Biomedical subjects

B Sivakumar

Publications and source records attributed to B Sivakumar.

At least 19 recordsLinked to original sources

PubMed2003

2-nitroso-1,3-diphenyl-1,2,3,4-tetrahydrobenzo[b][1,6]naphthyridine.

The title compound, C(24)H(19)N(3)O, crystallizes in the centrosymmetric space group P2(1)/a with one molecule in the asymmetric unit. The tetrahydropyridine ring has a boat conformation. The dihedral angle between the fused pyridine rings is 16.2 (1) degrees. The equatorial and axial orientations of the two phenyl groups with respect to the tetrahydropyridine ring are confirmed. The nitroso group is coplanar with the attached C-N-C group. The interplanar angle formed between the fused tetrahydropyridine and benzene planes is 13.4 (1) degrees. The crystal packing is stabilized by an intermolecular C-H.O hydrogen bond, which forms a C(9) graph-set chain running along the [001] direction.

Crystallography, X-Ray↗

PubMed2002

Inhibition of transthyretin amyloid fibril formation by 2,4-dinitrophenol through tetramer stabilization.

Transthyretin (TTR), a homotetrameric thyroxine transport protein found in the plasma and cerebrospinal fluid, circulates normally as a innocuous soluble protein. In some individuals, TTR polymerizes to form insoluble amyloid fibrils. TTR amyloid fibril formation and deposition have been associated with several diseases like familial amyloid polyneuropathy and senile systemic amyloidosis. Inhibition of the fibril formation is considered a potential strategy for the therapeutic intervention. The effect of small water-soluble, hydrophobic ligand 2,4-dinitrophenol (2,4-DNP) on TTR amyloid formation has been tested. 2,4-DNP binds to TTR both at acidic and physiological pH, as shown by the quenching of TTR intrinsic fluorescence. Interestingly, 2,4-DNP not only binds to TTR at acidic pH but also inhibits amyloid fibril formation as shown by the light scattering and Congo red-binding assay. Inhibition of fibril formation by 2,4-DNP appears to be through the stabilization of TTR tetramer upon binding to the protein, which includes active site. These findings may have implications for the development of mechanism based small molecular weight compounds as therapeutic agents for the prevention/inhibition of the amyloid diseases.

2,4-Dinitrophenol↗

PubMed2002

Double fortified salt at crossroads.

Iron Deficiency Anemia (IDA) and Iodine Deficiency Disorders (IDD) are the major public health problems often co-existing in many regions in our country. National Institute of Nutrition (NIN) has promoted the technology of double fortification of common salt with iodine and iron as a strategy to control both deficiencies under food-based approaches. Two other formulations of double fortified salt (DFS) have been subsequently developed by other agencies. NIN formulation & Nutrisalt have a stabilizer/promoter to maintain the stability of iodine in the presence of iron. The Micronutrient Initiative (MI) formulation uses physical separation of iodine by microencapsulation. NIN carried out extensive studies on stability, bioavailability, acceptability, safety and impact (including in community) of DFS. Feasibility both at factory level production and community level implementation have been worked out. MI salt had also undergone stability, acceptability and impact studies. No data is reported on the stability of Nutrisalt except that good stability is claimed in the available reports. In principle, the strategy of double fortification of salt with iron and iodine is sound with uniformly good impact on urinary iodine excretion and prevention of anemia. However, striking increments in hemoglobin (Hb) were not readily demonstrated since the intended purpose of DFS was only to provide iron at maintenance level and not therapeutic level. Complexities in the experimental designs, confounding variables and quality of the ingredients in salts also contributed to difficulties in interpretation of Hb status in studies involving DFS. Along with improvements contemplated in formulation to enhance the stability and bioavailibility, DFS should be able to fulfil the promise and realise its potential in reducing iron and iodine deficiency amongst our poor population in the next few years.

Anemia, Iron-Deficiency↗

PubMed2001

Prospects of fortification of salt with iron and iodine.

Fortification of salt with iron has been developed by the National Institute of Nutrition (NIN) as a strategy for the control of iron deficiency anaemia (IDA) in India, similar to iodization of salt for control of iodine deficiency disorders (IDD). Stability of the iron fortified salt (IFS), its bioavailability and organoleptic evaluation of food items containing the IFS have been demonstrated. Acceptability and effectiveness of the IFS in school children and in multicentric community trials have been demonstrated. With the introduction of universal iodization of salt as a national policy in 1988, NIN has developed a formulation for double fortification (DFS) of salt with iodine and iron. The stability of the nutrients under laboratory conditions along with their bioavailability were found to be good but varying with the quality of salt used. The DFS has been evaluated in controlled trials in tribal communities and in residential school children. The findings of these studies are discussed. Overall, in these trials, DFS effectively controlled iodine deficiency but a clear impact on reducing anaemia was not demonstrated. In residential schoolchildren, increased urinary excretion of iodine as well as reduced anaemia were observed. The quality of salt has been found to be an important determinant of the stability of iodine in DFS. Further evaluation of this potentially important intervention is in progress.

Adolescent↗

PubMed2000

Nutritional status affects intestinal carotene cleavage activity and carotene conversion to vitamin A in rats.

Validation of an in vivo method we developed recently and its application to assess the role of dietary factors in carotene conversion were tested in rats. We compared the ratio of area under plasma vitamin A time-curves (AUC(0-12h)) obtained after a dose of beta-carotene to that after a dose of vitamin A, with the in vitro intestinal supernatant beta-carotene dioxygenase activity. In separate experiments, vitamin A (AD) and protein deficiencies (PD) were produced in male WNIN weanling rats. Corresponding food-restricted (AR and PR) and unrestricted rats (AA and PA) served as controls. Three rats in each of the AD, AR and AA groups received oral doses of 50-300 microgram beta-carotene or 25-150 microgram vitamin A and four rats in each of the PD, PR and PA groups received only 100 microg beta-carotene or vitamin A. The plasma vitamin A AUC(0-12h) with beta-carotene or vitamin A were significantly and positively correlated (r = 0.714-0.918, n = 9-12, P < 0.05) with the dose in AD, AR and AA groups. The AUC(0-12h) slope ratios in AD, AR and AA rats were 0.33, 0.20 and 0.26, respectively. The beta-carotene dioxygenase activity (pmol retinal. h(-1). mg protein(-1)) was significantly higher in the AD group (14.9 +/- 2.43) compared to both AR (6.7 +/- 0.62) and AA (6.3 +/- 1.37) groups and was parallel with in vivo conversion of beta-carotene to vitamin A. The AUC(0-12h) ratio was lower in PD rats (0.13) compared to PR (0.26) and PA (0.5) groups. Similarly, the in vitro enzyme activity (pmol retinal. h(-1). mg protein(-1)) in PD rats was significantly lower (3.6 +/- 1.30) compared to PR (13.7 +/- 0.92) and PA groups (13.8 +/- 1.6). Thus the results validate the methodology and confirm the role of nutritional factors in carotene conversion to vitamin A.

Analysis of Variance↗

PubMed1998

Biological efficacy and plasma norethisterone levels of orally administered norethisterone enanthate in rat and hamster.

Norethisterone enanthate (NET-En) is a well known intramuscular contraceptive drug. The long acting nature of this preparation when administered orally was evaluated in female rats and hamsters using fertility inhibition test and from the plasma levels of norethisterone (NET). An oral dose of 20-60 mg NET-En was administered to random groups of six female rats and hamsters and were mated after five and ten days with males of proven fertility. The fertility inhibition rate was determined from vaginal delivery. A dose-dependent reduction in fertility was seen in rats 5 days after oral administration of NET-En. This effect was found to be less pronounced and not significant 10 days after administration of similar doses of NET-En. In hamsters, a similar but less pronounced effect was noted. The decrease in fertility was significant only at the 60 mg dose. The plasma levels of NET estimated by RIA over a period of 15 days, in a different set of treated rats, suggested rapid absorption of NET-En within a day, and drug concentration decreased slowly, the levels on the 4th day ranged from 0.9-2.3 with the 10 mg and 1.0-4.0 ng/ml with the 20 mg dose. Detection of adequate levels of NET in plasma during the estrous cycle in rats, and the fertility inhibition observed in female rats and at higher doses in hamsters, suggest that NET-En is orally active.

Animals↗

PubMed1998

Current controversies in carotene nutrition.

Most of the dietary vitamin A is derived from plant foods in the form of pro-vitamin A, the carotenoids. Though in 1930 it was first demonstrated that beta-carotene is the precursor for vitamin A and it is well accepted that 1 mole of beta-carotene is equivalent to one mole of vitamin A, the mechanism of conversion to vitamin A has been controversial. Some of the mechanisms suggested are central cleavage potentially yielding 2 molecules of vitamin A or excentric cleavage producing one molecule of vitamin A from beta-carotene which drastically varied the potency of carotene. A mucosal supernatant from rat intestine was shown to have beta-carotene dioxygenase activity which provided the basis for central cleavage. Many observations on enzyme activity in vitro and efficacy of carotene in vivo did not support the above findings and a re-evaluation of the whole problem was undertaken at the National Institute of Nutrition (NIN), Hyderabad. Intestinal conversion of beta-carotene to vitamin A both in vitro and in vivo in rats and in vivo in children was evaluated. A novel method of obtaining the in vivo conversion of carotene to vitamin A using the ratio of area under plasma vitamin A time curves after a dose of beta-carotene and vitamin A (> 100 micrograms) was developed in rats and later extended to children. In children a dose of 1.5 mg of beta-carotene and vitamin A was used. From these studies intestinal conversion of beta-carotene to vitamin A was found to be an enzymatic reaction involving central cleavage and which needed the presence of oxygen. The substrate was found to bind the enzyme at C-15,15'. The enzyme may be associated with inherent or contaminant enzyme which breaks of other part of the molecule released after central cleavage of carotene. The in vivo conversion of carotene to vitamin A was found to vary from 20 to 80 per cent depending on the nutritional status. Vitamin A deficiency was found to enhance both the in vitro and in vivo conversion and protein deficiency to decrease both. Thus the present results confirm the convertibility of dietary carotenoids to vitamin A and could facilitate further investigations on interactions of different dietary carotenoids on the absorption and cleavage of carotene to vitamin A in children.

Animals↗

PubMed1998

Impact evaluation of iron & iodine fortified salt.

As a novel approach to tackle the problems of iron deficiency anaemia and iodine deficiency disorders (IDDs), which often coexist, the National Institute of Nutrition has developed iron and iodine fortified common salt (double fortified salt-DFS) as a public health measure. This salt has undergone a battery of laboratory and field tests to evaluate its feasibility for use in a national programme. The DFS is designed to provide 1 mg of iron and 15 micrograms of iodine per gram of common salt. This was made possible by the inclusion of a polyphosphate stabilizer, sodium hexametaphosphate (SHMP) at 1 per cent level. The stability of iron and iodine was found to be good up to 6 months. However, the stability of iodine depended upon the quality of the salt used for fortification. The biological effects of long-term consumption of DFS were evaluated in experimental rats and in field trials. Both iron and iodine from the salt were found to be biologically available in regenerating haemoglobin and in increasing excretion of iodine in urine. When this salt was tested in tribal villages endemic for goitre and iron deficiency anaemia, the bioresponse was good with regard to the iodine status but was not uniform in all segments with regard to iron, probably due to confounding variables. In a study carried out in residential school children where such variables did not exist, DFS was found to have significant impact on haemoglobin status in anaemic children and improved their urinary iodine excretion. The consumption of DFS for 2 yr did not have any adverse effects in school children as well as in the tribal population. Parameters related to calcium homeostasis were not altered in children receiving DFS. Histopathological examination of tissues and radiological examination of bone did not reveal any abnormality in DFS fed rats. Similarly serum and urinary parameters related to calcium and phosphorus were not altered in DFS fed rats. Therefore, DFS is presented as a feasible and effective strategy to control the double deficiency of iron and iodine in our community.

Animals↗

PubMed1997

Pharmacokinetics of orally administered norethisterone enanthate in rabbit, monkey, and women.

Norethisterone enanthate (NET-En), an established intramuscular long-acting contraceptive agent, has previously been shown to be effective in inhibiting fertility in two rodent species even 4 days after oral ingestion. Pharmacokinetics of NET and NET-En were studied after oral and intramuscular doses in two animal species and a few women. The results suggest that the NET-En was absorbed within a day in all the species after oral dose. The estimates of relative bioavailability ranged from 13 to 51% in rabbits, monkeys, and women. The elimination half-life was 5-10 days. The presence of the active component, NET, in the circulation over the experimental period of 15 days suggests that NET-En could be useful as a long-acting oral pill. The suppression of progesterone levels during the luteal phase of menstrual cycle in women also supports this finding.

Administration, Oral↗

PubMed1997

Changes in biochemical indicators of iron status during iron repletion and depletion in monkeys.

Different modes of iron depletion and repletion were studied in monkeys to understand the sequential changes in and the relative importance of different biochemical indicators of iron status. Six control monkeys were divided into two groups, one was fed an iron-deficient diet (group 1) and the other underwent phlebotomy in addition to receiving an iron-deficient diet (group 2). Previously iron-depleted monkeys were subdivided into 4 groups of 3 animals each. While one group was continued on the iron-deficient diet (group 3), the second group received parenteral iron (group 4), the third group (group 5) received a sufficient-iron-containing diet, and the fourth group was fed 50% of the iron requirement. All indicators of iron status like hemoglobin (Hb), erythrocyte protoporphyrin (EPP), serum transferrin saturation and serum ferritin were monitored periodically, in addition to liver and bone marrow iron. all the indicators except serum ferritin and liver iron showed a decrease in group 2. On the other hand, animals receiving parenteral iron (group 4) showed an increase in all the parameters except serum ferritin. The dietary supplementation produced an increase in Hb and a decrease in EPP only (groups 5 and 6). There was a significant positive correlation between changes in bone marrow iron and Hb concentration depending on the severity of depletion and repletion. Both serum ferritin and liver iron did not respond to changes in dietary iron. Another parameter which responded to repletion was EPP. Serum ferritin and liver iron did not respond to changes in dietary iron or was not sensitive to subclinical iron deficiency. The results indicate that change in Hb is more sensitive to detect the deficiency of iron. It was also observed that different parameters respond variably under different modes of depletion and repletion.

Animals↗

PubMed1997

Vitamin A requirements assessed by plasma response to supplementation during pregnancy.

Plasma vitamin A responses were examined in 30 low income pregnant women before and after supplementation with vitamin A. In the groups of women who had an initial (at < 20 weeks) plasma vitamin A of less than 30 micrograms/dl retinol, typical changes representing a peak at mid gestation and a significant decline at term were observed. Supplementation with vitamin A tablets equivalent to 1800 micrograms of retinol daily for 12 weeks was able to raise the plasma vitamin A content at term. On the other hand, those women who had an initial plasma vitamin A concentration of more than 30 micrograms/dl did not show any appreciable changes even with vitamin A supplementation. Consistent beneficial effects of supplementation on maternal and cord vitamin A and maternal hemoglobin and progesterone were noted in our previous studies only when the supplementation lasted for 12 weeks and not after 10 weeks. Using these data with dietary intake obtained from other studies, an attempt was made to estimate the requirements of vitamin A during pregnancy. The approximate requirement of 780 retinol equivalents (RE) obtained, is in agreement with earlier recommendations of FAO and Indian Council of Medical Research (ICMR) Expert Committees, but is higher than the recent ICMR recommendations.

Female↗

PubMed1996

Isolation of acute-phase proteins from plasma for determination of fractional synthesis rates by a stable isotope tracer technique.

Because of the unavailability of convenient tracer methods, there is no information on the kinetic changes responsible for the increased or decreased pool sizes of the acute-phase proteins (APPs) during the metabolic response to trauma and infections. We have developed a stable isotope tracer method to measure the synthesis rates of the APPs transferrin, haptoglobin, and alpha1-antitrypsin. The proteins were isolated from plasma by either direct or sequential immunoprecipitation and purified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. With the exception of haptoglobin, the major band of each protein and its standard ran to a position corresponding to its molecular mass. The major band of haptoglobin and its standard ran to a position corresponding to a molecular mass of slightly less than 44 kDa, which corresponds to the haptoglobin beta chain, molecular mass 42.5 kDa. To measure the fractional synthesis rates (FSRs) of these proteins, three children were infused with 2H3-leucine for 8 h, and the amount of 2H3-leucine incorporated into the proteins was measured by gas chromatography-mass spectrometry. The plateau isotopic enrichment of very low density lipoprotein-apoB-100-bound leucine was used to estimate the isotopic enrichment of the hepatic protein synthetic precursor pool. FSRs (%/day) of the proteins were haptoglobin, 50 +/- 8; transferrin, 19 +/- 1.1; and "alpha"1-antitrypsin, 10 +/- 1. 5.

Acute-Phase Proteins↗

PubMed1996

Isolation and characterization of monkey liver ferritin.

Monkey liver ferritin was isolated and purified along with human liver ferritin and their physicochemical and immunological characteristics were compared. The apparent molecular weight of monkey liver ferritin was estimated to be 430 kDa as against 450 kDa of human liver ferritin. Both ferritins appeared to be made up of a 22.5 kDa polypeptide under denaturing conditions and the proteins contained neutral sugar (wt/wt) of 2.0% (monkey) and 2.4% (human). By immunoblots both human and monkey liver ferritins showed appreciable cross-reactivity with the polyclonal antibodies raised against either proteins. Monkey liver ferritin, however, was not recognised by the human monoclonal antibody. The amino acid composition of both ferritins was more or less similar. Isoelectric focusing indicated that monkey liver ferritin showed microheterogeneity with three bands at pI 5.4, 5.5 and 5.6, whereas human liver ferritin showed a single band at pI 5.6 confirming the relative acidic nature of monkey liver ferritin.

Adult↗

PubMed1994

Fractional synthesis rates of retinol-binding protein, transthyretin, and a new peptide measured by stable isotope techniques in neonatal pigs.

Our objective was to develop a stable isotopic method to measure the synthesis rates of retinol-binding protein (RBP) and transthyretin (TTR). Both proteins were isolated from human and pig plasma by sequential immunoprecipitation and purified by SDS-polyacrylamide gel electrophoresis under denaturing conditions. Both human and pig anti-RBP precipitates contained a peptide (TTR2) that had a molecular mass that was similar but not identical to that of TTR subunit. The N-terminal amino acid sequence of porcine TTR2 was highly but not completely homologous with porcine TTR. Human TTR2 showed no homology with TTR but was completely homologous with an internal sequence of human fibrinogen alpha chain. To measure the fractional rates of synthesis (FRS) of these peptides, six infant pigs were infused with [2H3]leucine at a constant rate for 6 h, and the amount of [2H3]leucine incorporated into the proteins was measured by negative chemical ionization gas chromatography-mass spectrometry. The plateau isotope ratio of plasma very low density lipoprotein apoB-100-bound leucine was used to estimate the isotopic enrichment of hepatic protein synthetic precursor pool. The mean FRS (% h +/- S.E.) of TTR (1.97 +/- 0.13) and RBP (3.89 +/- 0.07) were significantly different. The FRS of TTR2 was low (0.31 +/- 0.19) relative to that of RBP and TTR. Thus, three different peptides with different turnover rates seem to be involved in the transport of retinol.

Amino Acid Sequence↗

PubMed1994

Induction of dietary iron deficiency in rhesus monkeys: sequential changes in serum ferritin and other biochemical indicators of iron status.

The usefulness of serum ferritin as a measure of subclinical stages of iron deficiency has been tested in monkeys by inducing a mild iron deficiency dietarily over a period of 12 months. Various biochemical indicators of iron status were measured periodically along with analysis of liver iron and iron staining of bone marrow samples obtained by biopsy, at the end of the experiment. A mild form of iron deficiency was confirmed by bone marrow staining for iron. Of all the biochemical indicators tested, significant decreases were seen in hemoglobin and hematocrit at the 11th and 10th months, respectively. These changes were consistent with the changes later found in bone marrow grading for iron. Serum ferritin concentration and liver iron concentration did not show any significant difference between the controls and iron-deficient monkeys. Thus, these results do not support the existence of a latent stage of iron deficiency. In the mild form of iron deficiency, the functional compartment, represented by bone marrow iron and hemoglobin, is sensitive to depletion even when there were no changes in storage compartment represented by liver iron and serum ferritin.

Anemia, Iron-Deficiency↗

PubMed1993

Assessment of vitamin A status in pregnant women as reflected by in vitro destruction of vitamin A by hemolysates and urinary ammonium nitrogen to creatinine ratio.

To investigate the significance of the lowered plasma vitamin A during the last few weeks of pregnancy, the capacity of erythrocyte lysates to destroy vitamin A in vitro and the alteration in ammonium nitrogen to creatinine ratio (Am N/Cr) in random urine samples was followed up at different gestational ages in women from low income groups. One group received no supplementation and the other received supplements of 1800 retinol equivalents (RE) and at most points the number of observations were not less than 12. In the unsupplemented women there was a significant increase in the capacity of erythrocytes to destroy vitamin A in vitro, which reflects an increased oxidative stress as compared to the supplemented group. While differences in mean Am N/Cr did not follow any consistent pattern, there was a strong association between lowered plasma vitamin A (< 35 micrograms/dl) and increased Am N/Cr ratio (> 0.5). This was true only when combined data of both groups were considered till 26 weeks of gestation and not beyond. As expected in supplemented women there was no significant fall in the plasma vitamin A during term. These data reveal that the lowered plasma vitamin A levels are suggestive of greater risk of hypovitaminosis A during pregnancy as indicated by the oxidative stress in erythrocytes.

Chi-Square Distribution↗

PubMed1993

A new model for producing vitamin A deficiency in rats.

To produce a rapid depletion of vitamin A, an experimental approach based on partial hepatectomy (60%) to remove stores and feeding a vitamin A deficient diet during recovery was tested in weanling and adult wistar rats. Plasma and liver vitamin A levels were determined at appropriate time points along with food intakes and body weights. Adult rats fed a deficient diet for a period of one month during regeneration, exhibited significantly lower values (mean +/- SE) of liver vitamin A (176 +/- 19 micrograms/g) compared to controls (256 +/- 41 micrograms/g) receiving vitamin A supplements. However, these levels are not in the deficient range and the plasma vitamin A levels were not altered. Therefore, adult animals were not considered a suitable model for such experiments. In similar experiments with weanling rats, sham-operated controls kept on a vitamin A-free diet showed a liver vitamin A concentration of 16 +/- 1.2 micrograms/g after six weeks. Hepatectomized animals kept on a similar diet showed 5.2 +/- 1.1 micrograms/g liver in contrast to those fed on a vitamin A supplemented diet (328 +/- 27 micrograms/g). Also, the plasma vitamin A of hepatectomized animals on a vitamin A-deficient diet was very low (4.3 +/- 1.5 micrograms/dl) as compared to that in either supplemented or sham-operated controls. Thus rapid deficiency of nutrients like vitamin A could be produced using a hepatectomy and regeneration model in weanling rats, which otherwise may take much longer time.

Animals↗

PubMed1991

Effect of vitamin A supplementation of plasma progesterone and estradiol levels during pregnancy.

The effect of vitamin A supplementation on plasma estrogen and progesterone were studied in pregnant women. While there was no change in the estrogen concentration, the mean increment in plasma progesterone in the supplemented group was significant when compared to the unsupplemented group. It is suggested that vitamin A supplementation to undernourished pregnant women may have beneficial effect on feto-placental function.

Diet↗