Selective intermediate‐/small‐conductance calcium‐activated potassium channel (KCNN4) blockers are potent and effective therapeutics in experimental brain oedema and traumatic brain injury caused by acute subdural haematoma

Abstract

Early deterioration and death after brain injury is often the result of oedema in the injured and peri-lesional tissue. So far, no pharmacotherapy is available that exhibits significant brain oedema-reducing efficacy in patients. We selected two low molecular weight compounds from different chemical classes, a triazole (1-[(2-chlorophenyl)diphenylmethyl]-1,2,3-triazole) and a cyclohexadiene (methyl 4-[4-chloro-3-(trifluoromethyl)phenyl]-6-methyl-3-oxo-1,4,7-tetrahydroisobenzofuran-5-carboxylate) to characterize their pharmacological properties on KCNN4 channels (intermediate/small conductance calcium-activated potassium channel, subfamily N, member 4) in vitro as well as in vivo. In vitro we replaced potassium by rubidium (Rb+) and determined Rb+ fluxes evoked by 10 micro m of the calcium ionophore A23187 on C6BU1 rat glioma cells. Compared with known KCNN4 blockers, such as clotrimazole (IC50=360 +/- 12 nm) and charybdotoxin (IC50=3.3 +/- 1.9 nm), the triazole and cyclohexadiene were considerably more potent than clotrimazole and displayed similar potencies (IC50=12.1 +/- 8.8 and 13.3 +/- 4.7 nm, respectively). In the rat acute subdural haematoma model, both the triazole and cyclohexadiene displayed reduction of brain water content (-26% at 0.3 mg/kg and -24% at 0.01 mg/kg) and reduction of the intracranial pressure (-46% at 0.1 mg/kg and -60% at 0.003 mg/kg) after 24 h when administered as a 4-h infusion immediately after brain injury. When infarct volumes were determined after 7 days, the triazole as well as the cyclohexadiene displayed strong neuroprotective efficacy (-52% infarct volume reduction at 1.2 mg/kg and -43% at 0.04 mg/kg, respectively). It is concluded that blockade of KCNN4 channels is a new pharmacological approach to attenuate acute brain damage caused by traumatic brain injury.

Lysophosphatidylcholine Stimulates IL-1β Release from Microglia via a P2X7 Receptor-Independent Mechanism

“…It has been demonstrated that selective blockade of K Ca 3.1 Ca 2ϩ -activated K ϩ channels attenuates acute brain damage caused by traumatic brain injury (54) and ameliorates the outcome of experimental autoimmune encephalomyelitis (55,56). In experimental autoimmune encephalomyelitis mice, reduced IL-1␤ levels were detected following K ϩ channel inhibition (56), which could be related to inhibition of microglial activation in vivo.…”

The Ca2+-Activated K+ChannelKCNN4/KCa3.1 Contributes to Microglia Activation and Nitric Oxide-Dependent Neurodegeneration

“…Use of KCa3.1 channel blockers to treat CNS disorders is beginning to be addressed, and the results are encouraging. Bayer (Wuppertal, Germany) developed several KCa3.1 blockers, tested them in a rat model of traumatic brain injury (subdural hematoma), and found that several hours of intravenous administration of either a triazole or a cyclohexadiene compound significantly reduced the ensuing edema, intracranial pressure, and infarct volume (Mauler et al, 2004). KCa3.1 blockade reduced inflammatory cytokine production and damage in the spinal cord in a murine model of multiple sclerosis (Reich et al, 2005), but potential contributions of CNS cells were not determined.…”

Hydrophobic Interactions as Key Determinants to the KCa3.1 Channel Closed Configuration

“…The voltage-insensitive calcium-activated K ϩ channel of intermediate conductance KCa3.1 is now emerging as a therapeutic target for a large variety of health disorders such as autoimmune diseases, vascular inflammation, and cancer (1)(2)(3)(4)(5)(6)(7). Increasing evidence also supports a prominent role of KCa3.1 in respiratory diseases such as allergic asthma (8) and airway obstruction coming from tissues remodeling (8,9).…”

“…This conclusion followed from the observation that the small positively charged reagents MTSEA ϩ , EtHg ϩ , and Ag ϩ were accessible to cysteine residues engineered deep inside the channel central cavity with the channel in the closed configuration. In contrast, larger molecules such as the MTS reagent MTSET ϩ (5.8 Å diameter) showed a 10 3 -10 4 -fold difference in accessibility between the channel closed and open configurations (13). It was concluded that the bundle crossing region, predicted on the basis of the KcsA structure to be located at the C-terminal end of the S6 transmembrane segments, cannot form a tight seal impermeable to K ϩ ions when KCa3.1 is in the closed configuration.…”