Obesity has reached worldwide epidemic proportions and with this increased incidence of obesity, comes an increase in incidence of the comorbidities associated with obesity such as diabetes and cardiovascular disease (CVD). The underlying mechanisms which connect these diseases are still poorly understood. One system which has been shown to be up-regulated in the setting of obesity and diabetes is that of the G-protein coupled receptor-55/Lysophosphatidylinositol (GPR55/LPI). Despite being upregulated in the setting of obesity, the function of GPR55 in obesity and other disease states remains elusive. Therefore, the present study aimed to 1) investigate the role of GPR55 in obesity by characterising the phenotype of the GPR55 knockout (GPR55-/-) mouse when challenged with a high fat diet (HFD) intervention, 2) elucidate any effect of the GPR55 knockout and HFD intervention on the myocardial infarct size sustained following a period of ischaemia/reperfusion (I/R) and 3) make use of an in vitro model to elucidate the mechanisms by which changes occur in the adipose tissue of mice fed a HFD. GPR55-/- mice fed a HFD for 12-weeks gained significantly more weight in the form of fat mass, compared to wild-type (WT) controls and consequently become obese. Obese GPR55-/- mice displayed hypertrophic adipose tissue concurrent with the significant dysregulation of plasma lipids, increases in specific circulating LPI species, increased lipid deposition within the liver and a change in adipose tissue gene expression profile. These changes were not observed in GPR55-/- mice fed a standard diet or WT mice fed a HFD. Following a period of I/R, the myocardial infarct size in hearts from WT HFD fed mice was significantly smaller than in hearts from WT standard diet fed mice. This reduction in infarct size due to HFD intervention was not dependent on RISK-pathway activation and was not observed in hearts from GPR55-/- mice, therefore demonstrating that the cardio-protective effect of a HFD on infarct size is dependent on GPR55. In vitro studies using 3T3-L1 cells determined that the changes in adipose tissue gene expression of HFD fed mice was not due to enhanced stimulation with LPI or via hypoxic mechanisms. The results of these studies demonstrate that GPR55 has an anti-obesity function in vivo and also mediates the cardio-protective effect of a HFD on myocardial infarct size, through currently unknown mechanisms.

Artemisinin is herbal drug with a wide range of biological and physiological function. It is currently administered in the treatment against uncomplicated F.Palcifarum infections. It has also been shown to be cytotoxic against a variety of cancer cells. Despite the promise of many anti cancer drugs, drug induced cardiotoxicity has constantly threatened drug applicability especially in patients with co-morbities. Artemisinin has been shown to be cardioprotective, although the intracellular pathways remain to be elucidated. In this study, isolated perfused rat hearts were subjected to 35 minutes of ischaemia and 120 minutes reperfusion or primary cardiac myocytes subjected to 120 minutes hypoxia and 120 minutes reoxygenation where artemisinin (4.3μM) was administered in presence and absence of the PI3K inhibitor (wortmannin) (0.1μM), p70S6K inhibitor (rapamycin) (0.1μM), non selective nitric oxide synthase inhibitor (L-NAME) (100μM) and inducible nitric oxide synthase inhibitor (aminoguanidine) (100μM). At the end of the experiment, hearts underwent infarct size to risk ratio assessment via tri-phenyltetrazolium chloride staining or western blot analysis for p-Akt and p70S6K. Cardiac myocytes were assessed for either MTT analysis, cleaved-caspase 3 or for eNOS/iNOS or p-BAD activity using flow cytometry. In isolated hearts, artemisinin (0.1μM-100μM) showed a significant dose dependent decrease in infarct size (P<0.01-0.001 vs. I/R control). It was also shown to significantly improve cellular viability (66.5±6.3% vs. 29.3±6.1% in H/R, P<0.01) and decrease the levels of cleaved caspase-3 compared to the H/R control group (17.1±2.0% vs. 26.8±2.0% in H/R, P<0.001). Artemisinin was shown to confer protection via the activation of the PI3K-Akt-p70S6k cell survival pathway and presented an upregulation in p-eNOS and iNOS expression. Furthermore, co-administering artemisinin with doxorubicin showed artemisinin reverses I/R or H/R injury as well as doxorubicin-induced injury via the nitric oxide signalling pathway. Additionally, in HL-60 cells, the co-administration doubled artemisinins cytotoxicity while also implicating the nitric oxide pathway. This is the first study to shows that artemisinin ameliorates doxorubicin mediated cardiac injury whilst enhancing its cytotoxicity in HL-60 in a nitric oxide dependent manner. This study concluded that artemisinin was both anti apoptotic and protective against myocardial I/R injury via the PI3K-Akt-BAD/P70S6K and via the nitric oxide cell survival pathway as well as pro-apoptotic against HL-60 in a nitric oxide dependent manner.

Aims Toll-like receptor (TLR)-mediated signalling pathways have been implicated in myocardial ischaemia/reperfusion (I/R) injury. Activation of the phosphoinositide 3-kinase (PI3K)/Akt pathway protects the myocardium from ischaemic injury. We hypothesized that the modulation of TLR2 would induce cardioprotection against I/R injury via activation of the PI3K/Akt signalling. Methods and results Mice were treated with TLR2 ligands, peptidoglycan (PGN) or Pam3CSK4, respectively, 1 h before the hearts were subjected to ischaemia (1 h), followed by reperfusion (4 h). Infarct size was determined by triphenyltetrazolium chloride staining. Cardiac function and haemodynamic performance were evaluated. Infarct size was significantly reduced in PGN-or Pam3CSK4-treated mice compared with untreated I/R mice. Administration of TLR2 ligands improved cardiac function following I/R. PGN treatment increased the levels of phospho-Akt and phospho-GSK-3β (glycogen synthase kinase-3β), compared with untreated I/R hearts. PGN stimulation increased TLR2 tyrosine phosphorylation and association of the p85 subunit of PI3K with TLR2. To investigate the role of PI3K/Akt signalling in PGN-induced cardioprotection, we administered the PI3K inhibitor, Wortmannin, to the mice 15 min before PGN treatment. We also administered PGN to kinase-deficient Akt (kdAkt) transgenic mice 1 h before myocardial I/R. Both PI3K inhibition and kdAkt mice abolished the cardioprotection induced by PGN. To examine the role of TLR2 in PGN-induced cardioprotection, we administrated PGN to TLR2 knockout mice 1 h before the hearts were subjected to I/R. PGN-induced cardioprotection was lost in TLR2-deficient mice. Conclusion These results demonstrate that TLR2 ligands induced cardioprotection, which is mediated through a TLR2/PI3K/Akt-dependent mechanism.