L-arginine and antineutrophil serum enable venular control of capillary perfusion in hypercholesterolemic rats

7-O-methylpunctatin, a Novel Homoisoflavonoid, Inhibits Phenotypic Switch of Human Arteriolar Smooth Muscle Cells

Remodeling of arterioles is a pivotal event in the manifestation of many inflammation-based cardio-vasculopathologies, such as hypertension. During these remodeling events, vascular smooth muscle cells (VSMCs) switch from a contractile to a synthetic phenotype. The latter is characterized by increased proliferation, migration, and invasion. Compounds with anti-inflammatory actions have been successful in attenuating this phenotypic switch. While the vast majority of studies investigating phenotypic modulation were undertaken in VSMCs isolated from large vessels, little is known about the effect of such compounds on phenotypic switch in VSMCs of microvessels (microVSMCs). We have recently characterized a novel homoisoflavonoid that we called 7-O-methylpunctatin (MP). In this study, we show that MP decreased FBS-induced cell proliferation, migration, invasion, and adhesion. MP also attenuated adhesion of THP-1 monocytes to microVSMCs, abolished FBS-induced expression of MMP-2, MMP-9, and NF-κB, as well as reduced activation of ERK1/2 and FAK. Furthermore, MP-treated VSMCs showed an increase in early (myocardin, SM-22α, SM-α) and mid-term (calponin and caldesmon) differentiation markers and a decrease in osteopontin, a protein highly expressed in synthetic VSMCs. MP also reduced transcription of cyclin D1, CDK4 but increased protein levels of p21 and p27. Taken together, these results corroborate an anti-inflammatory action of MP on human microVSMCs. Therefore, by inhibiting the synthetic phenotype of microVSMCs, MP may be a promising modulator for inflammation-induced arteriolar pathophysiology.

Multidrug donor preconditioning protects steatotic liver grafts against ischemia-reperfusion injury

BACKGROUND

Graft dysfunction of steatotic livers (SL) still remains a major challenge in liver transplantation. Different mechanisms are thought to be involved in the impaired tolerance of SL to ischemia-reperfusion injury. Thus, different pharmacologic strategies may need to be combined to effectively protect SL and to reduce graft dysfunction after transplantation. Therefore, we analyzed the effectiveness of a multidrug donor preconditioning (MDDP) procedure to protect SL from cold ischemia-reperfusion injury.

METHODS

Liver steatosis was induced by a high-carbohydrate, fat-free diet. A total of 24 Sprague-Dawley rats were divided into 3 groups (n = 8 each), including a control group with nonsteatotic livers (Con), a vehicle-treated SL group (SL-Con), and a SL group undergoing MDDP (SL-MDDP), including pentoxyphylline, glycine, deferoxamine, N-acetylcysteine, erythropoietin, melatonin, and simvastatin. MDDP was applied before liver perfusion with 4°C histidine-tryptophan-ketoglutarate (HTK) solution and organ harvest. After 24 hours of cold storage in HTK, postischemic reperfusion was performed in an isolated liver reperfusion model using 37°C Krebs-Henseleit bicarbonate buffer.

RESULTS

After 60 minutes of reperfusion, SL showed a significant reduction of bile flow as well as a marked increase of liver enzyme levels and apoptotic cell death compared with Con. This was associated with an increased malondialdehyde formation, interleukin-1 production, and leukocytic tissue infiltration. MDDP completely abolished the inflammatory response and was capable of significantly reducing parenchymal dysfunction and injury.

CONCLUSIONS

MDDP decreases SL injury after cold storage and reperfusion. The concept of MDDP as a simple and safe preoperative regime, thus may be of interest in clinical use, expanding the donor pool from marginal donors.

Losartan and ozagrel reverse retinal arteriolar constriction in non-obese diabetic mice

OBJECTIVE

Reductions in retinal blood flow are observed early in diabetes. Venules may influence arteriolar constriction and flow; therefore, we hypothesized that diabetes would induce the constriction of arterioles that are in close proximity to venules, with the constriction mediated by thromboxane and angiotensin II.

METHODS

Using nonobese diabetic (NOD) mice, retinal measurements were performed three weeks following the age at which glucose levels exceeded 200 mg/dL, with accompanying experiments on age-matched normoglycemic NOD mice. The measurements included retinal arteriolar diameters and red blood cell velocities and were repeated following an injection of the thromboxane synthase inhibitor, ozagrel. Mice were subdivided into equal groups and given drinking water with or without the angiotensin II receptor antagonist, losartan.

RESULTS

Retinal arterioles were constricted in hyperglycemic mice, with a significant reduction in flow. However, not all arterioles were equally affected; the vasoconstriction was limited to arterioles that were in closer proximity to venules. The arteriolar vasoconstriction (mean arteriolar diameters = 51 +/- 1 vs. 61 +/- 1 microm in controls; p < 0.01) was eliminated by both ozagrel (61 +/- 2 microm) and losartan (63 +/- 2 microm).

CONCLUSIONS

Venule-dependent arteriolar vasoconstriction in NOD mice is mediated by thromboxane and/or angiotensin II.

T-Cell–Derived Interferon-γ Contributes to Arteriolar Dysfunction During Acute Hypercholesterolemia

OBJECTIVES

T-lymphocytes and interferon-gamma (IFN-gamma) contribute to leukocyte recruitment in postcapillary venules during hypercholesterolemia. Our objectives were to determine whether: (1) T-lymphocytes are the source of this IFN-gamma, and (2) whether T-cell-derived IFN-gamma also mediates the accompanying arteriolar dysfunction and platelet adhesion.

METHODS AND RESULTS

Intravital videomicroscopy was used to quantify arteriolar responses to acetylcholine, and leukocyte and platelet adhesion in postcapillary venules of wild-type (WT), immunodeficient (SCID), and IFN-gamma(-/-) mice on a normal (ND) or high-cholesterol (HC) diet. Acetylcholine-induced arteriolar dilation was impaired in WT-HC, compared with WT-ND. This endothelial dysfunction was absent in SCID-HC or IFN-gamma(-/-)-HC mice. Vasodilation was impaired by transfer of WT, but not IFN-gamma(-/-), T-cells to these immunodeficient mice. WT-HC mice exhibited elevated leukocyte and platelet adhesion in venules, versus WT-ND. This blood cell recruitment was attenuated to ND levels in SCID-HC and IFN-gamma(-/-)-HC mice, but restored to WT-HC levels by transfer of WT, but not IFN-gamma(-/-), T-lymphocytes.

CONCLUSIONS

These data reveal a novel role of T-lymphocyte-derived IFN-gamma in the development of endothelial dysfunction in arterioles during hypercholesterolemia and extend our previous observations that IFN-gamma mediates both inflammatory and thrombogenic responses to hypercholesterolemia in postcapillary venules.

Mediators of CD18/P-selectin-dependent constriction of venule-paired arterioles in hypercholesterolemia

This study addresses the role of venule-derived mediators in the arteriolar constriction that accompanies hypercholesterolemia. Constriction was assessed by measuring the tone of small arterioles closely paired with venules in the mesentery of normal cholesterol rats (NC), high cholesterol rats (HC), HC rats injected with antibodies against CD18 and P-selectin (HC/mAbs), HC rats treated with the thromboxane synthase inhibitor, ozagrel (HC/ozagrel), and HC rats pretreated with anti-platelet serum (HC/APS). Venule-paired arterioles in the untreated HC group demonstrated enhanced tone compared with arterioles in the NC group, while no difference was found between unpaired arterioles of the two groups. Perivascular nitric oxide (NO) concentrations were found to be significantly decreased in venule-paired arterioles of HC rats (238+/-14 nM) compared with those of NC rats (426+/-42 nM). The injection of anti-adhesion antibodies successfully attenuated the enhanced arteriolar tone and venular leukocyte adherence in the HC group, and tended to increase levels of NO in venule-paired arterioles by 33% (to 326+/-19 nM; still lower than that of the NC group). Ozagrel and platelet depletion attenuated the enhanced arteriolar tone by 53% and 33%, respectively, without affecting NO concentrations. These findings indicate that the mechanism of blood cell-dependent arteriolar constriction during hypercholesterolemia may be dependent on thromboxane, a decrease in NO, and the proximity of the arterioles to postcapillary venules.

P-selectin-mediated adhesion impairs endothelium-dependent arteriolar dilation in hypercholesterolemic mice

Hypercholesterolemia is associated with an attenuation of endothelium-dependent dilation in arterioles and an increase in leukocyte and platelet adhesion in venules. The proximity of closely paired arterioles and venules is thought to facilitate heat and mass transport between the two and could be involved in transport of inflammatory and/or vasoactive mediators from venule to arteriole. In the current study, we tested the hypothesis that the impaired arteriolar dilation associated with hypercholesterolemia might be dependent on P-selectin-dependent blood cell adhesion in the closely paired venules. Leukocyte and platelet recruitment in venules and the endothelium-dependent response to bradykinin in second-order arterioles were observed in the mouse intestinal submucosa using intravital microscopy. Four weeks of a high-cholesterol diet decreased bradykinin-induced arteriolar dilation more dramatically in closely paired arterioles than in distantly paired arterioles. The dysfunctional arteriolar dilation of closely paired arterioles in hypercholesterolemic mice was significantly improved when the experiments were repeated in P-selectin-deficient mice (given the high-cholesterol diet) or in hypercholesterolemic mice injected with a P-selectin monoclonal antibody. A similar improvement in dilation of closely paired arterioles was attained in hypercholesterolemic mice given the superoxide dismutase mimetic Tempol. These findings indicate that hypercholesterolemia-induced increases in venular leukocyte and platelet adhesion might contribute to the impaired endothelium-dependent dilation of closely paired arterioles via a mechanism that is distance limited and dependent on P-selectin and superoxide.

Microvascular responses to hypercholesterolemia: the interactions between innate and adaptive immune responses

Hypercholesterolemia is recognized as one of the major risk factors in cardiovascular disease. It promotes the development of a proinflammatory phenotype in large vessels, in particular arteries, with disease. Cells of the innate and adaptive immune system are localized within atherosclerotic plaques and participate in the initiation and progression of plaque formation. It is now recognized that each segment of the microvasculature also experiences inflammation due to hypercholesterolemia, and that this occurs long before events in the large vessels. More recently, it is has been established that the innate and adaptive immune systems participate in the responses of postcapillary venules, and possibly arterioles, to elevated cholesterol levels, and that T lymphocytes may be one of the early cell types activated by hypercholesterolemia. These cells initiate a series of steps that lead to leukocyte accumulation in postcapillary venules and endothelial dysfunction in the arterioles. This review discusses the microvascular alterations induced by hypercholesterolemia, with particular attention paid to the roles of the innate and adaptive immune responses, and how these two systems may communicate to induce the microvascular inflammation.

Long-term high-fat diet induces pancreatic injuries via pancreatic microcirculatory disturbances and oxidative stress in rats with hyperlipidemia

Relations between hyperlipidemia and chronic pancreatitis remain unclear. Microcirculatory disturbances and oxidative stress are involved in pathogeneses of a high numbers of diseases. The objective of this study was to induce hyperlipidemia in rats by long-term high-fat diet intake, then investigate the biochemical, microcirculatory, and histological alterations in blood and pancreatic tissues of these animals, and discuss their potential significances. Pancreatic blood flow was detected by intravital microscope; malondialdehyde (MDA) content and superoxide dismutase (SOD) activity were measured in pancreatic tissues for assessment of oxidative stress and alpha-smooth muscle actin (alpha-SMA) expression was determined by immunohistochemical staining and RT-PCR. The results showed that the velocity of pancreatic microvascular blood flow of rats with hyperlipidemia decreased significantly as compared to control value (p = 0.008). Pancreatic MDA content increased whereas SOD activity decreased in these rats (p = 0.022; p = 0.039, respectively). Histologically, microvesicles in acinar and islet cells, dilated rough endoplasmic reticulum, swollen mitochondrion and modified vascular endothelial cells were observed under light microscope and transmission electron microscope. In addition, alpha-SMA expression was up-regulated significantly (p < 0.05). These results suggest that long-term high-fat diet can induce chronic pancreatic injuries which could be considered as "nonalcoholic fatty pancreatic disease", and pancreatic microcirculatory disturbances and oxidative stress may play an important part in the underlying pathogenesis.

Leukocyte adherence inhibits adenosine-dependent venular control of arteriolar diameter and nitric oxide

Venular control of arteriolar perfusion has been the focus of several investigations in recent years. This study investigated 1) whether endogenous adenosine helps control venule-dependent arteriolar dilation and 2) whether venular leukocyte adherence limits this response via an oxidant-dependent mechanism in which nitric oxide (NO) levels are decreased. Intravital microscopy was used to assess changes in arteriolar diameters and NO levels in rat mesentery. The average resting diameter of arterioles (27.5 +/- 1.0 microm) paired with venules with minimal leukocyte adherence (2.1 +/- 0.3 per 100-microm length) was significantly larger than that of unpaired arterioles (24.5 +/- 0.8 microm) and arterioles (23.3 +/- 1.3 microm) paired with venules with higher leukocyte adherence (9.0 +/- 0.5 per 100-microm length). Local superfusion of adenosine deaminase (ADA) induced significant decreases in diameter and perivascular NO concentration in arterioles closely paired to venules with minimal leukocyte adherence. However, ADA had little effect on arterioles closely paired to venules with high leukocyte adherence or on unpaired arterioles. To determine whether the attenuated response to ADA for the high-adherence group was oxidant dependent, the responses were also observed in arterioles treated with 10(-4) M Tempol. In the high-adherence group, Tempol fully restored NO levels to those of the low-adherence group; however, the ADA-induced constriction remained attenuated, suggesting a possible role for an oxidant-independent vasoconstrictor released from the inflamed venules. These findings suggest that adenosine- and venule-dependent dilation of paired arterioles may be mediated, in part, by NO and inhibited by venular leukocyte adherence.

Venular constriction of submucosal arterioles induced by dextran sodium sulfate

BACKGROUND

Leukocyte and platelet adherence in postcapillary venules has been speculated to induce constriction of closely paired arterioles. This mechanism was investigated in the current study, in a model of intestinal inflammation induced by dextran sodium sulfate (DSS; 5,000 molecular weight).

METHODS

Closely paired, parallel arterioles and venules in the submucosa of the mouse intestine were observed using fluorescent intravital microscopy. Arterioles in control mice were compared to arterioles in mice given 5% DSS in drinking water for 11 days.

RESULTS

DSS induced an inflammatory response in which fluorescently labeled leukocytes and platelets were observed adhering to venules. Arterioles constricted and flow decreased significantly when the arterioles were paired with venules having adherent leukocytes and platelets, although the decreases in flow and diameter appeared to be more dependent on platelet than leukocyte adherence. No significant constriction was observed in arterioles paired with venules having minimal platelet adherence. Inhibition of thromboxane with 100 mg/kg ozagrel induced a significant dilation of arterioles in DSS mice that was absent in control mice.

CONCLUSION

The results are consistent with a proposed mechanism in which thromboxane constricts submucosal arterioles when the arterioles are closely paired with platelet-bearing venules in DSS-induced inflammation.

The microcirculation: a motor for the systemic inflammatory response and large vessel disease induced by hypercholesterolaemia?

There is abundant evidence that links hypercholesterolaemia to both vascular inflammation and atherogenesis. While atherosclerosis is a large vessel disease that is characterized by leucocyte infiltration and lipid deposition in the wall of lesion-prone arteries, the inflammatory response does not appear to be confined to these locations. There is evidence supporting a systemic inflammatory response that is characterized by endothelial cell activation in multiple vascular beds and the appearance of activated immune cells and a wide range of inflammatory mediators in blood. The mechanism(s) responsible for initiating this systemic response remain poorly defined, although several inciting factors have been proposed, including infectious agents and oxidative stress resulting from one or more of the cardiovascular risk factors (e.g. hypercholesterolaemia, hypertension). While cells within lesion-prone arteries are often inferred as the source of circulating inflammatory mediators during atherogenesis, the fact that endothelial cells throughout the vasculature are activated raises the possibility that the microvasculature (which encompasses a vast endothelial surface area) may contribute to creating the systemic inflammatory milieu that is linked to atherogenesis. This review addresses evidence that links the microvasculature to the inflammatory responses induced by hypercholesterolaemia and offers the hypothesis that inflammatory events initiated within the microcirculation may contribute to initiation and/or progression of large vessel disease.

Arteriovenous pairing: a determinant of capillary exchange

Venuloarteriolar signaling helps mediate microvascular function and dysfunction. Mediators produced at venular sites of inflammation appear to constrict arterioles and increase capillary permeability. In contrast, venules beneficially dilate arterioles to enhance capillary flow according to metabolic demand. These mechanisms are altered with cardiovascular risk factors, contributing to microvascular complications.