Angiotensin II in the Brain & Therapeutic Considerations

In a previous post I suggested that another cheap generic drug (an ACE inhibitor) could potentially be repurposed to treat schizophrenia and some autism. The original idea was related more to modifying the immune/inflammatory response in the body, rather than the brain.  There is however plenty of research regarding Angiotensin within the brain and the numerous roles it plays.

Juggling - maximizing effects, while minimizing
drug interventions

You may recall in the earlier post that in both schizophrenia and autism there is elevated angiotensin II.

In the brain there are two types of angiotensin receptor, AT1 and AT2.  Their actions are opposing each other.

In many kinds of disease we would want to stimulate AT2, but inhibit AT1.

AT2 is thought to be important for cognitive function and is now a target for Alzheimer’s research.

Using an ACE inhibitor you reduce the amount of angiotensin II and so in effect inhibit both AT1 and AT2.

In theory angiotensin II should not cross the blood brain barrier (BBB), so we should be dealing with centrally produced (i.e. inside the brain) angiotensin II.  In practical terms it seems that people with high levels of angiotensin II may have a permeable BBB.

This is relevant because most ACE inhibitors do not cross the BBB, but the original ACE inhibitor called Captopril does cross the BBB.  So if a centrally acting ACE inhibitor were found to be required, it was discovered 40 years ago.

A therapy would ideally be targeted selectively at AT1 or AT2 receptors.  An AT1 blocker might treat for stress-induced disorders.  An experimental AT2 receptor agonist, called compound 21, is now available and is expected to reduce inflammation and oxidative stress.

Compound 21, a selective agonist of angiotensin AT2 receptors, prevents endothelial inflammation and leukocyte adhesion in vitro and in vivo.

Angiotensin II receptor AT1 antagonists are widely used drugs indicated for hypertension, diabetic nephropathy and congestive heart failure. They block effect of Angiotensin on AT1 and might be good in the brain.

We would like to increase the effect on AT2, we could do that with more Angiotensin II, but then we would make things worse with AT1.

                          Do nothing  ACE inhibitor    AT1 antagonist      AT2 agonist

Effect on AT1               none                            good                                     good                          none

Effect on AT2               none                            bad                                       none                          good

AT1 antagonists are widely available and seen as well tolerated.

AT1 antagonists appear to protect against Alzheimer’s.

The only AT2 agonist is an experimental drug called Compound 21.

The only ACE inhibitor that should affect AT2 in the brain is Captopril and so may be an unwise choice. It will reduce Angiotensin II in the brain and in the rest of the body.


Why were we interested in Angiotensin?

Targeting Angiotensin in Schizophrenia and Some Autism

In the original Angiotensin post in this blog we saw that in schizophrenia and some autism, that Angiotensin II is elevated.  We also saw that:-

·        Blocking angiotensin-converting enzyme (ACE) induces those potent regulatory T cells that are lacking in autism and modulates Th1 and Th17 mediated autoimmunity.  See my last post on Th1, Th2 and Th17. 

·        In addition, Angiotensin II affects the function of the NKCC1/2 chloride cotransporters that are dysfunctional in much autism and at least some schizophrenia.

·        It should also reduce any troubling high levels of leptin, which we saw in another post is an issue in most autism

So the idea was that many broadly anti-inflammatory effects of reducing Angiotensin II might be helpful in autism.

But what about inside the brain?

Angiotensin in the Brain

Here we do get to the science, but I will start with the conclusion. We actually want more effect from the Angiotensin AT2 receptor, which should give numerous benefits, but have no means of achieving this. What we can do is make sure we do not reduce AT2 activity, this means better to use and AT1 antagonist, rather than an ACE inhibitor.

The science supporting the use of an AT agonist follows:-

In the text you will see ARB and compound 21. Both are doing good things. The suggestion is that by doing all these good things there should be improved cognitive function; this has yet to be proved in human tests.

ARB = Angiotensin Receptor AT1 Blocker

Compound 21 = Angiotensin Receptor AT2 agonist

Roles of Brain Angiotensin II in Cognitive Function and Dementia

The brain renin-angiotensin system (RAS) has been highlighted as having a pathological role in stroke, dementia, and neurodegenerative disease. Particularly, in dementia, epidemiological studies indicate a preventive effect of RAS blockade on cognitive impairment in Alzheimer disease (AD). Moreover, basic experiments suggest a role of brain angiotensin II in neural injury, neuroinflammation, and cognitive function and that RAS blockade attenuates cognitive impairment in rodent dementia models of AD. Therefore, RAS regulation is expected to have therapeutic potential for AD. Here, we discuss the role of angiotensin II in cognitive impairment and AD. Angiotensin II binds to the type 2 receptor (AT₂) and works mainly by binding with the type 1 receptor (AT₁). AT₂ receptor signaling plays a role in protection against multiple-organ damage. A direct AT₂ receptor agonist is now available and is expected to reduce inflammation and oxidative stress and enhance cell differentiation. We and other groups reported that AT₂ receptor activation enhances neuronal differentiation and neurite outgrowth in the brain. Here, we also review the effect of the AT₂ receptor on cognitive function. RAS modulation may be a new therapeutic option for dementia including AD in the future.

Figure 1: Possible effect of angiotensin II on neurovascular unit. AT₂: angiotensin II type 2 receptor, AchR: acetylcholine receptor, BBB: blood brain barrier, and TGF-β: transforming growth factor β.

Figure 2: Effect of angiotensin II type 2 receptor signaling on cognitive function. AT₂: angiotensin II type 2 receptor, ATIP: AT₂ receptor-interacting protein, Id1: inhibitor of DNA binding protein 1, MMS2: methyl methanesulfonate-sensitive 2, NO: nitric oxide, SHP-1: Src homology 2 domain-containing protein-tyrosine phosphatase 1, and Ubc-13: ubiquitin conjugating enzyme 13.

Figure 3: Effect of angiotensin II on cognitive function. ACE: angiotensin converting enzyme inhibitor, AT₁: angiotensin II type 1 receptor, AT₂: angiotensin II type 2 receptor, and ARB: angiotensin II type 1 receptor blocker.

Continuous stimulation with angiotensin II may damage neurons via multiple cascades through AT₁ receptor stimulation. On the other hand, stimulation of the AT₂ receptor is expected to prevent neural damage and cognitive impairment (Figure 3). However, it is difficult to perform clinical intervention studies to confirm the results of animal studies because of the long-term progression of cognitive impairment. Moreover, in clinical practice, it is not possible to exclude the antihypertensive effect of RAS blockade on cognition in patients with hypertension. However, RAS modulation may be a new therapeutic option for dementia including AD in the future. Therefore, the hypothesis that RAS regulation affects future cognitive function should be confirmed with carefully designed clinical studies.

Which ARB (Angiotensin Receptor Blocker) for Autism?

Very many biological markers are disturbed in autism and many of them seem to be best ignored, you cannot “correct” them all.

However, there will be an underlying reason behind each one of them being disturbed.

As we saw in the recent post on metabolic syndrome, it is not uncommon to find a cascade of downstream problems that might seem to indicate a huge list of drugs.  A different approach is required, it is necessary to treat the underlying (upstream) problems and have a much shorter list of therapies.

We saw in the post on leptin that the elevated levels in autism are treatable, but is there any point?

We have a long list of other things that might be useful in autism and it would be nice to have a single therapy that might address many of them.

It appears that selecting the optimal ARB might give the opportunity to address numerous issues at once.

Telmisartan seems to have numerous potentially useful additional effects:

·        Acts as a PPAR gamma agonist, like the glitazone drugs shown effective in autism trials

·        Acts as a PPAR delta agonist, which should activate the impaired PPARδ  PGC-1α signaling pathway, and enhance mitochondrial biogenesis. This should help people with mitochondrial disease and should be evident by increased exercise endurance and, in theory, improved cognitive function.

·        Telmisartan regulates the Bcl-2 cancer gene, implicated in autism

BDNF-Akt-Bcl2 antiapoptotic signaling pathway is compromised in the brain of autistic subjects

While the effect in autism is complex, Telmisartan is already seen as a potent target for prevention and treatment in human prostate cancer

·        Telmisartan and other ARBs appear to give protection from Alzheimer’s Disease (suggested to be via its effect on PPAR gamma). Perhaps useful for young adults with Down Syndrome, where early onset Alzheimer’s is expected?

·       Telmisartan and other ARBs have a tendency to increase the level of potassium in blood. Up to 10% of people would experience mild hyperkalemia.  For people with autism taking bumetanide, this effect on potassium might actually be helpful. They would need to reduce their potassium supplementation, or might need none at all.

Telmisartan in clinical trials related to autism

As is repeatedly the case, schizophrenia research is again more advanced than autism research. A quick check showed this:-

Telmisartan Completed Phase 4 Trials for Schizoaffective Disorders / Schizophrenia Treatment

This is a 12-week, randomized, double-blinded, placebo-controlled trial of telmisartan 80 mg/day as an adjunctive to clozapine or olanzapine therapy, in 70 schizophrenia subjects to examine telmisartan's effect on glucose metabolism, weight, food intake, resting energy expenditure, and body composition. In addition, the study will examine insulin's effects on psychopathology and cognition.

Conclusion

We currently have no possibility of something like Compound 21, but Telmisartan looks very interesting and it would nice if those psychiatrists who have trialed it in schizophrenia would do the same in autism.  

It looks like the beneficial effects should come at a lower dose than that used to lower blood pressure. In the schizophrenia trial I think they used a higher dose (80mg) than necessary, I suppose they wanted to maximize their chance of success.  In order to minimize any possible negative effects, I would suggest the psychiatrists trial 20mg in youth with autism.

There will be a post on PPAR delta and mitochondrial disease, because there are at least two other ways to target mitochondrial disease in this way, if you do not like Telmisartan.  There is the cheap drug Bezafibrate and the supplement berberine.

The Singing Statin, the BCL-2 Gene and Epigenetics

This post has something for both the casual reader and the scientists among you.  Today I will start with the science.

Epigenetics

Epigenetics are chemical markers that can appear on your DNA as the result of some environmental exposure, like diet or stress.  Methylation is a type of epigenetic change in which methyl groups are added to DNA and switch on or off the underlying gene.  This can have severe consequences depending on which gene is affected.

Identical Twins

It seems that if one identical twin has autism, there is a 70% chance that the other twin will be autistic.  In 30% of the cases the twin is neurotypical.  Researchers have very cleverly started to analyse pairs of twins from this 30% group and look for epigenetic marks.  This would highlight genetic causes of autism.

Apoptosis

Apoptosis is a tricky word to spell, for somebody like me, but is actually something quite simple; it is programmed cell death.  Apoptosis happens in all of us, all day long.  If it gets out of control, it becomes bad and something called atrophy will occur.  Too little apoptosis can result in irregular cell growth and cancer.

 

Candidate Genes

Using the epigenetics approach, in 2010 a study was published that identified two “candidate” genes linked to autism.  They were BCL-2 and RORA.

According to that study, BCL-2 is an anti-apoptotic protein located in the outer mitochondrial membrane that is important for cell survival under a variety of stressful conditions.  In other words BCL-2 inhibits cell death.

According to another source, BCL-2 is “one of the foremost anti-apoptotic molecules”.

A very recent study has identified more such genes, using the same approach.

 

If you are really interested in the genetics of autism, there is actually a database of all the indicated genes, maintained by the Simons Foundation.

  

BCL-2 and autism

Going back to 2001, researchers had already noted that the autistic brain was deficient in BCL-2 and they suggested that:-

“These results indicate for the first time that autistic cerebellum may be vulnerable to pro-apoptotic stimuli and to neuronal atrophy as a consequence of decreased BCL-2 levels.”

The study is called :- Reduction in anti-apoptotic protein Bcl-2 in autistic cerebellum

As we have already learned, in the autistic brain the important Purkinje Cells are reduced in number by half due to atrophy.  If BCL-2 can indeed reduce this excessive apoptosis, it should be a friend indeed.

 

Stimulating production of Bcl-2

Fortunately the clever people working with Professor Wood, at the University of Minnesota, have been studying cholesterol regulation in the brain for some time.  Here is what they have been up to:-

“The lab has recently made the novel discovery that statins both in vivo and in vitro stimulate gene expression and protein levels of one of the foremost anti-apoptotic molecules, Bcl-2. Currently, studies are focused on mechanisms of statin-induction of Bcl-2”

Or in plainer English, statin drugs increase your level of BCL-2 and so reduce cell death.
 

If you want to read more here is an open access paper:-  Simvastatin Stimulates Production of the Antiapoptotic Protein Bcl-2 via Endothelin-1 and NFATc3 in SH-SY5Y Cells

 

The Singing Statin

Now we have finished with the pure science and we move back to the practical world of applied science.

Monty, aged 9, has been taking atorvastatin for a few weeks.  After day one, he developed the urge to play the piano outside of lesson time.  Every day since, he has played more and more.  Now his piano teacher says she thinks he has absolute pitch.  It turns out that this is far more common in the autistic population and there is a great deal of research that has been done on this and music/autism in general.  Here is a short article on the subject.

Now in an earlier post we established the importance of the stress hormone cortisol and also the interesting finding that you can reduce it by singing.  Then I got people asking about, “what about just listening to music” or “what about playing an instrument”.  I did not do the research, but I think nothing works like a good sing.

So yesterday I was delighted to hear that Monty has started to sing spontaneously in his room.  He put on his Mozart CD and started to sing, with his own lyrics and not just in English, but also in his second language.

I have to thank Mr Pfizer and in fact Mr Bruce Roth for bringing us Atorvastatin (called Lipitor or Sortis, depending on where you live).  Mr Roth invented it in 1985.

Perhaps BCL-2 could be better named the Singing Gene?