Alterations in geometry, biomechanics, and mineral composition of juvenile rat femur induced by nonplanar PCB‐155 and/or planar PCB‐169

Abstract

Exposure to widespread lipophilic and bioaccumulative polychlorinated biphenyls (PCBs) induces diverse biochemical and toxicological responses in various organs, including the bone. The aim of this study was to evaluate the changes in growth rate, geometry, serum, and bone biochemical parameters and biomechanics of juvenile rat femur induced by lactational exposure to nonplanar PCB-155 and planar PCB-169 individually and in combination. Fifteen lactating Wistar rats were divided into four groups (PCB-169, PCB-155, PCB-155+169, and control), and PCBs were administered intraperitoneally at different time points after delivery. Femurs from 22-day-old offspring were analyzed by microCT, three-point bending test and inductively coupled plasma-mass spectrometry (ICP-MS) to obtain data on bone geometry, biomechanics and mineral composition. The serum levels of calcium, phosphate and alkaline phosphatase were also determined. Lactational exposure to planar PCB-169 resulted in shorter and thinner femurs, reduced endosteal and periosteal perimeters, smaller total cross-sectional and medullary areas, and lowered serum bone marker levels and calcium levels in the bone, while femur mechanical properties were not significantly altered. The changes observed in the combination exposure (PCB-155+169) group were similar to those observed in the PCB-169 group but were less pronounced. In summary, our results demonstrate that alterations in lactationally exposed offspring were primarily induced by planar PCB-169. The milder outcome in the combined group suggested that the PCB-169-mediated toxic effects on the bone might be reduced by a nonplanar PCB-155 congener. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1135-1146, 2017.

Lactational exposure to dioxin-like polychlorinated biphenyl 169 and nondioxin-like polychlorinated biphenyl 155: Effects on rat femur growth, biomechanics and mineral composition

“…Our preceding study on prepubertal rat offspring (PND 22) revealed inhibitory effects of dioxin-like PCB-169, but not nondioxin-like PCB-155, on femur growth and mineralization (Brankovič et al, 2017). However, we encountered problems when performing biomechanical measurements on the developing prepubertal bones, i.e., on PND 22, femurs were insufficiently mineralized to be precisely assessed in a three-6 point-bending test (Brankovič et al, 2017). This challenge was not the case in rats from PND 35 onwards (Finnilä et al, 2010;Indrekvam et al, 1991).…”

“…A cerealbased fixed-formula maintenance diet for the rats (Altromin 1324, Lage, Germany) and water were administered ad libitum. After delivery, the mothers and their offspring were randomly divided into four groups and the PCB congener administration regimes with loading and maintenance doses were executed as previously described (Brankovič et al, 2017;Grošelj et al, 2014). This protocol was based on the TEF of PCB-169 (van den Berg et al, 2006) and the previously established excretion patterns of PCB-155 and PCB-169 in milk (Vrecl et al, 2005).…”

“…Thawed femurs were evaluated using a microCT scanner (Siemens Inveon MultiModality, Knoxville, TN, USA) and "Inveon Research Workplace" software (Siemens Medical Solutions USA, Inc., PA, USA). The procedure and protocols were conducted as reported previously (Brankovič et al, 2017). Femur length was measured from the top of the femur head to the most distal point of the medial condyle.…”

“…Exposure to PCBs and environmental organochlorines has been shown to affect bone mineral density in humans (Hodgson et al, 2008) and wild animals including polar bears (Daugaard-Petersen; Sonne et al, 2015), Baltic grey seal (Lind et al, 2003) and freshwater turtle (Ming-Ch'eng Adams et al, 2016). Bone studies in experimental animals reported biochemical and toxicological responses after exposure to TCDD (Herlin et al, 2013;Jämsä et al, 2001;Lind et al, 2009;Nishimura et al, 2009), environmental and commercial mixtures of chemical pollutants (Daugaard-Petersen et al, 2018;Elabbas et al, 2011aElabbas et al, , 2011bRamajayam et al, 2007) or individual PCBs (Brankovič et al, 2017;Gutleb et al, 2010;Lind et al, 2000). In young animals, after in utero and lactational exposure to TCDD, bone growth and mechanical strength were affected in wild-type AhR rats on postnatal day (PND) 40 (Miettinen et al, 2005), and bone mineralization was impaired in mice on PND 21 (Nishimura et al, 2009).…”

“…Despite a decade of experiments on PCB effects in bone tissue, information on its biomechanical behavior is still not comprehensive and often opposing. Our preceding study on prepubertal rat offspring (PND 22) revealed inhibitory effects of dioxin-like PCB-169, but not nondioxin-like PCB-155, on femur growth and mineralization (Brankovič et al, 2017). However, we encountered problems when performing biomechanical measurements on the developing prepubertal bones, i.e., on PND 22, femurs were insufficiently mineralized to be precisely assessed in a three-6 point-bending test (Brankovič et al, 2017).…”