VEGF localisation in diabetic retinopathy

AIM

To determine the staining pattern of vascular endothelial growth factor (VEGF) at different stages of diabetic retinopathy (including post-laser photocoagulation) and to compare staining in excised fibrovascular and fibrocellular (non-diabetic) preretinal membranes.

METHODS

Immunohistochemical localisation of VEGF, using antibodies raised against VEGF165 and VEGF121,165,189, was carried out on specimens of normal human retina (n = 15), diabetic retinas ((a) with no overt retinopathy (n = 19), (b) with intraretinal vascular abnormalities but no proliferative retinopathy (n = 6), (c) with active proliferative retinopathy (n = 6), (d) with no residual proliferative retinopathy after photocoagulation therapy (n = 15)), excised diabetic fibrovascular membranes (n = 19), and non-diabetic fibrocellular membranes (n = 7). The degree and pattern of immunostaining was recorded.

RESULTS

In general, VEGF was absent from the majority of normal retinas. VEGF staining was apparent in most diabetic tissues but the staining pattern was dependent on both the specificity of the antibody used and the category of tissue. Staining with the VEGF165 antibody was generally confined to endothelial cells adn perivascular regions while the VEGF121,165,189 antibody was also associated with extravascular components of the inner retina. Intensity of immunostaining of diabetic eyes was dependent on the severity of retinopathy being least in diabetics with no overt retinopathy and greatest in retinas with proliferative retinopathy. Interestingly, the intensity of immunostaining in diabetic retinas which had undergone laser surgery for proliferative retinopathy was reduced to basal levels. Moderate to intense immunostaining was observed in all fibrovascular and fibrocellular membranes examined.

CONCLUSIONS

This study supports a circumstantial role for VEGF in the pathogenesis of both the preclinical and proliferative stages of diabetic retinopathy.

Blue light-induced singlet oxygen generation by retinal lipofuscin in non-polar media

Accumulation of lipofuscin (LF) is a prominent feature of aging in the human retinal pigment epithelium (RPE) cells. This age pigment exhibits substantial photoreactivity, which may increase the risk of retinal photodamage and contribute to age-related maculopathy. In a previous study, we detected singlet oxygen generation by lipofuscin granules excited with blue light. In this paper we investigated the ability of hydrophobic components of lipofuscin to photogenerate singlet oxygen in non-polar environments. Singlet oxygen was detected directly by monitoring its characteristic phosphorescence at ca 1270 nm. The action spectrum of singlet oxygen formation indicated that this process was strongly wavelength-dependent and its efficiency decreased with increasing wavelength by a factor of ten, comparing 420 nm and 520 nm. The quantum yield of singlet oxygen increased with increasing concentration of oxygen. Using laser flash photolysis we studied the possible mechanism of singlet oxygen formation. The observed transient, with a broad absorption spectrum peaking at around 440 nm, was identified as a triplet with lifetime ca 11 microseconds. It was quenched by both molecular oxygen and beta-carotene with concomitant formation of a beta-carotene triplet state. These results indicate the potential role of hydrophobic components of lipofuscin in blue light-induced damage to the RPE.

Increased expression of placenta growth factor in proliferative diabetic retinopathy

Proliferative diabetic retinopathy is thought to be mediated by the hypoxic regulation of angiogenic growth factors, in particular the vascular endothelial growth factor (VEGF) family. The aim of this study was to determine if placental growth factor (PIGF), a recently identified member of the VEGF family, was expressed in diabetic eyes undergoing preretinal neovascularization. Rabbit anti-PIGF antiserum was raised using a 20-amino acid N-terminal sequence to PIGF and did not cross react with VEGF165. Immunohistochemistry was performed on specimens of normal retina (n = 8), diabetic retina in the absence (n = 7) and presence (n = 4) of proliferative retinopathy, scatter laser-treated diabetic retina (n = 7), excised fibrovascular preretinal membranes (n = 12), and nondiabetic fibrocellular epiretinal (n = 7) membranes. PIGF levels were also determined in vitrectomy specimens from patients with either proliferative diabetic retinopathy or macular hole. PIGF immunoreactivity was intensely localized to the endothelial and perivascular regions of newly formed blood vessels of excised fibrovascular preretinal membranes. Intense localization of PIGF protein was also observed in superficial retinal vessels in diabetic retinae adjacent to neovascular preretinal membranes. Localization of PIGF was weak or absent in diabetic retinae that showed no evidence of neovascular proliferation. PIGF protein was also absent in normal retinae, in diabetic retinae that had received extensive treatment with scatter laser photocoagulation, and in nonvascularized epiretinal membranes. PIGF was present in all diabetic vitreous samples (mean 103 pg/ml) but nondetectable in control samples. These results strongly implicate a role for PIGF in the pathogenesis of proliferative diabetic retinopathy.

The effects of growth factors and conditioned media on the proliferation of human corneal epithelial cells and keratocytes

BACKGROUND

As growth factors play an important role in epithelial wound repair, we evaluated the effect of exogenous growth factors in the presence and absence of corneal epithelial and keratocyte conditioned medium on human corneal epithelial cell and keratocyte proliferation.

METHODS

Preconfluent cultures of human corneal epithelial cells or stromal keratocytes were exposed to varying concentrations of EGF, TGF-beta or bFGF in the presence or absence of human corneal epithelial or stromal keratocyte conditioned medium. Cell numbers were determined after 48 h incubation. RIA and ELISA were used to quantify the levels of EGF, TGF-beta and bFGF in conditioned media.

RESULTS

EGF and bFGF increased, while TGF-beta decreased, the proliferation of both cell types in a dose-dependent manner. Epithelial cell conditioned medium inhibited, and keratocyte conditioned medium stimulated, the proliferation of both cell types. The proliferative effects of EGF, TGF-beta and bFGF in the presence of keratocyte conditioned medium were additive for both cell types. By contrast, the addition of exogenous growth factors was unable to overcome the inhibitory potential of epithelial conditioned medium. Both conditioned media contained significant levels of bFGF, but TGF-beta levels in epithelial conditioned medium were up to 5 times greater than that in keratocyte conditioned medium.

CONCLUSIONS

The results indicate that corneal cells maintain tissue homeostasis and modulate the wound healing response via paracrine/autocrine pathways.

Determination of volumetric cerebrospinal fluid absorption into extracranial lymphatics in sheep

We estimated the volumetric clearance of cerebrospinal fluid (CSF) through arachnoid villi and extracranial lymphatics in conscious sheep. Catheters were inserted into both lateral ventricles, the cisterna magna, multiple cervical lymphatics, thoracic duct, and jugular vein. Uncannulated cervical vessels were ligated. 125I-labeled human serum albumin (HSA) was administered into both lateral ventricles. 131I-HSA was injected intravenously to permit calculation of plasma tracer loss and tracer recirculation into lymphatics. From mass balance equations, total volumetric absorption of CSF averaged 3.37 +/- 0.38 ml/h, with 2.03 +/- 0.29 ml/h (approximately 60%) removed by arachnoid villi and 1.35 +/- 0.46 ml/h (approximately 40%) cleared by lymphatics. With projected estimates for noncannulated ducts, total CSF absorption increased to 3.89 +/- 0.33 ml/h, with 1.86 +/- 0.49 ml/h (48%) absorbed by lymphatics. Additionally, we calculated total CSF drainage to be 3.48 +/- 0.52 ml/h, with 54 and 46% removed by arachnoid villi and lymphatics, respectively, using previously published mass transport data from our group. We employed estimates of CSF tracer concentrations that were extrapolated from relationships observed in the study reported here. We conclude that 40-48% of the total volume of CSF absorbed from the cranial compartment is removed by extracranial lymphatic vessels.

A role for vitamin A in the formation of ocular lipofuscin

BACKGROUND

Lipofuscin granules in the retinal pigment epithelium are lipid protein aggregates which are thought to represent the lifelong accumulation of the non-degradable end products from the phagocytosis of photoreceptor outer segments. Given the increasing evidence for a key role for vitamin A in the formation of ocular lipofuscin, the fluorophores generated by reacting vitamin A with lipid were assessed.

METHODS

Reaction mixtures consisting of vitamin A (retinol) or its aldehyde (retinal) and (a) isolated rod outer segments, (b) the lipid extract of rod outer segments, (c) protein, or (d) liposomes were incubated at either pH 4.5 or 7.0 for up to 42 days. The fluorescence characteristics and mobility of the chloroform soluble fluorophores generated were compared with those extracted from purified human lipofuscin. Finally, the effect of lysosomal degradation on fluorophores generated in the above mixtures was assessed.

RESULTS

Major spectral changes were observed when ROS or liposomes were incubated with retinal. These changes were pH dependent and did not occur if retinal was replaced with retinol. A number of the fluorophores generated exhibited similar fluorescence characteristics and chromatographic mobility to those of lipofuscin. Neither the presence of protein nor exposure to lysosomal enzymes had any effect on the spectral profile or fluorophore mobility of the fluorophores generated.

CONCLUSIONS

These results suggest that some of the chloroform soluble fluorophores of lipofuscin are formed as a direct reaction product of retinal and lipid.

Cell attachment to, and contraction of, the retina in vitro

PURPOSE

To examine the behavior of fibroblasts and retinal pigment epithelial cells after attachment to the retinal surface in vitro to elucidate the pathobiology of the early stages of epiretinal membrane formation.

METHODS

Human retinal pigment epithelial (HRPE) cells and bovine Tenon's capsule fibroblasts (BTFs) were seeded onto the surface of bovine retinal explants maintained in organ culture. The changes induced in the underlying retina, including contraction, were assessed during a period of up to 10 days. Immunohistochemistry was used to assess proliferation of the seeded cells and to determine deposition of extracellular matrix.

RESULTS

Explants of bovine neuroretina were maintained in organ culture, with good morphologic preservation of the inner limiting lamina and inner retinal layers, for 7 to 10 days. The HRPE cells and the BTFs attached to the retinal surface and exerted tractional forces, producing partial- and full-thickness retinal folding. Contraction commenced within 24 hours of attachment of the cells and continued for several days, with most of the contraction occurring within the next 48 to 72 hours. The HRPE cells and BTFs were found to be equally contractile. Deposition of cellular fibronectin (but not collagen type I) was demonstrated.

CONCLUSIONS

The contractile cellular membranes generated in this organ culture system exhibit many of the morphologic and functional features of epiretinal membranes found in the early stages of proliferative vitreoretinopathy.

Lymphatic drainage of the CNS: effects of lymphatic diversion/ligation on CSF protein transport to plasma

The plasma recovery of an intraventricularly administered protein was compared before and after lymph diversion/ligation in the same conscious sheep to determine the relative roles of arachnoid villi and lymphatics in the clearance of a cerebral spinal fluid tracer. 125I-human serum albumin was injected into both lateral ventricles, and venous blood was sampled. One day later, multiple cervical vessels and the thoracic duct were cannulated for lymph collection. Uncannulated vessels were ligated. The experiment was repeated with 131I-human serum albumin as the tracer. Before lymph diversion/ligation, the time-averaged tracer transport into the plasma was 6.4 +/- 1.0%/h, with an average 6-h plasma recovery of 38.2 +/- 5.7% (percentage of injected dose). After lymph diversion/ligation, the values dropped to 2.9 +/- 0.5%/h and 17.7 +/- 2.7%, respectively. The collected lymph contained 8.7 +/- 2.6% of the tracer. No significant differences were observed in sham-operated animals. In conclusion, extracranial lymphatic vessels in sheep transport approximately one-half of the protein tracer from the cerebral spinal fluid compartment into plasma.

Intravitreal growth factors in proliferative diabetic retinopathy: correlation with neovascular activity and glycaemic management

AIM

Many growth factors are implicated in proliferative diabetic retinopathy (PDR). It was decided to test the hypothesis that no one factor is predominant but that a regular profile of levels of different growth factors might be operating, and that the profile might differ according to whether or not insulin therapy was part of the patient's glycaemic management. The levels of several growth factors in vitrectomy samples were therefore determined from diabetic patients with tractional, non-haemorrhagic sequelae of PDR and these levels were correlated with (a) each other (growth factor profile), (b) neovascular activity, and (c) the method of glycaemic management (insulin treated (IT) or non-insulin treated (NIT)).

METHODS

72 samples of vitreous were obtained from either diabetic patients with PDR (n = 51) or non-diabetic (control) patients (n = 21). Levels of bFGF, IGF-I, EGF, and insulin were determined by radioimmunoassay; levels of TGF-beta 2 by ELISA; and levels of IGF-I binding protein by western ligand blotting. The data were analysed using appropriate statistics.

RESULTS

There was no regular growth factor profile. bFGF levels were significantly greater in vitreous from NIT patients compared with IT patients and controls. The highest levels of bFGF were found in NIT patients with actively vascularised membranes. TGF-beta 2 levels were significantly greater in vitreous from IT patients compared with NIT patients and controls The highest levels of TGF-beta 2 were found in IT patients with actively vascularised membranes. IGF-I levels were significantly greater in diabetics (irrespective of insulin treatment) than non-diabetics and the highest levels of IGF-I were found in IT patients with actively vascularised membranes. A 34 kDa IGFBP was the predominant IGFBP identified in vitreous and was found to be elevated in diabetics patients.

CONCLUSION

In PDR there is a correlation between intravitreal growth factor levels and both disease state (whether active or fibrotic) and method of glycaemic management.

The effect of scatter laser photocoagulation on intravitreal levels of growth factors in the miniature pig

PURPOSE

To characterise changes in intravitreal growth factor profiles following retinal photocoagulation in the miniature pig.

METHODS

Miniature pig eyes underwent scatter photocoagulation by either diode infrared or emerald green laser. Animals were sacrificed at various times (up to 42 days) post-laser. The eyes were than removed and vitreous samples analysed for basic fibroblast growth factor, insulin-like growth factor-I and epidermal growth factor by radioimmunoassay, transforming growth factor-beta 2 by ELISA and insulin-like growth factor binding proteins using Western ligand blotting.

RESULTS

Vitreous transforming growth factor-beta 2 levels were decreased at 1 h post diode laser and at 4 and 7 days post emerald laser but returned to normal by 21 and 42 days respectively. Vitreous insulin-like growth factor-I levels increased at 4 and 7 days post diode and emerald laser respectively but returned to normal by 21 days. Insulin-like growth factor Western ligand blotting demonstrated that a 34 kDa insulin-like growth factor binding protein was predominant in the pig vitreous; the levels of this binding protein followed an identical trend to those observed for insulin-like growth factor-I. No changes in vitreous levels of either basic fibroblast growth factor or epidermal growth factor were observed following laser treatment.

CONCLUSIONS

Our results demonstrate a significant shift in the balance of intravitreal growth factors following retinal laser photocoagulation. Such changes may be pertinent to the regression of preretinal new vessels after laser photocoagulation.

Drainage of CSF through lymphatic pathways and arachnoid villi in sheep: measurement of 125I-albumin clearance

We investigated lymphatic drainage pathways of the central nervous system in conscious sheep and quantified the clearance of a cerebrospinal fluid (CSF) tracer into lymph and blood. In the first group of studies, 125I-HSA was injected into the lateral ventricles of the brain or into lumbar CSF and after 6 h, various lymph nodes and tissues were excised and counted for radioactivity. Multiple lymphatic drainage pathways of cranial CSF existed in the head and neck region defined by elevated 125I-HSA in the retropharyngeal/cervical, thymic, pre-auricular and submandibular nodes. Implicated in spinal CSF drainage were mainly the lumbar and intercostal nodes. In a second group of experiments, multiple cervical vessels and the thoracic duct were cannulated and lymph diverted from the animals. Transport of tracer through arachnoid villi was taken from recoveries in venous blood. Following intraventricular administration, the 6 h recoveries of 125I-HSA in the lymph (sum of cervical and thoracic duct) and blood were 8.2% +/- 3.0 and 12.5% +/- 4.5 respectively and at 22 h, 25.1% +/- 6.9 and 20.8% +/- 4.1 respectively. When 125I-HSA was injected into lumbar CSF, the 6 h recoveries of tracer in thoracic duct and blood were 11.6% +/- 2.7 and 16.3% +/- 3.7 respectively. Total lymph and blood recoveries were not significantly different in any experiment. We conclude that the clearance of 125I-HSA from the CSF is almost equally distributed between lymphatic and arachnoid villi pathways.

Qualitative research in health care: II. A structured review and evaluation of studies

A hand search of the original papers in seven medical journals over 5 years was conducted in order to identify those reporting qualitative research. A total of 210 papers were initially identified, of which 70 used qualitative methods of both data collection and analysis. These papers were evaluated by the researchers using a checklist which specified the criteria of good practice. Overall, 2% of the original papers published in the journals reported qualitative studies. Papers were more frequently positively assessed in terms of having clear aims, reporting research for which a qualitative approach was appropriate and describing their methods of data collection. Papers were less frequently positively assessed in relation to issued of data analysis such as validity, reliability and providing representative supporting evidence. It is concluded that the full potential of qualitative research has yet to be realized in the field of health care.

Qualitative research in health care: I. The scope and validity of methods

It is increasingly argued that qualitative approaches have an important role in health care research. A wide range of methods are used to collect qualitative data, including in-depth interviews, focus groups and observational methods such as participant observation. The reliability and validity of qualitative studies can be addressed by a variety of techniques. Although there is less consensus about appropriate methods of analysing qualitative data, such analyses tend to be grounded in the data, and involve iterative procedures and the development and refinement of typologies, analogies and other forms of concept to make sense of data.

The views of general practitioners on community carrier screening for cystic fibrosis

BACKGROUND

Recent developments in molecular genetics have made it possible to identify carriers of the cystic fibrosis (CF) mutation, regardless of family history, before they have an affected child. Using these techniques, population or 'community' carrier screening can offer informed reproductive choice to individuals and couples who would not otherwise know of their risk of having a CF child.

AIM

This study set out to assess the views of general practitioners (GPs) on community carrier screening for CF and to consider the factors that influence their willingness to offer it themselves.

METHOD

A self-administered questionnaires was sent to all 616 GPs in four areas of North Thames (West) Region.

RESULTS

Two-thirds of respondents indicated that identifying carrier couples to offer genetic counselling before conception was a very important benefit of community carrier screening. Two-thirds felt that general practice was the most appropriate place in which to offer it, and similar proportions that the most appropriate times to do so were when a close relative was diagnosed and when seeking family planning. About half wanted to offer community carrier screening themselves; this was related to experience with CF patients and CF carrier testing, and estimates of the numbers of CF carriers in the practice.

CONCLUSIONS

There is considerable support among GPs for community carrier screening for CF in general practice, particularly in the context of family planning services. Knowledge and experience of CF increase GPs' willingness to offer it themselves.

Oxygen modulates the response of the retinal pigment epithelium to basic fibroblast growth factor and epidermal growth factor by receptor regulation

PURPOSE

To determine if low oxygen affects growth factor responsiveness in retinal pigment epithelial (RPE) cells and if such effects are mediated through changes in cell surface receptors.

METHODS

Proliferating human RPE cells were exposed to varying concentrations of exogenous basic fibroblast growth factor (bFGF) or epidermal growth factor (EGF) at different media oxygen tensions (16 to 147 mm Hg) and cell counts determined after 4 days. Receptor expression was determined by affinity cross-linking and saturation binding studies on confluent RPE cultures exposed to varying media oxygen tensions for 2 days.

RESULTS

Retinal pigment epithelial cells exhibited a greater proliferative response to exogenous growth factors at hypoxia than at higher media oxygen tensions, and they expressed bFGF and demonstrated that hypoxia caused both an increase in the number of EGF receptors per cell and a shift from low to high affinity receptors.

CONCLUSIONS

These results suggest that hypoxia not only can stimulate RPE cell proliferation per se, it also can "prime" cells t respond more markedly to exogenous growth factors. These observations may be important in elucidating the cause of proliferative vitreoretinopathy.

Gay men's accounts of unsafe sex

This paper provides a qualitative analysis of the explanations given by a sample of 78 gay men in England of the most recent occasion on which they engaged in anal intercourse without a condom. Explanations are analysed and interpreted from the sociological perspective of 'accounts': that is, they are not viewed as exact descriptions of the 'real' motives for behaviour but are seen as a powerful resource that can illuminate the knowledge, assumptions and values that inform behaviour. Four distinct types of accounts were identified from the men's descriptions of the circumstances and motivations surrounding their most recent unsafe sexual encounter. These related to: (i) their emotional needs and drives; (ii) the calculus of risk; (iii) issues of trust; and (iv) lapses of control. Each of these types of account is described and the implications of the typology are considered, both for our understanding of the meanings, considerations and constraints surrounding high-risk sexual behaviour and for developing more relevant health education interventions.