Effect of long-term treatment with low-dose phytoestrogens on the calcitonin-gene related peptide and substance p protein and gene expression of lumbosacral dorsal root ganglia in male rats

Abstract

Lumbosacral dorsal root ganglion (DRG) regulates pain and sexual behaviors through sensory neuropeptides calcitonin-gene related peptides (CGRP) and substance P (SP). These neuropeptide syntheses regulated by female sex steroids has been suggested. Soybean phytoestrogens, genistein or daidzein, revealed both estrogenic and anti-estrogenic effects in many organs. High-dose genistein or daidzein supplementation interrupted male reproductive organs growth and function but low doses of phytoestrogens contaminated in daily consuming products such as soymilk have never been investigated for their neuromodulatory effect in adult males. Therefore, this study aimed to examine genomic effects of low-doses of genistein and daidzein on CGRP- and SP- mRNA and protein expressions in DRG neurons of adult male rats using real time reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemical analysis (IHC), respectively. Adult male Wistar rats were daily subcutaneously injected with vehicle, 17-estradiol (E2 0.1-10 µg/kg BW), genistein or daidzein (250-1000 µg/kg BW) for consecutive 35 days. Body weight and food intake were daily recorded. DRGs (L1-S2) were collected and prepared for real-time RT-PCR or the IHC. The weight of testes and accessory sex organs were evaluated for the disrupted effects of chemical treatment. In the present study, genistein or daidzein did not exhibit any effects on reproductive organs in male rats, whereas E2 reduced body weight gain and accessory organ weight weight. However, daidzein but E2 or genistein induced PPT-A gene encoding substance P expression in both lumbar and sacral DRG by 3-4 folds. In contrast to mRNA expression, E2 increased sacral neuropeptides CGRP- and SP-expressed neuron subpopulations. However, genistein but daidzein significantly decreased CGRP- and SP-expressed neurons (>80%) in sacral DRG. Therefore, long-term exposure with low-dose genistein or daidzein but E2 has negatively regulatory effects on the expression of CGRP and SP neuropeptides that mediated pain and sensation without the male reproductive organs disruption. These evidences may provide the new insights for daily consuming of soybean phytoestrogens as an anti-nociceptive and anti-inflammatory compound in neuropathic pain