Ascorbic Acid (Vitamin C); a first generation medication for CMT 1A?

[Guest guest]

Dear ers,

Below is the English translation article From Med Sci (Paris). 2004

Oct;20(10):843-844 on Ascorbic Acid/Vitamin C.(with generous thanks to

Joyce in Sweden for her outstanding help!) (Thanks too, to Dr. Fontes,

for his generosity in sharing his review with us) Footnotes and the

Figures from are in pdf format along with the original article in our

Files section. ~ Gretchen

Ascorbic acid, a first generation medication for Charcot Marie Tooth

disease type 1A? by Michel Fontès; (Inserm U. 491 Génétique médicale et

développement Faculté de Médécine de la Tirnone, 27, boulevard Jean

Moulin, 13385 Marseille Cedex 5, France

Charcot-Marie Tooth (CMT) is the most frequent form of peripheral

demyelinating neuropathy and the neuomuscular disorder which affects 1

out of 2,500 persons) [1]. It is characterized by a progressive atrophy

of the distal muscles. The first symptoms appear between 20 and 30

years, but about 10% of the cases concerns children or teen-agers. This

disease is genetically heterogenous, but half of the patients are

affected by the disease type 1A.

It is a demyelinating form which is due to a partial trisomy of a little

region of the short arm of the chromosome 17 [2, 3], including the gene

PMP22 that is implied in the myelination processes [4]. In order to

understand more the physiopathology of CMT and to

propose therapeutical solutions, in 1996, along with collaboration with

C. Huxley, we have built an animal model of this disease, by inserting a

YAC (yeast artificial chromosome) of 560 kb containing the gene PMP22

human, in the genome murin [3]. This strategy of producing “humanized”

mice has been developed in such a manner that the observed abnormalities

have the same origin as by the patients, i.e. an abnormality in a human

gene.

In this case, the therapeutical target is identical by a humanized mouse

and by the patients in our study concerning the gene PMP22 human. Many

lineages of mice have been

obtained and the animals have developed a peripheral neuropathy

resembling to CMT1A [6]. We have used essentially the lineage showing

the most severe phenotype (lineage C22).

We have used mice CMT C22 as a pre-clinical model in order to test in

“clinical mice assays”, a therapeutic approach that could be applicable

by the human. Taking into account the difficulties of a genetic therapy

approach, we are privileged to use classical pharmacology.

In a prior intention, we researched the bibliography of data concerning

molecules “bound” to the myelinisation. Two publications have drawn our

attention [7, 8], showing that the ascorbic acid was an absolutely

necessary factor to the myelinisation in vitro in the cocultures between

axons and Schwann cells. Further research has revealed that persons

affected by the disease presented demyelinating peripheral neuropathies.

The toxicity of this molecule being well known, we were able to perform

immediate clinical tests of phase II/III. Hence, we carried out with the

following experience:

animals (males and females) of the lineage C22 transgenic for the gene

PMP22 human, have been administrated orally once a week a dose of

ascorbic acid corresponding to four grams by the human (no toxicological

data exists for larger doses).

On the other arm of the test, the animals were receiving a placebo. The

animals’ locomotoric abilities were evaluated at the end of three months

by using the well-known test of the rotarod (one measures the time

during which an animal is capable of staying on a tread mill turning at

a certain speed).

The males (more severely affected than the females) that were treated by

a placebo, or those that were not treated, were only able to stay on the

tread mill during an average of nine seconds whereas the animals which

received the ascorbic acid were able to stay 46 seconds in average. We

have carried out a second series of tests: males aged of

two months belonging to the same litter, divided into two groups, one

treated by a placebo, and the other by ascorbic acid. After three months

of treatment, the males that were not treated were not able to stay more

than one second on the tread mill (we have chosen litters that were very

affected) whereas the animals that were treated stayed

45 seconds (Figure A).

At last, a test concerning the muscular force (grip test) showed us that

the treated animals had doubled their muscular force during three months

of treatment (Figure 1B) [9]. The total of this data showed an

undiscussable therapeutical effect of the ascorbic acid. But what was

the mechanism?

In a first period of time, we have helped ourselves with the histologic

analysis.

Slices of sciatic nerve taken from transgenic animals treated by

ascorbic acid have shown a remyelination of fibers that did not exist by

non-transgenic animals, or by the transgenic animals treated by a

placebo. Furthermore, the gain of myelin found again in a normal shape

by the animals treated by the ascorbic acid. At last, the last test

concerning the effect of ascorbic acid, the restauration of the duration

of a normal life by the animals males of the lineage C22 treated by the

ascorbic acid, which is remarkable, because in this lineage, the

lethality of the affected males is very important, and this occurs for

unknown reasons [9].

The question remains concerning the molecular mechanism leading to the

remyelination and to the correction of the phenotype. The hypothesis

that came immediately to the mind was an action of the ascorbic acid on

the gene PMP22; this one possesses a minimal promoter of 300 pb allowing

a specific expression in the Schwann cells. However, this promoter’s

activity is repressed if the cells are not stimulated by some dibutyril

AMPc or forskolin [10]. However, the ascorbic acid interacts with the

pool of AMPc [11].

Hence, we have transfected the Schwann cells by a construction in which

the transcription of a (rapporteur) promoter gene is placed under the

control of a promoter of PMP22. The cells are incubated with dibutyril

AMPc used alone or in association with the ascorbic acid. In these

conditions, the ascorbic acid enters in competition with the stimulation

of the expression of PMP22 by the AMPc, diminishing it by half.

Afterwards we have showed by RT-PCR quantitative in real time that the

quantity of transcripts of PMP22 were weaker by the animals treated by

ascorbic cid than by those that have received the placebo. The

phenotypical correction that is observed by the animals receiving the

ascorbic acid is then explained by its action on the expression of the

gene PMP22 [9].

In conclusion, the ascorbic acid in a strong dose is capable of

correcting the phenotype of animals affected by a disease neighboring

that of the CMT1A human. So the road is open for clinical human tests,

which we hope that we can carry out with as soon as possible. It is

interesting to conclude by underlining that the results of many studies

have recently been published, making a reality of similar therapeutical

approaches

for many genetic diseases.

These works are all based on the same strategy: The use of known

molecules, or in development for other applications, in animal models

that have genetic diseases. Would the treatments of the first generation

for many genetic diseases be based on classical pharmacology?

[Guest guest]

Dear Gretchen,

It is lovely to read the article on the list. I'm grateful for you - thanks.

Reading about the positive benefits of Vitamine C is very encouraging.

I am also happy to take part of all the different researches and news that you

so generously present to us. The discussions with all the members here are also

very rewarding.

Joyce in Sweden