Mechanism of action of ascorbic acid: relationship with clinical trials

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(Oral presentation from Antwerp Consortium July 2009)

Mechanism of action of ascorbic acid: relationship with clinical trials.

S. Belin, F. Kaya, G. Duisit and M. Fontes

Therapy of Genetic Disorders, EA4263, FacuIte de Medecine, Marseille, France

Following our princeps work on partial correction of CMT mouse phenotypic

conection by high doses of ascOlbic acid (AA), we perform experimental work to

understand the basis of these observations.

Using transient transfection of Schwarm cell lines we demonstrated that AA

incubation inhibits the expression of PMP22 (IC50=440IlM) Same results have been

obtained with a C22 SC line. In addition we demonstrated that incubation of

Schwann cells with increasing concentrations of AA results in a decrease of the

intracellular pool ofcAMP (IC50=350 11M).

Using membranes isolated from schwann cell, we demonstrate that AA is a

competitive inhibitor of adenylate cyclase, explaining the decrease of cAMP pool

resulting from AA treatment From previous work on transgenic CMTIA mouse lines,

we deduced that PMP22 overexpression could be tolemted up to a threshold.

From Cl and C2 mouse lines, we know that 80% of overexpression of the human gene

is tolerated. From patients we know that 100% of overexpression leads to the

disease. Therefore, correcting only 20% of PMP22 verexpression is sufficient to

present a phenotypic impact.

Referring to our dosel response curve of PMP22 inhibition, we deduced that a

minimal extracellular concentration of 180llM of AA should be reached to reduce

the expression of PMP22 by 20% Referring to analysis of seric concentration of

AA, obtained from oral administration to healthy volunteers (Padayatty et ai,

2004), a minimal concentration higher that 2g per day is necessary to obtain a

concentration of 180 11M during more than 4/5 hours.

In conclusion, phenotypic correction of PMP22 overexpression by AA results from

competitive inhibition of adenylate cyclase lowering the cAMP pool and

inhibition of PMP22 expression. Additionally, if the treatment with AA works in

humans it could probably be

efficient only after a treatment by more than 2g in a single administration.