National Toxicology Program

No data were found in the literature on the prechunic effects of either DCA or TCA in humans.

1. Dichloroacetic Acid

   oral, rats:

   The toxic effects of DCA were studied in rats following a subchronic exposure. Male Sprague-Dawley rats were divided into four treatment groups, 10 animals/group and given DCA in their drinking water at concentrations of 0, 50.0, 500.0, or 5000.0 ppm for 90 days. The test animals were observed daily throughout the duration of the study. Their body weights were recorded weekly and water consumption was measured after approximately 60 days of exposure.

   At the conclusion of the study, the test animals were sacrificed and studies were performed to assess the toxic effects from DCA exposure. Serum samples were collected and the serum biochemical profile (blood urea nitrogen (BUN), creatinine, glucose, alanine-amino transferase (SGPT), alkaline phosphatase, cholesterol, total protein, albumin, calcium, phosphorus, creatinine phosphokinase (CPK), and gamma glutamyl transpeptidase (GGT)) was assessed. Immunological parameters including: T cell-dependent IgG antibody production, delayed-type hypersensitivity, natural killer cell cytotoxicity, and production of macrophage-derived prostaglandin E2 (PGE2) and lymphocyte-derived interleukin 2 (IL2), were examined. In addition, necropsies were performed on all the animals and the individual organ (liver, kidney, spleen, thymus, and testes) to body weight ratios were determined. Samples of brain, heart, lung, pancreas, adrenals, lymph nodes, gastrointestinal tract, urinary bladder, muscle, skin, liver, kidney, spleen, thymus, and testes were collected and stained with hematoxylin and eosin for histological examination. Liver samples were collected to measure the peroxisomal B-oxidation activity.

   The body weights for the animals receiving 500.0 and 5000.0 ppm DCA were significantly (P<0.05) reduced in a dose-dependent manner compared to the controls. Significant changes were evident after 4 weeks (5000.0 ppm) and 9 weeks (500.0 ppm). Significant (P<0.05) increases in organ/body weight ratios were observed in the liver and kidney (500.0 and 5000.0 ppm) and spleen (5000.0 ppm). There were no treatment-related changes observed in either the thymus or testes. A decrease in water consumption was observed after 2 months of exposure in all test groups, however, the decrease was significant (P<0.05) in the 500.0 and 5000.0 ppm treatment groups, only.

   The total serum protein levels were significantly (P<0.05) depressed in all of the animals treated with DCA in comparison to the controls. The measured total serum protein in the controls was 7.2±0.1 g/dl and in the DCA treatment groups following serum protein levels were measured: 6.8±0.1 (50 ppm), 6.7±0.1 (500.0 ppm), and 6.6±0.1 (5000.0 ppm) g/dl. Significant increases (P<0.05) in alkaline phosphatase levels (215.5±17.6 IU/l (500.0 ppm) and 293.7±17.6 IU/l (5000.0 ppm) and SGPT levels (82.4±9.9 IU/l (5000.0) were observed compared to controls (alkaline phosphatase-183.7±21.1 IU/l and SGPT-56.5±11.9 IU/l.) Peroxisomal B-oxidation activity in the liver were observed to be significantly (P<0.05) increased in the 5000.0 ppm dose group only. There was no evidence of treatment-related changes in any of the immunological parameters studied.

   Necropsy of the animals revealed that the livers weights of the animals given 5000.0 ppm DCA (21.4±0.7 g) were significantly (P<0.05) elevated compared to the controls (15.7±0.9 g) and liver enlargement was grossly evident. Microscopic evaluation revealed focal areas of hepatocellular enlargement. This swelling was most severe in the animals receiving 5000.0 ppm DCA. Other treatment-related abnormalities observed in the high dose group included pockets of proteinaceous fluid in the liver, diffuse degeneration of tubular epithelium and cells of the glomeruli in the kidney, and enlarged spleens.

   The authors suggest that the results of this study indicate that long-term exposure to DCA produces substantial systemic toxicity to the liver and kidney. The amount of DCA likely to cause harm exceeds levels of DCA that are expected to be found in the environment and chlorinated drinking water. Mather et al., concluded that the data indicate that the kidney and liver are the major target organs for DCA [Mather et al., 1990].

2. Trichloroacetic Acid

   oral, rats:

   The effects from prechronic exposure to low concentrations of TCA were studied in rats. Four groups (10 animals/group) of male Sprague-Dawley rats were given TCA, daily, in their drinking water at concentrations of 0, 50.0, 500.0, or 5000.0 ppm for 90 consecutive days. A serum biochemical profile was done on all of the animals surviving at the end of the 90 day study. Tests included blood urea nitrogen, creatinine, calcium, phosphorus, total protein, albumin, glucose, cholesterol, alkaline phosphatase, creatinine phosphokinase, and alanine aminotransferase. At the conclusion of the study, the animals were sacrificed and underwent complete necropsy and histopathological examinations. The animal's weights were recorded prior to treatment and at the time of sacrifice. Weights obtained from the liver, kidneys, spleen, and thymus at necropsy were used to determine organ body weight ratios.

   All gross lesions and tumors were recorded. The brain, heart, lung, pancreas, adrenals, lymph nodes, gastrointestinal tract, urinary bladder, muscle, skin, kidney, spleen, thymus, and testes were fixed, processed, and stained with hematoxylin and eosin to evaluate the number of GGT-positive foci.

   There were no significant differences in body or organ weights as a percentage of body weights between the test groups and the control group. In addition, there were no gross lesions that were attributed to the TCA exposure. Microscopic examination of the tissue was unremarkable.

   The serum cholesterol levels were significantly (P<0.05) decreased in all of the TCA treatment groups compared to the controls. A significant (P<0.05) increase, of approximately 50% over controls, in serum alanine aminotransferase was seen in the animals dosed with 5000.0 ppm TCA, only. No other significant differences between experimental groups were noted. The author stated that general toxicity of TCA, as determined by the parameters evaluated, is reasonably low in rats. The procedures and results for other studies which were conducted in conjunction with this 90 day study are described in sections V.D.2 and V.G.3 [Parnell, 1986].

   oral, rats:

   The toxic effects of TCA in rats were studied in a 90 day investigation in conjunction with the 90 day study on DCA [Mather et al., 1990] described above.. Male Sprague-Dawley rats were divided into four groups of 10 animals and given doses of TCA in their drinking water at concentrations of 0, 50.0, 500.0, or 5000.0 ppm. The test animals were observed daily throughout the duration of the study. Their body weights were recorded weekly and the amount of water consumption was measured after approximately 60 days of exposure.

   At the conclusion of the study, the test animals were sacrificed and studies were performed to assess the toxic effects from TCA exposure. Serum samples were collected and the serum biochemical profile (blood urea nitrogen, creatinine, glucose, alanine-amino transferase (SGPT), alkaline phosphatase, cholesterol, total protein, albumin, calcium, phosphorus, creatinine phosphokinase, and gamma glutamyl transpeptidase) was assessed. Immunological parameters including: T cell-dependent IgG antibody production, delayed-type hypersensitivity, natural killer cell cytotoxicity, and production of macrophage-derived prostaglandin E2 (PGE2) and lymphocyte-derived interleukin 2 (IL2), were evaluated. Necropsies were performed and individual organ (liver, kidney, spleen, thymus, and testes) to body weight ratios were determined. Samples of brain, heart, lung, pancreas, adrenals, lymph nodes, gastrointestinal tract, urinary bladder, muscle, skin, liver, kidney, spleen, thymus, and testes were collected and stained with hematoxylin and eosin for histological examination. Liver samples were collected to measure the peroxisomal B-oxidation activity.

   
   There were no significant changes in body weight for any of the test animals. A significant (P<0.05) decrease in water consumption was observed at the 2 highest levels. Significant (P<0.05) increases in organ/body weight ratios were observed in the liver (4.35±1.10%) and kidney (0.41±0.01%) of the 5000.0 ppm group compared to the control group (liver (4.07±0.10%), and kidney (0.37±0.01%)). There were no treatment-related weight changes observed in either the spleen, thymus, or testes. No consistent differences were seen in serum chemistry parameters of TCA-treated animals. The livers of animals exposed to 5000.0 ppm TCA had significantly (P<0.05) elevated peroxisomal B-oxidation activity. There was no evidence of treatment related changes in the immunity parameters.

   Microscopic evaluation revealed focal areas of hepatocellular enlargement among the high dose group. The intracellular swelling was less severe than that observed in a parallel study conducted by Mather et al., 1990 on DCA described above. It was observed that the TCA-treated rats livers accumulated less glycogen. The authors suggest that the results of this study indicate that long-term exposure to TCA produces substantial systemic toxicity to the liver and kidney. Mather et al., reports that the amount of TCA likely to cause harm exceeds levels that are expected to be found in the environment and chlorinated drinking water [Mather et al., 1990].

   dermal, rats:

   The effects of TCA when applied dermally to oral mucosa, submucosal connective tissue, pulp, alveolar bone, and periodontium were assessed in rat. The second objective of this study was to provide a theoretical basis to an apparently satisfactory clinical adjunctive measure in the treatment of invasive cervical resorption. Twenty-eight male, Sprague-Dawley Porten strain rats were topically treated with TCA (90% in aqueous solution) for 30 seconds at two locations: 1) midline junction of the soft and hard palate and 2) a cavity prepared between the first and second molar, originating at the palato-gingival margin continuing 3 mm into underlying periodontal ligament, bone, and tooth. A control cavity was prepared on the contralateral side and irrigated with saline. A group of untreated rats served as controls. The animals were sacrificed at 5 and 30 minutes, 1 and 16 hours, and 1, 2, 5, 7, 10, 14, 21, 28, and 42 days. Macroscopic observations were recorded at each experimental period. The animals were decapitated, the mandible and associated soft tissue were removed, and the cranium and soft tissue were fixed for histological evaluation.

   No signs of toxicity in the test animals were apparent at any time during the study. The formation of white lesions on the soft palate was observed within a few seconds after TCA was applied. Histological examinations of the soft palate revealed coagulation necrosis with a distinct line of demarcation between affected and nonaffected tissues. Separation of the necrotic tissue from the rapid-regenerating tissue underneath occurred on, or shortly after, the second day. The healing process continued uninterrupted until there was no evidence of residual pathology (on approximately the fifth day). The authors suggest that the lack of chronic inflammatory response in the tissues beneath the well-defined area of coagulation necrosis was a contributing factor towards the rapid and uncomplicated repair.

   Minor differences in the healing of gingival tissue, periodontium, subepithelial tissues, alveolar bone, and pulp between the test and control cavities were observed early in the study. The initial reaction to TCA (particularly 30 minutes and 1 and 16 hours) of the gingival and palatal mucosa were similar to the reactions observed in the soft palate. Red blood cells were absent in the test cavity after 5 minutes in one of the rats, but the authors repute that this may have been due to artefact or the haemostyptic effect of TCA. At all other experimental periods, the tissue responses in both the experimental and control sites followed a predictable pattern of repair. There were no observable reactions to TCA in the tooth pulp or the root.

   The authors state that the results of this study indicate that there are no substantial differences between the responses of rat tissue to mechanical trauma and 30 second application of TCA and controls receiving the same trauma. They further suggest that clinical application of TCA in the treatment of invasive cervical resorption will not apparently be hampered or undermined by any residual, medicament-related delayed healing of the traumatized periodontal and related tissues [Heithersay and Wilson, 1988].

   dermal mice:

   TCA was one of 27 compounds used in a preliminary validation study of the final design of the mouse ear sensitization assay. Sixteen female Balb/c mice received a 10% dose of TCA in ethanol on both sides of their right ear on days 0 and 2. On day 2 they also received a scapular sub-cutaneous injection of 0.5 ml Freunds's adjuvant. On day 9, an induction dose of 10% TCA was administered topically to both sides of the left ear and the ear thickness was measured immediately before compound administration and after 24 hours. The measured ear thickness immediately before the challenge was 21.81±1.69; after 24 hours the thickness was determined to be 21.55±1.84. (Ear thickness was determined to be 21.66+1.5 and 21.69+1.91 immediately before and 24 hours after challenge in control animals administered ethanol only.) The authors state that these results are not significant and that TCA is a nonsensitizing compound in the mouse ear sensitization assay [Descotes, 1988].