Toxic effects of exogenous retinoic acid on the neurodevelopment of zebrafish (Danio rerio) embryos

Pro-inflammatory effects of all-trans retinoic acid in experimental acute inflammation - insights into eosinophil and neutrophil dynamics

CONTEXT

All-trans retinoic acid (ATRA), a metabolite of vitamin A, regulates embryogenesis, regeneration, hematopoiesis, differentiation, and apoptosis. It also exerts immunomodulatory effects and is used in inflammatory disease models.

OBJECTIVE

This study aimed to investigate the paradoxical pro-inflammatory effects of ATRA on eosinophil and neutrophil recruitment and activation.

MATERIALS AND METHODS

We used thioglycolate- and zymosan-induced peritonitis models in mice to evaluate leukocyte recruitment following ATRA treatment. The roles of inducible nitric oxide synthase (iNOS), tumor necrosis factor (TNF), and the 5-lipoxygenase (5-LO) pathway were assessed using genetically deficient mice and pharmacological inhibitors.

RESULTS AND DISCUSSION

ATRA increased total leukocyte, eosinophil, and neutrophil counts in peritoneal exudates, enhancing the response to both thioglycolate and zymosan. The effects were microenvironment-dependent and likely mediated by local release of pro-inflammatory cytokines and chemokines. iNOS was required for eosinophil recruitment, while TNF contributed to both eosinophil and neutrophil recruitment. The 5-LO pathway was essential for eosinophil involvement. These findings suggest that ATRA can paradoxically enhance inflammation by modulating innate immune cell responses.

CONCLUSIONS

ATRA promotes inflammation through iNOS, TNF, and 5-LO-dependent pathways, revealing complex mechanisms of immune modulation with potential relevance for inflammatory disease management.

The effects of all-trans retinoic acid on prednisolone-induced osteoporosis in zebrafish larvae

Glucocorticoids (GCs) are extensively used as anti-inflammatory and immunosuppressive medications in the long-term treatment of rheumatic disorders, respiratory diseases, renal diseases, and organ transplantation. Prolonged use of GCs can reduce bone mineral density, leading to osteoporosis (Glucocorticoid Induced Osteoporosis, GIOP) and fracture. All-trans retinoic acid (ATRA) is an active vitamin A metabolite that regulates embryonic development and adult organ function. ATRA has been found in studies to enhance osteogenesis. To examine the interventional effects of ATRA on GIOP and the mechanisms of ATRA activities, we first performed bioinformatic analysis to identify potential gene targets of ATRA. Zebrafish larvae were recruited as experimental animals, and the frequently used GC, prednisolone, was administered to larvae to construct a GIOP model. We evaluated the influence of exogenous ATRA on the activities of bone metabolic enzymes, the expression of genes linked to osteoblasts and osteoclasts, and the restoration of bone mineral density and bone mass in GIOP zebrafish larvae. Furthermore, we studied the influence of RBM14, a transcriptional coactivator and negative reciprocal factor of ATRA, on the regulation of osteoblastic gene expression during the anti-GIOP process of ATRA using the morpholino knockdown approach. The findings of bone metabolic enzyme activity (alkaline phosphatase, ALP and tartrate-resistant acid phosphatase, TRAP) and expression assays of osteoblastic marker genes (Runx2a, Runx2b, SP7, Csf1a, RANKL, and CTSK) indicated that ATRA had bidirectional effects on osteogenesis. However, in the GIOP model, ATRA reversed the GIOP-induced osteoporosis phenotype by inhibiting the GIOP-induced suppression of osteoblastic metabolic enzyme (ALP) activities and osteoblastic marker gene expression (Runx2a, Runx2b, and SP7), and this antagonism was concentration-dependent. We also observed that ATRA inhibited RBM14 expression in zebrafish larvae, while ATRA alone and RBM14 knockdown showed a consistent induction of osteoblast marker gene expression, implying that ATRA's inhibitory effect on RBM14 expression may underlie ATRA's osteogenic effects. Based on these data, we postulated that ATRA may ameliorate GIOP by decreasing RBM14 expression, thereby enhancing osteoblastic marker gene expression.

Thallium - poisoner's poison: An overview and review of current knowledge on the toxicological effects and mechanisms

Thallium (Tl) is one of the most toxic metals and its historic use in homicides has led it to be known as "the poisoner's poison." This review summarizes the methods for identifying Tl and determining its concentrations in biological samples in recently reported poisoning cases, as well as the toxicokinetics, toxicological effects, toxicity mechanisms, and detoxication methods of Tl. Recent findings regarding Tl neurotoxicological pathways and toxicological effects of Tl during pregnancy are also presented. Confirmation of elevated Tl concentrations in blood, urine, or hair is indispensable for diagnosing Tl poisoning. The kidneys show the highest Tl concentration within 24 h after ingestion, while the brain shows the highest concentration thereafter. Tl has a very slow excretion rate due to its large distribution volume. Following acute exposure, gastrointestinal symptoms are observed at an early stage, and neurological dysfunction is observed later: Tl causes the most severe damage in the central nervous system. Alopecia and Mees' lines in the nails are observed within 1 month after Tl poisoning. The toxicological mechanism of Tl is considered to be interference of vital potassium-dependent processes with Tl+ because its ionic radius is similar to that of K+, as well as inhibition of enzyme reactions by the binding of Tl to -SH groups, which disturbs vital metabolic processes. Tl toxicity is also related to reactive oxygen species generation and mitochondrial dysfunction. Prussian blue is the most effective antidote, and metallothionein alone or in combination with Prussian blue was recently reported to have cytoprotective effects after Tl exposure. Because Tl poisoning cases are still reported, early determination of Tl in biological samples and treatment with an antidote are essential.