Mice need time to adjust

Plan for:

• Initial reduction in food intake and weight loss
• Daily observation of animal tolerance — consult your IACUC for monitoring metrics
• Intervene when necessary

Other researchers have the following advice

If intake seems to be a problem:

• Determine if a lower dose is effective for your model by conducting a tamoxifen dose feeding trial
• Gradually acclimate mice by mixing tamoxifen-containing pellets with regular feed pellets
• Wet the food, then place in a dish inside the cage (requires daily replacement)
• Feed tamoxifen diet on weekdays, regular diet on weekends
• Alternate weeks (two weeks on tamoxifen diet, one week off) for longer treatments

Safe handling of tamoxifen diets

• Tamoxifen is a selective estrogen receptor modulator (SERM) meaning it can repress actions of estrogen or have pro-estrogen effects
• Usual dose for therapeutic effects in humans is 20 mg/day. Tamoxifen diets for rodents typically contain ~one to two mg/pellet
• Accidental tamoxifen exposure can be minimized by using typical lab precautions of lab coat, gloves, and mask when handling the diet.
• Your chemical safety department should be contacted for additional institution specific guidelines for handling and disposal of tamoxifen containing diets.

Key points from literature

• Length of treatment varies from one to two weeks^1,2,5,6,7,8 to one to two months^3,4,8
• Pure tamoxifen1,5,8 and tamoxifen citrate^1,2,3,4,6,7 are both effective
  Usual tamoxifen doses are ~40-80 mg per kg body weight per day
• Typical inclusion for pure tamoxifen is 250 mg8 or 500 mg1,5 and for tamoxifen citrate is 400 mg per kg diet^1,2,3,4,6,7
• Initial weight loss of ten % is reported^1,2,4,7,8, associated with reduced food intake²
• Subsequent recovery of body weight after returning to regular diet may be compromised by gene inactivation^2,7

Selected tamoxifen references

¹ Andersson KB, Winer LH, Mork HK, Molkentin JD, Jaisser F. 2010. Tamoxifen administration routes and dosage for inducible Cre-mediated gene disruption in mouse hearts. Transgenic Res 19:715-725.

² Chiang PM, Ling J, Jeong YH, Price DL, Aja SM, Wong PC. 2010. Deletion of TDP-43 down-regulates Tbc1d1, a gene linked to obesity, and alters body fat metabolism. Proc Natl Acad Sci USA 107:16320-16324.

³ Kardakaris R, Gareus R, Xanthoulea S, Pasparakis M. 2011. Endothelial and macrophage-specific deficiency of P38alpha MAPK does not affect the pathogenesis of atherosclerosis in ApoE-/- mice. PLoS One 6:e21055.

⁴ Kiermayer C, Conrad M, Schneider M, Schmidt J, Brielmeier M. 2007. Optimization of spatiotemporal gene inactivation in mouse heart by oral application of tamoxifen citrate. Genesis 45:11-16.

⁵ Koitabashi N, Bedja D, Zaiman AL, Pinto YM, Zhang M, Gabrielson KL, Takimoto E, Kass DA. 2009. Avoidance of transient cardiomyopathy in cardiomyocyte-targeted tamoxifen-induced MerCreMer gene deletion models. Circ Res 105:12-15.

⁶ Kratsios P, Catela C, Salimova E, Huth M, Berno V, Rosenthal N, Mourkioti F. 2009. Distinct roles for cell-autonomous Notch signaling in cardiomyocytes of the embryonic and adult heart. PCirc Res 106:559-572.

⁷ Miro-Murillo M, Elorza A, Soro-Arnaiz I, Albacete-Albacete L, Ordonez A, Balsa E, Vara-Vega A, Vazquez S, Fuertes E, Fernandez-Criado C, Landazuri MO, Aragones J. 2011. Acute Vhl gene inactivation induces cardiac HIF-dependent erythropoietin gene expression. PLoS One 6:e22589.

⁸ Welle S, Burgess K, Thornton CA, Tawil R. 2009. Relation between extent of myostatin depletion and muscle growth in mature mice. Am J Physiol Endocrinol Metab.Oct;297(4):E935-40.