Sunday, December 3, 2023
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In South Africa, traditional herbal remedies are often used alongside conventional pharmaceuticals to treat diseases such as fever, asthma, constipation, esophageal cancer, and hypertension. Research is now being directed at providing a scientific rationale for the use of these herbal remedies. A team of researchers at the University of KwaZulu-Natal (Durban, South Africa) has investigated 16 nutritive plants growing in the KwaZulu-Natal region and concluded that 8 plant extracts may be of use in the treatment of hypertension. Their studies were presented during the 120th annual meeting of the American Physiological Society, being held as part of the Experimental Biology 2007 conference, April 28-May 2, 2007 in Washington, DC.[22,23]
Lead researcher Irene Mackraj, PhD, and her colleagues screened all 16 plants for ACE inhibitor activity using organic and aqueous extracts prepared with ground dried leaves. Ten grams of ground plant material was suspended in either a methanol or distilled water solution for 48 hours. Each solution was subsequently filtered and the filtrate left to air-dry, resulting in the specific test compound. ACE activity was determined using a fluorometric enzyme assay. Plasma ACE activity was determined using rat plasma. The IC50 (concentration producing 50% inhibition) of the conventional ACE inhibitor captopril was determined to test the sensitivity of the assay. At least 3 separate determinations were conducted for each test compound. A tannin test was only conducted on those plant extracts that inhibited the conversion of angiotensin I to angiotensin II by > 50% in the initial analysis.
Eight of the 16 plants demonstrated significant ACE inhibition activity in both extract forms:
These 8 plants were then subjected to a gelatin salt block test for tannins to eliminate any false-positive results. None of the plants tested positive for tannins.
Only Tulbaghia violacea (wild garlic, known as wilde knoffel in Afrikaans, isihaqa in Zulu, and itswele lomlambo in Xhosa), showed more than 50% ACE inhibition in both extract preparations (71% in the methanolic extract and 68% in the aqueous extract). These findings were consistent with those of an earlier study from the University of Natal Pietermaritzburg (Scottsville), which also reported > 50% ACE inhibition with T violacea extracts.[24] Dr. Mackraj and her colleagues further demonstrated the mechanism of ACE inhibition in vivo by administering exogenous angiotensin I along with organic crude leaf extracts of T violacea (50 mg/kg intravenously) followed by invasive blood pressure monitoring. Acute in-vivo blood pressure screening after administration of the same T violacea extract (50 mg/kg intraperitoneally, daily for 2 weeks) reduced blood SBP and DBP in the Dahl salt-sensitive rat model. Daily administration of the extract compared with captopril 10 mg/kg body weight in 3-month-old Dahl salt-sensitive rats over 2 weeks appeared to confirm that both treatments acted on blood pressure, urinary volume, and sodium excretion by interruption of the renin-angiotensin pathway. Both T violacea extract and captopril decreased angiotensin AT1a receptor mRNA expression in the kidneys compared with control animals treated with dimethylsulfoxide (DMSO). These decreases were mirrored by reductions in SBP (10.8% with T violacea extract and 11% with captopril). Urine output and sodium excretion increased in both groups.
T violacea is indigenous to the Eastern Cape, South Africa, where the leaves and/or bulbs are widely used as an herbal remedy for various ailments and eaten as vegetables. Its medicinal uses include fever and colds, asthma, tuberculosis, and stomach problems. The leaves of the plant are used to treat esophageal cancer. It has been suggested that T violacea extract may have therapeutic properties similar to those of commercial garlic (Allium sativum), as both plants belong to the Alliaceae family. The plant is also used as a snake repellent.
