Aquaporins in the Cornea

The cornea is an avascular, transparent tissue that allows light to enter the visual system. Accurate vision requires proper maintenance of the cornea's integrity and structure. Due to its exposure to the external environment, the cornea is prone to injury and must undergo proper wound healing to restore vision. Aquaporins (AQPs) are a family of water channels important for passive water transport and, in some family members, the transport of other small molecules; AQPs are expressed in all layers of the cornea. Although their functions as water channels are well established, the direct function of AQPs in the cornea is still being determined and is the focus of this review. AQPs, primarily AQP1, AQP3, and AQP5, have been found to play an important role in maintaining water homeostasis, the corneal structure in relation to proper hydration, and stress responses, as well as wound healing in all layers of the cornea. Due to their many functions in the cornea, the identification of drug targets that modulate the expression of AQPs in the cornea could be beneficial to promote corneal wound healing and restore proper function of this tissue crucial for vision.

Exploring Skin Wound Healing Models and the Impact of Natural Lipids on the Healing Process

Cutaneous wound healing is a complex biological process involving a series of well-coordinated events aimed at restoring skin integrity and function. Various experimental models have been developed to study the mechanisms underlying skin wound repair and to evaluate potential therapeutic interventions. This review explores the diverse array of skin wound healing models utilized in research, ranging from rodent excisional wounds to advanced tissue engineering constructs and microfluidic platforms. More importantly, the influence of lipids on the wound healing process is examined, emphasizing their role in enhancing barrier function restoration, modulating inflammation, promoting cell proliferation, and promoting remodeling. Lipids, such as phospholipids, sphingolipids, and ceramides, play crucial roles in membrane structure, cell signaling, and tissue repair. Understanding the interplay between lipids and the wound microenvironment provides valuable insights into the development of novel therapeutic strategies for promoting efficient wound healing and tissue regeneration. This review highlights the significance of investigating skin wound healing models and elucidating the intricate involvement of lipids in the healing process, offering potential avenues for improving clinical outcomes in wound management.

Risk factors and mortality in dialysis patients with abdominal aortic aneurysm: A retrospective cohort study

In the general population, abdominal aortic aneurysm (AAA) is synonymous with vascular disease and associated with increased mortality. Vascular disease is common in end-stage renal disease (ESRD) patients on dialysis, but there is limited information on AAA in this population. To address this issue, we queried the United States Renal Data System for risk factors associated with a diagnosis of AAA as well as the impact of AAA on ESRD patient survival. Incident dialysis patients from 2005 to 2014 with AAA and other clinical comorbidities were identified using ICD-9 and ICD-10 codes. Time to death was defined using the time from the start of dialysis to the date of death or to December 31, 2015. Cox proportional hazards (CPH) modeling was used to determine the adjusted hazard ratio (aHR) and 95% confidence intervals (CI) for death. From a total cohort of 820,826, we identified 21,631 subjects with a diagnosis of AAA. When compared to patients without AAA, AAA patients were older and more likely to be of white race and male gender, have a higher mean Charlson comorbidity index (CCI), have hypertension as the ESRD etiology, and use tobacco. Although a bivariate CPH model showed that AAA patients had an increased mortality risk compared to patients without the diagnosis, in the final CPH model, AAA patients had a decreased risk of mortality (aHR = 0.83, 95% CI 0.81-0.84) due to confounding with age. These results suggest that AAA is not associated with increased risk of death in ESRD patients after controlling for various demographic and clinical risk factors.

Deep neck space infections in end-stage renal disease patients: Prevalence and mortality

Deep neck space infections (DNSI) are severe infections within the layers of neck fascia that are known to be associated with underlying immunocompromised states. Although uremia associated with kidney disease is known to cause immune system dysfunction, DNSI in patients with kidney disease has been poorly studied. This study investigated the prevalence of DNSI and the associated risk of mortality within the United States end-stage renal disease (ESRD) population, using a retrospective cohort study design and the United States Renal Data System database of patients (ages 18-100) who initiated dialysis therapy between 2005 and 2019. International Classification of Disease-9 and -10 codes were used to identify the diagnosis of DNSI and comorbid conditions. Of the 705,891 included patients, 2.2% had a diagnosis of DNSI. Variables associated with increased risk of DNSI were female sex, black compared to white race, catheter, or graft compared to arteriovenous fistula (AVF) access, autoimmune disease, chronic tonsillitis, diagnoses in the Charlson Comorbidity Index (CCI), tobacco use, and alcohol dependence. DNSI diagnosis was an independent risk factor for mortality, which was also associated with other comorbidity factors such as older age, catheter or graft compared to AVF access, comorbidities in the CCI, tobacco use, and alcohol dependence. Because of the increased mortality risk of DSNI in the ESRD population, health professionals should encourage good oral hygiene practices and smoking cessation, and they should closely monitor these patients to reduce poor outcomes.

The Assessment of Infection Risk in Patients with Vitiligo Undergoing Dialysis for End-Stage Renal Disease: A Retrospective Cohort Study

Vitiligo is an autoimmune condition that causes patchy skin depigmentation. Although the mechanism by which vitiligo induces immunocompromise is unclear, other related autoimmune diseases are known to predispose those affected to infection. Individuals with vitiligo exhibit epidermal barrier disruption, which could potentially increase their susceptibility to systemic infections; patients with renal disease also show a predisposition to infection. Nevertheless, there is little research addressing the risk of infection in dialysis patients with vitiligo in comparison to those without it. A retrospective analysis was performed on patients with end-stage renal disease (ESRD) in the United States Renal Data System who started dialysis between 2004 and 2019 to determine if ESRD patients with vitiligo are at an increased risk of bacteremia, cellulitis, conjunctivitis, herpes zoster, or septicemia. Multivariable logistic regression modeling indicated that female sex, black compared to white race, Hispanic ethnicity, hepatitis C infection, and tobacco use were associated with an enhanced risk of vitiligo, whereas increasing age and catheter, versus arteriovenous fistula, and access type were associated with a decreased risk. After controlling for demographics and clinical covariates, vitiligo was found to be significantly associated with an increased risk of bacteremia, cellulitis, and herpes zoster but not with conjunctivitis and septicemia.

Sleep apnea in end-stage renal disease patients: Impact on cardiovascular and neurological outcomes

INTRODUCTION

Sleep apnea (SA) is an important comorbidity in end-stage renal disease (ESRD) patients. The association between SA and cardiac and neurological disease is known. This study investigates the relationship between SA and cardiovascular and cerebrovascular outcomes in the ESRD population.

METHODS

In a retrospective cohort study, the United States Renal Data System was queried to identify ESRD patients aged 18-100 years in whom hemodialysis had been initiated between 2005 and 2013. Diagnoses of SA and clinical comorbidities were determined from International Classification of Disease-9 codes. Demographic variables were obtained from Centers for Medicare and Medicaid Services Form-2728. Logistic regression was used to examine the association of SA with myocardial infarction (MI) or with stroke, controlling for demographic and clinical variables.

RESULTS

Of 858,131 subjects meeting the inclusion criteria, 587 had central SA, and 22,724 had obstructive SA. The SA cohort was younger, more likely to be male and Caucasian compared to the non-SA cohort. Patients with SA also had more tobacco and alcohol use, hypertension, heart failure, and diabetes. Central SA (aRR = 1.69, 95% CI = 1.28-2.23) and obstructive SA (aRR = 1.15, 95% CI = 1.09-1.21) were associated with an increased risk of stroke but not MI.

CONCLUSION

In the ESRD population, a diagnosis of central SA or obstructive SA increased the risk of stroke, but not MI. Early identification and treatment of SA in the ESRD population may help reduce the risk of stroke in these patients.

Atopic Dermatitis and the Risk of Infection in End-Stage Renal Disease

Background and Objectives: Atopic dermatitis (AD), also known as eczema, is a common chronic inflammatory skin condition affecting 16.5 million adults in the United States. AD is characterized by an impaired epidermal barrier that can predispose individuals to infection. End-stage renal disease (ESRD) is also commonly complicated by infections due to chronic vascular access and immune-system dysfunction, possibly related to uremia. Multiple studies have reported that renal disease is a common comorbidity in adults with atopic dermatitis. The aim of this study was to determine whether AD is a risk factor for certain infections in patients with ESRD. Materials and Methods: Using the United States Renal Data System, a retrospective cohort analysis was conducted on adult ESRD patients initiating dialysis between 2004 and 2019 to investigate associations between infections and AD in this population. Results: Of 1,526,266 patients, 2290 were identified with AD (0.2%). Infectious outcomes of interest were bacteremia, septicemia, cellulitis, herpes zoster, and conjunctivitis. In all infectious outcomes except for conjunctivitis, patients with the infectious outcomes were more likely to carry a diagnosis of AD. After controlling for demographic and clinical covariates, AD was associated with an increased risk of cellulitis (adjusted relative risk (aRR) = 1.39, 95% confidence interval (CI) = 1.31-1.47) and herpes zoster (aRR = 1.67, CI = 1.44-1.94), but not with bacteremia (aRR = 0.96, CI = 0.89-1.05), septicemia (aRR = 1.02, CI = 0.98-1.08), or conjunctivitis (aRR = 0.97, CI = 0.740-1.34). Conclusions: Overall, after controlling for demographic and clinical covariates and adjusting for person-years-at-risk, AD was associated with an increased risk for some, but not all, infections within the population of patients with ESRD.

Association of psoriasis and stroke in end-stage renal disease patients

BACKGROUND

Previous research in the general population suggests that the inflammatory skin disease psoriasis is associated with an increased risk of vascular events, such as stroke. Thus, psoriasis may also represent a risk factor for stroke in end-stage renal disease (ESRD) patients.

METHODS

We queried the United States Renal Data System for incident dialysis patients between 2004 and 2015. Psoriasis was defined as having at least two international classification of disease (ICD)-9 or ICD-10 diagnosis codes. ICD codes were also used to query the outcome of interest, stroke, as well as other clinical risk factors. Logistic regression was used to examine the association of psoriasis and other risk factors with stroke.

RESULTS

Of 966,399 ESRD patients, we identified 89,700 (9.3%) subjects with stroke and 6,286 (0.7%) with psoriasis. Of these psoriasis patients, 796 (0.9%) also had a stroke. Psoriasis was associated with an increased risk of stroke in an unadjusted model [odds ratio (OR)=1.16; 95% confidence interval (CI)=1.08-1.25]. However, after controlling for demographic and clinical risk factors, the final adjusted model showed that psoriasis was not associated with stroke (OR=0.96, CI=0.88-1.04). Congestive heart failure [adjusted OR of 1.79 (CI=1.75-1.83)] was a confounder of the association of psoriasis with stroke.

CONCLUSIONS

Contrary to prior research in the general population, psoriasis in ESRD patients was not associated with the risk of stroke after controlling for various demographic and clinical parameters. Our finding emphasizes the importance of controlling for a variety of factors in population studies examining associations of diseases and risk factors.

The Skin and Inflamm-Aging

With its unique anatomical location facing both the external and internal environment, the skin has crucial functions, including shielding the body from damage caused by ultraviolet radiation and chemicals, preventing water loss, acting as a primary barrier against pathogens, participating in metabolic processes like vitamin D production and temperature control and relaying information to the body through sensory and proprioceptor nerves. Like all organ systems, skin is known to undergo multiple changes with aging. A better understanding of the mechanisms that mediate aging-related skin dysfunction may allow the creation of targeted therapeutics that have beneficial effects not only on aged skin but also on other organs and tissues that experience a loss of or decline in function with aging. The skin is the largest organ of the body and can contribute to serum inflammatory mediator levels. One alteration known to occur with age is an impairment of skin barrier function; since disruption of the barrier is known to induce inflammation, skin may be a major contributor to the sustained, sub-clinical systemic inflammation associated with aging. Such "inflamm-aging" may underlie many of the deleterious changes observed in aged individuals. This review explores the role of age-related skin changes, skin inflammation and inflamm-aging.

Non-tuberculous mycobacterial infections in patients with end-stage renal disease: Prevalence, risk factors, and mortality

Non-tuberculous mycobacterial (NTM) disease has increased in prevalence in the USA, however, little is known on NTM in the population with end-stage renal disease (ESRD). Thus, we investigated patients with ESRD to determine risk factors for NTM disease and mortality. We queried the United States Renal Data System from 2005 to 2015 using International Classification of Diseases (ICD)-9/ICD-10 codes to identify NTM and risk factors. Logistic regression was used to examine the association of risk factors with NTM and Cox proportional hazards modeling was used to assess the association of NTM with mortality. Of 1,068,634 included subjects, 3232 (0.3%) individuals were identified with any NTM diagnosis. Hemodialysis versus peritoneal dialysis (OR=0.10, 95% CI=0.08 to 0.13) was protective for NTM, whereas black (OR=1.27, 95% CI=1.18 to 1.37) or other race compared with white race (OR=1.39, 95% CI=1.21 to 1.59) increased the risk of NTM. HIV (OR=15.71, 95% CI=14.24 to 17.33), history of any transplant (OR=4.25, 95% CI=3.93 to 4.60), kidney transplant (OR=3.00, 95% CI=2.75 to 3.27), diabetes (OR=1.32, 95% CI=1.23 to 1.43), rheumatologic disease (OR=1.92, 95% CI=1.77 to 2.08), and liver disease (OR=2.09, 95% CI=1.91 to 2.30) were associated with increased risk for NTM diagnosis. In multivariable analysis, there was a significant increase in mortality with any NTM diagnosis (HR=1.83, 95% CI=1.76 to 1.91, p≤0.0001). Controlling for relevant demographic and clinical risk factors, there was an increased risk of mortality associated with any diagnosis of NTM. Early diagnosis and treatment of NTM infection may improve survival in patients with ESRD.

Demographic and clinical risk factors for diagnosis of sleep disorders in ESRD patients

BACKGROUND

Sleep disturbances in patients with end-stage renal disease (ESRD) are common and more prevalent than in the general population. This study aims to assess the demographic and clinical risk factors for the diagnosis of sleep disorders in ESRD patients.

METHODS

This study is a retrospective analysis of the United States Renal Data System (USRDS) to evaluate risk factors for the diagnosis of sleep disorders, including hypersomnolence, insomnia, restless leg syndrome (RLS), or obstructive or central sleep apnea (OSA/CSA). All ESRD subjects enrolled in the USRDS between 2004-2015 were eligible for inclusion. The risk factors analyzed were age, race, sex, ethnicity, access type, dialysis modality, and the Charlson Comorbidity Index (CCI). All statistical analysis was performed using SAS 9.4, and statistical significance was assessed using an alpha level of 0.05. Descriptive statistics on all variables overall and by each sleep diagnosis were determined.

RESULTS

Increasing age, black race, other race, and Hispanic ethnicity were associated with decreased risk of each sleep diagnosis while CCI was associated with increased risk. Females were at increased risk of RLS and insomnia while males were at increased risk of OSA/CSA. Catheter and graft access decreased risk of RLS but increased risk of insomnia compared to AVF access. Catheter access increased risk of OSA/CSA compared to graft access. Hemodialysis increased risk of OSA/CSA compared to peritoneal dialysis.

CONCLUSIONS

Some ESRD patients are at an increased risk for diagnosis of sleep disorders based on age, race, sex, comorbid health conditions, and dialysis modality.

Risk factors and mortality in patients with listeriosis and end-stage renal disease

BACKGROUND

End-stage renal disease (ESRD) is a known immunocompromising status that predisposes patients to developing infections. Disease from Listeria monocytogenes may affect any host but tends to be more severe in the immunocompromised.

METHODS

We used a large population of patients with ESRD to identify risk factors for listeriosis and mortality. Patients with a diagnosis of Listeria and other risk factors for listeriosis were identified using claims data from the United States Renal Data System database from 2004-2015. Demographic parameters and risk factors associated with Listeria were modeled using logistic regression while association with mortality was assessed with Cox Proportional Hazards modeling.

RESULTS

A diagnosis of Listeria was identified in 291 (0.01%) of a total 1,071,712 patients with ESRD. Cardiovascular disease, connective tissue disease, upper gastrointestinal ulcerative disease, liver disease, diabetes, cancer, and human immunodeficiency virus were all associated with an increased risk of Listeria. Patients with Listeria had an increased risk of death relative to patients without Listeria (adjusted hazard ratio=1.79; 95% confidence interval 1.52-2.10).

CONCLUSIONS

Incidence of listeriosis in our study population was over 7 times higher than what has been reported for the general population. The independent association of a Listeria diagnosis with increased mortality is also consistent with the disease's high mortality in the general population. Due to limitations with diagnosis, providers should maintain high clinical suspicion for listeriosis when patients with ESRD present with a compatible clinical syndrome. Further prospective study may help precisely quantify the increased risk of listeriosis in patients with ESRD.

Hashimoto's thyroiditis and renal transplant rejection

PURPOSE

Hashimoto's thyroiditis (HT) is a common autoimmune thyroid disorder that can disrupt thyroid function and homeostasis. As HT results from a dysregulated immune system, we hypothesized that these patients might be more susceptible to transplant failure; however, literature on this association is limited. The purpose of this study is to examine the association of HT with the risk of renal transplant failure.

METHODS

We utilized the United States Renal Database System dataset collected from 2005 to 2014 and compared the time from first renal transplant to transplant failure in end-stage renal disease (ESRD) patients with a HT diagnosis to ESRD patients without a HT diagnosis that underwent renal transplant.

RESULTS

A total of 144 ESRD patients had International Classification of Disease-9 claim codes for HT prior to renal transplant, amongst a total cohort of 90,301 renal transplant patients aged 18-100 and meeting criteria. Patients with HT were significantly more likely to be female, white, and to have a diagnosis of cytomegalovirus compared to patients without. ESRD patients with a HT diagnosis that underwent renal transplant had a significantly increased risk of renal transplant failure compared to those ESRD renal transplant patients without an HT diagnosis. There was a significantly increased adjusted hazard ratio for graft failure in patients with a HT diagnosis compared to those without.

CONCLUSION

Thyroid health and HT may play a significant role in the development of the increased risk of renal transplant failure observed in this study. Additional studies are needed to investigate the underlying mechanisms for this association.

Pressure Ulcer Diagnosis Is Associated with Increased Mortality in Patients with End-Stage Renal Disease: A Retrospective Study

Pressure ulcers are associated with multiple comorbidities and annually affect approximately 3 million Americans, directly accounting for approximately 60,000 deaths per year. Because patients with end-stage renal disease (ESRD) are known to present with unique factors which impair wound healing, pressure ulcers diagnosed in ESRD patients might independently increase the risk of mortality. To investigate the association between pressure ulcer diagnosis and mortality risk in the ESRD population, a retrospective analysis of the United States Renal Data System (USRDS) database was performed. The records of 1,526,366 dialysis patients who began therapy between 1 January 2005 and 31 December 2018 were included. Our analysis showed that the diagnosis of pressure ulcers in this population was independently associated with mortality even after controlling for confounding factors (p < 0.001). A Kaplan-Meier survival analysis demonstrated reduced survival in patients with a pressure ulcer diagnosis compared to those without a pressure ulcer diagnosis. These results establish pressure ulcers as a significant independent risk factor for mortality, as well as suggesting several comorbidities as potential risk factors for pressure ulcers in the ESRD population.

Phosphatidylglycerol to Treat Chronic Skin Wounds in Diabetes

This review proposes the use of dioleoylphosphatidylglycerol (DOPG) to enhance diabetic wound healing. Initially, the characteristics of diabetic wounds are examined, focusing on the epidermis. Hyperglycemia accompanying diabetes results in enhanced inflammation and oxidative stress in part through the generation of advanced glycation end-products (AGEs), in which glucose is conjugated to macromolecules. These AGEs activate inflammatory pathways; oxidative stress results from increased reactive oxygen species generation by mitochondria rendered dysfunctional by hyperglycemia. These factors work together to reduce the ability of keratinocytes to restore epidermal integrity, contributing to chronic diabetic wounds. DOPG has a pro-proliferative action on keratinocytes (through an unclear mechanism) and exerts an anti-inflammatory effect on keratinocytes and the innate immune system by inhibiting the activation of Toll-like receptors. DOPG has also been found to enhance macrophage mitochondrial function. Since these DOPG effects would be expected to counteract the increased oxidative stress (attributable in part to mitochondrial dysfunction), decreased keratinocyte proliferation, and enhanced inflammation that characterize chronic diabetic wounds, DOPG may be useful in stimulating wound healing. To date, efficacious therapies to promote the healing of chronic diabetic wounds are largely lacking; thus, DOPG may be added to the armamentarium of drugs to enhance diabetic wound healing.

Phospholipase D mediates very low-density lipoprotein-induced aldosterone production, in part, via lipin-1

Aldosterone is considered to be a link between hypertension and obesity; obese individuals have high serum levels of very low-density lipoprotein (VLDL). VLDL has been shown to induce aldosterone production in multiple adrenal zona glomerulosa models, mediated in part by phospholipase D (PLD). PLD is an enzyme that hydrolyzes phosphatidylcholine to produce phosphatidic acid (PA), a lipid second messenger that can also be dephosphorylated by lipin to yield diacylglycerol (DAG), yet another lipid signal. However, it is unclear which of the two lipid second messengers, PA or DAG, underlies PLD's mediation of aldosterone production. We hypothesized that the key signal produced by PLD (indirectly) is DAG such that PLD mediates VLDL-induced aldosterone production via lipin-mediated metabolism of PA to DAG. To assess the role of lipin in VLDL-induced aldosterone production, lipin-1 was overexpressed (using an adenovirus) or inhibited (using propranolol) in HAC15 cells followed by treatment with or without VLDL. Lipin-1 overexpression enhanced the VLDL-stimulated increase in CYP11B2 expression (by 75%), and lipin-1 inhibition decreased the VLDL-stimulated increase in CYP11B2 expression (by 66%). Similarly, the VLDL-stimulated increase in aldosterone production was enhanced by lipin-1 overexpression (182%) and was decreased by lipin inhibition (80%). Our results are suggestive of DAG being the key lipid signal since manipulating lipin-1 levels/activity affects VLDL-stimulated steroidogenic gene expression and ultimately, aldosterone production. Our study warrants further investigation into VLDL-stimulated steroidogenic signaling pathways which may lead to the identification of novel therapeutic targets, such as lipin-1 and its downstream pathways, to potentially treat obesity-associated hypertension.

Association of psoriasis with myocardial infarction in end-stage renal disease patients

BACKGROUND

Previous research in non-dialysis patients suggests that the inflammatory skin disease psoriasis is associated with an increased risk of severe vascular events like myocardial infarction (MI). Thus, we determined whether psoriasis represents a significant risk factor for MI in end-stage renal disease (ESRD) patients.

METHODS

We queried the United States Renal Data System for ESRD patients starting dialysis between 2004 and 2015. ICD-9 and ICD-10 codes were used to identify those with at least two diagnoses of psoriasis, a diagnosis of MI, and other clinical risk factors. Logistic regression was used to examine the association of psoriasis and various risk factors with MI.

RESULTS

Of a cohort of 1,062,693, we identified 6823 (0.6%) subjects with psoriasis and 181,960 (17.1%) with MI. Of the 6823 patients with psoriasis, 1671 (24%) developed an MI. Psoriasis was associated with an increased risk of MI in an unadjusted model [odds ratio (OR) = 1.34; confidence interval (CI) = 1.26-1.42]. However, after controlling for demographics, dialysis modality, access type, and various conditions related to the Charlson Comorbidity Index, psoriasis was not associated with MI (OR = 0.95, CI = 0.89-1.01). Confounders of the association of psoriasis with MI included congestive heart failure (OR = 5.26, CI = 5.17-5.36), pulmonary disease (OR = 1.25, CI = 1.23-1.26), and diabetes with complications (OR = 1.82, CI = 1.79-1.85).

CONCLUSIONS

Contrary to prior research in the general population, in the ESRD population psoriasis was not associated with an increased risk of MI after controlling for various demographic and clinical parameters. These data emphasize the importance of an integrated approach since comorbidities may influence the choice of therapy for psoriasis and outcomes.

Sleep apnea in end-stage renal disease patients: risk factors and mortality

Sleep apnea (SA) is highly prevalent in the end-stage renal disease (ESRD) population. However, the impact of SA on mortality in ESRD is unclear. This study investigates the relationship between SA and mortality in ESRD. The United States Renal Data System was queried in a retrospective cohort study to identify ESRD patients aged 18-100 years who initiated hemodialysis between 2005 and 2013. Diagnoses of SA and comorbidities were determined from International Classification of Disease-9 codes and demographic variables from Centers for Medicare and Medicaid Services Form-2728. Cox proportional hazards models were used to examine the association of SA with mortality controlling for multiple variables. Of 858,131 subjects meeting inclusion criteria, 587 were found to have central SA (CSA) and 22,724 obstructive SA (OSA). The SA cohort was younger and more likely to be male and Caucasian compared to the non-SA cohort, with more diagnoses of tobacco and alcohol use, hypertension, heart failure, and diabetes. Both CSA (adjusted hazard ratio (aHR) = 1.42, 95% confidence interval (CI): 1.29-1.56) and OSA (aHR = 1.35, 95% CI: 1.32-1.37) were associated with increased mortality. Other variables associated with increased mortality included age, dialysis initiation with a catheter or graft, alcohol use, hypertension, and cardiovascular disease. Factors associated with decreased mortality included female sex, black race, Hispanic ethnicity, diagnosis of heart failure or diabetes, and an ESRD etiology of glomerulonephritis or polycystic kidney disease. Since a diagnosis of either OSA or CSA increases mortality risk, early identification of SA and therapy in this ESRD population may improve survival.

Dioleoylphosphatidylglycerol Inhibits Heat Shock Protein B4 (HSPB4)-Induced Inflammatory Pathways In Vitro

Our previous work shows that dioleoylphosphatidylglycerol (DOPG) accelerates corneal epithelial healing in vitro and in vivo by unknown mechanisms. Prior data demonstrate that DOPG inhibits toll-like receptor (TLR) activation and inflammation induced by microbial components (pathogen-associated molecular patterns, PAMPs) and by endogenous molecules upregulated in psoriatic skin, which act as danger-associated molecular patterns (DAMPs) to activate TLRs and promote inflammation. In the injured cornea, sterile inflammation can result from the release of the DAMP molecule, heat shock protein B4 (HSPB4), to contribute to delayed wound healing. Here, we show in vitro that DOPG inhibits TLR2 activation induced in response to HSPB4, as well as DAMPs that are elevated in diabetes, a disease that also slows corneal wound healing. Further, we show that the co-receptor, cluster of differentiation-14 (CD14), is necessary for PAMP/DAMP-induced activation of TLR2, as well as of TLR4. Finally, we simulated the high-glucose environment of diabetes to show that elevated glucose levels enhance TLR4 activation by a DAMP known to be upregulated in diabetes. Together, our results demonstrate the anti-inflammatory actions of DOPG and support further investigation into its development as a possible therapy for corneal injury, especially in diabetic patients at high risk of vision-threatening complications.

Cutaneous squamous cell carcinoma and mortality in end-stage renal disease

BACKGROUND

In the general population, cutaneous squamous cell carcinoma (cSCC) is associated with increased all-cause mortality. Transplant patients have been shown to have an increased risk of developing cSCC, and their cSCC is associated with an increased risk for mortality. In end-stage renal disease (ESRD) patients, there is extensive mortality and immune dysfunction. Because of this immune system dysfunction, we examined whether cSCC is associated with increased risk of all-cause mortality among ESRD patients, as well as the risk factors for cSCC.

METHODS

We analyzed ESRD patients in the United States Renal Data System from 2004-2014, excluding organ transplant recipients. We assessed mortality using a Cox Proportional Hazards (CPH) model to control for various demographic and clinical parameters, identified using international classification of diseases (ICD)-9 codes.

RESULTS

Of the 1,035,193 patients included, 624 (0.1%) were diagnosed with cSCC. The median survival time for those with cSCC was 3.91 years [95% confidence interval (CI) = 3.67-4.15], versus 2.92 years [95%CI = 2.92-2.93] for patients without cSCC. ESRD patients with cSCC were at lower risk of death [adjusted hazard ratio = 0.75; 95%CI = 0.69-0.82] compared to those without. Decreased risk of death was also associated with parameters such as black race, Hispanic ethnicity, tobacco dependence and actinic keratosis. Increased mortality risk was associated with increasing age, male sex, hemodialysis (versus peritoneal dialysis) and alcohol dependence.

CONCLUSIONS

Contrary to expectations, ESRD patients with a cSCC diagnosis showed reduced all-cause mortality risk relative to those without. The reason for this discrepancy remains unclear, suggesting the need for further study.

Update on the Role of Glucocorticoid Signaling in Osteoblasts and Bone Marrow Adipocytes During Aging

PURPOSE OF REVIEW

Bone marrow adipose tissue (BMAT) in the skeleton likely plays a variety of physiological and pathophysiological roles that are not yet fully understood. In elucidating the complex relationship between bone and BMAT, glucocorticoids (GCs) are positioned to play a key role, as they have been implicated in the differentiation of bone marrow mesenchymal stem cells (BMSCs) between osteogenic and adipogenic lineages. The purpose of this review is to illuminate aspects of both endogenous and exogenous GC signaling, including the influence of GC receptors, in mechanisms of bone aging including relationships to BMAT.

RECENT FINDINGS

Harmful effects of GCs on bone mass involve several cellular pathways and events that can include BMSC differentiation bias toward adipogenesis and the influence of mature BMAT on bone remodeling through crosstalk. Interestingly, BMAT involvement remains poorly explored in GC-induced osteoporosis and warrants further investigation. This review provides an update on the current understanding of the role of glucocorticoids in the biology of osteoblasts and bone marrow adipocytes (BMAds).

Innate Immune System Activation, Inflammation and Corneal Wound Healing

Corneal wounds resulting from injury, surgeries, or other intrusions not only cause pain, but also can predispose an individual to infection. While some inflammation may be beneficial to protect against microbial infection of wounds, the inflammatory process, if excessive, may delay corneal wound healing. An examination of the literature on the effect of inflammation on corneal wound healing suggests that manipulations that result in reductions in severe or chronic inflammation lead to better outcomes in terms of corneal clarity, thickness, and healing. However, some acute inflammation is necessary to allow efficient bacterial and fungal clearance and prevent corneal infection. This inflammation can be triggered by microbial components that activate the innate immune system through toll-like receptor (TLR) pathways. In particular, TLR2 and TLR4 activation leads to pro-inflammatory nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) activation. Similarly, endogenous molecules released from disrupted cells, known as damage-associated molecular patterns (DAMPs), can also activate TLR2, TLR4 and NFκB, with the resultant inflammation worsening the outcome of corneal wound healing. In sterile keratitis without infection, inflammation can occur though TLRs to impact corneal wound healing and reduce corneal transparency. This review demonstrates the need for acute inflammation to prevent pathogenic infiltration, while supporting the idea that a reduction in chronic and/or excessive inflammation will allow for improved wound healing.

Association of intermittent versus continuous hemodialysis modalities with mortality in the setting of acute stroke among patients with end-stage renal disease

Patients with end-stage renal disease (ESRD) are 8-10 times more likely to suffer from a stroke compared with the general public. Despite this risk, there are minimal data elucidating which hemodialysis modality is best for patients with ESRD following a stroke, and guidelines for their management are lacking. We retrospectively queried the US Renal Data System administrative database for all-cause mortality in ESRD stroke patients who received either intermittent hemodialysis (IHD) or continuous renal replacement therapy (CRRT). Acute ischemic stroke and hemorrhagic stroke were identified using the International Classification of Diseases 9th Revision (ICD-9)/ICD-10 codes, and hemodialysis modality was determined using Healthcare Common Procedure Coding System (HCPCS) codes. Time to death from the first stroke diagnosis was the outcome of interest. Cox proportional hazards modeling was used, and associations were expressed as adjusted HRs. From the inclusion cohort of 87,910 patients, 92.9% of patients received IHD while 7.1% of patients received CRRT. After controlling for age, race, sex, ethnicity, and common stroke risk factors such as hypertension, diabetes, tobacco use, atrial fibrillation, and hyperlipidemia, those who were placed on CRRT within 7 days of a stroke had an increased risk of death compared with those placed on IHD (HR=1.28, 95% CI 1.25 to 1.32). It is possible that ESRD stroke patients who received CRRT are more critically ill. However, even when the cohort was limited to only those patients in the intensive care unit and additional risk factors for mortality were controlled for, CRRT was still associated with an increased risk of death (HR=1.32, 95% CI 1.27 to 1.37). Therefore, further prospective clinical trials are warranted to address these findings.

Updated Perspectives on Keratinocytes and Psoriasis: Keratinocytes are More Than Innocent Bystanders

Psoriasis is a complex disease triggered by genetic, immunologic, and environmental stimuli. Many genes have been linked to psoriasis, like the psoriasis susceptibility genes, some of which are critical in keratinocyte biology and epidermal barrier function. Still, the exact pathogenesis of psoriasis is unknown. In the disease, the balance between the proliferative and differentiative processes of keratinocytes becomes altered. Multiple studies have highlighted the role of dysregulated immune cells in provoking the inflammatory responses seen in psoriasis. In addition to immune cells, accumulating evidence shows that keratinocytes are involved in psoriasis pathogenesis, as discussed in this review. Although certain immune cell-derived factors stimulate keratinocyte hyperproliferation, activated keratinocytes can also produce anti-microbial peptides, cytokines, and chemokines that can promote their proliferation, as well as recruit immune cells to help initiate and reinforce inflammatory feedback loops. Psoriatic keratinocytes also show intrinsic differences from normal keratinocytes even after removal from the in vivo inflammatory environment; thus, psoriatic keratinocytes have been found to exhibit abnormal calcium metabolism and possible epigenetic changes that contribute to psoriasis. The Koebner phenomenon, in which injury promotes the development of psoriatic lesions, also provides evidence for keratinocytes' contributions to disease pathogenesis. Furthermore, transgenic mouse studies have confirmed the importance of keratinocytes in the etiology of psoriasis. Finally, in addition to immune cells and keratinocytes, data in the literature support roles for other cell types, tissues, and systems in psoriasis development. These other contributors are all potential targets for therapies, suggesting the importance of a holistic approach when treating psoriasis.

The role of lipid second messengers in aldosterone synthesis and secretion

Second messengers are small rapidly diffusing molecules or ions that relay signals between receptors and effector proteins to produce a physiological effect. Lipid messengers constitute one of the four major classes of second messengers. The hydrolysis of two main classes of lipids, glycerophospholipids and sphingolipids, generate parallel profiles of lipid second messengers: phosphatidic acid (PA), diacylglycerol (DAG), and lysophosphatidic acid versus ceramide, ceramide-1-phosphate, sphingosine, and sphingosine-1-phosphate, respectively. In this review, we examine the mechanisms by which these lipid second messengers modulate aldosterone production at multiple levels. Aldosterone is a mineralocorticoid hormone responsible for maintaining fluid volume, electrolyte balance, and blood pressure homeostasis. Primary aldosteronism is a frequent endocrine cause of secondary hypertension. A thorough understanding of the signaling events regulating aldosterone biosynthesis may lead to the identification of novel therapeutic targets. The cumulative evidence in this literature emphasizes the critical roles of PA, DAG, and sphingolipid metabolites in aldosterone synthesis and secretion. However, it also highlights the gaps in our knowledge, such as the preference for phospholipase D-generated PA or DAG, as well as the need for further investigation to elucidate the precise mechanisms by which these lipid second messengers regulate optimal aldosterone production.

Loss of Indoleamine-2,3-Dioxygenase-1 (IDO1) in Knockout Mice Does Not Affect the Development of Skin Lesions in the Imiquimod-Induced Mouse Model of Psoriasis

Indoleamine-2,3-dioxygenase (IDO) degrades the essential amino acid tryptophan resulting in tryptophan depletion and the accumulation of catabolites such as kynurenine. The expression/activity of IDO in various cells, including macrophages and dendritic cells, results in an inhibition of T-cell responses in a number of situations, such as toward allogeneic fetuses and tissue grafts. Psoriasis is an immune-mediated skin disease involving T cells; kynureninase and its generation of catabolites downstream of IDO are reported to play an important role in this disease. We hypothesized that mice lacking the IDO1 gene would exhibit a hyperactive immune response and an exacerbation of skin lesions in the imiquimod-induced mouse model of psoriasis. Littermate wild-type and IDO1-knockout mice were treated with imiquimod for 5 days, and the severity of psoriasiform skin lesions assessed using the psoriasis area and severity index (PASI), ear edema measured using a digital caliper, and thickness of the epidermis determined by histology. Expression of pro-inflammatory mediators and tryptophan-metabolizing enzymes was monitored using quantitative RT-PCR. Imiquimod increased ear edema, PASI scores, and epidermal thickness in both WT and IDO1 knockout mice; however, there were no differences observed between the 2 genotypes. There were also no differences in imiquimod’s induction of skin inflammatory mediators, indicating no effect of IDO1 gene loss in this psoriasis model. Although these data suggest a lack of involvement of IDO1 in psoriatic skin inflammation, other possible mechanisms, such as compensatory changes in other pathways and the involvement of the IDO2 isoform, must also be considered.

The Glucocorticoid Receptor in Osterix-Expressing Cells Regulates Bone Mass, Bone Marrow Adipose Tissue, and Systemic Metabolism in Female Mice During Aging

Hallmarks of aging-associated osteoporosis include bone loss, bone marrow adipose tissue (BMAT) expansion, and impaired osteoblast function. Endogenous glucocorticoid levels increase with age, and elevated glucocorticoid signaling, associated with chronic stress and dysregulated metabolism, can have a deleterious effect on bone mass. Canonical glucocorticoid signaling through the glucocorticoid receptor (GR) was recently investigated as a mediator of osteoporosis during the stress of chronic caloric restriction. To address the role of the GR in an aging-associated osteoporotic phenotype, the current study utilized female GR conditional knockout (GR-CKO; GR^fl/fl :Osx-Cre+) mice and control littermates on the C57BL/6 background aged to 21 months and studied in comparison to young (3- and 6-month-old) mice. GR deficiency in Osx-expressing cells led to low bone mass and BMAT accumulation that persisted with aging. Surprisingly, however, GR-CKO mice also exhibited alterations in muscle mass (reduced % lean mass and soleus fiber size), accompanied by reduced voluntary physical activity, and also exhibited higher whole-body metabolic rate and elevated blood pressure. Moreover, increased lipid storage was observed in GR-CKO osteoblastic cultures in a glucocorticoid-dependent fashion despite genetic deletion of the GR, and could be reversed via pharmacological inhibition of the mineralocorticoid receptor (MR). These findings provide evidence of a role for the GR (and possibly the MR) in facilitating healthy bone maintenance with aging in females. The effects of GR-deficient bone on whole-body physiology also demonstrate the importance of bone as an endocrine organ and suggest evidence for compensatory mechanisms that facilitate glucocorticoid signaling in the absence of osteoblastic GR function; these represent new avenues of research that may improve understanding of glucocorticoid signaling in bone toward the development of novel osteogenic agents. © 2021 American Society for Bone and Mineral Research (ASBMR).

Incidence and risk factors for mucormycosis in renal transplant patients

BACKGROUND

Renal transplant patients are at increased risk for mucormycosis. Diabetes, neutropenia, deferoxamine therapy, and immunosuppressive medications have been associated with increased risk of mucormycosis in studies of solid organ transplant recipients. To focus on renal transplant patients, the US Renal Data System (USRDS) was queried to determine the incidence and risk factors for mucormycosis.

METHODS

All renal transplant patients in the USRDS from 1988 to 2015 were queried for a diagnosis of mucormycosis after the first transplant date using ICD-9 and ICD-10 codes. The International Classification of Diseases (ICD) codes, which currently exist in the ninth and tenth revisions, are a global system of classification used to code diagnoses, procedures, and symptoms. We defined proven mucormycosis by a histopathologic or fungal stain procedure code within 7 days of the diagnosis code. Logistic regression controlling for person-years at risk was used to examine demographic and clinical diagnosis risk factors for mucormycosis.

RESULTS

Of the 306,482 renal transplant patients, 222 (0.07%) had codes consistent with proven mucormycosis. The incidence of mucormycosis increased from 1990 to 2000 (peak 17.6 per 100,000 person-years) and subsequently demonstrated more variability. Hispanic ethnicity (OR=1.45), age 65 years or greater (OR=1.64), other or black race compared with white race (OR=1.96 and 1.74), cadaver or other donor type (OR=2.41), and receiving tacrolimus (OR=2.09) were associated with increased risk. Comorbidities associated with decreased risk of mucormycosis included female sex (OR=0.68), iron overload (OR=0.56), and receiving mycophenolate mofetil (OR=0.67) or azathioprine (OR=0.53).

CONCLUSIONS

In renal transplant patients, age, deceased donor graft transplant, tacrolimus administration, race other than white, and Hispanic ethnicity were associated with increased risk of mucormycosis. Unexpectedly, iron overload was protective. Mucormycosis is a rare infection in renal transplant patients which should be considered in patients with the above risk factors after more common infections have been ruled out.

Renal Contributions to Age-Related Changes in Mineral Metabolism

Aging results in a general decline in function in most systems. This is particularly true with respect to the skeleton and renal systems, impacting mineral homeostasis. Calcium and phosphate regulation requires tight coordination among the intestine, bone, parathyroid gland, and kidney. The role of the intestine is to absorb calcium and phosphate from the diet. The bone stores or releases calcium and phosphate depending on the body's needs. In response to low plasma ionized calcium concentration, the parathyroid gland produces parathyroid hormone, which modulates bone turnover. The kidney reabsorbs or excretes the minerals and serves as the final regulator of plasma concentration. Many hormones are involved in this process in addition to parathyroid hormone, including fibroblast growth factor 23 produced by the bone and calcitriol synthesized by the kidney. Sclerostin, calcitonin, osteoprotegerin, and receptor activator of nuclear factor‐κB ligand also contribute to tissue‐specific regulation. Changes in the function of organs due to aging or disease can perturb this balance. During aging, the intestine cannot absorb calcium efficiently due to decreased expression of key proteins. In the bone, the balance between bone formation and bone resorption tends toward the latter in older individuals. The kidney may not filter blood as efficiently in the later decades of life, and the expression of certain proteins necessary for mineral homeostasis declines with age. These changes often lead to dysregulation of organismal mineral homeostasis. This review will focus on how mineral homeostasis is impacted by aging with a particular emphasis on the kidney's role in this process. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Down-Regulated Calcium-Sensing Receptor in Keratinocytes and Skin from Aged Mice and Humans Impairs Function

The calcium-sensing receptor (CaSR) is important in the skin, contributing to several epidermal functions, including differentiation, water permeability barrier repair, and wound healing. Celli et al. (2021) show that CaSR levels are reduced in keratinocytes/skin from aged individuals, with resulting impairment of key functions. CaSR agonists can correct these defects, suggesting a possible therapy to combat aging-related delayed skin wound healing.

Tryptophan-Kynurenine Pathway in COVID-19-Dependent Musculoskeletal Pathology: A Minireview

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19), affecting multiple organ systems, including the respiratory tract and lungs. Several studies have reported that the tryptophan-kynurenine pathway is altered in COVID-19 patients. The tryptophan-kynurenine pathway plays a vital role in regulating inflammation, metabolism, immune responses, and musculoskeletal system biology. In this minireview, we surmise the effects of the kynurenine pathway in COVID-19 patients and how this pathway might impact muscle and bone biology.

Septic arthritis in the end-stage renal disease population

Septic arthritis is important to consider in any patient who presents with joint pain because it is a medical emergency with an 11% fatality rate. Diagnosis and treatment may improve prognosis; however, many patients do not regain full joint function. In patients with end-stage renal disease (ESRD), immune dysfunction due to uremia and chronic vascular access leads to increased risk of infection. We examined the incidence, risk factors and sequelae of septic arthritis in a cohort of hemodialysis patients. The US Renal Data System was queried for diagnoses of septic arthritis and selected sequelae using International Statistical Classification of Diseases and Related Health Problems-9 and Current Procedural Terminology-4 codes in patients who initiated hemodialysis between 2005 and 2010. Multivariable logistic regression was used to determine potential risk factors for septic arthritis and its sequelae. 7009 cases of septic arthritis were identified, an incidence of 514.8 per 100,000 persons per year. Of these patients, 2179 were diagnosed with a documented organism within 30 days prior to or 14 days after the septic arthritis diagnosis, with methicillin-resistant Staphylococcus aureus infections (57.4%) being the most common. Significant risk factors for septic arthritis included history of joint disease, immune compromise (diabetes, HIV, cirrhosis), bacteremia and urinary tract infection. One of the four sequelae examined (joint replacement, amputation, osteomyelitis, Clostridioides difficile infection) occurred in 25% of septic arthritis cases. The high incidence of septic arthritis and the potential for serious sequelae in patients with ESRD suggest that physicians treating individuals with ESRD and joint pain/inflammation should maintain a high clinical suspicion for septic arthritis.

Phenformin: AMP(K)ed for Potential Repurposing

The results in the article by Zhou et al. (2020) demonstrate that the antidiabetic drug phenformin inhibits skin tumor growth and promotes keratinocyte differentiation, and an underlying mechanism is also defined. In this commentary, additional potential mechanisms through which phenformin may exert its antitumorigenic effect are described. Thus, the proposed repurposing of phenformin to treat skin cancer has merit.

Nocardiosis in renal transplant patients

Renal transplant patients are immunosuppressed and are at increased risk of opportunistic infections, including Nocardia infection. In renal transplant patients, information on the incidence and risk factors associated with nocardiosis is limited. To address the incidence and risk factors associated with nocardiosis in a large renal transplant population, we used the US Renal Data System (USRDS). Sequelae of allograft failure or rejection after infection were also examined. Demographics, clinical risk factors, Nocardia diagnosis, and allograft failure following Nocardia infection were queried in USRDS renal transplant patients using International Classification of Diseases, Ninth Revision (ICD-9) codes in billing claims and Centers for Medicare and Medicaid Services Form 2728. Generalized linear models were used to determine the risk factors associated with nocardiosis, and Cox proportional hazards models were used to examine the association of risk factors with graft failure among patients with Nocardia infection. Of 203,233 renal transplant recipients identified from 2001 to 2011, 657 (0.32%) were diagnosed with Nocardia infection. Pneumonia was the most frequent presentation (15.2%), followed by brain abscess (8.4%). Numerous factors associated with increased Nocardia infection included age >65 years (OR=2.10, 95% CI 1.71 to 2.59), history of transplant failure (OR=1.28, CI 1.02 to 1.60) or history of rejection (OR=4.83, CI 4.08 to 5.72), receipt of a deceased donor transplant (OR=1.23, CI 1.03 to 1.46), and treatment with basiliximab (OR=1.25, CI 1.00 to 1.55), cyclosporine (OR=1.30, CI 1.03 to 1.65), tacrolimus (OR=2.45, CI 2.00 to 3.00), or thymoglobulin (OR=1.89, CI 1.59 to 2.25). In patients with nocardiosis administration of antithymocyte globulin (HR=2.76), chronic obstructive pulmonary disease (HR=2.47), and presentation of Nocardia infection with brain abscess (HR=1.85) were associated with an increased risk of graft failure. This study provides new information to enhance early recognition and targeted treatment of nocardiosis in renal transplant patients.

Treatment of psoriasis in end-stage renal disease patients is associated with decreased mortality: A retrospective cohort study

BACKGROUND

Psoriasis impairs the quality of life of approximately 7.5 million Americans and is associated with serious comorbidities. Because of chronic vascular access and epidermal dysfunction, end-stage renal disease (ESRD) patients with psoriasis may be at greater risk for infection, and psoriasis treatment could affect this risk.

METHODS

A retrospective cohort analysis was performed using the United States Renal Data System from 2004-2011 to investigate the association of psoriasis with infections common to ESRD patients, as well as the effect of psoriasis treatment on infection risk as well as mortality.

RESULTS

A total of 8,911 psoriasis patients were identified. Psoriasis was associated with a significantly increased risk for all queried infections, especially cellulitis (adjusted relative risk = 1.55), conjunctivitis (1.47), and onychomycosis (1.36). Psoriasis treatment (systemic, local, and light) was associated with a significantly decreased risk of some infections. Psoriasis treatment was also correlated with a significantly decreased risk of mortality, with systemic therapies (biologics and other immunosuppressants) showing the greatest reduction (adjusted hazard ratio = 0.55).

CONCLUSIONS

These results suggest that psoriasis-ESRD patients may have an increased risk of infection and treatment of psoriasis is associated with a reduced risk of some infections and improved survival.

Morbidity and Mortality of Spinal Epidural Abscess in End-Stage Renal Disease Patients: A Case-Control Study

BACKGROUND

Spinal epidural abscess (SEA) is an uncommon and highly morbid infection of the epidural space. End-stage renal disease (ESRD) patients are known to be at increased risk of developing SEA; however, there are no studies that have described the risk factors and outcomes of SEA in ESRD patients utilizing the United States Renal Data System (USRDS).

METHODS

To determine risk factors, morbidity, and mortality associated with SEA in ESRD patients, a retrospective case-control study was conducted using the USRDS. ESRD patients diagnosed with SEA between 2005 and 2010 were identified, and logistic regression was performed to examine correlates of SEA, as well as risk factors associated with mortality in SEA-ESRD patients.

RESULTS

The prevalence of SEA amongst ESRD patients was 0.39% (n = 1,697). Patients with SEA were more likely to be male [adjusted Odds Ratio (OR) = 1.22], black (OR = 1.19), diabetic (OR = 1.26), with catheter access (OR = 1.29), and less likely to be ≥65 years old (OR = 0.64). Osteomyelitis, bacteremia/septicemia, MRSA, and endocarditis were all significantly associated with increased risk of SEA (OR = 1.54-5.14). Age ≥65 years (HR = 1.45), urinary tract infections (HR = 1.26), decubitus ulcers (HR=1.37), and post-SEA paraplegia (HR = 1.25) were significantly associated with mortality among those with SEA.

CONCLUSIONS

As described in previous literature, risk factors for SEA included infections, diabetes, and indwelling catheters. Additionally, clinicians should be aware of the risk factors for mortality in SEA-ESRD patients. As the largest study of SEA to date, our report identifies important risk factors for SEA in ESRD patients, and novel data regarding their mortality-associated risk factors.

Phosphatidylglycerol and surfactant: A potential treatment for COVID-19?

A hypothesis concerning the potential utility of surfactant supplementation for the treatment of critically ill patients with COVID-19 is proposed, along with a brief summary of the data in the literature supporting this idea. It is thought that surfactant, which is already approved by the Food and Drug Administration for intratracheal administration to treat neonatal respiratory distress syndrome in pre-term infants, could benefit COVID-19-infected individuals by: (1) restoring surfactant damaged by lung infection and/or decreased due to the virus-induced death of the type II pneumocytes that produce it and (2) reducing surface tension to decrease the work of breathing and limit pulmonary edema. In addition, a constituent of surfactant, phosphatidylglycerol, could mitigate COVID-19-induced lung pathology by: (3) decreasing excessive innate immune system stimulation via its inhibition of toll-like receptor-2 and -4 activation by microbial components and cellular proteins released by damaged cells, thereby limiting inflammation and the resultant pulmonary edema, and (4) possibly blocking spread of the viral infection to non-infected cells in the lung. Therefore, it is suggested that surfactant preparations containing phosphatidylglycerol be tested for their ability to improve lung function in critically ill patients with COVID-19.

The Role of Tryptophan Metabolites in Musculoskeletal Stem Cell Aging

Although aging is considered a normal process, there are cellular and molecular changes that occur with aging that may be detrimental to health. Osteoporosis is one of the most common age-related degenerative diseases, and its progression correlates with aging and decreased capacity for stem cell differentiation and proliferation in both men and women. Tryptophan metabolism through the kynurenine pathway appears to be a key factor in promoting bone-aging phenotypes, promoting bone breakdown and interfering with stem cell function and osteogenesis; however, little data is available on the impact of tryptophan metabolites downstream of kynurenine. Here we review available data on the impact of these tryptophan breakdown products on the body in general and, when available, the existing evidence of their impact on bone. A number of tryptophan metabolites (e.g., 3-hydroxykynurenine (3HKYN), kynurenic acid (KYNA) and anthranilic acid (AA)) have a detrimental effect on bone, decreasing bone mineral density (BMD) and increasing fracture risk. Other metabolites (e.g., 3-hydroxyAA, xanthurenic acid (XA), picolinic acid (PIA), quinolinic acid (QA), and NAD+) promote an increase in bone mineral density and are associated with lower fracture risk. Furthermore, the effects of other tryptophan breakdown products (e.g., serotonin) are complex, with either anabolic or catabolic actions on bone depending on their source. The mechanisms involved in the cellular actions of these tryptophan metabolites on bone are not yet fully known and will require further research as they are potential therapeutic targets. The current review is meant as a brief overview of existing English language literature on tryptophan and its metabolites and their effects on stem cells and musculoskeletal systems. The search terms used for a Medline database search were: kynurenine, mesenchymal stem cells, bone loss, tryptophan metabolism, aging, and oxidative stress.

Dioleoylphosphatidylglycerol Accelerates Corneal Epithelial Wound Healing

Purpose

In contact with the external environment, the cornea can easily be injured. Although corneal wounds generally heal rapidly, the pain and increased risk of infection associated with a damaged cornea, as well as the impaired healing observed in some individuals, emphasize the need for novel treatments to accelerate corneal healing. We previously demonstrated in epidermal keratinocytes that the glycerol channel aquaporin-3 (AQP3) interacts with phospholipase D2 (PLD2) to produce the signaling phospholipid phosphatidylglycerol (PG), which has been shown to accelerate skin wound healing in vivo. We hypothesized that the same signaling pathway might be operational in corneal epithelial cells.

Methods

We used co-immunoprecipitation, immunohistochemistry, scratch wound healing assays in vitro, and corneal epithelial wound healing assays in vivo to determine the role of the AQP3/PLD2/PG signaling pathway in corneal epithelium.

Results

AQP3 was present in human corneas in situ, and AQP3 and PLD2 were co-immunoprecipitated from corneal epithelial cell lysates. The two proteins could also be co-immunoprecipitated from insect cells simultaneously infected with AQP3- and PLD2-expressing baculoviruses, suggesting a likely direct interaction. A particular PG, dioleoylphosphatidylglycerol (DOPG), enhanced scratch wound healing of a corneal epithelial monolayer in vitro. DOPG also accelerated corneal epithelial wound healing in vivo, both in wild-type mice and in a mouse model exhibiting impaired corneal wound healing (AQP3 knockout mice).

Conclusions

These results indicate the importance of the AQP3/PLD2/PG signaling pathway in corneal epithelial cells and suggest the possibility of developing DOPG as a pharmacologic therapy to enhance corneal wound healing in patients.

Incidence and risk factors for HPV-associated cancers in women with end-stage renal disease

Human papillomavirus (HPV) causes the majority of cervical, anal/rectal, and oropharyngeal cancers in women. End-stage renal disease (ESRD) is also associated with an increased risk of malignancy, but the incidence of and risk factors for HPV-associated cancers in US dialysis patients are not defined. We queried the US Renal Data System for women with HPV-associated cancers and assessed for incidence of cancer diagnosis and association of risk factors. From 2005 to 2011, a total of 1032 female patients with ESRD had 1040 HPV-associated cancer diagnoses. Patients had a mean age of 65 years, were mostly white (63%), and on hemodialysis (92%). Cervical cancer (54%) was the most common, followed by anal/rectal (34%), and oropharyngeal (12%). The incidence of HPV-associated cancers in patients with ESRD increased yearly, with up to a 16-fold increased incidence compared with the general population. Major risk factors associated with the development of any HPV-associated cancer included smoking (adjusted relative risk=1.89), alcohol use (1.87), HIV (2.21), and herpes infection (2.02). Smoking, HIV, and herpes infection were prominent risk factors for cervical cancer. The incidence of HPV-associated cancers in women with ESRD is rising annually and is overall higher than in women of the general population. Tobacco use is a universal risk factor. For cervical cancer, the presence of HIV and herpes are important comorbidities. Recognizing risk factors associated with these cancers may improve diagnosis and facilitate survival. The role of HPV vaccination in at-risk dialysis patients remains to be defined but warrants further study.

Age-related increase of kynurenine enhances miR29b-1-5p to decrease both CXCL12 signaling and the epigenetic enzyme Hdac3 in bone marrow stromal cells

Mechanisms leading to age-related reductions in bone formation and subsequent osteoporosis are still incompletely understood. We recently demonstrated that kynurenine (KYN), a tryptophan metabolite, accumulates in serum of aged mice and induces bone loss. Here, we report on novel mechanisms underlying KYN's detrimental effect on bone aging. We show that KYN is increased with aging in murine bone marrow mesenchymal stem cells (BMSCs). KYN reduces bone formation via modulating levels of CXCL12 and its receptors as well as histone deacetylase 3 (Hdac3). BMSCs responded to KYN by significantly decreasing mRNA expression levels of CXCL12 and its cognate receptors, CXCR4 and ACKR3, as well as downregulating osteogenic gene RUNX2 expression, resulting in a significant inhibition in BMSCs osteogenic differentiation. KYN's effects on these targets occur by increasing regulatory miRNAs that target osteogenesis, specifically miR29b-1-5p. Thus, KYN significantly upregulated the anti-osteogenic miRNA miR29b-1-5p in BMSCs, mimicking the up-regulation of miR-29b-1-5p in human and murine BMSCs with age. Direct inhibition of miR29b-1-5p by antagomirs rescued CXCL12 protein levels downregulated by KYN, while a miR29b-1-5p mimic further decreased CXCL12 levels. KYN also significantly downregulated mRNA levels of Hdac3, a target of miR-29b-1-5p, as well as its cofactor NCoR1. KYN is a ligand for the aryl hydrocarbon receptor (AhR). We hypothesized that AhR mediates KYN's effects in BMSCs. Indeed, AhR inhibitors (CH-223191 and 3',4'-dimethoxyflavone [DMF]) partially rescued secreted CXCL12 protein levels in BMSCs treated with KYN. Importantly, we found that treatment with CXCL12, or transfection with an miR29b-1-5p antagomir, downregulated the AhR mRNA level, while transfection with miR29b-1-5p mimic significantly upregulated its level. Further, CXCL12 treatment downregulated IDO, an enzyme responsible for generating KYN. Our findings reveal novel molecular pathways involved in KYN's age-associated effects in the bone microenvironment that may be useful translational targets for treating osteoporosis.

Pathogen-Associated Molecular Pattern-Induced TLR2 and TLR4 Activation Increases Keratinocyte Production of Inflammatory Mediators and is Inhibited by Phosphatidylglycerol

Skin serves not only as a protective barrier to microbial entry into the body but also as an immune organ. The outer layer, the epidermis, is composed predominantly of keratinocytes, which can be stimulated to produce proinflammatory mediators. Although some inflammation is useful to defend against infection, excessive or persistent inflammation can lead to the development of inflammatory skin diseases, such as psoriasis, a common skin disorder affecting approximately 2% of the US population. We have previously found that phosphatidylglycerol (PG) derived from soy can inhibit inflammation in a contact irritant ear edema mouse model. Here, we investigated the ability of soy PG to inhibit inflammatory mediator expression in response to activators of the pattern recognition receptors, toll-like receptor-2 (TLR2) and -4 (TLR4). We found that in epidermal keratinocytes, soy PG inhibited TLR2 and TLR4 activation and inflammatory mediator expression in response to a synthetic triacylated lipopeptide and lipopolysaccharide, respectively, as well as an endogenous danger-associated molecular pattern. However, at higher concentrations, soy PG alone enhanced the expression of some proinflammatory cytokines, suggesting a narrow therapeutic window for this lipid. Dioleoylphosphatidylglycerol (DOPG), but not dioleoylphosphatidylcholine, exerted a similar inhibitory effect, completely blocking keratinocyte inflammatory mediator expression induced by TLR2 and TLR4 activators as well as NFκB activation in a macrophage cell line (RAW264.7); however, DOPG was not itself proinflammatory even at high concentrations. Furthermore, DOPG had no effect on NFκB activation in response to a TLR7/8 agonist. Our results suggest that DOPG could be used to inhibit excessive skin inflammation. SIGNIFICANCE STATEMENT: Although inflammation is beneficial for clearing an infection, in some cases, the infection can be excessive and/or become chronic, thereby resulting in considerable tissue damage and pathological conditions. We show here that the phospholipid phosphatidylglycerol can inhibit the activation of toll-like receptors 2 and 4 of the innate immune system as well as the downstream inflammatory mediator expression in response to microbial component-mimicking agents in epidermal keratinocytes that form the physical barrier of the skin.

Picolinic acid, a tryptophan oxidation product, does not impact bone mineral density but increases marrow adiposity

Tryptophan is an essential amino acid catabolized initially to kynurenine (kyn), an immunomodulatory metabolite that we have previously shown to promote bone loss. Kyn levels increase with aging and have also been associated with neurodegenerative disorders. Picolinic acid (PA) is another tryptophan metabolite downstream of kyn. However, in contrast to kyn, PA is reported to be neuroprotective and further, to promote osteogenesis in vitro. Thus, we hypothesized that PA might be osteoprotective in vivo. In an IACUC-approved protocol, we fed PA to aged (23-month-old) C57BL/6 mice for eight weeks. In an effort to determine potential interactions of PA with dietary protein we also fed PA in a low-protein diet (8%). The mice were divided into four groups: Control (18% dietary protein), +PA (700 ppm); Low-protein (8%), +PA (700 ppm). The PA feedings had no impact on mouse weight, body composition or bone density. At sacrifice bone and stem cells were collected for analysis, including μCT and RT-qPCR. Addition of PA to the diet had no impact on trabecular bone parameters. However, marrow adiposity was significantly increased in PA-fed mice, and in bone marrow stromal cells isolated from these mice increases in the expression of the lipid storage genes, Plin1 and Cidec, were observed. Thus, as a downstream metabolite of kyn, PA no longer showed kyn's detrimental effects on bone but instead appears to impact energy balance.

Aquaporin-3 in the epidermis: more than skin deep

The skin is essential for terrestrial life. It is responsible for regulating water permeability and functions as a mechanical barrier that protects against environmental insults such as microbial infection, ultraviolet light, injury, and heat and cold, which could damage the cells of the body and compromise survival of the organism. This barrier is provided by the outer layer, the epidermis, which is composed predominantly of keratinocytes; keratinocytes undergo a program of differentiation to form the stratum corneum comprising the cornified squame "bricks" and lipid "mortar." Dysregulation of this differentiation program can result in skin diseases, including psoriasis and nonmelanoma skin cancers, among others. Accumulating evidence in the literature indicates that the water-, glycerol-, and hydrogen peroxide-transporting channel aquaporin-3 (AQP3) plays a key role in various processes involved in keratinocyte function, and abnormalities in this channel have been observed in several human skin diseases. Here, we discuss the data linking AQP3 to keratinocyte proliferation, migration, differentiation, and survival as well as its role in skin properties and functions like hydration, water retention, wound healing, and barrier repair. We also discuss the mechanisms regulating AQP3 levels, localization, and function and the anomalies in AQP3 that are associated with various skin diseases.