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IJPRD, 2014; Vol 6(03):May-2014 (130 - 137) International Standard Serial Number 0974 – 9446
Available online on www.ijprd.com
130
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ASSIOCIATION OF LIPID LEVELS AND INSULIN RESISTANCE: NOVEL APPROACH IN DYSLIPIDEMIA
Ketan R. Soni1
*,
Mustakim M. Mansuri1
, Sandipkumar V. Bhatt1
, Shrikalp S. Deshpande1
, Gaurang B. Shah1
*1
K. B. Institute Of Pharmaceutical Education and Research, Gandhinagar – 23, Gujarat, India
ABSTRACT
Dyslipidemia, the major constituent of the metabolic syndrome,
characterized by elevated free fatty acid, Triglycerides, Low
Density Lipoprotein and apo B levels, and reduced High Density
Lipoprotein levels. Hyperinsulinemia, which accompanies Insulin
resistance is a common condition which play important role in the
pathogenesis of the metabolic syndrome, obesity and Type 2
diabetes (T2DM), as well as cardiovascular disease.
Lipodystrophies on the other hand are associated with decreased
adipose mass but are, again, characterized by insulin resistance.
Excess abdominal adipose tissue has been shown to release
increased amounts of free fatty acids which directly affect insulin
signaling, diminish glucose uptake in muscle, drive exaggerated
triglyceride synthesis and induce gluconeogenesis in the liver.
Treatment approaches for patients of diabetic dyslipidemia are
treated with individual or combination niacin, thiazolidinedione,
fibrates and a statin shows promise for correcting the dyslipidemia
commonly observed in patients with type 2 diabetes.
Keywords: Dyslipidemia, Metabolic syndrome, Insulin resistance,
Type 2 diabetes
GENERAL OVERVIEW OF CHOLESTEROL
ABSORPTION:
Intestinal cholesterol absorption initiates with the
micellarsolubilisation of both dietary and biliary
cholesterol in the lumen of the small intestine. In
general, nearly two thirds of intestinal cholesterol
absorbed is from the bile and the other one third is
derived from the diet. The cholesterol is then
moved from the micelles to the surface of the
brush border membrane of the enterocyte, and
into the cytoplasmic compartment. Cholesterol
moves to the endoplasmic reticulum where it
esterified by acyl-CoA: cholesterol acyl-transferase
(ACAT) to form cholesteryl ester. Free cholesterol
and cholesteryl esters are packed into
chylomicrons, which are then secreted into the
mesenteric lymph. Once in the circulation, the liver
quickly clears chylomicrons and their remnants.
The significances of cholesterol absorption
inhibition include decreased cholesterol delivery to
Correspondence Author
Ketan R. Soni
K. B. Institute Of Pharmaceutical
Education and Research, Gandhinagar
– 23, Gujarat, India
Email: ketansoni1991@gmail.com
International Journal of Pharmaceutical Research & Development ISSN: 0974 – 9446
Available online on www.ijprd.com
131
the liver, decreased hepatocyte cholesterol stores,
reduced low-density lipoprotein (LDL) production,
increased LDL clearance and, then, decreased LDL
cholesterol levels.(1)
HYPERLIPIDEMIA:
Hyperlipidemia is the predictor of coronary artery
disease (CAD).(2) It is a heterogeneous disorder
commonly characterized by an increased flux of
free fatty acids (FFAs), high triglycerides (TGs), low-
density lipoprotein-cholesterol (LDL-c) and
apolipoprotein B (apoB) levels, as well as by a
reduced plasma high-density lipoprotein (HDL)
cholesterol concentration.(3, 4) The lipid
aberration in hyperlipidemia is an increase in
circulating (nonesterified) FFAs coining from
adipose tissue, and an insufficient esterification
and FFA metabolism. The reduced retention of
fatty acids (FAs) by adipose tissue leads to an
increased flux of FFA returning to the liver, which
stimulates hepatic TG production, promoting the
production of apoB and the assembly and secretion
of very low-density lipoprotein(VLDL).(5)
The progression of atherogenic dyslipidemia is
mediated largely by the effect of circulatory FFAs
on the liver, which stimulating synthesis of
triglycerides and secretion of very low density
lipoprotein cholesterol (VLDL-C). The increased
VLDL-C level is usually related with lowered HDL-C
because cholesteryl ester transfer protein (CETP)
transfers core lipids between the molecules.(6, 7)
Insulin often worsens the condition as it down
regulates the activity of lipoprotein lipase, an
enzyme that contributes to the breakdown of
VLDL-C. Therefore, hyperinsulinemia stimulates the
production and decreases the metabolism of VLDL-
C.(8)
Brousseau and coworker found that increased CETP
activity may be responsible for some of the lipid
abnormalities seen in the metabolic syndrome,
inhibition of CETP increases HDL-C levels and
provide a potential therapeutic approach for the
metabolic syndrome(9).
Which is characterized by the coexistence of
hyperinsulinemia, obesity, dyslipidemia, and
hypertension. Dyslipidemia is the hallmark of the
metabolic syndrome, which is summarized by:
Increased flux of FFAs; raised TG values; low HDL-c
values; increased of LDL-c values; and raised apoB
values.(3, 4, 10)
The primary defect is probably focused in the
inadequate esterification of the free fatty acids to
TGs by the adipose tissue, this leads to reduced
fatty acid trapping and subsequent retention by
the adipose tissue. The insulin resistance also
causes reduced retention of free fatty acids by the
adipocytes. These abnormalities lead to increased
flux of free fatty acids to the liver. However, it is
shown that hepatic fatty acid metabolism is
required for the development of insulin resistance.
Increased amount of free fatty acids from the
periphery to the liver in the insulin resistant state
stimulates hepatic TG synthesis, which stimulates
the gathering and secretion of TG containing VLDL,
as well as the apo B production in the liver. When
insulin resistance occurs, high level of insulin make
the liver resistant to the inhibitory effects of insulin
on VLDL production.(3)
One probability is that changed lipid flux in the liver
attributable to insulin resistance may decrease the
hepatic production of Apo A. However, there are
some studies showing that the diameter of HDL is
affected by insulin resistance. Alternatively, the
insulin resistance may cause the destabilization of
ATP binding cassette A1 transporter protein, a key
molecule that mediates the transfer of cellular
phospholipids and cholesterol to Apo A for the
formation of mature and functional HDL particles.
Mutations in the ATP binding cassette A1
transporter are related with Tangier disease, which
is characterized by enormously low HDL cholesterol
levels.
INSULIN RESISTANCE:
The term ‘insulin resistance’ in humans is
frequently used synonymously with ‘impaired
insulin-stimulated glucose disposal’, as measured
with the hyperinsulinaemic-euglycaemic clamp
technique. The area of insulin resistance as a
fundamental constituent of the pathogenesis of
International Journal of Pharmaceutical Research & Development ISSN: 0974 – 9446
Available online on www.ijprd.com
132
type 2 DM has focused on tissues responsible for
insulin-mediated glucose uptake, namely muscle
and, slightly to adipose tissue. However, it is known
that not only glucose uptake but also adipose
tissue lipolysis and destruction of hepatic glucose
production are regulated by insulin.(11)
Insulin resistance is generally defined as the
reduction in insulin ability to stimulate glucose
uptake from body peripheral tissues. At
physiological conditions, insulin activates glucose
uptake by stimulating the canonical I RS-PI 3K-Akt
pathway and by phosphorylating and deactivating
Akt substrate 160 (AS160), is a protein that
prevents glucose transporter (GLUT) 4
translocation to the membrane. Thus, by inhibiting
AS160, insulin increase the GLUT4 translocation
from internal vesicles, promoting fusion to the
plasma membrane and subsequently glucose
uptake.(12)
Dyslipidemia is well-known risk factor for CVD, as
well as a component of metabolic syndrome, and
role of HDL-C, triglycerides (TG) and low-density
lipoprotein cholesterol (LDL-C) are previously
established as predictors of CVD.(2, 4) On the other
hand, a characteristic dyslipidemia is too
associated with insulin resistance. Several studies
are reported that newly addressed lipid profiles
might be more beneficial than the traditional ones
used for CVD prediction, and measuring these
variables might help identify insulin resistance and
CVD. Total cholesterol (T-C)/HDL-C, TG/ HDL-C, and
LDL-C/HDL-C ratio, as well as TG and HDL-C are
independently linked with insulin resistance and
risk factors of CVD. The presence of hyper
triglyceridemia, low HDL-C concentrations, and
high TG/HDL-C ratios almost never occurred as
isolated disorders, and were nearly always
associated with insulin resistance because insulin
affects TG and HDL-C metabolism.(4)
Insulin resistance is a central pathophysiological
characteristic of type 2 diabetes and abdominal
obesity, and is usually associated with metabolic
dyslipidemia. The dyslipidemia accompanying
insulin resistance is characterized by distinct
changes from a normal plasma lipid and lipoprotein
profile. These changes include decreases in plasma
levels of HDL with elevated plasma FFA and
triglycerides (TG). These lipid changes are
commonly associated with elevated VLDL
production, a concomitant increase in ApoB, an
essential structural constituent of these
atherogenic lipoproteins, and increased plasma
levels of small dense low density lipoprotein
(LDL).(10)
Cellular mechanism of insulin resistance:
The increase in plasma free fatty acid
concentration is typically linked with insulin
resistance states. An inverse association between
fasting plasma fatty acid concentrations and insulin
sensitivity, which altered fatty acid metabolism
contributes to insulin resistance in patients with
type 2 diabetes. The gathering of intracellular fatty
acid acyl CoA or other fatty acid metabolite in
muscle and liver, either through increased delivery
or reduced metabolism.(13)
Randle et al. established that free fatty acid (FFA)
effectively complete with glucose for substrate
oxidation in rat and therefore speculated that
enhance fat oxidation might cause insulin
resistance associates with diabetes and obesity.
The mechanism they explain that insulin resistance
was that an increase in fatty acids caused an
increase in the intra mitochondrial acetyl CoA/CoA
and NADH/NAD+
ratios, with consequent
inactivation of pyruvate dehydrogenase, This in
turn would cause intracellular citrate
concentrations to rise, leading to inhibition of
phosphofructokinase, a key rate-controlling
enzyme in glycolysis. Consequent accumulation of
glucose-6-phosphate would prevent hexokinase II
activity, resulting in an increase in intracellular
glucose concentrations and reduced glucose
uptake.(12), which leads to the intracellular
accumulation of triglycerides, and, of intracellular
fatty acid metabolites (fatty acyl CoA’s,
diacylglycerol, and ceramides) in these insulin-
responsive tissues, which leads to developed
insulin signaling defects and insulin resistance.
International Journal of Pharmaceutical Research & Development
Available online on www.ijprd.com
Fig. 1 Cellular mechanisam of insulin resistance
ASSOCIATION OF LIPID LEVEL AND INSULIN
RESISTANCE.
Hyperlipidemia and its complications are a main
reason of mortality and morbidity among patients
with type 2 diabetes. Most studies show that
patients with type 2 diabetes have more
triglyceride and less HDL cholesterol (in particular,
a lower HDL2 sub fraction) than non
There is a direct connection between the
dyslipidemia seen in diabetics and the in
risk of CHD.(14, 15) Type 2 diabetes has been
associated with high synthesis and low absorption
of cholesterol independent of weight, indicating
that insulin resistance may be a link between
glucose and cholesterol metabolism.(16
The lipid profile of type 2 diabetes mellitus is
characterized by increased triglycerides (TGs),
decreased high-density lipoprotein cholesterol
(HDL-C), increased very low density lipoproteins
(VLDLs), and small, dense low density lipoprotein
particles, the combination of which is h
atherogenic.(17, 18)
Insulin resistance and loss of glucose homeostasis
International Journal of Pharmaceutical Research & Development
Fig. 1 Cellular mechanisam of insulin resistance
ASSOCIATION OF LIPID LEVEL AND INSULIN
Hyperlipidemia and its complications are a main
reason of mortality and morbidity among patients
diabetes. Most studies show that
patients with type 2 diabetes have more
triglyceride and less HDL cholesterol (in particular,
a lower HDL2 sub fraction) than non-diabetics.
There is a direct connection between the
dyslipidemia seen in diabetics and the increased
Type 2 diabetes has been
associated with high synthesis and low absorption
of cholesterol independent of weight, indicating
ulin resistance may be a link between
16)
diabetes mellitus is
characterized by increased triglycerides (TGs),
density lipoprotein cholesterol
C), increased very low density lipoproteins
(VLDLs), and small, dense low density lipoprotein
particles, the combination of which is highly
homeostasis
contribute to a lipid abnormalities and
vascular damage in the form of atherogenesis,
chronic inflammation, and pro thrombotic changes
are unique patterns of
related to increased cardiovascular
and pharmacologic involvements
successfully control insulin
unfavorable lipid profiles.
management, medications
sensitizers, and thiazolidinedione
well tolerated in the managing of
syndrome.(8)
Diabetic patients with type 2 diabetes mellitus are
at greater risk of developing vascular diseases
because of lipid changes. The prevalence of
dyslipidemia in diabetes mellitus is 95%.
increasing cardiovascular complications in type 2
diabetic patients it is important to observe the
correlation of type 2 diabetes mellitus and Lipid
abnormalities.(20)
Hyperglycemia and atherosclerosis are related in
type-2 diabetes.(21) Persistent hyperglycemia
ISSN: 0974 – 9446
133
abnormalities and subsequent
the form of atherogenesis,
chronic inflammation, and pro thrombotic changes
metabolic dysfunction
cardiovascular risk. Lifestyle
involvements can be used to
insulin resistance and
In addition to lifestyle
such as statins, insulin
and thiazolidinedione are effective and
managing of metabolic
Diabetic patients with type 2 diabetes mellitus are
at greater risk of developing vascular diseases
because of lipid changes. The prevalence of
dyslipidemia in diabetes mellitus is 95%.(19) Due to
increasing cardiovascular complications in type 2
diabetic patients it is important to observe the
correlation of type 2 diabetes mellitus and Lipid
lycemia and atherosclerosis are related in
Persistent hyperglycemia
International Journal of Pharmaceutical Research & Development ISSN: 0974 – 9446
Available online on www.ijprd.com
134
causes glycosylation of all proteins, particularly
collagen cross linking and matrix proteins of
arterial wall. This finally causes endothelial cell
dysfunction, contributing further to
atherosclerosis. There is detected that lipid
abnormality is in diabetic patients. Early detection
and treatment of hyperlipidemia in of diabetes
mellitus can prevent the progression of lipid
irregularities and minimize the risk for atherogenic
cardiovascular disorder and cerebrovascular
accident.(19)
The association between lipid profile and body fat
distribution had been much discussed during the
past decades Both lipid profile and body fat have
been shown to be the important predictors for
metabolic disturbances including dyslipidemia,
hypertension, diabetes, cardiovascular diseases,
hyperinsulinemia etc.(22) Diabetics had
significantly raised levels of total cholesterol, LDL
cholesterol and triglycerides with significantly
lower level of HDL cholesterol as compared to
control and males have higher values as compared
to females.(23) Insulin resistance is linked to
established risk factors for atherosclerosis such as
hypertension, hyperlipidemia, and obesity, which
subsequently accelerate the development and
progression of atherosclerosis. (24)Insulin
resistance and type 2 diabetes (T2DM) have been
constantly associated with high triglyceride and
low HDL-cholesterol levels. Increased synthesis of
VLDL particles in the liver has been proposed to be
the main cause of increased concentrations of
triglyceride-rich lipoproteins. (16) Fasting insulin
had a stronger association with increased
cholesterol synthesis that hepatic insulin resistance
so, it is the link between insulin resistance and
cholesterol metabolism. (25)
Increased plasma levels of triglycerides (TG) in very
low density lipoproteins (VLDL) are not only
common characteristics of the dyslipidemia
associated with insulin resistance and type 2
diabetes mellitus but are the central
pathophysiologic feature of the abnormal lipid
profile. Overproduction of VLDL leads to increased
plasma levels of TG by an exchange process
mediated by cholesterol ester transfer protein
(CETP), results in low levels of high density
lipoprotein (HDL) cholesterol and Apo lipoprotein,
and the generation of small, dense, cholesterol
ester depleted low density lipoproteins (LDL).This
combination of abnormalities, elevated blood
levels of triglycerides (TG), low levels of high
density lipoprotein (HDL) cholesterol, and relatively
normal levels of low density lipoprotein (LDL)
cholesterol carried in small, dense, cholesterol-
poor LDL particles, has been called the diabetic
dyslipidemia. Significant evidence supports a key
role for insulin resistance, which is a central
pathophysiologic feature of T2DM in the
development of the diabetic dyslipidemia.
Overproduction of VLDL, with increased secretion
of both triglyceride and apo B100, seems to be the
central and most important etiology of increased
plasma VLDL levels in patients with insulin
resistance or T2DM.
The presence of hypertriglyceridemia, low HDL-C
concentrations, and high TG/HDL-C ratios almost
never occurred as isolated disorders, and were
nearly always associated with insulin resistance
because insulin affects TG and HDL-C
metabolism.(4)
Because both states are associated with insulin
resistance, the possibility remained that insulin
resistance would affect primarily either absorption
or synthesis and then lead to compensatory
changes in the other pathway, resulting in the
observed changes in both cholesterol absorption
and synthesis. Based on this study, we propose
that a decrease in cholesterol absorption is
secondary to increased cholesterol synthesis in
subjects with insulin resistance for two reasons.
First, the association of insulin resistance with
markers of cholesterol synthesis was stronger than
with markers of cholesterol absorption. Second,
when we used factor analysis to separate two non-
correlating factors that describe cholesterol
absorption and synthesis, insulin resistance was
significantly linked to cholesterol synthesis factor
International Journal of Pharmaceutical Research & Development ISSN: 0974 – 9446
Available online on www.ijprd.com
135
not to absorption factor. This shows that
cholesterol synthesis is increased and cholesterol
absorption is decreased in insulin-resistant
normoglycemic men. Fasting insulin was more
strongly correlated with cholesterol synthesis.
These findings imply that the regulation of
cholesterol metabolism by hyperinsulinemia, itself
or as a marker of hepatic insulin resistance, is the
link between insulin resistance and cholesterol
metabolism.
Fig: 2 Insulin resistance, the metabolic syndrome, and cardiovascular disease risk.
Obesity and insulin resistance are closely
associated and appear to be important underlying
factors in the development of the metabolic
syndrome. This multi component disorder is
associated with several other situations such as
hypertension, dyslipidemia, and coagulation
abnormalities. The metabolic syndrome
significantly increases the risk of the progression of
both type 2 diabetes and atherosclerotic
cardiovascular disease.(10)
TREATMENT OF DIABETIC DYSLIPIDEMIA: EFFECT
ON INSULIN RESISTANCE
Glycemic Agents: Some of the therapeutic choices
available for the treatment of T2DM, such as
metformin and the thiazolidinedione, can lower
plasma triglyceride concentrations 10–15% and 15–
25%, respectively.(26)
Fibric acid derivatives: Fenofibrate and gemfibrozil
The Diabetes Atherosclerosis Intervention Study
(DAIS) showed that treatment with fenofibrate was
related with lower TG and higher HDL cholesterol
levels, and declines in focal coronary artery
disorder (CAD) by angiography in subjects with
T2DM.(27)
Nicotinic acid (Niacin): Niacin, when used in
pharmacologic doses (1–3 g/day), has the ability to
potently lower TG (25–40%) and elevation of HDL
cholesterol (10–25%). Niacin also decreased LDL
cholesterol (15–20%) and this adds to its potential
efficacy in a high risk population (28)
Ezetimibe: Ezetimibe is the first of the cholesterol
absorption inhibitors, a novel class of lipid
modifying drugs, which potently prevent the
absorption of biliary and dietary cholesterol from
the small intestine without affecting the absorption
of fat-soluble vitamins, triglycerides or bile acids.
International Journal of Pharmaceutical Research & Development ISSN: 0974 – 9446
Available online on www.ijprd.com
136
Ezetimibe situated in the brush border of the small
intestinal enterocytes and reduces the uptake of
cholesterol into the enterocytes. This has the net
effect of inhibiting cholesterol absorption by
keeping the cholesterol in the intestinal lumen,
allowing it to be excreted. Clinical trials was
demonstrated that Ezetimibe decreased LDL
cholesterol and triglycerides, and increased HDL
cholesterol in humans.(1)
Ezetimibe is currently available from this class
whose mechanism of action involves inhibition of
dietary cholesterol absorption without affecting
the absorption triglycerides and bile acids.
Ezetimibe binds to cholesterol transporter NPC1L1
(Niemann-pick C1-like1) protein in the brush
border of intestine as well as in hepatocytes.
Reduction in cholesterol absorption leads to
compensatory up-regulation of LDL receptors on
the cell surface and increased LDL cholesterol
uptake into cells and reductions of blood LDL
cholesterol content. Side effects of Ezetimibe are
diarrhea, abdominal pain, arthralgia, backache,
myalgia, headache, sinusitis, hepatitis, aphylaxis,
myopathy, and rhabdomyolysis. This drug is
contraindicated in active liver diseases.
CONCLUSION:
The diabetic dyslipidemia that accompanies the
metabolic syndrome is generally characterized by
increased plasma TG, LDL, and decreased HDL,
each of which is believed to be an independent risk
factor for cardiovascular disease. Insulin resistance
in diabetic dyslipidemia appears to result from a
combination of increased production and
decreased clearance of atherogenic lipoprotein
particles. Diabetic dyslipidemia treated with
individual or combination niacin, thiazolidinedione,
fibrates and/or statin help in correcting the
dyslipidemia and thereby may be beneficial in
preventing further risk of developing
cardiovascular diseases.
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*****

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ASSIOCIATION OF LIPID LEVELS AND INSULIN RESISTANCE

  • 1. IJPRD, 2014; Vol 6(03):May-2014 (130 - 137) International Standard Serial Number 0974 – 9446 Available online on www.ijprd.com 130 -------------------------------------------------------------------------------------------------------------------------------------------------- ASSIOCIATION OF LIPID LEVELS AND INSULIN RESISTANCE: NOVEL APPROACH IN DYSLIPIDEMIA Ketan R. Soni1 *, Mustakim M. Mansuri1 , Sandipkumar V. Bhatt1 , Shrikalp S. Deshpande1 , Gaurang B. Shah1 *1 K. B. Institute Of Pharmaceutical Education and Research, Gandhinagar – 23, Gujarat, India ABSTRACT Dyslipidemia, the major constituent of the metabolic syndrome, characterized by elevated free fatty acid, Triglycerides, Low Density Lipoprotein and apo B levels, and reduced High Density Lipoprotein levels. Hyperinsulinemia, which accompanies Insulin resistance is a common condition which play important role in the pathogenesis of the metabolic syndrome, obesity and Type 2 diabetes (T2DM), as well as cardiovascular disease. Lipodystrophies on the other hand are associated with decreased adipose mass but are, again, characterized by insulin resistance. Excess abdominal adipose tissue has been shown to release increased amounts of free fatty acids which directly affect insulin signaling, diminish glucose uptake in muscle, drive exaggerated triglyceride synthesis and induce gluconeogenesis in the liver. Treatment approaches for patients of diabetic dyslipidemia are treated with individual or combination niacin, thiazolidinedione, fibrates and a statin shows promise for correcting the dyslipidemia commonly observed in patients with type 2 diabetes. Keywords: Dyslipidemia, Metabolic syndrome, Insulin resistance, Type 2 diabetes GENERAL OVERVIEW OF CHOLESTEROL ABSORPTION: Intestinal cholesterol absorption initiates with the micellarsolubilisation of both dietary and biliary cholesterol in the lumen of the small intestine. In general, nearly two thirds of intestinal cholesterol absorbed is from the bile and the other one third is derived from the diet. The cholesterol is then moved from the micelles to the surface of the brush border membrane of the enterocyte, and into the cytoplasmic compartment. Cholesterol moves to the endoplasmic reticulum where it esterified by acyl-CoA: cholesterol acyl-transferase (ACAT) to form cholesteryl ester. Free cholesterol and cholesteryl esters are packed into chylomicrons, which are then secreted into the mesenteric lymph. Once in the circulation, the liver quickly clears chylomicrons and their remnants. The significances of cholesterol absorption inhibition include decreased cholesterol delivery to Correspondence Author Ketan R. Soni K. B. Institute Of Pharmaceutical Education and Research, Gandhinagar – 23, Gujarat, India Email: ketansoni1991@gmail.com
  • 2. International Journal of Pharmaceutical Research & Development ISSN: 0974 – 9446 Available online on www.ijprd.com 131 the liver, decreased hepatocyte cholesterol stores, reduced low-density lipoprotein (LDL) production, increased LDL clearance and, then, decreased LDL cholesterol levels.(1) HYPERLIPIDEMIA: Hyperlipidemia is the predictor of coronary artery disease (CAD).(2) It is a heterogeneous disorder commonly characterized by an increased flux of free fatty acids (FFAs), high triglycerides (TGs), low- density lipoprotein-cholesterol (LDL-c) and apolipoprotein B (apoB) levels, as well as by a reduced plasma high-density lipoprotein (HDL) cholesterol concentration.(3, 4) The lipid aberration in hyperlipidemia is an increase in circulating (nonesterified) FFAs coining from adipose tissue, and an insufficient esterification and FFA metabolism. The reduced retention of fatty acids (FAs) by adipose tissue leads to an increased flux of FFA returning to the liver, which stimulates hepatic TG production, promoting the production of apoB and the assembly and secretion of very low-density lipoprotein(VLDL).(5) The progression of atherogenic dyslipidemia is mediated largely by the effect of circulatory FFAs on the liver, which stimulating synthesis of triglycerides and secretion of very low density lipoprotein cholesterol (VLDL-C). The increased VLDL-C level is usually related with lowered HDL-C because cholesteryl ester transfer protein (CETP) transfers core lipids between the molecules.(6, 7) Insulin often worsens the condition as it down regulates the activity of lipoprotein lipase, an enzyme that contributes to the breakdown of VLDL-C. Therefore, hyperinsulinemia stimulates the production and decreases the metabolism of VLDL- C.(8) Brousseau and coworker found that increased CETP activity may be responsible for some of the lipid abnormalities seen in the metabolic syndrome, inhibition of CETP increases HDL-C levels and provide a potential therapeutic approach for the metabolic syndrome(9). Which is characterized by the coexistence of hyperinsulinemia, obesity, dyslipidemia, and hypertension. Dyslipidemia is the hallmark of the metabolic syndrome, which is summarized by: Increased flux of FFAs; raised TG values; low HDL-c values; increased of LDL-c values; and raised apoB values.(3, 4, 10) The primary defect is probably focused in the inadequate esterification of the free fatty acids to TGs by the adipose tissue, this leads to reduced fatty acid trapping and subsequent retention by the adipose tissue. The insulin resistance also causes reduced retention of free fatty acids by the adipocytes. These abnormalities lead to increased flux of free fatty acids to the liver. However, it is shown that hepatic fatty acid metabolism is required for the development of insulin resistance. Increased amount of free fatty acids from the periphery to the liver in the insulin resistant state stimulates hepatic TG synthesis, which stimulates the gathering and secretion of TG containing VLDL, as well as the apo B production in the liver. When insulin resistance occurs, high level of insulin make the liver resistant to the inhibitory effects of insulin on VLDL production.(3) One probability is that changed lipid flux in the liver attributable to insulin resistance may decrease the hepatic production of Apo A. However, there are some studies showing that the diameter of HDL is affected by insulin resistance. Alternatively, the insulin resistance may cause the destabilization of ATP binding cassette A1 transporter protein, a key molecule that mediates the transfer of cellular phospholipids and cholesterol to Apo A for the formation of mature and functional HDL particles. Mutations in the ATP binding cassette A1 transporter are related with Tangier disease, which is characterized by enormously low HDL cholesterol levels. INSULIN RESISTANCE: The term ‘insulin resistance’ in humans is frequently used synonymously with ‘impaired insulin-stimulated glucose disposal’, as measured with the hyperinsulinaemic-euglycaemic clamp technique. The area of insulin resistance as a fundamental constituent of the pathogenesis of
  • 3. International Journal of Pharmaceutical Research & Development ISSN: 0974 – 9446 Available online on www.ijprd.com 132 type 2 DM has focused on tissues responsible for insulin-mediated glucose uptake, namely muscle and, slightly to adipose tissue. However, it is known that not only glucose uptake but also adipose tissue lipolysis and destruction of hepatic glucose production are regulated by insulin.(11) Insulin resistance is generally defined as the reduction in insulin ability to stimulate glucose uptake from body peripheral tissues. At physiological conditions, insulin activates glucose uptake by stimulating the canonical I RS-PI 3K-Akt pathway and by phosphorylating and deactivating Akt substrate 160 (AS160), is a protein that prevents glucose transporter (GLUT) 4 translocation to the membrane. Thus, by inhibiting AS160, insulin increase the GLUT4 translocation from internal vesicles, promoting fusion to the plasma membrane and subsequently glucose uptake.(12) Dyslipidemia is well-known risk factor for CVD, as well as a component of metabolic syndrome, and role of HDL-C, triglycerides (TG) and low-density lipoprotein cholesterol (LDL-C) are previously established as predictors of CVD.(2, 4) On the other hand, a characteristic dyslipidemia is too associated with insulin resistance. Several studies are reported that newly addressed lipid profiles might be more beneficial than the traditional ones used for CVD prediction, and measuring these variables might help identify insulin resistance and CVD. Total cholesterol (T-C)/HDL-C, TG/ HDL-C, and LDL-C/HDL-C ratio, as well as TG and HDL-C are independently linked with insulin resistance and risk factors of CVD. The presence of hyper triglyceridemia, low HDL-C concentrations, and high TG/HDL-C ratios almost never occurred as isolated disorders, and were nearly always associated with insulin resistance because insulin affects TG and HDL-C metabolism.(4) Insulin resistance is a central pathophysiological characteristic of type 2 diabetes and abdominal obesity, and is usually associated with metabolic dyslipidemia. The dyslipidemia accompanying insulin resistance is characterized by distinct changes from a normal plasma lipid and lipoprotein profile. These changes include decreases in plasma levels of HDL with elevated plasma FFA and triglycerides (TG). These lipid changes are commonly associated with elevated VLDL production, a concomitant increase in ApoB, an essential structural constituent of these atherogenic lipoproteins, and increased plasma levels of small dense low density lipoprotein (LDL).(10) Cellular mechanism of insulin resistance: The increase in plasma free fatty acid concentration is typically linked with insulin resistance states. An inverse association between fasting plasma fatty acid concentrations and insulin sensitivity, which altered fatty acid metabolism contributes to insulin resistance in patients with type 2 diabetes. The gathering of intracellular fatty acid acyl CoA or other fatty acid metabolite in muscle and liver, either through increased delivery or reduced metabolism.(13) Randle et al. established that free fatty acid (FFA) effectively complete with glucose for substrate oxidation in rat and therefore speculated that enhance fat oxidation might cause insulin resistance associates with diabetes and obesity. The mechanism they explain that insulin resistance was that an increase in fatty acids caused an increase in the intra mitochondrial acetyl CoA/CoA and NADH/NAD+ ratios, with consequent inactivation of pyruvate dehydrogenase, This in turn would cause intracellular citrate concentrations to rise, leading to inhibition of phosphofructokinase, a key rate-controlling enzyme in glycolysis. Consequent accumulation of glucose-6-phosphate would prevent hexokinase II activity, resulting in an increase in intracellular glucose concentrations and reduced glucose uptake.(12), which leads to the intracellular accumulation of triglycerides, and, of intracellular fatty acid metabolites (fatty acyl CoA’s, diacylglycerol, and ceramides) in these insulin- responsive tissues, which leads to developed insulin signaling defects and insulin resistance.
  • 4. International Journal of Pharmaceutical Research & Development Available online on www.ijprd.com Fig. 1 Cellular mechanisam of insulin resistance ASSOCIATION OF LIPID LEVEL AND INSULIN RESISTANCE. Hyperlipidemia and its complications are a main reason of mortality and morbidity among patients with type 2 diabetes. Most studies show that patients with type 2 diabetes have more triglyceride and less HDL cholesterol (in particular, a lower HDL2 sub fraction) than non There is a direct connection between the dyslipidemia seen in diabetics and the in risk of CHD.(14, 15) Type 2 diabetes has been associated with high synthesis and low absorption of cholesterol independent of weight, indicating that insulin resistance may be a link between glucose and cholesterol metabolism.(16 The lipid profile of type 2 diabetes mellitus is characterized by increased triglycerides (TGs), decreased high-density lipoprotein cholesterol (HDL-C), increased very low density lipoproteins (VLDLs), and small, dense low density lipoprotein particles, the combination of which is h atherogenic.(17, 18) Insulin resistance and loss of glucose homeostasis International Journal of Pharmaceutical Research & Development Fig. 1 Cellular mechanisam of insulin resistance ASSOCIATION OF LIPID LEVEL AND INSULIN Hyperlipidemia and its complications are a main reason of mortality and morbidity among patients diabetes. Most studies show that patients with type 2 diabetes have more triglyceride and less HDL cholesterol (in particular, a lower HDL2 sub fraction) than non-diabetics. There is a direct connection between the dyslipidemia seen in diabetics and the increased Type 2 diabetes has been associated with high synthesis and low absorption of cholesterol independent of weight, indicating ulin resistance may be a link between 16) diabetes mellitus is characterized by increased triglycerides (TGs), density lipoprotein cholesterol C), increased very low density lipoproteins (VLDLs), and small, dense low density lipoprotein particles, the combination of which is highly homeostasis contribute to a lipid abnormalities and vascular damage in the form of atherogenesis, chronic inflammation, and pro thrombotic changes are unique patterns of related to increased cardiovascular and pharmacologic involvements successfully control insulin unfavorable lipid profiles. management, medications sensitizers, and thiazolidinedione well tolerated in the managing of syndrome.(8) Diabetic patients with type 2 diabetes mellitus are at greater risk of developing vascular diseases because of lipid changes. The prevalence of dyslipidemia in diabetes mellitus is 95%. increasing cardiovascular complications in type 2 diabetic patients it is important to observe the correlation of type 2 diabetes mellitus and Lipid abnormalities.(20) Hyperglycemia and atherosclerosis are related in type-2 diabetes.(21) Persistent hyperglycemia ISSN: 0974 – 9446 133 abnormalities and subsequent the form of atherogenesis, chronic inflammation, and pro thrombotic changes metabolic dysfunction cardiovascular risk. Lifestyle involvements can be used to insulin resistance and In addition to lifestyle such as statins, insulin and thiazolidinedione are effective and managing of metabolic Diabetic patients with type 2 diabetes mellitus are at greater risk of developing vascular diseases because of lipid changes. The prevalence of dyslipidemia in diabetes mellitus is 95%.(19) Due to increasing cardiovascular complications in type 2 diabetic patients it is important to observe the correlation of type 2 diabetes mellitus and Lipid lycemia and atherosclerosis are related in Persistent hyperglycemia
  • 5. International Journal of Pharmaceutical Research & Development ISSN: 0974 – 9446 Available online on www.ijprd.com 134 causes glycosylation of all proteins, particularly collagen cross linking and matrix proteins of arterial wall. This finally causes endothelial cell dysfunction, contributing further to atherosclerosis. There is detected that lipid abnormality is in diabetic patients. Early detection and treatment of hyperlipidemia in of diabetes mellitus can prevent the progression of lipid irregularities and minimize the risk for atherogenic cardiovascular disorder and cerebrovascular accident.(19) The association between lipid profile and body fat distribution had been much discussed during the past decades Both lipid profile and body fat have been shown to be the important predictors for metabolic disturbances including dyslipidemia, hypertension, diabetes, cardiovascular diseases, hyperinsulinemia etc.(22) Diabetics had significantly raised levels of total cholesterol, LDL cholesterol and triglycerides with significantly lower level of HDL cholesterol as compared to control and males have higher values as compared to females.(23) Insulin resistance is linked to established risk factors for atherosclerosis such as hypertension, hyperlipidemia, and obesity, which subsequently accelerate the development and progression of atherosclerosis. (24)Insulin resistance and type 2 diabetes (T2DM) have been constantly associated with high triglyceride and low HDL-cholesterol levels. Increased synthesis of VLDL particles in the liver has been proposed to be the main cause of increased concentrations of triglyceride-rich lipoproteins. (16) Fasting insulin had a stronger association with increased cholesterol synthesis that hepatic insulin resistance so, it is the link between insulin resistance and cholesterol metabolism. (25) Increased plasma levels of triglycerides (TG) in very low density lipoproteins (VLDL) are not only common characteristics of the dyslipidemia associated with insulin resistance and type 2 diabetes mellitus but are the central pathophysiologic feature of the abnormal lipid profile. Overproduction of VLDL leads to increased plasma levels of TG by an exchange process mediated by cholesterol ester transfer protein (CETP), results in low levels of high density lipoprotein (HDL) cholesterol and Apo lipoprotein, and the generation of small, dense, cholesterol ester depleted low density lipoproteins (LDL).This combination of abnormalities, elevated blood levels of triglycerides (TG), low levels of high density lipoprotein (HDL) cholesterol, and relatively normal levels of low density lipoprotein (LDL) cholesterol carried in small, dense, cholesterol- poor LDL particles, has been called the diabetic dyslipidemia. Significant evidence supports a key role for insulin resistance, which is a central pathophysiologic feature of T2DM in the development of the diabetic dyslipidemia. Overproduction of VLDL, with increased secretion of both triglyceride and apo B100, seems to be the central and most important etiology of increased plasma VLDL levels in patients with insulin resistance or T2DM. The presence of hypertriglyceridemia, low HDL-C concentrations, and high TG/HDL-C ratios almost never occurred as isolated disorders, and were nearly always associated with insulin resistance because insulin affects TG and HDL-C metabolism.(4) Because both states are associated with insulin resistance, the possibility remained that insulin resistance would affect primarily either absorption or synthesis and then lead to compensatory changes in the other pathway, resulting in the observed changes in both cholesterol absorption and synthesis. Based on this study, we propose that a decrease in cholesterol absorption is secondary to increased cholesterol synthesis in subjects with insulin resistance for two reasons. First, the association of insulin resistance with markers of cholesterol synthesis was stronger than with markers of cholesterol absorption. Second, when we used factor analysis to separate two non- correlating factors that describe cholesterol absorption and synthesis, insulin resistance was significantly linked to cholesterol synthesis factor
  • 6. International Journal of Pharmaceutical Research & Development ISSN: 0974 – 9446 Available online on www.ijprd.com 135 not to absorption factor. This shows that cholesterol synthesis is increased and cholesterol absorption is decreased in insulin-resistant normoglycemic men. Fasting insulin was more strongly correlated with cholesterol synthesis. These findings imply that the regulation of cholesterol metabolism by hyperinsulinemia, itself or as a marker of hepatic insulin resistance, is the link between insulin resistance and cholesterol metabolism. Fig: 2 Insulin resistance, the metabolic syndrome, and cardiovascular disease risk. Obesity and insulin resistance are closely associated and appear to be important underlying factors in the development of the metabolic syndrome. This multi component disorder is associated with several other situations such as hypertension, dyslipidemia, and coagulation abnormalities. The metabolic syndrome significantly increases the risk of the progression of both type 2 diabetes and atherosclerotic cardiovascular disease.(10) TREATMENT OF DIABETIC DYSLIPIDEMIA: EFFECT ON INSULIN RESISTANCE Glycemic Agents: Some of the therapeutic choices available for the treatment of T2DM, such as metformin and the thiazolidinedione, can lower plasma triglyceride concentrations 10–15% and 15– 25%, respectively.(26) Fibric acid derivatives: Fenofibrate and gemfibrozil The Diabetes Atherosclerosis Intervention Study (DAIS) showed that treatment with fenofibrate was related with lower TG and higher HDL cholesterol levels, and declines in focal coronary artery disorder (CAD) by angiography in subjects with T2DM.(27) Nicotinic acid (Niacin): Niacin, when used in pharmacologic doses (1–3 g/day), has the ability to potently lower TG (25–40%) and elevation of HDL cholesterol (10–25%). Niacin also decreased LDL cholesterol (15–20%) and this adds to its potential efficacy in a high risk population (28) Ezetimibe: Ezetimibe is the first of the cholesterol absorption inhibitors, a novel class of lipid modifying drugs, which potently prevent the absorption of biliary and dietary cholesterol from the small intestine without affecting the absorption of fat-soluble vitamins, triglycerides or bile acids.
  • 7. International Journal of Pharmaceutical Research & Development ISSN: 0974 – 9446 Available online on www.ijprd.com 136 Ezetimibe situated in the brush border of the small intestinal enterocytes and reduces the uptake of cholesterol into the enterocytes. This has the net effect of inhibiting cholesterol absorption by keeping the cholesterol in the intestinal lumen, allowing it to be excreted. Clinical trials was demonstrated that Ezetimibe decreased LDL cholesterol and triglycerides, and increased HDL cholesterol in humans.(1) Ezetimibe is currently available from this class whose mechanism of action involves inhibition of dietary cholesterol absorption without affecting the absorption triglycerides and bile acids. Ezetimibe binds to cholesterol transporter NPC1L1 (Niemann-pick C1-like1) protein in the brush border of intestine as well as in hepatocytes. Reduction in cholesterol absorption leads to compensatory up-regulation of LDL receptors on the cell surface and increased LDL cholesterol uptake into cells and reductions of blood LDL cholesterol content. Side effects of Ezetimibe are diarrhea, abdominal pain, arthralgia, backache, myalgia, headache, sinusitis, hepatitis, aphylaxis, myopathy, and rhabdomyolysis. This drug is contraindicated in active liver diseases. CONCLUSION: The diabetic dyslipidemia that accompanies the metabolic syndrome is generally characterized by increased plasma TG, LDL, and decreased HDL, each of which is believed to be an independent risk factor for cardiovascular disease. Insulin resistance in diabetic dyslipidemia appears to result from a combination of increased production and decreased clearance of atherogenic lipoprotein particles. Diabetic dyslipidemia treated with individual or combination niacin, thiazolidinedione, fibrates and/or statin help in correcting the dyslipidemia and thereby may be beneficial in preventing further risk of developing cardiovascular diseases. REFERENCES 1. Van Heek M, Davis H. Pharmacology of ezetimibe. European Heart Journal Supplements. 2002;4(suppl J):J5-J8. 2. Ghule BV, Ghante MH, Saoji AN, Yeole PG. Antihyperlipidemic effect of the methanolic extract from Lagenaria siceraria Stand. fruit in hyperlipidemic rats. Journal of Ethnopharmacology. 2009;124(2):333-7. 3. Kolovou GD, Anagnostopoulou KK, Cokkinos DV. Pathophysiology of dyslipidaemia in the metabolic syndrome. Postgrad Med J. 2005;81(956):358-66. 4. Kawamoto R, Tabara Y, Kohara K, Miki T, Kusunoki T, Takayama S, et al. Relationships between lipid profiles and metabolic syndrome, insulin resistance and serum high molecular adiponectin in Japanese community-dwelling adults. Lipids in Health and Disease. 2011;10(1):79. 5. Mahamuni SP, Khose RD, Menaa F, Badole SL. Therapeutic approaches to drug targets in hyperlipidemia. BioMedicine. 2012;2(4):137-46. 6. Eckel RH, Grundy SM, Zimmet PZ. The metabolic syndrome. Lancet. 2005;365(9468):1415-28. 7. Granberry MC, Fonseca VA. Insulin resistance syndrome: options for treatment. Southern medical journal. 1999;92(1):2-15. 8. Fonseca VA. The metabolic syndrome,hyperlipidemia, and insulin resistance. Clinical Cornerstone. 2005;7(2– 3):61-72. 9. Brousseau ME, Schaefer EJ, Wolfe ML, Bloedon LT, Digenio AG, Clark RW, et al. Effects of an inhibitor of cholesteryl ester transfer protein on HDL cholesterol. The New England journal of medicine. 2004;350(15):1505-15. 10. Avramoglu RK, Basciano H, Adeli K. Lipid and lipoprotein dysregulation in insulin resistant states. Clinica Chimica Acta. 2006;368(1–2):1- 19. 11. Kovacs P, Stumvoll M. Fatty acids and insulin resistance in muscle and liver. Best Practice & Research Clinical Endocrinology & Metabolism. 2005;19(4):625-35. 12. Roden M, Price TB, Perseghin G, Petersen KF, Rothman DL, Cline GW, et al. Mechanism of free fatty acid-induced insulin resistance in
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