Hepatic catabolism of rat and human lipoproteins in rats treated with 17 alpha-ethinyl estradiol

Formulating 10-hydroxycamptothecin into nanoemulsion with functional excipient tributyrin: An innovative strategy for targeted hepatic cancer chemotherapy

This study aimed to develop an innovative dosage form for 10-hydroxycamptothecin (HCPT), a chemotherapeutic agent with limited aqueous solubility and stability, to enhance its parenteral delivery and targeting to hepatic cancer. We formulated HCPT into a nanoemulsion using tributyrin, a dietary component with histone deacetylase inhibitor activity. The resulting HCPT-loaded tributyrin nanoemulsion (Tri-HCPT-E) underwent extensive evaluations. Tri-HCPT-E significantly improved the aqueous solubility, stability, and anti-cancer activities in HepG2 cells. Pharmacokinetic studies confirmed the increased stability and hepatic targeting, with Tri-HCPT-E leading to a 120-fold increase in plasma exposure of intact HCPT and a 10-fold increase in hepatic exposure compared to the commercial free solution. Co-administration of 17α-ethynylestradiol, an up-regulator of low-density lipoprotein (LDL) receptor, further enhanced the distribution and metabolism of HCPT, demonstrating an association between the LDL receptor pathway and hepatic targeting. Most importantly, Tri-HCPT-E exhibited superior in vivo anti-cancer efficacy in a mouse xenograft model compared to the commercial formulation, without causing escalated hepatic or renal toxicity. In conclusion, formulating HCPT into a nanoemulsion with tributyrin has proven to be an innovative and effective strategy for targeted hepatic cancer chemotherapy while tributyrin, a pharmacologically active dietary component, has emerged as a promising functional excipient for drug delivery.

Salvia officinalis mitigates uterus and liver damages induced by an estrogen deficiency in ovariectomized rats

The present study evaluated the antioxidant activity of Salvia officinalis (sage) and its protective effect on estrogen deficiency in ovariectomized rats. Female Wistar rats were treated during either 15 or 30 days as follows: group C: negative controls, group S: positive controls treated with sage leaves, ovariectomized rats (group OVX) and ovariectomized rats receiving either sage (OVX-S) or hormonal (Group OVX-E) treatments, respectively. After 15 and 30 days of treatments, OVX rats showed a gain in body weight and an increase of absolute and relative liver weights. Meanwhile, absolute and relative uterus weights were decreased. Moreover, ovariectomy altered plasma transaminases' activities, lipid profile, and disrupted the redox status of liver and uterine tissues. It affected also the reproductive tract by decreasing the uterus glycogen content and plasma LDH activity. Supplementation of sage via the diet reduced weight gain and oxidative stress resulting from estrogen deficiency. PRACTICAL APPLICATIONS: During menopause, sexual hormone deficiency, especially estrogen, causes several morphological and physiological disturbances in liver and uterus tissues. In fact, the body weight gain and disturbances of redox status in liver and uterus were the main health problems detected after menopause. Sage leaves, used as medicinal plant, exerted its beneficial effects in the management of menopause disorders. As an important source of antioxidants, sage leaves could prevent obesity and oxidative damage in the liver and uterus resulting from estrogen deficiency.

Low-density lipoprotein receptor deficiency impaired mice osteoblastogenesis in vitro

Postmenopausal osteoporosis affected most elderly women with co-existence of lipid and bone metabolism disorders. However, the cellular and molecular mechanisms underlying the parallel progression and cross-talk of these systems remained unclear. In the present study, low-density lipoprotein receptor knockout (LDLR^-/-) mice were chosen to elucidate the effect of LDLR in regulating the differentiation of osteoblasts, which were responsible for bone formation and modulation of osteoclastogenesis. Primary osteoblasts were isolated from the calvarium of newborn LDLR^-/- or wild-type mice followed by osteoblastic differentiation culture in vitro. Alkaline phosphatase activity was significantly decreased in LDLR^-/- osteoblasts compared to wild-type controls, combined with calcium deposit formation delay, implying impaired osteoblastogenesis in vitro. Consistent with these findings, the expression of runt-related transcription factor 2 (Runx2) was decreased 3 days after differentiation in LDLR^-/- osteoblasts compared to wild-type controls. Moreover, the expression of Osterix was decreased 7 days after differentiation in LDLR^-/- osteoblasts compared to wild-type controls, later than Runx2.However, the osteoclastogenesis modulation role of osteoblasts was unaffected by the LDLR deficiency, evidenced by the same level of osteoprotegerin (OPG)/receptor activator of nuclear factor-κ B ligand (RANKL) axis between LDLR^-/- and wild-type control osteoblasts. Our results provide a novel insight into the role of LDLR during osteoblastic differentiation and improve understanding of cross-talk between bone and lipid metabolisms.

Prophylactic effect of resveratrol against ethinylestradiol-induced liver cholestasis

Estrogens, and particularly glucuronides such as ethinylestradiol (EE), have been shown to cause cholestasis in animal studies, by reducing bile acid uptake by hepatocytes. The aim of the present article was to investigate anticholestatic activity of resveratrol (RES) against liver cholestasis induced by EE in adult female rats. The daily oral administration of the RES at a concentration of 25 mg/kg body weight for 15 days to rats treated with EE (100 μg/kg body weight for 5 days) resulted in a significant protection against EE-induced decrease in both serum cholesterol and bile acid levels as well as against an increase of serum bilirubin concentration. The treatment also resulted in a significant increase in hepatic superoxide dismutase, glutathione peroxidase, glutathione reductase, and catalase activities as well as hepatic protein-bound and nonprotein sulfhydryl groups. RES inhibited serum alkaline phosphatase, alanine aminotransferase, pi-glutathione-S-transferase, gamma-glutamyl transpeptidase, and alpha-glutathione-S-transferase activities, as well as reduced serum tumor necrosis factor-alpha, nitric oxide, and hepatic malondialdehyde as compared to EE-treated rats. The results clearly suggest that RES has a powerful prophylactic action in cholestasis induced by EE. Taken together, RES has potential as a preventive and therapeutic agent for cholestasis and deserves clinical trial in the near future as an adjuvant therapy in women treated with estrogen.

Triglyceride-rich lipoproteins and plasma lipid transport

This memoir provides a history of the triglyceride-rich lipoproteins of blood plasma over the last half-century. As precursors of low-density lipoproteins and in their own right, triglyceride-rich lipoproteins are essential to the formation of atherosclerotic plaques and to consequent ischemic vascular disease. The author recounts research at the National Heart Institute during 1953 to 1956 and continuing thereafter at the University of California San Francisco. Emphasis is placed on key insights arising from investigations of human disease, the interplay of fatty acid and triglyceride-transport involving the liver, small intestine, adipose tissue and muscle, and the role of the liver in the synthesis and catabolism of atherogenic lipoproteins.

Protective effect of Jasonia montana against ethinylestradiol-induced cholestasis in rats

Estrogens, and particularly glucuronides such as ethinylestradiol (EE), have been shown to cause cholestasis in animal studies, by reducing bile acid uptake by hepatocytes. The aim of the present article is to investigate anticholestatic activity of the ethanolic extract of the aerial parts of Jasonia montana against liver cholestasis induced by EE in adult female rats in an attempt to understand its mechanism of action, which may pave the way for possible therapeutic applications. Subcutaneous administration of 100 μg/kg b.w. ethinylestradiol to rats induced hepatocellular cholestasis with a significant decrease in serum cholesterol, bile acids and bilirubin levels as well as in hepatic superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR) activities and hepatic total, protein-bound and non-protein sulfhydryl groups. Also, treatment with EE produced significant increase in serum Pi-glutathione-s-transferase (Pi-GST), gamma glutamyl transpeptidase (γ-GT) and alpha-glutathione-s-transferase (α-GST) activities as well as serum nitric oxide (NO) and tumor necrosis factor alpha (TNF-α) level and hepatic malondialdehyde (MDA) level as compare to control group. Oral administration of the aerial parts of ethanolic extract at a concentration of 150 mg/kg b.w. daily to rats treated with EE for 15 days showed a significant protection against-induced decrease in serum cholesterol, bile acids and bilirubin levels. The treatment also resulted in a significant increase in hepatic SOD, GPx and GR activities as well as hepatic total, protein-bound and non-protein sulfhydryl groups. In addition, the extract could inhibit serum Pi-GST, γ-GT and α-GST activities as well as reduce serum TNF-α, NO and hepatic MDA as compare to ethinylestradiol treated rats. High content of flavonoids and phenolic compounds was found in ethanolic extract, which may be responsible for free radical activity. The results clearly suggest that the aerial parts of J. montana extract may effectively normalize the impaired antioxidant status in ethinylestradiol (EE)-cholestatic model. Thus the extract may have a therapeutic value in drug-induced biliary cholestasis as well as in hormonal therapy.

Comparing the effects of atamestane, toremifene and tamoxifen alone and in combination, on bone, serum lipids and uterus in ovariectomized rats

Complete estrogen blockade remains under investigation as a means to optimize anti-estrogen therapy in breast cancer thus both the efficacy and end-organ toxicities are of interest with combinations. We hypothesized that a steroidal aromatase inhibitor (AI) atamestane (ATA) alone, and in combination with the anti-estrogens tamoxifen (TAM) or toremifene (TOR) would have beneficial effects in ovariectomized (OVX) rats on key end-organ functions including bone and lipid metabolism and on the endometrium. Significant positive effects on bone were noted with ATA, TOR, TAM, ATA+TOR, or ATA+TAM. TOR, TAM, ATA+TOR, or ATA+TAM caused significant decreases in serum cholesterol and low-density lipoprotein cholesterol whereas ATA had no effect. Uterine weight and epithelium lining height were not increased by ATA but were by TOR and TAM. No significant differences were found in the key parameters outlined above between OVX rats given TOR and ATA+TOR, or TAM and ATA+TAM. Our data show that ATA in combination with TOR or TAM is equivalent to TOR or TAM alone in terms of end-organ effects within a range of clinically relevant doses. Further studies of combinations of AIs with anti-estrogens on end-organ function are merited.

Evaluation of the pharmacokinetics of all-trans-retinoic acid (ATRA) in Wistar rats after intravenous administration of ATRA loaded into tributyrin submicron emulsion and its cellular activity on caco-2 and HepG2 cell lines

The pharmacokinetics of all-trans-retinoic acid (ATRA), an anti-cancer drug was highly variable due to its poor aqueous solubility. In this study, we investigated the pharmacokinetics of ATRA in male Wistar rats following intravenous administration of the ATRA loaded tributyrin emulsion. In vitro, the ATRA emulsion was proved binding to apolipoprotein(s). In vivo, the clearance of ATRA was significantly reduced by formulating into the tributyrin emulsion, leading to higher AUCs. Co-administration with 17alpha-ethynylestradiol, a compound known to upregulate the activity of low-density lipoprotein receptors in tissues, significantly increased the K(e), V, and CL of ATRA. The variation of plasma AUCs after administering the ATRA emulsion to the healthy rats was two times less than that after the ATRA solution. The IC(50) in ATRA of the ATRA emulsion for the Caco-2 carcinoma cells was 3.8 microg/mL lower than 6 microg/mL of the ATRA solution. The IC(50) of the emulsion for the HepG2 carcinoma cells was 2.8 microg/mL, while IC(50) was not achieved with the ATRA solution over the test concentration range. The finding indicated that the tributyrin emulsion could be used as a carrier for ATRA and enhances the drug effect by reducing the clearance and increasing the in vitro activity.

Effect of OS-0544, a selective estrogen receptor modulator, on endothelial function and increased sympathetic activity in ovariectomized rats

Estrogens are known to contribute to endothelial function and sympathetic activity, both of which are strongly associated with the pathogenesis of ischemic heart disease. In addition, estrogens improve impaired lipid profile, a risk factor of endothelial dysfunction. In this study, we investigated the effects of OS-0544, a structurally new selective estrogen receptor modulator (SERM), on endothelial function, sympathetic activity, and plasma cholesterol level in ovariectomized (OVX) rats. Female Sprague-Dawley rats were ovariectomized and orally treated with OS-0544 (or OS-0689, the (R)-enantiomer of OS-0544), or 17beta-estradiol (E2) for 4 weeks, starting the next days after ovariectomy or for 1 week, starting 6 weeks after ovariectomy. Ovariectomy significantly increased vasopressin-induced mean blood pressure (AVP-MBP) (57+/-3.3 mm Hg vs. 46+/-3.5 mm Hg, P<0.05) and decreased acetylcholine (Ach)-induced maximum vasorelaxation response (69+/-5.6% vs. 81+/-4.0%, P<0.05). OS-0544 significantly inhibited AVP-MBP elevation (46+/-3.5 mm Hg vs. 57+/-3.3 mm Hg, P<0.05) and decreased Ach-induced maximum vasorelaxation response (90+/-3.3% vs. 69+/-5.6%, P<0.05) in OVX rats. In addition, OS-0689 as well as E2 significantly reduced (up to 67%) the increase in sympathetic activity in OVX rats. Moreover, like E2, OS-0544 significantly decreased plasma cholesterol level in OVX rats. These results demonstrate that OS-0544 has vascular protective effect on vascular function after ovariectomy. It is therefore believed that OS-0544 has vascular protective effect in postmenopausal woman.

The effects of atamestane and toremifene alone and in combination compared with letrozole on bone, serum lipids and the uterus in an ovariectomized rat model

We compared the effects of atamestane (ATA) and toremifene (TOR) alone and in combination, with letrozole (LET) on bone, serum lipids and the uterus in ovariectomized (OVX) rats after 16 weeks of treatment. Compared to OVX controls lumbar vertebral and femoral BMD as well as mechanical strength and trabecular bone volume were significantly greater in animals given ATA, TOR or ATA + TOR. The effects of ATA were not reversed by the androgen receptor blocker, flutamide (FLT). Serum cholesterol, low-density lipoprotein cholesterol and triglycerides were reduced by TOR and ATA + TOR whereas they remained unchanged in animals receiving ATA, ATA + FLT, and LET. The uterine epithelium in OVX animals was equally stimulated by TOR and ATA + TOR and unaffected by ATA or LET. Intact animals had significant atrophy of the uterine epithelium when receiving ATA. In summary, TOR alone or in combination with ATA had a predictable stimulatory effect on bone and the uterine epithelium while reducing key parameters of lipid metabolism. In contrast, ATA but not LET had an unexpected stimulatory effect on the OVX rat's bone and this was not reversed by the anti-androgen FLT leaving this finding unexplained for now. ATA is distinct from LET on end-organ function and this favorable profile makes clinical testing of this steroidal aromatase inhibitor of interest in the clinical setting.

Hypocholesterolemic action of the selective estrogen receptor modulator acolbifene in intact and ovariectomized rats with diet-induced hypercholesterolemia

Acolbifene (ACOL) is a fourth-generation selective estrogen receptor modulator (SERM) that has strong and pure antiestrogenic properties toward estrogen-sensitive cancers, but improves energy and lipid metabolism in an estrogen-like fashion in rodent models. The aim of this study was to determine the potency of ACOL to reduce cholesterolemia in a dietary model of hypercholesterolemia and to establish its mechanisms of action. Intact and ovariectomized (OVX) female rats were treated for 3 weeks with ACOL, and serum cholesterol and liver determinants of cholesterol metabolism were assessed. Acolbifene prevented both diet- and ovariectomy-induced weight gain and completely prevented diet-induced hypercholesterolemia. Relative to a reference chow diet, the high-cholesterol diet decreased the high-density lipoprotein (HDL) cholesterol fraction, which remained unaffected by ACOL, indicating that in hypercholesterolemic conditions, ACOL modulated only the non-HDL fraction. No impact of ACOL on determinants of liver cholesterol synthesis was observed. In contrast, ACOL increased hepatic low-density lipoprotein receptor protein in both intact and OVX rats, which was negatively correlated with serum total and non-HDL cholesterol (r=-0.59, P<.0001), suggesting a contribution of receptor-mediated hepatic uptake of cholesterol-rich lipoproteins to the hypocholesterolemic effect of ACOL. These findings establish that ACOL retains its powerful cholesterol-lowering action in diet-induced hypercholesterolemia and suggest that the SERM acts in such conditions through favoring hepatic low-density lipoprotein receptor-mediated uptake of cholesterol transported by non-HDL lipoprotein fractions.

Evaluation of Tributyrin Lipid Emulsion with Affinity to Low-Density Lipoprotein: Pharmacokinetics in Adult Male Wistar Rats and Cellular Activity on Caco-2 and HepG2 Cell Lines

The tributyrin lipid emulsion was proved to be able to bind to low-density lipoprotein (LDL) in vitro. The aim of this study was to investigate the pharmacokinetics of the emulsion in vivo and the cellular activity in vitro. The pharmacokinetics of tributyrin and its metabolite, butyrate, was evaluated in male Wistar rats after administration with pure tributyrin or tributyrin emulsion. After oral administration, maximal plasma concentration (C(max)), time to reach maximal plasma concentration (T(max)), and elimination half-life (T(1/2)) of butyrate were 87.6 muM and 25.3 and 63.0 min, respectively, for the pure tributyrin compared with 1344.5 microM and 8.5 and 19.8 min for the 10% (v/v) tributyrin emulsion. C(max) and mean residence time of tributyrin were 2.74 microM and 87.9 min and 4.2 microM and 132.0 min for pure tributyrin and 10% emulsion, respectively. The bioavailabilities of the pure tributyrin versus tributyrin emulsion were 15.3 versus 65.7% and 34.9 versus 64.5% calculated from butyrate and tributyrin, respectively. After the rats were treated with 17alpha-ethynylestradiol (an LDL receptor up-regulator), the distribution volumes calculated from both butyrate and tributyrin were significantly increased after oral administration or infusion of the 10% tributyrin emulsion. The increased distribution volume after coadministration with a LDL receptor up-regulator suggested the increased uptake of tributyrin/butyrate by tissues with increased expression of LDL receptors. The selective uptake of the emulsion by the cellular LDL receptors was further confirmed by testing the cellular viability in the presence of competing LDL. The viable cells can reach 92% of control at IC(50) in Caco-2 and 77% in HepG2 incubated with emulsion in the presence of LDL.

The selective estrogen receptor modulator acolbifene reduces cholesterolemia independently of its anorectic action in control and cholesterol-fed rats

The cancer-preventing selective estrogen receptor modulator (SERM) acolbifene (ACOL) exerts a potent and pure antiestrogenic action in the mammary gland and uterus, yet it displays beneficial, estrogen-like actions on energy and lipid metabolism in rodents. The compound reduces food intake and strongly decreases cholesterolemia in rats fed a cholesterol-free diet. This study was designed to establish whether the anorectic effect of ACOL is involved in its cholesterol-lowering action, and whether the compound retains its ability to lower cholesterol concentrations in rats with diet-induced hypercholesterolemia. Female rats were fed a purified diet devoid of cholesterol (reference diet) or containing 2% cholesterol (C-diet); they were either not treated or treated daily with ACOL or not treated and pair-fed to the ACOL-treated rats. The C-diet did not affect food intake or weight and fat gains. ACOL reduced food intake (16%) and weight gain (45%, mainly fat) similarly in both dietary cohorts. ACOL, but not pair feeding, reduced cholesterolemia by 33% in rats fed the reference diet. As expected, the C-diet raised serum total cholesterol almost 3-fold and this increase was largely prevented by ACOL but not by pair feeding. Cholesterol was reduced by ACOL, mainly in the HDL fraction, in rats fed the reference diet, but only in the non-HDL fraction in those fed the C-diet. In livers of rats fed the reference diet, ACOL, but not pair feeding, increased protein abundance of the scavenger receptor, class B, type 1, and the LDL receptor, thought to be involved in ACOL-mediated cholesterol lowering. These findings demonstrate that the potent hypocholesterolemic action of ACOL is independent of the concomitant reduction in food intake and fat accretion, and that such action occurs in rats with overt diet-induced hypercholesterolemia.

Estradiol and progesterone treatments change the lipid profile in naturally menopausal rats from different age groups

The effect of estradiol and progesterone therapy in serum and liver on the lipid profile of naturally menopausal albino rats of the Wistar strain of different age groups (12,18 and 24 months) have been measured and compared with the age matched groups. Three months old rats were used as young controls. The aged rats were administered subcutaneous injection of 17-beta-estradiol (0.1 microg/g body weight), progesterone (2.5 microg/g body weight) and similar concentrations of both in combined treatment for 1 month and the level of triglycerides (TG), total lipids (TL), total cholesterol (TC), high density lipoprotein (HDL), low density lipoprotein (LDL) and very low density lipoprotein (VLDL) were measured in serum and liver of 3, 12, 18 and 24 months old control as well as treated groups. The results show that TG, HDL, VLDL levels were increased significantly by 71%, 155%, 54%, respectively in liver of 24 months old rats by combination treatment when compared with age matched control animals. The levels of TL, TC and LDL were decreased by 20%, 31%, and 30%, respectively in serum of 12 months old rats in combination treatment group. The effect was more significant in 12 and 24 months old female rats with administration of estrogen and combined (EP) treatments. The results indirectly suggest that hormone replacement therapy (HRT) can reduce the risk of cardiovascular disease (CVD) thereby playing a cardio-protective role by restoring lipid and hormone levels to the similar levels as found in young female animals.

Effects of the steroidal aromatase inhibitor exemestane and the nonsteroidal aromatase inhibitor letrozole on bone and lipid metabolism in ovariectomized rats

PURPOSE

Exemestane (EXE) and letrozole (LET) are third-generation aromatase inhibitors currently prescribed for postmenopausal hormone-dependent breast cancer. The impact on end organs of estrogen depletion in menopausal women is of significant clinical importance. We studied the effects of EXE, its principal metabolite, 17-hydroexemestane (17-H-EXE), and LET on bone and lipid metabolism in ovariectomized (OVX) rats.

EXPERIMENTAL DESIGN

OVX rats were treated by weekly intramuscular injection for 16 weeks with 20, 50, and 100 mg/kg EXE, 20 mg/kg 17-H-EXE, and daily oral gavage of 1 mg/kg LET. At the end of the treatment period, bone mineral density (BMD), the bone resorption marker serum pyridinoline, the bone formation marker serum osteocalcin, bone mechanical properties, histomorphometry, and serum lipid concentrations were determined.

RESULTS

Lumbar vertebral and femoral BMD, bending strength of the femur, compressive strength of the fifth lumbar vertebra, and trabecular bone volume were significantly higher in OVX animals given EXE and 17-H-EXE than in OVX controls. EXE and 17-H-EXE significantly reduced an ovariectomy-induced increase in serum pyridinoline and serum osteocalcin. EXE and 17-H-EXE given to OVX rats caused significant reductions of serum cholesterol and low-density lipoprotein cholesterol. In contrast, OVX rats treated with LET had BMD, bone biomarkers, mechanical failure properties, and lipid levels similar to those of OVX controls.

CONCLUSIONS

EXE and 17-H-EXE significantly prevent bone loss, enhance bone mechanical strength, and lower serum cholesterol and low-density lipoprotein levels in OVX rats. These protective effects on end-organ function are not seen with the nonsteroidal inhibitor LET.

Regulation of Low-Density Lipoprotein Receptor Activity by Estrogens and Phytoestrogens in a HepG2 Cell Model

BACKGROUND/AIMS

Estrogen treatment is thought to lower low-density lipoprotein (LDL) cholesterol levels by increasing clearance through hepatic LDL receptors. This study aimed to determine the effect of estrogens and phytoestrogens on LDL receptor activity in a human hepatoma cell line, HepG2.

METHODS

HepG2 cells in culture were incubated for 24 h with estrogen or phytoestrogen and LDL receptor activity was measured by examining the cellular binding of colloidal gold-labelled LDL.

RESULTS

17Beta-estradiol significantly increased LDL receptor activity whereas estriol had negligible effects. Incubation with the isoflavonoids, formononetin, biochanin A and daidzein, caused significant elevations in receptor activity at concentrations above 40 microM. Coumestrol, a coumestan with a high level of estrogenic activity, caused a 3-fold increase in receptor activity at a concentration of 50 microM. Of the phytoestrogenic mammalian lignans enterolactone and enterodiol, only enterolactone displayed the ability to significantly upregulate LDL receptor activity at 50 microM.

CONCLUSION

This study suggests that the LDL receptor-stimulating effect of natural estrogens is mainly due to estradiol and that the cholesterol-lowering effect of diets high in phytoestrogens may be due in part to their ability to increase hepatic LDL receptor activity.

The selective estrogen receptor modulator SCH 57068 prevents bone loss, reduces serum cholesterol and blocks estrogen-induced uterine hypertrophy in ovariectomized rats

Our objective was to determine the effects of SCH 57068 alone and with 17 beta-estradiol (E(2)) on bone, lipids and uteri in ovariectomized (OVX) rats. In OVX animals lumbar vertebral and femoral bone mineral density (BMD) were significantly higher after 12 weeks of treatment with SCH 57068 than in untreated OVX controls. Similarly BMD was superior in OVX + E(2) + SCH 57068 treated animals than in OVX + E(2) controls. SCH 57068 also significantly reduced the increase in bone turnover markers, serum pyridinoline and serum osteocalcin levels, induced by OVX, and increased mechanical bone strength. SCH 57068 also significantly reduced the rise in serum cholesterol and low-density lipoprotein cholesterol induced by OVX. SCH 57068 had no stimulatory effect on uterine epithelium when given alone in OVX rats. SCH 57068 (1 and 2.5 mg/kg) reduced uterine weight and blocked endometrial stimulation induced by E(2). In summary, SCH 57068 adds to the positive effects of E(2) on bone and lipid metabolism but blocks the stimulatory effects of E(2) on the uterus. Potentially, E(2) + SCH 57068 could be combined for the treatment and prevention of breast cancer or as a novel hormone replacement therapy.

The aromatase knockout mouse presents with a sexually dimorphic disruption to cholesterol homeostasis

The aromatase knockout (ArKO) mouse cannot synthesize endogenous estrogens due to disruption of the Cyp19 gene. We have shown previously, that ArKO mice present with age-progressive obesity and hepatic steatosis, and by 1 yr of age both male and female ArKO mice develop hypercholesterolemia. In this present study 10- to 12-wk-old ArKO mice were challenged for 90 d with high cholesterol diets. Our results show a sexually dimorphic response to estrogen deficiency in terms of cholesterol homeostasis in the liver. ArKO females presented with elevated serum cholesterol; conversely, ArKO males had elevated hepatic cholesterol levels. In response to dietary cholesterol, 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase transcript levels were significantly reduced in females, whereas males showed more modest changes. Neither low density lipoprotein nor sterol regulatory element-binding protein expression levels were significantly altered by diet or genotype. The expression of Cyp7a, which encodes cholesterol 7 alpha-hydroxylase, was significantly reduced in ArKO females compared with wild-type females and was increased by cholesterol feeding. Cyp7a expression was significantly elevated in the wild-type males on the high cholesterol diet, although no difference was seen between genotypes on the control diet. The ATP-binding cassette G5 and ATP-binding cassette G8 transporters do not appear to be regulated by estrogen. The expression of acyl-coenzyme A:cholesterol acyltransferase 2 showed a sexually dimorphic response, where estrogen appeared to have a stimulatory effect in females, but not males. This study reveals a sexually dimorphic difference in mouse hepatic cholesterol homeostasis and roles for estrogen in the regulation of cholesterol uptake, biosynthesis, and catabolism in the female, but not in the male.

The aromatase knockout mouse presents with a sexually dimorphic disruption to cholesterol homeostasis

The aromatase knockout (ArKO) mouse cannot synthesize endogenous estrogens due to disruption of the Cyp19 gene. We have shown previously, that ArKO mice present with age-progressive obesity and hepatic steatosis, and by 1 yr of age both male and female ArKO mice develop hypercholesterolemia. In this present study 10- to 12-wk-old ArKO mice were challenged for 90 d with high cholesterol diets. Our results show a sexually dimorphic response to estrogen deficiency in terms of cholesterol homeostasis in the liver. ArKO females presented with elevated serum cholesterol; conversely, ArKO males had elevated hepatic cholesterol levels. In response to dietary cholesterol, 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase transcript levels were significantly reduced in females, whereas males showed more modest changes. Neither low density lipoprotein nor sterol regulatory element-binding protein expression levels were significantly altered by diet or genotype. The expression of Cyp7a, which encodes cholesterol 7 alpha-hydroxylase, was significantly reduced in ArKO females compared with wild-type females and was increased by cholesterol feeding. Cyp7a expression was significantly elevated in the wild-type males on the high cholesterol diet, although no difference was seen between genotypes on the control diet. The ATP-binding cassette G5 and ATP-binding cassette G8 transporters do not appear to be regulated by estrogen. The expression of acyl-coenzyme A:cholesterol acyltransferase 2 showed a sexually dimorphic response, where estrogen appeared to have a stimulatory effect in females, but not males. This study reveals a sexually dimorphic difference in mouse hepatic cholesterol homeostasis and roles for estrogen in the regulation of cholesterol uptake, biosynthesis, and catabolism in the female, but not in the male.

Hepatic endosomal trafficking of lipoprotein-bound endotoxin in rats

Triglyceride-rich lipoproteins (chylomicrons (CM), VLDL) can bind and protect against endotoxin (LPS)-induced shock and mortality in rodents. The protective effect of lipoproteins is in part due to the increased plasma clearance and biliary excretion of LPS. Specifically, CM-LPS complexes are principally removed from the circulation by the liver with a rapid plasma half-life approximating that for CM alone. Thus, we hypothesized that hepatocytes clear CM-bound LPS via known lipoprotein receptors and traffic the toxic macromolecule through the same endosomal pathway employed for the catabolism of triglyceride-rich lipoproteins. To examine the endosomal uptake and biliary excretion of LPS, we isolated early and late hepatic endosomal fractions and hepatic bile from rats following the injection of radiolabeled CM-bound LPS. The uptake of (125)I-LPS was compared in animals that overexpressed either the LDL receptor or the LDL receptor-related protein (LRP) versus untreated control with normal lipoprotein levels. Herein we present data indicating that both the LDL receptor and the LRP participate in the rapid internalization of CM-bound LPS by hepatocytes. Upregulation of the LDL receptor increased the accumulation of (125)I-LPS in late endosomes (P < 0.03). In contrast, increased levels of the LRP were associated with negligible movement of LPS into late endosomes but a trend toward the increased biliary excretion of the radiolabeled macromolecule. Taken together these data further elucidate the role of the liver in the host innate immune response to infection and potentially implicate distinct roles for the LDL receptor and LRP in the catabolism of CM-bound LPS.

Niacin, but not gemfibrozil, selectively increases LP-AI, a cardioprotective subfraction of HDL, in patients with low HDL cholesterol

Evidence indicates that the high density lipoprotein (HDL) subfraction containing apolipoprotein A-I without apolipoprotein AII (LP-AI) is more antiatherogenic than HDL particles containing apolipoprotein A-I and apolipoprotein A-II (LP-AI+AII). This study examined the effect of extended-release niacin (niacin-ER) and gemfibrozil on LP-AI and LP-AI+AII particles in patients with low levels of HDL cholesterol (HDL-C). Mechanisms by which these agents modulate HDL particles were investigated by in vitro studies using human hepatoblastoma (Hep G2) cells. A total of 139 patients with low HDL-C (</=40 mg/dL) were randomized to niacin-ER or gemfibrozil in a multicenter double-blind trial. Patients were dose-escalated with once-nightly niacin-ER (1 to 2 g) or gemfibrozil (1.2 g) for 19 weeks. Niacin-ER had a greater effect in raising HDL-C and apolipoprotein A-I levels than did gemfibrozil. Niacin-ER at 1- and 2-g doses increased LP-AI levels by 8.7+/-4.0% (P=0.033) and 24.0+/-4.4% (P<0.001), respectively. Gemfibrozil had no consistent effect on LP-AI levels. LP-AI+AII levels increased 5% to 8% by both agents. In vitro studies showed that niacin, but not gemfibrozil, selectively decreased the uptake of (125)I-labeled LP-AI holoparticles by Hep G2 cells. The uptake of [(3)H]cholesterol ester was approximately 75% greater from LP-AI versus LP-AI+AII particles, but neither niacin nor gemfibrozil affected cholesterol ester uptake. These data indicate that unlike gemfibrozil, niacin selectively increases LP-AI compared with LP-AI+AII particle concentration in patients with low HDL-C levels. The mechanism of action of increased LP-AI concentration appears to be mediated by decreased hepatic removal of LP-AI particles, which are more efficient in reverse cholesterol transport, thus suggesting an additional mechanism by which niacin mediates its antiatherogenic properties.

Metabolism of chylomicron cholesterol is delayed by estrogen. An in vivo study in the rat

In order to test the effects of estrogen on the clearance of cholesterol of dietary origin from the blood and its elimination from the body via the bile in an in vivo animal model, the fate of radioactivity from intravenously injected [3H]cholesterol-labeled chylomicrons was investigated in the rat. The labeled lipoproteins were administered intrajugularly to male rats previously given 17alpha ethinyl estradiol or the vehicle only, and the removal of the radioactivity from the blood and its uptake by the liver and secretion into bile was determined. Experiments were carried out in animals with or without prior drainage (20 hr) of the pool of bile acids in the enterohepatic circulation, to take account of the different demands of the liver for cholesterol in the two conditions. In rats without biliary drainage, estrogen treatment decreased the rate of removal of radioactivity from the blood by about 30% and the recovery of cholesterol in the liver by about 50% in the first 30 min after injection of the labeled chylomicrons. After biliary drainage, however, the recovery of label in the liver after 90 min was similar in estrogen-treated and control animals, although its secretion into bile was markedly reduced in the estrogen-treated group (total biliary secretion in 90 min was 26% of the value found in control rats). In addition, the apolipoprotein E (aopE) content of the serum total lipoproteins was markedly reduced by estrogen. These results provide direct evidence indicating that estrogen retards the elimination of dietary cholesterol from the body via the bile in the rat, and this is likely to be mainly due to a reduced level of apoE in chylomicrons. In view of this, we suggest that the hypothesis that estrogen increases the hepatic uptake of chylomicron cholesterol, and its excretion in the bile during contraceptive and hormone replacement therapy should be re-examined.

Obesity and disturbed lipoprotein profile in estrogen receptor-alpha-deficient male mice

Clinical case reports have documented disturbances of carbohydrate and lipid metabolism in aromatase deficient and estrogen resistant males. The aim of the present study was to explore the metabolic functions of estrogens in male mice and to dissect the estrogen receptor (ER) specificity of such effects. Total body fat content and serum levels of leptin were followed in ERalpha knockout (ERKO), ERbeta knockout (BERKO), and ERalpha/beta double knockout (DERKO) mice. Neither the total body fat nor serum leptin levels were altered in any group before or during sexual maturation. However, after sexual maturation ERKO and DERKO, but not BERKO, demonstrated a clear increase in total body fat and enhanced serum leptin levels. Serum cholesterol was increased and a qualitative change in the lipoprotein profile, including smaller LDL particles, was observed in ERKO and DERKO mice. In conclusion, ERalpha but not ERbeta-inactivated male mice develop obesity after sexual maturation.

Biochemical analysis of a caveolae-enriched plasma membrane fraction from rat liver

We isolated and characterized a subcellular fraction derived from the blood-sinusoidal plasma membrane of hepatocytes enriched in caveolin and containing several of the molecular components described to be present in caveolae isolated from other cell types. A morphological study by electron microscopy revealed that it was composed of caveolae-attached membrane profiles. Immunoelectron microscopy of isolated fraction showed the specific labeling of internal caveolae membranes with anti-caveolin antibody. Finally, one- and two-dimensional electrophoresis and Western blotting were used for the biochemical analysis of this new rat liver plasma membrane fraction. From the biochemical and the morphological characterization, we conclude that the caveolae-enriched plasma membrane fraction is a plasma membrane fraction, which originates from specialized regions of the sinusoidal plasma membrane, enriched in caveolae.

Prevention of bone loss by EM-800 and raloxifene in the ovariectomized rat

Some undesirable effects are associated with chronic estrogen and progestin administration used to prevent bone loss in postmenopausal women, thus leading to poor compliance and the need for improved therapeutic and preventive agents. We have thus studied the ability of the new antiestrogen EM-800 (SCH 57050) to prevent bone loss and lower serum cholesterol levels and compared its effects with those of raloxifene. Ovariectomized (OVX) female rats were treated by oral gavage for 37 weeks with increasing daily doses (0.01, 0.03, 0.1, 0. 3 or 1 mg/kg) of EM-800 or raloxifene. At 35 weeks after OVX, lumbar spine bone mineral density (BMD) was 19% lower than in intact animals (P<0.01), while the OVX animals given EM-800 or raloxifene had 90-93 and 85-90%, respectively, of the BMD values observed in intact rats. Similar effects were observed on femoral BMD. Bone histomorphometry measurements were performed on proximal tibia. At the 0.01 mg/kg dose, EM-800 prevented the effect of OVX on TBV by 34% (P<0.01), while raloxifene had no detectable effect. Treatment with 1 mg/kg EM-800 and raloxifene resulted in, respectively, 68% (P<0.01) and 64% (P<0.01) prevention of the OVX-induced decrease in TBV. In addition, the administration of 0.01 and 0.03 mg/kg EM-800 caused, respectively, 54% (P<0.01) and 56% (P<0.01) inhibitions of serum cholesterol levels, while raloxifene administered at the same doses caused, respectively, 24% (P<0.01) and 41% (P<0.01) decreases of the value of the same parameter. At the highest doses used (0.1-1 mg/kg), both compounds lowered serum cholesterol levels by approximately 65% (P<0.01). No stimulatory effect of EM-800 was observed on the endometrial epithelial cells at doses up to 1 mg/kg, while hypertrophy of uterine epithelium was observed with raloxifene. EM-800 and raloxifene achieve the same degree of effectiveness on bone and serum cholesterol at higher doses, but EM-800 is at least three to ten times more potent than raloxifene at lower concentrations and has no stimulatory effect on uterine epithelium. The present data show the potent effect of EM-800 preventing bone loss and lower serum cholesterol levels without the negative effect on the endometrium, thus suggesting the particular interest of this new fully tissue-specific selective estrogen receptor modulator.

EGF triggers caveolin redistribution from the plasma membrane to the early/sorting endocytic compartment of hepatocytes

In this study, we demonstrate that, in rat liver, epidermal growth factor (EGF) is responsible for the partial redistribution of caveolin-1 from the plasma membrane into the early/sorting endocytic compartment. Highly purified endosomes and plasma membrane fractions were isolated from control rat liver and from rats injected with EGF or pIgA for different times. Whereas in subcellular fractions from control hepatocytes most of caveolin was concentrated in the plasma membrane and the receptor-recycling fractions, after EGF injection there was a significant redistribution of caveolin toward the early/sorting (CURL) endocytic fractions. The recruitment of caveolin into the endocytic compartment was not induced by pIgA.

Charting the fate of the "good cholesterol": identification and characterization of the high-density lipoprotein receptor SR-BI

Risk for cardiovascular disease due to atherosclerosis increases with increasing concentrations of low-density lipoprotein (LDL) cholesterol and is inversely proportional to the levels of high-density lipoprotein (HDL) cholesterol. The receptor-mediated control of plasma LDL levels has been well understood for over two decades and has been a focus for the pharmacologic treatment of hypercholesterolemia. In contrast, the first identification and characterization of a receptor that mediates cellular metabolism of HDL was only recently reported. This receptor, called scavenger receptor class B type I (SR-BI), is a fatty acylated glycoprotein that can cluster in caveolae-like domains on the surfaces of cultured cells. SR-BI mediates selective lipid uptake from HDL to cells. The mechanism of selective lipid uptake is fundamentally different from that of classic receptor-mediated endocytic uptake via coated pits and vesicles (e.g. the LDL receptor pathway) in that it involves efficient receptor-mediated transfer of the lipids, but not the outer shell proteins, from HDL to cells. In mice, SR-BI plays a key role in determining the levels of plasma HDL cholesterol and in mediating the regulated, selective delivery of HDL-cholesterol to steroidogenic tissues and the liver. Significant alterations in SR-BI expression can result in cardiovascular and reproductive disorders. SR-BI may play a similar role in humans; thus, modulation of its activity may provide the basis of future approaches to the treatment and prevention of atherosclerotic disease.

Biphasic effects of the natural estrogen 17beta-estradiol on hepatic cholesterol metabolism in intact female rats

The protective influence of estrogens in cardiovascular disease is believed to be partly due to beneficial effects on cholesterol metabolism. Much of the experimental data are based on models in which synthetic estrogens have been used in pharmacological doses, and therefore, the physiological role of estrogens in cholesterol metabolism is uncertain. To evaluate this important issue, we performed experiments in intact female rats with use of the natural estrogen 17beta-estradiol (E2) administered either subcutaneously or orally. After physiological doses of E2 (< or =0.04 mg. kg(-1). d(-1)) were administered, plasma levels of high density lipoprotein (HDL) cholesterol and apolipoprotein (apo) A-I were increased. In the liver, 3-hydroxy-3-methylglutaryl coenzyme A reductase and cholesterol 7alpha-hydroxylase activities were increased, as well as cholesterol 7alpha-hydroxylase mRNA levels. These effects were abolished during treatment with higher doses of E2, whereas apo A-I mRNA increased in a dose-dependent way. After treatment with pharmacological doses of E2 (> or =0.2 mg. kg(-1). d(-1)), the number of hepatic low density lipoprotein receptors increased and plasma cholesterol was reduced. These effects were similar after both oral and subcutaneous administration of E2. Our results show that the responses to E2 are biphasic: plasma HDL, apo A-I, and hepatic enzyme activities governing bile acid and cholesterol synthesis increased only at physiological doses of E2. At pharmacological doses of E2, hepatic low density lipoprotein receptors are stimulated and plasma cholesterol is reduced. Therefore, under physiological conditions, E2 exerts its major effects on hepatic cholesterol metabolism through mechanisms other than stimulation of low density lipoprotein receptor expression.

Effects of reserpine on expression of the LDL receptor in liver and on plasma and tissue lipids, low density lipoprotein and fibrinogen in rabbits in vivo

The effects of administering reserpine (0.1 mg/kg) or 17alpha-ethinyloestradiol (2.5 mg/kg) to New Zealand White rabbits on low density lipoprotein receptors in liver, on plasma low density lipoprotein and fibrinogen and on plasma and tissue lipids were determined. Blood pressure and heart rate were also followed. The drugs were injected subcutaneously into conscious unrestrained rabbits for 5 days. On the 6th day homologous 125I-tyramine cellobiose labelled low density lipoprotein (125I-TC-LDL) was injected intravenously and 24 h later the animals were killed. Compared to controls, reserpine significantly increased LDL receptor expression in the liver by about threefold, and reduced total cholesterol in plasma, aorta and heart, without affecting plasma triglycerides. The reductions in plasma cholesterol and heart were due to decreases in both unesterified and esterified cholesterol. Similar effects were observed with oestrogen, except that there was no change in esterified cholesterol in aorta. In liver, a decrease of 24% in total cholesterol was due mainly to decreased esterified cholesterol. In adrenal glands total cholesterol increased by 25%. Reserpine significantly accelerated the plasma clearance of intravenously injected homologous 125I-TC-LDL and reduced its accumulation in aortic wall. Neither reserpine nor oestradiol affected blood pressure, haematocrit or plasma fibrinogen. The results suggest that reserpine is an affective anti-atherogenic drug capable of decreasing cholesterol in plasma, arteries and heart by increasing high affinity LDL receptors in the liver.

Cellubrevin is present in the basolateral endocytic compartment of hepatocytes and follows the transcytotic pathway after IgA internalization

The endocytic compartment of polarized cells is organized in basolateral and apical endosomes plus those endocytic structures specialized in recycling and transcytosis, which are still poorly characterized. The complexity of the various populations of endosomes has been demonstrated by the exquisite repertoire of endogenous proteins. In this study we examined the distribution of cellubrevin in the endocytic compartment of hepatocytes, since its intracellular location and function in polarized cells are largely unknown. Highly purified rat liver endosomes were isolated from estradiol-treated rats, and the early/sorting endosomal fraction was further subfractionated in a multistep sucrose density gradient, and studied. Analysis of dissected endosomal fractions showed that cellubrevin was located in early/sorting endosomes, with Rab4, annexins II and VI, and transferrin receptor, but in a specific subpopulation of these early endosomes with the same density range as pIgA and Raf-1. Interestingly, only in those isolated endosomal fractions, endosomes enriched in transcytotic structures (of livers loaded with IgA), the polymeric immunoglobulin receptor specifically co-immunoprecipitated with cellubrevin. In addition, confocal and immuno-electron microscopy identification of cellubrevin in tubular structures underneath the sinusoidal plasma membrane together with the re-organization of cellubrevin, in the endocytic compartment, after the IgA loading, strongly suggest the involvement of cellubrevin in the transcytosis of pIgA.

Up-regulation of low density lipoprotein receptor by a novel isobenzofranone derivative, MD-700

Stimulatory effects of a novel isobenzofranone, MD-700, on low density lipoprotein (LDL) receptor activity were investigated in vitro and in vivo. MD-700 at 0.03 microg/ml elevated the expression of LDL receptor in HepG2 cells within 4 h. Corresponding to this, uptake of fluorescent labeled-LDL (3,3'-dioctadecylindocarbocyanine-LDL) by the cells increased linearly in time- and dose-dependent manner by MD-700 for up to 12 h. In the experiment using HepG2 cells transiently transfected with promoter-luciferase gene constructs, MD-700 increased luciferase activity in a dose-dependent manner from 0.03 to 0.1 microg/ml. In contrast, luciferase activity was not stimulated by MD-700 in construct with a deleted sterol regulatory element (SRE)-1, suggesting importance of SRE-1 in stimulation of the LDL receptor gene promoter by MD-700. Binding experiments on liver membranes from MD-700-treated hamsters showed about a 60% increase in 125I-labeled LDL binding. A Scatchard plot revealed that MD-700 increased the maximal binding without affecting binding affinity. In contrast to findings with an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, pravastatin, MD-700 had no effect on the sterol synthesis in hamster liver homogenates. These results suggest that MD-700 stimulates the expression of LDL receptor, presumably in a manner independent of change in sterol metabolism, and thereby promotes LDL clearance. Hypocholesterolemic actions of MD-700 in hamsters were then examined. MD-700 lowered serum cholesterol levels in hamsters fed normal chow or a high-fat diet. Fractionation of serum lipoproteins demonstrated that MD-700 selectively decreased LDL and very low density lipoprotein cholesterol. Dose-dependent decrease in serum cholesterol was also seen in hypercholesterolemic rats. Thus, the hypocholesterolemic action of MD-700 may be attributed to up-regulation of the LDL receptor, based on stimulation of the transcription of the LDL receptor gene. Although pravastatin stimulates LDL uptake and lowers serum cholesterol in a manner similar to that seen with MD-700, the mechanism responsible for hypocholesterolemic action appears to differ.

A tubular endosomal fraction from rat liver: biochemical evidence of receptor sorting by default

We previously have isolated an endosomal fraction from rat liver, termed receptor-recycling compartment (RRC), which is highly enriched in recycling receptors and in the transcytotic polymeric Ig receptor (pIgR). We now have analyzed the RRC fraction by immunoisolation and found that no uniquely transcytotic elements were present, because recycling receptors and the pIgR were coisolated on the same elements. In addition, RRC was very rich in proteins previously shown to be associated with recycling endosomes, such as rab 11, cellubrevin, and endobrevin, but relatively poor in early endosome antigen 1. As RRC contains mainly tubules and small vesicles, our results indicate that it is enriched in elements of a tubular endosomal compartment involved in receptor sorting. Biochemical analysis showed that the density of recycling receptors and transcytotic pIgR in RRC membranes was similar to that in early endosome membranes. This observation supports the idea that increasing membrane surface area by endosome tubulation is the main mechanism to ensure efficient receptor sorting and, at the same time, locates RRC in a common step of the endocytotic system before final receptor segregation into distinct recycling and transcytotic pathways.

Increased Clearance Explains Lower Plasma Levels of Tissue-Type Plasminogen Activator by Estradiol: Evidence for Potently Enhanced Mannose Receptor Expression in Mice

Several clinical studies have demonstrated an inverse relationship between circulating levels of estrogen and tissue-type plasminogen activator (t-PA). The present study was designed to test the hypothesis that estrogens lower plasma levels of t-PA by increasing its clearance from the bloodstream. 17-Ethinyl estradiol (EE) treatment resulted in a significant increase in the clearance rate of recombinant human t-PA in mice (0.46 mL/min in treated mice v 0.32 mL/min in controls; P < .01). The clearance of endogenous, bradykinin-released t-PA in rats was also significantly increased after EE treatment (area under the curve [AUC], 24.9 ng/mL · min in treated animals v 31.9 ng/mL · min in controls; P < .05). Two distinct t-PA clearance systems exist in vivo: the low-density lipoprotein receptor-related protein (LRP) on liver parenchymal cells and the mannose receptor on mainly liver endothelial cells. Inhibition of LRP by intravenous injection of receptor-associated protein (RAP) as a recombinant fusion protein with Salmonella japonicum glutathione S-transferase (GST) significantly retarded t-PA clearance in control mice (from 0.41 to 0.25 mL/min; n = 5, P < .001) and EE-treated mice (from 0.66 to 0.35 mL/min; n = 5, P < .005), but did not eliminate the difference in clearance capacity between the 2 experimental groups. Similar results were obtained in mice in which LRP was inhibited via overexpression of the RAP gene in liver by adenoviral gene transduction. In contrast, administration of mannan, a mannose receptor antagonist, resulted in identical clearances (0.22 mL/min in controls and 0.24 mL/min in EE-treated mice). Northern blot analysis showed a 6-fold increase in mannose receptor mRNA expression in the nonparenchymal liver cells of EE-treated mice, whereas the parenchymal LRP mRNA levels remained unchanged. These findings were confirmed at the protein level by ligand blotting and Western blotting analysis. Our results demonstrate that EE treatment results in increased plasma clearance rate of t-PA via induction of the mannose receptor and could explain for the inverse relationship between estrogen status and plasma t-PA concentrations as observed in humans.

Increased Clearance Explains Lower Plasma Levels of Tissue-Type Plasminogen Activator by Estradiol: Evidence for Potently Enhanced Mannose Receptor Expression in Mice

Several clinical studies have demonstrated an inverse relationship between circulating levels of estrogen and tissue-type plasminogen activator (t-PA). The present study was designed to test the hypothesis that estrogens lower plasma levels of t-PA by increasing its clearance from the bloodstream. 17-Ethinyl estradiol (EE) treatment resulted in a significant increase in the clearance rate of recombinant human t-PA in mice (0.46 mL/min in treated mice v 0.32 mL/min in controls; P &lt; .01). The clearance of endogenous, bradykinin-released t-PA in rats was also significantly increased after EE treatment (area under the curve [AUC], 24.9 ng/mL · min in treated animals v 31.9 ng/mL · min in controls; P &lt; .05). Two distinct t-PA clearance systems exist in vivo: the low-density lipoprotein receptor-related protein (LRP) on liver parenchymal cells and the mannose receptor on mainly liver endothelial cells. Inhibition of LRP by intravenous injection of receptor-associated protein (RAP) as a recombinant fusion protein with Salmonella japonicum glutathione S-transferase (GST) significantly retarded t-PA clearance in control mice (from 0.41 to 0.25 mL/min; n = 5, P &lt; .001) and EE-treated mice (from 0.66 to 0.35 mL/min; n = 5, P &lt; .005), but did not eliminate the difference in clearance capacity between the 2 experimental groups. Similar results were obtained in mice in which LRP was inhibited via overexpression of the RAP gene in liver by adenoviral gene transduction. In contrast, administration of mannan, a mannose receptor antagonist, resulted in identical clearances (0.22 mL/min in controls and 0.24 mL/min in EE-treated mice). Northern blot analysis showed a 6-fold increase in mannose receptor mRNA expression in the nonparenchymal liver cells of EE-treated mice, whereas the parenchymal LRP mRNA levels remained unchanged. These findings were confirmed at the protein level by ligand blotting and Western blotting analysis. Our results demonstrate that EE treatment results in increased plasma clearance rate of t-PA via induction of the mannose receptor and could explain for the inverse relationship between estrogen status and plasma t-PA concentrations as observed in humans.

Catabolism of HDL1 cholesteryl ester in the rat. Effect of ethinyl estradiol treatment

The present study was performed in control and ethinyl estradiol-treated rats in order to determine the mechanisms involved in the catabolism of HDL1 cholesteryl ester. Ligand blottings on liver membranes showed that purified HDL1, containing about 70% apolipoprotein E and 10% apolipoprotein AI, bind to the LDL receptor (130 kDa) and not to HB2 (100 kDa) or SR-BI (82 kDa), candidate HDL receptors. Immunoblots showed that the treatment increased the hepatic level of the LDL receptor five- to ten-fold, strongly decreased that of SRBI and did not change that of HB2. An in vivo kinetic study showed that the turnover of HDL1 cholesteryl ester is more rapid in treated than control rats. The liver participation (60%) in this clearance was not modified by the treatment. Therefore, it can be concluded that the catabolism of HDL1 cholesteryl ester, in control as in treated rats, is essentially ensured by the uptake of entire particles in the hepatocytes via LDL receptors.

The "early-sorting" endocytic compartment of rat hepatocytes is involved in the intracellular pathway of caveolin-1 (VIP-21)

The sinusoidal plasma membrane of the hepatocyte is organized into functional and structural microdomains whose origin, maintenance, and functioning are closely related with the endocytic compartment. Three different subcellular fractions, from rat liver, containing caveolin-1, the structural protein of caveolae, were morphologically and biochemically characterized. A caveolae-enriched plasma membrane fraction (CEF), contains large membrane structures surrounding attached internal plasmalemmal vesicles; the receptor-recycling compartment (RRC), contains tubules and vesicles with similar morphology to the internal vesicles observed by electron microscopy in CEF; and finally, caveolin-1 was also detected in early-sorting endosomes (CURL, compartment of uncoupling receptors and ligands). In this study, we show that following an intravenous administration of retinol-binding protein (RBP), there was a redistribution of caveolin-1 from the plasma membrane (CEF) to intracellular endocytic compartments (RRC and early-sorting endosomes). Thus, these results indicate that, in the hepatocyte, caveolae are dynamic structures actively interacting with the endocytic compartment.

EM-652 (SCH 57068), a third generation SERM acting as pure antiestrogen in the mammary gland and endometrium

Breast cancer is the most frequent cancer in women while it is the second cause of cancer death. Estrogens are well recognized to play the predominant role in breast cancer development and growth and much efforts have been devoted to the blockade of estrogen formation and action. The most widely used therapy of breast cancer which has shown benefits at all stages of the disease is the use of the antiestrogen Tamoxifen. This compound, however, possesses mixed agonist and antagonist activity and major efforts have been devoted to the development of compounds having pure antiestrogenic activity in the mammary gland and endometrium. Such a compound would avoid the problem of stimulation of the endometrium and the risk of endometrial carcinoma. We have thus synthesized an orally active non-steroidal antiestrogen, EM-652 (SCH 57068) and the prodrug EM-800 (SCH57050) which are the most potent of the known antiestrogens. EM-652 is the compound having the highest affinity for the estrogen receptor, including estradiol. It has higher affinity for the ER than ICI 182780, hydroxytamoxifen, raloxifene, droloxifene and hydroxytoremifene. EM-652 has the most potent inhibitory activity on both ER alpha and ER beta compared to any of the other antiestrogens tested. An important aspect of EM-652 is that it inhibits both the AF1 and AF2 functions of both ER alpha and ER beta while the inhibitory action of hydroxytamoxifen is limited to AF2, the ligand-dependent function of the estrogen receptors. AF1 activity is constitutive, ligand-independent and is responsible for mediation of the activity of growth factors and of the ras oncogene and MAP-kinase pathway. EM-652 inhibits Ras-induced transcriptional activity of ER alpha and ER beta and blocks SRC-1-stimulated activity of the two receptors. EM-652 was also found to block the recruitment of SRC-1 at AF1 of ER beta, this ligand-independent activation of AF1 being closely related to phosphorylation of the steroid receptors by protein kinase. Most importantly, the antiestrogen hydroxytamoxifen has no inhibitory effect on the SRC-1-induced ER beta activity while the pure antiestrogen EM-652 completely abolishes this effect, thus strengthening the need to use pure antiestrogens in breast cancer therapy in order to control all known aspects of ER-regulated gene expression. In fact, the absence of blockade of AF2 by hydroxytamoxifen could explain why the benefits of tamoxifen observed up to 5 years become negative at longer time intervals and why resistance develops to tamoxifen. EM-800, the prodrug of EM-652, has been shown to prevent the development of dimethylbenz(a)anthracene (DMBA)-induced mammary carcinoma in the rat, a well-recognized model of human breast cancer. It is of interest that the addition of dehydroepiandrosterone, a precursor of androgens, to EM-800, led to complete inhibition of tumor development in this model. Not only the development, but also the growth of established DMBA-induced mammary carcinoma was inhibited by treatment with EM-800. An inhibitory effect was also observed when medroxyprogesterone was added to treatment with EM-800. Uterine size was reduced to castration levels in the groups of animals treated with EM-800. An almost complete disappearance of estrogen receptors was observed in the uterus, vaginum and tumors in nude mice treated with EM-800. EM-652 was the most potent antiestrogen to inhibit the growth of human breast cancer ZR-75-1, MCF-7 and T-47D cells in vitro when compared with ICI 182780, ICI 164384, hydroxytamoxifen, and droloxifene. Moreover, EM-652 and EM-800 have no stimulatory effect on the basal levels of cell proliferation in the absence of E2 while hydroxytamoxifen and droloxifene had a stimulatory effect on the basal growth of T-47D and ZR-75-1 cells. EM-652 was also the most potent inhibitor of the percentage of cycling cancer cells. (ABSTRACT TRUNCATED)

The influence of estrogen on hepatic cholesterol metabolism and biliary lipid secretion in rats fed fish oil

Both estrogen and dietary n-3 polyunsaturated fatty acids are known to be hypocholesterolemic, but appear to exert their effects by different mechanisms. In this study, the interaction between dietary fish oil (rich in n-3 polyunsaturated fatty acids) and estrogen in the regulation of hepatic cholesterol metabolism and biliary lipid secretion in rats was studied. Rats fed a low fat or a fish oil-supplemented diet for 21 days were injected with 17alpha-ethinyl estradiol (5 mg/kg body weight) or the vehicle only (control rats) once per day for 3 consecutive days. Estrogen-treatment led to a marked reduction in plasma cholesterol levels in fish oil-fed rats, which was greater than that observed with either estrogen or dietary fish oil alone. The expression of mRNA for cholesterol 7alpha-hydroxylase was decreased by estrogen in rats fed a low fat or a fish oil-supplemented diet, while the output of cholesterol (micromol/h/kg b.wt.) in the bile was unchanged in both groups. Cholesterol levels in the liver were increased by estrogen in rats given either diet, but there was a significant shift from cholesterol esterification to cholesteryl ester hydrolysis only in the fish oil-fed animals. Estrogen increased the concentration of cholesterol (micromol/ml) in the bile in rats fed the fish oil, but not the low fat diet. However, the cholesterol saturation index was unaffected. The output and concentration of total bile acid was also unaffected, but changes in the distribution of the individual bile acids were observed with estrogen treatment in both low fat and fish oil-fed groups. These results show that interaction between estrogen-treatment and dietary n-3 polyunsaturated fatty acids causes changes in hepatic cholesterol metabolism and biliary lipid secretion in rats, but does not increase the excretion of cholesterol from the body.

Effects of apolipoprotein B-100 on the metabolism of a lipid microemulsion model in rats

In previous studies, it was shown that lipid microemulsions resembling LDL (LDE) but not containing protein, acquire apolipoprotein E when injected into the bloodstream and bind to LDL receptors (LDLR) using this protein as ligand. Aiming to evaluate the effects of apolipoprotein (apo) B-100 on the catabolism of these microemulsions, LDE with incorporated apo B-100 (LDE-apoB) and native LDL, all labeled with radioactive lipids were studied after intraarterial injection into Wistar rats. Plasma decay curves of the labels were determined in samples collected over 10 h and tissue uptake was assayed from organs excised from the animals sacrificed 24 h after injection. LDE-apo B had a fractional clearance rate (FCR) similar to native LDL (0.40 and 0.33, respectively) but both had FCR pronouncedly smaller than LDE (0.56, P<0.01). Liver was the main uptake site for LDE, LDE-apoB, and native LDL, but LDE-apoB and native LDL had lower hepatic uptake rates than LDE. Pre-treatment of the rats with 17alpha-ethinylestradiol, known to upregulate LDLR, accelerated the removal from plasma of both LDE and LDE-apoB, but the effect was greater upon LDE than LDE-apoB. These differences in metabolic behavior documented in vivo can be interpreted by the lower affinity of LDLR for apo B-100 than for apo E, demonstrated in in vitro studies. Therefore, our study shows in vivo that, in comparison with apo E, apo B is a less efficient ligand to remove lipid particles such as microemulsions or lipoproteins from the intravascular compartment.

Isolated endosomes from quiescent rat liver contain the signal transduction machinery. Differential distribution of activated Raf-1 and Mek in the endocytic compartment

In this study we identify the molecules involved in the MAPK signal transduction pathway (Ras, Raf-1, Mek, Mek-P and MAPK) in highly purified endosomal fractions isolated from rat liver. Biochemical analysis shows that only the early-sorting endocytic compartment contains activated Raf-1 and Mek. Finally, the exogenous administration of EGF led to redistribution of Raf-1 from the caveolin-enriched plasma membrane into the endosomes.

Prevention of development of dimethylbenz(a)anthracene (DMBA)-induced mammary tumors in the rat by the new nonsteroidal antiestrogen EM-800 (SCH57050)

The effect of EM-800, a new non-steroidal antiestrogen having pure antiestrogenic activity, was studied on chemical carcinogenesis induced by dimethylbenz(a)anthracene (DMBA) as well as on serum lipids and bone mass in the rat. Treatment with EM-800 orally, once daily, for 282 days (9 months), starting 3 days before DMBA administration, decreased the incidence of tumors from 95% in control animals to 60% (p < 0.01), 38% (p < 0.01), and 28% (p < 0.01) at the daily doses of 25 microg, 75 microg, and 250 microg, respectively. The average number of tumors per animal decreased from 4.5 +/- 0.5 tumors in the control group to 0.9 +/- 0.2 (p < 0.01), 0.5 +/-0.2 (p < 0.01), and 0.3 +/- 0.1 (p < 0.01) tumors in the rats treated with the above-indicated doses of the anti-estrogen. In addition, treatment with the increasing doses of EM-800 reduced serum cholesterol levels to 64%, 56%, and 48% of control, while serum triglycerides decreased to 31%, 28%, and 30% of control. Bone mineral content (BMC) and bone mineral density (BMD) of total skeleton, femur, and lumbar spine were not significantly affected following 282 days of treatment with EM-800. However, treatment with EM-800 inhibited the urinary ratio of hydroxyproline to creatinine (HP/Cr) from 14.0 +/- 3.90 micromol/mmol in controls to 7.6 +/-0.8 (p < 0.05), 6.8 +/- 0.8 (p < 0.01), and 6.8 +/- 1.1 (p < 0.01) micromol/mmol, respectively, while the same treatment had no effect on serum total alkaline phosphatase (tALP) activity or urinary calcium and phosphorus excretion. The 25 microg, 75 microg, and 250 microg daily doses of EM-800 inhibited uterine weight by 35% (p < 0.01), 62% (p < 0.01), and 66% (p < 0.01), while vaginal weight was reduced by 8% (p < 0.05), 30% (p < 0.01), and 38% (p < 0.01), respectively. In agreement with the 27% increment (p < 0.05) in ovarian weight at the highest anti-estrogen dose used, serum androstenedione (p < 0.05), androst-5-ene-3beta,17beta-diol (p < 0.01), testosterone (p < 0.05), and estradiol (p < 0.01) levels were increased. The present data show that EM-800 prevents the development of DMBA-induced mammary tumors while simultaneously inhibiting uterine and vaginal weight, reducing serum cholesterol and triglyceride levels, and having no adverse effect on bone mass following 9 months of treatment in the rat.

Effects of CP-336,156, a new, nonsteroidal estrogen agonist/antagonist, on bone, serum cholesterol, uterus and body composition in rat models

We have discovered a new, nonsteroidal, potent estrogen agonist/antagonist, CP-336,156. CP-336,156 binds selectively and with high affinity to the human estrogen receptor-alpha with a half-inhibition concentration of 1.5 nM, which is similar to that seen with estradiol (4.8 nM). When given orally to immature (3-week-old) female Sprague-Dawley rats for 3 days at doses of 0.1, 1.0, 10, or 100 microg/kg x day, unlike 17alpha-ethynyl estradiol, CP-336,156 had no effect on uterine wet or dry weight. Similarly, no uterine hypertrophy was observed in aged (17-month-old) female rats treated (p.o.) with CP-336,156 at 10 or 100 microg/kg x day for 28 days. We also found that CP-336,156 decreased total serum cholesterol and fat body mass and had no effect on lean body mass in these aged female rats. In 5-month-old ovariectomized (OVX) Sprague-Dawley female rats, CP-336,156 completely prevented OVX-induced increases in body weight gain, total serum cholesterol, and serum osteocalcin at doses between 10 and 1000 microg/kg x day after 4 weeks. At these doses, CP-336,156 completely prevented OVX-induced bone loss and inhibited the increased bone turnover associated with estrogen deficiency in lumbar vertebrae, proximal tibiae, and distal femora. Similar to estrogen, CP-336,156 induced apoptosis and p53 expression with a concomitant decrease in the number of tartrate-resistant acid phosphatase-positive multinuclear cells in rat bone marrow cell cultures in vitro, suggesting that the induction of apoptosis may be a mechanism for the estrogenic activities of CP-336,156 in bone. In summary, CP-336,156 is a new, orally active, nonsteroidal, potent estrogen agonist/antagonist that has similar effects in bone as estradiol but without the uterine-stimulating effects associated with estradiol in rats.

Sex steroids increase cholesterol 7alpha-hydroxylase mRNA in nonhuman primates

One mechanism that may account for our prior observation that oral contraceptives decrease the hepatic cholesterol concentration independently of the low-density lipoprotein (LDL) receptor in sexually intact nonhuman primates is that sex hormones increase biliary cholesterol secretion by increasing hepatic mRNA abundance for cholesterol 7alpha-hydroxylase, the rate-limiting enzyme in the conversion of cholesterol into bile acids. To examine the independent effect of estrogen, progestin, and combined estrogen and progestin on the hepatic cholesterol concentration and cholesterol 7alpha-hydroxylase mRNA abundance, 34 ovariectomized adult female cynomolgus monkeys were fed a moderately atherogenic diet for 12 weeks with either oral conjugated equine estrogen ([CEE] n = 8), medroxyprogesterone acetate ([MPA] n = 9), or combined CEE + MPA (n = 9) and compared with a control group (n = 8) that did not receive exogenous sex hormones. After 12 weeks, hepatic cholesterol was significantly lower in CEE-treated (6.2 +/- 1.2 mg/g liver) and CEE + MPA-treated (6.4 +/- 0.9 mg/g liver) animals compared with the control (12.6 +/- 1.9 mg/g liver) and MPA-treated (14.6 +/- 1.6 mg/g liver) groups. Hepatic cholesterol 7alpha-hydroxylase mRNA abundance was significantly increased in CEE-treated (0.553 +/- 0.08 pg/microg RNA), MPA-treated (0.734 +/- 0.12 pg/microg RNA), and CEE + MPA-treated (0.487 +/- 0.07 pg/microg RNA) animals compared with the controls (0.318 +/- 0.03 pg/microg RNA). There was no significant difference in the plasma LDL cholesterol concentration and hepatic LDL receptor mRNA abundance between the groups. These data support but do not prove the hypothesis that low-dose oral estrogen induces an increase in cholesterol 7alpha-hydroxylase mRNA abundance, which is correlated with biliary cholesterol secretion and may result in depletion of hepatic cholesterol.

Annexin VI defines an apical endocytic compartment in rat liver hepatocytes

Annexin VI has been demonstrated previously to be a marker for hepatic endosomes. By western blotting with an affinity purified anti-annexin VI antibody it was shown that annexin VI was present in the three morphologically and functionally different endosomal fractions from rat liver. We have quantified the gold-labeled endosomes by immunoelectron microscopy in ultrathin Lowicryl sections of rat liver and now demonstrate that 80% of the total labeling with anti-annexin VI was associated with endocytic structures surrounding the bile canaliculus, the apical domain of hepatocytes, whereas only 20% was found in the subsinusoidal endosomes. In double immuno-gold labeling experiments 80% of the Rab5 positive apical endosomes were also labeled with anti-annexin VI antibodies. However, there was no significant colocalization with antibodies to the polymeric immunoglobulin receptor. Finally, we demonstrate that 50% of endosomes containing internalized gold-labeled transferrin were double labeled with anti-annexin VI antibodies. Thus, annexin VI becomes the first known structural protein at the apical ‘early’ endocytic compartment of the hepatocyte that may be involved in the receptor recycling and transport to late endocytic/lysosomal compartment pathways.

Human recombinant apolipoprotein E-enriched liposomes can mimic low-density lipoproteins as carriers for the site-specific delivery of antitumor agents

Progressive hypocholesterolemia is a feature associated with a number of cancers of different origin, and it is caused by the high expression of low-density lipoprotein (LDL) receptors (LDLrs) on many tumor cell types. Selective delivery of chemotherapeutics using LDL as a carrier has therefore been proposed, but the endogenous nature of LDL hampers its pharmaceutical application. In the current study, we explored the possibility of synthesizing liposomes that mimic LDL from commercially available lipids and proteins. Small unilamellar liposomes were created (28.9 +/- 0.9 nm) and complexed with 5.8 +/- 0.7 molecules of human recombinant apolipoprotein E (apoE). On intravenous injection into rats, the liposomes retained their aqueous core, structural integrity, and the majority of the preassociated apoE. [3H]Cholesteryl oleate-labeled apoE-enriched liposomes showed a relatively long serum half-life (>5 hr), and a low uptake by cells of the reticuloendothelial system was observed (<0.8% of the injected dose at 30 min after injection). Pretreatment of rats with 17alpha-ethinyl estradiol, which induces the expression of the LDLr on the liver and adrenals, led to a 2.5-fold accelerated serum clearance (t1/2 = 123 +/- 10 min) and a selectively increased uptake of liposomes by the liver (2.0-fold) and adrenals (3.8-fold). The liver association of the liposomes was coupled to the lysosomal uptake route, similarly as for LDL. In vitro studies using B16 melanoma cells showed that the liposomes bound exclusively to the LDLr via their apoE moiety (90,000 liposomes/cell), with a 14-fold higher affinity (Kd = 0.77 +/- 0.09 nM) than LDL itself. Because of their favorable properties, we anticipate that these apoE-enriched liposomes are advantageous compared with native LDL in the development of a selective LDLr-targeted antitumor therapy.