Renal functional response to protein loading in type 1 (insulin-dependent) diabetic patients on normal or high salt intake

Insulin-dependent diabetes mellitus (IDDM) patients may have an increased intrarenal angiotensin II activity. In diabetic patients, captopril increases the renal hemodynamic response to an amino acid infusion. We investigated the effects of two salt diets on arterial pressure and renal response to a protein load in 10 normotensive (blood pressure < 140/90 mm Hg) IDDM patients (aged 30 +/- 3 years) who had diabetes for 7 +/- 4 years and normoalbuminuria levels [albumin excretion rate 4.8 (2.5-19.1) microg/min]. After 1 week of normal (approximately 100 mmol/day; approximately 100 mEq/l) and 1 week of high (approximately 300 mmol/day; approximately 300 mEq/l) salt intake, renal hemodynamic studies were performed at baseline and after a protein load (meat meal) of 100 g/1.73 m2. The mean 24-hour urinary sodium excretion levels were 99 +/- 27 and 293 +/- 80 mmol (mEq) with normal and high salt intake, respectively. No significant changes were seen in plasma sodium and glucose control with the normal and high salt diets, respectively: plasma sodium 135 +/- 3 vs. 137 +/- 1 mmol/l (mEq/l), (p = 0.08) and glycated hemoglobin 9.1 +/- 1.9 vs. 9.4 +/- 2.1% (p = 0.36). The body weight (70.9 +/- 12 vs. 71.8 +/- 13 kg; p = 0.015) was significantly higher with a high salt diet. The mean arterial pressure was similar with both diets (normal vs. high salt diet 91 +/- 9 vs. 89 +/- 6 mm Hg, p = 0.25). The plasma renin concentration [28 +/- 15 vs. 16 +/- 6 microU/ml(168 +/- 90 vs. 96 +/- 36 pmol/l), p = 0.013] and angiotensin II [8.8 +/- 4.4 vs. 6.4 +/- 3.5 pg/ml (0.052 +/- 0.025 vs. 0.038 +/- 0.021 nmol/l), p = 0.016] were significantly lower with the high salt diet. Following protein loading, the glomerular filtration rate increased with both diets: normal salt diet 114 +/- 26 vs. 128 +/- 30 ml/min/1.73 m2(1.9 +/- 0.43 vs. 2.13 +/- 0.50 ml/s/1.73 m2), p = 0.04; high salt diet 118 +/- 23 vs. 127 +/- 29 ml/min/1.73 m2 (1.97 +/- 0.38 vs. 2.12 +/- 0.48 ml/s/1.73 m2), p = 0.13. The change in renal plasma flow was similar to that of the glomerular filtration rate with normal and high salt intake, respectively: 566 +/- 94 vs. 617 +/- 142 ml/min/1.73 m2 (9.44 +/- 1.57 vs. 10.29 +/- 2.37 ml/s/173 m2), p = 0.0017; 572 +/- 125 vs. 600 +/- 110 ml/min/1.73 m2 (9.54 +/- 2.08 vs. 10.00 +/- 1.83 ml/s/1.73 m2), p = 0.057. In this subset of normotensive normoalbuminuric IDDM patients, a high salt intake did not promote an exaggerated renal response to the protein load despite inhibition of the renin-angiotensin system.

Purification and characterization of fully functional human osteoclast precursors

The identification and purification of human osteoclast precursors is essential to further our understanding of the mechanisms that control human osteoclast differentiation. Osteoclastoma tissue potentially provides a rich source of human osteoclast precursors, and in previous studies we have demonstrated the existence of a population of mononuclear cells within this tissue that is reactive with osteoclast-selective vitronectin receptor monoclonal antibodies. In this study, mononuclear cells expressing the vitronectin receptor, as defined by their ability to react with a murine monoclonal antibody to the beta 3 chain of the vitronectin receptor (87MEM1), were isolated from collagenase digests of osteoclastoma tissue using a fluorescence activated cell sorter. Based on their fluorescence signal and size, approximately 2-3% of the viable cells (typically 2 x 10(5)) were obtained and prepared for further phenotyping. The isolated cells demonstrated a number of phenotypic characteristics of osteoclasts: positive tartrate-resistant acid phosphatase (TRAP) activity, reactivity with human osteoclast-selective antibodies, expression of calcitonin receptors, cathepsin K (a novel osteoclast-selective cysteine proteinase) mRNA, and osteopontin mRNA and protein. These phenotypic characteristics were also detected in mononuclear cells within cryostat sections of the native osteoclastoma tissue as well as in resorption lacunae of sections of human bone. In contrast, isolated peripheral blood monocytes were negative for TRAP activity and osteopontin expression and, unlike the osteoclastoma-derived cells, demonstrated strong nonspecific esterase activity. Significantly, when the osteoclastoma-derived 87MEM1 positive cells were cocultured on whale dentine for 1-3 weeks with stromal cells, extensive resorption of the dentine surface was observed. This is the first demonstration of the purification of human osteoclast precursors. These cells provide an homogeneous cell population for studying cellular events that occur during human osteoclast differentiation.

Human osteoclastoma-derived stromal cells: correlation of the ability to form mineralized nodules in vitro with formation of bone in vivo

It has been suggested that the stromal element of human osteoclastomas contains osteoblastic cells. In this study, we demonstrate that osteoclast-depleted, passaged stromal cells express alkaline phosphatase and osteocalcin in vitro and form mineralized nodules under appropriate culture conditions. In addition, we describe a model in which severe combined immunodeficient (SCID) mice were used to support the differentiation of these putative human osteoblast progenitors in vivo. Lesions formed from human stromal cells were identified using the OKa blood group antigen and human procollagen type I antibodies. By 21 days, the lesion was a complete bone unit: a fully mineralized cortex, remodeling trabeculae, and a highly cellular marrow space. Stromal cells derived from six out of seven osteoclastomas produced identical lesions. Further studies have demonstrated that the capacity of the osteoclastoma-derived stromal cells to form bone in vivo and in vitro is passage dependent; early passages were osteogenic in both model systems, while later passages were not. In conclusion, we have developed a model in which the osteogenic nature of cells can be confirmed in vivo. Furthermore, human osteoclastoma-derived stromal cells provide a source of these osteogenic cells to study human osteoblast differentiation, both in vivo and in vitro.

Cathepsin K, but not cathepsins B, L, or S, is abundantly expressed in human osteoclasts

Random high throughput sequencing of a human osteoclast cDNA library was employed to identify novel osteoclast-expressed genes. Of the 5475 ESTs obtained, approximately 4% encoded cathepsin K, a novel cysteine protease homologous to cathepsins S and L; ESTs for other cathepsins were rare. In addition, ESTs for cathepsin K were absent or at low frequency in cDNA libraries from numerous other tissues and cells. In situ hybridization in osteoclastoma and osteophyte confirmed that cathepsin K mRNA was highly expressed selecively in osteoclasts; cathepsins S, L, and B were not detectable. Cathepsin K was not detected by in situ hybridization in a panel of other tissues. Western blot of human osteoclastoma or fetal rat humerus demonstrated bands of 38 and 27 kDa, consistent with sizes predicted for pro- and mature cathepsin K. Immunolocalization in osteoclastoma and osteophyte showed intense punctate staining of cathepsin K exclusively in osteoclasts, with a polar distribution that was more intense at the bone surface. The abundant expression of cathepsin K selectively in osteoclasts strongly suggests that it plays a specialized role in bone resorption. Furthermore, the data suggest that random sequencing of ESTs from cDNA libraries is a valuable approach for identifying novel cell-selective genes.

Human osteoclast and giant cell differentiation: the apparent switch from nonspecific esterase to tartrate resistant acid phosphatase activity coincides with the in situ expression of osteopontin mRNA

Animal model and in vitro cultures suggest that osteoclasts and cells of the mononuclear phagocyte system share a common precursor. However, the human osteoclast precursor has not been positively identified. We attempted to identify the precursor in situ by using a number of osteoclast- and macrophage-selective markers, together with the expression of osteopontin mRNA, previously shown to be abundant in human osteoclasts. Sections of osteophytic bone and a panel of inflammatory connective tissues were processed for in situ hybridization; serial sections were analyzed for tartrate-resistant acid phosphatase (TRAP) and nonspecific esterase (NSE) activity, selective cytochemical markers for the osteoclast and cells of the macrophage/monocyte lineage, respectively. The murine anti-human osteoclast monoclonal antibodies 23C6 (vitronectin receptor) and C35 (osteoclast-selective) were used to further identify the osteoclast phenotype. We compared osteoclasts, giant cells, and their respective putative mononuclear precursors. At resorption sites within osteophytic bone, osteopontin mRNA was expressed in osteoclasts and a distinct population of TRAP+, NSE- mononuclear cells. Adjacent clusters of mononuclear cells were TRAP- and NSE+ or were active for both enzymes; these cells demonstrated variable expression of osteopontin mRNA. In the inflammatory connective tissues, abundant macrophage-like cells (NSE+/TRAP-) did not express osteopontin mRNA. However, TRAP+ mononuclear cells observed among clusters of NSE+ cells did express osteopontin mRNA. At these sites, clusters of putative macrophage polykaryons removing fragments of bone debris were observed. These giant cells and associated mononuclear cells were NSE- and distinctly TRAP+, and expressed osteopontin mRNA, C35, and 23C6 (human osteoclast) reactivity. Therefore, cells involved in the remodeling (resorption) of bone or the removal of bone debris, together with their immediate precursors, switch from being NSE+/TRAP- to NSE-/TRAP+ cells that express osteopontin mRNA. We propose that the clusters of NSE+/TRAP- mononuclear cells represent the immature osteoclast precursor. In support of this, TRAP+/NSE+ cells were occasionally observed in both tissues, representing an intermediate stage in differentiation. These results further suggest that cells of the mononuclear phagocyte lineage within bone and inflammatory connective tissue have the potential to differentiate into osteoclasts.

Human osteoclasts, not osteoblasts, deposit osteopontin onto resorption surfaces: an in vitro and ex vivo study of remodeling bone

Osteopontin is a phosphorylated glycoprotein believed to be secreted by osteoblasts and deposited into the bone matrix to facilitate osteoclasts adhesion or to initiate osteoid mineralization. Previously we have presented contradictory evidence that osteoclasts express osteopontin mRNA in human remodeling bone. The aim of this study was to ascertain whether osteoclasts synthesize and deposit osteopontin in resorption lucunae. We characterized expression of osteopontin mRNA and protein expression in both intramembranous and endochondral ossification, as well as remodeling bone, in the human osteophyte. Osteopontin mRNA was expressed in osteoclast with tartrate-resistant acid phosphatase (TRAP) positivity within resorption lacunae. The osteoclasts and immediate resorption surfaces also expressed osteopontin. However, osteopontin mRNA and protein were weak (transient) or undetectable in osteoblasts at adjacent bone formation sites; no osteopontin expression was observed in the osteoid, although occasional reactivity was observed in osteocytes and the mineral-osteoid interface. In contrast, osteopontin was highly expressed in the osteoblasts and matrix of woven bone during intramembranous and endochondral ossification. The matrix expression correlated with mineralization; however, in some instances osteopontin deposition was observed prior to mineralization. Similarly, osteopontin expression was evident in cartilage matrix, solely at foci of mineralization. Chondroclasts expressed osteopontin mRNA and protein: the surfaces of resorbed calcified cartilage also expressed osteopontin. Abnormal, unmineralized matrices apparently lacked deposited osteopontin, but were nevertheless resorbed by osteoclasts; the osteoclasts and resorbed surfaces expressed no osteopontin protein. That osteoclasts are responsible for the deposition of osteopontin was confirmed in vitro, whereby resorption pits in whale dentine and bovine bone slices, produced by isolated human osteoclasts, contained deposited osteopontin. Osteopontin may facilitate the adhesion (or detachment) of the osteoclast to the bone surface. Alternatively, the possibility that osteopontin may act as a postresorptive signal to recruit osteoblasts, or to polarize and direct the mineralization of the formed osteoid, is discussed.

Differential distribution of annexins-I, -II, -IV, and -VI in synovium

OBJECTIVES

To examine the distribution of four annexins in non-inflamed rheumatoid arthritic and osteoarthritic synovial tissue.

METHODS

Frozen sections were stained with monoclonal antibodies (MAb) specific for annexins-I, -II, -IV, and -VI, and for cell lineage related markers including CD68 and CD14 (macrophages), prolyl hydroxylase (fibroblasts), and CD3 (T cells).

RESULTS

Each of the annexins was present in synovial tissues in significant amounts in the three groups studied. Annexin-I was predominantly found within the synovial lining layer and double labelling showed it to be present predominantly in cells of the macrophage lineage. In rheumatoid specimens there was increased staining within the lining layer, perivascularly and on macrophages within the tissue stroma. Annexin-II was present in a distribution similar to that of annexin-I, but with more prominent perivascular staining. Annexins-IV and -VI were seen chiefly in association with areas of lymphocyte infiltration in rheumatoid tissue, whereas annexins-I and -II were absent from these areas. Endothelial cells stained weakly positive for annexins-I and -II, and more strongly for -IV and -VI.

CONCLUSIONS

This study demonstrates that annexins (particularly annexin-I, a putative mediator of the anti-inflammatory activities of glucocorticoids) are abundant in rheumatoid and non-rheumatoid synovial tissue, annexins-IV and -VI having a distribution distinct from that of -I and -II.

Monoclonal antibodies with selective reactivity against osteoblasts and osteocytes in human bone

Monoclonal antibodies (MAb) may provide valuable tools for studying osteoblast differentiation. We therefore raised a panel of MAb reactive with cells of this phenotype using 1,25(OH)2D3-treated human trabecular osteoblast-like cells (HOBS) as the immunogen. Immunohistochemical studies on various tissues, including undecalcified cryostat sections of fetal and adult human bone, identified 11 bone cell-reactive MAb. Of these, 2 demonstrated particularly selective reactivities against osteocytes (OB/M) and osteoblasts (OB/L). These reactivities were also seen in developing bone from rat, rabbit, and marmoset. OB/L and OB/M demonstrated limited reactivity against a small number of human tissues from the extensive panel of substrates tested. Both MAb exhibited reactivity against discrete populations of cells in the large and small intestine. In addition, OB/L reacted with cells in the basal epidermis of skin and OB/M with cells in blood vessel walls. Both antibodies demonstrated reactivity against a variety of cultured osteoblast-like cell lines and other cultured cell types. These MAb may therefore provide a valuable means of studying osteoblast ontogeny.

Expression of mRNA for IL1 beta, IL6 and TGF beta 1 in developing human bone and cartilage

Using in situ hybridization, we investigated the expression of mRNA for interleukin-1 beta (IL1 beta), interleukin-6 (IL6), and transforming growth factor-beta-1 (TGF beta 1) in sections of developing bone in human osteophytes. The expression was related to the cellular activity of alkaline phosphatase to aid in the identification of pre-osteoblast populations. IL1 beta mRNA was localized in active osteoblasts within distinct areas of intramembranous ossification. However, the expression was sporadic and appeared to occur at a specific stage of the osteoblast life cycle. There was no IL1 beta mRNA expression in any cell types during endochondral ossification. IL6 mRNA expression was located within pre-osteoblasts and in newly differentiated and matrix-secreting osteoblasts; expression was absent or reduced in flattened, inactive osteoblasts. Weak or no IL6 expression was observed in chondroblasts and chondrocytes, respectively. However, there was a close association between IL6 mRNA expression and the differentiation of mesenchymal cells into osteoblasts. TGF beta 1 expression was localized to osteoblasts apposed to bone or cartilage matrix; the intensity of expression correlated with matrix secretion. Chondroblasts and chondrocytes expressed lower but significant levels of TGF beta 1 mRNA; the expression was lost with the progression to calcifying cartilage. The three cytokines studied were differentially expressed both temporally and spatially, suggesting different roles for each in osteoblast and chondrocyte function.

Microcytophotometric analysis of human osteoclast metabolism: lack of activity in certain oxidative pathways indicates inability to sustain biosynthesis during resorption

It has been proposed that highly biosynthetic cells oxidize fatty acids to generate ATP while maintaining high levels of glucose metabolism through the glycolytic and pentose shunt systems to supply biosynthetic intermediates. We investigated the metabolic strategies and substrate for ATP production in the osteoclast. We used in situ quantitative microcytophotometric techniques to determine the maximal activity of the pentose shunt (glucose-6-phosphate dehydrogenase; G6PD), the glycolytic pathway (glyceraldehyde-3-phosphate dehydrogenase and lactate dehydrogenase; G3PD and LDH), fatty acid oxidation (beta-hydroxyacyl dehydrogenase; HOAD), and the Krebs cycle (succinate dehydrogenase; SDH) in human osteoclasts in situ, and related these enzyme activities to the degree of involvement of the cells in resorption. Unlike other highly biosynthetic cells, such as chondrocytes and macrophage polykaryons, osteoclasts associated with bone resorption were deficient in G3PD, LDH, and G6PD activity. However, osteoclasts did demonstrate a capacity for fatty acid oxidation which increased in cells apposed to the bone surface. The lack of significant glycolytic and pentose shunt activity in the osteoclast provides good evidence that resorbing osteoclasts, unlike phagocytosing macrophage polykaryons, have the metabolic characteristics of cells with greatly reduced capabilities of de novo mRNA synthesis but which do maintain high rates of ATP production. The possibility that the loss of glycolytic activity is a prelude to cell death is discussed.

Early loading-related changes in the activity of glucose 6-phosphate dehydrogenase and alkaline phosphatase in osteocytes and periosteal osteoblasts in rat fibulae in vivo

The tibiae and fibulae of 14-week-old rats were subjected to a single 5 minutes period of cyclic longitudinal loading at 1 Hz. The activity of the enzymes glucose 6-phosphate dehydrogenase (G6PD) and alkaline phosphatase (ALP) in osteocytes and periosteal osteoblasts was measured immediately and 24 h after loading. In osteocytes G6PD activity was increased immediately after loading but returned to control values 24 h later. There was no detectable ALP activity in these cells regardless of loading history. In periosteal osteoblasts G6PD activity was raised immediately after loading and remained higher than controls 24 h later. ALP activity in periosteal cells was unaffected immediately after loading but 24 h later was substantially increased. These findings are consistent with osteocytes and periosteal cells both being immediately responsive to periods of intermittent loading in their adjacent matrices. In both cell types an early feature of this response is an increase in G6PD activity. In osteocytes this response is short-lived, suggesting that it is an early biochemical change associated with strain perception that does not progress to matrix synthesis. The increase in G6PD activity with unaffected ALP levels in periosteal cells immediately after loading is consistent with a similar response. In these cells the increase in G6PD accompanied by increased ALP levels 24 h after loading suggests that the loading-related response progresses to new bone formation.

Integrin subunit expression by human osteoblasts and osteoclasts in situ and in culture

The extracellular matrix may be considered as an insoluble local mediator which plays an important role in regulating cell function. Communication between the cell and its matrix occurs via the integrins, a family of transmembrane proteins composed of non-covalently linked alpha and beta subunits. The aim of this study was to establish which integrins are present on human bone cells in situ and in culture, using cryostat sections of undecalcified human bone, osteoclastoma tissue and cultured human osteoblasts. Integrin subunit expression was identified indirectly using alkaline phosphatase anti-alkaline phosphatase conjugates and FITC-labelled secondary antibodies. Subunits expressed by cultured human osteoblast-like cells were then quantified by FACS analysis. Staining patterns observed in situ show that osteoblasts and osteoclasts possess different integrin subunits. Osteoblasts primarily express alpha 1, alpha 3 and beta 1 and weakly express alpha 2. Osteoclasts express alpha 2, alpha V, beta 1 and beta 3. Subunits alpha 4, alpha 5, alpha 6, alpha L, alpha M and beta 2 were not expressed by either of these cell types. Expression of beta 1 by all cells of the osteoblastic lineage was constitutive, but alpha 1 and alpha 3 subunits were expressed by osteoblasts actively synthesizing bone and some of the osteoblast lining cells. All integrin subunits identified on osteoblasts in situ were maintained on culture but there was an increased expression of alpha 2 and alpha V subunits were weakly positive. Expression of alpha 2, alpha 3, alpha V and beta 1 subunits was independent of cell density but expression of alpha 1 was much greater in confluent cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Production and characterization of osteoclast-selective monoclonal antibodies that distinguish between multinucleated cells derived from different human tissues

Osteoclastoma-derived giant cells were used to produce 11 mouse monoclonal antibodies (MAb) reactive against human osteoclasts on undecalcified sections of adult human bone. All exhibited unique reactivities across a wide range of human tissues. Three in particular demonstrated distinctive reactivities; C35 was highly selective for bone osteoclasts, C27 showed selective reactivity for osteoclasts, tissue macrophages and blood-borne monocytes, and C22 showed selective membrane staining of osteoclasts. Consequently, C22 was used to coat Dynabeads to affinity-purify viable human osteoclasts from osteoclastoma-derived cell suspensions. Immunocytochemical staining of inflammatory osteoarthritic synovium/granulation tissue demonstrated positivity in the majority of giant cells with MAb C22 and C27. In contrast, C35 reacted with only very occasional giant cells. Furthermore, multinucleated cells formed in long-term human bone marrow cultures demonstrated similar selective staining. C27 stained all giant cells and the majority of mononuclear cells. C22 detected only a small proportion of giant cells. In contrast to its staining on bone osteoclasts, C22 demonstrated granular cytoplasmic staining in cultured giant cells. C35 stained no cells at all in these cultures. These MAb can therefore distinguish between giant cells of various origins and authentic mature osteoclasts. Alternatively, they can recognize antigens expressed at different stages of osteoclast differentiation and therefore provide an excellent tool for the study of the human osteoclast lineage.

Effect of low protein diet on the renal response to meat ingestion in diabetic nephropathy

We measured the renal haemodynamic and proteinuric response to a meat meal (MM) in ten persistently proteinuric insulin-dependent diabetic patients in a randomized cross-over study of 3 weeks on low protein diet (LPD) or normal protein intake (NPD). On LPD, protein intake (0.64 +/- 0.05 vs 1.15 +/- 0.09 g kg-1 body weight (BW) per day, P less than 0.001), plasma urea (6.6 +/- 1.3 vs 11.0 +/- 2.0 mmol l-1, P less than 0.01) and urea appearance (0.06 +/- 0.01 vs 0.16 +/- 0.03 gN kg-1 body weight per day, P less than 0.001) were lower. Baseline glomerular filtration rate (GFR), renal plasma flow (RPF) and renal vascular resistance (RVR) were similar on the two diets and there were no significant average changes in these variables after the meat meal on either diet (NPD, before vs after MM: GFR: 67 +/- 11 vs 71 +/- 13 ml min-1 1.73 m-2; RPF: 479 +/- 70 vs 512 +/- 81 ml min-1 1.73 m-2; RVR: 181 +/- 45 vs 179 +/- 52 mmHg min-1 l-1); (LPD, before vs after MM: GFR: 64 +/- 10 vs 67 +/- 11 ml min-1 1.73 m-2; RPF: 506 +/- 60 vs 533 + 52 ml min-1 1.73 m-2; RVR: 151 +/- 28 vs 146 +/- 32 mmHg min-1 l-1). However, all patients with baseline GFR above 60 ml min-1 1.73 m-2 showed a GFR rise in response to the meat meal on both diets, while patients with lower baseline values tended to reduce their GRF.(ABSTRACT TRUNCATED AT 250 WORDS)

Load-induced proteoglycan orientation in bone tissue in vivo and in vitro

Previous studies of Alcian blue-induced birefringence in adult avian cortical bone showed that a short period of intermittent loading rapidly produces an increased level of orientation of proteoglycans within the bone tissue. In the absence of further loading, this persists for over 24 hours. We have proposed that this phenomenon could provide a means for "capturing" the effects of transient strains, and so provide a persistent, constantly updated strain-related influence on osteocyte populations related to the bones' averaged recent strain history, in effect, a "strain memory" in bone tissue. In our present study, we use the Alcian blue-induced birefringence technique to demonstrate that proteoglycan orientation also occurs after intermittent loading of both cortical and cancellous mammalian bone in vivo and in vitro. We also show that the change in birefringence is proportional to the magnitude of the applied strain, and that the reorientation occurs rapidly, reaching a maximal value after only 50 loading cycles. Examination of electron micrographs of bone tissue after staining with cupromeronic blue allows direct visualization and quantification of the change in proteoglycan orientation produced by loading. This shows that intermittent loading is associated with a realignment of the proteoglycan protein cores, bringing them some 5 degrees closer to the direction of collagen fibrils in the bone matrix.

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.

A quantitative cytochemical method for ornithine decarboxylase activity

Although decarboxylases, particularly ornithine decarboxylase, are of considerable importance in cell metabolism, it has been impossible to demonstrate their activity histochemically, as this depends on trapping carbon dioxide at neutral pH values. A new reagent, lead hydroxyisobutyrate, has been shown capable of such trapping. It has been applied to the demonstration of ornithine decarboxylase activity in mouse kidney. Optimal concentrations of substrate, co-factor and trapping agent, as well as the pH optimum, have been determined for cryostat sections stabilized with a collagen polypeptide. The activity was inhibited by the specific ornithine decarboxylase inhibitor alpha-difluoromethyl ornithine.

Retinal break type and proliferative vitreoretinopathy in nontraumatic retinal detachment

In a retrospective study of 1180 consecutive eyes operated for retinal detachment, vitreous traction on the rent was the determining factor for the development of proliferative vitreoretinopathy (PVR). Round, multiple, small holes in equatorial degeneration (retinogenic) and macular holes in which no vitreous traction on the rent was found did not complicate with PVR. Retinal detachment caused by horseshoe or crescent-shaped tears with evidence of vitreous traction (vitreogenic) developed PVR to a variable degree: in 171 (25.8%) senile myopic, 19 (44.2%) senile-myopic aphakic, 23 (20.2%) typical aphakic, and 32 (78.1%) patients with giant tears. We also found that retinogenic retinal detachments affected younger age groups more than did vitreogenic retinal detachments.

Restriction of dietary protein and progression of renal failure in diabetic nephropathy

In a study of the effect of a low-protein diet on the progression of renal disease 19 insulin-dependent diabetic patients with persistent clinical proteinuria were observed for 12-39 (mean 29) months while they were on a normal-protein diet (1.13 [0.06] g/kg per day), then for 12-49 (mean 33) months on a low-protein diet (0.67 [0.03] g/kg per day). The low-protein diet had no adverse effect on nutrition or glycosylated haemoglobin concentration. Mean supine blood pressure (BP) fell slightly on the low-protein diet and was probably due to the start or modification of antihypertensive medication in 9 patients. The mean rate of decline in glomerular filtration rate fell from 0.61 (SEM 0.14) ml/min per month with the normal-protein diet to 0.14 (0.08) with the low-protein diet, and this effect remained highly significant after adjustment for blood pressure, energy intake, and glycosylated haemoglobin. The rise in the fractional clearance of albumin during a normal-protein diet stopped with the low-protein diet, and there was a significant fall in albumin excretion from 467 (95% CI 234-895) micrograms/24 h on the normal-protein to 340 (138-719) on the low-protein diet. Thus, a low-protein diet, with its reduction in protein and possibly other dietary components such as phosphate or fat, seems to retard the rate of decline of glomerular filtration rate in diabetic nephropathy independently of blood pressure changes and glycaemic control.

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.

Renal response to restricted protein intake in diabetic nephropathy

Proteinuria in diabetes is associated with progressive glomerular damage. We studied the effects of 3-wk dietary protein restriction on proteinuria and renal function in 10 insulin-dependent diabetic men with diabetic nephropathy. Patients were randomly assigned by a crossover design to 40-g low-protein diet (LPD) or usual-protein diet (UPD). Glomerular filtration rate and renal plasma flow were measured by inulin and p-aminohippurate clearance at the end of each period under conditions of sustained euglycemia. Total calorie intake, body weight, serum albumin and total protein concentrations, hematocrit, blood pressure, and glucose control were similar during the two diets. Achieved protein intake was 46 +/- 3 g/day during LPD and 81 +/- 4 g/day during UPD (P less than .001). Urinary urea appearance and plasma urea were significantly lower on LPD. Median total urinary protein was reduced from 3.9 g/day (range 0.5-12.3) on UPD to 2.4 (range 0.2-9.0) on LPD (P less than .006), and there was a significant fall in the median fractional clearance of albumin from 2.0 x 10(-4) (range 0.1-90.9) on UPD to 1.0 x 10(-4) (range 0.1-51.4) on LPD and IgG from 2.1 x 10(-5) (range 0.2-238) to 1.5 x 10(-5) (range 0.1-77) (P less than .006 and P less than .02, respectively). The reabsorption rate of beta 2-microglobulin was similar on the two diets and glomerular filtration rate, renal plasma flow, and filtration fraction remained unchanged. Thus, short-term dietary protein restriction reduces diabetic proteinuria independently of blood glucose or systemic blood pressure changes by improving glomerular permselectivity.

Electron microscopy of undecalcified human bone

An alternative approach for the electron microscopical examination of undecalcified human bone was investigated. The method required bone to be chilled to -70 degrees C, sectioned at 10 microns in a special bone cryostat, and these sections to be fixed and embedded for ultrathin sectioning. Good preservation of bone cells was seen. The advantages of this method are that it allows numerous particular regions of the 10 microns thick sections to be selected under normal light microscopy, and these regions to be then selected for electron microscopy. The 10 microns sections allow for excellent penetration of the fixative and thus better preservation of the tissue is more likely.

Major components of bone in subcapital and trochanteric fractures. A comparative study

Quantitative polarised light microscopy was applied to sections of unfixed, undecalcified bone taken at operation from patients with two types of proximal femoral fracture, subcapital and trochanteric. Specimens were also taken from the equivalent sites in otherwise normal subjects at autopsy, and from various other sites of traumatic fractures; these two latter groups acted as controls. Analysis of the 57 specimens disclosed changes in the nature of the bone at the site of subcapital fractures, namely the presence of relatively large crystals of hydroxyapatite and a change in the molecular orientation, but not total content, of the acidic proteoglycans of the bone matrix. Our results have confirmed and extended the findings of others on subcapital fractures, and have also shown very similar changes in the trochanteric fractures. It thus appears that the bony changes in the two types of proximal femoral fracture are not as different as has been suggested.