Doxorubicin-induced central nervous system toxicity and protection by xanthone derivative of Garcinia mangostana.

Doxorubicin (Dox) is a potent, broad-spectrum chemotherapeutic drug used around the world. Despite its effectiveness, it has a wide range of toxic side effects, many of which most likely result from its inherent pro-oxidant activity. It has been reported that Dox has toxic effects on normal tissues, including brain tissue. The present study tested the protective effect of a xanthone derivative of Garcinia Mangostana against Dox-induced neuronal toxicity. Xanthone can prevent Dox from causing mononuclear cells to increase the level of tumor necrosis factor-alpha (TNFα). We show that xanthone given to mice before Dox administration suppresses protein carbonyl, nitrotyrosine and 4-hydroxy-2'-nonenal (4HNE)-adducted proteins in brain tissue. The levels of the pro-apoptotic proteins p53 and Bax and the anti-apoptotic protein Bcl-xL were significantly increased in Dox-treated mice compared with the control group. Consistent with the increase of apoptotic markers, the levels of caspase-3 activity and TUNEL-positive cells were also increased in Dox-treated mice. Pretreatment with xanthone suppressed Dox-induced increases in all indicators of injury tested. Together, the results suggest that xanthone prevents Dox-induced central nervous system toxicity, at least in part, by suppression of Dox-mediated increases in circulating TNFα. Thus, xanthone is a good candidate for prevention of systemic effects resulting from reactive oxygen generating anticancer therapeutics.

A neuronal model of Alzheimer's disease: an insight into the mechanisms of oxidative stress-mediated mitochondrial injury.

Alzheimer's disease (AD) is associated with beta-amyloid accumulation, oxidative stress and mitochondrial dysfunction. However, the effects of genetic mutation of AD on oxidative status and mitochondrial manganese superoxide dismutase (MnSOD) production during neuronal development are unclear. To investigate the consequences of genetic mutation of AD on oxidative damages and production of MnSOD during neuronal development, we used primary neurons from new born wild-type (WT/WT) and amyloid precursor protein (APP) (NLh/NLh) and presenilin 1 (PS1) (P264L) knock-in mice (APP/PS1) which incorporated humanized mutations in the genome. Increasing levels of oxidative damages, including protein carbonyl, 4-hydroxynonenal (4-HNE) and 3-nitrotyrosine (3-NT), were accompanied by a reduction in mitochondrial membrane potential in both developing and mature APP/PS1 neurons compared with WT/WT neurons suggesting mitochondrial dysfunction under oxidative stress. Interestingly, developing APP/PS1 neurons were significantly more resistant to beta-amyloid 1-42 treatment, whereas mature APP/PS1 neurons were more vulnerable than WT/WT neurons of the same age. Consistent with the protective function of MnSOD, developing APP/PS1 neurons have increased MnSOD protein and activity, indicating an adaptive response to oxidative stress in developing neurons. In contrast, mature APP/PS1 neurons exhibited lower MnSOD levels compared with mature WT/WT neurons indicating that mature APP/PS1 neurons lost the adaptive response. Moreover, mature APP/PS1 neurons had more co-localization of MnSOD with nitrotyrosine indicating a greater inhibition of MnSOD by nitrotyrosine. Overexpression of MnSOD or addition of MnTE-2-PyP(5+) (SOD mimetic) protected against beta-amyloid-induced neuronal death and improved mitochondrial respiratory function. Together, the results demonstrate that compensatory induction of MnSOD in response to an early increase in oxidative stress protects developing neurons against beta-amyloid toxicity. However, continuing development of neurons under oxidative damage conditions may suppress the expression of MnSOD and enhance cell death in mature neurons.

Tumor necrosis factor alpha-mediated nitric oxide production enhances manganese superoxide dismutase nitration and mitochondrial dysfunction in primary neurons: an insight into the role of glial cells.

Tumor necrosis factor-alpha (TNF-alpha), a ubiquitous pro-inflammatory cytokine, is an important mediator in the immune-neuroendocrine system that affects the CNS. The present study demonstrates that treatment with TNF-alpha activates microglia to increase TNF-alpha production in primary cultures of glial cells isolated from wild-type (WT) mice and mice deficient in the inducible form of nitric oxide synthase (iNOSKO). However, mitochondrial dysfunction in WT neurons occurs at lower concentrations of TNF-alpha when neurons are directly treated with TNF-alpha or co-cultured with TNF-alpha-treated microglia than iNOSKO neurons similarly treated. Immunofluorescent staining of primary neurons co-cultured with TNF-alpha-treated microglia reveals that the antioxidant enzyme in mitochondria, manganese superoxide dismutase (MnSOD), is co-localized with nitrotyrosine in WT but not in iNOSKO primary neuronal cells. Importantly, the percentage of surviving neurons is significantly reduced in WT neurons compared with iNOSKO neurons under identical treatment conditions. Together, the results suggest that TNF-alpha activates microglia to produce high levels of TNF-alpha and that production of nitric oxide (NO) in neurons is an important factor affecting MnSOD nitration and subsequent mitochondrial dysfunction.