Alda-1, an aldehyde dehydrogenase-2 agonist, causes deterioration in renal functions following ischemia-reperfusion injury due to crystalline nephropathy

From Rare Disorders of Kidney Tubules to Acute Renal Injury: Progress and Prospective

Background

Acute kidney injury (AKI) is a severe condition marked by rapid renal function deterioration and elevated mortality, with traditional biomarkers lacking sensitivity and specificity. Rare tubulointerstitial diseases encompass a spectrum of disorders, primarily including monogenic diseases, immune-related conditions, and drug-induced tubulointerstitial diseases. The clinical manifestations vary from electrolyte and acid-base imbalances to kidney function insufficiency, which is associated with AKI in up to 20% of cases. Evidence indicated that rare tubulointerstitial diseases might provide new conceptual insights and perspectives for novel biomarkers and potential therapeutic strategies for AKI.

Summary

Autosomal dominant tubulointerstitial kidney disease (ADTKD) and Fanconi syndrome (FS) are rare tubulointerstitial diseases. In ADTKD, UMOD and REN are closely related to AKI by affecting oxidative stress and tubuloglomerular feedback, which provide potential new biomarkers for AKI. Both rare tubulointerstitial diseases and AKI share etiologies and treatment responses. From the mechanism standpoint, rare tubulointerstitial diseases and AKI involve tubular transporter injury, initially manifesting as tubular dysfunction in tubulointerstitial disorder and progressing to AKI because of the programmed cell death with apoptosis, pyroptosis, or necroptosis of proximal tubule cells. Additionally, mitochondrial dysfunction has been identified as a common mechanism in both tubulointerstitial diseases and AKI induced by drugs, pSS, or monoclonal diseases. In the end, both AKI and FS patients and animal models responded well to the therapy of the primary diseases.

Key Messages

In this review, we describe an overview of ADTKD and FS to identify their associations with AKI. Mitochondrial dysfunction contributes to rare tubulointerstitial diseases and AKI, which might provide a potential therapeutic target.

Aldehyde dehydrogenase 2 alleviates mitochondrial dysfunction by promoting PGC-1α-mediated biogenesis in acute kidney injury

Renal tubular epithelial cells are one of the high energy-consuming cell types, which mainly depend on mitochondrial energy supply. Aldehyde dehydrogenase 2 (ALDH2) is a key enzyme that is involved in alcohol metabolism and mitochondrial oxidative ATP production; however, its function in mitochondrial homoeostasis in acute kidney injury (AKI) is unclear. Here, we found that ALDH2 expression was predominantly decreased in cisplatin or maleic acid (MA) models both in vivo and in vitro. ALDH2 knockout (KO) mice exhibited exacerbated kidney impairment and apoptosis of tubular epithelial cells after cisplatin injection. In contrast, ALDH2 activation alleviated AKI and tubular cell apoptosis in both cisplatin- and MA-induced models. RNA sequencing revealed that the oxidative phosphorylation pathway was positively enriched in the renal tissues after Alda-1 pre-treatment in MA-induced mice. ALDH2 activation restored mitochondrial structure, mitochondrial membrane potential, and respiration rate, but downregulated glycolysis in MA-induced mice and human renal proximal tubular epithelial (HK-2) cells. Mechanistically, co-immunoprecipitation assays revealed that ALDH2 interacts with peroxisomal proliferator-γ coactivator-1α (PGC-1α), a master regulator of mitochondrial biogenesis, and advanced its nuclear translocation. Subsequently, PGC-1α knockdown almost abolished the improvement of ALDH2 activation on MA-induced tubular epithelial cells damage. Thus, our study revealed that ALDH2 activation alleviated mitochondrial dysfunction in AKI by enhancing PGC-1α-mediated mitochondrial biogenesis. Hence, ALDH2 may act as a potential therapeutic target to prevent AKI progression.

Aldehyde Dehydrogenase 2 Ameliorates LPS-Induced Acute Kidney Injury through Detoxification of 4-HNE and Suppression of the MAPK Pathway

Lipopolysaccharide (LPS)-induced septic acute kidney injury (AKI) is determined as a devastating organ dysfunction elicited by an inappropriate response to infection with high morbidity and mortality rates. Previous evidence has illustrated an indispensable role of mitochondrial aldehyde dehydrogenase 2 (ALDH2) in the pathogenesis of sepsis-induced multiorgan abnormalities. Specifically, this study investigated the potential role of ALDH2 in sepsis-induced AKI. After LPS administration, we observed a significant decline in renal function, increased inflammatory cytokines, oxidative stress, 4-hydroxy-2-nonenal (4-HNE) accumulation, and apoptosis via MAPK activation in ALDH2^-/- mice; in contrast, pretreatment with Alda-1 (an ALDH2 activator) alleviated the LPS-induced dysfunctions in mice. Moreover, in vitro analysis revealed that ALDH2 overexpression in mouse tubular epithelial cells (mTECs) improved the inflammatory response, oxidative stress, 4-HNE accumulation, and apoptosis via MAPK inhibition, whereas ALDH2 knockdown in mTECs aggravated these parameters via MAPK activation. Therefore, ALDH2 may protect against LPS-induced septic AKI by suppressing 4-HNE/MAPK pathway.

Neuroprotective effects of Alda-1 mitigate spinal cord injury in mice: involvement of Alda-1-induced ALDH2 activation-mediated suppression of reactive aldehyde mechanisms

Spinal cord injury (SCI) is associated with high production and excessive accumulation of pathological 4-hydroxy-trans-2-nonenal (4-HNE), a reactive aldehyde, formed by SCI-induced metabolic dysregulation of membrane lipids. Reactive aldehyde load causes redox alteration, neuroinflammation, neurodegeneration, pain-like behaviors, and locomotion deficits. Pharmacological scavenging of reactive aldehydes results in limited improved motor and sensory functions. In this study, we targeted the activity of mitochondrial enzyme aldehyde dehydrogenase 2 (ALDH2) to detoxify 4-HNE for accelerated functional recovery and improved pain-like behavior in a male mouse model of contusion SCI. N-(1,3-benzodioxol-5-ylmethyl)-2,6-dichlorobenzamide (Alda-1), a selective activator of ALDH2, was used as a therapeutic tool to suppress the 4-HNE load. SCI was induced by an impactor at the T9–10 vertebral level. Injured animals were initially treated with Alda-1 at 2 hours after injury, followed by once-daily treatment with Alda-1 for 30 consecutive days. Locomotor function was evaluated by the Basso Mouse Scale, and pain-like behaviors were assessed by mechanical allodynia and thermal algesia. ALDH2 activity was measured by enzymatic assay. 4-HNE protein adducts and enzyme/protein expression levels were determined by western blot analysis and histology/immunohistochemistry. SCI resulted in a sustained and prolonged overload of 4-HNE, which parallels with the decreased activity of ALDH2 and low functional recovery. Alda-1 treatment of SCI decreased 4-HNE load and enhanced the activity of ALDH2 in both the acute and the chronic phases of SCI. Furthermore, the treatment with Alda-1 reduced neuroinflammation, oxidative stress, and neuronal loss and increased adenosine 5′-triphosphate levels stimulated the neurorepair process and improved locomotor and sensory functions. Conclusively, the results provide evidence that enhancing the ALDH2 activity by Alda-1 treatment of SCI mice suppresses the 4-HNE load that attenuates neuroinflammation and neurodegeneration, promotes the neurorepair process, and improves functional outcomes. Consequently, we suggest that Alda-1 may have therapeutic potential for the treatment of human SCI. Animal procedures were approved by the Institutional Animal Care and Use Committee (IACUC) of MUSC (IACUC-2019-00864) on December 21, 2019.

A critical assessment of the potential of pharmacological modulation of aldehyde dehydrogenases to treat the diseases of bone loss

Chronic alcoholism (CA) decreases bone mass and increases the risk of hip fracture. Alcohol and its main metabolite, acetaldehyde impairs osteoblastogenesis by increasing oxidative stress. Aldehyde dehydrogenase (ALDH) is the rate-limiting enzyme in clearing acetaldehyde from the body. The clinical relevance of ALDH in skeletal function has been established by the discovery of single nucleotide polymorphism, SNP (rs671) in the ALDH2 gene giving rise to an inactive form of the enzyme (ALDH2*2) that causes increased serum acetaldehyde and osteoporosis in the affected individuals. Subsequent mouse genetics studies have replicated human phenotype in mice and confirmed the non-redundant role of ALDH2 in bone homeostasis. The activity of ALDH2 is amenable to pharmacological modulation. ALDH2 inhibition by disulfiram (DSF) and activation by alda-1 cause reduction and induction of bone formation, respectively. DSF also inhibits peak bone mass accrual in growing rats. On the other hand, DSF showed an anti-osteoclastogenic effect and protected mice from alcohol-induced osteopenia by inhibiting ALDH1a1 in bone marrow monocytes. Besides DSF, there are several classes of ALDH inhibitors with disparate skeletal effects. Alda-1, the ALDH2 activator induced osteoblast differentiation by increasing bone morphogenic protein 2 (BMP2) expression via ALDH2 activation. Alda-1 also restored ovariectomy-induced bone loss. The scope of structure-activity based studies with ALDH2 and the alda-1-like molecule could lead to the discovery of novel osteoanabolic molecules. This review will critically discuss the molecular mechanism of the ethanol and its principal metabolite, acetaldehyde in the context of ALDH2 in bone cells, and skeletal homeostasis.

Salusin-β mediates tubular cell apoptosis in acute kidney injury: Involvement of the PKC/ROS signaling pathway

Salusin-β is abundantly expressed in many organs and tissues including heart, blood vessels, brain and kidneys. Recent studies have identified salusin-β as a bioactive peptide that contributes to various diseases, such as atherosclerosis, hypertension, diabetes and metabolic syndrome. However, the role of salusin-β in the pathogenesis of acute kidney injury (AKI) is largely unclear. In the present study, we investigated the roles of salusin-β in cisplatin or lipopolysaccharide (LPS)-induced renal injury. Herein, we found that salusin-β expression was upregulated in both renal tubular cells and kidney tissues induced by both cisplatin and LPS. In vitro, silencing of salusin-β diminished, whereas overexpression of salusin-β exaggerated the increased PKC phosphorylation, oxidative stress, histone γH2AX expression, p53 activation and apoptosis in either cisplatin or LPS-challenged renal tubular cells. More importantly, salusin-β overexpression-induced tubular cell apoptosis were abolished by using the PKC inhibitor Go 6976, reactive oxygen species (ROS) scavenger NAC, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor apocynin (Apo) or p53 inhibitor Pifithrin-α. In animals, blockade of salusin-β alleviated PKC phosphorylation, ROS accumulation, DNA damage, and p53 activation as well as renal dysfunction in mice after administration of cisplatin or LPS. Taken together, these results suggest that overexpressed salusin-β is deleterious in AKI by activation of the PKC/ROS signaling pathway, thereby priming renal tubular cells for apoptosis and death.

Aldehyde dehydrogenase-2 activation by Alda-1 decreases necrosis and fibrosis after bile duct ligation in mice

BACKGROUND AND AIM

Liver fibrosis is a leading cause of mortality worldwide. Oxidative stress is a key component in the pathogenesis of liver fibrosis. We investigated the role of aldehyde formation resulting from lipid peroxidation in cholestatic liver injury and fibrosis.

METHODS

C57Bl/6J mice underwent bile duct ligation (BDL) or sham operation. One hour after surgery and daily thereafter, animals were given Alda-1 (20 mg/kg, s.c.), an aldehyde dehydrogenase-2 activator, or equivalent volume of vehicle. Blood and livers were collected after 3 and 14 days.

RESULTS

Serum alanine aminotransferase (ALT) increased from 39.8 U/L after sham operation to 537 U/L 3 days after BDL, which Alda-1 decreased to 281 U/L. Biliary infarcts with a periportal distribution developed with an area of 7.8% at 14 days after BDL versus 0% area after sham operation. Alda-1 treatment with BDL decreased biliary infarcts to 1.9%. Fibrosis detected by picrosirius red staining increased from 1.6% area in sham to 7.3% after BDL, which decreased to 3.8% with Alda-1. Alda-1 suppression of fibrosis was additionally confirmed by second harmonic generation microscopy. After BDL, collagen-I mRNA increased 12-fold compared to sham, which decreased to 6-fold after Alda-1 treatment. Smooth muscle α-actin expression in the liver, a marker of activated stellate cells, increased from 1% area in sham to 18.7% after BDL, which decreased to 5.3% with Alda-1. CD68-positive macrophages increased from 33.4 cells/field in sham to 134.5 cells/field after BDL, which decreased to 64.9 cells/field with Alda-1. Lastly, 4-hydroxynonenal adduct (4-HNE) immunofluorescence increased from 2.5% area in sham to 14.1% after BDL. Alda-1 treatment decreased 4-HNE to 2.2%.

CONCLUSION

Accelerated aldehyde degradation by Alda-1 decreases BDL-induced liver necrosis, inflammation, and fibrosis, implying that aldehydes play an important role in the pathogenesis of cholestatic liver injury and fibrosis.

The Effect of Arabic Gum on Renal Function in Reversible Unilateral Ureteric Obstruction

Arabic gum (AG) has antioxidant and anti-inflammatory properties. However, the effect of AG in ureteric obstruction (UO) has not been investigated yet. Male rats underwent reversible left unilateral UO (UUO) for 72 h. Group AG-1 (n = 12) received AG 15 g/kg/day dissolved in drinking water starting seven days before and continuing throughout the period of the UUO, whereas group Vx-1 (n = 8) had only water. Group AG-2 (n = 12) and Vx-2 (n = 8) had similar protocols as AG-1 and Vx-1, respectively, but underwent terminal experiments to measure renal functions, six days post-UUO reversal. Arabic gum significantly attenuated the UUO-induced increase in the tissue level of malonedialdehyde and superoxide dismutase and the rise in the gene expression of TNF-α, TGF-β1, and p53 in AG-1 compared to Vx-1. It also attenuated the severity of tubular dilatation. However, AG did not affect the alterations in the renal blood flow or glomerular filtration rate. The fractional sodium excretion was lower in AG-2 but did not reach statistical significance (0.40 ± 0.11 vs 0.74 ± 0.12, p = 0.07). AG attenuated the UUO-induced rise in oxidative stress markers and proinflammatory and profibrotic cytokines and the degree of renal tubular dilatation, indicating a protective effect in obstructive nephropathy.