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L S Ramsammy

Publications and source records attributed to L S Ramsammy.

16 recordsLinked to original sources
PubMed1993

Biophysical and biochemical alterations of renal cortical membranes in diabetic rat.

The objective of this study was to determine whether streptozotocin-induced diabetes mellitus in the rat causes alterations in the lipid composition and fluidity of renal brush border membranes (BBM) and basolateral membranes (BLM). Compared to membranes of non-diabetic rats, BBM and BLM of diabetic rats contained 31% and 26%, respectively, less arachidonic acid and 36% and 46%, respectively, more linoleic acid esterfied in phospholipids. These changes were accompanied by a decrease in the average number of double bonds per mole of fatty acid, a measure of fatty acid unsaturation. In diabetic rats BLM had a higher total phospholipid/protein ratio (567 +/- 20 vs. 482 +/- 15 nmol/mg protein, P < 0.01), less cholesterol (369 +/- 30 vs. 512 +/- 34 nmol/mg protein, P < 0.01), more phosphatidylcholine (+72%) and less sphingomyelin (-22%) than did BBM. These differences were identical to those observed between BLM and BBM of non-diabetic rats. In control rats BLM was more fluid than BBM as assessed by the steady state fluorescence anisotrophy of diphenylhexatriene and by glycerol permeability. In diabetic rats the fluidity of BLM was not different from that of BBM as assessed by the steady state fluorescence anisotrophy of diphenylhexatriene whereas BLM was slightly more fluid than BBM as assessed by glycerol permeability. By both measures BLM and BBM from diabetic rats were significantly less fluid than BLM and BBM from control rats. Removal of proteins and cholesterol in sequence was accompanied by an increase in membrane fluidity in both groups. However, in no instance did the removal of proteins or cholesterol abolish the difference between the fluidity of diabetic membranes and that of control membranes. From these data we conclude that the reduction in fluidity of renal BLM and BBM in the diabetic rat is due to the change in the composition of fatty acids esterified in membrane phospholipids.

Animals↗
PubMed1993

Mechanism of decreased arachidonic acid in the renal cortex of rats with diabetes mellitus.

The purpose of this study was to investigate the roles of decreased synthesis and increased consumption in the depression of arachidonic acid levels in renal cortex and glomeruli of rats with streptozotocin-induced diabetes mellitus. In diabetic rats, arachidonic acid was depressed 33.2% in renal cortex, 47.4% in liver and 66.1% in heart compared to values of control rats. delta 6 Desaturase activity was depressed in renal cortex, liver and heart of diabetic rats to 53.3, 55.5 and 63.7%, respectively, of control values. delta 5 Desaturase activity was also depressed 43.7, 55.5 and 47.6% in renal cortex, liver and heart of diabetic rats, respectively. In other rats the activities of five enzymes involved in the synthesis and esterification of arachidonic acid were measured in renal cortex and in isolated glomeruli. Both tissues from diabetic rats showed depressed activities of delta 5 and delta 6 desaturases, increased activities of long-chain acyl-CoA synthetase and 1-acyl-sn-glycero-3-phosphocholine acyltransferase and no change in the activity of elongase as compared to those in control tissues. Malondialdehyde, an end product of lipid peroxidation, was lower in the renal cortex of diabetic rats than in control rats, whereas beta-oxidation of linoleic acid and arachidonic acid were similar in diabetic and in control rats. Basal and stimulated prostaglandin E2 synthesis were significantly higher in isolated glomeruli from diabetic rats compared to those in control rats. In isolated tubules, prostaglandin E2 synthesis was similarly low in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Acyl-CoA Dehydrogenase, Long-Chain↗
PubMed1989

Effect of gentamicin on phospholipid metabolism in cultured rabbit proximal tubular cells.

We examined the hypothesis that the accumulation of phospholipid in cells exposed to gentamicin is due to impaired degradation. Experiments were performed in rabbit proximal tubular cells grown in primary culture. Cells exposed to 10(-3) M gentamicin manifested myeloid body formation and a progressive increase in total phospholipid that by day 6 was 44% higher than that of control cells and reflected increases of phosphatidylinositol of 235%, phosphatidylcholine of 60%, phosphatidylethanolamine of 90%, and phosphatidylserine of 55% above control values. Gentamicin impaired the degradation of these phospholipids. The t1/2 of the phospholipid pool labeled with [3H]myoinositol increased 146% from 1.17 (control) to 2.88 days (gentamicin); the t1/2 of the [3H]choline pool increased 34% from 1.77 to 2.38 days; the t1/2 of the [3H]ethanolamine pool increased 57% from 3.14 to 4.93 days; the t1/2 of the [3H] serine pool increased 37% from 6.30 to 8.63 days. Exposure of cells to gentamicin for 2 days also stimulated increased incorporation of [3H]myoinositol (68%) and [3H]ethanolamine (59%) into phospholipid. The data are consistent with the hypothesis that gentamicin inhibits the activity of lysosomal phospholipases that results in the accumulation of phospholipid within the lysosome in the form of myeloid bodies. Increased phospholipid synthesis may represent a compensatory response to the impaired lysosomal degradation of phospholipid. We postulate that the preferential increase of phosphatidylinositol reflects the capacity of the polycationic gentamicin to interact electrostatically with the anionic phosphoinositides and inhibit their turnover.

Animals↗
PubMed1989

Polyaspartic acid protects against gentamicin nephrotoxicity in the rat.

Polyamino acids including polyaspartic acid (PAA) have been reported to provide protection against the development of aminoglycoside-induced nephrotoxicity in the rat as assessed by histopathology scoring. We sought to confirm and extend these observations by determining whether PAA also prevented functional and biochemical lesions of gentamicin-nephrotoxicity in an animal model studied extensively in our laboratory. Rats were given injections of: 1) 0.9% NaCl at 2.5 ml/kg b.wt. per day; 2) PAA (mol.wt. 15,000) at 500 mg/kg per day; 3) gentamicin at 100 mg/kg per day or 4) gentamicin at 100 mg/kg per day and PAA at 500 mg/kg per day for 6 days. Rats injected with gentamicin exhibited: 1) increased urinary excretion of the brush border membrane enzyme alanine aminopeptidase and the lysosomal enzyme N-acetyl-beta-d-glucosaminidase after the first injection; 2) increased total phospholipid and malondialdehyde but decreased catalase activity in the renal cortex; 3) elevation of serum creatinine and depression of creatinine clearance and 4) extensive proximal tubular cell necrosis all determined 24 hr after the last injection of gentamicin. Rats injected with gentamicin plus PAA also exhibited increased urinary excretion of alanine aminopeptidase not different in magnitude from that of rats injected with gentamicin alone, whereas N-acetyl-beta-d-glucosaminidase rose more slowly and returned to base line by day 4. Total renal cortical phospholipid was elevated to the same extent in the two groups. Malondialdehyde was not different from control and catalase activity was significantly less depressed in rats injected with gentamicin plus PAA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

The effect of gentamicin on the biophysical properties of phosphatidic acid liposomes is influenced by the O-C = O group of the lipid.

We previously reported that gentamicin binds to liposomes composed of anionic phospholipids and depresses glycerol permeability and raises the activation energy for glycerol permeation in these liposomes. We postulated that these changes in the glycerol permeability and in the activation energy (Ea) for glycerol permeation were due to hydrogen bonding between O-C = O groups in the hydrogen belt and one or more amino groups of gentamicin. To test this hypothesis, we examined the effects of gentamicin on the membrane surface potential, the glycerol permeability coefficient (p), the Ea for glycerol permeation, and the aggregation of liposomes composed of 1:1 phosphatidylcholine (PC) and phosphatidic acid with the acyl chains of phosphatidic acid in either an ester (PA) or an ether (PA*) linkage. Gentamicin depressed the membrane surface electrostatic potential, measured by the partitioning of methylene blue between the bulk solution and the liposomal membrane, to an equivalent degree in PC-PA and PC-PA* liposomes, which indicates that substitution of the ether for the ester linkage did not interfere with the electrostatic interaction between the cationic drug and the negatively charged phosphate head group. Gentamicin caused a temperature-dependent decrease of p and raised Ea for glycerol permeation from 17.7 +/- 0.3 to 21.6 +/- 0.4 kcal/mol in PC-PA liposomes but had little or no effect on these parameters in PC-PA* liposomes. In contrast, gentamicin induced a significantly greater degree of aggregation of PC-PA* liposomes compared to that of PC-PA liposomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical Phenomena↗
PubMed1988

Gentamicin inhibits agonist stimulation of the phosphatidylinositol cascade in primary cultures of rabbit proximal tubular cells and in rat renal cortex.

A growing body of evidence indicates that aminoglycoside antibiotics interact with phosphoinositides and this has led to the hypothesis that these drugs perturb the phosphatidylinositol (PI) cascade. To test this hypothesis we examined the effect of gentamicin on agonist stimulation of the PI cascade in primary culture of rabbit proximal tubular cells (RPTC) and in rat renal cortex. Parathyroid (PTH) (10(-6) M) stimulated a significant increase in total inositol phosphates, inositol monophosphate and inositol trisphosphate, but not inositol bisphosphate in RPTC with the peak effect at 2 min. This effect was completely inhibited in RPTC exposed to 10(-3) M gentamicin for 48 and 24 hr. In other experiments we demonstrated that angiotensin II, phenylephrine, bradykinin and arginine vasopressin (all at 10(-6) M) stimulated inositol trisphosphate generation in control RPTC but not in cells exposed to 10(-3) M gentamicin for 24 h. In contrast gentamicin did not block PTH-stimulation of cyclic AMP generation, which indicates that gentamicin did not prevent PTH from interacting with its plasma membrane receptor. PTH also stimulated redistribution of protein kinase C from the cytosolic to the membrane fraction of RPTC. This effect was completely abolished in RPTC exposed to 10(-3) M gentamicin for 2 days. PTH given i.p. to rats stimulated the redistribution of protein kinase C from the cytosolic to the membrane fraction of renal cortex. This effect was completely inhibited in rats injected with gentamicin, 100 mg/kg per day for 2 days. The

Animals↗
PubMed1987

Failure of inhibition of lipid peroxidation by vitamin E to protect against gentamicin nephrotoxicity in the rat.

We tested the hypothesis that accelerated lipid peroxidation, possibly at the level of the lysosome, is linked causally to the pathogenesis of aminoglycoside nephrotoxicity by investigating whether administration of vitamin E would inhibit lipid peroxidation and prevent or ameliorate gentamicin-induced proximal tubular cell injury. Five groups of rats were injected with either saline, vitamin E (600 mg/kg per day) for 6 days, gentamicin (100 mg/kg per day) for 6 days, vitamin E for 6 days plus gentamicin for 6 days or vitamin E for 12 days and gentamicin for the last 6 days. Gentamicin alone induced a 16% increase in renal cortical phospholipids; vitamin E had no significant effect on this change. Gentamicin alone caused accelerated lipid peroxidation evident by a doubling of renal cortical malondialdehyde to 1.23 nmol/mg protein, and a sharp decline of esterified polyunsaturated fatty acids, especially arachidonic acid which fell 43%. These changes were accompanied by depressions of superoxide dismutase, catalase, and total glutathione and a shift from reduced to oxidized glutathione. Concurrent treatment of rats with vitamin E plus gentamicin for 6 days had no significant effect on the gentamicin-induced alterations of malondialdehyde, superoxide dismutase, catalase or the glutathione cascade; however, the shift from polyunsaturated to saturated fatty acids was largely reversed. In rats pretreated with vitamin E for 6 days, gentamicin failed to raise renal cortical malondialdehyde above that of saline-treated rats. The changes in esterified fatty acids were prevented almost entirely, and there were no significant alterations from control of the glutathione cascade. The depressions of superoxide dismutase and of catalase, however, were not reversed. Vitamin E did not affect the amount of gentamicin accumulated in renal cortex nor did it prevent the gentamicin-induced rise of serum creatinine. Examination of renal cortex by light and electron microscopy revealed that vitamin E did not prevent or even reduce the severity of gentamicin-induced proximal tubular cell lesions and necrosis. These results confirm those we obtained in a previous study with the antioxidant diphenyl-phenylenediamine. The observation that inhibition of lipid peroxidation by two distinct antioxidants failed to prevent proximal tubular cell injury and renal dysfunction associated with gentamicin administration leads us to conclude that lipid peroxidation is a consequence and not a cause of gentamicin-induced nephrotoxicity.

Animals↗
PubMed1987

Induction of nephrotoxicity by high doses of gentamicin in diabetic rats.

Rats with streptozotocin-induced diabetes mellitus (DM) are resistant to aminoglycoside (AG) nephrotoxicity presumably because of defective transport and accumulation of drug by proximal tubular cells. To test this hypothesis we injected DM rats with saline or with gentamicin, 100, 200, and 400 mg/kg per day for 6 days, to determine if the renal cortical concentration of gentamicin could be raised to toxic levels. Nephrotoxicity was assessed by monitoring for evidence of accelerated lipid peroxidation in the renal cortex, for elevation of the serum creatinine concentration, and for evidence of proximal tubular cell injury and necrosis by light and electron microscopy. At 100 mg/kg per day renal cortical gentamicin was 454 +/- 85 micrograms/g. Except for an increase in renal cortical phospholipids these rats manifested no evidence of accelerated lipid peroxidation or elevation of serum creatinine. At 200 mg/kg per day renal cortical gentamicin rose to 636 +/- 20 micrograms/g. These rats manifested mild functional and morphological evidence of toxicity. At 400 mg/kg renal cortical gentamicin rose to 741 +/- 43 micrograms/g. These rats developed severe nephrotoxic injury as manifested by a marked increase of lipid peroxidation evident by an increase of malondialdehyde from a control level of 0.48 +/- 0.02 to 1.72 +/- 0.12 nmole/mg protein, a shift from unsaturated to saturated fatty acids esterified in renal cortical phospholipids, depression of superoxide dismutase and catalase, and a shift from reduced to oxidized glutathione. The serum creatinine rose from a baseline level of 0.24 +/- 0.01 to 0.46 +/- 0.05 mg/dl. Light and electron microscopy revealed enlarged lysosomes distended with typical myeloid bodies and extensive proximal tubular cell necrosis. These observations provide compelling evidence in support of the view that the resistance of DM rats to AG nephrotoxicity is causally linked to the low rate of drug uptake by renal proximal tubular cells. When the renal cortical concentration reaches a critical level, it elicits a pattern of toxic injury indistinguishable from that of nondiabetic rats. Thus, there is nothing inherent to the diabetic state that prevents AGs from causing their usual adverse effects on the metabolism of renal proximal tubular cells once they gain access in sufficient quantity into these cells.

Animals↗
PubMed1986

Effects of diphenyl-phenylenediamine on gentamicin-induced lipid peroxidation and toxicity in rat renal cortex.

The hypothesis that lipid peroxidation is linked causally to the pathogenesis of aminoglycoside nephrotoxicity was tested by determining whether administration of the antioxidant, diphenyl-phenylenediamine (DPPD) would inhibit lipid peroxidation and ameliorate gentamicin-induced proximal tubular cell injury. Rats were injected with saline, gentamicin or gentamicin plus DPPD for 4 days and were sacrificed 48 hr later. Gentamicin increased malondialdehyde in renal cortex from a control level of 0.65 +/- 0.04 to 1.01 +/- 0.03 nmol/mg of protein, P less than .01; it was reduced to 0.20 +/- 0.03 by DPPD, P less than .01 compared to control. Arachidonic acid comprised 27.6 +/- 0.5% of the fatty acid in renal cortical phospholipid of control rats. Gentamicin lowered arachidonic acid to 16.7 +/- 0.9%, P less than .01, and promoted a shift toward saturated fatty acids. DPPD reversed these changes. Gentamicin depressed catalase activity from a control value of 0.211 k/min to 0.154 +/- 0.008 k/min, P less than .01. DPPD depressed catalase further to 0.095 +/- 0.066 k/min, P less than .01. Total glutathione and reduced glutathione were depressed whereas the fraction of total glutathione in the oxidized state was augmented by gentamicin. These changes were prevented by DPPD. The renal cortical phospholipidosis induced by gentamicin was not altered by DPPD. The increased urinary excretions of alanine aminopeptidase and N-acetyl-beta-glucosaminidase induced by gentamicin were augmented further by DPPD. In DPPD rats serum creatinine (0.45 +/- 0.04 mg/dl) was higher (P less than .01) than that of gentamicin rats (0.35 +/- 0.01 mg/dl), which was higher (P less than .01) than that of control rats (0.26 +/- 0.01 gm/dl).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylglucosaminidase↗
PubMed1984

Molecular interactions in the hydrogen belts of membranes. Glucose-6-phosphatase, lysophosphatidylcholine, and cholesterol.

Microsomal glucose-6-phosphatase from rat liver is activated by phosphatidylcholine but inhibited by lysophosphatidylcholine. Inhibition occurs not by membrane lysis but in an intact bilayer; it is reversible; and it is overcome by addition of cholesterol but not if the cholesterol-hydroxyl group is blocked. An analog of lysophosphatidylcholine deprived of hydrogen bonding sites, 1-ether-2- deoxylysophosphatidylcholine , is a partial activator, and its effect on the enzyme in a phosphatidylcholine bilayer is not modulated by cholesterol. It appears to be one of the functions of cholesterol to buffer the lysophospholipids in membranes by complexing with them through hydrogen bonding in the hydrogen belt region. Lysophosphatidylcholine/cholesterol association is favored over phosphatidylcholine/cholesterol association.

Animals↗
PubMed1984

Interactions in the hydrogen belts of membranes: cholesterol leaving phosphatidylcholine bilayers.

Cholesterol transfer from sonicated liposomes of phosphatidylcholine containing 10 or 30 mole percent cholesterol was measured with erythrocytes as acceptor. The activation energies of the (rate-limiting) bilayer-cholesterol dissociation were determined. In parallel experiments, phosphatidylcholine was replaced by an analog lacking the carbonyl oxygens, diether-phosphatidylcholine. The activation energies for dissociation of cholesterol from this phospholipid were three Cal/mole smaller than those for cholesterol-phosphatidylcholine dissociation, at both concentrations of cholesterol. These results demonstrate the involvement of the carbonyl oxygen in cholesterol-phospholipid bonding and support the hypothesis of lipid-lipid hydrogen bonding in the hydrogen belts of membranes.

Animals↗
PubMed1983

Association of cholesterol with lysophosphatidylcholine.

With equimolar cholesterol, lysophosphatidylcholine (lysoPC) or 1-ether-2-deoxylyso-phosphatidylcholine (etherdeoxylysoPC) form unilamellar vesicles of identical dimensions. 13C-NMR spectra of such vesicles are interpreted on the premise that suppression of a signal by broadening (i.e. decrease of T*2 relaxation time) indicates a decrease of motion of the carbon atom relative to its surroundings. The signals for sn-glycerol C-1 and C-2 are completely suppressed in the lysoPC-cholesterol vesicles. In contrast, in the vesicles containing etherdeoxylysoPC, all three glycerol carbon signals make their appearance, with the T*2 of C-2 approaching the T*2 in the monomolecularly dissolved lysolipid. This result argues for lipid-lipid complexing in the "hydrogen belts' of the lysoPC-cholesterol bilayer, specifically, for hydrogen bonding involving the hydroxyl and carbonyl groups of lysoPC and the hydroxyl of cholesterol.

Cholesterol↗
PubMed1982

Lysophosphatidylcholine-cholesterol complex.

Lysophosphatidylcholine (lysoPC) and cholesterol at 1:1 molar ratio form multilamellar and, on sonication, unilamellar liposomes in water. Calorimetric scannings of varied mixtures in water give evidence for the existence of a 1:1 complex of the lipids. The permeability of the 1:1 bilayer against glycerol, at 22-42 degrees C, is lower than that of phosphatidylcholine-cholesterol bilayers; the energy of activation of permeation is 73% higher. This implies a low groundstate of the entropy of activation of permeation. Unilamellar lysoPC-cholesterol 1:1 liposomes, isolated by gel exclusion chromatography, are able to incorporate no more than 8 to 10% excess lysoPC and no additional cholesterol at all. Their physical parameters such a outer radius (14.8 nm) and bilayer thickness (4.2 nm) are between those reported for phosphatidylcholine vesicles and phosphatidylcholine-cholesterol vesicles. The outside-inside distribution of lysoPC in the small vesicles (determined by 31P-NMR) is 2.0. A comparison of 13C-NMR spectra of lysoPC (in 2H2O) and lysoPC-cholesterol vesicles shows that in the vesicles the signals for the carboxyl carbon of lysoPC as well as those for carbons 1 and 2 (and, partly, 3) of motional restriction in this region of the molecule. The low groundstate of the entropy of activation of permeation, and the immobilization of the glycerol moiety of the lysoPC, argue for a high degree of structural organization in the "hydrogen belt" regions of the lysoPC-cholesterol bilayer, and for lipid-lipid complexing via hydrogen bonding in these regions.

Calorimetry↗