Preeclampsia (PE) is a significant health problem in pregnancy, affecting 6–7% of all gestations and leading to fetal growth retardation, infant morbidity and mortality, premature birth, and maternal death. Currently, effective treatment options for PE are limited. This study aimed to evaluate the therapeutic potential of olive leaf extract (OLE) and nifedipine, alone and in combination, in improving pregnancy outcomes in rats induced with Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME). Rats were treated with single and combination treatments of nifedipine and OLE for four weeks, after being induced with L-NAME for six weeks. Following gestational day assessment and systolic blood pressure testing, the rats were sacrificed, and blood samples were collected for Neutrophil Gelatinase-Associated Lipocalin (NGAL), Malondialdehyde (MDA), proteinuria and Creatinine (SCr) Levels examinations. The results revealed the combination of nifedipine and OLE significantly improved the results of several biomarker analyses associated with PE, including increased NGAL levels, a significant decrease in MDA levels, decrease in proteinuria and elevated creatinine levels. The combination nifedipine and OLE treatment also exhibited a significant antihypertensive effect compared to either nifedipine or OLE monotherapy, as evidenced by the reduction in systolic and diastolic blood pressure levels. This study provides novel evidence for the potential of olive leaf extract as a nutraceutical adjunct for the prevention and treatment of PE. The significant improvements observed in several pathological features associated with PE, including antihypertensive effects, warrant further investigation. Future research should focus on elucidating the underlying mechanisms of action and exploring the clinical applicability of olive leaf extract in human populations with PE.

nifedipine, olive leaf extract, preeclampsia, rat model

Preeclampsia (PE) is a critical clinical condition that occurs after 20 weeks of pregnancy, affecting 5–10% of all pregnancies (Hayes-Ryan et al. 2021), responsible for over 70,000 maternal deaths and 500,000 fetal deaths worldwide every year. (Mihalceanu et al. 2019). Characterized by hypertension, proteinuria, hematological complications, and uteroplacental disorders (Magee et al. 2014), PE is marked by dysregulation of angiogenic factors like Soluble Fms-Like Tyrosine Kinase-1 (sFlt-1), leading to diminished levels of vascular endothelial growth factor (VEGF) and placental growth factor (PlGF), exacerbating endothelial dysfunction and vascular damage (Mlambo et al. 2023; Velegrakis et al. 2023). Additionally, heightened levels of Neutrophil Gelatinase-associated Lipocalin (NGAL) reflect inflammatory status and epithelial damage (Romejko et al. 2023), while excessive apoptosis in the placenta of PE women inhibits trophoblast invasion into spiral arteries, exacerbating placental ischemia and systemic endothelial damage (Jena et al. 2020).

The etiology of PE involves placental/trophoblast ischemia and hypoxia, oxidative stress, genetic predispositions, immune dysregulation, and vascular endothelial injury, contributing significantly to maternal morbidity and mortality (Abalos et al. 2013; Staff et al. 2013). Oxidative stress, characterized by an imbalance between oxidants and antioxidants, emerges as a significant factor, with lipid peroxide/Malondialdehyde (MDA) levels often elevated in preeclamptic patients (Skytte et al. 2023). Excessive apoptosis in trophoblast villi can damage the placenta and lead to fetal death and developmental disorders. Once caspase-3 is activated, cell death in the form of apoptosis will occur (Suparman et al. 2018).

Effective and safe pharmacological treatment of PE is still lacking. The complex etiology and high demand for safety profiles because of pregnancy are major hurdles for drug development for pre-eclampsia. Currently, due to anti-platelet and anti-inflammatory properties, low-dose aspirin is recommended for preventing or delaying the onset of pre-eclampsia (Mirabito et al. 2020). Unfortunately, recent studies suggest that the efficiency of low-dose aspirin in pre-eclampsia appears only to be modest or even non-responsive (Yang et al. 2022) and high-dose aspirin is prohibited because of potential adverse effects such as birth defects (Muzaffar et al. 2023). This prompted researchers to pursue alternative treatment regimens to improve the clinical management of PE (Bonnet et al. 2021).

Medicinal plants have become a promising sources for drug development (Abdallah et al. 2023), Olive leaf extract (OLE/ Olea europaea L.), renowned for its antioxidant (Akbari et al. 2022), anti-inflammatory (Tasneem et al. 2019), and vasodilatory properties(McNeill and Jurgens 2006), has garnered attention for its potential in mitigating PE pathogenesis (Silvani et al. 2020). OLE contains bioactive compounds like oleuropein that may mitigate placental ischemia, oxidative stress, and apoptosis in PE (Yang et al. 2022). Moreover, study on the effects of OLE at a single dose and in combination with common medication such as nifedipine for the treatment of PE are still limited. Nifedipine, a calcium channel blocker, has shown promise in managing hypertension and oxidative stress in various clinical and experimental settings (Ding et al. 2017; Yang et al. 2022). However, their efficacy in treating PE warrants further investigation, particularly in preclinical models.

This study aimed to evaluate the therapeutic potential of olive leaf extract (OLE) to improve clinical outcomes (systolic and diastolic) and biomarkers in pre‑eclampsia Rats model induced by Nω-nitro-l-arginine methyl ester hydrochloride (L-NAME). L-NAME inhibits nitric oxide synthase (NOS), reducing nitric oxide (NO) production and leading to vasoconstriction (narrowing of blood vessels) and increased blood pressure, which are characteristic features of preeclampsia. It is considered a standard model for inducing preeclampsia-like symptoms in rats.

To the best of our knowledge, this is the first study to investigate the potential therapeutic effects of olive leaf extract (OLE) in clinical features (i.e., systolic and diastolic blood pressure) and several biomarkers, such as Neutrophil Gelatinase-Associated Lipocalin (NGAL), Malondialdehyde (MDA), proteinuria and Serum Creatinine (SCr) levels outcomes of rats with pre-eclampsia-like symptoms. This study showed that the combination of nifedipine and OLE significantly improved the results of several biomarkers compared to single treatments.

The progressive deterioration of key physiological parameters over the course of preeclampsia pathogenesis was evident in our study. The steady rise in systolic and diastolic blood pressure underscores the severity of hypertension associated with this condition (Angeli et al. 2011; Stuart et al. 2018). Elevated proteinuria levels are also indicative of glomerular endothelial dysfunction and impaired renal hemodynamics in pre-eclampsia (Garovic 2000). Furthermore, the marked increase in creatinine over time highlights the risk of renal injury and dysfunction (Faiz 2020; MacDonald et al. 2022).

The improved blood pressure regulation could be attributed to the antihypertensive action of nifedipine as a calcium channel blocker coupled with the vasodilatory effects of olive leaf phenolic compounds (Abu-Amara and Meselhy 2016). Reduced proteinuria indicates improved glomerular permeability, which may be mediated by lowered oxidative stress and reduced endothelial activation (Kermanshah et al. 2020). The reno-protective effects, as evidenced by declining creatinine, could arise from reduced renal apoptosis and improved renal hemodynamics (Lafayette et al. 1998). However, the exact molecular mechanisms underlying these physiological effects remain unclear.

OLE also exhibited significant antihypertensive effects, lowering both systolic and diastolic blood pressure in PE rats model. This reduction in blood pressure was consistent with previous studies in Italy highlighting the vasodilatory properties of olive phenolics, particularly oleuropein, which enhance nitric oxide (NO) bioavailability and endothelial function (Ahamad et al. 2019). By preserving nitric oxide signaling disrupted in PE and attenuating oxidative stress-induced vascular damage, OLE likely contributes to improved vascular health and blood pressure regulation. Furthermore, olive leaf extract supplementation markedly reduced proteinuria levels. Proteinuria stems from glomerular endothelial damage and podocyte dysfunction, and is a hallmark of PE predictive of adverse maternal and fetal outcomes (Garovic 2000). The nephroprotective effects of olive leaf extract may be mediated by enhanced endothelial integrity and mitigated oxidative stress and inflammation, suggesting potential to alleviate renal injury in PE (Abu-Amara and Meselhy 2016).

Additionally, biomarker analysis provided insights into molecular mechanisms. We observed that the combination of olive leaf extract (OLE) with nifedipine led to a more significant decrease in soluble Fms-like tyrosine kinase-1 (sFlt-1) levels compared to either treatment alone. This combination may have a synergistic effect in improving placental perfusion and maternal endothelial function. Nifedipine, a calcium channel blocker, is known for its antihypertensive effects, which can help alleviate hypertension in preeclampsia. Additionally, OLE’s ability to modulate dysregulation of these angiogenic factors contributes to endothelial dysfunction in PE (Levine et al. 2004; Agrawal et al. 2019). By restoring this balance between pro- and anti-angiogenic factors, olive leaf extract may improve placental perfusion and maternal endothelial function, promoting better pregnancy outcomes. The observed decrease in soluble Fms-like tyrosine kinase-1 (sFlt-1) and increase in placental growth factor (PlGF) provides insights into the molecular mechanisms of olive leaf extract. sFlt-1 is an anti-angiogenic factor produced by the placenta that sequesters and inhibits the pro-angiogenic PlGF, leading to widespread maternal endothelial dysfunction in preeclampsia (Levine et al. 2004). Oleuropein (OLE) and hydroxytyrosol, bioactive phenolics in olive leaf extract, have been shown to suppress sFlt-1 production and secretion by placental tissues and endothelial cells (Abu-Amara and Meselhy 2016). This may occur by downregulating hypoxia-inducible transcription factors and preventing sFlt-1 mRNA expression and protein accumulation induced by placental oxidative stress (Kermanshah et al. 2020). Additionally, olive leaf extract may directly stimulate PlGF secretion by activating the Akt/eNOS pathway and enhancing VEGF-mediated PlGF expression (Han et al. 2005). By suppressing placental sFlt-1 overproduction and stimulating endothelial PlGF secretion, olive leaf extract can restore balance between these factors. This combination therapy may improve placental vascular development, systemic endothelial quiescence, and vascular tone regulation, thereby alleviating hypertension and proteinuria to improve pregnancy outcomes in preeclampsia.

OLE treatment showed reduced caspase-3 expression, indicating suppressed apoptosis, which is implicated in improper placentation and trophoblast turnover in preeclampsia (Allaire et al. 2000). The bioactive phenolics in OLE, such as oleuropein and hydroxytyrosol can inhibit apoptosis by modulating Bcl-2 proteins, preventing cytochrome c release, and inhibiting caspase activation (Bulotta et al. 2013). OLE also lowered malondialdehyde (MDA) levels, indicating reduced lipid peroxidation resulting from placental oxidative damage in preeclampsia (Kermanshah et al. 2020). Oleuropein can attenuate MDA production by enhancing antioxidant enzyme activities, decreasing NADPH oxidase activity, and scavenging reactive oxygen species (ROS) (Abu-Amara and Meselhy 2016). Additionally, OLE reduced neutrophil gelatinase-associated lipocalin (NGAL) levels, a biomarker of renal tubular injury. This reno-protective effect may occur via suppressed renal macrophage infiltration and inflammation by downregulating NF-kB activity (Han et al. 2005). The antioxidant effects of olive leaf extract likely also protect against renal oxidative damage that can cause NGAL upregulation. Overall, the reduction in apoptosis, oxidative stress, and renal injury markers highlights the multifaceted therapeutic potential of olive leaf extract in preeclampsia through modulation of pathways including inflammation, oxidative stress, and apoptosis. The combination therapy of nifedipine and OLE led to a further decrease in average caspase-3 levels compared to OLE treatment alone, suggesting a synergistic effect in suppressing apoptosis. Nifedipine, known for its calcium channel blocking properties, may complement OLE’s anti-apoptotic effects by improving placental perfusion and reducing oxidative stress, thereby further reducing apoptosis. This combination therapy plays a crucial role in improving placental health and pregnancy outcomes in PE by targeting multiple pathways, including inflammation, oxidative stress, and apoptosis.

The synergistic effects observed with combination therapy of nifedipine and olive leaf extract suggest that olive leaf extract may complement standard antihypertensive drugs like nifedipine to enhance efficacy while minimizing side effects. Nifedipine is a calcium channel blocker that lowers blood pressure by relaxing vascular smooth muscle and dilating peripheral arteries and arterioles (Xu et al. 2021). Oleuropein and hydroxytyrosol in olive leaf extract have been shown to induce acute endothelium-independent vasodilation in animal models of hypertension, possibly by interfering with calcium influx into vascular smooth muscle (Abu-Amara and Meselhy 2016). This complementary vasodilatory mechanism may underlie the enhanced antihypertensive action of the combination therapy. Furthermore, long-term intake of oleuropein-enriched olive leaf extract has been found to reduce blood pressure in genetic hypertension by improving vascular function and attenuating inflammation and oxidative stress, effects associated with angiotensin converting enzyme (ACE) inhibition (Singh et al. 2008). The combination of these long-term vascular benefits with nifedipine’s acute vasodilatory effects likely contributes to the synergistic blood pressure lowering efficacy of the combination therapy. The multi-targeted actions of olive leaf bioactive on pathways like oxidative stress, ACE activity, and vascular function highlight the value of integrating this herbal therapy with conventional drugs like nifedipine for a more effective management of hypertension in preeclampsia.

While this study provides valuable insights into the potential therapeutic effects of olive leaf extract (OLE) and nifedipine in a rat model of preeclampsia, several limitations should be acknowledged. The study focused on a limited set of physiological and molecular parameters, and further research is needed to explore the broader effects of OLE and nifedipine on maternal and fetal outcomes. The mechanisms underlying the observed effects were not fully elucidated, and future studies should aim to clarify the molecular pathways involved. Additionally, the long-term safety and efficacy of OLE and nifedipine in pregnant individuals remain to be established. Finally, the study did not assess the potential interactions between OLE and nifedipine with other medications commonly used in pregnancy, which could be important for clinical application.

This study highlights the potential of olive leaf extract (OLE) as a nutraceutical adjunct in the management of preeclampsia, both alone and in combination with nifedipine. The results demonstrate that the combination therapy of OLE and nifedipine exhibits synergistic effects, suggesting that OLE may complement conventional antihypertensive drugs to enhance efficacy while minimizing side effects. However, further research is needed to elucidate the molecular mechanisms involved and to evaluate the clinical safety and efficacy of OLE in human trials, paving the way for the development of novel treatment strategies.

The author has no funding to report.

The author has declared that no competing interests exist.

This study was supported by the Ministry of Health of the Republic of Indonesia’s study leave fund. Thank you to Azwar Djaajsinga’s parents, in-laws, husband, children and extended family for all their support so far. The author also thanks Mr. Ikhwan Yuda Kusuma for his direction, input and motivation in making this article.