Extra-pineal gland sources of melatonin

Dual sources of melatonin and evidence for different primary functions

This article discusses data showing that mammals, including humans, have two sources of melatonin that exhibit different functions. The best-known source of melatonin, herein referred to as Source #1, is the pineal gland. In this organ, melatonin production is circadian with maximal synthesis and release into the blood and cerebrospinal fluid occurring during the night. Of the total amount of melatonin produced in mammals, we speculate that less than 5% is synthesized by the pineal gland. The melatonin rhythm has the primary function of influencing the circadian clock at the level of the suprachiasmatic nucleus (the CSF melatonin) and the clockwork in all peripheral organs (the blood melatonin) via receptor-mediated actions. A second source of melatonin (Source # 2) is from multiple tissues throughout the body, probably being synthesized in the mitochondria of these cells. This constitutes the bulk of the melatonin produced in mammals and is concerned with metabolic regulation. This review emphasizes the action of melatonin from peripheral sources in determining re-dox homeostasis, but it has other critical metabolic effects as well. Extrapineal melatonin synthesis does not exhibit a circadian rhythm and it is not released into the blood but acts locally in its cell of origin and possibly in a paracrine matter on adjacent cells. The factors that control/influence melatonin synthesis at extrapineal sites are unknown. We propose that the concentration of melatonin in these cells is determined by the subcellular redox state and that melatonin synthesis may be inducible under stressful conditions as in plant cells.

Inflammatory liver diseases and susceptibility to sepsis

Patients with inflammatory liver diseases, particularly alcohol-associated liver disease and metabolic dysfunction-associated fatty liver disease (MAFLD), have higher incidence of infections and mortality rate due to sepsis. The current focus in the development of drugs for MAFLD is the resolution of non-alcoholic steatohepatitis and prevention of progression to cirrhosis. In patients with cirrhosis or alcoholic hepatitis, sepsis is a major cause of death. As the metabolic center and a key immune tissue, liver is the guardian, modifier, and target of sepsis. Septic patients with liver dysfunction have the highest mortality rate compared with other organ dysfunctions. In addition to maintaining metabolic homeostasis, the liver produces and secretes hepatokines and acute phase proteins (APPs) essential in tissue protection, immunomodulation, and coagulation. Inflammatory liver diseases cause profound metabolic disorder and impairment of energy metabolism, liver regeneration, and production/secretion of APPs and hepatokines. Herein, the author reviews the roles of (1) disorders in the metabolism of glucose, fatty acids, ketone bodies, and amino acids as well as the clearance of ammonia and lactate in the pathogenesis of inflammatory liver diseases and sepsis; (2) cytokines/chemokines in inflammatory liver diseases and sepsis; (3) APPs and hepatokines in the protection against tissue injury and infections; and (4) major nuclear receptors/signaling pathways underlying the metabolic disorders and tissue injuries as well as the major drug targets for inflammatory liver diseases and sepsis. Approaches that focus on the liver dysfunction and regeneration will not only treat inflammatory liver diseases but also prevent the development of severe infections and sepsis.

Complement levels in patients with bloodstream infection due to Staphylococcus aureus or Gram-negative bacteria

The complement system is a vital component of the innate immune system, though its role in bacteremia is poorly understood. We present complement levels in Staphylococcus aureus bacteremia (SAB) and Gram-negative bacteremia (GNB) and describe observed associations of complement levels with clinical outcomes. Complement and cytokine levels were measured in serum samples from 20 hospitalized patients with SAB, 20 hospitalized patients with GNB, 10 non-infected hospitalized patients, and 10 community controls. C5a levels were significantly higher in patients with SAB as compared to patients with GNB. Low C4 and C3 levels were associated with septic shock and 30-day mortality in patients with GNB, and elevated C3 was associated with a desirable outcome defined as absence of (1) septic shock, (2) acute renal failure, and (3) death within 30 days of bacteremia. Low levels of C9 were associated with septic shock in patients with GNB but not SAB. Elevated IL-10 was associated with increased 30-day mortality in patients with SAB. Complement profiles differ in patients with SAB and those with GNB. Measurement of IL-10 in patients with SAB and of C4, C3, and C9 in patients with GNB may help to identify those at higher risk for poor outcomes.

Off to a slow start: under-development of the complement system in term newborns is more substantial following premature birth

Complement represents a keystone to the innate immune system, with three activation pathways that utilise foreign microbial pattern recognition as well as activation by the host's specific antibodies. However, innate immunity is not synonymous with neonatal immunity. The complement system in healthy term (38-42 weeks gestation) newborns is under-developed and, with only a few exceptions (e.g. C7 and factor D), the circulating complement component concentrations are between 10 and 80% of adult levels. Complement activation is tightly regulated and the circulating regulator levels are also low relative to adults, sometimes at almost undetectable levels (e.g. C4b-binding protein). For premature newborns, these relative deficiencies are even more marked. Newborns are known to be more susceptible to infection, and the importance of complement, not only through its decreased ability to directly lyse bacteria with the common terminal pathway, but also its reduced ability to recruit (chemotaxis) innate and adaptive leukocytes to sites of microbial invasion and reduced ability to enhance phagocytosis (opsonisation) will be discussed. Complement also holds a key role in enhancing and directing refinement of the specific antibody response to pathogens (as an adjuvant) that likely plays a role in the well-known under-performance of the humoral immune response in newborns.

The sensitivity ofEscherichia coli strains with K1 surface antigen and rods without this antigen to the bactericidal effect of serum

The susceptibility of Escherichia coli strains with K1 surface antigen (K1+) and rods without this antigen (K1-) to the bactericidal action of normal bovine serum and human normal cord serum was determined. Seventy E. coli strains (35 K1+ and 35 K1-) were isolated from urine obtained from children with urinary tract infections. The strains investigated showed variable sensitivity to the bactericidal action of the sera. E. coli K1+ strains were characterized by lower sensitivity to bactericidal effect of the sera in comparison with K1- rods. The role of the particular mechanisms of complement activation in the process of killing of the E. coli strains was also determined.

Effects of endotoxin administration and cerebral hypoxia-ischemia on complement activity and local transcriptional regulation in neonatal rats

It is not known whether up-regulation of complement components, either circulating or locally synthesized, contributes to an increased susceptibility to neonatal hypoxic-ischemic (HI) cerebral injury. Therefore, we tested the hypothesis that in neonatal rats subjected to a unilateral HI cerebral insult, prior administration of E. coli lipopolysaccharide (LPS) augments (1) complement-mediated serum hemolytic activity, and (2) C3 mRNA and C9 mRNA levels in hepatic and cerebral tissue. Pregnant rats were injected subcutaneously with sterile normal saline (NS) or 500 microg/kg of LPS on gestational days 18 and 19. Following birth, the pups received intraperitoneal injections of NS or 250 microg/kg of LPS on postnatal days 3 and 5. On postnatal day 7, each animal was subjected to ligation of the right common carotid artery followed by 2.5h of hypoxia (8% O(2)). At 3, 6,18, 24 and 48 h after hypoxia, the complement-mediated hemolytic activity of pooled serum was measured. Hepatic and cerebral C3 mRNA and C9 mRNA were quantified by qRT-PCR at 3, 6, and 18 h after HI. Serum hemolytic activity, hepatic C3 mRNA, and hepatic C9 mRNA were up-regulated after cerebral HI. LPS administration potentiated the effect of HI on serum hemolytic activity and increased cerebral C3 mRNA levels. Cerebral C9 mRNA was not detected and was not affected by HI, with or without the prior LPS administration. These observations support the theory that previously reported C9-mediated neurotoxicity following cerebral HI is induced by circulating, rather than locally synthesized C9.

The role of complement in neonatal hypoxic-ischemic cerebral injury

Complement activation participates in tissue injury after temporary loss of blood flow (ischemia-reperfusion injury). Recently reported evidence indicates that complement activation is a pathologic mechanism of injury in the post-hypoxic-ischemic neonatal brain. Therefore, recently developed complement inhibitors may find a role in the amelioration of neonatal hypoxic-ischemic cerebral injury. Further research is needed to better define the role of complement in human neonatal cerebral injury and to determine the neuroprotective effect and safety of pharmacologic agents designed to inhibit complement.

[Virulence factors associated with E. coli neonatal meningitis]

Escherichia coli K1 is the leading cause of gram-negative bacterial meningitis in neonates. It is associated with a mortality rate as high as 40%, and more than half of the survivors have neurologic sequelae. Bacterial meningitis is the result of bacterial translocation from gastrointestinal tract to the blood and from blood to the central nervous system. Successful crossing of the BBB by E. coli K1 requires (a) a high degree of bacteremia and (b) several E. coli determinants contributing to invasion of BMEC such as the K1 capsule, Sfa, Ibe proteins, and CNF1. A better understanding for the molecular basis of E. coli K1 penetration of the BBB could potentially lead to the development of novel therapeutic and preventative strategies for E. coli K1 meningitis.

Molecular aspects of complement-mediated bacterial killing. Periplasmic conversion of C9 from a protoxin to a toxin

As part of the membrane attack complex complement protein C9 is responsible for direct killing of bacteria. Here we show that in the periplasmic space of an Escherichia coli cell C9 is converted from a protoxin to a toxin by periplasmic conditions missing in spheroplasts. This conversion is independent of the pathway by which C9 enters the periplasm. Both, C9 shocked into the periplasm and plasmid-expressed C9 targeted to the periplasm via a signal sequence are toxic. Toxicity requires disulfide-linked C9 because export into the periplasm of cells defective in disulfide bond synthesis (dsbA and dsbB mutants) is not toxic unless N-acetylcysteine is added externally to promote cystines. A N-terminal fragment, C9[1-144], is not toxic nor is cytoplasmically expressed C9, even in trxB mutants that are able to form disulfide bonds in the cytoplasm. Importantly, expression of full-length C9 in complement-resistant cells has no effect on their viability. Expression and translocation into the periplasm may provide a novel model to identify molecular mechanisms of other bactericidal disulfide-linked proteins and to investigate the nature of bacterial complement resistance.

Complement component C9 enhances the capacity of beta-lactam antibiotics to kill Escherichia coli in vitro and in vivo

Complement component C9 is required for rapid complement-mediated killing of Escherichia coli. In this report, the influence of supplemental C9 on the bactericidal and protective effects of beta-lactam antibiotics in neonates was assessed. By rocket immunoelectrophoresis, the intrinsic C9 concentrations of pooled serum from both human and rat neonates was less than 20% of adult levels. Supplemental C9 purified from human plasma enhanced the capacity of ampicillin-treated serum from human neonates to impair the survival of E coli O7:K1:NM (P < 0.02). Similarly, supplemental C9 enhanced the capacity of cefotaxime-treated neonatal rat serum to impair the survival of E coli O1:K1:NM (P < 0.05). Moreover, the intraperitoneal administration of C9 enhanced the survival of cefotaxime-treated neonatal rats that were septic with E coli (P < 0.05). These observations may contribute to the development of new strategies, such as augmentation of complement component serum concentrations, to reduce the morbidity and mortality of neonatal E coli sepsis.

The administration of complement component C9 enhances the survival of neonatal rats with Escherichia coli sepsis

To determine the significance of neonatal C9 deficiency, an animal model was developed in the rat. By rocket immunoelectrophoresis, the concentration of C9 in pooled adult rat serum was 224 +/- 7.2 microg/mL. In contrast, the concentration of C9 in pooled serum from 1-d-old rats was only 43 +/- 3.8 microg/mL and increased during the first 3 wk of life to 170 +/- 20 microg/mL. Similarly, the capacities of neonatal rat serum to kill two pathogenic strains of Escherichia coli and to lyse sensitized sheep erythrocytes were diminished compared with adult serum but increased during the first 3 wk of life. Supplemental human C9 significantly enhanced the bactericidal and hemolytic activity of neonatal rat serum. The capacity of neonatal rats to survive after the intrapulmonary injection of E. coli was positively correlated with the serum C9 concentration, bactericidal activity, and hemolytic activity. In 2-d-old rats infected with E. coli, the intraperitoneal administration of human C9 significantly enhanced survival and also enhanced the protective effect of intraperitoneal human IgG antibodies. The data indicate that C9 deficiency predisposed neonatal rats to invasion by E. coli. The neonatal rat appears to be a suitable model with which to investigate the significance of C9 deficiency.