Multiplex quantification of C-terminal alpha-1-antitrypsin peptides provides a novel approach for characterizing systemic inflammation

Alpha1-antitrypsin improves survival in murine abdominal sepsis model by decreasing inflammation and sequestration of free heme

Background

Excessive inflammation, hemolysis, and accumulation of labile heme play an essential role in the pathophysiology of multi-organ dysfunction syndrome (MODS) in sepsis. Alpha1-antitrypsin (AAT), an acute phase protein with heme binding capacity, is one of the essential modulators of host responses to inflammation. In this study, we evaluate the putative protective effect of AAT against MODS and mortality in a mouse model of polymicrobial abdominal sepsis.

Methods

Polymicrobial abdominal sepsis was induced in C57BL/6N mice by cecal ligation and puncture (CLP). Immediately after CLP surgery, mice were treated intraperitoneally with three different forms of human AAT-plasma-derived native (nAAT), oxidized nAAT (oxAAT), or recombinant AAT (recAAT)-or were injected with vehicle. Sham-operated mice served as controls. Mouse survival, bacterial load, kidney and liver function, immune cell profiles, cytokines/chemokines, and free (labile) heme levels were assessed. In parallel, in vitro experiments were carried out with resident peritoneal macrophages (MPMΦ) and mouse peritoneal mesothelial cells (MPMC).

Results

All AAT preparations used reduced mortality in septic mice. Treatment with AAT significantly reduced plasma lactate dehydrogenase and s-creatinine levels, vascular leakage, and systemic inflammation. Specifically, AAT reduced intraperitoneal accumulation of free heme, production of cytokines/chemokines, and neutrophil infiltration into the peritoneal cavity compared to septic mice not treated with AAT. In vitro experiments performed using MPMC and primary MPMΦ confirmed that AAT not only significantly decreases lipopolysaccharide (LPS)-induced pro-inflammatory cell activation but also prevents the enhancement of cellular responses to LPS by free heme. In addition, AAT inhibits cell death caused by free heme in vitro.

Conclusion

Data from the septic CLP mouse model suggest that intraperitoneal AAT treatment alone is sufficient to improve sepsis-associated organ dysfunctions, preserve endothelial barrier function, and reduce mortality, likely by preventing hyper-inflammatory responses and by neutralizing free heme.

SERPINA1 long transcripts produce non-secretory alpha1-antitrypsin isoform: In vitro translation in living cells

SERPINA1 is a well-studied serpin gene due to its dramatic impact on human health. Translation initiation at the main SERPINA1 start codon produces the only known alpha1-antitrypsin (AAT) isoform intended for secretion. AAT performs essential functions by inhibiting proteases and modulating immunity. However, SERPINA1 expression at the level of translation is not sufficiently studied. Here we hypothesize that the main SERPINA1 ORF can be alternatively translated, producing a non-secretory AAT isoform by either masking or excluding a signal peptide. We defined SERPINA1 long mRNA isoforms specific for prostate (DU145) and liver (HepG2) cell lines and studied their individual expression by in vitro assay. We found that all long transcripts produce both glycosylated secretory AAT-eGFP fusion protein and non-glycosylated intracellular AAT-eGFP (initiated from an alternative AUG-2 start codon), with the proportion regulated by the SERPINA1 5'-UTR. Both fusion proteins localize to distinct cellular compartments: in contrast to a fusion with the secretory AAT accumulating in the ER, the intracellular one exhibits nuclear-cytoplasmic shuttling. We detected putative endogenous AAT isoform enriching the nuclear speckles. CONCLUSION: Alternative translation initiation might be a mechanism through which SERPINA1 expands the biological diversity of its protein products. Our findings open up new prospects for the study of SERPINA1 gene expression.

Association of the C-terminal 42-peptide fragment of alpha-1 antitrypsin with the severity of ARDS: A pilot study

BACKGROUND

Acute respiratory distress syndrome is a life-threatening condition with a hospital mortality rate of up to 40%. Biomarkers related to the pathophysiology of ARDS may not only identify patients at risk but may also serve as potential therapeutic targets. This study examined the association between the proteolytic C-terminal 42-peptide fragment of alpha-1 antitrypsin and ARDS severity.

METHODS

The 42-peptide fragment and interleukin-6 levels were measured in 21 patients with mild-to-moderate ARDS and 47 patients with moderate-to-severe ARDS on days 1, 3, and 5 after diagnosis/admission to the intensive care unit. To elucidate the association between both biomarkers and the PaO₂/FiO₂ ratio, the concentrations of both biomarkers were compared between the two groups, and a multivariate regression analysis was performed.

RESULTS

The concentrations of both biomarkers were higher in patients with moderate-to-severe ARDS. While the PaO₂/FiO₂ ratio increased from day 1 to day 3, the concentrations of both biomarkers decreased. Multivariate regression analysis revealed negative associations between the PaO₂/FiO₂ ratio and both the C-terminal 42-peptide of alpha-1 antitrypsin and interleukin-6 on day 1 (beta: -0.138, p = 0.052; beta: -0.096, p = 0.004) and on day 3 (beta: -0.157, p = 0.045; beta: -0.106, p = 0.043).

INTERPRETATION

The C-terminal 42-peptide of alpha-1 antitrypsin is a new biomarker associated with ARDS severity. Its predictive value in identifying patients at risk of developing moderate-to-severe ARDS must be investigated in additional, independent prospective studies.