial was initiated to evaluate the efficacy of cilostazol, an antiplatelet drug, in inhibiting restenosis after stent implantation in a native coronary artery as evaluated by quantitative coronary angiography. Preliminary results suggest that cilostazol reduces restenosis by 36% over standard therapy alone. Restenosis after coronary stenting is primarily attributed to neointimal formation. Cilostazol decreases the activity of phosphodiesterase type 3, leading to the accumulation of cyclic adenosine monophosphate, which initiates a cascade of events including upregulation of anti-oncogenes p53 and p21 and upregulation of hepatocyte growth factor (HGF). The increase in p53 protein blocks cell cycle progression and induces apoptosis in vascular smooth muscle cells (VSMCs), leading to an antiproliferative effect. Upregulation of local HGF stimulates rapid regeneration of endothelial cells, which inhibits neointimal formation via two mechanisms: inhibition of abnormal VSMC growth and improvement of endothelial function. These mechanisms may be responsible for the improvement in restenosis shown in the CREST trial and a number of other trials in patients who underwent percutaneous transluminal coronary angioplasty. These effects, in addition to antithrombotic and vasodilatory attributes of cilostazol, make it a potentially viable treatment option for preventing restenosis following coronary stenting.

Optimising Exercise Training in Peripheral Arterial Disease

Peripheral arterial disease (PAD) is an obstructive condition where the flow of blood through peripheral arteries is impeded. During periods of increased oxygen demand (e.g. during exercise), peripheral limb ischaemia occurs, resulting in the sensation of muscle pain termed 'claudication'. As a result of claudication, subjects' ability to exercise is greatly reduced affecting their quality of life. Although many treatment options for patients with PAD exist, exercise training is an effective and low-cost means of improving functional ability and quality of life. Currently, there are limited specific recommendations to assist the exercise prescription and programming of these individuals. This review summarises data from 28 exercise training studies conducted in patients with PAD and formulates recommendations based on their results. Exercise training for patients with PAD should involve three training sessions per week comprising 45 minutes of intermittent treadmill walking in a supervised environment for a time period of 20 weeks or more. Encouragement and direction is given to further research aimed at investigating the effectiveness of training programmes in these patients.

Role of phosphodiesterase 3 in NO/cGMP-mediated antiinflammatory effects in vascular smooth muscle cells

Atherosclerosis involves cellular immune responses and altered vascular smooth muscle cell (VSMC) function. Nitric oxide (NO)/cGMP is uniquely capable of inhibiting key processes in atherosclerosis. In this study, we determined the effects of NO/cGMP and their molecular mechanisms in the regulation of NF-kappaB-dependent gene expression in VSMCs. We found that cGMP-elevating agents such as the NO donor S-nitroso-N-acetylpenicillamine (SNAP) and C-type natriuretic peptide (CNP), reduced TNF-alpha-induced NF-kappaB-dependent reporter gene expression in rat aortic VSMCs in a cGMP-dependent manner. The effects of SNAP and CNP on NF-kappaB are mediated by cAMP-dependent protein kinase (PKA) but not cGMP-dependent protein kinase (PKG) based on the findings that the selective PKA inhibitor, PKI, abolished the effects of SNAP and CNP on NF-kappaB, whereas the PKG inhibitor Rp-8-Br-PET-cGMP had no effect. Inhibition of cGMP-inhibited cAMP-hydrolyzing phosphodiesterase 3 (PDE3) blocked SNAP- and CNP-elicited effects on NF-kappaB-dependent transcription. Furthermore, cGMP analogues such as 8-pCPT-cGMP, which selectively activates PKG but does not inhibit PDE3, had no effect on NF-kappaB-mediated transcription. Activation of PKA by SNAP or cAMP-elevating agents not only inhibited TNF-alpha-induced NF-kappaB-dependent reporter gene expression but also reduced endogenous NF-kappaB-dependent adhesion molecule and chemokine expression. These results suggest that SNAP and CNP exert inhibitory effects on NF-kappaB-dependent transcription by activation of PKA via cGMP-dependent inhibition of PDE3 activity. Therefore, PDE3 is a novel mediator of inflammation in VSMCs.