Search PubMed⌕ Search

Biomedical subjects

R Natarajan

Publications and source records attributed to R Natarajan.

At least 73 records · Page 4Linked to original sources
PubMed1998

Regulation of hepatic neutral cholesteryl ester hydrolase by hormones and changes in cholesterol flux.

To understand molecular events in regulation of hepatic neutral cholesteryl ester hydrolase (EC3.1.1.13; CEH), catalytic activity, protein mass, and mRNA levels were measured in rats with various perturbations of hepatic cholesterol metabolism. Cholesterol feeding decreased activity (56 +/- 2%), mass (44 +/- 2%), and mRNA (14 +/- 3%). The cholesterol precursor mevalonate also decreased activity (42 +/- 6%), mass (76 +/- 3%), and mRNA (23 +/- 16%). Inhibition of cholesterol biosynthesis by lovastatin increased activity (65 +/- 12%) and mRNA (31 +/- 24%). Stimulation of cholesterol efflux by chronic biliary diversion increased activity (138 +/- 34%), mass (29 +/- 7%), and mRNA (146 +/- 28%). Chenodeoxycholate feeding decreased activity (46 +/- 6%) and mRNA (26 +/- 12%). These data suggest rational regulation of CEH in response to changes in cholesterol flux through the liver. In primary hepatocytes, steady-state mRNA markedly decreased during 72-h cultures and addition of L-thyroxine and dexamethasone synergistically maintained mRNA levels near control values. Lovastatin increased mRNA levels by 103 +/- 15%. Taurocholate and phorbol 12-myristate 13-acetate suppressed mRNA (61 +/- 4% and 49 +/- 13%, respectively), suggesting that protein kinase C mediated effects of bile acids on CEH mRNA levels. These data suggest regulation of CEH by hormones and signal transduction in addition to changes in cholesterol flux.

Animals↗
PubMed1998

Pulsus paradoxus: an objective measure of severity in croup.

We used a noninvasive monitor of arterial pressure to determine the utility of pulsus paradoxus (PP) as an objective severity measure in croup. We performed a prospective, blinded comparison of PP in children with croup versus healthy control subjects, analyzed the relationship between PP and Westley croup score (WCS), and observed the effect of racemic epinephrine (RE) on PP and WCS in a subgroup of patients with severe croup. The PP and WCS were measured at presentation and in severe patients after treatment with RE. Mean PP was 6.1 +/- 1.8 (SD) mm Hg (n = 29) in control subjects compared with a mean of 17.8 +/- 11.2 (SD) mm Hg (n = 28) in patients with croup (p < 0.00001). There was significant concordance between baseline WCS and PP (Spearman's rho: 0.68; p = 0.0001). The mean decrease in PP after RE was 7.5 +/- 11.8 (SD) mm Hg (p = 0.05; n = 12). The magnitude of decrease in PP after RE has significant concordance with the concurrent decrease in WCS (Spearman's rho: 0.73; p < 0.007). PP is elevated in children with croup, and the magnitude of elevation correlates with severity as measured by the WCS. PP may have utility as a research tool to objectively measure the severity of upper airway obstruction in croup.

Adolescent↗
PubMed1998

Insulin potentiates platelet-derived growth factor action in vascular smooth muscle cells.

Correlative studies have indicated that hyperinsulinemia is present in many individuals with atherosclerosis. Insulin resistance has also been linked to cardiovascular disease. It has proved to be difficult to decipher whether hyperinsulinemia or insulin resistance plays the most important role in the pathogenesis of atherosclerosis and coronary artery disease. In this study, we demonstrate that insulin increases the amount of farnesylated p21Ras in vascular smooth muscle cells (VSMC), thereby augmenting the pool of cellular Ras available for activation by platelet-derived growth factor (PDGF). In VSMC incubated with insulin for 24 h, PDGF's influence on GTP-loading of Ras was significantly increased. Furthermore, in cells preincubated with insulin, PDGF increased thymidine incorporation by 96% as compared with a 44% increase in control cells (a 2-fold increment). Similarly, preincubation of VSMC with insulin increased the ability of PDGF to stimulate gene expression of vascular endothelial growth factor 5- to 8-fold. The potentiating influence of insulin on PDGF action was abrogated in the presence of a farnesyltransferase inhibitor. Thus, the detrimental influence of hyperinsulinemia on the arterial wall may be related to the ability of insulin to augment farnesyltransferase activity and provide greater amounts of farnesylated p21Ras for stimulation by various growth promoting agents.

Animals↗
PubMed1998

Pilot trial of albuterol in facioscapulohumeral muscular dystrophy. FSH-DY Group.

BACKGROUND/OBJECTIVE: Facioscapulohumeral muscular dystrophy (FSHD) is currently untreatable, and there have been few therapeutic trials of any agent in the disease. Animal studies have demonstrated that beta2-adrenergic agonists induce muscle hypertrophy and prevent atrophy after a variety of physical and biochemical insults, and two human studies have shown that these agents increase certain measures of strength in healthy volunteers. We conducted an open-label pilot trial of a beta2-agonist (albuterol) in patients with FSHD. METHODS: Fifteen FSHD patients were given sustained-release albuterol (16.0 mg/day) for 3 months. The primary outcome measure was lean body mass, which was assessed through dual energy X-ray absorptiometry (DEXA). Strength was evaluated through maximal voluntary isometric contraction testing (MVICT) and manual muscle testing. RESULTS: Albuterol significantly increased DEXA lean body mass (the skeletal muscle compartment) by 1.29 +/- 1.18 kg (mean +/- SD, p = 0.001). Strength assessed through composite MVICT scores also increased by an average of 0.33 +/- 0.60 (p = 0.05), representing an overall 12% improvement in strength. CONCLUSIONS: These encouraging results suggest that beta2-agonists may have a role in treating FSHD and possibly other neuromuscular diseases. The effects of albuterol in FSHD are currently being evaluated in a larger, randomized, double-blind, placebo-controlled trial lasting 1 year.

Absorptiometry, Photon↗
PubMed1997

Age-related changes in catalytic activity, enzyme mass, mRNA, and subcellular distribution of hepatic neutral cholesterol ester hydrolase in female rats.

Activity and protein mass of hepatic neutral cholesteryl ester hydrolase (CEH) were measured in liver cytosol and washed microsomes of female Sprague-Dawley rats aged 3, 4, 7, 9, 13, and 16 wk. CEH mRNA was also measured. The microsomal component varied with age and contributed a greater fraction of total activity in females than previously reported in males. Nevertheless, the cytosolic component accounted for 62-80% of activity and 77-94% of immunoreactive protein in postmitochondrial fractions. Cytosolic and microsomal CEH specific activities, relative to total protein, decreased 94 and 83%, respectively, from 3 to 4 wk, prior to onset of puberty at 5 wk, and increased 360 and 137%, respectively, from 12 to 16 wk. These results contrast with an earlier study, in which cytosolic CEH activity of males increased with puberty and declined after 12 wk. Although cytosolic CEH was activated by protein kinase A and inhibited by alkaline phosphatase treatment at all ages, protein kinase activation peaked at 4 wk, coinciding with the initial decrease in specific activity. Specific activity in cytosol and microsomes correlated with CEH mass at all ages, suggesting that this CEH accounts for most variation in cellular activity. In contrast, CEH mRNA varied little from 3-16 wk, indicating that transcriptional regulation does not make a major contribution to the variation in CEH activity and mass in females, although it may make an important contribution to male-female differences in CEH expression. Specific activities of cytosolic and microsomal CEH, relative to immunoreactive CEH protein mass, exhibited changes consistent with posttranslational regulation. These results indicate gender-specific multivalent regulation of hepatic CEH by posttranslational mechanisms during development of female rats.

Aging↗
PubMed1997

The role of nitric oxide in the regulation of aldosterone synthesis by adrenal glomerulosa cells.

The role of nitric oxide (NO) in the regulation of aldosterone synthesis in the adrenal glomerulosa is not known. In this study, we observed that liberators of NO such as S-nitroso-N-acetyl-penicillamine (SNAP), sodium nitroprusside (Snp) and spermine nonoate (SNO) could significantly inhibit angiotensin II (AII) and ACTH-induced aldosterone synthesis in isolated rat and cultured human adrenal glomerulosa cells. To evaluate more precisely whether glomerulosa cells express NO synthase, we performed immunoblotting experiments with antibodies specific for the endothelial type ecNO synthase as well as the neuronal NO synthase. This revealed the presence of the ecNO synthase in rat adrenal capsules, in normal and in adenomatous human adrenal glomerulosa tissue, as well as in freshly dispersed rat adrenal glomerulosa cells. Furthermore, on immunohistochemical analysis, rat adrenal glomerulosa cell sections showed strongly positive staining for ecNO synthase. These results suggest that NO may be an important negative modulator of adrenal glomerulosa steroidogenesis.

Adrenocorticotropic Hormone↗
PubMed1997

Air leaking through the mouth during nocturnal nasal ventilation: effect on sleep quality.

Air leaking through the mouth has been reported in kyphoscoliotic patients receiving nasal ventilation via volume-limited ventilators. This study accessed the frequency of occurrence and effect on sleep quality of air leaking through the mouth during nocturnal nasal ventilation in patients with chest wall and neuromuscular disease using pressure-limited ventilation. Overnight and daytime polysomnography was performed in six stable experienced users of nocturnal nasal noninvasive positive-pressure ventilation (NPPV) who had chronic respiratory failure due to neuromuscular disease or chest wall deformity. All patients used the BiPAP S/T-D ventilatory support system (Respironics, Inc., Murrysville, PA). Measures included sleep scoring, leak quantitation, diaphragm and submental electromyograms (EMGs), and tidal and leak volumes. All patients had air leaking through the mouth for the majority of sleep. Sleep quality was diminished because of poor sleep efficiency and reduced percentages of slow-wave and rapid eye movement (REM) sleep. Air leaking through the mouth was associated with frequent arousals during stages 1 and 2 and REM sleep that contributed to sleep fragmentation, but arousals were infrequent during slow-wave sleep. Despite prevalent leaking, oxygenation was well maintained in all but one patient. Patients used a-combination of passive and active mechanisms to control air leaking. Although nasal ventilation improves nocturnal hypoventilation and symptoms in patients with restrictive thoracic disorders, air leaking through the mouth is very common during use. The leaking is associated with frequent arousals during lighter stages of sleep that interfere with progression to deeper stages, compromising sleep quality. Portable pressure-limited ventilators compensate for leaks, maintaining ventilation and oxygenation, but further studies are needed to determine which interfaces and ventilator techniques best control air leaking and optimize sleep quality.

Adult↗
PubMed1997

Effects of high glucose on vascular endothelial growth factor expression in vascular smooth muscle cells.

Vascular endothelial growth factor (VEGF), in addition oto its growth-promoting effects on endothelial cells, can also increase vascular permeability and monocyte migration. It has therefore been implicated in the pathogenic neovascularization associated with diabetic retinopathy and atherosclerosis. However, the factors regulating VEGF expression in the vascular wall are not fully understood. In this study, we examined the regulation of VEGF expression in vascular smooth muscle cells (VSMC) by hyperglycemia as well as by angiotensin II (ANG II). We also examined whether the 12-lipoxygenase (12-LO) product 12-hydroxyeicosatetraenoic acid (12-HETE) can alter VEGF expression, since 12-LO products of arachidonic acid have angiogenic properties, and ANG II as well as high glucose (HG, 25 mM) can increase 12-LO activity and expression in VSMC. Studies were carried out in human (HSMC) or porcine VSMC (PSMC), which were cultured for at least two passages under normal glucose (NG, 5.5 mM) or HG conditions. HG culture alone increased the expression of VEGF mRNA and protein in both HSMC and PSMC. Furthermore, ANG II treatment significantly induced VEGF mRNA and protein expression only in VSMC cultured in HG and not NG. In addition, 12-HETE significantly increased VEGF mRNA and protein expression in HSMC cultured in NG as well as in HG. Cells cultured in HG also secreted significantly greater amounts of VEGF into the culture medium. These results suggest that elevated VEGF production under HG conditions may play a role in the accelerated vascular disease observed in diabetes.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1997

Regulation of 12-lipoxygenase by cytokines in vascular smooth muscle cells.

Increasing evidence suggests that cytokines such as interleukin-1beta (IL-1), IL-4, and IL-8 may play an important role in the chronic inflammation and cellular growth observed in cardiovascular diseases. The lipoxygenase (LO) pathway of arachidonate metabolism has also been related to the pathology of hypertension and atherosclerosis. LO products have chemotactic, hypertrophic, and mitogenic effects in vascular cells, and the LO enzyme has been implicated in the oxidation of LDL. Furthermore, earlier studies have shown that vascular smooth muscle cell (VSMC) growth factors such as angiotensin II and platelet-derived growth factor can increase LO activity and expression in VSMCs. In the present study, we have examined whether vasoactive and inflammatory cytokines such as IL-1, IL-4, and IL-8 can modulate 12-LO activity and expression in porcine VSMCs and also whether they have growth-promoting effects in these cells. Treatment of porcine VSMCs with these cytokines led to significant increases in the levels of a cell-associated 12-LO product, 12-hydroxyeicosatetraenoic acid, as well as intracellular 12-LO enzyme activity. Furthermore, each of these cytokines led to a dose-dependent increase in 12-LO mRNA expression (333-base pair PCR product) as well as 12-LO protein expression (72 kD). In addition, all three interleukins could induce significant increases in VSMC DNA synthesis as well as proliferation. These results suggest that these cytokines have mitogenic effects in VSMCs and are also potent positive regulators of the 12-LO pathway. Thus, enhanced 12-LO activity and expression may be a key mechanism for cytokine-induced VSMC migration and proliferation.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1997

Increased 12-lipoxygenase expression in breast cancer tissues and cells. Regulation by epidermal growth factor.

The interaction of growth factors, such as epidermal growth factor (EGF) with their receptors, on breast cancer cells can lead to the hydrolysis of phospholipids and release of fatty acids, such as arachidonic acid, which can be further metabolized by the lipoxygenase (LO) pathway. Several LO products have been shown to stimulate oncogenes and have mitogenic and chemotactic effects. In this study, we have evaluated the regulation of 12-LO activity and expression in breast cancer cells and tissues. Leukocyte-type 12-LO messenger RNA (mRNA) expression was studied by a specific RT-PCR method in matched, normal, uninvolved and cancer-involved breast tissue RNA samples from six patients. In each of these six patients, the cancer-involved section showed a much higher level of 12-LO mRNA than the corresponding normal section. 12-LO mRNA levels also were greater in two breast cancer cell lines, MCF-7 and COH-BR1, compared with the nontumorigenic breast epithelial cell line, MCF-10F. The growth of the MCF-7 cells was significantly inhibited by two specific LO blockers but not by a cyclooxygenase blocker. Treatment of serum-starved MCF-7 cells with EGF for 4 h led to a dose-dependent increase in the formation of the 12-LO product, 12-hydroxyeicosatetraenoic acid. EGF treatment also increased the levels of the leukocyte-type 12-LO protein expression at 24 h. These results suggest that activation of the 12-LO pathway may play a key role in basal and EGF-induced breast cancer cell growth.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1996

Catalytic properties of the purified rat hepatic cytosolic cholesteryl ester hydrolase.

The purified enzyme hydrolyzed cholesteryl oleate, cholesteryl linoleate, and triolein at similar rates over a broad range of concentrations. Hydrolytic activity was relatively low with p-nitrophenyl acetate, but much higher with PNP-esters of the more lipophilic C4-C18 fatty acids, in sharp contrast to microsomal esterases which hydrolyze PNP-acetate more efficiently. Zn2+, Cu2+, Cd2+, Hg2+, and phenylmethylsulfonyl fluoride inhibited, whereas N-ethyl maleimide and iodoacetamide stimulated activity of the pure enzyme. Limited trypsin digestion selectively inhibited cholesteryl esterase activity with retention of activity toward PNP-octanoate, suggesting involvement of a trypsin-labile loop in the lipophilic substrate binding pocket.

Animals↗
PubMed1996

Age-related changes in mRNA, protein and catalytic activity of hepatic neutral cholesterol ester hydrolase in male rats: evidence for transcriptional regulation.

Messenger RNA, protein mass and catalytic activity of hepatic neutral cholesteryl ester hydrolase (CEH) were measured in male Sprague-Dawley rats, aged 6, 8, 9.5, 12 and 24 weeks (wks). CEH mRNA increased 101% from 6 to 9.5 wks, corresponding to onset of puberty, and declined by 52% from 12 to 24 wks. CEH mass was highly correlated with mRNA levels at all ages, increasing 170% from 6 to 9.5 wks and declining 61% from 12 to 24 wks. CEH activity was highly correlated with mass and mRNA from 8-24 wks, but was greater at 6 wks than the activity predicted by the measured mass. In all age groups, activity was consistently increased by activation of endogenous protein kinase A and consistently inhibited by alkaline phosphatase, suggesting that age-related differences in catalytic activity were not due to differences in the level of enzyme phosphorylation. These data suggest transcriptional regulation and indicate an important role for CEH in cholesterol homeostasis in the developing rat.

Aging↗
PubMed1996

Continuous, noninvasive measurement of pulsus paradoxus in patients with acute asthma.

OBJECTIVE: To evaluate a continuous, noninvasive measurement technique for pulsus paradoxus (PP) as an objective asthma severity indicator. DESIGN: Prospective, masked assessment of the relationship between PP, peak expiratory flow rate, oxygen saturation, clinical scoring, and admission decisions. SETTING: An urban pediatric emergency department. PATIENTS: Children with acute asthma. INTERVENTIONS: Standardized treatment per National Heart, Lung, and Blood Institute guidelines. MAIN OUTCOME MEASURES: Peak expiratory flow rate, oxygen saturation, pulmonary index score, and masked disposition decision. RESULTS: Significant positive correlations existed between PP and the pulmonary index score at the initial evaluation (r = 0.44; P < .001) and after 30 minutes (r = 0.51; P < .001) and 60 minutes (r = 0.45; P < .001). Significant negative correlations existed between PP and the percent predicted peak expiratory flow rate (r = -0.31; P = .01) and the oxygen saturation (r = -0.30; P = .02). The mean PP was significantly greater in patients who were admitted for further treatment at all time points (P = .003 or P = .002). At 30 minutes after presentation, a PP greater than 15 mm Hg predicted admission for further treatment or relapse; the sensitivity was 0.42, the specificity was 0.89, and the likelihood ratio was 3.86. CONCLUSIONS: Our measurement technique for PP is a useful objective indicator of the severity of asthma. Pulsus paradoxus correlates with clinical score, peak expiratory flow rate, and oxygen saturation. Furthermore, an elevated PP is associated with the decision to admit a patient for further treatment. These results suggest that this technique may represent a useful research tool for the assessment of acute, severe asthma. Further development of the technology may allow for a clinical application.

Acute Disease↗
PubMed1996

Platelet-derived growth factor BB mediated regulation of 12-lipoxygenase in porcine aortic smooth muscle cells.

Platelet-derived growth factor BB (PDGF) is a potent mitogen and chemoattractant for vascular smooth muscle cells (VSMC). In the present study, we have examined the effect of PDGF on the 12-lipoxygenase (12-LO) pathway of arachidonate metabolism in porcine aortic VSMC (PVSMC). The rationale for this is previous studies showing that LO products have growth and chemotactic effects in VSMC and that another VSMC growth factor, angiotensin II, is a potent positive regulator of 12-LO activity and expression. We observed that PDGF causes a significant increase in the formation of the 12-LO product, 12-hydroxyeicosatetraenoic acid (12-HETE) in PVSMC. In addition, PDGF also markedly increased leukocyte-type 12-LO messenger RNA and protein expression. PDGF-induced PVSMC migration was inhibited significantly by two LO blockers but not by a cyclooxygenase blocker. Furthermore, although the proliferative effects of PDGF on PVSMC were not altered by cell culture under hyperglycemic conditions (25 mM glucose, HG), the chemotactic effects of PDGF as well as those of 10% fetal calf serum were significantly greater in cells cultured in HG as compared to normal glucose conditions (5.5 mM), thus indicating a potential new mechanism for the accelerated cardiovascular disease usually observed in diabetes. These results indicate a novel mechanism for the biological effects of PDGF in leading to cardiovascular disease.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1996

A computer program for sample size and power calculations in the design of multi-arm and factorial clinical trials with survival time endpoints.

This paper presents a computer program for use in the design of long-term clinical trials with multiple treatment arms in which the primary outcome variables are censored survival times. The treatment arms may be structured as a one-way or multi-way factorial design. It is assumed that patients are entered and randomized to a treatment arm during an accrual period. The patients are then followed for a fixed period during which there may be dropouts. Various distributional assumptions can be used to model the survival times. These include an option in which there is an effect of treatment duly after a lag or delay time. The program then computes the power of various statistical tests of hypotheses concerning treatment differences, interactions and trends. The power computations are "exact" in that they use the Monte Carlo method to obtain Type I and II error probabilities. However the program also outputs the normal approximations for comparison, although they are typically not accurate in these situations. Fisher's LSD method is used to adjust for the multiple comparisons. By comparing the power for various sets of design parameters, such as sample size, numbers of factor levels, patient accrual rate, and length of follow-up, an appropriate design can be constructed. Two examples are provided. The first is a simple one-way layout with multiple treatment arms; the second a two-way factorial design for a proposed large scale cancer chemoprevention trial.

Clinical Trials as Topic↗
PubMed1996

Mechanisms of ANG II-induced mitogenic responses: role of 12-lipoxygenase and biphasic MAP kinase.

The potential mechanisms of angiotensin II (ANG II)-induced mitogenesis were studied in a Chinese hamster ovary fibroblast cell line overexpressing the rat vascular type 1a ANG II receptor (CHO-AT1a). ANG II had potent mitogenic effects in these CHO-AT1a cells, leading to a sustained increase in cell number as well as a dose-dependent increase in DNA synthesis. ANG II treatment also induced a biphasic elevation of mitogen-activated protein (MAP) kinase activity of both p42MAPK and p44MAPK with a rapid early peak at 5 min (2- to 6-fold) followed by a second sustained increase that reached a peak at 3 h (1.5- to 3-fold). We have previously shown that the 12-lipoxygenase (12-LO) pathway of arachidonate metabolism plays a key role in ANG II-induced growth of vascular smooth muscle and adrenal cells. In the present study, ANG II (10(-7) M) increased the formation of the 12-LO product, 12-hydroxyeicosatetraenoic acid (12-HETE). ANG II-induced DNA synthesis was inhibited by a specific LO inhibitor, cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate (CDC, 10 microM). In contrast, a cyclooxygenase blocker of arachidonate metabolism such as ibuprofen had no effect on ANG II-induced DNA synthesis. ANG II-induced DNA synthesis was also partially (32%) blocked by pertussis toxin (PTX). CDC and PTX also selectively blocked only the late (3 h) peak of ANG II-induced MAP kinase activity, suggesting that the late sustained peak of MAP kinase activity may be linked to the mitogenic effect of ANG II. Direct addition of 12-HETE (10(-7) M) led to a sustained increase in cell number similar to the effect of ANG II. 12-HETE also caused an increase in MAP kinase activity, and 12-HETE effects were blocked by PTX. These results suggest that ANG II-induced mitogenic response is associated with sustained MAP kinase activation and that LO activation may play a key role in this process.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗