Retinal capillaries: proliferation of mural cells in vitro

Connection of pericyte-angiopoietin-Tie-2 system in diabetic retinopathy: friend or foe?

Pericytes are distinctive regulators of vascular morphologenesis and function during vascular development and homeostasis. Pericytes have recently come into focus as implications of aberrant interactions between pericytes and endothelial cells in number of pathological angiogenesis conditions, including diabetic retinopathy and tumor angiogenesis. Pericyte dropout is a hallmark of early diabetic retinopathy. Abnormal angiopoietin (Ang)-Tie-2 signaling is one principal system participating in pericyte/endothelial cell dissociation during early stages of diabetic retinopathy. Angiopoietin 2 (Ang-2) is among the relevant growth factors induced by hypoxia and plays an important role in the initiation of retinal neovascularization and cause pericyte loss. Furthermore, high levels of VEGF synergize Ang-Tie-2 signaling during the development of diabetic retinopathy. An accelerated rate of clinical development Ang-Tie-2-manipulating drugs requests a better mechanistic understanding the connection between pericytes and Ang-Tie-2 systems both under normal and disease conditions. We summarize recent advances in pericyte study in conjunction with Ang-Tie-2 signaling and also discuss possible therapeutic strategies for diabetic retinopathy by targeting pericytes through manipulating Ang-Tie-2 signaling.

VEGFR1-mediated pericyte ablation links VEGF and PlGF to cancer-associated retinopathy

VEGF coordinates complex regulation of cellular regeneration and interactions between endothelial and perivascular cells; dysfunction of the VEGF signaling system leads to retinopathy. Here, we show that systemic delivery of VEGF and placental growth factor (PlGF) by protein implantation, tumors, and adenoviral vectors ablates pericytes from the mature retinal vasculature through the VEGF receptor 1 (VEGFR1)-mediated signaling pathway, leading to increased vascular leakage. In contrast, we demonstrate VEGF receptor 2 (VEGFR2) is primarily expressed in nonvascular photoreceptors and ganglion cells. Moreover, blockade of VEGFR1 but not VEGFR2 significantly restores pericyte saturation in mature retinal vessels. Our findings link VEGF and PlGF to cancer-associated retinopathy, reveal the molecular mechanisms of VEGFR1 ligand-mediated retinopathy, and define VEGFR1 as an important target of antiangiogenic therapy for treatment of retinopathy.

Attenuation of proliferation and migration of retinal pericytes in the absence of thrombospondin-1

Perivascular supporting cells, including vascular smooth muscle cells (VSMCs) and pericytes (PCs), provide instructive signals to adjacent endothelial cells helping to maintain vascular homeostasis. These signals are provided through direct contact and by the release of soluble factors by these cells. Thrombospondin (TSP)1 is a matricellular protein and an autocrine factor for VSMCs. TSP1 activity, along with that of PDGF, regulates VSMC proliferation and migration. However, the manner in which TSP1 and PDGF impact retinal PC function requires further investigation. In the present study, we describe, for the first time, the isolation and culture of retinal PCs from wild-type (TSP1(+/+)) and TSP1-deficient (TSP1(-/-)) immortomice. We showed that these cells express early and mature markers of PCs, including NG2, PDGF receptor-beta, and smooth muscle actin as well as desmin, calbindin, and mesenchymal stem cell markers. These cells were successfully passaged and maintained in culture for several months without significant loss of expression of these markers. TSP1(+/+) PCs proliferated at a faster rate compared with TSP1(-/-) PCs. In addition, TSP1(+/+) PCs, like VSMCs, responded to PDGF-BB with enhanced migration and proliferation. In contrast, TSP1(-/-) PCs failed to respond to the promigratory and proliferative activity of PDGF-BB. This may be attributed, at least in part, to the limited interaction of PDGF-BB with TSP1 in null cells, which is essential for PDGF proliferative and migratory action. We observed no significant differences in the rates of apoptosis in these cells. TSP1(-/-) PCs were also less adherent, expressed increased levels of TSP2 and fibronectin, and had decreased amounts of N-cadherin and alpha(v)beta(3)-integrin on their surface. Thus, TSP1 plays a significant role in retinal PC proliferation and migration impacting retinal vascular development and homeostasis.

Cultured ocular cells and extracellular matrices: role of growth factors, retinoic acid and cell polarity

Culture of various types of cells on gelled, reconstituted extracellular matrices results in decreased cellular proliferation. In the present study, we evaluated several possible mechanisms for this inhibition, as applied to cultured bovine retinal microvascular endothelial cells (EC) or to retinal pigment epithelial (RPE) cells: whether the inhibition might be related to (a) inactivation of fibroblast growth factor (FGF) by binding of the molecules present in the medium to a matrix component; (b) release of an inhibitor by the matrix in culture; or (c) inhibitory properties of the matrix macromolecules themselves. Our results suggest that mechanism (c) is most likely. The reasons are, first, that culture of EC or RPE cells on several different extracellular matrix substrates in the presence of logarithmically increasing concentrations of acidic or basic fibroblast growth factors (aFGF or bFGF) leads to a vertical shift of the plots of cell number after 4 days in culture vs. log growth factor concentration for both types of cells. The same result obtains when cells are cultured with logarithmically increasing concentrations of all-trans retinoic acid, which inhibits EC but not RPE cell proliferation in a dose-dependent fashion. This is consistent with mechanism (b) or (c), but not (a), for which one would expect a horizontal shift. Second, washing the matrices prior to the plating of cells with 1M NaCl, which elutes aFGF and partially elutes bFGF molecules from basement membranes, does not alter the growth of cells plated after the wash. This suggests also that growth factor binding to the matrix is not a likely mechanism for the observed inhibition. Incubation of matrices with culture medium prior to plating cells does not usually alter the ability of the medium thus "conditioned" to support cell growth, arguing against the possibility that the matrices release a soluble activator or inhibitor of such growth. However, in some experiments performed with lots of Matrigel (a commercially available basement membrane extract from a murine tumor) obtained prior to mid-1991, media "conditioned" by incubation with this matrix did show enhanced ability to facilitate EC and RPE cell proliferation. Finally, if RPE cells or EC are plated on various substrates, allowed to attach for 24 hr., and then the same or other substrates are poured over the cells, the effect on proliferation of the matrices plated on the apical surfaces of the cells is often less than that of matrices plated adjacent to their basal surfaces. Although in most cases these differences are not statistically significant, there is an apparent trend.(ABSTRACT TRUNCATED AT 400 WORDS)

Capillary pericytes: perspectives and future trends

A complete understanding of the microcirculation requires full knowledge of the structure and function of each of the constituent cells, including pericytes. Vascular endothelium and smooth muscle cells have been investigated intensively during the last two decades, but much less is known about the metabolism and function of capillary pericytes. However, the development of new electron microscopy techniques and the application of new cell culture and molecular biology techniques should allow for the rapid elucidation of the cellular biochemistry and the microvascular function and pathology of this ubiquitous capillary cell.

The growth and behaviour of rat retinal Müller cells in vitro. 1. An improved method for isolation and culture

Eyeballs were enucleated from young (postnatal day 8-12) pigmented rats and the retinas were dissected free after soaking the globes overnight in growth medium. The retinas were digested with enzymes, dissociated and maintained in stationary culture in 10% serum supplemented growth medium. Cultures displayed extensive cellular outgrowth after 1-5 days, with abundant fusiform and epithelioid cells. Removal of aggregates and cellular debris after 6-7 days yielded a purified flat cell preparation, which could be maintained either as a primary culture for several weeks or passaged repeatedly as rapidly proliferating epithelioid cells. Staining with monoclonal antibodies RET-G1, G3 and G7, and polyclonal S-100, glutamine synthetase and carbonic acid anhydrase antisera, all markers for Müller cells, showed positive labelling of all cells present in these purified cultures, both primary and passaged cells. This contrasted with the use of RET-G2, anti Factor VIII and anti glial fibrillary acidic protein (GFAP) antibodies. RET-G2, another Müller cell marker, failed to recognize passaged cells. Anti Factor VIII also did not label any cells, and anti GFAP stained very few cells: these remained associated with aggregated material so that vigorous washing to remove loosely adherent tissue from primary cultures resulted in the total absence of GFAP positive cells. In addition, no GFAP positive cells were detected in passaged cells or in cells regrown following freezing and storage. The Müller cell nature of these flat cells in soaked retinal cultures was further supported by the specific uptake of 5-bromo-deoxyuridine by nuclei located within the inner nuclear layer of retinal fragments in vitro. Hence the soaking treatment greatly reduces the number of surviving astrocytes whilst stimulating the rapid growth of cells expressing many properties of mature retinal Müller cells.

Proliferative response and macromolecular synthesis by ocular cells cultured on extracellular matrix materials

To investigate the effects of extracellular matrix components on cellular function, we cultured several types of ocular cells on substrates composed of extracellular matrix materials that were layered on culture dishes either as dried films or as gels. We measured cellular proliferation on these substrates and on a series of gels composed of varying proportions of rat tail tendon type I collagen and Matrigel, a commercially available extract of a basement membrane-producing murine tumor. In addition, we studied the biosynthesis of collagens and of proteoglycans by these cultured cells using [3H]-L-proline and [35S]-sulfate. The proliferative abilities of the various types of ocular cells on the dried film substrates, on uncoated plastic culture vessels, and on pure type I collagen gel, were similar. However, proliferation of ocular cells cultured on gels composed of greater than or equal to 90% Matrigel was markedly reduced. There was little or no inhibition of growth of two types of non-ocular cells: rat C6 astrocytoma cells, and human dermal fibroblasts. Histologic studies showed that the ocular cells tested often formed long strands and capillary-like tubes, and tended to "burrow" beneath the surface of substrates containing high percentages of Matrigel. Fibroblasts infrequently formed tubes, and exhibited the burrowing property also on gels containing primarily type I collagen, while C6 cells showed neither of these behaviors on any of the matrices tested. The elution pattern of newly synthesized [3H]-labeled and [35S]-labeled macromolecules produced by all of the cultured cell types, and detected by Sepharose CL-4B chromatography in the medium and in the cell layer plus matrix fractions did not vary following culture on the different substrates. Approximately twofold more of the newly synthesized collagens and proteoglycans were deposited in the cell layer plus matrix, and proportionately less appeared in the medium, when cells were cultured on type I collagen gels and on Matrigel than on the dried film substrates. These experiments demonstrate the influence of the extracellular matrix on several aspects of cell behavior, and provide further evidence that modification of the composition of the extracellular matrix may be an important determinant of normal or pathological cell function.

ATP causes retinal pericytes to contract in vitro

We evaluated the contractility of bovine retinal microvascular pericytes in culture by permeabilizing the cells with 0.1% Triton X-100 and measuring their response to MgATP. Sequential photographs of the cells were taken over 20 min and their surface areas were measured. Our study directly demonstrates that pericytes are contractile cells, which respond to MgATP in a dose-dependent fashion over a relatively short time course (minutes). Pericytes did not contract in response to GTP, pyrophosphate or beta, gamma-methylene ATP. Immunofluorescence study showed the presence of muscle actin in Triton X-100-treated cells before and after contraction, indicating preservation of this cytoskeletal protein even after treatment with the detergent. Similar experiments on human umbilical vein endothelial cells, bovine lens epithelial cells and human retinal pigment epithelial cells showed that these cells were significantly less contractile than retinal pericytes. That pericytes show substantial contraction over a short time course indicates that these cells may play a major role in regulating blood flow in the microcirculation.

Analysis of glycosaminoglycans in bovine retinal microvessel basement membrane

Glycosaminoglycans (GAG) were isolated from bovine retinal microvessel basement membrane (RMV-BM) and quantitatively analyzed using a recently described competitive binding assay that is specific for and sensitive to nanogram amounts of heparan and chondroitin sulfates. Treatment of osmotically lysed retinal microvessels with the ionic detergent deoxycholate (DOC), required for liberation of the extracellular matrix for plasma membrane lipoproteins and purification of the insoluble matrix, solubilized less than 5% of the GAG in the water-insoluble material. Total GAG content in the DOC-insoluble basement membranes was approx. 0.52 micrograms/mg dry weight; about 70% of the measurable GAG was resistant to both chondroitinase ABC and chondroitinase AC digestion and was sensitive to nitrous acid treatment, indicating its heparan sulfate nature. Cellulose acetate electrophoresis revealed two bands, one of which had an electrophoretic mobility similar to heparan sulfate standard and was sensitive to nitrous acid; the other migrated in the same position as chondroitin sulfate standard and was sensitive to chondroitinase ABC and chondroitinase AC digestion. These results provide evidence that RMV-BM contains chondroitin sulfate(s) as well as heparan sulfate, and offer the first quantitative analysis of GAG in this extracellular matrix.

Characteristics of lung pericytes in culture including their growth inhibition by endothelial substrate

Pericytes and endothelial cells from the same sample of adult rat lung have been separately established in culture by use of selective growth media. The endothelial cells are positive and the pericytes negative for angiotensin-converting enzyme activity and tissue plasminogen activator. Morphologically in culture, the pericytes are similar to pericytes from bovine retina and other sites and show positive immunofluorescence to both human platelet (non-muscle) myosin and smooth muscle myosin. In this respect they resemble smooth muscle cells grown from the rat main pulmonary artery, but lack the myofilaments and dense bodies characteristic of muscle cells. Lung endothelial cells and fibroblasts are positive only for platelet myosin. Pericytes in culture demonstrate an unusual growth response to endothelial substrate, obtained by removing confluent endothelial monolayers with nonionic detergent or alkali. When plated onto this material at low density, pericyte growth is inhibited. By contrast, the substrate stimulates the growth of endothelial cells and has no effect on smooth muscle cells. Initial attachment of endothelial cells and pericytes to the substrate is similar.

The isolation and culture of endothelial cells and pericytes from the bovine retinal microvasculature: a comparative study with large vessel vascular cells

Endothelial cells (BREC) and pericytes (BRP) were isolated from the bovine retinal microvasculature. These cells were first identified by morphological criteria and by their differential staining for Factor VIII related antigen. BREC and BRP responded differently to a number of experimental parameters in vitro; for example, the plating efficiency of BREC was enhanced by the use of a gelatin substratum and medium conditioned by either endothelial cells or pericytes; oxygen tension had no effect. In contrast, the plating efficiency of BRP was only enhanced by low oxygen tension. Conditioned media also stimulated the proliferation of BREC, but not that of BRP. The saturation density reached by BREC was dependent on the initial plating density while BRP plated at different initial densities reached the same final density. The in vitro behavior of the retinal microvascular cells was also compared to that of large vessel (aorta) endothelial cells (BAEC) and smooth muscle cells (SMC). Aortic and retinal endothelial cells showed similar morphology and behavior. When initially plated as a homogeneous cell suspension within a collagen matrix, both BREC and BAEC self-associated to form three-dimensional meshworks; this morphogenesis was accomplished by cell migration and did not involve cell proliferation. By contrast, BRP and SMC divided and remained homogeneously distributed when plated within a collagen gel matrix. BRP and SMC did, however, behave differently when plated on the surface of a collagen gel; SMC migrated extensively into the gel while BRP remained confined to the gel surface. BRP grown on any substratum began to retract upon themselves shortly after confluence, producing characteristic nodules interconnected by cellular strands. BRP and SMC were able to contract a collagen gel substratum, while retinal and aortic endothelial cells were unable to do so. These results provide new means for the in vitro characterization of endothelial cells, smooth muscle cells and pericytes.

Aldose reductase activity and basement membrane thickening

Rats fed a high-galactose diet develop marked thickening of their retinal capillary basement membranes. The effect is prevented if the animals also receive the aldose reductase inhibitor sorbinil. The effect does not appear to be due to aldose reductase itself, since immunoreactive aldose reductase has not been found in the retinal microvasculature of the rat but rather to a related enzyme with similar substrate specificity. The detailed biochemical mechanism for basement membrane thickening is obscure, involving an alteration of the extracellular matrix, where aldose reductase and similar enzymes have not been described; osmotic damage to the microvascular cells, such as has been described following aldose reductase-induced sugar alcohol accumulation in lens epithelial cells, is not apparent in diabetic or galactosemic animals. It is possible that concentrations of intracellular sugar alcohols that do not substantially change the osmolarity of the cell cytosol alter intracellular enzyme activities. This, in turn, could affect the biosynthesis of extracellular matrix macromolecules, as suggested, for example, by the hypothesis of Rohrbach et al, based on studies of a basement membrane-producing tumor implanted in diabetic mice, which proposes that the hyperglycemia of diabetes mellitus causes a reduced synthesis of the heparan sulfate BM-1 proteoglycan with a subsequent overproduction of type IV collagen. This and other hypotheses of basement membrane thickening can be tested in diabetic or galactosemic rats, some of which receive aldose reductase inhibitors, or in retinal microvascular pericytes and endothelial cells grown in culture.

Collagens of the retinal microvascular basement membrane and of retinal microvascular cells in vitro

We have analysed the collagens present in vascular basement membranes isolated from bovine retinal and cerebral microvessels and bovine renal glomeruli, and from the non-vascular basement membrane of bovine lens capsule. These are compared with the collagens produced by cultured bovine retinal microvascular pericytes and lens epithelial cells, and by canine retinal microvascular endothelial cells, in vitro. Biochemical and immunocytochemical analyses indicate that all of the vascular basement membrane preparations have an identical collagenous composition, consisting of the same polypeptides present in lens capsule (primarily type IV collagen), together with other polypeptides that are identified as type I, and a small amount of type III collagen. Identification of the latter is based on two-dimensional gel electrophoresis in the presence and absence of a reducing agent. Immunocytochemical studies, however, demonstrate type I, type IV and some type V collagen in the basement membranes of the isolated microvessels. The cultured microvascular cells produce predominantly type I collagen molecules, but they also produce other collagen peptides that appear to be type IV, and, at least in some experiments, small amounts of type III collagen. The biochemical identification of collagens type I and IV is confirmed by immunocytochemistry. However, results with anti-type I collagen and procollagen antibodies in cultured pericytes vary with antibodies from different sources. The quantities of the type IV peptides produced by the cultured cells also vary in different experiments.

On the pathogenesis of diabetic retinopathy

Recent investigations of retinal vascular cells in tissue culture, animal models, and diabetic human subjects suggest several potential pathogenetic mechanisms for diabetic retinopathy. These include the enzyme aldose reductase, which appears to be responsible for basement membrane thickening in galactosemic rats (since the lesion is prevented by an aldose reductase inhibitor), and a picture, in galactosemic dogs, that closely resembles early, background diabetic retinopathy; insulin, which stimulates, and elevated glucose levels, which inhibit in vitro proliferation of retinal pericytes. Various hormones, including the sex hormone, the insulin-like growth factors and, perhaps independently, growth hormones, may influence the later stages of diabetic retinopathy. Chronic hyperglycemia appears to be the primary pathogenetic agent in diabetic retinopathy as well as in other complications of diabetes, but the different rates of onset and progression of these complications suggest that glucose acts through different biochemical pathways that are probably under different genetic control. Finally, the locus of the primary biochemical lesion in diabetic retinopathy may reside in the neuronal or glial cells of the retina, with the retinal blood vessels only secondarily involved.

Human retinal vessels in tissue culture. A preliminary report of the effect of acute glucose poisoning on cultured vascular cells

To delineate the factors involved in the pathogenesis of human retinal vasculopathies, as in vitro model of human retinal vascular cells was developed by using cadaver eyes enucleated four to eight hours after death and stored at +4 C for three to seven days. A pure, viable capillary explant was obtained by microdissection and gentle agitation; the more rapidly occurring postmortem changes in the surrounding nervous tissue of the retina facilitated separation of the vascular explants. Factor VIII indirect immunofluorescent staining revealed that 85% to 90% of the cells harvested from capillaries of 3- to 5-day-old cadaver eyes and all cells cultured from 1-week-old postmortem eyes reacted positively, indicating their endothelial nature. High-glucose medium caused degenerative changes in the cells of the initial explant as well as in the cells of confluent cultures within 24 to 72 hours. The cytotoxic effect of glucose was manifested by accumulation of PAS-positive granules, cytoplasmic vacuolation, and eventual cell degeneration.

Presence of glycosaminoglycans in retinal capillary basement membrane

Retinal microvessels were isolated from bovine eyes and the basement membranes were purified either directly or after incubation with [35S]sulfate and [14C]glucosamine. The basement membranes, which were purified by osmotic lysis and sequential treatment with detergents, had the general compositional features associated with basement membrane collagens, including high levels of hydroxyproline and hydroxylysine and the presence of 3-hydroxyproline and cystine. After pronase digestion, cellulose acetate electrophoresis of glycosaminoglycans from retinal microvessel basement membrane revealed material comigrating with heparan sulfate that was insensitive to digestion with Streptomyces hyaluronidase ad chondroitinase ABC. Retinal microvessels also incorporated [35S]- and [14C]glucosamine into glycosaminoglycans that were isolated following pronase digestion of the retinal microvessel basement membrane purified from these incubations. The findings provide the first demonstration that glycosaminoglycans are integral components of the retinal microvascular basement membrane and suggest that heparan sulfate is the major glycosaminoglycan species in this basement membrane.

Electron microscopic features of experimental choroidal neovascularization

We produced choroidal neovascularization in the rhesus monkey by diminishing the blood supply to the inner retina and producing defects in Bruch's membrane by photocoagulation. The neovascular fronds which developed either infiltrated the subretinal space or proliferated through necrotic and gliotic retina into the vitreous cavity. Sequential electron microscopic sections of neovascular fronds in the subretinal space demonstrated that the advancing capillary sprouts were composed of primitive endothelial tubes surrounded by pericytes and enmeshed in a loose basement-membrane-like substance. More mature capillaris and displayed endothelial fenestrations and endothelial-pericyte membranous contacts. Large neovascular fronds developed major feeding vessels that closely resembled normal small choroidal arteries and veins. Retinal pigment epithelial cells in various guises were in constant association with proliferating neovascular networks.

Recent advances in diabetic retinopathy

Despite the fact that we still do not understand what causes the development of retinopathy in diabetic subjects, major advances in its treatment have taken place. Photocoagulation clearly reduces the retinopathy although how early treatment should be initiated has not been clearly defined. Vitrectomy is capable of restoring vision in many already blind eyes but at some risk. We are inching closer to an understanding of the pathophysiology of retinopathy with development of retinal endothelial and pericyte cell culture techniques, studies of vascular permeability, flow and angiogenesis. Diabetic retinopathy is more common at early durations of diabetes than previously realized. This may allow for prospective intervention studies, using development of retinopathy as an endpoint. Diabetic retinopathy may be a reasonable index of short-term survival.

Cerebral microvessels and derived cells in tissue culture: isolation and preliminary characterization

Microvessels isolated from mouse forebrain were used as the source material for the derivation of cerebral vascular endothelium and smooth-muscle cells in culture. The microvessels were isolated by a mechanical dispersion and filtration technique, and were maintained in vitro as organoid cultures. A microvessel classification system was developed and proved to be useful as a tool in monitoring culture progress and in predicting the type(s) of microvessel(s) that would give rise to migrating and/or proliferating cells. The isolated cerebral microvessels were heterogeneous in diameter, size of individual vascular isolate, and proliferative potential. The isolated microvessels ranged in diameter from 4 micron to 25 micron and in size from a single microvascular segment to a large multibranched plexus with mural cells. The initial viability, determined by erythrosin B exclusion, was approximately 50% on a per cell basis. All microvessel classes had proliferative potential although the rate and extent of proliferation were both microvessel class- and density-dependent. The smaller microvessels gave rise to endothelial cells, whereas the large microvessels gave rise to endothelial and smooth-muscle cells. The viability and progress of a microvessel toward derived cell proliferation seemed to be directly proportional to the number of mural cells present.

Aldose reductase in diabetic complications of the eye

Aldose reductase (AR) appears to initiate the cataractous process in galactosemic and diabetic animals. Sugars in excess are converted to polyols by lens AR. In sugar cataracts, polyols accumulate to levels substantial enough to cause a hypertonicity leading to lens fiber swelling. All other changes appear secondary to polyol accumulation and lens swelling. The development of sugar cataracts can be duplicated in organ culture. In culture, the various changes that occur were minimized or did not occur when inhibitors of AR were included in the medium. Moreover, AR inhibitors were shown to effectively delay the onset of sugar cataract development in animals. A defect in the corneal epithelium of diabetics became apparent in vitrectomy. One manifestation of this problem was the delay in the reepithelialization of denuded corneas. In examining this problem experimentally, the epithelium was removed from the corneas of diabetic and normal rats. The regeneration of epithelium in corneas of diabetic rats required a longer period than in the normal. The possibility that AR, active in the epithelium, was involved in this phenomenon was investigated. The corneal epithelium was removed from both eyes of a diabetic rat. One eye was treated topically with the AR inhibitor CP-45,634 while the other served as control. The eye treated with CP-45,635 regenerated epithelium much more quickly than the untreated eye. Other AR inhibitors had similar beneficial effects.