Red cell enzymopathies in leukemias

Red cell glucose-6-phosphate dehydrogenase (G6PD) and pyruvate kinase (PK) levels were estimated in patients with leukemias, to see if there was a consistent enzyme defect and correlation of enzyme levels with stage of the disease with prognostic assessment. G6PD levels were found to be significantly increased or decreased in majority of the patients with acute leukemias. Increased activity was seen in majority of the patients with L1 and decreased activity in L2 subtype of acute lymphocytic leukemia (ALL). In chronic myeloid leukemia (CML) G6PD activity was consistently increased, with levels being highly elevated in chronic phase and moderately in blast phase. Variation in G6PD activity was found to be related to the stage of disease and was of prognostic significance. PK was found to be normal or decreased. Fetal haemoglobin levels were also estimated in 30 patients with leukemias and were found to be elevated in most patients. Red cell G6PD may be useful for staging of the disease, as prognostic indicator and predictor of relapse.

Chemistry and biology of DNA methyltransferases

Recognition of a specific DNA sequence by a protein is probably the best example of macromolecular interactions leading to various events. It is a prerequisite to understanding the basis of protein-DNA interactions to obtain a better insight into fundamental processes such as transcription, replication, repair, and recombination. DNA methyltransferases with varying sequence specificities provide an excellent model system for understanding the molecular mechanism of specific DNA recognition. Sequence comparison of cloned genes, along with mutational analyses and recent crystallographic studies, have clearly defined the functions of various conserved motifs. These enzymes access their target base in an elegant manner by flipping it out of the DNA double helix. The drastic protein-induced DNA distortion, first reported for HhaI DNA methyltransferase, appears to be a common mechanism employed by various proteins that need to act on bases. A remarkable feature of the catalytic mechanism of DNA (cytosine-5) methyltransferases is the ability of these enzymes to induce deamination of the target cytosine in the absence of S-adenosyl-L-methionine or its analogs. The enzyme-catalyzed deamination reaction is postulated to be the major cause of mutational hotspots at CpG islands responsible for various human genetic disorders. Methylation of adenine residues in Escherichia coli is known to regulate various processes such as transcription, replication, repair, recombination, transposition, and phage packaging.

Functional analysis of conserved motifs in EcoP15I DNA methyltransferase

EcoP15I DNA methyltransferase recognizes the sequence 5'-CAGCAG-3' and transfers a methyl group to N-6 of the second adenine residue in the recognition sequence. All N-6 adenine methyltransferases contain two highly conserved sequences, FxGxG (motif I), postulated to form part of the S-adenosyl-L-methionine binding site and (D/N/S)PP(Y/F) (motif IV) involved in catalysis. We have altered the second glycine residue in motif I to arginine and serine, and substituted tyrosine in motif IV with tryptophan in EcoP15I DNA methyltransferase, using site-directed mutagenesis. The mutant enzymes were overexpressed, purified and characterized by biochemical methods. The mutations in motif I completely abolished AdoMet binding but left target DNA recognition unaltered. Although the mutation in motif IV resulted in loss of enzyme activity, we observed enhanced crosslinking of S-adenosyl-L-methionine and DNA. This implies that DNA and AdoMet binding sites are close to motif IV. Taken together, these results reinforce the importance of motif I in AdoMet binding and motif IV in catalysis. Additionally, limited proteolysis and UV crosslinking experiments with EcoP15I DNA methyltransferase imply that DNA binds in a cleft formed by two domains in the protein. Methylation protection analysis provides evidence for the fact that EcoP15I DNA MTase makes contacts in the major groove of its substrate DNA. Interestingly, hypermethylation of the guanine residue next to the target adenine residue indicates that the protein probably flips out the target adenine residue.

Epidemiological observations on cancer of the oesophagus--a review of Indian studies

This is an epidemiological review on cancer of the oesophagus. In this attempt, all aspects of epidemiological factors based on national and international studies on oesophageal cancer have been brought out. The problem of this cancer in Indian context has been documented. The association of tobacco and alcohol habits with oesophageal cancer has been confirmed from the studies conducted in India. There is an urgent need to educate the common people about the harmful effect of these two habits and governments and voluntary organisation should take effective steps for its prevention.

1-Hydroxyethyl radical formation during NADPH- and NADH-dependent oxidation of ethanol by human liver microsomes

Ethanol can be oxidized to the 1-hydroxyethyl radical (HER) by rat and deer mice liver microsomal systems. Experiments were carried out to evaluate the ability of human liver microsomes to catalyze this reaction, compare the effectiveness of NADH with that of NADPH, and assess the possible role of cytochrome b5 in HER formation. HER was detected as the alpha-(4-pyridly-1 -oxide)-N-t-butylnitrone/HER adduct. Human liver microsomes catalyzed HER formation with either NADPH or NADH as cofactor; rates with NADH were approximately 50% those found with NADPH. Chelex-100 treatment of the reaction mixture produced marked inhibition of HER formation, suggesting that a transition metal, such as iron, was required to catalyze the reaction. The addition of ferric chloride restore HER formation. Catalase (2600 units/ml) and superoxide dismutases (500 units/ml) nearly completely inhibited the reaction with either NADPH or NADH. The NADH-dependent rates of superoxide production, detected as 5,5-dimethyl-1-pyrroline-N-oxide-O2H, were approximately 50% the NADPH-dependent rates, which is consistent with the rates of HER formation. Anti-cytochrome b5 IgG decreased NADPH- and NADH-dependent HER formation, and this was associated with inhibition of superoxide formation with both reductants. These results indicate that human liver microsomes can catalyze the oxidation of ethanol of HER with either NADPH or NADH as reductant. The effectiveness of NADH may be significant in view of the increased NADH/NAD+ redox ratio in the liver as a consequence of ethanol oxidation by alcohol dehydrogenase. HER formation by human liver microsomes seems to be catalyzed by an oxidant derived from the interaction of iron with superoxide or H2O2, and a close association exists between HER formation and superoxide production. Cytochrome b5 seems to play a role in HER formation, most likely due to its effect on superoxide production.

Leukocyte glucose 6 phosphate dehydrogenase (G6PD) as prognostic indicator in children with acute lymphocytic leukemia

G6PD activity, estimated in 37 patients with acute lymphocytic leukemia (ALL) prior to therapy was found to be significantly decreased in 78.37% of the patients with ALL while it was normal in other patients. Variation in G6PD was found to be dependent on the percentage of myelocytes. Correlation analysis of leukocyte G6PD activity with karyotype indicated that patients with normal karyotype with normal G6PD activity had good prognosis while those with abnormal G6PD with abnormal karyotype had poor prognosis. Subjects with normal karyotype and abnormal G6PD and vice versa had intermediate prognosis. Thus the results clearly indicate that leukocyte G6PD may be used as a diagnostic and prognostic tool.

Production of nitric oxide and other iron-containing metabolites during the reductive metabolism of nitroprusside by microsomes and by thiols

Sodium nitroprusside is used as a hypotensive agent because of its ability to produce nitric oxide (NO), although direct demonstration of this has not been reported in a biological system. Nitroprusside (NP) nitroxide radical anion, the first reduction product of NP generated in the presence of microsomes and NADPH, was found to undergo further metabolism. One of the products produced during this reductive metabolism was shown to be NO. By using N-methylglucamine dithiocarbamate-FeCl2 complex [(NMGD)2Fe(II)] as the NO trap, we have detected and characterized the mononitroso bis(N-methylglucamine dithiocarbamato) iron (II) complex (MNBI) (g = 2.040, and A(14N) = 13.3 G) as the product of NO trapping. The production of NO during the reductive metabolism of NP by submitochondrial particles and a human HepG2 hepatoblastoma cell line was also demonstrated using (NMGD)2Fe(II). In addition to MNBI, two other mononitrosyl iron complexes, the NP nitroxide radical anion and a second species designated as Fe(NO)(X)(Y) (g = 2.032, and A(14N) = 14.3 G), and additional unidentified paramagnetic products containing iron were also detected. Thiol compounds such as glutathione, cysteine, and cysteamine reduce NP to generate NP nitroxide radical anion and a paramagnetic species characterized as a dithiolated dinitroso iron complex (DDIC), Fe(NO)2(RS)2 g = 2.030, A(14N) = 2.2 G(2N), and A(1H) = 1.1 G(4H). At 77 K, DDIC generated from cysteine and NP has an axial symmetry, with g perpendicular = 2.040, and g parallel = 2.014. Two additional paramagnetic products, designated as species C (g = 2.020, linewidth = 4.8 G) and species D (g = 2.008, linewidth = 6.1 G), were also formed during NP reduction by thiol compounds. The characterization of these complexes has been hampered by the lack of hyperfine features in the ESR spectra. The production of NO during cysteamine reduction of NP was demonstrated by using (NMGD)2-Fe(II) as the spin-trap. These results directly demonstrate the production of NO during the reduction of NP by microsomes plus NADPH or by thiols. (NMGD)2-Fe(II) is a particularly useful spin-trap for the detection of NO in a strong reducing environment.

Humoral immune responses to the Plasmodium falciparum antigen Pf155 RESA in adults with differential clinical conditions from an Indian zone where malaria is endemic

Ring infected erythrocyte surface antigen of Plasmodium falciparum (Pf155/RESA) has been considered as a vaccine candidate. However, the relative immunogenicity of this antigen has not been studied in Indian populations. Pf155/RESA was investigated for its immunogenicity by studying humoral immune responses against Pf155/RESA and Pf155/RESA derived peptides (P1, P2 representing immunodominant epitopes from the 3' and P3 from the 5' repeat regions) by erythrocyte membrane immunofluorescence (EMIF) assay and by enzyme linked immunosorbent assay (ELISA) in P. falciparum primed donors living in hyperendemic malarious areas (Orissa State, India) where P. falciparum infections are highly prevalent. Subjects of different clinical status namely acute (A), clinically immune (CI) and acute with history of repeated P. falciparum infections (R) were included in this study. All the donors were seropositive against the crude antigen. There was considerable variation in the responses among the donors. While humoral responses in the plasmas against the P2 peptide (EENV)4 were significantly higher in magnitude and in frequency in the CI donors than in the A donors, no positive response was seen in the R donors. The responses to the peptides P1 (EENVEHDA)2 and P3 (DDEHVEEPTVA)2 were poor both in the A and in the CI groups. Whereas, most of the R donors were seropositive against the P3. The present results indicate that Pf155/RESA contains B cell epitopes which were recognized differently by the immune system of individuals living in malaria-hyperendemic areas of India who have been primed by natural infection. Our studies also suggest that in order to investigate the possible functional role of a given antigen, study of immune responses against the antigen in donors of different clinical status may be useful.

DNA recognition by the EcoP15I and EcoPI modification methyltransferases

The DNA-binding properties of the EcoP15I DNA methyltransferase (M.EcoP15I; MTase) were studied using electrophoretic mobility shift assays. We show by molecular size-exclusion chromatography and dimethyl suberimidate cross-linking that M.EcoP15I is a dimer in solution. While M.EcoP15I binds approx. threefold more tightly to its recognition sequence, 5'-CAGCAG-3', than to non-specific sequences in the presence of AdoMet or its analogs, the discrimination between specific and non-specific sequences significantly increases in presence of ATP. These results suggest for the first time a role for ATP in DNA recognition by type-III restriction-modification enzymes. Furthermore, we show that although c2 EcoPI mutant MTases are defective in AdoMet binding, they are still able to bind DNA in a sequence-specific manner.

Polytuftsin: its possible effects and mechanism during macrophage activation

Polytuftsin (PT) a 35-40 repeat unit of tuftsin (TKPR), when administered as a conjugate with the malarial peptide, ring-infected erythrocyte surface antigen (RESA), enhanced antigen-induced lymphoproliferation and antibody levels in mice as compared to RESA alone. This enhancement was unrelated to the H-2 background of the animals. The present study was undertaken with a view to understanding the mechanism(s) responsible for this immune enhancement. Peritoneal adherent cells (PAC) from H-2b and H-2d mice were incubated with RESA alone, PT-conjugated RESA, a physical mixture of RESA + PT and PT alone. They were subsequently evaluated for I-A expression using monoclonal antibodies and flow cytometry as well as cell-ELISA. Significant increase in I-A expression on PAC was observed in all 4 groups as compared to untreated cells. Whereas cells treated with PT-conjugated RESA showed highly significant increase in I-A (P < 0.001), the other groups showed moderate increase (P < 0.05). This enhancement was attributable to increase in the number of I-A-positive cells rather than I-A molecules per cell. Moreover, IL-1 release, as assayed by bioassay, was significantly higher in cells treated with conjugated RESA as compared to cells treated with RESA or PT alone (P < 0.05). Thus, it would appear that PT-conjugated RESA peptide of the malarial antigen selectively enhances major histocompatibility complex (MHC) class II molecules on antigen-presenting cells (APC) and may therefore improve immune functions by stimulating better antigen presentation and proliferation of T cells.

ATP hydrolysis is required for DNA cleavage by EcoPI restriction enzyme

The type III restriction endonuclease EcoPI, coded by bacteriophage P1, cleaves unmodified DNA in the presence of ATP and magnesium ions. We show that purified EcoPI restriction enzyme fails to cleave DNA in the presence of non-hydrolyzable ATP analogs. More importantly, this study demonstrates that EcoPI restriction enzyme has an inherent ATPase activity, and ATP hydrolysis is necessary for DNA cleavage. Furthermore, we show that the progress curve of the reaction with EcoPI restriction enzyme exhibits a lag which is dependent on the enzyme concentration. Kinetic analysis of the progress curves of the reaction suggest slow transitions that can occur during the reaction, characteristic of hysteretic enzymes. The role of ATP in the cleavage mechanism of type III restriction enzymes is discussed.

Interaction of EcoP15I DNA methyltransferase with oligonucleotides containing the asymmetric sequence 5'-CAGCAG-3'

EcoP15I DNA methyltransferase (Mtase) recognizes the asymmeteric sequence CAGCAG and catalyzes the transfer of a methyl group from S-adenosyl-L-methionine to the second adenine residue. We have investigated the DNA binding properties of EcoP15I DNA Mtase using gel mobility shift assays. EcoP15I DNA Mtase binds approximately threefold more tightly to DNA containing its recognition sequence, CAGCAG, than to non-specific sequences in the absence or presence of cofactors. Interestingly, in the presence of ATP the discrimination between specific and non-specific sequences increases significantly. These results suggest for the first time a role for ATP in DNA recognition by type III restriction-modification enzymes. In addition, we have shown that bromodeoxyuridine-containing oligonucleotides form complexes with EcoP15I DNA Mtase that are crosslinked upon irradiation. More importantly, we have shown that the crosslink site is at the site of DNA binding, since it can be suppressed by an excess of unmodified oligonucleotide. EcoP15I DNA Mtase exhibited Michaelis-Menten kinetics with both unmodified and bromodeoxyuridine-substituted DNA, with a higher specificity constant for the latter. Furthermore, gel mobility shift assays showed that proteolyzed EcoP15I DNA Mtase formed a specific complex with DNA, which had similar mobility as the native protein-DNA complex. Taken together these results form the basis for a detailed structure-function analysis of EcoP15I DNA Mtase.

Risk assessment of tobacco, alcohol and diet in oral cancer--a case-control study

A retrospective case-control study of 713 male oral-cancer patients seen at Tata Memorial Hospital, Bombay, during 1980-1984 was undertaken to assess the association between chewing, smoking and alcohol habits. Male controls were chosen among those persons who attended the hospital during the same period and were diagnosed as free from cancer, benign tumour and infectious disease. Statistical analysis was based on unconditional logistic regression and the confidence interval for RR was calculated using the standard error of the estimates. Established factors such as tobacco chewing and bidi smoking showed a significant association with oral cancer. For the alcohol habit, the relative risk was 1.42 and the dose-response relationship, in terms of frequency and duration of the habit, was also observed. The illiterate group showed an almost 2-fold significant excess risk compared to the literate group. After adjusting for confounding variables such as age, residence, illiteracy and known factors such as tobacco chewing and bidi smoking, the study has brought out the significance of a non-vegetarian diet as a high-risk factor for oral cancer compared to a vegetarian diet. Further studies are required to identify specific items in the non-vegetarian diet which may be associated with oral cancer.

Construction of a synthetic immunogen: use of the natural immunomodulator polytuftsin in malaria vaccines against RESA antigen of Plasmodium falciparum

Polytuftsin, a 35-40-unit repeat of the naturally occurring tetrapeptide tuftsin (TKPR), was chemically linked to EENVEHDA and DDEHVEEPTVA repeat sequences of ring-infected erythrocyte surface antigen protein (an asexual blood-stage antigen) of Plasmodium falciparum. These synthetic constructs were tested for their humoral and cellular immune responses in five inbred strains of mice with different genetic backgrounds (H-2a, H-2b, H-2d, H-2k and H-2i). Mice immunized with these constructs showed higher antibody titres, secondary immune responses and antigen-induced T-cell proliferation compared with the peptide dimers alone. Sera from mice immunized with both the constructs inhibited merozoite invasion of erythrocytes in vitro by 60-80% at 1:10 antisera dilution. Polytuftsin alone proved to be a very poor immunogen in our studies, since no anti-tuftsin antibodies could be detected in the sera. Therefore, we conclude that the synthetic constructs described here could be useful for the development of subunit malaria vaccines.

Role of reproductive factors in breast cancer in a low-risk area: a case-control study

A case-control study of 689 breast cancer patients seen at Tata Memorial Hospital during the period 1980-84 was carried out. During the same period 711 females who attended the hospital without a history of benign breast lesions or gynaecological complaints were selected as controls. Patients were interviewed by trained investigators to collect data on reproductive factors, menstrual history, tobacco smoking and chewing habit, dietary practices (vegetarian and non-vegetarian diet) and alcohol consumption. Cases and controls were stratified into four age groups (< 35 years, 35-44, 45-54 and 55+ years) and three places of residence (Bombay, Maharashtra, others). The adjusted relative risk (RR) for unmarried women compared with married women was 2.3. Nulliparous women had a 2.2-fold higher risk than parous women. Late age at marriage (30 years and above) and late age at first pregnancy (30 years and above) showed excess risks of 2.5 and 5.4 compared with women married at the age of 14 years and age at first pregnancy of < or = 14 years. Three or more pregnancies was associated with a 40-50% reduction in risk (P < 0.01). Non-vegetarian diet, literacy status and a history of stillbirth and abortion did not emerge as significant risk factors for breast cancer in our study. These findings, in a low-risk population, were consistent with those reported from high-risk populations.

Photolabeling of the EcoP15 DNA methyltransferase with S-adenosyl-L-methionine

Radioactivity from S-adenosyl-L-[methyl-3H]methionine ([methyl-3H]AdoMet) was bound to the EcoP15 DNA methyltransferase (M.EcoP15) following short-wave ultraviolet (UV) irradiation. The labeled protein was subjected to polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE), and detected by fluorography and autoradiography. Labeling was found to be dependent on the concentration of AdoMet and time of UV irradiation. The photolabeling by [methyl-3H]AdoMet was specific and blocked by S-adenosyl-L-homocysteine (AdoHcy) and sinefungin which are known to function as competitive inhibitors. Limited digestion of the M.EcoP15-AdoMet adduct by Staphylococcus aureus protease V8 generated three peptides of approx. 50, 32 and 30 kDa. Interestingly, only the 30-kDa peptide fragment contained radioactivity, as detected by SDS-PAGE, followed by fluorography and autoradiography. Further, sequencing of a few amino acids at the N-terminus of these peptides showed that the 30-kDa fragment was the N-terminal portion of M.EcoP15. These results suggest that photolabeling is at the AdoMet-binding site and that the N-terminal half of M.EcoP15 may be involved in substrate binding.

Interaction of EcoP1 modification methylase with S-adenosyl-L-methionine: a UV-crosslinking study

EcoP1 modification methylase was radioactively labeled when incubated with S-adenosyl-L-[methyl-3H]methionine in the presence of ultraviolet light. Crosslinking of the enzyme as detected by electrophoresis on sodium dodecyl sulfate-polyacrylamide gel followed by fluorography and autoradiography, was shown to be specific by a number of criteria. More importantly, EcoP1 modification methylase was also radioactively labeled with S-adenosyl-L-[carboxyl-14C]methionine demonstrating that labeling involved binding of the entire AdoMet molecule rather than methylation of the protein. Further, c2 EcoP1 mutant DNA modification methylases which show negligible or very little methylation activity, correspondingly formed a weak or no adduct upon crosslinking. These results suggest that photolabeling of EcoP1 DNA modification methylase occurs at the AdoMet binding site.

Modulation of peripheral blood derived monocytes/macrophages from leprosy patients using 'tuftsin' for production of reactive oxygen intermediates

Phagocytic cells respond to a variety of membrane stimulants by producing reactive oxygen intermediates (ROI), i.e. O2-, H2O2 and OH.metabolites. Plasma membrane activation is associated with superoxide generating NADPH oxidase, thereby causing the production of these toxic species. Stimulation of phagocytic cells also results in activation of purine catabolism, which directs the metabolic flux through xanthine oxidase to produce the superoxide anion. We previously observed that BL/LL macrophages (M phi) exhibited a premature inability to undergo tuftsin stimulated phagocytosis and microbicidal activity. The present study was undertaken to measure ROI levels in the absence and presence of 'tuftsin' pulsing as a function of in vitro culture age and also correlated these levels with adenosine deaminase (ADA) activity. The latter is known to be a contributor of O2- generation and is also involved in the maturation of the monocyte/macrophage system. The behaviour of normal and tuberculoid monocytes/macrophages were more or less the same, either in the presence or absence of tuftsin, i.e. they showed a progressive increase in ROI production until day 3, then tapered off in older cultures by day 7. In contrast, after day 1, the lepromatous macrophages were unable to undergo tuftsin mediated stimulation for the production of ROI and ADA activity. These findings indicate a defective M phi function in lepromatous patients towards tuftsin pulsing, thereby supporting our earlier observations. Thus BL/LL M phi behaved as if they were aged after 1 day of in vitro culture, which may account for an inability to handle Mycobacterium leprae for efficient killing.

Modulation of trenimon-induced cytotoxicity by DT-diaphorase in isolated rat hepatocytes under aerobic versus hypoxic conditions

Trenimon belongs to a class of aziridinylbenzoquinone anticancer drugs that cross the blood-brain barrier. In this study we have investigated the molecular mechanisms for trenimon-induced toxicity in aerobic versus hypoxic conditions with the use of freshly isolated rat hepatocytes. The following evidence suggests the mechanisms for trenimon detoxification involves reduction by DT-diaphorase, while the cytotoxic mechanism involves macromolecular alkylation under hypoxic conditions as well as oxidative stress under aerobic conditions. (a) Hepatocyte cytotoxicity induced by trenimon (250 microM) under aerobic conditions ensued following an initial induction of cyanide-resistant respiration and partial oxidation of glutathione to oxidized glutathione. Trenimon reduction to the hydroquinone by the hepatocytes was rapid. Inhibition of hepatocyte DT-diaphorase by dicumarol increased trenimon-induced cytotoxicity by approximately 10-fold, and markedly inhibited hydroquinone formation. Furthermore, both cyanide-resistant respiration and oxidized glutathione formation were markedly increased, resulting in depletion of oxygen in the media. Trenimon reduction to the hydroquinone then occurred. This suggests that DT-diaphorase in normal hepatocytes prevents the formation of the semiquinone that causes cytotoxic protein alkylation and oxidative stress. (b) Hepatocyte cytotoxicity induced by trenimon (350 microM) under hypoxic conditions ensued following glutathione depletion without oxidized glutathione formation. Inactivation of hepatocyte DT-diaphorase by dicumarol under hypoxic conditions increased trenimon-induced cytotoxicity by approximately 3.5-fold and increased semiquinone radical levels 2-fold without affecting its reduction rate. This suggests that the cytotoxic mechanism involves protein alkylation by semiquinone radicals formed by reductases catalyzing a one-electron reduction of trenimon.

Construction of synthetic immunogens: use of T- and B-cell epitopes of CS and RESA proteins of Plasmodium falciparum

An invariant T-helper epitope of the sequence ENDIEKKICKMEKCSSVFNV (residue no. 376-395) from the circumsporozoite (CS) protein was coupled chemically with the repeat sequences, namely (EENV)2, EENVEHDA and DDEHVEEPTVA, of ring-infected erythrocyte surface antigen (RESA) protein of Plasmodium falciparum. The CS sequence was tested for helper and proliferative activity in five inbred strains of mice of different haplotypes. The CS peptide showed dose-dependent lymphocyte proliferative response in all the strains tested. On the other hand, no proliferative response was observed with the dimers of the three RESA repeat sequences. The antibody levels in these strains immunized with RESA-CS hybrid structures showed high titres and a booster effect during subsequent immunization. Such a phenomenon was not observed with RESA peptides alone. The above CS sequence could be an ideal T-helper epitope which can be linked to hydrophilic B-cell epitopes of the RESA sequence to overcome major histocompatibility complex restriction in the host.

Enzyme immunoassay of phagocytosis stimulating tetrapeptide "tuftsin" in normal and leprosy sera

The serum concentrations of the phagocytosis stimulating the tetrapeptide, tuftsin, were determined by competitive enzyme immunoassay in borderline tuberculoid/tuberculoid (BT/TT, 16 cases), borderline lepromatous/lepromatous (BL/LL, 16 cases), and in healthy controls (20 cases). Using checkerboard titration, 10 ng/well of diphtheria toxoid-p-aminophenylacetyl tuftsin (DTPT) conjugate when incubated with tuftsin antisera at 1:15,000 dilution with a preincubation time of 60 min with the competitor (tuftsin) followed by a further 60-min incubation onto the DTPT-coated wells gave consistent results with a sensitivity of 5 ng/well tuftsin. The mean serum tuftsin concentration was significantly lower in BL/LL patients (134.42 +/- 48.7 ng/ml, p less than 0.01) than in healthy controls (262.86 +/- 59.8 ng/ml), while BT/TT sera (210.94 +/- 75.5 ng/ml) showed slightly decreased levels than did normals, which was not statistically significant. The mean serum IgG levels in BL/LL and BT/TT patients (37.26 +/- 10.99 mg/ml; 28.08 +/- 6.57 mg/ml, respectively) showed significantly (p less than 0.001) higher concentrations than did healthy controls (12.3 +/- 3.6 mg/ml). These observations on the serum concentrations of tuftsin and IgG in leprosy individuals suggest that there is splenic dysfunction in BL/LL patients in terms of the processing of leukokinin to release the free, active molecule tuftsin.

Reduction of paraquat and related bipyridylium compounds to free radical metabolites by rat hepatocytes

The toxicity of paraquat is due to the oxygen-derived radicals formed by the reaction of oxygen with bipyridylium radical cations. Although paraquat is known to cause lung toxicity, the related bipyridylium compounds such as diquat and morfamquat do not affect the lung as seriously, but rather cause liver toxicity. Paraquat, diquat, morfamquat, and benzyl viologen are reduced by rat hepatocytes to their respective radical cations. An intracellular component of the signal was detected from diquat and benzyl viologen radical cations. These radical cations generated inside the cell can cross the plasma membrane. Generation of the diquat radical cation by hepatocytes is not affected by the inhibition of cytochrome P-450 by carbon monoxide or metyrapone, suggesting that this enzyme is probably not involved in the reduction of diquat as had been proposed previously. The reduction of paraquat is generally attributed to NADPH-cytochrome P-450 reductase, and presumably diquat is also reduced by this flavoprotein. Some transition metal chelates such as ferric diethylenetriaminepentaacetic acid delay the detection of the diquat radical cation. This may be due to the reduction of the ferric chelate by the diquat radical cation resulting in the formation of the ferrous chelate and the parent bipyridylium dication. When all the ferric chelate has been reduced to the ferrous chelate, then the bipyridylium radical can be detected. Alternatively, if the ferric chelate enters the cell, it can compete with the parent bipyridylium dication for the reductase, which would also lead to delayed detection.

Reductive metabolism of nitroprusside in rat hepatocytes and human erythrocytes

The metabolism of nitroprusside by hepatocytes or subcellular fractions involves a one-electron reduction of nitroprusside to the corresponding metal-nitroxyl radical. Thiol compounds also reduced nitroprusside to the metal-nitroxyl radical apparently via a thiol adduct. The nitroprusside reduction by microsomes was shown to be due to cytochrome P450 reductase as an antibody to cytochrome P450 reductase inhibits the microsomal reduction of nitroprusside, and the inhibitors of cytochrome P450 such as carbon monoxide or metyrapone had no effect. The reduction of nitroprusside by mitochondria in the presence of NADH or NADPH also produced the metal-nitroxyl radical. In hepatocytes, both mitochondria and the cytochrome P450 reductase are involved in the reduction of nitroprusside. The reductive metabolism of nitroprusside was found to produce toxic by-products, namely, free cyanide anion and hydrogen peroxide. We have also detected thiyl radicals formed in the thiol compound reduction of NP. We propose that cyanide and hydrogen peroxide are important toxic species formed in the metabolism of nitroprusside. The rate of reductive metabolism of nitroprusside by rat hepatocytes was much higher than with human erythrocytes. Therefore the major site of nitroprusside metabolism in vivo may be liver and not blood as originally proposed.

Comparative assessment of pedal pressing rates of self-stimulation of hypothalamus and midbrain with both square wave and sine wave stimulus parameters

In Wistar rats, the regional differences of pedal pressing rates of self-stimulation (SS) of lateral hypothalamus (LH) and substantia nigra-ventral tegmental area (SN-VTA) were assessed with electrodes implanted in both regions in each subject. Average of SS rates of SN-VTA sites was significantly higher than that of LH sites, tested with both sine wave and square wave types of stimuli. There was no significant difference in SS rates between males and females, and also in the females between different days of oestrus cycles. The high rates of robust SS observed in this study relative to SS rates reported in past literature were probably due not only to the placements of electrodes in the main substrates of SS, but also to the parameters of stimulus used (0.25 sec trains of sine waves through bipolar electrodes).