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Endocrine Reviews Sep 2023Hyponatremia is the most common electrolyte disorder, affecting more than 15% of patients in the hospital. Syndrome of inappropriate antidiuresis (SIAD) is the most... (Review)
Review
Hyponatremia is the most common electrolyte disorder, affecting more than 15% of patients in the hospital. Syndrome of inappropriate antidiuresis (SIAD) is the most frequent cause of hypotonic hyponatremia, mediated by nonosmotic release of arginine vasopressin (AVP, previously known as antidiuretic hormone), which acts on the renal V2 receptors to promote water retention. There are a variety of underlying causes of SIAD, including malignancy, pulmonary pathology, and central nervous system pathology. In clinical practice, the etiology of hyponatremia is frequently multifactorial and the management approach may need to evolve during treatment of a single episode. It is therefore important to regularly reassess clinical status and biochemistry, while remaining alert to potential underlying etiological factors that may become more apparent during the course of treatment. In the absence of severe symptoms requiring urgent intervention, fluid restriction (FR) is widely endorsed as the first-line treatment for SIAD in current guidelines, but there is considerable controversy regarding second-line therapy in instances where FR is unsuccessful, which occurs in around half of cases. We review the epidemiology, pathophysiology, and differential diagnosis of SIAD, and summarize recent evidence for therapeutic options beyond FR, with a focus on tolvaptan, urea, and sodium-glucose cotransporter 2 inhibitors.
Topics: Humans; Hyponatremia; Inappropriate ADH Syndrome; Water-Electrolyte Balance; Neoplasms
PubMed: 36974717
DOI: 10.1210/endrev/bnad010 -
Nature Dec 2023Maintenance of renal function and fluid transport are essential for vertebrates and invertebrates to adapt to physiological and pathological challenges. Human patients...
Maintenance of renal function and fluid transport are essential for vertebrates and invertebrates to adapt to physiological and pathological challenges. Human patients with malignant tumours frequently develop detrimental renal dysfunction and oliguria, and previous studies suggest the involvement of chemotherapeutic toxicity and tumour-associated inflammation. However, how tumours might directly modulate renal functions remains largely unclear. Here, using conserved tumour models in Drosophila melanogaster, we characterized isoform F of ion transport peptide (ITP) as a fly antidiuretic hormone that is secreted by a subset of yki gut tumour cells, impairs renal function and causes severe abdomen bloating and fluid accumulation. Mechanistically, tumour-derived ITP targets the G-protein-coupled receptor TkR99D in stellate cells of Malpighian tubules-an excretory organ that is equivalent to renal tubules-to activate nitric oxide synthase-cGMP signalling and inhibit fluid excretion. We further uncovered antidiuretic functions of mammalian neurokinin 3 receptor (NK3R), the homologue of fly TkR99D, as pharmaceutical blockade of NK3R efficiently alleviates renal tubular dysfunction in mice bearing different malignant tumours. Together, our results demonstrate a novel antidiuretic pathway mediating tumour-renal crosstalk across species and offer therapeutic opportunities for the treatment of cancer-associated renal dysfunction.
Topics: Animals; Humans; Mice; Antidiuretic Agents; Cyclic GMP; Disease Models, Animal; Drosophila melanogaster; Kidney Diseases; Malpighian Tubules; Neoplasms; Nitric Oxide Synthase; Receptors, Neurokinin-3; Xenograft Model Antitumor Assays; Arginine Vasopressin; Drosophila Proteins; Neuropeptides
PubMed: 38057665
DOI: 10.1038/s41586-023-06833-8 -
American Journal of Physiology. Renal... Jan 2024Tolvaptan, a vasopressin antagonist selective for the V2-subtype vasopressin receptor (V2R), is widely used in the treatment of hyponatremia and autosomal-dominant...
Tolvaptan, a vasopressin antagonist selective for the V2-subtype vasopressin receptor (V2R), is widely used in the treatment of hyponatremia and autosomal-dominant polycystic kidney disease (ADPKD). Its effects on signaling in collecting duct cells have not been fully characterized. Here, we perform RNA-seq in a collecting duct cell line (mpkCCD). The data show that tolvaptan inhibits the expression of mRNAs that were previously shown to be increased in response to vasopressin including aquaporin-2, but also reveals mRNA changes that were not readily predictable and suggest off-target actions of tolvaptan. One such action is activation of the MAPK kinase (ERK1/ERK2) pathway. Prior studies have shown that ERK1/ERK2 activation is essential in the regulation of a variety of cellular and physiological processes and can be associated with cell proliferation. In immunoblotting experiments, we demonstrated that ERK1/ERK2 phosphorylation in mpkCCD cells was significantly reduced by vasopressin, in contrast to the increases seen in non-collecting-duct cells overexpressing V2R in prior studies. We also found that tolvaptan has a strong effect to increase ERK1/ERK2 phosphorylation in the presence of vasopressin and that tolvaptan's effect to increase ERK1/ERK2 phosphorylation is absent in mpkCCD cells in which both protein kinase A (PKA)-catalytic subunits have been deleted. Thus, it appears that the tolvaptan effect to increase ERK activation is PKA-dependent and is not due to an off-target effect of tolvaptan. We conclude that in cells expressing V2R at endogenous levels: ) vasopressin decreases ERK1/ERK2 activation; ) in the presence of vasopressin, tolvaptan increases ERK1/ERK2 activation; and ) these effects are PKA-dependent. Vasopressin is a key hormone that regulates the function of the collecting duct of the kidney. ERK1 and ERK2 are enzymes that play key roles in physiological regulation in all cells. The authors used collecting duct cell cultures to investigate the effects of vasopressin and the vasopressin receptor antagonist tolvaptan on ERK1 and ERK2 phosphorylation and activation.
Topics: Tolvaptan; Receptors, Vasopressin; Phosphorylation; MAP Kinase Signaling System; Kidney; Antidiuretic Hormone Receptor Antagonists; Vasopressins
PubMed: 37916285
DOI: 10.1152/ajprenal.00124.2023 -
The Surgical Clinics of North America Aug 2023Renovascular hypertension (RVH) is a secondary form of high blood pressure resulting from impaired blood flow to the kidneys with subsequent activation of the... (Review)
Review
Renovascular hypertension (RVH) is a secondary form of high blood pressure resulting from impaired blood flow to the kidneys with subsequent activation of the renin-angiotensin-aldosterone system. Often, this occurs due to abnormally small, narrowed, or blocked blood vessels supplying one or both kidneys (ie: renal artery occlusive disease) and is correctable. Juxtaglomerular cells release renin in response to decreased pressure, which in turn catalyzes the cleavage of circulating angiotensinogen synthesized by the liver to the decapeptide angiotensin I. Angiotensin-converting enzyme then cleaves angiotensin I to form the octapeptide angiotensin II, a potent vasopressor and the primary effector of renin-induced hypertension. The effects of angiotensin II are mediated by signaling downstream of its receptors. Angiotensin receptor type 1 is a G-protein-coupled receptor that activates vasoconstrictor and mitogenic signaling pathways resulting in peripheral arteriolar vasoconstriction and increased renal tubular reabsorption of sodium and water which promotes intravascular volume expansion. Angiotensin II stimulates the adrenal cortical release of aldosterone, which promotes renal tubular sodium reabsorption, resulting in volume expansion. Angiotensin II acts on glial cells and regions of the brain responsible for blood pressure regulation increasing renal sympathetic activation. Angiotensin II simulates the release of vasopressin from the pituitary which stimulates thirst and water reabsorption from the kidney to expand the intravascular volume and cause peripheral vasoconstriction (increased sympathetic tone). All of these mechanisms coalesce to increase arterial pressure by way of arteriolar constriction, enhanced cardiac output, and the retention of sodium and water.
Topics: Humans; Hypertension, Renovascular; Renin; Angiotensin II; Angiotensin I; Hypertension; Blood Pressure; Sodium
PubMed: 37455034
DOI: 10.1016/j.suc.2023.05.007 -
International Journal of Molecular... Oct 2023In patients with heart failure (HF), the neuroendocrine systems of the sympathetic nervous system (SNS), the renin-angiotensin-aldosterone system (RAAS) and the arginine... (Review)
Review
In patients with heart failure (HF), the neuroendocrine systems of the sympathetic nervous system (SNS), the renin-angiotensin-aldosterone system (RAAS) and the arginine vasopressin (AVP) system, are activated to various degrees producing often-observed tachycardia and concomitant increased systemic vascular resistance. Furthermore, sustained neurohormonal activation plays a key role in the progression of HF and may be responsible for the pathogenetic mechanisms leading to the perpetuation of the pathophysiology and worsening of the HF signs and symptoms. There are biomarkers of activation of these neurohormonal pathways, such as the natriuretic peptides, catecholamine levels and neprilysin and various newer ones, which may be employed to better understand the mechanisms of HF drugs and also aid in defining the subgroups of patients who might benefit from specific therapies, irrespective of the degree of left ventricular dysfunction. These therapies are directed against these neurohumoral systems (neurohumoral antagonists) and classically comprise beta blockers, angiotensin-converting enzyme (ACE) inhibitors/angiotensin receptor blockers and vaptans. Recently, the RAAS blockade has been refined by the introduction of the angiotensin receptor-neprilysin inhibitor (ARNI) sacubitril/valsartan, which combines the RAAS inhibition and neprilysin blocking, enhancing the actions of natriuretic peptides. All these issues relating to the neurohumoral activation in HF are herein reviewed, and the underlying mechanisms are pictorially illustrated.
Topics: Humans; Neprilysin; Tetrazoles; Angiotensin Receptor Antagonists; Heart Failure; Angiotensin-Converting Enzyme Inhibitors; Drug Combinations; Renin-Angiotensin System; Natriuretic Peptides; Aminobutyrates; Biphenyl Compounds
PubMed: 37895150
DOI: 10.3390/ijms242015472 -
Clinical and Molecular Hepatology Oct 2023Hyponatremia is primarily a water balance disorder associated with high morbidity and mortality. The pathophysiological mechanisms behind hyponatremia are... (Review)
Review
Hyponatremia is primarily a water balance disorder associated with high morbidity and mortality. The pathophysiological mechanisms behind hyponatremia are multifactorial, and diagnosing and treating this disorder remains challenging. In this review, the classification, pathogenesis, and step-by-step management approaches for hyponatremia in patients with liver disease are described based on recent evidence. We summarize the five sequential steps of the traditional diagnostic approach: 1) confirm true hypotonic hyponatremia, 2) assess the severity of hyponatremia symptoms, 3) measure urine osmolality, 4) classify hyponatremia based on the urine sodium concentration and extracellular fluid status, and 5) rule out any coexisting endocrine disorder and renal failure. Distinct treatment strategies for hyponatremia in liver disease should be applied according to the symptoms, duration, and etiology of disease. Symptomatic hyponatremia requires immediate correction with 3% saline. Asymptomatic chronic hyponatremia in liver disease is prevalent and treatment plans should be individualized based on diagnosis. Treatment options for correcting hyponatremia in advanced liver disease may include water restriction; hypokalemia correction; and administration of vasopressin antagonists, albumin, and 3% saline. Safety concerns for patients with liver disease include a higher risk of osmotic demyelination syndrome.
Topics: Humans; Hyponatremia; Liver Diseases; Antidiuretic Hormone Receptor Antagonists; Water
PubMed: 37280091
DOI: 10.3350/cmh.2023.0090