Gene dosage of the apolipoprotein E (APOE) epsilon 4 allele is a major risk factor for familial Alzheimer disease (AD) of late onset (after age 60). Here we studied a large series of 115 AD case subjects and 243 controls as well as 150 affected and 197 unaffected members of 66 AD families. Our data demonstrate a protective effect of the epsilon 2 allele, in addition to the dose effect of the epsilon 4 allele in sporadic AD. Although a substantial proportion (65%) of AD is attributable to the presence of epsilon 4 alleles, risk of AD is lowest in subjects with the epsilon 2/epsilon 3 genotype, with an additional 23% of AD attributable to the absence of an epsilon 2 allele. The opposite actions of the epsilon 2 and epsilon 4 alleles further support the direct involvement of APOE in the pathogenesis of AD.

Oxidative stress markers as well as high concentrations of copper are found in the vicinity of A␤ amyloid deposits in Alzheimer's disease. The neurotoxicity of A␤ in cell culture has been linked to H 2 O 2 generation by an unknown mechanism. We now report that Cu(II) markedly potentiates the neurotoxicity exhibited by A␤ in cell culture. The potentiation of toxicity is greatest for A␤1-42 > A␤1-40 > > mouse/rat A␤1-40, corresponding to their relative capacities to reduce Cu(II) to Cu(I), form H 2 O 2 in cell-free assays and to exhibit amyloid pathology. The copper complex of A␤1-42 has a highly positive formal reduction potential (Ϸ؉500 -550 mV versus Ag/AgCl) characteristic of strongly reducing cuproproteins. These findings suggest that certain redox active metal ions may be important in exacerbating and perhaps facilitating A␤-mediated oxidative damage in Alzheimer's disease.Oxidative damage in the neocortex coincides with A␤ accumulation both in Alzheimer's disease (AD) 1 (1) and in A␤ amyloid-bearing transgenic mice (2), but the mechanisms of oxidation are unknown. The possibility that A␤ accumulation causes oxidation, perhaps by radical formation (3), has been explored, but the nature of the chemistry involved in generating A␤-associated oxidation products such as lipid peroxides (4) remains to be elaborated. In culture, A␤-induced neurotoxicity is characterized by elevated cellular H 2 O 2 and is combated by antioxidants such as vitamin E and catalase (5). The origin of the toxic H 2 O 2 is unknown.Recently, we reported that Fe(III) interacts directly with A␤1-42 and A␤1-40 to produce H 2 O 2 and TBARS formation in a cell-free manner in vitro, through reduction of the metal ion (6), suggesting that a source of the H 2 O 2 that mediates toxicity in cell cultures exposed to A␤ is extracellular. Cu(II)and Fe(III) have been found in abnormally high concentrations in amyloid plaques (Ϸ0.4 and Ϸ1 mM, respectively) and AD-affected neuropil (7), and copper-selective chelators have been shown to dissolve A␤ deposits extracted from AD post-mortem brain specimens (8). Therefore, these metal ions may be important cofactors in A␤-associated oxidative damage. Importantly, we have also reported that the generation of both Cu(II) and Fe(III)-mediated TBARS is greatest for A␤1-42 Ͼ A␤1-40 Ͼ Ͼ rat A␤1-40 (6). This rank order is of interest because it mirrors the relative participation of the peptides in amyloid neuropathology, and because the most active one (A␤1-42) is overproduced in familial AD (9). Rats and mice do not develop amyloid (10), even in mice transgenic for familial-AD linked mutant presenilin that overexpress endogenous mouse A␤1-42 (11), probably due to the three amino acid substitutions in their homologue of A␤ (Arg 5 3 Gly, Tyr 10 3 Phe, and His 13 3 Arg) (12).Although Fe(III) mediates and potentiates A␤1-40 toxicity in cell culture (13), it is not clear whether this is due to metal interaction with the peptide or due to a nonspecific increase in reactive oxygen species (ROS) generation within the cell. R...

Recent studies suggest that insulin-degrading enzyme (IDE) in neurons and microglia degrades Abeta, the principal component of beta-amyloid and one of the neuropathological hallmarks of Alzheimer's disease (AD). We performed parametric and nonparametric linkage analyses of seven genetic markers on chromosome 10q, six of which map near the IDE gene, in 435 multiplex AD families. These analyses revealed significant evidence of linkage for adjacent markers (D10S1671, D10S583, D10S1710, and D10S566), which was most pronounced in late-onset families. Furthermore, we found evidence for allele-specific association between the putative disease locus and marker D10S583, which has recently been located within 195 kilobases of the IDE gene.

Proteins are designed to function in environments crowded by cosolutes, but most studies of protein equilibria are conducted in dilute solution. While there is no doubt that crowding changes protein equilibria, interpretations of the changes remain controversial. This review combines experimental observations on the effect of small uncharged cosolutes (mostly sugars) on protein stability with a discussion of the thermodynamics of cosolute-induced nonideality and critical assessments of the most commonly applied interpretations. Despite the controversy surrounding the most appropriate manner for interpreting these effects of thermodynamic nonideality arising from the presence of small cosolutes, experimental advantage may still be taken of the ability of the cosolute effect to promote not only protein stabilization but also protein self-association and complex formation between dissimilar reactants. This phenomenon clearly has potential ramifications in the cell, where the crowded environment could well induce the same effects.