T-cell acute leukaemia exhibits dynamic interactions with bone marrow microenvironments.

It is widely accepted that complex interactions between cancer cells and their surrounding microenvironment contribute to disease development, chemo-resistance and disease relapse. In light of this observed interdependency, novel therapeutic interventions that target specific cancer stroma cell lineages and their interactions are being sought. Here we studied a mouse model of human T-cell acute lymphoblastic leukaemia (T-ALL) and used intravital microscopy to monitor the progression of disease within the bone marrow at both the tissue-wide and single-cell level over time, from bone marrow seeding to development/selection of chemo-resistance. We observed highly dynamic cellular interactions and promiscuous distribution of leukaemia cells that migrated across the bone marrow, without showing any preferential association with bone marrow sub-compartments. Unexpectedly, this behaviour was maintained throughout disease development, from the earliest bone marrow seeding to response and resistance to chemotherapy. Our results reveal that T-ALL cells do not depend on specific bone marrow microenvironments for propagation of disease, nor for the selection of chemo-resistant clones, suggesting that a stochastic mechanism underlies these processes. Yet, although T-ALL infiltration and progression are independent of the stroma, accumulated disease burden leads to rapid, selective remodelling of the endosteal space, resulting in a complete loss of mature osteoblastic cells while perivascular cells are maintained. This outcome leads to a shift in the balance of endogenous bone marrow stroma, towards a composition associated with less efficient haematopoietic stem cell function. This novel, dynamic analysis of T-ALL interactions with the bone marrow microenvironment in vivo, supported by evidence from human T-ALL samples, highlights that future therapeutic interventions should target the migration and promiscuous interactions of cancer cells with the surrounding microenvironment, rather than specific bone marrow stroma, to combat the invasion by and survival of chemo-resistant T-ALL cells.

The effect of chronic L-arginine administration on vascular recovery following cold cardioplegic arrest in rats.

OBJECTIVE: Acute administration of L-arginine (LA), the physiological substrate of nitric oxide, has been used as a strategy for myocardial protection during ischemia-reperfusion. The aim of this study was to assess the effects of chronic oral LA administration on vascular functions and morphology after prolonged cold cardioplegic arrest. METHODS: Adult male Sprague-Dawley rats (600-650 g) were divided into control and LA groups, which received LA (4 mg/ml) for 6 weeks. Two experimental protocols were carried out. (1) Isolated rat heart perfusion was performed and hearts were subjected to ischemia for 4 h at 4 degrees C using cold crystalloid cardioplegia (n=8 in LA, n=7 in control). Endothelial and vascular smooth muscle functions were assessed through observations of pre- and post-ischemic coronary flow response to 5-hydroxytryptamine (5-HT) and glyceryl trinitrate (GTN) (%5-HT and %GTN, respectively). (2) Semi-quantitative assessment of tissue morphology was conducted after the same ischemia-reperfusion protocol (n=4 in each group). RESULTS: The LA group showed significantly better recovery (post-/pre-ischemic value) of %5-HT (97.0+/-65.6 versus 21.5+/-25.7%, P=0.015) and %GTN (124.5+/-117.6 versus 47.7+/-16.6%, P=0.021). The histological assessment showed no significant differences between the two groups. CONCLUSIONS: Chronic oral administration of LA significantly ameliorated the postischemic recovery of endothelial and vascular smooth muscle functions after cold cardioplegic arrest in rats.

Age-related changes in the protective effect of chronic administration of L-arginine on post-ischemic recovery of endothelial function.

OBJECTIVE: The aim of this study was to assess the effect of chronic administration of L-arginine (LA) on vascular functions as well as its age-related changes. METHODS: Male Sprague-Dawley rats aged 1, 4, 8 and 16 months were divided into control and LA groups, which were administered LA (4 mg/ml) for 6 weeks. Isolated heart perfusion was performed, followed by cardioplegic arrest for 4h at 4 degrees C and reperfusion. Vascular functions were assessed through observations of pre-/post-ischemic coronary flow response to 5-hydroxytryptamine (5-HT) and glyceryl trinitrate (GTN). Ultrastructure was studied after the same ischemia-reperfusion. RESULTS: A significant improvement of percentage recovery (post-/pre-ischemic value) of response to 5-HT were seen in 4 and 8 months LA group when compared to the control (84.2+/-14.0 vs. 33.9+/-12.5 (P<0.05) and 97.0+/-23.2 vs. 21.5+/-9.7 (P<0.05), respectively). Furthermore, 8 months LA group had better percentage recovery of response to GTN (124.5+/-41.6 vs. 47.7+/-6.3, P<0.05). Ultrastructural study showed no significant differences between the groups in any age. CONCLUSIONS: Chronic oral administration of LA enhanced the post-ischemic recovery of vascular function in the young adult and adult hearts, but not in the infant and elderly.