Essential role of growth hormone in ischemia-induced retinal neovascularization

Retinal neovascularization is the major cause of untreatable blindness. The role of growth hormone (GH) in ischemia-associated retinal neovascularization was studied in transgenic mice expressing a GH antagonist gene and in normal mice given an inhibitor of GH secretion (MK678). Retinal neovascularization was inhibited in these mice in inverse proportion to serum levels of GH and a downstream effector, insulin-like growth factor-I (IGF-I). Inhibition was reversed with exogenous IGF-I administration. GH inhibition did not diminish hypoxia-stimulated retinal vascular endothelial growth factor (VEGF) or VEGF receptor expression. These data suggest that systemic inhibition of GH or IGF-I, or both, may have therapeutic potential in preventing some forms of retinopathy.

Isolation of an APRT heterozygote from TK6 human lymphoblasts: predominance of multi-locus loss of heterozygosity among spontaneous APRT-mutants

The TK6 human B lymphoblastoid cell line contains two easily and widely used selectable markers: the X-linked, hemizygous hprt locus, and the heterozygous tk locus on chromosome 17q. In this study, rare APRT heterozygotes were directly isolated from the TK6 population by clonal selection in cell culture medium supplemented with 5 micrograms/ml of 8-azaadenine. One of nine isolated heterozygotes, AZH1, was characterized extensively. APRT- mutants can be recovered from AZH1 at a mutation rate of 1.5 x 10(-7), similar to rates previously determined for the selection of TK- and HPRT- mutants from TK6. A unique sequence alteration was identified in the non-functional aprt allele at position 1930. A G:C to A:T transition at this site alters the canonical AG splice acceptor dinucleotide in exon 3, and also results in the destruction of a Stul recognition sequence. This polymorphism was used to analyze loss of heterozygosity in a set of 32 spontaneous APRT- mutants by restriction analysis following PCR amplification. Analysis of flanking microsatellite dinucleotide polymorphisms demonstrated that LOH occurring in spontaneous APRT- mutants is nearly always a multi-locus event extending at least 7.5 cM along chromosome 16q. This pattern of LOH among APRT- mutants differs from extensive LOH in spontaneous, normal-growth TK- mutants derived from TK6 cells (p < 0.0001), and suggests that cis-acting factors may be equally important in shaping the mutational spectrum as trans-acting factors such as cellular apoptotic capacity.

Histopathology and vascular endothelial growth factor in untreated and diode laser-treated retinopathy of prematurity

OBJECTIVES

We had the unique opportunity to compare the eyes of a premature infant with stage 3 retinopathy of prematurity (ROP) in both eyes after the condition was treated by diode laser photocoagulation in one eye only. After the infant's death, we investigated the extent of structural damage incurred with the diode laser and examined the effect of treatment on vascular endothelial growth factor (VEGF) expression.

METHODS

The eyes were fixed and embedded in paraffin. Adjacent 6 microns sections were either stained for histopathologic analysis or used for in situ hybridization. VEGF messenger RNA (mRNA) was detected by using radiolabeled antisense riboprobes.

RESULTS

In the treated eye, histopathologic results demonstrated the clinically evident dose-response effect, with sparing of inner retinal elements with mild laser burns and full-thickness retinal cell disruption with severe burns. Scleral and ciliary nerve effects were absent. VEGF mRNA was localized primarily in the ganglion cell layer but was also found in the inner nuclear layer. In the untreated eye, an increase in VEGF mRNA was detected at the peripheral edge of the vascularized retina anterior to the ridge. In the laser-treated eye, VEGF mRNA expression was dramatically upregulated in the ganglion cell layer in areas adjacent to laser burns.

CONCLUSIONS

VEGF mRNA was found to be elevated in the peripheral, avascular retina of the untreated eye, consistent with the hypothesis that retinal hypoxia stimulates VEGF expression. In the treated eye with recurrent ROP, VEGF mRNA was not detected in the photocoagulated areas of retina but was increased between laser scars. This finding confirms the results of prior animal studies and validates the use of these models.

Directed mutagenesis of the Trypanosoma cruzi trans-sialidase enzyme identifies two domains involved in its sialyltransferase activity

Of the increasing number of sialidases found to be made by microorganisms, the trypanosome trans-sialidase is unique in its added ability to efficiently carry out a sialyltransferase reaction using preformed glycoconjugates. The enzyme is predicted to have a multidomain structure, with one domain containing sequence and expected structural features found in bacterial sialidases. The trans-sialidase is very similar in overall sequence to another trypanosome enzyme that has only sialidase activity. Hybrid expression constructs containing pieces of these trypanosome trans-sialidase and sialidase genes were used to determine which regions of trans-sialidase are required for sialyltransferase activity. Two domains were found to influence the enzymatic activity: the N-terminal catalytic domain, and a downstream domain that resembles an Fn3-like module.

Probes for narcotic receptor mediated phenomena. 23. Synthesis, opioid receptor binding, and bioassay of the highly selective delta agonist (+)-4-[(alpha R)-alpha-((2S,5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]- N,N-diethylbenzamide (SNC 80) and related novel nonpeptide delta opioid receptor ligands

The highly selective delta (delta) opioid receptor agonist SNC 80 [(+)-4- [(alpha R)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N ,N- diethylbenzamide, (+)-21] and novel optically pure derivatives were synthesized from the enantiomers of 1-allyl-trans-2,5-dimethylpiperazine (2). The piperazine (+/-)-2 was synthesized, and its enantiomers were obtained on a multigram scale in > 99% optical purity by optical resolution of the racemate with the camphoric acids. The absolute configuration of (+)-2 was determined to be 2S,5R by X-ray analysis of the salt with (+)-camphoric acid. Since the chirality of the starting material was known, and the relative configuration of compounds (-)-21, (-)-22, and (+)-23 were obtained by single-crystal X-ray analysis, the assignment of the absolute stereochemistry of the entire series could be made. Radioreceptor binding studies in rat brain preparations showed that methyl ethers (+)-21 (SNC 80) and (-)-25 exhibited strong selectivity for rat delta receptors with low nanomolar affinity to delta receptors and only micromolar affinity for rat mu (mu) opioid receptors. Compounds (-)-21, (-)-22, and (-)-23 showed micromolar affinities for delta opioid receptors. The unsubstituted derivative (+)-22 and the fluorinated derivative (-)-27 showed > 2659- and > 2105-fold delta/mu binding selectivity, respectively. The latter derivatives are the most selective ligands described in the new series. Studies with some of the compounds described in the isolated mouse vas deferens and guinea pig ileum bioassays revealed that all were agonists with different degrees of selectivity for the delta opioid receptor. These data show that (+)-21 and (+)-22 are potent delta receptor agonists and suggest that these compounds will be valuable tools for further study of the delta opioid receptor at the molecular level, including its function and role in analgesia and drug abuse.

Prevention of postoperative abdominal adhesions by a sodium hyaluronate-based bioresorbable membrane: a prospective, randomized, double-blind multicenter study

BACKGROUND

Postoperative abdominal adhesions are associated with numerous complications, including small bowel obstruction, difficult and dangerous reoperations, and infertility. A sodium hyaluronate and carboxymethylcellulose bioresorbable membrane (HA membrane) was developed to reduce formation of postoperative adhesions. The objectives of our prospective study were to assess the incidence of adhesions that recurred after a standardized major abdominal operation using direct laparoscopic peritoneal imaging and to determine the safety and effectiveness of HA membrane in preventing postoperative adhesions.

STUDY DESIGN

Eleven centers enrolled 183 patients with ulcerative colitis or familial polyposis who were scheduled for colectomy and ileal pouch-anal anastomosis with diverting-loop ileostomy. Before abdominal closure, patients were randomly assigned to receive or not receive HA membrane placed under the midline incision. At ileostomy closure eight to 12 weeks later, laparoscopy was used to evaluate the incidence, extent, and severity of adhesion formation to the midline incision.

RESULTS

Data were analyzed for 175 assessable patients. While only five (6 percent) of 90 control patients had no adhesions, 43 (51 percent) of 85 patients receiving HA membrane were free of adhesions (p < 0.00000000001). The mean percent of the incision length involved was 63 percent in the control group, significantly greater than the 23 percent observed in patients who received HA membrane (p < 0.001). Dense adhesions were observed in 52 (58 percent) of the 90 control patients, but in only 13 (15 percent) of the 85 receiving HA membrane (P < 0.0001). Comparison of the incidence of specific adverse events between the groups did not identify a difference (P > 0.05).

CONCLUSIONS

This study represents the first controlled, prospective evaluation of postoperative abdominal adhesion formation and prevention after general abdominal surgery using standardized, direct peritoneal visualization. In this study, HA membrane was safe and significantly reduced the incidence, extent, and severity of postoperative abdominal adhesions.

Regulation of vascular endothelial growth factor by oxygen in a model of retinopathy of prematurity

OBJECTIVES

To investigate the role of vascular endothelial growth factor (VEGF) in the pathogenesis of the first phase of retinopathy of prematurity (ROP) and to examine the mechanism by which supplemental oxygen therapy might inhibit neovascularization in the second phase of ROP.

METHODS

A novel combination of fluorescein-dextran perfusion and colorimetric whole-retina in situ hybridization was used to evaluate the expression of VEGF messenger RNA in relationship to the location of blood vessels in retinas from neonatal mice that were exposed to hyperoxia. Northern blot and immunoblot analyses were used to quantify the changes in VEGF messenger RNA and protein expression caused by hyperoxia. The ability of VEGF to prevent hyperoxia-induced vaso-obliteration was evaluated by injecting exogenous VEGF into the vitreous cavity prior to oxygen exposure.

RESULTS

Vascular endothelial growth factor messenger RNA was produced in a reticular pattern just anterior to the developing blood vessels in normal retina on postnatal day 7. The expression of VEGF in the peripheral retina was down-regulated by hyperoxia in conjunction with the arrest of growth and the loss of some of the developing vasculature. Total VEGF messenger RNA and protein levels in retinas from animals on postnatal day 7 were decreased 55% and 85%, respectively, after 6 hours in 75% oxygen. Vaso-obliteration was inhibited 57% by pretreatment of animals with exogenous VEGF. In animals with retinal ischemia secondary to loss of vasculature, treatment with supplemental oxygen therapy decreased stimulated retinal VEGF levels by approximately 70%.

CONCLUSIONS

Down-regulation of VEGF expression by hyperoxia may be partly responsible for the vaso-obliteration and cessation of normal retinal blood vessel growth observed in premature infants in whom ROP develops. Hyperoxia also has the potential to be used therapeutically to down-regulate VEGF expression in hypoxic retina in the hope of limiting the neovascular complications of ROP. Based on these findings about the regulation of VEGF expression in the retina, an explanation of the pathogenesis of ROP is proposed.

Transanal endoscopic microsurgery. Initial registry results

Transanal endoscopic microsurgery (TEM) was first used on a regular basis in the United States in 1990. Because there is a sole source of instrumentation, the surgeons who use this equipment are known to us. Thus, this earliest registry is a compilation of data based on most patients who underwent TEM in the United States from 1990 to 1994.

METHOD

One hundred fifty-three cases were voluntarily registered by six surgeons. Pathology included 54 carcinomas, 82 adenomas, and 17 other entities. Most resections were full thickness. Fifty percent of cases were out of reach of standard instruments. Complication rate, hospital stay, and blood loss were recorded. Technical difficulties at time of surgery (9 percent), early complications (15 percent), and late complications (5 percent) have been tabulated.

RESULTS

Recurrence rates for carcinoma were 10 percent for T1, 40 percent for T2, and 66 percent for T3 stages. Failures were treated by abdominoperineal resection or low anterior resection. Adenomas recurred in 11 percent, but these recurrences were small and easily treatable.

CONCLUSION

TEM has a low complication rate. By carefully selecting small, superficial cancers and adenomas, TEM results in superior outcome over other approaches to the mid and upper rectum.

Isolation and expression of an open reading frame encoding sialidase from Trypanosoma rangeli

Several protozoan parasites of human have been found to express enzymes capable of releasing terminal sialic acid residues from host glycans. These include enzymes similar in activity to bacterial and viral sialidases, as well as a novel type of enzyme, trans-sialidase, which can transfer sialic acid from one carbohydrate chain to another. Here we report the isolation of a gene and a gene fragment from the kinetoplastid Trypanosoma rangeli which encode products related in sequence to the trans-sialidase enzyme of T. cruzi. The gene fragment ORF is nearly identical to that of the complete gene, which encodes an enzymatically inactive protein. When the ORF of the gene fragment is fused to fragments from related genes, it encodes a product with sialidase activity. Both predicted T. rangeli protein products also have other potential structural features found in bacterial sialidases and in members of a previously described Trypanosoma trans-sialidase superfamily.

Oligodeoxynucleotides inhibit retinal neovascularization in a murine model of proliferative retinopathy

Diseases characterized by retinal neovascularization are among the principal causes of visual loss worldwide. The hypoxia-stimulated expression of vascular endothelial growth factor (VEGF) has been implicated in the proliferation of new blood vessels. We have investigated the use of antisense phosphorothioate oligodeoxynucleotides against murine VEGF to inhibit retinal neovascularization and VEGF synthesis in a murine model of proliferative retinopathy. Intravitreal injections of two different antisense phosphorothioate oligodeoxynucleotides prior to the onset of proliferative retinopathy reduced new blood vessel growth a mean of 25 and 31% compared with controls. This inhibition was dependent on the concentration of antisense phosphorothioate oligodeoxynucleotides and resulted in a 40-66% reduction in the level of VEGF protein, as determined by Western blot analysis. Control (sense, nonspecific) phosphorothioate oligodeoxynucleotides did not cause a significant reduction in retinal neovascularization or VEGF protein levels. These data further establish a fundamental role for VEGF expression in ischemia-induced proliferative retinopathies and a potential therapeutic use for antisense phosphorothioate oligodeoxynucleotides.

Excellent outcome using selective criteria for rectocele repair

PURPOSE

The aim of this study was to review our experience with patients with rectoceles using very selective criteria for operative repair and to critically review our surgical results.

METHODS

This is a review of patients selected for rectocele repair between 1989 and 1994.

RESULTS

Two hundred seventy-nine patients were evaluated for pelvic outlet symptoms in our clinic. Defecography was performed in 180 patients; rectocele was seen in 143 patients (79 percent; 135 females and 8 males). On physical examination, 132 patients had a palpable rectocele (73 percent). Rectocele repair was recommended for 35 patients (13 percent); 33 (32 females and 1 male) underwent this procedure. Mean age was 55 (range, 16-78) years. Although many patients complained of constipation, incontinence and pelvic pain, in these 33 patients criteria for repair included the sensation of a vaginal mass or bulge that required digital support and/or rectal digitizing for evacuation (58 percent), retention of barium in the rectocele on defecography (55 percent), or a very large rectocele with internal anterior rectal wall prolapse (6 percent). A hysterectomy had been performed previously in 47 percent of women repaired. Rectocele repair was performed by a standard transanal approach in 31 patients and transabdominally in 2 patients. Hospital stay averaged 3.7 (range, 1-8) days. Few postoperative complications occurred; urinary retention was the most common (18 percent). All patients were followed postoperatively, and 26 patients (79 percent) answered a standardized questionnaire. Mean follow-up was 31 (range, 5-64) months. Eighty percent of patients questioned who initially complained of a vaginal mass or bulge reported complete resolution (significant improvement by the sign test, P < 0.5). Subjectively, 92 percent of patients questioned reported improvement in their preoperative symptoms and satisfaction with the operation.

CONCLUSION

Rectoceles are frequently identified during defecography, which is performed for pelvic floor complaints, yet are often asymptomatic. In contrast to other recent reports of rectocele repair, our data indicate that careful selection of patients using specific criteria may result in very good clinical results.

Suppression of retinal neovascularization in vivo by inhibition of vascular endothelial growth factor (VEGF) using soluble VEGF-receptor chimeric proteins

The majority of severe visual loss in the United States results from complications associated with retinal neovascularization in patients with ischemic ocular diseases such as diabetic retinopathy, retinal vein occlusion, and retinopathy of prematurity. Intraocular expression of the angiogenic protein vascular endothelial growth factor (VEGF) is closely correlated with neovascularization in these human disorders and with ischemia-induced retinal neovascularization in mice. In this study, we evaluated whether in vivo inhibition of VEGF action could suppress retinal neovascularization in a murine model of ischemic retinopathy. VEGF-neutralizing chimeric proteins were constructed by joining the extracellular domain of either human (Flt) or mouse (Flk) high-affinity VEGF receptors with IgG. Control chimeric proteins that did not bind VEGF were also used. VEGF-receptor chimeric proteins eliminated in vitro retinal endothelial cell growth stimulation by either VEGF (P < 0.006) or hypoxic conditioned medium (P < 0.005) without affecting growth under nonstimulated conditions. Control proteins had no effect. To assess in vivo response, animals with bilateral retinal ischemia received intravitreal injections of VEGF antagonist in one eye and control protein in the contralateral eye. Retinal neovascularization was quantitated histologically by a masked protocol. Retinal neovascularization in the eye injected with human Flt or murine Flk chimeric protein was reduced in 100% (25/25; P < 0.0001) and 95% (21/22; P < 0.0001) 0.0001) of animals, respectively, compared to the control treated eye. This response was evident after only a single intravitreal injection and was dose dependent with suppression of neovascularization noted after total delivery of 200 ng of protein (P < 0.002). Reduction of histologically evident neovascular nuclei per 6-microns section averaged 47% +/- 4% (P < 0.001) and 37% +/- 2% (P < 0.001) for Flt and Flk chimeric proteins with maximal inhibitory effects of 77% and 66%, respectively. No retinal toxicity was observed by light microscopy. These data demonstrate VEGF's causal role in retinal angiogenesis and prove the potential of VEGF inhibition as a specific therapy for ischemic retinal disease.

Enamel hypoplasia, bilateral cataracts, and aqueductal stenosis: a new syndrome?

We report on a 12-year-old girl who presented with generalized enamel hypoplasia, cataracts, and enlargement of the cerebral ventricles secondary to aqueductal stenosis. Previously described syndromes of enamel defects with or without cataracts were excluded on the basis of clinical criteria and appearance of the dentition. Metabolic conditions which could have caused cataracts were excluded clinically and by biochemical tests. The combination of signs in this patient may represent a new syndrome.

Conjunctival biopsy in patients with Kawasaki disease

Kawasaki disease (KD) is an acute vasculitis of infants and young children that is associated with bilateral nonexudative conjunctivitis during the acute illness. Epidemiologic evidence has suggested an infectious cause but the etiology of KD remains unknown. We examined conjunctival biopsy specimens from seven patients with typical KD to characterize the pathologic changes during the acute disease. Light microscopic examination revealed nonspecific, mild inflammatory changes that included vascular dilatation, infiltration with scattered lymphocytes, increased numbers of plasma cells in the conjunctival stroma, and increased prominence of goblet cells in the epithelium. No pathogens were identified by special stains for bacteria and rickettsiae, nor were viral particles seen by electron microscopy. We conclude that the conjunctivitis of acute KD is characterized by vascular dilatation with a mild mononuclear cell response with no pathognomonic features. The conjunctiva can be readily sampled in these patients and biopsy may prove useful in selected patients to exclude other clinical entities in the differential diagnosis.

Intraoperative reasons for abandoning ileal pouch-anal anastomosis procedures

PURPOSE

Ileal pouch-anal anastomosis (IPAA) has become the operation of choice for most patients with chronic ulcerative colitis and familial adenomatous polyposis. However, because of technical or disease factors at the time of pouch construction, IPAA must sometimes be abandoned. A retrospective review was conducted to find reasons for IPAA failure or abandonment.

METHODS

Since 1981, 103 patients have had to have an IPAA procedure at the George Washington University Medical Center in Washington, DC. All charts were reviewed and data retrospectively collected.

RESULTS

Six of 103 patients (six percent) were unable to have IPAA constructed. Five patients ultimately received a standard end ileostomy, and one had an ileorectal anastomosis. The reasons for abandoning the IPAA procedure were an ischemic pouch, failure to reach the anus, poorly controlled presacral hemorrhage, desmoid of the mesentery, and finding incurable colon carcinoma.

CONCLUSIONS

Information regarding the risk of failure or abandonment during the IPAA procedure should be discussed with the patient during preoperative counseling and must be included as an element of informed consent.

Vascular endothelial growth factor/vascular permeability factor expression in a mouse model of retinal neovascularization

Neovascular diseases of the retina are a major cause of blindness worldwide. Hypoxia is thought to be a common precursor to neovascularization in many retinal diseases, but the factors involved in the hypoxic neovascular response have not been fully identified. To investigate the role of vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) in retinal neovascularization, the expression of VEGF/VPF mRNA and protein were studied in a mouse model of proliferative retinopathy. RNA (Northern) blot analysis revealed that retinal VEGF/VPF mRNA expression increased 3-fold between 6 and 12 hr of relative retinal hypoxia and remained elevated during the development of neovascularization. In situ hybridization localized VEGF/VPF mRNA to cells bodies in the inner nuclear layer of the retina. Immunohistochemical confocal microscopy demonstrated that VEGF/VPF protein levels increase with a time course similar to that of the mRNA. The cells in the inner nuclear layer of the retina that produce VEGF/VPF were identified morphologically as Müller cells. These data suggest that VEGF/VPF expression in the retina plays a central role in the development of retinal ischemia-induced ocular neovascularization.

Field-effect-transistor self-electro-optic-effect-device (FET-SEED) electrically addressed differential modulator array

We describe a 6 × 6 array of electrically addressed field-effect-transistor self-electro-optic-effect-device differential modulators in which each element has a single-stage amplifier to permit an input voltage of less than 1 V to control the output modulators, which can operate at as high as 10 V. The variations in the switching voltages across the array are less than ±70 mV, and the individual array elements are operated at as high as 2 Gbits/s. We also measure cross talk between adjacent elements within the array, measure the dependence of the switching time on the input voltage swing, and calculate the dependence of the switching time that is due to the photocurrent of the modulators.

Microbiology of human immunodeficiency virus anorectal disease

PURPOSE

Individuals who are seropositive for the human immunodeficiency virus are at high risk for opportunistic infection and anorectal disorders. Little prospective information is available regarding anorectal pathogens in these patients.

METHODS

One hundred sixty-three HIV-seropositive patients presented to the colorectal clinic between 1989 and 1992. Forty-seven (29 percent) patients were thought to have an infectious process and were prospectively studied using a standardized multiculture protocol.

RESULTS

Mean age was 33 (range, 19-59) years. All were male; high-risk behavior accounted for 87 percent of HIV transmissions. Presenting complaints included anorectal pain (79 percent), pus per anum (28 percent), and blood per anum (26 percent). Examination revealed perianal tenderness (60 percent), condyloma (38 percent), perianal ulcers (38 percent), and anal fissures (34 percent). Sixty-six sets of cultures were performed; 28 patients had one set, 15 had two sets, and 4 had three sets. Thirty-two of these 47 patients (68 percent) had positive cultures including herpes (50 percent), cytomegalovirus (25 percent), Neisseria gonorrhoeae (16 percent), chlamydia (16 percent), acidfast bacilli (2 percent), and others (9 percent). Six of 32 patients with positive cultures had more than one organism cultured. Sixteen (50 percent) patients with positive cultures were treated medically, 8 (25 percent) were treated surgically and 8 (25 percent) were treated with both modalities. Sixty-one procedures were performed on 17 patients for condylomata. Eighteen patients had 20 procedures for abscesses, 50 percent of whom had positive cultures for other than common bowel flora; all improved. Fourteen patients underwent 33 procedures for perianal fistulas. Mycobacterium fortuitum was cultured from one patient who required 13 procedures for abscesses and fistulas. Forty-five (96 percent) patients were followed for an average of 12.5 months +/- 2.9 SEM (range, 1-94 months). Symptoms were improved or resolved in 22 of 32 (69 percent) patients with positive cultures and in 11 of 13 (84 percent) with negative cultures.

CONCLUSIONS

Specific pathogens may often be identified in human immunodeficiency virus-seropositive patients with anorectal disorders if aggressively sought. Although patients without specific pathogens identified may be expected to improve with planned empiric treatment, positive identification allows more directed therapy.

Effect of light on oxygen-induced retinopathy in the mouse

PURPOSE

To examine the effect lf light on retinal neovascularization and vasculogenesis in a reproducible and quantifiable model of oxygen-induced proliferative retinopathy in the mouse.

METHODS

C57Bl/6J mice were reared in room air, 68% oxygen, or 75% oxygen and were exposed to darkness, low cyclical light (200-350 lux), or high-intensity continuous light (3000-4500 lux). The entire retinal vascular pattern was visualized in fluorescein-dextran perfused flat-mount preparations. Proliferative retinopathy was quantified by counting neovascular nuclei in 6 microns cross-sections of whole eyes.

RESULTS

Light exposure did not exacerbate the proliferative retinopathy that was seen after 68% oxygen exposure, which induced a meager proliferative response, nor after 75% oxygen exposure, which induced an exuberant proliferative response. In room air, retinas from all three illumination groups had normal vascular patterns.

CONCLUSIONS

In this model of oxygen-induced retinopathy, under the conditions tested, light neither exacerbated the hyperoxia-induced neovascularization nor affected normal retinal vascular development.

Oxygen-induced retinopathy in the mouse

PURPOSE

To develop oxygen-induced retinopathy in the mouse with reproducible and quantifiable proliferative retinal neovascularization suitable for examining pathogenesis and therapeutic intervention for retinal neovascularization in retinopathy of prematurity (ROP) and other vasculopathologies.

METHODS

One-week-old C57BL/6J mice were exposed to 75% oxygen for 5 days and then to room air. A novel fluorescein-dextran perfusion method has been developed to assess the vascular pattern. The proliferative neovascular response was quantified by counting the nuclei of new vessels extending from the retina into the vitreous in 6 microns sagittal cross-sections. Cross-sections were also stained for glial fibrillary acidic protein (GFAP).

RESULTS

Fluorescein-dextran angiography delineated the entire vascular pattern, including neovascular tufts in flat-mounted retinas. Hyperoxia-induced neovascularization occurred at the junction between the vascularized and avascular retina in the mid-periphery. Retinal neovascularization occurred in all the pups between postnatal day 17 and postnatal day 21. There was a mean of 89 neovascular nuclei per cross-section of 9 eyes in hyperoxia compared to less than 1 nucleus per cross-section of 8 eyes in the normoxia control (P < 0.0001). Proliferative vessels were not associated with GFAP-positive astrocyte processes.

CONCLUSIONS

The authors have described a reproducible and quantifiable mouse model of oxygen-induced retinal neovascularization that should prove useful for the study of pathogenesis of retinal neovascularization as well as for the study of medical intervention for ROP and other retinal angiopathies.

Genetic instability on chromosome 16 in a human B lymphoblastoid cell line

Mutagenesis at the aprt locus in TK6 human lymphoblasts has been found to occur at an unusually high rate (1.2 x 10(-9)) for a homozygous diploid locus. Evaluation of linked microsatellite polymorphisms demonstrated that loss of heterozygosity (LOH) accompanies conventional intragenic sequence alterations in each APRT- mutant. LOH occurred without allele preference. The extent of loss was highly uniform, ranging from 16q12 to 16qter in 36/38 APRT- mutants. Fluorescence in situ hybridization (FISH), used in conjunction with microsatellite analysis, demonstrated that the loss was not attributable to physical deletion, nondisjunction, or nondisjunction with reduplication of the remaining chromosome. LOH thus appears to be recombinationally mediated. FISH analysis also detected translocations affecting chromosome 16 in 4/20 APRT- mutants examined. APRT- mutants appear to arise as part of a genetic instability phenomenon since three distinct genetic alterations affecting chromosome 16 are recovered in single clones at a detectable rate. These events may be mechanistically related to early events in gene amplification.

Evidence for high-frequency allele loss at the aprt locus in TK6 human lymphoblasts

The aprt locus in TK6 human lymphoblasts has been previously shown to have an unusual mutation frequency (5 x 10(-8) and a gene dosage of 2. Measurements of mutation rate (1.2 x 10(-9)) reported here, confirm the mutation-frequency observations. These results are not easily accommodated by models of the gene as functionally homozygous or heterozygous. Characterization of all exon and intron sequences identified no polymorphism which could distinguish two heterozygous aprt alleles. Furthermore, autoradiographs of 16 spontaneous APRT- mutants demonstrate a variety of unique sequences. If aprt were heterozygous, wild-type sequence from the alternate allele would be observed at positions where mutations have occurred. These observations cannot be explained by conventional loss of heterozygosity in which the same mutated allele would be repeatedly recovered. We therefore propose that aprt is a functionally homozygous locus. APRT- mutants may arise by conventional mutation of one allele, and high-frequency loss or conversion of the alternate allele.

Microscopic visualization of the retina by angiography with high-molecular-weight fluorescein-labeled dextrans in the mouse

Methods currently available for the examination of the retinal vasculature of laboratory animals have significant drawbacks. Fluorescein angiography of rodent eyes is hampered by a poor view of the peripheral retina and difficulty in performing fundus photography. Methods of staining or filling retinal vessels are unreliable, labor-intensive, or have high backgrounds. We have developed a novel technique that is quick, simple, and accurate. Fluorescein-labeled 2 million molecular weight dextrans are used to fill the retinal vasculature of mice in vivo, followed by removal of the retina, fixation in paraformaldehyde, and examination of the vascular pattern in whole mount preparations by fluorescence microscopy. We found that fluorescein and fluorescein-labeled low-molecular-weight dextrans (40,000-500,000) are not suitable as they leak out of the vasculature to stain the entire retina in whole mount preparations. By contrast, fluorescein-labeled 2 million molecular weight dextrans remain in the vasculature for many months without diffusion or decay. Under low magnification, the entire retinal vasculature can be visualized at one time. By focusing from one plane to another, the superficial, connecting, or deep vascular layers are delineated. The background fluorescence is very low. We have successfully used this technique in over 20 mice per day to document retinal angiogenesis in a model of oxygen-induced proliferative retinopathy.