Anita Garlind

The Cerebrocortical Areas in Normal Brain Aging and in Alzheimer's Disease: Noticeable Differences in the Lipid Peroxidation Level and in Antioxidant Defense

The markers of oxidative stress were measured in four cerebrocortical regions of Alzheimers disease (AD) and age-matched control brains. In controls the levels of diene conjugates (DC) and lipid peroxides (LOOH) were significantly higher in the sensory postcentral and occipital primary cortex than in the temporal inferior or frontal inferior cortex. The antioxidant capacity (AOC) was highest in the temporal, and GSH in the frontal inferior cortex. The highest activity of superoxide dismutase (SOD) and catalase (CAT) was found in the occipital primary cortex. Compared with controls, significantly higher level of DC and LOOH and attenuated AOC were evident in AD temporal inferior cortex. In AD frontal inferior cortex moderate increase in LOOH was associated with positive correlation between SOD activity and counts of senile plaques. Our data suggest that in AD cerebral cortex, the oxidative stress is expressed in the reducing sequence: temporal inferior cortex > frontal inferior cortex > sensory postcentral cortex ≃ occipital primary cortex, corresponding to the histopathological spreading of AD from the associative to primary cortical areas.

Soluble interleukin-1 receptor type II levels are elevated in cerebrospinal fluid in Alzheimer's disease patients.

Evidence from epidemiological, clinical and experimental studies favour the hypothesis that inflammatory events are part of the neuropathology in Alzheimers disease. Proinflammatory cytokines such as interleukin-1 (IL-1), interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-alpha) have been found in activated microglia in the vicinity of amyloid plaques in Alzheimers disease brain. In the present study, the levels of soluble IL-1 receptor type II (sIL-1R type II), IL-1 receptor antagonist (IL-1ra), IL-1beta, IL-6 and TNF-alpha were analyzed in cerebrospinal fluid (CSF) samples from Alzheimers disease patients and control subjects. The levels of sIL-1R type II were significantly higher in CSF from Alzheimers disease patients than in CSF samples from control subjects (38.5+/-8 pg/ml (mean+/-S.E.M.) vs. 7.9+/-4 pg/ml, p<0.05). Measurements of the proinflammatory cytokines IL-6 and TNF-alpha showed no significant difference between the two groups, and the levels of IL-1beta and IL-1ra in the present material were too low to permit detection. The increased levels of sIL-1R type II may reflect a compensatory mechanism to balance an increased release of IL-1 receptor agonists in the Alzheimers disease brain.

Regional distribution of somatostatin receptor binding and modulation of adenylyl cyclase activity in Alzheimer's disease brain.

We have previously reported a reduction in the inhibitory effect of somatostatin on adenylyl cyclase activity in the superior temporal cortex of a group of Alzheimers disease cases, compared to a group of matched controls. In the present study, the levels of high affinity 125I-Tyr11-somatostatin-14 binding, its modulation by guanine nucleotides and the effects of somatostatin on adenylyl cyclase activity have been measured in preparations of frontal cortex, hippocampus, caudate nucleus and cerebellum from the same patient and control groups. A significant reduction in 125I-Tyr11-somatostatin-14 binding was observed in the frontal cortex, but not other regions, of the Alzheimers disease group, compared with control values. The profiles of inhibition of specific 125I-Tyr11-somatostatin-14 binding by Gpp(NH)p were similar in all regions in both groups. No significant differences in basal, forskolin-stimulated, or somatostatin and neuropeptide Y inhibitions of adenylyl cyclase activity were found between the two groups. The pattern of change of somatostatin binding in the Alzheimers disease cases observed in the present study differs from the reported pattern of loss of somatostatin neurons and may be secondary to the degeneration of somatostatin receptor-bearing cholinergic afferents arising from the nucleus basalis. The results of this study indicate that impaired somatostatin modulation of adenylyl cyclase is not a global phenomenon in Alzheimers disease brain and also that there are no major disruptions of somatostatin receptor-G-protein coupling or of adenylyl cyclase catalytic activity in this disorder.

Diminished [3H]inositol(1,4,5)P3 but not [3H]inositol(1,3,4,5)P4 binding in Alzheimer's disease brain

Levels of the calcium mobilising receptors for the phosphoinositide hydrolysis derived second messengers, inositol(1,4,5)trisphosphate [Ins(1,4,5)P3] and inositol(1,3,4,5) tetrakis-phosphate [Ins(1,3,4,5)P4] were compared in the cerebellum, superior temporal and superior frontal cortex of a series of Alzheimers disease and matched control cases. Membrane [3H]Ins(1,4,5)P3 radioligand binding experiments performed under steady state conditions revealed that the number of Ins(1,4,5)P3 recognition sites was significantly decreased in all three brain regions of the Alzheimers disease cases, compared to controls. In contrast, [3H]Ins(1,3,4,5)P4 binding levels, as assessed in competition analyses, were not significantly different between the groups in any brain region. Moreover, the Hill coefficients for inhibition of [3H]Ins(1,3,4,5)P4 binding by non-radioactive Ins(1,3,4,5)P4 were less than unity in both the control and Alzheimers disease brains, suggesting that the heterogeneity of these binding sites are also maintained in the disease. It is concluded that disruptions of the phosphoinositide hydrolysis pathway in Alzheimers disease brain are associated with a selective loss of calcium mobilising Ins(1,4,5)P3, but not Ins(1,3,4,5)P4 receptor sites. These alterations may contribute to an altered calcium homeostasis in Alzheimers disease, as well as providing one reason for the lack of success of cholinergic replacement therapies aimed at enhancing muscarinic receptor-mediated phosphatidylinositol hydrolysis.

Neurotransmitter-mediated inhibition of post-mortem human brain adenylyl cyclase.

The effects of a range of neurotransmitter agonists showing selectivity for receptor types inhibitorily coupled to adenylyl cyclase were compared in membrane preparations of hippocampus, frontal cortex and caudate nucleus/ striatum from previously frozen post-mortem human and rat brain. Agonists were tested against basal and forskolin stimulated activities, forskolin being a potent activator of the catalytic sub-unit of the enzyme. Of those agonists tested, only somatostatin (100 μM) and neuropeptide Y (10 μM) gave consistent inhibitions of basal and forskolin stimulated enzyme activities in all three regions of both human and rat brain. Somatostatin-mediated inhibition of human brain adenylyl cyclase was reduced in the absence of GTP and in the presence of the guanine nucleotide partial agonist, guanosine 5′-O-thiodiphosphate, consistent with a G-protein-linked receptor. No such GTP-dependence was found for the neuropeptide Y-mediated adenylyl cyclase inhibition. GTP-dependent somatostatin mediated inhibitions of human brain adenylyl cyclase activity were of highest magnitude in the thalamus, intermediate magnitude in the hippocampus and caudate nucleus and lowest magnitude in the frontal cortex. It is concluded that of a range of neurotransmitter receptor agonists tested, only somatostatin gives robust, GTP-dependent responses that are reproducible enough to be used with post-mortem tissue for the comparison of receptor function in human brain disorders.

Receptor-effector coupling dysfunctions in Alzheimer's disease.

There is now good evidence that in the AD brain, a number of neurotransmitter effector systems are defective. Such abnormalities include defective G, protein and protein kinase C function as well as a drastically reduced level of receptors for the second messenger Ins(1,4,5) P3. Such changes are probably not restricted to the late stages of the disease, and are found in regions of the brain that show little histopathological abnormality, such as the cerebellum. Whether these changes precede or are secondary to primary histopathological changes such as beta-amyloid deposition is not as yet clear. What is clear, however, is that such signal transduction abnormalities are likely to negate therapeutic benefits in clinical strategies based upon the tenet of neurotransmitter replacement.

Disturbances in signal transduction mechanisms in Alzheimer’s disease

Many of the treatments directed towards alleviation of symptoms in Alzheimer’s disease assume that target receptor systems are functionally intact. However, there is now considerable evidence that this is not the case. In human post-mortem brain tissue samples, the function of the GTP-binding protein Gs in regulating adenylyl cyclase is severely disabled, whereas that of G. is intact. This difference in the function of the two G-protein types is also found in G-protein regulation of high- and low-affinity receptor recognition site populations. Measurement of G-protein densities using selective antibodies has indicated that the dysfunction in Gs-stimulation of cAMP production correlates with the ratio of the large to small molecular weight isoforms of the Gsa subunit. With respect to intracellular second messenger effects, there is a dramatic decrease in the density of brain receptor recognition sites for Ins(l,4,5)P3 that is not accompanied by a corresponding change in the Ins(l,3,4,5)P4 recognition site density. Protein kinase C function is also altered in Alzheimer’s disease, a finding that may be of importance for the control of β-amyloid production. These studies indicate that signal transduction processes are severely compromised in Alzheimer’s disease. Some of these disturbances are also seen in cultured fibroblasts from Alzheimer’s disease patients, indicating that they are neither restricted to areas of histopathological change, nor non-specific changes found late in the course of the disease. Cellular models to investigate the relation between amyloid production and deficits in signal transduction are also discussed.

Cytokines and memory across the mature life span of women

Increasing evidence suggests a role of the immune system in modulation of cognition, but details on affected memory systems are largely lacking. We therefore aimed to study the relation between selected cytokines and subsets of memory, and the impact of age in these relations. From a random population-based sample (the Betula Prospective Cohort Study), 298 women (age 45-90) were studied in terms of episodic recall and recognition, semantic fluency and knowledge, and prospective memory. Circulating cytokines of relevance for cognition and aging were measured with ELISA. Levels of interleukin (IL)-6 and sIL-2R were significantly and negatively associated with most cognitive variables, while the opposite was true for IL-1β. Age shared substantial variance with both cytokines and memory, and turned most correlations non-significant when controlled for together with education, BMI and presence of disease. Interactions between age and cytokines were further analyzed in multiple regressions. For IL-6, significant negative interactions with age were found for semantic fluency (p<0.05) and prospective memory (p<0.01), and for sIL-2R in predicting semantic knowledge (p<0.05), indicating an increased negative impact of these cytokines on memory with increasing age. In conclusion, the study indicates a relation between cytokines and memory that appears to be largely mediated by age, and supports the suggestion that cytokine dysregulation with higher age may interact with cognitive aging.

Preservation of κ1 opioid receptor recognition site density and regulation by G-proteins in the temporal cortex of patients with Alzheimer's disease

Abstract The pharmacological properties of the κ 1 opioid receptor were investigated in human post-mortem temporal cortical membranes from control and Alzheimers disease brains, using the κ 1 -selective radioligand [ 3 H]U69593. [ 3 H]U69593 bound to a single high affinity site population with no significant difference between control ( B max 31 ± 4.14 fmol/mg protein, K D 1.01 ± 0.26 nM) and Alzheimers disease brains ( B max 37 ± 4.63 fmol/mg protein, K D 0.86 ± 0.08 nM). Competition studies with dynorphin B and α-neoendorphin gave flat inhibition curves with Hill coefficients of 0.31 ± 0.04 and 0.49 ± 0.09 in the control brains and 0.38 ± 0.05 and 0.48 ± 0.08 in the Alzheimers disease brains, respectively. The pI 50 values for dynorphin B and α-neoendorphin were 8.73 ± 0.17 and 8.48 ± 0.09, respectively, in the control brains and 9.30 ± 0.22 and 8.70 ± 0.15 in the Alzheimers disease brains. The guanine nucleotide analogue Gpp(NH)p inhibited binding by ca. 70% in both the control and Alzheimers disease brains, the residual binding being sensitive to NaCl in both cases. These results indicate that the pharmacological properties and the functional integrity of G-protein coupling of the κ 1 receptor recognition site are preserved in Alzheimers disease temporal cortex.

Characterization and regional distribution of adenylyl cyclase activity from human brain.

The characteristics of the human brain adenylyl cyclase complex were studied in membranes from post-mortem frontal cortex. Basal, guanine nucleotide, sodium fluoride and forskolin stimulated activities were highly magnesium-dependent. Sodium fluoride and guanine nucleotides gave bi-phasic responses, with both stimulation and inhibition of enzyme activity, the latter being more pronounced at lower magnesium concentrations. Enzyme activity was stimulated to a similar extent by GTP and its non-hydrolysable analogue Gpp(NH)p, suggesting a low GTPase activity in human post-mortem brain preparations. Guanine nucleotide stimulated enzyme activity was potently antagonized by guanosine 5?-O-(thiodiphosphate). Sodium fluoride stimulated activity was enhanced by aluminium chloride. In contrast to the effects seen with guanine nucleotides, the inhibition of sodium fluoride/aluminium chloride stimulated activity by guanosine 5?-O-(thiodiphosphate) was dependent upon pre-incubation of membranes with a neurotransmitter agonist. Basal, guanine nucleotide and sodium fluoride/aluminium chloride stimulated activities showed a marked regional distribution. Stimulated activities were highest in frontal and parietal cortex, intermediate in the nucleus caudatus and cerebellar cortex and lowest in occipital cortex, putamen, globus pallidus and ventral hippocampus. It is concluded that the regulation of human post-mortem brain adenylyl cyclase by guanine nucleotides is similar to that reported for studies on experimental animals.