Another study by the same team of researchers, published in the Journal of Food Science, found that the polyphenols present in hibiscus leaves may inhibit growth of and destroy melanoma cancer cells without damaging healthy human skin cells, scientists from Taiwan have found.
Hibiscus leaf is a rich source of polyphenols, which are thought to have hypolipidemic (lipid-lowering) and antioxidant effects.
The scientists claimed that this was the first study focusing on the polyphenols and their anti-melanoma mechanisms.
Commonly called roselle or zobo, Hibiscus sabdariffa belongs to the plant family Malvaceae. In folk herbal medicine, it is used to treat hypertension, pyrexia, and liver disorders, and is used for its immune-modulating effect in Asia.
An aqueous extract of dried flowers of H. sabdariffa L. has been used as an effective treatment against leukemia and gastric carcinoma, due to its high content in polyphenols. Previous studies have demonstrated that leaves of H. sabdariffa possess hypoglycemic, hypolipidemic, antioxidant, and estrogenic-like effects.
Recent studies suggested that H. sabdariffa is an interesting nutri-medicinal plant with multiple pharmacological activities, and H. sabdariffa leaf extract (HLE) has the potential to be developed as a chemotherapeutic agent. In anticancer studies, HLE-induced apoptosis through mediated intrinsic and extrinsic apoptotic pathways in human prostate cancer cells.
Chui and his team of researchers wrote: “Hibiscus sabdariffa leaf has been previously shown to possess hypoglycemic, hypolipidemic, and antioxidant effects, and induce tumor cell apoptosis. However, the molecular mechanisms involved in the anticancer activity of H. sabdariffa leaf extract (HLE) are poorly understood. The object of the study was to examine the anti-invasive potential of HLE. First, HLE was demonstrated to be rich in polyphenols.
“The results of wound-healing assay and in vitro transwell assay revealed that HLE dose-dependently inhibited the migration and invasion of human prostate cancer LNCaP (lymph node carcinoma of the prostate) cells under non-cytotoxic concentrations. Our results further showed that HLE exerted an inhibitory effect on the activity and expressions of matrix metalloproteinase-9 (MMP-9). The HLE-inhibited MMP-9 expression appeared to be a consequence of nuclear factor-kappaB (NF-κB) inactivation because its DNA-binding activity was suppressed by HLE. Molecular data showed all these influences of HLE might be mediated via inhibition of protein kinase B (PKB, also known as Akt)/NF-B/MMP-9 cascade pathway, as demonstrated by the transfection of Akt1 overexpression vector.
“Finally, the inhibitory effect of HLE was proven by its inhibition on the growth of LNCaP cells and the expressions of metastasis-related molecular proteins in vivo. These findings suggested that the inhibition of MMP-9 expression by HLE may act through the suppression of the Akt/NF-B signaling pathway, which in turn led to the reduced invasiveness of the cancer cells.”
Prostate cancer (CaP) is a very common male-specific malignancy, and the second most common cancer among men in the world. Thus, developing novel treatment options for CaP has become an important medical need. Since CaP is so highly sensitive to androgens, the intrinsic androgenic, glucocorticoid, and estrogenic-like activities of nutri-medicinal plants or herbs have potential for use in the treatment of CaP. In recent years, many anticancer agents appeared to target signaling intermediates in metastatic pathways. Current reports revealed that the inhibition of metastasis in CaP cells by tea polyphenols and curcumin was related to the signal transduction regulation.
Tumor metastasis occurs by a series of steps, including vessel formation, cell attachment, invasion, and cell proliferation, and is regulated by extremely complicated mechanisms. The degradation of basement membranes and the stromal extracellular matrix (ECM) are crucial steps for tumor invasion and metastasis. The matrix metalloproteinases (MMPs) family of human zinc-dependent endopeptidases is responsible for the degradation of the ECM. Among them, gelatinases (MMP-2 and MMP-9) efficiently degrade native collagen types IV and V, fibronectin, and elastin. The expression of the MMPs gene is primarily regulated at the transcriptional (through activator protein-1 (AP-1) or nuclear factor-kappaB (NF-κB) via mitogen-activated protein kinase (MAPK) or phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB, also known as Akt) pathways) and posttranscriptional levels, and at the protein level via their activators or inhibitors, and their cell surface localization. MMPs and their regulatory pathways have been considered promising targets for anticancer drugs and chemotherapeutic agents.
Previous studies on functions of HLE have been mainly focused on its antioxidant and apoptosis-inducing activities, whereas the effect of HLE on metastasis and invasion of tumor cells has not been clearly clarified. Since cancer metastasis and invasion are highly related to the degradation of the ECM, intercellular adhesion, and cellular motility, this study explored the effects of HLE on MMPs expression, as well as the activities of Akt, MAPK, and transcriptional factors (AP-1 and NF-κB) on LNCaP (lymph node carcinoma of the prostate) cells, an androgen-responsive human CaP cell line, to explore the underlying mechanism for the action of HLE in cancer cell invasion in vitro. Additionally, the effect of HLE was shown by its inhibition of the growth of LNCaP cells in xenograft tumor studies. The detailed signaling pathway involved in HLE-inhibited CaP metastasis in vivo is also included.
Melanoma is the least common but most fatal form of skin cancer and is resistant to most forms of treatment including chemotherapy. Rates of melanoma have doubled in the past 20 years.
“Melanoma has become an increasingly important public health issue and novel treatment options have become an important medical need,” say the researchers.
“Regarding the effect of Hibiscus leaf in vitro and in vivo studies, the effect of the polyphenolic extract in cancer is rarely reported. Thus, it is important to evaluate the potential of Hibiscus leaf polyphenols (HLP) as a functional food for anticancer.”
Chui and his team of researchers said that hibiscus leaf was consumed as a vegetable in Africa but ignored elsewhere around the world. They suggested that based on these results, published in the Journal of Food Science, HLP might be a useful anti-melanoma agent.
Using human melanoma cells, mice melanoma cells and normal human skin fibroblasts as a control, the researchers treated them with various concentrations of HLP for 24 hours in order to determine the effect on the cancer cells as well the mechanisms behind this.
They found that HLP, and, in particular, the polyphenol epicatechin gallate (ECG), had an inhibitory effect on the growth of both the human and mouse cancer cells – inhibiting 50 per cent of cancer cell viability when treated for 24 hours at a 250 microgram (μg) per millilitre (mL) dose. Significantly, the normal human skin cells did not change.
“These findings indicate that the HLP is likely to be a useful chemotherapeutic agent to eliminate cancer cells without significant harmful effects on normal cells,” said the researchers.
They also found that HPL and ECG led to “dose dependent and significant” levels of cancer cell death in the human cancer cells, in two ways – apoptosis, or programmed cell death and autophagy, or the catabolic breakdown of cells.
The scientists have called for more research into the extraction methods to yield a maximum amount of HLP.
They used methanol, hexane and ethyl acetate to extract the polyphenols from dried hibiscus sabdariffa leaves at 50°C.
Other health benefits of Zobo
Due to their perceived potential health benefits, commercial preparations of H. sabdariffa extracts (HSE) are currently marketed as supplements and these extracts have gained an important position in some local soft drink markets. In folk herbal medicine, it is used to treat hypertension, pyrexia, and liver disorders and it is also taken for its immunemodulating effects. The leaf of the plant is usually discarded around the world, except in Africa, where it is consumed as a vegetable. An ethanol extract of the dried leaves has been shown to reduce aflatoxin formation, and to have an in vitro inhibitory effect against some fungi that include Aspergillus fumigatus, Rhizopus nigricans, and Trichophyton mentagrophytes.
Studies with laboratory animals have demonstrated that an aqueous extract of H. sabdariffa leaves (HLE) caused a significant decrease in epididymal sperm counts, histological distortion of tubules, disruption of normal testicular epithelial organization, and disintegration of sperm cells. The authors postulated that these effects were related to interference of spermatogenesis by the extract, which may have been caused by an estrogenic-like action of the extract.
The Heart Insurance Tea, HIT
A professor of pharmacognosy and Chairman Bioresources Development Group (BDG) and Intercedd Health Products (IHP), Maurice Iwu, told The Guardian that zobo tea is an insurance cover for the heart. Iwu said: “Bissap Tea is a herbal Tea drink of an infusion made from the dried calyces of Hibiscus sabdariffa ﬂower which can be consumed both hot or cold by people around the world.
“The drink has been used as a home remedy in many Asian, African and the Caribbean countries for years. The Tea contains vitamin C, minerals and about 15 to 30 per cent organic acids.
“Bissap Tea promotes general good health through antioxidant which ﬁghts cellular damage and support the immune system. The natural chemicals in the drink also promote good cardiac function and prevent heart diseases, including hypertension.
“They also promote digestive and bowel regularity, water control, and weight loss and management.”
Zobo reduces diabetes-induced kidney disease risk
Results of a recent study suggest that aqueous extract of Hibiscus sabdariffa (HSE) has no harmful effect on the liver but when consumed in high doses could be harmful to the kidney. “Further research aimed at identifying the chemical composition and potential toxic agent(s) in HS is recommended,” the researchers wrote.
The study titled: “Toxicilogical effects of aqueous extract of Hibiscus Sabdariffa on the liver and kidney,” was published in Journal of College of Medicine.
The aim of the study is to show the effect of graded doses of aqueous extract of HS on major excretory organs (liver and kidney) of albino Wistar rats. This may be helpful in determining the safety or otherwise of its consumption at different concentrations.
The researchers wrote: “There were no significant changes in the histology of the liver throughout the period of HS administration in all the groups.
However, there were significant histological changes in the kidney, which were more pronounced at higher doses (80 and 160mg/kg). There was shrinkage of glomerular tuft, increase in urinary pole, an increase in the size of the tubular lumen and tubular damage.
These effects were more marked as the duration of administration of the extract progressed with the greatest effect observed at 12th week.”
Zobo tea bursts kidney stones
Another study found that Hibiscus sabdariffa might help treat kidney stones via uricosuric activity. The study titled: “Uricosuric effect of Roselle (Hibiscus sabdariffa) in normal and renal-stone former subjects,” was published in Journal of Ethnopharmacology.
Uricosuric agents are used to lowering the uric acid level in the blood and to prevent the formation of uric acid crystals in the joints and kidneys. These drugs are often used to treat gout, a disease in which uric acid crystals deposit in joints and cause pain. By decreasing plasma uric acid levels, these drugs decrease the deposition of crystals in joints, eventually decreasing inflammation and thereby reducing the pain of gout.
Researchers from Thailand conducted a study with nine subjects with no history of kidney stones and nine with a history of kidney stones. A cup of tea made from 1.5 grams of dry roselle was provided to subjects twice daily (morning and evening) for 15 days.
After taking the tea, both groups showed increases in oxalate and citrate. In the non-kidney stone group, increases in uric acid excretion and clearance were observed. In the patients with kidney stones, both uric acid excretion and clearance were significantly increased.
The study authors concluded that roselle has a uricosuric effect and they suggested that the chemical constituents exerting this effect should be identified.
Also, researchers have shown that aqueous (water) extracts of HSE is capable of reducing lipid peroxidation, increasing catalase and glutathione activities significantly in diabetic kidney, and decreasing the plasma levels of triglyceride, low-density lipoprotein (LDL) and increasing high-density lipoprotein (HDL) value.
The researchers concluded: “In conclusion, our results show that HSE possesses the potential effects to ameliorate diabetic nephropathy via improving the oxidative status and regulating Akt/Bad/14-3-3? signaling.”
Hibiscus tea lowers blood pressure, ‘bad’ cholesterol
Nigerian researchers have confirmed that drinking tea made with flower extracts of Hibiscus rosa-Sinensis (popularly called Hibiscus flower)- a close relative of Hibiscus sabdariffa (zobo)- lowered blood pressure in hypertensive patients.
Researchers have also demonstrated how the flower extracts of hibiscus could be used to reduce weight, prevent obesity and coronary heart diseases like atherosclerosis by lowering the blood levels of low density lipo-protein (LDL) ‘bad’ cholesterol.
Atherosclerosis, which involves deposits of fatty substances, cellular waste products, calcium and fibrin (is a fibrous protein involved in the clotting of blood); and is the leading cause of illness and death in most countries.
However, a local study has found that although hibiscus leaf extracts reduced blood pressure, the integrity of the kidney may be compromised if it is used in high doses for the treatment of hypertension.
Botanically called Hibiscus rosa-Sinensis, hibiscus belongs to the plant family Malvaceae. Hibiscus has many species and is a primary ingredient in many herbal teas.