Proteinuria: changes and mechanisms in toxic nephropathies

The nephrotoxicity of Aristolochia rotunda L. in rats: Mitochondrion as a target for renal toxicity of Aristolochic acids-containing plants

In recent years, there has been a growing trend in the usage of traditional medicine and herbal treatments. However, the misconception that they are completely safe resulted in irreversible complications and damages. The present study was conducted to investigate the potential renal toxicity of a commonly used drug in Iran's traditional medicine and pharmacy, known as Zaravand Gerd or Nokhod Alvand (Aristolochia rotunda L.). In Iranian traditional medicine, Zaravand Gerd is used as a remedy for respiratory system ailments, back pain, anxiety, headache and septic wounds. Fifty-six male rats were divided into seven groups (n = 8). The first group served as the control and received normal saline, while the second to seventh groups were administered varying doses of the aqueous extract of Zaravand Gerd (0.1, 0.5, 1.25, 2.5, and 5 g/kg) for a period of three weeks. Various parameters were measured to evaluate the potential kidney damage caused by the extract, including serum creatinine and BUN levels, as well as urine protein and glucose levels, which were analyzed using an autoanalyzer. Additionally, kidney tissue samples were examined pathologically, and mitochondria from the kidney tissue were isolated to assess mitochondrial parameters. The results of this study revealed that high doses of Zaravand Gerd extract led to a significant increase in urinary glucose and protein excretion compared to the control group. Pathological examination of the isolated kidney tissues indicated that the concentrations of 2.5 and 5 g/kg of Zaravand Gerd extract resulted in kidney damage and dilation of proximal convoluted tubules. Furthermore, the study demonstrated that high doses of the extract (2.5 and 5 g/kg) caused damage to the mitochondria. Based on the findings of this study, it can be concluded that the administration of high doses of Zaravand Gerd extract, which are not commonly used in traditional medicine, can have toxic effects on the kidneys in rats as an animal model. These results highlight the importance of considering the potential risks associated with herbal medicines and the necessity of usage based on scientific evidence.

Effect of mercury vapour exposure on urinary excretion of calcium, zinc and copper: relationship to alterations in functional and structural integrity of the kidney

Background: The kidney has a remarkable capacity to concentrate mercury (Hg) and as such is a primary target organ when exposure to Hg occurs, and it is also an organ for Hg excretion. Objective: The present work aims to investigate the effect of occupational Hg vapour exposure on the urinary excretion of calcium (Ca), zinc (Zn) and copper (Cu), and the possible association of this excretion to work duration as well as renal alterations. Methods: 83 non-smoker participants (36 referents, age: 35.69/9.5 years; 27 Hg vapour-exposed workers with 5/10 years work duration, age: 33.09/5.1 years; and 20 Hg vapour-exposed workers with]/11 years work duration, age: 39.509/8.50 years) were included in the present study. Urinary levels of microalbumin (U-Malb) and retinol-binding protein (U-RBP) as well as cytosolic glutathione S-transferase activity (U-GST) were measured to assess the glomerular and proximal tubular reabsorption functions as well as structural integrity of proximal tubules; respectively. In addition, blood Hg (B-Hg), serum levels of Hg (S-Hg) and Ca (S-Ca), and urinary levels of Hg (U-Hg), Ca (U-Ca), Zn (U-Zn), Cu (U-Cu) and creatinine (U-cr) were estimated. Results: In comparison to referents, all investigated parameters showed significant increase (except S-Ca and U-Zn/U-Cu ratio that significantly decreased among the workers as one group, S-Ca and U-Zn/U-Cu ratio that significantly and nonsignificantly decreased; respectively among workers with 5/10 years work duration, S-Ca and U-Zn/U-Cu ratio that significantly decreased among workers with]/11 years work duration). In addition, B-Hg was nonsignificantly increased and S-Ca was significantly decreased; also, both U-Hg and U-Zn/U-Cu were nonsignificantly decreased among workers with]/11 years work duration in comparison to those with 5/10 years work duration. Also, each of U-Hg, U-Ca, U-Zn and U-Cu was related to one another, while each of U-Ca, U-Zn and U-Cu was related to each of U-Malb, U-RBP and U-GST (except U-Zn was not related to U-GST). Conclusion: Hg vapour exposure leads to renal alterations which may parallel the change in proteinuria and enzymuria as well as the increased loss in urine of each of Ca, Zn and Cu. The urinary assessment of these metals may be used as a good indicator for renal dysfunction.

Should screening of renal markers be recommended in a working population?

INTRODUCTION

It is debated whether the general population should be screened for kidney disease. This study evaluated whether screening of albuminuria and estimated glomerular filtration rate (eGFR) in a working population should be recommended to detect subjects with chronic kidney disease.

METHODS

The unreferred renal insufficiency study is a cross-sectional study in 1,398 workers aged 17-65. Markers of cardiovascular and renal disease were measured. Cardiovascular risk (CVR) was defined by hypertension (n = 416), diabetes (n = 45), dyslipidemia (n = 159) and/or history of a cardiovascular event (n = 10).

RESULTS

In our population, 5 % of the workers had microalbuminuria, 0.5 % had macroalbuminuria and <0.1 % had eGFR <60 ml/min/1.73 m(2). All workers with an eGFR <60 ml/min/1.73 m(2) and/or macroalbuminuria (8/8) had at least one CVR factor, whereas this was the case in only half of workers with microalbuminuria (36/73, p = 0.007). In workers without CVR factors, the presence of microalbuminuria was associated with low body mass index (BMI, p < 0.001) or physiochemical exposure risk (p < 0.001).

CONCLUSIONS

Screening of renal markers in a working population, identified only a few subjects with an eGFR <60 ml/min/1.73 m(2) or macroalbuminuria. Although microalbuminuria was more prevalent, it might not necessarily indicate kidney disease, as it may have a completely different meanings depending of the phenotype of the screened subjects. Besides underlying CVR factors, microalbuminuria was also associated with low BMI in absence of any risk factor, suggesting presence of benign postural proteinuria. In addition, microalbuminuria also seemed to be related to physicochemical exposure. In view of the impossibility to further analyze this finding in the present study, the meaning of this observation needs to be further investigated.

Biomarkers of kidney integrity in children and adolescents with dental amalgam mercury exposure: findings from the Casa Pia children's amalgam trial

Mercury is toxic to the kidney, and dental amalgam is a source of mercury exposure. Few studies have evaluated the effects of dental amalgam on kidney function in a longitudinal context in children. Here, we evaluated urinary concentrations of glutathione S-transferases (GSTs) alpha and pi as biomarkers of renal proximal and distal tubular integrity, respectively, and albumin as a biomarker of glomerular integrity in children and adolescents 8-18 years of age over a 7-year course of dental amalgam treatment. Five hundred seven children, 8-12 years of age at baseline, participated in a clinical trial to evaluate the neurobehavioral and renal effects of dental amalgam in children. Subjects were randomized to either dental amalgam or resin composite treatments. Urinary GSTs alpha and pi, albumin, and creatinine concentrations were measured at baseline and annually in all subjects. Results were evaluated using linear regression analysis. GST-alpha concentrations were similar between treatment groups and in each sex and race (white vs. non-white) group in each follow-up year. GST-pi levels tended upward over the course of follow-up by four- to six-fold. This increase was seen in all groups irrespective of the treatment, race, or gender. Females had GST-pi levels approximately twice those of males at all ages. Albumin concentrations were constant throughout the follow-up period and did not differ by treatment, although females had 39% higher albumin levels than males. Additionally, we found no significant effects of amalgam treatment on the proportion of children with microalbuminuria (>30 mg/g creatinine). These findings are relevant within the context of children's health risk assessment as relates to the safety of mercury exposure from dental amalgam on kidney function. These data also provide normative values for sensitive indices of renal functional integrity that may serve in the evaluation of children and adolescents with renal disorders.

Acute, nonfatal intoxication with trichloroethylene

Nonfatal acute inhalation of trichloroethylene (TRI) at work was described. The subject, male, 54 years old, was drawn unconscious by a metal-degreasing machine and immediately sheltered in intensive care unit. Other than basic life support and common laboratory indices, blood and urine were collected to measure dose and kidney effect parameters such as TRI in blood and urine, trichloroethanol (TCE) and trichloroacetic acid (TCA) in urine, and total urinary proteins (TUP), urinary glutamine synthetase (GS) and urinary N-acetyl-beta-D-glucosaminidase (NAG). Two hours after accident, TRI in blood was 9 mg/l, but after 38 h it was below 1 mg/l. TCE and TCA have a peak 11 and 62 h after poisoning, respectively. Acute renal involvement was revealed by a peak of urinary proteins and enzymes 7 h after exposure with a second peak 74 h after. Seven day after hospitalisation the patient was dismissed with complete recovery. This nonfatal intoxication with TRI shows that the exposure was approximately 150 ppm, three times the ACGIH TLV (50 ppm) and that kidney was the only organ affected. Urinary enzymes, in particular GS, are good indices to monitor transient effects of TRI on the kidney.

Nephrotoxicity of organic solvents: biomarkers for early detection

OBJECTIVES

Evidence for a relationship between chronic kidney diseases or progression of already existing diseases (glomerulonephritides) and occupational solvent exposure has been found in case reports, in case-control studies and also in cross-sectional studies. An analysis of the available literature was performed with respect to markers measured in cross-sectional studies that might be useful for an early detection of solvent-induced effects on the kidney.

METHODS

The relevant cross-sectional studies were evaluated and the following markers were analyzed with respect to their suitability as biomarker for renal damage: total protein, albumin, transferrin, IgG, beta(2)-microglobulin, retinol-binding protein, N-acetyl-beta-D: -glucosaminidase, alanine aminopeptidase, beta-galactosidase, beta-glucuronidase, leucin aminopeptidase, alkaline phosphatase, lysozyme, Tamm-Horsfall protein and laminin fragments in urine as well as E-selectin, laminin and anti-laminin antibodies and anti-glomerular basement membrane antibodies in serum.

RESULTS

An increased albumin excretion was observed more frequently in groups of workers exposed to various solvents (like toluene, styrene, aliphatic/aromatic hydrocarbon mixtures, tetrachloroethene, mixtures of chlorinated hydrocarbons) than in controls. No clear pattern emerged for the other markers.

CONCLUSIONS

The determination of albumin excretion in the urine appears to be a useful parameter for monitoring solvent-exposed workers.

Maternal tobacco smoking and lung epithelium-specific proteins in amniotic fluid

The bronchiolar 16 kD Clara cell secretory protein (CC16) and the alveolar surfactant-associated protein A (SP-A) are secreted in the amniotic fluid (AF), where they reflect the growth and the maturity of the fetal lung. To evaluate the possible effects of in utero tobacco smoke exposure upon infant bronchoalveolar epithelium function and maturity, CC16 and SP-A levels were determined in AF obtained at term (36-41 wk) from 28 nonsmoking, 18 smoke-exposed, and 28 smoking mothers with uncomplicated pregnancies. Tobacco smoke exposure was assessed by questionnaire and the assay in AF and maternal urine of cotinine, a stable nicotine metabolite. The specificity of the changes of CC16 and SP-A concentrations in AF was assessed by comparison with nonpulmonary proteins of high- (albumin and transferrin) or low-molecular weight (beta2-microglobulin, retinol binding protein, cystatin-C). Pulmonary and nonpulmonary AF proteins were also compared by two-dimensional gel electrophoresis between smoking and nonsmoking mothers. The levels of CC16 and SP-A as well as low- and high-molecular-weight proteins were not significantly different between the three smoking categories. The protein pattern of AF, established by two-dimensional gel electrophoresis, did not reveal any quantitative or qualitative difference between nonsmoking (n = 10), smoke-exposed (n = 5), and smoking mothers (n = 5). By multiple regression analysis of possible determinants, tobacco smoke did not emerge as a significant predictor of CC16 and SP-A concentrations in AF. SP-A level was dependent only on gestational age at birth (r2 = 0.1, p = 0.001), whereas CC16 correlated only with the levels of low-molecular weight proteins (r2 = 0.2, p = 0.0001). The latter correlation suggests that CC16 enters AF not only as a result of its secretion at the surface of the respiratory tract but also partly following its elimination by the fetal kidney. This study suggests that maternal smoking during pregnancy is not associated with alterations of the secretory functions of the epithelium of the distal airways and the alveoli at term.

Historical control data on urinary and renal tissue biomarkers in naive male Wistar rats

Total proteins, angiotensin-converting enzyme, N-acetyl-beta-D-glucosaminidase, glutamine transaminase K and glutamine synthetase were determined in urine collected overnight (14 h: 6:00 p.m.-8:00 a.m.) from naive male Wistar rats; glutamine transaminase K and glutamine synthetase in the kidney 10,000 g supernatant and p-aminohippurate uptake in renal cortical slices also were measured. Urinary parameters were related both to urinary creatinine concentration and urinary flow rate; kidney parameters were related to protein concentration (enzymes) or slice/medium (S/M) ratio (p-aminohippurate uptake). The following reference ranges (1.0 and 99.0 percentiles) were obtained: urine: total urinary proteins (195 samples) 0.03-0.29 g mmol(-1) creatinine and 0.13-1.77 mg h(-1); angiotensin-converting enzyme (115 samples) 8.9-63.7 micromol mmol(-1) creatinine and 59.4-282.7 nmol h(-1); glutamine transaminase K (115 samples) 0-1.7 micromol mmol(-1) creatinine and 0-8.5 nmol h(-1); N-acetyl-beta-D-glucosaminidase (72 samples) 0.7-5.0 micromol mmol(-1) creatinine and 4.9-28.4 nmol h(-1) (naive male rats did not excrete glutamine synthetase); kidney: glutamine transaminase K (36 samples) 14.5-32.8 nmol mg(-1) protein; glutamine synthetase (22 samples) 13.9-48.6 nmol mg(-1) protein and p-aminohippurate (54 samples) 4.77-17.89 S/M. Urinary creatinine (r = -0.780), total urinary proteins (r = -0.521), angiotensin-converting enzyme (r = -0.650) and N-acetyl-beta-D-glucosaminidase (r = -0.796) but not glutamine transaminase K were well correlated with diuresis. In addition, the same parameters, but not glutamine transaminase K, were well correlated with creatinine (r = 0.604,0.701 and 0.747, respectively). Significant correlation also was observed between urinary indices adjusted to creatinine or urinary flow rate (total urinary proteins: r = 0.813; angiotensin-converting enzyme: r = 0.677; glutamine transaminase K: r = 0.939; N-acetyl-beta-D-glucosaminidase: r = 0.657). Finally, a low but significant correlation was found between total urinary proteins and angiotensin-converting enzyme (r = 0.293) and N-acetyl-beta-D-glucosaminidase (r = 0.471).

Differential toxicity expression of gentamicine in five-sixths nephrectomized rats assigned to three progressive stages of renal dysfunction--establishment of a new screening approach

Progressive renal dysfunction in 5/6 nephrectomized (NX) rats can be physiologically divided into three stages, coinciding with morphological stages, after definition of physiological parameters for identification of stage. Now, for the establishment of a toxicity screening approach using 5/6 NX rats, our concept, "Differential toxicity synchronized with renal dysfunction process could be identified using 5/6 NX rats" was examined by dosing gentamicin. Firstly, electrophoretic fractional changes of urinary proteins during gentamicin treatment were clarified with determination of amino acid sequences and the three differential features were proven, revealing the unpredictable depression of urinary albumin with progression of the stages in NX rats. Secondly, marked elevation of urinary lactate dehydrogenase (LDH) and glucose (GLU) was evident, indicating the intensified hypoxic conditions and glycolysis in tubular cells synchronized with increased tubular damage. Thirdly, these transit metabolic changes were proven as intensive cause for the advancement of renal dysfunction by the reduction of FRelectrolytes and water at the end of each dosing period. These results indicate that toxicity studies of newly developed drugs using 5/6 NX rats have potentiality prior to clinical dosing to the patients.

Effects of subchronic exposure of rats to dichloramine and trichloramine in drinking water

The subchronic toxicity of 0.2-200 ppm dichloramine and 0.2-90 ppm trichloramine in the drinking water of rats was investigated using biochemical, hematological, and histopathological parameters. Animals in the highest dose groups consumed 5-15% less fluid than controls with no significant decrease in body weight gain. No clinical signs of toxicity were observed in either case. Both males and females dosed with 90 ppm trichloramine had significantly increased relative kidney/body weights and the females had increased hepatic glutathione S-transferase and UPD-glucuronosyltransferase activities. No significant changes were detected in other xenobiotic metabolizing enzymes or in serum biochemistry, urine biochemistry, or hematology. Both dichloramine and trichloramine induced minimal to mild adaptive histopathological changes in thyroids and kidneys of animals of both sexes. Dichloramine, but not trichloramine, was associated with histological changes in the gastric cardia characterized by epithelial hyperplasia at concentrations of 2 ppm and above in the males and 200 ppm in the females. This study indicates that dichloramine produced mild histological effects at drinking water concentrations of >0.2 ppm in males (0.019 mg/kg/day) and >2 ppm in females (0.26 mg/kg/day) while trichloramine produced biochemical and mild histological effects at levels of >2 ppm both in males (0.23 mg/kg/day) and in females (0.29 mg/kg/day).

Evidence for an essential role of megalin in transepithelial transport of retinol

Transepithelial transport of retinol is linked to retinol-binding protein (RBP), which is taken up and also synthesized in a number of epithelia. By immunocytochemistry of human, rat, and mouse renal proximal tubules, a strong staining in apical endocytic vacuoles, lysosomes, endoplasmic reticulum, Golgi, and basal vesicles was observed, in accordance with luminal endocytic uptake as well as a constitutive synthesis and basal secretion of RBP. Analysis of mice with target disruption of the gene for the major endocytic receptor of proximal tubules, megalin, revealed no RBP in proximal tubules of these mice. Western blotting and HPLC of the urine of the megalin-deficient mice instead revealed a highly increased urinary excretion of RBP and retinol, demonstrating that glomerular filtered RBP-retinol of megalin-deficient mice escapes uptake by proximal tubules. A direct megalin-mediated uptake of purified RBP-retinol was indicated by surface plasmon resonance analysis and uptake in immortalized rat yolk sac cells. Uptake was partially inhibited by a polyclonal megalin antibody and the receptor-associated protein. The present data show that the absence of RBP-binding megalin causes a significantly increased loss of RBP and retinol in the urine, demonstrating a crucial role of megalin in vitamin A homeostasis.

Verapamil protection against mercuric chloride-induced renal glomerular injury in rats

We have examined the effects of the calcium channel blocker verapamil on the renal glomerular structural damage produced by mercuric chloride in rats. Verapamil (75 micrograms/kg body wt iv) was administered 30 min prior to mercuric chloride injection (HgCl2, 5 mg/kg body wt sc). Verapamil prevented the glomerular proteinuria observed in HgCl2-treated rats. Isolated glomeruli from mercury-treated rats 1 h after injection presented a diminished cross-sectional area as compared with control glomeruli (control [micron2], 26,310 +/- 2545; HgCl2 [micron2], 18,474 +/- 1828) and increased glomerular calcium content (control, 23 +/- 6 nmol/mg protein; HgCl2, 43 +/- 7 nmol/mg protein). Verapamil pretreatment prevented glomerular cross-sectional area (GCSA) diminution and glomerular calcium content rise (GCSA [micron2] Vp + Hg, 28,281 +/- 4654, Ca2+ [nmol/mg protein] Vp + Hg, 18 +/- 5). Renal sections prepared for immunohistochemical detection and histochemical analysis showed increased deposits of fibronectin and lipids and enhanced cellularity in glomerular structures from HgCl2-treated rats. Renal sections from animals pretreated with verapamil showed fibronectin and lipid contents not different from control sections and their histological studies did not show any changes when compared with control. Verapamil pretreatment also protected glomeruli from enhanced leukocyte content (myeloperoxidase activity/mg protein): control, 59 +/- 7; HgCl2, 134 +/- 10; Vp + Hg, 79 +/- 11). HgCl2 also contracts GCSA in vitro; Vp prevented this GCSA diminution. The results described in this study indicate that mercuric chloride nephrotoxicity may be associated not only with changes in renal glomerular haemodynamics, but also with a direct effect on glomerular cells.

Effects of subchronic exposure of monochloramine in drinking water on male rats

A subchronic rat study with paired-water control was conducted to resolve the question of whether monochloramine at 200 ppm in drinking water can cause reduced body weight gain and other changes observed in earlier investigations. Male Sprague-Dawley rats (93 +/- 5 g) were divided into three groups of 10 rats each: the treatment group was fed drinking water containing 200 ppm monochloramine, the control group was fed bicarbonate-buffered water ad libitum, and the paired-water control rats were given a daily volume of bicarbonate-buffered water equal to that consumed by the monochloramine treatment group. Compared to the control group, rats in the treatment group consumed an average of 42% less fluid and 16% less food over the 13-week treatment period and had 15-20% lower final body weight gain. Similar degrees of reduction in food consumption and body weight gain were observed in the paired-water rats. A decreased liver to body weight ratio occurred in the treatment and paired-water groups. Increased inorganic phosphate, albumin, total protein, and urea nitrogen were detected in sera from both the treatment group and the paired-water groups. The paired-water animals had lower levels of white blood cells and lymphocytes, while the paired-water and monochloramine-treated groups had reduced monocyte counts. Except for a slightly increased response to Con A observed in splenic lymphocytes of the monochloramine-treated rats (versus the paired-water), no significant changes were found in mitogen responsiveness to T cell, B cell, and B plus T cell mitogens or in splenic natural killer (NK) cell activities. There were no significant changes in serum levels of IgG, IgA, and IgM. The following biochemical parameters showed no significant variations among the three groups: serum thyroxin, liver phase I (PROD, EROD, and MROD) and phase II (UDPGT and GST) drug-metabolizing enzyme activities; serum and liver thiobarbituric acid-reactive substances (TBARS); bronchoalveolar lavage fluid protein and N-acetylgluosaminidase (NAGA) activity; and urinary ascorbic acid, protein, and NAGA activity. Histopathological examination revealed minimal to mild adaptive changes in the liver of the paired-water and monochloramine-treated rats and in the thyroid of the monochloramine-treated animals. No treatment-related cytological changes were found in red cells and bone marrow. The results indicate that the reduced body weight gain and the minor biochemical, hematological, immunological, and histopathological changes associated with subchronic exposure to 200 ppm monochloramine in drinking water (equivalent to an intake of 21.6 mg/kg/day) were largely related to the reduced water intake and food consumption and not caused by monochloramine.

The importance of urinary protein excretion during conservative management of severe preeclampsia

OBJECTIVES

We determined the natural course of urinary protein excretion during conservative management of severe preeclampsia and investigated whether changes in urinary protein excretion can predict maternal or perinatal outcome.

STUDY DESIGN

We reviewed the medical charts of 66 women with severe preeclampsia which was managed conservatively before 32 weeks of gestation and who had at least two 24-hour urinary protein determinations 4 or more days apart after admission.

RESULTS

Fifty-nine (89%) of 66 women had an increase in proteinuria during conservative management of severe preeclampsia. The median increase in protein excretion after admission was 660 mg/24 hours (range-4580 to 18,960 mg/24 hours). Patients were divided into two groups. The first group (n = 24) had an increase in 24-hour urinary protein excretion of > or = 2 gm; the second group (n = 42) had a 24-hour urinary protein excretion that decreased (n = 7) or increased by < 2 gm (n = 35). There were no cases of eclampsia or stillbirth in either group. The rate of HELLP (hemolysis, elevated liver enzyme levels, low platelet counts) syndrome, abruptio placentae, cesarean delivery because of fetal distress, 5-minute Apgar scores < or = 6, and the admission-to-delivery intervals were all similar in the two groups.

CONCLUSIONS

Proteinuria increases in most women with severe preeclampsia managed conservatively. No differences in maternal or fetal outcomes were found between pregnancies with marked increases in proteinuria and those with modest or no increases.

Angiotensin I converting enzyme in glycerol-induced acute renal failure in rats

Angiotensin I converting enzyme (ACE) activity was measured in serum, urine, and tissues of rats with acute renal failure (ARF) induced by glycerol. Glycerol-injected rats were subdivided in three groups according to the urinary volume: oliguric, nonoliguric, and polyuric. The damage to the proximal tubule was evident by (a) the histological analysis at light and electron microscopy level, (b) the augmented urinary excretion of the enzymes dipeptidyl aminopeptidase IV and N-acetyl-beta-D-glucosaminidase, and (c) the low molecular weight proteinuria pattern. On the other hand, the appearance of the glomeruli at the ultrastructural level was normal. These data suggest that the increased urinary excretion of enzymes and proteins in these rats is a consequence of the tubular injury. ARF was markedly higher in the oliguric rats. Urine ACE activity increased in the rats of the three groups, but statistical significance was reached only in the oliguric rats. Serum ACE activity increased in the oliguric rats and tissue ACE activity did not change. It is concluded that the high urinary ACE in glycerol-treated rats is associated with the damage to the kidney tubules. These data support the contention that urinary ACE may be another marker of injury to the proximal tubule.

Low-molecular-weight proteins as markers of organ toxicity with special reference to Clara cell protein

Low-molecular-weight (M(r) between 5 and 40 kDa) proteins present several features related to their small size making them potentially interesting biomarkers of toxicity. They are readily exchangeable and might serve as peripheral indicators of toxic events in relatively inaccessible target organs. They have a short half-life in plasma and may thus respond to both acute and chronic toxic effects. Their catabolism takes place in the proximal tubule which is the segment of nephron which is the most vulnerable to toxic injury. Low-M(r) proteins have been used hitherto in toxicology mainly in relation to their renal handling, i.e. as markers of proximal tubule dysfunction or of glomerular filtration rate, e.g. beta 2-microglobulin (beta 2-m), alpha 1-microglobulin (alpha 1-m) and retinol-binding protein (RBP). The potential of low-M(r) proteins as biomarkers of toxicity might go beyond the field of nephrotoxicity, as suggested by our investigations on a new low-M(r) protein called protein 1 or Clara cell protein (CC16). CC16 is a 16-kDa protein synthesised by non-ciliated cells of the tracheobronchial epithelium, among which the Clara cells which, because of their high xenobiotic-metabolizing activity, are particularly vulnerable to a number of air pollutants. CC16 secreted in the respiratory tract diffuses passively by transsudation into the serum where it may mirror changes occurring in the lung. Recent studies on subjects exposed to lung toxicants (e.g. tobacco smoke and silica) suggest that CC16 in serum or bronchoalveolar lavage fluid is a sensitive marker of bronchial tree injury. CC16 is handled by the kidney as other low-M(r) proteins and may also be used to detect proximal tubule dysfunction. In this respect too, CC16 shows a unique sensitivity and can detect very subtle defects in proximal tubular dysfunction that remain undetected when screening is based on the assay of classical urinary low-M(r) proteins (i.e. beta 2-m, alpha 1-m or RBP).

Association between NAG-B and cadmium in urine with no evidence of a threshold

OBJECTIVES

To explore the significance of the increase in urinary excretion of the lysosomal enzyme beta-N-acetylglucosaminidase (NAG) at low exposures to cadmium (Cd) that is frequently found in the absence of any other sign of renal dysfunction.

METHODS

The activity was measured of the two main isoenzymes of NAG (NAG-A secreted by exocytosis and NAG-B released with cell membranes) in the urine of 49 male workers employed in a Cd smelter and of 20 age matched controls.

RESULTS

An increased urinary excretion of low molecular weight proteins was noted only in subjects who excreted > 10 micrograms Cd/g creatinine. The urinary activity of NAG-B showed a dose related increase that was already significant in the group excreting 0.5-2 micrograms Cd/g creatinine. In multiple regression analysis the NAG-B activity correlated with the excretion of Cd but not with that of lead or mercury. The NAG-A activity was by contrast unaffected by exposure to Cd but correlated with the urinary excretion of lead and copper.

CONCLUSIONS

As NAG-B is considered to be the lesional form of NAG, the existence of a specific association between this enzyme and urinary Cd excretion with no detectable threshold suggests that this metal produces cellular alterations at exposures commonly found in the general population.

Renal handling of drugs and amino acids after impairment of kidney or liver function--influences of maturity and protective treatment

Renal tubular cells are involved both in secretion and in reabsorption processes within the kidney. Normally, most xenobiotics are secreted into the urine at the basolateral membrane of the tubular cell, whereas amino acids are reabsorbed quantitatively at the luminal side. Under different pathological or experimental circumstances, these transport steps may be changed, e.g., they may be reduced by renal impairment (reduction of kidney mass, renal ischemia, administration of nephrotoxins) or they may be enhanced after stimulation of transport carriers. Furthermore, a distinct interrelationship exists between excretory functions of the kidney and the liver. That means liver injury can influence renal transport systems also (hepato-renal syndrome). In this review, the following aspects were included: based upon general information concerning different transport pathways for xenobiotics and amino acids within kidney cells and upon a brief characterization of methods for testing impairment of kidney function, the maturation of renal transport and its stimulation are described. Similarities and differences between the postnatal development of kidney function and the increase of renal transport capacity after suitable stimulatory treatment by, for example, various hormones or xenobiotics are reviewed. Especially, renal transport in acute renal failure is described for individuals of different ages. Depending upon the maturity of kidney function, age differences in susceptibility to kidney injury occur: if energy-requiring processes are involved in the transport of the respective substance, then adults, in general, are more susceptible to renal failure than young individuals, because in immature organisms, anaerobic energy production predominates within the kidney. On the other hand, adult animals can better compensate for the loss of renal tissue (partial nephrectomy). With respect to stimulation of renal transport capacity after repeated pretreatment with suitable substances, age differences also exist: most stimulatory schedules are more effective in young, developing individuals than in mature animals. Therefore, the consequences of the stimulation of renal transport can be different in animals of different ages and are discussed in detail. Furthermore, the extent of stimulation is different for the transporters located at the basolateral and at the luminal membranes: obviously the tubular secretion at the contraluminal membrane can be stimulated more effectively than reabsorption processes at the luminal side.

Chronic nephrotoxicity of soluble nickel in rats

1. Male and female Wistar rats were given 100 mg L-1 of nickel (as nickel sulfate) in drinking water for 6 months. Lactate dehydrogenase, total proteins, N-acetyl-beta-D-glucosaminidase (NAG), albumin and beta 2-microglobulin were measured in 24 h urine after 3 and 6 months of exposure. Body and kidney weights were also recorded. 2. After 6 months, urinary excretion of albumin in control and exposed rats was 354 and 1319 micrograms 24 h-1 for female rats (P < 0.05) and 989 and 2065 micrograms 24 h-1 for male rats (P = non significant). Kidney weights were significantly increased in the exposed groups. No significant changes were observed in other parameters. 3. The results suggest that low-level oral exposure to soluble nickel either induces changes of glomerular permeability in female and possibly in male rats, or enhances the normal age-related glomerular nephritis lesions of ageing rats. The intake was probably not high enough to induce significant tubular changes. The female rat seems to be more sensitive to the nephrotoxic effect of nickel than the male rat.

Increased albumin excretion in industrial workers due to shift work rather than to prolonged exposure to low concentrations of chlorinated hydrocarbons

OBJECTIVES

It has been reported that groups of workers in petrochemical industries who have been exposed to low concentrations of chemicals for prolonged periods have an increased urinary albumin excretion compared with unexposed controls. This increase, however, seemed to be unrelated to the extent, duration, and type of exposure. The aim of the present study was to investigate the suggestion that the small increase in albumin excretion might be due to differences in physical workload between the exposed and control groups or to the fact that the exposed workers are shift workers whereas the controls are employed on day duty.

METHODS

To elucidate the effect of shift work, again a series of renal and hepatic variables were studied in organochlorine workers but now with two different control groups. One control group comprised shift workers and the other only workers on day duty. The exposed and both control groups had roughly equal physical workloads, although one control group comprised shift workers and the other workers who work only during day time.

RESULTS

There were no significant changes in the results of the liver tests between the exposed group and either of the control groups, nor between the two control groups. No significant differences for any renal test were found between the exposed workers and control shift workers, but albumin was significantly lower in the control day workers than in the exposed workers and control shift workers.

CONCLUSIONS

The results suggest that the previously reported small increase in albuminuria in industrial workers is due to alterations in circadian rhythms due to the shift work system rather than to prolonged exposure to low concentrations of potentially nephrotoxic chemicals.

Glutathione status, lipid peroxidation and kidney function in streptozotocin diabetic rats

In adult female rats diabetic nephropathy was induced by i.v. administration of streptozotocin (6 mg/100 g b.w.). The animals survive for 3 weeks when very low daily doses of insulin (0.3 IU/animal) are administered. High blood urea concentrations and distinct proteinuria indicate the impairment of kidney function in streptozotocin diabetic rats. Streptozotocin induces mild polyuria and increased renal excretion of potassium; there is also an increase in renal excretion of administered p-aminohippurate. Three weeks after administration of streptozotocin the formation of lipid peroxides is increased in the kidney. At this time glutathione content (GSH, GSSG) is unchanged in liver and kidney of streptozotocin diabetic rats. Impairment of kidney function in streptozotocin diabetic rats can be prevented by daily supplementation with sufficient doses of insulin (about 3 IU/animal).

Occupational hydrocarbon exposure and chronic nephropathy

This review aims at discussing the questions raised by the hydrocarbon-related chronic nephropathy and its possible consequence, the hydrocarbon-related chronic renal failure. It has been attempted to adopt the point of view of the clinician. Therefore, the most important part of the review is devoted to a presentation and an analysis of the available data on humans. The main features of the available studies on human subjects are presented, their conclusions discussed in the light of the possible methodological flaws, and practical conclusions drawn. After a discussion of the main difficulties encountered for selecting the suitable exposure indicator, the studies are discussed in order of decreasing quality of the study design (cohort, case-control, cross-sectional studies, and the case reports). It is concluded that a great deal of controversies about chronic hydrocarbon-related nephropathy is explained by differences in the study design and that hydrocarbon-induced nephropathy is probably more than a mere hypothesis, although a causal relationship has not yet been proven. Finally, some practical consequences for dealing with a hydrocarbon-exposed patient diagnosed with a kidney disease and the need for further research are discussed.

Effects of six months' white spirit inhalation exposure in adult and old rats

In two separate experiments in rats the irreversible effects of six months' exposure to white spirit (0, 400 p.p.m., and 800 p.p.m.) were studied. In one experiment the exposure started at the age of three months, in the other the rats were 15 months at the beginning of the exposure. After an exposure-free period of several months neurobehavioural, pathological, and neurochemical examinations were performed. A marked difference in motor activity between young and aged animals was found. A slight effect on kidney function was seen at 800 p.p.m. No macroscopic or histopathological changes related to dosing were found. The concentrations of noradrenaline, dopamine, and 5-hydroxytryptamine in various brain regions and in whole brain were irreversibly changed. In conclusion, the study revealed different changes within the CNS, but failed to demonstrate neurobehavioural white spirit-induced neurotoxicity.

Monitoring of early nephrotoxic effects of industrial chemicals

Long-term exposure to certain industrial chemicals (e.g. heavy metals, some halogenated hydrocarbons) may cause progressive degenerative changes in the kidney, possibly leading to renal insufficiency. The screening tests most widely used to assess the integrity of the kidney (i.e. serum creatinine or BUN and the quantitative or semi-quantitative measurement of total proteinuria) lack sensitivity; they do not permit the detection of renal disturbances at a stage when removal from exposure may prevent progression of the disease process and are not suitable to determine the no-effect levels of potentially nephrotoxic chemicals. During the last decades new markers have been proposed for the early detection of structural and/or functional changes at various sites of the renal parenchyma. Some tests mainly attempt to assess the integrity of the glomerulus (e.g. high Mr proteinuria such as transferrinuria and albuminuria; increased excretion of some components of the glomerular basement membrane or the mesangium matrix, increased plasma concentration of low Mr proteins such as beta 2-microglobulin and free retinol binding protein), the proximal tubule (e.g. urinary excretion of several low Mr plasma proteins, tubular enzymes and antigens), the loop of Henle and distal tubule (e.g. excretion of various prostanoids). Currently, the majority of these tests are of limited value at the individual level because their health significance, even when they are persistently abnormal, has not yet been sufficiently studied. In workers exposed to Cd, however, it has been shown that a persistent low Mr proteinuria is predictive of an exacerbation of the age-related decline of the GFR; this biological change should be considered as an adverse effect. Currently, the principal application of these tests lies in the framework of epidemiologic studies designed to assess permissible exposure levels to nephrotoxic pollutants. The study of dose-effects/response relationships based on a large battery of renal markers has allowed the better determination of the internal dose of Cd, which is not associated with significant renal risk.

Selective increase in the urinary excretion of protein 1 (Clara cell protein) and other low molecular weight proteins during normal pregnancy

The effect of normal pregnancy on the tubular transport of proteins has been studied by measuring four low molecular weight (Mr) proteins in the urine of pregnant women: protein 1 (a recently discovered urinary protein identical to Clara cell protein), beta 2-microglobulin, retinol-binding protein and alpha 1-microglobulin. The urinary excretion of albumin and beta-N-acetylglucosaminidase was also determined. One hundred and fourteen women with uncomplicated pregnancy were examined: 22 in the first trimester, 42 in the second and 50 in the third trimester. They were compared to 40 age-matched non-pregnant women. The urinary excretion of the four low Mr proteins was significantly increased during the second and third trimester of pregnancy. During the last trimester, the mean relative increases in the urinary excretion of these proteins ranged from 2.8 to 15.6 and prevalences of elevated values from 25 to 46%. This rise in low Mr urinary protein excretion was particularly important in some pregnant women, representing (e.g. for protein 1) more than a 100-fold increase above normal. The urinary excretion of beta-N-acetyl-D-glucosaminidase was also increased during pregnancy but the albuminuria remained stable. These changes in low Mr urinary proteins were reversible after delivery and most likely resulted from a transient decrease in the reabsorptive capacity of the proximal tubule associated with an increase of the filtered load. However, some women excreted high amounts of protein 1 which could not be accounted for by a decreased tubular reabsorption and which might originate from a secretion by the urogenital tract.

The use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis to detect renal damage in Sprague-Dawley rats treated with gentamicin sulfate

Renal toxicity is a common manifestation to the exposure of laboratory animals and humans to a wide range of xenobiotics. Traditional methods for evaluating renal damage by clinical chemistry such as blood urea nitrogen (BUN) and serum creatinine are not sensitive to early, mild changes. The use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to measure the molecular weight spectrum of urinary proteins allows for an evaluation of the functional changes associated with renal damage. The ability of the kidney to filter and reabsorb proteins is related to the functional ability of glomeruli and the proximal tubules. Gentamicin sulfate produces injury to the S-1 and S-2 segments of the proximal tubule in laboratory animals and humans. While severe damage to the tubules is associated with increased BUN, serum creatinine, and N-acetyl-beta-glucosiminadase (NAG), mild injury is not detected by these means. The evaluation of urinary proteins by SDS-PAGE demonstrated renal toxicity at a dose of 6 mg/kg after 2 days of sc treatment. The NAG: creatinine ratio was shown to be elevated after 2 days of treatment at 63 mg/kg. The use of SDS-PAGE as described in this paper provides a sensitive method for detecting renal injury.

Renal effects of in utero exposure to mercuric chloride in rats

The transplacental nephrotoxicity of mercuric chloride has been studied in female Sprague-Dawley rats. Mercuric chloride was injected s.c. to rats at the dose of 1 mg/kg during the last 8 gestational days or the whole pregnancy. Both mothers and newborns developed a transient renal dysfunction resulting in an increased urinary excretion of beta 2-microglobulin and albumin. In mothers and their female offspring, these effects were completely reversible and did not influence the subsequent evolution of the renal function. In the male offspring, however, transitory changes in protein excretion were again observed a few months later, concomitantly with an enhanced accumulation of alpha 2u-globulin in the kidney. The transfer of mercury from maternal to fetal tissues was very small. The kidney concentrations of mercury in newborns were more than 300 times lower than in mothers. The barrier role of the placenta is not sufficient to prevent the occurrence of renal effects in the offspring of rats treated with inorganic mercury during pregnancy.