Biomedical subjects

K D Tew

Publications and source records attributed to K D Tew.

At least 19 recordsLinked to original sources

PubMed2006

The ATP-binding cassette transporter ABCA2 as a mediator of intracellular trafficking.

ATP-binding cassette (ABC) transporters are a family of proteins that translocate molecules across cellular membranes. Substrates can include lipids, cholesterol and drugs. Mutations in ABC transporter genes can cause human pathologies and drug resistance phenotypes in cancer cells. ABCA2, the second member the A sub-family to be identified, was found at high levels in ovarian carcinoma cells resistant to the anti-cancer agent, estramustine (EM). In vitro models with elevated levels of ABCA2 are resistant to a variety of compounds, including estradiol, mitoxantrone and a free radical initiator, 2,2'-azobis-(2-amidinopropane) (AAPH). ABCA2 is most abundant in the central nervous system (CNS), ovary and macrophages. Enhanced expression of ABCA2 and related proteins, including ABCA1, ABCA4 and ABCA7, is found in human macrophages upon bolus cholesterol treatment. ABCA2 also plays a role in the trafficking of low-density lipoprotein (LDL)-derived free cholesterol and is coordinately expressed with genes involved in cholesterol homeostasis. Additionally, ABCA2 expression has been linked with gene cluster patterns consistent with pathologies including Alzheimer's disease (AD). A single-nucleotide polymorphism (SNP) in exon 14 of the ABCA2 gene was shown to be linked to early onset AD in humans, supporting the observation that ABCA2 expression influences levels of beta-amyloid peptide (Abeta), the primary component of senile plaques. ABCA2 may play a role in cholesterol transport and affect a cellular phenotype conducive to the pathogenesis of a variety of human diseases including AD, atherosclerosis and cancer.

ATP-Binding Cassette Transporters↗

PubMed2006

Glutathione S-transferase polymorphisms: cancer incidence and therapy.

The super family of glutathione S-transferases (GSTs) is composed of multiple isozymes with significant evidence of functional polymorphic variation. Over the last three decades, data from cancer studies have linked aberrant expression of GST isozymes with the development and expression of resistance to a variety of chemicals, including cancer drugs. This review addresses how differences in the human GST isozyme expression patterns influence cancer susceptibility, prognosis and treatment. In addition to the well-characterized catalytic activity, recent evidence has shown that certain GST isozymes can regulate mitogen-activated protein kinases or can facilitate the addition of glutathione to cysteine residues in target proteins (S-glutathionylation). These multiple functionalities have contributed to the recent efforts to target GSTs with novel small molecule therapeutics. Presently, at least two drugs are in late-stage clinical testing. The evolving functions of GST and their divergent expression patterns in individuals make them an attractive target for drug discovery.

Drug Resistance, Neoplasm↗

PubMed2004

Mitoxantrone resistance in a small cell lung cancer cell line is associated with ABCA2 upregulation.

The aim of this study was to find factors that could explain the accumulation difference of mitoxantrone in the BCRP1-negative GLC4-MITO cell line compared to GLC4. Comparative genomic hybridisation (CGH) was applied to determine chromosomal differences between GLC4 and GLC4-MITO. Comparative genomic hybridisation analysis revealed gain of 2q, 6p, 9q, 13q, 14q, 15q, 19q and Xp and loss of 1p, 2q, 3p, 3q, 4q, 6q, 8q, 11p, 16p, 17q, 18p, 20p and Xq. In the over-represented chromosomal areas, seven transporter genes were identified: ABCB6, ABCB2 (TAP1), ABCB3 (TAP2), ABCF1 (ABC50), ABCC10 (MRP7), ABCA2 (ABC2) and ABCC4 (MRP4). No RNA or protein upregulation was observed for ABCB6, ABCF1, ABCC10, ABCC4, ABCB2 and ABCB3, but an increased expression was detected for ABCA2 mRNA in GLC4-MITO. ABCA2 is known to be involved in resistance to estramustine. In the MTT assay, GLC4-MITO was two-fold resistant to estramustine compared to GLC4. Coincubation with estramustine and mitoxantrone increased mitoxantrone accumulation in GLC4-MITO, while this was not affected in GLC4. This suggests that estramustine is able to block mitoxantrone efflux in GLC4-MITO cells. These data reveal that cellular reduction of mitoxantrone in a mitoxantrone-resistant cell line is associated with overexpression of ABCA2.

ATP-Binding Cassette Transporters↗

PubMed2004

The role of carotenoids in the prevention of human pathologies.

Reactive oxygen species (ROS) and oxidative damage to biomolecules have been postulated to be involved in the causation and progression of several chronic diseases, including cancer and cardiovascular diseases, the two major causes of morbidity and mortality in Western world. Consequently dietary antioxidants, which inactivate ROS and provide protection from oxidative damage are being considered as important preventive strategic molecules. Carotenoids have been implicated as important dietary nutrients having antioxidant potential, being involved in the scavenging of two of the ROS, singlet molecular oxygen (1O2) and peroxyl radicals generated in the process of lipid peroxidation. Carotenoids are lipophilic molecules which tend to accumulate in lipophilic compartments like membranes or lipoproteins. Chronic ethanol consumption significantly increases hydrogen peroxide and decreases mitochondrial glutathione (GSH) in cells overexpressing CYP2E1. The depletion of mitochondrial GSH and the rise of hydrogen peroxide are responsible for the ethanol-induced apoptosis. Increased intake of lycopene, a major carotenoid in tomatoes, consumed as the all-trans-isomer attenuates alcohol induced apoptosis in 2E1 cells and reduces risk of prostate, lung and digestive cancers. Cancer-preventive activities of carotenoids have been associated as well as with their antioxidant properties and the induction and stimulation of intercellular communication via gap junctions which play a role in the regulation of cell growth, differentiation and apoptosis. Gap junctional communication between cells which may be a basis for protection against cancer development is independent of the antioxidant property.

Antioxidants↗

PubMed2003

Trace elements in human physiology and pathology. Copper.

Copper is a trace element, important for the function of many cellular enzymes. Copper ions can adopt distinct redox states oxidized Cu(II) or reduced (I), allowing the metal to play a pivotal role in cell physiology as a catalytic cofactor in the redox chemistry of enzymes, mitochondrial respiration, iron absorption, free radical scavenging and elastin cross-linking. If present in excess, free copper ions can cause damage to cellular components and a delicate balance between the uptake and efflux of copper ions determines the amount of cellular copper. In biological systems, copper homeostasis has been characterized at the molecular level. It is coordinated by several proteins such as glutathione, metallothionein, Cu-transporting P-type ATPases, Menkes and Wilson proteins and by cytoplasmic transport proteins called copper chaperones to ensure that it is delivered to specific subcellular compartments and thereby to copper-requiring proteins.

Adenosine Triphosphatases↗

PubMed2003

Phytosterols in the prevention of human pathologies.

Coronary heart disease is a major health problem in developed countries. Many studies have shown that elevated serum concentrations of total or low-density-lipoprotein cholesterol (LDL cholesterol) are high risk factors, whereas high concentrations of high-density-lipoprotein cholesterol (HDL cholesterol) or a low LDL to HDL cholesterol ratio may protect against coronary heart disease. Plant sterols and stanols derived from vegetable oils or wood pulp have been shown to lower total and LDL cholesterol levels in humans by inhibiting cholesterol absorption from the intestine. These findings may lead to new therapeutic options to treat hypercholesterolemia. In addition, phytosterols may influence cell growth and apoptosis of tumor cells. However, they can interfere with the absorption of fat soluble vitamins and carotenoids.

Anticholesteremic Agents↗

PubMed2002

Estrogens and environmental estrogens.

The natural female sex hormone estrogens binds once inside the cell to a protein receptor to form a 'ligand-hormone receptor complex'. The binding activates the hormone receptor, which triggers specific cellular processes. The activated hormone receptor then turns on specific genes, causing cellular changes that lead to responses typical of a ligand-hormone receptor complex. Estrogens (especially estradiol) bring out the feminine characteristics, control reproductive cycles and pregnancy, influence skin, bone, the cardiovascular system and immunity. Natural hormones are more potent than any of the known synthetic environmental estrogens (except drugs such as diethylstilbestrol [DES]). Estrogen production varies according to different factors (gender, age and reproductive cycles). Women produce more estrogen than men and the production is more abundant during fetal development than in the postmenopausal period. Most natural estrogens are short-lived, do not accumulate in tissue and are easily broken down in the liver. In contrast to natural estrogens, estrogenic drugs such as ethynylestradiol diethylstilbestrol (DES), synthetic environmental estrogens such as beta-hexachlorocyclohexane (beta-HCH), polychlorinated biphenyls (PCBs), o, p, p'DDT, 4-nonylphenol (NP) and phytoestrogens such as isoflavones or lignans, are more stable and remain in the body longer than natural estrogens. Because most of these compounds are lipophilic, they tend to accumulate within the fat and tissue of animals and humans. Thus, depending on the natural estrogen levels, environmental estrogens may have different influences (mimicking, blocking or cancelling out estrogen's effects) on estrogen activities.

Age Factors↗

PubMed2002

Polyphenols: do they play a role in the prevention of human pathologies?

Polyphenols are the most abundant antioxidants in our diets. The main classes of polyphenols are phenolic acids (mainly caffeic acid) and flavonoids (the most abundant in the diet are flavanols (catechins plus proanthocyanidins), anthocyanins and their oxidation products), which account for one- and two-thirds, respectively. Polyphenols are reducing agents, and together with other dietary reducing agents, such as vitamin C, vitamin E and carotenoids, referred to as antioxidants, protect the body's tissues against oxidative stress and associated pathologies such as cancers, coronary heart disease and inflammation. The biological properties, bioavailability, antioxidant activity, specific interactions with cell receptors and enzymes, are related to the chemical structure of polyphenols. It is, therefore, essential to know the nature of the main polyphenols ingested, their dietary origin, the amounts consumed in different diets, their bioavailability and the factors controlling their bioavailability.

Antioxidants↗

PubMed2002

Polyunsaturated fatty acids (PUFA) and eicosanoids in human health and pathologies.

Linoleic and alpha-linolenic acids, obtained from plant material in the diet are the precursors in tissues of two families with opposing effects which are referred to as "essential fatty acids" (EFA): arachidonic acid (AA) and pentaene (eicosapentaenoic acid: EPA) and hexaene (docosahexaenoic acid: DHA) acids. The role of EFA is crucial, without a source of AA or compounds which can be converted into AA, synthesis of prostaglandins (PGs) by a cyclooxygenase (COX) enzyme would be compromised, and this would seriously affect many normal metabolic processes. COX, also known as prostaglandin endoperoxide synthase (Pghs) or as prostaglandin G/H synthase, is a key membrane bound enzyme responsible for the oxidation of AA to PGs. Two COX isoforms have been identified, COX-1 and COX-2 that form PGH2, a common precursor for the biosynthesis of thromboxane A2 (TxA2), prostacyclin (PGI2) and PGs (PGD2, PGE2, PGF2alpha. COX-1 enzyme is expressed constitutively in most cells and tissues. Its expression remains constant under either physiological or pathological conditions controlling synthesis of those PGs primarily involved in the regulation of homeostatic functions. In contrast, COX-2 is an intermediate response gene that encodes a 71-kDa protein. COX-2 is normally absent from most cells but highly inducible in certain cells in response to inflammatory stimuli resulting in enhanced PG release. PGs formed by COX-2 primarily mediate pain and inflammation but have multiple effects that can favour tumorigenesis. They are more abundant in cancers than in normal tissues from which the cancers arise. COX-2 is a participant in the pathway of colon carcinogenesis, especially when mutation of the APC (Adenomatous Polyposis Coli) tumour suppressor gene is the initiating event. In addition, COX-2 up-regulation and elevated PGE2 levels are involved in breast carcinogenesis. It seems that there is a correlation between COX-2 level of expression and the size of the tumours and their propensity to invade underlying tissue. Inhibition by non-steroidal anti-inflammatory drugs (NSAIDs) of COX enzymes which significantly suppress PGE2 levels, reduced breast cancer incidence and protected against colorectal cancer. Therefore it is suggested that consumption of a diet enriched in n-3 PUFA (specifically EPA and DHA) and inhibition of COX-2 by NSAIDs may confer cardioprotective effects and provide a significant mechanism for the prevention and treatment of human cancers.

Cardiovascular Diseases↗

PubMed2002

I. Arginine.

L-Arginine (Arg) is classified as an essential amino acid for birds, carnivores and young mammals and a conditionally essential amino acid for adults. It is converted by arginase to L-ornithine, a precursor of polyamines and urea, which is important in the urea cycle. Arg serves as a precursor for creatine, which plays an essential role in the energy metabolism of muscle, nerve and testis and accounts for Arg catabolism and for the synthesis of agmatine and proteins. Via its ability to increase growth hormone secretion it influences immune function. Depending on nutritional status and developmental stage, normal plasma Arg concentrations in humans and animals range from 95 to 250 micromol/l. Systemic or oral Arg administration has been shown to improve cardiovascular function and reduce myocardial ischemia in coronary artery disease patients. It reduces blood pressure and renal vascular resistance in essential hypertensive patients with normal or insufficient renal function. Although Arg plasma concentrations are not altered in hypercholesterolemic individuals, oral or intravenous Arg administration can reverse endothelial dysfunction in hypercholesterolemic patients and in cigarette smokers. The main importance of Arg is attributed to its role as a precursor for the synthesis of nitric oxide (NO), a free radical molecule that is synthesized in all mammalian cells from L-Arg by NO synthase (NOS). NO appears to be a major form of the endothelium-derived relaxing factor (EDRF). NO and EDRF share similar chemical and pharmacological properties and are derived from the oxidation of a terminal guanidine group of L-Arg. Various mechanisms have been implicated in the defect in vascular relaxation. These include, increased diffusional barrier for NO, L-Arg depletion, altered levels of reactive oxygen, inactivation of NO by superoxide anions (O2-). The independent reactions of O2-, NO and their reaction yielding peroxynitrite are critical in the initiation and maintenance of the atherosclerotic state and contribute to the defect in vasorelaxation. NO also plays a role as a neurotransmitter, mediator of immune response and as signaling molecule. The NO synthesized by iNOS in macrophages contributes to their cytotoxic activity against tumor cells, bacteria and protozoa. Our aim here is to review on some amino acids with high functional priority such as Arg and to define their effective activity in human health and pathologies.

Animals↗

PubMed2002

II. Glutamine and glutamate.

Glutamine and glutamate with proline, histidine, arginine and ornithine, comprise 25% of the dietary amino acid intake and constitute the "glutamate family" of amino acids, which are disposed of through conversion to glutamate. Although glutamine has been classified as a nonessential amino acid, in major trauma, major surgery, sepsis, bone marrow transplantation, intense chemotherapy and radiotherapy, when its consumption exceeds its synthesis, it becomes a conditionally essential amino acid. In mammals the physiological levels of glutamine is 650 micromol/l and it is one of the most important substrate for ammoniagenesis in the gut and in the kidney due to its important role in the regulation of acid-base homeostasis. In cells, glutamine is a key link between carbon metabolism of carbohydrates and proteins and plays an important role in the growth of fibroblasts, lymphocytes and enterocytes. It improves nitrogen balance and preserves the concentration of glutamine in skeletal muscle. Deamidation of glutamine via glutaminase produces glutamate a precursor of gamma-amino butyric acid, a neurotransmission inhibitor. L-Glutamic acid is a ubiquitous amino acid present in many foods either in free form or in peptides and proteins. Animal protein may contain from 11 to 22% and plants protein as much as 40% glutamate by weight. The sodium salt of glutamic acid is added to several foods to enhance flavor. L-Glutamate is the most abundant free amino acid in brain and it is the major excitatory neurotransmitter of the vertebrate central nervous system. Most free L-glutamic acid in brain is derived from local synthesis from L-glutamine and Kreb's cycle intermediates. It clearly plays an important role in neuronal differentiation, migration and survival in the developing brain via facilitated Ca++ transport. Glutamate also plays a critical role in synaptic maintenance and plasticity. It contributes to learning and memory through use-dependent changes in synaptic efficacy and plays a role in the formation and function of the cytoskeleton. Glutamine via glutamate is converted to alpha-ketoglutarate, an integral component of the citric acid cycle. It is a component of the antioxidant glutathione and of the polyglutamated folic acid. The cyclization of glutamate produces proline, an amino acid important for synthesis of collagen and connective tissue. Our aim here is to review on some amino acids with high functional priority such as glutamine and to define their effective activity in human health and pathologies.

Animals↗

PubMed2001

Gene expression profiling using a novel method: amplified differential gene expression (ADGE).

Amplified differential gene expression (ADGE) is a novel technique, designed to profile gene expression of the whole transcriptome or to compare expression of a set of genes between two samples. ADGE employs hybridization to quadratically amplify the ratio of an expressed gene between control and tester samples before displaying. The subtle structures of adapters and primers are designed for displaying the amplified ratio of an expressed gene between two samples. Four selective nucleotides at the 3' end of primers are used to increase PCR efficiency for targeted molecules and to improve detection of PCR products. Double PCR with the same pair of primers expands the detection range, especially for genes of low abundance. Integration of these steps makes ADGE sensitive and accurate. Application to drug resistant human tumor cell lines showed that ADGE accurately profiled expression levels for induced, repressed or unchanged genes. The qualitative expression patterns for ADGE were verified with RT-PCR.

DNA Primers↗

PubMed2001

Cloning and characterization of human adenosine 5'-triphosphate-binding cassette, sub-family A, transporter 2 (ABCA2).

We have isolated the full-length cDNA for human ATP-binding cassette, sub-family A, member 2 transporter (ABCA2). The ORF of this cDNA encodes a protein consisting of 2436 amino acids with apparent molecular weight of M(r) 270,000. Accordingly, ABCA2 is the largest known mammalian ABC transporter described thus far. Analysis of mRNA expression levels indicated that ABCA2 is highest in human brain and has a broad expression pattern in a panel of tumor cell lines. Using specific antibodies to ABCA2 and various organelle marker proteins, ABCA2 was found to colocalize with the lysosomal/endosomal marker LAMP1, forming discrete, punctate intracellular vesicles. In ABCA2-transfected cells, the transporter also colocalized with a fluorescently labeled steroid analogue, estramustine. The sequestration of the steroid into the lysosomal/endosomal compartment indicates a potential substrate specificity for ABCA2. Furthermore, the presence of a lipocalin signature motif in the ABCA2 sequence suggests a possible broad role for this protein in the transport of steroids, lipids, and related molecules.

ATP-Binding Cassette Transporters↗

PubMed2001

Glutathione S-transferase P1-1 (GSTP1-1) inhibits c-Jun N-terminal kinase (JNK1) signaling through interaction with the C terminus.

c-Jun N-terminal kinase (JNK)-mediated cell signaling pathways are regulated endogenously in part by protein-protein interactions with glutathione S-transferase P1-1 (GSTP1-1) (). Using purified recombinant proteins, combined with fluorescence resonance energy transfer technology, we have found that the C terminus of JNK is critical to the interaction with GSTP1-1. The apparent K(d) for full-length JNK was 188 nm and for a C-terminal fragment (residues 200-424) 217 nm. An N-terminal fragment (residues 1-206) did not bind to GSTP1-1. Increased expression of the C-terminal JNK fragment in a tetracycline-inducible transfected NIH3T3 cell line produced a concentration-dependent increase in the kinase activity of JNK under normal, unstressed growth conditions indicating a dominant-negative effect. This suggests that the fragment can compete with endogenous full-length functional JNK resulting in dissociation of the GSTP1-1-JNK interaction and concomitant JNK enzyme activation. By using an antibody to hemagglutinin-tagged C-JNK, a concentration-dependent co-immunoprecipitation of GSTP1-1 was achieved. These data provide evidence for direct interactions between the C-terminal of JNK and GSTP1-1 and a rationale for considering GSTP1-1 as a critical ligand-binding protein with a role in regulating kinase pathways.

3T3 Cells↗

PubMed2001

Iron: deficiencies and requirements.

A report from the World Health Organization estimates that 46% of the world's 5- to 14-year-old children are anemic. In addition, 48% of the world's pregnant women are anemic. A majority of these cases of anemia are due to iron deficiency. Our aim here is to review the latest data on iron regulatory mechanisms, iron sources and requirements. Human and animal studies have shown that amino acids and peptides influence iron absorption from the intestinal lumen. Inter-organ transport and uptake of nonheme iron is largely performed by the complex transferring-transferring receptor system. Moreover, the discovery of cytoplasmic iron regulatory proteins (IRPs) has provided a molecular framework from which we understand the coordination of cellular iron homeostasis in mammals. IRPs and the iron responsive elements (IREs) to which they bind allow mammals to make use of the essential properties of iron while reducing its potentially toxic effect. Physiologic iron requirements are three times higher in pregnancy than they are in menstruating women (approximately 1200 mg must be acquired from the body's iron store or from the diet by the end of pregnancy). The administration of iron supplements weekly instead of daily in humans has been proposed and is being actively investigated as a viable means of controlling iron deficiency in populations, including pregnant women.

Adolescent↗

PubMed2001

Prevention of pathologies associated with oxidative stress and dietary intake deficiencies: folate deficiency and requirements.

Folate (folic acid, folacin) is an essential vitamin that is found in nature. Folates contain the core chemical structure of pteroylglutamic acid, but vary in their state of reduction, the single carbon moiety they bear and/or the length of the glutamate chain. At least 50% of whole body folate is stored in the liver. The influence of intracellular folate concentration depends largely on dietary intake. The supply of folate depends primarily on the quantity and bioavailability of ingested folate and the rate of loss by urinary and fecal routes and through catabolism.

Animals↗

PubMed2001

Cellular thiols and reactive oxygen species in drug-induced apoptosis.

In higher eukaryotes, reactive oxygen species (ROS) are generated during respiration in mitochondria in the course of reduction of molecular oxygen as well as by distinct enzyme systems. ROS have been implicated in the regulation of diverse cellular functions including defense against pathogens, intracellular signaling, transcriptional activation, proliferation, and apoptosis. The reduction-oxidation (redox) state of the cell is primarily a consequence of the precise balance between the levels of ROS and endogenous thiol buffers present in the cell, such as glutathione and thioredoxin, which protect cells from oxidative damage. Dramatic elevation of ROS, exceeding compensatory changes in the level of the endogenous thiol buffers, may result in the sustained activation of signaling pathways and expression of genes that induce apoptosis in affected cells. Many cytotoxic drugs function selectively to kill cancer cells by the abrogation of proliferative signals, leading to cell death, and numerous reports have demonstrated that ROS are generated following treatment with these drugs. In this review, we will summarize recent contributions to our understanding of the importance of cytotoxic drug-induced modulation of cellular redox status for signaling and transcription leading to activation of apoptotic effector mechanisms.

Animals↗

PubMed2001

Binding of the aminothiol WR-1065 to transcription factors influences cellular response to anticancer drugs.

The aminothiol WR-1065 (the active form of amifostine) protects normal tissues from the toxic effects of certain cancer drugs, while leaving their antitumor effects unchanged. The present data address the mechanism of action of this dichotomous effect. (35)S-Labeled WR-1065 bound directly to the transcription factors nuclear factor-kappaB, activator protein-1, and p53, resulting in enhanced binding of these proteins to target regulatory DNA sequences and subsequent transactivation of a number of downstream genes. Since other small molecular thiols could mimic WR-1065, the redox potential of the sulfhydryl is an important determinant of its activity. In nontransformed cells, WR-1065 protected cells from the cytotoxic effects of paclitaxel in a p53-dependent manner. However, in a transformed human tumor cell line, there was no cytoprotectivity by WR-1065, consistent with the premise that p53-dependent growth arrest is the basis for the protective effect of this compound, and that this pathway is abrogated in human tumors. The combined data support the principle that the cellular effects of the aminothiol WR-1065 are mediated through an impact on transcriptional regulation and are not only a consequence of radical scavenging.

Animals↗