Sucralose: lack of effects on sperm glycolysis and reproduction in the rat.

Certain chlorine-substituted sugars with chemical similarities to sucralose have been demonstrated previously to diminish or inhibit sperm glycolysis and fertility in the rat ([Ford]). In order to investigate this potential for sucralose, epididymal spermatozoa were recovered from rats exposed in vivo to oral doses of one of three of these substituted sugars: 6-chloroglucose (6-CG, 24mg/kg/day, positive control), sucralose (500mg/kg/day, over 300 times the expected human daily intake), or a 6'-substituted isomer of sucralose, trichloro de-oxy sucrose (TCDS, 100mg/kg/day, a potential trace impurity in commercial sucralose); distilled water served as the negative control. After incubation of the spermatozoa with D-[U-(14)C] glucose, measurements of (14)CO(2) and of ATP content showed no impairment of the glycolytic ability of spermatozoa in any of the groups except for a marked inhibition for those exposed to 6-CG, the positive control. In order to determine whether other parameters of reproduction and fertility could be affected, reproductive endpoints were examined following oral exposure of male and female rats to sucralose. Sucralose was fed in the diet at concentrations of 0, 0.3, 1.0 and 3.0% (approx. 100, 365 and 1150 times the EDI) to groups of 30 male and 30 female rats for 10 weeks prior to mating, and continued through two subsequent generations until weaning of the F(2) pups. Two litters were produced per generation. Food consumption and weight gain in the F(0) and F(1) generations were depressed in all sucralose groups before mating and in all four litters prior to weaning. The decrease in initial average weight for newborn pups probably reflects the increased litter sizes noted for sucralose-treated groups and the reduced food consumption of the dams during gestation and lactation. The latter is a result primarily of the unpalatability of sucralose to rats ([McNeil,]). Caecal enlargement (a common animal response to large doses of indigestible material) occurred in both the F(0) and F(1) parents. Increased kidney weights, possibly associated with increased water intake, were observed primarily among animals receiving 3% sucralose (no renal histopathology has been detected). Decreased thymus weights occurred in F(1) males and in both F(1) and F(2) females at the 3% level. Subsequent studies specifically designed to investigate the potential for adverse immune system effects of sucralose ([McNeil,]) showed no adverse effects. These findings are consistent with investigations by others showing that decreases in thymus weights occur in young rats in response to stressful conditions associated with reductions in weight gain. All reproductive indices (oestrous cycles, mating behaviour, fertility, gestation, maternal and foetal viability, foetal development, parturition, pup maturation and lactation) were comparable between the control and sucralose-treated groups. We conclude from these results that sucralose has no effect on sperm glycolysis or on male or female reproductive performance in the rat.

Sucralose: assessment of teratogenic potential in the rat and the rabbit.

The teratogenic potential of sucralose was examined following gavage administration to pregnant rats and rabbits during organogenesis. Groups of 20 mated rats were dosed on days 6-15 of gestation inclusive at 500, 1000 or 2000mg/kg/day; groups of 16 to 18 inseminated rabbits were dosed on days 6 to 19 of gestation inclusive at 175, 350 or 700mg/kg/day following preliminary studies at higher doses. Concurrent control groups received vehicle alone. Rats were killed on day 21 and rabbits on day 29 of gestation. Foetuses were evaluated at necropsy and after processing for possible soft tissue and skeletal alterations. There was no evidence of teratogenicity for either species. The only observed response to treatment in rats was a slight increase in water intake. Some adult rabbits receiving 700mg/kg/day exhibited marked gastrointestinal disturbance, also seen at higher doses in preliminary studies. Gastrointestinal effects such as these occur non-specifically in response to high doses of poorly absorbed compounds, and in the present study were considered to be responsible for two maternal deaths and four abortions. Full evaluation of rabbit foetuses in the main study (up to 700mg/kg/day) and necropsy of foetuses in a preliminary study with pregnant animals (up to 1000mg/kg/day) showed no evidence of adverse foetal response to sucralose. These teratology studies in both pregnant rodent and non-rodent animal models demonstrate that maternal consumption of high levels of sucralose during the period of organogenesis has no effect on normal foetal development in the rat or rabbit.

Alternative approaches to the safety assessment of macronutrient substitutes.

Traditional toxicological procedures have only limited application to the safety assessment of macronutrient substitutes. Experience indicates that spurious effects are often encountered when macronutrients or their replacements are fed to rodents at high dietary levels. These effects may results in nutritional imbalances that lead secondarily to adverse physiological consequences including cancer, renal disease, or reproductive effects. In approaching the safety assessment of macronutrient substitutes, consideration needs to be given to designing and implementing a safety assessment program which acknowledges the physical, chemical, and biological properties of the substance. Factors such as molecular size, physical state, solvent properties, hydrolysis potential, digestibility, absorption potential, and metabolic fate must be well established prior to selection of appropriate test models. Armed with this information, many potential undesirable physiological effects of the substances can be predicted, thus precluding the need for a full spectrum of animal testing. Predicted physiological and metabolic effects, however, should be characterized using in vitro methods and confirmed with in vivo models. Initial short-term toxicity screening tests with rodents should be carried out to identify unanticipated systemic toxicity. Testing in laboratory animals and trials in humans should then proceed with more appropriate models that are specially selected to assess the significance of predicted outcomes, to characterize dose-response relationships, and to identify possible needs to modify the product to mitigate adverse physiological consequences. These might include physical changes to alter particle size, chemical changes to modify digestibility, or nutrient supplementation to overcome impacts on nutrient availability. Thoughtful selection of appropriate and relevant models based on the physical, chemical, and biological properties of test substances will provide more rational approaches to safety assessments and avoid the pitfalls of routine application of traditional tests.

A review of the toxicology profile of rioprostil.

The toxicity of rioprostil was extensively investigated. Studies in rodents, dogs and monkeys indicate a low order of acute toxicity. Oral subchronic and chronic toxicity studies in rats and dogs produce effects that would be expected based on the pharmacological activity of the compound. In reproduction studies with rioprostil, male and female fertility is unaffected in rats at doses up to 2.0 mg/kg/day and there is no evidence of embryotoxicity, fetotoxicity, or teratogenicity in rats at doses up to 1.7 mg/kg/day. In rabbits a maternally toxic dose (1.5 mg/kg) also increases resorptions, reduces fetal weight, and increases the incidence of malformations. Evaluation of 24-month carcinogenicity studies in mice and rats at oral doses up to 2.0 and 1.5 mg/kg/day, respectively, are in progress. Mutagenicity studies are negative.

Strain differences in the immune response of mice to homologous sperm-specific lactate dehydrogenase (LDH-C4).

The sperm-specific isozyme of murine lactate dehydrogenase (LDH-C4) was injected into female mice of various strains. Two regulatory phenotypes characterize the resultant immunity to LDH-C4: one is manifested by high, intermediate or low levels of response, the other by the immediate or delayed maturation of peak titer. The response of several strains can be classified as high (SWR, SJL, BABL/c, C3H/He) and intermediate to low (A, CBA, DBA/2, DBA/1, C57BL/6) according to the level of antibody production and cell mediated immunity. BALB/c, SJL and SWR strains are immediate responders while DBA/2 and C3H/He mice are clearly delayed responders. Maturation and magnitude of response do not appear to be related. Both the antibody and cell mediated responses are T-dependent, but are not obviously associated with Ig allotype or H-2 regulation.