Lactoferrin moderates LPS-induced hypotensive response and gut injury in rats

Abstract

Hypotension is a physiologic state of low blood pressure, the causes of which range from dehydration to underlying serious medical disorders. The aim of this study was to assess the utility of lactoferrin (LF), a natural immunomodulator, to restrain LPS-induced hypotension in rats. LF has previously demonstrated a role in mediation of immune responses, including control of inflammatory cytokine production during acute inflammation. Rats were administered with LF by gavage at 1 h or 18 h prior to LPS injections. Heart rate (HR) and mean arterial blood pressure (MAP) were continuously recorded post LPS administration for 6 h. Simultaneously to hemodynamic measurements, serum was examined for TNF-α, IL-6, and TGF-β production. At termination, the proximal duodenum was subjected to histopathological analysis. LF administered at 1 h prior to LPS protected rats from the LPS-induced hypotension. The protective effect on MAP was also apparent when LF was administered as a pretreatment 18 h prior to LPS challenge, although the effect was lessened. For all groups, LF pretreatment led to a minor, but insignificant, improvement in HR post LPS administration. In addition, when rats were given LF 1 h before LPS, they showed a significant decrease in serum TNF-α and IL-6 production. LF did not affect the production level of serum TGF-β. Of high importance, LF was able to confer histo-pathological protection of intestinal tissue post LPS administration, for both the 1 h and 18 h LF pretreatment groups. These studies indicate a potential for clinical utility of LF to control hypotension.

Introduction

Medical conditions causing hypotension, a physiologic state of low blood pressure, include a wide variety of causes such as cardiac and endocrine dysfunctions, dehydration and blood loss, septicemia and allergic anaphylaxis, pregnancy, and even nutrient deficiency [1]. The clinical manifestations associated with vascular pressure change often result in damage to vital organs. In particular, septic shock-induced hypotension (systolic blood pressure < 90 mmHg, mean arterial blood pressure < 60 mmHg or a drop of ≥ 40 mmHg from baseline pressures) is difficult to manage due to severe tissue hypoperfusion. Even with restoration of adequate blood pressure and normal cardiac output, signs of tissue hypoperfusion and continued tissue damage may persist [2].

A commonly used experimental model to induce hypotension is by systemic administration of lipopolysaccharide (LPS), a component of the wall of Gram-negative bacteria which is also central to the septic shock pathogenesis. A variety of acute inflammatory responses are induced by LPS, including hypotension found in early stages of septic shock [3]. While there are medications for treatment of general hypotension, septic shock-induced hypotension requires a multi-directional approach to offset the imbalance in immune-homeostasis, and subsequent protection against multiple organ failure.

Lactoferrin (LF), a natural immune modulator and homeostatic agent, is a ubiquitous iron-binding protein found in mammalian body fluids and secondary granules of leukocytes. LF plays an important role in maintaining physiological homeostasis in mammals, and is considered as a basic component of innate immunity with the potential to modulate host response during microbial infections [4], [5], [6], [7], [8]. LF has direct antimicrobial activity, including an iron-dependent bacteriostatic property and iron-independent bacteriocidal action on LPS-bearing Gram-negative bacteria [9], [10]. Under inflammatory conditions, LF production is increased in the periphery by neutrophils [11], [12] and in the central nervous system (CNS) by the microglia [13]. LF is transported from blood to the cerebrospinal fluid through the blood–brain barrier via receptor-mediated transcytosis [14]. Of interest, oral administered bovine milk-derived LF (BLF) mediates many factors related to hypotension pathophysiology. For example, LF inhibits formalin-evoked nociception [15], carrageenan-induced inflammation [16], and vascular endothelial growth factor-mediated angiogenesis [17], [18]. More recently, LF was shown to inhibit pollen antigen-induced allergic airway inflammation assessed both by histological evaluation of airways and by examination of reactive oxygen species (ROS) in bronchial epithelial cells [19], [20]. LF has the ability to modulate cytokine production from monocytes and lymphocytes during foreign stimuli or mitogenic activation. This, coupled with the ability to affect production and activity of ROS, allows LF to serve as a unique regulator to a wide array of responses, including those involved in acute inflammation, and subsequent development of disease related pathologies.

Although the effects of LF as a key element to combat excessive inflammation have been extensively described in vitro and in vivo, little is known about its cardiovascular effects when administered orally. Hayashida et al. [21] suggested that LF administered IV causes hypotension via an endothelium-dependent vasodilation that is strongly mediated by nitric oxide (NO), with LF-induced hypotension mediated under central opioidergic control. It is hypothesized that LF would be an important physiological modulator of the cardiovascular system. The present studies were therefore undertaken to examine LF protective effects against LPS-induced hypotension. Specifically, the correlation between LF anti-inflammatory activity and its inhibitory hemodynamic effects were assessed in rats challenged with LPS.