Biomedical subjects

J M Larner

Publications and source records attributed to J M Larner.

At least 19 recordsLinked to original sources

PubMed2001

Disruption of spermatogenesis and Sertoli cell structure and function by the indenopyridine CDB-4022 in rats.

The present studies were undertaken to determine the testicular cell type(s) affected by the antispermatogenic indenopyridine CDB-4022. At the oral threshold dose (2.5 mg/kg), CDB-4022 induced infertility in all males. CDB-4022 did not alter (P > 0.05) Leydig cell function as assessed by circulating testosterone, seminal vesicle, and ventral prostate weights or body weight gain compared to controls. Conversely, CDB-4022 reduced (P < 0.05) testicular weight, spermatid head counts, and percentage of seminiferous tubules undergoing spermatogenesis. In a second study, adult male rats received a maximally effective oral dose of CDB-4022 (12.5 mg/kg), dipentylphthalate (DPP; 2200 mg/kg; a Sertoli cell toxicant), or vehicle and were necropsied 3, 6, or 12 h after dosing to determine acute effects. Serum inhibin B levels were suppressed (P < 0.05) by 6 h after CDB-4022 or DPP treatment, but epididymal androgen-binding protein (ABP) levels were not altered (P > 0.05), compared to controls. CDB-4022 and DPP increased (P < 0.05) the percentage of tubules with apoptotic germ cells, particularly differentiating spermatogonia and spermatocytes, by 12 h after dosing. Microscopic examination of the testis indicated a greater degree of vacuolation in Sertoli cells and initial signs of apical germ cell sloughing/shedding by 3 or 12 h after CDB-4022 or DPP treatment, respectively. In a third study, prepubertal male rats were treated with vehicle, 12.5 mg/kg of CDB-4022, or 2200 mg/kg of DPP, and the efferent ducts of the right testis were ligated 23 h before necropsy. Seminiferous tubule fluid secretion (difference in weight of testes), serum inhibin B levels, and ABP levels in the unligated epididymis were reduced (P < 0.05) at 24 and 48 h after dosing in CDB-4022- and DPP-treated rats compared to controls. Collectively, these data suggest that CDB-4022 disrupts spermatogenesis by inducing apoptosis in early stage germ cells via a direct action on the Sertoli cell.

Androgen-Binding Protein↗

PubMed2000

Histone H1 and H3 dephosphorylation are differentially regulated by radiation-induced signal transduction pathways.

We recently demonstrated that linker histone H1, which is thought to have a fundamental role in higher-order chromatin structure, becomes transiently dephosphorylated after ionizing radiation (IR) in a mutated ataxia telangiectasia (ATM) dependent manner. To establish whether H1 dephosphorylation was a component of a damage-response pathway that included dephosphorylation of other histones, we asked whether H3 was dephosphorylated in response to IR in a manner similar to H1. H1 and H3 are maximally phosphorylated in metaphase and both are dephosphorylated after IR. However, the duration of IR-induced H3 dephosphorylation is significantly longer than that of IR-induced H1 dephosphorylation. Moreover, H1 dephosphorylation is ATM-dependent, whereas H3 dephosphorylation is ATM-independent. These observations suggest that the damage-sensing pathways regulating H3 and H1 dephosphorylation diverge upstream of ATM.

Animals↗

PubMed2000

Circulating concentrations of the antiprogestins CDB-2914 and mifepristone in the female rhesus monkey following various routes of administration.

The overall aim of these studies was to investigate the oral and i.m. bioavailability of CDB-2914 in intact female rhesus monkeys, and to compare the serum concentrations of CDB-2914 with that of mifepristone following oral administration. In the first study, a 50 mg bolus of CDB-2914 per monkey was administered intravenously, orally or intramuscularly. The area under the serum concentration-time curve for 72 h (AUC(0-72)) following i.v. injection was 18 320 +/- 2718 ng/ml*h, and that for oral administration was 10 464 +/- 3248 ng/ml*h. Thus, the oral bioavailability of CDB-2914 equivalents was 56%. The AUC(0-168 h) following i.m. injection was 11 226 +/- 1130 ng/ml*h. Therefore, the i.m. bioavailability of CDB-2914 equivalents was 62%. In the second study, the serum concentrations of CDB-2914 and mifepristone equivalents were compared following an oral bolus dose in two different formulations. When administered at 5 mg/kg in aqueous suspending vehicle (ASV), the mean peak serum concentration (C(max)) of CDB-2914 equivalents (192 +/- 64 ng/ml) occurred at 5 +/- 1 h, whereas the C(max) of mifepristone equivalents (82 +/- 25 ng/ml) occurred at 3 +/- 1 h. Following administration in gelatin capsules (35 mg/monkey), the C(max) of CDB-2914 equivalents (129 +/- 24 ng/ml) occurred at 5 +/- 1 h, while the C(max) of mifepristone equivalents (31 +/- 8 ng/ml) occurred at 3 +/- 1 h. The serum concentration (AUC(0-120 h)) of CDB-2914 equivalents was 4.7- or 5. 3-fold greater than that of mifepristone equivalents when administered orally in ASV or gelatin capsules respectively. The serum protein binding characteristics of CDB-2914 were also studied. CDB-2914 bound to human alpha(1)-acid glycoprotein (AAG), but not with as high an affinity as mifepristone. In contrast, neither CDB-2914 nor mifepristone bound with high affinity to AAG, corticosteroid binding globulin or sex hormone binding globulin in monkey serum. Collectively, these results indicated that CDB-2914 was more efficiently absorbed than mifepristone following oral administration to female rhesus monkeys.

Administration, Oral↗

PubMed1999

Histone H1 dephosphorylation is mediated through a radiation-induced signal transduction pathway dependent on ATM.

Ionizing radiation is known to activate multiple signal transduction pathways, but the targets of these pathways are poorly understood. Phosphorylation of histone H1 is thought to have a role in chromatin condensation/decondensation, and we asked whether ionizing radiation (IR) would alter H1 phosphorylation. Our data demonstrate that low doses of IR result in a dramatic, but transient, dephosphorylation of H1 isoforms. The in vivo IR-induced dephosphorylation of H1 is completely blocked by wortmannin and is abrogated in ataxia telangiectasia cells. Furthermore, we measured radiation-induced inhibition of cyclin dependent kinase activity and activation of histone H1 phosphatase activity. Both activities were affected by radiation-induced signals in an ATM-dependent manner. Thus, the rapid IR-induced dephosphorylation of H1 involves a pathway including ATM and a wortmannin-sensitive step leading to both inhibition of cyclin-dependent kinase activities as well as activation of H1 phosphatase(s).

Androstadienes↗

PubMed1999

Radiation down-regulates replication origin activity throughout the S phase in mammalian cells.

An asynchronous culture of mammalian cells responds acutely to ionizing radiation by inhibiting the overall rate of DNA replication by approximately 50% for a period of several hours, presumably to allow time to repair DNA damage. At low and moderate doses, this S phase damage-sensing (SDS) pathway appears to function primarily at the level of individual origins of replication, with only a modest inhibition of chain elongation per se. We have shown previously that the majority of the inhibition observed in an asynchronous culture can be accounted for by late G1cells that were within 2-3 h of entering the S period at the time of irradiation and which then fail to do so. A much smaller effect was observed on the overall rate of replication in cells that had already entered the S phase. This raised the question whether origins of replication that are activated within S phase per se are inhibited in response to ionizing radiation. Here we have used a two-dimensional gel replicon mapping strategy to show that cells with an intact SDS pathway completely down-regulate initiation in both early- and late-firing rDNA origins in human cells. We also show that initiation in mid- or late-firing rDNA origins is not inhibited in cells from patients with ataxia telangiectasia, confirming the suggestion that these individuals lack the SDS pathway.

Animals↗

PubMed1999

Third ventricular lesion masquerading as suprasellar disease.

We discuss the case of a patient who presented with a bitemporal visual field disturbance thought to arise from chiasmatic compression secondary to a suprasellar mass. The patient was ultimately diagnosed with medulloblastoma with diffuse intraventricular disease. Careful review of magnetic resonance (MR) findings in this case demonstrate the apparent suprasellar mass to be within the suprachiasmatic recess of the third ventricle. The role of MR imaging in distinguishing between suprasellar disease involving the third ventricle and primary third ventricular lesions is discussed.

Adult↗

PubMed1999

The radiation-induced S-phase checkpoint is independent of CDKN1A.

We recently demonstrated that, in response to radiation, replication is down-regulated at the level of individual origins throughout S phase of the cell cycle. Since several in vitro studies demonstrate that CDKN1A (formerly known as p21) down-regulates replication by inhibiting PCNA, and since CDKN1A can retard progression of cells through S phase in vivo, the question arises whether CDKN1A is involved in the S-phase damage-sensing pathway. In the present study we analyzed the effect of ionizing radiation on CDKN1A+/+ and CDKN1A-/- cells derived from the HCT 116 cell line. Neither progression of cells through S phase nor survival after exposure to ionizing radiation is influenced by CDKN1A status in either synchronous or asynchronous cells. These results establish that CDKN1A is not necessary for the acute S-phase damage-sensing pathway that functions to prevent firing of replication origins during S phase.

Cells, Cultured↗

PubMed1998

Effects of two progestin-only contraceptives, Depo-Provera and Norplant-II, on the vaginal epithelium of rhesus monkeys.

The objective of this study was to determine whether progestin-only contraceptives induce thinning of the vaginal epithelium in nonhuman primates. Eight intact rhesus monkeys (four per group) were treated with either a single intramuscular injection of 30 mg of Depo-Provera or a subcutaneous insertion of Norplant-II (2 x 75 mg rods; day 0). Norplant-II rods were removed 90 days after insertion. Vaginal biopsies were obtained during a pretreatment menstrual cycle and following treatment on days 10, 30, 60, 118, and 146. Formalin-fixed vaginal biopsies were evaluated for epithelial thickness and the degree of keratinization. The circulating levels of estradiol, progesterone, medroxyprogesterone acetate (MPA), or levonorgestrel (LNG) were monitored throughout the study by specific radioimmunoassays. Circulating levels of estradiol and progesterone confirmed the stage of the menstrual cycle in which pretreatment biopsies were obtained. Following treatment with Depo-Provera, serum levels of MPA increased to 2.3 +/- 0.6 ng/ml (x +/- SE, n = 4) within 24 hr. Serum levels of MPA were maximal on day 14 (5.5 +/- 0.9 ng/ml), dropped below 1 ng/ml by day 50, and were nondetectable by day 70. Circulating levels of LNG were elevated 24 hr after insertion of Norplant-II (5.8 +/- 3.0 ng/ml), peaked on day 2 (7.6 +/- 4.2 ng/ml), remained between 1.4 and 6.2 ng/ml from days 14 to 90, and were nondetectable by day 118, the first serum sample after removal of Norplant-II. There were no significant differences (p > 0.05) in the epithelial thickness (microm), number of epithelial cell layers, or type of epithelium present in vaginal biopsies obtained during the follicular or luteal phases of the pretreatment menstrual cycle. Conversely, a pronounced effect of progestin treatment was observed on the vaginal epithelium. There were no significant differences (p > 0.05) between the two progestin treatment groups, but a significant effect (p < 0.05) over time was observed (two-way ANOVA). Compared with pretreatment menstrual cycle controls, the vaginal epithelial thickness was decreased (p < 0.05) by day 30 or 60 following Norplant-II insertion or Depo-Provera injection, respectively. The number of epithelial cell layers was also decreased (p < 0.05) on days 30 and/or 60 in progestin-treated monkeys compared with pretreatment control cycles. Following removal of Norplant-II or metabolic excretion of MPA, the vaginal epithellium regenerated and the thickness was no longer different (p > 0.05) from the pretreatment control cycle. These data demonstrate that progestin-only contraceptives induced thinning of the vaginal epithelium in rhesus monkeys, and this effect was rapidly reversible following physical or metabolic removal of the progestin.

Animals↗

PubMed1997

A p53-independent damage-sensing mechanism that functions as a checkpoint at the G1/S transition in Chinese hamster ovary cells.

In response to a moderate dose of radiation, asynchronous mammalian cell populations rapidly and transiently down-regulate the rate of DNA synthesis to approximately 50% of preirradiation values. We show here that only half of the reduction in overall replication rate can be accounted for by direct inhibition of initiation at origins in S-phase cells. The other half results from the operation of a newly defined cell cycle checkpoint that functions at the G1/S transition. This checkpoint senses damage incurred at any time during the last 2 hr of G1 and effectively prevents entry into the S period. The G1/S and S-phase checkpoints are both p53-independent and, unlike the p53-mediated G1 checkpoint, respond rapidly to radiation, suggesting that they may represent major damage-sensing mechanisms connecting the replication machinery with DNA repair pathways.

Animals↗

PubMed1997

Cloning and characterization of Chinese hamster p53 cDNA.

We have cloned and sequenced Chinese hamster p53 cDNA and have compared the p53 sequence in different Chinese hamster cell lines to several relevant phenotypes. Our results indicate that a mutation in CHO cells that changes Thr211 to Lys211 abrogates the ability to arrest in G1 and apparently renders cells capable of amplifying DNA. However, this mutation has no effect on the G2 checkpoint or on acute down-regulation of DNA replication after a radiation challenge.

Amino Acid Sequence↗

PubMed1997

S phase damage sensing checkpoints in mammalian cells.

Mammalian cells have evolved multiple responses for dealing with DNA damage. One response is to acutely downregulate DNA synthesis at the initiation step. Essentially nothing is known about the initial signal that activates this SDS pathway or the macromolecules involved in transducing the signal into the final inhibitory step at origins. Determining whether any radiation induced changes in known proteins involved in cell cycle regulation or in other signal transduction pathways are primary or secondary responses to DNA damage constitutes a major challenge to identifying members of the pathway. It may turn out to be easier to identify the final mediator in the pathway, namely the protein(s) whose interaction with origins is ultimately affected by radiation. Hopefully, mutations in SDS genes in genetically tractable systems such as S cerevisiae or Schizosaccharomyces pombe will allow the identification of homologous genes in mammals. Most tumour cells are TP53 negative, and yet it is not clear that TP53 status influences radiation sensitivity. The SDS pathway may therefore represent an important protective mechanism that stands in the way of effective tumour cell killing by radiation therapy. It is hoped that an understanding of this pathway will provide opportunities for developing novel antineoplastic targets and/or radiation sensitizers.

Animals↗

PubMed1995

A phase 1-2 trial of superselective carboplatin, low-dose infusional 5-fluorouracil and concurrent radiation for high-grade gliomas.

Recent trials have suggested that low-dose infusional 5-FU is more efficacious when given during radiotherapy than is bolus 5-FU. Additionally, intra-arterial cisplatin for brain tumors has been shown to be associated with both high response rates as well as significant toxicity. A dose escalation study was therefore performed using superselective carboplatin, a cisplatin analogue with a favorable CNS toxicity profile in combination with 6 weeks of infusional 5-FU at 225 mg/m2 and concurrent radiotherapy. Eight patients were treated at the starting dose of 200 mg/m2 carboplatin and 11 patients were treated at 300 mg/m2. No toxicity was observed that was attributable to infusional 5-FU. However, two ischemic events related to the superselective delivery of carboplatin were observed, and one patient was noted to have asymptomatic retinal toxicity from the carboplatin. Of 19 patients, 5 had objective responses with 25% or greater reduction in tumor volumes. Continuous infusional 5-FU can be given in combination with partial brain radiotherapy without significant toxicity. Superselective carboplatin delivery is associated with a low incidence of stroke, but no significant retinal toxicity.

Adult↗

PubMed1995

Desmoplastic fibroma: a role for radiotherapy?

Desmoplastic fibroma is a rare, locally aggressive, benign tumor that is considered the skeletal counterpart of the desmoid tumor of soft tissues. Although the treatment of choice of desmoplastic fibroma is surgical excision, radiation therapy should be considered when surgery is not a viable option.

Adult↗

PubMed1994

Esthesioneuroblastoma. Long-term outcome and patterns of failure--the University of Virginia experience.

BACKGROUND: Esthesioneuroblastoma is a rare tumor arising from olfactory epithelium. This retrospective review analyzed the patterns of failure and long term outcome of patients with esthesioneuroblastoma evaluated at a single institution. METHODS: Forty patients with esthesioneuroblastoma were evaluated at the University of Virginia, with a median follow-up of 130 months. In most cases, treatment consisted of combined-modality therapy, including radiotherapy and surgery for Stages A and B disease and the addition of chemotherapy for Stage C disease. Fifteen patients received chemotherapy that included cyclophosphamide plus vincristine. Thirty-eight patients received radiotherapy, with a median dose of 50 Gy. Initial surgery for 23 patients included craniofacial resection, whereas the remainder had less extensive surgery (3 had no initial surgery). Five patients were salvaged with high dose chemotherapy and autologous bone marrow transplantation (CTX/BMT). RESULTS: Actuarial survivals at 5, 10, and 15 years are 78%, 71%, and 65% respectively. Fifty-five percent of patients failed therapy, and 68% of the failures were locoregional. Thirty-nine percent of recurrences occurred later than 5 years from diagnosis. Three of the five patients were successfully salvaged with CTX/BMT compared with four of seventeen patients who underwent conventional salvage therapy. CONCLUSIONS: Esthesioneuroblastoma is associated with long term survival and late recurrences. Multimodality therapy should be used initially. Durable remissions of failures can be achieved with CTX/BMT:

Adolescent↗

PubMed1994

Radiation effects on DNA synthesis in a defined chromosomal replicon.

It has recently been shown that the tumor suppressor p53 mediates a signal transduction pathway that responds to DNA damage by arresting cells in the late G1 period of the cell cycle. However, the operation of this pathway alone cannot explain the 50% reduction in the rate of DNA synthesis that occurs within 30 min of irradiation of an asynchronous cell population. We are using the amplified dihydrofolate reductase (DHFR) domain in the methotrexate-resistant CHO cell line, CHOC 400, as a model replicon in which to study this acute radiation effect. We first show that the CHOC 400 cell line retains the classical acute-phase response but does not display the late G1 arrest that characterizes the p53-mediated checkpoint. Using a two-dimensional gel replicon-mapping method, we then show that when asynchronous cultures are irradiated with 900 cGy, initiation in the DHFR locus is completely inhibited within 30 min and does not resume for 3 to 4 h. Since initiation in this locus occurs throughout the first 2 h of the S period, this result implies the existence of a p53-independent S-phase damage-sensing pathway that functions at the level of individual origins. Results obtained with the replication inhibitor mimosine define a position near the G1/S boundary beyond which cells are unable to prevent initiation at early-firing origins in response to irradiation. This is the first direct demonstration at a defined chromosomal origin that radiation quantitatively down-regulates initiation.

Animals↗

PubMed1993

The isolation and characterization of estradiol-fatty acid esters in human ovarian follicular fluid. Identification of an endogenous long-lived and potent family of estrogens.

The estradiol-fatty acid esters are highly potent and long-lived estrogens that were first isolated and identified from in vitro biosynthetic experiments (Mellon-Nussbaum S., Ponticorvo, L., Schatz, F., and Hochberg, R. B. (1982) J. Biol. Chem. 257, 5678-5684). Other studies have indicated that these esters exist endogenously, but the evidence is indirect, resting solely on the presence of a nonpolar saponifiable metabolite. Although there are similar reports of other naturally occurring fatty acid esters of biologically active steroid hormones, likewise, none has been isolated and characterized. In this study we have found that follicular fluid from the ovaries of women stimulated with gonadotrophins contains relatively large amounts of a nonpolar saponifiable derivative of estradiol (approximately 10(-7)M), which we presumed to be fatty acid esters. Using a combination of chromatographic techniques we isolated these estradiol metabolites and identified them by mass spectral analysis. They are a mixture of five different estradiol-17 fatty acid esters. The amount of each present was determined by separating the esters by reversed phase high performance liquid chromatography and then quantifying each peak by radioimmunoassay and UV absorption. The esters of estradiol are predominantly unsaturated, with linoleate the most abundant comprising 43% of the total. The other esters are: palmitate (20%), arachidonate (19%), oleate (14%), and stearate (4%). Thus these studies conclusively demonstrate the existence of these unusually powerful estrogens.

Arachidonic Acid↗

PubMed1993

The dosimetric consequences of weighted fields using the same isocenter in radiosurgery.

One handicap in achieving ideal dosimetry with the Gamma Knife is the limited number of standard collimator sizes (4, 8, 14 and 18 mm). We report an approach that makes possible the creation of 50% or higher isodose lines, corresponding to collimator sizes from 4 to 18 mm. This technique, which uses the same icocenter, but with different sized and weighted collimators, improves matching for given isodose lines to the diameter of the lesion in a defined plane. However, when combination fields, designed to reproduce the 50% isodose diameter of the 8- and 14-mm collimators, are compared to the standard sizes, there are significant differences in the three-dimensional dosimetry.

Brain Neoplasms↗

PubMed1993

Extracranial absorbed doses with Gamma Knife radiosurgery.

Radiosurgery is used with increasing frequency, not only for the treatment of cerebral arteriovenous malformations (AVMs), but also for the treatment of other well-defined lesions including acoustic neuromas, meningiomas, pituitary adenomas as well as solitary metastases. Although investigators have addressed dosimetric aspects of stereotactic radiosurgery in terms of target volume, little if any attention has been focused on the absorbed doses received at extracranial sites. Therefore, absorbed doses to the eye, thyroid, sternum and gonads were measured in 111 patients (100 adults and 11 children) using thermoluminescent dosimetry (TLDs). For the 100 adults, the average maximum target absorbed dose was 35 +/- 8 Gy. The measured absorbed dose in selected organs of adults from Gamma Knife radiosurgery using one or more isocenters was 9 +/- 8 cGy for the eye, 15 +/- 7 cGy for the thyroid, 20 +/- 10 cGy for the sternum and 3 +/- 2 cGy for the gonads. The absorbed doses received by the children (13 years and younger) was similar with the exception of a marked increase in gonadal dose. The use of multiple isocenters is associated with higher absorbed doses to extracranial sites.

Adolescent↗