Chinese sweet leaf

Rubus suavissimus (of the family Rosaceae) is a small fruit bearing plant that is sometimes called Ten-Cha (Japan)^[1] or Chinese Sweet Leaf (China).^[2] Ten-Cha is actually a generic term for sweet Chinese teas in Japan, and the tea using rubus suavissimus is more specifically called tenyoukenkoushi among other possible optios of dojosan (Hydrangea aspera), gyuhakuto (Hedyotis hedyotidea), and tasuiseikayou (Lithocarpus polystachyus).^[1]

The leaves of this plant, almost always brewed as a tea, have been used traditionally to maintain kidney health, improve blood flow,^[3] promote appetite, induce expectoration, stop cough, and alleviate fever.^[1]

Rubus suavissimus is, essentially, a tea that has been used to improve symptoms of sickness and to aid the body in clearing mucus (coughing), clearing a fever, and improving appetite

The composition of rubus suavissimus leaves (unless otherwise specified) include:

• Rubusoside (also known as desglucostevioside), the β-D-glucosyl ester of 13-O-β-D-glucosyl-steviol at around 4.87% dry weight^[4][5] and present in the water extracts (tea);^[6] structurally similar to the steviol glycosides from stevia^[7]
• Steviol monoside (0.08% dry weight^[4])
• Suavioside A-J with C₁, D₁, and D₂ specified;^[8]
• Gallic acid (0.13% dry weight^[4]) and ellagic acid (0.71% dry weight)^[4][2]
• Rubusuaviins A-F (tannin structures)^[9]
• 1(β)-O-galloyl pedunculagin^[9]
• Strictinin^[9]
• Lambertianin A^[9]
• Sanguiin H-5, H-6, and 1-degalloylsanguiin H-6^[9]
• Rutin (0.11% dry weight^[4])
• Ent-13-hydroxy-kauran-16-en-19-oic acid and ent-kaura-16-en-19-oic-13-O-β-D-glucoside^[10]

27% of the weight of the leaves consists of rubusoside, gallic acid, and ellagic acid in approximately a 17.2:1.8:1.^[2]

The overall plant content appears to be mixed between diterpenoids and tannins; while the tannins likely confer a varity of health effects, the diterpenoids are structured similar to stevia diterpenoids and confer a sweet taste to the leaf

Rubusoside appears to have a slightly bitter aftertaste but 115-fold higher sweetness than sucrose,^[6] and this molecule underlies why rubus suavissimus is called 'Sweet tea' in China and Japan.

All suaviosides are sweet except for C₁, D₂, and F which possess a bitter taste.^[8]

Most diterpenoids in this leaf are sweet and the overall taste is sweet, although some isolated diterpenoids are bitter in taste

Due to appearing in the urine in their intact forms following oral administration to the rat rubusoside, ellagic acid, and gallic acid appear to be absorbed from the intestines.^[2]

After a dose of 1,000mg/kg rubus suavissimus extract (860mg rubusoside, 90mg ellagic acid, and 50mg gallic acid per 1,000mg extract) these three molecules appeared in the urine in an unmetabolized form;^[2] pharmacokinetics were not evaluated.

It appears that the two most well known tannins and the main flavorant (rubusoside) are not metabolized in the rat body following oral ingestion

The tannin structures in rubus suavissimus appear to have inhibitory potential on intestinal α-amylase, and at a concentration of 10µg/mL in vitro inhibitory potential appeared to be most potent with and rubusuaviin A and B (60.6-60.8%) with comparable inhibitory potential from rubusuaviin E (52.3+/-2.7%), 1(β)-O-galloyl pedunculagin (56.2+/-4.4%), and Lambertianin A (56.3+/-2.7%).^[9]

The tannin structures in the leaves appear to inhibit the α-amylase enzyme with respectable potency, but there are no studies in living models at this point in time

In rats fed a high fed diet with or without 3% rubus suavissimus in the feed (maximum dose of 220mg/kg), there was no significant influence on fasting blood glucose over nine weeks.^[2]

In isolated 3T3-L1 adipocytes, a hot water extract of the leaves (0.5% of the medium) appears to promote the early phases of adipogenesis associated with increasing PPARγ expression to 137-191% of control when measured after 24-48 hours and increased its gene products.^[11]

It appears that rubus suavissimus extract at 10μg/mL (86% rubusoside with the rest being ellagic and gallic acids) inhibits the growth of 3T3-L1 adipocytes by 20% yet causes a significant suppression of VEGF but not bFGF expression.^[2] This suppression of VEGF is thought to reflect a reduction in angiogenesis and, secondary to that, less growth of body fat since the two are highly correlated.^[12][13] This is probably related to the gallic acid content, as although adding 0.1-0.3% of the diet as gallic acid failed to inhibit angiogenesis (due to absorption issues) injections of 0.1% inhibited angiogenesis by 41%.^[14]

While there are some influences on the level of the fat cell suggesting it should proliferate, the influences on blood vessels that innervate the fat cells appear to be anti-obese. More research on the particular mechanisms of action and the molecule mediating these effects is needed

Rubus suavissimus at 3% of the diet (maximum dose of 220mg/kg) over nine weeks in rats fed a high fat diet did not influence food intake yet reduced weight gain (22%) and fat mass gain (48%) relative to high fat control, reaching a final body weight comparable to the low fat fed control.^[2]

The lone rat study noted pretty much an inhibition of the fat gain associated with a high fat diet in rats (being comparable to the normal chow control) suggesting a relatively potent anti-obese effect

In mouse macrophages transfected with a stable NF-kB reporter cell (to assess NF-kB interactions^[15]), a crude rubus suavissimus extract at 500µg/mL fully prevented NF-kB activity albeit with some toxicity, but a 20% methanolic was also fairly potent without apparent toxicity.^[16]

Possible antiinflammatory effects that occur at a high concentration and do not appear to be overly promising whatsoever

In isolated mast cells stimulated with compound 48/80, rubus suavissimus is able to inhibit COX enzyme activity with an IC₅₀ value of 170μg/mL (less than the reference drug of aspirin at 15μg/mL).^[17] It inhibited histamine release but did not influence on histamine-induced vascular permeability was not significant despite the inhibition of histamine secretion reaching significance.^[17] When tested elsewhere, the water extract of rubus suavissimus noted that 300μg/mL was able to inhibit release of histamine from stimulated mast cells (although to a potency that was noted with 100μg/mL of a 40% ethanolic garcinia mangostana extract) but failed to suppress PGE₂ secretion.^[18]

There appear to be some antiallergic properties associated with the tea extract, although it seems to be less potent than the reference drugs and other tested supplements

Rubus suavissimus in persons with confirmed dust mite allergies, supplementation of 400mg of the extract daily over the course of four weeks noted reductions in nasal congestion and runiness as well as sneezing although not to a degree significantly better than placebo;^[1] the overall rate of improvement was 31.9% in the rubus suavissimus group while it was 23.8% in placebo.^[1]

The aforementioned study^[1] did make note of two positive studies conducted by Ukai et al. (1995, 1998) which showed promise with 120mg of a supplement and 80mg of a tea in persons with perennial allergic rhinitus and cedar pollinosis, respectively; neither of these studies can be located online.

There appear to be two untracable studies noting benefit with the leaf extract, but the one accessible and controlled study on the subject matter failed to find a therapeutic effect of the tea on symptoms of allergies

Ingestion of 3% of the rat diet as rubus suavissimus (maximal dose of 220mg/kg) for nine weeks has failed to exert any biochemical or clinical side effects.^[2] There was an increase in serum potassium noted in the high fat fed supplement group that was not seen in high fat nor low fat control, but it was not deemed clinically relevant.^[2]

Currently no known toxicity associated with this tea