Hypertension Is Associated With Intestinal Microbiota Dysbiosis and Inflammation in a Brazilian Population

Hypertension is a major global health challenge, as it represents the main risk factor for stroke and cardiovascular disease. It is a multifactorial clinical condition characterized by high and sustained levels of blood pressure, likely resulting from a complex interplay of endogenous and environmental factors. The gut microbiota has been strongly supposed to be involved but its role in hypertension is still poorly understood. In an attempt to fill this gap, here we characterized the microbial composition of fecal samples from 48 hypertensive and 32 normotensive Brazilian individuals by next-generation sequencing of the 16S rRNA gene. In addition, the cytokine production of peripheral blood samples was investigated to build an immunological profile of these individuals. We identified a dysbiosis of the intestinal microbiota in hypertensive subjects, featured by reduced biodiversity and distinct bacterial signatures compared with the normotensive counterpart. Along with a reduction in Bacteroidetes members, hypertensive individuals were indeed mainly characterized by increased proportions of Lactobacillus and Akkermansia while decreased relative abundances of well-known butyrate-producing commensals, including Roseburia and Faecalibacterium within the Lachnospiraceae and Ruminococcaceae families. We also observed an inflamed immune profile in hypertensive individuals with an increase in TNF/IFN-\u3b3 ratio, and in TNF and IL-6 production when compared to normotensive ones. Our work provides the first evidence of association of hypertension with altered gut microbiota and inflammation in a Brazilian population. While lending support to the existence of potential microbial signatures of hypertension, likely to be robust to age and geography, our findings point to largely neglected bacteria as potential contributors to intestinal homeostasis loss and emphasize the high vulnerability of hypertensive individuals to inflammation-related disorders

Oral tolerance induction with altered forms of ovalbumin

As a T cell-dependent phenomenon, oral tolerance is not expected to depend necessarily on native configuration of antigens. We investigated the induction of oral tolerance with modified ovalbumin (Ova). Oral administration of heat-denatured (HD-Ova) and cyanogen bromide-degraded ovalbumin was less effective than native Ova in inducing oral tolerance in B6D2F1 mice. HD-Ova was effective in suppressing delayed-type hypersensitivity (DTH) reactions but did not suppress specific antibody formation. Injection of Ova directly into the stomach, but not into the ileum or cecum, suppressed subsequent immunization to DTH reactions. Gavage with protease inhibitors (aprotinin or ovomucoid) before gavage with Ova was ineffective in blocking tolerance induction. Treatment with hydroxyurea to destroy cycling cells 24 h before gavage with Ova blocked oral tolerance induction and also the possibility to passively transfer tolerance to naive recipients with the serum of mice gavaged with Ova 1 h before. The implications of these findings about oral tolerance induction are discusse

Ethanol-induced colitis prevents oral tolerance induction in mice

The gut mucosa is a major site of contact with antigens from food and microbiota. Usually, these daily contacts with natural antigens do not result in inflammatory reactions; instead they result in a state of systemic hyporesponsiveness named oral tolerance. Inflammatory bowel diseases (IBD) are associated with the breakdown of the immunoregulatory mechanisms that maintain oral tolerance. Several animal models of IBD/colitis are available. In mice, these include targeted disruptions of the genes encoding cytokines, T cell subsets or signaling proteins. Colitis can also be induced by intrarectal administration of chemical substances such as 2,4,6-trinitrobenzene sulfonic acid in 50% ethanol. We report here a novel model of colitis induced by intrarectal administration of 50% ethanol alone. Ethanol-treated mice develop an inflammatory reaction in the colon characterized by an intense inflammatory infiltrate in the mucosa and submucosa of the large intestine. They also present up-regulation of both interferon gamma (IFN-gamma) and interleukin-4 (IL-4) production by cecal lymph node and splenic cells. These results suggest a mixed type of inflammation as the substrate of the colitis. Interestingly, cells from mesenteric lymph nodes of ethanol-treated mice present an increase in IFN-gamma production and a decrease in IL-4 production indicating that the cytokine balance is altered throughout the gut mucosa. Moreover, induction of oral tolerance to ovalbumin is abolished in these animals, strongly suggesting that ethanol-induced colitis interferes with immunoregulatory mechanisms in the intestinal mucosa. This novel model of colitis resembles human IBD. It is easy to reproduce and may help us to understand the mechanisms involved in IBD pathogenesis

Interruption of recently induced immune responses by oral administration of antigen

Interest in oral tolerance has been renewed in the last few years as a possibility of intervention in human autoimmune diseases. An obstacle in this direction is that, although easily induced in animals virgin of contact with the antigen, oral tolerance becomes hard to induce in previously immunized animals. The present results show that there is an early period after primary immunization in which prolonged oral exposure to the antigen may arrest ongoing immune responses. Beyond this period, oral exposures to the antigen become ineffective and may actually boost immune responses. The end of the susceptible period coincides with the emergence of free specific antibodies in serum. However, the previous administration of purified anti-ovalbumin antibodies (40 µg) was unable to block the induction of oral tolerance to ovalbumin in normal mic

Immunoglobulin production is impaired in protein-deprived mice and can be restored by dietary protein supplementation

Most contacts with food protein and microbiota antigens occur at the level of the gut mucosa. In animal models where this natural stimulation is absent, such as germ-free and antigen-free mice, the gut-associated lymphoid tissue (GALT) and systemic immunological activities are underdeveloped. We have shown that food proteins play a critical role in the full development of the immune system. C57BL/6 mice weaned to a diet in which intact proteins are replaced by equivalent amounts of amino acids (Aa diet) have a poorly developed GALT as well as low levels of serum immunoglobulins (total Ig, IgG, and IgA, but not IgM). In the present study, we evaluated whether the introduction of a protein-containing diet in 10 adult Aa-fed C57BL/6 mice could restore their immunoglobulin levels and whether this recovery was dependent on the amount of dietary protein. After the introduction of a casein-containing diet, Aa-fed mice presented a fast recovery (after 7 days) of secretory IgA (from 0.33 to 0.75 mg/mL, while in casein-fed mice this value was 0.81 mg/mL) and serum immunoglobulin levels (from 5.39 to 10.25 mg/mL of total Ig). Five percent dietary casein was enough to promote the restoration of secretory IgA and serum immunoglobulin levels to a normal range after 30 days feeding casein diet (as in casein-fed mice - 15% by weight of diet). These data suggest that the defect detected in the immunoglobulin levels was a reversible result of the absence of food proteins as an antigenic stimulus. They also indicate that the deleterious consequences of malnutrition at an early age for some immune functions may be restored by therapeutic intervention later in life

Aging and immunoglobulin isotype patterns in oral tolerance

In the present review we address oral tolerance as an important biological phenomenon and discuss how it is affected by aging. Other factors such as frequency of feeding and previous digestion of the antigen also seem to influence the establishment of oral tolerance. We also analyze immunoglobulin isotypes of specific antibodies formed by tolerant and immunized animals of different ages submitted to different conditions of oral antigen administration. Isotypic patterns were studied as a parameter for assessing the pathways of B and T cell interactions leading to antibody productio