ANGIOGENESIS IN

HEALTH AND DISEASE

DR DIBYAJYOTI PRUSTY1ST Year PG

Moderator:Dr Pranati MohantyAsst. Professor

Department of PathologySCB Medical College, Cuttack

Cross section of blood vessels

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OVERVIEW OF VESSEL FORMATION

TYPES OF ANGIOGENESIS

The process of angiogenesis occurs as an orderly series of events :

1. Vasodilation and increased permeability2. Separation of pericytes3. Migration of endothelial cells4. Proloferation of endothelial cells behind the leading

‘tip’ cell5. Remodelling in to capillary tubes6. Recruitment of periendothelial cells7. Suppression of endothelial proliferation and deposition

of basement membrane

UNDERSTANDING ANGIOGENESIS

Folkman J, D’Amore PA. Blood vessel formation: what is its molecular basis? Cell 1996;87:1153-1155.

Angiogenic stimulators

REGULATION OF ANGIOGENESIS

METABOLIC FACTORS:a. Capillary growth is proportional to metabolic activityb. Increase in metabolic activity stimulates blood vessel growthc. Decrease in metabolic activity causes vascular regression ;d. Over oxygenation often leads to capillary rarefaction in sedentary

muscles by auto regulatory vasoconstriction of arterioles. e. Long term increase in BP leads to vascular rarefaction by auto

regulatory vasoconstriction mechanism.f. OXYGEN is the master signal in growth regulation of vascular

system. Chronic exposure to hypoxia leads to increase in arterial diameter .

g. Role of Adenosine:

Vasodialatory property- restores balance between O2 demand and supply

Serve as a negative signal to maintain tissue oxygenation in normal range.

MECHANICAL FACTORS:1. PHYSICAL FORCES acting on the wall of blood

vessels

Shear stress is sensed by the endothelium. This stress acts as a proangiogenic factor.

REGULATION OF ANGIOGENESIS

2.MECHANOSENSORY MECHANISMS EpNaC Proteins : Localised in ECs, Smooth muscle cell

membranes. Both these cells express alha-, beta-, and gamma-

subunits of EpNaC. Mechanosensory complex formed by - endothelium & smooth muscle cell(cytoskeletons and

EpNaCs) - extra cellula matrix It plays a critical role in angiogenic process- as

mechanosensor for migration of endothelial cells and smooth muscle cells.

Specific EpNaC inhibitor used- Benzanil- to prevent angiogenesis.

ROLE OF PERICYTES

Pericytes are single layer of periendothelial smooth muscle cells that modulate endothelial cell function.

Regulate vascular function: -vascular diameter -vascular permeability - endothelial survival

FACTORS AND RECEPTORS

VASCULAR ENDOTHELIAL GROWTH FACTOR

ANGIOPOETINS BASIC FIBROBLAST GROWTH FACTOR PLATELET DERIVED GROWTH FACTOR EPIDERMAL GROWTH FACTOR TRANSFORMING GROWTH FACTOR-

ALPHA

ACTIVATORS OF ANGIOGENESIS

VASCULAR ENDOTHELIAL GROWTH FACTOR Glycoproteins consisting of A-, B-, C-, D-, E- forms and Placental

Growth Factor (PlGF)

Within the six subtypes multiple isoforms exists

Loss of even a single VEGF-A allele results in embryonic lethality Angiogenesis is primarily mediated through interaction of VEGF-

A with VEGFR-2

VEGF RECEPTORS3 types of receptors- VEGFR-1, VEGFR-2 (KDR, Flk-1), VEGFR-3

Tyrosine kinases

VEGF production is under control of : hypoxia-inducible transcription factors(HIFs) VEGF receptor expression is up-regulated under:

hypoxic or ischemic conditions; (30-fold within minutes)

VEGF is a major player in angiogenesis initiation: it cause:1. Endothelial cell survival

2. Stimulates endothelial division, induce locomotion/migration

3. Induce the expression of proteases and receptors

4. Prevent endothelial cell apoptosis 

5. Increase in vascular permeability by upregulating second messengers such as NO

Fibroblast growth factor Basic Fibroblast growth factor (bFGF) family are also

potent inducers of angiogenesis. The effects of FGFs are mediated via high-affinity tyrosine kinase receptors.

Cellular responses mediated by FGFs include cell migration proliferation differentiation

Platelet-derived growth factor The platelet-derived growth factor (PDGF) regulates

the recruitment of PERICYTES and smooth muscle cells required for further stabilization of the new capillaries

ENDOSTATIN Produced by proteolytic cleavage of collagen

ANGIOSTATIN Produced by proteolytic cleavage of plasminogen,

THROMBOSPONDIN-1(TSP-1)Adhesive glycoprotein in matrix.P53 up regulates TSP-1

INHIBITORS OF ANGIOGENESIS

CELL ADHESION MOLECULES(CAM)

1. Integrins, cadherins2.Vascular cell adhesion molecule-1,3.P-selectin and E-selectin

Integrins are expressed at high levels in : tumor vasculature and wound-healing tissues ,

but at extremely low levels in normal blood vessels.

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PROTEASES

Matrix metalloproteases Plasminogen activator(PA) / (MMPs) plasmin system PAs activate the plasminogen degrade different into plasmin, which degrades protein types several components of extracellular matrix (ECM) Both PAs and MMPs are secreted together with their

inhibitors. It ensures a stringent control of local proteolytic activity.

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Why Tumors require Angiogenesis?A, Tumors less than 1 mm3 receive oxygen and nutrients by diffusion from host vasculature.

B, Larger tumors require new vessel network. Tumor secretes angiogenic factors that stimulate migration, proliferation, and neovessel formation by endothelial cells in adjacent established vessels.

C, Newly vascularized tumor no longer relies solely on diffusion from host vasculature, facilitating progressive growth.

STRUCTURE AND FUNCTION OF TUMOR VESSELS:

Chaotic architecture and heterogeneous blood flow that leads to abnormal growth

Excessively dilated blood vessels Extreme corkscrew like tortuosities Lack of pericyte support or abnormal pericytic function: Permeability strongly increased

-fenestrae-enlarged Junctions

No functional lymphatics inside the tumor-enlarged in surrounding,-increases metastasis

CHAOTIC ORGANIZATION OF TUMOR-ASSOCIATED VASCULATURE

ANGIOGENESIS ASSAYS 1. In-vitro assays-Proliferation assay-Migration assay-Tube formation assay-Rat and mouse aortic ring assay 2. In-vivo assays-Corneal angiogenesis assay-Chick choreoallantoic membrane angiogenesis assay-Matrigel Plug assay

The difficulties faced: -ECs are heterogeneous -In-vitro conditions rarely reflects in-vivo environment

IN HEALTH AND DISEASE

ANGIOGENESIS:ABNORMAL OR EXCESSIVE ORGANS INVOLVED DISEASES

Numerous Organs Cancers Infectious diseasesAutoimmune disorders

Blood vessels Vascular malformations, DiGorge syndromeAtherosclerosis,

Adipose tissue Obesity

Skin PsoriasisScar keloids, Pyogenic granuloma

ORGANS INVOLVED DISEASES

Eye Diabetic retinopathyRetinopathy of prematurityChoroidal neovascularisation

Lung Primary pulmonary hypertensionAsthma , Nasal polyps

Gastro-Intestinal

Bone, joints

Reproductive system

Inflammatory bowel disease,Ascitis,

Synovitis , OsteomyelitisOsteophyte formation

Endometriosis , Uterine bleeding, Ovarian cyst

ANGIOGENESIS:INSUFFICIENCY OR VESSEL REGRESSION

ORGANS INVOLVED DISEASES

Blood vessels Atherosclerosis, Hypertension,Diabetic ischemic limbs

Nervous system Alzheimer’s disease

Amyotrophic lateral sclerosisDiabetic neuropathy

Stroke

Gastrointestinal Gastric or oral ulcerationsChrohn’s disease

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ORGANS INVOLVED DISEASES

Skin Hair lossSkin purpura, Telangeactasia

Reproductive system Pre-eclampsia, Menorrhagia

Lungs

Kidney

Bones & joints

Neonatal respiratory distressEmphysema Pulmonary fibrosis

Nephropathy

Osteoporosis Impaired fracture healing

Heterotypic interactions as targets for therapeutic intervention

CURRENT ANGIOGENIC INHIBITORS IN CLINICAL USE AND CLINICAL TRIALS

Bevacizumab (Avastin™) Sunitinib (Sutent™) Sorafenib (Nexavar™) Cederanib (Recentin™ - AZD- 2171)

Many others in development

FUTURE DIRECTIONS-VEGF-TRAP

Composite decoy receptor based on VEGFR-1 and VEGFR-2 fused to a human Fc segment of IgG1 that binds VEGF

Decreases free VEGF to bind to receptors and prevent vessel growth

FDA approved for neovascular macular degeneration

THE CHALLENGES!!! Proangiogenic growth factor redundancy Selection of hypoxia-resistant cells Co-option of normal organ vasculature Vascular remodelling Angiogenesis contributing to growth of ‘liquid’

hematologic malignancies, not just solid tumors Circulating endothelial progenitor cells or precursor

cells Diverse array of molecular mediators of

angiogenesis

CONCLUSION Historically, angiogenesis is only implicated in cancer,

arthritis, psoriasis…etc. In recent years it is evident that excessive, insufficient or abnormal angiogenesis contributes many more disorders.

Both pro- & antiangiogenic therapy with single angiogenic molecule is more challenging than anticipated

Monotherapy with a single angiogenic inhibitor may not suffice to combat the angiogenic factors produced by cancer cells

Understanding the complex interplay of molecular signals in more integrated manner to develop efficient and safe therapies.

INHIBITION OF BLOOD VESSEL GROWTH WITHIN A TUMOR COULD PROLONG TUMOR DORMANCY AND IMPROVE SURVIVAL OF PATIENTS WITH MINIMAL TOXICITY.