Incorporation of Three Extracyclic Arginine Residues into a Melanocortin Macrocyclic Agonist (c[Pro-His-DPhe-Arg-Trp-Dap-Lys(Arg-Arg-Arg-Ac)-DPro]) Decreases Food Intake When Administered Intrathecally or Subcutaneously Compared to a Macrocyclic Ligand Lacking Extracyclic Arginine Residues (c[Pro-His-DPhe-Arg-Trp-Dap-Ala-DPro)]

Of the three Food and Drug Administration-approved melanocortin peptide drugs, two possess a cyclic scaffold, demonstrating that cyclized melanocortin peptides have therapeutic relevance. An extracyclic Arg residue, critical for pharmacological activity in the approved melanocortin cyclic drug setmelanotide, has also been demonstrated to increase the signal when fluorescently labeled cell-penetrating cyclic peptides are incubated with HeLa cells, with the maximal signal observed with three extracyclic Arg amino acids. Herein, a branching Lys residue was substituted into two macrocyclic melanocortin peptide agonists to incorporate 0-3 extracyclic Arg amino acids. Incorporation of the Arg residues resulted in equipotent or increased agonist potency at the mouse melanocortin receptors in vitro, suggesting that these substitutions were tolerated in the macrocyclic scaffolds. Further in vivo evaluation of one parent ligand (c[Pro-His-DPhe-Arg-Trp-Dap-Ala-Pro]) and the three Arg derivative (c[Pro-His-DPhe-Arg-Trp-Dap-Lys(Ac-Arg-Arg-Arg)-Pro)] demonstrated that the three Arg derivative further decreased food intake compared to the parent macrocycle when the compounds were administered either via intrathecal injection or subcutaneous dosing. This suggests that three extracyclic Arg amino acids may be beneficial in the design of cyclic melanocortin ligands and that in vitro pharmacological profiling may not predict the in vivo efficacy of melanocortin ligands.

Incorporation of Indoylated Phenylalanine Yields a Sub-Micromolar Selective Melanocortin-4 Receptor Antagonist Tetrapeptide

The melanocortin family is involved in many physiological functions, including pigmentation, steroidogenesis, and appetite. The centrally expressed melanocortin-3 and melanocortin-4 receptors (MC3R and MC4R) possess overlapping but distinct roles in energy homeostasis. Herein, the third and fourth positions of a tetrapeptide lead compound [Ac-Arg-Arg-(pI)DPhe-Tic-NH₂], previously reported to possess MC3R agonist and MC4R antagonist activities, were substituted with indoylated phenylalanine (Wsf/Wrf) residues in an attempt to generate receptor subtype selective compounds. At the third position, d-amino acids were required for melanocortin agonist activity, while both l- and d-residues resulted in MC4R antagonist activity. These results indicate that l-indoylated phenylalanine residues at the third position of the scaffold can generate MC4R over MC3R selective antagonist ligands, resulting in a substitution pattern that may be exploited for novel MC4R ligands that can be used to probe the in vivo activity of the MC4R without involvement of the MC3R.

Functional Mixture-Based Positional Scan Identifies a Library of Antagonist Tetrapeptide Sequences (LAtTeS) with Nanomolar Potency for the Melanocortin-4 Receptor and Equipotent with the Endogenous AGRP(86-132) Antagonist

The melanocortin-4 receptor (MC4R) plays an important role in appetite. Agonist ligands that stimulate the MC4R decrease appetite, while antagonist compounds increase food consumption. Herein, a functional mixture-based positional scan identified novel MC4R antagonist sequences. Mixtures comprising a library of 12,960,000 tetrapeptides were screened in the presence and absence of the NDP-MSH agonist. These results led to the synthesis of 48 individual tetrapeptides, of which 40 were screened for functional activity at the melanocortin receptors. Thirteen compounds were found to possess nanomolar antagonist potency at the MC4R, with the general tetrapeptide sequence Ac-Aromatic-Basic-Aromatic-Basic-NH₂. The most notable results include the identification of tetrapeptide 48 [COR1-25, Ac-DPhe(pI)-Arg-Nal(2')-Arg-NH₂], an equipotent MC4R antagonist to agouti-related protein [AGRP(86-132)], more potent than miniAGRP(87-120), and possessing 15-fold selectivity for the MC4R versus the MC3R. These tetrapeptides may serve as leads for novel appetite-inducing therapies to treat states of negative energy balance, such as cachexia and anorexia.

The melanocortin pathway and energy homeostasis: From discovery to obesity therapy

Background

Over the past 20 years, insights from human and mouse genetics have illuminated the central role of the brain leptin-melanocortin pathway in controlling mammalian food intake, with genetic disruption resulting in extreme obesity, and more subtle polymorphic variations influencing the population distribution of body weight. At the end of 2020, the U.S. Food and Drug Administration (FDA) approved setmelanotide, a melanocortin 4 receptor agonist, for use in individuals with severe obesity due to either pro-opiomelanocortin (POMC), proprotein convertase subtilisin/kexin type 1 (PCSK1), or leptin receptor (LEPR) deficiency.

Scope of review

Herein, we chart the melanocortin pathway's history, explore its pharmacology, genetics, and physiology, and describe how a neuropeptidergic circuit became an important druggable obesity target.

Major conclusions

Unravelling the genetics of the subset of severe obesity has revealed the importance of the melanocortin pathway in appetitive control; coupling this with studying the molecular pharmacology of compounds that bind melanocortin receptors has brought a new obesity drug to the market. This process provides a drug discovery template for complex disorders, which for setmelanotide took 25 years to transform from a single gene into an approved drug.

Multiresidue Tetrapeptide Substitutions Yield a 140-fold Selective Melanocortin-3 over Melanocortin-4 Receptor Agonist

The five melanocortin receptors regulate numerous physiological functions. Although many ligands have been developed for the melanocortin-4 receptor (MC4R), the melanocortin-3 receptor (MC3R) has been less-well characterized, in part due to the lack of potent, selective tool compounds. Previously an Ac-His-Arg-(pI)DPhe-Tic-NH₂ scaffold, inverting the Phe-Arg motif of the native melanocortin signal sequence, was identified to possess mMC3R over mMC4R selective agonist activity. In this study, a library of 12 compounds derived from this scaffold was synthesized and assayed at the mouse melanocortin receptors (MCRs), utilizing substitutions previously shown to increase mMC3R agonist potency and/or selectivity. One compound (8, Ac-Val-Gln-DBip-DTic-NH₂) was identified as greater than 140-fold selective for the mMC3R over the mMC4R, possessed 70 nM potency at the mMC3R, and partially stimulated the mMC4R at 100 μM concentrations without antagonist activity. This pharmacological profile may be useful in developing new tool and therapeutic ligands that selective signal through the MC3R.

Corrigendum. Intraoperative fluoroscopic imaging to treat cam deformities: correlation with 3-dimensional computed tomography

Ross JR, Bedi A, Stone RM, Sibilsky Enselman E, Leunig M, Kelly BT, Larson CM. Intraoperative fluoroscopic imaging to treat cam deformities: correlation with 3-dimensional computed tomography. Am J Sports Med. 2014;42(6):1370-1376. (Original DOI: 10.1177/0363546514529515 )

Hyperthyroidism enhances endothelium-dependent relaxation in the rat renal artery

OBJECTIVE

Hyperthyroidism has pronounced effects on vascular function and endothelium-dependent relaxation. The aim of the present study was to identify mechanisms underlying hyperthyroidism-induced alterations in endothelial function in rats.

METHODS

Animals were subjected to either a single injection (36 h) or 8 weeks treatment with the thyroid hormone triiodothyronine (T3, i.p.). Vascular reactivity and agonist-induced hyperpolarization were studied in isolated renal arteries. Endothelial nitric oxide (NO) synthase expression and cyclic AMP accumulation were determined in aortic segments.

RESULTS

Endothelium-dependent relaxations to acetylcholine (ACh) were enhanced by T3 36 h after injection and after treatment for 8 weeks. Thirty-six hours after T3 application, relaxation mediated by the endothelium-derived hyperpolarizing factor (EDHF) and by endothelium-derived NO were significantly enhanced. After 8 weeks treatment with T3, however, EDHF-mediated relaxation was impaired, whereas NO-mediated relaxation remained enhanced. KCl- and ACh-induced hyperpolarizations were more pronounced in arteries from rats treated with T3 for 36 h compared to control, whereas in arteries from rats treated with T3 for 8 weeks both responses were attenuated. In rats treated for 36 h, vascular cyclic AMP levels were enhanced in the aorta and inhibition of protein kinase A attenuated EDHF-mediated relaxations of the renal artery without affecting responses in arteries from the control group. In the aorta from rats treated with T3 for 8 weeks, the expression of the endothelial NO synthase was markedly up-regulated (463+/-68%).

CONCLUSIONS

These data indicate that short-term treatment with T3 increases endothelium-dependent relaxation, most probably by increasing vascular cyclic AMP content. Following treatment with T3 for 8 weeks, expression of the endothelial NO synthase was enhanced. During this phase, NO appears to be the predominant endothelium-derived vasodilator.

Thromboembolism after total knee arthroplasty: intermittent pneumatic compression and aspirin prophylaxis

This is a study of two consecutive antithromboembolism regimens after total knee arthroplasty. In group 1, 131 patients were given aspirin prophylaxis alone (650 mg by mouth twice a day). In group 2, 123 patients were treated with aspirin, knee-high compression stockings, and intermittent knee-high pneumatic compression devices, which were started intraoperatively. The prevalence of deep vein thrombosis in group 1 was 15.9% (21 of 131 patients). One patient had a possible symptomatic nonfatal pulmonary embolism, and one patient had a symptomatic calf thrombus. Asymptomatic thrombi were detected in calf veins in 9 patients, popliteal vein in 6 patients, and femoral vein in 5 patients. In Group 2, the prevalence was 7.4% (9 of 123 patients). Asymptomatic thrombi were located in calf veins in 6 patients, popliteal vein in 1 patient, and femoral vein in 2 patients. There was a significant difference in the prevalence of deep vein thrombosis between the two groups. A history of previous thromboembolism was a significant risk factor for a new thrombus. The prevalence after bilateral one-stage knee arthroplasty was 24.3% for group 1 and 12.5% for group 2. Aspirin and knee-high intermittent pneumatic compression together are more effective than aspirin alone for prevention of deep vein thrombosis after primary and revision knee arthroplasty.

One-peg versus three-peg patella component fixation in total knee arthroplasty

In many designs of total knee arthroplasty, the patella with one central peg has been replaced by a patella with three small pegs for cement fixation. There have been recent reports of failure of this design. This is a prospective, consecutive study of two types of patella component fixation in 228 posterior-stabilized knee arthroplasties done by one surgeon. A central peg all-polyethylene component was used for 84 consecutive knees in 63 patients (Group A) and a three-peg patella was used for the next 144 consecutive knees in 99 patients (Group B). The mean followup was 6.7 years (range, 2-10 years) for Group A and 3.5 years (range, 2-6 years) for Group B. Except for the patellar component fixation, all knees had the same posterior-stabilized prosthesis using a specific protocol for patellar resurfacing. No patient required reoperation for a patellofemoral complication. The prevalence of patella fracture was higher in Group A, 4.7% (four knees), compared with 2.1% (three knees) in Group B, but this difference was not statistically significant. The presence of anterior knee pain referable to the patella was 7.1% (five patients, six knees) in Group A (one patient with two knees had severe anterior knee pain) and 9% (13 knees in 13 patients) in Group B. There was no patella clunk syndrome, subluxation, or fracture of a fixation peg in either group. With this specific protocol for patella resurfacing, there was a higher rate of complications with the one central peg patella (4.7%) than with the three-peg patella (2.1%), but this did not reach statistical significance. The results do not support an increased risk of component failure with this three-peg patella design, but do not, at this length of followup, show any significant advantage of three-peg fixation.

Bone mineral density and fractures in boys with Duchenne muscular dystrophy

The relationships between bone density, mobility, and fractures were assessed in 41 boys with Duchenne muscular dystrophy. Bone density in the lumbar spine was only slightly decreased while the boys were ambulatory (mean z-score, -0.8), but significantly decreased with loss of ambulation (mean z-score, -1.7). In contrast, bone density in the proximal femur was profoundly diminished even when gait was minimally affected (mean z-score, -1.6), and then progressively decreased to nearly 4 standard deviations below age-matched normals (mean z-score, -3.9). These are consistent with the findings that 18 (44%) of the boys sustained a fracture, 66% of these fractures involved the lower extremities, and there were no spinal compression fractures. Furthermore, four (44%) of nine boys who were walking with aids or support at the time of fracture never resumed walking after the fracture. Osteoporosis is most profound in the lower extremities of boys with Duchenne muscular dystrophy, and begins to develop early while still ambulating. Frequent fractures that may result in loss of ambulation are the clinical consequences.

Patellofemoral complications with the Insall-Burstein II posterior-stabilized total knee arthroplasty

The Insall-Burstein and Insall-Burstein II posterior-stabilized (I-B II PS) prostheses have been reported to have a high prevalence of patellar complications. This is a prospective, consecutive study of 118 primary total knee arthroplasties in 82 patients with the I-B II PS prosthesis implanted by 1 surgeon, using a specific technique for patellar resurfacing. The mean follow-up time was 4.0 years (range, 2-8 years). Clinical evaluation was performed using a standard knee score system with specific additional evaluation of the patellofemoral joint. Radiographs were evaluated for fracture, loosening, and subluxation. Ninety-four knees (80%) were rated excellent, 21 knees (17%) good, and 3 knees (3%) fair. The mean flexion was 112 degrees postoperative. No knee required reoperation for the patellofemoral joint. There were 2 nondisplaced and 1 minimally displaced patellar fractures treated nonoperatively, no patellar clunk syndrome, and no subluxations. Using the patellar evaluation system, 109 knees had no anterior knee pain, 7 knees had mild pain, and 2 knees (1 patient) had moderate-to-severe pain only with rising from a chair. Patellofemoral crepitus with active flexion-extension in the seated position was noted in 16 knees (14%) but was painful in only 2 knees (1 patient). With this technique for patellar resurfacing with this prosthesis, patellofemoral complications were only 4.2%, and no knee required reoperation for the patella or for loosening. With attention to operative technique, patellofemoral resurfacing with this posterior-stabilized total knee arthroplasty can be highly successful.

Malignancy, mortality, and medicosurgical management of Clostridium septicum infection

BACKGROUND

Necrotizing Clostridium septicum infections (CSI) have a strong association with malignancy or immunosuppression. To clarify this relationship and determine how it impacted mortality, the experience with CSI at a single institution was reviewed.

METHODS

Records of all patients admitted to our hospital with culture proven clostridial infection from 1966 through 1993 were reviewed.

RESULTS

Among patients presenting with clinical gas gangrene, 281 had culture proven clostridial infection and 32 (11.4%) had CSI. The mortality among CSI patients was 56%, whereas 26% of all patients with clostridial infections died (p = 0.001). An associated malignancy was found in 50% of patients with CSI, whereas this was seen in only 11% of patients with other clostridial infections (p = 0.0001 for CSI versus clostridial infection overall). The remaining patients with spontaneous CSI all had evidence of immunosuppression.

CONCLUSIONS

The high mortality and likelihood of associated malignancy or hematologic disease underscore the importance of a high index of suspicion and the need to search for and treat associated conditions in all patients with CSI.

Multiple organ failure in patients with thermal injury

OBJECTIVE

To assess the frequency and significance of multiple organ failure in patients with burn injuries.

DESIGN

Retrospective review and prospective assessment of patients with acute burns.

SETTING

University hospital burn center.

PATIENTS AND METHODS

We reviewed 529 patients admitted for acute burn treatment whose lengths of stay exceeded 72 hrs. A new scoring system, the Thermal Injury Organ Failure Score, was used to assign scores from 0 (normal) to 6 (severe dysfunction) to each of 6 organ systems, which were then totaled to compile the overall score. This system was also used for prospective assessment of 83 adult burn patients, and compared with the Acute Physiology and Chronic Health Evaluation (APACHE) II scoring system during the first week of treatment.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

For 496 survivors, mean organ failure score was 3.28, compared with 23.1 in 33 nonsurvivors (p < .0001). All nonsurvivors but one had scores of > or = 15, indicating dysfunction of at least three organs. Scores and mortality rate increased with age and burn size. Pulmonary dysfunction was the most frequent form of organ failure seen, but correlated less with outcome than did cardiovascular or neurologic scores. Sepsis was present in 22 of 33 patients who died. In the prospective study, organ failure scores correlated with outcome more closely than did APACHE II scores. Weekly evaluation of these patients demonstrated progressive divergence in scores between survivors and nonsurvivors.

CONCLUSIONS

Multiple organ failure was almost invariably present in burn patients who died > 72 hrs after injury. Burn victims, who have been excluded from reviews of multiple organ failure, appear to manifest organ failure in a manner similar to that of other surgical populations. The scoring system reported here may prove useful in evaluating organ failure in thermally injured patients.

Lifestyle adjustments in elderly patients after burn injury

Although survival of older burn victims has improved significantly in recent years, controversy remains over the care that should be given to this group and the functional recovery of survivors. To assess the impact of burn injury on lifestyle in the elderly, we conducted a mail-in survey among surviving patients ages 45 years or older who were treated in our burn center from 1978 to the middle of 1987. The survey asked questions about living arrangements, personal care, family relations, social life, work status, and outlook on the future. Of 168 surveys mailed, 109 were completed and returned (64.9%). Responders consisted of 82 men and 27 women with a mean age of 57.8 years (range, 45 to 92 years). Ninety-seven percent of patients were able to return home after discharge, but 27% of the oldest patients (ages greater than 75 years) required permanent placement in extended care facilities. With increased age there was an increased tendency toward dependence and the need for assistance in daily living; half of the oldest patients required assistance in daily living. Even so, most of the patients in this survey remained independent and maintained a positive outlook on the future. These results appear to justify a policy of aggressive treatment for elderly burn victims.

The continuing challenge of burn care in the elderly

Recent improvements in survival have stimulated interest in the care of elderly patients with burn injuries. We reviewed 278 patients aged 45 years and older treated during a 10-year period. The survival rate was 80% overall and 67% for patients over 75 years of age. Mortality rates correlated with patient age, burn size, presence of inhalation injury, number of complications of care, and fluid resuscitation requirements, but not with the number of preexisting medical problems. Burn wound excision and skin grafting were performed frequently and were well tolerated. During this period, hospital charges increased fourfold and were twice as great in nonsurvivors. Reimbursements based on diagnosis-related groups during the last 3 years of the review (75 patients) resulted in a total deficit of $1.2 million. Aggressive care for most elderly patients with burn injuries appears justified by the improved outcomes demonstrated. This has increased the difficulty of decisions regarding patient salvability and the allotment of resources. Elderly patients with burn injuries illustrate many contemporary dilemmas in patient care in this era of cost consciousness.

A randomized trial of indirect calorimetry-based feedings in thermal injury

To assess the superiority of indirect calorimetry (IC)-based enteral nutrition in burned patients, 49 adults with mean burns of 47% TBSA received feedings based either on the Curreri formula (CURR), or on IC, using enteral formulas with nonprotein calorie:nitrogen ratios of either 86:1, or 125:1. Intake in CURR patients was a mean 3,490 kcal/day, which exceeded resting energy expenditure (REE) by 43%, while IC patients received 3,530 kcal/day (1.2 x REE; p less than 0.05). Both groups maintained body weight and lymphocyte counts; survival was equal. Complications (diarrhea, nausea, hyperglycemia) were frequent in both groups, but their incidence did not differ. Patients fed the lower calorie:nitrogen ratio had greater cumulative nitrogen balance, with no increase in nitrogen excretion. It appears advisable to nourish burned patients with the minimal effective intake. While use of IC facilitates this goal, use of the Curreri formula provides acceptable approximation of caloric requirements in the early postburn period.

The declining incidence of fatal sepsis following thermal injury

Successful management of burned patients requires effective prevention and management of infectious complications. This study reviews the incidence of fatal sepsis in our burn center and attempts to analyze factors which may predict septic mortality. From January 1, 1978, through May 31, 1988, 1,913 patients were admitted, with a mean age of 24.8 +/- 0.5 years, a mean burn size of 17.7 +/- 0.4% total body surface area (%TBSA), and a mean 10.1 +/- 0.5% TBSA full-thickness injury. Nine per cent of patients sustained concurrent inhalation injuries. Overall mortality was 7.4%, and 1.6% of patients died from sepsis. Regression analysis showed that overall burn size, presence of inhalation injury, and the extent of full-thickness burn injury were significant independent predictors of death from sepsis, in decreasing order of relative importance. During the period 1983-1988, the incidence of septic mortality was 0.7%, which was significantly lower than the earlier half (1978-1982) of the study period (p less than 0.01). These data indicate that fatal infections are becoming increasingly uncommon after thermal injury. The reasons for this decline are probably multiple, and they include the widespread practice of early excision, and improvements in fluid resuscitation and the general medical care of burned patients.

Complications of burn care in patients with neurologic disorders

Patients with neurologic disorders are frequently burned in mishaps related directly to their diseases. Once burned, these patients face a mortality rate significantly greater than that of the burn population as a whole. To assess the impact of neurologic disease on burn care, we reviewed the records of 37 patients admitted to our burn center with burns and neurologic illness. Thirty-three patients (89%) sustained injuries directly related to their neurologic problems, the most frequent being bathtub scalds (29.8%) and scald/spills (24.3%). We compared 31 of these patients having nonextensive burn injuries (less than or equal to 25% total body surface area) to a control population with similar-sized burns from our burn unit during the study period. This comparison revealed significantly longer length of stay for the neurologically impaired sample. We presume that costs of care are also increased for this sample. The high frequency of burn injury among neurologically impaired persons, coupled with the greater difficulty in caring for them, suggests that this group should receive intensive burn prevention educational efforts.