Antimicrobial, antiparasitic and anticancer properties of Hibiscus sabdariffa (L.) and its phytochemicals: in vitro and in vivo studies

Overview

In the last few decades, Hibiscus sabdariffa L. (Malvaceae; H. sabdariffa) has gained much attention in research field because of its potentially useful bioactivity as well as a great safety and tolerability. For decades, microbial, parasitic and cancer diseases remain a serious threat to human health and animals as well. To treat such diseases, a search for new sources such as plants that provide various bioactive compounds useful in the treatment of several physiological conditions is urgently needed, since most of the drugs currently used in the therapy have several undesirable side effects, toxicity, and drug resistance. In this paper, we aim to present an updated overview of in vitro and in vivo studies that show the significant therapeutic properties of the crude extracts and phytochemicals derived from H. sabdariffa as antimicrobial, antiparasitic, and anticancer agents. The future directions of the use of H. sabdariffa in clinical trials will be discussed.

Key words:
Hibiscus sabdariffa L. • antimicrobial agents • cancer preventive agents • antiparasitic drugs • natural products

Introduction

Hibiscus sabdariffa L. (Malvaceae; H. sabdariffa) is a medicinal plant which has a long history of herbal and edible uses across the world and is mainly cultivated in tropical and subtropical regions of Africa and Asia^1–3). It is an annual or perennial plant or woody-based shrub with serrate leaves, red calyces and red stems^{3, 4)}. The phytochemical and pharmacological activities of various parts of H. sabdariffa have been evaluated including antioxidant, antidiabetic, anti-inflammatory, antimicrobial, and anticancer properties^5–7). Nowadays, cancer, microbial, and parasitic diseases have become a global concern worldwide, since these diseases have threatened human and animal health^8–12). This review aims to provide a brief overview of the in vitro and in vivo studies that present the therapeutic potential of H. sabdariffa extract (HSE) and its bioactive substances in the treatment of cancer, bacterial, fungal, and parasitic diseases.

Phytochemical profile

H. sabdariffa has a long tradition as it contains a rich bioactive profile responsible for its therapeutic efficacy such as anthocyanins, flavonoids, polysaccharides, and organic acids including malic, ascorbic, hydroxycitric, and Hibiscus acids^13–15). Furthermore, HSE is rich in minerals such as iron and calcium with a low content of glucose, and 18 volatile compounds were identified via GC and GC-MS analyses¹⁶⁾. It has been reported that H. sabdariffa seeds contain a large amount of polyunsaturated fatty acids, tocopherol, and the major fatty acids of seeds were found to be oleic 37.92%, linoleic 35.01% and palmitic 19.65% acids^{16, 17)}. Another studies have explored that 1g of aqueous extract of H. sabdariffa contains anthocyanins (56.5 mg/g delphinidin-3-O-sambubioside and 20.8 mg/g cyanidin-3-O-sambubioside), 3.2 mg/g quercetin, 2.1 mg/g rutin and 2.7 mg/g chlorogenic acid, while ethanol was revealed as the best solvent for the extraction of anthocyanins (ranged from 17.3 to 32.2 mg of cyanidin-3-glucoside/g dry weight in the pigmented varieties)^{18, 19)}.

Antimicrobial and antiparasitic properties

Numerous studies have described the potential use of HSE and its phytochemicals as significant antimicrobial and antiparasitic agents in the treatment of various infections.

Antibacterial activities

Recently, Alshami and Alharbi²⁰⁾ explored the effective potential of HSE to prevent recurrent urinary tract infections (UTIs). HSE was found to exhibit bacteriostatic effect with potent inhibition of the growth of six Escherichia coli (E. coli) and two Klebsiella pneumoniae isolates (collected from patients with recurrent UTIs) and remarkable inhibition of biofilm production of all isolates. MIC (Minimum Inhibitory Concentration) values ranged from 0.5 to 4 mg/mL, and MBC (Minimum Bactericidal Concentration) ranged from 8 to 64 mg/mL. The effectiveness of aqueous extracts of H. sabdariffa were investigated for antimicrobial activity against E. coli and Staphylococcus aureus (S. aureus) strains in a microbiological medium and ultrahigh-temperature-processed milk with various fat percentages. The results showed that extracts treated by heat revealed higher antimicrobial activity than in microbiological medium²¹⁾. A methanol extract of H. sabdariffa was found to inhibit effectively the growth of E. coli O157:H7 (at a concentration of 10%) isolates from food, veterinary, and clinical samples, as determined by disk diffusion method²²⁾. Liu et al. reported that aqueous extract of H. sabdariffa and H. sabdariffa protocatechuic acid (PCA) at a concentration of 5 mg/mL inhibited notably the growth of methicillin-resistant Staphylococcus aureus (MRSA), Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae. In addition, PCA (in a dose-dependent manner) exerted higher antibacterial activity against tested pathogens in broth than in human plasma. Moreover, the antibacterial effect was independent from temperature, when treated by a heat²³⁾. The antibacterial effects of aqueous and ethanol extracts, and PCA of H. sabdariffa were examined against food spoilage bacteria Bacillus cereus, Salmonella typhimurium DT104, E. coli O157:H7, Listeria monocytogenes, and S. aureus. MICs of aqueous, ethanol extracts, and PCA against tested bacteria were in the range of 112–144, 72–96, and 24–44 μg/mL, respectively. The results revealed that ethanol extract exhibited greater antibacterial effects than aqueous extract²⁴⁾. Jung et al.¹⁶⁾ evaluated the antimicrobial properties of aqueous and ethanol extracts of H. sabdariffa against Bacillus subtilis, S. aureus, and E. coli. The results showed that ethanol extract against Bacillus subtilis and S. aureus explored higher activity than that of aqueous extract, while aqueous extract at concentrations of 25 and 50 mg/mL inhibited potently the growth of E. coli via the paper disc method. Olaleye²⁵⁾ investigated in vitro the inhibitory effect of aqueous-methanol extract of dried H. sabdariffa calyx against nine bacterial pathogens such as Clostridium sporogenes, S. aureus, Bacillus stearothermophilus, Micrococcus luteus, Serratia mascences, E. coli, Klebsiella pneumoniae, Pseudomonas fluorescens, and Bacillus cereus. The inhibitory effect was observed potently against all tested pathogens. Several studies have also demonstrated that HSE exerted antibacterial activity against bacteria causing oral cavity infections such as. Streptococcus mutans with MIC value of 2.5 mg/mL, while at concentrations ranging from 96–152 μg/mL exhibited also significant inhibitory activity against Campylobacter coli and Campylobacter fetus, which contaminate beef, pork, and chicken meat^{26, 27)}. The crude extracts of H. sabdariffa seeds were tested for inhibitory activity against three types of Gram-negative bacteria species Enterobacter, Salmonella, and Shigella. The higher antibacterial activity was observed against Salmonella sp. at a concentration of 200 mg/L²⁸⁾.

Antifungal activities

The anticandidal activity of methanol extract of H. sabdariffa fruit (at a concentration of 10 mg/mL) was evaluated against six pathogenic Candida species such as C. albicans, C. glabrata, C. guilliermondii, C. krusei, C. parapsilosis and C. tropicalis. The inhibitory activity was detected only against C. albicans²⁹⁾. El-Nagerabi et al.³⁰⁾ examined the inhibitory effect of aqueous extract of H. sabdariffa calyx at concentrations of 5, 7.5, 10 and 12.5 g/100 mL on the growth and aflatoxin B1 production by two fungal strains Aspergillus parasiticus (CBS 921.7) and Aspergillus flavus (SQU 21). The results indicated that no inhibitory effect was observed on the growth of both fungal strains, while the inhibition of aflatoxin B1 production by the different concentrations of H. sabdariffa calyx ranged between 91.5–97.9% and 87.1–93.3% for A. flavus and A. parasiticus strains, respectively. In addition, the study confirmed the metabolic effect of aqueous extract of H. sabdariffa calyx on aflatoxin biosynthesis pathway of both Aspergillus species, and a beneficial use in food industry as an effective biocontrol and non-toxic biopreservative agent.

Antiparasitic activities

Human lymphatic filariasis, a vector-borne disease, is distributed in tropical, subtropical regions, causing a public health problem. Saxena et al.³¹⁾ determined antifilarial activity of ethanolic extract of H. sabdariffa leaves by in vitro motility and MTT methods. The results showed that the extract affected both the adult worms and microfilariae of Brugia malayi. The butanol fraction exhibited remarkable inhibitory effect, which was related to anthocyanin-glycosides. Animal trypanosomosis, a parasitic disease is still the main factor of decreasing the growth of livestock in Africa. Umar and colleagues³²⁾ investigated in vivo the effect of aqueous extracts of H. sabdariffa calyces on the heamatological profile and organ pathological changes in Trypanasoma congolense-infected rats. The results showed that consumption of the extract (9.94 mg/100g/day) enhanced the pathological changes in blood and organs of T. congolense-infected rats.

Anticancer activity

The crude extracts and isolated substances from H. sabdariffa were found to be potential cancer chemopreventive agents. For instance, Hibiscus anthocyanins (HAs) exhibited an ability to promote cancer cell apoptosis, particularly in gastric cancer and leukemia, while PCA was found to suppress the carcinogenic action of various substances in different tissues of rat models in vivo^{33, 34)}. Tsai and co-workers³⁵⁾ have recently evaluated the protective effect of HAs on N-nitrosomethylurea (NMU)-induced leukemia of rats in vivo. The results indicated that oral administration of HAs (0.2%) significantly suppressed progression of NMU- -induced leukemia by approximately 33.3% in rats. Several studies have also evaluated the effectiveness of HAs including delphinidin-3-sambubioside on human leukemia cells. Interestingly, HAs effectively induced apoptotic cell death in human promyelocytic leukemia cells via the p38-FasL and Bid pathway, and ROS- -mediated the mitochondrial dysfunction pathway^{36, 37)}. Lo and colleagues³⁸⁾ also reported that HAs induced apoptosis of the proliferating smooth muscle cell via activation of P38 MAPK and p53 pathway. PCA, a phenolic acid was found to exert in vitro protective effects against cytotoxicity and genotoxicity of hepatocytes induced by tert-butylhydroperoxide (t-BHP). Mechanism of PCA’s protective effect may be related to its ability to inhibit DNA repair synthesis caused by t-BHP and by scavenging free radicals as well³⁹⁾. Tseng et al.^{40, 41)} presented in two studies that PCA exhibited remarkable inhibition of 12-O-tetradecanolyphorbol-13- -acetate (TPA)-induced skin tumor formation in female CD1-mice and the survival of human promyelocytic leukemia HL-60 cells. In their studies, they revealed that the mechanism by which PCA utilized anticancer activities is due to its ability to induce antitumor activities through DNA fragmentation, GI arrest, apoptosis, and decreasing reactive oxygen species (ROS). The apoptosis-inducing activity was implicated with the phosphorylation and degradation of RB and the suppression of Bcl-2 protein. Lin and colleagues⁴²⁾ studied the apoptotic effect of PCA on human gastric carcinoma (AGS) cells. The results suggested that the apoptotic effect may be mediated via p53 signaling and p38 MAPK/FasL cascade pathway. Olvera-Garcia and co-workers⁴³⁾ reported that PCA inhibited the mutagenicity of 1-nitropyrene and checked the proliferation of HeLa cells, both in a dose-response manner in human stomach adenocarcinoma AGS cells. In addition, the effect of Hibiscus sabdariffa extract induced cytotoxicity and apoptosis of the cancer cells in dose-dependent manner through JNK/p38 signaling cascade-mediated apoptosis. Saeed at al.⁴⁴⁾ reported that ethanolic extract of H. sabdariffa exerted moderate proliferative activity in cell-culture using estrogen-responsive breast cancer cell lines (MCF-7). Moreover, the results revealed that H. sabdariffa extract was found to be the richest in quercetin and daidzein as phytoestrogens among the other tested plants used in the study. Lin et al.⁴⁵⁾ studied the anticancer properties of H. sabdariffa leaf extracts against various human prostate cancer (CaP) cells in vitro and in vivo. The study explored that anti-apoptotic activity was mediated via both intrinsic (Bax/cytochrome c-mediated caspase 9) and extrinsic (Fas-mediated caspase 8/t-Bid) pathways and by inhibiting the growth of prostate tumor xenograft in athymic nude mice as well. The results suggested that leaf extracts contained higher amounts of polyphenolic compounds than extracts from calyces and hence, Hibiscus polyphenolic compounds provide effective anticancer agents. Chiu and co-workers⁴⁶⁾ evaluated in vitro anticancer activity of Hibiscus leaf polyphenolic (HLP) extract in melanoma cells. It has been found that HLP is rich in epicatechin gallate (ECG) and other polyphenols. The results explored that anticancer effect of HLP was associated with ECG by inducing the caspases cleavages, Bcl-2 family proteins regulation, and Fas/FasL activation in A375 cells. The apoptotic activity was determined by DAPI stain, cell-cycle analysis, and acidic vascular organelle (AVO) stain. Eventually, the study suggested that HLP could be a potential antimelanoma agent.

Conclusion and future directions

In summary, H. sabdariffa exerted various beneficial activities with no remarkable genotoxic effects as well as great tolerability. Hibiscus sabdariffa was found to be a great target as a source of many chemotherapeutic agents useful in food industry and drug discovery development. The most bioactive compounds in HSE that have been found to have significant therapeutic properties against microbial, parasitic and cancer diseases were PCA, HAs, and polyphenols. In this review, we summarized exclusively the potential use of HSE and its phytochemicals in the treatment of the most serious diseases which affect human and animal health such as cancer, bacterial, fungal, and parasitic diseases. H. sabdariffa has been examined both in in vitro and in vivo studies but more robust, randomized, and controlled clinical trials with well-characterized HSE preparations would be needed in future research to confirm the therapeutic potential.

Conflict of interest: none.

This study was funded by Internal Grant Agency (IGA) of the Faculty of Environmental Sciences, Czech University of Life Sciences Prague, Czech Republic. Project No. 20154247/2015.

Received 25 November 2015

Accepted 16 December 2015

Ing. Sherif T. S. Hassan 

Department of Natural Drugs, Faculty of Pharmacy

University of Veterinary and Pharmaceutical Sciences

Palackého tř. 1946/1,

612 42 Brno,

Czech Republic

e-mail: sherif.hassan@seznam.cz

S. T. S. Hassan • K. Berchová

Department of Applied Ecology, Faculty of Environmental Sciences

Czech University of Life Sciences,

Prague,

Czech Republic

M. Šudomová

Department of Archeology and Museology, Faculty of Arts

Masaryk University,

Brno,

Czech Republic