Lunocapitate versus four-corner fusion in scapholunate or scaphoid nonunion advanced collapse: a randomized controlled trial

This pragmatic randomized controlled trial compared lunocapitate fusion (LCF) and four-corner fusion (4CF) for scapholunate advanced collapse (SLAC) and scaphoid nonunion advanced collapse (SNAC) in 64 patients. The primary outcome was change in grip strength from preoperative to 1 year postoperatively. The secondary outcomes were Disability of the Hand, Arm, and Shoulder score, Patient Rated Wrist Evaluation score, EuroQol-5D-3L, range of motion, key pinch strength and complications 12 months postoperatively. Grip strength improved only to a small extent and there was no difference between the groups. No differences were found in the secondary outcomes. In conclusion, LCF is not inferior to 4CF regarding strength, range of motion or patient-reported outcome measures.Level of evidence: I.

Carpal fractures: epidemiology, classification and treatment of 6542 fractures from the Swedish Fracture Registry

This study describes the age and sex distribution, trauma mechanism, treatment and influence of patient-reported outcomes of 6542 carpal fractures from the Swedish Fracture Registry (SFR). The most commonly fractured carpal bone was the scaphoid (60%), followed by the triquetrum (25%), hamate (5%) and trapezium (4%). The mean age at injury was 41 years, and 69% of patients were male. The age and sex distribution of carpal fractures differed substantially between the different carpal bones. Men were more likely to sustain a carpal fracture after high-energy trauma and were more likely to be treated surgically. Carpal fractures had a small negative effect on the Short Musculoskeletal Function Assessment Hand/Arm Index and EQ-5D scores 1 year after the injury.Level of evidence: IV.

Finger fractures: Epidemiology and treatment based on 21341 fractures from the Swedish Fracture register

BACKGROUND

There is a lack of detailed epidemiological studies of finger fractures, the most common fracture of the upper extremity.

METHODS

Based on data of 21 341 finger fractures in the Swedish Fracture register, a national quality registry that collects data on all fractures, this study describes anatomical distribution, cause, treatment, age distribution, and result in terms of patient related outcome measures (PROMs).

RESULTS

The most common finger fracture was of the base of the 5th finger, followed by the distal phalanx in the 4th finger. Open fractures were most common in the distal phalanges, especially in the 3rd finger. Intraarticular fractures were most frequent in the middle phalanges. Fall accidents was the most common cause of a fracture. The mean age at injury was 40 years (38 for men, 43 for women). 86% of finger fractures in adults were treated non-operatively. Men were more frequently operated than women. Finger fractures did not affect hand function or quality of life and there were no relevant differences in PROMs between fracture type, treatment, or sex.

CONCLUSION

This study presents detailed information about the various types of finger fractures which can be used as point of reference in clinical work and for future studies.

Residual flexion deformity after scaphoid nonunion surgery: 7-year follow-up study

The clinical implication of a residual flexion deformity following surgery for scaphoid nonunion is unclear. Sixty-three patients who underwent scaphoid nonunion surgery were assessed after a mean of 7 years (range 5-10) to analyse the outcomes based on the presence of residual scaphoid deformity. Primary outcome was Disabilities of the Arm, Shoulder and Hand score. Secondary outcomes were Patient-Rated Wrist Evaluation score, wrist range of motion and strength. Patients were dichotomized to residual deformity or no deformity. Scaphoid deformity was calculated from CT scans based on the median difference between the height-length ratio of the operated versus the uninjured scaphoid. There were no differences between residual deformity (n = 33) and no deformity (n = 30) in any outcome variables, except for wrist extension which was slightly worse in the deformity group. The deformity group had a greater number of radiographic osteoarthritis, but all cases were mild, and osteoarthritis did not correlate to a worse outcome. We conclude that residual scaphoid deformity has no relevant negative impact on mid-term wrist function.Level of evidence: IV.

Non-operative treatment or volar locking plate fixation for dorsally displaced distal radius fractures in patients over 70 years - a three year follow-up of a randomized controlled trial

Background

Surgical treatment of displaced distal radius fractures (DRF) in older patients has increased, despite lacking evidence of its superiority over non-operative treatment. How treatment choice affects these patients after the initial 12-month period remains unknown. This study presents a clinical and radiographic follow up at an average of 3 years after treatment in the context of a randomized clinical trial comparing outcomes in patients aged ≥70 years, with a dorsally displaced distal radius fracture treated either surgically with volar locking plate or non-operatively.

Methods

Between 2009 and 2017, 140 patients aged ≥70 years with dorsally displaced DRF were randomized to surgery with volar locking plate (VLP) or non-operative treatment. At an average of 3 years after inclusion the participants were invited to an additional follow-up. The primary outcome was Patient Rated Wrist Evaluation (PRWE). Secondary outcomes included additional Patient Reported Outcome Measures (PROM), grip strength, range of motion, complications and radiological results.

Results

Sixty six patients were available for a 3 year follow-up, 33 in the non-operatively treated group and 33 in the VLP-group. The mean age at injury was 77 years. At 3 years the median PRWE was better (0 points) in the VLP-group than in the non-operative treatment group (9 points) p-value: 0.027. No statistically significant difference was found in Disabilities of the Arm, Hand, and Shoulder (DASH), EuroQol 5 Dimensions (EQ-5D) or grip strength. Total arc of range of motion was larger in the operatively treated group. No significant difference in osteoarthritis was found. Both groups had regained grip strength. The complication rate was similar. Outcomes improved from the 1 year to the 3 year follow-up.

Conclusions

Surgery with volar locking plate gave less long-term disability compared to non-operative treatment for severely displaced distal radius fractures in patients aged ≥70 years. Our findings were statistically significant but in the lower range of clinical importance.

Trial registration

The study was registered at : NCT02154620 03/06/2014 and NCT01268397 30/12/2010. Ethical approval was obtained from Ethical Committee in Stockholm, Sweden (2009/37–31/3, 2013/105–31/2, 2014/1041–32, 2017/611–32).

Effects of intra-articular Platelet-Rich Plasma (PRP) injections on osteoarthritis in the thumb basal joint and scaphoidtrapeziotrapezoidal joint

Intra-articular injection of platelet rich plasma (PRP) has been reported to decrease pain and improve function in knee osteoarthritis. There are few reports on the effect of PRP in the treatment of osteoarthritis in the hand. Our aim was to evaluate the effect of PRP-injections on pain and functional outcome in the short-term for osteoarthritis in the thumb basal joint and scaphoidtrapeziotrapezoidal (STT) joint. A retrospective analysis was performed of 29 patients treated with intra-articular PRP injection for painful osteoarthritis in the thumb basal joint (21 patients) or STT joint (eight patients). The patients received two consecutive, radiologically guided PRP injections at an interval of 3–4 weeks. Pain at rest and on load (numerical rating scale (NRS) 0–10), Patient-rated Wrist and Hand Evaluation (PRWHE) score (0–100), grip strength (Jamar) and key pinch were recorded pre-injection and 3 months after the second injection. Mean age was 63 (range 34–86) years and 17 patients were women. We used generalized estimating equations (GEE) to analyze the effect on the outcome variables. Possible predictors were included in the model (high pain level pre-injection, gender, age, manually demanding work, affected joint (thumb base or STT) and use of analgesic). The GEE analysis showed that PRP injections had no effect on reported pain, PRWHE score, grip strength or key pinch. 16/28 patients experience a positive effect according to a yes/no question. The short-term effect of PRP for osteoarthritis in the thumb base and STT-joint is doubtful and needs to be properly investigated in placebo-controlled studies.

Does proximal migration of the first metacarpal correlate with remaining pain after trapeziectomy?

Proximal migration of the thumb metacarpal has been suggested as a possible cause of remaining pain after trapeziectomy for trapeziometacarpal joint osteoarthritis. The aim of this study was to investigate if proximal migration after trapeziectomy is associated with a poorer long-term outcome in terms of pain and objective physical variables. We retrospectively examined 91 thumbs in 65 patients after a mean of 10 years following trapeziectomy with or without ligament reconstruction and tendon interposition. Proximal migration of the thumb metacarpal was measured on plain lateral radiographs of the thumb and correlated to visual analogue pain scale (VAS), thumb range of motion and strength. Most thumbs had a severe proximal migration of the first metacarpal, the mean scaphoid metacarpal distance was 2.7 mm. Most patients reported no or little pain, median VAS was 0 at rest and 1 after load. There were no differences in reported VAS pain at rest or after load between patients with severe (<2 mm scaphoid metacarpal joint space) or less severe (≥2 mm metacarpal joint space) proximal migration. Patients that reported more pain (VAS >2) did not exhibit more migration than patients reporting less or no pain. Thumbs with severe migration had weaker key pinch (3.4 vs. 4.6 kg, p = 0.008) and grip strength (15 vs. 21 kg p = 0.002). We conclude that proximal migration most likely does not cause residual or recurrent pain after trapeziectomy.

There is motion between the scaphoid and the lunate during the dart-throwing motion

Scaphoid and lunate mobility has been suggested to be minimal during the dart-throwing motion in studies based on serial computed tomography (CT) scans and cadaver studies. This study analyzes the direct motion between the scaphoid and the lunate during the dart-throwing motion in vivo. We examined nine individuals with standard CT scans of the wrist in radial extension and ulnar flexion. The paired CT scans were analyzed with a volume registration technique. The lunate was registered as fixed and the scaphoid as the mobile element. The motion of the scaphoid relative the lunate between the positions of radial extension and ulnar flexion was measured. There was considerable motion between the scaphoid and the lunate with both a distal to proximal translation and rotation during the dart-throwing motion, regardless of whether the scapholunate ligament was intact or not. These results suggest that aggressive dart-throwing exercises should not be implemented early on during rehabilitation following scapholunate repair.

Structural Changes in the Posterior Interosseous Nerve from Patients with Wrist Osteoarthritis and Asymptomatic Controls

Background  Posttraumatic morphological changes have been described in the posterior interosseous nerve (PIN) after mild wrist trauma, and it has been suggested that posttraumatic nerve changes may contribute to wrist pain. PIN excision has shown to relieve pain in some patients with wrist osteoarthritis. However, is not known if PINs from osteoarthritic wrist have pathological features. Objective  The aim of this study was to investigate whether PINs from osteoarthritic wrists show morphological changes that are not present in healthy wrists. Materials and Methods  PINs resected from 15 osteoarthritic wrists were analyzed with light microscopy regarding morphological changes and compared with five asymptomatic controls without osteoarthritis. Results  No significant differences in fascicular area, myelinated fiber density or myelinated fiber diameter were found. However, most patients and controls exhibited some degree of pathology, and a few samples from both groups exhibited severe pathological changes. Conclusions  Our findings of morphological changes in both patients with osteoarthritis and asymptomatic controls suggest that pathological changes of unknown significance might exist in the general population in the PIN at wrist level. We believe that the observed structural nerve changes in the PIN are unlikely to contribute to the symptoms of pain. Further studies of the normal histological appearance of the terminal PIN are needed. Level of Evidence  This is Level II study.

A registry based analysis of the patient reported outcome after surgery for trapeziometacarpal joint osteoarthritis

BACKGROUND

The aim of the study was to evaluate patient reported outcome measures (PROM) before and after trapeziectomy with or without ligament reconstruction and tendon interposition for trapeziometacarpal joint arthritis with special focus on possible differences due to gender, age and surgical method.

METHODS

Data from the Swedish quality registry for hand surgery (HAKIR) was analyzed preoperatively, 3 months and 1 year postoperatively for 1850 patients (mean age 63 years, 79% women).

RESULTS

One year postoperatively, mean pain at rest was reduced from 50 to 12 of maximum 100. However, pain on load and weakness had not abated to the same extent (mean 30 and 34 of 100, respectively). The mean improvement in PROM did not differ between age groups or gender. The result was similar after trapeziectomy with ligament reconstruction and tendon interposition (86% of the patients) and simple trapeziectomy but few patients were operated with the latter method.

CONCLUSION

Pain on load and weakness remains to some extent 1 year after surgery for trapeziometacarpal joint arthritis. The result is similar after trapeziectomy with or without ligament reconstruction and tendon interposition and the same improvement can be expected after surgery regardless of age and gender.

Nonoperative Treatment Compared with Volar Locking Plate Fixation for Dorsally Displaced Distal Radial Fractures in the Elderly: A Randomized Controlled Trial

BACKGROUND

The usage of volar locking plate fixation for distal radial fractures has increased in older patient populations, despite the fact that surgical treatment in the elderly population has not clearly been proven to be superior to nonoperative treatment. The purpose of the present study was to compare nonoperative treatment with volar locking plate fixation with regard to clinical outcome for elderly patients with dorsally displaced distal radial fractures.

METHODS

In this study, 140 patients were randomly allocated to nonoperative treatment with a plaster splint (n = 72) or volar locking plate fixation (n = 68). The outcome variables were the Patient-Rated Wrist Evaluation (PRWE) score, Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire score, EuroQol-5 Dimensions (EQ-5D) score, range of motion, grip strength, radiographic outcomes, and complications. Evaluation was performed at 3 and 12 months by unblinded observers.

RESULTS

At 3 months, 122 patients were evaluated, and at 12 months, 119 patients were evaluated. At 3 months, the volar locking plate group, compared with the nonoperative treatment group, had a better median PRWE score (10.3 compared with 35.5 points; p = 0.002), DASH score (14.4 compared with 29.2 points; p = 0.016), and grip strength (71.0% of the uninjured hand compared with 53.9%; p < 0.001). Significant differences in favor of the volar locking plate group remained at 12 months; compared with the nonoperative treatment group, the volar locking plate group had a better median PRWE score (7.5 points compared with 17.5 points; p = 0.014), DASH score (8.3 points compared with 19.9 points; p = 0.028), and grip strength (96.8% compared with 80.0%; p = 0.001). Radiographic measurements favored volar locking plate fixation at 3 and 12 months. Complication rates were similar, with 11% major complications in the nonoperative group compared with 14% major complications in the volar locking plate group (p = 0.606) and 11% minor complications in the nonoperative group compared with 20% minor complications in the volar locking plate group (p = 0.197).

CONCLUSIONS

The PRWE scores, DASH scores, and grip strength were better for the volar locking plate group compared with the nonoperative group at 3 and 12 months. The complication rates were similar. Our results imply that there is a benefit for the elderly patient with an unstable dorsally displaced distal radial fracture to be treated with a volar locking plate.

LEVEL OF EVIDENCE

Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Characterization of leptin intracellular trafficking

Leptin is produced by adipose tissue, and its concentration in plasma is related to the amount of fat in the body. The leptin receptor (OBR) is a member of the class I cytokine receptor family and several different isoforms, produced by alternative mRNA splicing are found in many tissues, including the hypothalamus. The two predominant isoforms includes a long form (OBR) with an intracellular domain of 303 amino acids and a shorter form (OBR) with an intracellular domain of 34 amino acids. Since OBR, is mainly expressed in the hypotalamus, it has been suggested to be the main signalling form. The peripheral production of leptin by adipocyte tissue and its effects as a signal of satiety in the central nervous system imply that leptin gains access to regions of the brain regulating in energy balance by crossing the blood-brain barrier. In an attempt to characterize the intracellular transport of leptin, we have followed binding internalization and degradation of leptin in HEK293 cells. We have also monitored the intracellular transport pathway of fluorescent conjugated leptin in HEK293 cells. Phenylarsine oxide, a general inhibitor of endocytosis, as well as incubation at mild hypertonic conditions, prevented the uptake of leptin, confirming a receptor-mediated internalization process. When internalized, 125I-leptin was rapidly accumulated inside the cells and reached a maximum after 10 min. After 70 minutes about 40-50% of total counts in each time point were found in the medium as TCA-soluble material. Leptin sorting, at the level of early endosomes, did not seem to involve recycling endosomes, since FITC-leptin was sorted from Cy3-transferrin containing compartments at 37 degrees C. At 45 minutes of continuos internalization, FITC-leptin appeared mainly accumulated in late endocytic structures colocalizing with internalized rhodamine coupled epidermial growth factor (EGF) and the lysosomal marker protein lamp-1. The transport of leptin was also shown to engage a monensin and bafilomycin sensitive degradation process in lysosomes. Together, our results provide novel data concerning the uptake, intracellular localization and transport of leptin.

Differential induction of peroxisomal populations in subcellular fractions of rat liver

In rat liver, peroxisome proliferators induce profound changes in the number and protein composition of peroxisomes, which upon subcellular fractionation is reflected in heterogeneity in sedimentation properties of peroxisome populations. In this study we have investigated the time course of induction of the peroxisomal proteins catalase, acyl-CoA oxidase (ACO) and the 70 kDa peroxisomal membrane protein (PMP70) in different subcellular fractions. Rats were fed a di(2-ethylhexyl)phthalate (DEHP) containing diet for 8 days and livers were removed at different time-points, fractionated by differential centrifugation into nuclear, heavy and light mitochondrial, microsomal and soluble fractions, and organelle marker enzymes were measured. Catalase was enriched mainly in the light mitochondrial and soluble fractions, while ACO was enriched in the nuclear fraction (about 30%) and in the soluble fraction. PMP70 was found in all fractions except the soluble fraction. DEHP treatment induced ACO, catalase and PMP70 activity and immunoreactive protein, but the time course and extent of induction was markedly different in the various subcellular fractions. All three proteins were induced more rapidly in the nuclear fraction than in the light mitochondrial or microsomal fractions, with catalase and PMP70 being maximally induced in the nuclear fraction already at 2 days of treatment. Refeeding a normal diet quickly normalized most parameters. These results suggest that induction of a heavy peroxisomal compartment is an early event and that induction of 'small peroxisomes', containing PMP70 and ACO, is a late event. These data are compatible with a model where peroxisomes initially proliferate by growth of a heavy, possibly reticular-like, structure rather than formation of peroxisomes by division of pre-existing organelles into small peroxisomes that subsequently grow. The various peroxisome populations that can be separated by subcellular fractionation may represent peroxisomes at different stages of biogenesis.

Rab11 regulates the compartmentalization of early endosomes required for efficient transport from early endosomes to the trans-golgi network

Several GTPases of the Rab family, known to be regulators of membrane traffic between organelles, have been described and localized to various intracellular compartments. Rab11 has previously been reported to be associated with the pericentriolar recycling compartment, post-Golgi vesicles, and the trans-Golgi network (TGN). We compared the effect of overexpression of wild-type and mutant forms of Rab11 on the different intracellular transport steps in the endocytic/degradative and the biosynthetic/exocytic pathways in HeLa cells. We also studied transport from endosomes to the Golgi apparatus using the Shiga toxin B subunit (STxB) and TGN38 as reporter molecules. Overexpression of both Rab11 wild-type (Rab11wt) and mutants altered the localization of the transferrrin receptor (TfR), internalized Tf, the STxB, and TGN38. In cells overexpressing Rab11wt and in a GTPase-deficient Rab11 mutant (Rab11Q70L), these proteins were found in vesicles showing characteristics of sorting endosomes lacking cellubrevin (Cb). In contrast, they were redistributed into an extended tubular network, together with Cb, in cells overexpressing a dominant negative mutant of Rab11 (Rab11S25N). This tubularized compartment was not accessible to Tf internalized at temperatures <20 degrees C, suggesting that it is of recycling endosomal origin. Overexpression of Rab11wt, Rab11Q70L, and Rab11S25N also inhibited STxB and TGN38 transport from endosomes to the TGN. These results suggest that Rab11 influences endosome to TGN trafficking primarily by regulating membrane distribution inside the early endosomal pathway.

Expression and intracellular localization of leptin receptor long isoform-GFP chimera

The leptin receptor (OBR) and its ligand leptin (OB) are key players in the regulation of body weight. The OBR is a member of the class I cytokine receptor family and is alternatively spliced into at least six different isoforms. The multiple forms are identical in their extracellular and transmembrane regions but differ in lengths. The two predominant isoforms include a long form (OBR(l)) with an intracellular domain of 303 amino acids and a shorter form (OBR(s)) with an intracellular domain of 34 amino acids. We have constructed a recombinant OBR(l) chimera with the green fluorescent protein (GFP) by fusing GFP to the C-terminus of the OBR(l). The OBR(l)-GFP chimera was transiently transfected and expressed in SHSY5Y and HEK293 cells. In a STAT-Luciferase assay we show that the GFP moiety in this chimera did not affect the signalling capacity of OBR(l)-GFP. In both SHSY5Y and HEK293 cells transfected with OBR(l)-GFP, a predominant intracellular green OBR(l)-GFP fluorescence was detected in vesicles also positive for internalized fluorophore conjugated leptin. We also found that treatment with the lysosomotropic reagent monensin did not relocalize OBR(l)-GFP together with the human transferrin receptor in recycling endosomes, indicating OBR(l)-GFP not to participate in this pathway. In biotinylation-streptavidin pulse chase experiments, using antibodies raised against GFP and OBR, we observed that the rate of early appearance of OBR(s) at the cell surface, upon leptin stimulation, was faster than that found for OBR(l)-GFP. Taken together, our results provide novel data concerning the intracellular trafficking of the two different isoforms of the leptin receptor.

Immunocytochemical localization of the 70 kDa peroxisomal membrane protein in connections between peroxisomes in rat liver: support for a reticular organization of peroxisomes maintained by the cytoskeleton

Recently it has been shown that peroxisomes interact with microtubules which affect the structure and intracellular distribution of the organelle (Schrader, M., J. K. Burkhardt, E. Baumgart, G. Lüers, H. Spring, A. Völkl, H. D. Fahimi: Interaction of microtubules with peroxisomes. Tubular and spherical peroxisomes in HepG2 cells and their alterations induced by microtubule-active drugs. Eur. J. Cell Biol. 69, 24-35 (1996)). In the present work, we have applied immunological techniques to study the organization of peroxisomes within the rat liver cell. Antibodies to a pentadecapeptide corresponding to amino acid residues 403-417 of the 70 kDa integral peroxisomal membrane protein (Kamijo, K., S. Taketani, S. Yokota, T. Osumi, T. Hashimoto: The 70-kDa peroxisomal membrane protein is a member of the Mdr (P-glycoprotein)-related ATP-binding protein super family. J. Biol. Chem. 265, 4534-4540 (1990)) were raised in rabbits and affinity purified. This antibody was found to be highly specific for peroxisomes as determined by ELISA and Western blot analysis. Immunoelectron microscopy of tissue sections from rat liver revealed that peroxisomal membranes were labeled with this antibody and, in addition, labeling was found on tubular extensions often connecting peroxisomes. Antibodies to alpha-tubulin were used to locate the microtubular system. Microtubules were often found in close connection to peroxisomes, suggesting interaction between peroxisomes and the cytoskeleton. Double-labeling experiments for the 70 kDa integral peroxisomal membrane protein and alpha-tubulin demonstrated that the tubular structures connecting peroxisomes did not colocalize with microtubules. These results suggest that peroxisomes are organized in reticular structures within rat liver cells and that the structure and localization of these reticuli may be determined by their association to the microtubular network.

Peroxisome proliferators differentially regulate long-chain acyl-CoA thioesterases in rat liver

We have investigated the effects of peroxisome proliferators on rat liver long-chain acyl-CoA thioesterase activities. Subcellular fractionations of liver homogenates from control, clofibrate- and di(2-ethylhexyl)phthalate-treated rats confirmed earlier studies which demonstrated that peroxisome-proliferating drugs induce long-chain acyl-CoA thioesterase activity mainly in the mitochondrial and cytosolic fractions. The aim of the present study was to investigate whether the induced activities were due to increases in normally expressed enzymes, or due to induction of novel enzymes. To investigate whether structurally different peroxisome proliferators differentially induced thioesterase activities, we tested the effects of di(2-ethylhexyl)phthalate (a plastisizer) and the hypolipidemic drug clofibrate. For this purpose, we established an analytical size exclusion chromatography method. Chromatography of solubilised mitochondrial matrix proteins showed that the activity in control mitochondria was mainly due to enzymes with molecular masses of about 50 kDa and 35 kDa. The activity in samples prepared from clofibrate- and di(2-ethylhexyl)phthalate-treated rats eluted as proteins of about 40 kDa and 110 kDa. Highly purified peroxisomes contained two peaks of activity, which were not induced, that corresponded to molecular masses of 40 kDa and 80 kDa. The 80-kDa peak was shown to be due to dimerization by addition of glycerol. Chromatography of cytosolic fractions from control rat livers indicated the presence of long-chain acyl-CoA thioesterases with molecular masses of approximately 35 kDa and 125 kDa and a broad peak corresponding to a high-molecular-mass protein. The activity in cytosolic fractions from peroxisome-proliferator-treated rats eluted mainly as peaks corresponding to 40, 110 and 150 kDa. In addition, in the 110-kDa peak, a different degree of induction and different chain-length specificities were caused by clofibrate and di(2-ethylhexyl)phthalate, suggesting that these peroxisome proliferators differentially regulate the cytosolic acyl-CoA thioesterase activities. Western blot analysis showed that enzymes in the 40-kDa peak of the peroxisomal and cytosolic fractions were structurally related, but not identical, to a 40-kDa mitochondrial very-long-chain acyl-CoA thioesterase. Our data show that the increased acyl-CoA thioesterase activities in mitochondria and cytosol were mainly due to induction of acyl-CoA thioesterases which are not, or only weakly, expressed under normal conditions.

Novel peroxisomal populations in subcellular fractions from rat liver. Implications for peroxisome structure and biogenesis

According to current concepts, new peroxisomes are formed by division of pre-existing peroxisomes or by budding from a peroxisomal reticulum. Recent cytochemical and biochemical data indicate that protein content in peroxisomes are heterogenous and that import of newly synthesized proteins may be restricted to certain protein import-competent peroxisomal subcompartments (Yamamoto, K., and Fahimi, H. D. (1987) J. Cell Biol. 105, 713-722; Heinemann, P., and Just, W. W. (1992) FEBS Lett. 300, 179-182; Lüers, G., Hashimoto, T., Fahimi, H. D., and Völkl, A. (1993) J. Cell Biol. 121, 1271-1280). We have observed that substantial amounts of peroxisomal proteins are found together with "microsomes" (100,000 x g pellet) after subcellular fractionation of rat liver homogenates. In this study we have investigated the origin of these peroxisomal proteins by modified gradient centrifugation procedures in Nycodenz and by analysis of enzyme activity distributions, Western blotting, and immunoelectron microscopy. It is concluded that much of this material is confined to novel populations of "peroxisomes." Immunocytochemistry on gradient fractions showed that some vesicles were enriched in acyl-CoA oxidase and peroxisomal multifunctional enzyme ("catalase-negative") whereas others were enriched in catalase and thiolase ("acyl-CoA oxidase-negative"). Double immunolabeling experiments verified the strong heterogeneity in the protein contents of these vesicles and also identified peroxisomes varying in size from about 0.5 microns ("normal peroxisomes") to extremely small vesicles of less than 100 nm in diameter. The possibility that these vesicles may be related to different subcompartments of a larger peroxisomal structure involved in protein import and biogenesis will be discussed.

Characterization of acyl-CoA thioesterase activity in isolated rat liver peroxisomes. Partial purification and characterization of a long-chain acyl-CoA thioesterase

A common function of peroxisomes in eukaryotic cells is beta-oxidation of fatty acids. In animal cells, beta-oxidation is compartmentalized to peroxisomes and mitochondria. Although regulation of beta-oxidation in mitochondria has been extensively studied, knowledge on its regulation in peroxisomes is still limited. We have considered the possibility that peroxisomes may contain acyl-CoA thioesterases with different substrate specificities that possibly regulate metabolism of different lipids by regulation of substrate availability. In the present study, we have investigated the presence of short-chain and long-chain acyl-CoA thioesterase activities in rat liver peroxisomes. Light-mitochondrial fractions, enriched in peroxisomes, were fractionated by Nycodenz density gradient centrifugation and gradient fractions were analyzed for acyl-CoA thioesterase and marker enzyme distributions. Fractionation of livers from normal rats showed that most of the long-chain acyl-CoA thioesterase activity was localized in microsomes and mitochondria, and only low activity was found in fractions containing peroxisomes. The gradient distribution of propionyl-CoA thioesterase activity showed this activity to be localized mainly in mitochondria and in fractions possibly representing lysosomes, with a small peak of activity in peroxisomal fractions. Di(2-ethylhexyl)phthalate treatment induced the specific propionyl-CoA thioesterase activity approximately threefold in the peak mitochondrial fractions and about onefold in peroxisomal fractions; the activity appeared to be almost exclusively localized to these organelles. The specific activity of myristoyl-CoA thioesterase was induced 1-2-fold in peroxisomal peak fractions and more than 10-fold in the mitochondrial peak fraction, whereas it was unchanged in microsomes. The chain-length specificity of acyl-CoA thioesterase activity in isolated peroxisomes suggests that peroxisomes contain an inducible short-chain thioesterase active on C2-C4 acyl-CoA species (possibly a 'propionyl-CoA' thioesterase). In addition, peroxisomes contain medium-chain to long-chain thioesterase activity, probably due to separate enzymes based on the different chain-length specificities observed in peroxisomes from normal and di(2-ethylhexyl)phthalate-treated rats. A long-chain acyl-CoA thioesterase was partially purified from isolated peroxisomes and found to be active only on fatty-acyl-CoA species longer than octanoyl-CoA. The protein is apparently a monomer of about 40 kDa and clearly different from microsomal long-chain acyl-CoA thioesterase. An induction of this long-chain thioesterase may explain the observed change in chain-length specificity in peroxisomes isolated from normal and di(2-ethylhexyl)phthalate-treated rats. Possible physiological functions of these thioesterases are discussed.

Alpha 1- and beta-adrenergic regulation of intracellular Ca2+ levels in brown adipocytes

In order to monitor changes in cytosolic Ca2+ levels, brown-fat cells were incubated with the fluorescent Ca2+-indicator fura-2 and the fluorescence intensity ratio followed. The addition of norepinephrine led to a rapid and persistent increase in the cytosolic Ca2+ level, which was dose-dependent with a maximal effect at about 1 microM. The response was diminished in the absence of extracellular Ca2+ and was inhibited more efficiently by phentolamine and prazosin than by propranolol or yohimbine, indicating alpha 1-adrenergic mediation. Accordingly, selective alpha 1-adrenergic stimulation also increased the cytosolic Ca2+ level. However, selective beta-adrenergic stimulation, as well as the adenylate cyclase activator forskolin, were also able to increase the cytosolic Ca2+ level in these cells to a certain extent. It was concluded that the major part of the increase in cytosolic Ca2+ was mediated, as in other cell types, via alpha 1-adrenergic receptors, but that Ca2+ levels were also positively modulated by a cAMP-mediated process. These observations are discussed in relation to known alpha 1/beta synergisms in brown adipose tissue.