Effects of hepatic impairment on the metabolism of fructose and 5-fluorouracil, as studied in fatty liver models using in vivo 31P-MRS and 19F-MRS

Effects of exercise training on intrahepatic lipid content in humans

Non-alcoholic fatty liver (NAFL) is the most common liver disorder in western society. Various factors may play a role in determining hepatic fat content, such as delivery of lipids to the liver, de novo lipogenesis, hepatic lipid oxidation, secretion of intrahepatic lipids to the circulation or a combination of these. If delivery of lipids to the liver outweighs the sum of hepatic lipid oxidation and secretion, the intrahepatic lipid (IHL) content starts to increase and NAFL may develop. NAFL is closely related to obesity and insulin resistance and a fatty liver increases the vulnerability to type 2 diabetes development. Exercise training is a cornerstone in the treatment and prevention of type 2 diabetes. There is a large body of literature describing the beneficial metabolic consequences of exercise training on skeletal muscle metabolism. Recent studies have started to investigate the effects of exercise training on liver metabolism but data is still limited. Here, first, we briefly discuss the routes by which IHL content is modulated. Second, we review whether and how these contributing routes might be modulated by long-term exercise training. Third, we focus on the effects of acute exercise on IHL metabolism, since exercise also might affect hepatic metabolism in the physically active state. This will give insight into whether the effect of exercise training on IHL could be explained by the accumulated effect of acute bouts of exercise, or whether adaptations might occur only after long-term exercise training. The primary focus of this review will be on observations made in humans. Where human data is missing, data obtained from well-accepted animal models will be used.

Effects of oral 5-fluorouracil drugs on hepatic fat content in patients with colon cancer

RATIONALE AND OBJECTIVES

The association between hepatic steatosis and oral 5-fluorouracil (5-FU) agents is clinically recognized but has not been systematically studied. The aim of this study was to determine the effects of 5-FU on hepatic fat content in patients undergoing oral 5-FU therapy and to compare the effects in three subgroups of 5-FU drugs.

MATERIALS AND METHODS

Fifty-one patients with postoperative colon cancer (mean 61.1 years) were retrospectively studied. Forty-three patients were given adjuvant oral 5-FU therapy for a mean 3.3 years (5-FU group), and eight patients were not (control group). All patients underwent preoperative and postoperative abdominal computed tomography (CT) studies. The liver/spleen ratio was calculated from the CT attenuation values for the liver and spleen. We also compared the effects on hepatic appearance under CT of three 5-FU drugs: fluorouracil (n = 13), doxifluridine (n = 14), or UFT (a mixture of tegafur and uracil; n = 9).

RESULTS

In the 5-FU group, the mean CT values for the liver were significantly reduced relative to values before therapy (P < .01) and to those of the control group (P < .0001). Fifteen of 43 patients (34.9%) developed steatosis. Of the three 5-FU drugs, fluorouracil and doxifluridine caused a significant decrease in hepatic CT values.

CONCLUSION

5-FU caused a significant decrease in CT attenuation, indicating an increase in hepatic fat content, and was associated with very frequent hepatic steatosis. UFT seemed less likely to cause hepatic fatty infiltration. CT examination was useful for early detection of drug-induced side effects on liver even before lab abnormality or clinical manifestation is observed.

5-Fluorouracil catabolism to 5-fluoro-5,6-dihydrouracil is reduced by acute liver impairment in mice

This study investigated the effect of acute liver damage on the inactivation of 5-fluorouracil (5-FU) to its main catabolite 5-fluoro-5,6-dihydrouracil (5-FUH2) in mice. Plasma pharmacokinetics of 5-FU and 5-FUH2 in mice receiving 5-FU (10, 30, and 90 mg/kg) were compared to those in mice pretreated with carbon tetrachloride and receiving the same 5-FU doses. Carbon tetrachloride-induced hepatic damage was histopathologically examined under light microscopy and serum transaminases and dihydropyrimidine dehydrogenase activities were also measured. Liver histopathology and elevated aminotransferase activity levels confirmed the presence of liver damage. 5-FU C(max) and AUC both increased up to 71% in mice with liver damage. This was reflected by decreased 5-FUH2 production, since 5-FUH2 C(max) and AUC levels decreased up to 47% and 61%, respectively. Metabolic ratios between 5-FUH2 and 5-FU AUCs were considerably decreased as well, further suggesting that liver damage caused a reduction in 5-FU catabolism. DPD activity was not altered in damaged livers. The present results indicate that 5-FU disposition in mice could be profoundly altered in the presence of severe liver impairment, potentially leading to enhanced anabolic activation of 5-FU. This effect seems to be ascribed to a reduction of viable hepatocytes, rather than to an inactivation of DPD activity.

Detection of the non-steroidal anti-inflammatory drug niflumic acid in humans: a combined 19F-MRS in vivo and in vitro study

This study describes for the first time results of a (19)F-MRS study on humans exposed to the fluorinated non-steroidal anti-inflammatory drug niflumic acid. The accumulation and elimination of this commercially available selective prostaglandin synthase inhibitor is studied after an oral bolus in the human liver, in blood plasma and in urine samples. The in vivo spectra of the liver display two resonances with a similar increase in signal intensity during the investigation period of 240 min. One resonance refers to the parent compound niflumic acid (P), whereas the second resonance corresponds to a metabolite (M1) formed by the biotransformation by liver enzymes. The spectroscopic comparison with model compounds suggests 4'-hydroxyniflumic acid as the metabolite. During the entire experiment the concentration ratios of these resonances (P/M1) ranged between 0.7 and 0.9, indicating a high metabolite concentration most probably due to an efficient first pass metabolism. Both resonances (P, M1) were observed in the in vitro study of the blood plasma samples after plasma protein denaturation. However, in comparison to the liver spectra, the amount of the metabolite M1 is very small with a P/M1-ratio of 36.6 after 90 min and 16.1 after the end of measurement. This finding suggests an efficient biliary excretion of the metabolite M1, which bypasses the blood circulation system. Both resonances are also identified in the native urine samples. The signal intensity of the parent compound dominates the spectra of all urine samples, whereas the signal intensity of M1 increases slowly reaching a similar value to the parent compound P at the end of the measurement. This observation demonstrates an effective renal elimination of niflumic acid and suggests the existence of an enterohepatic circuit with a re-entry mechanism for the biliary excreted metabolite M1. In the urine spectra, an additional metabolite M2 is found. This resonance exhibits a low but constant signal intensity. The chemical origin of this metabolite is unclear.