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Biomedical subjects

N P Johnson

Publications and source records attributed to N P Johnson.

At least 19 recordsLinked to original sources
PubMed1996

Strandedness discrimination in peptide-polynucleotide complexes.

Preferential binding to single- or double-stranded nucleic acids is important for the activity of many proteins that process RNA and DNA. We have investigated the mechanism of strandedness discrimination with peptides derived from the putative DNA-binding domain of the RecA protein, a bacterial recombinase that modulates its affinity for single-stranded DNA by means of ATP binding and hydrolysis. Contributions of electrostatic and non-electrostatic interactions to binding of these peptides with polynucleotides were evaluated by fluorescence spectroscopy as a function of salt concentration and peptide charge. Binding of these peptides to single- and double-stranded nucleic acids was dominated by non-electrostatic interactions. Small electrostatic contributions selectively enhanced peptide complexation with single-stranded nucleic acids. Similar results were observed in control experiments carried out with tripeptides containing charged and aromatic amino acid residues. It was possible to modify the strandedness preference of peptide-polynucleotide complexes by changing electrostatic contributions to the binding free energy. These observations suggest a mechanism whereby some proteins that interact with DNA or RNA might determine and regulate their relative affinity for single- and double-stranded nucleic acids.

Amino Acid Sequence↗
PubMed1996

Drinking problems of nursing students.

A sample of 315 nursing students in yearly cohorts (1988-1992) completed the Michigan Alcoholism Screening Test (MAST). A simple and quick instrument with established reliability and validity, the MAST had a reliability coefficient of .78 with this sample. The MAST scores of the nursing students indicated that 21.5% had probable alcoholism or were alcoholic. Drinking problems among these nursing students were similar to those of other nursing students and college students in general. Implications for nurse educators include recognition that nursing students need continuing self-assessment and monitoring to avoid drinking problems as a student and future practitioner. Alcoholism self-screening is an excellent introduction to client assessment for drinking problems. Implications for future research include identifying correlates and determinants of problem drinking behaviors and ultimately developing and testing educational interventions to eliminate the problem.

Adolescent↗
PubMed1996

The influence of race and gender on depressive and substance abuse symptoms in high-risk adolescents.

Concerns about the cultural competence of child mental health services has led to the examination of racial/ethnic and gender differences in the prevalence of psychiatric symptoms. This study examines racial and gender differences in depressive and substance abuse symptomatology in a high-risk population of adolescents living in five residential group homes in South Carolina. We surveyed 299 youth ages 12 to 17, including 101 African American and 198 Whites. They completed the Centers for Epidemiological Studies-Depression scale (CES-D) and questions on substance abuse, demographics, and psychosocial functioning. No significant differences were found in the percentages of Whites and African Americans scoring above 16+ and 23+ cutoff scores on the CES-D, but significant gender differences were identified. Neither race nor race by age group interactions were found to be significantly correlated in regression analyses with CES-D score nor multiple substance use, whereas gender (p < .001) and school performance were significantly correlated with CES-D score, and poverty was correlated with multiple substance use. Our results indicate that levels of depressive symptomatology as measured by the CES-D are much more sensitive to gender than to race in high-risk populations. Different gender cutoffs are indicated when using systematic instruments in the measurement of depressive symptoms.

Adolescent↗
PubMed1995

Does ethnicity influence obstetric intervention?

AIMS: To examine whether the high proportion of Polynesian women giving birth at Middlemore Hospital contributes to its low interventional delivery rate. METHODS: A study of a one-year cohort of women delivering at Middlemore Hospital. Delivery suite records were scrutinised to determine ethnicity and mode of delivery. Statistical comparisons were made. RESULTS: In Maori, Pacific Island and European women the caesarean section rates were 6.5%, 9.5% and 11.5% respectively. Maori women have a significantly lower rate of caesarean section than Pacific Island women and both groups have a significantly lower rate than European women. The spontaneous vaginal delivery rates in Maori, Pacific Island and European women were 89.0%, 87.4% and 74.8% respectively. CONCLUSION: The high proportion New Zealand Maori and Pacific Island women contributes to, but does not fully explain, the low interventional delivery rate at Middlemore Hospital.

Adult↗
PubMed1995

Assessment of the laparoscopic treatment of ectopic pregnancy.

AIMS: To assess the first 2 years experience of the laparoscopic surgical treatment of ectopic pregnancy in a regional referral centre. METHODS: All cases of ectopic pregnancy in a 2 year period from August 1991 were evaluated to assess the impact on the routine management of this condition. RESULTS: In the first year 14 cases were managed by laparoscopic means and took an average operating time of mean 73.8 (SD 17.2) minutes compared to mean 69.1 (17.9) minutes in the 26 cases managed this way in the second year. The 40 patients were hospitalised for an average of 1.4 days and 24 stayed one night only. There was no difference in operating time between registrars and consultants. The only major complication was a patient who required an emergency laparotomy because of continued bleeding. When all cases of ectopic surgery were evaluated in the second year, six of the 32 cases required laparotomy to complete the operation. CONCLUSION: The benefits of laparoscopic surgical treatment of ectopic pregnancy dictate that this should be employed as first line treatment for all cases of tubal ectopic gestation. Our experience suggests that achieving such a service, whilst not without pitfalls, should be possible in all gynaecology units provided that staff are motivated and that laparoscopic equipment is available.

Evaluation Studies as Topic↗
PubMed1994

Double-stranded DNA templates can induce alpha-helical conformation in peptides containing lysine and alanine: functional implications for leucine zipper and helix-loop-helix transcription factors.

Transcription factors of the basic-leucine zipper and basic-helix-loop-helix families specifically recognize DNA by means of intrinsically flexible peptide domains that assume an alpha-helical conformation upon binding to target DNA sequences. We have investigated the nonspecific interactions that underlie specific DNA recognition. Circular dichroism measurements showed that 20-bp double-stranded DNA oligonucleotides can act as templates to promote random coil-->alpha-helix transitions in short peptides containing alanine and lysine. This conformational change takes place without altering the structure of the DNA, and neither specific peptide-DNA contacts nor cooperative interactions between peptides are necessary. The conformational change does require (i) double-stranded (but not single-stranded) oligodeoxynucleotides in either the B or the B' conformation and (ii) peptides that can form positively charged amphipathic alpha-helices. In 10 mM Na2HPO4 (pH 7.5; 10 degrees C), the excess free-energy contribution of the DNA template to the stability of the alpha-helical form of the oligopeptides tested was delta Gex = -0.15 (+/- 0.07) kcal/mol per lysine residue. The implications of these results for the thermodynamics and kinetics of DNA target site selection by basic-leucine zipper and basic-helix-loop-helix regulatory proteins are discussed.

Alanine↗
PubMed1994

Purification and biochemical characterization of Escherichia coli RecA proteins mutated in the putative DNA binding site.

Escherichia coli RecA protein plays a central role both in DNA repair and in recombination. We report biochemical properties of three new RecA proteins mutated at positions 199 (RecA694), 207 (RecA659), and 211 (RecA611) in the putative DNA binding site. RecA694 had a wild-type phenotype, whereas RecA611 and RecA659 were deficient in promoting both the self-cleavage of LexA repressor and the DNA-strand exchange reaction. In order to determine the origin of this inhibition, we examined the capacity of wild-type and mutant proteins to bind to single-stranded DNA (with and without single-stranded binding protein, SSB), double-stranded DNA, and ATP. DNA strand exchange defects were correlated with the inability of mutant proteins to displace SSB from DNA. For the recA659 mutation this inhibition was reversed by equimolar wild-type protein. In contrast, mixtures of either wild-type/RecA659 or wild-type/RecA611 proteins remained deficient in LexA cleavage, suggesting that the dominant negative phenotype of the mutant proteins may be a consequence of the formation heterologous RecA complexes. Various mutations in the putative DNA binding site of RecA protein altered ATP binding, ATPase activity, displacement of SSB from single-stranded DNA, and protein-protein interactions. These results are consistent with the hypothesis that DNA binding to this site of RecA relays allosteric effects to several functional domains throughout the protein.

Adenosine Triphosphatases↗
PubMed1991

Effect of the amine non-leaving group on the structure and stability of DNA complexes with cis-[Pt(R-NH2)2(NO3)2].

The antitumor compound cis-[Pt(NH3)2Cl2] (cisplatin), conserves two ammine ligands during the reaction with its cellular target DNA. Modifications of these non-leaving groups change the antineoplastic properties of this compound and its genotoxic effects. It is therefore of interest to determine the influence of non-leaving groups on the structure and stability of DNA in vitro. We have investigated platinum-DNA adducts formed by cis-[Pt(R-NH2)2(NO3)2] (where R-NH2 = NH3, methylamine, cyclobutylamine, cyclopentylamine and cyclohexylamine) as a function of DNA binding. All compounds quantitatively reacted with DNA in less than 1 h at 37 degrees C. They formed bifunctional adducts with adjacent nucleotides judging from the displacement of the intercalating molecule ethidium bromide, ultraviolet absorption spectroscopy and circular dichroism. Substitution of a H on the NH3 ligand by alkyl groups dramatically destabilized the platinum-DNA complex. Thermal stability decreased progressively with an increasing number of carbon atoms, delta tm = -4.4 degrees C for 3 cyclohexylamine-platinum-DNA adducts/1000 nucleotides, conditions where cisplatin had no effect. DNA adducts with cyclobutylamine and cyclohexylamine ligands inhibited the hydrolysis of platinum-DNA complexes by S1 nuclease. Km for the digestion of DNA containing these lesions was 2.3 times greater than for cisplatin, indicating steric inhibition of enzyme-substrate complex formation. These results show that the non-leaving groups of substituted cis-Pt(II) compounds may destabilize DNA and interfere with protein-DNA interactions. These perturbations may have consequences for the genotoxic and antitumor activities of platinum compounds.

Antineoplastic Agents↗
PubMed1991

Teniposide and cisplatin given by intraperitoneal administration: preclinical and phase I/pharmacokinetic studies.

Cisplatin and teniposide given by intraperitoneal (IP) route exert a synergistic therapeutic effect against ascitic P388 leukemia in mice. As single agents, they display different dose-limiting toxicities and favourable pharmacokinetic characteristics in IP phase I trials. We administered cisplatin (fixed dose: 200 mg/m2) and teniposide (escalating doses) by IP route without dwell-time to investigate the toxicity, pharmacokinetics and clinical activity of this 2-drug combination. Nine patients received a total of 14 courses. Myelosuppression, nausea and vomiting were the most frequent toxicities. Leukopenia was the dose-limiting toxicity. The maximum tolerated dose of teniposide was 100 mg/m2 when administered with a fixed dose of 200 mg/m2 cisplatin. Pharmacokinetic analysis showed that the main parameters of both cisplatin and teniposide in the peritoneum and in the plasma were not modified when the drugs were combined. It appears that a pharmacodynamic interaction exists between cisplatin and teniposide which results in increased hematologic toxicity. Although an objective response has been observed in one patient with refractory ovarian cancer, such association should not be applicable for further clinical development due to marked toxicity and the low dose of teniposide recommended.

Adult↗
PubMed1991

Awareness of substance abuse in orthopedic patients: a survey of orthopedic surgeons.

We surveyed 178 orthopedic physicians in the Washington, DC, area to ascertain the effect on patient care of previous education in the area of drug and alcohol issues. The return rate was 75%. Of the respondents, 99% were male, average age was 46.7 years (+/- 9.3), and average number of years in practice was 15.2 (+/- 9.6). A majority of respondents indicated that they did not have training in the abuse potential of analgesics (92 [69%]), characteristics of benzodiazepine abuse (77 [58%]), or when to seek the assistance of an addiction medicine specialist for patients with chronic pain (106 [80%]). Only 41 (31%) of the orthopedists indicated that they inquire about alcohol and drug use before prescribing opiates for more than a week. We offer suggestions for self-education for interested physicians.

Alcoholism↗
PubMed1990

Kinetic studies of the hydrolysis of platinum-DNA complexes by nuclease S1.

The antitumor agent cis-diamminedichloroplatinum(II) (cis-DDP) reacts covalently with DNA and disrupts its secondary structure. Damaged DNA, but not native DNA, is readily digested by S1 nuclease, an endonuclease specific for single stranded polynucleotides. We have measured S1 nuclease digestion of platinated DNA by the release of platinum-DNA adducts and compared it with digestion of unplatinated DNA. The rate of hydrolysis of damaged substrate from platinum-DNA complexes was less than the overall rate of digestion of nucleotides. Similar results were observed for platinum-DNA complexes in native, denatured or renatured conformations. The hydrolysis of denatured platinum-DNA complexes, rb = 0.075 platinum per nucleotide, obeyed Michaelis-Menten kinetics. Taking into account the level of DNA damage, Vm, for the release of platinated adducts was 0.6 times smaller than for digestion of unplatinated DNA. Km values and competition experiments indicated that the enzyme bound equally well to platinated and unplatinated substrates. Similar results were obtained for denatured DNA complexes with trans-DDP while [PtCl(diethylenetriamine)]Cl had no influence on nuclease digestion. These results suggest that bifunctional platinum-DNA lesions have contradictory effects on the hydrolysis of double stranded DNA by S1 nuclease. On one hand they create nuclease sensitive substrate by disrupting DNA secondary structure. On the other, they inhibit digestion of the damaged strand by increasing the activation energy for hydrolysis.

Cisplatin↗
PubMed1990

Detection of DNA strand breaks in Escherichia coli treated with platinum(IV) antitumor compounds.

DNA strand breaks were observed in bacteria treated with Pt(IV) but not Pt(II) antitumor compounds by two methods. First, compounds which cause DNA strand breaks produced an SOS induction signal which was detected by a rapid bacterial assay. In addition, the capacity of these compounds to cut DNA in vivo was directly measured by agarose gel electrophoresis of pBR322 DNA extracted from bacteria treated with these drugs. cis-Diamminetetrachloroplatinum(IV) (cis-DTP) and cis-dichloro-trans-dihydroxo-cis-bis(isopropylamine)-platinum(IV) (iproplatin) produced strand breaks in both assays while cis-diamminedichloroplatinum(II) (cisplatin) did not. These results indicate that Pt(IV) antitumor complexes may cause DNA damage in vivo which is not produced by Pt(II) compounds.

Antineoplastic Agents↗
PubMed1990

Biophysical studies of the modification of DNA by antitumour platinum coordination complexes.

Cisplatin (cis-diamminedichloroplatinum(II] is widely used in the treatment of various human tumours. A large body of experimental evidence indicates that the reaction of cisplatin with DNA is responsible for the cytostatic action of this drug. Several platinum-DNA adducts have been identified and their effect on the conformation of DNA has been investigated. Structural studies of platinum-DNA adducts now permit a reasonably good explanation of the biophysical properties of platinated DNA. Antitumouractive platinum compounds induce in DNA, at low levels of binding, local conformational alterations which have the character of non-denaturing distortions. It is likely that these changes occur in DNA due to the formation of intrastrand cross-links between two adjacent purine residues. On the other hand, the modification of DNA by antitumour-inactive complexes results in the formation of more severe local denaturation changes. Conformational alterations induced in DNA by antitumour-active platinum compounds may be reparable with greater difficulty than those induced by the inactive complexes. Alternatively, non-denaturation change induced in DNA by antitumour platinum drugs could represent more significant steric hindrance against DNA replication as compared with inactive complexes.

Animals↗