Correcting for Multiple Comparisons in Statistical Analysis of Animal Bioassay Data

Disrupting lipid homeostasis with CAV2 in OSCC triggers apoptosis, lipolysis, and mitochondrial dysfunction by transcriptional repression of PPARγ

BACKGROUND

Abnormal lipid droplet (LD) dynamics in oral squamous cell carcinoma (OSCC) indicate lipid metabolism alterations that facilitate malignancy progression. However, the specific mechanisms by which disruptions in lipid homeostasis affect malignancy processes remain poorly understood. This study investigated the role of LD-associated protein Caveolin2 (CAV2) in OSCC lipid homeostasis and progression.

METHODS

The clinical relevance of CAV2 in OSCC was assessed through transcriptomics, single-cell sequencing, and functional validation in OSCC cells. CAV2 knockdown via shRNA was used to analyze its effects on growth, apoptosis, lipid homeostasis, and mitochondrial function. RNA sequencing, lipidomics, and molecular docking elucidated mechanisms of lipid metabolic disruption. Lipolysis was evaluated via glycerol release, lipidomics, and expression of related genes and proteins. Seahorse assays were used to evaluate mitochondrial dysfunction by analyzing mitochondrial respiration, while additional experiments assessed ROS levels, MMP, morphology, mass, and organelle interactions. In vivo, studies examined tumor progression in nude mice implanted with CAV2-knockdown OSCC cells. The regulatory role of PPARγ on CAV2 was explored through bioinformatics, correlation analysis, and dual-luciferase assays. Coimmunoprecipitation assessed CAV2 and NCOR1 binding with PPARγ, while the PPARγ inverse agonist T0070907 was used to enhance NCOR1-mediated repression of CAV2.

RESULTS

CAV2 was upregulated in OSCC and correlated with poor clinical outcomes. CAV2 knockdown increased apoptosis, reduced proliferation, and disrupted lipid homeostasis, elevating polyunsaturated fatty acids (PUFAs). Regulatory networks responsible for PUFA accumulation were mapped in CAV2-knockdown OSCC cells, from upstream regulators to downstream effects. Furthermore, lipolysis and mitochondrial dysfunction were also enhanced following CAV2 silencing. In vivo, CAV2 knockdown suppressed OSCC progression. Mechanistically, PPARγ regulated CAV2 transcription via NCOR1, but OSCC cells disrupted this repression. The PPARγ inverse agonist T0070907 restored NCOR1-mediated repression, synergistically enhancing the effects of CAV2 knockdown on apoptosis, lipolysis, and mitochondrial dysfunction.

CONCLUSIONS

Alteration of CAV2 disrupted lipid homeostasis and inhibited OSCC progression by affecting key processes, including apoptosis, lipolysis, and mitochondrial dysfunction. The disruption was driven by the dysregulation of the PPARγ/NCOR1 axis, highlighting the potential of targeting CAV2 and its interaction with PPARγ as a therapeutic strategy for OSCC.

A critical evaluation of rodent carcinogenicity studies on butyl methacrylate demonstrates a lack of carcinogenic potential

Assessments of a chemical agent's carcinogenicity based on rodent bioassays rely on their appropriate interpretation. This involves attention to study details, including reliable histopathologic diagnoses, and proper statistical analyses, including consideration of multiple comparisons, concurrent and historical controls. A major factor is evaluation of their likely mode of action and the human relevance of any identified tumors. We present a critical evaluation of the assessment of the 2-year inhalation bioassays of n-butyl methacrylate (n-BMA) in rats and mice performed by the Japan Bioassay Research Center (JBRC) and an assessment of the International Agency for Research on Cancer (IARC) review and classification as Group 2B, possible human carcinogen. The tumors of concern for assessment of its carcinogenicity included mononuclear cell leukemia (MCL) in male rats, thyroid C-cell tumors in female rats, liver tumors and histiocytic sarcomas in male mice, and hemangiosarcomas in female mice. Our review of these studies raises concerns regarding the accuracy of histopathology diagnoses and human relevance of MCL. Most critically, the statistical evaluation/interpretation of all tumor types indicates no carcinogenic effects, since the frequency of increases (at p < 0.05) in tumor incidences in the study is totally consistent with chance expectation (i.e. not treatment related). Furthermore, the plausibility of n-BMA being carcinogenic is questionable since it is non-genotoxic, and the weight of evidence including read-across to the close structural analog methyl methacrylate indicates no concern for cancer. After thorough review of these bioassays, we conclude that there is no convincing evidence of carcinogenicity for n-BMA, contrary to the conclusion of the JBRC and the decision by the IARC.

Using historical control data in bioassays for regulatory toxicology

Historical control data (HCD) consist of pooled control group responses from bioassays. These data must be collected and are often used or reported in regulatory toxicology studies for multiple purposes: as quality assurance for the test system, to help identify toxicological effects and their effect-size relevance and to address the statistical multiple comparison problem. The current manuscript reviews the various classical and potential new approaches for using HCD. Issues in current practice are identified and recommendations for improved use and discussion are provided. Furthermore, stakeholders are invited to discuss whether it is necessary to consider uncertainty when using HCD formally and statistically in toxicological discussions and whether binary inclusion/exclusion criteria for HCD should be revised to a tiered information contribution to assessments. Overall, the critical value of HCD in toxicological bioassays is highlighted when used in a weight-of-evidence assessment.