Can I take adenosylcobalamin at the same time as methylcobalamin?
Theoretically yes - ie taking the two different forms at the same time shouldn't matter though the amount of the total dose might. There is very limited capacity to absorb B12 via the oral or sublingual route (it appears that sublingual is actually oral. It appears to be more efficient because the lozenge dissolves slowly and the amount entering the gut for absorption is kept low, so more ends up being absorbed compared with the full dose going into the stomach at the same time.).
Having said that, the fact that you respond more favourably to the adenosyl form suggests that the normal B12 processing steps maybe don't apply to you and we enter the murky territory of poorly understood alternative pathways.
@Freddd has reported that for him at least, the two forms appear to compete and he takes them separately. As for the proportions of each that he finds helpful, I am sure that is an individual thing. You would need to determine your own response to each form.
In your case taking the two forms separately might be a wise precaution. In any case it is a good idea regardless of form to spread out doses.
You might want to consider alternative application routes, eg injection or topical. I'm not sure if the adenosyl form is available via injection - I seem to recall Freddd saying it is. You would need to check, certainly the methyl form is.
This is undoubtedly the best way to build up high levels and achieve the flooding of the CNS that Freddd talks about.
Alternatively there is the topical route.
These products have been tried by a number of people on PR, including myself. Some swear by them, others who needed high doses have returned to injections. I alternate between the methyl oil and a homemade version (see more below) plus a little adenosyl in sublingual form.
The scientist who runs the company is very helpful about answering questions. He says in experiments done to develop the product, he found about 80% absorption of these oils. Absorption from sublingual is at best around 10%. Absorption from injections close to 100%.
If you try the oils I would suggest you at least start with separate adenosyl and methyl forms.
The homemade version just uses
liquid methylcobalamin (not sure if a liquid adensoyl is available anywhere) mixed with a little body lotion in the palm of the hand and rubbed into the soft skin of the underarms, abdomen or buttocks.
Quadros ("Advances in the understanding of cobalamin assimilation and metabolism") has a section on absorption but I can't make sense of it. I did see you once post about haptocorrin and transcobalamin which are compounds, as far as I can tell, that seem to be involved in absorption but I really can't understand much about it.
Haptocorrin (HC) and transcobalamin 2 (TCN2) are carrier proteins which transport cobalamin in the blood. HC is also present in saliva.
Cobalamin is a very reactive molecule and the cobalt atom at its centre is very susceptible to oxidation. Consequently the molecule is not left naked in the body, it is always accompanied by some sort of protein which acts in a protective role.
Cobalamin in food is usually protein bound already but just in case, there is HC around in saliva. Once in the stomach the acid environment helps to separate cobalamin from protein and it then is bound to intrinsic factor (IF).
The IF-cobalamin is absorbed in the small intestine via a specific receptor for the complex, called cubilin. In the absence of IF, little absorption occurs. This is the case for pernicious anaemia.
Before it reaches the peripheral circulation, cobalamin is transferred from IF to HC and TCN2. About 80% of cobalamin in the blood is bound to HC, the rest to TCN2. It is only the later form that is taken up into cells in the body, again via a specific receptor for the complex. I have described what happens to the cobalamin-TCN2-receptor complex inside the cell in an earlier post.
I honestly don't know if TCN2 has a preference for one form of cobalamin over another. Undoubtedly I could find out by reading detailed studies about the carrier protein, but I haven't the energy for it. Normally, the predominant form in the blood is methylcobalamin. In the case where large amounts of other forms are supplemented (particular via injection where high concentrations could be reached), presumably those forms would be more abundant than methyl.
As far as I know they should all be bound to TCN2 and taken into the cell.
Also as far as I know naked cobalamin is not taken into the cell, it must be bound to a serum factor. In the alternative route of passive diffusion of cobalamin into the cell (ie not via the usual receptor mediated mechanism) which is usually referred to in studies but not further defined, I don't know if the protein is TCN2, nor have I seen any studies of what happens to cobalamin taken up via this route.
Freddd appears to have adult onset cblC disease. The genetic defect here lies in the processing which occurs after cobalamin has been separated from TCN2 inside the cell. Normally, the upper axial ligand (ie the methyl, adensoyl etc group) is then removed by the protein product of the gene
MMACHC.
Cobalamin is then routed to either the methionine synthase enzyme where it is methylated and used by that enzyme, or to the mitochondrion where it is adenylated and used by methylmalonyl CoA mutase.
When
MMACHC is defective, both B12 dependant enzymes receive insufficient cofactor and so both are unable to function properly. Consequently people with this defect show both elevated homocysteine and MMA.
In your case I am assuming that the defect may lie only in the mitochondrial pathway, but that is only an assumption. Have you had homocysteine measured?