2.1. Pharmacokinetics from Oral Intake
The amount of ginger active components that reach the bloodstream following oral intake is relatively low due to losses during gastroenteric absorption. Furthermore, gingerols, like most orally administered apolar phenolic compounds, undergo glucuronide and sulfate conjugation that takes place primarily in the intestinal mucosa and secondarily in the liver and other tissues
[20]. This way, plasma components of ginger are typically found in the conjugated forms rather than the free ones. This was demonstrated by a study on mice treated with 250 mg/kg of ginger extract. The study monitored the main active components of ginger in the free form, revealing very low seric levels
[21]. Also remarkable are the different absorption kinetics observed for each one of the components. The 6-gingerol plasma peak was observed at roughly two hours of administration (but with a large error, 27.18 ± 38.43 μg/L), while 10-gingerol peaked at 30 min (55.95 ± 31.61 μg/L) and 8-gingerol was practically undetected; 6-shogaol peaked at 10 min with only 4.04 ± 5.37 μg/L.
Pharmacokinetics of ginger in humans was investigated using an escalation study with 27 healthy subjects. A single oral dose of ginger extracts was administered, with concentrations standardised to 5% of total gingerols and ranging from 100 mg to 2.0 g. The subjects were monitored for 6-, 8-, 10-gingerols and 6-shogaol
[22]. The compounds were rapidly absorbed, with a t
max of 55 to 65.6 min (range: 45–120 min) and elimination half-lives (t
1/2β) of 75 to 120 min at the highest dose, 2.0 g. No free 6-, 8-, 10-gingerols or 6-shogaol were observed in the plasma, in agreement with the studies performed with mice. Instead, their circulating metabolites were detected, mostly glucuronides and/or sulphates ().
Table 1. Pharmacokinetic parameters for the main active components of ginger.
Component
|
Dose (mg)
|
Cmax (μg/mL)
|
AUC (μg·min·mL−1)
|
tmax (min)
|
t1/2β (min)
|
6-gingerol, total
|
1000
|
0.4 ± 0.2
|
12.6 ± 6.4
|
55.0 ± 7.7
|
—
|
1500
|
1.69 ± 2.31
|
75.6 ± 110.3
|
60.0 ± 0.0
|
—
|
2000
|
0.85 ± 0.43
|
65.6 ± 44.4
|
65.5 ± 22.6
|
110.0 ± 34.9
|
6-gingerol glucoronide
|
1000
|
0.16 ± 0.15
|
—
|
—
|
—
|
1500
|
0.62 ± 0.62
|
—
|
—
|
—
|
2000
|
0.62 ± 0.56
|
—
|
—
|
—
|
6-gingerol sulphate
|
1000
|
0.02 ± 0.03
|
—
|
—
|
—
|
1500
|
0.04 ± 0.04
|
—
|
—
|
—
|
2000
|
0.33 ± 0.41
|
—
|
—
|
—
|
8-gingerol, total
|
1000
|
0.1 ± 0.1
|
2.1 ± 2.2
|
52.5 ± 8.7
|
—
|
1500
|
0.1 ± 0.1
|
2.6 ± 2.0
|
60.0 ± 0.0
|
—
|
2000
|
0.23 ± 0.16
|
18.1 ± 20.3
|
73.1 ± 29.4
|
113.5 ± 41.1
|
10-gingerol, total
|
1000
|
0.1 ± 0.1
|
2.9 ± 3.2
|
60.0 ± 0.0
|
—
|
1500
|
0.1 ± 0.02
|
7.7 ± 5.3
|
80.0 ± 34.6
|
—
|
2000
|
0.53 ± 0.4
|
50.1 ± 49.3
|
75.0 ± 27.8
|
128.7 ± 38.8
|
6-shogaol, total
|
1000
|
0.1 ± 0.1
|
0.8 ± 1.5
|
55.0 ± 8.7
|
—
|
1500
|
0.4 ± 0.08
|
1.6 ± 2.8
|
60.0 ± 0.0
|
—
|
2000
|
0.15 ± 0.12
|
10.9 ± 13.0
|
65.6 ± 22.6
|
120.4 ± 42.0
|
Note: Cmax = maximum plasma concentration, AUC = area under the concentration-time curve, tmax = time point at which Cmax is observed, t1/2β = elimination half-life.
It should be noted that only 6-gingerol conjugates were detectable in subjects taking doses below 1.0 g, and for this reason, the low doses are not listed in the . The AUC values for the doses of 250 and 500 mg of ginger presented low values, of 2.8 and 5.3 μg·min·mL−1 respectively. For the two lowest doses of ginger tested, 100 and 250 mg, the Cmax of 6-gingerol conjugates had values of 0.3 and 0.4 μg/mL, respectively. Ginger was well tolerated in all subjects.
Ginger metabolism and excretion is still not fully determined. Studies using 6-gingerol as a model show that this molecule is extensively metabolised in the liver by enzymes of the uridine diphosphate glucuronosyltransferase family to form glucuronide conjugates
[20][23]. Roughly, half of the administered 6-gingerol is excreted through the bile as a glucuronide, with only 2–3% appearing in the urine in the free form
[20]. Other metabolites, formed by hepatic oxidation and eliminated in the urine, include 9-hydroxy-6-gingerol, vanillic acid, ferulic acid, (S)-(+)-4-hydroxy-6-oxo-8-(4-hydroxy-3-methoxyphenyl)octanoic acid, and 4-(4-hydroxy-3-methoxyphenyl)butanoic acid.
2.2. Safety and Interactions
Ginger is a very safe herbal medicine, able to be used even in pregnancy
[24][25]. Nevertheless, it is not completely free from side effects and it also displays a long list of interactions with other compounds, from pharmaceutical active ingredients (APIs) to vitamins and nutrients. In these interactions, ginger acts mostly as a bioenhancer, that is, an agent that enhances the bioavailability of other substances. This effect may be associated with the presence of piperine-like compounds in ginger
[26]. Piperine, the pungent compound in black pepper, is a well-known bioenhancer. However, ginger interactions with APIs are not fully predictable and reduction of bioavailability is also reported.
2.3. Biological Activity
Ginger is indicated in Ayurvedic, Chinese and Unani traditional medicines for a large variety of pathologies and ailments, often being considered a panacea or universal medicine. Most of this knowledge is, however, empirical, and only in the latest decades has clinical trial-based evidence been gathered on the activities of ginger.
3. Encapsulation of Ginger
3.1. Dispersion and Micronisation
Encapsulation of ginger essential oil or ginger oleoresin by forming a dispersion into a polymer or other carrier agent, with subsequent drying and micronisation (commonly in one step, by spray-drying), is a common solution for the protection of the active ingredients against volatilisation or against degradation by heat and light. In addition, liquid and semi-solid extracts are turned into powdered solids which are easier to store and handle.
In the case of ginger essential oil, encapsulation can be achieved with various agents including inulin, whey protein (WP)
[27] and a WP/maltodextrin blend
[28]. For ginger oleoresin, various methods and dispersing agents are described by Janayudin et al.
[29], including chitosan and blends of maltodextrin with caseinate or arabic gum. Chitosan
[30] and chitosan-alginate mixtures
[31] can also be used to form microcapsules with the oleoresin of red ginger, a subspecies of ginger containing higher amounts of 10-gingerol, 6-gingerdiol and its acetylated derivatives
[32].
3.2. Liposomal Ginger
Some liposomal ginger products are available on the market, namely a combination of ginger, curcumin and docosahexaenoic acid (an omega-3 fatty acid) named ‘Micelle Liposomal Curcumin Gold’
[33] and another comprising turmeric, lemon and ginger, called ‘Synchro Gold Lemon Ginger’
[34]. Inclusion of a lipophilic drug into liposomes aims usually at increasing its bioavailability, which, in the case of the two marketed herbal supplements, would refer to oral absorption, given that these are to be taken by this route. Nevertheless, to the best of our knowledge, the effect of liposomes on the oral bioavailability of the active components from ginger remains yet to be demonstrated by any in vivo studies or clinical trials.
Available research into the benefits of liposomes for ginger biotechnological applications includes the evaluation of stability and dermal bioavailability. Inclusion of ginger extract into nanoliposomes was shown to help preserve its antioxidant properties
[35] and its skin permeability, measured on an in vitro goat skin model
[36].
4. Novel Drug Delivery Technologies Based on Ginger
4.1. Ginger-Derived Nanoparticles (GDPs)
Fresh ginger juice can be used to afford, by a controlled methodology
[37][38][39], ginger-derived nanoparticles (GDPs) that are suitable for loading and carrying APIs or other compounds. GDPs from ginger contain lipids, mainly phosphatidic acids (41.9% of total lipids), digalactosyldiacylglycerol (27.4%) and monogalactosyldiacylglycerol (18.9%)
[40], as well as a fair amount of RNA
[39]. GDPs have, thus, an intrinsic immunomodulatory activity, inducing production of the cytokines IL-6 and IL-10 when incubated with macrophages. Furthermore, they are not destroyed in the stomach
[39], and they are able to enter liver cells (hepatocytes) in mice
[41], where they demonstrated a protective effect against alcohol-induced liver damage.
The high biocompatibility of GDPs and their ability to easily fuse with biological membranes owing to the high content in phosphatidic acids makes them excellent candidates for innovative biological therapies. Chronic diseases associated with genetic dysfunction, such as ulcerative colitis, can be treated by gene therapy or by knocking out a target gene using small interfering RNAs (siRNAs). SiRNAs are small double-strand sequences able to knock down specific genes, in this case CD98. GDPs loaded with siRNA-CD98 were tested both in vitro and in vitro as an innovative therapy for ulcerative colitis. In vitro studies on the RAW 264.7 and colon-26 cell lines show successful transfection, with distribution of the GDPs throughout the cells and inhibition of the expression of CD98 gene by roughly 20% in colon-26 cells and 50% in RAW cells. The GDPs have also good distribution in vivo, with studies on mice demonstrating that they have a preferential action (CD98 knock-out) on the ileum and the colon
[40].
4.2. Ginger-Derived Nano-Vectors (GDNVs)
GDPs can be transformed into other kinds of carriers by extracting the lipids they contain and leaving the RNA behind. The extracted lipids form, by sonication, nano-sized vesicles that received the acronym of GDNVs. These new carriers are taken up by intestinal cells, as demonstrated in vitro on the Colon-26 and HT-29 human colon adenocarcinoma cell lines, and biocompatible as demonstrated by the lack of toxicity in vivo on mice. Furthermore, they act effectively as carriers for oral administration of the antitumoral drug doxorubicin and this therapy successfully inhibited tumor growth in a Colon-26 xenograft tumor mouse model
[42].