Publisher Summary This chapter discusses the role of free radicals and catalytic metal ions in human disease. The importance of transition metal ions in mediating oxidant damage naturally leads to the question as to what forms of such ions might be available to catalyze radical reactions in vivo . The chapter discusses the metabolism of transition metals, such as iron and copper. It also discusses the chelation therapy that is an approach to site-specific antioxidant protection. The detection and measurement of lipid peroxidation is the evidence most frequently cited to support the involvement of free radical reactions in toxicology and in human disease. A wide range of techniques is available to measure the rate of this process, but none is applicable to all circumstances. The two most popular are the measurement of diene conjugation and the thiobarbituric acid (TBA) test, but they are both subject to pitfalls, especially when applied to human samples. The chapter also discusses the essential principles of the peroxidation process. When discussing lipid peroxidation, it is essential to use clear terminology for the sequence of events involved; an imprecise use of terms such as initiation has caused considerable confusion in the literature. In a completely peroxide-free lipid system, first chain initiation of a peroxidation sequence in a membrane or polyunsaturated fatty acid refers to the attack of any species that has sufficient reactivity to abstract a hydrogen atom from a methylene group.

Role of free radicals and catalytic metal ions in human disease: an overview.

Glutamate neurotoxicity and diseases of the nervous system

Radicals are species containing one or more unpaired electrons. The oxygen radical superoxide (O 2 - ) and the non-radical oxidants hydrogen peroxide (H2O2) and hypochlorous acid (HOCl) are produced during normal metabolism and perform several useful functions. Excessive production of O 2 - and H2O2 can result in tissue damage, which often involves generation of highly reactive hydroxy 1 radical (· OH) and other oxidants in the presence of “catalytic” iron or copper ions. A major form of antioxidant defence is the storage and transport of iron or copper ions in forms that will not catalyze formation of reactive radicals. Tissue injury, e. g., by ischaemia or trauma, can cause increased iron availability and accelerate free radical reactions. This may be especially important in the brain, since areas of this organ are rich in iron and cerebrospinal fluid cannot bind released iron ions. Oxidative stress upon nervous tissue can produce damage by several interacting mechanisms, including rises in intracellular free Ca2+ and, possibly, release of excitatory amino acids. Recent suggestions that free radical reactions are involved in the neurotoxicity of aluminium and in damage to the substantia nigra in Parkinson’s disease are reviewed. Finally, the nature of antioxidants is discussed, with a suggestion that antioxidant enzymes and chelators of iron ions may be more generally useful protective agents than chain-breaking antioxidants. Careful precautions must be taken in the design of antioxidants for therapeutic use.

Reactive Oxygen Species and the Central Nervous System

Privileged substructures are of potentially great importance in medicinal chemistry. These scaffolds are characterized by their ability to promiscuously bind to a multitude of receptors through a variety of favorable characteristics. This may include presentation of their substituents in a spatially defined manner and perhaps also the ability to directly bind to the receptor itself, as well as exhibiting promising characteristics to aid bioavailability of the overall molecule. It is believed that some privileged substructures achieve this through the mimicry of common protein surface elements that are responsible for binding, such as β- and gamma;-turns. As a result, these structures represent a promising means by which new lead compounds may be identified.

The combinatorial synthesis of bicyclic privileged structures or privileged substructures

Migraine is a common and sometimes debilitating disorder. This review describes the epidemiology, pathophysiology, and preventive and symptomatic treatment of migraine, with special attention to drug therapy with the triptans.

Migraine--current understanding and treatment.

Novel 21-amino steroids as potent inhibitors of iron-dependent lipid peroxidation.

Oxidation of ferrous iron during peroxidation of lipid substrates

Chloride channel expression with the tandem construct of alpha 6-beta 2 GABAA receptor subunit requires a monomeric subunit of alpha 6 or gamma 2.

Isochroman-6-carboxamides as Highly Selective 5-HT1D Agonists: Potential New Treatment for Migraine without Cardiovascular Side Effects

The alpha 1 beta 2 and alpha 1 beta 2 gamma 2 subtypes, common subtypes of gamma-aminobutyric acid (GABA)A receptors in the brain, are known to share many ligands, but only the latter interacts with benzodiazepines. In this study, we attempted to examine whether the presence of the gamma 2 subunit in the cloned receptors alters the binding properties of GABA and t-butylbicyclophosphorothionate (TBPS) (a highly sensitive probe for conformational changes in the chloride ionophore of GABAA receptors) and their interactions. Using a high-level expression system of SF-9 cells infected with baculovirus, we produced a group of cloned GABAA receptors with variations in the ratio (0 to 3) of the virion carrying the cDNA for the gamma 2 subunit to those carrying the cDNAs for the alpha 1 and beta 2 subunits. The number of benzodiazepine binding sites increased as the level of the gamma 2 virion was raised and reached that of GABA high affinity sites at a gamma 2 to alpha 1 beta 2 ratio of 0.5 or more. It appears that the conversion of the alpha 1 beta 2 to the alpha 1 beta 2 gamma 2 subtype is favorable and complete in the presence of a sufficient level of the gamma 2 subunit, assuming the number of the GABA sites to be equal to the total number of the cloned GABAA receptors. In all preparations, the dissociation constants for flunitrazepam, muscimol, and TBPS were fairly constant, and the maximal number of binding sites for TBPS appeared to be equal to that for muscimol, with no dependence on the gamma 2 virion levels. The effect of GABA on TBPS binding, however, were markedly altered by the gamma 2 subunit. With the alpha 1 beta 2 subtype GABA at concentrations occupying its high affinity sites markedly stimulated but at higher concentrations (micromolar ranges) inhibited TBPS binding, whereas with the alpha 1 beta 2 gamma 2 subtype GABA inhibited TBPS binding without the early stimulatory phase. We also confirmed the selective interaction of Zn2+ (50 microM) with the alpha 1 beta 2 subtype, as probed with TBPS binding, and observed a progressive disappearance of Zn2+ sensitivity as the gamma 2 virion level increased.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of interactions of [3H]muscimol, t-butylbicyclophosphoro[35S]thionate, and [3H]flunitrazepam with cloned gamma-aminobutyric acidA receptors of the alpha 1 beta 2 and alpha 1 beta 2 gamma 2 subtypes.

Jeffrey F Pregenzer

Papers

Novel 21-amino steroids as potent inhibitors of iron-dependent lipid peroxidation.

Oxidation of ferrous iron during peroxidation of lipid substrates

Chloride channel expression with the tandem construct of alpha 6-beta 2 GABAA receptor subunit requires a monomeric subunit of alpha 6 or gamma 2.

Isochroman-6-carboxamides as Highly Selective 5-HT1D Agonists: Potential New Treatment for Migraine without Cardiovascular Side Effects

Comparison of interactions of [3H]muscimol, t-butylbicyclophosphoro[35S]thionate, and [3H]flunitrazepam with cloned gamma-aminobutyric acidA receptors of the alpha 1 beta 2 and alpha 1 beta 2 gamma 2 subtypes.