Pilot study: Trehalose-induced remodelling of the human microbiota affects Clostridioides difficile infection outcome in an in vitro colonic model

Within the human intestinal tract, dietary, microbial- and host-derived compounds are used as signals by many pathogenic organisms, including Clostridioides difficile. Trehalose has been reported to enhance virulence of certain C. difficile ribotypes; however, such variants are widespread and not correlated with clinical outcomes for patients suffering from C. difficile infection (CDI). Here, we make preliminary observations to how to trehalose supplementation affects the microbiota in an in vitro model and show that trehalose can reduce the outgrowth of C. difficile, preventing simulated CDI. Three clinically reflective human gut models simulated the effects of sugar (trehalose or glucose) or saline ingestion on the microbiota. Models were instilled with sugar or saline and further exposed to C. difficile spores. The recovery of the microbiota following antibiotic treatment and CDI induction was monitored in each model. The human microbiota remodeled to utilise the bioavailable trehalose. Clindamycin induction caused simulated CDI in models supplemented with either glucose or saline; however, trehalose supplementation did not result in CDI, although limited spore germination did occur. The absence of CDI in trehalose model was associated with enhanced abundances of Finegoldia, Faecalibacterium and Oscillospira, and reduced abundances of Klebsiella and Clostridium spp., compared with the other models. Functional analysis of the microbiota in the trehalose model revealed differences in the metabolic pathways, such as amino acid metabolism, which could be attributed to prevention of CDI. Our data show that trehalose supplementation remodelled the microbiota, which prevented simulated CDI, potentially due to enhanced recovery of nutritionally competitive microbiota against C. difficile.

Time course of saline-induced recovery of the gustatory system in sodium-restricted rats

Placing pregnant rats on a Na(+)-restricted diet (0.03% NaCl) results in greatly reduced chorda tympani nerve responses to Na+ stimuli in the offspring. Normal responses can be permanently restored by providing offspring one-time access to saline. We tested whether saline-induced recovery occurs in taste receptor cells present at the time of saline intake. Chorda tympani responses were recorded 2 h, 6 h, 24 h, 10 days, and 20 days after saline ingestion. Chorda tympani Na+ responses from Na(+)-restricted rats at 2 h, 6 h, 24 h, and 10 days after saline intake were comparable to responses from control Na(+)-restricted rats. Twenty days after saline consumption, responses to Na+ were significantly elevated compared with control Na(+)-restricted rats. The results indicate that extant taste receptor cells are not substantially influenced by the saline ingestion. Instead, the delayed recovery suggests that taste receptor stem cells exclusively are influenced by saline intake.

Central oxytocin and ANP receptors mediate osmotic inhibition of salt appetite in rats

These studies evaluated the involvement of central oxytocin (OT) and atrial natriuretic peptide (ANP) receptors in the osmotic inhibition of hypovolemia-induced salt appetite. Rats were pretreated centrally with the A chain of the cytotoxin ricin conjugated to OT (rAOT) or ANP (rAANP) to selectively inactivate cells bearing these respective receptors, or rats were pretreated with the unconjugated A chain (rA) as a control. Hypovolemia was induced with subcutaneous colloid injections, and rats then were given either 2 M mannitol, which raises plasma osmolality but lowers plasma sodium, or 1 M NaCl, which raises both. Hypertonic mannitol inhibited saline ingestion in rA-treated control rats but stimulated ingestion in rAOT- and rAANP-treated rats, whereas hypertonic NaCl blunted saline ingestion in rA- and rAOT-treated rats but stimulated ingestion in rAANP-treated rats. Angiotensin II-induced saline intake was similarly potentiated in rAOT- and rAANP-treated rats, indicating that this treatment also activates central inhibitory OT and ANP pathways. These data suggest that central ANP receptors mediate both Na(+)- and osmolality-induced inhibition of NaCl ingestion, whereas central OT receptors primarily mediate osmolality-induced inhibition of NaCl ingestion in rats.

Plasma volume with alternative tilting: effect of fluid ingestion

The present study determines the effect of repeated 70 degrees head-up tilt (HUT) on plasma volume (PV) shifts by measuring blood density (BD), plasma density (PD), and hematocrit (Hct). Eight men (18–26 yr) underwent a predrink period with two supine (P1 and P3) and two HUT (P2 and P4) phases of 45 min each. At the end of P4 they drank 10 ml/kg body wt of isotonic (290 mosmol/kg) sodium chloride (Iso) or hypotonic (< 10 mosmol/kg) unsweetened tea (Hypo) or nothing [control (Con)]. The following periods continued the supine (P5, P7)/upright (P6) sequence. BD and PD were measured from ear lobe blood; they were different (P < 0.05) between Con, Hypo, and Iso P6 and P7. The density of fluid that moved between intra- and extravascular compartments was 1,008.2 +/- 0.4 g/l and did not differ with test situations. In Con (P3, P5, P7), supine PV steadily decreased compared with P1 (P < 0.05). PV in P1, P2, and P3 of all treatments averaged 120 +/- 1, 101 +/- 1, and 115 +/- 1%, respectively, of PV in P4. Tilt-induced PV shifts ranged from -9.7 to -16.7% compared with PV during the respective previous phases. After drinking, PV increased (P < 0.05) above Con values at the end of P7 by 12.9% with Iso and by 6.6% with Hypo. Progressive hemoconcentration occurred in the nondrink supine periods; isotonic saline ingestion increased supine PV to Con level but did not stop or reverse the decrease of upright hemoconcentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Relaxation responses of the human proximal stomach to distension during fasting and after food

The responses of the human proximal stomach to distension were studied in 22 healthy volunteers using an intragastric polyethylene bag, inflated progressively in 30-ml steps until the limit of tolerated volume was reached. Three successive inflations were carried out during the fasting state followed by a fourth inflation after ingestion of 250 ml of either a nutrient meal or isosmolar saline. The first inflation showed an initial nonlinear pressure rise (slope of logged pressure vs. volume = 114.6 +/- 10.0 log mmHg/ml x 10(-5)), which was then followed by the development of a plateau phase, in which further distension did not increase intragastric pressure. The slopes of the subsequent fasting inflations were significantly lower than that of the first inflation (P < 0.01) but were similar to each other (slope 83.0 +/- 5.4 and 79.8 +/- 5.7 log mmHg/ml x 10(-5)), indicating that distension-induced gastric relaxation had occurred. After saline ingestion, responses to distension were similar to those during the fasted state. After the nutrient meal ingestion, however, the slope decreased to 60.3 +/- 7.7 log mmHg/ml x 10(-5) (P < 0.01 vs. saline), indicating nutrient-induced gastric relaxation. Our study demonstrates that the pressure-volume characteristics of the proximal stomach are modulated both by distension and by the presence of nutrients in the upper gut, which appear to operate independently.

Transcapillary fluid responses to lower body negative pressure

The effect of lower body negative pressure (LBNP) on transcapillary fluid balance is unknown. Therefore, our objective was to assess leg interstitial fluid pressures (IFP), leg circumference, plasma volume (PV), and net whole body transcapillary fluid transport (TFT) during and after supine LBNP and to evaluate the addition of oral saline ingestion on transcapillary exchange. Six healthy men 23–41 yr old underwent 4 h of 30 mmHg LBNP, followed by 50 min of supine recovery on two separate occasions, once with and once without ingestion of 1 liter of isotonic saline. IFP was measured continuously in subcutis as well as superficial and deep regions of the tibialis anterior muscle by slit catheters. TFT was calculated by subtracting urine production and calculated insensible fluid loss from changes in PV. During exposure to LBNP, IFP decreased in parallel with chamber pressure, foot venous pressure did not change, leg circumference increased by 3 +/- 0.35% (SE) (P < 0.05), and PV decreased by 14 +/- 2.3%. IFP returned to near control levels after LBNP. At the end of minute 50 of recovery, PV remained decreased (by 7.5 +/- 5.2%) and leg circumference remained elevated (by 1 +/- 0.37%). LBNP alone produced significant movement of fluid into the lower body but no net TFT (-7 +/- 12 ml/h). During LBNP with saline ingestion, 72 +/- 4% of the ingested fluid volume filtered out of the vascular space (TFT = 145 +/- 10 ml/h), and PV decreased by 6 +/- 3%.(ABSTRACT TRUNCATED AT 250 WORDS)