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Biomedical subjects

P V Subbaiah

Publications and source records attributed to P V Subbaiah.

At least 73 records · Page 4Linked to original sources
PubMed1985

The measurement of arterial smooth muscle cell mitogens in the blood of oral contraceptive users.

We have previously shown that serum from young women receiving the same combined mestranol-norethindrone containing oral contraceptive (OC) preparation accelerated the proliferation of arterial smooth muscle cells (SMC) in tissue culture, and this in vitro effect was not a direct action of either of its estrogenic or progestogenic constituents. To identify the substance(s) which might contribute to this potentially atherogenic action, blood was obtained from 20 OC users and control women for the measurement of growth hormone, insulin, somatomedins (insulin-like growth factor IGF-I and IGF-II), and the platelet alpha-granule constituents platelet-derived growth factor (PDGF), beta-thromboglobulin, and platelet factor 4 (PF4). No difference was demonstrable between OC users and controls in the levels of any of these growth-promoting hormones, nor in plasma concentrations of any of the platelet alpha-granule proteins. These studies indicate that the enhanced mitogenicity found in OC sera is probably not attributable directly to these hormones or PDGF, and may instead result from an in vivo OC-induced alteration in other as yet unidentified mediators of cellular growth.

Adolescent↗
PubMed1985

Role of low density lipoprotein in the activation of plasma lysolecithin acyltransferase activity. Effect of chemical and enzymatic modifications of the lipoprotein on enzyme activity.

The effect of various chemical and enzymatic modifications of low density lipoprotein (LDL) on its ability to activate the isolated human plasma lysolecithin acyltransferase (LAT) was studied. Removal of all lipids from LDL resulted in the complete loss of LAT activation. Removal of only neutral lipids by extraction with heptane retained up to 50% of the original activity, which was not increased further by reconstitution of the LDL with the extracted lipids. Hydrolysis of the diacylphosphoglycerides of the LDL with phospholipases resulted in complete loss of LAT activation which was partially restored by the addition of egg lecithin. Hydrolysis of more than 4% of LDL protein by trypsin led to a linear decrease in activity with complete loss of activity occurring when about 25% of the LDL protein is hydrolyzed. Modification of the arginine groups of LDL reversibly inhibited the activation of LAT. Modification of lysine residues of LDL by acetylation, acetoacetylation or succinylation also abolished its ability to activate lysolecithin acylation.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1984

Increased lysolecithin acyltransferase activity in the plasma of type II hyperlipoproteinemic patients.

Lecithin-cholesterol acyltransferase (LCAT) in human plasma has been shown to acylate lysolecithin to lecithin in presence of low density lipoprotein (LDL). To determine the physiological importance of LDL in activating lysolecithin acyltransferase (LAT) activity, we assayed the LAT activity in 18 hypercholesterolemic (Type II) patients and 15 control subjects. The enzyme activity was about 60% higher in the patients compared with the controls. On the other hand, the LCAT activity, measured by 2 different procedures, as well as enzyme mass, determined by radioimmuno assay, were comparable in the controls and hypercholesterolemics. The LAT activity was highly correlated with LDL levels in the plasma, but the LCAT activity and the enzyme mass had no correlation with the LDL levels. These results show that the plasma LDL is the rate-limiting activator of the enzyme, and pathological conditions, resulting in higher LDL levels, also cause higher LAT activities.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1982

Polyamines and atherosclerosis. Platelet releasate and other mitogens stimulate putrescine transport in arterial smooth muscle cells.

Although polyamine (PA) levels are believed to increase in response to mitogenic stimuli in all cells during growth, their role in arterial smooth muscle cell (ASMC) proliferation, an essential step in atherogenesis, is unknown. To determine whether the arterial wall mitogen, platelet-derived growth factor (PDGF) influences PA metabolism when cell cycle traverse is initiated, we examined its effects on the transport of the PA precursor [3H]putrescine (PUT) in culture in bovine and human ASMC. PUT uptake was stimulated in a dose-response relationship by PDGF-containing human serum (2-10%), and abolished in 24 h without it. Inhibition of this uptake by spermidine and the lack of effect of thymidine, leucine and ornithine indicated that uptake was by a PA-specific mechanism. Without serum, platelet releasate containing PDGF stimulated PUT uptake but not that of leucine or glucose. While platelet-poor plasma alone also promoted PUT uptake, the combination of platelet releasate and platelet-poor plasma was required for maximal DNA synthesis. PUT uptake under these conditions reached a peak at 16 h, while the synthesis of DNA was maximal at 24 h. Supraphysiological concentrations of insulin, and fibroblast and epidermal growth factors, also stimulated the uptake of the labeled PUT both in the absence and presence of serum, but at much lower rates than those observed with platelet releasate. These findings indicate that the early replicative actions of a variety of mitogens for ASMC involve stimulation of PUT uptake and suggest that PA uptake must precede the initiation of DNA synthesis in ASMC during atherogenesis.

Arteries↗
PubMed1982

Studies on the cofactor requirement for the acylation and hydrolysis reactions catalyzed by purified lecithin-cholesterol acyltransferase. Effect of low density lipoproteins and apolipoprotein A-i.

Because lecithin-cholesterol acyltransferase (LCAT) has been shown to carry out acylation of lysolecithin as well as hydrolysis of lecithin in addition to an esterification of cholesterol, the cofactor requirements of the three reactions catalyzed by the enzyme were studied. The purified enzyme required apolipoprotein A-I (apo A-I) for both the phospholipase A2 activity (release of free fatty acids from lecithin) and cholesterol esterification, whereas, low density lipoprotein (LDL) was required for the acylation of lysolecithin. Apo A-I and lecithin liposomes could not substitute for LDL for the activation of lysolecithin acyltransferase activity. Removal of apo A-I from the LDL preparation by affinity chromatography did not affect the activation of lysolecithin acylation, indicating that the contaminating apo A-I is not responsible for the activation. LDL facilitates cholesterol esterification in presence of labelled lecithin liposomes by providing the unesterified cholesterol. Removal of contaminating apo A-I, however, abolishes this LCAT activity which could be restored by addition of pure apo A-I. Lysolecithin inhibits both phospholipase A2 and LCAT activities, but LDL appeared to attenuate the effects of lysolecithin, in addition to stimulating the acylation of lysolecithin. These results show that apo A-I is not obligatory for all the reactions carried out by the enzyme, and that LDL plays an important role in the regulation of the hydrolysis and acylation reaction carried out by the enzyme.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1982

Requirement of low density lipoproteins for the lysolecithin acyl transferase activity in human plasma: assay of enzyme activity in abetalipoproteinemic patients.

Previous studies from this laboratory have shown that the lecithin:cholesterol acyl transferase (LCAT) of normal human plasma can convert lysolecithin to lecithin in the presence of low density lipoproteins (LDL). In order to study the importance of LDL for the lysolecithin acyl transferase (LAT) activity, the LCAT and LAT activities were assayed in two patients with abetalipoproteinemia. The plasma from both patients had only 5%-6% of the LAT activity present in normal plasma. This activity was stimulated up to 22-fold by the addition of normal LDL but not very low density lipoproteins (VLDL) or high density lipoproteins. The LAT activity of normal plasma was only stimulated by two-threefold by LDL. The LCAT activity in both patients was reduced to 42%-46% of the control values. This activity was stimulated up to fourfold by the addition of LDL as well as VLDL which is comparable to the activation obtained with control plasma. These results therefore suggest that LDL is physiological activator of LAT reaction in normal human plasma.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1982

Host defense mellitus: defective membrane synthesis during phagocytosis.

During phagocytosis, polymorphonuclear leukocytes from poorly controlled diabetic patients convert lysolecithin to lecithin at a lower rate than cells from control subjects. This defect is partially reversed by treatment with insulin. By reducing the availability of structural lipid for formation of the phagocytic vacuole which normally takes place during phagocytosis, this impairment may compromise cellular host-defense mechanisms in some diabetic patients.

Adult↗
PubMed1982

Lecithin: cholesterol acyltransferase activity in dialyzed and undialyzed chronic uremic patients.

Lecithin cholesterol acyltransferase (LCAT) and lysolecithin acyltransferase (LAT) activities in plasma were significantly lower in undialyzed than in dialyzed uremic patients and controls. Both LCAT and LAT activities were normal in the maintenance dialysis group. The free/total cholesterol ratio was significantly increased in the undialyzed patients only. This ratio and LCAT were inversely related in the dialyzed group, unrelated in the undialyzed patients, and positively correlated in controls. Unlike non-uremic populations with hypertriglyceridemia in which LCAT is increased, no correlation was found between plasma triglyceride and LCAT in the uremic population studied. Our results show that both LCAT and LAT activities are reduced in undialyzed chronic uremic patients but are not significantly different from control levels in patients treated with chronic hemodialysis. These results indicate that the changes in LCAT activity contrast with those described in lipoprotein composition and metabolism which do not appear to be affected by chronic dialysis therapy.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1980

Low density lipoprotein-activated lysolecithin acylation by human plasma lecithin-cholesterol acyltransferase. Identity of lysolecithin acyltransferase and lecithin-cholesterol acyltransferase.

There is in normal plasma an enzyme activity which converts labeled lysolecithin to lecithin by an energy-independent low density lipoprotein-activated pathway. Studies were undertaken to compare the identity of this enzyme with lecithin-cholesterol acyltransferase. During purification of the enzyme by ultracentrifugation and by chromatography on high density lipoprotein affinity column, DEAE-Sepharose column, and hydroxylapatite column, both the lysolecithin acyltransferase activity and the lecithin-cholesterol acyl transferase activity were found in the same fractions and were enriched to the same extent at each step. The final purified preparation which had 16,000- to 24,000-fold higher specific activities than starting plasma gave a single protein band on polyacrylamide gel electrophoresis and this single band contained both the activities. Also, the effects of pH, heat, and chemical inhibitors on the enzyme activities were similar. Plasma from patients with familial lecithin-cholesterol acyltransferase deficiency also lacked lysolecithin acyltransferase activity. These results indicate that a single enzyme carries out both lecithin-cholesterol acyltransferase and lysolecithin acyltransferase activities. The purified enzyme required apolipoprotein A-I for lecithin-cholesterol acyltransferase activity, but required low density lipoprotein for lysolecithin acyltransferase activity.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1980

Studies of membrane formation in Tetrahymena. The identification of membrane proteins and turnover rates in nongrowing cells.

Membrane proteins within cell fractions of Tetrahymena have been separated by polyacrylamide gel electrophoresis and the turnover of these proteins has been studied in nongrowing cells using double labeling procedures. Lactoperoxidase iodination and two-dimensional gel separations have revealed over 20 surface-labeled proteins, two of which are responsible for the single peak found in ciliary and nonciliary surface membranes. Turnover measurements show that there is heterogeneity in the rates at which membrane proteins turn over. The data suggest that larger proteins may turn over at higher rates in the microsomal fraction, as previously shown in mammalian cells. This was not found in the surface membrane fractions of Tetrahymena. However, membrane-associated cytoskeletal proteins had lower turnover rates than integral membrane proteins, and significant heterogeneity was found among the integral proteins measured. The implications of these findings for possible modes of membrane biogenesis in Tetrahymena are discussed.

Animals↗
PubMed1980

The uptake and acylation of exogenous lysophosphatidylethanolamine by Escherichia coli cells.

Escherichia coli envelopes were fractionated to yield inner and outer membrane fractions. Both these fractions were found to convert [14C]lysophosphatidylethanolamine to its diacyl analogue. Intact Escherichia coli cells were capable of absorbing exogenous labelled lysophosphatidylethanolamine and converting it to phosphatidylethanolamine. When the 14C- and 32P-labelled lyso analogue was used, both the absorption process and the conversion to diacyl analogue proceeded without a significant change in isotope ratio either in the presence or in the absence of added inorganic phosphate. The absorption process was not markedly stimulated by Ca2+ in the medium; it proceeded to an amount representing 25--30% of the endogenous membrane lipid and was accompanied by some degradation to water-soluble products which accumulated in the cell mainly, but also in the incubation medium. The absorbed lipid was recovered in both the inner and outer membrane fractions of the cell envelope. The results indicate that Escherichia coli inner and outer membranes are capable of absorbing exogenous lysophosphoglyceride and converting it into structurally useful diacyl analogue.

Calcium↗
PubMed1980

Oral contraceptive steroids and atherosclerosis: lipogenesis in human arterial smooth muscle cells and dermal fibroblasts in presence of lipoprotein-deficient serum from oral contraceptive users.

The incorporation of [14C]-acetate into lipids by cultured human arterial smooth muscle cells and dermal fibroblasts was studied in the presence of lipoprotein-deficient serum from oral contraceptive users (OC) and control women. Exposure to OC serum: 1) significantly increased the synthesis of cholesterol above controls in both fibroblasts (+25-56%) and smooth muscle cells (+28-42%) without a significant change in the synthesis of lecithin; and 2) resulted in increased cholesterol/lecithin ratios in newly synthesized lipids which were higher than controls in both fibroblasts (+50%) and smooth muscle cells (+30%). In vitro addition of the steroid ingredients of the "pill" to the growth medium containing control serum did not result in a stimulation of lipogenesis by the cells. [3H] - mevalonate incorporation into cholesterol was no different with OC and control serum, indicating that the stimulation noted in cholesterol synthesis by OC serum was due to an increased HMG-CoA reductase activity. These findings suggest that increased sterol synthesis in arterial smooth muscle cells of oral contraceptive users may be one pathogenetic factor which adversely influences their risk of atherosclerosis.

Adult↗
PubMed1979

Association of lysolecithin acyltransferase with the high density lipoproteins and its activation by the low density lipoproteins in normal human plasma.

The lysolecithin acyltransferase of human plasma is shown to be associated with the high-density lipoprotein fraction. Although the low density lipoproteins do not have intrinsic enzyme activity, their presence activated the enzyme 3--7-fold. This activation is not affected by heat-treatment of the low density lipoproteins, but is abolished by the addition of heparin.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1979

Polyamines: an unrecognised cardiovascular risk factor in chronic dialysis?

The significance of raised polyamine (P.A.) levels in chronic-dialysis patients is unknown. Since these biologically active substances have hormone-like properties and promote cell-growth in plant and animal tissues, it is possible that they stimulate proliferation of arterial smooth-muscle cells (S.M.C.)--a central process in atherogenesis--and thereby contribute to the rapidly accelerated cardiovascular disease observed during dialysis. Such a role for P.A. is supported by tissue-culture studies, which show not only that P.A.-rich serum from dialysis patients stimulates S.M.C. growth, but also that this mitogenic effect is lost when P.A. are selectively removed from uraemic serum and restored by their addition. Although these observations provide new insights into possible mechanisms of atherogenesis, they are not surprising in view of the many known biological actions of P.A.

Arteries↗
PubMed1976

Interactions of the components of the prothrombinase complex.

The interaction of components of the prothrombinase complex, i.e. bovine Factor X or Factor Xa, bovine Factor V or Factor Va, phospholipid, and Ca2+, in various combinations was studied primarily by a gel filtration technique. In experiments, in which phospholipids ranging from those isolated from naturally occurring sources to those long chain (18 : 1) as well as short chain 6 : 0 and 7 : 0 fatty acids prepared by chemical and enzymatic synthesis were used, it was evident that a net negative surface charge on the lipid dispersions was one of the important requirements for interaction. Though the short chain fatty acid phospholipids interacted with the proteins of the prothrombinase complex, there was invariably a diminution in the activity of the enzyme complex. It was established that Factor V or Va did not bind Ca2+ and that the binding of either of these factors with phospholipids (with a net negative charge) was not dependent on Ca2+. However, the interaction of Factor X or Factor Xa with phospholipids with a negative charge required Ca2+. It was shown that Factor X could bind to the same type of lipid of lipid surface as that noted for Factor Xa. Of interest was the apparent difference in the phospholipid binding characteristics of the two variant forms of bovine plasma Factor X, i.e. X1 and X2, which might in part explain the differences in their specific activities. Of importance was the lack of demonstrable complex formation between Factors II, X and V in the absence of phospholipids and/or in the presence or absence of Ca2+. The significance of these results as they might apply to the configuration of the prothrombinase complex and its interaction with prothrombin plus the usefulness of the short chain fatty acid phospholipid in exploring these lipid-protein interactions are discussed.

Animals↗
PubMed1974

The mechanism of intestinal absorption of phosphatidylcholine in rats.

1. The mechanism of absorption of phosphatidylcholine was studied in rats by injecting into the intestine phosphatidylcholine specifically labelled either in the fatty acid or in the glycerol moiety or with (32)P, when considerable amounts of 1-acyl-lysophosphatidylcholine were found in the intestinal lumen. 2-([(14)C]Acyl)phosphatidylcholine gave markedly more radioactive unesterified fatty acids in the lumen, compared with the 1-([(14)C]acyl) derivative. Some of the radioactivity from either the fatty acid or the glycerol moiety of the injected phosphatidylcholine appeared in the mucosal triacylglycerols. 2. Injection of (32)P-labelled phosphatidylcholine or (32)P-labelled lysophosphatidylcholine led to the appearance of radioactive glycerylphosphorylcholine, glycerophosphate and P(i) in the mucosa. 3. Rat mucosa was found to contain a highly active glycerylphosphorylcholine diesterase. 4. It was concluded that the dietary phosphatidylcholine is hydrolysed in the intestinal lumen by the pancreatic phospholipase A to 1-acylglycerylphosphorylcholine, which on entering the mucosal cell is partly reacylated to phosphatidylcholine, and the rest is further hydrolysed to glycerylphosphorylcholine, glycerophosphate, glycerol and P(i). The fatty acids and glycerophosphate are then reassembled to give triacylglycerols via the Kennedy (1961) pathway.

Animals↗