The p53-regulated cyclin G gene promotes cell growth: p53 downstream effectors cyclin G and Gadd45 exert different effects on cisplatin chemosensitivity

Among the p53-regulated genes that have been identified thus far, cyclin G is a relatively recent one. We conducted a series of experiments aimed at elucidating cyclin G function. Ectopic overexpression of cyclin G in human RKO colon carcinoma cells accelerated cell growth. Transfection of normal human fibroblasts with the cyclin G expression vector promoted clonal expansion. Cyclin G immune complexes isolated from the transfected cells exhibited appreciable levels of cyclin-dependent kinase activity, as evidenced using histone H1 as a substrate. The retinoblastoma protein, pRb, was detectable in cyclin G immune complexes, raising the possibility that Rb may be one mediator of cyclin G action. Cyclin G-overexpressing cells were more sensitive to cisplatin cytotoxicity than the parent cells, probably because cyclin G overexpression overrides cell cycle checkpoint(s). Overexpression of another p53-regulated gene, GADD45, by contrast, protected cells from cisplatin killing. These findings suggest that different downstream effectors of the p53 pathway may exert different effects on cellular survival after treatment with cancer chemotherapy drugs such as cisplatin.

Necrosis of the substantia nigra, pars reticulate, in flurothyl-induced status epilepticus is ameliorated by the spin trap alpha phenyl-N-tert-butyl nitrone

The objective of the present study was to explore whether a diffusible free radical scavenger can ameliorate the pan-neurotic lesions of the substantia nigra, pars reticulate (SNPR), which are incurred in rats subjected to status epilepticus of more than 30 min duration. Vehicle-injected animals had flurothyl seizures induced for 45 min. The seizures were then terminated and the animals were recovered for 7 d to allow histopathological evaluation of the SNPR lesions. Drug-treated animals, which were otherwise treated identically, were given either 100-800 mg/ kg of dimethylthiourea (DMTU), a diffusible hydroxyl ion scavenger, or the diffusible spin trap alpha-phenyl N-tert-butyl nitrone (PBN) in a dose of 100 mg/kg i.p.. All animals given DMTU died 2 to 8 h after status epilepticus, but PBN was tolerated well by the animals. The amount of flurothyl required to sustain the electrographic seizures was identical in the vehicle- and drug-injected groups, demonstrating that PBN did not suppress seizure activity. Vehicle-injected animals had large bilateral infarcts localized to the SNPR. Of the six animals treated with PBN, one had a small, unilateral lesions, and in all other animals the SNPR had a normal histological appearance. The results strongly suggest that the pan-necrotic lesions of the SNPR incurred during ongoing seizure activity represent a free radical-mediated lesion.

Gas chromatographic/mass spectrometric detection of narcotine, papaverine, and thebaine in seeds of Papaver somniferum

In addition to codeine and morphine, three more compounds: narcotine (noscapine), papaverine, and thebaine were found in Indian and Netherlands poppy seeds (Papaver somniferum L). The compounds were detected by a GC/MS technique and the identities were confirmed by comparing retention times and ion ratios with the known references. The concentrations of codeine, morphine, thebaine, papaverine, and narcotine were 44, 167, 41, 67, and 230 micrograms/g in Indian poppy seeds, and were 1.8, 39, 1.0, 0.17, 0.84 micrograms/g in Netherlands poppy seeds, respectively. Because these compounds may be urinary products after poppy seed consumption, the lowest detectable concentrations of codeine, morphine, thebaine, papaverine, and narcotine in urine are of interest and were found to be 4, 4, 5, 0.4, and 4 ng/ml, respectively. The detection of urinary narcotine, papaverine, or thebaine may be utilized to differentiate poppy seed consumption from illicit codeine, morphine, or heroin use.

Antisense GADD45 expression results in decreased DNA repair and sensitizes cells to u.v.-irradiation or cisplatin

Loss of p53 function in cancer cells commonly results in a condition of genomic instability. This is believed to emanate from a loss of the G1 checkpoint response to DNA damage. While the role of p53 in the induction of a G1 arrest is well-accepted, additional p53 functions are being discovered. Cell cycle checkpoints presumably function to allow additional time for DNA repair after damage is incurred, however, genetic studies in yeast suggest that components of the checkpoint pathway may also be involved in DNA lesion processing (Lydall and Weinert, 1995). Recent evidence suggests that this may also be the case for p53, as suggested by numerous reports linking p53 function to DNA repair. Thus, loss of p53 function might contribute to genomic instability independent of G1-arrest. In the present study, we explored the effect of p53 disruption and consequences of antisense GADD45 expression on the DNA repair capacity of human colon carcinoma RKO cells. DNA repair was assayed using host-cell reactivation of u.v.-damaged reporter plasmids and unscheduled DNA synthesis experiments in transiently-transfected cells. We show that a number of transfected genes that suppress p53 function reduce the ability of cells to repair u.v.-induced DNA damage. Moreover, cells in which expression of the p53-regulated gene GADD45 was blocked by antisense vectors, also showed altered levels of DNA repair. Blocking Gadd45 expression by constitutive antisense expression sensitized cells to killing by u.v.-radiation or by cis-platinum (II) diamine-dichloride (CDDP, or cisplatin), a cancer chemotherapy drug which produces DNA cross-links. These findings suggest the involvement of downstream effectors of the p53 pathway in the coordination of cell cycle arrest and DNA repair.

MDA-MDMA concentrations in urine specimens

Urine specimens collected from active-duty U.S. Army personnel were submitted for analysis to the Tripler Army Medical Center, Forensic Toxicology Drug Testing Laboratory as part of the random drug testing program. During an 18-month drug-screening period, 34 specimens tested positive for amphetamines with the Roche Abuscreen Radioimmunoassay for Methamphetamine (High Specificity); based on gas chromatographic-mass spectrometric (GC-MS) analysis, the presence of 3,4-methylenedioxymethamphetamine (MDMA) was suspected. These samples were subsequently submitted to the Division of Forensic Toxicology, Office of the Armed Forces Medical Examiner, Armed Forces Institute of Pathology for further testing. All 34 samples screened positive using both the Abbott TDx Amphetamine/ Methamphetamine II assay and the Amphetamine class assay. Confirmation and quantitation by GC-MS revealed the presence of both MDMA and 3,4-methylenedioxyamphetamine (MDA) in all samples. The MDMA concentrations ranged from 0.38 to 96.2 mg/L (mean, 13.4 mg/L) and the MDA concentrations ranged from 0.15 to 8.6 mg/L (mean, 1.6 mg/L). The mean ratio of MDA, the N-demethylation metabolite of MDMA, to MDMA was 0.15, similar to the ratio of amphetamine, the N-demethylation metabolite of methamphetamine, to methamphetamine of 0.10. The presence of MDA in urine specimens at a concentration approximately 10-15% that of the MDMA present is consistent with MDMA metabolism, which may be indicative of the use of MDMA only, as compared with the combined use of both drugs.

One-step esterification of benzoylecgonine with dimethylformamide-dipropylacetal or dimethylformamide-diisopropylacetal in the presence of pyridine

A simple procedure was developed to derivatize benzoylecgonine extracted from urine for subsequent confirmation by gas chromatography-mass spectrometry. The compound was esterified with dimethylformamide-dipropylacetal (DMF-DPA) or dimethylformamide-diisopropylacetal (DMF-DIPA) to the corresponding propyl and isopropyl esters. The optimum reaction condition was found to be heating the reaction mixture in the presence of pyridine at 100 degrees C for 30 min. The procedure is a one-step esterification followed by evaporation of excess reagents. When benzoylecgonine was extracted from urine using a solid-phase extraction technique and derivatized with this procedure, the compound was detected at a level as low as 10 ng/mL. Quantitation was linear over the concentration range 10-8000 ng/mL.

Abrogation of p53 function affects gadd gene responses to DNA base-damaging agents and starvation

The tumor suppressor p53 is required for induction of its downstream effector genes such as GADD45 and CIP1/WAF1 by ionizing radiation (IR). This response is probably mediated through defined p53 binding sites located in the promoter of CIP1/WAF1 and in the third intron of GADD45. In contrast, the gadd gene stress response to base-damaging agents, such as methylmethane sulfonate (MMS) or UV radiation, or medium depletion (starvation) occurs in all mammalian cells examined to date regardless of p53 status for both GADD45 and also GADD153, which is not IR-responsive in many lines with functional p53. These agents strongly induce the p53 protein and raise the possibility that, although p53 is not required for the typical "gadd" response to these agents, p53 may contribute to these non-IR stress responses. This possibility was confirmed by the finding that disruption of p53 function by transfection with dominant-negative vectors expressing HPV E6, mutant p53, or SV40 T Ag reduced the induction of GADD45 and GADD153 as measured by increases in mRNA and protein levels in human lines with wild-type p53. Similarly, induction of these genes by MMS or UV radiation was consistently stronger in the parental mouse embryo fibroblasts compared to cells derived from mice where both p53 alleles had been deleted. Similar qualitative responses were also seen for CIP1/WAF1. In agreement with reduced induction of p53-regulated genes, the G1 checkpoint activated by MMS or UV radiation was markedly abrogated in p53-wt human MCF-7 breast carcinoma cells by E6 expression. Interestingly, induction of reporter constructs driven by the GADD45 or GADD153 promoters was substantially reduced in human cells transfected with mutant p53 or E6 expression vectors or in cells lacking p53 following treatment with MMS, UV radiation, or starvation. Because neither promoter is inducible by IR, and neither contains a strong p53 binding site, these results indicate that p53 has a synergistic or cooperative role in these non-IR stress responses for both GADD45 and GADD153, and that this role is not mediated through identifiable p53-binding sites.

Escape from het-6 incompatibility in Neurospora crassa partial diploids involves preferential deletion within the ectopic segment

Self-incompatible het-6OR/het-6PA partial diploids of Neurospora crassa were selected from a cross involving the translocation strain, T(IIL-->IIIR)AR18, and a normal sequence strain. About 25% of the partial diploids exhibited a marked increase in growth rate after 2 weeks, indicating that "escape" from het-6 incompatibility had occurred. Near isogenic tester strains with different alleles (het-6OR and het-6PA) were constructed and used to determine that 80 of 96 escape strains tested were het-6PA, retaining the het-6 allele found in the normal-sequence LGII position; 16 were het-6OR, retaining the allele in the translocated position. Restriction fragment length polymorphisms in 45 escape strains were examined with probes made from cosmids that spanned the translocated region. Along with electrophoretic analysis of chromosomes from three escape strains, RFLPs showed that escape is associated with deletion of part of one or the other of the duplicated DNA segments. Deletions ranged in size from approximately 70 kbp up to putatively the entire 270-kbp translocated region but always included a 35-kbp region wherein we hypothesize het-6 is located. The deletion spectrum at het-6 thus resembles other cases where mitotic deletions occur such as of tumor suppressor genes and of the hprt gene (coding for hypoxanthine-guanine phosphoribosyl-transferase) in humans.

PDGF AA as mediator in nicotine-dependent carcinogenesis

Effect of nicotine on PDGF AA and PDGF BB interaction with cervical cancer SiHa cells was tested. [125I]PDGF AA was internalized by cells and accumulated in the cytoplasm and nucleus (chromatin). In the absence of nicotine, maximal accumulation of [125I]PDGF AA inside the cells occurred after 1 day of incubation, which was followed by a progressive degradation of the growth factor during the next 2, 3 and 5 days of cell exposure. In the presence or 0.001 or 0.01% nicotine, accumulation of [125I]PDGF AA was slightly higher than in the absence of nicotine, and maximal accumulation occurred after 2 days or incubation. In the presence of 0.1 % nicotine, maximal accumulation occurred after 5 days of incubation and was 20 and 14 times higher in the cytoplasm and chromatin, respectively. Nicotine-postponed degradation and increased nuclear accumulation of PDGF AA resulted in activation of RNA synthesis and cell proliferation. PDGF BB, which was not internalized by cells did not respond to nicotine treatment. The proposed mechanism of nicotine-PDGF AA co-carcinogenesis may involve inhibition of growth factor degradation at the lysosomal level and an increased chromatin accumulation of the non-degraded PDGF.

Valsalva's maneuver revisited: a quantitative method yielding insights into human autonomic control

Seventeen healthy supine subjects performed graded Valsalva maneuvers. In four subjects, transesophageal echographic aortic cross-sectional areas decreased during and increased after straining. During the first seconds of straining, when aortic cross-sectional area was declining and peripheral arterial pressure was rising, peroneal sympathetic muscle neurons were nearly silent. Then, as aortic cross-sectional area and peripheral pressure both declined, sympathetic muscle nerve activity increased, in proportion to the intensity of straining. Poststraining arterial pressure elevations were proportional to preceding increases of sympathetic activity. Sympathetic inhibition after straining persisted much longer than arterial and right atrial pressure elevations. Similarly, R-R intervals changed in parallel with peripheral arterial pressure, until approximately 45 s after the onset of straining, when R-R intervals were greater and arterial pressures were smaller than prestraining levels. Our conclusions are as follows: opposing changes of carotid and aortic baroreceptor inputs reduce sympathetic muscle and increase vagal cardiac motor neuronal firing; parallel changes of barorsensory inputs provoke reciprocal changes of sympathetic and direct changes of vagal firing; and pressure transients lasting only seconds reset arterial pressure-sympathetic and -vagal response relations.

The product of the het-C heterokaryon incompatibility gene of Neurospora crassa has characteristics of a glycine-rich cell wall protein

Filamentous fungi are capable of hyphal fusion, but heterokaryon formation between different isolates is controlled by specific loci termed het loci. Heterokaryotic cells formed between strains of different het genotype are rapidly destroyed or strongly inhibited in their growth. In Neurospora crassa, at least 11 loci, including the mating type locus, affect the capacity to form a heterokaryon between different isolates. In this report, we describe the molecular characterization of the vegetative incompatibility locus, het-C. The het-COR allele was cloned by genetically identifying the het-C locus in a chromosome walk, and the activity of clones containing the het-COR allele was tested in a functional transformation assay. The het-COR allele encodes a 966-amino acid polypeptide with a putative signal peptide, a coiled-coil motif and a C-terminal glycine-rich domain, similar to glycine-rich domains detected in various extracellular and structural cell envelope proteins. Both the coiled-coil and one-third of the glycine-rich carboxyl terminal domains were required for full het-COR activity. Mutants of het-COR were obtained by repeat-induced point mutation (RIP); these mutants were indistinguishable from wild type during vegetative growth and sexual reproduction but displayed dual compatibility with both of two mutually incompatible het-COR and het-cPA strains.

Factor structure of mental health measures

This study investigated the factor structure of 18 scales that measure personal growth, subjective well-being, stress-resistant personality, self-deceptive positivity, and demographics. The sample of 338 persons was drawn from university students and community residents. A principal-components analysis with oblique rotation found a large factor for measures of subjective well-being as well as smaller factors for measures of personal growth, gender and age, and personality integration and education. Results provided support for the hypothesis that subjective well-being and personal growth are related, but not identical, constructs. Implications are discussed.

Characteristics of postischemic seizures in hyperglycemic rats

Normoglycemic animals subjected to 10-20 min of transient ischemia survive without major neurological symptoms, but incur delayed neuronal damage selectively affecting vulnerable neuronal populations. If the animals are hyperglycemic before ischemia is induced, cell damage develops more rapidly, and postischemic seizures appear after a delay of 18-24 h. This study was designed to assess whether the primary insult, i.e., transient ischemia in hyperglycemic animals, triggers early epileptogenic activity which 'matures' into clinical seizures, or if the seizures arise as a result of secondary events occurring after many hours of recirculation. EEG activity during 20-24 h of postischemic recirculation was recorded from electrodes implanted in the neocortex and hippocampus of freely moving rats which had been subjected to 10 min of ischemia under normoglycemic or hyperglycemic conditions. Normoglycemic animals showed a transient postischemic reduction of EEG amplitude and frequency, and sparse and temporary epileptiform activity. In contrast, hyperglycemic animals showed a more pronounced reduction of EEG amplitude and frequency, and early appearing epileptiform activity which was sustained, and ultimately transformed into overt electrographic seizures. The EEG changes were more pronounced in the neocortex than in the hippocampus. The results thus demonstrate that the initial ischemic insult, and not the secondary damage appearing many hours after the initiation of recirculation, triggers epileptiform activity that 'matures' into status epilepticus.

Religious insistence on medical treatment. Christian theology and re-imagination

Families and surrogates sometimes use religious themes to justify their insistence on aggressive end-of-life care. Their hope that "God will work a miracle" can halt negotiations with health care professionals and lead to litigation. The possibility of "re-imagining" religious themes, to broaden their scope and present a wider vision of the Christian tradition, may offer a solution.

Characterization of the GADD45 response to ionizing radiation in WI-L2-NS cells, a p53 mutant cell line

We have previously reported that WI-L2-NS, a human lymphoblastoid cell line, has very high basal levels of GADD45 mRNA and protein in spite of a p53 mutation at amino acid 237. Regardless of the amount of Gadd45 in this cell line, no growth suppression activity was detected. We report here that in WI-L2-NS, the mutated p53 protein adopts predominantly a wild type (wt) conformation and binds to the p53 binding site in the GADD45 third intron. In this cell line, the already high levels of mutated p53 protein can be induced further by ionizing radiation (IR) but the response of the p53 downstream effector genes is altered. Induction of GADD45 and CIP1/WAF1 is reduced compared to p53 wt cell lines but is still substantially higher than the average fold induction obtained from 39 p53 mutant cell lines. Induction of the MDM2 gene was not detected in WI-L2-NS following IR. The induction pattern of the three p53 effector genes by the alkylating agent methylmethane sulfonate (MMS) was also attenuated in WI-L2-NS cells. In TK6 cells, a WI-L2-NS sister cell line having a p53 wt genotype, the induction of the p53 downstream effectors is normal, i.e. induced, both at the protein and the mRNA levels. These results indicate that the DNA binding activity of the mutated p53 protein in WI-L2-NS might be responsible, at least in part, for the high basal levels of GADD45 but can not mediate the full induction of the p53 downstream effector genes. The reason(s) for the inability of Gadd45 to suppress growth in this cell line remains however unknown.

Mammalian DNA damage-inducible genes associated with growth arrest and apoptosis

Mammalian cells are exposed to a wide variety of genotoxic stresses from both endogenous and exogenous sources. Cells typically exhibit cell cycle delays, or checkpoints, in response to acute genotoxic stress. Other types of cellular responses to DNA damage include apoptosis and probably increases in DNA repair levels. These response pathways are altered in cancer cells, by genetic alterations such as overexpression or mutation of oncogenes, or loss of tumor suppressor gene functions. As cancer chemotherapy relies primarily on the selective killing of cancer cells by DNA-damaging agents, genetic alterations affecting cellular stress response pathways may affect the outcome of cancer treatment.

Determination of 207Pb2+ chemical shift tensors from precise powder lineshape analysis

207Pb solid state NMR powder spectra at 296 K are presented for PbSO4, PbMoO4, PbCrO4, PbCO3, PbTiO3, PbZrO3, Pb(NO3)2, Pb(SCN)2, and PbS. Analysis for principal values of the anisotropic chemical shift tensors of the generally very broad spectra included the frequency dependent excitation of the pulse sequence used. Commonly used solid and liquid secondary shift standards for lead were studied with high precision as a function of temperature between 295 K and 315 K to establish a clean 207Pb shift scale. Errors in the existing literature are discussed.

Recall of frequency of occurrence of self-generated and examiner-provided words after frontal or temporal lobectomy

Patients with unilateral excisions from the frontal or temporal lobe and normal control subjects were given two tasks requiring the recall of the frequency of occurrence of words that differed in the number of times they occurred in study lists. In one task, subjects were required to generate words in response to cues, whilst in the other they merely had to read responses that satisfied the cues. All subject groups gave higher frequency estimates to words they had generated than to words they had read. Across both tasks, the frontal-lobe groups (left more so than right) underestimated frequency of occurrence.

Gastro-intestinal protein loss in elderly patients with cardiac cachexia

Undernutrition resulting from chronic congestive heart failure (cardiac cachexia, CC) increases morbidity and mortality particularly in elderly people. The aetiology of CC is thought to be multifactorial. We have assessed the presence of gastro-intestinal protein loss in a group of patients with CC and a group of healthy age-and sex-matched controls. Gastro-intestinal protein loss was measured using the chromic chloride test in 29 patients with CC [mean age 76.1 (SD4.4) years] and 29 healthy controls [mean age 74.9 (SD 4.8) years]. The patients were undernourished in terms of anthropometric measurements compared to controls. The patients had a significantly lower mean ejection fraction [41.5(18.3)% vs. 65.5(2. 2)%] and higher mean pulmonary artery pressure [89.4(19.9)mmHg vs. 19.3(8.1) mmHg]. The recovery of radioactivity in a 5-day stool collection was similar in the two groups [patients vs. controls: 1. 0(0.7)% vs. 0.98(0.6)%, p=0.9]. These values are within the expected normal range. We conclude that gastro-intestinal protein loss is not a significant factor in the production of cardiac cachexia.

Regional brain-derived neurotrophic factor mRNA and protein levels following transient forebrain ischemia in the rat

Levels of BDNF mRNA and protein were measured in the rat brain using in situ hybridization and a two-site enzyme immunoassay. Under basal conditions, the highest BDNF concentration was found in the dentate gyrus (88 ng/g), while the levels in CA3 (50 ng/g), CA1 (18 ng/g) and parietal cortex (8 ng/g) were markedly lower. Following 10 min of forebrain ischemia, BDNF protein increased transiently in the dentate gyrus (to 124% of control at 6 h after the insult) and CA3 region (to 131% of control, at 1 week after the insult). In CA1 and parietal cortex, BDNF protein decreased to 73-75% of control at 24 h. In contrast, BDNF mRNA expression in dentate granule cells and CA3 pyramidal layer was transiently elevated to 287 and 293% of control, respectively, at 2 h, whereas no change was detected in CA1 or neocortex. The regional BDNF protein levels shown here correlate at least partly with regional differences in cellular resistance to ischemic damage, which is consistent with the hypothesis of a neuroprotective role of BDNF.

Fat malabsorption in elderly patients with cardiac cachexia

Malnutrition resulting from chronic congestive heart failure (cardiac cachexia, CC) is not uncommon and contributes to mortality and morbidity especially of elderly people. The aetiology of cardiac cachexia is probably multifactorial. We have assessed whether malabsorption of fat is associated with CC and if so whether it is due to small-bowel bacterial overgrowth. Three groups of subjects were studied: 29 (20 women) patients (mean age 76.1 years) with controlled congestive heart failure and weight loss (CC); 14 (seven women) patients (mean age 74.0 years) with controlled congestive heart failure and no weight loss (non-cachexia, NON-CC); and 29 (20 women) healthy controls (mean age 74.9 years). Fast absorption was quantified using the cumulative 6 h 14CO2 exhalation in the 14C-triolein breath test and small-bowel bacterial overgrowth was quantified using the cumulative 8 h 14CO2 exhalation in the 14C-glycocholic acid breath test. The cumulative 6 h 14CO2 exhalation in the triolein breath test was reduced in the CC group (p = 0.001) implying impaired fat absorption. There was no evidence of small-bowel bacterial overgrowth in any group. Impaired absorption of fat was related to the clinical severity of heart failure and its duration. Impaired fat absorption is associated with cardiac cachexia. It is not due to small-bowel bacterial overgrowth. The aetiology of fat malabsorption in heart failure requires further studies.

Reflex control of sympathetic activity during ventricular tachycardia in dogs: primary role of arterial baroreflexes

BACKGROUND

The determinants of hemodynamic outcome during ventricular tachycardia (VT) are not well understood. In the present study, we addressed the relative contributions of arterial and cardiopulmonary baroreflexes to the sympathetic and arterial pressure responses to VT or ventricular pacing (VP) in dogs with inducible VT.

METHODS AND RESULTS

Responses of renal sympathetic nerve activity (RSNA), pulmonary capillary wedge pressure (PCWP), and mean arterial pressure (MAP) to induced VT or VP (220 to 280 beats per minute) were determined in 12 dogs with a healed anteroapical infarction and inducible VT and in 8 control dogs. The responses were determined with all reflexes intact, after selective denervation of either arterial or cardiopulmonary baroreflexes, and after combined denervation. Differences between intact and denervated conditions were used to assess the relative effects of each baroreflex. In the infarct group, responses during VT were comparable to those during VP. RSNA and PCWP increased significantly (P<.01), whereas MAP decreased significantly (P<.001) during VT or VP with baroreflexes intact in both groups. The increase in RSNA and the recovery of MAP during sustained VP were greater in the infarct group (P<.05); in addition, the increase in PCWP was greater in the infarct group (P<.05). Arterial baroreflex denervation abolished the increased RSNA and recovery of MAP during VP in both groups. After cardiopulmonary baroreflex denervation, the increase in RSNA was augmented in both groups (control group more than infarct group), but recovery of MAP was increased further only in the control group.

CONCLUSIONS

These results suggest that arterial baroreflex mediated sympathoexcitation plays an important role in determining the hemodynamic outcome during VT, whereas cardiopulmonary baroreflexes play only a modest modulatory role.

An abnormality in the p53 pathway following gamma-irradiation in many wild-type p53 human melanoma lines

DNA-damaging agents such as ionizing radiation (IR) activate the tumor suppressor p53, and, in turn, p53 transactivates a number of downstream effector genes such as GADD45, CIP1/WAF1, and MDM2. The induction of these downstream genes following IR appears to be strictly dependent upon the presence of wild-type functional p53 known to evoke G1 arrest. In this study, we characterized 56 cell lines from 9 different tumor types with predetermined p53 genotype by measuring the induction of GADD45, CIP1/WAF1, and MDM2 relative mRNA levels after IR. A higher fraction of melanoma lines had wild-type (wt) p53 (5/8, or 63%) compared to the nonmelanoma lines (11/48, or 23%). Most wt p53 (nonmelanoma) cell lines (11/12, or 92%) showed clear induction of both GADD45 and CIP1/WAF1. On the other hand, many wt p53 melanoma lines (4/5, or 80%) showed normal induction of CIP1/WAF1, but little or no induction of GADD45. Despite this defect in GADD45 induction, we found that all wt p53 melanoma lines exhibited strong G1 arrest and increased levels of p53 protein after IR. The results demonstrated that radiation-induced G1 arrest could occur by the p53-CIP1/WAF1 pathway without appreciable induction of GADD45 in melanoma lines. Time course experiments demonstrated prolonged induced expression of CIP1/WAF1 mRNA transcripts in melanoma lines in which GADD45 induction was lacking, suggesting some sort of compensatory mechanism involving CIP1/WAF1, in cell lines with defective GADD45 induction. We could reproduce this compensatory effect in RKO colon carcinoma cells in which GADD45 expression was blocked by constitutive antisense vectors. These findings reveal that defective induction of GADD45 following IR is common in human melanoma cell lines.

Enalaprilat augments arterial and cardiopulmonary baroreflex control of sympathetic nerve activity in patients with heart failure

OBJECTIVES

This study sought to determine the effects of enalaprilat on reflex control of sympathetic nerve activity.

BACKGROUND

Angiotensin-converting enzyme inhibitors decrease mortality in patients with congestive heart failure. Their efficacy appears to be related importantly to antiadrenergic effects, the mechanism for which has not been determined. Because baroreflexes tonically inhibit sympathetic outflow, and baroreflexes are blunted in heart failure, we hypothesized that these agents reduce sympathetic activity by augmenting baroreflexes.

METHODS

We assessed baroreflex control of sympathetic nerve activity and heart rate in patients with congestive heart failure and in control subjects before and after enalaprilat (0.02 mg/kg body weight intravenously). Arterial baroreflexes were perturbed by bolus administration of sodium nitroprusside and phenylephrine. Cardiopulmonary baroreflexes were perturbed by lower body negative pressure and head-down tilt. Muscle sympathetic nerve activity was recorded by microneurography.

RESULTS

Enalaprilat decreased systolic blood pressure in patients with heart failure and control subjects. Sympathetic nerve activity increased in control subjects but decreased in patients with heart failure after enalaprilat despite reductions in central venous pressure in this group. Baroreflex control of sympathetic nerve activity was unchanged by enalaprilat in control subjects. In patients with heart failure, both arterial and cardiopulmonary baroreflex control of sympathetic nerve activity was enhanced by enalaprilat. Baroreflex control of heart rate was unchanged by enalaprilat in either group.

CONCLUSIONS

Enalaprilat augments both arterial and cardiopulmonary baroreflex control of sympathetic activity in heart failure. These augmented inhibitory influences are associated with a reduction in sympathetic outflow and may contribute to the beneficial effects of angiotensin-converting enzyme inhibitors in heart failure.

Simplified visual preperitoneal access to the space of Retzius for laparoscopic urethrocolpopexy

We developed a simplified method for the preperitoneal access to the space of Retzius under visualization. This extraperitoneal technique was used in 28 patients to perform a laparoscopic Burch procedure.

Mapping translocation breakpoints by orthogonal field agarose-gel electrophoresis

Orthogonal field agarose-gel electrophoresis (OFAGE) of chromosomes from translocation-bearing and normal Neurospora crassa strains was utilized, first, to recover cosmids from a translocated region, and second, to map translocation breakpoints. Surprisingly, the right breakpoints in two independently derived, interstitial translocations, T(II-->III) AR18 and T(II-->VI)P2869, are within about 5.6 kbp of each other suggesting that this region of linkage group (LG) II may be fragile or otherwise subject to chromosome breakage. Mapping translocation breakpoints through OFAGE, or other similar methods, should allow for DNA sequencing across breakpoints that are not associated with mutant phenotypes or that are not within walking distance of cloned markers.

Inhibition of cancer cell growth by internalized immuno-histone conjugates

MAb NS 88 directed against breast cancer cells, which is internalized and translocated to the cell nucleus, was conjugated with histone and labeled with 125I. 125I-MAb-histone complexes (M(r) 250,000) were internalized by breast and cervical cancer cells and localized in the cytoplasm and chromatin. Electrophoretic analysis of the cells extracted from the conjugates revealed the same molecular weights of the cytoplasmic and chromatin complexes as those of the native conjugate. Nicotine (0.1%), which suppresses lysosomal degradation, stabilized the conjugates within the cell and prolonged the presence of nondegraded complexes inside the cytoplasm and chromatin from 1 day to at least 3 days. MAb-histone complexes, but not MAb alone, inhibited RNA synthesis and proliferation of cervical and breast cancer cells. A new application of internalized MAbs as the vehicles for protein inhibitors of transcription or replication is discussed.

Characterization of p21Cip1/Waf1 peptide domains required for cyclin E/Cdk2 and PCNA interaction

The cyclin-dependent kinase inhibitor p21Cip1/Waf1 is responsible for the p53-dependent growth arrest of cells in G1 phase following DNA damage. In the present study we investigated regions of p21 involved in inhibition of the G1/S phase cyclin-dependent kinase, cyclin E/Cdk2, as well as regions of p21 important for binding to this kinase and recombinant PCNA. To perform these studies we synthesized a series of overlapping peptides spanning the entire p21 sequence and used them in in vitro assays with cyclin E/Cdk2-immune complexes and with recombinant p21 and PCNA proteins. One amino-terminal p21 peptide spanning amino acids 15-40, antagonized p21 binding and inhibition of cyclin E/Cdk2 kinase. Antagonism of p21 binding was, however, lost in a similar peptide lacking amino acids 15-20, or in a peptide in which cysteine-18 was substituted for a serine. These results suggest that this peptide region is important for p21 interaction with cyclin E/Cdk2. A second peptide (amino acids 58-77) also antagonized p21-activity, but this peptide did not affect the ability of p21 to interact with cyclin E/Cdk2. A region of p21 larger than 26 amino acids is presumably required for Cdk-inhibition because none of the peptides we tested inhibited cyclin E/Cdk2. We also found that a peptide spanning amino acids 21-45 bound recombinant p21 in ELISA assays, and additional studies revealed a requirement for amino acids 26 through 45 for this interaction. A p21 peptide spanning amino acids 139-164 was found to bind PCNA in a filter binding assay and this peptide suppressed recombinant p21-PCNA interaction. Conformational analysis revealed that peptides spanning amino acids 21-45 and 139-164 tended towards an alpha-helical conformation in trifluoroethanol buffer, indicating that these regions are probably in a coiled conformation in the native protein. Taken together, our results provide an insight into domains of p21 that are involved in cyclin E/Cdk2 and PCNA interaction. Our results also suggest that a potential p21 dimerization domain may lie in the amino-terminus of p21. Continued exploration of these domains could prove useful in assessing p21-mimetic strategies for cancer treatment.

Immunodetection of squamous cell carcinoma-associated variant of nuclear protein

A new monoclonal antibody, MAb C63.3, was developed by immunizing mice with the high molecular weight fraction of the cytoplasmic proteins from the cervical squamous cell carcinoma. In Western blotting, MAb C63.3 reacted with cytoplasmic and chromatin antigens expressed by cervical and vulvar squamous cell carcinomas and much weaker with normal cervical tissue and skin cells. Different molecular variants of C63.3 chromatin antigens were found in normal tissues (heavy variants, M(r) 65,000 and 59,000) compared to squamous cell carcinomas (light variant, M(r) 48,000). Diagnostic value of the cancer-associated M(r) 48,000 antigen is discussed. MAb C63.3 was internalized by cells and bound to the chromatin which suggests that antigen(s) C63.3 might represent a receptor for a yet unknown ligand (growth factor). It is suggested that the high molecular weight C63.3 antigens play a role in maintaining the nonmalignant phenotype.

Role of hypoxemia in sleep apnea-induced sympathoexcitation

The importance of hypoxemia in determining sympathoexcitation during obstructive sleep apnea was examined by comparing changes in efferent sympathetic nerve activity (SNA) during spontaneous obstructive apneas with hypoxemia alone of similar magnitude and duration induced by 1-4 breaths of 100% nitrogen in six patients with obstructive sleep apnea and with spontaneous apneas while breathing 100% oxygen (apnea without hypoxemia) in three patients. In addition, eight control subjects were studied during induced hypoxemia. The magnitude of sympathoexcitation during spontaneous apneas (103 +/- 15%) was more than twice that observed during induced hypoxemia (47 +/- 14%) during episodes in which the nadir of oxygen desaturation (78 +/- 2 and 75 +/- 2%, respectively) and duration of hypoxemia (27 +/- 3 and 33 +/- 3 s, respectively) were the same (P > 0.20). Similarly, in three patients SNA increased 115% during normoxic spontaneous obstructive apneas, but increased only 43% during hyperoxic spontaneous obstructive apneas in which oxygen saturation did not decrease significantly. Sympathetic neural responses to induced hypoxemia in control subjects (17 +/- 7%) were significantly less than that of the sleep apnea patients. We conclude that hypoxemia contributes importantly, but is not the sole determinant of the sympathoexcitation provoked during episodes of obstructive sleep apnea.

Diagnosis of osteomyelitis in neuropathic foot ulcers

We reviewed all patients with a clinically infected foot ulcer attending a specialised neuropathic foot clinic. Neuropathy was confirmed by the inability to feel a 5.07 Semmes-Weinstein hair, areflexia and impaired vibration sense, as measured by a biothesiometer. Of 40 patients who attended the clinic over a two-year period, six with ischaemic ulcers were excluded. The remaining 34 had plain radiographs of the foot followed by a 99mTc-MDP bone scan. If the latter was positive, an 111In-labelled WBC scan was performed with planar and/or tomographic dual-isotope studies where appropriate. Bone and WBC scans were performed in 31 patients. In ten, isotope imaging showed infection localised to the soft tissues only and conservative treatment was successful in them all. Eighteen patients were treated surgically with excision of the involved bone, which was sent for culture and histological examination. Dual-isotope scans had a sensitivity of 93% and a specificity of 83%. 99mTc-MDP bone scans with the appropriate In-labelled WBC scans can reliably determine the site and extent of osteomyelitis in the neuropathic diabetic foot.

Application of the USDA Forest Service National Hierarchical Framework of Ecological Units at the sub-regional level: The New England-New York example

Ecological regionalization according to the USDA Forest Service National Hierarchical Framework of Ecological Units was undertaken for the New England-New York region. A topdown, map-overlay approach was used to map sections and subsections. Where available, landscape level units (LTAs) were aggregated and evaluated to supplement the subsection mapping. A regional collaborative effort was undertaken to counterbalance the shortfalls of a purely mechanistic approach. As a result of this process, 17 section and 58 draft subsection units were delineated for the New England-New York region. The sub-regional units developed reflect the strong correspondence among climate, topography and geography at this scale. Geologic factors, due to their influence on landform and mineral availability, are also reflected in the ecological unit boundaries. Efforts to apply the multifactor model at the sub-regional level have been hampered by the lack of scale appropriate information on a number of factors particularly meso-scale climate and potential natural community composition and distribution. Further research and investigation are required before these criterion are adequately met.

Microsurgery in a rat lung transplant model: analysis of benefit

With the use of microsurgery, we have developed a method of measuring hemodynamic parameters in a rat not possible with previous technology. Three groups of rats were studied: a chemically induced pulmonary hypertensive group (PH); a chemically induced pulmonary hypertensive group treated with single lung transplantation (LT); and an untreated, control group (C). Cardiac output, heart rate, and pulmonary vascular resistance were then calculated in each group from data obtained by 1 mm high fidelity micromanometers and an ultrasonic flow probe. The results show that the data collected from the rodent model are reproducible within each group, and data quality is comparable to large animal models. With this new method, data can be collected in a small animal model at a fraction of the time and cost of large animal studies. Additionally, the complications of graft rejection in large animal studies are eliminated in an isogenic rodent model.

Direct interaction of Gadd45 with PCNA and evidence for competitive interaction of Gadd45 and p21Waf1/Cip1 with PCNA

We have previously shown (Smith et al., 1994) that antibodies raised against the growth arrest and DNA damage inducible protein Gadd45 co-precipitate proliferating cell nuclear antigen (PCNA), a protein involved in DNA replication and repair. Here we demonstrate that Gadd45 can directly bind to PCNA using a Far-western blotting approach. In this assay, a Gadd45 bacterial expression vector was modified to allow synthesis of purified 32P-labeled Gadd45 fusion protein. This protein was used to detect filter bound PCNA protein, while filter bound Gadd45 protein could also be detected by free PCNA molecules. Using recombinant proteins in conjunction with immunoprecipitation and immunoblotting, we show that Gadd45 competes with p21 for binding to PCNA and conversely, p21 blocks the ability of Gadd45 to bind PCNA. In addition, p21 appears to disrupt PCNA trimers whereas Gadd45 has a lesser effect. PCNA trimer disruption was also observed in UV-irradiated cells but not in repair-defective xeroderma pigmentosum group A (XP-A) cells.

Regulation of brain-derived neurotrophic factor gene expression after transient middle cerebral artery occlusion with and without brain damage

Levels of mRNA for c-fos, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), TrkB, and TrkC were studied using in situ hybridization in the rat brain at different reperfusion times after unilateral middle cerebral artery occlusion (MCAO). Short-term (15 min) MCAO, which does not cause neuronal death, induced elevated BDNF mRNA expression confined to ipsilateral frontal and cingulate cortices outside the ischemic area. With a longer duration of MCAO (2 h), which leads to cortical infarction, the increase was more marked and elevated BDNF mRNA levels were also detected bilaterally in dentate granule cells and CA1 and CA3 pyramidal neurons. Maximum expression was found after 2 h of reperfusion. At 24 h BDNF mRNA expression had returned to control values. In the ischemic core of the parietal cortex only scattered neurons were expressing high levels of BDNF mRNA after 15 min and 2 h of MCAO. Analysis of different BDNF transcripts showed that MCAO induced a marked increase of exon III mRNA but only small increases of exon I and II mRNAs in cortex and hippocampus. In contrast to BDNF mRNA, elevated expression of c-fos mRNA was observed in the entire ipsilateral cerebral cortex, including the ischemic core, after both 15 min and 2 h of MCAO. Two hours of MCAO also induced transient, bilateral increases of NGF and TrkB mRNA levels and a decrease of NT-3 mRNA expression, confined to dentate granule cells. The upregulation of BDNF mRNA expression in cortical neurons after MCAO is probably triggered by glutamate through a spreading depression-like mechanism. The lack of response of the BDNF gene in the ischemic core may be due to suppression of signal transduction or transcription factor synthesis caused by the ischemia. The observed pattern of gene expression after MCAO agrees well with a neuroprotective role of BDNF in cortical neurons. However, elevated levels of NGF and BDNF protein could also increase synaptic efficacy in the postischemic phase, which may promote epileptogenesis.

Mechanisms of secondary brain damage in global and focal ischemia: a speculative synthesis

The objective of this article is to amalgamate previous results into a speculative synthesis that sheds light on the causes of secondary brain damage following either global/forebrain or focal ischemia. The hypothesis is based on the well-founded assumption that the pathophysiology of the brain damage incurred by global or forebrain ischemia is different from that of focal ischemia. In the former, the ischemia is usually dense and of brief duration and, provided that reperfusion is adequate, cell damage is conspicuously delayed, mostly affecting selectively vulnerable neurons. In contrast, focal ischemia is either long-lasting or permanent, and it is usually less severe, particularly in the perifocal penumbral regions. The lesion is typically pan-necrotic ("infarction"), initially affecting the focus supplied by the occluded artery, later invading the penumbra zone. Available results allow a restatement of the calcium hypothesis of cell death. In global or forebrain ischemia, calcium influx through channels gated by voltage or glutamate receptors is envisaged to trigger reactions that limit the survival of neurons during reperfusion, leading to secondary neuronal death after hours or days of survival. It can be hypothesized that the initial insult leads to a sustained alteration of membrane calcium handling, resulting in slow, gradual calcium overload of mitochondria. Alternatively, a sustained perturbation of the intracellular signal transduction pathway leads to changes in transcription or translation, bereaving the cells of heat shock and stress proteins, of trophic factors, or of enzymes required for survival. However, with the possible exception of the gerbil, neither microvascular failure nor primary mitochondrial dysfunction is believed to be involved. In focal ischemia, similar reactions are probably triggered by calcium influx, whether this is sustained (the focus) or intermittent (the penumbra). However, these play a minor role in cell death since they are overridden by reactions producing mediators of rapidly developing secondary damage, affecting either microvessels or mitochondria. Very probably, some of these mediators are free radicals, or nitric oxide, or other reactive metabolites, emanating from lipid hydrolysis and arachidonic acid metabolism. During continuous ischemia, or during recirculation following 1-3 h of ischemia, these mediators activate adhesion molecules in endothelial cells or polymorphonuclear leucocytes, or oxidize key proteins. The result is either failure of microcirculation ("capillary plugging"), or sustained mitochondrial failure. Since calcium influx is an initial event, agents reducing presynaptic depolarization and calcium entry through glutamate receptor-gated and other calcium channels have predictably a narrow therapeutic window; however, since spin trapping agents of the nitrone class act many hours after the induction of focal ischemia, their therapeutic window is potentially very wide. This may be because expression of mRNAs for adhesion molecules and their synthesis are relatively slow processes, and because the nitrones act on events that involve adhesion of leukocytes to the endothelial cells, with plugging of capillaries and postcapillary venules, and on the ensuing inflammatory response.

The neurochemical and metabolic cascade following brain injury: moving from animal models to man

Experimental traumatic brain injury produces a series of cellular events contributing to a neurochemical and neurometabolic cascade. This cascade is defined by the release of neurotransmitters resulting in a massive ionic flux, which, consequently, produces an increase in glycolysis. This increase in glycolysis is followed by a metabolic diaschisis, which is related to the degree and extent of behavioral deficits. Clinical efforts have now determined that a similar cascade occurs in human head injury, validating the animal model as well as providing new assessment strategies for the management and treatment of brain injury.

Cholinergic and GABAergic neurons in the nucleus basalis region of young and aged rats

Antibodies directed against choline acetyltransferase and glutamic acid decarboxylase were used in combination with recently developed stereological techniques to quantify changes in cholinergic, GABAergic, and total neuron number (Nissl-stain) within adjacent tissue sections through the horizontal limb/nucleus basalis in young (3 months, n = 6) and aged (27 months, n = 6) Fischer-344 male rats. Unbiased estimates of total neuron number within these regions were produced using a three-dimensional optical probe, the optical disector, in combination with a systematic random sampling scheme. Estimates of cell counts in immunostained tissue sections were conducted throughout the entire horizontal limb/nucleus basalis region. A significant 30% decrease in both cholinergic and total neuron number was detected in the aged animals; GABAergic neuron number remained unchanged. Total neuron number was significantly correlated with both cholinergic (r = 0.94) and glial cell number (r = 0.63), but not with GABAergic cell number. Based on neuron counts within an individual thick tissue section, the cholinergic neurons comprised only 11-15% of all neurons in the nucleus basalis of young and aged animals. Cholinergic neuron loss accounted for only 20% of the total age-related neuron loss within the horizontal limb/nucleus basalis in Fischer-344 male rats. These results indicate that age-related cholinergic neuron loss within the basal forebrain is reflected in reductions in total neuron number; however, GABAergic neurons, many of which project to the cortex, are unaffected by age. The magnitude of the age-related total neuron loss cannot be entirely accounted for by cholinergic cell loss. Therefore, an unidentified non-cholinergic, non-GABAergic component within the basal forebrain is also lost during aging and may contribute to the cognitive deficits previously ascribed to cholinergic dysfunction.

The production and characterization of murine monoclonal antibodies to human Gadd45 raised against a recombinant protein

The production of two different murine monoclonal antibodies to human Gadd45, a protein that is induced in response to DNA damage, is reported. Antibodies were generated in a SJL mouse using a recombinant form of the human Gadd45 protein. Monoclonal antibody 4TCYA1, which recognizes the denatured form of human Gadd45 in Western blots, was selected based upon the recognition of Gadd45 induced by functional p53 in the human myeloid leukemia cell line, ML-1. A second monoclonal antibody, designated 30T.14, immunoprecipitates native human Gadd45 in lysates produced from RKO cells, a colorectal carcinoma cell line that expresses relatively high basal levels of Gadd45, as well as from cell lysates made from ML-1 cells after exposure to ionizing irradiation (IR). Since 4TCYA1 fails to immunoprecipitate Gadd45, and 30T.14 fails to bind to IR-induced Gadd45 in immunoblotting, these two monoclonal antibodies probably recognize different epitopes.

Baseline arterial pressure affects sympathoexcitatory responses to ventricular premature beats

The seconds to minutes before sudden cardiac death are characterized by fluctuations of arterial pressure, cardiac rhythm, and probably sympathetic nerve activity. We explored the interrelations among these factors in seven patients undergoing clinical electrophysiological testing. We measured muscle sympathetic nerve activity (SNA) and arterial pressure responses to ventricular premature beats induced throughout the cardiac cycle under three conditions: 1) lowered arterial pressure and elevated SNA produced by intravenous nitroprusside, 2) baseline arterial pressure and SNA during saline infusion, and 3) elevated arterial pressure and decreased SNA activity produced by intravenous phenylephrine. Sympathetic responses to premature beats were inversely related to diastolic pressure. The magnitude of the sympathetic response was directly related to the prevailing arterial pressure and inversely related to baseline SNA. These data demonstrate that sympathoexcitation evoked by ventricular dysrhythmias is determined importantly by the prevailing arterial pressure and possibly by the background R-R interval and level of sympathetic activity. This effect may influence hemodynamic and electrophysiological stability during dysrhythmias.

Stimulus and sex differences in performance of mental rotation: evidence from event-related potentials

We examined stimulus and sex differences in reaction time (RT) and event-related potentials (ERPs) during mental rotation of letters and abstract designs (PMA figures). RTs replicated stimulus and angle effects found in previous studies, but no sex differences were found for either set of stimuli. ERP latency data showed women began stimulus evaluation earlier, and PMA rotations began later over smaller angles, whereas letter rotations began later over larger angles. ERP amplitude data replicated hemisphere, electrode, and angle effects found in earlier studies. Amplitude measures also showed greater involvement of anterior cortical areas for evaluation of letter figures and posterior right temporal lobe for PMA figures, and greater positivity of women's waveforms than men's over late evaluation and early rotation components.

Psychosocial correlates of immune responsiveness and illness episodes in US Air Force Academy cadets undergoing basic cadet training

This study examined psychosocial correlates of immune function and illness in 89 male first-year US Air Force Academy cadets. A psychosocial questionnaire was administered to cadets prior to their arrival at the academy and was readministered during cadet orientation and during the stressful environment of Basic Cadet Training (BCT). Immune responsiveness was analyzed by PHA-, PMA-, or anti-CD3-stimulated thymidine uptake in mononuclear leucocytes. Illness episodes were assessed via medical chart review and self-reported symptoms. There were significant increases in distress levels as cadets entered BCT. No psychosocial measure assessed prior to arrival at the academy predicted level of PHA-, PMA-, and anti-CD3-stimulated thymidine uptake or risk of illness. However, hostility levels reported during BCT predicted risk of illness in the four weeks following psychosocial assessment (odds ratio = 7.1; 95% confidence interval: 1.4-36.1). Elevated response to environmental stressors and lower well-being levels also predicted impending illness, but only in the cohort of cadets who had not contracted food poisoning prior to assessment during BCT (OR = 9.3, CI = 1.9-46.7; OR = 0.09, CI = 0.02-0.53). These results suggest that self-report measures of hostility, response to environmental stressors and well-being may be useful predictors of impending illness episodes in males encountering high stress environments.

Simultaneous measurement of one-carbon and polyglutamate derivatives of folic acid in rat liver using enzymatic interconversions of folates followed by ternary complex formation with thymidylate synthetase and 5-fluorodeoxyuridylic acid: standardization of the method

A sensitive assay is needed for the measurement of individual folate derivatives in samples that contain low concentrations of folate. The ternary complex method for the determination of folylpolyglutamates has been combined with procedures for interconverting folate derivatives to provide a method capable of measuring 28 different folate derivatives in biological samples. The method takes advantage of the properties of the ternary complex formed with thymidylate synthetase, fluorodeoxyuridylic acid and 5,10-methylenetetrahydrofolic acid. In the presence of excess purified thymidylate synthetase and excess [3H]fluorodeoxyuridylic acid, limiting concentrations of folates were converted to 5,10-methylenetetrahydrofolate using purified folate interconverting enzymes. This process separated folate derivatives into four groups: Tetrahydrofolate + 5,10-methylenetetrahydrofolate; dihydrofolate; 5,10-methenyl-, 5-formyl-, and 10-formyltetrahydrofolates and 5-methyltetrahydrofolate. Within groups specificity was good, showing little overlap between folates. Sensitivities to 100 fmol of folate were achievable and to 1 pmol were standard. Recoveries were linear for each of the groups in this system to 50 pmol of folate. Ternary complexes containing different polyglutamates were separated by isoelectric focusing, visualized by fluorography and measured by densitometry. The densitometry was linear with folate concentration in the range 20-200 fmol for each of the polyglutamates. Primary and secondary coefficients of variation were determined. This method provides the sensitivity to measure individual folates in the femtomole range and the flexibility to determine the concentrations of 28 separate pools of folate derivatives, differentiating between derivatives of the pteridine moiety and glutamate chain length simultaneously.

Disruption of p53 function sensitizes breast cancer MCF-7 cells to cisplatin and pentoxifylline

The possibility that appropriately designed chemotherapy could act selectively against p53-defective tumor cells was explored in MCF-7 human breast cancer cells. These cells were chosen because they have normal p53 function but are representative of a tumor cell type that does not readily undergo p53-dependent apoptosis. Two sublines (MCF-7/E6 and MCF-7/mu-p53) were established in which p53 function was disrupted by transfection with either the human papillomavirus type-16 E6 gene or a dominant-negative mutant p53 gene. p53 function in MCF-7/E6 and MCF-7/mu-p53 cells was defective relative to control cells in that there were no increases in p53 or p21Waf1/Cip1 protein levels and no G1 arrest following exposure to ionizing radiation. Survival assays showed that p53 disruption sensitized MCF-7 cells to cisplatin (CDDP) but not to several other DNA-damaging agents. CDDP sensitization was not limited to MCF-7 cells since p53 disruption in human colon carcinoma RKO cells also enhanced sensitivity to CDDP. Contrary to the other DNA-damaging agents tested, CDDP-induced DNA lesions are repaired extensively by nucleotide excision, and in agreement with a defect in this process, MCF-7/E6 and MCF-7/mu-p53 cells exhibited a reduced ability to repair a CDDP-damaged chloramphenicol acetyltransferase-reporter plasmid transfected into the cells. Therefore, we attributed the increased CDDP sensitivity of MCF-7 cells with disrupted p53 to defects in G1 checkpoint control, nucleotide excision repair, or both. The G2 checkpoint inhibitor pentoxifylline exhibited synergism with CDDP in killing MCF-7/E6 cells but did not affect sensitivity of the control cells. Moreover, pentoxifylline inhibited G2 checkpoint function to a greater extent in MCF-7/E6 than in the parental cells. These results suggested that, in the absence of p53 function, cancer cells are more vulnerable to G2 checkpoint abrogators. Our results show that a combination of CDDP and pentoxifylline is capable of synergistic and preferential killing of p53-defective tumor cells that do not readily undergo apoptosis.

Induction of p53-, MDM2-, and WAF1/CIP1-like molecules in insect cells by DNA-damaging agents

Cellular responses following DNA damage are ubiquitous in the biological world. In response to DNA damage, cell cycle checkpoints are activated, which delay cell cycle progression and most likely serve to allow time for repair. One important checkpoint in mammalian cells, activated in the G1 phase of the cell cycle, is dependent on the p53 tumor suppressor gene product. While p53 is responsible for inducing G1 arrest, the product of the MDM2 gene is believed to alleviate the arrest, allowing continuation of the cell cycle after a transient delay. Inasmuch as MDM2 and WAF1/CIP1 are transactivated by p53, while MDM2 binds to and modulates the activity of p53, a "feedback loop" is thus created. This pathway has been highly conserved in mammalian cells, but its presence outside of vertebrates is unknown. By using human MDM2 and WAF1/CIP1 cDNA probes, and monoclonal antibodies to p53 and Mdm2, we demonstrate in insect cell lines evidence for the existence of p53-, MDM2-, and WAF1/CIP1-like molecules and a p53-regulated pathway following treatment by DNA-damaging agents.

Critical values for plasma glucose in aggravating ischaemic brain damage: correlation to extracellular pH

The objective of the present experiments was to characterize conditions under which pre-ischaemic hyperglycaemia aggravates brain damage following transient forebrain ischaemia. Specifically, we wished to explore whether accentuated damage is a threshold function of plasma glucose concentration or pH, as assessed by measurements of extracellular pH (pHe). Forebrain ischaemia of 10 min duration was induced in rats at varying degrees of hyperglycaemia, with continuous measurements of pHe, and the animals were allowed to survive for 7 days before histopathological evaluation of the density and distribution of brain damage. Ischaemic brain damage appeared as a threshold function of plasma glucose concentration. At values of 4-6 mM virtually no damage was observed in any other structure than the CA1 sector of the hippocampus and, even in that structure, damage was variable. At glucose concentrations of 8-12 mM moderate damage was observed infrequently in caudoputamen, parietal cortex, and thalamus. At values above 12 mM, damage increased dramatically in these areas, and additional structures were recruited in the damage process (cingulate cortex, the CA3 sector of the hippocampus, and substantia nigra). Measurements of pHe in parietal cortex showed a threshold for seizure induction at values of 6.4-6.5, probably corresponding to intracellular pH values of 6.2-6.3. The threshold for aggravation of histopathological damage was similar. It is concluded that a moderate increase in plasma glucose in the threshold range predisposes the tissue to aggravated damage, probably by activating biochemical reactions or pathophysiological events with a steep pH dependence.