Mechanisms of photo-induced vitreous liquefaction

Meteorological factors and rhegmatogenous retinal detachment in metropolitan France

Rhegmatogenous retinal detachment (RRD) is a sight-threatening condition with rising global incidence. Identifying factors contributing to seasonal variations in RRD would allow a better understanding of RRD pathophysiology. We therefore performed a retrospective case series study investigating the relationship between RRD occurrence and meteorological factors throughout metropolitan France (the METEO-POC study), particularly the mean temperature over the preceding 10-day period (T-1). Adult patients having undergone RRD surgery and residing in one of the three most populated urban areas of each French region were included (January 2011-December 2018). The study involved 21,166 patients with idiopathic RRD (61.1% males, mean age 59.8-65.1 years). RRD incidence per 100,000 inhabitants increased from 7.79 to 11.81. RRD occurrence was not significantly associated with mean temperature over T-1 in the majority of urban areas (31/36). In a minority of areas (5/36) we observed correlations between RRD incidence and mean temperature over T-1, however these were extremely weak (r = 0.1-0.2; p < 0.05). No associations were found between RRD incidence and secondary outcomes: mean daily temperature over the 10 days prior T-1, minimum/maximum temperatures, rainfall, duration of sunshine, atmospheric pressure, overall radiation, relative humidity, wind speed. Overall, we found no relationships between meteorological parameters and RRD occurrence.

Posterior vitreous detachment rates post-uncomplicated phacoemulsification surgery: a systematic review

PURPOSE

It is commonly accepted that phacoemulsification surgery is a risk factor for the development of posterior vitreous detachment (PVD) and may accelerate the process. This is an important consideration particularly in cases involving young patients who pre-operatively have no PVD, given the increased risk of retinal tears and detachments.

METHODS

A comprehensive literature search was conducted to identify studies reporting incidence of PVD post-uncomplicated phacoemulsification surgery. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement was used for search strategy. Of 3071 titles, 7 studies met the inclusion criteria; The outcomes measured were PVD occurrence by (1) time, (2) type, (3) age, (4) gender and (5) axial length, with all statistical analysis performed using Review Manager.

RESULTS

A total of 2034 eyes were included for analysis with a mean follow-up time of 28.3 months. 33.3% of patients developed a PVD, either partial or complete, with rates increasing in a time dependent manner. No significant difference was noted in sub-group analysis by age, gender or axial length.

CONCLUSIONS

The results from our systematic review show that uncomplicated phacoemulsification accelerates the physiological process of PVD development. Pre-operative evaluation of the vitreoretinal interface should be performed with careful post-operative follow-up advised in those without a pre-existing PVD.

Vitreous Antioxidants, Degeneration, and Vitreo-Retinopathy: Exploring the Links

The transparent vitreous body, which occupies about 80% of the eye’s volume, is laden with numerous enzymatic and non-enzymatic antioxidants that could protect the eye from oxidative stress and disease. Aging is associated with degeneration of vitreous structure as well as a reduction in its antioxidant capacity. A growing body of evidence suggests these age-related changes may be the precursor of numerous oxidative stress-induced vitreo-retinopathies, including vision degrading myodesopsia, the clinically significant entoptic phenomena that can result from advanced vitreous degeneration. Adequate intravitreal antioxidant levels may be protective against vitreous degeneration, possibly preventing and even improving vision degrading myodesopsia as well as mitigating various other vitreo-retinopathies. The present article is, therefore, a review of the different antioxidant molecules within vitreous and the inter-relationships between vitreous antioxidant capacity and degeneration.

Human vitreous in proliferative diabetic retinopathy: Characterization and translational implications

Diabetic retinopathy (DR) is one of the leading causes of visual impairment in the working-age population. DR is a progressive eye disease caused by long-term accumulation of hyperglycaemia-mediated pathological alterations in the retina of diabetic patients. DR begins with asymptomatic retinal abnormalities and may progress to advanced-stage proliferative diabetic retinopathy (PDR), characterized by neovascularization or preretinal/vitreous haemorrhages. The vitreous, a transparent gel that fills the posterior cavity of the eye, plays a vital role in maintaining ocular function. Structural and molecular alterations of the vitreous, observed during DR progression, are consequences of metabolic and functional modifications of the retinal tissue. Thus, vitreal alterations reflect the pathological events occurring at the vitreoretinal interface. These events are caused by hypoxic, oxidative, inflammatory, neurodegenerative, and leukostatic conditions that occur during diabetes. Conversely, PDR vitreous can exert pathological effects on the diabetic retina, resulting in activation of a vicious cycle that contributes to disease progression. In this review, we recapitulate the major pathological features of DR/PDR, and focus on the structural and molecular changes that characterize the vitreal structure and composition during DR and progression to PDR. In PDR, vitreous represents a reservoir of pathological signalling molecules. Therefore, in this review we discuss how studying the biological activity of the vitreous in different in vitro, ex vivo, and in vivo experimental models can provide insights into the pathogenesis of PDR. In addition, the vitreous from PDR patients can represent a novel tool to obtain preclinical experimental evidences for the development and characterization of new therapeutic drug candidates for PDR therapy.

Evaluation of posterior vitreous detachment after uneventful phacoemulsification surgery by optical coherence tomography and ultrasonography

BACKGROUND

The aim was to investigate the effect of uneventful phacoemulsification on vitreoretinal interface evaluated by optical coherence tomography (OCT) and ultrasound.

METHODS

One hundred and fifty eyes were evaluated for the presence or absence of posterior vitreous detachment by ultrasound and OCT prior to cataract surgery. Only those eyes with intact vitreoretinal adhesion were included in the study. All patients underwent cataract surgery. At one month, three months and six months, all patients were assessed with OCT and ultrasound. The data were analysed for statistical significance.

RESULTS

The study was carried out on 30 of 31 patients with no posterior vitreous detachment. The mean age of patients was 62.63 ± 7.15 years (range 49 to 75 years) and 15 were female. Posterior vitreous detachment developed in 17 patients (56.66 per cent) at one month, 21 patients (70 per cent) at three months and 22 patients (73.33 per cent) at six months following the surgery. No complications or acute symptoms were detected associated with posterior vitreous detachment.

CONCLUSION

Vitreoretinal interface changes and vitreoretinal separations and progression of separation can be easily evaluated by OCT. The current study confirms that posterior vitreous detachment occurs commonly soon after cataract surgery.

[Seasonal variation in the occurrence of rhegmatogenous retinal detachment at the beginning of the 21st century. Study results and literature review]

AIM

The present study aims to ascertain whether there are seasonal variations in the occurrence of rhegmatogenous retinal detachment at the beginning of the 21st century, compare these results with seasonal variations observed in the literature for the 20th century, and determine whether current general lifestyle changes in terms of the increased use of visual media (TV, PC) and a decrease in outdoor activity influence seasonal patterns of rhegmatogenous retinal detachment.

METHOD

A quantitative retrospective analysis of 2605 surgical protocols of retinal detachment repair procedures performed at the eye clinic of the Johannes Gutenberg University, Mainz, Germany, between 1998 and 2008 was carried out.

RESULTS

Rhegmatogenous retinal detachment was diagnosed in 1490 cases and, as such, was the most frequently occurring type of retinal detachment during the selected period of time (p = 0.001). A seasonal distribution was detected with statistically significant maximum and minimum incidences in July and October, respectively, (p = 0.008). These results are consistent with the findings of large studies conducted in the 20(th) century that observed a maximum in the summer months and a minimum in the winter months. Furthermore, in the period between 2003 and 2008 significantly more rhegmatogenous retinal detachments were observed than from 1998 to 2002 (p = 0.001). During school holiday periods 1.43% fewer rhegmatogenous retinal detachments were observed than had been estimated statistically. The increased number of hours of sunlight and increased average monthly temperatures had no significant impact on the occurrence of rhegmatogenous retinal detachment.

CONCLUSION

Current changes in lifestyle in terms of the increased use of visual media and a decrease in outdoor activity do not appear to have influenced the seasonal variation in rhegmatogenous retinal detachment. Factors other than light intensity and average temperature that have not yet been evaluated appear to be the cause of these seasonal variations.

Emerging nonsurgical methods for the treatment of vitreomacular adhesion: a review

With the dissemination of optical coherence tomography over the past two decades, the role of persistent vitreomacular adhesion (VMA) in the development of numerous macular pathologies - including idiopathic macular hole, vitreomacular traction syndrome, cystoid and diabetic macular edema, neovascularization in diabetic retinopathy and retinal vein occlusion, exudative age-related macular degeneration, and myopic traction maculopathy - has been established. While invasive vitreoretinal procedures have long been utilized to address complications related to these disorders, such an approach is hampered by incomplete vitreoretinal separation and vitreous removal, surgical complications, and high costs. In light of such limitations, investigators have increasingly looked to nonsurgical means for the treatment of persistent pathologic VMA. Chief among these alternative measures is the intravitreal application of pharmacologic agents for the induction of vitreous liquefaction and/or vitreoretinal separation, an approach termed pharmacologic vitreolysis. This article aims to review the available evidence regarding the use of pharmacologic agents in the treatment of VMA-related pathology. In addition, a discussion of vitreous molecular organization and principles of physiologic posterior vitreous detachment is provided to allow for a consideration of vitreolytic agent mode of action and molecular targets.

Pathogenesis of rhegmatogenous retinal detachment: predisposing anatomy and cell biology

BACKGROUND

The pathogenesis of rhegmatogenous retinal detachment is complex, and our knowledge of the exact mechanism of vitreoretinal attachment and detachment remains incomplete.

METHODS

We performed a Medline, Ovid, and EMBASE search using search words rhegmatogenous, retinal detachment, vitreous, and retinal adhesion. All appropriate articles were reviewed, and the evidence was compiled.

RESULTS

Cortical vitreous contains fibrillar collagens type II, V/XI, and IX. The inner limiting membrane of the retina contains collagens type I, IV, VI, and XVIII as well as numerous other glycoproteins and potential adhesion molecules. The distribution and age-related changes in the structure of these molecules play an important role in the formation of a retinal break, which may compromise and disrupt the normal mechanisms of neurosensory retinal adhesion.

CONCLUSION

Rhegmatogenous retinal detachment development is intimately related to changes in the fibrillar structure of the aging vitreous culminating in posterior vitreous detachment with regions of persistent and tangential vitreoretinal traction predisposing to retinal tear formation. A complex interplay of factors such as weakening of vitreoretinal adhesion, posterior migration of the vitreous base, and molecular changes at the vitreoretinal interface are important in predisposing to focal areas of vitreoretinal traction precipitating rhegmatogenous retinal detachment. Once formed, the passage of liquefied vitreous through a retinal break may overwhelm normal neurosensory-retinal pigment epithelium adhesion perpetuating and extending detachment and causing visual loss. To understand the molecular events underlying rhegmatogenous retinal detachment so that new therapies can be developed, it is important to appreciate the structural organization of the vitreous, the biology underlying vitreous liquefaction and posterior vitreous detachment, and the mechanisms of vitreoretinal attachment and detachment.

Oxidative damage to extracellular matrix and its role in human pathologies

The extracellular compartments of most biological tissues are significantly less well protected against oxidative damage than intracellular sites and there is considerable evidence for such compartments being subject to a greater oxidative stress and an altered redox balance. However, with some notable exceptions (e.g., plasma and lung lining fluid) oxidative damage within these compartments has been relatively neglected and is poorly understood. In particular information on the nature and consequences of damage to extracellular matrix is lacking despite the growing realization that changes in matrix structure can play a key role in the regulation of cellular adhesion, proliferation, migration, and cell signaling. Furthermore, the extracellular matrix is widely recognized as being a key site of cytokine and growth factor binding, and modification of matrix structure might be expected to alter such behavior. In this paper we review the potential sources of oxidative matrix damage, the changes that occur in matrix structure, and how this may affect cellular behavior. The role of such damage in the development and progression of inflammatory diseases is discussed.

Gel electrophoretic analysis of corneal collagen after photodynamic cross-linking treatment

PURPOSE

Photodynamic collagen cross-linking by using ultraviolet A (UVA) irradiation and the photosensitizer riboflavin has been recently introduced as a new possible treatment of progressive keratoconus. This is the first study, to our knowledge, investigating biochemical aspects of the new procedure. Its aim was to analyze the possible changes in the electrophoretic pattern of corneal collagen type I after collagen cross-linking treatment.

METHODS

Twenty fresh postmortem porcine corneas were cross-linked; another 20 porcine corneas treated with physiologic saline were used as controls. After removal of the central 10 mm of the epithelium, the corneas were treated with the photosensitizer riboflavin and UVA irradiation for 30 minutes by using a double UVA diode (370 nm, 3 mW/cm). For biochemical analysis, the central 10-mm corneal buttons were trephined, tissue was homogenized, and collagen type I was extracted. Subsequently, the collagen extracts were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

RESULTS

In the controls, the typical collagen pattern of normal cornea was found with 1 gamma trimer band, 2 beta dimer bands, and 2 alpha monomer bands. In the cross-linked samples, there was an additional intense polymer band in the stacking gel that was resistant to mercaptoethanol, heat, and pepsin treatment. Its molecular size was estimated to be at least 1000 kDa.

CONCLUSIONS

In the cross-linked corneas, a strong band of high-molecular-weight collagen polymers was shown as the biochemical correlate of the cross-linking effect, showing the efficiency of the new cross-linking procedure. This polymer band complies well with the morphologic correlate of an increased fiber diameter after cross-linking treatment. Its chemical stability supports hopes of a long-term effect of the new treatment.

Time course of posterior vitreous detachment in the second eye

PURPOSE OF REVIEW

Posterior vitreous detachment is the principal predisposing event for the development of retinal breaks and rhegmatogenous retinal detachments. Patients with unilateral posterior vitreous detachment are potentially at risk of developing the complications associated with posterior vitreous detachment in the fellow eye. Thus, to identify when posterior vitreous detachment develops in the fellow eye after it develops in the first eye is important for managing patients with unilateral posterior vitreous detachment.

RECENT FINDINGS

The main theme in the literature is research regarding the mechanism of the development of posterior vitreous detachment. Various pharmacologic vitreolysis agents can induce posterior vitreous detachment. Changes in the enzymatic activities in the vitreous and vitreoretinal interface tend to promote vitreous separation from the inner retinal surface with aging. Clinical studies have shown a significant increase in the occurrence of posterior vitreous detachment with aging, and the interval between the development of posterior vitreous detachment in the first eye and in the second eye is short.

SUMMARY

Posterior vitreous detachment is one of the most important age-related changes in human eyes, and age-related changes develop equally in both normal eyes; thus, posterior vitreous detachment may develop in the second eye within a few years of developing in the first eye.

Effects of Advanced Glycation End Products on Hyaluronan Photolysis: A New Mechanism of Diabetic Vitreopathy

PURPOSE

To test the effects of advanced glycation end products (AGEs), which are increased in vitreous of diabetic patients, on photolysis of hyaluronan.

METHODS

Pullulan standards were used as molecular weight (MW) markers to obtain a calibration curve. 0.02% hyaluronan solutions were divided into AGE-added and AGE-free samples; each sample was irradiated using a xenon lamp or kept in the dark. Retention time (RT) was measured for each sample using high-performance liquid chromatography.

RESULTS

RTs and logarithm of MW of pullulan standards were negatively correlated. In hyaluronan samples exposed to light, RT increased significantly for both AGE-added and AGE-free samples compared with samples kept in the dark. RT in AGE-added samples was greater by 3% than that in AGE-free samples (p = 0.02).

CONCLUSIONS

Exposure to light decreases MW of hyaluronan; addition of AGEs promotes this change. The photosensitizer activity of AGEs may be associated with accelerated depolymerization of hyaluronan in diabetic patients.

Cationic dye-sensitized degradation of sodium hyaluronate through photoinduced electron transfer in the upper excited state

The formation of ground-state complexes of methylene blue (MB) and thionine (TN) with sodium hyaluronate (NaHA) was clearly observed by means of absorption spectra in aqueous solution. Irradiation of the complexes using 313 nm light caused significant degradation of NaHA under oxygen and argon. However, the use of visible light over 400 nm, which gives the lowest excited singlet state of the cationic dyes, caused no degradation. MB and TN were more efficient sensitizers for the degradation of NaHA than rose bengal (RB), although RB is a more efficient singlet oxygen (1O2) sensitizer than the cationic dyes. Under similar conditions the polysaccharides with carboxyl groups, such as alginic acid and polygalacturonic acid, also photodecomposed. However, the polysaccharides without carboxyl groups, such as pullulan and methyl cellulose, did not. The irradiation of the polysaccharides in the presence of powdered titanium dioxide as a photocatalyst to generate the hydroxyl radical (.OH) in aerated aqueous solution caused the fragmentation of all the polymers. It was confirmed that methyl viologen, an electron-accepting sensitizer, formed a charge-transfer complex with NaHA, the irradiation of which caused the efficient degradation of NaHA. In the presence of beta- and gamma-cyclodextrins the MB- and TN-sensitized photodegradation of NaHA was markedly suppressed. This was probably due to the formation of the inclusion complexes comprising the cationic dyes and the cyclodextrins. On the basis of the results obtained we propose that the cationic dye-sensitized degradation of NaHA involves a photoinduced electron-transfer process between the upper excited dyes and the ground-state NaHA and that .OH and 1O2 do not participate in the degradation.

Microdialysis measurement of ascorbic acid in rabbit vitreous after photodynamic reaction

A method for long-term intravitreous microdialysis was used to measure endogenous reduced ascorbic acid in the vitreous of rabbits by HPLC-ECD before and after exposure to intense visible light in the presence of fluorescein. Cellulose microdialysis probes were implanted into the vitreous humor of each eye and after stabilization ascorbic acid measurements were recorded over a 14 day period. Under this experimental condition, normal ascorbic acid concentrations in vitreous varied from 98.0 +/- 9.8 to 106.9 +/- 20.3 microM(mean +/- S.D.). The eyes received light irradiation (25 000 lux) for 2 hr and fluorescein was used as the photosensitizer once or twice. No immediate effects on ascorbic acid concentrations could be observed in the eyes irradiated twice without fluorescein i.v. injections and in the twice fluorescein injected without irradiation. However, in the eyes irradiated once with fluorescein (30 mg kg(-1)), ascorbic acid concentration after irradiation significantly decreased from day 2 and continued over a period of 10 days compared with that before irradiation and maximal reduction was 32.6% (P < 0.005) on day 6 after irradiation. By day 13, the ascorbic acid concentration returned to control levels (P > 0.01). In the eyes irradiated twice with fluorescein injections, ascorbic acid concentration after irradiation decreased even more over the experimental period and the maximal reduction was 65.5% (P < 0.005) on day 5 after irradiation and did not recover over the next 9 days. In the eyes irradiated twice with fluorescein injections plus administration of ascorbic acid (150 mg kg(-1)) 30 min before irradiation, a significant increase (52.5%) of ascorbic acid (P < 0.005) was found on day 1 and control levels of ascorbic acid were maintained from day 2 onward. The protective role of ascorbic acid in the vitreous humor against photodynamic reaction is suggested.

Calcification resistance, biostability, and low immunogenic potential of porcine heart valves modified by dye-mediated photooxidation

The calcification potential, biostability, and immunogenic response of materials intended for long-term in vivo use, such as in heart-valve bioprostheses, are essential components of device performance. Here we explore these properties in photooxidized porcine heart valves. To study immunological sensitization, we injected tissue extracts intradermally into guinea pigs. Test and control animals received a challenge patch of the appropriate extract and were scored for dermal reactions. Neither cottonseed oil nor sodium chloride extracts of photooxidized heart-valve tissues caused any dermal inflammatory response. After implantation in the rat subcutaneous model for 90 days, the calcium content of 48-h-treated photooxidized cusp tissue [0.04 +/- 0.00 mg/g wet weight (gww)] was comparable to that of unimplanted control tissues (usually <1 mg/gww) and much lower than that of glutaraldehyde-treated controls (71 +/- 15 mg/gww). The porcine aortic wall calcium content (49 +/- 31 mg/gww) was comparable to that of glutaraldehyde-treated controls (59 +/- 8 mg/gww). Histologically, a time-dependent decrease in inflammation and vascularization with increasing photooxidation time was noted in the rat model along with an increase in the stability and organization of collagen bundles. In summary, porcine valve tissues treated by dye-mediated photooxidation were resistant to calcification, were biostable, and demonstrated a low immunogenic response, indicating potential for use in heart-valve bioprostheses.

Photodynamic biologic tissue glue in perforating rabbit corneal wounds

OBJECTIVE

To evaluate the in vivo wound modulating effects of a new biologic tissue adhesive.

BACKGROUND DATA

Biological tissue glue can serve as an important adjunct technology in the treatment of a number of ocular conditions, including closure of corneal wounds. These experiments were performed to evaluate the wound healing effects of a new photodynamic biologic tissue glue (PBTG) in perforating rabbit corneal incisions.

METHODS

Perforating corneal wounds were created in 12 pigmented rabbits. Two perforating incisions were made 180 degrees apart 2 mm from the limbus. One incision in each eye was closed with a single interrupted 10-0 nylon suture, and the other closed with PBTG. Rabbits were followed biomicroscopically and sacrificed at 1-, 3-, and 7-week intervals for histological evaluation of their corneal wounds.

RESULTS

There were no clinical signs of PBTG-related toxicity in any of the rabbits. Compared to control wounds, all glued corneas had greater epithelial filling, less stromal edema, and fewer inflammatory cells at the 1-, 3-, and 7-week stages and showed greater overall wound maturation.

CONCLUSION

Our data suggest that PBTG is an effective and nontoxic tissue adhesive that accelerates normal corneal wound healing.

Expression of the collagen-related heat shock protein HSP47 in fibroblasts treated with hyperthermia or photodynamic therapy

Heat shock protein (HSP) 47 is associated with collagen type I metabolism, both constitutively and after stress-inflicted injury. It has been claimed that, in contrast to hyperthermia (HT), photodynamic therapy (PDT) does not damage collagen, as measured at the level of tissue. We have studied HSP47 expression in normal murine skin fibroblasts (3T6) treated with hyperthermia or photodynamic therapy (PDT) mediated by three different photosensitizers: (1) haematoporphyrin ester (HpE), (2) meta tetra hydroxyphenyl chlorin (mTHPC) and (3) riboflavin (RB). Riboflavin is not an established photosensitizer for PDT and was chosen here because it is known to provoke collagen damage. The applied doses of the treatments were isoeffective in terms of 3T6 clonogenic cell survival. Analysis, at both transcriptional and translational levels, revealed HSP47 elevation after hyperthermia and after PDT with RB. PDT sensitized by HpE and mTHPC did not significantly alter HSP47 expression. These observations are consistent with our hypothesis that this collagen chaperone is up-regulated by laser-mediated modalities known to damage collagen (i.e. HT and RB PDT) but not by more conventional PDT treatments. Additionally, unexpected significant up-regulation of HSP47 was detected after illumination alone (no photosensitizer) of 3T6 cells at 653 nm laser light, but not at 630 nm.

Degradation of hyaluronic acid by photosensitized riboflavin in vitro. Modulation of the effect by transition metals, radical quenchers, and metal chelators

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.

Shrinkage temperature versus protein extraction as a measure of stabilization of photooxidized tissue

A rise in thermal denaturation temperature has been utilized as an indication of stabilization of collagen-containing materials such as pericardial tissue and porcine heart-valve leaflets following treatment with glutaraldehyde, Denacol, or other chemical agents. In contrast, stabilization of bovine pericardial tissue by dye-mediated photooxidation does not result in a significant rise in shrinkage temperature comparable with these treated materials. It was therefore hypothesized that a rise in shrinkage temperature is not a necessary indication for tissue stabilization. A sensitive protein extraction assay has been developed which can be used to monitor the stabilization of pericardial tissue by a variety of treatment methods, including photooxidation. A reduction in extractable protein, as analyzed by polyacrylamide gel electrophoresis, is noted for pericardial tissue treated with photooxidation, glutaraldehyde, or Denacol. Loss of extractable protein, as a function of treatment time, correlates well with a significant rise in shrinkage temperature for pericardium treated with glutaraldehyde or Denacol but not with photooxidation. This difference is attributed to the stabilization processes of glutaraldehyde and Denacol, which involve extensive crosslinking and polymer formation within and in addition to the native pericardial matrix, leading to a rise in matrix complexity and thermal stability. In contrast, photooxidation is a catalytic process involving modification and crosslink formation within existing matrix components, resulting in a material with little added matrix complexity.

Serum-induced collagen gel contraction

PURPOSE

To understand the molecular events underlying disease-related vitreous gel contraction, the effect of serum components on collagen was investigated.

METHODS

Bovine vitreous or dermal collagen was incubated with a mixture of transglutaminase (TG; factor XIIIa) and fibronectin (FN), and the biochemical changes of collagen were monitored by gel electrophoresis. In addition, serum-induced changes in the volume of the collagen gel were monitored.

RESULTS

Gel electrophoresis revealed a new high-molecular-weight band (M(r) 240,000) presumably due to intermolecular cross-links of collagen peptides and FN. The serum components also were shown to cause a significant decrease in the volume of the collagen gel. CONCLUSION. Collagen gel contraction could be attributed to the collagen-FN-collagen cross-links catalyzed by TG.