Renal tubular site of action of fluoride in Fischer 344 rats

The Footprints of Mitochondrial Fission and Apoptosis in Fluoride-Induced Renal Dysfunction

Fluoride (F) is widely distributed in the environment and poses serious health risks to humans and animals. Although a good body of literature demonstrates a close relationship between F content and renal system performance, there is no satisfactory information on the involved intracellular routes. Hence, this study used histopathology and mitochondrial fission to explore fluorine-induced nephrotoxicity further. For this purpose, mice were exposed to the F ion (0, 25, 50, 100 mg/L) for 90 days. The effects of different F levels on renal pathomorphology and ion metabolism were assessed using hematoxylin and eosin (H&E), periodic acid-Schiff stain (PAS), periodic acid-silver methenamine (PASM), Prussian blue (PB), and alkaline phosphatase (ALP) staining. The results showed that F could lead to glomerular atrophy, tubular degeneration, and vacuolization. Meanwhile, F also could increase glomerular and tubular glycoproteins; made thickening of the renal capsule membrane and thickening of the tubular basement membrane; led to the accumulation of iron ions in the tubules; and increased in glomerular alp and decreased tubular alp. Concomitantly, IHC results showed that F significantly upregulated the expression levels of mitochondrial fission-related proteins, including mitochondrial fission factor (Mff), fission 1 (Fis1), and mitochondrial dynamics proteins of 49 kDa (MiD49) and 51 kDa (MiD51), ultimately caused apoptosis. To sum up, excessive fluorine has a strong nephrotoxicity effect, disrupting the balance of mitochondrial fission and fusion, interfering with the process of mitochondrial fission, and then causing damage to renal tissue structure and apoptosis.

Stem Cells for Next Level Toxicity Testing in the 21st Century

The call for a paradigm change in toxicology from the United States National Research Council in 2007 initiates awareness for the invention and use of human-relevant alternative methods for toxicological hazard assessment. Simple 2D in vitro systems may serve as first screening tools, however, recent developments infer the need for more complex, multicellular organotypic models, which are superior in mimicking the complexity of human organs. In this review article most critical organs for toxicity assessment, i.e., skin, brain, thyroid system, lung, heart, liver, kidney, and intestine are discussed with regards to their functions in health and disease. Embracing the manifold modes-of-action how xenobiotic compounds can interfere with physiological organ functions and cause toxicity, the need for translation of such multifaceted organ features into the dish seems obvious. Currently used in vitro methods for toxicological applications and ongoing developments not yet arrived in toxicity testing are discussed, especially highlighting the potential of models based on embryonic stem cells and induced pluripotent stem cells of human origin. Finally, the application of innovative technologies like organs-on-a-chip and genome editing point toward a toxicological paradigm change moves into action.

Renal effects of general anesthesia from old to recent studies

Various types of anesthesia are being utilized to maintain physiologically secured surgical conditions. Nearly all categories of general anesthesia are characterized by various perioperative and postoperative complications. These shortcomings are important aspects that need to be considered by the anesthesiologist and surgeon before administration of these compounds. The renal effects of anesthesia play an important role in understanding possible systemic changes due to the fact that the kidney has a direct or indirect impact on nearly all the systems of the body. Various studies have been conducted to find out changes in renal parameters and its systemic effects upon administration of the anesthesia and its postoperative repercussions. Besides that, the impaired renal function might have an impact on the excretion of anesthetic metabolites, which can lead to long-term dysfunction. Patients with a previous history of disease ought to be brought under consideration because these chemicals can ameliorate pre-existent symptoms. This review is intended to discuss the early and latest studies based on the effects of general anesthesia on the renal system.

Exploring the role of excess fluoride in chronic kidney disease: A review

This review covers nearly 100 years of studies on the toxicity of fluoride on human and animal kidneys. These studies reveal that there are direct adverse effects on the kidneys by excess fluoride, leading to kidney damage and dysfunction. With the exception of the pineal gland, the kidney is exposed to higher concentrations of fluoride than all other soft tissues. Therefore, exposure to higher concentrations of fluoride could contribute to kidney damage, ultimately leading to chronic kidney disease (CKD). Among major adverse effects on the kidneys from excessive consumption of fluoride are immediate effects on the tubular area of the kidneys, inhibiting the tubular reabsorption; changes in urinary ion excretion by the kidneys disruption of collagen biosynthesis in the body, causing damages to the kidneys and other organs; and inhibition of kidney enzymes, affecting the functioning of enzyme pathways. This review proposes that there is a direct correlation between CKD and the consumption of excess amounts of fluoride. Studies particularly show immediate adverse effects on the tubular area of human and animal kidneys leading to CKD due to the consumption of excess fluoride. Therefore, it is very important to conduct more investigations on toxicity studies of excess fluoride on the human kidney, including experiments using human kidney enzymes, to study more in depth the impact of excess fluoride on the human kidney. Further, the interference of excess fluoride on collagen synthesis in human body and its effect on human kidney should also be further investigated.

The role of ions, heavy metals, fluoride, and agrochemicals: critical evaluation of potential aetiological factors of chronic kidney disease of multifactorial origin (CKDmfo/CKDu) and recommendations for its eradication

The pollution of water and food through human waste and anthropogenic activities, including industrial waste and agricultural runoff, is a mounting problem worldwide. Water pollution from microbes causes identifiable diarrhoeal illnesses. The consumption of water contaminated with heavy metals, fluoride, and other toxins causes insidious illnesses that lead to protracted, non-communicable diseases and death. Chronic kidney disease of unusual/uncertain/unknown aetiology is one such example, began to manifest in the mid-1960s in several dry-zonal agricultural societies in developing economies that are located around the equator. In Sri Lanka, such a disease is affecting the North Central Province, the rice bowl of the country that first appeared in the mid-1990s. Several potential causes have been postulated, including heavy metals, fluoride, cyanobacterial and algae toxins, agrochemicals, and high salinity and ionicity in water, but no specific source or causative factor has been identified for CKD of multifactorial origin (CKDmfo). Three large studies conducted in the recent past failed to find any of the postulated components (heavy metals, cyanobacterial toxins, fluoride, salinity, or agrochemicals) at levels higher than those deemed safe by the World Health Organization and the US Environmental Protection Agency. At the reported low levels in water and with the heterogeneous geographical distribution, it is unrealistic to expect any of these components individually could cause this disease. However, the additive or synergistic effects of a combination of factors and components, even at lower exposure levels, together with malnutrition and harmful behaviours, and/or a yet-unidentified (or not investigated) toxin, can cause this epidemic. Because the cause is unknown, scientists need to work on broader hypotheses, so that key causative elements are not missed. Taken together the plausibility of multiple factors in the genesis of this disease, the appropriate terminology is CKDmfo, a name that also indicates the need for multi-disciplinary research programs to facilitate identifying the cause(s) and the need for multiple approaches to eradicate it. While some potential causes remain to be investigated, existing data point to polluted water as the main source of this disease. This article evaluates pros and cons of each hypothesis and highlights the importance of among others, providing clean water to all affected and surrounding communities. Available data do not support any of the postulated agents, chemicals, heavy metals, fluoride, salinity/ionicity, or individual agrochemical components, such as phosphate or glyphosate, as causative factors for CKDmfo in Sri Lanka. However, as the CKDmfo name implies, a combination of these factors (or an unknown toxin) together with harmful behaviour and chronic dehydration may cause this disease. Irrespective of the cause, prevention is the only way forward for eradication.

Fluoride-induced apoptosis and expressions of caspase proteins in the kidney of carp (Cyprinus carpio)

The study was conducted to investigate oxidative stress, apoptosis, and protein expressions of caspase-3, 8, and 9 in kidney of the carp juveniles exposed to 0, 40, 80, 120, and 160 mg L(-1) of fluoride (in the form of NaF) for 90 days. The results showed that dose- and time-dependent decrease of SOD and GSH and dose- and time-dependent increase of MDA were observed in the carp juveniles, which suggested that fluoride induced oxidative damage accompanied with morphological changes and significant apoptosis in fish exposed to fluoride, especially in the higher doses. Fluoride exposure also significantly elevated the protein expressions of caspase-3, 8, and 9. In conclusion, these results indicate that chronic exposure to fluoride causes oxidative stress, damages the kidney structure, and results in renal apoptosis by caspase-dependent pathway.

Analgesic use of inhaled methoxyflurane: Evaluation of its potential nephrotoxicity

Methoxyflurane is a volatile, halogenated analgesic, self-administered in a controlled low dose from the Penthrox(®) inhaler for short-term pain relief. It was formerly used in significantly higher doses to produce anaesthesia, when it caused a specific type of dose-related renal tubular damage. The pathogenesis of the renal damage and clinical use of methoxyflurane are discussed here with evidence that a low but effective analgesic dose is not associated with the risk of renal adverse effects. The maximum dose employed to produce analgesia is limited to methoxyflurane 6 mL/day and 15 mL/week, producing a minimum alveolar concentration (MAC) of 0.59 MAC-hours. Renal damage is due to the metabolism of methoxyflurane and release of fluoride ions. Exposure of humans to methoxyflurane ≤2.0 MAC-hours, resulting in serum fluoride ≤40 µmol/L, has not been associated with renal tubular toxicity. The safety margin of analgesic use of methoxyflurane in the Penthrox ((®)) inhaler is at least 2.7- to 8-fold, based on methoxyflurane MAC-hours or serum fluoride level, with clinical experience suggesting it is higher. It is concluded from clinical experience in emergency medicine, surgical procedures and various experimental and laboratory investigations that the analgesic use of methoxyflurane in subanaesthetic doses in the Penthrox inhaler does not carry a risk of nephrotoxicity.

Effects of acute sodium fluoride exposure on kidney function, water homeostasis, and renal handling of calcium and inorganic phosphate

Fluoride compounds are abundant and widely distributed in the environment at a variety of concentrations. Further, fluoride induces toxic effects in target organs such as the liver and kidney. In this study, we performed an early analysis of renal function using a clearance technique in Wistar rats acutely exposed to fluoride at a plasma concentration of 0.625 μg/ml. Our results revealed that fluoride, at a concentration close to the concentration present in the serum after environmental exposure, induced a significant tubular dysfunction, resulting in diluted urine, impaired protein reabsorption, and increased calcium and phosphate urinary excretion. Our work demonstrates that even acute exposures to low concentrations of NaF may induce renal damage and confirms that, after exposure, the kidney participates directly in the calcium and phosphate deficiencies observed in fluoride-exposed populations.

The role of cytochrome P450 enzymes in hepatic and extrahepatic human drug toxicity

The human cytochrome P450 enzyme system metabolises a wide array of xenobiotics to pharmacologically inactive metabolites, and occasionally, to toxicologically active metabolites. Impairment of cytochrome P450 activity, which may be either genetic or environmental, may lead to toxicity caused by the parent compound itself. In practise, this usually only applies to drugs that have a narrow therapeutic index and when their clearance is critically dependent upon the fraction normally metabolised by that pathway. P450 enzymes may also convert the drug to a chemically reactive metabolite, which, if not detoxified, may lead to various forms of hepatic and extrahepatic toxicity, including cellular necrosis, hypersensitivity, teratogenicity, and carcinogenicity, depending on the site of formation and the relative stability of the metabolite, and the cellular macromolecule with which it reacts. Variation in the regulation and expression of the drug metabolising enzymes may play a key role in both interindividual variation in sensitivity to drug toxicity and tissue-specific damage. Avoidance of toxicity may be possible in rare instances by prediction of individual susceptibility or by designing new chemical entities that are metabolised by a range of enzymes (both cytochromes P450 and others) and do not undergo bioactivation.

[Changes in renal function induced by anesthesia]

The rate of urine formation and its composition are influenced by the different drugs used during surgery. Anaesthetics act on renal function, not only directly, but also by producing changes in cardiovascular function and in neuroendocrine activity. Many factors may be incriminated: lowered blood pressure and cardiac output, increased sympathetic outflow (renal nerve stimulation and increased plasma catecholamines), increased release of renin, angiotensin and vasopressin. The effects of anaesthetics on the kidney go beyond a simple change in basal haemodynamics and include, for some drugs, an alteration in the ability for the kidney to autoregulate its blood flow and glomerular filtration rate. Studies on toad bladders showed a decrease in transport of water, sodium and organic anions. But, in fact, renal effects of anaesthetics in man and animals depend on the species, the anaesthetic and the method used to study the effect. Most barbiturates and inhalational anaesthetics tend to decrease renal blood flow (RBF) and glomerular filtration rate (GFR). These trends are gradually reversed during recovery. The effects of ketamine and diazepam are not clearly defined. Morphine and fentanyl decrease urine flow and GFR, whilst RBF increases or decreases, depending on whether a direct or indirect measurement technique was used. Muscle relaxants have little effect on renal function. Spinal and epidural anaesthesia only slightly decrease GFR and RBF in proportion to the decrease in mean arterial pressure. Obviously, the preexisting intravascular volume and the quantity of intravenous fluids given strongly influence the renal response to spinal and epidural anaesthesia. Some studies have shown that urine flow rate, creatinine clearance, urinary sodium excretion and RBF are reduced during mechanical ventilation with positive end-expiratory pressure. Surgery itself influences renal function by inducing alterations in prerenal haemodynamics. Operative stress leads to an increase in circulating catecholamines and angiotensin. Significant fluid shifts, excessive blood loss and redistribution of a third space may lead to a prerenal oliguric state, increasing secretion of vasopressin. Acute renal failure (ARF) is a frequently lethal complication of critical surgical illness, due to a variety of factors which interfere with glomerular filtration and tubular reabsorption, such as renal hypoperfusion or nephrotoxic insults. In fact, the initiating aggression ultimately culminates in the development of one or more of the maintenance factors (decreased tubular function, tubular obstruction, decreased GFR and RBF) that reduce urine flow and osmolar excretion. Good management during the perioperative period tends to minimize the risk of developing ARF.

The effects of fluoridated water on rat urine and tissue cAMP levels

Male Wistar rats were fed a fluoride deficient diet (less than 0.5 parts/10(6) F), and either distilled water or fluoridated water (1.0 parts/10(6)). By week 3, the control group had urinary excretions of 106 +/- 5 nmol cAMP/day (mean +/- SEM) whereas the experimental group excreted 129 +/- 6 nmol cAMP/day. After 111 days, the control group excreted 270 +/- 26 nmol cAMP/day compared to 600 +/- 78 nmol cAMP/day for the experimental group. Body weight, food and water consumption, urine volume, and urinary creatinine and phosphate levels were not significantly different between the two groups. Tissue cAMP levels were determined after 4, 6 and 16 weeks. By week 4, the rats receiving the fluoridated water had significantly higher levels of cAMP in the liver (113 per cent) tibia (130 per cent), femur (89 per cent) and heart (35 per cent). At week 6, the liver (119 per cent), tibia (296 per cent), heart (168 per cent), kidney (73 per cent) and submandibular gland (27 per cent) had significantly higher levels of cAMP. By week 16, the liver, femur, kidney and submandibular gland continued to have elevated levels of cAMP. Liver glycolytic metabolites were determined after 6 weeks, and the results suggested a decrease in pyruvate kinase activity.

Effects of prolonged anesthesia with enflurane or halothane on renal function in dogs

Elevated serum inorganic fluoride levels (60-300 mumol/l), maintained over 6 h, influenced renal function in beagle dogs. Changes in water reabsorption were seen with an increased urine flow and free water clearance and decreased urinary concentration capacity. Possible nephrotoxicity as an effect of inorganic fluoride production during prolonged enflurane anesthesia was evaluated in a group of beagle dogs. Another group of dogs, anesthetized with halothane in equianesthetic doses, was studied for comparison. Serum inorganic fluoride levels and urinary oxalate excretion were determined and postanesthetic renal morphology was examined. Renal function was evaluated from endogenous clearances and concentration capacity before and after anesthesia. In the enflurane group, serum inorganic fluoride levels peaked at 22.5 mumol/l at the end of anesthesia and decreased rapidly in the postanesthetic period. Urinary oxalate excretion did not increase. No changes in renal morphology were found. Renal function tests did not reveal any disturbance after enflurane anesthesia. The two anesthetized groups did not differ in any of the parameters studied, except in serum inorganic fluoride levels.

Effects of renal function on serum fluoride level in dogs during and after enflurane anesthesia

To study the effect of renal function on the increased serum inorganic fluoride level produced by the metabolism of enflurane, three groups of beagle dogs were exposed to prolonged enflurane anesthesia, 1.25 MAC for 8 h. One group was studied both with and without renal function, one group only without renal function, and one group on two different occasions with renal function intact. Serum inorganic fluoride levels were determined every hour during the enflurane anesthesia and on termination for a further 4 h. In dogs with no renal function, the increase rate and the peak of serum inorganic fluoride level were significantly higher than in dogs with renal function. The average peak level in dogs with renal function was 21.4 mumol/l and in dogs with no renal function 38.4 mumol/l. Renal function was found to have the same capacity to increase the inorganic fluoride elimination from serum as other routes of elimination. At corresponding serum levels, the rate of decrease after terminating enflurane anesthesia was 3.5-4.0 mumol/l/h lower without renal function. Reanesthesia after 3 weeks did not significantly change the serum inorganic fluoride levels compared to the first anesthesia.

Enflurane anesthesia in living donor renal transplantation

Two groups of patients undergoing elective living donor renal transplantation were studied during enflurane or halothane supplemented anesthesia. The duration of anesthesia was similar in both groups. The mean administered enflurane dose was 243 vol % min; the corresponding halothane dose was 56 vol % min. In the enflurane group, the mean serum inorganic fluoride level peaked at 21.0 mumol/l 3 h after the end of anesthesia. The inorganic fluoride level in urine produced by the renal graft increased continuously, but did not peak, during the first 24 postanesthetic hours. The renal graft quickly started to function in all patients in both groups. The frequency of rejection reactions was higher in the enflurane group than in the halothane group. Serum creatinine levels decreased rapidly in both groups. Urine flow was high on the day of transplantation, but normalized on the first postanesthetic day. Renal sodium clearance decreased earlier in the enflurane group than in the halothane group. This difference was statistically significant on the first postanesthetic day. In the enflurane group, the required pancuronium dose was significantly lower than in the halothane group. In one patient in the enflurane group, the serum inorganic fluoride level increased to 37.5 mumol/l. In this patient renal tubular function may have been affected, but the change was not conclusive since a pronounced rejection of the graft became evident. Since increases in serum inorganic fluoride level approaching 75% of the threshold level for nephrotoxicity in normal kidneys may occur, enflurane should not be routinely used in anesthesia for renal transplantation.

Reduced fluoride sensitivity of liver cells from rats chronically exposed to fluoride

The fluoride sensitivity, determined as effect on protein synthesis (incorporation of 14C-leucine), of liver and kidney cells in suspension culture was exposed. The cells were freshly prepared by collagenase perfusion from rats given drinking water with or without addition of 100 p.p.m. (5.26 mM) fluoride for 9-28 weeks. The fluoride sensitivity of the liver cells from rats given fluoride sensitivity of the kidney cells from fluoride exposed and control rats appeared similar. Fluoride resistance (i.e. decreased sensitivity) may thus develop also in cells in vivo. When exposed to 3 mM NaF for 1 hour the intracellular concentration of fluoride in liver cells from fluoride exposed and controls animals were similar.

Anesthesia for cesarean section.--VI Late effects on the infant of enflurane anesthesia for cesarean section

Enflurane anesthesia for cesarean section has given favourable results with regard to anesthetic effect and lack of depression of the neonate. Enflurane is metabolized to fluoride. High serum levels of inorganic fluoride are nephrotoxic. The nephrotoxic level is known for healthy adult kidneys but not for neonatal kidneys. In a study on enflurane anesthesia for cesarean section serum analyses revealed increased inorganic fluoride levels in the neonates. To exclude unwanted effects on the children, a follow-up study was undertaken 6-12 months after delivery. General development and renal function were studied. No abnormalities were found, indicating that enflurane anesthesia for cesarean section has no persistent unfavourable effects on the children.

Renal function and fluoride formation and excretion during enflurane anaesthesia

Central circulation, renal function, and fluoride formation and excretion were studied in nine patients during enflurane anaesthesia and surgery. Cardiac output and mean systemic arterial pressure remained unchanged compared with preoperative control values. During anaesthesia and surgery, urine flow rate, inulin clearance, PAH clearance and fractional sodium excretion were 60, 65, 55, and 45% of control values, respectively. Mean peak plasma level of fluoride was 20.0 microM. It was reached 4 hours after termination of anaesthesia. Fluoride clearance (CF) decreased from 23.9 ml . min-1 to 2.7 ml . min-1 during anaesthesia. Postoperative, CF increased to 41.6 and 76.0 ml . min-1, respectively, during two consecutive measurement periods. There was no correlation between plasma fluoride levels and depression of any renal function variable.

Effects of enflurane anesthesia on the function of ischemically damaged kidneys

Enflurane is metabolized to inorganic fluoride. Serum levels of inorganic fluoride exceeding 50 microM/l are considered nephrotoxic for normal kidneys. Renal damage has not been observed after enflurane anesthesia in patients with normal renal function. Further impairment in patients with previously damaged kidneys has been reported. The restitution of function of ischemically damaged kidneys was studied in two groups of dogs. In one of the groups, dogs were submitted to a long duration enflurane anesthesia. The other group served as a control. In the first group the serum level of inorganic fluoride at the end of the anesthesia was 27.9 microM/l. Renal function was studied with endogenous clearances and concentration capacity. The inorganic fluoride level achieved by enflurane anesthesia did not influence the restitution of renal function.

Enflurane nephrotoxicity and pre-existing renal dysfunction

This study provides the first morphological evidence of significant structural damage following high doses of enflurane alone and confirms previous findings of transient renal functional abnormalities following high dosage enflurane. The study also indicates that enflurane may have a greater potential for renal toxicity in the presence of renal impairment. Treatment of Fischer 344 rats with a nephrotoxic dose of gentamicin prior to six hours of enflurane (GE) anaesthesia at 1 MAC resulted in increased serum concentration of the enflurance metabolite inorganic fluoride (GE, 43.9 +/- 1.5; E, 34.5 +/- 1.8 mu mol/L), increased urine flow rate and a greater degree of structural damage in renal proximal convoluted tubule cells than was observed with either gentamicin (G) or enflurane (E) alone. Treatment with gentamicin prior to enflurane also resulted in reduced urinary osmolality compared to enflurane or gentamicin alone (GE, 742 +/- 57; E, 1709 +/- 66; G, 985 +/- 32 m0sm/kg).

Osmometry. 2. Osmoregulation

The maintenance of osmolar constancy of the body fluids is dependent upon the recognition of osmolar disequilibrium and its correction by modifying the ingestion and excretion of fluid and solute. Osmolar changes are sensed by the hypothalamus which regulates the secretion of antidiuretic hormone to modify the renal excretion of water. The integrity of the system depends upon the renal ability to vary the solute concentration of urine.

A dose-response study in man of the metabolism of enflurane used as a supplement

The metabolism of enflurane, used as a supplement to muscle relaxant and nitrous oxide anaesthesia, was studied in 19 healthy adult male surgical patients; seven control patients received halothane.

Patients receiving enflurane were randomly allocated to three groups:

Group I—1/2 MAC for 1/2 hour (dosage=1/4 MAC hour)

Group II—1/2 MAC for 2 hours (dosage=1 MAC hour)

Group III—1/2 MAC for 4 hours (dosage=2 MAC hours)

Metabolism of enflurane to inorganic fluoride (F-) was indicated by elevated serum F-concentration and elevated urinary excretion of F-. Peak serum F- concentration was measured in samples collected immediately at the end of enflurane anaesthesia and fell thereafter, approaching pre-operative levels at 48 hours; mean peak serum F- was 23·6± 4·2 μmol/l after 2 MAC hours of enflurane, 17·7±2·8 μmol/l after 1 MAC hour and 10·5± 0·9 μmol/l after 1/4 MAC hour. Nephrotoxic levels of serum F- (50 μmol/l) were not reached in any patient. Post anaesthetic renal function, including response to vasopressin, was normal in all groups. A dose-response relationship between enflurane dose and F- in serum and urine was established.