Trevor Hardigan

Linagliptin treatment improves cerebrovascular function and remodeling and restores reduced cerebral perfusion in Type 2 diabetes

The antihyperglycemic agent linagliptin, a dipeptidyl peptidase-4 (DPP-IV) inhibitor, has been shown to reduce inflammation and improve endothelial cell function. In this study, we hypothesized that DPP-IV inhibition with linagliptin would improve impaired cerebral perfusion in diabetic rats, as well as improve insulin-induced cerebrovascular relaxation and reverse pathological cerebrovascular remodeling. We further postulated that these changes would lead to a subsequent improvement of cognitive function. Male Type-2 diabetic and nondiabetic Goto-Kakizaki rats were treated with linagliptin for 4 wk, and blood glucose and DPP-IV plasma levels were assessed. Cerebral perfusion was assessed after treatment using laser-Doppler imaging, and dose response to insulin (10(-13) M-10(-6) M) in middle cerebral arteries was tested on a pressurized arteriograph. The impact of DPP-IV inhibition on diabetic cerebrovascular remodeling was assessed over a physiologically relevant pressure range, and changes in short-term hippocampus-dependent learning were observed using a novel object recognition test. Linagliptin lowered DPP-IV activity but did not change blood glucose or insulin levels in diabetes. Insulin-mediated vascular relaxation and cerebral perfusion were improved in the diabetic rats with linagliptin treatment. Indices of diabetic vascular remodeling, such as increased cross-sectional area, media thickness, and wall-to-lumen ratio, were also ameliorated; however, improvements in short-term hippocampal-dependent learning were not observed. The present study provides evidence that linagliptin treatment improves cerebrovascular dysfunction and remodeling in a Type 2 model of diabetes independent of glycemic control. This has important implications in diabetic patients who are predisposed to the development of cerebrovascular complications, such as stroke and cognitive impairment.

TLR2 knockout protects against diabetes-mediated changes in cerebral perfusion and cognitive deficits

The risk of cognitive decline in diabetes (Type 1 and Type 2) is significantly greater compared with normoglycemic patients, and the risk of developing dementia in diabetic patients is doubled. The etiology for this is likely multifactorial, but one mechanism that has gained increasing attention is decreased cerebral perfusion as a result of cerebrovascular dysfunction. The innate immune system has been shown to play a role in diabetic vascular complications, notably through the Toll-like receptor (TLR)-stimulated release of proinflammatory cytokines and chemokines that lead to vascular damage. TLR2 has been implicated in playing a crucial role in the development of diabetic microvascular complications, such as nephropathy, and thus, we hypothesized that TLR2-mediated cerebrovascular dysfunction leads to decreased cerebral blood flow (CBF) and cognitive impairment in diabetes. Knockout of TLR2 conferred protection from impaired CBF in early-stage diabetes and from hyperperfusion in long-term diabetes, prevented the development of endothelium-dependent vascular dysfunction in diabetes, created a hyperactive and anxiolytic phenotype, and protected against diabetes-induced impairment of long-term hippocampal and prefrontal cortex-mediated fear learning. In conclusion, these findings support the involvement of TLR2 in the pathogenesis of diabetic vascular disease and cognitive impairment.

Diabetes-mediated middle cerebral artery remodeling is restored by linagliptin: Interaction with the vascular smooth muscle cell endothelin system.

INTRODUCTION Endothelin-1 (ET-1) mediates cerebrovascular remodeling in vascular smooth muscle layer of the middle cerebral arteries (MCA) in type-2 diabetic Goto-Kakizaki (GK) rats. While metformin, oral glucose lowering agent, prevent/restores vascular remodeling and reduce systemic and local ET-1 levels whether this effect was specific to metformin remained unknown. Our working hypotheses were 1) linagliptin, a DPP-IV inhibitor, can reverse diabetes-mediated cerebrovascular remodeling and this is associated with decreased ET-1, and 2) linagliptin prevents the high glucose induced increase in ET-1 and ET receptors in brain vascular smooth muscle cells (bVSMCs). METHODS Diabetic and non-diabetic GK rats were treated with linagliptin (4weeks). MCAs were fixed in buffered 4% paraformaldehyde and used for morphometry. Human bVSMCs incubated in normal glucose (5.5mM)/high glucose (25mM) conditions were treated with the linagliptin (100nM; 24h). ET-1 secretion and ET receptors were measured in media and cell lysate respectively. Immunostaining was performed for ET-A and ET-B receptor. ET receptors were also measured in cells treated with ET-1 (100nM) and linagliptin. RESULTS Linagliptin treatment regressed vascular remodeling of MCAs in diabetic animals but had no effect on blood glucose. bVSMCs in normal/high glucose condition did not show any significant difference in ET-1 secretion or ET-A and ET-B receptor expression. ET-1 treatment in high glucose condition significantly increased the ET-A receptors and this effect was inhibited by linagliptin. CONCLUSIONS Linagliptin is effective in reversing established pathological cerebrovascular remodeling associated with diabetes. Attenuation of the ET system could be a pleiotropic effect of linagliptin that provides vascular protection.

Linagliptin reduces effects of ET-1 and TLR2-mediated cerebrovascular hyperreactivity in diabetes.

AIMS The anti-hyperglycemic agent linagliptin, a dipeptidyl peptidase-4 inhibitor, has been shown to reduce inflammation and improve endothelial cell function. In this study, we hypothesized that DPP-IV inhibition with linagliptin would improve impaired cerebral blood flow in diabetic rats through improved insulin-induced cerebrovascular relaxation and reversal of pathological cerebrovascular remodeling that subsequently leads to improvement of cognitive function. MAIN METHODS Male type-2 diabetic Goto-Kakizaki (GK) and nondiabetic Wistar rats were treated with linagliptin, and ET-1 plasma levels and dose response curves to ET-1 (0.1-100nM) in basilar arteries were assessed. The impact of TLR2 antagonism on ET-1 mediated basilar contraction and endothelium-dependent relaxation to acetylcholine (ACh, 1nM-1M) in diabetic GK rats was examined with antibody directed against the TLR2 receptor (Santa Cruz, 5μg/mL). The expression of TLR2 in middle cerebral arteries (MCAs) from treated rats and in brain microvascular endothelial cells (BMVEC) treated with 100nM linagliptin was assessed. KEY FINDINGS Linagliptin lowered plasma ET-1 levels in diabetes, and reduced ET-1-induced vascular contraction. TLR2 antagonism in diabetic basilar arteries reduced ET-1-mediated cerebrovascular dysfunction and improved endothelium-dependent vasorelaxation. Linagliptin treatment in the BMVEC was able to reduce TLR2 expression in cells from both diabetic and nondiabetic rats. CONCLUSIONS These results suggest that inhibition of DPPIV using linagliptin improves the ET-1-mediated cerebrovascular dysfunction observed in diabetes through a reduction in ET-1 plasma levels and reduced cerebrovascular hyperreactivity. This effect is potentially a result of linagliptin causing a decrease in endothelial TLR2 expression and a subsequent increase in NO bioavailability.

The contribution of Toll-like receptors to placental inflammation in diet-induced maternal obesity

Toll-like receptor (TLR)-regulated protein kinases and inflammatory cytokines were activated in fetal vascular smooth muscle cells (VSMC) treated with palmitate. Tumor necrosis factor (TNFα) and interleukin-6 (IL6) were increased and correlated with expression of TLRs in the labyrinth placentae of high fat (HF)-fed rats with increased plasma lipids and visceral adiposity. Thus, local induction of TLR signaling via saturated fatty acids (SFA) may in part contribute to placental inflammation in diet-induced maternal obesity.

Gene and Stem Cell Therapy in Erectile Dysfunction

Erectile dysfunction (ED) is a complex, multifactorial issue commonly affecting men of all ages. ED is currently defined as “the inability to achieve and/or maintain penile erection sufficient to permit satisfactory sexual intercourse”, and has been associated with such risk factors as hypertension, diabetes, alcoholism, smoking, and pelvic surgery [1]. This condition has seriously impacted the men’s quality of life. Even though nowadays there are a large number of options to treat ED, a considerable number of patients do not answer adequately the conventional therapies available. Penile erection is achieved through a neurovascular response exhibiting an increase in arterial inflow, relaxation of corporal smooth muscle, and restriction of the venous outflow. Relatively recent pharmacological advances, namely oral phosphodiesterase-5 (PDE5) inhibitors, have become the first line of treatment in ED. PDE5 inhibitors allow the patient to achieve a penile erection via the effects on the nitric oxide (NO) signaling pathway, which is the principal mediator of corporal smooth muscle relaxation. The inhibition of the degradative actions of PDE5 on 3’,5’-cyclic guanosine monophosphate (cGMP), the second messenger molecule of NO signaling, lead to an increased bioavailability of NO in the corporal smooth muscle thus promoting vasodilation and penile erection. However, despite the widespread efficacy of these medications, there are still men for which oral PDE5 inhibitors are ineffective. ED in men with diabetes, for example, is typically more severe, exhibiting a less effective response to PDE5 inhibitors when compared to non-diabetic patients. The vascular injuries that accompanies diabetes is often too damaging to endothelial physiology to allow adequate penile erections [4] and thus complicates use of the oral medications as treatment for ED. Due to the vast array of potential causes of ED ranging from neurogenic and vasculogenic to hormonal issues, there exists a continuing need to address these deficiencies in patient management of ED and pursue new treatments. Two avenues showing a great deal of promise in ED treatment are gene therapy and stem cell therapy, both of which could possibly provide methods to prevent or even cure ED. This chapter will focus on recent studies in both gene and stem cell therapies in ED research, with the objective to establish that continued scientific exploration into these fields will yield clinically applicable approaches to combat this condition.

Cephalad Migration of Intradural Bullet from Thoracic Spine to Cervical Spine

BACKGROUND There are few reported instances of intraspinal migration of a bullet fragment. The majority of these migrations occur caudally, typically below the level of T10. Even fewer cases demonstrate cephalad migration from the sacral spine to the lumbar spine. We report here for the first time a case of a cephalad migration intradurally from the thoracic spine to cervical spine. CASE DESCRIPTION A 31-year old man presented to the emergency department with a suspected spinal cord injury following a GSW sustained to the left shoulder. A penetrating gunshot injury to the thoracic spine at the level of T2 was observed, and CT angiography revealed a cephalad migration of the bullet fragment to the level of C6. The patient had marked weakness of the bilateral upper extremities, with paraplegia of the lower extremities. There was a sensory deficit beginning at a level 1 cm below the clavicle, as well as a decrease in rectal tone. We performed a laminectomy at C6 with dural incision and removal of the main bullet fragment. Following the surgery, significant improvement in strength and sensation in the bilateral upper extremities was noted, but paraplegia and sensory loss below the level of T2 persisted. CONCLUSIONS In this report, we review the previously reported cases in which intraspinal migration of bullets have occurred, and discuss the unique finding in this study of cephalad migration of a bullet within the dura. In addition, we detail considerations in the management of such injuries.

Variations on a theme: ET-14 notes from mentor and trainees.

With this haiku, we ended the Thirteenth International Conference on Endothelin, ET-13, in Tokyo where we celebrated 25 years of Endothelin research. ET-13 was the first International Conference on Endothelin to include presenters who were born after the discovery of Endothelin [1]. The organizers uniquely brought the youngest presenters to center stage during the celebrations with a haiku contest. The haiku is a traditional form of Japanese poetry that is known for its simplicity in the form and depth in the significance, which sounded just like endothelin [2]. Nine young scientists under the age of 25 created beautiful haikus that weaved ET to their research and presented to the first generation of ET scientists during the gala dinner. Being part of this wonderful event as a member of the first generation of ET researchers and sharing the enthusiasm of young scientists led to lingering thoughts about the impact of ET research and International Endothelin Conferences on our academic careers In this editorial, we would like to share our experiences at the ET14 as a mentor, a young scientist just embarking her Ph.D. training, and a young physician scientist who just completed his M.D./Ph.D. training.

Linagliptin attenuates diabetes-induced cerebral pathological neovascularization in a blood glucose-independent manner: Potential role of ET-1

AIMS We have shown that glycemic control with metformin or endothelin-1 (ET-1) inhibition with bosentan prevents and restores diabetes-mediated cerebral pathological remodeling and neovascularization. Our recent data suggest that linagliptin, a member of the dipeptidyl peptidase-4 inhibitor class of glucose-lowering agents, prevents cerebrovascular remodeling and dysfunction independent of its blood glucose lowering effects. We hypothesized that linagliptin prevents pathological neovascularization via the modulation of the ET-1 system. MATERIALS AND METHODS 24-week old diabetic Goto-Kakizaki and nondiabetic Wistar rats were treated for 4weeks with either vehicle chow or chow containing 166mg/kg linagliptin. At termination, FITC-dextran was injected to visualize the vasculature. Brain sections were imaged by confocal microscopy for vascular density, tortuosity, vascular volume, and surface in both the cortex and striatum. Retinal acellular capillary formation was measured. Brain microvascular endothelial cells (BMVEC) isolated from control or diabetic rats were treated with linagliptin with or without ET-1 dual receptor antagonist and tested for angiogenic properties with cell migration and tube formation assays. KEY FINDING Linagliptin reduced all indices of cerebral neovascularization compared with control rats. In vitro, linagliptin normalized the augmented angiogenic properties of BMVECs isolated from diabetic animals and bosentan reversed this response. Cells from diabetic animals had higher ET-1 and less ETB receptors than in control cells. Linagliptin significantly decreased ET-1 levels and increased ETB receptors. SIGNIFICANCE ET system contributes to pathological neovascularization in diabetes as evidenced by restoration of functional angiogenesis by bosentan treatment and prevention of linagliptin-mediated improvement of angiogenesis in the in vitro model.