Azithromycin in Post Diarrheal Haemolytic and Uremic Syndrome

Hemolytic uremic syndrome (HUS) is defined by the combination of microangiopathic hemolytic anemia, thrombocytopenia and acute renal failure. The underlying lesion is thrombotic microangiopathy (TMA) affecting arteriole and capillary walls, with endothelial cells swelling and detachment and thrombi obstructing vascular lumina. Post- diarrheal HUS (D+HUS) is induced by an infection due to E. coli (STEC) producing a Shiga -like toxin (Stx) which is responsible of TMA. Serotype O157:H7 represents 63-97 % of STEC causing D+HUS. Other serotypes frequently implicated in outbreaks are O26:H11, O103:H2, O111:H8, O145:H28 (Mariani - Kurkdjian P et al, 2001) (Espié et al, 2008).

The D+HUS mainly affects children under 3 years and occurs after a prodromal bloody diarrhea. The onset of HUS surrounds 3 to 5 days after the onset of diarrhea. D+HUS is the leading cause of acute renal failure in children under 5 years (Decludt et al. 2000).

In France, 100 to 120 pediatric cases of D+HUS are reported each year. STEC infection was demonstrated in 85 % of cases. In 50 % of cases, one or more persons of the same family have STEC diarrhea without HUS. The death rate in the acute phase is about 2% and 50% of D+HUS requires dialysis. The predictive factors of a poor outcome are an anuria for more than 8 days a neutrophil count>20000/mm3, a severe bowel disease or central nervous system (CNS) involvement (Scheiring et al. 2008). In 65-80 % of cases, a seemingly ad integrum recovery of renal function was observed within the first year after D + HUS onset. However, D+HUS is responsible for a nephron loss that could lead to hypertension, proteinuria and chronic renal failure in the long term. A study performed on 218 patients undergoing D+HUS in the chidhood, highlighted the presence of renal sequelae in nearly 65 % of them with a median follow-up of nearly 20 years. (Fila et al, submitted).

Classically, humans are infected by contaminated food (minced meat undercooked products, unpasteurized milk and cheese...), by the animal environment (especially cattle) or by transmission from person to person. EHEC virulence is associated with the presence of toxins called Shigatoxins (Stx) and the presence of the eae gene, responsible for damage attachment - clearing in the colon and caecum. Two major types of Shigatoxin, Stx1 and Stx2, and many Stx1 or Stx2 variants were identified: three variants for Stx1 and at least, six variants for Stx2. The determination of different profiles variants Stx is considered as predictive of the severity of STEC infections with progression to HUS, especially Stx2d activated and Stx2c After ingestion of contaminated food, STEC are able to withstand the acidity of the stomach and colonize the digestive tract. Toxins produced by the bacteria go through the intestinal epithelium, join the circulatory system and reach their target organs, mainly kidneys and CNS. Indeed, toxins bind to a specific glycolipid receptor, globotriosylceramide (Gb3) on the surface of endothelial cells of target organs (digestive tract, kidney, CNS, pancreas) driving on the one hand, the release of pro-inflammatory factors (TNF- α, IL6, IL8) involved in the formation of lesions of microangiopathy and leading to apoptosis of the target cells (Hurley et al. 2001) (Thorpe et al, 1999) (Zoja et al.2010).

To this day, management of D+HUS requires only supportive care. All specific therapies (antithrombotic and anti inflammatory agents, specific antibodies against Shigatoxin, plasma transfusion and plasma exchange) did not show efficacy (Scheiring et al. 2008) (Loirat et al. 2012).

Several retrospective and prospective studies suggest that antibiotics increase the risk of HUS by release of Stx during bacterial lysis but also to certain types of antibiotics, increased synthesis of Shiga toxin. The meta-analysis performed by Wang et al on the use of antibiotics in patient with STEC diarrhea and D+HUS highlighted an increased risk of developing D+HUS in patients treated with antibiotics (Wang et al. 2000). A second meta-analysis bringing together 20 studies, that compared the risk of HUS occurrence in patients with STEC diarrhea treated or not with antibiotics, has not concluded (Panos et al. 2006). According to these results, antibiotherapy is actually not recommended for patients with diarrhea EHEC and patients with D+HUS (Scheiring et al. 2008). However, these studies did not distinguish between different classes of antibiotics, bringing together all the bacteriostatic antibiotics as well as bactericidal. But, in vitro studies have clearly shown that certain classes of antibiotics such as quinolones induced the production of Shigatoxin (multiplying production by a factor of 100 for ciprofloxacin) while others had a strong inhibitory action as the azithromycin (Ohara et al. 2002 ) .

Azithromycin, an antibiotic of the macrolide family, binds to the 50S subunit of the bacterial ribosome and inhibits protein synthesis by blocking transpeptidation. This mechanism inhibits the production and the release of Shiga toxin in STEC (Ohara et al. 2002). Studies on animal models of D+HUS (mice, piglet) showed a drastic reduction in mortality. Moreover, in addition to its inhibitory action on the synthesis of Stx, azithromycin has a modulating effect on the inflammatory reaction on the vascular endothelium induced by the Shigatoxin that contribute to thrombotic microangiopathy. Indeed, azithromycin dramatically decreased secretion of IL6, IL1 and TNFα (Gantzhorn et al. 2009) (Ohara et al. 2002) (Zhang Q et al. 2009).

Moreover, a recent work from Amran et al performed in a mouse model of D+HUS highlighted a protective effect of azithromycin on the occurrence of neurological inhibition of inflammatory mechanism induced by Shigatoxin in the vascular endothelium brain and neurons (Amran et al. 2013).

On the human being, the German outbreak of D+HUS in O104H4 helped highlight the importance of an early treatment with azithromycin on the eradication of carriage of the bacteria as well as the eradication of Stx in stool (Nitschke et al. 2012). In addition, preliminary data from a retrospective study of D+HUS in Robert Debré hospital showed a lower incidence of severe digestive tract impairment in patients with D+HUS who received treatment with azithromycin compared to the control group (unpublished data).

The objective of a prospective study on patients with D+HUS treated with azithromycin will be to prove its beneficial effects on renal, hematological, digestive tract and neurological impairment seen in D+HUS and to reduce the potential sequelae.