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Biomedical subjects

R Chanderbhan

Publications and source records attributed to R Chanderbhan.

At least 19 recordsLinked to original sources
PubMed1996

Effect of sesame oil on serum and liver lipid profiles in the rat.

In our previous study (Satchithanandam, S., Reicks, M., Calvert, R.J., Cassidy, M.M. and Kritchevsky, D. (1993) J. Nutr. 123, 1852-1858), we found that the absorption of lymphatic cholesterol by rats fed diets containing 24% sesame oil was about 50% less than that by rats fed the control diet containing no sesame oil. The effect of sesame oil on serum cholesterol levels was not determined at that time. In the present study, three groups of male Wistar rats (75-100 g) were fed a control diet or a diet containing 12 or 24% sesame oil. To increase serum cholesterol levels, 1% cholesterol and 0.5% cholic acid were added to each diet. After rats were fed for 4 weeks, total cholesterol, LDL-cholesterol, HDL-cholesterol, and triglyceride levels were measured in the serum. Liver weight and cholesterol and triglyceride levels were determined. Liver cholesterol levels were significantly lower in rats fed the 24% sesame oil diet, and the liver lipid level was significantly higher in the 24% sesame oil-fed group, compared with levels in the group fed the control diet. Liver weights and esterified cholesterol and liver triglyceride levels were not significantly different among the groups. Levels of serum total cholesterol and LDL-cholesterol were significantly lower in rats fed the 24% sesame oil diet, compared with levels in the control group. Serum triglyceride and HDL-cholesterol levels did not differ significantly among the groups. The mechanism by which a diet containing 24% sesame oil reduces levels of serum and liver cholesterol, liver LDL cholesterol, and liver lipids is not known. However, the high degree of unsaturation (85%) of sesame oil and the presence of linoleic acid may be important factors.

Animals↗
PubMed1992

Prevention of post-ischemic brain lipid conjugated diene production and neurological injury by hydroxyethyl starch-conjugated deferoxamine.

Hydroxyethyl starch conjugated deferoxamine (DFO) was administered to rats following resuscitation from 6.5 min cardiac arrest (CA) in an attempt to prevent the iron-catalyzed production of oxygen free radicals which may lead to neurologic injury and ultimately death following restoration of spontaneous circulation (ROSC). Brain conjugated dienes were analyzed spectrophotometrically 4 and 24 hr following ROSC, and were found to be significantly elevated when compared to non-ischemic controls. Hydroxyethyl starch-DFO treated rats demonstrated no increased conjugated diene production at either period. Neurologic injury was significantly less in drug treated rats surviving 24 or 72 hours when compared to controls. While mortality was similar in drug treated or control rats for the first 24 hours following ROSC, delayed mortality (days 1-10) was significantly less in drug treated animals, presumably as a result of neurologic protection afforded by post-ischemic drug administration. Administration of DFO conjugated to hydroxyethyl starch appears to modulate the neurologic injury which occurs during brain ischemia and reperfusion.

Alkenes↗
PubMed1988

Sterol carrier protein2-like activity in rat intestine.

A sterol carrier protein2 (SCP2)-like activity has been demonstrated in rat intestinal mucosal homogenates and in isolated intestinal cells from both crypt and villus zones. The results indicate the presence of a protein with similar molecular weight and antigenicity to that of authentic SCP2 purified from rat liver cytosol. Like liver SCP2, mucosal cytosol stimulates pregnenolone production in rat adrenal mitochondria and acyl coenzyme A:cholesterol acyltransferase activity of liver and mucosal microsomes. The distribution of SCP2-like activity as determined by radioimmunoassay indicates high levels in mitochondria and cytosol and relatively lower levels in microsomes and in brush-border membranes. The widespread distribution of SCP2-like protein in the intestine is consistent with potential transfer functions in all phases of cholesterol processing.

Animals↗
PubMed1985

Regulation of bile-acid synthesis. Role of sterol carrier protein 2 in the biosynthesis of 7 alpha-hydroxycholesterol.

Sterol carrier protein2 (SCP2) is known to stimulate utilization of cholesterol in enzymic reactions in which cholesterol is the substrate. Substantial recent experimental evidence indicates that SCP2: activates enzymic conversion of intermediates between lanosterol and cholesterol; stimulates the microsomal conversion of cholesterol into cholesterol ester in rat liver; and enhances mitochondrial utilization of cholesterol for pregnenolone formation in the adrenals. The conversion of cholesterol into 7 alpha-hydroxycholesterol is the rate-limiting step in bile-acid synthesis. We therefore investigated the effect of SCP2 on this physiologically critical reaction by using a gas-chromatography-mass-spectrometry procedure that measures the mass of 7 alpha-hydroxycholesterol formed. The results show that SCP2 enhances 7 alpha-hydroxycholesterol formation by rat liver microsomes (microsomal fractions), utilizing either endogenous membrane cholesterol, cholesterol supplied exogenously in serum or in the form of cholesterol/phospholipid liposomes. Microsomes immunotitrated with anti-SCP2 antibody exhibited considerably less capacity to synthesize 7 alpha-hydroxycholesterol, which was restored to control levels on addition of purified SCP2. These data are consistent with the suggestion that SCP2 may be of physiological significance in the overall metabolism of cholesterol.

Animals↗
PubMed1985

Phospholipids, sterol carrier protein2 and adrenal steroidogenesis.

Rat adrenocortical cells and preparations of plasma membrane and mitochondria have been employed to assess the effects of phospholipids and of sterol carrier protein2 (SCP2) on specific aspects of adrenal steroidogenesis. With intact cells, liposomal dispersions of cardiolipin caused significant stimulation of corticosterone output, while preparations of phosphatidylcholine, phosphatidylinositol, or the 4'-phosphate and the 4',5'-diphosphate derivatives of phosphatidylinositol were without effect. With the adrenal plasma membrane preparation, none of the added phospholipids affected either sodium fluoride or ACTH-responsive adenylate cyclase activity. With intact mitochondria, only cardiolipin, among the various phospholipids, tested, caused a concentration-dependent stimulation of pregnenolone production. However, even at the highest concentration of cardiolipin tested (500 microM), the stimulatory effect was only half that observed with 0.7 microM SCP2, and the two effectors were not synergistic. SCP2 caused a redistribution of cholesterol from mitochondrial outer to inner membranes, while cardiolipin, which is an activator of cytochrome P-450scc, had no effect on distribution of mitochondrial membrane cholesterol.

Adrenal Cortex↗
PubMed1985

Sterol carrier protein 2 and fatty acid-binding protein. Separate and distinct physiological functions.

Sterol carrier protein 2 (SCP-2) participates in the microsomal conversion of lanosterol to cholesterol, in the conversion of cholesterol to cholesterol ester, and in intracellular cholesterol transfers. The stoichiometry of binding between cholesterol and SCP-2 is 1:1. However, reports have appeared attributing sterol carrier protein activity to a protein preparation identical to hepatic fatty acid-binding protein (FABP). Therefore, the present investigation was conducted to compare homogeneous preparations of FABP and SCP-2 with respect to their capacities to participate as carrier proteins in reactions involving sterols or fatty acids. The results show that SCP-2 and FABP have separate and distinct physiological functions, with SCP-2 participating in reactions involving sterols and FABP participating in reactions involving fatty acid binding and/or transport. Furthermore, there is no overlap in substrate specificities, i.e. FABP does not possess sterol carrier protein activity and SCP-2 does not specifically bind or transport fatty acid. As long as only small quantities of organic solvent (1.6 volume %) were used for substrate addition, the sterol delta 7-reductase liver microsomal assay for SCP-2 correlated well with the physiologically relevant assays employed in the reconstituted adrenal system. The sterol carrier protein activity previously attributed to rat hepatic FABP is explained by the presence of significant quantities of propylene glycol (15 volume %) or Tween 80 in the assay procedure.

Adrenal Glands↗
PubMed1985

Sterol carrier and lipid transfer proteins.

The discovery of the sterol carrier and lipid transfer proteins was largely a result of the findings that cells contained cytosolic factors which were required either for the microsomal synthesis of cholesterol or which could accelerate the transfer or exchange of phospholipids between membrane preparations. There are two sterol carrier proteins present in rat liver cytosol. Sterol carrier protein 1 (SCP1) (Mr 47 000) participates in the microsomal conversion of squalene to lanosterol, and sterol carrier protein 2 (SCP2) (Mr 13 500) participates in the microsomal conversion of lanosterol to cholesterol. In addition SCP2 also markedly stimulates the esterification of cholesterol by rat liver microsomes, as well as the conversion of cholesterol to 7 alpha-hydroxycholesterol - the major regulatory step in bile acid formation. Also, SCP2 is required for the intracellular transfer of cholesterol from adrenal cytoplasmic lipid inclusion droplets to mitochondria for steroid hormone production, as well as cholesterol transfer from the outer to the inner mitochondrial membrane. SCP2 is identical to the non-specific phospholipid exchange protein. While SCP2 is capable of phospholipid exchange between artificial donors/acceptors, e.g. liposomes and microsomes, it does not enhance the release of lipids other than unesterified cholesterol from natural donors/acceptors, e.g. adrenal lipid inclusion droplets, and will not enhance exchange of labeled phosphatidylcholine between lipid droplets and mitochondria. Careful comparison of SCP2 and fatty acid binding protein (FABP) using six different assay procedures demonstrates separate and distinct physiological functions for each protein, with SCP2 participating in reactions involving sterols and FABP participating in reactions involving fatty acid binding and/or transport. Furthermore, there is no overlap in substrate specificities, i.e. FABP does not possess sterol carrier protein activity and SCP2 does not specifically bind or transport fatty acid. The results described in the present review support the concept that intracellular lipid transfer is a highly specific process, far more substrate-specific than suggested by the earlier studies conducted using liposomal techniques.

Amino Acids↗
PubMed1985

Adrenal cholesterol esters as substrate source for steroidogenesis.

Adrenocortical cells obtained from tissues of unstimulated rats and which contained a high concentration of endogenous esterified cholesterol, were labeled in vitro with unesterified [4-14C]cholesterol, or incubated in the presence of [2-14C]acetate or lipoprotein [4-14C]cholesterol oleate (LP-CE). Incubations were conducted in the absence and presence of ACTH, and changes in the specific radioactivity (SA) of the secreted corticosterone were used to assess the primary sources of cholesterol substrate used for steroidogenesis. Incubations of cells containing [4-14C]cholesterol with ACTH resulted in a marked increase in the output of corticosterone mass, but not of labeled corticosterone. Thus, the SA of corticosterone when cells were incubated with ACTH was only 6.5% of that obtained from cells incubated in the absence of ACTH. During incubations with [2-14C]acetate, the ACTH-induced increase in the output of corticosterone mass was not associated with increased isotope output, and the SA of corticosterone was only 15% of that in control incubations. This dilution was not altered in cells isolated from adrenals of rats treated with 4-aminopyrazalopyrimidine (4-APP), in which increased cholesterogenesis was demonstrable. The uptake, and hydrolysis of LP-CE, and formation of labeled corticosterone was lipoprotein concentration dependent, and was not influenced by ACTH. However, in the presence of ACTH, the SA of the secreted corticosterone was only 4-8% of that in unstimulated cells. The consistent dilution of the SA of corticosterone in ACTH-treated cells in all studies suggest that the large stores of cytoplasmic cholesterol esters in these cells may normally serve as a primary source of the immediate precursor sterol used for steroidogenesis.

Acetates↗
PubMed1984

Sterol carrier protein2 (SCP2)-mediated transfer of cholesterol to mitochondrial inner membranes.

Rats treated with cycloheximide accumulate cholesterol in the adrenal mitochondria. This cholesterol is largely associated with the mitochondrial outer membrane. The addition of homogeneous sterol carrier protein2 (SCP2) to these mitochondria stimulated pregnenolone production to a greater extent than with mitochondria from untreated rats. Adrenal mitochondria from cycloheximide-treated rats were incubated in the presence of aminoglutethimide and cycloheximide to prevent further utilization of cholesterol for pregnenolone synthesis. Outer and inner membrane fractions of these mitochondria incubated with and without 0.75 microM SCP2, were prepared following hypotonic disruption. Incubations of mitochondria in the presence of SCP2 caused a marked shift in cholesterol from outer to inner membrane fractions. The findings provide direct evidence for a role of SCP2 or a similar peptide in modulating transfer of cholesterol to the inner membrane site of cholesterol side chain cleavage.

Adrenal Glands↗
PubMed1983

Evidence for sterol carrier protein2-like activity in hepatic, adrenal and ovarian cytosol.

Purified sterol carrier protein2 (SCP2) from rat liver stimulated utilization of endogenous cholesterol for pregnenolone synthesis by adrenal mitochondria. Cytosolic preparations of rat liver, adrenal and luteinized ovary were also stimulatory in mitochondrial pregnenolone synthesis to different extents. Treatment of all preparations with rabbit anti-rat SCP2 IgG neutralized the stimulatory effects, and immunoprecipitated proteins gave similar patterns on SDS-gradient polyacrylamide gel electrophoresis. Treatment with rabbit pre-immune IgG had no effect on these parameters. Thus, proteins which are immunochemically compatible with hepatic SCP2 appear to be present in steroidogenic tissues and may play a role in control of mitochondrial cholesterol side chain cleavage activity.

Adrenal Glands↗
PubMed1983

Sterol carrier protein2. Identification of adrenal sterol carrier protein2 and site of action for mitochondrial cholesterol utilization.

Addition of homogeneous rat liver sterol carrier protein2 (SCP2) or an adrenal cytosolic fraction enhanced pregnenolone production by adrenal mitochondria. Pretreatment of SCP2 or adrenal cytosol with anti-SCP2 IgG abolished the stimulatory effect of both preparations on mitochondrial pregnenolone output. Incubation of mitochondria with aminoglutethimide, which blocks interaction of cholesterol with inner membrane cytochrome P-450scc, resulted in decreased pregnenolone production and a decreased level of mitoplast cholesterol. Addition of SCP2 to the incubation media caused an almost 2-fold increase in cholesterol associated with the mitoplast, but did not enhance mitochondrial pregnenolone production. Studies with reconstituted cytochrome P-450scc in phospholipid vesicles also suggested that SCP2 did not affect interaction of cholesterol with the hemoprotein. Treatment of rats with cycloheximide alone or with adrenocorticotropic hormone resulted in a dramatic increase in mitochondrial cholesterol. However, these mitochondria did not exhibit increased levels of pregnenolone output under control incubation conditions. When SCP2 was included in the mitochondrial incubation media, pregnenolone production was significantly increased over that observed with adrenal mitochondria from untreated or adrenocorticotropic hormone-treated rats. The results imply that SCP2 enhances mitochondrial pregnenolone production by improving transfer of mitochondrial cholesterol to cytochrome P-450scc on the inner membrane, but does not directly influence the interaction of substrate with the hemoprotein.

Adrenal Glands↗
PubMed1982

Sterol carrier protein2. Delivery of cholesterol from adrenal lipid droplets to mitochondria for pregnenolone synthesis.

The ability of sterol carrier protein2 (SCP2) to mediate transfer of unesterified cholesterol from adrenal lipid inclusion droplets to mitochondria has been tested in an in vitro model system. Unlike mitochondrial utilization of cholesterol added in acetone or dimethyl sulfoxide, the unesterified cholesterol of lipid droplets did not provide a readily available source of substrate for mitochondrial pregnenolone production, without the addition of a transport mediator. Addition of SCP2, but not albumin, stimulated mitochondrial utilization of droplet cholesterol in a concentration-dependent manner. In the absence of mitochondria, SCP2 sequestered lipid droplet cholesterol, and in the presence of mitochondria, which were unable to convert cholesterol to pregnenolone, this cholesterol was quantitatively accumulated by mitochondria. Both processes were concentration-dependent and demonstrated a molar ratio of SCP2 and cholesterol for both binding and transport of 1. SCP2 also enhanced pregnenolone formation by mitochondria which were incubated in the absence of an extramitochondrial source of cholesterol. However, SCP2 had no effect on steroid release from a crude particulate fraction. These studies suggest that the effects of SCP2 are related to delivery of cholesterol from preformed stores to and into mitochondria for initiation of steroid hormone synthesis, and may represent an important modulator of sterol metabolism in adrenal cortical cells.

Adrenal Glands↗
PubMed1979

Prostaglandin synthesis in rat adrenocortical cells.

The biosynthesis of prostaglandins by isolated rat adrenocortical cells has been studied by determinations of products formed during incubations with labeled arachidonic acid and by radioimmunoassays. Analysis by thin-layer chromatographic separation of silicic acid column fractions indicated that PGE2, PGA2, (B2) and PGF2 alpha were the predominant prostaglandins formed by rat adrenocortical cells. Approximately 75% of the incorporated isotope was associated with the prostaglandins of the PGE pathway [PGE2 + PGA2 (B2)]. This was a consistent finding whether cells were incubated directly with arachidonic acid or with cells prelabeled with the substrate prior to study. ACTH did not affect the uptake or oxidation of [1-14C]-arachidonate, but did significantly increase incorporation of labeled substrate into [14C]prostaglandins. Of the ACTH-induced increase, 92% was accounted for by an increase in prostaglandins of the E pathway. Studies with prelabeled cells indicated that 77% of the prostaglandins synthesized in both control and ACTH-stimulated adrenocortical cells was released into the incubation medium during the 2-hr study. These had the same composition [88% PGE2 + PGA2 (B2)] as did the intracellular prostaglandins. Analysis by radioimmunoassays gave comparable data on the distribution of E- and F-type prostaglandins in control cells and cells incubated with ACTH or dibutyryl cyclic AMP. Thus, with these techniques, 88-92% of the increased prostaglandin synthesis due to ACTH or cyclic AMP was produced by the PGE2 rather than the PGF2 alpha pathway.

Adrenal Cortex↗
PubMed1978

Cholesterol arachidonate as a prostaglandin precursor in adrenocortical cells.

Rat adrenocortical cells were incubated with labeled arachidonate, and the radioactivity in unesterified fatty acids was reduced by washing with 2% albumin solutions. These cells were then incubated for two hours in the absence and presence of 7.1 x 10(-10)M ACTH. During subsequent incubation of prelabeled cells with ACTH, both the mass and radioactivity of arachidonate in adrenocortical cholesteryl esters was depleted to the same extent (30--32%). The released arachidonate was in part incorporated into phospholipids, and there was also a significant increase in unesterified arachidonic acid. During this period, there was also increased incorporation of arachidonate into labeled prostaglandins. Of this increase, 92% by isotope analysis, and 88% by radioimmunoassay techniques was attributable to prostaglandins of the E pathway. These data demonstrate that prostaglandin E synthesis is specifically increased during ACTH stimulation of rat adrenocortical cells and suggest that a major source of the arachidonate substrate for this synthesis is derived from hormone-dependent hydrolysis of cortical cholesteryl esters.

Adrenal Cortex↗
PubMed1978

ACTH-induced hydrolysis of cholesteryl esters in rat adrenal cells.

Rat adrenal cortical cells have been prepared by collagenase dissociation of trypsin-treated adrenal tissue. The content and compositions of cholesteryl ester, phospholipid, and triglyceride fatty acids compare favorably with those of undissociated rat adrenal tissue. During 2-hour control incubations of adrenal cortical cells, steroidogenesis was not detected, and the levels of sterol ester, phospholipid, and triglyceride fatty acids were not significantly altered. Incubations with adrenocorticotropic hormone (ACTH) resulted in coricosterone production and significant depletions of sterol ester and triglyceride fatty acids, but not of phospholipid fatty acids. Although all fatty acid esters of cholesterol were hydrolyzed under these conditions, the greatest contributions to the net decrease in sterol esters were by oleate, arachidonate, and adrenate. Incubations with dibutyryl cyclic adenosine monophosphate (0.5 mM) resulted in significantly greater levels of corticosterone production than did ACTH (250 muunits), but the effects on cellular lipids were comparable to those seen with the tropic hormone. This study represents the first demonstration of hormone-induced hydrolysis of sterol esters in an in vitro cell suspension system. The results are discussed with respect to hormone-sensitive sterol ester hydrolase of adrenal cortex, and to the role of endogenous cholesteryl esters in the steroidogenic pathway.

Adrenal Cortex↗