The association between parent-reported provider communication quality and child obesity status: Variation by parent obesity and child race/ethnicity

ObjectiveTo examine the association between healthcare provider communication quality and child obesity status, and the role of parent obesity and child race/ethnicity regarding this association.MethodsWe conducted a cross-sectional secondary data analysis with the 2011–2013 Medical Expenditures Panel Survey of parents with children ages 6–12 (n = 5390). We used multivariable logistic regression to examine the association of parent-reported healthcare provider communication quality (explaining well, listening carefully, showing respect, and spending enough time) with child obesity status, and effect modification by parent obesity and child race/ethnicity.ResultsParents of obese children were more likely to report that their child’s healthcare provider listened carefully (OR = 1.41, p = 0.002) and spent enough time (OR = 1.33, p = 0.022) than parents of non-obese children. Non-obese parents of obese children experienced better communication in the domains of listening carefully (p < 0.001) and spending enough time (p = 0.007). Parents of obese non-Hispanic Asian children and non-Hispanic Black children were more likely to report that providers explained things well (p = 0.043) and listened carefully (p = 0.012), respectively.ConclusionParents of obese children experienced better communication if parents were non-obese or children were non-Hispanic Black or Asian.Practice implicationsHealthcare providers should ensure effective communication with obese parents of obese children.     

Metformin limits ceramide-induced senescence in C2C12 myoblasts

High lipid and ceramide concentrations are hallmarks of obese and/or insulin resistant skeletal muscle, yet little is known about its role on cell cycle and senescence. The purpose of this study was to examine the role of ceramide on muscle senescence, and whether metformin limited this response.MethodsLow passage, proliferating C2C12 myoblasts were treated with a control, 50 μM C2-ceramide (8 h), and/or 2 mM metformin, then examined for insulin sensitivity, cell senescence, cell proliferation, cell cycle, protein expression of cell cycle regulators.ResultsCeramide treatment caused a dephosphorylation (p < 0.05) of Akt and 4E-BP1, regardless of the presence of insulin. The ceramide treated myoblasts displayed higher β-galactosidase staining (p < 0.05), reduced BrDu incorporation and total number of cells (p < 0.05), and an increased proportion of cells in G2-phase (p < 0.05) versus control cultures. Ceramide treatment also upregulated (p < 0.05) p53 and p21 protein expression, that was reversed by either pifithrin-α or shRNA for p53. Metformin limited (p < 0.05) ceramide's effects on insulin signaling, senescence, and cell cycle regulation.ConclusionsHigh ceramide concentrations reduced myoblast proliferation that was associated with aberrant cell cycle regulation and a senescent phenotype, which could provide an understanding of skeletal muscle cell adaptation during conditions of high intramuscular lipid deposition and/or obesity.     

Counteractive functions are encrypted in the residues of CD154

CD40, as a single receptor that binds CD154 (CD40-ligand or CD40L), regulates counteractive effector functions such as production of pro- and anti-inflammatory cytokines. Therefore, we examined whether such dual messages are encrypted in CD40L. As such message encryption was never investigated, we hypothesized that mutation of certain amino acid residues should in principle enhance pro-inflammatory cytokine production whereas mutation of some others would enhance anti-inflammatory cytokine secretion. We mutated six such residues, which were previously showed to participate in CD40L function. Here, we report that the mutant CD154 129E → V was superior to the wild-type CD154 in killing of Leishmania donovani, induction of inducible nitric oxide synthase (iNOS) and production of IL-12 and relative phosphorylation of p38MAPK and ERK-1/2 in PBMC-derived macrophages. By contrast, 128S → V promoted L. donovani survival, reducing iNOS, but increasing IL-10 expression and predominant ERK-1/2 phosphorylation. The mutant 144G → V did not have significant effects. Other mutants (142E → V, 143K → A, 145Y → F) mimicked the wild-type CD154. Molecular dynamics simulation suggested that these mutations induced differential conformational changes in the CD40–CD154 complex. Therefore, assortment of the contrasting messages encrypted in a given ligand performing counteractive functions presents a novel fundamental biological principle that can be used for devising various therapies.     

Adolescents with at-risk eating and lifestyle behaviors are affected by after school schedules across the clinical weight spectrum

ObjectiveEvaluate adolescent lifestyle patterns to develop more effective health promotion programs.MethodsAn interview approach was employed to gain in-depth understanding of eating and activity behaviors. Adolescents aged 13–18 years (n = 43) from clinically normal and obese weight categories were enrolled. Nutrient intake and food group servings were obtained from a food frequency questionnaire.ResultsFour participant subgroups were identified and labeled: “Idle, Engaged, Balanced and Working.” “Idle” adolescents were sedentary, sometimes napped, and often snacked after dinner. “Engaged” adolescents participated in extra-curricular activities for the majority of their after school hours. “Balanced” adolescents participated in a single after-school activity followed by sedentary time; they consumed meals consistently and often snacked after dinner. “Working” adolescents were the least sedentary with limited sleep duration and inconsistent meals; they often substituted a meal with a snack. Weight status did not differentiate subgroups effectively.ConclusionsEach group demonstrated at-risk behaviors for obesity. Future programs should consider after-school schedules and use activity and meal pattern assessments, not simply weight status, for program tailoring.Practice implicationsPediatric health care providers could identify at-risk behaviors through routine assessment of diet and activity patterns in combination with weight monitoring.     

Mitochondrial DNA deletion and sarcopenia

PurposeAccumulation of mitochondrial DNA deletions and the resultant impaired oxidative phosphorylation may play a pathogenic role in the mediation of age-related sarcopenia.MethodsTwenty four participants of the New Mexico Aging Process Study were classified as normal lean (n = 15) or sarcopenic (n = 9) based on body composition determined by Dual Energy x-ray Absorptiometry. Complex I and Complex IV activities were measured in the skeletal muscle samples obtained from gastrocnemius muscle. A two-stage nested polymerase chain reaction strategy was used to identify the mitochondrial DNA deletions in the entire mitochondrial genome in the skeletal muscle samples.ResultsAlthough Complex I activity was not significantly different (5.5 ± 0.9 vs. 4.6 ± 0.7 mU/mg protein, P > 0.05), Complex IV activity was higher in sarcopenic subjects (1.4 ± 0.3 vs. 1.0 ± 0.1 mU/mg protein, P < 0.05). Mitochondrial DNA deletions were mostly located in the region of Complex I and spanned from nicotinamide adenine dinucleotide dehydrogenase 1 to nicotinamide adenine dinucleotide dehydrogenase 6. Deletions in the 8,577–10,407 bp and 10,233–11,249 bp regions were associated with a significant decrease in Complex I activity (P < 0.05 and P = 0.02, respectively). Total cumulative deletion, defined as the sum of individual length of deletions in a subject, was comparable in subjects with and without sarcopenia (1760 ± 726 vs. 1782 ± 888 bp, P > 0.05). The magnitude of mitochondrial DNA deletion, however, correlated positively with lean body mass (r = 0.43, P < 0.05).ConclusionThus, mitochondrial DNA deletions are common in elderly subjects and are negatively related to Complex I activity. The positive association between mitochondrial DNA deletions and lean body mass needs to be confirmed by studies in a larger study population.     

Obesity in autoimmune diseases: Not a passive bystander

In the last decades, autoimmune diseases have experienced a dramatic increase in Western countries. The involvement of environmental factors is strongly suspected to explain this rise. Particularly, over the same period, obesity has followed the same outbreak. Since the exciting discovery of the secretory properties of adipose tissue, the relationship between obesity and autoimmunity and the understanding of the underlying mechanisms have become of major interest. Indeed, the fat tissue has been found to produce a wide variety of “adipokines”, involved in the regulation of numerous physiological functions, including the immune response. By conducting a systematic literature review, we extracted 329 articles regarding clinical, experimental and pathophysiological data on the relationship between obesity, adipokines – namely leptin, adiponectin, resistin, visfatin – and various immune-mediated conditions, including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), inflammatory bowel disease (IBD), multiple sclerosis (MS), type-1 diabetes (T1D), psoriasis and psoriatic arthritis (PsA), and thyroid autoimmunity (TAI), especially Hashimoto thyroiditis (HT). The strongest levels of evidence support an increased risk of RA (OR = 1.2–3.4), MS (OR = 2), psoriasis and PsA (OR = 1.48–6.46) in obese subjects. A higher risk of IBD, T1D and TAI is also suggested. Moreover, obesity worsens the course of RA, SLE, IBD, psoriasis and PsA, and impairs the treatment response of RA, IBD, psoriasis and PsA. Extensive clinical data and experimental models demonstrate the involvement of adipokines in the pathogenesis of these autoimmune diseases. Obesity appears to be a major environmental factor contributing to the onset and progression of autoimmune diseases.     

Changes in the somatostatin (SOM)-like immunoreactivity within nervous structures of the porcine descending colon under various pathological factors

This study reports on changes in the somatostatin-like immunoreactive (SOM-LI) nerve structures of the enteric nervous system (ENS) in the porcine descending colon, caused by chemically driven inflammation, proliferative enteropathy (PE), which is a “natural” inflammation with proliferative changes and nerve injury (axotomy). The distribution pattern of SOM-LI structures was studied using the immunofluorescence technique in the circular muscle layer, the myenteric (MP), outer submucous (OSP) and inner submucous plexuses (ISP) and also in the mucosal layer. Under physiological conditions SOM-LI perikarya have been shown to constitute 1.97 ± 0.36%, 2.06 ± 0.33% and 4.23 ± 0.40% in the MP, OSP and ISP, respectively. Changes in SOM-immunoreactivity depended on the pathological factor and the part of the ENS studied. Numbers of the SOM-LI perikarya amounted 1.81 ± 0.30, 1.97 ± 0.24 and 11.15 ± 0.95 during chemically induced colitis and 3.21 ± 0.37%, 4.33 ± 0.33% and 4.42 ± 0.32% after axotomy in MP, OSP and ISP, respectively. Moreover during PE SOM-positive cell bodies were not observed at all in MP, whereas within OSP and ISP the number of SOM-LI perikarya amounted to 3.34 ± 0.36 and 10.92 ± 059, respectively. All processes studied resulted in a decrease in the number of SOM-LI nerve fibers in the mucosal layer, whereas within the circular muscle layer chemically induced inflammation and axotomy caused an increase in the number of the SOM-LI nerve fibers contrary to PE, which reduced the number of such fibers. The obtained results suggest that SOM-LI nerve structures of the ENS may participate in various pathological states within the porcine descending colon and their functions probably depend on the type of pathological factor.     

Circulating vitamin D concentration and age-related macular degeneration: Systematic review and meta-analysis

Vitamin D may be involved in ocular function in older adults, but there is no current consensus on a possible association between circulating concentrations of 25-hydroxyvitamin D (25OHD) and the occurrence of age-related macular degeneration (AMD). Our objective was to systematically review and quantitatively assess the association of circulating 25OHD concentration with AMD. A Medline search was conducted in November 2015, with no date limit, using the MeSH terms “Vitamin D” OR “Vitamin D deficiency” OR “Ergocalciferols” OR ‘Cholecalciferol’ combined with “Age-related macular degeneration” OR “Macular degeneration” OR “Retinal degeneration” OR “Macula lutea” OR “Retina”. Fixed and random-effects meta-analyses were performed to compute (i) standard mean difference in 25OHD concentration between AMD and non-AMD patients; (ii) AMD risk according to circulating 25OHD concentration. Of the 243 retrieved studies, 11 observational studies—10 cross-sectional studies and 1 cohort study—met the selection criteria. The number of participants ranged from 65 to 17,045 (52–100% women), and the number with AMD ranged from 31 to 1440. Circulating 25OHD concentration was 15% lower in AMD compared with non-AMD on average. AMD was inversely associated with the highest 25OHD quintile compared with the lowest (summary odds ratio (OR) = 0.83 [95%CI:0.71–0.97]), notably late AMD (summary OR = 0.47 [95%CI:0.28–0.79]). Circulating 25OHD < 50 nmol/L was also associated with late-stage AMD (summary OR = 2.18 [95%CI:1.34–3.56]), an association that did not persist when all categories of AMD were considered (summary OR = 1.26 [95%CI:0.90–1.76]). In conclusion, this meta-analysis provides evidence that high 25OHD concentrations may be protective against AMD, and that 25OHD concentrations below 50 nmol/L are associated with late AMD.     

Optimizing the structure and contractility of engineered skeletal muscle thin films

An experimental system was developed to tissue engineer skeletal muscle thin films with well-defined tissue architecture and to quantify the effect on contractility. Using the C2C12 cell line, the authors tested whether tailoring the width and spacing of micropatterned fibronectin lines can be used to increase myoblast differentiation into functional myotubes and maximize uniaxial alignment within a 2-D sheet. Using a combination of image analysis and the muscular thin film contractility assay, it was demonstrated that a fibronectin line width of 100 μm and line spacing of 20 μm is able to maximize the formation of anisotropic, engineered skeletal muscle with consistent contractile properties at the millimeter length scale. The engineered skeletal muscle exhibited a positive force–frequency relationship, could achieve tetanus and produced a normalized peak twitch stress of 9.4 ± 4.6 kPa at 1 Hz stimulation. These results establish that micropatterning technologies can be used to control skeletal muscle differentiation and tissue architecture and, in combination with the muscular thin film contractility, assay can be used to probe structure–function relationships. More broadly, an experimental platform is provided with the potential to examine how a range of microenvironmental cues such as extracellular matrix protein composition, micropattern geometries and substrate mechanics affect skeletal muscle myogenesis and contractility.     

Effects of whole-body vibration exercise on muscular strength and power,functional mobility and self-reported knee function in middle-aged and older Japanese women with knee pain

BackgroundWhole-body vibration training using vertical-vibration machines is called “acceleration training” (AT). The purpose of this study was to elucidate the effect of AT on lower-limb muscular strength and power, functional mobility and self-reported knee function in middle-aged and older Japanese women with knee pain.MethodsThirty-eight middle-aged and older Japanese women (aged 50–73 years) with knee pain were divided into two groups: (1) the AT group (n = 29) engaged in AT three times per week for eight weeks, and (2) the control group (C group, n = 9). The AT program consisted of flexibility training, strength training of mainly the quadriceps and surrounding muscles and cool-down exercises. The C group was encouraged to perform the same or similar exercises at home without vibratory stimulus. We evaluated knee strength and power, functional mobility (timed up and go: TUG) and self-reported knee function (Japanese Knee Osteoarthritis Measure: JKOM).ResultsNo one in the AT group dropped out during the program. All JKOM categories except degree of pain improved significantly post intervention indicating improved knee function, and TUG was significantly shorter in these participants. All knee strength and power parameters except isometric knee extension peak torque improved significantly. The degree of change in JKOM total score and TUG was significantly different between the two groups.ConclusionVibratory stimulus during an eight week AT programme can promote participation and safely improve functional mobility and self-reported knee function better than exercise without vibratory stimulus in middle-aged and older Japanese women with knee pain.Level of evidence: level 2.     

Metabolic activity of osteoarthritic knees correlates with BMI

Osteoarthritis of the knee has consistently been linked to obesity, defined as a body mass index (BMI) > 30 kg/m². It has been hypothesized that obesity may lead to osteoarthritis through increased joint pressure, accumulated microtrauma, and disruption of normal chondrocyte metabolism. These changes in chondrocyte metabolism have not been thoroughly investigated, and it is the purpose of this study to identify a relationship between BMI and altered chondrocyte metabolism in osteoarthritic tissue. Articular cartilage was harvested from the femoral condyles of patients after total knee arthroplasty, and analyzed in explant and alginate models. Glycosaminoglycan (GAG) content was measured using a dimethylmethylene blue assay and normalized to DNA content using a PicoGreen® assay. Studies have reported GAGs to be a reliable measurement of chondrocyte metabolism and osteoarthritis progression. Our results show a significant linear relationship of increasing BMI and increasing GAG content in both alginate and explant models (p < 0.001 and p = 0.001). Obese (BMI ≥ 30 kg/m²) and non-obese (BMI < 30 kg/m²) comparisons also demonstrated significant differences with higher GAG/DNA content in obese individuals compared to non-obese (p = 0.001 and p = 0.015). The study results reveal significant relationships between GAG content and BMI in this population of osteoarthritic patients. The significant difference in GAG content between the obese and non-obese patients supports the connection between osteoarthritis and obesity previously reported. Higher patient BMI (> 30 kg/m²) may be similar to dynamic compression injuries which cause increased GAG synthesis in response to cartilage damage.     

Characterisation and functional implications of the two new HLA-G alleles found in Amerindian and Caribbean populations

HLA-G polymorphism has been found to be relatively low in all world populations. In the present paper two new HLA-G molecules are described in ancient American natives. A new HLA-G molecule from a Ecuador Amerindian individual (male) showed four codon changes with respect to HLA-G*01:01:01. Silent changes at α1 domain (residue 57, Pro, CCG → CCA) and α2 domain (residue 93, His, CAC → CAT and residue 100, Gly, GGC → GGT) and one productive change in α3 domain (residue 219 changed from Arg to Trp). This α3 change may dramatically alter HLA-G interactions with beta-2 microglobulin, CD8, ILT-2 and ILT-4 ligands present in subsets of T, B, NK, monocytes, macrophages and dentritic cells. Another HLA-G new molecule was found in a woman from Hispaniola Island, Dominican Republic (Sto Domingo): it presented a silent change at α2 domain residue 107, Gly, GGA → GGT and non-silent change at residue 178, Met → Thr (with respect to HLA-G*01:01:01) which is close to class I molecule/clonotypic T cell receptor interaction sites. Functional implications of these findings are discussed.     

Genetic polymorphisms in TNFSF13 and FDX1 are associated with IgA nephropathy in the Han Chinese population

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide, and its pathogenesis is influenced by both genetic and environmental factors. In this study, we evaluated 23 tag single-nucleotide polymorphisms (tSNPs) in 21 IgAN-associated genes, in 200 subjects with IgAN and 310 healthy gender- and age-matched unrelated control subjects with no history of renal disease or hypertension. Using the co-dominant model, we found that two genotypes of rs3803800 in TNFSF13 were associated with an increased risk of IgAN: “GA” (OR = 1.03, 95% CI = 0.71–1.51, p = 0.018) and “AA” (OR = 2.45, 95% CI = 1.29–4.65, p = 0.018). The “AA” genotype was also associated with an increased risk of IgAN in the recessive model (OR = 2.41, 95% CI = 1.30–4.46, p = 0.018), as was the genotype “AA” rs10488764 in FDX1 (OR = 1.88, 95% CI = 1.01–3.53, p = 0.048). Interestingly, we found that the allele “A” of rs3803800 in TNFSF13 is associated with a decreased risk of IgAN in females (OR = 0.43, 95% CI = 0.20–0.95, p = 0.009), but with an increased risk in males (OR = 1.78, 95% CI = 0.86–3.66, p = 0.009). Our findings, combined with previously reported results, suggest that TNFSF13 and FDX1 have potential roles in IgAN in the Han Chinese population. This information may be useful in the development of early prognostics for IgAN.     

Serum fetuin A concentration is elevated in children with non-alcoholic fatty liver disease

PurposeTo assess the serum fetuin A concentration as a potential marker of subclinical atherosclerosis in obese children with NAFLD.Material/methodsA prospective analysis of 45 obese children initially diagnosed with liver pathology (elevated serum ALT activity and/or ultrasonographic liver brightness and/or hepatomegaly) was conducted. The diagnosis of NAFLD was established in the children with elevated serum ALT activity and liver steatosis on ultrasound examination. Viral hepatitis, autoimmune, metabolic liver diseases (Wilson disease, alpha-1-antitrypsin deficiency, cystic fibrosis) and drug and toxin-induced liver injury were excluded in all children. The degree of liver steatosis was graded according to Saverymuttu scale and the total liver lipids concentration was assessed using proton magnetic resonance spectroscopy (¹H MRS).ResultsSerum fetuin A concentration was significantly higher in examined children compared to the control group (n = 30) (p = 0.00002). Higher serum fetuin A concentration was also observed in children with NAFLD (n = 19) in comparison to the controls (p = 0.000026). Additionally, higher BMI values, waist circumferences, ALT and GGT activity, intensity of liver steatosis on ultrasound and total concentration of lipids in the liver in ¹H MRS were found in children with NAFLD compared to the rest of the examined obese patients (n = 26). There was not found any correlation of the investigated glycoprotein with any other assessed parameters both in children with NAFLD and obese children without NAFLD.ConclusionHigher serum fetuin A concentration found in children with NAFLD compared to the control group support the hypothesis that atherosclerotic processes may develop faster in hepatopatic obese patients.     

STEAP4 and HIF-1α gene expressions in visceral and subcutaneous adipose tissue of the morbidly obese patients

Aim and backgroundObesity is a multifactorial disease in which environmental and genetic factors play an integrated role. Determining such target genes will help to elucidate the mechanisms underlying complex diseases such as obesity and diabetes which are usually seen together. Present study investigates the expression levels of STEAP4 and HIF-1α in visceral and subcutaneous adipose tissue.Patients and methods30(6 M) morbidly obese patients undergoing bariatric surgery were included in the study. The patients were grouped according to the BMI as Group I (BMI <50 kg/m²) and Group II (BMI ≥50 kg/m²). Samples from visceral (omentum) and subcutaneous adipose tissues were obtained from each patient and real-time PCR (qPCR) was carried out for STEAP4 and HIF-1α gene expressions. Correlations between expression levels and clinical parameters were analyzed.ResultsMean age of the patients recruited to the study was 37.4 (18–64) years. Mean BMI was 46 (36–60) kg/m². STEAP4 expression in visceral adipose tissue was significantly higher than subcutaneous tissue. Visceral STEAP4 expression was also found to be reduced with increased BMI. It was also lower in patients with HbA₁C over 6. Furthermore, expression of subcutaneous and visceral HIF-1α was significantly higher in Group II. There was a significant correlation between BMI, glycosylated hemoglobin, STEAP4 and HIF-1α gene expression.ConclusionsObesity and related disease are linked with the fact that there is a low grade inflammation in the adipose tissue of the obese individuals. Counter-regulatory processes such as STEAP4 protein family are overwhelmed by the proinflammatory stimuli. HIF-1α expression is increased due to tissue hypoxia and pro-inflammatory stimuli in the obese individuals, which results in increased visceral STEAP4 expressions.     

No effect of obesity on limb and component alignment after computer-assisted total knee arthroplasty

PurposeThis retrospective study aimed to determine if computer navigation provides consistent accuracy for limb and component alignment during TKA irrespective of body mass index (BMI) by comparing limb and component alignment and the outlier rates in obese versus non-obese individuals undergoing computer-assisted TKA.MethodsSix hundred and thirty-five computer assisted total knee arthroplasties (TKAs) performed in non-obese individuals (BMI < 30 kg/m²) were compared with 520 computer-assisted TKAs in obese individuals (BMI ≥ 30 kg/m²) for postoperative limb and component alignment using full length standing hip-to-ankle radiographs.ResultsNo significant difference in postoperative limb alignment (179.7° ± 1.7° vs 179.6° ± 1.8°), coronal femoral (90.2° ± 1.6° vs 89.8° ± 1.9°) and tibial component (90.2° ± 1.6° vs 90.3° ± 1.7°) alignment and outlier rates (6.2% vs 7.5%) was found between non-obese and obese individuals. Similarly, alignment and the outlier rates were similar when non-obese individuals and a subgroup of morbidly obese individuals (BMI > 40 kg/m²) were compared.ConclusionsComputer navigation can achieve excellent limb and component alignment irrespective of a patient's BMI. Although obesity may not be an indication per se for using computer navigation during TKA, it will help achieve consistently accurate limb and component alignment in obese patients.Level of EvidenceLevel II     

The role of impulsivity in pediatric obesity and weight status: A meta-analytic review

Pediatric obesity has reached epidemic proportions over the last two decades; however little research has focused on the behavioral mechanisms that may contribute to the rise of obesity in youth and adolescents. Impulsivity has been examined as a mechanism underlying the displacement of physical activity and the increase in food consumption, however this research is limited. The present meta-analysis aimed to address mixed findings of previous research by determining a relative effect of impulsivity on pediatric obesity. A total of 23 articles met the inclusion criteria for the present meta-analysis for a total sample size of 3898 participants (k = 27) aged 2–21 years (M = 10.99). Using the statistical software, Comprehensive Meta-Analysis, version 2.0—Hedges' g was computed to estimate effect size. Results revealed a moderate effect size, such that impulsivity was greater among overweight/obese children, relative to healthy weight children (g = 0.406). Significant moderating effects were found for the type of measure used (g = 0.426) and the dimension of impulsivity examined (g = 0.402). The current study emphasizes the need for further research on the role of impulsivity in pediatric obesity as additional findings may aid in the enhancement of future prevention and intervention weight management programs.     

Dual pH- and temperature-responsive microparticles for protein delivery to ischemic tissues

Injectable “smart” microspheres that are sensitive to both temperature and pH have been fabricated and tested for controlled delivery of therapeutic proteins to ischemic skeletal muscle. A library of copolymers composed of N-isopropyl acrylamide (NIPAAm), propyl acrylic acid (PAA), and butyl acrylate (BA) was used to fabricate microspheres using a double emulsion method, and an optimal formulation made from copolymers composed of 57 mol.% NIPAAm, 18 mol.% PAA and 25 mol.% BA copolymers was identified. At 37 °C and pH representative of ischemic muscle (i.e. pH 5.2–7.2), these microspheres produced sustained, diffusion-controlled release, and at normal, physiological pH (i.e. pH 7.4), they underwent dissolution and rapid clearance. Delivery of fibroblast growth factor 2 was used to confirm that protein bioactivity was retained following microsphere encapsulation/release based on a dose-dependent increase in NIH3T3 fibroblast proliferation in vitro. Microsphere-loaded or free Cy5.5-labeled albumin was injected into ischemic and control gastrocnemii of mice following unilateral induction of hind limb ischemia to model peripheral arterial disease. In the ischemic limb at days 3.5 and 7, there was higher local retention of the protein delivered via microspheres relative to injected free protein (p < 0.05). However, clearance of protein delivered via microspheres was equivalent to free protein at later time points that correspond to ischemic recovery in this model. Finally, histological analysis of the gastrocnemius revealed that the polymeric microspheres did not produce any microscopic signs of toxicity near the injection site. These combined results suggest that the pH- and temperature-responsive microspheres presented herein are a promising technological platform for controlled protein delivery to ischemic tissue.