Effect of nicotine on RANKL and OPG and bone mineral density.
OBJECTIVE
The signaling pathway OPG/RANK/RANKL is a key in maintaining the balance between the activity of osteoblasts and osteoclasts in order to prevent bone loss. In this study, our aim was to assess the effects of long-term nicotine exposure on plasma RANKL and OPG levels, tissue RANKL and OPG immunoreactivities, and bone mineral density (BMD) scores in rats.


METHODS
Thirty-six Swiss Albino rats weighing 70 ± 10 g were divided into three groups. While the controls (n = 12) were only given normal drinking water, for low-dose nicotine (LDN) group (n = 12) 0.4 mg/kg/day; for high-dose nicotine (HDN) group (n = 12), 6.0 mg/kg/day nicotine was added to drinking water for a year. At the end of 12th month, BMD scores were measured using an X-ray absorptiometry and bone turnover was assessed by measuring plasma RANKL and OPG levels and RANKL and OPG immunoreactivities in tail vertebrae of the rats.


RESULTS
There was no statistically significant difference in BMD scores of lumbar spine and femoral regions of the nicotine groups in comparison to controls. Plasma OPG levels were found to be significantly higher in HDN group, in comparison to the controls and LDN groups (p = .001) unlike plasma RANKL levels. Tissue RANKL and OPG immunoreactivities decreased significantly in the LDN and HDN groups (p < .001, p < .01, respectively).


CONCLUSIONS
The results of this study show that nicotine is not primarily responsible for the decrease in BMD frequently seen in smokers. Measuring plasma RANKL and OPG levels did not reflect tissue immunoreactivities.
1Department of Medical Biochemistry, Faculty of Medicine, Ege University, Izmir, Turkey.
Soycan
S
Mizrak
Volkan
V
Turan
Sevinc
S
Inan
Aysegul
A
Uysal
Candeger
C
Yilmaz
Gülinnaz
G
Ercan
D015502:Absorptiometry, Photon; D000284:Administration, Oral; D000818:Animals; D015519:Bone Density / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005260:Female; D008297:Male; D023421:Models, Animal; D009538:Nicotine / Q000008:administration & dosage / Q000494:pharmacology*; D053244:Osteoprotegerin / Q000378:metabolism*; D053245:RANK Ligand / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012307:Risk Factors; D013131:Spine / Q000187:drug effects / Q000378:metabolism*
D053244:Osteoprotegerin; D053245:RANK Ligand; C506032:Tnfrsf11b protein, rat; D009538:Nicotine
BMD; Nicotine; OPG; RANKL; immunohistochemical staining; rat