Insulin resistance means that body cells do not respond appropriately when insulin is present. Unlike type 1 diabetes mellitus, insulin resistance is generally "post-receptor", meaning it is a problem with the cells that respond to insulin rather than a problem with the production of insulin³.

Types of diabetes mellitus:⁴

 Type 1 diabetes

 Type 2 diabetes

 Gestational diabetes

 Other types

Type 1 Diabetes:

Type 1 diabetes mellitus is characterized by loss of the insulin-producing beta cells of the islets of Langerhans in the pancreas leading to insulin deficiency. This type of diabetes can be further classified as immune-mediated or idiopathic. The majority of type 1 diabetes is of the immune-mediated nature, where beta cell loss is a T-cell mediated autoimmune attack. There is no known preventive measure against type 1 diabetes. Sensitivity and responsiveness to insulin are usually normal, especially in the early stages. Type 1 diabetes can affect children or adults but was traditionally termed “juvenile diabetes” because it represents a majority of the diabetes cases in children.

Type 2 Diabetes:

Type 2 diabetes mellitus is characterized by insulin resistance, which may be combined with relatively reduced insulin secretion. The defective responsiveness of body tissues to insulin is believed to involve the insulin receptor. Type 2 diabetes is the most common type.

In the early stage of type 2 diabetes, the predominant abnormality is reduced insulin sensitivity. At this stage, hyperglycaemia can be reversed by a variety of measures and medications that improve insulin sensitivity or reduce glucose production by the liver. As the disease progresses, the impairment of insulin secretion occurs, and therapeutic replacement of insulin may sometimes become necessary in certain patients.

Gestational Diabetes:

Gestational diabetes mellitus (GDM) resembles type 2 diabetes in several respects, involving a combination of relatively inadequate insulin secretion and responsiveness. It occurs in about 2–5% of all pregnancies and may improve or disappear after delivery. Gestational diabetes is fully treatable but requires careful medical supervision throughout the pregnancy. About 20–50% of affected women develop type 2 diabetes later in life.

Even though it may be transient, untreated gestational diabetes can damage the health of the fetus or mother. Risks to the baby include macrosomia (high birth weight), congenital cardiac and central nervous system anomalies, and skeletal muscle malformations. Increased fetal insulin may inhibit fetal surfactant production and cause respiratory distress syndrome. Hyperbilirubinemia may result from red blood cell destruction. In severe cases, perinatal death may occur, most commonly as a result of poor placental perfusion due to vascular impairment.

Other Types:

Pre-diabetes indicates a condition that occurs when a person’s blood glucose levels are higher than normal but not high enough for a diagnosis of type 2 diabetes. Many people destined to develop type 2 diabetes, spend many years in a state of pre-diabetes. Some cases of diabetes are caused by the body’s tissue receptors not responding to insulin (even when insulin levels are normal, which is what separates it from type 2 diabetes); this form is very uncommon. Genetic mutations (autosomal

or mitochondrial) can lead to defects in beta cell function. Abnormal insulin action may also have been genetically determined in some cases. Any disease that causes extensive damage to the pancreas may lead to diabetes (for example, chronic pancreatitis and cystic fibrosis). Diseases associated with excessive secretion of insulin-antagonistic hormones can cause diabetes (which is typically resolved once the hormone excess is removed). Many drugs impair insulin secretion and some toxins damage pancreatic beta cells.

Causes:

1. Life style⁵

2. Medical condition⁶

3. Genetics⁷

WHO Diabetes criteria

Diabetes mellitus is characterized by recurrent or persistent hyperglycemia, and is diagnosed by demonstrating any one of the following:

· Fasting plasma glucose level at or above 7.0 mmol / L (126 mg/dL).

· Plasma glucose at or above 11.1 mmol/L (200 mg/dL) two hours after a 75 g oral glucose load as in a glucose tolerance test.

· Symptoms of hyperglycemia and casual plasma glucose at or above 11.1 mmol /L (200 mg/dL).

· Glycated hemoglobin (hemoglobin A1C) at or above 6.5. (This criterion was recommended by the American Diabetes Association in 2010; it has yet to be adopted by the WHO.)

DRUGS:

· Thiazolidinedione (TZDs). These increase tissue insulin sensitivity by affecting gene expression

· α-glucosidase inhibitors, which interfere with absorption of some glucose containing nutrients, reducing (or at least slowing) the amount of glucose absorbed

· Meglitinides which stimulate insulin release quickly; they can be taken with food, unlike the sulfonylureas which must be taken prior to food (sometimes some hours before, depending on the drug)

· Peptide analogs which work in a variety of ways:

o Incretinmimetics which increase insulin output from the beta cells among other effects. These includes the Glucagon-like peptide (GLP) analog exenatide, sometimes referred to as lizard spit as it was first identified in Gila monster saliva

o Dipeptidyl peptidase-4 (DPP-4) inhibitors increase Incretin levels (sitagliptin) by decreasing their deactivation rates

o Amylin agonist analog, which slows gastric emptying and suppresses glucagon (pramlintide)

Management:

Diabetes mellitus is a chronic disease which is difficult to cure. Management concentrates on keeping blood sugar levels as close to normal (“euglycemia”) as possible without presenting undue patient danger. This can usually be with close dietary management, exercise, and use of appropriate medications (insulin only in the case of type 1 diabetes mellitus. Oral medications may be used in the case of type 2 diabetes, as well as insulin).

Lifestyle modifications:

There are roles for patient education, dietetic support, sensible exercise, with the goal of keeping both short-term and long-term blood glucose levels within acceptable bounds In addition, given the associated higher risks of cardiovascular disease, lifestyle modifications are recommended to control blood pressure in patients with hypertension, cholesterol in those with dyslipidemia, as well as exercising more, smoking less or ideally not at all, consuming a recommended diet. Patients with foot problems are also recommended to wear diabetic socks, and possibly diabetic shoes.

Anti oxidant activity:

Though pathophysiology of diabetes remains to be fully understood, experimental evidences suggest the involvement of free radicals in the pathogenesis of diabetes and more importantly in the development of diabetic complications⁸. Free radicals are capable of damaging cellular molecules, DNA, proteins and lipids leading to altered cellular functions. Many recent studies reveal that antioxidants capable of neutralizing free radicals are effective in preventing experimentally induced diabetes in animal models as well as reducing the severity of diabetic complications⁹.

For the development of diabetic complications, the abnormalities produced in lipids and proteins are the major etiologic factors. In diabetic patients, extra-cellular and long lived proteins, such as elastin, laminin and collagen are the major targets of free radicals. These proteins are modified to form glyco-proteins due to hyperglycaemia. The modification of these proteins present in tissues such as lens, vascular wall and basement membranes are associated with the development of complications of diabetes such as cataracts, microangiopathy, atherosclerosis and nephropathy¹⁰. During diabetes, lipo- proteins are oxidized by free radicals.

Cytochrome P450 (CYP) enzymes participate in the detoxification of xenobiotics. Paradoxically, they can produce reactive oxygen species (ROS) that can damage DNA, as well as lipids and proteins. Metabolism of xenobiotics leads to the production of reactive oxygen species (ROS), which leads to oxidative stress.

Many literatures have reported that, chronic oxidative stress is one of the important causes for the production of auto antibodies which leads to autoimmune diseases¹¹.

Lipid peroxidation in fats and fatty foods not only deteriorates their quality and brings about chemical spoilage, but also generates free radicals and reactive oxygen species which (ROS) are implicated in carcinogenesis, mutagenesis, inflammation, aging and cardiovascular diseases. ROS, which include free radicals such as superoxide anion radicals (O₂ - ), hydroxyl radicals (OH.) and non free radical species such as H₂O₂and singled oxygen ( 1 O₂ ), are various forms of activated oxygen¹².

MATERIALS AND METHODS:

(i) Chemicals

The analytical graded chemicals were used for all the experiments.

(ii) Collection and Authentication

Erythrina indica belonging to family Fabaceae has been selected for the study. The plant material was collected from Thirumala forest, Chittor district, Andhra Pradesh, India and authenticated by Dr. Madhava Chetty, botanist, Sri Venkateshwara University, Tirupathi. The bark was shade dried and ground into coarse powder.

(iii) Preparation of Extract

500g of powdered bark of Erythrina indica was extracted continuously using soxhlet apparatus with methanol for about 48 hours at 30°C. The extracts were concentrated under reduced pressure using rotary vacuum flash evaporator to get a constant volume.

(iv) Preliminary Phytochemical Screening

The plant material is subjected to preliminary phytochemical screening for the detection of various plant constituents.

Evaluation of anti diabetic activity

Drugs:

Streptozotocin (sigma chemicals), Glibenclamide (local market) were used during the experimental protocol.

Animals:

Healthy male Wistar rats of weighing about 175 - 200 g purchased from NIN, Hyderabad were used in the present investigation. All the rats were given a period of acclimatization for 7 days before starting the experiment. They were fed ad libitum everyday with standard chow diet and were given free access to water. Animals described as fasting were deprived of food for at least 18 h but were allowed free access to drinking water.

Toxicity studies:

The extracts were given at the doses of 100, 250 and 500 mg/kg/day of body weight. All the animals found to be safe at dose of 3000 mg/kg (as per OECD Guidelines).

Experimental Induction of diabetes

Streptozotocin was purchased from, Sigma chemicals Hyderabad, India and was freshly dissolved in 0.1 M citrate buffer (pH = 4.5) at the dose of 50 mg/kg body weight and injected intraperitoneally within 15 min of dissolution in a vehicle volume of 0.4 mL with 1 mL of tuberculin syringe fitted with 24 gauge needle, whereas normal control group was given citrate buffer only (0.4 mL). Diabetes was confirmed by the determination of fasting glucose concentration on the third day post administration of Streptozotocin¹³.

Experimental design:

Rats were divided into the following groups.

Group I:Consists 6 rats which served as normal control and were given only citrate buffer (0.4 ml pH 4.5) daily.

Group II:Consists 6 STZ induced diabetic rats and served as diabetic control and were given citrate buffer (0.4 ml pH 4.5) daily.

Group III:Consists 6 STZ induced diabetic rats and were treated orally with methanolic extract of Erythrina indica (MEEI) bark at the dose of 100 mg/kg body weight daily for 21 days, once a day.

Group IV:Consists 6 STZ induced diabetic rats and were treated orally with methanolic extract of Erythrina indica bark at the dose of 250 mg/kg body weight daily for 21 days, once a day.

Group V:Consists 6 STZ induced diabetic rats and were treated orally with methanolic extract of Erythrina indica bark at the dose of 500 mg/kg body weight daily for 21 days, once a day.

Group VI:Consists 6 STZ induced diabetic rats and were given Glibenclamide (GBC) at the dose of 10 mg/kg body weight daily for 21 days, once a day.

Collection and processing of blood for estimation of blood sugar levels:

After 21 days of herbal treatment experiments were terminated and observations were made. Body weight was taken before and after experiment with the help of single pan balance. Blood glucose level was estimated on 0 day 7^th, 14^th and 21^st day of experiment with the help of glucometer using strip method and blood was taken from tip of the tail.

RESULTS:

Table 1: Phyto chemical screening

S.NO.	TEST	Methanolic Extract
1	Carbohydrates (Benedict’s test)	+
2	Proteins (Biuret test)	+
3	Amino acids (Ninhydrin test)	+
4	Alkaloids (Mayer’s test)	+
5	Steroids (Salkowaski’s Test)	+
6	Phenolic compounds (FeCl₃)	+
7	Tannins	+
8	Cardiac Glycosides (Kellarkillani Test)	+
9	Saponins (Foam Test)	+

DISCUSSION:

Streptozotocin induced hyperglycaemia has been described as a useful experiment model to study the activity of hypoglycaemic agents¹⁴. Streptozotocin selectively destroys the pancreatic insulin B cells, leaving less active cell resulting in a diabetic state. Streptozotocin action in B cells is accompanied by characteristic alterations in blood insulin and glucose concentrations. Two hours after injection, the hyperglycaemia isobserved later hypoglycaemia occurs¹⁵. These changes in blood glucose and reflect abnormalities in B cell function. STZ impairs glucose oxidation and decreases insulin biosynthesis and secretion¹⁶. It was observed that STZ at first abolished the B cell response to glucose. Temporary return of responsiveness then appears which is followed by its permanent loss and cells are damaged¹⁷.

In the present study, the methanolic extract of bark of Erythrina indica (MEEI) produced a significant decrease in the blood glucose level at a dose level of 250 and 500 mg/kg in hyperglycaemic rats. The animals which are treated with 500 mg/kg of MEEI showed a significant decrease in the blood glucose levels when compared to the 250 and 100 mg/kg MEEI.

The fact that some herbal preparations enhance the beta cell regeneration and peripheral glucose utilization in Alloxan¹⁸ and Streptozotocin induced diabetic rats supports the above assumption.

The significant decrease in the blood glucose levels in diabetic rats treated with bark of MEEI may be by stimulation of the residual pancreatic mechanism, probably by increasing peripheral utilization of glucose¹⁹.

STZ was found to generate reactive oxygen species, which also contribute to¹⁸diabetogenic action and plants containing flavonoids, isoflavanoids, triterpenoids have been shown to be effective in diabetes due to their antioxidants property²⁰. This suggest that the antihyperglycemic activity of Erythrina indica may be due to free radical scavenging activity which enhance the beta cell regeneration against streptozotocin induced free radicals.

Table:2 Antidiabetic activity of Erythrina indica

Group	Treatment	Mean Fasting blood glucose level (mg/dl)
Group	Treatment	Basalvalue	1^st week	2^nd week	3^rd week
Group I	Normal Control	91.83±2.78	92.50±4.23	90.33±4.08	91.50±3.44
Group II	Diabetic Control	291.83±3.30	290.16±3.18	288.66±4.63	291±4.24
Group III	EIME 100 mg/kg	297.66±3.77^b	283.33±3.38^b	270.50±5^b	258.66±4.22^b
Group IV	EIME 250 mg/kg	290.16±4.79^b	265.83±3.96^b	260.33±4.36^b	251.83±2.85^b
Group V	EIME500 mg/kg	295.33±3.66^b	221.66±5.20^b	207±4.27^b	199.33±5.67^b
Group VI	Standard Glibenclamide 10 mg/kg	293.66±4.29^b	209.16±3.76^b	183.50±4.96^b	177.33±4.95^b

Values expressed as Mean ± SD; Number of animals in each group = 6.

P< 0.05*: a, P< 0.001**: b and P< 0.0001***: c

Table:3 Effect ofErythrina indica on body weight of diabetic animals

S.No	Treatment	Mean body weight (g)
S.No	Treatment	Initial	1^st week	2^nd week	3^rd week
Group I	Normal Control	186.33 ± 2.75	188.0 ± 2.60	191.60 ± 2.89	193.90 ± 2.53
Group II	Diabetic Control	187.83 ± 3.30	158.33 ± 3.96	144.50 ± 4.63	132.03 ± 4.24
Group III	ME 100 mg/kg	186.50 ± 3.47^b	160.08 ± 4.21^b	149.28 ± 3.91^b	141.35 ± 3.63^b
Group IV	ME 250 mg/kg	188 ± 4.36^b	181.28 ± 3.66^b	175.13 ± 5.20^b	166.21 ± 4.79^b
Group V	ME500 mg/kg	193.66 ± 3.76^b	187.03 ± 4.96^b	182.48 ± 4.63^b	173.35 ± 4.24^b
Group VI	Standard Glibenclamide 10 mg/kg	189.83 ± 4.29^b	186.22 ± 3.30^b	179.53 ± 4.44^b	176.22 ± 4.67^b

Values expressed as Mean ± SD; Number of animals in each group = 6.

P< 0.05*: a, P< 0.001**: b and P< 0.0001***: c

CONCLUSION:

The literature reports reveal that flavonoids and tannins present in some plant extracts are responsible for antidiabetic activity. In the present investigation also the observed antidiabetic potential ofMEEI may be due to presence of similar phytoconstituents which was evident by preliminary phytochemical screening.

Further pharmacological and biochemical investigations will clearly elucidate the mechanism of action and will be helpful in projecting this plant as a therapeutic target in diabetes.

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Received on 10.12.2011

Modified on 21.12.2011

Accepted on 01.01.2012

Research Journal of Pharmacognosy and Phytochemistry. 4(2): March-April 2012, 70-74