Role of chronic hypoxia and hypoxia inducible factor in kidney disease:

Functional foods from the tropics to relieve chronic normobaric hypoxia

Functional foods with antioxidant and anti-inflammatory properties are regarded as a complementary therapy to improve chronic diseases such as obesity and inflammatory bowel disease (IBD). Obesity is a chronic low-grade inflammatory state leading to organ damage with increased risk of common diseases including cardiovascular and metabolic disease, non-alcoholic fatty liver disease, osteoarthritis and some cancers. IBD is a chronic intestinal inflammation categorised as Crohn's disease and ulcerative colitis depending on the location of inflammation. These inflammatory states are characterised by normobaric hypoxia in adipose and intestinal tissues, respectively. Tropical foods especially from Australia and South America are discussed in this review to show their potential in attenuation of these chronic diseases. The phytochemicals from these foods have antioxidant and anti-inflammatory activities to reduce chronic normobaric hypoxia in the tissues. These health benefits of the tropical foods are relevant not only for health economy but also in providing a global solution by improving the sustainability of their cultivation and assisting the local economies.

Association between air pollutants and development of chronic kidney disease: A systematic review and meta-analysis

BACKGROUND

The association between incident chronic kidney disease (CKD) or end-stage renal disease (ESRD) and exposure to outdoor air pollution is under debate. We aimed to examine this relationship based on a systematic review with random-effects meta-analysis.

METHODS

We screened the literature on long-term air pollution exposure assessment in the general population using an electronic search of PubMed, Medline, Embase, and Cochrane Library from inception to 20 October 2019. Observational studies investigating the association between long-term exposure to gaseous (CO, SO₂, NO₂, O₃) or particulate (PM_2.5 or PM₁₀) outdoor air pollutants and CKD, ESRD, or renal dysfunction were included, and summary risks were estimated.

RESULTS

Of 4419 identified articles, 23 met our inclusion criteria after screening and 14 were included in the meta-analysis. Pooled effect estimates had the following summary risk ratios (RRs) for CKD: 1.10 (95% confidence intervals [CI] 1.00, 1.21; derived from four studies) per 10 μg/m³ increase in PM_2.5 and 1.16 (95% CI 1.05, 1.29; derived from four studies) for PM₁₀; 1.31 (95% CI 0.86, 2.00; derived from two studies) per 10 ppm increase in CO; and 1.11 (95% CI 1.09, 1.14; derived from three studies) per 10 ppb increase in NO₂. For the pooled effect on eGFR, increases in PM₁₀ and PM_2.5 (of 10 μg/m³) were associated with eGFR decline by -0.83 (95% CI -1.54, -0.12; derived from two studies) and -4.11 (95% CI -12.64, 4.42; derived from two studies) mL/min/1.73 m², respectively.

CONCLUSIONS

Air pollution was observed to be associated with CKD and renal function decline. Although more longitudinal studies are required, we argue that air pollution is pernicious to kidney health.

Autophagy and LRRK2 in the Aging Brain

Autophagy is a highly conserved process by which long-lived macromolecules, protein aggregates and dysfunctional/damaged organelles are delivered to lysosomes for degradation. Autophagy plays a crucial role in regulating protein quality control and cell homeostasis in response to energetic needs and environmental challenges. Indeed, activation of autophagy increases the life-span of living organisms, and impairment of autophagy is associated with several human disorders, among which neurodegenerative disorders of aging, such as Parkinson’s disease. These disorders are characterized by the accumulation of aggregates of aberrant or misfolded proteins that are toxic for neurons. Since aging is associated with impaired autophagy, autophagy inducers have been viewed as a strategy to counteract the age-related physiological decline in brain functions and emergence of neurodegenerative disorders. Parkinson’s disease is a hypokinetic, multisystemic disorder characterized by age-related, progressive degeneration of central and peripheral neuronal populations, associated with intraneuronal accumulation of proteinaceous aggregates mainly composed by the presynaptic protein α-synuclein. α-synuclein is a substrate of macroautophagy and chaperone-mediated autophagy (two major forms of autophagy), thus impairment of its clearance might favor the process of α-synuclein seeding and spreading that trigger and sustain the progression of this disorder. Genetic factors causing Parkinson’s disease have been identified, among which mutations in the LRRK2 gene, which encodes for a multidomain protein encompassing central GTPase and kinase domains, surrounded by protein-protein interaction domains. Six LRRK2 mutations have been pathogenically linked to Parkinson’s disease, the most frequent being the G2019S in the kinase domain. LRRK2-associated Parkinson’s disease is clinically and neuropathologically similar to idiopathic Parkinson’s disease, also showing age-dependency and incomplete penetrance. Several mechanisms have been proposed through which LRRK2 mutations can lead to Parkinson’s disease. The present article will focus on the evidence that LRRK2 and its mutants are associated with autophagy dysregulation. Studies in cell lines and neurons in vitro and in LRRK2 knock-out, knock-in, kinase-dead and transgenic animals in vivo will be reviewed. The role of aging in LRRK2-induced synucleinopathy will be discussed. Possible mechanisms underlying the LRRK2-mediated control over autophagy will be analyzed, and the contribution of autophagy dysregulation to the neurotoxic actions of LRRK2 will be examined.

Functional Magnetic Resonance Imaging of the Kidneys-With and Without Gadolinium-Based Contrast

Assessment of renal function with magnetic resonance imaging (MRI) has been actively explored in the past decade. In this review, we introduce the principle of MRI and review recent progress of MRI methods (contrast enhanced and noncontrast) in assessing renal function. Contrast-enhanced MRI using ultra-low dose of gadolinium-based agent has been validated for measuring single-kidney glomerular filtration rate and renal plasma flow accurately. For routine functional test, contrast-enhanced MRI may not replace the simple serum-creatinine method. However, for patients with renal diseases, it is often worthy to perform MRI to accurately monitor renal function, particularly for the diseased kidney. As contrast-enhanced MRI is already an established clinical tool for characterizing renal structural abnormalities, including renal mass and ureteral obstruction, it is possible to adapt the clinical MRI protocol to measure single-kidney glomerular filtration rate and renal plasma flow, as demonstrated by recent studies. What makes MRI unique is the promise of its noncontrast methods. These methods include arterial spin labeling for tissue perfusion, blood oxygen-level dependent for blood and tissue oxygenation, and diffusion-weighted imaging for water diffusion. For each method, we reviewed recent findings and summarized challenges.

Plumbagin ameliorates diabetic nephropathy via interruption of pathways that include NOX4 signalling

NADPH oxidase 4 (Nox4) is reported to be the major source of reactive oxygen species (ROS) in the kidneys during the early stages of diabetic nephropathy. It has been shown to mediate TGFβ1-induced differentiation of cardiac fibroblasts into myofibroblasts. Despite TGFβ1 being recognised as a mediator of renal fibrosis and functional decline role in diabetic nephropathy, the renal interaction between Nox 4 and TGFβ1 is not well characterised. The aim of this study was to investigate the role of Nox4 inhibition on TGFβ1-induced fibrotic responses in proximal tubular cells and in a mouse model of diabetic nephropathy. Immortalised human proximal tubular cells (HK2) were incubated with TGFβ1 ± plumbagin (an inhibitor of Nox4) or specific Nox4 siRNA. Collagen IV and fibronectin mRNA and protein expression were measured. Streptozotocin (STZ) induced diabetic C57BL/6J mice were administered plumbagin (2 mg/kg/day) or vehicle (DMSO; 50 µl/mouse) for 24 weeks. Metabolic, physiological and histological markers of nephropathy were determined. TGFβ1 increased Nox4 mRNA expression and plumbagin and Nox4 siRNA significantly inhibited TGF-β1 induced fibronectin and collagen IV expression in human HK2 cells. STZ-induced diabetic C57BL/6J mice developed physiological features of diabetic nephropathy at 24 weeks, which were reversed with concomitant plumbagin treatment. Histologically, plumbagin ameliorated diabetes induced upregulation of extracellular matrix protein expression compared to control. This study demonstrates that plumbagin ameliorates the development of diabetic nephropathy through pathways that include Nox4 signalling.