Obesity increases the odds of intervertebral disc herniation and spinal stenosis; an MRI study of 1634 low back pain patients

PURPOSE

The objective of this study was to examine the relationships between BMI and intervertebral disc degeneration (DD), disc herniation (DH) and spinal stenosis (SS) using a large, prospectively recruited and heterogeneous patient population.

METHODS

Patients were recruited through the European Genodisc Study. An experienced radiologist scored MRI images for DD, DH and SS. Multivariate linear and logistic regression analyses were used to model the relationship between these variables and BMI with adjustment for patient and MRI confounders.

RESULTS

We analysed 1684 patients with a mean age of 51 years and BMI of 27.2 kg/m2.
The mean DD score was 2.6 (out of 5) with greater DD severity with increasing age (R2 = 0.44). In the fully adjusted model, a 10-year increase in age and a 5 kg/m2 increase in BMI were associated, respectively, with a 0.31-unit [95% CI 0.29,0.34] and 0.04-unit [CI 0.01,0.07] increase in degeneration. Age (OR 1.23 [CI 1.06,1.43]) and BMI (OR 2.60 [CI 2.28,2.96]) were positively associated with SS. For DH, age was a negative predictor (OR 0.70 [CI 0.64,0.76]) but for BMI (OR 1.19 [CI 1.07,1.33]), the association was positive. BMI was the strongest predictor of all three features in the upper lumbar spine.

CONCLUSIONS

While an increase in BMI was associated with only a slight increase in DD, it was a stronger predictor for DH and SS, particularly in the upper lumbar discs, suggesting weight loss could be a useful strategy for helping prevent disorders associated with these pathologies.

ISSLS PRIZE in Clinical Science 2023: comparison of degenerative MRI features of the intervertebral disc between those with and without chronic low back pain. An exploratory study of two large female populations using automated annotation

OBJECTIVES

The relationship of degeneration to symptoms has been questioned. MRI detects apparently similar disc degeneration and degenerative changes in subjects both with and without back pain. We aimed to overcome these problems by re-annotating MRIs from asymptomatic and symptomatics groups onto the same grading system.

METHODS

We analysed disc degeneration in pre-existing large MRI datasets. Their MRIs were all originally annotated on different scales. We re-annotated all MRIs independent of their initial grading system, using a verified, rapid automated MRI annotation system (SpineNet) which reported degeneration on the Pfirrmann (1-5) scale, and other degenerative features (herniation, endplate defects, marrow signs, spinal stenosis) as binary present/absent. We compared prevalence of degenerative features between symptomatics and asymptomatics.

RESULTS

Pfirrmann degeneration grades in relation to age and spinal level were very similar for the two independent groups of symptomatics over all ages and spinal levels. Severe degenerative changes were significantly more prevalent in discs of symptomatics than asymptomatics in the caudal but not the rostral lumbar discs in subjects < 60 years. We found high co-existence of degenerative features in both populations. Degeneration was minimal in around 30% of symptomatics < 50 years.

CONCLUSIONS

We confirmed age and disc level are significant in determining imaging differences between asymptomatic and symptomatic populations and should not be ignored. Automated analysis, by rapidly combining and comparing data from existing groups with MRIs and information on LBP, provides a way in which epidemiological and 'big data' analysis could be advanced without the expense of collecting new groups.

LEVEL OF EVIDENCE I

Diagnostic: individual cross-sectional studies with consistently applied reference standard and blinding.

Delivering Focused Ultrasound to Intervertebral Discs Using Time-Reversal

Chronic low back pain causes more disability worldwide than any other condition and is thought to arise in part through loss of biomechanical function of degenerate intervertebral discs (IVDs). Current treatments can involve replacing part or all of the degenerate IVDs by invasive surgery. Our vision is to develop a minimally invasive approach in which high intensity focused ultrasound (HIFU) is used to mechanically fractionate degenerate tissue in an IVD; a fine needle is then used to first remove the fractionated tissue and then inject a biomaterial able to restore normal physiologic function. The goal of this manuscript is to demonstrate the feasibility of trans-spinal HIFU delivery using simulations of 3-D ultrasound propagation in models derived from patient computed tomography (CT) scans. The CT data were segmented into bone, fat and other soft tissue for three patients. Ultrasound arrays were placed around the waist of each patient model, and time-reversal was used to determine the source signals necessary to create a focus in the center of the disc. The simulations showed that for 0.5 MHz ultrasound, a focus could be created in most of the lumbar IVDs, with the pressure focal gain ranging from 3.2-13.7. In conclusion, it is shown that with patient-specific planning, focusing ultrasound into an IVD is possible in the majority of patients despite the complex acoustic path introduced by the bony structures of the spine.

Disc size markedly influences concentration profiles of intravenously administered solutes in the intervertebral disc: a computational study on glucosamine as a model solute

PURPOSE

Tests on animals of different species with large differences in intervertebral disc size are commonly used to investigate the therapeutic efficacy of intravenously injected solutes in the disc. We hypothesize that disc size markedly affects outcome.

METHODS

Here, using a small non-metabolized molecule, glucosamine (GL) as a model solute, we calculate the influence of disc size on transport of GL into rat, rabbit, dog and human discs for 10 h post intravenous-injection. We used transient finite element models and considered an identical GL supply for all animals.

RESULTS

Huge effects of disc size on GL concentration profiles were found. Post-injection GL concentration in the rat disc reached 70% blood concentration within 15 min but remained below 10% in the human disc nucleus throughout. The GL rapidly penetrated post-injection into smaller discs resulting in homogeneous concentrations. In contrast, GL concentration, albeit at much lower levels, increased with time in the human disc with a small outward flux at the annulus periphery at longer periods.

CONCLUSIONS

Changes in the disc size hugely influenced GL concentrations throughout the disc at all regions and times. Increases in administered dose can neither remedy the very low concentration levels in the disc center in larger human disc at early post-injection hours nor alter the substantial differences in concentration profiles estimated among various species. The size effect will only be exacerbated as molecular weight of the solute increases and as the endplate calcifies. Extrapolation of findings from animal to human discs on the efficacy of intravenously administered solutes must proceed with great caution.

Osmolarity effects on bovine articular chondrocytes during three-dimensional culture in alginate beads

OBJECTIVE

With the development of engineered cartilage, the determination of the appropriate culture conditions is vital in order to maximize extracellular matrix synthesis. As osmolarity could affect the fate of chondrocytes, the purpose of this study was to determine the effects of osmolarity on chondrocytes during relatively long-term culture.

DESIGN

Bovine articular chondrocytes were cultured in alginate beads in a biocarbonate free system at 280, 380 and 550 mOsm at pH 7.4 for up to 12 days, respectively. Cell volume, intracellular pH (pH(i)), cell number, glucosaminoglycan (GAG) and collagen retention were measured at day 5 and 12. Cell viability and volume were monitored over the 12 days of culture.

RESULTS

By day 5 and 12, compared to the cell volume at 380 mOsm, around 20% (P<0.01) swelling and 15% (P<0.05) shrinkage were observed when the cells were cultured at 280 and 550 mOsm. The pH(i) over the 12 days of culture varied with osmolarity of the culture medium. In comparison with fresh cells, pH(i) became slightly more acidic by 0.15 pH units at 280 mOsm at day 5. However, by day 12, an alkalization of pH(i), by 0.2 pH units, was noted. A higher proliferation rate was seen at 280 mOsm than at other osmolarities while less GAG was produced.

CONCLUSIONS

Chronic exposure to anisotonic conditions results in cell swelling at 280 mOsm and shrinkage at 550 mOsm. The osmolarity of 280 mOsm appears to encourage proliferation of chondrocytes, but inhibits matrix production.

Analysis of cell viability in intervertebral disc: Effect of endplate permeability on cell population

Responsible for making and maintaining the extracellular matrix, the cells of intervertebral discs are supplied with essential nutrients by diffusion from the blood supply through mainly the cartilaginous endplates (CEPs) and disc tissue. Decrease in transport rate and increase in cellular activity may adversely disturb the intricate supply-demand balance leading ultimately to cell death and disc degeneration. The present numerical study aimed to introduce for the first time cell viability criteria into nonlinear coupled nutrition transport equations thereby evaluating the dynamic nutritional processes governing viable cell population and concentrations of oxygen, glucose and lactic acid in the disc as CEP exchange area dropped from a fully permeable condition to an almost impermeable one. A uniaxial model of an in vitro cell culture analogue of the disc is first employed to examine and validate cell viability criteria. An axisymmetric model of the disc with four distinct regions was subsequently used to investigate the survival of cells at different CEP exchange areas. In agreement with measurements, predictions of the diffusion chamber model demonstrated substantial cell death as essential nutrient concentrations fell to levels too low to support cells. Cells died away from the nutrient supply and at higher cell densities. In the disc model, the nucleus region being farthest away from supply sources was most affected; cell death initiated first as CEP exchange area dropped below approximately 40% and continued exponentially thereafter to depletion as CEP calcified further. In cases with loss of endplate permeability and/or disruptions therein, as well as changes in geometry and fall in diffusivity associated with fluid outflow, the nutrient concentrations could fall to levels inadequate to maintain cellular activity or viability, resulting in cell death and disc degeneration.

Cytochrome c oxidase levels in chondrocytes during monolayer expansion and after return to three dimensional culture

OBJECTIVE

Here we investigate whether monolayer culture or culture at 21% oxygen influences activity of cytochrome c oxidase, the terminal enzyme in the respiratory chain whose activity is essential for oxidative metabolism and whether return to three dimensional (3-D) culture restores cytochrome c oxidase activity to original levels.

METHODS

Primary bovine articular chondrocytes were cultured in alginate beads (3-D) for 4 weeks or in monolayer under 1% and 21% oxygen for up to 9 days and then returned to 3-D culture for up to 4 weeks. Cells were stained to localise cytochrome c oxidase within the cells. Mitochondrial protein content and cytochrome c oxidase enzymatic activity were determined. Expression of cytochrome c oxidase subunits, COXI and COXIV, was assessed by qRT-PCR.

RESULTS

Cytochrome c oxidase staining remained minimal in chondrocytes cultured in alginate for 4 weeks under 21% oxygen. Mitochondrial protein content and cytochrome c oxidase activity increased significantly during 9 days of chondrocyte expansion in monolayer, accompanied by up-regulation of the COXI mitochondrial gene but not the COXIV nuclear-encoded gene. Cytochrome c oxidase staining increased from day 5 of monolayer culture and remained high even after the cells were returned to 3-D culture for 4 weeks.

CONCLUSIONS

Culture of chondrocytes in monolayer leads to a rapid increase in mitochondrial protein content and cytochrome c oxidase activity. The increase in cytochrome c oxidase activity is not reversed even after chondrocytes are returned to 3-D culture for 4 weeks; high oxygen tension alone does not appear to stimulate cytochrome c oxidase activity.

Solute transport in intervertebral disc: experiments and finite element modeling

Loss of nutrient supply to the human intervertebral disc (IVD) cells is thought to be a major cause of disc degeneration in humans. To address this issue, transport of molecules of different size have been analyzed by a combination of experimental and modeling studies. Solute transport has been compared for steady-state and transient diffusion of several different solutes with molecular masses in the range 3-70 kDa, injected into parts of the disc where degeneration is thought most likely to occur first and into the blood supply to the disc. Diffusion coefficients of fluorescently tagged dextran molecules of different molecular weights have been measured in vitro using the concentration gradient technique in thin specimens of disc outer annulus and nucleus pulposus. Diffusion coefficients were found to decrease with molecular weight following a nonlinear relationship. Diffusion coefficients changed more rapidly for solutes with molecular masses less than 10 kDa. Although unrealistic or painful, solutes injected directly into the disc achieve the largest disc coverage with concentrations that would be high enough to be of practical use. Although more practical, solutes injected into the blood supply do not penetrate to the central regions of the disc and their concentrations dissipate more rapidly. Injection into the disc would be the best method to get drugs or growth factors to regions of degeneration in IVDs quickly; else concentrations of solute must be kept at a high value for several hours in the blood supply to the discs.

Investigation of solute concentrations in a 3D model of intervertebral disc

As the disc is the largest avascular structure in the body, disc cells depend for their normal function on an adequate supply of nutrients (oxygen and glucose) and the removal of metabolic by-products (lactic acid) via blood vessels at the cartilaginous endplates and annulus periphery. Concentration gradients develop depending on the balance between the rates of transport and rates of cellular activity. Since consumption and production rates are coupled via extracellular pH, the gradients are interdependent. This is a novel model study which takes into account the realistic 3D geometry of a L5-S1 lumbar disc in solving the nonlinear coupled diffusion equations. Effects of perturbations (calcification, sclerosis) in endplates, increases in cell metabolic rates following growth factor injection and changes in lumbar posture (kyphotic or lordotic) on extreme values of nutrient and metabolite concentrations and their spatial locations are investigated. Solute concentrations, particularly those of glucose, substantially diminish as a consequence of disturbances in supply at the endplates, increases in cell metabolic rate and more lordotic postures. Results, when compared to those from simplified axisymmetric models, demonstrate the importance of consideration of realistic 3D disc geometry.

Influence of extracellular osmolarity and mechanical stimulation on gene expression of intervertebral disc cells

Intervertebral discs (IVD) have a higher extracellular osmolarity than most other tissues; moreover their osmolarity changes by around 25% during each diurnal cycle. In this study, changes in aggrecan, collagen I and collagen II expression of IVD cells were examined after exposure to osmotic environment alterations or mechanical stimulation under different osmotic conditions. Human and bovine IVD cells seeded in three-dimensional (3D) collagen type I matrices were cultured under hypo-osmotic (300 mOsm), iso-osmotic (400 mOsm), or hyperosmotic (500 mOsm) conditions. Osmolarity-induced changes in gene expression of IVD cells were measured after 5 days. Load-induced changes in gene expression under the different osmotic conditions were measured after application of hydrostatic pressure (0.25 MPa, 0.1 Hz, 30 min) or cyclic strain (4%, 1 Hz, 24 h). The results showed that IVD cells respond strongly to changes in the osmotic environment by altering mRNA expression. Human cells cultured over 5 days increased expression of aggrecan and collagen II in both nucleus and annulus cells under increasing osmolarity. In contrast, collagen I expression was inhibited at high osmolarity in both cell types. Mechanically induced alterations in gene expression appear to have only modest effects on matrix protein expression, but the same stimulus partly resulted in an inhibition or stimulation of gene expression, depending on the osmotic conditions. This study showed that the osmotic environment does not only have an appreciable effect on gene expression but also affects responses to mechanical stimuli. This suggests that the osmotic conditions cannot be ignored when examining physiological and pathological behavior of IVD cells.

Application of multiple parallel perfused microbioreactors and three-dimensional stem cell culture for toxicity testing

In this study, a multiple parallel perfused microbioreactor platform, TissueFlex, was developed which can be used to perform cell and tissue culture under almost uniform and precisely controlled environment in a mid-throughput and parallel manner. These microbioreactors were used to culture human bone marrow cells (hBMCs) in three-dimensional (3D) scaffolds and also in two-dimensional (2D) monolayer for comparison for upto 7 days. Several scaffolding materials were evaluated for this purpose in terms of easiness in handling, ability to support the hBMC growth, and feasibility for non-destructive optical assays. The feasibility and efficacy of using the developed 3D-hBMCs-based model tissue-constructs cultured in TissueFlex microbioreactors for drug evaluation and toxicity testing was then studied. As a demonstration case study, the cultured cells were challenged with two chemicals, trimethoprim and pyrimethamine, both known to be harmful to cellular activities, with different protocols. Cytotoxicity in terms of cell viability and growth was determined using the AlamarBlue assay. The 3D spatial variations in cell morphology and cell survival were also monitored using 3D optical imaging using non-linear multiphoton microscopy. The results show that (i) the data obtained from 3D hBMCs culture and from (2D) monolayer cultures on the effect of the tested chemicals on cell growth are significantly different, and that (ii) the perfused microbioreactor technology could provide a highly controlled and prolonged cell culture environment for testing of various drugs and chemicals. The outcome of this study demonstrated the feasibility and potentials of the using 3D stem cell based model tissues in TissueFlex microbioreactors for drug evaluation and toxicity testing of chemicals as an efficient and standardized alternative testing method.

In vivo measurement of tissue metabolism in tendons of the rotator cuff

We have undertaken an in vivo assessment of the tissue metabolism and cellular activity in torn tendons of the rotator cuff. Cellular oxygen consumption was measured in 13 patients undergoing mini-open repair of small, medium, large and massive full-thickness tears. Measurements were also taken from three control patients who were undergoing open stabilisation of the shoulder with grossly normal tendons. The level of oxygen and nitrous oxide was measured amperometrically using silver needle microelectrodes at the apex of the tear and 1.5 cm from its edge. With nitrous oxide indicating the degree of perfusion, oxygen consumption was calculated at each location to reflect cellular activity.

All of the torn tendons had lower levels of cellular activity than the control group. This activity was lower still in the tissue nearest to the edge of the tear with the larger tears showing the lowest activity. This indicated reduced levels of tissue metabolism and infers a reduction in tendon viability.

Our findings suggest that surgical repair of torn tendons of the rotator-cuff should include the more proximal, viable tissue, and may help to explain the high rate of re-rupture seen in larger tears.

Influences of buffer systems on chondrocyte growth during long-term culture in alginate

OBJECTIVE

Chondrocyte behavior is very sensitive to culture environment such as physical and biochemical conditions. As extracellular pH (pHo) and the existence of bicarbonate could affect the chondrocyte fate, hence, the purpose of this study is to investigate the buffer system effect on chondrocyte fate during relatively long-term culture.

METHODS

In order to examine whether effects seen were due to bicarbonate or to pHo, we had to devise a system which could differentiate between the two effects. Culture media buffered by N-2-hydroxyethyl piperazine-N'-2-ethanesulfonic acid (HEPES) only and the combination of HEPES and bicarbonate were used. Bovine articular chondrocytes were cultured in alginate beads for up to 12 days. pHo was kept constant by culture of 3 beads in 2 ml culture medium. Cell density, intracellular pH (pHi) and glycosaminoglycan (GAG) were measured at day 5 and day 12. Cell morphology, distribution and viability in alginate beads were monitored over 12 days of culture.

RESULTS

Compared to culture in the absence of bicarbonate, a higher proliferation rate of chondrocytes was observed in the presence of bicarbonate. pHi was more alkaline, about 0.2 pH unit, in the presence of bicarbonate than that in the absence of bicarbonate. About 50% more GAG was deposited in alginate beads when chondrocytes were cultured in the combination of HEPES and bicarbonate, compared to chondrocytes cultured in the absence of NaHCO3 at the end of 12 days of culture.

CONCLUSION

The presence of bicarbonate results in more alkaline in the pHi of bovine chondrocytes after long-term culture. The combination of bicarbonate and HEPES in culture medium improves cell growth, matrix production in three-dimensional alginate beads.

Computation of coupled diffusion of oxygen, glucose and lactic acid in an intervertebral disc

The present numerical study aims to investigate the disc nutrition and factors affecting it by evaluating the concentrations of oxygen, glucose and lactic acid in the disc while accounting for the coupling between these species via the pH level in the tissue and the nonlinear concentration-consumption (for glucose and oxygen) and concentration-production (for lactate) relations. The effects of changes in the endplate exchange area (EA) adjacent to the nucleus or the inner annulus for the transport of nutrients and in the disc geometry as well as tissue diffusivities under static compression loading on species concentrations are also studied. Moreover, alterations in solute diffusion following a central endplate fracture are investigated. An axisymmetric geometry with four distinct regions is considered. Supply sources are assumed at the outer annulus periphery and disc endplates. Coupling between different solutes, pH level, endplate disruptions (calcifications and fractures) and mechanical loads substantially influenced the distribution of nutrients throughout the disc as well as the magnitude and location of critical concentrations; maximum for the lactic acid and minimum for oxygen and glucose. In cases with loss of endplate permeability and/or disruptions therein, as well as changes in geometry and fall in diffusivity associated with fluid expression, the nutrient concentrations could fall to levels inadequate to maintain cellular activity or viability, thus initiating or accelerating disc degeneration.

Diurnal fluid expression and activity of intervertebral disc cells

The intervertebral discs are large cartilaginous structures situated between the vertebral bodies, occupying around one third of the length of the spinal column. They act as the joints of the spine and carry mechanical load arising from body weight and muscle activity. Loads change with every alteration of posture and activity and the discs thus undergo a diurnal loading pattern with high loads on the discs during the day's activity and low loads on it at night during rest. As the disc is an osmotic system, around 25% of the disc's fluid is expressed and re-imbibed during each diurnal cycle with consequent changes in the osmotic environment of the disc cells. Here, present information on the effect of osmotic changes in disc cell metabolism is reviewed; results indicate that prevailing osmolarity is a powerful regulator of disc cell activity.

Effects of rapid cooling on articular cartilage

In order to improve the technique and protocols of cryopreservation of articular cartilage, a study was carried out to assess the effects of rapid cooling on the intact articular cartilage. Cartilage slices with a thickness ranging from 0.2 to 0.5 mm taken from bovine metacarpal-phalangeal joints were subjected to rapid cooling by immersing them in liquid nitrogen with and without treatment of the VS55 cryoprotective agent (CPA). The ultrastructure, chondrocyte viability, swelling property, and glycosaminoglycan (GAG) content were then examined before and after cryopreservation to give qualitative and quantitative evaluation on the functional state of both chondrocytes and extracellular matrix. The transmission electron microscopy study demonstrated that damage to chondrocytes without CPA was far more pronounced than those with VS55 protection while the structure of the extracellular matrix altered little in either group. The cell viability assay showed that although the exposure to VS55 led to about 36% chondrocytes losing membrane integrity, the VS55 could provide protection to chondrocytes during rapid cooling and thawing, with approximately 51% of the cells having survived rapid cooling compared to fewer than 5% in the absence of CPA. There were no significant differences in degrees of swelling or the GAG contents of cartilage slices after cryopreservation indicating rapid freezing caused little damage to the matrix. Future research activities include searching improved CPA formulation, optimising the treatment protocol and investigating the long-term effects of rapid cooling on articular cartilage.

The effect of hip resurfacing on oxygen concentration in the femoral head

We inserted an electrode up the femoral neck into the femoral head of ten patients undergoing a metal-on-metal hip resurfacing arthroplasty through a posterior surgical approach and measured the oxygen concentration during the operation. In every patient the blood flow was compromised during surgery, but the extent varied. In three patients, the oxygen concentration was zero at the end of the procedure. The surgical approach caused a mean 60% drop (p < 0.005) in oxygen concentration while component insertion led to a further 20% drop (p < 0.04). The oxygen concentration did not improve significantly on wound closure. This study demonstrates that during hip resurfacing arthroplasty, patients experience some compromise to their femoral head blood supply and some have complete disruption.

Analysis of Nonlinear Coupled Diffusion of Oxygen and Lactic Acid in Intervertebral Discs

The transport of oxygen and lactate (i.e., lactic acid) in the human intervertebral disc was investigated accounting for the measured coupling between species via the pH level in the tissue. Uncoupled cases were also analyzed to identify the extent of the effect of such coupling on the solute gradients across the disc. Moreover, nonlinear lactic production rate versus lactic concentration and oxygen consumption rate versus oxygen concentration were considered. The nonlinear coupled diffusion equations were solved using an in-house finite element program and an axisymmetric model of the disc with distinct nucleus and anulus regions. A pseudotransient approach with a backward integration scheme was employed to improve convergence. Coupled simulations influenced the oxygen concentration and lactic acid concentration throughout the disc, in particular the gradient of concentrations along the disc mid-height to the nucleus-anulus boundary where the solutes reached their most critical values; minimum for the oxygen tension and maximum for the lactate. Results suggest that for realistic estimates of nutrient and metabolite gradients across the disc, it could be important to take into account the coupling between the rates of synthesis and overall local metabolite/nutrient concentration.

TNFalpha-stimulated gene product (TSG-6) and its binding protein, IalphaI, in the human intervertebral disc: new molecules for the disc

Inflammation and irritation of the nerve roots has been indicated as an important factor in the pain associated with symptomatic disc herniations. Tumour necrosis factor alpha (TNFalpha) is now believed to be involved in this pathway. TNFalpha causes connective tissue cells in culture to synthesise a glycoprotein, TNFalpha-stimulated gene-6 (TSG-6). TSG-6 is found in inflammatory diseases of related connective tissues, such as articular cartilage in rheumatoid arthritis, but is not present in unaffected individuals. In order to determine if TSG-6 occurred in intervertebral disc (and cartilage endplate), we have investigated the presence of TSG-6 and its binding protein, inter-alpha-inhibitor (IalphaI), in 58 herniated and 15 non-herniated discs. Immunostaining for the cytokines, IL-1alpha, IL-1beta and TNFalpha, has also been carried out. We have demonstrated that both TSG-6 and IalphaI occur commonly in human intervertebral disc matrix with at least some TSG-6 in 98% of discs studied and IalphaI in all of them. Staining for TSG-6 was greatest in herniated discs, particularly close to blood vessels. IalphaI immunostaining was frequently widespread throughout the disc but there was little in the cartilage endplate. It has been proposed that these molecules have widespread effects, including extracellular matrix stabilisation, down-regulation of the protease network and reduction of inflammation. Hence, the occurrence of TSG-6 and IalphaI in disc tissue could have implications in the aetiopathogenesis and future therapeutics of intervertebral disc disease.

The influence and interactions of hydrostatic and osmotic pressures on the intracellular milieu of chondrocytes

The intracellular milieu of chondroctyes is regulated by an array of proteins in the cell membrane which operate as transport pathways, allowing ions and nutrients such as glucose and amino acids and metabolites such as lactate to cross the plasma membrane. Here we investigated the influence of hydrostatic pressure on intracellular calcium concentrations ([Ca(2+)](i)) in isolated bovine articular chondrocytes. We found that short applications of high hydrostatic pressures led to a significant increase in [Ca(2+)](i). The pressure-induced rise was abolished for long (240 sec) but not short (30 sec) pressure applications by removal of extracellular Ca(2+). The rise in pressure was also blocked by the inhibitors neomycin and thapsigargin confirming that pressure, by generating IP(3), led to an increase in [Ca(2+)](i) by mobilising the pool of Ca(2+) ions contained within intracellular stores. We also found that intracellular [Na(+)] was affected by a rise in osmotic pressure and further affected by application of hydrostatic pressure. The effect of hydrostatic pressure on sulphate incorporation depended strongly on extracellular osmolality. Since significant gradients in extracellular osmolality exist across intact cartilage, the results imply that responses of chondrocytes to the same pressure will vary depending on location in the joint. The results also indicate that hydrostatic pressures can affect several different transporter systems thus influencing the intracellular milieu and chondrocyte metabolism.

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.

Intracellular pH changes in isolated bovine articular chondrocytes during the loading and removal of cryoprotective agents

The addition and removal of a cryoprotective agent (CPA) are necessary steps in the cryopreservation of natural or engineered tissue products. However, the introduction and removal of CPAs induces dramatic chemical changes inside tissues and cells and these could cause irreversible damage. This study examined the effect of CPA loading and removal on the intracellular pH of isolated bovine articular chondrocytes using a fluorimetric technique. Chondrocytes that had been isolated from bovine articular cartilage were loaded with the pH-sensitive fluorophore 2('),7(')-bis(carboxyethyl)-5(6)-carboxyfluorescein. After removal of the extracellular fluorophore, the intensity of fluorescence was used to measure the intracellular pH according to a pre-determined calibration curve. Changes of intracellular pH in chondrocytes were measured following their exposure to dimethyl sulfoxide (Me(2)SO) and glycerol at concentrations of 0.6, 0.9, and 1.2M and later to the isotonic or hypertonic solutions that were used to remove the CPA. The effect of the presence of NaCl on the intracellular pH during CPA removal was also examined. The temperature was maintained at 37 degrees C. Trypan blue exclusion was used to quantify cell membrane integrity after the addition and removal of CPA. It was found that when the cells were exposed to CPA, the intracellular pH decreased quickly and recovered gradually later. During CPA removal, the intracellular pH rose following exposure to isotonic Hepes-buffered medium, but the opposite was observed if the Hepes buffer solution contained no NaCl; this was ascribed to the role of NaCl in cell membrane transport. It was noted that the change in intracellular pH correlated with the cell volume excursion, which could be estimated by the Kedem-Katchalsky model, and was linked to cell survival. The resulting alteration of pH inside the cells might contribute to cell damage and loss of function after cryopreservation.

The role of the physicochemical environment in determining disc cell behaviour

The cells of the intervertebral disc exist in an unusual environment. They are embedded in a dense matrix containing a high concentration of aggrecan whose fixed negative charges regulate the extracellular ionic composition and osmolarity; both extracellular cation concentrations and osmolarity are considerably higher than those experienced by most cell types. The disc also is avascular. Oxygen levels in the centre of the nucleus, where cells may be 6-8 mm from the blood supply, are very low. Since metabolism is mainly by glycolysis, lactic acid is produced at high rates and hence the pH is acidic. Finally, the disc is subjected to mechanical forces at all times; these vary with posture and activity. In particular, because the disc is under low loads during rest and high loads during the day's activities, it loses and regains around 25% of its fluid over a diurnal cycle with consequent changes to the concentrations of extracellular matrix macromolecules and ions and hence extracellular osmolality. Here we will briefly review these factors and discuss the influence of changes in the physicochemical environment on cellular activity, in particular on the rate at which disc cells synthesize and degrade matrix macromolecules.

The effects of pressure on chondrocyte tumour necrosis factor receptor expression

This work was performed to determine whether one aspect of load, pressure, could alter tumour necrosis factor (TNF) receptor type I (RI) expression on chondrocytes. Encapsulated tsT/AC62, osteoarthritic (OA) or non-arthritic (NA) chondrocytes were centrifuged at speeds representing 5 or 20 MPa, incubated for specific periods, released from alginate and TNFRI and II (TNFRII) expression determined by flow cytometry. Significant (p<0.05, n=4) changes in tsT/AC62 chondrocyte TNFRI expression were apparent 24 hours after application of 20 MPa. Five or 20 MPa increased OA chondrocyte TNFRI expression; chondrocytes from some OA patients were markedly sensitive to 20 MPa. NA chondrocyte TNFRI expression usually decreased in response to 5 and 20 MPa. Significant pressure-induced differences in TNFRI expression between NA and OA groups were apparent at 5, but not 20 MPa. Pressure did not significantly alter TNRFII expression on tsT/AC62, NA or OA chondrocytes. These results suggest a mechanism whereby sensitivity of chondrocytes to the effects of TNFalpha may be increased, in susceptible individuals, in regions of the joint that experience peak loading.

The effect of mechanical stress on cartilage energy metabolism

Cartilage is routinely subjected to varying mechanical stresses which are known to affect matrix turnover by a variety of pathways. Here we show that mechanical loads which suppress sulphate incorporation or protein synthesis by articular chondrocytes, also inhibit rates of oxygen uptake and of lactate production. Although the mechanisms have not been definitively identified, it has been shown that high hydrostatic pressures reduce the activity of the glucose transporter GLUT. Furthermore, fluid expression consequent on static loading changes intracellular pH and ionic strength; intracellular changes which would reduce the activity of glycolytic enzymes. Both pathways would thus lead to a fall in rates of glycolysis and a reduction in intracellular ATP, and - since ATP concentrations directly affect sulphation of proteoglycans - a rapid fall in sulphate incorporation. Our results suggest that load-induced changes in matrix synthesis in cartilage can occur by means other than changes in gene expression.

Volume increase in growth plate chondrocytes during hypertrophy: the contribution of organic osmolytes

During the differentiation cascade of growth plate chondrocytes, cells undergo as much as a 10-15-fold increase in volume. This volume increase, which occurs to different extents in growth plates growing at different rates, has been demonstrated to be the single most significant variable in understanding the quantitative aspects of the cellular kinetics of long bone growth. Our hypothesis is that this volume increase, which occurs through cell swelling by water imbibition, requires intracellular accumulation of osmolytes through activation or upregulation of membrane transport mechanisms. Significant intracellular accumulation of inorganic osmolytes, such as Na+, K+, and Cl-, is potentially disruptive to normal cellular metabolism, whereas intracellular accumulation of organic osmolytes is considered to be more compatible with metabolic function. Thus, we concentrated on determining the contributions of organic osmolytes--betaine, amino acids, inositol, and sorbitol--to volume increase. Pooled cryostat sections of young bovine growth plates were extracted followed by automated analysis for their content of amino acids. Analysis for betaine and the sugar alcohols was done by extraction and derivatization, followed by high-performance liquid chromatography (HPLC). Parallel stereological analyses correlated osmolyte changes to stages of chondrocytic differentiation, specifically comparing intracellular concentration and amount in proliferative vs. hypertrophic chondrocytes. Calculations demonstrated that, maximally, these organic osmolytes, in total, account for 6%-7% of the intracellular osmolytes required to sustain the volume increase, and that the most significant contribution is from betaine. This suggests that intracellular accumulation of organic osmolytes is not a primary strategy used by growth plate chondrocytes during volume increase of their terminal differentiation. The data also suggest that there is a differential regulation of transporters of these osmolytes such that intracellular concentrations are constantly modified as cells proceed through the differentiation cascade.