Papers by Kavitha Thirumurugan
Background: a-glucosidase inhibitors regulate postprandial hyperglycemia (PPHG) by impeding the r... more Background: a-glucosidase inhibitors regulate postprandial hyperglycemia (PPHG) by impeding the rate of carbohydrate digestion in the small intestine and thereby hampering the diet associated acute glucose excursion. PPHG is a major risk factor for diabetic vascular complications leading to disabilities and mortality in diabetics. Cinnamomum zeylanicum, a spice, has been used in traditional medicine for treating diabetes. In this study we have evaluated the a-glucosidase inhibitory potential of cinnamon extract to control postprandial blood glucose level in maltose, sucrose loaded STZ induced diabetic rats. Methods: The methanol extract of cinnamon bark was prepared by Soxhlet extraction. Phytochemical analysis was performed to find the major class of compounds present in the extract. The inhibitory effect of cinnamon extract on yeast a-glucosidase and rat-intestinal a-glucosidase was determined in vitro and the kinetics of enzyme inhibition was studied. Dialysis experiment was performed to find the nature of the inhibition. Normal male Albino wistar rats and STZ induced diabetic rats were treated with cinnamon extract to find the effect of cinnamon on postprandial hyperglycemia after carbohydrate loading. Results: Phytochemical analysis of the methanol extract displayed the presence of tannins, flavonoids, glycosides, terpenoids, coumarins and anthraquinones. In vitro studies had indicated dose-dependent inhibitory activity of cinnamon extract against yeast a-glucosidase with the IC 50 value of 5.83 μg/ml and mammalian a-glucosidase with IC 50 value of 670 μg/ml. Enzyme kinetics data fit to LB plot pointed out competitive mode of inhibition and the membrane dialysis experiment revealed reversible nature of inhibition. In vivo animal experiments are indicative of ameliorated postprandial hyperglycemia as the oral intake of the cinnamon extract (300 mg/kg body wt.) significantly dampened the postprandial hyperglycemia by 78.2% and 52.0% in maltose and sucrose loaded STZ induced diabetic rats respectively, compared to the control. On the other hand, in rats that received glucose and cinnamon extract, postprandial hyperglycemia was not effectively suppressed, which indicates that the observed postprandial glycemic amelioration is majorly due to a-glucosidase inhibition.
The breakdown of stored fat deposits into its components is a highly regulated process that maint... more The breakdown of stored fat deposits into its components is a highly regulated process that maintains plasma levels of free fatty acids to supply energy to cells. Insulin-mediated transcription of Atgl, the enzyme that mediates the rate-limiting step in lipolysis, is a key point of this regulation. In conditions such as obesity or insulin resistance, Atgl transcription is often misregulated, which can contribute to overall disease progression. The mechanisms by which Atgl is induced during adipogenesis are not fully understood. We utilized computational approaches to identify putative transcriptional regulatory elements in Atgl and then tested the effect of these elements and the transcription factors that bind to them in cultured pre-and mature adipocytes. Herein, we report that Atgl is downregulated by the basal transcription factor Sp1 in preadipocytes, and that the magnitude of downregulation dependents on interactions between Sp1 and PPARγ. In mature adipocytes, when PPARγ is abundant, PPARγ abrogated the transcriptional repression by Sp1 at the Atgl promoter and upregulated Atgl mRNA expression. Targeting the PPARγ-Sp1 interaction could be a potential therapeutic strategy to restore insulin sensitivity by modulating Atgl levels in adipocytes. ________________________________________
Hormetins are compounds that mediate hormesis by being beneficial at low doses but detrimental at... more Hormetins are compounds that mediate hormesis by being beneficial at low doses but detrimental at high doses. Recent studies have highlighted that many compounds that extended lifespan in model organisms did so by mediating hormesis. Rutin is a glycosylate conjugate of quercetin and rutinose and is abundant in citrus fruits and buckwheat seeds. Rutin possess ROS scavenging, anti-cancer, cardio-protective, skin-regenerative and neuro-protective properties. Drosophila melanogaster is an attractive model organism for longevity studies owing to its homology of organ and cellularpathways with mammals. In this study, we aimed to understand the effect of rutin on extending longevity in Drosophila melanogaster. Male and female flies were administered with a range of rutin doses (100-800 lM) to analyse whether rutin mediated lifespan-extension by hormesis. Effect of rutin on physiological parameters like food intake, fecundity, climbing activity, development and resistance to various stresses was also studied.
Biogerontology, 2015
Naringenin, the predominant bioflavonoid found in grapefruit and tomato has diverse bioactive pro... more Naringenin, the predominant bioflavonoid found in grapefruit and tomato has diverse bioactive properties that encompass anti-carcinogenic, anti-inflammatory, anti-atherogenic, anti-estrogenic, anti-hyperlipidemic and anti-hyperglycemic characteristics. Naringenin has not been explored for its pro-longevity traits in fruit flies. Therefore, the current study explores its influence on longevity, fecundity, feeding rate, larval development, resistance to starvation stress and body weight in male and female wild-type Drosophila melanogaster Canton-S flies. Flies were fed with normal and high fat diets respectively. The results implied hormetic effects of naringenin on longevity and development in flies. In flies fed with standard and high fat diets, lower concentrations of naringenin (200 and 400 µM) augmented mean lifespan while higher concentrations (600 and 800 µM) were consistently lethal. However, enhanced longevity seen at 400 µM of naringenin was at the expense of reduced fecundity and food intake in flies. Larvae reared on standard diet having 200 µM of naringenin exhibited elevated pupation and emergence as flies. Eclosion time was hastened in larvae reared on standard diet having 200 µM of naringenin. Female flies fed with a standard diet having 200 and 400 µM of naringenin were more resistant to starvation stress. Reduction in body weight was observed in male and female flies fed with a high fat diet supplemented with 200 and 400 µM of naringenin respectively. Collectively, the results elucidated a context- and dose-dependent hormetic efficacy of naringenin that varied with gender, diet and stage of lifecycle in flies.
Biochemistry
TRIOBP is an actin-bundling protein associated with human deafness DFNB28. In vitro, TRIOBP isofo... more TRIOBP is an actin-bundling protein associated with human deafness DFNB28. In vitro, TRIOBP isoform 4 (TRIOBP-4) forms dense F-actin bundles resembling the inner ear hair cell rootlet structure. Deletion of TRIOBP isoforms 4 and 5 leads to hearing loss in mice due to their inability to form rootlets. Despite the importance of TRIOBP in hearing, the mechanism of actin bundle formation by TRIOBP is not fully understood. The amino acid sequences of TRIOBP isoforms 4 and 5 contain two repeated motifs, referred to as R1 and R2, respectively. To examine the potential role of R1 and R2 motifs in F-actin binding, we generated TRIOBP-4 mutant proteins deleted with R2, and/or R1, and assessed their actin-binding activity and bundle formation in vitro by actin co-sedimentation assay, fluorescence and electron microscopy. Cellular distributions of the TRIOBP-4 mutants were examined by confocal microscopy. We showed that deletion of both R1 and R2 motifs completely disrupted actin binding activi...
Asian Journal of Pharmaceutical and Clinical Research
Objective: To evaluate the α-amylase inhibitory potential of nine herbal plants in regulating pos... more Objective: To evaluate the α-amylase inhibitory potential of nine herbal plants in regulating postprandial hyperglycemia. Materials and Methods: In vitro α-amylase inhibition assay using starch-iodine was performed. α-amylase inhibition delays breakdown of starch and prevents glucose release to reduce postprandial hyperglycemia. Results: The plants screened were Artocarpus altilis, Aconitum heterophyllum, Acorus calamus, Berberis aristata, Cassia auriculata, Cyprus rotundus, Mesua ferrea, Plumbago zeylanicum and Terminalia arjuna. Positive control Acarbose showed IC 50 at 14.24 µg/ml. Methanolic extract of C. auriculata (flower), T. arjuna (bark) and P. zeylanicum (rhizome) exhibited the best inhibitory activity with IC 50 value of 37.28 µg/ml, 48.75 µg/ml and 68.66 µg/ml, respectively. Conclusion: From the present study, we conclude that C. auriculata flower had displayed maximum inhibition against α-amylase.
brane excitability and stabilization of neuronal resting potential; charge balance during endosom... more brane excitability and stabilization of neuronal resting potential; charge balance during endosome acidification; fluid secretion, and regulation of cell volume. As a consequence dysfunctions in regulating membrane chloride permeability originate various diseases. For instance cystic fibrosis arises from a genetic alteration of a transmembrane conductance regulatory channel (CFTR).
Alpha-glucosidase inhibitory activity of fifteen Indian medicinal plants has been evaluated by in... more Alpha-glucosidase inhibitory activity of fifteen Indian medicinal plants has been evaluated by in vitro enzyme assay. Methanol extracts of Cyperus rotundus (tubers), Plumbago zeylanica (root), Symplocos racemosa (bark), and Terminalia arjuna (bark) had displayed 100% inhibition with the IC50 value of 3.98 µg/ml, 3.46 µg/ml, 8.16 µg/ml and 0.69 µg/ml, respectively. Bark extract of Terminalia arjuna is highly effective against alphaglucosidase activity even at nanogram concentration. Plant parts of Piper retrofractum (stem), Zingiber officinale (rhizome), Acorus calamus (rhizome), Picrorhiza kurroa (rhizome), Marsdenia tenacissima (stem), Clerodendron serratum (root), and Rubia cordifolia (root) are not effective and they require high concentration to exhibit inhibition. Potential plants that show maximum inhibition at low concentration (<10 µg/ml) were subjected to kinetic analysis to determine the mode of inhibition of the enzyme. Cyperus rotundus, Symplocos racemosa and Terminalia arjuna exhibited uncompetitive inhibition and Plumbago zeylanica had displayed mixed inhibition to alpha-glucosidase enzyme activity. From the enzyme assay, we infer that Cyperus rotundus, Plumbago zeylanica, Symplocos racemosa and Terminalia arjuna contain potential alpha-glucosidase inhibitors that can be exploited for its use in the treatment of diabetes.
Scientifica, 2014
Nutraceutical compounds show antioxidant and prooxidant properties under stress conditions like c... more Nutraceutical compounds show antioxidant and prooxidant properties under stress conditions like cancer, diabetes, and other diseases. The objective of this study is to find the dichotomic behavior of caffeine, curcumin, and naringenin on DNA of diabetic and normal subjects in the presence and absence of copper, hydrogen peroxide, and complex of copper-hydrogen peroxide. Hydrogen peroxide releases hydroxyl free radicals ( • OH) on oxidation of Cu (I) to Cu (II) through Fenton-type reaction to cause DNA damage. In the results, agarose gel electrophoretic pattern speculates the prooxidant effect of caffeine and antioxidant effect of curcumin on DNA in the presence of copper and hydrogen peroxide. UV-Vis spectral analysis shows hyperchromism on addition of DNA to caffeine, hypochromism with curcumin, and subtle changes with naringenin. The chosen nutraceuticals act as inducers and quenchers of oxidative free radicals arising from diabetes.
Journal of Structural Biology, 2003
We describe here a second generation apparatus for studying transient reaction conformations in m... more We describe here a second generation apparatus for studying transient reaction conformations in macromolecules and their complexes by electron cryo-microscopy. Reactions are trapped by rapid freezing in times ranging from a few milliseconds to tens of seconds after initiation. Blotting of the electron microscope grid and freezing it in liquid ethane uses computer controlled microstepping motors. For the fastest time resolution, a blotted grid containing a thin film of one reactant is sprayed with small droplets containing a second reactant just before freezing. The spray is produced electrically (electrospray), which gives a dense cloud of droplets <1 lm in diameter from the 1-2 ll of solution required per grid. A second method in which two solutions are first mixed by turbulent flow and then blotted prior to freezing is used for reactions with time courses >1 s.
Journal of Molecular Biology, 2008
The giant protein titin has important roles in muscle sarcomere integrity, elasticity and contrac... more The giant protein titin has important roles in muscle sarcomere integrity, elasticity and contractile activity. The key role in elasticity was highlighted in recent years by single-molecule mechanical studies, which showed a direct relationship between the non-uniform structure of titin and the hierarchical mechanism of its force-extension behavior. Further advances in understanding mechanisms controlling sarcomere structure and elasticity require detailed knowledge of titin arrangement and interactions in situ.
Journal of Biological Chemistry, 2003
We have found that myosin V, an important actinbased vesicle transporter, has a folded conformati... more We have found that myosin V, an important actinbased vesicle transporter, has a folded conformation that is coupled to inhibition of its enzymatic activity in the absence of cargo and Ca 2؉ . In the absence of Ca 2؉ where the actin-activated MgATPase activity is low, purified brain myosin V sediments in the analytical ultracentrifuge at 14 S as opposed to 11 S in the presence of Ca 2؉ where the activity is high. At high ionic strength it sediments at 10 S independent of Ca 2؉ , and its regulation is poor. These data are consistent with myosin V having a compact, inactive conformation in the absence of Ca 2؉ and an extended conformation in the presence of Ca 2؉ or high ionic strength. Electron microscopy reveals that in the absence of Ca 2؉ the heads and tail are both folded to give a triangular shape, very different from the extended appearance of myosin V at high ionic strength. A recombinant myosin V heavy meromyosin fragment that is missing the distal portion of the tail domain is not regulated by calcium and has only a small change in sedimentation coefficient, which is in the opposite direction to that seen with intact myosin V. Electron microscopy shows that its heads are extended even in the absence of calcium. These data suggest that interaction between the motor and cargo binding domains may be a general mechanism for shutting down motor protein activity and thereby regulating the active movement of vesicles in cells. The abbreviations used are: CaM, calmodulin; HMM, heavy meromyosin; MOPS, 4-morpholinepropanesulfonic acid; cp, centapoise.
In this study, we report the synthesis of silver nanoparticles from cinnamon bark extract. The ph... more In this study, we report the synthesis of silver nanoparticles from cinnamon bark extract. The physical charactrization of these silver nanoparticles was verified using UV-visible spectroscopy, scanning electron microscopy, and powder X-ray diffraction. Size distribution of nanoparticles was in the range of 30 to 150 nm. The zeta potential was -32 mV, indicating dispersion ability. Superoxide anion radical scavenging assay showed 82% activity for silver nanoparticles derived from cinnamon bark extract.
Drosophila melanogaster is an ideal model organism for developmental studies. This study tests th... more Drosophila melanogaster is an ideal model organism for developmental studies. This study tests the potential of semolina-jaggery (SJ) diet as a new formulation for bulk rearing of flies. Semolina and jaggery are organic products obtained from wheat endosperm and cane sugar, respectively. Semolina is a rich source of carbohydrates and protein. Jaggery has a high content of dietary sugars. Moreover, preparation of semolina jaggery diet is cost-effective and easy. Thus, the current study aimed to compare survival and developmental parameters of flies fed the SJ diet to flies fed the standard cornmeal-sugar-yeast (CSY) diet. SJ diet enhanced survival of flies without affecting fecundity; male flies showed increased resistance to starvation. A higher number of flies emerged at F2 and F3 generation when fed the SJ diet than when fed the control CSY diet. SJ diet did not increase fly body weight and lipid percentage. Therefore, SJ diet can be used for bulk rearing of healthy flies at par with the standard cornmeal-sugar-yeast diet.
Endoplasmic reticulum stress elicits unfolded protein response to counteract the accumulating unf... more Endoplasmic reticulum stress elicits unfolded protein response to counteract the accumulating unfolded protein load inside a cell. The chemical chaperone, 4-Phenylbutyric acid (4-PBA) is a FDA approved drug that alleviates endoplasmic reticulum stress by assisting protein folding. It is found efficacious to augment pathological conditions like type 2 diabetes , obesity and neurodegeneration. This study explores the binding nature of 4-PBA with human serum albumin (HSA) through spectroscopic and molecular dynamics approaches, and the results show that 4-PBA has high binding specificity to Sudlow Site II (Fatty acid binding site 3, subdomain IIIA). Ligand displacement studies, RMSD stabilization profiles and MM-PBSA binding free energy calculation confirm the same. The binding constant as calculated from fluorescence spectroscopic studies was found to be k PBA = 2.69 x 10 5 M-1. Like long chain fatty acids, 4-PBA induces conformational changes on HSA as shown by circular dichroism, and it elicits stable binding at Sudlow Site II (fatty acid binding site 3) by forming strong hydrogen bonding and a salt bridge between domain II and III of HSA. This minimizes the fluctuation of HSA backbone as shown by limited conformational space occupancy in the principal component analysis. The overall hydrophobicity of W214 pocket (located at subdomain IIA), increases upon occupancy of 4-PBA at any FA site. Descriptors of this pocket formed by residues from other subdomains largely play a role in compensating the dynamic movement of W214.
Adipose tissue secretes adipokines that regulate insulin sensitivity in adipocytes and other peri... more Adipose tissue secretes adipokines that regulate insulin sensitivity in adipocytes and other peripheral tissues critical to glucose metabolism. Insulin resistance is associated with severe alterations in adipokines characterized by release of increased pro-inflammatory cytokines and decreased anti-inflammatory cytokines from adipose tissue. The role of Farnesoid X receptor (FXR) activation on adipokines in relation to adipose tissue inflammation and insulin resistance is not completely explored. For the first time, we have evaluated the ability of Chenodeoxycholic acid (CDCA), an endogenous FXR ligand, in restoring the disturbance in adipokine secretion and insulin resistance in palmitate treated 3T3-L1 cells and adipose tissues of High fat diet (HFD) rats. CDCA suppressed several of the tested pro-inflammatory adipokines (TNF-α, MCP-1, IL-6, Chemerin, PAI, RBP4, resistin, vaspin), and enhanced the major anti-inflammatory and insulin sensitizing adipokines (adiponectin, leptin). CDCA suppressed the activation of critical inflammatory regulators such as NF-κB and IKKβ which are activated by palmitate treatment in differentiated cells and HFD in rats. We show the altered adipokines in insulin resistance, its association with inflammatory regulators, and the role of CDCA in amelioration of insulin resistance by modulation of adipokines.
Obesity is a worldwide metabolic disorder affecting all types of people. The mechanism by which i... more Obesity is a worldwide metabolic disorder affecting all types of people. The mechanism by which increased body fat mass that leads to insulin resistance and type 2 diabetes is not yet clearly known. There is a possible crosstalk between leptin, an adipokine and insulin signaling. Leptin mediates insulin sensitivity in hepatocytes; however, its concentration has found to be increased in obese and diabetic subjects. These subjects also have high incidence of oxidative stress status. Therefore, knowing the level of leptin present in obese diabetic subjects will be informative along with its relation to oxidative stress.
A small population study was performed to explore the association between leptin concentration and oxidative stress status in control and obese type 2 diabetic subjects. Oxidative stress status parameters like malondialdehyde (MDA), superoxide dismutase activity (SOD), glutathione peroxidase activity (GSH-Px), and protein carbonyl (PCO) groups content was measured spectrophotometrically in serum of 43 subjects. Serum Leptin concentration was measured by quantikine sandwich ELISA assay.
The strong positive correlation between MDA (malondialdehyde) and leptin in obese diabetic patients (ρ = 0.787, P < 0.05) suggests close association between lipid peroxidation and hyperleptinemia. In addition, observed positive correlation between protein carbonyl groups and leptin level in obese diabetic subjects (ρ = 0.599, P = 0.001) suggest that hyperleptinemia might also be associated with increased protein oxidation. In multiple logistic regression analysis, leptin has shown a significant association with obese type 2 diabetes [odds ratio (OR): 1.161, 95% confidence interval (Cl): 1.027-1.312, P < 0.05], but the significance is lost after adjusting for Age, BMI, MDA and anti-oxidant parameters.
In the subjects with both obesity and diabetes, there is a significant degree of association between hyperleptinemia and oxidative stress. This association reinforces the existing understanding that obese subjects who also have diabetes are vulnerable to cardiovascular complications driven by increased oxidative stress and hyperleptinemia.
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Papers by Kavitha Thirumurugan
A small population study was performed to explore the association between leptin concentration and oxidative stress status in control and obese type 2 diabetic subjects. Oxidative stress status parameters like malondialdehyde (MDA), superoxide dismutase activity (SOD), glutathione peroxidase activity (GSH-Px), and protein carbonyl (PCO) groups content was measured spectrophotometrically in serum of 43 subjects. Serum Leptin concentration was measured by quantikine sandwich ELISA assay.
The strong positive correlation between MDA (malondialdehyde) and leptin in obese diabetic patients (ρ = 0.787, P < 0.05) suggests close association between lipid peroxidation and hyperleptinemia. In addition, observed positive correlation between protein carbonyl groups and leptin level in obese diabetic subjects (ρ = 0.599, P = 0.001) suggest that hyperleptinemia might also be associated with increased protein oxidation. In multiple logistic regression analysis, leptin has shown a significant association with obese type 2 diabetes [odds ratio (OR): 1.161, 95% confidence interval (Cl): 1.027-1.312, P < 0.05], but the significance is lost after adjusting for Age, BMI, MDA and anti-oxidant parameters.
In the subjects with both obesity and diabetes, there is a significant degree of association between hyperleptinemia and oxidative stress. This association reinforces the existing understanding that obese subjects who also have diabetes are vulnerable to cardiovascular complications driven by increased oxidative stress and hyperleptinemia.
A small population study was performed to explore the association between leptin concentration and oxidative stress status in control and obese type 2 diabetic subjects. Oxidative stress status parameters like malondialdehyde (MDA), superoxide dismutase activity (SOD), glutathione peroxidase activity (GSH-Px), and protein carbonyl (PCO) groups content was measured spectrophotometrically in serum of 43 subjects. Serum Leptin concentration was measured by quantikine sandwich ELISA assay.
The strong positive correlation between MDA (malondialdehyde) and leptin in obese diabetic patients (ρ = 0.787, P < 0.05) suggests close association between lipid peroxidation and hyperleptinemia. In addition, observed positive correlation between protein carbonyl groups and leptin level in obese diabetic subjects (ρ = 0.599, P = 0.001) suggest that hyperleptinemia might also be associated with increased protein oxidation. In multiple logistic regression analysis, leptin has shown a significant association with obese type 2 diabetes [odds ratio (OR): 1.161, 95% confidence interval (Cl): 1.027-1.312, P < 0.05], but the significance is lost after adjusting for Age, BMI, MDA and anti-oxidant parameters.
In the subjects with both obesity and diabetes, there is a significant degree of association between hyperleptinemia and oxidative stress. This association reinforces the existing understanding that obese subjects who also have diabetes are vulnerable to cardiovascular complications driven by increased oxidative stress and hyperleptinemia.