Edging closer to targeting neuro-inflammation in autism via FPR2

 

 A thoughtful mouse in Naples

For many years, autism research has focused primarily on neurotransmitters such as GABA and glutamate. More recently, however, increasing attention has turned to another major contributor to brain function: the immune system.

Numerous studies have reported evidence of chronic microglial activation and elevated inflammatory cytokines in at least a subset of autistic people. The obvious question has always been:-

Can reducing neuro-inflammation improve the core features of autism?

A newly published study from researchers at the University of Naples suggests we may be edging closer to answering that question.

Rather than simply suppressing inflammation, they have taken a much more sophisticated approach by activating one of the body's own inflammation-resolution pathways. Their target is a receptor called Formyl Peptide Receptor 2 (FPR2), which has not been covered in previous posts.

 

Agonist MR-39 Supports Synaptic Health in the BTBR Mouse and Features a Favorable Safety Profile

Chronic unresolved inflammation is a common feature of several Central Nervous System (CNS) disorders, including autism spectrum disorder (ASD). We previously demonstrated that Formyl Peptide Receptor 2 (FPR2) activation by our agonist MR-39 reduced several inflammatory markers and improved social behavior in two validated animal models of ASD. Therefore, we decided to delve deeper into the potential of MR-39 as a drug for treating ASD. We first investigated the molecular mechanisms underlying the beneficial effects of MR-39 in BTBR mice. MR-39 significantly normalized pro-inflammatory cytokine release and NF-κB expression in the hippocampus and cortex, resulting in upregulation of synaptophysin protein levels, which, in turn, promote plasticity and correct abnormalities in dendritic spine morphology. Next, we characterized the safety and pharmacokinetic profile of MR-39 with respect to potential advancement for further pre- and clinical studies. We found that MR-39 was not genotoxic and safe to use since it had limited interaction with the majority of the targets associated with the adverse drug reaction. Consistently, a repeated-dose administration study evidenced no clinical signs attributable to treatment-related toxicity. On the other hand, MR-39 exhibited rapid hepatocyte clearance and interaction with efflux systems in vitro, suggesting possible limitations due to its pharmacokinetic properties. Finally, we explored multiple strategies to overcome MR-39’s low aqueous solubility, finding that the cosolvent approach can greatly enhance solubility and wettability. Overall, our study confirmed that promoting inflammation resolution with MR-39 can open new therapeutic options for ASD and that this compound has potential as a drug.

 

Why FPR2 is different

Most anti-inflammatory therapies work by blocking inflammatory pathways.

For example:

• statins reduce inflammatory signalling through multiple mechanisms
• pioglitazone shifts microglia towards a more reparative state via PPAR-γ
• ibudilast suppresses activated microglia
• low-dose naltrexone appears to reduce chronic glial activation through TLR4
• clemastine may reduce microglial activation while simultaneously promoting remyelination.

These are all potentially useful approaches, but fundamentally they are trying to dampen inflammation.

FPR2 works differently.

Inflammation is not simply switched on and then allowed to fade away. The body possesses an active programme that tells the immune system when the danger has passed and it is time to stop fighting and begin repairing damaged tissue.

FPR2 is one of the master regulators of this resolution of inflammation.

This distinction may prove extremely important in neurological disorders where persistent inflammation itself may be preventing normal synaptic development and plasticity.

 

Where is FPR2 found?

One reason FPR2 has attracted so much attention is that it is expressed in many of the cells involved in both inflammation and tissue repair.

Within the brain, FPR2 is found on:

• microglia - the brain's resident immune cells that monitor the environment, remove debris and regulate inflammation
• astrocytes - which support neurons, maintain the blood-brain barrier and participate in immune signalling
• neurons - suggesting FPR2 may influence synaptic plasticity and neuronal survival directly as well as indirectly through the immune system
• brain endothelial cells - which regulate communication between the bloodstream and the brain

Outside the brain it is expressed on many components of the innate immune system including neutrophils, macrophages, monocytes and several other immune cell types.

This broad distribution explains why FPR2 is now being investigated in such diverse conditions as Alzheimer's disease, stroke, multiple sclerosis, inflammatory bowel disease, rheumatoid arthritis, myocardial infarction and now autism.

Unlike many receptors that are confined to a single tissue, FPR2 appears to function as one of the body's master regulators of inflammation resolution. It helps coordinate the transition from an active immune response to tissue repair and restoration of normal homeostasis.

For autism this is particularly interesting because activating FPR2 could simultaneously calm activated microglia, reduce inflammatory cytokines, improve blood-brain barrier function and create an environment in which neurons and synapses can remodel more effectively.

Its widespread expression suggests that FPR2 is not simply controlling inflammation—it is coordinating the body's transition from defence to repair.

 

The experimental drug MR-39

The researchers tested a small molecule called MR-39, an activator of FPR2.

Interestingly, MR-39 was not originally developed as an autism therapy.

It emerged from research into neuro-inflammatory disorders, particularly Alzheimer's disease, illustrating an increasingly important trend in autism research: extending therapies developed for one neurological disorder into another when they target shared biological mechanisms.

Rather than developing drugs specifically "for autism", researchers are increasingly asking:

Which biological pathways are abnormal in autism, and are there drugs already being developed for those pathways?

This strategy has already given us therapies such as bumetanide, metformin, pioglitazone, statins and calcium-channel blockers.

MR-39 is another example.

An additional reason this approach is particularly attractive is that several studies have reported reduced circulating levels of Lipoxin A4 (LXA₄) in autistic children. LXA₄ is not just another anti-inflammatory molecule—it is one of the body's own specialised pro-resolving mediators (SPMs) and one of the principal activators of FPR2, already present in your body.

 

Decreased plasma levels of lipoxin A4 in children with autism spectrum disorders

The aim of this study was to evaluate the plasma levels of lipoxin A4 (LXA4), a mediator involved in the resolution of inflammation in Chinese children with autism spectrum disorders (ASD). From January 2013 to June 2014, a total of 150 children (75 confirmed ASD cases and 75 their age-matched and sex-matched control cases) participated in this study after consent was obtained from their parents. Clinical information was collected. Plasma levels of LXA4 were measured at baseline. The severity of ASD was assessed at admission using the Childhood Autism Rating Scale total score. The results indicated that the mean plasma levels of LXA4 were significantly lower in autistic children compared with the normal children (P<0.0001). There was a significant negative relationship between circulating LXA4 levels and severity of autism evaluated by Childhood Autism Rating Scale scores (P=0.006) after adjustment for the possible covariates.

These results suggested that autistic children had lower plasma LXA4 levels, suggesting an increased susceptibility to recurring inflammation in these samples.

 

In other words, the body already possesses a natural mechanism for activating this receptor and switching inflammation into its resolution phase.

If LXA₄ levels are indeed reduced in at least some autistic individuals, that natural "stop fighting, start repairing" signal may be weakened. MR-39 can therefore be viewed not as introducing an entirely artificial pathway, but as pharmacologically replacing or amplifying a biological signal that may already be deficient.

This provides a much stronger biological rationale for targeting FPR2 in autism than simply identifying it as another interesting receptor.

 

What did the new Italian study find?

Using the well-established BTBR mouse model of autism, the researchers found that after only eight days of treatment MR-39:

• significantly reduced the inflammatory cytokines IL-1β and TNF-α
• normalised NF-κB signalling
• increased levels of synaptophysin, an important marker of healthy synapses
• corrected abnormalities in dendritic spine morphology
• built upon previous work from the same laboratory showing improvements in social behaviour

One particularly encouraging finding was that MR-39 did not simply increase the number of synapses.

Instead, it appeared to improve their maturity.

The abnormal dendritic spines seen in the BTBR mice became much more like those found in healthy animals.

This is important because many forms of autism are characterised not simply by having too many or too few synapses, but by synapses that have failed to mature normally.

The findings therefore suggest that reducing chronic neuro-inflammation may allow existing neural connections to complete a more normal developmental programme, rather than simply creating new ones.

This may explain why MR-39 improved synaptic proteins and dendritic spine morphology without dramatically altering synapse number. Rather than forcing neurons to form new connections, the drug appears to create the biological conditions that allow normal developmental and repair processes to resume.

 

More than another mouse study

Many animal studies simply report behavioural improvements.

This paper goes considerably further.

The authors also examined:

• pharmacokinetics
• liver toxicity
• cardiac safety
• off-target effects
• genotoxicity
• metabolism
• formulation chemistry

In other words, they were already thinking like drug developers rather than purely academic scientists.

That makes this one of the more substantial preclinical autism studies published in recent years.

 

The challenges

MR-39 is not yet ready for human trials.

The authors identified several important limitations including poor oral bioavailability, rapid metabolism and potential cardiac and liver toxicity.

Fortunately, none of these appear insurmountable, and the compound was well tolerated in mice at therapeutic doses.

Like many first-generation research compounds, MR-39 itself may never become the final medicine.

Its greatest contribution may simply be demonstrating that FPR2 is a worthwhile therapeutic target.

 

Autism as a network disorder

One theme that has appeared repeatedly on this blog is that autism is probably best viewed not as a single biochemical defect, but as a network disorder.

Genes, mitochondria, immune activation, metabolism, ion channels, neurotransmitters and synaptic plasticity all interact to produce a stable pattern of brain function. Once established, that pattern may become a new homeostasis—a stable but abnormal equilibrium.

This helps explain why there is unlikely ever to be a single "autism drug".

A calcium-channel blocker may improve neuronal excitability.

A statin may reduce neuro-inflammation.

Pioglitazone may reprogramme microglia.

Clemastine may promote remyelination.

Bumetanide may restore inhibitory signalling.

Each addresses one part of the network.

The hope is not that one intervention completely resets the brain, but that multiple interventions gradually shift the network towards a healthier and more stable state.

Viewing autism as a network disorder naturally leads to a different therapeutic philosophy.

Instead of expecting one drug to correct every abnormality, the aim becomes rational polytherapy—combining carefully selected interventions that each influence a different component of the biological network.

One treatment might reduce neuro-inflammation.

Another might improve mitochondrial metabolism.

Another might restore inhibitory neurotransmission.

Another might promote remyelination.

Another might improve synaptic plasticity.

Individually these therapies may each produce only modest benefits.

Together, however, they may shift the entire network towards a healthier and more stable equilibrium.

This approach is already becoming familiar in other areas of medicine. Multiple sclerosis (MS) provides an excellent example. Twenty years ago, the primary goal of treatment was to suppress immune attack on myelin. Today, researchers increasingly recognise that long-term success also requires promoting remyelination, protecting neurons and encouraging the brain's own repair mechanisms. As a result, therapies such as clemastine, specialised pro-resolving mediators, neuroprotective agents and regenerative approaches are being investigated alongside traditional immunomodulatory drugs.

The philosophy is changing from simply stopping damage to actively promoting recovery.

I believe autism research is beginning to move in the same direction.

FPR2 is particularly interesting because it sits relatively high in the hierarchy of inflammatory regulation. Rather than blocking one inflammatory pathway, it appears to activate one of the brain's own programmes for restoring homeostasis. As such, future FPR2 activators/agonists may eventually become one component of a broader polytherapy approach that aims not merely to suppress symptoms, but to help the brain repair and reorganise itself.

  

Linking FPR2 with the Cell Danger Response

One striking aspect of this work is how well it fits with Robert Naviaux's Cell Danger Response (CDR) hypothesis.

Naviaux proposes that when cells encounter infection, toxins, trauma or metabolic stress they switch into a protective emergency programme.

Mitochondria alter their metabolism.

ATP is released outside cells as a danger signal.

Inflammatory pathways become activated.

Normal cellular communication becomes secondary to survival.

This response is entirely normal.

The problem arises if cells fail to exit this emergency state after the original danger has passed.

Viewed in this way, FPR2 could represent one of the mechanisms that helps cells transition out of the Cell Danger Response and back towards normal homeostasis.

Although this link remains speculative, it provides an intriguing framework that connects mitochondrial signalling, neuroinflammation and synaptic repair.

Interestingly, the two fields approach the problem from opposite directions.

Naviaux focuses on danger signalling—how cells detect injury and enter an emergency programme.

The FPR2 researchers focus on resolution signalling—how the immune system recognises that the danger has passed and initiates tissue repair.

These may simply represent different stages of the same biological programme.

One explains how the emergency begins.

The other may explain how it ends.

Ultimately, both point towards the same biological transition:

 

Stop defending. Start repairing.

Rather than directly repairing neurons, FPR2 activation may simply remove one of the major barriers preventing the brain from repairing itself.

 

Helping the body repair itself

Perhaps the most interesting lesson from this paper extends well beyond autism.

For decades drug development has largely focused on blocking abnormal pathways.

Block an enzyme

Block a receptor

Block a cytokine

Increasingly, medicine appears to be moving towards a different philosophy.

Many of the body's repair mechanisms already exist.

Stem cells migrate to damaged tissue.

Microglia clear cellular debris.

Specialised lipid mediators resolve inflammation.

Neurons remodel synaptic connections.

Oligodendrocytes repair myelin.

The challenge is often not that these systems are absent, but that they have become stalled or trapped in an abnormal steady state.

FPR2 appears to be one of the molecular switches that tells the immune system:

"The danger has passed. Stop fighting. Start rebuilding."

That may explain why FPR2 is attracting attention not only in autism, but also in Alzheimer's disease, stroke, multiple sclerosis and cardiovascular disease.

Rather than overriding biology, it appears to encourage biology to resume doing what evolution designed it to do.

 

Can we simply increase Lipoxin A4 instead?

An obvious question is: if autistic children have reduced levels of Lipoxin, why not simply treat with Lipoxin? Unfortunately, this is not practical. Like many of the body's own signalling molecules, Lipoxin is chemically unstable and has a biological half-life measured in minutes. It is rapidly broken down after being produced, making it a poor drug candidate.

This is the main reason researchers focus on developing stable FPR2 activators like MR-39, which are engineered to mimic the beneficial effects of Lipoxin while remaining active in the body for much longer. 

Another strategy is to encourage the body to produce more of its own Lipoxin. Unlike the resolvins, which are derived from omega-3 fatty acids, Lipoxin is synthesised from arachidonic acid (AA)—an omega-6 fatty acid that is already abundant in most people's cell membranes. The limiting factor here is not the availability of raw materials, but the activity of the specific enzymes required to convert that arachidonic acid into Lipoxin. At present, no supplement has been convincingly shown to raise Lipoxin levels in humans. 

However, there is growing evidence that regular aerobic exercise promotes the production of the body's broader family of specialised pro-resolving mediators (SPMs). For now, until stable analogues or molecular activators clear clinical trials, optimizing these natural physiological pathways remains our best practical tool.

 

Conclusion

MR-39 itself may never become an approved medicine. What encourages me far more is the direction in which neuroscience is moving. Research is gradually shifting away from searching for a single defective molecule and towards understanding the brain as a dynamic biological network capable of adaptation, repair and recovery.

The same trend is appearing across medicine. Many of today's most exciting therapies no longer attempt to repair the body themselves. Instead, they help the body repair itself. Whether through inflammation-resolution pathways such as FPR2, remyelination with clemastine, metabolic reprogramming with pioglitazone, restoration of inhibitory signalling with bumetanide, or perhaps one day therapies based on the Cell Danger Response, the underlying philosophy is becoming remarkably similar. The objective is not simply to suppress disease. It is to restore the conditions under which the brain can heal itself.

Increasingly, researchers are discovering that many chronic diseases are characterized not simply by excessive inflammation, but by a failure of that inflammation to resolve properly. Rather than continually developing stronger anti-inflammatory drugs to stomp out symptoms, the future lies in identifying the biological signals that tell the brain it is finally safe to stop defending itself and start developing normally again. If that philosophy proves correct, future autism treatment may consist of carefully selected combinations of therapies, each nudging a different part of the network in the same direction. Individually they may produce modest improvements, but together they may help the brain escape an abnormal equilibrium and settle into a healthier one.

In my specific case, I think we have already achieved this with my son’s Polypill therapy.