Early strain-related changes in enzyme activity in osteocytes following bone loading in vivo.

The skeleton's architecture is matched to the changing loads to which it is subjected because mechanical loading directly or indirectly influences the activity of cell populations to deposit, maintain, or remove bone tissue as appropriate. This responsiveness to load bearing presupposes that certain cells are sensitive to load itself or to its consequences within the tissue. The nature of this effect and the cells concerned have not yet been determined. In this series of experiments, bones were exposed in vivo to a single short period of dynamic loading, which if repeated daily had been shown to result in increased new bone formation. There was an increase in the activity of glucose 6-phosphate dehydrogenase (G6PD) in the periosteal cells adjacent to the bone surface 6 min after this single period of loading. This increase was proportional to the strain magnitude in the bone tissue in the immediate vicinity of the cells. In osteocytes, although the G6PD activity in each individual cell was unchanged by loading, the number of cells displaying activity was increased. This increase was also directly proportional to the applied strain in that area of the cortex (52% compared with 26% active osteocytes at a strain of 0.002). Activation of G6PD was unaccompanied by any equivalent changes in the activities of either glyceraldehyde 3-phosphate dehydrogenase (GA3PD) or lactate dehydrogenase (LDH). This finding is consistent with loading increasing the activity of the oxidative part of the pentose monophosphate shunt pathway. It is also consistent with stimulation of a synthetic process, such as the production of RNA from ribose 5-phosphate.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrochemical detection of depressed circulating levels of vitamin K1 in osteoporosis.

If gamma-carboxylation, by the vitamin K1 - cycle, of glutamate residues of bone-matrix peptides is essential for the formation of bone, the circulating levels of this vitamin might indicate the potential efficiency of this process. Methods involving HPLC with electrochemical detection have very recently been developed for assaying the low levels of vitamin K1 that occur in normal plasma. Using such methods, we found that the circulating levels of vitamin K1 in osteoporotic patients (who had sustained either spinal crush-fractures or fractures of the neck of the femur) were significantly lower than those of age-matched control subjects.

Inhibition of cytochemical bioactivity of parathyroid hormone by plasma in pseudohypoparathyroidism type I.

Despite the high circulating levels of immunoreactive PTH in patients with pseudohypoparathyroidism type I (PSPI) the levels of bioactive PTH (bioPTH) have been found to be close to the normal range. To elucidate this dissociation, we have studied the recovery of the biological activity of bovine PTH added to the plasma of patients with either PSPI, or with hypoparathyroidism (PTX), primary hyperparathyroidism (HPT) or of normal subjects. In PSPI (n = 10) the recovery of biological activity was 5.6% +/- 3.6 (mean +/- SEM) whereas in PTX (n = 7), in HPT (n = 4) and in normal subjects (n = 8) it was 79% +/- 5, 75% +/- 9 and 68% +/- 4, respectively. In another PSPI patient, who had undergone total parathyroidectomy, bioPTH was undetectable but the recovery from the plasma of added PTH was 84%. Thus we have found inhibition of PTH bioactivity by plasma of PSPI patients which was absent after parathyroidectomy.

Dissociation of parathyroid hormone bioactivity and immunoreactivity in pseudohypoparathyroidism type I.

Circulating levels of parathyroid hormone (PTH) in six patients with pseudohypoparathyroidism type I (PSPI) have been measured by two immunoassays and by cytochemical bioassay and compared with measurements in normal subjects and patients with clinically defined hyper- and hypoparathyroidism. In all PSPI patients, the levels of immunoreactive PTH were in the hyperparathyroid range, whereas the bioactive levels were either in the normal or close to the normal range. In one patient from whom the dihydrotachysterol therapy was withdrawn, both immunoreactive and bioactive PTH concentrations increased. The finding that the PTH measured by RIA in these PSPI patients may have reduced biological activity may explain some of the clinical findings of hypoparathyroidism in this syndrome.

Putrescine may be a natural stimulator of glucose-6-phosphate dehydrogenase.

The possible relationship between pyridoxal phosphate-dependent ornithine decarboxylase (ODC) activity and glucose-6-phosphate dehydrogenase (G6PD) activity has been studied in the osteoblasts of the growth-plate of metatarsals of rats fed a pyridoxine-deficient diet, which caused depressed G6PD levels. The G6PD activity was fully restored when it was assayed in the presence of putrescine. It is suggested that this relationship may account for the correlation generally found between growth and ODC activity.

Abnormalities in fracture healing induced by vitamin B6-deficiency in rats.

Vitamin K1 is the intermediate carrier of reducing equivalents in mineralization. In fracture-healing in the rat metatarsal the primary source of these reducing equivalents appears to be NADPH, generated from glucose 6-phosphate dehydrogenase (G6PD) activity. Because recent evidence indicated that stimulation of G6PD activity can be induced by putrescine, derived from pyridoxal phosphate-dependent ornithine decarboxylase activity, the effect of pyridoxine (vitamin B6) deficiency has been studied in this system. Vitamin B6-deficiency caused marked diminution in the G6PD activity in the periosteal region of bone-formation and in the developing callus, with significant delay in the maturation of the callus and union. It also caused changes in the bone suggestive of imbalance in the coupling between osteoblasts and osteoclasts. These results suggest that the vitamin B6-status may be important in fracture-healing.

Selective depression of metabolic activities in cortical osteoblasts at the site of femoral neck fractures.

The aim of this investigation was to determine whether some metabolic defect might be related to the propensity of osteoporotic femoral necks to fracture acutely. To this end, the activities of two dehydrogenases of the glycolytic Embden-Meyerhof pathway, two of the pentose phosphate pathway, two mitochondrial enzymes, and alkaline phosphatase were measured in the cortical and in the trabecular osteoblasts. Comparison was made with such activities in iliac crest biopsies from patients with these fractures and from the equivalent femoral and iliac crest samples from patients with osteoarthritis of the hip, in biopsies from the iliac crests from seven patients with no bony abnormality, and in specimens from the fracture site of six traumatic fractures. The results showed a highly significant decrease in the activities of the two enzymes of the pentose phosphate pathway (p less than 0.001) in the cortical, but not in the trabecular, osteoblasts in the osteoporotic fractures. This could not be attributed to the trauma of acute fracture since it was not found in traumatic fractures. Other experimental evidence has indicated that a relationship may occur between depressed activity of these enzymes and a retardation of bone formation.

Altered organization of non-collagenous bone matrix in osteoporosis.

In osteoporosis it is postulated that while the amount of bone is diminished, the quality of the bone is unaltered. Recently relatively novel methods of analysis have shown that, at the fracture site of osteoporotic subcapital fractures, there is a marked change in the molecular orientation of components of the non-collagenous bone matrix. These procedures, now applied to iliac crest biopsies, confirm earlier findings of altered orientation of the proteoglycans at the subcapital fracture site but show that very similar changes occur even in the iliac crests from patients with both types of osteoporotic proximal femoral fracture. Thus, whereas the amount of these acidic moieties of the non-collagenous bone matrix was unchanged, the molecular orientation was markedly altered, albeit not to the same extent as that found at the fracture site. These results imply that the quality of the bone, as well as the quantity, may be generally affected in osteoporosis.

Comparative metabolic enzymatic activity in trabecular as against cortical osteoblasts.

On the basis of studies with bone-seeking isotopes, it is generally believed that the metabolic activity of osteoblasts of the trabecular bone is greater than that of the osteoblasts of the cortex. This implies that the oxidative activity, which provides the energy for biosyntheses, will also be greater in the former than in the latter. In the present study, direct measurement of the activities of representative enzymes of the major oxidative pathways, as well as of alkaline phosphatase, showed that the reverse pertained. However, owing to the greater cellularity of trabecular bone, the activity per unit mass of bone may be higher in the trabecular bone.

Depressed levels of circulating menaquinones in patients with osteoporotic fractures of the spine and femoral neck.

Vitamin K1 functions in the conversion of glutamate residues, present in certain bone peptides, into the putatively active gamma-carboxyglutamate form. We have shown previously that the circulating levels of vitamin K1 are depressed in osteoporotic patients. However, it is known that menaquinones (vitamin K2:MK) may be more effective than vitamin K1 in this conversion of the inactive to active form of glutamate residues. A procedure for measuring such menaquinones has now demonstrated a marked deficiency of MK-7 and MK-8 in patients with osteoporotic fractures. It is suggested that estimates of circulating levels of K1, MK-7, and MK-8 might provide a biochemical risk marker of osteoporotic fractures.

Measurement of nitric oxide synthase activity in sections of rat liver.

In the previous communication we described a histochemical method for measuring soluble guanylate cyclase (sGC) activity in sections of rat liver. In theory, this method could be used to assess nitric oxide synthase (NOS) activity by the increased sGC activity induced by the additional presence of the substrates for NOS activity. We found that this was correct provided that the concentration of the colloid stabilizer in the reaction medium was decreased to just below the concentration required to fully stabilize the guanylate cyclase activity in the sections. This was related to the fact that the site of NOS activity was different from that of the sGC activity in the hepatocytes, so that the NO generated had to diffuse from the Kupffer cells to the hepatocytes as could occur only in partially unstabilized sections. Optimal concentrations of arginine and of NADPH have been determined for demonstrating NOS activity; the increased reaction was shown to be largely inhibited by methyl-arginine.

Histochemistry of guanylate cyclase activity.

Guanylate cyclase liberates pyrophosphate from guanosine triphosphate (GTP). In studies published previously, this phosphate is trapped by lead ions even though it is known that free lead ions inactivate a considerable proportion of this enzymatic activity. To overcome the damaging effects of fixation, this study used fresh cryostat sections stabilized with a sufficient concentration of a collagen-derived polypeptide to ensure no measurable loss of guanylate cyclase activity. To avoid the damaging influence of free lead ions, we used a hidden metal capture reagent, i.e., a complex of lead ammonium citrate/acetate that does not react with GTP but which rapidly forms a precipitate with the pyrophosphate liberated by the enzyme. The lead precipitate is then converted into the colored sulfide which is measured in individual cells by microdensitometry. This system was used to measure guanylate cyclase activity in individual cells in unfixed sections of rat liver.

Myocardial preservation during aortic valve surgery. Assessment of five techniques by cellular chemical and biophysical methods.

Five different types of myocardial protection were employed in this series of 168 patients undergoing aortic valve replacement. Two methods of assessing myocardial preservation were used: cellular biological estimations and quantitative polarization measurements. Both parameters showed that either of two methods, continuous perfusion at 32 degrees C. with a beating heart or cardioplegic hypothermic arrest, protected the myocardum best. Intermittent perfusion at 30 degrees C. with a fibrillating heart was the worst means of preservation. Our investigations (both clinical and experimental) have also shown that changes in birefringence, indicative of deteriorating myocardial function, are often detectable before parallel cytochemical changes are apparent.

Cold cardioplegia or continuous coronary perfusion? Report on preliminary clinical experience as assessed cytochemically.

Myocardial preservation by continuous coronary perfusion is compared with cold cardioplegia. The 1 L. of St. Thomas' cardioplegic protective solution used for infusion into the coronary arteries was at 4 degrees C. and had a normal electrolyte content except for raised concentrations of magnesium and potassium and the addition of procaine. Myocardial preservation was assessed by cytochemical grading of myocardial biopsy specimens and also by the requirement for significant inotropic support postoperatively. In aortic valve replacements with an aortic occlusion time of 1 1/2 hours, both techniques afforded a similar degree of preservation, except that the inner half of the myocardium was markedly better preserved by cold cardioplegia. After 2 hours in double valve replacements, a single cardioplegic infusion was not as effective as continuous coronary perfusion, but this could be corrected by a second infusion of the cardioplegic solution after an hour.

Quantitative enzyme cytochemistry of leukaemic cells.

A new technique for the quantitative estimation of glycolytic and respiratory enzyme activity in intact and unfixed bone marrow and peripheral blood cells is described. The method gives a two- to three-fold increase in demonstrable enzyme activity per cell compared with existing techniques using fixed marrow film preparations, and is particularly applicable to the study of relatively fragile cells such as the leukaemic lymphoblast.

Feulgen-hydrolysis profiles in cells exfoliated from the cervix uteri: a potential aid in the diagnosis of malignancy.

By varying the time of hydrolysis for the Feulgen reaction, done under conditions that protect the backbone of the DNA, it is possible to distinguish three species of DNA that are characterised by their lability to acid hydrolysis. The most labile DNA was found, in greatest proportions, in malignant cells; this may be helpful in diagnostic cytology. The fact that the cytologically normal cells, in grade V smears, also show this labile DNA may well facilitate cytological screening even in those smears that contain very few neoplastic cells.

Lysosomal naphthylamidase activity as a possible aid in cytological screening.

Lysosomal naphthylamidase activity has been measured microdensitometrically in cells in samples obtained by cervical and vaginal irrigation from 22 cases cytologically graded I and II, 28 graded III (moderate to severe dysplasia), 22 graded IV (carcinoma in situ), and 15 cases (grade V) of invasive carcinoma. There was a statistically significant difference in this activity in the cells from cases of grade V as against those in the relatively normal samples (grades I and II; p < 0.001) and as against those of grade IV (p < 0.005). The method is sufficiently robust for routine use provided that it is recognised that elevated activities can be found as a consequence of other factors such as previous surgical intervention and infection with herpes simplex.

A modified tetrazolium reaction for identifying malignant cells from gastric and colonic cancer.

When non-malignant cells were reacted for glucose-6-phosphate dehydrogenase activity, with neotetrazolium chloride as the indicator of the activity, oxygen competed with the neotetrazolium and nullified the reaction. In contrast, about 30% of the activity was retained in malignant cells, in sections and in smears, from cancer of the stomach or colon. This could provide the basis of a qualitative (black-or-white) functional test for distinguishing malignant cells in these conditions.

The effect of ionized calcium, pH, and temperature on bioactive parathyroid hormone during and after open-heart operations.

Normal myocardial function is dependent on the metabolic balance of a number of electrolytes and hormones. The calcium ion plays a major role in muscle contraction and is rigorously controlled within narrow limits. Open-heart surgery imposes metabolic disturbances on both electrolytes and hormones, especially ionized calcium. Normally, ionized calcium levels are controlled by parathyroid hormone with a negative feedback from the ionized calcium controlling the system, but the results from this study suggest that during open-heart procedures, ionized calcium does not impose its normal negative feedback on bioactive parathyroid hormone secretion. The low blood pH levels that occurred during the operative conditions of the patients studied and the level of hypothermia imposed on the circulating blood during cardiopulmonary bypass appeared to influence the control of parathyroid hormone secretion, causing high levels of hormone to be secreted during this period.

Loading-related reorientation of bone proteoglycan in vivo. Strain memory in bone tissue?

The load-carrying capacity of the skeleton is achieved and maintained as the result of a continued functional stimulus to the cell populations responsible for bone remodeling. Although some bone cells have been assumed to be influenced by the load-induced changes in strain throughout the matrix, no evidence is available to indicate which cells are susceptible to such strain change or how such transient events provide a sustained influence on cell behaviour. In the present study, we showed that a short period of dynamic loading in vivo affects the orientation of proteoglycan within bone tissue. This reorientation declines only slowly, thus providing a persistent record of the tissue's recent strain history. Such a record has the ability not only to "capture" strain transients but also to "update" and "average" them. In this way, the bone cells could be presented with a sustained and coherent stimulus directly related to dynamic strain transients. These transients are the tissue's principal function variable.