Experimental animal models of coronary microvascular dysfunction

Coronary microvascular dysfunction (CMD) is commonly present in patients with metabolic derangements and is increasingly recognized as an important contributor to myocardial ischaemia, both in the presence and absence of epicardial coronary atherosclerosis. The latter condition is termed 'ischaemia and no obstructive coronary artery disease' (INOCA). Notwithstanding the high prevalence of INOCA, effective treatment remains elusive. Although to date there is no animal model for INOCA, animal models of CMD, one of the hallmarks of INOCA, offer excellent test models for enhancing our understanding of the pathophysiology of CMD and for investigating novel therapies. This article presents an overview of currently available experimental models of CMD-with an emphasis on metabolic derangements as risk factors-in dogs, swine, rabbits, rats, and mice. In all available animal models, metabolic derangements are most often induced by a high-fat diet (HFD) and/or diabetes mellitus via injection of alloxan or streptozotocin, but there is also a wide variety of spontaneous as well as transgenic animal models which develop metabolic derangements. Depending on the number, severity, and duration of exposure to risk factors-all these animal models show perturbations in coronary microvascular (endothelial) function and structure, similar to what has been observed in patients with INOCA and comorbid conditions. The use of these animal models will be instrumental in identifying novel therapeutic targets and for the subsequent development and testing of novel therapeutic interventions to combat ischaemic heart disease, the number one cause of death worldwide.

Animal models as tools to investigate antidiabetic and anti-inflammatory plants

Plants have been historically used for diabetes treatment and related anti-inflammatory activity throughout the world; few of them have been validated by scientific criteria. Recently, a large diversity of animal models has been developed for better understanding the pathogenesis of diabetes mellitus and its underlying inflammatory mechanism and new drugs have been introduced in the market to treat this disease. The aim of this work is to review the available animal models of diabetes and anti-inflammatory activity along with some in vitro models which have been used as tools to investigate the mechanism of action of drugs with potential antidiabetic properties and related anti-inflammatory mechanism. At present, the rigorous procedures for evaluation of conventional antidiabetic medicines have rarely been applied to test raw plant materials used as traditional treatments for diabetes; and natural products, mainly derived from plants, have been tested in chemically induced diabetes model. This paper contributes to design new strategies for the development of novel antidiabetic drugs and its related inflammatory activity in order to treat this serious condition which represents a global public health problem.

Mechanisms underlying the losartan treatment-induced improvement in the endothelial dysfunction seen in mesenteric arteries from type 2 diabetic rats

It is well known that type 2 diabetes mellitus is frequently associated with vascular dysfunction and an elevated systemic blood pressure, yet the underlying mechanisms are not completely understood. We previously reported that in mesenteric arteries from established type 2 diabetic Otsuka Long-Evans Tokushima fatty (OLETF) rats, which exhibit endothelial dysfunction, there is an imbalance between endothelium-derived vasodilators [namely, nitric oxide (NO) and hyperpolarizing factor (EDHF)] and vasoconstrictors [contracting factors (EDCFs) such as cyclooxygenase (COX)-derived prostanoids]. Here, we investigated whether the angiotensin II receptor antagonist losartan might improve endothelial dysfunction in OLETF rats at the established stage of diabetes. In mesenteric arteries isolated from OLETF rats [vs. those from age-matched control Long-Evans Tokushima Otsuka (LETO) rats]: (1) the acetylcholine (ACh)-induced relaxation was impaired, (2) the NO- and EDHF-mediated relaxations were reduced, (3) the ACh-induced EDCF-mediated contraction and the production of prostanoids were increased, and (4) superoxide generation was increased. After such OLETF rats had received losartan (25 mg/kg/day p.o. for 4 weeks), their isolated mesenteric arteries exhibited: (1) improvements in ACh-induced NO- and EDHF-mediated relaxations, (2) reduced EDCF- and arachidonic acid-induced contractions, (3) suppressed production of prostanoids, (4) reduced PGE(2)-mediated contraction, and (5) reduced superoxide generation. Within the timescale studied here, losartan did not change the protein expressions of endothelial NO synthase, COX1, or COX2 in mesenteric arteries from either OLETF or LETO rats. Losartan thus normalizes vascular dysfunction in this type 2 diabetic model, and the above effects may contribute to the reduction of adverse cardiovascular events seen in diabetic patients treated with angiotensin II receptor blockers.

Diabetes-associated changes and role of N epsilon-(carboxymethyl)lysine in big ET-1-induced coronary vasoconstriction

Using perfused hearts from streptozotocin-induced long-term diabetic rats, we studied the coronary vasoconstrictor effect of the endothelin-1 (ET-1) precursor big ET-1 and also whether this response was modulated by N(epsilon)-(carboxymethyl)lysine (CML; a representative advanced glycation end product that is implicated in the pathogenesis of diabetic vasculopathy). The big ET-1-induced vasoconstriction (a) developed more rapidly (i.e., was greater in the first 30 min) in the diabetic group than in the age-matched controls, and (b) in each group was largely suppressed by phosphoramidon [nonselective endothelin-converting enzyme (ECE)/neutral endopeptidase (NEP) inhibitor] or CGS35066 (selective ECE inhibitor), but not by thiorphan (selective NEP inhibitor). The ET-1 release occurring after treatment with big ET-1, which was greater in diabetic coronary arteries than in the controls, was reduced by CGS35066. The dose-response curve for ET-1 was shifted to the left in the diabetics, so that at some lower doses of ET-1 the vasoconstriction was greater than in the controls. CML enhanced big ET-1- or ET-1-induced vasoconstriction in the controls, but not in the diabetics. Finally, the plasma level of CML was higher in diabetic than in control rats. These findings suggest (a) that the increased responsiveness to big ET-1 shown by diabetic coronary arteries may be attributable both to a more rapid conversion of big ET-1 to ET-1 (by ECE), allowing it to exert its contractile activity, and to an increased vascular sensitivity to ET-1, and (b) that CML may be at least partly responsible for the diabetes-associated enhancement of big ET-1-mediated coronary vasoconstriction.