2016 updated EULAR evidence-based recommendations for the management of gout.

BACKGROUND: New drugs and new evidence concerning the use of established treatments have become available since the publication of the first European League Against Rheumatism (EULAR) recommendations for the management of gout, in 2006. This situation has prompted a systematic review and update of the 2006 recommendations. METHODS: The EULAR task force consisted of 15 rheumatologists, 1 radiologist, 2 general practitioners, 1 research fellow, 2 patients and 3 experts in epidemiology/methodology from 12 European countries. A systematic review of the literature concerning all aspects of gout treatments was performed. Subsequently, recommendations were formulated by use of a Delphi consensus approach. RESULTS: Three overarching principles and 11 key recommendations were generated. For the treatment of flare, colchicine, non-steroidal anti-inflammatory drugs (NSAIDs), oral or intra-articular steroids or a combination are recommended. In patients with frequent flare and contraindications to colchicine, NSAIDs and corticosteroids, an interleukin-1 blocker should be considered. In addition to education and a non-pharmacological management approach, urate-lowering therapy (ULT) should be considered from the first presentation of the disease, and serum uric acid (SUA) levels should be maintained at<6 mg/dL (360 µmol/L) and <5 mg/dL (300 µmol/L) in those with severe gout. Allopurinol is recommended as first-line ULT and its dosage should be adjusted according to renal function. If the SUA target cannot be achieved with allopurinol, then febuxostat, a uricosuric or combining a xanthine oxidase inhibitor with a uricosuric should be considered. For patients with refractory gout, pegloticase is recommended. CONCLUSIONS: These recommendations aim to inform physicians and patients about the non-pharmacological and pharmacological treatments for gout and to provide the best strategies to achieve the predefined urate target to cure the disease.

OARSI recommendations for the management of hip and knee osteoarthritis: part III: Changes in evidence following systematic cumulative update of research published through January 2009.

OBJECTIVE: To update evidence for available therapies in the treatment of hip and knee osteoarthritis (OA) and to examine whether research evidence has changed from 31 January 2006 to 31 January 2009. METHODS: A systematic literature search was undertaken using MEDLINE, EMBASE, CINAHL, AMED, Science Citation Index and the Cochrane Library. The quality of studies was assessed. Effect sizes (ESs) and numbers needed to treat were calculated for efficacy. Relative risks, hazard ratios (HRs) or odds ratios were estimated for side effects. Publication bias and heterogeneity were examined. Sensitivity analysis was undertaken to compare the evidence pooled in different years and different qualities. Cumulative meta-analysis was used to examine the stability of evidence. RESULTS: Sixty-four systematic reviews, 266 randomised controlled trials (RCTs) and 21 new economic evaluations (EEs) were published between 2006 and 2009. Of 51 treatment modalities, new data on efficacy have been published for more than half (26/39, 67%) of those for which research evidence was available in 2006. Among non-pharmacological therapies, ES for pain relief was unchanged for self-management, education, exercise and acupuncture. However, with new evidence the ES for pain relief for weight reduction reached statistical significance, increasing from 0.13 [95% confidence interval (CI) -0.12, 0.36] in 2006 to 0.20 (95% CI 0.00, 0.39) in 2009. By contrast, the ES for electromagnetic therapy which was large in 2006 (ES=0.77, 95% CI 0.36, 1.17) was no longer significant (ES=0.16, 95% CI -0.08, 0.39). Among pharmacological therapies, the cumulative evidence for the benefits and harms of oral and topical non-steroidal anti-inflammatory drugs, diacerhein and intra-articular (IA) corticosteroid was not greatly changed. The ES for pain relief with acetaminophen diminished numerically, but not significantly, from 0.21 (0.02, 0.41) to 0.14 (0.05, 0.22) and was no longer significant when analysis was restricted to high quality trials (ES=0.10, 95% CI -0.0, 0.23). New evidence for increased risks of hospitalisation due to perforation, peptic ulceration and bleeding with acetaminophen >3g/day have been published (HR=1.20, 95% CI 1.03, 1.40). ES for pain relief from IA hyaluronic acid, glucosamine sulphate, chondroitin sulphate and avocado soybean unsponifiables also diminished and there was greater heterogeneity of outcomes and more evidence of publication bias. Among surgical treatments further negative RCTs of lavage/debridement were published and the pooled results demonstrated that benefits from this modality of therapy were no greater than those obtained from placebo. CONCLUSION: Publication of a large amount of new research evidence has resulted in changes in the calculated risk-benefit ratio for some treatments for OA. Regular updating of research evidence can help to guide best clinical practice.

Integrin-regulated secretion of interleukin 4: A novel pathway of mechanotransduction in human articular chondrocytes.

Chondrocyte function is regulated partly by mechanical stimulation. Optimal mechanical stimulation maintains articular cartilage integrity, whereas abnormal mechanical stimulation results in development and progression of osteoarthritis (OA). The responses of signal transduction pathways in human articular chondrocytes (HAC) to mechanical stimuli remain unclear. Previous work has shown the involvement of integrins and integrin-associated signaling pathways in activation of plasma membrane apamin-sensitive Ca2+-activated K+ channels that results in membrane hyperpolarization of HAC after 0. 33 Hz cyclical mechanical stimulation. To further investigate mechanotransduction pathways in HAC and show that the hyperpolarization response to mechanical stimulation is a result of an integrin-dependent release of a transferable secreted factor, we used this response. Neutralizing antibodies to interleukin 4 (IL-4) and IL-4 receptor alpha inhibit mechanically induced membrane hyperpolarization and anti-IL-4 antibodies neutralize the hyperpolarizing activity of medium from mechanically stimulated cells. Antibodies to interleukin 1beta (IL-1beta) and cytokine receptors, interleukin 1 receptor type I and the common gamma chain/CD132 (gamma) have no effect on me- chanically induced membrane hyperpolarization. Chondrocytes from IL-4 knockout mice fail to show a membrane hyperpolarization response to cyclical mechanical stimulation. Mechanically induced release of the chondroprotective cytokine IL-4 from HAC with subsequent autocrine/paracrine activity is likely to be an important regulatory pathway in the maintenance of articular cartilage structure and function. Finally, dysfunction of this pathway may be implicated in OA.

Signalling cascades in mechanotransduction: cell-matrix interactions and mechanical loading.

Mechanical loading of articular cartilage stimulates the metabolism of resident chondrocytes and induces the synthesis of molecules to maintain the integrity of the cartilage. Mechanical signals modulate biochemical activity and changes in cell behavior through mechanotransduction. Compression of cartilage results in complex changes within the tissue including matrix and cell deformation, hydrostatic and osmotic pressure, fluid flow, altered matrix water content, ion concentration and fixed charge density. These changes are detected by mechanoreceptors on the cell surface, which include mechanosensitive ion channels and integrins that on activation initiate intracellular signalling cascades leading to tissue remodelling. Excessive mechanical loading also influences chondrocyte metabolism but unlike physiological stimulation leads to a quantitative imbalance between anabolic and catabolic activity resulting in depletion of matrix components. In this article we focus on the role of mechanical signalling in the maintenance of articular cartilage, and discuss how alterations in normal signalling can lead to pathology.

Gout in the UK and Germany: prevalence, comorbidities and management in general practice 2000-2005.

OBJECTIVE: To investigate and compare the prevalence, comorbidities and management of gout in practice in the UK and Germany. METHODS: A retrospective analysis of patients with gout, identified through the records of 2.5 million patients in UK general practices and 2.4 million patients attending GPs or internists in Germany, using the IMS Disease Analyzer. RESULTS: The prevalence of gout was 1.4% in the UK and Germany. Obesity was the most common comorbidity in the UK (27.7%), but in Germany the most common comorbidity was diabetes (25.9%). The prevalence of comorbidities tended to increase with serum uric acid (sUA) levels. There was a positive correlation between sUA level and the frequency of gout flares. Compared with those in whom sUA was <360 micromol/l (<6 mg/dl), odds ratios for a gout flare were 1.33 and 1.37 at sUA 360-420 micromol/l (6-7 mg/dl), and 2.15 and 2.48 at sUA >530 micromol/l ( >9 mg/dl) in the UK and Germany, respectively (p<0.01). CONCLUSIONS: The prevalence of gout in practice in the UK and Germany in the years 2000-5 was 1.4%, consistent with previous UK data for 1990-9. Chronic comorbidities were common among patients with gout and included conditions associated with an increased risk for cardiovascular disease, such as obesity, diabetes and hypertension. The importance of regular monitoring of sUA in order to tailor gout treatment was highlighted by data from this study showing that patients with sUA levels >or=360 micromol/l (>or=6 mg/dl) had an increased risk of gout flares.

Cod liver oil (n-3 fatty acids) as an non-steroidal anti-inflammatory drug sparing agent in rheumatoid arthritis.

OBJECTIVES: Dose-dependant gastrointestinal and cardiovascular side-effects limit the use of NSAIDs in the management of RA. The n-3 essential fatty acids (EFAs) have previously demonstrated some anti-inflammatory and NSAID-sparing properties. The objective of this study was to determine whether cod liver oil supplementation helps reduce daily NSAID requirement of patients with RA. METHODS: Dual-centre, double-blind placebo-controlled randomized study of 9 months' duration. Ninety-seven patients with RA were randomized to take either 10 g of cod liver oil containing 2.2 g of n-3 EFAs or air-filled identical placebo capsules. Documentation of NSAID daily requirement, clinical and laboratory parameters of RA disease activity and safety checks were done at 0, 4, 12, 24 and 36 weeks. At 12 weeks, patients were instructed to gradually reduce, and if possible, stop their NSAID intake. Relative reduction of daily NSAID requirement by >30% after 9 months was the primary outcome measure. RESULTS: Fifty-eight patients (60%) completed the study. Out of 49 patients 19 (39%) in the cod liver oil group and out of 48 patients 5 (10%) in the placebo group were able to reduce their daily NSAID requirement by >30% (P = 0.002, chi-squared test). No differences between the groups were observed in the clinical parameters of RA disease activity or in the side-effects observed. CONCLUSIONS: This study suggests that cod liver oil supplements containing n-3 fatty acids can be used as NSAID-sparing agents in RA patients.

Mechanical regulation of proteoglycan synthesis in normal and osteoarthritic human articular chondrocytes--roles for alpha5 and alphaVbeta5 integrins.

The importance of biomechanical forces in regulating normal chondrocyte metabolism is well established and the mechanisms whereby mechanical forces are transduced into biochemical responses by chondrocytes are beginning to be understood. Previous studies have indicated that cyclical mechanical stimulation induces increased aggrecan gene expression in normal but not osteoarthritic chondrocytes in monolayer. It remains unclear, however, whether these effects on gene expression are associated with changes in proteoglycan production and whether any changes in proteoglycan expression is dependent on integrins or integrin associated proteins. Normal and osteoarthritic articular chondrocytes in monolayer were exposed to 0.33 Hz mechanical stimulation for 20 min in the absence or presence of function modifying anti-integrin antibodies. Following stimulation GAG and proteoglycan (PG) synthesis was assessed by DMMB assay and western blotting. Mechanical stimulation of normal chondrocytes resulted in increased GAG synthesis that was blocked by the presence of antibodies to alpha5 and alphaVbeta5 integrins and CD47. Electrophoretic patterns of PGs released from normal chondrocytes following mechanical stimulation showed an increase in newly-synthesized aggrecan that was not fragmented or degraded. Chondrocytes from osteoarthritic cartilage showed lower levels of GAG production when compared to normal chondrocytes and synthesis was not influenced by mechanical stimulation. These studies show that chondrocytes derived from normal and OA cartilage have different matrix production responses to mechanical stimulation and suggest previously unrecognised roles for alphaVbeta5 integrin in regulation of chondrocyte responses to biomechanical stimulation.

Integrin and mechanosensitive ion channel-dependent tyrosine phosphorylation of focal adhesion proteins and beta-catenin in human articular chondrocytes after mechanical stimulation.

Mechanical forces influence chondrocyte metabolism and function. We have previously shown that 0.33 Hz cyclical pressure-induced strain (PIS) results in membrane hyperpolarization of normal human articular chondrocytes (HAC) by activation of Ca(2+)-dependent K+ small conductance potassium activated calcium (SK) channels. The mechanotransduction pathway involves alpha 5 beta 1-integrin, stretch-activated ion channels (SAC) actin cytoskeleton and tyrosine protein kinases, with subsequent release of the chondroprotective cytokine interleukin-4 (IL-4). The objective of this study was to examine in detail tyrosine phosphorylation events in the mechanotransduction pathway. The results show tyrosine phosphorylation of three major proteins, p125, p90, and p70 within 1 minute of onset of mechanical stimulation. Immunoblotting and immunoprecipitation show these to be focal adhesion kinase (pp125FAK), beta-catenin, and paxillin, respectively. Tyrosine phosphorylation of all three proteins is inhibited by RGD containing oligopeptides and gadolinium, which is known to block SAC. beta-catenin coimmunoprecipitates with FAK and is colocalized with alpha 5-integrin and pp125FAK. These results indicate a previously unrecognized role for an integrin-beta-catenin signaling pathway in human articular chondrocyte (HAC) responses to mechanical stimulation.

Pyoderma gangrenosum: clinical and laboratory findings in 15 patients with special reference to polyarthritis.

Fifteen consecutive patients with PG have been studied during the period 1971-78. Systemic disease was found in 13 of the patients and preceded the skin disease in 10 patients by 1-25 years. Only two patients had ulcerative colitis. One patient had paroxysmal nocturnal hemoglobinuria and three patients had an IgA myeloma. Eight patients had polyarthritis; this was classical seropositive rheumatoid arthritis in two patients, and a seronegative inflammatory polyarthritis in six patients. Four patients had an unusual progressive erosive seronegative polyarthritis without evidence of granulomatous bowel disease, psoriasis, genital, urinary tract or eye disease. In three of these four patients the arthritis preceded the PG. Synovial fluid analysis showed depressed complement levels and in one patient deposits of immunoglobulins and complement were demonstrated in the synovial membrane. The course of the arthritis was progressive with development of disabling joint deformities and erosive destruction of joints, despite treatment with penicillamine, corticosteroids and nonsteroidal anti-inflammatory drugs. One other patient had severe degenerative joint disease and chondrocalcinosis in association with a seronegative inflammatory polyarthritis, and another patient had ulcerative proctitis and severe degenerative joint disease secondary to chronic seronegative inflammatory polyarthritis. None of the patients had colitic arthritis, but in view of the association between PG and ulcerative colitis, some patients previously reported with PG and joint disease may have been suffering from the arthritis of ulcerative colitis. PG developed at the site of skin trauma in six patients. The natural history of the skin disease ran one of two courses: an acute, progressive course in which the ulcers rapidly enlarged until arrested by treatment; and a chronic course in which the lesions extended slowly and which after a period of weeks began to show signs of spontaneous healing. In only the patients with ulcerative colitis was there any correlation between the activity of the associated disease and the onset and progression of the skin disease. Serum complement levels were normal and no circulating cryoprecipitable immune complexes were found. Skin histology showed no evidence of vasculitis and direct immunofluorescence examination of involved skin was negative for IgG, IgM, IgA and C3. No consistent abnormality of cell-mediated immunity or neutrophil function was found and no significantly increased prevalence of any HLA antigen type was noted. Twelve patients have been treated with systemic corticosteroids. Six of these patients developed serious steroid complications and four patients have died, all from complications of steroid therapy.

Differential effects of mepacrine, chloroquine and hydroxychloroquine on superoxide anion generation, phospholipid methylation and arachidonic acid release by human blood monocytes.

The 4-aminoquinolines chloroquine (CQ) and hydroxychloroquine (HCQ), and previously the 9-aminoacridine mepacrine (quinacrine) (MP), have been widely used in the treatment of inflammatory disorders such as rheumatoid arthritis and systemic lupus erythematosus. Their effects are believed to be mediated through phagocytic cells but the precise biochemical basis remains uncertain. We have investigated the effects of these drugs on monocyte superoxide anion (SO) generation elicited by 5 different stimuli-opsonised zymosan (STZ), FMLP, A23187, TPA and fluoride--and sought correlations with effects on two processes which have been linked with monocyte activation, namely arachidonate (AA) release and transmethylation of phosphatidyl ethanolamine (PE) to phosphatidylcholine (PC). In all experiments conditions were adjusted to achieve leucocyte concentrations of drug comparable to those found during in vivo therapy. Neither CQ nor HCQ had any marked effect on SO release induced by TPA, A23187 or fluoride ion, excluding a significant effect on protein kinase C (PKC), calmodulin-dependent kinase(s) or the membrane-bound, superoxide generating NADP(H) oxidase. In contrast MP inhibited the response to TPA and A23187. Each drug also had different effects on surface receptor-dependent responses; thus HCQ inhibited FMLP- but not STZ-induced SO release, whereas CQ and MP inhibited the response to both stimuli. Each drug also displayed different effects on AA release and phospholipid (PL)-methylation; MP and HCQ, but not CQ, inhibited STZ-stimulated AA release while MP and CQ but not HCQ inhibited basal rates of PL-methylation in mononuclear cells (MNC). However, only MP inhibited PL-methylation in an enriched monocyte population. We conclude that despite their close structural similarity, MP, CQ and HCQ each have different metabolic effects and their actions cannot simply be attributed to inhibition of lysosomal functions. Other possible mechanisms of action are discussed. The selective effects of each drug also provide further evidence for multiple pathways of monocyte activation.

Stimulation of human purine synthesis de novo by fructose infusion.

In order to clarify the mechanism of hyperuricemia and hyperuricosuria resulting from rapid infusion of fructose in man, the effects of an intravenous infusion of 125-200 g of fructose given over 3-4 hr on the rate of purine synthesis de novo was measured in one individual with osteoarthritis and four patients with gout. The incorporation of 1-minus 14C glycine into urinary uric acid was measured, and the pool size and turnover of urate were assessed by renal excretion of simultaneously administered 15-N urate. Fructose caused an expansion of body urate pool in all subjects, while urate turnover was increased in four. The rate of incorporation of 14-C glycine into urinary uric acid corrected for extrarenal disposal was increased in all cases (21%-430%). In two patients, rates of incorporation of 14-C glycine into urinary creatinine were increased by 10% and 11%, while rates of incorporation into uric acid were increased 84% and 159%, respectively, as a result of fructose infusion. Specific enhancement of the rate of purine synthesis de novo was suggested by these findings. The rate of infusion appeared more important than total dose in determining the magnitude of this effect. Whether the increased rate of purine synthesis was a result of direct stimulation by a fructose metabolite or was secondary to fructose-induced purine nucleotide depletion is uncertain, since the kinetics of glycine incorporation were consistent with either mechanism. Erythrocyte PP-ribose-P concentrations, however, were diminished during infusion rather than increased as might be expected if fructose infusion stimulated purine synthesis by increasing availability of this regulatory substrate.

Hyperpolarisation of cultured human chondrocytes following cyclical pressure-induced strain: evidence of a role for alpha 5 beta 1 integrin as a chondrocyte mechanoreceptor.

Mechanical stimuli influence chondrocyte metabolism, inducing changes in intracellular cyclic adenosine monophosphate and proteoglycan production. We have previously demonstrated that primary monolayer cultures of human chondrocytes have an electrophysiological response after intermittent pressure-induced strain characterised by a membrane hyperpolarisation of approximately 40%. The mechanisms responsible for these changes are not fully understood but potentially involve signalling molecules such as integrins that link extracellular matrix with cytoplasmic components. The results reported in this paper demonstrate that the transduction pathways involved in the hyperpolarisation response of human articular chondrocytes in vitro after cyclical pressure-induced strain involve alpha 5 beta 1 integrin. We have demonstrated, using pharmacological inhibitors of a variety of intracellular signalling pathways, that the actin cytoskeleton, the phospholipase C calmodulin pathway, and both tyrosine protein kinase and protein kinase C activities are important in the transduction of the electrophysiological response. These results suggest that alpha 5 beta 1 is an important chondrocyte mechanoreceptor and a potential regulator of chondrocyte function.

The effects of morphine and nalorphine on the plasma 11-hydroxycorticosteroid response to insulin-induced hypoglycaemia in patients with rheumatoid arthritis.

Morphine in therapeutic dosage has been shown to impair the plasma 11-hydroxycorticosteroid response to the stress of insulin-induced hypoglycaemia. Nalorphoine in similar dosage produced no impairment of the response to hypoglycaemia.

Abnormalities in mineral metabolism suggestive of parathyroid over-activity in rheumatoid arthritis.

A three-part study on mineral metabolism in patients with classical rheumatoid arthritis is described. In the first two parts, biochemical abnormalities were revealed suggestive of parathyroid over-activity, and in the third part, observation on calcium absorption provides a hyperparathyroid pattern. The importance of these findings in relation to demineralisation of bone in rheumatoid arthritis is discussed.

Hypoxanthine-guanine phosphoribosyl transferase: assay using high performance liquid chromatography.

A method is described for the estimation of hypoxanthine-guanine phosphoribosyltransferase using high performance liquid chromatography. The inosine monophosphate (IMP) generated from hypoxanthine is determined, after separation on a C18 reversed phase silica column with a buffer-methanol gradient, by the absorbance at 254 nm. Simultaneous reciprocal measurement of hypoxanthine consumption is made. The assay is suitable for screening red cell lysates for hypoxanthine-guanine phosphoribosyltransferase deficiency; the results being expressed as nmol inosine monophosphate . h-1. mg-1 haemoglobin. The normal range found was 94 +/- 15 nmol IMP . h-1 . mg-1 haemoglobin and hypoxanthine-guanine phosphoribosyltransferase activities down to 1% of normal can be assayed accurately.

Measurement of hand bone mineral content using single-photon absorptiometry.

A single photon absorption imaging technique has been developed to assess the bone mass of the hand, especially in patients with rheumatoid arthritis or bronchial asthma. A modified rectilinear scanner images the hand by transmission scanning in a water bath with a 7.4 GBq 125I source. A microcomputer is used to calculate the bone mineral distribution, and the total bone mineral content (BMC) of the hand is determined from that distribution. The precision (coefficient of variation) of the measurement is 1.9%. A control population of 20 men and 58 women has been studied to determine normal variations in hand bone mineral content with age, sex, body size, hand volume and years since menopause. The normal men are found to have an average hand BMC of 25.1 g with a coefficient of variation (CV) of 22%, which is reduced to 12% by normalising for body size using span. The normal women had an average hand BMC of 18.0 g +/- 15%. The CV is reduced to 13% by normalising for span and years post-menopause.

Total and peripheral bone mass in patients with psoriatic arthritis and rheumatoid arthritis.

Psoriatic arthritis is thought to be associated with periarticular osteoporosis while rheumatoid arthritis may be associated with generalised as well as periarticular bone loss. To assess the extent of total and peripheral bone loss in these two diseases, total body calcium was measured by in vivo neutron activation analysis and peripheral bone mass was assessed by metacarpal indices in age-matched patients with psoriatic arthritis and rheumatoid arthritis treated with nonsteroidal anti-inflammatory drugs alone. In comparison with age and sex-matched normal controls, total and peripheral bone mass was normal in psoriatic arthritis. There were significant reductions in total (6.2% in men; 7.9% in women) and peripheral (10.9% in men; 12.8% in women) bone mass in patients with rheumatoid arthritis compared with controls. Peripheral bone mass was significantly correlated with the degree of radiographic damage in male and female patients with rheumatoid arthritis. The mean annual loss of total body calcium was insignificant in psoriatic arthritis (0.6% in men; 1.9% in women) but markedly greater in rheumatoid arthritis (4.4% in men; 2.7% in women). The data suggested that total and peripheral bone loss is greater in rheumatoid arthritis than psoriatic arthritis. Substantial reductions in peripheral bone mass in patients with rheumatoid arthritis not receiving corticosteroids may account in part for the small reductions in total bone mass.

Clinical and enzymological studies in a child with type I glycogen storage disease associated with partial deficiency of hepatic glucose-6-phosphatase.

1. GSD-I is described in a child with partial deficiency of hepatic glucose-6-phosphatase. 2. Growth retardation and hepatosplenomegaly were major clinical features. 3. Hyperlipidaemia, lactic acidaemia, hyperuricaemia and reduced uric acid clearance were major biochemical findings. 4. Although the glucose response to glucagon and galactose was impaired, there was a striking absence of hypoglycaemia which may be attributable to residual catalytic activity of the enzyme. 5. Preliminary studies of the crude liver enzyme showed it to have a normal pH inactivation profile and apparent Km with a reduced Vmax. 6. No evidence of increased PP-ribose-P availability in fresh liver tissue was detected. 7. Continuous glucose feeding resulted in accelerated growth without complete correction of lactic acidosis or hyperuricaemia. 8. GSD-I with partial deficiency of hepatic glucose-6-phosphatase should be considered in patients with gout or hyperuricaemia associated with hypertriglyceridaemia and lactic acidaemia even in the absence of hypoglycaemia.

Purine and pyrimidine nucleotide concentrations in cells with decreased hypoxanthine-guanine-phosphoribosyltransferase (HGPRT) activity.

1. In order to investigate the role of purine ribonucleotides in the regulation of de novo purine synthesis in living human cells deficient in HGPRT, intracellular ribonucleotide concentrations have been measured in HGPRT lymphoblasts, fibroblasts and erythrocytes and in appropriate HGPRT controls by high pressure liquid chromatography. 2. Purine Purine ribonucleotide concentrations were not reduced in HGPRT cells, supporting the hypothesis that accelerated purine biosynthesis de novo results from increased availability of PP-ribose-P and not from altered feedback regulation by purine ribonucleotides in HGPRT deficient cells. 3. Striking increases in intracellular concentrations of some pyrimidine nucleotides and nucleotide sugars were detected in HGPRT lymphoblasts and erythrocytes, but not in fibroblasts. 4. The possibiiity that this abnormality of pyrimidine metabolism might result from coordinate regulation of purine and pyrimidine synthesis de novo by PP-ribose-P was not substantiated by measurements of rates of pyrimidine synthesis and experimental elevation of intracellular concentrations of PP-ribose-P following incubation of cells with inorganic phosphate.

Differential responses of chondrocytes from normal and osteoarthritic human articular cartilage to mechanical stimulation.

Mechanical stimulation is critically important for the maintenance of normal articular cartilage integrity. Molecular events regulating responses of chondrocytes to mechanical forces are beginning to be defined. Chondrocytes from normal human knee joint articular cartilage show increased levels of aggrecan mRNA following 0.33 Hz mechanical stimulation whilst at the same time relative levels of MMP3 mRNA are decreased. This anabolic response, associated with membrane hyperpolarisation, is activated via an integrin-dependent interleukin (IL)-4 autocrine/paracrine loop. Work in our laboratory suggests that this chondroprotective response may be aberrant in osteoarthritis (OA). Chondrocytes from OA cartilage show no changes in aggrecan or MMP3 mRNA following 0.33 Hz mechanical stimulation. alpha5beta1 integrin is the mechanoreceptor in both normal and OA chondrocytes but downstream signalling pathways differ. OA chondrocytes show membrane depolarisation following 0.33 Hz mechanical stimulation consequent to activation of an IL1beta autocrine/paracrine loop. IL4 signalling in OA chondrocytes is preferentially through the type I (IL4alpha/cgamma) receptor rather than via the type II (IL4alpha/IL13R) receptor. Altered mechanotransduction and signalling in OA may contribute to changes in chondrocyte behaviour leading to increased cartilage breakdown and disease progression.