New players in old amyloid precursor protein-processing pathways

The amyloid precursor protein (APP) gives rise to beta-amyloid peptides, which are the main constituents of senile plaques in brains of Alzheimer's disease (AD) patients. The generation of beta-amyloid peptides requires the enzymatic activity of the beta-site APP-cleaving enzyme 1 (BACE1). BACE1 is primarily expressed by neurons and increased BACE1 protein concentrations and enzymatic activities have been reported in the brains of AD patients. However, there is accumulating evidence that, in addition to neurons, reactive astrocytes are capable of expressing BACE1 and, therefore, may contribute to beta-amyloid plaque formation. This suggests that conditions accompanied by chronic astrocyte activation may contribute to developing AD. Non-amyloidogenic processing of the APP can be stimulated by phorbol esters (PEs) and by intracellular diacylglycerol (DAG) generation. This led to the hypothesis that classical and novel protein kinase Cs (PKCs), which are activated by DAG/PEs, regulate APP processing. However, in addition to PKCs, there are other DAG/PE receptors present in neurons which may participate in the modulation of APP processing. Munc13-1, a presynaptic protein with an essential role in synaptic vesicle priming, represents such an alternative target of the DAG second messenger pathway. Using Munc13-1 knock-out mice and human neuroblastoma cells transfected with wild-type and mutant Munc13-1 constructs it was demonstrated that Munc13-1 acts independently of and in parallel with PKC to modulate APP metabolism. Therefore, agonists specific for the Munc13-1 C1-domain or small molecules mimicking the function of the endogenous Munc13-1 activator RIM1 may prove useful to shift APP processing towards the non-amyloidogenic pathway.     

Neurosteroid modulation of allopregnanolone and GABA effect on the GABA-A receptor

The neurosteroid allopregnanolone (ALLO) or 3α-OH-5α-pregnane-20-one interacts with the GABA type A receptor chloride ion channel complex and enhances the effect of GABA. Animal and human studies suggest that ALLO plays an important role in several disorders including premenstrual syndrome, anxiety, and memory impairment. In contrast to ALLO, steroids with a hydroxy group in the 3β position usually exert a reducing effect and have recently attracted interest due to their suggested role in counteracting the negative action of ALLO. In this study, five different 3β-steroids were tested for their ability to modulate GABA-mediated chloride ion uptake in the absence and presence of ALLO in rat brain microsacs preparations. In addition, the effects of the 3β-steroids and their interaction with ALLO were investigated by patch-clamp recordings of spontaneous inhibitory postsynaptic currents (sIPSCs) in rat hypothalamic neurons from the medial preoptic nucleus (MPN). All tested 3β-steroids reduced the ALLO-enhanced GABA response in cerebral cortex, in hippocampus and in MPN. In cerebellum, only one had this effect. However, in the absence of ALLO, two of the 3β-steroids potentiated GABA-evoked chloride ion uptake and prolonged the sIPSCs decay time, whereas the others had little or no effect. Therefore, it is possible that at least some 3β-steroids can act as positive GABA_A receptor modulators as well as negative modulators depending on whether or not ALLO is present. Finally, these results suggest that the 3β-steroids could be of interest as pharmacological agents that could counteract the negative effects of ALLO.     

Can supplementation of diet with omega-3 polyunsaturated fatty acids reduce coronary angioplasty restenosis rate?

The objective of this blinded, randomized, prospective study was to assess whether supplementation of normal diet with omega-3 polyunsaturated fatty acids can reduce angiographically defined restenosis following coronary angioplasty. The study included all patients undergoing coronary angioplasty in this institution between January 1988 and January 1989. One hundred and twenty patients enrolled, 60 in each treatment group. All were randomized to either supplementation of normal diet with 3 g of omega-3 polyunsaturated fatty acids per day started 1-2 days prior to angioplasty and continued for 6 months (treatment group), or to receive standard therapy only (control group). Quantitative angiographically defined restenosis was assessed at 6 months post angioplasty. Restenosis occurred in 27.8% (95% CI 18.0-37.7%) of lesions in the treatment group and in 28.3% (CI 16.9-39.7%) of lesions in the control group, but the difference was not statistically significant. The study showed that diet supplemented with 3 g of omega-3 polyunsaturated fatty acids started 1-2 days preceding angioplasty does not reduce angiographically defined restenosis rate.     

Pathogenesis of Mucocutaneous Lesions in Behçet's Disease

Behcet's disease (BD) is characterized by recurrent oral aphthae, skin lesions, eye lesions, and genital ulceration. To determine the pathogenesis of BD, we performed histological and immunohistochemical studies of these mucocutaneous lesions, an assay of neutrophil activity, and HLA typing. Dense dermal or subcutaneous infiltrations of polymorphonuclear cells (PMN) without leukocytoclastic vasculitis were found in 28 of 57 lesions. Immunohistochemically, deposits of C3 on the vessels were found in 12 of 31 lesions. Deposits of immunoglobulin were not found except for one of IgM. C3 deposits and PMN infiltrations were significantly related (p<0.05). PMN activity by polarization was enhanced; however, the results did not show a significant relationship with the PMN infiltrations or the C3 deposits. The incidence of HLA-B51 was significantly high in BD, but no significant relationship was found between HLA-B51 and the results of other examinations. These results suggest that the pathogenesis of BD lesions differs from that of collagen diseases and that C3 deposits on the vessels may play an important role in the development of mucocutaneous lesions where PMN have mainly infiltrated.     

Secretion and function of the third component of complement (C3) by murine leukocytes.

Our new finding of de novo synthesis and secretion of C3 by both murine peritoneal macrophages and polymorphonuclear leukocytes (PMN) was confirmed by the incorporation of [35S]methionine into C3 molecules and their complete inhibition by cycloheximide. The methods of secretion of C3 from these two types of cells were compared by examining the C3 contents in their culture supernatants. Completely different modes of secretion were observed, i.e. although macrophages synthesize and secrete C3 constitutively, PMN has a mechanism to store the already synthesized C3 in the cell and secrete it in response to stimuli. Protein kinase C (PKC) activators, e.g. 12-O-tetradecanoyl-phorbol 13-acetate, dioctanoyl glycerol, and mezerein, as well as calcium ionophore A23187 stimulate the secretion of C3 from PMN. These results suggest the involvement of PKC and the calmodulin pathway. A very sensitive method for measuring C3 activity was developed which enabled us to show for the first time that C3 secreted by PMN had opsonizing activity and that particles cultured with PMN were phagocytosed effectively.     

Epileptogenic actions of xanthines in relation to their affinities for adenosine A1 receptors in CA3 neurons of hippocampal slices (guinea pig)

In order to analyze the epileptogenic mechanisms of caffaine and related xanthines, putative effects of these drugs were studied on adenosine receptors of CA3 neurons in hippocampal slices. Epileptogenic concentrations of different xanthine derivatives strongly correlated with their affinities for the inhibitory A₁ adenosine receptor subtype. The A₁ receptor agonists adenosine and R-PIA reversibly depressed xanthine-induced epileptic activity without effects on the resting membrane potential or on spontaneously occuring action potentials. These findings suggest that the epileptogenic potency of xanthines is primarily due to the blockade of the A₁ receptors through an abnormal rise of intracellular cAMP and to the excessive transmembrane calcium fluxes underlying paroxysmal depolarization shifts.     

Fever and feeding in the rat: Actions of intrahypothalamic interleukin-6 compared to macrophage inflammatory protein-1β (MIP-1β)

The chemokines, macrophage inflammatory protein-1 (MIP-1) and its subunit MIP-1β, induce an intense fever in the rat when they are injected directly into the anterior hypothalamic, pre-optic area (AH/POA), a region containing thermosensitive neurons. The purpose of this study was to compare the central action on body temperature (T_b) of MIP-1β with that of interleukin-6 (IL-6), which also has been implicated in the cerebral mechanism underlying the pathogenesis of fever. Following the stereotaxic implantation in the AH/POA of guide cannulae for repeated micro-injections, radio transmitters which monitor T_b continuously were inserted intraperitoneally in each of 15 male Sprague-Dawley rats. Each micro-injection was made in a site in the AH/POA in a volume of 1.0 μl of pyrogen-free artificial CSF, recombinant murine MIP-1β, or recombinant human IL-6. MIP-1β in a dose of 25 pg evoked an intense fever characterized by a short latency, a mean maximum rise in T_b of 2.4 ± 0.21°C reached by 3.7 ± 0.42 hr, and a duration exceeding 6.5 hr. Injected into homologous sites in the AH/POA, IL-6 induced a dose dependent fever of similar latency and a mean maximal increase in T_b of 1.2 ± 0.25°C, 1.8 ± 0.15°C, and 2.1 ± 0.22°C and duration of 6.2 ± 1.28 hr, 6.7 ± 0.49 hr, and 6.8 ± 0.65 hr when given in doses of 25, 50, and 100 ng, respectively. These results show that MIP-1β and the highest dose of IL-6 induce a fever of comparable intensity, but MIP-1β exerts its action in a much lower concentration. Thus, the de novo synthesis and subsequent action of the MIP-1 family of cytokines on neurons of the AH/POA in response to a pyrogen challenge apparently play a functional role in the pathogenesis of fever. Further, the endogenous activity of IL-6 in the hypothalamus which is enhanced in response to a lipopolysaccharide also may reflect its essential part in the acute phase response to a bacterial challenge. Copyright © 1994 Wiley-Liss, Inc.     

Zinc ions and alkaline PH alter the phosphorylated state of proteins 3 and 4.2 in human erythrocyte membranes

The phosphorylation patterns of isolated red blood cell (RBC) membranes labeled with [ γ-³²p]ATP are altered by Zn⁺⁺ ions. Zn⁺⁺ ions caused an increased phosphate incorporation into a 72 KDa protein and several proteins in the 40–60 KDa region and a decrease in the labeling of a 53 KDa protein. The 72 KDa and 53 KDa proteins have been identified as protein 4.2 and a protease-cleaved fragment of protein 3, respectively. Evidence suggests that the changes in phosphorylation pattern may be due to the stimulation of endogenous membrane alkaline phosphatase(s). Our results suggest that Zn⁺⁺, at physiological concentrations in the intact erythrocyte, could modulate the phosphorylation of selected proteins which may regulate their association in the cytoskeletal network.