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Use of imaging biomarkers to assess perfusion and glucose metabolism in the skeletal muscle of dystrophic mice.

Ahmad N, Welch I, Grange R, Hadway J, Dhanvantari S, Hill D, Lee TY, Hoffman LM - BMC Musculoskelet Disord (2011)

Bottom Line: The disease is characterized by progressive muscle degeneration that results from mutations in or loss of the cytoskeletal protein, dystrophin, from the glycoprotein membrane complex, thus increasing the susceptibility of contractile muscle to injury.Histological analysis of H&E-stained tissue collected from parallel littermates demonstrates the presence of both inflammatory infiltrate and centrally-located nuclei, a classic hallmark of myofibrillar regeneration.The present study demonstrates the utility of non-invasive imaging biomarkers in characterizing muscle degeneration/regeneration in murine models of DMD.

View Article: PubMed Central - HTML - PubMed

Affiliation: Imaging Program, Lawson Health Research Institute, 268 Grosvenor St., London N6A4V2, Canada.

ABSTRACT

Background: Duchenne muscular dystrophy (DMD) is a severe neuromuscular disease that affects 1 in 3500 boys. The disease is characterized by progressive muscle degeneration that results from mutations in or loss of the cytoskeletal protein, dystrophin, from the glycoprotein membrane complex, thus increasing the susceptibility of contractile muscle to injury. To date, disease progression is typically assessed using invasive techniques such as muscle biopsies, and while there are recent reports of the use of magnetic resonance, ultrasound and optical imaging technologies to address the issue of disease progression and monitoring therapeutic intervention in dystrophic mice, our study aims to validate the use of imaging biomarkers (muscle perfusion and metabolism) in a longitudinal assessment of skeletal muscle degeneration/regeneration in two murine models of muscular dystrophy.

Methods: Wild-type (w.t.) and dystrophic mice (weakly-affected mdx mice that are characterized by a point mutation in dystrophin; severely-affected mdx:utrn⁻/⁻ (udx) mice that lack functional dystrophin and are for utrophin) were exercised three times a week for 30 minutes. To follow the progression of DMD, accumulation of ¹⁸F-FDG, a measure of glucose metabolism, in both wild-type and affected mice was measured with a small animal PET scanner (GE eXplore Vista). To assess changes in blood flow and blood volume in the hind limb skeletal muscle, mice were injected intravenously with a CT contrast agent, and imaged with a small animal CT scanner (GE eXplore Ultra).

Results: In hind limb skeletal muscle of both weakly-affected mdx mice and in severely-affected udx mice, we demonstrate an early, transient increase in both ¹⁸F-FDG uptake, and in blood flow and blood volume. Histological analysis of H&E-stained tissue collected from parallel littermates demonstrates the presence of both inflammatory infiltrate and centrally-located nuclei, a classic hallmark of myofibrillar regeneration. In both groups of affected mice, the early transient response was succeeded by a progressive decline in muscle perfusion and metabolism; this was also evidenced histologically.

Conclusions: The present study demonstrates the utility of non-invasive imaging biomarkers in characterizing muscle degeneration/regeneration in murine models of DMD. These techniques may now provide a promising alternative for assessing both disease progression and the efficacy of new therapeutic treatments in patients.

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H&E-stained sections of gastrocnemius muscles (GMs). H&E-stained sections of gastrocnemius muscles (GMs) isolated from: (a) wild-type (w.t.) mice at (i) baseline (6 weeks old), (ii) week 8, (iii) week 14, and (iv) at the termination of the study (20-22 weeks of age). Pathology is described in the text. Legend: solid arrow, points to eccentrically-located nuclei in myofibers; (b) non-exercised mdx at (i) baseline, (ii) week 8, (iii) week 14, and (iv) at the termination of the study. Legend: open arrowhead points to centrally-located nuclei in myofibers; closed arrowhead points to inflammatory infiltrate, solid arrow points to eccentrically-located nuclei in myofibers; (c) exercised mdx mice at (i) baseline, (ii) week 8, (iii) week 14, and (iv) at the termination of the study. The pathology observed in each group and at each time are described in the text. Legend: solid arrow points to eccentrically-located nuclei; open arrowhead points to centrally-located nuclei in myofibers; closed arrowhead points to inflammatory infiltrate; and thin solid arrow points to a mineralized lesion; (d) non-exercise udx mice at (i) baseline, (ii) week 8, (iii) week 14, and (iv) at the termination of the study. Legend: open arrowhead points to centrally-located nuclei in myofibers; closed arrowhead points to inflammatory infiltrate.
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Figure 5: H&E-stained sections of gastrocnemius muscles (GMs). H&E-stained sections of gastrocnemius muscles (GMs) isolated from: (a) wild-type (w.t.) mice at (i) baseline (6 weeks old), (ii) week 8, (iii) week 14, and (iv) at the termination of the study (20-22 weeks of age). Pathology is described in the text. Legend: solid arrow, points to eccentrically-located nuclei in myofibers; (b) non-exercised mdx at (i) baseline, (ii) week 8, (iii) week 14, and (iv) at the termination of the study. Legend: open arrowhead points to centrally-located nuclei in myofibers; closed arrowhead points to inflammatory infiltrate, solid arrow points to eccentrically-located nuclei in myofibers; (c) exercised mdx mice at (i) baseline, (ii) week 8, (iii) week 14, and (iv) at the termination of the study. The pathology observed in each group and at each time are described in the text. Legend: solid arrow points to eccentrically-located nuclei; open arrowhead points to centrally-located nuclei in myofibers; closed arrowhead points to inflammatory infiltrate; and thin solid arrow points to a mineralized lesion; (d) non-exercise udx mice at (i) baseline, (ii) week 8, (iii) week 14, and (iv) at the termination of the study. Legend: open arrowhead points to centrally-located nuclei in myofibers; closed arrowhead points to inflammatory infiltrate.

Mentions: Analysis of H&E-stained GM tissue sections revealed that, at baseline (6 weeks of age) and at all time points thereafter, the GMs of w.t. mice were predominantly comprised of eccentrically-located nuclei (arrow), were devoid of inflammatory cells, and displayed normal amounts of connective tissue amongst myofibers (Figure 5a). In contrast, the GMs harvested from either group of mdx mice (non-exercised and exercised) at baseline exhibited numerous centrally-located nuclei (open arrow head), and small amounts of inflammatory infiltrate (arrow head) in the interstitial space (Figure 5b &5c(i)). The severity of the degenerative process in udx mice, relative to that occurring in mildly-affected mdx mice, was evidenced by the predominance of centrally-located nuclei (open arrow head) and the widespread presence of inflammatory infiltrate within enlarged intercellular space (arrow head) (Figure 5d(i)). Two weeks post-baseline (8 weeks of age), non-exercised mdx mice still exhibited centrally-located nuclei (open arrow head), as well as modest inflammatory infiltrate (arrow head) (Figure 5b(ii)). Centrally-located nuclei were also observed in exercised mdx and udx mice (open arrow head), although most notable in both groups was the presence of a marked inflammatory infiltrate amongst myofibers (arrow head) (Figure 5c and 5d(ii)), and by the occasional appearance of mineralized tissue (Figure 5c(ii), thin arrow).


Use of imaging biomarkers to assess perfusion and glucose metabolism in the skeletal muscle of dystrophic mice.

Ahmad N, Welch I, Grange R, Hadway J, Dhanvantari S, Hill D, Lee TY, Hoffman LM - BMC Musculoskelet Disord (2011)

H&E-stained sections of gastrocnemius muscles (GMs). H&E-stained sections of gastrocnemius muscles (GMs) isolated from: (a) wild-type (w.t.) mice at (i) baseline (6 weeks old), (ii) week 8, (iii) week 14, and (iv) at the termination of the study (20-22 weeks of age). Pathology is described in the text. Legend: solid arrow, points to eccentrically-located nuclei in myofibers; (b) non-exercised mdx at (i) baseline, (ii) week 8, (iii) week 14, and (iv) at the termination of the study. Legend: open arrowhead points to centrally-located nuclei in myofibers; closed arrowhead points to inflammatory infiltrate, solid arrow points to eccentrically-located nuclei in myofibers; (c) exercised mdx mice at (i) baseline, (ii) week 8, (iii) week 14, and (iv) at the termination of the study. The pathology observed in each group and at each time are described in the text. Legend: solid arrow points to eccentrically-located nuclei; open arrowhead points to centrally-located nuclei in myofibers; closed arrowhead points to inflammatory infiltrate; and thin solid arrow points to a mineralized lesion; (d) non-exercise udx mice at (i) baseline, (ii) week 8, (iii) week 14, and (iv) at the termination of the study. Legend: open arrowhead points to centrally-located nuclei in myofibers; closed arrowhead points to inflammatory infiltrate.
© Copyright Policy - open-access
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Figure 5: H&E-stained sections of gastrocnemius muscles (GMs). H&E-stained sections of gastrocnemius muscles (GMs) isolated from: (a) wild-type (w.t.) mice at (i) baseline (6 weeks old), (ii) week 8, (iii) week 14, and (iv) at the termination of the study (20-22 weeks of age). Pathology is described in the text. Legend: solid arrow, points to eccentrically-located nuclei in myofibers; (b) non-exercised mdx at (i) baseline, (ii) week 8, (iii) week 14, and (iv) at the termination of the study. Legend: open arrowhead points to centrally-located nuclei in myofibers; closed arrowhead points to inflammatory infiltrate, solid arrow points to eccentrically-located nuclei in myofibers; (c) exercised mdx mice at (i) baseline, (ii) week 8, (iii) week 14, and (iv) at the termination of the study. The pathology observed in each group and at each time are described in the text. Legend: solid arrow points to eccentrically-located nuclei; open arrowhead points to centrally-located nuclei in myofibers; closed arrowhead points to inflammatory infiltrate; and thin solid arrow points to a mineralized lesion; (d) non-exercise udx mice at (i) baseline, (ii) week 8, (iii) week 14, and (iv) at the termination of the study. Legend: open arrowhead points to centrally-located nuclei in myofibers; closed arrowhead points to inflammatory infiltrate.
Mentions: Analysis of H&E-stained GM tissue sections revealed that, at baseline (6 weeks of age) and at all time points thereafter, the GMs of w.t. mice were predominantly comprised of eccentrically-located nuclei (arrow), were devoid of inflammatory cells, and displayed normal amounts of connective tissue amongst myofibers (Figure 5a). In contrast, the GMs harvested from either group of mdx mice (non-exercised and exercised) at baseline exhibited numerous centrally-located nuclei (open arrow head), and small amounts of inflammatory infiltrate (arrow head) in the interstitial space (Figure 5b &5c(i)). The severity of the degenerative process in udx mice, relative to that occurring in mildly-affected mdx mice, was evidenced by the predominance of centrally-located nuclei (open arrow head) and the widespread presence of inflammatory infiltrate within enlarged intercellular space (arrow head) (Figure 5d(i)). Two weeks post-baseline (8 weeks of age), non-exercised mdx mice still exhibited centrally-located nuclei (open arrow head), as well as modest inflammatory infiltrate (arrow head) (Figure 5b(ii)). Centrally-located nuclei were also observed in exercised mdx and udx mice (open arrow head), although most notable in both groups was the presence of a marked inflammatory infiltrate amongst myofibers (arrow head) (Figure 5c and 5d(ii)), and by the occasional appearance of mineralized tissue (Figure 5c(ii), thin arrow).

Bottom Line: The disease is characterized by progressive muscle degeneration that results from mutations in or loss of the cytoskeletal protein, dystrophin, from the glycoprotein membrane complex, thus increasing the susceptibility of contractile muscle to injury.Histological analysis of H&E-stained tissue collected from parallel littermates demonstrates the presence of both inflammatory infiltrate and centrally-located nuclei, a classic hallmark of myofibrillar regeneration.The present study demonstrates the utility of non-invasive imaging biomarkers in characterizing muscle degeneration/regeneration in murine models of DMD.

View Article: PubMed Central - HTML - PubMed

Affiliation: Imaging Program, Lawson Health Research Institute, 268 Grosvenor St., London N6A4V2, Canada.

ABSTRACT

Background: Duchenne muscular dystrophy (DMD) is a severe neuromuscular disease that affects 1 in 3500 boys. The disease is characterized by progressive muscle degeneration that results from mutations in or loss of the cytoskeletal protein, dystrophin, from the glycoprotein membrane complex, thus increasing the susceptibility of contractile muscle to injury. To date, disease progression is typically assessed using invasive techniques such as muscle biopsies, and while there are recent reports of the use of magnetic resonance, ultrasound and optical imaging technologies to address the issue of disease progression and monitoring therapeutic intervention in dystrophic mice, our study aims to validate the use of imaging biomarkers (muscle perfusion and metabolism) in a longitudinal assessment of skeletal muscle degeneration/regeneration in two murine models of muscular dystrophy.

Methods: Wild-type (w.t.) and dystrophic mice (weakly-affected mdx mice that are characterized by a point mutation in dystrophin; severely-affected mdx:utrn⁻/⁻ (udx) mice that lack functional dystrophin and are for utrophin) were exercised three times a week for 30 minutes. To follow the progression of DMD, accumulation of ¹⁸F-FDG, a measure of glucose metabolism, in both wild-type and affected mice was measured with a small animal PET scanner (GE eXplore Vista). To assess changes in blood flow and blood volume in the hind limb skeletal muscle, mice were injected intravenously with a CT contrast agent, and imaged with a small animal CT scanner (GE eXplore Ultra).

Results: In hind limb skeletal muscle of both weakly-affected mdx mice and in severely-affected udx mice, we demonstrate an early, transient increase in both ¹⁸F-FDG uptake, and in blood flow and blood volume. Histological analysis of H&E-stained tissue collected from parallel littermates demonstrates the presence of both inflammatory infiltrate and centrally-located nuclei, a classic hallmark of myofibrillar regeneration. In both groups of affected mice, the early transient response was succeeded by a progressive decline in muscle perfusion and metabolism; this was also evidenced histologically.

Conclusions: The present study demonstrates the utility of non-invasive imaging biomarkers in characterizing muscle degeneration/regeneration in murine models of DMD. These techniques may now provide a promising alternative for assessing both disease progression and the efficacy of new therapeutic treatments in patients.

Show MeSH
Related in: MedlinePlus