Unformatted text preview: 284 HORMO NES AND RELATED DRUGS Insulin receptor
Glucose I ~--GNE proteins GTP ~--..... GDP GLUT4 - t ~- ~rt' ~ - GLUT4 ::?,:' ,§<.
cascade Second messengers
(PIP3 ) I Activation / Inhibition of Enzymes
mRNA , . . . Cellular
differentiation Fig. 19.3: A model of insulin receptor and mediation of its metabolic and cellular actions
T- Tyrosine residue; GLUT4-lnsulin dependent glucose transporter; IRS- Insulin receptor substrate proteins;
PIP3- Phosphatidyl inositol trisphosphate; P l3 kinase-Phosphatidylinositol-3 kinase; GNE proteins-Guanine nucleotide exchange proteins; MAP kinase-Mitogen-activated protein kinase; T-PrK- Tyrosine protein kinase; Ras- Regulator of cell division and differentiation (protooncogene product). ca lled the rapid actions. Others involving D A
mediated synthesis o f glucose transporte r and
some enzymes of amino acid metabolism have
a latency of few hours-the intermediate actions. In addition insulin exerts major long-term
effects on multiplication and differe ntiation of
many types of cells.
Mechanism of action Insulin acts on specific rt!ceptors
located on the cell membrane of practically every cell. but
their density depends on the cell type: liver and fat cells
arc very rich. The insulin receptor is a receptor tyrosine
kinase ( RT K } which is a heterotetrameric glycoprotcin
consisting of 2 extracellular a and 2 transmembrane f3
subunits linked together by disulfide bonds. It is oriented
across the cell memhrane as a heterodimer (Fig. 19.3).
The a subunits carry insul in binding sites, whi le the f3
subunits have tyrosine protein kinase activity. Binding of i nsul in LO Cl subunits induces aggregation
and internalization of the receptor along with the bound
insulin molecules. This activates tyrosine kinase acti vity
subunits • pairs of f3 subunits phospho,y late
e:-pose the catalytic
tyro inc residues on each other •
site to phosphorylate tyrosine residues of Insulin Receptor
ubstrate proteins (I RS I. I RS2. etc) and other caveolar/
noncaveolar proteins. In tum, a cascade of phosphorylation
and dephosphorylation reactions involving phosphatidyl
inositol 3 kinase (Pl3 kinase) and other kinases is set into
motion which amplifies the signal and results in stimulation
or inhibition o f en7ymes involved in the rapid metabolic
actions of insulin.
Second messengers like phosphatidyl inosiLOI trisphosphate (PI P.) which arc generated through acti, ation of a
specific Pl3-kinase also mt:diale the action of insulin on
Insulin stimulates glucose transport across cell membrane
by ATP depende111 tra nslocation of gl ucose transporter INSULIN, ORAL ANTI DIABETIC DRUGS AND GLUCAGO N GLUT4 to the pla~ma membrane. The second messenger
PIP, and certain tyrosine phosphorylated guanine nucleotide
exchange proteins play crucial role in the insulin sensitive translocation of GLUT4 from cytosol to the plasma
membrane, especially in skeletal muscle and adipose tissue.
Over a period of time insulin also promotes expression of
the genes directing synth~sis of GLUT4. Genes for a large
number of enzymes and carriers arc regulated by insulin
through Ras/Raf and MAP-Kinase as well as through the
phosphorylation ca~cadc. Long-tem1 efTects of insulin are
exe11ed by generation of transcription factors promoting
proliferation and differentiation of specific cells.
The internalized receptor-insu lin complex is either
degraded intraccllularly or returned back to the surface from
where the insulin is released extracellularly. The relative
preponderance nf these two processes differs among differe11t tissues: maximum degradation occurs in liver. least
in vascular e11dothelium. Fate of insulin Insulin i s d istri buted on l y extracellularly. It i s a peptide, and gets degraded
in the g. i .t . if given o rall y. Injected in sul in
or that rel eased from pancreas is m etabolized
primarily in li ver and to a sma ller extent in
kidn ey and muscles. early hal f o f the insu lin entering portal vei n from p ancr eas i s inactivated in the first passage th rough li ver. Thus,
normally l iver i s exposed to a much higher
concentration (4-8 fold) of i nsulin than are other tissues. As noted above, degradation of
insul in after receptor m ediated internalization
occurs to variable extents i n most target cells.
During biotransformation the di sulfide bonds are
reduced- A and B chains arc separated. T hese are further broken down to the constin1ent amino
acids. The plasma t ½ of in su lin is 5- 9 min. Preparations of insulin
The older commercial insulin preparations were produced
from beef and pork pancreas. They contained - 1% ( I 0,000
ppm) of other proteins (proinsulin. other polypeptides,
pancreatic proteins. insulin derivati,es. etc.) which were
potentially antigenic. Such insulins are no longer produced
and have been totally replaced by highly purified pork/beef
insulins. recombinant human insulins and insulin analogues. Highly purified insulin preparations
I n the 1970s improved purification teclrniques like
gel fi l tration and ion-exc hange c hromatography
wer e appli ed to produce 'sing l e peak ' and
'monocomponent (M C)' insu l ins w hich contain
< IO ppm proinsul in. The MC insuli ns are more
stable and cause less insulin resistance or injecti on
si te lipodystrophy. T he immunogenicity of pork
MC insulin is similar to that of recombinant
human insulin. Table 19.1 : Types of 111suhn preparations and 111suhn analogues
Type Appearance Onset (hr) Peak (hr) Duration (hr) Can be mixed with Insulin lispro Clear 0.2--0.3 1-1.5 3-5 Regular, NPH Insulin aspart Clear 0.2--0.3 1- 1.5 3-5 Regular, NPH Insulin glulisine Clear 0.2-0.4 1- 2 3-5 Regular, NPH Clear 0.5-1 2-3 6-8 All preparations (except
detemir) Insulin zinc suspension or Lente• Cloudy 1- 2 8- 10 12-20 Regular Neutral protamine hagedorn
(NPH) or isophane insulin Cloudy 1-2 8- 10 12- 20 Regular Insulin glargine Clear 2-4 24 None Insulin detemir Clear 1-4 20-24 None Rapid acting Short acting Regular (soluble) insulin Intermediate acting Long acting • Lente insulin is a 7:3 mixture of ultralente (crystalline) and semilente (amorphous) insulin zinc suspension.
Ultralente (long-acting) and semilente (short-acting) are not separately marketed. The older protamine zinc insulin
is also not marketed. 285 286 HORMONES AND RELATED DRUGS Types of insulin preparations
Regular (soluble) insulin l t is a buffered neutral pH solution of unmodified insulin stabilized
by a small amount of zi nc. At the concentration
of the injectable solution, the insulin molecules
self aggregate to form hexamers around the 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 upto 6-8 hours.
The absorption pattern is also afTcctcd by dose;
highe r doses act longer. When injected s.c.
just before a meal, this pattern often creates a
mismatch between the need and the availabi lity
of insulin to result i11 early postprand ia l hyperglycaemia and late postprandial hypoglycaemia.
Regular insulin is optimall y injected I hour
before a meal. Regular insulin injected s.c. is
also not suitable fo r providing a low constant
basal level of action in the interdigestive period. However, the slow onset of action is not
applicable to i.v. injection, because the insulin
hexamer dissociates rapidl y to produce prompt
action. Regular insulin is the only insulin used
for i.v. inj ection.
To ove rco me the above problems, so me
long-acting ' modified' or ' retard ' preparations
of insulin were soon developed. Recently, both
rapidl y actin g as well as peakless a nd longacti ng insu lin analogues have become avai lab le.
For obtaining retard preparations, insulin is
rendered insoluble either by complexing it with
protamine (a sma ll molec ul ar bas ic prote in)
o r by precipitating it with excess zinc a nd
increasing the particle size.
Lente insulin (Insulin-zinc suspension): Two
types of insul in-zinc suspensions have been produced. The one with large particles is crystalli ne
and practically insoluble in water (ultra lente). It
is long-acting. The other has smaller particles
and is amorphous (semilente), is hort-acti ng.
The ir 7:3 ratio mixture is called ' Lente insulin '
and is intermediate-acting.
lsophane (Neutral Protamine Hagedorn or
NPH) insulin: Protamine is added in a quantity just sufficient to complex all insulin molecules;
nei ther insulin nor protamine is present in free
form and pH is neutral. On s .c. injection, the
complex di ssociates slowl y to yie ld an intermedi ate duration of action. However, the time
course o f absorption a nd in tensity of action
of NP H insulin is relative ly inconsistent. 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).
4. Highly purified (monocomponcnt) pork regular insulin:
ACTRAPID MC. RAPIDICA 40 U/ml inj.
High ly purified (MC) pork lentc insulin: LE TARD,
M01\JOTARD MC, LENTINSULIN-HPI, ZlNULIN 40
Highly purified (MC) pork isophane ( PH) insulin:
INSULATARD 40 U/ml inj.
Mixture or highly purified pork regular insulin (30%)
and isophanc insulin (70%): RAPIMIX, MIXTARD
40 U/ml inj. Human insulins In the 1980s, the human in ulin s ( ha ving the same am in o ac id
sequence as human insulin) were produced by
recomb ina nt DNA technology in Escherichia
co/i- 'proinsulin recombinant bacterial' (prb)
a nd in yeast- ' precursor yeast re combinant'
(pyr), or by 'enzymati c modification o f porcine
insulin ' (emp).
3. 4. 5.
6. HUMA'\i ACTRAPID: Human regular insulin: 40 U1
ml, 100 U/ml, ACTRAPID IIM PENrIL 100 U/ml
pen mj.• WOSU LI N-R 40 U/ml inj vial and JOO U/
ml pen injector canridge.
HUMAN MONOTRAD. IIUMINSULIN-L: Human
leme insulin; 40 U/ml, 100 Ulm!.
IIUMA INSULATARD, IIUMINSULIN-N: Human
1mphane insulin 40 Ulm!. WOSULIN-"l 40 U/ml inj
vial and 100 U/ml pen mjector canndgc.
HU\,IA' ACTRAPHA E, II UM J. SULIN 30/70,
II UMAN MIXTARD: lluman tol11hle insulin (30%)
and iwphane insulin (70%), 40 U/ml. and 100 U/ml
vials. WOSULIN 30nO: 40 U/ml vial and 100 U/ml
ACTRAPHANE HM PENFIL: Iluman soluble insulin
isophane insulin 70% 100 U/ml pen injector.
INSUMA "I 50/ 50: Human soluble insulin 50% +
i,uplwne insulin 50% 40 U/ml mj: II UMIJ\ SULIN
50:50. HUMAN MIXTARD 50: WOSuLIN 50/50 40
U/ml ,ial. 100 U/ml canndgc. In the USA pork and beef insulin s are no
longer manufactured, but they a re still available
in U.K., India and some European countries. In
Britain now > 90% diabetics who use insulin IN SULIN, ORAL ANTI DIABETIC DRUGS AND GLUCAGON
are taking human insulins or insuli n ana logues.
In India a lso human insulins and analogues are
commonly used, except for considerations of cost.
Human insu lin is more water soluble as well
as hydrophobic than porci ne or bovine insulin.
It has a s lig ht ly more rapid s.c. absorption,
earl ie r and more defined peak concen tration
and slightl y shorter durati on of action. I luman
insulin is a lso modi fied similarl y to produce
isopha ne (NPll) and let11e prepara tions. Lente
human insulin is no longer prepared in the USA.
The allegation that human in, ulin produce; more l,ypog(1·cae111ic unawareness has not been substantiated. However, after
prolonged treatment, irrespec1i,e of the type of insulin used,
many diabetics develop relative hypoglycaemic unawareness/
change in hypoglycaemic symptoms, because of autonomic
ncuropathy, changes in pcrception/a1111ude and other factors.
Clinical superiority of human insulin over pork MC
insulin has not been demonstrated. Though new patients
may be started on human insulin,, the only indication for
transfor from purified pork 10 human insulin is allergy to
pork insulin. It is unwise lO transfer stabili7ed patients from
one lo another species insulin without good reason. Insulin analogues
Us ing recombinant DNA technology, ana logues
of insulin have been prod uced which have
modified p hannacok inetics on s.c. injectio n,
but s imi lar p harmacodynamic effec ts and
immunogenicity. Greater stability and consistency
o f the preparations are the other advantages. Insulin lispro: Produced by reversi ng pro line
and lysine at the carboxy term inus B 28 and B
29 posi tions, it fonns very weak hexamers that
dissociate ra pidly after s.c. injecti on result ing
in a quick and more de fined peak as well as
sho rter duration of action. Individua l variability
in absorption is minimized. Unlike regular insulin. it is best injected s.c. 0-20 min before a
meal. A better control of meal-time glycaemia
and a lower incide nce of la te post-prandia l
hypoglycaem ia have been obtained. Usi ng a
regimen of 2-3 dai ly meal-time insulin lispro
injections, a slightl y greater reduction in HbA1c
compared to regula r insulin has been reported.
Fewer hypoglycaemic episodes occurred .
HUM A LOG I00 U/ml, 3 ml cartndge. IO ml, ial. Insulin aspart: The proline at B 28 o f human
insu lin is replaced by aspartic acid. T his change
reduces the tendency for sel f-aggregation, and
a time-action profi le s imilar to insulin lispro
is obtained. It more closely mimics the physiological insu lin release pallern a fter a meal,
with the same advantages as above.
NOVOLOG, NOVORAPID 100 U/ml inj. Biphasic insulin aspart: The 70:30 mi xture
of isopha ne complex or in sulin aspart w ith
uneomplexed insulin aspart has the advantage
of rapid a nd predictable onset a long w ith intermediate du ration of action. It is called 'biphasic
insulin aspart', and can be injected twice dai ly
j ust before each major meal.
NOVO\IIX JO fLEXPEN 100 U/mL in J mL inj., also
Insulin glu/tsine: Another rapidly actmg insulin analogue
\\•ith lysine replacing asparaginc at B 23 and glutamie acid
replacing lysine at O 29. Prop,:riie; and advantages are
similar to insulin lispro. It has heen particularly used for
continuous subcutaneous insulin infusion (CSII) by a pump.
a!> Insulin glargine: This long-acting biosynth etic
insulin has 2 additional arginine residues at the
carboxy tem1inus of B cha in and glycine replaces
asparagi ne at A 2 1. T his ana logue remains soluble
at pH4 of the formulation. but precipitates a t
neutral pH encountered o n s.e. injection. A
depot is created from which monomeric insulin
dissociates slowly to enter the circulation. Onset
of action is delayed, but relatively low blood
levels o f insu lin are main ta ined fo r upto 24
hours. A smooth 'peakless' effect is obtained.
Thus, it is suitable fo r once da ily injection to
provide background insulin action. Fasting and
interdigestive blood glucose le vels are effective ly lowered irrespecti ve of time of the day
when injected or the site of s.c. injection. It is
mostly injected at bed time. Lower incidence o f
night-time hypog lycaemic episodes compared to
isophane insulin has been reported. However, it
does not eono-o l meal-time g lycacm ia, for w h ich
a rapid acting insuli n or an oral hypoglycaemic
is used concurrently. Because of ac idic pH, it
cannot be mixed with any other insulin preparation; must be injected separate ly.
LANTUS OPTISET 100 U/ml in 5 ml vial and 3 ml
prefilled pen injector. 287 288 HORMONES AN D RELATED DRUGS
Insulin detemir Myristoyl (a fatty acid) radical
is attached to the amino group of lysine at 829
of insulin chain. As a result, it binds to albumin
after s.c. injection from which the free form
becomes avai lab le slowly. A pattern of insulin
action a lmost similar to that of insulin glargine is
obtained, but twice daily dosing may be needed.
LEVEM IR fLEXPEN 100 U/mL in 3 ml prefllled pen
injector. Insulin degludec It is a new ultra long-acting ins ul in
analogue with a flat p lasma glucose lowering effect lasting
for ~ 40 hours, suitable for meeting basal ms11/i11 req11iremem in type I and type 2 diabetic patients. After single
daily injection the day-to-day variability in response and
risk of nocturnal hypoglycaemia are less than with insulin
glargine. An alternate day regimen has also been tried, but
may not be satisfactory. II has also been cofonnulated with
rapid-acting insulin aspan. REACTIONS TO INSULIN 1. Hypoglycaemia This is the most frequent
and potemially the most serious reaction. Hypog lycaem ic episodes are more common in patients
of ' labile' di abetes in whom insulin requ irement
fluctuates unpred ictably. Hypoglycaem ia can occur
in any diabetic fo llowing inadvertent injection
of large dose, by missing a meal after injection or by perfonning vigorous exercise. The
symptoms can be divided into those due to
counter-regulatory sympathetic stimul ation, viz.
sweating, anx iety, palpitation, tremor; and those
due to deprivation of the brain of its essential
nutrient glucose (neuroglucopenic symptoms)dizziness, headache, behavioural changes, visual
disturbances, hunger, fatigue, weakness, muscular
incoordination and sometimes fall in BP. Generally, the reflex sympathetic symptoms occur,
before the ne uroglucopenic, but the warn ing
sympto ms of hypoglycaem ia d iffe r from patie nt
to patient and a lso depend on the rate of fall
in blood glucose level. Diabetic neuropathy can
abolish the autonomic symptoms. Hypoglycaemic
unawareness (loss of warning symptoms) tends
to deve lop in patients who experience freque nt
episodes of hypoglycaemia.
Fina lly, when blood glucose fa ll further (to
< 40 mg/ di) menta l confusion, abno rma l
behaviour, se iz ures and coma occur. Irreversible neurological deficits are the sequelae of
prolonged hypoglycaemia. Treatment Glucose (or g lucose yie lding carbohydrate, e.g. sugar) 15- 20 g orally reverses
the symptoms rapidly in most cases. l f no
improvement occurs, the sa me amount may
be repeated after 15- 20 mi n. In severe cases
30- 50 ml of 50% glucose may be injected
i.v. over 10 min. Glucagon 0.5- 1 mg i.v. or
Adr 0.2 mg s.c. (less des irable) may be g iven
as an expedient measure in patients who are
not able to take s ugar orally and injectable
glucose is not available.
2. Local reactions Swelling, crythema and stinging
sometimes occur at the injected site, especially in the
beginning. Lipodys1rophy o f the subcutaneous fat around
the injection s ite occurred occasionally with the older
pork/beef insulin preparations. This is rare with the newer
3. Allergy This is due to contaminating proteins, and is
, ery rare with human/highly purified insulins.
Un icaria, angioedema and anaphylaxis are the manifestations.
4. Edema Some patients develop shon-lived dependent
edema (due to Na· retemion) when insulin therapy is staned. Drug interactions
I. p adrenergic blockers prolong hypoglycaemia
by inhibiting compensatory mechanisms o perating
through p2 receptors (P 1 selective blockers are
less liable). Warning signs of hypoglycaemia
like palpitation, tremor and anxiety are masked. 2. Th iazides, furo se mid e , cort icostero id s,
oral contracepti ves, salbutamol, ni fedi pine tend
to raise blood sugar a nd red uce effectiveness
3. Acute ingestion of a lcohol can precipitate
hypoglycaemia by depleting hepatic glycogen.
4. Lithium, high dose aspi rin and theophyll ine may a lso accentuate hypoglycaemia by en hancing ins ulin secretion, as well as periphera l
glucose uti lization. USES OF INSULIN
Diabetes mellitus The purpose of therapy
in diabetes mellitus is to restore metabolism to
norma l, avoid symptoms due to hyperglycaemia
and glucosuria, prevent short-term complications
(infection, ketoacidosis, etc.) and long-term sequelae
(cardiovascular, retinal. neurological, renal, etc.). 289 INSULIN, ORAL ANTI DIABETIC DRUGS AND GLU CAGO N The generally accepted criteria for adequate
glycaemia control in an adult diabetic treated
with insulin or oral antidiabetics are:
• Fast ing (morning) blood glucose levels
• Blood glucose levels .:::150 mg/di 2 hours
• HbA1, levels < 7%.
Insulin is effective in all forms of...
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