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Metabolic profiles of retinal ganglion cell related tissues. (A) Seventy three low molecular weight metabolites could be reliably detected in retina (n = 8), optic nerve (n = 8) and superior colliculus (SC; n = 8 hemispheres) of Brown Norway rats. Within tissue correlation of metabolites is demonstrated by a circus plot with linkers between metabolites. The number of significantly correlated metabolites is shown as a bar graph in the outer circle. The SC (pink) showed the greatest degree of within tissue correlation of metabolites. (B) Tissue differences were explored by principle component analysis (PCA) which revealed a clear distinction of tissues predominantly along one component (PC1). (C) NAD and related metabolites NADH and nicotinamide were compared between tissues. The optic nerve was most abundant in NAD, NADH, and nicotinamide but had the lowest NAD:NADH ratio, whilst the retina was comparatively low in nicotinamide, and the SC comparatively low in NAD and NADH. **P < 0.01, ***P < 0.001, NS P > 0.05. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
Source publication
Nicotinamide adenine dinucleotide (NAD) is a REDOX cofactor and metabolite essential for neuronal survival. Glaucoma is a common neurodegenerative disease in which neuronal levels of NAD decline. We assess the effects of nicotinamide (a precursor to NAD) on retinal ganglion cells (the affected neuron in glaucoma) in normal physiological conditions...
Contexts in source publication
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... groups that matched the different tissues, confirming globally distinct metabolic profiles (Supplementary Fig. 2A). Metabolites were most highly abundant in the optic nerve, followed by the SC and retina respectively. Correlation of all individual metabolites for all samples demonstrated that the SC had the highest intra-tissue correlation (Fig. 3A). In order to identify distinct metabolic signatures of the discrete tissues we used principle component analysis (PCA). Unsupervised PCA separated samples into discrete tissue groups supporting the HC data with PC1 describing the vast majority of variation (95.3%; Fig. 3B). Creatine, hypotaurine, 2-aminobutyric acid, ...
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... samples demonstrated that the SC had the highest intra-tissue correlation (Fig. 3A). In order to identify distinct metabolic signatures of the discrete tissues we used principle component analysis (PCA). Unsupervised PCA separated samples into discrete tissue groups supporting the HC data with PC1 describing the vast majority of variation (95.3%; Fig. 3B). Creatine, hypotaurine, 2-aminobutyric acid, glycerophosphocholine, and cysteine were the highest contributing loading factors in to PC1 demonstrating that relative abundance remained the largest determinant of tissue type even after scaling to reduce its effects ( Supplementary Fig. 2B and C). We specifically queried how NAD, NADH, ...
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... Supplementary Fig. 2B and C). We specifically queried how NAD, NADH, and NAM vary across these tissues. NAD was higher in retina and optic nerve than in the SC, but NADH was much more abundant in the optic nerve. This results in a lower NAD:NADH ratio in the optic nerve. NAM was relatively low in the retina compared to both the optic nerve and SC (Fig. ...
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... largely similar to normal NT retina, but there was a clear distinction in metabolic profile in the optic nerve and SC (Fig. 4B). PCA demonstrated that NAM induced changes were not sufficient to drive group distinction (Fig. 4B). NAM treatment resulted in 9 changed metabolites (11%) in the retina, 24 in the optic nerve (30%), and 5 in the SC (6%) (Fig. 4C-F, Supplementary Dataset 3). Increased NAD, NADH, and threonine were common to all tissues, with glyceric acid also increased in both retina and optic nerve (Fig. 4G, Supple- mentary Fig. 3). These metabolites alone were sufficient to distinguish NT and NT-NAM samples by HC (Fig. 4G). NAM was only increased in the optic nerve, suggesting that conversion to NAD ...
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... were not sufficient to drive group distinction (Fig. 4B). NAM treatment resulted in 9 changed metabolites (11%) in the retina, 24 in the optic nerve (30%), and 5 in the SC (6%) (Fig. 4C-F, Supplementary Dataset 3). Increased NAD, NADH, and threonine were common to all tissues, with glyceric acid also increased in both retina and optic nerve (Fig. 4G, Supple- mentary Fig. 3). These metabolites alone were sufficient to distinguish NT and NT-NAM samples by HC (Fig. 4G). NAM was only increased in the optic nerve, suggesting that conversion to NAD may be saturated in the optic nerve at this dose ( Supplementary Fig. 3). The NAD:NADH ratio was only significantly altered in the optic nerve (40% increase), as ...
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... metabolites alone were sufficient to distinguish NT and NT-NAM samples by HC (Fig. 4G). NAM was only increased in the optic nerve, suggesting that conversion to NAD may be saturated in the optic nerve at this dose ( Supplementary Fig. 3). The NAD:NADH ratio was only significantly altered in the optic nerve (40% increase), as NAD was increased to a greater proportion than NADH (~2.4 fold compared to ~1.7 fold), suggesting a larger pool of free NAD (Supplementary Fig. 3). ...
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... optic nerve, suggesting that conversion to NAD may be saturated in the optic nerve at this dose ( Supplementary Fig. 3). The NAD:NADH ratio was only significantly altered in the optic nerve (40% increase), as NAD was increased to a greater proportion than NADH (~2.4 fold compared to ~1.7 fold), suggesting a larger pool of free NAD (Supplementary Fig. 3). Pathways analysis revealed that NAM induced changes are predicted to significantly impact nicotinate and nicotinamide metabolism across the retina and optic nerve (Fig. 4H, Supplementary Dataset 4). Arginine biosynthesis is predicted to be affected in the retina, The optic nerve was most abundant in NAD, NADH, and nicotinamide but ...
Citations
... 15 It has been reported that retinal and optic nerve NAD + levels significantly decrease in mice after 14 days of high intraocular pressure treatment. 44 Additionally, mice with diabetes combined with myocardial infarction exhibit a significant reduction in NAD + content in cardiac tissue. 45 Furthermore, the loss of CX43 has been found to significantly decrease NAD + levels in the mouse brain, leading to BBB damage. ...
... There is accumulating evidence that links metabolic failure with loss of RGCS. This includes disturbed glucose, pyruvate, and Nicotinamide adenine dinucleotide (NAD) metabolism in several experimental animal models as well as alterations in the metabolites of human tear and aqueous humor samples taken from primary open angle glaucoma patients (Baltan et al., 2010;Casson et al., 2021;Harder et al., 2020;Myer et al., 2020;Rossi et al., 2019;Tribble et al., 2021;Williams et al., 2017). In addition to playing an important role in cell energy supply, metabolites are also important constituents of neurotransmitters, such as glutamate or Gamma-aminobutyric acid (GABA) that are essential for neurotransmission along the visual pathway. ...
... Tissues were stored at − 80 • C until shipment on dry ice to the Swedish Metabolomics Centre. Measurements were performed as described previously (Tribble et al., 2021). Briefly, 200 µL extraction buffer (80/20 v/v methanol: water) including internal standards and 1 tungsten bead were added to each tube. ...
... Previous studies of RGC metabolism have relied on whole retinal tissue or the enriched total RGC population [16][17][18][19][20] . Although such results have been insightful, they are limited by the small proportional representation of RGCs in the whole retina (1% of cells) and the inability to examine differences among RGCs 21 . ...
... Energetic stress can be a driver of neurodegeneration, and metabolic substrate supplementation can protect RGCs from degenerative models 19,[38][39][40] . Therefore, native differences in metabolic homeostasis could influence neuronal resiliency. ...
... Our experiments provide in vivo proof for this realtime energetic adaptation at a cellular level, and suggest that OXPHOS is a requirement for this metabolic response.We paradoxically found that RGCs that survived ONC had lower baseline ATP levels when examining the surviving cohort as a whole or when isolating the less intrinsically resilient non-RGCs. Numerous studies in multiple neuronal contexts, including in models of RGC degeneration, have shown that neuronal death is associated with energy decline and can be ameliorated by inhibiting aberrant ATP consumption or supplementing energetic substrates19,[38][39][40]62,63 . However, the lower levels of homeostatic ATP we measured in more-resilient RGCs are unlikely to be near metabolic failure. ...
Neuronal function requires high energy expenditure that is likely customized to meet specific signaling demands. However, little is known about diversity of metabolic homeostasis among divergently-functioning types of neurons. To this end, we examined retinal ganglion cells (RGCs), a population of closely related, yet electrophysiologically distinct excitatory projection neurons. Using in vivo 2-photon imaging to measure ATP with single cell resolution, we identified differential homeostatic energy maintenance in the RGC population that correspond to distinct RGC types. In the presence of circuit activity, the most active RGC type (Alpha RGCs), had lower homeostatic ATP levels than other types and exhibited the greatest magnitude of ATP decline when ATP synthesis was inhibited. By simultaneously manipulating circuit activity and mitochondrial function, we found that while oxidative phosphorylation was required to meet ATP demands during circuit activity, it was expendable to maintain resting ATP levels. We also examined ATP signatures associated with survival and injury response after axotomy and report a correlation between low homeostatic ATP and increased survival. In addition, we observed transient ATP increases in RGCs following axon injury. Together, these findings identify diversity of energy handling capabilities of dynamically active neurons with implications for neuronal resilience.
... The findings of this study demonstrated that the pea starch diet significantly elevated the levels of acetyl-CoA and α-ketoglutaric acid within the TCA while having no impact on glucose levels. Acetyl-CoA and α-ketoglutaric acid are critical intermediates in the TCA cycle, a central pathway for energy metabolism [61], indicating that the pea starch diet activated the ileal mucosal energy metabolism pathway independent of glucose metabolism, potentially linked to AA metabolism. AAs such as Asp, Glu, and glutamine are metabolized into TCA cycle intermediates to supply energy [62]. ...
Background
The synchronized absorption of amino acids (AAs) and glucose in the gut is crucial for effective AA utilization and protein synthesis in the body. The study investigated how the starch digestion rate and AA levels impact intestinal AA digestion, transport and metabolism, breast muscle protein metabolism, and growth in grower broilers. A total of 720 21-day-old healthy male Arbor Acres Plus broilers were randomly assigned to 12 treatments, each with 6 replicates of 10 birds. The treatments comprised 3 different starch [corn: control, cassava: rapidly digestible starch (RDS), and pea: slowly digestible starch (SDS)] with 4 different AA levels [based on standardized ileal digestible lysine (SID Lys), 0.92%, 1.02% (as the standard), 1.12% and 1.22%].
Results
An interaction between dietary starch sources and SID Lys levels significantly affected breast muscle yield ( P = 0.033). RDS and SDS diets, or SID Lys levels of 0.92%, 1.02%, or 1.22%, significantly decreased the breast muscle yield of broilers in contrast to the corn starch diet with 1.12% SID Lys ( P = 0.033). The SID Lys levels of 1.12% and 1.22% markedly improved body weight (BW), body weight gain (BWG) from 22 to 42 days of age, and mRNA expression of y ⁺ LAT1 and mTOR while reducing feed intake (FI) and feed/gain ratio (F/G) compared to the 0.92% SID Lys level ( P < 0.05). The SDS diet significantly decreased BW and BWG of broilers from 22 to 42 days of age, distal ileal starch digestibility, jejunal amylase and chymotrypsin activities, and mRNA expression of GLUT2 and y ⁺ LAT1 compared to the corn starch diet ( P < 0.05). The RDS diet suppressed the breast muscle mass by down-regulating expression of mTOR , S6K1 , and eIF4E and up-regulating expression of MuRF , CathepsinB , Atrogin-1 , and M-calpain compared to the corn starch diet ( P < 0.05). Targeted metabolomics analysis revealed that the SDS diet significantly increased acetyl-CoA and α-ketoglutaric acid levels in the tricarboxylic acid (TCA) cycle ( P < 0.05) but decreased the ileal digestibility of Lys, Tyr, Leu, Asp, Ser, Gly, Pro, Arg, Ile, and Val compared to the corn starch group ( P < 0.05).
Conclusion
The SDS diet impaired broiler growth by reducing intestinal starch digestibility, which inhibited intestinal AA and glucose absorption and utilization, increased AA oxidation for energy supply, and lowered the efficiency of protein synthesis. Although the RDS diet resulted in growth performance similar to the corn starch diet, it reduced breast muscle mass by inhibiting protein synthesis and promoting degradation.
Graphical Abstract
... ｜×× 2025 NEURAL REGENERATION RESEARCH www.nrronline.org Perspective nicotinamide alone protects soma, axons, and dendrites as well as providing a strong metabolic neuroprotection in an ocular hypertensive rat model and rotenone-induced retinal ganglion cell degenerative mouse model (Tribble et al., 2021;Cimaglia et al., 2024;Otmani et al., 2024). These results have translated well into the clinic, where it has been demonstrated that nicotinamide supplementation in existing glaucoma patients improves visual function (Hui et al., 2020). ...
... Specifically, this new dietary supplement was designed to combine the action of several natural substances well known in the literature for their neuroprotective and antioxidant effect and IOP-lowering effects, such as citicoline [2,4,12,19], forskolin from Coleus forskohlii [7,18], homotaurine [13,17], epigallocatechin-3-gallate (EGCG) from green tea leaves extract [20][21][22][23][24], and vitamins, which are important cofactors in the metabolic processes necessary for human health and energy metabolism. Moreover, some of the ingredients are also endowed with antioxidant potential, such as thiamine (vitamin B1) [25,26], riboflavin (vitamin B2) [13,[26][27][28], nicotinamide (vitamin B3) [2,11,29,30], pyridoxine (vitamin B6) [13,25,31], folic acid (vitamin B9) [26,32], and α-tocopherol (vitamin E) [33,34]. ...
Background/Objectives: Retinal ganglion cell (RGC) protection represents an unmet need in glaucoma. This study assessed the neuroprotective, antioxidant, and anti-inflammatory effect of a new nutraceutical formulation named Epicolin, based on citicoline, homotaurine, epigallocatechin-3-gallate, forskolin, and vitamins, through in vitro and in vivo studies. Methods: The neuroprotective effect of Epicolin or its single components, and Epicolin compared to an untreated control and two marketed formulations [Formulation G (FG) and N (FN)], was evaluated in neuroblastoma cells (SH-SY5Y) challenged with staurosporine. The antioxidant potential and the scavenging activity of Epicolin compared to the untreated control, and FG and FN, was evaluated in SH-SY5Y cells and through oxygen radical absorbance capacity acellular assay, respectively. Moreover, the protective effect against hypoxic damage was evaluated in Muller cells (MIO-M1) subjected to hypoxia. The efficacy of Epicolin was also evaluated in DBA/2J glaucomatous mice through the use of a pattern electroretinogram (PERG), immunostaining, and real-time PCR. Results: Among the nutraceutical formulations tested, only Epicolin showed a significant neuroprotective effect on SH-SY5Y attributable to the synergistic action of its single ingredients. As for antioxidant and scavenging activity, Epicolin showed a higher efficacy compared to FG and FN. Furthermore, Epicolin showed the same protective effect on MIO-M1 cells reducing HIF-1α expression. Finally, Epicolin treatment on DBA/2J mice protected the RGCs from loss of function, as demonstrated by PERG analysis, and attenuated their death by enhancing brain-derived neurotrophic factor (BDNF) and reducing interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) expression. Conclusions: Epicolin, due to its neuroprotective, antioxidant, and anti-inflammatory properties, represents a promising potential treatment for glaucoma.
... In LHON, mtDNA defects are ubiquitously expressed but phenotypically limited to RGC neurodegeneration and visual loss highlighting the exquisite susceptibility of RGCs to mitochondrial dysfunction 9,13,[16][17][18] . The phenotypic similarities of inherited optic neuropathies and glaucoma have prompted evaluation of the role of mitochondria in the pathogenesis of POAG 9,11,12,19,20 and catalyzed clinical interest in the use of nicotinamide to provide metabolic support to RGCs [21][22][23][24] . ...
... In glaucoma, the primary site of pathological changes is the retinal ganglion cells (RGCs), which are only accessible for study in postmortem studies 43 . Murine studies have identified mitochondrial and metabolic defects in RGCs 14,22,50 and driven clinical studies investigating the role of nicotinamide to prevent neurodegeneration in glaucoma 21,23,24 . Human studies using RGCs are limited, and Tenon's ocular fibroblasts have been used as a surrogate to identify mitochondrial dysfunction in glaucoma by our group and others 27,45,51 . ...
Glaucoma is a sight threatening neurodegenerative condition of the optic nerve head associated with ageing and marked by the loss of retinal ganglion cells. Mitochondrial dysfunction plays a crucial role in the pathogenesis of neurodegeneration in the most prevalent type of glaucoma: primary open angle glaucoma (POAG). All previous mitochondrial genome sequencing studies in POAG analyzed mitochondrial DNA (mtDNA) isolated from peripheral blood leukocytes and have not evaluated cells derived from ocular tissue, which better represent the glaucomatous disease context. In this study, we evaluated mitochondrial genome variation and heteroplasmy using massively parallel sequencing of mtDNA in a cohort of patients with POAG, and in a subset assess the role of somatic mitochondrial genome mutations in disease pathogenesis using paired samples of peripheral blood leukocytes and ocular tissue (Tenon’s ocular fibroblasts). An enrichment of potentially pathogenic nonsynonymous mtDNA variants was identified in Tenon’s ocular fibroblasts from participants with POAG. The absence of oxidative DNA damage and predominance of transition variants support the concept that errors in mtDNA replication represent the predominant mutation mechanism in Tenon’s ocular fibroblasts from patients with POAG. Pathogenic somatic mitochondrial genome mutations were observed in people with POAG. This supports the role of somatic mitochondrial genome variants in the etiology of glaucoma.
... This micronutrient is found mostly in meat (poultry and fish), legumes, nuts and seeds [32]. It is notable, however, that the precise quantity of niacin in the four quartiles of intake was different between studies: in the South Korean population, Q1 corresponded to an intake of <10.15 mg/day [20], while in the United States populations, the lowest consumption was higher (under approximately 15 mg/day [27,29] or under 19-20 mg/day [28,29]). Similarly, the highest quartile of intake was different between studies. ...
Background: Glaucoma is a progressive optic neuropathy, characterised by a complex pathophysiology, with mitochondrial dysfunction playing a significant role in the cellular damage and apoptosis of ganglion cells. Niacin is a precursor to several molecules acting as coenzymes in the mitochondrial production of ATP, in DNA repair and in the reduction of reactive oxygen species. The objective of this systematic review is to assess the impact of daily niacin intake on glaucoma. Methods: Case–control and cohort studies regarding niacin and glaucoma, indexed in PubMed, Web of Science, Cochrane and Scopus, were included. Other study methodologies, studies regarding niacin in other ocular disease or other nutrients in glaucoma were excluded. Bias was assessed using the Newcastle–Ottawa Scale. The study protocol was registered in the PROSPERO database (no. CRD42024578889). Results: Five case–control studies were included. In the pooled analysis, a significantly higher proportion of patients with high niacin consumption was found in the group without glaucoma compared to those with glaucoma as defined by ISGEO criteria (p-value < 0.00001; OR = 0.66, 95% CI 0.55–0.79) or as defined by retinal imaging (p-value = 0.02; OR = 0.63, 95% CI 0.43–0.94). Conclusions: Daily dietary intake of niacin is significantly lower in patients with glaucoma compared to the general population. Given different average daily intakes of niacin in these populations, different glaucoma definitions and several confounding variables which weaken the associations, large sample, standardised randomised controlled trials are needed to confirm the potential benefits of niacin in glaucoma.
... WLD S and Nmnat gene therapy's preservation of RGC electrical function in ocular hypertensive mice, suggesting a role for NMNAT2 in maintaining RGC somal viability (5,7,8,56). It is also important to consider manipulations like WLD S and Nmnat1 gene therapy preserved both RGC somas and axons in DBA/2J mice (5)(6)(7)57). This could suggest protection of both the RGC soma and axon is required for protection of somal viability after glaucoma-relevant injury. ...
Glaucoma is characterized by programmed cell death of retinal ganglion cells (RGCs) after axonal injury. Several studies have shown the cell-intrinsic drivers of RGC degeneration act in a compartment-specific manor. Recently, the transcription factors JUN and DDIT3 were identified as critical hubs regulating RGC somal loss after mechanical axonal injury. It is possible somal DDIT3/JUN activity initiates axonal degeneration mechanisms in glaucoma. Alternatively, DDIT3/JUN may act downstream of inciting degenerative mechanisms and only drive RGC somal loss. The MAP2Ks MKK4 and MKK7 control all JNK/JUN activity and can indirectly activate DDIT3. Furthermore, MKK4/7 have been shown to drive RGC axonal degeneration after mechanical axonal injury. The present work investigated whether JUN and DDIT3, or their upstream activators MKK4 and MKK7, control degeneration of RGC axons and somas after glaucoma-relevant injury. Ddit3/Jun deletion did not prevent axonal degeneration in ocular hypertensive DBA/2J mice but prevented nearly all RGC somal loss. Despite robust somal survival, Ddit3/Jun deletion did not preserve RGC somal viability (as assessed by PERG decline and soma shrinkage) in DBA/2J mice or after glaucoma-relevant mechanical axonal injury. In contrast, Mkk4/7 deletion significantly lessened degeneration of RGC somas and axons, and preserved somal function and size after axonal injury. In summary, activation of MKK4 and MKK7 appears to be the inciting mechanism governing death of the entire RGC after glaucoma-relevant injury; driving death of the RGC soma (likely through activation of DDIT3 and JUN), decline in somal viability, and axonal degeneration via DDIT3/JUN-independent mechanisms.
... ROS clearance, mitochondrial protection, and CaMKII/CREB pathway activation are promising treatments for glaucoma. [36][37][38][39] In this study, we developed hypoxia and ROS dual response nano drugs (HOLN-NPs), which can release Nico and OA under hypoxic environments and ROS conditions. In vitro studies demonstrated HOLN-NPs scavenged ≈70% of H 2 O 2 and ≈90% of •ABTS + , showing excellent ROS scavenging ability. ...
Glaucoma is an irreversible blinding eye disease characterized by retinal ganglion cell (RGC) death.Previous studies have demonstrated that protecting mitochondria and activating the CaMKII/CREB signaling pathway can effectively protect RGC and axon. However, currently treatments are often unsatisfactory, and the pathogenesis of glaucoma requires further elucidation. In this study, a ROS‐responsive dual drug conjugate (OLN monomer) is first designed that simultaneously bonds nicotinamide and oleic acid. The conjugate self‐assembled into nanoparticles (uhOLN‐NPs) through the aggregation of multiple micelles and possesses ROS scavenging capability. Then, a polymer with a hypoxic response function is designed, which encapsulates uhOLN‐NPs to form nanoparticles with hypoxic and ROS responses (HOLN‐NPs). Under hypoxia in RGCs, the azo bond of HOLN‐NPs breaks and releases uhOLN‐NPs. Meanwhile, under high ROS conditions, the thioketone bond broke, leading to the dissociation of nano‐prodrug. The released nicotinamide and oleic acid co‐scavenge ROS and activate the CaMKII/CREB pathway, protecting mitochondria in RGCs. HOLN‐NPs exhibit a significantly superior protective effect on R28 cells in glutamate models of glaucoma. The accumulation of HOLN‐NPs in retinal RGCs lead to significant inhibition of RGC apoptosis and axonal damage in vivo. Notably, HOLN‐NPs provide a new therapeutic approach for patients with neurodegenerative disease.
