Radiotherapy for recurrent choroidal neovascularisation complicating age related macular degeneration

AIMS

To report the safety and visual outcome data of external beam irradiation for recurrent choroidal neovascularisation complicating age related macular degeneration.

METHODS

Eighteen consecutive eyes received external beam irradiation with seven fractions of 2 Gy (total dose 14 Gy). The next 16 consecutive eyes received external beam irradiation with five fractions of 3 Gy (total dose 15 Gy). Main outcome measure was change in visual acuity. Secondary outcome variables were contrast sensitivity and fundus photographic/fluorescein angiographic progression.

RESULTS

The 3 Gy fraction group lost fewer lines of distance visual acuity at the three and six month follow up. At one year follow up, this difference was not maintained with 2 Gy fraction and 3 Gy fraction eyes. At one year follow up a decrease in visual acuity of three or more lines (moderate visual loss) occurred in 58% of 2 Gy and 42% of 3 Gy fraction eyes (p<0.36). At one year follow up a decrease in visual acuity of six or more lines (severe visual loss) occurred in 41% of 2 Gy eyes and 17% of 3 Gy eyes (p<0.23). At three months follow up, 3 Gy eyes were less likely (0%) than 2 Gy eyes (47%) to show moderate visual loss (p<0.003). However, Kaplan Meier curves estimate a significantly lower rate of severe visual loss in the 3 Gy group (p = 0.02). There were no significant differences in contrast sensitivity loss or fluorescein angiographic stabilisation rates. No evidence of radiation toxicity was observed.

CONCLUSION

Our results are consistent with trends for a palliative benefit with higher fraction sizes and doses. The radiobiologic differences between low and high fraction size groups in this study are modest and correlate with the modest and short term difference in visual outcomes. These trends support further investigation of radiotherapy using fraction sizes of 4 Gy or higher.

Review of alternative therapies for treatment of menopausal symptoms

Many women use alternative therapies to treat hot flushes and other menopausal symptoms. The purpose of this review is to summarize current information on the efficacy and safety of phytoestrogens and the herbal medicine black cohosh. A preponderance of evidence indicates that phytoestrogens are ineffective in treating hot flushes. Trials of black cohosh, many of which are small, of limited duration and of poor methodological quality, provide conflicting results, and at present it is unclear whether black cohosh is more effective than placebo. Although phytoestrogens and black cohosh appear to be safe when used for short periods of time, much larger and longer studies are needed to detect infrequent but potentially serious adverse events. Women who do not wish to take hormone therapy to treat menopausal symptoms should be encouraged to consider using selective serotonin reuptake inhibitors and other conventional therapeutic options.

Sleep disorders: a risk factor for normal-tension glaucoma?

PURPOSE

To determine the prevalence of sleep-related symptoms and sleep-related breathing disorders by polysomnography in patients with normal-tension glaucoma (NTG).

PATIENTS AND METHODS

This comparative case series included 23 patients with NTG, 14 NTG suspects, and 30 comparison patients without NTG. A sleep history was obtained and determined to be positive or negative. Polysomnography was offered for patients with a positive sleep history. Prevalence of a positive sleep history and prevalence of sleep disorders were the main outcome measures.

RESULTS

The NTG, NTG suspect, and comparison groups did not differ with respect to age, body mass index, systemic disease, gender, or race. Thirteen (57%) of 23 patients with NTG, 6 (43%) of 14 NTG suspects, and 1 (3%) of 30 comparison patients had a positive sleep history (P = 0.001). Nine of 13 patients with NTG and four of six NTG suspects with a positive sleep history chose to undergo polysomnography. Seven (78%) of nine patients with NTG and all four NTG suspects undergoing polysomnography were diagnosed with a sleep disorder. Five patients with NTG had sleep apnea and two had sleep hypopnea. Two NTG suspects had sleep apnea; one had sleep hypopnea; and one had upper airway resistance syndrome. The one comparison patient with a positive sleep history had upper airway resistance syndrome by polysomnography.

CONCLUSIONS

Sleep-disturbed breathing may be a risk factor for NTG. Although we do not provide evidence for a cause-and-effect relationship, various physiologic factors produced by sleep-disturbed breathing may play a significant role in the pathogenesis of this optic neuropathy. We recommend obtaining a sleep history from patients with NTG and performing polysomnography in those patients with sleep disturbance symptoms.

Sleep disorders: a risk factor for pseudotumor cerebri?

OBJECTIVE

To determine whether sleep-related breathing disorders are common in patients with idiopathic intracranial hypertension.

MATERIALS AND METHODS

Medical records of 53 patients with idiopathic intracranial hypertension from a tertiary center neuroophthalmology practice were reviewed. Thirty-seven patients were identified who had a history of snoring, difficulty sleeping, or daytime somnolence. The data from polysomnograms were tabulated to determine the frequency of apneas, hypopneas, and arousals.

RESULTS

Fourteen of 37 patients with idiopathic intracranial hypertension and symptoms of sleep disturbance underwent polysomnography. There were two men and 12 women varying in age from 24 to 58 years (mean, 39.4 +/- 11.9). These patients were obese with body mass indexes varying from 33.0 to 63.2 (mean, 46.0 +/- 9.5). A diagnosis of sleep apnea was made in six and upper airway resistance syndrome in seven patients.

CONCLUSIONS

Sleep-related breathing problems were common in our patients with idiopathic intracranial hypertension. Obesity was common in these patients and may be playing a causative role in sleep apnea and idiopathic intracranial hypertension. It is suggested that idiopathic intracranial hypertension patients who have symptoms of sleep disturbance should be further evaluated for the presence of sleep-related breathing problems.

How should alternative medicine be taught to medical students and physicians?

Advocates of alternative medicine are critical of current medical curricula, and have proposed fundamental changes, including the introduction of "integrative medicine" programs to teach alternative medicine. Medical educators have not replied to these criticisms, and have not developed basic curricula in alternative medicine. The author analyzes the alleged deficiencies in medical education, which are based on misrepresentations of medicine and medical training. (For example, critics state that physicians ignore mind-body interactions; in response, several examples are given to show that training physicians to consider the whole person and to identify and address emotional and social problems-the biopsycho-social model-are central tenets of medical education.) The author also examines fundamental differences between traditional and alternative medicine (e.g., their different attitudes toward the importance of evidence; the vitalistic versus the biomedical models of health and disease) that are central to the issue of how alternative medicine should be taught. He concludes that physicians need additional education in order to provide guidance to patients, but teaching about alternative medicine should be evidence-based, not merely the transmission of unproven practices.

External beam irradiation of subfoveal choroidal neovascularization complicating age-related macular degeneration: one-year results of a prospective, double-masked, randomized clinical trial

OBJECTIVES

To determine the effects of low-dose external beam irradiation compared with observation on the visual function of eyes with subfoveal choroidal neovascularization (CNV) complicating age-related macular degeneration (ARMD).

DESIGN

Prospective, double-masked, randomized clinical trial. Patients randomized to the radiation group received external beam irradiation at a dose of 14 Gy in 7 fractions of 2 Gy. Patients randomized to the observation group received sham radiation.

SETTING

Tertiary care retinal referral practice.

PATIENTS

Individuals with classic, mixed, or occult subfoveal CNV secondary to ARMD.

MAIN OUTCOME MEASURES

Change in visual acuity from baseline to specified time periods. Secondary outcome variables were contrast sensitivity and fundus photographic/fluorescein angiographic progression.

RESULTS

Forty-two eyes were randomized to observation; 41 eyes, to radiation. Baseline characteristics and demographics did not differ between groups. The median distance visual acuity (DVA) in radiation-treated eyes decreased from 20/80 at baseline to 20/320 (mean loss rate, 4.14 lines) at 1-year follow-up. The median DVA in observation group eyes decreased from 20/125 at baseline to 20/250 (mean loss rate, 3.39 lines) at 1-year follow-up. There were no statistically significant differences in changes in DVA, contrast sensitivity, or fluorescein angiographic progression from baseline between groups at any follow-up period.

CONCLUSIONS

At 1-year follow-up, low-dose external beam irradiation at 14 Gy in 7 fractions of 2 Gy is neither beneficial nor harmful for subfoveal CNV complicating ARMD.

Reduced severity of oxygen-induced retinopathy in eNOS-deficient mice

PURPOSE

Exposure of premature human infants to hyperoxia results in the obliteration of developing retina capillaries, leading to a vision-threatening retinopathy termed retinopathy of prematurity (ROP). The authors hypothesized that this process may be mediated in part by endothelial nitric oxide (NO)-derived oxidants such as peroxynitrite and tested this hypothesis in a mouse model of ROP.

METHODS

Normal mice, mice treated with the nitric oxide synthase (NOS) inhibitor N:(G)-nitro-L-arginine (L-NNA), and knockout mice carrying a homozygous targeted disruption of the gene for endothelial NOS (eNOS) were studied in an experimental model of ROP. Retinas were compared for extent of capillary obliteration in hyperoxia, vascular endothelial growth factor (VEGF) expression, nitrotyrosine formation, and vitreous neovascularization.

RESULTS

Oxygen-induced retinal vaso-obliteration was significantly reduced by L-NNA treatment (43% decrease from controls). The eNOS-deficient mice showed a similar reduction in vaso-obliteration (46% decrease from controls), and vitreous neovascularization was also substantially reduced (threefold decrease). Retinal nitrotyrosine formation, a measure of in situ peroxynitrite modification of proteins, was significantly elevated in normal mice during hyperoxia, in a spatial and temporal pattern consistent with a role in oxygen-induced vaso-obliteration. This was not seen in eNOS-deficient mice. VEGF expression was similar in both groups of mice, although suppression in hyperoxia was slightly blunted in eNOS-deficient mice.

CONCLUSIONS

These data suggest a role for NO and peroxynitrite in the pathogenesis of ROP. Therapies aimed at modulation of eNOS activity may have therapeutic potential for preventing ROP.

Ultrastructural and ERG findings in mice with adenomatous polyposis coli gene disruption

PURPOSE

In order to continue the previous morphological studies of eyes from mice with adenomatous polyposis coli (APC) gene mutation at codon 1638, we determined the ultrastructural and electrophysiologic characteristics of these eyes.

METHODS

Thirty-eight eyes from 20 mice heterozygous for APC gene mutation and 22 eyes from 11 wild-type mice were examined by light microscopy. Six APC-modified eyes without light microscopic abnormalities, four APC-modified eyes with focal light microscopic abnormalities, and four wild-type eyes were examined by electron microscopy. Electroretinograms were recorded from four APC-modified and three wild-type mice.

RESULTS

Four of 38 APC-modified eyes demonstrated ultrastructural evidence of focal RPE cells with increased melanosome production and atrophy. Other areas of the RPE in these four eyes demonstrated no ultrastructural abnormalities. Three APC-modified eyes demonstrated electron and light microscopic evidence of RPE hyperplasia. Electron microscopic examination of APC-modified eyes without light microscopic evidence of abnormalities demonstrated no ultrastructural differences from age-matched controls. Electroretinography demonstrated no differences in the b-wave or c-wave amplitudes between APC-modified and wild-type mice.

CONCLUSIONS

While light microscopic RPE alterations are observed in these APC-modified mice, the absence of a generalized, ultrastructural murine RPE defect is in contradistinction to observations in electron microscopic investigations of humans with colonic polyposis, pigmented ocular fundus lesions, and APC gene mutations between codons 463 and 1444. Our results in mice with APC mutation at codon 1638, however, are consistent with a previously identified association between the expression of pigmented ocular fundus lesions and region-specific mutation in the human APC gene. The APC protein may possess a physiologic function for both retinal and RPE development.

Sham radiation in clinical trials assessing radiotherapy for exudative age-related macular degeneration

BACKGROUND

To evaluate the effectiveness of sham radiation treatments in masking patients to their randomization group in the Radiation of Age-Related Macular Degeneration (ROARMD) Study.

METHODS

Patients with choroidal neovascularization complicating age-related macular degeneration were randomized to a treatment (RAD) group that received external beam irradiation (seven treatment sessions) or to a control (SHAM) group that received sham radiation (one sham treatment session). During a telephone survey, 62 of 73 randomized patients responded to the following questions: Do you think you received radiation? Why do you feel that way? Did the vision in your study eye worsen after enrollment?

RESULTS

Eighty-one percent of the RAD group and 59% of the SHAM group thought that they had received radiation. In patients who thought that their vision had stabilized or improved, 82% thought that they had received radiation. In patients who thought that their vision was worse, only 39% thought that they had received radiation. In 54% of patients, subjective perception of vision influenced their guess as to whether they received radiation.

CONCLUSIONS

Subjective patient perception of visual outcome was the most influential variable for masking. Variation between radiation treatment and sham session techniques, such as equipment used and duration of treatments, played a lesser role in the masking of patients. Seven treatment days correlated with a higher number of patients who thought that they had received radiation. Although our procedures do not strictly mask the two groups, one sham radiation session was effective in keeping patients guessing their randomization group.

Use of peptide ligands to analyze the fine specificity of antibodies against asialo GM1

We recently described clone 10, a monoclonal Fab fragment that binds to asialo GM1 (GA1), and three mutated Abs derived from it that also bind GA1 and have a three to four times increase in avidity. We selected a phage display linear heptapeptide library with these four Abs, and an IgM mAb, 156, which binds to GM1 and GD1b, but not to GA1. Peptides with the same motif, KL/VWQXXX, were selected by clones 10 and the two heavy chain mutants 227 and 109. In contrast, the light chain mutant L3 58 selected an entirely different peptide motif, TFGLQSL. Moreover, a different motif, K/SWTNL/MPP, was selected by mAb 156. Although mAbs clone 10 and its mutants 109, 227 and L3 58 all bind only to GA1, differences in their fine specificity were revealed by binding to peptide ligands.

Discordant retinoblastoma in monozygotic twins

PURPOSE

We report cases of discordant retinoblastoma in twins confirmed to be monozygotic by DNA analysis.

METHODS

Twin A demonstrated severe, bilateral, multifocal retinoblastoma, which was recalcitrant to external beam irradiation and chemoreduction. Twin B has not demonstrated retinoblastoma. DNA analysis was performed with polymorphic microsatellite markers to confirm monozygosity. Single-stranded conformation polymorphism and Southern blot analysis of the retinoblastoma gene were performed.

RESULTS

Molecular genetic analyses confirmed monozygosity but failed to disclose a retinoblastoma gene mutation in either twin.

CONCLUSIONS

The extreme phenotypic discordance may best be explained by an unidentified, postzygotic retinoblastoma gene mutation in early embryonic development of the affected twin.

The effect of blood transfusion protocol on retinopathy of prematurity: A prospective, randomized study

OBJECTIVE

Controversy exists regarding the potential influence of anemia and blood transfusions on the rate of retinopathy of prematurity (ROP) in premature infants. A prospective, randomized, masked trial was performed to determine the influence of red blood cell transfusion protocol on ROP incidence and severity in a population of high-risk infants.

METHODS

A total of 50 infants with birth weights <1251 g were divided randomly into two groups beginning on day of life 29. Group 1 (n = 24) received red cell transfusions during the 6-week study period, only if certain symptom-based guidelines were met. Group 2 (n = 26) received red cell transfusions to maintain the hematocrit level above 40% for the entire 6 weeks. Infants were monitored for ROP, growth, and associated morbidity. Serial measurements of serum glucose, lactate, ferritin, total iron-binding capacity, and iron were performed.

RESULTS

ROP occurred in 83% of infants in group 1, and 73% of infants in group 2. There were no statistically significant differences in ROP severity, intraventricular hemorrhage, bronchopulmonary dysplasia, necrotizing enterocolitis, or any of the laboratory values except hemoglobin (10.8 vs 13.2 g/dL) and hematocrit (33.9% vs 41.8%) between the groups. Combining data from both groups, there was no association between hemoglobin or hematocrit ratios and ROP incidence or severity.

CONCLUSIONS

A transfusion policy aimed at limiting the amount of blood given to premature infants (symptom-based) during the neonatal period does not impart a significantly different risk for ROP or other associated conditions, than does a policy in which transfusions are given more liberally for replacement purposes.

Structure-function studies of an anti-asialo GM1 antibody obtained from a phage display library

Although gangliosides elicit human autoantibodies, they are extremely weak immunogens in mice. We obtained a monoclonal antibody Fab fragment (clone 10) that is specific for asialo GM1 (GA1), from a phage display library. The Vkappa domain of clone 10 could be replaced by two different Vkappa domains without changing the specificity of the antibody. Mutagenesis of the third hypervariable regions of the heavy and light chains of clone 10 yielded three mutants that exhibited a 3 to 4 times increase in avidity for GA1. A molecular model of clone 10 indicated that the putative antigen-binding site contained a shallow surface pocket. These data illustrate the use of recombinant DNA techniques to obtain anti-ganglioside antibodies, and to explore the molecular basis of their antigen-binding activity.

Treatment outcome in fellow eyes after laser photocoagulation for retinopathy of prematurity

PURPOSE

To determine the concordance in structural outcome between fellow eyes in patients undergoing diode laser peripheral retinal photocoagulation for threshold retinopathy of prematurity.

METHODS

Records from 103 patients undergoing bilateral diode laser peripheral retinal photocoagulation for retinopathy of prematurity at three academic medical centers were reviewed. Information regarding infant gestational ages, birth weights, characteristics of retinopathy of prematurity, laser treatment variables, complications, and structural outcomes were obtained. The data were analyzed to determine the rate of successful structural outcomes among all eyes as well as the interocular outcome concordance.

RESULTS

A successful structural outcome was observed in 182 (88%) of the 206 eyes. Eighty-eight patients (85.4%) had bilateral favorable outcomes. Nine patients (8.7%) had bilateral unfavorable outcomes, and six patients (5.8%) had one favorable and one unfavorable eye. The outcome was concordant between fellow eyes in 94.2% of patients. This rate was higher than predicted if fellow-eye outcomes were truly independent (P < .00001) and did not depend on study center, laser settings, or location of the retinopathy of prematurity. Serious complications related to treatment were uncommon.

CONCLUSIONS

Diode laser peripheral retinal photocoagulation is a safe and effective procedure for treating threshold retinopathy of prematurity. The concordance of structural outcomes between fellow eyes is higher than expected by chance and suggests that patient-specific factors play a key role in treatment response.

Telemedicine diagnosis of eye disorders by direct ophthalmoscopy. A pilot study

OBJECTIVE

To report a pilot study of telemedical direct ophthalmoscopy in the diagnosis of acquired immune deficiency syndrome (AIDS)-related retinopathy in a human immunodeficiency virus (HIV)-positive population and in the diagnosis of glaucoma, cataract, and retinopathy in a diabetic population.

DESIGN

Prospective comparative case series.

PARTICIPANTS

Seventeen HIV-positive and 20 diabetic patients.

METHODS

A direct ophthalmoscope custom-fitted with a digital microcamera capable of transmitting images from any of 61 sites within the Georgia Statewide Telemedicine Program was used by a nonophthalmologist to examine 34 eyes of 17 HIV-positive patients and 39 eyes of 20 patients with diabetes. Fundus images were transmitted in real-time to a reviewing ophthalmologist. An in-person, comprehensive examination including indirect ophthalmoscopy, was performed by a second ophthalmologist. Telemedical examination was compared to the in-person comprehensive examination.

RESULTS

For the HIV study, 21 eyes did not show HIV retinopathy (noninfectious retinopathy with cotton-wool spots) by in-person examination. Telemedical examination correctly identified 20 of these eyes as disease-free (specificity = 95%). HIV retinopathy was present in 12 of the 34 eyes by in-person evaluation with telemedical examination correctly diagnosing 10 of these eyes (sensitivity = 83%). One eye with dense cataract and retinal detachment was unable to be evaluated ophthalmoscopically by either in-person or telemedical examination. Telemedical and in-person assessments for HIV retinopathy were identical in 100% of eyes without cataract. Disagreement in diagnosis between telemedical and in-person examination was associated with cataract (P < 0.0007). For the diabetes study, because of an inadequate image, telemedical examination was unable to classify 46% and 36% of eyes for glaucoma and diabetic retinopathy, respectively. Inability to make a telemedical determination for glaucoma (P < 0.011), nonproliferative (P < 0.064) and proliferative (P < 0.064) diabetic retinopathy was associated with cataract. Of the eyes that were able to be assessed by telemedical examination for diabetic retinopathy (n = 25), glaucoma (n = 21), and cataract (n = 39), the accuracy was poor (sensitivity = 29%, 50%, and 41%, respectively). Telemedical examination for diabetic retinopathy and glaucoma was more likely to agree with in-person examination in eyes without cataract as compared to eyes with cataract (not statistically significant).

CONCLUSION

Telemedical direct ophthalmoscopic, real-time fundus imaging may provide a valuable means for providing ophthalmic consultation to the primary care physician in younger patients without lens or media opacity, but is inadequate for eyes with any degree of lens or media opacity.

Variations among cell lines in the synthesis of sphingolipids in de novo and recycling pathways

There are several pathways for the incorporation of sugars into glycosphingolipids (GSL). Sugars can be added to ceramide that contains sphinganine (dihydrosphingosine) synthesized de novo (pathway 1), to ceramide synthesized from sphingoid bases produced by hydrolysis of sphingolipids (pathway 2), and into GSL recycling from the endosomal pathway through the Golgi (pathway 3). We reported previously the surprising observation that SW13 cells, a human adrenal carcinoma cell line, synthesize most of their GSL in pathway 2. We now present data on the synthesis of GSL in four additional cell lines. Approximately 90% of sugar incorporation took place in pathway 2, and 10% or less in pathway 1, in human foreskin fibroblasts and NB41A3 neuroblastoma cells. In contrast, approximately 50-90% of sugar incorporation took place in pathway 1 in C2C12 myoblasts. The C2C12 cells divide more rapidly and synthesize 10-14 times as much GSL as the other three cell lines. In C6 glioma cells, approximately 30% of sugar incorporation occurred in pathway 1 and 60% in pathway 2. There was no relation between the utilization of pathways for GSL and sphingomyelin synthesis in foreskin fibroblasts and C2C12 cells. In both cells pathways 1 and 2 each accounted for 50% of incorporation of choline into sphingomyelin. In five of the six cell lines that we have studied, most GSL synthesis takes place in pathway 2. We suggest that when the need for synthesis is relatively low, as in slowly dividing cells, GSL are synthesized predominantly from sphingoid bases salvaged from the hydrolytic pathway. When cells are dividing more rapidly, the need for increased synthesis is met by upregulating the de novo pathway.

Modulation of VEGF production by pH and glucose in retinal Müller cells

PURPOSE

To investigate the influence of pH and glucose concentration, both of which represent significant biochemical variables in tissue ischemia, on the production of VEGF protein by retinal Müller cells and C6 glioma cells, under normoxic and hypoxic conditions.

METHODS

Rat retinal Müller cells and C6 glioma cells grown in tissue culture monolayers were studied. The effect of pH (range 7.0-8.0) and glucose concentration (0.6-25 mmol/L) on VEGF protein production, under both normoxic and hypoxic conditions, were evaluated by ELISA analysis of the conditioned media. Establishment of significant cell hypoxia was verified by measurement of lactate release into the conditioned media.

RESULTS

Hypoxia caused a 7.9-fold increase in VEGF production in C6 cells at 24 h, and a 3.4-fold increase in Müller cells after 48 h. Under hypoxic conditions, VEGF protein production was increased further by increasing pH and increasing glucose, and decreased by low pH and low glucose. Varying the glucose concentration or pH of the medium did not result in significant induction of VEGF protein production by either cell type under normoxic conditions.

CONCLUSIONS

Both glucose and pH significantly affected VEGF production induced by low oxygen. However, neither exerted a measurable stimulatory effect on VEGF production in normoxic conditions. Coexisting hypoxia and acidosis or hypoglycemia, as might occur in severe tissue ischemia, may render glial cells incapable of effectively upregulating VEGF synthesis, while alkalosis or hyperglycemia may augment hypoxia-induced VEGF production.

Decreased synthesis of glycosphingolipids in cells lacking vimentin intermediate filaments

We are studying defects in glycosphingolipid synthesis in cells lacking vimentin intermediate filaments (vimentin-). Sugars can be incorporated into glycolipids whose ceramide is synthesized either de novo (pathway 1) or from sphingoid bases salvaged from hydrolysis of sphingolipids (pathway 2) and into glycolipids recycling from the endosomal pathway through the Golgi (pathway 3). Vimentin- embryonic fibroblasts, obtained from vimentin-knockout mice, incorporate less sugar into glycolipids than vimentin+ fibroblasts. Using two inhibitors of ceramide synthesis, beta-chloroalanine and fumonisin B1, we found the major defect in synthesis to be in pathway 2 and not in de novo synthesis. We used two additional approaches to analyze the functions of pathways 2 and 3. First, we used exogenous glucosylthioceramide ([14C]C8-Glc-S-Cer), a synthetic, nonhydrolyzable glycosphingolipid, as a precursor for synthesis of larger glycolipids. Vimentin- SW13 cells and embryonic fibroblasts glycosylated [14C]C8-Glc-S-Cer less extensively than their vimentin+ counterparts. Second, we used chloroquine to inhibit the hydrolysis of sphingolipids in endosomes and lysosomes. Chloroquine markedly decreased the incorporation of sugars into glycolipids larger than glucosylceramide. The defect in glycolipid synthesis in vimentin- cells probably results from impaired intracellular transport of glycolipids and sphingoid bases between the endosomal/lysosomal pathway and the Golgi apparatus and endoplasmic reticulum. Intermediate filaments may accomplish this function by contributing to the organization of subcellular organelles and/or by binding proteins that participate in transport processes.

Trilateral retinoblastoma: insights into histogenesis and management

Trilateral retinoblastoma (TRb) is a syndrome involving midline intracranial malignancies in children with the heritable form of retinoblastoma. All cases of TRb reported from 1971 to 1997 were reviewed. The histopathologic findings, clinical features, treatment modalities, and survival rates from 80 cases were evaluated. Histopathologic findings from intracranial malignancies demonstrated primitive neuroectodermal tumors in 61.5% of cases. Various degrees of neuronal or photoreceptor differentiation were seen in the other 38.5% of cases. Autopsy, histopathologic, and radiologic examinations did not show a more definitive site of origin of these intracranial tumors, although "pinealoblastoma" was often the diagnosis reported. These findings, together with analysis of the histopathologic similarities among human primitive neuroectodermal tumors, pinealoblastoma, retinoblastoma, and ependymoblastoma, suggest that TRb more likely arises from a germinal layer of predisposed primitive subependymal neuroblasts that are not necessarily destined for pineal or photoreceptor differentiation. Trilateral tumors have also been found in transgenic mice expressing the simian virus 40 T-antigen. Transgenic murine intracranial tumors are primitive neuroectodermal tumors arising from the subependymal layer. Transgenic mice with the murine interphotoreceptor cell binding protein promoter and simian virus 40 T-antigen also develop pineal tumors. Trilateral retinoblastoma is usually fatal, with an average survival time of 11.2 months. Therapies include radiation, systemic chemotherapy, intrathecal chemotherapy, and surgical resection/craniotomy in combination with radiation and/or chemotherapy. Survival may be prolonged with combination chemotherapy (24.6 months) and if neuroradiologic screening identifies TRb before symptoms are present (23.5 months). Recent success with platinum-based chemoreduction of intraocular retinoblastoma may indicate a similar role for platinum-based chemotherapy in the treatment of TRb. Routine central nervous system imaging should be considered in the management of TRb.

Kinetics of fluid delivery from methylcellulose sponges

PURPOSE

The authors quantitatively evaluate the kinetics of fluid transfer from microsurgical sponges in a laboratory model to understand the kinetics of mitomycin C (MMC) delivery.

METHODS

The amount of fluid transferred from soaked methylcellulose (Weck-cel, Weck Inc., Durham, NC, U.S.A.) sponges to small pieces of hydrated or dry filter paper used to simulate episcleral tissue and Tenon fascia was measured as a function of time, sponge size, hydration status of the filter paper, and technique of sponge application.

RESULTS

The time course of fluid delivery from methylcellulose sponges to filter paper was nonlinear and characterized by a rapid delivery phase over the first 15 to 30 seconds, followed by a slow phase extending to at least 5 minutes. Sponge size and baseline hydration of the paper significantly influenced the rate and amount of fluid delivered, as did replacing the sponge every minute with a new sponge.

CONCLUSION

The transfer of fluid from a microsurgical sponge displays nonlinear kinetics, with the majority of delivery occurring in the first 15 to 30 seconds. Sponge size, hydration of the recipient tissue, and technique of sponge application are significant variables influencing the amount of fluid, and therefore mitomycin C, delivered.

Retinal pigment epithelium abnormalities in mice with adenomatous polyposis coli gene disruption

OBJECTIVE

To examine eyes from mice with targeted adenomatous polyposis coli (APC) gene disruption to determine if retinal pigment epithelium (RPE) abnormalities replicate the human counterpart.

METHODS

Thirty-two eyes from 16 mice heterozygous for APC gene disruption (chain-termination mutation in codon 1638 of exon 15) and 12 control eyes were examined by light microscopy.

RESULTS

Fifteen of 32 eyes from 12 of 16 APC-disrupted mice demonstrated abnormalities of the RPE and retina. The RPE abnormalities included RPE coloboma, unifocal and multifocal RPE hypertrophy, RPE hyperplasia, and RPE duplication with invasion in the areas of outer and inner segments. Retinal abnormalities included outer nuclear layer duplication and outer nuclear layer atrophy. There were no RPE and retinal abnormalities seen in the control eyes.

CONCLUSIONS

This study is consistent with the hypothesis that the APC gene is critical in the regulation of RPE proliferation and development. These findings also demonstrate that mutation of the APC gene in codon 1638, a location beyond the previously described critical region for human RPE abnormalities, leads to perturbation in the mouse RPE and retina. Further study of this murine model and the APC/RPE relationship may provide insight into regulatory mechanisms for RPE proliferation.

On knowing what one knows

The author presents vignettes of a type of experience that is familiar to many analysts. He suggests that analysts and analysands know much more about each other than is generally recognized and that much of the important communication is subliminal, out of conscious awareness. Evidence of our unconscious knowledge surfaces in the form of emotion, fantasy, images, intrusive thoughts, and physical feelings. Often it seems uncanny. Recent experimental evidence and neurobiological research seem to explain and validate these analytic experiences.

Detection and localization of steel intraocular foreign bodies using computed tomography. A comparison of helical and conventional axial scanning

PURPOSE

To compare the sensitivity and specificity of detection, and accuracy of localization, of small steel intraocular and episcleral foreign bodies, using conventional axial and helical computed tomographic scanning in an experimental model.

METHODS

Small steel foreign bodies ranging in size from 0.048 to 0.179 mm3 were placed in intraocular and episcleral locations in eye bank eyes mounted in the orbits of a human skull and scanned using helical and conventional axial techniques. Helical scanning was performed using 1-mm and 3-mm thick sections. Conventional axial scanning was performed using 3-mm thick sections. Images were reviewed by masked observers to determine sensitivity, specificity, and accuracy of localization for each imaging method.

RESULTS

Steel foreign bodies as small as 0.048 mm3 were detectable with each scanning protocol. Although the helical scans appeared to provide higher levels of sensitivity compared to conventional axial scanning, the difference in outcome between the scan types was not statistically significant. Sensitivity was dependent on the size of the foreign body and ranged from 45% to 65% for the smaller ones (< 0.06 mm3) to 100% for the larger ones (> 0.06 mm3). Multiplanar reformatting of images was helpful in achieving optimal accuracy.

CONCLUSION

In an experimental model of steel intraocular foreign body, helical computed tomographic scanning provided images of high quality similar to that of conventional axial scanning.

Inflammatory opacities of the vitreous in rifabutin-associated uveitis

PURPOSE

To describe rifabutin-associated uveitis with opacities in the inferior and posterior vitreous in three patients with acquired immunodeficiency syndrome.

METHOD

Case reports of the three patients are presented.

RESULTS

The patients, who were being treated with rifabutin and fluconazole, developed anterior and posterior uveitis. The posterior uveitis was characterized by white-yellow inflammatory opacities located in the inferior and posterior vitreous. Discontinuation of rifabutin and the start of topical corticosteroid therapy resulted in improvement of the uveitis and visual acuity.

CONCLUSION

Recognition of rifabutin-associated uveitis with opacities in the inferior and posterior vitreous may prevent unnecessary invasive diagnostic and therapeutic procedures.

High affinity antibodies against Lex and sialyl Lex from a phage display library

Our previous studies of seven murine mAbs against the carbohydrate Lex Ag demonstrated that they were all encoded by VH441 and V kappa 24B. To obtain higher affinity Abs, and to ascertain whether their L chains could be encoded by other genes, we constructed a phage display library in a modified pComb 8 vector. The library contained random L chains, and Fd segments enriched in VH domains encoded by the VHX24 gene family. We selected phage with an Lex-BSA Ag, and obtained two Fab mAbs, clones 23 and 24, whose affinities were more than 100-fold higher than hybridoma mAb PM81. Both new mAbs were encoded by VH441, and their L chains were encoded by genes of the V kappa Ox1 and V kappa 9 families. In contrast to hybridoma mAb PM81, which binds only Lex, clones 23 and 24 bound sialyl Lex (SLex) as well as Lex, and clone 23 also binds the backbone carbohydrate structure nLacCer. Analysis of the binding of these three mAbs to synthetic glycolipids that contained structural modifications indicated that they recognize different aspects of the Lex structure, and suggested that they bind to limited regions of the oligosaccharide.

High affinity antibodies against Lex and sialyl Lex from a phage display library

Our previous studies of seven murine mAbs against the carbohydrate Lex Ag demonstrated that they were all encoded by VH441 and V kappa 24B. To obtain higher affinity Abs, and to ascertain whether their L chains could be encoded by other genes, we constructed a phage display library in a modified pComb 8 vector. The library contained random L chains, and Fd segments enriched in VH domains encoded by the VHX24 gene family. We selected phage with an Lex-BSA Ag, and obtained two Fab mAbs, clones 23 and 24, whose affinities were more than 100-fold higher than hybridoma mAb PM81. Both new mAbs were encoded by VH441, and their L chains were encoded by genes of the V kappa Ox1 and V kappa 9 families. In contrast to hybridoma mAb PM81, which binds only Lex, clones 23 and 24 bound sialyl Lex (SLex) as well as Lex, and clone 23 also binds the backbone carbohydrate structure nLacCer. Analysis of the binding of these three mAbs to synthetic glycolipids that contained structural modifications indicated that they recognize different aspects of the Lex structure, and suggested that they bind to limited regions of the oligosaccharide.

Trilateral tumors in four different lines of transgenic mice expressing SV40 T-antigen

PURPOSE

A line of transgenic mice containing the simian virus (SV) 40 T-antigen (T-ag) gene driven by the beta-luteinizing hormone (BLH) promoter developed bilateral retinoblastoma and primitive neuroectodermal tumors (PNET) of the midbrain. Midbrain tumors arose from the subependymal layer of the cerebral aqueduct. Bilateral ocular and brain tumors ("trilateral") were found in three other SV40 T-ag transgenic murine lines containing different promoters (murine interphotoreceptor retinoid-binding protein (IRBP), human IRBP, and alpha A-crystallin). To gain insight into the regulatory mechanisms involved in central nervous system tumorigenesis, the authors examined brain tumors from four lines of SV40 T-ag mice with different promoters.

METHODS

Formalin-fixed brain tumors were examined from four lines of transgenic mice containing different promoters linked to the protein coding region of the enhancerless SV40 T-ag oncogene. Transgenes contained the following promoters: BLH, mouse 1.8-kb IRBP, human 1.3-kb IRBP, and alpha A-crystallin.

RESULTS

Mice with a 1.8-kb IRBP promoter develop retinal photoreceptor and pineal tumors. Intracranial tumors arising from the subependymal layer of the third ventricle also were observed. Mice with a 1.3-kb IRBP promoter exhibit bilateral retinal PNET and PNET originating from the subependymal layer of the third ventricle. Mice with the alpha A-crystallin promoter exhibit bilateral lens tumors and PNET of the midbrain.

CONCLUSIONS

Ocular tumors in these mice may be ascribed to the promoter-driven, tissue-specific expression of SV40 T-ag. The common finding of PNET arising from the subependymal layer of the diencephalon is unlikely to be promoter related. These findings indicate that a regulatory region specific to the subependymal layer of the cerebral aqueduct and third ventricle resides in the structural region of the SV40 T-ag gene.

Pathways of glycosphingolipid biosynthesis in SW13 cells in the presence and absence of vimentin intermediate filaments

We reported previously that the incorporation of sugars into glycosphingolipids (GSL) is diminished in SW13 cells that lack a vimentin intermediate filament (IF) network (vim-) compared to vim+ cells. To further analyze the nature of this abnormality, we double-labeled cells with 3H-serine and 14C-sugars. There was no difference between vim+ and vim- cells in the incorporation of serine into GSL, although the usual difference in sugar incorporation was observed. This indicated that the defect in vim- cells was not in the incorporation of sugars into ceramide synthesized de novo by acylation of sphinganine (pathway 1). Sugars can also be incorporated into ceramide synthesized from sphingosine that is derived from catabolism of sphingolipids (pathway 2), and into GSL that recycle through the Golgi apparatus from endosomes (pathway 3). The amount of galactose and glucosamine incorporated into GSL in these three pathways was analyzed by the use of two inhibitors of sphingolipid biosynthesis. beta-Chloroalanine inhibits the de novo synthesis of sphinganine (pathway 1), and fumonisin B1 inhibits the acylation of sphinganine and sphingosine (pathways 1 and 2). We were surprised to observe that in both vim+ and vim- cells only 20-40% of sugar incorporation into GSL took place in pathway 1, and 60-80% of sugar incorporation took place in the recycling pathways. Moreover, in contrast to larger GSL, GlcCer was not synthesized in pathway 3. Our observations indicate that vimentin IF facilitate the recycling of GSL and sphingosine, and that the differences between vim+ and vim- cells are predominantly in pathways 2 and 3. Furthermore, although it is generally believed that virtually all GSL are synthesized in the de novo pathway, these data indicate that the recycling pathways predominate in the incorporation of sugars into GSL in SW13 cells.

Posterior segment complications after vitrectomy for macular hole

PURPOSE

The purpose of this study is to assess the rate of posterior segment complications after vitreous surgery for macular holes and to evaluate the effect of such complications on final visual outcome.

METHODS

The authors reviewed retrospectively all cases of vitreous surgery for macular holes performed between June 1990 and October 1993. Among 98 patients with a followup of 3 months or more, all patients with posterior segment complications during the postoperative course were identified. The rate of complications was compared with that seen after vitreous surgery for macular pucker performed by the same surgeons.

RESULTS

Posterior segment complications were noted in 23 (23%) of 98 patients. These included peripheral retinal breaks (3%), rhegmatogenous retinal detachment from a peripheral retinal break (14%), enlargement of the hole (2%), late reopening of the hole (2%), retinal pigment epithelium loss under the hole (1%), photic toxicity (1%), and endophthalmitis (1%). In 40% of these eyes, the final visual acuity was two lines or more below preoperative visual acuity. When compared with the macular pucker group, the rate of posterior segment complications, in particular the rate of peripheral retinal tears and detachments, was significantly higher (P < or = 0.05).

CONCLUSIONS

The authors conclude that visually significant posterior segment complications may occur after vitrectomy for macular hole, and the rate of these complications appears to be higher than expected.

Choroidal and retinal detachment in antineutrophil cytoplasmic antibody-positive scleritis

PURPOSE/METHODS

A 72-year-old woman with antineutrophil cytoplasmic antibody-positive vasculitis had a combined detachment of the choroid and retina. This unique initial manifestation was also associated with systemic and orbital manifestations, including brow ptosis, dacryoadenitis, and pneumonitis.

RESULTS/CONCLUSIONS

This patient underwent vitrectomy for removal of a dense vitreitis and responded well to systemic cyclophosphamide. This case demonstrates that antineutrophil cytoplasmic antibody testing is useful for the diagnosis and treatment of Wegener's granulomatosis and microscopic polyarteritis-associated scleritis. The distinction between these two entities is often difficult to make.

Vitamin D inhibits angiogenesis in transgenic murine retinoblastoma

PURPOSE

Vitamin D compounds have been shown to inhibit tumor growth in a transgenic retinoblastoma murine model. The mechanism of action has not been defined clearly, although an antiangiogenic action has been proposed.

METHODS

Transgenic retinoblastoma mice received high (0.05 microgram) and low (0.025 microgram) doses of vitamin D3 by intraperitoneal injection 5 times per week for 5 weeks. Control animals were injected with mineral oil vehicle alone. At 5 months of age, the animals were killed and eyes were enucleated and processed for light microscopy. Paraffin-embedded sections were stained with an immunoperoxidase stain (GS-1) specific for mammalian vascular endothelium. Sections were graded by a single masked reviewer, and intraobserver reliability was assessed. Mean vessel counts were made for each group.

RESULTS

The high-dose group had the lowest mean vessel count (8.5), followed by the low-dose group (10.1). The control group had the highest mean vessel count (14.1). Vitamin D-treated animals (high- and low-dose groups combined) had significantly fewer vessels P = 0.001) than untreated controls.

CONCLUSIONS

These results support the hypothesis that inhibition of angiogenesis is a mechanism of action for vitamin D in the transgenic retinoblastoma mouse model.

Streptokinase-induced Tenon's hemorrhage after retinal detachment surgery

PURPOSE/METHODS

We studied a case in which a streptokinase-induced Tenon's hemorrhage developed after retinal detachment surgery. The patient received intravenous streptokinase for myocardial infarction two hours after pars plana vitrectomy and encircling scleral buckling surgery.

RESULTS/CONCLUSIONS

A Tenon's hemorrhage with an orbital compartment syndrome developed in the patient's left eye, and he underwent lateral canthotomy and inferior cantholysis. Symptoms of the compartment syndrome resolved and final visual acuity was 20/40. Although there are potential ocular-related side effects to thrombolytic therapy, there has been no permanent ocular morbidity reported after thrombolytic-related hemorrhage. We recommend not to defer such life-saving therapy after ocular surgery.

Biosynthesis of glycosphingolipids is reduced in the absence of a vimentin intermediate filament network

Our previous observations on the immunocytochemical colocalization of intermediate filaments and glycosphingolipids led us to analyze the role of filaments in the biosynthesis and intracellular transport of glycosphingolipids. Cells with (vim+) and without (vim-) vimentin intermediate filaments were cloned from the adrenal carcinoma cell line SW13. There was no difference between vim+ and vim- cells in the proportion of newly synthesized C6-NBD-glucosylceramide transported to the plasma membrane. The vim+ cells synthesized glycosphingolipids, especially lactosylceramide and globotriosylceramide, and to a lesser extent GM3 ganglioside, more rapidly than vim- cells. The altered rate of biosynthesis did not result from differences in the levels of the glycosyltransferases that synthesize those compounds. To determine whether the presence of a vimentin network was responsible for the differences in biosynthesis, mouse vimentin cDNA was transfected into vim- cells. Transfected cells that expressed a mouse vimentin network demonstrated a twofold or greater increase in the rate of biosynthesis of neutral glycosphingolipids and gangliosides. There was no difference between vim+ and vim- cells in the synthesis of ceramide or sphingomyelin, or in their content of phospholipids or cholesterol. The nature of the biochemical defect(s) underlying the diminished incorporation of radiolabeled sugars into glycosphingolipids is unclear. Possibilities include alterations in the ultrastructure of the Golgi and/or abnormalities in a portion of the endocytic pathway.

Specificity and structure of murine monoclonal antibodies against GM1 ganglioside

Anti-GM1 antibodies have been implicated in the pathogenesis of several neurological diseases, but the role of these antibodies is still controversial. An animal model could provide insight into the mechanisms of these human disorders, but obtaining specific anti-GM1 monoclonal antibodies (mAbs) has been extremely difficult because of the weak immunogenicity of GM1 ganglioside. Four murine mAbs against GM1 were elicited by immunization of mice with lyso GM1 coupled to BSA and GM1 glycolipid. All four IgM,k mAbs bound strongly to GM1, three antibodies (125, 360 and 494) also bound very weakly to asialo GM1 (GA1) and one (156) bound weakly to GD1b. Three antibodies (125, 360 and 494) were encoded by the same VH and V kappa genes. The VH gene exhibited 97% homology to VHOX1, a member of the VHQ52N gene family, the D segment was probably derived from DQ52 and JH was identical to JH2. The V kappa gene was approximately 99% homologous to V kappa RF and J kappa was germline J kappa 2. The VH gene of mAb 156 exhibited 98% homology to VH205.12, of the VHJ558 gene family, the D segment was derived from DFL16.1, and JH was germline JH2. The V kappa and J kappa genes of mAb were identical to V kappa 8 and J kappa 1, respectively. The genes encoding these anti-GM1 antibodies were close to germline sequences and have been used to encode other antibodies. This suggests that the unresponsiveness of mice to immunization is probably due to inactivation of self-reactive B cells. These rare anti-GM1 mAbs will be valuable reagents for studies of the pathogenesis of autoimmune neuropathy in animals, and also for analyzing the tissue distribution and functions of GM1.

Structure-function studies of anti-3-fucosyllactosamine (Le(x)) and galactosylgloboside antibodies

We are studying murine mAbs against two carbohydrate epitopes, 3-fucosyllactosamine (Le(x), CD15) and galactosylgloboside. The VH domains of both panels of Ab are encoded by VH441, a member of the X24 family of Ig genes. To evaluate the contribution of the heavy chain CDR3 to the affinity of the anti-3-fucosyllactosamine Ab, CDR3-H of PMN6, a low affinity Ab, was replaced by the CDR3 of PM81, a higher affinity Ab. The affinity of the chimeric 6/81 Ab was increased when the heavy chain was paired with the PM81 light chain, but not when paired with another light chain (M5), which differs from PM81 light chain by three amino acids. To evaluate the contribution of somatic mutations to the binding of GalGb4, the 3A9 VH sequence, which contains three amino acid substitutions, was replaced by a germ-line sequence encoded by either VH441 or VHX24. The chimeric Ab, 441/3A9 and X24/3A9, bound Ag as well as the wild-type 3A9 Ab. Computer models of the Fv fragments of PM81 and 3A9 were compared with the crystal structure of the Fv fragment of J539, a galactan-binding myeloma protein that is encoded by the same VH and VK genes as 3A9. The surfaces of 3A9 and J539 have shallow pockets that are potential Ag-binding sites. Replacement of CDR3-H Tyr99, which is a prominent component of the pocket, by Ala abolished the binding of Ag. In contrast, the Fv surface of PM81 contains a large cleft rather than a pocket. These models indicate how the same VH gene segment can be used to encode Abs that exhibit different specificities.

Structure-function studies of anti-3-fucosyllactosamine (Le(x)) and galactosylgloboside antibodies

We are studying murine mAbs against two carbohydrate epitopes, 3-fucosyllactosamine (Le(x), CD15) and galactosylgloboside. The VH domains of both panels of Ab are encoded by VH441, a member of the X24 family of Ig genes. To evaluate the contribution of the heavy chain CDR3 to the affinity of the anti-3-fucosyllactosamine Ab, CDR3-H of PMN6, a low affinity Ab, was replaced by the CDR3 of PM81, a higher affinity Ab. The affinity of the chimeric 6/81 Ab was increased when the heavy chain was paired with the PM81 light chain, but not when paired with another light chain (M5), which differs from PM81 light chain by three amino acids. To evaluate the contribution of somatic mutations to the binding of GalGb4, the 3A9 VH sequence, which contains three amino acid substitutions, was replaced by a germ-line sequence encoded by either VH441 or VHX24. The chimeric Ab, 441/3A9 and X24/3A9, bound Ag as well as the wild-type 3A9 Ab. Computer models of the Fv fragments of PM81 and 3A9 were compared with the crystal structure of the Fv fragment of J539, a galactan-binding myeloma protein that is encoded by the same VH and VK genes as 3A9. The surfaces of 3A9 and J539 have shallow pockets that are potential Ag-binding sites. Replacement of CDR3-H Tyr99, which is a prominent component of the pocket, by Ala abolished the binding of Ag. In contrast, the Fv surface of PM81 contains a large cleft rather than a pocket. These models indicate how the same VH gene segment can be used to encode Abs that exhibit different specificities.

Nucleolar organizer regions in determining malignancy of pigmented conjunctival lesions

We assessed the usefulness of silver staining of nucleolar organizer regions in the diagnosis of pigmented conjunctival tumors. Fifty-one biopsy specimens were silver stained to identify the nucleolar organizer regions. Nineteen nevi without atypia, three nevi with atypia, eight primary acquired melanosis lesions, and 14 melanomas were studied. In each specimen, silver staining of the nucleolar organizer regions was counted in 100 cells to yield an average of the silver staining of the nucleolar organizer region count. The mean silver staining of the nucleolar organizer region counts per cell was correlated with the degree of malignancy of pigmented conjunctival lesions as follows: nevi, 3.0; primary acquired melanosis, 3.2; nevi with atypia, 3.9; primary acquired melanosis with atypia, 5.0; and melanoma, 5.7 (Spearman correlation [rS] = .83, P = .0001; analysis of variance [ANOVA] F test = 20.9, P = .0001). A cutoff value of 4.0 (mean silver staining of nucleolar organizer regions per cell) will differentiate melanoma and primary acquired melanosis with atypia from other lesions (sensitivity, 100%; specificity, 96%). The silver staining of nucleolar organizer regions is a useful adjunct in determining the malignancy of pigmented conjunctival tumors.

Variable subcellular localization of glycosphingolipids

Although most glycosphingolipids (GSLs) are thought to be located in the outer leaflet of the plasma membrane, recent evidence indicates that GSLs are also associated with intracellular organelles. We now report that the subcellular localization of GSLs varies depending on the GSL structure and cell type. GSL localization was determined by indirect immunofluorescence microscopy of fixed permeabilized cells. A single GSL exhibited variable subcellular localization in different cells. For example, antibody to GalCer is localized primarily to the plasma membrane of HaCaT II-3 keratinocytes, but to intracellular organelles in other epithelial cells. GalCer is localized to small vesicles and tubulovesicular structures in MDCK cells, and to the surface of phase-dense lipid droplets in HepG2 hepatoma cells. Furthermore, within a single cell type, individual GSLs were found to exhibit different patterns of subcellular localization. In HepG2 cells, LacCer was associated with small vesicles, which differed from the phase-dense vesicles stained by anti-GalCer, and Gb4Cer was associated with the intermediate filaments of the cytoskeleton. Both anti-GalCer and monoclonal antibody A2B5, which binds polysialogangliosides, localized to mitochondria. The distinct subcellular localization patterns of GSLs raise interesting questions about their functions in different organelles. Together with published data on the enrichment of GSLs in specific organelles and in apical plasma membrane, these findings indicate the existence of specific sorting mechanisms that regulate the intracellular transport and localization of GSLs.