Type 2 diabetes mellitus (T2DM), a disease on the rise and with huge economic burden to health care systems around the globe, results from defects in insulin action (termed insulin resistance) combined with impaired insulin secretion. Current methods of prevention and treatments for insulin resistance and T2DM are lacking in number and efficacy and, therefore, there is a need for new preventative measures and targeted therapies. In recent years, chemicals found in plants/herbs have attracted attention for their use as functional foods or nutraceuticals for preventing and treating insulin resistance and T2DM. Rosemary is an evergreen shrub indigenous to the Mediterranean region and South America, which contains various polyphenols. Rosemary extract and its polyphenolic constituents have been reported to have antioxidant, anti-inflammatory, anticancer, and anti-hyperglycemic properties. The current review summarizes the existing in vitro and in vivo studies examining the anti-diabetic effects of rosemary extract and its polyphenolic components and highlights the known mechanism of action.

Stimulation of the energy sensor AMP-activated kinase (AMPK) has been viewed as a targeted approach to increase glucose uptake by skeletal muscle and control blood glucose homeostasis. Rosemary extract (RE) has been reported to activate AMPK in hepatocytes and reduce blood glucose levels in vivo but its effects on skeletal muscle are not known. In the present study, we examined the effects of RE and the mechanism of regulation of glucose uptake in muscle cells. RE stimulated glucose uptake in L6 myotubes in a dose- and time-dependent manner. Maximum stimulation was seen with 5 μg/mL of RE for 4 h (184% ± 5.07% of control, p < 0.001), a response comparable to maximum insulin (207% ± 5.26%, p < 0.001) and metformin (216% ± 8.77%, p < 0.001) stimulation. RE did not affect insulin receptor substrate 1 and Akt phosphorylation but significantly increased AMPK and acetyl-CoA carboxylase phosphorylation. Furthermore, the RE-stimulated glucose uptake was significantly reduced by the AMPK inhibitor compound C, but remained unchanged by the PI3K inhibitor, wortmannin. RE did not affect GLUT4 or GLUT1 glucose transporter translocation in contrast with a significant translocation of both transporters seen with insulin or metformin treatment. Our study is the first to show a direct effect of RE on muscle cell glucose uptake by a mechanism that involves AMPK activation.

Skeletal muscle is a major insulin-target tissue and plays an important role in glucose homeostasis. Impaired insulin action in muscles leads to insulin resistance and type 2 diabetes mellitus. 5′ AMP-activated kinase (AMPK) is an energy sensor, its activation increases glucose uptake in skeletal muscle and AMPK activators have been viewed as a targeted approach in combating insulin resistance. We previously reported AMPK activation and increased muscle glucose uptake by rosemary extract (RE). In the present study, we examined the effects and the mechanism of action of rosmarinic acid (RA), a major RE constituent, in L6 rat muscle cells. RA (5.0 µM) increased glucose uptake (186 ± 4.17% of control, p < 0.001) to levels comparable to maximum insulin (204 ± 10.73% of control, p < 0.001) and metformin (202 ± 14.37% of control, p < 0.001). Akt phosphorylation was not affected by RA, while AMPK phosphorylation was increased. The RA-stimulated glucose uptake was inhibited by the AMPK inhibitor compound C and was not affected by wortmannin, an inhibitor of phosphoinositide 3-kinase (PI3K). The current study shows an effect of RA to increase muscle glucose uptake and AMPK phosphorylation. RA deserves further study as it shows potential to be used as an agent to regulate glucose homeostasis.

Compounds that increase the activity of the energy sensor AMP-activated kinase (AMPK) have the potential to regulate blood glucose levels. Although rosemary extract (RE) has been reported to activate AMPK and reduce blood glucose levels in vivo, the chemical components responsible for these effects are not known. In the present study, we measured the levels of the polyphenol carnosic acid (CA) in RE and examined the effects and the mechanism of action of CA on glucose transport system in muscle cells. High performance liquid chromatography (HPLC) was used to measure the levels of CA in RE. Parental and GLUT4myc or GLUT1myc overexpressing L6 rat myotubes were used. Glucose uptake was assessed using [ H]-2-deoxy-d-glucose. Total and phosphorylated levels of Akt and AMPK were measured by immunoblotting. Plasma membrane GLUT4myc and GLUT1myc levels were examined using a GLUT translocation assay. Statistics included analysis of variance (ANOVA) followed by Tukey's post-hoc test. At concentrations found in rosemary extract, CA stimulated glucose uptake in L6 myotubes. At 2.0 μmol/L CA a response (226 ± 9.62% of control, P=.001), similar to maximum insulin (201 ± 7.86% of control, P=.001) and metformin (213 ± 10.74% of control, P=.001) was seen. Akt phosphorylation was not affected by CA while AMPK and ACC phosphorylation was increased and the CA-stimulated glucose uptake was significantly reduced by the AMPK inhibitor compound C. Plasma membrane GLUT4 or GLUT1 glucose transporter levels were not affected by CA. Our study shows increased muscle cell glucose uptake and AMPK activation by low CA concentrations, found in rosemary extract, indicating that CA may be responsible for the antihyperglycemic properties of rosemary extract seen in vivo.

Goals: The authors sought to characterize predominantly alveolar exhaled nitric oxide (eNO) in hepatopulmonary syndrome (HPS) compared with non-HPS, changes after liver transplantation, and diagnostic properties. Background: HPS is defined by liver disease, intrapulmonary vascular dilatations (IPVDs), and hypoxemia. Rat models and small human studies suggest that NO overproduction may cause IPVDs. Study: A retrospective review of the Canadian HPS Database (2007 to 2017) and prospective eNO measurement (main outcome) in healthy controls (measurement expiratory flow, 200 mL/s). HPS was defined as: (1) liver disease; (2) contrast echocardiography consistent with IPVDs; and (3) partial pressure of arterial oxygen <70 mm Hg with alveolar-arterial gradient >20 mm Hg; subclinical HPS as criteria (1) and (2) only; and no HPS as criterion (1) only. Current smokers and subjects with asthma or pulmonary hypertension were excluded. A linear mixed effects model was used to compare eNO between groups and before and after transplantation. Results: eNO was 10.4±0.7 ppb in HPS (n=26); 8.3±0.6 ppb in subclinical HPS (n=38); 7.1±1.0 ppb in no HPS (n=15); and 5.6±0.7 ppb in controls (n=30) (P<0.001). eNO decreased from 10.9±0.8 ppb preliver to 6.3±0.8 ppb postliver transplant (n=6 HPS, 6 subclinical HPS) (P<0.001). eNO <6 ppb was 84.4% (73.1% to 92.2%) sensitive and ≥12 ppb was 78.1% (69.4% to 85.3%) specific for HPS (vs. subclinical HPS). Conclusions: HPS subjects have higher alveolar eNO than non-HPS subjects, levels normalize with liver transplantation. Applying eNO cutoff values may aid in HPS diagnosis.