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Biomedical subjects

R K Saxena

Publications and source records attributed to R K Saxena.

At least 37 records · Page 2Linked to original sources
PubMed2001

Biocatalytic potential of Fusarium globulosum lipase in selective acetylation/deacetylation reactions and in ester synthesis.

AIMS: The present study was carried out to assess the potential of Fusarium globulosum lipase (FGL) for chemoselective and regioselective biotransformations for the synthesis of industrially important organic compounds. METHODS AND RESULTS: Different acetylation/deacetylation reactions and ester synthesis reactions were carried out in organic media. Fusarium globulosum lipase showed exclusive selectivity for the acetylation of the alcoholic hydroxyl group over the phenolic hydroxyl group of the hydroxymethylated phenols and aryl alkyl ketones. This also led to the enantiomeric resolution of the aryl alkyl ketone. In contrast, the lipase showed reversed selectivity in deacetylation where it preferred the phenolic acetoxy group over the alcoholic acetoxy moiety of the peracetates of hydroxymethylated compounds. The enzyme also exhibited strict regioselection for deacetylation at the para position of the peracetate of an aryl alkyl ketone. In addition, the lipase also synthesized a variety of industrially important fatty acid esters of sugars, sugar alcohols, alcohols and ascorbic acid with high preference for middle-chain fatty acids. CONCLUSION: Fusarium globulosum lipase shows versatile catalytic potential in terms of chemo-, enantio- and regioselectivity and fatty acid specificity in carrying out a variety of industrially important biotransformations. SIGNIFICANCE AND IMPACT OF THE STUDY: The biocatalytic potential of FGL can thus be utilized for the synthesis and modification of different types of polyphenolic compounds and esters. These compounds find widespread uses as surfactants, bioactive analogues, antioxidants and flavour components in the food, detergent, pharmaceutical and cosmetic industries.

Acetylation↗
PubMed2001

Acute renal failure complicating rifampicin therapy.

BACKGROUND: Since 1971, 55 case-reports of rifampicin-induced acute renal failure (ARF) have been published. Covic et al described 60 consecutive cases of rifampicin-induced ARF during a period of eight years (1987-1995) from Iasi Dialysis Centre, Romania. The systenic data on this condition are not available, in view of the anecdotal nature of the observation from our country. OBJECTIVE: The aims of study were to analyze clinical features, course and outcome of ARF complicating rifampicin therapy at our centre. METHODS: We retrospectively studied prevalence, clinical presentations and renal histology and outcome of 11 cases (eight males, three females, aged 42-72 years) who were referred to Nephrology Unit of University Hospital, Varanasi for acute renal failure following retreatment with rifampicin between period of 1994-1999. RESULTS: The gastrointestinal symptoms (abdominal pain, nausea and vomiting) and 'flu like' (fever, weakness and body ache) syndrome were the most frequent presenting features. The clinical signs of intravascular hemolysis were observed in four cases. The commonest laboratory findings included: Anaemia (7), leukocytosis (5), thrombocytopenia (3) and toxic hepatitis in (2) patients. Toxic hepatitis, hemolysis and ARF was seen in one patient in combination. The typical clinical features of allergic interstitial nephritis and acute tubular necrosis were seen in six and two patients respectively. Renal biopsy in three cases revealed; crescentic GN (1) and ATN in (2) patients. Acute renal failure complicating rifampicin accounted for 1.8% (11/607) of all ARF cases hospitalized in our centre during the study period. Renal function returned to normal in nine cases and one patient died on account of hepatic failure (toxic hepatitis). The patients with crescentic GN remained anuric and became dialysis dependent. Thus, clinical course of rifampicin induced ARF was favourable; with only one mortality, compared to a 18% mortality rate among all ARF patients. CONCLUSION: Acute renal failure complicating rifampicin therapy is not an uncommon condition, and typically occurs after reintroduction of rifampicin. The renal prognosis is usually favourable. Intermittent or interrupted therapy appears to be a significant risk factor for the development of acute renal failure.

Acute Kidney Injury↗
PubMed2000

In vitro erythrocidal activity of activated spleen cells from young and old mice.

We have recently reported that activated mouse spleen mononuclear cells (MNCs) efficiently lyse autologous erythrocytes in vitro (Saxena and Chandrasekhar, 2000). In the present study, we have investigated erythrocyte-depleting ability (EDA) of spleen MNCs from young and old mice. Time kinetics of survival of erythrocytes in mitogen-activated spleen cell cultures indicated that the erythrocyte depletion was significantly faster in young spleen cell cultures than in the old. Poorer EDA of old MNCs was in spite of the fact that the susceptibility to lysis actually increased in erythrocytes from old mice. Erythrocytes opsonized by a hamster anti mouse Fas monoclonal antibody, were destroyed with a much greater efficiency by young MNCs, whereas the corresponding effect of opsonization was only moderate for old MNCs. Depletion of macrophages from MNC preparations by plastic adherence as well as carbonyl-iron and magnet treatment had a marginal if any effect on EDA of young and old mouse MNCs, indicating that a lower lymphocyte-associated erythrocidal activity as one of the factors responsible for overall lower EDA associated with spleen derived MNCs of old mice.

Aging↗
PubMed2000

Alumina-supported synthesis of antibacterial quinolines using microwaves.

7-(5'-Alkyl-1',3',4'-thiadiazol/oxadiazol-2'-ylthio)-6 -fluoro-2,4-dimethylquinolines and 3-formyl-2-(2'-hydroxy- 1',4'-naphthoquinon-3'-yl)-4-methyl/6-methyl/7-quinolines have been synthesised by the reaction of 5-alkyl-1,3,4-thiadiazol/oxadiazol-2-thiols with 7-chloro-6-fluoro-2,4-dimethylquinoline and by the reaction of 2-hydroxy-1,4-naphthoquinone with 2-chloro-3-formyl-4-methyl/6-methyl/7-methyl/8-methylquinolines respectively on basic alumina using microwaves, the reaction time has been brought down from hours to seconds with improved yield as compared to conventional heating. The compounds were tested for their in vitro antibacterial activity. All compounds showed promising antibacterial activity. The best activity was observed by compounds 3a and 3f.

4-Quinolones↗
PubMed2000

A novel nonphagocytic mechanism of erythrocyte destruction involving direct cell-mediated cytotoxicity.

The number of erythrocytes fell when co-cultured with cell preparations derived from mouse spleen, thymus, bone marrow, or peritoneal exudate (PE) cells. Erythrocyte-depletion activities (EDA) of different leukocyte preparations were in the order PE > spleen > thymus > bone marrow. Adherent, nonadherent, T-depleted, and T-enriched cell subpopulations had comparable EDA. Spleen cells from athymic nude mice, however, lacked significant EDA. In addition, EDA was boosted by Concanavalin A (Con A) but not by lipopolysaccharide, indicating that T cells may play a crucial role in inducing EDA in spleen cells. Paraformaldehyde-fixed spleen or PE cells, as well as membrane preparations isolated from spleen cells, efficiently lysed erythrocytes. Erythrocyte ghost membranes inhibited erythrocyte lysis by control or paraformaldehyde-fixed spleen cells. Treatment with hamster anti-mouse Fas or anti-mouse tumor necrosis factor receptor (TNFR) antibody could opsonize erythrocytes for faster depletion by spleen cells, suggesting an expression of Fas and TNFR on erythrocytes. TNF alpha could lyse erythrocytes in a dose-dependent fashion. Additionally, enhanced spleen cell EDA induced in response to succenyl Con-A could be blocked by anti-TNF alpha antibodies. Our results provide evidence for a direct cell-mediated cytotoxicity (CMC) of erythrocytes by leukocytes. A role of molecules of Fas and the TNF family in CMC of erythrocytes has also been suggested. Further work is needed to understand if, and to what extent, CMC of erythrocytes contributes to erythrocyte destruction in vivo and to determine its patho-physiological significance.

Animals↗
PubMed2000

Efficacy of culture filtrate protein preparations from Indian isolates of M. tuberculosis to activate T cells derived from healthy donors.

SETTING: While culture filtrate proteins (CFPs) of Mycobacterium tuberculosis appear to be good vaccine candidates for tuberculosis, only CFPs derived from certain popular laboratory strains of M. tuberculosis have been studied for this purpose. OBJECTIVE: To compare the relative efficacies of CFP preparations from two laboratory strains and four contemporary clinical isolates of M. tuberculosis to induce T-cell activation. DESIGN: CFPs were isolated from six strains of M. tuberculosis and were used to induce 1) T-cell proliferation, 2) IFN-gamma secretion, and 3) IL-12 secretion from peripheral blood derived mononuclear cell (PBMC) preparations from 33 healthy donors. RESULTS: Significant amounts of IL-12 were spontaneously secreted by PBMC preparations; CFP preparations from two clinical isolates (JNU-7 and JNU-51) significantly boosted this response. All six CFP preparations induced IFN-gamma secretion by PBMCs, but those from two contemporary strains of M. tuberculosis (JNU-7 and JNU-22) were most effective in this regard. The effect of CFPs from JNU-7 and JNU-22 was significantly better than those from the laboratory strains (H37Ra and Erdman). Similar results were obtained with the T-cell proliferation parameter. CONCLUSION: These results suggest that CFPs derived from selected clinical isolates of M. tuberculosis may outperform those of standard laboratory strains, and may therefore be a better source of potential candidates for a tuberculosis vaccine.

Bacterial Proteins↗
PubMed2000

Effect of serum dilution in diagnosis of malaria in community.

Recently, it has been shown that immunological methods can be used for the diagnosis of malaria other than sero-epidemiology. A study has been done to investigate optimum binding capacity of antigen-antibody (Ag-Ab) at different serum dilutions. For validating antigen-antibody (Ag-Ab) reaction at 1:100, 1:1000 and 1:1000 serum dilutions, have been tested in two different laboratories to establish validation of the ELISA method. Inter laboratory test on synthetic peptide (RI) ELISA was found comparable and meaningful for assessing malaria transmission in defined locality at 1:100 dilution. Results also showed that 1:1000 serum dilution can be useful for diagnostic purpose.

Binding Sites, Antibody↗
PubMed1999

Upregulation of KIR expression on murine bone marrow cells by paraformaldehyde fixed tumor cells.

We have previously shown that the activation of mouse spleen NK cells by IL2 is markedly boosted if paraformaldehyde fixed tumor target cells are added during the activation phase. In the present study, we have shown that such a boosting effect is not seen if mouse bone marrow (BM) cells are used instead of spleen cells. Addition of fixed tumor cells (1:100 ratio of tumor cells to BM cells) however resulted in a marked increase in the expression of Ly49 molecules on BM cells. The enhancement of Ly49 expression was not seen if fixed allogeneic BM cells were added, suggesting that Ly49 upregulation was tumor specific. Expression of Ly49A as well as Ly49C isotypes were augmented by fixed tumor cells. Moreover, increased Ly49 expression was seen on cell populations expressing TCRbeta as well as NK1.1 markers. These results indicate that exposure to tumor cells may be an important factor regulating KIR expression on NK and T cells. Implications of these results are discussed.

Animals↗
PubMed1999

Cytolytic activity of mitogen activated old and young mouse spleen cells against tumor target cells expressing high or low levels of Fas antigen.

Sensitivity of Fas expressing tumor cells (high levels in Hut78 & Jurkat; low levels in P815) toward the cytotoxic Con-A (5 microg/ml) activated spleen cells from young (12 to 16 week old males) and old (2 year old males) mice were studied. The spleen cells from young mice activated for a day showed high levels of cytotoxic activity against Hut78 and Jurkat cell lines but not against P815 cells. The cytotoxic activity against P815 cells were detected in the spleen cells from old but not young mice following a longer period of Con-A activation (three days). Comparable levels of cytotoxic activity against Hut78 and Jurkat cells were observed in the spleen cells from both young and old mice following three days of activation. Treatment of Hut78 cells with anti-Fas antibody affected the tumor cells become resistant against the cytotoxic activity of the spleen cells from young mice in a dose dependent manner however P815 cells were not affect by the anti-Fas antibody treatment. These results show that there are differences in the sensitivity of target tumor cells toward Con-A induced cytotoxic spleen cells from young and old mouse. Mitogen-induced cytotoxic lymphocytes from young mouse spleen appear to kill targets through mechanisms involving Fas antigen, specially, in early stage (1 day) of activation. Old mouse spleen cells generated high levels of cytotoxic cells in later phase (3 days), which appear to kill through Fas-unrelated mechanisms.

Age Factors↗
PubMed1999

Sorption and desorption of cobalt by Oscillatoria anguistissima.

Oscillatoria anguistissima rapidly adsorbs appreciable amounts of cobalt from the aqueous solutions within 15 min of initial contact with the metal solution. O. anguistissima showed a high sequestration of cobalt at low equilibrium concentrations, and it followed the Freundlich model of adsorption. The adsorption is a strongly pH-dependent and temperature-independent phenomenon. The presence of Mg2+ and Ca2+ (100-200 ppm) resulted in decline in Co2+ adsorption capacity of Oscillatoria biomass. Sulphate and nitrate (0. 75-10 mM) drastically reduced the extent of Co2+ biosorption. The biosorption of cobalt is an ion-exchange process as the Co2+ binding was accompanied by release of a large amounts of Mg2+ ions. Na2CO3 (1.0 mM) resulted in about 76% desorption of Co2+ from the loaded biomass.

Adsorption↗
PubMed1998

Induction of proliferation in resting B-cells by a factor released by activated mouse spleen cells.

Mouse spleen cells activated in a mixed lymphocyte reaction release a soluble factor, which induces a significant proliferative response in fresh mouse spleen cells. This proliferation inducing factor (PIF) was found to be heat stable (90 degrees C for 45 min) and also resistant to trypsin or chymotrypsin treatment. By using a sizing HPLC column, the molecular weight of PIF appears to be 25 kDa. Mouse spleen cells treated with anti-thy-1 + complement lost Con-A induced proliferative responses but responded well to PIF. B cell depleted spleen cells obtained by negative selection panning, did not respond to PIF. These results indicate that B cells proliferated in response to PIF. Polymixin-B, which blocks the B cell proliferative response to LPS, did not inhibit PIF induced proliferation.

Animals↗
PubMed1998

Potential use of a novel lipase from Aspergillus carneus in deacetylation reactions.

A novel lipase from Aspergillus carneus has been used in organic solvents for efficient regioselective and chemoselective deacetylation of the peracetates of polyphenolic aromatic ketones, esters and amides. A reversal of regioselectivity was observed as compared with the results obtained during deacetylation with porcine pancreatic lipase (PPL).

Acetates↗
PubMed1998

Partial purification and characterization of a novel murine factor that augments the expression of class I MHC antigens on tumor cells.

A soluble factor which augments the expression of major histocompatibility complex class I (MHC I) antigens on a number of murine tumor cell lines, has been isolated from the culture supernatants of mixed lymphocyte reaction of spleen cells derived from C57B1/6, Balb/c and Swiss mice. The factor, termed MHC-augmenting factor (MHC-AF) has been partially purified by Sephadex G-100 column chromatography and reverse phase HPLC. MHC-AF activity is associated with an 18 kDa molecule. MHC-AF activity was resistant to pH 2.0 treatment and partially purified MHC-AF preparations did not have any activity in L929 cell/vesicular stomatitis virus (VSV) interferon bioassay system. Antibodies to IFN-gamma did not block the activity of MHC-AF. These results indicate that a MHC-AF distinct from IFN-gamma, is produced by mouse spleen cells undergoing a mixed lymphocyte reaction.

Animals↗
PubMed1998

Lipase production by Aspergillus and Penicillium species.

Forty each of aspergilli and penicillia were screened for extracellular lipase production on agar plates and in liquid medium containing olive oil as substrate. Twenty-nine aspergilli and twenty-six penicillia produced lipase. Out of these, 19 aspergilli and 22 penicillia showed activity both on Nile blue sulfate and glycerol tributyrate agar plates while only 10 aspergilli and 4 penicillia showed a positive response to glycerol tributyrate agar alone. The screening revealed 11 Aspergillus spp. and 15 Penicillium spp. as new lipase producers. Pig fat as an economic substrate for lipase production was also investigated.

Animals↗
PubMed1998

Tumor specific boosting of IL-2 induced NK activation by paraformaldehyde fixed tumor cells.

NK activation in C57B1/6 mouse spleen cells was carried out with IL-2 in the presence or absence of paraformaldehyde fixed YAC tumor cells. Generation of anti-YAC cytolytic activity was markedly higher when activation was carried out in the presence of fixed tumor cells. In addition the cytotoxic effector cells generated were resistant to anti-Thy-1 + C treatment, indicating that the effector cells were not T lymphocytes. IL-2 activation of NK cells was compared When fixed YAC or EL4 tumor cells were added during the IL-2 activation phase, it was found that the addition of either of these tumor cells significantly boosted the levels of cytotoxic activity generated against both targets. Significantly higher anti-YAC cytotoxic activity was however generated when fixed YAC cells instead of EL4 cells were present during the activation phase. Similarly, significantly greater cytolytic activity was generated against EL4 cells, when fixed EL4 rather than YAC cells were present during the activation phase. Addition of paraformaldehyde fixed syngeneic or allogenic spleen cells instead of tumor cells, did not boost NK activation in response to IL-2, indicating that the boosting of NK activation did not result from exposure to alloantigens during the activation phase. These results indicate that an exposure to tumor cells during IL-2 activation phase, may boost the activation of NK cells in a tumor specific manner.

Animals↗