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Impaired liver metabolic function is related to mortality in severely malnourished children. Here the authors report a role for the tryptophan-NAD + pathway in reduced hepatic mitochondrial function and liver steatosis in a mouse model of severe malnutrition.

Summary: Background: The intestine of children with severe malnutrition (SM) shows structural and functional changes that are linked to increased infection and mortality. SM dysregulates the tryptophan-kynurenine pathway, which may impact processes such as SIRT1- and mTORC1-mediated autophagy and mitochondrial homeostasis. Using a mouse and organoid model of SM, we studied the repercussions of these dysregulations on malnutrition enteropathy and the protective capacity of maintaining autophagy activity and mitochondrial health. Methods: SM was induced through feeding male weanling C57BL/6 mice a low protein diet (LPD) for 14-days. Mice were either treated with the NAD+-precursor, nicotinamide; an mTORC1-inhibitor, rapamycin; a SIRT1-activator, resveratrol; or SIRT1-inhibitor, EX-527. Malnutrition enteropathy was induced in enteric organoids through amino-acid deprivation. Features of and pathways to malnutrition enteropathy were examined, including paracellular permeability, nutrient absorption, and autophagic, mitochondrial, and reactive-oxygen-species (ROS) abnormalities. Findings: LPD-feeding and ensuing low-tryptophan availability led to villus atrophy, nutrient malabsorption, and intestinal barrier dysfunction. In LPD-fed mice, nicotinamide-supplementation was linked to SIRT1-mediated activation of mitophagy, which reduced damaged mitochondria, and improved intestinal barrier function. Inhibition of mTORC1 reduced intestinal barrier dysfunction and nutrient malabsorption. Findings were validated and extended using an organoid model, demonstrating that resolution of mitochondrial ROS resolved barrier dysfunction. Interpretation: Malnutrition enteropathy arises from a dysregulation of the SIRT1 and mTORC1 pathways, leading to disrupted autophagy, mitochondrial homeostasis, and ROS. Whether nicotinamide-supplementation in children with SM could ameliorate malnutrition enteropathy should be explored in clinical trials. Funding: This work was supported by the Bill and Melinda Gates Foundation, the Sickkids Research Institute, the Canadian Institutes of Health Research, and the University Medical Center Groningen.

Abstract Malnutrition impacts approximately 50 million children worldwide and is linked to 45% of global mortality in children below the age of five. Severe acute malnutrition (SAM) is associated with intestinal barrier breakdown and epithelial atrophy. Extracellular vesicles including exosomes (EVs; 30–150 nm) can travel to distant target cells through biofluids including milk. Since milk-derived EVs are known to induce intestinal stem cell proliferation, this study aimed to examine their potential efficacy in improving malnutrition-induced atrophy of intestinal mucosa and barrier dysfunction. Mice were fed either a control (18%) or a low protein (1%) diet for 14 days to induce malnutrition. From day 10 to 14, they received either bovine milk EVs or control gavage and were sacrificed on day 15, 4 h after a Fluorescein Isothiocyanate (FITC) dose. Tissue and blood were collected for histological and epithelial barrier function analyses. Mice fed low protein diet developed intestinal villus atrophy and barrier dysfunction. Despite continued low protein diet feeding, milk EV treatment improved intestinal permeability, intestinal architecture and cellular proliferation. Our results suggest that EVs enriched from milk should be further explored as a valuable adjuvant therapy to standard clinical management of malnourished children with high risk of morbidity and mortality.

Purpose BRAF V600E is a potentially highly targetable mutation detected in a subset of pediatric low-grade gliomas (PLGGs). Its biologic and clinical effect within this diverse group of tumors remains unknown. Patients and Methods A combined clinical and genetic institutional study of patients with PLGGs with long-term follow-up was performed (N = 510). Clinical and treatment data of patients with BRAF V600E mutated PLGG (n = 99) were compared with a large international independent cohort of patients with BRAF V600E mutated-PLGG (n = 180). Results BRAF V600E mutation was detected in 69 of 405 patients (17%) with PLGG across a broad spectrum of histologies and sites, including midline locations, which are not often routinely biopsied in clinical practice. Patients with BRAF V600E PLGG exhibited poor outcomes after chemotherapy and radiation therapies that resulted in a 10-year progression-free survival of 27% (95% CI, 12.1% to 41.9%) and 60.2% (95% CI, 53.3% to 67.1%) for BRAF V600E and wild-type PLGG, respectively ( P < .001). Additional multivariable clinical and molecular stratification revealed that the extent of resection and CDKN2A deletion contributed independently to poor outcome in BRAF V600E PLGG. A similar independent role for CDKN2A and resection on outcome were observed in the independent cohort. Quantitative imaging analysis revealed progressive disease and a lack of response to conventional chemotherapy in most patients with BRAF V600E PLGG. Conclusion BRAF V600E PLGG constitutes a distinct entity with poor prognosis when treated with current adjuvant therapy.