Environmental fluoride exposure and implications on potential pediatric kidney health risks: an approach with urinary biomarkers

BACKGROUND

Environmental fluoride exposure at elevated levels is potentially linked to kidney injury, and may contribute to chronic kidney disease of uncertain etiology (CKDu) as a risk factor. However, this link remains unclear, and examining the risk of kidney damage from early life fluoride exposure may provide important insights. Hence, this study aimed to investigate associations of fluoride exposure with pediatric kidney health in CKDu impacted and unimpacted communities in Sri Lanka.

METHODS

Considering the geographical variations in environmental fluoride, climate, and prevalence of CKDu, four study groups were established within selected education zones in CKDu-endemic dry zone regions (D-En), and CKDu-nonendemic regions within the dry (D-NE), wet (W-NE), and intermediate (I-NE) climatic zones. The study population included 922 school students (11-18 years of age). Participants in each group were divided into four subgroups based on quartiles of respective urinary fluoride (UF) distribution for comparison of urinary kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), and albumin-creatinine ratio (ACR).

RESULTS

UF levels in participants particularly in CKDu endemic dry zone regions were significantly high compared to the other regions. Significantly high median urinary NGAL (in D-NE) and ACR (in D-EN, and W-NE) levels were observed in subgroups of higher UF quartiles. Albuminuria was not particularly identified in subjects with high UF excretion. Urinary KIM-1 showed no significant variation across the UF quartile subgroups. Linear regression identified weak associations of UF with kidney injury biomarkers.

CONCLUSIONS

Fluoride exposure is particularly high in CKDu-endemic dry zone communities. As implied by kidney injury biomarkers, a strong link between fluoride exposure and pediatric kidney health was not evident at the observed exposure levels in the study regions.

Body mass index and implications for pediatric kidney health: a cross-sectional study with urinary biomarkers

BACKGROUND

Extremes of unhealthy body weight, particularly obesity, are known to increase the risk of chronic kidney diseases. However, the current knowledge of kidney health outcomes associated with unhealthy body weight remains incomprehensive, especially in pediatrics. Therefore, the present study aimed to evaluate body mass index (BMI) and its potential associations with kidney health in a selected subset of school students in Sri Lanka.

METHODS

This cross-sectional study was conducted among students of both sexes in the range of 11-18 years of age (N = 1078) in education zones with no reported cases of chronic kidney disease of uncertain etiology. Based on sex- and age-specific BMI percentiles (LMS method), the participants were classified into five BMI groups (severely thin, thin, healthy, overweight, and obese) for measurement of urinary biomarkers of kidney injury: kidney injury molecule (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), and albumin creatinine ratio (ACR).

RESULTS

The median urinary levels of NGAL, ACR, and particularly KIM-1, which is a more sensitive indicator of kidney injury, showed no significant differences across the BMI strata. Importantly, moderate correlations of BMI with KIM-1 and NGAL were identified in severely thin girls.

CONCLUSIONS

According to the present study, these findings do not produce plausibly strong evidence to establish a potential association of BMI with altered kidney function in the studied pediatric communities. Particularly, a likelihood of abnormal kidney health outcomes associated with undernutrition is apparent in severely thin girls. However, in-depth studies are warranted to develop a comprehensive understanding of the associations of nutritional status with pediatric kidney health in Sri Lanka. A higher resolution version of the Graphical abstract is available as Supplementary information.

Environmental heat exposure and implications on renal health of pediatric communities in the dry climatic zone of Sri Lanka: An approach with urinary biomarkers

Prolonged heat exposure during outdoor physical exertion can result in adverse renal health outcomes, and it is also supposed to be a driver of chronic kidney disease of uncertain etiology (CKDu) in tropical regions. School students are more likely to experience high heat exposure during outdoor sports practices, and the current knowledge on potential renal health outcomes associated with heat exposure carries many knowledge gaps. Hence, the present study aimed to perform biomarker-based assessment of the likelihood of pediatric renal injury focusing the communities in the dry climatic zone in Sri Lanka, where it prevails relatively harsh climate and high prevalence of CKDu. School students who engaged in regular outdoor sports practices (high-heat exposure), and an age-matched control of students who did not engage in sports practices (low-heat exposure) from four educational zones: Padavi Sripura (N = 159) and Medirigiriya (N = 171), Uhana (N = 165) and Thanamalwila (N = 169) participated in this cross-sectional study representing CKDu endemic and non-endemic regions. Effective temperature (ET), wet-bulb globe temperature (WBGT), heat index (HI) and humidex were used for comparison of thermal comfort in the environment. The intensity of environmental heat measured by thermal comfort indices showed no significant difference (p > 0.05) among the study regions. Urinary kidney injury molecule (KIM-1) and albumin-creatinine ratio (ACR) in participants with high heat exposure did not differ significantly from those in the control groups in the four study zones, where urinary neutrophil gelatinase-associated lipocalin showed substantial differences in some groups. Irrespective of heat exposure, increased KIM-1 excretion was observed (p < 0.01) in participants of CKDu endemic regions compared to those in non-endemic areas. Within the context of our findings, there is no plausibly strong evidence to establish potential association of heat exposure with the likelihood of developing renal injury or abnormal renal outcomes in dry zone school students in Sri Lanka.

Arsenic and human health effects: A review

Arsenic (As) is ubiquitous in nature and humans being exposed to arsenic via atmospheric air, ground water and food sources are certain. Major sources of arsenic contamination could be either through geological or via anthropogenic activities. In physiological individuals, organ system is described as group of organs that transact collectively and associate with other systems for conventional body functions. Arsenic has been associated with persuading a variety of complications in body organ systems: integumentary, nervous, respiratory, cardiovascular, hematopoietic, immune, endocrine, hepatic, renal, reproductive system and development. In this review, we outline the effects of arsenic on the human body with a main focus on assorted organ systems with respective disease conditions. Additionally, underlying mechanisms of disease development in each organ system due to arsenic have also been explored. Strikingly, arsenic has been able to induce epigenetic changes (in utero) and genetic mutations (a leading cause of cancer) in the body. Occurrence of various arsenic induced health effects involving emerging areas such as epigenetics and cancer along with their respective mechanisms are also briefly discussed.

The Reck tumor suppressor protein alleviates tissue damage and promotes functional recovery after transient cerebral ischemia in mice

The extracellular matrix (ECM) is important for both structural integrity and functions of the brain. Matrix metalloproteinases (MMPs) play major roles in ECM-remodeling under both physiological and pathological conditions. Reversion-inducing cysteine-rich protein with Kazal motifs (Reck) is a membrane-anchored MMP-regulator implicated in coordinated regulation of pericellular proteolysis. Although patho-physiological importance of MMPs and another group of MMP-regulators, tissue inhibitor of metalloproteinases, in brain ischemia has been demonstrated, little is known about the role of Reck in this process. In this study, we found that Reck is up-regulated in hippocampus and penumbra of subventricular zone after transient cerebral ischemia in mice. Most of the Reck-positive cells found at day 2 after ischemia are positive for Nestin as well as Ki67 and localized to the CA2 region of the hippocampus. At day 7 after ischemia, the Reck-positive cells increased in number, extended processes, expressed the reactive astrocyte marker GFAP and the neuronal marker NF200, and were widely distributed in the hippocampus. In the mutant mice carrying single functional Reck allele (Reck+/-), tissue damage and cell death after cerebral ischemia were augmented, the recovery of long-term potentiation in the hippocampus was compromised, NR2C subunit of NMDA receptor was up-regulated, gelatinolytic activity of MMPs were up-regulated and laminin-immunoreactivity was reduced. Our data implicate Reck in protection of ECM/tissue integrity and promotion of functional recovery in the brain after transient cerebral ischemia.

Localization of the membrane-anchored MMP-regulator RECK at the neuromuscular junctions

Nerve apposition on nicotinic acetylcholine receptor clusters and invagination of the post-synaptic membrane (i.e. secondary fold formation) occur by embryonic day 18.5 at the neuromuscular junctions (NMJs) in mouse skeletal muscles. Finding the molecules expressed at the NMJ at this stage of development may help elucidating how the strong linkage between a nerve terminal and a muscle fiber is established. Immunohistochemical analyses indicated that the membrane-anchored matrix metalloproteinase regulator RECK was enriched at the NMJ in adult skeletal muscles. Confocal and electron microscopy revealed the localization of RECK immunoreactivity in secondary folds and subsynaptic intracellular compartments in muscles. Time course studies indicated that RECK immunoreactivity becomes associated with the NMJ in the diaphragm at around embryonic day 18.5 and thereafter. These findings, together with known properties of RECK, support the hypothesis that RECK participates in NMJ formation and/or maintenance, possibly by protecting extracellular components, such as synaptic basal laminae, from proteolytic degradation.

RECK modulates Notch signaling during cortical neurogenesis by regulating ADAM10 activity

We report that during cortical development in the mouse embryo, reversion-inducing cysteine-rich protein with Kazal motifs (RECK) critically regulates Notch signaling by antagonizing the ectodomain shedding of Notch ligands, which is mediated by a disintegrin and metalloproteinase domain 10 (ADAM10). In the embryonic brain, RECK is specifically expressed in Nestin-positive neural precursor cells (NPCs). Reck-deficient NPCs undergo precocious differentiation that is associated with downregulated Nestin expression, impaired Notch signaling and defective self-renewal. These phenotypes were substantially rescued either by enhancing Notch signaling or by suppressing endogenous ADAM10 activity. Consequently, we found that RECK regulates the ectodomain shedding of Notch ligands by directly inhibiting the proteolytic activity of ADAM10. This mechanism appeared to be essential for Notch ligands to properly induce Notch signaling in neighboring cells. These findings indicate that RECK is a physiological inhibitor of ADAM10, an upstream regulator of Notch signaling and a critical modulator of brain development.