Prospective Study of a System-Wide Adrenal Incidentaloma Quality Improvement Initiative

BACKGROUND

Appropriate follow-up of incidental adrenal masses (IAMs) is infrequent. We implemented a quality improvement (QI) program to improve management of IAMs.

STUDY DESIGN

This system-wide initiative targeted primary care providers (PCPs) after IAM detection. It incorporated (1) chart-based messages and emails to PCPs, (2) an evidence-based IAM evaluation algorithm, (3) standardized recommendations in radiology reports, and (4) access to a multispecialty adrenal clinic. Patients diagnosed with an IAM from January 1, 2018, to December 31, 2019, were prospectively included (the "QI cohort") and compared with a historical, preintervention cohort diagnosed with IAMs in 2016. The primary outcomes were the initiation of an IAM investigation by the PCP, defined as relevant clinical history-taking, laboratory screening, follow-up imaging, or specialist referral.

RESULTS

The QI cohort included 437 patients and 210 in the historical cohort. All patients had 12 months or more of follow-up. In the QI cohort, 35.5% (155 of 437) met the primary endpoint for PCP-initiated evaluation, compared with 27.6% (58 of 210) in the historical cohort (p = 0.0496). Among the subgroup with a documented PCP working within our health system, 46.3% (74 of 160) met the primary endpoint in the QI cohort vs 33.3% (38 of 114) in the historical cohort (p = 0.035). After adjusting for insurance status, presence of current malignancy, initial imaging setting (outpatient, inpatient, or emergency department), and having an established PCP within our health system, patients in the QI cohort had 1.70 times higher odds (95% CI 1.16 to 2.50) of undergoing a PCP-initiated IAM evaluation. Adrenal surgery was ultimately performed in 2.1% (9 of 437) of QI cohort patients and 0.95% (2 of 210) of historical cohort patients (p = 0.517).

CONCLUSIONS

This simple, moderately labor-intensive QI intervention was associated with increased IAM evaluation initiated by PCPs.

Point-of-care access to clinical guidelines may improve management of incidental findings in the primary care setting

RATIONALE

Incidental radiographic findings are common, and primary care providers (PCPs) are often charged with the conducting or initiating an appropriate evaluation. Clinical guidelines are available for management of common 'incidentalomas' including lung and adrenal nodules, but guidelines-adherent evaluations are not always performed; for example, in the setting of incidental adrenal masses (IAMs), recent literature suggests that an evidence-based evaluation occurs in <25% of patients for whom it is warranted-a quality and safety concern.

AIMS AND OBJECTIVES

The objective of this study was to examine whether point-of-care access to concise clinical guidelines would promote appropriate evaluations of two common incidentalomas: IAMs and lung nodules.

METHOD

This study was a survey-based, single-blinded, randomized experiment of decision-making within clinical vignettes. Respondents were PCPs in a variety of clinical practice settings, and half were randomly assigned to surveys that included concise clinical guidelines while the other half served as controls without access to guidelines. Scenarios involved patients with IAMs and lung nodules, and the scenarios included both higher-risk and lower-risk lesions. Our primary analysis examined safe versus inappropriate clinical decisions, while a secondary analysis compared guidelines-concordant versus guidelines-discordant responses.

RESULTS

For both the higher-risk IAM and higher-risk lung nodule scenarios, safe answer choices were selected at a similar rate by respondents regardless of whether they had access to guidelines or not. However, for the lower risk scenarios, inappropriate answer choices were chosen substantially more frequently by respondents without access to guidelines compared to those with the guidelines (lung: 29.3% vs. 4.5%, p = 0.003, adrenal: 31.6% vs. 7.0%, p = 0.01). There was less variation in the secondary analysis.

CONCLUSION

Survey respondents were significantly more likely to make safe management decisions in lower-risk clinical scenarios when clinical guidelines were available. Point-of-care access to clinical guidelines for incidentalomas is an intervention that may reduce management errors and improve patient safety.

Germline SUCLG2 Variants in Patients with Pheochromocytoma and Paraganglioma

BACKGROUND

Pheochromocytoma and paraganglioma (PPGL) are neuroendocrine tumors with frequent mutations in genes linked to the tricarboxylic acid cycle. However, no pathogenic variant has been found to date in succinyl-CoA ligase (SUCL), an enzyme that provides substrate for succinate dehydrogenase (SDH; mitochondrial complex II; CII), a known tumor suppressor in PPGL.

METHODS

A cohort of 352 subjects with apparently sporadic PPGL underwent genetic testing using a panel of 54 genes developed at the National Institutes of Health, including the SUCLG2 subunit of SUCL. Gene deletion, succinate levels, and protein levels were assessed in tumors where possible. To confirm the possible mechanism, we used a progenitor cell line, hPheo1, derived from a human pheochromocytoma, and ablated and re-expressed SUCLG2.

RESULTS

We describe eight germline variants in the GTP-binding domain of SUCLG2 in 15 patients (15 of 352, 4.3%) with apparently sporadic PPGL. Analysis of SUCLG2-mutated tumors and SUCLG2-deficient hPheo1 cells revealed absence of SUCLG2 protein, decrease in the level of the SDHB subunit of CII and faulty assembly of the complex, resulting in aberrant respiration and elevated succinate accumulation.

CONCLUSIONS

Our study suggests SUCLG2 as a novel candidate gene in the genetic landscape of PPGL. Large-scale sequencing may uncover additional cases harboring SUCLG2 variants and provide more detailed information about their prevalence and penetrance.

A Case of Paraneoplastic Hypoglycemia From Squamous Cell Carcinoma of Undetermined Primary

Case: A 57 year old man with squamous cell carcinoma (SCC) of the tongue with complete response to chemoradiation was found unresponsive with a reading of “low” by a POC glucometer. He was treated with an IV dextrose bolus but had recurrent hypoglycemia requiring a continuous dextrose infusion. He was diagnosed with COVID-19 pneumonia, acute hepatitis (elevated liver enzymes), and acute kidney injury (elevated serum creatinine 1.2 mg/dL). Other labs: elevated TSH 8.44 uIU/mL, normal AM cortisol 16.4 ug/dl. A 5.1 cm mass was discovered in the left lung with bilateral nodules, biopsi revealed SCC of unclear origin (either lung or metastatic disease from prior tongue cancer). He was malnourished from prior cancer related dysphagia and nutritional supplements were added. Despite this and improvement in liver and kidney function, he had persistent hypoglycemia. He became hypoglycemic within 4-hrs while performing a 72-hr fast with labs: serum glucose 45 mg/dL, insulin &lt 2 uU/mL, c-peptide &lt 0.1 ng/mL, proinsulin &lt 4 pmol/L, beta hydroxybutyrate 0.17 mmol/L, IGF1 &lt 16 ng/mL (ref: 50 - 317), IGF2 147 ng/mL (ref: 267-616), negative hypoglycemia panel and insulin antibody. This was consistent with a paraneoplastic hypoglycemia known as non-islet cell tumor hypoglycemia (NICTH). To discontinue the dextrose infusion, he was started on prednisone 20 mg daily titrated up to 60 mg daily, intermittent tube feeds and palliative chemotherapy. With this, hypoglycemia improved, and the dextrose infusion was discontinued. Unfortunately, he had ischemic bowel perforation leading to cardiac arrest and death. Discussion: Our patient had NICTH as suggested by the 72-hr fast (non-insulin mediated hypoglycemia, IGF2/IG1 ratio &gt 10) and the presence of a tumor. It is mediated by tumor-produced IGF-2 causing increased glucose utilization, decreased gluconeogenesis, glycogenolysis and ketogenesis. Curiously, IGF-2 may not be elevated if the tumor produces a partially processed “big IGF-2” for which there is no commercial assay. Instead, an IGF2/IGF1 ratio close to or more 10 is indicative of NICTH. Mesenchymal and hepatic tumors are the most common cause of this rare entity with an incidence of one per million people years. A literature search showed very few reports of SCC-mediated-NICTH, with one case of esophageal SCC. Our patients’ primary tumor was undetermined (lung vs tongue) - but in either case this could be a novel association. A multidisciplinary approach is required centered around the tumor (surgery, chemotherapy, or radiation). High dose prednisone 30 to 60 mg daily can be used in the interim as it decreases IGF-2 but is not always successful. Recombinant hGH and glucagon are alternatives or can be combined with steroids. In summary IGF2/IGF1 ratio should be calculated, palliative tumor directed therapy should be initiated with prednisone and supplemental nutrition as adjuncts.

Strategies to optimize management of incidental radiographic findings in the primary care setting: A mixed methods study

BACKGROUND

Incidental adrenal masses (IAMs) are common. Primary care providers (PCPs) are frequently responsible for incidentaloma evaluations. We evaluated whether PCPs view this paradigm effective, barriers faced, and strategies to optimize care delivery.

METHODS

This is a sequential explanatory study, comprised of surveys followed by focus groups of PCPs. Because lung nodules are another type of common incidental finding, we compared PCP views on management of lung nodules to their views on IAMs.

RESULTS

For IAMs, 22.3% of PCPs "always refer" to specialists, but for lung nodules this was 11.5% (p = 0.026). For lung nodules, the most significant barrier was insufficient time/support to longitudinally follow results (69%), but for IAMs it was uncertainty about which tests to order (68%). Fear of litigation was equal (lung = 22.5%, IAMs = 21.3%). Consistent themes regarding the "ideal" system included specific recommendations in radiology reports; automation of orders for follow-up tests; longitudinal tracking tools; streamlined consultations; and decision guides embedded within the electronic health record.

CONCLUSIONS

Respondents are more comfortable with lung nodules than IAMs. Management of "incidentalomas" is within their scope of practice, but the current system can be optimized.

Effect of Protein Intake on Lean Body Mass in Functionally Limited Older Men: A Randomized Clinical Trial

Importance

The Institute of Medicine set the recommended dietary allowance (RDA) for protein at 0.8 g/kg/d for the entire adult population. It remains controversial whether protein intake greater than the RDA is needed to maintain protein anabolism in older adults.

Objective

To investigate whether increasing protein intake to 1.3 g/kg/d in older adults with physical function limitations and usual protein intake within the RDA improves lean body mass (LBM), muscle performance, physical function, fatigue, and well-being and augments LBM response to a muscle anabolic drug.

Design, Setting, and Participants

This randomized clinical trial with a 2 × 2 factorial design was conducted in a research center. A modified intent-to-treat analytic strategy was used. Participants were 92 functionally limited men 65 years or older with usual protein intake less thanor equal to 0.83 g/kg/d within the RDA. The first participant was randomized on September 21, 2011, and the last participant completed the study on January 19, 2017.

Interventions

Participants were randomized for 6 months to controlled diets with 0.8 g/kg/d of protein plus placebo, 1.3 g/kg/d of protein plus placebo, 0.8 g/kg/d of protein plus testosterone enanthate (100 mg weekly), or 1.3 g/kg/d of protein plus testosterone. Prespecified energy and protein contents were provided through custom-prepared meals and supplements.

Main Outcomes and Measures

The primary outcome was change in LBM. Secondary outcomes were muscle strength, power, physical function, health-related quality of life, fatigue, affect balance, and well-being.

Results

Among 92 men (mean [SD] age, 73.0 [5.8] years), the 4 study groups did not differ in baseline characteristics. Changes from baseline in LBM (0.31 kg; 95% CI, -0.46 to 1.08 kg; P = .43) and appendicular (0.04 kg; 95% CI, -0.48 to 0.55 kg; P = .89) and trunk (0.24 kg; 95% CI, -0.17 to 0.66 kg; P = .24) lean mass, as well as muscle strength and power, walking speed and stair-climbing power, health-related quality of life, fatigue, and well-being, did not differ between men assigned to 0.8 vs 1.3 g/kg/d of protein regardless of whether they received testosterone or placebo. Fat mass decreased in participants given higher protein but did not change in those given the RDA: between-group differences were significant (difference, -1.12 kg; 95% CI, -2.04 to -0.21; P = .02).

Conclusions and Relevance

Protein intake exceeding the RDA did not increase LBM, muscle performance, physical function, or well-being measures or augment anabolic response to testosterone in older men with physical function limitations whose usual protein intakes were within the RDA. The RDA for protein is sufficient to maintain LBM, and protein intake exceeding the RDA does not promote LBM accretion or augment anabolic response to testosterone.

Trial Registration

clinicaltrials.gov Identifier: NCT01275365.

Effects of Testosterone Administration for 3 Years on Subclinical Atherosclerosis Progression in Older Men With Low or Low-Normal Testosterone Levels: A Randomized Clinical Trial

IMPORTANCE

Testosterone use in older men is increasing, but its long-term effects on progression of atherosclerosis are unknown.

OBJECTIVE

To determine the effect of testosterone administration on subclinical atherosclerosis progression in older men with low or low-normal testosterone levels.

DESIGN, SETTING, AND PARTICIPANTS

Testosterone's Effects on Atherosclerosis Progression in Aging Men (TEAAM) was a placebo-controlled, double-blind, parallel-group randomized trial involving 308 men 60 years or older with low or low-normal testosterone levels (100-400 ng/dL; free testosterone <50 pg/mL), recruited at 3 US centers. Recruitment took place between September 2004 and February 2009; the last participant completed the study in May 2012.

INTERVENTIONS

One hundred fifty-six participants were randomized to receive 7.5 g of 1% testosterone and 152 were randomized to receive placebo gel packets daily for 3 years. The dose was adjusted to achieve testosterone levels between 500 and 900 ng/dL.

MAIN OUTCOMES AND MEASURES

Coprimary outcomes included common carotid artery intima-media thickness and coronary artery calcium; secondary outcomes included sexual function and health-related quality of life.

RESULTS

Baseline characteristics were similar between groups: patients were a mean age of 67.6 years; 42% had hypertension; 15%, diabetes; 15%, cardiovascular disease; and 27%, obesity. The rate of change in intima-media thickness was 0.010 mm/year in the placebo group and 0.012 mm/year in the testosterone group (mean difference adjusted for age and trial site, 0.0002 mm/year; 95% CI, -0.003 to 0.003, P = .89). The rate of change in the coronary artery calcium score was 41.4 Agatston units/year in the placebo group and 31.4 Agatston units/year in the testosterone group (adjusted mean difference, -10.8 Agatston units/year; 95% CI, -45.7 to 24.2; P = .54). Changes in intima-media thickness or calcium scores were not associated with change in testosterone levels among individuals assigned to receive testosterone. Sexual desire, erectile function, overall sexual function scores, partner intimacy, and health-related quality of life did not differ significantly between groups. Hematocrit and prostate-specific antigen levels increased more in testosterone group.

CONCLUSIONS AND RELEVANCE

Among older men with low or low-normal testosterone levels, testosterone administration for 3 years vs placebo did not result in a significant difference in the rates of change in either common carotid artery intima-media thickness or coronary artery calcium nor did it improve overall sexual function or health-related quality of life. Because this trial was only powered to evaluate atherosclerosis progression, these findings should not be interpreted as establishing cardiovascular safety of testosterone use in older men.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00287586.

Effects of testosterone replacement in men with opioid-induced androgen deficiency: a randomized controlled trial

Symptomatic androgen deficiency is common in patients taking opioid analgesics, as these drugs potently suppress the hypothalamic-pituitary-gonadal axis. However, the efficacy of testosterone replacement in this setting remains unclear. The objective of this trial was to evaluate the efficacy of testosterone replacement on pain perception and other androgen-dependent outcomes in men with opioid-induced androgen deficiency. We conducted a randomized, double-blind, parallel placebo-controlled trial at an outpatient academic research center. Participants were men aged 18 to 64 years on opioid analgesics for chronic noncancer pain, and total testosterone levels were <350 ng/dL. Participants were randomly assigned to 14 weeks of daily transdermal gel that contained 5 g of testosterone or placebo. Primary outcomes were changes in self-reported clinical pain and objectively assessed pain sensitivity. Sexual function, quality of life, and body composition were also assessed. The mean age was 49 years. The median total and free testosterone levels at baseline were 243 ng/dL and 47 pg/mL and 251 ng/dL and 43 pg/mL in the testosterone and placebo arm, respectively. Of the 84 randomized participants, 65 had follow-up data on efficacy outcomes. Compared with men assigned to the placebo arm, those assigned to testosterone replacement experienced greater improvements in pressure and mechanical hyperalgesia, sexual desire, and role limitation due to emotional problems. Testosterone administration was also associated with an improvement in body composition. There were no between-group differences in changes in self-reported pain. In conclusion, in men with opioid-induced androgen deficiency, testosterone administration improved pain sensitivity, sexual desire, body composition, and aspects of quality of life.

Effect of testosterone replacement on response to sildenafil citrate in men with erectile dysfunction: a parallel, randomized trial

BACKGROUND

Erectile dysfunction and low testosterone levels frequently occur together.

OBJECTIVE

To determine whether addition of testosterone to sildenafil therapy improves erectile response in men with erectile dysfunction and low testosterone levels.

DESIGN

Randomized, double-blind, parallel, placebo-controlled trial. (ClinicalTrials.gov registration number: NCT00512707)

SETTING

Outpatient academic research center.

PARTICIPANTS

Men aged 40 to 70 years with scores of 25 or less for the erectile function domain (EFD) of the International Index of Erectile Function, total testosterone levels less than 11.45 nmol/L (<330 ng/dL), or free testosterone levels less than 173.35 pmol/L (<50 pg/mL).

INTERVENTION

Sildenafil dose was optimized, and 140 participants were then randomly assigned to 14 weeks of daily transdermal gel that contained 10-g testosterone for 70 participants and placebo for the remaining 70 participants. All participants were included in the primary analysis, although 10 in the testosterone group and 12 in the placebo group did not complete the study.

RESULTS

At baseline, the 2 groups had similar EFD scores. Administration of sildenafil alone was associated with a substantial increase in EFD score (mean, 7.7 [95% CI, 6.5 to 8.8]), but change in EFD score after randomization did not differ between the groups (difference, 2.2 [CI, -0.8 to 5.1]; P = 0.150). The findings were similar for other domains of sexual function in younger men, more obese men, and men with lower baseline testosterone levels or an inadequate response to sildenafil alone. Frequency of adverse events was similar for testosterone and placebo groups.

LIMITATION

Whether testosterone could improve erectile function without sildenafil was not studied.

CONCLUSION

Sildenafil plus testosterone was not superior to sildenafil plus placebo in improving erectile function in men with erectile dysfunction and low testosterone levels.

PRIMARY FUNDING SOURCE

National Institute of Child Health and Human Development.

Effect of testosterone supplementation with and without a dual 5α-reductase inhibitor on fat-free mass in men with suppressed testosterone production: a randomized controlled trial

CONTEXT

Steroid 5α-reductase inhibitors are used to treat benign prostatic hyperplasia and androgenic alopecia, but the role of 5α-dihydrotestosterone (DHT) in mediating testosterone's effects on muscle, sexual function, erythropoiesis, and other androgen-dependent processes remains poorly understood.

OBJECTIVE

To determine whether testosterone's effects on muscle mass, strength, sexual function, hematocrit level, prostate volume, sebum production, and lipid levels are attenuated when its conversion to DHT is blocked by dutasteride (an inhibitor of 5α-reductase type 1 and 2).

DESIGN, SETTING, AND PATIENTS

The 5α-Reductase Trial was a randomized controlled trial of healthy men aged 18 to 50 years comparing placebo plus testosterone enthanate with dutasteride plus testosterone enanthate from May 2005 through June 2010.

INTERVENTIONS

Eight treatment groups received 50, 125, 300, or 600 mg/wk of testosterone enanthate for 20 weeks plus placebo (4 groups) or 2.5 mg/d of dutasteride (4 groups).

MAIN OUTCOME MEASURES

The primary outcome was change in fat-free mass; secondary outcomes: changes in fat mass, muscle strength, sexual function, prostate volume, sebum production, and hematocrit and lipid levels.

RESULTS

A total of 139 men were randomized; 102 completed the 20-week intervention. Men assigned to dutasteride were similar at baseline to those assigned to placebo. The mean fat-free mass gained by the dutasteride groups was 0.6 kg (95% CI, -0.1 to 1.2 kg) when receiving 50 mg/wk of testosterone enanthate, 2.6 kg (95% CI, 0.9 to 4.3 kg) for 125 mg/wk, 5.8 kg (95% CI, 4.8 to 6.9 kg) for 300 mg/wk, and 7.1 kg (95% CI, 6.0 to 8.2 kg) for 600 mg/wk. The mean fat-free mass gained by the placebo groups was 0.8 kg (95% CI, -0.1 to 1.7 kg) when receiving 50 mg/wk of testosterone enanthate, 3.5 kg (95% CI, 2.1 to 4.8 kg) for 125 mg/wk, 5.7 kg (95% CI, 4.8 to 6.5 kg) for 300 mg/wk, and 8.1 kg (95% CI, 6.7 to 9.5 kg) for 600 mg/wk. The dose-adjusted differences between the dutasteride and placebo groups for fat-free mass were not significant (P = .18). Changes in fat mass, muscle strength, sexual function, prostate volume, sebum production, and hematocrit and lipid levels did not differ between groups.

CONCLUSION

Changes in fat-free mass in response to graded testosterone doses did not differ in men in whom DHT was suppressed by dutasteride from those treated with placebo, indicating that conversion of testosterone to DHT is not essential for mediating its anabolic effects on muscle.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00493987.

Clinical meaningfulness of the changes in muscle performance and physical function associated with testosterone administration in older men with mobility limitation

CONTEXT

Testosterone in Older Men with Mobility Limitations Trial determined the effects of testosterone on muscle performance and physical function in older men with mobility limitation. Trial's Data and Safety Monitoring Board recommended enrollment cessation due to increased frequency of adverse events in testosterone arm. The changes in muscle performance and physical function were evaluated in relation to participant's perception of change.

METHODS

Men aged 65 years and older, with mobility limitation, total testosterone 100-350 ng/dL, or free testosterone less than 50 pg/mL, were randomized to placebo or 10 g testosterone gel daily for 6 months. Primary outcome was leg-press strength. Secondary outcomes included chest-press strength, stair-climb, 40-m walk, muscle mass, physical activity, self-reported function, and fatigue. Proportions of participants exceeding minimally important difference in study arms were compared.

RESULTS

Of 209 randomized participants, 165 had follow-up efficacy measures. Mean (SD) age was 74 (5.4) years and short physical performance battery score 7.7 (1.4). Testosterone arm exhibited greater improvements in leg-press strength, chest-press strength and power, and loaded stair-climb than placebo. Compared with placebo, significantly greater proportion of men receiving testosterone improved their leg-press and chest-press strengths (43% vs 18%, p = .01) and stair-climbing power (28% vs 10%, p = .03) more than minimally important difference. Increases in leg-press strength and stair-climbing power were associated with changes in testosterone levels and muscle mass. Physical activity, walking speed, self-reported function, and fatigue did not change.

CONCLUSIONS

Testosterone administration in older men with mobility limitation was associated with patient-important improvements in muscle strength and stair-climbing power. Improvements in muscle strength and only some physical function measures should be weighed against the risk of adverse events in this population.

The effects of injected testosterone dose and age on the conversion of testosterone to estradiol and dihydrotestosterone in young and older men

BACKGROUND

During testosterone (T) therapy, T is partly converted to 17beta-estradiol (E2) and 5alpha-dihydrotestosterone (DHT). Effects of age, testosterone dose, and body composition on total and free E2 and DHT levels are unknown.

OBJECTIVE

We evaluated age and dose-related differences in E2 and DHT levels in response to graded doses of testosterone enanthate in young and older men.

METHODS

Fifty-one young (aged 19-35 yr) and 52 older (aged 59-75 yr) men completed treatment with monthly injections of a GnRH agonist plus randomly assigned weekly doses of testosterone enanthate (25, 50, 125, 300, or 600 mg) for 5 months.

RESULTS

During testosterone administration, total and free E2 levels increased dose-dependently (dose effect, P<0.001) in both young and older men. Total and free E2 levels and E2:T ratios during T administration were higher in older than young men, but age-related differences in free E2 and free E2:T ratios were not significant after adjusting for testosterone levels, percentage fat mass, and SHBG. DHT levels and DHT:T ratios were dose-related but did not differ between young and older men. Mechanistic modeling of free hormone data revealed that the conversions of T to E2 and DHT were both consistent with saturable Michaelis-Menten kinetics. The in vivo Km values were estimated to be 1.83 nm for aromatase and 3.35 nm for 5alpha-reductase, independent of age. The Vmax parameter for E2 was 40% higher in older men than younger men, but Vmax for DHT was not significantly different between age groups.

CONCLUSIONS

During im testosterone administration, E2 and DHT levels exhibit saturable increases with dose. The rate of whole body aromatization is higher in older men, partly related to their higher percentage fat mass, SHBG, and testosterone levels.

Adverse events associated with testosterone administration

BACKGROUND

Testosterone supplementation has been shown to increase muscle mass and strength in healthy older men. The safety and efficacy of testosterone treatment in older men who have limitations in mobility have not been studied.

METHODS

Community-dwelling men, 65 years of age or older, with limitations in mobility and a total serum testosterone level of 100 to 350 ng per deciliter (3.5 to 12.1 nmol per liter) or a free serum testosterone level of less than 50 pg per milliliter (173 pmol per liter) were randomly assigned to receive placebo gel or testosterone gel, to be applied daily for 6 months. Adverse events were categorized with the use of the Medical Dictionary for Regulatory Activities classification. The data and safety monitoring board recommended that the trial be discontinued early because there was a significantly higher rate of adverse cardiovascular events in the testosterone group than in the placebo group.

RESULTS

A total of 209 men (mean age, 74 years) were enrolled at the time the trial was terminated. At baseline, there was a high prevalence of hypertension, diabetes, hyperlipidemia, and obesity among the participants. During the course of the study, the testosterone group had higher rates of cardiac, respiratory, and dermatologic events than did the placebo group. A total of 23 subjects in the testosterone group, as compared with 5 in the placebo group, had cardiovascular-related adverse events. The relative risk of a cardiovascular-related adverse event remained constant throughout the 6-month treatment period. As compared with the placebo group, the testosterone group had significantly greater improvements in leg-press and chest-press strength and in stair climbing while carrying a load.

CONCLUSIONS

In this population of older men with limitations in mobility and a high prevalence of chronic disease, the application of a testosterone gel was associated with an increased risk of cardiovascular adverse events. The small size of the trial and the unique population prevent broader inferences from being made about the safety of testosterone therapy. (ClinicalTrials.gov number, NCT00240981.)

Self-monitoring of blood glucose with finger tip versus alternative site sampling: effect on glycemic control in insulin-using patients with type 2 diabetes

OBJECTIVE

This study compared glycemic control in finger tip versus forearm sampling methods of self-monitoring of blood glucose (SMBG).

RESEARCH DESIGN AND METHODS

One hundred seventy-four insulin-using patients with type 2 diabetes were randomized to SMBG using either finger-tip testing (FT) or forearm alternative site testing (AST) and followed up for 7 months. Hemoglobin A1C (HbA1C) was measured at baseline, month 4, and month 7. The study was designed to test the noninferiority of the AST method for the primary end point of change in HbA1C from baseline to month 7. Adherence with the testing schedule and frequency of hypoglycemic episodes were also measured.

RESULTS

The FT (n = 85) and AST (n = 89) groups each had significant decreases in mean HbA1C from baseline to month 7 (FT, -0.4 +/- 1.4%, P = 0.008; AST, -0.3 +/- 1.2%, P = 0.045), and noninferiority between groups was demonstrated with a margin of equivalence of 0.5 (P = 0.043). There was no observable difference in HbA1C change between the groups (P = 0.442). Adherence was better in the FT (87%) than the AST (78%) group (P = 0.003), which may have been because of the difficulty some subjects had in obtaining blood samples for AST. The number of hypoglycemic episodes was too small to assess for a difference between groups.

CONCLUSIONS

SMBG by the AST, rather than FT, method did not have a detrimental effect on long-term glycemic control in insulin-using patients with type 2 diabetes. Although adherence with testing was expected to be better in the AST group, it was actually better in the FT group.

Effects of a supraphysiological dose of testosterone on physical function, muscle performance, mood, and fatigue in men with HIV-associated weight loss

Testosterone increases fat-free mass (FFM) in men infected with human immunodeficiency virus (HIV), but its effects on muscle performance, physical function, mood, and quality of life are poorly understood. Sixty-one HIV-infected men with weight loss were randomized to receive weekly intramuscular injections of 300 mg of testosterone enanthate or placebo for 16 wk. The primary outcome of interest was physical function (walking speed, stair-climbing power, and load-carrying ability). Secondary outcome measures included body weight and composition, muscle performance, sexual function, mood, and quality of life. Serum nadir free and total testosterone levels increased (+188.0 +/- 29.6 and +720 +/- 86 ng/dl) in the testosterone, but not placebo, group. Testosterone administration was associated with increased FFM (2.8 +/- 0.5 kg), which was significantly greater than in the placebo group (P < 0.0001). Leg press strength increased significantly in testosterone-treated (P = 0.027), but not placebo-treated, men; the difference between groups was not significant. Other measures of muscle performance and physical function did not change significantly in either group. Men receiving testosterone demonstrated significantly greater improvements in mental health and quality-of-life scores than those receiving placebo and improvements in fatigue/energy and mood scores that were not significantly different from those receiving placebo. Sexual function scores did not change in either group. In HIV-infected men with weight loss, a supraphysiological dose of testosterone significantly increased FFM but did not improve self-reported or performance-based measures of physical function. Improvements in mood, fatigue, and quality-of-life measures in the testosterone group, although clinically important, need further confirmation.

Caspase-3 activity is reduced after spinal cord injury in mice lacking dynorphin: differential effects on glia and neurons

Dynorphins are endogenous opioid peptide products of the prodynorphin gene. An extensive literature suggests that dynorphins have deleterious effects on CNS injury outcome. We thus examined whether a deficiency of dynorphin would protect against tissue damage after spinal cord injury (SCI), and if individual cell types would be specifically affected. Wild-type and prodynorphin(-/-) mice received a moderate contusion injury at 10th thoracic vertebrae (T10). Caspase-3 activity at the injury site was significantly decreased in tissue homogenates from prodynorphin(-/-) mice after 4 h. We examined frozen sections at 4 h post-injury by immunostaining for active caspase-3. At 3-4 mm rostral or caudal to the injury, >90% of all neurons, astrocytes and oligodendrocytes expressed active caspase-3 in both wild-type and knockout mice. At 6-7 mm, there were fewer caspase-3(+) oligodendrocytes and astrocytes than at 3-4 mm. Importantly, caspase-3 activation was significantly lower in prodynorphin(-/-) oligodendrocytes and astrocytes, as compared with wild-type mice. In contrast, while caspase-3 expression in neurons also declined with further distance from the injury, there was no effect of genotype. Radioimmunoassay showed that dynorphin A(1-17) was regionally increased in wild-type injured versus sham-injured tissues, although levels of the prodynorphin processing product Arg(6)-Leu-enkephalin were unchanged. Our results indicate that dynorphin peptides affect the extent of post-injury caspase-3 activation, and that glia are especially sensitive to these effects. By promoting caspase-3 activation, dynorphin peptides likely increase the probability of glial apoptosis after SCI. While normally beneficial, our findings suggest that prodynorphin or its peptide products become maladaptive following SCI and contribute to secondary injury.

Endogenous sex hormones and cardiovascular disease incidence in men

BACKGROUND

Data suggest that endogenous sex hormones (testosterone, dehydroepiandrosterone sulfate [DHEA-S], and estradiol) influence cardiovascular disease (CVD) risk factors and vascular function. Yet, prospective studies relating sex hormones to CVD incidence in men have yielded inconsistent results.

OBJECTIVE

To examine the association of circulating sex hormone levels and CVD risk in men.

DESIGN

Prospective cohort study.

SETTING

Community-based study in Framingham, Massachusetts.

PARTICIPANTS

2084 middle-aged white men without CVD at baseline.

MEASUREMENTS

The authors used multivariable Cox regression to relate baseline levels of testosterone, DHEA-S, and estradiol to the incidence of CVD (coronary, cerebrovascular, or peripheral vascular disease or heart failure) during 10 years of follow-up.

RESULTS

During follow-up, 386 men (18.5%) experienced a first CVD event. After adjustment for baseline standard CVD risk factors, higher estradiol level was associated with lower risk for CVD (hazard ratio per SD increment in log estradiol, 0.90 [95% CI, 0.82 to 0.99]; P = 0.035). The authors observed effect modification by age: Higher estradiol levels were associated with lower CVD risk in older (median age >56 years) men (hazard ratio per SD increment, 0.86 [CI, 0.78 to 0.96]; P = 0.005) but not in younger (median age < or =56 years) men (hazard ratio per SD increment, 1.11 [CI, 0.89 to 1.38]; P = 0.36). The association of higher estradiol level with lower CVD incidence remained robust in time-dependent Cox models (updating standard CVD risk factors during follow-up). Serum testosterone and DHEA-S levels were not statistically significantly associated with incident CVD.

LIMITATIONS

Sex hormone levels were measured only at baseline, and the findings may not be generalizable to women and nonwhite people.

CONCLUSIONS

In the community-based sample, a higher serum estradiol level was associated with lower risk for CVD events in older men. The findings are consistent with the hypothesis that endogenous estrogen has vasculoprotective influences in men.

Molecular targets of opiate drug abuse in neuroAIDS

Opiate drug abuse, through selective actions at mu-opioid receptors (MOR), exacerbates the pathogenesis of human immunodeficiency virus-1 (HIV-1) in the CNS by disrupting glial homeostasis, increasing inflammation, and decreasing the threshold for pro-apoptotic events in neurons. Neurons are affected directly and indirectly by opiate-HIV interactions. Although most opiates drugs have some affinity for kappa (KOR) and/or delta (DOR) opioid receptors, their neurotoxic effects are largely mediated through MOR. Besides direct actions on the neurons themselves, opiates directly affect MOR-expressing astrocytes and microglia. Because of their broad-reaching actions in glia, opiate abuse causes widespread metabolic derangement, inflammation, and the disruption of neuron-glial relationships, which likely contribute to neuronal dysfunction, death, and HIV encephalitis. In addition to direct actions on neural cells, opioids modulate inflammation and disrupt normal intercellular interactions among immunocytes (macrophages and lymphocytes), which on balance further promote neuronal dysfunction and death. The neural pathways involved in opiate enhancement of HIV-induced inflammation and cell death, appear to involve MOR activation with downstream effects through PI3-kinase/Akt and/or MAPK signaling, which suggests possible targets for therapeutic intervention in neuroAIDS.

Dynorphin A (1–17) induces apoptosis in striatal neurons in vitro through α-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate receptor-mediated cytochrome C release and caspase-3 activation

Dynorphin A (1-17), an endogenous opioid neuropeptide, can have pathophysiological consequences at high concentrations through actions involving glutamate receptors. Despite evidence of excitotoxicity, the basic mechanisms underlying dynorphin-induced cell death have not been explored. To address this question, we examined the role of caspase-dependent apoptotic events in mediating dynorphin A (1-17) toxicity in embryonic mouse striatal neuron cultures. In addition, the role of opioid and/or glutamate receptors were assessed pharmacologically using dizocilpine maleate (MK(+)801), a non-equilibrium N-methyl-D-aspartate (NMDA) antagonist; 6-cyano-7-nitroquinoxaline-2,3-dione, a competitive alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)/kainate antagonist; or (-)-naloxone, a general opioid antagonist. The results show that dynorphin A (1-17) (>or=10 nM) caused concentration-dependent increases in caspase-3 activity that were accompanied by mitochondrial release of cytochrome c and the subsequent death of cultured mouse striatal neurons. Moreover, dynorphin A-induced neurotoxicity and caspase-3 activation were significantly attenuated by the cell permeable caspase inhibitor, caspase-3 inhibitor-II (z-DEVD-FMK), further suggesting an apoptotic cascade involving caspase-3. AMPA/kainate receptor blockade significantly attenuated dynorphin A-induced cytochrome c release and/or caspase-3 activity, while NMDA or opioid receptor blockade typically failed to prevent the apoptotic response. Last, dynorphin-induced caspase-3 activation was mimicked by the ampakine CX546 [1-(1,4-benzodioxan-6-ylcarbonyl)piperidine], which suggests that the activation of AMPA receptor subunits may be sufficient to mediate toxicity in striatal neurons. These findings provide novel evidence that dynorphin-induced striatal neurotoxicity is mediated by a caspase-dependent apoptotic mechanism that largely involves AMPA/kainate receptors.

Endogenous opioids and oligodendroglial function: possible autocrine/paracrine effects on cell survival and development

Previous work has shown that oligodendrocytes (OLs) express both micro- and kappa-opioid receptors. In developing OLs, micro receptor activation increases OL proliferation, while the kappa-antagonist nor-binaltorphimine (NorBNI) affects OL differentiation. Because exogenous opioids were not present in our defined culture medium, we hypothesized that NorBNI blocked endogenous opioids produced by the OLs themselves. To test this, intact and partially processed proenkephalin and prodynorphin-derived peptides were assessed in OLs using immunocytochemistry or Western blot analysis, or both. Immature OLs possessed large amounts of intact and partially processed proenkephalin precursors, as well as posttranslational products of prodynorphin including dynorphin A (1-17). With maturation, however, intact or partially processed proenkephalin was expressed by only about 50% of OLs, while dynorphin A (1-17) was undetectable. To assess the function of OL-derived opioids, the effect of kappa-agonists/antagonists on OL differentiation and death was explored. kappa-Agonists alone had no effect. In contrast, NorBNI significantly increased OL death. Additive OL losses were evident when NorBNI was paired with toxic levels of glutamate, suggesting that kappa-receptor blockade alone is sufficient to induce OL death. Thus, the results indicate that OLs express proenkephalin and prodynorphin peptides in a developmentally regulated manner, and further suggest that opioids produced by OLs modulate OL maturation and survival through local (i.e., autocrine and/or paracrine) mechanisms.

Structure-activity analysis of dynorphin A toxicity in spinal cord neurons: intrinsic neurotoxicity of dynorphin A and its carboxyl-terminal, nonopioid metabolites

Dynorphin A [dynorphin A (1-17)] is an endogenous opioid peptide that is antinociceptive at physiological concentrations. Levels of dynorphin A increase markedly following spinal cord trauma and may contribute to secondary neurodegeneration. Both kappa opioid and N-methyl-d-aspartate (NMDA) receptor antagonists can modulate the effects of dynorphin, suggesting that dynorphin is acting through kappa opioid and/or NMDA receptor types. Despite these findings, few studies have critically examined the mechanisms of dynorphin A neurotoxicity at the cellular level. To better understand how dynorphin affects cell viability, structure-activity studies were performed examining the effects of dynorphin A and dynorphin A-derived peptide fragments on the survival of mouse spinal cord neurons coexpressing kappa opioid and NMDA receptors in vitro. Time-lapse photography was used to repeatedly follow the same neurons before and during experimental treatments. Dynorphin A caused significant neuronal losses that were dependent on concentration (> or = 1 microM) and duration of exposure. Moreover, exposure to an equimolar concentration of dynorphin A fragments (100 microM) also caused a significant loss of neurons. The rank order of toxicity was dynorphin A (1-17) > dynorphin A (1-13) congruent with dynorphin A (2-13) congruent with dynorphin A (13-17) (least toxic) > dynorphin A (1-5) ([Leu(5)]-enkephalin) or dynorphin A (1-11). Dynorphin A (1-5) or dynorphin A (1-11) did not cause neuronal losses even following 96 h of continuous exposure, while dynorphin A (3-13), dynorphin A (6-17), and dynorphin A (13-17) were neurotoxic. The NMDA receptor antagonist MK-801 (dizocilpine) (10 microM) significantly attenuated the neurotoxic effects of dynorphin A and/or dynorphin-derived fragments except dynorphin A (13-17), suggesting that the neurotoxic effects of dynorphin were largely mediated by NMDA receptors. Thus, toxicity resides in the carboxyl-terminal portion of dynorphin A and this minimally includes dynorphin A (3-13) and (13-17). Our findings suggest that dynorphin A and/or its metabolites may contribute significantly to neurodegeneration during spinal cord injury and that alterations in dynorphin A biosynthesis, metabolism, and/or degradation may be important in determining injury outcome.

Neuronal interaction determines the expression of the alpha-2 isoform of Na, K-ATPase in oligodendrocytes

Na,K-ATPase is an integral membrane enzyme responsible for maintenance of the transmembrane Na+/K+ gradient which generates membrane excitability. Previous studies showed that oligodendrocytes within the CNS robustly expressed the alpha2 isoform of the Na,K-ATPase while oligodendrocytes in isolated cultures did not. We tested whether the levels of this isoform might be modulated by interactions with neurons. Western blots showed alpha2 protein expression was very low in rat optic nerve immediately after birth, but that expression was greatly increased by days 5 and 14. In adult optic nerves, levels were barely detectable. Since the first myelinated axons are observed in rat optic nerve at day 5, and the next 2 weeks are considered the period of peak myelination, this timing suggested a relationship between oligodendrocyte-neuron contact, myelination onset and the upregulation of the alpha2 isoform. In further experiments we plated oligodendrocytes in isolation or in co-culture with neurons dissociated from cerebral cortex at the day of birth. After 6 days in vitro, 45% of oligodendrocytes co-cultured with neurons expressed abundant alpha2 protein which was detected by immunohistochemistry, a six-fold increase over cells expressing alpha2 protein in isolated cultures. Conditioned medium from neuronal cultures did not affect alpha2 levels in oligodendrocytes. These results suggest that neurons may play a role in upregulating glial expression of the alpha2 isoform during peak periods of myelination, and that the effect is likely to be dependent on contact.

Abnormal Ca(2+) regulation in oligodendrocytes from the dysmyelinating jimpy mouse

Jimpy (jp) is a point mutation in the gene on the X chromosome which codes for the major myelin proteolipid protein. Most oligodendrocytes (OLs) in the jp mouse undergo cell death at the time when they should be actively myelinating. Loss of mature OLs results in severe CNS dysmyelination. Dying jp OLs have the morphology of apoptotic cells but it is not clear how the mutation activates biochemical pathways which lead to programmed death of OLs in jp CNS. There is compelling evidence from a number of systems that high levels of intracellular Ca(2+) ([Ca2+]i) can activate downstream processes which result in both apoptotic and necrotic cell death. To determine whether [Ca2+](i) dysregulation might be involved in the death of jp OLs, we used ratiometric imaging to determine levels of [Ca2+](i) in OLs cultured from jp and normal CNS and in immortalized cell lines derived from jp and normal OLs. Immortalized jp OLs and OLs isolated directly from jp brain both showed a similar elevation in [Ca2+](i) ranging from 60% to 150% over control values. A higher baseline [Ca2+](i) in jp OLs might increase their vulnerability to other insults due to abnormal protein processing or changes in signaling pathways which act as a final trigger for cell death.

Activation of the caspase-3 apoptotic cascade in traumatic spinal cord injury

Traumatic spinal cord injury often results in complete loss of voluntary motor and sensory function below the site of injury. The long-term neurological deficits after spinal cord trauma may be due in part to widespread apoptosis of neurons and oligodendroglia in regions distant from and relatively unaffected by the initial injury. The caspase family of cysteine proteases regulates the execution of the mammalian apoptotic cell death program. Caspase-3 cleaves several essential downstream substrates involved in the expression of the apoptotic phenotype in vitro, including gelsolin, PAK2, fodrin, nuclear lamins and the inhibitory subunit of DNA fragmentation factor. Caspase-3 activation in vitro can be triggered by upstream events, leading to the release of cytochrome c from the mitochondria and the subsequent transactivation of procaspase-9 by Apaf-1. We report here that these upstream and downstream components of the caspase-3 apoptotic pathway are activated after traumatic spinal cord injury in rats, and occur early in neurons in the injury site and hours to days later in oligodendroglia adjacent to and distant from the injury site. Given these findings, targeting the upstream events of the caspase-3 cascade has therapeutic potential in the treatment of acute traumatic injury to the spinal cord.

Programmed cell death without DNA fragmentation in the jimpy mouse: secreted factors can enhance survival

Jimpy is one of many related mutations affecting the myelin proteolipid protein gene that causes severe hypomyelination in the central nervous system (CNS). Underlying the hypomyelination is a failure of oligodendrocytes (OLs) to differentiate, and the premature death of large numbers of OLs during the developmental period. Previous light and electron microscopic evidence suggested that jimpy OLs die in a manner consistent with programmed cell death. We have used TUNEL staining as a biochemical marker for apoptosis in conjunction with immunostaining for OL and myelin markers. At 13 - 14 days postnatal, a time when the number of dying OLs in jimpy CNS is increased more than five times normal, there are only modest increases (70% in spinal cord; 20% in cerebral cortex) in TUNEL labeled cells in mutant CNS tissues. The results in vitro are similar, and only a small per cent of TUNEL labeled cells have the antigenic phenotype of OLs. The discrepancy between numbers of dying and TUNEL labeled cells suggests either that most jimpy OLs do not undergo programmed cell death or that the biochemical pathways leading to their death do not involve DNA fragmentation which is detected by the TUNEL method. We also present evidence that jimpy OLs show increased survival and enhanced differentiation when they are grown in vitro in medium conditioned by cells lines which express products of the proteolipid protein gene. Cell lines expressing proteolipid protein and the alternatively spliced DM20 protein have differential effects on cell numbers and production of myelin-like membranes.

Anti-death properties of TNF against metabolic poisoning: mitochondrial stabilization by MnSOD

The cytokine tumor necrosis factor (TNF) is toxic to some mitotic cells, but protects cultured neurons from a variety of insults by mechanisms that are unclear. Pretreatment of neurons or astrocytes with TNF caused significant increases in MnSOD activity, and also significantly attenuated 3-nitropropionic acid (3-NP) induced superoxide accumulation and loss of mitochondrial transmembrane potential. In oligodendrocytes, however, MnSOD activity was not increased, and 3-NP toxicity was unaffected by TNF. Genetically engineered PC6 cells that overexpress MnSOD also were resistant to 3-NP-induced damage. TNF pretreatment and MnSOD overexpression prevented 3-NP induced apoptosis, and shifted the mode of death from necrosis to apoptosis in response to high levels of 3-NP. Mitochondria isolated from either MnSOD overexpressing PC6 cells or TNF-treated neurons maintained resistance to 3-NP-induced loss of transmembrane potential and calcium homeostasis, and showed attenuated release of caspase activators. Overall, these results indicate that MnSOD activity directly stabilizes mitochondrial transmembrane potential and calcium buffering ability, thereby increasing the threshold for lethal injury. Additional studies showed that levels of oxidative stress and striatal lesion size following 3-NP administration in vivo are increased in mice lacking TNF receptors.

Endogenous opioid system in developing normal and jimpy oligodendrocytes: mu and kappa opioid receptors mediate differential mitogenic and growth responses

The early development of both neurons and neuroglia may be modulated by signaling through opioid mediated pathways. Neurons and astroglia not only express specific types of opiate receptors, but also respond functionally to opioids with altered rates of proliferation and growth. The present study was undertaken to determine if opioids also modulate development of the other major CNS macroglial cell, the oligodendrocyte (OL). Using well-characterized polyclonal antibodies specific for delta-, kappa-, and mu-opiate receptors, OLs grown in vitro were shown to express mu-receptors at a very immature stage prior to expression of kappa-receptors. This developmentally regulated sequence differs from the pattern of expression in neurons and astroglia. delta-receptors are apparently absent from cultured OLs. OLs also have physiologic responses to selective mu- and kappa-receptor agonists and antagonists. Exposure of relatively immature O4+ OLs to the mu-receptor agonist PL017 [H-Tyr-Pro-Phe(N-Me)-D-Pro-NH2] resulted in a significant enhancement in the rate of DNA synthesis. This effect, which was not observed in more mature MBP+ OLs, was entirely blocked by the antagonist naloxone. Although the kappa-receptor pathway appeared to be uninvolved in controlling proliferation, the kappa-receptor antagonist nor-binaltorphimine significantly increased the size of myelin-like membranes produced by the cultured OLs. Interestingly, OLs derived from the jimpy mouse, a mutant characterized by an almost complete lack of CNS myelin and premature death of OLs, were found to be deficient in kappa-opiate receptors. Our findings clearly show that OLs not only express specific opiate receptors, but also respond to changes in their level of stimulation in ways that could profoundly impact nervous system morphology and function. If opiate receptors are expressed by OLs in vivo, their pharmacological manipulation might provide a novel pathway for modulating OL and myelin production both during development and in demyelinated conditions.

Injury stimulates outgrowth and motility of oligodendrocytes grown in vitro

Oligodendrocytes which form myelin within the CNS develop from small, highly motile cells that are largely bipolar into mature cells which extend many processes and which produce myelin membranes around multiple axons. The production of myelin sheaths is thought to anchor mature oligodendrocytes (OLs), limiting their motility. When the brain sustains an injury, OLs do not make a significant effort to remyelinate, a fact attributed to both their lack of proliferation and their inability to migrate or extend processes into areas of injury. To test the motility and growth potential of mature OLs, we have designed an in vitro system in which individual cells can undergo long-term observation. Additionally, cells can be mechanically injured by transection of processes using a low-power laser beam. Both control and injured OLs undergo several types of structural change, including extension and retraction of processes and membranes, as well as changes in process caliber. Some OLs exhibit a high degree of motility, moving several hundred micrometers within days. Rather than interfering with the cells' ability to undergo structural change, injury actually stimulated outgrowth of new processes and motility. Neither injury nor addition of basic fibroblast growth factor (bFGF) increased the rate of OL division. However, bFGF paradoxically caused an increase in uptake of the DNA synthesis marker bromodeoxyuridine and had negative effects on OL survival. The unexpected findings that OLs with a mature phenotype are motile and undergo constant structural modification in vitro and that injury induces certain behaviors suggest that myelin-forming OLs in the brain may be capable of a high degree of plasticity under certain conditions.

mu-Opioid receptor activation enhances DNA synthesis in immature oligodendrocytes

Opioids disrupt nervous system development by inhibiting the proliferation of neuronal and glial progenitors. These studies explored the hypothesis that mu opioid receptors are expressed by immature oligodendrocytes (OLs) and are functionally related to growth. Antibodies identifying the cloned mu opioid receptor demonstrated that cultured OLs expressed mu opioid receptor immunoreactivity very early during development. Cultures were treated with the selective mu opioid receptor agonist H-Tyr-Pro-Phe (N-Me)-D-Pro-NH2 (PL017; 1 microM), or PL017 (1 microM) plus the antagonist naloxone (3 microM). Opioid-dependent changes in DNA synthesis were assessed by determining the proportion of bromodeoxyuridine (BrdU)-labeled O4-immunoreactive OLs. Treatment with PL017 caused a 311% increase in the proportion of O4-immunoreactive OLs incorporating BrdU compared to untreated controls, and these effects were prevented by co-administering naloxone. These preliminary results indicate that (i) immature OLs express mu opioid receptors and that (ii) the activation of this receptor type is functionally coupled to DNA synthesis and the cell division cycle. The expression of opioid receptors by OLs suggests that the endogenous opioid system is widely distributed among glial types.

Epigenetic factors up-regulate expression of myelin proteins in the dysmyelinating jimpy mutant mouse

Proteolipid protein (PLP) is a major structural component of central nervous system (CNS) myelin. Evidence exists that PLP or the related splice variant DM-20 protein may also play a role in early development of oligodendrocytes (OLs), the cells that form CNS myelin. There are several naturally occurring mutations of the PLP gene that have been used to study the roles of PLP both in myelination and in OL differentiation. The PLP mutation in the jimpy (jp) mouse has been extensively characterized. These mutants produce no detectable PLP and exhibit an almost total lack of CNS myelin. Additionally, most OLs in affected animals die prematurely, before producing myelin sheaths. We have studied cultures of jp CNS in order to understand whether OL survival and myelin formation require production of normal PLP. When grown in primary cultures, jp OLs mimic the relatively undifferentiated phenotype of jp OLs in vivo. They produce little myelin basic protein (MBP), never immunostain for PLP, and rarely elaborate myelin-like membranes. We report here that jp OLs grown in medium conditioned by normal astrocytes synthesize MBP and incorporate it into membrane expansions. Some jp OLs grown in this way stain with PLP antibodies, including an antibody to a peptide sequence specific for the mutant jp PLP. This study shows that: (1) an absence of PLP does not necessarily lead to dysmyelination or OL death; (2) OLs are capable of translating at least a portion of the predicted jp PLP; (3) the abnormal PLP made in the cultured jp cells is not toxic to OLs. These results also highlight the importance of environmental factors in controlling OL phenotype.

Differential expression of Na,K-ATPase isoforms in oligodendrocytes and astrocytes

Using Western blot and immunocytochemistry to detect protein, and in situ hybridization and Northern blot to detect RNA, we studied the expression of Na,K-ATPase subunit isoforms in cultured astrocytes and oligodendrocytes in vitro, and in glial cells in the brain. We found that astrocytes in culture express alpha 1 and alpha 2 isoforms of the catalytic subunit and both beta 1 and beta 2 isoforms of the regulatory subunit. Oligodendrocytes in culture express only alpha 1, but in vivo high levels of alpha 2 are seen in oligodendrocytes of white matter tracts. These results suggest that expression of the alpha 2 isoform in mature oligodendrocytes may be regulated by axonal contact and related to myelination.

Proteolipid protein: is it more than just a structural component of myelin?

Proteolipid protein (PLP) is the most abundant protein of central nervous system (CNS) myelin. Because of its predicted topography, PLP has been assumed to function as a structural component of myelin, providing stability and maintaining the compact lamellar structure. However, developmental studies have shown that the PLP gene is active long before myelination begins. This and other evidence from various PLP mutants and transgenic models has fueled speculation that PLP or other products of the gene have additional, nonstructural roles both within and outside the CNS. PLP is structurally related to a family of ion channel proteins which includes the connexins, synaptophysins and various neurotransmitter receptors, and there is some experimental evidence which supports a role for PLP in ion gating. Other provocative ideas are that the PLP gene may influence autocrine signaling within oligodendrocytes or that PLP mRNAs have a function apart from protein coding.

Postmitotic oligodendrocytes generated during postnatal cerebral development are derived from proliferation of immature oligodendrocytes

The phenotype of proliferating glia is examined during postnatal rodent development by combining immunocytochemistry (ICC) with 3H-thymidine autoradiography (ARG) to identify cells in the S phase of the cell cycle. Antibodies (ABs) which are specific for cells in the oligodendrocyte (OL) lineage were utilized, with emphasis placed upon the proliferation of OLs as it remains unclear whether this cell type divides in situ. The results show that proliferating cells stain with ABs which are specific for OLs and myelin glycolipids. The proliferating OLs (oligodendroblasts), although they do not appear to have formed myelin sheaths, have quite elaborate and distinctive morphologies. These oligodendroblasts give rise to very long, thin processes which in turn have additional branches. Their cytoarchitecture corresponds closely to cells described as oligodendroblasts with electron microscopy and whose processes often appear to be in the initial phase of myelination (Skoff et al: J. Comp. Neurol. 169:291-312, 1976a). These proliferating OLs are still quite immature because the expression of myelin specific proteins is only occasionally observed in 3H-thymidine labeled cells. The phenotype of the oligodendroblasts is quite different from that of proliferating astrocytes (astroblasts). As shown in previous studies (Skoff; Dev. Biol. 139:149-163, 1990), the astroblasts, which are identified by the presence of glial fibrillary acidic protein (GFAP), usually have thick, stubby processes, and both their nucleus and cytoplasm are larger and of lighter density than those found in oligodendroblasts. In early myelinating regions of the cerebrum, glycolipid positive cells account for the majority of the 3H-thymidine labeled cells. This data, when combined with the quantification of proliferating astrocytes (ASs) from previous immunocytochemical and electron microscopic studies, indicate that oligodendroblasts and astroblasts constitute the vast majority of the proliferating glia in the brain and in optic nerve at times when ASs and OLs are being generated. In normal postnatal cerebral development, the immature ASs and OLs which proliferate are the direct, immediate precursors for most postmitotic ASs and OLs.

Characterization and development of glial and other non-neuronal cells in chick Edinger Westphal cultures

Cultures of dissociated Edinger Westphal nuclei, dissected from embryonic chick brainstems, were screened immunohistochemically for a variety of non-neuronal cell markers. In young cultures, small clusters of cells were stained by the oligodendrocyte-specific antibodies 04 and 01. In older cultures, larger groups of cells were 04 and 01 positive, sheets of myelin-like membrane were elaborated, and immunoreactivity for proteolipid protein appeared. This sequence resembles that observed in well-characterized rodent brain cultures and suggests that oligodendrocytes in chick Edinger Westphal cultures differentiate in a pattern similar to rodent oligodendrocytes in culture. Variable numbers of cells were immunoreactive for glial fibrillary acidic protein. Many vimentin positive cells were observed, some of which morphologically resembled flat astrocytes. Together with the widespread presence of vimentin, large patches of fibronectin-like immunoreactivity suggested the presence of fibroblasts and/or endothelial cells. An anti-thymocyte polyclonal antibody stained a subset of cobblestone-shaped cells, possibly endothelial cells, in both Edinger Westphal cultures and control cultures of skin fibroblasts. Staining for smooth muscle myosin was detected in several patches of cells, tentatively identifying them as pericytes or smooth muscle cells. In conclusion, Edinger Westphal cultures contain a diverse and varying population of non-neuronal cells loosely organized in large, overlapping islands of cell types and including oligodendrocytes, astrocytes, possibly fibroblasts, endothelial cells, pericytes and/or smooth muscle cells.

The pH of jimpy glia is increased: intracellular measurements using fluorescent laser cytometry

The jimpy mutation lies in the gene which codes for myelin proteolipid protein, and the brains and spinal cords of jimpy mice contain little myelin and no measurable proteolipid protein. It has been thought that the mutation affected only the myelin forming oligodendroglial cells, but there is now considerable evidence that astroglia are also a target of the mutation since jimpy astrocytes exhibit a prominent gliosis along with defects in metabolism and proliferation. Because cell proliferation is associated with an increase in intracellular pH, we investigated whether the pH of jimpy glia was abnormal. Using a pH sensitive fluorescent dye and a laser cytometry system we measured the intracellular pH of individual cells in cultures derived from both jimpy and normal brains. The relative pH of flat astrocytes in jimpy cultures was higher than in normal cultures by an average of 0.24 pH units, and these increased values were evident 2-3 days after plating. At this in vitro age the cultures contain only a few oligodendrocytes, none of which express detectable proteolipid protein. The pH of the process-bearing cell population, which contains the oligodendrocytes as well as some astrocytes and presumptive glial precursors, was also increased but not until 7 days in culture. The finding that a mutation in the myelin proteolipid protein gene can alter the normal pH of astrocytes is quite unexpected since, as far as is known, astrocytes do not make proteolipid protein. These results and others discussed in this paper support the hypothesis that either proteolipid protein itself, or some other product of the gene, may have an important role in central nervous system development.

Jimpy mutation affects astrocytes: lengthening of the cell cycle in vitro

The jimpy mutation has been identified as a point mutation in the gene coding for the major myelin proteolipid protein. The most prominent effect of the mutation is an extreme reduction in central nervous system myelin in affected mice. However, both oligodendrocytes and astrocytes, the two types of central nervous system macroglia, have been shown to exhibit more subtle developmental and metabolic changes as a result of the mutation. These include early death and proliferation abnormalities in jimpy oligodendrocytes, and hypertrophy, increased pH and abnormal responses to high K+ in jimpy astrocytes. In the present study, we examine the effect of the mutation of the cell cycle of astrocytes. Using an immunocytochemical method to chart the percent of labeled mitoses, we find the total cell cycle to be lengthened in jimpy astrocytes by 5-6 h, with increases in several different phases. Since there is no evidence that astrocytes make myelin proteolipid protein, the results support previous studies which suggest that this gene may code for other proteins playing an important role in the development of many cell types.

The cell cycle of glial cells grown in vitro: an immunocytochemical method of analysis

Studies of cell cycles have traditionally employed [3H]- and [14C]-thymidine to label the DNA of proliferating cells and autoradiography to reveal the thymidine label. The development of antibodies to the thymidine analogue 5-bromodeoxyuridine (BrdU) has allowed the development of an immunocytochemical method analogous to the thymidine autoradiographic technique. In direct comparisons, we found that the immunocytochemical method consistently detected a larger number of proliferating cells. This suggests that it may be a more sensitive index of proliferation than thymidine autoradiography in some systems. We used the BrdU method to analyze the cycle of astroglia cultured from neonatal mouse cerebral cortex. Cells were exposed to BrdU for 1 hr to label a discrete subpopulation of proliferating cells. At 2-36 hr after the pulse, a combination of anti-BrdU immunocytochemistry and counterstaining with propidium iodide was used to identify proliferating cells. The length of the cell cycle was determined by charting the percent of BrdU-labeled mitotic cells vs time after the pulse. We found the average length of the cell cycle of astrocytes grown in vitro to be 20.5 hr. The combined G2 + M phases were 2-3 hr. These values are virtually identical with those found for glial cells in vivo, suggesting that the culture environment does not interfere with the normal control of cell cycle length.

Cellular dimensions affecting the nucleocytoplasmic volume ratio

Although it has long been appreciated that larger eukaryotic cells have larger nuclei, little is known about how this size relationship is maintained. Here we describe a method for measuring the aqueous volume ratio of nucleus to cytoplasm, two compartments which are interconnected via the pores in the nuclear envelope. We then use that method to identify proportional cellular dimensions in variously treated cells and in different cell types. Cells were scrape loaded with a mixture of fluorescent dextrans: Texas red dextran, average mol wt = 10,000 (TRDx10), and fluorescein isothiocyanate dextran, average mol wt = 70,000 (FDx70). After introduction into the cytoplasmic space, the TRDx10 distributed into both the nucleus and cytoplasm, whereas the FDx70 was restricted to cytoplasm, due to size exclusion by the nuclear pores. The aqueous nucleocytoplasmic volume ratio (RN/C) was determined by measuring, from fluorescence images of spread cells, total cellular fluorescence of each of the two probes and the fluorescence ratio of those probes in the cytoplasm. RN/C was unaffected by the measurement procedure or by varying temperatures between 23 degrees and 37 degrees C. Loading excess unlabeled dextrans had little effect on RN/C, with the single exception that high concentrations of large dextrans could lower RN/C in endothelial cells. Expanding intracellular membranous compartments of macrophages by phagocytosis of latex beads decreased RN/C. Expanding the same compartment by pinocytosis of sucrose, which nearly doubled total cell volume, had little effect on RN/C, indicating that nuclear volume was more closely linked to the cytoplasmic volume, exclusive of vesicular organelles, than to total cell volume. RN/C was the same in mononucleate and binucleate endothelial cells. Finally, measurements of RN/C in murine bone marrow-derived macrophages, bovine aortic endothelial cells, Swiss 3T3 fibroblasts, PtK2 cells, and CV-1 cells revealed that nuclear volume scaled allometrically with cell volume. The allometric relationship indicated that cell volume was proportional to nuclear surface area.

Studies of glial lineage and proliferation in vitro using an early marker for committed oligodendrocytes

The potential of immature glial cells to differentiate into astrocytes (ASs) or oligodendrocytes (OLs) has been examined using a monoclonal antibody (007) that is specific for OLs in vivo. Cells were dissociated from 2-day postnatal mouse cortex and labeled with the 007 antibody 2 hr after plating. The cells which were labeled during this single, brief exposure to the antibody retained the antibody on their surfaces over the course of the experiments. Cells were double stained at various timepoints for residual 007 antibody and either galactocerebroside (GC) or glial fibrillary acidic protein (GFAP). Shortly after plating, most 007+ cells were GC- and none expressed GFAP. These cells were round, although some had begun to extend very short processes. After 96 hr, greater than 95% of cells with residual 007 on their surfaces also expressed GC. By this time, all the 007+ cells had several processes of varying lengths extending from their cell bodies. Cells expressing both 007 and GFAP were never seen. The 007+/GC+ OLs were not induced to differentiate from 007+ bipotential progenitors since they were grown in fetal calf serum. These results show that under our culture conditions the 007 antibody is OL specific. Immunostaining for bromodeoxyuridine, a marker for dividing cells, revealed that some 007+ cells were proliferating. The majority of these proliferating cells had already extended three or more processes. We therefore conclude that immature, process-bearing cells can be committed to the OL lineage at times before they express detectable amounts of GC. Since these young 007+ OLs are actively proliferating, committed cells can serve as an important source of new OLs.

Division of astroblasts and oligodendroblasts in postnatal rodent brain: evidence for separate astrocyte and oligodendrocyte lineages

What precursor cells are the source of the macroglia generated during postnatal development? In order to answer this question, we studied the expression of glial specific antigens in proliferating neuroglia in postnatal rodent brain and optic nerve. Immunocytochemistry using antibodies to oligodendrocyte (OL) specific markers (sulfatide and galactocerebroside) and an astrocyte (AS) specific marker (glial fibrillary acidic protein) was combined with thymidine autoradiography. During the first week of postnatal development when most ASs are being generated, one third to one half of the proliferating cells in the optic system are positive for glial fibrillary acidic protein after a 1 h injection of thymidine (Skoff, Dev. Biol., 139:149-168, 1990). During the second postnatal week when OLs are being generated, 30 to 100% of the proliferating cells in presumptive white matter tracts are sulfatide positive and at least 10% are galactocerebroside positive. This finding demonstrates that ASs and OLs divide during postnatal development. These results confirm previous electron microscopic autoradiographic studies showing that the vast majority of proliferating cells in postnatal rat optic nerve have the morphologic characteristics of differentiating ASs or OLs (Skoff, J. Comp. Neurol., 169:291-312, 1976). Since proliferating ASs (astroblasts) and OLs (oligodendroblasts) constitute the majority of the dividing cells at the time that ASs and OLs are being generated, these glioblasts must be the major source for the macroglia generated postnatally. The findings strongly suggest that separate lineages exist for ASs and OLs during postnatal development. There is no compelling in vivo evidence for a bipotential progenitor cell that generates the majority of OLs and certain ASs in postnatal rodent brain. There may, of course, be distinct lineages for the subtypes of ASs and possibly even for subtypes of OLs. We review the concepts of commitment and plasticity and apply these terms to glial differentiation. In situ, the presence of oligodendroblasts and astroblasts demonstrates the COMMITMENT of proliferating cells to a specific glial lineage during normal development. Culture conditions may provide an environment that permits proliferating glial cells to vacillate in their selection of a specific lineage. This situation demonstrates developmental PLASTICITY and the ability of glia to adapt to an altered environment. Whether committed glial cells in situ can be induced to switch their lineage when normal CNS conditions are altered is an intriguing question that remains to be answered.

Plasticity of the tubular lysosomal compartment in macrophages

Because bone marrow-derived macrophages differentiate in culture, their lysosomal compartment is largely devoid of the undigested particles that are common in macrophages removed from tissues. The morphology of this nearly vacant lysosomal compartment was observed, after labeling with fluorescent endocytic tracers such as Lucifer Yellow, to be an extensive, tubuloreticular network, which underwent extensive rearrangements in accommodating endocytic loads. It was converted to spherical organelles when the lysosomal compartment was loaded with osmotically active solutes such as sucrose or Acridine Orange. Enzymatic degradation of intravacuolar sucrose by pinocytosed invertase resulted in the shrinkage of vacuoles and the re-formation of the tubular network. After phagocytosis of opsonized erythrocytes or latex beads, tubular lysosomes wrapped around the phagosomes, then merged to form phagolysosomes. The disappearance of tubules was proportional to the total surface area of particles ingested. Degradation of the phagocytosed contents permitted shrinkage of the phagolysosome and concomitant re-formation of the tubuloreticular network. Nondegradable contents such as latex beads prevented re-formation of the tubular network. These rearrangements of the lysosomal compartment indicate that the organelle exhibits considerable plasticity and interconnectedness, and that maturation of lysosomes after endocytosis does not necessarily entail irreversible morphological changes.

Death of individual oligodendrocytes in jimpy brain precedes expression of proteolipid protein

Immunocytochemistry and thymidine autoradiography were combined to determine the time elapsed between cell division and the expression of proteolipid protein (PLP) in individual oligodendrocytes in normal mouse brain. In jimpy (jp) brains, autoradiography was used to determine the time elapsed between cell division in an individual oligodendrocyte and evidence of cell death. Oligodendrocytes in normal mouse brain do not express PLP until 72 h after a single injection of [3H]-thymidine. In contrast, oligodendrocytes in jp brains begin to die within 9-11 h after an injection of thymidine. The jp mouse is one of several X-linked, hypomyelinated mutants in which a defect has been demonstrated in the gene coding for PLP. It has been presumed that the lack of this protein in the myelin sheath is responsible for the jp phenotype. However, the present study shows that individual jp oligodendrocytes begin to die long before they would normally have synthesized detectable levels of PLP. Therefore, it seems unlikely that the death of jp oligodendrocytes is due to the absence of PLP in myelin sheaths. Oligodendrocyte death and other early jp abnormalities may be due to the presence of abnormal PLP message which may interfere with glial differentiation. Alternatively, the PLP message may code for another protein which is important for normal development of neuroglia.

Differences in levels of neuroglial cell death in jimpy male mice and carrier females

Jimpy (jp) is an X-linked disorder which results in a variety of glial cell abnormalities and the virtual absence of myelin in the central nervous system (CNS) of affected males. Female heterozygote carriers of the jp gene are mosaics. The wild-type genome will be expressed in roughly half of their cells, while in the other half the jp genome will be expressed. We have exploited this characteristic in order to determine whether the premature oligodendroglial death previously described in jp males is a primary effect of the mutation. Mosaic spinal cords were examined at the light-microscopic level for the presence of pyknotic cells at ages when oligodendroglial death is quite pronounced in jp males. The percentage of pyknotic glial cells (less than 0.6%) is not statistically different in normal and mosaic females at 5 and 30 days. At 14-15 days there is a slight increase in mosaic cords (1.2 vs. 0.75%) but there are still 10 times more dying glia in jp male cords of the same age. The low level of oligodendroglial death in mosaic spinal cords suggests that it is secondary to some other jp abnormality. Small increases in glial death over a protracted period of time could result in lower numbers of oligodendrocytes in older mosaics. Even if this occurs, the data still support the idea that the phenotype of genetically jp cells can be favorably altered by the mosaic environment.