An inducible genetic tool for tracking and manipulating specific microglial states in development and disease

Recent single-cell RNA sequencing studies have revealed distinct microglial states in development and disease. These include proliferative region-associated microglia (PAM) in developing white matter and disease-associated microglia (DAM) prevalent in various neurodegenerative conditions. PAM and DAM share a similar core gene signature and other functional properties. However, the extent of the dynamism and plasticity of these microglial states, as well as their functional significance, remains elusive, partly due to the lack of specific tools. Here, we report the generation of an inducible Cre driver line, Clec7a-CreERT2, designed to target PAM and DAM in the brain parenchyma. Utilizing this tool, we profile labeled cells during development and in several disease models, uncovering convergence and context-dependent differences in PAM/DAM gene expression. Through long-term tracking, we demonstrate surprising levels of plasticity in these microglial states. Lastly, we specifically depleted DAM in cuprizone-induced demyelination, revealing their roles in disease progression and recovery.

Skin basal cell carcinomas assemble a pro-tumorigenic spatially organized and self-propagating Trem2+ myeloid niche

Cancer immunotherapies have revolutionized treatment but have shown limited success as single-agent therapies highlighting the need to understand the origin, assembly, and dynamics of heterogeneous tumor immune niches. Here, we use single-cell and imaging-based spatial analysis to elucidate three microenvironmental neighborhoods surrounding the heterogeneous basal cell carcinoma tumor epithelia. Within the highly proliferative neighborhood, we find that TREM2+ skin cancer-associated macrophages (SCAMs) support the proliferation of a distinct tumor epithelial population through an immunosuppression-independent manner via oncostatin-M/JAK-STAT3 signaling. SCAMs represent a unique tumor-specific TREM2+ population defined by VCAM1 surface expression that is not found in normal homeostatic skin or during wound healing. Furthermore, SCAMs actively proliferate and self-propagate through multiple serial tumor passages, indicating long-term potential. The tumor rapidly drives SCAM differentiation, with intratumoral injections sufficient to instruct naive bone marrow-derived monocytes to polarize within days. This work provides mechanistic insights into direct tumor-immune niche dynamics independent of immunosuppression, providing the basis for potential combination tumor therapies.

[Application of mixed reality technology in the field of hepatobiliary surgery]

Mixed reality is a new three-dimensional presentation technology that combines the virtual digital world with the real world, which has been initially applied in the field of hepatobiliary surgery. Compared with virtual reality, augmented reality and three-dimensional visualization technology, mixed reality technology has unique advantages in preoperative evaluation and formulation of surgical plan, real-time accurate navigation during operation and three-dimensional virtual teaching. And it is a new generation of auxiliary tool for precision hepatobiliary surgery. This paper describes the application and research progress of mixed reality technology in the field of hepatobiliary surgery, and discusses its application potential and current limitations.

[Impact of psoas muscle index on early postoperative mortality and complications after liver transplantation]

Objective: To investigate the relationship between psoas muscle index (PMI) and early postoperative survival rate and the incidence of complications after liver transplantation in adults. Methods: The clinical data of 225 patients (male, n=184; female, n=41) underwent liver transplantation at the Organ Transplantation Department of First Central Clinic Institute of Tianjin Medical University from January 2014 to December 2016 were analyzed, retrospectively.Original disease: hepatitis B liver cirrhosis(44 cases), hepatitis C cirrhosis(10 cases), autoimmune liver cirrhosis(29 cases), other benign liver diseases(24 cases), liver cirrhosis with liver cancer(116 cases), hilar cholangiocarcinoma(1 case) and hepatic vascular sarcoma(1 case). The area of bilateral psoas muscle on the lower edge level of the third lumbar vertebral body was measured through preoperative CT image.The PMI was calculated using this formula: bilateral psoas muscle area (mm(2))/the square of the body height (m(2)). According to the receiver operating characteristic curve and cut-off values, the male and female patients were divided into low PMI group and high PMI group respectively.The χ(2) test, Fisher exact test and t-test was used to compare the differences in perioperative data, survival rate and postoperative complications between the two groups, respectively. Results: There were 44 patients in the low PMI group, and 181 patients in the high PMI group. ICU time was longer (82.5(62.0-128.0) hours vs.69.1(56.0-104.0) hours; P=0.006) and preoperative blood urea nitrogen level (5.86(4.35-15.52) mmol/L vs. 4.94(4.05-7.06) mmol/L; P=0.012) was higher in the low PMI group than those in the high PMI group. Incidence rates of grade 5 complication (18.2%) and grade 4a complication (18.2%) were higher in the low PMI group, and 120-day cumulative survival rate was lower than that in high PMI group(81.8% vs. 95.6%, P=0.001). On the other hand, there were no significant differences in preoperative white blood cell count level, serum creatinine level, operative time, anhepatic period time, intraoperative blood loss, and incidence of postoperative grade 3 complications between the two groups(all P>0.05). Conclusions: There is a significant correlation between PMI and early postoperative survival rate and incidence of complications.Patients with lower PMI has poor prognosis after liver transplantation.

Mindfulness Meditation for Primary Headache Pain: A Meta-Analysis

Background:

Several studies have reported that mindfulness meditation has a potential effect in controlling headaches, such as migraine and tension-type headache; however, its role remains controversial. This review assessed the evidence regarding the effects of mindfulness meditation for primary headache pain.

Methods:

Only English databases (PubMed, Cochrane Central Register of Controlled Trials [the Cochrane Library], PsycINFO, Psychology and behavioral science collection, PsyArticles, Web of Science, and Scopus) were searched from their inception to November 2016 with the keywords (“meditation” or “mindfulness” or “vipassana” or “dzogchen” or “zen” or “integrative body-mind training” or “IBMT” or “mindfulness-based stress reduction” or “MBSR” or “mindfulness-based cognitive therapy” or “MBCT” and “Headache” or “Head pain” or “Cephalodynia” or “Cephalalgia” or “Hemicrania” or “Migraine”). Titles, abstracts, and full-text articles were screened against study inclusion criteria: controlled trials of structured meditation programs for adult patients with primary headache pain. The quality of studies included in the meta-analysis was assessed with the Yates Quality Rating Scale. The meta-analysis was conducted with Revman 5.3.

Results:

Ten randomized controlled trials and one controlled clinical trial with a combined study population of 315 patients were included in the study. When compared to control group data, mindfulness meditation induced significant improvement in pain intensity (standardized mean difference, −0.89; 95% confidence interval, −1.63 to −0.15; P = 0.02) and headache frequency (−0.67; −1.24 to −0.10; P = 0.02). In a subgroup analysis of different meditation forms, mindfulness-based stress reduction displayed a significant positive influence on pain intensity (P < 0.000). Moreover, 8-week intervention had a significant positive effect (P < 0.000).

Conclusions:

Mindfulness meditation may reduce pain intensity and is a promising treatment option for patients. Clinicians may consider mindfulness meditation as a viable complementary and alternative medical option for primary headache.

S1PR3 Signaling Drives Bacterial Killing and Is Required for Survival in Bacterial Sepsis

RATIONALE

Efficient elimination of pathogenic bacteria is a critical determinant in the outcome of sepsis. Sphingosine-1-phosphate receptor 3 (S1PR3) mediates multiple aspects of the inflammatory response during sepsis, but whether S1PR3 signaling is necessary for eliminating the invading pathogens remains unknown.

OBJECTIVES

To investigate the role of S1PR3 in antibacterial immunity during sepsis.

METHODS

Loss- and gain-of-function experiments were performed using cell and murine models. S1PR3 levels were determined in patients with sepsis and healthy volunteers.

MEASUREMENTS AND MAIN RESULTS

S1PR3 protein levels were up-regulated in macrophages upon bacterial stimulation. S1pr3^-/- mice showed increased mortality and increased bacterial burden in multiple models of sepsis. The transfer of wild-type bone marrow-derived macrophages rescued S1pr3^-/- mice from lethal sepsis. S1PR3-overexpressing macrophages further ameliorated the mortality rate of sepsis. Loss of S1PR3 led to markedly decreased bacterial killing in macrophages. Enhancing endogenous S1PR3 activity using a peptide agonist potentiated the macrophage bactericidal function and improved survival rates in multiple models of sepsis. Mechanically, the reactive oxygen species levels were decreased and phagosome maturation was delayed in S1pr3^-/- macrophages due to impaired recruitment of vacuolar protein-sorting 34 to the phagosomes. In addition, S1RP3 expression levels were elevated in monocytes from patients with sepsis. Higher levels of monocytic S1PR3 were associated with efficient intracellular bactericidal activity, better immune status, and preferable outcomes.

CONCLUSIONS

S1PR3 signaling drives bacterial killing and is essential for survival in bacterial sepsis. Interventions targeting S1PR3 signaling could have translational implications for manipulating the innate immune response to combat pathogens.

Sphingosine 1-phosphate receptor 2 signaling suppresses macrophage phagocytosis and impairs host defense against sepsis (INM3P.416)

Background: Sepsis is characterized by an inappropriate systemic inflammatory response and bacteremia that promote multiorgan failure and mortality. Sphingosine 1-phosphate receptor 2 (S1PR2) modulates endotoxin induced inflammation in endothelium. However, as a highly expressed S1P receptor in macrophage, its role in regulating macrophage response to bacterial infection remains unclear. Methods: Sepsis was induced in wild-type mice treated with S1PR2 antagonist or S1PR2-deficient mice. The antibacterial ability of cell specific S1PR2 was tested in bone marrow reconstitution or macrophage deletion mice. Signaling molecules responsible for S1PR2 mediated phagocytosis were also measured in bone marrow-derived macrophages. Results: Both genetic deletion and pharmaceutical inhibition of S1PR2 significantly limited bacterial burden, reduced lung damage, and improved survival in experimental sepsis. This protection was attributed to the enhanced phagocytic function of S1PR2-deficient macrophages. Absence of S1PR2 in macrophage inhibits RhoA-dependent cell contraction and promotes IQGAP1-Rac1-dependent lamellipodial protrusion, the different signalings of which depends on the extracellular stimulators. Conclusions: This study implies that S1PR2 as a critical receptor in macrophage, impairs phagocytosis and antimicrobial defense in the pathogenesis of sepsis. Interventions targeting S1PR2 signaling may serve as a promising therapeutic approach for sepsis.

Sphingosine 1-phosphate receptor-3 contributes to host defense against polymicrobial sepsis via modulating macrophage chemotaxis (CAM4P.161)

Objective Sphingosine 1-phosphate receptor-3 (S1P3) is an important G protein-coupled receptor regulating host immune response. However, the role of S1P3 in polymicrobial sepsis remains unclear. Method Sepsis was induced in wild-type (WT) and S1PR3-deficient mice via cecal ligation and puncture (CLP). The mortality of mice, as well as organ injury and bacterial clearance during sepsis were assessed. The role of S1PR3 in sepsis was further confirmed by administration of an agonist peptide representing part of the intracellular domain of S1PR3 (GPS-725.017) in septic WT mice. Results S1PR3 deficient mice showed reduced survival rate, increased lung and liver damage, and more bacterial burden during sepsis. There was also significantly less macrophages chemotactic into the peritoneal cavity in the S1PR3 deficient mice. GPS-725.017 could active S1PR3, including internalization of the membrane protein S1PR3 into cytoplasm and activation of MAPKs signaling. In vivo, GPS-725.017 treatment increased recruitment of phagocyte into the peritoneal cavity, enhanced bacterial clearance and improved survival during sepsis. Conclusion The present findings uncover S1PR3 might be a critical modulator of macrophage chemotaxis in the pathogenesis of sepsis. The detailed mechanisms need to be further addressed.

Sphingosine 1-phosphate receptor-3 enhances pro-inflammatory activity in human monocytes (P1384)

Objective: Sphingosine 1-phosphate receptor-3(S1P3) is a G protein-coupled receptor constitutively expressed in human monocytes and plays important roles in the innate immune response. This study is aimed to determine the level of S1P3 in septic patients and explore its role in signaling pro-inflammation activity. Method: Patients with sepsis, non-sepsis and trauma were enrolled, and S1P3 levels in monocytes were determined by real-time PCR and flow cytometry. The S1P3 levels were also measured in primary monocytes from healthy donors and THP-1 cell line after 100 ng/ml LPS or 10 ng/ml TNF-α stimulation for 24 hours. Furthermore, the S1P3 receptor was interfered by agonist (GPS-725.017), antagonist (suramin) or S1P3-specific shRNA to explore the relative intracellular signaling pathway. Results: The levels of S1P3 in septic patients were higher than those in non-septic controls and traumatic patients. LPS or TNF-α stimulation upregulated both mRNA and protein levels of S1P3. Furthermore, the LPS-induced MAPK activity and NF-κB activity in THP-1 cells could be enhanced by GPS-725.017 while reduced by suramin. Knock-down of S1P3 expression in THP-1 monocytes also reduced LPS-induced IL-1β and TNF-α production. Conclusion: The levels of S1P3 in human monocytes could be up-regulated by LPS and TNF-α. S1P3 could enhance LPS-induced pro-inflammatory activity, which involved MAPK and NF-κB pathways.

Risk factors for syphilis among incarcerated women in Rhode Island

Syphilis remains a significant problem in the United States. The prison environment is an ideal location to identify and treat syphilis. We undertook this study to describe the correlates and risk factors for syphilis among incarcerated women in Rhode Island. The study design was a review of all cases of syphilis identified through routine screening in the state prison and a case control study. Between 1992 and 1998, among 6,249 incarcerated women, 86 were found to have syphilis; of these, 29 were primary and secondary cases representing 49% of infectious cases of syphilis in women in the state. The prison environment offers a unique opportunity for the diagnosis and treatment of syphilis.

[Inhibitory effect of selenium on complement activation and its clinical significance]

In immunopathological study of complement activation, we recognised a marked inhibitory effect of sodium selenite on the haemolysis induced by complement fixation in vitro, thereafter on mouse complement activation in vivo induced by endotoxin, inulin or aggregated IgG indicated by a special rocket immunoelectrophoresis test of C3 split products. The effective inhibition usually began at the concentration of 0.002 mol/L of selenite in vitro, and 20 micrograms/25 g BW intravenously in vivo. The inhibitory effect was found evident on alternative pathway. This inhibitory effect was further identified in cases of epidemic haemorrhagic fever (EHF) treated by multiple dosages of 2 mg selenite per day in the first 9 days of hospitalization other than general management of 80 severe cases, including fulminant and moderate grade EHF cases. C3 activation was inhibited accordingly and the mortalities also dropped markedly from 100% of the non-treated group to 36% of the selenite treated group of fulminant type, and from 22% to zero of severe type group.

Effects of severe diabetes and insulin on the femoral neck of the immature rat

The interactive effects of severe diabetes and insulin therapy on the geometrical, biomechanical, and histomorphological characteristics of the femoral neck were studied in rats that had streptozotocin-induced, insulin-dependent (Type-I) diabetes. Thirty-six female Sprague-Dawley rats (8 weeks of age) were assigned randomly to one of three groups: 12 to control (C), 12 to severe diabetes mellitus (SDM), and 12 to severe diabetes with insulin treatment (SDI). At the conclusion of 10 weeks, the femoral necks were loaded to failure via cantilever-bending tests, and the geometrical, structural, and material properties of the femoral neck were measured and correlated with fracture-surface cross sections. Decalcified cross sections of the femoral necks were analyzed histomorphometrically to determine the porosity, the bone-cell counts, and the bone spicule/marrow space ratio. Rats with severe insulin-dependent diabetes had significantly lower total body mass than did control rats, as well as significantly less femur mass, femur length, total-bone cross-sectional area, and cortical-shell cross-sectional area. Insulin therapy ameliorated some, but not all, of the detrimental effects of diabetes on femoral neck geometry. Compared with control and SDI rats, SDM rats had lower values for femoral neck structural properties, although differences in structural properties may have been related to retarded growth as well as to diabetes. SDM rats had a significantly lower bone spicule/marrow space ratio and number of osteoclasts than did either the control or SDI rats and had significantly greater porosity in the femoral neck cortex than did control rats. Decrements in femoral neck material properties--which were independent of differences in body size--were significantly and linearly correlated with severity of diabetes (as measured by blood glucose level).

Reproducibility of the measurement of insulin sensitivity by the modified insulin suppression test

A significant increase in insulin resistance has been implicated in many human diseases and the absence of a simple, accurate, reproducible measurement of in vivo insulin sensitivity has become a major concern. In order to evaluate the reproducibility of insulin sensitivity measured by the modified insulin suppression test, 12 healthy young Chinese men were subjected to the same test two weeks apart. After three days on a standard diet and an overnight fast, somatostatin (350 micrograms/h), insulin (25 mU/m2/min) and glucose (240 mg/m2/min) were infused concomitantly for three hours. A steady state plasma glucose (SSPG) concentration achieved during the last 30 minutes of infusion represented the measurement of insulin sensitivity. Comparisons between the metabolic clearance rate of insulin (MCRi), plasma total triglyceride and lipoprotein cholesterol fractions on two different days were carried out. The results indicated that mean SSPG concentrations on Day 1 (5.73 +/- 0.43 mmol/L) correlated with mean SSPG concentrations on Day 14 (5.51 +/- 0.38 mmol/L; r = 0.82, p < 0.002). The relationship slope did not differ from 1 (0.74, p > 0.05), the intercept was close to the origin (1.24 mmol/L, p > 0.05) and the mean coefficient of intra-individual variation was 10.3%. There was no difference between the MCRi for Day 1 and Day 14 (529 +/- 26 vs 526 +/- 24 mL/m2/min, p = NS), with a mean coefficient of intra-individual variation of 6.9%.(ABSTRACT TRUNCATED AT 250 WORDS)

[Salvia miltiorrhizae in the treatment of the viral myocarditis]

In Order to evaluate the effect of Salvia miltiorrhizae (SM) on the acute viral myocarditis (AVM), 60 children with AVM were studied. The patients were divided in random into two groups, group 1 treated with vit. C, ATP, CoA (n = 30), group II with SM plus vit. C, ATP, CoA (n = 30). The levels of plasma lipid peroxide (LPO), erythrocyte membrane microviscosity (EMMV), LDH, CPK, GOT and ECG in each patient were determined before and after one course of treatments respectively. The results revealed that before treatment the levels of plasma LPO and EMMV in both groups increased significantly compared with those of normal controls (n = 30, P < 0.01) respectively. There was a close correlation between LPO and EMMV (r = 0.6774, P < 0.01) and a close correlation between LPO and LDH (r = 0.5703, P < 0.01). After one course, the levels of plasma LPO and EMMV in both groups decreased significantly (compared with those before treatment, P < 0.01, respectively). But the LPO level and EMMV in group I were much higher than those in normal controls yet (P < 0.05, respectively). And LDH, GOT and ECG in nearly half of the patients in group I did not recover after one course while most patients in group II recovered. The results suggested that free radical plays an important role in the pathogenesis of AVM. SM as a good antioxidant, could protect myocardium from repairing membrane damage and clearing away free radical. This provided a new approach to treatment of viral myocarditis.

Experimental diabetes, insulin treatment, and femoral neck morphology and biomechanics in rats

To investigate the effects of diabetes and insulin treatment on trabecular bone, the morphologic and biomechanical characteristics of the femoral neck in rats with streptozotocin-induced diabetes were studied. Young Sprague-Dawley rats were divided into three groups, control, diabetic (DM), and diabetic with insulin (DI), and maintained for ten weeks. Cantilever-bending tests to failure were conducted on the proximal femur, and fracture-surface cross sections were analyzed. Morphologically, the femoral necks in diabetic rats decreased in the relative size of their cortical shell and increased their trabecular core. Structurally, the load and the energy at the proportional limit and the total energy in diabetic femoral necks were significantly less than controls. In material properties, the diabetic femoral necks had significantly less stress at the proportional limit. Compared to the DM group, the DI femoral necks had significantly greater load and energy at the proportional limit and significantly greater total energy. Femoral neck mechanical and morphologic properties in diabetic rats were significantly lower than controls, but insulin treatment ameliorated diabetic osteopathy in the rat femoral neck.

Structural and mechanical adaptations of immature trabecular bone to strenuous exercise

Effects of strenuous exercise on immature bone were examined in two clinically important regions, femoral neck (FN) and lumbar vertebra (L6). Female Sprague-Dawley rats (n = 20, 8 wk of age, 150-170 g) were exercised progressively 5 days/wk for approximately 1 h/day for 10 wk at 75-80% of maximum oxygen capacity on a motor-driven treadmill. Caged age-matched rats served as controls (n = 20). Rat FNs were tested in cantilever bending, and vertebral bodies were compressed to 50% of their initial height at a fast strain rate. In response to the strenuous exercise, the relative area of the FN trabecular core increased significantly at the expense of the cortical shell. With that structural change, the exercised FN had significantly less energy to proportional limit than controls. The FN material properties (normal stresses at proportional limit and maximum) were significantly diminished after 10 wk of strenuous exercise. At the same time, no differences were found in vertebral geometry or structural and material properties. In the immature rate, the differential responses of the FN vs. L6 may relate to load history rather than a general systemic response to the strenuous exercise.

Changes in geometrical and biomechanical properties of immature male and female rat tibia

Tibial geometry and mechanical properties in male and female rapidly growing rats were measured to provide comparative data for spaceflight, exercise, or disease experiments that use immature rats as an animal model. A total of 68 immature Sprague-Dawley rats (43-58 d of age) were divided into 8 groups according to age and sex. Tibial length and middiaphysial cross-sectional data were analyzed, and tibial mechanical properties were obtained via three-point bending tests to failure. Results indicated that tibial geometry and mechanical properties were changed significantly during this 15-d period of rapid growth, with male rats having greater increases than female rats. Both male and female tibial lengths nevertheless increased significantly during this growth period, as did middiaphysical cross-sectional area. Tibial flexural rigidity increased significantly for both sexes during this growth period. The male tibiae changed primarily in structural characteristics, but some material properties also changed with age. In the female rats, however, the major changes in mechanical properties of the tibia were attributable only to structural changes in the bone.

High fat-sucrose diet effects on femoral neck geometry and biomechanics

Diets high in fat and sucrose may affect calcium metabolism, by decreasing calcium absorption in the gastrointestinal tract and decreasing calcium reabsorption in distal renal tubules, but information about the effects of high fat-sucrose diet on immature-bone material and structural properties is lacking. The present study examined the effects of a high fat-sucrose diet on the geometrical and biomechanical properties of the femoral neck in rapidly-growing rats. Sprague-Dawley female rats were assigned randomly to a high fat-sucrose diet group or a control-diet group for 10 weeks. Cantilever-bending tests to failure were conducted, and geometrical and material properties were calculated from fracture-surface cross-sections and were correlated with mechanical data. Geometrically, the high fat-sucrose diet decreased the relative size of the femoral neck cortical shell and increased the trabecular core. The femoral necks of rats fed the high fat-sucrose diet had signiflcanctly lower structural rigidity, load at proportional limit, maximum load, energy at proportional limit, total energy, normal stress at proportional limit and maximum normal stress than the controls.

[In vivo study of the inhibitory effect of sodium selenite on mouse complement activation]

A simple and sensitive rocket immunoelectrophoresis technique for the assessment of complement activation was employed to study the effect of sodium selenite on mouse complement activation. It was shown that selenite can cause both in vitro and in vivo inhibition of mouse complement activation. The most significant effect was observed in the inulin-activated group; and not in the mouse aggregated IgG activated group. These results suggest that selenite has some inhibiting effect on the alternative complement activation pathway but not on the classical pathway. Therefore, sodium selenite may be applicable in the alleviation or prevention of symptoms of diseases accompanied by alternative pathway complement activation.

[Circulating immune complex (CIC) and antitumor antibody in the serum of rats with thyroid carcinoma induced by 132I]

The antibody against thyroid cancer in serum of 29 rats was tested by indirect immunofluorescent technique and CIC levels were determined by polyethylene glycol (PEG) precipitation during the process of thyroid cancer being induced by 132I. The results showed that the antibody against thyroid cancer is not observed and CIC levels are significantly higher in groups with induced thyroid cancer (0.0316 +/- 0.0072), degeneration and focal epithelial proliferation (0.0211 +/- 0.0107) than that of the normal control group (0.0126 +/- 0.0066) (P less than 0.001). The CIC levels are gradually increased as the thyroid histopathology changes from degeneration and focal epithelial proliferation, benign tumor to malignancy. The causes of CIC increase and their significance are discussed.

Dynamic aspects of whole-body nitrogen metabolism in uremic patients on dietary therapy

15N-glycine administered orally to 3 patients with chronic renal failure and 15N-ammonium chloride given by intravenous infusion to 5 patients were used as tracers in studying the total body nitrogen metabolism during the course of dietary therapy. Patients on a diet providing 1.2 g protein per kilogram body weight per day had significantly lowered total nitrogen flux (Q) and rates of total body protein synthesis (S) and catabolism (C) as compared with the normal controls. A reduction in daily protein intake to 0.6 g/kg/day resulted in marked increases in all these parameters, so that the values actually approached that of the normal controls. While in the normal subjects low-protein intake did not affect the total body protein turnover significantly, it tended to decrease Q and to raise S, C, and S/Q. The results of the present study suggest that the adaptive response to restriction in protein intake is a more efficient utilization of nitrogen entering the metabolic pool for anabolic purposes, and less nitrogen excreted as urea. This response becomes manifest and essential to patients with chronic renal failure and forms the basis for low-protein diet therapy.