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Neutrophils accumulate in insulin-sensitive tissues during obesity and may play a role in impairing insulin sensitivity. The major serine protease expressed by neutrophils is neutrophil elastase (NE), which is inhibited endogenously by a1-antitrypsin A (A1AT). We investigated the effect of exogenous (A1AT) treatment on diet-induced metabolic dysfunction. Male C57Bl/6j mice fed a chow or a high-fat diet (HFD) were randomized to receive intraperitoneal injections three times weekly of either Prolastin (human A1AT; 2 mg) or vehicle (PBS) for 10 wk. Prolastin treatment did not affect plasma NE concentration, body weight, glucose tolerance, or insulin sensitivity in chow-fed mice. In contrast, Prolastin treatment attenuated HFD-induced increases in plasma and white adipose tissue (WAT) NE without affecting circulatory neutrophil levels or increases in body weight. Prolastin-treated mice fed a HFD had improved insulin sensitivity, as assessed by insulin tolerance test, and this was associated with higher insulin-dependent IRS-1 (insulin receptor substrate) and AktSer473 phosphorylation, and reduced inflammation markers in WAT but not liver or muscle. In 3T3-L1 adipocytes, Prolastin reversed recombinant NE-induced impairment of insulin-stimulated glucose uptake and IRS-1 phosphorylation. Furthermore, PDGF mediated p-AktSer473 activation and glucose uptake (which is independent of IRS-1) was not affected by recombinant NE treatment. Collectively, our findings suggest that NE infiltration of WAT during metabolic overload contributes to insulin resistance by impairing insulin-induced IRS-1 signaling. [ABSTRACT FROM AUTHOR]

Neutrophil elastase (NE) is a serine protease expressed by neutrophils which is inhibited endogenously by α1-Antitrypsin A (AAT). Obesity is associated with increased plasma NE:AAT ratios and adipose tissue NE accumulation, which may drive obesity-associated metabolic dysfunction. Exogenous AAT is now an FDA approved treatment for AAT deficiency, therefore we investigated whether AAT treatment may also have potential therapeutic benefits for diet induced metabolic dysfunction. Standard Chow and high-fat diet (HFD) fed male C57Bl6 mice were randomized to receive 3x weekly IP injections of either AAT (2mg) or vehicle (PBS) for 10 weeks. Chow fed mice treated with recombinant AAT showed no differences in plasma NE, body weight or metabolic phenotype compared to vehicle treated control mice. However, during HFD feeding AAT treatment attenuated increases in plasma NE and white adipose tissue (WAT) NE and neutrophil accumulation without affecting circulatory neutrophil levels or body weight. Consistent with NE knockout mice being partially protected from HFD glucose intolerance, treatment of HFD fed mice with AAT enhanced whole body insulin sensitivity which was attributed to higher insulin-dependent p-AktSer473 and reduced inflammation markers in WAT but no other peripheral tissues. Treatment of 3T3L1 adipocytes with recombinant NE impaired insulin-stimulated glucose uptake andp-AktSer473, suggesting that inhibition of NE in WAT is the primary mechanism through which AAT treatment enhances insulin sensitivity. Collectively, our data suggests AAT may play a potential role in mitigating diet-induced neutrophil infiltration in WAT insulin resistance. Disclosure: R.F. D'Souza: None. J.S.T. Woodhead: None. S.W. Masson: None. S.L. James: None. C. Hedges: None. T.L. Merry: None. Funding: Health Research Council of New Zealand [ABSTRACT FROM AUTHOR]