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Biomedical subjects

S N Mathur

Publications and source records attributed to S N Mathur.

At least 73 records · Page 4Linked to original sources
PubMed1983

Phospholipid fatty acid modification of rat liver microsomes affects acylcoenzyme A:cholesterol acyltransferase activity.

The effect of phospholipid fatty acyl composition on the activity of acylcoenzyme A:cholesterol acyltransferase was investigated in rat liver microsomes. Specific phosphatidylcholine replacements were produced by incubating the microsomes with liposomes and bovine liver phospholipid-exchange protein. Although the fatty acid composition of the microsomes was modified appreciably, there was no change in the microsomal phospholipid or cholesterol content. As compared to microsomes enriched for 2 h with dioleoylphosphatidylcholine, those enriched with dipalmitoylphosphatidylcholine exhibited 30-45% less acyl-CoA:cholesterol acyltransferase activity. Enrichment with 1-palmitoyl-2-linoleoylphosphatidylcholine increased acyl-CoA:cholesterol acyltransferase activity by 20%. By contrast, dilinoleoylphosphatidylcholine abolished microsomal acyl-CoA:cholesterol acyltransferase activity almost completely. Addition of cofactors that stimulated microsomal lipid peroxidation inhibited acyl-CoA:cholesterol acyltransferase activity by only 10%, however, and did not increase the inhibition produced by submaximal amounts of dilinoleoylphosphatidylcholine. Certain of the phosphatidylcholine replacements produced changes in palmitoyl-CoA hydrolase, NADPH-dependent lipid peroxidase, glucose-6-phosphatase and UDPglucuronyl transferase activities, but they did not closely correlate with the alterations in acyl-CoA:cholesterol acyltransferase activity. Electron spin resonance measurements with the 5-nitroxystearate probe indicated that microsomal lipid ordering was reduced to a roughly similar extent by dioleoyl- or by dilinoleoylphosphatidylcholine enrichment. Since these enrichments produce widely different effects on acyl-CoA:cholesterol acyltransferase activity, changes in bulk membrane lipid fluidity cannot be the only factor responsible for phospholipid fatty acid compositional effect on acyl-CoA:cholesterol acyltransferase. The present results are more consistent with a modulation resulting from either changes in the lipid microenvironment of acyl-CoA:cholesterol acyltransferase or a direct interaction between specific phosphatidylcholine fatty acyl groups and acyl-CoA:cholesterol acyltransferase.

Acyl Coenzyme A↗
PubMed1983

Regulation of acyl CoA:cholesterol acyltransferase by 25-hydroxycholesterol in rabbit intestinal microsomes and absorptive cells.

The regulation of rabbit intestinal acyl CoA:cholesterol acyltransferase (ACAT) by 25-hydroxycholesterol was studied. 25-Hydroxycholesterol significantly increased jejunal microsomal ACAT activity. The stimulation of ACAT activity by 25-hydroxycholesterol was inversely related to microsomal cholesterol content. In enterocytes, 25-hydroxycholesterol stimulated cholesteryl ester synthesis 6-fold. The esterification of cholesterol, taken up by enterocytes from liposomes or bile salt micelles, was increased by 25-hydroxycholesterol. This, however, did not affect the rate of uptake of cholesterol by the cells. In intestinal cells from rabbits fed cholesterol, the effect of 25-hydroxycholesterol on cholesteryl ester synthesis was 50% of that in cells prepared from animals fed no cholesterol. 25-Hydroxycholesterol stimulated the esterification of newly synthesized cholesterol. As new free cholesterol increased in enterocytes, 25-hydroxycholesterol lost its effect. Despite large amounts of newly synthesized cholesterol, oleic acid incorporation into cholesteryl ester was not increased. We conclude that 25-hydroxycholesterol increases intestinal ACAT activity. The effect of 25-hydroxycholesterol on ACAT is dependent upon the availability of cholesterol to the enzyme. At cholesterol concentrations below saturation, the oxygenated sterol has a stimulatory effect. If ACAT is saturated, 25-hydroxycholesterol has no effect. ACAT catalyzes the esterification of two separate pools of cholesterol within the enterocyte, i.e., newly synthesized cholesterol and membrane cholesterol. 25-Hydroxycholesterol increases the esterification rate of cholesterol in both pools.

Acyltransferases↗
PubMed1983

beta-sitosterol: esterification by intestinal acylcoenzyme A: cholesterol acyltransferase (ACAT) and its effect on cholesterol esterification.

Rabbits were fed either 10% coconut oil, 10% coconut oil and 1% beta-sitosterol, 10% coconut oil and 1% cholesterol, or 10% coconut oil and 1% beta-sitosterol plus 1% cholesterol for 4 weeks. Microsomal membranes from intestines of animals fed the 1% beta-sitosterol diet had 48% less cholesterol and were enriched twofold in beta-sitosterol compared to membranes from animals fed the coconut oil diet alone. Acylcoenzyme A:cholesterol acyltransferase (ACAT) activity in jejunum and ileum was decreased significantly in animals fed the plant sterol alone. In membranes from animals fed 1% beta-sitosterol and 1% cholesterol, beta-sitosterol content increased 50% whereas cholesterol was modestly decreased compared to their controls fed only cholesterol. Intestinal ACAT was unchanged in the animals fed both sterols when compared to their controls. beta-Sitosterol esterification was determined by incubating intestinal microsomal membranes with either [(14)C]beta-sitosterol-albumin emulsion or [(14)C]beta-sitosterol:dipalmitoyl phosphatidylcholine (DPPC) liposomes to radiolabel the endogenous sterol pool. Oleoyl-CoA was then added. The CoA-dependent esterification rate of beta-sitosterol was very slow compared to that of cholesterol using both techniques. An increased amount of endogenous microsomal beta-sitosterol, which occurs in animals fed 1% beta-sitosterol, did not interfere with the stimulation of ACAT activity secondary to cholesterol enrichment of the membranes. Enriching microsomal membranes three- to five-fold with beta-sitosterol did not affect ACAT activity. Freshly isolated intestinal cells were incubated for 1 hour with [(3)H]oleic acid and beta-sitosterol:DPPC or 25-hydroxycholesterol:DPPC. Incorporation of oleic acid into cholesteryl esters did not change in the presence of beta-sitosterol but increased fourfold after the addition of 25-hydroxycholesterol. We conclude that the CoA-dependent esterification rate of cholesterol is at least 60 times greater than that of beta-sitosterol. Membrane beta-sitosterol does not interfere with nor compete with cholesterol esterification. Inadequate esterification of this plant sterol may play a role in the poor absorption of beta-sitosterol by the gut.-Field, F. J., and S. N. Mathur. beta-Sitosterol: esterification by intestinal acylcoenzyme A:cholesterol acyltransferase (ACAT) and its effect on cholesterol esterification.

Acyl Coenzyme A↗
PubMed1982

Effect of liposome composition on the activity of detergent-solubilized acylcoenzyme A: cholesterol acyltransferase.

Acylcoenzyme A:cholesterol acyltransferase (ACAT) was solubilized from Ehrlich ascites cell microsomes with Triton X-100. After removal of the detergent, ACAT activity per mg protein was reduced by 50 to 65% as compared with untreated microsomes. When this microsomal extract was combined with liposomes composed of cholesterol and egg phosphatidylcholine, the ACAT activity increased 5.4- to 6.7-fold. Under these conditions sucrose density gradient centrifugation indicated that more than 50% of the added lipid was incorporated into vesicles having the same density as the ACAT activity, suggesting the formation of a complex. ACAT activity increased 2.9-fold when the phosphatidylcholine content of the liposomes was raised from 0.5 to 5.0 mumol/mg microsomal protein. By contrast, the ACAT activity increased only 42% when the cholesterol content of the liposomes was raised from 0.17 to 0.57 mumol/mg microsomal protein. Addition of phosphatidylethanolamine to the liposomes produced little change in ACAT activity, whereas the activity was reduced by 25 and 50%, respectively, when sphingomyelin or phosphatidylserine was added. ACAT activity was five times higher when the liposomes were prepared from dioleoylphosphatidylcholine than from saturated phosphatidylcholines, including hydrogenated egg yolk, dimyristoyl or dipalmitoyl phosphatidylcholine. Likewise, the ACAT activity with liposomes made from soybean or egg yolk phosphatidylcholine was almost 3.5-fold greater than with those prepared from the saturated phosphatidylcholines. These results are consistent with the view that the activity of ACAT can be modified by changes in the composition of the membrane lipids with which the enzyme is associated.

Acyltransferases↗
PubMed1981

Effect of fatty acid saturation on NADPH-dependent lipid peroxidation in rat liver microsomes.

NADPH-dependent lipid peroxidation in liver microsomes, as measured by malondialdehyde formation, decreased by 90% when rats were fed a diet containing 16% coconut oil. This reduction occurred within 1 to 3 days after the rats were placed on this highly saturated diet. The decrease in peroxidation activity was associated with a reduction in the polyunsaturated fatty acid content of the microsomal phospholipids, particularly arachidonic acid. When the rats were transferred to a highly polyunsaturated diet containing 16% sunflower seed oil, microsomal lipid peroxidation and arachidonic acid content were restored to normal values within 10 days. Arachidonic acid contained in the microsomal choline and ethanolamine phosphoglycerides was the main substrate for peroxidation. Addition of diarachidonyl phosphatidylcholine, but not free arachidonic acid, to the assay system restored peroxidation activity in tahe micraosomes prepared from ahe livers of the rats fed saturated fat. Likewise, prior incubation of these microsomes with a mixture of phospholipid exchange protein and liposomes containing diarachidonyl phosphatidylcholine restored peroxidation activity. These results indicate that diets rich in saturated fat reduce microsomal lipid peroxidation by decreasing the availability of polyunsaturated fatty acids in substrate phospholipids.

Adenosine Diphosphate↗
PubMed1981

Hepatic acylcoenzyme A: cholesterol acyltransferase activity during diet-induced hypercholesterolemia in cynomolgus monkeys.

Acylcoenzyme A: cholesterol acyltransferase (ACAT) activity was studied in hepatic microsomes of cynomolgus monkeys fed either commercial chow or an atherogenic diet of high cholesterol and saturated fat content. ACAT activity (pmol/min per mg protein) was 35 in liver microsomes from control monkeys, and 142 and 161 at 10 and 100 days, respectively, after starting the high cholesterol diet. The cholesterol-fed monkeys had about 1.5-fold increase in cholesterol content of hepatic microsome was compared to control monkeys (94 nmol/mg protein in controls versus 142 nmol/mg protein in the cholesterol fed group). There was no difference between the two groups in microsomal fatty acids in saturated, monoenoic, or polyenoic acid classes. However, the cholesterol-fed monkeys had relatively lower amounts of linoleic acid and higher amounts of arachidonic acid in the microsomes. To determine whether the increased microsomal cholesterol content might be responsible for the increase in ACAT activity, liver microsomes from control monkeys were incubated for 15-120 min with liposomes composed of cholesterol and dipalmitoyl phosphatidylcholine, 2:1 (mol/mol). The microsomal cholesterol content increased from 90 to 128 nmol/mg protein as the incubation progressed. There was a corresponding increase in ACAT activity from 80 to 240 pml/min per mg protein. This observation is consistent with the view that the high hepatic ACAT activity in the cholesterol-fed monkeys is due to the larger amount of cholesterol contained in the microsomes. The increase in hepatic ACAT activity occurs soon after cholesterol feeding is started; this response may be involved in the production of cholesteryl ester-rich lipoprotein by the liver, and thereby may be related to the atherogenic process in these primates.

Acyltransferases↗
PubMed1980

Chest injury.

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Adolescent↗
PubMed1978

Effects of dietary fat composition on the Ehrlich ascites tumor fluid lipoproteins.

Mice bearing the Ehrlich ascites tumor were fed diets rich in either coconut oil or sunflower oil. From 20 to 40% less lipid was present in the ascites tumor fluid when the mice were fed the sunflower oil diet. This was associated with a reduction in the amount of very low density lipoproteins (VLDL) and high density lipoproteins (HDL), the main lipoprotein fractions present in the ascites tumor fluid. The VLDL from the mice fed sunflower oil contained more cholesteryl esters and a lower free to esterified cholesterol ratio than those from the mice fed coconut oil. Very little change occurred in the composition of the HDL. All of the lipids contained in both lipoprotein fractions exhibited appreciable differences in fatty acid composition. Much more monoenoic and less polyenoic fatty acid were present in the lipids from the mice fed the coconut oil diet, but no appreciable change in saturated fatty acid content occurred. Similar changes in fatty acid composition were observed in the blood plasma of the tumor-bearing mice. There was no qualitative difference in the apolipoprotein patterns of either the ascites fluid VLDL or HDL. Pyrene fluorescence studies indicated that the fluidity of the VLDL was increased when the mice were fed the sunflower oil diets. No difference in HDL fluidity, however, was observed by this technique. These results indicate that the amount, composition, and physical properties of certain of the lipoproteins contained in the ascites tumor fluid can be modified by changing the composition of the dietary fat fed to mice bearing the Ehrlich ascites tumor.

Animals↗
PubMed1977

Tinidazole and metronidazole in the treatment of amoebic liver abscess.

Tinidazole, a new drug effective against E histolytica, was studied in patients with amoebic liver abscess proved by aspiration of pus. A preliminary open evaluation in fourteen patients provided a cure in all cases. A subsequent comparative study against metronidazole in another twenty-two patients led to a cure in all eleven patients treated with tinidazole and in ten out of eleven patients treated with metronidazole. The response was faster in patients treated with tinidazole. Tinidazole was totally free from side-effects. Tinidazole is a noteworthy addition to anti-amoebic therapy.

Adult↗
PubMed1976

Studies on the relative biopotencies and intestinal absorption of different apo-beta-carotenoids in rats and chickens.

1. The biopotencies relative to beta-carotene of several apocarotenoids, such as 8'-, 10'- and 12'-apo-beta-carotenal and methyl 8'-apo-beta-carotenoate, were investigated in rats, on a molar basis, by both curative-growth assay and liver-storage tests. 2. In the curative-growth assays, on a molar basis the biopotencies of 8'-, 10'- and 12'-apo-beta-carotenal and methyl 8'-apo-beta-carotenoate were 72, 78, 72 and 53% respectively, whereas on a weight basis the corresponding values were 93, 111, 111 and 63%, with respect to beta-carotene taken as 100%. In terms of yield of vitamin A, these values were much lower in the liver-storage tests. 3. When 8'-apo-beta-carotenal was fed, the unchanged aldehyde together with small amounts of the corresponding alcohol and larger proportions of the acid rapidly appeared in the tissues of both rats and chickens. The 8'-apocarotenol, 8'-apocarotenoic acid and its methyl ester were absorbed unchanged. The free acid disappeared most rapidly from the tissues, but its methyl ester persisted in the tissues longest. 4. On the basis of these observations it is suggested that most of an apocarotenal is oxidized to the corresponding acid, which, in turn, is mostly degraded to retinoic acid, with small proportions of it being attacked by the dioxygenase system giving retinal.

Animals↗
PubMed1976

Characterization of the Ehrlich ascites tumor plasma lipoproteins.

1. The lipoproteins of the Ehrlich ascites tumor plasma were separated into 3 distinct fractions, very low density, low density and high density lipoproteins by preparative ultracentrifugation combined with agarose column chromatography. 2. High density lipoproteins contained 74% of the total protein in the lipoproteins. By contrast, most of the lipids were present in the very low density lipoprotein fraction. 3. The fatty acid compositions of the cholesteryl esters were appreciably different in the very low, low and high density lipoproteins, whereas phospholipid and triacylglycerol fatty acid compositions were quite similar in the 3 lipoprotein fractions. 4. Very low and high density apoprotein electrophoretic patterns on sodium dodecyl sulfate-acrylamide gels were similar to those observed in the corresponding lipoprotein fractions obtained from other mammalian species. The low density fraction, however, contained 7 apoprotein bands, and 32% of the low density apoprotein was soluble in tetramethyl urea. 5. The average molecular weights as determined by analytical ultracentrifugation were 2-10(7) (very low density), 6-10(6) (low density) and 4.4-10(5) (high density).

Animals↗
PubMed1976

Studies on the metabolism of beta-carotene and apo-beta-carotenoids in rats and chickens.

(1)The relative abilities of the various fractions of rat and chicken liver to oxidize and reduce retinal and 8'-and 12'-apo-beta-carotenal were investigatjed and it has been shown that, while retinal is exclusely oxidized by the soluble fraction, the apocarotenals are mostly oxidized by the particulate fractions of the homogenate. (2) Addition of NAD+ or NADP+ markedly activated the oxidation of the apocarotenals, but not of retinal by the particulate fractions. (3) Considerable amounts of retinal and 8'-, 10'- and 12'-apo-beta-carotenal were isolated from the intestine of chickens fed beta-carotene and these apocarotenoids were conclusively identified. (4) Significant amounts of 8'-, 10'- and 12'-apo-beta-carotenoic acids were isolated from the intestine of rats given 8'-apo-beta-carotenal and these apocarotenoic acids were also conclusively identified. (5) In the light of these observations it is suggested that during conversion to vitamin A, the beta-carotene molecule is simultaneously attacked by the dioxygenase at several double bonds, the primary attack being at the central double bond and a tentative scheme for the mechanism of conversion is proposed.

Animals↗
PubMed1976

Congestive heart failure in two patients of lepromatous leprosy.

Two cases of lepromatous leprosy are presented with heart disease, one with cardiomegaly and the other with ischaemic heart disease. It is very difficult to say whether heart disease was due to any other cause associated with leprosy or due to leprous affection of myocardium. As there are no references in the literature regarding these, two cases are presented as problem cases.

Adult↗