Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive dementia. Amyloid-beta peptide (Abeta), a 39-43 amino acid peptide derived from beta-amyloid precursor protein, forms insoluble fibrillar aggregates that have been linked to neuronal and vascular degeneration in AD and cerebral amyloid angiopathy. Here we demonstrate that Abeta 1-40 and a truncated fragment, Abeta 25-35, induced death of oligodendrocytes (OLGs) in vitro in a dose-dependent manner with similar potencies. Abeta-induced OLG death was accompanied by nuclear DNA fragmentation, mitochondrial dysfunction, and cytoskeletal disintegration. Abeta activation of redox-sensitive transcription factors NF-kappaB and AP-1 and antioxidant prevention of Abeta-mediated OLG death suggest that oxidative injury contributes to Abeta cytotoxicity in OLGs. Recent demonstration of Abeta deposition and white matter abnormalities in AD implies a potential pathophysiological role for Abeta-mediated cytotoxicity of OLGs in this neurodegenerative disease.

Amyloid beta peptide (A beta), a 39 to 43 amino acid fragment of the beta-amyloid precursor protein (betaAPP), forms insoluble fibrillar accumulation in neurofibrillary tangles and vascular plaques. A beta has been implicated in neuronal and vascular degeneration in brain regions susceptible to plaque formation because of its cytotoxic effect on neurons and endothelial cells (ECs). The authors used a murine cerebral endothelial cell (CEC) line and primary cultures of bovine CECs to explore the cytotoxic mechanism of A beta. A beta 1-40 and A beta 25-35 peptides caused cell death in a dose-dependent and time-dependent manner. Exposure to either A beta 25-35 or A beta 1-40 at 10 micromol/L for 48 hours caused at least 40% cell death. Cerebral endothelial cell death was characterized by nuclear condensation, mitochondrial dysfunction, and nuclear and mitochondrial DNA damage. A beta 25-35 activated both caspase-8 and caspase-3 in murine CECs. zVAD-fmk, a broad-spectrum caspase inhibitor, prevented A beta 25-35-induced increase in caspase-3 activity and CEC death. N-acetyl-cysteine, an antioxidant, also prevented A beta-induced cell death. Together, these findings indicate that A beta-mediated CEC death is an apoptotic process that is characterized by increased oxidative stress, caspase activation, mitochondrial dysfunction, and nuclear and mitochondrial DNA damage.

No abstract

Although accumulating evidence demonstrates that white matter degeneration contributes to pathology in Alzheimer's disease (AD), the underlying mechanisms are unknown. In order to study the roles of the amyloid-b peptide in inducing oxidative stress damage in white matter of AD, we investigated the effects of amyloid-b peptide 25-35 (Ab) on proinflammatory cytokine tumor necrosis factor-a (TNF-a)-induced inducible nitric oxide synthase (iNOS) in cultured oligodendrocytes (OLGs). Although Ab 25-35 by itself had little effect on iNOS mRNA, protein, and nitrite production, it enhanced TNFa-induced iNOS expression and nitrite generation in OLGs. Ab, TNF-a, or the combination of both, increased neutral sphingomyelinase (nSMase) activity, but not acidic sphingomyelinase (aSMase) activity, leading to ceramide accumulation. Cell permeable C2-ceramide enhanced TNF-ainduced iNOS expression and nitrite generation. Moreover, the specific nSMase inhibitor, 3-O-methyl-sphingomyelin (3-OMS), inhibited iNOS expression and nitrite production induced by TNF-a or by the combination of TNF-a and Ab. Overexpression of a truncated mutant of nSMase with a dominant negative function inhibited iNOS mRNA production. 3-OMS also inhibited nuclear factor jB (NF-jB) binding activity induced by TNF-a or by the combination of TNF-a and Ab. These results suggest that neutral sphingomyelinase/ ceramide pathway is required but may not be sufficient for iNOS expression induced by TNF-a and the combination of TNF-a and Ab. Keywords: amyloid beta-peptide 25-35, ceramide, inducible nitric oxide synthase, neutral sphingomyelinase, oligodendrocyte, tumor necrosis factor-a. The amyloid-b peptide (Ab), a 39-43 amino acid fragment, derived from b-amyloid precursor protein, forms insoluble fibrillar aggregates that are deposited in the brains of the Alzheimer's disease (AD) patients (Selkoe 1999). These Ab depositions have been implicated in neuronal and vascular degeneration, potentially contributing to progressive dementia, the characteristic of the disease (Selkoe 2000). Although the majority of previous studies focused on grey matter pathology in AD, accumulating data demonstrate that white matter degeneration contributes to pathology in AD as well. A high percentage of AD patients show evidence of white matter degeneration with severe loss of oligodendrocytes (OLGs) caused by apoptosis (Brown et al. 2000). The observed white matter pathology, including loss of myelin and axons (Brun and Englund 1986;Lassmann et al. 1995), as well as OLG apoptosis, might be indirect consequences of neuron damage in gray matter. Alternatively, such damage could be mediated directly by Ab deposition, which has been reported in OLGs (Wilkins et al. 2001) and in animal models (Holtzman et al. 2000).It has been shown that Ab fibrils stimulate the production of proinflammatory cytokines including tumor necrosis factor-a (TNF-a) and interleukin-1b and nitric oxide (NO) Received March 15, 2005; accepted March 16, 2005. Address correspondence and reprint requests to ...

had cirrhosis with Child-Pugh score <8. The prescribed dose was 40 Gy in four fractions. Dose reduction was permitted for normal organ dose constrains. The bile duct (BD) was delineated from the common bile duct to the first bifurcation of left and right intrahepatic duct. In addition, the central hepatobiliary tract (cHBT) was defined by a 10 or 15 mm expansion of the portal vein from the splenic confluence to the first bifurcation of left and right portal veins. We analyzed the clinical and dosimetric parameters, including multiple dose-volume histogram endpoints: D max (the maximum point dose), D mean (the mean dose), V 40Gy (volume of cHBT that received 40 Gy), V 37Gy , V 34Gy. Receiver operator curves (ROC) defined optimal dosimetric thresholds for analysis. HB toxicities were graded according to Common Terminology Criteria for Adverse Events version 4.0 and we defined grade 3+ HB toxicity as a severe HB toxicity. Results: Median follow-up duration was 9.9 months after SABR. Eight out of 28 patients (28.6%) experienced severe HB toxicity. Among clinical and dosimetric parameters, V 40Gy of cHBT with 10 mm expansion were highly associated with severe HB toxicity: V 40Gy >40 cm 3 (relative risk [RR] Z 3.2, P < 0.011). However, clinical or other dosimetric factors, D max or D mean of BD and cHBT, did not have predictive value. The risk of severe HB toxicity for V 40Gy 20 cm 3 , > 20 cm 3 , > 30 cm 3 , and > 40 cm 3 are 8.3% (n Z 1/12), 41.2% (n Z 7/17), 46.2% (n Z 6/13), and 54.5% (n Z 6/11), respectively. Conclusion: SABR to the central liver lesions should be used with caution due to the risk of HB toxicity. Radiation doses to cHBT are associated with development of severe HB toxicity. We suggest that V 40Gy <20 cm 3 as a potential dose constraint for cHBT when delivered in four fractions.