The selective Na+-Ca2+ exchange inhibitor attenuates brain edema after radiofrequency lesion in rats

The NCX1 calcium exchanger is implicated in delayed axotomy after peripheral nerve stretch injury

BACKGROUND AND AIMS

After peripheral nerve stretch injury, most degenerating axons are thought to become disconnected at the time of injury, referred to as primary axotomy. The possibility of secondary axotomy-a delayed and potentially reversible form of disconnection-has not been evaluated. Here, we investigated secondary axotomy in a rat model of sciatic nerve stretch injury. We also evaluated whether axon sparing and functional improvement results from pharmacological blockade of the sodium-calcium exchanger 1 (NCX1), which is widely believed to contribute to traumatic axon degeneration but was previously only investigated in vitro.

METHODS

We studied peripheral nerve secondary axotomy in a clinically relevant rat model of sciatic nerve rapid stretch injury with immunolabeling and fluorescence microscopy. The role of NCX1 in secondary axotomy was studied with pharmacological inhibition with SEA0400 and immunolabeling, immunoblot, and behavioral assays.

RESULTS

We found that early after injury, many axons remained in-continuity and that degeneration of axons was delayed, consistent with the occurrence of secondary axotomy. βAPP, a marker of secondary axotomy, accumulated at regions of axon swelling and disconnection, and NCX1 was upregulated and co-localized to βAPP axonal swellings. Pharmacological blockade of NCX1 after injury reduced calpain activation, proteolytic degradation of neurofilaments, βAPP accumulation, distal axon degeneration, and improved hindlimb function.

INTERPRETATION

Our data demonstrate a major role for secondary axotomy in peripheral nerve stretch injury and identify NCX1 as a promising therapeutic target to reduce secondary axotomy and improve functional outcome after nerve injury.

Sodium-Calcium Exchanger 2: A Pivotal Role in Oxaliplatin Induced Peripheral Neurotoxicity and Axonal Damage?

Oxaliplatin (OHP)-induced peripheral neurotoxicity (OIPN) is a frequent adverse event of colorectal cancer treatment. OIPN encompasses a chronic and an acute syndrome. The latter consists of transient axonal hyperexcitability, due to unbalance in Na+ voltage-operated channels (Na+VOC). This leads to sustained depolarisation which can activate the reverse mode of the Na+/Ca2+ exchanger 2 (NCX2), resulting in toxic Ca2+ accumulation and axonal damage (ADa). We explored the role of NCX2 in in vitro and in vivo settings. Embryonic rat Dorsal Root Ganglia (DRG) organotypic cultures treated with SEA0400 (SEA), a NCX inhibitor, were used to assess neuroprotection in a proof-of-concept and pilot study to exploit NCX modulation to prevent ADa. In vivo, OHP treated mice (7 mg/Kg, i.v., once a week for 8 weeks) were compared with a vehicle-treated group (n = 12 each). Neurophysiological and behavioural testing were performed to characterise acute and chronic OIPN, and morphological analyses were performed to detect ADa. Immunohistochemistry, immunofluorescence, and western blotting (WB) analyses were also performed to demonstrate changes in NCX2 immunoreactivity and protein expression. In vitro, NCX inhibition was matched by ADa mitigation. In the in vivo part, after verifyingboth acute and chronic OIPN had ensued, we confirmed via immunohistochemistry, immunofluorescence, and WB that a significant NCX2 alteration had ensued in the OHP group. Our data suggest NCX2 involvement in ADa development, paving the way to a new line of research to prevent OIPN.

Potential Therapies for Cerebral Edema After Ischemic Stroke: A Mini Review

Stroke is the leading cause of global mortality and disability. Cerebral edema and intracranial hypertension are common complications of cerebral infarction and the major causes of mortality. The formation of cerebral edema includes three stages (cytotoxic edema, ionic edema, and vasogenic edema), which involve multiple proteins and ion channels. A range of therapeutic agents that successfully target cerebral edema have been developed in animal studies, some of which have been assessed in clinical trials. Herein, we review the mechanisms of cerebral edema and the research progress of anti-edema therapies for use after ischemic stroke.

Drug development in targeting ion channels for brain edema

Cerebral edema is a pathological hallmark of various central nervous system (CNS) insults, including traumatic brain injury (TBI) and excitotoxic injury such as stroke. Due to the rigidity of the skull, edema-induced increase of intracranial fluid significantly complicates severe CNS injuries by raising intracranial pressure and compromising perfusion. Mortality due to cerebral edema is high. With mortality rates up to 80% in severe cases of stroke, it is the leading cause of death within the first week. Similarly, cerebral edema is devastating for patients of TBI, accounting for up to 50% mortality. Currently, the available treatments for cerebral edema include hypothermia, osmotherapy, and surgery. However, these treatments only address the symptoms and often elicit adverse side effects, potentially in part due to non-specificity. There is an urgent need to identify effective pharmacological treatments for cerebral edema. Currently, ion channels represent the third-largest target class for drug development, but their roles in cerebral edema remain ill-defined. The present review aims to provide an overview of the proposed roles of ion channels and transporters (including aquaporins, SUR1-TRPM4, chloride channels, glucose transporters, and proton-sensitive channels) in mediating cerebral edema in acute ischemic stroke and TBI. We also focus on the pharmacological inhibitors for each target and potential therapeutic strategies that may be further pursued for the treatment of cerebral edema.

The Effect of Candesartan Alone and Its Combination With Estrogen on Post-traumatic Brain Injury Outcomes in Female Rats

Aim: The aim of this study was to evaluate the effect of candesartan (angiotensin II type I receptor blocker) alone and its combination with estrogen on the changes in brain edema, intracranial pressure (ICP), and cerebral perfusion pressure (CPP) following diffuse traumatic brain injury (TBI) in female rats.

Methods: TBI was induced in ovariectomized female rats using Marmarou's method. The treatment groups received low-dose (LC) and high-dose (HC) candesartan, estrogen (E2), a combination of estrogen vehicle and candesartan vehicle (oil + vehicle), or a combination of estrogen with low-dose (E2 + LC), or with high-dose (E2 + HC) candesartan. ICP and CPP were measured before and several times after TBI, and the brain water content (brain edema) was measured 24 h after TBI.

Results: After the TBI, brain edema and ICP in the estrogen group were lower than in the vehicle and TBI groups. Brain edema and ICP in the HC group were lower than in the vehicle group after TBI. Although there was no significant difference in brain edema and ICP between the LC and vehicle groups, significant differences in these variables were observed when the E2 + LC and E2 + HC groups were compared with the oil + vehicle group after TBI. A significant increase in CPP was observed in the estrogen group 4 and 24 h post-TBI, while this increase was found in the HC and E2 + LC groups 24 h post-TBI.

Conclusions: A low dose of candesartan did not exert a protective effect on TBI outcomes, but such an effect did appear after combination with estrogen. This finding suggests that interaction between low-dose candesartan and estrogen improves TBI-induced consequences.

Blood-brain barrier transport of an essential amino acid after cerebral ischemia reperfusion injury

Under pathophysiological conditions such as -cerebral ischemia-reperfusion (IR), damage to cerebrovascular endothelial cells causes alterations in the blood-brain barrier (BBB) function that can exacerbate neuronal cell injury and death. Clarifying changes in BBB transport in the early period of IR is important for understanding BBB function during therapy after cerebral ischemia. The present study was aimed at clarifying changes during IR in the BBB transport of L-phenylalanine (Phe) as a substrate of L-type amino acid transporter 1. An IR model was produced in mice by blood recirculation following occlusion of the middle cerebral artery. Permeability of the BBB to [(3)H]Phe was measured after IR injury using the brain perfusion method. Confocal microscopy of the IR injury showed no brain penetration of fluorescent tracer, thus confirming BBB integrity during 45 min of ischemia. Tight junction opening was not observed at 30 min after reperfusion following ischemia for 45 min. At the time of IR, [(3)H]Phe uptake into the brain appeared saturated. The Michaelis constant and maximum transport velocity in the IR group was reduced by 22 % compared with those in controls. These results suggest that the intrinsic transport clearance of Phe is slightly decreased in the early phase of IR.

Effect of sex steroid hormones on brain edema, intracranial pressure, and neurologic outcomes after traumatic brain injury

Recent studies have reported that estrogen and progesterone have a neuroprotective effect after traumatic brain injury (TBI); however, the mechanism(s) for this effect have not yet been elucidated. The aim of the present study was to investigate the role of sex steroid hormones on changes in brain edema, intracranial pressure (ICP), and cerebral perfusion pressure (CPP) after TBI in ovariectomized (OVX) rats. In this study, 50 female rats were divided into 5 groups: control (intact), sham, and 3 TBI groups consisting of vehicle, estrogen (1 mg/kg), and progesterone (8 mg/kg). TBI was induced by the Marmarou method, and the hormones were injected i.p. 30 min after TBI. ICP was measured in the spinal cord, and CPP was calculated by subtracting the mean arterial pressure (MAP) from ICP. The results revealed that brain water content after TBI was lower (p < 0.001) in the estrogen and progesterone groups than in the vehicle group. After trauma, ICP was significantly higher in TBI rats (p < 0.001). The ICP in the estrogen and progesterone groups decreased at 4 and 24 h after TBI compared with vehicle (p < 0.001 and p < 0.05, respectively). The CPP in the estrogen and progesterone groups increased after 24 h compared with vehicle (p < 0.001). Also after TBI, the neurological score (veterinary coma scale) was significantly higher than vehicle at 1 h (p < 0.01) and 24 h (p < 0.001) in the group treated with estrogen. In conclusion, pharmacological doses of estrogen and progesterone improved ICP, CPP, and neurological scores after TBI in OVX rats, which implies that these hormones play a neuroprotective role in TBI.

SEA0400: A Novel Sodium-Calcium Exchange Inhibitor with Cardioprotective Properties1

The cardiac sodium-calcium exchanger (NCX) plays an important role in calcium homeostasis. It is the primary mechanism for removing calcium ions that enter myocytes through L-type calcium channels on a beat-to-beat basis. Its direction of transport is determined by the membrane potential and the ionic concentrations of Na+ and Ca2+, with the forward (or Ca2+-efflux) mode of transport being the dominant mode under physiological conditions. In contrast, the Ca2+-influx mode (or reverse mode) of NCX becomes important in certain pathophysiological conditions, such as myocardial ischemia and reperfusion. Recent discovery of compounds that inhibit the Ca2+-influx mode (or reverse mode) of NCX has generated intense research interest in the pharmacology of NCX. Among the newer NCX inhibitors described to date, 2-[4-[(2,5-difluorophenyl)methoxy]-phenoxy]-5-ethoxyaniline (SEA0400) appears particularly promising in attenuating cardiac, renal, and cerebral ischemia/reperfusion injuries in various experimental models. Moreover, the mixed results that have emerged from clinical trials evaluating the efficacy and safety of inhibitors of the sodium-hydrogen exchanger (an upstream target in relation to the sodium-calcium exchanger) in myocardial protection stimulated interest in evaluating NCX as an alternative therapeutic target. This article reviews the pharmacological profile of SEA0400, as presented in the published literature, and discusses the therapeutic potential of this compound in attenuating myocardial ischemia/reperfusion injury.

Inhibition by SEA0400, a Selective Inhibitor of Na+/Ca2+ Exchanger, of Na+-Dependent Ca2+ Uptake and Catecholamine Release in Bovine Adrenal Chromaffin Cells

The effects of SEA0400, a selective inhibitor of the Na(+)/Ca(2+) exchanger (NCX), on Na(+)-dependent Ca(2+) uptake and catecholamine (CA) release were examined in bovine adrenal chromaffin cells that were loaded with Na(+) by treatment with ouabain and veratridine. SEA0400 inhibited Na(+)-dependent (45)Ca(2+) uptake and CA release, with the IC(50) values of 40 and 100 nM, respectively. The IC(50) values of another NCX inhibitor KB-R7943 were 1.8 and 3.7 microM, respectively. These results indicate that SEA0400 is about 40 times more potent than KB-R7943 in inhibiting NCX working in the reverse mode. In intact cells, SEA0400 and KB-R7943 inhibited CA release induced by acetylcholine and DMPP. The IC(50) values of SEA0400 were 5.1 and 4.5 microM and the values of KB-R7943 were 2.6 and 2.1 microM against the release induced by acetylcholine and DMPP, respectively, indicating that the potency of SEA0400 is about a half of that of KB-R7943 in inhibiting the nicotinic receptor-mediated CA release. The binding of [(3)H]nicotine with nicotinic receptors was inhibited by SEA0400 (IC(50) = 90 microM) and KB-R7943 (IC(50) = 12 microM). From these results, it is concluded that unlike KB-R7943, SEA0400 has a potent and selective action on NCX in bovine adrenal chromaffin cells.

Functional proteins involved in regulation of intracellular Ca(2+) for drug development: pharmacology of SEA0400, a specific inhibitor of the Na(+)-Ca(2+) exchanger

The Na(+)-Ca(2+) exchanger (NCX) is involved in regulation of intracellular Ca(2+) concentration. A specific inhibitor of NCX has been required for clarification of the physiological and pathological roles of NCX. We have developed 2-[4-[(2,5-difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline (SEA0400), a highly potent and selective inhibitor of NCX. SEA0400 in the concentration range that inhibits NCX exhibits negligible affinities for the Ca(2+) channels, Na(+) channels, K(+) channels, noradrenaline transporter, and 14 receptors; and it does not affect the activities of the store-operated Ca(2+) channel, Na(+)-H(+) exchanger, and several enzymes including Na(+),K(+)-ATPase and Ca(2+)-ATPase. Furthermore, recent studies show that SEA0400 attenuates ischemia-reperfusion injury in the brain, heart, and kidney and radiofrequency lesion-induced edema in rat brain. These findings suggest that NCX plays a key role in ischemia-reperfusion injury and may be a target molecule for treatment of reperfusion injury-related diseases.

Forefront of Na+/Ca2+ Exchanger Studies: Molecular Pharmacology of Na+/Ca2+ Exchange Inhibitors

The Na+/Ca2+ exchanger (NCX) is an ion transporter that exchanges Na+ and Ca2+ in either Ca2+ efflux or Ca2+ influx mode, depending on membrane potential and transmembrane ion gradients. In myocytes, neurons, and nephron cells, NCX is thought to play an important role in the regulation of intracellular Ca2+ concentration. Recently, the benzyloxyphenyl derivatives KB-R7943, SEA0400, and SN-6 have been developed as selective NCX inhibitors. Currently, SEA0400 is the most potent and selective inhibitor. These inhibitors possess different isoform-selectivities, although they have similar properties, such as Ca2+ influx mode-selectivity and I1 inactivation-dependence. Recent site-directed mutagenesis has revealed that these inhibitors possess some molecular determinants (Phe-213, Val-227, Tyr-228, Gly-833, and Asn-839) for interaction with NCX1. These benzyloxyphenyl derivatives are expected to be useful tools to study the physiological roles of NCX. Moreover, such inhibitors may have therapeutic potential as a new remedy for ischemic disease, arrhythmias, heart failure, and hypertension.