Biomedical subjects

R E Johnson

Publications and source records attributed to R E Johnson.

At least 37 records · Page 2Linked to original sources

PubMed2001

Effects of a signature on rates of change: a randomized controlled trial involving continuing education and the commitment-to-change model.

PURPOSE: Physicians frequently are asked to sign commitments to change practice, based upon their involvement in continuing medical education (CME) activities. Although use of the commitment-to-change model is increasingly widespread in CME, the effect of signing such commitments on rates of change is not well understood. METHOD: Immediately after a CME session, 110 physicians were asked to specify a change they intended to make in practice and to designate a level of commitment to change. To determine the effects of a signature on rates of change, physicians were randomly assigned to control (signature) and experimental (non-signature) groups. Follow-up surveys were conducted at two and three months to determine rates of change. RESULTS: In all, 88 physicians completed the first questionnaire, and 64 of them completed the follow-up. Consistent with prior studies involving the commitment-to-change model, those expressing an intention to change were significantly more likely to change on follow-up (p =.035). There was no significant difference between signature and non-signature groups (p =.99), regardless of age or gender. CONCLUSIONS: Signatures appear unimportant to assuring compliance with commitments to change used in CME conferences. A physician's behavior can be expected to change if the specified change is consistent with the physician's beliefs and sense of what is important. The relative influences of components of the commitment-to-change model require further study to determine more clearly their roles in causation and measurement.

Adult↗

PubMed2001

Requirement of DNA polymerase eta for error-free bypass of UV-induced CC and TC photoproducts.

The yeast RAD30-encoded DNA polymerase eta (Poleta) bypasses a cis-syn thymine-thymine dimer efficiently and accurately. Human DNA polymerase eta functions similarly in the bypass of this lesion, and mutations in human Poleta result in the cancer prone syndrome, the variant form of xeroderma pigmentosum. UV light, however, also elicits the formation of cis-syn cyclobutane dimers and (6-4) photoproducts at 5'-CC-3' and 5'-TC-3' sites, and in both yeast and human DNA, UV-induced mutations occur primarily by 3' C to T transitions. Genetic studies presented here reveal a role for yeast Poleta in the error-free bypass of cyclobutane dimers and (6-4) photoproducts formed at CC and TC sites. Thus, by preventing UV mutagenesis at a wide spectrum of dipyrimidine sites, Poleta plays a pivotal role in minimizing the incidence of sunlight-induced skin cancers in humans.

Alleles↗

PubMed2001

Role of DNA polymerase eta in the bypass of a (6-4) TT photoproduct.

UV light-induced DNA lesions block the normal replication machinery. Eukaryotic cells possess DNA polymerase eta (Poleta), which has the ability to replicate past a cis-syn thymine-thymine (TT) dimer efficiently and accurately, and mutations in human Poleta result in the cancer-prone syndrome, the variant form of xeroderma pigmentosum. Here, we test Poleta for its ability to bypass a (6-4) TT lesion which distorts the DNA helix to a much greater extent than a cis-syn TT dimer. Opposite the 3' T of a (6-4) TT photoproduct, both yeast and human Poleta preferentially insert a G residue, but they are unable to extend from the inserted nucleotide. DNA Polzeta, essential for UV induced mutagenesis, efficiently extends from the G residue inserted opposite the 3' T of the (6-4) TT lesion by Poleta, and Polzeta inserts the correct nucleotide A opposite the 5' T of the lesion. Thus, the efficient bypass of the (6-4) TT photoproduct is achieved by the combined action of Poleta and Polzeta, wherein Poleta inserts a nucleotide opposite the 3' T of the lesion and Polzeta extends from it. These biochemical observations are in concert with genetic studies in yeast indicating that mutations occur predominantly at the 3' T of the (6-4) TT photoproduct and that these mutations frequently exhibit a 3' T-->C change that would result from the insertion of a G opposite the 3' T of the (6-4) TT lesion.

Animals↗

PubMed2001

Physical and functional interactions of human DNA polymerase eta with PCNA.

Human DNA polymerase eta (hPoleta) functions in the error-free replication of UV-damaged DNA, and mutations in hPoleta cause cancer-prone syndrome, the variant form of xeroderma pigmentosum. However, in spite of its key role in promoting replication through a variety of distorting DNA lesions, the manner by which hPoleta is targeted to the replication machinery stalled at a lesion site remains unknown. Here, we provide evidence for the physical interaction of hPoleta with proliferating cell nuclear antigen (PCNA) and show that mutations in the PCNA binding motif of hPoleta inactivate this interaction. PCNA, together with replication factor C and replication protein A, stimulates the DNA synthetic activity of hPoleta, and steady-state kinetic studies indicate that this stimulation accrues from an increase in the efficiency of nucleotide insertion resulting from a reduction in the apparent K(m) for the incoming nucleotide.

Amino Acid Sequence↗

PubMed2000

A comparison of levomethadyl acetate, buprenorphine, and methadone for opioid dependence.

BACKGROUND: Opioid dependence is a chronic, relapsing disorder with important public health implications. METHODS: In a 17-week randomized study of 220 patients, we compared levomethadyl acetate (75 to 115 mg), buprenorphine (16 to 32 mg), and high-dose (60 to 100 mg) and low-dose (20 mg) methadone as treatments for opioid dependence. Levomethadyl acetate and buprenorphine were administered three times a week. Methadone was administered daily. Doses were individualized except in the group assigned to low-dose methadone. Patients with poor responses to treatment were switched to methadone. RESULTS: There were 55 patients in each group; 51 percent completed the trial. The mean (+/-SE) number of days that a patient remained in the study was significantly higher for those receiving levomethadyl acetate (89+/-6), buprenorphine (96+/-4), and high-dose methadone (105+/-4) than for those receiving low-dose methadone (70+/-4, P<0.001). Continued participation was also significantly more frequent among patients receiving high-dose methadone than among those receiving levomethadyl acetate (P=0.02). The percentage of patients with 12 or more consecutive opioid-negative urine specimens was 36 percent in the levomethadyl acetate group, 26 percent in the buprenorphine group, 28 percent in the high-dose methadone group, and 8 percent in the low-dose methadone group (P=0.005). At the time of their last report, patients reported on a scale of 0 to 100 that their drug problem had a mean severity of 35 with levomethadyl acetate, 34 with buprenorphine, 38 with high-dose methadone, and 53 with low-dose methadone (P=0.002). CONCLUSIONS: As compared with low-dose methadone, levomethadyl acetate, buprenorphine, and high-dose methadone substantially reduce the use of illicit opioids.

Adult↗

PubMed2000

Mismatch extension ability of yeast and human DNA polymerase eta.

DNA polymerase eta (Poleta) functions in error-free replication of UV-damaged DNA, and in vitro it efficiently bypasses a cis-syn T-T dimer by incorporating two adenines opposite the lesion. Steady state kinetic studies have shown that both yeast and human Poleta are low-fidelity enzymes, and they misincorporate nucleotides with a frequency of 10(-2)-10(-3) on both undamaged and T-T dimer-containing DNA templates. To better understand the role of Poleta in error-free translesion DNA synthesis, here we examine the ability of Poleta to extend from base mismatches. We find that both yeast and human Poleta extend from mismatched base pairs with a frequency of approximately 10(-3) relative to matched base pairs. In the absence of efficient extension of mismatched primer termini, the ensuing dissociation of Poleta from DNA may favor the excision of mismatched nucleotides by a proofreading exonuclease. Thus, we expect DNA synthesis by Poleta to be more accurate than that predicted from the fidelity of nucleotide incorporation alone.

Base Pair Mismatch↗

PubMed2000

Eukaryotic polymerases iota and zeta act sequentially to bypass DNA lesions.

DNA lesions can often block DNA replication, so cells possess specialized low-fidelity, and often error-prone, DNA polymerases that can bypass such lesions and promote replication of damaged DNA. The Saccharomyces cerevisiae RAD30 and human hRAD30A encode Pol eta, which bypasses a cis-syn thymine-thymine dimer efficiently and accurately. Here we show that a related human gene, hRAD30B, encodes the DNA polymerase Pol iota, which misincorporates deoxynucleotides at a high rate. To bypass damage, Pol iota specifically incorporates deoxynucleotides opposite highly distorting or non-instructional DNA lesions. This action is combined with that of DNA polymerase Pol zeta, which is essential for damage-induced mutagenesis, to complete the lesion bypass. Pol zeta is very inefficient in inserting deoxynucleotides opposite DNA lesions, but readily extends from such deoxynucleotides once they have been inserted. Thus, in a new model for mutagenic bypass of DNA lesions in eukaryotes, the two DNA polymerases act sequentially: Pol iota incorporates deoxynucleotides opposite DNA lesions, and Pol zeta functions as a mispair extender.

Base Pairing↗

PubMed2000

Apurinic endonuclease activity of yeast Apn2 protein.

Abasic (apurinic/apyrimidinic; AP) sites are generated in vivo through spontaneous base loss and by enzymatic removal of bases damaged by alkylating agents and reactive oxygen species. In Saccharomyces cerevisiae, the APN1 and APN2 genes function in alternate pathways of AP site removal. Apn2-like proteins have been identified in other eukaryotes including humans, and these proteins form a distinct subfamily within the exonuclease III (ExoIII)/Ape1/Apn2 family of proteins. Apn2 and other members of this subfamily contain a carboxyl-terminal extension not present in the ExoIII/Ape1-like proteins. Here, we purify the Apn2 protein from yeast and show that it is a class II AP endonuclease. Deletion of the carboxyl terminus does not affect the AP endonuclease activity of the protein, but this protein is defective in the removal of AP sites in vivo. The carboxyl terminus may enable Apn2 to complex with other proteins, and such a multiprotein assembly may be necessary for the efficient recognition and cleavage of AP sites in vivo.

Amino Acid Sequence↗

PubMed2000

Nalmefene: blockade of intravenous morphine challenge effects in opioid abusing humans.

No studies have assessed the dose-effect or duration of opioid blockade in opioid abusers produced by oral nalmefene, a micro-opioid antagonist. The present study examined the profile and time course of oral nalmefene blockade of subjective and physiological effects produced by intravenous morphine. To assess these effects, seven opioid abusers received oral nalmefene (0, 50 and 100 mg) followed by intravenous morphine (0, 10 and 20 mg) challenges every 24 h for 96 h using a Latin square randomized cross-over design. The duration of blockade varied by measure and dose. Both 50 and 100 mg nalmefene blocked morphine's effects up to 48 h.

Adult↗

PubMed2000

The human DINB1 gene encodes the DNA polymerase Poltheta.

The human DINB1 gene shares a high degree of homology with the Escherichia coli dinB gene. Here, we purify the hDINB1-encoded protein and show that it is a DNA polymerase. Because hDinB1 is the eighth eukaryotic DNA polymerase to be described, we have named it DNA polymerase (Pol) theta. hPoltheta is unable to bypass a cis-syn thymine-thymine dimer, nor does it bypass a (6-4) photoproduct or an abasic site. We also examine the fidelity of hPoltheta on nondamaged DNA templates by steady-state kinetic analyses and find that hPoltheta misincorporates deoxynucleotides with a frequency of about 10(-3) to 10(-4). We discuss the relationship between the fidelity of hPoltheta and its inability to bypass DNA damage.

Base Sequence↗

PubMed2000

Accuracy of thymine-thymine dimer bypass by Saccharomyces cerevisiae DNA polymerase eta.

The Saccharomyces cerevisiae RAD30 gene functions in error-free replication of UV-damaged DNA. RAD30 encodes a DNA polymerase, Pol eta, which inserts two adenines opposite the two thymines of a cis-syn thymine-thymine (T-T) dimer. Here we use steady-state kinetics to determine the accuracy of DNA synthesis opposite the T-T dimer. Surprisingly, the accuracy of DNA synthesis opposite the damaged DNA is nearly indistinguishable from that opposite nondamaged DNA, with frequencies of misincorporation of about 10(-2) to 10(-3). These studies support the hypothesis that unlike most DNA polymerases, Pol eta is able to tolerate distortions in DNA resulting from damage, which then enables the polymerase to utilize the intrinsic base pairing ability of the T-T dimer.

Base Sequence↗

PubMed2000

Fidelity of human DNA polymerase eta.

Xeroderma pigmentosum (XP) patients are highly sensitive to sunlight, and they suffer from a high incidence of skin cancers. The variant form of XP results from mutations in the hRAD30A gene, which encodes the DNA polymerase in humans, hPol(eta). Of the eukaryotic DNA polymerases, only human Pol(eta) and its yeast counterpart have the ability to replicate DNA containing a cis-syn thymine-thymine (T-T) dimer. Here we measure the fidelity of hPol(eta) on all four nondamaged template bases and at each thymine residue of a cis-syn T-T dimer. Opposite all four nondamaged template bases, hPol(eta) misincorporates nucleotides with a frequency of approximately 10(-2)-10(-3), and importantly, hPol(eta) synthesizes DNA opposite the T-T dimer with the same accuracy and efficiency as opposite the nondamaged DNA. The low fidelity of hPol(eta) may derive from a flexible active site that renders the enzyme more tolerant of geometric distortions in DNA and enables it to synthesize DNA past a T-T dimer.

DNA Damage↗

PubMed2000

Buprenorphine and naloxone for heroin dependence.

The pharmacology of buprenorphine is unique because of its partial agonist profile at the mu-opioid receptor (ie, high affinity, low intrinsic activity and slow dissociation). This unique profile results in greater safety, less physical dependence, and greater flexibility in dose scheduling. Buprenorphine has been investigated in combination with the opioid antagonist, naloxone, with the goal of decreasing abuse, misuse, and diversion. When combined with naloxone in a sublingual tablet, buprenorphine has been shown to be effective 1) in retaining patients in treatment, 2) in reducing opioid use and craving, and 3) when dosed less-than-daily. The pharmacologic effects of buprenorphine are not altered by the addition of naloxone when administered to the population in an appropriate combination ratio. However, if taken intravenously by individuals dependent on short- or long-acting opioids a precipitated withdrawal syndrome is observed, which should reduce its abuse potential. This review discusses the rationale for development and evidence supporting the use of a buprenorphine/naloxone combination product. The buprenorphine/naloxone combination product should be considered for use in primary care office-based settings as a safe and effective treatment that is likely to increase the availability of agonist treatment for opioid dependence.

Buprenorphine↗

PubMed2000

A one-year audit of topics and domains in the Journal of the American Medical Association and the New England Journal of Medicine.

BACKGROUND: The relative emphasis that major medical journals give to topic areas has a potential effect on priorities in patient care, policy decisions, and public awareness. We measured the distribution of topics in two journals, by disease categories and domains, over a calendar year. METHODS: All original investigations, reviews, editorials, and special articles published in 1998 by the Journal of the American Medical Association and the New England Journal of Medicine were classified by article type, disease category, and domain. The 12 domains ranged from basic science to health policy, and included primary and secondary prevention. RESULTS: The 1159 articles published in 1998 included 889 (77%) articles about specific diseases-590 falling within eight specialties-and 190 (16%) articles on generic topics. Eighty (7%) articles concerned the behaviors that cause disease. Primary prevention and screening were the subject of 71 (6%) and 29 (3%) articles, respectively. Most of these concerned uncommon issues in patient care. Although 27 (2%) articles dealt with essential health promotion (e.g., diet, exercise), and none included a study on how to help patients to exercise, stop smoking, or eat a healthy diet. In contrast, 451 (39%) articles concerned the diagnosis and treatment of patients with disease. CONCLUSIONS: The relative emphasis that journals gave to prevention during the sample period seems discordant with its importance to patients and public health. Potential explanations include poor volume and quality of submitted research and editorial concerns about importance and reader appeal.

Bibliometrics↗

PubMed2000

Evaluating the administration of an office-based health survey in a primary care practice.

Self-administered waiting room questionnaires are popular tools for gathering health information from patients, but these data cannot be used for research purposes without confirming adequate sampling of the practice population and assessing the completeness and accuracy of patients' responses. Long-term data collection also requires avoiding an imposition on clinic operations. We developed a protocol to test these questions in a 9-week pilot study of 884 survey-eligible patients visiting a family practice clinic. We found an adequate proportion of eligible patients were approached (74%) and participated (89%), they provided relatively complete (82-98%) and accurate responses, and the impact on office operations was minimal (<2 min of staff time per participant). Some demographic differences in participation and survey item completion were identified. A systematic process for testing survey performance allowed us to not only document these findings, but also to rapidly identify problems and introduce solutions while the survey was in progress.

Adolescent↗

PubMed2000

Controlled trials of CQI and academic detailing to implement a clinical practice guideline for depression.

BACKGROUND: The release of the Agency for Health Care Policy and Research (AHCPR)'s Guideline for the Detection and Treatment of Depression in Primary Care created an opportunity to evaluate under naturalistic conditions the effectiveness of two clinical practice guideline implementation methods: continuous quality improvement (CQI) and academic detailing. A study conducted in 1993-1994 at Kaiser Permanente Northwest Division, a large, not-for-profit prepaid group practice (group-model) HMO, tested the hypotheses that each method would increase the number of members receiving depression treatment and would relieve depressive symptoms. METHODS: Two trials were conducted simultaneously among adult primary care physicians, physician assistants, and nurse practitioners, using the same guideline document, measurement methods, and one-year follow-up period. The academic detailing trial was randomized at the clinician level. CQI was assigned to one of the setting's two geographic areas. To account for intraclinician correlation, both trials were evaluated using generalized equations analysis. RESULTS: Most of the CQI team's recommendations were not implemented. Academic detailing increased treatment rates, but--in a cohort of patients with probable chronic depressive disorder--it failed to improve symptoms and reduced measures of overall functional status. CONCLUSIONS: New organizational structures may be necessary before CQI teams and academic detailing can substantially change complex processes such as the primary care of depression. New research and treatment guidelines are needed to improve the management of persons with chronic or recurring major depressive disorder.

Adult↗

PubMed2000

Bovine gingival lysate: a novel substrate for rapid diagnosis of autoimmune vesiculo-bullous diseases. A preliminary observation.

Immunoblot assays have been developed to characterize the autoantigens and to detect autoantibodies in muco-cutaneous autoimmune vesiculo-bullous diseases using different substrates. However the results have been inconsistent, because availability and standardization of different substrates has been a major problem. The aim of this study was to develop an immunoblot assay using bovine gingival lysate as substrate because it is easily and readily available as well as inexpensive. Sera from patients with different vesiculo-bullous diseases were studied. These included 25 patients with pemphigus vulgaris (PV), 8 with paraneoplastic pemphigus (PNP), 12 with pemphigus foliaceus (PF), 25 with bullous pemphigoid (BP), and 22 with cicatricial pemphigoid (CP). Serum samples from 40 normal human volunteers were also studied. The autoantibody titers were determined based on the binding pattern of each disease and compared to those obtained by routine indirect immunofluorescence (IIF). Our observations suggest that the titers from immunoblot assays were significantly higher than titers obtained by IIF (P<0.0001). When the autoantibody titers were compared using bovine gingival lysate and human epidermal lysate as substrate, statistically significant differences were not observed. The use of bovine gingival lysate as a substrate will facilitate the rapid and early serological diagnosis of patients with vesiculobullous diseases. It may also be of benefit to laboratory investigators studying these autoantibodies.

Animals↗

PubMed2000

Efficient and accurate replication in the presence of 7,8-dihydro-8-oxoguanine by DNA polymerase eta.

Oxidative damage to DNA has been proposed to have a role in cancer and ageing. Oxygen-free radicals formed during normal aerobic cellular metabolism attack bases in DNA, and 7, 8-dihydro-8-oxoguanine (8-oxoG) is one of the adducts formed. Eukaryotic replicative DNA polymerases replicate DNA containing 8-oxoG by inserting an adenine opposite the lesion; consequently, 8-oxoG is highly mutagenic and causes G:C to T:A transversions. Genetic studies in yeast have indicated a role for mismatch repair in minimizing the incidence of these mutations. In Saccharomyces cerevisiae, deletion of OGG1, encoding a DNA glycosylase that functions in the removal of 8-oxoG when paired with C, causes an increase in the rate of G:C to T:A transversions. The ogg1Delta msh2Delta double mutant displays a higher rate of CAN1S to can1r forward mutations than the ogg1Delta or msh2Delta single mutants, and this enhanced mutagenesis is primarily due to G:C to T:A transversions. The gene RAD30 of S. cerevisiae encodes a DNA polymerase, Poleta, that efficiently replicates DNA containing a cis-syn thymine-thymine (T-T) dimer by inserting two adenines across from the dimer. In humans, mutations in the yeast RAD30 counterpart, POLH, cause the variant form of xeroderma pigmentosum (XP-V), and XP-V individuals suffer from a high incidence of sunlight-induced skin cancers. Here we show that yeast and human POLeta replicate DNA containing 8-oxoG efficiently and accurately by inserting a cytosine across from the lesion and by proficiently extending from this base pair. Consistent with these biochemical studies, a synergistic increase in the rate of spontaneous mutations occurs in the absence of POLeta in the yeast ogg1Delta mutant. Our results suggest an additional role for Poleta in the prevention of internal cancers in humans that would otherwise result from the mutagenic replication of 8-oxoG in DNA.

DNA↗