Measurement of DNA in intervertebral disc and other autofluorescent cartilages using the dye hoechst 33258

Changes in human intervertebral disc biochemical composition and bony end plates between middle and old age

Objective

This study evaluates molecular, nutritional and biochemical alterations in human intervertebral discs between middle and old age.

Methods

Twenty-eight human lumbar intervertebral discs from donors were evaluated and separated into two groups: Middle-aged (35–50 years old, relatively non-degenerate discs of Pfirrmann grades 1–3, n = 15) and Old-aged (≥80 years old, all degenerate Pfirrmann grade 4 or 5, n = 13). Parameters which might be expected to to be related to nutrient supply and so the health of disc cells (eg the porosity of the vertebral endplate, cell viability and cell density) and to disc extracellular composition (ie quantification of glycosaminoglycan disaccharides and hyaluronic acid molecular weight) and collagen organization, were analyzed. Three regions of the intervertebral disc (anterior annulus fibrosus, nucleus pulposus, and posterior annulus fibrosus) were examined.

Results

The old-aged group showed a decrease in content of sulphated and non-sulphated glycosaminoglycans relative to middle-aged and there were also alterations in the proportion of GAG disaccharides and a decrease of collagen fiber size. Hyaluronic acid molecular weight was around 200 kDa in all regions and ages studied. The anterior annulus differed from the posterior annulus particularly in relation to cell density and GAG content. Additionally, there were changes in the bony endplate, with fewer openings observed in the caudal than cranial endplates of all discs in both groups.

Conclusions

Results show the cranial vertebral endplate is the main vascular source for the intervertebral discs. Hylauronic acid molecular weight is the same through the intervertebral disc after age of 50 years.

Ionic and biochemical characterization of bovine intervertebral disk

INTRODUCTION

Intervertebral disks have been associated with low back pain, and many therapies have been proposed for its treatment. The cellular and molecular knowledge of intervertebral disks composition and precise methods to quantify disk components are important for any type of proposed therapy. Thus, the aim of this study was to correlate glycosaminoglycans presence with the quantitation of cells, ions and collagen fiber distributions in different intervertebral disk sections.

METHODS

In total, 14 intervertebral disks were used from cattle. All of the disks were dehydrated, separated in seven sections and digested in sodium-free papain buffer. Glycosaminoglycan measurements were performed in the samples according to agarose electrophoresis method; total cells were measured using the PicoGreen® technique, ions were quantified, and collagen fiber birefringence was analyzed with polarized light.

RESULTS

Cations Na+ and K+ are more concentrate in the nucleus (Na(+) = 1688.50 ± 110 mmol/L; K(+) = 111.9 ± 28 mmol/L) of intervertebral disks than the annulus (Na(+) = 652.80 ± 75 mmol/L; K(+) = 55.6 ± 8 mmol/L). A negative correlation between cells number and sodium/potassium was observed (p < 0.001) Additionally, thin collagen fibers were largest in the nucleus, similar to hyaluronate distribution.

CONCLUSIONS

The results suggest that annulus fibrosus cells are also sensitive to changes in ionic concentrations such as nucleus pulposus cells. Additionally, hyaluronate is related to thin collagen fibers type II.

Factors regulating viable cell density in the intervertebral disc: blood supply in relation to disc height

The intervertebral disc is an avascular tissue, maintained by a small population of cells that obtain nutrients mainly by diffusion from capillaries at the disc-vertebral body interface. Loss of this nutrient supply is thought to lead to disc degeneration, but how nutrient supply influences viable cell density is unclear. We investigated two factors that influence nutrient delivery to disc cells and hence cell viability: disc height and blood supply. We used bovine caudal discs as our model as these show a gradation in disc height. We found that although disc height varied twofold from the largest to the smallest disc studied, it had no significant effect on cell density, unlike the situation found in articular cartilage. The density of blood vessels supplying the discs was markedly greater for the largest disc than the smallest disc, as was the density of pores allowing capillary penetration through the bony endplate. Results indicate that changes in blood vessels in the vertebral bodies supplying the disc, as well as changes in endplate architecture appear to influence density of cells in intervertebral discs.

Age- and site-associated biomechanical weakening of human articular cartilage of the femoral condyle

OBJECTIVE

To determine the time sequence of biochemical and structural events associated with, and hypothesized to underlie, age-associated tensile weakening of macroscopically normal adult human articular cartilage of the knee.

METHODS

Macroscopically normal human articular cartilage of the lateral and medial femoral condyles (LFC and MFC) from Young (21-39 yrs), Middle (40-59 yrs), and Old (>/=60 yrs) age donors were analyzed for tensile properties, surface wear, and cell and matrix composition.

RESULTS

Variations in tensile, compositional, and surface structural properties were indicative of early, intermediate, and late stages of age-associated cartilage deterioration, occurring at an earlier age in the MFC than the LFC. Differences between Young and Middle age groups (indicative of early-to-intermediate stage changes) included decreased mechanical function in the superficial zone, with a loss of (or low) tensile integrity, and surface wear, with faint striations and mild staining on the articular surface after application of India ink. Differences between Middle and Old age groups (indicative of intermediate-to-late stage changes) included maintenance of moderate level biomechanical function, a decrease in cellularity, and a decrease in matrix glycosaminoglycan content. Tissue fluorescence increased steadily with age.

CONCLUSIONS

Many of these age-associated differences are identical to those regarded as pathological features of cartilage degeneration in early osteoarthritis. These findings provide evidence for the roles of mechanical wear, cell death, and enzymatic degradation in mediating the progression through successive and distinguishable stages of early cartilage deterioration.

Factors influencing the oxygen concentration gradient from the synovial surface of articular cartilage to the cartilage-bone interface: A modeling study

OBJECTIVE

There is very little information on the gradients of oxygen concentration from the synovial surface to the subchondral bone in articular cartilage. Cartilage is usually regarded as hypoxic, even though cellular metabolism is inhibited at low oxygen concentrations. We therefore measured rates of cellular consumption of oxygen and used these rates to calculate oxygen tension profiles across articular cartilage.

METHODS

The rate of oxygen consumption by bovine articular chondrocytes was measured in vitro, either in intact cartilage slices or in isolated chondrocytes. The oxygen tension profile across articular cartilage was predicted by solving a 1-dimensional reaction-diffusion equation. The effect of synovial fluid oxygen concentration, cell density, cartilage thickness, and influx of oxygen from the subchondral bone on the oxygen profile in the tissue was examined.

RESULTS

Oxygen consumption rates were relatively independent of oxygen tension at high oxygen tensions (5-21%), where they were approximately 10 nmoles/10(6) cells/hour for both isolated chondrocytes and for cartilage slices. Below 5% oxygen, the rate fell in an oxygen tension-dependent manner. Analysis showed that the oxygen profile across cartilage fell steeply in all but the thinnest cartilage samples but only fell to approximately 1% for low oxygen tensions in synovial fluid, with no supply from the subchondral bone.

CONCLUSION

The oxygen tension in normal cartilage is not likely to fall to 1% except under abnormal conditions. Oxygen tensions within cartilage are strongly affected by a number of factors, including oxygen concentrations in synovial fluid, cartilage thickness, cell density, and cellular oxygen consumption rates. Supply from the subchondral bone may be of particular importance.

Differential effects of aging on transport properties of anterior and posterior human sclera

The transport properties and composition of 44 pairs of human sclera, 37-91 years were compared. Solute transport, diffusion and partition coefficients of posterior sclera for solutes ranging in mass from 0.023-70kDa were higher than those of anterior sclera; the posterior region was also more hydrated. The differences in partition coefficient between anterior and posterior sclera became more pronounced as solute molecular weight increased. Partition coefficients and hydration of both regions decreased with increasing age. Chondroitinase ABC digestion, which removed the majority of glycosaminoglycans, increased partition coefficients of both regions significantly. These results suggest that for regions of equal scleral thickness, neglecting the influence of vascular factors, drug delivery will be more readily achieved across the posterior sclera than the anterior sclera in the age group studied and that, for both regions, ease of delivery will decrease with decreasing age.

A compositional analysis of human nasal septal cartilage

BACKGROUND

Nasal septal cartilage is well established as an autograft material. Tissue engineering methods are now being developed to synthesize cartilage constructs with the properties of this type of cartilage. However, important baseline data on the composition of native septal cartilage is sparse.

OBJECTIVES

To characterize quantitatively the major biochemical constituents of native adult human septal cartilage and determine age- or sex-related variation in composition.

METHODS

Cartilage was harvested from the inferior region of the nasal septum in 33 patients (mean +/- SD age, 47.0 +/- 13.5 years; range, 24-80 years) during routine septoplasty or septorhinoplasty. Biochemical assays were used to determine the quantities, relative to wet weight, of the major constituents of cartilage: water, collagen (from hydroxyproline), sulfated glycosaminoglycan (sGAG), and chondrocytes (from DNA).

RESULTS

On average, each gram of wet cartilage contained 77.7% water, 7.7% collagen, 2.9% sGAG, and 24.9 million cells. Hydration and collagen content showed no significant age variation. Advancing age was associated with a reduction in sGAG content (7.7% per decade, P =.02) and cellularity (7.4% per decade, P =.05). No significant sex differences were found in any of these cartilage constituents.

CONCLUSIONS

This study represents the first biochemical characterization of the composition of native human septal cartilage. The data serve as a baseline for future comparison of the properties of tissue-engineered neocartilage constructs. Furthermore, the age-associated variations in cartilage composition have implications for patient selection for reconstructive procedures.

Functional replacement of oxygen by other oxidants in articular cartilage

OBJECTIVE

Articular cartilage chondrocytes consume remarkably little O(2) in comparison with most other animal cells; glycolysis forms the principal source of ATP in this cartilage. Although not lethal for many days, imposition of anoxia immediately lowers intracellular ATP, inhibits rates of glycolysis, and prevents articular chondrocytes from producing extracellular matrix macromolecules. This study was undertaken to investigate the role of O(2) in articular chondrocyte metabolism.

METHODS

We examined the effects of oxygen and of several other classes of exogenous oxidants, i.e., 1) the dyes methylene blue and 2,6-dichlorophenol-indophenol, 2) the iron (III) complex ferricyanide, and 3) the keto-acids oxaloacetate and pyruvate (and phosphoenolpyruvate, a metabolic precursor of pyruvate), on rates of glycolysis and of sulfate incorporation by bovine articular cartilage in vitro.

RESULTS

Lactate production was lowest under conditions of anoxia and was stimulated severalfold by addition of O(2) (air-saturated medium). Under strict anoxia, other oxidants restored lactate production to rates at least comparable with those seen in aerobic controls; under aerobic conditions, they had little effect. Oxygen and all of the other oxidants examined stimulated sulfate incorporation more strongly than lactate production. The compounds that promoted glycolysis and hence sulfate incorporation in cartilage under anoxia were themselves reduced; that is, they functioned as oxidants in lieu of O(2).

CONCLUSION

For normal function, articular cartilage appears to require exogenous oxidants to stimulate glycolysis and produce ATP and extracellular matrix. Under physiologic conditions, oxygen acts as this oxidant, but its role can be adequately assumed by other agents.

Cell viability in scoliotic discs in relation to disc deformity and nutrient levels

STUDY DESIGN

Intervertebral disc tissue was analyzed during or removed at routine surgery for correction of scoliosis. Tissue was analyzed for glucose, lactate, oxygen, glycosaminoglycan, collagen concentrations, and cell viability.

OBJECTIVES

To investigate the cell viability of the scoliotic disc on the concave and convex sides and in relation to curve apex, and to relate cell viability to concentrations of nutrients, metabolites, and extracellular matrix components.

SUMMARY OF BACKGROUND DATA

Compositional differences have been measured in relation to the deformation of scoliotic discs. However, the causes of these in relation to cellular activity or viability are unknown.

METHODS

Oxygen concentration was measured at surgery using a microelectrode. A segment of disc then was removed and sections at defined locations measured for cell viability and glucose, lactate, glycosaminoglycan, and collagen concentrations. RESULTS Cell viability was lower toward the convex side of the curve, with the greatest difference between the sides in the apical disc. The apical disc had the lowest oxygen and highest lactate concentrations, and lowest total number of cells. Glucose concentration correlated with the number of live cells. Concentrations of glycosaminoglycans and collagen per dry weight of tissue were similar on both sides of the disc.

CONCLUSIONS

Differences in cell viability correlated with changes in nutrient and metabolite levels, and also with disc deformity (convex concave and distance from curve apex). Thus asymmetrical loads, tissue deformation, and nutrient supply may work separately or in combination to cause cell death. A loss of matrix macromolecules was not seen, possibly because the period between cell death and surgery was too short, as compared with long matrix turnover times. Cell death is expected eventually to have a deleterious effect on cell matrix and disc function.

Development of selective tolerance to interleukin-1beta by human chondrocytes in vitro

Interleukin-1 induces release of NO and PGE(2) and production of matrix degrading enzymes in chondrocytes. In osteoarthritis (OA), IL-1 continually, or episodically, acts on chondrocytes in a paracrine and autocrine manner. Human chondrocytes in chondron pellet culture were treated chronically (up to 14 days) with IL-1beta. Chondrons from OA articular cartilage were cultured for 3 weeks before treatment with IL-1beta (0.05-10 ng/ml) for an additional 2 weeks. Spontaneous release of NO and IL-1beta declined over the pretreatment period. In response to IL-1beta (0.1 ng/ml), NO and PGE(2) release was maximal on Day 2 or 3 and then declined to near basal level by Day 14. Synthesis was recovered by addition of 1 ng/ml IL-1beta on Day 11. Expression of inducible nitric oxide synthase (iNOS), detected by immunofluorescence, was elevated on Day 2 and declined through Day 14, which coordinated with the pattern of NO release. On the other hand, IL-1beta-induced MMP-13 synthesis was elevated on Day 3, declined on Day 5, and then increased again through Day 14. IL-1beta increased glucose consumption and lactate production throughout the treatment. IL-1beta stimulated proteoglycan degradation in the early days and inhibited proteoglycan synthesis through Day 14. Chondron pellet cultures from non-OA cartilage released the same amount of NO but produced less PGE(2) and MMP-13 in response to IL-1beta than OA cultures. Like the OA, IL-1beta-induced NO and PGE(2) release decreased over time. In conclusion, with prolonged exposure to IL-1beta, human chondrocytes develop selective tolerance involving NO and PGE(2) release but not MMP-13 production, metabolic activity, or matrix metabolism.

Biochemical quantification of DNA in human articular and septal cartilage using PicoGreen and Hoechst 33258

OBJECTIVE

To compare two fluorometric assays, utilizing (1) the bisbenzimidazole Hoechst 33258 and (2) PicoGreen, for determining DNA content in human cartilage.

METHODS

Human articular and nasal septal cartilage explants were digested using proteinase K. Portions of sample digest were analysed for intrinsic and dye-enhanced fluorescence with either Hoechst 33258 or PicoGreen.

RESULTS

Intrinsic tissue fluorescence in both articular and septal cartilage increased with age and was prominent at wavelengths used for Hoechst 33258 but relatively low at wavelengths used for PicoGreen. The relative contribution of intrinsic fluorescence to total dye-enhanced fluorescence of human cartilage was markedly greater for Hoechst 33258 (19-57%) than for PicoGreen (2-7%). Thus, in many situations, DNA in human cartilage can be assayed using PicoGreen without the need to correct for intrinsic cartilage fluorescence. The enhancement of fluorescence by each dye was found to be specific for DNA, as shown by fluorescence spectra, >90% sensitivity to DNase, and resistance to RNase. In addition, little or no interference was caused by non-DNA tissue components, since DNA caused an equal enhancement in the absence or presence of proteinase K digested human cartilage, once intrinsic cartilage fluorescence was subtracted. PicoGreen was more sensitive for assaying DNA (0.9ng DNA/ml) than Hoechst 33258 (6ng DNA/ml) and can also be used in a microplate reader.

CONCLUSION

PicoGreen can be used in a rapid and sensitive assay to quantify DNA in small samples of human cartilage.

Cells from different regions of the intervertebral disc: effect of culture system on matrix expression and cell phenotype

STUDY DESIGN

This study examined how the culture system and region of cellular origin affect disc cell morphology and extracellular matrix production.

OBJECTIVE

To determine the role of the cell populations in the different regions of the adult intervertebral disc in maintaining gradients in composition across the disc.

SUMMARY OF BACKGROUND DATA

It is not known whether the steep profiles in composition across the intervertebral disc are maintained by distinct cell populations or whether differences in cell metabolism are determined by changes in the physical environment across the disc. Very little information exists on the matrix produced by cells from the mature, non-notochordal nucleus pulposus.

METHODS

Cells were extracted from articular cartilage, nucleus pulposus, and the inner and outer anulus fibrosus of caudal discs from 18- to 24-month-old steers cultured in alginate or collagen gels or in monolayer. The effect of culture system and cell origin on cell morphology and matrix synthesis was measured using 35S-sulphate labeling and indirect immunolocalization.

RESULTS

Distinct morphologic differences between cells from different regions cultured in monolayer were retained through two passages. The rate of sulfate incorporation varied with cell type. Immediately after isolation, it was two- to threefold greater for nucleus cells than for cells from the disc inner anulus or articular cartilage. The rate was lowest for outer anulus cells. It also varied with culture system. For all cell types, the incorporation rate was highest in alginate and lowest in monolayer. Immunolocalization showed that nucleus cells stained strongly for all proteoglycan epitopes, whereas outer anulus cells stained least and in monolayer produced little proteoglycan.

CONCLUSIONS

The disc has at least three distinct cell populations, which differ in morphology and in amount and type of matrix they produce. Cells from mature nucleus pulposus produced sulfated glycosaminoglycans at a high rate in contrast to reported results for notochordal nucleus cells. Alginate, although an appropriate culture system for inner anulus and nucleus cells, may not be a suitable medium for outer anulus cells.

Intervertebral disc composition in neuromuscular scoliosis: changes in cell density and glycosaminoglycan concentration at the curve apex

STUDY DESIGN

An analysis of the variation in glycosaminoglycan, water content, and cell density with disc level in patients with neuromuscular scoliosis.

OBJECTIVES

To determine whether the composition of the apical disc differed from that of adjacent discs in the same spine.

SUMMARY OF BACKGROUND DATA

Compositional differences between the convex and concave sides of scoliotic discs have been noted and are thought to be secondary to altered loading. However, there is little information on changes relative to the apex.

METHODS

Intact wedges of disc obtained during anterior fusion procedures were taken from 23 discs of 6 patients with neuromuscular scoliosis. Radial profiles of glycosaminoglycan, water content, and cell density were measured. Concentrations were compared at a standard distance (5 mm) into the disc and plotted versus spinal level.

RESULTS

Glycosaminoglycan and water content were lowest in the outer annulus and increased steadily toward the disc center, whereas the cell density was highest in the outer 2 mm, fell steeply and then remained constant. At 5 mm from the annulus edge, cell density was lowest in apical discs and, in most cases, was noticeably higher in adjacent discs of the same spine. At the same point, there was no consistent change in glycosaminoglycan/dry weight from disc to disc, indicating no significant proteoglycan loss. However, glycosaminoglycan/tissue water, and therefore swelling pressure, was highest in the apical discs, suggesting that these discs were the most heavily loaded.

CONCLUSIONS

The loss of cells from the disc at the curve apex probably arose because this disc experiences greater mechanical stress or is more deformed than its neighbors. The decrease in cell density was not associated with major changes in tissue composition, possibly because rates of degradation and of synthesis were reduced, leaving the matrix largely unchanged.

The effect of hydration and matrix composition on solute diffusion in rabbit sclera

There is increasing interest in the possibility for drug delivery into the vitreous humor across the conjunctiva and sclera as an alternative route to the conjunctiva-cornea pathway. As a preliminary to human studies we have investigated the influence of scleral composition and hydration on solute transport in the rabbit sclera. Intermuscular sclera was excised from adult New Zealand rabbits. Tissue samples were either examined directly (controls), digested using chondroitinase ABC or crosslinked using glutaraldehyde. The effect of these treatments on the ultrastructural appearance of the sclera was assessed. Diffusion and partition coefficients for solutes of different molecular weights [sodium chloride (23 MW),(14)C sucrose (342 MW) and dextran-fluoresceins (3, 10, 40 and 70 kDa)] were measured in relation to tissue treatment. The results were used to determine the effect of tissue structure and composition on solute movement. We have found that: (1) diffusion and partition coefficients are sensitive to solute MW, decreasing as MW increases; (2) diffusion and partition coefficients are sensitive to tissue hydration, increasing as hydration increases; (3) crosslinking of the sclera by glutaraldehyde reduced the partition coefficients significantly for solutes with MW over 3 kDa; and (4) removal of glycosaminoglycans has only a small effect on either diffusion or the partition coefficient.