Leukotrienes: clinical significance

Recent insights into the causes of chronic leg ulceration in venous diseases and implications on other types of chronic wounds

Venous ulceration represents the most prevalent form of difficult-to-heal wounds and these problematic wounds require a significant amount of healthcare resources for their treatment. In order to develop effective treatment regimens a clearer understanding of the underlying pathological processes that lead to skin breakdown is required. However, to date, most of these studies have tended to focus on describing the pathology of already-established ulcers. By bringing together relevant aspects of diverse disciplines such as inflammation, cardiovascular, and connective tissue biology, we aim to provide an insight into how circulatory abnormalities that are caused by the underlying disease etiology can induce local tissue inflammation resulting in tissue breakdown. Initially this results in internal tissue damage but if the underlying disease is not treated, the internal tissue damage can worsen and lead to open ulceration. This article discusses the cause-and-effect relationships between chronic venous insufficiency and venous ulceration, focusing particularly on the biological processes that lead from the underlying disease condition to overt ulceration. Available evidence also suggests that formation of pressure, diabetic foot and arterial ulcers, and ulcers as results of blood disorders, is also likely to share some of the same biological processes as venous ulcers.

Dihomo-gamma-linolenic acid inhibits tumour necrosis factor-alpha production by human leucocytes independently of cyclooxygenase activity

Dietary oils (such as borage oil), which are rich in gamma-linolenic acid (GLA), have been shown to be beneficial under inflammatory conditions. Dihomo-GLA (DGLA) is synthesized directly from GLA and forms a substrate for cyclooxygenase (COX) enzymes, resulting in the synthesis of lipid mediators (eicosanoids). In the present study, the immunomodulatory effects of DGLA were investigated and compared with those of other relevant fatty acids. Freshly isolated human peripheral blood mononuclear cells (PBMC) were cultured in fatty acid (100 microm)-enriched medium for 48 hr. Subsequently, cells were stimulated with lipopolysaccharide (LPS) for 20 hr and the cytokine levels were measured, in supernatants, by enzyme-linked immunosorbent assay (ELISA). Phospholipids were analysed by gas chromatography. Fatty acids were readily taken up, metabolized and incorporated into cellular phospholipids. Compared with the other fatty acids tested, DGLA exerted pronounced modulatory effects on cytokine production. Tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-10 levels were reduced to 60% of control levels, whereas IL-6 levels were not affected by DGLA. Kinetic studies showed that peak levels of TNF-alpha, occurring early after LPS addition, were inhibited strongly, whereas IL-10 levels were not affected until 15 hr after stimulation. Both the reduction of cytokine levels and the decrease in arachidonic acid levels in these cells, induced by DGLA, were dose dependent, suggesting a shift in eicosanoid-subtype synthesis. However, although some DGLA-derived eicosanoids similarly reduced TNF-alpha levels, the effects of DGLA were probably not mediated by COX products, as the addition of indomethacin did not alter the effects of DGLA. In conclusion, these results suggest that DGLA affects cytokine production by human PBMC independently of COX activation.

Effects of arachidonic acid metabolites in a murine model of squamous cell carcinoma

BACKGROUND

A murine model (C3H mice) of squamous cell carcinoma (SCCVII) has been used to investigate the role of arachidonic acid (AA) metabolites in head and neck cancer. Inhibition of tumor growth by cyclooxygenase (COX) and lipoxygenase (LOX) inhibitors of AA metabolism has been associated with changes in levels of AA metabolites in tumor tissues and inflammatory cell infiltrates. To characterize this model further, the effects of exogenous AA metabolites on tumor growth in vitro and in vivo were investigated.

METHODS

Following subcutaneous inoculation with SCCVII tumor cells, control (16 mice) and treatment (24 mice) groups were injected with peritumoral vehicle or AA metabolite. Peritumoral injections of prostaglandin E2 (PGE2), leukotriene B4 (LTB4), and 12-hydroxyeicosatetraenoic acid (12-HETE) were performed for 16-21 days, and final excised tumor weights were measured. In vitro production of PGE2 and LTB4 was assayed in 2-5 day cultures of SCCVII. Exogenous PGE2 effects on tumor cell growth was assessed with the MTT assay in vitro.

RESULTS

Tumor growth was significantly inhibited (p =.03) following peritumoral injection of PGE2. Final tumor weights were not affected by LTB4 or 12-HETE. Tumor inhibition by PGE2 was associated with increased tumor tissue levels of LTB4 (p =.04). In vitro, SCCVII produced minimal amounts of PGE2 and LTB4, and PGE2 had minimal effect on growth.

CONCLUSIONS

In this model, tumor inhibition by exogenous PGE2 is primarily mediated by affecting host-tumor interactions, although there may be some direct effect on tumor cells. Changes in tumor tissue levels of LTB4 following peritumoral PGE2 administration may be attributable to negative feedback inhibition of the COX pathway with shunting into the LOX pathway. SCCVII cells are probably not a significant source of prostaglandins and leukotrienes in vivo. These data provide insight into the mechanism of action of inhibitors of AA metabolism on tumor growth.

Antiinflammatory effect of tepoxalin: blood and synovial tissue studied in patients with knee arthrosis

Our aim was to determine the amounts of eicosanoids in blood and synovial tissue of patients with knee arthrosis and to examine the effects of 2 doses of tepoxalin (50 mg twice, 200 mg twice), administered p.o. for 3.5 days. Concentrations of leukotriene B4 (LTB4, LTC4, and thromboxane B2 (TXB2) were measured in blood before and after oral administration of tepoxalin and release of prostaglandin E2 (PGE2), 6-keto-PGF1alpha, and LTC4 was measured in incubation media of synovial tissue, taken at surgery from patients treated with tepoxalin. Radioimmunoassay (RIA) was used to determine the levels of the eicosanoids. LT and TXB2 release was reduced by tepoxalin in both doses used. Under these conditions, PGE2, 6-keto-PGF1alpha, and LTC4 release from synovial tissue was detectable only after stimulation with calcium ionophore A23187. Washed synovial tissue, in which tepoxalin concentrations should be reduced, released higher amounts of all eicosanoids measured than directly incubated synovial tissue did. Pain after tepoxalin administration was significantly reduced. Relevant drug concentrations were detected in plasma and synovial fluid. Tepoxalin was well tolerated and had no marked adverse effects. At 400 mg, tepoxalin is a dual inhibitor of cyclooxygenase (CO) and 5-lipoxygenase (5-LO) in blood and synovial tissue.

Role of arachidonic acid metabolites in tumor growth inhibition by nonsteroidal antiinflammatory drugs

PURPOSE

A murine model of squamous cell carcinoma (SCC) was used to determine the role of arachidonic acid (AA) metabolites in the growth of SCC of the head and neck.

MATERIALS AND METHODS

C3H/HeJ mice bearing SCC (SCC VII) were treated with cyclooxygenase inhibitors (piroxicam and nabumetone) or a 5-lipoxygenase inhibitor (ketoconazole). Growth curves were established, and final tumor weights were measured. Following sacrifice, tumor tissue homogenates were assayed for prostaglandin E2 (PGE2) and 12-hydroxyeicosatetraenoic acid (12-HETE) by enzyme-linked immunosorbent assay (ELISA), and leukotriene B4 (LTB4) by radioimmunoassay (RIA). Inflammatory cell infiltrate was assessed histologically.

RESULTS

A significant inhibition of tumor growth (P = .001) and final tumor weight (P = .002) was noted in mice treated with piroxicam and nabumetone. Inhibition of tumor growth was associated with increased tumor tissue levels of PGE2 (P = .04) and lymphocytic infiltration (P = .07). Significant inhibition of tumor growth (P = .002) and final tumor weight (P = .05) was also noted in mice treated with ketoconazole.

CONCLUSION

These data suggest that both cyclooxygenase and lipoxygenase metabolites of AA affect tumor growth in this model and that inhibition of tumor growth by inhibitors of AA metabolism may be caused by an enhanced inflammatory cell response at the tumor site.

Pharmacokinetics and pharmacodynamics of tepoxalin after single oral dose administration to healthy volunteers

This study was conducted to examine the pharmacokinetics and pharmacodynamics of tepoxalin in healthy volunteers, an antiinflammatory compound that inhibits cyclooxygenase and lipoxygenase. Tepoxalin was absorbed after oral administration of single doses from 35 to 300 mg, after which it was rapidly converted to an acidic metabolite, RWJ 20142, which inhibits cyclooxygenase but not lipoxygenase. The areas under the concentration-time curve (AUC) of tepoxalin and RWJ 20142 in plasma increased in a dose-dependent fashion. Administration of the lowest dose of tepoxalin completely inhibited whole blood cyclooxygenase for the entire period of observation. This inhibition correlated closely with that of secretion and aggregation induced by collagen of platelets obtained from these subjects. Similarly, administration of tepoxalin was associated with significant inhibition of lipoxygenase in whole blood. Lipoxygenase was inhibited a maximum of 60% in a time-dependent fashion, and the duration of inhibition was dose-dependent. These studies demonstrate that tepoxalin inhibits whole blood cyclooxygenase, lipoxygenase, and platelet function after oral administration in humans.

Prognostic significance of prostaglandin E2 production by mononuclear cells and tumor cells in squamous cell carcinomas of the head and neck

Prostaglandin E2 (PGE2) has been implicated as a cause of immunosuppression in patients with head and neck cancer. To determine the relative contribution of tumor cells and mononuclear cells to PGE2 levels in vivo, tumor cells and tumor-infiltrating mononuclear cells (TIMC) were isolated from fresh tumor biopsy specimens of 23 patients with squamous cell carcinoma of the head and neck (SCCHN) by using enzymatic digestion and differential gradient centrifugation. Peripheral blood mononuclear cells (PBMC) and lymph node mononuclear cells (LNMC) from metastatic and nonmetastatic lymph nodes were also isolated. Cell fractions were cultured for 24 hours, and PGE2 levels of supernatant were determined by radioimmunoassay. PGE2 production by LNMC was significantly decreased compared to tumor cells, TIMC, and PBMC (P = .0002). LNMC from metastatic lymph nodes produced significantly higher levels of PGE2 (P = .02) compared to nonmetastatic lymph nodes. Although T stage was not correlated with PGE2 production by TIMC or tumor cells, advanced N stage (N1-3) was associated with decreased PGE2 production by TIMC (P = .006). These results suggest that both tumor cells and TIMC are sources of PGE2 in tumor tissues of patients with SCCHN and that decreased PGE2 production by host inflammatory cells may have clinical significance in the development of cervical metastases.

Psoriasis and drugs: influence of tetracyclines on the course of psoriasis

Patients with psoriasis vulgaris (462) were studied by questionnaire to find the effect on psoriasis of drug therapy for intercurrent diseases or focal infections. Of 462 patients with psoriasis, in 76 (16.45%) the disease became more severe during drug therapy. Of these, 19 worsened after administration of tetracyclines, and in five psoriasis was precipitated after therapy with drugs of the tetracycline family. We suggest that tetracyclines should be avoided in patients with psoriasis and in healthy persons with a genetic predisposition (positive family history, human leukocyte antigens B13, B17, B27).

Basic mechanisms in the healing cutaneous wound

The process of wound healing can be divided into substrate, proliferative, and remodeling phases. The basic biologic and physiologic events which transpire during these stages are examined in detail. Particular emphasis is placed on the interactions between platelets, macrophages, and other inflammatory cells, and fibroblasts in the healing wound. Recent advances in the roles played by interleukins, fibronectin, and epidermal growth factor are discussed.

Topical application of nonsteroidal anti-inflammatory drugs prevents vehicle-induced improvement of psoriasis

In a double-blind fashion, we compared the effect of topical application of 1% indomethacin cream or 1% meclofenamate cream with the effect of vehicle therapy alone in thirty patients with psoriasis. After 4 weeks' treatment of bilaterally symmetric psoriatic plaques, the indomethacin-treated sides were worse than the vehicle-treated sides in fourteen of twenty patients (p less than 0.01); the meclofenamate-treated sides were worse than the vehicle-treated sides in seven of ten patients (p less than 0.05). We suspect that the nonsteroidal anti-inflammatory drugs contributed to the maintenance of our patients' psoriasis by altering the arachidonic acid transformation cascade.