Cost effectiveness of single-dose nevirapine regimen for mothers and babies to decrease vertical HIV-1 transmission in sub-Saharan Africa

BACKGROUND

Identification of economical interventions to decrease HIV-1 transmission to children is an urgent public-health priority in sub-Saharan Africa. We assessed the cost effectiveness of the HIVNET 012 nevirapine regimen.

METHODS

We assessed cost effectiveness in a hypothetical cohort of 20,000 pregnant women in sub-Saharan Africa. Our main outcome measures were programme cost, paediatric HIV-1 cases averted, cost per case averted, and cost per disability-adjusted life-year (DALY). We compared HIVNET 012 with other short-course antiretroviral regimens. We also compared two implementation strategies: counselling and HIV-1 testing before treatment (targeted treatment), or nevirapine for all pregnant women (universal treatment, no counselling and testing). We did univariate and multivariate sensitivity analyses.

FINDINGS

For universal treatment with 30% HIV-1 seroprevalence, the HIVNET 012 regimen would avert 603 cases of HIV-1 in babies, cost US$83,333, and generate 15,862 DALYs. The associated cost-effectiveness ratios were $138 per case averted or $5.25 per DALY. At 15% seroprevalence, the universal treatment option would cost $83,333 and avert 302 cases at $276 per case averted or $10.51 per DALY. For targeted treatment at 30% seroprevalence, HIVNET 012 would cost $141,922 and avert 476 cases at $298 per case averted or $11.29 per DALY. With seroprevalence higher than 3.0% for universal and 4.5% for targeted treatment, the HIVNET 012 regimen was likely to be as cost effective as other public-health interventions. The cost effectiveness of HIVNET 012 was robust under a wide range of parameters in the sensitivity analysis.

INTERPRETATION

The HIVNET 012 regimen can be highly cost-effective in high seroprevalence settings. In lower seroprevalence areas, when multidose regimens are not cost effective, nevirapine therapy could have a major public-health impact at a reasonable cost.

Intrapartum and neonatal single-dose nevirapine compared with zidovudine for prevention of mother-to-child transmission of HIV-1 in Kampala, Uganda: HIVNET 012 randomised trial

BACKGROUND

The AIDS Clinical Trials Group protocol 076 zidovudine prophylaxis regimen for HIV-1-infected pregnant women and their babies has been associated with a significant decrease in vertical HIV-1 transmission in non-breastfeeding women in developed countries. We compared the safety and efficacy of short-course nevirapine or zidovudine during labour and the first week of life.

METHODS

From November, 1997, to April, 1999, we enrolled 626 HIV-1-infected pregnant women at Mulago Hospital in Kampala, Uganda. We randomly assigned mothers nevirapine 200 mg orally at onset of labour and 2 mg/kg to babies within 72 h of birth, or zidovudine 600 mg orally to the mother at onset of labour and 300 mg every 3 h until delivery, and 4 mg/kg orally twice daily to babies for 7 days after birth. We tested babies for HIV-1 infection at birth, 6-8 weeks, and 14-16 weeks by HIV-1 RNA PCR. We assessed HIV-1 transmission and HIV-1-free survival with Kaplan-Meier analysis.

FINDINGS

Nearly all babies (98.8%) were breastfed, and 95.6% were still breastfeeding at age 14-16 weeks. The estimated risks of HIV-1 transmission in the zidovudine and nevirapine groups were: 10.4% and 8.2% at birth (p=0.354); 21.3% and 11.9% by age 6-8 weeks (p=0.0027); and 25.1% and 13.1% by age 14-16 weeks (p=0.0006). The efficacy of nevirapine compared with zidovudine was 47% (95% CI 20-64) up to age 14-16 weeks. The two regimens were well tolerated and adverse events were similar in the two groups.

INTERPRETATION

Nevirapine lowered the risk of HIV-1 transmission during the first 14-16 weeks of life by nearly 50% in a breastfeeding population. This simple and inexpensive regimen could decrease mother-to-child HIV-1 transmission in less-developed countries.

A shift in the equilibrium constant at the catalytic site of proton-translocating transhydrogenase: significance for a 'binding-change' mechanism

In mitochondria and bacteria, transhydrogenase uses the transmembrane proton gradient (Deltap) to drive reduction of NADP+ by NADH. We have investigated the pre-steady-state kinetics of NADP+ reduction by acetylpyridine adenine dinucleotide (AcPdADH, an analogue of NADH) in complexes formed from the two, separately prepared, recombinant, peripheral subunits of the enzyme: the dI component, which binds NAD+ and NADH, and the dIII component, which binds NADP+ and NADPH. In the stopped-flow spectrophotometer the reaction proceeds as a single-turnover burst of hydride transfer to NADP+ on dIII before product NADPH release becomes limiting in steady state. The burst is biphasic. The results indicate that the fast phase represents direct hydride transfer from AcPdADH to NADP+ in dI:dIII complexes, and that the slow phase, which predominates when [dI]<[dIII], corresponds to dissociation of the protein complexes during multiple turnovers of dI. Measurements on the amplitude of the burst, and on the apparent first-order rate constant of the fast phase, indicate that the equilibrium constant of the hydride-transfer step on the enzyme is shifted relative to that in solution. This has consequences for a model proposed earlier, in which Deltap is used, not at the hydride-transfer step, but to change the binding affinities of NADP+ and NADPH.

Thalidomide for the treatment of esophageal aphthous ulcers in patients with human immunodeficiency virus infection. National Institute of Allergy and Infectious Disease AIDS Clinical Trials Group

A multicenter, double-blind, randomized, placebo-controlled clinical trial was conducted to determine the safety and efficacy of thalidomide for treating esophageal aphthous ulceration in persons infected with human immunodeficiency virus (HIV). Twenty-four HIV-infected patients with biopsy-confirmed aphthous ulceration of the esophagus were randomly assigned to receive either oral thalidomide, 200 mg/day, or oral placebo daily for 4 weeks. Eight (73%) of 11 patients randomized to receive thalidomide had complete healing of aphthous ulcers at the 4-week endoscopic evaluation, compared with 3 (23%) of 13 placebo-randomized patients (odds ratio, 13.82; 95% confidence interval, 1.16-823.75; P=.033). Odynophagia and impaired eating ability caused by esophageal aphthae were improved markedly by thalidomide treatment. Adverse events among patients receiving thalidomide included somnolence (4 patients), rash (2 patients), and peripheral sensory neuropathy (3 patients). Thalidomide is effective in healing aphthous ulceration of the esophagus in patients infected with HIV.

The mobile loop region of the NAD(H) binding component (dI) of proton-translocating nicotinamide nucleotide transhydrogenase from Rhodospirillum rubrum: complete NMR assignment and effects of bound nucleotides

The dI component of transhydrogenase binds NAD+ and NADH. A mobile loop region of dI plays an important role in the nucleotide binding process, and mutations in this region result in impaired hydride transfer in the complete enzyme. We have previously employed one-dimensional 1H-NMR spectroscopy to study wild-type and mutant dI proteins of Rhodospirillum rubrum and the effects of nucleotide binding. Here, we utilise two- and three-dimensional NMR experiments to assign the signals from virtually all of the backbone and side-chain protons of the loop residues. The mobile loop region encompasses 17 residues: Asp223-Met239. The assignments also provide a much strengthened basis for interpreting the structural changes occurring upon nucleotide binding, when the loop closes down onto the surface of the protein and loses mobility. The role of the mobile loop region in catalysis is discussed with particular reference to a newly-developed model of the dI protein, based on its homology with alanine dehydrogenase.

Comparison of cytomegalovirus loads in plasma and leukocytes of patients with cytomegalovirus retinitis. The Cytomegalovirus Retinitis and Viral Resistance Study Group

Cytomegalovirus (CMV) DNA loads in paired leukocyte and plasma samples from 199 patient visits by 66 patients with CMV retinitis were determined. Leukocyte CMV load determinations had a greater range of values (mean, 24,587 copies/10(6) leukocytes; maximum, 539, 000) than did plasma CMV load determinations (mean, 10,302 copies/ml; maximum, 386,000), and leukocyte viral loads were detectable in a greater proportion of patients at the time of diagnosis of CMV retinitis prior to initiation of anti-CMV therapy (82%) than were plasma viral loads (64%) (P = 0.0078). Agreement with CMV blood cultures was slightly better for plasma (kappa = 0. 68) than for leukocytes (kappa = 0.53), due to a greater proportion of patients with detectable viral loads in leukocytes having negative blood cultures.

A catalytically active complex formed from the recombinant dI protein of Rhodospirillum rubrum transhydrogenase, and the recombinant dIII protein of the human enzyme

Transhydrogenase is a proton pump. It has three components: dI and dIII protrude from the membrane and contain the binding sites for NAD(H) and NADP(H), respectively, and dII spans the membrane. We have expressed dIII from Homo sapiens transhydrogenase (hsdIII) in Escherichia coli. The purified protein was associated with stoichiometric amounts of NADP(H) bound to the catalytic site. The NADP+ and NADPH were released only slowly from the protein, supporting the suggestion that nucleotide-binding by dIII is regulated by the membrane-spanning dII. HsdIII formed a catalytically active complex with recombinant dI from Rhodospirillum rubrum (rrdI), even in the absence of dII. The rates of forward and reverse transhydrogenation catalysed by this complex are probably limited by slow release from dIII of NADPH and NADP+, respectively. The hybrid complex also catalysed high rates of 'cyclic' transhydrogenation, indicating that hydride transfer, and exchange of nucleotides with dI, are rapid. Stopped-flow experiments revealed a rapid, monoexponential, single-turnover burst of reverse transhydrogenation in pre-steady-state. The apparent first-order rate constant of the burst increased with the concentration of rrdI. A deuterium isotope effect (kH/kD approximately 2 at 27 degrees C) was observed when [4B-1H]NADPH was replaced with [4B-2H]NADPH. The characteristics of the burst of transhydrogenation with rrdI:hsdIII differed from those previously reported for rrdI:rrdIII (J.D. Venning et al., Eur. J. Biochem. 257 (1998) 202-209), but the differences are readily explained by a greater dissociation constant of the hybrid complex. The steady-state rate of reverse transhydrogenation by the rrdI:hsdIII complex was almost independent of pH, but there was a single apparent pKa ( approximately 9.1) associated with the cyclic reaction. The reactions of the dI:dIII complex probably proceed independently of those protonation/deprotonation reactions which, in the complete enzyme, are associated with H+ translocation.

A phase I/II study of the safety and pharmacokinetics of nevirapine in HIV-1-infected pregnant Ugandan women and their neonates (HIVNET 006)

OBJECTIVE

To determine the safety, pharmacokinetics, tolerance, antiretroviral activity, and infant HIV infection status after giving a single dose of nevirapine to HIV-1-infected pregnant women during labor and their newborns during the first week of life.

DESIGN

An open label phase I/II study.

SETTING

Tertiary care hospital, Kampala, Uganda.

PATIENTS AND INTERVENTIONS

Nevirapine, 200 mg, was given as a single dose during labor to 21 HIV-1-infected pregnant Ugandan women. In cohort 1, eight infants did not receive nevirapine whereas in cohort 2, 13 infants received a single dose of nevirapine, 2 mg/kg, at 72 h of age.

OUTCOMES

The number and type of adverse events; nevirapine concentrations in the plasma and breast milk; maternal plasma HIV-1 RNA copy number before and up to 6 weeks after delivery; and HIV-1 infection status of the infants were monitored.

RESULTS

Nevirapine was well tolerated by women and infants; no serious adverse events that were related to nevirapine were observed. Median nevirapine concentration in the women at delivery was 1623 ng/ml (range 238-2356 ng/ml); median cord/maternal blood ratio of 0.75 (0.37-0.93). The median half-life in women was 61.3 h (27-90 h) and the transplacental nevirapine half-life in infants who did not receive a neonatal dose was 54 h. The median half-life after a single dose at 72 h in infants was 46.5 h. During the first week of life, the median colostrum/breast milk to maternal plasma nevirapine concentration was 60.5% (25-122%). The median nevirapine concentration in breast milk 1 week after delivery was 103 ng/ml (25-309 ng/ml). Plasma nevirapine concentrations were above 100 ng/ml in all infants from both cohorts tested at age 7 days. Maternal HIV-1 RNA levels decreased by a median of 1.3 logs at 1 week postpartum, and returned to baseline by 6 weeks postpartum. Detectable plasma HIV-1 RNA was observed in one out of 22 (4.5%) infants at birth; three out of 21 (14%) at 6 weeks; and four out of 21 (19%) at 6 months of age.

CONCLUSION

The administration of a single dose of nevirapine to women during labor and to their newborns at 72 h was well tolerated and showed potent antiretroviral activity in the women at 1 week after dosing without rebound above baseline 6 weeks after a single dose. The nevirapine concentration was maintained above the target of 100 ng/ml in infants at age 7 days, even in those infants not receiving a neonatal dose. This regimen has promise as prophylaxis against intrapartum and early breast milk transmission in a breastfeeding population.

Catalytic properties of hybrid complexes of the NAD(H)-binding and NADP(H)-binding domains of the proton-translocating transhydrogenases from Escherichia coli and Rhodospirillum rubrum

Transhydrogenase couples reversible hydride transfer from NADH to NADP+ to proton translocation across the inner membrane in mitochondria and the cytoplasmic membrane in bacteria. The enzyme is composed of three parts. Domain I (dI) and domain III (dIII) are water soluble and contain the binding sites for NAD(H) and NADP(H), respectively; domain II (dII) spans the membrane. In the present investigation, dI from Rhodospirillum rubrum (rrI) and Escherichia coli (ecI), and dIII from R. rubrum (rrIII) and E. coli (ecIII) were overexpressed in E. coli and subsequently purified. Also, a preparation of a partially degraded E. coli transhydrogenase (ecbeta) was examined. Catalytic activities were analyzed in various dI+dIII and dI+ecbeta combinations. The abilities of the different dI+dIII combinations to catalyze cyclic transhydrogenation, i.e., the reduction of AcPyAD+ by NADH mediated via tightly bound NADP(H) in dIII, varied in the order: rrI+ecIII approximately rrI+rrIII > rrI+ecbeta >> ecI+ecIII; no measurable activities for ecI+rrIII and ecI+ecbeta were detected. Thus, rrI has a much greater apparent affinity than ecI for ecIII or rrIII or ecbeta. The pH dependences of the cyclic reaction seem to be determined by scalar protonation events on dI, both in rrI+rrIII and ecI+ecIII mixtures as well as in the wild-type R. rubrum and possibly in the E. coli enzyme. Higher reverse activities for rrI+ecbeta than for rrI+ecIII confirmed the regulatory role of dII for the association and dissociation rates of NADP(H).

Mutation of amino acid residues in the mobile loop region of the NAD(H)-binding domain of proton-translocating transhydrogenase

The effects of single amino acid substitutions in the mobile loop region of the recombinant NAD(H)-binding domain (dI) of transhydrogenase have been examined. The mutations lead to clear assignments of well-defined resonances in one-dimensional 1H-NMR spectra. As with the wild-type protein, addition of NADH, or higher concentrations of NAD+, led to broadening and some shifting of the well-defined resonances. With many of the mutant dI proteins more nucleotide was required for these effects than with wild-type protein. Binding constants of the mutant proteins for NADH were determined by equilibrium dialysis and, where possible, by NMR. Generally, amino acid changes in the mobile loop region gave rise to a 2-4-fold increase in the dI-nucleotide dissociation constants, but substitution of Ala236 for Gly had a 10-fold effect. The mutant dI proteins were reconstituted with dI-depleted bacterial membranes with apparent docking affinities that were indistinguishable from that of wild-type protein. In the reconstituted system, most of the mutants were more inhibited in their capacity to perform cyclic transhydrogenation (reduction of acetyl pyridine adenine dinucleotide, AcPdAD+, by NADH in the presence of NADP+) than in either the simple reduction of AcPdAD+ by NADPH, or the light-driven reduction of thio-NADP+ by NADH, which suggests that they are impaired at the hydride transfer step. A cross-peak in the 1H-1H nuclear Overhauser enhancement spectrum of a mixture of wild-type dI and NADH was assigned to an interaction between the A8 proton of the nucleotide and the betaCH3 protons of Ala236. It is proposed that, following nucleotide binding, the mobile loop folds down on to the surface of the dI protein, and that contacts, especially from Tyr235 in a Gly-Tyr-Ala motif with the adenosine moiety of the nucleotide, set the position of the nicotinamide ring of NADH close to that of NADP+ in dIII to effect direct hydride transfer.

Stopped-flow kinetics of hydride transfer between nucleotides by recombinant domains of proton-translocating transhydrogenase

Transhydrogenase catalyses the transfer of reducing equivalents between NAD(H) and NADP(H) coupled to proton translocation across the membranes of bacteria and mitochondria. The protein has a tridomain structure. Domains I and III protrude from the membrane (e.g. on the cytoplasmic side in bacteria) and domain II spans the membrane. Domain I has the binding site for NAD+/NADH, and domain III for NADP+/NADPH. We have separately purified recombinant forms of domains I and III from Rhodospirillum rubrum transhydrogenase. When the two recombinant proteins were mixed with substrates in the stopped-flow spectrophotometer, there was a biphasic burst of hydride transfer from NADPH to the NAD+ analogue, acetylpyridine adenine dinucleotide (AcPdAD+). The burst, corresponding to a single turnover of domain III, precedes the onset of steady state, which is limited by very slow release of product NADP+ (k approximately 0.03 s(-1)). Phase A of the burst (k approximately 600 s(-1)) probably arises from fast hydride transfer in complexes of domains I and III. Phase B (k approximately 10-50 s(-1)), which predominates when the concentration of domain I is less than that of domain III, probably results from dissociation of the domain I:III complexes and further association and turnover of domain I. Phases A and B were only weakly dependent on pH, and it is therefore unlikely that either the hydride transfer reaction, or conformational changes accompanying dissociation of the I:III complex, are directly coupled to proton binding or release. A comparison of the temperature dependences of AcPdAD+ reduction by [4B-2H]NADPH, and by [4B-1H]NADPH, during phase A shows that there may be a contribution from quantum mechanical tunnelling to the process of hydride transfer. Given that hydride transfer between the nucleotides is direct [Venning, J. D., Grimley, R. L., Bizouarn, T., Cotton, N. P. J. & Jackson, J. B. (1997) J. Biol. Chem. 272, 27535-27538], this suggests very close proximity of the nicotinamide rings of the two nucleotides in the I:III complex.

Interdomain hydride transfer in proton-translocating transhydrogenase

We describe the use of the recombinant, nucleotide-binding domains (domains I and III) of transhydrogenase to study structural, functional and dynamic features of the protein that are important in hydride transfer and proton translocation. Experiments on the transient state kinetics of the reaction show that hydride transfer takes place extremely rapidly in the recombinant domain I:III complex, even in the absence of the membrane-spanning domain II. We develop the view that proton translocation through domain II is coupled to changes in the binding characteristics of NADP+ and NADPH in domain III. A mobile loop region which emanates from the surface of domain I, and which interacts with NAD+ and NADH during nucleotide binding has been studied by NMR spectroscopy and site-directed mutagenesis. An important role for the loop region in the process of hydride transfer is revealed.

Variability and prognostic values of virologic and CD4 cell measures in human immunodeficiency virus type 1-infected patients with 200-500 CD4 cells/mm(3) (ACTG 175). AIDS Clinical Trials Group Protocol 175 Team

Virologic measurements are increasingly used to evaluate prognosis and treatment responses in human immunodeficiency virus (HIV) type 1 infection. Markers of HIV-1 replication, including infectious HIV-1 titer from peripheral blood mononuclear cells, serum HIV-1 p24 antigen, plasma HIV-1 RNA, CD4 cell numbers, and viral syncytium-inducing (SI) phenotype, were determined in 391 virology substudy participants in AIDS Clinical Trials Group study 175. The subjects had 200-500 CD4 cells/mm3. All markers of viral replication significantly correlated with one another and were inversely related to CD4 cell number. Disease progression to an AIDS-defining event or death or loss of >50% of CD4 cells was associated with infectious HIV-1 titer (P < .001), HIV-1 RNA (P < .001), and HIV-1 p24 antigen (P = .007). In multivariate proportional hazards models, p24 antigen was never significant when HIV-1 RNA level was included. In a model containing infectious HIV-1 titer (P = .038), HIV-1 RNA (P < .001), SI phenotype (P < .001), and CD4 cell number (P = .18), only the virologic parameters remained significantly associated with progression.

Role of methionine-239, an amino acid residue in the mobile-loop region of the NADH-binding domain (domain I) of proton-translocating transhydrogenase

Transhydrogenase couples the transfer of hydride equivalents between NAD(H) and NADP(H) to proton translocation across a membrane. The one-dimensional proton NMR spectrum of the recombinant NAD(H)-binding domain (domain I) of transhydrogenase from Rhodospirillum rubrum reveals well-defined resonances, several of which arise from a mobile loop at the protein surface. Four have been assigned to Met residues (MetA-MetD). Substitution of Met239 with either Ile (dI.M239I) or Phe (dI.M239F) resulted in loss of MetA from the NMR spectrum. Broadening and shifting of the mobile loop resonances consequent on NAD(H) binding indicate that the loop closes down on the protein surface. More NAD(H) had to be added to mutant domain I than to wild type to give comparable resonance broadening. The Kd of domain I for NADH, measured by equilibrium dialysis, was increased about three-fold by the Met239 mutations. Mutant and wild-type domain I were reconstituted with domain I-depleted membranes from R. rubrum, and with recombinant domain III of transhydrogenase. With membranes, the Km for acetylpyridine adenine dinucleotide during reverse transhydrogenation was 5x and > 6x greater in dI.M239I and dI.M239F, respectively, than in wild-type. Cyclic transhydrogenation (in membranes and the recombinant system) was substantially more inhibited (70% in dI.M239I, and 84% in dI.M239F) than either forward or reverse transhydrogenation. The docking affinities of dI.M239I and dI.M239F to the depleted membranes were similar to those of wild-type. It is concluded that Met239 is MetA in the mobile loop of domain I, and that in proteins with amino acid substitutions at this position, the binding affinity of NAD(H) is decreased, and the hydride transfer step is inhibited.

Serologic and phylogenetic characterization of HIV-1 subtypes in Uganda

OBJECTIVES

To determine the HIV genetic subtypes present in HIV-1-infected asymptomatic blood donors in Uganda and to evaluate serologic detection of infection by commercial immunoassays; to evaluate samples for HIV-1 group O infections.

METHODS

Sixty-four HIV-seropositive plasma samples were collected from the Nakasero Blood Bank, Kampala, Uganda. The plasma were evaluated using commercial HIV enzyme immunoassays (EIA) and a research immunoblot. HIV-1 group M and O infections were identified on the basis of discordant seroreactivity in EIA and reactivity to group M and O antigens on the immunoblot. Regions of gag p24 and env gp41 were amplified using reverse transcriptase polymerase chain reaction, and genetic subtypes were determined by phylogenetic analysis.

RESULTS

Serologic testing confirmed that 63 out of 64 plasma units were positive for HIV-1 group M infection and showed no evidence of HIV-1 group O infections. Genetic subtyping determined that 25 samples were subtype A, three subtype C, 22 subtype D, and nine were heterogeneous for subtypes A and D.

CONCLUSIONS

Despite the sequence variation observed in Uganda, commercial EIA based on HIV-1 subtype B proteins detected all the infections. In contrast, a peptide-based assay failed to detect three infections by subtype D viruses. This emphasizes the negative impact of HIV genetic variation on assays that rely on peptides to detect HIV infections. The number of infections with heterogeneous subtype (due to mixed infections or recombinant viruses) is high and reflects the growing complexity of the HIV epidemic in endemic regions where multiple subtypes are present in the population.

The pH dependences of reactions catalyzed by the complete proton-translocating transhydrogenase from Rhodospirillum rubrum, and by the complex formed from its recombinant nucleotide-binding domains

Transhydrogenase couples the translocation of protons across a membrane to the transfer of reducing equivalents between NAD(H) and NADP(H). Using transhydrogenase from Rhodospirillum rubrum we have examined the pH dependences of the 'forward' and 'reverse' reactions, and of the 'cyclic' reaction (NADP(H)-dependent reduction of the analogue, acetyl pyridine adenine dinucleotide, by NADH). In the case of the membrane-bound protein in chromatophores, the imposition of a protonmotive force through the action of the light-driven electron-transport system, stimulated forward transhydrogenation, inhibited reverse transhydrogenation, but had no effect on the cyclic reaction. The differential response at a range of pH values provides evidence that hydride transfer per se is not coupled to proton translocation and supports the view that energy transduction occurs at the level of NADP(H) binding. Chromatophore transhydrogenase and the detergent-dispersed enzyme both have bell-shaped pH dependences for forward and reverse transhydrogenation. The cyclic reaction, however, is rapid at low and neutral pH, and is attenuated only at high pH. A mixture of recombinant purified NAD(H)-binding domain I, and NADP(H)-binding domain III, of R. rubrum transhydrogenase carry out the cyclic reaction with a similar pH profile to that of the complete enzyme, but the forward and reverse reactions were much less pH dependent. The rates of release of NADP+ and of NADPH from isolated domain III were pH independent. The results are consistent with a model for transhydrogenation, in which proton binding from one side of the membrane is consequent upon the binding of NADP+ to the enzyme, and then proton release on the other side of the membrane precedes NADPH release.

Evidence that the transfer of hydride ion equivalents between nucleotides by proton-translocating transhydrogenase is direct

The molecular masses of the purified, recombinant nucleotide-binding domains (domains I and III) of transhydrogenase from Rhodospirillum rubrum were determined by electrospray mass spectrometry. The values obtained, 40,273 and 21,469 Da, for domains I and III, respectively, are similar to those estimated from the amino acid sequences of the proteins. Evidently, there are no prosthetic groups or metal centers that can serve as reducible intermediates in hydride transfer between nucleotides bound to these proteins. The transient-state kinetics of hydride transfer catalyzed by mixtures of recombinant domains I and III were studied by stopped-flow spectrophotometry. The data indicate that oxidation of NADPH, bound to domain III, and reduction of acetylpyridine adenine dinucleotide (an NAD+ analogue), bound to domain I, are simultaneous and very fast. The transient-state reaction proceeds as a biphasic burst of hydride transfer before establishment of a steady state, which is limited by slow release of NADP+. Hydride transfer between the nucleotides is evidently direct. This conclusion indicates that the nicotinamide rings of the nucleotides are in close apposition during the hydride transfer reaction, and it imposes firm constraints on the mechanism by which transhydrogenation is linked to proton translocation.

Mutations at tyrosine-235 in the mobile loop region of domain I protein of transhydrogenase from Rhodospirillum rubrum strongly inhibit hydride transfer

Transhydrogenase from mitochondrial and bacterial membranes couples proton translocation to hydride transfer between NAD(H) and NADP(H). The enzyme has three domains, of which domains I and III protrude from the membrane. These possess the NAD(H)- and NADP(H)-binding sites, respectively, whereas domain II spans the membrane. In domain I there is a mobile loop which emanates from the surface of the protein, but which closes down upon NAD(H) binding. In this report we show that the NADP(H)-dependent reduction of acetylpyridine adenine dinucleotide by NADH catalysed by Rhodospirillum rubrum transhydrogenase has 'ping-pong' kinetics, confirming that the reaction is cyclic. We then describe the kinetic and thermodynamic properties of mutants of recombinant domain I protein from the R. rubrum enzyme, in which Tyr-235 in the mobile loop has been substituted with Phe or Asn residues (dI.Y235F and dI.Y235N, respectively). (1) Equilibrium dialysis measurements show that dI.Y235F and dI.Y235N bind NADH more weakly than wild-type domain I protein (the Kd increases twofold and fourfold, respectively). (2) Reverse transhydrogenation rates (in steady state) of domain I-depleted membrane vesicles reconstituted with either dI.Y235F or dI.Y235N are inhibited by about 50% and 78%, respectively, relative to those obtained in reconstitutions with wild-type domain I protein. (3) Reverse transhydrogenation rates (in steady state) of mixtures of recombinant domain III protein and either dI.Y235F or dI.Y235N are inhibited only by about 10% and 20%, respectively, relative to those obtained in mixtures with wild-type protein. (4) Forward transhydrogenation rates (in both the complete enzyme and in domain I:III complexes) are inhibited even less by the mutations than the reverse reactions. (5) In contrast with (1), (2) and (3), cyclic transhydrogenation was strongly inhibited in both the reconstituted membrane system and in the recombinant domain I:III complexes (only 7-8% activity remains with dI.Y235F, and only 2-3% with dI.Y235N). It was recently established that, in contrast to forward and reverse transhydrogenation, the cyclic reaction is substantially limited by the rate of hydride transfer. It is therefore concluded that mutations at Tyr-235 in the mobile loop severely disrupt the hydride transfer step in the catalytic reaction of transhydrogenase.

Thalidomide for the treatment of oral aphthous ulcers in patients with human immunodeficiency virus infection. National Institute of Allergy and Infectious Diseases AIDS Clinical Trials Group

BACKGROUND

In patients with advanced human immunodeficiency virus (HIV) infection, aphthous ulceration of the mouth and oropharynx can become extensive and debilitating. Preliminary reports suggest that thalidomide may promote the healing of oral aphthous ulcers.

METHODS

We performed a double-blind, randomized, placebo-controlled study of thalidomide as therapy for oral aphthous ulcers in HIV-infected patients. The patients received a four-week course of either 200 mg of thalidomide or placebo orally once per day. They were evaluated weekly for the condition of the ulcers, their quality of life, and evidence of toxicity. Assays were performed for plasma tumor necrosis factor alpha (TNF-alpha), soluble TNF-alpha receptors, and HIV RNA.

RESULTS

Sixteen of 29 patients in the thalidomide group (55 percent) had complete healing of their aphthous ulcers after four weeks, as compared with only 2 of 28 patients in the placebo group (7 percent; odds ratio, 15; 95 percent confidence interval after adjustment for group sequential testing, 1.8 to 499; unadjusted P<0.001). Pain diminished and ability to eat improved with thalidomide treatment. The adverse effects noted with thalidomide included somnolence and rash (7 patients each), and 6 of the 29 patients discontinued treatment because of toxicity. Thalidomide treatment increased HIV RNA levels (median increase, 0.42 log10 copies per milliliter; increase with placebo, 0.05; P=0.04). With thalidomide treatment there were unexpected increases in the plasma concentrations of TNF-alpha and soluble TNF-alpha receptors.

CONCLUSIONS

Thalidomide is an effective treatment for aphthous ulceration of the mouth and oropharynx in patients with HIV infection.

The reduction of acetylpyridine adenine dinucleotide by NADH: is it a significant reaction of proton-translocating transhydrogenase, or an artefact?

Transhydrogenase is a proton pump. It has separate binding sites for NAD+/NADH (on domain I of the protein) and for NADP+/NADPH (on domain III). Purified, detergent-dispersed transhydrogenase from Escherichia coli catalyses the reduction of the NAD+ analogue, acetylpyridine adenine dinucleotide (AcPdAD+), by NADH at a slow rate in the absence of added NADP+ or NADPH. Although it is slow, this reaction is surprising, since transhydrogenase is generally thought to catalyse hydride transfer between NAD(H)--or its analogues and NADP(H)--or its analogues, by a ternary complex mechanism. It is shown that hydride transfer occurs between the 4A position on the nicotinamide ring of NADH and the 4A position of AcPdAD+. On the basis of the known stereospecificity of the enzyme, this eliminates the possibilities of transhydrogenation(a) from NADH in domain I to AcPdAD+ wrongly located in domain III; and (b) from NADH wrongly located in domain III to AcPdAD+ in domain I. In the presence of low concentrations of added NADP+ or NADPH, detergent-dispersed E. coli transhydrogenase catalyses the very rapid reduction of AcPdAD+ by NADH. This reaction is cyclic; it takes place via the alternate oxidation of NADPH by AcPdAD+ and the reduction of NADP+ by NADH, while the NADPH and NADP+ remain tightly bound to the enzyme. In the present work, it is shown that the rate of the cyclic reaction and the rate of reduction of AcPdAD+ by NADH in the absence of added NADP+/NADPH, have similar dependences on pH and on MgSO4 concentration and that they have a similar kinetic character. It is therefore suggested that the reduction of AcPdAD+ by NADH is actually a cyclic reaction operating, either with tightly bound NADP+/NADPH on a small fraction (< 5%) of the enzyme, or with NAD+/NADH (or AcPdAD+/AcPdADH) unnaturally occluded within the domain III site. Transhydrogenase associated with membrane vesicles (chromatophores) of Rhodospirillum rubrum also catalyses the reduction of AcPdAD+ by NADH in the absence of added NADP+/NADPH. When the chromatophores were stripped of transhydrogenase domain I, that reaction was lost in parallel with 'normal reverse' transhydrogenation (e.g., the reduction of AcPdAD+ by NADPH). The two reactions were fully recovered upon reconstitution with recombinant domain I protein. However, after repeated washing of the domain I-depleted chromatophores, reverse transhydrogenation activity (when assayed in the presence of domain I) was retained, whereas the reduction of AcPdAD+ by NADH declined in activity. Addition of low concentrations of NADP+ or NADPH always supported the same high rate of the NADH-->AcPdAD+ reaction independently of how often the membranes were washed. It is concluded that, as with the purified E. coli enzyme, the reduction of AcPdAD+ by NADH in chromatophores is a cyclic reaction involving nucleotides that are tightly bound in the domain III site of transhydrogenase. However, in the case of R. rubrum membranes it can be shown with some certainty that the bound nucleotides are NADP+ or NADPH. The data are thus adequately explained without recourse to suggestions of multiple nucleotide-binding sites on transhydrogenase.

Detection of human immunodeficiency virus type 1 (HIV-1) antibody by western blotting and HIV-1 DNA by PCR in patients with AIDS

The human immunodeficiency virus type 1 (HIV-1) Western blotting (immunoblotting) band patterns and the sensitivity of an HIV-1 DNA PCR assay were determined by testing the blood of patients with AIDS. Plasma and cell pellets processed from the peripheral blood of 199 patients with absolute CD4 cell counts of less than 200 cells per mm3 were tested by a licensed enzyme immunoassay (EIA; Abbott HIV-1) and Western blot assay (Cambridge-Biotech) for HIV-1 antibody. The Roache HIV-1 AMPLICOR DNA PCR assay was used to test cell pellets from 125 of the 199 patients for HIV-1 gag DNA sequences. All plasma samples from these 199 sequential patients were reactive for HIV-1 antibody by EIA and were positive by Western blot assay using the criteria recommended by the Centers for Disease Control and Prevention. The majority of samples (192 of 199; 96.5%) displayed at least six of nine bands characteristic of the virus by Western blotting, with the lowest number of bands characteristic of the virus displayed by any sample being three. However, 39 and 48% of all patients exhibited no bands to p17 and p55 antigens, respectively, whereas 0 to 7.5% of all patients exhibited no bands to the other antigens. HIV-1 gag DNA sequences were detected in 117 (93.6%) of 125 cell pellets processed from the peripheral blood of these same patients. All eight patients initially negative by PCR tested positive when a second pellet which had been produced from the same blood sample was tested. Despite a decrease in antibody reactivity to HIV Gag and Pol proteins, patients with advanced HIV-1 infection remained positive for HIV-1 antibody by EIA and Western blot testing. Confirmation by the HIV-1 Western blot assay still appears to be the more sensitive assay for the diagnosis of HIV-1 infection in those individuals with advanced HIV-1 infection in the United States.