Slow encephalopathies, inflammatory responses and arachis oil

Molecular Mechanisms in the Genesis of Seizures and Epilepsy Associated With Viral Infection

Seizures are a common presenting symptom during viral infections of the central nervous system (CNS) and can occur during the initial phase of infection ("early" or acute symptomatic seizures), after recovery ("late" or spontaneous seizures, indicating the development of acquired epilepsy), or both. The development of acute and delayed seizures may have shared as well as unique pathogenic mechanisms and prognostic implications. Based on an extensive review of the literature, we present an overview of viruses that are associated with early and late seizures in humans. We then describe potential pathophysiologic mechanisms underlying ictogenesis and epileptogenesis, including routes of neuroinvasion, viral control and clearance, systemic inflammation, alterations of the blood-brain barrier, neuroinflammation, and inflammation-induced molecular reorganization of synapses and neural circuits. We provide clinical and animal model findings to highlight commonalities and differences in these processes across various neurotropic or neuropathogenic viruses, including herpesviruses, SARS-CoV-2, flaviviruses, and picornaviruses. In addition, we extensively review the literature regarding Theiler's murine encephalomyelitis virus (TMEV). This picornavirus, although not pathogenic for humans, is possibly the best-characterized model for understanding the molecular mechanisms that drive seizures, epilepsy, and hippocampal damage during viral infection. An enhanced understanding of these mechanisms derived from the TMEV model may lead to novel therapeutic interventions that interfere with ictogenesis and epileptogenesis, even within non-infectious contexts.

The Effects of Immune System Modulation on Prion Disease Susceptibility and Pathogenesis

Prion diseases are a unique group of infectious chronic neurodegenerative disorders to which there are no cures. Although prion infections do not stimulate adaptive immune responses in infected individuals, the actions of certain immune cell populations can have a significant impact on disease pathogenesis. After infection, the targeting of peripherally-acquired prions to specific immune cells in the secondary lymphoid organs (SLO), such as the lymph nodes and spleen, is essential for the efficient transmission of disease to the brain. Once the prions reach the brain, interactions with other immune cell populations can provide either host protection or accelerate the neurodegeneration. In this review, we provide a detailed account of how factors such as inflammation, ageing and pathogen co-infection can affect prion disease pathogenesis and susceptibility. For example, we discuss how changes to the abundance, function and activation status of specific immune cell populations can affect the transmission of prion diseases by peripheral routes. We also describe how the effects of systemic inflammation on certain glial cell subsets in the brains of infected individuals can accelerate the neurodegeneration. A detailed understanding of the factors that affect prion disease transmission and pathogenesis is essential for the development of novel intervention strategies.

Neuroinflammation, Microglia, and Cell-Association during Prion Disease

Prion disorders are transmissible diseases caused by a proteinaceous infectious agent that can infect the lymphatic and nervous systems. The clinical features of prion diseases can vary, but common hallmarks in the central nervous system (CNS) are deposition of abnormally folded protease-resistant prion protein (PrPres or PrPSc), astrogliosis, microgliosis, and neurodegeneration. Numerous proinflammatory effectors expressed by astrocytes and microglia are increased in the brain during prion infection, with many of them potentially damaging to neurons when chronically upregulated. Microglia are important first responders to foreign agents and damaged cells in the CNS, but these immune-like cells also serve many essential functions in the healthy CNS. Our current understanding is that microglia are beneficial during prion infection and critical to host defense against prion disease. Studies indicate that reduction of the microglial population accelerates disease and increases PrPSc burden in the CNS. Thus, microglia are unlikely to be a foci of prion propagation in the brain. In contrast, neurons and astrocytes are known to be involved in prion replication and spread. Moreover, certain astrocytes, such as A1 reactive astrocytes, have proven neurotoxic in other neurodegenerative diseases, and thus might also influence the progression of prion-associated neurodegeneration.

Evolution in pharmacologic thinking around the natural analgesic palmitoylethanolamide: from nonspecific resistance to PPAR-α agonist and effective nutraceutical

The history of development of new concepts in pharmacology is a highly interesting topic. This review discusses scientific insights related to palmitoylethanolamide (PEA) and its progression over a period of six decades, especially in light of the work of the science sociologists, Ludwig Fleck and Thomas Kuhn. The discovery of the cannabis receptors and the nuclear peroxisome proliferator-activated receptors was the beginning of a completely new understanding of many important homeostatic physiologic mechanisms in the human body. These discoveries were necessary for us to understand the analgesic and anti-inflammatory activity of PEA, a body-own fatty amide. PEA is a nutrient known already for more than 50 years. PEA is synthesized and metabolized in animal cells via a number of enzymes and has a multitude of physiologic functions related to metabolic homeostasis. PEA was identified in the 1950s as a therapeutic principle with potent anti-inflammatory properties. Since 1975, its analgesic properties have been noted and explored in a variety of chronic pain states. Since 2008, PEA has been available as a nutraceutical under the brand names Normast® and PeaPure®. A literature search on PEA meanwhile has yielded over 350 papers, all referenced in PubMed, describing the physiologic properties of this endogenous modulator and its pharmacologic and therapeutic profile. This review describes the emergence of concepts related to the pharmacologic profile of PEA, with an emphasis on the search into its mechanism of action and the impact of failing to identify such mechanism in the period 1957–1993, on the acceptance of PEA as an anti-inflammatory and analgesic compound.

Intraperitoneal infection with scrapie is established within minutes of injection and is non-specifically enhanced by a variety of different drugs

Single intraperitoneal (i.p.) doses of 16 different drugs were given to mice 2 h before injecting scrapie i.p. Scrapie was injected as serial ten-fold dilutions of standard inocula and the effective titres obtained were used as a measure of the relative efficiency of infection in treated compared to saline injected mice. Despite the wide variety of drugs tested, most of them increased, non-specifically, the efficiency of infection by 0.6 to 2.1 log10 i.p. LD50 units (i.e., 4 to 126-fold), but only when both drug and scrapie were given i.p. The effect was greatest with a 2 h or a 6 h interval suggesting an involvement either of resident peritoneal cells or of elicited cells such as polymorphonuclear neutrophils. There was no increase in the efficiency of infection after intervals of 2 or 7 days when induced macrophages would predominant. The reverse sequence of injections (scrapie-0.5 h-drug) had no effect despite the persistence of high scrapie titre in the peritoneum at the time of drug injection. However, the effect was restored by a second injection of scrapie in the sequence, scrapie-drug-scrapie. It is concluded that scrapie infection is established within minutes of injection but much of the inoculum is associated with peritoneal cells which are irrelevant to pathogenesis. Drugs may enhance the infection of relevant peritoneal cells or their targeting to the visceral lymphoreticular tissues where early replication takes place.

Ionising radiation has no influence on scrapie incubation period in mice

Scrapie has an early non-clinical stage when replication of agent occurs in lymphoreticular organs. Whole-body irradiation failed to alter the incubation or neuropathology of the disease. Many experiments were carried out with different strains of scrapie agent and host, doses and timing of irradiation. The results suggest that mitotically quiescent cells are involved in agent replication.

Suppression of scrapie infection in mice by heteropolyanion 23, dextran sulfate, and some other polyanions

Studies of polyanions that suppress scrapie have been done to pinpoint the cell types in the lymphoreticular system which are important in pathogenesis and to suggest possible prophylactic or therapeutic strategies for the unconventional slow viruses. A regime of three daily injections of the inorganic heteropolyanion HPA-23 reduced the effective scrapie dose by more than 99%; i.e., some mice survived peripherally injected doses of 100 50% lethal dose units. The effect was greatest when the first dose of HPA-23 was given 4 h after injecting scrapie, but it declined rapidly as this interval was increased, and there was virtually no effect 2 days after infection. A single dose of high-molecular-weight organic polyanions such as carrageenan or dextran sulfate (DS-500) greatly reduced (i.e., greater than 99%) the efficiency of scrapie infection. In contrast to HPA-23, DS-500 was equally effective whether given 4 days before or 8 h after the time of infection. The antiscrapie effect of DS-500 appeared to be independent of its activity as a B-cell mitogen and of its ability to produce a cytotoxic blockade of phagocytic cells. DS-500 probably caused the aggregation and loss from blood of scrapie inoculum which was present immediately after injection, but it had additional effects on scrapie at later times.

Pathogenesis of mouse scrapie: distribution of agent in the pulp and stroma of infected spleens

Fourteen spleens were collected from mice infected with the 139A strain of scrapie, at a time when the concentration of agent in spleen was at a plateau. Scrapie infectivity was present in both the pulp and stromal fractions, but the concentration in stroma was about 10 times greater than that in pulp. On average, 1000 pulp cells were required to give 1 LD50 unit of scrapie infectivity. Linear regression analysis of data from 64 mouse spleens showed that the total infectivity correlated with tissue weight (P less than 0.001). The titres of the 14 stromal fractions were significantly correlated with whole spleen weight (P less than 0.02) and with the weight of stroma (P less than 0.02), but not with pulp weight. Hence, the titres in the isolated stroma probably reflect those of the stroma in vivo. In contrast, there was no correlation between total pulp titre and spleen weight, pulp weight or pulp cell number. Moreover, gentle washing of pulp cells removed about 80% of the total infectivity. This suggests that much of the pulp titre is adventitiously associated with cells and is in fact agent released from damaged stroma.

The activity of an anti-allergic compound, proxicromil, on models of immunity and inflammation

A tricyclic chromone, proxicromil (sodium 6,7,8,9-tetrahydro-5-hydroxy-4-oxo-10-propyl-naphtho (2,3-b) pyran-2-carboxylate), has been tested for activity against certain immunological and inflammatory reactions. When given parenterally it suppressed the development of delayed hypersensitivity reactions in sensitized mice and guinea-pigs but did not affect the rejection of skin allografts in mice. The compound had no activity against certain in vitro correlates of delayed hypersensitivity reactions (lymphocyte transformation and lymphokine activity), but did have an inhibitory effect on lymphokine (MIF) productions at 10(-4) M but not at 10(-5) M. Proxicromil was also found to be active in non-immunologically mediated models of inflammation and in models having an immunological component which are known to be sensitive to non-steroidal anti-inflammatory drugs (adjuvant arthritis, reversed passive Arthus reaction). The activity of this compound was enhanced when administered in arachis oil when compared to its activity in saline. Proxicromil has not direct activity on the development of immune responsiveness but appear to suppress the expression of delayed hypersensitivity and immune complex mediated hypersensitivity reactions by virtue and its anti-inflammatory properties. This activity is not associated with inhibition of cyclo-oxygenase.