Livingston, E. W. | bioRxiv Science

bioRxiv2025

Temporal evolution of hemodynamics in murine arteriovenous fistula: a micro-CT based computational fluid dynamics study

In this study, we investigated the hemodynamic characteristics of arteriovenous fistulae (AVF) in murine models using micro-CT based computational fluid dynamics (CFD). By combining high-resolution micro-CT imaging with ultrasound flow measurements, our methodology offers a cost-effective and efficient alternative to traditional MRI-based approaches. CFD simulations performed at 7 and 21 days post-surgery revealed significant temporal changes in both geometry and hemodynamics. Geometric analysis showed that: the proximal artery diameter increased from 0.29 mm to 0.38 mm, while the initial 2 mm fistula segment showed a 21.6% decrease (0.74 mm to 0.58 mm). Blood flow through the AVF nearly doubled from 1.33 mL/min to 2.57 mL/min. Time-averaged wall shear stress (TAWSS) peak values increased from 142 Pa (day 7) within the proximal artery to 200 Pa (day 21), in the stenotic region. The oscillatory shear index (OSI) showed marked elevation at the anastomosis (increasing from 0.22 to 0.48), indicating disturbed flow development. An inverse relationship between TAWSS and OSI was identified consistent with previous studies. Our methodology demonstrates the capability to analyze relationships between early hemodynamics and subsequent geometric changes. This approach could enable identification of regions susceptible to stenosis development and monitoring of AVF maturation, which could ultimately lead to quantitative metrics to evaluate surgical outcomes and early therapeutic interventions.

bioengineering↗

bioRxiv2022

Small Molecule Screen Identifies Pyrimethamine as an Inhibitor of NRF2-driven Esophageal Hyperplasia

ObjectiveNRF2 is a master transcription factor that regulates the stress response. NRF2 is frequently mutated and activated in human esophageal squamous cell carcinoma (ESCC), which drives resistance to chemotherapy and radiation therapy. Therefore, a great need exists for NRF2 inhibitors for targeted therapy of NRF2high ESCC. DesignWe performed high-throughput screening of two compound libraries from which hit compounds were further validated in human ESCC cells and a genetically modified mouse model. The mechanism of action of one compound was explored by biochemical assays. ResultsUsing high-throughput screening of two small molecule compound libraries, we identified 11 hit compounds as potential NRF2 inhibitors with minimal cytotoxicity at specified concentrations. We then validated two of these compounds, pyrimethamine and mitoxantrone, by demonstrating their dose- and time-dependent inhibitory effects on the expression of NRF2 and its target genes in two NRF2Mut human ESCC cells (KYSE70 and KYSE180). RNAseq and qPCR confirmed the suppression of global NRF2 signaling by these two compounds. Mechanistically, pyrimethamine reduced NRF2 half-life by promoting NRF2 ubiquitination and degradation in KYSE70 and KYSE180 cells. Expression of an Nrf2E79Q allele in mouse esophageal epithelium (Sox2CreER;LSL-Nrf2E79Q/+) resulted in an NRF2high phenotype, which included squamous hyperplasia, hyperkeratinization, and hyperactive glycolysis. Treatment with pyrimethamine (30mg/kg/day, p.o.) suppressed the NRF2high esophageal phenotype with no observed toxicity. ConclusionWe have identified and validated pyrimethamine as an NRF2 inhibitor that may be rapidly tested in the clinic as a radiation and chemotherapy sensitizer for NRF2high ESCC. SummaryO_ST_ABSWhat is already known on this topic - summarise the state of scientific knowledge on this subject before you did your study and why this study needed to be doneC_ST_ABSO_LIMutational activation of the NRF2 transcription factor drives ESCC progression and therapeutic resistance. Targeted therapies to block NRF2 have not yet been realized, despite great needs. C_LI What this study adds - summarise what we now know as a result of this study that we did not know beforeO_LIA screen of >35,000 small molecules identified eleven potential NRF2 inhibitors. Pyrimethamine and mitoxantrone were validated to inhibit the expression of NRF2 and NQO1 in human ESCC cells in both dose- and time-dependent manners. C_LIO_LIPyrimethamine enhanced NRF2 protein ubiquitination and degradation, resulting a decreased half-life. C_LIO_LIA genetically modified mouse model was established to express the Nrf2E79Q mutant allele in the mouse esophageal epithelium upon tamoxifen induction. Pyrimethamine suppressed the NRF2high esophageal phenotype induced by the mutant allele. C_LI How this study might affect research, practice or policy - summarise the implications of this studyO_LIAs an FDA-approved drug, Pyrimethamine has the potential for immediate translation to a clinical trial on NRF2high ESCC in humans. C_LIO_LIFurther exploration of its mechanisms of action may lead to more potent NRF2 inhibitors for future use. C_LI

cancer biology↗