Effects of age and sex on hexachloro-1,3-butadiene toxicity in the Fischer 344 rat

Sex-related differences in renal toxicodynamics in rodents

INTRODUCTION

An issue yet to be addressed, in the investigation of the xenobiotic toxicity, is a detailed characterization of the sex differences in toxicological responses. The 'sex issue' is particularly significant in nephrotoxicology as the kidney is a relevant target organ for xenobiotics and few studies have approached this subject in the past. There is a strong need to improve our understanding regarding the influence of sex in toxicology, given their increased requirement to establish the limits of exposure to chemicals in the environment and at work.

AREAS COVERED

In this review, the authors provide the reader with the current knowledge of sex differences in kidney toxicity for rats and mice. To make the review easier to consult, these studies have been organized according to the class of xenobiotic.

EXPERT OPINION

From the analysis of the present knowledge emerges a dramatic need for information on sex differences in xenobiotics toxicity. Although animals are reasonably good predictors of adverse renal effects in patients, there is need to identify alternative methods (e.g. in vitro/ex vivo) to better study sex differences in organ toxicity.

Evaluation of aging influence on renal toxicity caused by segment-specific nephrotoxicants of the proximal tubule in rat

Little is known concerning the sensitivity of aged rats to xenobiotics inducing kidney damage. To increase this knowledge, the age-dependent response of the kidney to hexachloro-1 : 3-butadiene (HCBD) or potassium dichromate (chromate) was investigated. Rats were treated at different ages with a single dose of segment-specific nephrotoxicants of the proximal tubule, chosen on the basis of their specificity for S(3) and for S(1)-S(2) segments, respectively. The toxicological impact of these xenobiotics has been evaluated through biochemical and genomic markers, and histopathological investigation of kidney samples. HCBD treatment induced tubular necrosis of the S(3) segment of the proximal tubule associated with changes of toxicological markers unrelated to the age. In contrast, chromate treatment induced an increased kidney damage related to the rat age. In fact, histopathological investigation revealed that at 1 month of age tubular vacuolar degeneration was seen affecting S(1)-S(2) segments of the proximal tubule, whereas at 3 months of age tubular necrosis occurred in the same segments associated with tubular dilation of the distal portions. Consistently, biochemical analysis confirmed a direct correlation among genomic and biochemical marker variability and animal age. Altogether, the results show that during aging there is an increased sensitivity of kidney to chromate but not to HCBD-induced damage and evidence differential age-related selectivity of rats for nephrotoxic compounds. Significance for human risk assessment is discussed.

An analysis of the need for an additional uncertainty factor for infants and children

Uncertainty factors have been used for over 40 years to establish safe intakes of threshold toxicants. Tenfold factors are used to allow for species differences and for human variability, with extra factors for database inadequacies. The proposal to introduce an additional 10-fold factor for pesticides when exposure of infants and children is anticipated implies either age-related differences between species or differences within humans which exceed those present in adults. Alternatively, the extra factor could be related to deficiencies of current testing methods or concerns over irreversibility in developing organ systems. Available data do not provide a scientific rationale for the extra factor due to inadequacy of inter- and intraspecies uncertainty factors. Justification for the factor therefore must relate to the adequacy and sensitivity of current methods or concern about irreversible effects in the developing organism.