Biomedical subjects

Matthias Lüke

Publications and source records attributed to Matthias Lüke.

9 recordsLinked to original sources

PubMed2007

Effects of the protein tyrosine kinase inhibitor genistein and taurine on retinal function in isolated superfused retina.

BACKGROUND: Genistein has the potential to act as an intraocular antiangiogenic agent. Its therapeutical use, however, is limited by toxic side effects on the retina. This study was designed to evaluate the simultaneous use of taurine as a neuroprotective drug. METHODS: Bovine retinas were isolated and perfused with an oxygen-preincubated nutrient solution. The electroretinogram (ERG) was recorded as a transretinal electrical potential using Ag/AgCl electrodes. At stable ERG amplitudes, genistein at concentrations of 11, 37, and 150 microM was added to the nutrient solution for 45 min, in the absence or presence of taurine (3 mM). Thereafter, the retina was reperfused with the nutrient solution for another 100 min. The percentage of b-wave reduction during genistein and genistein/taurine application was calculated. RESULTS: The b-wave amplitude was reduced by a smaller amount during the application of genistein (11 and 37 microM) in the presence of taurine compared with genistein alone. For both, genistein/taurine and genistein alone the b-wave recovered completely during the wash-out of the drugs. However, during the application of the highest tested concentration of genistein (150 microM), taurine did not protect completely, leading to an irreversible b-wave reduction. CONCLUSIONS: The adjuvant use of taurine reduces the genistein-induced retinal toxicity to a certain degree. However, the protective effect of taurine is limited and there is only a narrow therapeutic index for a combined intravitreal administration of genistein in coapplication with taurine to inhibit pathological ocular neovascularization.

Animals↗

PubMed2006

Influence of different purification techniques on triamcinolone yield and particle size spectrum.

BACKGROUND: To systematically investigate the common purification techniques for commercially available triamcinolone acetonide preparations and the influence of different filter parameters on final yield, reproducibility and particle size spectrum. METHODS: Two non-filter techniques using either sedimentation or centrifugation, and two different filter techniques were tested. Filters with different characteristics were investigated with the pore size ranging from 0.1 to 5.0 microm, and the filter diameter ranging from 4 to 30 mm. Only sterile standard syringe filters with low adsorptive characteristics (hydrophilic cellulose filter membranes) for pharmaceutical use were employed. For quantification, triamcinolone acetonide was dissolved in 60% methanol and measured spectrophotometrically at 239 nm. The crystal size spectrum was determined using a particle size analyzer that combines electronic pulse area analysis and resistance measurement. RESULTS: Depending on the purification technique used the resulting triamcinolone doses differed significantly. While the centrifugation method achieved purification without relevant loss, the sedimentation method yielded only 28.7% compared to the original commercial suspension, and in addition, the predictability was low (range 8.1-17.2 mg). With filter techniques high and consistent doses with a good reproducibility were achieved, but results were highly dependent on the filter characteristics. The final triamcinolone amount inversely correlated with the filter diameter due to a uniform loss of crystalline particles. In contrast, enlarging the pore size caused a substantial shift in the particle size spectrum due to a selective loss of small crystalline particles. CONCLUSIONS: The most common purification techniques vary notably in regard to final triamcinolone doses, reproducibility and particle size spectrum. The appropriate choice of the filter parameters seems to be more important than assumed, as pore size and filter diameter substantially influence both the final TA doses and the particle size of the TA crystals.

Centrifugation↗

PubMed2006

Expression of VEGF and PEDF in choroidal neovascular membranes following verteporfin photodynamic therapy.

PURPOSE: To examine the impact of photodynamic therapy (PDT) on pigment epithelium derived factor (PEDF) expression in human choroidal neovascularization (CNV) membranes with regard to vascular endothelial growth factor (VEGF) expression. DESIGN: Interventional case series. METHODS: Retrospective review of interventional case series of 42 patients (42 eyes) who underwent removal of CNV. CNV was secondary to age-related macular degeneration (AMD) in all cases. Fifteen patients were treated with PDT, 3 to 246 days before surgery. CNV were stained for CD34, CD105, cytokeratin 18, VEGF, and PEDF. Twenty-seven CNV without previous treatment were used as control. RESULTS: Specimens without pretreatment disclosed varying degrees of vascularization, VEGF, and PEDF expression by different cells. Specimens treated by PDT, three days previously showed mostly occluded vessels lined with damaged endothelial cells (EC). In contrast, specimens excised at later time points after PDT were highly vascularized with healthy EC. This chronology was associated with an impressive VEGF immunoreactivity increased considerably in retinal pigment epithelial cells as well as significantly reduced PEDF expression in EC and stroma. CONCLUSIONS: PDT induces a selective vascular damage in CNV. The effectiveness of PDT, however, seems to be jeopardized by a rebound effect initiated by an enhanced VEGF and reduced PEDF expression in CNV.

Aged↗

PubMed2006

Ultrastructural changes after artificial retinal detachment with modified retinal adhesion.

PURPOSE: Artificial retinal detachment is increasingly used in submacular surgery. However, overcoming physiological retinal adhesiveness by subretinal fluid injection is suspected to cause cellular damage and thus to limit visual rehabilitation. This experimental study was designed to examine the ultrastructural changes induced by retinal detachment under vitrectomy conditions and to evaluate factors that reduce adhesiveness and minimize cellular damage. METHODS: Twenty-one pigmented rabbits underwent vitrectomy, and the vitreous cavity was perfused for 10 minutes with various solutions. These included variations in osmolarity (314 and 500 mOsM), Ca(2+) ion concentration (Ca(2+)-supplemented, low Ca(2+), active Ca(2+) deprivation via 1 mM EDTA), temperature (19 degrees C and 34 degrees C), and ischemia (5 minutes). Nonvitrectomized eyes served as the control. Consecutively, an artificial bleb detachment was created underneath the visual streak by injecting 1 mL of buffered saline solution subretinally. Eyes were enucleated within 3 minutes, fixed with 2% glutaraldehyde/0.1 M cacodylate buffer (pH 7.4) containing 100 mM sucrose and processed for transmission electron microscopy and scanning electron microscopy. RESULTS: If a Ca(2+)-containing standard solution was used during vitrectomy, retinal adhesiveness was strong, and a forced bleb detachment caused substantial cellular damage characterized by swollen and fragmented photoreceptor outer segments and disruption of retinal pigment epithelial cells. Use of a Ca(2+)-free solution moderately reduced the adhesive strength with consequently less ultrastructural damage. Active Ca(2+)-deprivation further reduced the retinal adhesion, but may have induced damage as suggested by intracellular vacuolization. Hyperosmolarity and ischemic conditions had toxic effects on both the photoreceptors and RPE cells. In contrast, the use of a preheated Ca(2+)-free solution (34 degrees C) substantially reduced retinal adhesiveness under vitrectomy conditions and hence ultrastructural damage. CONCLUSIONS: Artificial retinal detachment causes substantial ultrastructural damage in eyes with physiological retinal adhesiveness if performed under vitrectomy conditions similar to surgery in humans. The use of a preheated Ca(2+)-free physiologic saline solution seems to be suitable to reduce retinal adhesion sufficiently, without causing significant cellular damage.

Adhesiveness↗

PubMed2005

The isolated perfused bovine retina--a sensitive tool for pharmacological research on retinal function.

The electroretinogram (ERG) of the isolated bovine retina serves as a proven criterion of retinal activity. It is used as a sensitive pharmacological tool for testing effects of applied drugs and toxins on photoreceptors, and higher order neurons that contribute to the generation of the b-wave. Following isolation and detachment from the underlying pigment epithelium, part of the retina was mounted into a closed chamber and perfused by a nutrient solution. Flow rate of the nutrient solution and its ingredients, incubation temperature and light intensity were optimised empirically to achieve a maximum b-wave amplitude. Under these conditions, a reproducible, high-resolution ERG can be stably recorded for more than 10 h with sufficient oxygenation found to be a prerequisite for the long-lasting stability. Addition of L(+)glutamate to the nutrient solutions was not anymore beneficial for the b-wave amplitude. A well-known inhibitor of oxidative phosphorylation (KCN) and antagonists of voltage-gated Ca2+ channels (isradipine, omega-conotoxin-GVIA and NiCl2) were used to prove the validity of the test system. The recording of the ERG from the isolated and perfused bovine retina serves as a valuable physiological model for a neuronal network in which important questions related to the retinal signalling and metabolism can be investigated.

Animals↗

PubMed2005

A Ni(2+)-sensitive component of the ERG b-wave from the isolated bovine retina is related to E-type voltage-gated Ca(2+) channels.

BACKGROUND: Voltage-dependent Ca(2+) channels trigger and control important cellular processes like neurotransmitter release and secretion, long-term potentiation, and gene expression in excitable cells. During retinal signal perception and processing, presynaptic Ca(2+) channels facilitate neurotransmitter release in photoreceptors and bipolar neurons, at nonspiking synapses which generate graded potentials. METHODS: The nature of voltage-gated Ca(2+) channels involved in retinal signal transduction is investigated in the present report by recording the electroretinogram (ERG) from the isolated and perfused bovine retina. Transcripts of the E/R- and T-type Ca(2+) channels are detected by RT-PCR. RESULTS: Using the Ca(2+) channel antagonists (+/-)-isradipine, NiCl(2), mibefradil, and SNX-482 results in either stimulatory or inhibitory effects on the ERG b-wave amplitude. On the transcript level, mRNA is detected for the E/R-type and a T-type voltage-gated Ca(2+) channel containing Ca(v)2.3 and Ca(v)3.1 as ion-conducting subunits, respectively. CONCLUSION: Blocking of the E/R-type Ca(2+) channels by NiCl(2) (10 microM) and SNX-482 (30 nM) contributes to the stimulatory effect, whereas antagonism of T-type as well as L-type Ca(2+) channels meditates the inhibitory action on the b-wave amplitude. Thus, a novel function for E/R-type voltage-gated Ca(2+) channels is probably associated with the visual signal transduction in the mammalian retina.

Animals↗

PubMed2005

Effects of daunorubicin and CD95L on retinal function in superfused vertebrate retina.

Alternative treatments of proliferative vitreoretinopathy (PVR) are needed. The intravitreal application of daunorubicin combined with CD95 ligand (CD95L) could provide a new therapeutic strategy. The effects of this application on bovine retinal function were investigated. Bovine retina preparations were perfused with a standard solution preequilibrated with oxygen. The b-wave and, after the addition of aspartate, the photoreceptor potential P III of the electroretinogram (ERG) were recorded using Ag/AgCl electrodes. Stable ERG amplitudes were recorded, then daunorubicin was added to the solution for 45 minutes, also with the addition of CD95L antibody. Subsequently, the preparation was reperfused with the standard solution for 100 minutes, to allow for recovery. The reduction in b-wave amplitude was reversible and not significantly changed by the addition of 0.25 microg/mL CD95L antibody to 13 microM of daunorubicin. The reduction of the b-wave amplitude was significantly changed and only partly reversible within the recovery time using 40 microM and 80 microM of daunorubicin. The photoreceptor potential P III amplitude was not significantly changed for up to 80 microM of daunorubicin. The ERG showed toxic effects of daunorubicin above a concentration of 13 microM used therapeutically in humans. The combination with CD95L did not increase retinal toxicity. It is, therefore, concluded that daunorubicin may be applied intraocularly, combined with CD95L, without interfering with retinal function.

Animals↗

PubMed2005

Effects of phosphodiesterase type 5 inhibitor sildenafil on retinal function in isolated superfused retina.

After the oral ingestion of sildenafil, visual abnormalities have been reported constantly. The mechanism of these adverse events has been presumed to be a result of the interaction of sildenafil with the retinal phosphodiesterase (PDE) type 6. To investigate the physiological basis of the effects of sildenafil on retinal function, bovine retinas were isolated and perfused with an oxygen pre-equilibrated standard solution. The electroretinogram (ERG) was recorded as a transretinal potential using silver/silver-chloride electrodes. After reaching stable ERG amplitudes, sildenafil was added to the nurient solution at different concentrations, and its effect on the a- and b-wave amplitude was studied separately. The 0.1 microM and higher concentrations of sildenafil reduced the b-wave amplitude, while a reduction of the a-wave amplitude was observed at an elevated threshold of 0.3 microM. The changes of the ERG amplitudes were fully reversible for the b-wave at a concentration of 0.1 microM and for the a-wave at 0.3 microM sildenafil. At higher concentrations, sildenafil was found to be only partially reversible within recovery time. In conclusion, besides an inhibitory influence on photoreceptors, sildenafil performs additional effects on the postsynaptic neuronal network. Higher concentrations of sildenafil were found to have a potential for retinal degeneration, suggesting that further trials should be designed to evaluate the long-term effects of sildenafil. The physiological consequences of an abuse or long-term, daily use of sildenafil are not clear.

3',5'-Cyclic-GMP Phosphodiesterases↗

PubMed2003

Electro-oculographic findings after 360 degrees retinotomy and macular translocation for subfoveal choroidal neovascularisation in age-related macular degeneration.

PURPOSE: To evaluate potential electro-oculographic changes after 360 degrees retinotomy and macular translocation for subfoveal choroidal neovascularisation in patients with age-related macular degeneration (AMD) in a randomised comparative (self-controlled) trial. METHODS: A consecutive series of 30 patients suffering from subfoveal choroidal neovascularisation secondary to age-related macular degeneration underwent 360 degrees retinotomy and macular translocation. The EOG served as the main parameter of the study and was recorded 1 day prior to the translocation surgery and no earlier than 21 days after the silicone oil removal. RESULTS: Postoperatively, a statistically significant decrease in mean dark trough by 64% was found for treated eyes (P<0.001). The mean dark trough of the fellow eye remained stable after surgery (P=0.33). The postoperative difference between the treated und untreated eyes proved to be statistically significant (P<0.001). The Arden ratio remained stable in the treated and untreated eyes with mean values of 204% (P=0.81) and 213% (P=0.18), respectively. A significant correlation between the reduction of the dark trough and the visual acuity at the 1-year follow-up was found. CONCLUSIONS: A persistent decrease in the corneofundal potential is associated with 360 degrees retinotomy and macular translocation for exudative AMD. This indicates a substantial postoperative malfunction of retinal pigment epithelial cells and an impaired photoreceptor regeneration. The impeded recovery of the RPE-photoreceptor complex can be interpreted as the result of the surgical trauma on the basis of prediseased RPE. A severe postoperative decrease in dark trough forecasts an incomplete recovery of visual acuity.

Choroidal Neovascularization↗