Occurrence of foam cells in the choroid plexus of rats injected intraperitoneally with methylcellulose

Repeated Intraperitoneal Administration of Low-Concentration Methylcellulose Leads to Systemic Histologic Lesions Without Loss of Preclinical Phenotype

Methylcellulose (MC; 0.5% concentration) is commonly used when evaluating investigational agents for efficacy in preclinical models of disease. When administered by the oral (PO) route, MC is considered a Food and Drug Administration "generally recognized as safe" compound. Yet, there is limited data pertaining to the tolerability and impact on model fidelity of repeated intraperitoneal administration of 0.5% MC. Chronic administration of high-concentration MC (2%-2.5%) has been used to induce anemia, splenomegaly, and lesions in multiple organ systems in several preclinical species. Histopathological findings from a diagnostic pathologic analysis of a single mouse from our laboratory with experimentally induced chronic seizures that had received repeated intraperitoneal administration of antiseizure drugs delivered in MC revealed similar widespread lesions. This study thus tested the hypothesis that chronic administration of intraperitoneal, but not PO, MC incites histologic lesions without effects on preclinical phenotype. Male CF-1 mice (n = 2-14/group) were randomized to receive either 6 weeks of twice weekly 0.5% MC or saline (intraperitoneal or PO) following induction of chronic seizures. Histology of a subset of mice revealed lesions in kidney, liver, mediastinal lymph nodes, mesentery, aorta, and choroid plexus only in intraperitoneal MC-treated mice (n = 7/7). Kindled mice that received MC PO (n = 5) or saline (intraperitoneal n = 6, PO n = 3) had no lesions. There were no effects of intraperitoneal MC treatment on body weight, appearance, seizure stability, or behavior. Nonetheless, our findings suggest that repeated intraperitoneal, but not PO, MC elicits systemic organ damage without impacting the model phenotype, which may confound interpretation of investigational drug-induced histologic lesions. SIGNIFICANCE STATEMENT: Methylcellulose (0.5% concentration) is commonly used when evaluating investigational agents for efficacy in preclinical models of disease. Herein, we demonstrate that repeated administration of 0.5% methylcellulose by the intraperitoneal, but not oral, route results in systemic inflammation and presence of foam-laden macrophages but does not impact the behavioral phenotype of a rodent model of neurological disease.

Vulnerability of fourth ventricle choroid plexus in sudden unexplained fetal and infant death syndromes related to smoking mothers

The human choroid plexuses in the ventricular system represent the main source of cerebrospinal fluid secretion and constitute a major barrier interface that controls the brain's environment. The present study focused on the choroid plexus of the fourth ventricle, the main cavity of the brainstem containing important nuclei and/or structures mediating autonomic vital functions. In serial sections of 84 brainstems of subjects aged from 17 gestational weeks to 8 postnatal months of life, the deaths due to both known and unknown causes, we examined the cytoarchitecture and the developmental steps of the fourth ventricle choroid plexus to determine whether this structure shows morphological and/or functional alterations in unexplained perinatal deaths (Sudden Infant Death Syndrome and Sudden Intrauterine Unexplained Death Syndrome). High incidence of histological and immunohistochemical alterations (prevalence of epithelial dark cells, the presence of cystic cells in the stroma, decreased number of blood capillaries, hyperexpression of Substance P and apoptosis) were prevalently observed in unexplained death victims (p<0.05 vs. controls). A significant correlation was found between maternal smoking in pregnancy and choroidal neuropathological parameters (p<0.01). This work underscores the negative effects of prenatal exposure to nicotine on the development of the autonomic nervous system, and in particular of the fourth ventricle choroid plexus that is a very vulnerable structure in the developing CSF-brain system.

The distributional nexus of choroid plexus to cerebrospinal fluid, ependyma and brain: toxicologic/pathologic phenomena, periventricular destabilization, and lesion spread

Bordering the ventricular cerebrospinal fluid (CSF) are epithelial cells of choroid plexus (CP), ependyma and circumventricular organs (CVOs) that contain homeostatic transporters for mediating secretion/reabsorption. The distributional pathway ("nexus") of CP-CSF-ependyma-brain furnishes peptides, hormones, and micronutrients to periventricular regions. In disease/toxicity, this nexus becomes a conduit for infectious and xenobiotic agents. The sleeping sickness trypanosome (a protozoan) disrupts CP and downstream CSF-brain. Piperamide is anti-trypanosomic but distorts CP epithelial ultrastructure by engendering hydropic vacuoles; this reflects phospholipidosis and altered lysosomal metabolism. CP swelling by vacuolation may occlude CSF flow. Toxic drug tools delineate injuries to choroidal compartments: cyclophosphamide (vasculature), methylcellulose (interstitium), and piperazine (epithelium). Structurally perturbed CP allows solutes to penetrate the ventricles. There, CSF-borne pathogens and xenobiotics may permeate the ependyma to harm neurogenic stem cell niches. Amoscanate, an anti-helmintic, potently injures rodent ependyma. Ependymal/brain regions near CP are vulnerable to CSF-borne toxicants; this proximity factor links regional barrier breakdown to nearby periventricular pathology. Diverse diseases (e.g., African sleeping sickness, multiple sclerosis) take early root in choroidal, circumventricular, or perivascular loci. Toxicokinetics informs on pathogen, anti-parasitic agent, and auto-antibody distribution along the CSF nexus. CVOs are susceptible to plasma-borne toxicants/pathogens. Countering the physico-chemical and pathogenic insults to the homeostasis-mediating ventricle-bordering cells sustains brain health and fluid balance.