title: P-glycoprotein activity in human Caucasian male lymphocytes does not follow its increased expression during aging.
abstract: P-glycoprotein (P-gp) is a transmembrane protein that mediates the efflux of innumerous structurally unrelated compounds. It was initially found over-expressed in tumor cells, associated to a multidrug resistance phenotype (MDR). Then, P-gp was found constitutively expressed in excretory cells/tissues and in circulating cells, such as lymphocytes. Considering the importance of this transporter in the establishment of therapeutic protocols and the existence of contradictory results, this study aimed at evaluating the influence of aging in the expression and function of P-gp in human lymphocytes, comparing two different methodologies to assess both parameters. P-gp activity and expression were evaluated in lymphocytes isolated from whole blood samples of 65 healthy caucasian male donors, divided into two groups according to age (group 1: under 30-years old; group 2: above 60-years old). P-gp expression was assessed using the anti-P-gp monoclonal antibody, UIC2, in the presence and in absence of vinblastine (Vbl). P-gp activity was evaluated measuring the efflux rate of the fluorescent P-gp substrate rhodamine 123 (Rho 123) and also using UIC2 shift assay. Flow cytometric analysis was performed to assess all the proceedings. Furthermore, P-gp expression and each of the P-gp activity determination methods were compared, through correlation analysis and linear regression models. We observed a significant age-dependent increase in mean P-gp expression (p = 0.029), which was not reflected in the transporter's activity (p > 0.050). Statistical analysis allowed selection of UIC2 shift assay over Rho 123 efflux assay as a more selective method to assess P-gp activity. Despite the significant correlation between P-gp expression and P-gp activity found in lymphocytes (Gp1(group 1)-r = 0.609, p < 0.001; Gp2-r = 0.461, p = 0.012), using UIC2 shift assay, these data reinforce the need for P-gp activity assessment, rather than P-gp expression determination alone, when starting new therapeutic regimens with P-gp substrates, especially in men older than 60 years of age.
authors: Departamento de Ciências Biológicas, Universidade do Porto, Rua Aníbal, Cunha, Porto, Portugal. v_vilasboas@yahoo.com
authors: Vânia
authors: V
authors: Vilas-Boas
authors: Renata
authors: R
authors: Silva
authors: A Rita
authors: AR
authors: Gaio
authors: Ana Margarida
authors: AM
authors: Martins
authors: Sofia Costa
authors: SC
authors: Lima
authors: Anabela
authors: A
authors: Cordeiro-da-Silva
authors: Maria
authors: M
authors: de Lourdes Bastos
authors: Fernando
authors: F
authors: Remião
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging / Q000235:genetics / Q000378:metabolism*; D000911:Antibodies, Monoclonal / Q000032:analysis*; D000972:Antineoplastic Agents, Phytogenic / Q000737:chemistry; D005434:Flow Cytometry / Q000379:methods*; D005456:Fluorescent Dyes / Q000032:analysis; D015870:Gene Expression; D006801:Humans; D008214:Lymphocytes / Q000166:cytology / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D012044:Regression Analysis; D020112:Rhodamine 123 / Q000032:analysis*; D014747:Vinblastine / Q000737:chemistry; D044465:White People
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000911:Antibodies, Monoclonal; D000972:Antineoplastic Agents, Phytogenic; D005456:Fluorescent Dyes; D020112:Rhodamine 123; D014747:Vinblastine