Browsing by Author "Mahmood, Akhtar"
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Item Characteristics and physiological role of surfactant-like particles secreted by entrocytes.(2006-07-29) Turan, Aasma; Gupta, Shiffalli; Mahmood, AkhtarIntestinal epithelium secretes novel unilamellar membranes having characteristics similar to lung surfactants and thus has been named Surfactant-like particles (SLP). The chemical analysis of the membranes revealed cholesterol/phospholipid molar ratio of 0.68-0.78, which is much distinct from that of the underlying microvillus membranes (1.34-1.49). The membrane contains 4-6 proteins with a molar weight of 30-120 kDa and is enriched with alkaline phosphatase, contains low amounts of disaccharidases but no Na+, K(+)-ATPase activity. The secretion of SLP is stimulated by fat feeding. Chronic ethanol ingestion also induces the formation of SLP in rat intestine. A number of physiological functions have been attributed to SLP, which include: (i) as a protective lubricant in intestinal lumen, (ii) a role in triacylglycerol transport, (iii) as a vehicle for the transport of luminal proteins into blood, (iv) as a stratum for the adhesion of microorganisms in intestinal lumen, and (v) a role in trans-signalling mechanism across the basolateral surface of enterocytes.Item Coordinated secretion of alkaline phosphatase into serum and intestine in fat-fed rats.(2004-09-16) Grewal, R; Mahmood, AkhtarBACKGROUND: Fat feeding increases the activity of intestinal alkaline phosphatase in the serum. The mechanism underlying this increase is unknown. Surfactant-like particles (SLP) secreted by enterocytes have been implicated in this phenomenon. OBJECTIVE: To study the effect of feeding fish oil and protein synthesis inhibitors on alkaline phosphatase activity in serum and in different intestinal fractions. METHODS: Male albino rats were fed 2 mL of fish oil and were injected cycloheximide or actinomycin D. Alkaline phosphatase activity was determined in the serum and intestinal fractions (SLP, mucosa, muscularis). RESULT: Feeding fish oil significantly elevated alkaline phosphatase activity in serum (p< 0.001) and intestinal mucosa (p< 0.01). Administration of cycloheximide or actinomycin D significantly reduced alkaline phosphatase activity in serum (p< 0.01) and in intestinal mucosa (p< 0.05). BCIP staining of brush border alkaline phosphatase activity in acrylamide gels yielded similar results. CONCLUSIONS: These findings suggest a co-ordination between alkaline phosphatase synthesis and its assembly into lipoprotein vesicles, such as SLP, secreted by enterocytes in response to fat feeding.Item Effect of gallic acid on alkaline phosphatase and peptidase activities in rat intestine.(2009-10) Mahajan, Nidhi; Mahmood, AkhtarGallic acid is a normal constituent of many edible foods, thus directly interacts with epithelial tissue in intestine. In the present study, the effect of gallic acid on intestinal alkaline phosphatase (IAP) and peptidase activities in rat intestine was evaluated. Gallic acid (0.27-0.5 mM) inhibited activities of leucine aminopeptidase (LAP) and -glutamyl transpeptidase (-GTP) by over 90%, compared to controls in rat intestine. In contrast, 0.1-0.6 mM gallic acid either had no effect or stimulated the activity of IAP in rat intestine. The observed inhibition of peptidases by gallic acid was reversible in nature. Kinetic analysis revealed no change in Vmax of LAP (0.42-0.44 units/mg protein) and -GTP (0.22-0.24 units/mg protein), while the values of apparent Km were increased 6-7 fold, exhibiting competitive-type of enzyme inhibition by gallic acid. The values of Ki for LAP and -GTP were 0.037 mM and 0.017 mM, respectively. These observations indicate that gallic acid is a potent inhibitor of brush border peptidases, and thus may interfere in the digestion and absorption of proteins in the intestine.Item Effect of Na+ ions on pH-dependent conformational changes in brush border sucrase-isomaltase in mice intestine.(2008-12-26) Gupta, Shiffalli; Mahmood, Safrun; Khan, Rizwan Hasan; Mahmood, AkhtarIntestinal brush border sucrase-isomaltase (sucrose D-glucosidase E.C. 3.2.1.48, E.C. 3.2.1.10) exhibits pH-dependent stimulatory or inhibitory effects in response to Na+ ions. However, whether the enzyme undergoes conformational modulations as a function of pH and in the presence of alkali metal ions is not known. In this paper, we investigated the structural and functional relationship of purified murine sucrase in response to pH and Na+ ions using UV-CD fluorescence and spectroscopic studies. Kinetic studies revealed that at pH 5.0, the enzyme activation by Na+ ions was V-type, which changed to K-type at pH 7.2, whereas at alkaline pH (8.5), Na+ ions inhibited the enzyme activity and inhibition was uncompetitive in nature, affecting both the Km and Vmax components. Far UV-CD spectra of protein at pH 7.2 in the absence and presence of Na+ were almost overlapping, suggesting that secondary structure of protein was not affected upon addition of the salt. However, near UV-CD spectra indicated marked alterations in the tertiary structure of protein in presence of 50 mM Na+ ions. Increase in pH from 7.2 to 8.5 resulted in a marked rise in fluorescence intensity and red shift in lambda max due to tryptophan residues in the enzyme molecule. These findings suggested that alterations in enzyme activity as a function of pH and Na+ ions was associated with ionization of key amino acid residues together with structural modifications in the enzyme conformation around neutral or alkaline pH.Item Effect of tannic acid on brush border disaccharidases in mammalian intestine.(2007-04-05) Chauhan, Ayesha; Gupta, Shiffalli; Mahmood, AkhtarTannic acid is a glucoside (penta-m-digallolyl-glucose), which exhibits a wide variety of physiological functions. Around neutral pH, 0.4 mM tannic acid produced 84% inhibition of rat brush border sucrase activity, but 35-40% enzyme inhibition was observed in the rabbit intestine at 0.08 mM concentration. In the mice, 74-77% enzyme inhibition was observed at 0.05 mM concentration of tannic acid. The observed inhibition was reversible in rat intestine. Tannic acid (0.2 mM) also inhibited lactase (18% in adult and 71% in suckling animals), maltase (76%) and trehalase (88%) activities in rat intestine. pH versus activity curves showed that 0.2 mM tannic acid inhibited enzyme activity in rat by 91% at pH 5.5 which was reduced to 14% at pH 8.5 compared to the respective controls. In the rabbit 18-60% enzyme inhibition was noticed below pH 7.0, however at pH 8.5, it was of the order of 38%. Kinetic analysis revealed that tannic acid is a competitive inhibitor of rat brush border sucrase at pH 6.8. Effect of tannic acid together with various -SH group reacting reagents revealed that the enzyme inhibition is additive in nature, suggesting the distinct nature of binding sites on the enzyme for these compounds. The results suggest that tannic acid is a potent inhibitor of intestinal brush border disaccharidases, and could modulate the intestinal functions.Item Effects of fluoride and ethanol administration on lipid peroxidation systems in rat brain.(2013-03) Chauhan, Shailender Singh; Ojha, Sudarshan; Mahmood, AkhtarExposure to fluoride and excessive ethanol consumption has been identified as a serious public health problem in many parts of the world, including India. Thus, the effect of co-exposure to fluoride and ethanol for 3-6 weeks was studied on lipid peroxidation (LPO) and oxidative stress related parameters in the rat brain. After 3 weeks, co-treated animals showed 95% increase in LPO levels compared to control. However, the levels of reduced glutathione, total and protein thiols were decreased. These changes were accompanied by a decrease in the activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and glutathione-S-transferase. Rats exposed to fluoride together with ethanol for 6 weeks resulted in 130% increase in LPO and decrease in the reduced glutathione levels. The activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and glutathione-S-transferase were reduced under these conditions. Brain histology revealed excessive lymphocytes, edema and spongeosis in the cortical region after six weeks of fluoride and ethanol treatment. These results suggest that exposure to fluoride together with ethanol enhances lipid peroxidation by affecting antioxidant defence systems in the rat brain.Item Ethanol-induced changes in lipid peroxidation of enterocytes across the crypt–villus axis in rats.(2010-01) Kalra, Amandeep Kaur; Gupta, Shiffalli; Turan, Aasma; Mahmood, Safrun; Mahmood, AkhtarBackground Reactive oxygen species (ROS) have been implicated in the turnover of epithelial cells in the rat intestine. The metabolism of ethanol generates ROS, which are implicated in cellular injury, but the levels of lipid peroxidation in intestine in chronic alcoholism are unknown. Aim To investigate the effects of ethanol ingestion on lipid peroxidation, and anti- and pro-oxidant enzyme systems in enterocytes across the crypt–villus axis in intestine. Methods Wistar rats (90–100 g) were administered 1 mL of 30% ethanol daily for 39 days. Intestinal epithelial cells were isolated in fractions. Malondialdehyde levels, and activities of glutathione-S-transferase (GST), glutathione reductase (GR), superoxide dismutase (SOD) and catalase were determined in various cell fractions. Incorporation of H3- thymidine into DNA of enterocytes was also determined. Results Lipid peroxidation was elevated by two- to threefolds in both villus and crypt cells in ethanol-fed animals compared to controls. The activities of GST and GR were four- to six-folds higher in villus tip cells compared to crypt base cells. The activities of SOD and catalase were five- to seven-fold higher in crypt base cells compared to villus tip cells. Ethanol feeding elevated the activities of SOD (76-190%) and catalase (20-150%) in enterocytes all along the crypt–villus axis compared to the controls. H3 thymidine incorporation into DNA of enterocytes was reduced by half in ethanol-fed rats compared to controls. Conclusions There is a gradient in the concentration of lipid peroxides in enterocytes across the crypt–villus axis, being high at the villus tip and low at the crypt base in the rat intestine. Ethanol feeding enhanced lipid peroxidation in both villus and crypt cells.Item Hypolactasia as a molecular basis of lactose intolerance.(2006-10-01) Kaur, Kamaljit; Mahmood, Safrun; Mahmood, AkhtarLactase-phlorizin hydrolase (LPH), a membrane-bound glycoprotein present in the luminal surface of enterocytes in the intestine is responsible for lactose intolerance, a phenomenon prevalent in humans worldwide. In the rodent intestine, the post-natal development of the LPH follows a specific pattern, such that the enzyme levels are high in the peri-natal period, but declines considerably upon maturation. The observed maturational decline in the LPH activity is very similar to adult-type hypolactasia observed in humans. Majority of the studies have been carried out using animal models or cell lines and a number of hypotheses have been put forward to explain the maturational decline of lactase activity such as: (a) decreased amount of lactase protein, (b) defect in post-translational modification of precursor lactase to the mature enzyme, and (c) synthesis of an inactive, high molecular weight lactase with altered glycosylation, however, the precise underlying mechanism of adult-type hypolactasia remains undefined. The present review describes the recent developments in understanding the regulation of lactase expression and the possible mechanism of adult-type hypolactasia, as a cause of lactose intolerance.Item In vitro translation of RNA to lactase during postnatal development of rat intestine.(2005-03-12) Kaur, Jaspreet; Kaur, Kamaljit; Mahmood, Akhtar; Mahmood, SafrunmRNA levels encoding lactase were detected by Northern blot analysis using two different probes in developing rat intestine. Probe I and probe II corresponding to second half of prolactase gene showed a 6.8 kb mRNA transcript in 7, 14, 21 and 30 day old rat intestine. There was no change in quantity of lactase mRNA detected using probe II, but hybridization with probe I showed a progressive decrease in mRNA transcript encoding lactase with age. At day 7 and 14 of postnatal development, the lactase mRNA was quite high, but it reduced upon weaning. The in vitro translation products of RNA detected by Western blot analysis using brush border lactase antibodies showed several isoforms of lactase antigen with molecular weight ranging from 100-220 kDa. Analysed at days 7 and 30 of postnatal development, lactase isoforms of molecular weight 130 kDa and 220 kDa were similar to those found in purified brush border membranes. The translation of RNA to 220 kDa lactase protein was high in 7 and 14 day old pups, but it was markedly reduced in 30 day old animals. These findings support the contention that translation of mRNA to lactase is impaired in weaned animals, which may also be responsible for the maturational decline in lactase activity in adult rat intestine.Item Inhibition of dextransucrase activity in Streptococcus mutans by plant phenolics.(2013-02) Goyal, Dimple; Sharma, Sukesh; Mahmood, AkhtarStreptococcus mutans is responsible for causing dental caries in humans and utilizes sucrose for its growth. The dextransucrase (EC 2.4.1.5) is responsible for sucrose metabolism, which exhibits both hydrolytic and glucosyltransferase activities. In this study, we examined the effects of the plant phenols, namely gallic, tannic and syringic acids and aqueous extracts of certain traditionally used chewing sticks (Acacia arabica, Azadirachta indica, Pongamia pinnata and Salvadora persica) for prevention of dental caries on hydrolytic activity of dextransucrsae in S. mutans. Gallic acid (4-5 mM) produced 80-90% inhibition of the enzyme, while tannic acid (0.2 mM) and syringic acid (5 mM) inhibited the enzyme activity 80% and 48%, respectively in vitro. The aqueous extracts of chewing sticks produced 35-40% inhibition of dextransucrase activity at 5 mg phenol concentration. Kinetic analysis revealed mixed-type of enzyme inhibition by polyphenols, where both Km and Vmax were altered. The value of Ki for tannic, gallic and syringic acids were 0.35, 1.6 and 1.94 mM, respectively. The enzyme inhibition by polyphenols was optimum at pH 7-7.5, while by plant extract was maximum at pH 5-6. These results suggest that plant polyphenols may find potential applications in the prevention and control of dental caries by inhibiting dextransucrase activity in S. mutans.Item Modulation of intestinal brush border membrane chemical composition during postnatal development in rats : Effect of gestational diabetes.(2012-01) Sharma, Ruchi; Chauhan, Shailender Singh; Mahmood, AkhtarThere was a significant increase in fucose (52%), total hexoses (16%) and hexosamine (56%) except sialic acid, which was reduced (77%) in the microvillus membrane of infants born to rat mothers made diabetic by injecting alloxan on day 3 of gestation. Expressed on the protein basis there were a significant increase in membrane, triglyceride, total cholesterol, and phospholipids content of brush border in pups from diabetic group between 5-45 days of postnatal age. Intestinal morphology in diabetic group showed, regression of tubular glands, distorted cellular organization of mucosal cells, reduction in the mucosal cell height and number of secretory goblet cells. These findings suggest that the gestational diabetes affects the sugar and lipid composition of the intestinal brush border membrane in rats during early stages of the postnatal development, which may be associated with compromised tissue functions later in life.Item Postnatal development of alcohol dehydrogenase in liver and intestine of rats exposed to ethanol in utero.(2005-01-17) Bhalla, Sonali; Kaur, Kamaljit; Mahmood, Akhtar; Mahmood, SafrunBACKGROUND AND OBJECTIVES: Ethanol exposure during gestation induces marked aberrations in growth and development of offsprings collectively known as foetal alcohol syndrome (FAS);. However, its effects on the postnatal development of alcohol dehydrogenase (ADH) are not adequately investigated. Therefore, ADH activity in liver and intestine of rats exposed to ethanol during gestation was studied in relation to postnatal development. METHODS: Pregnant female rats beginning at day 1 of gestation were fed 1 ml of 30 per cent ethanol daily during the entire gestation period. ADH activity was determined in liver and intestine postnatally at day 4, 8, 14, 20 and 30. DNA and RNA contents and intestinal histology were also examined. RESULTS: During the first two weeks of postnatal life, there was no difference in ADH levels of rat liver and intestine in control and prenatally ethanol exposed pups but ADH levels were significantly reduced at 3-4 wk in ethanol fed group compared to control. A similar decrease in DNA and RNA contents of intestine and changes in tissue morphology were observed in ethanol exposed pups during postnatal development. INTERPRETATION AND CONCLUSION: The findings of our study suggested that prenatal ethanol exposure modified ADH activity in liver and intestine during postnatal development. This could affect ethanol metabolism under these conditions.Item Susceptibility of lactase to luminal proteases in developing rat intestine.(2006-07-16) Kaur, Kamaljit; Mahmood, Safrun; Mahmood, AkhtarBACKGROUND: Postnatal development of rat intestine is associated with a decline in brush-border lactase activity. This phenomenon is similar to the adulthood hypolactasia in humans. However, the mechanism underlying this process is not understood. METHODS: The effect of luminal proteases from adult rat intestine on the intestinal lactase activity in animals aged 7, 14, 21 and 30 days was studied in in vitro experiments. Lactase levels were estimated using enzyme assays and Western blot analysis. RESULTS: Incubation of purified brush borders with increasing concentrations of luminal proteases reduced the lactase activity in intestine of 7-day-old rats, but not in that of adult animals. Western blot analysis revealed low signal of the 220-kDa lactase protein in 7-day-old animals, but not that of older weaned animals. CONCLUSIONS: Our findings suggest that luminal proteases may be responsible for the maturational decline in intestinal lactase activity.