Potential pharmacodynamic interactions of losartan and common herbal medicines, cumin, green tea, and cinnamon in L-NAME-induced hypertensive rats

2.1 Study protocol and animal groups

This study was approved by the Research Ethics Committee at King Saud University (KSU-SE-18–27, 24/12/2018). This study was conducted under a well-controlled environment (23°C/50-55% RH) using an ISO cage N-Biocontainment System type ISO36NSA^® (Tecniplast^®, Varese, Italy) in addition to a regular 12 h day/night cycle, and animals were provided with ad libitum access to food and water. Wistar rats were divided into five groups (n = 5) and received the following treatments. Group I, normal rats; Group II, animals were given a single daily oral dose of L-NAME (40 mg/kg) only. Group III, animals received a single oral daily dose of L-NAME (40 mg/kg) and CU 200 mg/kg. Group IV, animals were treated with a single oral daily dose of L-NAME (40 mg/kg) and GT 200 mg/kg. Group V, animals were administered a single oral daily dose of L-NAME (40 mg/kg) and CN 200 mg/kg was given to hypertensive rats. Following treatment with a single oral dose of LT (10 mg/kg), the groups were designated as follows: Group II as LT, Group III as CU + LT, Group IV as GT + LT, and Group V as CN + LT. Animals from Group II to Group V were treated with L-NAME (40 mg/kg) once per day for 2 weeks in order to induce HTN (Ahad et al. 2020). The L-NAME/herbal treatment was carried out for 14 days. Rats were defined as hypertensive when their systolic blood pressure (SBP) reached or exceeded 150 mm Hg.

The rats were fasted overnight on the 13^th day. On day 14, the initial blood pressure measurement was recorded at a time point of 0 h. Subsequently, the respective doses of L-NAME + herb were administered, and blood pressure was monitored at predefined time points over a 12-h period. Water and food were then available to the animals without restrictions. On day 15, the daily dose of L-NAME and the respective herb were administered. Later on, on the 15^th day, the rats were subjected to overnight fasting. On the 16^th day, the initial blood pressure measurement was recorded at 0 h. Subsequently, the respective doses of L-NAME + the herb + drug were administered, and then the blood pressure was measured at the predetermined time points.

2.2 Induction of HTN

To study the effects of herbs (CU, GT, and CN) on the pharmacodynamics of antihypertensive agent (LT), HTN was induced in healthy h albino Wistar rats (250 ± 50 g) by oral administration of L-NAME. L-NAME induced HTN model, which is known for its rapid induction of HTN as well as the ability to mimic the target-organ damage associated with HTN complications in humans (Lerman et al. 2019). L-NAME induces HTN by inhibiting the endothelial nitric oxide synthase (eNOS) enzyme, causing the depletion of NO and, therefore, making it impossible for the blood vessels to dilate, which, in turn, causes the endothelial wall to stiffen. Further, L-NAME administration causes the structural alteration of arteries by increasing the expression of the cyclooxygenase-2 enzyme as well as the formation of cyclooxygenase-2-dependent endothelium-derived constricting factors (Paulis et al. 2008) such as prostacyclin and thromboxane A₂. Furthermore, the superoxide (O^-₂) formed through the endothelial cyclooxygenase pathway reacts with NO to produce peroxynitrite, so in addition to inhibiting NO production, the NO, which is produced reacts with the superoxide, thereby further reducing the NO level (Lüscher et al. 1992). It should also be noted that L-NAME has the ability to produce pathological manifestations such as endothelial dysfunction and organ damage affecting the heart and kidneys that are similar to those seen in hypertensive patients through the indirect oxidation of tetrahydrobiopterin (Chia et al. 2021; Sonoda et al. 2017). This causes eNOS to uncouple and produce reactive oxygen species whilst also further elevating the oxidative stress level (Chia et al. 2021; Sonoda et al. 2017). Additionally, (Rincón et al. 2015) showed that NO inhibition causes renal damage due to the overexpression of the angiotensin II type 1 receptor (AT1) in the kidneys. Furthermore, supporting evidence has been provided of HTN being induced by L-NAME via the activation of the sympathetic nerve system and renin-angiotensin-aldosterone system (Biancardi et al. 2007).

2.3 Preparation and administration of herbs and losartan

The selected herbs CU, GT, and CN were ground into coarse/fine powder. Fresh dispersions of herbs were prepared each day prior to administration. The herb powder was dispersed into a small volume of normal saline before gradually adding the remaining volume of normal saline while stirring continuously until the desired volume was reached. This was followed by a sonication. The herbal dispersions of CU, GT, and CN were given to the respective animal groups orally at a dose equivalent to 200 mg/kg (Abd El-Baky 2013; Abdelrahman et al. 2023a; Abdelrahman et al. 2023b; Kalaivani et al. 2013; Sharafeldin Rizvi 2015; Srinivasan 2018a). LT tablets were crushed in a mortar and dissolved in normal saline with a final concentration of 1 mg/mL. Rats treated with LT received a dose equivalent to 10 mg/kg.

2.4 Monitoring the rats’ blood pressure

A non-invasive tail-cuff method was used to measure rats’ blood pressure using the Visitech BP-2000 series II instrument. To minimize stress-induced variations in blood pressure, rats were acclimatized to the restraint procedure for seven days prior to data collection. This training ensured the animals were familiar with the experimental conditions. A pharmacodynamic study of LT with and without herbs was performed by recording SBP, DBP, MAP, and HR values of each animal for up to 12 hours.

2.5 Statistical analysis

The statistical comparison was calculated using one-way ANOVA Dunnett’s test, significance level p<0.05, using GraphPad InStat^®.

3.1 Cumin - losartan pharmacodynamic interactions

CU treatment demonstrated a modest effect on the rats’ blood pressure. Both the SBP and DBP of rats treated with CU started to decline at a slow rate after 4 h (Fig. 1). The lowest reading for SBP was 157.80 ± 7.73 mmHg at 12 h. Similarly, DBP reached its lowest level of 108.20 ± 6.65 mmHg at 12 h. The reduction of 7.07% and 7.36% for SBP and DBP was noted at 12 h in comparison with rats in the hypertensive control group.

Rats treated with CU + LT presented a maximum drop in SBP and DBP at 4 h, with SBP and DBP values of 142.40 ± 4.22 mmHg and 80.40 ± 3.58 mmHg, respectively (Fig. 1). There was a reduction in SBP and DBP by 18.35% and 30.93% at 4 h as compared to the hypertensive control group. The duration of the antihypertensive effect of the combination of CU and LT was slightly longer than when LT alone was administered, and the SBP was not elevated as much, 145.60 ± 5.81 mmHg at 12 h compared to 155.00 ± 4.69 for LT alone. When CU and LT are used together, the improvements in HR are comparable to those achieved with LT alone (Fig. 1).

3.2 Green tea - losartan pharmacodynamic interactions

This study also demonstrated that the GT treatment had a notable antihypertensive effect over 12 h. Rats treated with GT showed SBP of 160.00 ± 5.48 mmHg, DBP of 103.40 ± 10.21 mmHg, and MAP of 121.60 ± 8.08 mmHg, which are lower by 7.3%, 13.69% and 10.98% respectively, compared to the hypertensive control group at the 0 h time point (Fig. 2).

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Fig. 2.

Illustration showing effect of LT, GT, and GT + LT on rats (a) SBP (b) DBP (c) MAP and (d) HR, *p<0.05 in comparison with hypertensive controls.

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The mean HR value was found 368.60 ± 10.31 beats/min, which is improved by 10.82% (Fig. 2). While at 12 h, GT presented SBP of 151.60 ± 4.56 mmHg, DBP of 100.80 ± 3.83 mmHg, and MAP 117.20 ± 3.11mmHg which are lower by 10.72%, 13.70% and 12.41% respectively, in comparison to the hypertensive control rats at 12 h time point (Fig. 2). The mean HR value was found 343.20 ± 4.92 beat/min, which is improved by 3.19% only (Fig. 2). The maximum effect on SBP was observed 12 h after the administration of GT with SBP of 151.60 ± 4.56 mmHg. Meanwhile, 95.00 ± 4.36 mmHg was the maximum reduction in DBP achieved after 8 h of herb administration. Surprisingly, a relatively lower SPB (151.60 ± 4.56 mmHg) was recorded in the GT alone group after 12 h compared to 155.00 ± 4.69 mmHg in the LT alone treated group. The antihypertensive effect of LT was augmented when used in combination with GT, important to note that the maximum reduction of SBP at 4 h (133.40 ± 7.54 mmHg, 23.51%) and DBP at 2 h (84.60 ± 5.27 mmHg, 31.99%) than hypertensive control group.

3.3 Cinnamon - losartan pharmacodynamic interactions

CN-treated animals showed a similar alteration in blood pressure pattern as GT-treated animals (Fig. 3). The rats treated with CN demonstrated SBP 161.40 ± 5.98 mmHg, DBP 13.60 ± 11.41 mmHg, and MAP of 128.80 ± 8.53 mmHg at the 0 h time point. After 12 h, SBP of 152.20 ± 3.27 mmHg, DBP 107.00 ± 7.04 mmHg, and MAP of 121.60 ± 4.62 mmHg were observed. The HR of 350.00 ± 11.14 beats/min and 352.00 ± 13.54 beats/min was noted at 0 and 12 h, respectively.

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Fig. 3.

Illustration showing the effect of LT, CN, and CN + LT on rats (a) SBP (b) DBP (c) MAP and (d) HR, *p<0.05 in comparison with hypertensive controls.

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In this study, each of the investigated herbs alone exhibits anti-hypertensive activity in varying degrees. Furthermore, it enhanced and prolonged the pharmacodynamic effects of the investigated drug for up to 12 h. As expected, LT treatment lowered the rats’ blood pressure. When CU was co-administered with LT, the results showed modest changes in SBP, DBP, and MAP compared to the group that received CU alone. After CU administration to rats, a reduction of 7.07% and 7.36% for SBP and DBP was noted at 12 h compared to the hypertensive control group of rats. These findings indicate that CU has a compounding action with LT, improving its anti-hypertensive action. CU’s potential antihypertensive effects are believed to stem from its ability to enhance NO production, reduce oxidative stress, and promote vasodilation, thereby lowering vascular resistance and blood pressure (Srinivasan 2018b). Additionally, CU has diuretic properties, which can aid in lowering blood pressure by reducing blood volume (Keshamma 2015). These mechanisms, combined with CU’s effects on CYP450 enzyme activity, suggest potential interactions with LT.

In comparison with the hypertensive control group at 0 h, GT consumption decreased SBP by 7.3%, DBP by 13.69%, and MAP by 10.98%. These findings suggest the possible benefits of GT to mitigate HTN. The findings demonstrate a substantial influence on cardiovascular health, emphasizing its therapeutic effectiveness. Further, the present study implies that the concurrent administration of LT and GT reduces blood pressure synergistically. The findings of this study demonstrate the possibility of using GT as an adjunct therapy for HTN management. The cardiovascular effects of GT are primarily attributed to its catechins, which promote endothelial cell function by enhancing NO production, reducing oxidative stress, and improving arterial elasticity (Maternia et al. 2023). GT catechins have also been shown to inhibit the renin-angiotensin system (Ryu et al. 2010). The polyphenolic compounds present in these herbs may exert antioxidant effects and lower oxidative stress and, in turn, control the blood pressure (Hodgson 2006). Another suggested mechanism is GT’s ability to inhibit the release of inflammatory cytokines (Szulińska et al. 2017). Additionally, EGCG and other catechins modulate the activity of CYP450 enzymes, particularly CYP3A4 and CYP2C9, which could influence the metabolism of LT and potentially alter its efficacy and safety profile when used concomitantly (Han et al. 2019; Yao et al. 2014). A detailed investigation is required to determine its long-term consequences and mechanisms of action.

Further CN considerably lowers the blood pressure in hypertensive rats and improves heart rate profiles. Furthermore, the co-administration of CN with LT further enhanced the efficacy of the treatment. Notably, CN co-administration with LT restored heart rate levels closer to the normal group, suggesting a protective effect on the cardiovascular system. Several mechanisms have been implicated in CN’s antihypertensive effects such as vasodilation, inhibition of angiotensin converting enzyme inhibitors, and modulation of nitric oxide synthesis (Mao et al. 2019), also the reported vasodilatory effect was attributed to the inhibition of calcium channels, resulting in decreased vascular resistance (Alvarez-Collazo et al. 2014). Additionally, CN has been found to improve glucose and lipid metabolism, making it beneficial for patients with metabolic syndrome and HTN (Baker et al. 2008; Hariri Ghiasvand 2016). Potential pharmacokinetic interactions between CN and LT could occur due to the modulation of CYP450 enzymes by CN’s constituents, such interactions could necessitate adjustments in LT dosing and careful monitoring of blood pressure and potential side effects (Ahad et al. 2022). This study found that combining herbal remedies with modern pharmaceuticals helped treat HTN more effectively, but close monitoring of blood pressure and dose is recommended. An interaction of LT and examined herbs, particularly GT and CN, produced a synergistic beneficial effect on HTN. Nevertheless, the simultaneous consumption of drugs, especially those metabolized by CYP2C9 and CYP3A4, with the tested herbal medicines needs to be taken into consideration with caution.