Histopathologic features of neovascularization in sickle cell retinopathy

Retrospective Cohort Study of Sickle Cell Disease and Large Vessel Retinal Vascular Occlusion Risk in a National United States Database

OBJECTIVE

To determine if differences exist in the risk of developing large vessel retinal vascular occlusions in patients with sickle cell states.

DESIGN

Retrospective cohort study.

PARTICIPANTS

Patients with sickle cell disease (SCD) or trait evaluated by an ophthalmologist were compared with matched controls without SCD or sickle cell trait (SCT) also evaluated by an ophthalmologist.

METHODS

This study used deidentified data from a national database (2006-2024), using International Classification of Diseases 10 codes to select for retinal vascular occlusions. Propensity score matching was performed with respect to age, sex, race, ethnicity, smoking, hypertension, diabetes, dyslipidemias, and obesity, resulting in hemoglobin SS (HbSS), hemoglobin SC (HbSC), and SCT cohorts and matched control cohorts.

MAIN OUTCOME MEASURES

Risk ratios (RRs) and 95% confidence intervals (CIs) of retinal vascular occlusion diagnosis, including central retinal artery occlusion (CRAO), branch retinal artery occlusion (BRAO), central retinal vein occlusion, branch retinal vein occlusion, and corneal dystrophy as a negative control, given SCD or SCT.

RESULTS

After propensity score matching, HbSS (n = 10 802; mean age ± standard deviation, 38.6 ± 20.6 years), HbSC (n = 4296, 34.3 ± 17.8 years), and SCT (n = 15 249, 39.8 ± 23.7 years) cohorts were compared with control cohorts (n = 10 802, 38.7 ± 20.7 years; n = 4296, 34.6 ± 18.0 years; n = 15 249, 39.9 ± 23.8 years, respectively). Patients with SCD (HbSS) had higher risk of developing any retinal vascular occlusion (RR, 2.33; 95% CI, 1.82-3.00), CRAO (RR, 2.71; 95% CI, 1.65-4.47), and BRAO (RR, 4.90; 95% CI, 2.48-9.67) than matched controls. Patients with HbSC disease had higher risk (RR, 3.14; 95% CI, 1.95-5.06) of developing any retinal vascular occlusion than matched controls without SCD. Patients with SCT did not have higher risk of developing retinal vascular occlusions (RR, 1.01; 95% CI, 0.81-1.26) than matched controls.

CONCLUSIONS

In a retrospective cohort study, patients with HbSS SCD have an increased risk of developing retinal vascular occlusions, and more specifically CRAO and BRAO, compared with patients without SCD.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Evaluation of Ocular Complications by Using Optical Coherence Tomography in Children With Sickle Cell Disease Eye Findings in Children With Sickle Cell Disease

OBJECTIVE

The aim of this study was to compare optical coherence tomography (OCT) findings in pediatric patients with sickle cell disease (SCD) and healthy individuals and to investigate associations between these data and the patients' systemic findings.

MATERIALS AND METHODS

The study included 108 eyes of 54 patients with SCD with no visual symptoms and a control group consisting of 110 eyes of 55 healthy subjects with no systemic or ocular pathology. After best-corrected visual acuity assessment, the study participants underwent a complete ophthalmologic examination including intraocular pressure. After examination and pupil dilation induced with 1% tropicamide, 9×9 mm macular sections were obtained with spectral-domain OCT. The macular sections were evaluated according to Early Treatment Diabetic Retinopathy Study (ETDRS) map and internal and external retinal thicknesses were measured using the software included in the OCT device.

RESULTS

The patient group showed significantly more foveal flattening, temporal thinning, and vascular tortuosity than the control group (P<0.0001 for all). Foveal width was significantly greater in the patient group (1592.39±175.56 µm) compared with the control group (1391.01±175.56 µm) (P<0.0001), whereas foveal depth was significantly lower in the patient group (121.15±26.83 µm) than in the control group (146.1±12.25 µm) (P<0.0001). The mean total retinal thickness was 253.53±22.31 µm in the patient group and 261.03±18.48 µm in the control group (P=0.007). Similarly, central retinal thickness was significantly lower in the patient group (219.35±10.53 µm) compared with the control group (235.32±12.51 µm) (P<0.0001).

DISCUSSION

Our study shows that pediatric patients with SCD may have subclinical retinal involvement and that temporal thinning, in particular, is an important OCT finding. This strongly suggests that OCT imaging would be a beneficial addition to routine ophthalmologic examination in the diagnosis and follow-up of this patient group.

Funduscopic examination and SD-OCT in detecting sickle cell retinopathy among pediatric patients

PURPOSE

To compare the results of fundus examination and spectral domain optic coherence tomography (SD-OCT) in detecting retinal changes in pediatric patients with sickle cell disease at a single center.

METHODS

In this prospective study, conducted over a period of 19 months, consecutive African American patients with sickle cell disease underwent complete ophthalmologic examination, and SD-OCT images of the maculas of both eyes were obtained.

RESULTS

A total of 69 (37 males) patients aged 5-20 years (mean 12.89 ± 4.09; range, 2-20) with sickle cell disease (SC, 26; SS, 36; Sβ+, 5; Sβ0 thalassemia, 2) were examined. Patients' visual acuity range was 20/20 to 20/40. On funduscopic examination, 11 of 69 showed signs of retinopathy, whereas 47 of 68 showed inner retina thinning in the watershed zone temporal to the fovea on SD-OCT. On average, SD-OCT diagnosed disease 1.78 years earlier than fundus examination. Of patients <10 years of age, 1 was diagnosed with retinopathy by funduscopy, whereas retinal changes were evident on SD-OCT in 12 of 22. Fundus examination showed no significant difference in retinal findings between SS/Sβ0 and SC genotypes. On SD-OCT, SS/Sβ0 showed worse disease process than SC in frequency of diagnosis (82% vs 56%), bilateral involvement (87% vs 43%), and foveal involvement (18% vs 0).

CONCLUSIONS

The peripheral retina could be visualized on fundus examination but not easily imaged on SD-OCT, which, however, had a higher detection rate and offered earlier diagnosis. In our patient cohort SD-OCT showed that the severity of retinal change was associated with more severe sickle cell disease genotypes (SS and Sβ0).

Retinal Photocoagulation for Proliferative Sickle Cell Retinopathy: A Prospective Clinical Trial with New Sea Fan Classification

Purpose

To compare the clinical outcome of stage III proliferative sickle cell retinopathy (PSR) treated by peripheral retinal scatter photocoagulation to natural course disease.

Methods

Long-term follow-up of 101 patients enrolled in a prospective trial of photocoagulation for PSR has been completed. Among 202 eyes of 101 patients enrolled at the University Eye Clinic of Créteil, 73 eyes showed a stage III PSR, which the authors further divided into five new grades (A, B, C, D, E) considering size, hemorrhage, fibrosis, and visible vessels. Grading was based on a three-mirror fundus examination, 360° color photographs, and fluorescein angiography. Mean follow-up was 4 years.

Results

Thirty-eight treated eyes and 35 untreated eyes were included in this study. The evolution was not statistically significant between treated and untreated groups concerning flat sea fan p<1 MPS disc area (grade A) or elevated sea fan with partial fibrosis (grade C). Progression and regression were compared between the two groups for grade B, resulting statistically significant (pp<0.05). Nine complications (13%) were observed, which only occurred in untreated patients with elevated sea fan and hemorrhage (grade B) or complete fibrosed sea fan with well defined vessels (grade E) (pp<0.05).

Conclusions

These data suggest that patients with grade A or C new sea fan classification should not be initially treated but observed.

New Ways to Detect Pediatric Sickle Cell Retinopathy: A Comprehensive Review

Sickle retinopathy reflects disease-related vascular injury of the eye, which can potentially result in visual loss from vitreous hemorrhage or retinal detachment. Here we review sickle retinopathy among children with sickle cell disease, describe the epidemiology, pediatric risk factors, pathophysiology, ocular findings, and treatment. Newer, more sensitive ophthalmological imaging modalities are available for retinal imaging, including ultra-widefield fluorescein angiography, spectral-domain optical coherence tomography, and optical coherence tomography angiography. Optical coherence tomography angiography provides a noninvasive view of retinal vascular layers that could previously not be imaged and can be quantified for comparative or prospective analyses. Ultra-widefield fluorescein angiography provides a more comprehensive view of the peripheral retina than traditional imaging techniques. Screening for retinopathy by standard fundoscopic imaging modalities detects a prevalence of approximately 10%. In contrast, these more sensitive methods allow for more sensitive examination that includes the retina perimeter where sickle retinopathy is often first detectable. Use of these new imaging modalities may detect a higher prevalence of early sickle pathology among children than has previously been reported. Earlier detection may help in better understanding the pathogenesis of sickle retinopathy and guide future screening and treatment paradigms.

Expression Pattern of HIF-1α and VEGF Supports Circumferential Application of Scatter Laser for Proliferative Sickle Retinopathy

Purpose

Retinal vascular occlusions in sickle cell anemia patients cause tissue ischemia and the release of angiogenic mediators that promote the development of retinal neovascularization, initiating proliferative sickle retinopathy (PSR). Laser photocoagulation (LPC) has emerged as the most common treatment for PSR. Nonetheless, only two randomized controlled clinical trials have evaluated the use of LPC for PSR, and both failed to definitively demonstrate efficacy of this approach. This may be due to a lack of knowledge regarding the appropriate location for placement of laser coagulations in PSR eyes. To help address this question, we examined the expression of hypoxia-inducible factor (HIF)-1α and vascular endothelial growth factor (VEGF) in PSR eyes.

Methods

The expression pattern of HIF-1α and VEGF in PSR (n = 5) and control (n = 3) eyes was examined by immunohistochemistry in different retinal regions defined by the presence or absence of retinal vessels.

Results

Hypoxia-inducible factor 1α and VEGF were expressed in the inner retina of 5/5 untreated PSR eyes adjacent to retinal neovascularization; expression of HIF-1α was not detected (and VEGF only lightly detected) in normal retinal and choroidal vasculature of 3/3 control eyes. Hypoxia-inducible factor 1α and VEGF were strongly expressed in retinal cells within avascular (nonperfused) retina, anterior to the boundary between perfused and nonperfused retina, as well as in posterior ischemic retina in the presence or absence of neovascular sea fans.

Conclusions

If the goal of LPC in PSR is to quench the expression of HIF-1–driven angiogenic mediators, our results support broad application of peripheral laser for its treatment.

Comparative analysis of the retinal microvasculature visualized with fluorescein angiography and the retinal function imager

PURPOSE

To assess the visualization of the retinal microvasculature with intravenous fluorescein angiography (IVFA) compared to the Retinal Function Imager (RFI).

DESIGN

Multicenter, retrospective, observational case series.

METHODS

Seven normal eyes and 26 eyes with various ocular diseases were imaged with both IVFA and the RFI. The ability to assess vessel loops, vertical collateral vessels, the size of the foveal avascular zone (FAZ), and degree of vessel branching were compared between IVFA and RFI images.

RESULTS

The RFI visualized a greater number of vessel loops (1.3 vs 0.4 per eye) and vertical collateral vessels (4.42 vs 0.97 per eye) than IVFA. On average, higher order of vessel branching was seen with the RFI compared to IVFA (5.2 vs 4.6). The foveal avascular zone (FAZ) was more clearly delineated using the RFI and was significantly smaller when measured on RFI (0.35 vs 0.75 mm(2)).

CONCLUSIONS

RFI, a noninvasive retinal imaging instrument, revealed vessel loops, vertical collateral vessels, the area of the FAZ, and order of vessel branching in greater detail than IVFA. This instrument may be helpful in understanding dynamic retinal vascular changes in a number of common ocular diseases, as well as in normal eyes.

Beyond the definitions of the phenotypic complications of sickle cell disease: an update on management

The sickle hemoglobin is an abnormal hemoglobin due to point mutation (GAG → GTG) in exon 1 of the β globin gene resulting in the substitution of glutamic acid by valine at position 6 of the β globin polypeptide chain. Although the molecular lesion is a single-point mutation, the sickle gene is pleiotropic in nature causing multiple phenotypic expressions that constitute the various complications of sickle cell disease in general and sickle cell anemia in particular. The disease itself is chronic in nature but many of its complications are acute such as the recurrent acute painful crises (its hallmark), acute chest syndrome, and priapism. These complications vary considerably among patients, in the same patient with time, among countries and with age and sex. To date, there is no well-established consensus among providers on the management of the complications of sickle cell disease due in part to lack of evidence and in part to differences in the experience of providers. It is the aim of this paper to review available current approaches to manage the major complications of sickle cell disease. We hope that this will establish another preliminary forum among providers that may eventually lead the way to better outcomes.

Pathology of sickle cell disease

Sickle cell disease (SCD) is a hereditary chronic hemolytic anemia with numerous clinical consequences. Intravascular sickling of red blood cells leads to multiorgan dysfunction. Although the pathophysiology of SCD has been well studied, there remains a lack of effective treatment. Refinements in overall care have improved quality of life; however, premature death is still not uncommon. SCD usually presents in childhood and is common in areas where malaria is (or was) common. The association with malaria is apparently of benefit to the individual because these individuals tend to contract a milder form of the disease. This review highlights the spectrum of pathology seen in people with SCD, with an emphasis on the pathogenesis of sudden death.

Retinal and optic nerve head pathology in Susac's syndrome

PURPOSE

This article describes the first retinal histopathologic findings in a patient with Susac's syndrome (SS).

DESIGN

Observational case report.

PARTICIPANT

A 51-year-old white woman diagnosed with SS.

METHODS

Eyes from a 51-year-old white woman diagnosed with SS were obtained at autopsy. One retina was dissected and processed for adenosine diphosphatase (ADPase) flat embedding. Selected areas were processed further for transmission electron microscopy.

MAIN OUTCOME MEASURES

Histopathologic examination using ADPase flat-embedding technique.

RESULTS

There were vaso-occlusive changes in the retinal periphery resulting in small areas of capillary dropout. Cross-sections demonstrated serous filled spaces between the retinal blood vessels and the internal limiting membrane. Lumens adjacent to these spaces appeared compressed and sometimes closed, but without thrombosis. Decreased ADPase activity in some peripheral blood vessels suggested endothelial cell dysfunction and vaso-occlusion. In the optic nerve head, numerous corpora amylacea were observed in the vicinity of capillaries with thickened walls and narrow lumens. Transmission electron microscopy demonstrated thickened and amorphous vascular basal lamina and open endothelial cell junctions in some retinal blood vessels.

CONCLUSIONS

The serous deposits with compression of retinal vessel lumens observed histologically probably represent the so-called string of pearls described clinically in SS. Chronic extension of these serous deposits along the vessel wall possibly are the cause of retinal arterial wall plaques as described by Gass and other investigators. In the optic nerve head, corpora amylacea are probably a result of microinfarcts resulting from optic nerve head capillary angiopathy. Accumulation of amorphous material in the basal lamina, loss of viable endothelial cells, and capillary dropout suggest that SS may be an endotheliopathy.

[Epidemiology and prognostic factors for sickle cell retinopathy in Ouagadougou (Burkina Faso)]

INTRODUCTION

The frequency of sickle cell disease varies from 5% to 20% in Africa.

PATIENTS AND METHOD

This retrospective study investigated 173 patients in an ambulatory setting from August 2000 to July 2006. The study included 98 women and 75 men, aged 15-62 years, with a mean age of 26.7 years.

RESULTS

Only 89 patients (71 SC and 18 SS) were seen in ophthalmology, 44 (49%) had sickle cell retinopathy with 26 (29%) cases nonproliferative and 18 cases proliferative (20%). Among the 71 SC patients, 35 (50%) had sickle cell retinopathy, with 40% the proliferative form. Of the 18 SS patients, nine had a retinopathy (50%), with four cases proliferative.

DISCUSSION

Retinopathy is a frequent complication of sickle cell disease, which can lead to blindness, and its management better accessibility to the ophthalmologic examination and preventive treatment by laser photo coagulation.

Sickle cell disease vasculopathy: a state of nitric oxide resistance

Sickle cell disease (SCD) is a hereditary hemoglobinopathy characterized by microvascular vaso-occlusion with erythrocytes containing polymerized sickle (S) hemoglobin, erythrocyte hemolysis, vasculopathy, and both acute and chronic multiorgan injury. It is associated with steady state increases in plasma cell-free hemoglobin and overproduction of reactive oxygen species (ROS). Hereditary and acquired hemolytic conditions release into plasma hemoglobin and other erythrocyte components that scavenge endothelium-derived NO and metabolize its precursor arginine, impairing NO homeostasis. Overproduction of ROS, such as superoxide, by enzymatic (xanthine oxidase, NADPH oxidase, uncoupled eNOS) and nonenzymatic pathways (Fenton chemistry), promotes intravascular oxidant stress that can likewise disrupt NO homeostasis. The synergistic bioinactivation of NO by dioxygenation and oxidation reactions with cell-free plasma hemoglobin and ROS, respectively, is discussed as a mechanism for NO resistance in SCD vasculopathy. Human physiological and transgenic animal studies provide experimental evidence of cardiovascular and pulmonary resistance to NO donors and reduced NO bioavailability that is associated with vasoconstriction, decreased blood flow, platelet activation, increased endothelin-1 expression, and end-organ injury. Emerging epidemiological data now suggest that chronic intravascular hemolysis is associated with certain clinical complications: pulmonary hypertension, cutaneous leg ulcerations, priapism, and possibly stroke. New therapeutic strategies to limit intravascular hemolysis and ROS generation and increase NO bioavailability are discussed.

The initial fetal human retinal vasculature develops by vasculogenesis

There is increasing evidence that the hemangioblast, a common progenitor for hematopoietic cells and endothelial cells, participates in embryonic and extra-embryonic vasculogenesis in some organs. Whether resident angioblasts or endothelial progenitor cells (EPCs) contribute to human retinal vasculogenesis is still a matter of controversy. To address this controversy, fetal human retinas of 6-23 weeks gestation (WG) were examined using immunohistochemistry and a panel of antibodies against endothelial cell markers (CD34, CD31), a marker for retinal angioblasts and endothelium (CD39/ecto-ADPase), and a marker for precursors and hemangioblasts (CXCR4). Confocal microscopic spectral analysis and double labeling with Ki67 was used to identify the proliferating cell types. In the inner neuroblastic layer of the 6-8 WG retina and in the putative ganglion cell layer in avascular regions of older eyes (14 WG-20 WG), scattered CD39+ angioblasts were well in advance of forming vasculature. There was a layer of CXCR4+ cells in the inner retina that was reduced in size with development. As blood vessels formed, CD39+ cells were always well in advance of the vascular front and they expressed CXCR4. This demonstrates that a pool of resident angioblasts express CD39 and CXCR4 as they differentiate and participate in vasculogenesis in the fetal human. They retain expression of CD39 as endothelial cells in the newly formed retinal vasculature but they down-regulate CXCR4 expression.

Expression of protein kinase CK2 in astroglial cells of normal and neovascularized retina

We previously documented protein kinase CK2 involvement in retinal neovascularization. Here we describe retinal CK2 expression and combined effects of CK2 inhibitors with the somatostatin analog octreotide in a mouse model of oxygen-induced retinopathy (OIR). CK2 expression in human and rodent retinas with and without retinopathy and in astrocytic and endothelial cultures was examined by immunohistochemistry, Western blotting, and reverse transcriptase-polymerase chain reaction. A combination of CK2 inhibitors, emodin or 4,5,6,7-tetrabromobenzotriazole, with octreotide was injected intraperitoneally from postnatal (P) day P11 to P17 to block mouse OIR. All CK2 subunits (alpha, alpha', beta) were expressed in retina, and a novel CK2alpha splice variant was detected by reverse transcriptase-polymerase chain reaction. CK2 antibodies primarily reacted with retinal astrocytes, and staining was increased around new intraretinal vessels in mouse OIR and rat retinopathy of prematurity, whereas preretinal vessels were negative. Cultured astrocytes showed increased perinuclear CK2 staining compared to endothelial cells. In the OIR model, CK2 mRNA expression increased modestly on P13 but not on P17. Octreotide combined with emodin or 4,5,6,7-tetrabromobenzotriazole blocked mouse retinal neovascularization more efficiently than either compound alone. Based on its retinal localization, CK2 may be considered a new immunohistochemical astrocytic marker, and combination of CK2 inhibitors and octreotide may be a promising future treatment for proliferative retinopathies.

Phosphatase enzyme histochemistry for studying vascular hierarchy, pathology, and endothelial cell dysfunction in retina and choroid

Phosphatase enzymes cleave an inorganic phosphate from a substrate. Phosphatase enzyme histochemistry followed by flat-embedding in glycol methacrylate is extremely useful in studying retinal and choroidal vascular development and loss, since only viable blood vessels have these enzyme activities. Sites of occlusion and remodeling can be identified and analysed, resulting in new insights into the cause of occlusion. The phosphatase activities are elevated in neovascularization making possible high resolution analysis of neovascularization, the feeder vessels, and the retinal milieu in which angiogenesis occurs. Adenosine diphosphatase (ADPase) catalyzes ADP to an inorganic phosphate plus adenosine monophosphate, preventing accumulation of ADP, one of the most potent stimuli for platelet aggregation. The ADPase technique can be used in any species but this report highlights its use in dog and human retinas. The ADPase technique has yielded important insights into vaso-occlusive and vasoproliferative processes in retinopathy of prematurity, sickle cell and diabetic retinopathies. The alkaline phosphatase flatembedding technique is useful in evaluating dog, cat, and human choroidal vasculatures. It has permitted quantification of the loss of choriocapillaris in diabetic choroidopathy and of the RPE and choriocapillaris in geographic atrophy and exudative age-related macular degeneration.

Effects of Sickle Cell Disease on the Eye: Clinical Features and Treatment

Ocular complications of the sickling disorders are multiple and require continuing assessment to detect lesions early enough for effective prophylactic therapy to maximize visual functioning. The disease requires close monitoring of the patient for progression or regression of lesions in determining the selection of therapeutic options.

Expression of pigment epithelium-derived factor (PEDF) and vascular endothelial growth factor (VEGF) in sickle cell retina and choroid

Pigment epithelium-derived factor (PEDF) has been shown to be an inhibitor of angiogenesis as well as a multipotent neurotrophic factor in the mammalian eye. Changes in PEDF levels have been correlated with development of retinal neovascularization in oxygen-induced retinopathy. The purpose of this study was to determine the localization and relative level of PEDF in human retinas and choroids using immunohistochemistry and evaluate the changes in PEDF and vascular endothelial growth factor (VEGF) localization and their relation to the progression of proliferative sickle cell retinopathy. Cryopreserved tissues from eyes of normal subjects and subjects with non-proliferative or proliferative sickle cell retinopathy were used with streptavidin peroxidase immunohistochemistry. A rabbit polyclonal antibody was made against recombinant human PEDF. Binding of the antibody was blocked by preincubation of the antibody with excess human recombinant PEDF. Relative levels of immunoreactivity were scored with a seven-point grading system and by microdensitometric analysis.The most prominent sites of PEDF localization in the normal eye were the vitreous condensed at the internal limiting membrane and RPE-Bruch's membrane-choriocapillaris complex. PEDF was also prominent in choroidal stroma. There was limited immunoreactivity in some cells of the neural retinas, in blood vessels and in the interphotoreceptor matrix (IPM). There was no difference in ratio (1.47 vs. 1.44) of PEDF/VEGF or the relative levels of either growth factor in the retinal vasculatures of the control subjects and perfused area of non-proliferative sickle cell retinas. The ratio was increased in the non-perfused area of the non-proliferative sickle cell retinas (2.24). In eyes with proliferative sickle cell retinopathy, elevated PEDF and VEGF immunostaining was present in viable vessels of sea fan neovascular formations as well as feeder vessels of sea fans. The PEDF/VEGF ratio in sea fans was 1.0. Immunoreactivity for PEDF was prominent in retinal vessels in non-perfused regions and in atrophic sea fans, while VEGF immunoreactivity was weak or absent in these structures. In conclusion, PEDF and VEGF were both significantly elevated in viable sea fan formations in sickle cell disease (p<0.05) but only PEDF was present in non-viable sea fans. The highest levels of PEDF in all eyes were associated with extracellular matrices (vitreous, choroidal stroma, IPM, and walls of blood vessels). PEDF might play an important role in inhibiting angiogenesis and inducing the regression of sea fans. Progression of angiogenesis may be dependent on the ratio of PEDF/VEGF.

Neutrophils and leucocyte adhesion molecules in sickle cell retinopathy

AIMS

The expression of the adhesion molecules ICAM-1, VCAM-1, and P-selectin, and the distribution and number of polymorphonuclear leucocytes (PMNs) were investigated in sickle cell retinopathy (SCR) and compared to the normal retina.

METHODS

Postmortem ocular tissue was obtained from five subjects (16, 21, 28, 40, and 41 years of age) with sickle haemoglobinopathies and from one control subject. Tissue was cryopreserved, and streptavidin peroxidase immunohistochemistry was performed with antibodies against ICAM-1, VCAM-1, and P-selectin. Immunohistochemical reaction product was scored, and PMN numbers were counted in sections stained with non-specific esterase.

RESULTS

Increased ICAM-1, VCAM-1, and P-selectin immunoreactivities were observed in sickle cell subjects compared to the control subject. The highest ICAM and P-selectin immunoreactivity was associated with intraretinal vessels adjacent to the preretinal neovascular formation in subjects with proliferative retinopathy. This was not the case with VCAM-1 immunoreactivity, which was highest in intraretinal vessels adjacent to the sea fan when the sea fan was still "in statu nascendi." Fully formed, "older" sea fans had the highest levels of VCAM-1. The increase in adhesion molecule immunoreactivity was paralleled by an increase in intraretinal PMNs. The number of intraretinal PMNs increased with progression of the disease and the numbers surpassed those in control subjects by threefold. In the sea fan with the greatest VCAM-1 immunoreactivity, there were 20 times more PMNs were observed than in the rest of the retina in the same subject.

CONCLUSION

These data suggest that adhesion molecule mediated leucocyte adhesion might play an important part in the vaso-occlusive phase of sickle cell retinopathy and in autoinfarction of sea fan formations.

Pleiotropic and epistatic effects in sickle cell anemia

Sickle cell anemia is the first monogenic disease ever described, and it became the paradigm for a disease traceable to a single mutation in a single gene. Pauling's concept of "molecular disease," based on this discovery, opened a new chapter in the history of medicine. Nevertheless, at the phenotypic level, sickle cell anemia is not a monogenic disease; it is a multigenic disease. The latter is the product of pleiotropic genes (involved in secondary pathophysiologic events) and epistatic genes (same gene but with significant pathophysiologic consequences among individual=polymorphism). These secondary events are an important part of the phenotype and explain the intense interindividual differences in the severity of the disease, in spite of all the patients having the same sickle globin gene in the homozygote form. In the last decade a number of epistatic genes and pleiotropic genes have been defined, and many others are potential candidates. CHIP technology and high-throughput sequencing promise to accelerate our full multigenic understanding of this disease, contributing to a more individualized concept of disease in conjunction as we enter the new millennium.

Nonperfusion of retina and choroid in transgenic mouse models of sickle cell disease

PURPOSE

To determine if vascular occlusion and nonperfusion is associated with the outer retinal atrophy, retinopathy, and choroidopathy (chorioretinopathy) that occurs in the alpha H beta S[beta MDD] and alpha H beta S [alpha MD beta MDD] transgenic mouse models of sickle cell disease.

METHODS

Mice from the alpha H beta S[beta MDD] and alpha H beta S[alpha MD beta MDD] transgenic mouse lines that express high levels of human beta S globin were anesthetized and administered horseradish peroxidase (HRP) intracardially. After 1 min, the animals were sacrificed, and the retina from one eye was excised, fixed, and developed in diaminobenzidine (DAB). The contralateral eye was fixed, embedded whole in glycol methacrylate, and HRP developed in 2.5 microns sections.

RESULTS

HRP reaction product (HRP-RP) and stained erythrocytes (RBCs) (due to endogenous peroxidase) were diffusely distributed within all vascular lumens in flatmount retinas from control animals (littermates homozygous for the mouse Beta Major deletion not expressing the beta S transgene). In 42.5% of the transgenic mice expressing beta S without any proliferative retinopathy, many blood vessels contained RBC plugs and lacked lumenal HRP-RP. In addition to packed RBCs, fibrin was sometimes present at sites of occlusion. In sections from whole eyes of the same animals, foci of photoreceptor degeneration were associated with areas of choriocapillaris nonperfusion (lumen that lacked HRP-PR). In areas with normal photoreceptors, the choriocapillaris appeared perfused (HRP-RP was present). In animals with proliferative chorioretinopathy, some neovascular formations lacked luminal HRP-RP, suggesting autoinfarction.

CONCLUSIONS

Nonperfused retinal and choroidal vessels were observed in mice from the alpha H beta S[beta MDD] and alpha H beta S[alpha MD beta MDD] lines without retinal and choroidal neovascularization, whereas, all mice with neovascularization had nonperfused areas. Furthermore, small foci of PR loss were associated with areas of nonperfused choriocapillaris. These results suggest that sickle cell-mediated vaso-occlusions are an initial event in the chorioretinopathy and outer retinal atrophy that occurs in these models.