PubMed Health⌕ Search

Biomedical subjects

K V Rao

Publications and source records attributed to K V Rao.

At least 19 recordsLinked to original sources
PubMed1992

The cytotoxic properties of malachite green are associated with the increased demethylase, aryl hydrocarbon hydroxylase and lipid peroxidation in primary cultures of Syrian hamster embryo cells.

Malachite green (MG), an industrial compound and potential environmental health hazard, is highly cytotoxic to mammalian cells in culture. In an attempt to define the biochemical basis, we have compared the cytotoxic effects and morphological alterations shown by MG in Syrian hamster embryo (SHE) cells with the levels of lipid peroxidation and the activities of aryl hydrocarbon hydroxylase, aminopyrine-N-demethylase, superoxide dismutase and catalase. Treatment of SHE cells with MG results into an induction of the mono-oxygenase system, lipid peroxidation and catalase in a dose-dependent way, indicating the formation of reactive free radicals. Accordingly, the possible involvement of reactive free radicals especially hydroxymethyl radicals in the observed high cytotoxicity due to exposure to MG is postulated.

Animals↗
PubMed1992

Identification of a new group-specific determinant on hepatitis B surface antigen with a synthetic peptide.

In a recent study we demonstrated that a synthetic peptide representing residues 124-147 of the major protein of hepatitis B surface Ag (HBsAg) undergoes spontaneous oligomerization to reconstruct one or more conformational group-specific determinants on HBsAg. The present study was undertaken to identify and characterize the HBsAg-related antigenic determinants on this oligomeric peptide (peptide OS[124-147]). A panel of nine analogs of this peptide was generated by either deleting, substituting, or chemical side chain modification of specific amino acid residues. With HBsAg subtype-specific antisera a single "a" epitope was identified as one that includes Met133 and Lys141. In addition a "d" epitope toward the amino-terminal end of the sequence was also observed. Perturbation of certain amino acid residues was found to enhance a antigenicity and subsequent experiments indicated that maximal expression of this a antigenicity is dependent in part on accessibility of the Lys141 side chain and in part on the primary sequence. With a total of 50 human anti-HBsAg serum samples obtained from individuals vaccinated against hepatitis B, it was demonstrated that these sera recognize the Met133-Lys141-dependent a epitope as the dominant, and in many cases the only, determinant on peptide OS[124-147]. Finally, on immunization, peptide OS[124-147] elicits an anti-HBsAg response that is predominantly anti-a though a lesser contribution from an anti-d response was also obtained.

Amino Acid Sequence↗
PubMed1992

A synthetic peptide spontaneously self-assembles to reconstruct a group-specific, conformational determinant of hepatitis B surface antigen.

A cysteine-rich peptide of sequence 124 to 147 of the major protein of hepatitis B surface Ag (HBsAg) was synthesized. On cleavage and subsequent work-up it was found that all of the cysteine sulfhydryl groups had spontaneously formed disulfide bonds to yield a heterogenous mixture of multiple forms with molecular masses ranging from 8 to 35 kDa (peptide OS[124-147]). In a direct ELISA peptide OS[124-147] showed a high degree of cross-reactivity with polyclonal anti-HBsAg antiserum whereas the HBsAg-related antigenicity of its disulfide-reduced analogs was insignificant. Peptide OS[124-147] was also recognized by all 15 of the anti-HBsAg-positive human sera tested. Further studies revealed that peptide OS[124-147] represents the conformational, disulfide-dependent "a" determinant of HBsAg and elicits antibodies that cross-react with a variety of HBsAg subtypes. Anti-peptide antibodies bound to the corresponding native epitope with an apparent affinity higher than that of homologous antisera. Finally, polyclonal anti-OS[124-147] antibodies could also immunoprecipitate purified Dane particles in solution. Together these studies indicate that peptide OS[124-147] represents an excellent candidate component of a peptide-based vaccine for hepatitis B.

Amino Acid Sequence↗
PubMed1992

Design and synthesis of a self-assembling peptide derived from the envelope proteins of HIV type 1. An approach to heterovalent immunogens.

A chimeric peptide that included sequences from gp120 and gp41 of HIV type 1 was synthesized. Cleavage from solid support yielded a composite of self-oligomerized products with molecular masses ranging from 5 to about 9 kDa. The oligomer but not its reduced, monomeric form was recognized by human anti-HIV sera and at least one of the two lysines in the sequence was involved in antibody binding. The oligomeric peptide was immunogenic, yielding a conformation-specific antibody response. Co-oligomerization of a hepatitis B surface Ag-derived peptide and the HIV type 1-derived peptide yielded a bivalent product in which conformational integrity of the individual components was maintained. Immunization with this hybrid peptide resulted in conformation-specific antibodies to both epitopes in all four murine strains tested. Lymphocyte proliferation assays revealed that the T epitopes resident in both peptide sequences remained active in the hybrid peptide. These results demonstrate the potential of this approach in generating multi- and heterovalent immunogens which may eventually find application as vaccines.

Amino Acid Sequence↗
PubMed1992

Hepatitis B virus envelope epitopes: gene assembly and expression in Escherichia coli of an immunologically reactive novel multiple-epitope polypeptide 1 (MEP-1).

A novel synthetic 323-bp gene with the open reading frame of a multiple-epitope polypeptide has been assembled and cloned. The gene is engineered by contiguous alignment of selected epitopes and functional domains of the hepatitis B virus envelope proteins separated by pairs of glycine residues. High-level bacterial production of this 100-amino acid (approx. 10 kDa) protein has been achieved and the gene product is stable. ELISA and Western blot experiments using epitope-specific antisera confirm that the corresponding epitopes are present in the engineered protein.

Amino Acid Sequence↗
PubMed1992

Receptor for pre-S1(21-47) component of hepatitis B virus on the liver cell: role in virus cell interaction.

Attachment of hepatitis B virus to a hepatoblastoma cell line (HepG2) was examined using a synthetic peptide corresponding to the pre-S1 (21-47) region of the envelope protein. Scatchard analysis revealed a single class binding site of Kd 104 +/- 27 nM/l and 5.4 +/- 1.2 x 10(5) sites per cell. Competition of HBV with pre-S1 peptides was dose dependent, and demonstrated it as the dominant binding site. In view of the suggested sequence homology between the peptide and IgA, cross-competition studies were carried out. The results indicate no direct role of IgA receptor in HBV binding. The receptor for the pre-S1 peptide was identified as a single major peptide of molecular weight 31 kD using in-situ ligand receptor crosslinking.

Amino Acid Sequence↗
PubMed1992

Comparison of immune responses to a native viral antigen and a synthetic peptide derived from it: implications for vaccine development.

Murine immune responses to the hepatitis B surface antigen (HBsAg) and a synthetic peptide derived from it were compared at the humoral level. Six of nine strains used responded to either peptide or HBsAg, though restriction profiles were not superimposable. Two of three strains non-responsive to HBsAg produced an antibody response on immunization with peptide which was cross-reactive with both peptide and HBsAg. In in vitro lymphocyte stimulation assays, lymphocyte from all six peptide-immunized mouse strains could be induced to proliferate on challenge with HBsAg. However, of the HBsAg-immunized groups, lymphocytes from only three of six responder strains proliferated on in vitro HBsAg challenge. Cumulatively, these results suggest that a vaccine formulation that includes both protein antigens and synthetic peptides derived from these proteins may be more effective at eliciting an immune response in a broader cross-section of target population.

Animals↗
PubMed1992

Macromolecular self-association of a synthetic peptide derived from the hepatitis B surface antigen: construction of a quaternary epitope.

A major impediment to the development of peptide vaccines has been the inability accurately to mimic conformationally constrained epitopes on the envelope proteins of pathogens. This limitation is further compounded by the fact that several viral envelope proteins exist either as covalently or non-covalently associated homo-oligomers in the native state. Evidence is now accumulating to indicate that, at least in some instances, these homo-oligomers display antigenic determinants that are not present in the dissociated monomer units. Clearly this problem will have to be addressed if peptide-based vaccines are ever to become feasible alternatives. In this report we demonstrate that an oligomerized synthetic peptide that was derived from the hepatitis B surface antigen aggregates in solution to form macromolecular structures. These aggregates appear to represent a 'native' form of the group-specific determinant presented by the hepatitis B surface antigen.

Amino Acid Sequence↗
PubMed1992

Diagnosis of renal transplant rejection in the cyclosporine era.

The introduction in 1983 of cyclosporine as a prophylactic immunosuppressive agent has contributed to improved renal allograft survival at many transplant centers. However, in view of its profound nephrotoxic potential, the use of this drug in renal transplant patients has caused diagnostic confusion. An accurate assessment of whether the allograft dysfunction is from drug overdose or from acute rejection is important before one can manage the problem appropriately. The two practical measures that would help in distinguishing acute rejection from cyclosporine-induced toxicity are 1) a trial of cyclosporine dose-reduction and subsequent assessment of renal function, and 2) histologic assessment of the renal allograft biopsy specimen. In recent years, several new diagnostic techniques to assess the immunologic activity within the graft environment have been developed that could further enhance our discriminating ability. However, these sophisticated techniques are not readily available to most clinicians who are currently managing patients with graft dysfunction. This article focuses on the different methods of distinguishing rejection from cyclosporine-induced toxicity. The data were abstracted from relevant papers published in the scientific literature during the past 12 months.

Cyclosporine↗
PubMed1992

Animal models for chemoprevention of respiratory cancer.

Of the several models for lung carcinogenesis, two appear appropriate for chemoprevention studies based upon dose response, tumor type, and tumor localization. One model utilizes the direct-acting carcinogen methylnitrosourea (MNU), and the other utilizes a carcinogen (diethylnitrosamine) requiring metabolic activation. Tumors appear rapidly in both models (within 6 months), and the model systems are responsive to modulation by several classes of potential chemopreventive agents. For example, the retinoid N-(4-hydroxyphenyl) retinamide reduces the incidence of lung adenosquamous carcinoma, but retinol or beta-carotene are ineffective when administered alone. However, concomitant administration of these compounds reduces the incidence of non-neoplastic dysplasias as well as adenosquamous carcinomas of the lung. In the MNU system, retinoids in general have been ineffective in reducing the incidence of tracheobronchial squamous-cell carcinomas.

Animals↗
PubMed1992

Immune response to hepatitis B virus surface antigen peptides during HBV infection.

Antibody responses of patients with acute (n = 73), fulminant (n = 30) and chronic (n = 51) hepatitis B virus (HBV) infection as well as recovered individuals (n = 7) were studied against three synthetic peptides, Pre-S1 amino acids (aa. 12-32), Pre-S2 amino acids (aa. 120-145), and S amino acids (aa. 124-147) of the envelope region (HBsAg). T cell blastogenic response was investigated in a proportion of the patients (27 acute, nine fulminant, 13 chronic hepatitis and seven recovered individuals) along with seven HBV vaccinated and three normal individuals. The presence of T cell response against S peptide was observed in all the cases (9/9, 100%) during early acute hepatitis. This was suppressed during late stages (8/18, 44%) followed by partial reversal during recovery (5/7, 71%). T cell response and antibodies to Pre-S1 and Pre-S2 peptides were present only in one-third of the patients throughout these periods. The T cell blastogenic response as well as antibody reactivity against these peptides were absent and minimal in chronic hepatitis. Immune response against envelope protein appears to play a major role in acute hepatic injury due to HBV infection and help in virus clearance.

Acute Disease↗
PubMed1992

BCG vaccination in malnourished child population.

The efficacy of BCG vaccination is still a subject of controversy. In the present study the protective role of BCG vaccination, the influence of nutritional status and justification for revaccination in children were investigated. Of the 504 preschool children suffering from tuberculosis who were registered for the study, 345 children did not receive BCG vaccine while the others had it during early infancy. Vaccinated children showed a significantly greater tendency to localise the tubercular lesions while most of the unvaccinated children suffered from progressive forms of the infection. Vaccination had similar effects even when there was associated malnutrition. Age did not seem to influence the severity of the disease in unvaccinated children while older children (greater than 3 yrs) had a greater tendency to localise the lesion in the vaccinated group. These data do not support the proposal of administering a booster dose of BCG to children who were vaccinated during early infancy.

Antibodies, Bacterial↗
PubMed1991

Kelthane residues in tissues of the tropical penaeid prawn, Metapenaeus monoceros (Fabricius), under sublethal chronic exposure--a monitoring study.

Monitoring the biodegradation and bioaccumulation of kelthane residues were undertaken during reclamation through oxygen consumption (respiration) and target enzyme activity assays. Even after 30 days of reclamation, non-recovery in respiration and target enzyme assays revealed the accumulation of kelthane as a residue in tissues. Thin-layer chromatography demonstrated the presence of kelthane residues as spots in tissue extracts of midgut gland and muscle after a 30-day recovery period. This confirms that kelthane is a persistent insecticide of low biodegradability and capable of accumulating in tissues as residues even at sublethal concentration under chronic exposure.

Animals↗
PubMed1991

Comparative evaluation of the immunogenicity of yeast-derived (recombinant) and plasma-derived hepatitis B vaccine in infants.

The immunogenicity of plasma-derived (HB Vax,MSD) and recombinant hepatitis B virus (Engerix B, SK&F) vaccines was evaluated in infants born to hepatitis B virus carrier mothers. The vaccination was carried out at 1 day, 1 month, and 6 months of age using 10 micrograms of the vaccine given intramuscularly. A total of 83/88 (94.3%) and 74/79 (93.6%) of the infants receiving the plasma-derived vaccine and yeast-derived vaccine showed antibody to hepatitis B surface antigen (anti-HBs). None of the maternal factors studied apart from the HBeAg positivity corellated with vaccine failure. The yeast-derived vaccine gives marginally lower antibody titre than the plasma-derived vaccine. The group-specific anti-"a" antibody was less than 10% of the total anti-HBsAg titre. It was observed that the vaccine alone without prior administration of hepatitis B immunoglobulin is effective in perinatal infection.

Biomarkers↗