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.
Kodavanti
P R
PR
Cellular and Molecular Toxicology Branch, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711.
Ward
T R
TR
McKinney
J D
JD
Tilson
H A
HA
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