Ipamorelin, a new growth-hormone-releasing peptide, induces longitudinal bone growth in rats.

<-it was new in 1999 when this study was published.

“Ipamorelin is a potent synthetic pentapeptide which has distinct and specific growth hormone (GH)-releasing properties. With the objective of investigating the effects on longitudinal bone growth rate (LGR), body weight (BW), and GH release, ipamorelin in different doses (0, 18, 90 and 450 microg/day) was injected s.c. three times daily for 15 days to adult female rats. After intravital tetracycline labelling on days 0, 6, and 13, LGR was determined by measuring the distance between the respective fluorescent bands in the proximal tibia metaphysis. Ipamorelin dose-dependently increased LGR from 42 microm/day in the vehicle group to 44, 50, and 52 microm/day in the treatment groups{So there was no cap at the dosage so far but there was a point of dimishing returns}. There was also a pronounced and dose-dependent effect on BW gain. The treatment did not affect total IGF-I levels, IGFBPs, or serum markers of bone formation and resorption. The number of tartrate-resistant acid phosphatase-positive multinuclear cells in the metaphysis of the tibia did not change significantly with treatment. The responsiveness of the pituitary to a provocative i.v. dose of ipamorelin or GHRH showed that the plasma GH response was marginally reduced after ipamorelin, but unchanged after GHRH{So there is a negative feedback mechanism in response to ipamorelin}. The pituitary GH content was unchanged by ipamorelin treatment.”

4-month old Sprague-Dawley rats were used.  Unlike with longitudinal bone growth there were no diminishing returns with body weight gain.

This study doesn’t quite give enough evidence to be confident in Ipamorelin’s height increasing abilities such as growth plate images for example but it’s definitely worth investigating.

Automated Cell Detection and Morphometry on Growth Plate Images of Mouse Bone.

“The resting zone contains relatively quiescent small, round, densely packed cells. Upon entry in the proliferating zone, cells elongate medial-laterally and undergo division by mitosis. At each division, the newly produced daughter cell remains closely situated with respect to the mother cell but may be far apart from other cells. The cells begin to form stacks. In pre-hypertrophic and hypertrophic zones, chondrocytes become arranged in columns. Such cells begin to enlarge and express Indian Hedgehog while the expression of Sox9 is reduced. In the hypertrophic zone, the terminal enlarged chondrocytes are larger than in the rest of the growth plate, either round or elongated in the longitudinal direction, and packed closely to one another. The bottom of this region is marked by ossification. Correlations exist among height of hypertrophic chondrocytes, growth plate length, and limb length[remember that correlation does not equal causation]”

“the mean cell area is significantly smaller in the resting zone than in the proliferative zone”

“the mean cell area is significantly smaller in the proliferative zone than in the hypertrophic zone; and that the mean orientation differs significantly between resting and proliferative, but not between proliferative and hypertrophic zones. Further, the mean isoperimetric ratio IR is significantly different between resting and proliferative zones, and between proliferative and hypertrophic zones, indicating that the cells become less circular as they progress from the resting to proliferative, and from proliferative to hypertrophic zone. ”

“the chondrocytes of the Smad1/5CKO mutant [havea] rounder shape, and the orientation off the horizontal (medial-lateral) direction,  in comparison with the control WT mouse”

The spine doesn’t react very positively to stretching but what about other cartilagenous regions?  In one post, we discovered that articular cartilage can undergo endochondral ossification and can undergo grow in size.

A big question is whether articular can contribute to height:

The use of knee height to estimate maximum stature in elderly Chinese.

“In a study of 247 (130 men and 117 women) adult ethnic Chinese living in Melbourne, Australia, we tested the hypothesis that knee height is independent of age{thus that articular cartilage degeneration would not affect knee height} and attempted to devise an equation for the estimation of maximum stature (MS) in the this elderly group (aged 65 yrs) of this population. Anthropometric indices, including body weight, stature, arm-span, and knee height were twice measured using standard methods. In both men and women, the younger adults were taller and had a greater arm-span than their elderly counterparts: however, there was no difference in knee height or body weight between the two groups. Knee height was not associated with age, while stature and arm-span{But arm span would be affected by articular cartilage too only} correlated negatively with age.  Knee height provides for a valid estimate of MS during early adulthood than arm-span. Knee height is independent of age and does not appear to decreased over time, in spite of an expected cohort effect in this population. Arm-span, however, appears to change with a cohort as well as with age. Thus, there is a place in a life-time nutritional assessment of the aged to measure both arm-span as an index of cohort status and knee height for an individual’s maximum achieved stature.”

According to Figure 1, the knee height measurement would incorporate the articular cartiage regions of the ankle and the knee.  There was a negative correlation between age and knee height it was just not statistically significant.  Interestingly arm span decreased more than overall stature despite discs not being a factor.

Micromechanical response of articular cartilage to tensile load measured using nonlinear microscopy.

“This work investigates the inhomogeneous distribution of strain in loaded AC by tracking the movement and morphological changes of individual chondrocytes using point pattern matching and Bayesian modeling.”

“Articular cartilage (AC) is a connective tissue found at the ends of articulating bones within the synovial joints of mammals. Healthy AC is composed primarily of a gel of hydrophilic proteoglycan molecules and interstitial fluid, constrained by a dense network of collagen fibres.”

“Tensile loading reveals the interconnectivity of the fibrous protein networks, and facilitates continuity of load transmission through the matrix”

“As well as resisting shear load associated with joint articulation, the superficial zone also provides a strain-limiting surface that restricts bulging close to regions that experience high compressive load.”

“Ridges in the surface of bovine AC that appeared as the tissue was stretched, and attributed these to protruding collagen fibres. Although these were slightly thinner than those found in the present investigation, the size difference could be associated with width contraction under load and the resolution limitations of the camera. The thick palmar cartilage showed regions of blurred and filamented signal near the surface, and filamented patterns throughout the middle and deep zones. Dorsal and cortical ridge samples showed patches of high intensity and varying signal orientation in the middle zone, which are possibly leaves of collagen overlapping at different angles. In the deep zone, images contained streaks of high signal intensity, which are unlikely to be due to tangentially aligned collagen. It is possible that these patterns arise from the interweaving in the horizontal plane of the predominantly perpendicular fibres. Chondrocytes (which appear dark under PLM) are arranged in columns perpendicular to the underlying bone, and regular spacing of these columns may cause the surrounding matrix to appear filamented when viewed en face.”

“Cartilage is thickest in regions that experience the least compressive load”

“The average cellular strain values of 2% in the long axis and −5% in short axis indicate that the cells experienced a mean in-plane compressive force and that ellipticity increased despite an outward force being applied to the sample. This overall compressive strain was not significantly different to that of the surrounding matrix, despite the low mechanical stiffness of chondrocytes”

Epiphysiodesis involves either removing the growth plate or taking it and modifying it before reinsertion.  Prophylactic Fixation involves inserting a metal into the bone.  A cannulated screw has a hollow central shaft.

Persisting Growth After Prophylactic Single-Screw Epiphysiodesis in Upper Femoral Epiphysis.

“Prophylactic fixation of the contralateral hip in cases of slipped upper femoral epiphysis is controversial. Using a single-cannulated screw has been widely accepted. Differing reports exist on the occurrence of persisting growth after prophylactic epiphysiodesis. The aim of this study was to evaluate the presence of persisting growth of the upper femoral epiphysis after prophylactic fixation.
From 2006 until 2009, 11 children underwent prophylactic pinning using a single-cannulated 6.5-mm cancellous screw. Time to fusion, persisting growth, and overgrowing of the screw were measured on plain radiographs taken postoperatively and at least after the growth plate was fused.
All patients except 1 (91%) showed a persisting growth of the epiphysis, and in 2 cases a hardware replacement was necessary. The mean increase of the femoral neck length was 8.2% (SEM 1.46%). Mean follow-up was 37 months (range, 12 to 49 mo). All patients had a Risser sign grade 0 at the time of surgery, and equal or less than grade 3, when the growth plate was fused{Riser 5 equals cessation of growth}.
Prophylactic fixation using a single-cannulated cancellous screw showed in our series growth persistence was the rule and in some cases the physeal overgrowth necessitates a hardware replacement.”

“After placing the guidewire under fluoroscopic guidance in a central position and drilling with a 5.0-mm drill just over the proximal femoral growth plate, the insertion of the 6.5-mm cannulated cancellous screw was carried out through a 0.5-inch incision.”

“The mean increase of femoral neck length at the time of physeal closure in patients without further surgeries was 8.6%, 7.5% in the 16mm threaded group and 10% in the 32mm threaded group.”<-The bigger the screw the larger the overgrowth.

Maybe placing a screw in adult bone will also cause a length increase?

 Insulin-Like Growth Factor I (IGF-1) Ec/Mechano Growth Factor – A Splice Variant of IGF-1 within the Growth Plate

“Human insulin-like growth factor 1 Ec (IGF-1Ec), also called mechano growth factor (MGF), is a splice variant of insulin-like growth factor 1 (IGF-1), which has been shown in vitro as well as in vivo to induce growth and hypertrophy in mechanically stimulated or damaged muscle. Growth, hypertrophy and responses to mechanical stimulation are important reactions of cartilaginous tissues, especially those in growth plates.  We wanted to ascertain if MGF is expressed in growth plate cartilage and if it influences proliferation of chondrocytes, as it does in musculoskeletal tissues. MGF expression was analyzed in growth plate and control tissue samples from piglets aged 3 to 6 weeks. Furthermore, growth plate chondrocyte cell culture was used to evaluate the effects of the MGF peptide on proliferation. MGF is expressed in considerable amounts in the tissues evaluated. We found the MGF peptide to be primarily located in the cytoplasm, and in some instances, it was also found in the nucleus of the cells. Addition of MGF peptides was not associated with growth plate chondrocyte proliferation.”

“IGF-1 and MGF are up-regulated in exercised and damaged skeletal muscle, probably inducing muscle growth and hypertrophy. MGF has been shown to stimulate proliferation and suppress differentiation, while IGF-1 also supported differentiation”

“Cyclic stretching of osteoblasts enhanced cell proliferation and induced expression of Mgf on the mRNA level. MGF has been observed to inhibit osteoblast differentiation and mineralization in osteoblast cell culture medium”

“Injecting MGF into [a] bone defect gap for 5 consecutive days resulted in accelerated bone healing”

“Comparison of mRNA expression revealed that the Mgf fraction of total Igf1 ratios varied between the tissues examined ranging from 8% in muscle to 31% in Ranvier’s groove “<-So MGF and IGF-1 correlates between muscle, bone, and cartilage tissue.

“Igf1 and Mgf expressions were lower in the proliferative zone than in the resting and hypertrophic zones”

“[No] statistically significant effects of the MGF peptides on the proliferation of monolayer growth plate chondrocytes in concentrations ranging from 0.1 to 500 ng/ml. Differences between concentrations could be detected when growth plate explants were treated with IGF-1 alone”

“In contrast to mature IGF-1, MGF has been reported to activate ERK1/2 without influencing Akt phosphorylation”

Human growth is associated with distinct patterns of gene expression in evolutionarily conserved networks.

“the expression of 688 genes (ANOVA false discovery rate modified p-value, q < 0.1) was associated with age, and subsets of these genes formed clusters that correlated with the phases of growth — infancy, childhood, puberty and [adult] height.”<-It seems that the genes are correlated with stage of development and not directly associated with differences in height.

“Network analysis on these clusters identified evolutionarily conserved growth pathways (NOTCH, VEGF, TGFB, WNT and glucocorticoid receptor)”

“Similar biological pathways were observed to be associated with development-related gene expression in other tissues (conjunctival epithelia, temporal lobe brain tissue and bone marrow) suggesting the existence of a tissue-independent genetic program for human growth and maturation.”

Gene expression from peripheral blood mononuclear cells were obtained.

Pathways associated with Adult Stage of Growth:

Ephrin Receptor Signaling:

Related genes upregulated by LSJL:

Epha5, Epha3

Downregulated:

Efnb3

Erythropoietin Signaling(associated with red blood cell production which means that bone marrow could be linked to height)

Related genes downregulated by LSJL:

Zc3h15

Wnt-Beta-Catening Signaling

Related Genes Upregulated by LSJL:

Fzd3, Fzd2, Dkk3,

Downregulated:

Fbxw2, Dvl1, Csnk1e, Hbp1, Tcf7, Csnk1d, Tle2, Senp2

Chemokine Signaling(Chemokines are related to inflammatory and leukocyte signaling)

LSJL Upregulated:

Ccr1, Cxcr7

Downregulated:

Ccrl2, Ccr9

Reelin Signaling Neurons(mostly associated with the brain which is why it’s not detected in LSJL.

Pathways Correlated with height in infancy and puberty are more traditional like BMP, GH, and TGF-Beta.

Pathways associated with Development in Infancy:
PDGF Signaling
VEGF Family Lig and-Receptor Interactions
VEGF Signaling
Angiopoietin Signaling
NGF Signaling
Melanocyte Development and Pigmentation Signaling
Renin-Angiotensin Signaling
NF-B Signaling
Notch Signaling
IGF-1 Signaling
Erythropoietin Signaling
Chemokine Signaling
Wnt/Beta-catenin Signaling
TGF-Beta Signaling
BMP signaling pathway
Neurotrophin/TRK Signaling
Ephrin Receptor Signaling
Growth Hormone Signaling
Axonal Guidance Signaling

Pathways Associated with Development in Puberty:

IGF-1 Signaling
Chemokine Signaling
Actin Cytoskeleton Signaling
Axonal Guidance Signaling
Wnt/B-catenin Signaling
TGFB- Signaling
Ephrin Receptor Signaling
VEGF Signaling
VEGF Family Lig and-Receptor Interactions
Renin-Angiotensin Signaling
NF-B Signaling
Notch Signaling

Regarding Reelin Signaling Neurons and Bone:

 Adult Rat Bones Maintain Distinct Regionalized Expression of Markers Associated with Their Development

“Limb bones contain greater amounts of polysulphated glycosaminoglycan stained with Alcian Blue and have significantly higher osteocyte densities than skull bone. Site-specific patterns persist in cultured adult bone-derived cells both phenotypically (proliferation rate, response to estrogen and cell volumes), and at the level of specific gene expression (collagen triple helix repeat containing 1, reelin and ras-like and estrogen-regulated growth inhibitor). Based on genome-wide mRNA expression and cluster analysis, we demonstrate that bones and cultured adult bone-derived cells segregate according to site of derivation. We also find the differential expression of genes associated with embryological development (Skull: Zic, Dlx, Irx, Twist1 and Cart1; Limb: Hox, Shox2, and Tbx genes) in both adult bones and isolated adult bone-derived cells.”

Reeln expression is elevated in limb versus skull bones.  Reeln is speculated to be involved in the osteocytic mechanical response of long bones.

Both Reeln and Cthrc1 are mentioned as therapeutic targets albeit for bone mass and not height growth.