The mystery of 4-FA

[aced126]

I'm still not satisfied with how one para fluorine substitution can trigger such a big change in selectivity for 5HT release over amphetamine which is very much selective towards dopamine and norepinephrine release. Hydrogen bonding in halogens is very weak, and a fluorine on an aromatic is very slightly more hydrophilic than the hydrogen couterpart. The radii of both atoms are very similar instead.

I'm now starting to think that there is something more to just binding in explaining the changed selectivity in this compound. Any new readers to this thread can refer back to this (http://www.bluelight.org/vb/threads...And-methamphetamine-only-releases-1-10-of-5HT) which contains much more information about binding at SERT.

Could anyone hazard a guess as to other factors playing a part in the selectivity of this molecule. Both activated and deactivated rings can bind to SERT, so that rules out the effect of fluorine on the ring. Fluorine is a weak hydrogen bond acceptor ruling out the theory of a possible hydrogen bond. The radius of fluorine is very similar to hydrogen so steric clash is unlikely.

I'm now starting to think that there is an endogenous mechanism by which phenethylamine is able to work in a similar way to amphetamine (it is the body's natural amphetamine you could say; a massive surge of it is released when doing high intensity excercise). However there is another problem. Phenethylamine is only present in the cytosol of neurons mostly and both dopaminergic and serotonergic vesicles will be very close to identical. VMAT2 and TAAR1 has the identical protein structure in both neurons. There is no phenethylamine in the serotonergic neuron (I think), and so 4-FA has to be getting into the serotonergic neuron to facilitate its effects. Amphetamine does not have these effects.

Thus the only way 4-FA can do what it does is by getting into the 5HT neuron way better than amphetamine does. Am I missing a really obvious binding interaction. Fluorines are often substituted onto compouds to tinker with the compounds metabolism while retaining target efficacy.

TLDR; I think there is a possible logical biological explanation for this observation rather than a purely molecular approach.

 

[Seppi]

I wrote this in the other thread, but I'll repeat it here since this coupling mechanism likely triggers CAMKII phosphorylation; if so, differences between the interactions of different drugs on the coupled transporter/channel may produce variability in calcium influx and, in turn, different neurotransmitter release profiles between those drugs.

Just to clear up a point of confusion in this thread:
Amphetamine has one additional transporter phosphorylation mechanism (CAMKIIα) that is independent of TAAR1 and which produces neurotransmitter efflux from neurons.
TAAR1 mediates PKA and PKC signaling cascades that phosphorylate transporters, but not the CAMKIIα cascade. I'm fairly certain that the triggering mechanism for the CAMKIIα cascade has just recently been identified, but I can't be sure until I get my hands on this paper: https://www.ncbi.nlm.nih.gov/pubmed/26162812

If DAT & L-type calcium channel coupling does mediate CAMKII phosphorylation, then it is likely that transporter/channel coupling also mediates 5-HT release since SERT and L-type calcium channels have also been shown to couple -https://www.ncbi.nlm.nih.gov/pubmed/24854234 - in turn, this represents another target that accounts for variability between releasing efficacy of different compounds. Unlike PKA and PKC, CAMKII phosphorylation has no effect on neurotransmitter reuptake.

 

[un kle fukka]

I truly believe that stuff is harmfull

 

[un kle fukka]

observation primarily! PEACE

 

[un kle fukka]

WHAT IS ITS ph THEN?

 

[belligerent drunk]

I believe unclefucker is just a troll - he's been spamming the forum for some time.

 

[dopamimetic]

Yeah.. trolls are a really curious species somehow. Interesting where they take the energy and motivation off to do what they do. Sometimes it's difficult to tell if it's a case of psychosis or just trollitis, too... Don't know what the best comparison would be. Cockroaches? But the imagination of a troll animal is somewhat more appealing

Sorry for OT.

 

[belligerent drunk]

At first I thought this particular individual suffered from severe amphetamine-induced psychosis. It is likely, no? Maybe he still hasn't slept.

Sorry for OT as well.

 

[serotonin2A]

Aced126, the other part of the explaination that you are not taking into account is that 4-F also alters DAT affinity. You can potentially increase selectivity for 5-HT neurons vs DA neurons by enhancing SERT affinity or by reducing DAT affinity. 4-Fluoroamphetamine has lower affinity than amphetamine for DAT, which apparently shifts its action toward 5-HT release.

Things like CaMIIK may play a role in monoamine release induced by amphetamines, but those mechanisms cannot explain the selectivity (because they are downstream of the transporters, which is where the drugs are actually acting).

 

[belligerent drunk]

Aced126, the other side of the explaination that you are missing is what 4-F does to DAT affinity. You could potentially increase selectivity for 5-HT neurons vs DA neurons by enhancing SERT affinity or by reducing DAT affinity. 4-Fluoroamphetamine has lower affinity than amphetamine for DAT, which apparently shifts its action toward 5-HT release.

Things like CaMIIK may play a role in monoamine release induced by amphetamines, but would have nothing to do with the selectivity issue (because they are downstream of the transporter, which is where the drugs are actually acting).

What facilitates such change in affinity though? I'm curious about the exact mechanism as well. I don't believe that 4-fluoro is the same as 4-hydrogeno(sp?) as much as aced suggests, but still. Is there a generally accepted model of how these types of drugs bind to relative transporters?

 

[aced126]

Serotonin, are you suggesting that since less 4-FA is uptaken by DAT, more is available for SERT to uptake? If this was so, could an experiment be designed to test this: DAT is blocked by a high affinity ligand. Then administer say amphetamine and it should now releasee way more 5HT than usual because it can't be uptaken by DAT and so has to be taken up by SERT.

 

[Seppi]

Aced126, the other side of the explaination that you are missing is what 4-F does to DAT affinity. You could potentially increase selectivity for 5-HT neurons vs DA neurons by enhancing SERT affinity or by reducing DAT affinity. 4-Fluoroamphetamine has lower affinity than amphetamine for DAT, which apparently shifts its action toward 5-HT release.

Things like CaMIIK may play a role in monoamine release induced by amphetamines, but would have nothing to do with the selectivity issue (because they are downstream of the transporter, which is where the drugs are actually acting).

I was actually only referring to different releasing profiles across different drugs, not the releasing profile of one drug across different types of monoamine neurons. Nonetheless, the coupling mechanism mentioned in that paper suggests that the different monoamine transporters (DAT/SERT) couple to a distinct set of L-type calcium channels (evidence for NET suggests that it couples to calcium channels, but no further research has been conducted). The fact that the transporter/channel coupling differs does create the potential for more selective channel activity in different monoamine neurons for a given drug; however, again, more research would be needed to determine if it really is a source of selective release in different monoamine neurons.

In any event, that paper came to the same conclusion that I did about these channels and CAMKII phosphorylation:

"One example of interest is CaMKII, which has been well characterized as an effector of Ca2+ currents downstream of L-type Ca2+ channels [21,22]. Interestingly, DAT is a CaMKII substrate and phosphorylated DAT favors the reverse transport of dopamine [48,49], constituting a possible mechanism by which electrical activity and L-type Ca2+ channels may modulate DAT states and dopamine release."
- PMID 26162812

 

[Seppi]

Serotonin, are you suggesting that since less 4-FA is uptaken by DAT, more is available for SERT to uptake? If this was so, could an experiment be designed to test this: DAT is blocked by a high affinity ligand. Then administer say amphetamine and it should now releasee way more 5HT than usual because it can't be uptaken by DAT and so has to be taken up by SERT.

That basically boils down to a form of competitive uptake between neurons for substrates. Blocking DAT would probably make a difference in SERT uptake in such cases, but that difference would not be large.

 

[serotonin2A]

Serotonin, are you suggesting that since less 4-FA is uptaken by DAT, more is available for SERT to uptake? If this was so, could an experiment be designed to test this: DAT is blocked by a high affinity ligand. Then administer say amphetamine and it should now releasee way more 5HT than usual because it can't be uptaken by DAT and so has to be taken up by SERT.

That's not what I'm suggesting. The proportion of 4-FA molecules that are sequestered in nerve terminals and cell bodies relative to the concentration in the extracellular space is very low -- pumping less of the drug into dopaminergic terminals wouldn't change the extracellular concentration.

The response to 4-FA is a function of its affinity/efficacy at its molecular targets AND the concentration (which depends on the dose taken). If 4-FA only worked through DAT, then lowering its affinity for DAT wouldn't matter -- you could just take a higher dose to offset the reduction in potency. But 4-FA also works by releasing serotonin. Because of its effects on 5-HT, it may not be possible to raise the dose high enough to offset the loss of DAT affinity; high levels of 5-HT release are known to inhibit the dopaminergic system (dysphoria!!), and can produce intolerable side-effects (hyperthermia).

So if you reduce the affinity of amphetamine for dopamine terminals, without producing a parallel reduction of the affinity for serotonergic terminals, then you are effectively turning it into a moderately-selective serotonin releaser (e.g., 4-FA).

 

[bofh453]

I wrote this in the other thread, but I'll repeat it here since this coupling mechanism likely triggers CAMKII phosphorylation; if so, differences between the interactions of different drugs on the coupled transporter/channel may produce variability in calcium influx and, in turn, different neurotransmitter release profiles between those drugs.

Here you go. In short, use sci-hub.io. Also, fuck Elsevier.

 

[aced126]

That's not what I'm suggesting. The proportion of 4-FA molecules that are sequestered in nerve terminals and cell bodies relative to the concentration in the extracellular space is very low -- pumping less of the drug into it dopaminergic terminals wouldn't change the extracellular concentration.

So if you reduce the affinity of amphetamine for dopamine terminals, without producing a parallel reduction of the affinity for serotonergic terminals, then you are effectively turning it into a moderately-selective serotonin releaser (e.g., 4-FA).

If the extracellular concentration of 4-FA approximately remains constant, how can this final statement be true. Is it because the reduced DA affinity and the resulting increase in 5HT to DA affinity ratio means that a higher dosage can be taken to achieve serotonergic effects whereby the dopaminergic effects are suppressed and therefore don't overwhelm the former?

And how can a reduction in affinity for dopamine terminals be achieved without actually altering the ligand structure itself?

Also referring back to the experiment I suggested, if one blocked dopamine terminals with high affinity antagonist, surely a much higher dosage of 4-FA could be administered without significant DA release, and more 5HT release will occur due to the small affinity the molecule does have for SERT?

 

[dopamimetic]

In short, use sci-hub.io. Also, fuck Elsevier.

Yeah, thanks for sharing that sci-hub thing!

Knowledge is power

 

[neurotic]

I think it's pretty much what 5ht2a said.

4-FA might not (compared to amphetamine) have a high affinity for SERT but rather a lower affinity for the catecholamines, because in the end it's the overall ratio between the monoamines that matters. 4-FA doses are on the 100mg range.

I guess it's the same with meth and MDMA... I.e. meth might be a potent 5ht releaser but because its a much more potent catecholamine releaser this effect is overshadowed, which doesn't happen with MDMA. At 100+mg doses meth might release a lot of 5ht...

Now that's an interesting way of thinking when designing a new empathogen...

 

[aced126]

I think we should be careful when considering human dosage levels and relating that to monoamine releasing efficacy without taking into account pharmacokinetic properties of each specific molecule. Having said that, these molecules have relatively similar kinetics.

If all this is true, why is it that when a patient on an SSRI regime takes MDMA, the effects are completely nullified? Surely there should be DA release and subjective effects of DA releasers like amphetamine should be observed? Yet it seems the SSRI blocks all effects. I mean, yeah a lot of the supposed DA effects of MDMA might be downstream as a result of 5HT release but you would still expect it to get into DA terminals a bit?

 

[serotonin2A]

I think it's pretty much what 5ht2a said.

4-FA might not (compared to amphetamine) have a high affinity for SERT but rather a lower affinity for the catecholamines, because in the end it's the overall ratio between the monoamines that matters. 4-FA doses are on the 100mg range.

I guess it's the same with meth and MDMA... I.e. meth might be a potent 5ht releaser but because its a much more potent catecholamine releaser this effect is overshadowed, which doesn't happen with MDMA. At 100+mg doses meth might release a lot of 5ht...

Now that's an interesting way of thinking when designing a new empathogen...

Yes, that is pretty much what I was saying.

I think we have to consider that possibility when thinking about the MDMA SAR. Most people think that when Shulgin made MDMA, he was going from MDA > MDMA, but you can also think about the progression from methamphetamine to MDMA. He didn't know it at the time, but he made a methamphetamine derivative where the catecholaminergic activity is greatly attenuated, allowing the dose to be pushed much higher. It turns out MDMA produces a ton of 5-HT release if you push the dose up to ~75 mg, which gives you a very different effect compared to methamphetamine.

There are two differences between (S)-METH and (S)-MDMA: compared to (S)-METH, (S)-MDMA has higher affinity for SERT AND lower affinity for DAT.

If all this is true, why is it that when a patient on an SSRI regime takes MDMA, the effects are completely nullified? Surely there should be DA release and subjective effects of DA releasers like amphetamine should be observed? Yet it seems the SSRI blocks all effects. I mean, yeah a lot of the supposed DA effects of MDMA might be downstream as a result of 5HT release but you would still expect it to get into DA terminals a bit?

I don't think the effects of MDMA are completely nullified by SSRIs. There is definite attenuation of the effects of MDMA, but the effects are not completely blocked. The catecholamine-releasing effects of MDMA are not extraordinary at normal doses, so you wouldn't expect to see much of a stimulant response induced by MDMA when the effect on 5-HT release is blocked. It's possible that MDMA would act more like methamphetamine in SSRI treated subjects if they took very high doses, but we won't know until someone tries it (I'm not actually recommending that someone should try that).

If we look at the MDMA/SSRI interaction studies:

(1) In: http://www.ncbi.nlm.nih.gov/pubmed/10731626

Vollenweider gave 40 mg (iv) citalopram prior to ~100 mg (po) MDMA. If you look at the 5D-ASC data (Figure 1 and Table 1), you can see that the combination of MDMA and citalopram was able to produce a substantial response, but it was no where near as intense as the response to MDMA alone. It looks like MDMA/citalopram produced about 40% of the effect induced by MDMA on positive mood.

If you look at their Adjective Mood Rating Scale data (Figure 2), there was actually very little difference between the effects of MDMA vs. citalopram and MDMA.

(2) in: http://www.ncbi.nlm.nih.gov/pubmed/17047932

Tancer and Chris-Ellyn Johanson gave 20 mg/day fluoxetine for 5 days and then gave subjects ~100 mg MDMA. Many of the effects of MDMA were only partially blocked.