Pharmacological Properties of Ginger Combinations

2.1 Determination of combination activities

The mode of interaction between plant extracts or pure compounds or standard approved drugs is determined using fractional inhibition or interaction factor. Fractional inhibition is used to determine the pharmacological activities of extract-drug combinations, and drug-drug combinations [19]. Fractional inhibition (FI) or combination index (CI) is the inhibition that is attributable to each of the extracts, compounds, or drugs in the combination. Pharmacological activity for each combination is calculated to give a combination index (CI) or 50% fractional inhibition concentration (FIC₅₀) using 50% inhibition concertation (IC₅₀). These CI values are grouped into synergism (CI < 1), additivity (CI = 1), and antagonism (CI > 1), see Figure 1.

The Sum CI values are used to generate scatter plots (isobolographs) that explain the potency of a given combination by plotting at least all the triplicate assays on one plane. These isobole curves are used to express the activities based on the dose-response of single components when used alone and in combination at different concentrations [20]. Sum FIC₅₀ for each extract-drug, and drug-drug combination ratios are also determined using the equation below [4]:

Interaction factor (IF) also explains mode of interactions between components in extract-drug and drug-drug combinations. It is also based on isobole graphs and grouped just like fractional inhibition concentration; synergism (IF < 1), additivity (IF = 1), and antagonism (IF > 1) [14, 20].

The IF is calculated as shown below:

AM = am measure of activity of a mixture of samples

AT = theoretically calculated activity of the mixture that is based on the dose-response of single components in the combination at different concentrations.

2.2 Antimicrobial activities of ginger combinations

Ginger has been used widely against microbial activities [21]. When used alone, extracts of ginger showed antimicrobial activity with a mean inhibition zone, a 50% microbial inhibition (MIC₅₀) value of 11.72 ± 0.62 mm and lemon (Citrus limon L.) showed MIC₅₀ value of 27.89 ± 1.12 mm against Streptococcus mutans. The activity of ginger when used in combination with lemon was revealed to have a mean inhibition zone with an MIC₅₀ value of 17.94 ± 0.46 mm [22]. This study reveals that the antimicrobial activities of ginger are enhanced when used in combination with ginger C. limon. Therefore C. limon potentiates ginger against S. mutans.

Synergism was observed when ginger was combined with barley (Hordeum vulgare L.) against Staphylococcus aureus and Aeromonas hydrophila [23]. Similar synergism was also observed when ginger was combined with pomegranate (Punica granatum L.) against A. hydrophila. The synergism resulted in complete inhibition of A. hydrophila. Combinations of ginger and licorice (Glycyrrihza glabra L.), and ginger and sage (Salvia officinalis L) tested against A. hydrophila and Escherichia coli both showed synergism [23]. Combined activity of a plethora of phytochemicals in ginger extracts combined with other plant extracts is responsible for the observed synergism when tested for antimicrobial activities. These studies indicate the potential use of ginger in combination with other plant extracts against microbial diseases.

In another study, methanol extracts from ginger showed antibacterial activities against 32 S. aureus strains with an MIC₉₀ value of 3.56 mg/mL when used alone. Synergism was observed with CI₉₀ values of less than 0.9 when two standard antibacterial drugs, tetracycline and netilmicin were each combined with ginger extracts [24]. This shows the potential use of ginger extracts in combination with tetracycline and netilmicin in controlling antimicrobial diseases and reduction of antimicrobial drug resistance. In the same study, additivity and antagonism were observed when ginger was combined with chloramphenicol, erythromycin, gentamycin, vancomycin, ampicillin, cefoxitin, cotrimoxazole, and ofloxacin, all tested against S. aureus [24]. In another comparative study, methanol and water leaves and rhizome ginger extracts were shown to be more effective against S. aureus and S. pyogenes than three standard antibiotics: chloramphenicol, ampicillin, and tetracycline. This depicts the possible use of ginger alongside standard antibiotics in the treatment of microbial diseases [12].

One of the major burdens of disease control is the emergence of drug-resistant strains. When two drugs that have different mechanisms of action are used in combination the likelihood of the emergence of drug-resistant strains is reduced. The pace of emergence of drug resistance is also reduced since a lower amount of each drug is used in combination treatment [19]. Therefore, these studies underpin the use of ginger combinations against antimicrobial diseases. The potential use of ginger in combination with other plants used against microbial diseases and a combination of ginger with standard antibiotic drugs is also depicted in overcoming antimicrobial drug resistance.

2.3 Antioxidant activities of ginger combinations

Ginger has been reported to have high phenolic content and high antioxidant activity [7]. The combination of ginger and coffee (Coffea arabica L.) has shown antioxidant synergistic effects. A combination of ethanol extracts of coffee and ginger showed the highest 2,2-dipheny-1-picryl-hydrazyl-hydrate (DPPH) radical scavenging activity than when used singly. Similarly, combined ginger and tea aqueous extracts showed the highest ABTS radical scavenging activity [13]. This shows that the antioxidant activities of ginger and tea are higher when used in combination than when used singly.

Juice extracts of ginger, kesum (Polygonum minus H.), and turmeric (Curcuma longa L.) without using any solvent showed were tested for antioxidant activities using DPPH radical scavenging assay and ferric-reducing antioxidant power (FRAP) assay [25]. When tested singly for FRAP ginger showed antioxidant activities of 26.2 μmol/g, kesum 46.3 μmol/g, and turmeric 23.3 μmol/g (μmol of Fe II/g of extracts). When the three plant species were combined at a ratio of 1:1:1, they had an antioxidant activity of 23.1 μmol/g which shows that kesum and turmeric juice extracts potentiate antioxidant activities of ginger. When ginger was combined separately with kesum (1:1) and turmeric (1:1) for FRAP, antagonism was displayed with CI_5o values of greater than 1. For DPPH radical scavenging activities, juice extracts of ginger, kesum, and turmeric showed percentage antioxidant activities of 79.0%, 82.6%, and 64.6%, respectively, when tested singly. When ginger was combined separately with extracts of both kesum (1:1) and turmeric (1:1) and when they were all combined (1:1:1) for DPPH radical scavenging activities, they showed additivity with CI_5o values of 1 [25].

In another study, the combination of ginger, garlic (Allium sativum L.), and cayenne pepper (Capsicum fructensces L.) extract at a ratio of 1:1:1 showed synergism with CI_5o values of less than 1. All extracts showed higher antioxidant activities than when these three natural spices are used alone [26] indicating that the extracts potentiate each other’s antioxidant activities. This is probably because the many phytochemicals in the combination increase the superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GRed) enzymes. These enzymes catalyze the conversion of reactive oxygen species to harmless species [26].

Ethanol extracts of ginger and secang wood (Caesalpinia sappan L.) were tested for antioxidant activities using DPPH method both in combination and singly [27]. The concertation of antioxidant compounds was highest in a combination of scang and ginger (2:1) with an IC₅₀ value of 90,14; absorbance was measured using UV. When tested singly, the IC₅₀ for scang and ginger was 54,53 and 197,74, respectively [27]. In another similar study, ginger combination with eucalyptus honey (Eucalyptus globulus Labill.) portrayed synergistic activities with CI_5o values of less than 1 in which antioxidant activities were increased where H6G5 displayed 60.0% and 90.0% using DPPH method [28].

2.4 Anticancer activities of ginger combinations

Shogaol and gingerol compounds and their derivatives isolated from ginger have shown activity against different types of cancers; breast cancer, lung cancer, cervical cancer, prostate cancer, liver cancer, blood cancer, and colorectal cancer [29]. Combinations of pure ginger phytochemicals, 6-gingerol (6G), 8-gingerol (8G), 10-gingerol (10G), and 6-shogoal (6S) have shown strong synergistic antiproliferative activities against prostate cancer cell lines with CI₅₀ values ranging between 0.03 and 0.88 [15]. The highest synergistic activities were observed in 6G + 8G, 8G + 10G, 10G + 6G, and 6S + 10G combinations with CI₅₀ values below 0.4 when tested against human prostate cancer cell lines [15]. In another follow-up study, a combination of 6-gingerol, a pure compound isolated from a Chinese Tongling White Ginger, with standard drugs depicted synergistic anticancer activities when tested against human cervical adenocarcinoma cells [30]. The combination of 6-gingerol with 5-FU (inhibition of S-phase of cell cycle and PI3K signaling pathway inhibitor) and Ptx (inhibition of G2/M-phase of cell cycle and mTOR inhibitor) at different concentrations showed synergism after 48 h treatment on Hela cells. A combination of 6-gingerol (45 μM) with Ptx (0.36 μM) inhibited 83.2% growth of the treated cells and a combination of 6-gingerol (45 μM) with 5-FU (22.5 μM) inhibited 52% growth of the cells. All nine combinations of 6-gingerol with Ptx portrayed strong synergism with CI values of less than 0.4 [30]. This study displays the synergistic interactions of ginger phytochemicals when used in combination with each other. This shows the value of using whole extracts in traditional medicine and therefore the popularity of herbal medication unlike the use of synthetic drugs that are based on one active ingredient.

Synergism has been observed when crude water ginger extract was combined with Gelam honey and tested against colorectal cancer cell line HT29 [31]. The 3-(4,5-dimethylthiazol-2-ly)-2,5-diphenyltetrazolium bromide (MTT) assay of these combinations depicted synergism with CI₅₀ values of less than 1 [32]. When tested singly against human colorectal adenocarcinoma cell line HT29, ginger extracts showed anticancer activity with an IC₅₀ value of 5.2 mg/mL and Gelam honey showed an IC₅₀ value of 80 mg/mL while a combination of an IC₅₀ value of 0.3 mg/mL was observed [32]. These results indicate the activity of ginger is more effective when used in combination than when used alone against colorectal cancer [31, 32]. In a similar study, a combination of ginger extracts with Gelam honey showed synergistic activities (CI <1) with higher apoptotic activities when each is combined with 5-FU and tested against HCT 116 colon cancer cell lines [9].

Combinations of ginger extracts, especially combination of ginger phytochemicals, have possible use in treatment of cancer and reduction of emergence of anticancer drug resistance. With the increased emergence of anticancer drug resistance and the side effects of anticancer drugs, the use of safe and effective anticancer ginger combinations that do not have side effects is indispensable.

2.5 Antidiabetic activities of ginger combinations

Extracts of ginger, green tea (Camellia sinensis L.), and cinnamon (Cinnamomum verum J.Presl) were tested separately and then combined against diabetes and postprandial glucose patterns. The three herbs, ginger, green tea, and cinnamon, exerted a glycemic index (GI) of 72, 79, and 63, respectively, when tested singly using healthy human volunteers of both genders. Synergism was depicted when all extracts were combined with a GI of 60 [33]. Therefore, the highest effect of lowering postprandial glucose in humans was portrayed when the herbs were used in combination showing the potential use of ginger, green tea, and cinnamon combinations in controlling blood sugar level.

In another study by Ali et al. [34], aqueous ginger extracts showed anti-hyperglycemia and anti-inflammatory activities when tested alone against type 2 diabetes in rats, in vivo [35]. When the same aqueous extracts were combined with probiotics of eight good bacteria, they portrayed synergism. The combination showed substantial improvement in oral glucose tolerance test, serum insulin, C-peptide, and lipid abnormalities than when the species extracts were used alone [35].

Extracts of three commonly used culinary natural spices, ginger, garlic (Allium sativum L.), and cayenne pepper (C. fructensces) have shown prophylactic and therapeutic activities against cardiovascular diseases, atherosclerosis, and antidiabetic diseases [26, 36]. Synergism was observed when the three spices were tested in combination (1:1:1:1) against hypercholesterolemic activity.

The various phytochemicals in extracts of the spices acting in a beneficial manner explain the observed anti-hypercholesterolemic activity that was higher in combination through synergism than when the three spices were tested singly [26]. The use of ginger combinations in blood sugar regulation in traditional medicine is, therefore, preferred to the synthetic antidiabetic drugs, which rely on one single active ingredient. These studies depict a possible use of ginger combinations in blood sugar balance.

2.6 Antidepressant activities of ginger combinations

Depression is mainly caused by an imbalance of neurotransmitters; serotonin, norepinephrine, and dopamine. Antidepressants are used to maintain a balance of neurotransmitters, especially serotonin. Honokiol and magnolol (HMM) from magnolia bark (Magnoliae officinalis Rehd. Et Wils), and ginger essential oils (GEO) and polysaccharides (PGR) from both plant species were combined and tested for antidepressant activities in mice by measuring serotonin and noradrenaline levels in the hippocampus, prefrontal cortex, and striatum [37]. Most combinations of the compounds from the two plant species showed synergism. The most effective antidepressant synergistic effects were observed when 39 mg/kg of OGR were combined with 15 mg/kg of HMM after two weeks of antidepressant treatment. This resulted in a significant increase in serotonin and noradrenaline in the prefrontal cortex [37]. These results are in agreement with similar synergistic antidepressant effects of OGR in combination with HMM as reported by Qiang et al. [38].

Anxiety and depression are increased by mercury II chloride (HgCl₂) in mice [39]. In a study by Benkermiche et al. [40], ginger extracts combined with black cumin (Nigella sativa L.) oil showed prophylaxis synergistic effects on anxiety and depression behavior in Wistar rats that had been exposed to HgCl₂ [34]. This could be attributed to the pure compounds like 6-gingerol, isolated from ginger, which has shown neuroprotective effects in rodents [41], and the antidepressant activities of thymoquinone, the active ingredient in N. sativa which act synergistically when combined [14]. With increased reports of anxiety, depression, and even suicide, these studies are crucial as they are suggestive of possible use of ginger combinations both as a prophylaxis and therapeutic against depression.

2.7 Pharmacological activities of ginger combinations for herbal tea formulations

In production of herbal teas, various parts of medicinal plants are used; roots, stems, leaves, barks, flowers, and seeds. Most of these herbal teas are usually used in combination, packed in bags, and sold for use in different countries [42]. The herbal tea formulations are preferred because use of medicinal plants in combination leads to presence of various bioactive phytochemicals in one package, which has shown to reverse and prevent various metabolic diseases [40]. Studies of tea and herbal infusion combinations have shown increased pharmacological activities against various diseases [38]. Apart from the medicinal benefits, the use of these herbal tea formulations is promoted because consumers believe that they are natural and safe without any side effects [43]. In addition, herbal formulations, especially with ginger, provide tea with the desired taste and aroma [4].

In a study by Yusuf et al. [44], herbal tea formulations of powdered dried leaves of mango tree (Mangifera indica L.), leaves of drumstick tree (Moringa oleifera Lam.), and ginger powder have shown to have potential nutritional and health benefits in prevention of various metabolic diseases. Presence of bioactive phytochemical compounds such as tannins, flavonoids, terpenoids, and cardiac glycosides in these formulations indicate that such a composite blend is a reservoir of various antioxidants acting together in a beneficial way through synergism when used in combination thereby promoting health due to the therapeutic and healing properties of the phytochemicals contained in these plants [45]. In addition to the medicinal properties of ginger when used as a herbal tea formulation in combination with leaves of mango and drumstick tree, the combination provides herbal teas with the desired and appealing sensory attributes such as color, aroma, flavor, texture, taste, mouth feel, and overall acceptability [40]. This makes the medicinal use of ginger herbal tea formulations when combined with other natural spices preferable than standard approved drugs.

Ginger is used in coffee (Coffea arabica L.) herbal tea drinks. When used as an oxidant, ginger offers protection to the human body from various diseases that are attributed to reactions of radicals [7]. In this protection, ginger acts as a radical-scavenger, by inhibiting peroxidation and other free radical-mediated processes [13, 43]. When used alone, water extracts of ginger and coffee showed antiradical activities with EC₅₀ values of 3.82 mg/mL and 1.78 mg/mL. Chlorogenic acid a pure compound isolated from ginger showed antiradical activity with an EC₅₀ value of 36.76 μg/mL and caffeic acid isolated from coffee showed antiradical activity with an EC₅₀ value of 22.37 μg/mL [13]. When coffee and ginger were combined, synergism was observed by the antiradical scavengers from extracts of the two plant species. This explains the medicinal benefits of the use of ginger when used in combination with herbal tea formulations for prevention of diseases.

When the plant extracts are digested, which imitates the drinking of herbal teas, the synergism increased in vitro. The combination of the pure compounds, chlorogenic acid from ginger and caffeic acid from coffee, showed antagonism for antiradical activity [13]. Phenolic compounds in ginger and coffee that are used in herbal teas act as an anti-inflammation through inhibition of pro-oxidative enzymes such as lipoxygenase (LOX) mediated arachidonic acid metabolism [20]. Water extracts of ginger and coffee showed LOX-inhibition activities with EC₅₀ values of 3.83 mg/mL and 4.85 mg/mL, respectively. The combination of these extracts showed synergism as the Lox-inhibition activities of the pure compounds increased when digested in vitro [20]. Pure compounds, chlorogenic acid from ginger and caffeic acid from coffee, had a LOX-inhibition activity with EC₅₀ values of 41.05 μg/mL and 22.86 μg/mL, respectively. When these compounds were combined, they showed stronger synergism [13]. Therefore, the ability of ginger to scavenge free radicals and inhibit lipoxygenase (LOX) is increased when ginger is used in combination with coffee. Since tea is the second most popular drink, second to water [12], the use of ginger in tea is, therefore, highly recommended as it makes the drink medicinal while improving the taste and aroma of tea.

2.8 Other pharmacological activities of ginger combinations

Synergism was shown when ginger was combined with nifedipine (a drug used to treat high blood pressure) in hypersensitive and normal patients. A combination of 1 g of ginger and 10 mg of nifedipine showed that a percentage inhibition of platelet induced by collagen, adenosine diphosphate (ADP), and epinephrine was 64.2%, 63.8%, 61.1%, respectively [44]. Ginger potentiated the antiplatelet aggression activity of nifedipine. The inhibition of platelet aggression suggests the use of ginger and nifedipine combination against cardiovascular and cerebrovascular complications [44].

Cisplatin is an anticancer drug in which reactive oxygen molecules (ROM) are involved in nephrotoxicity. Combinations of ginger ethanol extract (250 mg/kg of body weight) with vitamin E (α-tocopherol) (250 mg/kg) showed synergism against cisplatin-induced renal failure in mice [46]. In this combination, the activities of renal antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione (GSH) were increased while the level of malondialdehyde (MDA) was reduced [46]. The activity of the combination against cisplatin-induced acute renal failure is by increasing the antioxidant body’s defense system. Therefore, the ginger-cisplatin combination aids the body’s natural defense mechanism against renal failure. This study showed a potential use of ginger in combination with vitamin E against cisplatin-induced renal failure.

A specific ginger and glucosamine combination (Zinaxin Glucosamine; 170 mg EV.EXT 35 mixture and 500 mg glucosamine, as glucosamine sulfate, per capsule) showed potential use for mucosa protection by increased synthesis of mucosa prostaglandins (E1, E2, F2α, and 6-keto PGF1α) in knee and hip of osteoarthritis patients [47]. The gastrointestinal pain and dyspepsia were greatly reduced when compared with diclofenac. The study showed that this combination is as effective as diclofenac but has a better potential use as it concurrently provides gastro-protection, pain relief, and efficacy in osteoarthritis patients [47]. These extra health benefits in the use of natural remedies in phytomedicine make herbal medication popular, unlike pharmaceutical drugs that have adverse side effects. These results are in agreement with another recent study by Rondanelli et al. [48] on the use of ginger to relieve pain in osteoarthritis patients [49].

A study by Mustafa et al. [50] has shown that a combination of ginger powder and zinc supplements has potential pharmacological use in human health. This combination showed activity against oxidative damage, inflammation, and autophagy induced by fructose in rats with metabolic syndrome (MS). The combination also showed potential use in controlling glucose and lipid metabolism and the zinc homeostasis in rats with MS. The ginger powder and zinc supplement combination was shown to downregulate the expression of NF-κB, SREBP-1c, and mTORC1c genes and upregulate the expression of Nrf-2 and PPAR-α in the liver of rats with MS [51].

In another study, nanoparticles NP_S-PEG-FA loaded with the active ginger phytochemical 6-shogaol, demonstrated activity by alleviating colitis symptoms and increased colitis wound healing using mice model [30]. These results are suggestive of the therapeutic use of this approach in treatment of inflammatory bowels. In a similar study, semisolid poly (vinyl alcohol) hydrogels of ginger essential oil (GEO) encapsulation with chitosan nanoparticles (CNPs) displayed activity in wound healing. Increasing the amount of GEO in the hydrogels leads to a decrease in percentage encapsulation efficiency and increased percentage loading capacity [52, 53].

These studies on combination of ginger with standard approved drugs and nanoparticles reveal potential use of the medicinal plant species combinations in prevention and treatment of diseases. The use of these natural herbs combinations is also likely to reduce the emergence of resistance to these diseases.