Sexual dimorphism in endotoxin susceptibility after partial hepatectomy in rats

Myeloid-specific deletion of group VIA calcium-independent phospholipase A2 induces pro-inflammatory LPS response predominantly in male mice via MIP-1α activation

Polymorphisms of group VIA calcium-independent phospholipase A2 (PLA2G6) are associated with blood C-reactive protein suggesting its role in inflammation. We showed that myeloid-specific Pla2g6-deficiency in Pla2g6M-/- mice led to exaggerated inflammation and fibrosis in a lean fatty liver model. We here investigated whether these mutants display alteration in immune response after treatment with E. coli lipopolysaccharides (LPS) under acute (a single dose) and persistent (four doses) conditions. Without LPS treatment, male Pla2g6M-/- (but not Flox) mice at 12 months of age exhibited splenomegaly and hepatic necrosis, and ~ 30 % of them exhibited autoimmune hepatitis showing lymphoplasma cells with CD3(+) and CD45R(+) staining. Under acute LPS, male mutants showed an elevation of plasma MIP-1α and immunoglobulinA as well as upregulation of hepatic apoptosis and fibrosis PARP-1, Bax, MCP-1, α-SMA, and collagen I proteins. Their bone-marrow-derived macrophages also showed an elevation of MIP-1α release upon LPS stimulation in vitro. Female mutants under acute LPS showed a moderate increase in plasma KC/CXCL1, MCP-1, and IL10, and they showed no remarkable increase in hepatic fibrosis under acute or persistent LPS. Male mutants under persistent LPS displayed an elevation of aspartate aminotransferase, blood eosinophils, and hepatic apoptosis. Moreover, ~30 % of these mutants exhibited eosinophilic sclerosing portal hepatitis associated with an upregulated protein expression of hepatic CD8α, CD68, eosinophilic cationic protein, and Ly6G. Thus, myeloid-PLA2G6 deficiency led to an autoimmune and LPS-induced inflammatory liver disease via MIP-1α in a male-predominant manner. Our results may be applicable to patients with PLA2G6 mutations who undergo bacterial infection and sepsis.

NAFLD as a Sexual Dimorphic Disease: Role of Gender and Reproductive Status in the Development and Progression of Nonalcoholic Fatty Liver Disease and Inherent Cardiovascular Risk

Nonalcoholic fatty liver disease (NAFLD) spans steatosis through nonalcoholic steatohepatis, cirrhosis, and hepatocellular carcinoma (HCC) associated with striking systemic features and excess cardiovascular and liver-related mortality. The pathogenesis of NAFLD is complex and multifactorial. Endocrine derangements are closely linked with dysmetabolic traits. For example, in animal and human studies, female sex is protected from dysmetabolism thanks to young individuals’ ability to partition fatty acids towards ketone body production rather than very low density lipoprotein (VLDL)-triacylglycerol, and to sex-specific browning of white adipose tissue. Ovarian senescence facilitates both the development of massive hepatic steatosis and the fibrotic progression of liver disease in an experimental overfed zebrafish model. Consistently, estrogen deficiency, by potentiating hepatic inflammatory changes, hastens the progression of disease in a dietary model of nonalcoholic steatohepatitis (NASH) developing in ovariectomized mice fed a high-fat diet. In humans, NAFLD more often affects men; and premenopausal women are equally protected from developing NAFLD as they are from cardiovascular disease. It would be expected that early menarche, definitely associated with estrogen activation, would produce protection against the risk of NAFLD. Nevertheless, it has been suggested that early menarche may confer an increased risk of NAFLD in adulthood, excess adiposity being the primary culprit of this association. Fertile age may be associated with more severe hepatocyte injury and inflammation, but also with a decreased risk of liver fibrosis compared to men and postmenopausal status. Later in life, ovarian senescence is strongly associated with severe steatosis and fibrosing NASH, which may occur in postmenopausal women. Estrogen deficiency is deemed to be responsible for these findings via the development of postmenopausal metabolic syndrome. Estrogen supplementation may at least theoretically protect from NAFLD development and progression, as suggested by some studies exploring the effect of hormonal replacement therapy on postmenopausal women, but the variable impact of different sex hormones in NAFLD (i.e., the pro-inflammatory effect of progesterone) should be carefully considered.

Estrogen Accelerates Cell Proliferation through Estrogen Receptor α during Rat Liver Regeneration after Partial Hepatectomy

Although estrogen is implicated in the regulation of cell growth and differentiation in many organs, the exact mechanism for liver regeneration is not completely understood. We investigated the effect of estrogen on liver regeneration in male and female Wistar rats after 70% partial hepatectomy (PHx) and performed immunohistochemistry, western blotting and Southwestern histochemistry. 17β-estradiol (E₂) and ICI 182,780 were injected into male rats on the day before PHx. The proliferating cell nuclear antigen (PCNA) labeling index reached a maximum at 48 hr after PHx in males, and at 36 hr in females and E₂-treated male rats. Estrogen receptor α (ERα) was expressed in zones 1 and 2 in male rats, but was found in all zones in female rats. Interestingly, ERα was not detected at 6-12 hr after PHx but was found at 24-168 hr in male rats. However, ERα expression was found at all sampling time-points in female and E₂-treated male rats. The activity of estrogen responsive element binding proteins was detected from 12 hr after PHx in male rats but was found from 6 hr in female and E₂-treated male rats. ERα was co-expressed with PCNA during liver regeneration. These results indicate that estrogen may play an important role in liver regeneration through ERα.

Sex-based differential regulation of bacterial-induced bone resorption

BACKGROUND AND OBJECTIVE

Periodontal disease pathogenesis is comprised of the complex inflammatory immune response to oral bacterial dysbiosis. Like other inflammatory diseases, there is sexual dimorphism evident in periodontal diseases. During periodontitis, inflammatory chemokines direct neutrophils to migrate to the site of infection to neutralize the pathogen. Interestingly, these same chemokines are also involved in regulating pathogen-induced osteoclast formation. Previous reports show differences in bone turnover and lymphocyte recruitment between sexes. We hypothesize that chemokine expression is differentially regulated by sex and thus results in differential osteoclast formation.

MATERIAL AND METHODS

Male and female mice were utilized to isolate neutrophils based on expression of Ly6G-specific, as well as defined osteoclast progenitors. Cells were stimulated with lipopolysaccharide (LPS; 100 ng/mL) then analyzed for neutrophil infiltration and gene expression. Defined osteoclast progenitors were primed: macrophage-colony stimulating factor (25 ng/mL), receptor activator of NF-κB ligand (50 ng/mL), then stimulated with LPS. Osteoclasts were enumerated via TRAP stain and mRNA isolated for gene expression analysis via quantitative polymerase chain reaction.

RESULTS

In response to LPS, male neutrophils in vitro respond with increased chemokine expression and significantly more osteoclast formed in response to LPS compared to females.

CONCLUSIONS

Findings support observations in humans regarding a sexual dimorphism in oral bacterial infections of alveolar bone loss. Males have a strong inflammatory response to bacterial infection, resulting in increased inflammatory microenvironment, reduced pathogenic bacteria clearance and increased osteoclast-driven bone loss in response to differential expression of key chemokines.

Hormonal regulation of pro-inflammatory and lipid peroxidation processes in liver of old ovariectomized female rats

There is now a large body of evidence suggesting that the decline in ovarian function with menopause is associated with spontaneous increases in pro-inflammatory cytokines. On the other hand, oxidative stress has been implicated in the pathogenesis of several alterations due to menopause, and can arise through the increased production of lipid peroxides (LPO) and/or a deficiency of antioxidant defense. The aim of the present study was to investigate the effect of aging and ovariectomy on various physiological parameters related to inflammation and oxidative stress in livers obtained from old female rats and the influence of chronic exogenous administration of estrogens, phytoestrogens and growth hormone on these. Thirty-six female Wistar rats of 22 months of age were used in the present study. Twelve of them remained intact, and the other 24 had been ovariectomized at 12 months of age. Intact animals were divided into two groups and treated for 10 weeks with GH or saline, and ovariectomized animals were divided into four groups and treated for the same time with GH, estrogens, phytoestrogens or saline. A group of 2 month old intact female rats was used as young control. Protein expression of iNOS, HO-1, IL-6, TNFalpha, and IL-1beta were determined by Western blot analysis. The levels of NO( x ), LPO, TNFalpha, IL-1beta, IL-6 and IL-10 were determined in different fractions of the liver. Levels of LPO in the liver homogenates as well as iNOS protein expression and NO( x ) levels were increased in old rats as compared to young animals; this effect was more evident in ovariectomized animals. Pro-inflammatory cytokines TNF-alpha, IL-1beta and IL-6 were significantly increased and anti-inflammatory IL-10 decreased during ageing and after ovariectomy. Aging also significantly increased expression of HO-1 protein and ovariectomized rats showed an additional increase. Hormonal administration to the ovariectomized groups decreased NO( x ), LPO levels and pro-inflammatory cytokines as compared with untreated rats. Significant rise in IL-10 and reductions in the iNOS, IL-6, TNFalpha and IL-1beta proteins expression were also found. Oxidative stress and inflammation induced during aging in the liver are more marked in castrated than in intact old females. Administration of the different hormonal replacement therapies was able to inhibit the induction of pro-inflammatory cytokines and iNOS, decreased the levels of oxidative stress markers and had therapeutic potential in the prevention of liver injury.

Acute oral toxicity of colchicine in rats: effects of gender, vehicle matrix and pre-exposure to lipopolysaccharide

The oral toxicity of a single administration by gavage (10, 20 or 30 mg kg(-1) body weight) of colchicine (COL) was determined in young, mature male and female Sprague-Dawley rats. The effect of COL was evaluated in the presence or absence of additional treatment variables that included vehicle and lipopolysaccharide (LPS) pre-exposure. The vehicle for COL was either Half and Half cream (H & H) or saline, and each group included pretreatment with either saline or a low, minimally toxic dose (83 microg kg(-1) body weight) of LPS. Colchicine toxicity in both male and female age-matched rats was characterized by progressively more severe dose-related clinical signs of toxicity. These included mortality, decreased body weight and feed intake during the first several days after dosing, with recovery thereafter in surviving animals. There were differences in the severity of the toxic response to COL between male and female rats. The most notable sex-related difference was in COL lethality. Female rats were two times more susceptible to the lethal effects of COL than male rats. Saline or H & H delivery vehicles did not result in any apparent qualitative or quantitative differences in COL toxicity. LPS pretreatment significantly potentiated COL lethality in both males and females, although the potentiation in males was greater than in females. LPS pretreatment modestly increased the COL induced anorexic effect in surviving males, but not in surviving female animals. LPS did not appear to modulate either the body weights or clinical signs of COL induced toxicity in surviving males or females.

Which Gender is Better Positioned in the Process of Liver Surgery? Male or Female?

Liver surgery is a process which induces various types of stress on the liver including the total occlusion of the blood inflow, hemorrhage, massive volume reduction, and postoperative infection. Animal studies have shown a gender dimorphic response of the liver for various stresses such as ischemia/reperfusion, hemorrhage/resuscitation, hepatectomy, portal branch ligation, and endotoxemia. Most of these studies demonstrated the female liver to be more tolerant under stressful conditions than the male liver. Estrogen, which is a representative female sex hormone, may be one of the responsible factors for this gender dimorphism. The mechanism of estrogen's salutary effect includes circulatory improvement, a reduced inflammatory response, a reduced oxygen radical production, and an improved hepatic regeneration. However, the clinical evidence that supports the results of these experimental studies is still insufficient. A well-controlled prospective clinical study is necessary to clarify the role of gender or sex hormone in the process of liver surgery. This may not only lead to a deeper understanding of the liver pathophysiology, but also to the possibility of hepatoprotective therapy using sex hormone modulators. This review summarizes the current understanding of gender dimorphism in the tolerance of the liver to various hepatic stresses, which occur during the process of major liver surgery.

Sex differences in inflammatory cytokine production in hepatic ischemia-reperfusion

BACKGROUND

The inflammatory response to hepatic ischemia-reperfusion (I/R) is associated with an increase in cytokine production. Studies have documented that sex hormones modulate both the innate and adaptive immune responses, and that females are more robust than males. The aim of this study was to determine whether a sex difference in cytokine response to hepatic I/R exists under normal pathophysiologic condition without hormone intervention.

METHODS

Adult C57BL/6 mice underwent 90 min of hepatic ischemia followed by various reperfusion periods (0, 1.5, 3, 6 hr). Plasma cytokine TNF-alpha, IL-6, MIP-2, and KC were measured. Liver injury was assessed by plasma alanine transaminase (ALT) levels and liver histopathology.

RESULTS

A reperfusion time-dependent increase in hepatocellular injury was observed in both males and females, as indicated by increasing levels of plasma ALT and liver histopathology. The plasma cytokines were significantly increased in both female and male I/R groups compared to their respective sham counterparts. However, there was a significant difference in cytokine kinetics between the female and male I/R groups. Female mice initially had a higher level of IL-6, KC, and MIP-2 in response to I/R, which began to decline after 3 hr of reperfusion and were significantly lower than the male I/R counterparts by 6 hr of reperfusion. In contrast, the hepatocellular injury and TNF production were only moderately lower in female IR than male IR.

CONCLUSION

The study underscores role of the gender in differential inflammatory cytokine expression in response to hepatic I/R, which may reflect the host response outcome.

Sexual dimorphism in innate immune responses to infectious organisms

Gender has long been known to be a contributory factor in the incidence and progression of disorders associated with immune system dysregulation. More recently, evidence has accumulated that gender may also play an important role in infectious disease susceptibility. In general, females generate more robust and potentially protective humoral and cell-mediated immune responses following antigenic challenge than their male counterparts. In contrast, males have frequently been observed to mount more aggressive and damaging inflammatory immune responses to microbial stimuli. In this article we review the evidence for sexual dimorphism in innate immune responses to infectious organisms and describe our recent studies that may provide a mechanism underlying gender-based differences in conditions such as bacterial sepsis.

Sexual dimorphism in expression of receptors for bacterial lipopolysaccharides in murine macrophages: A possible mechanism for gender-based differences in endotoxic shock susceptibility

Gender-based differences in the incidence and severity of bacterial sepsis render males more susceptible to septic shock than females. However, the mechanisms that underlie this sexual dimorphism remain unclear. In the present study we confirm that males produce significantly higher levels of the inflammatory cytokine IL-6 and the acute phase protein LPS-binding protein (LBP) than females following in vivo lipopolysaccharide (LPS) exposure. It has also been verified that LPS-challenged male-derived macrophages produce higher levels of IL-1beta and lower levels of PGE(2) than similarly treated female-derived cells. Importantly, we demonstrated that male-derived macrophages produce significantly higher levels of the inflammatory chemokine IP-10 following LPS challenge than their female counterparts. It has been demonstrated further that, although resting macrophage levels of mRNA encoding Toll-like receptor 4 (TLR4) and its co-receptor CD14, are not significantly different between genders, male-derived macrophages constitutively express higher levels of these proteins on their cell surface. Elevated circulating levels of LBP and constitutively higher cell surface expression of TLR4 and CD14 on macrophages in males could result in the observed sexual dimorphism in LPS-induced inflammatory mediator production and the greater susceptibility of males to bacterial sepsis.