Browsing by Author "B.N. Tripathi"

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Differential sensitivity of Anabaena doliolum to Cu and Zn in batch and semicontinuous cultures
(Academic Press, 2003) B.N. Tripathi; S.K. Mehta; J.P. Gaur
Elevated concentrations of Cu and Zn inhibited Anabaena doliolum more severely in semicontinuous culture than in batch culture with growth and protein, chlorophyll a, and carotenoid contents generally more than two-fold more sensitive in the former culture system. The greater sensitivity of A. doliolum to test metals in semicontinuous culture was associated with their greater accumulation. The level of inhibition of various parameters of the test organism remained almost constant in semicontinuous culture, but considerable alleviation of the inhibitory effect occurred in batch culture with time concomitant with a regular decline in metal content of cells. However, metal content of cells in semicontinuous culture remained more or less constant with time, thereby causing no change in the level of inhibition. Unlike semicontinuous culture, batch culture showed considerable depletion of phosphate from the medium and a rise in pH (from 7 to 7.8). In conclusion, batch culture is not appropriate for long-term assessment of metal toxicity as it might substantially underestimate toxic effects of heavy metals. © 2003 Elsevier Science (USA). All rights reserved.
Drug-induced reactive oxygen species–mediated inhibitory effect on growth of Trypanosoma evansi in axenic culture system
(Springer Science and Business Media Deutschland GmbH, 2020) Rajender Kumar; Ruma Rani; Saroj Kumar; Khushboo Sethi; Shikha Jain; Kanisht Batra; Sanjay Kumar; B.N. Tripathi
Trypanosoma evansi, an extracellular haemoflagellate, has a wide range of hosts receptive and susceptible to infection, in which it revealed highly inconsistent clinical effects. Drugs used for the treatment of trypanosomosis have been utilized for more than five decades and have several problems like local and systemic toxicity. In the present investigation, imatinib and sorafenib were selected as drugs as they are reported to have the potential to cause reactive oxygen species (ROS)–mediated effect in cancer cells. Both have also been reported to have potential against T. brucei, T. cruzi and Leishmania donovani. To date, imatinib and sorafenib have not evaluated for their growth inhibitory effect against T. evansi. Imatinib and sorafenib showed significant (p < 0.001) inhibition on parasite growth and multiplication with IC50 (50% inhibitory concentration) values 6.12 μM and 0.33 μM respectively against T. evansi. Both the drug molecules demonstrated for the generation of ROS in T. evansi and were found up to 65% increased level of ROS as compared with negative control in the axenic culture system. Furthermore, different concentrations of imatinib and sorafenib were found non-toxic on horse peripheral blood mononuclear cells and Vero cell lines. Also, in conclusion, our results demonstrated that imatinib- and sorafenib-induced generation of ROS contributed inhibitory effect on the growth of Trypanosoma evansi in an axenic culture system. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
Enhanced sorption of Cu2+ and Ni2+ by acid-pretreated Chlorella vulgaris from single and binary metal solutions
(2002) S.K. Mehta; B.N. Tripathi; J.P. Gaur
The influence of HCl pretreatment (0.1 mM) on sorption of Cu2+ and Ni2+ by Chlorella vulgaris was tested using single and binary metal solutions. The optimal initial pH for sorption was 3.5 for Cu2+ and 5.5 for Ni2+. Second order rate kinetics described well sorption by untreated and acid-pretreated cells. The kinetic constant qe (metal sorption at equilibrium) for sorption of test metals from single and binary metal solutions was increased after pretreatment of the biomass with HCl. The Langmuir adsorption isotherm was developed for describing the various results for metal sorption. In single metal solution, acid pretreatment enhanced qmax for Cu2+ and Ni2+ sorption by approximately 70% and 65%, respectively. Cu2+ and Ni2+ mutually interfered with sorption of the other metal in the binary system. The combined presence of Cu2+ and Ni2+ led to their decreased sorption by untreated biomass by 19% and 88%, respectively. However, acid-pretreated biomass decreased Cu2+ and Ni2+ sorption by 15 and 22%, respectively, when both the metals were present in the solution. The results suggest a reduced mutual interference in sorption of Cu2+ and Ni2+ from the binary metal system due to the acid pretreatment. Acid-pretreated cells sorbed twice the amount of Cu2+ and ten times that of Ni2+ than the untreated biomass from the binary metal system. Acid pretreatment more effectively enhanced the sorption of Ni2+ form the binary metal solution. The total metal sorption by untreated and acid-pretreated biomass depended on the Cu2+: Ni2+ ratio in the binary metal system. Acid pretreatment of C. vulgaris could be an effective and inexpensive strategy for enhancing Cu2+ and Ni2+ sorption from single and binary metal solutions.
Influence of pH, temperature, culture age and cations on adsorption and uptake of Ni by Chlorella vulgaris
(Elsevier GmbH, 2000) S.K. Mehta; B.N. Tripathi; J.P. Gaur
Nickel accumulation by C. vulgaris was studied distinguishing adsorption and intracellular accumulation. The surface adsorption contributed maximally (<80%) to total Ni accumulation by the test alga. It was maximal and of equal magnitude at pH 3.5 and 5.5 accordingly suggesting the participation of strong and weak acidic functional groups of C. vulgaris with relatively low and high affinity for Ni adsorption. Nickel uptake was greatly reduced at acidic pH. The cultures in the decline phase of growth showed highest adsorption of Ni but the rate of Ni uptake was greatly reduced when cultures were in the decline or stationary phase of growth. A better exposure of Ni binding sites, or generation of new sites was perhaps responsible for greater Ni adsorption by old cultures of C. vulgaris. Sodium and K caused mixed inhibition whereas Ca and Mg caused noncompetitive inhibition of adsorption and uptake of Ni. Chromium was not able to competitively inhibit adsorption and uptake of Ni by the test alga. The competitive inhibition of Ni adsorption by Cu and Zn seems to be related to their similar ionic properties. Cu stimulated Ni uptake due possibly to increased permeability of the plasma membrane. The present study disagrees with the general conception that cations are competitive inhibitors of metal adsorption and uptake by algae.
Metal/metal oxide nanoparticles: Toxicity concerns associated with their physical state and remediation for biomedical applications
(Elsevier Inc., 2021) Anju Manuja; Balvinder Kumar; Rajesh Kumar; Dharvi Chhabra; Mayukh Ghosh; Mayank Manuja; Basanti Brar; Yash Pal; B.N. Tripathi; Minakshi Prasad
Metal/metal oxide nanoparticles show promise for various applications, including diagnosis, treatment, theranostics, sensors, cosmetics, etc. Their altered chemical, optical, magnetic, and structural properties have differential toxicity profiles. Depending upon their physical state, these NPs can also change their properties due to alteration in pH, interaction with proteins, lipids, blood cells, and genetic material. Metallic nanomaterials (comprised of a single metal element) tend to be relatively stable and do not readily undergo dissolution. Contrarily, metal oxide and metal alloy-based nanomaterials tend to exhibit a lower degree of stability and are more susceptible to dissolution and ion release when introduced to a biological milieu, leading to reactive oxygen species production and oxidative stress to cells. Since NPs have considerable mobility in various biological tissues, the investigation related to their adverse effects is a critical issue and required to be appropriately addressed before their biomedical applications. Short and long-term toxicity assessment of metal/metal oxide nanoparticles or their nano-formulations is of paramount importance to ensure the global biome's safety; otherwise, to face a fiasco. This article provides a comprehensive introspection regarding the effects of metal/metal oxides’ physical state, their surface properties, the possible mechanism of actions along with the potential future strategy for remediation of their toxic effects. © 2021 The Author(s)
Oxidative stress in Scenedesmus sp. during short- and long-term exposure to Cu2+ and Zn2+
(2006) B.N. Tripathi; S.K. Mehta; Anshu Amar; J.P. Gaur
Algae are exposed to elevated levels of heavy metals in water bodies generally for a long-term, and occasionally for a short-term duration. The present study deals with oxidative stress in Scenedesmus sp., commonly found in nutrient-rich freshwaters, during short- (6 h) and long-term (7 d) exposure to Cu2+ and Zn2+. The cells accumulated almost 2- and 4-times more Cu2+ and Zn2+ inside the cells during long-term than during short-term exposure to these metals. But the data on photosynthetic O2 evolution and cell viability suggest that Scenedesmus sp. experienced lesser metal stress in long-term than in short-term experiment. Although malondialdehyde content was slightly higher in the long-term experiment, the amount produced by one unit intracellular metal was significantly lower than that in the short-term experiment. Superoxide dismutase activity of Scenedesmus sp. was >30% higher during long-term than during short-term exposure to Cu2+ and Zn2+. But, catalase and ascorbate peroxidase activities increased only at 2.5 μM Cu2+ and 25 μM Zn2+ when oxidative stress was mild, but were inhibited at 10 μM Cu2+ under intense oxidative stress. Cu2+ and Zn2+ reduced glutathione reductase activity and total SH content of Scenedesmus sp. in both the experiments, with greater reduction occurring in the long-term experiment. The depletion of total thiol was positively related with the intracellular level of metals. Thiols might have helped Scenedesmus sp. in overcoming metal-induced oxidative stress, but depletion of thiol pool is known to make cells vulnerable to oxidative stress. The study suggests that antioxidant enzymes play a role only under mild oxidative stress. An increased accumulation of proline seems to be an important strategy for alleviating metal-induced oxidative stress in Scenedesmus sp. The study shows that Scenedesmus sp. could acclimatize during long-term exposure to toxic concentrations of the test metals. © 2005 Elsevier Ltd. All rights reserved.
Physiological behavior of Scenedesmus sp. during exposure to elevated levels of Cu and Zn and after withdrawal of metal stress
(2006) B.N. Tripathi; J.P. Gaur
A 48 h exposure of Scenedesmus sp. to sublethal concentrations of Cu (2.5 and 10 μM) and Zn (5 and 25 μM) caused a concentration-dependent inhibition of growth, photosynthesis, respiration, NO3 - uptake, and nitrate reductase (EC 1.6.6.1) activity, and a reduction in protein, carbohydrate, and photosynthetic-pigment levels with a concomitant increase in intracellular levels of the test metals. After exposure, algal cells were transferred to the basal medium without the excess level of test metals, to study the recovery of various processes. The growth of the test algae had not recovered up to 12 h after transfer to the basal medium, but some physiological parameters such as photosynthesis and respiration recovered within 6 h. The quicker recovery of photosynthesis and respiration might be used as acclimatory responses as they prepare a background for the recovery of other parameters, including growth, of the test alga by generating energy, forming photosynthate, and establishing the usual catabolism to attain normal conditions. Most of the processes recovered completely or almost completely after being stressed with 2.5 μM Cu or 5 μM Zn. However, the maintenance of a relatively high level of Cu and Zn in the cells previously exposed to 10 μM Cu and 25 μM Zn slowed down the recovery of different processes, which did not fully recover even at the end of the experiment after 96 h. The present study demonstrates that a chain of metabolic events, beginning with respiration and photosynthesis and continuing with assimilation and uptake of nutrients and subsequent restoration of other metabolic processes, is involved in the recovery of the algae from Cu and Zn stress. Each studied parameter seems to play an important role in balancing the cellular homeostasis during recovery from metal stress. © 2006 Springer-Verlag.
Relationship between copper- and zinc-induced oxidative stress and proline accumulation in Scenedesmus sp.
(Springer Verlag, 2004) B.N. Tripathi; J.P. Gaur
A 4-h exposure of Scenedesmus sp. to Cu or Zn enhanced intracellular levels of both test metals and proline. The level of intracellular proline increased markedly up to 10 μM Cu, but higher concentrations were inhibitory. However, intracellular proline consistently increased with increasing concentration of Zn in the medium. Cu and Zn induced oxidative stress in the test alga by increasing lipid peroxidation and membrane permeability, and by reducing SH content. Pretreatment of the test alga with 1 mM proline for 30 min completely alleviated Cu-induced lipid peroxidation, minimized K+ efflux and also reduced depletion of the SH pool. But proline pretreatment could only slightly reduce Zn-induced oxidative stress. Interestingly, proline pretreatment increased the level of Cu (25-54%) and Zn (19-49%) inside the cells. It did not affect the activities of superoxide dismutase, ascorbate peroxidase or catalase, but improved glutathione reductase activity under Cu and Zn stress. A comparison of the effects of proline pretreatment on lipid peroxidation by Cu, Zn, methyl viologen and ultraviolet-B radiation suggests that proline protects cells from metal-induced oxidative stress by scavenging reactive oxygen species rather than by chelating metal ions. Pretreatment of cells with a known antioxidant (ascorbate) and a hydroxyl radical scavenger (sodium benzoate) considerably reduced metal-induced lipid peroxidation and proline accumulation. However, sodium benzoate had a very mild effect on Zn-induced lipid peroxidation and proline accumulation. The present study demonstrates that proline possibly acts by detoxifying reactive oxygen species, mainly hydroxyl radicals, rather than by improving the antioxidant defense system under metal stress. © Springer-Verlag 2004.