Interanimal variability in preexisting collaterals is a major factor determining outcome in experimental angiogenesis trials

Abstract

Despite numerous animal trials reporting that cell therapy promotes collateral flow, clinical trials have not convincingly shown benefit. Patient-related risk factors are often used to explain these discrepancies. However, during the course of our own angiogenesis studies using mice, we noted large anatomical variability in collateral vessels. The purpose of the present investigation was to define how important this factor might be in determining intervention outcomes. Hindlimb ischemia was induced in BALB/c mice by ligating the superficial femoral artery. After 24 h, animals were treated by injecting the adductor muscle with either control media or cultured mesenchymal stem cells (MSCs). Blood flow recovery was measured using laser-Doppler [laser-Doppler perfusion imaging (LDPI) ratio]. In a second experiment, mice were stratified 24 h after arterial ligation before treatment by using a simple clinical score of the ligated leg: 1, able to flex, mild discoloration; 2, no flexion, mild discoloration; 3, severe discoloration; and 4, any necrosis. Without stratification, blood flow recovery significantly increased in the MSC-treated group ( P < 0.05, n = 6 MSC group, n = 7 media group). In the experiment employing stratification, all differences between the groups disappeared ( n = 11 MSC group, n = 10 media group; P = 0.3). Furthermore, we found a striking inverse correlation between clinical score on day 1 and the LDPI ratio on day 28 ( P < 0.0001; n = 79). Anatomical confirmation of the disparity in preexisting collaterals was found in two different mouse strains using microscopic computed tomography. In conclusion, there is substantial interanimal variability in preexisting collateral flow, and this variability can importantly influence outcome. To overcome this, either animals must be stratified before treatment, the number of animals must be increased substantially, or, preferably, both.

Interneuron Progenitors Attenuate the Power of Acute Focal Ictal Discharges

“…In addition, as electrophysiologically and neurochemically-defined cortical interneurons have recently been generated from embryonic stem cells, it may soon be possible to generate specific interneuron types from this resource [44], opening up the possibility of studies that determine which interneuron subclass is most efficacious for blocking different types of discharges. Furthermore, inter-animal variability has important implications in cell therapy [45]. Seizure duration, susceptibility to therapy and response can all be animal-dependent.…”

Vascular Reactivity in Newly-Formed and Mature Arterialized Collateral Capillaries

“…In addition to pharmacological evaluation of arterialized collateral capillaries (ACCs), we also sought to gain insight into the nature of impaired vasodilation of ACCs independent from genetic variation between strains by evaluating pre-existing collaterals (PECs), a more studied collateral vessel form (11,43,79). Because the smooth-muscle layer is already present within the PECs at the time of ligation, we anticipated that the vessels would undergo a less dramatic remodeling than the ACCs, and, therefore, provide insight into the role of cell rearrangement and proliferation versus cell recruitment as the primary impetus for smooth muscle-based dysfunction (11,79).…”

“…Because the smooth-muscle layer is already present within the PECs at the time of ligation, we anticipated that the vessels would undergo a less dramatic remodeling than the ACCs, and, therefore, provide insight into the role of cell rearrangement and proliferation versus cell recruitment as the primary impetus for smooth muscle-based dysfunction (11,79). The anatomical differences in size and layout may also contribute to vessel function through varied shear stress, as the PECs tend to be large, tortuous, and singular, while ACCs tend to be smaller, less tortuous, and more numerous.…”

“…Collaterals are beneficial in the event of arterial occlusion by providing patient circulation with an alternative path to reach downstream tissue (62,79). The spinotrapezius muscle within the Balb/C mouse strain serves as a model for an extreme case of low-density collateral networks within the vasculature (11,12,79).…”

“…The spinotrapezius muscle within the Balb/C mouse strain serves as a model for an extreme case of low-density collateral networks within the vasculature (11,12,79). In this model, the capillaries connecting dendritic arterial branches arterialize when an upstream artery is occluded to support a circulatory bypass route (25).…”