Prkd1 regulates the formation and repair of plasma membrane disruptions (PMD) in osteocytes.

We and others have seen that osteocytes sense high-impact osteogenic mechanical loading via transient plasma membrane disruptions (PMDs) which initiate downstream mechanotransduction. However, a PMD must be repaired for the cell to survive this wounding event. Previous work suggested that the protein Prkd1 (also known as PKCµ) may be a critical component of this PMD repair process, but the specific role of Prkd1 in osteocyte mechanobiology had not yet been tested. We treated MLO-Y4 osteocytes with Prkd1 inhibitors (Go6976, kbNB 142-70, staurosporine) and generated an osteocyte-targeted (Dmp1-Cre) Prkd1 conditional knockout (CKO) mouse. PMD repair rate was measured via laser wounding and FM1-43 dye uptake, PMD formation and post-wounding survival were assessed via fluid flow shear stress (50 dyn/cm2), and in vitro osteocyte mechanotransduction was assessed via measurement of calcium signaling. To test the role of osteocyte Prkd1 in vivo, Prkd1 CKO and their wildtype (WT) littermates were subjected to 2 weeks of unilateral axial tibial loading and loading-induced changes in cortical bone mineral density, geometry, and formation were measured. Prkd1 inhibition or genetic deletion slowed osteocyte PMD repair rate and impaired post-wounding cell survival. These effects could largely be rescued by treating osteocytes with the FDA-approved synthetic copolymer Poloxamer 188 (P188), which was previously shown to facilitate membrane resealing and improve efficiency in the repair rate of PMD in skeletal muscle myocytes. In vivo, while both WT and Prkd1 CKO mice demonstrated anabolic responses to tibial loading, the magnitude of loading-induced increases in tibial BMD, cortical thickness, and periosteal mineralizing surface were blunted in Prkd1 CKO as compared to WT mice. Prkd1 CKO mice also tended to show a smaller relative difference in the number of osteocyte PMD in loaded limbs and showed greater lacunar vacancy, suggestive of impaired post-wounding osteocyte survival. While P188 treatment rescued loading-induced increases in BMD in the Prkd1 CKO mice, it surprisingly further suppressed loading-induced increases in cortical bone thickness and cortical bone formation. Taken together, these data suggest that Prkd1 may play a pivotal role in the regulation and repair of the PMD response in osteocytes and support the idea that PMD repair processes can be pharmacologically targeted to modulate downstream responses, but suggest limited utility of PMD repair-promoting P188 in improving bone anabolic responses to loading.

Orchiectomy sensitizes cortical bone in male mice to the harmful effects of kynurenine.

Kynurenine (Kyn) is a tryptophan metabolite that increases with age and promotes musculoskeletal dysfunction. We previously found a sexually dimorphic pattern in how Kyn affects bone, with harmful effects more prevalent in females than males. This raises the possibility that male sex steroids might exert a protective effect that blunts the effects of Kyn in males. To test this, orchiectomy (ORX) or sham surgeries were performed on 6-month-old C57BL/6 mice, after which mice received Kyn (10 mg/kg) or vehicle via intraperitoneal injection, once daily, 5×/week, for four weeks. Bone histomorphometry, DXA, microCT, and serum marker analyses were performed after sacrifice. In vitro studies were performed to specifically test the effect of testosterone on activation of aryl hydrocarbon receptor (AhR)-mediated signaling by Kyn in mesenchymal-lineage cells. Kyn treatment reduced cortical bone mass in ORX- but not sham-operated mice. Trabecular bone was unaffected. Kyn's effects on cortical bone in ORX mice were attributed primarily to enhanced endosteal bone resorption activity. Bone marrow adipose tissue was increased in Kyn-treated ORX animals but was unchanged by Kyn in sham-operated mice. ORX surgery increased mRNA expression of the aryl hydrocarbon receptor (AhR) and its target gene Cyp1a1 in the bone, suggesting a priming and/or amplification of AhR signaling pathways. Mechanistic in vitro studies revealed that testosterone blunted Kyn-stimulated AhR transcriptional activity and Cyp1a1 expression in mesenchymal-linage cells. These data suggest a protective role for male sex steroids in blunting the harmful effects of Kyn in cortical bone. Therefore, testosterone may play an important role in regulating Kyn/AhR signaling in musculoskeletal tissues, suggesting crosstalk between male sex steroids and Kyn signaling may influence age-associated musculoskeletal frailty.

Five-Lumen Antibiotic-Impregnated Femoral Central Venous Catheters in Severely Burned Patients: An Investigation of Device Utility and Catheter-Related Bloodstream Infection Rates.

The objective of this study is to determine the catheter-related bloodstream infection (CRBSI) rate in a severely burned patient population, many of whom required prolonged use of central venous catheters (CVCs). Between January 2008 and June 2012, 151 patients underwent placement of 455 five-lumen minocycline/rifampin-impregnated CVCs. CRBSI was defined as at least one blood culture (>100,000 colonies) and one simultaneous roll-plate CVC tip culture (>15 colony forming units) positive for the same organism. Most patients had accidental burns (81.5%) with a mean TBSA of 50%. A mean of three catheters were inserted per patient (range, 1-25). CVCs were inserted in the femoral vein (91.2%), subclavian vein (5.3%), and internal jugular vein (3.3%). Mean overall catheter indwell time was 8 days (range, 0-39 days). The overall rate of CRBSI per 1000 catheter days was 11.2; patients with a TBSA >60% experienced significantly higher rates of CRBSI than patients with a TBSA ≤60% (16.2 vs 7.3, P = .01). CVCs placed through burned skin were four times more likely to be associated with CRBSI than CVCs placed through intact skin. The most common infectious organism was Acinetobacter baumannii. Deep venous thrombosis developed in eleven patients (7%). The overall rate of CRBSI was 11.2, consistent with published rates of CRBSI in burn patients. Thus, femoral placement of 5-lumen CVCs did not result in increased CRBSI rates. These data support the safety of femoral CVC placement in burn patients, contrary to the Centers for Disease Control recommendation to avoid femoral CVC insertion.

Thromboembolic complications in burn patients and associated risk factors.

Early mobilization and deep venous thrombosis (DVT) prophylaxis have been shown to reduce the incidence of DVT and pulmonary embolism among hospitalized patients, yet thromboembolic complications remain a great concern, especially to those who remain immobilized for an extended period of time. There are many risk factors associated with the development of thromboembolism, especially DVT. The main objective of this retrospective study is to estimate the occurrence of DVT in burn patients and to investigate some burn-related risk factors. A retrospective examination of DVT cases was conducted among the acute burn patients admitted to our Regional Burn Center during 2008. The analysis included the demographic factors, preexisting medical conditions, ventilator support, number of surgeries and blood transfusions, and use of central line. There was a total of 97 diagnosed patients with DVT and among them 86 were adult acute burn patients. There were 113 diagnosed with DVTs in 86 burn patients, including 22 patients diagnosed with DVT at multiple sites either in one screening or in subsequent screenings. Incidence of DVT at the center was 5.92 per 100 adult acute burn admissions. Men had more DVT than women (6.87 vs. 3.34%, relative risk 2.05, P < .05). The average percentage of %TBSA was smaller in the patients who were more than 50 years of age compared with the patients who were 49 years or younger (21.97 vs. 34.77%, P < .05). Among the patients with DVT, 80 (93%) had a central venous catheter before DVT developed and the other six never had a central venous catheter. The most common site for DVT development was common femoral vein site 89%. The average number of procedures before DVT was 7.84 ± 8.36, and blood transfusions were 39.55 ± 108.37 units. Six patients (7%) died in the hospital within these study cohorts and there was no indication that pulmonary embolism was the cause of the deaths. The study showed that the incidence of DVT in the burn center was comparable with the incidences reported in the literature. Being of male sex, a smoker, an alcoholic, high-age group, high %TBSA, use of central line, increased number of surgeries, and increased number of blood transfusions are identified as possible predisposing factors for DVTs. Further meaningful evaluation to determine the incidence of DVT in burn patients and its associated risk factors will require large multicenter, well-controlled, prospective designed study.

Treating necrotizing fasciitis with or without hyperbaric oxygen therapy.

There is not enough clinical data to support the benefit of adjuvant HBO2 therapy for necrotizing fasciitis (NF). We retrospectively reviewed our 67 NF cases to compare the outcomes of adjuvant HBO2 therapy versus non-HBO2 therapy. The overall outcome and morbidity criteria were compared between a group of 29 NF patients who received the adjuvant HBO2 and a group of the remaining 38 NF patients treated by only surgery and other standards of care. This study did not find any difference between the groups in average length of hospital stay, and their mortality. However, six (25%) of the non-HBO2 group patients required amputation of extremities compared to one of the HBO2 group (Fisher exact p = 0.09). Although the benefit of adjuvant HBO2 therapy remains controversial for NF, and the outcomes of this study are not statistically significant, there is a trend in clinical outcomes which shows that the therapy has the potential to reduce the number of amputation and salvage extremities. These findings necessitate multicenter, prospective, case control study to assess the possible benefit of adjuvant HBO2 therapy for NF.

Burns in mobile home fires--descriptive study at a regional burn center.

Death from fires and burns are the sixth most common cause of unintentional injury death in the United States. More than (3/4) of burn deaths occurring in the United States are in the home. Mobile home fires carry twice the death rate as other dwellings. The aim of the study was to describe the characteristics of deaths and injuries in mobile home fire admitted in a regional Burn Center and to identify possible risk factors. A cross-sectional retrospective study was carried out among all burn patients admitted to a regional Burn Center between January 2002 and December 2004 (3469 patients). The study included patients who suffered a burn injury from a mobile home fire. The demographic characteristics of the patients, location of mobile home, associated inhalation injury, source of fire, comorbidity of the victims, employment status, insurance status, family history of burns, and outcomes of the treatment were incorporated in a data collection record. There were 65 burn patients in mobile home fires admitted to the Burn Center during the studied period. The average age of the patients was 39 years (ranging from 2 to 81 years, SD=16.06), 77% were male, 67% were white, and 79% were the residents in the suburban areas of Georgia, South Carolina, North Carolina, and Florida. The average TBSA of burns was about 21% (ranging from 1 to 63%, SD=17.66), 63% of the patients had associated inhalation, three inhalation injury only, and 69% patients required ventilator support. The average length of stay per TBSA percentage of burn was 1.01 days (P=0.00), controlling for age, preexisting medical comorbidities, and inhalation injury. About 88% of the patients had preexisting medical comorbid conditions, 74% were smokers, 64% reported as alcoholic, and 72% had at least some form of health insurance coverage. In 40% of the cases, the cause of the fire was unknown, 31% were caused by accidental explosions, such as electric, gasoline, or kerosene appliances, and 29% were due to other causes. About 40% of burns took place between December and February. Among the studied cohorts, 32% were unemployed, 15% were disabled, and 14% did not have any information about their employment status. One in every four patients had a family history of a burn. Eight (12%) died in the hospital during treatment. There was a higher prevalence of inhalation injury and higher case fatality among the burn patients in mobile home fires compared with the statistics of the Burn Center. Observation showed a higher number of smokers and alcoholics among the burn patients. The main sources of fire were from home appliances. Fewer people had health insurance coverage than the national standard and more people suffered from some sort of chronic illness compared with the national morbidity data.

Purpura fulminans: a case series managed at a regional burn center.

Purpura fulminans (PF) is a protein C deficiency disease process with a high case fatality rate; however, overall incidence of the disease remains relatively very low. The similarity between skin necrosis secondary to PF and full-thickness skin burns provides the rationale for treating PF case in a burn center. In this case series we reviewed our experiences in managing PF and their associated favorable outcomes. Retrospective chart review of five PF cases managed between September 2004 and August 2006 at our Burn Center with 100% survival. Management of cases following the standard care of the Burn Center for a full-thickness burn included antibiotics, fluid resuscitation, surgical debridement with skin grafting, and activated protein C (Drotrecogin alfa) replacement. Two patients required amputations of extremities and all had surgical debridement. One required hemodialysis and two needed both hemodialysis and positive-pressure mechanical ventilator. No patient experienced any bleeding complications during or after surgery while receiving activated protein C. Early diagnosis and treatment at a burn center may reduce mortality and morbidity and loss of extremities in PF cases.

Clinical utility and economic impact of introducing a bowel management system.

PURPOSE: The primary objective of this study was to compare rates of urinary tract and soft tissue infections in critically ill burn patients before and following introduction of a Bowel Management System (BMS). We also analyzed the economic impact of the BMS as compared to reactive management of fecal soiling via cleansing and dressing changes. METHODS AND MATERIALS: A retrospective case-matched before-after study was completed. Critically ill burn patients using a BMS were matched with similar patients managed before introduction of the device based on gender, total body surface area burned, burn location, ventilation days, and hospital length of stay. RESULTS: Reductions in hospital-acquired urinary tract infections and skin and soft tissue infections were observed after introduction of the BMS. Despite its initial cost, it proved more cost effective than a reactive bowel management strategy based on cleansing and dressing changes when fecal soiling occurs. CONCLUSIONS: Proactive use of a bowel management device appears to reduce some infectious sequelae in a complicated burn care population and proved cost-effective for our facility.