In situ Analysis of Coronary Terminal Arteriole Diameter Responses: Technical Report of a New Experimental Model

Cell Size Critically Determines Initial Retention of Bone Marrow Mononuclear Cells in the Heart after Intracoronary Injection: Evidence from a Rat Model

Intracoronary injection of bone marrow mononuclear cells (BMMNC) is an emerging treatment for heart failure. Initial donor cell retention in the heart is the key to the success of this approach, but this process remains insufficiently characterized. Although it is assumed that cell size of injected cells may influence their initial retention, no scientific evidence has been reported. We developed a unique model utilizing an ex-vivo rat heart perfusion system, enabling quantitative assessment of retention of donor cells after intracoronary injection. The initial (5 minutes after intracoronary injection) retention rate of BMMNC was as low as approximately 20% irrespective of donor cell doses injected (1×10⁶, 8×10⁶, 4×10⁷). Quantitative cell-size assessment revealed a positive relationship between the size of BMMNC and retention ratio; larger subpopulations of BMMNC were more preferentially retained compared to smaller ones. Furthermore, a larger cell type—bone marrow-derived mesenchymal stromal cells (median size = 11.5μm versus 7.0μm for BMMNC)—had a markedly increased retention rate (77.5±1.8%). A positive relationship between the cell size and retention ratio was also seen in mesenchymal stromal cells. Flow-cytometric studies showed expression of cell-surface proteins, including integrins and selectin-ligands, was unchanged between pre-injection BMMNC and those exited from the heart, suggesting that biochemical interaction between donor cells and host coronary endothelium is not critical for BMMNC retention. Histological analyses showed that retained BMMNC and mesenchymal stromal cells were entrapped in the coronary vasculature and did not extravasate by 60 minutes after transplantation. Whilst BMMNC did not change coronary flow after intracoronary injection, mesenchymal stromal cells reduced it, suggesting coronary embolism, which was supported by the histological finding of intravascular cell-clump formation. These data indicate that cell-size dependent, passive (mechanical), intravascular entrapment is responsible for the initial donor cell retention after intracoronary injection of BMMNC in the heart having normal vasculatures (at least).

A review of methods for assessment of coronary microvascular disease in both clinical and experimental settings

Obstructive disease of the large coronary arteries is the prominent cause for angina pectoris. However, angina may also occur in the absence of significant coronary atherosclerosis or coronary artery spasm, especially in women. Myocardial ischaemia in these patients is often associated with abnormalities of the coronary microcirculation and may thus represent a manifestation of coronary microvascular disease (CMD). Elucidation of the role of the microvasculature in the genesis of myocardial ischaemia and cardiac damage-in the presence or absence of obstructive coronary atherosclerosis-will certainly result in more rational diagnostic and therapeutic interventions for patients with ischaemic heart disease. Specifically targeted research based on improved assessment modalities is needed to improve the diagnosis of CMD and to translate current molecular, cellular, and physiological knowledge into new therapeutic options.

The subepicardial microcirculation in heterotopically transplanted mouse hearts: An intravital multifluorescence microscopy study

OBJECTIVE

We developed a model for intravital microscopic analysis of the coronary microcirculation in transplanted murine hearts and assessed the influence of cold ischemia on postischemic microcirculatory dysfunctions.

METHODS

Murine hearts were exposed to 60 (n = 12) and 240 minutes (n = 8) of cold ischemia before syngeneic heterotopic transplantation. Intravital fluorescence microscopy allowed detailed analysis of the right ventricular coronary microcirculation, including feeding arterioles, nutritive capillaries, and postcapillary venules. With this technique, we further studied leukocyte-endothelial cell interactions, microvascular permeability, tissue oxygenation, and microlymphatics.

RESULTS

Cold ischemia of 240 minutes aggravated nutritive capillary perfusion failure, indicated by a significant reduction of functional capillary density and capillary flow velocity by 63% and 45% (P < .05 vs 60-minute cold ischemic isografts). The mitochondrial redox state, visualized by nicotinamide adenine dinucleotide hydrogen autofluorescence, was markedly deteriorated after 240-minute cold ischemia (P < .05), indicating a persistent mismatch between oxygen supply and demand resulting from pronounced capillary no-reflow. Prolonged ischemia further resulted in 6- and 11-fold higher numbers of rolling and firmly adherent leukocytes in postcapillary venules (P < .05), together with increased microvascular permeability.

CONCLUSIONS

We introduce a novel approach to visualize in detail the murine coronary microcirculation in vivo by multifluorescence microscopy. Our data demonstrate that prolonged cold ischemia provokes posttransplant capillary no-reflow, leukocytic inflammation, and persistent tissue hypoxia.

Adrenomedullin treatment abolishes ileal mucosal hypoperfusion induced by Staphylococcus aureus α-toxin—An intravital microscopic study on an isolated rat ileum

OBJECTIVE

Disturbances of intestinal microcirculation associated with sepsis and septic shock result in diminished mucosal oxygenation. Tissue hypoxia as well as mediator formation may lead to intestinal mucosa dysfunction. As a consequence, bacteria and their products as well as gut-derived inflammatory mediators may further perpetuate septic and inflammatory events. Adrenomedullin is produced in the mucosa of the gastrointestinal tract and has been shown to improve survival in experimental sepsis. Using pore-forming Staphylococcus aureus alpha-toxin as a potent initiator of inflammatory reactions, we tested the hypothesis that exogenously added adrenomedullin improves ileal mucosal perfusion.

DESIGN

Prospective, experimental study.

SETTING

University laboratory.

SUBJECTS

Isolated perfused ileum from male Sprague-Dawley rats

INTERVENTIONS

Adrenomedullin treatment of S. aureus alpha-toxin infused ileum.

MEASUREMENT AND MAIN RESULTS

An infusion of alpha-toxin (0.05 microg/mL) induced a significant decrease of red blood cell velocity in villus terminal arterioles from 1.7 to 0.7 mm/sec assessed by intravital microscopy. This was accompanied by a significant reduction of mucosal hemoglobin oxygenation from 71.8% to 17.5% and impaired oxygen uptake. At constant bulk flow and oxygen delivery, these data indicate a redistribution of blood perfusion away from mucosa. Subsequent intervention with 0.1 microM adrenomedullin redistributed blood flow back toward the mucosa, causing an improvement of mucosal hemoglobin oxygenation and of organ oxygen uptake.

CONCLUSION

These data suggest that exogenously added adrenomedullin protects ileum mucosa by diminishing alpha-toxin-induced microcirculatory disturbances. Further investigations will have to clarify the therapeutic potential of adrenomedullin in sepsis-related gut dysfunction.