title: Smoke carcinogens cause bone loss through the aryl hydrocarbon receptor and induction of Cyp1 enzymes.
abstract: Smoking is a major risk factor for osteoporosis and fracture, but the mechanism through which smoke causes bone loss remains unclear. Here, we show that the smoke toxins benzo(a)pyrene (BaP) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) interact with the aryl hydrocarbon receptor (Ahr) to induce osteoclastic bone resorption through the activation of cytochrome P450 1a/1b (Cyp1) enzymes. BaP and TCDD enhanced osteoclast formation in bone marrow cell cultures and gavage with BaP stimulated bone resorption and osteoclastogenesis in vivo. The osteoclastogenesis triggered by BaP or RANK-L was reduced in Ahr(-/-) cells, consistent with the high bone mass noted in Ahr(-/-) male mice. The receptor activator of NF-κB ligand (RANK-L) also failed to induce the expression of Cyp1 enzymes in Ahr(-/-) cells. Furthermore, the osteoclastogenesis induced by TCDD was lower in Cyp1a1/1a2(-/-) and Cyp1a1/1a2/1b1(-/-) cultures, indicating that Ahr was upstream of the Cyp enzymes. Likewise, the pharmacological inhibition of the Cyp1 enzymes with tetramethylsilane or proadifen reduced osteoclastogenesis. Finally, deletion of the Cyp1a1, Cyp1a2, and Cyp1b1 in triple knockout mice resulted in reduced bone resorption and recapitulated the high bone mass phenotype of Ahr(-/-) mice. Overall, the data identify the Ahr and Cyp1 enzymes not only in the pathophysiology of smoke-induced osteoporosis, but also as potential targets for selective modulation by new therapeutics.
authors.affiliation: Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19147, USA.
authors.forename: Jameel
authors.initials: J
authors.lastname: Iqbal
authors.forename: Li
authors.initials: L
authors.lastname: Sun
authors.forename: Jay
authors.initials: J
authors.lastname: Cao
authors.forename: Tony
authors.initials: T
authors.lastname: Yuen
authors.forename: Ping
authors.initials: P
authors.lastname: Lu
authors.forename: Itai
authors.initials: I
authors.lastname: Bab
authors.forename: N Adrian
authors.initials: NA
authors.lastname: Leu
authors.forename: Satish
authors.initials: S
authors.lastname: Srinivasan
authors.forename: Sagie
authors.initials: S
authors.lastname: Wagage
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Hunter
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Nebert
authors.forename: Mone
authors.initials: M
authors.lastname: Zaidi
authors.forename: Narayan G
authors.initials: NG
authors.lastname: Avadhani
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000096:biosynthesis* / Q000172:deficiency / Q000235:genetics; D001564:Benzo(a)pyrene / Q000633:toxicity; D001862:Bone Resorption / Q000209:etiology* / Q000378:metabolism* / Q000473:pathology; D002273:Carcinogens / Q000633:toxicity*; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics; D019388:Cytochrome P-450 CYP1A2 / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics; D065633:Cytochrome P-450 CYP1B1; D004195:Disease Models, Animal; D004790:Enzyme Induction / Q000235:genetics; D005260:Female; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity; D018336:Receptors, Aryl Hydrocarbon / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D012906:Smoke / Q000009:adverse effects*; D012907:Smoking / Q000009:adverse effects / Q000235:genetics; D014026:Nicotiana / Q000633:toxicity
chemical_list: D002273:Carcinogens; D000072317:Polychlorinated Dibenzodioxins; D018336:Receptors, Aryl Hydrocarbon; D012906:Smoke; D001564:Benzo(a)pyrene; D001189:Aryl Hydrocarbon Hydroxylases; C585496:CYP1B1 protein, human; C585498:Cyp1b1 protein, mouse; D019363:Cytochrome P-450 CYP1A1; D019388:Cytochrome P-450 CYP1A2; D065633:Cytochrome P-450 CYP1B1
keywords: bone formation; osteoblast; skeletal remodeling; toxicology