Reduction of intestinal mucosal immune function in heat-stressed rats and bacterial translocation

Dietary Zn proteinate with moderate chelation strength alleviates heat stress-induced intestinal barrier function damage by promoting expression of tight junction proteins via the A20/NF-κB p65/MMP-2 pathway in the jejunum of broilers

BACKGROUND

The aim of this study was to determine whether and how Zn proteinate with moderate chelation strength (Zn-Prot M) can alleviate heat stress (HS)-induced intestinal barrier function damage of broilers. A completely randomized design was used for comparatively testing the effects of Zn proteinate on HS and non-HS broilers. Under high temperature (HT), a 1 (Control, HT-CON) + 2 (Zn source) × 2 (added Zn level) factorial arrangement of treatments was used. The 2 added Zn sources were Zn-Prot M and Zn sulfate (ZnS), and the 2 added Zn levels were 30 and 60 mg/kg. Under normal temperature (NT), a CON group (NT-CON) and pair-fed group (NT-PF) were included.

RESULTS

The results showed that HS significantly reduced mRNA and protein expression levels of claudin-1, occludin, junctional adhesion molecule-A (JAMA), zonula occludens-1 (ZO-1) and zinc finger protein A20 (A20) in the jejunum, and HS also remarkably increased serum fluorescein isothiocyanate dextran (FITC-D), endotoxin and interleukin (IL)-1β contents, serum diamine oxidase (DAO) and matrix metalloproteinase (MMP)-2 activities, nuclear factor kappa-B (NF-κB) p65 mRNA expression level, and protein expression levels of NF-κB p65 and MMP-2 in the jejunum. However, dietary supplementation with Zn, especially organic Zn as Zn-Prot M at 60 mg/kg, significantly decreased serum FITC-D, endotoxin and IL-1β contents, serum DAO and MMP-2 activities, NF-κB p65 mRNA expression level, and protein expression levels of NF-κB p65 and MMP-2 in the jejunum of HS broilers, and notably promoted mRNA and protein expression levels of claudin-1, ZO-1 and A20.

CONCLUSIONS

Our results suggest that dietary Zn, especially 60 mg Zn/kg as Zn-Prot M, can alleviate HS-induced intestinal barrier function damage by promoting the expression of TJ proteins possibly via induction of A20-mediated suppression of the NF-κB p65/MMP-2 pathway in the jejunum of HS broilers.

Alleviating effect of methionine on intestinal mucosal injury induced by heat stress

Climate change is an increasing concern of stakeholders worldwide. The intestine is severely impacted by the heat stress. This study aimed to investigate the alleviating effects of methionine on the intestinal damage induced by heat stress in mice. The mice were divided into four groups: control group (C), methionine deficiency group (MD), methionine + heat stress group (MH), and methionine deficiency + heat stress group (MDH). Histopathological techniques, PAS-Alcian blue staining, immunohistochemistry method, biochemical quantification method, ELISA, and micro method were used to study the changes in the intestinal mucosal morphology, the number of goblet cells, the expression of tight junction proteins, the peroxide product contents and antioxidant enzyme activities, the intestinal mucosal damage, the content of immunoglobulins and HSP70, the activity of Na+/K+-ATPase. The results showed that methionine can improve intestinal mucosal morphology (increase the villi height, V/C value, and muscle layer thickness, decrease crypt depth), increase the expression of tight junction proteins (Claudin-1, Occludin, ZO-1) and the content of DAO, decrease the content of intestinal mucosa damage markers (ET, FABP2) and peroxidation products (MDA), increase the activity of antioxidant enzymes (GR, GSH-Px, SOD), the number of goblet cells, the contents of immunoglobulins (sIgA, IgA, IgG, IgM) and stress protein (HSP70), and the activity of Na+/K+-ATPase. It is suggested that methionine can alleviate intestinal damage in heat-stressed mice.

The protective effect of L-theanine on the intestinal barrier in heat-stressed organisms

Heat stress caused by heatwaves, extreme temperatures, and other weather can damage the intestinal barrier of organisms. L-Theanine (LTA) attenuates heat stress-induced oxidative stress, inflammatory responses, and impaired immune function, but its protective effect on the intestinal barrier of heat-stressed organisms is unclear. In this study, low (100 mg kg-1 d-1), medium (200 mg kg-1 d-1), and high (400 mg kg-1 d-1) dosages of LTA were used in the gavage of C57BL/6J male mice that were experimented on for 50 d. These mice were subjected to heat stress for 2 h d-1 at 40 ± 1 °C and 60 ± 5% RH in the last 7 d. LTA attenuated the heat stress-induced decreases in body mass and feed intake, and the destruction of intestinal villi and crypt depth; reduced the serum levels of FITC-dextran and D-LA, as well as the DAO activity; and upregulated the colonic tissues of Occludin, Claudin-1, and ZO-1 mRNA and occludin protein expression. The number of goblet cells in the colon tissue of heat-stressed organisms increased in the presence of LTA, and the expression levels of Muc2, Muc4 mRNA, and Muc2 protein were upregulated. LTA increased the abundance of Bifidobacterium and Turicibacter, and decreased the abundance of Enterorhabdus and Desulfovibrio in the intestinal tract of heat-stressed organisms and restored gut microbiota homeostasis. LTA promoted the secretion of IL-4, IL-10, and sIgA and inhibited the secretion of TNF-α and IFN-γ in the colon of heat-stressed organisms. The expressions of Hsf1, Hsp70, Hsph1, TLR4, P38 MAPK, p-P65 NF-κB, MLCK mRNA, and proteins were downregulated by LTA in the colon of heat-stressed organisms. These results suggest that LTA protects the intestinal barrier in heat-stressed organisms by modulating multiple molecular pathways. Therefore, this study provides evidence on how tea-containing LTA treatments could be used to prevent and relieve intestinal problems related to heat stress.

Effects of Hyperthermia and Hyperthermic Intraperitoneal Chemoperfusion on the Peritoneal and Tumor Immune Contexture

Hyperthermia combined with intraperitoneal (IP) drug delivery is increasingly used in the treatment of peritoneal metastases (PM). Hyperthermia enhances tumor perfusion and increases drug penetration after IP delivery. The peritoneum is increasingly recognized as an immune-privileged organ with its own distinct immune microenvironment. Here, we review the immune landscape of the healthy peritoneal cavity and immune contexture of peritoneal metastases. Next, we review the potential benefits and unwanted tumor-promoting effects of hyperthermia and the associated heat shock response on the tumor immune microenvironment. We highlight the potential modulating effect of hyperthermia on the biomechanical properties of tumor tissue and the consequences for immune cell infiltration. Data from translational and clinical studies are reviewed. We conclude that (mild) hyperthermia and HIPEC have the potential to enhance antitumor immunity, but detailed further studies are required to distinguish beneficial from tumor-promoting effects.

Critical illness aspects of heatstroke: A hot topic

Heatstroke represents the most severe end of the heat illness spectrum, and is increasingly seen in those undergoing exercise or exertion ('exertional heatstroke') and those exposed to high ambient temperatures, for example in heatwaves ('classical heatstroke'). Both forms may be associated with significant thermal injury, leading to organ dysfunction and the need for admission to an intensive care unit. The process may be exacerbated by translocation of bacteria or endotoxin through an intestinal wall rendered more permeable by the hyperthermia. This narrative review highlights the importance of early diagnosis, rapid cooling and effective management of complications. It discusses the incidence, clinical features and treatment of heatstroke, and discusses the possible role of intestinal permeability and advances in follow-up and recovery of this condition. Optimum treatment involves an integrated input from prehospital, emergency department and critical care teams, along with follow-up by rehabilitation teams and, if appropriate, sports or clinical physiologists.

Mild heat stress-induced adaptive immune response in blood mononuclear cells and leukocytes from mesenteric lymph nodes of primiparous lactating Holstein cows

Heat stress negatively affects the metabolism and physiology of the bovine gut. However, it is not known whether heat stress induces an inflammatory response in mesenteric lymph nodes (MLN), the primary origin of gut immune cells, and thus contributes to inflammatory processes in the circulation. Therefore, our objective was to elucidate the effects of chronic heat stress on the systemic activation of acute-phase response in blood, proinflammatory cytokine production in peripheral blood mononuclear cells (PBMC), and the activation of the toll-like receptor signaling (TLR) 2/4 pathway in MLN leucocytes and their chemokines and chemokine receptor profiles in Holstein cows. Primiparous Holstein cows (n = 30; 169 ± 9 d in milk) were exposed to a temperature-humidity index (THI) of 60 [16°C, 63% relative humidity (RH)] for 6 d. Thereafter, cows were evenly assigned to 3 groups: heat-stressed (HS; 28°C, 50% RH, THI = 76), control (CON; 16°C, 69% RH, THI = 60), or pair-feeding (PF; 16°C, 69% RH, THI = 60) for 7 d. On d 6, PBMC were isolated and on d 7 MLN. Plasma haptoglobin, TNFα, and IFNγ concentrations increased more in HS than CON cows. Concomitantly, TNFA mRNA abundance was higher in PBMC and MLN leucocytes of HS than PF cows, whereas IFNG mRNA abundance tended to be higher in MLN leucocytes of HS than PF cows, but not for chemokines (CCL20, CCL25) or chemokine receptors (ITGB7, CCR6, CCR7, CCR9). Furthermore, the TLR2 protein expression tended to be more abundant in MLN leucocytes of HS than PF cows. These results suggest that heat stress induced an adaptive immune response in blood, PBMC, and MLN leukocytes involving the acute-phase protein haptoglobin, proinflammatory cytokine production, and TLR2 signaling in MLN leucocytes. However, chemokines regulating the leucocyte trafficking between MLN and gut seem not to be involved in the adaptive immune response to heat stress.

Mogroside-rich extract from Siraitia grosvenorii fruits protects against heat stress-induced intestinal damage by ameliorating oxidative stress and inflammation in mice

Global warming makes humans and animals more vulnerable to heat stress. Heat stress can cause multiorgan dysfunction, especially in the intestine, primarily via oxidative stress and inflammation. Mogroside-rich extract (MGE) is the active ingredient of Siraitia grosvenorii and has significant antioxidant and anti-inflammatory activity. However, whether MGE can alleviate the intestinal damage caused by heat stress has not been explored. In this study, mice were given 600 mg kg^-1 MGE followed by exposure to high temperature (40 °C for 2 h per day), and the structures and molecular changes in the ileum were examined. Our findings showed that body weight was decreased by heat stress, while the activity of serum superoxide dismutase (SOD) was increased. We further found that heat stress impaired the intestinal barrier by reducing the number of goblet cells and mRNA levels of the tight junction proteins zona occludens protein 1 (ZO-1), Occludin (OCLD) and recombinant mucin 2 (MUC2 mucin), but it increased the mRNA level of trefoil factor 3 (TFF3). Interestingly, MGE treatment reversed these changes. Furthermore, heat stress increased the activity of SOD in the intestine, downregulated the expression of the oxidative stress-related genes glutathione peroxidase 1 (GPX1), SOD2 and nuclear factor erythroid 2-related factor 2 (NRF2), and upregulated the expression of catalase (CAT). Moreover, heat stress increased tumor necrosis factor-α (TNF-α) levels in the intestine and upregulated the expression of the inflammation-related genes interleukin 10 (IL-10), TNF-α, Interferon-γ (IFN-γ), toll like receptor 4 (TLR4) and nuclear factor-kappa B (NF-kB). However, MGE treatment effectively reduced TNF-α levels and restored the normal activity of SOD and normal mRNA levels for both oxidative stress-related and inflammation-related genes. In summary, our results showed that MGE can protect against heat stress-induced intestinal damage by ameliorating inflammation and oxidative stress.

Effect of coconut water and milk on heat stress-induced gastrointestinal tract dysmotility in rats: Role of oxidative stress and inflammatory response

The potential effects of coconut water (CCW) and milk (CCM) on gastrointestinal motility {intestinal transit (IT), intestinal fluid accumulation (IFA) and colonic motility}, tissue oxidative, and inflammatory responses in heat-stressed rats were investigated. There were four (4) temperature exposure groups; (i) Control at 30°C, (CON), (ii) heat-stressed (HS) group exposed to the ambiance of 40°C, (iii) heat-stressed pre-treated with coconut water (HS+ CCW), and (iv) coconut milk (HS + CCM). Skin temperatures (ST) and rectal temperatures (RT) were taken daily, before and after 2 hr heat exposure. GE, IT, and IFA were assessed using standard methods while colonic motility was assessed by colonic bead expulsion (CBE) time after the 14-day exposure. Serum cortisol and lipid peroxidation, antioxidant enzyme activities, inflammatory cytokines in intestinal samples were assessed. Stomach and intestinal morphology were equally examined on histomorphometry. Increased GE, IT, IFA, and colonic motility were observed in HS. CCW and CCM reversed the increases in GE, IT, IFA, and colonic motility in the heat-stressed rats (p < .05). Elevated serum cortisol level and intestinal MDA were significantly reduced in the CCW and CCM treated. Tissue GPx, T-AOC, and T-SOD were all enhanced in HS + CCW and HS + CCM. While tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were suppressed in the HS group, interleukin-4 (IL-4) and interleukin-10 (IL-10) were enhanced with CCW and CCM. Altered intestinal morphology in the HS was also significantly mitigated by CCW and CCM. We showed that coconut water and milk could ameliorate intestinal dysmotility associated with heat stress via oxidative stress reduction and suppression of inflammatory responses. PRACTICAL APPLICATIONS: Heat stress impacts negatively on intestinal health and integrity in both humans and animals via oxidative stress and inflammation. Conversely, coconut has demonstrated anti-oxidative and anti-inflammatory properties in health and medicinal applications. From the findings of this study, coconut water and milk display beneficial potentials against the untoward heat stress effect on gastrointestinal health.

Selenium exerts protective effects against heat stress-induced barrier disruption and inflammation response in jejunum of growing pigs

BACKGROUND

Heat stress (HS) has a negative impact on the intestinal barrier and immune function of pigs. Selenium (Se) may improve intestinal health through affecting selenoproteins. Thus we investigate the protective effect of new organic Se (2-hydroxy-4-methylselenobutanoic acid, HMSeBA) on jejunal damage in growing pigs upon HS and integrate potential roles of corresponding selenoproteins.

RESULTS

HS decreased the villus height and increased (P < 0.05) the protein abundance of HSP70, and downregulated (P < 0.05) protein levels of tight junction-related proteins (CLDN-1 and OCLD). HS-induced jejunal damage was associated with the upregulation of four inflammation-related genes and ten selenoprotein-encoding genes, downregulation (P < 0.05) of four selenoprotein-encoding genes and decreased (P < 0.05) the protein abundance of GPX4 and SELENOS. Compared with the HS group, HMSeBA supplementation not only elevated the villus height and the ratio of V/C (P < 0:05), but also reduced (P < 0.05) the protein abundance of HSP70 and MDA content, and increased (P < 0.05) the protein abundance of OCLD. HMSeBA supplementation downregulated the expression of seven inflammation-related genes, changed the expression of 12 selenoprotein-encoding genes in jejunum mucosa affected by HS, and increased the protein abundance of GPX4, TXNRD1 and SELENOS.

CONCLUSION

Organic Se supplementation beyond nutritional requirement alleviates the negative effect of HS on the jejunum of growing pigs, and its protective effect is related to the response of corresponding selenoproteins. © 2021 Society of Chemical Industry.

Baicalin Alleviates LPS-Induced Oxidative Stress via NF-κB and Nrf2–HO1 Signaling Pathways in IPEC-J2 Cells

Baicalin is a natural plant extract with anti-inflammatory and anti-oxidant activities. However, the molecular mechanism of baicalin on oxidative stress in IPEC-J2 cells exposed to LPS remains to be unclear. In this study, LPS stimulation significantly increased Toll-like receptor 4, tumor necrosis factor-α, and interleukins (IL-6 and IL-1β) expression in IPEC-J2 cells, and it activated the nuclear factor (NF-κB) expression. While, baicalin exerted anti-inflammatory effects by inhibiting NF-κB signaling pathway. LPS stimulation significantly increased the levels of the oxidative stress marker MDA, inhibited the anti-oxidant enzymes catalase and superoxide dismutase, which were all reversed by baicalin pre-treatment. It was found that baicalin treatment activated the nuclear import of nuclear factor-erythroid 2 related factor 2 (Nrf2) protein, and significantly increased the mRNA and protein expression of its downstream anti-oxidant factors such as heme oxygenase-1 and quinone oxidoreductase-1, which suggested that baicalin exerted anti-oxidant effects by activating the Nrf2-HO1 signaling pathway. Thus, pretreatment with baicalin inhibited LPS - induced oxidative stress and protected the normal physiological function of IPEC-J2 cells via NF-κB and Nrf2–HO1 signaling pathways.

Alterations in intestinal microbiota composition coincide with impaired intestinal morphology and dysfunctional ileal immune response in growing-finishing pigs under constant chronic heat stress

Background

Previous studies had shown that short-term acute heat stress (HS) affected the host’s metabolism and intestinal microbiota independent of feed intake (FI) reduction, and long-term calorie restriction caused intestinal morphological injuries and gut microbial alterations. However, research on the effects of constant chronic HS on intestinal microbial composition and the roles of FI reduction played in is limited. This study aimed to investigate the effects of 7-day constant chronic HS on the composition of intestinal microbes in growing-finishing pigs, and its relationship with pigs’ performance, intestinal morphology, and ileal immune response. Twenty-four growing-finishing pigs (Duroc × Large White × Landrace, 30 ± 1 kg body weight) were randomly assigned to three treatments (n = 8), 1) thermal neutral (TN) conditions (25 ± 1 °C) with ad libitum FI, 2) HS conditions (35 ± 1 °C) with ad libitum FI, 3) pair-fed (PF) with HS under TN conditions to discriminate the confounding effects of dissimilar FI, and the FI was the previous day’s average FI of HS. The small intestinal segments (duodenum, jejunum, and ileum) and feces were collected on d 8.

Results

Results indicated that HS drastically declined (P < 0.05) average daily gain (ADG) and average daily feed intake (ADFI) (about 61%) in comparison with TN, and caused hyperpyrexia, meanwhile PF caused hypothermia. Morphological observation by light and electron microscopes showed that both HS and PF treatment decreased (P < 0.05) the villus and microvillus height compared with TN. Additionally, HS increased (P < 0.05) protein expression of heat shock protein 70 in the duodenum, jejunum, and ileum. Furthermore, the expression of tight junction protein zonula occluden-1 (ZO-1) in the duodenum and ileum, and Occludin in the ileum were enhanced (P < 0.05) compared with TN and PF. Moreover, HS significantly enhanced (P < 0.05) the mRNA relative expression of inflammatory cytokines (TLR-2, TLR-4, and tumor necrosis factor-α (TNF-α), IL-6, IL-8, PG1–5, β-defensin 2 (pBD-2)), mucins (mucin-1 and mucin-2) and P65 protein level in the ileal mucosa tissue. Intestinal microbiota analysis by 16S rRNA sequencing showed lower (P < 0.10) α diversity in both HS and PF, and a separated cluster of β diversity among groups. Compared with TN, HS but not PF mainly reduced (FDR < 0.05) Bacteroidetes (phylum), Bacteroidia (class) and elevated the proportions of Proteobacteria (phylum, FDR < 0.05), Bacillales (order, FDR < 0.05), Planococcaceae (family, FDR < 0.05), Kurthia (genus, FDR < 0.05), Streptococcaceae (family, FDR < 0.10) and Streptococcus (genus, FDR < 0.10). Notably, Lactobacillales (order) was decreased (FDR < 0.05) by PF alone. Furthermore, the Spearman correlation analysis indicated that the microbes prevalent in HS were positively (P < 0.05) associated with intestinal morphological injuries indicators and ileal immune response parameters, and the microbes reduced in HS were negatively (P < 0.05) with the performance data.

Conclusions

Intestinal morphological injuries and ileal immune response caused by constant chronic HS independent of FI showed close connections with alterations in intestinal microbiota in growing-finishing pigs.

Microbiota-gut-brain axis and nutritional strategy under heat stress

Heat stress is a very universal stress event in recent years. Various lines of evidence in the past literatures indicate that gut microbiota composition is susceptible to variable temperature. A varied microbiota is necessary for optimal regulation of host signaling pathways and disrupting microbiota-host homeostasis that induces disease pathology. The microbiota–gut–brain axis involves an interactive mode of communication between the microbes colonizing the gut and brain function. This review summarizes the effects of heat stress on intestinal function and microbiota–gut–brain axis. Heat stress negatively affects intestinal immunity and barrier functions. Microbiota-gut-brain axis is involved in the homeostasis of the gut microbiota, at the same time, heat stress affects the metabolites of microbiota which could alter the function of microbiota–gut–brain axis. We aim to bridge the evidence that the microbiota is adapted to survive and thrive in an extreme environment. Additionally, nutritional strategies for alleviating intestinal heat stress are introduced.

Heat Stress-Mediated Activation of Immune-Inflammatory Pathways

Physiological changes in animals exposed to elevated ambient temperature are characterized by the redistribution of blood toward the periphery to dissipate heat, with a consequent decline in blood flow and oxygen and nutrient supply to splanchnic tissues. Metabolic adaptations and gut dysfunction lead to oxidative stress, translocation of lumen contents, and release of proinflammatory mediators, activating a systemic inflammatory response. This review discusses the activation and development of the inflammatory response in heat-stressed models.

Effect of chitosan on blood profile, inflammatory cytokines by activating TLR4/NF-κB signaling pathway in intestine of heat stressed mice

Heat stress can significantly affect the immune function of the animal body. Heat stress stimulates oxidative stress in intestinal tissue and suppresses the immune responses of mice. The protecting effects of chitosan on heat stress induced colitis have not been reported. Therefore, the aim of this study was to investigate the protective effects of chitosan on immune function in heat stressed mice. Mice were exposed to heat stress (40 °C per day for 4 h) for 14 consecutive days. The mice (C57BL/6J), were randomly divided into three groups including: control group, heat stress, Chitosan group (LD: group 300 mg/kg/day, MD: 600 mg/kg/day, HD: 1000 mg/kg/day). The results showed that tissue histology was improved in chitosan groups than heat stress group. The current study showed that the mice with oral administration of chitosan groups had improved body performance as compared with the heat stress group. The results also showed that in chitosan treated groups the production of HSP70, TLR4, p65, TNF-α, and IL-10 was suppressed on day 1, 7, and 14 as compared to the heat stress group. In addition Claudin-2, and Occludin mRNA levels were upregulated in mice receiving chitosan on day 1, 7, and 14 of heat stress. Furthermore, the IL-6, IL-10, and TNF-α plasma levels were down-regulated on day 1, 7, and 14 of heat stress in mice receiving the oral administration of chitosan. In conclusion, the results showed that chitosan has an anti-inflammatory ability to tolerate hot environmental conditions.

Terpinen4-ol inhibits heat stress induced inflammation in colonic tissue by Activating Occludin, Claudin-2 and TLR4/NF-κB signaling pathway

Heat stress has severe implications on the health of mice involving intestinal mucosal barrier damage and dysregulated mucosal immune response. This study was designed with long-term heat stress to detect the protective effect of terpinen4-ol on body weight, colon length, organ index, morphological structure, inflammatory cytokines expression, Claudin-2, Occludin, and TLR4 signaling pathway of colonic tissue in mice under heat stress. A study found that oral administration of terpinen4-ol helped against mortality and intestinal inflammation in a mouse model of acute colitis induced by heat stress (40 °C per day for 4 h) exposed for 14 consecutive days. The mice were divided into five groups including control, heat stress, terpinen4-ol low dose (TER LD: 5 mg/kg), medium dose (TER MD: 10 mg/kg), and high dose (TER HD: 20 mg/kg) group. Our study showed that the heat-stress terpinen4-ol group had improved body weight, colon length, and organ index, the number of white blood cells, lymphocytes, and neutrophils in the blood as compared to the heat stress group. In addition, results showed that heat stress upregulated the expression of TLR4, p65, TNF-α, and IL-10. While, in mice receiving the oral administration of terpinen4-ol, the production of TNF-α, IL-10, TLR4, and p65 was suppressed on day 1, 7, and 14 of heat stress. In addition Claudin-2, Occludin mRNA levels were upregulated in mice receiving terpinen4-ol on day 1, 7, and 14 of heat stress. Furthermore, the IL-6, IL-10, TNF-α serum levels were also upregulated in mice under heat stress, but in mice receiving the oral administration of terpinen4-ol, the IL-6, IL-10, TNF-α level was down-regulated on day 1, 7, and 14 of heat stress. Histomorphological examination found that as compared to the control group, the muscle layer thickness and villi height of mice in the heat stress group were significantly reduced, while the changes of the above indicators in the terpinene4-ol groups were improved than those in the heat stress group. In conclusion, the terpinen4-ol has a protective effect on colonic tissue damage induced by heat stress.

Effect of heat stress on growth and production performance of livestock and poultry: Mechanism to prevention

Heat stress is a widespread phenomenon in domestic animal feeding in tropical and sub-tropical areas that are subjected to a growing negative effect in livestock and poultry due to global warming. It leads to reduced food intake, retarded growth, intestinal disequilibrium, lower reproductive performance, immunity and endocrine disorders in livestock and poultry. Many studies show that the pathogenesis of heat stress is mainly related to oxidative stress, hormone secretion disorder, cytokine imbalance, cell apoptosis, cell autophagy, and abnormal cell function. Its mechanism refers to activation of mitogen-activated protein kinase (MAPK) signaling pathway and nuclear factor kappa B (NF-κB) signaling pathway, the fluctuation of tight junction protein and heat shock protein expression, and protein epigenetic modification. This manuscript reviews the mechanism of heat stress through an insight into the digestive, reproductive, immune, and endocrine system. Lastly, the progress in prevention and control techniques of heat stress has been summarized.

Jejunal mucosa proteomics unravel metabolic adaptive processes to mild chronic heat stress in dairy cows

Climate change affects the duration and intensity of heat waves during summer months and jeopardizes animal health and welfare. High ambient temperatures cause heat stress in dairy cows resulting in a reduction of milk yield, feed intake, and alterations in gut barrier function. The objectives of this study were to investigate the mucosal amino acid, glucose and lactate metabolism, as well as the proteomic response of the small intestine in heat stressed (HS) Holstein dairy cows. Cows of the HS group (n = 5) were exposed for 4 days to 28 °C (THI = 76) in a climate chamber. Percentage decrease in daily ad libitum intake of HS cows was calculated to provide isocaloric energy intake to pair-fed control cows kept at 15 °C (THI = 60) for 4 days. The metabolite, mRNA and proteomic analyses revealed that HS induced incorrect protein folding, cellular destabilization, increased proteolytic degradation and protein kinase inhibitor activity, reduced glycolysis, and activation of NF-κB signaling, uronate cycling, pentose phosphate pathway, fatty acid and amino acid catabolism, mitochondrial respiration, ATPase activity and the antioxidative defence system. Our results highlight adaptive metabolic and immune mechanisms attempting to maintain the biological function in the small intestine of heat-stressed dairy cows.

Intestinal Homeostasis under Stress Siege

Intestinal homeostasis encompasses a complex and balanced interplay among a wide array of components that collaborate to maintain gut barrier integrity. The appropriate function of the gut barrier requires the mucus layer, a sticky cushion of mucopolysaccharides that overlays the epithelial cell surface. Mucus plays a critical anti-inflammatory role by preventing direct contact between luminal microbiota and the surface of the epithelial cell monolayer. Moreover, mucus is enriched with pivotal effectors of intestinal immunity, such as immunoglobulin A (IgA). A fragile and delicate equilibrium that supports proper barrier function can be disturbed by stress. The impact of stress upon intestinal homeostasis results from neuroendocrine mediators of the brain-gut axis (BGA), which comprises a nervous branch that includes the enteric nervous system (ENS) and the sympathetic and parasympathetic nervous systems, as well as an endocrine branch of the hypothalamic-pituitary-adrenal axis. This review is the first to discuss the experimental animal models that address the impact of stress on components of intestinal homeostasis, with special emphasis on intestinal mucus and IgA. Basic knowledge from animal models provides the foundations of pharmacologic and immunological interventions to control disturbances associated with conditions that are exacerbated by emotional stress, such as irritable bowel syndrome.

Nutritional considerations to counteract gastrointestinal permeability during exertional heat stress

Intestinal barrier integrity and function are compromised during exertional heat stress (EHS) potentially leading to consequences that range from minor gastrointestinal (GI) disturbances to fatal outcomes in exertional heat stroke or septic shock. This mini-review provides a concise discussion of nutritional interventions that may protect against intestinal permeability during EHS and suggests physiological mechanisms responsible for this protection. Although diverse nutritional interventions have been suggested to be protective against EHS-induced GI permeability, the ingestion of certain amino acids, carbohydrates, and fluid per se is potentially effective strategy, whereas evidence for various polyphenols and pre/probiotics is developing. Plausible physiological mechanisms of protection include increased blood flow, epithelial cell proliferation, upregulation of intracellular heat shock proteins, modulation of inflammatory signaling, alteration of the GI microbiota, and increased expression of tight junction (TJ) proteins. Further clinical research is needed to propose specific nutritional candidates and recommendations for their application to prevent intestinal barrier disruption and elucidate mechanisms during EHS.

Preventive Effects of Bacillus licheniformis on Heat Stroke in Rats by Sustaining Intestinal Barrier Function and Modulating Gut Microbiota

Heat stroke (HS) models in rats are associated with severe intestinal injury, which is often considered as the key event at the onset of HS. Probiotics can regulate the gut microbiota by inhibiting the colonization of harmful bacteria and promoting the proliferation of beneficial bacteria. Here, we investigated the preventive effects of a probiotic Bacillus licheniformis strain (BL, CMCC 63516) on HS rats as well as its effects on intestinal barrier function and gut microbiota. All rats were randomly divided into four groups: control (Con) + PBS (pre-administration with 1 ml PBS twice a day for 7 days, without HS induction), Con + BL group (pre-administration with 1 ml 1 × 10⁸ CFU/ml BL twice a day for 7 days, without HS induction), HS + PBS (PBS, with HS induction), and HS + BL (BL, with HS induction). Before the study, the BL strain was identified by genomic DNA analysis. Experimental HS was induced by placing rats in a hot and humid chamber for 60 min until meeting the diagnostic criterion of HS onset. Body weight, core body temperature, survival rate, biochemical markers, inflammatory cytokines, and histopathology were investigated to evaluate the preventive effects of BL on HS. D-Lactate, I-FABP, endotoxin, and tight-junction proteins were investigated, and the fluorescein isothiocyanate-dextran (FD-4) test administered, to assess the degree of intestinal injury and integrity. Gut microbiota of rats in each group were analyzed by 16S rRNA sequencing. The results showed that pre-administration with BL significantly attenuated hyperthermia, reduced HS-induced death, alleviated multiple-organ injury, and decreased the levels of serum inflammatory cytokines. Furthermore, BL sustained the intestinal barrier integrity of HS rats by alleviating intestinal injury and improving tight junctions. We also found that BL significantly increased the ratios of two probiotic bacteria, Lactobacillus and Lactococcus. In addition, Romboutsia, a candidate biomarker for HS diagnosis, was unexpectedly detected. In summary, BL pre-administration for 7 days has preventative effects on HS that may be mediated by sustaining intestinal barrier function and modulating gut microbiota.

Mild heat stress changes the microbiota diversity in the respiratory tract and the cecum of layer-type pullets

The present study aimed to research the effects of cyclic heat environment on the microbial diversity and structure of respiratory tract and cecum of chicken. A total of 360 layer-type pullets at 11 wk of age were subjected to different temperature treatments for 10 wk: constant 22°C; cyclic temperature 22°C to 24°C, 22°C to 26°C, 22°C to 28°C, 22°C to 30°C; the ambient temperature increased from 10:00, reached the set point within 1 h, and maintained until 18:00, thereafter the temperature was restored to 22°C; and the relative humidity was maintained at 60%. The result showed that feed intake of the chickens on ambient temperature 30°C group was significantly lower than that of the chickens on ambient temperature 24°C. The white blood cell, red blood cell, lymphocyte, hemoglobin, and pecked-cell volume content were highest at 24°C on 14, 16, and 18 wk. The ratio of CD3⁺CD4⁺/CD3⁺CD8⁺ T cells was lowest at 30°C. Meanwhile, the abundance of cecum bacteria in chickens at 30°C was lower than that at 24°C. Cyclic heat environment temperature treatment did not significantly affect the concentration of secretory immunoglobulin A in chicken bronchoalveolar lavage fluid (BALF) levels during 10 wk of trial. The diversity index analysis showed that the effect of 24°C on the cecum flora of chickens was optimal. Abundance of Firmicutes bacteria in the lung flora and cecum flora was lower at 30°C than at 24°C group. Similarly, the microorganism, Brevibacillus in the BALF was also significantly lower at 24°C. In conclusion, cyclic 24°C treatment was beneficial for the feed intake, blood routine indexes, microflora structure of the cecum, and respiratory tract in laying pullets.

Salivary Immunoglobulin A Secretion and Polymeric Ig Receptor Expression in the Submandibular Glands Are Enhanced in Heat-Acclimated Rats

Salivary immunoglobulin A (IgA) plays a critical role in mucosal immunity. Chronic exposure to moderate heat induces heat acclimation, which modifies salivary functions. However, the changes in salivary IgA secretion in heat-acclimated rats are unclear. In this study, we investigated salivary IgA secretion and the expression of polymeric Ig receptor (pIgR), a key mediator of mucosal IgA secretion, in the submandibular glands (SMGs) of heat-acclimated rats. Following maintenance at an ambient temperature (T_a) of 24 ± 0.1 °C for 10 days, male Wistar rats were subjected to T_a of 32 ± 0.2 °C for 5 days (HE group) for heat acclimation or maintained at T_a of 24 ± 0.1°C (CN group). The rats were then anesthetized, pilocarpine (0.5 mg/kg) was intraperitoneally injected, and saliva was collected. Afterward, the SMGs and plasma were sampled. The salivary IgA concentration and IgA flow rate were significantly higher in the HE group than in the CN group. Similarly, SMG pIgR expression was significantly higher in HE rats. The levels of plasma cytokines, including interleukin (IL)-5, IL-6, and interferon-γ, were significantly greater in HE rats than in CN rats. Heat acclimation may enhance oral immunity through salivary IgA secretion and pIgR upregulation in the SMGs.

Effect of heat stress on the quantitative expression patterns of different cytokine genes in Malabari goats

A study was conducted to determine the influence of exposure to hot environment on different cytokine gene expression patterns in Malabari goat. The study was conducted in 12 (10 months to 1 year old) goats of Malabari breed for 45-day duration. The control (n = 6; C) group goats were kept under comfortable condition in the shaded pens while heat stress (n = 6; HS) group goats were kept out in the open hot environment during summer season for the study duration between 10.00 h to 16.00 h. The representative mesenteric lymph node (MLN) samples were collected from the slaughtered goats at the end of study for assessing the different cytokine gene expression and histopathological changes. Compared with C group, the expression patterns of interleukin 18 (IL-18), tumor necrosis factor-α (TNF-α), interferon-β (IFN-β), and IFN-γ downregulated (P < 0.05) in the HS group. The histopathological changes of MLNs showed paucity of lymphocyte distribution in follicular areas as wells as decreased density of lymphocytes in the germinal centers of the HS group (P < 0.05). The findings from this study reflected the compromised immune functions during heat stress in Malabari goats. Further, the study established that IL-18, TNF-α, IFN-β, and IFN-γ genes could serve as reliable immunological markers for quantifying heat stress-mediated immune response alterations in Malabari goats.

Heat exposure affects jejunal tight junction remodeling independently of adenosine monophosphate-activated protein kinase in 9-day-old broiler chicks

Dysfunction of the intestinal epithelial barrier under elevated temperatures is assumed to prompt pathological conditions and to eventually impede chickens' growth, resulting in massive economic losses in broiler industries. The aims of this research were to determine the impact of acute heat stress on the intestinal tight junction network of broiler chicks (Gallus domesticus L.) and to elucidate whether adenosine monophosphate-activated protein kinase (AMPK) was involved in the integrated response of the broiler's gastrointestinal tract to heat stress. A total of 80 9-day-old Arbor Acres chicks were subjected to temperature treatment (thermoneutral versus heat stress) and AMPK inhibition treatment (5 mg/kg body weight intraperitoneal injection of compound C vs. sham treatment) for 72 h. In addition to monitoring growth performance, the mRNA and protein levels of key tight junction proteins, target components of the AMPK pathway, and biomarkers of intestinal inflammation and oxidative stress were assessed in the jejunum under both stressors at 24 and 72 h. An increase of the major tight junction proteins, claudin-1 and zonula occludens-1, was implemented in response to an exacerbated expression of the AMP-activated protein kinase. Heat stress did not affect zootechnical performance but was confirmed by an increased gene expression of heat shock proteins 70 and 90 as well as heat shock factor-1. In addition, hyperthermia induced significant effects on tight junction proteins, although it was independent of AMPK.

Protective effects of zymosan on heat stress-induced immunosuppression and apoptosis in dairy cows and peripheral blood mononuclear cells

Dairy cows exposed to heat stress (HS) show decreased performance and immunity, but increased heat shock protein expressions and apoptosis. Zymosan, an extract from yeast cell walls, has been shown to modulate immune responses and defense against oxidative stress. However, few literatures are available about the effects of zymosan on immune responses and other parameters of the dairy cows under HS. Here, both primary peripheral blood mononuclear cell (PBMC) and dairy cow models were established to assess the effects of zymosan on performance, immunity, heat shock protein, and apoptosis-related gene expressions of dairy cows under HS. In vitro study showed that proliferation, IL-2 production, and Bcl-2/Bax-α ratio of cow primary PBMC were reduced, whereas hsp70 mRNA and protein expressions, as well as Annexin V-bing, were increased when PBMCs were exposed to heat. In contrast, zymosan significantly reversed these above changes induced by the HS. In the in vivo study, 40 Holstein dairy cows were randomly selected and assigned into zymosan group (supplemental zymosan; n = 20) and control group (no supplemental zymosan; n = 20). The results showed that zymosan improved significantly the dry matter intake and milk yield, increased IgA, IL-2, and tumor necrosis factor-α (TNF-α) contents in sera, as well as hepatic Bcl-2/Bax-α ratio, but decreased respiration rate and hepatic hsp70 expressions in the dairy cows under HS. Taken together, zymosan could alleviate HS-induced immunosuppression and apoptosis and improve significantly the productive performance and immunity of dairy cows under HS.

Effect of patchouli alcohol on the regulation of heat shock-induced oxidative stress in IEC-6 cells

Purpose Patchouli alcohol (PA) is used to treat gastrointestinal dysfunction. The purpose of this study was to ascertain the function of PA in the regulated process of oxidative stress in rat intestinal epithelial cells (IEC-6). Materials and methods Oxidative stress was stimulated by exposing IEC-6 cells to heat shock (42 °C for 3 h). IEC-6 cells in treatment groups were pretreated with various concentrations of PA (10, 40, and 80 ng/mL) for 3 h before heat shock. Results Heat shock caused damage to the morphology of IEC-6 cells, and increased reactive oxygen species (ROS) level and malondialdehyde (MDA) content. Moreover, mRNA and protein expression by target genes related to oxidative stress in heat shock were also altered. Specifically, the mRNA expression by HSP70, HSP90, GSH-px, NRF2 nd HO-1were all increased, and Nrf2 and Keap1 protein expression were increased after heat shock. However, pretreatment with PA weakened the level of damage to the cellular morphology, and decreased the MDA content caused by heat shock, indicating PA had cytoprotective activities. Pretreatment with PA at high dose significantly increased generation of intracellular ROS. Compared with the heat shock group alone, PA pretreatment significantly decreased the mRNA expression by HSP70, HSP90, SOD, CAT, GSH-px, KEAP1 and HO-1. Furthermore, the high dose of PA significantly increased Nrf2 protein expression, while both the intermediate and high dose of PA significantly increased HO-1 protein expression. Conclusion Heat-shock-induced oxidative stress in IEC-6 cells, and PA could alleviate the Nrf2-Keap1 cellular oxidative stress responses.

Intestinal epithelial barrier function and tight junction proteins with heat and exercise

A single layer of enterocytes and tight junctions (intercellular multiprotein complexes) form the intestinal epithelial barrier that controls transport of molecules through transcellular and paracellular pathways. A dysfunctional or "leaky" intestinal tight junction barrier allows augmented permeation of luminal antigens, endotoxins, and bacteria into the blood stream. Various substances and conditions have been shown to affect the maintenance of the intestinal epithelial tight junction barrier. The primary focus of the present review is to analyze the effects of exertional or nonexertional (passive hyperthermia) heat stress on tight junction barrier function in in vitro and in vivo (animals and humans) models. Our secondary focus is to review changes in tight junction proteins in response to exercise or hyperthermic conditions. Finally, we discuss some pharmacological or nutritional interventions that may affect the cellular mechanisms involved in maintaining homeostasis of the intestinal epithelial tight junction barrier during heat stress or exercise.

Microarray analysis of intestinal immune-related gene expression in heat-stressed rats

PURPOSE

This study aimed to investigate immune-related gene expression in rat small intestine after heat stress.

MATERIALS AND METHODS

Twelve Sprague Dawley (SD) rats were randomly divided into control and heat-stressed groups. Rats in both groups were housed at 25 °C with 60% relative humidity. The heat-stressed group was subjected to 40 °C for 2 h/day for 3 days. After heat stress, the mRNA expression profile of small intestine epithelial tissue was evaluated by microarray analysis.

RESULTS

A total of 23 genes related to immune responses were significantly altered, of which 12 genes were up-regulated and 11 genes were down-regulated.

CONCLUSIONS

Microarray analysis demonstrated the JAK-STAT pathway had a potentially important role in the regulation of inflammation in the small intestine, and changes in antigen presentation might reduce intestinal immune responses after heat stress.

Stress modulates intestinal secretory immunoglobulin A

Stress is a response of the central nervous system to environmental stimuli perceived as a threat to homeostasis. The stress response triggers the generation of neurotransmitters and hormones from the hypothalamus pituitary adrenal axis, sympathetic axis and brain gut axis, and in this way modulates the intestinal immune system. The effects of psychological stress on intestinal immunity have been investigated mostly with the restraint/immobilization rodent model, resulting in an up or down modulation of SIgA levels depending on the intensity and time of exposure to stress. SIgA is a protein complex formed by dimeric (dIgA) or polymeric IgA (pIgA) and the secretory component (SC), a peptide derived from the polymeric immunoglobulin receptor (pIgR). The latter receptor is a transmembrane protein expressed on the basolateral side of gut epithelial cells, where it uptakes dIgA or pIgA released by plasma cells in the lamina propria. As a result, the IgA-pIgR complex is formed and transported by vesicles to the apical side of epithelial cells. pIgR is then cleaved to release SIgA into the luminal secretions of gut. Down modulation of SIgA associated with stress can have negative repercussions on intestinal function and integrity. This can take the form of increased adhesion of pathogenic agents to the intestinal epithelium and/or an altered balance of inflammation leading to greater intestinal permeability. Most studies on the molecular and biochemical mechanisms involved in the stress response have focused on systemic immunity. The present review analyzes the impact of stress (mostly by restraint/immobilization, but also with mention of other models) on the generation of SIgA, pIgR and other humoral and cellular components involved in the intestinal immune response. Insights into these mechanisms could lead to better therapies for protecting against pathogenic agents and avoiding epithelial tissue damage by modulating intestinal inflammation.