Maaike Goris

Activation of liver X receptor-alpha reduces activation of the renal and cardiac renin-angiotensin-aldosterone system

Liver X receptor (LXR)-α is a pivotal player in reverse cholesterol metabolism. Recently, LXR-α was implicated as an immediate regulator of renin expression in a cAMP-responsive manner. To determine whether long-term LXR-α activation affects activation of the renal and cardiac renin–angiotensin–aldosterone system (RAAS), we treated mice with T0901317 (T09, a specific synthetic LXR agonist) in combination with the RAAS inducer isoproterenol (ISO). LXR-α-deficient (LXR-α−/−) and wild-type (WT) C57Bl/6J mice were treated with ISO, T09 or both for 7 days. Low-dose ISO treatment, not associated with an increase in blood pressure, caused an increase in renal renin mRNA, renin protein and ACE protein in WT mice. WT mice treated with both ISO and T09 had decreased renal renin, ACE and AT1R mRNA expression compared with mice treated with ISO only. Cardiac ACE mRNA expression was also reduced in the hearts of WT mice treated with ISO and T09 compared with those treated with ISO alone. The transcriptional changes of renin, ACE and AT1R were mostly absent in mice deficient for LXR-α, suggesting that these effects are importantly conferred through LXR-α. In conclusion, LXR-α activation blunts ISO-induced increases in mRNA expression of renin, AT1R and ACE in the heart and kidney. These findings suggest a role for LXR-α in RAAS regulation.

Platelet dynamics during natural and pharmacologically induced torpor and forced hypothermia.

Hibernation is an energy-conserving behavior in winter characterized by two phases: torpor and arousal. During torpor, markedly reduced metabolic activity results in inactivity and decreased body temperature. Arousal periods intersperse the torpor bouts and feature increased metabolism and euthermic body temperature. Alterations in physiological parameters, such as suppression of hemostasis, are thought to allow hibernators to survive periods of torpor and arousal without organ injury. While the state of torpor is potentially procoagulant, due to low blood flow, increased viscosity, immobility, hypoxia, and low body temperature, organ injury due to thromboembolism is absent. To investigate platelet dynamics during hibernation, we measured platelet count and function during and after natural torpor, pharmacologically induced torpor and forced hypothermia. Splenectomies were performed to unravel potential storage sites of platelets during torpor. Here we show that decreasing body temperature drives thrombocytopenia during torpor in hamster with maintained functionality of circulating platelets. Interestingly, hamster platelets during torpor do not express P-selectin, but expression is induced by treatment with ADP. Platelet count rapidly restores during arousal and rewarming. Platelet dynamics in hibernation are not affected by splenectomy before or during torpor. Reversible thrombocytopenia was also induced by forced hypothermia in both hibernating (hamster) and non-hibernating (rat and mouse) species without changing platelet function. Pharmacological torpor induced by injection of 5′-AMP in mice did not induce thrombocytopenia, possibly because 5′-AMP inhibits platelet function. The rapidness of changes in the numbers of circulating platelets, as well as marginal changes in immature platelet fractions upon arousal, strongly suggest that storage-and-release underlies the reversible thrombocytopenia during natural torpor. Possibly, margination of platelets, dependent on intrinsic platelet functionality, governs clearance of circulating platelets during torpor.

Losartan protects mesenteric arteries from ROS-associated decrease in myogenic constriction following 5/6 nephrectomy

Background: Chronic renal failure (CRF) is associated with hypertension, proteinuria, loss of myogenic constriction (MC) of mesenteric arteries and increased production of reactive oxygen species (ROS) under experimental conditions. Previous results showed that ACE (angiotensin-converting enzyme activity) inhibitor therapy is effective in slowing down the progression of disease. Therefore, we wanted to study whether the inverse AT1 (angiotensin II type 1) receptor agonist, losartan (LOS) was effective in preventing loss of MC in a rat model of CRF and whether acute ROS scavengers could improve MC. Methods: Rats underwent 5/6 nephrectomy (5/6 Nx) and were treated with vehicle or LOS (20 mg/kg/day; 5/6 Nx + LOS) for 12 weeks. Thereafter, the MC of the mesenteric arteries were measured in the presence and/or absence of tempol and catalase. Systolic blood pressure and proteinuria were measured weekly. Results: Systolic blood pressure and proteinuria in the 5/6 Nx + LOS group were significantly lower than in the 5/6 Nx group. Moreover, the MC of 5/6 Nx + LOS arteries was significantly increased compared with the untreated 5/6 Nx group (maximum MC, 32.3 ± 6.9 vs 8.9 ± 3.8% (p < 0.01)). Tempol + catalase significantly increased the MC in the 5/6 Nx group, but not in the 5/6 Nx + LOS group (increase in MC, 59.7 ± 13.0 (p < 0.05) vs. 17.0 ± 15.1%). Conclusion: These results support the roles of the RAAS (renin—angiotensin—aldosterone system) and ROS in the vascular dysfunction of systemic vessels in CRF.

Genetic deletion of growth differentiation factor 15 augments renal damage in both type 1 and type 2 models of diabetes

Growth differentiation factor 15 (GDF15) is emerging as valuable biomarker in cardiovascular disease and diabetic kidney disease. Also, GDF15 represents an early response gene induced after tissue injury and studies performed in GDF15 knockout (KO) mice suggest that GDF15 plays a protective role after injury. In the current study, we investigated the role of GDF15 in the development of diabetic kidney damage in type 1 and type 2 models of diabetes. Renal damage was assessed in GDF15 KO mice and wild-type (WT) mice in streptozotocin type 1 and db/db type 2 diabetic models. Genetic deletion of GDF15 augmented tubular and interstitial damage in both models of diabetes, despite similar diabetic states in KO and WT mice. Increased tubular damage in KO animals was associated with increased glucosuria and polyuria in both type 1 and type 2 models of diabetes. In both models of diabetes, KO mice showed increased interstitial damage as indicated by increased α-smooth muscle actin staining and collagen type 1 expression. In contrast, glomerular damage was similarly elevated in diabetic KO and WT mice. In type 1 diabetes, GDF15 KO mice demonstrated increased expression of inflammatory markers. In type 2 diabetes, elevated levels of plasma creatinine indicated impaired kidney function in KO mice. GDF15 protects the renal interstitium and tubular compartment in experimental type 1 and 2 diabetes without affecting glomerular damage.

Effects of Ivabradine and Metoprolol on Cardiac Angiogenesis and Endothelial Dysfunction in Rats With Heart Failure

Myocardial infarction (MI)-induced remodeling is associated with disturbed myocardial perfusion through vascular changes, such as reduced capillary density and endothelial dysfunction. Heart rate reduction (HRR) initiated immediately after MI stimulates angiogenesis and attenuates left ventricular dysfunction. We aimed to investigate the effects of long-term HRR on cardiac angiogenesis and endothelial function in a rat model of post-MI heart failure. Rats received early or late ivabradine or metoprolol for 12 or 9 weeks, respectively, and compared with untreated MI and sham animals 12 weeks after MI. Heart rate was measured in the conscious rat. MI resulted in an increased heart weight to body weight ratio, a decline in capillary density and a marked reduction in acetylcholine-induced relaxation. Early and late HRR by either ivabradine or metoprolol significantly increased capillary to myocyte ratio. Moreover, this ratio was significantly correlated to heart rate (r = −0.324 and P = 0.036). Neither early nor late chronic HRR prevented endothelial dysfunction, except a moderate improvement in late MI ivabradine group. In MI rats, HRR either by ivabradine or metoprolol treatment increases cardiac angiogenesis. Late HRR strategy was comparable to early HRR, suggesting that the beneficial effects are independent of the time of onset of therapy after MI.

Dopamine treatment attenuates acute kidney injury in a rat model of deep hypothermia and rewarming – The role of renal H2S-producing enzymes

Hypothermia and rewarming produces organ injury through the production of reactive oxygen species. We previously found that dopamine prevents hypothermia and rewarming-induced apoptosis in cultured cells through increased expression of the H2S-producing enzyme cystathionine β-Synthase (CBS). Here, we investigate whether dopamine protects the kidney in deep body cooling and explore the role of H2S-producing enzymes in an in vivo rat model of deep hypothermia and rewarming. In anesthetized Wistar rats, body temperature was decreased to 15°C for 3h, followed by rewarming for 1h. Rats (n≥5 per group) were treated throughout the procedure with vehicle or dopamine infusion, and in the presence or absence of a non-specific inhibitor of H2S-producing enzymes, amino-oxyacetic acid (AOAA). Kidney damage and renal expression of three H2S-producing enzymes (CBS, CSE and 3-MST) was quantified and serum H2S level measured. Hypothermia and rewarming induced renal damage, evidenced by increased serum creatinine, renal reactive oxygen species production, KIM-1 expression and influx of immune cells, which was accompanied by substantially lowered renal expression of CBS, CSE, and 3-MST and lowered serum H2S levels. Infusion of dopamine fully attenuated renal damage and maintained expression of H2S-producing enzymes, while normalizing serum H2S. AOAA further decreased the expression of H2S-producing enzymes and serum H2S level, and aggravated renal damage. Hence, dopamine preserves renal integrity during deep hypothermia and rewarming likely by maintaining the expression of renal H2S-producing enzymes and serum H2S.

Pioglitazone, a PPARγ agonist, provides comparable protection to angiotensin converting enzyme inhibitor ramipril against adriamycin nephropathy in rat.

Peroxisome proliferator-activated receptor γ (PPARγ) agonists have been shown to ameliorate diabetic nephropathy, but much less are known about their effects in non-diabetic nephropathies. In the present study, metabolic parameters, blood pressure, aortic endothelial function along with molecular and structural markers of glomerular and tubulointerstitial renal damage, were studied in a rat model of normotensive nephropathy induced by adriamycin and treated with PPARγ agonist pioglitazone (12mg/kg, po), angiotensin converting enzyme (ACE) inhibitor ramipril (1mg/kg, po) or their combination. Pioglitazone had no effect on systolic blood pressure, marginally reduced glycemia and improved aortic endothelium-dependent relaxation. In the kidney, pioglitazone prevented the development of proteinuria and focal glomerulosclerosis to the similar extent as blood-pressure lowering ramipril. Renoprotection provided by either treatment was associated with a reduction in the cortical expression of profibrotic plasminogen activator inhibitor-1 and microvascular damage-inducing endothelin-1, and a limitation of interstitial macrophage influx. Treatment with PPARγ agonist, as well as ACE inhibitor comparably affected renal expression of the renin-angiotensin system (RAS) components, normalizing increased renal expression of ACE and enhancing the expression of Mas receptor. Interestingly, combined pioglitazone and ramipril treatment did not provide any additional renoprotection. These results demonstrate that in a nondiabetic renal disease, such as adriamycin-induced nephropathy, PPARγ agonist pioglitazone provides renoprotection to a similar extent as an ACE inhibitor by interfering with the expression of local RAS components and attenuating related profibrotic and inflammatory mechanisms. The combination of the both agents, however, does not lead to any additional renal benefit.

Reduction of body temperature governs neutrophil retention in hibernating and nonhibernating animals by margination

Hibernation consists of periods of low metabolism, called torpor, interspersed by euthermic arousal periods. During deep and daily (shallow) torpor, the number of circulating leukocytes decreases, although circulating cells, is restored to normal numbers upon arousal. Here, we show that neutropenia, during torpor, is solely a result of lowering of body temperature, as a reduction of circulating also occurred following forced hypothermia in summer euthermic hamsters and rats that do not hibernate. Splenectomy had no effect on reduction in circulating neutrophils during torpor. Margination of neutrophils to vessel walls appears to be the mechanism responsible for reduced numbers of neutrophils in hypothermic animals, as the effect is inhibited by pretreatment with dexamethasone. In conclusion, low body temperature in species that naturally use torpor or in nonhibernating species under forced hypothermia leads to a decrease of circulating neutrophils as a result of margination. These findings may be of clinical relevance, as they could explain, at in least part, the benefits and drawbacks of therapeutic hypothermia as used in trauma patients and during major surgery.

Metformin Improves Endothelial Function and Reduces Blood Pressure in Diabetic Spontaneously Hypertensive Rats Independent from Glycemia Control: Comparison to Vildagliptin

Metformin confers vascular benefits beyond glycemia control, possibly via pleiotropic effects on endothelial function. In type-1-diabetes-mellitus (T1DM-)patients metformin improved flow-mediated dilation but also increased prostaglandin(PG)-F2α, a known endothelial-contracting factor. To explain this paradoxical finding we hypothesized that metformin increased endothelial-vasodilator mediators (e.g. NO and EDHF) to an even larger extent. Spontaneously-hypertensive-rats (SHR) display impaired endothelium-dependent relaxation (EDR) involving contractile PGs. EDR was studied in isolated SHR aortas and the involvement of PGs, NO and EDHF assessed. 12-week metformin 300 mg/kg/day improved EDR by up-regulation of NO and particularly EDHF; it also reduced blood pressure and increased plasma sulphide levels (a proxy for H2S, a possible mediator of EDHF). These effects persisted in SHR with streptozotocin (STZ)-induced T1DM. Vildagliptin (10 mg/kg/day), targeting the incretin axis by increasing GLP-1, also reduced blood pressure and improved EDR in SHR aortas, mainly via the inhibition of contractile PGs, but not in STZ-SHR. Neither metformin nor vildagliptin altered blood glucose or HbA1c. In conclusion, metformin reduced blood pressure and improved EDR in SHR aorta via up-regulation of NO and particularly EDHF, an effect that was independent from glycemia control and maintained during T1DM. A comparison to vildagliptin did not support effects of metformin mediated by GLP-1.