The effects of green cardamom supplementation on blood glucose, lipids profile, oxidative stress, sirtuin-1 and irisin in type 2 diabetic patients: a study protocol for a randomized placebo-controlled clinical trial

Diabetes Mellitus (DM) is a non-communicable disease that affects many persons annually. In 2000, 171 million people suffered fromDM globally, and it has been estimated to reach 366 million people in 2030 [1]. DM increases the risk of cardiovascular disease (CVD) by 2 to 4-fold. Dyslipidemia plays an important role in the pathogenesis of CVD in type 2 diabetes mellitus (T2DM) patients [2].

Studies have shown that high glucose level by stimulating reactive oxygen species (ROS) production damages β-cells and leads to impaired insulin release and insulin resistance [3, 4]. The antioxidant defence system is responsible for the neutralization of ROS; however, β-cells have a poor antioxidant defence system. Therefore, antioxidant supplementation by elevating antioxidant defence capacity can protect against β-cells dysfunction [5].

Many investigations have been executed regarding the relationship between sirtuin-1 (SIRT1) and irisin with the occurrence of DM. SIRT1 is a class III protein deacetylase that is associated with aging, inflammation and CVD [6]. Moreover, it has been suggested that SIRT1 plays an important role in glucose metabolism by stimulating pancreatic insulin release and insulin signaling pathway [7]. Investigations have stated that activation of SIRT1 leads to deacetylation of nuclear factor (NF)-κB, peroxisome proliferator activated receptor (PPAR)-γ and PPAR-γ coactivator 1α (PGC-1α) which have beneficial effect on glycemic indices, obesity and mitochondrial function [6, 7]. PGC-1α is a transcriptional coactivator that regulates energy balance and expression of fatty acids oxidation genes. In addition, it is involved in the improvement of mitochondrial function, insulin sensitivity and alleviation of oxidative stress. PPAR-γ and NF-κB are transcriptional factors that regulate fat metabolism and inflammation, respectively. Therefore, the inhibition of PPAR-γ and NF-κB activity by SIRT1 deacetylation suppresses fat accumulation and inflammatory processes in the human body [6, 8]. Studies have shown that lower SIRT1 activity is involved in the pathogenesis of DM and insulin resistance. Therefore, interventions that increase SIRT1 activity may be beneficial in improvement of insulin resistance and control of DM [7, 8]. Studies have shown that dietary polyphenols by stimulation of SIRT1 activity result in the suppression of NF-κB and activation of PGC-1α; hence improving insulin resistance and lipid metabolism [6].

Irisin is a recently known exercise-mediated myokine that regulates glucose hemeostasis [9]. Irisin contributes to the browning of white adipose tissue by increasing uncoupling protein-1 (UCP-1) in these cells, which results in the improvement of insulin sensitivity and glucose metabolism. UCP-1 is a key molecule that regulates energy expenditure [10]. Studies have indicated that a lower level of irisin is associated with DM and insulin resistance [9]. The activation of PGC-1α is the main stimulator of irisin release, therefore the elevation of irisin level may be a therapeutic approach in the management of insulin resistance and DM. It has been suggested that flavonoids such as quercetin and resveratrol by activation of PGC-1α- and the SIRT1-related signaling pathway contribute to mitochondrial biogenesis [11]. Mitochondria regulates oxidative metabolism in muscle, hence increase in mitochondrial biogenesis results in higher insulin-related glucose uptake by muscle which subsequently improves insulin sensitivity [12].

Green cardamom (Elettaria cardamomum) is a dietary spice (in the ginger family) with nutraceutical effects that has antioxidant, anti-inflammatory and anti-carcinogenic properties [13, 14]. In a recent study, Ahmed et al. indicated that cardamom supplementation by supression of α-amylase and α-glucosidase enzymes has anti-diabetic effects and may regulate glucose metabolism [15]. Cardamom volatile oil is composed of terpenes, esters, flavonoids, 1,8-cineole, alpha-terpinyl acetateand limonene [16]. Previous studies have indicated that 1,8-cineole has antioxidant and lipid-lowering effects [17, 18]. Cardamom is high in polyphenolic compounds such as quercetin, kaempferol, luteolin and pelargonidin which possess antioxidant properties [19]. It has been reported that resveratrol and quercetin can increase the deacetylation effect of SIRT1 by 13-fold and 4.6-fold, respectively [20]. Therefore, it has been hypothesized that cardamom antioxidant and anti-inflammatory activities may improve DM. Kandikattu et al. in an experimental model has shown that cardamom can stimulate in vitro superoxide dismutase (SOD), catalase and glutathione activity [21]. However, in two randomized clinical trials, cardamom (3 g/d) had no significant effect on oxidatve stress biomarkers in pre-diabetic and diabetic patients [22, 23]. To the best of our knowledge, there is no clinical trial that has investigated the effects of cardamom on SIRT1 secretion and subsequently PGC-1α, irisin and insulin sensitivity in diabetic patients. Therefore, this study has designed to investigate the effect of Elettaria cardamomum on blood glucose, lipid profile and oxidative stress biomarkers in T2DM patients. To determine the mechanism of cardamom effect on blood glucose and lipid levels, blood irisin, and SIRT1 will be assessed.

This clinical trial will be conducted after approval by the Ethics Committee of Tehran University of Medical Sciencesand after obtaining informed consent from the participants. Whenever a person is unable to continue supplementation, he/she will be excluded from the study.

One of the limitations of this study is the lack of cooperation of some patients who were replaced with other patients.

T2DM is a common chronic disease worldwide. Recently, herbal medicine has become more popular due to their beneficial effects [30]. Cardamom (E. cardamomum) is an expensive spice with an old history [31]. Today, cardamom is grown in India, Thailand, Guatemala, Ceylon and Malay Archipelago [26]. The main characteristics of cardamom include sweet odor, warm nature and mild strong taste that make it a popular spice [31]. Cardamom is rich in antioxidant compounds that cause elevation and activation of the antioxidant defense system [32].

To the best of our knowledge, this is the first randomized controlled trial that will determine the effect of cardamom on glycemic status, lipid profile, oxidative stress biomarkers, SIRT1 and irisin in T2DM. The selection of patients with T2DM is the main strength of the present study. The results of this trial will provide clinical evidence on the effectiveness and safety of cardamom supplementation in patients with T2DM.