Pallu Reddanna

Bio: Pallu Reddanna is an academic researcher from University of Hyderabad. The author has contributed to research in topics: Arachidonic acid & Lipoxygenase. The author has an hindex of 43, co-authored 190 publications receiving 5909 citations. Previous affiliations of Pallu Reddanna include Sri Venkateswara University & Yahoo!.

High-throughput screening assays for cyclooxygenase-2 and 5-lipoxygenase, the targets for inflammatory disorders.

Abstract: High-throughput screening (HTS) involves testing of compound libraries against validated drug targets using quantitative bioassays to identify 'hit' molecules that modulate the activity of target, which forms the starting point of a drug discovery effort. Eicosanoids formed via cyclooxygenase (COX) and lipoxygenase (LOX) pathways are major players in various inflammatory disorders. As the conventional non-steroidal anti-inflammatory drugs (NSAIDs) that inhibit both the constitutive (COX-1) and the inducible (COX-2) isoforms have gastric and renal side effects and the recently developed COX-2 selective anti-inflammatory drugs (COXIBs) have cardiac side effects, efforts are being made to develop more potent and safer antiinflammatory drugs. Current assay methods for these enzymes, such as oxygraphic, radioisotopic, spectrophotometric etc. are not compatible for screening of large number of compounds as in drug discovery programs. In the present study, HTS-compatible assays for COX-1, COX-2 and 5-LOX were developed for screening of compound libraries with the view to identify potential anti-inflammatory drug candidates. A spectrophotometric assay involving co-oxidation of tetramethyl-p-phenylene diamine (TMPD) during the reduction of prostaglandin G2 (PGG2) to PGH2 was adopted and standardized for screening of compounds against COX-1 and COX-2. Similarly, the HTS-compatible FOX (ferrous oxidation-xylenol orange) based spectrophotometric assay involving the formation of Fe3+/xylenol orange complex showing absorption in the visible range was developed for screening of compounds against 5-LOX.

Use of quantum mechanics/molecular mechanics-based FEP method for calculating relative binding affinities of FBPase inhibitors for type-2 diabetes

Abstract: A quantum mechanics (QM)/molecular mechanics (MM)-based free energy perturbation (FEP) method, developed recently, provides most accurate estimation of binding affinities. The validity of the method was evaluated for a large set of diverse inhibitors for fructose 1,6-bisphosphatase (FBPase), a target enzyme for type-II diabetes mellitus. The validation set comprises of 22 important structurally different mutations. The calculated relative binding free energies using the QM/MM-based FEP method reproduce the experimental values with exceptional precision of less than ±0.5 kcal/mol. The CPU requirements for QM/MM-based FEP are about fivefold greater than conventional FEP methods, but it is superior in accuracy of predictions. In addition, the QM/MM-based FEP method eliminates the need for time-consuming development of MM force field parameters, which are frequently required for novel inhibitors described by MM. Future automation of the method and parallelization of the code for 128/256/512 cluster computers is expected to enhance the speed and increase its use for drug design and lead optimization. The present application of QM/MM-based FEP method for structurally diverse set of analogs serves to enhance the scope of FEP method and demonstrate the utility of QM/MM-based FEP method for its potential in drug discovery.

Effects of (15S)‐hydroperoxyeicosatetraenoic acid and (15S)‐hydroxyeicosatetraenoic acid on the acute‐ lymphoblastic‐leukaemia cell line Jurkat: activation of the Fas‐mediated death pathway

Abstract: The antiproliferative effects of 15-LOX (15-lipoxygenase) metabolites of arachidonic acid {(15S)-HPETE [(15S)-hydroperoxyeicosatetraenoic acid] and (15S)-HETE [(15S)-hydroxyeicosatetraenoic acid]} and the mechanism(s) involved were studied in the human T-cell leukaemia cell line Jurkat. (15S)-HPETE, the hydroperoxy metabolite of 15-LOX, inhibited the growth of Jurkat cells 3 h after exposure and with an IC(50) value of 10 microM. The hydroxy metabolite of 15-LOX, (15S)-HETE, on the other hand, inhibited the growth of Jurkat cells after 6 h of exposure and with an IC(50) value of 40 microM. The cells exposed to 10 microM (15S)-HPETE for 3 h or to 40 microM (15S)-HETE for 6 h showed increased expression of Fas ligand and FADD (Fas-associated death domain), caspase 8 activation, Bid (BH3-interacting domain death agonist) cleavage, decrease in mitochondrial membrane potential, cytochrome c release, caspase 3 activation, PARP-1 [poly(ADP-ribose) polymerase-1] cleavage and DNA fragmentation, suggesting the involvement of both extrinsic and intrinsic death pathways. Further studies on ROS (reactive oxygen species) generation revealed the involvement of NADPH oxidase. In conclusion, the present study indicates that NADPH oxidase-induced ROS generation activates the Fas-mediated death pathway.

Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition)

Abstract: In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. For example, a key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process versus those that measure flux through the autophagy pathway (i.e., the complete process including the amount and rate of cargo sequestered and degraded). In particular, a block in macroautophagy that results in autophagosome accumulation must be differentiated from stimuli that increase autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. It is worth emphasizing here that lysosomal digestion is a stage of autophagy and evaluating its competence is a crucial part of the evaluation of autophagic flux, or complete autophagy. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. Along these lines, because of the potential for pleiotropic effects due to blocking autophagy through genetic manipulation, it is imperative to target by gene knockout or RNA interference more than one autophagy-related protein. In addition, some individual Atg proteins, or groups of proteins, are involved in other cellular pathways implying that not all Atg proteins can be used as a specific marker for an autophagic process. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular assays, we hope to encourage technical innovation in the field.

Lipid peroxidation: production, metabolism, and signaling mechanisms of malondialdehyde and 4-hydroxy-2-nonenal.

Abstract: Lipid peroxidation can be described generally as a process under which oxidants such as free radicals attack lipids containing carbon-carbon double bond(s), especially polyunsaturated fatty acids (PUFAs). Over the last four decades, an extensive body of literature regarding lipid peroxidation has shown its important role in cell biology and human health. Since the early 1970s, the total published research articles on the topic of lipid peroxidation was 98 (1970–1974) and has been increasing at almost 135-fold, by up to 13165 in last 4 years (2010–2013). New discoveries about the involvement in cellular physiology and pathology, as well as the control of lipid peroxidation, continue to emerge every day. Given the enormity of this field, this review focuses on biochemical concepts of lipid peroxidation, production, metabolism, and signaling mechanisms of two main omega-6 fatty acids lipid peroxidation products: malondialdehyde (MDA) and, in particular, 4-hydroxy-2-nonenal (4-HNE), summarizing not only its physiological and protective function as signaling molecule stimulating gene expression and cell survival, but also its cytotoxic role inhibiting gene expression and promoting cell death. Finally, overviews of in vivo mammalian model systems used to study the lipid peroxidation process, and common pathological processes linked to MDA and 4-HNE are shown.

The glutathione S-transferase supergene family: regulation of GST and the contribution of the isoenzymes to cancer chemoprotection and drug resistance.

Abstract: The glutathione S-transferases (GST) represent a major group of detoxification enzymes. All eukaryotic species possess multiple cytosolic and membrane-bound GST isoenzymes, each of which displays distinct catalytic as well as noncatalytic binding properties: the cytosolic enzymes are encoded by at least five distantly related gene families (designated class alpha, mu, pi, sigma, and theta GST), whereas the membrane-bound enzymes, microsomal GST and leukotriene C, synthetase, are encoded by single genes and both have arisen separately from the soluble GST. Evidence suggests that the level of expression of GST is a crucial factor in determining the sensitivity of cells to a broad spectrum of toxic chemicals. In this article the biochemical functions of GST are described to show how individual isoenzymes contribute to resistance to carcinogens, antitumor drugs, environmental pollutants, and products of oxidative stress.A description of the mechanisms of transcriptional and posttranscriptional regulat...