Biomedical subjects

B V Harmon

Publications and source records attributed to B V Harmon.

32 records · Page 2Linked to original sources

PubMed1992

Spermatogonial apoptosis has three morphologically recognizable phases and shows no circadian rhythm during normal spermatogenesis in the rat.

In this study we examined the possibility that regular or circadian fluctuations occur in the frequency of spontaneous spermatogonial apoptosis. Apoptosis of A2, A3 and A4 type spermatogonia occurring spontaneously in the normal rat testis was studied by light and electron microscopy. Normal and apoptotic A3 spermatogonia were quantified in 36 animals killed at two-hourly intervals over a 24 h period. Three sequential phases of spermatogonial apoptosis were defined and quantified separately: (i) an early phase in which cells showed margination of nuclear chromatin, (ii) an intermediate phase in which phagocytosed apoptotic bodies were partly degraded and (iii) a late phase in which only debris of degraded apoptotic bodies was evident. Groups of spermatogonia linked by intercellular bridges underwent apoptosis synchronously. Normal and apoptotic A3 spermatogonia occurred at a mean frequency of 33.4 and 9.6 per 10 seminiferous tubule profiles respectively; there was a large variation in these frequencies between animals, but no peaks or circadian periodicity were detected. Progressive degradation of apoptotic bodies was evident, the average ratios of intermediate and late bodies to early bodies being 1.5 and 3.5, respectively. Absence of a circadian rhythm in these data does not exclude the possibility that initiation of apoptosis in susceptible spermatogonial clones is synchronous, and that affected clones undergo lag periods of differing duration before expressing morphological apoptosis.

Animals↗

PubMed1992

Cell death induced by vincristine in the intestinal crypts of mice and in a human Burkitt's lymphoma cell line.

Although vincristine is widely used clinically in the treatment of some human cancers, its mechanism of action has not been clearly established. In this study, the patterns of cell death induced by vincristine in the intestinal crypts of mice and in a human Burkitt's lymphoma cell line were investigated by light and electron microscopy. Vincristine was found to enhance apoptosis of interphase cells in both systems and also to cause the arrest of cells in mitosis, the latter effect being more pronounced in the intestinal crypts. Arrested mitotic cells went on to die by a process that had a number of features in common with apoptosis. These include compaction of chromatin (following coalescence of chromosomes), condensation of the cytoplasm, initial preservation of organelle integrity, and eventually the fragmentation of the cell into a number of membrane-enclosed bodies which are morphologically similar to conventional apoptotic bodies. The results suggest that the cytocidal effect of vincristine is not solely dependent on metaphase arrest but is a cumulative one, resulting both from apoptosis of interphase cells and the 'apoptotic-like' death of cells arrested in metaphase.

Animals↗

PubMed1991

Apoptosis induced by mild hyperthermia in human and murine tumour cell lines: a study using electron microscopy and DNA gel electrophoresis.

Mild hyperthermia is known to enhance apoptosis in a range of normal and neoplastic cell populations. Studies of tumours previously shown to respond to heating in this manner might be expected to provide insights not only into the mechanism of hyperthermic cell killing, but also into the apoptotic process in general. In the present study, cell death induced by 43 degrees C heating for 30 min in two human Burkitt's lymphoma lines, BM 13674 and WW1, and in murine mastocytoma P-815 x 2.1 was found to be exclusively apoptotic in type, identification being based on light and electron microscopic appearances and on the presence of internucleosomal cleavage of DNA into fragments that are multiples of 180-200 base pairs, which was demonstrated by agarose gel electrophoresis. The heat-induced apoptosis was prevented by the presence of zinc sulphate, an inhibitor of the endonuclease considered to be responsible for the DNA cleavage, but was not suppressed by the protein synthesis inhibitor cycloheximide. The findings question the validity of the widely held view that active protein synthesis is an invariable prerequisite for the execution of apoptosis. It is suggested that an inositol triphosphate-mediated increase in cytosolic Ca2+, resulting from limited membrane damage, might be the critical event responsible for activation of apoptosis by mild hyperthermia.

Animals↗

PubMed1991

Effects of cycloheximide on B-chronic lymphocytic leukaemic and normal lymphocytes in vitro: induction of apoptosis.

A number of reports indicate that protein synthesis is a requirement for the occurrence of apoptosis. In this study, the effect of the protein synthesis inhibitor cycloheximide (CHM) on spontaneous apoptosis of B-chronic lymphocytic leukaemia (B-CLL) cells, previously shown to occur when they are cultured in RPMI-1640 medium with autologous or heterologous serum, was examined. No definite inhibition of apoptosis was observed. Indeed, CHM-treatment augmented apoptosis in the B-CLL cultures and also induced apoptosis of cultured normal peripheral blood lymphocytes. Augmentation was dose-dependent for B-CLL cells over the concentration range 10(-6) M (0.28 micrograms ml-1) to 10(-2) M (2800 micrograms ml-1), resulting in 9% to 98% apoptosis respectively by 24 h of culture (r = 0.619, P = 0.0008). Normal lymphocytes were affected by CHM over the range 10(-4) M to 10(-2) M, resulting in 7% to 74% apoptosis respectively (r = 0.794, P = 0.0001). Inhibition of protein synthesis in these cells by CHM was virtually complete at a concentration of 10(-3) M. The findings are in accord with some recent reports indicating that suppression of protein synthesis by CHM does not inhibit apoptosis in all circumstances. They also illustrate the marked susceptibility of B-CLL cells, compared with normal lymphocytes, to the induction of apoptosis by this drug. The manner in which CHM triggers apoptosis of some cell types is at present uncertain.

Antigens, CD↗

PubMed1991

The role of apoptosis in the response of cells and tumours to mild hyperthermia.

There is now abundant evidence that apoptosis, the cell death mechanism responsible for physiological deletion of cells, can be triggered by mild hyperthermia. However, the overall importance of this mode of death in heated tumours has not yet been established. In this light and electron microscopic study, apoptosis induced by 43 degrees C or 44 degrees C water bath heating for 30 min in a range of murine and human tumours growing in vitro and in four murine tumours growing as solid nodules in vivo, was identified on the basis of its characteristic morphology, and the amount present quantified. Apoptosis was found to play a variable role in the response of tumours to heating, with the lowest levels produced in human melanoma lines (less than 1%) and the highest levels in some Burkitt's lymphoma lines (up to 97%). In these latter tumours the induction of apoptosis is clearly a major component of the hyperthermic response.

Animals↗

PubMed1990

Cell death induced in a murine mastocytoma by 42-47 degrees C heating in vitro: evidence that the form of death changes from apoptosis to necrosis above a critical heat load.

The pathogenesis of heat-induced cell death is controversial. Categorizing the death occurring after various heat loads as either apoptosis or necrosis might help to elucidate this problem, since it has been shown that these two processes differ in their mode of initiation as well as in their morphological and biochemical features. Log-phase cultures of mastocytoma P-815 x 2.1 were heated at temperatures ranging from 42 to 47 degrees C for 30 min. After 42 degrees C heating a slight increase in apoptosis was observed morphologically. However, after heating at 43, 43.5 and 44 degrees C, there was marked enhancement of apoptosis, and electrophoresis of DNA showed characteristic internucleosomal cleavage. With heating at 45 degrees C both apoptosis and necrosis were enhanced, whereas at 46 and 47 degrees C only necrosis was produced. DNA extracted from the 46 and 47 degrees C cultures showed virtually no degradation, which contrasts with the random DNA breakdown observed in necrosis produced by other types of injury; lysosomal enzymes released during heat-induced necrosis may be inactivated at the higher temperatures. It is suggested that apoptosis following heating may be triggered either by a limited increase in cytosolic calcium levels resulting from mild membrane changes or by DNA damage. Necrosis, on the other hand, is likely to be a consequence of severe membrane disruption.

Animals↗

PubMed1989

Cell death by apoptosis in acute leukaemia.

We have previously demonstrated that when freshly isolated childhood T-cell acute lymphoblastic leukaemia cells are incubated in growth medium after isolation from blood, chromatin is rapidly cleaved into nucleosomal sized fragments that are multiples of 200 bp. The fragmentation is similar to that observed in other types of cells undergoing apoptosis or programmed cell death. In this study we describe a more comprehensive approach to the study of DNA fragmentation in leukaemia. Fragmentation was observed in freshly isolated cells from patients with T-cell acute lymphoblastic leukaemia and in one with common acute lymphoblastic leukaemia. Frozen samples of T-cell acute lymphoblastic leukaemia, common acute lymphoblastic leukaemia, and acute myeloid leukaemia cells also showed fragmentation of DNA. However, no fragmentation was evident in normal leukocytes treated under the same conditions. Ultrastructural studies on the isolated leukaemia cells demonstrate that the chromatin cleavage observed biochemically is associated with morphological changes characteristic of apoptosis.

Cell Survival↗

PubMed1989

Spontaneous programmed death (apoptosis) of B-chronic lymphocytic leukaemia cells following their culture in vitro.

When B-chronic lymphocytic leukaemia (B-CLL) cells derived from peripheral blood were cultured in vitro, a substantial proportion of them spontaneously died by apoptosis. This type of cell death is morphologically and biochemically distinct from necrosis and has previously been found to occur under physiologic and certain pathologic conditions where cell deletion appears controlled and biologically meaningful. By 30 h of culture, approximately 20% of the unfractionated B-CLL cells were affected. There was no significant difference in the incidence of apoptosis in T-cell depleted and undepleted cultures or when either autologous or normal human serum was used. Furthermore, seeding densities of 2 x 10(6) and 5 x 10(5) cells/ml resulted in a similar incidence of apoptosis, indicating that cell density was unlikely to be a contributing factor in producing the death. The finding that B-CLL cells spontaneously die in vitro has at least two important implications. Firstly, previous work relating to some of the functions of B-CLL cells and their interactions with T cells may require re-evaluation. Secondly, an understanding of the mechanisms involved in the induction of apoptosis in this disease may have therapeutic consequences.

Blood Cell Count↗

PubMed1988

Cell death by apoptosis following X-irradiation of the foetal and neonatal rat kidney.

A light and electron microscopic study was undertaken to determine the type of cell death induced by X-irradiation in the developing kidney. Five-day-old Sprague-Dawley rats were exposed to a whole-body dose of either 2 or 5 Gy, and foetuses in the eighteenth day of development were exposed to a dose of 4 Gy. The kidneys were examined at 4, 8 and 24 h, and at 1 and 2 weeks post-irradiation. The dying cells from both control and treated kidneys showed the morphological features of apoptosis, a distinct form of cell death that has been identified in mammalian tissues under physiological as well as pathological conditions. Necrosis was not detected. Apoptosis was infrequent in control kidneys and insignificant in extent when compared with the proliferative activity of the cells of the superficial nephrons. There was a pronounced increase in apoptosis during the first day after irradiation. The findings are in agreement with recent ultrastructural studies which report the presence of apoptosis following irradiation of rapidly proliferating adult cell populations, and irradiation of other immature mammalian tissues. There is evidence that apoptosis involves active cellular self-destruction, and it has been suggested that activation of apoptosis might bring about selective elimination of cells with critical DNA damage in irradiated tissues, thus minimizing propagation of genetic abnormalities.

Animals↗

PubMed1988

Patterns of cell death.

Cell death takes two distinct forms, necrosis and apoptosis. Necrosis is a degenerative phenomenon that follows irreversible injury. Apoptosis, in contrast, appears to be an active process requiring protein synthesis for its execution; it is implicated in physiological regulation of tissue size, and, where it occurs pathologically, a homeostatic role for the death is often evident. Morphologically, apoptosis involves condensation of the nuclear chromatin and cytoplasm, fragmentation of the nucleus, and budding of the whole cell to produce membrane-bounded bodies in which organelles are initially intact. These bodies are disposed of by adjacent cells without inflammation. Biochemically, there is distinctive internucleosome cleavage of DNA in apoptosis, which is quite different from the random DNA degradation observed in necrosis.

Adult↗

PubMed1988

Sertoli cell death by apoptosis in the immature rat testis following x-irradiation.

The importance of the morphological study of cell death has recently been emphasized by the recognition that the ultrastructural features of dying cells allow categorization of the death as either apoptosis or necrosis. This classification enables inferences to be drawn about the mechanism and biological significance of the death occurring in a particular set of circumstances. In this study, Sertoli cell death induced in the immature testis of three and four day old rats by 5 Gy (500 rads) x-irradiation was described by light and transmission electron microscopy with the objective of categorizing the death as apoptosis or necrosis. The testes were examined 1, 2, 3, 4, 8, and 24 h after irradiation. Following irradiation, there was a wave of apoptosis of the Sertoli cells starting in three to four hours and reaching a peak between four and eight hours. At 24 hours, only 61% of the expected number of Sertoli cells remained. These findings are in accord with recent ultrastructural reports that ionizing radiation induces cell death by apoptosis in rapidly proliferating cell populations. New insights into the pathogenesis of radiation-induced cell death might thus be expected to stem from future elucidation of the general molecular events involved in triggering apoptosis.

Animals↗

PubMed1988

X-ray-induced cell death by apoptosis in the immature rat cerebellum.

The cells of the external granular layer (EGL) of the developing cerebellum are known to be particularly sensitive to radiation. In the past, changes induced in this layer by irradiation have been referred to by non-specific terms such as "pyknotic cells" and the mode of cell death has been assumed to be necrosis. However, in published light micrographs of these dying cells, the appearance is suggestive of apoptosis, a distinctive mode of cell death which occurs spontaneously in normal adult and embryonic tissues and can also be triggered by certain pathological stimuli. This light and transmission electron microscopic study of control and irradiated (7 h post-irradiation) rat cerebellum from 18 day fetuses and 5 day-old neonates showed that the cell death was effected by apoptosis. The apoptosis was markedly enhanced by x-irradiation and quantification of the cell death in the EGL of 5 day-old rats exposed to 4, 8, 25, 100, and 400 cGy x-irradiation demonstrated that there was a positive dose response relationship. The extent of cell death by apoptosis which was 0.2% in control, ranged from 0.8% after 4 cGy to 62.3% after 400 cGy x-irradiation. The recognition that cell death by apoptosis can be a major component of x-irradiation damage has important implications for radiobiological studies.

Animals↗

PubMed1987

An ultrastructural study of spontaneous cell death in a mouse mastocytoma with particular reference to dark cells.

The morphology and frequency of the various types of cell death occurring spontaneously in a mouse mastocytoma growing as intramuscular nodules were investigated. In addition to necrosis and apoptosis, which have been well documented in malignant neoplasms in the past, a third morphological pattern of cell death, the formation of dark cells, was observed. Necrosis first appeared in confluent patches about 5 days after tumour inoculation, and these increased in size as the tumours grew. Apoptosis, on the other hand, was present at all stages of tumour growth, and remained at a reasonably constant level. Dark cells were first observed at about 6 days, and increased in numbers thereafter. Dark cells were characterised by overall cellular condensation and gross swelling of mitochondria. Their cytoplasm became squeezed out between adjacent cells and then fragmented. Remnants of dark cells were eventually phagocytosed and degraded by macrophages. The distribution of dark cells in the tumours suggested that crowding and compression may contribute to their development.

Animals↗

PubMed1986

The morphologic categorization of cell death induced by mild hyperthermia and comparison with death induced by ionizing radiation and cytotoxic drugs.

This paper presents a summary of the morphological categorization of cell death, results of two in vivo studies on the cell death induced by mild hyperthermia in rat small intestine and mouse mastocytoma, and a comparison of the cell death induced by hyperthermia, radiation and cytotoxic drugs. Two distinct forms of cell death, apoptosis and necrosis, can be recognized on morphologic grounds. Apoptosis appears to be a process of active cellular self-destruction to which a biologically meaningful role can usually be attributed, whereas necrosis is a passive degenerative phenomenon that results from irreversible cellular injury. Light and transmission electron microscopic studies showed that lower body hyperthermia (43 degrees C for 30 min) induced only apoptosis of intestinal epithelial cells, and of lymphocytes, plasma cells, and eosinophils. In the mastocytoma, hyperthermia (43 degrees C for 15 min) produced widespread tumor necrosis and also enhanced apoptosis of tumor cells. Ionizing radiation and cytotoxic drugs are also known to induce apoptosis in a variety of tissues. It is attractive to speculate that DNA damage by each agent is the common event which triggers the same process of active cellular self-destruction that characteristically effects selective cell deletion in normal tissue homeostasis.

Animals↗