Category Archives: PGE2

Vitamin K2 (MK4) Inhibits Bone Resorption Through Inhibition of PGE2 In Vitro

Abstract

Menatetrenone inhibits bone resorption partly through inhibition of PGE2 synthesis in vitro.

We studied the effect of menatetrenone, a vitamin K2 homolog, on bone resorption stimulated by interleukin-1 alpha (IL-1 alpha), prostaglandin E2 (PGE2), parathyroid hormone (PTH), and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Bone-resorbing activity was assessed by measurement of calcium and hydroxyproline in the media and calvariae. IL-1 alpha (0.1-100 U/ml), 1,25-(OH)2D3 (10(-10)-10(-7) M), PGE2 (10(-9)-10(-6) M), and PTH (3 x 10(-8)-3 x 10(-7) M) dose dependently increased the levels of calcium and hydroxyproline in the medium. Indomethacin (10(-6) M) completely inhibited bone resorption induced by IL-1 alpha and partially inhibited bone resorption induced by 1,25-(OH)2D3. However, indomethacin did not affect the action of PGE2 or PTH. Menatetrenone (3 x 10(-6)-3 x 10(-5) M) inhibited the bone resorption induced by IL-1 alpha (2 U/ml), PGE2 (10(-7) M), PTH (3 x 10(-7) M), and 1,25-(OH)2D3 (3 x 10(-10) M) in a dose-dependent manner. Menatetrenone also inhibited the PGE2 production stimulated by IL-1 alpha. These results indicate that menatetrenone may inhibit bone resorption through at least two different mechanisms; one possibly is an inhibitory effect on prostaglandin production.

Hara K, Akiyama Y, Tajima T, Shiraki M
J. Bone Miner. Res. May 1993
PMID: 8511981

Review: PGE2 is Complicated

The prostaglandin E(2) system: a toolbox for skeletal repair?

Gelse K, Beyer C
Arthritis Rheum. Apr 2011
PMID: 21190302 | Free Full Text

Prostaglandin E2 (PGE2), the most widely produced member of the prostaglandin group, originates from arachidonic acid that is released from the cell membrane by phospholipase A2, followed by enzymatic conversion by cyclooxygenase (COX) and PGE synthase 1 (PGES-1). PGE2 not only triggers pain and inflammation but also promotes matrix degradation and tissue damage by stimulating the expression of matrix-degrading enzymes (2). Inflammatory cytokines such as interleukin-1 or tumor necrosis factor ’ strongly increase PGE2 levels, but PGE2 secretion may also increase in response to other stimuli including growth factors, hypoxia, and a number of hormones.

Apart from the well-defined role of PGE2 in tissue inflammation, there is increasing evidence that it is involved in the maintenance and repair of the skeletal system. At first glance, the effects of PGE2 on tissue homeostasis of bone and cartilage seem confusing, because they conflict with the long-known destructive potential of the prostaglandins. Nevertheless, both catabolic and anabolic effects have already been described for PGE2 in these tissues. In terms of catabolism, PGE2 can promote osteoclastic bone resorption (3,4) and enhance breakdown of the extracellular matrix by increasing the expression of matrix metalloproteinase 3 (MMP-3) or MMP-13 (2,5). Regarding its anabolic aspects, PGE2 may stimulate chondrogenesis, chondrocyte proliferation (6), cartilage matrix synthesis (7), as well as osteoblast activity (8). To shed light on the apparent ambivalent role of PGE2, a multidimensional view is necessary that addresses the developmental stage, type of tissue, disease status, concentration of PGE2, and specific receptor status of the different cell types.

 

PGE2 Stimulates Bone Formation and Resorption In Mouse Cells

Abstract

Prostaglandin E2 stimulates osteoclast-like cell formation and bone-resorbing activity via osteoblasts: role of cAMP-dependent protein kinase.

Prostaglandin E2 (PGE2) is an important local regulator in bone. The present study was performed to investigate the effect of PGE2 on osteoclast-like cell formation and bone-resorbing activity of mature osteoclasts in the presence or absence of osteoblasts, PGE2 (10(-8) to 10(-6) M) significantly stimulated osteoclast-like cell formation in osteoblast-containing mouse bone cell cultures, although it did not affect osteoclast-like cell formation from hemopoietic blast cells supported by granulocyte-macrophage colony-stimulating factor in osteoblast-free mouse spleen cell cultures. The conditioned medium from osteoblastic UMR-106 cells pretreated with PGE2 (10(-8) and 10(-6) M) significantly stimulated osteoclast-like cell formation from hemopoietic blast cells. PGE2 also significantly stimulated the bone-resorbing activity of mature osteoclasts in osteoblast-containing mouse bone cell cultures. In contrast, PGE2 significantly inhibited the bone-resorbing activity and osteopontin mRNA expression in isolated rabbit osteoclasts. Rp-cAMPS, a direct protein kinase (PKA) antagonist, significantly inhibited PGE2-stimulated osteoclast-like cell formation and the bone-resorbing activity of mature osteoclasts, although protein kinase C inhibitors, dantrolene (an inhibitor of calcium release from the intracellular calcium pool) and voltage-dependent calcium channel blockers did not affect PGE2-stimulated osteoclast-like cell formation. In conclusion, PGE2 stimulated osteoclast-like cell formation and bone-resorbing activity in mouse bone cell cultures presumably through osteoblasts. The activation of PKA is linked to PGE2-stimulated osteoclast-like cell formation and bone-resorbing activity.

Kaji H, Sugimoto T, Kanatani M, Fukase M…
J. Bone Miner. Res. Jan 1996
PMID: 8770698

PGE2 Increases Bone Formation and Mass in Aging Rats

Abstract

Systemic prostaglandin E2 increases cancellous bone formation and mass in aging rats and stimulates their bone marrow osteogenic capacity in vivo and in vitro.

Prostaglandin E(2) (PGE(2)) has been shown to exert a bone anabolic effect in young and adult rats. In this study we tested whether it possesses a similar effect on bone formation and bone mass in aging rats. Fifteen-month-old rats were injected daily with either PGE(2) at 5 mg/kg or vehicle for 14 days. PGE(2) treatment stimulated the rate of cancellous bone formation (a approximately 5.5-fold increase in bone formation rate), measured by the incorporation of calcein into bone-forming surfaces at the tibial proximal metaphysis. This effect resulted in increased cancellous bone area (+54%) at the same site. Since PGE(2) treatment resulted in a much higher proportion of bone surface undergoing bone formation and thus lined with osteoblasts, we tested the hypothesis that PGE(2) stimulates osteoblast differentiation from bone marrow precursor cells both in vivo and in vitro. We found that ex vivo cultures of bone marrow stromal cells from rats injected for 2 weeks with PGE(2) at 5 mg/kg per day yielded more ( approximately 4-fold) mineralized nodules and exhibited a greater (by 30-40%) alkaline phosphatase activity compared with cultures from vehicle-injected rats, attesting to a stimulation of osteoblastic differentiation by PGE(2). We also compared the osteogenic capacity of bone marrow from aging (15-month-old) versus young (5-week-old) rats and its regulation by PGE(2) in vitro. Bone marrow stromal cell cultures from aging rats exhibited a greatly diminished osteogenic capacity, reflected in reduced nodule formation ( approximately 6% of young animals) and lower alkaline phosphatase activity ( approximately 60% of young animals). However, these parameters could be stimulated in both groups of animals by incubation with 10-100 nM PGE(2). The magnitude of this stimulation was greater in cultures from aging rats (+550% vs +70% in nodule formation of aging compared with young rats). In conclusion, we demonstrate here that PGE(2) exerts a bone anabolic effect in aging rats, similar to the effect we and others have reported in young, growing rats. The PGE(2)-stimulated bone formation, which augments bone mass, most likely results from recruitment of osteoblasts from their bone marrow stromal precursors.

Keila S, Kelner A, Weinreb M
J. Endocrinol. Jan 2001
PMID: 11139777 | Free Full Text

Review: Vitamin K Reviewed by European Vitamin K Experts

Abstract

Beyond deficiency: potential benefits of increased intakes of vitamin K for bone and vascular health.

Vitamin K is well known for its role in the synthesis of a number of blood coagulation factors. During recent years vitamin K-dependent proteins were discovered to be of vital importance for bone and vascular health. Recommendations for dietary vitamin K intake have been made on the basis of the hepatic requirements for the synthesis of blood coagulation factors. Accumulating evidence suggests that the requirements for other functions than blood coagulation may be higher. This paper is the result of a closed workshop (Paris, November 2002) in which a number of European vitamin K experts reviewed the available data and formulated their standpoint with respect to recommended dietary vitamin K intake and the use of vitamin K-containing supplements.

Vermeer C, Shearer MJ, Zittermann A, Bolton-Smith C…
Eur J Nutr Dec 2004
PMID: 15309455 | Free Full Text

Accumulating evidence suggests that in many aspects arterial calcification mimics bone formation, which prompts interest in the effects of vitamin K on the vasculature. Previous population-based studies reported a significant reduction in aortic calcification with high vitamin K1 [62] and vitamin K2 intake [63], and a significant inverse correlation was found between vitamin K2 intake, and the incidence of both ischaemic heart disease and cardiovascular mortality [63]. Based on these findings the effect of treatment on arterial characteristics was monitored in the Maastricht osteostudy. These unpublished findings clearly demonstrated that supplementation with vitamin K1 can protect against vascular hardening and loss of arterial elasticity. High dose MK-4 also seems to have cholesterol lowering properties as shown in studies in rabbits [64] and humans [65].

[…]

Extremely high doses (45–90mg/day) of MK-4 have been used for the treatment of postmenopausal osteoporosis in Japan for several years [66, 67]. After the positive outcomes of the first clinical trials, the treatment is now used on a large scale; thus far, no adverse side-effects have been reported. A number of independent groups have claimed that this medication results in complete prevention of further bone loss in postmenopausal women, and in some women even a significant gain in BMD [68, 69]. The treatment was also reported to be successful in other groups at risk for bone loss such as haemodialysis patients and those treated with corticosteroids.

[…]

In considering the potential efficacy of pharmacological doses of MK-4 it should be noted that there is evidence for a secondary function of this analogue over and above its role in glutamate carboxylation. The available evidence (mainly from cell culture experiments) suggests that MK-4 (but not K1) may also be associated with production of interleukin-6, regulate the synthesis of PGE2 [83], or inhibit the mevalonate pathway in a comparable way to bisphosphonates [84], but at present only preliminary data exist.

[…]

Any risks associated with relatively high consumption of either K1 or K2 appear minimal, with intakes up to 1 mg/d K1 and 45 mg/d MK-4 often having been used without observed adverse events. Two possible exceptions exist. Firstly a potential problem relates to interference with oral anticoagulants. However, a systematic dose-response study among subjects on oral anticoagulant treatment demonstrated that the stability of anticoagulation was not significantly affected by vitamin K supplements at doses below 100 μg/day [14]. Secondly, preliminary studies have suggested that high vitamin K1 supplementation (i. e. above 1 mg/day) can contribute to periodontal disease via a bacterial mechanism on gingival tissue (S. Hodges, unpublished data).

 

 

PGE2 Stimulates Bone Resorption and Formation In Vitro

Abstract

PGE2 stimulates both resorption and formation of bone in vitro: differential responses of the periosteum and the endosteum in fetal rat long bone cultures.

The ability of PGE2 to stimulate bone resorption in vitro and in vivo is well established but the effects of this compound on bone formation are still controversial. Recent clinical reports have suggested that long-term infusion of PGE in infants with cyanotic heart diseases led to a stimulation of periosteal bone formation and to hyperostosis. In the present report, we describe the effects of PGE2 (10(-5) M) in bone organ cultures on bone resorption, measured by the release of 45Calcium and the number of osteoclasts in sections of cultured bones, and bone volume, by measuring separately medullary and cortical areas. PGE2 induced a marked increase in 45Ca release and in cortical and medullary osteoclast numbers over 4 days in vitro; despite this increase in bone resorption, cortical bone volume remained constant, indicating a parallel increase in bone resorption and formation at this site. Morphological and quantitative data demonstrated a higher extent of osteoblastic surface along the periosteum of PGE2-treated bones when compared with control cultures. Medullary bone volume, on the other hand, decreased sharply during the culture period, demonstrating a lack of parallel increase in bone formation at this site. It is concluded that, under these experimental conditions, prostaglandin E2 stimulated both resorption and formation along the periosteum and only bone resorption along the endosteum of the cultured bones. The overall effect of PGE2 on bone as a whole, however, was net bone loss.

Nefussi JR, Baron R
Anat. Rec. Jan 1985
PMID: 3985383

PGE2 Increases Bone Strength in Rats

Abstract

Prostaglandin E2 increases bone strength in intact rats and in ovariectomized rats with established osteopenia.

It is well documented that prostaglandin E2 (PGE2) has the ability to stimulate bone formation, improve bone structure, and increase bone mass in intact or osteopenic rat models. However, the effects of PGE2 on the mechanical properties of bone have not been investigated previously.The purpose of our study was to determine the effects of PGE2 on the mechanical strength of bones in rapidly growing, adult, and ovariectomized rat models. In study I, PGE2 at 3 mg/kg per day, or vehicle, was given by daily subcutaneous injections for 30 days to rapidly growing (3-month-old) intact male rats. Compared with controls, PGE2 significantly increased initial maximal load and stiffness of cancellous bone at the distal femoral metaphysis (DFM) as determined by an indentation test. As determined by a compression test, rats treated with PGE2 showed a significant increase in maximal load, and a nonsignificant increase in stiffness in the fifth lumbar vertebral body (L5) when compared with controls. In study II, PGE2 at 3 mg/kg per day, or vehicle, was given by daily subcutaneous injection for 30 days to mature (10-month-old) intact male rats. PGE2 treatment significantly increased initial maximal load and stiffness of the DFM and L5. PGE2 induced a significant increase in maximal load, but not stiffness, in the femoral neck (FN), as determined by a cantilever compression test. There was an increase in maximal load in a three-point bending test at the femoral shaft (FS) although the increase did not achieve statistical significance. No change in stiffness in the FS was found after PGE2 treatment. In study III, 3-month-old female rats were sham-operated or ovariectomized (ovx) for 30 days. Thereafter, PGE, at 1 or 3 mg/kg, or vehicle, were given by daily subcutaneous injection to these rats for 30 days. After 30 and 60 days, ovx induced a significant decrease in initial maximal load and stiffness of cancellous bone at the DFM as compared with sham controls. In ovx rats with established osteopenia, PGE2 at 1 mg/kg per day nonsignificantly increased the initial maximal load and stiffness, whereas, at 3 mg/kg per day, PGE2 completely restored the initial maximal load and stiffness of DFM to sham control levels. Similarly, maximal load and stiffness of L5 decreased significantly in ovx rats compared with sham controls at 30 days postsurgery. PGE2 at 1 mg/kg per day partially restored the maximal load, whereas, at 3 mg/kg per day, it completely restored the maximal load and stiffness of L5 in the established osteopenia, ovx rats. At the FS, PGE2 at 3 mg/kg per day nonsignificantly increased maximal load (+11%) and significantly increased stiffness (+25%) compared with ovx controls. Neither ovx nor PGE2 treatment caused a significant change in the maximal load and stiffness of the FN in this study. These results reveal that PGE2 significantly increased the mechanical strength at various skeletal sites in rapidly growing and mature male rats, although the increase in femoral shafts was not statistically different. Furthermore, PGE2 completely restored mechanical strength to the cancellous bone in ovx rats with established osteopenia.

Ke HZ, Shen VW, Qi H, Crawford DT…
Bone Sep 1998
PMID: 9737347