Renal expression of sodium transporters and aquaporin-2 in hypothyroid rats

Thyroid hormone replacement therapy in dialysis/renal insufficiency patients

Dialysis/renal insufficiency patients are often accompanied by hypothyroidism due to renal damage, the mechanisms of which are complex. The use of thyroid hormone replacement therapy in such patients has become an important clinical issue. This article reviews the mechanism of hypothyroidism in dialysis/renal insufficiency patients and describes the importance and precautions of thyroid hormone replacement therapy to provide a reference for clinical diagnosis and treatment.

Disrupted uromodulin trafficking is rescued by targeting TMED cargo receptors

The trafficking dynamics of uromodulin (UMOD), the most abundant protein in human urine, play a critical role in the pathogenesis of kidney disease. Monoallelic mutations in the UMOD gene cause autosomal dominant tubulointerstitial kidney disease (ADTKD-UMOD), an incurable genetic disorder that leads to kidney failure. The disease is caused by the intracellular entrapment of mutant UMOD in kidney epithelial cells, but the precise mechanisms mediating disrupted UMOD trafficking remain elusive. Here, we report that transmembrane Emp24 protein transport domain-containing (TMED) cargo receptors TMED2, TMED9, and TMED10 bind UMOD and regulate its trafficking along the secretory pathway. Pharmacological targeting of TMEDs in cells, in human kidney organoids derived from patients with ADTKD-UMOD, and in mutant-UMOD-knockin mice reduced intracellular accumulation of mutant UMOD and restored trafficking and localization of UMOD to the apical plasma membrane. In vivo, the TMED-targeted small molecule also mitigated ER stress and markers of kidney damage and fibrosis. Our work reveals TMED-targeting small molecules as a promising therapeutic strategy for kidney proteinopathies.

ClC-Kb pore mutation disrupts glycosylation and triggers distal tubular remodeling

Mutations in the CLCNKB gene (1p36), encoding the basolateral chloride channel ClC-Kb, cause type 3 Bartter syndrome. We identified a family with a mixed Bartter/Gitelman phenotype and early-onset kidney failure and by employing a candidate gene approach, identified what we believe is a novel homozygous mutation (CLCNKB c.499G>T [p.Gly167Cys]) in exon 6 of CLCNKB in the index patient. We then validated these results with Sanger and whole-exome sequencing. Compared with wild-type ClC-Kb, the Gly167Cys mutant conducted less current and exhibited impaired complex N-linked glycosylation in vitro. We demonstrated that loss of Gly-167, rather than gain of a mutant Cys, impairs complex glycosylation, but that surface expression remains intact. Moreover, Asn-364 was necessary for channel function and complex glycosylation. Morphologic evaluation of human kidney biopsies revealed typical basolateral localization of mutant Gly167Cys ClC-Kb in cortical distal tubular epithelia. However, we detected attenuated expression of distal sodium transport proteins, changes in abundance of distal tubule segments, and hypokalemia-associated intracellular condensates from the index patient compared with control nephrectomy specimens. The present data establish what we believe are novel regulatory mechanisms of ClC-Kb activity and demonstrate nephron remodeling in humans, caused by mutant ClC-Kb, with implications for renal electrolyte handling, blood pressure control, and kidney disease.

Old woman with Sheehan's syndrome suffered severe hyponatremia following percutaneous coronary intervention: a case report and review of literature

Glucocorticoid deficiency can lead to hypoglycemia, hypotension, and electrolyte disorders. Acute glucocorticoid deficiency under stress is very dangerous. Here, we present a case study of an elderly patient diagnosed with Sheehan's syndrome, manifesting secondary adrenal insufficiency and secondary hypothyroidism, managed with daily prednisone and levothyroxine therapy. She was admitted to our hospital due to acute non-ST segment elevation myocardial infarction. The patient developed nausea and limb twitching post-percutaneous coronary intervention, with subsequent diagnosis of hyponatremia. Despite initial intravenous sodium supplementation failed to rectify the condition, and consciousness disturbances ensued. However, administration of 50 mg hydrocortisone alongside 6.25 mg sodium chloride rapidly ameliorated symptoms and elevated blood sodium levels. Glucocorticoid deficiency emerged as the primary etiology of hyponatremia in this context, exacerbated by procedural stress during percutaneous coronary intervention. Contrast agent contributed to blood sodium dilution. Consequently, glucocorticoid supplementation emerges as imperative, emphasizing the necessity of stress-dose administration of glucocorticoid before the procedure. Consideration of shorter intervention durations and reduced contrast agent dosages may mitigate severe hyponatremia risks. Moreover, it is crucial for this patient to receive interdisciplinary endocrinologist management. In addition, Sheehan's syndrome may pose a risk for coronary atherosclerotic disease.

Salt-losing nephropathy associated with severe hypothyroidism

Here, we present a case of an older man presenting with worsening confusion. Laboratory tests showed serum sodium of 120 mmol/L with severe hypothyroidism and renal salt wasting that improved with treatment of hypothyroidism, normalising the serum sodium.

The effect of hypothyroidism on the risk of diabetes and its microvascular complications: a Mendelian randomization study

Context

Several observational studies have found that hypothyroidism is associated with diabetes and its microvascular complications. However, the cause and effect have not been clarified.

Objective

The aim of the study was to examine the causality of such associations by a Mendelian randomization study.

Methods

Two-sample Mendelian randomization analysis was conducted to investigate the associations. Summary statistics for hypothyroidism were from the UK Biobank, and diabetes and its microvascular complications were from the largest available genome-wide association studies. MR-Egger, weighted median, inverse variance weighted, simple mode and weighted mode were used to examine the causal associations, and several sensitivity analyses were used to assess pleiotropy.

Results

Inverse variance weighted estimates suggested that hypothyroidism was associated with type 1 diabetes and type 1 diabetes with renal complications (β= 9.059926, se= 1.762903, P = 2.76E-07 and β= 10.18375, se= 2.021879, P = 4.73E-07, respectively) but not type 2 diabetes and type 2 diabetes with renal complications. In addition, hypothyroidism was positively associated with severe nonproliferative diabetic retinopathy and proliferative diabetic retinopathy (β= 8.427943, se= 2.142493, P = 8.36E-05 and β= 3.100939, se= 0.74956, P=3.52E-05, respectively).

Conclusions

The study identified the causal roles of hypothyroidism in diabetes and its microvascular complications. Hypothyroidism can lead to type 1 diabetes, type 1 diabetes with renal complications, severe nonproliferative diabetic retinopathy and proliferative diabetic retinopathy.

Subclinical Hypothyroidism, Kidney, and Heart from Normal to Uremic Milieu

Thyroid hormone (TH) imbalances, particularly subclinical hypothyroidism (SCHT), are associated with chronic kidney disease (CKD) and end-stage kidney disease (ESKD). SCHT is more prevalent in CKD and ESKD patients than in the general population, and this condition increases the risk of cardiovascular disease (CVD) morbidity and mortality. The risk of CVD is higher in CKD and ESKD patients compared with the general population. Traditional and nontraditional risk factors, including TH abnormalities, contribute to the high CVD burden in CKD and ESKD patients. The review discusses the link between CKD and hypothyroidism, with a focus on SCHT, and the mechanisms that lead to CVD burden.

Kidney disease and thyroid dysfunction: the chicken or egg problem

Patients with non-dialysis-dependant chronic kidney disease (NDD-CKD) and dialysis-dependant chronic kidney disease (DD-CKD) frequently also suffer from thyroid disorders, especially hypothyroidism which is found two to five times more often among them compared to the general population. Emerging research has illustrated the potential prognostic implications of this association as NDD-CKD and DD-CKD patients with hypothyroidism have been shown to have higher mortality rates, and treatment of subclinical hypothyroidism in NDD-CKD patients has been reported to attenuate the decline of glomerular filtration rate over time. This review illustrates the bidirectional, multi-layered interplay between the kidneys and the thyroid gland explaining how pathologies in one organ will affect the other and vice versa. Additionally, it outlines the impact of thyroid disorders on routine parameters of kidney function (especially serum creatinine and serum cystatin C) that nephrologists should be aware of in their clinical practice. Lastly, it summarizes the emerging evidence from clinical studies on how treatment of subclinical hypothyroidism in NDD-CKD and DD-CKD patients may potentially have beneficial effects on kidney function as well as mortality. While most of the research in this area has been performed on adult patients, we specifically discuss what is currently known about thyroid dysfunctions in paediatric CKD patients as well and provide management suggestions. The evidence accumulated so far clearly indicates that further, prospective studies with meticulous methodology are warranted to refine our understanding of thyroid disorders in paediatric and adult CKD patients and establish optimal treatment pathways.

Masked CKD in hyperthyroidism and reversible CKD status in hypothyroidism

INTRODUCTION

While it is well known that thyroid function may affect kidney function, the transition of the chronic kidney disease (CKD) status before and after treatment for thyroid disorders, as well as the factors affecting this change, remains to be explored. In the present study, we focused on the change in kidney function and their affecting factors during the treatment for both hyperthyroidism and hypothyroidism.

METHODS

Eighty-eight patients with hyperthyroidism and fifty-two patients with hypothyroidism were enrolled in a retrospective and longitudinal case series to analyze the changes in kidney function and their affecting factors after treatment for thyroid disorders.

RESULTS

Along with the improvement of thyroid function after treatment, there was a significant decrease in estimated glomerular filtration rate (eGFR) in hyperthyroidism (an average ΔeGFR of -41.1 mL/min/1.73 m²) and an increase in eGFR in hypothyroidism (an average ΔeGFR of 7.1 mL/min/1.73 m²). The multiple linear regression analysis revealed that sex, eGFR, free thyroxine (FT4) and free triiodothyronine (FT3) could be considered independent explanatory variables for ΔeGFR in hyperthyroidism, while age, eGFR, and FT3 were detected as independent explanatory variables in hypothyroidism. In addition, the stratification by kidney function at two points, pre- and post-treatment for thyroid disorders, revealed that 4.5% of the participants with hyperthyroidism were pre-defined as non-CKD and post-defined as CKD, indicating the presence of "masked" CKD in hyperthyroidism. On the other hand, 13.5% of the participants with hypothyroidism presented pre-defined CKD and post-defined non-CKD, indicating the presence of "reversible" CKD status in hypothyroidism.

CONCLUSIONS

We uncovered the population of masked CKD in hyperthyroidism and reversible CKD status in hypothyroidism, thereby re-emphasizing the importance of a follow-up to examine kidney function after treatment for hyperthyroidism and the routine evaluation of thyroid function in CKD patients as well as the appropriate hormone therapy if the patient has hypothyroidism.

The Interplay Between Thyroid Dysfunction and Kidney Disease

Hypothyroidism is a highly prevalent endocrine complication in chronic kidney disease (CKD) patients. A large body of evidence has shown that there is a bidirectional relationship between thyroid dysfunction and kidney disease, yet there are many remaining gaps in knowledge in regards to the clinical management of CKD patients with hypothyroidism, including those receiving hemodialysis and peritoneal dialysis. Given that hypothyroidism has been associated with many deleterious outcomes including a higher risk of (1) mortality, (2) cardiovascular disease, (3) impaired health-related quality of life, and (4) altered body composition in both non-CKD and CKD patients, future research is needed to establish the appropriate screening, diagnosis, and treatment approaches in these populations.

Evaluation of biochemical markers of kidney function in patients with subclinical hypothyroidism in comparison with euthyroid people

Background:

Subclinical hypothyroidism (SCH) as a compensated or preclinical type of primary and overt hypothyroidism (OHT) can affect approximately 4–10% of the general population. Treating SCH can slowdown the progression to OHT, the formation of cardiovascular diseases, neuropsychiatric symptoms, and other miscellaneous problems.

Materials and Methods:

The present study is a case-control study that was conducted on 239 adults who were referred to 501 Imam Reza Hospital from March 2019 up to September 2019. Of the 239 patients and their families admitted to the hospital, 121 (50.6%) were euthyroid (as control group) and the remaining participants (118, 49.4%) were SCH (as case group). The serum levels of thyroid stimulating hormone (TSH), urea, uric acid, creatinine, T3, and T4 were asked to be determined at a single laboratory. Biochemical markers of kidney function and the level of thyroid hormones were compared between the two groups of euthyroid and SCH.

Results:

TSH was significantly higher in SCH (7.25 (4.4-18.15)) compared to euthyroid (1.4 (0.2-3.7)) patients (P < 0.001). Among biochemical markers, creatinine (P < 0.001) and uric acid (P = 0.006) had higher serum levels in the case group. There was no remarkable difference in the thyroxine hormone levels and urea between the euthyroid and SCH patients (P > 0.05). Within the SCH group, there was a significant positive correlation between TSH and the level of creatinine (P = 0.001, r = 0.302).

Conclusion:

Regular monitoring of the major function of the kidneys in patients with hypothyroidism and SCH can help early diagnosis of kidney dysfunction, thus increasing the chance of restoring normal kidney function.

Thyroid Function Modulates Lung Fluid and Alveolar Viscoelasticity in Mechanically Ventilated Rat

BACKGROUND

Mechanical ventilation (MV) is life saving; yet it may induce severe lung injury and lead to multisystem organ failure and death. Thyroid hormones (THs) promote alveolar fluid clearance and alleviates hypoxia-induced lung injury. Given that the mechanism involved in hypoxia-induced lung injury is different from that of ventilator-induced lung injury, we examined the effects of thyroid function on lung extravascular fluid (LF), aquaporin 5 (AQP 5) expression, and alveolar viscoelasticity (AVE) in mechanically ventilated rat.

METHODS

Hypothyroid (hypo) and hyperthyroid (hyper) animals were generated by administration of metimazole and L-thyroxine, respectively. Lung injury was induced by high-tidal volume MV. The LF was estimated by lung wet weight-to-dry weight ratio assessment. Expression of AQP 5 was evaluated by western blotting and in situ immunohistochemistry. The AVE was judged by elastic lung pressure/volume curve recording.

RESULTS

Injurious MV significantly reduced lung AQP 5 expression and altered LF and AVE in a thyroid function-dependent manner. Regardless of animals' ventilation mode, hyper state caused significant reductions in LF and lung AQP 5 protein. It also improved AVE irrespective of animals' ventilation mode. The effects of hypo condition on LF, AQP 5 expression, and AVE were in contrast to that of hyper state.

CONCLUSIONS

These data indicate that thyroid function has profound effects on LF, AQP 5, and AVE in mechanically ventilated lungs. Given that the effects of thyroidal status were as prominent as that of injurious MV, we suggest that thyroid function should be considered when patients are to be subjected to MV.

WNK bodies cluster WNK4 and SPAK/OSR1 to promote NCC activation in hypokalemia

K⁺ deficiency stimulates renal salt reuptake via the Na⁺-Cl^- cotransporter (NCC) of the distal convoluted tubule (DCT), thereby reducing K⁺ losses in downstream nephron segments while increasing NaCl retention and blood pressure. NCC activation is mediated by a kinase cascade involving with no lysine (WNK) kinases upstream of Ste20-related proline-alanine-rich kinase (SPAK) and oxidative stress-responsive kinase-1 (OSR1). In K⁺ deficiency, WNKs and SPAK/OSR1 concentrate in spherical cytoplasmic domains in the DCT termed "WNK bodies," the significance of which is undetermined. By feeding diets of varying salt and K⁺ content to mice and using genetically engineered mouse lines, we aimed to clarify whether WNK bodies contribute to WNK-SPAK/OSR1-NCC signaling. Phosphorylated SPAK/OSR1 was present both at the apical membrane and in WNK bodies within 12 h of dietary K⁺ deprivation, and it was promptly suppressed by K⁺ loading. In WNK4-deficient mice, however, larger WNK bodies formed, containing unphosphorylated WNK1, SPAK, and OSR1. This suggests that WNK4 is the primary active WNK isoform in WNK bodies and catalyzes SPAK/OSR1 phosphorylation therein. We further examined mice carrying a kidney-specific deletion of the basolateral K⁺ channel-forming protein Kir4.1, which is required for the DCT to sense plasma K⁺ concentration. These mice displayed remnant mosaic expression of Kir4.1 in the DCT, and upon K⁺ deprivation, WNK bodies developed only in Kir4.1-expressing cells. We postulate a model of DCT function in which NCC activity is modulated by plasma K⁺ concentration via WNK4-SPAK/OSR1 interactions within WNK bodies.

Chronic Overexpression of Bradykinin in Kidney Causes Polyuria and Cardiac Hypertrophy

Acute intra-renal infusion of bradykinin increases diuresis and natriuresis via inhibition of vasopressin activity. However, the consequences of chronically increased bradykinin in the kidneys have not yet been studied. A new transgenic animal model producing an excess of bradykinin by proximal tubular cells (KapBK rats) was generated and submitted to different salt containing diets to analyze changes in blood pressure and other cardiovascular parameters, urine excretion, and composition, as well as levels and expression of renin-angiotensin system components. Despite that KapBK rats excrete more urine and sodium, they have similar blood pressure as controls with the exception of a small increase in systolic blood pressure (SBP). However, they present decreased renal artery blood flow, increased intrarenal expression of angiotensinogen, and decreased mRNA expression of vasopressin V1A receptor (AVPR1A), suggesting a mechanism for the previously described reduction of renal vasopressin sensitivity by bradykinin. Additionally, reduced heart rate variability (HRV), increased cardiac output and frequency, and the development of cardiac hypertrophy are the main chronic effects observed in the cardiovascular system. In conclusion: (1) the transgenic KapBK rat is a useful model for studying chronic effects of bradykinin in kidney; (2) increased renal bradykinin causes changes in renin angiotensin system regulation; (3) decreased renal vasopressin sensitivity in KapBK rats is related to decreased V1A receptor expression; (4) although increased renal levels of bradykinin causes no changes in mean arterial pressure (MAP), it causes reduction in HRV, augmentation in cardiac frequency and output and consequently cardiac hypertrophy in rats after 6 months of age.

Patients with hypokalemia develop WNK bodies in the distal convoluted tubule of the kidney

Hypokalemia contributes to the progression of chronic kidney disease, although a definitive pathophysiological theory to explain this remains to be established. K⁺ deficiency results in profound alterations in renal epithelial transport. These include an increase in salt reabsorption via the Na⁺-Cl^- cotransporter (NCC) of the distal convoluted tubule (DCT), which minimizes electroneutral K⁺ loss in downstream nephron segments. In experimental conditions of dietary K⁺ depletion, punctate structures in the DCT containing crucial NCC-regulating kinases have been discovered in the murine DCT and termed "WNK bodies," referring to their component, with no K (lysine) kinases (WNKs). We hypothesized that in humans, WNK bodies occur in hypokalemia as well. Renal needle biopsies of patients with chronic hypokalemic nephropathy and appropriate controls were examined by histological stains and immunofluorescence. Segment- and organelle-specific marker proteins were used to characterize the intrarenal and subcellular distribution of established WNK body constituents, namely, WNKs and Ste20-related proline-alanine-rich kinase (SPAK). In both patients with hypokalemia, WNKs and SPAK concentrated in non-membrane-bound cytoplasmic regions in the DCT, consistent with prior descriptions of WNK bodies. The putative WNK bodies were located in the perinuclear region close to, but not within, the endoplasmic reticulum. They were closely adjacent to microtubules but not clustered in aggresomes. Notably, we provide the first report of WNK bodies, which are functionally challenging structures associated with K⁺ deficiency, in human patients.

Hyponatremia in kidney transplant patients: its pathophysiologic mechanisms

Kidney transplant patients (KTPs), and particularly those with advanced chronic kidney rejection, may be affected by opportunistic infections, metabolic alterations and vascular and oncologic diseases that promote clinical conditions that require a variety of treatments, the combinations of which may predispose them to hyponatremia. Salt and water imbalance can induce abnormalities in volemia and/or serum sodium depending on the nature of this alteration (increase or decrease), its absolute magnitude (mild or severe) and its relative magnitude (body sodium:water ratio). Hyponatremia appears when the body sodium:water ratio is reduced due to an increase in body water or a reduction in body sodium. Additionally, hyponatremia is classified as normotonic, hypertonic and hypotonic and while hypotonic hyponatremia is classified in hyponatremia with normal, high or low extracellular fluid. The main causes of hyponatremia in KTPs are hypotonic hyponatremia secondary to water and salt contraction with oral hydration (gastroenteritis, sepsis), free water retention (severe renal failure, syndrome of inappropriate antidiuretic hormone release, hypothyroidism), chronic hypokalemia (rapamycin, malnutrition), sodium loss (tubular dysfunction secondary to nephrocalcinosis, acute tubular necrosis, tubulitis/rejection, interstitial nephritis, adrenal insufficiency, aldosterone resistance, pancreatic drainage, kidney–pancreas transplant) and hyponatremia induced by medication (opioids, cyclophosphamide, psychoactive, potent diuretics and calcineurinic inhibitors). In conclusion, KTPs are predisposed to develop hyponatremia since they are exposed to immunologic, infectious, pharmacologic and oncologic disorders, the combinations of which alter their salt and water homeostatic capacity.

With no lysine kinase 4 modulates sodium potassium 2 chloride cotransporter activity in vivo

With no lysine kinase 4 (WNK4) is essential to activate the thiazide-sensitive NaCl cotransporter (NCC) along the distal convoluted tubule, an effect central to the phenotype of familial hyperkalemic hypertension. Although effects on potassium and sodium channels along the connecting and collecting tubules have also been documented, WNK4 is typically believed to have little role in modulating sodium chloride reabsorption along the thick ascending limb of the loop of Henle. Yet wnk4^-/- mice (knockout mice lacking WNK4) do not demonstrate the hypocalciuria typical of pure distal convoluted tubule dysfunction. Here, we tested the hypothesis that WNK4 also modulates bumetanide-sensitive Na-K-2Cl cotransporter (NKCC2) function along the thick ascending limb. We confirmed that w nk4^-/- mice are hypokalemic and waste sodium chloride, but are also normocalciuric. Results from Western blots suggested that the phosphorylated forms of both NCC and NKCC2 were in lower abundance in wnk4^-/- mice than in controls. This finding was confirmed by immunofluorescence microscopy. Although the initial response to furosemide was similar in wnk4^-/- mice and controls, the response was lower in the knockout mice when reabsorption along the distal convoluted tubule was inhibited. Using HEK293 cells, we showed that WNK4 increases the abundance of phosphorylated NKCC2. More supporting evidence that WNK4 may modulate NKCC2 emerges from a mouse model of WNK4-mediated familial hyperkalemic hypertension in which more phosphorylated NKCC2 is present than in controls. These data indicate that WNK4, in addition to modulating NCC, also modulates NKCC2, contributing to its physiological function in vivo.

Evaluation of renal function in subclinical hypothyroidism

INTRODUCTION

Patients with subclinical hypothyroidism (SCH) have a few or no symptoms or signs of thyroid dysfunction and thus by its very nature, SCH is a laboratory diagnosis. Serum creatinine is elevated and glomerular filtration rate (GFR) values are reversibly reduced in overt hypothyroid patients. We hypothesize that SCH also may be associated with low GFR.

AIMS AND OBJECTIVES

The objective of this study was (1) to know the effect of SCH on kidney function, (2) to find the correlation between the renal function parameter creatinine, estimated GFR (eGFR), and thyroid-stimulating hormone (TSH), and (3) to know if creatinine values can be predicted by TSH values in SCH cases.

MATERIALS AND METHODS

This is a hospital-based cross-sectional study for 1 year. A total of 608 subjects of either sex were included in the study and were divided into 3 groups: (1) SCH, (2) overt hypothyroidism (OHT), and (3) euthyroidism (ET). TSH, free triiodothyronine, free thyroxine, and serum creatinine were estimated and eGFR was calculated using modification of diet in renal disease study equation and the chronic kidney disease epidemiology collaboration equations.

RESULTS

Serum creatinine levels were higher and eGFR was lower significantly in the subclinical hypothyroid group when compared to the control ET group (P < 0.001). The overtly hypothyroid group had significantly higher levels of serum creatinine and lower eGFR when compared to both the groups (P < 0.001). Significant correlation between TSH, creatinine, and eGFR was found in OHT group only. Linear regression analysis showed the regression in creatinine upon TSH is attributable to 44.5% among OHT group, 48.2% in SCH group.

CONCLUSION

It can be concluded that the SCH group behaves biochemically similar to OHT group and changes in serum creatinine reflect tissue hypothyroidism in SCH cases.

Changes in Thyroid Hormones Levels and Metabolism in Dairy Cows around Calving

The hormonal activity of the thyroid gland has an important role in ruminants for the modulation of metabolic variables. In this study changes in thyroid hormones and biochemical parameters in dairy cows around calving were evaluated and the critical thyroid hormones thresholds for predicting the risk of ketosis were estimated. Blood samples were collected from 82 dairy cows at 5±3 days pre-partum and 5±3 days postpartum. Serum values of triiodothyronine (T3), thyroxine (T4), thyroid-stimulating hormone (TSH), non-esterified fatty acids (NEFA), β-hydroxybutyrate (BHB), insulin, glucose, Ca, Cl, Mg, P, K, Na, aspartate transaminase (AST), alanine transaminase (ALT) and urea were evaluated. Signifi cant decrease in the levels of T3, T4 and TSH was found in the postpartum period. The values of T3 and T4 were negatively correlated with NEFA and BHB levels, and TSH values were negatively correlated with NEFA. A critical T3 threshold was found by means of ROC analysis for predicting the risk of ketosis. T3 values < 1.23 nmol/L were associated with BHB > 1.10 mmol/L in postpartum, which represents the BHB threshold commonly used as the indicator of hyperketonaemia. The results confirm that the peripartum period is accompanied by marked changes in circulating thyroid hormone profile that is correlated with lipomobilization predictors.

Thyroid dysfunction and kidney disease: An update

Thyroid hormones influence renal development, kidney hemodynamics, glomerular filtration rate and sodium and water homeostasis. Hypothyroidism and hyperthyroidism affect renal function by direct renal effects as well as systemic hemodynamic, metabolic and cardiovascular effects. Hypothyroidism has been associated with increased serum creatinine and decreased glomerular filtration rate. The reverse effects have been reported in thyrotoxicosis. Most of renal manifestations of thyroid dysfunction are reversible with treatment. Kidney disease may also cause thyroid dysfunction by several mechanisms. Nephrotic syndrome has been associated to changes in serum thyroid hormone concentrations. Different forms of glomerulonephritis and tubulointerstitial disease may be linked to thyroid derangements. A high prevalence of thyroid hormone alteration has been reported in acute kidney injury. Thyroid dysfunction is highly prevalent in chronic kidney disease patients. Subclinical hypothyroidism and low triiodothyronine syndrome are common features in patients with chronic kidney disease. Patients treated by both hemodialysis and peritoneal dialysis, and renal transplantation recipients, exhibit thyroid hormone alterations and thyroid disease with higher frequency than that found in the general population. Drugs used in the therapy of thyroid disease may lead to renal complications and, similarly, drugs used in kidney disorders may be associated to thyroid alterations. Lastly, low thyroid hormones, especially low triiodothyronine levels, in patients with chronic kidney disease have been related to a higher risk of cardiovascular disease and all-cause mortality. Interpretation of the interactions between thyroid and renal function is a challenge for clinicians involved in the treatment of patients with thyroid and kidney disease.

Unusual Presentation of Central Diabetes Insipidus in a Patient With Neurosarcoidosis

Hypernatremia is a frequent cause of intensive care unit admission. The patient presented in this article had hypernatremia refractory to D5W (dextrose 5% water) therapy, which led to a complex investigation. Workup revealed central diabetes insipidus most likely secondary to flare up of neurosarcoidosis. The challenge in terms of diagnosis was a presentation with low urine output in the setting of hypernatremia resistant to treatment with desmopressin. This case unfolded the role of hypothyroidism causing secondary renal dysfunction and hence needed continued treatment with thyroxine in addition to treatment for hypernatremia.

Assessment of renal function and electrolytes in patients with thyroid dysfunction in Addis Ababa, Ethiopia: a cross sectional study

Introduction

Studies demonstrated that abnormal thyroid functions may result in decreased or increased kidney size, kidney weight, and affect renal functions. In this regard, studies on the association of abnormal thyroid functions and renal function tests are scarcely found in Ethiopia.

Objective

To assess renal function and electrolytes in patients with thyroid dysfunction, in Addis Ababa, Ethiopia.

Methods

Cross sectional study was conducted from March 21/2015-May 27/2015 at Arsho Advanced Medical Laboratory. During the study period, 71 patients with thyroid dysfunction were eligible, and socio demographic data collected by structured questionnaire. Then blood sample was collected for thyroid function tests, renal function and blood electrolyte analysis. The collected data was analyzed by SPSS version 20. ANOVA and binary logistic regression were employed to evaluate the mean deference and associations of thyroid hormone with renal function and electrolyte balances.

Results

Among the renal function tests, serum uric acid, and creatinine mean values were significantly decreased in hyperthyroid patients; whereas, eGFR mean value was significantly increased in hyperthyroid study patients (P<0.05). Meanwhile, from the electrolyte measurements made, only the mean serum sodium value was significantly increased in hyperthyroid study participants. Binary logistic regression analysis on the association of thyroid dysfunction with electrolyte balance and renal function tests indicated that serum sodium, creatinine, eGFR values and hyperthyroidism have a statistical significant association at AOR 95% CI of 0.141(0.033-0.593, P=0.008); 16.236(3.481-75.739, P=0.001), and 13.797(3.261-58.67, P=0.001) respectively.

Conclusion

The current study reveals, thyroid abnormalities may lead to renal function alterations and also may disturb electrolyte balance. Knowledge of this significant association has worthwhile value for clinicians, to manage their patients' optimally.

SPAK and OSR1 play essential roles in potassium homeostasis through actions on the distal convoluted tubule

KEY POINTS

STE20 (Sterile 20)/SPS-1 related proline/alanine-rich kinase (SPAK) and oxidative stress-response kinase-1 (OSR1) phosphorylate and activate the renal Na(+) -K(+) -2Cl(-) cotransporter 2 (NKCC2) and Na(+) Cl(-) cotransporter (NCC). Mouse models suggest that OSR1 mainly activates NKCC2-mediated sodium transport along the thick ascending limb, while SPAK mainly activates NCC along the distal convoluted tubule, but the kinases may compensate for each other. We hypothesized that disruption of both kinases would lead to polyuria and severe salt-wasting, and generated SPAK/OSR1 double knockout mice to test this. Despite a lack of SPAK and OSR1, phosphorylated NKCC2 abundance was still high, suggesting the existence of an alternative activating kinase. Compensatory changes in SPAK/OSR1-independent phosphorylation sites on both NKCC2 and NCC and changes in sodium transport along the collecting duct were also observed. Potassium restriction revealed that SPAK and OSR1 play essential roles in the emerging model that NCC activation is central to sensing changes in plasma [K(+) ].

ABSTRACT

STE20 (Sterile 20)/SPS-1 related proline/alanine-rich kinase (SPAK) and oxidative stress-response kinase-1 (OSR1) activate the renal cation cotransporters Na(+) -K(+) -2Cl(-) cotransporter (NKCC2) and Na(+) -Cl(-) cotransporter (NCC) via phosphorylation. Knockout mouse models suggest that OSR1 mainly activates NKCC2, while SPAK mainly activates NCC, with possible cross-compensation. We tested the hypothesis that disrupting both kinases causes severe polyuria and salt-wasting by generating SPAK/OSR1 double knockout (DKO) mice. DKO mice displayed lower systolic blood pressure compared with SPAK knockout (SPAK-KO) mice, but displayed no severe phenotype even after dietary salt restriction. Phosphorylation of NKCC2 at SPAK/OSR1-dependent sites was lower than in SPAK-KO mice, but still significantly greater than in wild type mice. In the renal medulla, there was significant phosphorylation of NKCC2 at SPAK/OSR1-dependent sites despite a complete absence of SPAK and OSR1, suggesting the existence of an alternative activating kinase. The distal convoluted tubule has been proposed to sense plasma [K(+) ], with NCC activation serving as the primary effector pathway that modulates K(+) secretion, by metering sodium delivery to the collecting duct. Abundance of phosphorylated NCC (pNCC) is dramatically lower in SPAK-KO mice than in wild type mice, and the additional disruption of OSR1 further reduced pNCC. SPAK-KO and kidney-specific OSR1 single knockout mice maintained plasma [K(+) ] following dietary potassium restriction, but DKO mice developed severe hypokalaemia. Unlike mice lacking SPAK or OSR1 alone, DKO mice displayed an inability to phosphorylate NCC under these conditions. These data suggest that SPAK and OSR1 are essential components of the effector pathway that maintains plasma [K(+) ].

Water, electrolytes, and acid-base alterations in human immunodeficiency virus infected patients

The clinical spectrum of human immunodeficiency virus (HIV) infection associated disease has changed significantly over the past decade, mainly due to the wide availability and improvement of combination antiretroviral therapy regiments. Serious complications associated with profound immunodeficiency are nowadays fortunately rare in patients with adequate access to care and treatment. However, HIV infected patients, and particularly those with acquired immune deficiency syndrome, are predisposed to a host of different water, electrolyte, and acid-base disorders (sometimes with opposite characteristics), since they have a modified renal physiology (reduced free water clearance, and relatively increased fractional excretion of calcium and magnesium) and they are also exposed to infectious, inflammatory, endocrinological, oncological variables which promote clinical conditions (such as fever, tachypnea, vomiting, diarrhea, polyuria, and delirium), and may require a variety of medical interventions (antiviral medication, antibiotics, antineoplastic agents), whose combination predispose them to undermine their homeostatic capability. As many of these disturbances may remain clinically silent until reaching an advanced condition, high awareness is advisable, particularly in patients with late diagnosis, concomitant inflammatory conditions and opportunistic diseases. These disorders contribute to both morbidity and mortality in HIV infected patients.

The Controversies of Hyponatraemia in Hypothyroidism: Weighing the evidence

Hyponatraemia is a common electrolyte disturbance, with moderate (serum sodium: 125-129 mmol/L) to severe (serum sodium: ≤125 mmol/L) forms of the disease occurring in 4-15% of hospitalised patients. While it is relatively common, determining the underlying cause of this condition can be challenging and may require extensive laboratory investigations. To this end, it is important to ascertain the efficacy of laboratory tests in determining the cause of hyponatraemia. Up to 10% of patients with hypothyroidism also have hyponatraemia. Routine evaluation of thyroid function is often advocated in cases of low serum sodium. A review and discussion of the available literature is presented here to examine this recommendation.

Hyperkalemia develops in some thyroidectomized patients undergoing thyroid hormone withdrawal in preparation for radioactive iodine ablation for thyroid carcinoma

OBJECTIVE

Hyponatremia is observed in hypothyroidism, but it is not known if hypo- or hyperkalemia is associated with hypothyroidism. To study these questions, we determined serum potassium (K(+)) levels in thyroidectomized patients undergoing levothyroxine withdrawal before radioactive iodine (RAI) therapy for thyroid carcinoma.

METHODS

We retrospectively studied the records of 108 patients who had undergone total thyroidectomy for thyroid carcinoma followed by levothyroxine withdrawal and then ablation with RAI at Nagasaki University Hospital from 2009-2013. Blood samples were analyzed for serum K(+) concentrations when patients were euthyroid just before levothyroxine withdrawal and hypothyroid 21 days after levothyroxine withdrawal. We determined the proportion of patients who developed hyperkalemia (K(+) ≥5 mEq/L) and hypokalemia (K(+) ≤3.5 mEq/L).

RESULTS

Five (4.6%) patients developed hyperkalemia and 2 (1.9%) patients developed hypokalemia after levothyroxine withdrawal. The mean serum K(+) level after levothyroxine withdrawal was significantly higher than before levothyroxine withdrawal (4.23 ± 0.50 mEq/L vs. 4.09 ± 0.34 mEq/L; P<.001). After levothyroxine withdrawal, serum K(+) values were significantly correlated with age, serum sodium and creatinine levels, and the estimated glomerular filtration rate but not with serum free thyroxine or thyroid-stimulating hormone concentrations. The finding of an elevated serum K(+) of >0.5 mEq/L after levothyroxine withdrawal was more prevalent with age >60 years (odds ratio [OR], 4.66; P = .026) and with the use of angiotensin-II receptor blockers or angiotensin-converting enzyme inhibitors (OR, 3.53; P = .033) in a multivariate analysis.

CONCLUSION

Hyperkalemia develops in a small percentage of hypothyroid patients after thyroid hormone withdrawal, especially in patients over 60 years of age who are using antihypertensive agents that inhibit the reninangiotensin-aldosterone system.

Hypothyroidism affects differentially the cell size of epithelial cells among oviductal regions of rabbits

Oviductal regions show particular histological characteristics and functions. Tubal pathologies and hypothyroidism are related to primary and secondary infertility. The impact of hypothyroidism on the histological characteristics of oviductal regions has been scarcely studied. Our aim was to analyse the histological characteristics of oviductal regions in control and hypothyroid rabbits. Hypothyroidism was induced by oral administration of methimazole (MMI) for 30 days. For both groups, serum concentrations of thyroid and gonadal hormones were determined. Sections of oviductal regions were stained with the Masson's trichrome technique to analyse both epithelial and smooth muscle layers. The percentage of proliferative epithelial cells (anti-Ki67) in diverse oviductal regions was also quantified. Data were compared with Student t-test, Mann-Whitney U-test, or Fischer's test. In comparison with the control group, the hypothyroid group showed: (i) a low concentration of T3 and T4, but a high level of TSH; (ii) similar values of serum estradiol, progesterone and testosterone; (iii) a large size of ciliated cells in the ampulla (AMP), isthmus (IST) and utero-tubal junction (UTJ); (iv) a large size of secretory cells in the IST region; (v) a low percentage of proliferative secretory cells in the fimbria-infundibulum (FIM-INF) region; and (vi) a similar thickness of the smooth muscle layer and the cross-sectional area in the AMP and IST regions. Modifications in the size of the oviductal epithelium in hypothyroid rabbits could be related to changes in the cell metabolism that may impact on the reproductive functions achieved by oviduct.

Hyperkalemic hypertension-associated cullin 3 promotes WNK signaling by degrading KLHL3

Familial hyperkalemic hypertension (FHHt) is a monogenic disease resulting from mutations in genes encoding WNK kinases, the ubiquitin scaffold protein cullin 3 (CUL3), or the substrate adaptor kelch-like 3 (KLHL3). Disease-associated CUL3 mutations abrogate WNK kinase degradation in cells, but it is not clear how mutant forms of CUL3 promote WNK stability. Here, we demonstrated that an FHHt-causing CUL3 mutant (CUL3 Δ403-459) not only retains the ability to bind and ubiquitylate WNK kinases and KLHL3 in cells, but is also more heavily neddylated and activated than WT CUL3. In cells, activated CUL3 Δ403-459 depleted KLHL3, preventing WNK degradation, despite increased CUL3-mediated WNK ubiquitylation; therefore, CUL3 loss in kidney should phenocopy FHHt in murine models. As predicted, nephron-specific deletion of Cul3 in mice did increase WNK kinase levels and the abundance of phosphorylated Na-Cl cotransporter (NCC). Over time, however, Cul3 deletion caused renal dysfunction, including hypochloremic alkalosis, diabetes insipidus, and salt-sensitive hypotension, with depletion of sodium potassium chloride cotransporter 2 and aquaporin 2. Moreover, these animals exhibited renal inflammation, fibrosis, and increased cyclin E. These results indicate that FHHt-associated CUL3 Δ403-459 targets KLHL3 for degradation, thereby preventing WNK degradation, whereas general loss of CUL3 activity - while also impairing WNK degradation - has widespread toxic effects in the kidney.

Salt-losing nephropathy in hypothyroidism

A 35-year-old man presented with recurrent lower extremity weakness associated with polyuria later progressing to generalised weakness with difficulty in breathing. The patient was hypotensive and dry, with normal thyroid and chest examination, weak lower extremity and carpopedal spasm. Workup revealed hypokalaemia, hyponatraemia, hypocalcaemia, hypomagnesaemia, hypochloraemia and hypophosphataemia. Arterial blood gas showed respiratory alkalosis with good oxygenation. Twenty-four-hour urine collection showed normal volume with electrolyte wasting. Thyroid function test revealed overt hypothyroidism with negative antithyroid peroxidase. The patient was well after treatment with levothyroxine, volume and electrolyte replacement and was discharged. Thyroid hormones are related to the expression of the Na-K-ATPase, Na-Pi cotransporter, Mg-ATPase and Na-Ca exchanger pumps in the renal tubules. Sodium, potassium, phosphate, calcium, magnesium and water losses result from decreased expression of these pumps.

Annexin A2 mediates apical trafficking of renal Na⁺-K⁺-2Cl⁻ cotransporter

The furosemide-sensitive Na(+)-K(+)-2Cl(-) cotransporter (NKCC2) is responsible for urine concentration and helps maintain systemic salt homeostasis. Its activity depends on trafficking to, and insertion into, the apical membrane, as well as on phosphorylation of conserved N-terminal serine and threonine residues. Vasopressin (AVP) signaling via PKA and other kinases activates NKCC2. Association of NKCC2 with lipid rafts facilitates its AVP-induced apical translocation and activation at the surface. Lipid raft microdomains typically serve as platforms for membrane proteins to facilitate their interactions with other proteins, but little is known about partners that interact with NKCC2. Yeast two-hybrid screening identified an interaction between NKCC2 and the cytosolic protein, annexin A2 (AnxA2). Annexins mediate lipid raft-dependent trafficking of transmembrane proteins, including the AVP-regulated water channel, aquaporin 2. Here, we demonstrate that AnxA2, which binds to phospholipids in a Ca(2+)-dependent manner and may organize microdomains, is codistributed with NKCC2 to promote its apical translocation in response to AVP stimulation and low chloride hypotonic stress. NKCC2 and AnxA2 interact in a phosphorylation-dependent manner. Phosphomimetic AnxA2 carrying a mutant phosphoacceptor (AnxA2-Y24D-GFP) enhanced surface expression and raft association of NKCC2 by 5-fold upon low chloride hypotonic stimulation, whereas AnxA2-Y24A-GFP and PKC-dependent AnxA2-S26D-GFP did not. As the AnxA2 effect involved only nonphosphorylated NKCC2, it appears to affect NKCC2 trafficking. Overexpression or knockdown experiments further supported the role of AnxA2 in the apical translocation and surface expression of NKCC2. In summary, this study identifies AnxA2 as a lipid raft-associated trafficking factor for NKCC2 and provides mechanistic insight into the regulation of this essential cotransporter.

Nitric oxide and AQP2 in hypothyroid rats: a link between aging and water homeostasis

OBJECTIVE

Hypothyroid state and aging are associated with impairment in water reabsorption and changes in aquaporin water channel type 2 (AQP2). Nitric oxide (NO) is involved in AQP2 trafficking to the apical plasma membrane in medullary collecting duct cells. The purpose of this study was to investigate whether aging and hypothyroidism alter renal function, and whether medullary NO and AQP2 are implicated in maintaining water homeostasis.

MATERIALS/METHODS

Sprague-Dawley rats aged 2 and 18months old were treated with 0.02% methimazole (w/v) during 28days. Renal function was examined and NO synthase (NOS) activity ([(14)C (U)]-L-arginine to [(14)C (U)]-L-citrulline assays), NOS, caveolin-1 and -3 and AQP2 protein levels were determined in medullary tissue (Western blot). Plasma membrane fraction and intracellular vesicle fraction of AQP2 were evaluated by Western blot and immunohistochemistry.

RESULTS

A divergent response was observed in hypothyroid rats: while young rats exhibited polyuria with decreased medullary NOS activity, adult rats exhibited a decrease in urine output with increased NOS activity. AQP2 was increased with hypothyroidism, but while young rats exhibited increased AQP2 in plasma membrane, adult rats did so in the cytosolic site.

CONCLUSIONS

Hypothyroidism contributes in a differential way to aging-induced changes in renal function, and medullary NO and AQP2 would be implicated in maintaining water homeostasis.

A SPAK isoform switch modulates renal salt transport and blood pressure

The renal thick ascending limb (TAL) and distal convoluted tubule (DCT) play central roles in salt homeostasis and blood pressure regulation. An emerging model suggests that bumetanide- and thiazide-sensitive NaCl transporters (NKCC2 and NCC) along these segments are phosphorylated and activated by WNK kinases, via SPAK and OSR1. Here, we show that a kidney-specific SPAK isoform, which lacks the kinase domain, inhibits phosphorylation of NCC and NKCC2 by full-length SPAK in vitro. Kidney-specific SPAK is highly expressed along the TAL, whereas full-length SPAK is more highly expressed along the DCT. As predicted from the differential expression, SPAK knockout in animals has divergent effects along TAL and DCT, with increased phosphorylated NKCC2 along TAL and decreased phosphorylated NCC along DCT. In mice, extracellular fluid volume depletion shifts SPAK isoform abundance to favor NaCl retention along both segments, indicating that a SPAK isoform switch modulates sodium avidity along the distal nephron.

Generation and analyses of R8L barttin knockin mouse

Barttin, a gene product of BSND, is one of four genes responsible for Bartter syndrome. Coexpression of barttin with ClC-K chloride channels dramatically induces the expression of ClC-K current via insertion of ClC-K-barttin complexes into plasma membranes. We previously showed that stably expressed R8L barttin, a disease-causing missense mutant, is retained in the endoplasmic reticulum (ER) of Madin-Darby canine kidney (MDCK) cells, with the barttin β-subunit remaining bound to ClC-K α-subunits (Hayama A, Rai T, Sasaki S, Uchida S. Histochem Cell Biol 119: 485-493, 2003). However, transient expression of R8L barttin in MDCK cells was reported to impair ClC-K channel function without affecting its subcellular localization. To investigate the pathogenesis in vivo, we generated a knockin mouse model of Bartter syndrome that carries the R8L mutation. These mice display disease-like phenotypes (hypokalemia, metabolic alkalosis, and decreased NaCl reabsorption in distal tubules) under a low-salt diet. Immunofluorescence and immunoelectron microscopy revealed that the plasma membrane localization of both R8L barttin and the ClC-K channel was impaired in these mice, and transepithelial chloride transport in the thin ascending limb of Henle's loop (tAL) as well as thiazide-sensitive chloride clearance were significantly reduced. This reduction in transepithelial chloride transport in tAL, which is totally dependent on ClC-K1/barttin, correlated well with the reduction in the amount of R8L barttin localized to plasma membranes. These results suggest that the major cause of Bartter syndrome type IV caused by R8L barttin mutation is its aberrant intracellular localization.

Phosphate transporters in renal, gastrointestinal, and other tissues

Inorganic phosphate (Pi) is essential for all living organisms. Bound to organic molecules, Pi fulfills structural, metabolic, and signaling tasks. Therefore, cell growth and maintenance depends on efficient transport of Pi across cellular membranes into the intracellular space. Uptake of Pi requires energy because the substrate is transported against its electrochemical gradient. Till recently, 2 major families of physiologically relevant Pi-specific transporters have been identified: the solute carrier families Slc34 and Slc20. Interestingly, phylogenetic links can be detected between prokaryotic and eukaryotic transporters in both families. Because less complex model organisms are often instrumental in establishing paradigms for protein function in human beings, a brief assessment of Slc34 and Slc20 phylogeny is of interest.

Severe hyponatremia in association with I(131) therapy in a patient with metastatic thyroid cancer

Hyponatremia is a common clinical problem that results from various causes. Hypothyroidism is known to be one of the causes of this disorder. We report a case of metastatic thyroid cancer presenting with severe hyponatremia in association with hypothyroidism induced by pretreatment of I(131) therapy, such as a low-iodine diet and withdrawal of thyroid hormone. Serum arginine vasopressin (AVP) was elevated and urine osmolality was higher than that of serum. Saline infusion and thyroid hormone replacement normalized serum sodium and AVP. Inappropriate secretion of AVP in hypothyroid state was thought to be one of the causes of this hyponatremia.

Influences of hypertonic and hypovolemic treatments on vasopressin response in propylthiouracil (PTU) induced hypothyroid rat and effect on supplementation with L-thyroxine

This study was performed to investigate the effects of L-thyroxine treatment on plasma vasopressin (AVP) levels in rats with hypothyroidism induced by propylthiouracil (PTU). Animals were separated into three groups each having 6 rats: control, PTU, PTU+L-thyroxine groups. Then, the groups were further divided into 3 sub-groups including 6 rats (a; basal, b; hypertonic stimulated and c; hypovolemic stimulated). At the end of the experiments all rats were decapitated in order to obtain plasma samples for analysis in terms of Hct, osmolality, TT 3 , TT 4 and vasopressin. Haematocrit (Hct) levels were the highest in hypovolemic stimulated sub-group (P < 0.001). Osmolality levels were higher in hypertonic stimulated sub-groups (P < 0.001). Total T 3 and T 4 values were the lowest in the PTU group and the highest in the L-thyroxine treated group (P < 0.001). Plasma AVP levels were reduced by hypothyroidism. However, L-thyroxine treatment after the hypothyroidism prevented this reduction (P < 0.001). Vasopressin responses to basal, hypovolemic and hypertonic stimulations were the lowest in the PTU group (P < 0.001). The results of the present study show that basal and stimulated plasma vasopressin levels are reduced in PTU-induced hypothyroidism. However, L-thyroxine treatment following hypothyroidism prevents this reduction.

Alterations in osmotic fragility of the red blood cells in hypo- and hyperthyroid patients

BACKGROUND

Changes in concentration of thyroid hormones can affect Na+-K+-ATPase number and activity and phospholipid composition of the cell membranes leading to changes in the surface to volume ratio and strength of membrane.

AIM

In this study, the osmotic fragility of the red blood cells from non-treated hypo- and hyperthyroid patients was compared to that of control subjects.

MATERIAL/SUBJECTS AND METHODS

After 3 washings with normal saline, red blood cells were placed in varying concentrations of sodium chloride (Na- Cl) (0-0.9%) and fragility was assessed with colorimetric method; to do this, after the incubation period, tubes were centrifuged and the optical density of the tubes was measured. Hemolysis percentage in tubes was calculated based on 100% hemolysis in the tubes containing no NaCl (0%).

RESULTS

Osmotic fragility of the cells from hyperthyroid patients in 0.45% NaCl was significantly lower than control subjects (74.6%+/-30.2 vs 93.8%+/-9.1, p<0.01). The osmotic fragility of red blood cells in 0.5% concentration of sodium chloride in hyperthyroid patients was significantly lower compared to that of controls (27.8%+/-26.0 vs 63.5%+/-27.5, p<0.001). No significant difference was observed between the osmotic fragility of the hypothyroid patients compared with control subjects.

CONCLUSIONS

Alteration in osmotic fragility is seen in patients with hyperthyroidism; however, anemia reported in hypo- or hyperthyroid patients is not due to high osmotic fragility of red blood cells and other causes need to be investigated.

Renal Na+-K+-Cl- cotransporter activity and vasopressin-induced trafficking are lipid raft-dependent

Apical bumetanide-sensitive Na(+)-K(+)-2Cl(-) cotransporter (NKCC2), the kidney-specific member of a cation-chloride cotransporter superfamily, is an integral membrane protein responsible for the transepithelial reabsorption of NaCl. The role of NKCC2 is essential for renal volume regulation. Vasopressin (AVP) controls NKCC2 surface expression in cells of the thick ascending limb of the loop of Henle (TAL). We found that 40-70% of Triton X-100-insoluble NKCC2 was present in cholesterol-enriched lipid rafts (LR) in rat kidney and cultured TAL cells. The related Na(+)-Cl(-) cotransporter (NCC) from rat kidney was distributed in LR as well. NKCC2-containing LR were detected both intracellularly and in the plasma membrane. Bumetanide-sensitive transport of NKCC2 as analyzed by (86)Rb(+) influx in Xenopus laevis oocytes was markedly reduced by methyl-beta-cyclodextrin (MbetaCD)-induced cholesterol depletion. In TAL, short-term AVP application induced apical vesicular trafficking along with a shift of NKCC2 from non-raft to LR fractions. In parallel, increased colocalization of NKCC2 with the LR ganglioside GM1 and their polar translocation were assessed by confocal analysis. Apical biotinylation showed twofold increases in NKCC2 surface expression. These effects were blunted by mevalonate-lovastatin/MbetaCD-induced cholesterol deprivation. Collectively, these findings demonstrate that a pool of NKCC2 distributes in rafts. Results are consistent with a model in which LR mediate polar insertion, activity, and AVP-induced trafficking of NKCC2 in the control of transepithelial NaCl transport.

Renal Na+-K+-Cl- cotransporter activity and vasopressin-induced trafficking are lipid raft-dependent

Apical bumetanide-sensitive Na(+)-K(+)-2Cl(-) cotransporter (NKCC2), the kidney-specific member of a cation-chloride cotransporter superfamily, is an integral membrane protein responsible for the transepithelial reabsorption of NaCl. The role of NKCC2 is essential for renal volume regulation. Vasopressin (AVP) controls NKCC2 surface expression in cells of the thick ascending limb of the loop of Henle (TAL). We found that 40-70% of Triton X-100-insoluble NKCC2 was present in cholesterol-enriched lipid rafts (LR) in rat kidney and cultured TAL cells. The related Na(+)-Cl(-) cotransporter (NCC) from rat kidney was distributed in LR as well. NKCC2-containing LR were detected both intracellularly and in the plasma membrane. Bumetanide-sensitive transport of NKCC2 as analyzed by (86)Rb(+) influx in Xenopus laevis oocytes was markedly reduced by methyl-beta-cyclodextrin (MbetaCD)-induced cholesterol depletion. In TAL, short-term AVP application induced apical vesicular trafficking along with a shift of NKCC2 from non-raft to LR fractions. In parallel, increased colocalization of NKCC2 with the LR ganglioside GM1 and their polar translocation were assessed by confocal analysis. Apical biotinylation showed twofold increases in NKCC2 surface expression. These effects were blunted by mevalonate-lovastatin/MbetaCD-induced cholesterol deprivation. Collectively, these findings demonstrate that a pool of NKCC2 distributes in rafts. Results are consistent with a model in which LR mediate polar insertion, activity, and AVP-induced trafficking of NKCC2 in the control of transepithelial NaCl transport.

Wilms' tumor protein (-KTS) modulates renin gene transcription

Renin plays a crucial role in the control of various physiological processes such as blood pressure and body fluid homeostasis. Here, we show that a splice variant of the Wilms' tumor protein lacking three amino acids WT1(-KTS) suppresses renin gene transcription. Using bioinformatics tools, we initially predicted that a WT1-binding site exists in a regulatory region about 12 kb upstream of the renin promoter; this was confirmed by reporter gene assays and gel shift experiments in heterologous cells. Co-expression of Wt1 and renin proteins was found in rat kidney sections, mouse kidney blood vessels, and a cell line derived from the juxtaglomerular apparatus that produces renin. Knockdown of WT1 protein by siRNA significantly increased the cellular renin mRNA content, while overexpression of WT1(-KTS) reduced renin gene expression in stable and transiently transfected cells. A mutant WT1(-KTS) protein found in Wilms' tumors failed to suppress renin gene reporter activity and endogenous renin expression. Our findings show that renin gene transcription is regulated by the WT1(-KTS) protein and this may explain findings in patients with WT1 gene mutations of increased plasma renin and hypertension.