Chicory (Cichorium intybus L.) is an indigenous vegetable widely cultivated in Europe, America and Asia. In ancient times, the leaves, flowers, seeds, and roots have been used as a wealth of health benefits including its tonic effects, the ability to ease digestive problems and to detoxify liver. In Indian traditional therapy, chicory was known to possess antidiabetic effect. In the traditional medicine of Bulgaria and Italy, chicory was used as hypoglycemic decoctions. We wanted to obtain the complete chemical composition of the natural chicoric acid extract (NCRAE), a chicory root extract rich in chicoric acid, which previously showed its glucose tolerance effect in normal rats. To investigate if the whole NCRAE is required to be effective, we performed a comparative in vivo experiment on STZ diabetic rats treated either with NCRAE or a mixture composed of the two major compounds of NCRAE. LC-MS method has been used to analyze the exhaustive composition of NCRAE: we have determined that chicoric acid and chlorogenic acid represented 83.8% of NCRAE. So, we have prepared a solution mixture of chicoric acid and chlorogenic acid named SCCAM, in order to compare in vivo the antidiabetic effects of this last and NCRAE in streptozotocin diabetic rats. In vitro experiments were performed on L6 cell line both for glucose uptake and for the protective effect against H2O2 oxidative stress. Also, we have evaluated DPPH and ORAC (Oxygen Radical Absorbance Capacity) antioxidative capacities of the two compositions. The LC-MS analysis confirmed the high abundance of chicoric acid (64.2%) in NCRAE and a second part of NCRAE is composed of caffeoylquinic acids (CQAs) at 19.6% with among them the chlorogenic acid. This result has permitted us to prepare a mixture of synthetic L-chicoric acid (70%) and synthetic chlorogenic acid (30%): the solution is designated SCCAM. Our results showed that both NCRAE and SCCAM are able to improve a glucose tolerance in STZ diabetic rats after a subchronic administration of seven days. Alone NCRAE allows to significantly decrease the basal hyperglycemia after six days of treatment. To explain these difference of effects between NCRAE and SCCAM, we have compared their in vitro effects on the L6 muscle cell line both for the insulin sensitizing effect and for their protective action in pretreatment against H2O2. We have also compared their antioxidant capacities. In conclusion, we demonstrated that NCRAE, a natural extract of chicory (Cichorium intybus) rich in CRA and CQAs improves glucose tolerance and reduces the basal hyperglycemia in STZ diabetic rats.

Plant bioactive extracts represent a major resource for identifying drugs and adjuvant therapy for type 2 diabetes. To promote early screening of plants’ antidiabetic potential, we designed a four in vitro tests strategy to anticipate in vivo bioactivity. Two antidiabetic plants were studied: Ocimum gratissimum L. (Oc) leaf extract and Musanga cecropoides R. Br. ex Tedlie (Mu) stem bark extract. Chemical compositions were analyzed by LCMS and HPLC. Antidiabetic properties were measured based on (1) INS-1 cells for insulin secretion, (2) L6 myoblast cells for insulin sensitization (Glut-4 translocation), (3) L6 myoblast cells for protection against hydrogen peroxide (H₂O₂) oxidative stress (cell mortality), and (4) liver microsomial fraction for glucose-6-phosphastase activity (G6P). Oc extract increased insulin secretion and insulin sensitivity, whereas it decreased oxidative stress-induced cell mortality and G6P activity. Mu extract decreased insulin secretion and had no effect on insulin sensitivity or G6P activity, but it increased oxidative stress-induced cell mortality. Results were compared with NCRAE, an antidiabetic plant extract used as reference, previously characterized and reported with increased insulin secretion and insulin sensitivity, protection against oxidative stress, and decreased G6P activity. The proposed set of four in vitro tests combined with chemical analysis provided insight into the interest in rapid early screening of plant extract antidiabetic potential to anticipate pharmaco-toxicological in vivo effects.

Metabolic syndrome (METS) is a complex disorder that predisposes an affected person to an increased risk of diabetes and cardiovascular disease. Bitter Asteraceae plants contain several compounds active against METS that can be used as an alternative preventive therapy. Our previous work showed that a natural chicory extract (NCRAE) containing chicoric acid (CRA) and chlorogenic acid (CGA) in a molar ratio of 70/30 exhibited an antioxidant, insulin sensitization and anti-hyperglycemic effect. The present study was designed to evaluate the preventive effects of an NCRAE-like extract against METS in a complementary natural pharmacotherapeutic approach. An original Asteraceae infused drink containing the NCRAE CRA/CGA molecular ratio equivalent was prepared from dandelion (Taraxacum officinale L.) and burdock (Arctium lappa L.). The anti-METS effect of this drink was evaluated on the fructose-rat model for 8 weeks. Body weight, blood biochemistry, hepatic glucose-6-phosphatase, arterial blood pressure glucose and insulin tolerance were evaluated after 8 weeks. Our results show that daily oral intake of the Asteraceae infused drink led to a reduction of body weight gain, hyperglycemia, hypertriglyceridemia, insulin resistance and hypertension. Moreover, rat-by-rat analysis of the insulinemia measures revealed two types of responders. One sub-group of subjects demonstrated normal insulinemia and the other subgroup demonstrated hyperinsulinemia. This hyperinsulinemia, associated with the inhibition of the glucose-6-phosphatase activity in the liver tissue, may suggest an insulin release caused by CGA. The present study suggests that this original infusion of dandelion leaves and burdock roots may be used as an adjuvant therapy to prevent metabolic syndrome.

The aim of our study was to identify novel molecules able to induce an adaptative response against oxidative stress during the first stages of metabolic syndrome. A cellular survival in vitro test against H₂O₂-based test was applied after pretreatment with various natural bitter Asteraceae extracts. This screening revealed potent protection from burdock leaf extract. Using chromatography and LC-MS—RMN, we then isolated and identified an original sesquiterpene lactone bioactive molecule: the Xanthatin-13-(pyrrolidine-2-carboxylic acid) (XPc). A real-time RT-qPCR experiment was carried out on three essential genes involved in oxidative stress protection: GPx, SOD, and G6PD. In presence of XPc, an over-expression of the G6PD gene was recorded, whereas no modification of the two others genes could be observed. A biochemical docking approach demonstrated that XPc had a high probability to directly interact with G6PD at different positions. One of the most probable docking sites corresponds precisely to the binding site of AG1, known to stabilize the G6PD dimeric form and enhance its activity. In conclusion, this novel sesquiterpene lactone XPc might be a promising prophylactic bioactive agent against oxidative stress and inflammation in chronic diseases such as metabolic syndrome or type 2 diabetes.

Chicoric and chlorogenic acids (CRA and CGA), two caffeic acid derivatives found in a large variety of plants, particularly in Asteraceae, are known to modulate glucose-6-phosphatase (G6Pase) in hepatic and muscle cells. The aim of the present study is to use CRA/CGA to explore the modulation role and molecular mechanism of endocrine pancreatic beta-cells’ insulin secretion. The G6Pase enzyme activity influenced by caffeic and derivatives alone or in combination was assessed on microsomal fractions of INS1-beta-cells and hepatocytes. Overall, our results show inverse effects of CGA/CRA, allowing us to investigate the G6Pase activity modulation under low and high glucose concentrations. Our data strongly suggests the existence of two putative forms of the G6Pase enzyme. Based on these observations, we formulate the hypothesis of an adaptative bi-conformational model of G6Pase enzyme activity modulation depending on the level of the beta-cell glucose exposure.

Protein inhibitor of neuronal NO synthase (PIN) or dynein light chain 8 (LC8) is a highly conserved protein interacting with multiple partners, like neuronal NO synthase (nNOS) or myosin Va to modulate a variety of cellular functions. As PIN is expressed in skeletal muscle, our aim was to investigate a possible role of PIN in glucose uptake in L6 and primary muscle cells. PIN overexpression resulted into a decrease in glucose uptake with reduced GLUT4 expression and translocation at the plasma membrane, similarly to the pharmacological blockade of nNOS with L-NAME. PIN effect is mediated by a reduction in nNOS protein level and a direct interaction with nNOS leading to a reduced NO production in L6 myocytes. Surprisingly, a siRNA targeting PIN decreased glucose uptake and GLUT4 translocation, suggesting the involvement of nNOS-independent effects. We therefore focused on myosin Va which interacts with PIN in L6 myocytes. Myosin Va silencing provoked a decrease in glucose uptake. As PIN siRNA also reduced myosin Va expression, this confirms the essential role of myosin Va in the observed effects of PIN silencing on glucose uptake. We conclude that PIN modulates glucose uptake and GLUT4 translocation in rat muscle cells, through NO-dependent and -independent mechanisms.