Leukocyte modulation inhibits endotoxin-induced disruption of intracellular calcium homeostasis

ATP in red blood cells as biomarker for sepsis in humans

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to an infection. Due to the lack of causative immune treatment, mortality of sepsis remains at a high level and represents one of the main disease burdens globally. Adenosine 5' triphosphate (ATP) levels in red blood cells (RBC) are modulated by various factors during sepsis, including a decrease in ATP production, an increase in ATP catabolism and alterations in ATP release. Therefore, we hypothesize that intracellular ATP levels in RBC can serve as potential biomarker for sepsis and support sepsis diagnosis. This will facilitate early treatment and could improve the outcome of this serious condition.

The Effect of Sepsis on the Erythrocyte

Sepsis induces a wide range of effects on the red blood cell (RBC). Some of the effects including altered metabolism and decreased 2,3-bisphosphoglycerate are preventable with appropriate treatment, whereas others, including decreased erythrocyte deformability and redistribution of membrane phospholipids, appear to be permanent, and factors in RBC clearance. Here, we review the effects of sepsis on the erythrocyte, including changes in RBC volume, metabolism and hemoglobin's affinity for oxygen, morphology, RBC deformability (an early indicator of sepsis), antioxidant status, intracellular Ca²⁺ homeostasis, membrane proteins, membrane phospholipid redistribution, clearance and RBC O₂-dependent adenosine triphosphate efflux (an RBC hypoxia signaling mechanism involved in microvascular autoregulation). We also consider the causes of these effects by host mediated oxidant stress and bacterial virulence factors. Additionally, we consider the altered erythrocyte microenvironment due to sepsis induced microvascular dysregulation and speculate on the possible effects of RBC autoxidation. In future, a better understanding of the mechanisms involved in sepsis induced erythrocyte pathophysiology and clearance may guide improved sepsis treatments. Evidence that small molecule antioxidants protect the erythrocyte from loss of deformability, and more importantly improve septic patient outcome suggest further research in this area is warranted. While not generally considered a critical factor in sepsis, erythrocytes (and especially a smaller subpopulation) appear to be highly susceptible to sepsis induced injury, provide an early warning signal of sepsis and are a factor in the microvascular dysfunction that has been associated with organ dysfunction.

Red blood cell physiology in critical illness

OBJECTIVE

Reduction in red blood cell mass, as well as structural and functional alterations of erythrocytes, occurs in critical illness. This review discusses these changes in red blood cell physiology, emphasizing the pathogenesis of anemia in intensive care unit patients.

DATA SOURCE

Studies published in biomedical journals.

DATA SYNTHESIS AND CONCLUSION

Anemia in intensive care unit patients resembles the anemia of chronic disease, being characterized by diminished erythropoietin production relative to decreased hematocrit, altered iron metabolism, and impaired proliferation and differentiation of erythroid progenitors in the bone marrow. Inflammatory mediators play a major role in the development of insufficient erythropoiesis and altered iron metabolism. Furthermore, a proinflammatory milieu promotes structural and functional alterations of erythrocytes, impairing their deformability and possibly impairing microvascular perfusion. Collectively, these changes in red blood cell physiology can impair oxygen transport to tissues and, thereby, might contribute to the development of multiple organ failure in critical illness.

Red blood cell rheology in sepsis

Changes in red blood cell (RBC) function can contribute to alterations in microcirculatory blood flow and cellular dysoxia in sepsis. Decreases in RBC and neutrophil deformability impair the passage of these cells through the microcirculation. While the role of leukocytes has been the focus of many studies in sepsis, the role of erythrocyte rheological alterations in this syndrome has only recently been investigated. RBC rheology can be influenced by many factors, including alterations in intracellular calcium and adenosine triphosphate (ATP) concentrations, the effects of nitric oxide, a decrease in some RBC membrane components such as sialic acid, and an increase in others such as 2,3 diphosphoglycerate. Other factors include interactions with white blood cells and their products (reactive oxygen species), or the effects of temperature variations. Understanding the mechanisms of altered RBC rheology in sepsis, and the effects on blood flow and oxygen transport, may lead to improved patient management and reductions in morbidity and mortality.

Hypocalcemia in patients with acute pancreatitis: a putative role for systemic endotoxin exposure

INTRODUCTION

Hypocalcemia is not uncommon during acute pancreatitis and is associated with a poor outcome. Whilst the mechanisms responsible for its development remain unclear, there is evidence to implicate endotoxemia in other models of sepsis.

AIM

To investigate the potential role of systemic endotoxin exposure in the development of hypocalcemia in patients with acute pancreatitis.

METHODOLOGY

Adjusted serum calcium was measured daily, and the lowest value within 72 hours of admission for acute pancreatitis was determined. Serum endotoxin and both IgG and IgM antiendotoxin core antibodies (EndoCAbs) were measured on admission. Attacks were classified as mild (n = 51) or severe (n = 21) according to the criteria of the Atlanta International Symposium of 1992.

RESULTS

Hypocalcemia was significantly more frequent (86% versus 39%, p < 0.001) and reached significantly lower levels during severe attacks than during mild attacks (median [interquartile range], 2.06 [1.78-2.17] mmol/L, versus 2.23 [2.15-2.30] mmol/L; p < 0.001). Endotoxemia was present in a significantly greater proportion of patients with severe disease (71% versus 41%; p = 0.037), and serum IgM and IgG EndoCAbs were significantly depleted during severe attacks in comparison with mild attacks (p = 0.007 and p = 0.039, respectively). A negative and significant correlation was observed between endotoxemia and both the admission and lowest serum concentrations of adjusted calcium (r = -0.424 and p = 0.022; r = -0.383 and p = 0.037, respectively), and the latter correlated significantly with serum IgG EndoCAb concentrations (r = 0.251; p = 0.036).

CONCLUSION

Systemic endotoxin exposure appears to play a significant role in the development of hypocalcemia in patients with acute pancreatitis.

Allopurinol blocks shock-wave-induced rises in cytosolic calcium levels in MDCK cells

Allopurinol has been reported to ameliorate the side effects in patients following shock wave lithotripsy (SWL); however, the mechanism has not been studied. We have examined the protective effect of allopurinol on Madin-Darby canine kidney (MDCK) cells after shock wave exposure (SWE) by determining the release of aspartate aminotransferase (ASAT) and lactate dehydrogenase (LD), and the resting cytosolic Ca2+ concentration ([Ca2+]i). In SWE-treated cells, the release of ASAT and LD increased immediately, but largely transiently, by approximately 23% and 5-fold over control, respectively. Within 1-6 h after SWE there was a gradual rise in the resting [Ca2+]i of 16-137% above control. Allopurinol did not affect the transient enzyme release but blocked the long-term rises in the resting [Ca2+]i. The transient changes in [Ca2+]i evoked by two hormones, ATP and bradykinin, and a drug that releases Ca2+ from internal Ca2+ stores, thapsigargin, were only slightly affected in allopurinol-treated cells. We conclude that the protection conferred by allopurinol on patients treated with SWL might involve a direct protection of the kidney cells by maintaining a normal resting [Ca2+]i.