The detrimental effects of acute hyperglycemia on myocardial glucose uptake

Abstract

AimsAlthough acute hyperglycemic (AHG) episodes are linked to lower glucose uptake, underlying mechanisms remain unclear. We hypothesized that AHG triggers reactive oxygen species (ROS) production and increases non-oxidative glucose pathway (NOGP) activation, i.e. stimulation of advanced glycation end products (AGE), polyol pathway (PP), hexosamine biosynthetic pathway (HBP), PKC; thereby decreasing cardiac glucose uptake. Main methodsH9c2 cardiomyoblasts were exposed to 25mM glucose for 24h vs. 5.5mM controls±modulating agents during the last hour of glucose exposure: a) antioxidant #1 for mitochondrial ROS (250μM 4-OHCA), b) antioxidant #2 for NADPH oxidase-generated ROS (100μM DPI), c) NOGP inhibitors — 100μM aminoguanidine (AGE), 5μM chelerythrine (PKC); 40μM DON (HBP); and 10μM zopolrestat (PP). ROS levels (mitochondrial, intracellular) and glucose uptake were evaluated by flow cytometry. Key findingsAHG elevated ROS, activated NOGPs and blunted glucose uptake. Transketolase activity (pentose phosphate pathway [PPP] marker) did not change. Respective 4-OHCA and DPI treatment blunted ROS production, diminished NOGP activation and normalized glucose uptake. NOGP inhibitory studies identified PKCβII as a key downstream player in lowering insulin-mediated glucose uptake. When we employed an agent (benfotiamine) known to shunt flux away from NOGPs (into PPP), it decreased ROS generation and NOGP activation, and restored glucose uptake under AHG conditions. SignificanceThis study demonstrates that AHG elicits maladaptive events that function in tandem to reduce glucose uptake, and that antioxidant treatment and/or attenuation of NOGP activation (PKC, polyol pathway) may limit the onset of insulin resistance.