Steroid receptor coactivators, HER-2 and HER-3 expression is stimulated by tamoxifen treatment in DMBA-induced breast cancer.

BACKGROUND: Steroid receptor coactivators (SRCs) may modulate estrogen receptor (ER) activity and the response to endocrine treatment in breast cancer, in part through interaction with growth factor receptor signaling pathways. In the present study the effects of tamoxifen treatment on the expression of SRCs and human epidermal growth factor receptors (HERs) were examined in an animal model of ER positive breast cancer. METHODS: Sprague-Dawley rats with DMBA-induced breast cancer were randomized to 14 days of oral tamoxifen 40 mg/kg bodyweight/day or vehicle only (controls). Tumors were measured throughout the study period. Blood samples and tumor tissue were collected at sacrifice and tamoxifen and its main metabolites were quantified using LC-MS/MS. The gene expression in tumor of SRC-1, SRC-2/transcription intermediary factor-2 (TIF-2), SRC-3/amplified in breast cancer 1 (AIB1), ER, HER-1, -2, -3 and HER-4, as well as the transcription factor Ets-2, was measured by real-time RT-PCR. Protein levels were further assessed by Western blotting. RESULTS: Tamoxifen and its main metabolites were detected at high concentrations in serum and accumulated in tumor tissue in up to tenfolds the concentration in serum. Mean tumor volume/rat decreased in the tamoxifen treated group, but continued to increase in controls. The mRNA expression levels of SRC-1 (P = 0.035), SRC-2/TIF-2 (P = 0.002), HER-2 (P = 0.035) and HER-3 (P = 0.006) were significantly higher in tamoxifen treated tumors compared to controls, and the results were confirmed at the protein level using Western blotting. SRC-3/AIB1 protein was also higher in tamoxifen treated tumors. SRC-1 and SRC-2/TIF-2 mRNA levels were positively correlated with each other and with HER-2 (P ≤ 0.001), and the HER-2 mRNA expression correlated with the levels of the other three HER family members (P < 0.05). Furthermore, SRC-3/AIB1 and HER-4 were positively correlated with each other and Ets-2 (P < 0.001). CONCLUSIONS: The expression of SRCs and HER-2 and -3 is stimulated by tamoxifen treatment in DMBA-induced breast cancer. Stimulation and positive correlation of coactivators and HERs may represent an early response to endocrine treatment. The role of SRCs and HER-2 and -3 should be further studied in order to evaluate their effects on response to long-term tamoxifen treatment.

Combination of fish oil and fish protein hydrolysate reduces the plasma cholesterol level with a concurrent increase in hepatic cholesterol level in high-fat-fed Wistar rats.

OBJECTIVE: This study investigated the potential additive or synergistic effect of fish oil (FO) and fish protein hydrolysate (FPH) on cholesterol concentration in plasma and the liver. METHODS: Male Wistar rats were fed high-fat diets (30% fat, 20% protein, wt/wt) containing FO (5%), FPH (10%), a combination of FO and FPH, or a high-fat control diet. After 7 wk of feeding, the rats were fasted for 12 h before lipid levels in plasma and the liver and hepatic activities of acyl-coenzyme A:cholesterol acyltransferase, 3-hydroxy-3-methylglutaryl coenzyme A reductase, and fatty acid synthase were measured. RESULTS: The combination of FO and FPH in the diet profoundly reduced the plasma cholesterol level, mainly due to lowering of high-density lipoprotein cholesterol, whereas the hepatic total cholesterol concentration was elevated compared with control rats and rats fed diets containing FPH or FO alone. The elevated cholesterol concentration in the liver was caused by an increased amount of cholesteryl esters and was in correlation to an increased activity of acyl-coenzyme A:cholesterol acyltransferase. There was a reduced fatty acid synthase activity that could lead to a reduced lipogenesis in the rats fed a combination of FO and FPH. CONCLUSION: A dietary combination of FO and FPH resulted in lower levels of plasma cholesterol and higher levels of hepatic cholesterol compared with dietary FO or FPH alone. Further studies are warranted to confirm whether the hypocholesterolemic effect was due to a reduced secretion of very low-density lipoprotein from the liver.

Causes and prevention of tamoxifen-induced accumulation of triacylglycerol in rat liver.

Tamoxifen can induce hepatic steatosis in women. In this study, we wanted to elucidate the mechanism behind the tamoxifen-induced accumulation of triacylglycerol in liver in female rats, and we hoped to prevent this development by combination treatment with the modified fatty acid tetradecylthioacetic acid (TTA). The increased hepatic triacylglycerol level after tamoxifen treatment was accompanied by decreased acetyl-coenzyme A carboxylase (ACC) and FAS activities, increased glycerol-3-phosphate acyltransferase (GPAT) activity, and a tendency to increased diacylglycerol acyltransferase (DGAT) activity. The activities and mRNA levels of enzymes involved in beta-oxidation, ketogenesis, and uptake of lipids from liver were unaffected by tamoxifen, whereas the uptake of lipoproteins was unchanged and the uptake of fatty acids was decreased. Combination treatment with tamoxifen and TTA (Tam+TTA) normalized the hepatic triacylglycerol level and increased the activities of ACC, FAS, GPAT, and DGAT compared with tamoxifen-treated rats. The activities and mRNA levels of enzymes involved in beta-oxidation, ketogenesis, and uptake of lipids were increased after Tam+TTA treatment. In conclusion, tamoxifen increased the hepatic triacylglycerol level, probably as a result of increased triacylglycerol biosynthesis combined with unchanged beta-oxidation. The tamoxifen-induced accumulation of triacylglycerol was prevented by cotreatment with TTA, through mechanisms of increased mitochondrial and peroxisomal beta-oxidation.