Effects of preformed proline and proline amino acid precursors (including glutamine) on collagen synthesis in human fibroblast cultures

Proline metabolism shapes the tumor microenvironment: from collagen deposition to immune evasion

Proline is a nonessential amino acid, and its metabolism has been implicated in numerous malignancies. Together with a direct role in regulating cancer cells' proliferation and survival, proline metabolism plays active roles in shaping the tumor microenvironment (TME). Cancer-associated fibroblasts (CAFs) display high rates of proline biosynthesis to support the production of collagen for the extracellular matrix (ECM). Indeed, impaired proline metabolism in CAFs results in reduced collagen deposition and compromises the growth and metastatic spread of cancer. Moreover, the rate of proline metabolism regulates intracellular reactive oxygen species (ROS) levels, which influence the production and release of cytokines from cancer cells, contributing toward an immune-permissive TME. Hence, targeting proline metabolism is a promising anticancer strategy that could improve patients' outcome and response to immunotherapy.

Mitochondrial Pyruvate Carrier Inhibition Attenuates Hepatic Stellate Cell Activation and Liver Injury in a Mouse Model of Metabolic Dysfunction-associated Steatotic Liver Disease

Hepatic stellate cells (HSC) are non-parenchymal liver cells that produce extracellular matrix comprising fibrotic lesions in chronic liver diseases. Prior work demonstrated that mitochondrial pyruvate carrier (MPC) inhibitors suppress HSC activation and fibrosis in a mouse model of metabolic dysfunction-associated steatohepatitis (MASH). In the present study, pharmacologic or genetic inhibition of the MPC in HSC decreased expression of markers of activation in vitro. MPC knockdown also reduced the abundance of several intermediates of the TCA cycle, and diminished α-ketoglutarate played a key role in attenuating HSC activation by suppressing hypoxia inducible factor-1α signaling. On high fat diets, mice with HSC-specific MPC deletion exhibited reduced circulating transaminases, numbers of HSC, and hepatic expression of markers of HSC activation and inflammation compared to wild-type mice. These data suggest that MPC inhibition modulates HSC metabolism to attenuate activation and illuminate mechanisms by which MPC inhibitors could prove therapeutically beneficial for treating MASH.

Proline conjugated chitosan as wound healing material: In vitro studies on the influence of the scaffold on collagen production and wound healing

The present study reports the development of L-proline conjugated chitosan scaffold for wound healing application. Proline plays a beneficial role in collagen synthesis, and as a biochemical, it has the potential to modulate wound healing. In this regard, amino acid L-proline was conjugated onto chitosan, and the scaffolds were synthesised. FTIR and NMR analysis confirmed amino acid conjugation. The prepared scaffold was characterized by studies such as swelling, dissolution, tensile strength, porosity, water-vapor transmission rate and in-vitro healing properties. Cell viability assay showed that the scaffold has no cytotoxicity against the L929 and HaCaT cells. The in-vitro wound healing potential of the scaffold by scratch wound assay on the L929 cell line showed 53.35 ± 2.3 %, 72.96 ± 2.2 %, and 50.89 ± 0.3 % wound closure for CS-P 200, CS-P 400 and CS-P 600, respectively when compared to native CS scaffold (38.86 ± 1.6 %). A similar observation was found with HaCaT cells too. The studies showed that the modified scaffold promotes collagen deposition from fibroblast cells. These findings suggest that scaffold cues remodel the wound microenvironment for a better wound-healing state, and the L-proline conjugated scaffold may have considerable potential as a wound dressing to improve wound healing.

Ascorbic Acid (Vitamin C) as a Cosmeceutical to Increase Dermal Collagen for Skin Antiaging Purposes: Emerging Combination Therapies

Ascorbic acid (AA) is an essential nutrient and has great potential as a cosmeceutical that protects the health and beauty of the skin. AA is expected to attenuate photoaging and the natural aging of the skin by reducing oxidative stress caused by external and internal factors and by promoting collagen gene expression and maturation. In this review, the biochemical basis of AA associated with collagen metabolism and clinical evidence of AA in increasing dermal collagen and inhibiting skin aging were discussed. In addition, we reviewed emerging strategies that have been developed to overcome the shortcomings of AA as a cosmeceutical and achieve maximum efficacy. Because extracellular matrix proteins, such as collagen, have unique amino acid compositions, their production in cells is influenced by the availability of specific amino acids. For example, glycine residues occupy 1/3 of amino acid residues in collagen protein, and the supply of glycine can be a limiting factor for collagen synthesis. Experiments showed that glycinamide was the most effective among the various amino acids and amidated amino acids in stimulating collagen production in human dermal fibroblasts. Thus, it is possible to synergistically improve collagen synthesis by combining AA analogs and amino acid analogs that act at different stages of the collagen production process. This combination therapy would be useful for skin antiaging that requires enhanced collagen production.

Cancer-associated fibroblasts require proline synthesis by PYCR1 for the deposition of pro-tumorigenic extracellular matrix

Elevated production of collagen-rich extracellular matrix is a hallmark of cancer-associated fibroblasts (CAFs) and a central driver of cancer aggressiveness. Here we find that proline, a highly abundant amino acid in collagen proteins, is newly synthesized from glutamine in CAFs to make tumour collagen in breast cancer xenografts. PYCR1 is a key enzyme for proline synthesis and highly expressed in the stroma of breast cancer patients and in CAFs. Reducing PYCR1 levels in CAFs is sufficient to reduce tumour collagen production, tumour growth and metastatic spread in vivo and cancer cell proliferation in vitro. Both collagen and glutamine-derived proline synthesis in CAFs are epigenetically upregulated by increased pyruvate dehydrogenase-derived acetyl-CoA levels. PYCR1 is a cancer cell vulnerability and potential target for therapy; therefore, our work provides evidence that targeting PYCR1 may have the additional benefit of halting the production of a pro-tumorigenic extracellular matrix. Our work unveils new roles for CAF metabolism to support pro-tumorigenic collagen production.

Combination of Glycinamide and Ascorbic Acid Synergistically Promotes Collagen Production and Wound Healing in Human Dermal Fibroblasts

The purpose of this study is to present a novel strategy to enhance collagen production in cells. To identify amino acid analogs with excellent collagen production-enhancing effects, human dermal fibroblasts (HDFs) were treated with 20 kinds of amidated amino acids and 20 kinds of free amino acids, individually at 1 mM. The results showed that glycinamide enhanced collagen production (secreted collagen level) most effectively. Glycine also enhanced collagen production to a lesser degree. However, other glycine derivatives, such as N-acetyl glycine, N-acetyl glycinamide, glycine methyl ester, glycine ethyl ester, and glycyl glycine, did not show such effects. Glycinamide increased type I and III collagen protein levels without affecting COL1A1 and COL3A1 mRNA levels, whereas transforming growth factor-β1 (TGF-β1, 10 ng mL−1) increased both mRNA and protein levels of collagens. Ascorbic acid (AA, 1 mM) increased COL1A1 and COL3A1 mRNA and collagen I protein levels. Unlike TGF-β1, AA and glycinamide did not increase the protein level of α-smooth muscle actin, a marker of differentiation of fibroblasts into myofibroblasts. The combination of AA and glycinamide synergistically enhanced collagen production and wound closure in HDFs to a level similar to that in cells treated with TGF-β1. AA derivatives, such as magnesium ascorbyl 3-phosphate (MAP), 3-O-ethyl ascorbic acid, ascorbyl 2-O-glucoside, and ascorbyl tetraisopalmitate, enhanced collagen production, and the mRNA and protein levels of collagens at 1 mM, and their effects were further enhanced when co-treated with glycinamide. Among AA derivatives, MAP had a similar effect to AA in enhancing wound closure, and its effect was further enhanced by glycinamide. Other AA derivatives had different effects on wound closure. This study provides a new strategy to enhance cell collagen production and wound healing using glycinamide in combination with AA.

Regulation of Extracellular Matrix Production in Activated Fibroblasts: Roles of Amino Acid Metabolism in Collagen Synthesis

Cancer associated fibroblasts (CAFs) are a major component of the tumour microenvironment in most tumours, and are key mediators of the response to tissue damage caused by tumour growth and invasion, contributing to the observation that tumours behave as 'wounds that do not heal'. CAFs have been shown to play a supporting role in all stages of tumour progression, and this is dependent on the highly secretory phenotype CAFs develop upon activation, of which extracellular matrix (ECM) production is a key element. A collagen rich, stromal ECM has been shown to influence tumour growth and metastasis, exclude immune cells and impede drug delivery, and is associated with poor prognosis in many cancers. CAFs also extensively remodel their metabolism to support cancer cells, however, it is becoming clear that metabolic rewiring also supports intrinsic functions of activated fibroblasts, such as increased ECM production. In this review, we summarise how fibroblasts metabolically regulate ECM production, focussing on collagen production, at the transcriptional, translational and post-translational level, and discuss how this can provide possible strategies for effectively targeting CAF activation and formation of a tumour-promoting stroma.

The role of metabolic reprogramming and de novo amino acid synthesis in collagen protein production by myofibroblasts: implications for organ fibrosis and cancer

Fibrosis is a pathologic condition resulting from aberrant wound healing responses that lead to excessive accumulation of extracellular matrix components, distortion of organ architecture, and loss of organ function. Fibrotic disease can affect every organ system; moreover, fibrosis is an important microenvironmental component of many cancers, including pancreatic, cervical, and hepatocellular cancers. Fibrosis is also an independent risk factor for cancer. Taken together, organ fibrosis contributes to up to 45% of all deaths worldwide. There are no approved therapies that halt or reverse fibrotic disease, highlighting the great need for novel therapeutic targets. At the heart of almost all fibrotic disease is the TGF-β-mediated differentiation of fibroblasts into myofibroblasts, the primary cell type responsible for the production of collagen and other matrix proteins and distortion of tissue architecture. Recent advances, particularly in the field of lung fibrosis, have highlighted the role that metabolic reprogramming plays in the pathogenic phenotype of myofibroblasts, particularly the induction of de novo amino acid synthesis pathways that are required to support collagen matrix production by these cells. In this review, we will discuss the metabolic changes associated with myofibroblast differentiation, focusing on the de novo production of glycine and proline, two amino acids which compose over half of the primary structure of collagen protein. We will also discuss the important role that synthesis of these amino acids plays in regulating cellular redox balance and epigenetic state.

Proline-dependent regulation of collagen metabolism

This review is focused on recent data on the role of proline (Pro) in collagen biosynthesis and cellular metabolism. It seems obvious that one of the main substrates for collagen biosynthesis Pro is required to form collagen molecule. The question raised in this review is whether the Pro for collagen biosynthesis is synthesized "de novo", comes directly from degraded proteins or it is converted from other amino acids. Recent data provided evidence that extracellular Pro (added to culture medium) had significant, but relatively little impact on collagen biosynthesis in fibroblasts (the main collagen synthesized cells) cultured in the presence of glutamine (Gln). However, extracellular Pro drastically increased collagen biosynthesis in the cells cultured in Gln-free medium. It suggests that Pro availability determines the rate of collagen biosynthesis and demand for Pro in fibroblasts is predominantly met by conversion from Gln. The potential mechanism of this process as well as possible implication of this knowledge in pharmacotherapy of connective tissue diseases is discussed in this review.

Metabolism in the Tumor Microenvironment

Experiments in culture systems where one cell type is provided with abundant nutrients and oxygen have been used to inform much of our understanding of cancer metabolism. However, many differences have been observed between the metabolism of tumors and the metabolism of cancer cells grown in monoculture. These differences reflect, at least in part, the presence of nonmalignant cells in the tumor microenvironment and the interactions between those cells and cancer cells. However, less is known about how the metabolism of various tumor stromal cell types differs from that of cancer cells, and how this difference might inform therapeutic targeting of metabolic pathways. Emerging data have identified both cooperative and competitive relationships between different cell types in a tumor, and this review examines how four abundant stromal cell types in the tumor microenvironment, fibroblasts, T cells, macrophages, and endothelial cells, contribute to the metabolism of tumors.

Gaping of pectoralis minor muscles: magnitude and characterization of an emerging quality issue in broilers

Recently, a certain number of broiler abattoirs located in different Countries around the World have signaled an emerging quality issue termed "gaping" because of the separation of the fiber bundles affecting the external portion of the bipinnate pectoralis minor muscle. Thus, after defining the criteria to classify the muscles as Normal (NORM), Moderate (MOD), or Severe (SEV) cases, the incidence of gaping under commercial conditions was assessed on a total of 8,600 P. minor obtained from broiler chickens belonging to 43 flocks during a 6-mo period. Then, a total of 180 P. minor were selected based on previously defined criteria to evaluate the main quality traits (pH, color, water-holding/-binding capacity and tenderness), proximate composition, water mobility, and thermal properties as well as metabolic profile through 1H-Nuclear Magnetic Resonance spectroscopy. The average incidence of gaping defect was found to be 16.8% (8.8 and 8.0% MOD and SEV cases, respectively). As for the main quality traits, a reduction in ultimate pH was observed as the severity of the gaping defect increased, with SEV muscles displaying significantly lower values in comparison with NORM (5.96 vs. 6.02; P < 0.01), while MOD showed intermediate values (5.99). Concurrently, if compared with their NORM counterpart, MOD and SEV exhibited higher lightness (53.6 and 54.2 vs. 51.8; P < 0.01) coupled with higher (P < 0.05) cooking losses and longer (P < 0.05) transversal relaxation time of extra-myofibrillar water fraction. Overall, no significant differences were found concerning proximate composition and thermal properties. With regard to the metabolic profile, a significantly lower (P < 0.001) glutamine concentration was found in MOD and SEV muscles that, concurrently, revealed significant (P < 0.05) variations in the metabolites involved in energy-generating pathways. Overall, these findings evidenced that the gaping defect affecting broilers' P. minor muscles have strong similarities with the pale-soft-exudative condition previously described in poultry and likely results from the biochemical processes taking place during the post-mortem conversion of muscle to meat.

A Randomized Controlled Trial to Evaluate the Role and Efficacy of Oral Glutamine in the Treatment of Chemo-radiotherapy-induced Oral Mucositis and Dysphagia in Patients with Oropharynx and Larynx Carcinoma

AIM

To determine the role and efficacy of oral glutamine in the treatment of chemo-radiotherapy-induced oral mucositis and dysphagia in patients with carcinoma of the oropharynx and larynx. The primary objective of this study was to compare the incidence and severity of oral mucositis and dysphagia between the glutamine group (oral glutamine, along with concurrent chemo-radiotherapy) and the control group (concurrent chemo-radiotherapy alone, no glutamine). Secondary objectives were to compare the time to onset of oral mucositis and dysphagia, the incidence of treatment breaks (more than three consecutive radiation fractions missed), and significant weight loss (more than 3 kilograms of weight loss from the baseline) between the two groups.

METHOD

A total of 60 patients with locally advanced carcinoma of the oropharynx and larynx (Stage III - IV) who were receiving concurrent chemo-radiotherapy were randomised to the glutamine group (study arm, n = 30) and the non-glutamine group (control arm, n = 30). All patients were treated by radiotherapy to a total dose of 70 Gy in 35 fractions, along with concurrent weekly injections of cisplatin (40 mg/m²) chemotherapy. Patients in the study arm received 10 gm of oral glutamine two hours before radiotherapy (five days a week during the seven-week course of radiotherapy). In the control arm, glutamine was not given to patients during the chemo-radiotherapy treatment. All patients were assessed for oral mucositis, dysphagia, weight loss, and compliance/gap in the treatment (greater than three consecutive days of radiation missed) until the completion of chemo-radiotherapy. Grading of oral mucositis and dysphagia was done as per the National Cancer Institute, Common Terminology Criteria for Adverse Events version 4.03.

RESULTS

Out of 60 patients, 56 patients (93.33%) completed the full course of chemo-radiotherapy treatment. Twenty-seven patients (96.43%) in the control arm developed Grade III oral mucositis compared to only 12 patients (42.83%) in the glutamine arm (p < 0.001). Twenty-six patients (93%) in the control arm developed Grade III dysphagia compared to only 11 patients (39%) in the glutamine arm (p < 0.001). Glutamine significantly decreased the incidence and severity of mucositis and dysphagia. Glutamine delayed the onset of mucositis and dysphagia. As severe dysphagia was more prevalent in the control arm, feeding by Ryle's tube was required in 17 patients (56.67%) in the control arm versus only in eight patients (26.67%) in the glutamine arm (p = 0.03). Significant weight loss during the treatment was seen in all patients of the control arm (100% patients) compared to only 71% of the patients in the glutamine arm (p = 0.004). In the control arm, 46.67% patients had treatment interruption (gap) compared to 16.67% in the glutamine arm (p = 0.025). Sixteen patients (53%) from the control arm required admission (inpatient care) in the hospital to manage the treatment-toxicity (mucositis and dysphagia) compared to seven patients (23%) from the glutamine arm (p = 0.03).

CONCLUSION

Glutamine significantly decreased the incidence and severity of chemo-radiotherapy-induced oral mucositis and dysphagia. It delayed the onset of oral mucositis and dysphagia, improved the compliance to the chemo-radiotherapy treatment, and reduced the requirement for hospitalization for the management of treatment-induced toxicities in patients with locally advanced carcinoma of the oropharynx and larynx.

The efficacy of sodium azulene sulfonate L-glutamine for managing chemotherapy-induced oral mucositis in cancer patients: a prospective comparative study

Background

The efficacy of sodium azulene sulfonate L-glutamine (GA) in treating oral mucositis caused by the administration of anticancer agents has not been previously elucidated. Therefore, this prospective comparative study was conducted to evaluate the efficacy of GA in treating oral mucositis caused by chemotherapy regimens involving fluorinated pyrimidine anticancer drugs.

Methods

The subjects of this study were patients with oral mucositis of grade 2 or higher while on outpatient chemotherapy regimens involving fluorinated pyrimidine anticancer drugs for colorectal or breast cancer. The subjects were randomly divided into a group that received GA (the GA group) or a group that did not receive GA (the control group) by using the closed-envelope method. GA was administered three times a day every day from the first day of the regimen until the final day. The primary endpoint was the development of oral mucositis of grade 2 or higher. The secondary endpoint was the severity of oral pain, which was judged using an 11-stage numerical rating scale (NRS) ranging from 0 to 10.

Results

The proportion of patients with oral mucositis of grade 2 or higher was 32.4% in the GA group and 57.6% in the control group. The GA group had a significantly lower frequency of occurrence. The changes in the NRS scores before and after the trial began were − 2.9 ± 0.6 in the GA group and − 1.2 ± 0.5 in the control group. The NRS score decreased more significantly in the GA group than in the control group (P = 0.046). One patient stopped GA treatment voluntarily due to nausea; other than nausea, no GA-related side effects were observed.

Conclusions

GA protects against oral mucositis and reduces the severity of prevailing oral mucositis symptoms. Our findings indicate that GA is a highly safe and convenient drug.

Exogenous proline stimulates type I collagen and HIF-1α expression and the process is attenuated by glutamine in human skin fibroblasts

Abundance of proline (Pro) in collagen molecule led us to investigate whether Pro supply affects collagen biosynthesis in human skin fibroblasts. Treatment of the cells with milimolar concentrations (5 and 10 mM) of Pro for 24 and 48 h contributed to increase in α₁ subunit of collagen type I (COL1A1) expression in both cells and culture medium. However, the effect was more pronounced in glutamine-free medium. In such condition, Pro induced collagen expression by about twofold in the cells, while in the medium only by about 30% during 24 h incubation, compared to control. In the presence of glutamine (Gln), exogenous Pro stimulated intracellular collagen expression only by about 30% during 24 h of fibroblasts incubation, and it was not accompanied by adequate increase of collagen secretion into medium. Gln alone stimulated the processes by about 2–3 fold during the course of the experiment. Pro-dependent increase in collagen expression in Gln-free medium was accompanied by increase in prolidase activity and expression of pAkt. In both Gln-free medium and Gln-supplemented medium, Pro induced expression of p53 and HIF-1α. The data suggest that availability of Gln, as a substrate for Pro biosynthesis, determine the utilization of exogenous Pro for the collagen biosynthesis.

The Aryl Hydrocarbon Receptor and Its Ligands Inhibit Myofibroblast Formation and Activation: Implications for Thyroid Eye Disease

Thyroid eye disease (TED) is a degenerative disease that manifests with detrimental tissue remodeling, myofibroblast accumulation, and scarring in the orbit of affected individuals. Currently, there are no effective therapies for TED that target or prevent the excessive tissue remodeling caused by myofibroblast formation and activation. The canonical cytokine that induces myofibroblast formation is transforming growth factor (TGF)-β. The TGF-β signaling pathway is influenced by aryl hydrocarbon receptor (AHR) signaling pathways. We hypothesized that AHR agonists can prevent myofibroblast formation in fibroblasts from patients with TED, and thus AHR ligands are potential therapeutics for the disease. Orbital fibroblasts explanted from patients with TED were treated with TGF-β to induce myofibroblast formation, contraction, and proliferation. We found that AHR ligands prevent TGF-β-dependent myofibroblast formation, and this ability is dependent on AHR expression. The AHR and AHR ligands block profibrotic Wnt signaling by inhibiting the phosphorylation of GSK3β to prevent myofibroblast formation. These results provide new insight into the molecular pathways underlying orbital scarring in TED. These novel studies highlight the potential of the AHR and AHR ligands as future therapeutic options for eye diseases and possibly also for other scarring conditions.

L-glutamine decreases the severity of mucositis induced by chemoradiotherapy in patients with locally advanced head and neck cancer: a double-blind, randomized, placebo-controlled trial

The incidence of severe mucositis in the oral cavity, pharynx and larynx is high among patients with head and neck cancer (HNC) receiving chemoradiotherapy (CRT), resulting in significant pain and impairment of quality of life. The present study investigated whether L-glutamine (glutamine) decreases the severity of mucositis in the oral cavity, pharynx and larynx induced by CRT. This double-blind, randomized, placebo-controlled trial included 40 untreated patients with squamous cell carcinoma of the nasopharynx, oropharynx, hypopharynx or larynx. Patients received 66 or 70 Gy of total radiation at the rate of 2 Gy/fraction daily and 5 fractions/week. Cisplatin (20 mg/m²) and docetaxel (10 mg/m²) were intravenously co-administered once a week for 6 weeks. Patients were randomized to orally receive either glutamine (group G) or placebo (group P) at a dose of 10 g 3 times a day throughout the CRT course. Mucositis was assessed using the National Cancer Institute Common Terminology Criteria for Adverse Events version 3.0. The primary end point was mucositis severity. Mucositis developed in all patients. A maximal mucositis grade of G4 was observed in 0 and 25% group G and P patients, respectively, while that of G2 was observed in 10 and 0% group G and P patients, respectively (p=0.023). Glutamine significantly decreased the maximal mucositis grade (group G, 2.9±0.3; group P, 3.3±0.4; p=0.005) and pain score at weeks 4, 5 and 6. Glutamine significantly decreased mucositis severity in the oral cavity, pharynx and larynx induced by CRT in patients with HNC.

Combination of BCAAs and glutamine enhances dermal collagen protein synthesis in protein-malnourished rats

Skin collagen decreases in protein-malnourished states. Amino acids regulate protein metabolism, glutamine stimulates collagen synthesis through the conversion process to proline and provides 75 % of the intracellular free proline in fibroblasts. However, the impact of these amino acids on collagen synthesis under malnutrition has not been examined. We investigated the effect of amino acids on dermal tropocollagen synthesis in protein-malnourished rats. The fractional synthesis rate (FSR, %/h) of dermal tropocollagen was evaluated by the incorporation of L-[ring-(2)H(5)]-phenylalanine after 4 h infusion of each amino acid and the stable isotope. None of the infused 12 single amino acids (glutamine, proline, alanine, arginine, glutamate, glycine, aspartate, serine, histidine, lysine, phenylalanine and threonine) significantly increased the FSR (P = 0.343, one-way ANOVA). In contrast, amino acid mixtures of essential amino acids + glutamine + arginine (EAARQ) and branched-chain amino acids + glutamine (BCAAQ) significantly increased the FSR compared to saline, but the branched-chain amino acids (BCAAs) and amino acid mixture of collagen protein (AAC) did not alter the FSR (saline, 0.96 ± 0.24 %/h; EAARQ, 1.76 ± 0.89 %/h; BCAAQ 1.71 ± 0.36 %/h; BCAAs, 1.08 ± 0.20 %/h and AAC 1.39 ± 0.35 %/h, P < 0.05, Tukey's test). Proline conversion from glutamine represented only 3.9 % of the free proline in skin, as evaluated by the primed-constant infusion of L-d7-proline and L-α-15N-glutamine in rats. These results suggested that the combination of BCAAQ is a key factor for the enhancement of skin collagen synthesis in protein-malnourished rats. The contribution of extracellular free glutamine on de novo proline synthesis and collagen synthesis is very low in vivo compared to the contribution in vitro.

Importance of amino acid composition to improve skin collagen protein synthesis rates in UV-irradiated mice

Skin collagen metabolism abnormalities induced by ultraviolet (UV) radiation are the major causes of skin photoaging. It has been shown that the one-time exposure of UV irradiation decreases procollagen mRNA expression in dermis and that chronic UV irradiation decreases collagen amounts and induces wrinkle formation. Amino acids are generally known to regulate protein metabolism. Therefore, we investigated the effects of UV irradiation and various orally administered amino acids on skin collagen synthesis rates. Groups of 4–5 male, 8-week-old HR-1 hairless mice were irradiated with UVB (66 mJ/cm²) twice every other day, then fasted for 16 h. The fractional synthesis rate (FSR; %/h) of skin tropocollagen was evaluated by incorporating l-[ring-²H₅]-phenylalanine. We confirmed that the FSR of dermal tropocollagen decreased after UVB irradiation. The FSR of dermal tropocollagen was measured 30 min after a single oral administration of amino acids (1 g/kg) to groups of 5–16 UVB-irradiated mice. Branched-chain amino acids (BCAA, 1.34 ± 0.32), arginine (Arg, 1.66 ± 0.39), glutamine (Gln, 1.75 ± 0.60), and proline (Pro, 1.48 ± 0.26) did not increase the FSR of skin tropocollagen compared with distilled water, which was used as a control (1.56 ± 0.30). However, essential amino acids mixtures (BCAA + Arg + Gln, BCAA + Gln, and BCAA + Pro) significantly increased the FSR (2.07 ± 0.58, 2.04 ± 0.54, 2.01 ± 0.50 and 2.07 ± 0.59, respectively). This result suggests that combinations of BCAA and glutamine or proline are important for restoring dermal collagen protein synthesis impaired by UV irradiation.

Management of oral mucositis in patients who have cancer

Oral mucositis is a clinically important and sometimes dose-limiting complication of cancer therapy. Mucositis lesions can be painful, affect nutrition and quality of life, and have a significant economic impact. The pathogenesis of oral mucositis is multifactorial and complex. This review discusses the morbidity, economic impact, pathogenesis and clinical course of mucositis. Current clinical management of oral mucositis is largely focused on palliative measures such as pain management, nutritional support and maintenance of good oral hygiene. However, several promising therapeutic agents are in various stages of clinical development for the management of oral mucositis. These agents are discussed in the context of recently updated evidence-based clinical management guidelines.

Randomized, placebo-controlled trial of Saforis for prevention and treatment of oral mucositis in breast cancer patients receiving anthracycline-based chemotherapy

BACKGROUND

Oral mucositis (OM) is a frequent complication of mucotoxic cancer therapy, causing significant oral pain, increased infection risk, and impaired functioning. The efficacy and safety of Saforis (glutamine) powder in UpTec for oral suspension was evaluated for the prevention and treatment of OM.

METHODS

Three hundred twenty-six patients developing World Health Organization (WHO) grade >or=2 OM during a chemotherapy screening cycle were randomized to Saforis (n = 163) or placebo (n = 163) 3 times/day during their next chemotherapy cycle (Treatment Cycle 1). Patients were crossed over to the alternate treatment during Treatment Cycle 2. As prespecified in the statistical plan, because of a carryover effect in Treatment Cycle 2 the primary efficacy analysis was based on Treatment Cycle 1 only.

RESULTS

Compared with placebo, Saforis significantly reduced the incidence of clinically significant WHO grade >or=2 OM (38.7% vs. 49.7%; P = .026) and severe WHO grade >or=3 OM (1.2% vs. 6.7%; P = .005) in Treatment Cycle 1. Saforis also significantly reduced the worst Oral Mucositis Assessment Scale ulceration score in Treatment Cycle 1 compared with placebo (mean, 0.23 +/- 0.39 vs. 0.32 +/- 0.45; P = .013). Patients receiving Saforis in Treatment Cycle 1 had a lower-than-expected OM incidence when crossed over to placebo in Treatment Cycle 2, indicating a significant carryover effect (P = .027). The incidence of treatment-emergent adverse events was similar between groups.

CONCLUSIONS

Saforis is safe and effective for preventing and treating OM in patients receiving mucotoxic cancer chemotherapy.

Molecular mechanisms of glutamine action

Glutamine is the most abundant free amino acid in the body and is known to play a regulatory role in several cell specific processes including metabolism (e.g., oxidative fuel, gluconeogenic precursor, and lipogenic precursor), cell integrity (apoptosis, cell proliferation), protein synthesis, and degradation, contractile protein mass, redox potential, respiratory burst, insulin resistance, insulin secretion, and extracellular matrix (ECM) synthesis. Glutamine has been shown to regulate the expression of many genes related to metabolism, signal transduction, cell defense and repair, and to activate intracellular signaling pathways. Thus, the function of glutamine goes beyond that of a simple metabolic fuel or protein precursor as previously assumed. In this review, we have attempted to identify some of the common mechanisms underlying the regulation of glutamine dependent cellular functions.

Global expression profiling of fibroblast responses to transforming growth factor-beta1 reveals the induction of inhibitor of differentiation-1 and provides evidence of smooth muscle cell phenotypic switching

Transforming growth factor-beta1 (TGF-beta1) plays a central role in promoting extracellular matrix protein deposition by promoting the transformation of fibroblasts to myofibroblasts. To gain new insights into the transcriptional programs involved, we profiled human fetal lung fibroblast global gene expression in response to TGF-beta1 up to 24 hours using oligonucleotide microarrays. In this report, we present data for 146 genes that were up-regulated at least twofold at two time points. These genes group into several major functional categories, including genes involved in cytoskeletal reorganization (n = 30), matrix formation (n = 25), metabolism and protein biosynthesis (n = 27), cell signaling (n = 21), proliferation and survival (n = 13), gene transcription (n = 9), and of uncertain function (n = 21). For 80 of these genes, this is the first report that they are TGF-beta1-responsive. The early induction of two members of the inhibitor of differentiation (ID) family of transcriptional regulators, ID1 and ID3, was followed by the up-regulation of a number of genes that are usually expressed by highly differentiated smooth muscle cells, including smooth muscle myosin heavy chain, basic calponin, and smoothelin. These findings were confirmed at the protein level for primary adult lung fibroblasts. ID1 further behaved like a typical immediate-early gene and, unlike ID3, was expressed and induced at the protein level. Immunohistochemical analysis showed that ID1 was highly expressed by (myo)fibroblasts within fibrotic foci in experimentally induced pulmonary fibrosis. ID1 acts as a dominant-negative antagonist of basic helix-loop-helix transcription factors that drive cell lineage commitment and differentiation. These findings have important implications for our understanding of fibroblast transcriptional programming in response to TGF-beta1 during development, oncogenesis, tissue repair, and fibrosis.

Glitazones regulate glutamine metabolism by inducing a cellular acidosis in MDCK cells

We studied the effect of the antihyperglycemic glitazones, ciglitazone, troglitazone, and rosiglitazone, on glutamine metabolism in renal tubule-derived Madin-Darby canine kidney (MDCK) cells. Troglitazone (25 microM) enhanced glucose uptake and lactate production by 108 and 92% (both P < 0.001). Glutamine utilization was not inhibited, but alanine formation decreased and ammonium formation increased (both P < 0.005). The decrease in net alanine formation occurred with a change in alanine aminotransferase (ALT) reactants, from close to equilibrium to away from equilibrium, consistent with inhibition of ALT activity. A shift of glutamine's amino nitrogen from alanine into ammonium was confirmed by using L-[2-(15)N]glutamine and measuring the [(15)N]alanine and [(15)N]ammonium production. The glitazone-induced shift from alanine to ammonium in glutamate metabolism was dose dependent, with troglitazone being twofold more potent than rosiglitazone and ciglitazone. All three glitazones induced a spontaneous cellular acidosis, reflecting impaired acid extrusion in responding to both an exogenous (NH) and an endogenous (lactic acid) load. Our findings are consistent with glitazones inducing a spontaneous cellular acidosis associated with a shift in glutamine amino nitrogen metabolism from predominantly anabolic into a catabolic pathway.

The potential mechanism for glutamine-induced collagen biosynthesis in cultured human skin fibroblasts

Although glutamine (Gln) is known as an important stimulator of collagen biosynthesis in collagen-producing cells, the mechanism and endpoints by which it regulate the process remain largely unknown. Intermediates of Gln interconversion: glutamate (Glu) and pyrroline-5-carboxylate (P5C) stimulate collagen biosynthesis in cultured cells but evoke different maxima of collagen biosynthesis stimulating activity at different times of incubation. P5C was found to be the most potent stimulator of collagen biosynthesis after 6 h of incubation (approx. three-fold increase); after 12 h, it induced increase in collagen biosynthesis to 260%, while at 24 h, the process was decreased to approximately 80% of control values. Glu induced increase in collagen biosynthesis to approximately 180%, 400% and 120% of control values, after 6, 12 and 24 h, respectively, suggesting that after 12 h of incubation, Glu was the most potent stimulator of collagen biosynthesis. Glu was also the most potent stimulator of type I procollagen expression at this time. After 6, 12 and 24 h incubation, Gln induced collagen biosynthesis to approximately 112, 115 and 230% of control values, respectively. Since prolidase is known to be involved in collagen metabolism, the enzyme activity assay was performed in fibroblasts cultured in the presence of Gln, Glu and P5C. While Gln and Glu required 24 h for maximal stimulation of prolidase activity, P5C induced it after 6-12 h. The data suggest that P5C induced collagen biosynthesis and prolidase activity in a shorter time than Gln and Glu. We considered that P5C directly stimulates the processes, while Gln acts through its intermediate-P5C. Reduction of P5C to proline is coupled to the conversion of glucose-6-phosphate (G6P) to 6-phospho-gluconate, catalyzed by G6P dehydrogenase. We have found that dehydroepiandrosterone (DHEA), a potent inhibitor of G6P dehydrogenase, inhibited a stimulatory effect of P5C on collagen synthesis, expression of type I collagen and prolidase activity. Our results postulate a potential mechanism of glutamine-induced collagen biosynthesis through its intermediate - P5C. P5C-dependent activation of nucleotide biosynthesis, prolidase activity and P5C conversion into proline may contribute to the stimulation of collagen biosynthesis.

Glutamine increases collagen gene transcription in cultured human fibroblasts

We have previously shown that glutamine stimulates the synthesis of collagen in human dermal confluent fibroblast cultures (Bellon, G. et al. [1987] Biochim. Biophys. Acta, 930, 39-47). In this paper, we examine the effects of glutamine on collagen gene expression. A dose-dependent effect of glutamine on collagen synthesis was demonstrated from 0 to 0.25 mM followed by a plateau up to 10 mM glutamine. Depending on the cell population, collagen synthesis was increased by 1.3-to 2.3-fold. The mean increase in collagen and non-collagen protein synthesis was 63% and 18% respectively. Steady-state levels of alpha 1(I) and alpha 1(III) mRNAs, were measured by hybridizing total RNA to specific cDNA probes at high stringency. Glutamine increased the steady-state level of collagen alpha 1(I) and alpha 1(III) mRNAs in a dose-dependent manner. At 0.15 mM glutamine, collagen mRNAs were increased by 1.7-and 2.3-fold respectively. Nuclear run-off experiments at this concentration of glutamine indicated that the transcriptional activity was increased by 3.4-fold for the pro alpha 1(I) collagen gene. The effect of glutamine on gene transcription was also supported by the measurement of pro alpha 1(I) collagen mRNA half-life since glutamine did not affect its stability. Protein synthesis seemed to be required for the glutamine-dependent induction of collagen gene expression since cycloheximide suppressed the activation. The effect of glutamine appeared specific because analogues and/or derivatives of glutamine, such as acivicin, 6-diazo-5-oxo-L-norleucine, homoglutamine, ammonium chloride and glutamate did not replace glutamine. The influence of amino acid transport systems through plasma membrane was assessed by the use of 2(methylamino)-isobutyric acid and beta 2-aminobicyclo-(2.2.1)-heptane-2-carboxylic acid. The glutamine-dependent induction of collagen gene expression was found to be independent of transport system A but dependent on transport system L whose inhibition induced a decrease in pro alpha 1(I) collagen gene transcription by an unknown mechanism. Thus, glutamine, at physiological concentrations, indirectly regulates collagen gene expression.

Differential expression of thrombospondin, collagen, and thyroglobulin by thyroid-stimulating hormone and tumor-promoting phorbol ester in cultured porcine thyroid cells

In the present study, we have investigated the potential regulation of thyroglobulin (Tg) and extracellular matrix components synthesis by thyroid-stimulating hormone (TSH) and tetradecanoyl phorbol-13-acetate (TPA) on thyroid cells. Porcine thyroid cells isolated by trypsin-EGTA digestion of thyroid glands were maintained in serum containing medium on poly (L-lysine)-coated dishes. Cells differentiated into follicular or vesicular-like structures were distinguished by their ability to organify Na[125I] and to respond to TSH stimulation. After an incubation of the cells with radiolabeled proline or methionine, two major proteins were identified, p450-480 and p290 (so named because of their molecular masses). Tg (p290) synthesis was demonstrated by the synthesis of [131I]-labeled polypeptides with electrophoretic properties identical to those of authentic Tg molecules. P450-480 resolved to M(r) 190,000 under reducing sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) conditions. It was identified as thrombospondin by its reactivity with a monoclonal anti-human thrombospondin and by peptide sequencing of some of its tryptic fragments that displayed identity to thrombospondin I. Collagen synthesis was demonstrated by the formation of radioactive hydroxyproline and by the synthesis of pepsin-resistant polypeptides ranging from M(rs) 120,000 to 200,000. When the cells were cultured in the presence of 100 nM TPA, the culture medium contents of thrombospondin and collagen were increased by 2.7 and 1.6-fold, respectively, whereas Tg content was decreased by a factor 3.9. In contrast, the acute treatment of control cells with TPA induced a decrease in both Tg and collagen content by factors 3.0 and 1.5, respectively, and an increase in thrombospondin content by a factor 2.5. In the presence of 100 nM TPA, TSH (1 mU/ml) did not counteract the stimulating effect of TPA on extracellular matrix components synthesis. In contrast, when cells were cultured in the presence of TSH alone at concentrations higher than 0.1 mU/ml, collagen and thrombospondin in the medium were decreased by a factor 2.0 and 1.9, respectively, and TSH preferentially activated Tg synthesis. However, no acute response to TSH was observed in cells incubated for 2 days without effectors (control cells). On TSH differentiated cells, TPA decreased both collagen and Tg accumulation by factors 1.2 and 1.8, respectively, whereas it increased the one of thrombospondin by a factor 2. These results, together with the stimulating effect of TPA on TSH mediated cell proliferation, argue for a role of thrombospondin in cell adhesion and migration events within the thyroid epithelium.

Age-related changes in collagen synthesis and degradation in rat tissues. Importance of degradation of newly synthesized collagen in regulating collagen production

During developmental growth, collagens are believed to be continuously deposited into an extracellular matrix which is increasingly stabilized by the formation of covalent cross-links throughout life. However, the age-related changes in rates of synthetic and degradative processes are less well understood. In the present study we measured rates of collagen synthesis in vivo using a flooding dose of unlabelled proline given with [14C]proline and determining production of hydroxy[14C]proline. Degradation of newly synthesized collagen was estimated from the amount of free hydroxy [14C]proline in tissues 30 min after injection. Collagen fractional synthesis rates ranged from about 5%/day in skeletal muscle to 20%/day in hearts of rats aged 1 month. At 15 months of age, collagen fractional synthesis rates had decreased markedly in lung and skin, but in skeletal muscle and heart, rates were unchanged. At 24 months of age, synthesis rates had decreased by at least 10-fold in all tissues, compared with rates at 1 month. The proportion of newly synthesized collagen degraded ranged from 6.4 +/- 0.4% in skin to 61.6 +/- 5.0% in heart at 1 month of age. During aging the proportion degraded increased in all tissues to maximal values at 15 months, ranging from 56 +/- 7% in skin to 96 +/- 1% in heart. These data suggest that there are marked age-related changes in rates of collagen metabolism. They also indicate that synthesis is active even in old animals, where the bulk of collagens produced are destined to be degraded.

The effect of transforming growth factor beta on rates of procollagen synthesis and degradation in vitro

Transforming growth factor beta (TGF beta) is known to stimulate procollagen production and steady-state levels of procollagen mRNAs, but its ability to affect post-translational processing of procollagen has been little studied. This paper demonstrates the application of recently developed ultrasensitive methods for measuring hydroxyproline to assess rates of procollagen synthesis and degradation in vitro with and without TGF beta. Foetal rat fibroblasts synthesized 8.63 +/- 0.21 pmol hydroxyproline/micrograms DNA per h, which corresponds to approx. 40 molecules of procollagen/cell per s. Addition of TGF beta to cultures increased total amounts of procollagen synthesized and degraded by 112% and 82%, respectively, but there was a significant decrease in the proportion of procollagen degraded (control, 38.0 +/- 1.1%; TGF beta, 32.3 +/- 0.9%; P less than 0.005). This study demonstrates a novel mechanism which may contribute to the TGF beta-induced increase in procollagen production by fibroblasts.

Minocycline-treatment of diabetic rats normalizes skin collagen production and mass: possible causative mechanisms

Daily minocycline-treatment of streptozotocin-induced diabetic rats not only prevented a diabetes-caused atrophy of skin collagen mass (10-mos old rats), but also normalized skin collagen mass to match that of growing (ca. 1%/d) non-diabetic controls (4- and 5-mos old rats). The causative mechanism by which minocycline-treatment normalizes skin collagen mass must, in part, be related to a general anabolic effect on growth (body weight) because the effect on skin collagen mass correlates strongly to that on body weight. Consequently, a minocycline-stimulated increase of a systemic factor (such as insulin-like growth factor) is not unlikely. The anabolic effect of minocycline-treatment of diabetic rats is also expressed as a normalized cellular ribosome mass (an index of total protein synthetic capacity) and a normalized absolute rate of collagen production. (Calculation of an absolute rate was justified by an apparent maximum saturation of the prolyl-tRNA pool(s) of skin, maximum saturation obtained by the pool-flooding approach). The normalized skin ribosome amount does not, however, explain a selective effect of minocycline-treatment on collagen production as opposed to that for non-collagen protein, this selective effect measured as relative collagen production. To explain such selectivity, the inhibition of diabetes-induced excess skin collagenase activity seems unlikely. (This inference is based on results from a preliminary study indicating that recently [less than 2 h] synthesized collagen is not degraded by the excess collagenase in skin of diabetic rats). Thus, the principal collagen fraction acted on by pathologically excess collagenase might be collagen at a later stage (greater than 2 h after synthesis) in its life cycle. (Another possibility for the selective effect of minocycline on collagen production, as yet untested, is reduced intracellular procollagen degradation.) Overall, this is the first study aimed at discerning the mechanism(s) by which minocycline-treatment enhances the rate of collagen production in tissues of a diabetic rat. For future studies, the extent to which the positive effect on growth, ribosome mass, and rate of collagen production contributes to the change of collagen mass must, along with the known minocycline-inhibition of collagenase activity, be quantified. Such quantification is a prerequisite for evaluating the chemotherapeutic efficacy of minocycline-treatment on collagen-degradative diseases.

Stimulation of collagen synthesis in fibroblast cultures by a triterpene extracted from Centella asiatica

The drug "Titrated Extract from Centella asiatica" (TECA), used for its stimulating properties on the healing of wounds, is a mixture of 3 terpenes extracted from a tropical plant: asiatic acid (30%, w/w), madecassic acid (30%, w/w) and asiaticoside (40%, w/w). The effects of TECA and its individual components were checked on human foreskin fibroblast monolayer cultures. TECA increased the collagen synthesis in a dose-dependent fashion whereas a simultaneous decrease in the specific activity of neosynthesized collagen was observed. Asiatic acid was found to be the only component responsible for collagen synthesis stimulation. TECA and all three terpenes increased the intracellular free proline pool. This effect was independent of the stimulation of collagen synthesis.

Collagen synthesis in explants from rat intestine

Collagen is the major structural component of the intestinal wall and its metabolism is of special interest for intestinal strength. We describe collagen synthesis in short-term (3 h) incubations of rat intestinal tissue, as measured in terms of incorporation of [3H]proline in collagenase-digestible protein and percentage relative collagen synthesis. In this time span, incorporation of [3H]proline in collagen increases linearly with time and tissue weight. Addition of unlabeled proline during incubation, in excess of the 0.1 microM [3H]proline always present, strongly increases both total protein and collagen synthesis, suggesting that proline transport is rate limiting. Further experiments have been performed in the presence of labeled proline alone and with the addition of 0.35 mM unlabeled proline. Collagen synthesis is significantly higher in colon than in ileum, comprising 0.37 and 0.21%, respectively, of total protein synthesis. Also, collagen synthesis decreases considerably with age, both in ileum and colon. The results presented here demonstrate that rat intestinal explants synthesize measurable amounts of collagen in vitro and that the system used is able to detect changes in in vivo synthetic capability such as those induced by ageing.

Parathyroid hormone alteration of free and tRNA-bound proline specific activities in cultured mouse osteoblast-like cells

The effects of the synthetic amino-terminal fragment of parathyroid hormone [bPTH-(1-34)] on proline uptake and on the specific activities of intracellular free proline and tRNA-bound proline were studied in confluent primary cultures of osteoblast-like cells isolated from neonatal mouse calvaria. Pretreatment of cells for 4 hours with 24 nM bPTH-(1-34) increased subsequent proline uptake by approximately 50-60%; also increased were the specific activities of both intracellular free proline and tRNA-bound proline when [3H]proline was included in the extracellular uptake solution. Specific activities of the free and tRNA-bound proline pools remained elevated after proline uptake times of as long as 30 minutes and 120 minutes, respectively. These results indicate that experiments in which radiolabeled proline is used to evaluate PTH-induced protein synthesis in bone cells must be interpreted cautiously, since apparent changes in protein synthesis might actually reflect, at least in part, PTH-induced changes in the specific activities of precursor pools.