An Investigation into the Immunomodulatory Activities of <i>Sutherlandia frutescens</i> in Healthy Mice

<div><p><i>Sutherlandia frutescens</i> is a medicinal plant that has been traditionally used in southern Africa for cancers, infections, and inflammatory conditions. We recently published experiments demonstrating that an aqueous extract of <i>S</i>. <i>frutescens</i> possessed potent immune-stimulatory activity. This work was carried out with murine macrophages, an immune cell type that plays a pivotal role in host defense from infection and in shaping host inflammatory and immune responses. Here, we conducted a series of follow-up experiments to explore the impact of consuming <i>S</i>. <i>frutescens</i> on host response to bacterial challenge using healthy mice. We found that feeding mice a diet containing <i>S</i>. <i>frutescens</i> failed to significantly alter host response to systemic infection by either a gram-positive or gram-negative bacterium (i.e., <i>L</i>. <i>monocytogenes</i> and <i>E</i>. <i>coli</i>, respectively). In contrast to the <i>in vitro</i> observations, we found no evidence that <i>S</i>. <i>frutescens</i> consumption stimulated <i>in vivo</i> inflammatory responses; instead, consumption of <i>S</i>. <i>frutescens</i> tended to diminish <i>in vivo</i> inflammatory responses. Several possible reasons for this are discussed.</p></div

Impact of <i>S</i>. <i>frutescens</i> Consumption on Host Clearance of an Experimental Infection with <i>L</i>. <i>monocytogenes</i>.

<p>Female and male BALB/c (<i>L</i>. <i>monocytogenes</i>) mice were randomly assigned to one of three treatment groups: 0, 0.25, or 1.0% (wt/wt) <i>S</i>. <i>frutescens</i> in an AIN93G-type diet. After consuming diets for ~4 wks, all mice received an intravenous injection with ~10⁴ cfu of <i>L</i>. <i>monocytogenes</i> (EGD strain) in 0.2 mL of sterile, endotoxin-free phosphate-buffered saline. Liver and spleen samples were harvested three days after challenge and colony-forming units (<i>cfu</i>) were determined by a fluorescence-based microplate assay of tissue homogenates. Each symbol represents the data from a single mouse with the median and intra-quartile range shown.</p

Impact of <i>S</i>. <i>frutescens</i> Consumption on Host Clearance of an Experimental Infection with <i>E</i>. <i>coli</i>.

<p>Weanling female and male C57Bl/6 mice were randomly assigned to one of three treatment groups: 0, 0.25, or 1.0% (wt/wt) <i>S</i>. <i>frutescens</i> in an AIN93G-type diet. After consuming diets for ~4 wks, all mice were injected intraperitoneally with ~10⁸ colony-forming units (<i>cfu</i>) of <i>E</i>. <i>coli</i> (K-12 strain) in 1 mL of sterile PBS. Liver and spleen samples were harvested three days after challenge and colony-forming units (<i>cfu</i>) were determined by a fluorescence-based microplate assay of tissue homogenates. Each symbol represents the data from a single mouse with the median and intra-quartile range shown.</p

Dietary <i>S</i>. <i>frutescens</i> Has No Impact on Spontaneous Activity (i.e., sickness behavior) of Mice After an Experimental Infection with <i>E</i>. <i>coli</i>.

<p>Conditions were similar to those described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0160994#pone.0160994.g003" target="_blank">Fig 3</a>, except in this experiment the mice were C57Bl/6 mice and the challenge consisted of an intraperitoneal injection with ~10⁸ cfu of <i>E</i>. <i>coli</i> (K-12 strain).</p

<i>S</i>. <i>frutescens</i> (SF) Consumption Failed to Impact Circulating Cytokines and Chemokines in BALB/c Mice 24 hr Following an <i>in vivo</i> Challenge with <i>L</i>. <i>monocytogenes</i>.^<i>a</i>

<p><i>S</i>. <i>frutescens</i> (SF) Consumption Failed to Impact Circulating Cytokines and Chemokines in BALB/c Mice 24 hr Following an <i>in vivo</i> Challenge with <i>L</i>. <i>monocytogenes</i>.<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0160994#t002fn001" target="_blank">^<i>a</i></a></p

Dietary <i>S</i>. <i>frutescens</i> Has No Impact on Spontaneous Activity (i.e., sickness behavior) of Mice After an Experimental Infection with <i>L</i>. <i>monocytogenes</i>.

<p>Healthy female BALB/c weanling mice were fed experimental diets containing one of three doses of <i>S</i>. <i>frutescens</i> (i.e., 0, 0.25 or 1% by wt) for 3–4 wks. Mice were housed in pairs in a vivarium with a 12 hr light:dark cycle at a room temperature between 22–25°C and a relative humidity of 50–60% for the entirety of the study. One of each pair of mice had a mini-emitter surgically implanted under the skin along their spine between their shoulders. At ~1 week post-surgery mice received an intravenous injection of 10⁴ <i>cfu</i> of <i>L</i>. <i>monocytogenes</i>, EGD strain. Each mouse’s movement/activity was recorded every 5 seconds and reported as accumulated events for every 20 minute period. Each tick mark on the X-axis represents an hour. Data shown represent the mean activity (#events) of four mice in each diet treatment group (n = 4/diet treatment group).</p