Increased [3H]phorbol ester binding in rat cerebellar granule cells by polychlorinated biphenyl mixtures and congeners: structure-activity relationships.
Our previous reports indicate that polychlorinated biphenyl (PCB) congeners in vitro perturbed cellular Ca2+ homeostasis and protein kinase C (PKC) translocation. We have now studied the structure-activity relationship (SAR) of 3 PCB mixtures, 24 PCB congeners, and 1 dibenzofuran for their effects on PKC translocation by measuring [3H]phorbol ester ([3H]PDBu) binding in cerebellar granule cells (7 days in culture). All the PCB mixtures studied increased [3H]PDBu binding significantly and in a concentration-dependent manner. However, Aroclor 1016 and Aroclor 1254 were more potent than Aroclor 1260. Of the 24 congeners studied, di-ortho congeners such as 2,2',5,5'-tetrachlorobiphenyl (-TeCB), 2,2',4,6,6'-pentachlorobiphenyl (-PeCB), 2,2',4,6-TeCB, and 2,2'-dichlorobiphenyl (-DCB) were the most potent (E50 = 28-43 microM) while non-ortho congeners such as 3,3',4,4'-TeCB and 3,3',4,4'5-PeCB were not effective. The potential contaminant of PCB mixtures, 1,2,3,7,8-pentachlorodibenzofuran had no significant effect on [3H]PDBu binding. The SAR among these congeners revealed: (i) congeners with ortho-chlorine substitution such as 2,2'-DCB (EC50 = 43 +/- 3 microM) or ortho-lateral (meta, para) chlorine substitution such as 2,2',5,5'-TeCB (EC50 = 28 +/- 3 microM) and 2,2'4,6-TeCB (E50 = 41 +/- 6 microM) were most potent; (ii) congeners with only para-substitution such as 4,4'-DCB or high lateral content in the absence of ortho-substitution such as 3,3',4,4',5,5'-HCB were not effective; and (iii) increased chlorination was not clearly related to the effectiveness of these congeners, although hexa- and heptachlorination was less effective than di- and tetrachlorination. Low lateral substitution, especially without para-substitution, or lateral content in the presence of ortho-substitution, may be the most important structural requirement for the in vitro activity of these PCB congeners in neuronal preparations.
Cellular and Molecular Toxicology Branch, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711.
P R
PR
Kodavanti
T R
TR
Ward
J D
JD
McKinney
H A
HA
Tilson
D000704:Analysis of Variance; D000818:Animals; D001140:Aroclors / Q000633:toxicity; D001572:Benzofurans / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D001665:Binding Sites; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D020111:Chlorodiphenyl (54% Chlorine); D003198:Computer Simulation; D004305:Dose-Response Relationship, Drug; D005260:Female; D015240:Phorbol 12,13-Dibutyrate / Q000378:metabolism*; D011078:Polychlorinated Biphenyls / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D011247:Pregnancy; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
D001140:Aroclors; D001572:Benzofurans; C026987:aroclor 1260; D020111:Chlorodiphenyl (54% Chlorine); C027386:Aroclor 1016; D015240:Phorbol 12,13-Dibutyrate; C023614:dibenzofuran; D011078:Polychlorinated Biphenyls; D011493:Protein Kinase C