Trial of Supplementation With Aged Garlic Extract to Improve Endothelial Function in Patients With Metabolic Syndrome

Cardiovascular diseases (CVD) have become the main cause of death worldwide. It is estimated that 3.8 million men and 3.4 million women die every year from this cause (WHO 2006). In addition, an increase of 47 to 83 million disability-adjusted life years (DALY) between 1990 and 2020 has been projected for this disease (WHO 2006b). It is calculated that 5.3 million deaths by CVD occur in developed countries, while 8 to 9 million deaths occur in developing countries (Yusuf et al 2001; Lopez 1993). In Colombia, the death rate for CHD in 20-84 year old subjects increased from 58.5 per 100.000 in 1980 to 103.2 in 1996. Only 30% of this increase could be attributed to population aging (Lopez-Jaramillo et al 2001). From 1997 to 2001 acute myocardial infarction (AMI), stroke and diabetes mellitus type 2 (DM 2) were responsible for 213.150 deaths (19.6%). Together, these deaths exceeded those due to violent causes, which for several years were the first cause of death in this country.

The INTERHEART study (Yusuf 2004) identified the risk factors associated with AMI in 52 developed and developing countries. Smoking, hypertension, abnormal lipids, abdominal obesity (AO), diabetes and psychosocial stress were associated with ischemic disease in all regions of the world with no differences in age and gender. However, Lanas et al. (2007) reported the results of 1237 Latin American subjects from Brazil, Argentina, Chile and Colombia, included in the INTERHEART study, demonstrated that central obesity was the most important risk factor associated with AMI in this population, much more than in the entire population of the study. We have proposed that the biological response to obesity in developed countries is different than in developing countries, and that this response is modulated through epigenetic regulation (Lopez-Jaramillo et al 2008).

The consumer society has given rise to an increase in the prevalence of overweight, obesity, hypertension, diabetes mellitus type 2 (DM2) and finally metabolic syndrome (MS). Changes in the nutritional and physical habits are the main characteristics involved in the fast economic transition, where the over nutrition and the increased consumption of saturated fat and cholesterol, low intakes of polyunsaturated fat and lower physical activity are common determinants (Pi-Sunyer 2002).

The metabolic syndrome is a set of risk factors for diabetes mellitus type 2 and cardiovascular disease, characterized by the presence of resistance to insulin and compensating hyperinsulinemia, associate to alterations of carbohydrates and lipids metabolism, elevated arterial blood pressure and obesity (Pineda 2008). In 1988, Reaven observed that several risk factors (dislipidemia, hypertension, hyperglycemia) tended to be together. This set was named syndrome X (Reaven 1988). The name metabolic syndrome like a diagnostic entity with defined criteria was introduced by the WHO in 1998 (Alberti, Zimmet 1998). The metabolic syndrome prevalence varies according to some factors such as gender, age, ethnic group, but it is located between 15% to a 40%, being greater in the population of hispanic origin (Ford et al 2002). Metabolic syndrome is important in Colombia, where the population have a major sensibility to the development of an atherogenic lipid profile (Perez et al 2003), and low grade inflammation correlated to lower levels of abdominal obesity have been described (Garcia et al 2007). These factors are associated with an increase of the vascular reactivity to the angiotensin II stimulus (Rueda-Clausen et al 2007), hormone that is also produced in the visceral adiposity (17). The latter, at the endothelial level, increases the TNF production (Arenas et al 2004), a proinflammatory citokine that stimulates the hepatic production of C reactive protein (CRP), which in our population in situations such as abdominal obesity in adults (Garcia et al 2007) and children (Lopez-Jaramillo 2008b), arterial hypertension (Rueda-Clausen et al 2007), endothelial dysfunction (Garcia et al 2007b) and pregnancy induced hypertension (Teran et al 2001) is presented in higher levels than in other populations.

Recent studies have shown that obesity, insulin resistance and diabetes type 2 are proinflammatory states (Grundy et al 2004). It has been demonstrated that enlargement of adipocytes is frequently observed in obesity and in pre-diabetic individuals and in type 2 diabetics (Lundgren et al 2007). The increased adipocyte size may represent a failure in the recruitment of new adipocytes due to impaired differentiation; it has recently been shown that fat cell enlargement is an independent marker of insulin resistance (Rotter et al 2003). Cell size expansion leads to a reduction in the production of anti-inflammatory adipokines (like adiponectin) while proinflammatory cytokines (like IL-6, and PCR) are markedly increased (Rotter et al 2003).

Recent therapies have been introduced to achieve a control of metabolic disorders and reduce the endothelium damage of the metabolic syndrome. The garlic (Allium sativum) has been shown to improve blood lipids (Zlatkis et al 1953; Chi 1982; Shoetan et al 1984; Gebhart 1991;Welch et al 1992; Gebhart 1993; Yeh, Yeh 1994;), to have antithrombotic effects (Srivastava, Tyagi 1993), to decrease antiplatelet aggregation (Kiesewetter et al 1993) and to have antioxidative properties, (Sendl et al 1992; Yamasaki et al 1993). Besides, it has been reported that garlic stimulates the phagocytotic function of macrophage and lymphocyte proliferation (Tadi et al 1990). These effects are produced largely due to its high content of organosulfur compounds and antioxidant activity. However fresh garlic may cause indigestion and its pungent odor that lingers on the breath and skin can be a social deterrent. These disagreeable effects of fresh garlic are due to allicin, an oxidant released upon cutting or chewing the clove.

An alternative source of garlic that is odorless and rich in antioxidants is aged garlic extract (AGE) (Amagase et al 2001; Borek 2001). The well-standardized and highly bioavailable supplement is produced by prolonged extraction and aging of organic fresh garlic at a stable room temperature. The process converts unstable compounds, such as allicin, to stable substances and produces high levels of water-soluble organosulfur compounds. These include S-allylcysteine (SAC), AGE's major component, and S-allylmercaptocysteine, unique to AGE. Among other compounds present are low amounts of oil-soluble organosulfur compounds, flavonoids, a phenol, allixin, selenium, and saponins.

AGE has demonstrated to be useful in the reduction of the arterial tension; Steiner et al (Steiner et al 1996) realized a double-blind crossover study comparing the effect of aged garlic extract with placebo on blood lipids in a group of 41 moderately hypercholesterolemic men. Their results show that there was a 5.5% decrease in systolic blood pressure and a modest reduction of diastolic blood pressure in response to aged garlic extract. Slowing et al (2001) found that intake of garlic can prevent diet-induced hypercholesterolemia and vascular alteration in the endothelium-dependent relaxation associated with atherosclerosis, Macan et al (2006) administered AGE or placebo at a dose of 5 mL twice a day for 12 wk. to patients whom also received warfarin for 12 weeks, after this period the levels of HDL in the garlic group was higher compared with the placebo group.

Most of the effects of age garlic extract (AGE) can be explain because its levels of antioxidant compounds, whom increases nitric oxide production and decreases the output of inflammatory cytokines, the latter has been demonstrated in cultured cells.

Nitric oxide (NO) is an important intercellular and intracellular messenger with a major role in controlling the physiological function of the cardiovascular system (Palmer et al 1987; Moncada et al 1991). It is synthesized from L-arginine by NO synthases (NOSs) in many of the cells of the cardiovascular system, including endothelial cells, macrophages, smooth muscle cells, platelets and fibroblasts (42). Three kinds of NOSs, neuronal constitutive NOS (ncNOS), inducible NOS (iNOS) and endothelial constitutive NOS (ecNOS), were reported to be responsible for NO biosynthesis in these cells (Kerwin et al 1995). NO derived from ecNOS was reported to modulate vasomotor tone, inhibition of platelet aggregation and adhesion, inhibition of leucocyte migration, suggesting that NO could explain the anti-atherogenicity actions of the vascular endothelium (Moncada et al 1991).

Flow-mediated dilation (FMD), a noninvasive method that uses high-resolution ultrasonography, is an established test to assess endothelial function. The FMD technique measures the changes in the brachial artery diameter as a response to shear stress, and it is partially dependent on the capacity of endothelial cells to release nitric oxide (Celermajer et al 1992). This method has been validated in Colombian population (Accini et al 2001; Lopez-Jaramillo et al 2004) and has been used to evaluated the effect of AGE in endothelial function. Williams et al (2005) conducted a trial in 15 men with angiographically proven coronary artery disease in a randomized, placebo-controlled, cross-over design with 2-week treatment and washout periods. During AGE supplementation, FMD increased significantly (p = 0.04) from the baseline (44%) and mainly in men with lower baseline FMD. Levels of FMD at the end of AGE treatment were significantly (p = 0.03) higher compared with the corresponding levels at the end of placebo treatment.

However, at the moment there is not data about the effect of supplementation with AGE in the endothelial function in patients with metabolic syndrome. Thus, the purpose of this study is to investigate if the supplementation of Kyolic® can alter the levels of inflammatory markers and the endothelial function (measured by VMF) in patient with metabolic syndrome.