Izhak Nir

Ultrastructural localization of lectin binding sites on the surface of retinal photoreceptors and pigment epithelium.

Abstract The ferritin-lectin complexes of Ricinus communis agglutinin (RCA-120), wheat germ agglutinin (WGA), concanavalin A (con A), soybean agglutinin (SBA) and fucose binding protein (FBP) have been used to study the distribution of sugars along the plasma membranes of frog photoreceptor and pigment epithelial cells. The tissues were fixed prior to labeling in order to prevent the lectin-induced rearrangement of binding sites. The plasma membrane of different regions of the rod and cone photoreceptor cells bound each lectin to a different extent. In all cases, the outer segment plasma membrane bound more of the ferritin-lectin complex than did the inner segment plasma membrane. This might reflect the specific differentiation of the outer segment plasma membranes, related to their role in the visual process. The intensity of binding of each lectin to the pigment epithelium plasma membrane was similar to its binding to the rod outer segment plasma membrane. In cone outer segments, where one side of the disk membrane is accessible to the incubation medium, direct binding of lectin to the disk edges, as well as to the plasma membrane, was seen. Cone outer segments bound more of the α-D-N-acetylgalactosamine and D-galactose specific lectin, SBA, than did rod outer segments. No differences were observed in the binding of ferritin-lectin complexes to rod outer segments from dark or light adapted frogs.

Cisplatin ototoxicity in guinea pigs with special reference to toxic effects in the stria vascularis

The toxic effects of cisplatin (cis‐diamminedichloroplatinum [II]) on the organ of Corti are well established. Few and conflicting data on this drugs effects on the stria vascularis exist. The present study presents animal experiments on the toxic effects of cisplatin in the stria vascularis and in the organ of Corti. Cisplatin‐induced toxicity in albino and pigmented guinea pigs was evaluated morphologically and functionally, using light and transmission electron microscopy as well as auditory brainstem‐evoked potentials on the organ of Corti and the stria vascularis. The results showed variability in hearing thresholds, ranging from no change to hearing loss of 30 dB, and prominent damage in the organ of Corti and in the stria vascularis. The toxic effects to both the organ of Corti and the stria vascularis should be considered when cisplatin is used in chemotherapy.

The binding of concanavalin A to the rod outer segments and pigment epithelium of normal and RCS rats

Abstract We have studied the binding of ferritin conjugated concanavalin A to the plasma membranes of the rod outer segments and the pigment epithelium of normal rats, and rats suffering from hereditary retinal degeneration (RCS rats). Both fixed and unfixed tissues show an irregular distribution of the conjugated lectin along the plasma membranes of these cell types. This indicates that the lectin receptors are not homogeneously distributed in the membranes. The connecting cilium shows much heavier binding of ferritin-concanavalin A than do other parts of the photoreceptor cell. No significant differences were found between the binding of the lectin conjugate to retinal tissues from normal rats and RCS rats.

Toxic effects of cisplatin alone and in combination with gentamicin in stria vascularis of guinea pigs.

The toxic effects on the stria vascularis of treatment with cisplatin alone and combined with the aminoglycoside antibiotic, gentamicin, were studied in guinea pigs. The toxicity induced in albino and pigmented guinea pigs was investigated morphologically with light and transmission electron microscopy, and functionally by brainstem‐evoked response audiometry. The results of hearing thresholds were variable, ranging from no change in one ear in some of the animals to a hearing loss of 20 dB in one or both ears when treated with low‐dose cisplatin alone or in combination with gentamicin. Bilateral deafness resulted from high‐dose cisplatin combined with gentamicin. The combined treatment produced prominent structural damage in the stria vascularis. The results should be considered when aminoglycoside therapy is required in conjunction with cisplatin.

Permeability of blood vessels in experimental gliomas: uptake of 99mTc-glucoheptonate and alteration in blood-brain barrier as determined by cytochemistry and electron microscopy.

Experimental gliomas were induced in rats by prenatal exposure to ethyl nitrosourea. Changes in the blood-brain barrier were determined by the uptake of a water-soluble compound, 99mTc-glucoheptonate. Increased uptake of 99mTc-glucoheptonate was measured in intact tumors and in various sectors of dissected tumors. The extent of 99mTc-glucoheptonate uptake greatly varied among different tumors and among different sectors of the same tumor. Ultrastructural and cytochemical analysis of the capillary endothelial wall revealed major alterations in tight junctions, which became permeable to horseradish peroxidase. In brain tissue around the tumors, uptake of 99mTc-glucoheptonate and ultrastructure of tight junctions were comparable to normal brain capillaries. The results of the present study indicate that altered endothelial tight junctions may provide the main route of transport of 99mTc-glucoheptonate through the endothelial wall.

Quantitative Analysis of Tight Junctions and the Uptake of 99mTc in Human Gliomas

The structural dimensions of capillary tight junctions and the uptake of 99mTc pertechnetate in human gliomas were studied. Quantitative analysis revealed a correlation between the uptake of radionuclides and the length of endothelial tight junctions. It is suggested that brain scintigraphy might be used for the selection of malignant brain tumors with altered tight junctions which might be accessible to chemotherapy with water-soluble agents.

Cytochemical evaluation of anionic sites on the surface of cultured pigment epithelium cells from normal and dystrophic RCS rats

Anionic sites on the surface of cultured pigment epithelium cells from normal and dystrophic rats were studied. Cytochemical procedures and quantitative analysis were employed in order to determine distribution patterns and labeling densities. Anionic sites, in general, were localized with cationized ferritin at pH 7.0. The presence and density of sialic acid residues on the pigment epithelium cell surface were evaluated with colloidal iron at pH 1.8. Dystrophic cells contained 20% more cationized ferritin-binding sites as compared with normal pigment epithelium cells. With colloidal iron, an 18% increase in labeling density was measured in dystrophic pigment epithelium cells. Pretreatment with neuraminidase reduced subsequent labeling with colloidal iron by 93-97%. Thus, the presence of sialic acid residues on the surface of pigment epithelium cells and a significant increase in its content on the surface of dystrophic cells were established.

Correlation between radionuclides uptake and ultrastructural features of tight junctions in the capillary wall of meningiomas.

The uptake of Tc-99m pertechnetate and Co-57 bleomycin and the ultrastructure of small blood vessels were studied in 10 cases of meningioma. When thin sections of 120 contact areas between adjacent endothelial cells were examined, 92% of the intercellular contacts contained one to three punctate tight junctions. Freeze fracture preparations revealed fascia occludens with one to four sealing strands. These findings are consistent with the high permeability the meningiomas displayed for both of the radiopharmaceuticals.

Ultrastructural and Clinical Observations on Skin Metastases from Breast Cancer Patients following Intralesional Treatment with MER/BCG Vaccine

Ultrastructural and clinical investigations were carried out on skin metastases in patients with advanced breast cancer, following intralesional therapy with MER/BCG vaccine. A total of 65 tumoral lesions in 5 patients were injected with MER. Clinical responses were correlated with light and electron microscopic observations. Regressing tumor lesions showed substantial macrophage and lymphocyte infiltration and severe damage to tumor cells. Activated macrophages with secondary lysosomes and contacts between macrophages and tumor cells were widely observed. In 1 patient with limited cellular immune response, clinical regression was not evident and many tumor cells were ultrastructurally intact.

Pigment Epithelium and Rod Outer Segment Cell-Surface Interactions in Normal and RCS Rats

Phagocytosis of rod outer segment tips by the pigment epithelium (PE) is required for normal development of retinal photoreceptors (Young 1976). In RCS rats with retinitis pigmentosa, the balance between membrane renewal and removal is disturbed due to a defective phagocytosis process. This leads to accumulation of rod outer segment (ROS) membrane debris in the subretinal space and to subsequent retinal dystrophy (Bok & Hall 1971).