Effects of 1,2-dimethylhydrazine treatment and feeding regimen on rat colonic epithelial cell proliferation.

The present study was designed to test the hypothesis that 1,2-dimethylhydrazine dihydrochloride (DMH) induces preneoplasia in rat colonic epithelium and that this DMH-altered epithelium will respond differently to various nutritional challenges in comparison to normal colonic epithelium. Preneoplasia was arbitrarily defined as an altered and irreversible state of colonic epithelial cell proliferation induced by a carcinogen (DMH). In summary, DMH was found to be specific for the enhancement of rat colonic epithelial cell proliferation compared to other rapidly renewing cell populations, i.e., ileal epithelium and ear epidermis. DMH-induced changes in rat colonic epithelial cell proliferation and crypt cellularity were found to be irreversible following a 2- to 8-week recovery period. The p.o. administration of the solid and liquid diets, regardless of chemical constituents, supported a DMH-induced increase in colonic epithelial cell proliferation; however, a DMH-induced increase in epithelial cell proliferation was not observed in rats maintained on total parenteral nutrition. Thus, the route of administration has a significant influence on epithelial cell proliferation in colonic epithelium of DMH-treated rats. The importance of these results, along with previous studies, is the establishment and initial characterization of an exploitable preneoplastic system in rat colonic epithelium. Particularly revealing was the finding that significant changes in crypt kinetic parameters induced by DMH treatment did not revert to control values following a 2- to 8-week recovery period. Based on an altered and irreversible state of colonic epithelial cell proliferation induced by DMH, it is concluded that: (a) the preneoplastic state is a committed state and is not dependent upon the continued presence of the carcinogen; and (b) all cryptal epithelium is preneoplastic, although not all cells progress to the overtly transformed state. In addition, total parenteral nutrition prevented the expression of a DMH-induced preneoplastic state of altered epithelial cell proliferation.

Embryo cryopreservation in cynomolgus monkeys.

An improved knowledge of cryopreservation of primate embryos will have important research and clinical application. Fifty-six 4- to 8-cell in vitro fertilized embryos were frozen in HEPES-buffered Tyrode's solution containing 1.5 M dimethylsulfoxide (DMSO) and cooled at the rate of 0.3 degrees C/minute to -39 degrees C before being transferred into liquid nitrogen. Embryos were rapidly thawed at room temperature for 2 minutes. DMSO was diluted with medium in three steps at 5-minute intervals. Of the 56 embryos, 39 (70%) were classified as viable on the basis of surviving the freezing process with greater than 50% of their blastomeres intact. Twelve of the 39 embryos were cultured overnight, and 11 cleaved at least once. Twenty-five embryos were transferred to nine synchronized, unstimulated recipient monkeys 24 to 48 hours after ovulation. Three pregnancies (33.3%) resulted from the nine transfers.

Changes in nuclear shape and mitochondrial structure do not accompany the loss of division potential in human fibroblasts in vitro.

Previous studies on ultrastructural changes that occur in cultured human fibroblasts during their in vitro life-span indicate that "senescent" cells characteristically possess structurally altered mitochondria, highly lobed nuclei, and an abundance of secondary lysosomes when compared to early passage cells. In the present study, we demonstrate that improper preparative methods can induce altered mitochondrial morphology in preparations of both IMR-90 and HF730A fibroblasts, regardless of passage level. We also show that nuclei of both living and fixed IMR-90 fibroblasts are ovoid in shape, not lobulate, in well-spread cells, regardless of either the passage level or the proliferative capacity of the cell. Fibroblasts contain lobulated nuclei only when they have not spread completely on the culture substrate. Lobulations can be induced at any passage level by collagenase/trypsin or trypsin/EDTA treatment prior to fixation, but not by cytochalasin B treatment or by cold temperatures. We conclude that any treatment that affects cytoskeleton-membrane-culture substrate interactions will induce this aberrant nuclear morphology, but that this is not indicative of "senescence" and does not relate to proliferative decline.

Quantitative morphological analysis of proliferating and nonproliferating subpopulations of IMR-90 fibroblasts during aging in vitro.

Early-, mid- and late-passage cultures (population doubling levels 12, 35, and 51, respectively) of IMR-90 fibroblasts were exposed to 3H-thymidine for 48 h prior to fixation in situ for morphometric analysis in order to determine quantitatively what ultrastructural changes accompany the loss of proliferative capacity during aging in vitro. Analysis of autoradiographs, both at the light and electron microscopic levels, with an image analyzer followed by ANOVA statistical scrutiny demonstrated that a significant increase in relative cell area, an indicator of cell size, was characteristic of cells unable to incorporate 3H-TdR at both mid- and late-passage, but not at early-passage levels. Nuclear size also increased significantly with progressive passage level but was not related to proliferative capacity. No significant difference in the area fraction of nucleoli per unit area of nucleus or of mitochondria, Golgi, or lysosomes was seen in either subpopulation at any passage level. Dilated cisternae of rough endoplasmic reticulum in early-passage cells were seen if cells were harvested with trypsin and fixed either before or after centrifugation, but were not seen in labeled or unlabeled cells from any passage level when cultures were fixed in situ. We conclude that a significant increase in cell size is the only significant morphological change associated with the loss of proliferative capacity of IRM-90 fibroblasts. Furthermore, our data indicate that there is no accumulation of secondary lysosomes in human diploid fibroblasts during aging in vitro; we therefore cannot support any hypothesis of aging or proliferative decline that is based mechanistically upon this phenomenon.