Mouse cerebral prostaglandins, but not oxidative damage, change with age and are responsive to indomethacin treatment

Flies, worms and the Free Radical Theory of ageing

Drosophila and Caenorhabditis elegans have provided the largest body of evidence addressing the Free Radical Theory of ageing, however the evidence has not been unequivocally supportive. Oxidative damage to DNA is probably not a major contributor, damage to lipids is assuming greater importance and damage to proteins probably the source of pathology. On balance the evidence does not support a primary role of oxidative damage in ageing in C. elegans, perhaps because of its particular energy metabolic and stress resistance profile. Evidence is more numerous, varied and consistent and hence more compelling for Drosophila, although not conclusive. However there is good evidence for a role of oxidative damage in later life pathology. Future work should: 1/ make more use of protein oxidative damage measurements; 2/ use inducible transgenic systems or pharmacotherapy to ensure genetic equivalence of controls and avoid confounding effects during development; 3/ to try to delay ageing, target interventions which reduce and/or repair protein oxidative damage.

T. brucei infection reduces B lymphopoiesis in bone marrow and truncates compensatory splenic lymphopoiesis through transitional B-cell apoptosis

African trypanosomes of the Trypanosoma brucei species are extracellular protozoan parasites that cause the deadly disease African trypanosomiasis in humans and contribute to the animal counterpart, Nagana. Trypanosome clearance from the bloodstream is mediated by antibodies specific for their Variant Surface Glycoprotein (VSG) coat antigens. However, T. brucei infection induces polyclonal B cell activation, B cell clonal exhaustion, sustained depletion of mature splenic Marginal Zone B (MZB) and Follicular B (FoB) cells, and destruction of the B-cell memory compartment. To determine how trypanosome infection compromises the humoral immune defense system we used a C57BL/6 T. brucei AnTat 1.1 mouse model and multicolor flow cytometry to document B cell development and maturation during infection. Our results show a more than 95% reduction in B cell precursor numbers from the CLP, pre-pro-B, pro-B, pre-B and immature B cell stages in the bone marrow. In the spleen, T. brucei induces extramedullary B lymphopoiesis as evidenced by significant increases in HSC-LMPP, CLP, pre-pro-B, pro-B and pre-B cell populations. However, final B cell maturation is abrogated by infection-induced apoptosis of transitional B cells of both the T1 and T2 populations which is not uniquely dependent on TNF-, Fas-, or prostaglandin-dependent death pathways. Results obtained from ex vivo co-cultures of living bloodstream form trypanosomes and splenocytes demonstrate that trypanosome surface coat-dependent contact with T1/2 B cells triggers their deletion. We conclude that infection-induced and possibly parasite-contact dependent deletion of transitional B cells prevents replenishment of mature B cell compartments during infection thus contributing to a loss of the host's capacity to sustain antibody responses against recurring parasitemic waves.

African trypanosomiasis caused by Trypanosoma brucei species is fatal in both humans and animals and cannot be combated by vaccination because of extensive parasite antigenic variation. Effective trypanosome control and clearance from the bloodstream involves the action of antibodies specific for the parasite's highly diverse variable surface glycoprotein antigens. However, experimental infections in mice have shown that trypanosomiasis elicits a rapid process of B cell exhaustion and loss of protective antibody responses. Indeed, both marginal zone B cells, the first line of defense against blood-borne pathogens like T. brucei parasites, and follicular B cells, which are the major source for developing high-affinity antibody-producing plasma cells and memory B cells, become depleted during infection. In addition, existing B-cell memory, both against parasite antigens and non related pathogens, is destroyed early on in infection. Here, we demonstrate that during infection, B cell development is decreased in the bone marrow and early B cell development is taken over by the spleen. However, full maturation of developing B cells is abrogated by the occurrence of transitional B cell apoptosis. This impairs the replenishment of the mature marginal zone and follicular B cell pools and prevents the buildup of protective immunity against successive parasitemic waves.

Brain fixation for analysis of brain lipid-mediators of signal transduction and brain eicosanoids requires head-focused microwave irradiation: an historical perspective

To microwave or not to microwave, that is the question that has confounded the neurochemist as the quest for reducing changes in neurochemicals associated with post-mortem delay has evolved over the years. Rapid changes in brain constituents during the post-mortem delay have been recognized for years as a problem. What is real and what is artifact? What are true basal levels of molecules found in the brain? In the 1920s, neurochemists recognized this issue and determined freezing of the brain was most advantageous for halting rapid breakdown of some molecules and rapid formation of others. By the early 1970s, a number of laboratories noted that freezing the brain in situ or upon removing it from the cranial vault was not sufficient to reduce alterations in brain chemistry. Groups began experimenting with two different techniques to attack this problem, freeze-blowing and head-focused microwave irradiation. My laboratory and others have found that the utilization of head-focused microwave irradiation to halt enzymic alterations in lipids is an essential tool to limit alterations post-mortem. Recently, we and others have demonstrated that this technique is essential in reliably assessing brain eicosanoid levels, without such fixation true basal levels of eicosanoids are impossible to determine and the high concentrations seen in some paradigms may be merely an artifact produced during handling of the brain. Thus, for eicosanoid analysis and other applications in measuring brain lipid levels, head-focused microwave irradiation is an essential tool for the lipid neurochemist.

Relationship between levels of oxidative DNA damage, lipid peroxidation and mitochondrial membrane potential in young and old F344 rats

The extent of in vivo oxidative damage has been known to be cumulative over the period of the life of mammals. Our hypothesis is that there should be a positive correlation between the levels of 8-hydroxy-2'-deoxyguanosine (8OHdG) and 8-iso-prostaglandin F(2alpha) (8-iso-PGF(2alpha)) in major rat tissues. We also investigated whether increased level of oxidative stress causes a decrease in the mitochondrial membrane potential of peripheral lymphocytes of old rats using the MitoTracker Red fluorochrome. Our results show positive correlations between 8OHdG and 8-iso-PGF(2alpha) for liver, brain and kidney measured by HPLC-UV-ECD (electrochemical detector) and EIA methods, respectively. However, heart tissues show a negative correlation. The mitochondrial membrane potential of old rat lymphocytes records significant decrease compared with the young lymphocytes. Based on our results, we conclude that in ageing studies, specific tissues need to be examined in order to measure the localised DNA damage and lipid peroxidation as different tissues display different extent of oxidative damage. We believe this approach of using combined markers is useful to verify the true efficacy of health intervention studies in animals and humans. In addition, the isoprostane assay can be further developed looking at lipid peroxidation as a potential marker in ageing studies.

The effect of cyclooxygenase-2 inhibition on renal hemodynamic function in humans with type 1 diabetes

OBJECTIVE

Studies in animal models suggest that cyclooxygenase-2 (COX2) plays a role in the regulation of the renal microcirculation in diabetes. Accordingly, we examined the role of COX2 in the control of renal hemodynamic function and in the renal response to hyperglycemia in humans with uncomplicated type 1 diabetes. We hypothesized that COX2 inhibition would alleviate the hyperfiltration state and would abrogate the hyperglycemia-mediated rise in glomerular filtration rate (GFR). RESEARCH DESIGN AND METHODS; Renal function was assessed during clamped euglycemia and hyperglycemia on 2 consecutive days before and then again after 14 days of COX2 inhibition using 200 mg celecoxib once daily by mouth. For analysis, the cohort was then divided into two groups based on the baseline GFR: 9 subjects exhibited hyperfiltration (GFR >or=135 ml/min per 1.73 m(2)), and 12 subjects exhibited normofiltration (GFR <135 ml/min per 1.73 m(2)).

RESULTS

Under euglycemic conditions, COX2 inhibition resulted in a significant decline in GFR in the hyperfiltration group (150 +/- 5 to 139 +/- 5 ml/min per 1.73 m(2)) but increased GFR in the normofiltration group (118 +/- 5 to 138 +/- 5 ml/min per 1.73 m(2)). COX2 inhibition did not blunt the hyperglycemia-associated rise in GFR in the normofiltration group and was instead associated with an augmented rise in GFR.

CONCLUSIONS

In summary, our results support the hypothesis that COX2 is an important determinant of renal hemodynamic function in subjects with type 1 diabetes. The renal response to COX2 inhibition emphasizes that hyperfiltration and normofiltration are distinct physiological states.

Neuronal overexpression of cyclooxygenase-2 increases cerebral infarction

Increases in COX-2 enzymatic activity and prostaglandin production have been associated with neuronal injury in both acute and age-related degenerative neurological diseases. In this study, we tested the effects of increased COX-2 activity in a model of transient focal ischemia using a transgenic mouse model in which human COX-2 is constitutively expressed selectively in neurons of the striatum, cerebral cortex, and hippocampus. These COX-2 transgenic mice harbor elevated levels of PGE(2) that are 10-fold higher than nontransgenic levels. A significant increase in infarct volume was observed after middle cerebral artery occlusion with 4 days of reperfusion in COX-2 transgenic mice as compared with nontransgenic littermates. Pretreatment of nontransgenic mice with the selective COX-2 inhibitor SC58236 resulted in a significant reduction of infarct volume in nontransgenic mice, consistent with previous pharmacological studies. However, transgenic COX-2 mice treated with SC58236 did not show a significant reduction. This suggests that chronic increases in COX-2 expression and enzymatic activity, which can occur in aging and in pathological states characterized by oxidative stress and chronic inflammatory processes, can lead to downstream cellular changes that have a negative impact on neuronal survival in cerebrovascular disease.