PubMed Health⌕ Search

Biomedical subjects

C R Libertin

Publications and source records attributed to C R Libertin.

At least 19 recordsLinked to original sources
PubMed1997

HIV expression is induced in dying cells.

Using HeLa cells stably transfected with an HIV-LTR-CAT construct, we demonstrated a peak in CAT induction that occurs in viable (but not necessarily cell-division-competent) cells 24 h following exposure to some cell-killing agents. gamma rays were the only cell-killing agent which did not induce HIV transcription; this can be attributed to the fact that gamma-ray-induced apoptotic death requires functional p53, which is not present in HeLa cells. For all other agents, HIV-LTR induction was dose-dependent and correlated with the amount of cell killing that occurred in the culture. Doses which caused over 99% cell killing induced HIV-LTR transcription maximally, demonstrating that cells that will go on to die by 14 days are the cells expressing HIV-LTR-CAT.

Cell Death↗
PubMed1996

Dysregulation of temperature and liver cytokine gene expression in immunodeficient wasted mice.

Wasted mice bear the spontaneous autosomal recessive mutation wst/wst; this genotype is associated with weight loss beginning at 21 days of age, neurologic dysfunction, immunodeficiency at mucosal sites, and increased sensitivity to the killing effects of ionizing radiation. The pathology underlying the disease symptoms is unknown. Experiments reported here were designed to examine thermoregulation and liver expression of specific cytokines in wasted mice and in littermate and parental controls. Our experiments found that wasted mice begin to show a drop in body temperature at 21-23 days following birth, continuing until death at the age of 28 days. Concomitant with that, livers from wasted mice expressed increased amounts of mRNAs specific for cytokines IL-6 and IL-1, the acute phase reactant C-reactive protein, c-jun, and apoptosis-associated Rp-8 when compared to littermate and parental control animals. Levels of beta-transforming growth factor, c-fos, proliferating cell nuclear antigen, and ornithine amino transferase transcripts were the same in livers from wasted mice and controls. These results suggest a relationship between an acute phase reactant response in wasted mice and temperature dysregulation.

Abnormalities, Multiple↗
PubMed1996

Expression of enhanced spontaneous and gamma-ray-induced apoptosis by lymphocytes of the wasted mouse.

Mice bearing the autosomal recessive mutation wasted (wst/wst) display a disease pattern including increased sensitivity of lymphocytes to ionizing radiation, neurologic dysfunction, and immunodeficiency. Many of the features of this mouse model have suggested a premature or increased spontaneous frequency of apoptosis in thymocytes. Past work has documented an inability to establish cultured T cell lines, and abnormally high death rate of stimulated T cells in culture, and an increased sensitivity of T cells to the killing effects of ionizing radiations in the wst/wst mouse relative to controls. The experiments reported here were designed to examine splenic and thymic lymphocytes from the wasted and control mouse for signs of early apoptosis. Our results revealed enhanced expression of Rp-8 mRNA (which has been associated with apoptosis) in thymic lymphocytes and to a lesser extent in spinal cord in the wst/wst mouse relative to controls; expression of Rp-2 and Tcl-30 mRNA (also reported to be induced during apoptosis) were not detectable in spleen or thymus. Expression of Rp-2, Rp-8, and Tcl-30 mRNA in other affected tissues of the wasted mouse (brain and liver) were similar in the wasted mouse and controls. Thymus and spleen from the wasted mouse have reduced numbers of viable cells relative to controls. Higher spontaneous DNA fragmentation was observed in lymphocytes from the wasted mouse than in controls; however, gamma-ray-induced DNA fragmentation peaked at a lower dose and occurred to a greater extent in lymphocytes derived from the wasted mouse relative to controls. These results suggest that high spontaneous and gamma-ray-induced apoptosis in T cells of the wasted mouse may contribute to the mechanism underlying the observed lymphocyte and DNA repair abnormalities.

Animals↗
PubMed1996

Regulation of thymus PCNA expression is altered in radiation-sensitive wasted mice.

Mice bearing the autosomal recessive mutation 'wasted' (wst/wst) express a disease syndrome characterized by neurologic dysfunction, immunodeficiency, and increased sensitivity to the killing effects of ionizing radiation relative to normal littermates (wst/-) and to parental control mice (BCF1, BALB/c, and C57BL/6). Many of these abnormalities, evident as early as 21 days of age, have been localized to thymic tissues and T-lymphocyte populations. Comparison of two-dimensional gel electrophoresis patterns of proteins from wst/wst and control mouse thymus revealed that an acidic protein with a molecular mass of approximately 30 kDa was consistently expressed at lower levels in wasted mice than in controls. Microsequencing of this protein revealed a sequence of 19 N-terminal amino acids identical to the sequence of murine proliferating cell nuclear antigen (PCNA). Northern blot analyses of PCNA expression in thymus and spleen demonstrated lower accumulation of PCNA-specific transcripts in wasted mice compared with that in controls. Because PCNA expression is associated with cell cycle progression, the percentages of thymic and splenic cells in each stage of the cell cycle were examined; there were no differences in the cell stage distribution of lymphocytes freshly isolated from wasted mice compared with littermate or parental controls. After activation with concanavalin A, however, splenocytes from wst/wst mice showed a lower percentage of cells in S phase compared with that in controls. Southern blots with PCNA probes showed that the PCNA loci from the wasted mice and their normal littermates have the same restriction maps. While differences in polymerase chain reaction (PCR) priming were obtained, these could be attributed to strain-specific differences in mouse PCNA pseudogenes. These results suggest the presence of an alteration in the pathway leading to PCNA expression in radiation-sensitive tissues of wasted mice.

Animals↗
PubMed1995

Salicylic acid inhibits ultraviolet- and cis-platinum-induced human immunodeficiency virus expression.

Previous studies have shown that exposure of HeLa cells stably transfected with an HIV-long terminal repeat-chloramphenicol acetyltransferase (HIV-LTR-CAT) construct to many DNA-damaging agents (such as UV light) induces expression from the HIV LTR. By culturing the cells with salicylic acid we demonstrated dose-dependent repression of this UV-or cis-platinum (cis-Pt)-induced HIV expression. While salicylic acid treatment, indomethacin treatment, UV exposure, or cis-Pt treatment alone decreased viability by up to 50%, equal numbers of viable cells were used for the CAT assays. Repression was evident if salicylic acid was administered 2 h before, at the same time as, or up to 6 h after exposure to the DNA-damaging agent. The kinetics were similar for UV- and for cis-Pt-induced HIV expression, and induction was dependent on the UV dose or cis-Pt concentration added to the culture. pH changes of the media alone in the absence of salicylic acid did not affect HIV expression. Indomethacin (100 microM) did not affect UV- or cis-Pt-induced HIV expression. These results suggest a role for the prostaglandins or the cyclo-oxygenase pathway or both in HIV induction mediated by DNA-damaging agents.

Chloramphenicol O-Acetyltransferase↗
PubMed1995

The effects of multiple UV exposures on HIV-LTR expression.

Previous studies have shown that cellular stress agents such as UV radiation induce transcription from the long terminal repeat (LTR) of the human immunodeficiency virus (HIV). Using HeLa cells stably transfected with the HIV-LTR sequence, which transcriptionally drives the chloramphenicol acetyl transferase (CAT) reporter gene, we examined the effects of multiple exposures to UVC (254 nm) on HIV-LTR-CAT expression. Low doses (< or = 5 J m-2) had no effect on CAT expression, but up to 29-fold induction was observed with 10 J m-2 when cells were harvested 48 h after completion of the exposure. Little difference was noted in induction levels when cells were exposed to one 25 J m-2 dose, viable cells were harvested at 24 h, 48 h or 72 h, and cell lysates were assayed for CAT expression. Two sequential 12.5 J m-2 exposures, given 24 h apart, resulted in an additive effect on CAT expression; these two exposures produced CAT activity equivalent to that induced following a single 25 J m-2 dose. This additive effect was not evident at the lower doses (< or = 5 J m-2) or at the higher doses. Maximal induction was observed using doses from 25 to 37.5 J m-2. Multiple exposures with either the low (< or = 5 J m-2) or high doses (> 25 J m-2) did not result in an additive effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Chloramphenicol O-Acetyltransferase↗
PubMed1994

Cytokine and T-cell subset abnormalities in immunodeficient wasted mice.

Wasted mice bear an autosomal recessive mutation (wst/wst) that manifests itself in neurologic abnormalities, immunologic deficiency, and faulty DNA repair evident by 21 days of age. The immunodeficiency is characterized by a reduction in the thymus-to-body weight ratio, low levels of IgA plasma cells at secretory sites, and increased sensitivity of T-cells to the killing effects of ionizing radiation. Experiments were designed to examine measures of T-cell activity in wasted mice. The initial experiments established that wst/wst mice have percentages of thymic and splenic Thy1+ cells equivalent to those of control littermates. Further studies of T-cell subpopulations with thymocytes revealed normal percentages of CD4+ and CD8+ cells in wst/wst mice; however, double-labeling experiments showed that CD8+ cells were predominantly CD4- in wst/wst mice, whereas in controls most CD8+ cells also expressed CD4+. Mesenteric lymph node T-cell subpopulations were similar in wasted and control mice. Because cytokines play a significant role in the regulation of the immune response and also interact with a variety of cellular systems, we examined the expression of different cytokine and related genes (IL1, IL2, IL2R, TNF, IL5, gamma-interferon, beta-TGF) in lymphoid tissues from wasted mice as well as from littermate and parental controls. Studies of RNA from lymphoid tissues of wasted mice using dot blot and Northern blot hybridizations revealed a deficiency of IL5 mRNA in thymus and spleen, decreased expression of IL2R in thymus (but not spleen), increased expression of IL1 in spleen (but not thymus), and increased expression of IL2, gamma-interferon, and beta-TGF in both spleen and thymus, relative to controls. Expression of TNF mRNA in lymphoid tissues was unaffected by the wasted mutation. These results suggest a role for cytokine imbalance in the pathogenesis of the immunodeficiency and other abnormalities of wasted mice.

Animals↗
PubMed1994

Subnormal albumin gene expression is associated with weight loss in immunodeficient/DNA-repair-impaired wasted mice.

OBJECTIVE: Mice bearing the autosomal recessive mutation wst express a disease syndrome of immunodeficiency, neurologic dysfunction, increased sensitivity to the killing effects of ionizing radiation, and dramatic weight loss that begins at 21 days of age and progresses until death at 28-32 days of age. Because of the reported association between abnormal liver status and weight loss, we designed experiments to examine expression of a variety of liver-specific genes in wst/wst mice relative to littermates (wst/.) and parental strain (BCF1) controls. METHOD: Animals were individually weighed from ages 21-28 days to determine relative weight comparisons between wst/wst mice and controls. Dot blot hybridizations were set up to quantitate the accumulation of transcripts specific for alpha-fetoprotein, albumin and other liver-specific gene products. RESULTS: These results showed a 67% reduction in albumin mRNA expression in livers derived from wst/wst mice relative to both controls. Expression of alpha-fetoprotein, as well as a variety of other liver-specific genes [secretory component (SC), metallothionein (MT-2), cytochrome P1-450 (Cyt P1-450), transferrin receptor (Tf Rec), tumor necrosis factor (TNF), and immune-associated antigen (Ia)], was unaffected. CONCLUSIONS: These results suggest a relationship between low albumin expression and wasting syndromes in mice. In addition, our data suggest that the wasted mouse may serve as a unique model for subnormal albumin expression.

Animals↗
PubMed1994

Effects of gamma rays, ultraviolet radiation, sunlight, microwaves and electromagnetic fields on gene expression mediated by human immunodeficiency virus promoter.

Previous work by our group and others has shown the modulation of human immunodeficiency virus (HIV) promoter or long terminal repeat (LTR) after exposure to neutrons and ultraviolet radiations. Using HeLa cells stably transfected with a construct containing the chloramphenicol acetyl transferase (CAT) gene, the transcription of which is mediated by the HIV-LTR, we designed experiments to examine the effects of exposure to different types of radiation (such as gamma rays, ultraviolet and sunlight irradiations, electromagnetic fields and microwaves) on HIV-LTR-driven expression of CAT. These results demonstrated ultraviolet-light-induced transcription from the HIV promoter, as has been shown by others. Exposure to other DNA-damaging agents such as gamma rays and sunlight (with limited exposures) had no significant effect on transcription mediated by HIV-LTR, suggesting that induction of HIV is not mediated by just any type of DNA damage but rather may require specific types of DNA damage. Microwaves did not cause cell killing when cells in culture were exposed in high volumes of medium, and the same cells showed no changes in expression. When microwave exposure was carried out in low volumes of medium (so that excessive heat was generated) induction of HIV-LTR transcription (as assayed by CAT activity) was evident. Electromagnetic field exposures had no effect on expression of HIV-LTR. These results demonstrate that not all types of radiation and not all DNA-damaging agents are capable of inducing HIV. We hypothesize that induction of HIV transcription may be mediated by several different signals after exposure to radiation.

Chloramphenicol O-Acetyltransferase↗
PubMed1994

Low doses of neutrons induce changes in gene expression.

Studies were designed to identify genes induced in fibroblasts after exposure to low-dose neutron radiation but not after gamma rays. Our past work had shown similar modulation of transcripts for alpha-tubulin, beta- and gamma-actins, ornithine decarboxylase and interleukin 1 after exposure to either neutrons or gamma rays. However, differences in the expression of beta-protein kinase C and c-fos genes were observed, with both being induced after exposure to gamma rays but not neutrons. Recently we have identified two genes that are induced after exposure to neutrons but not gamma rays: Rp-8 (a gene associated with apoptosis) and the long terminal repeat (LTR) of the human immunodeficiency virus (HIV). Induction of Rp-8 mRNA was demonstrated in Syrian hamster embryo (SHE) fibroblasts and was found to be induced in cells exposed to neutrons administered at low (0.005 Gy/min) and high dose rate (0.12 Gy/min). No induction of other genes associated with apoptosis such as Rp-2, bcl-2 and Tcl-30 was observed. The induction of transcription from the LTR of HIV was demonstrated in HeLa cells bearing a transfected construct of the chloramphenicol acetyl transferase (CAT) gene driven by the HIV-LTR promoter. Measurements of CAT activity and CAT transcripts after irradiation demonstrated an unresponsiveness to gamma rays over a broad range of doses (0.1-3 Gy). Twofold induction of the HIV-LTR was detected after exposure to neutrons (0.48 Gy) administered at low (0.05 Gy/min) but not high (0.12 Gy/min) dose rates. Ultraviolet-mediated HIV-LTR induction, however, was inhibited by exposure to low-dose-rate neutron irradiation. These results are interesting in light of reports that Rp-8 is induced during apoptosis and that HIV causes apoptosis.

Animals↗
PubMed1993

Human neutrophil oxidative response and phagocytic killing of clinical and laboratory strains of Enterococcus faecalis.

Many clinical isolates of Enterococcus faecalis produce a hemolysin/bacteriocin that is plasmid mediated. Recent human epidemiologic studies and animal research suggest that this hemolysin/bacteriocin may enhance the pathogenicity of hemolysin-producing enterococci compared with non-hemolysin-producing strains. These studies determined that clinical strains that produce hemolysin/bacteriocin differed from non-hemolysin-producing clinical and laboratory strains in their ability to induce the production of reactive oxygen intermediates in human peripheral blood neutrophils and in their susceptibility to phagocytic killing in vitro. The induction of superoxide anion generation by neutrophils was demonstrated to be directly proportional to the presence of the hemolysin/bacteriocin plasmid and was transferable to a non-hemolysin-producing laboratory strain by transconjugation. The presence of the plasmid, however, did not effect killing by phagocytic cells in vitro. It is proposed that hemolysin/bacteriocin-producing strains of enterococcus may be more pathogenic due to reactive oxygen product-induced tissue injury in vitro.

Conjugation, Genetic↗
PubMed1992

The hemolysin/bacteriocin produced by enterococci is a marker of pathogenicity.

The hemolysin/bacteriocin produced by some strains of Enterococcus faecalis is active in the lysis of human, rabbit, and horse erythrocytes, but not those from sheep. In this study, we determined that 20% of clinical enterococcal isolates tested in the clinical microbiology laboratory produced hemolysin and that pathogenic human E. faecalis were more likely to be hemolysin-producing isolates. Among the organisms isolated from different anatomic sites, variability in the degree of hemolysin production existed. We used an isogenic pair of E. faecalis organisms to demonstrate that hemolysin production was due to a hemolysin/bacteriocin determinant transmissible by a plasmid and was not strain dependent. This determinant may be linked to antibiotic resistance genes in some instances. Also, the erythrocyte lysis occurred only when hemolysin was in the presence of E. faecalis organisms, suggesting a bacterial cell dependency for activity of the hemolysin.

Bacteremia↗
PubMed1991

Modulation of expression of virus-like elements following exposure of mice to high- and low-LET radiations.

Modulation of virus expression has been reported following exposure to a variety of cellular stresses, including UV radiation and heat-shock. The experiments reported here were designed to examine expression of endogenous VL30 (virus-like 30 S) elements following exposure of whole mice to ionizing radiations. Whole mice were exposed to doses of neutrons (50 cGy) or gamma-rays (300 cGy) shown to be equally efficient in cancer production in the whole animal, and tissues were harvested at 10 and 60 min following completion of the exposure. RNA extracted from these tissues and from tissues of untreated controls was examined for VL30 RNA accumulation by dilution dot blot and Northern blot analyses. These studies revealed that neutrons repressed VL30 RNA accumulation evident within 10 min following exposure in brain, gut, thymus and spleen but not in liver, in which VL30 RNA was unaffected by radiation exposure. During this same time interval, gamma-rays induced VL30 expression in gut and brain and to a lesser extent in liver. These experiments suggest the presence of a differential molecular response following whole-body exposure to high- versus low-LET radiations. In addition, this work demonstrates that ionizing radiations may affect expression of murine endogenous viral sequences.

Animals↗
PubMed1990

Disseminated intravascular coagulation in association with cavitary tuberculosis.

Coagulopathy due to tuberculosis is rare. We believe ours is only the second reported case of cavitary tuberculosis associated with disseminated intravascular coagulation. Our review of all 13 cases to date shows that the patients are generally black, middle-aged, male, alcoholic, and febrile. The tuberculosis is generally military, and is associated with a high mortality. Eight of the patients had associated adult respiratory distress syndrome. Only one (our case) had an acute tuberculous peritonitis. In six cases the coagulopathy began after the start of therapy; steroids did not appear to affect survival. The exact pathophysiologic mechanisms involved in the development of DIC are unknown.

Adult↗
PubMed1990

Engyodontium album endocarditis.

This is the first reported case of native valve endocarditis caused by Engyodontium album. This fungus, rarely seen as a human pathogen, is separated from Tritirachium species by its lack of pigmentation and from Beauveria species by the presence of conidiogenous cells in whorls.

Endocarditis↗
PubMed1990

Gentamicin-resistant enterococcal endocarditis: the need for routine screening for high-level resistance to aminoglycosides.

We have reported a case of high-level gentamicin-resistant enterococcal endocarditis as a complication of intravenous narcotic abuse. Because routine screening of enterococcal blood isolates for high-level aminoglycoside resistance was not done, the patient possibly received suboptimal therapy. This case amplifies the necessity of a systematic screening program for enterococcal blood isolates to detect high-level resistance to gentamicin and streptomycin in clinical laboratories.

Adult↗