Gut Microorganisms and Autism: the Latest Research

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Mitochondrial Defect and LPS

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1: J Autism Dev Disord. 2004 Dec;34(6):615-23.
Relative carnitine deficiency in autism.
Filipek PA, Juranek J, Nguyen MT, Cummings C, Gargus JJ.

Department of Pediatrics, College of Medicine, University of California, Irvine, CA, USA.

A random retrospective chart review was conducted to document serum carnitine levels on 100 children with autism. Concurrently drawn serum pyruvate, lactate, ammonia, and alanine levels were also available in many of these children. Values of free and total carnitine (p < 0.001), and pyruvate (p = 0.006) were significantly reduced while ammonia and alanine levels were considerably elevated (p < 0.001) in our autistic subjects. The relative carnitine deficiency in these patients, accompanied by slight elevations in lactate and significant elevations in alanine and ammonia levels, is suggestive of mild mitochondrial dysfunction. It is hypothesized that a mitochondrial defect may be the origin of the carnitine deficiency in these autistic children.

PMID: 15679182 [PubMed - indexed for MEDLINE]

LPS produces a decrease in acetylcarnitine concentration and an increase in lactate.

1: J Physiol. 2008 Mar 15;586(6):1767-75. Epub 2008 Jan 24.

Temporal changes in the involvement of pyruvate dehydrogenase complex in muscle lactate accumulation during lipopolysaccharide infusion in rats.

Alamdari N, Constantin-Teodosiu D, Murton AJ, Gardiner SM, Bennett T, Layfield R, Greenhaff PL.

Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Boston, MA 02215, USA.

A characteristic manifestation of sepsis is muscle lactate accumulation. This study examined any putative (causative) association between pyruvate dehydrogenase complex (PDC) inhibition and lactate accumulation in the extensor digitorum longus (EDL) muscle of rats infused with lipopolysaccharide (LPS), and explored the involvement of increased transcription of muscle-specific pyruvate dehydrogenase kinase (PDK) isoenzymes. Conscious, male Sprague-Dawley rats were infused i.v. with saline (0.4 ml h(-1), control) or LPS (150 mug kg(-1) h(-1)) for 2 h, 6 h or 24 h (n = 6-8). Muscle lactate concentration was elevated after 2, 6 and 24 h LPS infusion. Muscle PDC activity was the same at 2 h and 6 h, but was 65% lower after 24 h of LPS infusion (P < 0.01), when there was a 47% decrease in acetylcarnitine concentration (P < 0.05), and a 24-fold increase in PDK4 mRNA expression (P < 0.001). These changes were preceded by marked increases in tumour necrosis factor-alpha and interleukin-6 mRNA expression at 2 h. The findings indicate that the early (2 and 6 h) elevation in muscle lactate concentration during LPS infusion was not attributable to limited muscle oxygen availability or ATP production (evidenced by unchanged ATP and phosphocreatine (PCr) concentrations) or to PDC inhibition, whereas after 24 h, muscle lactate accumulation appears to have resulted from PDC activation status limiting pyruvate flux, most probably due to cytokine-mediated up-regulation of PDK4 transcription.

PMID: 18218678 [PubMed - indexed for MEDLINE]

PMCID: PMC2375698 [Available on 03/15/09]

Increase of ammonia levels by LPS

1: Hepatology. 2005 May;41(5):1065-73.

Lipopolysaccharide-induced tyrosine nitration and inactivation of hepatic glutamine synthetase in the rat.

Görg B, Wettstein M, Metzger S, Schliess F, Häussinger D.

Clinic for Gastroenterology, Hepatology, and Infectiology, Heinrich-Heine-University, Düsseldorf, Germany.

Glutamine synthetase (GS) in the liver is restricted to a small perivenous hepatocyte population and plays an important role in the scavenging of ammonia that has escaped the periportal urea-synthesizing compartment. We examined the effect of a single intraperitoneal injection of lipopolysaccharide (LPS) in vivo on glutamine synthesis in rat liver. LPS injection induced expression of inducible nitric oxide synthase, which was maximal after 6 to 12 hours but returned toward control levels within 24 hours. Twenty-four hours after LPS injection, an approximately fivefold increase in tyrosine-nitrated proteins in liver was found, and GS protein expression was decreased by approximately 20%, whereas GS activity was lowered by 40% to 50%. GS was found to be tyrosine-nitrated in response to LPS, and immunodepletion of tyrosine-nitrated proteins decreased GS protein by approximately 50% but had no effect on GS activity. Together with the finding via mass spectrometry that peroxynitrite-induced inactivation of purified GS is associated with nitration of the active site tyrosine residue, our data suggest that tyrosine nitration critically contributes to inactivation of the enzyme. In line with GS inactivation, glutamine synthesis from ammonia (0.3 mmol/L) in perfused livers from 24-hour LPS-treated rats was decreased by approximately 50%, whereas urea synthesis was not significantly affected. In conclusion, LPS impairs hepatic ammonia detoxification by both downregulation of GS and its inactivation because of tyrosine nitration. The resulting defect of perivenous scavenger cell function with regard to ammonia elimination may contribute to sepsis-induced development of hyperammonemia in patients who have cirrhosis.

PMID: 15830392 [PubMed - indexed for MEDLINE]

LPS induces increased hepatic uptake of alanine

1: Am J Physiol. 1999 Jul;277(1 Pt 1):G91-100.

Effects of LPS on transport of indocyanine green and alanine uptake in perfused rat liver.

Lund M, Kang L, Tygstrup N, Wolkoff AW, Ott P.

Medical Department A, National University Hospital, 2100 O Copenhagen, Denmark.

Lipopolysaccharide (LPS) initiates cholestasis. Whether this process is mediated by tumor necrosis factor-alpha (TNF-alpha) and whether the cholestatic response to LPS is associated with intrahepatic accumulation of possibly toxic substances are under debate. To study these questions the hepatic uptake and biliary excretion of indocyanine green (ICG) was examined in the isolated perfused rat liver 18 h after intravenous treatment of rats with either saline, 1 mg/kg body wt LPS, or LPS and intraperitoneal pentoxifylline (POF) (n = 6 in each group). POF inhibits TNF-alpha release after LPS administration. LPS induced a typical acute-phase response with increased mRNA for acute-phase proteins, reduced albumin mRNA, and increased hepatic uptake of alanine. Intrinsic hepatic clearance of ICG in controls (1.01 +/- 0.05 ml. min(-1). g liver(-1)) was similarly decreased by LPS alone (0.62 +/- 0.04 ml. min(-1). g(-1); P = 0.002 vs. control) or combined with POF (0.66 +/- 0.06 ml. min(-1). g(-1)). A kinetic analysis indicated that LPS reduced both uptake and excretion processes in a balanced manner, so that intrahepatic ICG content was unaffected or even slightly reduced, as confirmed by measurement of ICG contents in the perfused livers. In livers from parallel-treated nonperfused rats, mRNA for the organic anion transporting protein-1 (Oatp1, which is likely to mediate ICG uptake) was unaffected by LPS, whereas the concentration of Oatp1 protein was reduced. Thus LPS induced an acute-phase response that included downregulation of ICG uptake by reduction of Oatp1 protein concentration, possibly at a posttranscriptional level. TNF-alpha appears not to be the mediator because POF did not modify these LPS effects.

PMID: 10409155 [PubMed - indexed for MEDLINE]

Endotoxin (LPS)induces very low levels of pyruvate

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1: Brain Res. 2002 Jun 28;942(1-2):87-94. Interleukin-10 reverses acute detrimental effects of endotoxin-induced inflammation on perinatal cerebral hypoxia-ischemia.

Frøen JF, Munkeby BH, Stray-Pedersen B, Saugstad OD.

Department of Pediatric Research, The National Hospital, University of Oslo, N-0027 Oslo, Norway.

Perinatal brain injuries and the subsequent development of cerebral palsy are closely associated with intrauterine infections and inflammatory response. Antibiotics have proven futile in reducing perinatal brain injuries. We tested whether treatment with the anti-inflammatory cytokine IL-10 could have beneficial effects during a concomitant endotoxin and cerebral hypoxic-ischemic challenge. Thirty-three newborn piglets were randomized to pretreatment with: Controls: placebo, Endotoxin: 2 kU/kg bolus and infusion of 1 kU/kg per h of endotoxin, or Endotoxin+IL-10: endotoxin in addition to 50 microg/kg of porcine recombinant IL-10. We induced cerebral hypoxia-ischemia by bilateral clamping of the common carotid arteries and ventilation with 8% oxygen for 20 min followed by 3 h of reoxygenation/reperfusion. Extracellular lactate, pyruvate, glycerol and glutamate, microcirculation and tissue oxygenation were monitored in the striatum by microdialysis, laser Doppler flow and oxygen tension probe, respectively. During and/or after cerebral hypoxia-ischemia, Endotoxin caused marked deterioration of the cerebral metabolic situation with higher lactate/pyruvate ratio (P=0.003), compared to Controls and Endotoxin+IL-10. This was caused mainly by very low levels of pyruvate (P=0.001). During the following reoxygenation, Endotoxin compromised cerebral microcirculation (P=0.038) and tissue oxygenation (P=0.012) compared to Controls and Endotoxin+IL-10. After a period of remission, a secondary energy failure and a new rise in the lactate/pyruvate ratio was seen in Endotoxin (P=0.002), but not in Controls or Endotoxin+IL-10. At the end of observation, only the Endotoxin+IL-10 group had regained their baseline values in all variables. Thus IL-10 counteracts acute effects of endotoxin on cerebral metabolism, microcirculation and oxygen tension during hypoxia-ischemia in the perinatal brain.

PMID: 12031856 [PubMed - indexed for MEDLINE]