Antioxidant, antiinflammatory and neuroprotective actions of chondroitin sulfate and proteoglycans.

The antiinflammatory and antiapoptotic effects of chondroitin sulfate (CS) are being used to treat osteoarthritis. Recent evidence has revealed that those peripheral effects of CS may also have therapeutic interest in diseases of the central nervous system (CNS). We review here such evidence. Perineuronal nets (PNNs) formed by chondroitin sulfate proteoglycans (CSPGs) may have a neuroprotective action against oxidative stress potentially involved in neurodegeneration. On the other hand, in human neuroblastoma SH-SY5Y cells CS has antioxidant and neuroprotective effects by activating the signaling pathway PKC/PI3K/Akt and inducing the antioxidant enzyme hemoxygenase-1. Consistent with this is the observation that protein kinase C (PKC) blockade overcomes inhibition of neurite outgrowth elicited by CSPGs. In addition, CS protects cortical neurons against excytotoxic death by phosphorylation of intracellular signals and the suppression of caspase-3 activation. Of interest is the finding that a disaccharide derived from CSPG degradation (CSGP-DS) protects neurons against toxicity both in vitro and in vivo. Furthermore, CSGP-DS efficiently protects against neuronal loss in experimental autoimmune encephalomyelitis and uveitis, decreases secretion of tumor necrosis factor-alpha (TNF-alpha) and block necrosis factor kappa B (NF-kappaB) translocation. In conclusion, CS may have neuroprotective properties linked to its antioxidant and antiinflammatory effects.

Chondroitin sulfate inhibits lipopolysaccharide-induced inflammation in rat astrocytes by preventing nuclear factor kappa B activation.

Chondroitin sulfate (CS) is a glucosaminoglycan (GAG) currently used for the treatment of osteoarthritis because of its antiinflammatory and antiapoptotic actions. Recent evidence has revealed that those peripheral effects of CS may also have therapeutic interest in diseases of the CNS. Since neuroinflammation has been implicated in different neuronal pathologies, this study was planned to investigate how CS could modulate the inflammatory response in the CNS by using rat astrocyte cultures stimulated with lipopolysaccharide (LPS). We have evaluated different proteins implicated in the nuclear factor kappa B (NFkappaB) and Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathways employing RT-PCR, western blot and immunofluorescence techniques. At 10 microM, CS prevented translocation of p65 to the nucleus, reduced tumour necrosis factor alpha (TNF-alpha) mRNA and mitigated cyclooxygenase 2 (COX-2) and inducible nitric oxide synthase (iNOS) induction by LPS. However, it did not modify LPS-induced IP-10 and SOCS-1 mRNA, proteins that participate in the JAK/STAT pathway. The results of this study indicate that CS can potentially reduce neuroinflammation by inhibition of NFkappaB. Therefore endogenous GAGs could afford neuroimmunomodulatory actions under neurotoxic conditions.

Effect of chondroitin sulphate in a rabbit model of atherosclerosis aggravated by chronic arthritis.

BACKGROUND AND PURPOSE: Among the agents employed to manage osteoarthritis, chondroitin sulphate (CS) is a natural glycosaminoglycan with an anti-inflammatory effect on joint cells. CS might also influence the inflammatory component of atherosclerosis. Our aim was to examine the effect of CS administration on vascular injury and on markers of systemic inflammation in a rabbit model of atherosclerosis aggravated by systemic inflammation provoked by chronic antigen-induced arthritis. EXPERIMENTAL APPROACH: Atherosclerosis was induced in rabbits by maintaining them on a hyperlipidaemic diet after producing an endothelial lesion in the femoral arteries. Simultaneously, chronic arthritis was induced in these animals by repeated intraarticular injections of ovalbumin in previously immunized rabbits. A group of these rabbits were treated prophylactically with CS (100 mg kg(-1)day(-1)) and when the animals were killed, serum and peripheral blood mononuclear cells (PBMC) were isolated. Furthermore, femoral arteries and thoracic aorta were used for gene expression studies and histological examination. KEY RESULTS: CS administration reduced the concentration of the proinflammatory molecules C-reactive protein and IL-6 in serum. Likewise, CS inhibited the expression of CCL2/monocyte chemoattractant protein (MCP)-1 and cyclooxygenase (COX)-2 in PBMC, and reduced the nuclear translocation of nuclear factor-kappaB. In the femoral lesion, CS also diminished the expression of CCL2 and COX-2, as well as the ratio of the intima/media thickness. Moreover, CS decreased the percentage of rabbits with atherosclerosis and chronic arthritis that developed vascular lesions in the aorta. CONCLUSIONS AND IMPLICATIONS: These findings suggest that CS treatment may to some extent impede the progression of atherosclerosis.

Overexpression of protein targeting to glycogen in cultured human muscle cells stimulates glycogen synthesis independent of glycogen and glucose 6-phosphate levels.

There is growing evidence that glycogen targeting subunits of protein phosphatase-1 play a critical role in regulation of glycogen metabolism. In the current study, we have investigated the effects of adenovirus-mediated overexpression of a specific glycogen targeting subunit known as protein targeting to glycogen (PTG) in cultured human muscle cells. PTG was overexpressed both in muscle cells cultured at high glucose (glycogen replete) or in cells incubated for 18 h in the absence of glucose and then incubated in high glucose (glycogen re-synthesizing). In both glycogen replete and glycogen resynthesizing cells, PTG overexpression caused glycogen to be synthesized at a linear rate 1-5 days after viral treatment, while in cells treated with a virus lacking a cDNA insert (control virus), glycogen content reached a plateau at day 1 with no further increase. In the glycogen replete PTG overexpressing cells, glycogen content was 20 times that in controls at day 5. Furthermore, in cells undergoing glycogen resynthesis, PTG overexpression caused a doubling of the initial rate of glycogen synthesis over the first 24 h relative to cells treated with control virus. In both sets of experiments, the effects of PTG on glycogen synthesis were correlated with a 2-3-fold increase in glycogen synthase activity state, with no changes in glycogen phosphorylase activity. The alterations in glycogen synthase activity were not accompanied by changes in the intracellular concentration of glucose 6-phosphate. We conclude that PTG overexpression activates glycogen synthesis in a glucose 6-phosphate-independent manner in human muscle cells while overriding glycogen-mediated inhibition. Our findings suggest that modulation of PTG expression in muscle may be a mechanism for enhancing muscle glucose disposal and improving glucose tolerance in diabetes.

Glycogen depletion rather than glucose 6-P increments controls early glycogen recovery in human cultured muscle.

In glycogen-containing muscle, glycogenesis appears to be controlled by glucose 6-phosphate (6-P) provision, but after glycogen depletion, an autoinhibitory control of glycogen could be a determinant. We analyzed in cultured human muscle the contribution of glycogen depletion versus glucose 6-P in the control of glycogen recovery. Acute deglycogenation was achieved by engineering cells to overexpress glycogen phosphorylase (GP). Cells treated with AdCMV-MGP adenovirus to express 10 times higher active GP showed unaltered glycogen relative to controls at 25 mM glucose, but responded to 6-h glucose deprivation with more extensive glycogen depletion. Glycogen synthase (GS) activity ratio was double in glucose-deprived AdCMV-MGP cells compared with controls, despite identical glucose 6-P. The GS activation peak (30 min) induced by glucose reincubation dose dependently correlated with glucose 6-P concentration, which reached similar steady-state levels in both cell types. GS activation was significantly blunted in AdCMV-MGP cells, whereas it strongly correlated, with an inverse relationship, with glycogen content. An initial (0-1 h) rapid insulin-independent glycogen resynthesis was observed only in AdCMV-MGP cells, which progressed up to glycogen levels approximately 150 micrograms glucose/mg protein; control cells, which did not deplete glycogen below this concentration, showed a 1-h lag time for recovery. In summary, acute deglycogenation, as achieved by GP overexpression, caused the activation of GS, which inversely correlated with glycogen replenishment independent of glucose 6-P. During glycogen recovery, the activation promoted by acute deglycogenation rendered GS effective for controlling glycogenesis, whereas the transient activation of GS induced by the glucose 6-P rise had no impact on the resynthesis rate. We conclude that the early insulin-independent glycogen resynthesis is dependent on the activation of GS due to GP-mediated exhaustion of glycogen rather than glucose 6-P provision.

Expression of glucokinase in cultured human muscle cells confers insulin-independent and glucose concentration-dependent increases in glucose disposal and storage.

Insulin resistance, as is found in skeletal muscle of individuals with obesity and NIDDM, appears to involve a reduced capacity of the hormone to stimulate glucose uptake and/or phosphorylation. The glucose phosphorylation step, as catalyzed by hexokinase II, has been described as rate limiting for glucose disposal in muscle, but overexpression of this enzyme under control of a muscle-specific promoter in transgenic mice has had limited metabolic impact. In the current study, we investigated in a cultured muscle model whether expression of glucokinase, which in contrast to hexokinase II is not inhibited by glucose-6-phosphate (G-6-P), would have a pronounced metabolic impact. We used a recombinant adenovirus containing the cDNA-encoding rat liver glucokinase (AdCMV-GKL) to increase the glucose phosphorylating activity in cultured human muscle cells by fourfold. G-6-P levels increased in AdCMV-GKL-treated cells in a glucose concentration-dependent manner over the range of 1-30 mmol/l, whereas the much smaller increases in G-6-P in control cells were maximal at glucose concentrations <5 mmol/l. Further, cells expressing glucokinase accumulated 17 times more 2-deoxyglucose-6-phosphate than control cells. In AdCMV-GKL-treated cells, the time-dependent rise in G-6-P correlated with an increase in the activity ratio of glycogen synthase. AdCMV-GKL-treated cells also exhibited a 2.5- to 3-fold increase in glycogen content and a four- to fivefold increase in glycolytic flux, proportional to the increase in glucose phosphorylating capacity. All of these observations were made in the absence of insulin. Thus we concluded that expression of glucokinase in cultured human muscle cells results in proportional increases in insulin-independent glucose disposal, and that muscle glucose storage and utilization becomes controlled in a glucose concentration-dependent manner in AdCMV-GKL-treated cells. These results encourage testing whether delivery of glucokinase to muscle in vivo has an impact on glycemic control, which could be a method for circumventing the failure of insulin to stimulate glucose uptake and/or phosphorylation in muscle normally in insulin-resistant subjects.

Overexpression of glycogen phosphorylase increases GLUT4 expression and glucose transport in cultured skeletal human muscle.

Skeletal muscle glucose utilization, a major factor in the control of whole-body glucose tolerance, is modulated in accordance with the muscle metabolic demand. For instance, it is increased in chronic contraction or exercise training in association with elevated expression of GLUT4 and hexokinase II (HK-II). In this work, the contribution of increased metabolic flux to the regulation of the glucose transport capacity was analyzed in cultured human skeletal muscle engineered to overexpress glycogen phosphorylase (GP). Myocytes treated with an adenovirus-bearing muscle GP cDNA (AdCMV-MGP) expressed 10 times higher GP activity and exhibited a twofold increase in the Vmax for 2-deoxy-D-[3H]glucose (2-DG) uptake, with no effect on the apparent Km. The stimulatory effect of insulin on 2-DG uptake was also markedly enhanced in AdCMV-MGP-treated cells, which showed maximal insulin stimulation 2.8 times higher than control cells. No changes in HKII total activity or the intracellular compartmentalization were found. GLUT4, protein, and mRNA were raised in AdCMV-MGP-treated cells, suggesting pretranslational activation. GLUT4 was immunodetected intracellularly with a perinuclear predominance. Culture in glucose-free or high-glucose medium did not alter GLUT4 protein content in either control cells or AdCMV-MGP-treated cells. Control and GP-overexpressing cells showed similar autoinhibition of glucose transport, although they appeared to differ in the mechanism(s) involved in this effect. Whereas GLUT1 protein increased in control cells when they were switched from a high-glucose to a glucose-free medium, GLUT1 remained unaltered in GP-expressing cells upon glucose deprivation. Therefore, the increased intracellular metabolic (glycogenolytic-glycolytic) flux that occurs in muscle cells overexpressing GP causes an increase in GLUT4 expression and enhances basal and insulin-stimulated glucose transport, without significant changes in the autoinhibition of glucose transport. This mechanism of regulation may be operative in the postexercise situation in which GLUT4 expression is upregulated in coordination with increased glycolytic flux and energy demand.