Preclinical Studies

A.   Reduction in blood glucose levels

D-400, a formula containing the main ingredients, Gymnema sylvestre, Eugenia jambolana, Tinospora cordifolia, Pterocarpus marsupium, and Momordica charantia, markedly reduced the blood sugar levels of normal rat as compared to untreated control groups. In addition, it potentiated the hypoglycemic action of insulin in alloxan-induced diabetic rats as well as in rats pretreated with tolbutamide. Significant reductions in blood and urine sugar were also observed in alloxan-induced diabetic rats given D-400.

An alcoholic extract of P. marsupium wood administered to glycemic albino rabbits i.p. significantly lowered their blood sugar levels and improved glucose tolerance as shown in Figures 1 and 2.

Effect of the alcoholic extract of P.marsupium on the fasting blood glucose levels of rabbits.

Figure 1 Effect of the alcoholic extract of P.marsupium on the fasting blood glucose levels of rabbits.

Effect of the alcoholic extract of P. marsupium on the glucose tolerance of rabbits.

Figure 2 Effect of the alcoholic extract of P. marsupium on the glucose tolerance of rabbits.

Other researchers observed mild to moderate hypoglycemic effects in animal models.

The three major phenolic constituents present in the heartwood of P. marsupium, marsupsin, pterosupin, and pterostilbene, were  evaluated for their antihyperglycemic activity in streptozotocin-induced hyperglyce mic rats.

Plasma glucose levels were measured prior to and 72 hours after rats received an injection of streptozotocin (40 mg/kg body weight). Rats with glucose levels above 275 mg/100 ml were divided into 5 groups, each containing 5 animals. Groups I, II, and III received 20 mg/kg body weight of marsupsin, pterosupin and pterostilbene. A 3% aqueous propylene glycol solution was used as the vehicle for both marsupsin and pterosupin, while pure propylene glycol was used to dissolve pterostilbene. Group IV received 30 mg/kg body weight of the reference compound, metformin (1,1-dimethylbiguanide), a known hypoglycemic agent. The fifth group served as the controls; they received 3% aqueous propylene glycol (0.5 ml) in an amount equivalent to the drug treatments. Treatments for each group continued for 3 days before plasma glucose levels were measured.

Marsupsin and pterostilbene significantly reduced the plasma glucose levels of the streptozotocin-induced hyperglycemic rats, and the effect was comparable to metformin (Figure 3 and Figure 4).

 Effect of the major phenolic constituents of P. marsupium on the plasma glucose levels of streptozotocin-induced hyperglycemic rats.

Figure 2 Effect of the major phenolic constituents of P. marsupium on the plasma glucose levels of streptozotocin-induced hyperglycemic rats.

 Effect of the major phenolic constituents of P. marsupium on the plasma glucose levels of streptozotocin-induced hyperglycemic rats. (% Activity represents + percent increase or "-" percent decrease in the blood glucose level.)

Figure 4 Effect of the major phenolic constituents of P. marsupium on the plasma glucose levels of streptozotocin-induced hyperglycemic rats. (% Activity represents "+" percent increase or "-" percent decrease in the blood glucose level.)

B. Pancreatic b-cell regeneration

Several researchers have reported that extracts of P. marsupium and one of its constituents, (-)-epicatechin, have restorative and protective effects in diabetic animals (in which diabetes was induced by treatment with alloxan, a chemical compound that causes irreversible damage to pancreatic b-cells and induces persistent hyperglycemic levels).

Pancreatic beta-cell regeneration was observed in alloxan-induced diabetic rats that received the flavonoid fraction (XE) from the bark of P. marsupium.

As shown in Figure 3, the Pterocarpus marsupium extract restored the beta-cell population of the alloxan-treated animals (Group E) to their

Restorative and protective effects of P. marsupium against the action of alloxan on beta-cells in the pancreatic islets of albino rats.

Figure 3 Restorative and protective effects of P. marsupium against the action of alloxan on beta-cells in the pancreatic islets of albino rats.

Group A- Normal controls
Group B- 24 hour Alloxan controls (rats sacrificed 24 h after i.p. injection of alloxan)
Group C- 24 hour XE protected alloxan group (rats were pretreated with 7 doses of XE over 24 hrs. before receiving alloxan)
Group D- 4 day Alloxan controls (rats were sacrificed 4 days after alloxan administration)
Group E- XE-treated alloxan group (rats were treated with XE for 3 days (6 doses) 24 hours after receiving alloxan).

In addition, administration of the extract before the animals were treated with alloxan protected the animals against beta-cell necrosis (beta-cell death).

The blood sugar of hyperglycemic animals treated with (-)-epicatechin for four days after administration of alloxan for 24 hours was lowered within 24 hours and returned to normal on the 4th and 5th day after alloxan administration. The blood sugar of some animals remained low on the 8th day even though (-)-epicatechin administration was ceased on the 5th day. Survey of these (-)-epicatechin-treated animals revealed pancreatic islets that were filled with beta-cells. In addition, the b-cell counts were normal and showed evidence of mitosis. The results of this study are shown in Figure 4.

Antidiabetic effect of (-)-epicatechin in alloxan-induced diabetic rats

Figure 4 Antidiabetic effect of (-)-epicatechin in alloxan-induced diabetic rats

In another study, Chakravarthy et al. reported favorable results for (-)-Epicatechin when administered prior to alloxan administration. Albino rats received an aqueous extract of (-)-epicatechin in doses of 30 mg/kg i.p. for two days prior to alloxan administration (150 mg/kg i.p.). For the next 24 and 48 hours the animals were protected against the diabetogenic effects of alloxan as shown in Figure 5.

Protective action of (-)-epicatechin on the blood sugar and pancreatic beta-cell counts of alloxan-induced diabetic rats.<br />Group A = Normal controls

Figure 5 Protective action of (-)-epicatechin on the blood sugar and pancreatic beta-cell counts of alloxan-induced diabetic rats.
Group A = Normal controls;
Group B = Alloxan Controls-24 hours;
Group C = Alloxan Controls-48 hours;
Group D = Alloxan-induced, (-)-epicatechin pretreated animals- 24 hours;
Group E = Alloxan-induced, (-)-epicatechin pretreated animals- 48 hours) For all groups N=20 for blood sugar experiments and N=10 for beta cell experiments.

In addition to regenerating beta-cells, (-)-epicatechin has similar properties to the P.marsupium extracts of the heartwood and bark. Other studies have reported that (-)-epicatechin protects normal rat islets from alloxan toxicity, normalizes blood glucose levels, increases insulin secretion, and raises the insulin content of islets in rats.

Pterostilbene obtained from the heartwood was proven to lower blood sugar levels in animal models. Intravenous administration of 10 mg/kg produced fall in blood sugar levels (26-50%) in dogs, over a five hour period.

C.  Comparative blood sugar lowering effects of herbal extracts:

The antihyperglycemic action of 5 Ayurvedic, antidiabetic, medicinal plant preparations in alloxan-induced diabetic rats was investigated.

The plant extracts tested included an aqueous extract of P. marsupium heartwood, an aqueous decoction of Caesaria esculenta roots, an extract of Momordica charantia fruit pulp, an extract of the fresh leaves of Melia azadirachta (Neem), and an extract of the fresh leaves of Ocimum sanctum (Tulsi).

Each extract was diluted 10 times and 2.5 ml/200 g body weight (P. marsupium only) and 2ml/200 g body weight doses for all other extracts was administered to the animals.

The rats were divided into 3 groups based on the number of doses they received, Group A (1 dose), Group B (7 doses), and Group C (12 doses). Significant reductions in hyperglycemia were observed in  alloxan  induced diabetic rats for all plant extracts tested after just one dose of the plant extracts (Figure 1).

Blood sugar levels of non-diabetic, diabetic, and treated rats.

Figure 1 Blood sugar levels of non-diabetic, diabetic, and treated rats.
(All values are expressed as mean ± S.D., N=7)

Similarly, the administration of 7 and 12 doses of the plant extracts also produced significantly lower blood sugar levels. Coincidentally, this normoglycemic condition was stable until the end of the experiment.