Properties Permitting the Renal Cortex to Be the Oxygen Sensor for the Release of Erythropoietin: Clinical Implications

β-Thalassemia minor & renal tubular dysfunction: is there any association?

Objective

Beta(β)-thalassemia is one of the most common hereditary hematologic disorders. Patients with thalassemia minor (TM) are often asymptomatic and the rate of renal dysfunction is unknown in these patients. Due to the high prevalence of renal dysfunction in Iran, the current study aimed to determine renal tubular dysfunction in patients with beta-TM.

Methods

In this case-control study, 40 patients with TM and 20 healthy subjects were enrolled and urinary and blood biochemical analysis was done on their samples. Renal tubular function indices were determined and compared in both groups. Data was analyzed by SPSS software, version 20.0.

Results

The fraction excretion (FE) of uric acid was 8.31 ± 3.98% in the case and 6.2 ± 34.71% in the control group (p = 0.048). Also, FE of potassium was significantly higher in patients with TM (3.22 ± 3.13 vs. 1.91 ± 0.81; p = 0.036). The mean Plasma NGAL level was 133.78 ± 120.28 ng/mL in patients with thalassemia and 84.55 ± 45.50 ng/mL in the control group (p = 0.083). At least one parameter of tubular dysfunction was found in 45% of patients with thalassemia.

Conclusion

Based on the results of this study, the prevalence of tubular dysfunction in beta-thalassemia minor patients is high. Due to the lack of knowledge of patients about this disorder, periodic evaluation of renal function in TM patients can prevent renal failure by early diagnosis.

The potential role of Na-K-ATPase and its signaling in the development of anemia in chronic kidney disease

Chronic kidney disease (CKD) is one of the most prominent diseases affecting our population today. According to the Factsheet published by Centers for Disease Control and Prevention (CDC), it effects approximately 15% of the total population in the United States in some way, shape, or form. Within the myriad of symptomatology associated with CKD, one of the most prevalent factors in terms of affecting quality of life is anemia. Anemia of CKD cannot be completely attributed to one mechanism or cause, but rather has a multifactorial origin in the pathophysiology of CKD. While briefly summarizing well-documented risk factors, this review, as a hypothesis, aims to explore the possible role of Na-K-ATPase and its signaling function [especially recent identified reactive oxygen species (ROS) amplification function] in the interwoven mechanisms of development of the anemia of CKD.

Renal microvascular oxygen tension during hyperoxia and acute hemodilution assessed by phosphorescence quenching and excitation with blue and red light

PURPOSE

The kidney plays a central physiologic role as an oxygen sensor. Nevertheless, the direct mechanism by which this occurs is incompletely understood. We measured renal microvascular partial pressure of oxygen (P_kO₂) to determine the impact of clinically relevant conditions that acutely change P_kO₂ including hyperoxia and hemodilution.

METHODS

We utilized two-wavelength excitation (red and blue spectrum) of the intravascular phosphorescent oxygen sensitive probe Oxyphor PdG4 to measure renal tissue PO₂ in anesthetized rats (2% isoflurane, n = 6) under two conditions of altered arterial blood oxygen content (C_aO₂): 1) hyperoxia (fractional inspired oxygen 21%, 30%, and 50%) and 2) acute hemodilutional anemia (baseline, 25% and 50% acute hemodilution). The mean arterial blood pressure (MAP), rectal temperature, arterial blood gases (ABGs), and chemistry (radiometer) were measured under each condition. Blue and red light enabled measurement of P_kO₂ in the superficial renal cortex and deeper cortical and medullary tissue, respectively.

RESULTS

P_kO₂ was higher in the superficial renal cortex (~ 60 mmHg, blue light) relative to the deeper renal cortex and outer medulla (~ 45 mmHg, red light). Hyperoxia resulted in a proportional increase in P_kO₂ values while hemodilution decreased microvascular P_kO₂ in a linear manner in both superficial and deeper regions of the kidney. In both cases (blue and red light), P_kO₂ correlated with C_aO₂ but not with MAP.

CONCLUSION

The observed linear relationship between C_aO₂ and P_kO₂ shows the biological function of the kidney as a quantitative sensor of anemic hypoxia and hyperoxia. A better understanding of the impact of changes in P_kO₂ may inform clinical practices to improve renal oxygen delivery and prevent acute kidney injury.

Anesthesia for Patients with Anemia

Anemia is a common and often ignored condition in surgical patients. Anemia is usually multifactorial and iron deficiency and inflammation are commonly involved. An exacerbating factor in surgical patients is iatrogenic blood loss. Anemia has been repeatedly shown to be an independent predictor of worse outcomes. Patient blood management (PBM) provides a multimodality framework for prevention and management of anemia and related risk factors. The key strategies in PBM include support of hematopoiesis and improving hemoglobin level, optimizing coagulation and hemostasis, use of interdisciplinary blood conservation modalities, and patient-centered decision making throughout the course of care.

Stability of tissue PO2 in the face of altered perfusion: a phenomenon specific to the renal cortex and independent of resting renal oxygen consumption

1. Oxygen tension (PO(2)) in renal cortical tissue can remain relatively constant when renal blood flow changes in the physiological range, even when changes in renal oxygen delivery (DO(2)) and oxygen consumption (VO(2)) are mismatched. In the current study, we examined whether this also occurs in the renal medulla and skeletal muscle, or if it is an unusual property of the renal cortex. We also examined the potential for dysfunction of the mechanisms underlying this phenomenon to contribute to kidney hypoxia in disease states associated with increased renal VO(2) . 2. In both the kidney and hindlimb of pentobarbitone anaesthetized rabbits, whole organ blood flow was reduced by intra-arterial infusion of angiotensin-II and increased by acetylcholine infusion. In the kidney, this was carried out before and during renal arterial infusion of the mitochondrial uncoupler, 2,4-dinitrophenol (DNP), or its vehicle. 3. Angiotensin-II reduced renal (-34%) and hindlimb (-25%) DO(2) , whereas acetylcholine increased renal (+38%) and hindlimb (+66%) DO(2) . However, neither renal nor hindlimb VO(2) were altered. Tissue PO(2) varied with local perfusion in the renal medulla and biceps femoris, but not the renal cortex. DNP increased renal VO(2) (+38%) and reduced cortical tissue PO(2) (-44%), but both still remained stable during subsequent infusion of angiotensin-II and acetylcholine. 4. We conclude that maintenance of tissue PO(2) in the face of mismatched changes in local perfusion and VO(2) is an unusual property of the renal cortex. The underlying mechanisms remain unknown, but our current findings suggest they are not compromised when resting renal VO(2) is increased.

A revisit to O2 sensing and transduction in the carotid body chemoreceptors in the context of reactive oxygen species biology

Oxygen-sensing and transduction in purposeful responses in cells and organisms is of great physiological and medical interest. All animals, including humans, encounter in their lifespan many situations in which oxygen availability might be insufficient, whether acutely or chronically, physiologically or pathologically. Therefore to trace at the molecular level the sequence of events or steps connecting the oxygen deficit with the cell responses is of interest in itself as an achievement of science. In addition, it is also of great medical interest as such knowledge might facilitate the therapeutical approach to patients and to design strategies to minimize hypoxic damage. In our article we define the concepts of sensors and transducers, the steps of the hypoxic transduction cascade in the carotid body chemoreceptor cells and also discuss current models of oxygen- sensing (bioenergetic, biosynthetic and conformational) with their supportive and unsupportive data from updated literature. We envision oxygen-sensing in carotid body chemoreceptor cells as a process initiated at the level of plasma membrane and performed by a hemoprotein, which might be NOX4 or a hemoprotein not yet chemically identified. Upon oxygen-desaturation, the sensor would experience conformational changes allosterically transmitted to oxygen regulated K+ channels, the initial effectors in the transduction cascade. A decrease in their opening probability would produce cell depolarization, activation of voltage dependent calcium channels and release of neurotransmitters. Neurotransmitters would activate the nerve endings of the carotid body sensory nerve to convey the information of the hypoxic situation to the central nervous system that would command ventilation to fight hypoxia.

Myeloproliferative disorders and the hyperviscosity syndrome

Myeloproliferative disorders and the serum hyperviscosity syndrome can rapidly manifest with emergent presentations. Hyperviscosity occurs from pathologic elevations of either the cellular or acellular (protein) fractions of the circulating blood. Classic hyperviscosity syndrome presents with the triad of bleeding diathesis, visual disturbances, and focal neurologic signs. Emergency medicine providers should be aware of these conditions and be prepared to rapidly initiate supportive and early definitive management, including plasma exchange and apharesis. Early consultation with a hematologist is essential to managing these complex patients.

Review article: How cells sense oxygen: lessons from and for the kidney

The kidney has contributed two critical insights to an understanding of the mechanism by which all mammalian cells sense oxygen. The first followed from the detailed characterization of the regulation of expression of erythropoietin by oxygen and led to the discovery of the hypoxically regulated transcription factor, HIF (hypoxia-inducible factor). The second insight developed from the exploration of the molecular pathogenesis of von Hippel Lindau disease protein whose mutation is characterized by the development of renal cancers. The essential role for the von Hippel Lindau disease protein in the oxygen-dependent degradation of HIF led directly to the discovery of the oxygen sensing mechanism that regulates HIF by oxygen-dependent peptidyl hydroxylation. This understanding now generates novel therapeutic possibilities and is providing insights into the mechanisms of other renal diseases.

Intrarenal oxygenation: unique challenges and the biophysical basis of homeostasis

The kidney is faced with unique challenges for oxygen regulation, both because its function requires that perfusion greatly exceeds that required to meet metabolic demand and because vascular control in the kidney is dominated by mechanisms that regulate glomerular filtration and tubular reabsorption. Because tubular sodium reabsorption accounts for most oxygen consumption (Vo2) in the kidney, renal Vo2 varies with glomerular filtration rate. This provides an intrinsic mechanism to match changes in oxygen delivery due to changes in renal blood flow (RBF) with changes in oxygen demand. Renal Vo2 is low relative to supply of oxygen, but diffusional arterial-to-venous (AV) oxygen shunting provides a mechanism by which oxygen superfluous to metabolic demand can bypass the renal microcirculation. This mechanism prevents development of tissue hyperoxia and subsequent tissue oxidation that would otherwise result from the mismatch between renal Vo2 and RBF. Recent evidence suggests that RBF-dependent changes in AV oxygen shunting may also help maintain stable tissue oxygen tension when RBF changes within the physiological range. However, AV oxygen shunting also renders the kidney susceptible to hypoxia. Given that tissue hypoxia is a hallmark of both acute renal injury and chronic renal disease, understanding the causes of tissue hypoxia is of great clinical importance. The simplistic paradigm of oxygenation depending only on the balance between local perfusion and Vo2 is inadequate to achieve this goal. To fully understand the control of renal oxygenation, we must consider a triad of factors that regulate intrarenal oxygenation: local perfusion, local Vo2, and AV oxygen shunting.