Plant Extracts as Antihypertensive Agents

Hypertension (HTN) also known as High Blood Pressure (HBP) is a chronic medical condition in which the human blood pressure is above the threshold range. It can be classified as primary (essential) or secondary [1]. About 90-95% of the cases are primary, whereas 5-10% is secondary. Secondary HTN are caused by conditions that affect the kidneys, arteries, heart or endocrine system. Blood Pressure (BP) can be defined as the pressure exerted by the blood inside the blood vessels. There are two types of BP: systolic blood pressure, SBP<120mmHg) and diastolic blood pressure (DBP<80mmHg). Hypertension (HTN) is one of the risks factors for strokes, heart attacks, heart failure and arterial aneurysm. It is also the leading cause of chronic kidney failure [2]. HTN has several sub classifications such as HTN stage 1, HTN stage II and isolated systolic HTN. Isolated systolic HTN is elevated systolic pressure with normal diastolic pressure. Its common in elderly. Persons older than 50 years are classified as HTN if their BP is higher than 130/80mmHg. HTN is also classified as resistant if medications don’t reduce BP to norm [3]. Another classification is exercise HTN during exercise. For exercise HTN, the systolic range accepted is between 200 and 230mmHg [4].

There are many factors that are responsible for high blood pressure [5-7]. These are
a. Lifestyle: Sedentary lifestyle increases the risk of hypertension
b. Stress: Increasing stress, elevates blood pressure
c. Visceral obesity
d. Potassium deficiency (hypokalemia)
e. Obesity: A body mass index greater than 25 is responsible for than 85% of the cases
f. Salt (NaCl) sensitivity: A higher salt intake will increase the blood pressure.
g. Alcohol intake
h. Vitamin D deficiency
i. Aging
j. Inherited genetic mutations
k. Family history of HTN

Hypertension is one of the leading cause of death. It’s the most common and main contributor to the pathogenesis of myocardial infarction, stroke and renal diseases. WHO reports that over 60million people suffer from hypertension. This is more than 10% of the worldwide population [8]. The hypertension profile varies from one country to another. Secondary HTN results from an identifiable cause and its treated differently from essential HTN. This include Cushing’s syndrome, a condition whereby the adrenal gland over produce the hormone cortisol [9]. Several synthetic drugs of various classification have been developed over the years to lower the blood pressure and lower the risk from hypertension. These are shown in Table 1. Each of these drugs has its own mechanism of action. For example, blood pressure lowering by clonidine results from a reduction in the cardiac output due to a decrease in heart rate and relaxation of capacitance vessels. It also results in a reduction in peripheral vascular resistance. This is also accompanied by a decrease in renal vascular resistance and maintenance of renal blood flow [10]. Vasodilators work by relaxing smooth muscles of the arterioles and thus decreasing systemic vascular resistance which decreases blood pressure. Figure 1 shows the structure of some selected anti-hypertensive drugs. The side effects and the cost of synthesizing synthetic antihypertensive agents have resulted over the years in the use of herbal medicines which is far cheaper, commercially available and having little or no side effects. Besides, synthetic anti-hypertensive agents, when expired have to be dumped and this creates an environmental problem.

Figure 1:The structure of some selected anti-hypertensive drugs.

Table 1:Conventional synthetic medicines used in the treatment of hypertension.

Thus, research has intensified over the years in finding plants or plant extracts that can be used as antihypertensive agents. Thus, a literature review was done and results summarized. Table 2 shows a List of plants used as antihypertensive agents. Each of the above plants, like synthetic medicines, has its own mode or mechanism of action. For example, Tribulus terrestris herb is used habitually for the treatment of coronary heart disease, cerebral arteriosclerosis, myocardial infarction, thrombosis and hypertension [11-13]. Its suggested that the anti-hypertensive effects of the plant is due to its capability to boost up the discharge of Nitric Oxide (NO) from the nitrergic nerve endings and endothelium. Also, the anti-hypertensive effects may be associated with its Angiotensin Converting Enzyme (ACE) inhibitory action[14]. Crocus sativus (saffron), main chemical constituents are crocin, safranal, picrocrocin and crocetin. These compounds act as anti-hypertensive agents via a vasorelaxant action [15].

Table 2:List of plants with antihypertensive activities.

Plants have been mankind first medicine and still will have to be resorted to, considering that synthetic medicines produce side effects which are usually irreversible. In addition, synthetic drugs are environmentally unsafe and the cost of synthesizing a drug is an expensive endeavour. A wide range of synthetic drugs have been used over the years to treat hypertension. The mechanism of action of these drugs are variable. Plant herbal antihypertensive agents will be a good remedy to offset the disadvantages of synthetic anti-hypertensive agents, both from a medicinal and economic perspective.

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3. Osman SM, Khattab SN, Aly (2017) 1,3,5-Triazine-based polymer, synthesis, characterization and application for immobilization of silver nanoparticles. J Polym Res 24(231).
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6. Yun Suk, introduced a microporous Covalent Triazine Polymer (CTP) network with a high surface area was synthesized via the friedel–crafts reaction and employed as a potential transport system for drug delivery and controlled release. The CTP was transformed to the nanoscale region by intense ultrasonication followed by filtration to yield nanoscale CTP (NCTP).
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8. Khattab, reports the synthesis of a library of new s-triazine polyamides containing glycine and thioglycolic acid. The feasibility of the synthesized polymers as drug Nano delivery systems was investigated. The nanoparticles were loaded with celecoxib (CXB), an anti-inflammatory drug with a highly promising anti-cancer effect, resulting in high entrapment efficiency levels.