PubMed Health⌕ Search

Biomedical subjects

R K Jain

Publications and source records attributed to R K Jain.

At least 73 records · Page 4Linked to original sources
PubMed2000

Aggregation chaperones enhance aggregation and storage of secretory proteins in endocrine cells.

Calcium-induced aggregation has been proposed to play a role in the sorting and storage of secretory proteins in secretory granules of endocrine cells. The regulation of this process is not known. Hexahistidine epitope tags were used to create aggregation chaperones that enhance the calcium-induced aggregation of secretory granule proteins in vitro. Indeed, 100% recovery of the aggregating target protein was achieved without any modification of the target protein. The aggregation chaperone is not trapped in the aggregates. Co-expression of His(6)-tagged secreted alkaline phosphatase and the regulated secretory protein chromogranin A resulted in an increased chromogranin storage in secretory granules, and stimulated secretion of chromogranin A increased 50%. However, secretion of secreted alkaline phosphatase was not affected by the hexahistidine epitope tag. Thus, calcium-induced aggregation is not a passive process; rather, aggregation and sorting of secretory proteins can be regulated by aggregation chaperones in the secretory pathway of endocrine cells.

Animals↗
PubMed2000

Chemotaxis and biodegradation of 3-methyl- 4-nitrophenol by Ralstonia sp. SJ98.

3-Methyl-4-nitrophenol is one of the major breakdown products of fenitrothion [O,O-dimethyl O-(3-methyl-4-nitrophenyl) thiophosphate], a recalcitrant organophosphate insecticide used in agriculture. Being the non-polar methylated aromatic compound, 3-methyl-4-nitrophenol is highly toxic and, therefore, a complete degradation of this compound is important for environmental decontamination/bioremediation purposes. A gram negative, motile Ralstonia sp. SJ98 was isolated by selective screening from a soil sample contaminated with pesticides. The microorganism was capable of utilizing 3-methyl-4-nitrophenol as the sole source of carbon and energy. Thin layer chromatography (TLC), gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), and high performance liquid chromatography (HPLC) were performed to determine the possible intermediates in the degradative pathway of this compound. Taken together, catechol was found to be one of the major intermediate of the pathway. Furthermore, the chemotactic behavior of Ralstonia sp. SJ98 towards 3-methyl-4-nitrophenol was tested using three different methods i.e., drop assay, swarm plate assay and capillary assay, which were found to be positive towards this compound. This is the first report clearly indicating the involvement of a microorganism in the chemotaxis and biodegradation of methyl-4-nitrophenol and formation of catechol as an intermediate in the degradative pathway.

Amiloride↗
PubMed2000

Absence of functional lymphatics within a murine sarcoma: a molecular and functional evaluation.

Despite a clinically recognized association between the lymphatics and metastasis, the biology of tumor-lymphatic interaction is not clearly understood. We report here that functional lymphatic capillaries are absent from the interior of a solid tumor, despite the presence within the tumor of the lymphangiogenic molecule vascular endothelial growth factor (VEGF)-C and endothelial cells bearing its receptor, VEGF receptor 3. Functional lymphatics, enlarged and VEGF receptor 3 positive, were detected in some tumors only at the tumor periphery (within 100 microm of the interface with normal tissue). We conclude that although lymphangiogenic factors are present, formation of functional lymphatic vessels is prevented, possibly due to collapse by the solid stress exerted by growing cancer cells.

Animals↗
PubMed2000

Tumor oxygenation in hormone-dependent tumors during vascular endothelial growth factor receptor-2 blockade, hormone ablation, and chemotherapy.

Tumor oxygenation is critical for tumor survival as well as for response to therapy, e.g., radiation therapy. Hormone ablation therapy in certain hormone-dependent tumors and antiangiogenic therapy lead to vessel regression and have also shown beneficial effects when combined with radiation therapy. These findings are counterintuitive because vessel regression should reduce oxygen tension (pO2) in tumors, decreasing the effectiveness of radiotherapy. Here we report on the dynamics of pO2 and oxygen consumption in a hormone-dependent tumor following hormone ablation and during treatment with an anti-VEGFR-2 monoclonal antibody (mAb) or a combination of doxorubicin and cyclophosphamide; the latter combination is not known to cause vessel regression at doses used clinically. Androgen-dependent male mouse mammary carcinoma (Shionogi) was implanted into transparent dorsal skin-fold chambers in male severe combined immunodeficient mice. Thirteen days after the tumors were implanted, mice were treated with antiangiogenic therapy (anti-VEGFR-2 mAb, 1.4 mg/30 g body weight), hormone ablation by castration, or doxorubicin (6.5 mg/kg every 7 days) and cyclophosphamide (100 mg/kg every 7 days). A non-invasive in vivo method was used to measure pO2 profiles and to calculate oxygen consumption rates (Q(O2)) in tumors. Tumors treated with anti-VEGFR-2 mAb exhibited vessel regression and became hypoxic. Initial vessel regression was followed by a "second wave" of angiogenesis and increases in both pO2 and Q(O2). Hormone ablation led to tumor regression followed by an increase in pO2 coincident with regrowth. Chemotherapy led to tumor growth arrest characterized by constant Q(O2) and elevated pO2. The increased pO2 during anti-VEGFR-2 mAb and hormone ablation therapy may explain the observed beneficial effects of combining antiangiogenic or hormone therapies with radiation treatment. Thus, understanding the microenvironmental dynamics is critical for optimal scheduling of these treatment modalities.

Androgens↗
PubMed2000

Kinetics of biodegradation of p-nitrophenol by different bacteria.

Three bacterial species, i.e., Ralstonia sp. SJ98, Arthrobacter protophormiae RKJ100, and Burkholderia cepacia RKJ200, have been examined for their efficiency and kinetics behavior toward PNP degradation. All the three bacteria utilized PNP as the sole source of carbon, nitrogen, and energy. The rates of radiolabeled [U-(14)C]PNP degradation by all the bacteria were higher in the nitrogen-free medium compared to the medium with nitrogen. The apparent K(m) values of PNP degradation by SJ98, RKJ100, and RKJ200 were 0.32, 0.28, and 0.23 mM, respectively, as determined from the Michaelis-Menten curves. The maximum rates of PNP degradation (V(max)) according to Lineweaver-Burk's plots were 11.76, 7.81, and 3.84 micromol PNP degraded/min/mg dry biomass, respectively. The interpretation drawn from the Lineweaver-Burk's plots showed that the PNP degradation by SJ98 was stimulated by 4-nitrocatechol and 1, 2,4-benzenetriol. Benzoquinone and hydroquinone inhibited PNP degradation by RKJ100 noncompetitively and competitively, respectively, whereas in the case of RKJ200, benzoquinone and hydroquinone inhibited PNP degradation in an uncompetitive manner. beta-Ketoadipate did not affect the rate of PNP degradation in any case.

Arthrobacter↗
PubMed2000

Oncotic pressure in solid tumors is elevated.

Oncotic and hydrostatic pressure differences control the movement of fluid and large molecules across the microvascular wall of normal and tumor tissues. Recent studies have shown that the interstitial fluid pressure in tumors is elevated and is approximately equal to the microvascular pressure. Whereas oncotic pressure in blood plasma of various species is known, no data are available on the oncotic pressure in the interstitial space of tumors. We hypothesize that because of the leaky nature of tumor vessels, oncotic pressure in tumor interstitium should be close to that in plasma. To this end, we first developed a chronic wick method for the direct measurement of oncotic pressures in the interstitial fluid of tumors grown in mice. We found interstitial oncotic pressures in four human tumor xenografts to be higher than in s.c. tissue and comparable to that in plasma [rhabdomyosarcoma (RD), 24.2+/-4.7; squamous cell carcinoma (FaDu), 19.9+/-1.9; small cell lung carcinoma (54A), 21.1+/-2.8; colon adenocarcinoma (LIS174T), 16.7+/-3.0 mm Hg; s.c. tissue, 8.2+/-2.3; plasma, 20.0+/-1.6 mm Hg]. These results support our hypothesis that the oncotic pressure difference across the tumor microvascular wall is low. The high oncotic pressure in tumors is consistent with the elevated interstitial fluid pressure, and it contributes to the suboptimal delivery of large therapeutic agents to neoplastic cells.

Animals↗
PubMed2000

Fractals and cancer.

Recent studies have shown that fractal geometry, a vocabulary of irregular shapes, can be useful for describing the pathological architecture of tumors and, perhaps more surprisingly, for yielding insights into the mechanisms of tumor growth and angiogenesis that complement those obtained by modern molecular methods. This article outlines the basic methods of fractal geometry and discusses the value and limitations of applying this new tool to cancer research.

Algorithms↗
PubMed2000

Protein surface recognition by synthetic receptors based on a tetraphenylporphyrin scaffold.

[structure: see text] Receptors based on a tetraphenylporphyrin scaffold bearing different charged and hydrophobic groups have been synthesized. The interactions of these with horse heart cytochrome c were studied by fluorescence spectroscopy. Receptor 4 was identified to be the strongest synthetic receptor (K(d) = 20 nM) for cytochrome c. The differences in affinity among the receptors reflected a dependence on the number of anionic and hydrophobic groups.

Animals↗
PubMed2000

Role of extracellular matrix assembly in interstitial transport in solid tumors.

The extracellular matrix (ECM) may contribute to the drug resistance of a solid tumor by preventing the penetration of therapeutic agents. We measured differences in interstitial resistance to macromolecule (IgG) motion in four tumor types and found an unexpected correspondence between transport resistance and the mechanical stiffness. The interstitial diffusion coefficient of IgG was measured in situ by fluorescence redistribution after photobleaching. Tissue elastic modulus and hydraulic conductivity were measured by confined compression of excised tissue. In apparent contradiction to an existing paradigm, these functional properties are correlated with total tissue content of collagen, not glycosaminoglycan. An extended collagen network was observed in the more penetration-resistant tumors. Collagenase treatment of the more penetration-resistant tumors significantly increased the IgG interstitial diffusion rate. We conclude that collagen influences the tissue resistance to macromolecule transport, possibly by binding and stabilizing the glycosaminoglycan component of the ECM. These findings suggest a new method to screen tumors for potential resistance to macromolecule-based therapy. Moreover, collagen and collagen-proteoglycan bonds are identified as potential targets of treatment to improve macromolecule delivery.

Biological Transport↗
PubMed2000

Plasmid-encoded degradation of p-nitrophenol and 4-nitrocatechol by Arthrobacter protophormiae.

Arthrobacter protophormiae strain RKJ100 is capable of utilizing p-nitrophenol (PNP) as well as 4-nitrocatechol (NC) as the sole source of carbon, nitrogen and energy. The degradation of PNP and NC by this microorganism takes place through an oxidative route, as stoichiometry of nitrite molecules was observed when the strain was grown on PNP or NC as sole carbon and energy sources. The degradative pathways of PNP and NC were elucidated on the basis of enzyme assays and chemical characterization of the intermediates by TLC, GC, (1)H NMR, GC-MS, UV spectroscopy, and HPLC analyses. Our studies clearly indicate that the degradation of PNP proceeds with the formation of p-benzoquinone (BQ) and hydroquinone (HQ) and is further degraded via the beta-ketoadipate pathway. Degradation of NC involved initial oxidation to generate 1,2,4-benzenetriol (BT) and 2-hydroxy-1,4-benzoquinone; the latter intermediate is then reductively dehydroxylated, forming BQ and HQ, and is further cleaved via beta-ketoadipate to TCA intermediates. It is likely, therefore, that the same set of genes encode the further metabolism of HQ in PNP and NC degradation. A plasmid of approximately 65 kb was found to be responsible for harboring genes for PNP and NC degradation in this strain. This was based on the fact that PNP(-) NC(-) derivatives were devoid of the plasmid and had simultaneously lost their capability to grow at the expense of these nitroaromatic compounds.

Arthrobacter↗
PubMed2000

Irradiation of a primary tumor, unlike surgical removal, enhances angiogenesis suppression at a distal site: potential role of host-tumor interaction.

Changes in distal angiogenesis in response to irradiation of primary tumors are not known. To this end, PC-3, a human prostate carcinoma, and FSA-II, a murine fibrosarcoma, were grown in the gastrocnemius muscles of male nude mice. Distal angiogenesis was measured in gel containing human recombinant basic fibroblast growth factor placed in the cranial windows of these mice. PC-3-bearing mice showed inhibition of distal angiogenesis, as compared with non-tumor-bearing controls. Surgical removal of tumors tended to accelerate distal angiogenesis; in comparison, after irradiation of the PC-3 primary tumor, rates of angiogenesis in the cranial window were retarded. Irradiation of the non-tumor-bearing leg or of non-tumor-bearing animals showed no measurable effect on rate of growth of vessels in the cranial window. Similar results were found with the FSA-II tumors, with slowed distal angiogenesis in tumor-bearing animals and further suppression in animals with irradiated tumors. These results demonstrate that the effect of irradiation of a primary tumor on angiogenesis at a distal site may differ from the effect of surgical removal of the primary tumor. Unlike surgery, irradiation of a tumor may enhance angiogenic suppression at a distal site, and this difference may involve host-tumor interaction.

Analysis of Variance↗
PubMed2000

Chemotaxis of a Ralstonia sp. SJ98 toward different nitroaromatic compounds and their degradation.

A Ralstonia sp. SJ98, isolated by a chemotactic enrichment technique, was capable of utilizing different nitroaromatic compounds (NACs). It utilized p-nitrophenol, 4-nitrocatechol, o-nitrobenzoic acid, and p-nitrobenzoic acid as the sole source of carbon and energy. It was observed that Ralstonia sp. SJ98 was chemotactic to the above-mentioned NACs as tested by the drop assay, swarm plate assay, and capillary assay. However, it failed to show chemotactic behavior toward those compounds which were not degraded by the microorganism. This is the first report which shows the chemotaxis of a microorganism toward different NACs and their subsequent degradation. Some of the intermediates of the NACs' degradative pathways have been identified using TLC, GC, and GC-MS studies. The results presented here indicate a correlation between chemotaxis and biodegradation of NACs.

Betaproteobacteria↗
PubMed2000

Local imbalance of proangiogenic and antiangiogenic factors: a potential mechanism of focal necrosis and dormancy in tumors.

Solid tumors produce both stimulators and inhibitors of angiogenesis. The suppression of metastases by some primary tumors has been attributed to the longer circulatory half-lives of the inhibitors. We propose that intrinsic differences in the physicochemical properties of these regulators may also explain focal suppression of angiogenesis within the primary tumor. We present a mathematical framework that describes production, diffusion, and degradation of these factors in tumor and host tissue and their effect on angiogenesis at local and distal sites. Results show focal suppression of angiogenesis, provide an explanation for tumor dormancy and focal necrosis, and predict a suppressive influence of primary tumors on angiogenesis at metastatic sites. They suggest generally that diffusible factors produced by tumors can stimulate responses in adjacent host tissue, preparing it for further tumor invasion. This study presents a new paradigm for the development of tumor necrosis and offers new insight into angiogenesis regulation and therapy. The framework established for modeling the competing effects of diffusible stimulators and inhibitors can be applied more generally to growth factors/inhibitors and other opposing factors produced in the tumor environment.

Angiogenesis Inducing Agents↗
PubMed2000

Degradation of o-nitrobenzoate via anthranilic acid (o-aminobenzoate) by Arthrobacter protophormiae: a plasmid-encoded new pathway.

An Arthrobacter protophormiae strain RKJ100, isolated by selective enrichment, was capable of utilizing o-nitrobenzoate (ONB(+)) as the sole carbon, nitrogen, and energy source. The degradation of ONB proceeds through an oxygen insensitive reductive route as shown by the release of ammonia in the culture medium aerobically rather than nitrite ions. Thin-layer chromatography, gas chromatography, and gas chromatography-mass spectrometry of the intermediates have shown that ONB is degraded by a two-electron reduction of the nitro moiety, yielding o-hydroxylaminobenzoate and anthranilic acid. Quantitation of the intermediates, inhibition studies, and simultaneous induction studies have shown that anthranilic acid is produced as the terminal aromatic intermediate of a catabolic energy-yielding pathway and not as a side reaction taking place concurrently which is the first such report. A plasmid of approximately 65 kb was found to be responsible for harboring genes for ONB degradation in this strain. The same plasmid also encoded resistance to cobalt ions.

Aerobiosis↗
PubMed2000

Choline import into chloroplasts limits glycine betaine synthesis in tobacco: analysis of plants engineered with a chloroplastic or a cytosolic pathway.

The biosynthesis of the osmoprotectant glycine betaine (GlyBet) is a target for metabolic engineering to enhance stress resistance in crops. Certain plants synthesize GlyBet in chloroplasts via a two-step oxidation of choline (Cho). In previous work, a chloroplastic GlyBet synthesis pathway was inserted into tobacco (which lacks GlyBet) by expressing spinach choline monooxygenase (CMO). The transformants had low CMO enzyme activity, and produced little GlyBet (less than or = 70 nmol g(-1) fresh wt). In this study, transformants with up to 100-fold higher CMO activity showed no further increase in GlyBet. In contrast, tobacco expressing a cytosolic GlyBet synthesis pathway accumulated significantly more GlyBet (430 nmol g(-1) fresh wt), suggesting that subcellular localization influences pathway flux. Modeling of the labeling kinetics of Cho metabolites observed when [14C]Cho was supplied to engineered plants demonstrated that Cho import into chloroplasts indeed limits the flux to GlyBet in the chloroplastic pathway. A high-activity Cho transporter in the chloroplast envelope may therefore be an integral part of the GlyBet synthesis pathway in species that accumulate GlyBet naturally, and hence a target for future engineering.

Alcohol Oxidoreductases↗
PubMed2000

Effect of vascular endothelial growth factor on cultured endothelial cell monolayer transport properties.

Vascular endothelial growth factor (VEGF) is a potent enhancer of microvascular permeability in vivo. To date, its effects on hydraulic conductivity (L(p)) and diffusive albumin permeability (P(e)) of endothelial monolayers have not been thoroughly assessed in vitro. We hypothesized that VEGF affects endothelial transport properties differently depending on vessel location and endothelial phenotype. Using three well-established endothelial cell culture models-human umbilical vein endothelial cells (HUVECs), bovine aortic endothelial cells (BAECs), and bovine retinal microvascular cells (BRECs)-grown on porous, polycarbonate filters we were able to produce baseline transport properties characteristic of restrictive barriers. Our results show 3.1-fold and 5.7-fold increases in endothelial L(p) for BAEC and BREC monolayers, respectively, at the end of 3 h of VEGF (100 ng/ml) exposure. HUVECs, however, showed no significant alteration in L(p) after 3 h (100 ng/ml) or 24 h (25 ng/ml) of incubation with VEGF even though they were responsive to the inflammatory mediators, thrombin (1 U/ml; 27-fold increase in L(p) in 25 min) and bradykinin (10 microM; 4-fold increase in L(p) in 20 min). Protein kinase C (PKC) and nitric oxide (NO) are downstream effectors of VEGF signaling. BAEC L(p) was responsive to activation of NO (SNAP) and PKC (PMA), whereas these agents had no effect in altering HUVEC L(p). Moreover, BAECs exposed to the PKC inhibitor, staurosporine (50 ng/ml), exhibited significant attenuation of VEGF-induced increase in L(p), but inhibition of nitric oxide synthase (NOS) with L-NMMA (100 microM) had no effect in altering the VEGF-induced increase in L(p). These data provide strong evidence that in BAECs, the VEGF-induced increase in L(p) is mediated by a PKC-dependent mechanism. Regarding diffusive albumin P(e), at the end of 3 h, BAECs and BRECs showed 6.0-fold and 9. 9-fold increases in P(e) in response to VEGF (100 ng/ml), whereas VEGF had no significant effect after 3 h (100 ng/ml) or 24 h (25 ng/ml) in changing HUVEC P(e). In summary, these data indicate that VEGF affects endothelial transport properties differently depending on the vessel type and that differences in cell signaling pathways underlie the differences in VEGF responsiveness.

Animals↗