Endothelin–an emerging role in proinflammatory pathways in brain

Possible role of endothelin receptor against hyperhomocysteinemia and β-amyloid induced AD type of vascular dementia in rats

Vascular dementia (VaD) is considered as the second commonest form of dementia after Alzheimer's disease (AD). The study was designed to investigate the effect of endothelin receptor against β-amyloid induced AD type of vascular dementia. This disease was induced by combine administration of single ICV (intracerebroventricle) infusion of β-amyloid (Aβ) once and chronic oral administration of l-Methionine for 21 days. Bosentan (dual endothelin receptor antagonist) was administered for 21 days. Behavioral alterations were observed during different time interval of the study. Animals were killed immediately following the last behavior session. Oxidative parameters, acetylcholinesterase activity, neuro-inflammatory markers, amyloid beta levels were determined in hippocampus and cortex while serum homocysteine, serum nitrite carotid artery superoxide anion level were also determined. Endothelial function was measured on isolated carotid artery using myograph instrument. Aβ+l-Methionine showed more significant development of cognitive and vascular endothelial deficits, manifested in terms of increase in serum homocysteine level, endothelial dysfunction, impairment of learning and memory, enhanced brain acetylcholinesterase activity, marked mito-oxidative damage in rats. We have observed that l-Methionine and combination of Aβ+l-Methionine significantly enhanced Aβ level both in cortex as well as hippocampus. Treatment of bosentan attenuated Aβ+l-Methionine induced impairment of learning and memory, enhanced Aβ level, mitochondrial and endothelial dysfunction. The results of present study concluded that bosentan offers protection against β-amyloid-induced vascular dementia in rats. Endothelin receptor may be considered as a potential pharmacological target for the management of AD type of vascular dementia.

Cellular Microbiology of Mycoplasma canis

Mycoplasma canis can infect many mammalian hosts but is best known as a commensal or opportunistic pathogen of dogs. The unexpected presence of M. canis in brains of dogs with idiopathic meningoencephalitis prompted new in vitro studies to help fill the void of basic knowledge about the organism's candidate virulence factors, the host responses that it elicits, and its potential roles in pathogenesis. Secretion of reactive oxygen species and sialidase varied quantitatively (P < 0.01) among strains of M. canis isolated from canine brain tissue or mucosal surfaces. All strains colonized the surface of canine MDCK epithelial and DH82 histiocyte cells and murine C8-D1A astrocytes. Transit through MDCK and DH82 cells was demonstrated by gentamicin protection assays and three-dimensional immunofluorescence imaging. Strains further varied (P < 0.01) in the extents to which they influenced the secretion of tumor necrosis factor alpha (TNF-α) and the neuroendocrine regulatory peptide endothelin-1 by DH82 cells. Inoculation with M. canis also decreased major histocompatibility complex class II (MHC-II) antigen expression by DH82 cells (P < 0.01), while secretion of gamma interferon (IFN-γ), interleukin-6 (IL-6), interleukin-10 (IL-10), and complement factor H was unaffected. The basis for differences in the responses elicited by these strains was not obvious in their genome sequences. No acute cytopathic effects on any homogeneous cell line, or consistent patterns of M. canis polyvalent antigen distribution in canine meningoencephalitis case brain tissues, were apparent. Thus, while it is not likely a primary neuropathogen, M. canis has the capacity to influence meningoencephalitis through complex interactions within the multicellular and neurochemical in vivo milieu.

Role of endothelin receptors in the control of central nervous system parasitism in Trypanosoma cruzi infection in rats

Endothelin has been implicated in the pathogenesis of experimental and human Chagas disease. In the present study, we investigated whether the treatment with bosentan, an antagonist of both ET(A)/ET(B) endothelin receptors, modified parasite load and inflammation in the central nervous system (CNS) of Trypanosomacruzi-infected rats. The cerebellum was the most affected region in the CNS with marked parasitism and inflammation. Treatment with bosentan enhanced parasitemia and CNS parasitism, but control of infection was eventually attained. There was also an increase in the levels of the cytokines TNF-alpha, IL-10, IFN-gamma, CCL2/MCP-1, CCL3/MIP-1alpha and CCL5/RANTES in the brain of infected animals at days 9, 13 and 18 after infection. Overall, bosentan has some effects on the expression of certain cytokines and this may be related to the initial enhanced parasite load. Altogether, our data suggest that endothelin action via ET(A) and ET(B) receptors may play a role in the initial resistance of the CNS to T. cruzi infection in rats.

A fluorescent photoprobe for the imaging of endothelin receptors

A novel fluorescent photoprobe for the imaging of endothelin A receptors (ET(A)R) was developed. Based on the nonpeptidyl, high-affinity, and selective ET(A)R antagonist 3-benzo[1,3]dioxol-5-yl-5-hydroxy-5-(4-methoxyphenyl)-4-(3,4,5-trimethoxybenzyl)-5H-furan-2-one (PD 156707), a modification of the lead structure with a PEG-spacer containing an amino moiety was performed. Labeling of this precursor with the fluorescent marker Cy 5.5 NHS-ester was accomplished by adaption of common peptide labeling procedures. The affinity of the Cy 5.5-labeled receptor antagonist was evaluated using human carcinoma cell lines with different degrees of ET(A)R expression. Fluorescence microscopy revealed that ET(A)R-positive MCF-7 human breast adenocarcinoma and HT-1080 human fibrosarcoma cells effectively bind the photoprobe at very low doses (nM), while ET(A)R-negative MDA-MB-435 human breast cancer cells showed no fluorescence signal. Binding specificity of the probe could be demonstrated by predosing with a specific ET(A)R antibody or the parent antagonist PD 156707 as a competing inhibitor. The results suggest that the modified photoprobe tightly binds to ET(A) receptors and thus may be a possible candidate for the imaging of ET(A)R-overexpressing tissues in vivo.

Thermoregulation: some concepts have changed. Functional architecture of the thermoregulatory system

While summarizing the current understanding of how body temperature (Tb) is regulated, this review discusses the recent progress in the following areas: central and peripheral thermosensitivity and temperature-activated transient receptor potential (TRP) channels; afferent neuronal pathways from peripheral thermosensors; and efferent thermoeffector pathways. It is proposed that activation of temperature-sensitive TRP channels is a mechanism of peripheral thermosensitivity. Special attention is paid to the functional architecture of the thermoregulatory system. The notion that deep Tb is regulated by a unified system with a single controller is rejected. It is proposed that Tb is regulated by independent thermoeffector loops, each having its own afferent and efferent branches. The activity of each thermoeffector is triggered by a unique combination of shell and core Tbs. Temperature-dependent phase transitions in thermosensory neurons cause sequential activation of all neurons of the corresponding thermoeffector loop and eventually a thermoeffector response. No computation of an integrated Tb or its comparison with an obvious or hidden set point of a unified system is necessary. Coordination between thermoeffectors is achieved through their common controlled variable, Tb. The described model incorporates Kobayashi’s views, but Kobayashi’s proposal to eliminate the term sensor is rejected. A case against the term set point is also made. Because this term is historically associated with a unified control system, it is more misleading than informative. The term balance point is proposed to designate the regulated level of Tb and to attract attention to the multiple feedback, feedforward, and open-loop components that contribute to thermal balance.