Download VT PHAK EYE DROPS

VT PHAK EYE DROPS
THE CRYSTALLINE LENS AND SENILE CATARACTS
What is the lens? (1)
The crystalline lens is located just behind the iris. It is a transparent, biconvex structure that refracts light and
focuses it on the retina. The lens can be divided into several areas, from the surface to the center:
The capsule, a structure of exchange between the lens and the aqueous and vitreous humour.
The epithelium, a layer of cuboidal cells present within the anterior capsule only. It is the single
regenerating tissue in the lens; throughout life, epithelial cells divide, move to the equator, elongate,
loose their nucleus and become new lens fibers.
The lens fibers are the bulk of the lens, divided into the cortex and the nucleus:
-
The Cortex is composed of recent lens fibers. The cytoplasm of the lens fiber cells contains
crystallines, a class of water-soluble proteins.
-
The Nucleus, the innermost part of the lens, contains the old lens fibers which have lost all
major organelles. All lens fibers produced during the life of the animal are packed in the
nucleus and divided in thin concentric layers along time.
The lens is maintained by thin but very strong suspensory ligaments, the zonules of Zinn, attached one end to the
lens capsule and on the other end to the ciliary processes of the ciliary body.
The lens is an avascular structure that depends integrally on the aqueous and vitreous humours for nutrition. The
lens capsule and the epithelium regulate most of the exchanges between the aqueous humour and crystalline
cells.
The lens serves a dual function:
1. The lens makes adjustments for close or distance vision, by changes in its curvature. This process
is called accommodation. The lens gradually gets firmer with age, diminishing the ability to accommodate.
2. The lens protects the retina by absorbing ultra-violets.
VT PHAK EYE DROPS
The role of Glutathione in the lens (4)
Glutathione is a tri-peptide made of the amino acids glutamate, cysteine, and glycine and is also called
glutamylcysteinylglycine or GSH.
Glutathione exerts essential physiological functions aimed at preserving lens transparency:
Prevention of oxidative cell damage
Throughout life, the lens is exposed to ultra-violets radiations that induce free radicals production. These free
radicals are continuously inactivated by antioxidant systems. Glutathione is the most important antioxidant system
of the lens.
Amino acid transport
The lens is rich in proteins (35%). 85% of these proteins are water-soluble. They are called crystallines and are
responsible for lens transparency. The components used to produce these crystallines come from the aqueous
humour. These components are amino-acids and their transfer to the lens requires a polypeptide found on lens
epithelium, glutathione.
Protein synthesis and enzyme activation
Crystallines production requires glutathione as an enzyme activator and a source of amino-acids.
CRYSTALLINE
LENS
AQUEOUS
HUMOUR
VITREOUS
HUMOUR
PROTEIN SYNTHESIS
NEW
CRYSTALLINES
UV
GLUTATHIONE
Glutathione
Amino-acids
Free radicals
Free radicals destruction
The role of Glutathione in the maintenance of lens transparency
VT PHAK EYE DROPS
The Crystalline lens maturation process (senile cataract) & glutathione role (2, 5)
Glutathione availability decreases with age, leading to free-radicals accumulation and a decrease in
protein synthesis. Thus, crystallines are not regenerated and free-radicals induce crystallines
aggregation and opacification leading to a loss in lens transparency. Senile cataract is occurring.
CRYSTALLINE
LENS
AQUEOUS
HUMOUR
VITREOUS
HUMOUR
PROTEIN SYNTHESIS
NEW
CRYSTALLINES
UV
GLUTATHIONE
AGGREGATION
+ OPACIFIACTION
OF CRYSTALLINES
Glutathione
Amino-acids
Free radicals
Free radicals destruction
The degenerating process occuring in the old crystalline lens
Advanced cataracts are a leading cause of blindness in dogs and are generally recognised by pet
owners either through the cloudy, whitish-blue appearance of the eye, or by the resulting decrease
in the dog's vision.
VT PHAK EYE DROPS
VT PHAK EYE DROPS INGREDIENTS AIM AT SLOWING DOWN SENILE CATARACT
EVOLUTION
INGREDIENTS
CYTOCHROM C
GLYCINE
VITAMINE PP
(NICOTINAMIDE)
BORIC ACID
AND ITS SODIUM
SALT
PROPERTIES
BENEFITS
• Reduces damages induced by
• Free radical scavenger
free radicals (aggregation and
opacification of crystallines)
• Antioxidant
• Amino-acid part of Glutathione
• Glutathione regeneration
(6)
• Opacification slow down
composition
• Glutathione regeneration
• Regenerates the reduced
Glutathione pool
(7)
• Opacification slow down
• Antimicrobial agent
• Microbiological growth reduction
Cytochrome C metabolites protect lens cells from the oxidative stress induced by free radicals. (3, 8)
CRYSTALLINE
LENS
AQUEOUS
HUMOUR
VITREOUS
HUMOUR
P
ROTEIN SYNTHESIS
GLYCINE
N
EW
CRYSTALLINES
UV
CYTOCHROME
C
Glutathione
Amino-acids
GLUTATHIONE
Free radicals
Glycine
Mode of action of VT Phak ingredients in the lens
VITAMINE PP
Free radicals destruction
VT PHAK EYE DROPS
CONDITIONS FOR USE
VT Phak eye drops can be used in the early stages of
senile lens opacification.
DIRECTIONS FOR USE:
Instil 1 drop per eye twice daily for 20 days a month.
For increased efficacy, VT Phak eye drops can be associated with VT Phak Syrup.
1.
2.
3.
4.
5.
6.
7.
8.
CLERC B, (1997).
Cristallin.
In : Ophtalmologie Vétérinaire, 2ème Edition, Editions du Point Vétérinaire, 375-410.
JAIN NK, RAWAL UM, (1999).
Influence of UV-irradiation on enzymes in mouse ocular lens: in vitro studies.
Indian J Ophthalmol, 47, 25-29.
MA W, WANG RR, KLEIMAN NJ, (1997).
Microperoxidases catalytically degrade reactive oxygen species and may be anti-cataract agents.Spector A.
Exp Eye Res., 65, 4, 457-470.
PARRIS M. KIDD.
Glutathione: Systemic Protectant Against Oxidative and Free Radical Damage
http://www.thorne.com/altmedrev/fulltext/glut.html
ROSELEN G, (2005).
Le vieillissement de l’oeil chez l’animal.
Bull. Acad. Vet. France, 158, 3, 195-211.
TESHIGAWARA M, MATSUMOTO S, TSUBOI S, OHMORI S, (1995).
Changes in levels of glutathione and related compounds and activities of glutathione-related enzymes during rat liver regeneration.
Res Exp Med (Berl), 195, 2, 55-60.
VOGEL R, WIESINGER H, HAMPRECHT B, DRINGEN R, (1999).
The regeneration of reduced glutathione in rat forebrain mitochondria identifies metabolic pathways providing the NADPH required.
Neurosci Lett., 12, 275, 2, 97-100.
ZHOU W, MA W, CHIGNELL CF, RESZKA KJ, (2000).
Investigation of the mechanism of action of microperoxidase-11, (MP11), a potential anti-cataract agent, with hydrogen peroxide and
ascorbate.Spector A.
Exp Eye Res., 71, 2, 183-194.