Biomedical subjects

Aftab Ahmad

Publications and source records attributed to Aftab Ahmad.

16 recordsLinked to original sources

PubMed2006

Purinergic signaling and kinase activation for survival in pulmonary oxidative stress and disease.

Stimulus-induced release of endogenous ATP into the extracellular milieu has been shown to occur in a variety of cells, tissues, and organs. Extracellular ATP can propagate signals via P2 receptors that are essential for growth and survival of cells. Abundance of P2 receptors, their multiple isoforms, and their ubiquitous distribution indicate that they transmit vital signals. Pulmonary epithelium and endothelium are rich in both P2X and P2Y receptors. ATP release from lung tissue and cells occurs upon stimulation both in vivo and in vitro. Extracellular ATP can activate signaling cascades composed of protein kinases including extracellular signal-regulated kinase (ERK) and phosphatidylinositol-3-kinase (PI3K). Here we summarize progress related to release of endogenous ATP and nucleotide signaling in pulmonary tissues upon exposure to oxidant stress. Hypoxic, hyperoxic, and ozone exposures cause a rapid increase of extracellular ATP in primary pulmonary endothelial and epithelial cells. Extracellular ATP is critical for survival of these cells in high oxygen and ozone concentrations. The released ATP, upon binding to its specific receptors, triggers ERK and PI3K signaling and renders cells resistant to these stresses. Impairment of ATP release and transmission of such signals could limit cellular survival under oxidative stress. This may further contribute to disease pathogenesis or exacerbation.

Adenosine Triphosphate↗

PubMed2006

Update of the Providence Health System experience with the CarboMedics prosthesis.

BACKGROUND AND AIM OF THE STUDY: The study aim was to update the authors' experience with the CarboMedics bileaflet mechanical prosthesis in terms of early and long-term outcomes. METHODS: Between July 1994 and April 2005, a total of 774 CarboMedics valves was implanted at two Providence Health System hospitals in Portland Service Area. Of these valves, 406 (59%) were aortic valve replacements (AVR), 196 (28.5%) were mitral valve replacements (MVR), and 86 pairs (12.5%) were double valve replacements (DVR). RESULTS: The mean and maximum follow up was 4.6 and 10.2 years, respectively; total follow up was 3,150 patient-years (pt-yr) (total 3,503 valve-years). Operative mortality was 5.7% (4.4% for AVR, 7.7% for MVR, 7.0% for DVR). Five- and 10-year survivals respectively were 79 +/- 2% and 55 +/- 10% for AVR, 74 +/- 3% and 57 +/- 8% for MVR, and 64 +/- 6% and 39 +/- 11% for DVR (p = 0.009). Freedom from valve explant at five and 10 years respectively was 98 +/- 1% and 97 +/- 10% for AVR, 98 +/- 1% and 86 +/- 12% for MVR, and 96 +/- 3% and 96 +/- 3% for DVR (p = 0.950). Freedom from thromboembolism at five and 10 years respectively was 93 +/- 1% and 91 +/- 2% for AVR, 97 +/- 1% and 95 +/- 2% for MVR, and 90 +/- 4% and 90 4% for DVR (p = 0.226). Freedom from bleeding at five and 10 years respectively was 98 +/- 1% and 97 +/- 1% for AVR, 97 +/- 1% and 96 +/- 2% for MVR, and 91 +/- 4% and 91 +/- 4% for DVR (p = 0.006). Freedom from endocarditis at five and 10 years respectively was 99 +/- 1% and 99 +/- 1% for AVR, 98 +/- 1% and 98 +/- 1% for MVR, and 95 +/- 3% and 91 +/- 4% for DVR (p = 0.030). There were nine perivalvular leaks (six after AVR, three after MVR), and three valve thromboses (two after MVR, one after DVR). Freedom from overall valve-related events at five and 10 years respectively was 80 +/- 2% and 74 +/- 3% for AVR, 82 +/- 3% and 57 +/- 11% for MVR, and 69 +/- 6% and 66 +/- 6% for DVR (p = 0.074). CONCLUSION: Long-term experience with the CarboMedics valve shows the clinical performance of the valve to be very good, with results comparable to those obtained with other mechanical valves.

Adolescent↗

PubMed2005

Activation of a novel isoform of methionine adenosyl transferase 2A and increased S-adenosylmethionine turnover in lung epithelial cells exposed to hyperoxia.

S-Adenosylmethionine (SAM, AdoMet) is the most important methyl donor used for synthesis of nucleic acids, phospholipids, creatine, and polyamines and for methylation of many bioactive molecules. The metabolic response of the lung to oxidative stress of hyperoxia requires increased RNA and protein synthesis for energy metabolism, growth arrest, and antioxidant defense. We studied the production of SAM and other aspects of methionine metabolism in lung epithelial cells exposed to hyperoxia. Human lung epithelial-like (A549) and primary small airway epithelial (SAE) cells were exposed to normoxia (21% O(2)) or hyperoxia (95% O(2)). Cell methionine and S-adenosylmethionine content increased in response to hyperoxia in SAE and A549 cells. Because methionine adenosyl transferase (MAT) is the rate-limiting enzyme of the pathway, we examined the expression of a lung epithelial isoform of MAT 2A in hyperoxia. Western blots revealed a novel MAT 2A isoform expressed in both cell types, with a lower molecular mass than that described in Jurkat cells. Cloning and sequencing of the MAT 2A cDNA revealed one silent nucleotide substitution compared to that expressed in Jurkat. The lower mass of MAT 2A in both lung epithelial cells indicated that the absence of the major posttranslational modification of MAT 2A found in Jurkat. MAT 2A protein progressively increased during hyperoxic exposure in both transformed and primary lung epithelium. Increased flux of (13)C-labeled methionine to S-adenosylhomocysteine (SAH) in A549 demonstrated that SAM's methyl group was utilized, and increased formation of cystathionine indicated that at least part of SAM generated was directed toward cysteine/GSH in the transsulfuration pathway. These results indicate activation of MAT 2A and the transmethylation pathway in the metabolic response to hyperoxia in lung epithelium.

Cell Line, Tumor↗

PubMed2005

Endothelial Akt activation by hyperoxia: role in cell survival.

High oxygen concentrations (hyperoxia), often required in the treatment of preterm infants and critically ill patients, cause lung injury, targeting especially the endothelium. Exposure of primary human lung microvascular endothelial cells (HLMVEC) to hyperoxia caused transient Akt activation after 60 min, as determined by Western blot analysis of phosphorylated Ser 473 of Akt. Akt phosphorylation was also increased after 24 h of hyperoxic exposure, which declined at 48 h. Adenoviral (Ad)-mediated expression of constitutively active myrAkt protected HLMVEC against hyperoxic injury. Cell death due to hyperoxia (95% O2, 8 days), which was primarily necrotic, was substantial in control and Ad-LacZ-transduced cells, but was diminished by almost half in myrAkt-transduced cells. Hyperoxia caused increased cellular glucose consumption, an effect that was amplified in cells transduced with myrAkt compared to the LacZ-transduced or the nontransduced controls. Increased glucose consumption in myrAkt-expressing cells was accompanied by increased phosphorylation of mTOR and p70 S6-kinase. Rapamycin treatment decreased glucose consumption in myrAkt-transduced cells to levels comparable to those in control and LacZ-transduced cells exposed to hyperoxia. Ultrastructural morphometric analyses demonstrated that mitochondria and endoplasmic reticulum were less swollen in myrAkt cells relative to controls exposed to hyperoxia. These studies demonstrate that early activation of Akt occurs in hyperoxia in HLMVEC. That this event is a beneficial response is suggested by the finding that constitutive activation of Akt protects against hyperoxic stress, at least in part, by maintaining mitochondrial integrity.

Cell Survival↗

PubMed2005

Stimulation of HIF-1alpha, HIF-2alpha, and VEGF by prolyl 4-hydroxylase inhibition in human lung endothelial and epithelial cells.

Diminished alveolar and vascular development is characteristic of bronchopulmonary dysplasia (BPD) affecting many preterm newborns. Hypoxia promotes angiogenic responses in developing lung via, for example, vascular endothelial growth factor (VEGF). To determine if prolyl 4-hydroxylase (PHD) inhibition could augment hypoxia-inducible factors (HIFs) and expression of angiogenic proteins essential for lung development, HIF-1alpha and -2alpha proteins were assessed in human developing and adult lung microvascular endothelial cells and alveolar epithelial-like cells treated with either the HIF-PHD-selective inhibitor PHI-1 or the nonselective PHD inhibitors dimethyloxaloylglycine (DMOG) and deferoxamine (DFO). PHI-1 stimulated HIF-1alpha and -2alpha equally or more effectively than did DMOG or DFO, enhanced VEGF release, and elevated glucose consumption, whereas it was considerably less cytotoxic than DMOG or DFO. Moreover, VEGF receptor Flt-1 levels increased, whereas KDR/Flk-1 decreased. PHI-1 treatment also increased PHD-2, but not PHD-1 or -3, protein. These results provide proof of principle that HIF stimulation and modulation of HIF-regulated angiogenic proteins through PHI-1 treatment are feasible, effective, and nontoxic in human lung cells, suggesting the use of PHI-1 to enhance angiogenesis and lung growth in evolving BPD.

Basic Helix-Loop-Helix Proteins↗

PubMed2005

Lung epithelial cells release ATP during ozone exposure: signaling for cell survival.

The common air pollutant ozone causes acute toxicity to human airways. In primary and transformed epithelial cells from all levels of human or rat airways, ozone levels relevant to air pollution (50-200 ppb) increased extracellular [ATP] within 7-30 min. A human bronchial epithelial cell line (16HBE14o(-)) that forms electrically resistant polarized monolayers had up to 10-fold greater apical than basolateral surface extracellular [ATP] within 7 min of ozone exposure. Increased extracellular [ATP] appeared due to ATP secretion or release because (1) inhibition of ectonucleotidase (cell surface enzyme(s) which degrade ATP) by ozone did not occur until >120 min of ozone exposure and (2) brefeldin A, a secretory inhibitor, eliminated elevation of extracellular [ATP] without affecting intracellular ATP. Extracellular ATP protected against ozone toxicity in a P2Y receptor-dependent manner as (1) removal of ATP and adenosine by apyrase and adenosine deaminase, respectively, potentiated ozone toxicity, (2) extracellular supplementation with ATP, a poorly hydrolyzable ATP analog ATPgammaS, or UTP inhibited apoptotic and necrotic ozone-mediated cell death, and (3) ATP-mediated protection was eliminated by P2 and P2Y receptor inhibitors suramin and Cibacron blue (reactive blue 2), respectively. The decline in glucose uptake caused by prolonged ozone exposure was prevented by supplemental extracellular ATP, an effect blocked by suramin. Further, Akt and ERK phosphorylation resulted from exposure to supplemental extracellular ATP. Thus, extracellularly released ATP signals to prevent ozone-induced death and supplementation with ATP or its analogs can augment protection, at least in part via Akt and /or ERK signaling pathways and their metabolic effects.

Adenosine↗

PubMed2005

Effect of preterm birth on hypoxia-inducible factors and vascular endothelial growth factor in primate lungs.

Diminished vascular and alveolar development is characteristic of bronchopulmonary dysplasia (BPD). The low fetal O(2) tension promotes angiogenic responses during ontogenesis, while preterm birth interrupts normal lung growth. Most of the angiogenic responses are governed by hypoxia-inducible factors (HIFs), the expressions of which are unknown in the lungs of preterm primates. Lung tissue was harvested from fetal third-trimester baboons as well as from preterm baboons (67% or 75% of term gestation) treated with mechanical ventilation and either pro re nata (PRN) or 100% O(2). Both groups of preterm animals developed lung hypoplasia similar to human BPD. Expression of HIF-1alpha protein by Western blotting of nuclear extracts of fetal baboon samples differed from that of HIF-2alpha in that both were high at early third trimester, but at term, HIF-1alpha was absent, whereas HIF-2alpha remained unchanged. Moreover, the expression of prolyl hydroxylase domain-containing proteins 2 and 3 (PHD-2 and -3), which degrade HIFs, was increased following term birth. HIF-1alpha was diminished both in 125-day and 140-day BPD models, whereas HIF-2alpha was reduced only in the latter. Surprisingly, vascular endothelial growth factor (VEGF) was enhanced in preterm baboons with BPD as compared with age-matched fetal controls, and there was a negative correlation between HIF-1alpha and/or HIF-2alpha and VEGF in BPD. Moreover, VEGF receptors KDR and/or Flt-1 were decreased in BPD. Preterm birth also prevented the end-gestational increase in the expression of endothelial cell marker platelet-endothelial cell adhesion molecule 1. These results suggest that selective downregulation of HIFs in lungs of preterm neonates may contribute to the pathophysiology of BPD.

Actins↗

PubMed2005

PREOS NPS (Allelix/Nycomed).

NPS Allelix and Nycomed are developing PREOS, an injectable recombinant human parathyroid hormone, for the potential treatment of osteoporosis. In May 2005, NPS filed a market authorization application for PREOS in the US which was accepted for review in July 2005.

Animals↗

PubMed2004

Extracellular ATP-mediated signaling for survival in hyperoxia-induced oxidative stress.

Respiratory failure is a serious consequence of lung cell injury caused by treatment with high inhaled oxygen concentrations. Human lung microvascular endothelial cells (HLMVEC) are a principal target of hyperoxic injury (hyperoxia). Cell stress can cause release of ATP, and this extracellular nucleotide can activate purinoreceptors and mediate responses essential for survival. In this investigation, exposure of endothelial cells to an oxidative stress, hyperoxia, caused rapid but transient ATP release (20.03 +/- 2.00 nm/10(6) cells in 95% O(2) versus 0.08 +/- 0.01 nm/10(6) cells in 21% O2 at 30 min) into the extracellular milieu without a concomitant change in intracellular ATP. Endogenously produced extracellular ATP-enhanced mTOR-dependent uptake of glucose (3467 +/- 102 cpm/mg protein in 95% oxygen versus 2100 +/- 112 cpm/mg protein in control). Extracellular addition of ATP-activated important cell survival proteins like PI 3-kinase and extracellular-regulated kinase (ERK-1/2). These events were mediated primarily by P2Y receptors, specifically the P2Y2 and/or P2Y6 subclass of receptors. Extracellular ATP was required for the survival of HLMVEC in hyperoxia (55 +/- 10% surviving cells with extracellular ATP scavengers [apyrase + adenosine deaminase] versus 95 +/- 12% surviving cells without ATP scavengers at 4 d of hyperoxia). Incubation with ATP scavengers abolished ATP-dependent ERK phosphorylation stimulated by hyperoxia. Further, ERK activation also was found to be important for cell survival in hyperoxia, as treatment with PD98059 enhanced hyperoxia-mediated cell death. These findings demonstrate that ATP release and subsequent ATP-mediated signaling events are vital for survival of HLMVEC in hyperoxia.

Adenosine Triphosphate↗

PubMed2004

Cigarette smoke extract increases S-adenosylmethionine and cystathionine in human lung epithelial-like (A549) cells.

The effect of cigarette smoke extract (CSE) on S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), and sulfur amino acid metabolism was examined in human lung epithelial-like (A549) cells exposed to various CSE concentrations (2.5-100%) for 24 or 48 h. Intracellular SAM and SAM/SAH ratio were elevated after exposure to CSE for 48 h. Cell SAH content decreased, but the effect was not consistent. Cellular cystathionine, cysteine, and methionine levels were increased after CSE exposure for 48h. Sub-acute exposure to CSE induced increases in cellular SAM and SAM/SAH ratio. The transsulfuration pathway was likely activated by CSE since cystathionine increased, potentially contributing to the increased total intracellular GSH content.

Amino Acids, Sulfur↗

PubMed2003

Hypoxia protects human lung microvascular endothelial and epithelial-like cells against oxygen toxicity: role of phosphatidylinositol 3-kinase.

Hypoxic preconditioning is protective against oxidant-related damage in various organs, such as the heart. We previously showed that rats exposed to hypoxia also exhibit resistance to lethal pulmonary oxygen toxicity. The underlying mechanism and whether similar preconditioning is applicable to cellular models is unknown. In the present study, it was found that hypoxic pre-exposure induces a significant protective effect against hyperoxia-induced cell death in human lung microvascular endothelial cells (HLMVECs) and epithelial type II-like A549 cells. This effect of hypoxia is mediated by the phosphatidylinositol 3-kinase (PI3-K) signaling pathway because the presence of the PI3-K inhibitors, LY294002 and wortmannin, during pre-exposure to hypoxia completely blocks subsequent protection. Further, the hypoxia-dependent protection from hyperoxia was found to be associated with a 2-fold increase in PI3-K activity in hypoxia. Transient overexpression of a catalytically active class IA PI3-K p110alpha isoform also enhanced survival of A549 cells 2-fold compared with the empty vector control. These results indicate that hypoxia-induced activation of PI3-K is an important event in the acquisition of resistance against subsequent hyperoxic toxicity.

Cell Division↗

PubMed2003

Longitudinal change in left ventricular hypertrophy in the elderly on antihypertensive therapy.

Left ventricular hypertrophy is an independent risk factor for adverse cardiovascular events. Factors related to left ventricular hypertrophy progression or regression in the extremely elderly population including role of antihypertensive therapy, are not well recognized. We conducted a structured retrospective chart review analysis of a cohort of 100 homebound elderly, predominately female African American subjects. All persons had at least two 2-D echocardiograms interpreted by the same cardiologist prior to the initiation of this study. Information was collected on demographics, functional status, comorbid conditions, use of medication, and progression or regression of left ventricle hypertrophy between baseline and follow-up echocardiogram. At baseline and follow-up echocardiogram, 47% (n = 47) and 56% had evidence of hypertrophy, respectively. There was no association between treatment with beta-blocker, calcium channel-blocker, or diuretic therapy, and left ventricular hypertrophy at follow-up echocardiogram. Only angiotensin converting enzyme inhibitor therapy was associated with the progression of left ventricular hypertrophy in all subjects. Logistic regression analysis based on all subjects revealed that risk of left ventricular hypertrophy on follow-up echocardiogram was lower with increasing age (OR 0.95, CI 0.904-0.997) and higher with angiotensin converting enzyme inhibitor therapy (OR 3.27, CI 1.41-7.63). Among subjects with no evidence of left ventricular hypertrophy at baseline, only the presence of hypertension was associated with left ventricular hypertrophy (OR 4.4, CI 1.19-16.3). Treatment of hypertension in the elderly with angiotensin converting enzyme inhibitor seemed to worsen left ventricle hypertrophy in this patient population.

Adrenergic beta-Antagonists↗

PubMed2002

Evaluation of hepatoprotective potential of jigrine post-treatment against thioacetamide induced hepatic damage.

Jigrine a polypharmaceutical herbal formulation containing aqueous extracts of 14 medicinal plants developed on the principles of unani system of medicine is used for liver ailments. The hepatoprotective potential of jigrine post-treatment at the dose of 0.5 ml/kg per day p.o. for 21 days was evaluated against thiocetamide induced liver damage in rats. Biochemical parameters like AST, ALT in serum and TBARS and glutathione in tissues were estimated to assess liver function. Data on the biochemical parameters revealed hepatoprotective potential of jigrine post-treatment against thioacetamide induced hepatotoxicity in rats. Silymarin used as reference standard also exhibited significant hepatoprotective activity on post-treatment against thioacetamide-induced hepatotoxity in rats. The biochemical observations were supplemented with histopathological examination of rat liver sections.

Analysis of Variance↗

PubMed2002

Elevated expression of hexokinase II protects human lung epithelial-like A549 cells against oxidative injury.

Increased glucose utilization and hexokinase (HK)-II expression are adaptive features of lung cells exposed to hypoxia or hyperoxia. HK-II is the most regulated isoform of HK. Whether its overexpression could be protective against oxidative stress was explored in human lung epithelial-like (A549) cells. HK-II was overexpressed in A549 cells in a tetracycline-repressible retroviral vector system. Elevated expression of HK-II was confirmed by Western blot and activity measurements. Cell death caused by exposure to hyperoxia was decreased in HK-II-overexpressing cells. This effect was reversed when HK-II expression was suppressed with doxycycline. A similar protective effect was observed in HK-II-overexpressing cells after treatment with 1 mM hydrogen peroxide for 48 h. At baseline, fluorescence microscopy showed that overexpressed HK-II was localized to mitochondria. Electron microscopic studies showed that hyperoxia-exposed HK-II overexpressors had better-preserved and quantitatively smaller mitochondria than those in which the HK-II expression was suppressed or in the nontransduced A549 cells. Mitochondrial membrane potential was increased in HK-II-overexpressing cells exposed to hyperoxia compared with the nontransduced control cells under similar conditions. The present study demonstrates that HK-II protects human lung epithelial-like A549 cells against oxidative insults by protecting the mitochondria.

Cell Line↗

PubMed2002

Clinical evaluation of the carbomedics prosthesis: experience at providence health system in Portland.

BACKGROUND AND AIMS OF THE STUDY: This study details the authors' experience with the CarboMedics bileaflet mechanical prosthesis, and assesses the valve's efficacy in terms of early mortality and long-term morbidity. METHODS: Between July 1994 and December 2000, a total of 696 CarboMedics valves was implanted in 616 patients. Aortic valve replacement (AVR) was performed in 350 (57%) patients, mitral valve replacement (MVR) in 161 (26%), double (aortic + mitral) valve replacement (DVR) in 79 (13%), and other procedures in 26 (4%). RESULTS: There were 32 operative deaths. Operative mortality was 4.3% for AVR, 6.8% for MVR, and 7.6% for DVR. Linearized rates for late death were 3.4%/patient-year (pt-yr), 5.5%/pt-yr and 7.7%/pt-yr for AVR, MVR and DVR, respectively. Survival at five years was 80.1% for AVR, 73.0% for MVR, and 64.6% for DVR (p = 0.004). Freedom from reoperation at five years was 97.6% for AVR, 98.1% for MVR, and 94.1% for DVR (p = 0.718); freedom from thromboembolism at five years was 96.3% for AVR, 98.6% for MVR, and 88.3% for DVR (p = 0.04). Linearized rates of late thromboembolism were 0.7%/pt-yr, 0.4%/pt-yr and 2.3%/pt-yr, respectively. Freedom from PVE at five years was 98.4% for AVR, 97.0% for MVR, and 89.7% for the DVR group (p = 0.172). Linearized rates of PVE were 0.5%/pt-yr, 0.9%/pt-yr and 1.8%/pt-yr, respectively. Freedom from anticoagulant-related bleeding at five years was 98.0% in the AVR group, 97.8% in the MVR group, and 88.3% in the DVR group (p <0.001); linearized rates of this event were 0.4%/pt-yr, 0.6%/pt-yr and 3.2%/pt-yr, respectively. One valve thrombosis was found after MVR, and another in the mitral position after DVR. CONCLUSION: Early and intermediate-term follow up of the CarboMedics prosthesis indicates that the clinical performance of this valve is satisfactory, and results are comparable with those obtained for other mechanical valves.

Adolescent↗

PubMedDate not supplied

Cholesterol interferes with the MTT assay in human epithelial-like (A549) and endothelial (HLMVE and HCAE) cells.

Metabolically active cells are able to convert the MTT [3-(4,5-dimethythiazol-2-yl)-2,5-diphenyltetrazolium bromide] dye to blue formazan. This is the basis of the MTT assay, which is among the most widely used screening methods to evaluate cell viability and proliferation. When testing the effects of cholesterol products on the viability of human pulmonary epithelial-like A549 cells using trypan blue staining (cell numbers) and the MTT assay, results were inconsistent. The MTT assay indicated greater than 50% loss of viability with exposure of cells to cholesterol, whereas there was no decrease in viability indicated by trypan blue exclusion and propidium iodide uptake. A similar decrease in MTT reduction was obtained upon cholesterol treatment in human lung microvascular endothelial cells (HLMVECs) and human coronary artery endothelial cells (HCAECs) without loss of viability. This suggested a direct interference of cholesterol with the assay. However, using a cell-free system, there was no decrease in the reduction of MTT by ascorbic acid during incubation with a similar concentration of cholesterol. Light microscopy revealed enhanced exocytosis of formazan granules in presence of cholesterol. Incubation with apolipoprotein A-1 decreased cholesterol-mediated inhibition of MTT assay. These studies indicate decreased MTT reduction as a result of enhanced exocytosis of formazan due to cholesterol. A careful validation of viability assay procedures is therefore suggested in experiments where cholesterol is a constituent, to avoid a potential bias in concluding results of cytotoxicity studies.

Apolipoprotein A-I↗