Lagerstroemia speciosa Ameliorated Blood Pressure in LNAME Induced Hypertension in Experimental Rats through NO/cGMP and Oxidative Stress Modulation.

Cardiovascular disease is the primary reason for chronic heart diseases and mortality worldwide. Hypertension (HTN) is the utmost dominant risk factor for the evolution of several diseases. Herbal medicines, traditional medicinal herbs, and their extracts are widely utilized to treat and monitor HTN. Herbal components have been shown to help relax arteries and lower oxidative stress. The current study assesses the probable role of herbal plant extract Lagerstroemia speciosa (LS) in the LNAME induced HTN in rats. LNAME (50 mg/100 mL) in drinkable water was given to rats for five weeks. There was a significant upsurge in LNAME-treated hypertensive rats' blood pressure (BP). On treatment with LS, it ameliorates blood pressure. Further, LS also improved body weight, reduced heart weight, and heart hypertrophy. The NO/cGMP concentration was lowered along with a substantial upsurge in the level of glutathione and a decline in MDA level. The LS extract also reduced the inflammatory cytokine markers in the systemic circulation. In conclusion, thus, the extract of LS treatment can efficiently alleviate the BP, oxidative stress markers, and inflammation and improve NO/cGMP concentration in LNAME induced HTN in rats.

1. Introduction

Hypertension (HTN) is a crucial risk element for heart attacks, heart failure, and strokes [1, 2]. HTN is a significant indicator of the potential danger of progressing cardiovascular disorder [3]. HTN is typically costly as problems arising due to it are peripheral vascular disease (PVR), coronary artery disease (CAD), chronic renal and heart failure, cerebrovascular disease, [3] and diabetic cardiomyopathy [4]. HTN has been one of the globe's most frequent manifestations linked to early disease and mortality. As per the Centres for Disease Control and Prevention, HTN is accountable for >5.8% of all deaths and greater than 45 percent of all heart disease-related deaths. Antihypertensive therapy reduces the risk of severe cardiovascular risk by decreasing blood pressure (BP) and improving HTN risk factors [1, 2]. Without treatment, even a slight elevation in BP enhances the chance of attaining cardiovascular disease (CVD) and organ damage [5]. By reducing vascular resistance and increasing blood flow, vasorelaxation can help control HTN [6].

One of the factors that are supposed to involve in the progression as well as development of HTN is reactive oxygen species (ROS), which includes a number of metabolic signalling pathways. Aerobic animals continuously generate ROS, which are chief regulators of various physiological functions. Consequently, ROS is toxic at enhanced levels and produces widespread damage to the cell and tissue and poorly marks numerous physiological activities [6]. Numerous pathways by which ROS induces HTN comprise reduced bioavailability of nitric oxide (NO) [7], enhanced expression of ACE [8], and stimulation of AT1 receptor [9]. Owing to their antioxidant potential, several natural flavonoids are demonstrated to have the effect of antihypertensive by increasing the nitric oxide bioavailability [10, 11]. Findings have shown that ROS scavenging is also essential for treating HTN and that ACEI, such as antioxidant phenols, is a preferred antihypertensive agent. Medicinal plants as well as phytopharmaceuticals have been used for the treatment of severe diseases and have least adverse effects [12-16].

Lagerstroemia speciosa (LS or LSE) is usually known by name banaba. It has antidiabetic [17], antiobesity [18], α-glucosidase inhibitors [19], and anti-inflammatory properties [20]. Additionally, it also has effects against diabetic nephtopathy [21]. Since the antihypertensive activity of LS has not been reported, and no research have been done to date on the antihypertensive activity of LS. This research, therefore, explored the antihypertensive efficacy of LS in Nω-Nitro-L-arginine methyl ester hydrochloride (LNAME) induced HTN in rats.

2. Material and Methods

Animal experimental studies have been conducted according to Imam Mohammed Ibn Saud Islamic University's rules, Saudi Arabia–IRB. No. HAPO-01-R-0011. Throughout the duration of the trial, the animals had access to both food and water ad libitum. The Sprague Dawley (SD) rats were used in the present study. The rats were of the weight 150-180 g and aged 5-6 weeks old. The standard drug used was captopril (CAPT) 10 mg/kg, for six weeks [22]. The blood pressure of LNAME group was compared with extract-treated LS, and CAPT group (Supplementary Figures S1–S4).

2.1. LNAME Induced HTN in Rats

In total, four groups of 180-200 grams male SD rats were used for the experiment, containing 6 animals. The groupings of rats were as follows:

Control group: SD rats were served as control

LNAME group: LNAME (50 mg/100 ml water) in water was provided for consumption to the rats for four weeks served as a hypertensive group

LNAME+LS group: LNAME (50 mg/100 ml water) were treated with LS (400 mg/kg) for six weeks

2.2. BP Measurement

The induction of hypertension in the rats was confirmed by the use noninvasive blood pressure measurement technique (Columbus, U.S.A.) [1].

2.3. Determination of Body Weight (BW), Heart Weight and Cardiac Indices

Animals were anaesthetized with urethane at the end of the experiment, and blood was taken from the abdominal aorta. The heart was removed and cleaned, and the weights were determined. The heart weight indices were estimated by dividing the weight of the heart by the weight of the body.

2.4. Determination of NO, cGMP and Inflammatory Cytokines Level

The plasma NO level, cGMP concentration, and inflammatory cytokines were estimated by using NO Colorimetric Assay Kit, cGMP immunoassay EIA kit (Cayman Chemical, USA) assay kit, and TNFα, IL6, and IL1β ELISA kits (Elabscience, U.S.A.) as per the defined manufacturer's protocols.

2.5. Determination of ROS and Oxidative Enzymes

ROS was determined in heart tissue following the defined protocol [1, 3]. In tris buffer, the cardiac tissue was homogenized and then it was filtered. After that, cardiac tissue homogenate was incubated with DCFDA at 37°C for half an hour. The reading was taken at the excitation and emission wavelength of 488 nm and 530 nm. The antioxidant enzymes malondialdehyde (MDA), superoxide dismutase (SOD), and reduced glutathione (GSH) was estimated according to the methods described before [14, 15].

2.6. Hematoxylin and Eosin (H&E) Staining

After measuring the hemodynamic parameters, the hearts were subsequently removed, placed in a solution of 4% formalin, and allowed to remain there for 24 hours. The heart tissue samples were then encased in blocks made up of paraffin. The tissue samples were cut to a thickness of 5 micrometres and stained with H&E dye [3].

2.7. Real-Time PCR

The heart tissue was used for the isolation of RNA using trizol method. After the RNA isolation from the heart tissue by trizole, was then its OD was measured using nanodrop (Thermo fischer) and then it was transcribed into cDNA using reverse transcriptase kit of cDNA, and the RT qPCR was performed according to the defined protocol [1, 15]. The list of primer is given in supplementary table 1.

2.8. Data Analysis

For statistical analysis, Prism software version 8.0 (USA) have been used. To assess statistical significance, a one-way analysis of variance was performed, followed by the Newman-Keuls Multiple Comparison Test and the t-test. Data are represented as Mean ± Standard error of mean (SEM), ∗Control vs LNAME; # LNAME vs LNAME+LSE ∗∗P < 0.01, ∗∗∗P < 0.001; #P < 0.05, ##P < 0.01, ###P < 0.001.

3. Results

3.1. Effect of LS on Hemodynamic Parameters

HTN was induced by LNAME given orally to the rats in drinking water. The BP was increased to 171.19 ± 1.26 mmHg in LNAME group as equated to the control group 113.66 ± 2.26 mmHg, respectively (Figure 1). On treatment with the LS for six weeks, the BP was significantly ameliorated to 126.90 ± 1.36 mmHg compared to the diseased group rats' 171.19 ± 1.26 mmHg (Figure 1).

Figure 1

Effect of L.S.E. on BP (a) systolic blood pressure (SBP); (b) diastolic blood pressure (DBP); (c) mean arterial pressure (MAP); and (d) heart rate (HR).

3.2. Effect of LS on the Morphometric Parameters

Diseased group (LNAME) rats showed a considerable loss of BW (P < 0.01) equated to the normal group. LS treated for 6 weeks improves the decline in BW (P < 0.01) significantly as compared to the LNAME group rats. The heart weight and cardiac indices were found to upsurge substantially in the LNAME group rats. LS mitigates the heart weight and cardiac index significantly (Figure 2).

Figure 2

Effect of LSE on (a) body weight (BW); (b) heart weight (HW); (c) heart weight/body weight (HW/BW) (d) left ventricle weight (LVW); (e) left ventricle weight/body weight (LVW/BW).

3.3. Effect of LS on NO, cGMP Level, and eNOS Expression

The plasma level of N.O., cGMP, and eNOS expression was found to be declined significantly in the LNAME group rats (Figure 3). The NO, cGMP level, and the eNOS expression were markedly improved after the treatment.

Figure 3

Effect of LSE on (a) total nitrate (NOx) level (b) eNOS mRNA expression (c) cGMP concentration.

3.4. Effect of LS on ROS Production, Oxidative Stress (OS), and Myocardial Inflammation

The ROS generation was assessed in heart tissue by fluorometry. The ROS level was increased in LNAME rats. LS treated group displayed significantly reduced level. Besides, the level of various OS markers, such as GSH, MDA, and SOD were abnormal in diseased group rats (Figure 4).

Figure 4

Effect of LSE on (a) fluorescence intensity, (b) MDA level, (c) GSH level, (d) SOD activity.

On the other hand, treatment with LS, in the above levels were improved significantly parallel to the normal group. The LNAME heart depicted hypertrophy, and the architecture was abnormal in the tissue (Figure 5).

Figure 5

Images of the heart stained with H&E dye.

The level of inflammatory markers, TNFα, IL1β, and IL6 were augmented in LNAME group rats significantly, which was reduced by treatment with LS. Additionally, qPCR analysis of the gene expression of the above heart inflammatory cytokines and the mRNA level in heart tissue ascertained the above inflammatory cytokines in hypertensive rats (Figure 6).

Figure 6

Effect of LSE on inflammatory cytokine markers (a) TNF-α level, (b) IL6 level, (c) IL-1β level, (d) mRNA TNF-α expression, (e) mRNA IL6 expression, and (f) mRNA IL-1β expression.

4. Discussion

The continuous detrimental effect of HTN on one's health, despite the availability of efficient medications, necessitates the development of new pharmacological treatments [9]. Due to their minimal side-effect profiles, complementary, and alternative remedies may be more beneficial to many people having cardiovascular problems, and there is a demand for natural medicines. HTN and associated diseases are routinely treated using traditional medicine [1, 2].

LNAME induced HTN is due to the obstruction of enzyme nitric oxide synthase (NOS) due to which there is a deficiency of nitric oxide in the body. This leads to endothelial dysfunction and increase in BP. The blockade of NOS leads to generation of ROS [23]. Phenolics, such as flavonoids, inhibit the ROS production and have antioxidant potential, recently studied [1, 24]. Therefore, the current study shows that in vivo LS treatment to LNAME induced hypertensive rats, effectively decreases BP and enhances eNOS expression and improves NO/cGMP level. The BP decrease in the extract treatment group by the LS administration was equivalent to the group treated by standard drug captopril. The positive control drug captopril ameliorated the BP significantly in the CAPT group in line with LS treatment (Supplementary Figures S1–S4).

We found no toxicological effects in the rats during the six weeks of LS treatment, as evidenced by their demeanour. Furthermore, the BW of the LS-fed groups was similar to that of the control group, indicating that six weeks of LS administration is safe. As a result of the antihypertensive evaluation, LS revealed a considerable reduction in BP. Through the synthesis of endothelial-derived relaxing factors, such as NO/cGMP, the endothelium modulates vascular activity by modifying the effect of contractile chemicals on the vascular smooth muscle layer of the blood arteries [25, 26]. When comparing to the control group, the NO/cGMP level in the LNAME group was reduced. Vasoconstriction of the arteries occurs when NO levels are low, resulting in an augmented CO and BP. Flavonoids cause vasodilation because they have an antioxidant effect, preventing the generation of peroxynitrite and so improving the bioavailability of NO, causing vasodilation and reducing BP [27]. On further treatment with LS containing flavonoids, there was an increase in plasma NO levels compared to LNAME, hypertensive groups.

Endothelial dysfunction (ED) is delineated by reduced NO production in the aorta, which is linked to lowered eNOS [28]. The activity of p-eNOS has been observed to be ameliorated in the LNAME group rats aorta [29].

In HTN, there is an higher OS [30], leading to enhanced ROS production and inflammation in the body [31]. ROS causes inflammation in blood arteries by numerous pathways, one of which is an upsurge in inflammatory cytokines including TNFα, IL6, and IL1β [32]. MDA is the end-product of lipid peroxidation enhanced by ROS production [33]. Injury to the different organs from enhanced ROS generation leads to development of HTN [34]. LS decreases the formation of ROS, MDA level, and recovers the level of GSH in body. MDA production is employed as a predictor of OS-induced lipid peroxidation [35, 36]. Compared to the control group, the LNAME group had lower SOD and GSH levels. The MDA level was augmented significantly in the LNAME group. On treatment with LS, it enhanced the SOD, GSH, and decreased the MDA content. LS, therefore, had some antioxidant activities and were able to inhibit free radical production.

5. Conclusion

The antihypertensive effect of LS declined the increase in BP in LNAME induced hypertension rats. It enhanced the level of NO/cGMP, thereby enhancing the eNOS expression in the heart tissue. It also ameliorated the generation of ROS production, oxidative stress enzymes, and inflammatory cytokines. Thus, it was found that LS has antihypertensive property. Furthermore, the chemical elements from this plant need to be isolated and validated for their antihypertensive activity to be employed in the clinical trial investigation.