Morphological investigations into the structure of frozen-thawed rat islets of Langerhans

Cryosurgery: ultrastructural changes in pancreas tissue after low temperature exposure

A number of theoretical and experimental studies, both in vitro and in vivo, have been performed to explain the action of low temperatures on tissue. It is now evident that the thermal parameters used in the past for freezing during cryosurgery were not precise; this may have resulted in the failure of treatment. For the first time, this report describes the early ultrastructural features of pancreatic parenchyma after low temperature exposure, i.e., cryosurgery, in vivo. We demonstrate the effect of freeze-thawing processes using temperatures of various intensities. The cryosurgical response of pancreas parenchyma, i.e., ultrastructural cellular changes in pancreas tissue, was investigated. The electronic microscopic analysis showed that, after local cryodestruction at temperatures of -80 degrees C and -180 degrees C, similar processes occurred within the pancreas tissue in the early postcryosurgical phase -- immediately and up to 24 hours after low temperature exposure on tissue. The exocrine pancreatic cells in the center of the cryozone changed upon thawing. Ultrastructural changes in the exocrine pancreatic cells, where the first signs of dystrophic processes had been noticed, were increased. These ultrastructural changes in the pancreatic cells provide a platform to better understand the mechanisms of damage and the pathogenesis of frostbite after cryosurgery. The properties of the pancreas parenchyma response after low temperature exposure provide important insights into the mechanisms of damage and the cryogenic lesion immediately after thawing in cryosurgery. Our new insights prove on the cell level that suddenly and progressively damaged pancreatic cells in the postcryosurgical zone lead to aseptic cryonecrosis and then to aseptic cryoapoptosis of vital normal tissue. The vascular capillary changes and circulatory stagnation demonstrate the anti-angiogenesis mechanism, which, together with cryoaponecrosis and cryoapoptosis, are some of the main mechanisms of biological tissue injury following the low temperature exposure.

Ultrastructural features of medullary chromaffin cell cultures

The ultrastructural organization on the fourth day of culture of chromaffin cells isolated from the bovine adrenal medulla was characterized based on electron microscopic and morphological analysis. We established that medullary chromaffin cells could be divided into four morphologically different subtypes. Most cells (49.1% of those examined) had a dense cytoplasm and fine dense granules. Cells with dense cytoplasm and large granules represented a second type of chromaffin cell (21.1%). Cells of the third type had a light cytoplasm, granules with a light halo and a well-developed Golgi apparatus (26.3%). The fourth type of chromaffin cell was characterized by moderately dense cytoplasm with well-expressed varicose rough endoplasmic reticulum (about 3.5%). Among concomitant cell types, cortical adrenal cells from the zona fasciculata and zona glomerulosa, epithelial cells, fibroblasts, lymphocytes, brown lipoblasts and glial Schwann cells were present. Morphological analysis implies that cells with dense cytoplasm and fine granules and those with light cytoplasm and haloed granules (75.4% in total) are adrenaline-containing cells, whereas the cells with dense cytoplasm and large granules (26.3%) contain noradrenaline. Cells with moderately dense cytoplasm and varicose reticulum share common morphological properties with classical glandular cells and, by their properties, were closer to noradrenaline-containing cells. It is concluded that chromaffin cells, which are the main cell type among cultured cells from adult bovine adrenal medulla, are morphologically quite heterogeneous. Other cell types of different nature may also be present in the culture and can locally influence the properties of the investigated medullary chromaffin cells used in electrophysiological experiments.

Three-dimensional distribution of damaged cells in cryopreserved pancreatic islets as determined by laser scanning confocal microscopy

The technique of serial optical sectioning by confocal microscopy, in conjunction with off-line digital image analysis, was used to quantify the radial distribution of damaged cells in rat pancreatic islets following cryopreservation. The process consists of imaging frozen-thawed islets of Langerhans using laser scanning confocal microscopy (LSCM). The three-dimensional (3-D) distribution and analysis of the two populations of viable and damaged cells was visualized via acridine orange/propidium iodide (AO/PI) fluorescent staining. In preparation for cryopreservation, isolated and cultured rat pancreatic islets were brought to a 2 M concentration of dimethyl sulphoxide (DMSO) by serial addition at decreasing temperatures. Ice was nucleated in the islet suspension at -10 degrees C, and individual specimens were frozen to -70 degrees C at cooling rates of 1, 3, 10 and 30 degrees C/min in a programmable bulk freezer and subsequently stored in liquid nitrogen. After rapid thawing and serial dilution to remove DMSO, individual islets were prepared with AO/PI stains for imaging on the LSCM. Serial sections of the islets, 2-7 microns in thickness, were obtained and processed to obtain high-contrast images. Analysis algorithms consisted of template masking, grey-level thresholding, median filtering and 3-D blob colouring. The radial distribution of damaged cells in the islets was determined by isolating the cell and computing its distance from the centroid of the 3-D islet volume. An increase in the number of blobs corresponding to single and/or aggregates of damaged cells was observed progressively with distance from the centre towards the periphery of the islet. This pattern of freeze-induced killing of cells within the islet was found to occur consistently in the numerous individual specimens processed.

Cryopreservation of hamster pancreatic islets using a rapid cooling rate

To clarify the possibility of developing a rapid cooling rate for islet cryopreservation, we used a cooling rate of 25 degrees C/min for hamster pancreatic islet cryopreservation using 15 per cent dimethylsulfoxide as a cryoprotectant. After preservation, these islets were examined for their morphology and function by assaying the insulin release after glucose stimulation and the contents of the insulin and DNA in 10 islets. In addition, islet cell replicatory activity was investigated by an autoradiographic technique. The effects of transplantation of the islets upon isogeneic and xenogeneic transplantation were also examined. Freezing using a rapid cooling rate of 25 degrees C/min was found to be as effective as a slow cooling rate of 1 degree C/min for hamster islet cryopreservation. Morphologically, the cryopreserved islets appeared to be similar to the non-frozen cultured islets. The glucose-stimulated insulin release and cell replicatory activities in vitro also remained unchanged, whereas the number of cells per islet decreased slightly after cryopreservation. The grafting of cryopreserved islets normalized streptozotocin induced hyperglycemia following isogeneic transplantation. On the other hand, no prolongation of graft survivals in the case of the xenogeneic transplantation of hamster islets to rats was observed. The isogeneically transplanted islets exhibited the same cell replicatory activities in vivo, which was even higher compared that of normal hamster pancreatic islets in situ. In conclusion, the present findings indicate that hamster pancreatic islets can be successfully cryopreserved using a rapid cooling rate, however, it does not appear that this treatment reduces islet vulnerability to xenogeneic graft rejection.