title: Identification of a P-glycoprotein-deficient subpopulation in the CF-1 mouse strain using a restriction fragment length polymorphism.
abstract: There is a subpopulation of the CF-1 mouse strain that is very sensitive to the neurotoxicity induced by the avermectins, a class of natural products widely used in veterinary and human medicine as anti-parasitic agents. This sensitivity results from a lack of P-glycoprotein in the intestine and brain of sensitive animals, allowing increased penetration of these compounds in the blood and brain, respectively. We describe a restriction fragment length polymorphism that is able to predict which animals will be deficient in this protein, confirming at the genetic level a heterogeneous population of this mouse strain. Breeding studies demonstrated that the inheritance of the markers follows a normal Mendelian autosomal pattern. Sensitive "-/-" animals are deficient in P-glycoprotein in those tissues known to express primarily mdr1a, but have normal P-glycoprotein levels in tissues known to express primarily mdr1b or mdr2, suggesting that the defect in the sensitive animals is limited to the mdr1a gene. The P-glycoprotein expression in the brain is dependent on the genotype, which also determines the susceptibility to the avermectin-induced neurotoxicity, with the "-/-" animals being most sensitive, and the "+/-" animals having less P-glycoprotein and therefore increased CNS sensitivity compared to the "+/+" animals. The ability to segregate this strain into -/- and +/+ animals may prove useful for examining the physiological role of P-glycoprotein in drug absorption and distribution and related toxicity. These data also provide a warning that experiments carried out with P-glycoprotein substrates in the heterogeneous population of the CF-1 mouse must be interpreted with caution.
authors.affiliation: Department of Safety Assessment, Merck Research Laboratories, West Point, Pennsylvania 19486, USA.
authors.forename: D R
authors.initials: DR
authors.lastname: Umbenhauer
authors.forename: G R
authors.initials: GR
authors.lastname: Lankas
authors.forename: T R
authors.initials: TR
authors.lastname: Pippert
authors.forename: L D
authors.initials: LD
authors.lastname: Wise
authors.forename: M E
authors.initials: ME
authors.lastname: Cartwright
authors.forename: S J
authors.initials: SJ
authors.lastname: Hall
authors.forename: C M
authors.initials: CM
authors.lastname: Beare
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000172:deficiency / Q000235:genetics*; D000818:Animals; D005260:Female; D005838:Genotype; D007559:Ivermectin / Q000633:toxicity; D008297:Male; D051379:Mice; D012150:Polymorphism, Restriction Fragment Length
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D007559:Ivermectin