Search

We have measured liver heme oxygenase, a heat shock protein known to be increased under conditions of oxidative stress, to obtain additional evidence for an oxidative stress mechanism in hepatic uroporphyria induced by hexachlorobenzene (HCB). We have studied heme oxygenase at different times during HCB treatment and in two strains of rats (Agus and Wistar strains), which are known to differ in their sensitivity to the porphyria-inducing properties of HCB, in order to ascertain whether the same time course and genetic differences known to exist for the induction of porphyria also apply to hepatic oxidative stress. HCB induced heme oxygenase and accumulation of porphyrins in the liver of rats of both strains; no significant difference was found between the two strains in the HCB-induced heme oxygenase activity. The increased activity of the enzyme was first detected during the early phases of treatment, when a modest increase in liver porphyrins was observed; heme oxygenase remained at induced levels for several weeks during HCB treatment, and was still raised when an increase in total liver iron content and the onset of marked porphyria were also found. In contrast to the effects of HCB, phenobarbitone sodium (given in the drinking water for up to 4 weeks) produced similar elevations of total liver cytochrome P450 as HCB, but did not stimulate heme oxygenase or increase the total liver content of either iron or porphyrins. These results are compatible with an oxidative stress mechanism in HCB-induced liver toxicity and porphyria, but also suggest the existence of successive stages in the induction of hepatic porphyria, with more than one mechanism contributing to the marked accumulation of uroporphyrin.

OBJECTIVES--To identify any differences in hepatic function between workers exposed to carbon tetrachloride and controls, and to identify the best variable with which to examine any effects. METHODS--In a cross sectional study of hepatic function in workers occupationally exposed to carbon tetrachloride, 135 exposed employees were compared with 276 non-exposed controls. The exposed group was taken from three sites in the north west of England and the control group included non-exposed workers from one of these sites and another site located nearby. Demographic and alcohol consumption data were collected from both groups by questionnaire. Each member of the study group was allotted a notional estimated exposure to carbon tetrachloride, calculated from historic personal monitoring data and job category. A fasting sample of blood was taken from all participants and analysed for a variety of biochemical and haematological variables. The techniques of univariate and multivariate analysis of variance were used to investigate the effect on biochemical and haematological indices of a range of factors. RESULTS--Multivariate analysis of variance of four core liver function variables, alanine transaminase, aspartate transaminase, alkaline phosphatase, and gamma-glutamyl transferase, showed a significant difference between exposed and non-exposed workers. The univariate analyses identified increases in only alkaline phosphatase and gamma-glutamyl transferase within the exposed group and these did not show a significant dose-response relation. Univariate analysis of variance did show effects of alcohol and age on several variables. Significant differences between exposed and control groups for three haematological variables, haemoglobin, packed cell volume, and red blood count, were thought not to be due to the effects of exposure. Clinical review of exposed subjects with abnormal results did not show clinically evident disease that could have been associated with exposure to carbon tetrachloride. Also, a follow up study conducted three years after the cross sectional study at the site with highest exposures to carbon tetrachloride showed no evidence of any further changes in liver function variables. CONCLUSIONS--The most sensitive statistical methods have shown significant differences in the liver function variables measured between people exposed to carbon tetrachloride and the control group. The interpretation of the data collected was that these differences may be due to exposure to carbon tetrachloride but this was not clearly shown. Furthermore, the changes found have not given rise to any clinical disease.

There are a wide variety of laboratory tests available to assess damage to and functional impairment of the kidneys, although the effectiveness of these tests varies greatly depending upon the site specificity of the damage and to a lesser extent upon the animal species involved. Several traditional tests of renal dysfunction and damage, including plasma creatinine and urea, and urinalysis (dipstick and/or quantitative protein), can be used in the first instance to detect nephrotoxicity. A second tier of specific, targetted indicators (concentration test, urinary enzymes, clearance of analytes, specific proteins, etc.) may then be applied to identify further the site of the lesion and the functional status of the kidneys. The glomerular filtration rate (GFR) may be estimated from the clearance of exogenous and endogenous substances. The difficulty in obtaining accurately timed urine samples limits the value of these tests in small animals, although methods that do not involve urine collection are available. The kidney is the origin of several enzymes found in urine that can be used to monitor the toxic effects of chemicals and therapeutic substances. Selective measurement of enzyme activities in urine can be used to detect the site of the renal lesion after traditional tests have established the presence of renal injury. Separation of proteins in urine by electrophoretic techniques may also be used to discriminate damage to different parts of the nephron. Renal cell excretion in urine is a sensitive but unreliable indicator of acute damage to the proximal tubule. The rate of cell excretion is not a good predictor of the severity of tubular injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Groups of 12 male and 12 female rats were fed diets containing 0 or 8ppm trimethyltin chloride for up to 25 days. All the animals were observed prior to the study start and daily throughout the study for any changes in clinical condition. In addition, detailed clinical observations, including quantitative assessments of landing foot splay, sensory perception, muscle weakness and locomotor activity were monitored during the study. At the end of the study, the rats were killed and subjected to a full Post-mortem. Selected nervous system tissues were removed, processed and examined microscopically. Clinical signs typical of trimethyltin neurotoxicity (e.g. aggression, shaking and convulsions) were seen in rats receiving diets containing 8ppm trimethyltin chloride for as little as 22 days. Neuropathological lesions consisting of extensive neuronal cell necrosis in the limbic region of the brain, vacuolar degeneration of ventral horn cells of the spinal cord and a marginal increase in Wallerian-type degeneration were seen. The study demonstrates that trimethyltin neurotoxicity can be induced by dietary administration and that both male and female rats are equally sensitive.

Acute experimental models of renal damage to the proximal tubular, glomerular, and papillary regions of the rat were produced by administration of hexachloro-1:3-butadiene (HCBD), puromycin aminonucleoside (PAN), and 2-bromoethylamine (BEA), respectively. Several routine indicators of nephrotoxicity, the enzymes alkaline phosphatase and N-acetyl-beta-glucosaminidase, and the molecular weight of protein excretion were determined on urine samples. Tubular damage produced by HCBD or BEA was discriminated both quantitatively and qualitatively from glomerular damage produced by PAN. The latter was characterized by a pronounced increase in protein excretion, especially proteins with molecular weight greater than 40,000 Da. In contrast, protein excretion in tubular damage was raised only slightly and characterized by excretion of proteins of a wide range of molecular weights. Proximal tubular damage caused by HCBD and papillary damage caused by BEA were distinguished both by conventional urinalysis (volume and specific gravity) and by measurement of the two urinary enzymes. Alkaline phosphatase and glucose were markedly and transiently elevated in proximal tubular damage and N-acetyl-beta-glucosaminidase showed a sustained elevation in papillary damage. It is concluded that both selective urinary enzymes and the molecular weight pattern of urinary proteins can be used to provide diagnostic information about the possible site of renal damage.

Summary. Chronic feeding of hexachlorobenzene to rats increases the levels of certain hepatic haemoproteins prior to the onset of hepatic porphyria. The onset of hepatic porphyria is slow and only water soluble porphyrins accumulate in the livers. The accumulation of hexachlorobenzene by the liver is progressive but no direct correlation exists between the amount of HCB in the liver, the extent of hepatic porphyria and the changes in haemoprotein concentration. Similarities between experimental hepatic porphyria induced by hexachlorobenzene and those seen in human symptomatic porphyria are presented and emphasize the usefulness of the hexachlorobenzene model with which to study the human disease.

1. After an intraperitoneal injection of 59Fe the recovery of radioactivity in the liver, but not in other tissues, was increased in cobalt-pretreated rats. There was no proportional increase in the radioactivity recovered from liver haem. 2. Rats were injected intravenously with serum containing protein-bound 59Fe and 125I-labelled albumin as a marker. At various times after injection the specific radioactivities of iron in plasma and of non-haem iron in liver were determined; corrections were applied for the content of plasma in samples of liver. In cobalt-pretreated rats there was a more rapid loss of 59Fe radioactivity from the plasma and a corresponding increase in the uptake of 59Fe into liver non-haem iron. 3. The results are discussed in relation to the possible sites of action of cobalt, and the possibility is considered that only a fraction of the liver non-haem iron may be involved.

A comparison of the composition of fluid entering and leaving the kidney shows that many of the normal plasma constituents are handled individually — some are eliminated, some are conserved. For example, we have to account for the near absence of glucose and protein and for the appearance of high concentrations of creatinine and urea. To fulfil its role in maintaining a relatively constant internal environment the kidney is able to perform many complex and diverse functions simultaneously. These major functions include filtration, reabsorption, secretion and excretion. Changes in any of these functions will be reflected by a change in the composition of the urine. It is widely accepted that a variety of chemical substances can alter renal function, and the ability to produce a mild and reversible change is important from a pharmacological viewpoint, e.g. diuresis. However, in some instances irreversible effects may occur following incidental exposure to toxic substances. There are several reasons why the kidney may be particularly susceptible to injury. Firstly, renal blood flow is approximately 25% of cardiac output and as such delivers large quantities of blood and contents to the kidney. Secondly, the anatomical and functional properties of the kidney ensure that ample and often unwanted exposure to chemicals occurs by virtue of the blood supply to peritubular membranes and by virtue of tubular fluid at the brush-border membranes in the proximal tubule. Thirdly, the ability to concentrate the glomerular fluid may mean an increase in concentration of 100–1000 fold of certain chemical substances at critical regions of the nephron, e.g. the proximal tubule.

Although man has been exposed to naturally occurring poisons since the beginning of his existence, it is only in the past 80 years that there has been a dramatic increase in the number of synthetic chemicals, a few of which have subsequently been shown to cause health problems following human exposure. However, health in this country is better than in past times and the expectation of life in this chemical age is longer than ever before[l]. There is no evidence of mass harm to the population from new substances[2,3]. In the chemical industry, past history has shown that health effects have usually resulted from specific exposures; for example: bladder cancer from exposure to aromatic amines, fibrotic lung disease from exposure to silica dust, mesothelioma from asbestos, occupational asthma from exposure to platinum salts and more recently angiosarcoma of the liver from exposure to vinyl chloride monomer. As well as in the industrial situation, man is exposed to chemicals in pharmaceutical preparations, domestic products, food additives, pesticide residues and from accidental contamination of the environment.