Short-term oral oleoyl-estrone treatment increases plasma cholesterol turnover in the rat

OBJECTIVE

Oral treatment with oleoyl-estrone induces the loss of body fat and improvement of insulin resistance. Since cholesterol levels are deeply affected by oleoyl-estrone, we investigated here whether short-term treatment affected cholesterol turnover and overall metabolite changes.

DESIGN

Wistar female rats received a single oral dose of 10 mumol/kg oleoyl-estrone in 0.2 ml of sunflower oil. Groups of animals were killed at timed intervals and blood samples were taken. In a second experiment series, rats had implanted carotid and jugular cannulas and were given a single gavage of oleoyl-estrone. These rats were used for the measurement of the cholesterol turnover rate.

MEASUREMENTS

Body weight change and food intake: Glucose, total and HDL-cholesterol, triacylglycerols, 3-hydroxybutyrate, nonesterified fatty acids, insulin, HOMA score in the rats of the first series. Cholesterol: Cholesterol pool changes and cholesterol turnover rates in the rats of the second series.

RESULTS

OE induced early effects, decreasing food intake, cholesterol and HDL-cholesterol levels, and increasing insulin sensitivity (HOMA score). OE also increased cholesteryl-ester turnover, and decreased circulating total cholesterol, especially esterified cholesterol pools.

CONCLUSIONS

The role of early changes in insulin sensitivity induced by oral OE cannot explain per se the deep changes in cholesterol handling, essentially a consequence of accelerated lipoprotein turnover. However, the increase in cholesteryl-ester turnover observed with OE treatment may be, at least in part, a consequence of the decrease in insulin resistance. The compounded effect of increased insulin sensitivity and accelerated lipoprotein turnover may help explain the early and marked hypocholesterolaemic effects of OE.

Effect of oral oleoyl-estrone on adipose tissue composition in male rats

OBJECTIVE

To determine whether the oral administration of oleoyl-estrone has similar mass-decreasing effects on the main different sites of white adipose tissue (WAT).

DESIGN

Adult male Zucker lean rats were given a daily oral gavage of oleoyl-estrone (OE, 10 micromol/kg) in 0.2 ml of sunflower oil for 10 days, and were compared with controls receiving only the oil. The mass of the main WAT sites: subcutaneous, epididymal, mesenteric, retroperitoneal, gluteal, perirenal and interscapular, as well as perirenal and interscapular brown adipose tissue (BAT), were dissected and studied.

MEASUREMENTS

The tissue weight, DNA, protein, lipid and total cholesterol content, together with the levels of leptin and acyl-estrone in the larger WAT and BAT masses, were measured.

RESULTS

The weights of WAT depots were correlated with body weight but those of BAT were not. Cell size was maximal for epididymal and mesenteric and minimal for subcutaneous and retroperitoneal WAT and BAT. Differences were detected in DNA, and in protein and lipid content between distinct WAT sites. OE treatment tended to decrease cell number and cell size in WAT; only small differences in composition were found between WAT locations inside the visceral cavity and those outside. Decreases in lipid content were maximal in mesenteric fat. Leptin and acyl-estrone content were fairly uniform at the different WAT sites, except for high concentrations in gluteal WAT. OE induced a greater decrease in leptin and acyl-estrone than in DNA and lipids; changes in these hormones were fairly parallel in all sites.

CONCLUSIONS

In general, the differences in composition between visceral and peripheral subcutaneous WAT and their responses to OE were less marked than the individual differences observed between specific sites, regardless of location. WAT sites are fairly diverse in composition, but their response to OE treatment was uniform. OE decreased the weight of WAT through reduction of both cell numbers and size; but did not change the mass or composition of BAT significantly. The effects of OE are more marked in the hormonal signals (leptin and acyl-estrone) from the tissue than in its composition and mass.

Modulation by leptin, insulin and corticosterone of oleoyl-estrone synthesis in cultured 3T3 L1 cells

Preadipocytes (3T3 L1) were used between 7 and 14 days after differentiation; they were incubated with 44 nM 3H-esterone. The medium was supplemented with 1 microM recombinant murine leptin, 10 nM recombinant human insulin, or 1 microM corticosterone for up to 72 hr. In a second series of experiments, cells were incubated for 48 hr with different concentrations of leptin, insulin or corticosterone, and compared with controls (plain medium). Cells were harvested, washed in buffer and homogenized, and protein was measured. Lipid extracts of cell homogenates were used for HPLC; the label distribution in free and acylestrone peaks was measured. Overall uptake of estrone (i.e., the sum of free and acylestrone) by cells was not affected by leptin or corticosterone, but strongly reduced by insulin. Leptin and corticosterone increased the synthesis of acyl-esterone in a dose- and time-dependent way. Insulin decreased acyl-estrone synthesis at low concentrations and with little change over time. The results suggest that control of oleoyl-estrone deposition in adipocytes is modulated in at least two distinct steps: (a) estrone uptake, affected by insulin in the physiological range; and (b) synthesis of oleoyl-estrone from cell estrone. The latter may be affected by insulin, but leptin and corticosterone enhance the process.

Intestinal handling of an oral oleoyl-estrone gavage by the rat

Adult Zucker lean (Fa/?) female rats received a single 250 nmol oral gavage of 3H-labelled oleoylestrone in 0.2 ml of sunflower oil. After one hour, samples of arterial, portal and suprahepatic blood, and lymph were obtained and fractioned to determine the amount of radioactivity present in the form of free estrone, acyl-estrone and hydrophilic estrone esters in the blood of each vessel. Lipoprotein fractions (chylomicra + VLDL, LDL, HDL and lipoprotein-depleted plasma) were also analysed as well as the distribution of absorbed 3H-estrone in the intestine, specific organs and carcass. About one third of the oleoyl-estrone dose recovered was found in the tissues, mainly in the blood, the rest remaining relatively untouched in the intestinal content. High hypothalamic estrone uptake (compared with the rest of the brain) was observed. Data from non-radioactive estrone measurements showed a similar pattern of absorption and tissue distribution to that obtained by 3H-estrone tracking alone. In both cases, most of the estrone present in the intestinal lumen was absorbed as intact oleoyl-estrone, but a significant part was absorbed as free estrone. There is a net transfer of 3H-estrone into portal blood HDL, and part of the 3H-estrone is also loaded into lymph-carried chylomicra. A large share of free estrone is filtered by the liver, but most of the acyl-estrone absorbed passes unaltered. The oral administration of oleoyl-estrone results in significant absorption of the unaltered molecule, which is transferred to lymph-carried chylomicra and also directly to plasma HDLs. It may be inferred that the HDL fraction contains the physiological carrier of oleoyl-estrone in its role of ponderostat signal.