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Background: Previous human studies reported inconsistent effects of dietary protein and branched-chain amino acids (BCAAs) on insulin action and glucose metabolism. Similarly, it is unclear whether saturated fat (SF) intake influences these metabolic variables. Objective: The objective of this study was to test the effects of high [30% of energy (%E)] vs. moderate (20% E) intakes of protein (primarily whey) on insulin action and lipid and lipoprotein concentrations in the context of both high (15%E) and low (7%E) SF diets. Methods: The study was conducted as a randomized controlled trial in 158 overweight and obese men and women. After a 4-wk baseline diet [55%E carbohydrate, 15%E protein, 30%E fat (7%E SF)], participants were randomly assigned to 4 wk of either the baseline diet or 1 of 4 test diets containing 35%E carbohydrate and either 20%E or 30%E protein and either 7%E or 15%E SF. Frequently sampled i.v. glucose tolerance tests were administered after each dietary period. Results: Other than significantly higher fasting glucose concentrations for high vs. moderate protein intakes with a low-fat diet (difference ±SE:0 .4 7 ± 0.14 mmol/L; P= 0.001), there were no significant effects of dietary protein or SF on glucose metabolism, plasma insulin, or concentrations of lipids and lipoproteins. Changes in plasma BCAAs across all diets were negatively correlated with changes in the metabolic clearance rate of insulin (p = -0.18, P= 0.03) and positively correlated with changes in the acute insulin response to glucose (p = 0.15, P= 0.05). Conclusions: These findings suggest that short-term intake of BCAAs can influence insulin dynamics. However, in this group of overweight and obese individuals, neither high protein nor SF intake affected insulin sensitivity or plasma concentrations of lipids and lipoproteins. This trial was registered at clinicaltrials.gov as NCT00508937. [ABSTRACT FROM AUTHOR]

Inherited pathogenic succinate dehydrogenase (SDHx) gene mutations cause the hereditary pheochromocytoma and paraganglioma tumor syndrome. Syndromic tumors exhibit elevated succinate, an oncometabolite that is proposed to drive tumorigenesis via DNA and histone hypermethylation, mitochondrial expansion, and pseudohypoxia-related gene expression. To interrogate this prevailing model, we disrupt mouse adrenal medulla SDHB expression, which recapitulates several key molecular features of human SDHx tumors, including succinate accumulation but not 5hmC loss, HIF accumulation, or tumorigenesis. By contrast, concomitant SDHB and the neurofibromin 1 tumor suppressor disruption yields SDHx-like pheochromocytomas. Unexpectedly, in vivo depletion of the 2-oxoglutarate (2-OG) dioxygenase cofactor ascorbate reduces SDHB-deficient cell survival, indicating that SDHx loss may be better tolerated by tissues with high antioxidant capacity. Contrary to the prevailing oncometabolite model, succinate accumulation and 2-OG-dependent dioxygenase inhibition are insufficient for mouse pheochromocytoma tumorigenesis, which requires additional growth-regulatory pathway activation. [Display omitted] • Generation and phenotypic characterization of chromaffin cell SDHB knockout mice • SDHB loss and succinate accumulation are insufficient for pheochromocytoma initiation • Dual SDHB/NF1 chromaffin cell knockout mice develop SDHx-like pheochromocytomas • Robust survival of SDHB-deficient chromaffin cells requires an ample redox environment SDHB knockout in mouse chromaffin cells is not tumorigenic despite ample succinate accumulation and conveyance of cardinal features of SDHB-deficient pheochromocytomas. Armstrong et al. find that dual knockout of SDHB and NF1 yields SDHB-like tumors with accumulation of succinate and H3K9me3, in addition to swollen mitochondria and loss of 5hmC. [ABSTRACT FROM AUTHOR]