As a simulation of the etiological factors known for Itai-Itai disease, a syndrome characterized by renal dysfunction and osteomalacia in its Japanese victims, female mice were subjected to the individual and combined stresses of dietary Cd, nutrient-deficient diet, multiparity and ovariectomy. Renal function as affected by the etiological factors was periodically evaluated by determination of protein, amino acid, glucose and Cd concentrations in urine; periodic changes in skeletal Ca status were assessed relative to current renal function. Renal metabolism of Cd, Zn and Cu was also examined. At age 68 days, female mice were given nutrient-sufficient (+) or -deficient (−), purified diets containing either 0.25 (environmental), 5, or 50 ppm Cd as CdCl 2; the nutritional composition of (−) diet simulated that of food consumed by Japanese victims of Itai-Itai disease. At age 70 days, half of the females began a breeding regimen of six consecutive, 42-day rounds of pregnancy/lactation (PL mice); the remainder were maintained as virgin, non-pregnant controls (NP mice). Limited numbers of PL and NP mice were sacrificed at the end of each reproductive round. PL(+) mice taken in a given round had successively borne litters in that round and all preceding ones. PL(−) females taken at the end of round (R)-l, -2 and -3 had successively borne litters through those rounds; those taken at the end of R-5 or R-6 had nonsuccessively borne litters in four of five or three of six rounds, respectively. At the conclusion of the 252-day reproductive period, remaining females entered the 392-day, post-reproductive phase of the experiment. At age 546 days (mid-R-12), PL females having successfully borne at least three litters were ovariectomized (OV) to mimic human menopause; at the same time, NP females were either ovariectomized or sham-operated (SO). After surgery, all females were maintained to age 714 days (mid-R-16), then sacrificed. Spot urine samples were taken from individual mice at the end of most reproductive rounds (R-2 → 6), prior to surgery (rnid-R-10), and prior to final sacrifice (late-R-15); samples were also collected via metabolism cages at the end of R-10. Food consumption, monitored on a weekly basis over the first nine rounds, was generally not significantly affected by dietary Cd level or nutrient deficiencies in females of the same reproductive status; consumption was increased about 2.5-fold in PL versus NP groups during the reproductive period and about 1.4-fold during the post-reproductive period. At each of the three dietary Cd levels and after all reproductive rounds, mean renal Cd concentrations were 1.2- to 5.6-fold higher in PL than NP mice. After six reproductive rounds, renal Cd concentrations in PL(+) and (−) groups exposed to 50 ppm Cd had reached 155 and 179μg Cd/g kidney, respectively. Although these levels fell within a concentration range (145–200 μg Cd/g) where cadmium-induced renal dysfunction could be anticipated, no significant, Cd-dependent changes in mean urinary amino acid or protein concentrations were found. Moreover, among the same population, a 12% incidence of elevated urinary Cd (≥ 250 ng/ml) was noted, however none of the affected individuals exhibited depressed total calcium content (TCa) or calcium:dry weight ratios (Ca:DW) for femur. Such results suggested that the Cd-induced, skeletal demineralization observed in mice during the reproductive period (Bhattacharyya et al., Toxicology 1988a; 50: 193–204; Whelton et al., Toxicology 1994; 91: 235–251) likely occurred in the general absence of cadmium-induced renal dysfunction. By the end of the post-reproductive period, the incidence of elevated urinary Cd increased to 26% among ovariectomized females; of these, 89% with urinary Cd ≥ 345 ng/ml exhibited decreases in TCa and/or Ca:DW values for femur or lumbar vertebrae that exceeded one S.D. of their group mean. Such results suggested that skeletal demineralization observed at this time (Whelton et al., Toxicology 1997a; 119: 103–121) likely occurred, for at least a portion of the population, in the presence of an ovariectomy-enhanced, cadmium-induced nephrotoxicity. During the reproductive period, small increases in Zn and Cu concentrations (ca. 1.8- and 1.5-fold, respectively) were observed for kidneys of (−) diet mice with very large increases in renal Cd concentrations (ca. 7700-fold) analogous to results previously found for (+) diet mice (Bhattacharyya et al., Toxicology 1988b; 50: 205–215). A threshold Cd concentration below which the concentration of Zn was relatively constant and independent of Cd concentration was identified (13.6 μg Cd/g kidney); no similar threshold could be observed for Cu. At the end of six rounds, less Zn was found in the kidneys of PL(−) mice exposed to Cd at the 50 than 5 ppm level, however more Cu was found in the kidneys of both NP and PL(−) mice.
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Aug 29, 2023
Xian Liang Sun + 9
Open Access