Enzymatic and nonenzymatic production of free radicals from the carcinogens 4-nitroquinoline N-oxide and 4-hydroxylaminoquinoline N-oxide

The anion radicals of 4-nitroquinoline N-oxide (4-NQO) and 4-nitrosoquinoline N-oxide (4-NOQO) carcinogens were detected and characterized by electron spin resonance (ESR) spectroscopy. The structures of the radical intermediates were examined by density functional theory (DFT) at the level of hybrid unrestricted uBecke3LYP. The formation of superoxide anion radical catalyzed by flavin-containing enzymes such as cytochrome P450 reductase or xanthine oxidase in the presence of 4-NQO or 4-nitroquinoline N-oxide was studied by spin-trapping experiments. In this case, the ESR signal of the 5,5-dimethyl-1-pyrroline N-oxide (DMPO)-superoxide radical adduct was observed, and its formation was inhibited by superoxide dismutase (SOD). No ESR signal was detected when the two-electron-transferring flavoenzyme DT-diaphorase (NADPH-quinone oxidoreductase) was used. The above is consistent with a one-electron reduction in the metabolism of these nitro compounds to anion free radicals by various flavoenzyme reductases.

Stability improvements for an interferometer through study of spectral interference patterns

Conventional Mach-Zehnder interferometer configuration is modified to enhance its stability from the vibrations. To study the effects of vibrations on the Mach-Zehnder interferometer, we used spectral interference fringes from a broadband nanosecond dye laser source. We observed an improvement in the stability of the interferometer by a factor of 3.

Bioactive fragment of human interleukin-1beta (163-171) modulates the immune response to synthetic peptides of RESA of Plasmodium falciparum

In this study a bioactive fragment, residues 163-171 of human interleukin-1beta (hu IL-1beta), that mimics the functions of the whole IL-1 molecule was chemically linked to two peptide sequences of the ring erythrocyte surface antigen (RESA), an asexual blood stage antigen of Plasmodium falciparum. The immunogenicity of different formulations was studied in different haplotypes of inbred mice. The peptide-IL-1beta conjugates delivered in liposomes showed the maximal antibody production. Antigen entrapped in liposomes at a dose of 5 microg showed antibody levels comparable to that of peptide conjugate in alum. The IgG subclass profile with different RESA peptides and its conjugates at various doses in liposomes induced predominantly IgG2a/2b isotypes while alum-delivered formulations showed both IgG1 and IgG2a/2b isotypes. In vitro studies of merozoite reinvasion showed varying degree (50-85%) of inhibition, maximum being with the peptide conjugates in liposomes (80-87%). Thus, this approach suggests that linking of hu IL-1beta is instrumental in augmenting the immune response against otherwise poorly immunogenic synthetic peptides.

Interferometric measurement of the modulation transfer function of a spectrometer by using spectral modulations

We present our results on measurement of the modulation transfer function (MTF) of a given spectrometer by using the sinusoidally modulated spectrum from a Michelson interferometer with white light. We studied the MTF by varying the periodicity of the spectral fringes produced by the interferometer. Experimental data are fitted to a theoretical model to derive the spectral slit width from the measured MTF of the spectrometer.

Alcohol as an additional risk factor in laryngopharyngeal cancer in Mumbai--a case-control study

A retrospective case-control study of 1698 male pharyngeal and laryngeal cancers seen at the Tata Memorial Hospital, Mumbai from 1980 to 1984 was undertaken to assess the association between the cancers and chewing, smoking, and alcohol habits. Male controls were chosen from persons who attended the hospital during the same period and who were diagnosed as free from cancer, benign tumor, and infectious disease. Statistical analysis was based on unconditional logistic regression method. Bidi smoking and alcohol drinking emerged as significant factors for pharyngeal and laryngeal cancers. Illiterates had 50 to 60% excess risk for pharyngeal cancer only. Nonvegetarian diet did not emerge as significant factor in our study.

Influence of iron on growth and extracellular products of Acinetobacter baumannii

Iron is an important nutrient required by bacteria for optimal growth. Acquisition of iron from the host where iron is restricted is an important mediator of bacterial pathogenesis. In iron deplete chemically defined medium (CDM-Fe) growth of Acinetobacter baumannii was restricted as compared to iron replete medium (CDM + Fe). Bacteria developed four high molecular weight outer membrane proteins (OMPs) of 88, 84, 80 and 77 kDa in CDM-Fe medium which were absent in CDM + Fe medium, and are known iron regulated outer membrane proteins (IROMPs). A. baumannii secreted siderophores extracellularly into the medium which act as iron chelators which had been demonstrated in the supernatants of CDM-Fe media. The siderophore was of catechol type. This shows that A. baumannii under iron restricted conditions express IROMPs along with production of catechol type siderophore in order to acquire iron from the external milieu.

Probing the role of cysteine residues in the EcoP15I DNA methyltransferase

Chemical modification using thiol-directed agents and site-directed mutagenesis has been used to investigate the role of cysteine residues of EcoP15I DNA methyltransferase. Irreversible inhibition of enzymatic activity was provoked by chemical modification of the enzyme by N-ethylmaleimide and iodoacetamide. 5, 5'-Dithiobis(2-nitrobenzoic acid) titration of the enzyme under nondenaturing and denaturing conditions confirmed the presence of six cysteine residues without any disulfides in the protein. Aware that relatively bulky reagents inactivate the methyltransferase by directly occluding the substrate-binding site or by locking the methyltransferase in an inactive conformation, we used site-directed mutagenesis to sequentially replace each of the six cysteines in the protein at positions 30, 213, 344, 434, 553, and 577. All the resultant mutant methylases except for the C344S and C344A enzymes retained significant activity as assessed by in vivo and in vitro assays. The effects of the substitutions on the function of EcoP15I DNA methyltransferase were investigated by substrate binding assays, activity measurements, and steady-state kinetic analysis of catalysis. Our results clearly indicate that the cysteines at positions other than 344 are not essential for activity. In contrast, the C344A enzyme showed a marked loss of enzymatic activity. More importantly, whereas the inactive C344A mutant enzyme bound S-adenosyl-L-methionine, it failed to bind to DNA. Furthermore, in double and triple mutants where two or three cysteine residues were replaced by serine, all such mutants in which the cysteine at position 344 was changed, were inactive. Taken together, these results convincingly demonstrate that the Cys-344 is necessary for enzyme activity and indicate an essential role for it in DNA binding.

Construction of chimeric immunogens: Bioactive fragment of human IL-1β or polytuftsin (PT) capable of eliciting immune responses to HIV peptides

In this study, we have examined the effect of linking of bloactive fragment of human IL-1β (163-171) or polytuftsin (PT, a synthetic polymer of natural immunomodulator "tuftsin") with synthetic peptides of HIV on the induction of immune response to the synthetic peptides. A panel of synthetic peptides representing defined region of gp41, gp120 and gag were used as antigens. Immunomodulators linked peptides (i.e. peptide-IL-1β or peptide-PT) or peptide dimers were employed for immunization in Balb/c mice. Mice immunized with the peptide-immunomodulator develop effective T-cell proliferation,in vitro cytokine release and higher antibody production, but not with peptide dimers. We also found that peptide-immunomodulators induced high level of IgG2a antibody production. Furthermore, there was a positive correlation between the levels of cytokine (IL-2 & IFN-γ) and IgG isotype production. Thus it would appear that incorporation of IL-1β fragment or PT selectively enhances the Th1 type response to these peptides and may therefore be important for virus neutralization and clearance. However, the effect of IL-1β fragment was found to be more pronounced than polytuftsin. Such an approach may provide effective vaccination against other infectious diseases.

Risk assessment of tobacco, alcohol and diet in cancers of base tongue and oral tongue--a case control study

This is a retrospective case-control study of male tongue cancer patients seen at Tata memorial Hospital, Bombay, during the years 1980-84. The purpose of the study was to identify the association of tobacco, alcohol, diet and literacy status with respect to cancers of two sub sites of tongue namely anterior portion of the tongue (AT) (ICD 1411-1414) and base of the tongue (BT) (ICD 1410). There were 142 male AT patients and 495 BT patients interviewed during the period. 635 interviewed male patients who were free of any disease were considered as control. Bidi smoking was found to be a significant risk factor for BT patients and tobacco chewing for AT patients respectively. Alcohol drinkers showed about 45% to 79% excess risk for both sites of tongue cancer. Illiteracy and non vegetarian diet proved to be a significant factor for AT patients only. The study brings out that the location of cancer has got a direct bearing with the type of tobacco use and other related habits and this inturn may provide meaningful interpretation of variations observed in the incidence of tongue cancer around the world.

Influence of immunoadjuvants and a promiscous T-cell determinant on the immunogenicity of RESA peptide antigen of P. falciparum

Synthetic peptide antigens representing the repeat sequences of malarial antigens showed poor immunogenicity and protection in clinical trials. In the present study, RESA, an asexual blood stage antigen, containing (EENVEHDA)2 and (DDEHVEEPTVA)2 sequences were chemically linked to a promiscous T-cell determinant (CS.T3) of the circumsporozoite protein of P. falciparum. The synthetic constructs either alone or coentrapped with immunoadjuvants (nor muramyl dipeptide/lauroyl tetrapeptide) were administered in liposomes to mice of varying genetic background and the immunogenicity of different formulations were compared under identical experimental conditions. The RESA peptide formulations containing the T-cell determinant and the adjuvants generated high titre and affinity antibodies in all the strains, as compared to peptide(s) alone. The booster immunization induced a strong anamnestic response in each group. Though the major IgG isotype is of IgG1 and IgG2b interestingly, formulations containing CS.T3 have a higher proportion of cytophilic IgG2b isotype. There was a significant fall in the levels of IgG2b isotype while IgG1 levels were maintained same in the third bleed (day 60, without booster immunization). The mixed peptide group preparation containing the adjuvant is found to be a better immunogen than that of respective peptides itself. The in vitro merozoite reinvasion inhibition assay showed 76-96% inhibition with the formulations containing RESA peptide(s)-CS.T3 and the adjuvant, while with peptides alone the inhibition was 50-56%. This study highlights the importance of an alternative approach for developing peptide based immunogen against malaria.

Survival analysis of 5595 head and neck cancers--results of conventional treatment in a high-risk population

This is a study of 5595 head and neck cancer patients treated during 1987-89 at TMH, Mumbai. The study included 1970 oral cancers (ICD 140-145), 1495 oropharyngeal cancers (ICD 1410, 1453, 146), 1255 hypopharyngeal cancers (ICD 148), 125 nasopharyngeal cancers (ICD 147) and 750 laryngeal cancers (ICD 161). The clinical extent of disease at presentation was based on TNM group staging (UICC 1978). For the majority of sites, patients attended the hospital during stage III and stage IV of the disease; the only exception was for cancers of the lower lip, anterior tongue and vocal cord when between 46.2% and 56.5% of patients with localized cancer (stage I and II) were seen. Generally, surgery either alone or with radiation has been administered for oral cancer patients whereas radiation either alone or in combination with chemotherapy was administered for other head and neck sites. The overall 5-year survival rate was in the range of 20-43% for oral cancer, 8-25% for pharyngeal cancers and 25-62% for laryngeal cancer. The 5-year relative survival rates were more or less in agreement with the results published by the Eurocare study for head and neck cancers. The importance of primary prevention in head and neck cancer is stressed.

Functional analysis of conserved motifs in type III restriction-modification enzymes

EcoP1I and EcoP15I are members of type III restriction-modification enzymes. EcoPI and EcoP15I DNA methyltransferases transfer a methyl group from S-adenosyl-L-methionine (AdoMet) to the N6 position of the second adenine residues in their recognition sequences, 5'-AGACC-3' and 5'-CAGCAG-3' respectively. We have altered various residues in two highly conserved sequences, FxGxG (motif I) and DPPY (motif IV) in these proteins by site-directed mutagenesis. Using a mixture of in vivo and in vitro assays, our results on the mutational analysis of these methyltransferases demonstrate the universal role of motif I in AdoMet binding and a role for motif IV in catalysis. All six cysteine residues in EcoP15I DNA methyltransferase have been substituted with serine and the role of cysteine residues in EcoP15I DNA methyltransferase catalysed reaction assessed. The Res subunits of type III restriction enzymes share a distant sequence similarity with and contain the motifs characteristic of the DEAD box proteins. We have carried out site-directed mutagenesis of the conserved residues in two of the helicase motifs of the EcoP1I restriction enzyme in order to investigate the role of motifs in DNA cleavage by this enzyme. Our findings indicate that certain conserved residues in these motifs are involved in ATP hydrolysis while the other residues are involved in coupling restriction of DNA to ATP hydrolysis. Taken collectively, these results form the basis for a detailed structure-function analysis of EcoP1I and EcoP15I restriction enzymes.

Bioactive fragment of human IL-1beta [163-171] modulates the immune response to synthetic peptides of HIV

The activation of T helper cells specific for viral antigens is critical for antibody production and the generation of cytotoxic T cells during retroviral infection. In this study, we examined the effect of linking HIV peptides with a bioactive fragment of human interleukin-1beta (IL-1beta) (163-171) on the induction of immune response to the peptides. A panel of highly purified synthetic peptides representing defined regions of gp41, Gag and gp120 were used as antigens. Mouse spleen cells primed with the peptide conjugates produced greater proliferation on in vitro stimulation than spleen cells primed with peptide alone. In addition, antibody production as assessed by ELISA was observed after immunization with conjugated peptides but not with peptide alone, indicating B-cell activation. We also found that a high level of IgG2a antibody production correlated with a high level of IFN-gamma production. These findings favor the notion that IL-1beta plays an important role in immune responses. These observations support the formulation and design of synthetic vaccines against HIV using synthetic HIV peptides conjugated with immunomodulators. Such an approach may provide an effective vaccination against other infectious agents.

Estimate of cancer incidence in India in 1991

Cancer incidence and eighteen site-specific age standardised rates in India were estimated for the year 1991. With the establishment of National Cancer Registry Programme, incidence rates per 100,000 are available from six metropolitan registries and one rural registry. Using population census data for India in 1991, about 609,000 new cancer cases were estimated to have been diagnosed in the country in 1991. The estimated age standardised rates per 100,000 were 96.4 for males and 88.2 for females. The five most common cancers were lung (10.6%) pharynx (9.1%), oesophagus (6.7%), tongue (6.6%) and stomach (5.7%) among males and cervix (23.5%), breast (19.3%), ovary (5.5%) oesophagus (4.4%), and mouth (3.9%) among females. A comparison of estimated ASRs for two two largest countries in Asia (China and India) showed differences in the pattern of cancer.

Preparation & standardization of the goat lung surfactant extract

Exogenous goat lung surfactant extract (GLSE) was obtained by chloroform-methanol extraction of the centrifuged lung lavage. Four lungs provided around 250 mg of surfactant. GLSE has a phospholipid content of 50 percent, cholesterol of 1.5 percent and protein content under 1 percent. The preparation was bacteriologically sterile and had a shelf life of at least one month at 4 degrees C. Endotracheal administration of surfactant (50 mg/kg) in a rat lung model rendered surfactant deficient by saline lavage, restored the compliance characteristics to normal, thus documenting biological activity of the preparation. The cost of a course of 2 doses of surfactant replacement therapy was estimated to be as low as Rs 500/-. The study opens up the possibility of surfactant replacement therapy for the management of neonatal respiratory distress syndrome in India by an indigenous product at an affordable cost.

Modification of delivery system enhances MHC nonrestricted immunogenicity of V3 loop region of HIV-1 gp120

A successful peptide vaccine for AIDS is desired to elicit T-helper and cytotoxic T lymphocyte responses besides neutralizing antibodies. The V3 loop peptide of HIV-1 has been shown to contain the principal neutralizing domain, one of the most immunodominant regions, having both B-cell and T-cell determinants. In this study, the tip of the V3 loop region was mutated from GPGR to GPGQ based on the sequence of Indian isolates (CKRKIHIGPGQAFYT). To further enhance the immunogenicity of this epitope, two delivery systems of immune stimulating complexes (ISCOMs) and liposomes were used to incorporate the peptide. Mice of differing haplotypes, H-2b, H-2d, H-2k and H-2s, showed no MHC restriction when immunized with these formulations. The IgG levels as assessed by ELISA were found to be significantly higher (P < 0.05 to P < 0.001) for even five-fold lower doses of the peptide in ISCOMs and liposomes as compared to the conventional alum-based preparation. The major subtype elicited was IgG2a/IgG2b, suggestive of a Th1-like response for all the formulations. Thus, it would appear that the same peptide incorporated in ISCOMs and liposomes selects a Th1 response and may therefore be important not only for neutralization but also for virus clearance.

Immune response against the non-repeat region (293-310) of the circumsporozoite protein of Plasmodium vivax

Immunization by peptides based on the repeat sequences of Plasmodium falciparum or P. vivax antigen(s) have shown inconsistent results during clinical trials in humans. This could be attributed to the lack of T-cell help or antigenic polymorphism. Thus, attention has been focused towards the more conserved non-repeat regions. The present study was undertaken to map the antigenic determinant in the vicinity of region II (outside the repeat) of CS protein of P. vivax. The immunogenicity of the peptide was studied alone and after linking with polytuftsin (PT), using alum and Freund's adjuvant, in inbred strains of mice with different genetic backgrounds. The humoral response and antigen induced T-cell proliferation assays clearly demonstrated the immunomodulatory activity of PT. Comparable results were observed with antigen(s) administered either in alum or Freund's adjuvant. The induction of IgG2a and IgG2b antibody isotypes by both, peptide as well as the conjugate, may indicate that the T-helper response involved is of Th1 type. Further the immunofluorescence studies have shown that antibodies recognized the air dried sporozoites of P. cynomolgi. The results thus show that the above sequence has overlapping B and T-cell determinants and that alum can be substituted for Freund's adjuvant in generating an effective immune response.

Determination of the instrument function of a grating spectrometer by using white-light interferometry

We determined the instrument function or the response function of a grating spectrometer with finite slit widths in conditions of partial coherent illumination, by using a spectral-interference technique with white light. A Michelson interferometer of variable path delay is used to produce the spectral-interference fringes of required spacing. By deconvolution of the spectral visibility data for various exit and entrance slit widths, we have determined the exact form and frequency width of the instrument function for the spectrometer as well as the working region of the spectrometer for the least distorted output spectrum.

Mutations in the Res subunit of the EcoPI restriction enzyme that affect ATP-dependent reactions

The Res subunits of the type III restriction-modification enzymes share a statistically significant amino acid sequence similarity with several RNA and DNA helicases of the so-called DEAD family. It was postulated that in type III restriction enzymes a DNA helicase activity may be required for local unwinding at the cleavage site. The members of this family share seven conserved motifs, all of which are found in the Res subunit of the type III restriction enzymes. To determine the contribution, if any, of these motifs in DNA cleavage by EcoPI, a type III restriction enzyme, we have made changes in motifs I and II. While mutations in motif I (GTGKT) clearly affected ATP hydrolysis and resulted in loss of DNA cleavage activity, mutation in motif II (DEPH) significantly decreased ATP hydrolysis but had no effect on DNA cleavage. The double mutant R.EcoPIK90R-H229K showed no significant ATPase or DNA restriction activity though ATP binding was not affected. These results imply that there are at least two ATPase reaction centres in EcoPI restriction enzyme. Motif I appears to be involved in coupling DNA restriction to ATP hydrolysis. Our results indicate that EcoPI restriction enzyme does not have a strand separation activity. We suggest that these motifs play a role in the ATP-dependent translocation that has been proposed to occur in the type III restriction enzymes.

Quantitative assessment of tuftsin receptor expression and second messenger during in vitro differentiation of peripheral blood derived monocytes of leprosy patients

Tuftsin, a tetrapeptide (Thr-Lys-Pro-Arg) is known to potentiate the immunogenic activity of antigen-fed macrophages. The present study describes the mechanism of action of tuftsin in leprosy patients throughout the spectrum of the disease in vitro as a function of culture age in terms of (A) involvement of second messengers cAMP, cGMP and [Ca2+]i and (B) number of tuftsin binding sites/and their relative affinities on the monocytes/macrophages. There is apparently no direct involvement of either cAMP or cGMP while comparing the stimulated and unstimulated cultures during in vitro differentiation of monocytes (days 1, 3 and 7) or with the spectrum of the disease. Inhibition of superoxide anion release either by verapamil or with Quin 2 clearly demonstrated the involvement of [Ca2+]i as a second messenger during activation of monocytes/macrophages with tuftsin. Scatchard analysis of radiolabelled tuftsin binding data showed only one type of tuftsin receptor (low affinity) on BL/ LL monocytes/macrophages and normal and BT/TT cultures showed a gradual change in receptor number and affinities (low to high) with the maturation of monocytes to macrophages in contrast to BL/LL groups which displayed significantly less number of receptors. This study elicits a model which depicts that the biological responses/metabolic functions of early monocytes of normal and BT/TT gradually increase with the age of the culture till day 3 and tapers off thereafter in the older (day 7) cultures, whereas the monocytes/macrophages of BL/LL group are metabolically active only on day 1. The present study thereby implies that the clearance of leprosy bacilli from lepromatous leprosy lesions as a consequence of local or systemic immunotherapy (in the present study, the macrophage modulation by tuftsin) depends on the influx of new competent macrophages, rather than the local activation of resident lepromatous macrophages.

Release of reactive nitrogen intermediates from the peripheral blood-derived monocytes/macrophages of leprosy patients stimulated in vitro by tuftsin

The production of reactive nitrogen intermediates (RNI) by macrophages is critical to host defence, particularly for exerting the bactericidal and tumoricidal properties. Nitric oxide (NO) were measured in the peripheral blood-derived monocytes/macrophages of normal and leprosy patients (BT/TT and BL/LL) in the presence and absence of 'tuftsin' as a function of in vitro culture age (on 1, 3, 7 days). Macrophages from both groups of leprosy patients were able to produce NO during the unstimulated state but only BL/LL macrophages could be activated by tuftsin to produce significantly high levels of NO. This increase was highest on day 1, then gradually decreased with in vitro culture age. Surprisingly, tuftsin was unable to enhance the NO production in normal macrophages above the basal level. Further, normal and BT/TT macrophages had only Cu-Zn derived superoxide dismutase (SOD) activity whereas BL/LL cultures has Cu-Zn and Mn derived SOD activity. These studies indicate that in BL/LL cultures: a, apart from tuftsin, some additional signal is required to activate nitric oxide synthase (NOS) gene for NO production; and b, Mn-SOD produced by Mycobacterium leprae is playing a defensive role against toxic-free radicals. The final outcome of this mechanism is the survival of M. leprae inside the macrophages.

Leukocyte glucose 6 phosphate dehydrogenase as prognostic indicator in ANLL and CML

Glucose 6 phosphate dehydrogenase (G6PD) was estimated in the leucocytes of 35 patients with acute non-lymphocytic leukemia (ANLL) and 10 patients with chronic myeloid leukemia (CML). G6PD levels were found to be significantly decreased in majority of the patients with ANLL while it was increased in all CML patients. Variation in G6PD was found to be dependent on the percentage of myelocytes inANLL. Cytogenetic analysis was also carried out in these patients. Correlation analysis of leucocyte G6PD activity and karyotype with prognostic assessment clearly indicated the association of (s) high percentage of chromosomal abnormalities especially translocations, (b) low survival and remission rates, with patients having decreased G6PD activity when compared to patients with normal activity in ANLL. The studies indicate that leucocyte G6PD may be useful as a diagnostic and prognostic tool.

A comparative study of the redox-cycling of a quinone (rifamycin S) and a quinonimine (rifabutin) antibiotic by rat liver microsomes

Rifamycin S and rifabutin are clinical drugs used to treat tuberculosis and leprosy. The formation of reactive oxygen species during the redox-cycling of rifamycin S (quinone) and rifabutin (quinonimine) was evaluated. The semiquinone (or semiquinonimine) and hydroquinone (or hydroquinonimine) formed during the reduction of the parent molecules by microsomal electron transfer in the presence of nicotinamide-adenine dinucleotide phosphate, reduced (NADPH) or nicotinamide-adenine dinucleotide, reduced (NADH) reoxidizes in air to generate superoxide radical and hydrogen peroxide. In the presence of added iron, hydroxyl radicals, formed by the Fenton reaction, were detected using 5,5'-dimethyl-1-pyroline-N-oxide as the spin-trap. Rifamycin S, a quinone, redox cycles more efficiently than rifabutin, a quinonimine, as approximately five times the concentration of hydroxyl radical adduct of 5,5'-dimethyl-1-pyroline-N-oxide (DMPO) was detected, when compared with rifabutin. The NADPH-dependent microsomal production of hydroxyl radical in the presence of rifamycin S was somewhat higher than the NADH-rifamycin S system with most iron chelators. However, with rifabutin, NADH-dependent microsomal production of hydroxyl radical was higher than that found with the NADPH-rifabutin system. An exception was the iron chelator, diethylene-triamine-pentacetic acid (DTPA), in which NADPH-dependent rates exceeded the rates with NADH with both antibiotics. Rat liver sub-mitochondrial particles also generated hydroxyl radical in the presence of NADH and either rifamycin S or rifabutin. The electron transport chain inhibitors such as rotenone and antimycin A enhanced the signal intensity of DMPO-OH, suggesting NADH dehydrogenase (complex I) as the major component involved in the reduction of rifamycin S. Rifamycin S was shown to be readily reduced to rifamycin SV, the corresponding hydroquinone by Fe(II); under similar conditions Fe(II) did not reduce rifabutin. Using optical spectroscopy, we determined that rifamycin S forms a complex with Fe(II). The stoichiometry of the complex was Fe(rifamycin S)3 in phosphate buffer at pH 7.4. Rifabutin did not form a detectable complex with Fe(II). The redox cycling of rifamycin S and rifabutin did not cause microsomal lipid peroxidation. In fact, the Fe:ATP induced lipid peroxidation was completely inhibited by these two molecules. These results indicate that rifamycin S and rifabutin can interact with rat liver microsomes to undergo redox-cycling, with the subsequent production of hydroxyl radicals when iron complexes are present. Compared to NADPH, NADH is almost as effective (rifamycin S) or even more effective (rifabutin) in promoting these interactions. These interactions may play a role in the hepatotoxicity associated with the use of these antibiotics.

Advantage of dimeric peptide antigens in serodiagnosis of HIV-1 infection

The reactivity of antibodies with dimeric and monomeric peptide antigens was compared by ELISA. A panel of highly purified synthetic peptides of HIV-1 representing defined regions, 598-609 and 524-533 (fusion domain) of gp41 and 306-320 of gp120, were used as antigens in the ELISA. These peptides were selected and synthesized taking into account the level of sequence conservation of various strains and hydrophilicity. The analysis included sera from 52 HIV-1 infected individuals and 53 HIV-1 negative controls. Both peptides from gp41 were found to be particularly immunoreactive with sera from HIV-1 infected individuals. The frequency of reactivity to the selected peptide from gp120 (V3 loop) in infected individuals was 82%. An interesting observation was that the dimeric peptide antigens had a detection rate more than 4-fold higher than the monomeric antigens. We found that lower levels of antibodies could be detected with dimeric antigens. The peptides reacted with few sera other than HIV-1 positive sera. These results implicate the potential dimeric peptide antigens to be utilized in the serodiagnosis of HIV-1 infection.