Compromised Autoregulatory Control of Ocular Hemodynamics in Glaucoma Patients after Postural Change

PURPOSE

The autoregulatory control of retrobulbar blood flow in response to postural challenge was investigated in normal-tension glaucoma (NTG) patients in comparison with primary open-angle glaucoma (POAG) patients and healthy volunteers.

DESIGN

Prospective cohort study.

PARTICIPANTS AND CONTROLS

Twenty POAG patients, 20 NTG patients, and 20 control subjects.

METHODS

Peak systolic velocity (PSV), end diastolic velocity (EDV), and resistivity index (RI) in the short posterior ciliary artery (SPCA), central retinal artery (CRA) and ophthalmic artery (OA) were recorded after a change from sitting upright to a supine body position using color Doppler imaging.

MAIN OUTCOME MEASURES

Peak systolic velocity, EDV, and RI.

RESULTS

Ten minutes after postural change to a supine position, blood flow velocities in the SPCA remained unchanged in controls, whereas a significant increase of PSV and EDV was found in both glaucoma groups. The RI in the SPCA was significantly lowered in the NTG group. Recordings for the OA and CRA showed a significant increase in EDV and significant decrease in RI in all 3 groups; a significant increase in PSV in the CRA was detected only in the NTG group.

CONCLUSIONS

The unaltered flow velocities in the SPCA of healthy controls may indicate tight autoregulatory control, whereas the flow velocities in the CRA and OA appeared to follow alterations in hydrostatic pressure. In contrast, NTG and POAG patients demonstrated an insufficient compensatory response to postural change, leading to accelerated flow in the SPCA. This compromised autoregulatory control could represent another contributing factor in the pathogenesis of glaucoma.

Glaucoma progression is associated with decreased blood flow velocities in the short posterior ciliary artery

BACKGROUND

An altered perfusion of the optic nerve head has been proposed as a pathogenic factor in glaucoma.

AIM

To investigate potential differences in the ocular haemodynamics of patients having glaucoma with progressive versus stable disease, as well as healthy volunteers.

METHODS

Peak-systolic velocity (PSV), end-diastolic velocity (EDV) and resistivity index in the short posterior ciliary artery (SPCA), central retinal artery (CRA) and ophthalmic artery were recorded in 114 consecutive patients having glaucoma with an intraocular pressure (IOP) < or =21 mm Hg, as well as in 40 healthy volunteers, by colour Doppler imaging (CDI).

RESULTS

Of the 114 patients with glaucoma, 12 showed glaucoma progression (follow-up period: mean 295 (standard deviation (SD) (18) days). CDI measurements in these patients showed decreased PSV and EDV in the SPCA (p<0.001 and p<0.05, respectively) and decreased PSV in the CRA compared with patients with stable glaucoma and healthy controls (p<0.05). No differences in flow velocities were found for the ophthalmic artery. IOP and systemic blood pressure was similar in all the three groups.

CONCLUSIONS

Progressive glaucoma is associated with decreased blood flow velocities in the small retrobulbar vessels supplying the optic nerve head. The detected difference could represent a risk factor for progression of glaucomatous optic neuropathy.

In vivo confocal microscopy of pre-endothelial deposits

BACKGROUND

Deposits in various layers of the cornea might result from long-term medical therapy, photorefractive surgery, and longterm use of contact lenses or corneal dystrophies.

METHODS

A 46-year-old woman was referred to our department with the suspected diagnosis of posterior polymorphous dystrophy. Slit-lamp biomicroscopy revealed bilateral small-sized deposits in the posterior part of the cornea. In vivo confocal microscopy was performed to evaluate these deposits in detail.

RESULTS

In vivo confocal microscopy of the cornea identified hyperreflec-tive "dot-like" structures in the deep stromal layer and anterior to the endothelial cell layer. The morphology and number of keratocytes of the posterior stroma and of endothelial cells appeared normal.

CONCLUSIONS

In vivo confocal microscopy is a very useful tool to analyze and visualize pre-endothelial deposits. Because there is no family history of corneal disease, the exact origin of the pre-endothelial deposits in our case remains unclear.

Volumetric colour Doppler imaging: a useful tool for the determination of ocular blood flow in glaucoma patients?

PURPOSE

Disturbed ocular haemodynamics are discussed to contribute to the pathogenesis of glaucoma. Up to now there is no method available allowing direct determination of blood flow, which is the most relevant dimension for studies on haemodynamics. In this study, volumetric colour Doppler imaging (vCDI) is evaluated systematically in glaucoma patients.

METHODS

A Siemens Elegra ultrasound set-up with a linear 7.5 MHz probe was used for all CDI measurements. For vCDI, the cross-sectional area of a vessel and the flow velocity is determined. From both these parameters blood flow can be calculated. Ocular pulse amplitude (OPA) was assessed by the method of Langham using a pneumatic applanation tonometer.

RESULTS

(1) Velocity measurements using CDI in the ophthalmic artery and central retinal artery were highly reproducible (n=20). In contrast, reproducibility of vCDI measurements was low (n=20). Reproducibility improved if five vCDI measures were averaged. (2) Results from two different CDI-operators did not differ regarding the velocity measurements, but there was a difference in vCDI measurements (n=20). (3) Results from vCDI did not correlate with measurements of OPA in 69 patients. (4) In 15 patients, vCDI failed to detect changes of ocular perfusion induced by the application of dorzolamide.

CONCLUSION

vCDI is not applicable in ophthalmology at present.

Effects of glaucoma drugs on ocular hemodynamics in normal tension glaucoma: a randomized trial comparing bimatoprost and latanoprost with dorzolamide [ISRCTN18873428]

Background

Reduced choroidal perfusion is hypothesized to play a role in the pathogenesis of normal tension glaucoma. Thus the impact of antiglaucomatous eye drops on ocular perfusion has been the focus of recent research and the subject of intensive investigations. The present study investigates whether topically applied latanoprost or bimatoprost influence ocular perfusion in patients with normal tension glaucoma and compares these effects with that changes detected after the treatment with dorzolamide.

Methods

Ocular hemodynamics were assessed by color Doppler imaging (CDI) shortly before and after a one-month treatment with either latanoprost, bimatoprost or dorzolamide. Primary end-points of the study were peak systolic and end-diastolic blood flow velocities in the short posterior ciliary artery (SPCA) under the new therapy. Intraocular pressure (IOP) and additional perfusion parameters in the SPCA and other retrobulbar vessels were tracked as observational parameters. n = 42 patients with normal tension glaucoma were enrolled in the study.

Results

Systolic and diastolic blood flow velocities in the SPCA showed no significant alteration after the treatment with latanoprost or bimatoprost. Dorzolamide lead to increase of peak systolic velocity. IOP was reduced by all three agents in a range reported in the literature.

Conclusion

Topically applied latanoprost and bimatoprost act in a hemodynamically neutral manner and have the capability to lower IOP even in patients with normal tension glaucoma and low initial IOP level. Dorzolamide accelerates blood flow in systole. None of the tested compounds has a negative impact on hemodynamics in the short posterior ciliary arteries.

Differential and quantitative molecular analysis of ischemia complexity reduction by isotopic labeling of proteins using a neural embryonic stem cell model

The analysis of rapid changes of protein expression in living systems in response to insults requires rigorous methods of complexity reduction. To control dynamic pattern of hundreds or even thousands of protein isoforms, we applied a novel method of differential molecular analysis to a cellular model which is suited to study ischemia. Neural derivatives of murine embryonic stem cells were exposed to chemical ischemia. The model was used to obtain starting material for a quantitative differential proteomics analysis. Fractionation of phosphoproteins from these samples and subsequent identification by mass spectrometry of differential proteins provide proof of principle of how novel molecular analytical tools provide new insight into the network of neuroprotective molecular events during specific situations of neuronal stress and related pharmaceutical intervention. Our results indicate a particular role of an isoform of the acidic calcium-independent phospholipase A2 in this type of insult.

Reproducibility of blood flow velocity measurements using colour decoded Doppler imaging

BACKGROUND

It is taken for granted that glaucomatous damage is caused by changed haemodynamics of the retrobulbar vessel system besides other factors such as, for example, an elevated intraocular pressure. This was proven by various studies in which glaucoma patients were shown to have a changed retrobulbar blood flow velocity. In this study, the reliability of measurements of retrobulbar vessel perfusion by colour decoded Doppler imaging (CDI) was evaluated.

PATIENTS AND METHODS

A total of 18 healthy volunteers and 15 patients with various glaucoma types were enrolled in this study. Using a CDI system, type Siemens Sonoline Elegra with a combined applicator (7.5L40), retrobulbar vessel perfusions of the ophthalmic artery, the short posterior ciliary arteries, and the long posterior ciliary arteries of each patient were measured six times. In each measurement, pulse amplitude, end-diastolic velocity, maximum systolic velocity, pulsatility index, and resistivity index of the vessels were determined. The reproducibility of measurements was evaluated by the calculation of the intraclass correlation coefficient (ICC) for each parameter.

RESULTS

The ICCs for the ophthalmic artery varied from 0.89 to 0.98, for the short posterior ciliary artery from 0.75 to 0.91, and for the long posterior ciliary artery from 0.77 to 0.99 in both the groups.

CONCLUSIONS

The ICCs of the repeated measurements reflect a good reproducibility for both the groups with assumed different retrobulbar perfusion. These findings are prerequisites for the use of CDI in clinical practice and research.

Okuläre Hämodynamik beim Normaldruckglaukom: Effekte von Bimatoprost

BACKGROUND

Altered ocular perfusion plays a role in the pathophysiology of normal tension glaucoma. Prostaglandin-like substances are very effective in lowering intraocular pressure. Less data are available regarding the influence of these compounds on ocular perfusion. In the present study the effects of bimatoprost, which has recently been shown to increase the vascular tone of ciliary arteries in vitro, on the blood flow velocity are investigated.

PATIENTS AND METHODS

n = 9 eyes from 9 normal tension glaucoma patients were subjected to color Doppler imaging (CDI) before and during a 3 - 5 week therapy with bimatoprost.

RESULTS

Bimatoprost reduces intraocular pressure from 14.0 +/- 0.4 to 11.0 +/- 0.5 mmHg (n = 9; P < 0.001). Systolic as well as diastolic blood flow velocities, resistive index (RI) and pulsatility index (PI), measured by CDI, were unaltered in the presence of bimatoprost.

DISCUSSION

Bimatoprost does not influence blood flow velocities in the retrobulbar vessels. The in vitro observation of increased vascular tone in the presence of bimatoprost seems not to be relevant for ocular hemodynamics.

[Therapy of normal tension glaucoma: effect of brinzolamide on ocular haemodynamics]

BACKGROUND

Altered ocular perfusion plays a role in the pathophysiology of normal tension glaucoma. Dorzolamide, a locally applied inhibitor of carbonic anhydrase, is thought to increase ocular blood flow. Less data are available regarding the influence exercised on ocular perfusion by brinzolamide, another and different, locally administered, inhibitor of carbonic anhydrase.

PATIENTS AND METHODS

n = 15 eyes of 8 normal tension glaucoma patients were subjected to colour Doppler imaging and Langham-OBF (LOBF) before and during a therapy for 3 - 5 weeks with brinzolamide.

RESULTS

Brinzolamide reduces intraocular pressure from 15.8 +/- 0.9 to 12.6 +/- 0.9 mm Hg (n = 15; P < 0.05). Systolic as well as diastolic blood flow velocities, resistive (RI) and pulsatility index (PI), measured by CDI, remained unchanged in the presence of brinzolamide. LOBF values are also not influenced by brinzolamide (1014 + 115 before vs. 1113 +/- 178 microl under therapy; n = 15; n. s.).

DISCUSSION

Brinzolamide does not exercise any impact on ocular haemodynamics. This is different from the properties of dorzolamide that had been reported previously.

[Estimation of ocular perfusion: a practical oriented comparison of different methods]

BACKGROUND

Ocular haemodynamics play a prominent part in many ocular diseases. This leads to the need to determine ocular perfusion. Several studies reveal advantages of colour Doppler imaging (CDI) in ophthalmologic diagnostics. Little is known about correlation of CDI results with other methods.

PATIENTS AND METHODS

N = 56 eyes were examined with CDI, laser Doppler flowmetry (LDF) and Langham-OBF (LOBF). Correlations between the methods were identified by the Spearman correlation coefficient (R).

RESULTS

LDF correlated with time average maximum (TAMx) and mean (TAMn) velocity assessed by CDI in the long posterior ciliary artery (TAMx: R = 0.466, p = 0.038, n = 20; TAMn: R = 0.462; p = 0.040, n = 20), but not in the short posterior ciliary artery. LOBF correlated with pulsatility index (PI) and resistive index (RI) of CDI in short (PI: R = 0.514, p = 0.002, n = 35; RI: R = 0.438, p = 0.008, n = 35) and long posterior ciliary arteries (PI: R = 0.436, p = 0.009, n = 35; RI: R = 0.506, p = 0.002, n = 35).

DISCUSSION

Methods strengthen each other by partial correlation. CDI allows a more detailed insight into ocular perfusion than the other methods.

Estimation of choroid perfusion by colour Doppler imaging vs. other methods

Ocular haemodynamics play a prominent role in several ocular diseases. Recently, new methods for the determination of ocular perfusion were developed. Colour Doppler imaging (CDI) of orbital vessels has come up in the past decade and was shown to be useful in ophthalmological diagnostics. Little is known about measurement of choroid perfusion by CDI in comparison with other methods. Therefore, 49 eyes were examined with CDI, laser Doppler flowmetry (LDF) and the method of Langham (LOBF). Correlations between the methods were identified by the Spearman correlation coefficient (r). LDF readings correlated with time-averaged mean velocity assessed by CDI in the long posterior ciliary artery (r = 0.47; p = 0.039; n = 20), but not in the short posterior ciliary artery. LOBF measurements correlated with pulsatility index (PI) of CDI in short (r = 0.50; p = 0.005; n = 30) and long posterior ciliary arteries (r = 0.41; p = 0.024; n = 30). Methods strengthened each other by partial correlation. The study demonstrates that CDI allows a more detailed insight into ocular perfusion.

[Reproducibility of measuring retinal nerve fiber density. Comparison of optical coherence tomography with the nerve fiber analyzer and the Heidelberg retinal tomography device]

BACKGROUND

Glaucoma is associated with a progressive loss of retinal ganglion cell axons and the evaluation of the thickness of the retinal nerve fibre layer (RNFL) is important for early diagnosis and follow-up. Results of RNFL thickness measurements may vary according to the devices used. Therefore, the present study has analysed and compared the reproducibility of data obtained with three different instruments.

METHODS

RNFL thickness was determined using a circular identification line around the optic nerve head by optical coherence tomography (OCT), a Heidelberg Retina Tomograph (HRT) and a Nerve Fiber Analyser (NFA). Each eye was tested six times. The values for RNFL thickness were calculated for the superior, inferior, nasal and temporal areas. A one-way analysis of variance with random effects was chosen to estimate the variance components. The intraclass correlation coefficient (ICC) as a measure of reliability and the coefficient of variation (CV%) as a measure of precision were determined to estimate the reproducibility of RNFL thickness measurements.

RESULTS

With all three instruments, the reproducibility of measurements between the superior, inferior, temporal and nasal areas did not differ significantly suggesting that reproducibility does not depend on the thickness of the RNFL. Data obtained by NFA showed the highest ICC values (0.9) and lowest CV% values (7.0), followed by those obtained by HRT (reliability ICC 0.8; precision CV% 12). A markedly lower degree of reproducibility was found for the OCT compared to NFA and HRT (reliability ICC 0.5; precision CV% 15).

CONCLUSION

The comparison of RNFL thickness measurements with OCT, NFA, and HRT showed that the NFA yielded the most reliable results followed by HRT.

[Quantification of retinal nerve fiber thickness. A comparison of laser scanning ophthalmoscopy, polarimetry and optical coherence tomography in healthy and glaucomatous eyes]

PURPOSE

To evaluate the thickness of the retinal nerve fiber layer (RNFL) in healthy eyes and in eyes of patients with primary open angle glaucoma using the Heidelberg retina tomograph (HRT), the nerve fibre analyser (NFA) and the optical coherence tomograph (OCT).

METHODS

In this prospective cohort study, 40 normal eyes and 86 eyes of age-matched glaucoma patients were compared by confocal scanning laser tomography using the HRT, scanning laser polarimetry (NFA) and optical coherence tomography (OCT). The RNFL thickness was measured in the superior, inferior, nasal and temporal regions as well as the total circumference.

RESULTS

All three methods revealed a statistically significant difference between normal and glaucomatous eyes with respect to the mean RNFL thickness in the inferior and superior regions (p < 0.001). The mean RNFL thickness in the superior region was 329 microns (HRT), 87 microns (NFA) and 94 microns (OCT) in healthy volunteers compared to 275 microns (HRT), 72 microns (NFA) and 82 microns (OCT) in the patient group. In the inferior region, it was 323 microns (HRT), 87 microns (NFA) and 93 microns (OCT) in healthy subjects versus 240 microns (HRT), 74 microns (NFA) and 83 microns (OCT) in glaucoma patients. Cut-off points to differentiate between normal and glaucomatous eyes could not be defined. There was no difference in the RNFL thickness of right and left eyes.

CONCLUSIONS

In RNFL thickness measurements using HRT, NFA and OCT, glaucoma patients showed a significantly thinner RNFL in the superior and inferior areas compared to healthy volunteers. These results confirm the known histological and fundus photographic findings of RNFL thinning near the optic disc in glaucoma patients. Although RNFL thickness cannot be used to diagnose glaucoma in individual patients due to the high interindividual differences, the quantitative assessment of RNFL thickness may complement the diagnostic armamentarium as a sensitive parameter for diagnosing and monitoring glaucomas.

[Permanent embryonic mouse germ cell-lines, an in vitro alternative to in vivo germ cell mutagenicity tests]

Germ cell mutagenesis is required by the 7th amendment of the directive 67/548 EEC into the national regulations on existing chemicals. Officially accepted in vivo test systems for stage specific mutagenicity are the dominant lethal (DL) test and the specific locus test (SLT) in mice. An acceptable in vitro alternative designed to address germ cell mutagenesis and discriminate between male and female specific effects is not available at present. In order to offer a sensitive and predictive in vitro method to assess the genotoxic potential of chemical agents on male and female reproduction, we established primordial germ (PG) cell-derived permanent embryonic germ (EG) cell lines of the mouse (strain BALB/cJ). The differences in developmental sensitivity of the EG(3) cell line and differentiated fibroblast cells 3T3 were comparatively tested with cytotoxicity assay (MTT test ) and genotoxic studies (SCE-assay) under identical test conditions. The concentration-response curves reflected the female cell line EG(3) to be extremely sensitive concerning cytotoxic and genotoxic endpoints. Therefore this cell line was used to classify in vivo genotoxic and non-genotoxic test substances with different potential endpoints. Applying linear discriminant analysis three endpoints were identified for the correct classification (100%) of all test chemicals, namely the SCE(200) value (increase of 200% in the mean number of SCEs per metaphase spread) for EG(3) (3 hrs and 24 hrs assay) and the IC(5)0 value for EG(3) after 3 hrs of exposure to test chemicals.

Permanent embryonic germ cell lines of BALB/cJ mice--an in vitro alternative for in vivo germ cell mutagenicity tests

To offer a sensitive and predictive in vitro method to assess germ cell mutagenicity, we established primordial germ (PG) cell-derived permanent female and male embryonic germ (EG) cell lines of the mouse (strain BALB/cJ). The differences in developmental sensitivity of EG cells and differentiated fibroblast cells of the mouse cell line 3T3 to genotoxicants were tested comparatively under identical test conditions. Cytotoxicity assay was measured by the MTT test and genotoxic effects were determined by sister chromatid exchanges (SCE) rates induced by standard reference mutagens. Both methods are used to assign the chemicals to two classes of in vivo reproductive toxicity, non- and strongly genotoxic to germ cells. Applying linear discriminant analysis, a biostatistical prediction model (PM) was developed for the female cell line EG(3). This procedure identified a single variable, the Ig(SCE(200)EG(3)) as the statistically significant concentration related increase of 200% in the mean number of SCEs per metaphase spread after 3 h of exposure to be sufficient for separation into the classes: non- and strongly genotoxic to germ cells. Applying this PM to the training set of five genotoxic and three non-genotoxic test chemicals, 100% correct classifications were obtained.

Hybrid vigor, fetal overgrowth, and viability of mice derived by nuclear cloning and tetraploid embryo complementation

To assess whether heterozygosity of the donor cell genome was a general parameter crucial for long-term survival of cloned animals, we tested the ability of embryonic stem (ES) cells with either an inbred or F(1) genetic background to generate cloned mice by nuclear transfer. Most clones derived from five F(1) ES cell lines survived to adulthood. In contrast, clones from three inbred ES cell lines invariably died shortly after birth due to respiratory failure. Comparison of mice derived from nuclear cloning, in which a complete blastocyst is derived from a single ES cell, and tetraploid blastocyst complementation, in which only the inner cell mass is formed from a few injected ES cells, allows us to determine which phenotypes depend on the technique or on the characteristics of the ES cell line. Neonatal lethality also has been reported in mice entirely derived from inbred ES cells that had been injected into tetraploid blastocysts (ES cell-tetraploids). Like inbred clones, ES cell-tetraploid pups derived from inbred ES cell lines died shortly after delivery with signs of respiratory distress. In contrast, most ES cell-tetraploid neonates, derived from six F(1) ES cell lines, developed into fertile adults. Cloned pups obtained from both inbred and F(1) ES cell nuclei frequently displayed increased placental and birth weights whereas ES cell-tetraploid pups were of normal weight. The potency of F(1) ES cells to generate live, fertile adults was not lost after either long-term in vitro culture or serial gene targeting events. We conclude that genetic heterozygosity is a crucial parameter for postnatal survival of mice that are entirely derived from ES cells by either nuclear cloning or tetraploid embryo complementation. In addition, our results demonstrate that tetraploid embryo complementation using F(1) ES cells represents a simple, efficient procedure for deriving animals with complex genetic alterations without the need for a chimeric intermediate.

[Retinal nerve fiber layer thickness and peripapillary blood flow in glaucoma patients and healthy probands]

BACKGROUND

In progressive glaucoma there is increasing loss of retinal nerve fibers and therefore decreasing nerve fiber layer thickness. As measurements of capillary blood flow have been reported to depend on nerve fiber layer thickness, this could result in incorrectly high blood flow measurements in patients with advanced glaucoma.

METHODS

In 33 healthy controls and 59 glaucoma patients we measured retinal nerve fiber layer thickness by laser polarimetry and relative capillary blood flow by scanning laser doppler flowmetry three times on the nasal and temporal peripapillary retina. For statistical analysis a regression analysis was used.

RESULTS

The correlation coefficients for volume, velocity, and flow with nerve fiber layer thickness at the same location were 0.02/-0.03/-0.02 in the temporal retina and -0.22/-0.07/-0.19 in the nasal retina (all correlations nonsignificant).

CONCLUSION

No correlation was found between nerve fiber layer thickness and capillary blood flow. Measurement of capillary blood flow in glaucoma patients thus does not appear to be affected by decreasing nerve fiber layer thickness.

Dissection of bacteriophage lambda site-specific recombination using synthetic peptide combinatorial libraries

A wide variety of tools have been used to dissect biochemical pathways, inhibitors being chief among them. Combinatorial approaches have made the search for inhibitors much more efficient. We have applied such an approach to identify hexapeptides which inhibit different steps in a site-specific recombination reaction mediated by the bacteriophage lambda integrase protein. Integrase's mechanism is still incompletely understood, in large part because several pathway intermediates remain hard to isolate. Integrase-catalyzed recombination is very efficient, but if blocked, it is highly reversible to substrates; this combination makes some intermediates exceedingly transient. We have used synthetic peptide combinatorial libraries to screen for hexapeptides that affect the recombination pathway at different stages, and have identified two families of peptides: one probably blocks DNA cleavage, the other may stabilize the Holliday junction intermediates. These peptides do not resemble parts of integrase or any of the other helper functions in the pathway. The deconvolution of hexapeptide libraries based both on inhibition of an enzymatic reaction as well as on accumulation of reaction intermediates is a novel approach to finding useful tools for dissecting a biochemical pathway.

Peptide inhibitors of DNA cleavage by tyrosine recombinases and topoisomerases

The study of biochemical pathways requires the isolation and characterization of each and every intermediate in the pathway. For the site-specific recombination reactions catalyzed by the bacteriophage lambda tyrosine recombinase integrase (Int), this has been difficult because of the high level of efficiency of the reaction, the highly reversible nature of certain reaction steps, and the lack of requirements for high-energy cofactors or metals. By screening synthetic peptide combinatorial libraries, we have identified two related hexapeptides, KWWCRW and KWWWRW, that block the strand-cleavage activity of Int but not the assembly of higher-order intermediates. Although the peptides bind DNA, their inhibitory activity appears to be more specifically targeted to the Int-substrate complex, insofar as inhibition is resistant to high levels of non-specific competitor DNA and the peptides have higher levels of affinity for the Int-DNA substrate complex than for DNA alone. The peptides inhibit the four pathways of Int-mediated recombination with different potencies, suggesting that the interactions of the Int enzyme with its DNA substrates differs among pathways. The KWWCRW and KWWWRW peptides also inhibit vaccinia virus topoisomerase, a type IB enzyme, which is mechanistically and structurally related to Int. The peptides differentially affect the forward and reverse DNA transesterification steps of the vaccinia topoisomerase. They block formation of the covalent vaccinia topoisomerase-DNA intermediate, but have no apparent effect on DNA religation by preformed covalent complexes. The peptides also inhibit Escherichia coli topoisomerase I, a type IA enzyme. Finally, the peptides inhibit the bacteriophage T4 type II topoisomerase and several restriction enzymes with 2000-fold lower potency than they inhibit integrase in the bent-L pathway.

Embryotoxicity screening using embryonic stem cells in vitro: correlation to in vivo teratogenicity

Blastocyst-derived pluripotent embryonic stem (ES) cells of the mouse can be induced to differentiate in culture into a variety of cell types, including cardiac muscle cells. The embryonic stem cell test that makes use of the differentiation of ES cells into cardiomyocytes in a standardized in vitro model was developed to offer an alternative method to comprehensive in vivo studies in reproductive toxicology about toxic effects of chemicals. ES cells of the mouse cell line D3 are investigated for their preserved capability to differentiate following drug exposure, and both ES cells and differentiated fibroblast cells of the mouse cell line 3T3 are comparatively analyzed for effects on viability. The following endpoints are used to classify the embryotoxic potential of chemicals into three classes of in vitro embryotoxicity (non-, weakly or strongly embryotoxic). These endpoints are: (1) the inhibition of differentiation of ES cells into cardiomyocytes after 10 days of treatment, and the decrease of viability (cytotoxicity) of (2) 3T3 cells and (3) ES cells after 10 days of treatment, determined by a 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide (MTT) test. 50% inhibition concentrations for differentiation (ID(50)) and cytotoxicity (IC(50)D3 and IC(50)3T3) are calculated from concentration-response curves. Applying linear analysis of discriminance, a biostatistical prediction model (PM) was developed. This procedure identified three variables, the lg(IC(50)D3), the lg(IC(50)3T3) and the relative distance between IC(50)3T3 and ID(50), that improved the separation of the three classes of embryotoxicity compared to the prediction model that was originally proposed after test development. Unlike the original PM, the improved PM incorporates as one variable the relative distance between IC(50)3T3 and ID(50), instead of the ratio ID(50)/IC(50)D3 that was used previously.

Effect of topical dorzolamide on optic nerve head blood flow

PURPOSE

The topical carbonic anhydrase inhibitor dorzolamide has proven effective in lowering intraocular pressure in glaucoma patients. Because an impaired blood supply of the optic nerve has to be regarded as a major pathogenic risk factor it seems important to examine the effect of this new antiglaucomatous drug on capillary optic nerve head blood flow.

METHODS

In a double-masked, randomized clinical trial, dorzolamide eye drops were applied to both eyes of 15 healthy subjects (8 female, 7 male, mean age 30.6 years) three times daily for 3 days. The control group (15 healthy volunteers, 9 female, 6 male, mean age 30.8 years) received a placebo preparation according to the same protocol. Intraocular pressure (IOP), blood pressure, heart rate, capillary optic nerve head blood flow and retinal blood flow were measured at baseline (1D0), 90 min after single instillation (1D90), and after 3 days of therapy (3D). Scanning laser Doppler flowmetry (Heidelberg Retina Flowmeter) and laser Doppler flowmetry according to Riva (Oculix 4000) were used to measure optic nerve head blood flow.

RESULTS

IOP dropped in dorzolamide-treated subjects from 12.5 mmHg to 11.0/10.5 mmHg (1D0, 1D90, 3DO) and in the control group from 13.0 mmHg to 12.5/12.5 mmHg. Optic nerve blood flow as measured by scanning laser Doppler flowmetry showed no significant changes in dorzolamide-treated volunteers (temporal 310/329/315 AU, nasal 387/402/399 AU) or in the placebo group (temporal 238/306/276 AU, nasal 356/382/379 AU). Also as measured by laser Doppler flowmetry optic nerve head blood flow did not show significant changes in dorzolamide-treated volunteers (temporal 12.98/12.6/11.7 AU, nasal 16.6/16.9/15.7 AU) or in the placebo group (temporal 11.9/12.4/12.4 AU, nasal 16.1/15.8/17.7 AU). The systemic parameters blood pressure and heart rate remained unchanged during the treatment period.

CONCLUSION

The results showed the expected drop in IOP. However, capillary optic nerve head blood flow, measured by two different techniques, did not change during therapy. This may be due to the effective autoregulation in human optic nerve head circulation, which seems not to be affected by dorzolamide.

Regional distribution of optic nerve head blood flow

BACKGROUND

Advanced glaucoma typically results in damage of the temporal neuroretinal rim. As vascular factors are of pathogenic importance in the development of glaucomatous damage, the present study investigated whether regional differences in perfusion might be the reason for the preferential damage of the temporal neuroretinal rim.

MATERIAL AND METHODS

Blood flow of the neuroretinal rim was measured with the laser Doppler flowmeter (LDF) Oculix 4000 (continuous measurement of an area of 160 microm diameter) and the Heidelberg retina flowmeter (HRF). Both instruments measure the capillary blood flow (flow), the relative velocity of erythrocytes (velocity) and the relative volume of moving erythrocytes (volume). We examined one randomly chosen eye of 55 healthy subjects without history of glaucoma aged 22-57 years (mean 30 years). Each subject was measured with the LDF and HRF, each time nasally and temporally, away from visible vessels. The intraocular pressure (IOP) was measured with the Goldmann tonometer. Heart rate and systolic and diastolic blood pressure were measured.

RESULTS

The LDF measurements of the optic nerve head showed nasal flow of 12.4+/-5.6 AU and temporal flow of 9.8+/-3.6 AU. The HRF showed a nasal flow of 477+/-161 AU and a temporal flow of 368+/-166 AU. The volume measurements done by LDF showed nasally a value of 0.68+/-0.40 AU and temporally a value of 0.46+/-0.21 AU. The HRF volume measurements showed nasal values of 16.1+/-4.3 AU and temporal values of 13.0+/-4.0 AU. The LDF velocity values were nasally 0.22+/-0.05 kHz and temporally 0.26+/-0.05 kHz. HRF measurements showed velocity values of 1.7+/-0.5 kHz nasally and 1.3+/-0.6 kHz temporally. The differences were highly statistically significant for flow (LDF P=0.00007, HRF P=0.0005), volume (LDF P=0.00002, HRF P=0.00004) and velocity (LDF P=0.0002, HRF P=0.00004). The IOP was 12.6 mmHg. Blood pressure was 118/75 mmHg and the heart rate was 73 beats per minute. There was no correlation between age, IOP, BP and HR and the HRF/LDF measurements.

CONCLUSION

The measurements with two different methodologies showed a decreased blood flow of the temporal neuroretinal rim compared to the nasal side. These local differences might be one reason for the preferential damage of the temporal neuroretinal rim in advanced glaucoma.

Endothelial cell loss secondary to two different phacoemulsification techniques

BACKGROUND AND OBJECTIVE

The endothelial cell count after phacoemulsification serves as a sensitive indicator for the level of corneal damage caused by different phacoemulsification techniques.

PATIENTS AND METHODS

In a prospective and randomized study, the "Reversed Tip and Snip" technique and the "Divide and Conquer" technique were performed in groups of 30 patients each. The corneal endothelial cell count was measured preoperatively as well as 4 weeks and 3 months postoperatively.

RESULTS

The endothelial cell count showed significant (P < .001) reduction by approximately 10% after the "Reversed Tip and Snip" technique and by approximately 15% (P < .001) after the "Divide and Conquer" technique. The latter produced a significantly (P < .001) greater cell loss.

CONCLUSIONS

The "Reversed Tip and Snip" phacoemulsification technique produces less endothelial cell loss than the "Divide and Conquer" technique.

Utility of C57BL/6J x 129/SvJae embryonic stem cells for generating chromosomal deletions: tolerance to gamma radiation and microsatellite polymorphism

We have previously reported a method for making nested deletion complexes in mice by irradiation of ES cells. The key to this technology is that F1 hybrid ES cells (called v17.2) of the genotype (BALB/cTa x 129/SvJae) retain germline colonizing ability after exposure to levels of ionizing radiation that induce chromosomal deletions. In an effort to identify other genotypes of ES cells that are suitable for this technology, the radiation sensitivity of the cell line v6.4, which is of the genotype (C57BL/6J x 129/SvJae), was investigated. After treatment with a range of radiation exposures, the developmental potential of these cells was assayed by injecting them into blastocysts to generate chimeric mice. These experiments showed that while cell lethality increased as the level of radiation increased, the surviving ES cells retained full totipotency at all exposure levels, up to 400 Rads. Because polymorphism between parental microsatellite alleles in the F1 hybrid ES cells is important for ascertaining the sizes of induced deletions, the 129/SvJ and 129/SvJae allele sizes of 48 microsatellite loci on chromosome (Chr) 17 were determined. This revealed a higher level of polymorphism between 129 and C57BL/6J on Chr 17. The radiation tolerance, high polymorphism between parental strains, and presence of the widely used C57BL/6J strain component make v6.4 ES cells an attractive cell line for generating radiation-induced chromosomal deletions.

ES cells do not activate p53-dependent stress responses and undergo p53-independent apoptosis in response to DNA damage

BACKGROUND

Embryonic stem (ES) cells can contribute precursors to all adult cell lineages. Consequently, damage to ES cell genomes may cause serious developmental malfunctions. In somatic cells, cell-cycle checkpoints limit DNA damage by preventing DNA replication under conditions that may produce chromosomal aberrations. The tumor suppressor p53 is involved in such checkpoint controls and is also required to avoid a high rate of embryonic malformations. We characterized the cell-cycle and DNA-damage responses of ES cells to elucidate the mechanisms that prevent accumulation or transmission of damaged genomes during development.

RESULTS

ES cells derived from wild-type mice did not undergo cell-cycle arrest in response to DNA damage or nucleotide depletion, although they synthesized abundant quantities of p53. The p53 protein in ES cells was cytoplasmic and translocated inefficiently to the nucleus upon nucleotide depletion. Expression of high levels of active p53 from an adenovirus vector could not trigger cell cycle arrest. Instead, ES cells that sustained DNA damage underwent p53-independent apoptosis. The antimetabolite-induced p53-dependent arrest response was restored in ES cells upon differentiation.

CONCLUSIONS

Cell-cycle regulatory pathways in early embryos differ significantly from those in differentiated somatic cells. In undifferentiated ES cells, p53 checkpoint pathways are compromised by factors that affect the nuclear localization of p53 and by the loss of downstream factors that are necessary to induce cell-cycle arrest. A p53-independent programmed cell death pathway is effectively employed to prevent cells with damaged genomes from contributing to the developing organism. The p53-mediated checkpoint controls become important when differentiation occurs.

Regulation of ES cell differentiation by functional and conformational modulation of p53

Embryonic stem (ES) cell lines were used to examine the role of p53 during in vitro differentiation. Undifferentiated ES cells express high levels of p53 exclusively in the wild-type conformation, immunoprecipitable by monoclonal antibody PAb246, and p53 was found to be functionally active as determined by its ability to bind DNA specifically and to activate transcription of target genes. Differentiation in vitro resulted in a decrease in the levels of p53 and in a shift in its conformational status to the mutant form, detectable by monoclonal antibody PAb240, with a concomitant loss of functional activity. The presence of functional p53 in the undifferentiated ES cells renders them hypersensitive to UV irradiation, whereas the differentiated cells were resistant to UV treatment. ES cells lacking p53 exhibit enhanced proliferation in both the undifferentiated and differentiated state, and apoptosis accompanying differentiation was found to be reduced. Furthermore, wild-type ES cells undergoing apoptosis expressed functional p53. Expression of the temperature-sensitive p53val135 mutant in wild-type ES cells resulted in a reduction of apoptosis accompanying differentiation when it adopted a mutant conformation at 39 degrees C. These data demonstrate that functional inactivation of p53 allows differentiating cells to escape from apoptosis, and suggest that the conformational switch could regulate the inactivation process.

Chromosomal deletion complexes in mice by radiation of embryonic stem cells

Chromosomal deletions ("deficiencies') are powerful tools in the genetic analysis of complex genomes. They have been exploited extensively in Drosophila melanogaster, an organism in which deficiencies can be efficiently induced and selected. Spontaneous deletions in humans have facilitated the dissection of phenotypes in contiguous gene syndromes and led to the positional cloning of critical genes. In mice, deletion complexes created by whole animal irradiation experiments have enabled a systematic characterization of functional units along defined chromosomal regions. However, classical mutagenesis in mice is logistically impractical for generating deletion sets on a genome-wide scale. Here, we report a high-throughput method for generating radiation-induced deletion complexes at defined regions in the genome using ES cells. Dozens of deletions of up to several centiMorgans, encompassing a specific locus, can be created in a single experiment and transmitted through the germline. The ability to rapidly create deletion complexes along chromosomes will facilitate systematic functional analyses of the mammalian genome.

Targeting of a functional Escherichia coli RecA protein to the nucleus of plant cells

We have characterised a RecA protein fused to the simian virus 40 large T nuclear-localisation signal. The fusion protein was targeted to the nucleus in transgenic tobacco plants with high efficiency. By contrast, authentic RecA was not enriched in the nuclei of plant cells expressing comparable amounts of protein. For detailed characterisation of the strand-exchange activity of the nuclear-targeted RecA protein, a nearly identical protein was expressed in Escherichia coli and purified to homogeneity. This protein was found to bind to single-stranded DNA with the same stoichiometry and to promote the exchange of homologous DNA strands with the same kinetics as authentic RecA. It was concluded that the amino-terminal modification did not alter any of the essential properties of RecA and that the fusion protein is a fully functional strand-exchange protein. However, the ATPase activity of this protein was 20 times greater than that of RecA in the absence of single-stranded DNA. As with RecA, this activity was further stimulated by the addition of single-stranded DNA. Since ATPase activity is correlated with the ability of RecA to assume its high affinity state for DNA, the nuclear-targeted RecA protein might be regarded as a constitutively stimulated RecA variant, fully functional in promoting homologous recombination.

[Endothelial cell loss after phacoemulsification with the "reversed tip and snip" technique compared with the "divide and conquer" technique]

BACKGROUND

The endothelial cell count after phakoemulsification is a sensitive parameter to compare different phakoemulsification techniques.

PATIENTS AND METHOD

In a prospective study 30 patients in each group were operated upon the "Reversed Tip and Snip" and with the "Divide and Conquer"-Technique. The corneal endothelial cell count was measured before surgery and 4 weeks and 3 months after the operation.

RESULTS

The endothelial cell count was reduced significantly about 10% after the the "Reversed Tip and Snip" and about 15% after the "Divide and Conquer"-Technique. The first mentioned technique had a significantly reduced cell loss than the latter.

CONCLUSION

The "Reversed Tip and Snip" phakoemulsification technique causes less endothelial cell loss than the "Divide and Conquer"-Technique.

[Ultrasound biomicroscopy as a criterium of functional assessment of the supra-choroidal cleft after chamber angle surgical interventions]

BACKGROUND

The new technique of ultrasonic biomicroscopy provides detailed information about the extension and width of suprachoroidal clefts during the follow-up period after cyclodialysis ab interno.

PATIENTS AND METHODS

We examined a group of 9 patients suffering from dysgenetic glaucoma and secondary glaucoma. Ultrasonic biomicroscopy was performed before and after cyclodialysis ab interno. The results were compared to those of gonioscopy.

RESULTS

These examinations revealed that even cyclodialysis clefts which appeared to be closed by gonioscopy were still open. This was proven by a broad choroidal cleft in the cyclodialysis area.

CONCLUSIONS

Thus, ultrasonic biomicroscopy is a means of checking the outcome of cyclodialysis ab interno and may influence the indications for further surgical procedures.

RecA protein stimulates homologous recombination in plants

A number of RecA-like proteins have been found in eukaryotic organisms. We demonstrate that the prokaryotic recombination protein RecA itself is capable of interacting with genomic homologous DNA in somatic plant cells. Resistance to the DNA crosslinking agent mitomycin C requires homologous recombination as well as excision repair activity. Tobacco protoplasts expressing a nucleus-targeted RecA protein were at least three times as efficient as wild-type cells in repairing mitomycin C-induced damage. Moreover, homologous recombination at a defined locus carrying an endogenous nuclear marker gene was stimulated at least 10-fold in transgenic plant cells expressing nucleus-targeted RecA. The increase in resistance to mitomycin C and the stimulation of intrachromosomal recombination demonstrate that Escherichia coli RecA protein is functional in genomic homologous recombination in plants, especially when targeted to the plant nucleus.

[Glaucoma and aircraft pilot fitness]

Two completely different questions arise when considering glaucoma and fitness to fly: Firstly, what is the risk for a passenger with glaucoma? Secondly, what is the flight safety risk connected with pilots suffering from glaucoma? National requirements and international standards pay little regard to this disease. This is astonishing, given that the perception of flight information in the peripheral visual field is of great importance in the cockpit. On one hand, diagnostic glaucoma examinations for pilots are mainly insufficient, and on the other, progressive visual field deficiencies may go undetected because of long intervals between examinations. Intraocular pressure may increase while flying in aircraft, e.g. in the case of negative g-load. Frequent flights at high altitudes without pressurized cabin air and with decreased oxygen supply, and therefore decreased tissue oxygen saturation, may represent a risk, especially for patients with progressive nerve fibre loss.

Experimental use of space-retaining substances with extended duration: functional and morphological results

BACKGROUND

In glaucoma surgery, e.g. cyclodialysis ab interno, to date no viscous substances have been available that stay in the cyclodialysis cleft long enough to prevent scarring. We examined the qualities of two different viscoelastic substances that stay longer in the place of instillation than hyaluronic acid.

METHODS

We performed cyclodialysis ab interno in 12 eyes of six owl monkeys. The right eyes were treated with the gel with the higher molecular weight, the left eyes using the gel with the lower molecular weight. The baseline data of intraocular pressure and outflow facility were compared to the values measured postoperatively up to the 140th day. Histological examination of the eyes followed.

RESULTS

There was no statistically significant difference between the two substances. The mean intraocular pressure decrease was 7.9 (+/- 2.9) mmHg in the right eyes and 4.8 (+/- 2.7) mmHg in the left eyes. The histological examination showed that the gel had remained in the cyclodialysis cleft without signs of inflammation. In contrast to other viscoelastic substances studied previously, the substances in this study performed their space-retaining function without decreasing outflow facility.

CONCLUSION

Both substances are suitable means of improving the rate of success of cyclodialysis ab interno, as they remain where they are instilled long enough to prevent wound scarring in the cyclodialysis cleft.