SOME OBSERVATIONS ON EXPERIMENTAL BONE DISEASE

RICHARD H. FOLLIS, JR. Armed Forces Institute of Pathology, Washiiigton, 25, D.C.

THE normal sequences encountered in endochondral bone formation can be divided into three main categories: (1) growth of cartilage, (2) maintenance of a fine balance between osteoblastic and osteolytic activities of the bone cells and (3) deposition of inorganic materials in cartilage matrix and/or bone matrix (osteoid). Derangements in each of these three categories may be observed in bone disease naturally occurring in the growing child or in the adult. I n the experimental animal one can produce a t will changes which precisely duplicate many of the alterations seen in the human. One can sometimes go even farther and create changes which have no counterpart in human disease.

We should like t o present some interesting, though diversi- fied, examples of experimental bone disease which fit into these categories. The changes which we wish t o discuss will indicate a few of the large number of unsolved problems which concern the growth of normal cartilage and bone. This pre- sentation might better be entitled “ A miscellany of unrelated and peculiar changes which may be produced experimentally in cartilage and bone and which may some day throw light on the biochemical activities of these structures.”

When the dietary of an animal, or a human, too, for that matter, is restricted calorically or by the removal of one or more of any of the essential elements, amino acids, vitamins or fatty acids, growth of cartilage stops, sometimes very abruptly. The cells cease proliferating; in particular, the zone of hypertrophic cells becomes narrower and narrower (Fig. 1). Of course, the influence of the dietary restriction is

240

Bone Structure and Metabolism G. E. W. Wolstenholme.Cecil,ia M. O'Con,ner

Copyright 0 1956 Ciba Foundation Symposium

250 RICHARD H. FOLLIS, JR.

also apparent on the activities of the osteoblast. This is particularly true in ascorbic acid or copper deprivation. Ordinarily, though, the effects on cartilage are often much more pronounced. Certain simple histochemical procedures indicate, for instance, a decrease in glycogen and alkaline phosphatase activity (Follis, 1955~) . As is well known, when the dietary becomes adequate again, growth of the cartilage begins anew and there results an overproliferation of new bone on the framework provided by excessively produced calcified matrix of the cartilage.

The ease with which one can study alterations in the growth of cartilage by this means has prompted us to investigate the effects of purified growth hormone of the anterior lobe of the hypophysis" on the epiphyseal cartilage of rats which had completely stopped growing as a result of dietary restriction (Follis, 1955a). The problem, of course, was t o find out if this disturbance of growth was primarily due to lack of growth hormone, since the change is identical with what is seen in the hypophysectomized animal. It was found that when the hormone was administered in amounts more than necessary to promote growth in hypophysectomized rats, no effects could be elicited in the animals whose dietary had been restricted. It is thus apparent that the missing calories or specific nutrients are necessary for the cartilage cells to repro- duce and form matrix. It will be recalled that from the very beginnings of the modern science of nutrition, growth and reproduction have been used over and over again as yard- sticks for an optinid dietary.

A second and particularly intriguing alteration in the growth of cartilage results when sweet pea seeds (Lathrus odoratus) are incorporated in the diet (Ponseti, 1954). It has, of course, recently been shown that the active principle is p-amino- propionitrile (Bachhuber, Lalich and Angevine, 1955). When actively growing rats are placed on a diet containing 50 per cent ground sweet pea seeds? within 24 hours changes appear in

* Kindly supplied by Armour and Co. Chicago, 111. + Kindly supplied by Ferry Morse Seed Co., Detroit, Alich.

FIG. 1. A. Epiphyseal cartilage of normal rat to show width and orderly row formation of hypertrophic cells. R. Epiphpeel cartilage from rat on a protein-deficient diet for 3 weeks (same magnification as -4) to show great reduction in \iidth of rartilage.

All types of cells are affected.

[ f a c i n g pnge 250

FIG. 2. A. Epiphyseal cartilage from rat which had been on a ground sweet pea seed diet for 48 hours. S o t e clefts in cartilage matrix between cartilage cells. B. Epiphyseal cartilage after 8 days on the diet. There is complete disorganization of the cartilage

with large numbers of seemingly hypertrophic cells.

FIG. 3. A. Portion of metaphysis from control pig to show spicules of cal- cified cartilage matrix upon which bone is being deposited. Note large num- bers of osteoblasts. B. Same region from a copper-deficient pig to show

thin spicules of matrix devoid of bone. Sote also the lack of cellularity.

FIG. 4. Portion of cortex of tibia from rat which had received parenteral S r (18 mg.1100 q . ) each day for 8 days. Note large amount of light staining

material (outeoid) surrounding trabecrilae of bone.

OBSERVATIOSS ON EXPERIMENThL BOKE DISEASE 251

the epiphyseal cartilage (Follis, 1 9 5 5 ~ ) . There is an increase in the zone of hypertrophic cells, and as time goes on a thick jumble of such cells is found (Fig. 2). “Jumble” is used because the cells lose their orderly arrangement and form a thick band of large structures whose normal interrelation- ships are totally disorganized. From the beginning, too, a change is found in the matrix of the less differentiated cells. Clefts appear and the columns are spread apart. As time goes on the adherence of the cells to one another seems to become less and less so that when one cuts through the epiphyseal cartilage with a sharp razor the normal resistance is completely lost. The epiphyseal plate has become a sort of pulpy mass which appears in the fresh state, under the microscope, so lacking in cohesion that individual cells are found floating about by themselves. We are a t the present time studying certain histochemical aspects of this problem. The change should interest certain members of this group who are investi- gating the deposition of 355s in various areas, particularly cartilage.

When one comes to take up the many alterations which may result from disturbances in the fine balance between bone formation and destruction there are any number of experimental situations which might be discussed. We shall restrict our remarks on this subject to one: the very interesting reaction of the osteoblast to a deficiency of copper. Certain changes in the skeleton have been noted in animals grazing in areas whose soil is deficient in Cu. Gross alterations desig- nated as “ osteomalacia” had been reported (Davis, 1950). We were much intrigued several years ago when Drs. James Baxter and Judson Van Wyk brought us some bones from dogs which had been on a Cu-deficient regimen (Baxter and Van Wyk, 1953). Clinically, the disease was characterized by multiple spontaneous fractures with resultant deformities. X-ray studies revealed extreme rarefaction of the skeleton. Grossly, a t autopsy, the cortices of the long bones were extremely thin ; the epiphyses appeared wider than normal. When the cortex was studied microscopically (Baxter, Van

252 RICHARD €1. FOI,I.IS, JR.

Wyk and Follis, 1953), a marked decrease in thickness was found in the Cu-deficient animals. There was apparently a definite decrease in osteoblastic activity in the endosteal areas where destruction appeared to be proceeding in normal fashion. At the cartilage-shaft junctions of the Cu-deficient animals the epiphyseal cartilages were increased in width as compared with controls. The reason for this is not clear and need not detain us here. I n the metaphyseal regions an excess of calcified cartilage matrix upon which bone matrix was not being deposited was found. Our interpretation of this was that the matrix formative functions of the osteoblast were impaired by Cu deficiency, while those of the cartilage cell were not. This dissociation is frequently seen, for instance, in scurvy, osteogenesis imperfecta, etc.

More recently (Follis et al., 1955) we have studied a series of Cu-deficient swine. Changes in the epiphyseal cartilage were not pronounced in the swine. However, a prominent “lattice” of calcified cartilage matrix was present and was unsupported by bone (Fig. 3). There was a definite reduction in osteoblastic activity. This led t o fractures quite reminiscent of scurvy, though unlike this disease there was no osteoblastic prolifera- ation. From these two series of observations in dogs and swine i t would appear that Cu has a specific effect on osteo- blastic activity. Like ascorbic acid deficiency, a lack of Cu does not appear to affect chondrogenic activity.

We should now like to turn to two puzzling situations in which there is excess production of bone matrix which does not readily calcify. The first of these occurs when strontium is given to animals. You are all familiar with Lehnerdt’s (1910) observations on the appearance of a rickets-like condi- tion when excess Sr was administered to animals on a low cal- cium diet. This stimulated the Johns Hopkins group (Shipley et al., 1922), then working on rickets and vitamin D, to restudy Sr administration and to conclude that the changes observed by Lehnerdt had resulted from a lorn Ca, high P, diet and were not due per se to any action of Sr. The Baltimore investigators (Shipley et al., 1922) did note that the inclusion of Sr in the

OBSERVA4TIOSS O N EXPERIMEKTAL BOXE DISEASE 253

Ca-low diet stimulated growth in their rats. More recently Shorr and Carter (1952) have used Sr as an adjuvant to Ca in the “remineralization” of the skeleton in various bone diseases in man.

In some preliminary studies on rats, SrCO, was incorporated at a level of 4 per cent in a diet of adequate Ca and P content. We were impressed by the relatively slight changes a t the cartilage-shaft junction though the amounts of osteoid in the shaft were prodigious. This prompted us to administer various amounts of Sr intraperitoneally. The osteoid con- tinued to appear (Follis, 195%). When the animals were starved and bone growth had ceased, parenteral Sr stimulated the formation of new osteoid (Fig. 4). I n healing fractures and in old animals Sr administration led to the appearance of excess osteoid. It thus became apparent that Sr seemed to stimulate new matrix formation. This may have therapeutic implication and may explain some of the clinical results of Shorr and Carter (1952). The lack of calcification of the osteoid formed may be due to some inherent abnormality in i t or to some interference by Sr in the calcification mechanism, per- haps by competing with the metal complex of the enzyme systems of cells concerned with calcification.

Studies of certain chemical constituents of the serum of animals given parenteral Sr and showing excessive osteoid reveal no changes in Ca, P or alkaline phosphatase concentra- tions. The effects of Sr are to be investigated in several direc- tions in the near future.

The second puzzling situation which we would like to men- tion is found in rats to which toxic amounts of vitamin D are given. This state has for many years been known as “hyper- vitaminosis D rickets” (Ham and Lewis, 1934) and has been an enigma to a number of investigators, including ourselves. No changes are found in the epiphyseal cartilage; in fact, as a result of the toxicity there is cessation of growth of this tissue. There is, however, new formation of osteoid which fails t o calcify in the face of hypercalcaemia and hyperphosphataemia (Follis, 1 9 5 5 ~ ) . In the rat when levels of Ca and P are up t o

254 RICHARD H. FOLLIS, JR.

16 mg. per cent and 10 mg. per cent, respectively, and inor- ganic material is being deposited in many areas : myocardium, kidney, etc., this newly deposited organic matrix fails to show deposition of inorganic material in it ! We have found that the serum of vitamin D poisoned rats with hypercalcaemia and hyperphosphataemia will readily calcify rachitic rat cartilage in vitro. So, too, if the osteoid is incubated with normal rat serum, at Ca and P levels of say 10.0 and 9.0 mg. per cent, respectively, after 24 hours there appears to have been a deposition of inorganic material in it when compared with controls. We have detected this change histologically. Obviously, a more precise method would be to determine if there were a difference in ash content. Another peculiarity in hypervitaminosis D is the occurrence of alkalosis during a stage of toxicity. Usually a t death the whole blood pH is relatively normal, but several days before, we have en- countered pH levels of 7 . 8 at 37' C with the Beckman blood pH electrode. Another peculiarity is a fall in serum alkaline phosphatase activity. For example, a decrease from a normal figure of 18 to a terminal value of 5 may be encountered. This is of interest in view of the feeling that osteoblastic activity is going on at an accelerated rate.

These, then, are some examples of certain problems which have interested us in the past and which continue to intrigue us. What little we have told you should further indicate how much there is to be learned about cartilage and bone.

REFERENCES

BACHHUBER, T. E., LALICH, J. J., and ANGEVIKE, D. ill. (1955). Fed.

BAXTER, J. H., and VAN WYK, J. J. (1953). Johns Hopk. Hosp. Bull.,

BAXTER, J. H., VAN WYK, J. J., and FOLLIS, R. H., JR. (1953). Johns

DAVIS, G. K. (1950). A Symposium on Copper Deficiency, Baltimore:

FOLLIS, R. H., JR. ( 1 9 5 5 ~ ) . Unpublished. FOLLIS, R. H., JR. (19531). Fed. Proc., 14, 403. FOLLIS, R. H., JR. (1955~) . Amer. J . Path., 31, 568.

Proc., 14, 398.

9 3 , l .

Hopk. Hosp. Bull., 93, 25.

Johns Hopkins Press.

OBSERVATIONS OX EXPERIMESTAL BONE DISEASE 255

FOLLIS, R. H., JR., BUSH, J. A., CARTWRICHT, G. H., and WINTROBE, M. M. (1955). Johns Hopk. Hosp. Bull., 97, 405.

HAM, A. W., and LEWIS, 11. D. (1934). Brit. J . exp. Path., 15, 228. LEHNERDT, F. (1910). Beitr. path. Anat., 47, 215. PONSETI, I. V. (1954). J . Bone Jt. Surg., 36-A, 1031. SHIPLEY, P. G., PARK, E. A., MCCOLLUM, E. V., SIMMOXDS, N., and

KINNEY, E. M. (1922). Johns Hopk. Hosp. Bull., 33, 216. SHORR, E., and CARTER, A. C. (1952). Bull. Hosp. *Jt. Dis., 13, 59.

DISCUSSION

de Bernard: We did some experiments on the alteration of growth cartilage in thiamin deficiency, and found that the phosphatase content of this tissue was lowered.

Rogers: I was fascinated by your results with Lathrus odoratus, Prof. Follis. Are they due entireIy to the absence of glycogen?

Follis: There must be something wrong with the matrix, because the thing just goes to pieces. Some of the disorganization that you see in Fig. 2 is due to mechanical compression. It is just a mass of pulp.

Rogers: It is not only disorganization of the arrangement of cells. There is something wrong with the behaviour of the cartilage cells. Is it possible that the P-aminopropionitrile interferes with the formation of ground substance mucopolysaccharides ? A failure to form polymerized chondroitin sulphate might well lead to tissue disorganization under stress such as you have described. Have you tried anything other than P-aminopropionitrile ?

Meyer: I have heard that it can also be done with aminoacetonitrile. Bklunger: With Drs. Comar, Lotz and Visek of Oak Ridge, we have

just terminated a series of experiments on chronic fluorosis in pigs. In this case we observed hypertrophy and also dissociation of the plate, which are quite similar to that particular type of thing and also compar- able to the lesion of vitamin D deficiency. This condition is apparently related to a deficiency of the polysaccharides.

Bluzter: In cattle, in the county of Caithness in the north of Scotland, a condition of Cu deficiency associated with peatlands occurs, in which there is a marked lightening of the black coat colour, which is presumably an interference with melanin metabolism. One thing which has not been studied up there is the fact that these animals develop very thin bones and always walk with a very characteristic stilted gait. This same disease occurs also in certain parts of New Zealand. I wonder whether Prof. Follis has had any occasion to examine bones from animals which have been suffering from these so-called defective bone conditions due to Cu deficiency in cattle, or indeed the Cu deficiency syndromes which occur in sheep and which are associated with demyelination and loco- motor ataxy.

Follis: This has been described in Florida also, and has been called osteomalacia, erroneously I think, because the bones were not studied chemically and one should not use the term " osteomalacia )' indiscrimin- ately, even amongst animals,

256 DISCVSSION

Armstrong: How would you explain the exostoses and the osteo- sclerosis of chronic fluoride intoxication? Do we have to imagine that these are a result of overproduction of matrix?

Follis: I would think so. Of course a lot of this occurs a t the sites of insertion of tendons and muscles and one looks upon that as perhaps being analogous to this, in that an area of lowered resistance to stresses and strains with perhaps healing and overproduction of bone, such as we mentioned, might be the explanation of the changes IZodicek discussed in scurvy.

Kodicek: I take i t that these hypervitaminotic animals were rats; you find about 60 per cent ash in normal rats, and this seems rather high.

Follis: You can get it a little lower. It depends on which bone-this was fat-extracted bone.

Kodicek: Our results were on a fat-free basis, and we did not find lowering of the ash content in hypervitaminosis D.

Follis: Have you found a difference between hypervitaminosis D and cortisone ?

Kodicek: Not much; the ash content was 41 and 43 per cent respec- tively. I do not think the difference is significant. Histologically your picture and ours agree.

Dixon: Can you reconcile the rickets-producing action of Sr with Shorr's increased mineralization by Sr in human osteoporosis ?

Follis: Shorr gives fairly large quantities of Ca with the Sr, and what we have to do now perhaps is to give Ca and not Sr and see whether the excessive amounts of Ca will deposit in matrix.

Nicolaysen: Sr has a dual effect: it goes into the crystals and it inter- feres with metabolism a t the cellular level.

Follis: A third effect, perhaps, may be interference with the calcifica- tion mechanism, which has been demonstrated in vitro by Sobel.

Nicolaysen; This is a physicochemical concept. Panconi: I have seen many cases of hypervitaminosis D with osteo-

sclerosis of the metaphysis on the one hand and decalcification of the diaphysis on the other. We always have hypercalcaemia, in some cases a low or normal phosphate level, in others a high phosphate level. Very severe cases die of Ca poisoning.

Pollis: These animals probably die of renal insufficiency, the kidney tubules become congested.

Nordin: The alkalosis is interesting. What about K levels? Howard: I cannot tell you how it is produced, but we get a high CO,

and a low chloride in D intoxication, just the same as one sees in I< depletion. TVe have studied one person during D poisoning for a week. He was excreting more I< in the urine than he was taking in in the diet; but whether that was a typical week or whether K loss is the cause of the alkalosis, I do not know. It is most interesting.

Kordin: Dr. Howard, did you say there was uraemia there with a high phosphate ?

Howard: They had uraemia. There is something in uraemic serum that prevents bone and cartilage calcification a t much higher levels of Ca and P. TVe could not find what it was, it was not Mg or urea.

DISCUSSION 257

Kodicek: Reports have occasionally appeared in the literature that, in hypervitaminosis, people have found overproduction not of osteoid but of bone.

Follis: I think the length of time that the animals live may be a matter of dosage. This is the most extreme, when the animals die in six days.

Kodicek: Could i t be that there are two stages? Follis: Possibly; and you can give an animal a course of vitamin D

and not let him die, The osteoid which I showed in Fig. 4 has now calcified.

BONE 10