The role of tumor necrosis factor in health and disease.

The vast and growing array of cytokines is the subject of intense research for their potential to ameliorate a range of diseases that extends from autoimmune disorders to cancer and beyond. Among the cytokines, tumor necrosis factor-alpha (TNF-alpha) has proven to be a key ligand in triggering many intracellular processes, both physiological and pathological. Understanding its role in rheumatoid arthritis and Crohn's disease has produced effective new therapeutic agents, and there is reason to expect greater success as research proceeds. New synthetic macromolecules are effectively interfering with TNF and other ligands at and before the cellular membrane interface. This article reviews current knowledge of the molecular mechanics of TNF and the therapeutic inhibition of TNF action. Unraveling these processes has led to many insights into cytokine physiology and pathology.

Hypothalamic action of cachectin to alter pituitary hormone release.

Cachectin (tumor necrosis factor, TNF) is a macrophage hormone which is released during infection and after injection of bacterial lipopolysaccharides. We have already demonstrated that the peptide has direct action on the pituitary to alter pituitary hormone release in vitro. To evaluate its action in vivo, we injected it into the third ventricle (3V) of conscious, male rats and measured its effect on various anterior pituitary hormones. The peptide produced an elevation in rectal temperature measurable on first measurement at 1 hour postinjection which was maintained for 3 hours. The maximal increase in body temperature was 1-1.5 degrees C and maximal effect was obtained by a dose as low as 1 ng (0.3 pmol) of the peptide. Preinjection of indomethacin into the 3V 1 hour prior to injection of TNF completely blocked the effect on body temperature without producing an alteration in rectal temperature itself which suggests that the elevation in body temperature may be mediated by prostaglandins. Following the intraventricular injection of various doses of TNF, there was no significant effect on plasma adrenocorticotropin (ACTH) except with the highest, 100 ng dose tested, which evoked a small but significant increase in plasma ACTH with a delay of 1 to 2 hours. Thus, the dose necessary to release ACTH was much higher than that required to elevate body temperature. The effect was no longer significant in indomethacin-pretreated animals suggesting a role for prostaglandins in the effect. This highest dose of intraventricularly administered TNF also produced a relatively modest, but significant, delayed increase in plasma GH.(ABSTRACT TRUNCATED AT 250 WORDS)

Cachectin/tumor necrosis factor: production, distribution, and metabolic fate in vivo.

A highly specific radioreceptor assay for cachectin/tumor necrosis factor (TNF) was utilized to measure the time course of lipopolysaccharide (LPS)-induced hormone production in rabbits. Cachectin/TNF bioactivity was monitored in the same serum samples by measuring lipoprotein lipase (LPL) suppression in 3T3-L1 cells. Cachectin/TNF is produced in large quantities by LPS-treated rabbits without priming by bacillus Calmette Guérin, C. parvum, or other agents. Nanomolar concentrations of the hormone are achieved, with peak levels occurring at 2 hr postinjection; the hormone is rapidly cleared thereafter. In separate studies, mice were used to assess the distribution and metabolic fate of cachectin/TNF. Radioiodinated hormone is cleared from the plasma with a half-life of 6 to 7 min. Studies of the tissue distribution of label after injection demonstrate that liver, kidneys, skin, and gastrointestinal tract take up most of the hormone. Electrophoretic analysis of tissues recovered from injected animals suggests that the hormone is very rapidly degraded after binding.

Recombinant interleukin 1 suppresses lipoprotein lipase activity in 3T3-L1 cells.

Recombinant murine interleukin 1 (rIL 1) inhibits 3T3-L1 cell expression of lipoprotein lipase (LPL) activity when present in exceedingly dilute concentration (less than 10(-15) M). The extreme sensitivity of the adipocyte system to rIL 1 far exceeds that of the standard lymphocyte-activating factor assay. However, enzyme suppression is incomplete; even at micromolar concentrations, rIL 1 causes only about a 50% reduction in LPL activity. By contrast, cachectin (tumor necrosis factor) achieves nearly complete LPL suppression at subnanomolar concentrations. Concentrated solutions of rIL 1 are incapable of competing with radiolabeled cachectin for binding sites on 3T3-L1 cells. rIL 1-induced LPL suppression is abolished by the addition of a specific IL 1 neutralizing antiserum to the assay system. rIL 1 appears capable of influencing adipocyte expression of LPL, but apparently acts through a different mechanism than cachectin/TNF.

Lipopolysaccharide-treated RAW 264.7 cells produce a mediator that inhibits lipoprotein lipase in 3T3-L1 cells.

RAW 264.7 cells upon stimulation with lipopolysaccharide secrete a protein mediator(s) that suppresses lipoprotein lipase activity in differentiated 3T3-L1 cells. The mediator(s), which is absent from unstimulated culture supernatants, is nondialyzable and thermolabile. Preliminary characterization suggests that this mediator(s) may be the same as that previously found in medium from lipopolysaccharide-treated thioglycollate-elicited mouse peritoneal macrophage cultures.

A biochemically distinct sub-population of neurons in the human substantia gelatinosa. Study with G-6-PD histochemistry.

A method for localization of glucose-6-phosphate dehydrogenase (G-6-PD; D-glucose-6-phosphate: NADP+ oxidoreductase; E.C. 1.1.1.49) activity has been applied to human nervous tissue. Intensely staining cells, not definable by conventional histologic techniques, have been identified in the human spinal cord, with highest numbers present in the substantia gelatinosa of the sacral region. The cells have a neuron-like morphology and express neuronal-specific antigen but are heterogeneous in size and shape. They are not detectable in infant spinal cord, but stain heavily in adults. We propose that these cells are homologous to the G-6-PD-active dorsal medullary cells first noted by Sakharova et al. (1979) and together with the latter group, may comprise a hitherto unrecognized system of neurons in the human central nervous system.

The absence of unique kainic acid-like molecules in urine, serum, and CSF from Huntington's disease patients.

By means of a sensitive competition assay, serum, urine, and CSF from patients with Huntington's disease (HD) and controls were tested for the presence of molecules capable of displacing radioactive kainic acid (KA) from rat brain receptors. No difference was found between HD and control samples. It is unlikely that systemic production of an endogenous toxin structurally related to KA occurs in HD.