Search PubMed⌕ Search

Biomedical subjects

D L Stevens

Publications and source records attributed to D L Stevens.

At least 73 records · Page 4Linked to original sources
PubMed1997

Induction and rejoining of DNA double-strand breaks in Chinese hamster V79-4 cells irradiated with characteristic aluminum K and copper L ultrasoft X rays.

Characteristic aluminum K (AlK) (energy of 1.5 keV) and copper L (CuL) (energy of approximately 0.96 keV) ultrasoft X rays have been used to investigate the effectiveness of the numerous low-energy secondary electrons produced by low-linear energy transfer (LET) ionizing radiation. Cellular inactivation and induction and rejoining of DNA double-strand breaks (DSBs) in Chinese hamster V79-4 cells irradiated as monolayers with these ultrasoft X radiations have been studied under aerobic and anaerobic conditions. The mean cell thickness, determined by confocal laser scanning fluorescence microscopy, was used to calculate the mean dose to the nucleus of the irradiated cells. Relative to 60Co gamma rays, the relative biological effectiveness (RBE) for cellular inactivation at 10% survival is 1.7 +/- 0.1 and 2.3 +/- 0.3 for AIK and CuL ultrasoft X rays, respectively. The RBE values for induction of DSBs of 2.5 +/- 0.2 and 3.0 +/- 0.3 for AlK and CuL X rays, respectively, were determined after irradiation at 277 K using the technique of pulsed-field gel electrophoresis. Induction of DSBs is linearly dependent on dose. Oxygen enhancement ratios of 1.9 and 2.1 for cellular inactivation and DSB induction, respectively, were obtained with AIK X rays. These values are less than those for 60Co gamma radiation. The repair kinetics for rejoining of DSBs after a dose of 15 Gy is similar for both X-ray energies and 60Co gamma rays with a first half-life of 18-22 +/- 5 min. From these studies, it is suggested that induction of DSBs by low-LET radiations such as 60Co gamma rays reflects clustered damage produced predominantly by low-energy electron "track ends," which represent about 30% of the total dose.

Aerobiosis↗
PubMed1996

The toxic shock syndromes.

Because of the frequency with which Staphylococcus aureus and Streptococcus pyogenes infections occur, physicians are quite familiar with the diversity of their clinical presentations. In the 1970s, however, shock associated with multiorgan failure was described in menstruating female patients as well as in male patients following a variety of surgical procedures, such as rhinoplasty. This previously undescribed presentation of S. aureus infection, termed staphylococcal toxic shock syndrome, was associated with unique strains of S. aureus. In the mid-1980s, the emergence of streptococcal toxic shock syndrome was heralded by several case reports describing patients with group A streptococcal infections associated with shock and organ failure. This article compares the differences in the epidemiologic, clinical, and pathophysiologic features of the toxic shock syndromes.

Anti-Bacterial Agents↗
PubMed1996

Spread of serious disease-producing M3 clones of group A streptococcus among family members and health care workers.

Streptococcus pyogenes causes a variety of diseases ranging from mild pharyngitis to severe toxic shock syndrome (TSS) and acute rheumatic fever. Since 1987 there has been a resurgence of severe group A streptococcus infections including TSS, necrotizing fasciitis, and myositis. Using molecular and serotyping procedures, we recently studied two clusters of group A streptococcus disease that occurred within separate family units. The first cluster involved two family members (one with TSS and one with necrotizing fasciitis) and three health care workers who attended one of the index patients. The second cluster included a mother (with necrotizing fasciitis of the hand) and her three children. Group A streptococci isolated from individuals within both cluster groups were serotype M3;T3/13/B3264, and pulsed field gel electrophoresis revealed that all isolates except one had identical fingerprints of Sma I-digested chromosomal DNA. The findings demonstrate the potential for spread of serious group A streptococcus disease among individuals and the need for barrier protection when health care workers are exposed to secretions from infected individuals.

Adult↗
PubMed1996

Group A streptococcal bacteremia: the role of tumor necrosis factor in shock and organ failure.

Severe group A streptococcal infections associated with early onset shock and multiorgan failure define the streptococcal toxic shock syndrome. In the United States, group A streptococcal strains most commonly isolated are M types 1 and 3, which produce pyrogenic exotoxin type A. The role of tumor necrosis factor (TNF)-alpha and the dynamics of cardiovascular and laboratory abnormalities were investigated in a baboon model of group A Streptococcal bacteremia that mimics human Streptococcal toxic shock syndrome. Profound hypotension, leukopenia, metabolic acidosis, renal impairment, thrombocytopenia, and disseminated coagulopathy developed within 3 h after intravenous infusion of M type 3, pyrogenic exotoxin A-producing group A streptococci. Serum TNF-alpha peaked at 3 h and returned to baseline by 10 h. Mortality was 100%. Anti-TNF-alpha monoclonal antibody treatment markedly improved mean arterial blood pressure, tissue perfusion, and survival, suggesting that TNF-alpha plays an important role in the induction of shock and organ failure in group A streptococcal bacteremia.

Animals↗
PubMed1996

Genetic and phenotypic diversity among isolates of Streptococcus pyogenes from invasive infections.

To determine if recent cases of invasive group A streptococcal disease were caused by strains with a unique characteristic, 117 isolates Streptococcus pyogenes from patients with a variety of diseases, including necrotizing fasciitis and toxic shock syndrome, were analyzed. Significant genomic heterogeneity was observed among selected isolates, as determined using pulsed-field gel electrophoresis. The frequency of the bacteriophage-associated streptococcal erythrogenic toxin genes A and C (speA and speC) among the isolates was 44% (49/112) and 34% (38/112), respectively. Forty-three percent of speA-positive isolates produced streptococcal erythrogenic toxin (SPE) A in vitro. Seventy-six percent (85/112) of isolates produced SPE B in vitro, and in contrast to SPE A, little variation in the concentration of SPE B in broth culture supernatants was detected. The genetic and phenotypic heterogeneity observed among isolates from recent cases of severe infection does not support a clonal basis for the resurgence of invasive streptococcal infections.

Bacterial Proteins↗
PubMed1996

Phospholipase C and perfringolysin O from Clostridium perfringens upregulate endothelial cell-leukocyte adherence molecule 1 and intercellular leukocyte adherence molecule 1 expression and induce interleukin-8 synthesis in cultured human umbilical vein endothelial cells.

Clostridium perfringens phospholipase C (PLC) and perfringolysin O (PFO) differentially induced human umbilical vein endothelial cell expression and synthesis of endothelial cell-leukocyte adherence molecule-1 (ELAM-1), intracellular leukocyte adherence molecule-1 (ICAM-1), and interleukin-8 (IL-8). PLC strongly induced expression of ELAM-1, ICAM-1, and IL-8, while PFO stimulated early ICAM-1 expression but did not promote ELAM-1 expression or IL-8 synthesis. PLC caused human umbilical vein endothelial cells to assume a fibroblastoid morphology, whereas PFO, in high concentrations or after prolonged low-dose toxin exposure, caused cell death. The toxin-induced expression of proadhesive and activational proteins and direct cytopathic effects may contribute to the leukostasis, vascular compromise, and capillary leak characteristics of C. perfringens gas gangrene.

Bacterial Toxins↗
PubMed1996

Ultrasoft 1.5 keV aluminum K X rays are efficient producers of complex chromosome exchange aberrations as revealed by fluorescence in situ hybridization.

The electron pairs generated by ultrasoft 1.5 keV aluminum K X-ray photons deposit their energy in tracks of length < 70 nm and provide an ideal tool for analyzing the spatial distribution of breaks and misrepair processes. We have undertaken the analysis of changes in chromosome structure produced by aluminum K X rays in untransformed HF12 human fibroblasts in G1 phase using fluorescence in situ hybridization (FISH). Multicolored chromosome-specific DNA probes for chromosomes 1 and 2 and an alpha-satellite pan-centromeric probe were used to examine in vitro radiation-induced chromosome-type exchange aberrations. After mean doses of 0.37-2.93 Gy the relative frequencies of complex exchanges, derived from three or more breaks in two or more chromosomes, ranged from 15-35%. For the classic break-age-and-rejoining theory to hold, very large interaction distances are needed to account for this high frequency of multibreak interactions, unless many sites pre-exist where several different chromosomes come very close together. Alternatively, damaged DNA may be able to interact with adjacent undamaged DNA, obviating the need for large rejoining distances.

Aluminum↗
PubMed1996

Invasive group A streptococcal disease.

The emergence of severe group A streptococcal (GAS) infection since the 1980s has now been reported from most parts of the world. Many of these cases have been associated with deep-seated infection associated with shock and multiple-organ failure and are defined as streptococcal toxic shock syndrome (StrepTSS). Strains of GAS isolated from patients with invasive disease have been predominantly of M types 1 and 3, which produce either pyrogenic exotoxin A or B or both. In this article, the clinical and demographic features of streptococcal bacteremia, myositis, and necrotizing fasciitis are presented and compared with those of StrepTSS. Current concepts about the pathogenesis of invasive streptococcal infection are also discussed, in terms of the interaction between GAS virulence factors and host-defense mechanisms. Finally, the efficacy of clindamycin, the failure of penicillin, and new ideas for future treatment of serious streptococcal infections are outlined.

Age Factors↗
PubMed1995

Frequencies of complex chromosome exchange aberrations induced by 238Pu alpha-particles and detected by fluorescence in situ hybridization using single chromosome-specific probes.

We undertook an analysis of chromosome-type exchange aberrations induced by alpha-particles using fluorescence in situ hybridization (FISH) with whole chromosome-specific probes for human chromosomes 1 or 4, together with a pan-centromeric probe. Contact-inhibited primary human fibroblasts (in G1) were irradiated with 0.41-1.00 Gy 238Pu alpha-particles and aberrations were analysed at the next mitosis following a single chromosome paint. Exchange and aberration painting patterns were classified according to Savage and Simpson (1994a). Of exchange aberrations, 38-47% were found to be complex derived, i.e. resulting from three or more breaks in two or more chromosomes, and the variation with dose was minimal. The class of complex aberrations most frequently observed were insertions, derived from a minimum of three breaks in two chromosomes. There was also an elevated frequency of rings. The high level of complex aberrations observed after alpha-particle irradiation indicates that, when chromosome domains are traversed by high linear energy transfer alpha-particle tracks, there is an enhanced probability of production of multiple localized double-strand breaks leading to more complicated interactions.

Alpha Particles↗
PubMed1995

Antibiotic effects on bacterial viability, toxin production, and host response.

The efficacy of an antibiotic in human or experimental infection is presumed to be proportional to its in vitro antimicrobial activity, yet antibiotics having comparable in vitro activity may have markedly different efficacies in vivo. For example, we have reported that clindamycin is more efficacious than penicillin in experimental gas gangrene caused by Clostridium perfringens in animals. To explain these differences, we compared the dynamics of bacterial killing and suppression of toxin synthesis. In addition, we investigated the ability of clindamycin and penicillin to modulate lipopolysaccharide-induced cytokine production in human peripheral blood mononuclear cells. Our results suggest that clindamycin affects protein synthesis in both prokaryotic and eukaryotic cells. These data may, in part, explain why the efficacy of clindamycin is greater than that of penicillin and demonstrate that clindamycin may be important immune modulator.

Anti-Bacterial Agents↗
PubMed1995

Could nonsteroidal antiinflammatory drugs (NSAIDs) enhance the progression of bacterial infections to toxic shock syndrome?

Anecdotal reports suggest an association between the use of nonsteroidal antiinflammatory drugs (NSAIDs) and the progression of invasive group A streptococcal infections to shock and multiorgan failure. There is a biochemical rationale that could support this theory. Though NSAIDs are frequently used to relieve pain or reduce fever, they also attenuate granulocyte functions such as chemotaxis, phagocytosis, and bacterial killing. In addition, findings in recent studies involving human volunteers injected with endotoxin suggest that pretreatment with NSAIDs enhances production of tumor necrosis factor, which leads to higher blood levels of this cytokine, probably by preventing feedback inhibition by prostaglandin E2. Thus, NSAIDs may contribute to the sudden onset of shock, organ failure, and aggressive infection by inhibiting neutrophil function, augmenting cytokine production, and attenuating the cardinal manifestations of inflammation.

Animals↗
PubMed1995

Selective depletion of V beta-bearing T cells in patients with severe invasive group A streptococcal infections and streptococcal toxic shock syndrome. Ontario Streptococcal Study Project.

The V beta repertoire of T cells of patients with gram-positive group A streptococcal (GAS) and non-GAS infections was analyzed to seek evidence for the role of superantigens in streptococcal toxic shock syndrome. No evidence of V beta overexpression but a consistent pattern of depletion of V beta 1, V beta 5.1, and V beta 12 was observed in patients with severe GAS infections. This pattern of V beta depletion was not observed in patients with nonsevere GAS infections or with severe non-GAS gram-positive infections. T cells from patients with severe GAS infections showed evidence of apoptosis; no apoptosis was found when there was no evidence of V beta depletion. There was no correlation with streptococcal M or T serotype or known spe genes. The depletion of specific V beta-bearing T cells in patients with severe GAS infections supports the role of a superantigen in these infections. The in vivo pattern of V beta specificity implicates a novel superantigen(s) in this disease.

Adolescent↗
PubMed1995

Effects of Clostridium perfringens recombinant and crude phospholipase C and theta-toxin on rabbit hemodynamic parameters.

Clostridium perfringens exotoxins have been implicated as major virulence factors responsible for shock and organ failure in gas gangrene, yet the mechanism(s) by which they mediate cardiovascular dysfunction remain enigmatic. Recombinant (r) phospholipase C (PLC), r theta-toxin, culture supernatant (crude toxin), or 0.9% NaCl was infused intravenously into awake rabbits. Cardiac index (CI), mean arterial pressure (MAP), heart rate (HR), central venous pressure (CVP), arterial blood gases, and hematocrit were measured 1 h before and for 3 h after toxin infusion. Crude toxin and rPLC decreased CI, MAP, and HR and increased CVP; mortality was 87.5% and 83%, respectively. r theta-toxin did not decrease CI or MAP and mortality was 25%. Further, crude toxin and rPLC but not r theta-toxin inhibited cardiac contractility (dF/dt) in isolated rabbit atrial muscles. These results suggest that PLC-induced myocardial dysfunction contributes to shock in C. perfringens infection.

Animals↗
PubMed1995

Virulence studies on chromosomal alpha-toxin and theta-toxin mutants constructed by allelic exchange provide genetic evidence for the essential role of alpha-toxin in Clostridium perfringens-mediated gas gangrene.

The pathogenesis of clostridial myonecrosis, or gas gangrene, involves the growth of the anaerobic bacterium Clostridium perfringens in the infected tissues and the elaboration of numerous extracellular toxins and enzymes. The precise role of each of these toxins in tissue invasion and necrosis has not been determined. To enable genetic approaches to be used to study C. perfringens pathogenesis we developed an allelic exchange method which involved the transformation of C. perfringens cells with a suicide plasmid carrying a gene insertionally inactivated with an erythromycin-resistance determinant. The frequency with which double reciprocal crossover events were observed was increased to a workable level by increasing the amount of homologous DNA located on either side of the inactivated gene. Allelic exchange was used to isolate mutations in the chromosomal pfoA gene, which encodes an oxygen-labile haemolysin known as theta-toxin or perfringolysin O, and in the chromosomal plc gene, which encodes the alpha-toxin or phospholipase C. The resultant mutants failed to produce detectable theta-toxin or alpha-toxin activity, respectively, and could be complemented by recombinant plasmids that carried the respective wild-type genes. The resultant strains were virulence tested in a mouse myonecrosis model. The results showed that the plc mutants had demonstrably reduced virulence and therefore provided definitive genetic evidence for the essential role of alpha-toxin in gas gangrene or clostridial myonecrosis.

Alleles↗
PubMed1995

Calcium modulation of morphine analgesia: role of calcium channels and intracellular pool calcium.

Calcium (Ca++) administered into the i.c.v. space of mice has been reported to block opioid-induced antinociception dose dependently. These studies were conducted to test the hypothesis that Ca++ i.c.v. blocks the antinociceptive effects of morphine i.c.v. as a consequence of transmembrane Ca++ influx and Ca++ release from intracellular pools. Mice were injected with voltage-sensitive Ca++ channel antagonists at a dose that did not affect morphine antinociception to determine whether this pretreatment would prevent the inhibitory effects of Ca++. Nimodipine (12 nmol i.c.v.) was ineffective in preventing the inhibitory effects of Ca++ (100 nmol i.c.v.), whereas omega-conotoxin GVIA (3.3 pmol i.c.v.) completely prevented the inhibition by Ca++ of morphine antinociception. Other experiments were conducted to determine whether blocking Ca++ release from Ca++/caffeine-sensitive microsomal pools with ryanodine would prevent the inhibitory effects of Ca++. Ryanodine (2 nmol i.c.v.) significantly attenuated the inhibition by Ca++ of morphine antinociception. Another hypothesis to be tested was that stimulation of Ca++ release from intracellular pools would, like Ca++, block morphine antinociception. Thapsigargin (0.002-30 nmol i.c.v.), which increases cytosolic Ca++ by depleting Ca++ from inositol 1,4,5-trisphosphate-sensitive microsomal pools, dose-dependently blocked the antinociceptive effects of morphine. The results of this study indicate that Ca++ blocked morphine antinociception by stimulating Ca++ influx through omega-conotoxin GVIA-sensitive channels and by stimulating Ca++ release from Ca++/caffeine-sensitive microsomal pools.

Animals↗