1. Introduction
Metabolic syndrome (MetS) is defined as the coexistence of several risk factors of metabolic origin (with insulin resistance as the usual common pattern) that elevate the risk for cardiometabolic diseases [
1]. MetS is a major and escalating public health and clinical challenge worldwide in the wake of urbanization, surplus energy intake, increasing obesity, and sedentary life habits. Its prevalence has increased over time and is now reaching epidemic proportions, with an estimated prevalence of one-fifth of adult populations in western countries [
2]. All the cardiometabolic alterations that compound MetS are also key risk factors for the development and progression of non-alcoholic fatty liver disease (NAFLD), that is considered as a hepatic manifestation of MetS [
3].
The prevalence of NAFLD reaches alarming proportions, up to 80–90% of obese adults, 30–50% in those with diabetes, and up to 90% in hyperlipidemic subjects [
4]. It should be highlighted that liver fat has been associated with poor metabolic health, independent of the obesity state [
5,
6]. Despite its growing clinical burden, there are no specific drugs for the treatment of these subjects and their management is necessarily related to lifestyle changes. In recent years, there is a growing research focus on prevention and treatment of risk factors associated with both MetS and NAFLD. This includes the use of products of natural origin, also known as nutraceuticals, which can be used as supplements or even replace drugs, particularly in cases of intolerance or when side effects are present [
7]. Some nutraceuticals have shown to be effective in the management of different metabolic situations, including MetS and its associated complications, such as NAFLD [
8]. They could improve lipid infiltration of the liver but also several other risk factors, including anthropometric, hemodynamic, and biochemical parameters. Considering that NAFLD and cardiovascular diseases have common risk factors, guidelines for the prevention of cardiometabolic diseases make similar suggestions for their prevention and/or management [
9], and the role of nutraceuticals cannot be underestimated [
10].
Cynara spp. are plants that belong to the Asteraceae family that are widely consumed in the Mediterranean region and represent one of the world’s oldest medicinal plants with multiple health benefits due to the high concentration of biophenols [
11]. Extracts from different
Cynara species have shown several beneficial effects, such as anti-inflammatory, hepatoprotective, and lipid-lowering actions, including the ability to inhibit specific liver enzymes [
11]. Also, they have proven to be one of the safest nutraceuticals, showing no adverse effects on treated subjects [
12]. The extract of
Cynara cardunculus (L.) subsp.
scolymus Hayek, known as artichoke, showed an improvement of serum oxidized low-density lipoprotein-cholesterol (LDL) in subjects with MetS [
12]. Extract from artichoke leaves has also showed hepatoprotective properties and has been used in subjects with chronic liver disease [
13]. In addition, artichoke extract has been proven to inhibit oxidative stress in a dose-dependent way, and cynarine, chlorogenic acid, and luteolin seem to be the most active substances involved in this beneficial antioxidant activity [
14]. Previous studies have also shed light on the potential hepatoprotective activity and hypolipidemic effect of
Cynara cardunculus (L.) in the management of hepatic alterations [
15]. It has been shown that luteolin is effective in ameliorating ethanol-induced hepatic steatosis and injury in preclinical studies [
16]. This combination of effects induced by this flavone suggests that luteolin may be useful in the control of both NAFLD and cardiovascular risk [
17]. In addition, increasing evidence indicates that specific supplements or nutraceuticals have important hepatoprotective roles, improving liver enzymes as well as liver steatosis and its prognosis [
18].
Therefore, a hypothesis of the present study was that the supplementation of a Cynara cardunculus (L.) subsp. scolymus Hayek-based nutraceutical, named Altilix®, containing chlorogenic acid and its derivatives, and luteolin and its derivatives, can improve different cardio-metabolic markers in patients with metabolic syndrome (MetS) in a 6 month follow-up study. The primary objective was to assess whether Altilix® can improve different metabolic parameters including body weight, waist circumference, plasma lipids, plasma glycemia, plasma insulinemia, and HOMA (homeostatic model assessment) index, while secondary objectives were to assess whether Altilix® can reduce cardio-metabolic parameters including plasma cytokines (inflammatory markers and adipokines), carotid intima-media thickness, endothelial function, and fatty liver index.
4. Discussion
Literature data evidences that more efficient strategies are urgently needed in order to reduce the epidemiologic burden and adverse outcomes of the cardiometabolic implications of MetS and NAFLD.
A recent preclinical study reported the impact of flavonol derivatives rich in quercetin and kaempferol on fat storage in the liver. These molecules suppressed some signaling pathways involved in lipogenesis and adipogenesis, as well in the expression of key proteins of lipogenic liver metabolism [
27]. Our results point out the presence of such synergistic effects, showing an improvement in anthropometric (body weight, BMI, and waist circumference), glycemic, lipid, and liver parameters in Altilix
® (based on chlorogenic acid and its derivatives, and luteolin and its derivatives) supplemented subjects vs. placebo. These beneficial effects were maintained even when we stratified subjects according to the presence and degree of NAFLD. Our findings are in accord with recently published data of a pilot trial, in which an improvement of anthropometric variables after artichoke leaf extract supplementation in NAFLD subjects was present [
28]. Other preclinical and clinical studies have demonstrated several health-promoting properties of extracts of
Cynara spp., such as hypoglycemic, hypocholesterolemic, hypotriglyceridemic, other than antioxidant and hepatoprotective actions [
11]. In the present rigorous randomized, double-blind, placebo-controlled study, after 6 months of Altilix
® supplementation, we confirmed the beneficial effects on hepatic and cardiometabolic parameters. It may be considered that such results could be due to the impact on oxidative stress state elicited by
Cynara cardunculus phytochemicals, a key factor in the pathogenesis of NAFLD, as well as on inflammation [
11].
Our experimental data, for the first time, show the effect of artichoke extract on the improvement of two early atherosclerotic markers: cIMT and FMD, evidencing the clinical importance of the treatment as well as its nutraceutical properties on vascular function and remodeling, including beneficial action on the cardiovascular system and hepatoprotective activity [
10]. Firstly, after 6 months of Altilix
® supplementation, we found a significant improvement in endothelial function, and subsequently, we confirmed a preliminary observation of a beneficial effect of artichoke juice on brachial FMD, in a small group of hyperlipidemic subjects [
29].
The measured beneficial effect of cIMT in Altilix
® supplemented in comparison with placebo, is consistent with the positive influence of the treatment on LDL-cholesterol, and on the reduction in cardiovascular risk for MetS subjects. It is well known that elevated LDL-cholesterol levels are the major risk factor for coronary heart disease and, together with high cholesterol and triglycerides, are the main risk factors for atherosclerosis [
30]. Research on animal models showing that artichoke extract may prevent the development of atherosclerotic plaques [
31] has commented that the results are due to an antioxidant effect mediated by the reduction of LDL oxidation [
32] and the inhibition of cholesterol synthesis [
33].
We also showed that there is not a link between the degree of steatosis and improvement in cardiometabolic parameters; so, we hypothesize that Altilix® could act as a hepatic detoxifying agent with which supplementation could be considered very useful in the prevention of hepatic complications of MetS, particularly in NAFLD patients. This project could benefit from stratified analyses, based on variables such as NAFLD or other. Nevertheless, the sample sizes would decrease to get enough statistical power. Thus, we prefer to maintain the comparisons between the whole test and control groups; also, it should be considered that the test and control groups were randomly assigned.
In fact, we found in subjects from the Altilix
® supplemented vs. placebo groups, regarding MetS comorbidities, a significant improvement in glucose metabolism parameters (including HbA1c, insulin resistance, and pancreatic β-cell function), in agreement with some in vitro and in vivo literature data [
34,
35,
36]. In particular, among these, some in vivo studies with oral daily administration of
Cynara cardunculus (L.) subsp.
scolymus Hayek extract showed glycemic-lowering effects. Other studies reported in 39 overweight subjects, that the intake of tablets containing extract of artichoke during meals, resulted in a significant reduction of the HOMA index [
34]. Whereas, in vitro studies evidenced the role of chlorogenic acid on glucose regulation—antagonist in glucose transport, inhibitor of α-amylase and α-glucosidase, and therefore in the post-prandial glucose blood concentration [
34,
35,
36]. We also found, after Altilix
® supplementation, an improvement in both HOMA-IR (marker of insulin resistance), a marker useful in identifying individuals with metabolic NAFLD [
37] and HOMA-β (marker of pancreatic β-cell function).
Regarding the effect on cardiovascular/cardiometabolic diseases, our data concerning a significant reduction in TC, TG, and LDL-cholesterol, together with some not significant modifications in HDL-cholesterol levels, are also in line with previous reported effects of artichoke on lipid profile [
38] as well as on the inhibition of cholesterol synthesis exerted by luteolin, one of the components of Altilix
® [
33,
39]. However, this lipid-lowering effect could be, in turn, attributed to the presence in Altilix
® of chlorogenic acid, which is associated with a direct action on the liver, the excretion of biliary salts, and acids rich in cholesterol [
34,
40]. Therefore, our findings, proposing a direct effect of artichoke extract on lipids affecting liver-related parameters, particularly TG, result in being, again, of huge clinical value, since the accumulation of TG in hepatocytes is largely involved in NAFLD development and progression [
41].
To reinforce the values of Altilix
® supplementation in improving hepatic function in NAFLD patients, there is in our data the enhanced AST/ALT ratio, a reduction in both AST and ALT and FLI serum levels after 6 months of supplemented subjects compared with the placebo group, suggesting that subjects at high risk of developing hepatic complications of MetS could benefit from the mentioned supplementation. Previous evidence has shown, in fact, a possible activity of serum ALT as a predictor factor for general health, independent of the presence of liver disease, and particularly useful when liver disease is a component of MetS [
42].
Artichoke leaf extract has been proven, also, for its anti-inflammatory effects in non-alcoholic steatohepatitis induced in animal models [
43]. In addition, compounds derived from artichoke, too, have been previously described to act in the anti-inflammatory process, even in subjects with NAFLD [
15,
28]. These hepatoprotective effects may be surely ascribed to the antioxidant effects of phenols present in artichoke leaves. In fact, it may be considered that the intake of
Cynara cardunculus extract can lead to the removal of dangerous toxins, facilitation of bile production, assisting fat digestion and significantly preventing the lipid peroxidation process in cell membranes of liver tissues, as well as oxidative damage in hepatocyte membranes [
44,
45]. Finally, a significant rise of the serum levels of ghrelin was observed in the subjects that received the Altilix
® supplement. Lower levels of this hormone have been previously related to weight gain and adiposity, since it physiologically increases during fasting and decreases after food intake and has also a role in energy expenditure [
46]. Its levels have also been reported to be elevated by drugs such as Liraglutide [
47]. A previous study testing the effects in rodents of an extract of
Cosmos caudatus Kunth leaf, rich in chlorogenic acid, also showed an increase in ghrelin levels, as well as an improvement in lipid and obesity-related variables [
48].
It is well known that concentrations of IL-6 are drastically increased during inflammatory conditions [
49,
50]. We suppose that one of the reasons for the remarkable difference among the Altilix
® and placebo groups can be the increased inflammation associated with higher BMI and increased waist circumference in the placebo group that is further associated with visceral fat and its mediators in the inflammation process. Also, some other mediators, such as higher number of smokers in the placebo group, can be associated with higher inflammation in this group. The same reasons, at least in part, might explain that ghrelin is reduced in the placebo group, as it is known that plasma ghrelin levels decrease after a meal is consumed and in conditions of obesity, as well as that ghrelin levels are negatively correlated with BMI and insulin resistance [
51]. Yet, we cannot exclude the possibility that Altilix
® interferes in the mechanism of secretion of ghrelin and in the regulation of gastric emptying. In addition, in the placebo group, the cIMT increased after 6 months which also might, in part, explain lower levels of ghrelin as it is known that MetS is a predisposing factor to arterial stiffness, that persistent MetS circumstances can deteriorate the arterial stiffness severity, and that low concentrations of plasma ghrelin are meticulously connected to arterial stiffness [
52].
Such findings indicate the importance of a multifactorial approach on several components of MetS simultaneously, including lifestyle changes and promotion of non-smoking. It seems that different ingredients of the natural supplement used in the present study could have such multifactorial effects that can be of particular benefit for subjects with MetS.
The strengths of the study design are the inclusion of the placebo group, of the rigorous randomization, the double-blinded research, the high adherence to the treatment, as well as the blinded measurements of all parameters, including cIMT and FMD. This finding is of considerable clinical value, and we observed a general improvement in all groups. An improvement in cIMT and FMD in subjects with and without NAFLD in our study remains a valid therapeutic option, but the possible mechanisms of action on cardiovascular risk remains to be clarified. Studies with longer follow-ups are still necessary to confirm these effects. Also, the presented results have shown significant clinical effects in a real-world setting. Conversely, potential limitations may include the relatively short time frame of 6 months and the avoided acquisition of liver biopsy. However, this may be considered only an apparent limitation from both a clinical and ethical point of view; a liver biopsy could not be justified. On the other hand, the use of FLI for evaluating the presence and degree of NAFLD, as done in the present study, has been shown over the years very useful, since FLI is consistently able to detect unrecognized liver disease in the general population [
53]. Also, the American Association for the Study of Liver Diseases approves non-invasive methods, such as the assessment of serum markers, for screening liver dysfunction in subjects with metabolic risk factors, while liver biopsy has to be considered for disease confirmation only [
54].