Figure 1.
General scheme of protein distribution for the mini-array analysis.
Table 1.
Values of glycemia, fructosemia and insulinemia in rats subjected to either an oral glucose or fructose load.
Figure 2.
Mini-array analysis of the serine phosphorylation status of several proteins involved in overall cell function and the regulation of cell cycle in whole rat liver and skeletal muscle after oral loading of different amounts of glucose and fructose.
The mini-array analysis and the distribution of the proteins are described in the Material and Methods section and Figure 1. Healthy adult rats were subjected to an oral glucose or fructose load, as described in the Material and Methods section. The serine-phosphorylation levels of each spot in the mini-arrays were then analyzed. Control: rats that were not subjected to an oral load. Saline: rats subjected to a mock oral load with xx mL of saline solution (0.9%; w/v, NaCl in fresh drinking water). Glucose 1/4: animals subjected to an oral load of 65 mg glucose/100 g body weight. Glucose 1/2: animals subjected to an oral load of 125 mg glucose/100 g body weight. Glucose: animals subjected to an oral load of 250 mg glucose/100 g body weight. Fructose: animals subjected to an oral load of 280 mg fructose/100 g body weight. C-: negative controls. Liver: whole liver extracts. Muscle: whole skeletal muscle extracts. The Figures shows a representative image for five separate experiments. Negative controls were designed as described in the Material and Methods section.
Table 2.
Relative increase in serine phosphorylation levels of selected liver proteins in rats subjected to either an oral glucose or fructose load.
Table 3.
Relative increase in serine phosphorylation levels of selected skeletal muscle proteins in rats subjected to an oral glucose or fructose load.
Table 4.
Intracellular glucose 6-phosphate and ATP levels and relative increase in serine phosphorylation levels of selected proteins of hepatocytes incubated in the presence or absence of glucose or fructose.
Figure 3.
Mini-array analysis of the serine phosphorylation status of several proteins involved in overall cell function and the regulation of cell cycle in isolated hepatocytes and cultured skeletal muscle cells after incubation with a range of concentrations of glucose, fructose or glucose plus fructose.
The mini-array analysis and the distribution of the proteins are described in the Material and Methods section and Figure 1. Isolated hepatocytes and skeletal muscle cell cultures were obtained and incubated as described in the Material and Methods section. The serine-phosphorylation levels of each spot in the mini-arrays were then analyzed. Control: cells incubated for 5 min without the presence of any monosaccharide. Glucose: cells incubated for 5 min in the presence of 10 mM glucose. Fructose: hepatocytes incubated for 5 min in the presence of 10 mM fructose. Glucose+Fructose: cells incubated for 5 min in the presence of 10 mM glucose plus 75 µM fructose. Hepatocytes: isolated hepatocytes. Muscle: skeletal muscle cell cultures. The figures shows a representative image for five separate experiments.
Table 5.
Intracellular glucose 6-phosphate and ATP levels and relative increase in serine phosphorylation levels of selected proteins from cultured skeletal muscle cells incubated in the presence or absence of glucose or fructose.
Figure 4.
Diagram explaining the postulated hypothesis given to explain the specific effects of fructose and glucose on the overall function of liver and skeletal muscle cells after ingestion of/incubation with these sugars.
Following this hypothesis, peri-portal hepatocytes respond to glucose or fructose in a specific manner, depending on the sugar-specific changes that intracellular G 6P and ATP levels undergo in these cells and, perhaps, other unknown signalling mechanisms. The response of these cells is communicated to other hepatic cells and the liver as a whole signals peripheral tissues; this signalling, which is probably based on the presence or absence of micromolar concentrations of fructose in circulating blood, in addition to other putative, unknown signalling mechanisms, indicates that the circulating metabolites derive from either glucose or fructose. Peripheral tissues, like skeletal muscle, would then respond in a specific manner to these signals by changing the phospho-dephosphorylation levels of several key proteins, thus inducing an alteration in the physiology of these cells.