Arch Toxicol (1992) 6 6 : 3 1 5 - 3 2 0

Archives of

To:dcology 9 Springer-Verlag 1992

Decrease in bone strength of cadmium-treated young and old rats Kumiko Ogoshi 1, Yukuo Nanzai 2 and Tadashige Moriyama 1 1Dept of Public Health, Nara Medical University, Kashihara, Nara 634, Japan z Faculty of Engineering, Osaka City University, Sngimoto, Sumiyoshi-ku, Osaka 558, Japan Received 4 June 1991/Accepted 9 January 1992

Abstract. A decrease in mechanical strength of bones was observed both in young and old rats for long periods of administration of cadmium. Young (3-week-old) female rats were given 0 (control), 5 and 10 ppm cadmium in drinking water, respectively, for 20 weeks. Old (18-monthold) female rats were given 0 (control) and 40 ppm cadmium in drinking water, respectively, for 7 months. The compression strengths of bones of young rats which were given i0 ppm cadmium, and those of old rats which were given 40 ppm cadmium, significantly decreased at the distal end portion of femur. Cadmium contents in bones in the 10 ppm and 40 ppm groups were about 110 and 210 ng/g dry weight, respectively. The present result confirmed that cadmium has a lesional effect on the mechanical strength of bone at the concentration of 100-200 ng/g in dry weight of bone, for both young and old rats. Key words: Cadmium - R a t - Bone - Long-term administration

susceptible than kidney. Iguchi and Sano (1982) found that cadmium has an inhibitory effect on the crosslinking of collagen in bones of young rats. In our previous papers, it was shown that the mechanical strength of bones of young growing rats decreased with the administration of cadmium for 4 weeks, and that the decrease in mechanical strength of bones was correlated to the quantity of cadmium in the bones. The critical concentration of cadmium which affects the mechanical strength of bones is 100 ng/g dry weight of the bone (Ogoshi 1985; Ogoshi et al. 1989). It is considered that a small quantity of cadmium absorbed in a growing bone disturbs bone metabolism and as a result of the incomplete construction of the compact bone, the mechanical strength of bone decreases. In the present investigation, the effect of long term cadmium administration on the mechanical strength of bone was examined. It might happen, in the case of a long period of administration of a small amount of cadmium to young rats, that the bone would recover its normal mechanical strength after its Cd toxic effects were reduced in the process of its normal growth. This problem is addressed in the present study. The effect of a long period of administration of cadmium on the bones of aged rats was also tested.

Introduction There are some reports which suggest lesional effects of cadmium on bone (Yoshiki et al. 1975; Kawai et al. 1976; Iguchi and Sano 1982), but the direct effect of cadmium on bone still remains unclear. Kimura et al. (1974) found a histologic change in the bones of Cd-treated rats when no change in the hydroxylation of 25-OH-D3 in kidneys was observed. Yoshiki et al. (1975) observed that the osteoporotic change in bone preceded kidney damage in cadmium-treated rats. Kawai, Fukuda and Kimura (1976) observed bone damage in rats to which 10 ppm cadmium was administered for 8.5 months, while no damage took place in the kidneys in these rats. They asserted that bone is more

Offprint requests to: K. Ogoshi

Materials and methods Materials. We gave cadmium chloride solution as drinking water to two different age groups of rats, i. e. young rats and old rats, for long periods. The rats were free fed on normal diet MF (Oriental Yeast Inc., Japan). They were kept in the specific pathogen-free condition at a room temperature of 23_+1~ In experiment A, 97 female 21-day-old rats w e r e divided into three groups of 31, 31 and 35 rats. They were given drinking water containing 0 (as the control), 5 and 10 ppm cadmium, respectively, for 20 weeks. In experiment B, 27 female 18-month-old rats were divided into two groups, 9 and 18 rats. The first group was given distilled water as the control while the second group of 18 rats was given drinking water containing 40 ppm cadmium for 7 months. During the administration period, no observational signs of disorder were found among these rats, but one rat of the control group of experiment B was omitted from the experiment at the end of the administration because a tumor (histologically not identified) was found in its abdomen on dissection. At the end of the administration of cadmium, all the rats were anesthetized with

316 300

strength test, a bone shaft was supported horizontally by four fulcra, and the two inner fulcra were pulled perpendicularly to the bone's axis at a constant speed (1.65 mm/min). As the bending moment produced uniformly through the bone shaft by this four-point bending method, fracture occurred at the point which was most liable to break. For the compression test, a bone was cut into three portions, i. e. a proximal end portion, a middle shaft and a distal end portion, and the distal end portion and the middle shaft were separately compressed at a constant speed (1.65 mm/min) in the logitudinal direction of the bone's axis. The ultimate fracture force was measured and the stress at the fracture point was calculated. Details of the bending and compression strength tests were described elsewhere (Ogoshi et al. 1990).

(26)

T

b0 r

200 (IS)

o

:!:!:!:i:~:i:l

iiiiiiilililil ::i!i!:!i!i!::l iiiii ii!ilil !i!!!:i!i!i!i:l

(14)

!ii!!i:ii!:!:!~!~!a !!!!!::~

mo

ili i i!!ii i il !i!!ii~iiii!iil

i!!!i!i i i i l

(2o)

(8)

::::::::-..:

Control 5-

lO-ppm

young rats

Contml 40ppm

agedrats"

Fig. 1. Cadmium concentration in bone of young and aged rats. Each bar shows the mean + SD. The sample size is shown in parentheses on top of each bar

(n)

30(]

~

Determination of Cd. Zn, Mg and Fe in tissues. Cadmium concentration in bones, kidney cortex and liver was determined by atomic absorption spectrometry. The middle portions of femur, after being tested for compression strength, were collected individually, washed with physiological saline to remove the bone marrow, and dried to weigh. Then the bones were wet digested in hot nitric acid and after the adequate dilution the cadmium concentration was determined by the flameless atomic absorption analysis (FLA-100, AA-860, Nippon Jarrel Ash Inc., Japan). The kidney cortex and liver were dried, weighed, wet digested, and then the cadmium was determined by atomic absorption spectrometry (AA-860). Zinc, magnesium and iron contents of the wet digested bone samples were also determined by an inductively coupled plasma emission spectrochemical analyser (ICPS- 1000, Shimadzu Co., Japan). Hematological and biochemical tests. The blood drawn from the artery of rats was divided into two samples: for hematological tests and for biochemical tests. Hb content, Ht, MCV, MCH and MCHC valuesin blood were determined by the use of a Coulter Counter S. Alkaline phosphatase activity (Alp), Ca, P, Fe, total protein (TP), urea nitrogen (SUN), uric acid (UA), creatine (SCR) and creatinine (SEN) in serum were determined by PNPP, OCPC, molybdenum blue, iron electrode, Biuret, enzyme, enzyme, enzyme and Jaffe methods, respectively. Statistical analysis. The data were analysed statistically by Student's t-test. A test probability below 0.05 was considered significant. The correlation between the bone strength and the metal contents in bone was also tested in the Cd groups.

kidney cortex

20C

Results lOO (12)

Control

5 ppm lOppm

young rats

Control 40ppm aged rats

Fig. 2, Cadmium concentration in liver and kidney cortex of young and aged rats. Each bar shows the mean + SD. The sample size is shown in parentheses on top of each bar

ethyl ether, and their chests and abdomens were dissected to survey the organs. After checking that there was no abnormal signs in the rats, blood was drawn from the abdominal artery and the femurs, kidneys and the liver were dissected out for the following experiments. Mechanical strength tests of bones. Pairs of femurs of the rats, after being dissected out from their bodies, were prepared for the mechanical strength tests. One femur of a rat was examined for bending strength, and the other was examined for compression strength. For the bending

The results o f the m e c h a n i c a l strength test are shown in Tables 1 and 2. I n T a b l e 1, the body weight o f the 10 ppm Cd group of y o u n g rats in e x p e r i m e n t A decreased slightly, whereas the b o d y weight of the 40 p p m Cd group in experi m e n t B showed no significant change. The b o n e weight, except for o n e side of the b o n e s of the 10 p p m Cd group, showed no significant change, as s h o w n in Tables 1 and 2. In all c a d m i u m groups o f A a n d B, b e n d i n g strength showed no change, as c o m p a r e d with the controls. In Table 2, however, the decrease in c o m p r e s s i o n strength of the distal e n d portion (metaphysis) of the f e m u r was observed in the 10 p p m group of A and in the 40 p p m group of B. Decreases in c o m p r e s s i o n strength of these groups were observed in both b r e a k i n g load and stress. A slight decrease in c o m p r e s s i o n strength o f the distal end portion of the 5 p p m group of A was observed in both load and stress as s h o w n in T a b l e 2, but it was not statistically significant. N o change in the c o m p r e s s i o n strength of the m i d d l e shaft (diaphysis) o f the f e m u r was observed in any c a d m i u m groups of A and B. The c a d m i u m concentrations in bone, k i d n e y cortex and liver o f the groups o f A and B are s h o w n in Figs. 1 and 2.

317 Table 1. Bending strength of femur diaphysis of cadmium-treated female rats over long periods Body weight (g)

Femur weight (g)

Breaking moment M (10-2 Nm)

Breaking stress ~B (MPa)

327• 29 (31)

0.933• (24)

40.0___5.3 (24)

125.8+ 13.8 (24)

5 ppm

311 • (31)

0.920• (24)

39.6• (24)

128.5 _+11.9 (24)

10 ppm

306 +-28* (35)

0.909 --4-_0.066 (33)

38.0 ___4.2 (33)

124.4 _ 17.9 (33)

B: control

299+_ 19 (8)

0.769___0.031 (8)

28.5___0.9 (8)

159.7_+ 17.6 (8)

40 ppm

283+_24 (18)

0.771 +0.061 (18)

28.9+_2.4 (18)

158.1 ___17.9 (18)

A: control

A: 21-day-old rats, Cd-treated for 20 weeks B: 18-month-old rats, Cd-treated for 7 months Ivl:breaking bending moment 6B: breaking moment divided by the section modulus of diaphysis

(N): sample size *: value is statistically significant at the probability P

Decrease in bone strength of cadmium-treated young and old rats.

A decrease in mechanical strength of bones was observed both in young and old rats for long periods of administration of cadmium. Young (3-week-old) f...
519KB Sizes 0 Downloads 0 Views