Investigating the effects of an oral fructose challenge on hepatic ATP reserves in healthy volunteers: a 31P MRS study

Background: Impaired homeostasis of hepatic ATP has been associated with NAFLD. An intravenous fructose infusion has been shown to be an effective challenge to monitor the depletion and subsequent recovery of hepatic ATP reserves using 31P MRS. Aims: The purpose of this study was to evaluate the effects of an oral rather than intravenous fructose challenge on hepatic ATP reserves in healthy subjects. Methods: Self-reported healthy males were recruited. Following an overnight fast, baseline liver glycogen and lipid levels were measured using Magnetic Resonance Spectroscopy (MRS). Immediately after consuming a 500 ml 75 g fructose drink (1275 kJ) subjects were scanned continuously for 90 min to acquire dynamic 31P MRS measurements of liver ATP reserves. Results: A significant effect on ATP reserves was observed across the time course (P < 0.05). Mean ATP levels reached a minimum at 50 min which was markedly lower than baseline (80 ± 17% baseline, P < 0.05). Subsequently, mean values tended to rise but did not reach statistical significance above minimum. The time to minimum ATP levels across subjects was negatively correlated with BMI (R2 ¼ 0.74, P < 0.005). Rates of ATP recovery were not significantly correlated with BMI or liver fat levels, but were negatively correlated with baseline glycogen levels (R2 ¼ 0.7, P < 0.05). Conclusions: Depletion of ATP reserves can be measured non-invasively following an oral fructose challenge using 31P

A low calorie morning meal prevents the decline of hepatic glycogen stores: a pilot in vivo 13C magnetic resonance study

Previous studies have reported a meal-induced rise in hepatic glycogen stores from baseline levels following a fast and it is generally assumed that glycogen levels rise steadily following meals throughout the day. However, measurements are normally taken in conditions that are not typical of the Western breakfast, which is relatively carbohydrate rich with a lower calorific content than most experimental test meals. As such, little is known about the normal metabolic response to a realistic, low calorie morning meal. Therefore, the aim of this pilot study was to evaluate the effects of a low dose oral glucose intake on hepatic glycogen levels following an overnight fast in healthy subjects. Glycogen levels were monitored in vivo using 13C Magnetic Resonance Spectroscopy at baseline and hourly for 4 hours following either a 50 g glucose drink (773 kJ) or a control drink (0 kJ) given over two different visits. During the control visit hepatic glycogen levels decreased throughout the experiment with statistically significant decreases from baseline at 190 minutes (P < 0.05) and 250 minutes (P < 0.05). By contrast, the low dose glucose intake maintained glycogen concentrations with no significant decrease from baseline over 4 hours. A comparison between visits revealed that mean glycogen concentrations were significantly greater during the glucose visit (control visit, AUC = 218 ± 39 mol L−1 min−1; glucose visit, AUC = 305 ± 49 mol L−1 min−1; P < 0.05). Liver volume decreased significantly from baseline at 180 minutes (P < 0.05) post consumption in both groups, with no significant difference found between visits. Gastric content volumes were significantly higher for the glucose visit immediately following consumption (P < 0.001) and at 60 minutes (P = 0.007) indicating slower gastric emptying for the glucose compared with the control. In conclusion, following an overnight fast, a low dose oral glucose challenge prevents a reduction in hepatic glycogen content but does not increase it above fasted levels