Curr Eye Res. 1994 Jul;13(7):505-12.
Mechanisms of photo-induced vitreous liquefaction.
Akiba J, Ueno N, Chakrabarti B.
Schepens Eye Research Institute, Department of Ophthalmology, Harvard
Medical School, Boston, MA.
To understand the mechanisms of photo-induced vitreous liquefaction, this
study investigated the effects of free radicals on collagen and hyaluronic
acid (HA). Bovine vitreous collagen or HA was irradiated by visible light in
the presence of riboflavin (RF) as a photosensitizer. The changes in the
molecular weight of collagen and HA were monitored by sodium dodecyl
sulfate-polyacrylamide gel electrophoresis and high-performance liquid
chromatography, respectively.
Free radicals were shown to cause an increase
in the high-molecular-weight components and insolubilization of the vitreous
collagen and a decrease in the molecular weight of HA. The change in
molecular properties of the vitreous collagen could be attributed to
extensive crosslinks of the molecules. Since RF is present in the vitreous,
which is irradiated by visible light over a lifetime, both cross-links of
vitreous collagen and degradation of HA may contribute to age-related
vitreous liquefaction.
Nippon Ganka Gakkai Zasshi. 1992 Jun;96(6):731-6.
[Photodynamically induced vitreous liquefaction in vivo]
[Article in Japanese]
Akiba J.
Department of Ophthalmology, Asahikawa Medical College, Japan.
Photodynamically induced vitreous liquefaction in rabbit eye was
investigated. Photosensitizer, riboflavine phosphate, was injected into the
vitreous cavity of the rabbit before white-light irradiation. After the
irradiation (0, 1, 3, 6 hr) the rabbit vitreous body was separated into gel
and liquid portions. The liquid vitreous body was weighed, and the vitreous
liquefaction percentage was calculated.
One hour irradiation caused 38% of liquefaction of the eye; 3 hr, 50% liquefaction; 6 hr, 59% liquefaction. Although irradiated control eye (without photosensitizer) and the dark
adapted control eye (non-irradiated) showed 10-15% liquefaction throughout
the experimental period, the liquefaction percentage of the experimental
vitreous bodies was significantly larger than that of the control vitreous.
Inhibition experiment showed that the radical scavengers (Cu, Zn-superoxide
dismutase, catalase, and mannitol) could suppress the photodynamically
induced vitreous liquefaction.
Results indicated that free radicals, including hydroxyl radical and superoxide
anion, which are generated by photosensitizer and visible light irradiation,
may contribute to the age-related vitreous liquefaction of humans.
Albrecht Von Graefes Arch Klin Exp Ophthalmol. 1975;194(4 Suppl):277-81.
[The influence of riboflavin on vitreous homogenate (author's transl)]
[Article in German]
Hofmann H, Schmut O.
Sunlight causes a decrease of viscosity of a mixture of riboflavin and ox
vitreous homogenate while without riboflavin no reaction can be observed.
The mechanism of this reaction is not yet clarified. It is possible that the
reaction is closely related with the degradation of the viscosity of a
hyaluronic acid solution by ascorbic acid cause of the production of H2O2 in
both reactions. As an other mechanism the transfer of light energy on
hyaluronic acid by riboflavin can be assumed.
Nippon Ganka Gakkai Zasshi. 1995 Dec;99(12):1342-60.
[Changes in vitreous structure caused by oxygen free radicals]
[Article in Japanese]
Ueno N.
Department of Ophthalmology, Osaka University Medical School, Japan.
Vitreous liquefaction in humans is considered to be part of the normal
ocular aging process and is associated with vitreoretinal pathology. Because
hyaluronic acid (HA), one of the main components of the vitreous gel
structure, is degraded by reactive oxygen species (ROS) including oxygen
free radicals, the structural changes in the vitreous may be caused by ROS.
To investigate the effect of ROS on the vitreous gel structure, we treated
animal vitreous with ROS, which was generated from various sources. Using
riboflavin as a photosensitizer, calf vitreous was irradiated with visible
light (two 15-W fluorescent lamps) and found to be considerably liquefied.
The liquefaction resulted from HA depolymerization induced by ROS. Because
of the small amount of riboflavin naturally present in the vitreous, a
riboflavin-sensitized photochemical reaction may contribute to age-related
vitreous liquefaction.
Hematoporphyrin (HP), which is similar in chemical
structure to heme in blood, was also used as a photosensitizer. Irradiation with HP destroyed the calf vitreous gel structure and caused liquefaction. A HP-sensitized photochemical
reaction may contribute to vitreous liquefaction observed after vitreous
hemorrhage. Because metal ions, including Fe2+ and Cu2+, can catalyze to
generate ROS, liquefaction occurred when we treated calf vitreous with Fe2+
or Cu2+ at 4 degrees C. Adding ascorbic acid to the vitreous during the
reaction increased the rate of liquefaction. Therefore, metal ion catalyzed
ROS may also contribute to vitreous liquefaction, such as that found in an
injured eye with siderosis.
To investigate the relation between inflammatory
cell mediated ROS and vitreous liquefaction, an endotoxin-induced uveitis
model was created in the rabbit eye. Upon inflammation, the vitreous gel
contracted and released a water-like liquid. Because superoxide dismutase
can suppress the liquefaction, the destruction of the vitreous gel structure
resulted from ROS generated from inflammatory cells. Although many unknown factors contribute to vitreous liquefaction, ROS may be the main cause of vitreous structure alterations. To prevent or delay the progress of vitreous liquefaction in the normal
aging process or vitreous pathology, a new therapeutic procedure based on
clear scientific studies is needed.
Publication Types:
Review
Review, Tutorial
Free Radic Biol Med. 1997;22(7):1139-44.
Degradation of hyaluronic acid by photosensitized riboflavin in vitro.
Modulation of the effect by transition metals, radical quenchers, and metal
chelators.
Frati E, Khatib AM, Front P, Panasyuk A, Aprile F, Mitrovic DR.
INSERM-U.349, Lariboisiere Hospital, Paris, France.
The effect of photoexcited riboflavin (RF) on the viscosity of hyaluronic
acid (HA) solutions has been investigated. UV irradiation of RF causes under
aerobic conditions fragmentation of HA and a decrease in the viscosity of
its solutions.
A decrease of HA viscosity occurs in PO(4)-buffered solutions
and is accelerated by high pH, Fe2+ (but much less so by Fe3+), certain
metal chelators, and horseradish peroxidase (HRP); it is partially inhibited
by catalase and less so by superoxide dismutase (SOD). The reactivity of the
system was completely blocked by Tris, ethanol, aspirin, d-manitol,
dimethylthiourea (DMTU), dimethylsulfoxide (DMSO), and sodium azide. These
results indicate that the most likely chemical species involved in the
reaction is the hydroxyl radical. Singlet oxygen ((1)O(2)) generation is
suggested by the ability of NaN3 and DMSO to completely inhibit the
reactivity of the system.
These two agents, however, may also interact with
OH. radical, as well and suppress the reactivity of the system. H(2)O(2) and O(2).- seem also to be produced in significant amounts, because catalase and SOD partially block the
reactivity of the system. The effect of HRP may be due to hydrogen
subtraction from HA and H(2)O(2) reduction to water. Photoexcitation of RF
may potentially occur in vitro and in vivo in the organs and tissues that
are permeable to light, such as the eye or skin, and damage HA and other
cell-matrix components causing inflammation and accelerating aging.