4. Discussion
Ovariectomy is a preclinical model for post-menopausal osteoporosis and is considered the first choice, most commonly used for such studies (17,18), and recommended by the Food and Drug Administration (19). This experimental model has bone loss characteristics similar to osteoporosis in post-menopausal women. From the age of three months, when they are in the reproductive phase, rodents respond appropriately to the deficiency of sex hormones acquired due to ovariectomy. In this experimental model, in addition to bone loss, there is hypercholesterolemia, an increase in bone remodeling markers, a decrease in calcium absorption, and the protective effect of obesity on bone loss resulting from estrogen deficiency (20).
In this study, ovariectomized rats developed bone alterations similar to those observed during osteoporosis due to hypoestrogenism. As indicated by a decrease in femur weight, bone calcium content, an increase in alkaline phosphatase concentration, deformity of the microarchitecture of the epiphyses, a decrease in the number of osteocytes, and the absence of osteoblasts. Treatment with estrogen suppressed the effects of estrogen deficiency in most parameters. These results are in line with several studies that have used ovariectomy as a model for inducing osteoporosis in vivo (21-24).
In contrast to the clear bone-related benefits of HRT, its uncertain popularity has culminated in a clinical need for well-tolerated nutritional options that can be used safely after menopause and that effectively prevent bone loss and the development of osteoporosis. The phytonutraceutical OrmonaⓇ is a phytocomplex composed of 40% oil extract of annatto (Bixa orellana), with the same composition as ChronicⓇ (25,26). Among these 40%, ~10% are mainly δ-tocotrienols and ~28% are geranylgeraniol. In addition, it contains 20.8% red clover extract (Trifolium pratense), standardized with isoflavones such as daidzein, genistein, Biochanin A, and formononetin. 10% of the formulation is composed of a standardized extract of açaí (Euterpe oleracea) standardized with anthocyanins (mainly cyanidin 3-O-glucoside) (10).
Estrogens are directly involved in regulating energy homeostasis and are crucial in modulating food intake and energy expenditure. The literature reports that reduced levels of estradiol (E2, the main ovarian estrogen) after menopause in women and ovariectomy (OVX) in rodents lead to hyperphagia and reduced energy expenditure (EE), inducing overall weight gain (27-29). There is evidence that the effects of estradiol on food intake are regulated by estrogen receptors in the hypothalamus (for example, the arcuate nucleus - ARC and the hypothalamic paraventricular nucleus - PVN) and also in the nucleus of the solitary tract in the brainstem. However, which estrogen receptor is involved has yet to be made clear (30).
Contrary to what is observed in the literature (28,29,31), in this study, no increase in weight or food intake was observed in the OVX group. However, the "classical view" of estrogen action has been widely regarded as canonical dogma, as it integrates well not only the actions of E2 on the energy balance but also its effects on the hypothalamic-pituitary-gonadal (HPG) axis. A recent study (32) shows that the effect of E2 on eating depends on nutritional status.
However, there was a significant increase in weight in the ADS group. These animals’ higher food consumption could partly explain this. As weight gain occurred in parallel with food consumption in this study, demonstrating that the increase in weight induced by ovariectomy, which has been reported previously (33-35), can be attributed to food efficiency or possible changes in energy metabolism and deprivation of estrogenic activity since this was the only group that did not have estrogen hormone replacement.
The results of the hormonal profile showed that ovariectomy caused a significant decrease in the concentration of serum estradiol and progesterone in the OVX group. In contrast, the group treated only with the phytonutraceutical Ormona® showed a higher serum estradiol level (p < 0.005). Similar results were obtained in previous studies (36,37), which determined the dose-dependent pro-estrogenic profile in ovariectomized rats treated with increasing concentrations of T. pratense extract. Supplementation with T. pratense for 6 weeks increased estrogen and progesterone levels in mice. This result of estrogenic activity can be attributed to isoflavones (38).
Among the isoflavones found in the T. pratense species, four bind competitively to ERα and ERβ receptors (genistein > daidzein > biochanin A > formononetin) with affinities approximately one-thousandth of 17β-estradiol (39,40). In the phytonutraceutical Ormona®, 5.4% daidzein, 2.3% glycitein, and 3.6% genistein were identified (10), justifying the potent estrogenic activity performed by Ormona®.
In 2000, the North American Menopause Society (NAMS) published an evidence-based consensus on the role of isoflavones in menopausal health. Although the health effects observed in humans cannot be attributed to isoflavones alone, it has become clear that foods or products containing these substances have some physiological effects, mainly cardiovascular benefits. Since Ormona® phytonutraceutical is a product that combines various bioactives, the composition of this product favors its use for improving the health of premenopausal and menopausal women (41).
It was also observed that the group treated with the combination of Ormona® + estradiol showed a reduced osteogenic profile (p < 0.005). This result can be explained in part by the potential drug interaction between T. pratense and other anti-osteoporotic drugs, such as tamoxifen since studies report that preparations containing T. pratense can interfere with the steady-state mRNA levels of the main drug-metabolizing enzymes. This interference can be either by induction, as in the case of CYP3A2, or inhibition/suppression, as in the case of CYP 1A2, 2B1/2, 2C11, 2E1. Both situations can lead to changes in the metabolism of coadministered drugs (42).
Furthermore, it can be inferred that the ovariectomized rats model lacks an endogenous estrogen environment, as the higher endogenous estrogen environment can cause competition between isoflavones and estradiol for receptor binding sites, and therefore, the weaker estrogenic potency of isoflavones, as well as the different binding preferences to the α and β Estrogen Receptors (ERs) can lead to an anti-estrogenic effect. In a higher estrogen environment, isoflavones act in vitro as antiestrogens, while in a low estrogen environment, they act as estrogens, which is characteristic of a post-menopausal situation (40,43,44).
Another aspect to consider is the low serum estrogen concentration in the ORM+EST group. The competition for the same binding site between estradiol (an endogenous estrogen) and phytoestrogens (" plant-origin estrogens") is a topic discussed in the scientific literature. Some studies suggest phytoestrogens may have weaker estrogenic effects due to competition for estrogen receptors, leading to decreased serum estrogen levels. However, it is important to note that the extent of this competition and its effects on serum estrogen levels may vary according to several factors, including the amount and type of phytoestrogens consumed, the duration of exposure, and individual characteristics. In addition, studies on this topic can present conflicting results, and there needs to be a clear consensus on the effects of phytoestrogens on regulating serum estrogen levels (38,39).
In terms of biochemical parameters (
Figure 3), higher levels of cholesterol (TC), LDL, and triglycerides (TG) were observed in the OVW group, while HDL was not affected. These higher levels were explained by the increase in LDL cholesterol in the OVW group and corroborate other studies that have shown hypercholesterolemia in ovariectomized rats, reporting an association between estrogen deficiency and early onset changes in hepatic cholesterol and triacylglycerol synthesis (45-47).
Women in hypoestrogenic conditions are susceptible to various lipid metabolism disorders after menopause since epidemiological and prospective studies associate estrogen with a relevant role against metabolic syndrome precisely because it has effects on many organ systems that contribute to cardiovascular protection, including the regulation of hepatic lipid metabolism and serum lipoprotein levels (48,49).
The group treated with estrogen (EST) showed lower levels of TC, LDL, and higher HDL (p < 0.01), but it was unable to prevent an increase in TG compared to the negative control group. This can be explained by the hepatic action of estradiol (E2), which regulates the rate of synthesis of structural apolipoproteins for VLDL and HDL, reduces the rate of synthesis of apoB-100 while stimulating the synthesis of apoA-I and apoA-II. The HDL fraction containing apoA-I and apoA-II is necessary for the degradation of chylomicrons and VLDL and for the direct and indirect transportation of cholesterol to the liver. Furthermore, in hepatocytes, estrogens stimulate the synthesis of apoC-III while decreasing the synthesis of hepatic lipase (LH) (49-51).
Meanwhile, both OrmonaⓇ (ORM) and Ormona in combination with estrogen (ORM+EST) reduced TC and TG levels and increased HDL levels. These effects can be explained by the composition of the phytonutraceutical OrmonaⓇ, which has phytochemical markers such as geranylgeraniol and tocotrienols from B. orellana, which can reduce the biosynthesis of cholesterol and triglycerides by negatively regulating HMG-CoA reductase (HGMR) (14,52-54). In addition, reports show that supplementation with T. pratense (the main component of OrmonaⓇ) reduced LDL and TG levels in mice. Phytoestrogens, by inhibiting 7a-hydroxylase and estrogenic effects on the LDL receptor, modulate the PCSK9 enzyme to decrease LDL (37,55).
The significant increase in aspartate aminotransferase (AST) and alanine aminotransferase (ALT) following the administration of estradiol (EST) may be associated with various factors, including direct and indirect effects of estradiol on the liver or hyperandrogenemia. During hepatic metabolization, estradiol can increase blood flow to the liver. This hyperactivation of liver metabolism can cause damage to hepatocytes, releasing AST and ALT into the bloodstream. In addition, the liver can produce toxic by-products that can damage liver cells and release AST and ALT (56).
Although the OVW group showed a higher serum alkaline phosphatase (ALP) serum, the differences were not statistically significant (
Table 1). Despite this, the treated groups showed lower levels of ALP, demonstrating a modulating action on bone metabolism. Measuring biochemical markers of bone metabolism leads to understanding bone transition in advanced age. ALP is a component of the cell membrane of many body tissues, with the highest concentrations of this enzyme found in bone cells (osteoblasts) and the liver. ALP is increased in skeletal system diseases associated with increased osteoblastic activity and bone remodeling (57,58). Studies have reported increased ALP in ovariectomized rats (59-63).
The deposition of calcium salts in the process of osteogenesis is a process dependent on the nutritional state of the bone and immunological and biochemical factors (64). When assessing the total weight of the femur, the ORM group had a statistically higher bone mass (p < 0.05) compared to the OVW (
Figure 5). Similarly, the ORM group also had higher Ca2+ levels than the OVW and ADS groups (p < 0.05). These results were confirmed in the SEM images, where observation of the microstructure of the femur showed the epiphysis of the cancellous bone preserved (
Figure 6), indicating the osteoprotective action of Ormona
Ⓡ.
In the current study, histopathological evaluation revealed that treatment of ovariectomized rats with OrmonaⓇ resulted in an increase in the thickness of the femoral shaft compared to the OVW group and a decrease in the trabeculae. There was also an increase in the number of osteocytes, the presence of osteoblasts, and the absence of osteoclasts. These results align with the observations of other researchers, who have reported the protective action of T. pratense against bone alterations characteristic of osteoporosis due to hypoestrogenism (21,40,65-68).
Also present in OrmonaⓇ, geranylgeraniol (GGOH) may play an osteoprotective role, as observed in a previous study by our research group (14). Exogenous GGOH may inhibit osteoclast formation by suppressing the receptor activating NF-κB ligand expression (69). However, the mechanism of action proposed for the osteoprotective, and anabolic action of the phytoestrogens present in OrmonaⓇ is based on specific effects on osteoblasts and osteoclasts in vitro and in vivo.
The most abundant isoflavones in T. pratense, biochanin A and formononetin, are metabolized into genistein and daidzein, respectively (70,71). In vitro studies, it has been shown that the phytoestrogens daidzein (72,73), genistein (74,75), biochanin A, and formononetin (73,76,77) promote the differentiation and growth of osteoblasts and stimulate the formation and prevention of bone resorption by regulating calcium absorption, the intestinal microbiota, and various metabolic pathways. By mobilizing bone calcium into the circulation, isoflavones enhance calcium homeostasis during the calcium uptake (65,68,78).
Phytoestrogens are selective modulators of estrogen receptors (ER). Their main affinity is for the beta type (β-RE), which is more present in bone cells, especially in osteoblasts responsible for bone formation. Genistein, daidzein, biochanin A, and formononetin have been implicated in the estrogenic activity of T. pratense and have been shown to competitively bind to ERα and ERβ with similar affinities to 17-β estradiol (72,79,80).
Clinical data on the action of isoflavones shows that aglycones (most commonly found in fermented products) have beneficial effects against bone loss due to estrogen deficiency in women compared to the glycoside form of isoflavones. With this, the EFSA ratified the safety of isoflavones for women in a more comprehensive report (81).
Therefore, ascorbic acid from Myrciaria dubia extract tends to act as a catalyst, favoring the acid hydrolysis necessary to absorb these phytoestrogens. This is due to the pharmacokinetic aspect, since the absorption rates of isoflavones are favored at acidic pH, as it is necessary to break the bonds with the sugars present in the molecule, enabling the release of the aglycones present in glycosylated isoflavones, such as glycitein and daidzein (82).
Zhu et al. (82) showed that ascorbic acid prevented bone density loss in ovariectomized mice, suggesting that the nutrient may help prevent osteoporosis. The combined action of ascorbic acid and polyphenols present in M. dubia extract (approximately 1797.0 mg EAG.100g-1) provides antioxidant effects and benefits against menopausal symptoms (82).
Osteoprotegerin (OPG) and receptor activator ligand NF-j B (RANKL) are crucial in bone remodeling. The modulation of these factors has profound effects on bone formation and resorption. Interleukin 6 (IL-6) can inhibit apoptosis and directly increase the activity of osteoclasts, thus prolonging their lifespan and promoting bone loss by activating OPG/RANKL/RANK (osteoprotegerin/receptor activator of nuclear factor kappa B ligand/receptor activator of the nuclear factor kappa B) (83,84). In contrast, genistein and daidzein could suppress IL-6 release and increase OPG production dose-dependent (85).
In osteoblasts, genistein stimulates their proliferation (osteoblast-like cells MC3T3-E1) and protects against oxidative cell damage from free radicals (86), increases collagen synthesis, and prevents apoptosis in MC3T3-E1 (87). However, in vitro studies show that genistein can inhibit bone resorption by osteoclasts by inhibiting the formation and differentiation of osteoclastic cells from bone marrow cells and induces apoptosis of osteoclasts in their mature form through the mechanism of Ca 2+ channels. This suppressive effect of genistein on these bone cells is due to partial inhibition of protein tyrosine kinase and activation of protein tyrosine phosphatase (88-90).
In vivo tests with subcutaneous administration of genistein in ovariectomized rats showed an increase in the number of osteoblasts (91). Similarly, treatment with daidzein and 17β-estradiol has been shown to affect the maturation and activity of osteoclasts in vitro, providing evidence of inhibition of osteoclast differentiation by the mechanism of apoptosis of their specific precursors (92).
The formation of osteoclasts is regulated in response to the secretion of osteoclast differentiation factor (RANKL) and osteoprotegerin (OPG). RANKL is produced by osteoblasts or osteogenic stromal cells, and it is involved in the formation of osteoclast-like cells, the fusion of osteoclast precursor cells, and bone resorption. OPG inhibits osteoclastogenesis by masking RANKL in osteoblasts or osteogenic stromal cells. Phytoestrogens decreased RANKL mRNA levels and increased OPG mRNA levels through specific inhibition of topoisomerase II (topo II) and protein tyrosine kinase (93).
Therefore, this research shows that the results with the phytonutraceutical OrmonaⓇ were favorable for regulating the activities of bone cells, providing a possible way to support the regulation of menopause-related osteoporosis symptoms in women. However, simultaneous administration with synthetic estrogens requires greater attention, as possible anti-estrogenic activity has been observed. The effects of OrmonaⓇ on the skeletal system of estrogen-deficient rats differed from those exerted by estradiol, indicating a more complex mechanism of action.