Effects of a human recombinant alkaline phosphatase during impaired mitochondrial function in human renal proximal tubule epithelial cells

Mesenchymal stromal cells secretome restores bioenergetic and redox homeostasis in human proximal tubule cells after ischemic injury

BACKGROUND

Ischemia/reperfusion injury is the leading cause of acute kidney injury (AKI). The current standard of care focuses on supporting kidney function, stating the need for more efficient and targeted therapies to enhance repair. Mesenchymal stromal cells (MSCs) and their secretome, either as conditioned medium (CM) or extracellular vesicles (EVs), have emerged as promising options for regenerative therapy; however, their full potential in treating AKI remains unknown.

METHODS

In this study, we employed an in vitro model of chemically induced ischemia using antimycin A combined with 2-deoxy-D-glucose to induce ischemic injury in proximal tubule epithelial cells. Afterwards we evaluated the effects of MSC secretome, CM or EVs obtained from adipose tissue, bone marrow, and umbilical cord, on ameliorating the detrimental effects of ischemia. To assess the damage and treatment outcomes, we analyzed cell morphology, mitochondrial health parameters (mitochondrial activity, ATP production, mass and membrane potential), and overall cell metabolism by metabolomics.

RESULTS

Our findings show that ischemic injury caused cytoskeletal changes confirmed by disruption of the F-actin network, energetic imbalance as revealed by a 50% decrease in the oxygen consumption rate, increased oxidative stress, mitochondrial dysfunction, and reduced cell metabolism. Upon treatment with MSC secretome, the morphological derangements were partly restored and ATP production increased by 40-50%, with umbilical cord-derived EVs being most effective. Furthermore, MSC treatment led to phenotype restoration as indicated by an increase in cell bioenergetics, including increased levels of glycolysis intermediates, as well as an accumulation of antioxidant metabolites.

CONCLUSION

Our in vitro model effectively replicated the in vivo-like morphological and molecular changes observed during ischemic injury. Additionally, treatment with MSC secretome ameliorated proximal tubule damage, highlighting its potential as a viable therapeutic option for targeting AKI.

Human Recombinant Alkaline Phosphatase (Ilofotase Alfa) Protects Against Kidney Ischemia-Reperfusion Injury in Mice and Rats Through Adenosine Receptors

Adenosine triphosphate (ATP) released from injured or dying cells is a potent pro-inflammatory "danger" signal. Alkaline phosphatase (AP), an endogenous enzyme that de-phosphorylates extracellular ATP, likely plays an anti-inflammatory role in immune responses. We hypothesized that ilofotase alfa, a human recombinant AP, protects kidneys from ischemia-reperfusion injury (IRI), a model of acute kidney injury (AKI), by metabolizing extracellular ATP to adenosine, which is known to activate adenosine receptors. Ilofotase alfa (iv) with or without ZM241,385 (sc), a selective adenosine A_2A receptor (A_2AR) antagonist, was administered 1 h before bilateral IRI in WT, A_2AR KO (Adora2a^-/- ) or CD73^-/- mice. In additional studies recombinant alkaline phosphatase was given after IRI. In an AKI-on-chronic kidney disease (CKD) ischemic rat model, ilofotase alfa was given after the three instances of IRI and rats were followed for 56 days. Ilofotase alfa in a dose dependent manner decreased IRI in WT mice, an effect prevented by ZM241,385 and partially prevented in Adora2a^-/- mice. Enzymatically inactive ilofotase alfa was not protective. Ilofotase alfa rescued CD73^-/- mice, which lack a 5'-ectonucleotidase that dephosphorylates AMP to adenosine; ZM241,385 inhibited that protection. In both rats and mice ilofotase alfa ameliorated IRI when administered after injury, thus providing relevance for therapeutic dosing of ilofotase alfa following established AKI. In an AKI-on-CKD ischemic rat model, ilofotase alfa given after the third instance of IRI reduced injury. These results suggest that ilofotase alfa promotes production of adenosine from liberated ATP in injured kidney tissue, thereby amplifying endogenous mechanisms that can reverse tissue injury, in part through A_2AR-and non-A_2AR-dependent signaling pathways.

Targeting the Intestinal Barrier to Prevent Gut-Derived Inflammation and Disease: A Role for Intestinal Alkaline Phosphatase

Background

Intestinal alkaline phosphatase (IAP) as a tissue-specific isozyme of alkaline phosphatases is predominantly produced by enterocytes in the proximal small intestine. In recent years, an increasing number of pathologies have been identified to be associated with an IAP deficiency, making it very worthwhile to review the various roles, biological functions, and potential therapeutic aspects of IAP.

Summary

IAP primarily originates and acts in the intestinal tract but affects other organs through specific biological axes related to its fundamental roles such as promoting gut barrier function, dephosphorylation/detoxification of lipopolysaccharides (LPS), and regulation of gut microbiota.

Key Messages

Numerous studies reporting on the different roles and the potential therapeutic value of IAP across species have been published during the last decade. While IAP deficiency is linked to varying degrees of physiological dysfunctions across multiple organ systems, the supplementation of IAP has been proven to be beneficial in several translational and clinical studies. The increasing evidence of the salutary functions of IAP underlines the significance of the naturally occurring brush border enzyme.

Recent advances in intestinal alkaline phosphatase, inflammation, and nutrition

In recent years, much new data on intestinal alkaline phosphatase (IAP) have been published, and major breakthroughs have been disclosed. The aim of the present review is to critically analyze the publications released over the last 5 years. These breakthroughs include, for example, the direct implication of IAP in intestinal tight junction integrity and barrier function maintenance; chronic intestinal challenge with low concentrations of Salmonella generating long-lasting depletion of IAP and increased susceptibility to inflammation; the suggestion that genetic mutations in the IAP gene in humans contribute to some forms of chronic inflammatory diseases and loss of functional IAP along the gut and in stools; stool IAP as an early biomarker of incipient diabetes in humans; and omega-3 fatty acids as direct inducers of IAP in intestinal tissue. Many recent papers have also explored the prophylactic and therapeutic potential of IAP and other alkaline phosphatase (AP) isoforms in various experimental settings and diseases. Remarkably, nearly all data confirm the potent anti-inflammatory properties of (I)AP and the negative consequences of its inhibition on health. A simplified model of the body AP system integrating the IAP compartment is provided. Finally, the list of nutrients and food components stimulating IAP has continued to grow, thus emphasizing nutrition as a potent lever for limiting inflammation.

Organic anion transporters 1 and 3 influence cellular energy metabolism in renal proximal tubule cells

Organic anion transporters (OATs) 1 and 3 are, besides being uptake transporters, key in several cellular metabolic pathways. The underlying mechanisms are largely unknown. Hence, we used human conditionally immortalized proximal tubule epithelial cells (ciPTEC) overexpressing OAT1 or OAT3 to gain insight into these mechanisms. In ciPTEC-OAT1 and -OAT3, extracellular lactate levels were decreased (by 77% and 71%, respectively), while intracellular ATP levels remained unchanged, suggesting a shift towards an oxidative phenotype upon OAT1 or OAT3 overexpression. This was confirmed by increased respiration of ciPTEC-OAT1 and -OAT3 (1.4-fold), a decreased sensitivity to respiratory inhibition, and characterized by a higher demand on mitochondrial oxidative capacity. In-depth profiling of tricarboxylic acid (TCA) cycle metabolites revealed reduced levels of intermediates converging into α-ketoglutarate in ciPTEC-OAT1 and -OAT3, which via 2-hydroxyglutarate metabolism explains the increased respiration. These interactions with TCA cycle metabolites were in agreement with metabolomic network modeling studies published earlier. Further studies using OAT or oxidative phosphorylation (OXPHOS) inhibitors confirmed our idea that OATs are responsible for increased use and synthesis of α-ketoglutarate. In conclusion, our results indicate an increased α-ketoglutarate efflux by OAT1 and OAT3, resulting in a metabolic shift towards an oxidative phenotype.

Recombinant Alkaline Phosphatase Prevents Acute on Chronic Liver Failure

The lipopolysaccharide (LPS)– toll-like receptor-4 (TLR4) pathway plays an important role in liver failure. Recombinant alkaline phosphatase (recAP) deactivates LPS. The aim of this study was to determine whether recAP prevents the progression of acute and acute-on-chronic liver failure (ACLF). Eight groups of rats were studied 4-weeks after sham surgery or bile duct ligation and were injected with saline or LPS to mimic ACLF. Acute liver failure was induced with Galactosamine-LPS and in both models animals were treated with recAP prior to LPS administration. In the ACLF model, the severity of liver dysfunction and brain edema was attenuated by recAP, associated with reduction in cytokines, chemokines, liver cell death, and brain water. The activity of LPS was reduced by recAP. The treatment was not effective in acute liver failure. Hepatic TLR4 expression was reduced by recAP in ACLF but not acute liver failure. Increased sensitivity to endotoxins in cirrhosis is associated with upregulation of hepatic TLR4, which explains susceptibility to development of ACLF whereas acute liver failure is likely due to direct hepatoxicity. RecAP prevents multiple organ injury by reducing receptor expression and is a potential novel treatment option for prevention of ACLF but not acute liver failure.

Alkaline phosphatase: a potential biomarker for stroke and implications for treatment

Stroke is the fifth leading cause of death in the U.S., with more than 100,000 deaths annually. There are a multitude of risks associated with stroke, including aging, cardiovascular disease, hypertension, Alzheimer's disease (AD), and immune suppression. One of the many challenges, which has so far proven to be unsuccessful, is the identification of a cost-effective diagnostic or prognostic biomarker for stroke. Alkaline phosphatase (AP), an enzyme first discovered in the 1920s, has been evaluated as a potential biomarker in many disorders, including many of the co-morbidities associated with stroke. This review will examine the basic biology of AP, and its most common isoenzyme, tissue nonspecific alkaline phosphatase (TNAP), with a specific focus on the central nervous system. It examines the preclinical and clinical evidence which supports a potential role for AP in stroke and suggests potential mechanism(s) of action for AP isoenzymes in stroke. Lastly, the review speculates on the clinical utility of AP isoenzymes as potential blood biomarkers for stroke or as AP-targeted treatments for stroke patients.