Paradoxe

[yarsky]

J'ai trouve deux relativement anciennes publications sur KC. Une de 1978, une autre de 1985. Sur ce forum on n'a pas vu ces references. Peut-etre entre nous il ya des biochimistes (ou les pharmaciens) qui puissent eclerer ces deux directions de recherche. Alors
1) 1985
http://www.ncbi.nlm.nih.gov/entrez/quer ... b=pubmed&d opt=Abstract&list_uids=4096209

Biochemical studies of normal and keratoconus corneas.

Oxlund H, Simonsen AH.

Keratoconus corneas are characterized by a reduced mechanical stability. The mechanical strength depends primarily on the collagen. In the present study the cross-linking pattern is analysed because it is important for the mechanical properties; an analysis of the amino acids of the collagen is included. Surprisingly, we did not find any change in the cross-linking pattern of collagen from keratoconus corneas compared to normal corneas. Neither did we find any difference in the composition of amino acids of the collagens. Thus no alteration was found in the molecular structure which could explain the marked reduction in the mechanical stability of keratoconus corneas.

2)1978
http://www.ncbi.nlm.nih.gov/entrez/quer ... db=PubMed& list_uids=621128&dopt=Abstract

Collagen crosslinking in keratoconus.

Cannon DJ, Foster CS.

The examination of reducible collagen crosslinks in keratoconus cornea revealed the presence of lysinonorleucine in amounts far greater than in normal age-matched corneas. There was no indication of decreased hydroxylysine levels in keratoconus, and there were no clinical indications of a generalized connective tissue disorder. The abnormal levels of dehydrolysinonorleucine in the tissue may represent a change in hydroxylation of selected lysyl residues of normal collagen or the synthesis of abnormal collagen, perhaps an unusual type.

[yarsky]

Un autre etudes sur la difference entre KC cornee et cornee normal

3)1993

http://www.ncbi.nlm.nih.gov/entrez/quer ... t=Abstract

Modification of prostaglandin E2 and collagen synthesis in keratoconus fibroblasts, associated with an increase of interleukin 1 alpha receptor number.

Bureau J, Fabre EJ, Hecquet C, Pouliquen Y, Lorans G.

Laboratoire de Recherche, Ophtalmologique, INSERM U 86, Hotel-Dieu, Paris, France.

Keratoconus, a bilateral corneal disease, is characterized by modifications in corneal shape and thinning of the stroma. It affects young people. From a biochemical point of view, a decrease in collagen content, probably due to the high collagenase activity, has been reported. In these experiments, we have studied the membrane receptors for interleukin 1 alpha, and the corresponding dissociation constant (KD). We also investigated synthesis of prostaglandin E2 (PGE2) and collagen, as well as kinetics of cyclooxygenase. Data from normal human corneas and from keratoconus were compared. Fibroblasts from keratoconus proved to bear four fold more IL1 binding sites than those from normal cornea, with similar KD. Both types of cells synthesize prostaglandin E2, even if IL1 is not added to the medium, but the keratoconus cells produce ten times more than the normal cornea cells. When the cells are stimulated with IL1, synthesis of PGE2 strongly increases and the amounts produced by keratoconus cells are always higher than those of the normal cornea cells. Kinetics of the cyclooxygenase show that Vmax. is 10 times higher in keratoconus than in normal cornea cells; Km's are the same. The amounts of collagen synthesized by keratoconus cells are slightly lower than those of normal cornea cells. Addition of IL1 to the cultures enhances synthesis of collagenase by the cells and decreases collagen found in the culture media. The drop of collagen is more important in keratoconus than in normal cornea cell cultures.

[Florence BERGER]

Ah! Ben tiens! Yves Pouliquen ne nous est pas inconnu ...

[aldo]

Je m'y mets tout de suite!

[aldo]

Pour les deux premières, ma devise « on ne trouve que ce qu’on cherche ! ».
La première étude montre que la structure moléculaire du collagène est « normale », qu’il n’y a pas de différences au niveau de l’enchaînement des acides aminés constituant les protéines.
La deuxième semble montrer que la structure principale du collagène n’est pas altérée, seulement la « réticulation », [la façon dont les fibres s’entrecroisent], il est montré une augmentation de l’hydroxylation de certains acides aminés.
Par contre je dois dire que la troisième est vraiment très intéressante !
Si vous ne comprenez pas tout je vous l’expliquerai.

[Jacqueline]

Pour les deux premières, ma devise « on ne trouve que ce qu’on cherche ! ».

Curieuse devise. Moi, quand je perds quelque chose, c'est quand j'arrête de le chercher que je le trouve!

[yarsky]

aldo merci beaucoup!

c'est tres logique donc:
1. les colagen lui meme n'est pas change
2. que sont regroupement est different ainsi que les liens entre les fibrils

Dans la file voisine "structure et fonctionnement de la cornee" il y a un article avec des evidences, obtenues par la microscopie, que 1 et 2 sont vrai.