Influence of DPP-4 on Inflammatory Parameters in Diabetics: Gender Aspects

Influence of a Modern Oral Anti-diabetic Medication on Endothelial Dysfunction and Cardiovascular Risk in Diabetic Women and Men: Gender Aspects

Cardiovascular events are the most common cause for death in type 2 diabetes mellitus (T2DM) patients. Male diabetics have a 2 to 3 fold risk for cardiovascular disease (CVD) whereas female diabetes patients have a 3 to 7 fold risk for suffering from a CVD.

Endothelial dysfunction (ED) plays a central role in the development of atherosclerotic lesions. Moreover, ED represents an important diagnostic and prognostic parameter to estimate the cardiovascular risk in an early state. Experimental and clinical studies indicate that T2DM is closely associated with ED, which may be the consequence of a reduced bioactivity of nitric oxide (NO).

The success of diabetes therapy is monitored by the long-term parameter HbA1c. However, only two thirds of all patients with T2DM in the USA and Europe find themselves in the recommended HbA1c span (6.5-7.0 %). Consequently, oral anti-diabetic medication needs permanent adjustment and intensification in order to delaying the progress of T2DM.

Recently, two peptide hormones with insulinotropic effects were identified. These hormones, glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), are secreted by the gastrointestinal tract after exposure to glucose in nutrition. Physiological effects are increased insulin secretion, inhibition of glucagon secretion and reduction of body weight. Furthermore, these incretins are reduced in patients with impaired glucose tolerance. Thus, the therapeutic approach lies within the elevation of GLP-1 and GIP by preventing their degradation through the enzyme DPP-4 (dipeptidylpeptidase 4).

Thereby, the so-called gliptins inhibit the DPP-4 enzymes. Best results in HbA1c reduction were achieved when gliptins were combined with metformin, glimepiride or pioglitazone.

In this study, patients with T2DM, who are taking metformin as first line medication but do not achieve a HbA1c below 7.0 %, will routinely get an add-on therapy with gliptins (Vildagliptin or Sitagliptin) as second line therapy according to the guidelines of the Österreichische Diabetes Gesellschaft (ÖDG) prescribed by a medical doctor not involved in this study. This medication is a ÖDG standard therapy in T2DM, which patients receive anyway despite this study. Therefore, the therapy with gliptins is not a study medication and is not influenced by the study either. Only patients, who will meet the inclusion criteria of the study and voluntarily participate in the study, will be investigated.

The World Health Organization (WHO) estimates that more than 180 million people worldwide have diabetes. This number is likely to more than double by 2030. Further, the WHO proclaims that diabetes causes about 5 % of all deaths globally each year. Cardiovascular events are the most common cause for death in T2DM patients . According to the VERONA study, which observed 6000 T2DM patients over 10 years, 44 % of all deaths were caused by CVD, primarily heart attack and stroke . Interesting is the fact that male diabetics have a 2 to 3 fold risk for CVD whereas female T2DM patients have a 3 to 7 fold risk for suffering a cardiovascular event although there is no satisfying explanation for this phenomenon.

CVD is caused by atherosclerosis, a condition arising from ED. Hence, ED represents an important diagnostic and prognostic parameter to estimate the cardiovascular risk in a very early state. Such ED is frequently caused by a reduced bioactivity of NO. This molecule is synthesized in endothelial cells by oxidation of L-arginine in a reaction catalyzed by the endothelial nitric oxide synthase . NO is able to protect the vessel wall due to its vasodilatating, anti-adhesive and anti-proliferative activities. Experimental and clinical studies demonstrate that T2DM is closely associated with ED, which may be the consequence of a reduced bioactivity of NO. Central mechanisms explaining this defect in T2DM are the inactivation of NO by reactive oxygen species, the reduction in the amounts of co-factors necessary for NO-synthesis, such as biopterin and NADPH, as well as the inhibition of endothelial NO-synthase by phosphorylation (protein kinase C) and O-glycosylation (hexosamine pathway) .

Endostatin (ENST), an anti-angiogenetic factor, blocks endothelial cell proliferation and migration, induces endothelial cell apoptosis and inhibits thereby angiogenesis . Basal plasma levels of ENST are higher in T2DM patients and thus may be the missing link to explain the inactivation of NO as pro-angiogenetic factor in the process of atherosclerosis.

In T2DM, the high glucose load in the blood leads to swelling of the basement membrane and thus to microangiopathy. This favors the genesis of hypertension due to glomerulosclerosis. Eventually, three factors promote the increased risk for heart attack and stroke:

1. Hypertension
2. Increase of VLDL (due to low insulin levels)
3. and elevated clotting disposition (due to hyperglycemia induced production of fibrinogen, coagulation factor V and VIII) .

One of the difficulties in T2DM is the coexistence of polyneuropathy. As a result symptoms of angina pectoris under stress are painless so that silent infarcts are frequent and often the end point in the CVD progress . Thus, the most important aim in T2DM therapy is the prevention of secondary complications such as CVD. Therefore, the exact adjustment of blood glucose (monitored by HbA1c) plays a pivotal role in prevention. Unfortunately, only two thirds of all patients with T2DM in the USA and Europe find themselves in the recommended HbA1c span (6.5-7.0 %). Consequently, oral anti-diabetic medication needs permanent adjustment and intensification to delay the progress of T2DM. However, metformin and sulfonylurea derail the optimal treatment because of unwanted side effects, especially hypoglycemia and weight gain.

Recently, two peptide hormones, GLP-1 and GIP, with insulinotropic effects were identified. These so-called incretins are secreted by the gastrointestinal tract after exposure to glucose in nutrition. Physiological effects result in

• increased insulin secretion
• inhibition of glucagon secretion
• and reduction of body weight. It has been observed that incretin levels are reduced in patients with impaired glucose tolerance. Thus, the therapeutic approach lies within the elevation of GLP-1 and GIP by preventing their degradation through the enzyme DPP-4 (dipeptidylpeptidase 4), the so-called gliptins that inhibit the DPP-4 enzymes.

Best results in HbA1c reduction were achieved when gliptins were combined with metformin, glimepiride or pioglitazone .

In this study, patients with T2DM, who are taking metformin as first line medication but do not achieve a HbA1c below 7.0 % and with an intolerance against sulfonylurea (hypoglycemia during the night) and glitazones (obesity, weight gain and ankle edema), will routinely get an add-on therapy with gliptins (Vildagliptin or Sitagliptin) as second line therapy according to the guidelines of the Österreichische Diabetes Gesellschaft (ÖDG) prescribed by a medical doctor not involved in this study. This medication is a ÖDG standard therapy in T2DM, which patients receive anyway despite this study. Therefore, the therapy with gliptins is not a study medication and is not influenced by the study either. Only patients, who will meet the inclusion criteria of the study and voluntarily participate in the study, will be investigated.

Rationale of the study

This study aims to investigate the effects of a modern oral anti-diabetic medication according to the guidelines of the ÖDG on ED. A special focus will be put on the outcome between female and male patients to elucidate the different effects of the drugs on inflammatory parameters in women and men.

The following parameters will be measured:

• Catecholamine (norepinephrine, dopamine, epinephrine) Catecholamines are released by the adrenal gland in situations of stress such as psychological stress, physical stress or low blood sugar levels . They are water-soluble and 50 % bound to plasma proteins. The three major catecholamines that circulate in the blood are epinephrine, norepinephrine and dopamine. They are mainly produced from the adrenal medulla and the postganglionic fibers of the sympathetic nervous system. The measurement of the catecholamines serves as control parameter for the applied stress situations.
• ENST ENST, a 20-kDa C-terminal fragment derived from type XVIII collagen, is an endogenous protein that blocks the formation of blood vessels. It inhibits endothelial cell proliferation, migration and angiogenesis. There is evidence for several functions of neovascularisation in plaque growth that maintain perfusion beyond limits of diffusion from the artery lumen and outer adventitial vasa vasorum, deposit pro-atherogenic plasma molecules, recruit immune cells and progenitors, and promote intraplaque hemorrhage . ENST, as an angiostatic factor, might be the weapon of choice to battle these effects.
• BNP Brain natriuretic peptide (BNP) is a 32-amino acid peptide . It is synthesized predominantly in the left ventricle of the heart as the 108-amino acid pro-hormone preproBNP ( -BNP) . The hormone is a potent vasodilator and a natriuretic factor regulating salt and water homeostasis. BNP is stored in the human cardiac tissue mainly as BNP-32 with a lesser amount of the precursor preproBNP. The circulating plasma forms of BNP are BNP-32 and the NH2-terminal portion proBNP (Nt-proBNP) . Increased secretion of BNP and Nt-proBNP occurs mainly with increased tension in the ventricular walls, decreased oxygen supply, acute myocardial infarction, chronic cardiac heart failure, and in hypertrophy of the heart . The Nt-proBNP level was shown to be significantly elevated in the cohort of patients with T2DM. Taken together, both BNP and Nt-proBNP serve as sensitive markers of CVD .
• Intima-media thickness (by carotid-ultrasound) IMT is a measurement of the thickness of artery walls, usually by external ultrasound, to detect the presence and to track the progression of atherosclerotic lesions. Cross-sectional associations between common carotid artery IMT and cardiovascular risk factors have been demonstrated in several studies .
• Heart rate
• Blood pressure
• ECG

Inclusion Criteria:

• patients with T2DM
• metformin therapy
• HbA1c < 7%
• 25 - 69 years

Exclusion Criteria:

• pregnant women
• untreated thyroid dysfunction
• renal insufficiency (creatinine clearance < 60 ml/min)
• unstable coronary heart disease
• NYHA III or IV
• severe hepatic dysfunction except steatosis (GOT and GPT three times higher than ULN)
• patients undergoing cortisone therapy
• condition post stroke within the last 6 months