Making best use of existing NKCC1/2 Blockers in Autism

Azosemide C12H11ClN6O2S2  

Source: https://pubchem.ncbi.nlm.nih.gov/compound/azosemide

Today’s post may be of interest to those already using bumetanide for autism and for those considering doing so.  It does go into the details, because they really do matter and does assume some prior knowledge from earlier posts.

There has been a very thorough new paper published by a group at Johns Hopkins:-

Off-Label Use of Bumetanide for Brain Disorders: An Overview

It does cover all the usual issues and raises some points that have not been covered yet in this blog.  One point is treating autism prenatally. This issue was studied twice in rats, and the recent study was sent to me by Dr Ben Ari.  Short term treatment during pregnancy produced a permanent benefit.

Maternal bumetanide treatment prevents the overgrowth in the VPA condition

            

Brief maternal administration of bumetanide before birth restores low neuronal intracellular chloride concentration ([Cl⁻]_i) levels, produces an excitatory-to-inhibitory shift in the action of γ-aminobutyric acid (GABA), and attenuates the severity of electrical and behavioral features of ASD (9, 10), suggesting that [Cl⁻]_i levels during birth might play an important role in the pathogenesis of ASD (7). Here, the same bumetanide treatment significantly reduced the hippocampal and neocortical volumes of P0 VPA pups, abolishing the volume increase observed during birth in the VPA condition [hippocampus: P0 VPA versus P0 VPA + BUM (P = 0.0116); neocortex: P0 VPA versus P0 VPA + BUM (P = 0.0242); KWD] (Fig. 3B). Maternal bumetanide treatment also shifted the distribution of cerebral volumes from lognormal back to normal in the population of VPA brains, restoring smaller cerebral structure volumes (Fig. 3C). It also decreased the CA3 volume to CTL level after birth, suggesting that the increased growth observed in this region could be mediated by the excitatory actions of GABA (Fig. 3D). Therefore, maternal bumetanide administration prevents the enhanced growth observed in VPA animals during birth.

One issue with Bumetanide is that it affects both:-

·        NKCC2 in your kidneys, causing diuresis

·        NKCC1 in your brain and elsewhere, which is divided into two slightly different forms NKCC1a and NKCC1b

NKCC1 is also expressed in your inner ear where it is necessary for establishing the potassium-rich endolymph that bathes part of the cochlea, an organ necessary for hearing. 

If you block NKCC1 too much you will affect hearing.

Blocking NKCC1 in children and adults is seen as safe but the paper does query what the effect on hearing might be if given prenatally as the ear is developing.

Treating Down Syndrome Prenatally

While treating autism prenatally might seem a bit unlikely, treating Down Syndrome (DS) prenatally certainly is not.  Very often DS is accurately diagnosed before birth creating a valuable treatment window.  In most countries the vast majority of DS prenatal diagnoses lead to termination, but only a small percentage of pregnancies are tested for DS. In some countries such as Ireland a significant number of DS pregnancies are not terminated, these could be treated to reduce the deficits that will otherwise inevitably follow.

Timing of therapies for Down syndrome: the sooner, the better

The research does suggest that DS is another brain disorder that responds to bumetanide.

Back to autism and NKCC1

This should remind us that a defect in NKCC1 expression will not only cause elevated levels of chloride with in neurons, but will also affect the levels of sodium and potassium with neurons.

There are many ion channel dysfunctions (channelopathies) implicated in autism and elevated levels of sodium and potassium will affect numerous ion channels.  The paper does suggest that the benefit of bumetanide may go beyond modifying the effect of GABA, which is the beneficial mode of action put forward by Dr Ben Ari.

We have seen how hypokalemic sensory overload looks very similar to what often occurs in autism and that autistic sensory overload is reduced by taking an oral potassium supplement.

The paper also reminds us that loop diuretics like bumetanide and furosemide not only reduce inflow of chloride into neurons, but may also reduce the outflow. This is particularly known of furosemide, but also occurs with bumetanide at higher doses.

The chart below shows that the higher the concentration of bumetanide the strong its effect becomes on blocking NKCC1.

But at higher doses there will also be a counter effect of closing the NKCC2 transporter that allows chloride to leave neurons.

At some point a higher dose of bumetanide may have a detrimental effect on trying to lower chloride within neurons.

Since Dr Ben Ari’s objective is to lower chloride levels in neurons  it is important how freely these ions both enter and exit.  The net effect is what matters. (Loop diuretics block NKCC1 that lets chloride enter neurons but also block the KCC2 transporter via which they exit)

Is Bumetanide the optimal existing drug to lower chloride within neurons?  Everyone agrees that it is not, because only a tiny amount crosses into the brain. The paper gives details of the prodrugs like BUM5 that have been looked at previously in this blog; these are modified versions of bumetanide that can better slip across the blood brain barrier and then react in the brain to produce bumetanide itself.  It also highlights the recent research that suggests that Bumetanide may not be the most potent approved drug, it is quite conceivable that another old drug called Azosemide is superior.

The blood brain barrier is the problem, as is often the case.  Bumetanide has a low pH (it is acidic) which hinders its diffusion across the barrier.  Only about 1% passes through.

There is scepticism among researchers that enough bumetanide can cross into the brain to actually do any good.  This is reflected in the review paper.

The paper reminds us of the research showing how you can boost the level of bumetanide in the brain by adding Probenecid, an OAT3 inhibitor.  During World War 2 antibiotics were in short supply and so smaller doses were used, but their effect was boosted by adding Probenecid. By blocking OAT3, certain types of drug like penicillin and bumetanide are excreted at a slower rate and so the net level in blood increases.

The effect of adding Probenecid, or another less potent OAT3 inhibitors, is really no different to just increasing the dose of bumetanide.

The problem with increasing the dose of bumetanide is that via its effect on NKCC2 you cause even more diuresis, until eventually a plateau is reached.

Eventually, drugs selective for NKCC1a and/or NKCC1b will appear.

In the meantime, the prodrug BUM5 looks good. It crosses the BBB much better than bumetanide, but it still affects NKCC2 and so will cause diuresis.  But BUM5 should be better than Bumetanide + Probenecid, or a higher dose of Bumetanide.  BUM5 remains a custom-made research drug, never used in humans.

I must say that what again stands out to me is the old German drug, Azosemide.

In a study previously highlighted in this blog, we saw that Azosemide is 4 times more potent than Bumetanide at blocking NKCC1a and NKCC1b.

Azosemide is more potent than bumetanide and various other loop diuretics to inhibit the sodium-potassium-chloride-cotransporter human variants hNKCC1A and hNKCC1B

Azosemide is used in Japan, where recent research shows it is actually more effective than other diuretics

Azosemide, a Long-acting Loop Diuretic, is Superior to Furosemide in Prevention of Cardiovascular Death in Heart Failure Patients Without Beta-blockade 

As is often the case, Japanese medicine has taken a different course to Western medicine.

Years of safety information has already been accumulated on Azosemide.  It is not an untried research drug. It was brought to market in 1981 in Germany. It is available as Diart in Japan made by Sanwa Kagaku Kenkyusho and as a cheaper generic version by Choseido Pharmaceutical. In South Korea Azosemide is marketed as Uretin.

In any other sector other than medicine, somebody would have thought to check by now if Azosemide is better than Bumetanide.  It is not a matter of patents, Ben-Ari has patented all of the possible drugs, including Azosemide and of course Bumetanide.

So now we move on to Azosemide.

When researchers came to check the potency of the above drugs the results came as a surprise.  It turns out that the old German drug Azosemide is 4 times as potent as bumetanide.

The big question is how does it cross the blood brain barrier.

“The low brain concentrations of bumetanide obtained after systemic administration are thought to result from its high ionization (>99%) at physiological pH and its high plasma protein binding (>95%), which restrict brain entry by passive diffusion, as well as active efflux transport at the blood-brain barrier(BBB). The poor brain penetration of bumetanide is a likely explanation for its controversial efficacy in the treatment of brain diseases”

“… azosemide was more potent than any other diuretic, including bumetanide, to inhibit the two NKCC1 variants. The latter finding is particularly interesting because, in contrast to bumetanide, which is a relatively strong acid (pKa = 3.6), azosemide is not acidic (pKa = 7.38), which should favor its tissue distribution by passive diffusion. Lipophilicity (logP) of the two drugs is in the same range (2.38 for azosemide vs. 2.7 for bumetanide). Furthermore, azosemide has a longer duration of action than bumetanide, which results in superior clinical efficacy26 and may be an important advantage for treatment of brain diseases with abnormal cellular chloride homeostasis.”

Dosage equivalents of loop Diuretics

Bumetanide has very high oral bioavailablity, meaning almost all of what you swallow as a pill makes it into your bloodstream.

Furosemide and Azosemide have much lower bioavailability and so higher doses are needed to give the same effect.

Both Furosemide and Bumetanide are short acting, while Azosemide is long acting.

For a drug that needs to cross the blood brain barrier small differences might translate into profoundly different effects.

The limiting factor in all these drugs is their effect on NKCC2 that causes diuresis.

1mg of bumetanide is equivalent to 40mg of furosemide.

2mg of bumetanide is equivalent to 80mg of furosemide.

The standard dose for Azosemide in Japan, where people are smaller than in the West, is 30 mg or 60mg. 

Research suggests that the same concentration of Azosemide is 4x more potent than Bumetanide at blocking NKCC1 transporters, other factors that matter include:-

·        How much of the oral tablet ends up in the bloodstream.

·        How long does it stay in the blood stream

·        How much of the drug actually crosses the blood brain barrier

·        How does the drug bind to the NKCC1 transporters in neurons

·        How rapidly is the drug excreted from the brain

·        What effect is there on the KCC2 transporter that controls the exit of chloride ions from neurons.

All of this comes down to which is more effective in adults with autism 2mg of bumetanide or 60mg of Azosemide.

The side effects, which are mainly diuresis and loss of electrolytes will be similar, but Azosemide is a longer acting drug and so there will be differences. In fact Azosemide is claimed to be less troublesome than Bumetanide in lower potassium levels in your blood.

Conclusion  

The open question is whether generic Azosemide is “better” than generic Bumetanide for treating brain disorders in humans.

I did recently ask Dr Ben-Ari if he is aware of any data on this subject. There is none.

Many millions of dollars/euros are being spent getting Bumetanide approved for autism, so it would be a pity if Azosemide turns out to be better. (Dr Ben Ari’s company Neurochlore wants to develop a new molecule that will cross the blood brain barrier, block NKCC1 and not NKCC2 and so will not cause diuresis).

The hunch of the researchers from Hanover, Germany seems to be that the old German drug Azosemide will be better than Bumetanide.

I wonder if doctors at Johns Hopkins / Kennedy Krieger have started to prescribe bumetanide off-label to their patients with autism.  Their paper shows that they have a very comprehensive knowledge of the subject.

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I suggest readers consult the full version of the Johns Hopkins review paper on Bumetanide, it is peppered with links to all the relevant papers.

Off-Label Use of Bumetanide for Brain Disorders: An Overview

Bumetanide (BTN or BUM) is a FDA-approved potent loop diuretic (LD) that acts by antagonizing sodium-potassium-chloride (Na-K-Cl) cotransporters, NKCC1 (SLc12a2) and NKCC2. While NKCC1 is expressed both in the CNS and in systemic organs, NKCC2 is kidney-specific. The off-label use of BTN to modulate neuronal transmembrane Cl⁻gradients by blocking NKCC1 in the CNS has now been tested as an anti-seizure agent and as an intervention for neurological disorders in pre-clinical studies with varying results. BTN safety and efficacy for its off-label use has also been tested in several clinical trials for neonates, children, adolescents, and adults. It failed to meet efficacy criteria for hypoxic-ischemic encephalopathy (HIE) neonatal seizures. In contrast, positive outcomes in temporal lobe epilepsy (TLE), autism, and schizophrenia trials have been attributed to BTN in studies evaluating its off-label use. NKCC1 is an electroneutral neuronal Cl⁻importer and the dominance of NKCC1 function has been proposed as the common pathology for HIE seizures, TLE, autism, and schizophrenia. Therefore, the use of BTN to antagonize neuronal NKCC1 with the goal to lower internal Cl⁻ levels and promote GABAergic mediated hyperpolarization has been proposed. In this review, we summarize the data and results for pre-clinical and clinical studies that have tested off-label BTN interventions and report variable outcomes. We also compare the data underlying the developmental expression profile of NKCC1 and KCC2, highlight the limitations of BTN’s brain-availability and consider its actions on non-neuronal cells.

Btn Pro-Drugs and Analogs

To improve BTN accessibility to the brain, pro-drugs with lipophilic and uncharged esters, alcohol and amide analogs have been created. These pro-drugs convert to BTN after gaining access into the brain. There was a significantly higher concentration of ester prodrug, BUM5 (N,N – dimethylaminoethyl ester), in mouse brains compared to the parent BTN (10 mg/kg, IV of BTN and equimolar dose of 13 mg/kg, IV of BUM5) (Töllner et al., 2014). BUM5 stopped seizures in adult animal models where BTN failed to work (Töllner et al., 2014; Erker et al., 2016). BUM5 was also less diuretic and showed better brain access when compared to the other prodrugs, BUM1 (ester prodrug), BUM7 (alcohol prodrug) and BUM10 (amide prodrug). BUM5 was reported to be more effective than BTN in altering seizure thresholds in epileptic animals post-SE and post-kindling (Töllner et al., 2014). Furthermore, BUM5 (13 mg/kg, IV) was more efficacious than BTN (10 mg/kg, IV) in promoting the anti-seizure effects of PB, in a maximal electroshock seizure model (Erker et al., 2016). Compared to BUM5 which was an efficacious adjunct to PB in the above mentioned study, BTN was not efficacious when administered as an adjunct (Erker et al., 2016). In addition to seizure thresholds, further studies need to be conducted to assess effects of BUM5 on seizure burdens, ictal events, duration and latencies.

Recently, a benzylamine derivative, bumepamine, has been investigated in pre-clinical models. Since benzylamine derivatives lack the carboxylic group of BTN, it results in lower diuretic activity (Nielsen and Feit, 1978). This prompted Brandt et al. (2018) to explore the proposed lower diuretic activity, higher lipophilicity and lower ionization rate of bumepamine at physiological pH. Since it is known that rodents metabolize BTN quicker than humans, the study used higher doses of 10 mg/kg of bumepamine similar to their previous BTN studies (Olsen, 1977; Brandt et al., 2010; Töllner et al., 2014). Bumepamine, while only being nominally metabolized to BTN, was more effective than BTN to support anticonvulsant effects of PB in rodent models of epilepsy. This GABAergic response, however, was not due to antagonistic actions on NKCC1; suggesting bumepamine may have an off-target effect, which remains unknown. However, the anticonvulsive effects of bumepamine, in spite of its lack of action on NKCC1, are to be noted. Additionally, in another study by the same group, it was shown that azosemide was 4-times more potent an inhibitor of NKCC1 than BTN, opening additional avenues for better BBB penetration and NKCC1-antagonizing compounds for potential neurological drug discovery (Hampel et al., 2018).

Conclusion

The beneficial effects of BTN reported in cases of autism, schizophrenia and TLE, given its poor-brain bioavailability are intriguing. The mechanisms underlying the effects of BTN, as a neuromodulator for developmental and neuropsychiatric disorders could be multifactorial due to prominent NKCC1 function at neuronal and non-neuronal sites within the CNS. Investigation of the possible off-target and systemic effects of BTN may help further this understanding with the advent of a new generation of brain-accessible BTN analogs.

Modulating Neuronal Chloride via WNK

Today’s post is a little complicated, but should be relevant to parents already using bumetanide to reduce the severity of autism.

Tuning neurons via Cl-sensitive WNK

The science behind today’s post only started to evolve twenty years ago when it became understood how chloride enters and exits the neurons in your brain. Nonetheless there is now a vast amount of research and there are parts that have not yet been covered in this blog. 

A moving target

The first thing to realize is that trying to reduce the elevated level of chloride found in much autism is very much an ongoing battle. Chloride is flowing in too fast via NKCC1 and exiting too slowing via KCC2.

If you want to reduce the entry via NKCC1, or increase the exit via KCC2, either of these two strategies should lower the equilibrium level of chloride.  Most strategies in this blog target NKCC1, but in another disease (neuropathic pain) the target has been KCC2.

Whichever you target, the risk is that the body’s feedback loops come into play and undo some of your good work. This was highlighted recently in a paper by Kristopher Kahle at Yale, who looks likely to be joining this blog’s Dean’s List, which highlights the researchers who are really worth following. He is part of the new generation of higher quality researcherswho have an interest in autism.   

If all that was not complex, we have to realize that the number of these valves (cotransporters) that either let chloride enter or exit, is changing all the time.  Many factors relating to inflammation and pain affect the number of NKCC1 and KCC2 cotransporters, so in times of inflammation  you get a reduction KCC2 and/or an increase in NKCC1; hence a higher level of chloride in your neurons.

When people have a traumatic brain injury (TBI), they get an increase in NKCC1 and so an increase in neuronal chloride.  This makes the neurotransmitter GABA less inhibitory, this can lead to cognitive loss, behavioral changes and even a tendency to seizures.

In TBI not surprisingly you have elevated inflammatory signaling, such as via something called NF-κB. As pointed out by our reader AJ, when you take the supplement Astaxanthin, you reduce the expression of NKCC1 in TBI and this has been shown to be via NF-κB. So the potent antioxidant and broadly anti-inflammatory Astaxanthin is a good choice for people with elevated NF-κB.

Much is written in neuropathic pain research about KCC2 and drugs are being developed that could later be repurposed for autism (and indeed TBI). In neuropathic pain there is a lack of KCC2 expression and this is known to be linked to something called WNK1.  The WNK1 gene provides instructions for making multiple versions of the WNK1 protein. 

Mechanisms that control NKCC1 and KCC2

There are multiple mechanisms that affect the expression of NKCC1 and KCC2.  In some cases the two (NKCC1 and KCC2) are interrelated so either one is expressed or the other is expressed.  In the mature brain there should be KCC2, but little NKCC1.  

The current research by Kristopher Kahle is based on the recent discovery of a “rheostat” of chloride homeostasis, comprising the Cl^- sensitive WNK-SPAK kinases and the NKCC1/KCC2 cotransporters. This rheostat provides a way to reversibly tune the strength of inhibition in neurons.

In effect this means that inhibiting WNK should make GABA more inhibitory, which is the goal for all people who have elevated chloride in their neurons.   

Restoring GABA inhibition in a Rett syndrome mouse model by tuning a kinase-regulated Cl-rheostat

GABA_A receptors are ligand-gated Cl- channels. GABA_AR activation can elicit excitatory or inhibitory responses, depending on the intraneuronal Cl- concentration levels. Such levels are largely established by the Cl- co-transporters NKCC1 and KCC2. A progressive postnatal increase in KCC2 over NKCC1 activity drives the emergence of GABA_AR-mediated synaptic inhibition, and is critical for functional brain maturation. A delay in this NKCC1/KCC2 ‘switch’ contributes to the impairment of GABAergic inhibition observed in Rett syndrome, fragile X syndrome, and other neurodevelopmental conditions, such as epilepsy.

Kristopher Kahle and his colleagues aim to understand the mechanisms that govern these developmental changes in NKCC1/KCC2 activity. They hypothesize that an improved knowledge of these mechanisms will lead to the development of novel strategies for restoring GABAergic inhibition. The researchers propose to exploit their recent discovery of a ‘rheostat’ of Cl- homeostasis, comprising the Cl-sensitive WNK-SPAK kinases and the NKCC1/KCC2 cotransporters^1-3. This rheostat provides a phosphorylation-dependent way to reversibly tune the strength of synaptic inhibition in neurons.

The team will create genetic mouse models with inducible expression of phospho-mimetic or constitutively dephosphorylated WNK-SPAK-KCC2 pathway components. They will also develop novel WNK-SPAK kinase inhibitors that function as simultaneous NKCC1 inhibitors and KCC2 activators. These mouse models and compounds will be used to therapeutically restore GABA inhibition in the Rett syndrome MeCP2(R308/Y) mouse model. The researchers will use a combination of two-photon microscopy coupled with improved fluorescent optogenetic Cl- sensing, quantitative phosphoproteomics and patch-clamp electrophysiology to assess cellular and physiological changes in these mice.

Kinase-KCC2 coupling: Cl- rheostasis, disease susceptibility, therapeutic target.

The intracellular concentration of Cl⁻ ([Cl⁻]_i) in neurons is a highly regulated variable that is established and modulated by the finely tuned activity of the KCC2 cotransporter. Despite the importance of KCC2 for neurophysiology and its role in multiple neuropsychiatric diseases, our knowledge of the transporter's regulatory mechanisms is incomplete. Recent studies suggest that the phosphorylation state of KCC2 at specific residues in its cytoplasmic COOH terminus, such as Ser940 and Thr906/Thr1007, encodes discrete levels of transporter activity that elicit graded changes in neuronal Cl⁻ extrusion to modulate the strength of synaptic inhibition via Cl⁻-permeable GABA_A receptors. In this review, we propose that the functional and physical coupling of KCC2 to Cl⁻-sensitive kinase(s), such as the WNK1-SPAK kinase complex, constitutes a molecular “rheostat” that regulates [Cl⁻]_i and thereby influences the functional plasticity of GABA. The rapid reversibility of (de)phosphorylation facilitates regulatory precision, and multisite phosphorylation allows for the control of KCC2 activity by different inputs via distinct or partially overlapping upstream signaling cascades that may become more or less important depending on the physiological context. While this adaptation mechanism is highly suited to maintaining homeostasis, its adjustable set points may render it vulnerable to perturbation and dysregulation. Finally, we suggest that pharmacological modulation of this kinase-KCC2 rheostat might be a particularly efficacious strategy to enhance Cl⁻ extrusion and therapeutically restore GABA inhibition.

Dominant-negative mutation, genetic knockdown, or chemical inhibition of WNK1 in immature neurons (but not mature neurons) is sufficient to trigger a hyperpolarizing shift in GABA activity by enhancing KCC2-mediated Cl⁻ extrusion secondary to a reduction of Thr906/Thr1007 inhibitory phosphorylation (Friedel et al. 2015). These results extended previous work by Rinehart et al. (2009), who showed that KCC2 Thr906 phosphorylation inversely correlates with KCC2 activity in the developing mouse brain, and Inoue et al. (2012), who showed a phosphorylation-dependent inhibitory effect of taurine on KCC2 activity in immature neurons that was recapitulated by WNK1 overexpression in the absence of taurine. Together, these compelling data suggest that a postnatal decrease in WNK1-regulated inhibitory phosphorylation of KCC2 also contributes to increased KCC2 function (Fig. 5), and thus to the excitatory-to-inhibitory GABA shift that occurs during development. This also raises the possibility that dysfunctional phosphoregulation of these sites could be important in certain neurodevelopmental pathologies, like autism or neonatal seizures. An important issue of future investigation will be to determine how the increased levels of Cl⁻ in immature neurons affect WNK1 kinase activity. Could taurine, a factor known to activate WNK1 in immature neurons, achieve this by decreasing the sensitivity of WNK1 to Cl⁻?

Recently, a few groups have developed innovative high-throughput assays to screen for compounds that modulate KCC2 activity (Delpire et al. 2009, 2012; Gagnon et al. 2013), and one drug shows promise as a KCC2-dependent Cl⁻ extrusion enhancer with therapeutic effect in a model of neuropathic pain (Gagnon et al. 2013). These early but encouraging results require validation, but they establish the validity in vivo of the concept of GABA modulation via the pharmacological targeting of CCC-dependent Cl⁻ transport (Gagnon et al. 2013; Kahle et al. 2014a; Kaila et al. 2014). Could CCC phosphoregulatory mechanisms, normally employed to modulate transporter activity in response to perturbation or biological need, be harnessed to stimulate the KCCs (or inhibit NKCC1) for therapeutic benefit in disease states featuring an accumulation of intracellular Cl⁻?

Moreover, since the WNK kinases might also be the Cl⁻ sensors that detect changes in intracellular Cl⁻ (Piala et al. 2014), inhibiting these molecules might prevent feedback mechanisms that would counter the effects of targeting NKCC1 or KCC2 alone.

  

Chloride extrusion enhancers as novel therapeutics for neurological diseases

The K(+)-Cl(-) cotransporter KCC2 is responsible for maintaining low Cl(-) concentration in neurons of the central nervous system (CNS), which is essential for postsynaptic inhibition through GABA(A) and glycine receptors. Although no CNS disorders have been associated with KCC2 mutations, loss of activity of this transporter has emerged as a key mechanism underlying several neurological and psychiatric disorders, including epilepsy, motor spasticity, stress, anxiety, schizophrenia, morphine-induced hyperalgesia and chronic pain. Recent reports indicate that enhancing KCC2 activity may be the favored therapeutic strategy to restore inhibition and normal function in pathological conditions involving impaired Cl(-) transport. We designed an assay for high-throughput screening that led to the identification of KCC2 activators that reduce intracellular chloride concentration ([Cl(-)]i). Optimization of a first-in-class arylmethylidine family of compounds resulted in a KCC2-selective analog (CLP257) that lowers [Cl(-)]i. CLP257 restored impaired Cl(-) transport in neurons with diminished KCC2 activity. The compound rescued KCC2 plasma membrane expression, renormalized stimulus-evoked responses in spinal nociceptive pathways sensitized after nerve injury and alleviated hypersensitivity in a rat model of neuropathic pain. Oral efficacy for analgesia equivalent to that of pregabalin but without motor impairment was achievable with a CLP257 prodrug. These results validate KCC2 as a drugable target for CNS diseases.  

Chloride sensing by WNK1 kinase involves inhibition of autophosphorylation

WNK1 [with no lysine (K)] is a serine-threonine kinase associated with a form of familial hypertension. WNK1 is at the top of a kinase cascade leading to phosphorylation of several cotransporters, in particular those transporting sodium, potassium, and chloride (NKCC), sodium and chloride (NCC), and potassium and chloride (KCC). The responsiveness of NKCC, NCC, and KCC to changes in extracellular chloride parallels their phosphorylation state, provoking the proposal that these transporters are controlled by a chloride-sensitive protein kinase. Here, we found that chloride stabilizes the inactive conformation of WNK1, preventing kinase autophosphorylation and activation. Crystallographic studies of inactive WNK1 in the presence of chloride revealed that chloride binds directly to the catalytic site, providing a basis for the unique position of the catalytic lysine. Mutagenesis of the chloride binding site rendered the kinase less sensitive to inhibition of autophosphorylation by chloride, validating the binding site. Thus, these data suggest that WNK1 functions as a chloride sensor through direct binding of a regulatory chloride ion to the active site, which inhibits autophosphorylation.

The WNK-SPAK/OSR1 pathway: Master regulator of cation-chloride cotransporters

The WNK-SPAK/OSR1 kinase complex is composed of the kinases WNK (with no lysine) and SPAK (SPS1-related proline/alanine-rich kinase) or the SPAK homolog OSR1 (oxidative stress–responsive kinase 1). The WNK family senses changes in intracellular Cl⁻ concentration, extracellular osmolarity, and cell volume and transduces this information to sodium (Na⁺), potassium (K⁺), and chloride (Cl⁻) cotransporters [collectively referred to as CCCs (cation-chloride cotransporters)] and ion channels to maintain cellular and organismal homeostasis and affect cellular morphology and behavior. Several genes encoding proteins in this pathway are mutated in human disease, and the cotransporters are targets of commonly used drugs. WNKs stimulate the kinases SPAK and OSR1, which directly phosphorylate and stimulate Cl⁻-importing, Na⁺-driven CCCs or inhibit the Cl⁻-extruding, K⁺-driven CCCs. These coordinated and reciprocal actions on the CCCs are triggered by an interaction between RFXV/I motifs within the WNKs and CCCs and a conserved carboxyl-terminal docking domain in SPAK and OSR1. This interaction site represents a potentially druggable node that could be more effective than targeting the cotransporters directly. In the kidney, WNK-SPAK/OSR1 inhibition decreases epithelial NaCl reabsorption and K⁺ secretion to lower blood pressure while maintaining serum K⁺. In neurons, WNK-SPAK/OSR1 inhibition could facilitate Cl⁻ extrusion and promote γ-aminobutyric acidergic (GABAergic) inhibition. Such drugs could have efficacy as K⁺-sparing blood pressure–lowering agents in essential hypertension, nonaddictive analgesics in neuropathic pain, and promoters of GABAergic inhibition in diseases associated with neuronal hyperactivity, such as epilepsy, spasticity, neuropathic pain, schizophrenia, and autism. 

Regulation of OSR1 and the sodium, potassium, two chloride cotransporter by convergent signals

The Ste20 family protein kinases oxidative stress-responsive 1 (OSR1) and the STE20/SPS1-related proline-, alanine-rich kinase directly regulate the solute carrier 12 family of cation-chloride cotransporters and thereby modulate a range of processes including cell volume homeostasis, blood pressure, hearing, and kidney function. OSR1 andSTE20/SPS1-related proline-,alanine-rich kinase are activated by with no lysine [K] protein kinases that phosphorylate the essential activation loop regulatory site on these kinases. We found that inhibition of phosphoinositide 3-kinase (PI3K) reduced OSR1 activation by osmotic stress. Inhibition of the PI3K target pathway, the mammalian target of rapamycin complex 2 (mTORC2), by depletion of Sin1, one of its components, decreased activation of OSR1 by sorbitol and reduced activity of the OSR1 substrate, the sodium, potassium, two chloride cotransporter, in HeLa cells. OSR1 activity was also reduced with a pharmacological inhibitor of mTOR. mTORC2phosphorylated OSR1 on S339 in vitro, and mutation of this residue eliminated OSR1 phosphorylation by mTORC2. Thus, we identify a previously unrecognized connection ofthePI3K pathwaythroughmTORC2 to a Ste20 proteinkinase and ion homeostasis.

Significance

With no lysine [K] (WNK) protein kinases are sensitive to changes in osmotic stress. Through the downstream protein kinases oxidative stress-responsive 1 (OSR1) and STE20/SPS1related proline-, alanine-rich kinase, WNKs regulate a family of ion cotransporters and thereby modulate a range of processes including cell volume homeostasis, blood pressure, hearing, and kidney function. We found that a major phosphoinositide 3-kinase target pathway, the mammalian target of rapamycin complex 2, also phosphorylates OSR1, coordinating with WNK1 to enhance OSR1 and ion cotransporter function.

Changes in tonicity regulate the WNK-OSR1/SPAK pathway to control ion cotransporters for volume and ion homeostasis. We find that mTORC2 also contributes to enhanced OSR1 activity. Inhibiting mTORC2 does not inhibit WNK1 activity, indicating PF1 and PF2regions.

We conclude that cell homeostasis requires the multi level integration of WNK osmosensing and PI3K survival pathways.

The WNK-regulated SPAK/OSR1 kinases directly phosphorylate and inhibit the K+–Cl−co-transporters

These data demonstrate that the WNK-regulated SPAK/OSR1 kinases directly phosphorylate the N[K]CCs and KCCs, promoting their stimulation and inhibition respectively. Given these reciprocal actions with anticipated net effects of increasing Cl− influx, we propose that the targeting of WNK–SPAK/OSR1 with kinase inhibitors might be a novel potent strategy to enhance cellular Cl− extrusion, with potential implications for the therapeutic modulation of epithelial and neuronal ion transport in human disease states.

WNK Inhibitors

The first orally bioavailable pan-WNK-kinase inhibitor is WNK463.

“WNK463 is an orally bioavailable pan-WNK-kinase inhibitor. In vivo: WNK463, that exploits unique structural features of the WNK kinases for both affinity and kinase selectivity. In rodent models of hypertension, WNK463 affects blood pressure and body fluid and electro-lyte homeostasis, consistent with WNK-kinase-associated physiology and pathophysiology.”\

WNK463 is available as a research drug.

It looks like WNK2 is also very relevant, perhaps more so than WNK1, because we are interested specifically in the brain, where there is a lot of WNK2. WNK3 also looks very relevant. There is also WNK4.

WNK2 Kinase Is a Novel Regulator of Essential Neuronal Cation-Chloride Cotransporters

Here, we show that WNK2, unlike other WNKs, is not expressed in kidney; rather, it is a neuron-enriched kinase primarily expressed in neocortical pyramidal cells, thalamic relay cells, and cerebellar granule and Purkinje cells in both the developing and adult brain. Bumetanide-sensitive and Cl⁻-dependent ⁸⁶Rb⁺ uptake assays in Xenopus laevis oocytes revealed that WNK2 promotes Cl⁻ accumulation by reciprocally activating NKCC1 and inhibiting KCC2 in a kinase-dependent manner, effectively bypassing normal tonicity requirements for cotransporter regulation.  

Inhibition of WNK3 Kinase Signaling Reduces Brain Damage and Accelerates Neurological Recovery After Stroke.

WNK3 KO mice exhibited significantly decreased infarct volume and axonal demyelination, less cerebral edema, and accelerated neurobehavioral recovery compared to WNK3 WT mice subjected to MCA occlusion. The neuroprotective phenotypes conferred by WNK3 KO were associated with a decrease in stimulatory hyper-phosphorylations of the SPAK/OSR1 catalytic T-loop and of NKCC1 stimulatory sites Thr²⁰³/Thr²⁰⁷/Thr²¹², as well as with decreased cell surface expression of NKCC1. Genetic inhibition of WNK3 or siRNA knockdown of SPAK/OSR1 increased the tolerance of cultured primary neurons and oligodendrocytes to in vitro ischemia.

CONCLUSION

These data identify a novel role for the WNK3-SPAK/OSR1-NKCC1 signaling pathway in ischemic neuroglial injury, and suggest the WNK3-SPAK/OSR1 kinase pathway as a therapeutic target for neuroprotection following ischemic stroke.

  

Conclusion

I think we can simplify all of this into:-

We already know that many people with autism benefit from making GABA more inhibitory.

There are currently two types of therapy:

1.     Reducing intracellular chloride

2.     Modifying GABA_A α3 subunit sensitivity (low dose clonazepam from Professor Catterall)

Reducing intracellular chloride

This can be achieved by:

·        Reducing the inflow via NKCC1 using bumetanide and in future years using drugs which better pass the blood brain barrier, e.g. the research drug BUM5. Consider improving the potency of the current drug bumetanide using an OAT3 inhibitor that will increase its concentration and half-life, apparently already possible with acetazolamide.

·        Increasing the outflow via KCC2, possible with the research drug CLP257  

·        Reducing the inflow via AE3, possible with Diamox/acetazolamide

·        Substituting Br^- for Cl^-, using potassium bromide

·        Changing the relative expression of NKCC2/KCC1

Changing the relative expression of NKCC1/KCC2

·        This can be done today by treating any underlying inflammation.  Inflammation shifts the NKCC2/KCC1 balance in a way that makes GABA more excitatory, which is bad. This might be achieved by targeting IL-6, NF-κB or just treating any GI problems and allergies.  Always treat the comorbidities of autism.  

·        Using WNK inhibitors it will hopefully be possible to manually tune the NKCC1/KCC2 balance, just like tuning a piano. One pan-WNK-kinase inhibitor is WNK463.

·        I continue to believe that RORα could be an effective way to increase KCC2 expression and this is something that is not so hard to test.

The Purkinje-RORa-Estradiol-Neuroligin-KCC2 axis in Autism

I will be keeping a look out for further papers by Dr Kahle and be interested in any WNK-SPAK/OSR1 inhibitors he proposes.  If I was him I would start with WNK463.

There is more to the story, because naturally I want to see how estradiol relates to WNK and finally wrap up this subject. Then we will know how to treat the immature neurons often found in autism. A case of forever young.

In a following post I intend to do that; here is a sneak, but complex, preview.