Insulin (for diabetes patient)
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| Insulin injections| Insulin pen injection |
What is insulin and what does it do in the body?
Insulin was discovered in 1921 by Banting and
Best who demonstrated the hypoglycaemic action
of an extract of pancreas prepared after degeneration
of the exocrine part due to ligation of
pancreatic duct. It was first obtained in pure
crystalline form in 1926 and the chemical structure
was fully worked out in 1956 by Sanger.
Insulin is a two-chain polypeptide having 51
amino acids and MW about 6000. The A-chain
has 21 while B-chain has 30 amino acids. There
are minor differences between human, pork, and
beef insulins:
Thus, pork insulin is more homologous to human
insulin than is beef insulin. The A and B chains
are held together by two disulfide bonds.
Insulin is synthesized in the β cells of
pancreatic islets as a single chain peptide
Preproinsulin (110 AA) from which 24 AAs are
first removed to produce Proinsulin.
The connecting or ‘C’ peptide (35 AA) is split
off by proteolysis in Golgi apparatus; both insulin
and C peptide are stored in granules within the
cell. The C peptide is secreted in the blood along
with insulin.
Assay Insulin is bioassayed by measuring blood sugar
depression in rabbits (1 U reduces blood glucose of a fasting
rabbit to 45 mg/dl) or by its potency to induce hypoglycaemic
convulsions in mice. 1 mg of the International Standard of
insulin = 28 units. With the availability of pure preparations,
it can now be assayed chemically and quantity expressed
by weight. Plasma insulin can be measured by radioimmunoassay
or enzyme immunoassay.
Regulation of insulin secretion
Under the basal condition, ~1U insulin is secreted
per hour by the human pancreas. A much larger quantity
is secreted after every meal. The secretion of insulin
from β cells is regulated by chemical, hormonal
and neural mechanisms.
Chemical
The β cells have a glucose sensing
mechanism dependent on entry of glucose into
β cells (through the aegis of a glucose transporter
GLUT1) and its phosphorylation by glucokinase.
Glucose entry and metabolism leads to activation
of the glucose-sensor which indirectly inhibits the
ATP-sensitive K+ channel (K+
ATP) resulting in
partial depolarization of the β cells (see Fig. 19.6).
This increases intracellular Ca2+ availability (due
to the increased influx, decreased efflux, and release
from intracellular stores) → exocytotic release
of insulin storing granules. Other nutrients that
can evoke insulin release are—amino acids, fatty
acids and ketone bodies, but glucose is the
principal regulator and it stimulates the synthesis of
insulin as well. Glucose induces a brief pulse
of insulin output within 2 min (first phase)
followed by a delayed but more sustained second
the phase of insulin release.
Glucose and other nutrients are more effective in invoking
insulin release when given orally than i.v. They generate
chemical signals ‘incretins’ from the gut which act on β
cells in the pancreas to cause the anticipatory release of insulin.
The incretins involved are glucagon-like peptide-1 (GLP-
1), glucose-dependent insulinotropic polypeptide (GIP),
vasoactive intestinal peptide (VIP), pancreozymins-cholecystokinin,
etc.; but different incretin may mediate signal from
different nutrient. Glucagon and some of these peptides enhance
insulin release by increasing cAMP formation in the β cells.
Hormonal A number of hormones, e.g. growth
hormone, corticosteroids, thyroxine modify insulin
release in response to glucose. PGE has been
shown to inhibit insulin release. More important
are the intra-islet paracrine interactions between
the hormones produced by different types of islet
cells. The β cells constitute the core of the islets
and are the most abundant cell type. The α cells,
comprising 25% of the islet cell mass, surround
the core and secrete glucagon. The δ cells
(5–10%) elaborating somatostatin is interspersed
between the α cells. There is some PP (pancreatic
polypeptide containing) cells as well.
• Somatostatin inhibits the release of both insulin
and glucagon.
• Glucagon evokes the release of insulin as well as
somatostatin.
• Insulin inhibits glucagon secretion. Amylin,
another β cell polypeptide released with insulin,
inhibits glucagon secretion through a central
site of action in the brain.
The three hormones released from closely situated
cells influence each other’s secretion and
appear to provide fine-tuning of their output in
response to metabolic needs (Fig. 19.2).
Neural The islets are richly supplied by sympathetic
and vagal nerves.
• Adrenergic α2 receptor activation decreases
insulin release (predominant) by inhibiting β
cell adenylyl cyclase.
• Adrenergic β2 stimulation increases insulin
release (less prominent) by stimulating β cell
adenylyl cyclase.
• Cholinergic—muscarinic activation by ACh or
vagal stimulation causes insulin secretion
through IP3/DAG-increased intracellular Ca2+
in the β cells.
ACTIONS OF INSULIN
What is the role of insulin?
The overall effects of insulin are to dispose of meal-derived glucose, amino acids, fatty acids, and
favor storage of fuel. It is a major anabolic
hormone: promotes the synthesis of glycogen, lipids, and protein. The actions of insulin and the results
of its deficiency can be summarized as:
1. Insulin facilitates glucose transport across the cell
membrane; skeletal muscle and fat are highly
sensitive. The availability of glucose intracellularly
is the limiting factor for its utilization in
these and some other tissues. However, glucose
entry in the liver, brain, RBC, WBC, and renal medullary
cells is largely independent of insulin. Ketoacidosis
interferes with glucose utilization by the brain and
contributes to diabetic coma. Muscular activity
induces glucose entry in muscle cells without the
need for insulin. As such, exercise has an insulin
sparing effect.
The intracellular pool of vesicles containing
glucose transporter glycoproteins GLUT4 (insulin
activated) and GLUT1 is in dynamic equilibrium
with the GLUT vesicles inserted into the membrane.
This equilibrium is regulated by insulin
to favor translocation to the membrane.
Moreover, on a long-term basis, the synthesis of
GLUT4 is upregulated by insulin.
2. The first step in intracellular utilization of
glucose is its phosphorylation to form glucose-
6-phosphate. This is enhanced by insulin through
increased production of glucokinase. Insulin
facilitates glycogen synthesis from glucose in the liver,
muscle, and fat by stimulating the enzyme glycogen
synthase. It also inhibits glycogen degrading
enzyme phosphorylase → decreased glycogenolysis
in the liver.
3. Insulin inhibits gluconeogenesis (from protein,
FFA and glycerol) in the liver by gene mediated
decreased synthesis of phosphoenolpyruvate
carboxykinase. In insulin deficiency, proteins and
amino acids are funneled from peripheral tissues
to the liver where these substances are converted to
carbohydrate and urea. Thus, in diabetes there
is underutilization and overproduction of glucose
→ hyperglycemia → glycosuria.
4. Insulin inhibits lipolysis in adipose tissue
and favors triglyceride synthesis. In diabetes
the increased amount of fat is broken down due to
unchecked action of lipolytic hormones (glucagon,
ADR, thyroxine, etc.) → increased FFA and
glycerol in blood → taken up by liver to produce
acetyl-CoA. Normally acetyl-CoA is resynthesized
to fatty acids and triglycerides, but this process
is reduced in diabetics and acetyl CoA is diverted
to produce ketone bodies (acetone, acetoacetate,
β-hydroxybutyrate). The ketone bodies are released
in the blood—partly used up by muscle and heart
as an energy source, but when their capacity is
exceeded, ketonemia, and ketonuria result.
5. Insulin enhances transcription of vascular
endothelial lipoprotein lipase and thus increases
clearance of VLDL and chylomicrons.
6. Insulin facilitates AA entry and their synthesis
into proteins, as well as inhibits protein breakdown
in muscle and most other cells. Insulin deficiency
leads to protein breakdown → AAs are released in
blood → taken up by the liver and converted to pyruvate,
glucose, and urea. The excess urea produced is
excreted in urine resulting in a negative nitrogen
balance. Thus, catabolism takes the upper hand over
anabolism in the diabetic state.
Most of the above metabolic actions of insulin
are exerted within seconds or minutes and are
called the rapid actions. Others involving DNA
mediated synthesis of glucose transporter and
some enzymes of amino acid metabolism have
a latency of a few hours—the intermediate actions.
In addition, insulin exerts major long-term effects
on multiplication and differentiation of many types
of cells
Preparations of insulin|Insulin for diabetes|Insulin function
The older commercial preparations were produced
from beef and pork pancreas. They contained ~1%
(10,000 ppm) of other proteins (proinsulin, other
polypeptides, pancreatic proteins, insulin derivatives,
etc.) which were potentially antigenic. They
are no longer produced and have been totally
replaced by highly purified pork/beef insulins/
recombinant human insulins/insulin analogs.
Highly purified insulin preparations
In the 1970s improved purification techniques like
gel filtration and ion-exchange chromatography
were applied to produce ‘single peak’ and
‘monocomponent (MC)’ insulins which contain
<10 ppm proinsulin. The MC insulins are more
stable and cause less insulin resistance or injection
site lipodystrophy. The immunogenicity of pork
MC insulin is similar to that of recombinant human
insulin.
Types of insulin preparations |types of insulin
Regular (soluble) insulin It is a buffered
neutral pH solution of unmodified insulin stabilized
by a small amount of zinc. At the concentration
of the injectable solution, the insulin molecules
self aggregate to form hexamers around zinc ions.
After s.c. injection, insulin monomers are released
gradually by dilution, so that absorption occurs
slowly. Peak action is produced only after
2–3 hours and action continues up to 6–8 hours.
The absorption pattern is also affected by dose;
higher doses act longer. When injected s.c. just
before a meal, this pattern often creates a mismatch
between need and availability of insulin to result
in early postprandial hyperglycemia and late
postprandial hypoglycemia. It is generally
injected ½-1 hour before a meal. Regular insulin
injected s.c. is also not suitable for providing a
low constant basal level of action in the inner digestive
period. The slow onset of action is not applicable
to i.v. injection, because insulin hexamer
dissociates rapidly to produce prompt ac
To overcome the above problems, some long-acting
‘modified’ or ‘retard’ preparations of insulin
were soon developed. Recently, both rapidly acting
as well as peakless and long-acting insulin analogs
have become available.
For obtaining retard preparations, insulin is
rendered insoluble either by complexing it with
protamine (a small molecular basic protein) or
by precipitating it with excess zinc and increasing
the particle size.
Lente insulin (Insulin-zinc suspension):
Two types of insulin-zinc suspensions have been
produced. The one with large particles is
crystalline and practically insoluble in water
(ultralente). It is long-acting. The other has smaller
particles and is amorphous (semilente), which is short-acting.
Their 7:3 ratio mixture is called ‘Lente
insulin’ and is intermediate-acting.
Isophane (Neutral Protamine Hagedorn or
NPH) insulin: Protamine is added in a quantity
just sufficient to complex all insulin molecules;
neither of the two is present in free form and
The pH is neutral. On s.c. injection, the complex
dissociates slowly to yield an intermediate duration
of action. It is mostly combined with regular
insulin (70:30 or 50:50) and injected s.c. twice
daily before breakfast and before dinner (split mixed
regimen).
1. Highly purified (monocomponent) pork regular insulin:
ACTRAPID MC, RAPIDICA 40 U/ml injection.
2. Highly purified (MC) pork Lente insulin: LENTARD,
MONOTARD MC, LENTINSULIN-HPI, ZINULIN 40
U/ml
3. Highly purified (MC) pork isophane (NPH) insulin:
INSULATARD 40 U/ml injection.
4. Mixture of highly purified pork regular insulin (30%)
and isophane insulin (70%): RAPIMIX, MIXTARD
40 U/ml injection.
Human insulins In the 1980s, the human insulins
(having the same amino acid sequence as
human insulin) was produced by recombinant
DNA technology in Escherichia coli—‘proinsulin
recombinant bacterial’ (PRB) and in yeast—
‘precursor yeast recombinant’ (pyr), or by
‘enzymatic modification of porcine insulin’ (emp).
1. HUMAN ACTRAPID: Human regular insulin; 40 U/
ml, 100 U/ml, ACTRAPID HM PENFIL 100 U/ml pen
injection., WOSULIN-R 40 U/ml injection vial and 100 U/ml pen
injector cartridge.
2. HUMAN MONOTRAD, HUMINSULIN-L: Human lente
insulin; 40 U/ml, 100 U/ml.
3. HUMAN INSULATARD, HUMINSULIN-N: Human
isophane insulin 40 U/ml. WOSULIN-N 40 U/ml injection.
vial and 100 U/ml pen injector cartridge.
4. HUMAN ACTRAPHANE, HUMINSULIN 30/70,
HUMAN MIXTARD: Human soluble insulin (30%) and
isophane insulin (70%), 40 U/ml. and 100 U/ml vials.
WOSULIN 30/70: 40 U/ml vial and 100 U/ml cartridges.
5. ACTRAPHANE HM PENFIL: Human soluble insulin
30% + isophane insulin 70% 100 U/ml pen injector.
6. INSUMAN 50/50: Human soluble insulin 50% +
isophane insulin 50% 40 U/ml inj; HUMINSULIN 50:50,
HUMAN MIXTARD 50; WOSULIN 50/50 40 U/ml vial,
100 U/ml cartridge.
In the USA pork and beef insulins are no longer
manufactured, but they are still available in the U.K.,
India and some European countries. In Britain now
> 90% of diabetics who use insulin are taking human
insulins or insulin analogs. In India also human
insulins and analogs are commonly used, except
for considerations of cost. Human insulin is more
water-soluble as well as hydrophobic than porcine
or bovine insulin. It has a slightly more rapid s.c.
absorption, earlier and more defined peak, and
slightly shorter duration of action. Human insulin
is also modified similarly to produce isophane
(NPH) and Lente's preparations. Lente human insulin
is no longer prepared in the USA.
The allegation that human insulin produces more
hypoglycaemic unawareness has not been substantiated.
However, after prolonged treatment, irrespective of the type
of insulin, many diabetics develop relative hypoglycaemic
unawareness/change in hypoglycaemic symptoms, because of
autonomic neuropathy, changes in perception/attitude and
other factors.
Clinical superiority of human insulin over pork MC insulin
has not been demonstrated. Though new patients may be started
on human insulins, the only indication for transfer from purified
pork to human insulin is an allergy to pork insulin. It is unwise to
transfer stabilized patients from one to another species insulin
without good reason.
Insulin analogs
Using recombinant DNA technology, analogs
of insulin have been produced with modified
pharmacokinetics on s.c. injection, but similar
pharmacodynamic effects. Greater stability and
consistency are other advantages.
Insulin lispro:
Produced by reversing proline and
lysine at the carboxy terminus B 28 and B 29
positions, it forms very weak hexamers that
dissociate rapidly after s.c. injection resulting in
a quick and more defined peak as well as a shorter
duration of action. Unlike regular insulin, it needs
to be injected immediately before or even after
the meal, so that the dose can be altered according
to the quantity of food consumed. Better control
of meal-time glycemia and a lower incidence
of late postprandial hypoglycemia has been
obtained. Using a regimen of 2–3 daily mealtime
insulin lispro injections, a slightly greater
reduction in HbA1c compared to regular insulin
has been reported. Fewer hypoglycaemic episodes
occurred.
HUMALOG 100 U/ml, 3 ml cartridge, 10 ml vial.
Insulin Aspart: The proline at B 28 of human
insulin is replaced by aspartic acid. This change
reduces the tendency for self-aggregation, and a
time-action profile similar to insulin lispro is
obtained. It more closely mimics the physiological
insulin release pattern after a meal, with the same
advantages as above.
NOVOLOG, NOVORAPID 100 U/ml injection; Biphasic insulin
aspart - NOVO MIX 30 FEXPEN injector.
Insulin glulisine:
Another rapidly acting insulin analog
with lysine replacing asparagine at B 23 and glutamic acid
replacing lysine at B 29. Properties and advantages are similar
to insulin lispro. It has been particularly used for continuous
subcutaneous insulin infusion (CSII) by a pump.
Insulin glargine: This long-acting biosynthetic
insulin has 2 additional arginine residues at the
carboxy terminus of the B chain and glycine replaces
asparagine at A 21. It remains soluble at pH4
of the formulation, but precipitates at neutral pH
encountered on s.c. injection(insulin injection). A depot is created
from which monomeric insulin dissociates slowly
to enter the circulation. The onset of action is delayed,
but relatively low blood levels of insulin are
maintained for up to 24 hours. A smooth ‘peakless’
the effect is obtained. Thus, it is suitable for a once-daily injection to provide background insulin
action. Fasting and inner digestive blood glucose
levels are effectively lowered irrespective of the time
of the day when injected or the site of s.c.
injection. It is mostly injected at bedtime. Lower
incidence of night-time hypoglycaemic episodes
compared to isophane insulin has been reported.
However, it does not control meal-time glycemia,
for which rapid-acting insulin or an oral
hypoglycaemic is used concurrently. Because of
acidic pH, it cannot be mixed with any other
insulin preparation; must be injected separately.
LANTUS OPTISET 100 U/ml in 5 ml vial and 3 ml prefilled
pen injector. (insulin injection)
Insulin detemir Myristoyl (a fatty acid) radical is attached
to the amino group of lysine at B29 of the insulin chain. As
a result, it binds to albumin after s.c. injection(insulin injection) from which
the free form becomes available slowly. A pattern of insulin
action almost similar to that of insulin glargine is obtained,
but twice-daily dosing may be needed.
insulin for diabetes | insulin drug | insulin resistance
Why insulin is bad for you?
Insulin is not bad for you, Bad is its altered range means Increased insulin level or decreased insulin level. Under the basal condition, ~1U insulin is secreted per hour by the human pancreas. A much larger quantity is secreted after every meal. The secretion of insulin from β cells is regulated by chemical, hormonal and neural mechanisms.
What are the disadvantages of insulin?
The risk of Hypoglycaemia means it decreases normal glucose levels.
The problem of daily injection
Allergy of insulin
Increases weight or weight gain.
