Axonal swellings and spheroids: a new insight into the pathology of neurocysticercosis

Advanced Immunolabeling Method for Optical Volumetric Imaging Reveals Dystrophic Neurites of Dopaminergic Neurons in Alzheimer's Disease Mouse Brain

Optical brain clearing combined with immunolabeling is valuable for analyzing molecular tissue structures, including complex synaptic connectivity. However, the presence of aberrant lipid deposition due to aging and brain disorders poses a challenge for achieving antibody penetration throughout the entire brain volume. Herein, we present an efficient brain-wide immunolabeling method, the immuno-active clearing technique (iACT). The treatment of brain tissues with a zwitterionic detergent, specifically SB3-12, significantly enhanced tissue permeability by effectively mitigating lipid barriers. Notably, Quadrol treatment further refines the methodology by effectively eliminating residual detergents from cleared brain tissues, subsequently amplifying volumetric fluorescence signals. Employing iACT, we uncover disrupted axonal projections within the mesolimbic dopaminergic (DA) circuits in 5xFAD mice. Subsequent characterization of DA neural circuits in 5xFAD mice revealed proximal axonal swelling and misrouting of distal axonal compartments in proximity to amyloid-beta plaques. Importantly, these structural anomalies in DA axons correlate with a marked reduction in DA release within the nucleus accumbens. Collectively, our findings highlight the efficacy of optical volumetric imaging with iACT in resolving intricate structural alterations in deep brain neural circuits. Furthermore, we unveil the compromised integrity of DA pathways, contributing to the underlying neuropathology of Alzheimer's disease. The iACT technique thus holds significant promise as a valuable asset for advancing our understanding of complex neurodegenerative disorders and may pave the way for targeted therapeutic interventions.

Unveiling the role of iPLA2β in neurodegeneration: From molecular mechanisms to advanced therapies

Calcium-independent phospholipase A2β (iPLA2β), a member of the phospholipase A2 (PLA2s) superfamily, is encoded by the PLA2G6 gene. Mutations in the PLA2G6 gene have been identified as the primary cause of infantile neuroaxonal dystrophy (INAD) and, less commonly, as a contributor to Parkinson's disease (PD). Recent studies have revealed that iPLA2β deficiency leads to neuroinflammation, iron accumulation, mitochondrial dysfunction, lipid dysregulation, and other pathological changes, forming a complex pathogenic network. These discoveries shed light on potential mechanisms underlying PLA2G6-associated neurodegeneration (PLAN) and offer valuable insights for therapeutic development. This review provides a comprehensive analysis of the fundamental characteristics of iPLA2β, its association with neurodegeneration, the pathogenic mechanisms involved in PLAN, and potential targets for therapeutic intervention. It offers an overview of the latest advancements in this field, aiming to contribute to ongoing research endeavors and facilitate the development of effective therapies for PLAN.

Understanding the pathogenic mechanisms and therapeutic effects in neurocysticercosis

Despite being a leading cause of acquired seizures in endemic regions, the pathological mechanisms of neurocysticercosis are still poorly understood. This study aims to investigate the impact of anthelmintic treatment on neuropathological features in a rat model of neurocysticercosis. Rats were intracranially infected with Taenia solium oncospheres and treated with albendazole + praziquantel (ABZ), oxfendazole + praziquantel (OXF), or untreated placebo (UT) for 7 days. Following the last dose of treatment, brain tissues were evaluated at 24 h and 2 months. We performed neuropathological assessment for cyst damage, perilesional brain inflammation, presence of axonal spheroids, and spongy changes. Both treatments showed comparable efficacy in cyst damage and inflammation. The presence of spongy change correlated with spheroids counts and were not affected by anthelmintic treatment. Compared to white matter, gray matter showed greater spongy change (91.7% vs. 21.4%, p < 0.0001), higher spheroids count (45.2 vs. 0.2, p = 0.0001), and increased inflammation (72.0% vs. 21.4%, p = 0.003). In this rat model, anthelmintic treatment destroyed brain parasitic cysts at the cost of local inflammation similar to what is described in human neurocysticercosis. Axonal spheroids and spongy changes as markers of damage were topographically correlated, and not affected by anthelmintic treatment.

The Npc2Gt(LST105)BygNya mouse signifies pathological changes comparable to human Niemann-Pick type C2 disease

INTRODUCTION

Niemann-Pick type C2 disease (NP-C2) is a fatal neurovisceral disorder caused by defects in the lysosomal cholesterol transporter protein NPC2. Consequently, cholesterol and other lipids accumulate within the lysosomes, causing a heterogeneous spectrum of clinical manifestations. Murine models are essential for increasing the understanding of the complex pathology of NP-C2. This study, therefore, aims to describe the neurovisceral pathology in the NPC2-deficient mouse model to evaluate its correlation to human NP-C2.

METHODS

Npc2-/- mice holding the LST105 mutation were used in the present study (Npc2Gt(LST105)BygNya). Body and organ weight and histopathological evaluations were carried out in six and 12-week-old Npc2-/- mice, with a special emphasis on neuropathology. The Purkinje cell (PC) marker calbindin, the astrocytic marker GFAP, and the microglia marker IBA1 were included to assess PC degeneration and neuroinflammation, respectively. In addition, the pathology of the liver, lungs, and spleen was assessed using hematoxylin and eosin staining.

RESULTS

Six weeks old pre-symptomatic Npc2-/- mice showed splenomegaly and obvious neuropathological changes, especially in the cerebellum, where initial PC loss and neuroinflammation were evident. The Npc2-/- mice developed neurological symptoms at eight weeks of age, severely progressing until the end-stage of the disease at 12 weeks. At the end-stage of the disease, Npc2-/- mice were characterized by growth retardation, tremor, cerebellar ataxia, splenomegaly, foam cell accumulation in the lungs, liver, and spleen, brain atrophy, pronounced PC degeneration, and severe neuroinflammation.

CONCLUSION

The Npc2Gt(LST105)BygNya mouse model resembles the pathology seen in NP-C2 patients and denotes a valuable model for increasing the understanding of the complex disease manifestation and is relevant for testing the efficacies of new treatment strategies.

Impaired spatial working memory and reduced hippocampal neuronal density in a rat model of neurocysticercosis

Neurocysticercosis (NCC) is the most common parasitic disease affecting the nervous system and is a leading cause of acquired epilepsy worldwide, as well as cognitive impairment, especially affecting memory. The aim of this study was to evaluate the effect of NCC on spatial working memory and its correlation with hippocampal neuronal density, in a rat model of NCC. This experimental study was conducted on female (n = 60) and male (n = 73) Holtzman rats. NCC was induced by intracranial inoculation of T. solium oncospheres in 14 day-old-rats. Spatial working memory was assessed using the T-maze test at 3, 6, 9, and 12 months post-inoculation, and sensorimotor evaluation was performed at 12 months post-inoculation. Hippocampal neuronal density was evaluated by immunostaining of NeuN-positive cells of the CA1 region. Of the rats inoculated with T. solium oncospheres, 87.2% (82/94) developed NCC. The study showed a significant decline in spatial working memory over a 1-year follow-up period in rats experimentally infected with NCC. Males showed an early decline that started at 3 months, while females demonstrated it at 9 months. Additionally, a decrease in neuronal density was observed in the hippocampus of NCC-infected rats, with a more significant reduction in rats with cysts in the hippocampus than in rats with cysts in other brain areas and control rats. This rat model of NCC provides valuable support for the relationship between neurocysticercosis and spatial working memory deficits. Further investigations are required to determine the mechanisms involved in cognitive impairment and establish the basis for future treatments.

Experimental animal models and their use in understanding cysticercosis: A systematic review

BACKGROUND

Cysticercosis and Neurocysticercosis (NCC) can be studied using several animal species in experimental models which contributes to the understanding of the human form of the disease. Experimental infections of Taenia spp. are vital in explaining the modes of transmission of the parasite and helps the understanding of transmission of the parasite in humans and thus may be useful in designing therapeutic and immune-prophylactic studies to combat the disease. Thus, this systematic review aims to explore the existing experimental animal models to the understanding of cysticercosis in both humans and animals and elucidate the risk factors of cysticercosis and identify the Taenia spp. used in these models.

METHODOLOGY

We systematically identified all publications from the Web of Science, Google Scholar, and Pubmed regarding experimental animal models using Taenia spp. that cause cysticercosis in both humans and animals. 58 studies were identified for eligibility. Of these, only 48 studies met the inclusion criteria from which data extraction was done and presented descriptively.

RESULTS

Pigs, cattle, gerbils, mice, rats, voles, monkeys, cats, dogs, and goats were used in which T. solium, T. saginata, T. saginata asiatica, T. crassiceps and T. asiatica were studied. The routes used to induce disease were; oral, intravenous, subcutaneous, intramuscular, intraperitoneal, intraarterial, intracranial, intraduodenal, and surgical routes using eggs, oncospheres, and proglottids. Besides, the establishment of infection using eggs and oncospheres was affected by the route used to induce infection in the experimental animals. The cysticerci recovery rate in all the experimental studies was low and the number of animals used in these experiments varied from 1 to 84. Although not analysed statistically, sex, age, and breed of animals influenced the cysticerci recovery rate. Additionally, the cysticerci recovery rate and antibody-antigen levels were shown to increase with an increase in the dose of oncospheres and eggs inoculated in the animals. Contrasting results were reported in which the cysticerci recovery rate decreased with an increase in the dose of eggs inoculated.

CONCLUSION

This review describes the various animal experiments using Taenia species that cause cysticercosis highlighting the animals used, age and their breed, the routes of infection used to induce disease and the sample size used, and the cysticerci recovery rate in these animal models.

Frequency and Determinant Factors for Calcification in Neurocysticercosis

BACKGROUND

Neurocysticercosis is a major cause of acquired epilepsy. Larval cysts in the human brain eventually resolve and either disappear or leave a calcification that is associated with seizures. In this study, we assessed the proportion of calcification in parenchymal neurocysticercosis and risk factors associated with calcification.

METHODS

Data for 220 patients with parenchymal NCC from 3 trials of antiparasitic treatment were assessed to determine what proportion of the cysts that resolved 6 months after treatment ended up in a residual calcification at 1 year. Also, we evaluated the risk factors associated with calcification.

RESULTS

The overall proportion of calcification was 38% (188/497 cysts, from 147 patients). Predictors for calcification at the cyst level were cysts larger than 14 mm (risk ratio [RR], 1.34; 95% confidence interval [CI], 1.02-1.75) and cysts with edema at baseline (RR, 1.39; 95% CI, 1.05-1.85). At the patient level, having had more than 24 months with seizures (RR, 1.25; 95% CI, 1.08-1.46), mild antibody response (RR, 1.14; 95% CI, 1.002-1.27), increased dose albendazole regime (RR, 1.26; 95% CI, 1.14-1.39), lower doses of dexamethasone (RR, 1.36; 95% CI, 1.02-1.81), not receiving early antiparasitic retreatment (RR, 1.45; 95% CI, 1.08-1.93), or complete cure (RR, 1.48; 95% CI, 1.29-1.71) were associated with a increased risk of calcification.

CONCLUSIONS

Approximately 38% of parenchymal cysts calcify after antiparasitic treatment. Some factors associated with calcification are modifiable and may be considered to decrease or avoid calcification, potentially decreasing the risk for seizure relapses.

Brain calcification because of neurocysticercosis: a vast field to be explored

PURPOSE OF REVIEW

Neurocysticercosis is the most common helminthic infection of the central nervous system caused by the larval stage of the pork tapeworm, Taenia solium. Endemic regions include Latin American countries, sub-Saharan Africa, and large regions of Asia, including the Indian subcontinent and is a global health problem. Seizures are the most common manifestation and approximately 30% of adult-onset seizures in endemic regions are attributable to NCC. Calcifications because of neurocysticercosis is the most common finding on imaging in endemic regions and are important seizure foci contributing to the burden of epilepsy.

RECENT FINDINGS

After treatment with antiparasitics for multiple viable parenchymal disease, approximately 38% of cysts that resolved after 6 months of therapy will result in residual calcifications, which represents a significant burden of residual disease. Calcified disease has been referred to as 'inactive disease', but there is accumulating evidence to suggest that calcified granulomas are actually dynamic and substantially contribute to the development and maintenance of seizures.

SUMMARY

Calcified parenchymal neurocysticercosis contributes significantly to the development and maintenance of seizures in endemic regions. Understanding the pathogenesis of the role of calcified NCC in seizure development and risk factors for development of calcifications after treatment is critical to decreasing the burden of symptomatic disease in endemic regions.

Changes in inflammatory gene expression in brain tissue adjacent and distant to a viable cyst in a rat model for neurocysticercosis

BACKGROUND

The parasite Taenia solium causes neurocysticercosis (NCC) in humans and is a common cause of adult-onset epilepsy in the developing world. Hippocampal atrophy, which occurs far from the cyst, is an emerging new complication of NCC. Evaluation of molecular pathways in brain regions close to and distant from the cyst could offer insight into this pathology.

METHODS

Rats were inoculated intracranially with T. solium oncospheres. After 4 months, RNA was extracted from brain tissue samples in rats with NCC and uninfected controls, and cDNA was generated. Expression of 38 genes related to different molecular pathways involved in the inflammatory response and healing was assessed by RT-PCR array.

RESULTS

Inflammatory cytokines IFN-γ, TNF-α, and IL-1, together with TGF-β and ARG-1, were overexpressed in tissue close to the parasite compared to non-infected tissue. Genes for IL-1A, CSF-1, FN-1, COL-3A1, and MMP-2 were overexpressed in contralateral tissue compared to non-infected tissue.

CONCLUSIONS

The viable cysticerci in the rat model for NCC is characterized by increased expression of genes associated with a proinflammatory response and fibrosis-related proteins, which may mediate the chronic state of infection. These pathways appear to influence regions far from the cyst, which may explain the emerging association between NCC and hippocampal atrophy.

Inflammation in neurocysticercosis: clinical relevance and impact on treatment decisions

INTRODUCTION

Neurocysticercosis is caused by the localization of Taenia solium larvae in the central nervous system. The disease remains endemic in most countries of Latin America, Asia and Africa. While major improvements have been made in its diagnosis and treatment, uncertainties persist regarding the clinical implications and treatment of the inflammatory reaction associated with the disease.

AREAS COVERED

In this review, based on PubMed searches, the authors describe the characteristics of the immune-inflammatory response in patients with neurocysticercosis, its clinical implications and the treatment currently administered. The dual role of inflammation (participating in both, the death of the parasite, and the precipitation of serious complications) is discussed. New therapeutic strategies of potential interest are presented.

EXPERT OPINION

Inflammatory reaction is the main pathogenic mechanism associated to neurocysticercosis. Its management is mainly based on corticosteroids administration. This strategy had improved prognostic of patients as it allows for the control of most of the inflammatory complications. On the other side, it might be involved in the persistence of parasites in some patients, despite cysticidal treatment, due to its immunosuppressive properties. New strategies are needed to improve therapeutical management, particularly in the severest presentations.

Dual/double pathology in neurocysticercosis causing drug resistant epilepsy - Chance association or causal?

INTRODUCTION

Neurocysticercosis (NCC) as cause of drug resistant epilepsy (DRE) is commonly reported from India. We reviewed the neuropathological findings in patients undergoing resective surgery for DRE due to NCC, to determine the pathomechanism of epileptogenesis.

METHODS

Clinical, demographic and neuropathological findings of histologically confirmed cases of NCC causing DRE between 2005-2019 were reviewed. NeuN, GFAP, phosphorylated neurofilament, vimentin, CD34 for glial/ neuronal alterations, and Masson trichrome, Luxol Fast blue for evidence of fibrosis/ demyelination was used to determine cause of epileptogenesis.

RESULTS

There were 12 cases of NCC associated with dual/ double pathology, which constituted 3.02 % (12/398) of all the operated DRE. [Age range: 17-37y, Male:Female = 1.4:1]. Seizure duration ranged from 3-32y, with seizure onset between 4-27y. On MRI, lesions were of variable signal intensity on T1 and isointense on T2 with blooming on GRE/ SWI, and CT revealed calcification. Majority (11/12) had associated hippocampal sclerosis (HS) type 1 (dual pathology), localised to the same side as cysticercal cyst, suggesting it may be involved in the pathogenesis of HS. Ten had single cysticercal lesion involving ipsilateral hippocampus in 6, parahippocampal gyrus in 2, amygdala and temporal lobe in 1 case each. One had multiple NCC located in bilateral frontal, parietal and ipsilateral hippocampus. Adjacent cortex around the NCC evaluated in 6 cases, revealed inflammation, gliosis, axonal disruption/ beading, and variable synaptic/ neuronal dystrophic changes. There was a single case of NCC with Focal cortical dysplasia (FCD) type IIb (double pathology). In 11/12 cases Engel's post-surgery outcome was available with all having class I outcome.

CONCLUSION

HS was most common pathology associated with cysticercosis (Dual pathology), localised ipsilateral to the cysticercal cyst, suggesting that HS is a secondary/ epiphenomenon. Perilesional changes such as inflammation, gliosis, dystrophic synaptic and axonal pathology play a role in inducing or perpetuating the epileptiform activity. The association of FCD IIb with NCC in one case is likely to be a chance occurrence.

Taenia solium Cysticercosis and Its Impact in Neurological Disease

Taenia solium neurocysticercosis (NCC) is endemic in most of the world and contributes significantly to the burden of epilepsy and other neurological morbidity. Also present in developed countries because of immigration and travel, NCC is one of few diseases targeted for eradication. This paper reviews all aspects of its life cycle (taeniasis, porcine cysticercosis, human cysticercosis), with a focus on recent advances in its diagnosis, management, and control. Diagnosis of taeniasis is limited by poor availability of immunological or molecular assays. Diagnosis of NCC rests on neuroimaging findings, supported by serological assays. The treatment of NCC should be approached in the context of the particular type of infection (intra- or extraparenchymal; number, location, and stage of lesions) and has evolved toward combined symptomatic and antiparasitic management, with particular attention to modulating inflammation. Research on NCC and particularly the use of recently available genome data and animal models of infection should help to elucidate mechanisms of brain inflammation, damage, and epileptogenesis.

p75NTR and DR6 Regulate Distinct Phases of Axon Degeneration Demarcated by Spheroid Rupture

The regressive events associated with trophic deprivation are critical for sculpting a functional nervous system. After nerve growth factor withdrawal, sympathetic axons derived from male and female neonatal mice maintain their structural integrity for ∼18 h (latent phase) followed by a rapid and near unison disassembly of axons over the next 3 h (catastrophic phase). Here we examine the molecular basis by which axons transition from latent to catastrophic phases of degeneration following trophic withdrawal. Before catastrophic degeneration, we observed an increase in intra-axonal calcium. This calcium flux is accompanied by p75 neurotrophic factor receptor-Rho-actin-dependent expansion of calcium-rich axonal spheroids that eventually rupture, releasing their contents to the extracellular space. Conditioned media derived from degenerating axons are capable of hastening transition into the catastrophic phase of degeneration. We also found that death receptor 6, but not p75 neurotrophic factor receptor, is required for transition into the catastrophic phase in response to conditioned media but not for the intra-axonal calcium flux, spheroid formation, or rupture that occur toward the end of latency. Our results support the existence of an interaxonal degenerative signal that promotes catastrophic degeneration among trophically deprived axons.SIGNIFICANCE STATEMENT Developmental pruning shares several morphological similarities to both disease- and injury-induced degeneration, including spheroid formation. The function and underlying mechanisms governing axonal spheroid formation, however, remain unclear. In this study, we report that axons coordinate each other's degeneration during development via axonal spheroid rupture. Before irreversible breakdown of the axon in response to trophic withdrawal, p75 neurotrophic factor receptor-RhoA signaling governs the formation and growth of spheroids. These spheroids then rupture, allowing exchange of contents ≤10 kDa between the intracellular and extracellular space to drive death receptor 6 and calpain-dependent catastrophic degeneration. This finding informs not only our understanding of regressive events during development but may also provide a rationale for designing new treatments toward myriad neurodegenerative disorders.

In vitro model of postoncosphere development, and in vivo infection abilities of Taenia solium and Taenia saginata

Taenia solium is known to cause human cysticercosis while T. saginata does not. Comparative in vitro and in vivo studies on the oncosphere and the postoncospheral (PO) forms of T. solium and T. saginata may help to elucidate why cysticercosis can occur from one and not the other. The aim of this study was to use in vitro culture assays and in vivo models to study the differences in the development of the T. solium and T. saginata oncosphere. Furthermore, this study aimed to evaluate the expression of cytokines and metalloproteinases (MMPs) in human peripheral blood mononuclear cells (PBMCs), which were stimulated by these oncospheres and PO antigens. T. solium and T. saginata activated oncospheres (AO) were cultured in INT-407 and HCT-8 intestinal cells for 180 days. The T. solium began to die while the T. saginata grew for 180 days and developed to cysticerci in INT-407 cells. Rats were inoculated intracranially with AO and PO forms of either T. saginata or T. solium. Rats infected with T. solium AO and PO forms developed neurocysticercosis (NCC), while those infected with the T. saginata did not. Human PMBCs were stimulated with antigens of AO and PO forms of both species, and the production of cytokines and metalloproteinases (MMPs) was measured. The T. solium AO antigen stimulated a higher production of IL-4, IL-5, IL-13, IFN-γ, and IL-2 cytokines compared to T. saginata AO. In the PO form, the T. saginata PO antigen increased the production of IL-4, IL-5, IL-13, IFN-γ, IL-1β, IL-6, IL-10, TNF-α and IL-12 cytokines compared to T. solium, suggesting that this global immune response stimulated by different forms could permit survival or destruction of the parasite depending of their life-cycle stage. Regarding MMPs, T. solium AO antigen stimulated a higher production of MMP-9 compared to T. saginata AO antigen, which may be responsible for altering the permeability of intestinal cells and facilitating breakdown of the blood-brain barrier during the process of invasion of host tissue.

Taenia solium and Taenia saginata are two parasites that cause the tissue infection cysticercosis in their intermediate hosts, pigs and cows, respectively. One major difference between them is that T. solium can also cause neurocysticercosis in the human brain, while T. saginata cannot. Neurocysticercosis is thought to be the major cause of adult-onset seizures in developing countries. It is not well understood why only T. solium can survive in human tissue; however, the host inflammatory response likely plays an important role. The authors found that human immune cells stimulated with T. solium in the early stages of the parasite life cycle produced a more robust cytokine response than T. saginata. However, in the mature stage, which occurs once T. solium reaches the brain, T. solium antigens stimulated a lower inflammatory response compared to T. saginata, suggesting the parasite is able to manipulate the host immune response in some way to evade destruction. These findings may support the differences in growth observed by the authors when rat brains were inoculated with either parasite species. This study provides new insights into the different ways T. solium and T. saginata activate the immune response to survive and develop within the host.