Comitogenicity of eicosanoids and the peroxisome proliferator ciprofibrate in cultured rat hepatocytes

Abstract

Several hypolipidemic drugs and environmental contaminants induce hepatic peroxisome proliferation and hepatic tumors when administered to rodents. These chemicals increase the expression of the peroxisomal beta-oxidation pathway and the cytochrome P-450 4A family, which metabolize lipids, including eicosanoids and their precursor fatty acids. We previously found that the peroxisome proliferator ciprofibrate decreases the level of eicosanoids in the liver and in cultured hepatocytes. In this study, we examined the effect of prostaglandins E2 and F2 alpha (PGE2 and PGF2 alpha), leukotriene C4 (LTC4) and the peroxisome proliferator ciprofibrate on DNA synthesis in cultured hepatocytes. Primary rat hepatocytes were cultured on collagen gels in serum-free L-15 medium with varying concentrations of eicosanoids and ciprofibrate, and the absence or presence of growth factors. Ciprofibrate lowered hepatocyte eicosanoid concentrations; the addition of eicosanoids restored their levels. After a 48-h exposure with [3H]-thymidine, DNA synthesis was determined by measuring [3H]-thymidine incorporation into DNA. The addition of PGE2, PGF2 alpha, and LTC4 to cultures along with ciprofibrate increased DNA synthesis, whereas treatment with ciprofibrate or eicosanoids alone resulted in a much smaller increase. The addition of epidermal growth factor (EGF) to the eicosanoid-ciprofibrate combination increased DNA synthesis more than EGF or the eicosanoid-ciprofibrate combination alone. The PGF2 alpha-ciprofibrate combination also was comitogenic with transforming growth factor-alpha and hepatocyte growth factor. The addition of both ciprofibrate and prostaglandins also blocked the growth inhibitory effect of transforming growth factor-beta on DNA synthesis induced by EGF. These results show that the eicosanoids PGE2, PGF2 alpha, and LTC4 are comitogenic with the peroxisome proliferator ciprofibrate in cultured rat hepatocytes.

Stimulation of DNA synthesis by tumor promoters in primary rat hepatocytes is not mediated by arachidonic acid metabolites

“…On the other hand, PGE 2 and PGF 2α consistently had no additional growth‐stimulatory effect when EGF was present throughout the experiment but were found to be stimulatory in the presence of dexamethasone only. This is in contrast to previous reports demonstrating co‐mitogenic effects of PGE 2 and PGF 2α with EGF (Refnes et al, 1994, 1995; Hong and Glauert, 1996; Hashimoto et al, 1997). This discrepancy may be related to the timing of EGF addition.…”

“…As shown in Figure 2 (Panel A), in the absence of EGF stimulatory concentration‐dependent effects of both PGE 2 and PGF 2α were observed. Consistent with previous reports by others (Skouteris et al, 1988; Refnes et al, 1994, 1995; Dajani et al, 1996; Hong and Glauert, 1996), relatively high concentrations of prostaglandins (10 μM or more) were found to be required for significant effects. On the other hand, PGD 2 exhibited a concentration‐dependent growth‐stimulatory effect even in the presence of EGF (Fig.…”

“…However, some differences were noted among different studies. Prostaglandin concentrations in the micromolar range were required for stimulation of hepatocyte DNA synthesis in this and several other studies (Skouteris et al, 1988; Refnes et al, 1994, 1995; Hong and Glauert, 1996) while nanomolar concentration were reported to be effective in other studies, particularly in neonatal hepatocytes (Andreis et al, 1981; Armato and Andreis, 1983; Hashimoto et al, 1997). The present study systematically examined the auxilliary factors required to observe a stimulation of hepatocyte DNA synthesis by prostaglandins.…”

“…This report adds to the body of evidence showing that prostaglandins markedly enhance growth in neonatal (Andreis et al, 1981; Armato and Andreis, 1983) and adult rat hepatocytes (Skouteris et al, 1988; Refnes et al, 1994, 1995; Hong and Glauert, 1996; Hashimoto et al, 1997). However, some differences were noted among different studies.…”

Effects of Ochratoxin a on Cytotoxicity and Cell Differentiation in Cultured Rat Embryonic Cells

“…Cell growth rate was determined by [ 3 H]thymidine incorporation into DNA according to the method of Srinivasan et al (1990) and as described elsewhere (Hong & Glauert, 1996). The [ 3 H]thymidine was added to the embryonic cell culture 2 h after plating.…”