Bacteria-derived short-chain fatty acids as potential regulators of fungal commensalism and pathogenesis

The human gastrointestinal microbiome encompasses bacteria, fungi, and viruses forming complex bionetworks which, for organismal health, must be in a state of homeostasis. An important homeostatic mechanism derives from microbial competition, which maintains the relative abundance of microbial species in a healthy balance. Microbes compete for nutrients and secrete metabolites that inhibit other microbes. Short-chain fatty acids (SCFAs) are one such class of metabolites made by gut bacteria to very high levels. SCFAs are metabolised by microbes and host cells and have multiple roles in regulating cell physiology. Here, we review the mechanisms by which SCFAs regulate the fungal gut commensal Candida albicans. We discuss SCFA's ability to inhibit fungal growth, limit invasive behaviours and modulate cell surface antigens recognised by immune cells. We review the mechanisms underlying these roles: regulation of gene expression, metabolism, signalling and SCFA-driven post-translational protein modifications by acylation, which contribute to changes in acylome dynamics of C. albicans with potentially large consequences for cell physiology. Given that the gut mycobiome is a reservoir for systemic disease and has also been implicated in inflammatory bowel disease, understanding the mechanisms by which bacterial metabolites, such as SCFAs, control the mycobiome might provide therapeutic avenues.

The short-chain fatty acid crotonate reduces invasive growth and immune escape of Candida albicans by regulating hyphal gene expression

Microbes are exposed to nutritional and stress challenges in their environmental and host niches. To rise to these challenges, they regulate transcriptional programs that enable cellular adaptation. For instance, metabolite concentrations regulate post-translational modifications of chromatin, such as histone acetylation. In this way, metabolic signals are integrated with transcription. Over the last decade, several histone acylations have been discovered, including histone crotonylation. Their roles in microbial biology, environmental adaptation, and microbe-host interactions are incompletely defined. Here we show that the short-chain fatty acid crotonate, which is used to study histone crotonylation, changes cell morphology and immune interactions of Candida albicans. Crotonate reduces invasive hyphal morphogenesis of C. albicans within macrophages, thereby delaying macrophage killing and pathogen escape, as well as reducing inflammatory cytokine maturation. Crotonate's ability to reduce hyphal growth is environmentally contingent and pronounced within macrophages. Moreover, crotonate is a stronger hyphal inhibitor than butyrate under the conditions that we tested. Crotonate causes increased histone crotonylation in C. albicans under hyphal growth conditions and reduces transcription of hyphae-induced genes in a manner that involves the Nrg1 repressor pathway. Increasing histone acetylation by histone deacetylase inhibition partially rescues hyphal growth and gene transcription in the presence of crotonate. These results indicate that histone crotonylation might compete with acetylation in the regulation of hyphal morphogenesis. Based on our findings, we propose that diverse acylations of histones (and likely also non-histone proteins) enable C. albicans to respond to environmental signals, which in turn regulate its cell morphology and host-pathogen interactions.IMPORTANCEMacrophages curtail the proliferation of the pathogen Candida albicans within human body niches. Within macrophages, C. albicans adapts its metabolism and switches to invasive hyphal morphology. These adaptations enable fungal growth and immune escape by triggering macrophage lysis. Transcriptional programs regulate these metabolic and morphogenetic adaptations. Here we studied the roles of chromatin in these processes and implicate lysine crotonylation, a histone mark regulated by metabolism, in hyphal morphogenesis and macrophage interactions by C. albicans. We show that the short-chain fatty acid crotonate increases histone crotonylation, reduces hyphal formation within macrophages, and slows macrophage lysis and immune escape of C. albicans. Crotonate represses hyphal gene expression, and we propose that C. albicans uses diverse acylation marks to regulate its cell morphology in host environments. Hyphal formation is a virulence property of C. albicans. Therefore, a further importance of our study stems from identifying crotonate as a hyphal inhibitor.

136 DIABETES IS ASSOCIATED WITH IMPAIRED PERIPHERAL AND CEREBRAL HAEMODYNAMIC RESPONSES IN OLDER ADULTS

Background

Diabetes is associated with slower gait speed and adverse brain health outcomes in older adults. However, the putative mechanisms underlying these associations remain poorly explored. One such mechanism is via altered cerebral perfusion, which may represent an important intermediate phenotype in the association between diabetes and slower gait. We assessed the impact of diabetes on peripheral and cerebral haemodynamic responses during active stand as part of The Irish Longitudinal Study of Ageing (TILDA).

Methods

We assessed: (i) peripheral haemodynamic responses (heart rate, blood pressure, cardiac output) using finometry and (ii) Tissue Saturation Index (TSI) using Near-Infrared Spectroscopy (NIRS) during active stand in older adults.

Function-on-scalar regressions were used to model the impact of diabetes on the dynamic response to standing. Subsequently, multivariable linear models were used to model usual gait speed.

Results

Of 3,011 older adults (mean age: 64.2; 55.2% female) completing active stand, diabetes (n =193, 6.4%) was associated with significantly higher heart rate (mean 3.2, s.e. 0.02 bpm), higher cardiac output (mean 0.16, s.e. 0.04 L/min) and lower systolic blood pressure (mean –6.9, s.e. 1.8 mmHg) during standing. Additionally, diabetes was associated with significantly lower TSI from 10 seconds post-stand (mean –1.2%, s.e. 0.49%). Associations persisted following robust covariate adjustment. Diabetes was associated with significantly slower gait speed (-5.3 cm/s, CI (-8.4,-2.1)). In analysing the relationship between cerebral perfusion and gait speed, poorer recovery of TSI at 60-120 seconds post standing was associated with slower gait speed (0.53 cm/s slower gait speed per unit increase in TSI, p = 0.007).

Conclusion

Diabetes is associated with impaired peripheral and cerebral haemodynamic responses in addition to slower gait speed in community-dwelling older adults. Neuro-cardiovascular instability and altered cerebral perfusion may represent an important intermediate phenotype between diabetes and adverse health outcomes in older adults.

Cerebrospinal fluid levels of glial cell-derived neurotrophic factor correlate with spinal cord stimulation frequency in patients with neuropathic pain: a preliminary report

STUDY DESIGN

Case series.

OBJECTIVES

To evaluate relationships between spinal cord stimulation (SCS) parameters and levels of glial cell-derived neurotrophic factor (GDNF).

SETTING

Ambulatory pain clinic of St James's Hospital, Dublin, Ireland.

METHODS

Nine patients with an implanted SCS and Failed Back Surgery Syndrome (FBSS) were administered the Brief Pain Inventory and Short Form (36) Health Survey. Following a lumbar puncture, levels of GDNF in cerebrospinal fluid (CSF) were assayed and correlated with stimulation parameters. Controls were patients with arthritic back pain who were matched for age, gender and SF-36 score.

RESULTS

Concentrations of GDNF in CSF are higher in patients with FBSS than controls (P=0.002) and correlate with SCS frequency (P=0.029).

CONCLUSION

Concentrations of GDNF in CSF are higher in neuropathic pain and appear to be related to stimulation frequency. Further work is needed to evaluate this potential relationship, both in neuropathic pain and in other contexts such as locomotor dysfunction.

Spinal cord stimulation in pregnancy with failed back surgery syndrome

Women of child-bearing age who are candidates for trial and possible implantation of a spinal cord stimulator (SCS) may express concerns regarding its effect on their ability to become pregnant, to maintain a pregnancy and to breastfeed. Despite the large number of SCS implanted worldwide there is a paucity of data regarding its effect on fertility and the course of the pregnancy. We describe a case of 32 year old lady in our centre who became pregnant after SCS implantation and had an uneventful pregnancy with delivery of a healthy baby which was breastfed.

Polycythemia vera presenting as complex regional pain syndrome of the lower limbs

CASE REPORT

A 73-year-old woman with bilateral severe pain in her legs and feet was admitted to the hospital. The pain had started spontaneously without any known trauma a year earlier and had progressively worsened to the point that she was unable to walk. The patient complained of pain, discoloration, and sweating of the lower extremities. Physical examination revealed swollen, cold, wet, and blue extremities, with both allodynia and hyperalgesia, fulfilling criteria for a diagnosis of complex regional pain syndrome (CRPS) type 1. Laboratory findings demonstrated a hemoglobin level of 180 g/L(-1) and a hematocrit of 47%, leading to a diagnosis of polycythemia vera (PCV). Her condition slowly improved after repeated venesection, mild analgesics, and amitriptyline.

CONCLUSIONS

Polycythemia vera has not been described previously as a contributing factor in CRPS. In the present case, the diagnosis of PCV was important, because its treatment also improved the CRPS.

A prospective study comparing intravenous tenoxicam with rectal diclofenac for pain relief in day case surgery

In a prospective, randomized, double-blind study, we compared intravenous tenoxicam with rectal diclofenac for post-operative pain relief after day case arthroscopy or laparoscopic sterilization. Intravenous tenoxicam (40 mg) was administered as a single bolus at induction, or rectal diclofenac (100 mg) was administered immediately after induction. Both groups were similar with respect to age, weight, sex of the patients, the operation performed and the operative time. There were no significant differences observed between the groups for pain scores at 30 min, 60 min and 24 h post-operatively. The time to first analgesic requirement, the dose of pethidine administered and total analgesic requirements in the first 24 h post-operatively were equivalent in both groups. In view of the similar efficacy of both of these drugs, patient preference and ease of administration, the use of tenoxicam is appropriate in many patients undergoing day case surgery.

Elective tracheal intubation in cervical spine injuries

Patients presenting for surgical stabilisation of an unstable cervical spine are at risk of sustaining a further iatrogenic spinal cord injury during intubation of the trachea. Controversy exists regarding the optimal anaesthetic technique for securing the airway. We reviewed the techniques employed for intubating the trachea in our hospital over a five year period. Tracheal intubation was achieved using two different techniques: awake fibre-optic intubation with local anaesthesia, and general anaesthesia via the intravenous or inhalational route with neuromuscular blockade. Forty five patients were included. 16 patients demonstrated a pre-operative neurological deficit. Awake fibre-optic intubation was used in 27 cases, general anaesthesia was employed via the intravenous route in 17 cases and the inhalational route in 1 case. Weighted traction was employed in all cases to immobilize the cervical spine during intubation. There was no new neurological sequelae with any of these techniques. Our study suggests that there is no optimal anaesthetic technique for intubating the trachea in patients with cervical spine injuries and it is noteworthy that in line traction was used in every case.

Is repeat laparotomy of value in patients with suspected intra-abdominal sepsis in the intensive care unit?

The management of patients with suspected post laparotomy intra-abdominal sepsis poses a major therapeutic challenge to clinicians. The mortality is high and the optimal interventional modality remains ill-defined. We define the incidence, diagnostic methodology, pre- and postoperative findings and outcome of patients going from the intensive care unit for a repeat laparotomy in search of abdominal sepsis over a one year period. Fifteen patients were included with an overall mortality of 60 percent. In 6 cases more than one relaparotomy was performed with a mortality of 50 percent. Sepsis was found in 14 of the 15 cases with a mortality of 57 percent and the patient with a normal relaparotomy died. The primary surgery was elective in 26 percent of cases and the mortality was 50 percent. All the non-survivors required mechanical ventilation, inotropic support and continuous veno-veno haemodialysis while the survivors required less organ support. Radiological assessment (ultrasound scan and CT scan) were no better at predicting an abnormal relaparotomy than clinical assessment. Higher mortality rates were associated with increasing age and multi-system organ failure (p < 0.05).