Induction of protein catabolism and the ubiquitin-proteasome pathway by mild oxidative stress

Muscle wasting in cancer cachexia is associated with increased levels of malondialdehyde (MDA) in gastrocnemius muscles, suggesting an increased oxidative stress. To determine whether oxidative stress contributes to muscle protein catabolism, an in vitro model system, consisting of C2C12 myotubes, was treated with either 0.2 mM FeSO4, 0.1 mM H2O2, or both, to replicate the rise in MDA content in cachexia. All treatments caused an increased protein catabolism and a decreased myosin expression. There was an increase in the proteasome chymotrypsin-like enzyme activity, while immunoblotting showed an increased expression of the 20S proteasome α-subunits, p42, and the ubiquitin-conjugating enzyme, E214k. These results show that mild oxidative stress increases protein degradation in skeletal muscle by causing an increased expression of the major components of the ubiquitin-proteasome pathway. © 2002 Elsevier Science Ireland Ltd. All rights reserved.

Plasma levels of HDL and carotenoids are lower in dementia patients with vascular comorbidities

Elevated serum cholesterol concentrations in mid-life increase risk for Alzheimer's disease (AD) in later life. However, lower concentrations of cholesterol-carrying high density lipoprotein (HDL) and its principal apolipoprotein A1 (ApoA1) correlate with increased risk for AD. As HDL transports oxocarotenoids, which are scavengers of peroxynitrite, we have investigated the hypothesis that lower HDL and oxocarotenoid concentrations during AD may render HDL susceptible to nitration and oxidation and in turn reduce the efficiency of reverse cholesterol transport (RCT) from lipid-laden cells. Fasting blood samples were obtained from subjects with 1) AD without cardiovascular comorbidities and risk factors (AD); 2) AD with cardiovascular comorbidities and risk factors (AD Plus); 3) normal cognitive function; for carotenoid determination by HPLC, analysis of HDL nitration and oxidation by ELISA, and 3H-cholesterol export to isolated HDL. HDL concentration in the plasma from AD Plus patients was significantly lower compared to AD or control subject HDL levels. Similarly, lutein, lycopene, and zeaxanthin concentrations were significantly lower in AD Plus patients compared to those in control subjects or AD patients, and oxocarotenoid concentrations correlated with Mini-Mental State Examination scores. At equivalent concentrations of ApoA1, HDL isolated from all subjects irrespective of diagnosis was equally effective at mediating RCT. HDL concentration is lower in AD Plus patients' plasma and thus capacity for RCT is compromised. In contrast, HDL from patients with AD-only was not different in concentration, modifications, or function from HDL of healthy age-matched donors. The relative importance of elevating HDL alone compared with elevating carotenoids alone or elevating both to reduce risk for dementia should be investigated in patients with early signs of dementia.

P4-235 protein oxidation, lipid peroxidation and antioxidant status are similarly altered in Alzheimer disease and vascular dementia

Background: A large body of evidence supports a role of oxidative stress in Alzheimer disease (AD) and in cerebrovascular disease. A vascular component might be critical in the pathophysiology of AD. Objective(s): To evaluate the simultaneous behavior of a broad spectrum of peripheral antioxidants and biomarkers of oxidative stress in AD and vascular dementia (VaD). Methods: Sixty-three AD patients, 23 VaD patients and 55 controls were included in the study. We measured plasma levels of water-soluble (vitamin C and uric acid) and lipophilic (vitamin E, vitamin A, carotenoids including lutein, zeaxanthin, [3-cryptoxanthin, lycopene, c~- and [3-carotene) antioxidant micronutrients as well as levels of biomarkers of lipid peroxidation [malondialdehyde (MDA)] and of protein oxidation [immunoglobniin G (Ig G) levels of protein carbonyls and dityrosine] in patients and controls. Results: AD and VaD patients showed significantly decreased plasma levels of the water-soluble vitamin C and uric acid, of the lipophilic vitamin Eand vitamin A, and of the carotenoids lutein, zeaxanthin, 13-cryptoxanthin, lycopene and (x-carotene as compared to controls; among biomarkers of oxidative stress, only the content of dityrosine in Ig G was found to be significantly higher (p < 0.01) in AD patients as compared to controls; although a trend towards higher levels of dityrosine was also observed in VaD subjects compared to controls (6.3 4- 1.7 ~M in VaD patients vs. 5.1 4- 1.6 IxM in controls; p = 0.06), it did not reach statistical significance. In a cumulative analysis of all patient samples, a significant inverse association was found between plasma lycopene and MDA levels (r = -0.53, p < 0.0001). Conclusions: Independent of its nature-vascular or degenerativedementia is associated with the depletion of a large spectrum of antioxidant micronutrients and with increased protein oxidative modification. This might be relevant to the pathophysiology of dementing disorders, particularly in light of the recently suggested importance of the vascular component in AD development.

Metabolic and morphological alterations induced by proteolysis-inducing factor from Walker tumour-bearing rats in C2C12 myotubes

BACKGROUND: Patients with advanced cancer suffer from cachexia, which is characterised by a marked weight loss, and is invariably associated with the presence of tumoral and humoral factors which are mainly responsible for the depletion of fat stores and muscular tissue. METHODS: In this work, we used cytotoxicity and enzymatic assays and morphological analysis to examine the effects of a proteolysis-inducing factor (PIF)-like molecule purified from ascitic fluid of Walker tumour-bearing rats (WF), which has been suggested to be responsible for muscle atrophy, on cultured C2C12 muscle cells. RESULTS: WF decreased the viability of C2C12 myotubes, especially at concentrations of 20-25 mug.mL-1. There was an increase in the content of the pro-oxidant malondialdehyde, and a decrease in antioxidant enzyme activity. Myotubes protein synthesis decreased and protein degradation increased together with an enhanced in the chymotrypsin-like enzyme activity, a measure of functional proteasome activity, after treatment with WF. Morphological alterations such as cell retraction and the presence of numerous cells in suspension were observed, particularly at high WF concentrations. CONCLUSION: These results indicate that WF has similar effects to those of proteolysis-inducing factor, but is less potent than the latter. Further studies are required to determine the precise role of WF in this experimental model. © 2008 Yano et al; licensee BioMed Central Ltd.

Women outperform men in remembering to remember

The study of gender differences in prospective memory (i.e., remembering to remember) has received modest attention in the literature. The few reported studies investigating either subjective or objective evaluations of prospective memory have shown inconsistent data. In this study, we aimed to verify the presence of gender differences during the performance of an objective prospective memory test by considering the weight of specific variables such as length of delay, type of response, and type of cue. We submitted a sample of 100 healthy Italian participants (50 men and 50 women) to a test expressly developed to assess prospective memory: The Memory for Intentions Screening Test. Women performed better than men in remembering to do an event-based task (i.e., prompted by an external event) and when the task required a physical response modality. We discuss the behavioural differences that emerged by considering the possible role of sociological, biological, neuroanatomical, and methodological variables.

LDL-Lipids from patients with hypercholesterolaemia and Alzheimer's disease are inflammatory to microvascular endothelial cells:mitigation by statin intervention

Elevated LDL concentration in mid-life increases the risk of developing Alzheimer's disease (AD) in later life. Increased oxidative modification (oxLDL) and nitration is observed during dementia and hypercholesterolemia. We investigated the hypothesis that statin intervention in mid-life mitigates the inflammatory effects of oxLDL on the microvasculature. Human microvascular endothelial cells (HMVEC) were maintained on transwells to mimic the microvasculature and exposed to patient and control LDL. Blood was obtained from statin-naïve, normo- and hyperlipidaemic subjects, AD with vascular dementia (AD-plus) and AD subjects (n=10/group) at baseline. Only hyperlipidaemic subjects with normal cognitive function received 40mg simvastatin intervention/day for three months. Blood was re-analysed from normo- and hyper-lipidaemic subjects after three months. LDL isolated from statin-naïve hyperlipidaemic, AD and AD-plus subjects was more oxidised (agarose gel electrophoretic mobility, protein carbonyl content and 8-isoprostane F2α) compared to control subjects. Statin intervention decreased protein carbonyls (2.5±0.4 Vs 3.95±0.2nmol/mg; P<0.001) and 8-isoprostane F2α (30.4±4.0 pg/ml Vs 43.5±8.42 pg/ml; P<0.05). HMVEC treatment with LDL-lipids from hyperlipidaemic, AD and AD-plus subjects impaired endothelial tight junction expression and decreased total glutathione levels (AD; 18.61±1.3, AD-plus; 16.5±0.7nmol/mg protein) compared to untreated cells (23.8±1.2 vs nmol/mg protein). Basolateral IL-6 secretion was increased by LDL-lipids from hyperlipidaemic (78.4±1.9 pg/ml), AD (63.2±5.9 pg/ml) and AD-plus (80.8±0.9 pg/ml) groups compared to healthy subject lipids (18.6±3.6 pg/ml). LDL-Lipids isolated after statin intervention did not affect endothelial function. In summary, LDL-lipids from hypercholesterolaemic, AD and AD-plus patients are inflammatory to HMVEC. In vivo intervention with statins reduces the damaging effects of LDL-lipids on HMVEC.