Epidemiological, aetiological and prognostic aspects of canine primary bone cancer, with a view to its human counterpart

Osteosarcoma (OSA) is the most common histological subtype of primary bone cancer in both humans and dogs. The importance of this relatively rare malignancy in humans is underlined by the fact that it typically affects children and adolescents, constituting about 5% of paediatric cancers (<15 years (y) of age). Although a rare disease in the canine population as well, certain breeds of dogs have a lifetime risk approaching 10%, thereby affecting a large proportion of these dogs. Hence, OSA has a major impact on the health within such breeds. The overall incidence rate in canines outnumbers that of the human population, inspiring the use of dogs with naturally occurring OSA as models for its human counterpart. Furthermore, similar clinical and epidemiological features of this disease are seen in the 2 species. Knowledge regarding risk factors for developing OSA is scarce in both dogs and humans. A better understanding of the aetiology and pathogenesis could generate ideas for novel treatment options, and identifying markers for progression of the disease may help optimise individualised therapy.Osteosarkom (OSA) er den vanligste histologiske formen for primær benkreft hos både mennesker og hunder. Viktigheten av denne relativt sjeldne kreftformen understrekes av at den hovedsakelig rammer barn og ungdom; den utgjør omtrent 5 % av kreftsykdommene som rammer barn under 15 år. Osteosarkom er sjelden hos hunder også, men rammer opp til 10 % av hunder innen visse raser i løpet av livet. Sykdommen får derfor store konsekvenser for helsen til disse rasene. Alt i alt er OSA vanligere hos hund enn menneske, noe som har ført til bruk av hunder med naturlig forekomst av OSA som modeller for tilsvarende sykdom hos mennesker. Dette komparative aspektet styrkes av kliniske og epidemiologiske likheter ved denne kreftformen hos de to artene. Kunnskap om risikofaktorer for utviklingen av denne sykdommen er mangelfull hos både hund og menneske. En bedre forståelse av årsaksfaktorer for utvikling av OSA kan generere hypoteser som fører til nye behandlingsformer, samt identifisere markører som kan indikere progresjon av sykdommen og tilrettelegge for individuelle behandlingsprotokoller

An investigation of the effect of oestrogen on longitudinal growth

In the absence of readily available physiological models of human growth, the effects of oestradiol on the human C28/I2 chondrocyte cell line were studied. The classical oestrogen receptors, ERα and ERβ, were shown to be expressed in both murine and human chondrocyte cell lines. Oestradiol and related chemicals, which alter the function of the oestrogen receptors (ER), were exploited to tease out the different functions of each ER in the growth plate. In the absence of foetal bovine serum, oestradiol had no effect on proliferation, differentiation or apoptosis of chondrocyte cells in monolayer culture or on the growth of the foetal metatarsal culture system. In addition, oestradiol did not convey a protective effect on chondrocytes exposed to the pro-inflammatory cytokines, tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in monolayer culture. However, endogenous oestrogen appears to play an important role in maintaining chondrocyte proliferation in monolayer culture and mineralisation in metatarsal culture as reflected by the inhibitory effects of Faslodex, the non-specific ER antagonist, on chondrocytes and metatarsals in culture. In the presence of methyl-piperidino-pyrazole (MPP), a selective ERα antagonist, and raloxifene, a selective oestrogen receptor modulator with higher ERβ binding affinity, a reduction in chondrocyte proliferation and increase in apoptosis was observed in murine and human chondrocytes. Similarly, a marked reduction in linear growth occurred when foetal murine metatarsals were exposed to MPP and raloxifene in combination. A less marked reduction in growth was observed in MPP-treated metatarsals. These findings suggest that the oestrogen receptors may have opposing actions in the growth plate with ERβ acting like a brake on chondrocyte growth and ERα promoting growth. ERβ may regulate cell proliferation through control of cell cycle modulators affecting G1/S phase transition as MPP and raloxifene in combination reduced cyclin E and p53 levels on Western blot analysis. The aim of the second part of my thesis was to investigate the effect of oral oestrogen on linear growth in girls with primary ovarian insufficiency (POI). A retrospective review of girls with POI treated at a tertiary endocrinology clinic over an 11 year period was performed. As expected the majority of girls with POI had Turner syndrome (TS; 83.7%). Non-TS associated POI was rare and the leading cause was iatrogenic secondary to the effects of total body irradiation for bone marrow transplantation (12.8%). A significant proportion of these girls developed POI after full pubertal development so few cases were available to investigate the effect of oestrogen on growth. The oral oestrogen regime followed in individual patients with TS was highly variable so it was not possible to assess the effects of dose on height velocity or bone maturation in this retrospective audit. However, the second clinical study examined in detail the effect of oestrogen on growth in TS girls who received a standardised course of oral ethinylestradiol for pubertal induction and a standard dose of growth hormone (10 mg/m2/week). These girls participated in a prospective randomised double-blind placebo-controlled multi-centre study of growth promoting treatment in TS. The girls were initially randomised to oxandrolone or placebo at 9 years of age and further randomised to oral ethinylestradiol at 12 or 14 years of age. The results of this study are embargoed until published. The laboratory effects of oestradiol found in this thesis suggest that ERα may stimulate or maintain growth, and ERβ may inhibit growth. The obvious question is how these observations might be involved in the complex relationship between puberty, oestrogen and height velocity in humans. As affinity studies show that the half maximal effective concentration (EC50) of ERα is achieved at slightly lower concentrations of oestradiol than ERβ it is conceivable that the ERα effect could predominate at lower systemic oestradiol concentrations and that ERβ could become more important at higher concentrations for example in later puberty. Alternatively, it is possible that the expression of ERα reduces or ERβ increases in the growth plate after reaching peak height velocity

Normal bone growth requires optimal estrogen levels: negative effects of both high and low dose estrogen on the number of growth plate chondrocytes

Endochondral bone formation at epiphyseal growth plate consists of the synchronized processes of chondrogenesis and cartilage ossification. Estrogen, the major female sex hormone, plays an important role in this process, particularly during the pubertal growth spurt. However, its effects on the growth plate are not completely understood. The aims of this study were to clarify the effects of estrogen on the kinetics of chondrocytes in the growth plates of 10- to 25-week-old female rabbits by studying the effects of ovariectomy or high-dose administration of estrogen on the balance between cell proliferation and death. Forty-eight Japanese white rabbits were divided into three groups: sham operated, ovariectomized, or ovariectomized with subsequent weekly injection of high dose estrogen from 10 weeks. The chondrocyte kinetics was investigated by histomorphometry and immunohistochemistry, using antibodies for caspase-3, a marker of apoptosis, and for proliferating cell nuclear antigen. Both ovariectomized and estrogen-injected rabbits showed a declination of the chondrocyte number although the latter animals indicated a more dramatic effect. Estrogen-injected rabbits showed a decrease in the cell proliferating ability together with an increase in chondrocytes undergoing apoptosis while ovariectomy mainly reduced the cell proliferating ability. Given the known importance of estrogen for bone growth, one would expect that ovariectomy and high-dose administration of estrogen would have opposite effects. However, the present study indicated that both low and high concentration had a similar effect: a decrease in the chondrocyte number compared with control, suggesting that estrogen has to be maintained within a narrow range for optimal bone growth