Endometrial safety and tolerability of triphasic sequential hormone replacement estradiol valerate/medroxyprogesterone acetate therapy regimen

OBJECTIVE

Two randomized comparative multicenter studies were conducted to establish the endometrial safety and tolerability of a triphasic sequential hormone replacement estradiol valerate/medroxyprogesterone acetate (E2V/MPA) therapy regimen.

METHODS

Study 1 was a randomized, double-blind, clinical phase III study in 399 postmenopausal women, following parallel-group design with two groups. The duration of study treatment was 12 or 13 cycles of 28 days. A double-dummy technique was used to ensure blinding in the study. The investigational drugs were E2V/MPA triphasic and E2V/MPA biphasic (Diviseq and Divina, respectively; Orion Pharma). In study 2, a total of 341 subjects were randomly allocated by computer into two parallel groups receiving either E2V/MPA or estradiol/norethisterone acetate triphasic (E2/NETA, Trisequens; Novo Nordisk A/S) for 12-13 cycles. The study was an open, clinical phase III trial with a randomized, parallel-group design. Endometrial biopsies combined with transvaginal ultrasound were undertaken before and at the end of treatment during the progestogen phase. Bleeding patterns and symptom control were assessed throughout both studies.

RESULTS

E2V/MPA triphasic was found to have similar endometrial effects and bleeding patterns to those with E2V/MPA biphasic and E2/NETA triphasic. Climacteric symptoms were relieved as quickly and effectively as with the two comparator treatments. No adverse drug reactions specific to E2V/MPA triphasic were observed. At the end of the study, the proportions of secretory samples were 67.1% for the combined E2V/MPA triphasic groups, 65.6% for the E2V/MPA biphasic group and 71.6% for the E2/NETA triphasic group. One case of hyperplasia occurred in the E2V/MPA triphasic group. Thus the incidence of hyperplasia for the combined groups was 0.33%.

CONCLUSIONS

The triphasic E2V/MPA regimen was well tolerated and produced endometrial effects similar to those of the two comparators. Extending estrogen during the so-called treatment-free week with a lower dose of estradiol was effective in controlling vasomotor symptoms.

Effect of four oral contraceptives on hemostatic parameters

This is the first double-blind, controlled, randomized study comparing the effect of different estrogen components in oral contraceptives (OCs) on hemostasis variables. Four groups of 25 women each were treated for six cycles with monophasic combinations containing 21 tablets with either 30 microg ethinylestradiol (EE) + 2 mg dienogest (DNG) (30EE/DNG), 20 microg EE + 2 mg DNG (20EE/DNG), 10 microg EE + 2 mg estradiol valerate (EV) + 2 mg DNG (EE/EV/DNG) or 20 microg EE + 100 microg levonorgestrel (LNG) (EE/LNG). Blood samples were taken on Days 21-26 of the control cycle and on Days 18-21 of the first, third and sixth treatment cycle. Treatment with all four OCs caused an increase in levels of fibrinogen, prothrombin fragment 1+2, D-dimer, plasminogen, plasmin-antiplasmin complex and an increase in protein C activity, a decrease in antithrombin activity, tissue-plasminogen activator (t-PA) and plasminogen activator inhibitor (PAI), and a slight decrease in the sensitivity to activated protein C, but no significant change in that of the thrombin-antithrombin complex. In users of the DNG-containing OCs, the reduction in total and free protein S, and in t-PA and PAI was dependent on the EE dose, while factor VII activity was elevated, but not significantly different from EE/LNG. The results are in agreement with those of previous studies. The effects of EE/EV/DNG on total and free protein S and on t-PA and PAI were lower than those of 20EE/DNG, suggesting that the impact of 2 mg EV on several hemostasis variables is less than that of 10 microg EE. The results show an antagonistic effect of LNG on the EE-induced rise of factor VII activity and fragment 1+2 and on the EE-dependent reduction of total and free protein S.

Estrogen replacement therapy and Alzheimer's disease

Estrogen replacement therapy (ERT) is increasingly recommended for postmenopausal women due to its numerous beneficial effects on bone, cardiovascular system, brain function and quality of life. Data from retrospective epidemiological studies have shown that ERT has a potential to reduce the risk for developing Alzheimer's disease (AD) and to delay its progression. In addition, recent clinical studies have reported improvement of cognitive functions in women with AD. Findings from basic science indicated that the possible mechanisms of action by which estrogen may affect AD include interaction with cholinergic neurotransmitter system, cholinergic neurotrophic and neuroprotective effect, improvement of learning and memory, improvement of cerebral blood flow and metabolism, antioxidant and antiinflammatory action, and interference with beta-amyloid protein metabolism and toxicity. Estrogen use in postmenopausal women may offer a new approach for improving cognitive functions in nondemented and demented women, delaying the onset and progression of AD and reducing its occurrence. However, prospective clinical trials are required to establish the efficacy of ERT for prevention and treatment of AD.

Attitude of German women and gynecologists towards long-cycle treatment with oral contraceptives

Long-cycle regimens with continuous use of oral contraceptives (OCs) for 3 or 6 months followed by a hormone-free interval of 7 days may reduce or prevent cycle-dependent and menses-related complaints. A representative survey carried out with 1195 German women in different age groups revealed that only 26-35% of the women aged between 15 and 49 years preferred monthly bleeding, while 37-46% wished to never bleed. The reasons for the refusal of regular menstruations were fewer severe menstrual complaints, better hygiene, higher quality of life, and less blood loss. Among the women who preferred regular withdrawal bleeding during the use of OCs, the main reasons were fear of pregnancy, infertility and adverse effects, and that menstruations were natural. Between 32% and 54% of the women would suppress menstruation sporadically and 11-14% for a longer period of time. After continuous treatment with a combination of 30 microg ethinyl estradiol and 2 mg dienogest for 6 months, the majority of women preferred the long-cycle regimen as compared to the conventional OC regimen despite a higher rate of irregular bleeding. Bleeding occurred primarily in first-time users of OC, particularly during the administration of the second OC pack. A survey carried out with German gynecologists revealed that most physicians prescribed extended OC cycles primarily for medical reasons, e.g., dysmenorrhea, hypermenorrhea, endometriosis and premenstrual dysphoric disorder. The gynecologists preferred a regimen with three packs of extended use of OCs.

Effect of four oral contraceptives on thyroid hormones, adrenal and blood pressure parameters

In a double-blind, controlled, randomized, four-arm, bicentric clinical study, the effect of four oral contraceptives (OCs) on thyroid hormone parameters, cortisol, aldosterone, endothelin-1 and angiotensin II was investigated. Four groups composed of 25 volunteers each (ages between 18 and 35 years) were treated for six cycles with monophasic combinations containing 21 tablets with either 30 microg ethinylestradiol (EE) + 2 mg dienogest (DNG) (30EE/DNG), 20 microg EE + 2 mg DNG (20EE/DNG), 10 microg EE + 2 mg estradiol valerate (EV) + 2 mg DNG (EE/EV/DNG) or 20 microg EE + 100 microg levonorgestrel (LNG) (EE/LNG). The study was completed by 91 subjects. Blood samples were taken by venipuncture after at least 12 h fasting on Day 21-26 of the control cycle and on Day 18-21 of the first, third and sixth treatment cycle. There was a significant increase in triiodothyronine (T3) and thyroxine (T4) by 20-40% in all treatment cycles, while thyroid-stimulating hormone was significantly increased only with EE/EV/DNG. Treatment with the DNG-containing OCs caused no change in free T4 (FT4) and a transitory reduction in free T3 (FT3) levels during the first cycle. During intake of EE/LNG, FT4 rose slightly, while FT3 was not altered. The pronounced rise in the serum concentrations of cortisol appeared to be related to the EE dose. During the first three cycles of treatment, no effect on angiotensin II levels was observed, while in the sixth cycle a significant decrease was measured in all treatment groups. The four OCs did not influence the serum concentrations of endothelin-1 and no consistent effects were found concerning those of aldosterone. The results suggest that the three DNG-containing and the LNG-containing low-dose OCs may increase T3, T4 and cortisol due to an elevated binding to serum globulins, while the free proportion of the hormones is not or only slightly changed. Therefore, these OCs have only minor effects on thyroid function, adrenal and blood pressure serum parameters.

Effect of four different oral contraceptives on various sex hormones and serum-binding globulins

In a double-blind, controlled, randomized, four-arm, bicentric clinical study, the effect of four oral contraceptives (OCs) on various hormone parameters and serum-binding globulins was investigated. Four groups with 25 volunteers each (18-35 years of age) were treated for six cycles with monophasic combinations containing 21 tablets with either 30 microg ethinylestradiol (EE) + 2 mg dienogest (DNG) (30EE/DNG), 20 microg EE + 2 mg DNG (20EE/DNG), 10 microg EE + 2 mg estradiol valerate (EV) + 2 mg DNG (EE/EV/DNG) or 20 microg EE + 100 microg levonorgestrel (LNG) (EE/LNG). The study was completed by 91 subjects. Blood samples were taken after at least 12 h of fasting on Day 21-26 of the preceding control cycle and on Day 18-21 of the first, third and sixth treatment cycle. The serum concentrations of free testosterone were significantly decreased by about 40-60% in all four groups, while those of dehydroepiandrosterone sulfate (DHEAS) showed a time-dependent decrease during treatment. Except for EE/EV/DNG, which increased prolactin significantly during the third and sixth cycles, no change was observed with the EE-containing preparations. There was a significant increase in the levels of serum-binding globulins during treatment, which differed according to the composition of the OCs used. The rise in sex hormone-binding globulin (SHBG) was highest during intake of 30EE/DNG (+320%) and lowest with EE/LNG (+80%), while the effect of 20EE/DNG and EE/EV/DNG was similar (+270%). The thyroxine-binding globulin (TBG) levels increased significantly, by 50-60%, during treatment with the DNG-containing formulations, while the effect of EE/LNG was less significant (+30%). The rise in corticosteroid-binding globulin (CBG), which occurred in all groups, was most pronounced in women treated with 30EE/DNG (+90%) and least with EE/EV/DNG (+55%), indicating a strong influence of EE and no effect of the progestogen component. In all treatment groups, the frequency of intracyclic bleeding rose in the first treatment cycle and decreased thereafter. Cycle control was significantly better with 30EE/DNG or EE/LNG than with 20EE/DNG or EE/EV/DNG. There was no significant change in blood pressure, body mass index or pulse rate throughout the study. In conclusion, the DNG-containing OCs caused a higher rise in SHBG and TBG levels than the LNG-containing preparation. The effects on CBG suggest a lesser hepatic effect of 2 mg EV as compared to 20 or 30 microg EE. In contrast to EE, the use of estradiol in OCs appeared to increase prolactin release, while the cycle control was better with the OC containing 30 microg EE.

[Influence of the ovarian cycle on the central nervous system]

Estradiol, progesterone and some of their metabolites modulate the activity of neurotransmitters and neuropeptides in the CNS. The distribution and concentrations of sex steroids in the various CNS regions is partly dependent on the serum levels, but also on the local synthesis of the steroids. In general, estradiol and testosterone exert a stimulatory, progesterone an inhibitory effect on neuronal activities which are mediated by excitatory (e.g. glutamate, aspartate), and inhibitory amino acids (e.g. GABA) and neuropeptides (e.g. beta-endorphin), respectively. Gonadotropin release is primarily governed by the rhythm of pulsatile secretion of GnRH in the hypothalamus which is controlled by estradiol and progesterone by means of inhibitory or stimulatory modulation of the amplitude and frequency of GnRH pulses. The discharges of GnRH neurons triggered by excitatory amino acids are modulated by estradiol, while the inhibitory effect of progesterone is mediated by GABA and beta-endorphin which cause hyperpolarization of the GnRH neurons and consequently a reduced pulse frequency. The pulse amplitudes are primarily influenced by estradiol, but neuropeptide Y, neurotensin and noradrenaline contribute to their preovulatory enhancement. The postovulatory rise in core temperature is caused by the increasing level of progesterone and its metabolite 3 alpha-pregnanolone, respectively. Despite of this, up to 20% of ovulatory cycles do not show any rise in body temperature. Although 3 alpha-pregnanolone has sedative activities, there is no change in sleep quality during the luteal phase due to their low serum levels. It could be demonstrated that performance on tests of articulatory and fine motor skills are enhanced in the late follicular phase as compared to the menstruation phase, while spatial ability was better during menses. Estrogens may influence mood and well-being in a favorable manner, while in predisposed women progesterone may cause symptoms of premenstrual syndrome. In most women there are, however, no cycle-dependent mood changes. An increase in appetite can be observed during the periovulatory phase and before menses, while sexual interest increases in the follicular phase. Somatic complaints (back pain, abdominal pain, breast tenderness) which are highest before and during menstruation, are probably associated with a lowered pain threshold due to a fall in the beta-endorphin levels in the CNS.

Effect of dienogest-containing oral contraceptives on lipid metabolism

In a double-blind, controlled, randomized, four-arm, bicentric clinical study, the effect of four oral contraceptives (OCs) on lipid metabolism was investigated. Four groups composed of 25 volunteers each (mean age 26.1 +/- 4.5 years; body mass index 21.9 +/- 2.8 kg/m(2)) were treated for six cycles with monophasic combinations containing 21 tablets with either 30 microg ethinyl estradiol (EE) + 2 mg dienogest (DNG) (30 EE/DNG), 20 microg EE + 2 mg DNG (20 EE/DNG), 10 microg EE + 2 mg estradiol valerate (EV) + 2 mg DNG (EE/EV/DNG), or 20 microg EE + 100 microg levonorgestrel (LNG; EE/LNG). The study was completed by 91 women. Blood samples were taken by venipuncture after at least 12 h fasting on Days 21-26 of the control cycle and Days 18-21 of the first, third, and sixth treatment cycle. There were clear differences between the effects of EE/LNG and the formulations containing estrogens and DNG. Although EE/LNG did not change the triglycerides levels, a significant increase was observed during treatment with the DNG-containing preparations. Although EE/LNG significantly reduced HDL-CH and HDL(2)-CH, there was a nonsignificant increase with the DNG-containing OCs. No change was observed in the levels of HDL(3)-CH. A significant rise in apolipoprotein A1 occurred during intake with the three DNG-containing formulations, but not with EE/LNG. In contrast to the women treated with combinations of estrogens and DNG, apolipoprotein B rose significantly in the women in the EE/LNG group. Lipoprotein (a) was significantly reduced by 30 EE/DNG and EE/LNG and remained unaltered with 20 EE/DNG and EE/EV/DNG. Altogether, the changes in lipid metabolism caused by the DNG-containing formulations appeared to be more favorable than those observed with EE/LNG. In OCs with DNG, the EE dose does not seem to play a major role with respect to the effect on lipids.

Sex steroids used in hormonal treatment increase vascular procoagulant activity by inducing thrombin receptor (PAR-1) expression: role of the glucocorticoid receptor

BACKGROUND

The use of sex steroids in oral contraception or hormonal replacement therapy is associated with an increased risk of cardiovascular thromboembolic complications. Although both the estrogen and the progestin components have been involved, the underlying mechanisms responsible are unclear.

METHODS AND RESULTS

This study examined whether sex steroids promote hemostasis indirectly by increasing the procoagulant activity of blood vessels. Treatment of vascular smooth muscle cells with several progestins (progesterone, 3-keto-desogestrel, gestodene, and medroxyprogesterone acetate) upregulated proteolytically activatable thrombin receptor (PAR-1) expression, resulting in a potentiated thrombin-induced tissue factor expression and surface procoagulant activity. In contrast, neither the progestins levonorgestrel, norethisterone, and norgestimate nor the synthetic estrogen 17alpha-ethinylestradiol had such effects. The effect of the stimulatory progestins, which induce glucocorticoid-like effects in several cell systems, was mimicked by dexamethasone and inhibited by the progesterone and glucocorticoid receptor antagonist RU-38486. In addition, long-term administration of progesterone, 3-keto-desogestrel, or medroxyprogesterone acetate to ovariectomized rats increased PAR-1 protein level in the arterial wall, resulting in an increased responsiveness of isolated aortic rings to thrombin.

CONCLUSIONS

These data demonstrate that several progestins markedly potentiate the vascular procoagulant effects of thrombin by increasing the availability of membrane thrombin receptors in the smooth muscle, an effect that is most likely due to their glucocorticoid-like activity.

Validity of radioimmunological methods for determining free testosterone in serum

OBJECTIVE

To assess serum free testosterone (free T) concentrations in various groups of women by means of an ultrafiltration technique (UFT) or two RIAs and to investigate the influence of levonorgestrel (LNG) and norethisterone (NET) on free T.

DESIGN

Experimental study with serum samples from various groups of patients.

SETTING

Obstetrics and gynecology department of a university.

PATIENT(S)

Samples from 20 normal healthy women, 20 menopausal women, 21 pregnant women, 23 women using oral contraceptives (OC), 20 hyperandrogenemic women, 20 hirsute patients with normal total testosterone (total T), 18 patients with acne (normal total T), and 9 women with adrenogenital syndrome (AGS).

INTERVENTION(S)

Blood samples were taken by venipuncture.

MAIN OUTCOME MEASURE(S)

Serum concentrations of free T.

RESULT(S)

Mean free-T levels determined by UFT amounted to 5-6 pg/mL in most groups, except in patients with hyperandrogenemia (8.3 pg/mL) or AGS (10.7 pg/mL) and in women using OC (1.9 pg/mL). The values were twofold to fourfold and threefold to sevenfold higher than those determined with the RIAs. The proportion of free T as determined by UFT was 0.9-1.2% of total T and was 0.55% during OC treatment. The presence of 10 ng/mL of LNG or NET increased free-T levels by only 13%.

CONCLUSION(S)

Serum free-T levels determined with RIA are much lower than those measured with the UFT. The ratio between the UFT and RIA values may vary depending on the endocrine status. In women with normal or elevated sex hormone-binding globulin levels, nortestosterone derivatives increase free T levels only slightly.

[Cross-over comparison of the pharmacokinetics of estradiol during hormone replacement therapy with estradiol valerate or micronized estradiol]

OBJECTIVE

The aim of this randomized cross-over study was the comparison between a sequential 28-day hormone replacement therapy (HRT) using micronized estradiol and a cyclic 21-day HRT using estradiol valerate with regard to the pharmacokinetics of estradiol. -

MATERIAL AND METHODS

Fifty postmenopausal women were randomly assigned to be treated either with Trisequens(R) for 28 days or with Sisare(R) for 21 days. After a wash-out cycle, the women were treated for one cycle with the other preparation in a cross-over fashion. The pharmacokinetic profile of the serum concentrations of estradiol was measured on day 1, 21 and 28 each immediately before and 1, 2, 4, 6, 8, and 10 hours after intake of a tablet, and the AUC (area under the curve) was calculated. -

RESULTS

The serum concentrations of estradiol increased from a mean of 10 pg/ml up to 40 pg/ml (Trisequens(R)) and 30 pg/ml (Sisare(R)) on day 1, and to 80 pg/ml (Trisequens(R)) and 60 pg/ml (Sisare(R)) on day 21, and declined to 40 pg/ml (Trisequens(R)) and 10 pg/ml (Sisare(R)) on day 28. The AUC as calculated from both treatment cycles, was significantly higher on day 1, 21, and 28 during treatment with Trisequens(R) than with Sisare(R). This difference was, however, not signifcant on day 1 and 21 of the first treatment cycle. -

CONCLUSION

During treatment with 2 mg micronized estradiol the serum concentrations are significantly higher than with 2 mg estradiol valerate. On day 28 of treatment with Sisare(R), the estradiol levels decline to baseline values, while using Trisequens(R) they remain in the range of those measured on day 1.

[New gestagens--advantages and disadvantages]

Due to their high oral bioavailability synthetic progestagens are used for therapy, hormone replacement therapy and contraception There are different types of progestogens. There are progesterone derivatives, nortestosterone derivatives (13-methyl-gonanes and 13-ethyl-gonanes), spirolactone derivatives and norpregnance derivatives which differ in their efficacy and hormonal profile. All progestagens show antiestrogenic activities, inhibit the estrogen-induced proliferation of the endometrium and, hence, decrease the risk of endometrial hyperplasia. With the exception of Dienogest, the derivatives of 19-nortestosterone are characterized by a 17-alpha-ethynyl group and show slight androgenic properties which may antagonise some estrogen-dependent alterations of hepatic serum parameters. Tibolone which is a derivative of norethynodel also belongs to this group. Among the nortestosterone derivatives, there are the so-called "Prodrugs". Prodrugs are rapidly transformed after intake to the active progestagens. Progesterone derivatives partly exert moderate androgenic or antiandrogenic effects, while the spirolactone derivative Drospirenone shows antimineralocorticoid and antiandrogenic activities. The progesterone derivatives as well as Gestodene and Desogestrel have certain glucocorticoid activities which, at the doses used, are not clinically relevant, but possibly may influence vascular function. The effects of 19-norpregnane derivatives are comparable with those of progesterone derivatives. According to their different hormonal profiles and activities, the various available progestogens allow the choice of preparations which are best suitable for the individual woman for contraception or hormone replacement therapy.

Cell cycle-related expression and ligand binding of peripheral benzodiazepine receptor in human breast cancer cell lines

The aim of this study was to measure the expression of peripheral benzodiazepine receptors (PBR) as well as mitochondria content in different phases of the cell cycle of BT-20 and MCF-7 breast cancer cell lines, using two-parameter flow cytometric analyses. The PBR expression as well as mitochondria mass, were found to increase as cells pass through different stages of the cell cycle, whereas the amount of PBR in quiescent cells was very low. Binding capacity for the PBR ligand [3H]-Ro5-4864 was strongly related to the phase of the cell cycle with a positive correlation (r=0.98) with a high percentage of cells in S phase. Incubation of BT-20 cells in serum-deprived medium with nanomolar concentrations of Ro5-4864 caused an increase in S phase cells. This effect was not observed in MCF-7 cells. Using micromolar concentrations of Ro5-4864, both BT-20 and MCF-7 cells were reversibly arrested in the G(0/1) phase.

Relation of cell proliferation to expression of peripheral benzodiazepine receptors in human breast cancer cell lines

Peripheral benzodiazepine receptor (PBR) agonist [(3)H]Ro5-4864 has been shown to bind with high affinity to the human breast cancer cell line BT-20. Therefore, we investigated different human breast cancer cell lines with regard to binding to [(3)H]Ro5-4864 and staining with the PBR-specific monoclonal antibody 8D7. Results were correlated with cell proliferation characteristics. In flow cytometric analysis, the estrogen receptor (ER)-negative breast cancer cell lines BT-20, MDA-MB-435-S, and SK-BR-3 showed significantly higher PBR expression (relative fluorescence intensity) than the ER-positive cells T47-D, MCF-7 and BT-474 (P<0.05). Accordingly, BT-20 and MDA-MB-435-S had the highest capacity for binding [(3)H]-Ro5-4864, while the ER-positive cells exhibited only low binding of the benzodiazepine. PBR expression correlated inversely with cell doubling time (r = 0.78) and positively with Ki-67 expression (r = 0.77). The amount of mitochondria was significantly higher in cells with high PBR expression. As PBR could be demonstrated only after permeabilization of cells, PBR is suggested to be localized within the cytoplasm. Moreover, colocalization of PBR and mitochondria was shown by confocal microscopy analysis. The highest amounts of both PBR and mitochondria were found in cell lines with high mitotic activity. Therefore, it is concluded that the level of PBR is dependent on the number of mitochondria. PBR and its putative endogenous ligand diazepam-binding inhibitor are possibly involved in the regulation of cell proliferation of human breast cancer cell lines.

Towards structural determination of the water-splitting enzyme. Purification, crystallization, and preliminary crystallographic studies of photosystem II from a thermophilic cyanobacterium

A photosystem II preparation from the thermophilic cyanobacterium Synechococcus elongatus, which is especially suitable for three-dimensional crystallization in a fully active form was developed. The efficient purification method applied here yielded 10 mg of protein of a homogenous dimeric complex of about 500 kDa within 2 days. Detailed characterization of the preparation demonstrated a fully active electron transport chain from the manganese cluster to plastoquinone in the Q(B) binding site. The oxygen-evolving activity, 5000-6000 micromol of O(2)/(h.mg of chlorophyll), was the highest so far reported and is maintained even at temperatures as high as 50 degrees C. The crystals obtained by the vapor diffusion method diffracted to a resolution of 4.3 A. The space group was determined to be P2(1)2(1)2(1) with four photosystem II dimers per unit cell. Analysis of the redissolved crystals revealed that activity, supramolecular organization, and subunit composition were maintained during crystallization.

Specific binding of benzodiazepines to human breast cancer cell lines

Binding of [3H]Ro5-4864, a peripheral benzodiazepine receptor (PBR) agonist, to BT-20 human, estrogen- (ER) and progesterone- (PR) receptor negative breast cancer cells was characterized. It was found to be specific, dose-dependent and saturable with a single population of binding sites. Dissociation constant (K(D)) was 8.5 nM, maximal binding capacity (Bmax) 339 fM/10(6) cells. Ro5-4864 (IC50 17.3 nM) and PK 11195 (IC50 12.3 nM) were able to compete with [3H]Ro5-4864 for binding, indicating specificity of interaction with PBR. Diazepam was able to displace [3H]Ro5-4864 from binding only at high concentrations (>1 microM), while ODN did not compete for PBR binding. Thymidine-uptake assay showed a biphasic response of cell proliferation. While low concentrations (100 nM) of Ro5-4864, PK 11195 and diazepam increased cell growth by 10 to 20%, higher concentrations (10-100 microM) significantly inhibited cell proliferation. PK 11195, a potent PBR ligand, was able to attenuate growth of BT-20 cells stimulated by 100 nM Ro5-4864 and to reverse growth reduction caused by 1 and 10 microM Ro5-4864, but not by 50 microM and 100 microM. This indicates that the antimitotic activity of higher concentrations of Ro5-4864 is independent of PBR binding. It is suggested, that PBR are involved in growth regulation of certain human breast cancer cell lines, possibly by supplying proliferating cells with energy, as their endogenous ligand is a polypeptide transporting Acyl-CoA.

Localization of cyanobacterial photosystem II donor-side subunits by electron microscopy and the supramolecular organization ofphotosystem II in the thylakoid membrane

A large set of electron microscopy projections of photosystem II (PSII) dimers isolated from the cyanobacterium Synechococcus elongatus was characterized by single particle image analysis. In addition to previously published maps at lower resolution [Boekema, E.J., Hankamer, B., Bald, D., Kruip, J., Nield, J., Boonstra, A.F., Barber, J. & Rögner, M. (1995) Proc. Natl Acad. Sci. USA 92, 175-179], the new side-view projections show densities of all three lumenal extrinsic proteins, i.e. the 33-kDa, 12-kDa and the cytochrome c-550 subunit encoded by psbO, psbU and psbV, respectively. Analysis of the size and shape of the top-view projections revealed a small number of photosystem II particles of about double the size of the usual dimers. Size and quantity of these 'double dimers' correlates with a small fraction of 1000-kDa particles found with HPLC-size-exclusion chromatographic analysis. Because many cyanobacteria contain dimeric photosystem II complexes arranged in rows within the membrane, the double dimers can be considered as the breakdown fragments of these rows. Their analysis enabled the detection of the arrangement of photosystem II within the rows, in which the dimers interact with other dimers mostly with their tips, leaving a rather open center at the interfaces of two dimers. The dimers have a repeating distance of only 11.7 nm. As a consequence, the phycobilisomes, located on top of PSII and functioning in light-harvesting, must be closely packed or almost touch each other, in a manner similar to a recently suggested model [Bald, D., Kruip, J. & Rögner, M. (1996) Photosynthesis Res. 49, 103-118].