Mechanisms and clinical effects of thiazolidinediones.

Studies of pioglitazone, troglitazone, BRL 49653 and other thiazolidinediones in preclinical animal models of non-insulin dependent diabetes mellitus (NIDDM) and obesity led to the observation that these compounds were effective in reducing hyperglycaemia and hyperlipidaemia. In these models, animals treated with thiazolidinediones had notable improvements in blood glucose levels, hepatic glucose output, peripheral insulin resistance, and serum lipid levels. Mechanistic studies indicate that thiazolidinediones act at many intracellular sites and can influence several processes to increase cell sensitivity to insulin. These include influence on insulin receptor kinase activity, control of insulin receptor phosphorylation, change in number of insulin receptors, quantity and activity of GLUT-4, modulation of tumour necrosis factor (TNF) activity, activation of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) and alteration of hepatic glucose metabolism. Available data on pioglitazone and troglitazone from clinical studies support the efficacy and safety of this class of compounds in reducing hyperglycaemia, hypertriglyceridaemia and insulin resistance associated with NIDDM. Currently, only troglitazone is approved for use in the United States and only in combination with insulin. This new pharmacological class of drugs has great promise for the treatment of NIDDM and also as a valuable research tool to further the understanding of the mechanisms that underlie NIDDM and insulin resistance syndrome.

Regulation of synovial cell growth. Coexpression of transforming growth factor beta and basic fibroblast growth factor by cultured synovial cells.

OBJECTIVE: To demonstrate expression of transforming growth factor beta (TGF beta) and basic fibroblast growth factor (bFGF) by cultured rheumatoid arthritis (RA) synovial cells and to investigate their role as synovial cell mitogens. METHODS: Polypeptide growth factors were detected and identified by immunocytochemical staining and Western blot analysis. Messenger RNA (mRNA) transcripts encoding TGF beta and bFGF were identified by polymerase chain reaction analysis. The influence of neutralizing growth factor monoclonal antibodies (MAb) on RA synovial cell growth was investigated. TGF beta bioactivity was determined by Mv1Lu assay. RESULTS: Lysates of RA, as compared with normal, synovial cells contained greater amounts of TGF beta and bFGF. Western blot analysis identified a single TGF beta band (MW approximately 25 kd) in each of the cell lysates examined. Western blot analysis using MAb DE6 identified a doublet of bFGF bands (MW approximately 18.0 kd) in normal synovial cell lysates and 4 bFGF bands (MW approximately 18.0, 22.0, 22.6, and 25.2 kd) in RA synovial cell lysates. RA and normal synovial cells expressed mRNA transcripts encoding TGF beta 1 but not TGF beta 2, and FGF-2 (basic FGF). Additional mRNA transcripts encoding FGF-5 and FGF-7 were expressed by RA, but not normal, synovial cells in culture. In contrast to MAb 1D11.16, which caused a dose-dependent decrease in RA synovial cell growth, MAb DG2 (up to 100 micrograms/ml) had no effect on cell growth. CONCLUSION: RA and normal synovial cells cultured in serum-free medium express TGF beta 1 and native bFGF. However, only RA synovial cells in culture express higher molecular weight isoforms of bFGF. TGF beta 1 appears to regulate synovial cell growth in vitro through an external autocrine loop. Despite expression of high-affinity bFGF receptors on cultured synovial cells, the mechanisms by which bFGF modulates synovial cell growth are unknown.

Regulation of synovial cell growth: basic fibroblast growth factor synergizes with interleukin 1 beta stimulating phospholipase A2 enzyme activity, phospholipase A2 activating protein production and release of prostaglandin E2 by rheumatoid arthritis synovial cells in culture.

Cytokines have been implicated in the regulation of eicosanoid synthesis and synovial cell proliferation. To further define these mechanisms, we have compared the effects of basic fibroblast growth factor and platelet-derived growth factor on cell growth, prostaglandin E2 (PGE2) production and phospholipase A2 enzyme activity in long-term cultures of synovial cells from rheumatoid arthritis (RA) patients capable of proliferating in serum-free medium. Compared with serum-free medium alone, RA synovial cell growth was significantly enhanced by adding either basic fibroblast growth factor (bFGF) or platelet-derived growth factor (PDGF) to the culture medium. Growing RA synovial cells for 14 days in serum-free medium plus bFGF caused them to spontaneously release significant amounts of PGE2, an effect not seen if cells were grown in serum-free medium alone, or serum-free medium plus PDGF. Enhanced release of PGE2 occurred when arachidonic acid was added to bFGF but not PDGF-treated RA synovial cells, suggesting that bFGF increased cyclooxygenase enzyme activity in these cells. Moreover, phospholipase A2 (PLA2) enzyme activity was found to be significantly greater in RA synovial cells grown for 14 days in serum-free medium containing bFGF alone, or bFGF plus interleukin 1 beta (IL-1 beta) compared with cells grown in either serum-free medium alone, or serum-free medium plus PDGF. Similarly, bFGF plus IL-1 beta-stimulated release of PLA2 activating protein, a novel mammalian phospholipase stimulator found in high concentrations in RA synovial fluid.(ABSTRACT TRUNCATED AT 250 WORDS)

Polypeptide growth factors augment interleukin 1-induced release of prostaglandin E2 by rheumatoid arthritis synovial cells in vitro.

When stimulated with increasing amounts of interleukin 1 beta (IL 1 beta) rheumatoid arthritis (RA), as compared with osteoarthritis (OA), synovial cells grown in RPMI plus fetal bovine serum (FBS), released significantly more prostaglandin E2 (PGE2) (p less than 0.05; paired t test, two-tailed). PGE2 release by IL 1 beta-stimulated RA synovial cells grown for 14 days in serum-free RPMI was significantly less than that released by the same cells grown in medium plus 10% FBS (p less than 0.03; two-tailed). Since these data suggest that growth factors present in FBS may augment the effects of IL 1 beta, experiments were conducted to study the influence of four polypeptide growth factors--transforming growth factor-beta (TGF-beta), platelet-derived growth factor (PDGF), epidermal growth factor (EGF), and basic fibroblast growth factor (bFGF), on IL 1 beta-induced release of PGE2 by cultured RA synovial cells. Both EGF and bFGF significantly enhanced IL 1 beta-induced release of PGE2 (p less than 0.05; paired t test, one-tailed), while PDGF was synergistic with IL 1 beta, significantly increasing release of PGE2 by these cultured cells (p less than 0.02; two-tailed). No such effect was seen when TGF-beta was added to the culture medium. Taken together, these data lend support to the concept that within the synovial micro-environment small quantities of individual growth factors may potentiate the effects of IL 1 beta to amplify intra-articular inflammation.

Autocrine regulation of rheumatoid arthritis synovial cell growth in vitro.

Rheumatoid arthritis (RA), and not osteoarthritis (OA) synovial cells proliferate in serum-free medium, a finding that suggests that, in vitro, RA synovial cells may be stimulated to grow by the continuous autocrine production of at least one polypeptide growth factor. Adding monoclonal antibody 1D11.16, or rabbit polyclonal anti-tumor growth factor beta (anti-TGF-beta) antibodies (both neutralizing antibodies to TGF-beta 1 and TGF-beta 2) to RA synovial cells, in culture, caused a significant reduction in cell growth, an effect not seen when other growth factor antibodies (platelet-derived growth factor [PDGF], epidermal growth factor [EGF], or EGF receptor) were added to the culture medium. Taken together, these data are consistent with the concept that RA synovial cell growth in vitro is driven endogenous TGF-beta. Moreover, when EGF was added to the culture medium, this caused the numbers of RA, and not OA, synovial cells to increase significantly. This finding suggests that RA synovial cells are in G1 phase of the cell cycle; an effect that could be mediated by endogenous TGF-beta.

Allylamine-induced vascular toxicity in vitro: prevention by semicarbazide-sensitive amine oxidase inhibitors.

The present studies were designed to evaluate the role that metabolic activation plays in allylamine (AAM)-induced vascular toxicity. The effects of AAM were evaluated in primary cultures of rat vascular endothelial (VEC) and smooth muscle cells (SMC). Semicarbazide (SC) and diethyldithiocarbamate (DDC) were used as inhibitors of semicarbazide-sensitive amine oxidase (SSAO). Clorgyline and pargyline were used as inhibitors of monoamine oxidase (MAO) A and B, respectively. The effect of catalase, a hydrogen peroxide scavenger, on AAM-induced cytotoxicity was also evaluated. Lactate dehydrogenase (LDH) release and morphological alterations were chosen as indicators of cytotoxicity. Confluent cultures of VEC and SMC were exposed to various concentrations of AAM (2-200 microM) in the absence and presence of serum for 4, 12, or 24 hr. High concentrations of AAM (200 microM) alone produced a time-dependent increase in LDH release and morphologic alterations in cultures of both cell types. Lower concentrations of AAM did not compromise the structural integrity of the cells. Semicarbazide (200 microM) or DDC (2 mM), but not clorgyline (10 microM) or pargyline (10 microM), prevented the toxicity of AAM (200 microM). Allylamine-induced cytotoxicity was partially prevented by catalase (2500 U/ml). The presence of fetal bovine serum in the medium was not essential for the manifestation of cytotoxicity. Single cell suspensions of VEC or SMC formed acrolein (ACR) when incubated in the presence of AAM. The formation of ACR mediated by SMC was inhibited by SC (20 microM), but not clorgyline (10 microM). These results support the concept that AAM is oxidatively deaminated by an SSAO present in vascular cells to generate toxic metabolic by-products capable of causing extensive cellular injury.