Hormonal regulation of creatine kinase BB

Age and gender specific stimulation of creatine kinase specific activity by gonadal steroids in human bone-derived cells in culture

We previously reported a non-enzymatic method for isolation of human bone cells in culture that display osteoblastic features and respond to 1,25 dihydroxy vitamin D (1,25) and to parathyroid hormone (PTH). The present study was undertaken to analyze the response of cultured human bone cells to 17beta-estradiol (E2) and to dihydrotestosterone (DHT) as a function of gender and age. Cultured human bone cells, obtained from biopsies during orthopedic surgery, were divided into four groups defined by gender and age: pre- and post-menopausal healthy non-osteoporotic women that were not under hormone replacement therapy (HRT) and mature (<55-year-old) and older (>60-year-old) men. We found gender specific responses to gonadal steroids using the specific activity of the brain type (BB) isozyme of creatine kinase (CK) as a response marker. Constitutive levels of CK activity did not change with age or gender and the enzyme extracted from cells from the different sexes and ages did not respond to either progesterone (P) or to 1,25. CK from the different cells responded to gonadal steroids in a gender specific manner, i.e. CK from female derived cells responded to E2 only and the enzyme from male derived cells responded to DHT only. In female derived cells the response to E2 declined significantly with age, while the response to DHT in CK from male derived cells did not vary with age. This may be due to either decreased proportion of mature osteoblasts and/or their differentiation state and/or changes in the levels of estrogen receptor(s), coactivators or corepressors in these cells. These results extend our knowledge of human osteoblast biology (beyond murine cells) and are therefore more relevant for developing models for treatment of human metabolic bone diseases such as post-menopausal osteoporosis.

Effects of gonadal steroids and their antagonists on DNA synthesis in human vascular cells

The cardiovascular effect of estrogen is currently under intense investigation, but the role of androgens in vascular biology has attracted little attention. Because endothelial repair and vascular smooth muscle cell (VSMC) proliferation affect atherogenesis, we analyzed the effects of 17beta-estradiol (E2), dihydrotestosterone (DHT), and sex hormone antagonists on DNA synthesis in human umbilical VSMCs and in E304 cells (a human umbilical endothelial cell line). In VSMCs, both E2 and DHT had a biphasic effect on [3H]thymidine incorporation into DNA: low concentrations (0.3 nmol/L for E2, 3 nmol/L for DHT) stimulated [3H]thymidine incorporation (+35% and +41%, respectively), whereas high concentrations (30 nmol/L for E2, 300 nmol/L for DHT) inhibited [3H]thymidine incorporation (-40%). In contrast, E2 (0.3 to 300 nmol/L) and DHT (3 to 3000 nmol/L) dose-dependently enhanced [3H]thymidine incorporation in E304 cells (peak, +85% for both). In VSMCs, high concentrations of E2 and DHT inhibited platelet-derived growth factor (PDGF)-or insulin-like growth factor (IGF-1)-induced DNA synthesis (-50% to 80%), whereas PDGF- or IGF-1-dependent DNA synthesis in E304 cells was further increased by E2. The antiestrogens tamoxifen and raloxifene mimicked the effects of E2 on DNA synthesis in both VSMCs and E304 cells. However, when coincubated with a stimulatory concentration of E2 (0.3 nmol/L), tamoxifen and raloxifene blocked E2-induced [3H]thymidine incorporation in E304 cells but not in VSMCs. Finally, the androgen antagonist flutamide inhibited the biphasic effects of DHT on VSMCs and blocked the increase in DNA elicited by DHT in E304 cells. The results suggest complex, dose-dependent, and cell-specific interactions of estrogens, androgens, and their respective antagonists in the control of cellular proliferation in the vascular wall. Gonadal steroid-dependent inhibition of VSMC proliferation and stimulation of endothelial replication may contribute to vascular protection and remodeling responses to vascular injury.

Reduction of brain phosphocreatine in bipolar II disorder detected by phosphorus-31 magnetic resonance spectroscopy

Brain phosphorus metabolism was measured by 31P-MRS in 15 patients with bipolar II disorder (BP II) and 14 patients with bipolar I disorder (BP I). Phosphocreatine (PCr)levels were significantly lower in patients with BP II in all three psychiatric states compared to 59 normal controls (PCr (%) was 13.5 +/- 1.5 (mean +/- SD) for controls, and 12.2 +/- 1.7, 12.1 +/- 1.3, 12.0 +/- 1.9 for hypomanic, euthymic and depressed bipolar II patients respectively). High values of phosphomonoester (PME) were found in BP II patients in the hypomanic and depressive states, but PME values in the euthymic state did not differ significantly from controls. Intracellular pH of BP II patients in all three psychiatric phases was similar to control values, whereas euthymic BP I patients had lower pH values. These results suggest that brain high energy phosphate metabolism may be impaired in BP II and that there may be pathophysiological differences between BP I and BP II.

Intracellular alterations of the creatine kinase isoforms in brains of schizophrenic patients

Postmortem brain tissues of schizophrenic patients were found to contain 5-10 times less water-soluble creatine kinase (BB CK) and 1.5-3 times less mitochondrial creatine kinase as compared to control. The major part of BB CK in schizophrenic brain tissues, contrary to control, was found to be insoluble in water (particulate form of BB CK) and could be extracted from brain tissue with strong denaturating agents. The particulate form of BB CK did not have any enzymatic activity but activity was found after the solubilization of this isoenzyme. The observed BB CK translocation into the particulate inactive form and the decrease of mitochondrial CK content to schizophrenic brains may reflect changes in the synthesis and the utilization of creatine phosphate.

Elevated serum levels of creatine kinase BB in autosomal dominant osteopetrosis type II

Serum levels of creatine kinase isoenzyme BB (CK-BB) were measured spectrophotometrically and by electrophoresis in 17 patients with autosomal dominant osteopetrosis (ADO) and compared with those of age- and sex-matched controls. Eight patients had ADO type 1 and nine patients had ADO type II. CK-BB was significantly increased (p less than 0.002) in type II but normal in type I compared with controls. This finding supports heterogeneity of ADO, and it may indicate a potential role for CK-BB as a marker of immature osteoclasts.

Direct and sex-specific stimulation by sex steroids of creatine kinase activity and DNA synthesis in rat bone

A direct in vitro effect of 17 beta-estradiol (E2) was demonstrated on bone and cartilage cell energy metabolism. Sex-specific stimulation by E2 and testosterone was shown in diaphyseal bone of weanling rats. E2 (30 nM) caused, within 24 hr, a 70-200% increase in creatine kinase (CK; ATP:creatine N-phosphotransferase, EC 2.7.3.2) specific activity in ROS 17/2.8 rat osteogenic sarcoma cells, MC3T3-E1 mouse calvaria-derived cells, and rat fetal calvaria cells, and a 40% increase in rat epiphyseal cartilage cells. Stimulation of CK activity by E2 was dose and time dependent: in ROS 17/2.8 cells, a highly significant increase was found at 3 nM E2 and a greater than 100% increase in CK activity was found 1 hr after E2 administration. In female 20-day-old Wistar-derived rats, E2 (5 micrograms per rat) increased CK activity in diaphyseal bone by 82% within 1 hr of i.p. injection, with a maximal increase of 200% after 24 hr; neither the weakly estrogenic agonist 17 alpha-estradiol, testosterone, nor progesterone showed this effect. Conversely, in male rat diaphyseal bone, testosterone or dihydrotestosterone increased CK activity after 24 hr by approximately 100%, while E2 was ineffective. In epiphyseal cartilage, both E2 and testosterone increased CK activity. Stimulation of CK activity by sex hormones was paralleled by significant increases in [3H]thymidine incorporation into DNA. Therefore, it is possible that direct sex-specific actions of gonadal steroids may contribute to stimulating bone growth and maintaining balanced bone turnover.

The transduction of mechanical force into biochemical events in bone cells may involve activation of phospholipase A2

Mechanical forces applied to cultured bone cells induce the production of cAMP via stimulation of the formation of prostaglandin E2 (PGE2) and its release into the medium, resulting in stimulation of adenylate cyclase. In this paper we show that either the antibiotic gentamycin (100 micrograms/ml) or antiphospholipid antibodies (0.1%) which bind to membrane phospholipids abolish cAMP formation induced by mechanical forces; exogenously added arachidonic acid or PGE2 stimulates cAMP formation, even in the presence of these agents. Addition of exogenous phospholipase A2 (but not phospholipase C) causes an increase in the formation of cAMP in bone cells, a response that is also inhibited by gentamycin or antiphospholipase antibodies. These observations suggest that mechanical forces exert their effect on bone cells via the following chain of events: (1) activation of phospholipase A2, (2) release of arachidonic acid, (3) increased PGE synthesis, (4) augmented cAMP production.

Estrogen responsive creatine kinase in human breast cancer cells

The brain type (BB) isoenzyme of creatine kinase (CK) is a very sensitive marker of estrogen action in rat uterus and in experimental mammary tumors. In order to detect useful markers for estrogen dependent human breast cancer cell proliferation we measured CK levels and isoenzyme composition in the CG5 cells, an estrogen supersensitive variant of the MCF-7 human breast cancer cell line. Under basal conditions, CK-BB accounted for 10%-15% of total enzymatic activity, while the MM isoenzyme represented the overwhelming component. In cells cultured in the presence of 5% charcoal-treated fetal calf serum, physiological concentrations (0.1-1 nM) of estradiol increased CK-BB levels in a dose- and time-related fashion. The effect was specific for estrogens and was prevented by antiestrogens. Our results show that CK-BB is estrogen regulated in the CG5 cells and suggest a possible role for this enzyme as an additional marker of the hormonal responsiveness of breast cancer.