Endocrine Abstracts

Background: Endoplasmic reticulum (ER) stress and associated mitochondrial dysfunction contribute to the pathogenesis of obesity and type 2 diabetes mellitus (T2DM). Studies show broccoli can reduce inflammation in cancer and may therefore mitigate inflammation-induced cellular disruption that precedes insulin resistance in human adipocytes. Therefore these studies investigated the impact of freeze-dried broccoli extracts (BE) on ER stress and mitochondrial dysfunction in human adipocytes.

Methods: Differentiated human adipocytes (Chub-S7 cell line, n=6) were treated with tunicamycin (Tun; 750ng/ml) alone, to induce ER stress, or combined with a freeze-dried broccoli extract (BE; hybrid Brassica oleracea var. italic; 10ng/ml) acutely (24hr), and chronically (48hr, 72hr). ER stress changes were measured through marker genes (ATF4, ATF6 and CHOP) and proteins (BiP, p-eIF2α and eIF2α). Mitochondrial function was assessed via a Mito Stress Test, measuring oxygen consumption, and through marker genes (SIRT3). Mitochondrial morphology was assessed using live cells on a Nanolive microscope.

Results: Tun increased ER stress marker genes up to 4.5-fold (CHOP, 72hr, P<0.001), whilst BE+Tun reduced this expression up to 64% (P<0.001). Tun increased mitochondrial oxygen consumption rate by 77% (24hr, P<0.05) whilst BE mitigated this by 37%. BE increased the expression of SIRT3 up to 3-fold, regardless of Tun presence. Live cell imaging highlighted Tun-induced mitochondrial fragmentation, indicative of dysfunction, which progressed with time (48hr, 72hr). BE+Tun treated cells displayed a more efficient, elongated mitochondrial phenotype, similar to control.

Conclusion: These studies highlighted that BE can alleviate ER stress and associated mitochondrial dysfunction in human adipocytes. BE reduced markers of ER stress, prevented excessive mitochondrial oxygen consumption and maintained morphologically healthier mitochondria than cells exposed to Tun alone. These impacts occurred both acutely and chronically, with most notable protection from BE observed at 72hr. As such, BE may offer an agent to relieve obesity-induced inflammation and associated insulin resistance.