Herbal Research

Huang Qin

RADIX SCUTELLARIAE (BLACK SKULLCAP ROOT)

Huang Qin is the dried root of Scutellaria baicalensis (Labiatac). The herb is mainly produced in the provinces of Hebei, Inner Mongolia, Shanxi, Shandong and Shaanxi. It is collected in spring and autumn, and steamed or boiled before it is dried in the sun.

CHEMISTRY

Over 50 flavone derivatives have been isolated from the root of S. baicalensis. Baicalin and wogonoside are the two major compounds found in the root. Other flavonoids isolated from the root are listed in Table 7-1.

Table 7-1. Flavonoids isolated from Scutellaria baicalensis root1-6.

Classification	Compounds
Flavones	Chrysin Baicalein Wogonin Norwogonin 7-Methoxy-norwogonin Oroxylin A Baicalein-7-methylether 5-Hydroxy-7,8-dimethoxyflavofle 5,8~Dihydroxy-6,7-dimethoxyflavone 5,7,2'-Trihydroxy-8-methoxyflavone 5,8,2'-Trihydroxy-7-methoXyflavone 5,7,2'-Trihydroxy-6-methoxyflavone Skullcapflavone I Skullcapflavone II (neobaicalein) 5,8,2'-Trihydroxy-6,7-dimethyoxyflavone Tenaxin Scutellarein Hispidulin 5,7,4'-Trihydroxy-8-methoxy-flavone 5,7,2',3'-Tetrahydroxyflavone 5,7,2',6'-Tetrahydroxyflavone 7,2',6'-Trihydroxy-5-methoxyflavone 5,7,2'-Trihydroxy-6'-methoxyflavone Ganhuangenin Viscidulins I and II 5,7,2'5'-Tetrahydroxyflavone (-)Eriodictyol Rivularin
Flavone O-glycosides	Oroxylin A 7-O-b-D-glucopyranosiduronide Scutellarin Baicalein 7-O-b-D-glucopyranoside Wogonin 5-O-b-D-glucopyranoside Viscidulin III-2'-O-b-D-glucoside 5,2',6'-Trihydroxy-6,7,8-trimethoxyflavone 2'-O-glucoside 5,2',6'-Trihydroxy-6,7-dimethoxyflavone 2'-O-glucoside 3,5,7,2',6'-Pentahydroxyflavone 2'-O-glucoside (2S)-5,7-Dihydroxy-6-methoxyflavanone 7-O-glucoside Benzyl O-b-D-apiofuranosyl-(1 2)-b-D-glucopyranoside Chrysin 7-O-b-D-glucuronopyranoside 5,7,2'-Trihydroxy-6-methoxyflavone 7-O-b-D-glucuronopyranoside (+)Syringaresinol-O-b-D-glucuronopyranoside
Flavone C-glycosides	6-C-b-D-Glucopyranosyl-8-C-a-L-arabinopyranosylchrysin 6-C-a -L-Arabino-pyranosyl-8-C-b-D-glucopyranosylchrysin Chrysin 6-C-b-D-glucopyranoside Chrysin 8-C-b-D-glucopyranoside
Flavanones	Dihydrobaicalein Dihydrooroxylin A 5,7,2',6'-Tetrahydroxyflavanone 3,5,7,2'6'-Pentahydroxyflavone
Chalcone	2,6,2',4'-Tetrahydroxy-6'-methoxychalcone

PHARMACOLOGY

Antimicrobial Activity

The root has a wide antibacterial spectrum. Its decoction showed different degrees of antibacterial activity in vitro against hemolytic streptococcus, pneumococcus, meningococcus, Staphylococcus aureus, Bacillus diphtheriae, B. dysenteriae, B. anthracis, B. typhosus, B. paratyphosus, B. proteus, E. coli, Pseudomonas aeruginosa, Bordetella pertussis, and Vibrio comma. Baicalin is the major antibacterial active component7'8. In tests with selected oral bacteria, including suspected periodontopathogens, Bacterioides melamnogenicus intermedius was found to be most sensitive to a 2% decoction of S. baicalensis9.
The aqueous extract was shown in vitro to be active against 10 kinds of skin fungi including Trichophyton violaceum and Microsporum audouini, and the decoction was active against 9 skin fungi including Trichophyton violaceum and Microsporum can is7'8.
Crude extract of the herb or baicalin was shown to inhibit HIV antigen expression in H9 cell culture, with 50% inhibitory doses of 0.6 pg/ml and 3.3 gg/ml, respectively. They also inhibited P24 antigen production in H9 cells, with IC50 values of 1.94 lg/ml and 4.74 lg/ml, respectively10. Baicalin was found to be a non-competitive inhibitor of HIV reverse transcriptase (RT), with an IC50 of 22 lM11 ~. Baicalin inhibited HIV- 1 infection and replication as measured by a quantitative focal syncytium formation on CEM-ss monolayer cells and IIIV-1 specific core antigen p24 expression and retroviral reverse transcriptase (RT) activity in the HIV- 1 infected 119 cells. It was further found that the enzymatic activity of purified recombinant HIV- l/RT was inhibited by baicalin. In addition to lymphoid cell lines, the anti-HIV- 1 activity of baicalin was also observed in cultures of primary human peripheral blood mononuclear cells infected with HIV- 1 in vitro. Neither cytotoxic nor cytostatic effects on the inducator cells were found under the assay condition12. Another component of the root 5,7,4-trihydroxy-8-methoxyflavone was found to suppress replication of mouse-adapted influenza viruses A/Guizhouf54/89 and B/Ibarald/2/85 in Madin-Darby canine kidney (MDCK) cells in a dose-dependent manner by 50% at 20 lM and 90% at 40 lM, respectively13.

Antiallergic Effect

In egg white-sensitized guinea pigs, oral administration of 50 mg/kg of baicalin for one week protected the animals against allergic reaction due to re-inspiration of the antigen, significantly prolonging the latent period of convulsion. Baicalin and baicalein significantly inhibited allergic asthma in guinea pigs and allergic contraction reaction (Schultz-Dale reaction) of the isolated small intestine and trachea of sensitized guinea pigs. Baicalein was more potent than baicalin. Likewise, baicalein had a stronger inhibition than baicalin on the systemic passive allergic reaction of guinea pigs and mice, and skin passive allergic reaction of guinea pigs. This allergy inhibition is believed due to the inhibition of mercaptylase and consequently inhibition of the release of allergic mediators (histamine and SRS-A) during antigen-antibody interaction. Wogonin suppressed acetyleholine-induced spasm of the isolated mouse small intestine7'8. In tests for antiasthmatic effects using isolated tracheal muscle from guinea pigs as model, both baicalin and baicalein showed antihistaminic, anticholinergic and papaverine-like activities. A synergism between baicalin and ephedrine was observed14. Many of the flavone derivatives including wogonin, wogonoside, skullcapflavone II, and 5,7,2',5'-tetrahydroxyflavanone were active in inhibiting the histamine release from rat peritoneal mast cells induced by compound 48/80' ~. Using the rat basophilic leukemia cell line RBL-2H3 to test for inhibitory activity on antigen-induced histamine release from IgE-sensitized RBL-2H3 cells, baicalein and scutellarein showed strong inhibition, with IC50 values of 1.07 x
10-5 M and 3.15 x 10-6 M, respectively. Scutellarein was less cytotoxic than baicalein16.
Because the antiallegic drugs disodium cromoglycate (DSCG) and tranilast are strong inhibitors of hyaluronidase, the effect of baicalein on hyaluronidase was also tested. Baicalein showed a dose-dependent inhibitory effect'7. It has been found that basophil and its precursor numbers are increased in atopic patients. The effect of baicalein on human basophil growth was therefore examined in vitro using cord blood mononuclear cells as a basophil precursor source. It was found that baicalein at 1-100 lM dose-dependently inhibited basophil number and histamine content18.

Antiinflammatory Effect

Baicalin, baicalein and wogonin were found to be able to inhibit the increase of vascular permeability in mice induced by acetic acid and to reduce acute paw edema in rats induced by compound 48/80. They also suppressed development of secondary lesion in adjuvantinduced arthritis in rats19. Wagonin also inhibited carrageenin-induced paw edema in rats at 75 mg/kg20. Recently, It was found that the flavonoids from S. baicalensis possess a dual function both as an antiinflammatory agent and an enhancer of cellular activity in gingival fibroblasts21. The antiinflammatory effect of baicalein was greater in the chronic inflammation model (rat adjuvant arthritis, ED50 120.6 mg/kg) than in the rat carrageenininduced paw edema (ED50 > 200.0 mg/kg). Further study of the 5-lipoxygenase (5-LO) inhibitory activity of baicalein on leukotriene C4 (LTC4) biosynthesis by rat resident peritoneal macrophages stimulated with calcium ionophore showed that it significantly inhibited LTC4 production with an IC50 of 9.5 lM, suggesting that inhibition of the 5-LO pathway of arachidonic acid metabolism may be one of the mechanisms of baicalein's antiinflammatory activity22. Wagonin, baicalein and baicalin at 1 pg/mI expressed significant inhibition (>50 %) in LPS-induced production of IL-1b, similar to that of prednisolone. Moreover, the flavonoids inhibited IL-b induced synthesis of PGE2 and LTB4 considerably. In addition, they exerted a moderate inhibition (33%-36%) of collagenolytic activity, comparable to 40% inhibition by tetracycline. Meanwhile, the cellular activity of fibroblasts was augmented remarkably (40%) by baicalein and slightly by baicalin and wogonin. Consistent with the cellular activation, the flavonoids enhanced the synthesis of both collagen and total protein in fibroblasts, in contrast to growth factors which increased only the synthesis of total protein23.

Antipyretic Effect

Oral administration of the extract of the herb dose-dependently reduced the rectal temperature in conscious rats. The hypothermia was brought about solely by cutaneous vasodilation as estimated by an increase incutaneous temperature. There were no changes in either metabolic heat production or respiratory evaporative heat loss24. Baicalin also produced an significant antipyretic effect in rats with fever. However, it did not reduce the normal body temperature. The antipyretic activity of 4.5 mg/kg of baicalin was similar to that of 100 mg/kg of coantipyrine25.

Cardiovascular Effect

The blood pressure of anesthetized dogs was markedly decreased by intravenous administration of 0.5 g/kg of the fluid extract, oral administration 1 g/kg of the aqueous extract, intravenous administration of 60 mg/kg of the decoction, and oral, intramuscular or intravenous administration of 1 g/kg of the alcoholic extract of the root. Baicalin was found hypotensive-active at intravenous doses of 10-20 mg/kg. Oral or rectal administration of the tincture preparation lowered the blood pressure of dogs with neurogenic hypertension. A marked reduction of blood pressure was achieved in dogs with or without renal hypertension after giving the aqueous extract orally trice daily for 4 weeks. The hypotensive effect is believed to be related to its vasodilation effect and the inhibition of the vasomotor centers7'8.
Baicalin, wogonin, oroxylin A, skullcapflavone II and chrysin were inhibitory in vitro on collagen-induced blood platelet aggregation at a concentration of 0.1 mM. Chrysin also inhibited ADP-induced blood platelet aggregation, whereas baicalin and wogonin had an inhibitory action on arachidonic acid-induced platelet aggregation. Baicalein and baicalin further inhibited the conversion of fibrinogen to fibrin by thrombin. They also prevented the decrease of platelets and fibrinogen in rats with experimental DIC (disseminated intravascular coagulation) induced by endotoxin26.
Effects of the Scutellaria flavonoids on mammalian lipid metabolism were also studied. Wogonin inhibited deposition of liver triglycerides and increased serum high-density lipoprotein-cholesterol levels in rats fed on a corn oil-cholesterol-sodium cholate mixture. Skullcapflavone II reduced total cholesterol levels and liver triglyceride content in serum and increased serum high-density lipoprotein-cholesterol. Baicalein and baicalin reduced serum-free fatty acid and triglyceride levels and liver glyceride content27. The flavone derivatives also inhibited lipid peroxidation in rat liver homogenate stimulated by a mixture of FeCl2 and ascorbic acid or by a mixture of HADPH and ADP28'29.
In rabbits vascular smooth muscle cells, baicalein, baicalin and wogonin dose-dependently inhibited the proliferative response induced by 5% fetal calf serum at 10-6-10-4 M. Baicalein had a greater inhibitory effect than baicalin and wogonin, and may be a useful template for the development of better drugs to prevent the pathological changes of atherosclerosis and restenosis30.

Hepatoprotective and Choleretic Effects

The root or baicalin has protective effect against Cd4- or galactosalmine (GlaN)-caused liver injury. Given 3 and 20 h before GlaN treatment, an extract of the root showed protection against GlaN-induced lethal toxicity31. The flavonoid components of the root suppressed lipid peroxidation in the liver and inhibited the increase of triglyceride in serum and liver8. Baicalin can decrease the hepatotoxicity of strychnine, increasing the LD50 by
2.5 times7.
Intravenous injection of the decoction (0.5 g/kg) increased bile secretion in anesthetized
dogs. The aqueous, alcoholic extracts, or baicalin also increased bile secretion in rabbits. Intravenous administration of baicalin reduced the increased blood bilirubin level in rabbits caused by ligation of the common bile duct7.

Sedative and Diuretic Effects

The root showed sedative effect in mice, dogs and rabbits. Intraperitoneal administration of 2 g/kg of the decoction inhibited the positive conditioned reflex in mice, prolonging its latent period and the frequency of reinforcement. If the positive conditioned reflex was established before the negative one, the root could improve the negative conditioned reflex, thus intensifying the cortical inhibition. Intraperitoneal administration of baicalin (500 or 1000 mg/kg) also produced sedative effect in mice, lasting for 2 to 3 h. Mild sedation in rabbits was observed after intravenous administration of 1 g/kg of the aqueous extract. Central inhibition was increased and death could ensue by increasing the dose.
Intravenous administration of the aqueous extract, alcoholic extract, baicalin, baicalein or wogonin increased the urine output of anesthetized rabbits. Diuretic effect has also been observed in rabbits by oral administration of the alcoholic extract and in mice by intrapentoneal administration of baicalin or baicalein. The condensed water extract or baicalin was also diuretic in anesthetized dogs7.

THERAPEUTIC APPLICATIONS

Traditional Description

Huang Qin has a bitter taste and a cold property, acting on the lung, gallbladder, stomach and large intestine channels. It has the functions of:

(i) clearing away heat and dampness, used in various damp heat syndrome and acute febrile diseases;
(ii) purging fire and detoxicating, used in cough with yellow sputum due to heat in the lung; and
(iii) stopping bleeding and preventing miscarriage, used in bleeding due to invasion of blood by excessive heat, such as hematemesis, epistaxis, hematuria or hemafecia, metrorrhagia and metrostaxis.

Applications
Respiratory tract infection in children

The 50% decoction of the herb was used in the treatment of 51 cases of acute upper respiratory infection, 11 acute bronchitis and 1 acute tonsillitis at daily doses of 6-10 ml. Body temperature was normalized in 3 days in 51 cases7.

Scarlet fever

The decoction of the herb given orally to 1577 persons significantly decreased the incidence of scarlet fever7.

Carriers of epidemic cerebrospinal meningitis

Spraying of 2 ml the aerosol of the 20% decoction of the herb (equivalent to 0.4 g of the herb) to the throat was effective in all 209 cases tested7.

Infectious hepatitis

Baicalin was used in the treatment of icteric and nonicteric hepatitis and active chronic hepatitis. In effective cases, it restored the liver functions and improved the clinical symptoms. It was also reportedly effective against chronic hepatitis B and in those with persistently positive HBsAg for more than one year7.

Acute biliary infection

Intravenous infusion of baicalin in the treatment of 72 cases of acute biliary infection (30 biliary tract ascariasis complicated with cholecystitis and cholangitis, 25 acute cholecystitis, 10 acute retrograde pancreatitis, 5 cholecystitis complicated with cholelithiasis, 1 liver cirrhosis complicated with biliary infection and 1 biliary infection with secondary liver abscess) resulted in marked improvement in 45 cases and significant improvement in 20 other cases7.

Psoriasis

Baicalin has been recently reported to be effective in the treatment of psoriasis vulgaris. Of 38 patients treated with baicalin, 13.16% were cured and 10.23% were essentially cured. The effects were further increased by using baicalin together with the extract of rhubarb, 0.45 g each, administered orally trice daily. Table 7-2 shows the result of such a treatment regimen in 43 cases of psoriasis vulgaris, 1 case of psoriasis with postulation and 1 case of erythroderma psoriaticum32'33.

Table 1 Effects of baicalin plus rhubarb in the treatment of psoriasis.

Treatment	Cured	Essentially cured	Significantly improved	Improved	Ineffective	Total cases
1 month	1	1	3	3	0	8
2 months	3	1	2	1	0	7
3 months	2	4	3	0	1	10
4 months	3	6	1	3	0	13
5 months	3	2	1	0	0	6
6 months	0	1	0	0	0	1

Hypotension

The tincture of the herb was used in 51 hypertensive patients and produced hypotensive and symptom-relieving effects7.

SIDE EFFECTS AND TOXICITY

No side effects, except rare gastric discomfort and diarrhea, were associated with either oral administration of the crude preparation or injection of baicalin and baicalein. Rabbits receiving oral dose of 10 g/kg of the decoction or intravenous injection of 2 g/kg of the ethanolic extract appeared sedation; no death occurred. Intravenous administration of 2 g/kg of the aqueous extract also produced sedative and hypnotic effects in rabbits, but the animals died 8 to 12 h later. When the dosage was reduced to 1 g/kg, sedation but no death occurred. A single oral dose of 12 or 15 g/kg of the aqueous extract elicited no abnormal reactions in dogs during 48 h of observation, except emesis in the high dose group. Oral administration of 4 or 5 g/kg to dose trice daily for 8 weeks did not produce any significant abnormalities in routine blood test and histology of internal organs. Only lose stool happened to animals in the high dosage group but it disappeared upon discontinuation of the medication. The lethal doses of various preparations of the root in mice by subcutaneous administration are 6 g/kg for ethanolic extract and baicalin and 4 g/kg for wogonin. The LD50 of baicalin in mice by intraperitoneal administration was 3.081 g/kg7.

REFERENCES

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