Effects of cilostazol, an antiplatelet agent, on axonal regeneration following nerve injury in 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.

Cilostazol is an effective causal therapy for preventing paclitaxel-induced peripheral neuropathy by suppression of Schwann cell dedifferentiation

Chemotherapy-induced peripheral neuropathy (CIPN) can lead to discontinuation of chemotherapy and is consequently a serious impediment to effective cancer treatment. Due to our limited understanding of mechanisms underlying the pathogenesis of CIPN, no causal therapy has been approved for relief of this condition. We previously demonstrated that taxanes (paclitaxel and docetaxel) induce Schwann cell dedifferentiation, characterized by increased expression of p75 and galectin-3, ultimately leading to demyelination. These changes appear to be responsible for CIPN pathogenesis. This study was designed to identify a novel candidate therapeutic for CIPN with the ability to suppress paclitaxel-induced Schwann cell dedifferentiation. Given that elevation of cyclic adenosine monophosphate (cAMP) signaling participates in Schwann cell differentiation, we performed immunocytochemical screening of phosphodiesterase (PDE) inhibitors. We found that the PDE3 inhibitor cilostazol strongly promoted differentiation of primary cultures of rat Schwann cells via a mechanism involving cAMP/exchange protein directly activated by cAMP (Epac) signaling. Co-treatment with cilostazol prevented paclitaxel-induced dedifferentiation of Schwann cell cultures and demyelination in a mixed culture of Schwann cells and dorsal root ganglia neurons. Notably, continuous oral administration of cilostazol suppressed Schwann cell dedifferentiation within the sciatic nerve and the development of mechanical hypersensitivity in a mouse model of paclitaxel-related CIPN. Importantly, cilostazol potentiated, rather than inhibited, the anti-cancer effect of paclitaxel on the human breast cancer cell line MDA-MB-231. These findings highlight the potential utility of cilostazol as a causal therapeutic that avoids the development of paclitaxel-related CIPN without compromising anti-cancer properties.

Regeneration of diabetic axons is enhanced by selective knockdown of the PTEN gene

Diabetes mellitus renders both widespread and localized irreversible damage to peripheral axons while imposing critical limitations on their ability to regenerate. A major failure of regenerative capacity thereby imposes a 'double hit' in diabetic patients who frequently develop focal neuropathies such as carpal tunnel syndrome in addition to generalized diffuse polyneuropathy. The mechanisms of diabetic neuron regenerative failure have been speculative and few approaches have offered therapeutic opportunities. In this work we identify an unexpected but major role for PTEN upregulation in diabetic peripheral neurons in attenuating axon regrowth. In chronic diabetic neuropathy models in mice, we identified significant PTEN upregulation in peripheral sensory neurons of messenger RNA and protein compared to littermate controls. In vitro, sensory neurons from these mice responded to PTEN knockdown with substantial rises in neurite outgrowth and branching. To test regenerative plasticity in a chronic diabetic model with established neuropathy, we superimposed an additional focal sciatic nerve crush injury and assessed morphological, electrophysiological and behavioural recovery. Knockdown of PTEN in dorsal root ganglia ipsilateral to the side of injury was achieved using a unique form of non-viral short interfering RNA delivery to the ipsilateral nerve injury site and paw. In comparison with scrambled sequence control short interfering RNA, PTEN short interfering RNA improved several facets of regeneration: recovery of compound muscle action potentials, reflecting numbers of reconnected motor axons to endplates, conduction velocities of both motor and sensory axons, reflecting their maturation during regrowth, numbers and calibre of regenerating myelinated axons distal to the injury site, reinnervation of the skin by unmyelinated epidermal axons and recovery of mechanical sensation. Collectively, these findings identify a novel therapeutic approach, potentially applicable to other neurological conditions requiring specific forms of molecular knockdown, and also identify a unique target, PTEN, to treat diabetic neuroregenerative failure.

Cilostazol in Diabetic Neuropathy

Peripheral neuropathy remains a major chronic complication of diabetes mellitus. Its pathogenesis mainly involves chronic glucose toxicity and nerve ischemia. Preclinical studies have shown that cilostazol, a reversible selective inhibitor of phosphodiesterase-3A with antiplatelet, antithrombotic, and vasodilatory properties, exerts beneficial effects on nerve function in experimental diabetes. Clinical data, however, is sparse. Two recent randomized placebo-controlled clinical trials showed that cilostazol did not improve diabetic neuropathy in humans. Hence, more data is needed to confirm or refute the poor clinical efficacy of cilostazol. Importantly, future studies should include larger patient series, provide longer follow-up data, and employ more accurate diagnostic tools.

Cilostazol: a pilot study on safety and clinical efficacy in neuropathies of diabetes mellitus type 2 (ASCEND)

BACKGROUND

Diabetic polyneuropathy may have vascular and metabolic components in its pathophysiologic mechanism. Cilostazol, aside from its antiplatelet and vasodilatory properties, may increase nerve blood flow and potentially improve neuropathy.

OBJECTIVE

To assess the efficacy and safety of cilostazol in diabetic polyneuropathy.

METHODS

Forty-seven diabetic patients were randomized into placebo, low-dose (100 mg/d), and high-dose (200 mg/d) cilostazol groups. Primary efficacy parameter was a change in neuropathy symptom scores and secondary efficacy parameter was a change in walking speed from baseline to week 12. Safety parameters were changes in nerve conduction studies as well as reporting of adverse events.

RESULTS/CONCLUSION

Despite significant improvement in the neuropathy symptom scores in the overall motor and sensory categories of the 3 arms of the study from baseline to week 12, no significant differences were found among the groups, indicating nonsuperiority of cilostazol in regard to improvement of neuropathy symptoms over the short study span. However, cilostazol, at low dose, was effective in improving walking speed from baseline to week 12, implying an improved blood flow. No significant worsening nor improvement in motor and sensory nerve conduction parameters were observed, comparing the 3 study arms from baseline to weeks 4, 12, and 16, supporting cilostazol's safety. Overall, the adverse events of the 3 study arms did not significantly differ, and neither were there serious adverse events reported, also signifying safety and tolerability in our Filipino cohort of patients with neuropathy in diabetes mellitus treated with cilostazol.

The Vascular and Biochemical Effects of Cilostazol in Diabetic Patients With Peripheral Arterial Disease

Objectives: Cilostazol improves walking in patients with peripheral arterial disease (PAD). We hypothesized that cilostazol reduces diabetic complications in PAD patients.

Methods: Diabetic PAD patients were prospectively recruited to a randomized double-blinded, placebo-controlled trial, using cilostazol 100mg twice a day. Clinical assessment included ankle-brachial index, arterial compliance, peripheral transcutaneous oxygenation, treadmill walking distance and validated quality of life (QoL) questionnaires. Biochemical analyses included glucose and lipid profiles. All tests were at baseline, 6, and 24 weeks.

Results: 26 diabetic PAD patients (20 men) were recruited. Cilostazol improved absolute walking distance at 6 and 24 weeks (86.4% vs. 14.1%, P = .049; 143% vs. 23.2%, P = .086). Arterial compliance and lipid profiles improved as did some QoL indices for cilostazol at 6 and 24 weeks. Blood indices were similar at baseline and at follow-up points for both treatment groups.

Conclusions: Cilostazol is a well-tolerated and efficacious treatment, which improves claudication distances in diabetic PAD patients with further benefits in arterial compliance, lipid profiles, and QoL.

The Effects of Cilostazol on Peripheral Neuropathy in Diabetic Patients With Peripheral Arterial Disease

Background Evidence from diabetic animal models suggests that cilostazol, a cyclic AMP phosphodiesterase inhibitor used in the treatment of claudication, is efficacious in the treatment of peripheral neuropathy, although this is unproven in humans. The main aim of this study was to assess the effects of cilostazol on neuropathic symptomatology in diabetic patients with peripheral arterial disease (PAD). Methods Diabetic patients with PAD were prospectively recruited to a randomized double-blinded placebo-controlled trial. Baseline clinical data were recorded prior to trial commencement following medical optimization. Neurological assessment included the Toronto Clinical Neuropathy Scoring system (TCNS) and vibration perception thresholds (VPT) with a neurothesiometer at baseline, 6 weeks, and 24 weeks. Results Twenty-six patients were recruited from December 2004 to January 2006, which included 20 males. Baseline patient allocation to treatment arms was matched for age, sex, and medical comorbidities. There was no significant difference in neurological assessment between the treatment groups using the TCNS and VPT at 6 and 24 weeks. Conclusions Despite extensive animal-based evidence that cilostazol attenuates neuropathic symptomatology, our results do not support this effect in human diabetic PAD patients.

Potencial terapêutico para a prevenção e tratamento da nefropatia e neuropatia diabéticas: evidências do uso do cilostazol

O cilostazol é um inibidor seletivo da fosfodiesterase tipo III com ação vasodilatadora, antiagregante plaquetária e antitrombótica. É considerada a droga de primeira escolha na claudicação intermitente devido à doença arterial obstrutiva periférica. Vários estudos demonstraram melhora significativa na distância percorrida na caminhada sem dor e na qualidade de vida, sem aumentar o risco de sangramento. Essas ações também foram verificadas em pacientes diabéticos, pois o cilostazol não afeta o metabolismo da glicose. Estudos, principalmente experimentais, têm mostrado resultados satisfatórios na melhora do fluxo sangüíneo neural, na atividade da bomba de sódio e potássio, na resistência à insulina e na microalbuminúria. Neste artigo, apresentamos uma revisão do uso do cilostazol na prevenção e no tratamento das complicações do diabetes mellitus, como nefropatia e neuropatia. Ressalta-se a necessidade do controle adequado dos níveis glicêmicos, da hipertensão arterial sistêmica e do tabagismo. Um maior número de estudos clínicos é necessário para melhor compreensão desses efeitos benéficos.

Regenerative failure of diabetic nerves bridging transection injuries

BACKGROUND

Failed regeneration compounds the deficits imposed by diabetes from peripheral neuropathy. In this work, we addressed how diabetes or local glucose toxicity might impact peripheral nerve trunk regeneration and reconstitution across major sciatic nerve transection injuries of rats.

METHODS

Specific conduits, amendable to manipulation of infused glucose concentrations through a T connection, were perfused with 5 or 30 mmol/L glucose in nondiabetics or 5 mmol/L glucose in rats with experimental diabetes. Quantitative early and later regenerative outgrowth was measured.

RESULTS

Local glucose exposure had no impact on early axon or Schwann cell outgrowth or partnering nor later myelinated axon regeneration. Despite only mildly attenuated early sprouting of axons with Schwann cells, diabetic bridges exhibited massive later failure of reconstitution by 3 weeks after injury.

CONCLUSION

Diabetes is associated with severe limitations in regenerative success, despite appropriate early axon outgrowth.

Impaired peripheral nerve regeneration in diabetes mellitus

Diabetes mellitus impairs peripheral nerve regeneration. Regenerative failure likely exacerbates deficits from polyneuropathy or focal neuropathies in patients who might otherwise exhibit spontaneous improvement. Some focal neuropathies, like carpal tunnel syndrome, are common, yet render ongoing disability because of their delayed recovery. Why diabetic nerves fail to regenerate is an interesting question to consider because several mechanisms likely contribute. In this review, we examine a number of these causes. These causes include microangiopathy or disease of small blood vessels, failure to provide proper metabolic support for repair, defects in the entry and actions of inflammatory cells within the injury milieu, less robust support of axons by their Schwann cells, and lack of a full repertoire of trophic factors. A number of the mechanisms that generate neuropathy in the first place also likely contribute to failed regenerative programs, but how they do so is not clear.

Diabetic neuropathy and nerve regeneration

Diabetic neuropathy is the most common peripheral neuropathy in western countries. Although every effort has been made to clarify the pathogenic mechanism of diabetic neuropathy, thereby devising its ideal therapeutic drugs, neither convinced hypotheses nor unequivocally effective drugs have been established. In view of the pathologic basis for the treatment of diabetic neuropathy, it is important to enhance nerve regeneration as well as prevent nerve degeneration. Nerve regeneration or sprouting in diabetes may occur not only in the nerve trunk but also in the dermis and around dorsal root ganglion neurons, thereby being implicated in the generation of pain sensation. Thus, inadequate nerve regeneration unequivocally contributes to the pathophysiologic mechanism of diabetic neuropathy. In this context, the research on nerve regeneration in diabetes should be more accelerated. Indeed, nerve regenerative capacity has been shown to be decreased in diabetic patients as well as in diabetic animals. Disturbed nerve regeneration in diabetes has been ascribed at least in part to all or some of decreased levels of neurotrophic factors, decreased expression of their receptors, altered cellular signal pathways and/or abnormal expression of cell adhesion molecules, although the mechanisms of their changes remain almost unclear. In addition to their steady-state changes in diabetes, nerve injury induces injury-specific changes in individual neurotrophic factors, their receptors and their intracellular signal pathways, which are closely linked with altered neuronal function, varying from neuronal survival and neurite extension/nerve regeneration to apoptosis. Although it is essential to clarify those changes for understanding the mechanism of disturbed nerve regeneration in diabetes, very few data are now available. Rationally accepted replacement therapy with neurotrophic factors has not provided any success in treating diabetic neuropathy. Aside from adverse effects of those factors, more rigorous consideration for their delivery system may be needed for any possible success. Although conventional therapeutic drugs like aldose reductase (AR) inhibitors and vasodilators have been shown to enhance nerve regeneration, their efficacy should be strictly evaluated with respect to nerve regenerative capacity. For this purpose, especially clinically, skin biopsy, by which cutaneous nerve pathology including nerve regeneration can be morphometrically evaluated, might be a safe and useful examination.

Cilostazol prevents impairment of slow axonal transport in streptozotocin-diabetic rats

We studied the effects of cilostazol, an antiplatelet and vasodilating agent, on axonal transport patterns of cytoskeletal proteins in the motor fibers of sciatic nerve of streptozotocin-induced diabetic rats. Proteins labeled with L-[35S]methionine in 6-mm consecutive segments of the nerve were analyzed electrophoretically following fractionation into Triton-soluble and-insoluble subpopulations. Transport rates of proteins (particularly neurofilaments) in slow component a were reduced by 50% 2 weeks after labeling (4 weeks after streptozotocin). An apparent reduction of tubulin and actin was observed at later intervals after induction of diabetes. Actin transported in slow component b was also impaired, though to a lesser extent than in component a. Cilostazol prevented transport impairment of both slow components a and b without affecting hyperglycemia or reduction in body weight gain. These results suggest that in sciatic motor fibers early defects in slowly transported proteins are more marked in slow component a, and that impairment may be caused primarily by hemodynamic abnormalities.