Endotoxin-based molecular strategies for the prevention and treatment of gram-negative sepsis and septic shock

Agonistic and antagonistic properties of a Rhizobium sin-1 lipid A modified by an ether-linked lipid

LPS from Rhizobium sin-1 (R. sin-1) can antagonize the production of tumor necrosis factor alpha (TNF-alpha) by E. coli LPS in human monocytic cells. Therefore these compounds provide interesting leads for the development of therapeutics for the prevention or treatment of septic shock. Detailed structure activity relationship studies have, however, been hampered by the propensity of these compounds to undergo beta-elimination to give biological inactive enone derivatives. To address this problem, we have chemically synthesized in a convergent manner a R. sin-1 lipid A derivative in which the beta-hydroxy ester at C-3 of the proximal sugar unit has been replaced by an ether linked moiety. As expected, this derivative exhibited a much-improved chemical stability. Furthermore, its ability to antagonize TNF-alpha production induced by enteric LPS was only slightly smaller than that of the parent ester modified derivative demonstrating that the ether-linked lipids affect biological activities only marginally. Furthermore, it has been shown for the first time that R. sin-1 LPS and the ether modified lipid A are also able to antagonize the production of the cytokine interferon-inducible protein 10, which arises from the TRIF-dependent pathway. The latter pathway was somewhat more potently inhibited than the MyD88-dependent pathway. Furthermore, it was observed that the natural LPS possesses much greater activity than the synthetic and isolated lipid As, which indicates that di-KDO moiety is important for optimal biological activity. It has also been found that isolated R. sin-1 LPS and lipid A agonize a mouse macrophage cell line to induce the production of TNF-alpha and interferon beta in a Toll-like receptor 4-dependent manner demonstrating species specific properties.

A novel lipid A fromHalomonas magadiensis inhibits enteric LPS-induced human monocyte activation

Lipopolysaccharide (LPS) endotoxin is the bacterial product responsible for the clinical syndrome of Gram-negative septicemia and endotoxic shock. During sepsis, microbial antigens, such as LPS, activate monocytes and macrophages to produce several pro-inflammatory cytokines, among which tumor necrosis factor-alpha (TNF-alpha) appears to be very important for the development of endotoxic shock. The endotoxic properties of LPS principally reside in the lipid A (LIP A) component, which is the primary immunostimulatory center of Gram-negative bacteria. In recent years there has been a continuous effort to identify molecules able to antagonize the deleterious effects of endotoxic shock. In this study we show that a novel LIP A fraction from the LPS of Halomonas magadiensis (Hm), a Gram-negative extremophilic and alkaliphilic bacterium, significantly inhibits the synthesis of TNF-alpha by human monocytes activated by Escherichia coli LPS. LIP A from Hm exerts these effects by interfering with E. coli LPS for activation of Toll-like receptor 4 expressed in human cells. This result defines Hm LIP A as a novel class of LPS antagonist whose structural features could be utilized for the design of compounds for the treatment of Gram-negative sepsis.

Flavonoids protect mice from two types of lethal shock induced by endotoxin

The protective effect of flavonoids on two types of lethal endotoxic shock was studied. A lethal endotoxic shock was induced by administration of lipopolysaccharide (LPS) into D-galactosamine (D-GalN)-sensitized mice and another one was done by administration of a high dose of LPS into normal mice. Pretreatment with a series of flavonoids protected mice from two types of endotoxin lethality. Flavonoid pretreatment reduced the serum tumor necrosis factor-alpha (TNF-alpha) level in mice injected with D-GalN and LPS, but not in mice injected with a high dose of LPS. TNF-alpha-induced lethal shock in D-GalN-sensitized mice was also protected by pretreatment with flavonoids, suggesting that flavonoids augmented the resistance to TNF-alpha lethality. On the other hand, flavonoids reduced the plasma level of lipid peroxides in mice injected with a high dose of LPS, but not in D-GalN-sensitized mice. Taken together, these results indicated that flavonoids might protect mice from two types of endotoxin lethality. The protective mechanism of flavonoids in each endotoxin lethality is discussed.

The role of the Th-1 to Th-2 shift of the cytokine profiles of CD4 helper cells in the pathogenesis of autoimmune and hypercatabolic diseases

The task of the immune system is the continuous elimination of endogenous cellular debris and the elimination, when necessary, of exogenous structures. It therefore seems useful and practical to add to the paradigms 'self' and 'not self' the term 'altered self'. The concept of stress, introduced by W. B. Cannon and H. Selye in the 1930s, covers the wide range of aggressive environmental influences which for their part result in a uniform shift of the metabolism in the direction of catabolism. This results from the activation of the neuroendocrine stress axis, hypothalamus-pituitary-adrenals, and causes an increased release of catecholamines and glucocorticoids. These latter substances limit life-threatening acute-phase reactions by endogenous inflammation mediators. The purpose of the shift of the cytokine profiles of the CD4 lymphocytes from Th-1 to Th-2 is, with the return of a raised cortisol level to normal values, to temporarily take over the anti-inflammatory functions of the cortisol. A sustained Th-2 shift is an expression of a persistent hypercortisolism in autoimmune states. The suppression of the anti-inflammatory effects of cortisol as a result of states of excessive stress leads to hypercatabolic diseases such as AIDS, sepsis and toxic shock syndrome and protein calorie malnutrition (NAIDS). In the prevention and treatment of AIDS and NAIDS, besides the elimination of the causes of stress, the prophylactic and therapeutic efforts are based mainly on the activation of the mesenchymal production of anabolic matrix components, mainly glycosaminoglycans, and the neutralization of O2 and NO radicals and inflammation mediators from macrophages by polyanions and polyphenols. In our opinion, in sepsis and toxic shock syndromes, lasting reduction of the mortality rates for these diseases is best achieved through the early administration of high intravenous doses of gammaglobulins.