Macrophage depletion ameliorates glycerol-induced acute kidney injury in mice

Elevated plasma myoglobin level is closely associated with type 2 diabetic kidney disease

BACKGROUND

Diabetic kidney disease (DKD) is the most frequent complication in patients with type 2 diabetes mellitus (T2DM). It causes a chronic and progressive decline in kidney function, and ultimately patients require renal replacement therapy. To date, an increasing number of clinical studies have been conducted to explore the potential and novel biomarkers, which can advance the diagnosis, estimate the prognosis, and optimize the therapeutic strategies at the early stage of DKD. In the current study, we sought to investigate the association of plasma myoglobin with DKD.

METHODS

A total of 355 T2DM patients with DKD and 710 T2DM patients without DKD were enrolled in this study. Laboratory parameters including blood cell count, hemoglobin A1c, biochemical parameters, and plasma myoglobin were recorded. Patients were classified on admission according to the tertile of myoglobin and clinical parameters were compared between the groups. Pearson correlation analysis, linear regression, logistic regression, receiver operating characteristics (ROC) analysis, and spline regression were performed.

RESULTS

Plasma myoglobin significantly increased in patients with DKD and was associated with renal function and inflammatory parameters. Plasma myoglobin was an independent risk factor for the development of DKD. The area under ROC curve of myoglobin was 0.831. Spline regression showed that there was a significant linear association between DKD incidence and a high level of plasma myoglobin when it exceeded 36.4 mg/mL.

CONCLUSIONS

This study shows that elevated plasma myoglobin level is closely associated with the development of kidney injury in patients with T2DM.

Depletion of macrophages with clodronate liposomes partially attenuates renal fibrosis on AKI-CKD transition

Clodronate liposomes are bisphosphonates encapsulated by liposomes that are known to induce macrophage depletion in vivo. In a previous study, clodronate liposomes improved renal ischemia/reperfusion (I/R) injury in mice, which may be due to effects on macrophage phenotypes. However, how inflammatory cytokines secretion participates is unknown. In this study, we investigated the effect of macrophages in the I/R kidney by depleting macrophages with clodronate liposomes and changing inflammatory cytokines. C57BL/6 mice underwent I/R injury with or without clodronate liposomes administration on Days 5 and 15. Tubular injury, collagen deposition, and fibrosis were detected and analyzed by histological staining, immunocytochemistry (IHC), flow cytometry (FACS), and reverse transcription-polymerase chain reaction (RT-PCR). Inflammatory cytokines were detected and analyzed by Western blotting and RT-PCR. We found that clodronate liposomes alleviated renal fibrosis and tissue damage on both Days 5 and 15. KIM-1, IL-10, and TGF-β were reduced significantly in the clodronate liposomes treatment group. However, TNF-α was not different between the clodronate liposomes treatment group and the phosphate-buffered saline treatment group on either Day 5 or Day 15. Thus, clodronate liposomes can alleviate renal fibrosis and tissue damage and reduce the inflammatory cytokines IL-10 and TGF-β, suggesting that clodronate liposomes alleviate renal fibrosis may because of M1/M2 polarization.

Dietary docosahexaenoic acid plays an opposed role in ferroptotic and non-ferroptotic acute kidney injury

Ferroptosis due to polyunsaturated fatty acid (PUFA) peroxidation has been implicated in the pathogenesis of acute kidney injury (AKI), suggesting the risk of dietary intake of PUFA for people susceptible to AKI. Clinically, however, in addition to ferroptosis, other mechanisms also contribute to different types of AKI such as inflammation associated necroptosis and pyroptosis. Therefore, the role of PUFA, especially ω3 PUFA which is a common food supplement, in various AKIs deserves further evaluation. In this study, rhabdomyolysis- and folic acid-induced AKI (Rha-AKI and FA-AKI) were established in mice fed with different fatty acids Histology of kidney, blood urea nitrogen and creatinine, lipid peroxidation, and inflammatory factors were examined. Results showed that these two types of AKIs had diametrically different pathogenesis indicated by that ferrostatin-1 (Fer-1), a lipid antioxidant, can attenuate FA-AKI rather than Rha-AKI. Further, dietary DHA (provided by fish oil) reduced tubular injury and renal lesion by inhibiting peroxidation and inflammation in mice with Rha-AKI while increasing cell death, tissue damage, peroxidation and inflammation in mice with FA-AKI. In human renal tubular epithelial cell line HK-2, MTT assay and DHE staining showed that both myoglobin and ferroptosis inducers can cause cell death and oxidative stress. Ferroptosis inducer-induced cell death was promoted by DHA, while such result was not observed in myoglobin-induced cell death when adding DHA. This study illustrates that the mechanisms of AKI might be either ferroptosis dependent or -independent and the deterioration effect of dietary DHA depends on whether ferroptosis is involved.

Administration of a single dose of lithium ameliorates rhabdomyolysis-associated acute kidney injury in rats

Rhabdomyolysis is characterized by muscle damage and leads to acute kidney injury (AKI). Clinical and experimental studies suggest that glycogen synthase kinase 3β (GSK3β) inhibition protects against AKI basically through its critical role in tubular epithelial cell apoptosis, inflammation and fibrosis. Treatment with a single dose of lithium, an inhibitor of GSK3β, accelerated recovery of renal function in cisplatin and ischemic/reperfusion-induced AKI models. We aimed to evaluate the efficacy of a single dose of lithium in the treatment of rhabdomyolysis-induced AKI. Male Wistar rats were allocated to four groups: Sham, received saline 0.9% intraperitoneally (IP); lithium (Li), received a single IP injection of lithium chloride (LiCl) 80 mg/kg body weight (BW); glycerol (Gly), received a single dose of glycerol 50% 5 mL/kg BW intramuscular (IM); glycerol plus lithium (Gly+Li), received a single dose of glycerol 50% IM plus LiCl IP injected 2 hours after glycerol administration. After 24 hours, we performed inulin clearance experiments and collected blood / kidney / muscle samples. Gly rats exhibited renal function impairment accompanied by kidney injury, inflammation and alterations in signaling pathways for apoptosis and redox state balance. Gly+Li rats showed a remarkable improvement in renal function as well as kidney injury score, diminished CPK levels and an overstated decrease of renal and muscle GSK3β protein expression. Furthermore, administration of lithium lowered the amount of macrophage infiltrate, reduced NFκB and caspase renal protein expression and increased the antioxidant component MnSOD. Lithium treatment attenuated renal dysfunction in rhabdomyolysis-associated AKI by improving inulin clearance and reducing CPK levels, inflammation, apoptosis and oxidative stress. These therapeutic effects were due to the inhibition of GSK3β and possibly associated with a decrease in muscle injury.

Molecular Mechanisms of Rhabdomyolysis-Induced Kidney Injury: From Bench to Bedside

Rhabdomyolysis-induced acute kidney injury (RIAKI) occurs following damage to the muscular sarcolemma sheath, resulting in the leakage of myoglobin and other metabolites that cause kidney damage. Currently, the sole recommended clinical treatment for RIAKI is aggressive fluid resuscitation, but other potential therapies, including pretreatments for those at risk for developing RIAKI, are under investigation. This review outlines the mechanisms and clinical significance of RIAKI, investigational treatments and their specific targets, and the status of ongoing research trials.

Functional consequence of myeloid ferritin heavy chain on acute and chronic effects of rhabdomyolysis-induced kidney injury

Acute kidney injury (AKI) is a serious complication of rhabdomyolysis that significantly impacts survival. Myoglobin released from the damaged muscle accumulates in the kidney, causing heme iron-mediated oxidative stress, tubular cell death, and inflammation. In response to injury, myeloid cells, specifically neutrophils and macrophages, infiltrate the kidneys, and mediate response to injury. Ferritin, comprised of ferritin light chain and ferritin heavy chain (FtH), is vital for intracellular iron handling. Given the dominant role of macrophages and heme-iron burden in the pathogenesis of rhabdomyolysis, we studied the functional role of myeloid FtH in rhabdomyolysis-induced AKI and subsequent fibrosis. Using two models of rhabdomyolysis induced AKI, we found that during the acute phase, myeloid FtH deletion did not impact rhabdomyolysis-induced kidney injury, cell death or cell proliferation, suggesting that tubular heme burden is the dominant injury mechanism. We also determined that, while the kidney architecture was markedly improved after 28 days, tubular casts persisted in the kidneys, suggesting sustained damage or incomplete recovery. We further showed that rhabdomyolysis resulted in an abundance of disparate intra-renal immune cell populations, such that myeloid populations dominated during the acute phase and lymphoid populations dominated in the chronic phase. Fibrotic remodeling was induced in both genotypes at 7 days post-injury but continued to progress only in wild-type mice. This was accompanied by an increase in expression of pro-fibrogenic and immunomodulatory proteins, such as transforming growth factor-β, S100A8, and tumor necrosis factor-α. Taken together, we found that while the initial injury response to heme burden was similar, myeloid FtH deficiency was associated with lesser interstitial fibrosis. Future studies are warranted to determine whether this differential fibrotic remodeling will render these animals more susceptible to a second AKI insult or progress to chronic kidney disease at an accelerated pace.

Pifithrin-α ameliorates glycerol induced rhabdomyolysis and acute kidney injury by reducing p53 activation

Objectives

Rhabdomyolysis is a series of symptoms caused by the dissolution of striped muscle, and acute kidney injury (AKI) is a potential complication of severe rhabdomyolysis. The underlying causes of AKI are remarkably complex and diverse. Here, we aim to investigate whether pifithrin-α protected against rhabdomyolysis-induced AKI and to determine the involved mechanisms.

Methods

Intramuscular injection in the right thigh caudal muscle of C57BL/6J mice with 7.5 ml/kg saline (Group A) or of the same volume 50% glycerol was used to induce rhabdomyolysis and subsequent AKI (Group B). Pifithrin-α was injected intraperitoneally 4 h before (Group C) or 4 h after (Group D) the glycerol injection. Serum creatine kinase, blood urea nitrogen, and creatinine were determined, and the renal cortex was histologically analyzed. Renal expression levels of interested mRNAs and proteins were determined and compared, too.

Results

Intramuscular injection of glycerol induced rhabdomyolysis and subsequent AKI in mice (Groups B–D). Renal function reduction and histologic injury of renal tubular epithelial cells were associated with increased p53 activation, oxidative stress, and inflammation. Notably, compared with pifithrin-α rescue therapy (Group D), pretreatment of pifithrin-α (Group C) protected the mice from severe injury more effectively.

Conclusions

Our present study suggests that p53 may be a therapeutic target of AKI caused by glycerol, and the inhibition of p53 can block glycerol-mediated AKI by using pharmacological agents instead of genetic inhibitory approaches, which further supports that p53 played a pivotal role in renal tubular injury when challenged with glycerol.

Rhodomeroterpene alleviates macrophage infiltration and the inflammatory response in renal tissue to improve acute kidney injury

Inflammation is broadly recognized as an important factor in the pathogenesis of acute kidney injury (AKI), but pharmacological approaches to alleviate inflammation in AKI have not been proved successful in clinical trials. Macrophage infiltration into renal tissue promotes inflammatory responses that contribute to the pathogenesis of AKI. Suppression of renal tissue inflammatory responses is postulated to improve renal injury of patients and animals. Rhodomeroterpene (RMT) is a novel meroterpenoid isolated from the Rhododendron genus that was shown to exert anti-inflammatory action in vivo or in vitro in this study. We investigated the treatment effects of RMT on LPS-induced sepsis and two different AKI models. The results showed that pretreatment with RMT (30 mg kg^-1  d^-1 , ip, for 3 days) significantly inhibited acute inflammatory responses in LPS-induced septic mice. In both renal ischemia-reperfusion injury (I/R) and sepsis-induced AKI models, RMT (30 mg kg^-1  d^-1 , ip, for 3 days) ameliorated renal function and injury and alleviated inflammation by reducing the infiltration of immune cells, including macrophages and neutrophils. Furthermore, our study demonstrated that RMT inhibits inflammatory responses in macrophages. The anti-inflammatory effects of RMT may be due to the inactivation of the IKK/NF-κB and PI3K/PDK1/Akt inflammatory signaling pathways in macrophages. Collectively, our findings indicate that RMT ameliorates renal injury and alleviates the renal inflammatory state in different AKI models, suggesting that RMT may be a potential agent for the treatment of AKI.

Chloroquine inhibits pro-inflammatory effects of heme on macrophages and invivo

BACKGROUND

Chloroquine has been used successfully to treat Malaria, including by chloroquine-resistant Plasmodium sp., indicating that it has effects on disease itself. Since heme has inflammatory effects and contributes to the pathogenesis of hemolytic diseases, we hypothesize that the anti-inflammatory effect of chloroquine is partially due to its inhibitory effect on heme-induced macrophage activation and on inflammatory tissue damage.

METHODS

Bone marrow derived macrophages (BMDMs) were incubated with chloroquine before stimulation with heme, in different conditions, to evaluate cytokines secretion, ROS production, mitogen activated protein kinases (MAPK) or spleen tyrosine kinase (Syk) activation, alone or combined with LPS. The effects of chloroquine upon heme inflammation were also evaluated in vivo, through simultaneous i.p. injection of LPS and heme, intratracheal instillation of Poly-IC followed by heme injection, and in a rhabdomyolysis model.

RESULTS

Chloroquine inhibited TNF secretion, mitochondrial ROS production, MAPK, and Syk activation induced by heme. Inhibition of TNF production could be mimicked by zinc ionophore quercetin, but not by primaquine, a chloroquine analog with low affinity for heme. IL-6 and IL-1β secretions induced by heme in the presence of PRRs agonists were inhibited by chloroquine, but not by calcium chelator BAPTA or inhibitor of endosomal acidification concamycin B. Chloroquine also protected mice from heme inflammatory effects in vivo, inhibiting lethal synergism with PRR agonists, lung pathology caused by heme injection after intratracheal instillation of Poly-IC, and delaying death after rhabdomyolisis.

CONCLUSION

Our data indicate that chloroquine might be used as a supportive therapy to control heme-induced deleterious inflammation in different hemolytic diseases.

Thalidomide reduces glycerol-induced acute kidney injury by inhibition of NF-κB, NLRP3 inflammasome, COX-2 and inflammatory cytokines

Acute kidney injury (AKI) is an important clinical complication of rhabdomyolysis. The inflammatory processes are involved in the pathogenesis of AKI induced by rhabdomyolysis. Thalidomide is an anti-inflammatory agent that has been used in the treatment of inflammatory disorders. The aim of this study was to investigate the therapeutic effect of thalidomide and its underlying mechanisms on a mouse model of rhabdomyolysis-induced AKI. Mice were injected with a single dose of glycerol (50%, 10 ml/kg, im) to induce AKI, and treated with thalidomide (40 and 80 mg/kg/day, orally) for 2 days. Renal tissue and blood samples were collected for histological and biochemical analysis. In thalidomide treated mice, blood urea nitrogen (BUN) (59.3 ± 19.6 vs. 223 ± 33 mg/dl), plasma creatinine (0.58 ± 0.3 vs. 1.28 ± 0.3 mg/dl), relative kidney weight (0.93 ± 0.13% vs. 1.22 ± 0.1%) and histopathological damage (1.5 ± 0.8 vs. 3.3 ± 1.1 score) were significantly lower as compared to the glycerol group. The results also showed that the levels of malondialdehyde (MDA) (0.13 ± 0.02 vs. 0.2 ± 0.01 µM/mg), myeloperoxidase (MPO) (0.1 ± 0.05 vs. 0.25 ± 0.02 U/mg) and the expression of nuclear factor kappa B (NF-κB) (1.7-fold), NLRP3 inflammasome (1.4-fold) and cyclooxygenase (COX)-2 (3-fold) in renal tissue were significantly lower in thalidomide treated group than those in the glycerol group. Thalidomide treatment resulted in lower renal pro-inflammatory cytokines tumor necrosis factor (TNF)-α (6.7 ± 0.8 vs. 12.3 ± 1.2 ng/ml), interleukin (IL)-1β (3.2 ± 0.5 vs. 5.1 ± 0.3 pg/mg), IL-6 (24.7 ± 2.4 vs. 33 ± 3 pg/mg) and transforming growth factor (TGF)-β1 (0.6 ± 0.17 vs. 1.56 ± 0.24 ng/ml) than those in the glycerol treated mice. In addition the levels of monocyte chemoattractant protein (MCP)-1 (9.5 ± 1 vs. 12.8 ± 1.1 pg/mg) and intercellular adhesion molecule (ICAM)-1 (22.8 ± 7.8 vs. 53.3 ± 5.5 pg/mg) were significantly lower in renal tissue of mice treated with thalidomide as compared to the glycerol treated mice. In conclusion these data revealed that thalidomide may be a potential therapeutic approach against rhabdomyolysis-induced AKI through inhibition of inflammatory responses.

Emerging medical therapies in crush syndrome - progress report from basic sciences and potential future avenues

Crush injury is a disease that is commonly found in victims of earthquakes, debris flows, mine disasters, explosions, terrorist attacks, local wars, and other accidents. The complications that arise due to the crush injury inflicted on victims give rise to crush syndrome (CS). If not treated in time, the mortality rate of CS is very high. The most important measure that can be taken to reduce mortality in such situations is to immediately start treatment. However, the traditional treatment methods such as fluid resuscitation, diuresis, and hemodialysis are not feasible enough to be carried out at the disaster scene. So there is a need for developing new treatments that are efficient and convenient. Because it is difficult to diagnose in the disaster area and reach the treatment equipment and treat on time. It has become a new research needs to be directed into identifying new medical treatment targets and methods using the etiology and pathophysiological mechanisms of CS. In recent years, a large number of new anti-oxidant and anti-inflammatory drug therapies have been shown to be highly efficacious in CS rat/mouse models. Some of them are expected to become specific drugs for the emergency treatment of a large number of patients who may develop CS in the aftermath of earthquakes, wars, and other disasters in the future. Hence, we have reviewed the latest research on the medical therapy of CS as a source for anyone wishing to pursue research in this direction.

Toll-like receptor 4: An attractive therapeutic target for acute kidney injury

Acute kidney injury (AKI) is a progressive renal complication which significantly affects the patient's life with huge economic burden. Untreated acute kidney injury eventually progresses to a chronic form and end-stage renal disease. Although significant breakthroughs have been made in recent years, there are still no effective pharmacological therapies for the treatment of acute kidney injury. Toll-like receptor 4 (TLR4) is a well-characterized pattern recognition receptor, and increasing evidence has shown that TLR4 mediated inflammatory response plays a pivotal role in the pathogenesis of acute kidney injury. The expression of TLR4 has been seen in resident renal cells, including podocytes, mesangial cells, tubular epithelial cells and endothelial cells. Activation of TLR4 signaling regulates the transcription of numerous pro-inflammatory cytokines and chemokines, resulting in renal inflammation. Therefore, targeting TLR4 and its downstream effectors could serve as an effective therapeutic intervention to prevent renal inflammation and subsequent kidney damage. For the first time, this review summarizes the literature on acute kidney injury from the perspective of TLR4 from year 2010 to 2020. In the current review, the role of TLR4 signaling pathway in AKI with preclinical evidence is discussed. Furthermore, we have highlighted several compounds of natural and synthetic origin, which have the potential to avert the renal TLR4 signaling in preclinical AKI models and have shown protection against AKI. This scientific review provides new ideas for targeting TLR4 in the treatment of AKI and provides strategies for the drug development against AKI.

Abnormal liver function tests associated with severe rhabdomyolysis

Rhabdomyolysis is a syndrome of skeletal muscle injury with release of cellular constituents such as potassium, phosphate, urate and intracellular proteins such as myoglobin into the circulation, which may cause complications including acute kidney injury, electrolyte disturbance and cardiac instability. Abnormal liver function tests are frequently observed in cases of severe rhabdomyolysis. Typically, there is an increase in serum aminotransferases, namely aspartate aminotransferase and alanine aminotransferase. This raises the question of liver injury and often triggers a pathway of investigation which may lead to a liver biopsy. However, muscle can also be a source of the increased aminotransferase activity. This review discusses the dilemma of finding abnormal liver function tests in the setting of muscle injury and the potential implications of such an association. It delves into some of the clinical and experimental evidence for correlating muscle injury to raised aminotransferases, and discusses pathophysiological mechanisms such as oxidative stress which may cause actual liver injury. Serum aminotransferases lack tissue specificity to allow clinicians to distinguish primary liver injury from muscle injury. This review also explores potential approaches to improve the accuracy of our diagnostic tools, so that excessive or unnecessary liver investigations can be avoided.

The Impact of Versatile Macrophage Functions on Acute Kidney Injury and Its Outcomes

Acute kidney injury (AKI) is a common and devastating clinical condition with a high morbidity and mortality rate and is associated with a rapid decline of kidney function mostly resulting from the injury of proximal tubules. AKI is typically accompanied by inflammation and immune activation and involves macrophages (Mϕ) from the beginning: The inflamed kidney recruits “classically” activated (M1) Mϕ, which are initially poised to destroy potential pathogens, exacerbating inflammation. Of note, they soon turn into “alternatively” activated (M2) Mϕ and promote immunosuppression and tissue regeneration. Based on their roles in kidney recovery, there is a growing interest to use M2 Mϕ and Mϕ-modulating agents therapeutically against AKI. However, it is pertinent to note that the clinical translation of Mϕ-based therapies needs to be critically reviewed and questioned since Mϕ are functionally plastic with versatile roles in AKI and some Mϕ functions are detrimental to the kidney during AKI. In this review, we discuss the current state of knowledge on the biology of different Mϕ subtypes during AKI and, especially, on their role in AKI and assess the impact of versatile Mϕ functions on AKI based on the findings from translational AKI studies.

Curcumin relieved cisplatin-induced kidney inflammation through inhibiting Mincle-maintained M1 macrophage phenotype

BACKGROUND

Acute kidney injury (AKI) is a common kidney disease with a high risk of death and can develop into chronic kidney disease (CKD) and renal failure eventually. Curcumin, an herbal supplement, has been reported exhibiting a renoprotective role in AKI. However, the underlying mechanism is largely unclear.

PURPOSE

Recent research showed that Mincle (Macrophage-inducible C-type lectin) maintained M1 macrophage polarization, which plays a key role in kidney injury of AKI through up-regulating the expression and secretion of inflammatory cytokines. Here, we investigated the effects of Curcumin on Mincle expression and macrophage polarization in vitro using lipopolysaccharide (LPS) induced macrophage inflammatory cell model and in vivo using a cisplatin induced murine AKI (cis-AKI) model.

METHODS

Cell activation, inflammatory cytokines expression and secretion, protein levels, macrophage polarization and renal pathology were analyzed.

RESULTS

Our results showed that Curcumin markedly reduced the mRNA expression and secretion of IL-1β, IL-6, TNFα and MCP-1 in LPS stimulated RAW264.7 cell and the supernatant. The same results were found in Curcumin treated cis-AKI kidney and blood. The data also demonstrated that Curcumin remarkably down-regulated mRNA expression and protein level of Mincle in cis-AKI kidney and also reduced expression of iNOS (M1 macrophage marker) as well as inhibited the activation of Syk and NF-kB. Interestingly, although Mincle deletion in RAW264.7 cell largely decreased the LPS-induced protein level of iNOS, Curcumin cannot further reduce expression of iNOS without Mincle, indicating that Curcumin inhibits M1 macrophage with a Mincle-dependent pattern. Furthermore, flow cytometry results showed that Curcumin significantly decreased the iNOS positive macrophages and increased the CD206 (M2 macrophage marker) positive macrophages in vivo and in vitro.

CONCLUSION

Our findings prove that Curcumin protects kidney from cisplatin induced AKI through inhibiting Mincle maintained M1 macrophage phenotype, that may provide a specific renoprotection mechanism for Curcumin to develop it as a new therapeutic candidate for AKI.

Pharmacological Inhibition of Macrophage Toll-like Receptor 4/Nuclear Factor-kappa B Alleviates Rhabdomyolysis-induced Acute Kidney Injury

Background:

Acute kidney injury (AKI) is the most common and life-threatening systemic complication of rhabdomyolysis. Inflammation plays an important role in the development of rhabdomyolysis-induced AKI. This study aimed to investigate the kidney model of AKI caused by rhabdomyolysis to verify the role of macrophage Toll-like receptor 4/nuclear factor-kappa B (TLR4/NF-κB) signaling pathway.

Methods:

C57BL/6 mice were injected with a 50% glycerin solution at bilateral back limbs to induce rhabdomyolysis, and CLI-095 or pyrrolidine dithiocarbamate (PDTC) was intraperitoneally injected at 0.5 h before molding. Serum creatinine levels, creatine kinase, the expression of tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6, and hematoxylin and eosin stainings of kidney tissues were tested. The infiltration of macrophage, mRNA levels, and protein expression of TLR4 and NF-κB were investigated by immunofluorescence double-staining techniques, reverse transcriptase-quantitative polymerase chain reaction, and Western blotting, respectively. In vitro, macrophage RAW264.7 was stimulated by ferrous myoglobin; the cytokines, TLR4 and NF-κB expressions were also detected.

Results:

In an in vivo study, using CLI-095 or PDTC to block TLR4/NF-κB, functional and histologic results showed that the inhibition of TLR4 or NF-κB alleviated glycerol-induced renal damages (P < 0.01). CLI-095 or PDTC administration suppressed proinflammatory cytokine (TNF-α, IL-6, and IL-1β) production and macrophage infiltration into the kidney (P < 0.01). Moreover, in an in vitro study, CLI-095 or PDTC suppressed myoglobin-induced expression of TLR4, NF-κB, and proinflammatory cytokine levels in macrophage RAW264.7 cells (P < 0.01).

Conclusion:

The pharmacological inhibition of TLR4/NF-κB exhibited protective effects on rhabdomyolysis-induced AKI by the regulation of proinflammatory cytokine production and macrophage infiltration.

Kidney disease models: tools to identify mechanisms and potential therapeutic targets

Acute kidney injury (AKI) and chronic kidney disease (CKD) are worldwide public health problems affecting millions of people and have rapidly increased in prevalence in recent years. Due to the multiple causes of renal failure, many animal models have been developed to advance our understanding of human nephropathy. Among these experimental models, rodents have been extensively used to enable mechanistic understanding of kidney disease induction and progression, as well as to identify potential targets for therapy. In this review, we discuss AKI models induced by surgical operation and drugs or toxins, as well as a variety of CKD models (mainly genetically modified mouse models). Results from recent and ongoing clinical trials and conceptual advances derived from animal models are also explored.

Macrophage extracellular trap formation promoted by platelet activation is a key mediator of rhabdomyolysis-induced acute kidney injury

Rhabdomyolysis is a serious syndrome caused by skeletal muscle injury and the subsequent release of breakdown products from damaged muscle cells into systemic circulation. The muscle damage most often results from strenuous exercise, muscle hypoxia, medications, or drug abuse and can lead to life-threatening complications, such as acute kidney injury (AKI). Rhabdomyolysis and the AKI complication can also occur during crush syndrome, an emergency condition that commonly occurs in victims of natural disasters, such as earthquakes, and man-made disasters, such as wars and terrorism. Myoglobin released from damaged muscle is believed to trigger renal dysfunction in this form of AKI. Recently, macrophages were implicated in the disease pathogenesis of rhabdomyolysis-induced AKI, but the precise molecular mechanism remains unclear. In the present study, we show that macrophages released extracellular traps (ETs) comprising DNA fibers and granule proteins in a mouse model of rhabdomyolysis. Heme-activated platelets released from necrotic muscle cells during rhabdomyolysis enhanced the production of macrophage extracellular traps (METs) through increasing intracellular reactive oxygen species generation and histone citrullination. Here we report, for the first time to our knowledge, this unanticipated role for METs and platelets as a sensor of myoglobin-derived heme in rhabdomyolysis-induced AKI. This previously unknown mechanism might be targeted for treatment of the disease. Finally, we found a new therapeutic tool for prevention of AKI after rhabdomyolysis, which might rescue some sufferers of this pathology.

Phenotypic Characterization of Macrophages from Rat Kidney by Flow Cytometry

There is increasing evidence suggesting the important role of inflammation and, subsequently, macrophages in the development and progression of renal disease. Macrophages are heterogeneous cells that have been implicated in kidney injury. Macrophages may be classified into two different phenotypes: classically activated macrophages (M1 macrophages), that release pro-inflammatory cytokines and promote fibrosis; and alternatively activated macrophages (M2 macrophages) that are associated with immunoregulatory and tissue-remodeling functions. These macrophage phenotypes need to be discriminated and analyzed to determine their contribution to renal injury. However, there are scarce studies reporting consistent phenotypic and functional information about macrophage subtypes in inflammatory renal disease models, especially in rats. This fact may be related to the limited macrophage markers used in rats, contrary to mice. Therefore, novel strategies are necessary to quantify and characterize the renal content of these infiltrating cells in a reliable way. This manuscript details a protocol for kidney digestion and further phenotypic and quantitative analysis of macrophages from rat kidneys by flow cytometry. Briefly, kidneys were incubated with collagenase and total macrophages were identified according to the dual presence of CD45 (leukocytes common antigen) and CD68 (PAN macrophage marker) in live cells.This was followed by surface staining of CD86 (M1 marker) and CD163 (M2 marker). Rat peritoneal macrophages were used as positive control for macrophage marker detection by flow cytometry. Our protocol resulted in low cellular mortality and allowed characterization of different intracellular and surface protein markers, thus limiting the loss of cellular integrity observed in other protocols. Moreover, this procedure allows the use of macrophages for further techniques, including cell sorting and mRNA or protein expression studies, among others.

CD163-Macrophages Are Involved in Rhabdomyolysis-Induced Kidney Injury and May Be Detected by MRI with Targeted Gold-Coated Iron Oxide Nanoparticles

Macrophages play an important role in rhabdomyolysis-acute kidney injury (AKI), although the molecular mechanisms involved in macrophage differentiation are poorly understood. We analyzed the expression and regulation of CD163, a membrane receptor mainly expressed by anti-inflammatory M2 macrophages, in rhabdomyolysis-AKI and developed targeted probes for its specific detection in vivo by MRI. Intramuscular injection of glycerol in mice promoted an early inflammatory response, with elevated proportion of M1 macrophages, and partial differentiation towards a M2 phenotype in later stages, where increased CD163 expression was observed. Immunohistological studies confirmed the presence of CD163-macrophages in human rhabdomyolysis-AKI. In cultured macrophages, myoglobin upregulated CD163 expression via HO-1/IL-10 axis. Moreover, we developed gold-coated iron oxide nanoparticles vectorized with an anti-CD163 antibody that specifically targeted CD163 in kidneys from glycerol-injected mice, as determined by MRI studies, and confirmed by electron microscopy and immunological analysis. Our findings are the first to demonstrate that CD163 is present in both human and experimental rhabdomyolysis-induced AKI, suggesting an important role of this molecule in this pathological condition. Therefore, the use of probes targeting CD163-macrophages by MRI may provide important information about the cellular composition of renal lesion in rhabdomyolysis.

The natural behavior of mononuclear phagocytes in HTS formation

Hypertrophic scars (HTS) are caused by trauma or burn injuries to the deep dermis and are considered fibrosis in the skin. Monocytes, M1 and M2 macrophages are mononuclear phagocytes. Studies suggest that M2 macrophages are profibrotic and might contribute to HTS formation. Our lab has established a human HTS-like nude mouse model, in which the grafted human skin develops red, raised, and firm scarring, resembling HTS seen in humans. In this study, we observed the natural behavior of mononuclear phagocyte system in this nude mouse model of dermal fibrosis at multiple time points. Thirty athymic nude mice received human skin grafts and an equal number of mice received mouse skin grafts as controls. The grafted skin and blood were harvested at 1, 2, 3, 4, and 8 weeks. Wound area, thickness, collagen morphology and level, the cell number of myofibroblasts, M1- and M2-like macrophages in the grafted skin, as well as monocyte fraction in the blood were investigated at each time points. Xenografted mice developed contracted and thickened scars grossly. The xenografted skin resembled human HTS tissue based on enhanced thickness, fibrotic orientation of collagen bundles, increased collagen level, and infiltration of myofibroblasts. In the blood, monocytes dramatically decreased at 1 week postgrafting and gradually returned to normal in the following 8 weeks. In the xenografted skin, M1-like macrophages were found predominantly at 1-2 weeks postgrafting; whereas, M2-like macrophages were abundant at later time points, 3-4 weeks postgrafting coincident with the development of fibrosis in the human skin tissues. This understanding of the natural behavior of mononuclear phagocytes in vivo in our mouse model provides evidence for the role of M2-like macrophages in fibrosis of human skin and suggests that macrophage depletion in the subacute phases of wound healing might reduce or prevent HTS formation.

Leucine-rich repeat kinase 2 deficiency is protective in rhabdomyolysis-induced kidney injury

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common known genetic cause of Parkinson's disease, and LRRK2 is also linked to Crohn's and Hansen's disease. LRRK2 is expressed in many organs in mammals but is particularly abundant in the kidney. We find that LRRK2 protein is predominantly localized to collecting duct cells in the rat kidney, with much lower expression in other kidney cells. While genetic knockout (KO) of LRRK2 expression is well-tolerated in mice and rats, a unique age-dependent pathology develops in the kidney. The cortex and medulla of LRRK2 KO rat kidneys become darkly pigmented in early adulthood, yet aged animals display no overt signs of kidney failure. Accompanying the dark pigment we find substantial macrophage infiltration in LRRK2 KO kidneys, suggesting the presence of chronic inflammation that may predispose to kidney disease. Unexpectedly, the dark kidneys of the LRRK2 KO rats are highly resistant to rhabdomyolysis-induced acute kidney injury compared with wild-type rats. Biochemical profiling of the LRRK2 KO kidneys using immunohistochemistry, proteomic and lipidomic analyses show a massive accumulation of hemoglobin and lipofuscin in renal tubules that account for the pigmentation. The proximal tubules demonstrate a corresponding up-regulation of the cytoprotective protein heme oxygenase-1 (HO-1) which is capable of mitigating acute kidney injury. The unusual kidney pathology of LRRK2 KO rats highlights several novel physiological roles for LRRK2 and provides indirect evidence for HO-1 expression as a protective mechanism in acute kidney injury in LRRK2 deficiency.