Outcomes based on blood pressure in patients on continuous flow left ventricular assist device support: An Interagency Registry for Mechanically Assisted Circulatory Support analysis

BACKGROUND

An optimal blood pressure (BP) range to mitigate morbidity and mortality on left ventricular assist device (LVAD) support has not been clearly defined.

METHODS

Average Doppler opening pressure, mean arterial pressure (MAP), and/or systolic blood pressure (SBP) were calculated in operative survivors (n = 16,155) of LVAD support in the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS). BP distributions were used to group patients into low (BP <25th percentile), normal (25-75th percentile), high (75th-95th percentile), and very high (>95th percentile). Associations between BP and adverse events were evaluated using Cox regression (hazard ratio[HR], 95% confidence interval).

RESULTS

The median (25th, 75th) MAP, Doppler, and SBP (mm Hg) during continuous flow LVAD support were 84 (77, 90), 85 (80, 92), and 99 (90, 107) mm Hg, respectively. BP had a bimodal risk association with survival. At 3 years, survival was 58% ± 1.8% in those with low MAP (≤75 mm Hg) vs 70% ± 0.9%, 71% ± 1.5%, and 63% ± 3.0% in the those with normal, high, or very high average MAP, respectively. Patients with chronically low MAP (≤75 mm Hg), Doppler (≤80 mm Hg), and SBP (<90 mm Hg) had 35%-42% higher adjusted hazards of death than patients with normal or high BP (p ≤ 0.0001). Patients with MAP >100 mm Hg, Doppler ≥105 mm Hg, and SBP ≥120 mm Hg had 17%-20% higher adjusted hazards of death than those with normal pressures (p < 0.05). In patients on axial flow LVADs, elevated SBP (HR 1.08 [95% confidence interval, 1.04-1.13] per 10 mm Hg increase) but not MAP correlated with increased incident of stroke.

CONCLUSIONS

In INTERMACS, BP extremes during LVAD support increase the risk for adverse events, supporting a MAP goal >75 mm Hg and <90 mm Hg. Hypotension conferred the highest risk for mortality. Excessive BP control should be avoided, and Doppler opening pressure should not be assumed to represent MAP in all patients.

Modelling the human immune response: can mice be trusted? Commentary

The mouse is now the animal of choice for laboratory-based medical research. Although its contribution to advancing understanding of our inner workings is indisputable, we should acknowledge that mice and humans are tangibly different. This article highlights, and attempts some rationale for, discrepancies between the two species' immune systems.

CD5-positive and CD5-negative human B cells converge to an indistinguishable population on signalling through B-cell receptors and CD40

Whether CD5 on B cells marks a subset functionally distinct from the conventional CD5 negative (CD5neg) adult population or is more an indicator of activation, remains contentious. Here we have investigated whether CD5 positive (CD5pos) and CD5neg B cells can be distinguished in terms of their response to surrogate signals aimed to model, in vitro, T-cell dependent (TD) and T-independent (TI) encounters with antigen in vivo: the predominantly CD5pos B-cell population found in cord blood, CD5 B cells positively selected from tonsils and their CD5neg counterparts, were compared. Neonatal B cells displayed a near-identical phenotype to that of adult CD5pos B cells, being characterized by uniform immunoglobulin M (IgM), immunoglobulin D (IgD), CD23 and CD44 coexpression. When cultured with anti-IgM maintained at high density on CD32-tranfected mouse L cells to model TI responses or on CD40 ligand (CD40L)-bearing L cells (with or without captured anti-IgM) to model TD encounters, DNA synthesis was stimulated to a similar extent in all three populations. Focusing on CD5 and CD23, we found that - although the signals delivered promoted distinct profiles of expression - under each condition of activation, the phenotypes that emerged for adult CD5pos and CD5neg B cells were remarkably similar. Neonatal B cells displayed a greater diminution in CD5 expression than adult CD5pos B cells following CD40 signals but otherwise the two populations again behaved similarly. The inclusion of interleukin-4 (IL-4) to cultures where cells were costimulated via surface (s)IgM and CD40 resulted in a complete loss of CD5 expression and a corresponding hyperexpression of CD23, irrespective of the population studied. The near-identical response of CD5pos and CD5neg B cells to surrogate TD or TI signals in vitro and their convergence to indistinguishable phenotypes is wholly supportive of CD5 being a fluctuating marker of activation rather than it delineating functionally distinct subsets.

Mechanisms of antigen receptor-dependent apoptosis of human B lymphoma cells probed with a panel of 27 monoclonal antibodies

The present study has used a panel of 23 monoclonal antibodies to IgM and 4 to IgD in order to probe parameters influencing sIg-dependent apoptosis in an IgM/IgD-expressing Burkitt lymphoma line. No direct correlation was observed between the capacity of the different anti-mu to drive cells into apoptosis and either their domain specificity or their affinity for sIgM. There was, however, a direct correlation between the functional outcome and the ability of the monoclonal antibodies to elicit a rise in intracellular Ca2+. For apoptosis to occur, the Ca2+ response had to attain a threshold value of approximately 100 nM. A direct role for Ca2+ in the delivery of the apoptotic signal was demonstrated using thapsigargin to raise intracellular Ca2+ levels. Antigen receptor ligation was linked to Ca2+ increases by tyrosine kinases as revealed by direct analysis of protein tyrosine phosphorylation and the effects of selective protein tyrosine kinase-inhibiting tyrphostins. These findings reveal a central role for the antigen receptor-generated Ca2+ signal in driving apoptosis in human B lymphoma cells and stresses the need to use a panel of reagents when probing function with presumed ligand-mimetic monoclonal antibodies.

Signals for survival and apoptosis in normal and neoplastic B lymphocytes

B lymphocytes are subject to selection within germinal centers following somatic hyper-mutation on immunoglobulin variable region genes based on their ability to bind antigen with high affinity. Non-selected cells die by apoptosis. Tumors with features of germinal center B cells include follicular center cell lymphoma and Burkitt's lymphoma. We have used the latter extensively as a neoplastic model of germinal center cells and have compared directly the behaviour of cell lines derived from biopsy material with that of the normal counterparts. Here we describe some of our findings in the two systems with regard to signals regulating survival and apoptosis.

Engagement of CD20 suppresses apoptosis in germinal center B cells

In a screen of 67 monoclonal antibodies (mAb) included in the Blind Panel of B cell antibodies for the 5th International Workshop on Human Leukocyte Differentiation Antigens, only the CD20 mAb--included as a positive control for immunophenotyping studies--was found to suppress the spontaneous apoptosis which occurs in human germinal center (GC) B cells when placed in tissue culture at 37 degrees C. Further detailed study using the 1F5 mAb confirmed this observation, showing that rescue from apoptosis via CD20, while not as efficient as that obtained on ligating CD40, was of similar magnitude to that achieved on engagement of surface immunoglobulin (sIg) by immobilized antibody. Also similar to anti-Ig, the CD20 mAb rescued from apoptosis without priming for the proliferation of GC B cells: this was quite different to its action on resting, non-GC B cells, where it provides a potent priming signal for cell cycle progression in response to IL-4 or anti-CD40. Unlike the survival signal engendered via sIg, CD20 engagement neither mobilized Ca2+ from intracellular stores or opening of a Ca2+ channel with 1F5, nor did it affect the ability of anti-Ig to open a Ca2+ gate in GC B cells. An unexpected feature of CD20-mediated rescue of GC B cells from apoptosis was a failure to turn on Bcl-2 expression.

Regulation of myo-inositol transport during the growth and differentiation of thyrocytes: a link with thyroid-stimulating hormone-induced phospholipase A2 activity

The Vmax of myo-inositol transport increased 3-fold during epidermal growth factor (EGF)-induced growth and thyroid-stimulating hormone. (TSH)-induced differentiation in primary cultures of sheep and human thyrocytes. The Km remained unaltered. This up-regulation required the presence of insulin. The TSH-induced rise in myo-inositol transport commenced 8 to 16 h after the initial stimulus and achieved a plateau at 24 h. In human thyrocytes the change in Vmax was accompanied by an increase in the steady-state levels of mRNA for the myo-inositol transporter following treatment with either ligand. Examination of the metabolites of myo-inositol showed few significant changes after treatment of sheep thyrocytes with EGF for 24 h. This is consistent with maintenance of the intracellular concentration of myo-inositol as the cells enlarge in preparation for cell division. In TSH-treated cells, however, up-regulation of myo-inositol transport was linked with increased myo-inositol cycling across the cell membrane, increased phospholipase A2-mediated turnover of phosphatidylinositol and a concomitant increase in arachidonic acid turnover. Increased levels of myo-inositol phosphates were also noted 24 h after TSH treatment. These results indicate the initiation of secondary signalling events many hours after the primary stimulus.

Effect of Mg2+ on Na(+)-dependent inositol transport. Role for Mg2+ in etiology of diabetic complications

Diabetes mellitus is associated with a significant reduction in the serum concentration of Mg2+. Several studies have suggested that hypomagnesemia may be implicated in the etiology of diabetic complications; however, no mechanism has been proposed. This study demonstrates that Mg2+ is a positive effector of inositol transport and is capable of promoting a 2.5-fold increase in the affinity of the transporter for inositol. Analysis of the kinetics of inositol transport shows that, at physiological concentrations of inositol, the reductions in Mg2+ concentrations that occur in diabetic patients would result in a significant decline in the rate of inositol transport (1.5- to 2-fold). We suggest that hypomagnesemia may be linked to the development of diabetic complications via reduction in the rate of inositol transport and subsequent intracellular inositol depletion. This assertion allows hypomagnesemia and the polyol theory to be unified into one mechanistic model for the development of diabetic complications.

Changes in the kinetics of inositol transport during TPA-induced differentiation of HL60 cells towards monocytes

When exposed to the phorbol ester TPA, HL60 cells undergo growth arrest and differentiate towards monocytes. During TPA-induced differentiation there was a 2.6-fold increase in the rate of inositol transport (Vmax), a 2.1-fold increase in intracellular inositol and a 1.5-fold increase in inositol lipid. An increase in the Vmax of inositol transport did not occur when the variant cell line HL60Ast3 was exposed to TPA, which has been shown in this cell line to induce growth arrest but not differentiation. This observation suggests that the change in inositol transport during HL60 monocyte differentiation is specifically associated with the process of cell differentiation as opposed to growth arrest.

Sodium dependent inositol transport in HL60 cells is not related to Na+/K+ ATPase activity

In HL60 cells, inositol transport is sodium-dependent but functionally independent of Na+/K+ ATPase activity. This observation has implications for the currently proposed theory for the development of diabetic complications.