Biomedical subjects

L S Brown

Publications and source records attributed to L S Brown.

At least 37 records · Page 2Linked to original sources

PubMed1998

Buprenorphine maintenance treatment of opiate dependence: a multicenter, randomized clinical trial.

AIMS: To evaluate the safety and efficacy of an 8 mg/day sublingual dose of buprenorphine in the maintenance treatment of heroin addicts by comparison with a 1 mg/day dose over a 16-week treatment period. As a secondary objective, outcomes were determined concurrently for patients treated with two other dose levels. DESIGN: Patients were randomized to four dosage groups and treated double-blind. SETTING: Twelve outpatient opiate maintenance treatment centers throughout the United States. PARTICIPANTS: Two hundred and thirty-nine women and 497 men who met the DSM-III-R criteria for opioid dependence and were seeking treatment. INTERVENTION: Patients received either 1, 4, 8 or 16 mg/day of buprenorphine and were treated in the usual clinical context, including a 1-hour weekly clinical counseling session. MEASUREMENT: Retention in treatment, illicit opioid use as determined by urine toxicology, opioid craving and global ratings by patient and staff. Safety outcome measures were provided by clinical monitoring and by analysis of the reported adverse events. FINDINGS: Outcomes in the 8 mg group were significantly better than in the 1 mg group in all four efficacy domains. No deaths occurred in either group. The 8 mg group did not show an increase in the frequency of adverse events. Most reported adverse effects were those commonly seen in patients treated with opioids. CONCLUSIONS: The findings support the safety and efficacy of buprenorphine and suggest that an adequate dose of buprenorphine will be a useful addition to pharmacotherapy.

Buprenorphine↗

PubMed1998

Rates of tuberculosis infection in healthcare workers providing services to HIV-infected populations. Terry Beirn Community Programs for Clinical Research on AIDS.

OBJECTIVE: To assess the prevalence of tuberculosis (TB) or a positive skin test in healthcare workers (HCWs) providing services to human immunodeficiency virus (HIV)-infected individuals and to determine prospectively the incidence of new infections in this population. DESIGN: This prospective cohort study enrolled 1,014 HCWs working with HIV-infected populations from 10 metropolitan areas. Purified protein derivative (PPD) tuberculin skin tests were placed at baseline and every 6 months afterwards on those without a history of TB or a positive PPD. Demographic, occupational, and TB exposure data also were collected. SETTING: Outpatient clinics, hospitals, private practice offices, and drug treatment programs providing HIV-related healthcare and research programs. PARTICIPANTS: A voluntary sample of staff and volunteers from 16 Community Programs for Clinical Research on AIDS units. RESULTS: Factors related to prior TB or a positive skin test at baseline included being foreign-born, increased length of time in health care, living in New York City, or previous bacille Calmette-Guerin vaccination. The rate of PPD conversion was 1.8 per 100 person years of follow-up. No independent relation was found between the amount or type of contact with HIV-infected populations and the risk of TB infection. CONCLUSION: These data provide some reassurance that caring for HIV-infected patients is not related to an increased rate of TB infection among HCWs in these settings.

AIDS-Related Opportunistic Infections↗

PubMed1997

Transient channel-opening in bacteriorhodopsin: an EPR study.

Active translocation of ions across membranes requires alternating access of the ion binding site inside the pump to the two membrane surfaces. Proton translocation by bacteriorhodopsin (bR), the light-driven proton pump in Halobacterium salinarium, involves this kind of a change in the accessibility of the centrally located retinal Schiff base. This key event in bR's photocycle ensures that proton release occurs to the extracellular side and proton uptake from the cytoplasmic side. To study the role of protein conformational changes in this reprotonation switch, spin labels were attached to pairs of engineered cysteine residues in the cytoplasmic interhelical loops of bR. Light-induced changes in the distance between a spin label on the EF interhelical loop and a label on either the AB or the CD interhelical loop were observed, and the changes were monitored following photoactivation with time-resolved electron paramagnetic resonance (EPR) spectroscopy. Both distances increase transiently by about 5 A during the photocycle. This opening occurs between proton release and uptake, and may be the conformational switch that changes the accessibility of the retinal Schiff base to the cytoplasmic surface after proton release to the extracellular side.

Bacteriorhodopsins↗

PubMed1997

A controlled trial of isoniazid in persons with anergy and human immunodeficiency virus infection who are at high risk for tuberculosis. Terry Beirn Community Programs for Clinical Research on AIDS.

BACKGROUND: Patients with human immunodeficiency virus (HIV) infection and latent tuberculosis are at substantial risk for the development of active tuberculosis. As a public health measure, prophylactic treatment with isoniazid has been suggested for HIV-infected persons who have anergy and are in groups with a high prevalence of tuberculosis. METHODS: We conducted a multicenter, randomized, double-blind, placebo-controlled trial of six months of prophylactic isoniazid treatment in HIV-infected patients with anergy who have risk factors for tuberculosis infection. The primary end point was culture-confirmed tuberculosis. RESULTS: The study was conducted from November 1991 through June 1996. Over 90 percent of the patients had two or more risk factors for tuberculosis infection, and nearly 75 percent of patients were from greater New York City. After a mean follow-up of 33 months, tuberculosis was diagnosed in only 6 of 257 patients in the placebo group and 3 of 260 patients in the isoniazid group (risk ratio, 0.48; 95 percent confidence interval, 0.12 to 1.91; P=0.30). There were no significant differences between the two groups with regard to death, death or the progression of HIV disease, or adverse events. CONCLUSIONS: Even in HIV-infected patients with anergy and multiple risk factors for latent tuberculosis infection, the rate of development of active tuberculosis is low. This finding does not support the use of isoniazid prophylaxis in high-risk patients with HIV infection and anergy unless they have been exposed to active tuberculosis.

AIDS-Related Opportunistic Infections↗

PubMed1997

A local electrostatic change is the cause of the large-scale protein conformation shift in bacteriorhodopsin.

During light-driven proton transport bacteriorhodopsin shuttles between two protein conformations. A large-scale structural change similar to that in the photochemical cycle is produced in the D85N mutant upon raising the pH, even without illumination. We report here that (i) the pKa values for the change in crystallographic parameters and for deprotonation of the retinal Schiff base are the same, (ii) the retinal isomeric configuration is nearly unaffected by the protein conformation, and (iii) preventing rotation of the C13-C14 double bond by replacing the retinal with an all-trans locked analogue makes little difference to the Schiff base pKa. We conclude that the direct cause of the conformational shift is destabilization of the structure upon loss of interaction of the positively charged Schiff base with anionic residues that form its counter-ion.

Bacteriorhodopsins↗

PubMed1997

Time-resolved fourier transform infrared study of structural changes in the last steps of the photocycles of Glu-204 and Leu-93 mutants of bacteriorhodopsin.

The last intermediate in the photocycle of the light-driven proton pump bacteriorhodopsin is the red-shifted O state. The structure and dynamics of the last step in the photocycle were characterized with time-resolved Fourier transform infrared spectroscopy of the mutants of Glu-204 and Leu-93, which accumulate this intermediate in much larger amounts than the wild type. The results show that E204Q and E204D give distorted all-trans-retinal chromophore like the O intermediate of the wild type. This is simply due to the perturbation of the proton acceptor function of Glu-204 in the O-to-BR transition in the Glu-204 mutants. The corresponding red-shifted intermediates of L93M, L93T, and L93S have a 13-cis chromophore like the N intermediate of the wild type, as reported from analysis of extracted retinal [Delaney, J. K., Schweiger, U., & Subramaniam, S. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 11120-11124]. In spite of their different chromophore structures from the O intermediate, the red-shifted intermediates are similar to the O intermediate but not to the N intermediate of the wild type with respect to structural changes in the peptide carbonyls. The structural changes around Asp-96 in the N intermediate are completely restored also in the red-shifted intermediates of the Leu-93 mutants like in the O intermediate. These results imply that the protein structural changes in the last step proceed regardless of thermal isomerization of the chromophore. Time-resolved Fourier transform infrared spectroscopy with the Glu-204 mutants suggests that the response of Asp-204 (Glu-204 in the wild type) to the protonation of Asp-85 during formation of the M intermediate, which results in proton release, is slow and may occur through structural changes.

Bacteriorhodopsins↗

PubMed1997

Guanidinium restores the chromophore but not rapid proton release in bacteriorhodopsin mutant R82Q.

Replacement of the Arg residue at position 82 in bacteriorhodopsin by Gln or Ala was previously shown to slow the rate of proton release and raise the pK of Asp 85, indicating that R82 is involved both in the proton release reaction and in stabilizing the purple form of the chromophore. We now find that guanidinium chloride lowers the pK of D85, as monitored by the shift of the 587-nm absorbance maximum to 570 nm (blue to purple transition) and increased yield of photointermediate M. The absorbance shift follows a simple binding curve, with an apparent dissociation constant of 20 mM. When membrane surface charge is taken into account, an intrinsic dissociation constant of 0.3 M fits the data over a range of 0.2-1.0 M cation concentration (Na+ plus guanidinium) and pH 5.4-6.7. A chloride counterion is not involved in the observed spectral changes, as chloride up to 0.2 M has little effect on the R82Q chromophore at pH 6, whereas guanidinium sulfate has a similar effect to guanidinium chloride. Furthermore, guanidinium does not affect the chromophore of the double mutant R82Q/D85N. Taken together, these observations suggest that guanidinium binds to a specific site near D85 and restores the purple chromophore. Surprisingly, guanidinium does not restore rapid proton release in the photocycle of R82Q. This result suggests either that guanidinium dissociates during the pump cycle or that it binds with a different hydrogen-bonding geometry than the Arg side chain of the wild type.

Bacteriorhodopsins↗

PubMed1997

Sexual risk behaviour among subgroups of heterosexual HIV infected patients in an urban setting.

OBJECTIVE: To determine the frequency of characteristics associated with unprotected heterosexual intercourse in HIV infected adults in an urban area. DESIGN: Retrospective comparison of sexual risk transmission behaviour between HIV infected men and women from a drug treatment site and between women from the drug site and HIV infected women from an urban medical centre. METHODS: HIV infected women and men were asked questions on sexual behaviour for a 1 year period before enrollment. The outcome variable was heterosexual risk behaviour (HRB) defined as having vaginal sex at least once in the previous year and not always using condoms. RESULTS: 73% of the drug clinic females, 72% of the drug clinic males, and 42% of the medical centre female engaged in HRB. Using logistic regression analysis, women and men in drug treatment engaged in similar rates of HRB; however, women in drug treatment were four times (95% CI = 2.0-8.3) more likely to engage in HRB risk behaviour than women from the medical centre. CONCLUSION: The data suggest that a surprisingly large portion of HIV infected patients under treatment engaged in HRB, especially former drug users. Without specifically targeted interventions, the heterosexual spread of HIV in urban areas will continue to be a serious problem.

Adult↗

PubMed1996

Interaction of proton and chloride transfer pathways in recombinant bacteriorhodopsin with chloride transport activity: implications for the chloride translocation mechanism.

When the protonated retinal Schiff base dissociates in the photocycle of the proton pump bacteriorhodopsin, asp-85 is the proton acceptor. Replacing this residue with threonine confers halorhodopsin-like properties on the protein, including chloride transport [Sasaki, J., Brown, L.S., Chon, Y.-S., Kandori, H., Maeda, A., Needleman, R., & Lanyi, J.K. (1995) Science 269, 73-75]. However, the electrostatic interaction between the vicinity of residue 85 and glu-204, a residue located about 10 A away near the extracellular surface, that is a part of the proton transport mechanism, should still exist. We find that in the D85T mutant glu-204 becomes protonated when chloride is added. This indicates that the binding of chloride at thr-85 must be equivalent to deprotonation of asp-85. The protonation state of glu-204 reports therefore on the presence or absence of chloride bound at thr-85. During the chloride-transport cycle of D85T, but not D85T/E204Q, fluorescein and pyranine detect the transient release of protons from the protein to the surface and the bulk. The release and the subsequent uptake of the protons occur during the rise and decay of a red-shifted photointermediate, respectively, and confirm the earlier suggestion that this state has the same role in the chloride transport as the M intermediate in the proton transport. Consistent with the red-shift of the absorption maximum, the chloride bound near the Schiff base had already moved away, presumably to be released at the cytoplasmic surface, but another chloride ion has not yet been taken up from the extracellular surface. The switch of the connectivity of the chloride binding site from the cytoplasmic to the extracellular membrane surface must occur therefore during the lifetime of this photointermediate.

Aspartic Acid↗

PubMed1996

Lack of a pharmacologic interaction between rifabutin and methadone in HIV-infected former injecting drug users.

Rifampin, an agent known to decrease the half-life of methadone, and rifabutin are two rifamycins that are structurally similar and share mechanisms of action. Hence the possibility of a drug-drug interaction between rifabutin and methadone was evaluated in 24 methadone-maintained, former injecting drug users infected with the human immunodeficiency virus. The study was an open-label, drug-drug interaction and safety trial in which patients were followed for 15 days. Each patient received rifabutin 300 mg as a single dose concomitantly with their individualized methadone dosage. No significant differences in methadone peak plasma concentration, time to peak plasma concentration, area under the plasma concentration-time curve, systemic clearance or renal clearance was observed in the presence of rifabutin. Seventy-five percent of the patients reported at least one symptom of narcotic withdrawal during the study, however, these symptoms were mild. A relationship between the development of narcotic withdrawal and methadone systemic exposure could not be established. Concurrent administration of rifabutin and methadone appeared to be safe in human immunodeficiency virus-infected injecting drug users maintained on stable doses of methadone and is not expected to produce any significant changes in the pharmacokinetics of methadone in these patients.

AIDS-Related Opportunistic Infections↗

PubMed1996

Hydration of the counterion of the Schiff base in the chloride-transporting mutant of bacteriorhodopsin: FTIR and FT-raman studies of the effects of anion binding when Asp85 is replaced with a neutral residue.

The chromophores of the D85T and D85N mutants of bacteriorhodopsin are blue but become purple like the wild type when chloride or bromide binds near the Schiff base. In D85T this occurs near neutral pH, but in D85N only at pH < 4. The structures of the L and the unphotolyzed states of these proteins were examined with Fourier transform infrared spectroscopy. The difference spectra of the purple forms, but not the blue forms in the absence of these anions, resembled the spectrum of the wild-type protein. Shift of the ethylenic band toward lower frequency upon replacing chloride by bromide confirmed the contribution of the negative charge of the anions to the Schiff base counterion. These anions restored the change of water, which is bound near the protonated Schiff base but is absent in the blue form of the D85N mutant, though with stronger H-bonding than in the wild type. The C = N stretching vibration of the Schiff base in H2O and 2H2O was detected by Fourier transform Raman spectroscopy. The H-bonding strength of the Schiff base in the unphotolyzed state was weaker when chloride or bromide was bound to the mutants than with Asp85 as the counterion in the wild type. Thus, although the geometry of the environment is different, there is at least one water molecule coordinated to the bound halide in these mutants, in a way similar to water bound to Asp85 in the wild type.

Anions↗

PubMed1996

Steric interaction between the 9-methyl group of the retinal and tryptophan 182 controls 13-cis to all-trans reisomerization and proton uptake in the bacteriorhodopsin photocycle.

The hypothesis was tested whether in bacteriorhodopsin (BR) the reduction of the steric interaction between the 9-methyl group of the chromophore all-trans-retinal and the tryptophan at position 182 causes the same changes as observed in the photocycle of 9-demethyl-BR. For this, the photocycle of the mutant W182F was investigated by time-resolved UV-vis and pH measurements and by static and time-resolved FT-IR difference spectroscopy. We found that the second half of the photocycle was similarly distorted in the two modified systems: based on the amide-I band, the protonation state of D96, and the kinetics of proton uptake, four N intermediates could be identified, the last one having a lifetime of several seconds; no O intermediate could be detected; the proton uptake showed a pronounced biphasic time course; and the pKa of group(s) on the cytoplasmic side in N was reduced from 11 in wild type BR to around 7.5. In contrast to 9-demethyl-BR, in the W182F mutant the first part of the photocycle does not drastically deviate from that of wild type BR. The results demonstrate the importance of the steric interaction between W182 and the 9-methyl group of the retinal in providing tight coupling between chromophore isomerization and the late proton transfer steps.

Halobacterium↗

PubMed1996

Proton transport by halorhodopsin.

In halorhodopsin from Natronobacterium pharaonis, a light-driven chloride pump, the chloride binding site also binds azide. When azide is bound at this location the retinal Schiff base transiently deprotonates after photoexcitation with light > 530 nm, like in the light-driven proton pump bacteriorhodopsin. As in the photocycle of bacteriorhodopsin, pyranine detects the release of protons to the bulk. The subsequent reprotonation of the Schiff base is also dependent on azide, but with different kinetics that suggest a shuttling of protons from the surface as described earlier for halorhodopsin from Halobacterium salinarium. This azide-dependent, bacteriorhodopsin-like photocycle results in active electrogenic proton transport in the cytoplasmic to extracellular direction, detected in cell envelope vesicle suspensions both with a potential-sensitive electrode and by measuring light-dependent pH change. We conclude that in halorhodopsin an azide bound to the extracellular side of the Schiff base, and another azide shuttling between the Schiff base and the cytoplasmic surface, fulfill the functions of Asp-85 and Asp-96, respectively, in bacteriorhodopsin. Thus, although halorhodopsin is normally a chloride ion pump, it evidently contains all structural requirements, except an internal proton acceptor and a donor, of a proton pump. This observation complements our earlier finding that when a chloride binding site was created in bacteriorhodopsin through replacement of Asp-85 with a threonine, that protein became a chloride ion pump.

Azides↗

PubMed1996

A linkage of the pKa's of asp-85 and glu-204 forms part of the reprotonation switch of bacteriorhodopsin.

Because asp-85 is the acceptor of the retinal Schiff base proton during light-driven proton transport by bacteriorhodopsin, modulation of its pKa in the photocycle is to be expected. The complex titration of asp-85 in the unphotolyzed protein was suggested [Balashov, S. P., Govindjee, R., Imasheva, E. S., Misra, S., Ebrey, T. G., Feng, Y., Crouch, R. K., & Menick, D. R (1995) Biochemistry 34, 8820-8834] to reflect the dependence of this residue on the protonation state of another, unidentified group. From the pH dependencies of the rate constant for the thermal equilibration of retinal isomeric states (dark adaptation) and the deprotonation kinetics of the Schiff base during the photocycle in the E204Q and E204D mutants, we identify the residue as glu-204. The nature of its interaction with asp-85 is that at neutral pH either residue can be anionic but not both. This is consistent with our recent finding that glu-204 is the origin of the proton released to the extracellular surface upon protonation of asp-85 during the transport. We propose, therefore, that the following series of events occur in the photocycle. Protonation of asp-85 in the proton equilibrium with the Schiff base of the photoisomerized retinal results in the dissociation of glu-204 and proton release to the extracellular surface. The deprotonation of glu-204, in turn, raises the pK(a) of asp-85, and the equilibrium with the Schiff base shifts toward complete proton transfer. This constitutes the first phase of the reprotonation switch because it excludes asp-85 as a donor in the reprotonation of the Schiff base that follows. The sequential structural changes of the protein that ensue, detected earlier by diffraction, are suggested to facilitate the change of the access of the Schiff base toward the cytoplasmic side as the second phase of the switch, and the lowering the pKa of asp-96, so as to make it a proton donor, as the third phase.

Amino Acid Sequence↗

PubMed1996

Determination of the transiently lowered pKa of the retinal Schiff base during the photocycle of bacteriorhodopsin.

Reprotonation of the transiently deprotonated retinal Schiff base in the bacteriorhodopsin photocycle is greatly slowed when the proton donor Asp-96 is removed with site-specific mutagenesis, but its rate is restored upon adding azide or other weak acids such as formate and cyanate. As expected, between pH 3 and 7 the rate of Schiff base protonation in the photocycle of the D96N mutant correlates with the concentrations of the acid forms of these agents. Dissection of the rates in the biexponential reprotonation kinetics of the Schiff base between pH 7 and 9 yielded calculated rate constants for the protonation equilibrium. Their dependencies on pH and azide or cyanate concentrations are consistent with both earlier suggested mechanisms: (i) azide and other weak acids may function as proton carriers in the protonation equilibrium of the Schiff base, or (ii) the binding of their anionic forms may catalyze proton conduction to and from the Schiff base. The measured rate constants allow the calculation of the pKa of the Schiff base during its reprotonation in the photocycle of D96N. It is 8.2-8.3, a value much below the pKa determined earlier in unphotolyzed bacteriorhodopsin.

Azides↗

PubMed1996

Evidence for response set effects in structured research interviews.

The Addiction Severity Index and NIMH Diagnostic Interview Schedule data of 20 methadone-maintained subjects with "fake bad" invalid profiles on the Personality Assessment Inventory, 15 methadone-maintained subjects with "fake good" invalid profiles, and 158 methadone-maintained subjects with valid profiles were compared. The findings revealed a number of significant group differences on both measures with the highest scores for the fake bad subjects and lowest scores for the fake good subjects. These findings suggest that the response sets exhibited in response to the Personality Assessment Inventory questionnaire extended to performance during the two semi-structured interviews. There was no indication that interviewers were aware of misrepresentation. The limitations of the findings and alternative interpretations of the data are considered.

Adult↗

PubMed1996

Natural history of HIV-1 infection and predictors of survival in a cohort of HIV-1 seropositive injecting drug users.

Injecting drug users represent a pivotal and increasing component of acquired immunodeficiency syndrome (AIDS) case reporting in the United States. This article describes the natural history of human immunodeficiency virus (HIV) disease in a New York City cohort of 328 HIV-infected injecting drug users. The study sample of nearly two-thirds men (predominately African Americans and Latino Americans) underwent follow-up from December 1988 through December 1993. Male injecting drug users reported a longer injecting drug use history and were more likely to share needles/works than female injecting drug users. Eighty-nine of 328 study subjects died during the 5 years of observation. Comparing African Americans and Latinos, race/ethnicity was not related to survival. Survival was related to baseline CD4 count and hemoglobin level. Zidovudine use and PCP prophylaxis did not predict survival. Because of the continuing and increasing impact of HIV disease on injecting drug users and communities of color, there remains an unquestionable need to develop effective prevention programs, to understand the natural history of HIV disease, and to develop appropriate therapeutic interventions to treat those with HIV disease.

Adult↗

PubMed1996

Nicotine dependence and depression among methadone maintenance patients.

There recently has been increasing interest at substance abuse treatment centers in smoking cessation treatment. Because a history of depression has been shown in other populations to complicate cessation efforts, the relationship between depression and nicotine dependence was tested in 726 methadone patients. Elevated odds of nicotine dependence given depression were found with three of four depression measures. Additional research is recommended to determine whether smoking cessation treatment will be more successful for methadone patients with a history of depression if it also addresses depression.

Adult↗