N-(4-hydroxyphenyl)retinamide-induced death in human lymphoblastoid cells: 50 kb DNA breakage as a means of distinguishing apoptosis from necrosis.

Experimental studies of N-(4-hydroxyphenyl)retinamide, a potential cancer chemopreventive agent, have primarily involved breast cancer and neuroblastoma cell populations together with an investigation of myeloid leukemia cells and have principally been concerned with the induction of apoptosis. This investigation of N-(4-hydroxyphenyl)retinamide-induced apoptosis using T-cell-derived human lymphoblastoid lines extends these studies by indicating distinctive features associated with this drug. The induction of apoptosis is restricted to a limited concentration range, which, if exceeded, results in cell death by necrosis. While morphological changes typical of apoptosis induced by many agents are readily demonstrable after treatment of lymphoblastoid cells with 3 microM N-(4-hydroxyphenyl)retinamide, distinctive features evident using the retinoid include the absence of cell cycle arrest along with the mode and pattern of DNA breakage. Analysis by conventional gel electrophoresis indicated that internucleosomal fragmentation of DNA was an unreliable indicator of apoptosis. On the other hand, higher order DNA breakage was consistently detected during drug-induced apoptosis, but not as a result of treatment causing necrosis.

Involvement of apoptosis in 4-vinylcyclohexene diepoxide-induced ovotoxicity in rats.

Previous studies have determined that 4-vinylcyclohexene diepoxide (VCD) causes specific destruction of oocytes contained in small pre-antral (primordial and primary) ovarian follicles of Fischer 344 rats following 30 days of daily dosing with VCD. The purposes of this study were to identify the type of VCD-induced cell death occurring in small pre-antral follicles and to determine the earliest time following the onset of dosing when evidence of follicular destruction could first be detected. A significant decrease in the number of oocytes contained in small pre-antral follicles in ovaries of rats after 15 days of daily dosing (ip) with VCD (80 mg/kg) had been observed in preliminary experiments. Therefore, a study was conducted to determine the time of the onset of this follicular destruction by examination of follicular DNA integrity. Female Fischer 344 rats were dosed daily (80 mg/kg, i.p.) for 6, 8, 10, 12, or 14 days, and ovaries were removed 1, 4, or 24 hr after the final dose. Small pre-antral follicles (25-100 microns) were isolated by gentle dissociation of ovaries with collagenase, and follicles were sorted with micropipets. Genomic DNA was isolated from follicles and radiolabeled with [32P]dideoxy ATP, and the degree of fragmentation quantified by agarose gel electrophoresis and autoradiography. Degradation of DNA was evaluated by 32P content in low-molecular-weight fragments ( < 4 kilobase pairs). Degradation of DNA was not observed in follicles collected 24 hr after the final dose on any day. However, a random pattern of DNA degradation was observed, and was significantly greater (p < 0.05) compared with controls, when follicles were collected 4 hr following VCD administration on Days 10 and 12, but not on Days 6 or 8, of dosing. Although not significant, there was also evidence of DNA degradation in dosed animals on Day 14. Histological evaluation of small pre-antral follicles in ovarian sections during the early stages of VCD-induced DNA degradation (Day 10; 4 hr) demonstrated margination of chromatin along the nuclear membrane in oocytes and disruptions in focal contact between granulosa cells and oocytes, both features indicative of apoptosis. Furthermore, there was no sign of ruptured membranes in granulosa cells or oocytes or of an inflammatory response, characteristics of necrosis (pathological cell death). Whereas biochemical and morphological evidence of follicular destruction was seen 4 hr after dosing on Day 10, numbers of oocyte-containing primordial and primary follicles in VCD-treated animals were not different from controls at that time. These results demonstrate that the initial evidence of impending destruction of small pre-antral follicles is first consistently visualized following 10 days of daily dosing with VCD, although a measurable reduction in oocyte numbers has not yet occurred. Despite the fact that internucleosomal cleavage of genomic DNA was not observed, morphological evaluations support that granulosa cells and oocytes in primordial and primary follicles are destroyed via the induction of apoptosis.

Enhanced expression of bax in small preantral follicles during 4-vinylcyclohexene diepoxide-induced ovotoxicity in the rat.

4-Vinylcyclohexene diepoxide (VCD) destroys small preantral (25-100 microns) ovarian follicles after repeated dosing in mice and rats. A previous study determined this follicular destruction is via apoptosis (physiological cell death). The purposes of this study were to examine the effects of VCD on amounts of mRNA for several genes that might be involved in this ovotoxic response and to determine the specificity of this response for small preantral follicles. The genes of interest were bax, a cell death gene; three forms of the antioxidant enzyme, superoxide dismutase (mitochondrial manganese-containing or MnSOD, cytosolic copper/zinc-containing or Cu/ZnSOD, and secreted or secSOD); and microsomal epoxide hydrolase (mEH), involved in detoxification of VCD. Female Fischer 344 rats were administered daily doses (10 days) of vehicle control (sesame oil) or VCD (80 mg/kg, ip). Four hours after the last injection, livers and ovaries were removed. Small (25-100 microns) and large (100-250 microns) preantral follicles were separated from the ovaries by gentle dissociation and collected by mouth pipeting. Total RNA was extracted from all tissues, reverse transcribed into first-strand cDNA, and amplified by polymerase chain reaction using oligonucleotide primers specific for each gene. Relative levels of mRNA were visualized by agarose gel electrophoresis and autoradiography and quantified by densitometric analysis. Coamplification of ribosomal protein L19 (constitutively expressed in ovarian tissue) was used for normalization in each sample. Increased levels of mRNA for bax (172 +/- 20% of control, p < 0.05), MnSOD (248 +/- 70% of control, p < 0.05), and mEH (352 +/- 120% of control, p < 0.05) were measured in 25- to 100-microns follicles collected from VCD-treated compared with control rats. Unlike 25- to 100-microns follicles (the targets of ovotoxicity), in 100- to 250-microns follicles (nontargets) there were no changes (p > 0.05) in mRNA levels for bax or MnSOD in VCD-treated rats; however, mRNA levels for mEH were significantly decreased (79 +/- 4% of control, p < 0.05), compared with control. No changes in levels of mRNA for mEH were observed in liver from VCD-treated rats relative to control. Additionally, in liver VCD caused a significant decrease in mRNA levels for bax (31 +/- 5% of control, p < 0.05) and Cu-ZnSOD (56 +/- 17% of control, p < 0.05). In summary, dosing of rats with VCD enhanced expression of mRNA encoding several genes that might respond during the induction of ovotoxicity. The selective increase in bax in the population of follicles destroyed by repeated dosing with VCD may reflect their susceptibility to apoptosis.

Follicular mechanisms associated with 4-vinylcyclohexene diepoxide-induced ovotoxicity in rats.

The mechanism of 4-vinylcyclohexene diepoxide (VCD)-induced oocyte destruction in small preantral follicles of rats and mice has not been elucidated. This study examined the effects of daily dosing of female rats with VCD on protein synthesis and follicle viability. An investigation of granulosa cells as a target for VCD was also made. Small preantral follicles (25 to 100 microns) isolated from untreated immature rats (day 28) as well as from rats injected daily for 10 d with VCD (0.57 mmol/kg, IP) or vehicle control (sesame oil) were incubated for 3, 6, or 10 h in vitro with or without VCD. Viability (trypan blue dye exclusion) or protein synthesis (3H-leucine incorporation) in follicles was measured. Large preantral follicles (100 to 250 microns), isolated oocytes or granulosa cells from small preantral follicles, hepatocytes, and adrenal cells served as controls. Viability was not compromised in small follicles isolated from untreated or VCD-injected rats. However, following in vitro incubation of small preantral follicles with VCD, there was a significant decrease in viability by 6 h. This loss in viability was observed in granulosa cells and was even greater in follicles from dosed as compared with undosed animals. The various cell types were incubated in vitro with or without VCD for 3 h and the rate of protein synthesis was measured by 3H-leucine incorporation during the last hour of incubation. Incubation of small preantral follicles from untreated animals with VCD for 3 h produced significant inhibition in the rate of protein synthesis. This effect was reversed and significantly stimulated after 6 and 10 h of incubation with VCD. Follicles from animals that had been dosed daily with VCD for 10 d demonstrated similar inhibition of protein synthesis following 3 h in vitro incubation with VCD; however, unlike those from undosed rats, follicles from dosed rats did not recover from this inhibition after 6 or 10 h of in vitro incubation with VCD. In vitro incubation with VCD stimulated the rate of protein synthesis in large preantral follicles; however, no effect on the rate of protein synthesis was observed in isolated oocytes and granulosa cells, hepatocytes, or adrenal cells. These observations suggest that VCD affects follicular viability via an effect on granulosa cells and that daily dosing of rats with VCD makes small preantral follicles more susceptible to ovotoxicity by VCD.