Pleiotropic Effects of GLP-1. Cardiovascular Evidence of Effectiveness

doi:10.4236/pp.2013.49091

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Pharmacology & Pharmacy, 2013, 4, 647-650

Published Online December 2013 (http://www.scirp.org/journal/pp)

http://dx.doi.org/10.4236/pp.2013.49091

Open Access PP

647

Pleiotropic Effects of GLP-1. Cardiovascular Evidence of

Effectiveness

Pedro Pujante Alarcón1, Ana Belén Hernández Cascales1, Alfonso López Ruiz2,

María Ángeles Ibañez Gil3, Alicia Hernández Torres4, María Dolores Hellín Gil1

1Endocrinology and Nutrition Service of the Hospital University Virgen de la Arrixaca, Murcia, Spain; 2Pharmaceutical Care

Research at the University of Granada, Granada, Spain; 3Health Center Mariano Yago, Yecla, Murcia, Spain; 4Infectious Internal

Medicine of the Hospital University Virgen de la Arrixaca, Murcia, Spain.

Email: [email protected]

Received September 8th, 2013; revised October 16th, 2013; accepted October 29th, 2013

License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

Patients with diabetes are characterized by the development of cardiovascular complications: nephropathy, retinopathy,

neuropathy, ischemia or hypertensive etc. Therefore, the cardiovascular involvement is the leading cause of death in

patients with Diabetes Mellitus type 2 (DM2). Despite intensive treatment on classical factors of cardiovascular disease

(blood pressure levels, LDL cholesterol, etc.), patients with diabetes have a high number of cardiovascular events and

the onset and prognosis of these are related to glycemic control parameters, glycosylated hemoglobin (HbA1c). On the

other hand, the question of the cardiovascular protective effect of some hypoglycemic treatments has been raised, ask-

ing what he has done to know more accurately about the safety and cardiovascular effects of the treatments we have

today. The two most important incretin hormones are GIP (gastric inhibitory polypeptide) and GLP-1 (glucagon-like

peptide-1). Treatment based on GLP-1 is a novel weapon in T2DM that achieves a reduction in HbA1c with other

metabolic effects: weight loss and extra effect in dyslipidemia and blood pressure. In the last years other beneficial ac-

tions such a protector effect against myocardium ischemia and other actions in basals were reported. In this article we

will try to explain the evidence of GLP-1 treatments and its cardiovascular effects.

Keywords: GLP-1; T2DM; Myocardium Ischemia

1. Introduction

The incidence of type 2 diabetes is a health problem now

and with future prospects uncertain. It is estimated to

reach 300 million diabetic patients in the coming years

[1]. Patients with diabetes are characterized by the de-

velopment of cardiovascular complications: nephropathy,

retinopathy, neuropathy, ischemia or hypertensive etc.

[2]. Therefore, the cardiovascular involvement is the

leading cause of death in patients with Diabetes Mellitus

type 2 [3]. Despite intensive treatment on classical fac-

tors of cardiovascular disease (blood pressure levels,

LDL cholesterol, etc.), patients with diabetes have a high

number of cardiovascular events and the onset and prog-

nosis of these are related to glycemic control parameters,

glycosylated hemoglobin (HbA1c) [4].

On the other hand, it has raised the question of the

cardiovascular protective effect of some hypoglycemic

treatments, rosiglitazone, [5,6] asking what he has done

to know more accurately about the safety and cardiovas-

cular effects of the treatments we have today.

2. Incretins

The incretin effect is known as the amplification of the

insulin response that occurs after oral ingestion of glu-

cose in the administration of an equivalent amount intra-

venously. This effect is responsible for up to 60% of the

increase in insulin secretion after ingesta [7].

Incretins are intestinal peptides original in response to

intake. Among its effects include stimulation of insulin

production, suppression of glucagon thereby reducing

hepatic glucose production and inhibition of β-cell apop-

tosis [8]. Nauck et al. [9], showed in 1986 that the in-

cretin effect was decreased in patients with type 2 diabe-

tes because they decrease in the concentrations of GLP-1

Pleiotropic Effects of GLP-1. Cardiovascular Evidence of Effectiveness

648

(and GIP), after ingestion. Its efficacy is mediated by its

action on GLP-1 receptor abundantly expressed in the

gastrointestinal tract but may be present also in pancre-

atic tissue, lung and stomach, nervous system, heart,

vascular smooth muscle cells and macrophages. For this

reason, besides the already mentioned hypoglycemic

effect, GLP-1 effects are attributed regulation about the

appetite, decreased gastric emptying, increased periph-

eral insulin sensitivity, as well as neuro and cardiopro-

tective effects [4,10]

Thus, treatments aimed at acquiring an incretin effect

have been for many years an attractive therapeutic target

that nowadays is part of our medical arsenal. Also we

have drugs GLP-1 analogues resistant to inactivation of

the enzyme DPP-4 (liraglutide), incretin mimetics resis-

tant to DPP-4 (exenatide) and inhibitors of the enzyme

DPP-4 (vildagliptin, siltagliptin, saxagliptin).

3. GLP-1 and Cardiovascular Risk Factors

Exenatide has shown a reduction of about 1% in HbA1c

in patients without prior treatment or with sulfonylureas

and metformin alone or in combination. It also adds a

beneficial effect on fasting blood glucose and postpran-

dial glucose [11-14], with a reduction in weight up to 5.3

kg in those studies for 3 years [15]. Similarly Liraglutide

reduces HbA1c over 1% in patients with different com-

binations of antidiabetic orales [16-18] and even com-

pared to glargine insulin [19] with a beneficial effect on

weight. In those studies comparing the effect of liraglu-

tide vs. exenatide, liraglutide shows a greater reduction

in HbA1c (−1.12% vs. 0.79%, P < 0.05) with similar ef-

fect on weight loss (3 kg approximately) in 26 studies

weeks [20].

Furthermore, liraglutide and exenatide have shown a

reduction in cardiovascular risk factors including dyslip-

idemia and blood pressure. In a meta-analysis of 6 stud-

ies performed more than 2000 patients exanatide showed

a reduction systolic (SBP) without changes in diastolic

blood pressure (DBP). This effect could not be explained

completely by weight loss [21]. Liraglutide has demon-

strated in the 6 studies LEAD a reduction of 2.5 mmHg

SBP. This effect has been demonstrated in the first 2

weeks before the weight loss [22]. Regarding the lipid

profile exenatide has demonstrated a decrease in the

concentration of triglycerides by 12%, 5% total choles-

terol, LDL 6% and increased HDL cholesterol by 24% in

studies conducted at 3 years[15].

In addition to these cardiovascular effects have been

reported in animal studies and human in vitro different

actions of analogues of GLP-1 on macrophages and

monocytes by decreasing their accumulation in athero-

sclerotic plaques and reducing production of inflamma-

tory mediators such as TNF-α or CD11b expression [23].

4. GLP-1 in the Cardiovascular System

Vascular function:

Different studies in healthy patients have been con-

ducted to determine the effect of acute or chronic analogs

of GLP-1 in the endothelium. First, the acute treatment

has been shown to increase blood flow to endothe-

lium-dependent vascular level in non diabetic patients

[24] and in diabetics with stable coronary disease [25].

Moreover chronic treatment with GLP-1 analogs has

shown improvement in endothelial function and vaso-

constriction in rats diabetes induced with estreptozocine

[26]. In addition, some studies suggest that this im-

provement in endothelial dysfunction provides vasodila-

tion and improved blood flow to areas distal, common

site for the development of complications associated with

diabetes [4]. One of the potential mechanisms by which

GLP-1 analogs affect the vascular tree is due to the re-

duction of the toxic effect of glucose on the endothelial

cell. GLP-1 has been shown to decrease the deleterious

effect of advanced glycation products (AGE) in the en-

dotelium [27].

Cardiac function:

Most studies designed to determine the effect of

GLP-1 on cardiovascular function have focused on mod-

els of ischemia and reperfusion. Studies in vivo and in

vitro with cardiomyocytes in mice have shown that after

a period of ischemia and subsequent reperfusion, the

mice treated with GLP-1 analogs significantly reduce the

size of the infarct zone post-ischemia improve cardiac

contractility, systolic function and diastolic function [28].

Similar experiments have given similar results in canine

models of dilated cardiomyopathy [29] and porks [30]. In

humans, a small, non-randomized study in patients, most

non-diabetics, who had undergone coronary revasculari-

zation after acute myocardial infarction and to which he

had been given an infusion of GLP-1 analogs for 72

hours, an improvement in ejection fraction and better left

ventricular myocardial contractility had been reported. In

this sense Sokos et al. [31] selected 20 patients who un-

derwent aortocoronary bypass and who infused GLP-1

analogues. Observed in the treated group that the use of

vasoactive or inoprotic drug was lower and there were

fewer arrhythmias. In additional studies, infusion of

GLP-1 analogs for 48 hours in patients non-diabetics and

heart failure reduced fasting glucose levels and insulin

levels increased compared to placebo associated with an

increased heart rate and blood pressure but no impact

hemodynamics.

The mechanism by which it acts is not clarified. It is

thought that the myocardium after ischemia increases

glucose uptake. This increase improves glucose oxida-

tion and producing more ATP than from the free fatty

acids. In addition to this increased supply of glucose to

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Pleiotropic Effects of GLP-1. Cardiovascular Evidence of Effectiveness 649

myocardial ischemia occurs a minor ischemic damage.

That has been regarded as a cardioprotective effect of the

myocardium with consequent smaller necrosis [32] zone.

What we do not known if this action is mediated by

GLP-1 receptor exclusively or by an intermediate me-

tabolites such GLP-1 (9 - 36), an antagonist receptor

have also shown beneficial effect after isquemia [4].

5. Conclusion

Therapies based on incretins, GLP-1 have proven to be

an effective treatment for glycemic control with very

beneficial effects on weight, blood pressure and lipid

profile. Moreover, although the results are preliminary,

we observe a beneficial effect on associated complica-

tions of DM2. The modifications to the atherosclerotic

plaques and improving endothelial dysfunction make us

foresee a very beneficial effect on cardiovascular disease

prevention. On the other hand, with the data in models of

ischemic heart disease, and the cardioprotective effect of

GLP-1, demonstrated in animal and human experiments,

we do consider the possibility of a beneficial effect be-

yond the treatment of cardiovascular risk factors. How-

ever, the data in the treatment in diabetes and heart fail-

ure are not as conclusive. In these patients, we must not

forget the side effects of current therapies against type 2

diabetes: the water retention of glitazons and insulin or

the contraindicated indication of metformin in patients

with renal failure. Although larger, prospective, random-

ized studies are needed in order to determine the safety

of GLP-1 analogs in heart failure, we can not discard

them when planning the best treatment for this kind of

patients.

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