1.1. Origin and Composition
Dimocarpus longan (of the Sapindaceae family) is a tree bearings fruits known as Longan, which are sometimes referred to either Dragon Eyes (with the word Longan being translated into Dragon Eye), Euphoria Longan, or Lumyai (Thai) with a more colloquiol name for Lognan fruits "the little brother of Lychee".
Traditional usage includes as a tonic and for the treatment of forgetfulness, insomnia, or palpitations caused by fright. The seeds and fruits tend to be used in traditional medicine, while the flowers tend to be sold in supermarkets for usage as an aromatic tea.
Traditional usage of Longan fruits is to support memory and cognitive function
Some constituents of Longan include:
Polyphenolics (6.3-8.09% dry weight) consisting of ellagic acid (25.84g/kg, the range of 8.13-12.65g/kg also being reported in the fruits; up to 156g/kg in the seeds), corilagin (13.31g/kg, 643g/kg, and 50.64g/kg; quite variable), chebulagic acid (13.06g/kg), isomallotinic acid (8.56g/kg), ellagic acid 4-O-α-l-arabinofuranoside (9.93g/kg), geraniin (5.79g/kg), and gallic acid (9.18-23.04g/kg)
An A type proanthocyanidin trimer (1.63g/kg), an A2 dimer, and Procyanidin B2; with procyanidins consisting of 112.5 +/-5.2mg/g of the flower water extract and 186.7 +/- 7.8mg/g of the ethanolic flower extract
(-)-epicatechin (1.13g/kg whole seeds)
Methyl brevifolin carboxylate (0.16g/kg)
Paltmitic acid and Oleic acid, comprising 35% and 28% of the oils
Adenosine and Adenine
Uridine and 5-Methyluridine
Chlorogenic acid, ferulic acid, vanillic acid, and gentisic acid
Sinapic Acid, syringic acid, and p-coumaric acid
Gallic Acid/Glucose combination structures (monogalloyl-glucose, digalloyl-glucose...heptagalloyl-glucose)
In regards to the non-caloric bioactives, there does not appear to really be anything unique in Longan that has yet been reported. Overall though, it appears to have a very large amount of antioxidant potential due to the large tannin and procyanidin content
Some polysaccharides (carbohydrate content) include:
Longan Pulp Polysaccharide LP3, named subsequently after LP1 and LP2; all nitrogen containing polysaccharides
Pericarp oligosaccharide rich in Galactose (71.5%), Glucose (24.6%), and Galacturonic acid (3.9%)
Polysaccharides may be involved in the immune system and possibly cancer metabolism aspects
Polyphenolic compounds tend to be highest in the seeds (with higher levels in dry seeds on a weight basis, due to the loss of water), followed the fruits and then by the pulps and rinds which are negligible sources of polyphenolics.
Extracts of the flowers can lead to remarkably high concentrations of phenolic compounds (47.7% of total weight of the ethanolic extract; 54.8% of the water extract) and flavonoids (15.6% of the total weight of the ethanolic extract; 13.9% of the water extract) with similar levels of condensed tannins as flavonoids. The methanolic extract results in 50.9% phenolics by weight and 14.2% flavonoids (comparable to the previous two extracts), 11.1% tannins and 15.2% procyanidins; both the ethyl acetate and n-hexane extracts have poor phenolic and flavonoid content.
The polysaccharides of Longan fruits, when intragastically administered to rats at 0.05-0.2g/kg for 14 days prior to cerebral ischemia (MCAO injury), the size of the subsequent infarct is reduced in a dose-dependent manner at 0.05g/kg (8%), 0.1g/kg (13%), and 0.2g/kg (29.5%) outperforming the active control of nimodipine at 0.02g/kg (14%). The edema associated with brain injury was also dose-dependently reduced (almost normalized at the highest dose) and acted to normalize alterations in antioxidative enzymes and inflammatory cytokines, although the root cause of these protective effects was not noted. Protective effects may also exist with the hot water extract of the flowers (125-500mg/kg), where administration of the Parkinson's neurotoxin MPP+- after a week of Longan extract had progressively less effects on dopaminergic neurons on the substantia nigra, with 500mg/kg abolishing the effects of the toxin (lipid peroxidation, dopamine content of cells, ED-1 induction).
Remarkably, the hot water extract of the flowers was more potent than both Trolox (water soluble analogue of Vitamin E) and glutathione itself in preventing lipid peroxidation in vitro; lipid peroxidation protection was noted in brain slices of rats fed the powder, suggesting it is biologically relevant although a suppression of microglia activation may also be an underlying cause. This anti-oxidant capabilities of the flowers has been noted elsewhere, where Vitamin E and Vitamin C were outperformed and the water extract was comparable to isolated catechin.
Some neuroprotective effects appear to exist with Dragon Eye fruits, which may be related to the anti-oxidant capabilities. These protective effects seem quite potent to be honest, but limited evidence on the subject matter
2.2. Memory and Learning
Mechanistically, Oral ingestion of 200mg/kg Longan fruit (water extract) appears to enhance Brain-Derived Neurotrophic Factor (BDNF) immunopositive regions in the hippocampal CA1 and DG regions with increased phosphorylated CREB and ERK in these regions, and this increased cell count is though to be due to preserving cell survival rather than inducing proliferation.
The aqueous extraction of Longan fruits fed at 100-400mg/kg bodyweight to ICR mice over a period of 14 days is able to enhance memory performance on a step-down latency task, with all doses (100, 200, and 400mg/kg) being equally effective as 400mg/kg Piracetam used as active control.
Two studies in rats suggesting improvements in memory possibly related to BNDF induction, but more studies are needed; looks promising
In rats given either a normal or hypercaloric diet paired with 1.25-2.5% water extract of the flowers of Lognan, the higher dose was able to attenuate the rate of weight gain over 9 weeks (with 1.25% being ineffective), bringing the 36.65% weight increase seen in hypercaloric control to 30.71% (with normal fed control at 27.99%) without affecting food intake. This study noted a polyphenolic intake of 112.01mg/kg daily in the high dose group, and also noted increased fecal triglyceride content (possible lipase inhibition) and noted normalized PPARα activity that was hindered with high caloric feeding.
Possible anti-obese effects associated with Longan fruit, unknown practical relevance
4Skeletal Muscle and Physical Performance
A study using the polysaccharides from Longan seeds noted that 100-400mg/kg of the polysaccharides orally for 30 days to mice enhances hepatic glycogen content in a dose-dependent manner; improvements in swimming time and reductions in serum urea and lactate were both noted (and thought to be due to anti-fatigue effects) but were inconsistent with no dose response.
Possible performance enhancing effects, but more studies are needed to confirm
Dimocarpus longan is thought to have an anabolic effect on isolated osteoblasts (MC3T3-E1 cells) at 500 μg/mL of an extract secondary to activating the Runx2 via ERK1/2.
6Inflammation and Immunology
Oral administration of LP3 polysaccharide from Longan (50-200mg/kg) to mice who were currently undergoing immunosuppression increased serum hemolysin production, macrophage phagocytosis, NK cell cytotoxicity, and splenic lymphocyte proliferation; all of which were most effective at 100mg/kg and on par with Ganoderan (50mg/kg; bioactive from Ganoderma Lucidum). These effects suggest protection from immunosuppression, and appear to extend to LP1 and LP2 as well.
The polysaccharides of Longan fruit (100-400mg/kg), in response to DTH (research model of immunity due to T-cells mediating DTH being similar to those that are protective against intracellular infections) immunity appeared to be enhanced with 400mg/kg being similar to an 0.02g/kg injection of lentinan (shiitake polysaccharide) and 100-200mg/kg outperforming; this was extended to macrophagocytosis, where 200mg/kg of Longan fruit polysaccharide increased phagocytosis to 514.3% of control levels, and to both splenocyte proliferation as well as tumor cytotoxicity via the immune system (S180 model; 82.64-83.22% inhibition at 100-200mg/kg with Lentinan at 33.14%).
Appears to enhance proliferation of immune cells and exert an immunopotentiating effect, which can help alleviate immunosuppression
In vitro, water extracts of Lognan with a polyphenolic content (2.65% ellagic acid, 0.81% epicatechin) appear to inhibit LPS-induced NO release in macrophages with an IC50 of 179.8μg/mL; with isolated ellagic acid and gallic acid possessing IC50 values of 5.2uM and 18.8uM respectively. Similar results have been noted elsewhere, where both water and ethanolic extracts weakly inhibited macrophage activation in response to LPS and other parts of the plant which possess polyphenolics (twig and flower) have also shown efficacy.
When looking at individual macrophages, the polyphenolics within longan appear to have an anti-inflammatory effect. This extends to all parts of the plant that possess polyphenolics (so potentially everything except the rind).
A test using the water extract of Longan pericarp (100-400mg/kg) taken 2 hours prior to Carrageenan-induced inflammation in mice was able to exert anti-inflammatory effects, as evidenced by a reduction in edema up to 58% after 5 hours relative to control; when relative to the active control (10mg/kg Indomethacin), the reduction by Indomethacin to 39% was seen as statistically similar.
Water extracts of Longan appear to exert antiinflammatory effects of moderate potency in vivo
7Peripheral Organ Systems
Logan seeds were initially found to have the ability to inhibit the xanthine oxidase enzyme in vitro which was later found to be most potent in an ethyl acetate fraction of the flower (IC50 of 115.8 μg/mL) which was traced back to proanthocyanidin A2 and acetonylgeraniin A. When testing this property in rats two studies using 80mg/kg and 50-100mg/kg have found that dimocarpus longan is capable of reducing uric acid levels with changes in urate transporters having been noted (induction of GLUT9 and suppression of GLUT1).
Components of longan appear to have the ability to inhibit xanthine oxidase which may be able to reduce uric acid levels
8Interactions with Cancer Metabolism
One study (duplicated in Medline) using SW480 and Colo 320DM colorectal cell lines noted that the water extract of the flower was able to induce apoptosis in a concentration and time dependent manner with a potency comparable to EGCG (the main catechin of the four green tea catechins), with cancer cells reaching under 20% viability with 400mcg/mL for 48 hours. The mechanism of apoptosis was related to caspase-3 release and PARP cleavage from reductions in mitochondrial membrane potential, and this has been replicated elsewhere where an antiproliferative effect was also noted with longan seeds.
May induce apoptosis in cancer cells, but only one study has so far been conducted
9Interactions with Aesthetics
Longan appears to have anti-oxidative properties due mostly to the gallic acid and ellagic acid components, as in a DPPH assay both compounds are more effective in sequestering free radicals as the reference compound Vitamin C and dried seeds seem somewhat comparable to Camellia Sinensis (source of green tea catechins). These effects may underlie tyrosinase inhibitory potential, with IC50 values of 2.9 and 3.2mg/mL (fresh and dried seeds respectively) both of which are significantly weaker than the reference compound Kojic Acid (8.9ug/mL).
Weak protective effects on the skin
Smilax is a phytonutrient combination therapy of Hordeum vulgare, Polygonatum multiﬂorum, Longan, Ligusticum sinense, Lilium brownii, Gynura pinnatiﬁda, Coreopsis lanceolata, Juniperus communis, and Ginger in a 30:2:4:10:20:20:2:2:1 ratio. After administration of liquid drops thrice a day for 6 weeks to obese persons (totalling a daily dose of 40mg dry weight of the combination) noted a decrease in body weight of 8.5% that, although exceeding placebo, was not statistically significant; relative to their own baseline, the Smilax group lost BMI, weight, and hip circumference while the placebo group did not.
A later in vitro test noted that incubation of human adipocytes with Smilax resulted in less lipid accumulation and increased glycerol release; suggesting lipolysis.
One study using a combination therapy known as Smilax noted significant reductions in weight loss associated with treatment; this study has not yet been replicated
In a preliminary toxicology test, up to 13 weeks of daily consumption of Longan seed extract (up to 800mg/kg for 4 weeks and 500mg/kg for 13 weeks) was not associated with any overt toxicological effects (some fluctuations of food intake that were not dose or time dependent and thought to be due to chance, a random significant spike in eosinophil % in male mice). Ingestion of 5g/kg in mice for up to 14 days was not associated with any toxicological signs.
No apparent toxicity associated with Longan fruits in high doses