Cellular migration and replication in endothelial regeneration: a study using irradiated endothelial cultures

Cellular migration and replication were studied during repair of mechanical injuries produced in cultured monolayers of vascular endothelium. Human endothelial cells were obtained by collagenase perfusion of term umbilical cord veins and were grown on glass cover slips in replicate primary cultures. Following standardized mechanical denudation ("wounding") of narrow linear areas in postconfluent cultures, cellular migration and DNA synthesis were assessed at intervals after terminal 3H-thymidine incubation. Migration of cells from the edges of the wound into the denuded area was consistently underway by 12 hours, and by 24 hours there was considerable repopulation of the wound. A significant increase in 3H-thymidine labeling was not observed in the wound area until 36 hours. When cultures were exposed to 1500 rads of x-rays 1 hour prior to wounding, labeling was nearly abolished at 48 and 72 hours despite continuous incubation with 3H-thymidine. However, migration occurred as usual and resulted in repopulation similar to that in nonirradiated replicate cultures. These studies indicate that small endothelial defects can be significantly repaired by migration of adjacent viable cells. Thus, factors influencing both migration and replication should be considered in studies dealing with endothelial regeneration in vivo.

Regeneration of endothelium in rat aorta after local freezing. A scanning electron microscopic study

Immediately after freezing the abdominal aorta of rats by applying a cold probe, the endothelium is desquamated or necrotic and platelets adhere to desquamated areas (at the earliest observable time) but not to necrotic endothelium or endothelium adjacent to the injury. Preferential adhesion of platelets to fenestrations of the internal elastic laimina appears to lead to their active migration into the media, where a large number may be present up to 8 days after injury. Platelets seems to be removed from the surface by the action of the advancing edge of the regenerating endothelium, moving at a maximum mean rate of 590 mu daily. An increase in area of individual cells appears to relate better than an increase in their number to the advance of the edge of the regenerating sheet.

The migration of lymphocytes across specialized vascular endothelium. III. Concanavalin A delays lymphocytes in normal traffic areas

Radioactively labelled rat lymphocytes were treated in vitro with concanavalin A (con A) and injected intravenously into syngeneic recipients. By examining the blood and tissues at intervals from 30 min to 48 h after injection, it was confirmed that con A altered the distribution of lymphocytes. Comparison was made with the localization of alternatively labelled untreated lymphocytes injected into the same recipients and with untreated lymphocytes injected into other recipients. Within 1 h of injection there was a surplus of treated cells in the lungs and liver and deficits (of equal magnitude) in the blood, spleen and lymphonodes. By 24 h after injection there was a twofold surplus of treated cells in the spleen but a persisting deficit in lymphnodes. These perturbations can be ascribed to the prolonged retention of lymphocytes in normal sites of localization; there is no evidence that con A either hinders the migration of lymphocytes from the blood or diverts them to abnormal sites. It is not clear whether the delay in the recipients' tissues requires an active response to con A but, if so, then it does not proceed to blastic transformation.

The intimal healing of microvascular anastomoses

Examination with the S.E.M. shows that 5 days after surgery the microanastomoses area is covered with pseudointima, and the regeneration of the intima is completed within two weeks. Comparing the two different suture techniques (large bites and small bites), there are no differences between them in the resultant patency rates. The large bites produce less immediate leakages. There were no significant differences in the process of intimal healing.

Clonal growth of bovine vascular endothelial cells: fibroblast growth factor as a survival agent

Bovine vascular endothelial cells do not grow when cultured at low density unless fibroblast growth factor is included in the culture medium. When endothelial cells obtained from the intimal surface of fetal and adult aortas were seeded at low density (8 cells per cm2), they formed small colonies of large, irregular, vacuolated cells. At very low density (0.3 cells per cm2) they did not survive. The addition of fibroblast growth factor to endothelial cells maintained at such low densities resulted in the formation of vigorously growing colonies of small, uniform cells. Electron microscopy showed that the cultured endothelial cells had the fine structure characteristics of endothelial cells. Immunofluorescence microscopy revealed antihemophilic factor (Factor VIII) antigen in the cells. Our results demonstrated that fibroblast growth factor permits the survival of endothelial cells plated at extremely low cell density. With the use of fibroblast growth factor, endothelial cell clones are easily produced.

The blood-retinal barriers

The Blood-Retinal Barrier (BRB) is a situation of restricted permeability which is present between the blood and the retina. This barrier has a well defined anatomic substrate, particular permeability characteristics and appears to play a role of major importance in the pathophysiology and therapeutics of retinal disease. The BRB phenomenon operates fundamentally at two levels, retinal vessels and chorioepithelial interface, forming which may be better called an inner BRB and an outer BRB. The main structures involved are, for the inner BRB, the endothelial membrane of the retinal vessels, and for the outer BRB, the retinal pigment epithelium. 'Zonulae occludentes' are present in these membranes forming complete belts around the cells, sealing off the spaces between them. Other structures appear to play an accessory role. Both barriers show an apparent predominance of processes of active transport over mechanisms of passive transfer, these being extremely restricted. Much information on the pathophysiology of the BRB mechanism has been obtained from studies of its experimental breakdown. In this way, a breakdown of the inner BRB may be induced by acute distension of the vessel walls, ischaemia, chemical influences, defects in the endothelial cells and failure of the active transport system, whereas experimental ischaemia, mechanical distension of the pigment epithelial membrane, defects in the pigment epithelium and failure of the active transport systems can cause a breakdown of the outer BRB. The increased permeability of the inner BRB, and of the outer BRB, appears to be related to changes in the vascular endothelial membrane and retinal pigment epithelium, respectively. In clinical ophthalmology there are two methods for the diagnosis of breakdown of the BRB, fundus fluorescein angiography and vitreous fluorophotometry. Vitreous fluorophotometry being capable of detecting functional alterations of the barrier before any pathological changes are apparent. There is evidence of an intimate relationship between breakdown of the BRB and almost every retinal disease, particularly the vascular retinopathies and the pigment epitheliopathies. Diabetic retinopathy, hypertensive retinopathy, retinal vein obstruction, blood diseases, trauma or surgery to the eye, temporary arterial obstruction, perivasculitis, Behçet's and Coats' diseases, retinoblastoma, hemangioblastoma and retinal neovascularization are examples of situations where a breakdown of the inner BRB has been demonstrated. On the other hand, examples of breakdown of the outer BRB include situations of choroidal ischaemia, detachment of the pigment epithelium, choroidal neovascularization, photocoagulation, retinal detachment, Koyanagi's disease, central serous choroidopathy, multifocal inner choroiditis and acute placoid pigment epitheliopathy.

A method for studying endothelial regeneration in small vessels

A simple, accurate method for demonstrating very small areas of endothelium is described. Some possible fields for further investigation are suggested. An outline of the possible normal mechanism of endothelial regeneration is described.

Human corneal endothelial layer repair during organ culture

Circular freeze-thaw endothelial wounds were created on paired human corneas. Ultrastructural and physiological studies were performed after organ culture (OC) incubation at 37 C from 1 to 21 days as well as on fresh noncultured controls. As early as 24 hours after injury, OC corneas demonstrated ultrastructurally intact endothelial cells at the margin of the wound, elongating and sliding toward its center. All OC corneas were completely covered by ultrastructurally intact and physiologically functioning endothelial cells by seven days of OC. These cells were approximately twice normal size. Enlarged endothelial cells that maintained deturgescence function were seen in the wounded area after 14 and 21 days of OC. None of the fresh controls demonstrated deturgescence function and in none could ultrastructurally intact endothelial cells be found in the area of the wound. This confirms our hypothesis that during 37 C OC incubation, human corneal endothelium repairs defects in its layer by cells that are physiologically and ultrastructurally intact.

Homocystine-induced arteriosclerosis. The role of endothelial cell injury and platelet response in its genesis

The atherogenic mechanism of homocystinemia has been defined by measuring endothelial cell loss and regeneration, platelet consumption, and intimal lesion formation in a primate model. Three groups of baboons were studied: (a) 8 control animals; (b) 15 animals after 3 mo of continuous homocystinemia; and (c) 11 animals after 3 mo of combined homocystinemia and oral treatment with dipyridamole. Experimental homocystinemia caused patchy endothelial desquamation comprising about 10% of the aortic surface despite a 25-fold increase in endothelial cell regeneration. Neither endothelial cell loss nor regeneration was changed significantly by dipyridamole. Homocystine-induced vascular deendothelialization produced a threefold increase in platelet consumption that was interrupted by dipyridamole inhibition of platelet function. All homocystinemic animals developed typical arteriosclerotic or preatherosclerotic intimal lesions composed of proliferating smooth muscle cells averaging 10-15 cell layers surrounded by large amounts of collagen, elastic fibers, glycosaminoglycans, and sometimes lipid. Intimal lesion formation was prevented by dipyridamole therapy. We conclude that homocystine-induced endothelial cell injury resulted in arteriosclerosis through platelet-mediated intimal proliferation of smooth muscle cells that can be prevented by drug-induced platelet dysfunction.

Lymphocyte homing into lymph nodes: in vitro demonstration of the selective affinity of recirculating lymphocytes for high-endothelial venules

An in vitro model is described for studying the interaction between lymphocytes and high-endothelial venules (HEV) of lymph nodes. Rat or mouse lymphocytes which were layered over fixed sections of syngeneic lymph nodes adhered selectively to the endothelium of HEV but did not bind to other vascular endothelia. Evidence is presented that adherence to HEV in vitro is a property of recirculating lymphocytes and not a characteristic of cells which are unable to home into lymph nodes in vivo.

Penetrating keratoplasty using 37 C organ cultured cornea

Sixty-three penetrating keratoplasties were performed in 63 patients using donor corneas stored by 37 C organ culture incubation for an average of 13 days (range 2 to 35 days). No grafts failed before four weeks, except one which was stored at 4 C for 48 hours prior to transplantation, indicating that endothelial viability is maintained when proper storage conditions are maintained. Sixteen grafts have failed as a result of factors other than the storage method. This clinical study confirms our previous laboratory conclusions that 37 C OC incubation up to 35 days improves the quality of donor endothelium compared with other methods of storage, and it represents a significant advance in corneal preservation.

On the interpretation of depth dependent light scattering measurements in normal corneas

In recent studies other investigatiors have presented traces of "light scattering" versus depth into the cornea. The present investigation demonstrates that these traces do not measure the actual light scatter intensity and that a proper interpretation of such traces shows that most of the scattering is from within the stroma.

Hydrostatic pressure effects on deswelling of de-epithelialized and de-endothelialized corneas

The effects of varying hydrostatic pressure on the thinning rate of preswollen de-epithelialized or de-endothelialized corneas has been determined in the specular microscope. The appropriate membrane was removed, the cornea given access to Ringer to swell, and then fluid exchange at that surface blocked with oil. De-epithelialized corneas thin more slowly as hydrostatic pressure on the posterior surface is increased, until fluid movement ceases at 60 to 70 mm. Hg. Fluid movement can occur, therefore, against a considerable hydrostatic pressure. De-endothelialized corneas thin at a higher rate as hydrostatic pressure is increased; this effect is probably a mechanical one with increasing pressure forcing fluid out across the epithelium.

Permeability of the small intestine after intra-arterial injection of histamine-type mediators and irradiation

Permeability and selectivity of rabbit small intestine were estimated by a perfusion technique after intra-arterial injection of histamine-type mediators and intestinal irradiation. It was shown that the histamine-type mediators caused an increase in capillary permeability which produced an overall moderate increase in transmucosal permeability with a moderate loss of selectivity. Local intestinal irradiation caused a very marked increase in permeability and a profound loss of selectivity. It was felt that this was produced partly by an increase in capillary permeability but largely by damage to the epithelial basement membrane. It is concluded that the intestinal capillary endothelium is both rate-limiting and selective, though not to a major degree in either case. The epithelial basement membrane, however, appears to be both rate-limiting and markedly selective.

[Pachymetry in the study of preservation of the cornea]

Rabbit corneas were preserved for between 7 and 14 days at + 4 degrees C in a whole eye in synthetic media (T.C. 199 and T.C. Earle) with or without added Dextran. In the absence of Dextran the corneas preserved at + 4 degrees C became thick. This thickening increased with the length of conservation. Dextran limited the hydration of the stroma. Measurement of the variations of corneal thickness during perfusion for 6 hours at 30 degrees C in T.C. Earle could be used as an index of the function of the corneal endothelium. Even after 14 days of preservation at + 4 degrees C the corneal endothelium retained the ability to reduce or prevent hydration during perfusion at 30 degrees C. Histological studies showed good conservation of the cellular structure after 7 days at + 4 degrees C. Pyknosis appeared after 14 days conservation. T.C. 199 preserved endothelial function better than T.C. Earle.

Endothelial contractility - an undecided problem in vascular research

The rather old conception that endothelial cells possess an autonomous contractile capability has been reevaluated by several suthors during the past ten years on the basis of three different arguments of various validity: (1) After the topical application of inflammatory mediators tmajno et al. regularly found the endothelial nuclei furnished with numerous identations together with many interendothelial "gaps"; Both findings are assumed to be the morphological correlate of an endothelial shortening due to the contraction of the cells. While nuclear indentations seemed to be a rather weak argument to substantiate contractile capabilities, a mechanism other than contraction is outlined for the formation of "gaps"; (2) The second argument in favour of endothelial contractility is the occurrence of cytoplasmic filaments that occasionally form cross striated bundles and/or show a "thick" and "thin" variety. If all these data are assumed to be the morphological evidence for the contractile capability of cells then the conclusion: the more filaments the higher the contractile activity, must be valid. But when compiling those endothelia that are particularly rich in filaments this conclusion does not make sense, because e.g. the endothelium covering the venous valves is crowded with filaments yet an especially high "contractile activity" does not seem very probabble. On the other hand, the supposition that endothelial conttractility is entirely independent of the existence of cytoplasmic filaments leaves the question unanswered what then are the filaments for if not serving mechanical purposes. This line of reasoning is supported by both the localization of the filaments predominantly in those endothelia that have to sustain higher degrees of various mechanical stresses and the fact that filamentous structures significatnly increase in number under the influence of hypertension. (3) The final argument brought forward to substantiate endothelial contractility is the demonstration of actin and tropomyosin in the endothelium of various types of blood vessels that also occur under the influence of hypertension; tbut the significance of these findings as a proof for endothelial contractility is curtailed by the fact that the occurrence of actin alone is not conclusive for any contractile capabilities; Furthermore, a convincing demonstration of myosin in endothelial cells is still lacking and the "thick" filaments are believed to be noncontractile. Hence we suggest that the endothelial filaments together with the myoid proteins do not serve as a means for "contractility" in a true sense but simply act as a design to originate tensile strength.