What are the limits to mRNA?
December 20, 2020 9:22 AM Subscribe
The new vaccine is frankly, completely bonkers. It's the equivalent of winning a war by dropping leaflets. What are the limits for mRNA getting into our cells? Could you eat it or inhale it?
It took me a few tries to understand it, but the Moderna and Pfizer vaccines contain no virus, or even proteins, and consist entirely of messenger RNA. The entire vaccine is the code to make the spike protein, which is picked up by our cells, that then fabricate the characteristic spike protein of the coronavirus. The immune system recognizes the protein, and boom, immunity! So what are the limits here? Could you eat a bunch of mRNA and make your body fabricate proteins? What about inhaling it into the lungs, or putting some on a mucus membrane like inside your nose? Could you use the mRNA to construct other proteins that are currently too delicate to put in a pill or shot? I'm curious about the possibilities.
It took me a few tries to understand it, but the Moderna and Pfizer vaccines contain no virus, or even proteins, and consist entirely of messenger RNA. The entire vaccine is the code to make the spike protein, which is picked up by our cells, that then fabricate the characteristic spike protein of the coronavirus. The immune system recognizes the protein, and boom, immunity! So what are the limits here? Could you eat a bunch of mRNA and make your body fabricate proteins? What about inhaling it into the lungs, or putting some on a mucus membrane like inside your nose? Could you use the mRNA to construct other proteins that are currently too delicate to put in a pill or shot? I'm curious about the possibilities.
Typically the major issue with mRNA is that it's not very stable -- it's constantly getting broken down. The amount of time it hangs around will differ dramatically depending on the species you're putting it into & the sequence of the mRNA itself, but the breakdown can be on a minutes to hours timescale. I was actually (pleasantly!) surprised to hear that the mRNA vaccines worked, I was expecting them to degrade so rapidly that they wouldn't produce much immune response.
Anyway, this is why you're hearing a lot about special temperature storage conditions (-80 C freezers) for the vaccine. Off the top of my head, I would expect eaten mRNA to be completely broken down by stomach acids, but you could do something similar with regular old DNA (a plasmid). You can look at gene guns (pretty much what it sounds like), electroporation, or transfection -- those are all fairly standard lab techniques to introduce foreign DNA.
Once you get past all the efficiency and RNA fragility problems, yes, in principle mRNA can code for any protein as long as the host species has the necessary amino acids present.
posted by angst at 10:02 AM on December 20, 2020 [2 favorites]
Anyway, this is why you're hearing a lot about special temperature storage conditions (-80 C freezers) for the vaccine. Off the top of my head, I would expect eaten mRNA to be completely broken down by stomach acids, but you could do something similar with regular old DNA (a plasmid). You can look at gene guns (pretty much what it sounds like), electroporation, or transfection -- those are all fairly standard lab techniques to introduce foreign DNA.
Once you get past all the efficiency and RNA fragility problems, yes, in principle mRNA can code for any protein as long as the host species has the necessary amino acids present.
posted by angst at 10:02 AM on December 20, 2020 [2 favorites]
If you ate or breathed the vaccine it, your body would break it down. That's why you need to get a shot.
posted by tivalasvegas at 10:18 AM on December 20, 2020
posted by tivalasvegas at 10:18 AM on December 20, 2020
I love this question because it's a great chance to understand how biochemistry matters at the atom by atom level. Leaving aside the way that they are modified, folded up, located within the cell, and bound to different proteins, there are two key differences between DNA and RNA. The first one gets taught in middle and high school: thymine nucleobases in DNA are replaced by uracil in RNA. The second one gets a little less attention, but is far more important to your question: the five-carbon sugar those As, Cs, Gs, Ts, and Us are attached to differs by a single atom at a single position between RNA and DNA, and that single change makes a huge difference in the stability of the two molecules. DNA has a hydrogen at the 2´ ("two-prime") position on the ring. RNA has a hydroxyl (-OH) at the same location, meaning the two molecules differ by a single oxygen atom.
When the hydroxyl is deprotonated (loses its hydrogen; happens all the time), that oxygen acquires a negative charge, allowing the oxygen (now playing the role of a nucleophile) to literally attack the backbone structure of the RNA molecule, so that in effect, the RNA destroys itself. To make matters worse, intracellular nucleases (degrading enzymes) take advantage of this Achilles heel of RNA molecules in a variety of ways, often interacting with the 2´-OH to in ways that allow them to coordinate ripping off the hydrogen to literally generate the negatively charged oxygen and then shove it up against the phosphodiester backbone to cleave RNA more rapidly. Together, these explain many of the reasons why RNA has a much shorter half-life than DNA.
So you may be wondering: how do we make RNA therapeutics that survive long enough to be administered to a person and produce an effect? Three answers:
1. Keep them cold (to reduce auto-hydrolysis and keep them below the temperatures at which nucleases are active).
2. Give them a protective coat (the lipid layer hermanubis mentions).
3. Stabilize the RNA biochemically to help them last a little longer. This is not being done for the COVID-19 vaccines, but a handful of RNA-based injectable drugs (like nusinersen) now actually replace the 2´-OH with a more stable biochemical group that still looks enough like an RNA to a cell, but which confers additional stability and resistance to enzymatic degradation, and also reinforce the phosphodiester backbone with stronger linkages.
However, as an RNA biologist who cares a lot about this kind of thing, even if I stabilized the heck out of an RNA molecule, I'd have low hopes for it surviving the mammalian digestive system. I haven't tried it, though.
posted by deludingmyself at 10:31 AM on December 20, 2020 [52 favorites]
When the hydroxyl is deprotonated (loses its hydrogen; happens all the time), that oxygen acquires a negative charge, allowing the oxygen (now playing the role of a nucleophile) to literally attack the backbone structure of the RNA molecule, so that in effect, the RNA destroys itself. To make matters worse, intracellular nucleases (degrading enzymes) take advantage of this Achilles heel of RNA molecules in a variety of ways, often interacting with the 2´-OH to in ways that allow them to coordinate ripping off the hydrogen to literally generate the negatively charged oxygen and then shove it up against the phosphodiester backbone to cleave RNA more rapidly. Together, these explain many of the reasons why RNA has a much shorter half-life than DNA.
So you may be wondering: how do we make RNA therapeutics that survive long enough to be administered to a person and produce an effect? Three answers:
1. Keep them cold (to reduce auto-hydrolysis and keep them below the temperatures at which nucleases are active).
2. Give them a protective coat (the lipid layer hermanubis mentions).
3. Stabilize the RNA biochemically to help them last a little longer. This is not being done for the COVID-19 vaccines, but a handful of RNA-based injectable drugs (like nusinersen) now actually replace the 2´-OH with a more stable biochemical group that still looks enough like an RNA to a cell, but which confers additional stability and resistance to enzymatic degradation, and also reinforce the phosphodiester backbone with stronger linkages.
However, as an RNA biologist who cares a lot about this kind of thing, even if I stabilized the heck out of an RNA molecule, I'd have low hopes for it surviving the mammalian digestive system. I haven't tried it, though.
posted by deludingmyself at 10:31 AM on December 20, 2020 [52 favorites]
Oh, and for what it's worth, the RNA would do just fine in the acid environment of the stomach. Acidic environments are great for RNA because an excess of hydrogen ions (the literal definition of acidity) means it's less likely for the 2´-OH to lose a hydrogen to the surrounding liquid. (In contrast, when I want to fragment RNA quickly for an experiment, I heat it up in a basic solution for a minute or two and it shreds right up.) The problem is the digestive enzymes in the stomach, of which you have many. Just as you've got enzymes to rip apart starches and proteins, your stomach is also ground zero for dismantling RNA and DNA you consume. Weirdly enough, it seems like this is performed by pepsin, an enzyme I think of purely as a protease, but it seems to multitask: Digestion of Nucleic Acids Starts in the Stomach.
posted by deludingmyself at 10:45 AM on December 20, 2020 [14 favorites]
posted by deludingmyself at 10:45 AM on December 20, 2020 [14 favorites]
To borrow the asker's war analogy, there's a huge difference between randomly dropping leaflets out of an airplane and hoping enemy soldiers nearby will just happen to pick it up, vs having a spy on the inside feeding information directly to the admirals and generals in getting your body to do what we want. Your skin is actually an amazing protective organ, and injecting a vaccine gets it right where it needs to be. Eating or inhaling it does very little to teach your body about the antibodies it needs. Your body is good at ejecting, sometimes violently, things you've eaten that it thinks is poisonous, through vomiting or diarrhea (though it's not foolproof). Inhaling things is also of limited benefit because of your bodies natural defense defense there, with mucous/snot.
It's a bit tricky to understand, since inhaling the SARS-Cov-2 virus is how most people are catching it. However, that's just how the virus gets into you. From your lungs, it develops further into full blown COVID-19. (It's not simply a respiratory virus. Here's a UCSF article talking about why that's not right.) In developing antibodies, your body is on the look-out for these specific kinds of foreign virus particles, and ready to repel them in a way that eating or snorting the mRNA particles simply isn't able to teach your body.
posted by fragmede at 11:26 AM on December 20, 2020 [2 favorites]
It's a bit tricky to understand, since inhaling the SARS-Cov-2 virus is how most people are catching it. However, that's just how the virus gets into you. From your lungs, it develops further into full blown COVID-19. (It's not simply a respiratory virus. Here's a UCSF article talking about why that's not right.) In developing antibodies, your body is on the look-out for these specific kinds of foreign virus particles, and ready to repel them in a way that eating or snorting the mRNA particles simply isn't able to teach your body.
posted by fragmede at 11:26 AM on December 20, 2020 [2 favorites]
I found this Nature article very useful in understanding how mRNA vaccines work and were developed. It looks like a pretty technical article but I managed to understand most of it.
As folks have said, it's quite a challenge to package the mRNA, keep it stable, and get it inside cells. That's what took so long to develop working ones.
posted by Nelson at 8:47 AM on December 21, 2020
As folks have said, it's quite a challenge to package the mRNA, keep it stable, and get it inside cells. That's what took so long to develop working ones.
posted by Nelson at 8:47 AM on December 21, 2020
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If you ingest the vaccine this lipid layer will be broken down by the digestive system, and the mRNA will subsequently be broken down and have no effect.
Nasal administration would get the vaccine into the bloodstream, though it might require a slightly different wrapping layer to promote uptake. See this paper (in mice).
Currently, continued administration of mRNA nanoparticles is too dangerous for treatments that require continual dosage due to the lipid encapsulation's liver toxicity. Moderna started out with mRNA as a general drug platform to treat almost any disease, then pivoted to rare diseases caused by errors in specific proteins, then to vaccines that require much less dosage. However, of course, research continues and further advancements are possible that make it a more general technology.
posted by hermanubis at 9:57 AM on December 20, 2020 [19 favorites]