Phytoestrogenic Effects of Equisetum arvense (Horsetail) Extract in an Oestrogen-deficient Rat Model: An Experimental Study

Introduction: Postmenopausal osteoporosis, primarily driven by oestrogen deficiency, is characterised by reduced bone mass, compromised microarchitecture, and increased fracture risk. Hormone Replacement Therapy (HRT) is effective but associated with serious adverse effects such as increased risks of breast cancer and cardiovascular events prompting interest in plant-based phytoestrogens. Equisetum arvense (EA) (field horsetail), rich in flavonoids and silica, is traditionally used for bone health, yet its oestrogenic potential in oestrogen deficient models remains underexplored. Aim: To assess the oestrogen-like activity of EA (horsetail) extract in an oestrogen deficient rat model (ovariectomised rats) by analysing both histological features and biochemical parameters. Materials and Methods: The present preclinical experimental animal study was conducted at Cape Bio Lab and Research Centre, Marthandam, Tamil Nadu, India, between January and June 2023, 54 female Albino Wistar rats (three-month-old, 200- 220 g) were bilaterally ovariectomised to induce oestrogen deficiency. One-month postsurgery, rats were divided into sham operated, Ovariectomised (OVX) control, and treatment groups. The treatment groups received both E. arvense extract (60 mg/ kg/day) and estradiol for 45 and 90 days. After overnight fasting, blood samples were collected via retro-orbital plexus under anaesthesia. Serum samples were analysed for biochemical parameters, including osteocalcin, Alkaline Phosphatase (ALP), Liver Function Tests (LFTs), and Renal Function Tests (RFTs). Femur bones were harvested for histological examination at the end of treatment. Results: Phytochemical analysis of EA's ethanolic extract revealed a diverse array of secondary metabolites, including carbohydrates, proteins, flavonoids, saponins, glycosides, tannins, phenolics, and fixed oils. OVX rats displayed notable bone loss and elevated markers of bone resorption, hepatic stress, and renal dysfunction. Treatment with E. arvense, especially over 90 days, significantly improved bone architecture (p<0.01), lowered Osteocalcin and ALP levels (p=0.63) and normalised LFT (p<0.001) and RFT markers (p=0.004). Protein profiles also returned to near-normal levels (p<0.05). The effects were comparable to those observed in estradiol-treated groups, with no statistically significant difference between the two treatment arms. The current study revealed that supplementation with EA notably enhanced bone microarchitecture and normalised critical biochemical markers in OVX rats. Conclusion: The EA exhibited significant phytoestrogenic, bone-protective, hepatoprotective, and nephroprotective effects in OVX rats. These findings highlight its promise as a natural alternative to Oestrogen replacement therapy for managing postmenopausal symptoms, warranting further clinical evaluation.