Female gut and genital tract microbiota-induced crosstalk and differential effects of short-chain fatty acids on immune sequelae

The gut and genital tract microbiota of females represent very complex biological ecosystems that are in continuous communication with each other. The crosstalk between these two ecosystems impacts host physiological, immunological and metabolic homeostasis and vice versa. The vaginal microbiota evolved through a continuous translocation of species from the gut to the vagina or through a mother-to-child transfer during delivery. Though the organisms retain their physio-biochemical characteristics while in the vagina, the immune responses elicited by their metabolic by-products appear to be at variance with those in the gut. This has critical implications for the gynecological, reproductive as well as overall wellbeing of the host and by extension her offspring. The homeostatic and immunomodulatory effects of the bacterial fermentation products (short chain fatty acids, SCFAs) in the gut are better understood compared to the genital tract. While gut SCFAs prevent a leakage of bacteria and bacterial products from the gut in to circulation (leaky gut) and consequent systemic inflammation (anti-inflammatory/protective role); they have been shown to exhibit dysbiotic and proinflammatory effects in the genital tract that can lead to unfavorable gynecological and reproductive outcomes. Therefore, this review was conceived to critically examine the correlation between the female gut and genital tract microbiota. Secondly, we explored the metabolic patterns of the respective microbiota niches; and thirdly, we described the diverse effects of products of bacterial fermentation on immunological responses in the vaginal and rectal ecosystems

Analysis of cervicovaginal fluid metabolome and microbiome in relation to preterm birth.

The biochemical activities and resultant metabolic by-products of the vaginal microbial community during gestation can provide useful insight into the pathophysiology of preterm birth (PTB), as well as help in identifying women at risk. These metabolic changes leave specific signature fingerprints that can be investigated by Magnetic resonance spectroscopy (MRS). Therefore, we hypothesised that women who ultimately deliver prematurely will have significantly different vaginal microbiota metabolite signatures compared to their term counterparts even in the absence of clinical infection. In order to characterise and validate the cervicovaginal fluid (CVF) metabolite profiles and determine their predictive capacities for PTB, high-vaginal swabs were obtained from asymptomatic and symptomatic pregnant women sub-classified depending on a previous history of PTB and/or short cervix (< 25 mm) into: asymptomatic low risk (ALR) women with no prior PTB nor short cervix, 20-22 gestational weeks (w), n = 183; and asymptomatic high risk (AHR) women with prior history of PTB and/or short cervix, 20-22 w, n = 186. A subset of these women were assessed again at 26-28 w (due to their high-risk status), n = 129. The fourth cohort comprised women presenting with symptoms of threatened preterm labour (PTL) 24-36 w, n = 89 (SYM). CVF dissolved in phosphate buffered saline was analysed with a 9.4T MR spectrometer. Metabolites were identified, integrated for peak area and normalised to the total spectrum integral (excluding water signal). Acetate concentrations (AceConc) were also determined from a randomly selected subset of SYM women (n = 57), by a spectrophotometric technique. Additionally, clinical parameters such as cervical length (CL), fetal fibronectin (FFN), and vaginal pH were recorded and correlated to the metabolites. Furthermore, the 16S rDNA of vaginal bacterial species were PCR-amplified and the vaginal cytology was also determined by Gram, Hematoxylin and eosin, and Papanicolaou staining methods. We observed that acetate normalised integral (N.I.) (P = 0.002), and acetate/lactate ratio (P = 0.002) were higher in the SYM women who delivered preterm. These were also predictive of PTB < 37 w (AUROC: acetate N.I. = 0.75; acetate/lactate ratio = 0.76), < 32 w (AUROC: acetate N.I. = 0.73; acetate/lactate ratio = 0.79), and within 2 weeks of the index assessment (AUROC: acetate N.I. = 0.77; acetate/lactate ratio = 0.78), whilst glutamine/glutamate N.I.s was predictive of PTB < 32 w (AUROC = 0.71), and within 2 weeks of the index assessment (AUROC = 0.68) only. Also, in the AHR20-22w and ALR women, acetate (AUROC = 0.61) and branched chain amino acids N.I.s (AUROC = 0.75) were predictive of PTB < 37 w respectively. Normalised integrals of succinate, formate, lactate, and glucose did not differ in relation to PTB in any of the groups. Like the acetate N.I.s, AceConc in the SYM women was higher (P = 0.006) in the preterm-delivered women and was predictive of PTB 0.53 g/l. AceConc also correlated with acetate N.I. (r = 0.69; P < 0.0001). PCR revealed a higher prevalence of potentially pathogenic anaerobic bacteria species in the preterm-delivered women across the groups except the ALR women. Apart from correlating with clinical parameters, the prediction of PTB was improved especially in the SYM women when metabolite N.I.s, CL and FFN were combined. In conclusion, elevated CVF acetate showed clinically useful discriminative propensity for preterm delivery and delivery within 2 weeks of presentation in symptomatic women. A ratio of acetate to lactate showed similar discriminatory capacity in symptomatic women, whilst branched chain amino acids appeared predictive of preterm delivery in asymptomatic women at low risk of PTB. These metabolite differences were supported with the association of higher prevalence of mixed anaerobes in the vaginal melieu and preterm birth

Gene-related prevalence of metabolically healthy obesity in different racio-ethnic groups

The metabolically healthy obesity (MHO) phenotype is partly influenced by race/ethnicity and genetic factors being relatively more prevalent in some groups compared to others. This review examines current evidence on the prevalence of MHO amongst children, adolescents and adults of different racio-ethnic groups; and explores gene variants and single nucleotide polymorphisms (SNPs) that may confer cardioprotection in some racio-ethnic groups compared to others. Literature search of articles published in English was conducted using PubMed, Medline and Google scholar databases, with search terms related to the prevalence of metabolically healthy obesity as well as genetic variants that decrease or increase the risk of metabolic syndrome (MetS). MHO prevalence differed across racio-ethnic groups and gene variants that confer cardioprotection were higher in some racio-ethnic groups compared to others. Lower prevalence of MHO across all ages was particularly reported in the Middle East, while high prevalence was reported in Africans, Americans and some Asian adult population. Excluding environmental and other risk factors, we observed that Caucasians were carriers of gene variants that confer protection against cardiometabolic diseases, whilst Asians showed high frequency of gene variants that increase susceptibility to MetS. A robust understanding of the role of these gene variants, their frequency distribution and racio-ethnic variations may facilitate conceptualisation of appropriate genome wide association studies (GWAS) to determine significant associations between various genetic factors and observed phenotype or disease. This will guide policy formulation and serve as a useful tool in pharmacogenomics and precision medicine. Keywords: Obesity, metabolically healthy obesity, single nucleotide polymorphism, ethnicity, race, metabolic syndrome, gene variant

Thirst perception, drinking, arginine vasopressin activity and associated neurohumoral factors

Thirst, drinking, and arginine vasopressin (AVP) secretion are essential correlated osmoregulatory mechanisms that are crucial for normal physiologic function and overall survival of humans. These homeostatic mechanisms require or are operated via complex central and peripheral neural connections with influence from other peptides and hormones including angiotensin II, atrial natriuretic peptide and relaxin. The effectiveness of these mechanisms declines with age, and the consequences manifest during hyperosmotic challenges as decreased thirst and urine concentrating ability. The neurohumoral cascades involved in the physiological response to alterations in fluid and electrolyte balance are examined.Keywords: Thirst perception, drinking, arginine vasopressin, angiotensin II, atrial natriuretic peptide, relaxi

The vaginal microenvironment: the physiologic role of lactobacilli

In addition to being a passage for sperm, menstruum, and the baby, the human vagina and its microbiota can influence conception, pregnancy, the mode and timing of delivery, and the risk of acquiring sexually transmitted infections. The physiological status of the vaginal milieu is important for the wellbeing of the host as well as for successful reproduction. High estrogen states, as seen during puberty and pregnancy, promote the preservation of a homeostatic (eubiotic) vaginal microenvironment by stimulating the maturation and proliferation of vaginal epithelial cells and the accumulation of glycogen. A glycogen-rich vaginal milieu is a haven for the proliferation of Lactobacilli facilitated by the production of lactic acid and decreased pH. Lactobacilli and their antimicrobial and anti-inflammatory products along with components of the epithelial mucosal barrier provide an effective first line defense against invading pathogens including bacterial vaginosis, aerobic vaginitis-associated bacteria, viruses, fungi and protozoa. An optimal host-microbial interaction is required for the maintenance of eubiosis and vaginal health. This review explores the composition, function and adaptive mechanisms of the vaginal microbiome in health and those disease states in which there is a breach in the host-microbial relationship. The potential impact of vaginal dysbiosis on reproduction is also outlined

Matrix metalloproteinase-induced cervical extracellular matrix remodelling in pregnancy and cervical cancer

The phenomenal extracellular matrix (ECM) remodelling of the cervix that precedes the myometrial contraction of labour at term or preterm appears to share some common mechanisms with the occurrence, growth, invasion and metastasis of cervical carcinoma. Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that are pivotal to the complex extracellular tissue modulation that includes degradation, remodelling and exchange of ECM components, which contribute to homeostasis under normal physiological conditions such as cervical remodelling during pregnancy and puerperium. However, in cancer such as that of the uterine cervix, this extensive network of extracellular tissue modulation is altered leading to disrupted cell–cell and cell–basement membrane adhesion, abnormal tissue growth, neovascularization and metastasis that disrupt homeostasis. Cervical ECM remodelling during pregnancy and puerperium could be a physiological albeit benign neoplasm. In this review, we examined the pathophysiologic differences and similarities in the role of MMPs in cervical remodelling and cervical carcinoma

Microbial dysbiosis-induced obesity: role of gut microbiota in homoeostasis of energy metabolism

The global obesity epidemic has necessitated the search for better intervention strategies including the exploitation of the health benefits of some gut microbiota and their metabolic products. Therefore, we examined the gut microbial composition and mechanisms of interaction with the host in relation to homoeostatic energy metabolism and pathophysiology of dysbiosis-induced metabolic inflammation and obesity. We also discussed the eubiotic, health-promoting effects of probiotics and prebiotics as well as epigenetic modifications associated with gut microbial dysbiosis and risk of obesity. High-fat/carbohydrate diet programmes the gut microbiota to one predominated by Firmicutes (Clostridium), Prevotella and Methanobrevibacter but deficient in beneficial genera/species such as Bacteroides, Bifidobacterium, Lactobacillus and Akkermansia. Altered gut microbiota is associated with decreased expression of SCFA that maintain intestinal epithelial barrier integrity, reduce bacterial translocation and inflammation and increase expression of hunger-suppressing hormones. Reduced amounts of beneficial micro-organisms also inhibit fasting-induced adipocyte factor expression leading to dyslipidaemia. A low-grade chronic inflammation (metabolic endotoxaemia) ensues which culminates in obesity and its co-morbidities. The synergy of high-fat diet and dysbiotic gut microbiota initiates a recipe that epigenetically programmes the host for increased adiposity and poor glycaemic control. Interestingly, these obesogenic mechanistic pathways that are transmittable from one generation to another can be modulated through the administration of probiotics, prebiotics and synbiotics. Though the influence of gut microbiota on the risk of obesity and several intervention strategies have been extensively demonstrated in animal models, application in humans still requires further robust investigation

Mid-gestational changes in cervicovaginal fluid cytokine levels in asymptomatic pregnant women are predictive markers of inflammation-associated spontaneous preterm birth

OBJECTIVES: Perturbation of the choriodecidual space before the onset of spontaneous preterm birth (sPTB) could lead to a concomitant rise in both cervicovaginal fluid (CVF) cytokine and fetal fibronectin (FFN), and assessing the concentrations of both markers could improve the prediction of sPTB (delivery before 37 completed weeks of gestation). Therefore, we prospectively determined mid-trimester changes in CVF cytokine and FFN concentrations, and their predictive capacity for sPTB in asymptomatic pregnant women. STUDY DESIGN: CVF collected at 20+0-22+6 weeks (n = 47: Preterm-delivered = 22, Term-delivered = 25) and 26+0-28+6 weeks (n = 50: Preterm-delivered = 17, Term-delivered = 33) from 63 asymptomatic pregnant women at risk of sPTB were examined. Cytokine and FFN concentrations were determined by multiplexed bead-based immunoassay and 10Q Rapid analysis (Hologic, MA, USA) respectively. The 20+0-22+6/26+0-28+6 weeks ratios of cytokines and FFN concentrations were compared between preterm- and term-delivered women using Receiver Operating Characteristics curves to predict sPTB. Also, bacterial 16S rDNA from 64 samples (20+0-22+6 weeks n = 36, 26+0-28+6 weeks n = 28) was amplified by polymerase chain reaction to determine associations between vaginal microflora, cytokine and FFN concentrations. RESULTS: Changes in RANTES and IL-1β concentrations between 20+0-22+6 and 26+0-28+6 weeks, expressed as a ratios, were predictive of sPTB, RANTES (AUC = 0.82, CI = 0.62-0.94) more so than IL-1β (AUC = 0.71, CI = 0.53-0.85) and FFN (not predictive). Combining these markers (AUC = 0.83, CI = 0.63-0.95) showed similar predictive capacity as RANTES alone. FFN concentrations at 26+0-28+6 weeks correlated with IL-1β (r = 0.4, P = 0.002) and RANTES (r = 0.3, P = 0.03). In addition, there was increased prevalence of vaginal anaerobes including Bacteroides, Fusobacterium and Mobiluncus between gestational time points in women who experienced sPTB compared to the term women (P = 0.0006). CONCLUSIONS: CVF RANTES and IL-1β in mid-trimester of pregnancy correlate with quantitative FFN. The levels of CVF RANTES and IL-1β decline significantly in women who deliver at term unlike women who deliver preterm. This observation suggests that sPTB may be characterised by sustained choriodecidual inflammation and may have clinical value in serial screening for sPTB if confirmed by larger studies

Exploring the antimicrobial properties of vaginal Lactobacillus crispatus against preterm birth-associated bacteria

The need to develop new treatments to prevent unprompted premature delivery before 37 weeks of pregnancy remains pressing and unmet. Bacteria (Lactobacillus species) that promote vaginal health produce biochemical compounds that prevent the growth of microbes such as Gardnerella vaginalis. Overgrowth of G. vaginalis can cause vaginal infection with smelly discharge and increase a woman’s risk of sexually transmitted infections and premature delivery. In this study, we examined how normal health-promoting (L. crispatus) and potentially harmful (G. vaginalis) vaginal bacteria interact in a laboratory setting. This was in order to observe natural and effective agent(s) from L. crispatus that can hinder the growth of G. vaginalis and accompanying immune response. We observed that L. crispatus clears G. vaginalis by itself and with several biochemical compounds that it produces. Such biochemical compounds can be developed into treatment for vaginal infections and premature delivery due to infection and inappropriate immune response

Placental microbial–metabolite profiles and inflammatory mechanisms associated with preterm birth

There is growing emphasis on the potential significance of the placental microbiome and microbiome–metabolite interactions in immune responses and subsequent pregnancy outcome, especially in relation to preterm birth (PTB). This review discusses in detail the pathomechanisms of placental inflammatory responses and the resultant maternal–fetal allograft rejection in both microbial-induced and sterile conditions. It also highlights some potential placental-associated predictive markers of PTB for future investigation. The existence of a placental microbiome remains debatable. Therefore, an overview of our current understanding of the state and role of the placental microbiome (if it exists) and metabolome in human pregnancy is also provided. We critical evaluate the evidence for a placental microbiome, discuss its functional capacity through the elaborated metabolic products and also describe the consequent and more established fetomaternal inflammatory responses that stimulate the pathway to preterm premature rupture of membranes, preterm labour and spontaneous PTB