Accelerated atherosclerosis in beta-thalassemia.

Children with beta-thalassemia (BT) present with an increase in carotid intima-medial thickness, an early sign suggestive of premature atherosclerosis. However, it is unknown if there is a direct relationship between BT and atherosclerotic disease. To evaluate this, wild-type (WT, littermates) and BT (Hbbth3/+) mice, both male and female, were placed on a 3-mo high-fat diet with low-density lipoprotein receptor suppression via overexpression of proprotein convertase subtilisin/kexin type 9 (PCSK9) gain-of-function mutation (D377Y). Mechanistically, we hypothesize that heme-mediated oxidative stress creates a proatherogenic environment in BT because BT is a hemolytic anemia that has increased free heme and exhausted hemopexin, heme's endogenous scavenger, in the vasculature. We evaluated the effect of hemopexin (HPX) therapy, mediated via an adeno-associated virus, to the progression of atherosclerosis in BT and a phenylhydrazine-induced model of intravascular hemolysis. In addition, we evaluated the effect of deferiprone (DFP)-mediated iron chelation in the progression of atherosclerosis in BT mice. Aortic en face and aortic root lesion area analysis revealed elevated plaque accumulation in both male and female BT mice compared with WT mice. Hemopexin therapy was able to decrease plaque accumulation in both BT mice and mice on our phenylhydrazine (PHZ)-induced model of hemolysis. DFP decreased atherosclerosis in BT mice but did not provide an additive benefit to HPX therapy. Our data demonstrate for the first time that the underlying pathophysiology of BT leads to accelerated atherosclerosis and shows that heme contributes to atherosclerotic plaque development in BT.NEW & NOTEWORTHY This work definitively shows for the first time that beta-thalassemia leads to accelerated atherosclerosis. We demonstrated that intravascular hemolysis is a prominent feature in beta-thalassemia and the resulting increases in free heme are mechanistically relevant. Adeno-associated virus (AAV)-hemopexin therapy led to decreased free heme and atherosclerotic plaque area in both beta-thalassemia and phenylhydrazine-treated mice. Deferiprone-mediated iron chelation led to deceased plaque accumulation in beta-thalassemia mice but provided no additive benefit to hemopexin therapy.

Intestinal barrier dysfunction in murine sickle cell disease is associated with small intestine neutrophilic inflammation, oxidative stress, and dysbiosis.

The intestinal microbiome has emerged as a potential contributor to the severity of sickle cell disease (SCD). We sought to determine whether SCD mice exhibit intestinal barrier dysfunction, inflammation, and dysbiosis. Using the Townes humanized sickle cell mouse model, we found a 3-fold increase in intestinal permeability as assessed via FITC-dextran (4 kDa) assay in SS (SCD) mice compared to AA (wild type) mice (n = 4, p < 0.05). This was associated with 25 to 50% decreases in claudin-1, 3, and 15 and zonula occludens-1 gene expression (n = 8-10, p < 0.05) in the small intestine. Increased Ly6G staining demonstrated more neutrophils in the SS small intestine (3-fold, n = 5, p < 0.05) associated with increased expression of TNFα, IL-17A, CXCL1, and CD68 (2.5 to 5-fold, n = 7-10, p < 0.05). In addition, we observed 30 to 55% decreases in superoxide dismutase-1, glutathione peroxidase-1, and catalase antioxidant enzyme expression (n = 7-8, p < 0.05) concomitant to an increase in superoxide (2-fold, n = 4, p < 0.05). Importantly, all significant observations of a leaky gut phenotype and inflammation were limited to the small intestine and not observed in the colon. Finally, characterization of the composition of the microbiome within the small intestine revealed dysbiosis in SS mice compared to their AA littermates with 47 phyla to species-level significant alterations in amplicon sequence variants. We conclude that the intestinal barrier is compromised in SCD, associated with decreased gene expression of tight junction proteins, enhanced inflammation, oxidative stress, and gut microbiome dysbiosis, all specific to the small intestine.

Adhesion molecules and cerebral microvascular hemodynamic abnormalities in sickle cell disease.

Cerebrovascular abnormalities are a common feature of sickle cell disease that may be associated with risk of vaso-occlusive pain crises, microinfarcts, and cognitive impairment. An activated endothelium and adhesion factors, VCAM-1 and P-selectin, are implicated in sickle cell vasculopathy, including abnormal hemodynamics and leukocyte adherence. This study examined the association between cerebral expression of these adhesion factors and cortical microvascular blood flow dynamics by using in-vivo two-photon microscopy. We also examined the impact of blood transfusion treatment on these markers of vasculopathy. Results showed that sickle cell mice had significantly higher maximum red blood cell (RBC) velocity (6.80 ± 0.25 mm/sec, p ≤ 0.01 vs. 5.35 ± 0.35 mm/sec) and more frequent blood flow reversals (18.04 ± 0.95 /min, p ≤ 0.01 vs. 13.59 ± 1.40 /min) in the cortical microvasculature compared to controls. In addition, sickle cell mice had a 2.6-fold (RFU/mm2) increase in expression of VCAM-1 and 17-fold (RFU/mm2) increase in expression of P-selectin compared to controls. This was accompanied by an increased frequency in leukocyte adherence (4.83 ± 0.57 /100 µm/min vs. 2.26 ± 0.37 /100 µm/min, p ≤ 0.001). We also found that microinfarcts identified in sickle cell mice were 50% larger than in controls. After blood transfusion, many of these parameters improved, as results demonstrated that sickle cell mice had a lower post-transfusion maximum RBC velocity (8.30 ± 0.98 mm/sec vs. 11.29 ± 0.95 mm/sec), lower frequency of blood flow reversals (12.80 ± 2.76 /min vs. 27.75 ± 2.09 /min), and fewer instances of leukocyte adherence compared to their pre-transfusion imaging time point (1.35 ± 0.32 /100 µm/min vs. 3.46 ± 0.58 /100 µm/min). Additionally, we found that blood transfusion was associated with lower expression of adhesion factors. Our results suggest that blood transfusion and adhesion factors, VCAM-1 and P-selectin, are potential therapeutic targets for addressing cerebrovascular pathology, such as vaso-occlusion, in sickle cell disease.

Increasing nitric oxide bioavailability fails to improve collateral vessel formation in humanized sickle cell mice.

Sickle cell disease (SCD) is associated with repeated bouts of vascular insufficiency leading to organ dysfunction. Deficits in revascularization following vascular injury are evident in SCD patients and animal models. We aimed to elucidate whether enhancing nitric oxide bioavailability in SCD mice improves outcomes in a model of vascular insufficiency. Townes AA (wild type) and SS (sickle cell) mice were treated with either L-Arginine (5% in drinking water), L-NAME (N(ω)-nitro-L-arginine methyl ester; 1 g/L in drinking water) or NO-generating hydrogel (PA-YK-NO), then subjected to hindlimb ischemia via femoral artery ligation and excision. Perfusion recovery was monitored over 28 days via LASER Doppler perfusion imaging. Consistent with previous findings, perfusion was impaired in SS mice (63 ± 4% of non-ischemic limb perfusion in AA vs 33 ± 3% in SS; day 28; P < 0.001; n = 5-7) and associated with increased necrosis. L-Arginine treatment had no significant effect on perfusion recovery or necrosis (n = 5-7). PA-YK-NO treatment led to worsened perfusion recovery (19 ± 3 vs. 32 ± 3 in vehicle-treated mice; day 7; P < 0.05; n = 4-5), increased necrosis score (P < 0.05, n = 4-5) and a 46% increase in hindlimb peroxynitrite (P = 0.055, n = 4-5). Interestingly, L-NAME worsened outcomes in SS mice with decreased in vivo lectin staining following ischemia (7 ± 2% area in untreated vs 4 ± 2% in treated mice, P < 0.05, n = 5). Our findings demonstrate that L-arginine and direct NO delivery both fail to improve postischemic neovascularization in SCD. Addition of NO to the inflammatory, oxidative environment in SCD may result in further oxidative stress and limit recovery.

PPARγ increases HUWE1 to attenuate NF-κB/p65 and sickle cell disease with pulmonary hypertension.

Sickle cell disease (SCD)-associated pulmonary hypertension (PH) causes significant morbidity and mortality. Here, we defined the role of endothelial specific peroxisome proliferator-activated receptor γ (PPARγ) function and novel PPARγ/HUWE1/miR-98 signaling pathways in the pathogenesis of SCD-PH. PH and right ventricular hypertrophy (RVH) were increased in chimeric Townes humanized sickle cell (SS) mice with endothelial-targeted PPARγ knockout (SSePPARγKO) compared with chimeric littermate control (SSLitCon). Lung levels of PPARγ, HUWE1, and miR-98 were reduced in SSePPARγKO mice compared with SSLitCon mice, whereas SSePPARγKO lungs were characterized by increased levels of p65, ET-1, and VCAM1. Collectively, these findings indicate that loss of endothelial PPARγ is sufficient to increase ET-1 and VCAM1 that contribute to endothelial dysfunction and SCD-PH pathogenesis. Levels of HUWE1 and miR-98 were decreased, and p65 levels were increased in the lungs of SS mice in vivo and in hemin-treated human pulmonary artery endothelial cells (HPAECs) in vitro. Although silencing of p65 does not regulate HUWE1 levels, the loss of HUWE1 increased p65 levels in HPAECs. Overexpression of PPARγ attenuated hemin-induced reductions of HUWE1 and miR-98 and increases in p65 and endothelial dysfunction. Similarly, PPARγ activation attenuated baseline PH and RVH and increased HUWE1 and miR-98 in SS lungs. In vitro, hemin treatment reduced PPARγ, HUWE1, and miR-98 levels and increased p65 expression, HPAEC monocyte adhesion, and proliferation. These derangements were attenuated by pharmacological PPARγ activation. Targeting these signaling pathways can favorably modulate a spectrum of pathobiological responses in SCD-PH pathogenesis, highlighting novel therapeutic targets in SCD pulmonary vascular dysfunction and PH.

Whole Blood Transcriptome Analysis in Children with Sickle Cell Anemia.

Whole transcriptome RNA-sequencing was performed to quantify RNA expression changes in whole blood samples collected from steady state sickle cell anemia (SCA) and control subjects. Pediatric SCA and control subjects were recruited from Atlanta (GA)-based hospital(s) systems and consented for RNA sequencing. RNA sequencing was performed on an Ion Torrent S5 sequencer, using the Ion Total RNA-seq v2 protocol. Data were aligned to the hg19 reference genome and analyzed in the Partek Genomics studio package (v7.0). 223 genes were differentially expressed between SCA and controls (± 1.5 fold change FDR p < 0.001) and 441 genes show differential transcript expression (± 1.5 fold FDR p < 0.001). Differentially expressed RNA are enriched for hemoglobin associated genes and ubiquitin-proteasome pathway genes. Further analysis shows higher gamma globin gene expression in SCA (33-fold HBG1 and 49-fold HBG2, both FDR p < 0.05), which did not correlate with hemoglobin F protein levels. eQTL analysis identified SNPs in novel non-coding RNA RYR2 gene as having a potential regulatory role in HBG1 and HBG2 expression levels. Gene expression correlation identified JHDM1D-AS1(KDM7A-DT), a non-coding RNA associated with angiogenesis, enhanced GATA1 and decreased JAK-STAT signaling to correlate with HBG1 and HBG2 mRNA levels. These data suggest novel regulatory mechanisms for fetal hemoglobin regulation, which may offer innovative therapeutic approaches for SCA.

Role of age and neuroinflammation in the mechanism of cognitive deficits in sickle cell disease.

IMPACT STATEMENT: This study provides crucial information that could be helpful in the development of new or repurposing of existing therapies for the treatment of cognitive deficit in individuals with sickle cell disease (SCD). Its impact is in demonstrating for the first time that neuroinflammation and along with abnormal neuroplasticity are among the underlying mechanism of cognitive and behavioral deficits in SCD and that drugs such as minocycline which targets these pathophysiological mechanisms could be repurposed for the treatment of this life altering complication of SCD.

Higher prevalence of spontaneous cerebral vasculopathy and cerebral infarcts in a mouse model of sickle cell disease.

Stroke is a dramatic complication of sickle cell disease (SCD), which is associated with cerebral vasculopathies including moya moya, intravascular thrombi, cerebral hyperemia, and increased vessel tortuosity. The spontaneous occurrence of these pathologies in the sickle cell mouse model has not been described. Here, we studied Townes humanized sickle cell and age-matched control mice that were 13 months old. We used in vivo two-photon microscopy to assess blood flow dynamics, vascular topology, and evidence of cerebral vasculopathy. Results showed that compared to controls, sickle cell mice had significantly higher red blood cell (RBC) velocity (0.73 mm/s vs. 0.55 mm/s, p = 0.013), capillary vessel diameter (4.84 µM vs. 4.50 µM, p = 0.014), and RBC volume flux (0.015 nL/s vs. 0.010 nL/s, p = 0.021). Also, sickle cell mice had significantly more tortuous capillary vessels ( p < 0.0001) and significantly shorter capillary vessel branches ( p = 0.0065) compared to controls. Sickle cell mice also had significantly higher number of capillary occlusive events (3.4% vs. 1.9%, p < 0.0001) and RBC stalls (3.8% vs. 2.1%, p < 0.0001) in the cerebral capillary bed. In post-mortem immunohistochemical analyses, sickle cell mice had a 2.5-fold higher frequency of cortical microinfarcts compared to control mice. Our results suggest that aged Townes sickle cell mice spontaneously develop SCD-associated cerebral vasculopathy.

Renal protection by atorvastatin in a murine model of sickle cell nephropathy.

Recent studies have demonstrated pleiotropic effects of statins in various mouse models of kidney disease. In this study, Townes humanized sickle cell mice were treated for 8 weeks with atorvastatin at a dose of 10 mg/kg/day starting at 10 weeks of age. Treatment with atorvastatin significantly reduced albuminuria, and improved both urine concentrating ability and glomerular filtration rate. Atorvastatin also decreased markers of kidney injury and endothelial activation, and ameliorated oxidant stress in renal tissues and peripheral macrophages. Atorvastatin downregulated the expression of mRNA levels of the NADPH oxidases, Cybb (also termed Nox2) and Nox4, which are major sources of oxidant stress in the kidney. These findings highlight the pleiotropic effects of atorvastatin and suggest that it may provide beneficial effects in sickle cell nephropathy.

Impaired Collateral Vessel Formation in Sickle Cell Disease.

OBJECTIVE: The adaptive response to vascular injury is the formation of functional collateral vessels to maintain organ integrity. Many of the clinical complications associated with sickle cell disease can be attributed to repeated bouts of vascular insufficiency, yet the detailed mechanisms of collateral vessel formation after injury are largely unknown in sickle cell disease. Here, we characterize postischemic neovascularization in sickle cell disease and the role of neutrophils in the production of reactive oxygen species. APPROACH AND RESULTS: We induced hindlimb ischemia by ligation of the femoral artery in Townes SS (sickle cell) mice compared with AA (wild type) mice. Perfusion recovery, ascertained using LASER (light amplification by stimulated emission of radiation) Doppler perfusion imaging, showed significant diminution in collateral vessel formation in SS mice after hindlimb ischemia (76±13% AA versus 34±10% in SS by day 28; P<0.001; n=10 per group). The incidence of amputation (25% versus 5%) and foot necrosis (80% versus 15%) after hindlimb ischemia was significantly increased in the SS mice. Motor function recovery evaluation by the running wheel assay was also impaired in SS mice (36% versus 97% at 28 days post-hindlimb ischemia; P<0.001). This phenotype was associated with persistent and excessive production of reactive oxygen species by neutrophils. Importantly, neutrophil depletion or treatment with the antioxidant N-acetylcysteine reduced oxidative stress and improved functional collateral formation in the SS mice. CONCLUSIONS: Our data suggest dysfunctional collateral vessel formation in SS mice after vascular injury and provide a mechanistic basis for the multiple vascular complications of sickle cell disease.

Losartan therapy decreases albuminuria with stable glomerular filtration and permselectivity in sickle cell anemia.

Sickle cell nephropathy begins with hyperfiltration and microalbuminuria and may progress to renal failure. The aim of this study was to determine the effects of losartan on glomerular function and albumin excretion in sickle cell anemia (SCA). Individuals with SCA on hydroxyurea with persistent albuminuria were enrolled in a 1-year study of losartan. Glomerular filtration rate (GFR) measured by iohexol clearance, albumin excretion rate (AER), and fractional clearance of dextran were assessed at baseline, short-term (1-2month), and long-term (≥12month) intervals. Twelve subjects (6 microalbuminuria, 6 macroalbuminuria) completed short-term studies; 8 completed long-term studies. Baseline GFR was 112ml/min/1.73m2 (71-147ml/min/1.73m2). AER decreased significantly at the short-term (median decrease -134 mcg/min, p=0.0063). GFR was not significantly-different at short-term or long-term intervals. Dextran clearance improved for diameters smaller than albumin (<36Å) but not larger sizes. Losartan therapy for ≥1year in sickle nephropathy results in lower albumin excretion with stable GFR. Filtration of neutral molecules ≥36Å was not changed by losartan, suggesting that the effect of losartan is a mechanism other than alteration of glomerular filtration size-selectivity.

Sickle Mice Are Sensitive to Hypoxia/Ischemia-Induced Stroke but Respond to Tissue-Type Plasminogen Activator Treatment.

BACKGROUND AND PURPOSE: The effects of lytic stroke therapy in patients with sickle cell anemia are unknown, although a recent study suggested that coexistent sickle cell anemia does not increase the risk of cerebral hemorrhage. This finding calls for systemic analysis of the effects of thrombolytic stroke therapy, first in humanized sickle mice, and then in patients. There is also a need for additional predictive markers of sickle cell anemia-associated vasculopathy. METHODS: We used Doppler ultrasound to examine the carotid artery of Townes sickle mice tested their responses to repetitive mild hypoxia-ischemia- and transient hypoxia-ischemia-induced stroke at 3 or 6 months of age, respectively. We also examined the effects of tPA (tissue-type plasminogen activator) treatment in transient hypoxia-ischemia-injured sickle mice. RESULTS: Three-month-old sickle cell (SS) mice showed elevated resistive index in the carotid artery and higher sensitivity to repetitive mild hypoxia-ischemia-induced cerebral infarct. Six-month-old SS mice showed greater resistive index and increased flow velocity without obstructive vasculopathy in the carotid artery. Instead, the cerebral vascular wall in SS mice showed ectopic expression of PAI-1 (plasminogen activator inhibitor-1) and P-selectin, suggesting a proadhesive and prothrombotic propensity. Indeed, SS mice showed enhanced leukocyte and platelet adherence to the cerebral vascular wall, broader fibrin deposition, and higher mortality after transient hypoxia-ischemia. Yet, post-transient hypoxia-ischemia treatment with tPA reduced thrombosis and mortality in SS mice. CONCLUSIONS: Sickle mice are sensitive to hypoxia/ischemia-induced cerebral infarct but benefit from thrombolytic treatment. An increased resistive index in carotid arteries may be an early marker of sickle cell vasculopathy.

Albuminuria Is Associated with Endothelial Dysfunction and Elevated Plasma Endothelin-1 in Sickle Cell Anemia.

BACKGROUND: The pathogenesis of albuminuria in SCD remains incompletely understood. We evaluated the association of albuminuria with measures of endothelial function, and explored associations of both albuminuria and measures of endothelial function with selected biological variables (vascular endothelial growth factor [VEGF], endothelin-1 [ET-1], soluble fms-like tyrosine kinase-1 [sFLT-1], soluble vascular cell adhesion molecule-1 [soluble VCAM-1] and plasma hemoglobin). METHODS: Spot urine measurements for albumin-creatinine ratio (UACR) and 24-hour urine protein were obtained. Endothelial function was assessed using brachial artery ultrasound with measurements of flow-mediated dilation (FMD), nitroglycerin-mediated dilation (NTMD) and hyperemic velocity. RESULTS: Twenty three subjects with varying degrees of albuminuria were evaluated. UACR was significantly correlated with FMD (ρ = -0.45, p = 0.031). In univariate analysis, UACR was correlated with VEGF (ρ = -0.49; 95% CI: -0.75 --0.1, p = 0.015), plasma hemoglobin (ρ = 0.50; 95% CI: 0.11-0.75, p = 0.013) and ET-1 (ρ = 0.40; 95% CI: -0.03-0.69, p = 0.06). Multivariable analysis showed significant associations of ET-1 (estimate: 455.1 [SE: 198.3], p = 0.02), VEGF (estimate: -1.1 [SE: 0.53], p = 0.04) and sFLT-1 (estimate: -1.14 [SE: 0.49], p = 0.02) with UACR. Only ET-1 (estimate: -8.03 [SE: 3.87], p = 0.04) was significantly associated with FMD in multivariable analyses. Finally, UACR was correlated with both 24-hour urine protein (ρ = 0.90, p < 0.0001) and urine aliquots for albumin-creatinine ratio obtained from the 24-hour urine collection (ρ = 0.97, p < 0.0001). CONCLUSION: This study provides more definitive evidence for the association of albuminuria with endothelial dysfunction in SCD. Elevated circulating levels of ET-1 may contribute to SCD-related glomerulopathy by mediating endothelial dysfunction.

GBT440 increases haemoglobin oxygen affinity, reduces sickling and prolongs RBC half-life in a murine model of sickle cell disease.

A major driver of the pathophysiology of sickle cell disease (SCD) is polymerization of deoxygenated haemoglobin S (HbS), which leads to sickling and destruction of red blood cells (RBCs) and end-organ damage. Pharmacologically increasing the proportion of oxygenated HbS in RBCs may inhibit polymerization, prevent sickling and provide long term disease modification. We report that GBT440, a small molecule which binds to the N-terminal α chain of Hb, increases HbS affinity for oxygen, delays in vitro HbS polymerization and prevents sickling of RBCs. Moreover, in a murine model of SCD, GBT440 extends the half-life of RBCs, reduces reticulocyte counts and prevents ex vivo RBC sickling. Importantly, oral dosing of GBT440 in animals demonstrates suitability for once daily dosing in humans and a highly selective partitioning into RBCs, which is a key therapeutic safety attribute. Thus, GBT440 has the potential for clinical use as a disease-modifying agent in sickle cell patients.

Nonhematopoietic Nrf2 dominantly impedes adult progression of sickle cell anemia in mice.

The prevention of organ damage and early death in young adults is a major clinical concern in sickle cell disease (SCD). However, mechanisms that control adult progression of SCD during the transition from adolescence are poorly defined with no cognate prophylaxis. Here, we demonstrate in a longitudinal cohort of homozygous SCD (SS) mice a link between intravascular hemolysis, vascular inflammation, lung injury, and early death. Prophylactic Nrf2 activation in young SS mice stabilized intravascular hemolysis, reversed vascular inflammation, and attenuated lung edema in adulthood. Enhanced Nrf2 activation in endothelial cells in vitro concurred with the dramatic effect on vascular inflammation in the mice. BM chimeric SS mice lacking Nrf2 expression in nonhematopoietic tissues were created to dissect the role of nonerythroid Nrf2 in SCD progression. The SS chimeras developed severe intravascular hemolysis despite having erythroid Nrf2. In addition, they developed premature vascular inflammation and pulmonary edema and died younger than donor littermates with intact nonhematopoietic Nrf2. Our results reveal a dominant protective role for nonhematopoietic Nrf2 against tissue damage in both erythroid and nonerythroid tissues in SCD. Furthermore, we show that prophylactic augmentation of Nrf2-coordinated cytoprotection effectively impedes onset of the severe adult phenotype of SCD in mice.

Body composition and grip strength are improved in transgenic sickle mice fed a high-protein diet.

Key pathophysiology of sickle cell anaemia includes compensatory erythropoiesis, vascular injury and chronic inflammation, which divert amino acids from tissue deposition for growth/weight gain and muscle formation. We hypothesised that sickle mice maintained on an isoenergetic diet with a high percentage of energy derived from protein (35 %), as opposed to a standard diet with 20 % of energy derived from protein, would improve body composition, bone mass and grip strength. Male Berkeley transgenic sickle mice (S; n 8-12) were fed either 20 % (S20) or 35 % (S35) diets for 3 months. Grip strength (BIOSEB meter) and body composition (dual-energy X-ray absorptiometry scan) were measured. After 3 months, control mice had the highest bone mineral density (BMD) and bone mineral content (BMC) (P < 0·005). S35 mice had the largest increase in grip strength. A two-way ANOVA of change in grip strength (P = 0·043) attributed this difference to genotype (P = 0·025) and a trend in type of diet (P = 0·067). l-Arginine (l-Arg) supplementation of the 20 % diet was explored, as a possible mechanism for improvement obtained with the 35 % diet. Townes transgenic sickle mice (TS; n 6-9) received 0·8, 1·6, 3·2 or 6·4 % l-Arg based on the same protocol and outcome measures used for the S mice. TS mice fed 1·6 % l-Arg for 3 months (TS1.6) had the highest weight gain, BMD, BMC and lean body mass compared with other groups. TS3.2 mice showed significantly more improvement in grip strength than TS0·8 and TS1.6 mice (P < 0·05). In conclusion, the high-protein diet improved body composition and grip strength. Outcomes observed with TS1.6 and TS3.2 mice, respectively, confirm the hypothesis and reveal l-Arg as part of the mechanism.