Lecture : 7
I- Introduction.
II- Induction of
diabetes.
III- Screening of
hypoglycemic drugs.
IV-Practical example
❑Diabetes Mellitus:
Is a chronic metabolic disorder characterized by high
blood glucose level due to insulin deficiency or decreased
sensitivity of insulin receptors (insulin resistance)
Result*
Fasting
Glucose
Blood Sugar Tolerance
Test
Test
99 mg/dL or
below
Prediabetes 100 – 125
mg/dL
126 mg/dL or
Diabetes
above
Normal
140 mg/dL or
below
140 – 199
mg/dL
200 mg/dL or
above
❑Complications of diabetes:
It is a serious endocrine syndrome with poor metabolic
control and responsible for increased risk of:
1) Metabolic: Diabetic ketoacidosis (DKA)
2) Non-metabolic:
x Microvascular complications: retinopathy, neuropathy and
nephropathy.
x Macrovascular complications: atherosclerosis, hypertension
and peripheral vascular disease.
❑Types of diabetes:
Type-1 diabetes:
[insulin dependent diabetes mellitus (IDDM)].
Due to loss of the insulin-producing beta cells of the
islets of langerhans in the pancreas leading to insulin
deficiency may be immune-mediated or idiopathic.
Treatment:
Insulin injection.
Type-2 diabetes
[Non- insulin dependent diabetes mellitus (NIDDM)].
Due to :
- Defects in insulin secretion ,
- Reduced sensitivity of the tissue
to insulin : (insulin resistance)
- Combination of both.
The defective responsiveness of body tissues to insulin is
believed to involve the insulin receptor.
Treatment of type 2 diabetes:
1) Insulin Secretagogues: Sulphonylureas (Glimepiride)
They act by stimulation of insulin release and inhibition of glucagon release
2) Insulin Sensitizers: Metformin (Glucophage®)
They Increase insulin sensitivity in peripherals and stimulates glucose uptake and
utilization
3) Alpha Glucosidase Inhibitors: Acarbose and Miglitol
They act by inhibition of α-glucosidase enzyme leading to inhibition of digestion
of oligosaccharides to monosaccharides.
Treatment of type 2 diabetes:
4) GLP-1 receptor agonists: Exenatide
5) DPP-IV inhibitors: Sitagliptin
6) Amylin analogue: Pramlintide
❑
❑
Animal models of diabetes are greatly useful and advantageous
in biomedical studies because they offer promise of new insights
into human diabetes.
Methods of induction in laboratory animals :
1- Chemically
2- Surgically
3- Genetically
4- Viral induction
5- Large oral glucose
6- Insulin Antibodies-induced diabetes
7- In-vitro models for diabetes
Chemical agents which produce diabetes :(diabetogenic
agent) include agents that:
Damage ß- cell, cause temporary inhibition of insulin
production and/ or secretion and diminish the metabolic
efficacy of insulin in target tissue.
1) Streptozocin (STZ) induced diabetes
•
•
STZ induces diabetes in almost all species.
Diabetes can be induced by STZ either by single injection or
by multiple low dose injection of STZ.
• STZ is the most commonly used drug for induction of
diabetes in rats.
2) Alloxan induced diabetes:
• Alloxan is a uric acid derivative .
• Generates reactive oxygen species in a cyclic redox
reaction, in a final step produces hydroxyl radicals. These
hydroxyl radicals are responsible for the death of the beta
cells.
❑ Alloxan causes triphasic response in animals:
• Stage I-early hyperglycemia of short duration (about 1-4
hr) due to a sudden decrease of insulin release.
• Stage II-hyperglycemia lasting up to 48 hrs and often
resulting in convulsion and death.
• Stage III-chronic diabetic phase consequence of insulin
lack histologically only a few ß- cells.
• If any are detectable in animals with fully developed alloxan
diabetes.
• Exogenous insulin readily restores normal blood glucose
levels
• This method consists of complete or partial
pancreatectomy in animals used for the induction of type-1
or type-2 diabetes respectively.
• Historically, the diabetic dog model through surgical
complete pancreatectomy has been considered to be the
first animal model of diabetes and is rarely now used for
the investigation.
• Few researchers have employed this model to explore
effects of natural products with animal species such as rats,
pigs, dogs.
❑ Limitations to surgically induced diabetes:
• Requires high level of technical expertise and adequate
surgical room environment.
• High risk of animal infection.
• Adequate post-operative analgesia and antibiotic
administration, supplementation with pancreatic enzymes
are needed to prevent malabsorption and loss of pancreatic
counter regulatory response to hypoglycemia.
• Spontaneous diabetic animals of type-2 diabetes may be
obtained from the animals with one or several genetic
mutations transmitted from generation to generation or by
selected from non-diabetic out bred animals by repeated
breeding over several generation.
• These animals generally inherit diabetes either as single or
multigene defects.
• Polygenic animals represent the human condition more
closely when compared to monogenic animals.
• Viruses produce diabetes mellitus by destroying and
infecting pancreatic beta cells.
•
This method is often referred to as physiological
induction of diabetes mellitus because the blood glucose
level of the animal is transiently increased with no damage
to the pancreas.
• Bovine insulin to guinea pigs produces anti-insulin
antibodies.
• Intravenous injection of 0.25-1.0 ml guinea pig anti-serum to
rats induces a dose dependent increase in blood glucose
levels up to 300 mg/dl.
• This effect is due to neutralization of endogenous insulin by
insulin antibodies.
• It persists as long as the antibodies are capable of reacting
with insulin remaining in the circulation.
• The need for alternative strategies for the prevention and
treatment of diabetes is growing rapidly as type-2 diabetes is
reaching epidemic status in our society.
• Many in vitro techniques have been developed to elucidate
the varied mechanisms of action of hypoglycaemic agents
discovered by in vivo bioassays.
Three aspects of the hypoglycaemic response
commonly studied in vitro:
1- Insulin release from the pancreatic islets.
2-Peripheral insulin binding and glucose uptake.
3-Effects on hepatic enzymes.
are
❑ Animal used:
• Rats – Mice – Dogs – Cats – Monkeys.
❑ Steps:
1- Animals are starved 18 hr.
2- Fasting blood sugar is analyzed.
3- Test or standard hypoglycemic agent either : orally or
parentrally (insulin).
4- Blood samples are taken at different time intervals to
record blood glucose level.
5- Compare the Test & Standard hypoglycemic effect.
Induction of diabetes in rats
Streptozotocin
Rosiglitazone
55 mg/kg I.P
8 mg/kg P.O.
72 hrs
Days
1
80-100
mg/dl
2
3
4
200-300
mg/dl
5
6