Vascular smooth muscle contractility assays for inflammatory and immunological mediators

Freestanding hydrogel lumens for modeling blood vessels and vasodilation

Lumen structures exist throughout the human body, and the vessels of the circulatory system are essential for carrying nutrients and oxygen and regulating inflammation. Vasodilation, the widening of the blood vessel lumen, is important to the immune response as it increases blood flow to a site of inflammation, raises local temperature, and enables optimal immune system function. A common method for studying vasodilation uses excised vessels from animals; major drawbacks include heterogeneity in vessel shape and size, time-consuming procedures, sacrificing animals, and differences between animal and human biology. We have developed a simple, user-friendly in vitro method to form freestanding cell-laden hydrogel rings from collagen and quantitatively measure the effects of vasodilators on ring size. The hydrogel rings are composed of collagen I and can be laden with human vascular smooth muscle cells, a major cellular and structural component of blood vessels, or lined with endothelial cells in the lumen. The methods presented include a 3D printed device (which is amenable to future fabrication by injection molding) and commercially available components (e.g., Teflon tubing or a syringe) to form hydrogel rings between 2.6-4.6 mm outer diameter and 0.79-1.0 mm inner diameter. Here we demonstrate a significant difference in ring area in the presence of a known vasodilator, fasudil (p < 0.0001). Our method is easy to implement and provides a foundation for a medium-throughput solution to generating vessel model structures for future investigations of the fundamental mechanisms of vasodilation (e.g., studying uncharacterized endogenous molecules that may have vasoactivity) and testing vasoactive drugs.

Naïve, Regulatory, Activated, and Memory Immune Cells Co-exist in PVATs That Are Comparable in Density to Non-PVAT Fats in Health

Perivascular adipose tissue (PVAT), the fat surrounding peripheral blood vessels, is protective and reduces the contraction of blood vessels in health. PVAT is composed of adipocytes, stromal cells, and immune cells. Recent work supports eosinophils as one of the cell types key to the anti-contractile nature of PVAT in health. Hence, we hypothesized that there exists a basally activated immune cell community in healthy PVAT that is distinctly different from non-PVAT fats. PVATs were from around mesenteric resistance vessels (MRPVAT – white fat) and thoracic aorta (APVAT – brown fat). Non-PVATs included retroperitoneal (RP fat – white fat) and subscapular (SS fat – brown fat) while the spleen was a positive control. Tissues were harvested from adult male and female Sprague Dawley rats. Six primary immune cell types were identified in PVATs. T cells (CD4 and CD8), B cells, natural killer (NK) cells, macrophages, mast cells, and neutrophils in the stromal vascular fraction of each fat were identified using nine-color flow cytometry. PVATs contained a higher number of total immune cells vs. their respective non-PVAT fats in females. Females had a higher number of T cells in MRPVAT vs. males. Females also had a greater number of T cells and total immune cells in APVAT vs. males. Further, activation, differentiation, and/or polarization of various immune cell types were similarly determined by flow cytometry. PVATs were similar to their respective non-PVAT fats in density of recently activated B cells (B220+ CD25+). However, MRPVAT in females had a higher number of naïve CD4 T cells vs. MRPVAT in males and APVAT in females. MRPVAT also had denser naïve CD8 T cells vs. APVAT in females. Overall, this research for the first time has identified a community of discrete populations of immune cells (naive/recently activated/regulatory/memory) in healthy PVATs. Contrary to our hypothesis, PVATs are more similar than different in density to their respective non-PVAT fats.

D-Arg0-Bradykinin-Arg-Arg, a Latent Vasoactive Bradykinin B2 Receptor Agonist Metabolically Activated by Carboxypeptidases

We previously reported hypotensive and vasodilator effects from C-terminally extended bradykinin (BK) sequences that behave as B₂ receptor (B₂R) agonists activated by vascular or plasma peptidases. D-Arg⁰-BK-Arg-Arg (r-BK-RR) is a novel prodrug peptide hypothetically activated by two catalytic cycles of Arg-carboxypeptidases (CPs) to release the direct agonist D-Arg⁰-BK. N-terminally extending the BK sequence with D-Arg⁰ in the latter peptide was meant to block the second kinin inactivation pathway in importance, aminopeptidase P. The affinity of r-BK and r-BK-RR for recombinant B₂R was assessed using a [³H]BK binding displacement assay. Their pharmacology was evaluated in human isolated umbilical vein, a contractile bioassay for the B₂R, in a morphological assay involving the endocytosis of B₂R-green fusion protein (GFP) and in anesthetized rats instrumented to record hemodynamic responses to bolus intravenous injection of both peptides. r-BK exhibited an affinity equal to that of BK for the rat B₂R, while r-BK-RR was 61-fold less potent. In the vein and the B₂R-GFP internalization assay, r-BK was a direct agonist unaffected by the blockade of angiotensin converting enzyme (ACE) with enalaprilat, or Arg-CPs with Plummer’s inhibitor. However, the in vitro effects of r-BK-RR were reduced by these inhibitors, more so by enalaprilat. In anesthetized rats, r-BK and r-BK-RR were equipotent hypotensive agents and their effects were inhibited by icatibant (a B₂R antagonist). The hypotensive effects of r-BK were potentiated by enalaprilat, but not influenced by the Arg-CPs inhibitor, which is consistent with a minor role of Arg-CPs in the metabolism of r-BK. However, in rats pretreated with both enalaprilat and Plummer’s inhibitor, the hypotensive responses and the duration of the hypotensive episode to r-BK were significantly potentiated. The hypotensive responses to r-BK-RR were not affected by enalaprilat, but were reduced by pre-treatment with the Arg-CPs inhibitor alone or combined with enalaprilat. Therefore, in vivo, Arg-CPs activity is dominant over ACE to regenerate the B₂R agonist r-BK from r-BK-RR, a prodrug activator of the B₂R. A B₂R agonist activated only at the level of the microcirculation by resident peptidases could be developed as an intravenously infused drug for ischemic diseases.

Species-specific pharmacology of maximakinin, an amphibian homologue of bradykinin: putative prodrug activity at the human B2 receptor and peptidase resistance in rats

Maximakinin (MK), an amphibian peptide possessing the C-terminal sequence of bradykinin (BK), is a BK B₂ receptor (B₂R) agonist eliciting prolonged signaling. We reinvestigated this 19-mer for species-specific pharmacologic profile, in vivo confirmation of resistance to inactivation by angiotensin converting enzyme (ACE), value as a module for the design of fusion proteins that bind to the B₂R in mammalian species and potential activity as a histamine releaser. Competition of the binding of [³H]BK to recombinant human myc-B₂Rs in cells that express these receptors revealed that MK possessed a tenuous fraction (<0.1%) of the affinity of BK, despite being only ∼20-fold less potent than BK in a contractility assay based on the human isolated umbilical vein. These findings are reconciled by the generation of C-terminal fragments, like Lys-Gly-Pro-BK and Gly-Pro-BK, when the latent MK is incubated with human venous tissue (LC-MS), supporting activation via hydrolysis upstream of the BK sequence. At the rat recombinant myc-B₂R, MK had a lesser affinity than that of BK, but with a narrower margin (6.2-fold, radioligand binding competition). Accordingly, MK (10 nM) stimulated calcium transients in cells that expressed the rat receptors, but not the human B₂R. Recombinant MRGPRX2, a receptor that mediates cationic peptide-induced mast cell secretion, minimally responded by increased [Ca⁺²]_i to MK at 10 µM. Enhanced green fluorescent protein fused to MK (EGFP-MK) labeled cells that expressed rat, but not human B₂Rs. Intravenous MK induced dose-dependent hypotensive, vasodilator and tachycardic responses in anesthetized rats and the effects were antagonized by pretreatment with icatibant but not modified by pyrilamine or enalaprilat. Strong species-specific responses to the toxin-derived peptide MK and its prodrug status in the isolated human vein were evidenced. Accordingly, MK in the EGFP-MK fusion protein is a pharmacophore module that confers affinity for the rat B₂R, but not for the human form of the B₂R. MK is unlikely to be an efficient mast cell activator, but its resistance to inactivation by ACE was confirmed in vivo.

Infrared-emitting, peptidase-resistant fluorescent ligands of the bradykinin B2 receptor: application to cytofluorometry and imaging

BACKGROUND

We have previously reported the design, pharmacological properties and imaging application of bradykinin (BK) B₂ receptor (B₂R) ligands conjugated with fluorophores such as fluorescein derivatives at their N-terminus. To take advantage of the high penetration of infrared light into living tissues and their low autofluorescence in this region of the spectrum, additional probes conjugated with cyanine dye 7 (Cy7) were synthesized and characterized.

RESULTS

The antagonist B-9430 (D-Arg-[Hyp³,Igl⁵,D-Igl⁷,Oic⁸]-BK) and the agonist B-9972 (D-Arg-[Hyp³,Igl⁵,Oic⁷,Igl⁸]-BK) were N-terminally extended with the infrared fluorophore Cy7, producing the peptides B-10665 and B-10666, respectively. Pharmacological studies indicated that the agonist B-10666 lost much affinity for the B₂R vs. the parent peptide, whereas the antagonist B-10665 better retained its potency vs. B-9430 (competition of [³H]BK binding to human B₂R, contractility of the human isolated umbilical vein for which potency losses were more important in each case). Both probes stained HEK 293 cells that expressed the B₂R-green fluorescent protein (GFP) construction in a specific manner (confocal microscopy) and with very extensive co-localization of the green and infrared fluorescence in either case. The agonist B-10666 at 100 nM promoted the endocytosis of B₂R-GFP in live cells, but not the antagonist version at 10-25 nM. The Cy7-labeled peptides did not label cells expressing the β₂-adrenoceptor-GFP construction. B-10665 at low nanomolar concentrations was an effective probe for the recombinant B₂Rs in cytofluorometry and macroscopic imaging of cell wells (IVIS imaging system operated for infrared fluorescence detection).

CONCLUSIONS

Despite a propensity for non-specific binding when used at high concentrations and limited sensitivity, Cy7-conjugated peptidase-resistant B₂R ligands support original imaging and cytofluorometric applications.

The isolated human umbilical vein as a bioassay for kinin-generating proteases: An in vitro model for therapeutic angioedema agents

AIMS

The isolated human umbilical vein is a robust contractile bioassay for ligands of the bradykinin (BK) B2 receptor (B2R), also extendable to B1 receptor (B1R) pharmacology. We hypothesized that, as a freshly isolated vessel, it also contains traces of plasma proteins that may confer responses to exogenous proteases via the formation of kinins.

MAIN METHODS

Rings of human umbilical veins were mounted in organ baths containing Krebs buffer maintained at 37°C and purified proteases were introduced in the bathing fluid along with additional drugs/proteins that permit mechanistic analysis of effects.

KEY FINDINGS

The previously described contractile response to human recombinant tissue kallikrein (KLK-1, 1-10nM) is not influenced by metabolic inhibitors, suggesting its dependence on a preexisting reservoir of low molecular weight-kininogen (LK). Active plasma kallikrein (apK, ≤5nM) was inactive in fresh tissues, unless high molecular weight-kininogen (HK, 39-197nM) replenishment was applied. The effects of KLK-1 and HK+apK are abolished by pretreating tissues with icatibant, but not with tranexamic acid. C1-esterase inhibitor inhibited only HK+apK. Purified plasmin and neutrophil proteinase-3 produced small contractions in the presence of HK only, and tissue plasminogen activator, none. B1R stimulation was pharmacologically evidenced in response to KLK-1 if LK was supplied.

SIGNIFICANCE

The pharmacology of KLK-1 and HK+apK in the human isolated umbilical vein is essentially based on the activity of locally generated kinins and this assay models the inhibitory action of some therapeutic agents active in angioedema states. Proteases that indirectly generate kinins have little activity in the system.

Gastrointestinal Congestion Dilates the Hepatic Artery Through the P38 MAPK Signal Transduction Pathway During Liver Transplantation

During the neohepatic stage of liver transplantation, hemodynamics change markedly. The current study aimed to investigate whether gastrointestinal congestion caused by inferior vena cava and hepatic portal vein clamping can dilate the hepatic artery and to determine the associated mechanisms. Ring segments of the hepatic artery were treated with the plasma from gastrointestinal congestion or the superior vena cava. The fractions in gastrointestinal congestion and the superior vena cava plasma were tested, and the effect of these fractions on the tone of the hepatic artery ring was examined. Different signal transduction blockers and different inhibitors were then used to determine the exact signal transduction pathway involved. In addition, endothelial cell structure was observed by transmission electron microscopy after treatment with the gastrointestinal congestion plasma or the superior vena cava plasma. Gastrointestinal congestion plasma contained more inflammatory cytokines than superior vena cava plasma, and these cytokines could cause hepatic artery ring dilatation. A P38 mitogen-activated protein kinase (P38 MAPK) signal transduction pathway blocker and nitric oxide (NO), prostaglandin (PGI2), nuclear factor-κB (NF-κB), and adenosine triphosphate (ATP)-sensitive K (KATP) channel inhibitors were able to significantly reverse the ring tension caused by gastrointestinal congestion plasma. The normal endothelium was also injured by treatment with gastrointestinal congestion plasma. The inflammatory cytokines in gastrointestinal congestion can cause hepatic artery ring dilatation through the P38 MAPK signal transduction pathway, and this phenomenon is also associated with NO, PGI2, NF-κB, and the KATP channel. These inflammatory cytokines can injure endothelial cells in the hepatic artery.

Pharmacological effects of recombinant human tissue kallikrein on bradykinin B2 receptors

Tissue kallikrein (KLK-1), a serine protease, initiates the release of bradykinin (BK)-related peptides from low-molecular weight kininogen. KLK-1 and the BK B₂ receptor (B₂R) mediate beneficial effects on the progression of type 2 diabetes and renal disease, but the precise role of KLK-1 independent of its kinin-forming activity remains unclear. We used DM199, a recombinant form of human KLK-1, along with the isolated human umbilical vein, a robust bioassay of the B₂R, to address the previous claims that KLK-1 directly binds to and activates the human B₂R, with possible receptor cleavage. DM199 (1–10 nmol/L) contracted the isolated vein via the B₂R, but in a tachyphylactic, kinin-dependent manner, without desensitization of the tissue to exogenously added BK. In binding experiments with recombinant N-terminally tagged myc-B₂Rs expressed in HEK 293a cells, DM199 displaced [³H]BK binding from the rabbit myc-B₂R, but not from the human or rat myc-B₂Rs. No evidence of myc-B₂R degradation by immunoblot analysis was apparent following treatment of these 3 myc-B₂R constructs with DM199 (30 min, ≤10 nmol/L). In HEK 293 cells stably expressing rabbit B₂R-GFP, DM199 (11–108 pmol/L) elicited signaling-dependent endocytosis and reexpression, while a higher concentration (1.1 nmol/L) induced a partially irreversible endocytosis of the construct (microscopy), paralleled by the appearance of free GFP in cells (immunoblotting, indicative of incomplete receptor down-regulation). The pharmacology of DM199 at relevant concentrations (<10 nmol/L) is essentially based on the activity of locally generated kinins. Binding to and mild down-regulation of the B₂R is possibly a species-dependent idiosyncratic response to DM199.

Endotoxin-induced monocytic microparticles have contrasting effects on endothelial inflammatory responses

Septic shock is a severe disease state characterised by the body's life threatening response to infection. Complex interactions between endothelial cells and circulating monocytes are responsible for microvasculature dysfunction contributing to the pathogenesis of this syndrome. Here, we intended to determine whether microparticles derived from activated monocytes contribute towards inflammatory processes and notably vascular permeability. We found that endotoxin stimulation of human monocytes enhances the release of microparticles of varying phenotypes and mRNA contents. Elevated numbers of LPS-induced monocytic microparticles (mMP) expressed CD54 and contained higher levels of transcripts for pro-inflammatory cytokines such as TNF, IL-6 and IL-8. Using a prothrombin time assay, a greater reduction in plasma coagulation time was observed with LPS-induced mMP than with non-stimulated mMP. Co-incubation of mMP with the human brain endothelial cell line hCMEC/D3 triggered their time-dependent uptake and significantly enhanced endothelial microparticle release. Unexpectedly, mMP also modified signalling pathways by diminishing pSrc (tyr416) expression and promoted endothelial monolayer tightness, as demonstrated by endothelial impedance and permeability assays. Altogether, these data strongly suggest that LPS-induced mMP have contrasting effects on the intercellular communication network and display a dual potential: enhanced pro-inflammatory and procoagulant properties, together with protective function of the endothelium.

Pharmacological evidence of bradykinin regeneration from extended sequences that behave as peptidase-activated B2 receptor agonists

While bradykinin (BK) is known to be degraded by angiotensin converting enzyme (ACE), we have recently discovered that Met-Lys-BK-Ser-Ser is paradoxically activated by ACE. We designed and evaluated additional "prodrug" peptides extended around the BK sequence as potential ligands that could be locally activated by vascular or blood plasma peptidases. BK regeneration was estimated using the contractility of the human umbilical vein as model of vascular functions mediated by endogenous B2 receptors (B2Rs) and the endocytosis of the fusion protein B2R-green fluorescent protein (B2R-GFP) expressed in Human Embryonic Kidney 293 cells. Of three BK sequences extended by a C-terminal dipeptide, BK-His-Leu had the most desirable profile, exhibiting little direct affinity for the receptor but a significant one for ACE (as shown by competition of [(3)H]BK binding to B2R-GFP or of [(3)H]enalaprilat to recombinant ACE, respectively). The potency of the contractile effect of this analog on the vein was reduced 18-fold by the ACE inhibitor enalaprilat, pharmacologically evidencing BK regeneration in situ. BK-Arg, a potential substrate of arginine carboxypeptidases, had a low affinity for B2Rs and its potency as a contractile agent was reduced 15-fold by tissue treatment with an inhibitor of these enzymes, Plummer's inhibitor. B2R-GFP internalization in response to 100 nM of the extended peptides recapitulated these findings, as enalaprilat selectively inhibited the effect of BK-His-Leu and Plummer's inhibitor, that of BK-Arg. The two peptidase inhibitors did not affect BK-induced effects in either assay. The novel C-terminally extended BKs had no or very little affinity for the kinin B1 receptor (competition of [(3)H]Lys-des-Arg(9)-BK binding). The feasibility of peptidase-activated B2R agonists is illustrated by C-terminal extensions of the BK sequence.