Annual Review of Pharmacology and Toxicology - Volume 47, 2007
Volume 47, 2007
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Allosteric Modulation of G Protein–Coupled Receptors
Vol. 47 (2007), pp. 1–51More LessAbstractThe past decade has witnessed a significant growth in the identification of allosteric modulators of G protein–coupled receptors (GPCRs), i.e., ligands that interact with binding sites that are topographically distinct from the orthosteric site recognized by the receptor's endogenous agonist. Because of their ability to modulate receptor conformations in the presence of orthosteric ligand, allosteric modulators can “fine-tune” classical pharmacological responses. This is advantageous in terms of a potential for engendering greater GPCR subtype-selectivity, but represents a significant challenge for detecting and validating allosteric behaviors. Although allosteric sites need not have evolved to accommodate endogenous ligands, there are a number of examples of where such modulators have been shown to contribute to physiological or pathophysiological processes. Studies are also beginning to unravel the structural basis of allosteric modulation of GPCRs. It remains to be determined whether such modulation represents interactions within monomers versus across dimers.
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Pharmacogenomic and Structural Analysis of Constitutive G Protein–Coupled Receptor Activity
Vol. 47 (2007), pp. 53–87More LessAbstractG protein–coupled receptors (GPCRs) respond to a chemically diverse plethora of signal transduction molecules. The notion that GPCRs also signal without an external chemical trigger, i.e., in a constitutive or spontaneous manner, resulted in a paradigm shift in the field of GPCR pharmacology. The discovery of constitutive GPCR activity and the fact that GPCR binding and signaling can be strongly affected by a single point mutation drew attention to the evolving area of GPCR pharmacogenomics. For a variety of GPCRs, point mutations have been convincingly linked to human disease. Mutations within conserved motifs, known to be involved in GPCR activation, might explain the properties of some naturally occurring, constitutively active GPCR variants linked to disease. In this review, we provide a brief historical introduction to the concept of constitutive receptor activity and the pharmacogenomic and structural aspects of constitutive receptor activity.
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Cell Survival Responses to Environmental Stresses Via the Keap1-Nrf2-ARE Pathway
Vol. 47 (2007), pp. 89–116More LessAbstractKeap1-Nrf2-ARE signaling plays a significant role in protecting cells from endogenous and exogenous stresses. The development of Nrf2 knockout mice has provided key insights into the toxicological importance of this pathway. These mice are more sensitive to the hepatic, pulmonary, ovarian, and neurotoxic consequences of acute exposures to environmental agents and drugs, inflammatory stresses, as well as chronic exposures to cigarette smoke and other carcinogens. Under quiescent conditions, the transcription factor Nrf2 interacts with the actin-anchored protein Keap1, largely localized in the cytoplasm. This quenching interaction maintains low basal expression of Nrf2-regulated genes. However, upon recognition of chemical signals imparted by oxidative and electrophilic molecules, Nrf2 is released from Keap1, escapes proteasomal degradation, translocates to the nucleus, and transactivates the expression of several dozen cytoprotective genes that enhance cell survival. This review highlights the key elements in this adaptive response to protection against acute and chronic cell injury provoked by environmental stresses.
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Cell Signaling and Neuronal Death
Vol. 47 (2007), pp. 117–141More LessAbstractThe past few decades have revealed that cell death can be precisely programmed with two principal forms, apoptosis and necrosis. Besides pathophysiological alterations, physiologic processes, such as the pruning of neurons during normal development and the involution of the thymus, involve apoptosis. This review focuses on the role of inter- and intracellular signaling systems in cell death, especially in the nervous system. Among neurotransmitters, glutamate and nitric oxide have been most extensively characterized and contribute to cell death in excitotoxic damage, especially in stroke and possibly in neurodegenerative diseases. Within cells, calcium, the most prominent of all intracellular messengers, mediates diverse forms of cell death with actions modulated by many proteins, including IP3 receptors, calcineurin, calpain, and cytochrome c.
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Mitochondrial Oxidative Stress: Implications for Cell Death
Vol. 47 (2007), pp. 143–183More LessAbstractIn addition to the established role of the mitochondria in energy metabolism, regulation of cell death has emerged as a second major function of these organelles. This seems to be intimately linked to their generation of reactive oxygen species (ROS), which have been implicated in mtDNA mutations, aging, and cell death. Mitochondrial regulation of apoptosis occurs by mechanisms, which have been conserved through evolution. Thus, many lethal agents target the mitochondria and cause release of cytochrome c and other pro-apoptotic proteins into the cytoplasm. Cytochrome c release is initiated by the dissociation of the hemoprotein from its binding to the inner mitochondrial membrane. Oxidation of cardiolipin reduces cytochrome c binding and increases the level of soluble cytochrome c in the intermembrane space. Subsequent release of the hemoprotein occurs by pore formation mediated by pro-apoptotic Bcl-2 family proteins, or by Ca2+ and ROS-triggered mitochondrial permeability transition, although the latter pathway might be more closely associated with necrosis. Taken together, these findings have placed the mitochondria in the focus of current cell death research.
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AMP-Activated Protein Kinase as a Drug Target
Vol. 47 (2007), pp. 185–210More LessAbstractThe AMP-activated protein kinase (AMPK) system is a regulator of energy balance at both the cellular and whole-body levels that, once activated by low energy status, effects a switch from ATP-consuming anabolic pathways to ATP-producing catabolic pathways. It now appears to be the major target for two existing classes of drug used to treat type 2 diabetes, i.e., the biguanides and thiazolidinediones. However, in both cases these activate AMPK indirectly, and an interesting question concerns whether a drug that directly activated AMPK would retain the therapeutic benefits of the existing drugs while eliminating unwanted side effects. AMPK activators also now have potential as anticancer drugs.
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Intracellular Targets of Matrix Metalloproteinase-2 in Cardiac Disease: Rationale and Therapeutic Approaches
Vol. 47 (2007), pp. 211–242More LessAbstractA new paradigm of matrix metalloproteinase-2 (MMP-2) action in the heart undergoing oxidative stress has emerged. Although best known for its role in the proteolysis of extracellular protein targets, MMP-2 is also localized to the sarcomere within the cardiomyocyte. Oxidative stress activates full-length MMP-2 without need for proteolytic processing and inactivates an endogenous inhibitor, tissue inhibitor of metalloproteinase-4. MMP-2 proteolyzes specific targets within the cell to cause acute, reversible contractile dysfunction. Inhibitors of MMPs are discussed and their possible use for the therapy of acute heart injury caused by oxidative stress is examined.
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Arsenic: Signal Transduction, Transcription Factor, and Biotransformation Involved in Cellular Response and Toxicity
Vol. 47 (2007), pp. 243–262More LessAbstractArsenic is a naturally occurring metalloid that causes oxidative stress. Exposure of humans, experimental animals, and cultured cells to arsenic results in a variety of diverse health effects, dysfunction of critical enzymes, and cell damage. In this context, one area of arsenic study has been the role of its metabolism. Like organic chemicals, arsenic undergoes reduction, methylation, and glutathione conjugation to yield polar metabolites that are substrates for transporters. These events suggest that transcription factor(s) controlling the upregulation of antioxidant proteins, Phase II xenobiotic-metabolizing enzymes, and Phase III transporters should affect arsenic-mediated oxidative stress and the steady-state level of arsenic in the cells. In this review, we summarize recent progress in arsenic toxicity in terms of disrupted signal transduction cascades, the transcription factors involved, and arsenic biotransformation, including a novel pathway.
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Aldo-Keto Reductases and Bioactivation/Detoxication
Yi Jin, and Trevor M. PenningVol. 47 (2007), pp. 263–292More LessAbstractAldo-keto reductases (AKRs) are soluble NAD(P)(H) oxidoreductases that primarily reduce aldehydes and ketones to primary and secondary alcohols, respectively. The ten known human AKR enzymes can turnover a vast range of substrates, including drugs, carcinogens, and reactive aldehydes. They play central roles in the metabolism of these agents, and this can lead to either their bioactivation or detoxication. AKRs are Phase I drug metabolizing enzymes for a variety of carbonyl-containing drugs and are implicated in cancer chemotherapeutic drug resistance. They are involved in tobacco-carcinogenesis because they activate polycyclic aromatic trans-dihydrodiols to yield reactive and redox active o-quinones, but they also catalyze the detoxication of nicotine derived nitrosamino ketones. They also detoxify reactive aldehydes formed from exogenous toxicants, e.g., aflatoxin, endogenous toxicants, and those formed from the breakdown of lipid peroxides. AKRs are stress-regulated genes and play a central role in the cellular response to osmotic, electrophilic, and oxidative stress.
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Carbonyl Reductases: The Complex Relationships of Mammalian Carbonyl- and Quinone-Reducing Enzymes and Their Role in Physiology
Vol. 47 (2007), pp. 293–322More LessAbstractCarbonyl groups are frequently found in endogenous or xenobiotic compounds. Reactive carbonyls, formed during lipid peroxidation or food processing, and xenobiotic quinones are able to covalently modify DNA or amino acids. They can also promote oxidative stress, the products of which are thought to be an important initiating factor in degenerative diseases or cancer. Carbonyl groups are reduced by an array of distinct NADPH-dependent enzymes, belonging to several oxidoreductase families. These reductases often show broad and overlapping substrate specificities and some well-characterized members, e.g., carbonyl reductase (CBR1) or NADPH-quinone reductase (NQO1) have protective roles toward xenobiotic carbonyls and quinones because metabolic reduction leads to less toxic products, which can be further metabolized and excreted. This review summarizes the current knowledge on structure and function relationships of the major human and mammalian carbonyl reductases identified.
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Drug Targeting to the Brain
Vol. 47 (2007), pp. 323–355More LessAbstractThe central nervous system (CNS) is a sanctuary site and is protected by various barriers. These regulate brain homeostasis and the transport of endogenous and exogenous compounds by controlling their selective and specific uptake, efflux, and metabolism in the brain. Unfortunately, potential drugs for the treatment of most brain diseases are therefore often not able to cross these barriers. As a result, various drug delivery and targeting strategies are currently being developed to enhance the transport and distribution of drugs into the brain. Here we discuss briefly the biology and physiology of the blood-brain barrier (BBB) and the blood-cerebro-spinal-fluid barrier (BCSFB), and, in more detail, the possibilities for delivering large-molecular-weight drugs by local and global delivery and by viral and receptor-mediated nonviral drug delivery to the (human) brain.
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Mechanism-Based Pharmacokinetic-Pharmacodynamic Modeling: Biophase Distribution, Receptor Theory, and Dynamical Systems Analysis
Vol. 47 (2007), pp. 357–400More LessAbstractMechanism-based PK-PD models differ from conventional PK-PD models in that they contain specific expressions to characterize, in a quantitative manner, processes on the causal path between drug administration and effect. This includes target site distribution, target binding and activation, pharmacodynamic interactions, transduction, and homeostatic feedback mechanisms. As the final step, the effects on disease processes and disease progression are considered. Particularly through the incorporation of concepts from receptor theory and dynamical systems analysis, important progress has been made in the field of mechanism-based PK-PD modeling. This has yielded models with much-improved properties for extrapolation and prediction. These models constitute a theoretical basis for rational drug discovery and development.
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The Functional Impact of SLC6 Transporter Genetic Variation
Vol. 47 (2007), pp. 401–441More LessAbstractSolute carrier 6 (SLC6) is a gene family of ion-coupled plasma membrane cotransporters, including transporters of neurotransmitters, amino acids, and osmolytes that mediate the movement of their substrates into cells to facilitate or regulate synaptic transmission, neurotransmitter recycling, metabolic function, and fluid homeostasis. Polymorphisms in transporter genes may influence expression and activity of transporters and contribute to behavior, traits, and disease. Determining the relationship between the monoamine transporters and complex psychiatric disorders has been a particular challenge that is being met by evolving approaches. Elucidating the functional consequences of and interactions among polymorphic sites is advancing our understanding of this relationship. Examining the influence of environmental influences, especially early-life events, has helped bridge the gap between genotype and phenotype. Refining phenotypes, through assessment of endophenotypes, specific behavioral tasks, medication response, and brain network properties has also improved detection of the impact of genetic variation on complex behavior and disease.
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mTOR Pathway as a Target in Tissue Hypertrophy
Vol. 47 (2007), pp. 443–467More LessAbstractRecent work has shown that the mTOR (mammalian target of rapamycin) pathway is an integral cell growth regulator. The mTOR pathway involves two functional complexes, TORC1 and TORC2, which have been defined by both their association with raptor or rictor, respectively, and their sensitivity to short-term rapamycin inhibition. Loss of tumor suppressors TSC1 or TSC2 leads to aberrant activation of TORC1, which has been implicated in the control of cell size. As a result, both physiologic and pathologic tissue hypertrophy are associated with TORC1 activation. Some clinical examples include skeletal and cardiac muscle hypertrophy, vascular restenosis, and compensatory nephrotic hypertrophy. Clarification of the mTOR pathway may lead to increased understanding of both the etiology and consequences of aberrant cell size regulation. This review covers some of the biochemical regulation of the mTOR pathway that may be important to the regulation of cell size, and it will present several potential clinical applications where the control of cell size may be biologically significant.
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Diseases Caused by Defects in the Visual Cycle: Retinoids as Potential Therapeutic Agents
Vol. 47 (2007), pp. 469–512More LessAbstractAbsorption of a photon by an opsin pigment causes isomerization of the chromophore from 11-cis-retinaldehyde to all-trans-retinaldehyde. Regeneration of visual chromophore following light exposure is dependent on an enzyme pathway called the retinoid or visual cycle. Our understanding of this pathway has been greatly facilitated by the identification of disease-causing mutations in the genes coding for visual cycle enzymes. Defects in nearly every step of this pathway are responsible for human-inherited retinal dystrophies. These retinal dystrophies can be divided into two etiologic groups. One involves the impaired synthesis of visual chromophore. The second involves accumulation of cytotoxic products derived from all-trans-retinaldehyde. Gene therapy has been successfully used in animal models of these diseases to rescue the function of enzymes involved in chromophore regeneration, restoring vision. Dystrophies resulting from impaired chromophore synthesis can also be treated by supplementation with a chromophore analog. Dystrophies resulting from the accumulation of toxic pigments can be treated pharmacologically by inhibiting the visual cycle, or limiting the supply of vitamin A to the eyes. Recent progress in both areas provides hope that multiple inherited retinal diseases will soon be treated by pharmaceutical intervention.
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Idiosyncratic Drug Reactions: Current Understanding
Vol. 47 (2007), pp. 513–539More LessAbstractClinical characteristics and circumstantial evidence suggest that idiosyncratic drug reactions are caused by reactive metabolites and are immune-mediated; however, there are few definitive data and there are likely exceptions. There are three principal hypotheses for how reactive metabolites might induce an immune-mediated idiosyncratic reaction: the hapten hypothesis, the danger hypothesis, and the PI hypothesis. It has been proposed that some idiosyncratic reactions, especially those involving the liver, represent metabolic idiosyncrasy; however, there are even less data to support this hypothesis. The unpredictable nature of these reactions makes mechanistic studies difficult. There is a very strong association with specific human leukocyte antigen (HLA) genes for certain reactions, but this has only been demonstrated for very few drugs. Animal models represent a very powerful tool for mechanistic studies, but the number of valid models is also limited. There may be biomarkers of risk; however, much more work needs to be done.
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Non-Nicotinic Therapies for Smoking Cessation
Vol. 47 (2007), pp. 541–564More LessAbstractCigarette smoking is the primary cause of numerous preventable diseases; as such, the goals of smoking cessation are both to reduce health risks and to improve the quality of life. Currently, the first-line smoking cessation therapies include nicotine replacement products and bupropion. The nicotinic receptor partial agonist varenicline has recently been approved by the FDA for smoking cessation. A newer product currently under development and seeking approval by the FDA are nicotine vaccines. Clonidine and nortriptyline have demonstrated some efficacy but side effects may limit their use to second-line therapeutic products. Other therapeutic drugs that are under development include rimonabant, mecamylamine, monoamine oxidase inhibitors, and dopamine receptor D3 antagonists. Inhibitors of nicotine metabolism are also promising candidates for smoking reduction and cessation. In conclusion, promising new therapeutic products are emerging and they will provide smokers additional options to assist in achieving smoking cessation.
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The Obesity Epidemic: Current and Future Pharmacological Treatments
Vol. 47 (2007), pp. 565–592More LessAbstractThe unabated rise in the prevalence of obesity is a challenge for global health care systems. Efforts to reverse this trend by dietary or behavioral counseling have not been successful, which has stimulated efforts to find a role for pharmacotherapy. Currently only a small number of antiobesity drugs are approved for long-term use and only a few compounds are in clinical development. Despite recent progress in the understanding of the regulation of energy balance, drug discovery has been less productive than expected. In the present review, the clinically available antiobesity agents are discussed. Examples of drug candidates that are currently in development are given and the possible future range of antiobesity agents is illustrated by the targets being addressed in drug discovery. Finally, the efficacy of antiobesity agents and their value in the treatment of obesity are assessed in comparison with other therapeutic approaches, such as surgery and changes in lifestyle.
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Circadian Rhythms: Mechanisms and Therapeutic Implications
Vol. 47 (2007), pp. 593–628More LessAbstractThe mammalian circadian system is organized in a hierarchical manner in that a central pacemaker in the suprachiasmatic nucleus (SCN) of the brain's hypothalamus synchronizes cellular circadian oscillators in most peripheral body cells. Fasting-feeding cycles accompanying rest-activity rhythms are the major timing cues in the synchronization of many, if not most, peripheral clocks, suggesting that the temporal coordination of metabolism and proliferation is a major task of the mammalian timing system. The inactivation of noxious food components by hepatic, intestinal, and renal detoxification systems is among the metabolic processes regulated in a circadian manner, with the understanding of the involved clock output pathways emerging. The rhythmic control of xenobiotic detoxification provides the molecular basis for the dosing time-dependence of drug toxicities and efficacy. This knowledge can in turn be used in improving or designing chronotherapeutics for the patients who suffer from many of the major human diseases.
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Targeting Antioxidants to Mitochondria by Conjugation to Lipophilic Cations
Vol. 47 (2007), pp. 629–656More LessAbstractMitochondrial oxidative damage contributes to a range of degenerative diseases. Consequently, the selective inhibition of mitochondrial oxidative damage is a promising therapeutic strategy. One way to do this is to invent antioxidants that are selectively accumulated into mitochondria within patients. Such mitochondria-targeted antioxidants have been developed by conjugating the lipophilic triphenylphosphonium cation to an antioxidant moiety, such as ubiquinol or α-tocopherol. These compounds pass easily through all biological membranes, including the blood-brain barrier, and into muscle cells and thus reach those tissues most affected by mitochondrial oxidative damage. Furthermore, because of their positive charge they are accumulated several-hundredfold within mitochondria driven by the membrane potential, enhancing the protection of mitochondria from oxidative damage. These compounds protect mitochondria from damage following oral delivery and may therefore form the basis for mitochondria-protective therapies. Here we review the background and work to date on this class of mitochondria-targeted antioxidants.
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Previous Volumes
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Volume 65 (2025)
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Volume 64 (2024)
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Volume 63 (2023)
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Volume 62 (2022)
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Volume 61 (2021)
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Volume 60 (2020)
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Volume 59 (2019)
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Volume 58 (2018)
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Volume 57 (2017)
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Volume 56 (2016)
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Volume 55 (2015)
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Volume 54 (2014)
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Volume 53 (2013)
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Volume 52 (2012)
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Volume 51 (2011)
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Volume 50 (2010)
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Volume 49 (2009)
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Volume 48 (2008)
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Volume 47 (2007)
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Volume 46 (2006)
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Volume 45 (2005)
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Volume 44 (2004)
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Volume 43 (2003)
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Volume 42 (2002)
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Volume 41 (2001)
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Volume 40 (2000)
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Volume 39 (1999)
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Volume 38 (1998)
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Volume 37 (1997)
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Volume 36 (1996)
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Volume 35 (1995)
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Volume 34 (1994)
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Volume 33 (1993)
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Volume 32 (1992)
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Volume 31 (1991)
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Volume 30 (1990)
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Volume 29 (1989)
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Volume 28 (1988)
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Volume 27 (1987)
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Volume 26 (1986)
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Volume 25 (1985)
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Volume 24 (1984)
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Volume 23 (1983)
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Volume 22 (1982)
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Volume 21 (1981)
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Volume 20 (1980)
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Volume 19 (1979)
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Volume 18 (1978)
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Volume 17 (1977)
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Volume 16 (1976)
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Volume 15 (1975)
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Volume 14 (1974)
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Volume 13 (1973)
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Volume 12 (1972)
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Volume 11 (1971)
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Volume 10 (1970)
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Volume 9 (1969)
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Volume 8 (1968)
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Volume 7 (1967)
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Volume 6 (1966)
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Volume 5 (1965)
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Volume 4 (1964)
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Volume 3 (1963)
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Volume 2 (1962)
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Volume 1 (1961)
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Volume 0 (1932)