Elsevier

Toxicology Letters

Volume 98, Issue 3, 15 September 1998, Pages 195-202
Toxicology Letters

Effect of three polychlorinated biphenyls on f-met-leu-phe-induced degranulation in rat neutrophils

https://doi.org/10.1016/S0378-4274(98)00117-9Get rights and content

Abstract

It has been known that polychlorinated biphenyl (PCB) mixtures and individual congeners produce degranulation of rat neutrophils. Structure–activity relationships for congeners PCB 8 (2,4′-dichlorobiphenyl), PCB 126 (3,3′,4,4′,5-pentachlorobiphenyl) and PCB 128 (2,2′,3,3′,4,4′-hexachlorobiphenyl) were examined by correlating the extent of degranulation and cytotoxicity with molecular and physico-chemical parameters. Neutrophils were exposed to PCB congeners and then to the neutrophil activator f-met-leu-phe (fmlp). Degranulation and cytotoxicity were quantified by measuring released myeloperoxidase and lactate dehydrogenase activities, respectively. Degranulation in the absence of fmlp, that is in quiescent neutrophils, was detected only for PCB 8. Inhibition of fmlp-induced degranulation was observed for both PCB 8 (50 μM) and PCB 128 (10 and 50 μM). PCB 126 did not affect degranulation of quiescent or fmlp-stimulated neutrophils. Thus, effects on degranulation were observed only for ortho-substituted congeners. Cytotoxicity was observed under all conditions with PCB 8, in quiescent neutrophils with PCB 128, and in activated neutrophils with PCB 126. Structure–activity relationships revealed that effects of PCBs on neutrophil degranulation correlate with the energy of the lowest unoccupied molecular orbital but not with torsional angle 2,1,1′,2′. This study demonstrates the importance of molecular, electronic parameters in PCB-induced effects on neutrophil degranulation.

Introduction

Polychlorinated biphenyls (PCBs) are organic compounds which are present as environmental contaminants in almost the entire food web (Evans et al., 1991). Their slow rates of metabolism and high liposolubilities allow them to bioaccumulate in an extension which may depend on the content of total lipid in the organism (Ali et al., 1997). A broad spectrum of biological effects has been associated with individual PCB congeners as well as mixtures, including induction of hepatic enzymes (McFarland and Clarke, 1989), cancer, alterations in reproduction, immunotoxicity (Safe, 1994), and neurobehavioral effects (Kimbrough, 1995).

In addition to effects on cells of the specific immune system, PCBs affect the function of polymorphonuclear neutrophils involved in inflammation. Activation of neutrophils initiates a cascade of intracellular events that leads to enzyme release, oxidative burst, chemotaxis and aggregation. These responses are essential for killing pathogens (Sha'afi and Molski, 1988). Exposure of isolated, rat neutrophils to Aroclor mixtures of PCBs causes them to generate superoxide anion and to undergo degranulation (Ganey et al., 1993). Moreover, pretreatment with PCBs alters the response of neutrophils to subsequent exposure to other stimuli. Phorbol ester-induced superoxide anion production is increased by exposure to PCBs, whereas degranulation stimulated by the peptide N-formyl-met-leu-phe (fmlp) is inhibited. It has been established that some PCBs activate neutrophils to undergo oxidative burst through stimulation of the production of inositol phosphates (Tithof et al., 1995) and arachidonic acid (Tithof et al., 1996), as well as through calcium-dependent mechanisms (Brown and Ganey, 1995). These activities are, in general, associated with ortho-substituted PCB congeners and not with coplanar, dioxin-like PCBs. Less is known about mechanisms involved in PCB-induced degranulation of neutrophils, and only limited structure–activity data are available. In this work we report the effect of in vitro exposure to three different PCB congeners on neutrophil degranulation in quiescent and fmlp-activated cells. The molecular properties that may be responsible for this action are discussed.

Section snippets

Chemicals

PCB congeners 8 (2,4′-dichlorobiphenyl), 126 (3,3′,4,4′,5-pentachlorobiphenyl) and 128 (2,2′,3,3′,4,4′-hexachlorobiphenyl) were purchased from ChemService, (West Chester, PA). Fmlp and cytochalasin B were obtained from Sigma (St. Louis, MO).

Isolation of rat, peritoneal neutrophils

Neutrophils were isolated from the peritoneum of male, Sprague–Dawley, retired breeder rats by glycogen elicitation as described previously (Hewett and Roth, 1988). Isolated neutrophils were resuspended in 1 ml Hanks' balanced salt solution (HBSS), pH 7.35,

Results

Fig. 2Fig. 3Fig. 4 show the effects of PCB congeners on degranulation and cytotoxicity of neutrophils, expressed as percentage of total MPO and LDH released, respectively. In the absence of stimulation with fmlp, PCB 8 caused neutrophil degranulation at 10 and 50 μM. Neither PCB 126 nor PCB 128 stimulated release of MPO (Fig. 2A). PCB 8 was cytotoxic to quiescent neutrophils at 10 and 50 μM, PCB 128 caused release of LDH at 50 μM, and PCB 126 was not cytotoxic at any concentration tested (Fig. 2

Discussion

Stimulation of degranulation in quiescent neutrophils and attenuation of fmlp-induced degranulation in the same cells have been observed for the PCB mixture Aroclor 1242 and for the congener PCB 47 (2,2′4,4′-tetrachlorobiphenyl) (Ganey et al., 1993). From the studies presented here it is clear that the patterns of activity for PCB congeners are structure dependent. For this study, three PCB congeners were chosen which differ in chlorine content (di, penta and hexa) and pattern of chlorine

Acknowledgements

This work was supported by NIH Grant ESO4911. The authors give thanks to SGI facility (NSF Grant CHE9321436) from the Chemistry Department of Michigan State University. Jesus Olivero is sponsored by the Scholarship Colciencias-Fulbright-Laspau, Santa Fé de Bogota, Colombia.

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